Exciton generation/dissociation/charge-transfer enhancement in inorganic/organic hybrid solar cells by robust single nanocrystalline LnPxOy (Ln = Eu, Y) doping.

PubMed

Jin, Xiao; Sun, Weifu; Chen, Zihan; Wei, Taihuei; Chen, Chuyang; He, Xingdao; Yuan, Yongbiao; Li, Yue; Li, Qinghua

2014-06-11

Low-temperature solution-processed photovoltaics suffer from low efficiencies because of poor exciton or electron-hole transfer. Inorganic/organic hybrid solar cell, although still in its infancy, has attracted great interest thus far. One of the promising ways to enhance exciton dissociation or electron-hole transport is the doping of lanthanide phosphate ions. However, the underlying photophysical mechanism remains poorly understood. Herein, by applying femtosecond transient absorption spectroscopy, we successfully distinguished hot electron, less energetic electron, hole transport from electron-hole recombination. Concrete evidence has been provided that lanthanide phosphate doping improves the efficiency of both hot electron and "less energetic" electron transfers from donor to acceptor, but the hole transport almost remains unchanged. In particular, the hot electron transfer lifetime was shortened from 30.2 to 12.7 ps, that is, more than 60% faster than pure TiO2 acceptor. Such improvement was ascribed to the facts that the conduction band (CB) edge energy level of TiO2 has been elevated by 0.2 eV, while the valence band level almost remains unchanged, thus not only narrowing the energy offset between CB levels of TiO2 and P3HT, but also meanwhile enlarging the band gap of TiO2 itself that permits one to inhibit electron-hole recombination within TiO2. Consequently, lanthanide phosphate doped TiO2/P3HT bulk-heterojunction solar cell has been demonstrated to be a promising hybrid solar cell, and a notable power conversion efficiency of 2.91% is therefore attained. This work indicates that lanthanide compound ions can efficiently facilitate exciton generation, dissociation, and charge transport, thus enhancing photovoltaic performance.

Sandwiched confinement of quantum dots in graphene matrix for efficient electron transfer and photocurrent production

PubMed Central

Zhu, Nan; Zheng, Kaibo; Karki, Khadga J.; Abdellah, Mohamed; Zhu, Qiushi; Carlson, Stefan; Haase, Dörthe; Žídek, Karel; Ulstrup, Jens; Canton, Sophie E.; Pullerits, Tõnu; Chi, Qijin

2015-01-01

Quantum dots (QDs) and graphene are both promising materials for the development of new-generation optoelectronic devices. Towards this end, synergic assembly of these two building blocks is a key step but remains a challenge. Here, we show a one-step strategy for organizing QDs in a graphene matrix via interfacial self-assembly, leading to the formation of sandwiched hybrid QD-graphene nanofilms. We have explored structural features, electron transfer kinetics and photocurrent generation capacity of such hybrid nanofilms using a wide variety of advanced techniques. Graphene nanosheets interlink QDs and significantly improve electronic coupling, resulting in fast electron transfer from photoexcited QDs to graphene with a rate constant of 1.3 × 109 s−1. Efficient electron transfer dramatically enhances photocurrent generation in a liquid-junction QD-sensitized solar cell where the hybrid nanofilm acts as a photoanode. We thereby demonstrate a cost-effective method to construct large-area QD-graphene hybrid nanofilms with straightforward scale-up potential for optoelectronic applications. PMID:25996307

Sandwiched confinement of quantum dots in graphene matrix for efficient electron transfer and photocurrent production

NASA Astrophysics Data System (ADS)

Zhu, Nan; Zheng, Kaibo; Karki, Khadga J.; Abdellah, Mohamed; Zhu, Qiushi; Carlson, Stefan; Haase, Dörthe; Žídek, Karel; Ulstrup, Jens; Canton, Sophie E.; Pullerits, Tõnu; Chi, Qijin

2015-05-01

Quantum dots (QDs) and graphene are both promising materials for the development of new-generation optoelectronic devices. Towards this end, synergic assembly of these two building blocks is a key step but remains a challenge. Here, we show a one-step strategy for organizing QDs in a graphene matrix via interfacial self-assembly, leading to the formation of sandwiched hybrid QD-graphene nanofilms. We have explored structural features, electron transfer kinetics and photocurrent generation capacity of such hybrid nanofilms using a wide variety of advanced techniques. Graphene nanosheets interlink QDs and significantly improve electronic coupling, resulting in fast electron transfer from photoexcited QDs to graphene with a rate constant of 1.3 × 109 s-1. Efficient electron transfer dramatically enhances photocurrent generation in a liquid-junction QD-sensitized solar cell where the hybrid nanofilm acts as a photoanode. We thereby demonstrate a cost-effective method to construct large-area QD-graphene hybrid nanofilms with straightforward scale-up potential for optoelectronic applications.

Direct Observation of Excimer-Mediated Intramolecular Electron Transfer in a Cofacially-Stacked Perylene Bisimide Pair.

PubMed

Sung, Jooyoung; Nowak-Król, Agnieszka; Schlosser, Felix; Fimmel, Benjamin; Kim, Woojae; Kim, Dongho; Würthner, Frank

2016-07-27

We have elucidated excimer-mediated intramolecular electron transfer in cofacially stacked PBIs tethered by two phenylene-butadiynylene loops. The electron transfer between energetically equivalent PBIs is revealed by the simultaneous observation of the PBI radical anion and cation bands in the transient absorption spectra. The fluorescence decay time of the excimer states is in good agreement with the rise time of PBI radical bands in transient absorption spectra suggesting that the electron transfer dynamics proceed via the excimer state. We can conclude that the excimer state effectuates the efficient charge transfer in the cofacially stacked PBI dimer.

Three-dimensional hollow graphene efficiently promotes electron transfer of Ag3PO4 for photocatalytically eliminating phenol

NASA Astrophysics Data System (ADS)

Song, Shaoqing; Meng, Aiyun; Jiang, Shujuan; Cheng, Bei

2018-06-01

The effective transport of photo-induced carriers over semiconductor photocatalyst is critical for enhancing the photocatalytic performance under light excitation. Although oxidized graphene (GO) and/or reduced graphene oxide (rGO) has been used as cocatalyst to promote the transfer and utilization of electrons, however, random diffusion and transfer of photo-induced charges are inevitable from all sides over these actual graphene owing to the limitation of the preparation process and theory. Herein, we utilized three-dimensional hollow carbon graphene (HCG) to promote the efficient electron transfer of Ag3PO4 in the photocatalytic process. Owing to the confinement-induced electron field of HCG, the constructed HCG-Ag3PO4 photocatalytic system demonstrated the enhanced visible-light adsorption, improved transfer of photo-induced charges, and suitable redox potentials as revealed by transient photo-current spectroscopic, surface photovoltage spectroscopy, and electron paramagnetic resonance (EPR). EPR spectra of oxygen species and gas chromatography-mass spectra exhibited high efficiency activity over HCG-Ag3PO4 with Z-scheme photocatalytic mechanism for phenol decomposition by reaction between hexanoic acid and radOH and radO2-. It is noteworthy that photocatalytic performance over optimal HCG-Ag3PO4 is 6, 3.43, 1.92 times of pristine Ag3PO4, GO-Ag3PO4, and rGO-Ag3PO4, respectively. The results may supply a novel perspective to enhance transfer of photo-induced charges for the promotion of photocatalytic technology.

Photo-induced electron transfer method

DOEpatents

Wohlgemuth, Roland; Calvin, Melvin

1984-01-01

The efficiency of photo-induced electron transfer reactions is increased and the back transfer of electrons in such reactions is greatly reduced when a photo-sensitizer zinc porphyrin-surfactant and an electron donor manganese porphyrin-surfactant are admixed into phospho-lipid membranes. The phospholipids comprising said membranes are selected from phospholipids whose head portions are negatively charged. Said membranes are contacted with an aqueous medium in which an essentially neutral viologen electron acceptor is admixed. Catalysts capable of transfering electrons from reduced viologen electron acceptor to hydrogen to produce elemental hydrogen are also included in the aqueous medium. An oxidizable olefin is also admixed in the phospholipid for the purpose of combining with oxygen that coordinates with oxidized electron donor manganese porphyrin-surfactant.

Role of Surface-Capping Ligands in Photoexcited Electron Transfer between CdS Nanorods and [FeFe] Hydrogenase and the Subsequent H 2 Generation

DOE PAGES

Wilker, Molly B.; Utterback, James K.; Greene, Sophie; ...

2017-12-08

Complexes of CdS nanorods and [FeFe] hydrogenase from Clostridium acetobutylicum have been shown to photochemically produce H 2. This study examines the role of the ligands that passivate the nanocrystal surfaces in the electron transfer from photoexcited CdS to hydrogenase and the H 2 generation that follows. We functionalized CdS nanorods with a series of mercaptocarboxylate surface-capping ligands of varying lengths and measured their photoexcited electron relaxation by transient absorption (TA) spectroscopy before and after hydrogenase adsorption. Rate constants for electron transfer from the nanocrystals to the enzyme, extracted by modeling of TA kinetics, decrease exponentially with ligand length, suggestingmore » that the ligand layer acts as a barrier to charge transfer and controls the degree of electronic coupling. Relative light-driven H 2 production efficiencies follow the relative quantum efficiencies of electron transfer, revealing the critical role of surface-capping ligands in determining the photochemical activity of these nanocrystal-enzyme complexes. Our results suggest that the H 2 production in this system could be maximized with a choice of a surface-capping ligand that decreases the distance between the nanocrystal surface and the electron injection site of the enzyme.« less

Role of Surface-Capping Ligands in Photoexcited Electron Transfer between CdS Nanorods and [FeFe] Hydrogenase and the Subsequent H 2 Generation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wilker, Molly B.; Utterback, James K.; Greene, Sophie

Complexes of CdS nanorods and [FeFe] hydrogenase from Clostridium acetobutylicum have been shown to photochemically produce H 2. This study examines the role of the ligands that passivate the nanocrystal surfaces in the electron transfer from photoexcited CdS to hydrogenase and the H 2 generation that follows. We functionalized CdS nanorods with a series of mercaptocarboxylate surface-capping ligands of varying lengths and measured their photoexcited electron relaxation by transient absorption (TA) spectroscopy before and after hydrogenase adsorption. Rate constants for electron transfer from the nanocrystals to the enzyme, extracted by modeling of TA kinetics, decrease exponentially with ligand length, suggestingmore » that the ligand layer acts as a barrier to charge transfer and controls the degree of electronic coupling. Relative light-driven H 2 production efficiencies follow the relative quantum efficiencies of electron transfer, revealing the critical role of surface-capping ligands in determining the photochemical activity of these nanocrystal-enzyme complexes. Our results suggest that the H 2 production in this system could be maximized with a choice of a surface-capping ligand that decreases the distance between the nanocrystal surface and the electron injection site of the enzyme.« less

Efficient Yttrium(III) Chloride-Treated TiO2 Electron Transfer Layers for Performance-Improved and Hysteresis-Less Perovskite Solar Cells.

PubMed

Li, Minghua; Huan, Yahuan; Yan, Xiaoqin; Kang, Zhuo; Guo, Yan; Li, Yong; Liao, Xinqin; Zhang, Ruxiao; Zhang, Yue

2018-01-10

Hybrid organic-inorganic metal halide perovskite solar cells have attracted widespread attention, owing to their high performance, and have undergone rapid development. In perovskite solar cells, the charge transfer layer plays an important role for separating and transferring photogenerated carriers. In this work, an efficient YCl 3 -treated TiO 2 electron transfer layer (ETL) is used to fabricate perovskite solar cells with enhanced photovoltaic performance and less hysteresis. The YCl 3 -treated TiO 2 layers bring about an upward shift of the conduction band minimum (E CBM ), which results in a better energy level alignment for photogenerated electron transfer and extraction from the perovskite into the TiO 2 layer. After optimization, perovskite solar cells based on the YCl 3 -treated TiO 2 layers achieve a maximum power conversion efficiency of about 19.99 % (19.29 % at forward scan) and a steady-state power output of about 19.6 %. Steady-state and time-resolved photoluminescence measurements and impedance spectroscopy are carried out to investigate the charge transfer and recombination dynamics between the perovskite and the TiO 2 electron transfer layer interface. The improved perovskite/TiO 2 ETL interface with YCl 3 treatment is found to separate and extract photogenerated charge rapidly and suppress recombination effectively, which leads to the improved performance. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Organic Solar Cells: Understanding the Role of Förster Resonance Energy Transfer

PubMed Central

Feron, Krishna; Belcher, Warwick J.; Fell, Christopher J.; Dastoor, Paul C.

2012-01-01

Organic solar cells have the potential to become a low-cost sustainable energy source. Understanding the photoconversion mechanism is key to the design of efficient organic solar cells. In this review, we discuss the processes involved in the photo-electron conversion mechanism, which may be subdivided into exciton harvesting, exciton transport, exciton dissociation, charge transport and extraction stages. In particular, we focus on the role of energy transfer as described by Förster resonance energy transfer (FRET) theory in the photoconversion mechanism. FRET plays a major role in exciton transport, harvesting and dissociation. The spectral absorption range of organic solar cells may be extended using sensitizers that efficiently transfer absorbed energy to the photoactive materials. The limitations of Förster theory to accurately calculate energy transfer rates are discussed. Energy transfer is the first step of an efficient two-step exciton dissociation process and may also be used to preferentially transport excitons to the heterointerface, where efficient exciton dissociation may occur. However, FRET also competes with charge transfer at the heterointerface turning it in a potential loss mechanism. An energy cascade comprising both energy transfer and charge transfer may aid in separating charges and is briefly discussed. Considering the extent to which the photo-electron conversion efficiency is governed by energy transfer, optimisation of this process offers the prospect of improved organic photovoltaic performance and thus aids in realising the potential of organic solar cells. PMID:23235328

Millisecond newly born pulsars as efficient accelerators of electrons

NASA Astrophysics Data System (ADS)

Osmanov, Zaza; Mahajan, Swadesh; Machabeli, George; Chkheidze, Nino

2015-09-01

The newly born millisecond pulsars are investigated as possible energy sources for creating ultra-high energy electrons. The transfer of energy from the star rotation to high energy electrons takes place through the Landau damping of centrifugally driven (via a two stream instability) electrostatic Langmuir waves. Generated in the bulk magnetosphere plasma, such waves grow to high amplitudes, and then damp, very effectively, on relativistic electrons driving them to even higher energies. We show that the rate of transfer of energy is so efficient that no energy losses might affect the mechanism of particle acceleration; the electrons might achieve energies of the order of 1018 eV for parameters characteristic of a young star.

Ultrafast Interlayer Electron Transfer in Incommensurate Transition Metal Dichalcogenide Homobilayers.

PubMed

Li, Yuanyuan; Cui, Qiannan; Ceballos, Frank; Lane, Samuel D; Qi, Zeming; Zhao, Hui

2017-11-08

Two-dimensional materials, such as graphene, transition metal dichalcogenides, and phosphorene, can be used to construct van der Waals multilayer structures. This approach has shown potentials to produce new materials that combine novel properties of the participating individual layers. One key requirement for effectively harnessing emergent properties of these materials is electronic connection of the involved atomic layers through efficient interlayer charge or energy transfer. Recently, ultrafast charge transfer on a time scale shorter than 100 fs has been observed in several van der Waals bilayer heterostructures formed by two different materials. However, information on the transfer between two atomic layers of the same type is rare. Because these homobilayers are essential elements in constructing multilayer structures with desired optoelectronic properties, efficient interlayer transfer is highly desired. Here we show that electron transfer between two monolayers of MoSe 2 occurs on a picosecond time scale. Even faster transfer was observed in homobilayers of WS 2 and WSe 2 . The samples were fabricated by manually stacking two exfoliated monolayer flakes. By adding a graphene layer as a fast carrier recombination channel for one of the two monolayers, the transfer of the photoexcited carriers from the populated to the drained monolayers was time-resolved by femtosecond transient absorption measurements. The observed efficient interlayer carrier transfer indicates that such homobilayers can be used in van der Waals multilayers to enhance their optical absorption without significantly compromising the interlayer transport performance. Our results also provide valuable information for understanding interlayer charge transfer in heterostructures.

Simple structured hybrid WOLEDs based on incomplete energy transfer mechanism: from blue exciplex to orange dopant.

PubMed

Zhang, Tianyou; Zhao, Bo; Chu, Bei; Li, Wenlian; Su, Zisheng; Yan, Xingwu; Liu, Chengyuan; Wu, Hairuo; Gao, Yuan; Jin, Fangming; Hou, Fuhua

2015-05-15

Exciplex is well known as a charge transfer state formed between electron-donating and electron-accepting molecules. However, exciplex based organic light emitting diodes (OLED) often performed low efficiencies relative to pure phosphorescent OLED and could hardly be used to construct white OLED (WOLED). In this work, a new mechanism is developed to realize efficient WOLED with extremely simple structure by redistributing the energy of triplet exciplex to both singlet exciplex and the orange dopant. The micro process of energy transfer could be directly examined by detailed photoluminescence decay measurement and time resolved photoluminescence analysis. This strategy overcomes the low reverse intersystem crossing efficiency of blue exciplex and complicated device structure of traditional WOLED, enables us to achieve efficient hybrid WOLEDs. Based on this mechanism, we have successfully constructed both exciplex-fluorescence and exciplex-phosphorescence hybrid WOLEDs with remarkable efficiencies.

Simple structured hybrid WOLEDs based on incomplete energy transfer mechanism: from blue exciplex to orange dopant

NASA Astrophysics Data System (ADS)

Zhang, Tianyou; Zhao, Bo; Chu, Bei; Li, Wenlian; Su, Zisheng; Yan, Xingwu; Liu, Chengyuan; Wu, Hairuo; Gao, Yuan; Jin, Fangming; Hou, Fuhua

2015-05-01

Exciplex is well known as a charge transfer state formed between electron-donating and electron-accepting molecules. However, exciplex based organic light emitting diodes (OLED) often performed low efficiencies relative to pure phosphorescent OLED and could hardly be used to construct white OLED (WOLED). In this work, a new mechanism is developed to realize efficient WOLED with extremely simple structure by redistributing the energy of triplet exciplex to both singlet exciplex and the orange dopant. The micro process of energy transfer could be directly examined by detailed photoluminescence decay measurement and time resolved photoluminescence analysis. This strategy overcomes the low reverse intersystem crossing efficiency of blue exciplex and complicated device structure of traditional WOLED, enables us to achieve efficient hybrid WOLEDs. Based on this mechanism, we have successfully constructed both exciplex-fluorescence and exciplex-phosphorescence hybrid WOLEDs with remarkable efficiencies.

Simple structured hybrid WOLEDs based on incomplete energy transfer mechanism: from blue exciplex to orange dopant

PubMed Central

Zhang, Tianyou; Zhao, Bo; Chu, Bei; Li, Wenlian; Su, Zisheng; Yan, Xingwu; Liu, Chengyuan; Wu, Hairuo; Gao, Yuan; Jin, Fangming; Hou, Fuhua

2015-01-01

Exciplex is well known as a charge transfer state formed between electron-donating and electron-accepting molecules. However, exciplex based organic light emitting diodes (OLED) often performed low efficiencies relative to pure phosphorescent OLED and could hardly be used to construct white OLED (WOLED). In this work, a new mechanism is developed to realize efficient WOLED with extremely simple structure by redistributing the energy of triplet exciplex to both singlet exciplex and the orange dopant. The micro process of energy transfer could be directly examined by detailed photoluminescence decay measurement and time resolved photoluminescence analysis. This strategy overcomes the low reverse intersystem crossing efficiency of blue exciplex and complicated device structure of traditional WOLED, enables us to achieve efficient hybrid WOLEDs. Based on this mechanism, we have successfully constructed both exciplex-fluorescence and exciplex-phosphorescence hybrid WOLEDs with remarkable efficiencies. PMID:25975371

Accompanying coordinate expansion and recurrence relation method using a transfer relation scheme for electron repulsion integrals with high angular momenta and long contractions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hayami, Masao; Seino, Junji; Nakai, Hiromi, E-mail: nakai@waseda.jp

An efficient algorithm for the rapid evaluation of electron repulsion integrals is proposed. The present method, denoted by accompanying coordinate expansion and transferred recurrence relation (ACE-TRR), is constructed using a transfer relation scheme based on the accompanying coordinate expansion and recurrence relation method. Furthermore, the ACE-TRR algorithm is extended for the general-contraction basis sets. Numerical assessments clarify the efficiency of the ACE-TRR method for the systems including heavy elements, whose orbitals have long contractions and high angular momenta, such as f- and g-orbitals.

Squarylium-triazine dyad as a highly sensitive photoradical generator for red light.

PubMed

Kawamura, Koichi; Schmitt, Julien; Barnet, Maxime; Salmi, Hanene; Ley, Christian; Allonas, Xavier

2013-09-16

New dyads, based on squarylium dye and substituted-triazine, were synthesized that exhibit an intramolecular photodissociative electron-transfer reaction. The compounds were used as a red-light photoradical generator. The photochemical activity of the dyad was compared to the corresponding unlinked systems (S+T) by determining the rate constant of electron transfer. The efficiency of the radical generation from the dyad compared to the unlinked system was demonstrated by measuring the maximum rate of free radical polymerization of acrylates in film. An excellent relationship between the rate of electron transfer and the rate of polymerization was found, evidencing the interest of this new approach to efficiently produce radicals under red light. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Direct evidence of two interatomic relaxation mechanisms in argon dimers ionized by electron impact

PubMed Central

Ren, Xueguang; Jabbour Al Maalouf, Elias; Dorn, Alexander; Denifl, Stephan

2016-01-01

In weakly bound systems like liquids and clusters electronically excited states can relax in inter-particle reactions via the interplay of electronic and nuclear dynamics. Here we report on the identification of two prominent examples, interatomic Coulombic decay (ICD) and radiative charge transfer (RCT), which are induced in argon dimers by electron collisions. After initial ionization of one dimer constituent ICD and RCT lead to the ionization of its neighbour either by energy transfer to or by electron transfer from the neighbour, respectively. By full quintuple-coincidence measurements, we unambiguously identify ICD and RCT, and trace the relaxation dynamics as function of the collisional excited state energies. Such interatomic processes multiply the number of electrons and shift their energies down to the critical 1–10 eV range, which can efficiently cause chemical degradation of biomolecules. Therefore, the observed relaxation channels might contribute to cause efficient radiation damage in biological systems. PMID:27000407

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kar, Durga P.; Nayak, Praveen P.; Bhuyan, Satyanarayan

In order to power or charge electronic devices wirelessly, a bi-directional wireless power transfer method has been proposed and experimentally investigated. In the proposed design, two receiving coils are used on both sides of a transmitting coil along its central axis to receive the power wirelessly from the generated magnetic fields through strongly coupled magnetic resonance. It has been observed experimentally that the maximum power transfer occurs at the operating resonant frequency for optimum electric load connected across the receiving coils on both side. The optimum wireless power transfer efficiency is 88% for the bi-directional power transfer technique compared 84%more » in the one side receiver system. By adopting the developed bi-directional power transfer method, two electronic devices can be powered up or charged simultaneously instead of a single device through usual one side receiver system without affecting the optimum power transfer efficiency.« less

Balancing the Electron and Hole Transfer for Efficient Quantum Dot Light-Emitting Diodes by Employing a Versatile Organic Electron-Blocking Layer.

PubMed

Jin, Xiao; Chang, Chun; Zhao, Weifeng; Huang, Shujuan; Gu, Xiaobing; Zhang, Qin; Li, Feng; Zhang, Yubao; Li, Qinghua

2018-05-09

The electron-blocking layer (EBL) is important to balance the charge carrier transfer and achieve highly efficient quantum dot light-emitting diodes (QLEDs). Here, we report the utilization of a soluble tert-butyldimethylsilyl chloride-modified poly( p-phenylene benzobisoxazole) (TBS-PBO) as an EBL for simultaneous good charge carrier transfer balance while maintaining a high current density. We show that the versatile TBS-PBO blocks excess electron injection into the quantum dots (QDs), thus leading to better charge carrier transfer balance. It also restricts the undesired QD-to-EBL electron-transfer process, which preserves the superior emission capabilities of the emitter. As a consequence, the TBS-PBO device delivers an external quantum efficiency (EQE) maximum of 16.7% along with a remarkable current density as high as 139 mA/cm 2 with a brightness of 5484 cd/m 2 . The current density of our device is higher than those of insulator EBL-based devices because of the higher conductivity of the TBS-PBO versus insulator EBL, thus helping achieve high luminance values ranging from 1414 to 20 000 cd/cm 2 with current densities ranging from 44 to 648 mA/cm 2 and EQE > 14%. We believe that these unconventional features of the present TBS-PBO-based QLEDs will expand the wide use of TBS-PBO as buffer layers in other advanced QLED applications.

Direct Electron Transfer of Dehydrogenases for Development of 3rd Generation Biosensors and Enzymatic Fuel Cells.

PubMed

Bollella, Paolo; Gorton, Lo; Antiochia, Riccarda

2018-04-24

Dehydrogenase based bioelectrocatalysis has been increasingly exploited in recent years in order to develop new bioelectrochemical devices, such as biosensors and biofuel cells, with improved performances. In some cases, dehydrogeases are able to directly exchange electrons with an appropriately designed electrode surface, without the need for an added redox mediator, allowing bioelectrocatalysis based on a direct electron transfer process. In this review we briefly describe the electron transfer mechanism of dehydrogenase enzymes and some of the characteristics required for bioelectrocatalysis reactions via a direct electron transfer mechanism. Special attention is given to cellobiose dehydrogenase and fructose dehydrogenase, which showed efficient direct electron transfer reactions. An overview of the most recent biosensors and biofuel cells based on the two dehydrogenases will be presented. The various strategies to prepare modified electrodes in order to improve the electron transfer properties of the device will be carefully investigated and all analytical parameters will be presented, discussed and compared.

[Promoting efficiency of microbial extracellular electron transfer by synthetic biology].

PubMed

Li, Feng; Song, Hao

2017-03-25

Electroactive bacteria, including electrigenic bacteria (exoelectrogens) and electroautotrophic bacteria, implement microbial bioelectrocatalysis processes via bi-directional exchange of electrons and energy with environments, enabling a wide array of applications in environmental and energy fields, including microbial fuel cells (MFC), microbial electrolysis cells (MEC), microbial electrosynthesis (MES) to produce electricity and bulk fine chemicals. However, the low efficiency in the extracellular electron transfer (EET) of exoelectrogens and electrotrophic microbes limited their industrial applications. Here, we reviewed synthetic biology approaches to engineer electroactive microorganisms to break the bottleneck of their EET pathways, to achieve higher efficiency of EET of a number of electroactive microorganisms. Such efforts will lead to a breakthrough in the applications of these electroactive microorganisms and microbial electrocatalysis systems.

Interaction of photosystem I from Phaeodactylum tricornutum with plastocyanins as compared with its native cytochrome c6: Reunion with a lost donor.

PubMed

Bernal-Bayard, Pilar; Pallara, Chiara; Carmen Castell, M; Molina-Heredia, Fernando P; Fernández-Recio, Juan; Hervás, Manuel; Navarro, José A

2015-12-01

In the Phaeodactylum tricornutum alga, as in most diatoms, cytochrome c6 is the only electron donor to photosystem I, and thus they lack plastocyanin as an alternative electron carrier. We have investigated, by using laser-flash absorption spectroscopy, the electron transfer to Phaeodactylum photosystem I from plastocyanins from cyanobacteria, green algae and plants, as compared with its own cytochrome c6. Diatom photosystem I is able to effectively react with eukaryotic acidic plastocyanins, although with less efficiency than with Phaeodactylum cytochrome c6. This efficiency, however, increases in some green alga plastocyanin mutants mimicking the electrostatics of the interaction site on the diatom cytochrome. In addition, the structure of the transient electron transfer complex between cytochrome c6 and photosystem I from Phaeodactylum has been analyzed by computational docking and compared to that of green lineage and mixed systems. Taking together, the results explain why the Phaeodactylum system shows a lower efficiency than the green systems, both in the formation of the properly arranged [cytochrome c6-photosystem I] complex and in the electron transfer itself. Copyright © 2015 Elsevier B.V. All rights reserved.

Ultrashort electromagnetic pulse control of intersubband quantum well transitions

PubMed Central

2012-01-01

We study the creation of high-efficiency controlled population transfer in intersubband transitions of semiconductor quantum wells. We give emphasis to the case of interaction of the semiconductor quantum well with electromagnetic pulses with a duration of few cycles and even a single cycle. We numerically solve the effective nonlinear Bloch equations for a specific double GaAs/AlGaAs quantum well structure, taking into account the ultrashort nature of the applied field, and show that high-efficiency population inversion is possible for specific pulse areas. The dependence of the efficiency of population transfer on the electron sheet density and the carrier envelope phase of the pulse is also explored. For electromagnetic pulses with a duration of several cycles, we find that the change in the electron sheet density leads to a very different response of the population in the two subbands to pulse area. However, for pulses with a duration equal to or shorter than 3 cycles, we show that efficient population transfer between the two subbands is possible, independent of the value of electron sheet density, if the pulse area is Π. PMID:22916956

Ultrashort electromagnetic pulse control of intersubband quantum well transitions.

PubMed

Paspalakis, Emmanuel; Boviatsis, John

2012-08-23

: We study the creation of high-efficiency controlled population transfer in intersubband transitions of semiconductor quantum wells. We give emphasis to the case of interaction of the semiconductor quantum well with electromagnetic pulses with a duration of few cycles and even a single cycle. We numerically solve the effective nonlinear Bloch equations for a specific double GaAs/AlGaAs quantum well structure, taking into account the ultrashort nature of the applied field, and show that high-efficiency population inversion is possible for specific pulse areas. The dependence of the efficiency of population transfer on the electron sheet density and the carrier envelope phase of the pulse is also explored. For electromagnetic pulses with a duration of several cycles, we find that the change in the electron sheet density leads to a very different response of the population in the two subbands to pulse area. However, for pulses with a duration equal to or shorter than 3 cycles, we show that efficient population transfer between the two subbands is possible, independent of the value of electron sheet density, if the pulse area is Π.

A bio-inspired N-doped porous carbon electrocatalyst with hierarchical superstructure for efficient oxygen reduction reaction

NASA Astrophysics Data System (ADS)

Miao, Yue-E.; Yan, Jiajie; Ouyang, Yue; Lu, Hengyi; Lai, Feili; Wu, Yue; Liu, Tianxi

2018-06-01

The bio-inspired hierarchical "grape cluster" superstructure provides an effective integration of one-dimensional carbon nanofibers (CNF) with isolated carbonaceous nanoparticles into three-dimensional (3D) conductive frameworks for efficient electron and mass transfer. Herein, a 3D N-doped porous carbon electrocatalyst consisting of carbon nanofibers with grape-like N-doped hollow carbon particles (CNF@NC) has been prepared through a simple electrospinning strategy combined with in-situ growth and carbonization processes. Such a bio-inspired hierarchically organized conductive network largely facilitates both the mass diffusion and electron transfer during the oxygen reduction reactions (ORR). Therefore, the metal-free CNF@NC catalyst demonstrates superior catalytic activity with an absolute four-electron transfer mechanism, strong methanol tolerance and good long-term stability towards ORR in alkaline media.

Experimental insights on the electron transfer and energy transfer processes between Ce{sup 3+}-Yb{sup 3+} and Ce{sup 3+}-Tb{sup 3+} in borate glass

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sontakke, Atul D., E-mail: sontakke.atul.55a@st.kyoto-u.ac.jp; Katayama, Yumiko; Tanabe, Setsuhisa

2015-03-30

A facile method to describe the electron transfer and energy transfer processes among lanthanide ions is presented based on the temperature dependent donor luminescence decay kinetics. The electron transfer process in Ce{sup 3+}-Yb{sup 3+} exhibits a steady rise with temperature, whereas the Ce{sup 3+}-Tb{sup 3+} energy transfer remains nearly unaffected. This feature has been investigated using the rate equation modeling and a methodology for the quantitative estimation of interaction parameters is presented. Moreover, the overall consequences of electron transfer and energy transfer process on donor-acceptor luminescence behavior, quantum efficiency, and donor luminescence decay kinetics are discussed in borate glass host.more » The results in this study propose a straight forward approach to distinguish the electron transfer and energy transfer processes between lanthanide ions in dielectric hosts, which is highly advantageous in view of the recent developments on lanthanide doped materials for spectral conversion, persistent luminescence, and related applications.« less

A Strategy to Enhance the Efficiency of Quantum Dot-Sensitized Solar Cells by Decreasing Electron Recombination with Polyoxometalate/TiO2 as the Electronic Interface Layer.

PubMed

Chen, Li; Chen, Weilin; Li, Jianping; Wang, Jiabo; Wang, Enbo

2017-07-21

Electron recombination occurring at the TiO 2 /quantum dot sensitizer/electrolyte interface is the key reason for hindering further efficiency improvements to quantum dot sensitized solar cells (QDSCs). Polyoxometalate (POM) can act as an electron-transfer medium to decrease electron recombination in a photoelectric device owing to its excellent oxidation/reduction properties and thermostability. A POM/TiO 2 electronic interface layer prepared by a simple layer-by-layer self-assembly method was added between fluorine-doped tin oxide (FTO) and mesoporous TiO 2 in the photoanode of QDSCs, and the effect on the photovoltaic performance was systematically investigated. Photovoltaic experimental results and the electron transmission mechanism show that the POM/TiO 2 electronic interface layer in the QDSCs can clearly suppress electron recombination, increase the electron lifetime, and result in smoother electron transmission. In summary, the best conversion efficiency of QDSCs with POM/TiO 2 electronic interface layers increases to 8.02 %, which is an improvement of 25.1 % compared with QDSCs without POM/TiO 2 . This work first builds an electron-transfer bridge between FTO and the quantum dot sensitizer and paves the way for further improved efficiency of QDSCs. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Synchronized energy and electron transfer processes in covalently linked CdSe-squaraine dye-TiO2 light harvesting assembly.

PubMed

Choi, Hyunbong; Santra, Pralay K; Kamat, Prashant V

2012-06-26

Manipulation of energy and electron transfer processes in a light harvesting assembly is an important criterion to mimic natural photosynthesis. We have now succeeded in sequentially assembling CdSe quantum dot (QD) and squaraine dye (SQSH) on TiO(2) film and couple energy and electron transfer processes to generate photocurrent in a hybrid solar cell. When attached separately, both CdSe QDs and SQSH inject electrons into TiO(2) under visible-near-IR irradiation. However, CdSe QD if linked to TiO(2) with SQSH linker participates in an energy transfer process. The hybrid solar cells prepared with squaraine dye as a linker between CdSe QD and TiO(2) exhibited power conversion efficiency of 3.65% and good stability during illumination with global AM 1.5 solar condition. Transient absorption spectroscopy measurements provided further insight into the energy transfer between excited CdSe QD and SQSH (rate constant of 6.7 × 10(10) s(-1)) and interfacial electron transfer between excited SQSH and TiO(2) (rate constant of 1.2 × 10(11) s(-1)). The synergy of covalently linked semiconductor quantum dots and near-IR absorbing squaraine dye provides new opportunities to harvest photons from selective regions of the solar spectrum in an efficient manner.

Molecular implementation of molecular shift register memories

NASA Technical Reports Server (NTRS)

Beratan, David N. (Inventor); Onuchic, Jose N. (Inventor)

1991-01-01

An electronic shift register memory (20) at the molecular level is described. The memory elements are based on a chain of electron transfer molecules (22) and the information is shifted by photoinduced (26) electron transfer reactions. Thus, multi-step sequences of charge transfer reactions are used to move charge with high efficiency down a molecular chain. The device integrates compositions of the invention onto a VLSI substrate (36), providing an example of a molecular electronic device which may be fabricated. Three energy level schemes, molecular implementation of these schemes, optical excitation strategies, charge amplification strategies, and error correction strategies are described.

Efficient etching-free transfer of high quality, large-area CVD grown graphene onto polyvinyl alcohol films

NASA Astrophysics Data System (ADS)

Marta, Bogdan; Leordean, Cosmin; Istvan, Todor; Botiz, Ioan; Astilean, Simion

2016-02-01

Graphene transfer is a procedure of paramount importance for the production of graphene-based electronic devices. The transfer procedure can affect the electronic properties of the transferred graphene and can be detrimental for possible applications both due to procedure induced defects which can appear and due to scalability of the method. Hence, it is important to investigate new transfer methods for graphene that are less time consuming and show great promise. In the present study we propose an efficient, etching-free transfer method that consists in applying a thin polyvinyl alcohol layer on top of the CVD grown graphene on Cu and then peeling-off the graphene onto the polyvinyl alcohol film. We investigate the quality of the transferred graphene before and after the transfer, using Raman spectroscopy and imaging as well as optical and atomic force microscopy techniques. This simple transfer method is scalable and can lead to complete transfer of graphene onto flexible and transparent polymer support films without affecting the quality of the graphene during the transfer procedure.

Acid proliferation to improve the sensitivity of EUV resists: a pulse radiolysis study

NASA Astrophysics Data System (ADS)

Enomoto, Kazuyuki; Arimitsu, Koji; Yoshizawa, Atsutaro; Yamamoto, Hiroki; Oshima, Akihiro; Kozawa, Takahiro; Tagawa, Seiichi

2011-04-01

The yields of acid have been measured in the electron-beam irradiation of triphenylsulfonium triflate (TPS-Tf) and pinanediol monosulfonates, which consist of tosylate (PiTs), 4-fluorobenzenesulfonate (Pi1F), or 4-trifluoromethylbenzenesulfonate (Pi3F), as an acid amplifier blended in 4-hydroxystyrene matrixes. The acid yields efficiency decreases when PiTs is present, while its efficiency increases in the presence of Pi3F. Reactions of the electrons with TPS-Tf and pinanediol monosulfonates have been studied using pulse radiolysis in liquid tetrahydrofuran (THF) to evaluate the kinetic contributions to acid production. The THF-solvated electrons react with PiTs, Pi1F, and Pi3F to produce the corresponding radical anions; the rate constants are estimated to be 4.1, 5.1, and 9.2 × 1010 M-1 s-1, respectively. Electron transfer from PiTs•-, Pi1F•-, and Pi3F•- radical anions to TPS-Tf occurs with the rate constants of 5.7×1010, 1.2×1011, and 6.3 × 1010 M-1 s-1, respectively. The long-lived Pi3F•- efficiently undergoes the electron transfer to TPS-Tf to form the TPS-Tf•-, which subsequently decompose to generate TfOH. On the other hand, the decay channels of PiTs•- and Pi1F•-, which possess a relatively short lifetime, are presumably dependent on its reactions with solvated protons (charge recombination) rather than the electron transfer to TPS-Tf. The novel acid production pathway via the electron transfer from pinanediol monosulfonate radical anions to TPS-Tf is presented.

Photoinduced electron transfer from semiconductor quantum dots to metal oxide nanoparticles

PubMed Central

Tvrdy, Kevin; Frantsuzov, Pavel A.; Kamat, Prashant V.

2011-01-01

Quantum dot-metal oxide junctions are an integral part of next-generation solar cells, light emitting diodes, and nanostructured electronic arrays. Here we present a comprehensive examination of electron transfer at these junctions, using a series of CdSe quantum dot donors (sizes 2.8, 3.3, 4.0, and 4.2 nm in diameter) and metal oxide nanoparticle acceptors (SnO2, TiO2, and ZnO). Apparent electron transfer rate constants showed strong dependence on change in system free energy, exhibiting a sharp rise at small driving forces followed by a modest rise further away from the characteristic reorganization energy. The observed trend mimics the predicted behavior of electron transfer from a single quantum state to a continuum of electron accepting states, such as those present in the conduction band of a metal oxide nanoparticle. In contrast with dye-sensitized metal oxide electron transfer studies, our systems did not exhibit unthermalized hot-electron injection due to relatively large ratios of electron cooling rate to electron transfer rate. To investigate the implications of these findings in photovoltaic cells, quantum dot-metal oxide working electrodes were constructed in an identical fashion to the films used for the electron transfer portion of the study. Interestingly, the films which exhibited the fastest electron transfer rates (SnO2) were not the same as those which showed the highest photocurrent (TiO2). These findings suggest that, in addition to electron transfer at the quantum dot-metal oxide interface, other electron transfer reactions play key roles in the determination of overall device efficiency. PMID:21149685

Photoinduced electron transfer from semiconductor quantum dots to metal oxide nanoparticles.

PubMed

Tvrdy, Kevin; Frantsuzov, Pavel A; Kamat, Prashant V

2011-01-04

Quantum dot-metal oxide junctions are an integral part of next-generation solar cells, light emitting diodes, and nanostructured electronic arrays. Here we present a comprehensive examination of electron transfer at these junctions, using a series of CdSe quantum dot donors (sizes 2.8, 3.3, 4.0, and 4.2 nm in diameter) and metal oxide nanoparticle acceptors (SnO(2), TiO(2), and ZnO). Apparent electron transfer rate constants showed strong dependence on change in system free energy, exhibiting a sharp rise at small driving forces followed by a modest rise further away from the characteristic reorganization energy. The observed trend mimics the predicted behavior of electron transfer from a single quantum state to a continuum of electron accepting states, such as those present in the conduction band of a metal oxide nanoparticle. In contrast with dye-sensitized metal oxide electron transfer studies, our systems did not exhibit unthermalized hot-electron injection due to relatively large ratios of electron cooling rate to electron transfer rate. To investigate the implications of these findings in photovoltaic cells, quantum dot-metal oxide working electrodes were constructed in an identical fashion to the films used for the electron transfer portion of the study. Interestingly, the films which exhibited the fastest electron transfer rates (SnO(2)) were not the same as those which showed the highest photocurrent (TiO(2)). These findings suggest that, in addition to electron transfer at the quantum dot-metal oxide interface, other electron transfer reactions play key roles in the determination of overall device efficiency.

Enhancement of extracellular electron transfer and bioelectricity output by synthetic porin.

PubMed

Yong, Yang-Chun; Yu, Yang-Yang; Yang, Yun; Liu, Jing; Wang, Jing-Yuan; Song, Hao

2013-02-01

The microbial fuel cell (MFC), is a promising environmental biotechnology for harvesting electricity energy from organic wastes. However, low bacterial membrane permeability of electron shuttles is a limiting factor that restricts the electron shuttle-mediated extracellular electron transfer (EET) from bacteria to electrodes, thus the electricity power output of MFCs. To this end, we heterologously expressed a porin protein OprF from Pseudomonas aeruginosa PAO1 into Escherichia coli, which dramatically increased its membrane permeability, delivering a much higher current output in MFCs than its parental strain (BL21). We found that the oprF-expression strain showed more efficient EET than its parental strain. More strikingly, the enhanced membrane permeability also rendered the oprF-expression strain an efficient usage of riboflavin as the electron shuttle, whereas its parental strain was incapable of. Our results substantiated that membrane permeability is crucial for the efficient EET, and indicated that the expression of synthetic porins could be an efficient strategy to enhance bioelectricity generation by microorganisms (including electrogenic bacteria) in MFCs. Copyright © 2012 Wiley Periodicals, Inc.

Core-shell nanophosphor architecture: toward efficient energy transport in inorganic/organic hybrid solar cells.

PubMed

Li, Qinghua; Yuan, Yongbiao; Chen, Zihan; Jin, Xiao; Wei, Tai-huei; Li, Yue; Qin, Yuancheng; Sun, Weifu

2014-08-13

In this work, a core-shell nanostructure of samarium phosphates encapsulated into a Eu(3+)-doped silica shell has been successfully fabricated, which has been confirmed by X-ray diffraction, transmission electron microscopy (TEM), and high-resolution TEM. Moreover, we report the energy transfer process from the Sm(3+) to emitters Eu(3+) that widens the light absorption range of the hybrid solar cells (HSCs) and the strong enhancement of the electron-transport of TiO2/poly(3-hexylthiophene) (P3HT) bulk heterojunction (BHJ) HSCs by introducing the unique core-shell nanoarchitecture. Furthermore, by applying femtosecond transient absorption spectroscopy, we successfully obtain the electron transport lifetimes of BHJ systems with or without incorporating the core-shell nanophosphors (NPs). Concrete evidence has been provided that the doping of core-shell NPs improves the efficiency of electron transfers from donor to acceptor, but the hole transport almost remains unchanged. In particular, the hot electron transfer lifetime was shortened from 30.2 to 16.7 ps, i.e., more than 44% faster than pure TiO2 acceptor. Consequently, a notable power conversion efficiency of 3.30% for SmPO4@Eu(3+):SiO2 blended TiO2/P3HT HSCs is achieved at 5 wt % as compared to 1.98% of pure TiO2/P3HT HSCs. This work indicates that the core-shell NPs can efficiently broaden the absorption region, facilitate electron-transport of BHJ, and enhance photovoltaic performance of inorganic/organic HSCs.

High Throughput Engineering to Revitalize a Vestigial Electron Transfer Pathway in Bacterial Photosynthetic Reaction Centers*

PubMed Central

Faries, Kaitlyn M.; Kressel, Lucas L.; Wander, Marc J.; Holten, Dewey; Laible, Philip D.; Kirmaier, Christine; Hanson, Deborah K.

2012-01-01

Photosynthetic reaction centers convert light energy into chemical energy in a series of transmembrane electron transfer reactions, each with near 100% yield. The structures of reaction centers reveal two symmetry-related branches of cofactors (denoted A and B) that are functionally asymmetric; purple bacterial reaction centers use the A pathway exclusively. Previously, site-specific mutagenesis has yielded reaction centers capable of transmembrane charge separation solely via the B branch cofactors, but the best overall electron transfer yields are still low. In an attempt to better realize the architectural and energetic factors that underlie the directionality and yields of electron transfer, sites within the protein-cofactor complex were targeted in a directed molecular evolution strategy that implements streamlined mutagenesis and high throughput spectroscopic screening. The polycistronic approach enables efficient construction and expression of a large number of variants of a heteroligomeric complex that has two intimately regulated subunits with high sequence similarity, common features of many prokaryotic and eukaryotic transmembrane protein assemblies. The strategy has succeeded in the discovery of several mutant reaction centers with increased efficiency of the B pathway; they carry multiple substitutions that have not been explored or linked using traditional approaches. This work expands our understanding of the structure-function relationships that dictate the efficiency of biological energy-conversion reactions, concepts that will aid the design of bio-inspired assemblies capable of both efficient charge separation and charge stabilization. PMID:22247556

Efficient photosensitized splitting of the thymine dimer/oxetane unit on its modifying beta-cyclodextrin by a binding electron donor.

PubMed

Tang, Wen-Jian; Song, Qin-Hua; Wang, Hong-Bo; Yu, Jing-Yu; Guo, Qing-Xiang

2006-07-07

Two modified beta-cyclodextrins (beta-CDs) with a thymine dimer and a thymine oxetane adduct respectively, TD-CD and Ox-CD, have been prepared, and utilized to bind an electron-rich chromophore, indole or N,N-dimethylaniline (DMA), to form a supramolecular complex. We have examined the photosensitized splitting of the dimer/oxetane unit in TD-CD/Ox-CD by indole or DMA via an electron-transfer pathway, and observed high splitting efficiencies of the dimer/oxetane unit. On the basis of measurements of fluorescence spectra and splitting quantum yields, it is suggested that the splitting reaction occurs in a supramolecular complex by an inclusion interaction between the modified beta-CDs and DMA or indole. The back electron transfer, which leads low splitting efficiencies for the covalently-linked chromophore-dimer/oxetane compounds, is suppressed in the non-covalently-bound complex, and the mechanism has been discussed.

Role of coherence and delocalization in photo-induced electron transfer at organic interfaces

NASA Astrophysics Data System (ADS)

Abramavicius, V.; Pranculis, V.; Melianas, A.; Inganäs, O.; Gulbinas, V.; Abramavicius, D.

2016-09-01

Photo-induced charge transfer at molecular heterojunctions has gained particular interest due to the development of organic solar cells (OSC) based on blends of electron donating and accepting materials. While charge transfer between donor and acceptor molecules can be described by Marcus theory, additional carrier delocalization and coherent propagation might play the dominant role. Here, we describe ultrafast charge separation at the interface of a conjugated polymer and an aggregate of the fullerene derivative PCBM using the stochastic Schrödinger equation (SSE) and reveal the complex time evolution of electron transfer, mediated by electronic coherence and delocalization. By fitting the model to ultrafast charge separation experiments, we estimate the extent of electron delocalization and establish the transition from coherent electron propagation to incoherent hopping. Our results indicate that even a relatively weak coupling between PCBM molecules is sufficient to facilitate electron delocalization and efficient charge separation at organic interfaces.

Stable Organic Radicals as Hole Injection Dopants for Efficient Optoelectronics.

PubMed

Bin, Zhengyang; Guo, Haoqing; Liu, Ziyang; Li, Feng; Duan, Lian

2018-02-07

Precursors of reactive organic radicals have been widely used as n-dopants in electron-transporting materials to improve electron conductivity and enhance electron injection. However, the utilization of organic radicals in hole counterparts has been ignored. In this work, stable organic radicals have been proved for the first time to be efficient dopants to enhance hole injection. From the absorbance spectra and the ultraviolet photoelectron spectra, we could observe an efficient electron transfer between the organic radical, (4-N-carbazolyl-2,6-dichlorophenyl)bis(2,4,6-trichlorophenyl)methyl (TTM-1Cz), and the widely used hole injection material, 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HAT-CN). When the unpaired electron of TTM-1Cz is transferred to HAT-CN, it would be oxidized to a TTM-1Cz cation with a newly formed lowest unoccupied molecular orbital which is quite close to the highest occupied molecular orbital (HOMO) of the hole-transporting material (HTM). In this way, the TTM-1Cz cation would promote the electron extraction from the HOMO of the HTM and improve hole injection. Using TTM-1Cz-doped HAT-CN as the hole injection layer, efficient organic light-emitting diodes with extremely low voltages can be attained.

Conductive properties of methanogenic biofilms.

PubMed

Li, Cheng; Lesnik, Keaton Larson; Liu, Hong

2018-02-01

Extracellular electron transfer between syntrophic partners needs to be efficiently maintained in methanogenic environments. Direct extracellular electron transfer via electrical current is an alternative to indirect hydrogen transfer but requires construction of conductive extracellular structures. Conductive mechanisms and relationship between conductivity and the community composition in mixed-species methanogenic biofilms are not well understood. The present study investigated conductive behaviors of methanogenic biofilms and examined the correlation between biofilm conductivity and community composition between different anaerobic biofilms enriched from the same inoculum. Highest conductivity observed in methanogenic biofilms was 71.8±4.0μS/cm. Peak-manner response of conductivity upon changes over a range of electrochemical potentials suggests that electron transfer in methanogenic biofilms occurs through redox driven super-exchange. The strong correlation observed between biofilm conductivity and Geobacter spp. in the metabolically diverse anaerobic communities suggests that the efficiency of DEET may provide pressure for microbial communities to select for species that can produce electrical conduits. Copyright © 2017 Elsevier B.V. All rights reserved.

Charge Transfer Dynamics of Highly Efficient Cyanidin-3-O- Glucoside Sensitizer for Dye-Sensitized Solar Cells

NASA Astrophysics Data System (ADS)

Prima, E. C.; Yuliarto, B.; Suyatman; Dipojono, H. K.

2016-08-01

This paper reports the novel efficiency achievement of black rice-based natural dye- sensitized solar cells. The higher dye concentration, the longer dye extraction as well as dye immersion onto a TiO2 film, and the co-adsorption addition are key strategies for improved-cell performance compared to the highest previous achievement. The black rice dye containing 1.38 mM cyanidin-3-O-glucoside has been extracted without purification for 3 weeks at dark condition and room temperature. The anatase TiO2 photoanode was dipped into dye solution within 4 days. Its electrode was firmly sealed to be a cell and was filled by I-/I3- electrolyte using vacuum technique. As a result, the overall solar-to-energy conversion efficiency was 1.49% at AM 1.5 illumination (100 mW.cm-2). The voltametric analysis has reported the interfacial electronic band edges of TiO2-Dye-Electrolyte. Furthermore, electrochemical impedance spectroscopy has shown the kinetic of interfacial electron transfer dynamics among TiO2-dye-electrolyte. The cell has the transfer resistance (Rt) of 12.5 ω, the recombination resistance (Rr) of 266.8 ω, effective electron diffusion coefficients (Dn) of 1.4 × 10-3 cm2/s, Dye-TiO2 effective electron transfer (τd) of 26.6 μs, effective diffusion length (Ln)of 33.78 μm, chemical capacitance (Cμ) of 12.43 μF, and electron lifetime (τn) of 3.32 ms.

Out-of-plane heat transfer in van der Waals stacks through electron-hyperbolic phonon coupling

NASA Astrophysics Data System (ADS)

Tielrooij, Klaas-Jan; Hesp, Niels C. H.; Principi, Alessandro; Lundeberg, Mark B.; Pogna, Eva A. A.; Banszerus, Luca; Mics, Zoltán; Massicotte, Mathieu; Schmidt, Peter; Davydovskaya, Diana; Purdie, David G.; Goykhman, Ilya; Soavi, Giancarlo; Lombardo, Antonio; Watanabe, Kenji; Taniguchi, Takashi; Bonn, Mischa; Turchinovich, Dmitry; Stampfer, Christoph; Ferrari, Andrea C.; Cerullo, Giulio; Polini, Marco; Koppens, Frank H. L.

2018-01-01

Van der Waals heterostructures have emerged as promising building blocks that offer access to new physics, novel device functionalities and superior electrical and optoelectronic properties1-7. Applications such as thermal management, photodetection, light emission, data communication, high-speed electronics and light harvesting8-16 require a thorough understanding of (nanoscale) heat flow. Here, using time-resolved photocurrent measurements, we identify an efficient out-of-plane energy transfer channel, where charge carriers in graphene couple to hyperbolic phonon polaritons17-19 in the encapsulating layered material. This hyperbolic cooling is particularly efficient, giving picosecond cooling times for hexagonal BN, where the high-momentum hyperbolic phonon polaritons enable efficient near-field energy transfer. We study this heat transfer mechanism using distinct control knobs to vary carrier density and lattice temperature, and find excellent agreement with theory without any adjustable parameters. These insights may lead to the ability to control heat flow in van der Waals heterostructures.

Catalytic four-electron reduction of O2 via rate-determining proton-coupled electron transfer to a dinuclear cobalt-μ-1,2-peroxo complex.

PubMed

Fukuzumi, Shunichi; Mandal, Sukanta; Mase, Kentaro; Ohkubo, Kei; Park, Hyejin; Benet-Buchholz, Jordi; Nam, Wonwoo; Llobet, Antoni

2012-06-20

Four-electron reduction of O(2) by octamethylferrocene (Me(8)Fc) occurs efficiently with a dinuclear cobalt-μ-1,2-peroxo complex, 1, in the presence of trifluoroacetic acid in acetonitrile. Kinetic investigations of the overall catalytic reaction and each step in the catalytic cycle showed that proton-coupled electron transfer from Me(8)Fc to 1 is the rate-determining step in the catalytic cycle.

Efficient charge transfer and utilization of near-infrared solar spectrum by ytterbium and thulium codoped gadolinium molybdate (Gd2(MoO4)3:Yb/Tm) nanophosphor in hybrid solar cells.

PubMed

Sun, Weifu; Chen, Zihan; Zhang, Qin; Zhou, Junli; Li, Feng; Jin, Xiao; Li, Dongyu; Li, Qinghua

2016-11-09

In this work, thulium and ytterbium codoped gadolinium molybdate (Gd 2 (MoO 4 ) 3 :Yb/Tm) nanophosphors (NPs) have been synthesized, followed by being incorporated into a photo-catalytic titania (TiO 2 ) nanoparticle layer. In detail, morphology and phase identification of the prepared NPs are first characterized and then the up-conversion of the Gd 2 (MoO 4 ) 3 :Yb/Tm NPs is studied. Electron transfer dynamics after interfacing with bare or NP-doped electron donor TiO 2 and the corresponding photovoltaic performance of solar cells are explored. The results show that Gd 2 (MoO 4 ) 3 :Yb/Tm NPs excited at 976 nm exhibit intense blue (460-498 nm) and weak red (627-669 nm) emissions. The lifetime of electron transfer is shortened from 817 to 316 ps after incorporating NPs and correspondingly the electron transfer rate outstrips by 3 times that of the bare TiO 2 . Consequently, a notable power conversion efficiency of 4.15% is achieved as compared to 3.17% of pure TiO 2 /PTB7. This work demonstrates that the co-doping of robust rare earth ions with different unique functions can widen the harvesting range of the solar spectrum, boost electron transfer rate and eventually strengthen device performance, without complicated interfacial and structural engineering.

Interfacial Charge Transfer States in Condensed Phase Systems

NASA Astrophysics Data System (ADS)

Vandewal, Koen

2016-05-01

Intermolecular charge transfer (CT) states at the interface between electron-donating (D) and electron-accepting (A) materials in organic thin films are characterized by absorption and emission bands within the optical gap of the interfacing materials. CT states efficiently generate charge carriers for some D-A combinations, and others show high fluorescence quantum efficiencies. These properties are exploited in organic solar cells, photodetectors, and light-emitting diodes. This review summarizes experimental and theoretical work on the electronic structure and interfacial energy landscape at condensed matter D-A interfaces. Recent findings on photogeneration and recombination of free charge carriers via CT states are discussed, and relations between CT state properties and optoelectronic device parameters are clarified.

Effects of oxidants and reductants on the efficiency of excitation transfer in green photosynthetic bacteria

NASA Technical Reports Server (NTRS)

Wang, J.; Brune, D. C.; Blankenship, R. E.

1990-01-01

The efficiency of energy transfer in chlorosome antennas in the green sulfur bacteria Chlorobium vibrioforme and Chlorobium limicola was found to be highly sensitive to the redox potential of the suspension. Energy transfer efficiencies were measured by comparing the absorption spectrum of the bacteriochlorophyll c or d pigments in the chlorosome to the excitation spectrum for fluorescence arising from the chlorosome baseplate and membrane-bound antenna complexes. The efficiency of energy transfer approaches 100% at low redox potentials induced by addition of sodium dithionite or other strong reductants, and is lowered to 10-20% under aerobic conditions or after addition of a variety of membrane-permeable oxidizing agents. The redox effect on energy transfer is observed in whole cells, isolated membranes and purified chlorosomes, indicating that the modulation of energy transfer efficiency arises within the antenna complexes and is not directly mediated by the redox state of the reaction center. It is proposed that chlorosomes contain a component that acts as a highly quenching center in its oxidized state, but is an inefficient quencher when reduced by endogenous or exogenous reductants. This effect may be a control mechanism that prevents cellular damage resulting from reaction of oxygen with reduced low-potential electron acceptors found in the green sulfur bacteria. The redox modulation effect is not observed in the green gliding bacterium Chloroflexus aurantiacus, which contains chlorosomes but does not contain low-potential electron acceptors.

Crystal Structure and Catalytic Mechanism of 7-Hydroxymethyl Chlorophyll a Reductase*

PubMed Central

Wang, Xiao; Liu, Lin

2016-01-01

7-Hydroxymethyl chlorophyll a reductase (HCAR) catalyzes the second half-reaction in chlorophyll b to chlorophyll a conversion. HCAR is required for the degradation of light-harvesting complexes and is necessary for efficient photosynthesis by balancing the chlorophyll a/b ratio. Reduction of the hydroxymethyl group uses redox cofactors [4Fe-4S] cluster and FAD to transfer electrons and is difficult because of the strong carbon-oxygen bond. Here, we report the crystal structure of Arabidopsis HCAR at 2.7-Å resolution and reveal that two [4Fe-4S]clusters and one FAD within a very short distance form a consecutive electron pathway to the substrate pocket. In vitro kinetic analysis confirms the ferredoxin-dependent electron transport chain, thus supporting a proton-activated electron transfer mechanism. HCAR resembles a partial reconstruction of an archaeal F420-reducing [NiFe] hydrogenase, which suggests a common mode of efficient proton-coupled electron transfer through conserved cofactor arrangements. Furthermore, the trimeric form of HCAR provides a biological clue of its interaction with light-harvesting complex II. PMID:27072131

Nonadiabatic dynamics of photo-induced proton-coupled electron transfer reactions via ring-polymer surface hopping

NASA Astrophysics Data System (ADS)

Shakib, Farnaz; Huo, Pengfei

Photo-induced proton-coupled electron transfer reactions (PCET) are at the heart of energy conversion reactions in photocatalysis. Here, we apply the recently developed ring-polymer surface-hopping (RPSH) approach to simulate the nonadiabatic dynamics of photo-induced PCET. The RPSH method incorporates ring-polymer (RP) quantization of the proton into the fewest-switches surface-hopping (FSSH) approach. Using two diabatic electronic states, corresponding to the electron donor and acceptor states, we model photo-induced PCET with the proton described by a classical isomorphism RP. From the RPSH method, we obtain numerical results that are comparable to those obtained when the proton is treated quantum mechanically. This accuracy stems from incorporating exact quantum statistics, such as proton tunnelling, into approximate quantum dynamics. Additionally, RPSH offers the numerical accuracy along with the computational efficiency. Namely, compared to the FSSH approach in vibronic representation, there is no need to calculate a massive number of vibronic states explicitly. This approach opens up the possibility to accurately and efficiently simulate photo-induced PCET with multiple transferring protons or electrons.

Preliminary design development of 100 KW rotary power transfer device

NASA Technical Reports Server (NTRS)

Weinberger, S. M.

1981-01-01

Contactless power transfer devices for transferring electrical power across a rotating spacecraft interface were studied. A power level of 100 KW was of primary interest and the study was limited to alternating current devices. Rotary transformers and rotary capacitors together with the required dc to ac power conditioning electronics were examined. Microwave devices were addressed. The rotary transformer with resonant circuit power conditioning was selected as the most feasible approach. The rotary capacitor would be larger while microwave devices would be less efficient. A design analysis was made of a 100 KW, 20 kHz power transfer device consisting of a rotary transformer, power conditioning electronics, drive mechanism and heat rejection system. The size, weight and efficiency of the device were determined. The characteristics of a baseline slip ring were presented. Aspects of testing the 100 KW power transfer device were examined. The power transfer device is a feasible concept which can be implemented using presently available technologies.

Optical determination of charge transfer times from indoline dyes to ZnO in solid state dye-sensitized solar cells

NASA Astrophysics Data System (ADS)

Meyenburg, I.; Hofeditz, N.; Ruess, R.; Rudolph, M.; Schlettwein, D.; Heimbrodt, W.

2018-05-01

We studied the electron transfer at the interface of organic-inorganic hybrids consisting of indoline derivatives (D149 and D131) on ZnO substrates using a new optical method. We revealed the electron transfer times from the excited dye, e.g. the excitons formed in the dye aggregates to the ZnO substrate by analyzing the photoluminescence transients of the excitons after femtosecond excitation and applying kinetic model calculations. We reveal the changes of the electron transfer times by applying electrical bias. Pushing the Fermi energy of the ZnO substrate towards the excited dye level the transfer time gets longer and eventually the electron transfer is suppressed. The level alignment between the excited dye state and the ZnO Fermi-level is estimated. The excited state of D131 is about 100 meV higher than the respective state of D149 compared to the ZnO conduction band. This leads to shorter electron transfer times and eventually to higher quantum efficiencies of the solar cells.

Comparative study of alkylthiols and alkylamines for the phase transfer of gold nanoparticles from an aqueous phase to n-hexane.

PubMed

Li, Lingxiangyu; Leopold, Kerstin; Schuster, Michael

2013-05-01

An efficient ligand-assisted phase transfer method has been developed to transfer gold nanoparticles (Au-NPs, d: 5-25 nm) from an aqueous solution to n-hexane. Four different ligands, namely 1-dodecanethiol (DDT), 1-octadecanethiol (ODT), dodecylamine (DDA), and octadecylamine (ODA) were investigated, and DDT was found to be the most efficient ligand. It appears that the molar ratio of DDT to Au-NPs is a critical factor affecting the transfer efficiency, and 270-310 is found to be the optimum range, under which the transfer efficiency is >96%. Moreover, the DDT-assisted phase transfer can preserve the shape and size of the Au-NPs, which was confirmed by UV-vis spectra and transmission electron microscopy (TEM). Additionally, the transferred Au-NPs still can be well dispersed in the n-hexane phase and remain stable for at least 2 weeks. On the other hand, the ODT-, DDA-, and ODA-assisted phase transfer is fraught with problems either related to transfer efficiency or NPs aggregation. Overall, the DDT-assisted phase transfer of Au-NPs provides a rapid and efficient method to recover Au-NPs from an aqueous solution to n-hexane. Copyright © 2013 Elsevier Inc. All rights reserved.

LASER APPLICATIONS AND OTHER TOPICS IN QUANTUM ELECTRONICS: Hydrodynamic efficiency of laser-induced transfer of matter

NASA Astrophysics Data System (ADS)

Isakov, Vladimir A.; Kanavin, Andrey P.; Nasibov, A. S.

2007-04-01

A one-dimensional analytic hydrodynamic model of the direct laser-induced transfer of matter is considered. The efficiency of pulsed laser radiation energy conversion to the kinetic energy of the ejected matter is determined. It is shown that the hydrodynamic efficiency of the process for the layers of matter of thickness exceeding the laser radiation absorption depth is determined by the adiabatic index of the evaporated matter.

Efficiency of ablative loading of material upon the fast-electron transfer of absorbed laser energy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gus'kov, Sergei Yu; Kasperczuk, A; Pisarczyk, T

2006-05-31

We present the results of experiments on the short-term irradiation of a solid material by a laser beam. The data testify to a rise in efficiency of the energy transfer from the laser pulse to a shock wave due to the fast-electron energy transfer. The experiments were performed with massive aluminium targets on the PALS iodine laser, whose pulse duration (0.4 ns) was much shorter than the time of shock decay and crater formation in the target (50-200 ns). The irradiation experiments were carried out using the fundamental laser harmonic (1.315 {mu}m) with an energy of 360 J. The greatermore » part of the experiments were performed for the radiation intensity exceeding 10{sup 15} W cm{sup -2}, which corresponded to the efficient generation of fast electrons under the conditions where the relatively long-wavelength iodine-laser radiation was employed. The irradiation intensity was varied by varying the laser beam radius for a specified pulse energy. (interaction of laser radiation with matter. laser plasma)« less

Hot phonon effect on electron velocity saturation in GaN: A second look

NASA Astrophysics Data System (ADS)

Khurgin, Jacob; Ding, Yujie J.; Jena, Debdeep

2007-12-01

A theoretical model is developed for electron velocity saturation in high power GaN transistors. It is shown that electron velocity at high electric fields is reduced due to heating of electron gas since the high density of nonequilibrium LO phonons cannot efficiently transfer heat to the lattice. However, the resulting degradation of electron velocity is found to be weaker than previously reported. The results are compared with experimental data, and the ways to improve the efficiency of cooling the electron gas to increase the drift velocity are discussed.

Improving the efficiency of water splitting in dye-sensitized solar cells by using a biomimetic electron transfer mediator

PubMed Central

Zhao, Yixin; Swierk, John R.; Megiatto, Jackson D.; Sherman, Benjamin; Youngblood, W. Justin; Qin, Dongdong; Lentz, Deanna M.; Moore, Ana L.; Moore, Thomas A.; Gust, Devens; Mallouk, Thomas E.

2012-01-01

Photoelectrochemical water splitting directly converts solar energy to chemical energy stored in hydrogen, a high energy density fuel. Although water splitting using semiconductor photoelectrodes has been studied for more than 40 years, it has only recently been demonstrated using dye-sensitized electrodes. The quantum yield for water splitting in these dye-based systems has, so far, been very low because the charge recombination reaction is faster than the catalytic four-electron oxidation of water to oxygen. We show here that the quantum yield is more than doubled by incorporating an electron transfer mediator that is mimetic of the tyrosine-histidine mediator in Photosystem II. The mediator molecule is covalently bound to the water oxidation catalyst, a colloidal iridium oxide particle, and is coadsorbed onto a porous titanium dioxide electrode with a Ruthenium polypyridyl sensitizer. As in the natural photosynthetic system, this molecule mediates electron transfer between a relatively slow metal oxide catalyst that oxidizes water on the millisecond timescale and a dye molecule that is oxidized in a fast light-induced electron transfer reaction. The presence of the mediator molecule in the system results in photoelectrochemical water splitting with an internal quantum efficiency of approximately 2.3% using blue light. PMID:22547794

Fragment-based Quantum Mechanical/Molecular Mechanical Simulations of Thermodynamic and Kinetic Process of the Ru2+-Ru3+ Self-Exchange Electron Transfer.

PubMed

Zeng, Xiancheng; Hu, Xiangqian; Yang, Weitao

2012-12-11

A fragment-based fractional number of electron (FNE) approach, is developed to study entire electron transfer (ET) processes from the electron donor region to the acceptor region in condensed phase. Both regions are described by the density-fragment interaction (DFI) method while FNE as an efficient ET order parameter is applied to simulate the electron transfer process. In association with the QM/MM energy expression, the DFI-FNE method is demonstrated to describe ET processes robustly with the Ru 2+ -Ru 3+ self-exchange ET as a proof-of-concept example. This method allows for systematic calculations of redox free energies, reorganization energies, and electronic couplings, and the absolute ET rate constants within the Marcus regime.

A Combined Theoretical and Experimental Study of Dissociation of Charge Transfer States at the Donor-Acceptor Interface of Organic Solar Cells.

PubMed

Tscheuschner, Steffen; Bässler, Heinz; Huber, Katja; Köhler, Anna

2015-08-13

The observation that in efficient organic solar cells almost all electron-hole pairs generated at the donor-acceptor interface escape from their mutual coulomb potential remains to be a conceptual challenge. It has been argued that it is the excess energy dissipated in the course of electron or hole transfer at the interface that assists this escape process. The current work demonstrates that this concept is unnecessary to explain the field dependence of electron-hole dissociation. It is based upon the formalism developed by Arkhipov and co-workers as well as Baranovskii and co-workers. The key idea is that the binding energy of the dissociating "cold" charge-transfer state is reduced by delocalization of the hole along the polymer chain, quantified in terms of an "effective mass", as well as the fractional strength of dipoles existent at the interface in the dark. By covering a broad parameter space, we determine the conditions for efficient electron-hole dissociation. Spectroscopy of the charge-transfer state on bilayer solar cells as well as measurements of the field dependence of the dissociation yield over a broad temperature range support the theoretical predictions.

Interplay between structure, stoichiometry, and electron transfer dynamics in SILAR-based quantum dot-sensitized oxides.

PubMed

Wang, Hai; Barceló, Irene; Lana-Villarreal, Teresa; Gómez, Roberto; Bonn, Mischa; Cánovas, Enrique

2014-10-08

We quantify the rate and efficiency of picosecond electron transfer (ET) from PbS nanocrystals, grown by successive ionic layer adsorption and reaction (SILAR), into a mesoporous SnO2 support. Successive SILAR deposition steps allow for stoichiometry- and size-variation of the QDs, characterized using transmission electron microscopy. Whereas for sulfur-rich (p-type) QD surfaces substantial electron trapping at the QD surface occurs, for lead-rich (n-type) QD surfaces, the QD trapping channel is suppressed and the ET efficiency is boosted. The ET efficiency increase achieved by lead-rich QD surfaces is found to be QD-size dependent, increasing linearly with QD surface area. On the other hand, ET rates are found to be independent of both QD size and surface stoichiometry, suggesting that the donor-acceptor energetics (constituting the driving force for ET) are fixed due to Fermi level pinning at the QD/oxide interface. Implications of our results for QD-sensitized solar cell design are discussed.

Enhanced Ionization of Embedded Clusters by Electron-Transfer-Mediated Decay in Helium Nanodroplets.

PubMed

LaForge, A C; Stumpf, V; Gokhberg, K; von Vangerow, J; Stienkemeier, F; Kryzhevoi, N V; O'Keeffe, P; Ciavardini, A; Krishnan, S R; Coreno, M; Prince, K C; Richter, R; Moshammer, R; Pfeifer, T; Cederbaum, L S; Mudrich, M

2016-05-20

We report the observation of electron-transfer-mediated decay (ETMD) involving magnesium (Mg) clusters embedded in helium (He) nanodroplets. ETMD is initiated by the ionization of He followed by removal of two electrons from the Mg clusters of which one is transferred to the He ion while the other electron is emitted into the continuum. The process is shown to be the dominant ionization mechanism for embedded clusters for photon energies above the ionization potential of He. For Mg clusters larger than five atoms we observe stable doubly ionized clusters. Thus, ETMD provides an efficient pathway to the formation of doubly ionized cold species in doped nanodroplets.

Enhanced Electron Affinity and Exciton Confinement in Exciplex-Type Host: Power Efficient Solution-Processed Blue Phosphorescent OLEDs with Low Turn-on Voltage.

PubMed

Ban, Xinxin; Sun, Kaiyong; Sun, Yueming; Huang, Bin; Jiang, Wei

2016-01-27

A benzimidazole/phosphine oxide hybrid 1,3,5-tris(1-(4-(diphenylphosphoryl)phenyl)-1H-benzo[d]imidazol-2-yl)benzene (TPOB) was newly designed and synthesized as the electron-transporting component to form an exciplex-type host with the conventional hole-transporting material tris(4-carbazoyl-9-ylphenyl)amine (TCTA). Because of the enhanced triplet energy and electron affinity of TPOB, the energy leakage from exciplex-state to the constituting molecule was eliminated. Using energy transfer from exciplex-state, solution-processed blue phosphorescent organic light-emitting diodes (PHOLEDs) achieved an extremely low turn-on voltage of 2.8 V and impressively high power efficiency of 22 lm W(-1). In addition, the efficiency roll-off was very small even at luminance up to 10 000 cd m(-2), which suggested the balanced charge transfer in the emission layer. This study demonstrated that molecular modulation was an effective way to develop efficient exciplex-type host for high performanced PHOLEDs.

Robust Stacking-Independent Ultrafast Charge Transfer in MoS2/WS2 Bilayers.

PubMed

Ji, Ziheng; Hong, Hao; Zhang, Jin; Zhang, Qi; Huang, Wei; Cao, Ting; Qiao, Ruixi; Liu, Can; Liang, Jing; Jin, Chuanhong; Jiao, Liying; Shi, Kebin; Meng, Sheng; Liu, Kaihui

2017-12-26

Van der Waals-coupled two-dimensional (2D) heterostructures have attracted great attention recently due to their high potential in the next-generation photodetectors and solar cells. The understanding of charge-transfer process between adjacent atomic layers is the key to design optimal devices as it directly determines the fundamental response speed and photon-electron conversion efficiency. However, general belief and theoretical studies have shown that the charge transfer behavior depends sensitively on interlayer configurations, which is difficult to control accurately, bringing great uncertainties in device designing. Here we investigate the ultrafast dynamics of interlayer charge transfer in a prototype heterostructure, the MoS 2 /WS 2 bilayer with various stacking configurations, by optical two-color ultrafast pump-probe spectroscopy. Surprisingly, we found that the charge transfer is robust against varying interlayer twist angles and interlayer coupling strength, in time scale of ∼90 fs. Our observation, together with atomic-resolved transmission electron characterization and time-dependent density functional theory simulations, reveals that the robust ultrafast charge transfer is attributed to the heterogeneous interlayer stretching/sliding, which provides additional channels for efficient charge transfer previously unknown. Our results elucidate the origin of transfer rate robustness against interlayer stacking configurations in optical devices based on 2D heterostructures, facilitating their applications in ultrafast and high-efficient optoelectronic and photovoltaic devices in the near future.

Ultra high energy electrons powered by pulsar rotation.

PubMed

Mahajan, Swadesh; Machabeli, George; Osmanov, Zaza; Chkheidze, Nino

2013-01-01

A new mechanism of particle acceleration, driven by the rotational slow down of the Crab pulsar, is explored. The rotation, through the time dependent centrifugal force, can efficiently excite unstable Langmuir waves in the electron-positron (hereafter e(±)) plasma of the star magnetosphere. These waves, then, Landau damp on electrons accelerating them in the process. The net transfer of energy is optimal when the wave growth and the Landau damping times are comparable and are both very short compared to the star rotation time. We show, by detailed calculations, that these are precisely the conditions for the parameters of the Crab pulsar. This highly efficient route for energy transfer allows the electrons in the primary beam to be catapulted to multiple TeV (~ 100 TeV) and even PeV energy domain. It is expected that the proposed mechanism may, unravel the puzzle of the origin of ultra high energy cosmic ray electrons.

Photoinduced triplet-triplet energy transfer in a 2-ureido-4(1H)-pyrimidinone-bridged, quadruply hydrogen-bonded ferrocene-fullerene assembly.

PubMed

Feng, Ke; Yu, Mao-Lin; Wang, Su-Min; Wang, Ge-Xia; Tung, Chen-Ho; Wu, Li-Zhu

2013-01-14

2-Ureido-4(1H)-pyrimidinone-bridged ferrocene-fullerene assembly I is designed and synthesized for elaborating the photoinduced electron-transfer processes in self-complementary quadruply hydrogen-bonded modules. Unexpectedly, steady-state and time-resolved spectroscopy reveal an inefficient electron-transfer process from the ferrocene to the singlet or triplet excited state of the fullerene, although the electron-transfer reactions are thermodynamically feasible. Instead, an effective intra-assembly triplet-triplet energy-transfer process is found to be operative in assembly I with a rate constant of 9.2×10(5) s(-1) and an efficiency of 73% in CH(2)Cl(2) at room temperature. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Simulation-Based Approach to Determining Electron Transfer Rates Using Square-Wave Voltammetry.

PubMed

Dauphin-Ducharme, Philippe; Arroyo-Currás, Netzahualcóyotl; Kurnik, Martin; Ortega, Gabriel; Li, Hui; Plaxco, Kevin W

2017-05-09

The efficiency with which square-wave voltammetry differentiates faradic and charging currents makes it a particularly sensitive electroanalytical approach, as evidenced by its ability to measure nanomolar or even picomolar concentrations of electroactive analytes. Because of the relative complexity of the potential sweep it uses, however, the extraction of detailed kinetic and mechanistic information from square-wave data remains challenging. In response, we demonstrate here a numerical approach by which square-wave data can be used to determine electron transfer rates. Specifically, we have developed a numerical approach in which we model the height and the shape of voltammograms collected over a range of square-wave frequencies and amplitudes to simulated voltammograms as functions of the heterogeneous rate constant and the electron transfer coefficient. As validation of the approach, we have used it to determine electron transfer kinetics in both freely diffusing and diffusionless surface-tethered species, obtaining electron transfer kinetics in all cases in good agreement with values derived using non-square-wave methods.

Charge Transfer from n-Doped Nanocrystals: Mimicking Intermediate Events in Multielectron Photocatalysis.

PubMed

Wang, Junhui; Ding, Tao; Wu, Kaifeng

2018-06-12

In multielectron photocatalytic reactions, an absorbed photon triggers charge transfer from the light-harvester to the attached catalyst, leaving behind a charge of the opposite sign in the light-harvester. If this charge is not scavenged before the absorption of the following photons, photoexcitation generates not neutral but charged excitons from which the extraction of charges should become more difficult. This is potentially an efficiency-limiting intermediate event in multielectron photocatalysis. To study the charge dynamics in this event, we doped CdS nanocrystal quantum dots (QDs) with an extra electron and measured hole transfer from n-doped QDs to attached acceptors. We find that the Auger decay of charged excitons lowers the charge separation yield to 68.6% from 98.4% for neutral excitons. In addition, the hole transfer rate in the presence of two electrons (1290 ps) is slower than that in the presence one electron (776 ps), and the recombination rate of charge separated states is about 2 times faster in the former case. This model study provides important insights into possible efficiency-limiting intermediate events involved in photocatalysis.

Acid/base-regulated reversible electron transfer disproportionation of N–N linked bicarbazole and biacridine derivatives† †Electronic supplementary information (ESI) available: Experimental information, synthesis and characterization data, NMR spectra, solid state NMR data, X-ray data, ESR spectra, UV-Vis-NIR spectra, fluorescence spectra, kinetic experiments, theoretical calculations, Tables S1–S8, Scheme S1, Fig. S1–12, References. CCDC 1025063, 1038914, 1049677 and 1040722. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c5sc00946d

PubMed Central

Pandit, Palash; Yamamoto, Koji; Nakamura, Toshikazu; Nishimura, Katsuyuki; Kurashige, Yuki; Yanai, Takeshi; Nakamura, Go; Masaoka, Shigeyuki; Furukawa, Ko; Yakiyama, Yumi; Kawano, Masaki

2015-01-01

Regulation of electron transfer on organic substances by external stimuli is a fundamental issue in science and technology, which affects organic materials, chemical synthesis, and biological metabolism. Nevertheless, acid/base-responsive organic materials that exhibit reversible electron transfer have not been well studied and developed, owing to the difficulty in inventing a mechanism to associate acid/base stimuli and electron transfer. We discovered a new phenomenon in which N–N linked bicarbazole (BC) and tetramethylbiacridine (TBA) derivatives undergo electron transfer disproportionation by acid stimulus, forming their stable radical cations and reduced species. The reaction occurs through a biradical intermediate generated by the acid-triggered N–N bond cleavage reaction of BC or TBA, which acts as a two electron acceptor to undergo electron transfer reactions with two equivalents of BC or TBA. In addition, in the case of TBA the disproportionation reaction is highly reversible through neutralization with NEt3, which recovers TBA through back electron transfer and N–N bond formation reactions. This highly reversible electron transfer reaction is possible due to the association between the acid stimulus and electron transfer via the acid-regulated N–N bond cleavage/formation reactions which provide an efficient switching mechanism, the ability of the organic molecules to act as multi-electron donors and acceptors, the extraordinary stability of the radical species, the highly selective reactivity, and the balance of the redox potentials. This discovery provides new design concepts for acid/base-regulated organic electron transfer systems, chemical reagents, or organic materials. PMID:29218181

Storage and retrieval of quantum information with a hybrid optomechanics-spin system

NASA Astrophysics Data System (ADS)

Feng, Zhi-Bo; Zhang, Jian-Qi; Yang, Wan-Li; Feng, Mang

2016-08-01

We explore an efficient scheme for transferring the quantum state between an optomechanical cavity and an electron spin of diamond nitrogen-vacancy center. Assisted by a mechanical resonator, quantum information can be controllably stored (retrieved) into (from) the electron spin by adjusting the external field-induced detuning or coupling. Our scheme connects effectively the cavity photon and the electron spin and transfers quantum states between two regimes with large frequency difference. The experimental feasibility of our protocol is justified with accessible laboratory parameters.

Engineering coherence among excited states in synthetic heterodimer systems.

PubMed

Hayes, Dugan; Griffin, Graham B; Engel, Gregory S

2013-06-21

The design principles that support persistent electronic coherence in biological light-harvesting systems are obscured by the complexity of such systems. Some electronic coherences in these systems survive for hundreds of femtoseconds at physiological temperatures, suggesting that coherent dynamics may play a role in photosynthetic energy transfer. Coherent effects may increase energy transfer efficiency relative to strictly incoherent transfer mechanisms. Simple, tractable, manipulable model systems are required in order to probe the fundamental physics underlying these persistent electronic coherences, but to date, these quantum effects have not been observed in small molecules. We have engineered a series of rigid synthetic heterodimers that can serve as such a model system and observed quantum beating signals in their two-dimensional electronic spectra consistent with the presence of persistent electronic coherences.

The charger transfer electronic coupling in diabatic perspective: A multi-state density functional theory study

NASA Astrophysics Data System (ADS)

Guo, Xinwei; Qu, Zexing; Gao, Jiali

2018-01-01

The multi-state density functional theory (MSDFT) provides a convenient way to estimate electronic coupling of charge transfer processes based on a diabatic representation. Its performance has been benchmarked against the HAB11 database with a mean unsigned error (MUE) of 17 meV between MSDFT and ab initio methods. The small difference may be attributed to different representations, diabatic from MSDFT and adiabatic from ab initio calculations. In this discussion, we conclude that MSDFT provides a general and efficient way to estimate the electronic coupling for charge-transfer rate calculations based on the Marcus-Hush model.

Photoinduced electron transfer interaction of anthraquinones with aniline quenchers: Influence of methyl substitution in aniline donors

NASA Astrophysics Data System (ADS)

Sivakumar, V.; Ponnamma, Deepalekshmi; Hussein, Yasser H. A.

2017-02-01

Photoinduced electron transfer between triplet state of 9,10-anthraquinone (AQ) and its two derivatives: 2-chloro-9,10-anthraquinone (CAQ) and sodium anthraquinone-2-sulfonate (AQS) and ground state aniline (AN) and its dimethyl substitutions: 2,3-dimethylaniline (2,3-DMA), 2,6-dimethylaniline (2,6-DMA), 3,5-dimethylaniline (3,5-DMA) and N,N-dimethylaniline (N,N-DMA) is studied using nanosecond laser flash photolysis at room temperature. Detection of radical bands of quinone anions and aniline cations along with their formation and/or decay kinetics are used to confirm the electron transfer (ET) process. In MeCN medium, AN quenches the triplet state of CAQ (CAQT) but not the triplets AQT or AQST. However in aqueous medium, AN quenches AQST and forms radical ion pair. All the DMAs can react through ET with all the triplet quinones at different degrees of efficiency in MeCN medium. Noticeably, the ring substituted DMAs are less efficient in electron donation to AQT or AQST while the N,N-DMA shows high efficiency in donating electron to all triplet quinones in MeCN medium. Charge distribution of donor molecules, in MeCN medium is calculated using density functional theory (DFT), and shows an enhancement of electron density of the ring of N,N-DMA, making it an ideal electron donor for ET studies compared to other DMAs. This systematic selection and usage of anilines with electrochemically tunable quinones can be viewed as a working model of donor-acceptor system that can be utilized in photoinduced ET applications.

Effect of proton transfer on the electronic coupling in DNA

NASA Astrophysics Data System (ADS)

Rak, Janusz; Makowska, Joanna; Voityuk, Alexander A.

2006-06-01

The effects of single and double proton transfer within Watson-Crick base pairs on donor-acceptor electronic couplings, Vda, in DNA are studied on the bases of quantum chemical calculations. Four dimers [AT,AT], [GC,GC], [GC,AT] and [GC,TA)] are considered. Three techniques - the generalized Mulliken-Hush scheme, the fragment charge method and the diabatic states method - are employed to estimate Vda for hole transfer between base pairs. We show that both single- and double proton transfer (PT) reactions may substantially affect the electronic coupling in DNA. The electronic coupling in [AT,AT] is predicted to be most sensitive to PT. Single PT within the first base pair in the dimer leads to increase in the hole transfer efficiency by a factor of 4, while proton transfer within the second pair should substantially, by 2.7 times, decrease the rate of charge transfer. Thus, directional asymmetry of the PT effects on the electronic coupling is predicted. The changes in the Vda matrix elements correlate with the topological properties of orbitals of donor and acceptor and can be qualitatively rationalized in terms of resonance structures of donor and acceptor. Atomic pair contributions to the Vda matrix elements are also analyzed.

Quantitative Kα line spectroscopy for energy transport in ultra-intense laser plasma interaction

NASA Astrophysics Data System (ADS)

Zhang, Z.; Nishimura, H.; Namimoto, T.; Fujioka, S.; Arikawa, Y.; Nakai, M.; Koga, M.; Shiraga, H.; Kojima, S.; Azechi, H.; Ozaki, T.; Chen, H.; Pakr, J.; Williams, G. J.; Nishikino, M.; Kawachi, T.; Sagisaka, A.; Orimo, S.; Ogura, K.; Pirozhkov, A.; Yogo, A.; Kiriyama, H.; Kondo, K.; Okano, Y.

2012-10-01

X-ray line spectra ranging from 17 to 77 keV were quantitatively measured with a Laue spectrometer, composed of a cylindrically curved crystal and a detector. The absolute sensitivity of the spectrometer system was calibrated using pre-characterized laser-produced x-ray sources and radioisotopes, for the detectors and crystal respectively. The integrated reflectivity for the crystal is in good agreement with predictions by an open code for x-ray diffraction. The energy transfer efficiency from incident laser beams to hot electrons, as the energy transfer agency for Au Kα x-ray line emissions, is derived as a consequence of this work. By considering the hot electron temperature, the transfer efficiency from LFEX laser to Au plate target is about 8% to 10%.

Ultrafast Electron Transfer across a Nanocapsular Wall: Coumarins as Donors, Viologen as Acceptor, and Octa Acid Capsule as the Mediator.

PubMed

Chuang, Chi-Hung; Porel, Mintu; Choudhury, Rajib; Burda, Clemens; Ramamurthy, V

2018-01-11

Results of our study on ultrafast electron transfer (eT) dynamics from coumarins (coumarin-1, coumarin-480, and coumarin-153) incarcerated within octa acid (OA) capsules as electron donors to methyl viologen dissolved in water as acceptor are presented. Upon photoexcitation, coumarin inside the OA capsule transfers an electron to the acceptor electrostatically attached to the capsule leading to a long-lived radical-ion pair separated by the OA capsular wall. This charge-separated state returns to the neutral ground state via back electron transfer on the nanosecond time scale. This system allows for ultrafast electron transfer processes through a molecular wall from the apolar capsular interior to the highly polar (aqueous) environment on the femtosecond time scale. Employing femtosecond transient absorption spectroscopy, distinct rates of both forward (1-25 ps) and backward eT (700-1200 ps) processes were measured. Further understanding of the energetics is provided using Rehm-Weller analysis for the investigated photoinduced eT reactions. The results provide the rates of the eT across a molecular wall, akin to an isotropic solution, depending on the standard free energy of the reaction. The insights from this work could be utilized in the future design of efficient electron transfer processes across interfaces separating apolar and polar environments.

Hybrid fusions show that inter-monomer electron transfer robustly supports cytochrome bc{sub 1} function in vivo

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ekiert, Robert; Czapla, Monika; Sarewicz, Marcin

2014-08-22

Highlights: • We used hybrid fusion bc{sub 1} complex to test inter-monomer electron transfer in vivo. • Cross-inactivated complexes were able to sustain photoheterotrophic growth. • Inter-monomer electron transfer supports catalytic cycle in vivo. • bc{sub 1} dimer is functional even when cytochrome b subunits come from different species. - Abstract: Electronic connection between Q{sub o} and Q{sub i} quinone catalytic sites of dimeric cytochrome bc{sub 1} is a central feature of the energy-conserving Q cycle. While both the intra- and inter-monomer electron transfers were shown to connect the sites in the enzyme, mechanistic and physiological significance of the lattermore » remains unclear. Here, using a series of mutated hybrid cytochrome bc{sub 1}-like complexes, we show that inter-monomer electron transfer robustly sustains the function of the enzyme in vivo, even when the two subunits in a dimer come from different species. This indicates that minimal requirement for bioenergetic efficiency is to provide a chain of cofactors for uncompromised electron flux between the catalytic sites, while the details of protein scaffold are secondary.« less

Distal [FeS]-Cluster Coordination in [NiFe]-Hydrogenase Facilitates Intermolecular Electron Transfer

PubMed Central

Petrenko, Alexander; Stein, Matthias

2017-01-01

Biohydrogen is a versatile energy carrier for the generation of electric energy from renewable sources. Hydrogenases can be used in enzymatic fuel cells to oxidize dihydrogen. The rate of electron transfer (ET) at the anodic side between the [NiFe]-hydrogenase enzyme distal iron–sulfur cluster and the electrode surface can be described by the Marcus equation. All parameters for the Marcus equation are accessible from Density Functional Theory (DFT) calculations. The distal cubane FeS-cluster has a three-cysteine and one-histidine coordination [Fe4S4](His)(Cys)3 first ligation sphere. The reorganization energy (inner- and outer-sphere) is almost unchanged upon a histidine-to-cysteine substitution. Differences in rates of electron transfer between the wild-type enzyme and an all-cysteine mutant can be rationalized by a diminished electronic coupling between the donor and acceptor molecules in the [Fe4S4](Cys)4 case. The fast and efficient electron transfer from the distal iron–sulfur cluster is realized by a fine-tuned protein environment, which facilitates the flow of electrons. This study enables the design and control of electron transfer rates and pathways by protein engineering. PMID:28067774

Energy level engineering in ternary organic solar cells: Evaluating exciton dissociation at organic semiconductor interfaces

NASA Astrophysics Data System (ADS)

Feron, Krishna; Thameel, Mahir N.; Al-Mudhaffer, Mohammed F.; Zhou, Xiaojing; Belcher, Warwick J.; Fell, Christopher J.; Dastoor, Paul C.

2017-03-01

Electronic energy level engineering, with the aim to improve the power conversion efficiency in ternary organic solar cells, is a complex problem since multiple charge transfer steps and exciton dissociation driving forces must be considered. Here, we examine exciton dissociation in the ternary system poly(3-hexylthiophene): [6,6]-phenyl-C61-butyric acid methyl ester:2,4-bis[4-(N,N-diisobutylamino)-2,6-dihydroxyphenyl] squaraine (P3HT:PCBM:DIBSq). Even though the energy level diagram suggests that exciton dissociation at the P3HT:DIBSq interface should be efficient, electron paramagnetic resonance and external quantum efficiency measurements of planar devices show that this interface is not capable of generating separated charge carriers. Efficient exciton dissociation is still realised via energy transfer, which transports excitons from the P3HT:DIBSq interface to the DIBSq:PCBM interface, where separated charge carriers can be generated efficiently. This work demonstrates that energy level diagrams alone cannot be relied upon to predict the exciton dissociation and charge separation capability of an organic semiconductor interface and that energy transfer relaxes the energy level constraints for optimised multi-component organic solar cells.

The effect of twisted D–D–π–A configuration on electron transfer and photo-physics characteristics

NASA Astrophysics Data System (ADS)

Liu, Yunpeng; Li, Yuanzuo; Song, Peng; Ma, Fengcai; Yang, Yanhui

2018-05-01

Two D-D-π-A organic dyes (M45, M46) with dithieno[3,2-b:2‧,3‧-d]pyrrole (DTP) units as election donors in two perpendicular directions, were investigated using density functional theory (DFT) and time-dependent DFT. The ground-state geometries, the absorption, the electronic structures, the charge density difference and molecular electrostatic potential were obtained. To simulate a more realistic performance, all calculations were based on gas condition and dichloromethane solvent. Photoelectric parameters were evaluated by the following factors: the light harvesting efficiency, electron injection driving force, the excited lifetime and vertical dipole moment. Meanwhile, the polarisability and hyperpolarisability were investigated to further explain the relationship between non-linear optical properties and efficiency. The direction of the DTP obviously affects the twisted degree of molecule, forming a better coplanarity on the donor 2 of M45, which results in stronger charge transfer interactions. Furthermore, M45 possesses significant advantages in geometric structure, absorption band and intramolecular charge transfer mechanism. These critical parameters supported the higher performance of M45 in comparison with M46. Moreover, four dyes were designed by the substitution of donor 2, which further verify the influence of the twisted donor 2 on electron transfer and photoelectric properties of D-D-π-A configuration.

Exciplex-triplet energy transfer: A new method to achieve extremely efficient organic light-emitting diode with external quantum efficiency over 30% and drive voltage below 3 V

NASA Astrophysics Data System (ADS)

Seo, Satoshi; Shitagaki, Satoko; Ohsawa, Nobuharu; Inoue, Hideko; Suzuki, Kunihiko; Nowatari, Hiromi; Yamazaki, Shunpei

2014-04-01

A novel approach to enhance the power efficiency of an organic light-emitting diode (OLED) by employing energy transfer from an exciplex to a phosphorescent emitter is reported. It was found that excitation energy of an exciplex formed between an electron-transporting material with a π-deficient quinoxaline moiety and a hole-transporting material with aromatic amine structure can be effectively transferred to a phosphorescent iridium complex in an emission layer of a phosphorescent OLED. Moreover, such an exciplex formation increases quantum efficiency and reduces drive voltage. A highly efficient, low-voltage, and long-life OLED based on this energy transfer is also demonstrated. This OLED device exhibited extremely high external quantum efficiency of 31% even without any attempt to enhance light outcoupling and also achieved a low drive voltage of 2.8 V and a long lifetime of approximately 1,000,000 h at a luminance of 1,000 cd/m2.

Electron-Induced Displacement Damage Effects in CCDs

NASA Technical Reports Server (NTRS)

Becker, Heidi N.; Elliott, Tom; Alexander, James W.

2006-01-01

We compare differences in parametric degradation for CCDs irradiated to the same displacement damage dose with 10-MeV and 50-MeV electrons. Charge transfer efficiency degradation was observed to not scale with NIEL for small signals.

Theoretical studies on effective metal-to-ligand charge transfer characteristics of novel ruthenium dyes for dye sensitized solar cells.

PubMed

Wang, Huei-Tang; Taufany, Fadlilatul; Nachimuthu, Santhanamoorthi; Jiang, Jyh-Chiang

2014-05-01

The development of ruthenium dye-sensitizers with highly effective metal-to-ligand charge transfer (MLCT) characteristics and narrowed transition energy gaps are essential for the new generation of dye-sensitized solar cells. Here, we designed a novel anchoring ligand by inserting the cyanovinyl-branches inside the anchoring ligands of selected highly efficient dye-sensitizers and studied their intrinsic optical properties using theoretical methods. Our calculated results show that the designed ruthenium dyes provide good performances as sensitizers compared to the selected efficient dyes, because of their red-shift in the UV-visible absorption spectra with an increase in the absorption intensity, smaller energy gaps and thereby enhancing MLCT transitions. We found that, the designed anchoring ligand acts as an efficient "electron-acceptor" which boosts electron-transfer from a -NCS ligand to this ligand via a Ru-bridge, thus providing a way to lower the transition energy gap and enhance the MLCT transitions.

Ultrafast charge transfer between MoTe2 and MoS2 monolayers

NASA Astrophysics Data System (ADS)

Pan, Shudi; Ceballos, Frank; Bellus, Matthew Z.; Zereshki, Peymon; Zhao, Hui

2017-03-01

High quality and stable electrical contact between metal and two-dimensional materials, such as transition metal dichalcogenides, is a necessary requirement that has yet to be achieved in order to successfully exploit the advantages that these materials offer to electronics and optoelectronics. MoTe2, owing to its phase changing property, can potentially offer a solution. A recent study demonstrated that metallic phase of MoTe2 connects its semiconducting phase with very low resistance. To utilize this property to connect other two-dimensional materials, it is important to achieve efficient charge transfer between MoTe2 and other semiconducting materials. Using MoS2 as an example, we report ultrafast and efficient charge transfer between MoTe2 and MoS2 monolayers. In the transient absorption measurements, an ultrashort pump pulse is used to selectively excite electrons in MoTe2. The appearance of the excited electrons in the conduction band of MoS2 is monitored by using a probe pulse that is tuned to the resonance of MoS2. We found that electrons transfer to MoS2 on a time scale of at most 0.3 ps. The transferred electrons give rise to a large transient absorption signal at both A-exciton and B-exciton resonances due to the screening effect. We also observed ultrafast transfer of holes from MoS2 to MoTe2. Our results suggest the feasibility of using MoTe2 as a bridge material to connect MoS2 and other transition metal dichalcogenides, and demonstrate a new transition metal dichalcogenide heterostructure involving MoTe2, which extends the spectral range of such structures to infrared.

A highly sensitive and selective fluorimetric probe for intracellular peroxynitrite based on photoinduced electron transfer from ferrocene to carbon dots.

PubMed

Zhu, Jiali; Sun, Shan; Jiang, Kai; Wang, Yuhui; Liu, Wenqing; Lin, Hengwei

2017-11-15

Herein, a highly sensitive and selective fluorimetric nanoprobe for peroxynitrite (ONOO - ) detection based on photoinduced electron transfer (PET) from ferrocene (Fc) to carbon dots (CDs) is reported. The nanoprobe (named CDs-Fc) can be facilely constructed through covalently conjugating CDs and ferrocenecarboxylic acid. Further studies reveal that the energy level of highest occupied molecular orbital (HOMO) of the CDs is lowered with the addition of ONOO - due to its oxidation and nitration capabilities. Thus, an efficient electron transfer from Fc to the excited states of CDs could occur, leading to obvious fluorescence quenching. The fluorescence quenching of the nanoprobe was determined to be peroxynitrite concentrations dependence with a linear range between 4nM to 0.12μM. Thanks to the excellent optical properties of the CDs and efficient electron transfer efficiency from Fc to the excited CDs, the nanoprobe exhibits very high sensitivity to ONOO - with a limit of detection (LOD) of 2.9nM. To the best of our knowledge, this LOD is the highest reported value till today for the detection of peroxynitrite. Besides, the nanoprobe also shows excellent selectivity to ONOO - among a broad range of substances, even including other reactive oxygen/nitrogen species (ROS/RNS). Finally, the nanoprobe was verified to be very low cytotoxicity, and was successfully applied for intracellular ONOO - detection. This work would provide a promising tool for the research of ONOO - in cytobiology and disease diagnosis. Copyright © 2017 Elsevier B.V. All rights reserved.

Photoinduced electron transfer in a molecular dyad by nanosecond pump-pump-probe spectroscopy.

PubMed

Ha-Thi, M-H; Pham, V-T; Pino, T; Maslova, V; Quaranta, A; Lefumeux, C; Leibl, W; Aukauloo, A

2018-06-01

The design of robust and inexpensive molecular photocatalysts for the conversion of abundant stable molecules like H2O and CO2 into an energetic carrier is one of the major fundamental questions for scientists nowadays. The outstanding challenge is to couple single photoinduced charge separation events with the sequential accumulation of redox equivalents at the catalytic unit for performing multielectronic catalytic reactions. Herein, double excitation by nanosecond pump-pump-probe experiments was used to interrogate the photoinduced charge transfer and charge accumulation on a molecular dyad composed of a porphyrin chromophore and a ruthenium-based catalyst in the presence of a reversible electron acceptor. An accumulative charge transfer state is unattainable because of rapid reverse electron transfer to the photosensitizer upon the second excitation and the low driving force of the forward photodriven electron transfer reaction. Such a method allows the fundamental understanding of the relaxation mechanism after two sequential photon absorptions, deciphering the undesired electron transfer reactions that limit the charge accumulation efficiency. This study is a step toward the improvement of synthetic strategies of molecular photocatalysts for light-induced charge accumulation and more generally, for solar energy conversion.

Enhancement of the inverted polymer solar cells via ZnO doped with CTAB

NASA Astrophysics Data System (ADS)

Sivashnamugan, Kundan; Guo, Tzung-Fang; Hsu, Yao-Jane; Wen, Ten-Chin

2018-02-01

A facile approach enhancing electron extraction in zinc oxide (ZnO) electron transfer interlayer and improving performance of bulk-heterojunction (BHJ) polymer solar cells (PSCs) by adding cetyltrimethylammonium bromide (CTAB) into sol-gel ZnO precursor solution was demonstrated in this work. The power conversion efficiency (PCE) has a 24.1% increment after modification. Our results show that CTAB can dramatically influence optical, electrical and morphological properties of ZnO electron transfer layer, and work as effective additive to enhance the performance of bulk- heterojunction polymer solar cells.

Photoinduced electron transfer interaction of anthraquinones with aniline quenchers: Influence of methyl substitution in aniline donors.

PubMed

Sivakumar, V; Ponnamma, Deepalekshmi; Hussein, Yasser H A

2017-02-15

Photoinduced electron transfer between triplet state of 9,10-anthraquinone (AQ) and its two derivatives: 2-chloro-9,10-anthraquinone (CAQ) and sodium anthraquinone-2-sulfonate (AQS) and ground state aniline (AN) and its dimethyl substitutions: 2,3-dimethylaniline (2,3-DMA), 2,6-dimethylaniline (2,6-DMA), 3,5-dimethylaniline (3,5-DMA) and N,N-dimethylaniline (N,N-DMA) is studied using nanosecond laser flash photolysis at room temperature. Detection of radical bands of quinone anions and aniline cations along with their formation and/or decay kinetics are used to confirm the electron transfer (ET) process. In MeCN medium, AN quenches the triplet state of CAQ (CAQ T ) but not the triplets AQ T or AQS T . However in aqueous medium, AN quenches AQS T and forms radical ion pair. All the DMAs can react through ET with all the triplet quinones at different degrees of efficiency in MeCN medium. Noticeably, the ring substituted DMAs are less efficient in electron donation to AQ T or AQS T while the N,N-DMA shows high efficiency in donating electron to all triplet quinones in MeCN medium. Charge distribution of donor molecules, in MeCN medium is calculated using density functional theory (DFT), and shows an enhancement of electron density of the ring of N,N-DMA, making it an ideal electron donor for ET studies compared to other DMAs. This systematic selection and usage of anilines with electrochemically tunable quinones can be viewed as a working model of donor-acceptor system that can be utilized in photoinduced ET applications. Copyright © 2016 Elsevier B.V. All rights reserved.

Theoretical investigation of the charge-transfer properties in different meso-linked zinc porphyrins for highly efficient dye-sensitized solar cells.

PubMed

Namuangruk, Supawadee; Sirithip, Kanokkorn; Rattanatwan, Rattanawelee; Keawin, Tinnagon; Kungwan, Nawee; Sudyodsuk, Taweesak; Promarak, Vinich; Surakhot, Yaowarat; Jungsuttiwong, Siriporn

2014-06-28

The charge transfer effect of different meso-substituted linkages on porphyrin analogue 1 (A1, B1 and C1) was theoretically investigated using density functional theory (DFT) and time-dependent DFT (TDDFT) calculations. The calculated geometry parameters and natural bond orbital analysis reveal that the twisted conformation between porphyrin macrocycle and meso-substituted linkages leads to blocking of the conjugation of the conjugated backbone, and the frontier molecular orbital plot shows that the intramolecular charge transfer of A1, B1 and C1 hardly takes place. In an attempt to improve the photoinduced intramolecular charge transfer ability of the meso-linked zinc porphyrin sensitizer, a strong electron-withdrawing group (CN) was introduced into the anchoring group of analogue 1 forming analogue 2 (A2, B2 and C2). The density difference plot of A2, B2 and C2 shows that the charge transfer properties dramatically improved. The electron injection process has been performed using TDDFT; the direct charge-transfer transition in the A2-(TiO2)38 interacting system takes place; our results strongly indicated that introducing electron-withdrawing groups into the acceptor part of porphyrin dyes can fine-tune the effective conjugation length of the π-spacer and improve intramolecular charge transfer properties, consequently inducing the electron injection process from the anchoring group of the porphyrin dye to the (TiO2)38 surface which may improve the conversion efficiency of the DSSCs. Our calculated results can provide valuable information and a promising outlook for computation-aided sensitizer design with anticipated good properties in further experimental synthesis.

Direct Electron Transfer of Enzymes in a Biologically Assembled Conductive Nanomesh Enzyme Platform.

PubMed

Lee, Seung-Woo; Lee, Ki-Young; Song, Yong-Won; Choi, Won Kook; Chang, Joonyeon; Yi, Hyunjung

2016-02-24

Nondestructive assembly of a nanostructured enzyme platform is developed in combination of the specific biomolecular attraction and electrostatic coupling for highly efficient direct electron transfer (DET) of enzymes with unprecedented applicability and versatility. The biologically assembled conductive nanomesh enzyme platform enables DET-based flexible integrated biosensors and DET of eight different enzyme with various catalytic activities. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Enhanced charge separation of rutile TiO2 nanorods by trapping holes and transferring electrons for efficient cocatalyst-free photocatalytic conversion of CO2 to fuels.

PubMed

Wu, Jing; Lu, Hongwei; Zhang, Xuliang; Raziq, Fazal; Qu, Yang; Jing, Liqiang

2016-04-11

Modification with chloride and phosphate anions, and coupling with carbon nanotubes could effectively trap holes and transfer the electrons of rutile nanorods, respectively, so as to greatly promote photogenerated charge separation, leading to an obviously-improved cocatalyst-free photocatalytic conversion of CO2 to CH4 and CO, along with the positive effects of constructed phosphate bridges.

Theoretical Study of Ultrafast Electron Injection into a Dye/TiO2 System in Dye-Sensitized Solar Cells

NASA Astrophysics Data System (ADS)

Lin, Chundan; Xia, Qide; Li, Kuan; Li, Juan; Yang, Zhenqing

2018-06-01

The ultrafast injection of excited electrons in dye/TiO2 system plays a critical role, which determines the device's efficiency in large part. In this work, we studied the geometrical structures and electronic properties of a dye/TiO2 composite system for dye-sensitized solar cells (DSSCs) by using density functional theory, and we analyzed the mechanism of ultrafast electron injection with emphasis on the power conversion efficiency. The results show that the dye SPL103/TiO2 (101) surface is more stable than dye SPL101. The electron injection driving force of SPL103/TiO2 (101) is 3.55 times that of SPL101, indicating that SPL103/TiO2 (101) has a strong ability to transfer electrons. SPL103 and SPL101/TiO2 (101) both have fast electron transfer processes, and especially the electron injection time of SPL103/TiO2 (101) is only 1.875 fs. The results of this work are expected to provide a new understanding of the mechanism of electron injection in dyes/TiO2 systems for use in highly effective DSSCs.

High efficiency ZnO-based dye-sensitized solar cells with a 1H,1H,2H,2H-perfluorodecyltriethoxysilane chain barrier for cutting on interfacial recombination

NASA Astrophysics Data System (ADS)

Xie, Yahong; Zhou, Xiaofeng; Mi, Hongyu; Ma, Junhong; Yang, Jianya; Cheng, Jian

2018-03-01

Charge recombination at the ZnO photoanode/electrolyte interface is one of the major limitations for high performance dye-sensitized solar cells (DSSCs) toward their theoretical power conversion efficiency (PCE). Here, we proposed an efficient approach for reducing this interfacial losses and consequently facilitating charge transfer by decorating a hydrophobic thin-film on the surface of the dye-coated zinc oxide photoanode via 1H,1H,2H,2H-perfluorodecyltriethoxysilane (PFDTES) hexane solution immersing. As a result, a high PCE of 8.22% was obtained, which far exceeded the efficiency of 5.40% in a conventional DSSC without PFDTES treatment. Furthermore, PFDTES treatment also largely elongated the lifetime of photogenerated electrons, and maintained a good photo-response at the photoelectrode. This work provides a comprehensive explanation of electron injection, transfer and recombination at the ZnO photoanode/electrolyte interface, and a promising strategy to explore high efficiency ZnO-based DSSCs.

Enhanced photocurrent production by bio-dyes of photosynthetic macromolecules on designed TiO2 film

PubMed Central

Yu, Daoyong; Wang, Mengfei; Zhu, Guoliang; Ge, Baosheng; Liu, Shuang; Huang, Fang

2015-01-01

The macromolecular pigment-protein complex has the merit of high efficiency for light-energy capture and transfer after long-term photosynthetic evolution. Here bio-dyes of A. platensis photosystem I (PSI) and spinach light-harvesting complex II (LHCII) are spontaneously sensitized on three types of designed TiO2 films, to assess the effects of pigment-protein complex on the performance of bio-dye sensitized solar cells (SSC). Adsorption models of bio-dyes are proposed based on the 3D structures of PSI and LHCII, and the size of particles and inner pores in the TiO2 film. PSI shows its merit of high efficiency for captured energy transfer, charge separation and transfer in the electron transfer chain (ETC), and electron injection from FB to the TiO2 conducting band. After optimization, the best short current (JSC) and photoelectric conversion efficiency (η) of PSI-SSC and LHCII-SSC are 1.31 mA cm-2 and 0.47%, and 1.51 mA cm-2 and 0.52%, respectively. The potential for further improvement of this PSI based SSC is significant and could lead to better utilization of solar energy. PMID:25790735

Charge transfer in photorechargeable composite films of TiO2 and polyaniline

NASA Astrophysics Data System (ADS)

Nomiyama, Teruaki; Sasabe, Kenichi; Sakamoto, Kenta; Horie, Yuji

2015-07-01

A photorechargeable battery (PRB) is a photovoltaic device having an energy storage function in a single cell. The photoactive electrode of PRB is a bilayer film consisting of bare porous TiO2 and a TiO2-polyaniline (PANi) mixture that work as a photovoltaic current generator and an electrochemical energy storage by ion dedoping, respectively. To study the charge transfer between TiO2 and PANi, the photorechargeable quantum efficiency QE ([electron count on discharge]/[incident photon count on photocharge]) was measured by varying the thickness LS of the TiO2-PANi mixture. The quantum efficiency QEuv for UV photons had a maximum of ˜7% at LS ˜ 7 µm. The time constant τTP for the charge transfer was about 10-1 s, which was longer ten times or more than the lifetime of excited electrons within TiO2. These facts reveal that the main rate-limiting factor in the photocharging process is the charge transfer between TiO2 and PANi.

Controllable fabrication of Pt nanocatalyst supported on N-doped carbon containing nickel nanoparticles for ethanol oxidation.

PubMed

Yu, Jianguo; Dai, Tangming; Cao, Yuechao; Qu, Yuning; Li, Yao; Li, Juan; Zhao, Yongnan; Gao, Haiyan

2018-08-15

In this paper, platinum nanoparticles were deposited on a carbon carrier with the partly graphitized carbon and the highly dispersive carbon-coated nickel particles. An efficient electron transfer structure can be fabricated by controlling the contents of the deposited platinum. The high resolution transmission electron microscopy images of Pt 2 /Ni@C N-doped sample prove the electron transfer channel from Pt (1 1 1) crystal planes to graphite (1 0 0) or Ni (1 1 1) crystal planes due to these linked together crystal planes. The Pt 3 /Ni@C N-doped with low Pt contents cannot form the electron transfer structure and the Pt 1 /Ni@C N-doped with high Pt contents show an obvious aggregation of Pt nanoparticles. The electrochemical tests of all the catalysts show that the Pt 2 /Ni@C N-doped sample presents the highest catalytic activity, the strongest CO tolerance and the best catalytic stability. The high performance is attributed to the efficient electronic transport structure of the Pt 2 /Ni@C N-doped sample and the synergistic effect between Pt and Ni nanoparticles. This paper provides a promising method for enhancing the conductivity of electrode material. Copyright © 2018 Elsevier Inc. All rights reserved.

Influence of the ambient temperature on the cooling efficiency of the high performance cooling device with thermosiphon effect

NASA Astrophysics Data System (ADS)

Nemec, Patrik; Malcho, Milan

2018-06-01

This work deal with experimental measurement and calculation cooling efficiency of the cooling device working with a heat pipe technology. The referred device in the article is cooling device capable transfer high heat fluxes from electric elements to the surrounding. The work contain description, working principle and construction of cooling device. The main factor affected the dissipation of high heat flux from electronic elements through the cooling device to the surrounding is condenser construction, its capacity and option of heat removal. Experimental part describe the measuring method cooling efficiency of the cooling device depending on ambient temperature in range -20 to 40°C and at heat load of electronic components 750 W. Measured results are compared with results calculation based on physical phenomena of boiling, condensation and natural convection heat transfer.

Energy-Efficient and Environmentally Friendly Solid Oxide Membrane Electrolysis Process for Magnesium Oxide Reduction: Experiment and Modeling

NASA Astrophysics Data System (ADS)

Guan, Xiaofei; Pal, Uday B.; Powell, Adam C.

2014-06-01

This paper reports a solid oxide membrane (SOM) electrolysis experiment using an LSM(La0.8Sr0.2MnO3-δ)-Inconel inert anode current collector for production of magnesium and oxygen directly from magnesium oxide at 1423 K (1150 °C). The electrochemical performance of the SOM cell was evaluated by means of various electrochemical techniques including electrochemical impedance spectroscopy, potentiodynamic scan, and electrolysis. Electronic transference numbers of the flux were measured to assess the magnesium dissolution in the flux during SOM electrolysis. The effects of magnesium solubility in the flux on the current efficiency and the SOM stability during electrolysis are discussed. An inverse correlation between the electronic transference number of the flux and the current efficiency of the SOM electrolysis was observed. Based on the experimental results, a new equivalent circuit of the SOM electrolysis process is presented. A general electrochemical polarization model of SOM process for magnesium and oxygen gas production is developed, and the maximum allowable applied potential to avoid zirconia dissociation is calculated as well. The modeling results suggest that a high electronic resistance of the flux and a relatively low electronic resistance of SOM are required to achieve membrane stability, high current efficiency, and high production rates of magnesium and oxygen.

Efficient generation and transportation of energetic electrons in a carbon nanotube array target

NASA Astrophysics Data System (ADS)

Ji, Yanling; Jiang, Gang; Wu, Weidong; Wang, Chaoyang; Gu, Yuqiu; Tang, Yongjian

2010-01-01

Laser-driven energetic electron propagation in a carbon nanotube-array target is investigated using two-dimensional particle-in-cell simulations. Energetic electrons are efficiently generated when the array is irradiated by a short intense laser pulse. Confined and guided transportation of energetic electrons in the array is achieved by exploiting strong transient electromagnetic fields created at the wall surfaces of nanotubes. The underlying mechanisms are discussed in detail. Our investigation shows that the laser energy can be transferred more effectively to the target electrons in the array than that of in the flat foil due to the hole structures in the array.

Single-crystal charge transfer interfaces for efficient photonic devices (Conference Presentation)

NASA Astrophysics Data System (ADS)

Alves, Helena; Pinto, Rui M.; Maçôas, Ermelinda M. S.; Baleizão, Carlos; Santos, Isabel C.

2016-09-01

Organic semiconductors have unique optical, mechanical and electronic properties that can be combined with customized chemical functionality. In the crystalline form, determinant features for electronic applications such as molecular purity, the charge mobility or the exciton diffusion length, reveal a superior performance when compared with materials in a more disordered form. Combining crystals of two different conjugated materials as even enable a new 2D electronic system. However, the use of organic single crystals in devices is still limited to a few applications, such as field-effect transistors. In 2013, we presented the first system composed of single-crystal charge transfer interfaces presenting photoconductivity behaviour. The system composed of rubrene and TCNQ has a responsivity reaching 1 A/W, corresponding to an external quantum efficiency of nearly 100%. A similar approach, with a hybrid structure of a PCBM film and rubrene single crystal also presents high responsivity and the possibility to extract excitons generated in acceptor materials. This strategy led to an extended action towards the near IR. By adequate material design and structural organisation of perylediimides, we demonstrate that is possible to improve exciton diffusion efficiency. More recently, we have successfully used the concept of charge transfer interfaces in phototransistors. These results open the possibility of using organic single-crystal interfaces in photonic applications.

Single Pt Atoms Confined into a Metal-Organic Framework for Efficient Photocatalysis.

PubMed

Fang, Xinzuo; Shang, Qichao; Wang, Yu; Jiao, Long; Yao, Tao; Li, Yafei; Zhang, Qun; Luo, Yi; Jiang, Hai-Long

2018-02-01

It is highly desirable yet remains challenging to improve the dispersion and usage of noble metal cocatalysts, beneficial to charge transfer in photocatalysis. Herein, for the first time, single Pt atoms are successfully confined into a metal-organic framework (MOF), in which electrons transfer from the MOF photosensitizer to the Pt acceptor for hydrogen production by water splitting under visible-light irradiation. Remarkably, the single Pt atoms exhibit a superb activity, giving a turnover frequency of 35 h -1 , ≈30 times that of Pt nanoparticles stabilized by the same MOF. Ultrafast transient absorption spectroscopy further unveils that the single Pt atoms confined into the MOF provide highly efficient electron transfer channels and density functional theory calculations indicate that the introduction of single Pt atoms into the MOF improves the hydrogen binding energy, thus greatly boosting the photocatalytic H 2 production activity. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Proton-Coupled Electron Transfer in Artificial Photosynthetic Systems.

PubMed

Mora, S Jimena; Odella, Emmanuel; Moore, Gary F; Gust, Devens; Moore, Thomas A; Moore, Ana L

2018-02-20

Artificial photosynthetic constructs can in principle operate more efficiently than natural photosynthesis because they can be rationally designed to optimize solar energy conversion for meeting human demands rather than the multiple needs of an organism competing for growth and reproduction in a complex ecosystem. The artificial photosynthetic constructs described in this Account consist primarily of covalently linked synthetic chromophores, electron donors and acceptors, and proton donors and acceptors that carry out the light absorption, electron transfer, and proton-coupled electron transfer (PCET) processes characteristic of photosynthetic cells. PCET is the movement of an electron from one site to another accompanied by proton transfer. PCET and the transport of protons over tens of angstroms are important in all living cells because they are a fundamental link between redox processes and the establishment of transmembrane gradients of proton electrochemical potential, known as proton-motive force (PMF), which is the unifying concept in bioenergetics. We have chosen a benzimidazole phenol (BIP) system as a platform for the study of PCET because with appropriate substitutions it is possible to design assemblies in which one or multiple proton transfers can accompany oxidation of the phenol. In BIP, oxidation of the phenol increases its acidity by more than ten pK a units; thus, electrochemical oxidation of the phenol is associated with a proton transfer to the imidazole. This is an example of a PCET process involving transfer of one electron and one proton, known as electron-proton transfer (EPT). When the benzimidazole moiety of BIP is substituted at the 4-position with good proton acceptor groups such as aliphatic amines, experimental and theoretical results indicate that two proton transfers occur upon one-electron oxidation of the phenol. This phenomenon is described as a one-electron-two-proton transfer (E2PT) process and results in translocation of protons over ∼7 Å via a Grotthuss-type mechanism, where the protons traverse a network of internally H-bonded sites. In the case of the E2TP process involving BIP analogues with amino group substituents, the thermodynamic price paid in redox potential to move a proton to the final proton acceptor is ∼300 mV. In this example, the decrease in redox potential limits the oxidizing power of the resulting phenoxyl radical. Thus, unlike the biological counterpart, the artificial construct is thermodynamically incapable of effectively advancing the redox state of a water oxidation catalyst. The design of systems where multiple proton transfer events are coupled to an oxidation reaction while a relatively high redox potential is maintained remains an outstanding challenge. The ability to control proton transfer and activity at defined distances and times is key to achieving proton management in the vicinity of catalysts operating at low overpotential in myriad biochemically important processes. Artificial photosynthetic constructs with well-defined structures, such as the ones described in this Account, can provide the means for discovering design principles upon which efficient redox catalysts for electrolysis and fuel cells can be based.

Ultrafast electron and hole transfer dynamics of a solar cell dye containing hole acceptors on mesoporous TiO2 and Al2O3.

PubMed

Scholz, Mirko; Flender, Oliver; Boschloo, Gerrit; Oum, Kawon; Lenzer, Thomas

2017-03-08

The stability of dye cations against recombination with conduction band electrons in mesoporous TiO 2 electrodes is a key property for improving light harvesting in dye-sensitised solar cells. Using ultrafast transient broadband absorption spectroscopy, we monitor efficient intramolecular hole transfer in the solar cell dye E6 having two peripheral triarylamine acceptors. After photoexcitation, two hole transfer mechanisms are identified: a concerted mechanism for electron injection and hole transfer (2.4 ps) and a sequential mechanism with time constants of 3.9 ps and 30 ps. This way the dye retards unwanted recombination with a TiO 2 conduction band electron by quickly moving the hole further away from the surface. Contact of the E6/TiO 2 surface with the solvent acetonitrile has almost no influence on the electron injection and hole transfer kinetics. Fast hole transfer (2.8 ps) is also observed on a "non-injecting" Al 2 O 3 surface generating a radical cation-radical anion species with a lifetime of 530 ps. The findings confirm the good intramolecular hole transfer properties of this dye on both thin films. In contrast, intramolecular hole transfer does not occur in the mid-polar organic solvent methyl acetate. This is confirmed by TDDFT calculations suggesting a polarity-induced reduction of the driving force for hole transfer. In methyl acetate, only the relaxation of the initially photoexcited core chromophore is observed including solvent relaxation processes of the electronically excited state S 1 /ICT.

A quantitative structure–function relationship for the Photosystem II reaction center: Supermolecular behavior in natural photosynthesis

PubMed Central

Barter, Laura M. C.; Durrant, James R.; Klug, David R.

2003-01-01

Light-induced charge separation is the primary photochemical event of photosynthesis. Efficient charge separation in photosynthetic reaction centers requires the balancing of electron and excitation energy transfer processes, and in Photosystem II (PSII), these processes are particularly closely entangled. Calculations that treat the cofactors of the PSII reaction center as a supermolecular complex allow energy and electron transfer reactions to be described in a unified way. This calculational approach is shown to be in good agreement with experimentally observed energy and electron transfer dynamics. This supermolecular view also correctly predicts the effect of changing the redox potentials of cofactors by site-directed mutagenesis, thus providing a unified and quantitative structure–function relationship for the PSII reaction center. PMID:12538865

Peel-and-Stick: Mechanism Study for Efficient Fabrication of Flexible/Transparent Thin-film Electronics

NASA Astrophysics Data System (ADS)

Lee, Chi Hwan; Kim, Jae-Han; Zou, Chenyu; Cho, In Sun; Weisse, Jeffery M.; Nemeth, William; Wang, Qi; van Duin, Adri C. T.; Kim, Taek-Soo; Zheng, Xiaolin

2013-10-01

Peel-and-stick process, or water-assisted transfer printing (WTP), represents an emerging process for transferring fully fabricated thin-film electronic devices with high yield and fidelity from a SiO2/Si wafer to various non-Si based substrates, including papers, plastics and polymers. This study illustrates that the fundamental working principle of the peel-and-stick process is based on the water-assisted subcritical debonding, for which water reduces the critical adhesion energy of metal-SiO2 interface by 70 ~ 80%, leading to clean and high quality transfer of thin-film electronic devices. Water-assisted subcritical debonding is applicable for a range of metal-SiO2 interfaces, enabling the peel-and-stick process as a general and tunable method for fabricating flexible/transparent thin-film electronic devices.

Peel-and-stick: mechanism study for efficient fabrication of flexible/transparent thin-film electronics.

PubMed

Lee, Chi Hwan; Kim, Jae-Han; Zou, Chenyu; Cho, In Sun; Weisse, Jeffery M; Nemeth, William; Wang, Qi; van Duin, Adri C T; Kim, Taek-Soo; Zheng, Xiaolin

2013-10-10

Peel-and-stick process, or water-assisted transfer printing (WTP), represents an emerging process for transferring fully fabricated thin-film electronic devices with high yield and fidelity from a SiO2/Si wafer to various non-Si based substrates, including papers, plastics and polymers. This study illustrates that the fundamental working principle of the peel-and-stick process is based on the water-assisted subcritical debonding, for which water reduces the critical adhesion energy of metal-SiO2 interface by 70 ~ 80%, leading to clean and high quality transfer of thin-film electronic devices. Water-assisted subcritical debonding is applicable for a range of metal-SiO2 interfaces, enabling the peel-and-stick process as a general and tunable method for fabricating flexible/transparent thin-film electronic devices.

Highly efficient biosensors by using well-ordered ZnO/ZnS core/shell nanotube arrays

NASA Astrophysics Data System (ADS)

Tarish, Samar; Xu, Yang; Wang, Zhijie; Mate, Faten; Al-Haddad, Ahmed; Wang, Wenxin; Lei, Yong

2017-10-01

We have studied the fabrication of highly efficient glucose sensors using well-ordered heterogeneous ZnO/ZnS core/shell nanotube arrays (CSNAs). The modified electrodes exhibit a superior electrochemical response towards ferrocyanide/ferricyanide and in glucose sensing. Further, the fabricated glucose biosensor exhibited good performance over an acceptable linear range from 2.39 × 10-5 to 2.66 × 10-4 mM, with a sensitivity of 188.34 mA mM-1 cm-2, which is higher than that of the ZnO nanotube array counterpart. A low limit of detection was realized (24 μM), which is good compared with electrodes based on conventional structures. In addition, the enhanced direct electrochemistry of glucose oxidase indicates the fast electron transfer of ZnO/ZnS CSNA electrodes, with a heterogeneous electron transfer rate constant (K s) of 1.69 s-1. The fast electron transfer is attributed to the high conductivity of the modified electrodes. The presented ZnS shell can facilitate the construction of future sensors and enhance the ZnO surface in a biological environment.

Cellobiose Dehydrogenase Aryl Diazonium Modified Single Walled Carbon Nanotubes: Enhanced Direct Electron Transfer through a Positively Charged Surface

PubMed Central

2011-01-01

One of the challenges in the field of biosensors and biofuel cells is to establish a highly efficient electron transfer rate between the active site of redox enzymes and electrodes to fully access the catalytic potential of the biocatalyst and achieve high current densities. We report on very efficient direct electron transfer (DET) between cellobiose dehydrogenase (CDH) from Phanerochaete sordida (PsCDH) and surface modified single walled carbon nanotubes (SWCNT). Sonicated SWCNTs were adsorbed on the top of glassy carbon electrodes and modified with aryl diazonium salts generated in situ from p-aminobenzoic acid and p-phenylenediamine, thus featuring at acidic pH (3.5 and 4.5) negative or positive surface charges. After adsorption of PsCDH, both electrode types showed excellent long-term stability and very efficient DET. The modified electrode presenting p-aminophenyl groups produced a DET current density of 500 μA cm−2 at 200 mV vs normal hydrogen reference electrode (NHE) in a 5 mM lactose solution buffered at pH 3.5. This is the highest reported DET value so far using a CDH modified electrode and comes close to electrodes using mediated electron transfer. Moreover, the onset of the electrocatalytic current for lactose oxidation started at 70 mV vs NHE, a potential which is 50 mV lower compared to when unmodified SWCNTs were used. This effect potentially reduces the interference by oxidizable matrix components in biosensors and increases the open circuit potential in biofuel cells. The stability of the electrode was greatly increased compared with unmodified but cross-linked SWCNTs electrodes and lost only 15% of the initial current after 50 h of constant potential scanning. PMID:21417322

Cellobiose dehydrogenase aryl diazonium modified single walled carbon nanotubes: enhanced direct electron transfer through a positively charged surface.

PubMed

Tasca, Federico; Harreither, Wolfgang; Ludwig, Roland; Gooding, John Justin; Gorton, Lo

2011-04-15

One of the challenges in the field of biosensors and biofuel cells is to establish a highly efficient electron transfer rate between the active site of redox enzymes and electrodes to fully access the catalytic potential of the biocatalyst and achieve high current densities. We report on very efficient direct electron transfer (DET) between cellobiose dehydrogenase (CDH) from Phanerochaete sordida (PsCDH) and surface modified single walled carbon nanotubes (SWCNT). Sonicated SWCNTs were adsorbed on the top of glassy carbon electrodes and modified with aryl diazonium salts generated in situ from p-aminobenzoic acid and p-phenylenediamine, thus featuring at acidic pH (3.5 and 4.5) negative or positive surface charges. After adsorption of PsCDH, both electrode types showed excellent long-term stability and very efficient DET. The modified electrode presenting p-aminophenyl groups produced a DET current density of 500 μA cm(-2) at 200 mV vs normal hydrogen reference electrode (NHE) in a 5 mM lactose solution buffered at pH 3.5. This is the highest reported DET value so far using a CDH modified electrode and comes close to electrodes using mediated electron transfer. Moreover, the onset of the electrocatalytic current for lactose oxidation started at 70 mV vs NHE, a potential which is 50 mV lower compared to when unmodified SWCNTs were used. This effect potentially reduces the interference by oxidizable matrix components in biosensors and increases the open circuit potential in biofuel cells. The stability of the electrode was greatly increased compared with unmodified but cross-linked SWCNTs electrodes and lost only 15% of the initial current after 50 h of constant potential scanning. © 2011 American Chemical Society

Photoinduced Charge Shifts and Electron Transfer in Viologen-Tetraphenylborate Complexes: Push-Pull Character of the Exciplex.

PubMed

Santos, Willy G; Budkina, Darya S; Deflon, Victor M; Tarnovsky, Alexander N; Cardoso, Daniel R; Forbes, Malcolm D E

2017-06-14

Viologen-tetraarylborate ion-pair complexes were prepared and investigated by steady-state and time-resolved spectroscopic techniques such as fluorescence and femtosecond transient absorption. The results highlight a charge transfer transition that leads to changes in the viologen structure in the excited singlet state. Femtosecond transient absorption reveals the formation of excited-state absorption and stimulated emission bands assigned to the planar (k obs < 10 12 s -1 ) and twisted (k obs ∼ 10 10 s -1 ) structures between two pyridinium groups in the viologen ion. An efficient photoinduced electron transfer from the tetraphenylborate anionic moiety to the viologen dication was observed less than 1 μs after excitation. This is a consequence of the push-pull character of the electron donor twisted viologen structure, which helps formation of the borate triplet state. The borate triplet state is deactivated further via a second electron transfer process, generating viologen cation radical (V •+ ).

Interfacial electron transfer of glucose oxidase on poly(glutamic acid)-modified glassy carbon electrode and glucose sensing.

PubMed

Zhou, Xuechou; Tan, Bingcan; Zheng, Xinyu; Kong, Dexian; Li, Qinglu

2015-11-15

The interfacial electron transfer of glucose oxidase (GOx) on a poly(glutamic acid)-modified glassy carbon electrode (PGA/GCE) was investigated. The redox peaks measured for GOx and flavin adenine dinucleotide (FAD) are similar, and the anodic peak of GOx does not increase in the presence of glucose in a mediator-free solution. These indicate that the electroactivity of GOx is not the direct electron transfer (DET) between GOx and PGA/GCE and that the observed electroactivity of GOx is ascribed to free FAD that is released from GOx. However, efficient electron transfer occurred if an appropriate mediator was placed in solution, suggesting that GOx is active. The PGA/GCE-based biosensor showed wide linear response in the range of 0.5-5.5 mM with a low detection limit of 0.12 mM and high sensitivity and selectivity for measuring glucose. Copyright © 2015 Elsevier Inc. All rights reserved.

Enhanced interfacial electron transfer of inverted perovskite solar cells by introduction of CoSe into the electron-transporting-layer

NASA Astrophysics Data System (ADS)

Chen, Shanshan; Yang, Songwang; Sun, Hong; Zhang, Lu; Peng, Jiajun; Liang, Ziqi; Wang, Zhong-Sheng

2017-06-01

To improve the electron transfer at the interface between the perovskite film and the electron-transporting-material (ETM) layer, CoSe doped [6,6]-phenyl C61-butyric acid methyl ester (PCBM) is employed as the ETM layer for the inverted planar perovskite solar cell with NiO as the hole-transporting-material layer. Introduction of CoSe (5.8 wt%) into the PCBM layer improves the conductivity of the ETM layer and decreases the photoluminescence intensity, thus enhancing the interfacial electron extraction and reducing the electron transfer resistance at the perovskite/ETM interface. As a consequence, the power conversion efficiency is enhanced from 11.43% to 14.91% by 30% due to the noted increases in short-circuit current density from 17.95 mA cm-2 to 19.85 mA cm-2 and fill factor from 0.60 to 0.70. This work provides a new strategy to improve the performance of inverted perovskite solar cells.

Synthesis of an A-D-A type of molecule used as electron acceptor for improving charge transfer in organic solar cells

NASA Astrophysics Data System (ADS)

Zhang, Chao-Zhi; Gu, Shu-Duo; Shen, Dan; Yuan, Yang; Zhang, Mingdao

2016-08-01

Electron-accepting molecules play an important role in developing organic solar cells. A new type of A-D-A molecule, 3,6-di([7-(5-bromothiophen-2-yl)-1,5,2,4,6,8-dithiotetrazocin-3-yl]thiophen-2-yl)-9-(2-ethylhexyl)carbazole, was synthesized. The lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) energy levels are -3.55 and -5.85 eV, respectively. Therefore, the A-D-A type of compound could be used as electron acceptor for fabricating organic solar cell with a high open circuit voltage. Gibbs free energy (-49.2 kJ/mol) reveals that the process of A-D-A acceptor accepting an electron from poly(3-hexylthiophene) at excited state is spontaneous. The value of entropy (118 J/mol) in the process of an electron transferring from P3HT to the A-D-A acceptor at organic interface suggests that electrons generated from separation of electron-hole pairs at donor/acceptor interface would be delocalized efficiently. Therefore, the A-D-A molecule would be a potential acceptor for efficient organic BHJ solar cells.

Biological photovoltaics: intra- and extra-cellular electron transport by cyanobacteria.

PubMed

Bradley, Robert W; Bombelli, Paolo; Rowden, Stephen J L; Howe, Christopher J

2012-12-01

A large variety of new energy-generating technologies are being developed in an effort to reduce global dependence on fossil fuels, and to reduce the carbon footprint of energy generation. The term 'biological photovoltaic system' encompasses a broad range of technologies which all employ biological material that can harness light energy to split water, and then transfer the resulting electrons to an anode for power generation or electrosynthesis. The use of whole cyanobacterial cells is a good compromise between the requirements of the biological material to be simply organized and transfer electrons efficiently to the anode, and also to be robust and able to self-assemble and self-repair. The principle that photosynthetic bacteria can generate and transfer electrons directly or indirectly to an anode has been demonstrated by a number of groups, although the power output obtained from these devices is too low for biological photovoltaic devices to be useful outside the laboratory. Understanding how photosynthetically generated electrons are transferred through and out of the organism is key to improving power output, and investigations on this aspect of the technology are the main focus of the present review.

Electron Transfer Mechanisms of DNA Repair by Photolyase

NASA Astrophysics Data System (ADS)

Zhong, Dongping

2015-04-01

Photolyase is a flavin photoenzyme that repairs two DNA base damage products induced by ultraviolet (UV) light: cyclobutane pyrimidine dimers and 6-4 photoproducts. With femtosecond spectroscopy and site-directed mutagenesis, investigators have recently made significant advances in our understanding of UV-damaged DNA repair, and the entire enzymatic dynamics can now be mapped out in real time. For dimer repair, six elementary steps have been characterized, including three electron transfer reactions and two bond-breaking processes, and their reaction times have been determined. A unique electron-tunneling pathway was identified, and the critical residues in modulating the repair function at the active site were determined. The dynamic synergy between the elementary reactions for maintaining high repair efficiency was elucidated, and the biological nature of the flavin active state was uncovered. For 6-4 photoproduct repair, a proton-coupled electron transfer repair mechanism has been revealed. The elucidation of electron transfer mechanisms and two repair photocycles is significant and provides a molecular basis for future practical applications, such as in rational drug design for curing skin cancer.

Boiling and quenching heat transfer advancement by nanoscale surface modification.

PubMed

Hu, Hong; Xu, Cheng; Zhao, Yang; Ziegler, Kirk J; Chung, J N

2017-07-21

All power production, refrigeration, and advanced electronic systems depend on efficient heat transfer mechanisms for achieving high power density and best system efficiency. Breakthrough advancement in boiling and quenching phase-change heat transfer processes by nanoscale surface texturing can lead to higher energy transfer efficiencies, substantial energy savings, and global reduction in greenhouse gas emissions. This paper reports breakthrough advancements on both fronts of boiling and quenching. The critical heat flux (CHF) in boiling and the Leidenfrost point temperature (LPT) in quenching are the bottlenecks to the heat transfer advancements. As compared to a conventional aluminum surface, the current research reports a substantial enhancement of the CHF by 112% and an increase of the LPT by 40 K using an aluminum surface with anodized aluminum oxide (AAO) nanoporous texture finish. These heat transfer enhancements imply that the power density would increase by more than 100% and the quenching efficiency would be raised by 33%. A theory that links the nucleation potential of the surface to heat transfer rates has been developed and it successfully explains the current finding by revealing that the heat transfer modification and enhancement are mainly attributed to the superhydrophilic surface property and excessive nanoscale nucleation sites created by the nanoporous surface.

Boosting surface charge-transfer doping efficiency and robustness of diamond with WO3 and ReO3

NASA Astrophysics Data System (ADS)

Tordjman, Moshe; Weinfeld, Kamira; Kalish, Rafi

2017-09-01

An advanced charge-transfer yield is demonstrated by employing single monolayers of transition-metal oxides—tungsten trioxide (WO3) and rhenium trioxide (ReO3)—deposited on the hydrogenated diamond surface, resulting in improved p-type sheet conductivity and thermal stability. Surface conductivities, as determined by Hall effect measurements as a function of temperature for WO3, yield a record sheet hole carrier concentration value of up to 2.52 × 1014 cm-2 at room temperature for only a few monolayers of coverage. Transfer doping with ReO3 exhibits a consistent narrow sheet carrier concentration value of around 3 × 1013 cm-2, exhibiting a thermal stability of up to 450 °C. This enhanced conductivity and temperature robustness exceed those reported for previously exposed surface electron acceptor materials used so far on a diamond surface. X-ray photoelectron spectroscopy measurements of the C1s core level shift as a function of WO3 and ReO3 layer thicknesses are used to determine the respective increase in surface band bending of the accumulation layers, leading to a different sub-surface two-dimensional hole gas formation efficiency in both cases. This substantial difference in charge-exchange efficiency is unexpected since both surface acceptors have very close work functions. Consequently, these results lead us to consider additional factors influencing the transfer doping mechanism. Transfer doping with WO3 reveals the highest yet reported transfer doping efficiency per minimal surface acceptor coverage. This improved surface conductivity performance and thermal stability will promote the realization of 2D diamond-based electronic devices facing process fabrication challenges.

Materials and systems for unassisted photoelectrochemical solar fuels production (Conference Presentation)

NASA Astrophysics Data System (ADS)

Lee, Jae Sung

2016-10-01

About 400 semiconductor solids are known to have photocatalytic activity for water splitting. Yet there is no single material that could satisfy all the requirements for desired photocatalysts: i) suitable band gap energy (1.7 eV< Eg < 2.3 eV) for high efficiency, ii) proper band position for reduction and/or oxidation of water, iii) long-term stability in aqueous solutions, iv) low cost, v) high crystallinity, and vi) high conductivity. Hence, in the selection of photocatalytic materials, we better start from intrinsically stable materials made of earth-abundant elements. The band bap energy is also the primary consideration to absorb ample amount of solar energy of wide wavelength spectrum. It sets the limit of theoretically maximum efficiency and it could also be extended by band engineering techniques. Upon selection of the candidate materials, we can also modify the materials for full utilization their potentials. The main path of efficiency loss in PEC water splitting process is recombination of photoelectrons and holes. We discuss the material designs including i) p-n heterojunction photoanodes for effective electron-hole separation, ii) electron highway to facilitate interparticle electron transfer, iii) metal or anion doping to improve conductivity of the semiconductor and to extend the range of light absorption, iv) one-dimensional nanomaterials to secure a short hole diffusion distance and vectoral electron transfer, and v) loading co-catalysts for facile charge separation. High efficiency has been demonstrated for all these examples due to efficient electron-hole separation. Finally, total systems for unassisted solar fuel production are demonstrated.

Efficient modulation of optical and electrical properties of X-shaped thermally activated delayed fluorescence emitters by substitution.

PubMed

Fan, Jianzhong; Wang, Xin; Lin, Lili; Wang, Chuankui

2016-08-01

A series of X-shaped thermally activated delayed fluorescence (TADF) emitters are systematically studied by first-principles calculations. Effects of the cyano group adding to the acceptor unit and the hydroxyl group adding to the donor part on the optical and electrical properties are analyzed. It is found that both kinds of groups can efficiently increase the emission wavelength to realize full-color emission. Although they play different roles in modulating the energy level of frontier orbitals, the S-T energy gap, the reorganization energy and transfer integral for different molecules, they can efficiently increase the charge transfer rate and reduce the difference of electron transfer rate and hole transfer rate. These results indicate that these designed strategies are efficient to achieve balanced charge transfer rates and modulate emission colors. By analyzing the energy matching between the TADF emitters and three kinds of hosts, the emission spectra of the 3,5-bis(N-carbazolyl)benzene (mcp) and the absorption spectra of most TADF emitters have a large overlap, which provides helpful information in application of these TADF molecules.

Molecular helices as electron acceptors in high-performance bulk heterojunction solar cells

DOE PAGES

Yu M. Zhong; Nam, Chang -Yong; Trinh, M. Tuan; ...

2015-09-18

Despite numerous organic semiconducting materials synthesized for organic photovoltaics in the past decade, fullerenes are widely used as electron acceptors in highly efficient bulk-heterojunction solar cells. None of the non-fullerene bulk heterojunction solar cells have achieved efficiencies as high as fullerene-based solar cells. Design principles for fullerene-free acceptors remain unclear in the field. Here we report examples of helical molecular semiconductors as electron acceptors that are on par with fullerene derivatives in efficient solar cells. We achieved an 8.3% power conversion efficiency in a solar cell, which is a record high for non-fullerene bulk heterojunctions. Femtosecond transient absorption spectroscopy revealedmore » both electron and hole transfer processes at the donor–acceptor interfaces. Atomic force microscopy reveals a mesh-like network of acceptors with pores that are tens of nanometres in diameter for efficient exciton separation and charge transport. As a result, this study describes a new motif for designing highly efficient acceptors for organic solar cells.« less

Molecular helices as electron acceptors in high-performance bulk heterojunction solar cells.

PubMed

Zhong, Yu; Trinh, M Tuan; Chen, Rongsheng; Purdum, Geoffrey E; Khlyabich, Petr P; Sezen, Melda; Oh, Seokjoon; Zhu, Haiming; Fowler, Brandon; Zhang, Boyuan; Wang, Wei; Nam, Chang-Yong; Sfeir, Matthew Y; Black, Charles T; Steigerwald, Michael L; Loo, Yueh-Lin; Ng, Fay; Zhu, X-Y; Nuckolls, Colin

2015-09-18

Despite numerous organic semiconducting materials synthesized for organic photovoltaics in the past decade, fullerenes are widely used as electron acceptors in highly efficient bulk-heterojunction solar cells. None of the non-fullerene bulk heterojunction solar cells have achieved efficiencies as high as fullerene-based solar cells. Design principles for fullerene-free acceptors remain unclear in the field. Here we report examples of helical molecular semiconductors as electron acceptors that are on par with fullerene derivatives in efficient solar cells. We achieved an 8.3% power conversion efficiency in a solar cell, which is a record high for non-fullerene bulk heterojunctions. Femtosecond transient absorption spectroscopy revealed both electron and hole transfer processes at the donor-acceptor interfaces. Atomic force microscopy reveals a mesh-like network of acceptors with pores that are tens of nanometres in diameter for efficient exciton separation and charge transport. This study describes a new motif for designing highly efficient acceptors for organic solar cells.

Novel multistep BRET-FRET energy transfer using nanoconjugates of firefly proteins, quantum dots, and red fluorescent proteins

NASA Astrophysics Data System (ADS)

Alam, Rabeka; Zylstra, Joshua; Fontaine, Danielle M.; Branchini, Bruce R.; Maye, Mathew M.

2013-05-01

Sequential bioluminescence resonance energy transfer (BRET) and fluorescence resonance energy transfer (FRET) from firefly luciferase to red fluorescent proteins using quantum dot or rod acceptor/donor linkers is described. The effect of morphology and tuned optical properties on the efficiency of this unique BRET-FRET system was evaluated.Sequential bioluminescence resonance energy transfer (BRET) and fluorescence resonance energy transfer (FRET) from firefly luciferase to red fluorescent proteins using quantum dot or rod acceptor/donor linkers is described. The effect of morphology and tuned optical properties on the efficiency of this unique BRET-FRET system was evaluated. Electronic supplementary information (ESI) available: Experimental details, Fig. S1 and Table S1-S4. See DOI: 10.1039/c3nr01842c

48 CFR 23.705 - Electronic products environmental assessment tool.

Code of Federal Regulations, 2010 CFR

2010-10-01

... REGULATION SOCIOECONOMIC PROGRAMS ENVIRONMENT, ENERGY AND WATER EFFICIENCY, RENEWABLE ENERGY TECHNOLOGIES... standard for personal computer products— (i) Was issued by the Institute of Electrical and Electronics.... 104-113, the “National Technology Transfer and Advancement Act of 1995”, (see 11.102(c)); (iii) Meets...

48 CFR 23.704 - Electronic products environmental assessment tool.

Code of Federal Regulations, 2011 CFR

2011-10-01

... REGULATION SOCIOECONOMIC PROGRAMS ENVIRONMENT, ENERGY AND WATER EFFICIENCY, RENEWABLE ENERGY TECHNOLOGIES... standard for personal computer products— (i) Was issued by the Institute of Electrical and Electronics.... 104-113, the “National Technology Transfer and Advancement Act of 1995”, (see 11.102(c)); (iii) Meets...

48 CFR 23.704 - Electronic product environmental assessment tool.

Code of Federal Regulations, 2014 CFR

2014-10-01

... REGULATION SOCIOECONOMIC PROGRAMS ENVIRONMENT, ENERGY AND WATER EFFICIENCY, RENEWABLE ENERGY TECHNOLOGIES... Electrical and Electronics Engineers, Inc., on March 5, 2010; October 19, 2012, and October 19, 2012.... 272 note), the “National Technology Transfer and Advancement Act of 1995,” (see 11.102(c)); (iii...

48 CFR 23.704 - Electronic products environmental assessment tool.

Code of Federal Regulations, 2012 CFR

2012-10-01

... REGULATION SOCIOECONOMIC PROGRAMS ENVIRONMENT, ENERGY AND WATER EFFICIENCY, RENEWABLE ENERGY TECHNOLOGIES... standard for personal computer products— (i) Was issued by the Institute of Electrical and Electronics.... 104-113, the “National Technology Transfer and Advancement Act of 1995”, (see 11.102(c)); (iii) Meets...

Electronic Modulation of Electrocatalytically Active Center of Cu7S4 Nanodisks by Cobalt-Doping for Highly Efficient Oxygen Evolution Reaction.

PubMed

Li, Qun; Wang, Xianfu; Tang, Kai; Wang, Mengfan; Wang, Chao; Yan, Chenglin

2017-12-26

Cu-based electrocatalysts have seldom been studied for water oxidation because of their inferior activity and poor stability regardless of their low cost and environmentally benign nature. Therefore, exploring an efficient way to improve the activity of Cu-based electrocatalysts is very important for their practical application. Modifying electronic structure of the electrocatalytically active center of electrocatalysts by metal doping to favor the electron transfer between catalyst active sites and electrode is an important approach to optimize hydrogen and oxygen species adsorption energy, thus leading to the enhanced intrinsic electrocatalytic activity. Herein, Co-doped Cu 7 S 4 nanodisks were synthesized and investigated as highly efficient electrocatalyst for oxygen evolution reaction (OER) due to the optimized electronic structure of the active center. Density-functional theory (DFT) calculations reveal that Co-engineered Cu 7 S 4 could accelerate electron transfer between Co and Cu sites, thus decrease the energy barriers of intermediates and products during OER, which are crucial for enhanced catalytic properties. As expected, Co-engineered Cu 7 S 4 nanodisks exhibit a low overpotential of 270 mV to achieve current density of 10 mA cm -2 as well as decreased Tafel slope and enhanced turnover frequencies as compared to bare Cu 7 S 4 . This discovery not only provides low-cost and efficient Cu-based electrocatalyst by Co doping, but also exhibits an in-depth insight into the mechanism of the enhanced OER properties.

Applications of free-electron lasers to measurements of energy transfer in biopolymers and materials

NASA Astrophysics Data System (ADS)

Edwards, Glenn S.; Johnson, J. B.; Kozub, John A.; Tribble, Jerri A.; Wagner, Katrina

1992-08-01

Free-electron lasers (FELs) provide tunable, pulsed radiation in the infrared. Using the FEL as a pump beam, we are investigating the mechanisms for energy transfer between localized vibrational modes and between vibrational modes and lattice or phonon modes. Either a laser-Raman system or a Fourier transform infrared (FTIR) spectrometer will serve as the probe beam, with the attribute of placing the burden of detection on two conventional spectroscopic techniques that circumvent the limited response of infrared detectors. More specifically, the Raman effect inelastically shifts an exciting laser line, typically a visible frequency, by the energy of the vibrational mode; however, the shifted Raman lines also lie in the visible, allowing for detection with highly efficient visible detectors. With regards to FTIR spectroscopy, the multiplex advantage yields a distinct benefit for infrared detector response. Our group is investigating intramolecular and intermolecular energy transfer processes in both biopolymers and more traditional materials. For example, alkali halides contain a number of defect types that effectively transfer energy in an intermolecular process. Similarly, the functioning of biopolymers depends on efficient intramolecular energy transfer. Understanding these mechanisms will enhance our ability to modify biopolymers and materials with applications to biology, medecine, and materials science.

Improved electron transfer and plasmonic effect in dye-sensitized solar cells with bi-functional Nb-doped TiO2/Ag ternary nanostructures.

PubMed

Park, Jung Tae; Chi, Won Seok; Jeon, Harim; Kim, Jong Hak

2014-03-07

TiO2 nanoparticles are surface-modified via atom transfer radical polymerization (ATRP) with a hydrophilic poly(oxyethylene)methacrylate (POEM), which can coordinate to the Ag precursor, i.e. silver trifluoromethanesulfonate (AgCF3SO3). Following the reduction of Ag ions, a Nb2O5 doping process and calcination at 450 °C, bi-functional Nb-doped TiO2/Ag ternary nanostructures are generated. The resulting nanostructures are characterized by energy-filtering transmission electron microscopy (EF-TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV-visible spectroscopy. The dye-sensitized solar cell (DSSC) based on the Nb-doped TiO2/Ag nanostructure photoanode with a polymerized ionic liquid (PIL) as the solid polymer electrolyte shows an overall energy conversion efficiency (η) of 6.9%, which is much higher than those of neat TiO2 (4.7%) and Nb-doped TiO2 (5.4%). The enhancement of η is mostly due to the increase of current density, attributed to the improved electron transfer properties including electron injection, collection, and plasmonic effects without the negative effects of charge recombination or problems with corrosion. These properties are supported by intensity modulated photocurrent/voltage spectroscopy (IMPS/IMVS) and incident photon-to-electron conversion efficiency (IPCE) measurements.

Microwave Driven Magnetic Plasma Accelerator Studies (CYCLOPS)

NASA Technical Reports Server (NTRS)

Crimi, G. F.; Eckert, A. C.; Miller, D. B.

1967-01-01

A microwave-driven cyclotron resonance plasma acceleration device was investigated using argon, krypton, xenon, and mercury as propellants. Limited ranges of propellant flow rate, input power, and magnetic field strength were used. Over-all efficiencies (including the 65% efficiency of the input polarizer) less than 10% were obtained for specific impulse values between 500 and 1500 sec. Power transfer efficiencies, however, approached 100% of the input power available in the right-hand component of the incident circularly polarized radiation. Beam diagnostics using Langmuir probes, cold gas mapping, r-f mapping and ion energy analyses were performed in conjunction with an engine operating in a pulsed mode. Measurements of transverse electron energies at the position of cyclotron resonant absorption yielded energy values more than an order of magnitude lower than anticipated. The measured electron energies were, however, consistent with the low values of average ion energy measured by retarding potential techniques. The low values of average ion energy were also consistent with the measured thrust values. It is hypothesized that ionization and radiation limit the electron kinetic energy to low-values thus limiting the energy which is finally transferred to the ion. Thermalization by electron-electron collision was also identified as an additional loss mechanism. The use of light alkali metals, which have relatively few low lying energy levels to excite, with the input power to mass ratio selected so as to limit the electron energies to less than the second ionization potential, is suggested. It is concluded, however, that the over-all efficiency for such propellants would be less than 40 per cent.

Experimental evaluation of cooling efficiency of the high performance cooling device

NASA Astrophysics Data System (ADS)

Nemec, Patrik; Malcho, Milan

2016-06-01

This work deal with experimental evaluation of cooling efficiency of cooling device capable transfer high heat fluxes from electric elements to the surrounding. The work contain description of cooling device, working principle of cooling device, construction of cooling device. Experimental part describe the measuring method of device cooling efficiency evaluation. The work results are presented in graphic visualization of temperature dependence of the contact area surface between cooling device evaporator and electronic components on the loaded heat of electronic components in range from 250 to 740 W and temperature dependence of the loop thermosiphon condenser surface on the loaded heat of electronic components in range from 250 to 740 W.

Single-Molecule Interfacial Electron Transfer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lu, H. Peter

This project is focused on the use of single-molecule high spatial and temporal resolved techniques to study molecular dynamics in condensed phase and at interfaces, especially, the complex reaction dynamics associated with electron and energy transfer rate processes. The complexity and inhomogeneity of the interfacial ET dynamics often present a major challenge for a molecular level comprehension of the intrinsically complex systems, which calls for both higher spatial and temporal resolutions at ultimate single-molecule and single-particle sensitivities. Combined single-molecule spectroscopy and electrochemical atomic force microscopy approaches are unique for heterogeneous and complex interfacial electron transfer systems because the static andmore » dynamic inhomogeneities can be identified and characterized by studying one molecule at a specific nanoscale surface site at a time. The goal of our project is to integrate and apply these spectroscopic imaging and topographic scanning techniques to measure the energy flow and electron flow between molecules and substrate surfaces as a function of surface site geometry and molecular structure. We have been primarily focusing on studying interfacial electron transfer under ambient condition and electrolyte solution involving both single crystal and colloidal TiO 2 and related substrates. The resulting molecular level understanding of the fundamental interfacial electron transfer processes will be important for developing efficient light harvesting systems and broadly applicable to problems in fundamental chemistry and physics. We have made significant advancement on deciphering the underlying mechanism of the complex and inhomogeneous interfacial electron transfer dynamics in dyesensitized TiO 2 nanoparticle systems that strongly involves with and regulated by molecule-surface interactions. We have studied interfacial electron transfer on TiO 2 nanoparticle surfaces by using ultrafast single-molecule spectroscopy and electrochemical AFM metal tip scanning microscopy, focusing on understanding the interfacial electron transfer dynamics at specific nanoscale electron transfer sites with high-spatially and temporally resolved topographic-and-spectroscopic characterization at individual molecule basis, characterizing single-molecule rate processes, reaction driving force, and molecule-substrate electronic coupling. One of the most significant characteristics of our new approach is that we are able to interrogate the complex interfacial electron transfer dynamics by actively pin-point energetic manipulation of the surface interaction and electronic couplings, beyond the conventional excitation and observation.« less

Modular Homogeneous Chromophore–Catalyst Assemblies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mulfort, Karen L.; Utschig, Lisa M.

2016-05-17

Photosynthetic reaction center (RC) proteins convert incident solar energy to chemical energy through a network of molecular cofactors which have been evolutionarily tuned to couple efficient light-harvesting, directional electron transfer, and long-lived charge separation with secondary reaction sequences. These molecular cofactors are embedded within a complex protein environment which precisely positions each cofactor in optimal geometries along efficient electron transfer pathways with localized protein environments facilitating sequential and accumulative charge transfer. By contrast, it is difficult to approach a similar level of structural complexity in synthetic architectures for solar energy conversion. However, by using appropriate self-assembly strategies, we anticipate thatmore » molecular modules, which are independently synthesized and optimized for either light-harvesting or redox catalysis, can be organized into spatial arrangements that functionally mimic natural photosynthesis. In this Account, we describe a modular approach to new structural designs for artificial photosynthesis which is largely inspired by photosynthetic RC proteins. We focus on recent work from our lab which uses molecular modules for light-harvesting or proton reduction catalysis in different coordination geometries and different platforms, spanning from discrete supramolecular assemblies to molecule–nanoparticle hybrids to protein-based biohybrids. Molecular modules are particularly amenable to high-resolution characterization of the ground and excited state of each module using a variety of physical techniques; such spectroscopic interrogation helps our understanding of primary artificial photosynthetic mechanisms. In particular, we discuss the use of transient optical spectroscopy, EPR, and X-ray scattering techniques to elucidate dynamic structural behavior and light-induced kinetics and the impact on photocatalytic mechanism. Two different coordination geometries of supramolecular photocatalyst based on the [Ru(bpy)3]2+ (bpy = 2,2'-bipyridine) light-harvesting module with cobaloxime-based catalyst module are compared, with progress in stabilizing photoinduced charge separation identified. These same modules embedded in the small electron transfer protein ferredoxin exhibit much longer charge-separation, enabled by stepwise electron transfer through the native [2Fe-2S] cofactor. We anticipate that the use of interchangeable, molecular modules which can interact in different coordination geometries or within entirely different structural platforms will provide important fundamental insights into the effect of environment on parameters such as electron transfer and charge separation, and ultimately drive more efficient designs for artificial photosynthesis.« less

Effect of generation on the electronic properties of light-emitting dendrimers

NASA Astrophysics Data System (ADS)

Burn, Paul L.; Halim, Mounir; Pillow, Jonathan N. G.; Samuel, Ifor D. W.

1999-12-01

We have compared the optical and electronic properties of a series of porphyrin centered dendrimers containing stilbene dendrons. The first and second generation dendrimers could be spin-coated from solution to form good quality thin films. Incorporation into single layer light-emitting diodes gave red-light emission with maximum external quantum efficiencies of 0.02% and 0.04% for the first and second generation dendrimers respectively. We have determined by photoluminescence studies that energy can be transferred efficiently from the stilbene dendrons to the porphyrin core and that PL emission is from the core. Cyclic voltammetry studies on the dendrimers show that the reductions are porphyrin centered with the dendrons only affecting the rate of heterogeneous electron transfer between the electrode and the dendrimers. This suggests that charge mobility within a dendrimer film in an LED will be affected by the porphyrin edge to porphyrin edge distance. We have studied the hydrodynamic radii of the dendrimers by gel permeation chromatography and found as expected that the average porphyrin edge to dendron edge distance increases with generation. This is consistent with the slowing of heterogeneous electron transfer observed in the cyclic voltammetry on increasing the generation number and suggests that the dendrons are interleaved in the solid state to facilitate charge transport.

Trapped in imidazole: how to accumulate multiple photoelectrons on a black-absorbing ruthenium complex.

PubMed

Zedler, Linda; Kupfer, Stephan; de Moraes, Inês Rabelo; Wächtler, Maria; Beckert, Rainer; Schmitt, Michael; Popp, Jürgen; Rau, Sven; Dietzek, Benjamin

2014-03-24

Ruthenium dyes incorporating a 4H-imidazole chromophore as a ligand exhibit a spectrally broad absorption in the UV/Vis region. Furthermore, they show the ability to store two electrons within the 4H-imidazole ligand. These features render them promising molecular systems, for example, as inter- or intramolecular electron relays. To optimize the structures with respect to their electron-storage capability, it is crucial to understand the impact of structural changes accompanying photoinduced charge transfer in the electronic intermediates of multistep electron-transfer processes. The photophysical properties of these (reactive) intermediates might impact the function of the molecular systems quite substantially. However, the spectroscopic study of short-lived intermediates in stepwise multielectron-transfer processes is experimentally challenging. To this end, this contribution reports on the electrochemical generation of anions identical to intermediate structures and their spectroscopic characterization by in situ resonance Raman and UV/Vis spectroelectrochemistry and computational methods. Thereby, an efficient two-electron pathway to the 4H-imidazole electron-accepting ligand is identified. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Efficiency of photochemical stages of photosynthesis in purple bacteria (a critical survey).

PubMed

Borisov, A Yu

2014-03-01

Based on currently available data, the energy transfer efficiency in the successive photophysical and photochemical stages has been analyzed for purple bacteria. This analysis covers the stages starting from migration of the light-induced electronic excitations from the bulk antenna pigments to the reaction centers up to irreversible stage of the electron transport along the transmembrane chain of cofactors-carriers. Some natural factors are revealed that significantly increase the rates of efficient processes in these stages. The influence on their efficiency by the "bottleneck" in the energy migration chain is established. The overall quantum yield of photosynthesis in these stages is determined.

Time-resolved measurement of intramolecular photoinduced electron transfer processes in perylene diimides (Conference Presentation)

NASA Astrophysics Data System (ADS)

Döring, Robin Carl; Baal, Eduard; Sundermeyer, Jörg; Chatterjee, Sangam

2017-02-01

Perylene-3,4,9,10-tetracarboxylic acid (PTCDA) and respective derivatives (e.g. perylene diimide - PDI) are widely used as dyes but also for device applications such as organic field effect transistors or in organic photovoltaics. Due to their intrinsically high quantum efficiencies they are also used as spectroscopic standards. One major drawback of these materials is their low solubility in organic solvents which can be addressed by long alkyl substitutions. When introducing a tertiary amine into the molecule a mechanism known as photoinduced electron transfer (PET) can occur. Here, following an optically excited HOMO-LUMO transition of the core, an electron from the electron lone pair of the amine is transferred to the HOMO of the perylene core. Hence, radiative recombination is disallowed and photoluminescence effectively quenched. Here, we perform a systematic study of the distance dependence of the PET by introducing alkyle groups as spacer units between PDI core and the tertiary amine. Dynamics of the PET are extracted from ultrafast time-resolved photoluminescence measurement data. A rate equation model, simulating a three level system, reveals rate constant of the back electron transfer, otherwise not accessible with our experimental methods. Assuming a Marcus model of electron transfer, electronic coupling strength between the electronic states involved in the respective transitions can be calculated. In addition to the distance dependence, the effects of protonation and methylation of the the tertiary amine units are studied.

Ero1-α and PDIs constitute a hierarchical electron transfer network of endoplasmic reticulum oxidoreductases

PubMed Central

Araki, Kazutaka; Iemura, Shun-ichiro; Kamiya, Yukiko; Ron, David; Kato, Koichi; Natsume, Tohru

2013-01-01

Ero1-α and endoplasmic reticulum (ER) oxidoreductases of the protein disulfide isomerase (PDI) family promote the efficient introduction of disulfide bonds into nascent polypeptides in the ER. However, the hierarchy of electron transfer among these oxidoreductases is poorly understood. In this paper, Ero1-α–associated oxidoreductases were identified by proteomic analysis and further confirmed by surface plasmon resonance. Ero1-α and PDI were found to constitute a regulatory hub, whereby PDI induced conformational flexibility in an Ero1-α shuttle cysteine (Cys99) facilitated intramolecular electron transfer to the active site. In isolation, Ero1-α also oxidized ERp46, ERp57, and P5; however, kinetic measurements and redox equilibrium analysis revealed that PDI preferentially oxidized other oxidoreductases. PDI accepted electrons from the other oxidoreductases via its a′ domain, bypassing the a domain, which serves as the electron acceptor from reduced glutathione. These observations provide an integrated picture of the hierarchy of cooperative redox interactions among ER oxidoreductases in mammalian cells. PMID:24043701

Charge Transfer Dynamics at Dye-Sensitized ZnO and TiO2 Interfaces Studied by Ultrafast XUV Photoelectron Spectroscopy

PubMed Central

Borgwardt, Mario; Wilke, Martin; Kampen, Thorsten; Mähl, Sven; Xiao, Manda; Spiccia, Leone; Lange, Kathrin M.; Kiyan, Igor Yu.; Aziz, Emad F.

2016-01-01

Interfacial charge transfer from photoexcited ruthenium-based N3 dye molecules into ZnO thin films received controversial interpretations. To identify the physical origin for the delayed electron transfer in ZnO compared to TiO2, we probe directly the electronic structure at both dye-semiconductor interfaces by applying ultrafast XUV photoemission spectroscopy. In the range of pump-probe time delays between 0.5 to 1.0 ps, the transient signal of the intermediate states was compared, revealing a distinct difference in their electron binding energies of 0.4 eV. This finding strongly indicates the nature of the charge injection at the ZnO interface associated with the formation of an interfacial electron-cation complex. It further highlights that the energetic alignment between the dye donor and semiconductor acceptor states appears to be of minor importance for the injection kinetics and that the injection efficiency is dominated by the electronic coupling. PMID:27073060

A Biomimetic-Computational Approach to Optimizing the Quantum Efficiency of Photovoltaics

NASA Astrophysics Data System (ADS)

Perez, Lisa M.; Holzenburg, Andreas

The most advanced low-cost organic photovoltaic cells have a quantum efficiency of 10%. This is in stark contrast to plant/bacterial light-harvesting systems which offer quantum efficiencies close to unity. Of particular interest is the highly effective quantum coherence-enabled energy transfer (Fig. 1). Noting that quantum coherence is promoted by charged residues and local dielectrics, classical atomistic simulations and time-dependent density functional theory (DFT) are used to identify charge/dielectric patterns and electronic coupling at exactly defined energy transfer interfaces. The calculations make use of structural information obtained on photosynthetic protein-pigment complexes while still in the native membrane making it possible to establish a link between supramolecular organization and quantum coherence in terms of what length scales enable fast energy transport and prevent quenching. Calculating energy transfer efficiencies between components based on different proximities will permit the search for patterns that enable defining material properties suitable for advanced photovoltaics.

Photocurrent generation by direct electron transfer using photosynthetic reaction centres

NASA Astrophysics Data System (ADS)

Mahmoudzadeh, A.; Saer, R.; Jun, D.; Mirvakili, S. M.; Takshi, A.; Iranpour, B.; Ouellet, E.; Lagally, E. T.; Madden, J. D. W.; Beatty, J. T.

2011-09-01

Photosynthetic reaction centres (RCs) convert light into separated charges with nearly perfect quantum efficiency, and have been used to generate photocurrent. Previous work has shown that electron tunnelling rates between redox centres in proteins depend exponentially on the tunnelling distance. In this work the RC from Rhodobacter sphaeroides was genetically modified with the aim of achieving the shortest tunnelling distances yet demonstrated between the RC's electron-accepting P site and underlying graphite and gold electrodes, and between the electron donor Q site and graphite electrodes. Opposite charges are carried to counter electrodes using mobile mediators, as in dye-sensitised solar cells. Native RCs are bound to graphite surfaces through N-(1-pyrene)iodoacetamide. Although the linker's length is only 4 Å, the electron transfer pathway between the Q electron donor site on the RC and the electrode surface is still too large for current to be significant. A mutant version with the electron acceptor P side close to the graphite surface produced currents of 15 nA cm-2 upon illumination. Direct binding of RCs to a gold surface is shown, resulting in currents of 5 nA cm-2. In both cases the current was unaffected by mediator concentration but increased with illumination, suggesting that direct electron transfer was achieved. The engineering of an RC to achieve direct electron transfer will help with long term efforts to demonstrate RC-based photovoltaic devices.

A fluorescent probe for ecstasy.

PubMed

Masseroni, D; Biavardi, E; Genovese, D; Rampazzo, E; Prodi, L; Dalcanale, E

2015-08-18

A nanostructure formed by the insertion in silica nanoparticles of a pyrene-derivatized cavitand, which is able to specifically recognize ecstasy in water, is presented. The absence of effects from interferents and an efficient electron transfer process occurring after complexation of ecstasy, makes this system an efficient fluorescent probe for this popular drug.

Efficient Energy Transfer from Near-Infrared Emitting Gold Nanoparticles to Pendant Ytterbium(III).

PubMed

Crawford, Scott E; Andolina, Christopher M; Kaseman, Derrick C; Ryoo, Bo Hyung; Smith, Ashley M; Johnston, Kathryn A; Millstone, Jill E

2017-12-13

Here, we demonstrate efficient energy transfer from near-infrared-emitting ortho-mercaptobenzoic acid-capped gold nanoparticles (AuNPs) to pendant ytterbium(III) cations. These functional materials combine the high molar absorptivity (1.21 × 10 6 M -1 cm -1 ) and broad excitation features (throughout the UV and visible regions) of AuNPs with the narrow emissive properties of lanthanides. Interaction between the AuNP ligand shell and ytterbium is determined using both nuclear magnetic resonance and electron microscopy measurements. In order to identify the mechanism of this energy transfer process, the distance of the ytterbium(III) from the surface of the AuNPs is systematically modulated by changing the size of the ligand appended to the AuNP. By studying the energy transfer efficiency from the various AuNP conjugates to pendant ytterbium(III) cations, a Dexter-type energy transfer mechanism is suggested, which is an important consideration for applications ranging from catalysis to energy harvesting. Taken together, these experiments lay a foundation for the incorporation of emissive AuNPs in energy transfer systems.

Enhancing the performance of Escherichia coli-inoculated microbial fuel cells by introduction of the phenazine-1-carboxylic acid pathway.

PubMed

Feng, Jiao; Qian, Ying; Wang, Zhen; Wang, Xin; Xu, Sheng; Chen, Kequan; Ouyang, Pingkai

2018-06-10

Microbial fuel cells (MFCs) are a renewable green energy source that uses microorganisms to catalytically convert chemical energy into electrical energy. The efficiency of extracellular electron transfer (EET) from the microbe cell to the anode electrode plays a key role in the MFC. However, the insulating properties of the cell membrane limit the efficiency of EET. Herein, EET efficiency was improved by introducing a phenazine synthesis pathway into Escherichia coli. Through the heterologous expression of phzA1B1C1D1E1F1G1, phenazine-1-carboxylic acid production increased, and the maximum power density increased from 16.7 mW/m 2 to 181.1 mW/m 2 . Furthermore, the charge transfer resistance of 6.7 Ω decreased to 4.2 Ω, which reflected the enhancement of the EET efficiency and the electricity power output. Our results imply that introducing a heterologous electron shuttle into E. coli could be an efficient approach to improving the EET efficiency and performance of an MFC. Copyright © 2018 Elsevier B.V. All rights reserved.

Electron transfer function versus oxygen delivery: a comparative study for several hexacoordinated globins across the animal kingdom.

PubMed

Kiger, Laurent; Tilleman, Lesley; Geuens, Eva; Hoogewijs, David; Lechauve, Christophe; Moens, Luc; Dewilde, Sylvia; Marden, Michael C

2011-01-01

Caenorhabditis elegans globin GLB-26 (expressed from gene T22C1.2) has been studied in comparison with human neuroglobin (Ngb) and cytoglobin (Cygb) for its electron transfer properties. GLB-26 exhibits no reversible binding for O(2) and a relatively low CO affinity compared to myoglobin-like globins. These differences arise from its mechanism of gaseous ligand binding since the heme iron of GLB-26 is strongly hexacoordinated in the absence of external ligands; the replacement of this internal ligand, probably the E7 distal histidine, is required before binding of CO or O(2) as for Ngb and Cygb. Interestingly the ferrous bis-histidyl GLB-26 and Ngb, another strongly hexacoordinated globin, can transfer an electron to cytochrome c (Cyt-c) at a high bimolecular rate, comparable to those of inter-protein electron transfer in mitochondria. In addition, GLB-26 displays an unexpectedly rapid oxidation of the ferrous His-Fe-His complex without O(2) actually binding to the iron atom, since the heme is oxidized by O(2) faster than the time for distal histidine dissociation. These efficient mechanisms for electron transfer could indicate a family of hexacoordinated globin which are functionally different from that of pentacoordinated globins.

Biochar as an electron shuttle for reductive dechlorination of pentachlorophenol by Geobacter sulfurreducens

PubMed Central

Yu, Linpeng; Yuan, Yong; Tang, Jia; Wang, Yueqiang; Zhou, Shungui

2015-01-01

The reductive dechlorination of pentachlorophenol (PCP) by Geobacter sulfurreducens in the presence of different biochars was investigated to understand how biochars affect the bioreduction of environmental contaminants. The results indicated that biochars significantly accelerate electron transfer from cells to PCP, thus enhancing reductive dechlorination. The promotion effects of biochar (as high as 24-fold) in this process depend on its electron exchange capacity (EEC) and electrical conductivity (EC). A kinetic model revealed that the surface redox-active moieties (RAMs) and EC of biochar (900 °C) contributed to 56% and 41% of the biodegradation rate, respectively. This work demonstrates that biochars are efficient electron mediators for the dechlorination of PCP and that both the EC and RAMs of biochars play important roles in the electron transfer process. PMID:26592958

Origin of Plasmon Lineshape and Enhanced Hot Electron Generation in Metal Nanoparticles.

PubMed

You, Xinyuan; Ramakrishna, S; Seideman, Tamar

2018-01-04

Plasmon-generated hot carriers are currently being studied intensively for their role in enhancing the efficiency of photovoltaic and photocatalytic processes. Theoretical studies of the hot electrons subsystem have generated insight, but we show that a unified quantum-mechanical treatment of the plasmon and hot electrons reveals new physical phenomena. Instead of a unidirectional energy transfer process in Landau damping, back energy transfer is predicted in small metal nanoparticles (MNPs) within a model-Hamiltonian approach. As a result, the single Lorentzian plasmonic line shape is modulated by a multipeak structure, whose individual line width provides a direct way to probe the electronic dephasing. More importantly, the hot electron generation can be enhanced greatly by matching the incident energy to the peaks of the modulated line shape.

Electron Transfer Dissociation: Effects of Cation Charge State on Product Partitioning in Ion/Ion Electron Transfer to Multiply Protonated Polypeptides

PubMed Central

Liu, Jian; McLuckey, Scott A.

2012-01-01

The effect of cation charge state on product partitioning in the gas-phase ion/ion electron transfer reactions of multiply protonated tryptic peptides, model peptides, and relatively large peptides with singly charged radical anions has been examined. In particular, partitioning into various competing channels, such as proton transfer (PT) versus electron transfer (ET), electron transfer with subsequent dissociation (ETD) versus electron transfer with no dissociation (ET,noD), and fragmentation of backbone bonds versus fragmentation of side chains, was measured quantitatively as a function of peptide charge state to allow insights to be drawn about the fundamental aspects of ion/ion reactions that lead to ETD. The ET channel increases relative to the PT channel, ETD increases relative to ET,noD, and fragmentation at backbone bonds increases relative to side-chain cleavages as cation charge state increases. The increase in ET versus PT with charge state is consistent with a Landau-Zener based curve-crossing model. An optimum charge state for ET is predicted by the model for the ground state-to-ground state reaction. However, when the population of excited product ion states is considered, it is possible that a decrease in ET efficiency as charge state increases will not be observed due to the possibility of the population of excited electronic states of the products. Several factors can contribute to the increase in ETD versus ET,noD and backbone cleavage versus side-chain losses. These factors include an increase in reaction exothermicity and charge state dependent differences in precursor and product ion structures, stabilities, and sites of protonation. PMID:23264749

Impact of undamped and damped intramolecular vibrations on the efficiency of photosynthetic exciton energy transfer

NASA Astrophysics Data System (ADS)

Juhász, Imre Benedek; Csurgay, Árpád I.

2018-04-01

In recent years, the role of molecular vibrations in exciton energy transfer taking place during the first stage of photosynthesis attracted increasing interest. Here, we present a model formulated as a Lindblad-type master equation that enables us to investigate the impact of undamped and especially damped intramolecular vibrational modes on the exciton energy transfer, particularly its efficiency. Our simulations confirm the already reported effects that the presence of an intramolecular vibrational mode can compensate the energy detuning of electronic states, thus promoting the energy transfer; and, moreover, that the damping of such a vibrational mode (in other words, vibrational relaxation) can further enhance the efficiency of the process by generating directionality in the energy flow. As a novel result, we show that this enhancement surpasses the one caused by pure dephasing, and we present its dependence on various system parameters (time constants of the environment-induced relaxation and excitation processes, detuning of the electronic energy levels, frequency of the intramolecular vibrational modes, Huang-Rhys factors, temperature) in dimer model systems. We demonstrate that vibrational-relaxation-enhanced exciton energy transfer (VREEET) is robust against the change of these characteristics of the system and occurs in wide ranges of the investigated parameters. With simulations performed on a heptamer model inspired by the Fenna-Matthews-Olson (FMO) complex, we show that this mechanism can be even more significant in larger systems at T = 300 K. Our results suggests that VREEET might be prevalent in light-harvesting complexes.

Photochemical charge separation in zeolites: Electron transfer dynamics, nanocrystals and zeolitic membranes. Final technical report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dutta, Prabir K.

2001-09-30

Aluminosilicate zeolites provide an excellent host for photochemical charge separation. Because of the constraints provided by the zeolite, the back electron transfer from the reduced acceptor to the oxidized sensitizer is slowed down. This provides the opportunity to separate the charge and use it in a subsequent reaction for water oxidation and reduction. Zeolite-based ruthenium oxide catalysts have been found to be efficient for the water splitting process. This project has demonstrated the usefulness of zeolite hosts for photolytic splitting of water.

Study of intermediates from transition metal excited-state electron-transfer reactions

NASA Astrophysics Data System (ADS)

Hoffman, M. Z.

1984-03-01

Attention during the past year focused on MV(+)., the reduced methyl viologen radical cation, which is a precursor to the formation of H2 in the photosensitized reduction of water. Through the use of photochemical and radiation chemical techniques, the efficiency of interaction of MV(+). with colloidal Pt, the stability of MV(+). as a function of pH, the quantum yield of formation of MV(+). in the Ru(bpy)3(2+)/MV(2+)/EDTA system, and the formation of photoactive charge-transfer complexes between MV(2+) and sacrificial electron donors were studied.

Electron transfer from plastocyanin to photosystem I.

PubMed Central

Haehnel, W; Jansen, T; Gause, K; Klösgen, R B; Stahl, B; Michl, D; Huvermann, B; Karas, M; Herrmann, R G

1994-01-01

Mutant plastocyanins with Leu at position 10, 90 or 83 (Gly, Ala and Tyr respectively in wildtype) were constructed by site-specific mutagenesis of the spinach gene, and expressed in transgenic potato plants under the control of the authentic plastocyanin promoter, as well as in Escherichia coli as truncated precursor intermediates carrying the C-terminal 22 amino acid residues of the transit peptide, i.e. the thylakoid-targeting domain that acts as a bacterial export signal. The identity of the purified plastocyanins was verified by matrix-assisted laser desorption/ionization mass spectrometry. The formation of a complex between authentic or mutant spinach plastocyanin and isolated photosystem I and the electron transfer has been studied from the biphasic reduction kinetics of P700+ after excitation with laser flashes. The formation of the complex was abolished by the bulky hydrophobic group of Leu at the respective position of G10 or A90 which are part of the conserved flat hydrophobic surface around the copper ligand H87. The rate of electron transfer decreased by both mutations to < 20% of that found with wildtype plastocyanin. We conclude that the conserved flat surface of plastocyanin represents one of two crucial structural elements for both the docking at photosystem I and the efficient electron transfer via H87 to P700+. The Y83L mutant exhibited faster electron transfer to P700+ than did authentic plastocyanin. This proves that Y83 is not involved in electron transfer to P700 and suggests that electron transfer from cytochrome f and to P700 follows different routes in the plastocyanin molecule. Plastocyanin (Y83L) expressed in either E. coli or potato exhibited different isoelectric points and binding constants to photosystem I indicative of differences in the folding of the protein. The structure of the binding site at photosystem I and the mechanism of electron transfer are discussed. Images PMID:8131737

Reversible Quantum Brownian Heat Engines for Electrons

NASA Astrophysics Data System (ADS)

Humphrey, T. E.; Newbury, R.; Taylor, R. P.; Linke, H.

2002-08-01

Brownian heat engines use local temperature gradients in asymmetric potentials to move particles against an external force. The energy efficiency of such machines is generally limited by irreversible heat flow carried by particles that make contact with different heat baths. Here we show that, by using a suitably chosen energy filter, electrons can be transferred reversibly between reservoirs that have different temperatures and electrochemical potentials. We apply this result to propose heat engines based on mesoscopic semiconductor ratchets, which can quasistatically operate arbitrarily close to Carnot efficiency.

Reversible quantum heat engines for electrons

NASA Astrophysics Data System (ADS)

Linke, Heiner; Humphrey, Tammy E.; Newbury, Richard; Taylor, Richard P.

2002-03-01

Brownian heat engines use local temperature gradients in asymmetric potentials to move particles against an external force. The energy efficiency of such machines is generally limited by irreversible heat flow carried by particles that make contact with different heat baths. Here we show that, by using a suitably chosen energy filter, electrons can be transferred reversibly between reservoirs that have different temperatures and electrochemical potentials. We apply this result to propose heat engines based on quantum ratchets, which can quasistatically operate at Carnot efficiency.

Electronic structural dependence of the photophysical properties of fluorescent heteroditopic ligands - implications in designing molecular fluorescent indicators.

PubMed

Younes, Ali H; Zhang, Lu; Clark, Ronald J; Davidson, Michael W; Zhu, Lei

2010-12-07

Two fluorescent heteroditopic ligands (2a and 2b) for zinc ion were synthesized and studied. The efficiencies of two photophysical processes, intramolecular charge transfer (ICT) and photoinduced electron transfer (PET), determine the magnitudes of emission bathochromic shift and enhancement, respectively, when a heteroditopic ligand forms mono- or dizinc complexes. The electron-rich 2b is characterized by a high degree of ICT in the excited state with little propensity for PET, which is manifested in a large bathochromic shift of emission upon Zn(2+) coordination without enhancement in fluorescence quantum yield. The electron-poor 2a displays the opposite photophysical consequence where Zn(2+) binding results in greatly enhanced emission without significant spectral shift. The electronic structural effects on the relative efficiencies of ICT and PET in 2a and 2b as well as the impact of Zn(2+)-coordination are probed using experimental and computational approaches. This study reveals that the delicate balance between various photophysical pathways (e.g. ICT and PET) engineered in a heteroditopic ligand is sensitively dependent on the electronic structure of the ligand, i.e. whether the fluorophore is electron-rich or poor, whether it possesses a donor-acceptor type of structure, and where the metal binding occurs.

Intramolecular Charge Transfer of Conjugated Liquid Crystal Ferrocene Macromolecules - Synthesis and Characterization

DTIC Science & Technology

2016-04-12

AFRL-AFOSR-CL-TR-2016-0012 Intramolecular Charge Transfer of Conjugated Liquid Crystal Ferrocene Macromolecules Ronald Ziolo CIQA Final Report 07/07...3. DATES COVERED (From - To)  15 Aug 2014 to 14 Jan 2016 4. TITLE AND SUBTITLE Intramolecular Charge Transfer of Conjugated Liquid Crystal Ferrocene...characterization of a new series of conjugated macromolecules bearing ferrocene as a highly efficient electron donor material coupled to 2,5-di(alcoxy) benzene

A Synthetic Approach to the Transfer Matrix Method in Classical and Quantum Physics

ERIC Educational Resources Information Center

Pujol, O.; Perez, J. P.

2007-01-01

The aim of this paper is to propose a synthetic approach to the transfer matrix method in classical and quantum physics. This method is an efficient tool to deal with complicated physical systems of practical importance in geometrical light or charged particle optics, classical electronics, mechanics, electromagnetics and quantum physics. Teaching…

Controllable Spatial Configuration on Cathode Interface for Enhanced Photovoltaic Performance and Device Stability.

PubMed

Li, Jiangsheng; Duan, Chenghao; Wang, Ning; Zhao, Chengjie; Han, Wei; Jiang, Li; Wang, Jizheng; Zhao, Yingjie; Huang, Changshui; Jiu, Tonggang

2018-05-08

The molecular structure of cathode interface modification materials can affect the surface morphology of the active layer and key electron transfer processes occurring at the interface of polymer solar cells in inverted structures mostly due to the change of molecular configuration. To investigate the effects of spatial configuration of the cathode interfacial modification layer on polymer solar cells device performances, we introduced two novel organic ionic salts (linear NS2 and three-dimensional (3D) NS4) combined with the ZnO film to fabricate highly efficient inverted solar cells. Both organic ionic salts successfully decreased the surface traps of the ZnO film and made its work function more compatible. Especially NS4 in three-dimensional configuration increased the electron mobility and extraction efficiency of the interfacial film, leading to a significant improvement of device performance. Power conversion efficiency (PCE) of 10.09% based on NS4 was achieved. Moreover, 3D interfacial modification could retain about 92% of its initial PCE over 160 days. It is proposed that 3D interfacial modification retards the element penetration-induced degradation without impeding the electron transfer from the active layer to the ZnO film, which significantly improves device stability. This indicates that inserting three-dimensional organic ionic salt is an efficient strategy to enhance device performance.

Tuning of Hemes b Equilibrium Redox Potential Is Not Required for Cross-Membrane Electron Transfer.

PubMed

Pintscher, Sebastian; Kuleta, Patryk; Cieluch, Ewelina; Borek, Arkadiusz; Sarewicz, Marcin; Osyczka, Artur

2016-03-25

In biological energy conversion, cross-membrane electron transfer often involves an assembly of two hemesb The hemes display a large difference in redox midpoint potentials (ΔEm_b), which in several proteins is assumed to facilitate cross-membrane electron transfer and overcome a barrier of membrane potential. Here we challenge this assumption reporting on hemebligand mutants of cytochromebc1in which, for the first time in transmembrane cytochrome, one natural histidine has been replaced by lysine without loss of the native low spin type of heme iron. With these mutants we show that ΔEm_b can be markedly increased, and the redox potential of one of the hemes can stay above the level of quinone pool, or ΔEm_b can be markedly decreased to the point that two hemes are almost isopotential, yet the enzyme retains catalytically competent electron transfer between quinone binding sites and remains functionalin vivo This reveals that cytochromebc1can accommodate large changes in ΔEm_b without hampering catalysis, as long as these changes do not impose overly endergonic steps on downhill electron transfer from substrate to product. We propose that hemesbin this cytochrome and in other membranous cytochromesbact as electronic connectors for the catalytic sites with no fine tuning in ΔEm_b required for efficient cross-membrane electron transfer. We link this concept with a natural flexibility in occurrence of several thermodynamic configurations of the direction of electron flow and the direction of the gradient of potential in relation to the vector of the electric membrane potential. © 2016 by The American Society for Biochemistry and Molecular Biology, Inc.

Estimates of electronic coupling for excess electron transfer in DNA

NASA Astrophysics Data System (ADS)

Voityuk, Alexander A.

2005-07-01

Electronic coupling Vda is one of the key parameters that determine the rate of charge transfer through DNA. While there have been several computational studies of Vda for hole transfer, estimates of electronic couplings for excess electron transfer (ET) in DNA remain unavailable. In the paper, an efficient strategy is established for calculating the ET matrix elements between base pairs in a π stack. Two approaches are considered. First, we employ the diabatic-state (DS) method in which donor and acceptor are represented with radical anions of the canonical base pairs adenine-thymine (AT) and guanine-cytosine (GC). In this approach, similar values of Vda are obtained with the standard 6-31G* and extended 6-31++G** basis sets. Second, the electronic couplings are derived from lowest unoccupied molecular orbitals (LUMOs) of neutral systems by using the generalized Mulliken-Hush or fragment charge methods. Because the radical-anion states of AT and GC are well reproduced by LUMOs of the neutral base pairs calculated without diffuse functions, the estimated values of Vda are in good agreement with the couplings obtained for radical-anion states using the DS method. However, when the calculation of a neutral stack is carried out with diffuse functions, LUMOs of the system exhibit the dipole-bound character and cannot be used for estimating electronic couplings. Our calculations suggest that the ET matrix elements Vda for models containing intrastrand thymine and cytosine bases are essentially larger than the couplings in complexes with interstrand pyrimidine bases. The matrix elements for excess electron transfer are found to be considerably smaller than the corresponding values for hole transfer and to be very responsive to structural changes in a DNA stack.

Role of Electron-Driven Proton-Transfer Processes in the Ultrafast Deactivation of Photoexcited Anionic 8-oxoGuanine-Adenine and 8-oxoGuanine-Cytosine Base Pairs.

PubMed

Wu, Xiuxiu; Karsili, Tolga N V; Domcke, Wolfgang

2017-01-14

It has been reported that 8-oxo-7,8-dihydro-guanosine (8-oxo-G), which is the main product of oxidative damage of DNA, can repair cyclobutane pyrimidine dimer (CPD) lesions when incorporated into DNA or RNA strands in proximity to such lesions. It has therefore been suggested that the 8-oxo-G nucleoside may have been a primordial precursor of present-day flavins in DNA or RNA repair. Because the electron transfer leading to the splitting of a thymine-thymine pair in a CPD lesion occurs in the photoexcited state, a reasonably long excited-state lifetime of 8-oxo-G is required. The neutral (protonated) form of 8-oxo-G exhibits a very short (sub-picosecond) intrinsic excited-state lifetime which is unfavorable for repair. It has therefore been argued that the anionic (deprotonated) form of 8-oxo-G, which exhibits a much longer excited-state lifetime, is more likely to be a suitable cofactor for DNA repair. Herein, we have investigated the exited-state quenching mechanisms in the hydrogen-bonded complexes of deprotonated 8-oxo-G - with adenine (A) and cytosine (C) using ab initio wave-function-based electronic-structure calculations. The calculated reaction paths and potential-energy profiles reveal the existence of barrierless electron-driven inter-base proton-transfer reactions which lead to low-lying S₁/S₀ conical intersections. The latter can promote ultrafast excited-state deactivation of the anionic base pairs. While the isolated deprotonated 8-oxo-G - nucleoside may have been an efficient primordial repair cofactor, the excited states of the 8-oxo-G - -A and 8-oxo-G - -C base pairs are likely too short-lived to be efficient electron-transfer repair agents.

Enhanced photocatalytic activity of graphitic carbon nitride/carbon nanotube/Bi2WO6 ternary Z-scheme heterojunction with carbon nanotube as efficient electron mediator.

PubMed

Jiang, Deli; Ma, Wanxia; Xiao, Peng; Shao, Leqiang; Li, Di; Chen, Min

2018-02-15

All-solid-state Z-scheme heterojunction has attracted much attention in photocatalytic field because of its strong ability in charge separation and transfer. In the present study, all-solid-state ternary Z-scheme heterojunction constructed by graphitic carbon nitride (CN) nanosheet, carbon nanotube (CNT), and Bi 2 WO 6 (BWO) nanosheet, in which CNT was employed as the electron mediator. The CN/CNT/BWO ternary Z-scheme heterojunction shows the enhanced photocatalytic activity towards the degradation of tetracycline hydrochloride (TC) as compared to the pristine g-C 3 N 4 , Bi 2 WO 6 , CNT/BWO, CNT/CN, and CN/BWO. The significantly improved photocatalytic activity can be mainly ascribed to the formed CNT-mediated Z-scheme heterojunction, which facilitates the separation and transfer of photogenerated electron-hole pairs. Our work provides a rational design of all-solid-state Z-scheme heterojunction with CNT as the electron mediator for highly efficient photocatalysis. Copyright © 2017 Elsevier Inc. All rights reserved.

Metal-Free Photoinduced Electron Transfer-Atom Transfer Radical Polymerization Integrated with Bioinspired Polydopamine Chemistry as a Green Strategy for Surface Engineering of Magnetic Nanoparticles.

PubMed

Yang, Yang; Liu, Xuegang; Ye, Gang; Zhu, Shan; Wang, Zhe; Huo, Xiaomei; Matyjaszewski, Krzysztof; Lu, Yuexiang; Chen, Jing

2017-04-19

Developing green and efficient technologies for surface modification of magnetic nanoparticles (MNPs) is of crucial importance for their biomedical and environmental applications. This study reports, for the first time, a novel strategy by integrating metal-free photoinduced electron transfer-atom transfer radical polymerization (PET-ATRP) with the bioinspired polydopamine (PDA) chemistry for controlled architecture of functional polymer brushes from MNPs. Conformal PDA encapsulation layers were initially generated on the surfaces of MNPs, which served as the protective shells while providing an ideal platform for tethering 2-bromo-2-phenylacetic acid (BPA), a highly efficient initiator. Metal-free PET-ATRP technique was then employed for controlled architecture of poly(glycidyl methacrylate) (PGMA) brushes from the core-shell MNPs by using diverse organic dyes as photoredox catalysts. Impacts of light sources (including UV and visible lights), photoredox catalysts, and polymerization time on the composition and morphology of the PGMA brushes were investigated. Moreover, the versatility of the PGMA-functionalized core-shell MNPs was demonstrated by covalent attachment of ethylenediamine (EDA), a model functional molecule, which afforded the MNPs with improved hydrophilicity, dispersibility, and superior binding ability to uranyl ions. The green methodology by integrating metal-free PET-ATRP with facile PDA chemistry would provide better opportunities for surface modification of MNPs and miscellaneous nanomaterials for biomedical and electronic applications.

Energy transfer dynamics in Light-Harvesting Dendrimers

NASA Astrophysics Data System (ADS)

Melinger, Joseph S.; McMorrow, Dale; Kleiman, Valeria D.

2002-03-01

We explore energy transfer dynamics in light-harvesting phenylacetylene symmetric and asymmetric dendrimers. Femtosecond pump-probe spectroscopy is used to probe the ultrafast dynamics of electronic excitations in these dendrimers. The backbone of the macromolecule consists of branches of increasing conjugation length, creating an energy gradient, which funnels energy to an accepting perylene trap. In the case of the symmetric dendrimer (nanostar), the energy transfer efficiency is known to approach nearly unity, although the nature and timescale of the energy transfer process is still unknown. For the asymmetric dendrimers, energy transfer efficiencies are very high, with the possibility of more complex transfer processes. We experimentally monitor the transport of excitons through the light-harvesting dendrimer. The transients show a number of components, with timescales ranging from <300fs to several tens of picoseconds, revealing the complex photophysics taking place in these macromolecules. We interpret our results in terms of the Förster mechanism in which energy transfer occurs through dipole-dipole interactions.

Delayed Triplet-State Formation through Hybrid Charge Transfer Exciton at Copper Phthalocyanine/GaAs Heterojunction.

PubMed

Lim, Heeseon; Kwon, Hyuksang; Kim, Sang Kyu; Kim, Jeong Won

2017-10-05

Light absorption in organic molecules on an inorganic substrate and subsequent electron transfer to the substrate create so-called hybrid charge transfer exciton (HCTE). The relaxation process of the HCTE states largely determines charge separation efficiency or optoelectronic device performance. Here, the study on energy and time-dispersive behavior of photoelectrons at the hybrid interface of copper phthalocyanine (CuPc)/p-GaAs(001) upon light excitation of GaAs reveals a clear pathway for HCTE relaxation and delayed triplet-state formation. According to the ground-state energy level alignment at the interface, CuPc/p-GaAs(001) shows initially fast hole injection from GaAs to CuPc. Thus, the electrons in GaAs and holes in CuPc form an unusual HCTE state manifold. Subsequent electron transfer from GaAs to CuPc generates the formation of the triplet state in CuPc with a few picoseconds delay. Such two-step charge transfer causes delayed triplet-state formation without singlet excitation and subsequent intersystem crossing within the CuPc molecules.

Long distance electron-transfer mechanism in peptidylglycine alpha-hydroxylating monooxygenase: a perfect fitting for a water bridge.

PubMed

de la Lande, Aurélien; Martí, Sergio; Parisel, Olivier; Moliner, Vicent

2007-09-26

The active sites of copper enzymes have been the subject of many theoretical and experimental investigations from a number of years. Such studies have embraced topics devoted to the modeling of the first coordination sphere at the metallic cations up to the development of biomimetic, or bioinspired, catalytic systems. At least from the theoretical viewpoint, fewer efforts have been dedicated to elucidate how the two copper cations act concertedly in noncoupled dicopper enzymes such as peptidylglycine alpha-hydroxylating monooxygenase (PHM) and dopamine beta-monooxygenase (DbetaM). In these metalloenzymes, an electronic transfer is assumed between the two distant copper cations (11 A). Recent experimental results suggest that this transfer occurs through water molecules, a phenomenon which has been theoretically evidenced to be of high efficiency in the case of cytochrome b5 (Science, 2005, 310, 1311). In the present contribution dedicated to PHM, we overpass the common theoretical approaches dedicated to the electronic and geometrical structures of sites CuM or CuH restricted to their first coordination spheres and aim at directly comparing theoretical results to the experimentally measured activity of the PHM enzyme. To achieve this goal, molecular dynamics simulations were performed on wild-type and various mutants of PHM. More precisely, we provide an estimate of the electron-transfer efficiency between the CuM and CuH sites by means of such molecular dynamics simulations coupled to Marcus theory joined to the Beratan model to approximate the required coupling matrix elements. The theoretical results are compared to the kinetics measurements performed on wild and mutated PHM. The present work, the dynamic aspects of which are essential, accounts for the experimental results issued from mutagenesis. It supports the conclusion that an electronic transfer can occur between two copper(I) sites along a bridge involving a set of hydrogen and chemical bonds. Residue Gln170 is evidenced to be the keystone of this water-mediated pathway.

High Efficiency Electron-Laser Interactions in Tapered Helical Undulators

NASA Astrophysics Data System (ADS)

Duris, Joseph Patrick

Efficient coupling of relativistic electron beams with high power radiation lies at the heart of advanced accelerator and light source research and development. The inverse free electron laser is a stable accelerator capable of harnessing very high intensity laser electric fields to efficiently transfer large powers from lasers to electron beams. In this dissertation, we first present the theoretical framework to describe the interaction, and then apply our improved understanding of the IFEL to the design and numerical study of meter-long, GeV IFELs for compact light sources. The central experimental work of the dissertation is the UCLA BNL helical inverse free electron laser experiment at the Accelerator Test Facility in Brookhaven National Laboratory which used a strongly tapered 54cm long, helical, permanent magnet undulator and a several hundred GW CO2 laser to accelerate electrons from 52 to 106MeV, setting new records for inverse free electron laser energy gain (54MeV) and average accelerating gradient (100MeV/m). The undulator design and fabrication as well as experimental diagnostics are presented. In order to improve the stability and quality of the accelerated electron beam, we redesigned the undulator for a slightly reduced output energy by modifying the magnet gap throughout the undulator, and we used this modified undulator to demonstrated capture of >25% of the injected beam without prebunching. In the study of heavily loaded GeV inverse free electron lasers, we show that a majority of the power may be transferred from a laser to the accelerated electron beam. Reversing the process to decelerate high power electron beams, a mechanism we refer to as tapering enhanced stimulated superradiant amplification, offers a clear path to high power light sources. We present studies of radiation production for a wide range of wavelengths (10mum, 13nm, and 0.3nm) using this method and discuss the design for a deceleration experiment using the same undulator used for acceleration in this experiment. By accounting for the evolving radiation field in the design of the undulator tapering, a large fraction of energy may be transferred between the electrons and laser, enabling compact, high-current GeV accelerators and various wavelength light-sources of unprecedented peak powers.

Enhanced Photoelectrocatalytic Activity of BiOI Nanoplate-Zinc Oxide Nanorod p-n Heterojunction.

PubMed

Kuang, Pan-Yong; Ran, Jing-Run; Liu, Zhao-Qing; Wang, Hong-Juan; Li, Nan; Su, Yu-Zhi; Jin, Yong-Gang; Qiao, Shi-Zhang

2015-10-19

The development of highly efficient and robust photocatalysts has attracted great attention for solving the global energy crisis and environmental problems. Herein, we describe the synthesis of a p-n heterostructured photocatalyst, consisting of ZnO nanorod arrays (NRAs) decorated with BiOI nanoplates (NPs), by a facile solvothermal method. The product thus obtained shows high photoelectrochemical water splitting performance and enhanced photoelectrocatalytic activity for pollutant degradation under visible light irradiation. The p-type BiOI NPs, with a narrow band gap, not only act as a sensitizer to absorb visible light and promote electron transfer to the n-type ZnO NRAs, but also increase the contact area with organic pollutants. Meanwhile, ZnO NRAs provide a fast electron-transfer channel, thus resulting in efficient separation of photoinduced electron-hole pairs. Such a p-n heterojunction nanocomposite could serve as a novel and promising catalyst in energy and environmental applications. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Facile fabrication of BiVO4 nanofilms with controlled pore size and their photoelectrochemical performances

NASA Astrophysics Data System (ADS)

Feng, Chenchen; Jiao, Zhengbo; Li, Shaopeng; Zhang, Yan; Bi, Yingpu

2015-12-01

We demonstrate a facile method for the rational fabrication of pore-size controlled nanoporous BiVO4 photoanodes, and confirmed that the optimum pore-size distributions could effectively absorb visible light through light diffraction and confinement functions. Furthermore, in situ X-ray photoelectron spectroscopy (XPS) reveals more efficient photoexcited electron-hole separation than conventional particle films, induced by light confinement and rapid charge transfer in the inter-crossed worm-like structures.We demonstrate a facile method for the rational fabrication of pore-size controlled nanoporous BiVO4 photoanodes, and confirmed that the optimum pore-size distributions could effectively absorb visible light through light diffraction and confinement functions. Furthermore, in situ X-ray photoelectron spectroscopy (XPS) reveals more efficient photoexcited electron-hole separation than conventional particle films, induced by light confinement and rapid charge transfer in the inter-crossed worm-like structures. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr06584d

Impact of interfacial molecular orientation on radiative recombination and charge generation efficiency

DOE PAGES

Ran, Niva A.; Roland, Steffen; Love, John A.; ...

2017-07-19

Here, a long standing question in organic electronics concerns the effects of molecular orientation at donor/acceptor heterojunctions. Given a well-controlled donor/acceptor bilayer system, we uncover the genuine effects of molecular orientation on charge generation and recombination. These effects are studied through the point of view of photovoltaics—however, the results have important implications on the operation of all optoelectronic devices with donor/acceptor interfaces, such as light emitting diodes and photodetectors. Our findings can be summarized by two points. First, devices with donor molecules face-on to the acceptor interface have a higher charge transfer state energy and less non-radiative recombination, resulting inmore » larger open-circuit voltages and higher radiative efficiencies. Second, devices with donor molecules edge-on to the acceptor interface are more efficient at charge generation, attributed to smaller electronic coupling between the charge transfer states and the ground state, and lower activation energy for charge generation.« less

Enhanced Internal Quantum Efficiency in Dye-Sensitized Solar Cells: Effect of Long-Lived Charge-Separated State of Sensitizers.

PubMed

Sun, Haiya; Liu, Dongzhi; Wang, Tianyang; Lu, Ting; Li, Wei; Ren, Siyao; Hu, Wenping; Wang, Lichang; Zhou, Xueqin

2017-03-22

Effective charge separation is one of the key determinants for the photovoltaic performance of the dye-sensitized solar cells (DSSCs). Herein, two charge-separated (CS) sensitizers, MTPA-Pyc and YD-Pyc, have been synthesized and applied in DSSCs to investigate the effect of the CS states of the sensitizers on the device's efficiency. The CS states with lifetimes of 64 and 177 ns for MTPA-Pyc and YD-Pyc, respectively, are formed via the photoinduced electron transfer (PET) from the 4-styryltriphenylamine (MTPA) or 4-styrylindoline (YD) donor to the pyrimidine cyanoacrylic acid (Pyc) acceptor. DSSCs based on MTPA-Pyc and YD-Pyc exhibit high internal quantum efficiency (IQE) values of over 80% from 400 to 600 nm. In comparison, the IQEs of the charge transfer (CT) sensitizer cells are 10-30% lower in the same wavelength range. The enhanced IQE values in the devices based on the CS sensitizers are ascribed to the higher electron injection efficiencies and slower charge recombination. The results demonstrate that taking advantage of the CS states in the sensitizers can be a promising strategy to improve the IQEs and further enhance the overall efficiencies of the DSSCs.

Immobilization of glucose oxidase into a nanoporous TiO₂ film layered on metallophthalocyanine modified vertically-aligned carbon nanotubes for efficient direct electron transfer.

PubMed

Cui, Hui-Fang; Zhang, Kuan; Zhang, Yong-Fang; Sun, Yu-Long; Wang, Jia; Zhang, Wei-De; Luong, John H T

2013-08-15

Glucose oxidase (GOD) was adsorbed into a nanoporous TiO₂ film layered on the surface of an iron phthalocyanine (FePc) vertically-aligned carbon nanotube (CNT) modified electrode. A Nafion film was then dropcast on the electrode's surface to improve operational and storage stabilities of the GOD-based electrode. Scanning electron microscopy (SEM) micrographs revealed the formation of FePc and nanoporous TiO₂ nanoparticles along the sidewall and the tip of CNTs. Cyclic voltammograms of the GOD electrode in neutral PBS exhibited a pair of well-defined redox peaks, attesting the direct electron transfer of GOD (FAD/FADH₂) with the underlying electrode. The potential of glucose electro-oxidation under nitrogen was ∼+0.12 V with an oxidation current density of 65.3 μA cm(-2) at +0.77 V. Voltammetric and amperometric responses were virtually unaffected by oxygen, illustrating an efficient and fast direct electron transfer. The modification of the CNT surface with FePc resulted in a biosensor with remarkable detection sensitivity with an oxygen-independent bioelectrocatalysis. In deaerated PBS, the biosensor displayed average response time of 12 s, linearity from 50 μM to 4 mM, and a detection limit of 30 μM (S/N=3) for glucose. Copyright © 2013 Elsevier B.V. All rights reserved.

Reduced energy offset via substitutional doping for efficient organic/inorganic hybrid solar cells.

PubMed

Jin, Xiao; Sun, Weifu; Zhang, Qin; Ruan, Kelian; Cheng, Yuanyuan; Xu, Haijiao; Xu, Zhongyuan; Li, Qinghua

2015-06-01

Charge carrier transport in bulk heterojunction that is central to the device performance of solar cells is sensitively dependent on the energy level alignment of acceptor and donor. However, the effect of energy level regulation induced by nickel ions on the primary photoexcited electron transfer and the performance of P3HT/TiO₂ hybrid solar cells remains being poorly understood and rarely studied. Here we demonstrate that the introduction of the versatile nickel ions into TiO₂ nanocrystals can significantly elevate the conduction and valence band energy levels of the acceptor, thus resulting in a remarkable reduction of energy level offset between the conduction band of acceptor and lowest unoccupied molecular orbital of donor. By applying transient photoluminescence and femtosecond transient absorption spectroscopies, we demonstrate that the electron transfer becomes more competitive after incorporating nickel ions. In particular, the electron transfer life time is shortened from 30.2 to 16.7 ps, i.e., more than 44% faster than pure TiO₂ acceptor, thus leading to a notable increase of power conversion efficiency in organic/inorganic hybrid solar cells. This work underscores the promising virtue of engineering the reduction of 'excess' energy offset to accelerate electron transport and demonstrates the potential of nickel ions in applications of solar energy conversion and photon detectors.

Enhancement of Perovskite Solar Cells Efficiency using N-Doped TiO2 Nanorod Arrays as Electron Transfer Layer.

PubMed

Zhang, Zhen-Long; Li, Jun-Feng; Wang, Xiao-Li; Qin, Jian-Qiang; Shi, Wen-Jia; Liu, Yue-Feng; Gao, Hui-Ping; Mao, Yan-Li

2017-12-01

In this paper, N-doped TiO 2 (N-TiO 2 ) nanorod arrays were synthesized with hydrothermal method, and perovskite solar cells were fabricated using them as electron transfer layer. The solar cell performance was optimized by changing the N doping contents. The power conversion efficiency of solar cells based on N-TiO 2 with the N doping content of 1% (N/Ti, atomic ratio) has been achieved 11.1%, which was 14.7% higher than that of solar cells based on un-doped TiO 2 . To get an insight into the improvement, some investigations were performed. The structure was examined with X-ray powder diffraction (XRD), and morphology was examined by scanning electron microscopy (SEM). Energy dispersive spectrometer (EDS) and Tauc plot spectra indicated the incorporation of N in TiO 2 nanorods. Absorption spectra showed higher absorption of visible light for N-TiO 2 than un-doped TiO 2 . The N doping reduced the energy band gap from 3.03 to 2.74 eV. The photoluminescence (PL) and time-resolved photoluminescence (TRPL) spectra displayed the faster electron transfer from perovskite layer to N-TiO 2 than to un-doped TiO 2 . Electrochemical impedance spectroscopy (EIS) showed the smaller resistance of device based on N-TiO 2 than that on un-doped TiO 2 .

Microbial Electrochemistry and its Application to Energy and Environmental Issues

NASA Astrophysics Data System (ADS)

Hastings, Jason Thomas

Microbial electrochemistry forms the basis of a wide range of topics from microbial fuel cells to fermentation of carbon food sources. The ability to harness microbial electron transfer processes can lead to a greener and cleaner future. This study focuses on microbial electron transfer for liquid fuel production, novel electrode materials, subsurface environments and removal of unwanted byproducts. In the first chapter, exocellular electron transfer through direct contact utilizing passive electrodes for the enhancement of bio-fuel production was tested. Through the application of microbial growth in a 2-cell apparatus on an electrode surface ethanol production was enhanced by 22.7% over traditional fermentation. Ethanol production efficiencies of close to 95% were achieved in a fraction of the time required by traditional fermentation. Also, in this chapter, the effect of exogenous electron shuttles, electrode material selection and resistance was investigated. Power generation was observed using the 2-cell passive electrode system. An encapsulation method, which would also utilize exocellular transfer of electrons through direct contact, was hypothesized for the suspension of viable cells in a conductive polymer substrate. This conductive polymer substrate could have applications in bio-fuel production. Carbon black was added to a polymer solution to test electrospun polymer conductivity and cell viability. Polymer morphology and cell viability were imaged using electron and optical microscopy. Through proper encapsulation, higher fuel production efficiencies would be achievable. Electron transfer through endogenous exocellular protein shuttles was observed in this study. Secretion of a soluble redox active exocellular protein by Clostridium sp. have been shown utilizing a 2-cell apparatus. Cyclic voltammetry and gel electrophoresis were used to show the presence of the protein. The exocellular protein is capable of reducing ferrous iron in a membrane separated chamber. In experiments where the redox active protein was allowed to pass through the permeable membrane, iron dissolution was 14-fold greater than experiments where the protein was held to one chamber by a non-permeable membrane. Confirmation of a redox active protein could reshape or understanding of subsurface redox processes. The final topic in this study discusses electron transfer within the cell for production of fermentation products. Glycerol, which is an unwanted side-product of biodiesel transesterfication, is utilized as a carbon source for fermentation. Bacterial samples harvested from Galena Creek soil (NGC) are shown in this study to be efficient consumers of glycerol. NGC microbe was characterized through 16s rDNA genetic sequencing and determined to belong to genus Clostridium. Clostridium NGC was able to consume glycerol at 29.7gpl within 72hrs grown in a media containing 50gpl glycerol. All observed fermentation metabolites were characterized and quantified through an HPLC. Glycerol consumption rates and metabolite production rates were observed using varying media recipes. This study has found that NGC has higher selectivity for low weight acids at lower yeast extract concentration and higher selectivity for larger acids and alcohols at higher yeast extract concentrations.

Low potential manganese ions as efficient electron donors in native anoxygenic bacteria.

PubMed

Deshmukh, Sasmit S; Protheroe, Charles; Ivanescu, Matei-Alexandru; Lag, Sarah; Kálmán, László

2018-04-01

Systematic control over molecular driving forces is essential for understanding the natural electron transfer processes as well as for improving the efficiency of the artificial mimics of energy converting enzymes. Oxygen producing photosynthesis uniquely employs manganese ions as rapid electron donors. Introducing this attribute to anoxygenic photosynthesis may identify evolutionary intermediates and provide insights to the energetics of biological water oxidation. This work presents effective environmental methods that substantially and simultaneously tune the redox potentials of manganese ions and the cofactors of a photosynthetic enzyme from native anoxygenic bacteria without the necessity of genetic modification or synthesis. A spontaneous coordination with bis-tris propane lowered the redox potential of the manganese (II) to manganese (III) transition to an unusually low value (~400 mV) at pH 9.4 and allowed its binding to the bacterial reaction center. Binding to a novel buried binding site elevated the redox potential of the primary electron donor, a dimer of bacteriochlorophylls, by up to 92 mV also at pH 9.4 and facilitated the electron transfer that is able to compete with the wasteful charge recombination. These events impaired the function of the natural electron donor and made BTP-coordinated manganese a viable model for an evolutionary alternative. Copyright © 2018 Elsevier B.V. All rights reserved.

Physical stage of photosynthesis charge separation

NASA Astrophysics Data System (ADS)

Yakovlev, A. G.; Shuvalov, V. A.

2016-06-01

An analytical review is given concerning the biophysical aspects of light-driven primary charge separation in photosynthesis reaction centers (RCs) which are special pigment-protein complexes residing in a cell membrane. The primary (physical) stage of charge separation occurs in the pico- and femtosecond ranges and consists of transferring an electron along the active A-branch of pigments. The review presents vast factual material on both the general issues of primary photosynthesis and some more specific topics, including (1) the role of the inactive B-branch of pigments, (2) the effect of the protein environment on the charge separation, and (3) the participation of monomeric bacteriochlorophyll BA in primary electron acceptance. It is shown that the electron transfer and stabilization are strongly influenced by crystallographic water and tyrosine M210 molecules from the nearest environment of BA. A linkage between collective nuclear motions and electron transfer upon charge separation is demonstrated. The nature of the high quantum efficiency of primary charge separation reactions is discussed.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Wenting; Zhang, Qinggang; Wang, Ruiqin

Unsaturated metal species (UMS) confined in nanomaterials play important roles for electron transfer in a wide range of catalytic reactions. However, the limited fabrication methods of UMS restrict their wider catalytic applications. Here in this paper, we report on the synergy of unsaturated Zn and Cu dopants confined in carbon dots (ZnCu-CDs) to produce enhanced electron transfer and photooxidation processes in the doped CDs. The Zn/Cu species chelate with the carbon matrix mainly through Cu-O(N)-Zn-O(N)-Cu complexes. Within this structure, Cu 2+ acts as a mild oxidizer that facilely increases the unsaturated Zn content and also precisely tunes the unsaturated Znmore » valence state to Zn d+, where d is between 1 and 2, instead of Zn. With the help of UMS, electron-transfer pathways are produced, enhancing both the electron donating (7.0 times) and-accepting (5.3 times) abilities relative to conventional CDs. Because of these synergistic effects, the photocatalytic efficiency of CDs in photooxidation reactions is shown to improve more than 5-fold.« less

A review on the bioenergetics of anaerobic microbial metabolism close to the thermodynamic limits and its implications for digestion applications.

PubMed

Leng, Ling; Yang, Peixian; Singh, Shubham; Zhuang, Huichuan; Xu, Linji; Chen, Wen-Hsing; Dolfing, Jan; Li, Dong; Zhang, Yan; Zeng, Huiping; Chu, Wei; Lee, Po-Heng

2018-01-01

The exploration of the energetics of anaerobic digestion systems can reveal how microorganisms cooperate efficiently for cell growth and methane production, especially under low-substrate conditions. The establishment of a thermodynamically interdependent partnership, called anaerobic syntrophy, allows unfavorable reactions to proceed. Interspecies electron transfer and the concentrations of electron carriers are crucial for maintaining this mutualistic activity. This critical review summarizes the functional microorganisms and syntroph partners, particularly in the metabolic pathways and energy conservation of syntrophs. The kinetics and thermodynamics of propionate degradation to methane, reversibility of the acetate oxidation process, and estimation of microbial growth are summarized. The various routes of interspecies electron transfer, reverse electron transfer, and Poly-β-hydroxyalkanoate formation in the syntrophic community are also reviewed. Finally, promising and critical directions of future research are proposed. Fundamental insight in the activities and interactions involved in AD systems could serve as a guidance for engineered systems optimization and upgrade. Copyright © 2017 Elsevier Ltd. All rights reserved.

Theoretical investigation of the electron transfer dynamics and photodegradation pathways in a hydrogen-evolving ruthenium-palladium photocatalyst.

PubMed

Staniszewska, Magdalena; Kupfer, Stephan; Guthmuller, Julien

2018-05-16

Time-dependent density functional theory calculations combined with the Marcus theory of electron transfer (ET) were applied on the molecular photocatalyst [(tbbpy)2Ru(tpphz)PdCl2]2+ in order to elucidate the light-induced relaxation pathways populated upon excitation in the longer wavelength range of its absorption spectrum. The computational results show that after the initial excitation, metal (Ru) to ligand (tpphz) charge transfer (MLCT) triplet states are energetically accessible, but that an ET toward the catalytic center (PdCl2) from these states is a slow process, with estimated time constants above 1 ns. Instead, the calculations predict that low-lying Pd-centered states are efficiently populated - associated to an energy transfer toward the catalytic center. Thus, it is postulated that these states lead to the dissociation of a Cl- and are consequently responsible for the experimentally observed degradation of the catalytic center. Following dissociation, it is shown that the ET rates from the MLCT states to the charge separated states are significantly increased (i.e. 10^5-10^6 times larger). This demonstrates that alteration of the catalytic center generates efficient charge separation. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electron Transfer as a Probe of the Interfacial Quantum Dot-Organic Molecule Interaction

NASA Astrophysics Data System (ADS)

Peterson, Mark D.

This dissertation describes a set of experimental and theoretical studies of the interaction between small organic molecules and the surfaces of semiconductor nanoparticles, also called quantum dots (QDs). Chapter 1 reviews the literature on the influence of ligands on exciton relaxation dynamics following photoexcitation of semiconductor QDs, and describes how ligands promote or inhibit processes such as emission, nonradiative relaxation, and charge transfer to redox active adsorbates. Chapter 2 investigates the specific interaction of alkylcarboxylated viologen derivatives with CdS QDs, and shows how a combination of steady-state photoluminescence (PL) and transient absorption (TA) experiments can be used to reveal the specific binding geometry of redox active organic molecules on QD surfaces. Chapter 3 expands on Chapter 2 by using PL and TA to provide information about the mechanisms through which methyl viologen (MV 2+) associates with CdS QDs to form a stable QD/MV2+ complex, suggesting two chemically distinct reactions. We use our understanding of the QD/molecule interaction to design a drug delivery system in Chapter 4, which employs PL and TA experiments to show that conformational changes in a redox active adsorbate may follow electron transfer, "activating" a biologically inert Schiff base to a protein inhibitor form. The protein inhibitor limits cell motility and may be used to prevent tumor metastasis in cancer patients. Chapter 5 discusses future applications of QD/molecule redox couples with an emphasis on efficient multiple charge-transfer reactions -- a process facilitated by the high degeneracy of band-edge states in QDs. These multiple charge-transfer reactions may potentially increase the thermodynamic efficiency of solar cells, and may also facilitate the splitting of water into fuel. Multiple exciton generation procedures, multi-electron transfer experiments, and future directions are discussed.

Resonant energy transfer and trace-level sensing using branched Ag-rod-supported carbon dots

NASA Astrophysics Data System (ADS)

Nair, Radhika V.; Arya, M.; Vijayan, C.

2018-05-01

We report on the resonant energy transfer in branched Ag rod-supported carbon dots (C-dots) and its applications for the trace-level sensing of highly reactive oxygen species and organic pollutants based on surface plasmon enhanced energy transfer (SPEET) and surface enhanced Raman spectroscopy (SERS). The branched morphology of Ag is found to significantly enhance visible light absorption and thus increases the spectral overlap with C-dot emission. In addition, branched morphology results in the formation of a large number of plasmonic hotspots and efficient propagation of plasmons through the interconnections, as also supported by finite-difference time-domain simulations. Branched Ag-rod—C-dot composite is found to be able to detect 0.02 µM of hydrogen peroxide based on SPEET. The efficient transfer of electrons from C-dots to the Ag rod enhances the SERS efficiency of Ag resulting in an enhancement factor of the order of 108 and enables the composite to detect 10‑10 M of the organic pollutant Rhodamine 6G.

Carbon fiber enhanced bioelectricity generation in soil microbial fuel cells.

PubMed

Li, Xiaojing; Wang, Xin; Zhao, Qian; Wan, Lili; Li, Yongtao; Zhou, Qixing

2016-11-15

The soil microbial fuel cell (MFC) is a promising biotechnology for the bioelectricity recovery as well as the remediation of organics contaminated soil. However, the electricity production and the remediation efficiency of soil MFC are seriously limited by the tremendous internal resistance of soil. Conductive carbon fiber was mixed with petroleum hydrocarbons contaminated soil and significantly enhanced the performance of soil MFC. The maximum current density, the maximum power density and the accumulated charge output of MFC mixed carbon fiber (MC) were 10, 22 and 16 times as high as those of closed circuit control due to the carbon fiber productively assisted the anode to collect the electron. The internal resistance of MC reduced by 58%, 83% of which owed to the charge transfer resistance, resulting in a high efficiency of electron transfer from soil to anode. The degradation rates of total petroleum hydrocarbons enhanced by 100% and 329% compared to closed and opened circuit controls without the carbon fiber respectively. The effective range of remediation and the bioelectricity recovery was extended from 6 to 20cm with the same area of air-cathode. The mixed carbon fiber apparently enhanced the bioelectricity generation and the remediation efficiency of soil MFC by means of promoting the electron transfer rate from soil to anode. The use of conductively functional materials (e.g. carbon fiber) is very meaningful for the remediation and bioelectricity recovery in the bioelectrochemical remediation. Copyright © 2016 Elsevier B.V. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nemec, Patrik, E-mail: patrik.nemec@fstroj.uniza.sk; Malcho, Milan, E-mail: milan.malcho@fstroj.uniza.sk

This work deal with experimental evaluation of cooling efficiency of cooling device capable transfer high heat fluxes from electric elements to the surrounding. The work contain description of cooling device, working principle of cooling device, construction of cooling device. Experimental part describe the measuring method of device cooling efficiency evaluation. The work results are presented in graphic visualization of temperature dependence of the contact area surface between cooling device evaporator and electronic components on the loaded heat of electronic components in range from 250 to 740 W and temperature dependence of the loop thermosiphon condenser surface on the loaded heatmore » of electronic components in range from 250 to 740 W.« less

The fine tuning of carotenoid-chlorophyll interactions in light-harvesting complexes: an important requisite to guarantee efficient photoprotection via triplet-triplet energy transfer in the complex balance of the energy transfer processes

NASA Astrophysics Data System (ADS)

Di Valentin, Marilena; Carbonera, Donatella

2017-08-01

Triplet-triplet energy transfer (TTET) from the chlorophyll to the carotenoid triplet state is the process exploited by photosynthetic systems to protect themselves from singlet oxygen formation under light-stress conditions. A deep comprehension of the molecular strategies adopted to guarantee TTET efficiency, while at the same time maintaining minimal energy loss and efficient light-harvesting capability, is still lacking. The paramagnetic nature of the triplet state makes electron paramagnetic resonance (EPR) the method of choice when investigating TTET. In this review, we focus on our extended comparative study of two photosynthetic antenna complexes, the Peridinin-chlorophyll a-protein of dinoflagellates and the light-harvesting complex II of higher plants, in order to point out important aspects of the molecular design adopted in the photoprotection strategy. We have demonstrated that a proper analysis of the EPR data allows one to identify the pigments involved in TTET and, consequently, gain an insight into the structure of the photoprotective sites. The structural information has been complemented by a detailed description of the electronic structure provided by hyperfine spectroscopy. All these elements represent the fundamental building blocks toward a deeper understanding of the requirements for efficient photoprotection, which is fundamental to guarantee the prolonged energy conversion action of photosynthesis.

Intermolecular interaction approach for TADF (Conference Presentation)

NASA Astrophysics Data System (ADS)

Wong, Ken-Tsung

2016-09-01

Materials with thermally activated delayed fluorescence (TADF) have recently emerged as new fluorescent emitters for highly efficient organic light-emitting diodes (OLEDs). Molecule with TADF behavior needs to have a small singlet-triplet energy difference (ΔES-T) that allows the up-conversion from nonradiative triplet state (T1) to radiative singlet state (S1) via reverse intersystem crossing (RISC) process. Generally, molecules with small ΔES-T can be obtained via carefully manipulate the degree of "intramolecular" charge transfer (ICT) between electron-donating and -accepting components, such that the electron exchange energy that contributes to ΔES-T, can be minimized. Alternatively, excited state with small ΔES-T can be feasibly realized via "intermolecular" charge transfer occurring at the interface between spatially separating donor (D) and acceptor (A) molecules. Because the exchange energy decreases as the HOMO-LUMO separation distance increases, theoretically, the intermolecular D/A charge transfer state (or exciplex) should have rather small ΔES-T, leading to efficient TADF. However, it is still a challenge to access highly efficient exciplex systems. This is mainly because exciplex formation is commonly accompanied with a large red shift of emission spectra and long radiative lifetime, which tend to diminish photoluminescence quantum yield (PLQY) as well as electroluminescence (EL) performance. Until now, exciplex-based OLEDs with external quantum efficiency (EQE) above 10% are still limited. By judicious selection of donor and acceptor, the formation of efficient exciplex can be feasibly achieved. In this conference, our recent efforts on highly efficient exciplexes using C3-symmetry triazine acceptors and various donors, and their device characteristics will be presented.

IR-Driven Ultrafast Transfer of Plasmonic Hot Electrons in Nonmetallic Branched Heterostructures for Enhanced H2 Generation.

PubMed

Zhang, Zhenyi; Jiang, Xiaoyi; Liu, Benkang; Guo, Lijiao; Lu, Na; Wang, Li; Huang, Jindou; Liu, Kuichao; Dong, Bin

2018-03-01

The ultrafast transfer of plasmon-induced hot electrons is considered an effective kinetics process to enhance the photoconversion efficiencies of semiconductors through strong localized surface plasmon resonance (LSPR) of plasmonic nanostructures. Although this classical sensitization approach is widely used in noble-metal-semiconductor systems, it remains unclear in nonmetallic plasmonic heterostructures. Here, by combining ultrafast transient absorption spectroscopy with theoretical simulations, IR-driven transfer of plasmon-induced hot electron in a nonmetallic branched heterostructure is demonstrated, which is fabricated through solvothermal growth of plasmonic W 18 O 49 nanowires (as branches) onto TiO 2 electrospun nanofibers (as backbones). The ultrafast transfer of hot electron from the W 18 O 49 branches to the TiO 2 backbones occurs within a timeframe on the order of 200 fs with very large rate constants ranging from 3.8 × 10 12 to 5.5 × 10 12 s -1 . Upon LSPR excitation by low-energy IR photons, the W 18 O 49 /TiO 2 branched heterostructure exhibits obviously enhanced catalytic H 2 generation from ammonia borane compared with that of W 18 O 49 nanowires. Further investigations by finely controlling experimental conditions unambiguously confirm that this plasmon-enhanced catalytic activity arises from the transfer of hot electron rather than from the photothermal effect. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electronic coupling matrix elements from charge constrained density functional theory calculations using a plane wave basis set

NASA Astrophysics Data System (ADS)

Oberhofer, Harald; Blumberger, Jochen

2010-12-01

We present a plane wave basis set implementation for the calculation of electronic coupling matrix elements of electron transfer reactions within the framework of constrained density functional theory (CDFT). Following the work of Wu and Van Voorhis [J. Chem. Phys. 125, 164105 (2006)], the diabatic wavefunctions are approximated by the Kohn-Sham determinants obtained from CDFT calculations, and the coupling matrix element calculated by an efficient integration scheme. Our results for intermolecular electron transfer in small systems agree very well with high-level ab initio calculations based on generalized Mulliken-Hush theory, and with previous local basis set CDFT calculations. The effect of thermal fluctuations on the coupling matrix element is demonstrated for intramolecular electron transfer in the tetrathiafulvalene-diquinone (Q-TTF-Q-) anion. Sampling the electronic coupling along density functional based molecular dynamics trajectories, we find that thermal fluctuations, in particular the slow bending motion of the molecule, can lead to changes in the instantaneous electron transfer rate by more than an order of magnitude. The thermal average, ( {< {| {H_ab } |^2 } > } )^{1/2} = 6.7 {mH}, is significantly higher than the value obtained for the minimum energy structure, | {H_ab } | = 3.8 {mH}. While CDFT in combination with generalized gradient approximation (GGA) functionals describes the intermolecular electron transfer in the studied systems well, exact exchange is required for Q-TTF-Q- in order to obtain coupling matrix elements in agreement with experiment (3.9 mH). The implementation presented opens up the possibility to compute electronic coupling matrix elements for extended systems where donor, acceptor, and the environment are treated at the quantum mechanical (QM) level.

Electronic energy transfer in bimetallic Ru-Os complexes containing the 3,5-bis(pyridin-2-yl)-1,2,4-triazolate bridging ligand

NASA Astrophysics Data System (ADS)

De Cola, Luisa; Barigelletti, Francesco; Balzani, Vincenzo; Hage, Ronald; Haasnoot, Jaap G.; Reedijk, Jan; Vos, Johannes G.

1991-04-01

The luminescence and photochemical properties of the two isomeric heterobimetallic [(bpy) 2Ru(bpt)Os(bpy) 2] 3+ and [(bpy) 2Os(bpt)Ru(bpy) 2] 3+ complexes have been investigated (bpy=2,2'-pyridine; bpt -=3,5-bis(pyridin-2-yl)-1,2,4-triazolate ion). The properties of the two isomeric compounds are compared with those of the corresponding dinuclear homometallic inert and exhibit luminescence only from the Os-based component. Excitation in the Ru-based component is followed by ≈ 100% efficient energy transfer to the Os-based component. The energy-transfer mechanism is briefly discussed. The one-electron oxidation products (which contain Os in the 3+ oxidation state) are not luminescent because of the presence of a low-energy intervalence transfer level.

Enhanced bimolecular exchange reaction through programmed coordination of a five-coordinate oxovanadium complex for efficient redox mediation in dye-sensitized solar cells.

PubMed

Oyaizu, Kenichi; Hayo, Noriko; Sasada, Yoshito; Kato, Fumiaki; Nishide, Hiroyuki

2013-12-07

Electrochemical reversibility and fast bimolecular exchange reaction found for VO(salen) gave rise to a highly efficient redox mediation to enhance the photocurrent of a dye-sensitized solar cell, leading to an excellent photovoltaic performance with a conversion efficiency of 5.4%. A heterogeneous electron-transfer rate constant at an electrode (k0) and a second-order rate constant for an electron self-exchange reaction (k(ex)) were proposed as key parameters that dominate the charge transport property, which afforded a novel design concept for the mediators based on their kinetic aspects.

Positive effects of bio-nano Pd (0) toward direct electron transfer in Pseudomona putida and phenol biodegradation.

PubMed

Niu, Zhuyu; Jia, Yating; Chen, Yuancai; Hu, Yongyou; Chen, Junfeng; Lv, Yuancai

2018-06-08

This study constructed a biological-inorganic hybrid system including Pseudomonas putida (P. putida) and bioreduced Pd (0) nanoparticles (NPs), and inspected the influence of bio-nano Pd (0) on the direct electron transfer and phenol biodegradation. Scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDX) showed that bio-nano Pd (0) (~10 nm) were evenly dispersed on the surface and in the periplasm of P. putida. With the incorporation of bio-nano Pd (0), the redox currents of bacteria in the cyclic voltammetry (CV) became higher and the oxidation current increased as the addition of lactate, while the highest increase rates of two electron transfer system (ETS) rates were 63.97% and 33.79%, respectively. These results indicated that bio-nano Pd (0) could directly promote the electron transfer of P. putida. In phenol biodegradation process, P. putida-Pd (0)- 2 showed the highest k (0.2992 h -1 ), μ m (0.035 h -1 ) and K i (714.29 mg/L) and the lowest apparent K s (76.39 mg/L). The results of kinetic analysis indicated that bio-nano Pd (0) markedly enhanced the biocatalytic efficiency, substrate affinity and the growth of cells compared to native P. putida. The positive effects of bio-nano Pd (0) to the electron transfer of P. putida would promote the biodegradation of phenol. Copyright © 2018 Elsevier Inc. All rights reserved.

Bio-Photoelectrochemical Solar Cells Incorporating Reaction Center and Reaction Center Plus Light Harvesting Complexes

NASA Astrophysics Data System (ADS)

Yaghoubi, Houman

Harvesting solar energy can potentially be a promising solution to the energy crisis now and in the future. However, material and processing costs continue to be the most important limitations for the commercial devices. A key solution to these problems might lie within the development of bio-hybrid solar cells that seeks to mimic photosynthesis to harvest solar energy and to take advantage of the low material costs, negative carbon footprint, and material abundance. The bio-photoelectrochemical cell technologies exploit biomimetic means of energy conversion by utilizing plant-derived photosystems which can be inexpensive and ultimately the most sustainable alternative. Plants and photosynthetic bacteria harvest light, through special proteins called reaction centers (RCs), with high efficiency and convert it into electrochemical energy. In theory, photosynthetic RCs can be used in a device to harvest solar energy and generate 1.1 V open circuit voltage and ~1 mA cm-2 short circuit photocurrent. Considering the nearly perfect quantum yield of photo-induced charge separation, efficiency of a protein-based solar cell might exceed 20%. In practice, the efficiency of fabricated devices has been limited mainly due to the challenges in the electron transfer between the protein complex and the device electrodes as well as limited light absorption. The overarching goal of this work is to increase the power conversion efficiency in protein-based solar cells by addressing those issues (i.e. electron transfer and light absorption). This work presents several approaches to increase the charge transfer rate between the photosynthetic RC and underlying electrode as well as increasing the light absorption to eventually enhance the external quantum efficiency (EQE) of bio-hybrid solar cells. The first approach is to decrease the electron transfer distance between one of the redox active sites in the RC and the underlying electrode by direct attachment of the of protein complex onto Au electrodes via surface exposed cysteine residues. This resulted in photocurrent densities as large as ~600 nA cm-2 while still the incident photon to generated electron quantum efficiency was as low as %3 x 10-4. 2- The second approach is to immobilize wild type RCs of Rhodobacter sphaeroides on the surface of a Au underlying electrode using self-assembled monolayers of carboxylic acid terminated oligomers and cytochrome c charge mediating layers, with a preferential orientation from the primary electron donor site. This approach resulted in EQE of up to 0.06%, which showed 200 times efficiency improvement comparing to the first approach. In the third approach, instead of isolated protein complexes, RCs plus light harvesting (LH) complexes were employed for a better photon absorption. Direct attachment of RC-LH1 complexes on Au working electrodes, resulted in 0.21% EQE which showed 3.5 times efficiency improvement over the second approach (700 times higher than the first approach). The main impact of this work is the harnessing of biological RCs for efficient energy harvesting in man-made structures. Specifically, the results in this work will advance the application of RCs in devices for energy harvesting and will enable a better understanding of bio and nanomaterial interfaces, thereby advancing the application of biological materials in electronic devices. At the end, this work offers general guidelines that can serve to improve the performance of bio-hybrid solar cells.

Electronic Delocalization, Vibrational Dynamics and Energy Transfer in Organic Chromophores

DOE PAGES

Nelson, Tammie Renee; Fernandez Alberti, Sebastian; Roitberg, Adrian; ...

2017-06-12

The efficiency of materials developed for solar energy and technological applications depends on the interplay between molecular architecture and light-induced electronic energy redistribution. The spatial localization of electronic excitations is very sensitive to molecular distortions. Vibrational nuclear motions can couple to electronic dynamics driving changes in localization. The electronic energy transfer among multiple chromophores arises from several distinct mechanisms that can give rise to experimentally measured signals. Atomistic simulations of coupled electron-vibrational dynamics can help uncover the nuclear motions directing energy flow. Through careful analysis of excited state wave function evolution and a useful fragmenting of multichromophore systems, through-bond transportmore » and exciton hopping (through-space) mechanisms can be distinguished. Such insights are crucial in the interpretation of fluorescence anisotropy measurements and can aid materials design. Finally, this Perspective highlights the interconnected vibrational and electronic motions at the foundation of nonadiabatic dynamics where nuclear motions, including torsional rotations and bond vibrations, drive electronic transitions.« less

Layer-by-layer films and colloidal dispersions of graphene oxide nanosheets for efficient control of the fluorescence and aggregation properties of the cationic dye acridine orange.

PubMed

Hansda, Chaitali; Chakraborty, Utsav; Hussain, Syed Arshad; Bhattacharjee, Debajyoti; Paul, Pabitra Kumar

2016-03-15

Chemically derived graphene oxide (GO) nanosheets have received great deal of interest for technological application such as optoelectronic and biosensors. Aqueous dispersions of GO become an efficient template to induce the association of cationic dye namely Acridine Orange (AO). Interactions of AO with colloidal GO was governed by both electrostatic and π-π stacking cooperative interactions. The type of dye aggregations was found to depend on the concentration of GO in the mixed ensemble. Spectroscopic calculations revealed the formation of both H and J-type dimers, but H-type aggregations were predominant. Preparation of layer-by-layer (LbL) electrostatic self-assembled films of AO and GO onto poly (allylamine hydrochloride) (PAH) coated quartz substrate is also reported in this article. UV-Vis absorption, steady state and time resolve fluorescence and Raman spectroscopic techniques have been employed to explore the detail photophysical properties of pure AO, AO/GO mixed solution and AO/GO LbL films. Scanning electron microscopy was also used for visual evidence of the synthesized nanodimensional GO sheets. The fluorescence quenching of AO in the presence of GO in aqueous solution was due to the interfacial photoinduced electron transfer (PET) from photoexcited AO to GO i.e. GO acts as an efficient quenching agent for the fluorescence emission of AO. The quenching is found to be static in nature. Raman spectroscopic results also confirmed the interaction of AO with GO and the electron transfer. The formation of AO/GO complex via very fast excited state electron transfer mechanism may be proposed as to prepare GO-based fluorescence sensor for biomolecular detection without direct labeling the biomolecules by fluorescent probe. Copyright © 2015 Elsevier B.V. All rights reserved.

Layer-by-layer films and colloidal dispersions of graphene oxide nanosheets for efficient control of the fluorescence and aggregation properties of the cationic dye acridine orange

NASA Astrophysics Data System (ADS)

Hansda, Chaitali; Chakraborty, Utsav; Hussain, Syed Arshad; Bhattacharjee, Debajyoti; Paul, Pabitra Kumar

2016-03-01

Chemically derived graphene oxide (GO) nanosheets have received great deal of interest for technological application such as optoelectronic and biosensors. Aqueous dispersions of GO become an efficient template to induce the association of cationic dye namely Acridine Orange (AO). Interactions of AO with colloidal GO was governed by both electrostatic and π-π stacking cooperative interactions. The type of dye aggregations was found to depend on the concentration of GO in the mixed ensemble. Spectroscopic calculations revealed the formation of both H and J-type dimers, but H-type aggregations were predominant. Preparation of layer-by-layer (LbL) electrostatic self-assembled films of AO and GO onto poly (allylamine hydrochloride) (PAH) coated quartz substrate is also reported in this article. UV-Vis absorption, steady state and time resolve fluorescence and Raman spectroscopic techniques have been employed to explore the detail photophysical properties of pure AO, AO/GO mixed solution and AO/GO LbL films. Scanning electron microscopy was also used for visual evidence of the synthesized nanodimensional GO sheets. The fluorescence quenching of AO in the presence of GO in aqueous solution was due to the interfacial photoinduced electron transfer (PET) from photoexcited AO to GO i.e. GO acts as an efficient quenching agent for the fluorescence emission of AO. The quenching is found to be static in nature. Raman spectroscopic results also confirmed the interaction of AO with GO and the electron transfer. The formation of AO/GO complex via very fast excited state electron transfer mechanism may be proposed as to prepare GO-based fluorescence sensor for biomolecular detection without direct labeling the biomolecules by fluorescent probe.

The effect of a longitudinal density gradient on electron plasma wake field acceleration

NASA Astrophysics Data System (ADS)

Tsiklauri, David

2016-12-01

Three-dimensional, particle-in-cell, fully electromagnetic simulations of electron plasma wake field acceleration in the blow-out regime are presented. Earlier results are extended by (i) studying the effect of a longitudinal density gradient, (ii) avoiding the use of a co-moving simulation box, (iii) inclusion of ion motion, and (iv) studying fully electromagnetic plasma wake fields. It is established that injecting driving and trailing electron bunches into a positive density gradient of 10-fold increasing density over 10 cm long lithium vapour plasma results in spatially more compact and three times larger, compared with the uniform density case, electric fields (-6.4×1010 V m-1), leading to acceleration of the trailing bunch up to 24.4 GeV (starting from an initial 20.4 GeV), with energy transfer efficiencies from the leading to trailing bunch of 75%. In the uniform density case, a -2.5×1010 V m-1 wake is created leading to acceleration of the trailing bunch up to 22.4 GeV, with energy transfer efficiencies of 65%. It is also established that injecting the electron bunches into a negative density gradient of 10-fold decreasing density over 10 cm long plasma results in spatially more spread and two and a half smaller electric fields (-1.0×1010 V m-1), leading to a weaker acceleration of the trailing bunch up to 21.4 GeV, with energy transfer efficiencies of 45%. Taking ion motions into consideration shows that in the plasma wake ion number density can increase over a few times the background value. It is also shown that transverse electromagnetic fields in a plasma wake are of the same order as the longitudinal (electrostatic) ones.

Inhibited proton transfer enhances Au-catalyzed CO2-to-fuels selectivity.

PubMed

Wuttig, Anna; Yaguchi, Momo; Motobayashi, Kenta; Osawa, Masatoshi; Surendranath, Yogesh

2016-08-09

CO2 reduction in aqueous electrolytes suffers efficiency losses because of the simultaneous reduction of water to H2 We combine in situ surface-enhanced IR absorption spectroscopy (SEIRAS) and electrochemical kinetic studies to probe the mechanistic basis for kinetic bifurcation between H2 and CO production on polycrystalline Au electrodes. Under the conditions of CO2 reduction catalysis, electrogenerated CO species are irreversibly bound to Au in a bridging mode at a surface coverage of ∼0.2 and act as kinetically inert spectators. Electrokinetic data are consistent with a mechanism of CO production involving rate-limiting, single-electron transfer to CO2 with concomitant adsorption to surface active sites followed by rapid one-electron, two-proton transfer and CO liberation from the surface. In contrast, the data suggest an H2 evolution mechanism involving rate-limiting, single-electron transfer coupled with proton transfer from bicarbonate, hydronium, and/or carbonic acid to form adsorbed H species followed by rapid one-electron, one-proton, or H recombination reactions. The disparate proton coupling requirements for CO and H2 production establish a mechanistic basis for reaction selectivity in electrocatalytic fuel formation, and the high population of spectator CO species highlights the complex heterogeneity of electrode surfaces under conditions of fuel-forming electrocatalysis.

Tip-Enhanced Photoinduced Electron Transfer and Ionization on Vertical Silicon Nanowires.

PubMed

Chen, Xiaoming; Wang, Tao; Lin, Leimiao; Wo, Fangjie; Liu, Yaqin; Liang, Xiao; Ye, Hui; Wu, Jianmin

2018-05-02

Nanostructured semiconductors are one of the most potent candidates for matrix-free laser desorption/ionization mass spectrometric (LDI-MS) analysis of low-molecular-weight molecules. Herein, the enhanced photoinduced electron transfer and LDI on the tip of a vertical silicon nanowire (SiNW) array were investigated. Theoretical simulation and LDI detection of indigo and isatin molecules in negative ion mode revealed that the electric field can be enhanced on the tip end of SiNWs, thereby promoting the energy and electron transfer to the analytes adsorbed on the tip of SiNWs. On the basis of this finding, a tip-contact sampling method coupled with LDI-MS detection was established. In this strategy, the tip of SiNWs can be regarded as microextraction heads for the sampling of molecules when they come in contact with analytes. Impression of skin, tissue, and pericarp on the vertical SiNW array can effectively transfer endogenous metabolites or exogenous substances onto the tip. Upon laser irradiation, the adsorbed molecules on the SiNW tip can be efficiently ionized and detected in negative ion mode because of the tip-enhanced electron transfer and LDI effect. We believe this work may significantly expand the application of LDI-MS in various fields.

An efficient signal-on aptamer-based biosensor for adenosine triphosphate detection using graphene oxide both as an electrochemical and electrochemiluminescence signal indicator.

PubMed

Huang, Xiang; Li, Yuqin; Zhang, Xiaoshan; Zhang, Xin; Chen, Yaowen; Gao, Wenhua

2015-09-07

An efficient aptasensor was developed in which graphene oxide (GO) was employed as an indicator for both electrochemical impedance spectroscopy and electrochemiluminescence (ECL) signal generation. The aptasensor was fabricated by self-assembling the ECL probe of a thiolated adenosine triphosphate binding aptamer (ABA) tagged with a Ru complex (Ru(bpy)3(2+) derivatives) onto the surface of gold nanoparticle (AuNP) modified glassy carbon electrode (GCE). ABA immobilized onto AuNP modified GCE could strongly adsorb GO due to the strong π-π interaction between ABA and graphene oxide; ECL quenching of the Ru complex then takes place because of energy transfer and electron transfer, and a large increase of the electron transfer resistance (Ret) of the electrode. While in the presence of target adenosine triphosphate (ATP), the ABA prefers to form ABA-ATP bioaffinity complexes, which have weak affinity to graphene oxide and keep the graphene oxide away from the electrode surface, thus allowing the ECL signal enhancement, and in conjunction with the decrease of the Ret. Because of the high ECL quenching efficiency, unique structure, and electronic properties of graphene oxide, the Ret and ECL intensity versus the logarithm of ATP concentration was linear in the wide range from 10 pM to 10 nM with an ultra-low detection limit of 6.7 pM to 4.8 pM, respectively. The proposed aptasensor exhibited excellent reproducibility, stability, and outstanding selectivity, and ATP could be effectively distinguished from its analogues. More significantly, this efficient ECL aptasensor strategy based on GO acting both as an electrochemical and ECL signal indicator is general and can be easily extended to other biological binding events.

BiF(AO+, v’) Radiative Lifetimes and Rate Coefficients for V yields T Transfer and Electronic Quenching.

DTIC Science & Technology

1987-04-24

8217) Radiative Lifetimes and Rate Coefficients for V - T Transfer and Electronic Quenching R. F. HEIDNER Ill, H . HELVAJIAN ,J. S. HOLLOWAY, and J. B...ofoffene. 9. ~ ~ ~ ~ ~ ~ ~ ~ ~ ia U91FO01NGOGNIAIO AE N DDESIIIA T NR.ASK II.~~~~~~~~ WSPIUIOk:TTMET:. .I epn *~~ h Approsp c...collisions of the metastable NF(a 1 h ) state with ground-state BI? molecules, a chemical pumping scheme made efficient by the large densities of NF(a) that can

Direct determination of resonance energy transfer in photolyase: structural alignment for the functional state.

PubMed

Tan, Chuang; Guo, Lijun; Ai, Yuejie; Li, Jiang; Wang, Lijuan; Sancar, Aziz; Luo, Yi; Zhong, Dongping

2014-11-13

Photoantenna is essential to energy transduction in photoinduced biological machinery. A photoenzyme, photolyase, has a light-harvesting pigment of methenyltetrahydrofolate (MTHF) that transfers its excitation energy to the catalytic flavin cofactor FADH¯ to enhance DNA-repair efficiency. Here we report our systematic characterization and direct determination of the ultrafast dynamics of resonance energy transfer from excited MTHF to three flavin redox states in E. coli photolyase by capturing the intermediates formed through the energy transfer and thus excluding the electron-transfer quenching pathway. We observed 170 ps for excitation energy transferring to the fully reduced hydroquinone FADH¯, 20 ps to the fully oxidized FAD, and 18 ps to the neutral semiquinone FADH(•), and the corresponding orientation factors (κ(2)) were determined to be 2.84, 1.53 and 1.26, respectively, perfectly matching with our calculated theoretical values. Thus, under physiological conditions and over the course of evolution, photolyase has adopted the optimized orientation of its photopigment to efficiently convert solar energy for repair of damaged DNA.

Efficient two-component relativistic method for large systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nakai, Hiromi; Research Institute for Science and Engineering, Waseda University, Tokyo 169-8555; CREST, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012

This paper reviews a series of theoretical studies to develop efficient two-component (2c) relativistic method for large systems by the author’s group. The basic theory is the infinite-order Douglas-Kroll-Hess (IODKH) method for many-electron Dirac-Coulomb Hamiltonian. The local unitary transformation (LUT) scheme can effectively produce the 2c relativistic Hamiltonian, and the divide-and-conquer (DC) method can achieve linear-scaling of Hartree-Fock and electron correlation methods. The frozen core potential (FCP) theoretically connects model potential calculations with the all-electron ones. The accompanying coordinate expansion with a transfer recurrence relation (ACE-TRR) scheme accelerates the computations of electron repulsion integrals with high angular momenta and longmore » contractions.« less

Interfacial charge separation and photovoltaic efficiency in Fe(ii)-carbene sensitized solar cells.

PubMed

Pastore, Mariachiara; Duchanois, Thibaut; Liu, Li; Monari, Antonio; Assfeld, Xavier; Haacke, Stefan; Gros, Philippe C

2016-10-12

The first combined theoretical and photovoltaic characterization of both homoleptic and heteroleptic Fe(ii)-carbene sensitized photoanodes in working dye sensitized solar cells (DSSCs) has been performed. Three new heteroleptic Fe(ii)-NHC dye sensitizers have been synthesized, characterized and tested. Despite an improved interfacial charge separation in comparison to the homoleptic compounds, the heteroleptic complexes did not show boosted photovoltaic performances. The ab initio quantitative analysis of the interfacial electron and hole transfers and the measured photovoltaic data clearly evidenced fast recombination reactions for heteroleptics, even associated with un unfavorable directional electron flow, and hence slower injection rates, in the case of homoleptics. Notably, quantum mechanics calculations revealed that deprotonation of the not anchored carboxylic function in the homoleptic complex can effectively accelerate the electron injection rate and completely suppress the electron recombination to the oxidized dye. This result suggests that introduction of strong electron-donating substituents on the not-anchored carbene ligand in heteroleptic complexes, in such a way of mimicking the electronic effects of the carboxylate functionality, should yield markedly improved interfacial charge generation properties. The present results, providing for the first time a detailed understanding of the interfacial electron transfers and photovoltaic characterization in Fe(ii)-carbene sensitized solar cells, open the way to a rational molecular engineering of efficient iron-based dyes for photoelectrochemical applications.

Beyond superquenching: Hyper-efficient energy transfer from conjugated polymers to gold nanoparticles

PubMed Central

Fan, Chunhai; Wang, Shu; Hong, Janice W.; Bazan, Guillermo C.; Plaxco, Kevin W.; Heeger, Alan J.

2003-01-01

Gold nanoparticles quench the fluorescence of cationic polyfluorene with Stern–Volmer constants (KSV) approaching 1011 M—1, several orders of magnitude larger than any previously reported conjugated polymer–quencher pair and 9–10 orders of magnitude larger than small molecule dye–quencher pairs. The dependence of KSV on ionic strength, charge and conjugation length of the polymer, and the dimensions (and thus optical properties) of the nanoparticles suggests that three factors account for this extraordinary efficiency: (i) amplification of the quenching via rapid internal energy or electron transfer, (ii) electrostatic interactions between the cationic polymer and anionic nanoparticles, and (iii) the ability of gold nanoparticles to quench via efficient energy transfer. As a result of this extraordinarily high KSV, quenching can be observed even at subpicomolar concentrations of nanoparticles, suggesting that the combination of conjugated polymers with these nanomaterials can potentially lead to improved sensitivity in optical biosensors. PMID:12750470

Bimolecular Rate Constants for FAD-Dependent Glucose Dehydrogenase from Aspergillus terreus and Organic Electron Acceptors.

PubMed

Tsuruoka, Nozomu; Sadakane, Takuya; Hayashi, Rika; Tsujimura, Seiya

2017-03-10

The flavin adenine dinucleotide-dependent glucose dehydrogenase (FAD-GDH) from Aspergillus species require suitable redox mediators to transfer electrons from the enzyme to the electrode surface for the application of bioelectrical devices. Although several mediators for FAD-GDH are already in use, they are still far from optimum in view of potential, kinetics, sustainability, and cost-effectiveness. Herein, we investigated the efficiency of various phenothiazines and quinones in the electrochemical oxidation of FAD-GDH from Aspergillus terreus . At pH 7.0, the logarithm of the bimolecular oxidation rate constants appeared to depend on the redox potentials of all the mediators tested. Notably, the rate constant of each molecule for FAD-GDH was approximately 2.5 orders of magnitude higher than that for glucose oxidase from Aspergillus sp. The results suggest that the electron transfer kinetics is mainly determined by the formal potential of the mediator, the driving force of electron transfer, and the electron transfer distance between the redox active site of the mediator and the FAD, affected by the steric or chemical interactions. Higher k ₂ values were found for ortho-quinones than for para-quinones in the reactions with FAD-GDH and glucose oxidase, which was likely due to less steric hindrance in the active site in the case of the ortho-quinones.

Early bacteriopheophytin reduction in charge separation in reaction centers of Rhodobacter sphaeroides.

PubMed

Zhu, Jingyi; van Stokkum, Ivo H M; Paparelli, Laura; Jones, Michael R; Groot, Marie Louise

2013-06-04

A question at the forefront of biophysical sciences is, to what extent do quantum effects and protein conformational changes play a role in processes such as biological sensing and energy conversion? At the heart of photosynthetic energy transduction lie processes involving ultrafast energy and electron transfers among a small number of tetrapyrrole pigments embedded in the interior of a protein. In the purple bacterial reaction center (RC), a highly efficient ultrafast charge separation takes place between a pair of bacteriochlorophylls: an accessory bacteriochlorophyll (B) and bacteriopheophytin (H). In this work, we applied ultrafast spectroscopy in the visible and near-infrared spectral region to Rhodobacter sphaeroides RCs to accurately track the timing of the electron on BA and HA via the appearance of the BA and HA anion bands. We observed an unexpectedly early rise of the HA⁻ band that challenges the accepted simple picture of stepwise electron transfer with 3 ps and 1 ps time constants. The implications for the mechanism of initial charge separation in bacterial RCs are discussed in terms of a possible adiabatic electron transfer step between BA and HA, and the effect of protein conformation on the electron transfer rate. Copyright © 2013 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Watching the dynamics of electrons and atoms at work in solar energy conversion.

PubMed

Canton, S E; Zhang, X; Liu, Y; Zhang, J; Pápai, M; Corani, A; Smeigh, A L; Smolentsev, G; Attenkofer, K; Jennings, G; Kurtz, C A; Li, F; Harlang, T; Vithanage, D; Chabera, P; Bordage, A; Sun, L; Ott, S; Wärnmark, K; Sundström, V

2015-01-01

The photochemical reactions performed by transition metal complexes have been proposed as viable routes towards solar energy conversion and storage into other forms that can be conveniently used in our everyday applications. In order to develop efficient materials, it is necessary to identify, characterize and optimize the elementary steps of the entire process on the atomic scale. To this end, we have studied the photoinduced electronic and structural dynamics in two heterobimetallic ruthenium-cobalt dyads, which belong to the large family of donor-bridge-acceptor systems. Using a combination of ultrafast optical and X-ray absorption spectroscopies, we can clock the light-driven electron transfer processes with element and spin sensitivity. In addition, the changes in local structure around the two metal centers are monitored. These experiments show that the nature of the connecting bridge is decisive for controlling the forward and the backward electron transfer rates, a result supported by quantum chemistry calculations. More generally, this work illustrates how ultrafast optical and X-ray techniques can disentangle the influence of spin, electronic and nuclear factors on the intramolecular electron transfer process. Finally, some implications for further improving the design of bridged sensitizer-catalysts utilizing the presented methodology are outlined.

Charge transfer mechanism in titanium-doped microporous silica for photocatalytic water-splitting applications

DOE PAGES

Sapp, Wendi; Koodali, Ranjit; Kilin, Dmitri

2016-02-29

Solar energy conversion into chemical form is possible using artificial means. One example of a highly-efficient fuel is solar energy used to split water into oxygen and hydrogen. Efficient photocatalytic water-splitting remains an open challenge for researchers across the globe. Despite significant progress, several aspects of the reaction, including the charge transfer mechanism, are not fully clear. Density functional theory combined with density matrix equations of motion were used to identify and characterize the charge transfer mechanism involved in the dissociation of water. A simulated porous silica substrate, using periodic boundary conditions, with Ti 4+ ions embedded on the innermore » pore wall was found to contain electron and hole trap states that could facilitate a chemical reaction. A trap state was located within the silica substrate that lengthened relaxation time, which may favor a chemical reaction. A chemical reaction would have to occur within the window of photoexcitation; therefore, the existence of a trapping state may encourage a chemical reaction. Furthermore, this provides evidence that the silica substrate plays an integral part in the electron/hole dynamics of the system, leading to the conclusion that both components (photoactive materials and support) of heterogeneous catalytic systems are important in optimization of catalytic efficiency.« less

Costs and cost-efficiency of a mobile cash transfer to prevent child undernutrition during the lean season in Burkina Faso: a mixed methods analysis from the MAM'Out randomized controlled trial.

PubMed

Puett, Chloe; Salpéteur, Cécile; Houngbe, Freddy; Martínez, Karen; N'Diaye, Dieynaba S; Tonguet-Papucci, Audrey

2018-01-01

This study assessed the costs and cost-efficiency of a mobile cash transfer implemented in Tapoa Province, Burkina Faso in the MAM'Out randomized controlled trial from June 2013 to December 2014, using mixed methods and taking a societal perspective by including costs to implementing partners and beneficiary households. Data were collected via interviews with implementing staff from the humanitarian agency and the private partner delivering the mobile money, focus group discussions with beneficiaries, and review of accounting databases. Costs were analyzed by input category and activity-based cost centers. cost-efficiency was analyzed by cost-transfer ratios (CTR) and cost per beneficiary. Qualitative analysis was conducted to identify themes related to implementing electronic cash transfers, and barriers to efficient implementation. The CTR was 0.82 from a societal perspective, within the same range as other humanitarian transfer programs; however the intervention did not achieve the same degree of cost-efficiency as other mobile transfer programs specifically. Challenges in coordination between humanitarian and private partners resulted in long wait times for beneficiaries, particularly in the first year of implementation. Sensitivity analyses indicated a potential 6% reduction in CTR through reducing beneficiary wait time by one-half. Actors reported that coordination challenges improved during the project, therefore inefficiencies likely would be resolved, and cost-efficiency improved, as the program passed the pilot phase. Despite the time required to establish trusting relationships among actors, and to set up a network of cash points in remote areas, this analysis showed that mobile transfers hold promise as a cost-efficient method of delivering cash in this setting. Implementation by local government would likely reduce costs greatly compared to those found in this study context, and improve cost-efficiency especially by subsidizing expansion of mobile money network coverage and increasing cash distribution points in remote areas which are unprofitable for private partners.

Synthesis of TiO2-poly(3-hexylthiophene) hybrid particles through surface-initiated Kumada catalyst-transfer polycondensation.

PubMed

Boon, Florian; Moerman, David; Laurencin, Danielle; Richeter, Sébastien; Guari, Yannick; Mehdi, Ahmad; Dubois, Philippe; Lazzaroni, Roberto; Clément, Sébastien

2014-09-30

TiO2/conjugated polymers are promising materials in solar energy conversion where efficient photoinduced charge transfers are required. Here, a "grafting-from" approach for the synthesis of TiO2 nanoparticles supported with conjugated polymer brushes is presented. Poly(3-hexylthiophene) (P3HT), a benchmark material for organic electronics, was selectively grown from TiO2 nanoparticles by surface-initiated Kumada catalyst-transfer polycondensation. The grafting of the polymer onto the surface of the TiO2 nanoparticles by this method was demonstrated by (1)H and (13)C solid-state NMR, X-ray photoelectron spectrometry, thermogravimetric analysis, transmission electron microscopy, and UV-visible spectroscopy. Sedimentation tests in tetrahydrofuran revealed improved dispersion stability for the TiO2@P3HT hybrid material. Films were produced by solvent casting, and the quality of the dispersion of the modified TiO2 nanoparticles was evaluated by atomic force microscopy. The dispersion of the P3HT-coated TiO2 NPs in the P3HT matrix was found to be homogeneous, and the fibrillar structure of the P3HT matrix was maintained which is favorable for charge transport. Fluorescence quenching measurements on these hybrid materials in CHCl3 indicated improved photoinduced electron-transfer efficiency. All in all, better physicochemical properties for P3HT/TiO2 hybrid material were reached via the surface-initiated "grafted-from" approach compared to the "grafting-onto" approach.

Multi-gigaelectronvolt acceleration of positrons in a self-loaded plasma wakefield.

PubMed

Corde, S; Adli, E; Allen, J M; An, W; Clarke, C I; Clayton, C E; Delahaye, J P; Frederico, J; Gessner, S; Green, S Z; Hogan, M J; Joshi, C; Lipkowitz, N; Litos, M; Lu, W; Marsh, K A; Mori, W B; Schmeltz, M; Vafaei-Najafabadi, N; Walz, D; Yakimenko, V; Yocky, G

2015-08-27

Electrical breakdown sets a limit on the kinetic energy that particles in a conventional radio-frequency accelerator can reach. New accelerator concepts must be developed to achieve higher energies and to make future particle colliders more compact and affordable. The plasma wakefield accelerator (PWFA) embodies one such concept, in which the electric field of a plasma wake excited by a bunch of charged particles (such as electrons) is used to accelerate a trailing bunch of particles. To apply plasma acceleration to electron-positron colliders, it is imperative that both the electrons and their antimatter counterpart, the positrons, are efficiently accelerated at high fields using plasmas. Although substantial progress has recently been reported on high-field, high-efficiency acceleration of electrons in a PWFA powered by an electron bunch, such an electron-driven wake is unsuitable for the acceleration and focusing of a positron bunch. Here we demonstrate a new regime of PWFAs where particles in the front of a single positron bunch transfer their energy to a substantial number of those in the rear of the same bunch by exciting a wakefield in the plasma. In the process, the accelerating field is altered--'self-loaded'--so that about a billion positrons gain five gigaelectronvolts of energy with a narrow energy spread over a distance of just 1.3 metres. They extract about 30 per cent of the wake's energy and form a spectrally distinct bunch with a root-mean-square energy spread as low as 1.8 per cent. This ability to transfer energy efficiently from the front to the rear within a single positron bunch makes the PWFA scheme very attractive as an energy booster to an electron-positron collider.

On non-local energy transfer via zonal flow in the Dimits shift

NASA Astrophysics Data System (ADS)

St-Onge, Denis A.

2017-10-01

The two-dimensional Terry-Horton equation is shown to exhibit the Dimits shift when suitably modified to capture both the nonlinear enhancement of zonal/drift-wave interactions and the existence of residual Rosenbluth-Hinton states. This phenomenon persists through numerous simplifications of the equation, including a quasilinear approximation as well as a four-mode truncation. It is shown that the use of an appropriate adiabatic electron response, for which the electrons are not affected by the flux-averaged potential, results in an nonlinearity that can efficiently transfer energy non-locally to length scales of the order of the sound radius. The size of the shift for the nonlinear system is heuristically calculated and found to be in excellent agreement with numerical solutions. The existence of the Dimits shift for this system is then understood as an ability of the unstable primary modes to efficiently couple to stable modes at smaller scales, and the shift ends when these stable modes eventually destabilize as the density gradient is increased. This non-local mechanism of energy transfer is argued to be generically important even for more physically complete systems.

Intrinsic non-radiative voltage losses in fullerene-based organic solar cells

NASA Astrophysics Data System (ADS)

Benduhn, Johannes; Tvingstedt, Kristofer; Piersimoni, Fortunato; Ullbrich, Sascha; Fan, Yeli; Tropiano, Manuel; McGarry, Kathryn A.; Zeika, Olaf; Riede, Moritz K.; Douglas, Christopher J.; Barlow, Stephen; Marder, Seth R.; Neher, Dieter; Spoltore, Donato; Vandewal, Koen

2017-06-01

Organic solar cells demonstrate external quantum efficiencies and fill factors approaching those of conventional photovoltaic technologies. However, as compared with the optical gap of the absorber materials, their open-circuit voltage is much lower, largely due to the presence of significant non-radiative recombination. Here, we study a large data set of published and new material combinations and find that non-radiative voltage losses decrease with increasing charge-transfer-state energies. This observation is explained by considering non-radiative charge-transfer-state decay as electron transfer in the Marcus inverted regime, being facilitated by a common skeletal molecular vibrational mode. Our results suggest an intrinsic link between non-radiative voltage losses and electron-vibration coupling, indicating that these losses are unavoidable. Accordingly, the theoretical upper limit for the power conversion efficiency of single-junction organic solar cells would be reduced to about 25.5% and the optimal optical gap increases to 1.45-1.65 eV, that is, 0.2-0.3 eV higher than for technologies with minimized non-radiative voltage losses.

The influence of the distance between the donor-acceptor groups of polymethine dyes on their photovoltaic properties

NASA Astrophysics Data System (ADS)

Seliverstova, E.; Ibrayev, N.

2018-01-01

Spectral-luminescent and photovoltaic properties of polymethine dyes of various structures are studied. It is shown that an increase in the length of the methylene chain between the active chromophores leads to a red-wave shift of the absorption and fluorescence spectra. Significant changes in the absorptivity and lifetime of fluorescence do not occur in this case. The best photovoltaic parameters have cells sensitized with shorter dye molecules. It is shown, that for a longer dye the resistance associated with electron recombination on the TiO2/electrolyte surface is much higher than the electron transfer resistance in the semiconductor, which reduces the efficiency of electron transfer in the solar cell, sensitized with longer dye molecules.

Concentration-dependent photophysical switching in mixed self-assembled monolayers of pentacene and perylenediimide on gold nanoclusters.

PubMed

Kato, Daiki; Sakai, Hayato; Araki, Yasuyuki; Wada, Takehiko; Tkachenko, Nikolai V; Hasobe, Taku

2018-03-28

Photophysical control and switching on organic-inorganic hybrid interfaces are of great interest in diverse fundamental and applicative research areas. 6,13-Bis(triisopropylsilylethynyl)pentacene (TP) is well-known to exhibit efficient singlet fission (SF) for generation of high-yield triplet excited states in aggregated forms, whereas perylenediimide (PDI) ensembles show the characteristic excimer formation. Additionally, a combination of pentacene (electron donor: D) and PDI (electron acceptor: A) is expected to undergo an efficient photoinduced electron transfer (PET), and absorption of two chromophores combined covers the entire visible region. Therefore, the concentration-dependent mixed self-assembled monolayers (SAMs) composed of two chromophores enable us to control and switch the photophysical processes on a surface. In this work, a series of mixed SAMs composed of TP and PDI units on gold nanoclusters (GNCs) were newly synthesized by changing the relative molecular concentration ratios. Structural control of mixed SAMs on a gold surface based on the concentration ratios was successfully achieved. Time-resolved femtosecond and nanosecond transient absorption measurements clearly demonstrate photophysical control and switching of the above competitive reactions such as SF, electron transfer (ET) and excimer formation. The maximum quantum yields of triplet states (ΦT = ∼170%) and electron transfer (ΦET = ∼95%) were quantitatively evaluated by changing the concentration ratios. The rate constants of SF and excimer processes are largely dependent on the concentration ratios, whereas the rate constants of ET processes approximately remain constant. These findings are also discussed based on the statistical framework of the assembly of chromophores on the gold surface.

Preparation and Degradation of Polysilylenes

DTIC Science & Technology

1991-05-02

Grignard reagent formation from Mg and alkyl iodides in comparison with less reactive alkyl chlorides 2 3 . Electron transfer to the chlorides occur at...stoichiometric balance of reagents and nearly complete conversions (e.g. DPN-100 at 99% conversion in a homogeneous polycondensation with exact stoichiometric...the magnesium surface, whereas alkyl iodides accept electrons through Ŝ. larger distance and could not efficiently form organomagneslum reagents but

Exploring the effect of band alignment and surface states on photoinduced electron transfer from CuInS2/CdS core/shell quantum dots to TiO2 electrodes.

PubMed

Sun, Mingye; Zhu, Dehua; Ji, Wenyu; Jing, Pengtao; Wang, Xiuying; Xiang, Weidong; Zhao, Jialong

2013-12-11

Photoinduced electron transfer (ET) processes from CuInS2/CdS core/shell quantum dots (QDs) with different core sizes and shell thicknesses to TiO2 electrodes were investigated by time-resolved photoluminescence (PL) spectroscopy. The ET rates and efficiencies from CuInS2/CdS QDs to TiO2 were superior to those of CuInS2/ZnS QDs. An enhanced ET efficiency was surprisingly observed for 2.0 nm CuInS2 core QDs after growth of the CdS shell. On the basis of the experimental and theoretical analysis, the improved performances of CuInS2/CdS QDs were attributed to the passivation of nonradiative traps by overcoating shell and enhanced delocalization of electron wave function from core to CdS shell due to lower conduction band offset. These results indicated that the electron distribution regulated by the band alignment between core and shell of QDs and the passivation of surface defect states could improve ET performance between donor and acceptor.

Carbon dot-Au(i)Ag(0) assembly for the construction of an artificial light harvesting system.

PubMed

Jana, Jayasmita; Aditya, Teresa; Pal, Tarasankar

2018-03-06

Artificial light harvesting systems (LHS) with inorganic counterparts are considered to be robust as well as mechanistically simple, where the system follows the donor-acceptor principle with an unchanged structural pattern. Plasmonic gold or silver nanoparticles are mostly chosen as inorganic counterparts to design artificial LHS. To capitalize on its electron accepting capability, Au(i) has been considered in this work for the synergistic stabilization of a system with intriguingly fluorescing silver(0) clusters produced in situ. Thus a stable fluorescent Au(i)Ag(0) assembly is generated with electron accepting capabilities. On the other hand, carbon dots have evolved as new fluorescent probes due to their unique physicochemical properties. Utilizing the simple electronic behavior of carbon dots, an electronic interaction between the fluorescent Au(i)Ag(0) and a carbon dot has been investigated for the construction of a new artificial light harvesting system. This coinage metal assembly allows surface energy transfer where it acts as an acceptor, while the carbon dot behaves as a good donor. The energy transfer efficiency has been calculated experimentally to be significant (81.3%) and the Au(i)Ag(0)-carbon dot assembly paves the way for efficient artificial LHS.

Biological construction of single-walled carbon nanotube electron transfer pathways in dye-sensitized solar cells.

PubMed

Inoue, Ippei; Watanabe, Kiyoshi; Yamauchi, Hirofumi; Ishikawa, Yasuaki; Yasueda, Hisashi; Uraoka, Yukiharu; Yamashita, Ichiro

2014-10-01

We designed and mass-produced a versatile protein supramolecule that can be used to manufacture a highly efficient dye-sensitized solar cell (DSSC). Twelve single-walled carbon-nanotube (SWNT)-binding and titanium-mineralizing peptides were genetically integrated on a cage-shaped dodecamer protein (CDT1). A process involving simple mixing of highly conductive SWNTs with CDT1 followed by TiO2 biomineralization produces a high surface-area/weight TiO2 -(anatase)-coated intact SWNT nanocomposite under environmentally friendly conditions. A DSSC with a TiO2 photoelectrode containing 0.2 wt % of the SWNT-TiO2 nanocomposite shows a current density improvement by 80% and a doubling of the photoelectric conversion efficiency. The SWNT-TiO2 nanocomposite transfers photon-generated electrons from dye molecules adsorbed on the TiO2 to the anode electrode swiftly. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ran, Niva A.; Roland, Steffen; Love, John A.

Here, a long standing question in organic electronics concerns the effects of molecular orientation at donor/acceptor heterojunctions. Given a well-controlled donor/acceptor bilayer system, we uncover the genuine effects of molecular orientation on charge generation and recombination. These effects are studied through the point of view of photovoltaics—however, the results have important implications on the operation of all optoelectronic devices with donor/acceptor interfaces, such as light emitting diodes and photodetectors. Our findings can be summarized by two points. First, devices with donor molecules face-on to the acceptor interface have a higher charge transfer state energy and less non-radiative recombination, resulting inmore » larger open-circuit voltages and higher radiative efficiencies. Second, devices with donor molecules edge-on to the acceptor interface are more efficient at charge generation, attributed to smaller electronic coupling between the charge transfer states and the ground state, and lower activation energy for charge generation.« less

Enhancement of photoelectrochemical activity of SnS thin-film photoelectrodes using TiO2, Nb2O5, and Ta2O5 metal oxide layers

NASA Astrophysics Data System (ADS)

Vequizo, Junie Jhon M.; Yokoyama, Masanori; Ichimura, Masaya; Yamakata, Akira

2016-06-01

Tin sulfide (SnS) fine photoelectrodes fabricated by three-step pulsed electrodeposition were active for H2 evolution. The incident-photon-conversion-efficiency increases from 900 nm and offers a good fit with the absorption spectrum. The activity was enhanced by 3.4, 3.0, and 1.8 times compared to bare SnS by loading Nb2O5, TiO2, and Ta2O5, respectively. Nb2O5 was most efficient because its conduction band is low enough to facilitate effective electron transfer from SnS; it also has sufficiently high potential for H2 evolution. The overall activity is determined by the competitive interfacial electron transfer between SnS/metal-oxide and metal-oxide/water. Therefore, constructing appropriate heterojunctions is necessary for further improving photoelectrochemical systems.

Enhancement of the efficiency of dye-sensitized solar cell with multi-wall carbon nanotubes/polypyrrole composite counter electrodes prepared by electrophoresis/electrochemical polymerization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luo, Jun; Niu, Hai-jun; Wen, Hai-lin

2013-03-15

Graphical abstract: The overall energy conversion efficiency of the DSSC employing the MWCNT/PPy CE reached 3.78%. Compared with a reference DSSC using single MWCNT film CE with efficiency of 2.68%, the energy conversion efficiency was increased by 41.04%. Highlights: ► MWCNT/PPy composite film prepared by electrodeposition layer by layer was used as counter electrode in DSSC. ► The overall energy conversion efficiency of the DSSC was 3.78% by employing the composite film. ► The energy conversion efficiency increased by 41.04% compared with efficiency of 2.68% by using the single MWCNT film. ► We analyzed the mechanism and influence factor ofmore » electron transfer in the composite electrode by EIS. - Abstract: For the purpose of replacing the precious Pt counter electrode in dye-sensitized solar cells (DSSCs) with higher energy conversion efficiency, multi-wall carbon nanotube (MWCNT)/polypyrrole (PPy) double layers film counter electrode (CE) was fabricated by electrophoresis and cyclic voltammetry (CV) layer by layer. Atom force microscopy (AFM), scanning electron microscopy (SEM) and transmission electron microscope (TEM) demonstrated the morphologies of the composite electrode and Raman spectroscopy verified the PPy had come into being. The overall energy conversion efficiency of the DSSC employing the MWCNT/PPy CE reached 3.78%. Compared with a reference DSSC using single MWCNT film CE with efficiency of 2.68%, the energy conversion efficiency was increased by 41.04%. The result of impedance showed that the charge transfer resistance R{sub ct} of the MWCNT/PPy CE had the lowest value compared to that of MWCNT or PPy electrode. These results indicate that the composite film with high conductivity, high active surface area, and good catalytic properties for I{sub 3}{sup −} reduction can potentially be used as the CE in a high-performance DSSC.« less

Wireless Power Transfer to Millimeter-Sized Gastrointestinal Electronics Validated in a Swine Model.

PubMed

Abid, Abubakar; O'Brien, Jonathan M; Bensel, Taylor; Cleveland, Cody; Booth, Lucas; Smith, Brian R; Langer, Robert; Traverso, Giovanni

2017-04-27

Electronic devices placed in the gastrointestinal (GI) tract for prolonged periods have the potential to transform clinical evaluation and treatment. One challenge to the deployment of such gastroresident electronics is the difficulty in powering millimeter-sized electronics devices without using batteries, which compromise biocompatibility and long-term residence. We examined the feasibility of leveraging mid-field wireless powering to transfer power from outside of the body to electronics at various locations along the GI tract. Using simulations and ex vivo measurements, we designed mid-field antennas capable of operating efficiently in tissue at 1.2 GHz. These antennas were then characterized in vivo in five anesthetized pigs, by placing one antenna outside the body, and the other antenna inside the body endoscopically, at the esophagus, stomach, and colon. Across the animals tested, mean transmission efficiencies of -41.2, -36.1, and -34.6 dB were achieved in vivo while coupling power from outside the body to the esophagus, stomach, and colon, respectively. This corresponds to power levels of 37.5 μW, 123 μW and 173 μW received by antennas in the respective locations, while keeping radiation exposure levels below safety thresholds. These power levels are sufficient to wirelessly power a range of medical devices from outside of the body.

Wireless Power Transfer to Millimeter-Sized Gastrointestinal Electronics Validated in a Swine Model

NASA Astrophysics Data System (ADS)

Abid, Abubakar; O'Brien, Jonathan M.; Bensel, Taylor; Cleveland, Cody; Booth, Lucas; Smith, Brian R.; Langer, Robert; Traverso, Giovanni

2017-04-01

Electronic devices placed in the gastrointestinal (GI) tract for prolonged periods have the potential to transform clinical evaluation and treatment. One challenge to the deployment of such gastroresident electronics is the difficulty in powering millimeter-sized electronics devices without using batteries, which compromise biocompatibility and long-term residence. We examined the feasibility of leveraging mid-field wireless powering to transfer power from outside of the body to electronics at various locations along the GI tract. Using simulations and ex vivo measurements, we designed mid-field antennas capable of operating efficiently in tissue at 1.2 GHz. These antennas were then characterized in vivo in five anesthetized pigs, by placing one antenna outside the body, and the other antenna inside the body endoscopically, at the esophagus, stomach, and colon. Across the animals tested, mean transmission efficiencies of -41.2, -36.1, and -34.6 dB were achieved in vivo while coupling power from outside the body to the esophagus, stomach, and colon, respectively. This corresponds to power levels of 37.5 μW, 123 μW and 173 μW received by antennas in the respective locations, while keeping radiation exposure levels below safety thresholds. These power levels are sufficient to wirelessly power a range of medical devices from outside of the body.

Ab initio quantum chemical calculation of electron transfer matrix elements for large molecules

NASA Astrophysics Data System (ADS)

Zhang, Linda Yu; Friesner, Richard A.; Murphy, Robert B.

1997-07-01

Using a diabatic state formalism and pseudospectral numerical methods, we have developed an efficient ab initio quantum chemical approach to the calculation of electron transfer matrix elements for large molecules. The theory is developed at the Hartree-Fock level and validated by comparison with results in the literature for small systems. As an example of the power of the method, we calculate the electronic coupling between two bacteriochlorophyll molecules in various intermolecular geometries. Only a single self-consistent field (SCF) calculation on each of the monomers is needed to generate coupling matrix elements for all of the molecular pairs. The largest calculations performed, utilizing 1778 basis functions, required ˜14 h on an IBM 390 workstation. This is considerably less cpu time than would be necessitated with a supermolecule adiabatic state calculation and a conventional electronic structure code.

Efficient Auger Charge-Transfer Processes in ZnO

NASA Astrophysics Data System (ADS)

Stehr, J. E.; Chen, S. L.; Svensson, B. G.; Buyanova, I. A.; Chen, W. M.

2018-05-01

Photoluminescence and magneto-optical measurements are performed on a line peaking at 3.354 eV (labeled as NBX) in electron-irradiated ZnO. Even though the energy position of the NBX line is close to that for bound excitons in ZnO, it has distinctively different magneto-optical properties. Photoelectron paramagnetic resonance measurements reveal a connection and a charge-transfer process involving NBX and Fe and Al centers. The experimental results are explained within a model which assumes that the NBX is a neutral donor bound exciton at a defect center located near a Fe impurity and an Auger-type charge-transfer process occurs between NBX and Fe3 + . While the NBX dissociates, its hole is captured by an excited state of Fe3 + and the released energy is transferred to the NBX electron, which is excited to the conduction band and subsequently trapped by a substitutional AlZn shallow donor.

DFT/TD-semiempirical study on the structural and electronic properties and absorption spectra of supramolecular fullerene-porphyrine-metalloporphyrine triads based dye-sensitized solar cells.

PubMed

Rezvani, M; Darvish Ganji, M; Jameh-Bozorghi, S; Niazi, A

2018-04-05

In the present work density functional theory (DFT) and time-dependent semiempirical ZNIDO/S (TD-ZNIDO/S) methods have been used to investigate the ground state geometries, electronic structures and excited state properties of triad systems. The influences of the type of metal in the porphyrin ring, change in bridge position and porphyrine-ZnP duplicate on the energies of frontier molecular orbital and UV-Vis spectra has been studied. Geometry optimization, the energy levels and electron density of the Highest Occupied Molecular Orbital (HOMO) and the Lowest Unoccupied Molecular Orbital (LUMO), chemical hardness (η), electrophilicity index (ω), electron accepting power (ω + ) were calculated using ZINDO/S method to predict which molecule is the most efficient with a great capability to be used as a triad molecule in solar industry. Moreover the light harvesting efficiency (LHE) was calculated by means of the oscillator strengths which are obtained by TD-ZINDO/S calculation. Theoretical studies of the electronic spectra by ZINDO/S method were helpful in interpreting the observed electronic transitions. This aspect was systematically explored in a series of C 60 -Porphyrine-Metalloporphyrine (C 60 -P-Mp) triad system with M being Fe, Co, Ni, Ti, and Zn. Generally, transition metal coordination compounds are used as effective sensitizers, due to their intense charge-transfer absorption over the whole visible range and highly efficient metal-to-ligand charge transfer. We aim to optimize the performance of the title solar cells by altering the frontier orbital energy gaps. The results reveal that cell efficiency can be enhanced by metal functionalization of the free base porphyrin. Ti-porphyrin was found to be the most efficient dye sensitizer for dye sensitized solar cells (DSSCs) based on C 60 -P-Mptriad system due to C 60 -Por-TiP complex has lower chemical hardness, gap energy and chemical potential as well as higher electron accepting power among other complexes. In addition, the performance of solar cells favors better with doubly and increasing the π conjugated of the bridge. Copyright © 2018 Elsevier B.V. All rights reserved.

DFT/TD-semiempirical study on the structural and electronic properties and absorption spectra of supramolecular fullerene-porphyrine-metalloporphyrine triads based dye-sensitized solar cells

NASA Astrophysics Data System (ADS)

Rezvani, M.; Darvish Ganji, M.; Jameh-Bozorghi, S.; Niazi, A.

2018-04-01

In the present work density functional theory (DFT) and time-dependent semiempirical ZNIDO/S (TD-ZNIDO/S) methods have been used to investigate the ground state geometries, electronic structures and excited state properties of triad systems. The influences of the type of metal in the porphyrin ring, change in bridge position and porphyrine-ZnP duplicate on the energies of frontier molecular orbital and UV-Vis spectra has been studied. Geometry optimization, the energy levels and electron density of the Highest Occupied Molecular Orbital (HOMO) and the Lowest Unoccupied Molecular Orbital (LUMO), chemical hardness (η), electrophilicity index (ω), electron accepting power (ω+) were calculated using ZINDO/S method to predict which molecule is the most efficient with a great capability to be used as a triad molecule in solar industry. Moreover the light harvesting efficiency (LHE) was calculated by means of the oscillator strengths which are obtained by TD-ZINDO/S calculation. Theoretical studies of the electronic spectra by ZINDO/S method were helpful in interpreting the observed electronic transitions. This aspect was systematically explored in a series of C60-Porphyrine-Metalloporphyrine (C60-P-Mp) triad system with M being Fe, Co, Ni, Ti, and Zn. Generally, transition metal coordination compounds are used as effective sensitizers, due to their intense charge-transfer absorption over the whole visible range and highly efficient metal-to-ligand charge transfer. We aim to optimize the performance of the title solar cells by altering the frontier orbital energy gaps. The results reveal that cell efficiency can be enhanced by metal functionalization of the free base porphyrin. Ti-porphyrin was found to be the most efficient dye sensitizer for dye sensitized solar cells (DSSCs) based on C60-P-Mptriad system due to C60-Por-TiP complex has lower chemical hardness, gap energy and chemical potential as well as higher electron accepting power among other complexes. In addition, the performance of solar cells favors better with doubly and increasing the π conjugated of the bridge.

Towards Efficient and Accurate Description of Many-Electron Problems: Developments of Static and Time-Dependent Electronic Structure Methods

NASA Astrophysics Data System (ADS)

Ding, Feizhi

Understanding electronic behavior in molecular and nano-scale systems is fundamental to the development and design of novel technologies and materials for application in a variety of scientific contexts from fundamental research to energy conversion. This dissertation aims to provide insights into this goal by developing novel methods and applications of first-principle electronic structure theory. Specifically, we will present new methods and applications of excited state multi-electron dynamics based on the real-time (RT) time-dependent Hartree-Fock (TDHF) and time-dependent density functional theory (TDDFT) formalism, and new development of the multi-configuration self-consist field theory (MCSCF) for modeling ground-state electronic structure. The RT-TDHF/TDDFT based developments and applications can be categorized into three broad and coherently integrated research areas: (1) modeling of the interaction between moleculars and external electromagnetic perturbations. In this part we will first prove both analytically and numerically the gauge invariance of the TDHF/TDDFT formalisms, then we will present a novel, efficient method for calculating molecular nonlinear optical properties, and last we will study quantum coherent plasmon in metal namowires using RT-TDDFT; (2) modeling of excited-state charge transfer in molecules. In this part, we will investigate the mechanisms of bridge-mediated electron transfer, and then we will introduce a newly developed non-equilibrium quantum/continuum embedding method for studying charge transfer dynamics in solution; (3) developments of first-principles spin-dependent many-electron dynamics. In this part, we will present an ab initio non-relativistic spin dynamics method based on the two-component generalized Hartree-Fock approach, and then we will generalized it to the two-component TDDFT framework and combine it with the Ehrenfest molecular dynamics approach for modeling the interaction between electron spins and nuclear motion. All these developments and applications will open up new computational and theoretical tools to be applied to the development and understanding of chemical reactions, nonlinear optics, electromagnetism, and spintronics. Lastly, we present a new algorithm for large-scale MCSCF calculations that can utilize massively parallel machines while still maintaining optimal performance for each single processor. This will great improve the efficiency in the MCSCF calculations for studying chemical dissociation and high-accuracy quantum-mechanical simulations.

Nuclear conversion theory: molecular hydrogen in non-magnetic insulators

NASA Astrophysics Data System (ADS)

Ilisca, Ernest; Ghiglieno, Filippo

2016-09-01

The hydrogen conversion patterns on non-magnetic solids sensitively depend upon the degree of singlet/triplet mixing in the intermediates of the catalytic reaction. Three main `symmetry-breaking' interactions are brought together. In a typical channel, the electron spin-orbit (SO) couplings introduce some magnetic excitations in the non-magnetic solid ground state. The electron spin is exchanged with a molecular one by the electric molecule-solid electron repulsion, mixing the bonding and antibonding states and affecting the molecule rotation. Finally, the magnetic hyperfine contact transfers the electron spin angular momentum to the nuclei. Two families of channels are considered and a simple criterion based on the SO coupling strength is proposed to select the most efficient one. The denoted `electronic' conversion path involves an emission of excitons that propagate and disintegrate in the bulk. In the other denoted `nuclear', the excited electron states are transients of a loop, and the electron system returns to its fundamental ground state. The described model enlarges previous studies by extending the electron basis to charge-transfer states and `continui' of band states, and focuses on the broadening of the antibonding molecular excited state by the solid conduction band that provides efficient tunnelling paths for the hydrogen conversion. After working out the general conversion algebra, the conversion rates of hydrogen on insulating and semiconductor solids are related to a few molecule-solid parameters (gap width, ionization and affinity potentials) and compared with experimental measures.

Reactive Black 5 as electron donor and/or electron acceptor in dual chamber of solar photocatalytic fuel cell.

PubMed

Khalik, Wan Fadhilah; Ho, Li-Ngee; Ong, Soon-An; Voon, Chun-Hong; Wong, Yee-Shian; Yusuf, Sara Yasina; Yusoff, NikAthirah; Lee, Sin-Li

2018-07-01

The role of azo dye Reactive Black 5 (RB5) as an electron donor and/or electron acceptor could be distinguished in dual chamber of photocatalytic fuel cell (PFC). The introduction of RB5 in anode chamber increased the voltage generation in the system since degradation of RB5 might produce electrons which also would transfer through external circuit to the cathode chamber. The removal efficiency of RB5 with open and closed circuit was 8.5% and 13.6%, respectively and removal efficiency for open circuit was low due to the fact that recombination of electron-hole pairs might happen in anode chamber since without connection to the cathode, electron cannot be transferred. The degradation of RB5 in cathode chamber with absence of oxygen showed that electrons from anode chamber was accepted by dye molecules to break its azo bond. The presence of oxygen in cathode chamber would improve the oxygen reduction rate which occurred at Platinum-loaded carbon (Pt/C) cathode electrode. The V oc , J sc and P max for different condition of ultrapure water at cathode chamber also affected their fill factor. The transportation of protons to cathode chamber through Nafion membrane could decrease the pH of ultrapure water in cathode chamber and undergo hydrogen evolution reaction in the absence of oxygen which then increased degradation rate of RB5 as well as its electricity generation. Copyright © 2018 Elsevier Ltd. All rights reserved.

Efficient recyclable organic solar cells on cellulose nanocrystal substrates with a conducting polymer top electrode deposited by film-transfer lamination

Treesearch

Yinhua Zhou; Talha M. Khan; Jen-Chieh Liu; Canek Fuentes-Hernandez; Jae Won Shim; Ehsan Najafabadi; Jeffrey P. Youngblood; Robert J. Moon; Bernard Kippelen

2014-01-01

We report on efficient solar cells on recyclable cellulose nanocrystal (CNC) substrates with a new device structure wherein polyethylenimine-modified Ag is used as the bottom electron-collecting electrode and high-conductivity poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS, PH1000) is used as the semitransparent top holecollecting electrode. The...

Production of Highly Polarized Positrons Using Polarized Electrons at MeV Energies

NASA Astrophysics Data System (ADS)

Abbott, D.; Adderley, P.; Adeyemi, A.; Aguilera, P.; Ali, M.; Areti, H.; Baylac, M.; Benesch, J.; Bosson, G.; Cade, B.; Camsonne, A.; Cardman, L. S.; Clark, J.; Cole, P.; Covert, S.; Cuevas, C.; Dadoun, O.; Dale, D.; Dong, H.; Dumas, J.; Fanchini, E.; Forest, T.; Forman, E.; Freyberger, A.; Froidefond, E.; Golge, S.; Grames, J.; Guèye, P.; Hansknecht, J.; Harrell, P.; Hoskins, J.; Hyde, C.; Josey, B.; Kazimi, R.; Kim, Y.; Machie, D.; Mahoney, K.; Mammei, R.; Marton, M.; McCarter, J.; McCaughan, M.; McHugh, M.; McNulty, D.; Mesick, K. E.; Michaelides, T.; Michaels, R.; Moffit, B.; Moser, D.; Muñoz Camacho, C.; Muraz, J.-F.; Opper, A.; Poelker, M.; Réal, J.-S.; Richardson, L.; Setiniyaz, S.; Stutzman, M.; Suleiman, R.; Tennant, C.; Tsai, C.; Turner, D.; Ungaro, M.; Variola, A.; Voutier, E.; Wang, Y.; Zhang, Y.; PEPPo Collaboration

2016-05-01

The Polarized Electrons for Polarized Positrons experiment at the injector of the Continuous Electron Beam Accelerator Facility has demonstrated for the first time the efficient transfer of polarization from electrons to positrons produced by the polarized bremsstrahlung radiation induced by a polarized electron beam in a high-Z target. Positron polarization up to 82% have been measured for an initial electron beam momentum of 8.19 MeV /c , limited only by the electron beam polarization. This technique extends polarized positron capabilities from GeV to MeV electron beams, and opens access to polarized positron beam physics to a wide community.

Production of Highly Polarized Positrons Using Polarized Electrons at MeV Energies

DOE PAGES

Abbott, D.; Adderley, P.; Adeyemi, A.; ...

2016-05-27

The Polarized Electrons for Polarized Positrons experiment at the injector of the Continuous Electron Beam Accelerator Facility has demonstrated for the first time the efficient transfer of polarization from electrons to positrons produced by the polarized bremsstrahlung radiation induced by a polarized electron beam in a high-Z target. Positron polarization up to 82% have been measured for an initial electron beam momentum of 8.19~MeV/c, limited only by the electron beam polarization. We report that this technique extends polarized positron capabilities from GeV to MeV electron beams, and opens access to polarized positron beam physics to a wide community.

Simulation of solution phase electron transfer in a compact donor-acceptor dyad.

PubMed

Kowalczyk, Tim; Wang, Lee-Ping; Van Voorhis, Troy

2011-10-27

Charge separation (CS) and charge recombination (CR) rates in photosynthetic architectures are difficult to control, yet their ratio can make or break photon-to-current conversion efficiencies. A rational design approach to the enhancement of CS over CR requires a mechanistic understanding of the underlying electron-transfer (ET) process, including the role of the environment. Toward this goal, we introduce a QM/MM protocol for ET simulations and use it to characterize CR in the formanilide-anthraquinone dyad (FAAQ). Our simulations predict fast recombination of the charge-transfer excited state, in agreement with recent experiments. The computed electronic couplings show an electronic state dependence and are weaker in solution than in the gas phase. We explore the role of cis-trans isomerization on the CR kinetics, and we find strong correlation between the vertical energy gaps of the full simulations and a collective solvent polarization coordinate. Our approach relies on constrained density functional theory to obtain accurate diabatic electronic states on the fly for molecular dynamics simulations, while orientational and electronic polarization of the solvent is captured by a polarizable force field based on a Drude oscillator model. The method offers a unified approach to the characterization of driving forces, reorganization energies, electronic couplings, and nonlinear solvent effects in light-harvesting systems.

Reaction Dynamics of Proton-Coupled Electron Transfer from Reduced ZnO Nanocrystals.

PubMed

Braten, Miles N; Gamelin, Daniel R; Mayer, James M

2015-10-27

The creation of systems that efficiently interconvert chemical and electrical energies will be aided by understanding proton-coupled electron transfers at solution-semiconductor interfaces. Steps in developing that understanding are described here through kinetic studies of reactions of photoreduced colloidal zinc oxide (ZnO) nanocrystals (NCs) with the nitroxyl radical TEMPO. These reactions proceed by proton-coupled electron transfer (PCET) to give the hydroxylamine TEMPOH. They occur on the submillisecond to seconds time scale, as monitored by stopped-flow optical spectroscopy. Under conditions of excess TEMPO, the reactions are multiexponential in character. One of the contributors to this multiexponential kinetics may be a distribution of reactive proton sites. A graphical overlay method shows the reaction to be first order in [TEMPO]. Different electron concentrations in otherwise identical NC samples were achieved by three different methods: differing photolysis times, premixing with an unphotolyzed sample, or prereaction with TEMPO. The reaction velocities were consistently higher for NCs with higher numbers of electrons. For instance, NCs with an average of 2.6 e(-)/NC reacted faster than otherwise identical samples containing ≤1 e(-)/NC. Surprisingly, NC samples with the same average number of electrons but prepared in different ways often had different reaction profiles. These results show that properties beyond electron content determine PCET reactivity of the particles.

Function of CN group in organic sensitizers: The first principle study.

PubMed

Liu, Yun; Shao, Di; Bai, Xiaohui; Yang, Zhenqing; Lin, Chundan; Shao, Changjin

2017-05-15

The cyano group (CN) of the acceptor in organic sensitizers plays an important role for highly efficient dye-sensitized solar cells. In this paper, three 5, 6-difluoro-2,1,3-benzothiadiazole (DFBTD) organic molecules with different number of CN units, named ME15, ME16 and ME17, were investigated by the density functional theory (DFT) and time-dependent DFT (TDDFT). We analyzed the CNs effects on the electronic structures, optical properties, adsorption modes and electron transfer and injection. The result shows that ME17 has the largest maximum absorption wavelength (λ max ) among these new designed dyes due to the strong electron withdrawing ability of two CNs. In addition, CN greatly influence the adsorption modes of dye/TiO 2 and electron injection mechanism. ME16 with one CN also has good optical absorption properties and its acceptor has the strongest coupling strength with the TiO 2 semiconductor which is favorable for electron transfer and injection. Thus, we believe that the number of CN groups in acceptor should be moderate and one CN in D-A-π-A structure dyes may be the more appropriate focusing on the light harvesting ability, electron transfer and electron injection. Copyright © 2017 Elsevier B.V. All rights reserved.

Exciton Energy Transfer from Halide Terminated Nanocrystals to Graphene in Solar Photovoltaics

NASA Astrophysics Data System (ADS)

Ajayi, Obafunso; Abramson, Justin; Anderson, Nicholas; Owen, Jonathan; Zhao, Yue; Kim, Phillip; Gesuele, Felice; Wong, Chee Wei

2011-03-01

Graphene, a zero-gap semiconductor, has been identified as an ideal electrode for nanocrystal solar cell photovoltaic applications due to its high carrier mobility. Further advances in efficient current extraction are required towards this end. We investigate the resonant energy transfer dynamics between photoexcited nanocrystals and graphene, where the energy transfer rate is characterized by the fluorescent quenching of the quantum dots in the presence of graphene. Energy transfer has been shown to have a d -4 dependence on the nanocrystal distance from the graphene surface, with a correction due to blinking statistics. We investigate this relationship with single and few layer graphene. We study halide-terminated CdSe quantum dots; where the absence of the insulating outershell improves the electronic coupling of the donor-acceptor system leads to improved electron transfer. We observe quenching of the halide terminated nanocrystals on graphene, with the quenching factor ρ defined as IQ /IG (the relative intensities on quartz and graphene).

Utilizing Energy Transfer in Binary and Ternary Bulk Heterojunction Organic Solar Cells.

PubMed

Feron, Krishna; Cave, James M; Thameel, Mahir N; O'Sullivan, Connor; Kroon, Renee; Andersson, Mats R; Zhou, Xiaojing; Fell, Christopher J; Belcher, Warwick J; Walker, Alison B; Dastoor, Paul C

2016-08-17

Energy transfer has been identified as an important process in ternary organic solar cells. Here, we develop kinetic Monte Carlo (KMC) models to assess the impact of energy transfer in ternary and binary bulk heterojunction systems. We used fluorescence and absorption spectroscopy to determine the energy disorder and Förster radii for poly(3-hexylthiophene-2,5-diyl), [6,6]-phenyl-C61-butyric acid methyl ester, 4-bis[4-(N,N-diisobutylamino)-2,6-dihydroxyphenyl]squaraine (DIBSq), and poly(2,5-thiophene-alt-4,9-bis(2-hexyldecyl)-4,9-dihydrodithieno[3,2-c:3',2'-h][1,5]naphthyridine-5,10-dione). Heterogeneous energy transfer is found to be crucial in the exciton dissociation process of both binary and ternary organic semiconductor systems. Circumstances favoring energy transfer across interfaces allow relaxation of the electronic energy level requirements, meaning that a cascade structure is not required for efficient ternary organic solar cells. We explain how energy transfer can be exploited to eliminate additional energy losses in ternary bulk heterojunction solar cells, thus increasing their open-circuit voltage without loss in short-circuit current. In particular, we show that it is important that the DIBSq is located at the electron donor-acceptor interface; otherwise charge carriers will be trapped in the DIBSq domain or excitons in the DIBSq domains will not be able to dissociate efficiently at an interface. KMC modeling shows that only small amounts of DIBSq (<5% by weight) are needed to achieve substantial performance improvements due to long-range energy transfer.

N-type molecular electrical doping in organic semiconductors: formation and dissociation efficiencies of charge transfer complex

NASA Astrophysics Data System (ADS)

Kim, Jae-Min; Yoo, Seung-Jun; Moon, Chang-Ki; Sim, Bomi; Lee, Jae-Hyun; Lim, Heeseon; Kim, Jeong Won; Kim, Jang-Joo

2016-09-01

Electrical doping is an important method in organic electronics to enhance device efficiency by controlling Fermi level, increasing conductivity, and reducing injection barrier from electrode. To understand the charge generation process of dopant in doped organic semiconductors, it is important to analyze the charge transfer complex (CTC) formation and dissociation into free charge carrier. In this paper, we correlate charge generation efficiency with the CTC formation and dissociation efficiency of n-dopant in organic semiconductors (OSs). The CTC formation efficiency of Rb2CO3 linearly decreases from 82.8% to 47.0% as the doping concentration increases from 2.5 mol% to 20 mol%. The CTC formation efficiency and its linear decrease with doping concentration are analytically correlated with the concentration-dependent size and number of dopant agglomerates by introducing the degree of reduced CTC formation. Lastly, the behavior of dissociation efficiency is discussed based on the picture of the statistical semiconductor theory and the frontier orbital hybridization model.

Effective immobilization of alcohol dehydrogenase on carbon nanoscaffolds for ethanol biofuel cell.

PubMed

Umasankar, Yogeswaran; Adhikari, Bal-Ram; Chen, Aicheng

2017-12-01

An efficient approach for immobilizing alcohol dehydrogenase (ADH) while enhancing its electron transfer ability has been developed using poly(2-(trimethylamino)ethyl methacrylate) (MADQUAT) cationic polymer and carbon nanoscaffolds. The carbon nanoscaffolds were comprised of single-walled carbon nanotubes (SWCNTs) wrapped with reduced graphene oxide (rGO). The ADH entrapped within the MADQUAT that was present on the carbon nanoscaffolds exhibited a high electron exchange capability with the electrode through its cofactor β-nicotinamide adenine dinucleotide hydrate and β-nicotinamide adenine dinucleotide reduced disodium salt hydrate (NAD + /NADH) redox reaction. The advantages of the carbon nanoscaffolds used as the support matrix and the MADQUAT employed for the entrapment of ADH versus physisorption were demonstrated via cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Our experimental results showed a higher electron transfer, electrocatalytic activity, and rate constant for MADQUAT entrapped ADH on the carbon nanoscaffolds. The immobilization of ADH using both MADQUAT and carbon nanoscaffolds exhibited strong potential for the development of an efficient bio-anode for ethanol powered biofuel cells. Copyright © 2017 Elsevier B.V. All rights reserved.

In situ fabrication of green reduced graphene-based biocompatible anode for efficient energy recycle.

PubMed

Cheng, Ying; Mallavarapu, Megharaj; Naidu, Ravi; Chen, Zuliang

2018-02-01

Improving the anode configuration to enhance biocompatibility and accelerate electron shuttling is critical for efficient energy recovery in microbial fuel cells (MFCs). In this paper, green reduced graphene nanocomposite was successfully coated using layer-by-layer assembly technique onto carbon brush anode. The modified anode achieved a 3.2-fold higher power density of 33.7 W m -3 at a current density of 69.4 A m -3 with a 75% shorter start period. As revealed in the characterization, the green synthesized nanocomposite film affords larger surface roughness for microbial colonization. Besides, gold nanoparticles, which anchored on graphene sheets, promise the relatively high electroactive sites and facilitate electron transfer from electricigens to the anode. The reduction-oxidation peaks in cyclic voltammograms indicated the mechanism of surface cytochromes facilitated current generation while the electrochemical impedance spectroscopy confirmed the enhanced electron transfer from surface cytochrome to electrode. The green synthesis process has the potential to generate a high performing anode in further applications of MFCs. Copyright © 2017 Elsevier Ltd. All rights reserved.

Hole transfer from CdSe nanoparticles to TQ1 polymer in hybrid solar cell device

NASA Astrophysics Data System (ADS)

Sohail, Muhammad; Shah, Zawar Hussain; Saeed, Shomaila; Bibi, Nasreen; Shahbaz, Sadia; Ahmed, Safeer; Shabbir, Saima; Siddiq, Muhammad; Iqbal, Azhar

2018-05-01

In view of realizing the economic viability, we fabricate a solar cell device containing low band gap and easily processable polymer 5-yl-8-(thiophene-2,5-diyl)-2,3-bis(3-(octyloxy)phenyl) quinoxaline (TQ1) and CdSe nanoparticles (NPs) and investigate its charge transport properties. When the TQ1 is combined with the CdSe NPs a strong photoluminescence quenching and shortening of photoluminescence lifetime of the TQ1 is observed indicating exciton transfer from TQ1 to the CdSe NPs. The time-resolved photoluminescence further reveals that the exciton transfer from the polymer to CdSe NPs is very efficient (68%) and it occurs in <1 ns. The exciton transfer from TQ1 to the NPs and electron-hole pair separation followed by hole transfer from the NPs to the TQ1 at the interface indeed increases the lifetime of the charge carriers. This in turn increases the efficiency of the solar cell as compared to polymer only device. These observations suggest the importance of other II-VI semiconductor NPs to achieve higher efficiency for photovoltaic devices containing TQ1 polymer.

Ultrafast Spectroscopy Reveals Electron-Transfer Cascade That Improves Hydrogen Evolution with Carbon Nitride Photocatalysts.

PubMed

Corp, Kathryn L; Schlenker, Cody W

2017-06-14

Solar hydrogen generation from water represents a compelling component of a future sustainable energy portfolio. Recently, chemically robust heptazine-based polymers known as graphitic carbon nitrides (g-C 3 N 4 ) have emerged as promising photocatalysts for hydrogen evolution using visible light while withstanding harsh chemical environments. However, since g-C 3 N 4 electron-transfer dynamics are poorly understood, rational design rules for improving activity remain unclear. Here, we use visible and near-infrared femtosecond transient absorption (TA) spectroscopy to reveal an electron-transfer cascade that correlates with a near-doubling in photocatalytic activity from 2050 to 3810 μmol h -1 g -1 when we infuse a suspension of bulk g-C 3 N 4 with 10% mass loading of chemically exfoliated carbon nitride. TA spectroscopy indicates that exfoliated carbon nitride quenches photogenerated electrons on g-C 3 N 4 at rates approaching the molecular diffusion limit. The TA signal for photogenerated electrons on g-C 3 N 4 decays with a time constant of 1/k e ' = 660 ps in the mixture versus 1/k e = 4.1 ns in g-C 3 N 4 alone. Our TA measurements suggest that the charge generation efficiency in g-C 3 N 4 is greater than 65%. Exfoliated carbon nitride, which liberates only trace hydrogen levels when photoexcited directly, does not appear to independently sustain appreciable long-lived charge generation. Thus, the activity enhancement in the two-component infusion evidently results from a cooperative effect in which charge is generated on g-C 3 N 4 , followed by electron transfer to exfoliated carbon nitride containing photocatalytic chain terminations. This correlation between electron transfer and photocatalytic activity provides new insight into structural modifications for controlling charge separation dynamics and activity of carbon-based photocatalysts.

Using Hyperfine Electron Paramagnetic Resonance Spectroscopy to Define the Proton-Coupled Electron Transfer Reaction at Fe-S Cluster N2 in Respiratory Complex I.

PubMed

Le Breton, Nolwenn; Wright, John J; Jones, Andrew J Y; Salvadori, Enrico; Bridges, Hannah R; Hirst, Judy; Roessler, Maxie M

2017-11-15

Energy-transducing respiratory complex I (NADH:ubiquinone oxidoreductase) is one of the largest and most complicated enzymes in mammalian cells. Here, we used hyperfine electron paramagnetic resonance (EPR) spectroscopic methods, combined with site-directed mutagenesis, to determine the mechanism of a single proton-coupled electron transfer reaction at one of eight iron-sulfur clusters in complex I, [4Fe-4S] cluster N2. N2 is the terminal cluster of the enzyme's intramolecular electron-transfer chain and the electron donor to ubiquinone. Because of its position and pH-dependent reduction potential, N2 has long been considered a candidate for the elusive "energy-coupling" site in complex I at which energy generated by the redox reaction is used to initiate proton translocation. Here, we used hyperfine sublevel correlation (HYSCORE) spectroscopy, including relaxation-filtered hyperfine and single-matched resonance transfer (SMART) HYSCORE, to detect two weakly coupled exchangeable protons near N2. We assign the larger coupling with A( 1 H) = [-3.0, -3.0, 8.7] MHz to the exchangeable proton of a conserved histidine and conclude that the histidine is hydrogen-bonded to N2, tuning its reduction potential. The histidine protonation state responds to the cluster oxidation state, but the two are not coupled sufficiently strongly to catalyze a stoichiometric and efficient energy transduction reaction. We thus exclude cluster N2, despite its proton-coupled electron transfer chemistry, as the energy-coupling site in complex I. Our work demonstrates the capability of pulse EPR methods for providing detailed information on the properties of individual protons in even the most challenging of energy-converting enzymes.

Long-lived, charge-shift states in heterometallic, porphyrin-based dendrimers formed via click chemistry.

PubMed

Le Pleux, Loïc; Pellegrin, Yann; Blart, Errol; Odobel, Fabrice; Harriman, Anthony

2011-05-26

A series of multiporphyrin clusters has been synthesized and characterized in which there exists a logical gradient for either energy or electron transfer between the porphyrins. A central free-base porphyrin (FbP), for example, is equipped with peripheral zinc(II) porphyrins (ZnP) which act as ancillary light harvesters and transfer excitation energy to the FbP under visible light illumination. Additional energy-transfer steps occur at the triplet level, and the series is expanded by including magnesium(II) porphyrins and/or tin(IV) porphyrins as chromophores. Light-induced electron transfer is made possible by incorporating a gold(III) porphyrin (AuP(+)) into the array. Although interesting by themselves, these clusters serve as control compounds by which to understand the photophysical processes occurring within a three-stage dendrimer comprising an AuP(+) core, a second layer formed from four FbP units, and an outer layer containing 12 ZnP residues. Here, illumination into a peripheral ZnP leads to highly efficient electronic energy transfer to FbP, followed by charge transfer to the central AuP(+). Charge recombination within the resultant charge-shift state is intercepted by secondary hole transfer to the ZnP, which occurs with a quantum yield of around 20%. The final charge-shift state survives for some microseconds in fluid solution at room temperature.

Single-Nanoparticle Photoelectrochemistry at a Nanoparticulate TiO2 -Filmed Ultramicroelectrode.

PubMed

Peng, Yue-Yi; Ma, Hui; Ma, Wei; Long, Yi-Tao; Tian, He

2018-03-26

An ultrasensitive photoelectrochemical method for achieving real-time detection of single nanoparticle collision events is presented. Using a micrometer-thick nanoparticulate TiO 2 -filmed Au ultra-microelectrode (TiO 2 @Au UME), a sub-millisecond photocurrent transient was observed for an individual N719-tagged TiO 2 (N719@TiO 2 ) nanoparticle and is due to the instantaneous collision process. Owing to a trap-limited electron diffusion process as the rate-limiting step, a random three-dimensional diffusion model was developed to simulate electron transport dynamics in TiO 2 film. The combination of theoretical simulation and high-resolution photocurrent measurement allow electron-transfer information of a single N719@TiO 2 nanoparticle to be quantified at single-molecule accuracy and the electron diffusivity and the electron-collection efficiency of TiO 2 @Au UME to be estimated. This method provides a test for studies of photoinduced electron transfer at the single-nanoparticle level. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Dispersion of bamboo type multi-wall carbon nanotubes in calf-thymus double stranded DNA.

PubMed

Primo, Emiliano N; Cañete-Rosales, Paulina; Bollo, Soledad; Rubianes, María D; Rivas, Gustavo A

2013-08-01

We report for the first time the use of double stranded calf-thymus DNA (dsDNA) to successfully disperse bamboo-like multi-walled carbon nanotubes (bCNT). The dispersion and the modified electrodes were studied by different spectroscopic, microscopic and electrochemical techniques. The drastic treatment for dispersing the bCNT (45min sonication in a 50% (v/v) ethanol:water solution), produces a partial denaturation and a decrease in the length of dsDNA that facilitates the dispersion of CNT and makes possible an efficient electron transfer of guanine residues to the electrode. A critical analysis of the influence of different experimental conditions on the efficiency of the dispersion and on the performance of glassy carbon electrodes (GCE) modified with bCNT-dsDNA dispersion is also reported. The electron transfer of redox probes and guanine residues was more efficient at GCE modified with bCNT dispersed in dsDNA than at GCE modified with hollow CNT (hCNT) dispersed in dsDNA, demonstrating the importance of the presence of bCNT. Copyright © 2013 Elsevier B.V. All rights reserved.

Charge-transfer excited state in pyrene-1-carboxylic acids adsorbed on titanium dioxide nanoparticles

NASA Astrophysics Data System (ADS)

Krawczyk, S.; Nawrocka, A.; Zdyb, A.

2018-06-01

The electronic structure of excited photosensitizer adsorbed at the surface of a solid is the key factor in the electron transfer processes that underlie the efficiency of dye-sensitized solar cells and photocatalysts. In this work, Stark effect (electroabsorption) spectroscopy has been used to measure the polarizability and dipole moment changes in electronic transitions of pyrene-1-carboxylic (PCA), -acetic (PAA) and -butyric (PBA) acids in ethanol, both free and adsorbed on colloidal TiO2, in glassy ethanol at low temperature. The lack of appreciable increase of dipole moment in the excited state of free and adsorbed PAA and PBA points that two or more single bonds completely prevent the expansion of π-electrons from the aromatic ring towards the carboxylic group, thus excluding the possibility of direct electron injection into TiO2. In free PCA, the pyrene's forbidden S0 → S1 transition has increased intensity, exhibits a long progression in 1400 cm-1 Ag mode and is associated with |Δμ| of 2 D. Adsorption of PCA on TiO2 causes a broadening and red shift of the S0 → S1 absorption band and an increase in dipole moment change on electronic excitation to |Δμ| = 6.5 D. This value increased further to about 15 D when the content of acetic acid in the colloid was changed from 0.2% to 2%, and this effect is ascribed to the surface electric field. The large increase of |Δμ| points that the electric field effect can not only change the energetics of electron transfer from the excited sensitizer into the solid, but can also shift the molecular electronic density, thus directly influencing the electronic coupling factor relevant for electron transfer at the molecule-solid interface.

Magnetic Field Effect: An Efficient Tool To Investigate The Mechanism Of Reactions Using Laser Flash Photolysis Technique

DOE Office of Scientific and Technical Information (OSTI.GOV)

Basu, Samita; Bose, Adity; Dey, Debarati

2008-04-24

Magnetic field effect combined with laser flash photolysis technique have been used to study the mechanism of interactions between two drug-like quinone molecules, Menadione (1,4-naphthoquinone, MQ) and 9, 10 Anthraquinone (AQ) with one of the DNA bases, Adenine in homogeneous acetonitrile/water and heterogeneous micellar media. A switchover in reaction mode from electron transfer to hydrogen abstraction is observed with MQ on changing the solvent from acetonitrile/water to micelle; whereas, AQ retains its mode of interaction towards Adenine as electron transfer in both the media due to its bulky structure compared to MQ.

Plasmon-enhanced scattering and charge transfer in few-layer graphene interacting with buried printed 2D-pattern of silver nanoparticles

NASA Astrophysics Data System (ADS)

Carles, R.; Bayle, M.; Bonafos, C.

2018-04-01

Hybrid structures combing silver nanoparticles and few-layer graphene have been synthetized by combining low-energy ion beam synthesis and stencil techniques. A single plane of metallic nanoparticles plays the role of an embedded plasmonic enhancer located in dedicated areas at a controlled nanometer distance from deposited graphene layers. Optical imaging, reflectance and Raman scattering mapping are used to measure the enhancement of electronic and vibrational properties of these layers. In particular electronic Raman scattering is shown as notably efficient to analyze the optical transfer of charge carriers between the systems and the presence of intrinsic and extrinsic defects.

Magnetic Field Effect: An Efficient Tool To Investigate The Mechanism Of Reactions Using Laser Flash Photolysis Technique

NASA Astrophysics Data System (ADS)

Basu, Samita; Bose, Adity; Dey, Debarati

2008-04-01

Magnetic field effect combined with laser flash photolysis technique have been used to study the mechanism of interactions between two drug-like quinone molecules, Menadione (1,4-naphthoquinone, MQ) and 9, 10 Anthraquinone (AQ) with one of the DNA bases, Adenine in homogeneous acetonitrile/water and heterogeneous micellar media. A switchover in reaction mode from electron transfer to hydrogen abstraction is observed with MQ on changing the solvent from acetonitrile/water to micelle; whereas, AQ retains its mode of interaction towards Adenine as electron transfer in both the media due to its bulky structure compared to MQ.

Plasmon-enhanced scattering and charge transfer in few-layer graphene interacting with buried printed 2D-pattern of silver nanoparticles.

PubMed

Carles, R; Bayle, M; Bonafos, C

2018-04-27

Hybrid structures combing silver nanoparticles and few-layer graphene have been synthetized by combining low-energy ion beam synthesis and stencil techniques. A single plane of metallic nanoparticles plays the role of an embedded plasmonic enhancer located in dedicated areas at a controlled nanometer distance from deposited graphene layers. Optical imaging, reflectance and Raman scattering mapping are used to measure the enhancement of electronic and vibrational properties of these layers. In particular electronic Raman scattering is shown as notably efficient to analyze the optical transfer of charge carriers between the systems and the presence of intrinsic and extrinsic defects.

Breaking the barriers of all-polymer solar cells: Solving electron transporter and morphology problems

NASA Astrophysics Data System (ADS)

Gavvalapalli, Nagarjuna

All-polymer solar cells (APSC) are a class of organic solar cells in which hole and electron transporting phases are made of conjugated polymers. Unlike polymer/fullerene solar cell, photoactive material of APSC can be designed to have hole and electron transporting polymers with complementary absorption range and proper frontier energy level offset. However, the highest reported PCE of APSC is 5 times less than that of polymer/fullerene solar cell. The low PCE of APSC is mainly due to: i) low charge separation efficiency; and ii) lack of optimal morphology to facilitate charge transfer and transport; and iii) lack of control over the exciton and charge transport in each phase. My research work is focused towards addressing these issues. The charge separation efficiency of APSC can be enhanced by designing novel electron transporting polymers with: i) broad absorption range; ii) high electron mobility; and iii) high dielectric constant. In addition to with the above parameters chemical and electronic structure of the repeating unit of conjugated polymer also plays a role in charge separation efficiency. So far only three classes of electron transporting polymers, CN substituted PPV, 2,1,3-benzothiadiazole derived polymers and rylene diimide derived polymers, are used in APSC. Thus to enhance the charge separation efficiency new classes of electron transporting polymers with the above characteristics need to be synthesized. I have developed a new straightforward synthetic strategy to rapidly generate new classes of electron transporting polymers with different chemical and electronic structure, broad absorption range, and high electron mobility from readily available electron deficient monomers. In APSCs due to low entropy of mixing, polymers tend to micro-phase segregate rather than forming the more useful nano-phase segregation. Optimizing the polymer blend morphology to obtain nano-phase segregation is specific to the system under study, time consuming, and not trivial. Thus to avoid micro-phase segregation, nanoparticles of hole and electron transporters are synthesized and blended. But the PCE of nanoparticle blends are far less than those of polymer blends. This is mainly due to the: i) lack of optimal assembly of nanoparticles to facilitate charge transfer and transport processes; and ii) lack of control over the exciton and charge transport properties within the nanoparticles. Polymer packing within the nanoparticle controls the optoelectronic and charge transport properties of the nanoparticle. In this work I have shown that the solvent used to synthesize nanoparticles plays a crucial role in determining the assembly of polymer chains inside the nanoparticle there by affecting its exciton and charge transport processes. To obtain the optimal morphology for better charge transfer and transport, we have also synthesized nanoparticles of different radius with surfactants of opposite charge. We propose that depending on the radius and/or Coulombic interactions these nanoparticles can be assembled into mineral structure-types that are useful for photovoltaic devices.

Theoretical study of anisotropic mobility in ladder-type molecule organic semiconductors

NASA Astrophysics Data System (ADS)

Wei, Hui-Ling; Liu, Yu-Fang

2014-09-01

The properties of two ladder-type semiconductors {M1: 2,2'-(2,7-dihexy1-4,9-dihydro- s-indaceno[1,2- b:5,6- b']dithiophene-4,9-diylidene) dimalononitrile and M2: 2,7-dihexy1-4,9-dihydro- s-indaceno[1,2- b:5,6- b']dithiophene-4,9-dione} as the n-type and ambipolar organic materials are systematically investigated using the first-principle density functional theory combined with the Marcus-Hush electron transfer theory. It is found that the substitution of M1 induces large changes in its electron-transfer mobility of 1.370 cm2 V-1 s-1. M2 has both large electron- and hole-transfer mobility of 0.420 and 0.288 cm2 V-1 s-1, respectively, which indicates that M2 is potentially a high efficient ambipolar organic semiconducting material. Both the M1 and M2 crystals show remarkable anisotropic behavior. A proper design of the n-type and ambipolar organic electronic materials, which may have high mobility performance, is suggested based on the investigated two molecules.

Synergies between Unsaturated Zn/Cu Doping Sites in Carbon Dots Provide New Pathways for Photocatalytic Oxidation

DOE PAGES

Wu, Wenting; Zhang, Qinggang; Wang, Ruiqin; ...

2017-12-07

Unsaturated metal species (UMS) confined in nanomaterials play important roles for electron transfer in a wide range of catalytic reactions. However, the limited fabrication methods of UMS restrict their wider catalytic applications. Here in this paper, we report on the synergy of unsaturated Zn and Cu dopants confined in carbon dots (ZnCu-CDs) to produce enhanced electron transfer and photooxidation processes in the doped CDs. The Zn/Cu species chelate with the carbon matrix mainly through Cu-O(N)-Zn-O(N)-Cu complexes. Within this structure, Cu 2+ acts as a mild oxidizer that facilely increases the unsaturated Zn content and also precisely tunes the unsaturated Znmore » valence state to Zn d+, where d is between 1 and 2, instead of Zn. With the help of UMS, electron-transfer pathways are produced, enhancing both the electron donating (7.0 times) and-accepting (5.3 times) abilities relative to conventional CDs. Because of these synergistic effects, the photocatalytic efficiency of CDs in photooxidation reactions is shown to improve more than 5-fold.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Weihuan; France, David M.; Yu, Wenhua

At present, single-phase liquid, forced convection cooled heat sinks with fins are used to cool power electronics in hybrid electric vehicles (HEVs). Although use of fins in the cooling channels increases heat transfer rates considerably, a second low-temperature radiator and associated pumping system are still required in HEVs. This additional cooling system adds weight and cost while decreasing the efficiency of HEVs. With the objective of eliminating this additional low-temperature radiator and pumping system in HEVs, an alternative cooling technology, subcooled boiling in the cooling channels, was investigated in the present study. Numerical heat transfer simulations were performed using subcooledmore » boiling in the power electronics cooling channels with the coolant supplied from the existing main engine cooling system. Results show that this subcooled boiling system is capable of removing 25% more heat from the power electronics than the conventional forced convection cooling technology, or it can reduce the junction temperature of the power electronics at the current heat removal rate. With the 25% increased heat transfer option, high heat fluxes up to 250 W/cm(2) (typical for wideband-gap semiconductor applications) are possible by using the subcooled boiling system.« less

Solvent-assisted multistage nonequilibrium electron transfer in rigid supramolecular systems: Diabatic free energy surfaces and algorithms for numerical simulations

NASA Astrophysics Data System (ADS)

Feskov, Serguei V.; Ivanov, Anatoly I.

2018-03-01

An approach to the construction of diabatic free energy surfaces (FESs) for ultrafast electron transfer (ET) in a supramolecule with an arbitrary number of electron localization centers (redox sites) is developed, supposing that the reorganization energies for the charge transfers and shifts between all these centers are known. Dimensionality of the coordinate space required for the description of multistage ET in this supramolecular system is shown to be equal to N - 1, where N is the number of the molecular centers involved in the reaction. The proposed algorithm of FES construction employs metric properties of the coordinate space, namely, relation between the solvent reorganization energy and the distance between the two FES minima. In this space, the ET reaction coordinate zn n' associated with electron transfer between the nth and n'th centers is calculated through the projection to the direction, connecting the FES minima. The energy-gap reaction coordinates zn n' corresponding to different ET processes are not in general orthogonal so that ET between two molecular centers can create nonequilibrium distribution, not only along its own reaction coordinate but along other reaction coordinates too. This results in the influence of the preceding ET steps on the kinetics of the ensuing ET. It is important for the ensuing reaction to be ultrafast to proceed in parallel with relaxation along the ET reaction coordinates. Efficient algorithms for numerical simulation of multistage ET within the stochastic point-transition model are developed. The algorithms are based on the Brownian simulation technique with the recrossing-event detection procedure. The main advantages of the numerical method are (i) its computational complexity is linear with respect to the number of electronic states involved and (ii) calculations can be naturally parallelized up to the level of individual trajectories. The efficiency of the proposed approach is demonstrated for a model supramolecular system involving four redox centers.

Pattern transfer printing by kinetic control of adhesion to an elastomeric stamp

DOEpatents

Nuzzo, Ralph G [Champaign, IL; Rogers, John A [Champaign, IL; Menard, Etienne [Urbana, IL; Lee, Keon Jae [Tokyo, JP; Khang, Dahl-Young [Urbana, IL; Sun, Yugang [Champaign, IL; Meitl, Matthew [Champaign, IL; Zhu, Zhengtao [Urbana, IL

2011-05-17

The present invention provides methods, systems and system components for transferring, assembling and integrating features and arrays of features having selected nanosized and/or microsized physical dimensions, shapes and spatial orientations. Methods of the present invention utilize principles of `soft adhesion` to guide the transfer, assembly and/or integration of features, such as printable semiconductor elements or other components of electronic devices. Methods of the present invention are useful for transferring features from a donor substrate to the transfer surface of an elastomeric transfer device and, optionally, from the transfer surface of an elastomeric transfer device to the receiving surface of a receiving substrate. The present methods and systems provide highly efficient, registered transfer of features and arrays of features, such as printable semiconductor element, in a concerted manner that maintains the relative spatial orientations of transferred features.

Electron Flow in Multiheme Bacterial Cytochromes is a Balancing Act Between Heme Electronic Interaction and Redox Potentials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Breuer, Marian; Rosso, Kevin M.; Blumberger, Jochen

The naturally widespread process of electron transfer from metal reducing bacteria to extracellular solid metal oxides entails unique biomolecular machinery optimized for long-range electron transport. To perform this function efficiently microorganisms have adapted multi-heme c-type cytochromes to arrange heme cofactors into wires that cooperatively span the cellular envelope, transmitting electrons along distances greater than 100 Angstroms. Implications and opportunities for bionanotechnological device design are self-evident. However, at the molecular level how these proteins shuttle electrons along their heme wires, navigating intraprotein intersections and interprotein interfaces effciently, remains a mystery so far inaccessible to experiment. To shed light on this criticalmore » topic, we carried out extensive computer simulations to calculate Marcus theory quantities for electron transfer along the ten heme cofactors in the recently crystallized outer membrane cytochrome MtrF. The combination of electronic coupling matrix elements with free energy calculations of heme redox potentials and reorganization energies for heme-to-heme electron transfer allows the step-wise and overall electron transfer rate to be estimated and understood in terms of structural and dynamical characteristics of the protein. By solving a master equation for electron hopping, we estimate an intrinsic, maximum possible electron flux through solvated MtrF of 104-105 s-1, consistent with recently measured rates for the related MtrCAB protein complex. Intriguingly, this flux must navigate thermodynamically uphill steps past low potential hemes. Our calculations show that the rapid electron transport through MtrF is the result of a clear correlation between heme redox potential and the strength of electronic coupling along the wire: Thermodynamically uphill steps occur only between electronically well connected stacked heme pairs. This suggests that the protein evolved to harbor low potential hemes, presumably necessary for reduction of certain soluble substrates, without slowing down electron ow. These findings are particularly profound in light of the apparently well conserved staggered cross heme wire structural motif in functionally related outer-membrane proteins.« less

Photoinduced Electron Transfer-based Halogen-free Photosensitizers: Covalent meso-Aryl (Phenyl, Naphthyl, Anthryl, and Pyrenyl) as Electron Donors to Effectively Induce the Formation of the Excited Triplet State and Singlet Oxygen for BODIPY Compounds.

PubMed

Zhang, Xian-Fu; Feng, Nan

2017-09-19

Pristine BODIPY compounds have negligible efficiency to generate the excited triplet state and singlet oxygen. In this report, we show that attaching a good electron donor to the BODIPY core can lead to singlet oxygen formation with up to 58 % quantum efficiency. For this purpose, BODIPYs with meso-aryl groups (phenyl, naphthyl, anthryl, and pyrenyl) were synthesized and characterized. The fluorescence, excited triplet state, and singlet oxygen formation properties for these compounds were measured in various solvents by UV/Vis absorption, steady-state and time-resolved fluorescence methods, as well as laser flash photolysis technique. In particular, the presence of anthryl and pyrenyl showed substantial enhancement on the singlet oxygen formation ability of BODIPY with up to 58 % and 34 % quantum efficiency, respectively, owing to their stronger electron-donating ability. Upon the increase in singlet oxygen formation, the fluorescence quantum yield and lifetime values of the aryl-BODIPY showed a concomitant decrease. The increase in solvent polarity enhances the singlet oxygen generation but decreases the fluorescence quantum yield. The results are explained by the presence of intramolecular photoinduced electron transfer from the aryl moiety to BODIPY core. This method of promoting T 1 formation is very different from the traditional heavy atom effect by I, Br, or transition metal atoms. This type of novel photosensitizers may find important applications in organic oxygenation reactions and photodynamic therapy of tumors. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Chemoselective Hydrodehalogenation of Organic Halides Utilizing Two-Dimensional Anionic Electrons of Inorganic Electride [Ca2N]+·e^.

PubMed

Kim, Ye Ji; Kim, Sun Min; Yu, Chunghyeon; Yoo, YoungMin; Cho, Eun Jin; Yang, Jung Woon; Kim, Sung Wng

2017-01-31

Halogenated organic compounds are important anthropogenic chemicals widely used in chemical industry, biology, and pharmacology; however, the persistence and inertness of organic halides cause human health problems and considerable environmental pollution. Thus, the elimination or replacement of halogen atoms with organic halides has been considered a central task in synthetic chemistry. In dehalogenation reactions, the consecutive single-electron transfer from reducing agents generates the radical and corresponding carbanion and thus removes the halogen atom as the leaving group. Herein, we report a new strategy for an efficient chemoselective hydrodehalogenation through the formation of stable carbanion intermediates, which are simply achieved by using highly mobile two-dimensional electrons of inorganic electride [Ca 2 N] + ·e - with effective electron transfer ability. The consecutive single-electron transfer from inorganic electride [Ca 2 N] + ·e - stabilized free carbanions, which is a key step in achieving the selective reaction. Furthermore, a determinant more important than leaving group ability is the stability control of free carbanions according to the s character determined by the backbone structure. We anticipate that this approach may provide new insight into selective chemical formation, including hydrodehalogenation.

Energy transfer in a mechanically trapped exciplex.

PubMed

Klosterman, Jeremy K; Iwamura, Munetaka; Tahara, Tahei; Fujita, Makoto

2009-07-15

Host-guest complexes involving M(6)L(4) coordination cages can display unusual photoreactivity, and enclathration of the very large fluorophore bisanthracene resulted in an emissive, mechanically trapped intramolecular exciplex. Mechanically linked intramolecular exciplexes are important for understanding the dependence of energy transfer on donor-acceptor distance, orientation, and electronic coupling but are relatively unexplored. Steady-state and picosecond time-resolved fluorescence measurements have revealed that selective excitation of the encapsulated guest fluorophore results in efficient energy transfer from the excited guest to an emissive host-guest exciplex state.

Nuclear conversion theory: molecular hydrogen in non-magnetic insulators

PubMed Central

Ghiglieno, Filippo

2016-01-01

The hydrogen conversion patterns on non-magnetic solids sensitively depend upon the degree of singlet/triplet mixing in the intermediates of the catalytic reaction. Three main ‘symmetry-breaking’ interactions are brought together. In a typical channel, the electron spin–orbit (SO) couplings introduce some magnetic excitations in the non-magnetic solid ground state. The electron spin is exchanged with a molecular one by the electric molecule–solid electron repulsion, mixing the bonding and antibonding states and affecting the molecule rotation. Finally, the magnetic hyperfine contact transfers the electron spin angular momentum to the nuclei. Two families of channels are considered and a simple criterion based on the SO coupling strength is proposed to select the most efficient one. The denoted ‘electronic’ conversion path involves an emission of excitons that propagate and disintegrate in the bulk. In the other denoted ‘nuclear’, the excited electron states are transients of a loop, and the electron system returns to its fundamental ground state. The described model enlarges previous studies by extending the electron basis to charge-transfer states and ‘continui’ of band states, and focuses on the broadening of the antibonding molecular excited state by the solid conduction band that provides efficient tunnelling paths for the hydrogen conversion. After working out the general conversion algebra, the conversion rates of hydrogen on insulating and semiconductor solids are related to a few molecule–solid parameters (gap width, ionization and affinity potentials) and compared with experimental measures. PMID:27703681

Direct observation of multistep energy transfer in LHCII with fifth-order 3D electronic spectroscopy.

PubMed

Zhang, Zhengyang; Lambrev, Petar H; Wells, Kym L; Garab, Győző; Tan, Howe-Siang

2015-07-31

During photosynthesis, sunlight is efficiently captured by light-harvesting complexes, and the excitation energy is then funneled towards the reaction centre. These photosynthetic excitation energy transfer (EET) pathways are complex and proceed in a multistep fashion. Ultrafast two-dimensional electronic spectroscopy (2DES) is an important tool to study EET processes in photosynthetic complexes. However, the multistep EET processes can only be indirectly inferred by correlating different cross peaks from a series of 2DES spectra. Here we directly observe multistep EET processes in LHCII using ultrafast fifth-order three-dimensional electronic spectroscopy (3DES). We measure cross peaks in 3DES spectra of LHCII that directly indicate energy transfer from excitons in the chlorophyll b (Chl b) manifold to the low-energy level chlorophyll a (Chl a) via mid-level Chl a energy states. This new spectroscopic technique allows scientists to move a step towards mapping the complete complex EET processes in photosynthetic systems.

Charge separation and carrier dynamics in donor-acceptor heterojunction photovoltaic systems.

PubMed

Teuscher, Joël; Brauer, Jan C; Stepanov, Andrey; Solano, Alicia; Boziki, Ariadni; Chergui, Majed; Wolf, Jean-Pierre; Rothlisberger, Ursula; Banerji, Natalie; Moser, Jacques-E

2017-11-01

Electron transfer and subsequent charge separation across donor-acceptor heterojunctions remain the most important areas of study in the field of third-generation photovoltaics. In this context, it is particularly important to unravel the dynamics of individual ultrafast processes (such as photoinduced electron transfer, carrier trapping and association, and energy transfer and relaxation), which prevail in materials and at their interfaces. In the frame of the National Center of Competence in Research "Molecular Ultrafast Science and Technology," a research instrument of the Swiss National Science Foundation, several groups active in the field of ultrafast science in Switzerland have applied a number of complementary experimental techniques and computational simulation tools to scrutinize these critical photophysical phenomena. Structural, electronic, and transport properties of the materials and the detailed mechanisms of photoinduced charge separation in dye-sensitized solar cells, conjugated polymer- and small molecule-based organic photovoltaics, and high-efficiency lead halide perovskite solar energy converters have been scrutinized. Results yielded more than thirty research articles, an overview of which is provided here.

A PEG/copper(i) halide cluster as an eco-friendly catalytic system for C-N bond formation.

PubMed

Li, Cheng-An; Ji, Wei; Qu, Jian; Jing, Su; Gao, Fei; Zhu, Dun-Ru

2018-05-22

The catalytic activities of eight copper(i) halide clusters assembled from copper(i) halide and ferrocenyltelluroethers, 1-8, were investigated in C-N formation under various conditions. A catalytic procedure using poly(ethylene glycol) (PEG-400) as a greener alternative organic solvent has been developed. The PEG-400/5 system can achieve 99% targeted yield with a mild reaction temperature and short reaction time. After the isolation of the products by extraction with diethyl ether, this PEG-400/cluster system could be easily recycled. Spectroscopic studies elucidate a stepwise mechanism: firstly, proton-coupled electron transfer (PCET) involving the transfer of an electron from Cu+ and a proton from imidazole results in the formation of a labile penta-coordinated Cu2+ and aryl radical; the following effective electron transfer from the ferrocene unit reduces Cu2+ and forms the target product; finally, the ferrocenium unit is reduced by the I- anion. The merits of this eco-friendly synthesis are the efficient utilization of reagents and easy recyclability.

Construction and direct electrochemistry of orientation controlled laccase electrode.

PubMed

Li, Ying; Zhang, Jiwei; Huang, Xirong; Wang, Tianhong

2014-03-28

A laccase has multiple redox centres. Chemisorption of laccases on a gold electrode through a polypeptide tag introduced at the protein surface provides an isotropic orientation of laccases on the Au surface, which allows the orientation dependent study of the direct electrochemistry of laccase. In this paper, using genetic engineering technology, two forms of recombinant laccase which has Cys-6×His tag at the N or C terminus were generated. Via the Au-S linkage, the recombinant laccase was assembled orientationally on gold electrode. A direct electron transfer and a bioelectrocatalytic activity toward oxygen reduction were observed on the two orientation controlled laccase electrodes, but their electrochemical behaviors were found to be quite different. The orientation of laccase on the gold electrode affects both the electron transfer pathway and the electron transfer efficiency of O2 reduction. The present study is helpful not only to the in-depth understanding of the direct electrochemistry of laccase, but also to the development of laccase-based biofuel cells. Copyright © 2014 Elsevier Inc. All rights reserved.

Cross-benzoin and Stetter-type reactions mediated by KOtBu-DMF via an electron-transfer process.

PubMed

Ragno, Daniele; Zaghi, Anna; Di Carmine, Graziano; Giovannini, Pier Paolo; Bortolini, Olga; Fogagnolo, Marco; Molinari, Alessandra; Venturini, Alessandro; Massi, Alessandro

2016-10-18

The condensation of aromatic α-diketones (benzils) with aromatic aldehydes (benzoin-type reaction) and chalcones (Stetter-type reaction) in DMF in the presence of catalytic (25 mol%) KOtBu is reported. Both types of umpolung processes proceed with good efficiency and complete chemoselectivity. On the basis of spectroscopic evidence (MS analysis) of plausible intermediates and literature reports, the occurrence of different ionic pathways have been evaluated to elucidate the mechanism of a model cross-benzoin-like reaction along with a radical route initiated by an electron-transfer process to benzil from the carbamoyl anion derived from DMF. This mechanistic investigation has culminated in a different proposal, supported by calculations and a trapping experiment, based on double electron-transfer to benzil with formation of the corresponding enediolate anion as the key reactive intermediate. A mechanistic comparison between the activation modes of benzils in KOtBu-DMF and KOtBu-DMSO systems is also described.

Heterojunction-Assisted Co3 S4 @Co3 O4 Core-Shell Octahedrons for Supercapacitors and Both Oxygen and Carbon Dioxide Reduction Reactions.

PubMed

Yan, Yibo; Li, Kaixin; Chen, Xiaoping; Yang, Yanhui; Lee, Jong-Min

2017-12-01

Expedition of electron transfer efficiency and optimization of surface reactant adsorption products desorption processes are two main challenges for developing non-noble catalysts in the oxygen reduction reaction (ORR) and CO 2 reduction reaction (CRR). A heterojunction prototype on Co 3 S 4 @Co 3 O 4 core-shell octahedron structure is established via hydrothermal lattice anion exchange protocol to implement the electroreduction of oxygen and carbon dioxide with high performance. The synergistic bifunctional catalyst consists of p-type Co 3 O 4 core and n-type Co 3 S 4 shell, which afford high surface electron density along with high capacitance without sacrificing mechanical robustness. A four electron ORR process, identical to the Pt catalyzed ORR, is validated using the core-shell octahedron catalyst. The synergistic interaction between cobalt sulfide and cobalt oxide bicatalyst reduces the activation energy to convert CO 2 into adsorbed intermediates and hereby enables CRR to run at a low overpotential, with formate as the highly selective main product at a high faraday efficiency of 85.3%. The remarkable performance can be ascribed to the synergistic coupling effect of the structured co-catalysts; heterojunction structure expedites the electron transfer efficiency and optimizes surface reactant adsorption product desorption processes, which also provide theoretical and pragmatic guideline for catalyst development and mechanism explorations. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Theoretical study of electronic transfer current rate at dye-sensitized solar cells

NASA Astrophysics Data System (ADS)

AL-Agealy, Hadi J. M.; AlMaadhede, Taif Saad; Hassooni, Mohsin A.; Sadoon, Abbas K.; Ashweik, Ahmed M.; Mahdi, Hind Abdlmajeed; Ghadhban, Rawnaq Qays

2018-05-01

In this research, we present a theoretical study of electronic transfer kinetics rate in N719/TiO2 and N719/ZnO dye-sensitized solar cells (DSSC) systems using a simple model depending on the postulate of quantum mechanics theory. The evaluation of the electronic transition current rate in DSSC systems are function of many parameters such that; the reorientation transition energies ΛSe m D y e , the transition coupling parameter ℂT(0), potential exponential effect e-(E/C-EF ) kBT , unit cell volume VSem, and temperature T. Furthermore, the analysis of electronic transfer current rate in N719/TiO2 and N719/ZnO systems show that the rate upon dye-sensitization solar cell increases with increases of transition coupling parameter, decreasing potential that building at interface a results of different material in this devices and increasing with reorientation transition energy. On the other hand, we can find the electronic transfer behavior is dependent of the dye absorption spectrum and mainly depending on the reorientation of transition energy. The replacement of the solvents in both DSSC system caused increasing of current rates dramatically depending on polarity of solvent in subset devices. This change in current rate of electron transfer were attributed to much more available of recombination sites introduced by the solvents medium. The electronic transfer current dynamics are shown to occurs in N719/TiO2 system faster many time compare to ocuures at N719/ZnO system, this indicate that TiO2 a is a good and active material compare with ZnO to using in dye sensitized solar cell devices. In contrast, the large current rate in N719/TiO2 comparing to ZnO of N719/ZnO systems indicate that using TiO2 with N719 dye lead to increasing the efficiency of DSSC.

Imaging Plasmon Hybridization of Fano Resonances via Hot-Electron-Mediated Absorption Mapping.

PubMed

Simoncelli, Sabrina; Li, Yi; Cortés, Emiliano; Maier, Stefan A

2018-06-13

The inhibition of radiative losses in dark plasmon modes allows storing electromagnetic energy more efficiently than in far-field excitable bright-plasmon modes. As such, processes benefiting from the enhanced absorption of light in plasmonic materials could also take profit of dark plasmon modes to boost and control nanoscale energy collection, storage, and transfer. We experimentally probe this process by imaging with nanoscale precision the hot-electron driven desorption of thiolated molecules from the surface of gold Fano nanostructures, investigating the effect of wavelength and polarization of the incident light. Spatially resolved absorption maps allow us to show the contribution of each element of the nanoantenna in the hot-electron driven process and their interplay in exciting a dark plasmon mode. Plasmon-mode engineering allows control of nanoscale reactivity and offers a route to further enhance and manipulate hot-electron driven chemical reactions and energy-conversion and transfer at the nanoscale.

Peripheral Hole Acceptor Moieties on an Organic Dye Improve Dye‐Sensitized Solar Cell Performance

PubMed Central

Hao, Yan; Gabrielsson, Erik; Lohse, Peter William; Yang, Wenxing; Johansson, Erik M. J.; Hagfeldt, Anders

2015-01-01

Investigation of charge transfer dynamics in dye‐sensitized solar cells is of fundamental interest and the control of these dynamics is a key factor for developing more efficient solar cell devices. One possibility for attenuating losses through recombination between injected electrons and oxidized dye molecules is to move the positive charge further away from the metal oxide surface. For this purpose, a metal‐free dye named E6 is developed, in which the chromophore core is tethered to two external triphenylamine (TPA) units. After photoinduced electron injection into TiO2, the remaining hole is rapidly transferred to a peripheral TPA unit. Electron–hole recombination is slowed down by 30% compared to a reference dye without peripheral TPA units. Furthermore, it is found that the added TPA moieties improve the electron blocking effect of the dye, retarding recombination of electrons from TiO2 to the cobalt‐based electrolyte. PMID:27722076

Modeling Electronic-Nuclear Interactions for Excitation Energy Transfer Processes in Light-Harvesting Complexes.

PubMed

Lee, Mi Kyung; Coker, David F

2016-08-18

An accurate approach for computing intermolecular and intrachromophore contributions to spectral densities to describe the electronic-nuclear interactions relevant for modeling excitation energy transfer processes in light harvesting systems is presented. The approach is based on molecular dynamics (MD) calculations of classical correlation functions of long-range contributions to excitation energy fluctuations and a separate harmonic analysis and single-point gradient quantum calculations for electron-intrachromophore vibrational couplings. A simple model is also presented that enables detailed analysis of the shortcomings of standard MD-based excitation energy fluctuation correlation function approaches. The method introduced here avoids these problems, and its reliability is demonstrated in accurate predictions for bacteriochlorophyll molecules in the Fenna-Matthews-Olson pigment-protein complex, where excellent agreement with experimental spectral densities is found. This efficient approach can provide instantaneous spectral densities for treating the influence of fluctuations in environmental dissipation on fast electronic relaxation.

Quantum coherence spectroscopy reveals complex dynamics in bacterial light-harvesting complex 2 (LH2).

PubMed

Harel, Elad; Engel, Gregory S

2012-01-17

Light-harvesting antenna complexes transfer energy from sunlight to photosynthetic reaction centers where charge separation drives cellular metabolism. The process through which pigments transfer excitation energy involves a complex choreography of coherent and incoherent processes mediated by the surrounding protein and solvent environment. The recent discovery of coherent dynamics in photosynthetic light-harvesting antennae has motivated many theoretical models exploring effects of interference in energy transfer phenomena. In this work, we provide experimental evidence of long-lived quantum coherence between the spectrally separated B800 and B850 rings of the light-harvesting complex 2 (LH2) of purple bacteria. Spectrally resolved maps of the detuning, dephasing, and the amplitude of electronic coupling between excitons reveal that different relaxation pathways act in concert for optimal transfer efficiency. Furthermore, maps of the phase of the signal suggest that quantum mechanical interference between different energy transfer pathways may be important even at ambient temperature. Such interference at a product state has already been shown to enhance the quantum efficiency of transfer in theoretical models of closed loop systems such as LH2.

Quantum coherence spectroscopy reveals complex dynamics in bacterial light-harvesting complex 2 (LH2)

PubMed Central

Harel, Elad; Engel, Gregory S.

2012-01-01

Light-harvesting antenna complexes transfer energy from sunlight to photosynthetic reaction centers where charge separation drives cellular metabolism. The process through which pigments transfer excitation energy involves a complex choreography of coherent and incoherent processes mediated by the surrounding protein and solvent environment. The recent discovery of coherent dynamics in photosynthetic light-harvesting antennae has motivated many theoretical models exploring effects of interference in energy transfer phenomena. In this work, we provide experimental evidence of long-lived quantum coherence between the spectrally separated B800 and B850 rings of the light-harvesting complex 2 (LH2) of purple bacteria. Spectrally resolved maps of the detuning, dephasing, and the amplitude of electronic coupling between excitons reveal that different relaxation pathways act in concert for optimal transfer efficiency. Furthermore, maps of the phase of the signal suggest that quantum mechanical interference between different energy transfer pathways may be important even at ambient temperature. Such interference at a product state has already been shown to enhance the quantum efficiency of transfer in theoretical models of closed loop systems such as LH2. PMID:22215585

Vitamin C: electron emission, free radicals and biological versatility.

PubMed

Getoff, Nikola

2013-01-01

The many-sided biological role of vitamin C (ascorbate) is briefly illustrated by specific examples. It is demonstrated that in aqueous solutions, vitamin C emits solvated electrons (e(aq)(-)), when excited in single state. Vitamin C can also react with e(aq)(-) as well as transfer them to other biological systems and thereby acts as efficient electron mediator. Based on its chemical and biological properties, it is clear that vitamin C plays a very important role in various functions in the organism alongside biochemical processes.

Charge Transfer Enhancement in the D-π-A Type Porphyrin Dyes: A Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT) Study.

PubMed

Kang, Guo-Jun; Song, Chao; Ren, Xue-Feng

2016-11-25

The electronic geometries and optical properties of two D-π-A type zinc porphyrin dyes (NCH₃-YD2 and TPhe-YD) were systematically investigated by density functional theory (DFT) and time-dependent density functional theory (TD-DFT) to reveal the origin of significantly altered charge transfer enhancement by changing the electron donor of the famous porphyrin-based sensitizer YD2-o-C8. The molecular geometries and photophysical properties of dyes before and after binding to the TiO₂ cluster were fully investigated. From the analyses of natural bond orbital (NBO), extended charge decomposition analysis (ECDA), and electron density variations (Δρ) between the excited state and ground state, it was found that the introduction of N(CH₃)₂ and 1,1,2-triphenylethene groups enhanced the intramolecular charge-transfer (ICT) character compared to YD2-o-C8. The absorption wavelength and transition possess character were significantly influenced by N(CH₃)₂ and 1,1,2-triphenylethene groups. NCH₃-YD2 with N(CH₃)₂ groups in the donor part is an effective way to improve the interactions between the dyes and TiO₂ surface, light having efficiency (LHE), and free energy change (ΔG inject ), which is expected to be an efficient dye for use in dye-sensitized solar cells (DSSCs).

Effect of gold nanoparticles on the structure and electron-transfer characteristics of glucose oxidase redox polyelectrolyte-surfactant complexes.

PubMed

Cortez, M Lorena; Marmisollé, Waldemar; Pallarola, Diego; Pietrasanta, Lía I; Murgida, Daniel H; Ceolín, Marcelo; Azzaroni, Omar; Battaglini, Fernando

2014-10-06

Efficient electrical communication between redox proteins and electrodes is a critical issue in the operation and development of amperometric biosensors. The present study explores the advantages of a nanostructured redox-active polyelectrolyte-surfactant complex containing [Os(bpy)2Clpy](2+) (bpy=2,2'-bipyridine, py= pyridine) as the redox centers and gold nanoparticles (AuNPs) as nanodomains for boosting the electron-transfer propagation throughout the assembled film in the presence of glucose oxidase (GOx). Film structure was characterized by grazing-incidence small-angle X-ray scattering (GISAXS) and atomic force microscopy (AFM), GOx incorporation was followed by surface plasmon resonance (SPR) and quartz-crystal microbalance with dissipation (QCM-D), whereas Raman spectroelectrochemistry and electrochemical studies confirmed the ability of the entrapped gold nanoparticles to enhance the electron-transfer processes between the enzyme and the electrode surface. Our results show that nanocomposite films exhibit five-fold increase in current response to glucose compared with analogous supramolecular AuNP-free films. The introduction of colloidal gold promotes drastic mesostructural changes in the film, which in turn leads to a rigid, amorphous interfacial architecture where nanoparticles, redox centers, and GOx remain in close proximity, thus improving the electron-transfer process. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Highly galloylated tannin fractions from witch hazel (Hamamelis virginiana) bark: electron transfer capacity, in vitro antioxidant activity, and effects on skin-related cells.

PubMed

Touriño, Sonia; Lizárraga, Daneida; Carreras, Anna; Lorenzo, Sonia; Ugartondo, Vanessa; Mitjans, Montserrat; Vinardell, María Pilar; Juliá, Luis; Cascante, Marta; Torres, Josep Lluís

2008-03-01

Witch hazel ( Hammamelis virginiana) bark is a rich source of both condensed and hydrolizable oligomeric tannins. From a polyphenolic extract soluble in both ethyl acetate and water, we have generated fractions rich in pyrogallol-containing polyphenols (proanthocyanidins, gallotannins, and gallates). The mixtures were highly active as free radical scavengers against ABTS, DPPH (hydrogen donation and electron transfer), and HNTTM (electron transfer). They were also able to reduce the newly introduced TNPTM radical, meaning that they included some highly reactive components. Witch hazel phenolics protected red blood cells from free radical-induced hemolysis and were mildly cytotoxic to 3T3 fibroblasts and HaCat keratinocytes. They also inhibited the proliferation of tumoral SK-Mel 28 melanoma cells at lower concentrations than grape and pine procyanidins. The high content in pyrogallol moieties may be behind the effect of witch hazel phenolics on skin cells. Because the most cytotoxic and antiproliferative mixtures were also the most efficient as electron transfer agents, we hypothesize that the final putative antioxidant effect of polyphenols may be in part attributed to the stimulation of defense systems by mild prooxidant challenges provided by reactive oxygen species generated through redox cycling.

What is beta-carotene doing in the photosystem II reaction centre?

PubMed Central

Telfer, Alison

2002-01-01

During photosynthesis carotenoids normally serve as antenna pigments, transferring singlet excitation energy to chlorophyll, and preventing singlet oxygen production from chlorophyll triplet states, by rapid spin exchange and decay of the carotenoid triplet to the ground state. The presence of two beta-carotene molecules in the photosystem II reaction centre (RC) now seems well established, but they do not quench the triplet state of the primary electron-donor chlorophylls, which are known as P(680). The beta-carotenes cannot be close enough to P(680) for triplet quenching because that would also allow extremely fast electron transfer from beta-carotene to P(+)(680), preventing the oxidation of water. Their transfer of excitation energy to chlorophyll, though not very efficient, indicates close proximity to the chlorophylls ligated by histidine 118 towards the periphery of the two main RC polypeptides. The primary function of the beta-carotenes is probably the quenching of singlet oxygen produced after charge recombination to the triplet state of P(680). Only when electron donation from water is disturbed does beta-carotene become oxidized. One beta-carotene can mediate cyclic electron transfer via cytochrome b559. The other is probably destroyed upon oxidation, which might trigger a breakdown of the polypeptide that binds the cofactors that carry out charge separation. PMID:12437882

Surface Charge Transfer Doping via Transition Metal Oxides for Efficient p-Type Doping of II-VI Nanostructures.

PubMed

Xia, Feifei; Shao, Zhibin; He, Yuanyuan; Wang, Rongbin; Wu, Xiaofeng; Jiang, Tianhao; Duhm, Steffen; Zhao, Jianwei; Lee, Shuit-Tong; Jie, Jiansheng

2016-11-22

Wide band gap II-VI nanostructures are important building blocks for new-generation electronic and optoelectronic devices. However, the difficulty of realizing p-type conductivity in these materials via conventional doping methods has severely handicapped the fabrication of p-n homojunctions and complementary circuits, which are the fundamental components for high-performance devices. Herein, by using first-principles density functional theory calculations, we demonstrated a simple yet efficient way to achieve controlled p-type doping on II-VI nanostructures via surface charge transfer doping (SCTD) using high work function transition metal oxides such as MoO 3 , WO 3 , CrO 3 , and V 2 O 5 as dopants. Our calculations revealed that these oxides were capable of drawing electrons from II-VI nanostructures, leading to accumulation of positive charges (holes injection) in the II-VI nanostructures. As a result, Fermi levels of the II-VI nanostructures were shifted toward the valence band regions after surface modifications, along with the large enhancement of work functions. In situ ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy characterizations verified the significant interfacial charge transfer between II-VI nanostructures and surface dopants. Both theoretical calculations and electrical transfer measurements on the II-VI nanostructure-based field-effect transistors clearly showed the p-type conductivity of the nanostructures after surface modifications. Strikingly, II-VI nanowires could undergo semiconductor-to-metal transition by further increasing the SCTD level. SCTD offers the possibility to create a variety of electronic and optoelectronic devices from the II-VI nanostructures via realization of complementary doping.

Tuning charge balance in PHOLEDs with ambipolar host materials to achieve high efficiency

DOE Office of Scientific and Technical Information (OSTI.GOV)

Padmaperuma, Asanga B.; Koech, Phillip K.; Cosimbescu, Lelia

2009-08-27

The efficiency and stability of blue organic light emitting devices (OLEDs) continue to be a primary roadblock to developing organic solid state white lighting. For OLEDs to meet the high power conversion efficiency goal, they will require both close to 100% internal quantum efficiency and low operating voltage in a white light emitting device.1 It is generally accepted that such high quantum efficiency, can only be achieved with the use of organometallic phosphor doped OLEDs. Blue OLEDs are particularly important for solid state lighting. The simplest (and therefore likely the lowest cost) method of generating white light is to downmore » convert part of the emission from a blue light source with a system of external phosphors.2 A second method of generating white light requires the superposition of the light from red, green and blue OLEDs in the correct ratio. Either of these two methods (and indeed any method of generating white light with a high color rendering index) critically depends on a high efficiency blue light component.3 A simple OLED generally consists of a hole-injecting anode, a preferentially hole transporting organic layer (HTL), an emissive layer that contains the recombination zone and ideally transports both holes and electrons, a preferentially electron-transporting layer (ETL) and an electron-injecting cathode. Color in state-of-the-art OLEDs is generated by an organometallic phosphor incorporated by co-sublimation into the emissive layer (EML).4 New materials functioning as hosts, emitters, charge transporting, and charge blocking layers have been developed along with device architectures leading to electrophosphorescent based OLEDs with high quantum efficiencies near the theoretical limit. However, the layers added to the device architecture to enable high quantum efficiencies lead to higher operating voltages and correspondingly lower power efficiencies. Achievement of target luminance power efficiencies will require new strategies for lowering operating voltages, particularly if this is to be achieved in a device that can be manufactured at low cost. To avoid the efficiency losses associated with phosphorescence quenching by back-energy transfer from the dopant onto the host, the triplet excited states of the host material must be higher in energy than the triplet excited state of the dopant.5 This must be accomplished without sacrificing the charge transporting properties of the composite.6 Similar problems limit the efficiency of OLED-based displays, where blue light emitters are the least efficient and least stable. We previously demonstrated the utility of organic phosphine oxide (PO) materials as electron transporting HMs for FIrpic in blue OLEDs.7 However, the high reluctance of PO materials to oxidation and thus, hole injection limits the ability to balance charge injection and transport in the EML without relying on charge transport by the phosphorescent dopant. PO host materials were engineered to transport both electrons and holes in the EML and still maintain high triplet exciton energy to ensure efficient energy transfer to the dopant (Figure 1). There are examples of combining hole transporting moieties (mainly aromatic amines) with electron transport moieties (e.g., oxadiazoles, triazines, boranes)8 to develop new emitter and host materials for small molecule and polymer9 OLEDs. The challenge is to combine the two moieties without lowering the triplet energy of the target molecule. For example, coupling of a dimesitylphenylboryl moiety with a tertiary aromatic amine (FIAMBOT) results in intramolecular electron transfer from the amine to the boron atom through the bridging phenyl. The mesomeric effect of the dimesitylphenylboryl unit acts to extend conjugation and lowers triplet exciton energies (< 2.8 eV) rendering such systems inadequate as ambipolar hosts for blue phosphors.« less

Spin-photon interface and spin-controlled photon switching in a nanobeam waveguide

NASA Astrophysics Data System (ADS)

Javadi, Alisa; Ding, Dapeng; Appel, Martin Hayhurst; Mahmoodian, Sahand; Löbl, Matthias Christian; Söllner, Immo; Schott, Rüdiger; Papon, Camille; Pregnolato, Tommaso; Stobbe, Søren; Midolo, Leonardo; Schröder, Tim; Wieck, Andreas Dirk; Ludwig, Arne; Warburton, Richard John; Lodahl, Peter

2018-05-01

The spin of an electron is a promising memory state and qubit. Connecting spin states that are spatially far apart will enable quantum nodes and quantum networks based on the electron spin. Towards this goal, an integrated spin-photon interface would be a major leap forward as it combines the memory capability of a single spin with the efficient transfer of information by photons. Here, we demonstrate such an efficient and optically programmable interface between the spin of an electron in a quantum dot and photons in a nanophotonic waveguide. The spin can be deterministically prepared in the ground state with a fidelity of up to 96%. Subsequently, the system is used to implement a single-spin photonic switch, in which the spin state of the electron directs the flow of photons through the waveguide. The spin-photon interface may enable on-chip photon-photon gates, single-photon transistors and the efficient generation of a photonic cluster state.

Electronic Transport Properties of Carbon-Nanotube Networks: The Effect of Nitrate Doping on Intratube and Intertube Conductances

NASA Astrophysics Data System (ADS)

Ketolainen, T.; Havu, V.; Jónsson, E. Ö.; Puska, M. J.

2018-03-01

The conductivity of carbon-nanotube (CNT) networks can be improved markedly by doping with nitric acid. In the present work, CNTs and junctions of CNTs functionalized with NO3 molecules are investigated to understand the microscopic mechanism of nitric acid doping. According to our density-functional-theory band-structure calculations, there is charge transfer from the CNT to adsorbed molecules indicating p -type doping. The average doping efficiency of the NO3 molecules is higher if the NO3 molecules form complexes with water molecules. In addition to electron transport along individual CNTs, we also study electron transport between different types (metallic, semiconducting) of CNTs. Reflecting the differences in the electronic structures of semiconducting and metallic CNTs, we find that in addition to turning semiconducting CNTs metallic, doping further increases electron transport most efficiently along semiconducting CNTs as well as through the junctions between them.

Electron transfer from a solid-state electrode assisted by methyl viologen sustains efficient microbial reductive dechlorination of TCE.

PubMed

Aulenta, Federico; Catervi, Alessandro; Majone, Mauro; Panero, Stefania; Reale, Priscilla; Rossetti, Simona

2007-04-01

The ability to transfer electrons, via an extracellular path, to solid surfaces is typically exploited by microorganisms which use insoluble electron acceptors, such as iron-or manganese-oxides or inert electrodes in microbial fuel cells. The reverse process, i.e., the use of solid surfaces or electrodes as electron donors in microbial respirations, although largely unexplored, could potentially have important environmental applications, particularly for the removal of oxidized pollutants from contaminated groundwater or waste streams. Here we show, for the first time, that an electrochemical cell with a solid-state electrode polarized at -500 mV (vs standard hydrogen electrode), in combination with a low-potential redox mediator (methyl viologen), can efficiently transfer electrochemical reducing equivalents to microorganisms which respire using chlorinated solvents. By this approach, the reductive transformation of trichloroethene, a toxic yet common groundwater contaminant, to harmless end-products such as ethene and ethane could be performed. Furthermore, using a methyl-viologen-modified electrode we could even demonstrate that dechlorinating bacteria were able to accept reducing equivalents directly from the modified electrode surface. The innovative concept, based on the stimulation of dechlorination reactions through the use of solid-state electrodes (we propose for this process the acronym BEARD: Bio-Electrochemically Assisted Reductive Dechlorination), holds promise for in situ bioremediation of chlorinated-solvent-contaminated groundwater, and has several potential advantages over traditional approaches based on the subsurface injection of organic compounds. The results of this study raise the possibility that immobilization of selected redox mediators may be a general strategy for stimulating and controlling a range of microbial reactions using insoluble electrodes as electron donors.

Design principle for efficient charge separation at the donor-acceptor interface for high performance organic solar cell device

NASA Astrophysics Data System (ADS)

Nie, Wanyi; Gupta, Gautam; Crone, Brian; Wang, Hsing-Lin; Mohite, Aditya; MPA-11 Material synthesis and integrated device Team; MPA-chemistry Team

2014-03-01

The performance of donor (D) /acceptor (A) structure based organic electronic devices, such as solar cell, light emitting devices etc., relays on the charge transfer process at the interface dramatically. In organic solar cell, the photo-induced electron-hole pair is tightly bonded and will form a charge transfer (CT) state at the D/A interface after dissociation. There is a large chance for them to recombine through CT state and thus is a major loss that limit the overall performance. Here, we report three different strategies that allow us to completely suppress the exciplex (or charge transfer state) recombination between any D/A system. We observe that the photocurrent increases by 300% and the power conversion efficiency increases by 4-5 times simply by inserting a spacer layer in the form of an a) insulator b) Oliogomer or using a c) heavy atom at the donor-acceptor interface in a P3HT/C60 bilayer device. By using those different functional mono layers, we successfully suppressed the exciplex recombination in evidence of increased photocurrent and open circuit voltage. Moreover, these strategies are applicable universally to any donor-acceptor interface. And we demonstrated such strategies in a bulk-heterojunction device which improved the power conversion efficiency from 3.5% up to 4.6%.

Fe2P as a novel efficient catalyst promoter in Pd/C system for formic acid electro-oxidation in fuel cells reaction

NASA Astrophysics Data System (ADS)

Wang, Fulong; Xue, Huaiguo; Tian, Zhiqun; Xing, Wei; Feng, Ligang

2018-01-01

Developing catalyst promoter for Pd/C catalyst is significant for the catalytic ability improvement in energy transfer related electrochemical reactions. Herein, we demonstrate Fe2P as an efficient catalyst promoter in Pd/C catalyst system for formic acid electro-oxidation in fuel cells reactions. Adding Fe2P in the Pd/C catalyst system greatly increases the performances for formic acid oxidation by 3-4 times; the CO stripping technique displays two kinds of active sites formation in the Pd-Fe2P/C catalyst system coming from the interaction of Pd, Fe2P and Pd oxide species and both are more efficient for formic acid and CO-species electrooxidation. The smaller charge transfer resistance and Tafel slope for formic acid oxidation indicate the improvements in kinetics by Fe2P in the Pd-Fe2P/C system. The nanostructured hybrid units of Pd, Fe2P and carbon are evidently visible in the high resolution microscopy images and XPS technique confirmes the electronic effect in the catalyst system. The promotion effect of Fe2P in the catalyst system arising from the structure, composition and electronic effect changes is discussed with the help from multiple physical and electrochemical techniques. It is concluded that Fe2P as a significant catalyst promoter will have potential application in energy transfer related electrochemical reactions.

Theoretical study on naphthobischalcogenadiazole conjugated polymer systems and C61 derivative as organic photovoltaic semiconductors

NASA Astrophysics Data System (ADS)

Fujita, Takehiro; Matsui, Toru; Sumita, Masato; Imamura, Yutaka; Morihashi, Kenji

2018-02-01

We investigated the charge-transfer reactions of solar cells including a quaterthiophene copolymer with naphtho-bis-thiadiazole (PNTz4T) and naphtho-bis-oxadiazole (PNOz4T) using constrained density functional theory (CDFT). According to our calculations, the high electron-transfer rate results in a highly efficient solar cell, and the stable charge-transfer state results in low energy loss. Our computations imply that the following three factors are crucial to improve the performance of semiconducting polymers: (i) large structural changes following charge-transfer, (ii) narrow band gap, and (iii) spatially delocalized lowest unoccupied molecular orbital (LUMO) of the ground state.

Improvement of efficiency in graphene/gallium nitride nanowire on Silicon photoelectrode for overall water splitting

NASA Astrophysics Data System (ADS)

Bae, Hyojung; Rho, Hokyun; Min, Jung-Wook; Lee, Yong-Tak; Lee, Sang Hyun; Fujii, Katsushi; Lee, Hyo-Jong; Ha, Jun-Seok

2017-11-01

Gallium nitride (GaN) nanowires are one of the most promising photoelectrode materials due to their high stability in acidic and basic electrolytes, and tunable band edge potentials. In this study, GaN nanowire arrays (GaN NWs) were prepared by molecular beam epitaxy (MBE); their large surface area enhanced the solar to hydrogen conversion efficiency. More significantly, graphene was grown by chemical vapor deposition (CVD), which enhanced the electron transfer between NWs for water splitting and protected the GaN NW surface. Structural characterizations of the prepared composite were performed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The photocurrent density of Gr/GaN NWs exhibited a two-fold increase over pristine GaN NWs and sustained water splitting up to 70 min. These improvements may accelerate possible applications for hydrogen generation with high solar to hydrogen conversion efficiency.

Highly Efficient Inverted Perovskite Solar Cells with CdSe QDs/LiF Electron Transporting Layer

NASA Astrophysics Data System (ADS)

Tan, Furui; Xu, Weizhe; Hu, Xiaodong; Yu, Ping; Zhang, Weifeng

2017-12-01

Organic/inorganic hybrid perovskite solar cell has emerged as a very promising candidate for the next generation of near-commercial photovoltaic devices. Here in this work, we focus on the inverted perovskite solar cells and have found that remarkable photovoltaic performance could be obtained when using cadmium selenide (CdSe) quantum dots (QDs) as electron transporting layer (ETL) and lithium fluoride (LiF) as the buffer, with respect to the traditionally applied and high-cost [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). The easily processed and low-cost CdSe QDs/LiF double layer could facilitate convenient electron-transfer and collection at the perovskite/cathode interface, promoting an optoelectric conversion efficiency of as high as 15.1%, very close to that with the traditional PCBM ETL. Our work provides another promising choice on the ETL materials for the highly efficient and low-cost perovskite solar cells.

Engineering high charge transfer n-doping of graphene electrodes and its application to organic electronics.

PubMed

Sanders, Simon; Cabrero-Vilatela, Andrea; Kidambi, Piran R; Alexander-Webber, Jack A; Weijtens, Christ; Braeuninger-Weimer, Philipp; Aria, Adrianus I; Qasim, Malik M; Wilkinson, Timothy D; Robertson, John; Hofmann, Stephan; Meyer, Jens

2015-08-14

Using thermally evaporated cesium carbonate (Cs2CO3) in an organic matrix, we present a novel strategy for efficient n-doping of monolayer graphene and a ∼90% reduction in its sheet resistance to ∼250 Ohm sq(-1). Photoemission spectroscopy confirms the presence of a large interface dipole of ∼0.9 eV between graphene and the Cs2CO3/organic matrix. This leads to a strong charge transfer based doping of graphene with a Fermi level shift of ∼1.0 eV. Using this approach we demonstrate efficient, standard industrial manufacturing process compatible graphene-based inverted organic light emitting diodes on glass and flexible substrates with efficiencies comparable to those of state-of-the-art ITO based devices.

Investigation of Stability of Photosynthetic Reaction Center and Quantum Dot Hybrid Films.

PubMed

Lukashev, E P; Knox, P P; Oleinikov, I P; Seifullina, N Kh; Grishanova, N P

2016-01-01

The efficiency of interaction (efficiency of energy transfer) between various quantum dots (QDs) and photosynthetic reaction centers (RCs) from the purple bacterium Rhodobacter sphaeroides and conditions of long-term stability of functioning of such hybrid complexes in film preparations were investigated. It was found that dry films containing RCs and QDs and maintained at atmospheric humidity are capable to keep their functional activity for at least some months as judging by results of measurement of their spectral characteristics, efficiency of energy transfer from QDs to RCs, and RC electron-transport activity. Addition of trehalose to the films giving them still greater stability is especially expressed for films maintained at low humidity. These stable hybrid film structures are promising for further biotechnological studies for developing new phototransformation devices.

Analysis of transformations of the ultrafast electron transfer photoreaction mechanism in liquid solutions by the rate distribution approach.

PubMed

Kuzmin, Michael G; Soboleva, Irina V

2014-05-01

Representation of the experimental reaction kinetics in the form of rate distribution is shown to be an effective method for the analysis of the mechanisms of these reactions and for comparisons of the kinetics with QC calculations, as well as with the experimental data on the medium mobility. The rate constant distribution function P(k) can be obtained directly from the experimental kinetics N(t) by an inverse Laplace transform. The application of this approach to kinetic data for several excited-state electron transfer reactions reveals the transformations of their rate control factors in the time domain of 1-1000 ps. In neat electron donating solvents two components are observed. The fastest component (k > 1 ps(-1)) was found to be controlled by the fluctuations of the overall electronic coupling matrix element, involving all the reactant molecules, located inside the interior of the solvent shell, rather than for specific pairs of reactant molecules. The slower component (1 > k > 0.1 ps(-1)) is controlled by the medium reorganization (longitudinal relaxation times, τL). A substantial contribution from the non-stationary diffusion controlled reaction is observed in diluted solutions ([Q] < 1 M). No contribution from the long-distance electron transfer (electron tunneling) proposed earlier for the excited-state electron transfer between perylene and tetracyanoethylene in acetonitrile is observed. The rate distribution approach provides a simple and efficient method for the quantitative analysis of the reaction mechanism and transformation of the rate control factors in the course of the reactions.

Blue Thermally Activated Delayed Fluorescence Polymers with Nonconjugated Backbone and Through-Space Charge Transfer Effect.

PubMed

Shao, Shiyang; Hu, Jun; Wang, Xingdong; Wang, Lixiang; Jing, Xiabin; Wang, Fosong

2017-12-13

We demonstrate novel molecular design for thermally activated delayed fluorescence (TADF) polymers based on a nonconjugated polyethylene backbone with through-space charge transfer effect between pendant electron donor (D) and acceptor (A) units. Different from conventional conjugated D-A polymers with through-bond charge transfer effect, the nonconjugated architecture avoids direct conjugation between D and A units, enabling blue emission. Meanwhile, spatial π-π interaction between the physically separated D and A units results in both small singlet-triplet energy splitting (0.019 eV) and high photoluminescence quantum yield (up to 60% in film state). The resulting polymer with 5 mol % acceptor unit gives efficient blue electroluminescence with Commission Internationale de l'Eclairage coordinates of (0.176, 0.269), together with a high external quantum efficiency of 12.1% and low efficiency roll-off of 4.9% (at 1000 cd m -2 ), which represents the first example of blue TADF nonconjugated polymer.

Unravelling the pH-dependence of a molecular photocatalytic system for hydrogen production† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c5sc01349f Click here for additional data file.

PubMed Central

Pastor, Ernest; Gross, Manuela A.; Selim, Shababa

2015-01-01

Photocatalytic systems for the reduction of aqueous protons are strongly pH-dependent, but the origin of this dependency is still not fully understood. We have studied the effect of different degrees of acidity on the electron transfer dynamics and catalysis taking place in a homogeneous photocatalytic system composed of a phosphonated ruthenium tris(bipyridine) dye (RuP) and a nickel bis(diphosphine) electrocatalyst (NiP) in an aqueous ascorbic acid solution. Our approach is based on transient absorption spectroscopy studies of the efficiency of photo-reduction of RuP and NiP correlated with pH-dependent photocatalytic H2 production and the degree of catalyst protonation. The influence of these factors results in an observed optimum photoactivity at pH 4.5 for the RuP–NiP system. The electron transfer from photo-reduced RuP to NiP is efficient and independent of the pH value of the medium. At pH <4.5, the efficiency of the system is limited by the yield of RuP photo-reduction by the sacrificial electron donor, ascorbic acid. At pH >4.5, the efficiency of the system is limited by the poor protonation of NiP, which inhibits its ability to reduce protons to hydrogen. We have therefore developed a rational strategy utilising transient absorption spectroscopy combined with bulk pH titration, electrocatalytic and photocatalytic experiments to disentangle the complex pH-dependent activity of the homogenous RuP–NiP photocatalytic system, which can be widely applied to other photocatalytic systems. PMID:28717491

Plasmon enhanced heterogeneous electron transfer with continuous band energy model

NASA Astrophysics Data System (ADS)

Zhao, Dandan; Niu, Lu; Wang, Luxia

2017-08-01

Photoinduced charge injection from a perylene dye molecule into the conduction band of a TiO2 system decorated by a metal nanoparticles (MNP) is studied theoretically. Utilizing the density matrix theory the charge transfer dynamics is analyzed. The continuous behavior of the TiO2 conduction band is accounted for by a Legendre polynomials expansion. The simulations consider optical excitation of the dye molecule coupled to the MNP and the subsequent electron injection into the TiO2 semiconductor. Due to the energy transfer coupling between the molecule and the MNP optical excitation and subsequent charge injection into semiconductor is strongly enhanced. The respective enhancement factor can reach values larger than 103. Effects of pulse duration, coupling strength and energetic resonances are also analyzed. The whole approach offers an efficient way to increase charge injection in dye-sensitized solar cells.

Delocalization Drives Free Charge Generation in Conjugated Polymer Films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pace, Natalie A.; Reid, Obadiah G.; Rumbles, Garry

We demonstrate that the product of photoinduced electron transfer between a conjugated polymer host and a dilute molecular sensitizer is controlled by the structural state of the polymer. Ordered semicrystalline solids exhibit free charge generation, while disordered polymers in the melt phase do not. We use photoluminescence (PL) and time-resolved microwave conductivity (TRMC) measurements to sweep through polymer melt transitions in situ. Free charge generation measured by TRMC turns off upon melting, whereas PL quenching of the molecular sensitizers remains constant, implying unchanged electron transfer efficiency. The key difference is the intermolecular order of the polymer host in the solidmore » state compared to the melt. We propose that this order-disorder transition modulates the localization length of the initial charge-transfer state, which controls the probability of free charge formation.« less

Delocalization Drives Free Charge Generation in Conjugated Polymer Films

DOE PAGES

Pace, Natalie A.; Reid, Obadiah G.; Rumbles, Garry

2018-02-19

We demonstrate that the product of photoinduced electron transfer between a conjugated polymer host and a dilute molecular sensitizer is controlled by the structural state of the polymer. Ordered semicrystalline solids exhibit free charge generation, while disordered polymers in the melt phase do not. We use photoluminescence (PL) and time-resolved microwave conductivity (TRMC) measurements to sweep through polymer melt transitions in situ. Free charge generation measured by TRMC turns off upon melting, whereas PL quenching of the molecular sensitizers remains constant, implying unchanged electron transfer efficiency. The key difference is the intermolecular order of the polymer host in the solidmore » state compared to the melt. We propose that this order-disorder transition modulates the localization length of the initial charge-transfer state, which controls the probability of free charge formation.« less

Multi-stage Depressed Collectors (MDC) for efficiency improvements of UHF broadcast klystrons

NASA Technical Reports Server (NTRS)

Kosmahl, H. G.

1982-01-01

The consumed primary power is reduced and the efficiency of traveling wave tubes is raised through the use of depressed collectors which passively convert potential energy into electric energy. Efficiency was kept with constant within a 3 dB range while the output power varied by 10 dB. Aspects to be considered in transferring this technology to UHF klystrons are the electron energy spectrum of the klystron and the magnitude of the injection angle required.

Engineering of Porphyrin Molecules for Use as Effective Cathode Interfacial Modifiers in Organic Solar Cells of Enhanced Efficiency and Stability.

PubMed

Tountas, Marinos; Verykios, Apostolis; Polydorou, Ermioni; Kaltzoglou, Andreas; Soultati, Anastasia; Balis, Nikolaos; Angaridis, Panagiotis A; Papadakis, Michael; Nikolaou, Vasilis; Auras, Florian; Palilis, Leonidas C; Tsikritzis, Dimitris; Evangelou, Evangelos K; Gardelis, Spyros; Koutsoureli, Matroni; Papaioannou, George; Petsalakis, Ioannis D; Kennou, Stella; Davazoglou, Dimitris; Argitis, Panagiotis; Falaras, Polycarpos; Coutsolelos, Athanassios G; Vasilopoulou, Maria

2018-06-20

In the present work, we effectively modify the TiO 2 electron transport layer of organic solar cells with an inverted architecture using appropriately engineered porphyrin molecules. The results show that the optimized porphyrin modifier bearing two carboxylic acids as the anchoring groups and a triazine electron-withdrawing spacer significantly reduces the work function of TiO 2 , thereby reducing the electron extraction barrier. Moreover, the lower surface energy of the porphyrin-modified substrate results in better physical compatibility between the latter and the photoactive blend. Upon employing porphyrin-modified TiO 2 electron transport layers in PTB7:PC 71 BM-based organic solar cells we obtained an improved average power conversion efficiency up to 8.73%. Importantly, porphyrin modification significantly increased the lifetime of the devices, which retained 80% of their initial efficiency after 500 h of storage in the dark. Because of its simplicity and efficacy, this approach should give tantalizing glimpses and generate an impact into the potential of porphyrins to facilitate electron transfer in organic solar cells and related devices.

Role of electron transfer in Ce{sup 3+} sensitized Yb{sup 3+} luminescence in borate glass

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sontakke, Atul D., E-mail: sontakke.atul.55a@st.kyoto-u.ac.jp; Katayama, Yumiko; Zhuang, Yixi

2015-01-07

In a Ce{sup 3+}-Yb{sup 3+} system, two mechanisms are proposed so far namely, the quantum cutting mechanism and the electron transfer mechanism explaining Yb{sup 3+} infrared luminescence under Ce{sup 3+} excitation. Among them, the quantum cutting mechanism, where one Ce{sup 3+} photon (ultraviolet/blue) gives rise to two Yb{sup 3+} photons (near infrared) is widely sought for because of its huge potential in enhancing the solar cell efficiency. In present study on Ce{sup 3+}-Yb{sup 3+} codoped borate glasses, Ce{sup 3+} sensitized Yb{sup 3+} luminescence at ∼1 μm have been observed on Ce{sup 3+} 5d state excitation. However, the intensity of sensitized Yb{supmore » 3+} luminescence is found to be very weak compared to the strong quenching occurred in Ce{sup 3+} luminescence in Yb{sup 3+} codoped glasses. Moreover, the absolute luminescence quantum yield also showed a decreasing trend with Yb{sup 3+} codoping in the glasses. The overall behavior of the luminescence properties and the quantum yield is strongly contradicting with the quantum cutting phenomenon. The results are attributed to the energetically favorable electron transfer interactions followed by Ce{sup 3+}-Yb{sup 3+} ⇌ Ce{sup 4+}-Yb{sup 2+} inter-valence charge transfer and successfully explained using the absolute electron binding energies of dopant ions in the studied borate glass. Finally, an attempt has been presented to generalize the electron transfer mechanism among opposite oxidation/reduction property dopant ions using the vacuum referred electron binding energy (VRBE) scheme for lanthanide series.« less

Pivotal Role of Iron in the Regulation of Cyanobacterial Electron Transport.

PubMed

González, A; Sevilla, E; Bes, M T; Peleato, M L; Fillat, M F

2016-01-01

Iron-containing metalloproteins are the main cornerstones for efficient electron transport in biological systems. The abundance and diversity of iron-dependent proteins in cyanobacteria makes those organisms highly dependent of this micronutrient. To cope with iron imbalance, cyanobacteria have developed a survey of adaptation strategies that are strongly related to the regulation of photosynthesis, nitrogen metabolism and other central electron transfer pathways. Furthermore, either in its ferrous form or as a component of the haem group, iron plays a crucial role as regulatory signalling molecule that directly or indirectly modulates the composition and efficiency of cyanobacterial redox reactions. We present here the major mechanism used by cyanobacteria to couple iron homeostasis to the regulation of electron transport, making special emphasis in processes specific in those organisms. © 2016 Elsevier Ltd. All rights reserved.

Photoinduced energy and electron transfer processes in hexapyropheophorbide a- fullerene [C(60)] molecular systems.

PubMed

Regehly, Martin; Ermilov, Eugeny A; Helmreich, Matthias; Hirsch, Andreas; Jux, Norbert; Röder, Beate

2007-02-08

The photophysical properties of the novel hexapyropheophorbide a (P6), and hexakis (pyropheophorbide a)-C60 (FP6) were studied and compared with those of hexakis (pyropheophorbide a)-fullerene [5:1] hexaadduct (FHP6). It was found that after light absorption the pyropheophorbide a molecules in all three compounds undergo very efficient energy transfer as well as partly excitonic interactions. The last process results in the formation of energy traps, which could be resolved experimentally. For P6, due to shorter distances between neighboring dye molecules, stronger interactions between pyropheophorbide a units than for FHP6 were observed. As a consequence, the excitation energy is delivered rapidly to traps formed by stacked pyropheophorbide a molecules resulting in the reduction of fluorescence, intersystem crossing, and singlet oxygen quantum yields compared to the values of FHP6. For FP6 the reduction of these values is much stronger due to an additional fast and efficient deactivation process, namely photoinduced electron transfer from pyropheophorbide a to the fullerene moiety. Consequently, FP6 can be considered as a combination of a light-harvesting system consisting of several separate pyropheophorbide a molecules and a charge-separating center.

On non-local energy transfer via zonal flow in the Dimits shift

DOE PAGES

St-Onge, Denis A.

2017-10-10

The two-dimensional Terry–Horton equation is shown to exhibit the Dimits shift when suitably modified to capture both the nonlinear enhancement of zonal/drift-wave interactions and the existence of residual Rosenbluth–Hinton states. This phenomenon persists through numerous simplifications of the equation, including a quasilinear approximation as well as a four-mode truncation. It is shown that the use of an appropriate adiabatic electron response, for which the electrons are not affected by the flux-averaged potential, results in anmore » $$\\boldsymbol{E}\\times \\boldsymbol{B}$$ nonlinearity that can efficiently transfer energy non-locally to length scales of the order of the sound radius. The size of the shift for the nonlinear system is heuristically calculated and found to be in excellent agreement with numerical solutions. The existence of the Dimits shift for this system is then understood as an ability of the unstable primary modes to efficiently couple to stable modes at smaller scales, and the shift ends when these stable modes eventually destabilize as the density gradient is increased. This non-local mechanism of energy transfer is argued to be generically important even for more physically complete systems.« less

Wireless Power Transfer to Millimeter-Sized Gastrointestinal Electronics Validated in a Swine Model

PubMed Central

Abid, Abubakar; O’Brien, Jonathan M.; Bensel, Taylor; Cleveland, Cody; Booth, Lucas; Smith, Brian R.; Langer, Robert; Traverso, Giovanni

2017-01-01

Electronic devices placed in the gastrointestinal (GI) tract for prolonged periods have the potential to transform clinical evaluation and treatment. One challenge to the deployment of such gastroresident electronics is the difficulty in powering millimeter-sized electronics devices without using batteries, which compromise biocompatibility and long-term residence. We examined the feasibility of leveraging mid-field wireless powering to transfer power from outside of the body to electronics at various locations along the GI tract. Using simulations and ex vivo measurements, we designed mid-field antennas capable of operating efficiently in tissue at 1.2 GHz. These antennas were then characterized in vivo in five anesthetized pigs, by placing one antenna outside the body, and the other antenna inside the body endoscopically, at the esophagus, stomach, and colon. Across the animals tested, mean transmission efficiencies of −41.2, −36.1, and −34.6 dB were achieved in vivo while coupling power from outside the body to the esophagus, stomach, and colon, respectively. This corresponds to power levels of 37.5 μW, 123 μW and 173 μW received by antennas in the respective locations, while keeping radiation exposure levels below safety thresholds. These power levels are sufficient to wirelessly power a range of medical devices from outside of the body. PMID:28447624

Molecular level energy and electron transfer processes at nanocrystalline titanium dioxide interfaces

NASA Astrophysics Data System (ADS)

Farzad, Fereshteh

This thesis describes photo-induced molecular electron and energy transfer processes occurring at nanocrystalline semiconductor interfaces. The Introductory Chapter provides background and describes how these materials may be useful for solar energy conversion. In Chapter 2, results describing excitation of Ru(deeb)(bpy)2 2+, bis(2,2'-bipyridine)(2,2'-bipyridine-4,4 '-diethylester)ruthenium(II) hexafluorophosphate, bound to nanocrystalline TiO2 thin films, immersed in an acetonitrile bath are presented. The data indicates that light excitation forms predominately long-lived metal-to-ligand charge-transfer, MLCT, excited states under these conditions. Modeling of the data as a function of irradiance has been accomplished assuming parallel unimolecular and bimolecular excited state deactivation processes. The quantum yield for excited state formation depends on the excitation irradiance, consistent with triplet-triplet annihilation processes that occur with k > 1 x 108 s-1. Chapter 3 extends the work described in Chapter 2 to LiClO4 acetonitrile solutions. Li+ addition results in a red shift in the MLCT absorption and photoluminescence, PL, and a concentration dependent quenching of the PL intensity on TiO2. The Li+ induced spectroscopic changes were found to be reversible by varying the electrolyte composition. A second-order kinetic model quantified charge recombination transients. A model is proposed wherein Li+ ion adsorption stabilizes TiO2 acceptor states resulting in energetically more favorable interfacial electron transfer. The photophysical and photoelectrochemical properties of porous nanocrystalline anatase TiO2 electrodes modified with Ru(deeb)(bpy)2 2+, Os(deeb)(bpy)22+, and mixtures of both are described in Chapters 4 and 5. In regenerative solar cells with 0.5 M LiI/0.05 M I2 acetonitrile electrolyte, both compounds efficiently inject electrons into TiO2 producing monochromatic incident photon-to-current efficiencies (IPCE), IPCE (460 nm) = 0.70 + 0.05 for Ru(dcb)(bpy)2 2+/TiO2 and 0. 10 + 0.05 for Os(dcb)(bpy)2 2+/TiO2. Os(dcb)(bpy)22+ extends the spectral sensitivity of the TiO2 material beyond 700 rim. Application of a negative bias to the derivatized TiO2 surfaces results in inefficient interfacial electron transfer and no significant photocurrent. Instead, lateral energy transfer cross the nanocrystalline TiO2 surface from Ru(dcb)(bpy)22+* to Os(dcb)(bpy) 22+ is observed. The energy transfer process can be switched off with a positive applied bias ten times with no significant deterioration. The results demonstrate control of molecular excited states at nanostructured interfaces.

Alternative mitochondrial electron transfer for the treatment of neurodegenerative diseases and cancers: Methylene blue connects the dots.

PubMed

Yang, Shao-Hua; Li, Wenjun; Sumien, Nathalie; Forster, Michael; Simpkins, James W; Liu, Ran

2017-10-01

Brain has exceptional high requirement for energy metabolism with glucose as the exclusive energy source. Decrease of brain energy metabolism and glucose uptake has been found in patients of Alzheimer's, Parkinson's and other neurodegenerative diseases, providing a clear link between neurodegenerative disorders and energy metabolism. On the other hand, cancers, including glioblastoma, have increased glucose uptake and rely on aerobic glycolysis for energy metabolism. The switch of high efficient oxidative phosphorylation to low efficient aerobic glycolysis pathway (Warburg effect) provides macromolecule for biosynthesis and proliferation. Current research indicates that methylene blue, a century old drug, can receive electron from NADH in the presence of complex I and donates it to cytochrome c, providing an alternative electron transfer pathway. Methylene blue increases oxygen consumption, decrease glycolysis, and increases glucose uptake in vitro. Methylene blue enhances glucose uptake and regional cerebral blood flow in rats upon acute treatment. In addition, methylene blue provides protective effect in neuron and astrocyte against various insults in vitro and in rodent models of Alzheimer's, Parkinson's, and Huntington's disease. In glioblastoma cells, methylene blue reverses Warburg effect by enhancing mitochondrial oxidative phosphorylation, arrests glioma cell cycle at s-phase, and inhibits glioma cell proliferation. Accordingly, methylene blue activates AMP-activated protein kinase, inhibits downstream acetyl-coA carboxylase and cyclin-dependent kinases. In summary, there is accumulating evidence providing a proof of concept that enhancement of mitochondrial oxidative phosphorylation via alternative mitochondrial electron transfer may offer protective action against neurodegenerative diseases and inhibit cancers proliferation. Copyright © 2015 Elsevier Ltd. All rights reserved.

Synthesis of Dual NIR Two-photon Absorptive [60]fullerenyl Multiadducts for Nonlinear Light-transmittance Reduction Application

DTIC Science & Technology

2014-11-01

INTRODUCTION Nonlinear optical characteristics of [60] fullerene -derived C60-(antenna)x nanostructure conjugates are based on excited singlet state...two-photon absorption (2PA) processes in the NIR region [3]. Fullerene cages exhibit high electronegativity and electron-accepting characteristics...photoenergy by the donor DPAF-Cn antenna was able to undergo efficient intramolecular electron- or energy-transfer to the fullerene acceptor moiety in

Reduced graphene oxide-mediated Z-scheme BiVO4/CdS nanocomposites for boosted photocatalytic decomposition of harmful organic pollutants.

PubMed

Clament Sagaya Selvam, N; Kim, Yeong Gyeong; Kim, Dong Jin; Hong, Won-Hwa; Kim, Woong; Park, Sung Hyuk; Jo, Wan-Kuen

2018-09-01

The efficient photocatalytic degradation of harmful organic pollutants (isoniazid (ISN) and 1,4-dioxane (DX)) via the Z-scheme electron transfer mechanism was accomplished using a photostable composite photocatalyst consisting of BiVO 4 , CdS, and reduced graphene oxide (RGO). Compared to their pristine counterparts, the RGO-mediated Z-scheme CdS/BiVO 4 (CdS/RGO-BiVO 4 ) nanocomposites exhibited superior degradation activities, mainly attributed to the prolonged charge separation. RGO was found to be involved in visible-light harvesting and acted as a solid-state electron mediator at the CdS/BiVO 4 interface to realize an effective Z-scheme electron transfer pathway, avoid photocatalyst self-oxidation, and lengthen the life span of charge carriers. The results of reactive species scavenging experiments, photoluminescence measurements, and transient photocurrent measurements, as well as the calculated band potentials of the synthesized photocatalysts, supported the Z-scheme electron/hole pair separation mechanism. Additionally, the intermediates formed during the degradation of ISN and DX were identified, and a possible fragmentation pattern was proposed. This systematic work aims to develop photostable Z-scheme composites as unique photocatalytic systems for the efficient removal of harmful organic pollutants. Copyright © 2018 Elsevier B.V. All rights reserved.

Enhanced performances for top-emitting white organic light-emitting diodes by utilizing green phosphor as energy transfer medium

NASA Astrophysics Data System (ADS)

Deng, Lingling; Bao, Yiyang; Zhang, Yanan; Peng, Ling; Zhu, Wenjing; Zhao, Yue; Xu, Yewen; Chen, Shufen

2016-06-01

In top-emitting white organic light-emitting diodes (TWOLEDs), the device performances attribute to the several important factors, such as exciton profile, energy transfer, and microcavity effect. In this paper, a TWOLED containing a heterojunction blue emission layer (EML) and a red EML is reported. A host material with high triplet energy level is employed for the adjacent blue and red EML, while the inefficient red emission reduces the emission efficiency of the TWOLED. In order to enhance the red emission efficiency, mixed-host and co-doping technologies are used in the red EML. By mixing the hole transporting and electron transporting host materials, the exciton recombination zone extends to the red EML to increase the red emission intensity and reduce the efficiency roll-off. And by co-doping a green phosphor into the red EML as the energy transfer medium, the energy transfer rate is enhanced, and then the current efficiency increases. Besides, both the mixed-host and co-doping change the carrier transport and the exciton recombination zone, which further affects the microcavity resonance in the devices. Due to the enhancement on the red emission intensity and the shift of resonant wavelength, the chromaticity of the TWOLED is improved.

Microwave assisted synthesis of porous ZnO/SnS heterojunction and its application in visible light degradation of ciprofloxacin

NASA Astrophysics Data System (ADS)

Makama, A. B.; Salmiaton, A.; Saion, E. B.; Choong, T. S. Y.; Abdullah, N.

2016-07-01

Porous ZnO/SnS heterojunctions were successfully synthesized via microwave-assisted heating of aqueous solutions containing different amounts of SnS precursors (SnCl2 and Na2S) in the presence of fixed amount of ZnCO3 nanoparticles. The experimental results revealed that the heterojunctions exhibited much higher visible light-driven photocatalytic activity for the degradation of the ciprofloxacin than pure SnS nanocrystals. The photocatalytic degradation efficiency (1-Ct/C0) of the pollutant for the most active heterogeneous nanostructure is about four times more efficient than pure SnS. The enhanced photocatalytic efficiency is ascribed to the synergic effect of high photon absorption and reduction in the recombination of electrons and holes because of efficient separation and electron transfer from the SnS to ZnO nanoparticles.

UV-radiation-induced electron emission by hormones. Hypothesis for specific communication mechanisms

NASA Astrophysics Data System (ADS)

Getoff, Nikola

2009-11-01

The highlights of recently observed electron emission from electronically excited sexual hormones (17β-estradiol, progesterone, testosterone) and the phytohormone genistein in polar media are briefly reviewed. The electron yield, Q(e aq-), dependence from substrate concentration, hormone structure, polarity of solvent, absorbed energy and temperature are discussed. The hormones reactivity with e aq- and efficiency in electron transfer ensure them the ability to communicate with other biological systems in an organism. A hypothesis is presented for the explanation of the mechanisms of the distinct recognition of signals transmitted by electrons, originating from different types of hormones to receiving centres. Biological consequences of the electron emission in respect to cancer are mentioned.

Unravelling electronic and structural requisites of triplet-triplet energy transfer by advanced electron paramagnetic resonance and density functional theory

NASA Astrophysics Data System (ADS)

Di Valentin, M.; Salvadori, E.; Barone, V.; Carbonera, D.

2013-10-01

Advanced electron paramagnetic resonance (EPR) techniques, in combination with Density Functional theory (DFT), have been applied to the comparative study of carotenoid triplet states in two major photosynthetic antenna complexes, the Peridinin-chlorophyll a-protein of dinoflagellates and the light-harvesting complex II of higher plants. Carotenoid triplet states are populated by triplet-triplet energy transfer (TTET) from chlorophyll molecules to photoprotect the system from singlet oxygen formation under light-stress conditions. The TTET process is strongly dependent on the relative arrangement and on the electronic properties of the triplet states involved. The proposed spectroscopic approach exploits the concept of spin conservation during TTET, which leads to recognisable spin polarisation effects in the time-resolved and field-swept echo-detected EPR spectra. The electron spin polarisation produced at the carotenoid acceptor site depends on the initial polarisation of the chlorophyll donor and on the relative geometrical arrangement of the donor-acceptor zero-field splitting axes. We have demonstrated that a proper analysis of the spectra in the framework of spin angular momentum conservation allows to derive the pathways of TTET and to gain insight into the structural requirements of this mechanism for those antenna complexes, whose X-ray structure is available. We have further proved that this method, developed for natural antenna complexes of known X-ray structure, can be extended to systems lacking structural information in order to derive the relative arrangement of the partners in the energy transfer process. The structural requirements for efficient TTET, obtained from time-resolved and pulse EPR, have been complemented by a detailed description of the electronic structure of the carotenoid triplet state, provided by pulse Electron-Nuclear DOuble Resonance (ENDOR) experiments. Triplet-state hyperfine couplings of the α- and β-protons of the carotenoid conjugated chain have been assigned with the aid of quantum chemical calculation. DFT predictions of the electronic structure of the carotenoid triplet state, in terms of spin density distribution, frontier orbital description and orbital excitation represent suitable building blocks toward a deeper understanding of electronic requirements for efficient TTET.

New acceptor-bridge-donor strategy for enhancing NLO response with long-range excess electron transfer from the NH2...M/M3O donor (M = Li, Na, K) to inside the electron hole cage C20F19 acceptor through the unusual σ chain bridge (CH2)4.

PubMed

Bai, Yang; Zhou, Zhong-Jun; Wang, Jia-Jun; Li, Ying; Wu, Di; Chen, Wei; Li, Zhi-Ru; Sun, Chia-Chung

2013-04-04

Using the strong electron hole cage C20F19 acceptor, the NH2...M/M3O (M = Li, Na, and K) complicated donors with excess electron, and the unusual σ chain (CH2)4 bridge, we construct a new kind of electride molecular salt e(-)@C20F19-(CH2)4-NH2...M(+)/M3O(+) (M = Li, Na, and K) with excess electron anion inside the hole cage (to be encapsulated excess electron-hole pair) serving as a new A-B-D strategy for enhancing nonlinear optical (NLO) response. An interesting push-pull mechanism of excess electron generation and its long-range transfer is exhibited. The excess electron is pushed out from the (super)alkali atom M/M3O by the lone pair of NH2 in the donor and further pulled inside the hole cage C20F19 acceptor through the efficient long σ chain (CH2)4 bridge. Owing to the long-range electron transfer, the new designed electride molecular salts with the excess electron-hole pair exhibit large NLO response. For the e(-)@C20F19-(CH2)4-NH2...Na(+), its large first hyperpolarizability (β0) reaches up to 9.5 × 10(6) au, which is about 2.4 × 10(4) times the 400 au for the relative e(-)@C20F20...Na(+) without the extended chain (CH2)4-NH2. It is shown that the new strategy is considerably efficient in enhancing the NLO response for the salts. In addition, the effects of different bridges and alkali atomic number on β0 are also exhibited. Further, three modulating factors are found for enhancing NLO response. They are the σ chain bridge, bridge-end group with lone pair, and (super)alkali atom. The new knowledge may be significant for designing new NLO materials and electronic devices with electrons inside the cages. They may also be the basis of establishing potential organic chemistry with electron-hole pair.

Communication: Microsecond dynamics of the protein and water affect electron transfer in a bacterial bc1 complex

NASA Astrophysics Data System (ADS)

Martin, Daniel R.; Matyushov, Dmitry V.

2015-04-01

Cross-membrane electron transport between cofactors localized in proteins of mitochondrial respiration and bacterial photosynthesis is the source of all biological energy. The statistics and dynamics of nuclear fluctuations in these protein/membrane/water heterogeneous systems are critical for their energetic efficiency. The results of 13 μs of atomistic molecular dynamics simulations of the membrane-bound bc1 bacterial complex are analyzed here. The reaction is affected by a broad spectrum of nuclear modes, with the slowest dynamics in the range of time-scales ˜0.1-1.6 μs contributing half of the reaction reorganization energy. Two reorganization energies are required to describe protein electron transfer due to dynamical arrest of protein conformations on the observation window. This mechanistic distinction allows significant lowering of activation barriers for reactions in proteins.

Two-Dimensional Fourier Transform Electronic Spectroscopy of Peridinin and Peridinin Analogs

NASA Astrophysics Data System (ADS)

Khosravi, Soroush; Bishop, Michael; Obaid, Razib; Whitelock, Hope; Carroll, Ann Marie; Lafountain, Amy; Frank, Harry; Beck, Warren; Gibson, George; Berrah, Nora

2016-05-01

The peridinin chlorophyll- a protein (PCP) is a light harvesting complex in dinoflagellates that exhibits a carotenoid-to-chlorophyll (Chl) a excitation energy transfer (EET) efficiency of 85-95%. Unlike most light harvesting complexes, where the number of carotenoids is less than Chl, each subunit of PCP contains eight tightly-packed peridinins surrounding two Chl a molecules. The unusual solvent polarity dependence of the lowest excited S1 state of peridinin suggests the presence of an intramolecular charge-transfer (ICT) state. The nature of the ICT state, its coupling to the S1 of peridinin, and whether it enables the high EET efficiency is still unclear. Two-dimensional electronic Fourier transform spectroscopy (2DES) is a powerful method capable of examining these issues. The present work examines the ICT state of peridinin and peridinin analogs that have diminished ICT character. 2DES data adding new insight into the spectral signatures and nature of the ICT state in peridinin will be presented. Funded by the DoE-BES, Grant No. DE-SC0012376.

Light-Induced Activation of a Molybdenum Oxotransferase Model within a Ru(II)-Mo(VI) Dyad.

PubMed

Ducrot, Aurélien B; Coulson, Ben A; Perutz, Robin N; Duhme-Klair, Anne-Kathrin

2016-12-19

Nature uses molybdenum-containing enzymes to catalyze oxygen atom transfer (OAT) from water to organic substrates. In these enzymes, the two electrons that are released during the reaction are rapidly removed, one at a time, by spatially separated electron transfer units. Inspired by this design, a Ru(II)-Mo(VI) dyad was synthesized and characterized, with the aim of accelerating the rate-determining step in the cis-dioxo molybdenum-catalyzed OAT cycle, the transfer of an oxo ligand to triphenyl phosphine, via a photo-oxidation process. The dyad consists of a photoactive bis(bipyridyl)-phenanthroline ruthenium moiety that is covalently linked to a bioinspired cis-dioxo molybdenum thiosemicarbazone complex. The quantum yield and luminescence lifetimes of the dyad [Ru(bpy) 2 (L 2 )MoO 2 (solv)] 2+ were determined. The major component of the luminescence decay in MeCN solution (τ = 1149 ± 2 ns, 67%) corresponds closely to the lifetime of excited [Ru(bpy) 2 (phen-NH 2 )] 2+ , while the minor component (τ = 320 ± 1 ns, 31%) matches that of [Ru(bpy) 2 (H 2 -L 2 )] 2+ . In addition, the (spectro)electrochemical properties of the system were investigated. Catalytic tests showed that the dyad-catalyzed OAT from dimethyl sulfoxide to triphenyl phosphine proceeds significantly faster upon irradiation with visible light than in the dark. Methylviologen acts as a mediator in the photoredox cycle, but it is regenerated and hence only required in stoichiometric amounts with respect to the catalyst rather than sacrificial amounts. It is proposed that oxidative quenching of the photoexcited Ru unit, followed by intramolecular electron transfer, leads to the production of a reactive one-electron oxidized catalyst, which is not accessible by electrochemical methods. A significant, but less pronounced, rate enhancement was observed when an analogous bimolecular system was tested, indicating that intramolecular electron transfer between the photosensitizer and the catalytic center is more efficient than intermolecular electron transfer between the separate components.

Electrostatic Steepening of Whistler Waves

NASA Astrophysics Data System (ADS)

Vasko, I. Y.; Agapitov, O. V.; Mozer, F. S.; Bonnell, J. W.; Artemyev, A. V.; Krasnoselskikh, V. V.; Tong, Y.

2018-05-01

We present surprising observations by the NASA Van Allen Probes spacecraft of whistler waves with substantial electric field power at harmonics of the whistler wave fundamental frequency. The wave power at harmonics is due to a nonlinearly steepened whistler electrostatic field that becomes possible in the two-temperature electron plasma due to the whistler wave coupling to the electron-acoustic mode. The simulation and analytical estimates show that the steepening takes a few tens of milliseconds. The hydrodynamic energy cascade to higher frequencies facilitates efficient energy transfer from cyclotron resonant electrons, driving the whistler waves, to lower energy electrons.

Hybrid super electron donors - preparation and reactivity.

PubMed

Garnier, Jean; Thomson, Douglas W; Zhou, Shengze; Jolly, Phillip I; Berlouis, Leonard E A; Murphy, John A

2012-01-01

Neutral organic electron donors, featuring pyridinylidene-imidazolylidene, pyridinylidene-benzimidazolylidene and imidazolylidene-benzimidazolylidene linkages are reported. The pyridinylidene-benzimidazolylidene and imidazolylidene-benzimidazolylidene hybrid systems were designed to be the first super electron donors to convert iodoarenes to aryl radicals at room temperature, and indeed both show evidence for significant aryl radical formation at room temperature. The stronger pyridinylidene-imidazolylidene donor converts iodoarenes to aryl anions efficiently under appropriate conditions (3 equiv of donor). The presence of excess sodium hydride base has a very important and selective effect on some of these electron-transfer reactions, and a rationale for this is proposed.

Nonplasmonic Hot-Electron Photocurrents from Mn-Doped Quantum Dots in Photoelectrochemical Cells.

PubMed

Dong, Yitong; Rossi, Daniel; Parobek, David; Son, Dong Hee

2016-03-03

We report the measurement of the hot-electron current in a photoelectrochemical cell constructed from a glass/ITO/Al2 O3 (ITO=indium tin oxide) electrode coated with Mn-doped quantum dots, where hot electrons with a large excess kinetic energy were produced through upconversion of the excitons into hot electron hole pairs under photoexcitation at 3 eV. In our recent study (J. Am. Chem. Soc. 2015, 137, 5549), we demonstrated the generation of hot electrons in Mn-doped II-VI semiconductor quantum dots and their usefulness in photocatalytic H2 production reaction, taking advantage of the more efficient charge transfer of hot electrons compared with band-edge electrons. Here, we show that hot electrons produced in Mn-doped CdS/ZnS quantum dots possess sufficient kinetic energy to overcome the energy barrier from a 5.4-7.5 nm thick Al2 O3 layer producing a hot-electron current in photoelectrochemical cell. This work demonstrates the possibility of harvesting hot electrons not only at the interface of the doped quantum dot surface, but also far away from it, thus taking advantage of the capability of hot electrons for long-range electron transfer across a thick energy barrier. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Equilibrium and ultrafast kinetic studies manipulating electron transfer: A short-lived flavin semiquinone is not sufficient for electron bifurcation

DOE PAGES

Hoben, John P.; Lubner, Carolyn E.; Ratzloff, Michael W.; ...

2017-06-14

Flavin-based electron transfer bifurcation is emerging as a fundamental and powerful mechanism for conservation and deployment of electrochemical energy in enzymatic systems. In this process, a pair of electrons is acquired at intermediate reduction potential (i.e. intermediate reducing power) and each electron is passed to a different acceptor, one with lower and the other with higher reducing power, leading to 'bifurcation'. It is believed that a strongly reducing semiquinone species is essential for this process, and it is expected that this species should be kinetically short-lived. We now demonstrate that presence of a short-lived anionic flavin semiquinone (ASQ) is notmore » sufficient to infer existence of bifurcating activity, although such a species may be necessary for the process. We have used transient absorption spectroscopy to compare the rates and mechanisms of decay of ASQ generated photochemically in bifurcating NADH-dependent ferredoxin-NADP + oxidoreductase and the non-bifurcating flavoproteins nitroreductase, NADH oxidase and flavodoxin. We found that different mechanisms dominate ASQ decay in the different protein environments, producing lifetimes ranging over two orders of magnitude. Capacity for electron transfer among redox cofactors vs. charge recombination with nearby donors can explain the range of ASQ lifetimes we observe. In conclusion, our results support a model wherein efficient electron propagation can explain the short lifetime of the ASQ of bifurcating NADH-dependent ferredoxin-NADP + oxidoreductase I, and can be an indication of capacity for electron bifurcation.« less

Equilibrium and ultrafast kinetic studies manipulating electron transfer: A short-lived flavin semiquinone is not sufficient for electron bifurcation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hoben, John P.; Lubner, Carolyn E.; Ratzloff, Michael W.

Flavin-based electron transfer bifurcation is emerging as a fundamental and powerful mechanism for conservation and deployment of electrochemical energy in enzymatic systems. In this process, a pair of electrons is acquired at intermediate reduction potential (i.e. intermediate reducing power) and each electron is passed to a different acceptor, one with lower and the other with higher reducing power, leading to 'bifurcation'. It is believed that a strongly reducing semiquinone species is essential for this process, and it is expected that this species should be kinetically short-lived. We now demonstrate that presence of a short-lived anionic flavin semiquinone (ASQ) is notmore » sufficient to infer existence of bifurcating activity, although such a species may be necessary for the process. We have used transient absorption spectroscopy to compare the rates and mechanisms of decay of ASQ generated photochemically in bifurcating NADH-dependent ferredoxin-NADP + oxidoreductase and the non-bifurcating flavoproteins nitroreductase, NADH oxidase and flavodoxin. We found that different mechanisms dominate ASQ decay in the different protein environments, producing lifetimes ranging over two orders of magnitude. Capacity for electron transfer among redox cofactors vs. charge recombination with nearby donors can explain the range of ASQ lifetimes we observe. In conclusion, our results support a model wherein efficient electron propagation can explain the short lifetime of the ASQ of bifurcating NADH-dependent ferredoxin-NADP + oxidoreductase I, and can be an indication of capacity for electron bifurcation.« less

Equilibrium and ultrafast kinetic studies manipulating electron transfer: A short-lived flavin semiquinone is not sufficient for electron bifurcation.

PubMed

Hoben, John P; Lubner, Carolyn E; Ratzloff, Michael W; Schut, Gerrit J; Nguyen, Diep M N; Hempel, Karl W; Adams, Michael W W; King, Paul W; Miller, Anne-Frances

2017-08-25

Flavin-based electron transfer bifurcation is emerging as a fundamental and powerful mechanism for conservation and deployment of electrochemical energy in enzymatic systems. In this process, a pair of electrons is acquired at intermediate reduction potential ( i.e. intermediate reducing power), and each electron is passed to a different acceptor, one with lower and the other with higher reducing power, leading to "bifurcation." It is believed that a strongly reducing semiquinone species is essential for this process, and it is expected that this species should be kinetically short-lived. We now demonstrate that the presence of a short-lived anionic flavin semiquinone (ASQ) is not sufficient to infer the existence of bifurcating activity, although such a species may be necessary for the process. We have used transient absorption spectroscopy to compare the rates and mechanisms of decay of ASQ generated photochemically in bifurcating NADH-dependent ferredoxin-NADP + oxidoreductase and the non-bifurcating flavoproteins nitroreductase, NADH oxidase, and flavodoxin. We found that different mechanisms dominate ASQ decay in the different protein environments, producing lifetimes ranging over 2 orders of magnitude. Capacity for electron transfer among redox cofactors versus charge recombination with nearby donors can explain the range of ASQ lifetimes that we observe. Our results support a model wherein efficient electron propagation can explain the short lifetime of the ASQ of bifurcating NADH-dependent ferredoxin-NADP + oxidoreductase I and can be an indication of capacity for electron bifurcation.

Size and Temperature Dependence of Electron Transfer between CdSe Quantum Dots and a TiO 2 Nanobelt

DOE PAGES

Tafen, De Nyago; Prezhdo, Oleg V.

2015-02-24

Understanding charge transfer reactions between quantum dots (QD) and metal oxides is fundamental for improving photocatalytic, photovoltaic and electronic devices. The complexity of these processes makes it difficult to find an optimum QD size with rapid charge injection and low recombination. We combine time-domain density functional theory with nonadiabatic molecular dynamics to investigate the size and temperature dependence of the experimentally studied electron transfer and charge recombination at CdSe QD-TiO 2 nanobelt (NB) interfaces. The electron injection rate shows strong dependence on the QD size, increasing for small QDs. The rate exhibits Arrhenius temperature dependence, with the activation energy ofmore » the order of millielectronvolts. The charge recombination process occurs due to coupling of the electronic subsystem to vibrational modes of the TiO 2 NB. Inelastic electron-phonon scattering happens on a picosecond time scale, with strong dependence on the QD size. Our simulations demonstrate that the electron-hole recombination rate decreases significantly as the QD size increases, in excellent agreement with experiments. The temperature dependence of the charge recombination rates can be successfully modeled within the framework of the Marcus theory through optimization of the electronic coupling and the reorganization energy. Our simulations indicate that by varying the QD size, one can modulate the photoinduced charge separation and charge recombination, fundamental aspects of the design principles for high efficiency devices.« less

Regulation of the photosynthetic apparatus under fluctuating growth light.

PubMed

Tikkanen, Mikko; Grieco, Michele; Nurmi, Markus; Rantala, Marjaana; Suorsa, Marjaana; Aro, Eva-Mari

2012-12-19

Safe and efficient conversion of solar energy to metabolic energy by plants is based on tightly inter-regulated transfer of excitation energy, electrons and protons in the photosynthetic machinery according to the availability of light energy, as well as the needs and restrictions of metabolism itself. Plants have mechanisms to enhance the capture of energy when light is limited for growth and development. Also, when energy is in excess, the photosynthetic machinery slows down the electron transfer reactions in order to prevent the production of reactive oxygen species and the consequent damage of the photosynthetic machinery. In this opinion paper, we present a partially hypothetical scheme describing how the photosynthetic machinery controls the flow of energy and electrons in order to enable the maintenance of photosynthetic activity in nature under continual fluctuations in white light intensity. We discuss the roles of light-harvesting II protein phosphorylation, thermal dissipation of excess energy and the control of electron transfer by cytochrome b(6)f, and the role of dynamically regulated turnover of photosystem II in the maintenance of the photosynthetic machinery. We present a new hypothesis suggesting that most of the regulation in the thylakoid membrane occurs in order to prevent oxidative damage of photosystem I.

Visible Light Driven Benzyl Alcohol Dehydrogenation in a Dye-Sensitized Photoelectrosynthesis Cell

DOE Office of Scientific and Technical Information (OSTI.GOV)

Song, Wenjing; Vannucci, Aaron K.; Farnum, Byron H.

2014-06-27

Light-driven dehydrogenation of benzyl alcohol (BnOH) to benzaldehyde and hydrogen has been shown to occur in a dye-sensitized photoelectrosynthesis cell (DSPEC). In the DSPEC, the photoanode consists of mesoporous films of TiO2 nanoparticles or of core/shell nanoparticles with tin-doped In2O3 nanoparticle (nanoITO) cores and thin layers of TiO2 deposited by atomic layer deposition (nanoITO/TiO2). Metal oxide surfaces were coderivatized with both a ruthenium polypyridyl chromophore in excess and an oxidation catalyst. Chromophore excitation and electron injection were followed by cross-surface electron-transfer activation of the catalyst to RuIV=O2+, which then oxidizes benzyl alcohol to benzaldehyde. The injected electrons are transferred tomore » a Pt electrode for H2 production. The nanoITO/TiO2 core/shell structure causes a decrease of up to 2 orders of magnitude in back electron-transfer rate compared to TiO2. At the optimized shell thickness, sustained absorbed photon to current efficiency of 3.7% was achieved for BnOH dehydrogenation, an enhancement of ~10 compared to TiO2.« less

Observation of Internal Photoinduced Electron and Hole Separation in Hybrid Two-Dimentional Perovskite Films.

PubMed

Liu, Junxue; Leng, Jing; Wu, Kaifeng; Zhang, Jun; Jin, Shengye

2017-02-01

Two-dimensional (2D) organolead halide perovskites are promising for various optoelectronic applications. Here we report a unique spontaneous charge (electron/hole) separation property in multilayered (BA) 2 (MA) n-1 Pb n I 3n+1 (BA = CH 3 (CH 2 ) 3 NH 3 + , MA = CH 3 NH 3 + ) 2D perovskite films by studying the charge carrier dynamics using ultrafast transient absorption and photoluminescence spectroscopy. Surprisingly, the 2D perovskite films, although nominally prepared as "n = 4", are found to be mixture of multiple perovskite phases, with n = 2, 3, 4 and ≈ ∞, that naturally align in the order of n along the direction perpendicular to the substrate. Driven by the band alignment between 2D perovskites phases, we observe consecutive photoinduced electron transfer from small-n to large-n phases and hole transfer in the opposite direction on hundreds of picoseconds inside the 2D film of ∼358 nm thickness. This internal charge transfer efficiently separates electrons and holes to the upper and bottom surfaces of the films, which is a unique property beneficial for applications in photovoltaics and other optoelectronics devices.

Microbial interspecies electron transfer via electric currents through conductive minerals

PubMed Central

Kato, Souichiro; Hashimoto, Kazuhito; Watanabe, Kazuya

2012-01-01

In anaerobic biota, reducing equivalents (electrons) are transferred between different species of microbes [interspecies electron transfer (IET)], establishing the basis of cooperative behaviors and community functions. IET mechanisms described so far are based on diffusion of redox chemical species and/or direct contact in cell aggregates. Here, we show another possibility that IET also occurs via electric currents through natural conductive minerals. Our investigation revealed that electrically conductive magnetite nanoparticles facilitated IET from Geobacter sulfurreducens to Thiobacillus denitrificans, accomplishing acetate oxidation coupled to nitrate reduction. This two-species cooperative catabolism also occurred, albeit one order of magnitude slower, in the presence of Fe ions that worked as diffusive redox species. Semiconductive and insulating iron-oxide nanoparticles did not accelerate the cooperative catabolism. Our results suggest that microbes use conductive mineral particles as conduits of electrons, resulting in efficient IET and cooperative catabolism. Furthermore, such natural mineral conduits are considered to provide ecological advantages for users, because their investments in IET can be reduced. Given that conductive minerals are ubiquitously and abundantly present in nature, electric interactions between microbes and conductive minerals may contribute greatly to the coupling of biogeochemical reactions. PMID:22665802

Electrical contacting of an assembly of pseudoazurin and nitrite reductase using DNA-directed immobilization.

PubMed

Tepper, Armand W J W

2010-05-12

A method for the electrical contacting of redox enzymes that obtain oxidizing or reducing equivalents from small electron-transfer proteins is demonstrated. The electrochemical contacting of redox enzymes through their immobilization onto electrode supports offers great potential for technological applications and for fundamental studies, but finding appropriate methods to immobilize the enzymes in an orientation allowing rapid electron transfer with the electrode has proven difficult. The copper enzyme nitrite reductase (NiR) and its natural electron-exchange partner pseudoazurin (Paz) are conjugated to a specific DNA tag and immobilized to a gold electrode into a stoichiometrically defined assembly. The DNA tethered to the electrode surface acts as flexible place-holder for the protein components, allowing both proteins to move within the construct. It is shown that Paz efficiently shuttles electrons between the electrode and the NiR enzyme, allowing the electrochemically driven NiR catalysis to be monitored. The activity of the NiR enzyme remains unperturbed by the immobilization. The rate-limiting step of the system is tentatively ascribed to the dissociation of the Paz/NiR complex. The electrochemical response of the system reports not only on the NiR catalysis and on interfacial electron transfer but also on the interaction between NiR and Paz.

CdSe quantum dot-fullerene hybrid nanocomposite for solar energy conversion: electron transfer and photoelectrochemistry.

PubMed

Bang, Jin Ho; Kamat, Prashant V

2011-12-27

The development of organic/inorganic hybrid nanocomposite systems that enable efficient solar energy conversion has been important for applications in solar cell research. Nanostructured carbon-based systems, in particular C(60), offer attractive strategies to collect and transport electrons generated in a light harvesting assembly. We have assembled CdSe-C(60) nanocomposites by chemically linking CdSe quantum dots (QDs) with thiol-functionalized C(60). The photoinduced charge separation and collection of electrons in CdSe QD-C(60) nanocomposites have been evaluated using transient absorption spectroscopy and photoelectrochemical measurements. The rate constant for electron transfer between excited CdSe QD and C(60) increased with the decreasing size of the CdSe QD (7.9 × 10(9) s(-1) (4.5 nm), 1.7 × 10(10) s(-1) (3.2 nm), and 9.0 × 10(10) s(-1) (2.6 nm)). Slower hole transfer and faster charge recombination and transport events were found to dominate over the forward electron injection process, thus limiting the deliverance of maximum power in CdSe QD-C(60)-based solar cells. The photoinduced charge separation between CdSe QDs and C(60) opens up new design strategies for developing light harvesting assemblies.

Numerical investigation of thermal performance of a water-cooled mini-channel heat sink for different chip arrangement

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tikadar, Amitav, E-mail: amitav453@gmail.com; Hossain, Md. Mahamudul; Morshed, A. K. M. M.

Heat transfer from electronic chip is always challenging and very crucial for electronic industry. Electronic chips are assembled in various manners according to the design conditions and limitationsand thus the influence of chip assembly on the overall thermal performance needs to be understand for the efficient design of electronic cooling system. Due to shrinkage of the dimension of channel and continuous increment of thermal load, conventional heat extraction techniques sometimes become inadequate. Due to high surface area to volume ratio, mini-channel have the natural advantage to enhance convective heat transfer and thus to play a vital role in the advancedmore » heat transfer devices with limited surface area and high heat flux. In this paper, a water cooled mini-channel heat sink was considered for electronic chip cooling and five different chip arrangements were designed and studied, namely: the diagonal arrangement, parallel arrangement, stacked arrangement, longitudinal arrangement and sandwiched arrangement. Temperature distribution on the chip surfaces was presented and the thermal performance of the heat sink in terms of overall thermal resistance was also compared. It is found that the sandwiched arrangement of chip provides better thermal performance compared to conventional in line chip arrangement.« less

Biomass production from electricity using ammonia as an electron carrier in a reverse microbial fuel cell.

PubMed

Khunjar, Wendell O; Sahin, Asli; West, Alan C; Chandran, Kartik; Banta, Scott

2012-01-01

The storage of renewable electrical energy within chemical bonds of biofuels and other chemicals is a route to decreasing petroleum usage. A critical challenge is the efficient transfer of electrons into a biological host that can covert this energy into high energy organic compounds. In this paper, we describe an approach whereby biomass is grown using energy obtained from a soluble mediator that is regenerated electrochemically. The net result is a separate-stage reverse microbial fuel cell (rMFC) that fixes CO₂ into biomass using electrical energy. We selected ammonia as a low cost, abundant, safe, and soluble redox mediator that facilitated energy transfer to biomass. Nitrosomonas europaea, a chemolithoautotroph, was used as the biocatalyst due to its inherent capability to utilize ammonia as its sole energy source for growth. An electrochemical reactor was designed for the regeneration of ammonia from nitrite, and current efficiencies of 100% were achieved. Calculations indicated that overall bioproduction efficiency could approach 2.7±0.2% under optimal electrolysis conditions. The application of chemolithoautotrophy for industrial bioproduction has been largely unexplored, and results suggest that this and related rMFC platforms may enable biofuel and related biochemical production.

Biomass Production from Electricity Using Ammonia as an Electron Carrier in a Reverse Microbial Fuel Cell

PubMed Central

West, Alan C.; Chandran, Kartik; Banta, Scott

2012-01-01

The storage of renewable electrical energy within chemical bonds of biofuels and other chemicals is a route to decreasing petroleum usage. A critical challenge is the efficient transfer of electrons into a biological host that can covert this energy into high energy organic compounds. In this paper, we describe an approach whereby biomass is grown using energy obtained from a soluble mediator that is regenerated electrochemically. The net result is a separate-stage reverse microbial fuel cell (rMFC) that fixes CO2 into biomass using electrical energy. We selected ammonia as a low cost, abundant, safe, and soluble redox mediator that facilitated energy transfer to biomass. Nitrosomonas europaea, a chemolithoautotroph, was used as the biocatalyst due to its inherent capability to utilize ammonia as its sole energy source for growth. An electrochemical reactor was designed for the regeneration of ammonia from nitrite, and current efficiencies of 100% were achieved. Calculations indicated that overall bioproduction efficiency could approach 2.7±0.2% under optimal electrolysis conditions. The application of chemolithoautotrophy for industrial bioproduction has been largely unexplored, and results suggest that this and related rMFC platforms may enable biofuel and related biochemical production. PMID:23028643

Investigating the association between photosynthetic efficiency and generation of biophotoelectricity in autotrophic microbial fuel cells

PubMed Central

Ciniciato, Gustavo P. M. K.; Ng, Fong-Lee; Phang, Siew-Moi; Jaafar, Muhammad Musoddiq; Fisher, Adrian C.; Yunus, Kamran; Periasamy, Vengadesh

2016-01-01

Microbial fuel cells operating with autotrophic microorganisms are known as biophotovoltaic devices. It represents a great opportunity for environmentally-friendly power generation using the energy of the sunlight. The efficiency of electricity generation in this novel system is however low. This is partially reflected by the poor understanding of the bioelectrochemical mechanisms behind the electron transfer from these microorganisms to the electrode surface. In this work, we propose a combination of electrochemical and fluorescence techniques, giving emphasis to the pulse amplitude modulation fluorescence. The combination of these two techniques allow us to obtain information that can assist in understanding the electrical response obtained from the generation of electricity through the intrinsic properties related to the photosynthetic efficiency that can be obtained from the fluorescence emitted. These were achieved quantitatively by means of observed changes in four photosynthetic parameters with the bioanode generating electricity. These are the maximum quantum yield (Fv/Fm), alpha (α), light saturation coefficient (Ek) and maximum rate of electron transfer (rETRm). The relationship between the increases in the current density collected by the bioanode to the decrease of the rETRm values in the photosynthetic pathway for the two microorganisms was also discussed. PMID:27502051

Investigating the association between photosynthetic efficiency and generation of biophotoelectricity in autotrophic microbial fuel cells

NASA Astrophysics Data System (ADS)

Ciniciato, Gustavo P. M. K.; Ng, Fong-Lee; Phang, Siew-Moi; Jaafar, Muhammad Musoddiq; Fisher, Adrian C.; Yunus, Kamran; Periasamy, Vengadesh

2016-08-01

Microbial fuel cells operating with autotrophic microorganisms are known as biophotovoltaic devices. It represents a great opportunity for environmentally-friendly power generation using the energy of the sunlight. The efficiency of electricity generation in this novel system is however low. This is partially reflected by the poor understanding of the bioelectrochemical mechanisms behind the electron transfer from these microorganisms to the electrode surface. In this work, we propose a combination of electrochemical and fluorescence techniques, giving emphasis to the pulse amplitude modulation fluorescence. The combination of these two techniques allow us to obtain information that can assist in understanding the electrical response obtained from the generation of electricity through the intrinsic properties related to the photosynthetic efficiency that can be obtained from the fluorescence emitted. These were achieved quantitatively by means of observed changes in four photosynthetic parameters with the bioanode generating electricity. These are the maximum quantum yield (Fv/Fm), alpha (α), light saturation coefficient (Ek) and maximum rate of electron transfer (rETRm). The relationship between the increases in the current density collected by the bioanode to the decrease of the rETRm values in the photosynthetic pathway for the two microorganisms was also discussed.

Versatile Molecular Functionalization for Inhibiting Concentration Quenching of Thermally Activated Delayed Fluorescence.

PubMed

Lee, Jiyoung; Aizawa, Naoya; Numata, Masaki; Adachi, Chihaya; Yasuda, Takuma

2017-01-01

Concentration quenching of thermally activated delayed fluorescence is found to be dominated by electron-exchange interactions, as described by the Dexter energy-transfer model. Owing to the short-range nature of the electron-exchange interactions, even a small modulation in the molecular geometric structure drastically affects the concentration-quenching, leading to enhanced solid-state photoluminescence and electroluminescence quantum efficiencies. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Combined high and low-thrust geostationary orbit insertion with radiation constraint

NASA Astrophysics Data System (ADS)

Macdonald, Malcolm; Owens, Steven Robert

2018-01-01

The sequential use of an electric propulsion system is considered in combination with a high-thrust propulsion system for application to the propellant-optimal Geostationary Orbit insertion problem, whilst considering both temporal and radiation flux constraints. Such usage is found to offer a combined propellant mass saving when compared with an equivalent high-thrust only transfer. This propellant mass saving is seen to increase as the allowable transfer duration is increased, and as the thrust from the low-thrust system is increased, assuming constant specific impulse. It was found that the required plane change maneuver is most propellant-efficiently performed by the high-thrust system. The propellant optimal trajectory incurs a significantly increased electron flux when compared to an equivalent high-thrust only transfer. However, the electron flux can be reduced to a similar order of magnitude by increasing the high-thrust propellant consumption, whilst still delivering an improved mass fraction.

Vibrational Relaxation and Electronic Quenching-Rate Coefficients for BiF (A0+,v1) by SF6

DTIC Science & Technology

1988-08-22

REPORT SD-TR-88-83 LO Vibrational Relaxation and Electronic Quenching-Rate N Coefficients for BiF (AO+ , v ) by SF 6 0) 0) H . HELVAJIAN , J. S...1. J. M. Herbelin and R. A. Klingberg, Int. J. Chem. Kinet. 16, 849 (19824). 2. R. F. Heidner III, H . Helvajian , J. S. Holloway, and J. B. Koffend, J...driven electronic-transfer laser based on the efficient H + NF2 NF(a) + HF reaction. More recently, the rate coefficients for spontaneous emission

Molecular dynamics and charge transport in organic semiconductors: a classical approach to modeling electron transfer† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c6sc04547b Click here for additional data file.

PubMed Central

Vázquez-Mayagoitia, Álvaro; Ratcliff, Laura E.; Tretiak, Sergei; Bair, Raymond A.; Gray, Stephen K.; Van Voorhis, Troy; Larsen, Ross E.; Darling, Seth B.

2017-01-01

Organic photovoltaics (OPVs) are a promising carbon-neutral energy conversion technology, with recent improvements pushing power conversion efficiencies over 10%. A major factor limiting OPV performance is inefficiency of charge transport in organic semiconducting materials (OSCs). Due to strong coupling with lattice degrees of freedom, the charges form polarons, localized quasi-particles comprised of charges dressed with phonons. These polarons can be conceptualized as pseudo-atoms with a greater effective mass than a bare charge. We propose that due to this increased mass, polarons can be modeled with Langevin molecular dynamics (LMD), a classical approach with a computational cost much lower than most quantum mechanical methods. Here we present LMD simulations of charge transfer between a pair of fullerene molecules, which commonly serve as electron acceptors in OSCs. We find transfer rates consistent with experimental measurements of charge mobility, suggesting that this method may provide quantitative predictions of efficiency when used to simulate materials on the device scale. Our approach also offers information that is not captured in the overall transfer rate or mobility: in the simulation data, we observe exactly when and why intermolecular transfer events occur. In addition, we demonstrate that these simulations can shed light on the properties of polarons in OSCs. Much remains to be learned about these quasi-particles, and there are no widely accepted methods for calculating properties such as effective mass and friction. Our model offers a promising approach to exploring mass and friction as well as providing insight into the details of polaron transport in OSCs. PMID:28553494

Amino-Acid-Induced Preferential Orientation of Perovskite Crystals for Enhancing Interfacial Charge Transfer and Photovoltaic Performance.

PubMed

Shih, Yen-Chen; Lan, Yu-Bing; Li, Chia-Shuo; Hsieh, Hsiao-Chi; Wang, Leeyih; Wu, Chih-I; Lin, King-Fu

2017-06-01

Interfacial engineering of perovskite solar cells (PSCs) is attracting intensive attention owing to the charge transfer efficiency at an interface, which greatly influences the photovoltaic performance. This study demonstrates the modification of a TiO 2 electron-transporting layer with various amino acids, which affects charge transfer efficiency at the TiO 2 /CH 3 NH 3 PbI 3 interface in PSC, among which the l-alanine-modified cell exhibits the best power conversion efficiency with 30% enhancement. This study also shows that the (110) plane of perovskite crystallites tends to align in the direction perpendicular to the amino-acid-modified TiO 2 as observed in grazing-incidence wide-angle X-ray scattering of thin CH 3 NH 3 PbI 3 perovskite film. Electrochemical impedance spectroscopy reveals less charge transfer resistance at the TiO 2 /CH 3 NH 3 PbI 3 interface after being modified with amino acids, which is also supported by the lower intensity of steady-state photoluminescence (PL) and the reduced PL lifetime of perovskite. In addition, based on the PL measurement with excitation from different side of the sample, amino-acid-modified samples show less surface trapping effect compared to the sample without modification, which may also facilitate charge transfer efficiency at the interface. The results suggest that appropriate orientation of perovskite crystallites at the interface and trap-passivation are the niche for better photovoltaic performance. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ice-assisted transfer of carbon nanotube arrays.

PubMed

Wei, Haoming; Wei, Yang; Lin, Xiaoyang; Liu, Peng; Fan, Shoushan; Jiang, Kaili

2015-03-11

Decoupling the growth and the application of nanomaterials by transfer is an important issue in nanotechnology. Here, we developed an efficient transfer technique for carbon nanotube (CNT) arrays by using ice as a binder to temporarily bond the CNT array and the target substrate. Ice makes it an ultraclean transfer because the evaporation of ice ensures that no contaminants are introduced. The transferred superaligned carbon nanotube (SACNT) arrays not only keep their original appearance and initial alignment but also inherit their spinnability, which is the most desirable feature. The transfer-then-spin strategy can be employed to fabricate patterned CNT arrays, which can act as 3-dimensional electrodes in CNT thermoacoustic chips. Besides, the flip-chipped CNTs are promising field electron emitters. Furthermore, the ice-assisted transfer technique provides a cost-effective solution for mass production of SACNTs, giving CNT technologies a competitive edge, and this method may inspire new ways to transfer other nanomaterials.

Unravelling the pH-dependence of a molecular photocatalytic system for hydrogen production.

PubMed

Reynal, Anna; Pastor, Ernest; Gross, Manuela A; Selim, Shababa; Reisner, Erwin; Durrant, James R

2015-08-01

Photocatalytic systems for the reduction of aqueous protons are strongly pH-dependent, but the origin of this dependency is still not fully understood. We have studied the effect of different degrees of acidity on the electron transfer dynamics and catalysis taking place in a homogeneous photocatalytic system composed of a phosphonated ruthenium tris(bipyridine) dye ( RuP ) and a nickel bis(diphosphine) electrocatalyst ( NiP ) in an aqueous ascorbic acid solution. Our approach is based on transient absorption spectroscopy studies of the efficiency of photo-reduction of RuP and NiP correlated with pH-dependent photocatalytic H 2 production and the degree of catalyst protonation. The influence of these factors results in an observed optimum photoactivity at pH 4.5 for the RuP - NiP system. The electron transfer from photo-reduced RuP to NiP is efficient and independent of the pH value of the medium. At pH <4.5, the efficiency of the system is limited by the yield of RuP photo-reduction by the sacrificial electron donor, ascorbic acid. At pH >4.5, the efficiency of the system is limited by the poor protonation of NiP , which inhibits its ability to reduce protons to hydrogen. We have therefore developed a rational strategy utilising transient absorption spectroscopy combined with bulk pH titration, electrocatalytic and photocatalytic experiments to disentangle the complex pH-dependent activity of the homogenous RuP - NiP photocatalytic system, which can be widely applied to other photocatalytic systems.

Electrical Matching at Metal/Molecule Contacts for Efficient Heterogeneous Charge Transfer.

PubMed

Sato, Shino; Iwase, Shigeru; Namba, Kotaro; Ono, Tomoya; Hara, Kenji; Fukuoka, Atsushi; Uosaki, Kohei; Ikeda, Katsuyoshi

2018-02-27

In a metal/molecule hybrid system, unavoidable electrical mismatch exists between metal continuum states and frontier molecular orbitals. This causes energy loss in the electron conduction across the metal/molecule interface. For efficient use of energy in a metal/molecule hybrid system, it is necessary to control interfacial electronic structures. Here we demonstrate that electrical matching between a gold substrate and π-conjugated molecular wires can be obtained by using monatomic foreign metal interlayers, which can change the degree of d-π* back-donation at metal/anchor contacts. This interfacial control leads to energy level alignment between the Fermi level of the metal electrode and conduction molecular orbitals, resulting in resonant electron conduction in the metal/molecule hybrid system. When this method is applied to molecule-modified electrocatalysts, the heterogeneous electrochemical reaction rate is considerably improved with significant suppression of energy loss at the internal electron conduction.

Improvement of Charge Transportation in Si Quantum Dot-Sensitized Solar Cells Using Vanadium Doped TiO2.

PubMed

Seo, Hyunwoong; Ichida, Daiki; Hashimoto, Shinji; Itagaki, Naho; Koga, Kazunori; Shiratani, Masaharu; Nam, Sang-Hun; Boo, Jin-Hyo

2016-05-01

The multiple exciton generation characteristics of quantum dots have been expected to enhance the performance of photochemical solar cells. In previous work, we first introduced Si quantum dot for sensitized solar cells. The Si quantum dots were fabricated by multi-hollow discharge plasma chemical vapor deposition, and were characterized optically and morphologically. The Si quantum dot-sensitized solar cells had poor performance due to significant electron loss by charge recombination. Although the large Si particle size resulted in the exposure of a large TiO2 surface area, there was a limit to ho much the particle size could be decreased due to the reduced absorbance of small particles. Therefore, this work focused on decreasing the internal impedance to improve charge transfer. TiO2 was electronically modified by doping with vanadium, which can improve electron transfer in the TiO2 network, and which is stable in the redox electrolyte. Photogenerated electrons can more easily arrive at the conductive electrode due to the decreased internal impedance. The dark photovoltaic properties confirmed the reduction of charge recombination, and the photon-to-current conversion efficiency reflected the improved electron transfer. Impedance analysis confirmed a decrease in internal impedance and an increased electron lifetime. Consequently, these improvements by vanadium doping enhanced the overall performance of Si quantum dot-sensitized solar cells.

Visible light-driven water oxidation promoted by host-guest interaction between photosensitizer and catalyst with a high quantum efficiency.

PubMed

Li, Hua; Li, Fei; Zhang, Biaobiao; Zhou, Xu; Yu, Fengshou; Sun, Licheng

2015-04-08

A highly active supramolecular system for visible light-driven water oxidation was developed with cyclodextrin-modified ruthenium complex as the photosensitizer, phenyl-modified ruthenium complexes as the catalysts, and sodium persulfate as the sacrificial electron acceptor. The catalysts were found to form 1:1 host-guest adducts with the photosensitizer. Stopped-flow measurement revealed the host-guest interaction is essential to facilitate the electron transfer from catalyst to sensitizer. As a result, a remarkable quantum efficiency of 84% was determined under visible light irradiation in neutral aqueous phosphate buffer. This value is nearly 1 order of magnitude higher than that of noninteraction system, indicating that the noncovalent incorporation of sensitizer and catalyst is an appealing approach for efficient conversion of solar energy into fuels.

Amorphous MoS{sub x} on CdS nanorods for highly efficient photocatalytic hydrogen evolution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Xiaofang; Tang, Chaowan; Zheng, Qun

Loading cocatalyst on semiconductors was crucially necessary for improving the photocatalytic hydrogen evolution. Amorphous MoS{sub x} as a novel and noble metal-free cocatalyst was loaded on CdS nanorods by a simple photodeposition method. Efficient hydrogen evolution with amount of 15 mmol h{sup −1} g{sup −1} was observed over the MoS{sub x} modified CdS nanorods, which was about 6 times higher than that by using Pt as cocatalyst. Meanwhile, with MoS{sub x} cocatalyst, the efficiency of CdS nanorods was superior to that of CdS nanoparticles and bulk CdS. No deactivation could be observed in the efficiency of MoS{sub x} modified CdSmore » nanorods under irradiation for successive 10 h. Further experimental results indicated that the efficient electrons transfer, low overpotential of hydrogen evolution and active S atoms over the MoS{sub x} modified CdS nanorods were responsible for the higher efficiency. Our results provided guidance for synthesizing noble metal-free materials as cocatalyst for photocatalytic hydrogen evolution. - Graphical abstract: Photodeposition of amorphous MoS{sub x} on CdS nanorods for highly efficient photocatalytic hydrogen evolution. - Highlights: • Amorphous MoSx cocatalyst was loaded on CdS NRs by a simple photodeposition. • MoS{sub x}/CdS NRs exhibited 6 times higher hydrogen evolution efficiency than Pt/CdS NRs. • The hydrogen evolution of MoS{sub x}/CdS NRs linearly increased with prolonging time. • Lower overpotential and efficient electron transfer were observed over MoS{sub x}/CdS NRs.« less

One Electron-Initiated Two-Electron Oxidation of Water by Aluminum Porphyrins with Earth's Most Abundant Metal.

PubMed

Kuttassery, Fazalurahman; Mathew, Siby; Sagawa, Shogo; Remello, Sebastian Nybin; Thomas, Arun; Yamamoto, Daisuke; Onuki, Satomi; Nabetani, Yu; Tachibana, Hiroshi; Inoue, Haruo

2017-05-09

We report herein a new molecular catalyst for efficient water splitting, aluminum porphyrins (tetra-methylpyridiniumylporphyrinatealuminum: AlTMPyP), containing earth's most abundant metal as the central ion. One-electron oxidation of the aluminum porphyrin initiates the two-electron oxidation of water to form hydrogen peroxide as the primary reaction product with the lowest known overpotential (97 mV). The aluminum-peroxo complex was detected by a cold-spray ionization mass-spectrometry in high-resolution MS (HRMS) mode and the structure of the intermediate species was further confirmed using laser Raman spectroscopy, indicating the hydroperoxy complex of AlTMPyP to be the key intermediate in the reaction. The two-electron oxidation of water to form hydrogen peroxide was essentially quantitative, with a Faradaic efficiency of 99 %. The catalytic reaction was found to be highly efficient, with a turnover frequency up to ∼2×10 4  s -1 . A reaction mechanism is proposed involving oxygen-oxygen bond formation by the attack of a hydroxide ion on the oxyl-radical-like axial ligand oxygen atom in the one-electron-oxidized form of AlTMPyP(O - ) 2 , followed by a second electron transfer to the electrode. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Designing interfaces of hydrogenase-nanomaterial hybrids for efficient solar conversion.

PubMed

King, Paul W

2013-01-01

The direct conversion of sunlight into biofuels is an intriguing alternative to a continued reliance on fossil fuels. Natural photosynthesis has long been investigated both as a potential solution, and as a model for utilizing solar energy to drive a water-to-fuel cycle. The molecules and organizational structure provide a template to inspire the design of efficient molecular systems for photocatalysis. A clear design strategy is the coordination of molecular interactions that match kinetic rates and energetic levels to control the direction and flow of energy from light harvesting to catalysis. Energy transduction and electron-transfer reactions occur through interfaces formed between complexes of donor-acceptor molecules. Although the structures of several of the key biological complexes have been solved, detailed descriptions of many electron-transfer complexes are lacking, which presents a challenge to designing and engineering biomolecular systems for solar conversion. Alternatively, it is possible to couple the catalytic power of biological enzymes to light harvesting by semiconductor nanomaterials. In these molecules, surface chemistry and structure can be designed using ligands. The passivation effect of the ligand can also dramatically affect the photophysical properties of the semiconductor, and energetics of external charge-transfer. The length, degree of bond saturation (aromaticity), and solvent exposed functional groups of ligands can be manipulated to further tune the interface to control molecular assembly, and complex stability in photocatalytic hybrids. The results of this research show how ligand selection is critical to designing molecular interfaces that promote efficient self-assembly, charge-transfer and photocatalysis. This article is part of a Special Issue entitled: Metals in Bioenergetics and Biomimetics Systems. Copyright © 2013 Elsevier B.V. All rights reserved.

Photosynthetic antenna-reaction center mimicry with a covalently linked monostyryl boron-dipyrromethene-aza-boron-dipyrromethene-C60 triad.

PubMed

Shi, Wen-Jing; El-Khouly, Mohamed E; Ohkubo, Kei; Fukuzumi, Shunichi; Ng, Dennis K P

2013-08-19

An efficient functional mimic of the photosynthetic antenna-reaction center has been designed and synthesized. The model contains a near-infrared-absorbing aza-boron-dipyrromethene (ADP) that is connected to a monostyryl boron-dipyrromethene (BDP) by a click reaction and to a fullerene (C60 ) using the Prato reaction. The intramolecular photoinduced energy and electron-transfer processes of this triad as well as the corresponding dyads BDP-ADP and ADP-C60 have been studied with steady-state and time-resolved absorption and fluorescence spectroscopic methods in benzonitrile. Upon excitation, the BDP moiety of the triad is significantly quenched due to energy transfer to the ADP core, which subsequently transfers an electron to the fullerene unit. Cyclic and differential pulse voltammetric studies have revealed the redox states of the components, which allow estimation of the energies of the charge-separated states. Such calculations show that electron transfer from the singlet excited ADP ((1) ADP*) to C60 yielding ADP(.+) -C60 (.-) is energetically favorable. By using femtosecond laser flash photolysis, concrete evidence has been obtained for the occurrence of energy transfer from (1) BDP* to ADP in the dyad BDP-ADP and electron transfer from (1) ADP* to C60 in the dyad ADP-C60 . Sequential energy and electron transfer have also been clearly observed in the triad BDP-ADP-C60 . By monitoring the rise of ADP emission, it has been found that the rate of energy transfer is fast (≈10(11)  s(-1) ). The dynamics of electron transfer through (1) ADP* has also been studied by monitoring the formation of C60 radical anion at 1000 nm. A fast charge-separation process from (1) ADP* to C60 has been detected, which gives the relatively long-lived BDP-ADP(.+) C60 (.-) with a lifetime of 1.47 ns. As shown by nanosecond transient absorption measurements, the charge-separated state decays slowly to populate mainly the triplet state of ADP before returning to the ground state. These findings show that the dyads BDP-ADP and ADP-C60 , and the triad BDP-ADP-C60 are interesting artificial analogues that can mimic the antenna and reaction center of the natural photosynthetic systems. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ultrafast exciton dynamics and light-driven H2 evolution in colloidal semiconductor nanorods and Pt-tipped nanorods.

PubMed

Wu, Kaifeng; Zhu, Haiming; Lian, Tianquan

2015-03-17

Colloidal quantum confined one-dimensional (1D) semiconductor nanorods (NRs) and related semiconductor-metal heterostructures are promising new materials for efficient solar-to-fuel conversion because of their unique physical and chemical properties. NRs can simultaneously exhibit quantum confinement effects in the radial direction and bulk like carrier transport in the axial direction. The former implies that concepts well-established in zero-dimensional quantum dots, such as size-tunable energetics and wave function engineering through band alignment in heterostructures, can also be applied to NRs; while the latter endows NRs with fast carrier transport to achieve long distance charge separation. Selective growth of catalytic metallic nanoparticles, such as Pt, at the tips of NRs provides convenient routes to multicomponent heterostructures with photocatalytic capabilities and controllable charge separation distances. The design and optimization of such materials for efficient solar-to-fuel conversion require the understanding of exciton and charge carrier dynamics. In this Account, we summarize our recent studies of ultrafast charge separation and recombination kinetics and their effects on steady-state photocatalytic efficiencies of colloidal CdS and CdSe/CdS NRs and related NR-Pt heterostructures. After a brief introduction of their electronic structure, we discuss exciton dynamics of CdS NRs. By transient absorption and time-resolved photoluminescence decay, it is shown that although the conduction band electrons are long-lived, photogenerated holes in CdS NRs are trapped on an ultrafast time scale (∼0.7 ps), which forms localized excitons due to strong Coulomb interaction in 1D NRs. In quasi-type II CdSe/CdS dot-in-rod NRs, a large valence band offset drives the ultrafast localization of holes to the CdSe core, and the competition between this process and ultrafast hole trapping on a CdS rod leads to three types of exciton species with distinct spatial distributions. The effect of the exciton dynamics on photoreduction reactions is illustrated using methyl viologen (MV(2+)) as a model electron acceptor. The steady-state MV(2+) photoreduction quantum yield of CdSe/CdS dot-in-rod NRs approaches unity under rod excitation, much larger than CdSe QDs and CdSe/CdS core/shell QDs. Detailed time-resolved studies show that in quasi-type II CdSe/CdS NRs and type II ZnSe/CdS NRs strong quantum confinement in the radial direction facilitates fast electron transfer and hole removal, whereas the fast carrier mobility along the axial direction enables long distance charge separation and slow charge recombination, which is essential for efficient MV(2+) photoreduction. The NR/MV(2+) relay system can be coupled to Pt nanoparticles in solution for light-driven H2 generation. Alternatively, Pt-tipped CdS and CdSe/CdS NRs provide fully integrated all inorganic systems for light-driven H2 generation. In CdS-Pt and CdSe/CdS-Pt hetero-NRs, ultrafast hole trapping on the CdS rod surface or in CdSe core enables efficient electron transfer from NRs to Pt tips by suppressing hole and energy transfer. It is shown that the quantum yields of photodriven H2 generation using these heterostructures correlate well with measured hole transfer rates from NRs to sacrificial donors, revealing that hole removal is the key efficiency-limiting step. These findings provide important insights for designing more efficient quantum confined NR and NR-Pt based systems for solar-to-fuel conversion.

Influence of silver nanoparticles on relaxation processes and efficiency of dipole – dipole energy transfer between dye molecules in polymethylmethacrylate films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bryukhanov, V V; Borkunov, R Yu; Tsarkov, M V

The fluorescence and phosphorescence of dyes in thin polymethylmethacrylate (PMMA) films in the presence of ablated silver nanoparticles has been investigated in a wide temperature range by methods of femtosecond and picosecond laser photoexcitation. The fluorescence and phosphorescence times, as well as spectral and kinetic characteristics of rhodamine 6G (R6G) molecules in PMMA films are measured in a temperature range of 80 – 330 K. The temperature quenching activation energy of the fluorescence of R6G molecules in the presence of ablated silver nanoparticles is found. The vibrational relaxation rate of R6G in PMMA films is estimated, the efficiency of themore » dipole – dipole electron energy transfer between R6G and brilliant green molecules (enhanced by plasmonic interaction with ablated silver nanoparticles) is analysed, and the constants of this energy transfer are determined. (nanophotonics)« less

FOB-SH: Fragment orbital-based surface hopping for charge carrier transport in organic and biological molecules and materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Spencer, J.; Gajdos, F.; Blumberger, J., E-mail: j.blumberger@ucl.ac.uk

2016-08-14

We introduce a fragment orbital-based fewest switches surface hopping method, FOB-SH, designed to efficiently simulate charge carrier transport in strongly fluctuating condensed phase systems such as organic semiconductors and biomolecules. The charge carrier wavefunction is expanded and the electronic Hamiltonian constructed in a set of singly occupied molecular orbitals of the molecular sites that mediate the charge transfer. Diagonal elements of the electronic Hamiltonian (site energies) are obtained from a force field, whereas the off-diagonal or electronic coupling matrix elements are obtained using our recently developed analytic overlap method. We derive a general expression for the exact forces on themore » adiabatic ground and excited electronic state surfaces from the nuclear gradients of the charge localized electronic states. Applications to electron hole transfer in a model ethylene dimer and through a chain of ten model ethylenes validate our implementation and demonstrate its computational efficiency. On the larger system, we calculate the qualitative behaviour of charge mobility with change in temperature T for different regimes of the intermolecular electronic coupling. For small couplings, FOB-SH predicts a crossover from a thermally activated regime at low temperatures to a band-like transport regime at higher temperatures. For higher electronic couplings, the thermally activated regime disappears and the mobility decreases according to a power law. This is interpreted by a gradual loss in probability for resonance between the sites as the temperature increases. The polaron hopping model solved for the same system gives a qualitatively different result and underestimates the mobility decay at higher temperatures. Taken together, the FOB-SH methodology introduced here shows promise for a realistic investigation of charge carrier transport in complex organic, aqueous, and biological systems.« less

FOB-SH: Fragment orbital-based surface hopping for charge carrier transport in organic and biological molecules and materials

NASA Astrophysics Data System (ADS)

Spencer, J.; Gajdos, F.; Blumberger, J.

2016-08-01

We introduce a fragment orbital-based fewest switches surface hopping method, FOB-SH, designed to efficiently simulate charge carrier transport in strongly fluctuating condensed phase systems such as organic semiconductors and biomolecules. The charge carrier wavefunction is expanded and the electronic Hamiltonian constructed in a set of singly occupied molecular orbitals of the molecular sites that mediate the charge transfer. Diagonal elements of the electronic Hamiltonian (site energies) are obtained from a force field, whereas the off-diagonal or electronic coupling matrix elements are obtained using our recently developed analytic overlap method. We derive a general expression for the exact forces on the adiabatic ground and excited electronic state surfaces from the nuclear gradients of the charge localized electronic states. Applications to electron hole transfer in a model ethylene dimer and through a chain of ten model ethylenes validate our implementation and demonstrate its computational efficiency. On the larger system, we calculate the qualitative behaviour of charge mobility with change in temperature T for different regimes of the intermolecular electronic coupling. For small couplings, FOB-SH predicts a crossover from a thermally activated regime at low temperatures to a band-like transport regime at higher temperatures. For higher electronic couplings, the thermally activated regime disappears and the mobility decreases according to a power law. This is interpreted by a gradual loss in probability for resonance between the sites as the temperature increases. The polaron hopping model solved for the same system gives a qualitatively different result and underestimates the mobility decay at higher temperatures. Taken together, the FOB-SH methodology introduced here shows promise for a realistic investigation of charge carrier transport in complex organic, aqueous, and biological systems.

Effect of anode polarization on biofilm formation and electron transfer in Shewanella oneidensis/graphite felt microbial fuel cells.

PubMed

Pinto, David; Coradin, Thibaud; Laberty-Robert, Christel

2018-04-01

In microbial fuel cells, electricity generation is assumed by bacterial degradation of low-grade organics generating electrons that are transferred to an electrode. The nature and efficiency of the electron transfer from the bacteria to the electrodes are determined by several chemical, physical and biological parameters. Specifically, the application of a specific potential at the bioanode has been shown to stimulate the formation of an electro-active biofilm, but the underlying mechanisms remain poorly understood. In this study, we have investigated the effect of an applied potential on the formation and electroactivity of biofilms established by Shewanella oneidensis bacteria on graphite felt electrodes in single- and double-chamber reactor configurations in oxic conditions. Using amperometry, cyclic voltammetry, and OCP/Power/Polarization curves techniques, we showed that a potential ranging between -0.3V and +0.5V (vs. Ag/AgCl/KCl sat.) and its converse application to a couple of electrodes leads to different electrochemical behaviors, anodic currents and biofilm architectures. For example, when the bacteria were confined in the anodic compartment of a double-chamber cell, a negative applied potential (-0.3V) at the bioanode favors a mediated electron transfer correlated with the progressive formation of a biofilm that fills the felt porosity and bridges the graphite fibers. In contrast, a positive applied potential (+0.3V) at the bioanode stimulates a direct electron transfer resulting in the fast-bacterial colonization of the fibers only. These results provide significant insight for the understanding of the complex bacteria-electrode interactions in microbial fuel cells. Copyright © 2017 Elsevier B.V. All rights reserved.

Styrene-spaced copolymers including anthraquinone and β-O-4 lignin model units: synthesis, characterization and reactivity under alkaline pulping conditions.

PubMed

Megiatto, Jackson D; Cazeils, Emmanuel; Ham-Pichavant, Frédérique; Grelier, Stéphane; Gardrat, Christian; Castellan, Alain

2012-05-14

A series of random copoly(styrene)s has been synthesized via radical polymerization of functionalized anthraquinone (AQ) and β-O-4 lignin model monomers. The copolymers were designed to have a different number of styrene spacer groups between the AQ and β-O-4 lignin side chains aiming at investigating the distance effects on AQ/β-O-4 electron transfer mechanisms. A detailed molecular characterization, including techniques such as size exclusion chromatography, MALDI-TOF mass spectrometry, and (1)H, (13)C, (31)P NMR and UV-vis spectroscopies, afforded quantitative information about the composition of the copolymers as well as the average distribution of the AQ and β-O-4 groups in the macromolecular structures. TGA and DSC thermal analysis have indicated that the copolymers were thermally stable under regular pulping conditions, revealing the inertness of the styrene polymer backbone in the investigation of electron transfer mechanisms. Alkaline pulping experiments showed that close contact between the redox active side chains in the copolymers was fundamental for an efficient degradation of the β-O-4 lignin model units, highlighting the importance of electron transfer reactions in the lignin degradation mechanisms catalyzed by AQ. In the absence of glucose, AQ units oxidized phenolic β-O-4 lignin model parts, mainly by electron transfer leading to vanillin as major product. By contrast, in presence of glucose, anthrahydroquinone units (formed by reduction of AQ) reduced the quinone-methide units (issued by dehydration of phenolic β-O-4 lignin model part) mainly by electron transfer leading to guaiacol as major product. Both processes were distance dependent.

Charge separation and carrier dynamics in donor-acceptor heterojunction photovoltaic systems

PubMed Central

Teuscher, Joël; Brauer, Jan C.; Stepanov, Andrey; Solano, Alicia; Boziki, Ariadni; Chergui, Majed; Wolf, Jean-Pierre; Rothlisberger, Ursula; Banerji, Natalie; Moser, Jacques-E.

2017-01-01

Electron transfer and subsequent charge separation across donor-acceptor heterojunctions remain the most important areas of study in the field of third-generation photovoltaics. In this context, it is particularly important to unravel the dynamics of individual ultrafast processes (such as photoinduced electron transfer, carrier trapping and association, and energy transfer and relaxation), which prevail in materials and at their interfaces. In the frame of the National Center of Competence in Research “Molecular Ultrafast Science and Technology,” a research instrument of the Swiss National Science Foundation, several groups active in the field of ultrafast science in Switzerland have applied a number of complementary experimental techniques and computational simulation tools to scrutinize these critical photophysical phenomena. Structural, electronic, and transport properties of the materials and the detailed mechanisms of photoinduced charge separation in dye-sensitized solar cells, conjugated polymer- and small molecule-based organic photovoltaics, and high-efficiency lead halide perovskite solar energy converters have been scrutinized. Results yielded more than thirty research articles, an overview of which is provided here. PMID:29308415

Scanning electrochemical microscopy based evaluation of influence of pH on bioelectrochemical activity of yeast cells - Saccharomyces cerevisiae.

PubMed

Ramanavicius, A; Morkvenaite-Vilkonciene, I; Kisieliute, A; Petroniene, J; Ramanaviciene, A

2017-01-01

In this research scanning electrochemical microscopy was applied for the investigation of immobilized yeast Saccharomyces cerevisiae cells. Two redox mediators based system was applied in order to increase the efficiency of charge transfer from yeast cells. 9,10-phenanthrenequinone (PQ) was applied as a lipophilic redox mediator, which has the ability to cross the cell's membrane; another redox mediator was ferricyanide, which acted as a hydrophylic electron acceptor able to transfer electrons from the PQ to the working electrode of SECM. Hill's function was applied to determine the optimal pH for this described SECM-based system. The influence of pH on cell viability could be well described by Hill's function. It was determined that at pH 6.5 the PQ has a minimal toxic influence on yeast cells, and the kinetics of metabolic processes in cells as well as electron transfer rate achieved in consecutive action of both redox mediators were appropriate to achieve optimal current signals. Copyright © 2016 Elsevier B.V. All rights reserved.

Electron-transfer reactions in cyanine borate ion pairs: photopolymerization initiators sensitive to visible light

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chatterjee, S.; Gottschalk, P.; Davis, P.D.

1988-03-30

Photoinitiation of polymerization is a process of immense practical, economic, and theoretical importance. In typical examples the polymerization of an acrylate or styrene-derived monomer is initiated by irradiation of a sensitizer with ultraviolet light. The excited state of the sensitizer may dissociate directly to form active free radicals as in the case of the benzoin ethers, or it may first undergo a bimolecular electron-transfer reaction whose products initiate polymerization as is the case in the benzophenone-dimethylaniline system. Efforts to extend the range of useful photoinitiators of free-radical polymerization to the visible region of the spectrum have heretofore met with onlymore » modest success. These special initiators typically are sensitive only to blue light or suffer from thermal instability and have low quantum efficiencies. The authors report herein the discovery that triphenylalkylborate salts of cyanine dyes (Chart I) are photoinitiators of free-radical polymerization whose sensitivity throughout the entire visible spectral region is the result of a novel intra-ion-pair electron-transfer reaction.« less

High-performance blue phosphorescent OLEDs using energy transfer from exciplex.

PubMed

Seino, Yuki; Sasabe, Hisahiro; Pu, Yong-Jin; Kido, Junji

2014-03-12

An efficient energy transfer from an exciplex between a sulfone and an arylamine derivatives to a blue phosphorescent emitter enables OLED performances among the best, of over 50 lm W(-1) at 100 cd m(-2) . The formation of the exciplex realizes a barrier-free hole-electron recombination pathway, thereby leading to high OLED performances with an extremely low driving voltage of 2.9 V at 100 cd m(-2) . © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Photoinduced electron transfer and persistent spectral hole-burning in natural emerald.

PubMed

Riesen, Hans

2011-06-02

Wavelength-selective excited-state lifetime measurements and absorption, luminescence, and hole-burning spectra of a natural African emerald crystal are reported. The (2)E excited-state lifetime displays an extreme wavelength dependence, varying from 190 to 37 μs within 1.8 nm of the R(1)-line. Overall, the excited state is strongly quenched, in comparison to laboratory-created emerald (τ=1.3 ms), with an average quenching rate of ∼6 × 10(3) s(-1) at 2.5 K. This quenching is attributed to photoinduced electron transfer caused by a relatively high concentration of Fe(2+) ions. The forward electron-transfer rate, k(f), from the nearest possible Fe(2+) sites at around 5 Å is estimated to be ∼20 × 10(3) s(-1) at 2.5 K. The photoreductive quenching of the excited Cr(3+) ions by Fe(2+) is followed by rapid electron back-transfer in the ground state upon deactivation. The exchange interaction based quenching can be modeled by assuming a random quencher distribution within the possible Fe(2+) sites with the forward electron-transfer rate, k(f), given as a function of acceptor-donor separation R by exp[(R(f)-R)/a(f)]; R(f) and a(f) values of 13.5 and 2.7 Å are obtained at 2.5 K. The electron transfer/back-transfer reorganizes the local crystal lattice, occasionally leading to a minor variation of the short-range structure around the Cr(3+) ions. This provides a mechanism for spectral hole-burning for which a moderately high quantum efficiency of about ∼0.005% is observed. Spectral holes are subject to spontaneous hole-filling and spectral diffusion, and both effects can be quantified within the standard two-level systems for non-photochemical hole-burning. Importantly, the absorbance increases on both sides of broad spectral holes, and isosbestic points are observed, in accord with the expected distribution of the "photoproduct" in a non-photochemical hole-burning process. © 2011 American Chemical Society

Biofuel Cells Select for Microbial Consortia That Self-Mediate Electron Transfer

PubMed Central

Rabaey, Korneel; Boon, Nico; Siciliano, Steven D.; Verhaege, Marc; Verstraete, Willy

2004-01-01

Microbial fuel cells hold great promise as a sustainable biotechnological solution to future energy needs. Current efforts to improve the efficiency of such fuel cells are limited by the lack of knowledge about the microbial ecology of these systems. The purposes of this study were (i) to elucidate whether a bacterial community, either suspended or attached to an electrode, can evolve in a microbial fuel cell to bring about higher power output, and (ii) to identify species responsible for the electricity generation. Enrichment by repeated transfer of a bacterial consortium harvested from the anode compartment of a biofuel cell in which glucose was used increased the output from an initial level of 0.6 W m−2 of electrode surface to a maximal level of 4.31 W m−2 (664 mV, 30.9 mA) when plain graphite electrodes were used. This result was obtained with an average loading rate of 1 g of glucose liter−1 day−1 and corresponded to 81% efficiency for electron transfer from glucose to electricity. Cyclic voltammetry indicated that the enhanced microbial consortium had either membrane-bound or excreted redox components that were not initially detected in the community. Dominant species of the enhanced culture were identified by denaturing gradient gel electrophoresis and culturing. The community consisted mainly of facultative anaerobic bacteria, such as Alcaligenes faecalis and Enterococcus gallinarum, which are capable of hydrogen production. Pseudomonas aeruginosa and other Pseudomonas species were also isolated. For several isolates, electrochemical activity was mainly due to excreted redox mediators, and one of these mediators, pyocyanin produced by P. aeruginosa, could be characterized. Overall, the enrichment procedure, irrespective of whether only attached or suspended bacteria were examined, selected for organisms capable of mediating the electron transfer either by direct bacterial transfer or by excretion of redox components. PMID:15345423

The Development of Layered Photonic Band Gap Structures Using a Micro-Transfer Molding Technique

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sutherland, Kevin Jerome

Photonic band gap (PBG) crystals are periodic dielectric structures that manipulate electromagnetic radiation in a manner similar to semiconductor devices manipulating electrons. Whereas a semiconductor material exhibits an electronic band gap in which electrons cannot exist, similarly, a photonic crystal containing a photonic band gap does not allow the propagation of specific frequencies of electromagnetic radiation. This phenomenon results from the destructive Bragg diffraction interference that a wave propagating at a specific frequency will experience because of the periodic change in dielectric permitivity. This gives rise to a variety of optical applications for improving the efficiency and effectiveness of opto-electronicmore » devices. These applications are reviewed later. Several methods are currently used to fabricate photonic crystals, which are also discussed in detail. This research involves a layer-by-layer micro-transfer molding ({mu}TM) and stacking method to create three-dimensional FCC structures of epoxy or titania. The structures, once reduced significantly in size can be infiltrated with an organic gain media and stacked on a semiconductor to improve the efficiency of an electronically pumped light-emitting diode. Photonic band gap structures have been proven to effectively create a band gap for certain frequencies of electro-magnetic radiation in the microwave and near-infrared ranges. The objective of this research project was originally two-fold: to fabricate a three dimensional (3-D) structure of a size scaled to prohibit electromagnetic propagation within the visible wavelength range, and then to characterize that structure using laser dye emission spectra. As a master mold has not yet been developed for the micro transfer molding technique in the visible range, the research was limited to scaling down the length scale as much as possible with the current available technology and characterizing these structures with other methods.« less

Light harvesting and charge management by Ni4S3 modified metal-organic frameworks and rGO in the process of photocatalysis.

PubMed

Liu, Duanduan; Jin, Zhiliang; Zhang, Yongke; Wang, Guorong; Ma, Bingzhen

2018-06-01

Harvesting and charge management is obtained by means of Ni 4 S 3 modified Metal-organic Frameworks (MOF) and rGO, namely, the Uio-66 (Zr)/rGO combined with Ni 4 S 3 photocatalyst was successfully prepared with the solvothermal method. The Ni 4 S 3 acted as the electron transfer agent greatly improve the electrons transmission from the excited state dye to the rGO/MOF surface for proton reduction reaction. The hydrogen production amount over EY-sensitized rGO/MOF/Ni 4 S 3 photocatalyst has reached 280 μmol for 5 h, which is about 14 times than that of the pure Ni 4 S 3 photocatalyst and 185 times than that of the pure rGO/MOF photocatalyst under visible light irradiation (λ ≥ 420 nm). In the composite, the rGO acts as electron-transfer mediator and Ni 4 S 3 serves as H 2 -evolution active site. A series of studies shown that the Ni 4 S 3 modified MOF and rGO provided more active sites and improved the efficiency of photo-generated charge separation by means of several characterizations such as SEM, XRD, XPS, Element Mapping, UV-vis DRS, BET, Photocurrent, Voltammetric Scanning, Fluorescence Spectra and FTIR. and the results of which were in good agreement with each other. The photoelectron migration rate and photogenerated charge separation efficiency of the composite can be obviously increased with graphene as a good electron acceptor and transfer medium and Ni 4 S 3 as hydrogen producing active site. Copyright © 2018 Elsevier Inc. All rights reserved.

Heterogeneous electron transfer of a two-centered heme protein: redox and electrocatalytic properties of surface-immobilized cytochrome C(4).

PubMed

Monari, Stefano; Battistuzzi, Gianantonio; Borsari, Marco; Di Rocco, Giulia; Martini, Laura; Ranieri, Antonio; Sola, Marco

2009-10-15

The recombinant diheme cytochrome c(4) from the psycrophilic bacterium Pseudoalteromonas haloplanktis TAC 125 and its Met64Ala and Met164Ala variants, which feature a hydroxide ion axially bound to the heme iron at the N- and C-terminal domains, respectively, were found to exchange electrons efficiently with a gold electrode coated with a SAM of 11-mercapto-1-undecanoic acid. The mutation-induced removal of the redox equivalence of the two heme groups and changes in the net charge of the protein lobes yield two-centered protein systems with unprecedented properties in the electrode-immobilized state. The heterogeneous and intraheme electron transfer processes were characterized for these species in which the high- and low-potential heme groups are swapped over in the bilobal protein framework and experience a constrained (M64A) and unconstrained (M164A) orientation toward the electrode. The reduction thermodynamics for the native and mutated hemes were measured for the first time for a diheme cytochrome c. In the diffusing regime, they reproduce closely those for the corresponding centers in single-heme class-I cytochromes c, despite the low sequence identity. Larger differences are observed in the thermodynamics of the immobilized species and in the heterogeneous electron transfer rate constants. T-dependent kinetic measurements show that the proteins are positioned approximately 7 A from the HOOC-terminated SAM-coated electrode. Protein-electrode orientation and efficient intraheme ET enable the His,OH(-)-ligated heme A of the immobilized Met64Ala variant to carry out the reductive electrocatalysis of molecular oxygen. This system therefore constitutes a novel two-centered heme-based biocatalytic interface to be exploited for "third-generation" amperometric biosensing.

Ab Initio Simulation of Charge Transfer at the Semiconductor Quantum Dot/TiO 2 Interface in Quantum Dot-Sensitized Solar Cells

DOE PAGES

Xin, Xukai; Li, Bo; Jung, Jaehan; ...

2014-07-24

Quantum dot-sensitized solar cells (QDSSCs) have emerged as a promising solar architecture for next-generation solar cells. The QDSSCs exhibit a remarkably fast electron transfer from the quantum dot (QD) donor to the TiO 2 acceptor with size quantization properties of QDs that allows for the modulation of band energies to control photoresponse and photoconversion efficiency of solar cells. In order to understand the mechanisms that underpin this rapid charge transfer, the electronic properties of CdSe and PbSe QDs with different sizes on the TiO 2 substrate are simulated using a rigorous ab initio density functional method. Our method capitalizes onmore » localized orbital basis set, which is computationally less intensive. Quite intriguingly, a remarkable set of electron bridging states between QDs and TiO 2 occurring via the strong bonding between the conduction bands of QDs and TiO 2 is revealed. Such bridging states account for the fast adiabatic charge transfer from the QD donor to the TiO 2 acceptor, and may be a general feature for strongly coupled donor/acceptor systems. All the QDs/TiO 2 systems exhibit type II band alignments, with conduction band offsets that increase with the decrease in QD size. This facilitates the charge transfer from QDs donors to TiO 2 acceptors and explains the dependence of the increased charge transfer rate with the decreased QD size.« less

Molecular dynamics and charge transport in organic semiconductors: a classical approach to modeling electron transfer

DOE PAGES

Pelzer, Kenley M.; Vázquez-Mayagoitia, Álvaro; Ratcliff, Laura E.; ...

2017-01-01

Organic photovoltaics (OPVs) are a promising carbon-neutral energy conversion technology, with recent improvements pushing power conversion efficiencies over 10%. A major factor limiting OPV performance is inefficiency of charge transport in organic semiconducting materials (OSCs). Due to strong coupling with lattice degrees of freedom, the charges form polarons, localized quasi-particles comprised of charges dressed with phonons. These polarons can be conceptualized as pseudo-atoms with a greater effective mass than a bare charge. Here we propose that due to this increased mass, polarons can be modeled with Langevin molecular dynamics (LMD), a classical approach with a computational cost much lower thanmore » most quantum mechanical methods. Here we present LMD simulations of charge transfer between a pair of fullerene molecules, which commonly serve as electron acceptors in OSCs. We find transfer rates consistent with experimental measurements of charge mobility, suggesting that this method may provide quantitative predictions of efficiency when used to simulate materials on the device scale. Our approach also offers information that is not captured in the overall transfer rate or mobility: in the simulation data, we observe exactly when and why intermolecular transfer events occur. In addition, we demonstrate that these simulations can shed light on the properties of polarons in OSCs. In conclusion, much remains to be learned about these quasi-particles, and there are no widely accepted methods for calculating properties such as effective mass and friction. Lastly, our model offers a promising approach to exploring mass and friction as well as providing insight into the details of polaron transport in OSCs.« less

Different electronic and charge-transport properties of four organic semiconductors Tetraazaperopyrenes derivatives

NASA Astrophysics Data System (ADS)

Shi, Yarui; Wei, Huiling; Liu, Yufang

2015-03-01

Tetraazaperopyrenes (TAPPs) derivatives are high-performance n-type organic semiconductor material families with the remarkable long-term stabilities. The charge carrier mobilities in TAPPs derivatives crystals were calculated by the density functional theory (DFT) method combined with the Marcus-Hush electron-transfer theory. The existence of considerable C-H…F-C bonding defines the conformation of the molecular structure and contributes to its stability. We illustrated how it is possible to control the electronic and charge-transport parameters of TAPPs derivatives as a function of the positions, a type of the substituents. It is found that the core substitution of TAPPs has a drastic influence on the charge-transport mobilities. The maximum electron mobility value of the core-brominated 2,9-bis (perfluoroalkyl)-substituted TAPPs is 0.521 cm2 V-1 s-1, which appear in the orientation angle 95° and 275°. The results demonstrate that the TAPPs with bromine substituents in ortho positions exhibit the best charge-transfer efficiency among the four different TAPP derivatives.

Active space debris charging for contactless electrostatic disposal maneuvers

NASA Astrophysics Data System (ADS)

Schaub, Hanspeter; Sternovsky, Zoltán

2014-01-01

The remote charging of a passive object using an electron beam enables touchless re-orbiting of large space debris from geosynchronous orbit (GEO) using electrostatic forces. The advantage of this method is that it can operate with a separation distance of multiple craft radii, thus reducing the risk of collision. The charging of the tug-debris system to high potentials is achieved by active charge transfer using a directed electron beam. Optimal potential distributions using isolated- and coupled-sphere models are discussed. A simple charging model takes into account the primary electron beam current, ultra-violet radiation induced photoelectron emission, collection of plasma particles, secondary electron emission and the recapture of emitted particles. The results show that through active charging in a GEO space environment high potentials can be both achieved and maintained with about a 75% transfer efficiency. Further, the maximum electrostatic tractor force is shown to be insensitive to beam current levels. This latter later result is important when considering debris with unknown properties.

Local light-induced magnetization using nanodots and chiral molecules.

PubMed

Dor, Oren Ben; Morali, Noam; Yochelis, Shira; Baczewski, Lech Tomasz; Paltiel, Yossi

2014-11-12

With the increasing demand for miniaturization, nanostructures are likely to become the primary components of future integrated circuits. Different approaches are being pursued toward achieving efficient electronics, among which are spin electronics devices (spintronics). In principle, the application of spintronics should result in reducing the power consumption of electronic devices. Recently a new, promising, effective approach for spintronics has emerged, using spin selectivity in electron transport through chiral molecules. In this work, using chiral molecules and nanocrystals, we achieve local spin-based magnetization generated optically at ambient temperatures. Through the chiral layer, a spin torque can be transferred without permanent charge transfer from the nanocrystals to a thin ferromagnetic layer, creating local perpendicular magnetization. We used Hall sensor configuration and atomic force microscopy (AFM) to measure the induced local magnetization. At low temperatures, anomalous spin Hall effects were measured using a thin Ni layer. The results may lead to optically controlled spintronics logic devices that will enable low power consumption, high density, and cheap fabrication.

Charge Transfer Reactions

NASA Astrophysics Data System (ADS)

Dennerl, Konrad

2010-12-01

Charge transfer, or charge exchange, describes a process in which an ion takes one or more electrons from another atom. Investigations of this fundamental process have accompanied atomic physics from its very beginning, and have been extended to astrophysical scenarios already many decades ago. Yet one important aspect of this process, i.e. its high efficiency in generating X-rays, was only revealed in 1996, when comets were discovered as a new class of X-ray sources. This finding has opened up an entirely new field of X-ray studies, with great impact due to the richness of the underlying atomic physics, as the X-rays are not generated by hot electrons, but by ions picking up electrons from cold gas. While comets still represent the best astrophysical laboratory for investigating the physics of charge transfer, various studies have already spotted a variety of other astrophysical locations, within and beyond our solar system, where X-rays may be generated by this process. They range from planetary atmospheres, the heliosphere, the interstellar medium and stars to galaxies and clusters of galaxies, where charge transfer may even be observationally linked to dark matter. This review attempts to put the various aspects of the study of charge transfer reactions into a broader historical context, with special emphasis on X-ray astrophysics, where the discovery of cometary X-ray emission may have stimulated a novel look at our universe.

Enhancing Bidirectional Electron Transfer of Shewanella oneidensis by a Synthetic Flavin Pathway.

PubMed

Yang, Yun; Ding, Yuanzhao; Hu, Yidan; Cao, Bin; Rice, Scott A; Kjelleberg, Staffan; Song, Hao

2015-07-17

Flavins regulate the rate and direction of extracellular electron transfer (EET) in Shewanella oneidensis. However, low concentration of endogenously secreted flavins by the wild-type S. oneidensis MR-1 limits its EET efficiency in bioelectrochemical systems (BES). Herein, a synthetic flavin biosynthesis pathway from Bacillus subtilis was heterologously expressed in S. oneidensis MR-1, resulting in ∼25.7 times' increase in secreted flavin concentration. This synthetic flavin module enabled enhanced bidirectional EET rate of MR-1, in which its maximum power output in microbial fuel cells increased ∼13.2 times (from 16.4 to 233.0 mW/m(2)), and the inward current increased ∼15.5 times (from 15.5 to 255.3 μA/cm(2)).

Free energy landscape of electrocatalytic CO2 reduction to CO on aqueous FeN4 center embedded graphene studied by ab initio molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Sheng, Tian; Sun, Shi-Gang

2017-11-01

Experiments have found that the porphyrin-like FeN4 site in Fe-N-C materials is highly efficient for the electrochemical reduction of CO2 into CO. In this work, we investigated the reduction mechanisms on FeN4 embedded graphene layer catalyst with some explicit water molecules by combining the constrained ab initio molecular dynamics simulations and thermodynamic integrations. The reaction free energy and electron transfer in each elementary step were identified. The initial CO2 activation was identified to go through the first electron transfer to form adsorbed CO2- anion and the CO desorption was the rate limiting step in the overall catalytic cycle.

Theoretical insights into multiscale electronic processes in organic photovoltaics

NASA Astrophysics Data System (ADS)

Tretiak, Sergei

Present day electronic devices are enabled by design and implementation of precise interfaces that control the flow of charge carriers. This requires robust and predictive multiscale approaches for theoretical description of underlining complex phenomena. Combined with thorough experimental studies such approaches provide a reliable estimate of physical properties of nanostructured materials and enable a rational design of devices. From this perspective I will discuss first principle modeling of small-molecule bulk-heterojunction organic solar cells and push-pull chromophores for tunable-color organic light emitters. The emphasis is on electronic processes involving intra- and intermolecular energy or charge transfer driven by strong electron-phonon coupling inherent to pi-conjugated systems. Finally I will describe how precise manipulation and control of organic-organic interfaces in a photovoltaic device can increase its power conversion efficiency by 2-5 times in a model bilayer system. Applications of these design principles to practical architectures like bulk heterojunction devices lead to an enhancement in power conversion efficiency from 4.0% to 7.0%. These interface manipulation strategies are universally applicable to any donor-acceptor interface, making them both fundamentally interesting and technologically important for achieving high efficiency organic electronic devices.

High-efficient photo-electron transport channel in SiC constructed by depositing cocatalysts selectively on specific surface sites for visible-light H{sub 2} production

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Da; Peng, Yuan; Wang, Qi

2016-04-18

Control cocatalyst location on a metal-free semiconductor to promote surface charge transfer for decreasing the electron-hole recombination is crucial for enhancing solar energy conversion. Based on the findings that some metals have an affinity for bonding with the specific atoms of polar semiconductors at a heterostructure interface, we herein control Pt deposition selectively on the Si sites of a micro-SiC photocatalyst surface via in-situ photo-depositing. The Pt-Si bond forming on the interface constructs an excellent channel, which is responsible for accelerating photo-electron transfer from SiC to Pt and then reducing water under visible-light. The hydrogen production is enhanced by twomore » orders of magnitude higher than that of bare SiC, and 2.5 times higher than that of random-depositing nano-Pt with the same loading amount.« less

Layered-metal-hydroxide nanosheet arrays with controlled nanostructures to assist direct electronic communication at biointerfaces.

PubMed

An, Zhe; Lu, Shan; Zhao, Liwei; He, Jing

2011-10-18

In this work, ordered vertical arrays of layered double hydroxide (LDH) nanosheets have been developed to achieve electron transfer (eT) at biointerfaces in electrochemical devices. It is found that tailoring the gap size of LDH nanosheet arrays could significantly promote the eT rate. This research has successfully extended nanomaterials for efficient modifications of electrode surfaces from nanoparticles, nanowires, nanorods, and nanotubes to nanosheets. © 2011 American Chemical Society

Does the position of the electron-donating nitrogen atom in the ring system influence the efficiency of a dye-sensitized solar cell? A computational study.

PubMed

Biswas, Abul Kalam; Barik, Sunirmal; Das, Amitava; Ganguly, Bishwajit

2016-06-01

We have reported a number of new metal-free organic dyes (2-6) that have cyclic asymmetric benzotripyrrole derivatives as donor groups with peripheral nitrogen atoms in the ring, fluorine and thiophene groups as π-spacers, and a cyanoacrylic acid acceptor group. Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations were employed to examine the influence of the position of the donor nitrogen atom and π-conjugation on solar cell performance. The calculated electron-injection driving force (ΔG inject), electron-regeneration driving force (ΔG regen), light-harvesting efficiency (LHE), dipole moment (μ normal), and number of electrons transferred (∆q) indicate that dyes 3, 4, and 6 have significantly higher efficiencies than reference dye 1, which exhibits high efficiency. We also extended our comparison to some other reported dyes, 7-9, which have a donor nitrogen atom in the middle of the ring system. The computed results suggest that dye 6 possesses a higher incident photon to current conversion efficiency (IPCE) than reported dyes 7-9. Thus, the use of donor groups with peripheral nitrogen atoms appears to lead to more efficient dyes than those in which the nitrogen atom is present in the middle of the donor ring system. Graphical Abstract The locations of the nitrogen atoms in the donor groups in the designed dye molecules have an important influence on DSSC efficiency.

Photo-electrochemical properties of graphene wrapped hierarchically branched nanostructures obtained through hydrothermally transformed TiO2 nanotubes

NASA Astrophysics Data System (ADS)

Rambabu, Y.; Jaiswal, Manu; Roy, Somnath C.

2017-10-01

Hierarchically structured nanomaterials play an important role in both light absorption and separation of photo-generated charges. In the present study, hierarchically branched TiO2 nanostructures (HB-MLNTs) are obtained through hydrothermal transformation of electrochemically anodized TiO2 multi-leg nanotubes (MLNT) arrays. Photo-anodes based on HB-MLNTs demonstrated 5 fold increase in applied bias to photo-conversion efficiency (%ABPE) over that of TiO2 MLNTs without branches. Further, such nanostructures are wrapped with reduced graphene oxide (rGO) films to enhance the charge separation, which resulted in ∼6.5 times enhancement in %ABPE over that of bare MLNTs. We estimated charge transport (η tr) and charge transfer (η ct) efficiencies by analyzing the photo-current data. The ultra-fine nano branches grown on the MLNTs are effective in increasing light absorption through multiple scattering and improving charge transport/transfer efficiencies by enlarging semiconductor/electrolyte interface area. The charge transfer resistance, interfacial capacitance and electron decay time have been estimated through electrochemical impedance measurements which correlate with the results obtained from photocurrent measurements.

Energy Transfer Kinetics in Photosynthesis as an Inspiration for Improving Organic Solar Cells.

PubMed

Nganou, Collins; Lackner, Gerhard; Teschome, Bezu; Deen, M Jamal; Adir, Noam; Pouhe, David; Lupascu, Doru C; Mkandawire, Martin

2017-06-07

Clues to designing highly efficient organic solar cells may lie in understanding the architecture of light-harvesting systems and exciton energy transfer (EET) processes in very efficient photosynthetic organisms. Here, we compare the kinetics of excitation energy tunnelling from the intact phycobilisome (PBS) light-harvesting antenna system to the reaction center in photosystem II in intact cells of the cyanobacterium Acaryochloris marina with the charge transfer after conversion of photons into photocurrent in vertically aligned carbon nanotube (va-CNT) organic solar cells with poly(3-hexyl)thiophene (P3HT) as the pigment. We find that the kinetics in electron hole creation following excitation at 600 nm in both PBS and va-CNT solar cells to be 450 and 500 fs, respectively. The EET process has a 3 and 14 ps pathway in the PBS, while in va-CNT solar cell devices, the charge trapping in the CNT takes 11 and 258 ps. We show that the main hindrance to efficiency of va-CNT organic solar cells is the slow migration of the charges after exciton formation.

Advanced Chemical Design for Efficient Lignin Bioconversion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xie, Shangxian; Sun, Qining; Pu, Yunqiao

Here, lignin depolymerization mainly involves redox reactions relying on the effective electron transfer. Even though electron mediators were previously used for delignification of paper pulp, no study has established a bioprocess to fragment and solubilize the lignin with an effective laccase–mediator system, in particular, for subsequent microbial bioconversion. Efficient lignin depolymerization was achieved by screening proper electron mediators with laccase to attain a nearly 6-fold increase of kraft lignin solubility compared to the control kraft lignin without laccase treatment. Chemical analysis suggested the release of a low molecular weight fraction of kraft lignin into the solution phase. Moreover, NMR analysismore » revealed that an efficient enzyme–mediator system can promote the lignin degradation. More importantly, the fundamental mechanisms guided the development of an efficient lignin bioconversion process, where solubilized lignin from laccase–HBT treatment served as a superior substrate for bioconversion by Rhodococcus opacus PD630. The cell growth was increased by 10 6 fold, and the lipid titer reached 1.02 g/L. Overall, the study has manifested that an efficient enzyme–mediator–microbial system can be exploited to establish a bioprocess to solubilize lignin, cleave lignin linkages, modify the structure, and produce substrates amenable to bioconversion.« less

Advanced Chemical Design for Efficient Lignin Bioconversion

DOE PAGES

Xie, Shangxian; Sun, Qining; Pu, Yunqiao; ...

2017-01-30

Here, lignin depolymerization mainly involves redox reactions relying on the effective electron transfer. Even though electron mediators were previously used for delignification of paper pulp, no study has established a bioprocess to fragment and solubilize the lignin with an effective laccase–mediator system, in particular, for subsequent microbial bioconversion. Efficient lignin depolymerization was achieved by screening proper electron mediators with laccase to attain a nearly 6-fold increase of kraft lignin solubility compared to the control kraft lignin without laccase treatment. Chemical analysis suggested the release of a low molecular weight fraction of kraft lignin into the solution phase. Moreover, NMR analysismore » revealed that an efficient enzyme–mediator system can promote the lignin degradation. More importantly, the fundamental mechanisms guided the development of an efficient lignin bioconversion process, where solubilized lignin from laccase–HBT treatment served as a superior substrate for bioconversion by Rhodococcus opacus PD630. The cell growth was increased by 10 6 fold, and the lipid titer reached 1.02 g/L. Overall, the study has manifested that an efficient enzyme–mediator–microbial system can be exploited to establish a bioprocess to solubilize lignin, cleave lignin linkages, modify the structure, and produce substrates amenable to bioconversion.« less

Heterogeneous Single-Atom Catalyst for Visible-Light-Driven High-Turnover CO2 Reduction: The Role of Electron Transfer.

PubMed

Gao, Chao; Chen, Shuangming; Wang, Ying; Wang, Jiawen; Zheng, Xusheng; Zhu, Junfa; Song, Li; Zhang, Wenkai; Xiong, Yujie

2018-03-01

Visible-light-driven conversion of CO 2 into chemical fuels is an intriguing approach to address the energy and environmental challenges. In principle, light harvesting and catalytic reactions can be both optimized by combining the merits of homogeneous and heterogeneous photocatalysts; however, the efficiency of charge transfer between light absorbers and catalytic sites is often too low to limit the overall photocatalytic performance. In this communication, it is reported that the single-atom Co sites coordinated on the partially oxidized graphene nanosheets can serve as a highly active and durable heterogeneous catalyst for CO 2 conversion, wherein the graphene bridges homogeneous light absorbers with single-atom catalytic sites for the efficient transfer of photoexcited electrons. As a result, the turnover number for CO production reaches a high value of 678 with an unprecedented turnover frequency of 3.77 min -1 , superior to those obtained with the state-of-the-art heterogeneous photocatalysts. This work provides fresh insights into the design of catalytic sites toward photocatalytic CO 2 conversion from the angle of single-atom catalysis and highlights the role of charge kinetics in bridging the gap between heterogeneous and homogeneous photocatalysts. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Artificial photosynthetic antennas and reaction centers

DOE PAGES

Llansola-Portoles, Manuel J.; Gust, Devens; Moore, Thomas A.; ...

2017-03-01

Presently, the world is experiencing an unprecedented crisis associated with the CO2 produced by the use of fossil fuels to power our economies. As evidenced by the increasing levels in the atmosphere, the reduction of CO2 to biomass by photosynthesis cannot keep pace with production with the result that nature has lost control of the global carbon cycle. In order to restore control of the global carbon cycle to solar-driven processes, highly efficient artificial photosynthesis can augment photosynthesis in specific ways and places. The increased efficiency of artificial photosynthesis can provide both renewable carbon-based fuels and lower net atmospheric levelsmore » of CO2, which will preserve land and support the ecosystem services upon which all life on Earth depends. The development of artificial photosynthetic antennas and reaction centers contributes to the understanding of natural photosynthesis and to the knowledge base necessary for the development of future scalable technologies. This review focuses on the design and study of molecular and hybrid molecular-semiconductor nanoparticle based systems, all of which are inspired by functions found in photosynthesis and some of which are inspired by components of photosynthesis. In addition to constructs illustrating energy transfer, photoinduced electron transfer, charge shift reactions and proton coupled electron transfer, our review covers systems that produce proton motive force.« less

Energy relay from an unconventional yellow dye to CdS/CdSe quantum dots for enhanced solar cell performance.

PubMed

Narayanan, Remya; Das, Amrita; Deepa, Melepurath; Srivastava, Avanish Kumar

2013-12-02

A new design for a quasi-solid-state Forster resonance energy transfer (FRET) enabled solar cell with unattached Lucifer yellow (LY) dye molecules as donors and CdS/CdSe quantum dots (QDs) tethered to titania (TiO2 ) as acceptors is presented. The Forster radius is experimentally determined to be 5.29 nm. Sequential energy transfer from the LY dye to the QDs and electron transfer from the QDs to TiO2 is followed by fluorescence quenching and electron lifetime studies. Cells with a donor-acceptor architecture (TiO2 /CdS/CdSe/ZnS-LY/S(2-)-multi-walled carbon nanotubes) show a maximum incident photon-to-current conversion efficiency of 53 % at 530 nm. This is the highest efficiency among Ru-dye free FRET-enabled quantum dot solar cells (QDSCs), and is much higher than the donor or acceptor-only cells. The FRET-enhanced solar cell performance over the majority of the visible spectrum paves the way to harnessing the untapped potential of the LY dye as an energy relay fluorophore for the entire gamut of dye sensitized, organic, or hybrid solar cells. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Artificial photosynthetic antennas and reaction centers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Llansola-Portoles, Manuel J.; Gust, Devens; Moore, Thomas A.

Presently, the world is experiencing an unprecedented crisis associated with the CO2 produced by the use of fossil fuels to power our economies. As evidenced by the increasing levels in the atmosphere, the reduction of CO2 to biomass by photosynthesis cannot keep pace with production with the result that nature has lost control of the global carbon cycle. In order to restore control of the global carbon cycle to solar-driven processes, highly efficient artificial photosynthesis can augment photosynthesis in specific ways and places. The increased efficiency of artificial photosynthesis can provide both renewable carbon-based fuels and lower net atmospheric levelsmore » of CO2, which will preserve land and support the ecosystem services upon which all life on Earth depends. The development of artificial photosynthetic antennas and reaction centers contributes to the understanding of natural photosynthesis and to the knowledge base necessary for the development of future scalable technologies. This review focuses on the design and study of molecular and hybrid molecular-semiconductor nanoparticle based systems, all of which are inspired by functions found in photosynthesis and some of which are inspired by components of photosynthesis. In addition to constructs illustrating energy transfer, photoinduced electron transfer, charge shift reactions and proton coupled electron transfer, our review covers systems that produce proton motive force.« less

Hot Charge Carrier Transmission from Plasmonic Nanostructures

NASA Astrophysics Data System (ADS)

Christopher, Phillip; Moskovits, Martin

2017-05-01

Surface plasmons have recently been harnessed to carry out processes such as photovoltaic current generation, redox photochemistry, photocatalysis, and photodetection, all of which are enabled by separating energetic (hot) electrons and holes—processes that, previously, were the domain of semiconductor junctions. Currently, the power conversion efficiencies of systems using plasmon excitation are low. However, the very large electron/hole per photon quantum efficiencies observed for plasmonic devices fan the hope of future improvements through a deeper understanding of the processes involved and through better device engineering, especially of critical interfaces such as those between metallic and semiconducting nanophases (or adsorbed molecules). In this review, we focus on the physics and dynamics governing plasmon-derived hot charge carrier transfer across, and the electronic structure at, metal-semiconductor (molecule) interfaces, where we feel the barriers contributing to low efficiencies reside. We suggest some areas of opportunity that deserve early attention in the still-evolving field of hot carrier transmission from plasmonic nanostructures to neighboring phases.

Photoanode Thickness Optimization and Impedance Spectroscopic Analysis of Dye-Sensitized Solar Cells based on a Carbazole-Containing Ruthenium Dye

NASA Astrophysics Data System (ADS)

Choi, Jongwan; Kim, Felix Sunjoo

2018-03-01

We studied the influence of photoanode thickness on the photovoltaic characteristics and impedance responses of the dye-sensitized solar cells based on a ruthenium dye containing a hexyloxyl-substituted carbazole unit (Ru-HCz). As the thickness of photoanode increases from 4.2 μm to 14.8 μm, the dye-loading amount and the efficiency increase. The device with thicker photoanode shows a decrease in the efficiency due to the higher probability of recombination of electron-hole pairs before charge extraction. We also analyzed the electron-transfer and recombination characteristics as a function of photoanode thickness through detailed electrochemical impedance spectroscopy analysis.

Design of an efficient photoanode for dye-sensitized solar cells using electrospun one-dimensional GO/N-doped nanocomposite SnO2/TiO2

NASA Astrophysics Data System (ADS)

Mohamed, Ibrahim M. A.; Dao, Van-Duong; Yasin, Ahmed S.; Barakat, Nasser A. M.; Choi, Ho-Suk

2017-04-01

This study presents the combination of N, graphene oxide (GO) and SnO2 as efficient dopants into TiO2 nanofibers (NFs) photoanode substrate for highly efficient dye-sensitized solar cells (DSCs). The developed NFs are synthesized by electrospinning and hydrothermal processes and characterized by FESEM, TEM, XPS, FT-IR, Raman and EDX-studies. The formation of short NFs is confirmed through FESEM and TEM measurements. As the results, the major crystal structure of TiO2 in the prepared NFs has anatase (85.23%) and rutile-structure (14.67%). XPS and EDX studies affirm that the material has Ti, O, Sn, N and C elements. In addition, FT-IR and Raman spectra give an indication about the GO-content. Typically, the DSC based on the novel NFs shows 6.18% efficiency. The Jsc, Voc, FF and Rct are estimated and found to be 10.32 mA cm-2, 0.825 V, 0.73 and 21.66 Ω, respectively. The high-power efficiency is contributed by three reasons. The first one is the high dye-loading (2.16 × 10-7 mol cm-2). The second reason is the enhanced charge transfer and decreasing of the electrons/holes recombination through formation of wide band-gap oxide (3.246 eV). Finally, the third one is GO-doping which may create new routes for the electron transfer in working electrode layer.

Enhancing stability and efficiency of perovskite solar cells with crosslinkable silane-functionalized and doped fullerene

DOE PAGES

Bai, Yang; Dong, Qingfeng; Shao, Yuchuan; ...

2016-10-05

The instability of hybrid perovskite materials due to water and moisture arises as one major challenge to be addressed before any practical application of the demonstrated high efficiency perovskite solar cells. Here we report a facile strategy that can simultaneously enhance the stability and efficiency of p-i-n planar heterojunction-structure perovskite devices. Crosslinkable silane molecules with hydrophobic functional groups are bonded onto fullerene to make the fullerene layer highly water-resistant. Methylammonium iodide is introduced in the fullerene layer for n-doping via anion-induced electron transfer, resulting in dramatically increased conductivity over 100-fold. With crosslinkable silane-functionalized and doped fullerene electron transport layer, themore » perovskite devices deliver an efficiency of 19.5% with a high fill factor of 80.6%. Furthermore, a crosslinked silane-modified fullerene layer also enhances the water and moisture stability of the non-sealed perovskite devices by retaining nearly 90% of their original efficiencies after 30 days’ exposure in an ambient environment.« less

Enhancing stability and efficiency of perovskite solar cells with crosslinkable silane-functionalized and doped fullerene

PubMed Central

Bai, Yang; Dong, Qingfeng; Shao, Yuchuan; Deng, Yehao; Wang, Qi; Shen, Liang; Wang, Dong; Wei, Wei; Huang, Jinsong

2016-01-01

The instability of hybrid perovskite materials due to water and moisture arises as one major challenge to be addressed before any practical application of the demonstrated high efficiency perovskite solar cells. Here we report a facile strategy that can simultaneously enhance the stability and efficiency of p–i–n planar heterojunction-structure perovskite devices. Crosslinkable silane molecules with hydrophobic functional groups are bonded onto fullerene to make the fullerene layer highly water-resistant. Methylammonium iodide is introduced in the fullerene layer for n-doping via anion-induced electron transfer, resulting in dramatically increased conductivity over 100-fold. With crosslinkable silane-functionalized and doped fullerene electron transport layer, the perovskite devices deliver an efficiency of 19.5% with a high fill factor of 80.6%. A crosslinked silane-modified fullerene layer also enhances the water and moisture stability of the non-sealed perovskite devices by retaining nearly 90% of their original efficiencies after 30 days' exposure in an ambient environment. PMID:27703136

Interface design principles for high-performance organic semiconductor devices

DOE PAGES

Nie, Wanyi; Gupta, Gautam; Crone, Brian K.; ...

2015-03-23

Organic solar cells (OSCs) are a promising cost-effective candidate in next generation photovoltaic technology. However, a critical bottleneck for OSCs is the electron/hole recombination loss through charge transfer state at the interface, which greatly limits the power conversion efficiency. W. Nie, A. Mohite, and co-workers demonstrate a simple strategy of suppressing the recombination rate by inserting a spacer layer at the donor-acceptor interface, resulting in a dramatic increase in power conversion efficiency.

Deposition of thin silicon layers on transferred large area graphene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lupina, Grzegorz, E-mail: lupina@ihp-microelectronics.com; Kitzmann, Julia; Lukosius, Mindaugas

2013-12-23

Physical vapor deposition of Si onto transferred graphene is investigated. At elevated temperatures, Si nucleates preferably on wrinkles and multilayer graphene islands. In some cases, however, Si can be quasi-selectively grown only on the monolayer graphene regions while the multilayer islands remain uncovered. Experimental insights and ab initio calculations show that variations in the removal efficiency of carbon residuals after the transfer process can be responsible for this behavior. Low-temperature Si seed layer results in improved wetting and enables homogeneous growth. This is an important step towards realization of electronic devices in which graphene is embedded between two Si layers.

Enhanced Fenton-like removal of nitrobenzene via internal microelectrolysis in nano zerovalent iron/activated carbon composite.

PubMed

Hu, Sihai; Wu, Yaoguo; Yao, Hairui; Lu, Cong; Zhang, Chengjun

2016-01-01

The efficiency of Fenton-like catalysis using nano zerovalent iron (nZVI) is limited by nZVI aggregation and activity loss due to inactive ferric oxide forming on the nZVI surface, which hinders electron transfer. A novel iron-carbon composite catalyst consisting of nZVI and granular activated carbon (GAC), which can undergo internal iron-carbon microelectrolysis spontaneously, was successfully fabricated by the adsorption-reduction method. The catalyst efficiency was evaluated in nitrobenzene (NB) removal via the Fenton-like process (H2O2-nZVI/GAC). The results showed that nZVI/GAC composite was good for dispersing nZVI on the surface of GAC, which permitted much better removal efficiency (93.0%) than nZVI (31.0%) or GAC (20.0%) alone. Moreover, iron leaching decreased from 1.28 to 0.58 mg/L after reaction of 240 min and the oxidation kinetic of the Fenton-like reaction can be described well by the second-order reaction kinetic model (R2=0.988). The composite catalyst showed sustainable catalytic ability and GAC performed as a medium for electron transfer in internal iron-carbon microelectrolysis to promote Fe2+ regeneration and Fe3+/Fe2+ cycles. Therefore, this study represents an important method to design a low cost and high efficiency Fenton-like catalyst in practical application.

Enhancing extracellular electron transfer between Pseudomonas aeruginosa PAO1 and light driven semiconducting birnessite.

PubMed

Ren, Guiping; Sun, Yuan; Ding, Yang; Lu, Anhuai; Li, Yan; Wang, Changqiu; Ding, Hongrui

2018-06-02

In recent years, considerable research effort has explored the interaction between semiconducting minerals and microorganisms, such relationship is a promising way to increase the efficiency of bioelectrochemical systems. Herein, the enhancement of electron transfer between birnessite photoanodes and Pseudomonas aeruginosa PAO1 under visible light was investigated. Under light illumination and positive bias, the light-birnessite-PAO1 electrochemical system generated a photocurrent of 279.57 μA/cm 2 , which is 322% and 170% higher than those in the abiotic control and dead culture, suggesting photoenhanced electrochemical interaction between birnessite and Pseudomonas. The I-t curves presented repeatable responses to light on/off cycles, and multi-conditions analyses indicated that the enhanced photocurrent was attributed to the additional redox species associated with P. aeruginosa PAO1 and with the biofilm on birnessite. Electroconductibility analysis was conducted on the biofilm cellularly by conductive atomic force microscope. Pyocyanin was isolated as the biosynthesized extracellular shuttle and characterized by cyclic voltammetry and surface-enhanced Raman spectroscopy. Rapid bioelectron transfer driven by light was observed. The results suggest new opportunities for designing photo-bioelectronic devices and expanding our understanding of extracellular electron transfer with semiconducting minerals under light in nature environments. Copyright © 2018. Published by Elsevier B.V.

Exciton Resonances in Novel Silicon Carbide Polymers

NASA Astrophysics Data System (ADS)

Burggraf, Larry; Duan, Xiaofeng

2015-05-01

A revolutionary technology transformation from electronics to excitionics for faster signal processing and computing will be advantaged by coherent exciton transfer at room temperature. The key feature required of exciton components for this technology is efficient and coherent transfer of long-lived excitons. We report theoretical investigations of optical properties of SiC materials having potential for high-temperature excitonics. Using Car-Parinello simulated annealing and DFT we identified low-energy SiC molecular structures. The closo-Si12C12 isomer, the most stable 12-12 isomer below 1100 C, has potential to make self-assembled chains and 2-D nanostructures to construct exciton components. Using TDDFT, we calculated the optical properties of the isomer as well as oligomers and 2-D crystal formed from the isomer as the monomer unit. This molecule has large optical oscillator strength in the visible. Its high-energy and low-energy transitions (1.15 eV and 2.56 eV) are nearly pure one-electron silicon-to-carbon transitions, while an intermediate energy transition (1.28 eV) is a nearly pure carbon-to-silicon one-electron charge transfer. These results are useful to describe resonant, coherent transfer of dark excitons in the nanostructures. Research supported by the Air Force Office of Scientific Research.

MutY: optimized to find DNA damage site electronically?

NASA Astrophysics Data System (ADS)

Lin, Jong-Chin; Cox, Daniel; Singh, Rajiv

2006-03-01

Iron sulfur clusters are present in the DNA repair protein MutY in a region highly homologous in species as diverse as E. Coli and Homo Sapiens, yet their function remains unknown. In MutY, this mixed valence cluster exists in two oxidation states, [Fe4S4]^2+/3+, with the stability depending upon the presence of DNA. We have studied the electronic structure and stability of these clusters using the local orbital based SIESTA implementation of density functional theory. We find that the iron-sulfur cluster in MutY can undergo 2+ to 3+ oxidation when coupling to DNA through hole transfer, especially when MutY is near an oxoguanine modified base(oxoG). Employing the Marcus theory for electron transfer, we find (i) near optimal Frank-Condon(FC) factor for 2+ transfer to oxoG; (ii) reduced FC factor for transfer to G due to a high oxidation potential; (iii) reduced FC factor with the mutation L154F; (iv) reduced tunning matrix element with the mutation R149W. Both L154F and R149W mutations dramatically reduce or eliminate repair efficiency. Hence, redox modulation of MutY search and binding appears plausible and may have broader implications for DNA-protein interactions.

Are hot charge transfer states the primary cause of efficient free-charge generation in polymer:fullerene organic photovoltaic devices? A kinetic Monte Carlo study.

PubMed

Jones, Matthew L; Dyer, Reesha; Clarke, Nigel; Groves, Chris

2014-10-14

Kinetic Monte Carlo simulations are used to examine the effect of high-energy, 'hot' delocalised charge transfer (HCT) states for donor:acceptor and mixed:aggregate blends, the latter relating to polymer:fullerene photovoltaic devices. Increased fullerene aggregation is shown to enhance charge generation and short-circuit device current - largely due to the increased production of HCT states at the aggregate interface. However, the instances where HCT states are predicted to give internal quantum efficiencies in the region of 50% do not correspond to HCT delocalisation or electron mobility measured in experiments. These data therefore suggest that HCT states are not the primary cause of high quantum efficiencies in some polymer:fullerene OPVs. Instead it is argued that HCT states are responsible for the fast charge generation seen in spectroscopy, but that regional variation in energy levels are the cause of long-term, efficient free-charge generation.

Probing and Exploiting the Interplay between Nuclear and Electronic Motion in Charge Transfer Processes.

PubMed

Delor, Milan; Sazanovich, Igor V; Towrie, Michael; Weinstein, Julia A

2015-04-21

The Born-Oppenheimer approximation refers to the assumption that the nuclear and electronic wave functions describing a molecular system evolve and can be determined independently. It is now well-known that this approximation often breaks down and that nuclear-electronic (vibronic) coupling contributes greatly to the ultrafast photophysics and photochemistry observed in many systems ranging from simple molecules to biological organisms. In order to probe vibronic coupling in a time-dependent manner, one must use spectroscopic tools capable of correlating the motions of electrons and nuclei on an ultrafast time scale. Recent developments in nonlinear multidimensional electronic and vibrational spectroscopies allow monitoring both electronic and structural factors with unprecedented time and spatial resolution. In this Account, we present recent studies from our group that make use of different variants of frequency-domain transient two-dimensional infrared (T-2DIR) spectroscopy, a pulse sequence combining electronic and vibrational excitations in the form of a UV-visible pump, a narrowband (12 cm(-1)) IR pump, and a broadband (400 cm(-1)) IR probe. In the first example, T-2DIR is used to directly compare vibrational dynamics in the ground and relaxed electronic excited states of Re(Cl)(CO)3(4,4'-diethylester-2,2'-bipyridine) and Ru(4,4'-diethylester-2,2'-bipyridine)2(NCS)2, prototypical charge transfer complexes used in photocatalytic CO2 reduction and electron injection in dye-sensitized solar cells. The experiments show that intramolecular vibrational redistribution (IVR) and vibrational energy transfer (VET) are up to an order of magnitude faster in the triplet charge transfer excited state than in the ground state. These results show the influence of electronic arrangement on vibrational coupling patterns, with direct implications for vibronic coupling mechanisms in charge transfer excited states. In the second example, we show unambiguously that electronic and vibrational movement are coupled in a donor-bridge-acceptor complex based on a Pt(II) trans-acetylide design motif. Time-resolved IR (TRIR) spectroscopy reveals that the rate of electron transfer (ET) is highly dependent on the amount of excess energy localized on the bridge following electronic excitation. Using an adaptation of T-2DIR, we are able to selectively perturb bridge-localized vibrational modes during charge separation, resulting in the donor-acceptor charge separation pathway being completely switched off, with all excess energy redirected toward the formation of a long-lived intraligand triplet state. A series of control experiments reveal that this effect is mode specific: it is only when the high-frequency bridging C≡C stretching mode is pumped that radical changes in photoproduct yields are observed. These experiments therefore suggest that one may perturb electronic movement by stimulating structural motion along the reaction coordinate using IR light. These studies add to a growing body of evidence suggesting that controlling the pathways and efficiency of charge transfer may be achieved through synthetic and perturbative approaches aiming to modulate vibronic coupling. Achieving such control would represent a breakthrough for charge transfer-based applications such as solar energy conversion and molecular electronics.

A 4-dimethylaminobenzoate-functionalized Ti6-oxo cluster with a narrow band gap and enhanced photoelectrochemical activity: a combined experimental and computational study.

PubMed

Lv, Hai-Ting; Cui, Ying; Zhang, Yu-Min; Li, Hua-Min; Zou, Guo-Dong; Duan, Rui-Huan; Cao, Jun-Tao; Jing, Qiang-Shan; Fan, Yang

2017-09-28

Organic donor-π-bridge-acceptor (D-π-A) dyes with arylamines as an electron donor have been widely used as photosensitizers for dye-sensitized solar cells (DSSCs). However, titanium-oxo clusters (TOCs) functionalized with this kind of D-π-A structured dye-molecule have rarely been explored. In the present study, the 4-dimethylaminobenzoate-functionalized titanium-oxo cluster [Ti 6 (μ 3 -O) 6 (OiPr) 6 (DMABA) 6 ]·2C 6 H 5 CH 3 (DMABA = 4-dimethylaminobenzoate) was synthesized and structurally characterized by single-crystal X-ray diffraction. For comparison, two other Ti 6 -oxo clusters, namely [Ti 6 (μ 3 -O) 6 (OiPr) 6 (AD) 6 ] (AD = 1-adamantanecarboxylate) and [Ti 6 (μ 3 -O) 2 (μ 2 -O)(μ 2 -OiPr) 4 (OiPr) 10 (DMM) 2 ] (DMM = dimethylmalonate), were also studied. The DMABA-functionalized cluster exhibits a remarkably reduced band gap of ∼2.5 eV and much enhanced photocurrent response in comparison with the other two clusters. The electronic structures and electronic transitions of the clusters were studied by DFT and TDDFT calculations. The computational results suggest that the low-energy transitions of the DMABA-functionalized cluster have a substantial charge-transfer character arising from the DMABA → {Ti 6 } cluster core ligand-to-core charge transfer (LCCT), along with the DMABA-based intra-ligand charge transfer (ILCT). These low-energy charge transfer transitions provide efficient electron injection pathways for photon-to-electron conversion.

Utilizing Electrical Characteristics of Individual Nanotube Devices to Study the Charge Transfer between CdSe Quantum Dots and Double-Walled Nanotubes

DOE PAGES

Zhu, Yuqi; Zhou, Ruiping; Wang, Lei; ...

2017-03-02

To study the charge transfer between cadmium selenide (CdSe) quantum dots (QDs) and double-walled nanotubes (DWNTs), various sizes of CdSe-ligand-DWNT structures are synthesized, and field-effect transistors (FETs) from individual functionalized DWNTs rather than networks of the same are fabricated. From the electrical measurements, two distinct electron transfer mechanisms from the QD system to the nanotube are identified. By the formation of the CdSe-ligand-DWNT heterostructure, an effectively n-doped nanotube is created due to the smaller work function of CdSe as compared with the nanotube. In addition, once the QD-DWNT system is exposed to laser light, further electron transfer from the QDmore » through the ligand, i.e. 4-mercaptophenol (MTH), to the nanotube occurs and a clear QD-size dependent tunneling process is observed. Furthermore, the detailed analysis of a large set of devices and the particular methodology employed here for the first time allowed for extracting a wavelength and quantum dot size dependent charge transfer efficiency – a quantity that is evaluated for the first time through electrical measurement.« less

Utilizing Electrical Characteristics of Individual Nanotube Devices to Study the Charge Transfer between CdSe Quantum Dots and Double-Walled Nanotubes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Yuqi; Zhou, Ruiping; Wang, Lei

To study the charge transfer between cadmium selenide (CdSe) quantum dots (QDs) and double-walled nanotubes (DWNTs), various sizes of CdSe-ligand-DWNT structures are synthesized, and field-effect transistors (FETs) from individual functionalized DWNTs rather than networks of the same are fabricated. From the electrical measurements, two distinct electron transfer mechanisms from the QD system to the nanotube are identified. By the formation of the CdSe-ligand-DWNT heterostructure, an effectively n-doped nanotube is created due to the smaller work function of CdSe as compared with the nanotube. In addition, once the QD-DWNT system is exposed to laser light, further electron transfer from the QDmore » through the ligand, i.e. 4-mercaptophenol (MTH), to the nanotube occurs and a clear QD-size dependent tunneling process is observed. Furthermore, the detailed analysis of a large set of devices and the particular methodology employed here for the first time allowed for extracting a wavelength and quantum dot size dependent charge transfer efficiency – a quantity that is evaluated for the first time through electrical measurement.« less

Nanocrystal Size-Dependent Efficiency of Quantum Dot Sensitized Solar Cells in the Strongly Coupled CdSe Nanocrystals/TiO2 System.

PubMed

Yun, Hyeong Jin; Paik, Taejong; Diroll, Benjamin; Edley, Michael E; Baxter, Jason B; Murray, Christopher B

2016-06-15

Light absorption and electron injection are important criteria determining solar energy conversion efficiency. In this research, monodisperse CdSe quantum dots (QDs) are synthesized with five different diameters, and the size-dependent solar energy conversion efficiency of CdSe quantum dot sensitized solar cell (QDSSCs) is investigated by employing the atomic inorganic ligand, S(2-). Absorbance measurements and transmission electron microscopy show that the diameters of the uniform CdSe QDs are 2.5, 3.2, 4.2, 6.4, and 7.8 nm. Larger CdSe QDs generate a larger amount of charge under the irradiation of long wavelength photons, as verified by the absorbance results and the measurements of the external quantum efficiencies. However, the smaller QDs exhibit faster electron injection kinetics from CdSe QDs to TiO2 because of the high energy level of CBCdSe, as verified by time-resolved photoluminescence and internal quantum efficiency results. Importantly, the S(2-) ligand significantly enhances the electronic coupling between the CdSe QDs and TiO2, yielding an enhancement of the charge transfer rate at the interfacial region. As a result, the S(2-) ligand helps improve the new size-dependent solar energy conversion efficiency, showing best performance with 4.2-nm CdSe QDs, whereas conventional ligand, mercaptopropionic acid, does not show any differences in efficiency according to the size of the CdSe QDs. The findings reported herein suggest that the atomic inorganic ligand reinforces the influence of quantum confinement on the solar energy conversion efficiency of QDSSCs.

Communication: Coherences observed in vivo in photosynthetic bacteria using two-dimensional electronic spectroscopy

NASA Astrophysics Data System (ADS)

Dahlberg, Peter D.; Norris, Graham J.; Wang, Cheng; Viswanathan, Subha; Singh, Ved P.; Engel, Gregory S.

2015-09-01

Energy transfer through large disordered antenna networks in photosynthetic organisms can occur with a quantum efficiency of nearly 100%. This energy transfer is facilitated by the electronic structure of the photosynthetic antennae as well as interactions between electronic states and the surrounding environment. Coherences in time-domain spectroscopy provide a fine probe of how a system interacts with its surroundings. In two-dimensional electronic spectroscopy, coherences can appear on both the ground and excited state surfaces revealing detailed information regarding electronic structure, system-bath coupling, energy transfer, and energetic coupling in complex chemical systems. Numerous studies have revealed coherences in isolated photosynthetic pigment-protein complexes, but these coherences have not been observed in vivo due to the small amplitude of these signals and the intense scatter from whole cells. Here, we present data acquired using ultrafast video-acquisition gradient-assisted photon echo spectroscopy to observe quantum beating signals from coherences in vivo. Experiments were conducted on isolated light harvesting complex II (LH2) from Rhodobacter sphaeroides, whole cells of R. sphaeroides, and whole cells of R. sphaeroides grown in 30% deuterated media. A vibronic coherence was observed following laser excitation at ambient temperature between the B850 and the B850∗ states of LH2 in each of the 3 samples with a lifetime of ˜40-60 fs.

Capillary atmospheric pressure electron capture ionization (cAPECI): a highly efficient ionization method for nitroaromatic compounds.

PubMed

Derpmann, Valerie; Mueller, David; Bejan, Iustinian; Sonderfeld, Hannah; Wilberscheid, Sonja; Koppmann, Ralf; Brockmann, Klaus J; Benter, Thorsten

2014-03-01

We report on a novel method for atmospheric pressure ionization of compounds with elevated electron affinity (e.g., nitroaromatic compounds) or gas phase acidity (e.g., phenols), respectively. The method is based on the generation of thermal electrons by the photo-electric effect, followed by electron capture of oxygen when air is the gas matrix yielding O2(-) or of the analyte directly with nitrogen as matrix. Charge transfer or proton abstraction by O2(-) leads to the ionization of the analytes. The interaction of UV-light with metals is a clean method for the generation of thermal electrons at atmospheric pressure. Furthermore, only negative ions are generated and neutral radical formation is minimized, in contrast to discharge- or dopant assisted methods. Ionization takes place inside the transfer capillary of the mass spectrometer leading to comparably short transfer times of ions to the high vacuum region of the mass spectrometer. This strongly reduces ion transformation processes, resulting in mass spectra that more closely relate to the neutral analyte distribution. cAPECI is thus a soft and selective ionization method with detection limits in the pptV range. In comparison to standard ionization methods (e.g., PTR), cAPECI is superior with respect to both selectivity and achievable detection limits. cAPECI demonstrates to be a promising ionization method for applications in relevant fields as, for example, explosives detection and atmospheric chemistry.

Time-Domain Ab Initio Analysis of Excitation Dynamics in a Quantum Dot/Polymer Hybrid: Atomistic Description Rationalizes Experiment.

PubMed

Long, Run; Prezhdo, Oleg V

2015-07-08

Hybrid organic/inorganic polymer/quantum dot (QD) solar cells are an attractive alternative to the traditional cells. The original, simple models postulate that one-dimensional polymers have continuous energy levels, while zero-dimensional QDs exhibit atom-like electronic structure. A realistic, atomistic viewpoint provides an alternative description. Electronic states in polymers are molecule-like: finite in size and discrete in energy. QDs are composed of many atoms and have high, bulk-like densities of states. We employ ab initio time-domain simulation to model the experimentally observed ultrafast photoinduced dynamics in a QD/polymer hybrid and show that an atomistic description is essential for understanding the time-resolved experimental data. Both electron and hole transfers across the interface exhibit subpicosecond time scales. The interfacial processes are fast due to strong electronic donor-acceptor, as evidenced by the densities of the photoexcited states which are delocalized between the donor and the acceptor. The nonadiabatic charge-phonon coupling is also strong, especially in the polymer, resulting in rapid energy losses. The electron transfer from the polymer is notably faster than the hole transfer from the QD, due to a significantly higher density of acceptor states. The stronger molecule-like electronic and charge-phonon coupling in the polymer rationalizes why the electron-hole recombination inside the polymer is several orders of magnitude faster than in the QD. As a result, experiments exhibit multiple transfer times for the long-lived hole inside the QD, ranging from subpicoseconds to nanoseconds. In contrast, transfer of the short-lived electron inside the polymer does not occur beyond the first picosecond. The energy lost by the hole on its transit into the polymer is accommodated by polymer's high-frequency vibrations. The energy lost by the electron injected into the QD is accommodated primarily by much lower-frequency collective and QD modes. The electron dynamics is exponential, whereas evolution of the injected hole through the low density manifold of states of the polymer is highly nonexponential. The time scale of the electron-hole recombination at the interface is intermediate between those in pristine polymer and QD and is closer to that in the polymer. The detailed atomistic insights into the photoinduced charge and energy dynamics at the polymer/QD interface provide valuable guidelines for optimization of solar light harvesting and photovoltaic efficiency in modern nanoscale materials.

Dark States in the Light-Harvesting complex 2 Revealed by Two-dimensional Electronic Spectroscopy

PubMed Central

Ferretti, Marco; Hendrikx, Ruud; Romero, Elisabet; Southall, June; Cogdell, Richard J.; Novoderezhkin, Vladimir I.; Scholes, Gregory D.; van Grondelle, Rienk

2016-01-01

Energy transfer and trapping in the light harvesting antennae of purple photosynthetic bacteria is an ultrafast process, which occurs with a quantum efficiency close to unity. However the mechanisms behind this process have not yet been fully understood. Recently it was proposed that low-lying energy dark states, such as charge transfer states and polaron pairs, play an important role in the dynamics and directionality of energy transfer. However, it is difficult to directly detect those states because of their small transition dipole moment and overlap with the B850/B870 exciton bands. Here we present a new experimental approach, which combines the selectivity of two-dimensional electronic spectroscopy with the availability of genetically modified light harvesting complexes, to reveal the presence of those dark states in both the genetically modified and the wild-type light harvesting 2 complexes of Rhodopseudomonas palustris. We suggest that Nature has used the unavoidable charge transfer processes that occur when LH pigments are concentrated to enhance and direct the flow of energy. PMID:26857477

Hydrodynamic liver gene transfer mechanism involves transient sinusoidal blood stasis and massive hepatocyte endocytic vesicles.

PubMed

Crespo, A; Peydró, A; Dasí, F; Benet, M; Calvete, J J; Revert, F; Aliño, S F

2005-06-01

The present study contributes to clarify the mechanism underlying the high efficacy of hepatocyte gene transfer mediated by hydrodynamic injection. Gene transfer experiments were performed employing the hAAT gene, and the efficacy and differential identification in mouse plasma of human transgene versus mouse gene was assessed by ELISA and proteomic procedures, respectively. By applying different experimental strategies such as cumulative dose-response efficacy, hemodynamic changes reflected by venous pressures, intravital microscopy, and morphological changes established by transmission electron microscopy, we found that: (a) cumulative multiple doses of transgene by hydrodynamic injection are efficient and well tolerated, resulting in therapeutic plasma levels of hAAT; (b) hydrodynamic injection mediates a transient inversion of intrahepatic blood flow, with circulatory stasis for a few minutes mainly in pericentral vein sinusoids; (c) transmission electron microscopy shows hydrodynamic injection to promote massive megafluid endocytic vesicles among hepatocytes around the central vein but not in hepatocytes around the periportal vein. We suggest that the mechanism of hydrodynamic liver gene transfer involves transient inversion of intrahepatic flow, sinusoidal blood stasis, and massive fluid endocytic vesicles in pericentral vein hepatocytes.

Dark States in the Light-Harvesting complex 2 Revealed by Two-dimensional Electronic Spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ferretti, Marco; Hendrikx, Ruud; Romero, Elisabet

Energy transfer and trapping in the light harvesting antennae of purple photosynthetic bacteria is an ultrafast process, which occurs with a quantum efficiency close to unity. However the mechanisms behind this process have not yet been fully understood. Recently it was proposed that low-lying energy dark states, such as charge transfer states and polaron pairs, play an important role in the dynamics and directionality of energy transfer. However, it is difficult to directly detect those states because of their small transition dipole moment and overlap with the B850/B870 exciton bands. Here we present a new experimental approach, which combines themore » selectivity of two-dimensional electronic spectroscopy with the availability of genetically modified light harvesting complexes, to reveal the presence of those dark states in both the genetically modified and the wild-type light harvesting 2 complexes of Rhodopseudomonas palustris. In conclusion, we suggest that Nature has used the unavoidable charge transfer processes that occur when LH pigments are concentrated to enhance and direct the flow of energy.« less

Dark States in the Light-Harvesting complex 2 Revealed by Two-dimensional Electronic Spectroscopy

DOE PAGES

Ferretti, Marco; Hendrikx, Ruud; Romero, Elisabet; ...

2016-02-09

Energy transfer and trapping in the light harvesting antennae of purple photosynthetic bacteria is an ultrafast process, which occurs with a quantum efficiency close to unity. However the mechanisms behind this process have not yet been fully understood. Recently it was proposed that low-lying energy dark states, such as charge transfer states and polaron pairs, play an important role in the dynamics and directionality of energy transfer. However, it is difficult to directly detect those states because of their small transition dipole moment and overlap with the B850/B870 exciton bands. Here we present a new experimental approach, which combines themore » selectivity of two-dimensional electronic spectroscopy with the availability of genetically modified light harvesting complexes, to reveal the presence of those dark states in both the genetically modified and the wild-type light harvesting 2 complexes of Rhodopseudomonas palustris. In conclusion, we suggest that Nature has used the unavoidable charge transfer processes that occur when LH pigments are concentrated to enhance and direct the flow of energy.« less

Exciton-to-Dopant Energy Transfer in Mn-Doped Cesium Lead Halide Perovskite Nanocrystals.

PubMed

Parobek, David; Roman, Benjamin J; Dong, Yitong; Jin, Ho; Lee, Elbert; Sheldon, Matthew; Son, Dong Hee

2016-12-14

We report the one-pot synthesis of colloidal Mn-doped cesium lead halide (CsPbX 3 ) perovskite nanocrystals and efficient intraparticle energy transfer between the exciton and dopant ions resulting in intense sensitized Mn luminescence. Mn-doped CsPbCl 3 and CsPb(Cl/Br) 3 nanocrystals maintained the same lattice structure and crystallinity as their undoped counterparts with nearly identical lattice parameters at ∼0.2% doping concentrations and no signature of phase separation. The strong sensitized luminescence from d-d transition of Mn 2+ ions upon band-edge excitation of the CsPbX 3 host is indicative of sufficiently strong exchange coupling between the charge carriers of the host and dopant d electrons mediating the energy transfer, essential for obtaining unique properties of magnetically doped quantum dots. Highly homogeneous spectral characteristics of Mn luminescence from an ensemble of Mn-doped CsPbX 3 nanocrystals and well-defined electron paramagnetic resonance spectra of Mn 2+ in host CsPbX 3 nanocrystal lattices suggest relatively uniform doping sites, likely from substitutional doping at Pb 2+ . These observations indicate that CsPbX 3 nanocrystals, possessing many superior optical and electronic characteristics, can be utilized as a new platform for magnetically doped quantum dots expanding the range of optical, electronic, and magnetic functionality.

Theoretical study on phosphorescence efficiency and color tuning from orange to blue-green of Ir(III) complexes based on substituted 2-phenylimidazo[1,2-a]pyridine ligand.

PubMed

Li, Xiao-Na; Wu, Zhi-Jian; Li, Xi-Yan; Zhang, Hong-Jie; Liu, Xiao-Juan

2011-04-30

The geometrical structures, phosphorescence quantum yields, and electroluminescence (EL) efficiency of six iridium(III) complexes containing 2-phenylimidazo[1,2-a]pyridine ligand are investigated by density functional theory (DFT), which show a wide color tuning of photoluminescence from orange (λ(em) = 550 nm) to blue-green (λ(em) = 490 nm). The calculated results shed some light on the reasons of the remarkably manipulated excited-state and EL properties through substitution effect. The Mulliken charge calculation reveals that attached -CF(3) groups on phenyl and imidazo[1,2-a]pyridine (impy) moieties (4) can make both of them as electron-deficient region, which will lead to the contraction of the whole coordination sphere and strengthen the metal-ligand interaction. While attaching two -CF(3) groups on phenyl ring can make it more electron-deficient, which will induce electron transferring from acac and impy fragment to phenyl ring, and also result in the contracted structure. The largest metal-to-ligand charge transfer ((3)MLCT) character and the smaller S(1)-T(1) energy gap (ΔE(S(1)-T(1))) value increase the emission quantum yields of 4 and 6 than other complexes. For EL efficiency, because of the similar highest occupied molecular orbital (HOMO) levels of 4 and 6 to that of holes injection material poly(N-vinylcarbazole) (PVK) and the larger dipole moments, majority hole will be accumulated on the HOMO of 4 and 6. Combination with the lower lowest unoccupied molecular orbital energy levels compared with PVK, the recombination zones of 4 and 6 can be well confined within emitting material layer (EML) and lead to the higher EL efficiency. Copyright © 2010 Wiley Periodicals, Inc.

Nanoamplifiers synthesized from gadolinium and gold nanocomposites for magnetic resonance imaging

NASA Astrophysics Data System (ADS)

Tian, Xiumei; Shao, Yuanzhi; He, Haoqiang; Liu, Huan; Shen, Yingying; Huang, Wenlin; Li, Li

2013-03-01

We have synthesized an efficient and highly sensitive nanoamplifier composed of gadolinium-doped silica nanoparticles and gold nanoparticles (AuNPs). Magnetic resonance imaging (MRI) in vitro and in vivo assays revealed enhancement of signal sensitivity, which may be explained by electron transfer between water and gadolinium-doped nanoparticles, apparent in the presence of gold. In vitro and in vivo evaluation demonstrated nanoamplifier incurred minimal cytotoxicity and immunotoxicity, increased stability, and gradual excretion patterns. Tumor targeted properties were preliminarily determined when the nanoamplifier was injected into mouse models of colon cancer liver metastasis. Furthermore, although AuNPs departed from the nanoamplifiers in specific mice tissues, optical and magnetic resonance imaging was efficient, especially in metastatic tumors. These assays validate our nanoamplifier as an effective MRI signal enhancer with sensitive cancer diagnosis potential.We have synthesized an efficient and highly sensitive nanoamplifier composed of gadolinium-doped silica nanoparticles and gold nanoparticles (AuNPs). Magnetic resonance imaging (MRI) in vitro and in vivo assays revealed enhancement of signal sensitivity, which may be explained by electron transfer between water and gadolinium-doped nanoparticles, apparent in the presence of gold. In vitro and in vivo evaluation demonstrated nanoamplifier incurred minimal cytotoxicity and immunotoxicity, increased stability, and gradual excretion patterns. Tumor targeted properties were preliminarily determined when the nanoamplifier was injected into mouse models of colon cancer liver metastasis. Furthermore, although AuNPs departed from the nanoamplifiers in specific mice tissues, optical and magnetic resonance imaging was efficient, especially in metastatic tumors. These assays validate our nanoamplifier as an effective MRI signal enhancer with sensitive cancer diagnosis potential. Electronic supplementary information (ESI) available: Protocols for the characterization, immunotoxicity and pharmacokinetics analyses. Additional supporting figures. See DOI: 10.1039/c3nr00170a

Carbon materials for enhancing charge transport in the advancements of perovskite solar cells

NASA Astrophysics Data System (ADS)

Hu, Ruiyuan; Chu, Liang; Zhang, Jian; Li, Xing'ao; Huang, Wei

2017-09-01

Organic-inorganic halide perovskite solar cells (PSCs) have become a new favorite in the photovoltaic field, due to the boosted efficiency up to 22.1%. Despite a flow of achievements, there are certain challenges to simultaneously meet high efficiency, large scale, low cost and high stability. Due to the low cost, extensive sources, high electrical conductivity and chemical stability, carbon materials have made undeniable contributions to play positive roles in developing PSCs. Carbon materials not only have the favorable conductivity but also bipolar advantage, which can transfer both electrons and holes. In this review, we will discuss how the carbon materials transfer charge or accelerate charge transport by incorporation in PSCs. Carbon materials can replace transparent conductive oxide layers, and enhance electron transport in electron transport layers. Moreover, carbon materials with continuous structure, especially carbon nanotubes and graphene, can provide direct charge transport channel that make them suitable additives or even substitutes in hole transport layers. Especially, the successful application of carbon materials as counter electrodes makes the devices full-printable, low temperature and high stability. Finally, a brief outlook is provided on the future development of carbon materials for PSCs, which are expected to devote more contributions in the future photovoltaic market.

Use of one- and two-mediator systems for developing a BOD biosensor based on the yeast Debaryomyces hansenii.

PubMed

Zaitseva, A S; Arlyapov, V A; Yudina, N Yu; Alferov, S V; Reshetilov, A N

2017-03-01

We investigated the use of one- and two-mediator systems in amperometric BOD biosensors (BOD, biochemical oxygen demand) based on the yeast Debaryomyces hansenii. Screening of nine mediators potentially capable of electron transfer - ferrocene, 1,1'-dimethylferrocene, ferrocenecarboxaldehyde, ferroceneacetonitrile, neutral red, 2,6-dichlorophenolindophenol, thionine, methylene blue and potassium ferricyanide - showed only ferrocene and neutral red to be efficient electron carriers for the eukaryotes studied. Two-mediator systems based on combinations of the investigated compounds were used to increase the efficiency of electron transfer. The developed two-mediator biosensors exceeded their one-mediator analogs by their characteristics. The most preferable two-mediator system for developing a BOD biosensor was a ferrocene-methylene blue combination that ensured a satisfactory long-time stability (43 days), selectivity, sensitivity (the lower limit of the determined BOD 5 concentrations, 2.5mg О 2 /dm 3 ) and speed (assay time for one sample, not greater than 10min) of BOD determination. Analysis of water samples showed that the use of a ferrocene-methylene blue two-mediator system and the yeast D. hansenii enabled registration of data that highly correlated with the results of the standard method (R=0.9913). Copyright © 2017 Elsevier Inc. All rights reserved.

A Decaheme Cytochrome as a Molecular Electron Conduit in Dye-Sensitized Photoanodes

PubMed Central

Hwang, Ee Taek; Sheikh, Khizar; Orchard, Katherine L; Hojo, Daisuke; Radu, Valentin; Lee, Chong-Yong; Ainsworth, Emma; Lockwood, Colin; Gross, Manuela A; Adschiri, Tadafumi; Reisner, Erwin; Butt, Julea N; Jeuken, Lars J C

2015-01-01

In nature, charge recombination in light-harvesting reaction centers is minimized by efficient charge separation. Here, it is aimed to mimic this by coupling dye-sensitized TiO2 nanocrystals to a decaheme protein, MtrC from Shewanella oneidensis MR-1, where the 10 hemes of MtrC form a ≈7-nm-long molecular wire between the TiO2 and the underlying electrode. The system is assembled by forming a densely packed MtrC film on an ultra-flat gold electrode, followed by the adsorption of approximately 7 nm TiO2 nanocrystals that are modified with a phosphonated bipyridine Ru(II) dye (RuP). The step-by-step construction of the MtrC/TiO2 system is monitored with (photo)electrochemistry, quartz-crystal microbalance with dissipation (QCM-D), and atomic force microscopy (AFM). Photocurrents are dependent on the redox state of the MtrC, confirming that electrons are transferred from the TiO2 nanocrystals to the surface via the MtrC conduit. In other words, in these TiO2/MtrC hybrid photodiodes, MtrC traps the conduction-band electrons from TiO2 before transferring them to the electrode, creating a photobioelectrochemical system in which a redox protein is used to mimic the efficient charge separation found in biological photosystems. PMID:26180522

Analytical and toxicological evaluation of flavor chemicals in electronic cigarette refill fluids.

PubMed

Behar, Rachel Z; Luo, Wentai; McWhirter, Kevin J; Pankow, James F; Talbot, Prue

2018-05-29

Thousands of electronic cigarette refill fluids are commercially available. The concentrations of nicotine and the solvents, but not the flavor chemicals, are often disclosed on product labels. The purpose of this study was to identify and quantify flavor chemicals in 39 commercial refill fluids that were previously evaluated for toxicity. Twelve flavor chemicals were identified with concentrations ≥1 mg/ml: cinnamaldehyde, menthol, benzyl alcohol, vanillin, eugenol, p-anisaldehyde, ethyl cinnamate, maltol, ethyl maltol, triacetin, benzaldehyde, and menthone. Transfer of these flavor chemicals into aerosols made at 3V and 5V was efficient (mean transfer = 98%). We produced lab-made refill fluids containing authentic standards of each flavor chemical and analyzed the toxicity of their aerosols produced at 3V and 5V using a tank Box Mod device. Over 50% of the refill fluids in our sample contained high concentrations of flavor chemicals that transferred efficiently to aerosols at concentrations that produce cytotoxicity. When tested with two types of human lung cells, the aerosols made at 5V were generally more toxic than those made at 3V. These data will be valuable for consumers, physicians, public health officials, and regulatory agencies when discussing potential health concerns relating to flavor chemicals in electronic cigarette products.

Graphene Derivative in Magnetically Recoverable Catalyst Determines Catalytic Properties in Transfer Hydrogenation of Nitroarenes to Anilines with 2-Propanol.

PubMed

Das, Vijay Kumar; Mazhar, Sumaira; Gregor, Lennon; Stein, Barry D; Morgan, David Gene; Maciulis, Nicholas A; Pink, Maren; Losovyj, Yaroslav; Bronstein, Lyudmila M

2018-06-14

Here, we report transfer hydrogenation of nitroarenes to aminoarenes using 2-propanol as a hydrogen source and Ag-containing magnetically recoverable catalysts based on partially reduced graphene oxide (pRGO) sheets. X-ray diffraction and X-ray photoelectron spectroscopy data demonstrated that, during the one-pot catalyst synthesis, formation of magnetite nanoparticles (NPs) is accompanied by the reduction of graphene oxide (GO) to pRGO. The formation of Ag 0 NPs on top of magnetite nanoparticles does not change the pRGO structure. At the same time, the catalyst structure is further modified during the transfer hydrogenation, leading to a noticeable increase of sp 2 carbons. These carbons are responsible for the adsorption of substrate and intermediates, facilitating a hydrogen transfer from Ag NPs and creating synergy between the components of the catalyst. The nitroarenes with electron withdrawing and electron donating substituents allow for excellent yields of aniline derivatives with high regio and chemoselectivity, indicating that the reaction is not disfavored by these functionalities. The versatility of the catalyst synthetic protocol was demonstrated by a synthesis of an Ru-containing graphene derivative based catalyst, also allowing for efficient transfer hydrogenation. Easy magnetic separation and stable catalyst performance in the transfer hydrogenation make this catalyst promising for future applications.

Tautomeric selectivity of the excited-state lifetime of guanine/cytosine base pairs: The role of electron-driven proton-transfer processes

PubMed Central

Sobolewski, Andrzej L.; Domcke, Wolfgang; Hättig, C.

2005-01-01

The UV spectra of three different conformers of the guanine/cytosine base pair were recorded recently with UV-IR double-resonance techniques in a supersonic jet [Abo-Riziq, A., Grace, L., Nir, E., Kabelac, M., Hobza, P. & de Vries, M. S. (2005) Proc. Natl. Acad. Sci. USA 102, 20–23]. The spectra provide evidence for a very efficient excited-state deactivation mechanism that is specific for the Watson–Crick structure and may be essential for the photostability of DNA. Here we report results of ab initio electronic-structure calculations for the excited electronic states of the three lowest-energy conformers of the guanine/cytosine base pair. The calculations reveal that electron-driven interbase proton-transfer processes play an important role in the photochemistry of these systems. The exceptionally short lifetime of the UV-absorbing states of the Watson–Crick conformer is tentatively explained by the existence of a barrierless reaction path that connects the spectroscopic 1π π * excited state with the electronic ground state via two electronic curve crossings. For the non-Watson–Crick structures, the photochemically reactive state is located at higher energies, resulting in a barrier for proton transfer and, thus, a longer lifetime of the UV-absorbing 1π π * state. The computational results support the conjecture that the photochemistry of hydrogen bonds plays a decisive role for the photostability of the molecular encoding of the genetic information in isolated DNA base pairs. PMID:16330778

Effect of π-bridge units on properties of A-π-D-π-A-type nonfullerene acceptors for organic solar cells.

PubMed

Wang, Yan-Ling; Li, Quan-Song; Li, Ze-Sheng

2018-05-15

Acceptor-π-donor-π-acceptor (A-π-D-π-A)-types of small molecules are very promising nonfullerene acceptors to overcome the drawbacks of fullerene derivatives such as the weak absorption ability and electronic adjustability. However, only few attempts have been made to develop π-bridge units to construct highly efficient acceptors in OSCs. Herein, taking the reported acceptor P1 as a reference, five small-structured acceptors (P2, P3, P4, P5, and P6) have been designed via the replacement of the π-bridge unit. A combination of quantum chemistry and Marcus theory approaches is employed to investigate the effect of different π-bridge units on the optical, electronic, and charge transport properties of P1-P6. The calculation results show that the designed molecules P2 and P5 can become potential acceptor replacements of P1 due to their red-shifted absorption bands, appropriate energy levels, low exciton binding energy, and high electron affinity and electron mobility. Additionally, compared with P3HT/P1, P3HT/P2 and P3HT/P5 exhibit stronger and wider absorption peaks, larger electron transfer distances (DCT), greater transferred charge amounts (Δq), and smaller overlaps (Λ), which shows that P2 and P5 have more significant electron transfer characteristics and favorable exciton dissociation capabilities for enhancing the short-circuit current density (JSC) and thus, they are potential acceptors in OSCs.

Nonlinear whistler waves

NASA Astrophysics Data System (ADS)

Vasko, I.; Agapitov, O. V.; Mozer, F.; Bonnell, J. W.; Krasnoselskikh, V.; Artemyev, A.; Drake, J. F.

2017-12-01

Chorus waves observed in the Earth inner magnetosphere sometimes exhibit significantly distorted (nonharmonic) parallel electric field waveform. In spectrograms these waveform features show up as overtones of chorus wave. In this work we show that the chorus wave parallel electric field is distorted due to finite temperature of electrons. The distortion of the parallel electric field is described analytically and reproduced in the numerical fluid simulations. Due to this effect the chorus energy is transferred to higher frequencies making possible efficient scattering of low ( a few keV) energy electrons.

Protein's electronic polarization contributes significantly to its catalytic function

NASA Astrophysics Data System (ADS)

Xiang, Yun; Duan, Lili; Zhang, John Z. H.

2011-05-01

Ab initio quantum mechanical/molecular mechanical method is combined with the polarized protein-specific charge to study the chemical reactions catalyzed by protein enzymes. Significant improvement in the accuracy and efficiency of free-energy simulation is demonstrated by calculating the free-energy profile of the primary proton transfer reaction in triosephosphate isomerase. Quantitative agreement with experimental results is achieved. Our simulation results indicate that electronic polarization makes important contribution to enzyme catalysis by lowering the energy barrier by as much as 3 kcal/mol.

Electrochemically enhanced microbial CO conversion to volatile fatty acids using neutral red as an electron mediator.

PubMed

Im, Chae Ho; Kim, Changman; Song, Young Eun; Oh, Sang-Eun; Jeon, Byong-Hun; Kim, Jung Rae

2018-01-01

Conversion of C1 gas feedstock, including carbon monoxide (CO), into useful platform chemicals has attracted considerable interest in industrial biotechnology. Nevertheless, the low conversion yield and/or growth rate of CO-utilizing microbes make it difficult to develop a C1 gas biorefinery process. The Wood-Ljungdahl pathway which utilize CO is a pathway suffered from insufficient electron supply, in which the conversion can be increased further when an additional electron source like carbohydrate or hydrogen is provided. In this study, electrode-based electron transference using a bioelectrochemical system (BES) was examined to compensate for the insufficient reducing equivalent and increase the production of volatile fatty acids. The BES including neutral red (BES-NR), which facilitated electron transfer between bacteria and electrode, was compared with BES without neutral red and open circuit control. The coulombic efficiency based on the current input to the system and the electrons recovered into VFAs, was significantly higher in BES-NR than the control. These results suggest that the carbon electrode provides a platform to regulate the redox balance for improving the bioconversion of CO, and amending the conventional C1 gas fermentation. Copyright © 2017 Elsevier Ltd. All rights reserved.

Exploring Step‐by‐Step Assembly of Nanoparticle:Cytochrome Biohybrid Photoanodes

PubMed Central

Hwang, Ee Taek; Orchard, Katherine L.; Hojo, Daisuke; Beton, Joseph; Lockwood, Colin W. J.; Adschiri, Tadafumi

2017-01-01

Abstract Coupling light‐harvesting semiconducting nanoparticles (NPs) with redox enzymes has been shown to create artificial photosynthetic systems that hold promise for the synthesis of solar fuels. High quantum yields require efficient electron transfer from the nanoparticle to the redox protein, a property that can be difficult to control. Here, we have compared binding and electron transfer between dye‐sensitized TiO2 nanocrystals or CdS quantum dots and two decaheme cytochromes on photoanodes. The effect of NP surface chemistry was assessed by preparing NPs capped with amine or carboxylic acid functionalities. For the TiO2 nanocrystals, binding to the cytochromes was optimal when capped with a carboxylic acid ligand, whereas for the CdS QDs, better adhesion was observed for amine capped ligand shells. When using TiO2 nanocrystals, dye‐sensitized with a phosphonated bipyridine Ru(II) dye, photocurrents are observed that are dependent on the redox state of the decaheme, confirming that electrons are transferred from the TiO2 nanocrystals to the surface via the decaheme conduit. In contrast, when CdS NPs are used, photocurrents are not dependent on the redox state of the decaheme, consistent with a model in which electron transfer from CdS to the photoanode bypasses the decaheme protein. These results illustrate that although the organic shell of NPs nanoparticles crucially affects coupling with proteinaceous material, the coupling can be difficult to predict or engineer. PMID:28920010

Graphite from the University of Idaho Thermolyzed Asphalt Reaction (GUITAR): Fundamental Electrochemical Characterizations

NASA Astrophysics Data System (ADS)

Gyan, Isaiah Owusu

This dissertation details electrochemical characterization of GUITAR (Graphite from the University of Idaho Thermolyzed Asphalt Reaction), a new allotrope of carbon. Applications based on fundamental electrochemical properties of this material are also presented. The dissertation is presented in five chapters. Chapter one presents a summary of the discovery and physical characterizations of GUITAR and how its physical properties position it among carbon materials. In chapter two, fundamental electrochemical properties covering aqueous potential window and electron transfer kinetics with common dissolved redox couples are presented. This chapter highlights significant electrochemical differences between GUITAR and other sp2 carbon materials, notably, fast electron transfer across basal plane GUITAR, contrary to reports at basal planes of graphite and graphene electrodes. In chapter three, the concept of electron transfer facility is extended with biologically relevant molecules. GUITAR is shown to be suitable for biosensing with properties such as; facile electron transfer, low detection limit, high resistance to fouling and stability to anodic regeneration procedures. Chapter four presents further exploration of GUITAR's wide cathodic potential limits in other aqueous electrolytes and preliminary studies towards the exploitation of this property in the negative half of vanadium redox flow battery, where GUITAR-based electrodes are expected to increase coulombic efficiency and increase battery performance due to low hydrogen evolution. Chapter five concludes this dissertation with point-by-point presentation of significant discoveries that highlights GUITAR's uniqueness. This chapter also describes how the various fundamental electrochemical properties of GUITAR make it useful for various applications.

Torsional Dynamics, Intramolecular Charge Transfer, and Solvent Friction in the S2 (11Bu+) Excited State of Peridinin: A Mechanism for Enhanced Mid-Visible Light Harvesting in the Peridinin-Chlorophyll a Protein

NASA Astrophysics Data System (ADS)

Beck, Warren; Roscioli, Jerome; Ghosh, Soumen; Bishop, Michael; Lafountain, Amy; Frank, Harry

The structural mechanism that allows peridinin to provide one of the highest quantum efficiencies for excitation energy transfer to chlorophyll (Chl) a acceptors in the peridinin-chlorophyll a protein (PCP) from dinoflagellates involves an order-of-magnitude slowing of the S2 (11Bu+)--> S1 (21Ag-)nonradiative decay pathway compared to carotenoids lacking carbonyl substitution. Using femtosecond transient grating spectroscopy with heterodyne detection, we have determined for the first time that the decay of an intermediate state termed Sx, which we assign to a twisted form of the S2 state, is substantially slowed by solvent friction in peridinin due to its intramolecular charge transfer (ICT) character. The Sx intermediate exhibits a long enough lifetime to serve as an efficient excitation energy transfer donor to Chl a in PCP. The possibility that the Franck-Condon S2 state also transfers excitation via quantum coherent mechanisms is being considered currently using broadband two-dimensional electronic spectroscopy. Support from the DOE/BES Photosynthetic Systems Program, Grant DE-SC0010847.

DOE Office of Scientific and Technical Information (OSTI.GOV)

St-Onge, Denis A.

The two-dimensional Terry–Horton equation is shown to exhibit the Dimits shift when suitably modified to capture both the nonlinear enhancement of zonal/drift-wave interactions and the existence of residual Rosenbluth–Hinton states. This phenomenon persists through numerous simplifications of the equation, including a quasilinear approximation as well as a four-mode truncation. It is shown that the use of an appropriate adiabatic electron response, for which the electrons are not affected by the flux-averaged potential, results in anmore » $$\\boldsymbol{E}\\times \\boldsymbol{B}$$ nonlinearity that can efficiently transfer energy non-locally to length scales of the order of the sound radius. The size of the shift for the nonlinear system is heuristically calculated and found to be in excellent agreement with numerical solutions. The existence of the Dimits shift for this system is then understood as an ability of the unstable primary modes to efficiently couple to stable modes at smaller scales, and the shift ends when these stable modes eventually destabilize as the density gradient is increased. This non-local mechanism of energy transfer is argued to be generically important even for more physically complete systems.« less

Electroluminescent Yb2O3:Er and Yb2Si2O7:Er nanolaminate films fabricated by atomic layer deposition on silicon

NASA Astrophysics Data System (ADS)

Ouyang, Zhongtao; Yang, Yang; Sun, Jiaming

2018-06-01

Atomic layer doped Yb2O3:Er and Yb2Si2O7:Er nanolaminate films are fabricated on silicon by atomic layer deposition, and ∼1530 nm electroluminescence (EL) is obtained from the metal-oxide-semiconductor light-emitting devices (MOSLEDs) based on these films. The Yb2O3 films transfer to Yb2Si2O7 phase after annealing above 1000 °C. Intense photoluminescence from Yb2Si2O7 film confirms high efficiency and energy transfer under optical excitation, but the limited electron conduction restricts the EL performance. EL from the Yb2O3:Er MOSLED outperforms, presenting an external quantum efficiency up to 8.5% and the power efficiency of 1 × 10-3. The EL is derived to result from the impact excitation of Er3+ ions by hot electrons, which stem from Fowler-Nordheim tunneling mechanism under sufficient bias voltage. The critical distance for the cross relaxation of doped Er3+ ions in nanolaminate Yb2O3 matrix is experimentally determined to be ∼3 nm. Such devices manifest the technological potential of Er-doped Yb-oxides for applications in silicon-based optoelectronics.

Directional charge transfer mediated by mid-gap states: A transient absorption spectroscopy study of CdSe quantum dot/β-Pb 0.33V 2O 5 heterostructures

DOE PAGES

Milleville, Christopher C.; Pelcher, Kate E.; Sfeir, Matthew Y.; ...

2016-02-15

For solar energy conversion, not only must a semiconductor absorb incident solar radiation efficiently but also its photoexcited electron—hole pairs must further be separated and transported across interfaces. Charge transfer across interfaces requires consideration of both thermodynamic driving forces as well as the competing kinetics of multiple possible transfer, cooling, and recombination pathways. In this work, we demonstrate a novel strategy for extracting holes from photoexcited CdSe quantum dots (QDs) based on interfacing with β-Pb 0.33V 2O 5 nanowires that have strategically positioned midgap states derived from the intercalating Pb 2+ ions. Unlike midgap states derived from defects or dopants,more » the states utilized here are derived from the intrinsic crystal structure and are thus homogeneously distributed across the material. CdSe/β-Pb 0.33V 2O 5 heterostructures were assembled using two distinct methods: successive ionic layer adsorption and reaction (SILAR) and linker-assisted assembly (LAA). Transient absorption spectroscopy measurements indicate that, for both types of heterostructures, photoexcitation of CdSe QDs was followed by the transfer of electrons to the conduction band of β-Pb 0.33V 2O 5 nanowires and holes to the midgap states of β-Pb 0.33V 2O 5 nanowires. Holes were transferred on time scales less than 1 ps, whereas electrons were transferred more slowly on time scales of ~2 ps. In contrast, for analogous heterostructures consisting of CdSe QDs interfaced with V 2O 5 nanowires (wherein midgap states are absent), only electron transfer was observed. Interestingly, electron transfer was readily achieved for CdSe QDs interfaced with V 2O 5 nanowires by the SILAR method; however, for interfaces incorporating molecular linkers, electron transfer was observed only upon excitation at energies substantially greater than the bandgap absorption threshold of CdSe. Furthermore, transient absorbance decay traces reveal longer excited-state lifetimes (1–3 μs) for CdSe/β-Pb 0.33V 2O 5 heterostructures relative to bare β-Pb 0.33V 2O 5 nanowires (0.2 to 0.6 μs); the difference is attributed to surface passivation of intrinsic surface defects in β-Pb 0.33V 2O 5 upon interfacing with CdSe.« less

A Nonfullerene Small Molecule Acceptor with 3D Interlocking Geometry Enabling Efficient Organic Solar Cells.

PubMed

Lee, Jaewon; Singh, Ranbir; Sin, Dong Hun; Kim, Heung Gyu; Song, Kyu Chan; Cho, Kilwon

2016-01-06

A new 3D nonfullerene small-molecule acceptor is reported. The 3D interlocking geometry of the small-molecule acceptor enables uniform molecular conformation and strong intermolecular connectivity, facilitating favorable nanoscale phase separation and electron charge transfer. By employing both a novel polymer donor and a nonfullerene small-molecule acceptor in the solution-processed organic solar cells, a high-power conversion efficiency of close to 6% is demonstrated. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Exciplex: An Intermolecular Charge-Transfer Approach for TADF.

PubMed

Sarma, Monima; Wong, Ken-Tsung

2018-04-03

Organic materials that display thermally activated delayed fluorescence (TADF) are a striking class of functional materials that have witnessed a booming progress in recent years. In addition to pure TADF emitters achieved by the subtle manipulations of intramolecular charge transfer processes with sophisticated molecular structures, a new class of efficient TADF-based OLEDs with emitting layer formed by blending electron donor and acceptor molecules that involve intermolecular charge transfer have also been fabricated. In contrast to pure TADF materials, the exciplex-based systems can realize small ΔEST (0-0.05 eV) much more easily since the electron and hole are positioned on two different molecules, thereby giving small exchange energy. Consequently, exciplex-based OLEDs have the prospective to maximize the TADF contribution and achieve theoretical 100% internal quantum efficiency. Therefore, the challenging issue of achieving small ΔEST in organic systems could be solved. In this article, we summarize and discuss the latest and most significant developments regarding these rapidly evolving functional materials, wherein the majority of the reported exciplex forming systems are categorized into two sub-groups, viz. (a) exciplex as TADF emitters and (b) those as hosts for fluorescent, phosphorescent and TADF dopants according to their structural features and applications. The working mechanisms of the direct electroluminescence from the donor/acceptor interface and the exciplex-forming systems as co-host for the realization of high efficiency OLEDs are reviewed and discussed. This article delivers a summary of the current progresses and achievements of exciplex-based researches and points out the future challenges to trigger more research endeavors to this growing field.

Using quantum dynamics simulations to follow the competition between charge migration and charge transfer in polyatomic molecules

NASA Astrophysics Data System (ADS)

Spinlove, K. E.; Vacher, M.; Bearpark, M.; Robb, M. A.; Worth, G. A.

2017-01-01

Recent work, particularly by Cederbaum and co-workers, has identified the phenomenon of charge migration, whereby charge flow occurs over a static molecular framework after the creation of an electronic wavepacket. In a real molecule, this charge migration competes with charge transfer, whereby the nuclear motion also results in the re-distribution of charge. To study this competition, quantum dynamics simulations need to be performed. To break the exponential scaling of standard grid-based algorithms, approximate methods need to be developed that are efficient yet able to follow the coupled electronic-nuclear motion of these systems. Using a simple model Hamiltonian based on the ionisation of the allene molecule, the performance of different methods based on Gaussian Wavepackets is demonstrated.

Ultrafast dynamics of colloidal semiconductor nanocrystals relevant to solar fuels production

NASA Astrophysics Data System (ADS)

Cogan, Nicole M. B.; Liu, Cunming; Qiu, Fen; Burke, Rebeckah; Krauss, Todd D.

2017-05-01

Artificial conversion of sunlight to chemical fuels has attracted attention for several decades as a potential source of clean, renewable energy. We recently found that CdSe quantum dots (QDs) and simple aqueous Ni2+ salts in the presence of a sacrificial electron donor form a highly efficient, active, and robust system for photochemical reduction of protons to molecular hydrogen. Ultrafast transient absorption spectroscopy studies of electron transfer (ET) processes from the QDs to the Ni catalysts reveal extremely fast ET, and provide a fundamental explanation for the exceptional photocatalytic H2 activity. Additionally, by studying H2 production of the Ni catalyst with CdSe/CdS nanoparticles of various structures, it was determined that surface charge density plays an important role in charge transfer and ultimately H2 production activity.

Enhanced Charge Separation and FRET at Heterojunctions between Semiconductor Nanoparticles and Conducting Polymer Nanofibers for Efficient Solar Light Harvesting

PubMed Central

Sardar, Samim; Kar, Prasenjit; Remita, Hynd; Liu, Bo; Lemmens, Peter; Kumar Pal, Samir; Ghosh, Srabanti

2015-01-01

Energy harvesting from solar light employing nanostructured materials offer an economic way to resolve energy and environmental issues. We have developed an efficient light harvesting heterostructure based on poly(diphenylbutadiyne) (PDPB) nanofibers and ZnO nanoparticles (NPs) via a solution phase synthetic route. ZnO NPs (~20 nm) were homogeneously loaded onto the PDPB nanofibers as evident from several analytical and spectroscopic techniques. The photoinduced electron transfer from PDPB nanofibers to ZnO NPs has been confirmed by steady state and picosecond-resolved photoluminescence studies. The co-sensitization for multiple photon harvesting (with different energies) at the heterojunction has been achieved via a systematic extension of conjugation from monomeric to polymeric diphenyl butadiyne moiety in the proximity of the ZnO NPs. On the other hand, energy transfer from the surface defects of ZnO NPs (~5 nm) to PDPB nanofibers through Förster Resonance Energy Transfer (FRET) confirms the close proximity with molecular resolution. The manifestation of efficient charge separation has been realized with ~5 fold increase in photocatalytic degradation of organic pollutants in comparison to polymer nanofibers counterpart under visible light irradiation. Our results provide a novel approach for the development of nanoheterojunctions for efficient light harvesting which will be helpful in designing future solar devices. PMID:26611253

Energy harvesting of non-emissive triplet excitons in tetracene by emissive PbS nanocrystals

NASA Astrophysics Data System (ADS)

Thompson, Nicholas J.; Wilson, Mark W. B.; Congreve, Daniel N.; Brown, Patrick R.; Scherer, Jennifer M.; Bischof, Thomas S.; Wu, Mengfei; Geva, Nadav; Welborn, Matthew; Voorhis, Troy Van; Bulović, Vladimir; Bawendi, Moungi G.; Baldo, Marc A.

2014-11-01

Triplet excitons are ubiquitous in organic optoelectronics, but they are often an undesirable energy sink because they are spin-forbidden from emitting light and their high binding energy hinders the generation of free electron-hole pairs. Harvesting their energy is consequently an important technological challenge. Here, we demonstrate direct excitonic energy transfer from ‘dark’ triplets in the organic semiconductor tetracene to colloidal PbS nanocrystals, thereby successfully harnessing molecular triplet excitons in the near infrared. Steady-state excitation spectra, supported by transient photoluminescence studies, demonstrate that the transfer efficiency is at least (90 ± 13)%. The mechanism is a Dexter hopping process consisting of the simultaneous exchange of two electrons. Triplet exciton transfer to nanocrystals is expected to be broadly applicable in solar and near-infrared light-emitting applications, where effective molecular phosphors are lacking at present. In particular, this route to ‘brighten’ low-energy molecular triplet excitons may permit singlet exciton fission sensitization of conventional silicon solar cells.

High-yield transfer printing of metal-insulator-metal nanodiodes.

PubMed

Bareiss, Mario; Ante, Frederik; Kälblein, Daniel; Jegert, Gunther; Jirauschek, Christian; Scarpa, Giuseppe; Fabel, Bernhard; Nelson, Edward M; Timp, Gregory; Zschieschang, Ute; Klauk, Hagen; Porod, Wolfgang; Lugli, Paolo

2012-03-27

Nanoscale metal-insulator-metal (MIM) diodes represent important devices in the fields of electronic circuits, detectors, communication, and energy, as their cutoff frequencies may extend into the "gap" between the electronic microwave range and the optical long-wave infrared regime. In this paper, we present a nanotransfer printing method, which allows the efficient and simultaneous fabrication of large-scale arrays of MIM nanodiode stacks, thus offering the possibility of low-cost mass production. In previous work, we have demonstrated the successful transfer and electrical characterization of macroscopic structures. Here, we demonstrate for the first time the fabrication of several millions of nanoscale diodes with a single transfer-printing step using a temperature-enhanced process. The electrical characterization of individual MIM nanodiodes was performed using a conductive atomic force microscope (AFM) setup. Our analysis shows that the tunneling current is the dominant conduction mechanism, and the electrical measurement data agree well with experimental data on previously fabricated microscale diodes and numerical simulations. © 2012 American Chemical Society

Ultrafast electron transport across nano gaps in nanowire circuits

DOE Office of Scientific and Technical Information (OSTI.GOV)

Potma, Eric O.

In this Program we aim for a closer look at electron transfer through single molecules. To achieve this, we use ultrafast laser pulses to time stamp an electron tunneling event in a molecule that is connected between two metallic electrodes, while reading out the electron current. A key aspect of this project is the use of metallic substrates with plasmonic activity to efficiently manipulate the tunneling probability. The first Phase of this program is concerned with developing highly sensitive tools for the ultrafast optical manipulation of tethered molecules through the evanescent surface field of plasmonic substrates. The second Phase ofmore » the program aims to use these tools for exercising control over the electron tunneling probability.« less

Prediction of FAD binding sites in electron transport proteins according to efficient radial basis function networks and significant amino acid pairs.

PubMed

Le, Nguyen-Quoc-Khanh; Ou, Yu-Yen

2016-07-30

Cellular respiration is a catabolic pathway for producing adenosine triphosphate (ATP) and is the most efficient process through which cells harvest energy from consumed food. When cells undergo cellular respiration, they require a pathway to keep and transfer electrons (i.e., the electron transport chain). Due to oxidation-reduction reactions, the electron transport chain produces a transmembrane proton electrochemical gradient. In case protons flow back through this membrane, this mechanical energy is converted into chemical energy by ATP synthase. The convert process is involved in producing ATP which provides energy in a lot of cellular processes. In the electron transport chain process, flavin adenine dinucleotide (FAD) is one of the most vital molecules for carrying and transferring electrons. Therefore, predicting FAD binding sites in the electron transport chain is vital for helping biologists understand the electron transport chain process and energy production in cells. We used an independent data set to evaluate the performance of the proposed method, which had an accuracy of 69.84 %. We compared the performance of the proposed method in analyzing two newly discovered electron transport protein sequences with that of the general FAD binding predictor presented by Mishra and Raghava and determined that the accuracy of the proposed method improved by 9-45 % and its Matthew's correlation coefficient was 0.14-0.5. Furthermore, the proposed method enabled reducing the number of false positives significantly and can provide useful information for biologists. We developed a method that is based on PSSM profiles and SAAPs for identifying FAD binding sites in newly discovered electron transport protein sequences. This approach achieved a significant improvement after we added SAAPs to PSSM features to analyze FAD binding proteins in the electron transport chain. The proposed method can serve as an effective tool for predicting FAD binding sites in electron transport proteins and can help biologists understand the functions of the electron transport chain, particularly those of FAD binding sites. We also developed a web server which identifies FAD binding sites in electron transporters available for academics.

Biochar assisted thermophilic co-digestion of food waste and waste activated sludge under high feedstock to seed sludge ratio in batch experiment.

PubMed

Li, Qian; Xu, Manjuan; Wang, Gaojun; Chen, Rong; Qiao, Wei; Wang, Xiaochang

2018-02-01

Batch experiments were conducted using biochar (BC) to promote stable and efficient methane production from thermophilic co-digestion of food waste (FW) and waste activated sludge (WAS) at feedstock/seed sludge (F/S) ratios of 0.25, 0.75, 1.5, 2.25, and 3. The results showed that the presence of BC dramatically shortened the lag time of methane production and increased the methane production rate with increased organic loading. The higher buffer capacity and large specific surface area of BC promoted microorganism growth and adaption to VFAs accumulation. Additionally, the electron exchange in syntrophic oxidation of butyrate and acetate as intermediate products was significantly facilitated by BC possibly due to the selective succession of bacteria and methanogens which may have participated in direct interspecies electron transfer, in contrast with the control group with low-efficient electron ferried between syntrophic oxidizers and methanogens using hydrogen as the electron carrier. Copyright © 2017 Elsevier Ltd. All rights reserved.

Boron doped graphene wrapped silver nanowires as an efficient electrocatalyst for molecular oxygen reduction

NASA Astrophysics Data System (ADS)

Nair, Anju K.; Thazhe Veettil, Vineesh; Kalarikkal, Nandakumar; Thomas, Sabu; Kala, M. S.; Sahajwalla, Veena; Joshi, Rakesh K.; Alwarappan, Subbiah

2016-12-01

Metal nanowires exhibit unusually high catalytic activity towards oxygen reduction reaction (ORR) due to their inherent electronic structures. However, controllable synthesis of stable nanowires still remains as a daunting challenge. Herein, we report the in situ synthesis of silver nanowires (AgNWs) over boron doped graphene sheets (BG) and demonstrated its efficient electrocatalytic activity towards ORR for the first time. The electrocatalytic ORR efficacy of BG-AgNW is studied using various voltammetric techniques. The BG wrapped AgNWs shows excellent ORR activity, with very high onset potential and current density and it followed four electron transfer mechanism with high methanol tolerance and stability towards ORR. The results are comparable to the commercially available 20% Pt/C in terms of performance.

Electronic structure and charge transfer excited states of endohedral fullerene containing electron donoracceptor complexes utilized in organic photovoltaics

NASA Astrophysics Data System (ADS)

Amerikheirabadi, Fatemeh

Organic Donor-Acceptor complexes form the main component of the organic photovoltaic devices (OPVs). The open circuit voltage of OPVs is directly related to the charge transfer excited state energies of these complexes. Currently a large number of different molecular complexes are being tested for their efficiency in photovoltaic devices. In this work, density functional theory as implemented in the NRLMOL code is used to investigate the electronic structure and related properties of these donor-acceptor complexes. The charge transfer excitation energies are calculated using the perturbative delta self-consistent field method recently developed in our group as the standard time dependent density functional approaches fail to accurately provide them. The model photovoltaics systems analyzed are as follows: Sc3N C 80--ZnTPP, Y3 N C80-- ZnTPP and Sc3 N C80-- ZnPc. In addition, a thorough analysis of the isolated donor and acceptor molecules is also provided. The studied acceptors are chosen from a class of fullerenes named trimetallic nitride endohedral fullerenes. These molecules have shown to possess advantages as acceptors such as long lifetimes of the charge-separated states.

Stretchable interconnections for flexible electronic systems.

PubMed

Jianhui, Lin; Bing, Yan; Xiaoming, Wu; Tianling, Ren; Litian, Liu

2009-01-01

Sensors, actuators and integrated circuits (IC) can be encapsulated together on an elastic substrate, which makes a flexible electronic system. In this system, electrical interconnections that can sustain large and reversible stretching are in great need. This paper is devoted to the fabrication of highly stretchable metal interconnections. Transfer printing technology is utilized, which mainly involves the transfer of 100-nm-thick gold ribbons from silicon wafers to pre-stretched elastic substrates. After the elastic substrates relax from the pre-strain, the gold ribbons buckle and form wavy geometries. These wavy geometries change in shapes to accommodate the applied strain and can be reversely stretched without cracks or fractures occurring, which will greatly raise the stretchability of the gold ribbons. As an application example, some of these wavy ribbons can accommodate high levels of stretching (up to 100%) and bending (with curvature radius down to 1.20 mm). Moreover, the efficiency and reliability of the transfer, especially for slender ribbons, have been increased due to the improvement of the technology. All the characteristics above will permit making stretchable gold conductors as interconnections for flexible electronic systems such as implantable medical systems and smart clothes.

Long-range energy transfer in self-assembled quantum dot-DNA cascades

NASA Astrophysics Data System (ADS)

Goodman, Samuel M.; Siu, Albert; Singh, Vivek; Nagpal, Prashant

2015-11-01

The size-dependent energy bandgaps of semiconductor nanocrystals or quantum dots (QDs) can be utilized in converting broadband incident radiation efficiently into electric current by cascade energy transfer (ET) between layers of different sized quantum dots, followed by charge dissociation and transport in the bottom layer. Self-assembling such cascade structures with angstrom-scale spatial precision is important for building realistic devices, and DNA-based QD self-assembly can provide an important alternative. Here we show long-range Dexter energy transfer in QD-DNA self-assembled single constructs and ensemble devices. Using photoluminescence, scanning tunneling spectroscopy, current-sensing AFM measurements in single QD-DNA cascade constructs, and temperature-dependent ensemble devices using TiO2 nanotubes, we show that Dexter energy transfer, likely mediated by the exciton-shelves formed in these QD-DNA self-assembled structures, can be used for efficient transport of energy across QD-DNA thin films.The size-dependent energy bandgaps of semiconductor nanocrystals or quantum dots (QDs) can be utilized in converting broadband incident radiation efficiently into electric current by cascade energy transfer (ET) between layers of different sized quantum dots, followed by charge dissociation and transport in the bottom layer. Self-assembling such cascade structures with angstrom-scale spatial precision is important for building realistic devices, and DNA-based QD self-assembly can provide an important alternative. Here we show long-range Dexter energy transfer in QD-DNA self-assembled single constructs and ensemble devices. Using photoluminescence, scanning tunneling spectroscopy, current-sensing AFM measurements in single QD-DNA cascade constructs, and temperature-dependent ensemble devices using TiO2 nanotubes, we show that Dexter energy transfer, likely mediated by the exciton-shelves formed in these QD-DNA self-assembled structures, can be used for efficient transport of energy across QD-DNA thin films. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr04778a

Dynamics of Back Electron Transfer in Dye-Sensitized Solar Cells Featuring 4-tert-Butyl-Pyridine and Atomic-Layer-Deposited Alumina as Surface Modifiers.

PubMed

Katz, Michael J; Vermeer, Michael J DeVries; Farha, Omar K; Pellin, Michael J; Hupp, Joseph T

2015-06-18

A series of dye-sensitized solar cells (DSCs) was constructed with TiO2 nanoparticles and N719 dye. The standard I3(-)/I(-) redox shuttle and the Co(1,10-phenanthroline)3(3+/2+) shuttle were employed. DSCs were modified with atomic-layered-deposited (ALD) coatings of Al2O3 and/or with the surface-adsorbing additive 4-tert-butyl-pyridine. Current-voltage data were collected to ascertain the influence of each modification upon the back electron transfer (ET) dynamics of the DSCs. The primary effect of the additives alone or in tandem is to increase the open-circuit voltage. A second is to alter the short-circuit current density, JSC. With dependence on the specifics of the system examined, any of a myriad of dynamics-related effects were observed to come into play, in both favorable (efficiency boosting) and unfavorable (efficiency damaging) ways. These effects include modulation of (a) charge-injection yields, (b) rates of interception of injected electrons by redox shuttles, and (c) rates of recombination of injected electrons with holes on surface-bound dyes. In turn, these influence charge-collection lengths, charge-collection yields, and onset potentials for undesired dark current. The microscopic origins of the effects appear to be related mainly to changes in driving force and/or electronic coupling for underlying component redox reactions. Perhaps surprisingly, only a minor role for modifier-induced shifts in conduction-band-edge energy was found. The combination of DSC-efficiency-relevant effects engendered by the modifiers was found to vary substantially as a function of the chemical identity of the redox shuttle employed. While types of modifiers are effective, a challenge going forward will be to construct systems in ways in which the benefits of organic and inorganic modifiers can be exploited in fully additive, or even synergistic, fashion.

Vibronic Wavepackets and Energy Transfer in Cryptophyte Light-Harvesting Complexes.

PubMed

Jumper, Chanelle C; van Stokkum, Ivo H M; Mirkovic, Tihana; Scholes, Gregory D

2018-06-21

Determining the key features of high-efficiency photosynthetic energy transfer remains an ongoing task. Recently, there has been evidence for the role of vibronic coherence in linking donor and acceptor states to redistribute oscillator strength for enhanced energy transfer. To gain further insights into the interplay between vibronic wavepackets and energy-transfer dynamics, we systematically compare four structurally related phycobiliproteins from cryptophyte algae by broad-band pump-probe spectroscopy and extend a parametric model based on global analysis to include vibrational wavepacket characterization. The four phycobiliproteins isolated from cryptophyte algae are two "open" structures and two "closed" structures. The closed structures exhibit strong exciton coupling in the central dimer. The dominant energy-transfer pathway occurs on the subpicosecond timescale across the largest energy gap in each of the proteins, from central to peripheral chromophores. All proteins exhibit a strong 1585 cm -1 coherent oscillation whose relative amplitude, a measure of vibronic intensity borrowing from resonance between donor and acceptor states, scales with both energy-transfer rates and damping rates. Central exciton splitting may aid in bringing the vibronically linked donor and acceptor states into better resonance resulting in the observed doubled rate in the closed structures. Several excited-state vibrational wavepackets persist on timescales relevant to energy transfer, highlighting the importance of further investigation of the interplay between electronic coupling and nuclear degrees of freedom in studies on high-efficiency photosynthesis.

Hydrogenated TiO2 Thin Film for Accelerating Electron Transport in Highly Efficient Planar Perovskite Solar Cells.

PubMed

Yao, Xin; Liang, Junhui; Li, Yuelong; Luo, Jingshan; Shi, Biao; Wei, Changchun; Zhang, Dekun; Li, Baozhang; Ding, Yi; Zhao, Ying; Zhang, Xiaodan

2017-10-01

Intensive studies on low-temperature deposited electron transport materials have been performed to improve the efficiency of n-i-p type planar perovskite solar cells to extend their application on plastic and multijunction device architectures. Here, a TiO 2 film with enhanced conductivity and tailored band edge is prepared by magnetron sputtering at room temperature by hydrogen doping (HTO), which accelerates the electron extraction from perovskite photoabsorber and reduces charge transfer resistance, resulting in an improved short circuit current density and fill factor. The HTO film with upward shifted Fermi level guarantees a smaller loss on V OC and facilitates the growth of high-quality absorber with much larger grains and more uniform size, leading to devices with negligible hysteresis. In comparison with the pristine TiO 2 prepared without hydrogen doping, the HTO-based device exhibits a substantial performance enhancement leading to an efficiency of 19.30% and more stabilized photovoltaic performance maintaining 93% of its initial value after 300 min continuous illumination in the glove box. These properties permit the room-temperature magnetron sputtered HTO film as a promising electron transport material for flexible and tandem perovskite solar cell in the future.

Enhancing Performance and Uniformity of Perovskite Solar Cells via a Solution-Processed C70 Interlayer for Interface Engineering.

PubMed

Zhou, Ya-Qing; Wu, Bao-Shan; Lin, Guan-Hua; Li, Yang; Chen, Di-Chun; Zhang, Peng; Yu, Ming-Yu; Zhang, Bin-Bin; Yun, Da-Qin

2017-10-04

Although some kinds of semiconductor metal oxides (SMOs) have been applied as electron selective layers (ESLs) for planar perovskite solar cells (PSCs), electron transfer is still limited by low electron mobility and defect film formation of SMO ESLs fabricated via low-temperature solution process. Herein, the C 70 interlayer between TiO 2 and (HC(NH 2 ) 2 PbI 3 ) x (CH 3 NH 3 PbCl 3 ) 1-x is prepared by spin-coating and low-temperature annealing for planar n-i-p PSCs. The resultant TiO 2 /C 70 ESL shows good surface morphology, efficient electron extraction, and facilitation of high-quality perovskite film formation, which can be attributed to the suitable nanosize and the superior electronic property of C 70 molecules. In comparison with pristine TiO 2 -based PSCs, the efficiency and hysteresis index are, respectively, enhanced 28% and reduced 76% by adding the C 70 interlayer between TiO 2 and perovskite on the basis of statistical data of more than 50 cells. With the main advantages of low-temperature process and optimized interface, the champion efficiency of PSCs on flexible substrates could exceed 12% in contrast with the above 18% on rigid substrate.

Progress and Perspectives of Plasmon-Enhanced Solar Energy Conversion.

PubMed

Cushing, Scott K; Wu, Nianqiang

2016-02-18

Plasmonics allows extraordinary control of light, making it attractive for application in solar energy harvesting. In metal-semiconductor heterojunctions, plasmons can enhance photoconversion in the semiconductor via three mechanisms, including light trapping, hot electron/hole transfer, and plasmon-induced resonance energy transfer (PIRET). To understand the plasmonic enhancement, the metal's geometry, constituent metal, and interface must be viewed in terms of the effects on the plasmon's dephasing and decay route. To simplify design of plasmonic metal-semiconductor heterojunctions for high-efficiency solar energy conversion, the parameters controlling the plasmonic enhancement can be distilled to the dephasing time. The plasmonic geometry can then be further refined to optimize hot carrier transfer, PIRET, or light trapping.

Modulation of ICT probability in bi(polyarene)-based O-BODIPYs: towards the development of low-cost bright arene-BODIPY dyads.

PubMed

Gartzia-Rivero, Leire; Sánchez-Carnerero, Esther M; Jiménez, Josue; Bañuelos, Jorge; Moreno, Florencio; Maroto, Beatriz L; López-Arbeloa, Iñigo; de la Moya, Santiago

2017-09-12

We report the synthesis, and spectroscopic and electrochemical properties of a selected library of novel spiranic O-BODIPYs bearing a phenol-based bi(polyarene) unit tethered to the boron center through oxygen atoms. These dyes constitute an interesting family of arene-BODIPY dyads useful for the development of photonic applications due to their synthetic accessibility and tunable photonic properties. It is demonstrated that the electron-donor capability of the involved arene moiety switches on a non-emissive intramolecular charge transfer (ICT) state, which restricts the fluorescence efficiency of the dyad. Interestingly, the influence of this non-radiative deactivation channel can be efficiently modulated by the substitution pattern, either at the dipyrrin ligand or at the polyarene moiety. Thus, dyads featuring electron-rich dipyrrin and electron-poor polyarene show lower or almost negligible ICT probability, and hence display bright fluorescence upon dual excitation at far-away spectral regions. This synthetic approach has allowed the easy development of low-cost efficient ultraviolet-absorbing visible-emitting cassettes by selecting properly the substitution pattern of the involved key units, dipyrrin and bi(polyarene), to modulate not only absorption and emission wavelengths, but also fluorescence efficiencies.

Effect of introduction of a new electronic anesthesia record (Epic) system on the safety and efficiency of patient care in a gastrointestinal endoscopy suite-comparison with historical cohort.

PubMed

Goudra, B; Singh, P M; Borle, A; Gouda, G

2016-01-01

Use of electronic medical record systems has increased in the recent years. Epic is one such system gaining popularity in the USA. Epic is a private company, which invented the electronic documentation system adopted in our hospital. In spite of many presumed advantages, its use is not critically analyzed. Some of the perceived advantages are increased efficiency and protection against litigation as a result of accurate documentation. In this study, retrospective data of 305 patients who underwent endoscopic retrograde cholangiopancreatography (wherein electronic charting was used - "Epic group") were compared with 288 patients who underwent the same procedure with documentation saved on a paper chart ("paper group"). Time of various events involved in the procedure such as anesthesia start, endoscope insertion, endoscope removal, and transfer to the postanesthesia care unit were routinely documented. From this data, the various time durations were calculated. Both "anesthesia start to scope insertion" times and "scope removal to transfer" times were significantly less in the Epic group compared to the paper group. Use of Epic system led to a saving of 4 min of procedure time per patient. However, the mean oxygen saturation was significantly less in the Epic group. In spite of perceived advantages of Epic documentation system, significant hurdles remain with its use. Although the system allows seamless flow of patients, failure to remove all artifacts can lead to errors and become a source of potential litigation hazard.

Molecular Electronic Coupling Controls Charge Recombination Kinetics in Organic Solar Cells of Low Bandgap Diketopyrrolopyrrole, Carbazole, and Thiophene Polymers

PubMed Central

2013-01-01

Low-bandgap diketopyrrolopyrrole- and carbazole-based polymer bulk-heterojunction solar cells exhibit much faster charge carrier recombination kinetics than that encountered for less-recombining poly(3-hexylthiophene). Solar cells comprising these polymers exhibit energy losses caused by carrier recombination of approximately 100 mV, expressed as reduction in open-circuit voltage, and consequently photovoltaic conversion efficiency lowers in more than 20%. The analysis presented here unravels the origin of that energy loss by connecting the limiting mechanism governing recombination dynamics to the electronic coupling occurring at the donor polymer and acceptor fullerene interfaces. Previous approaches correlate carrier transport properties and recombination kinetics by means of Langevin-like mechanisms. However, neither carrier mobility nor polymer ionization energy helps understanding the variation of the recombination coefficient among the studied polymers. In the framework of the charge transfer Marcus theory, it is proposed that recombination time scale is linked with charge transfer molecular mechanisms at the polymer/fullerene interfaces. As expected for efficient organic solar cells, small electronic coupling existing between donor polymers and acceptor fullerene (Vif < 1 meV) and large reorganization energy (λ ≈ 0.7 eV) are encountered. Differences in the electronic coupling among polymer/fullerene blends suffice to explain the slowest recombination exhibited by poly(3-hexylthiophene)-based solar cells. Our approach reveals how to directly connect photovoltaic parameters as open-circuit voltage to molecular properties of blended materials. PMID:23662167

Uphill energy transfer from long-wavelength absorbing chlorophylls to PS II in Ostreobium sp. is functional in carbon assimilation.

PubMed

Wilhelm, Christian; Jakob, Torsten

2006-03-01

From the algal genus Ostrobium two species are known which express a chlorophyll antenna absorbing between 710 and 725 nm to a different extent. In a comparative study with these two species it is shown that quanta absorbed by this long wavelength antenna can be transferred to PS II leading to significant PS II-related electron transfer. It is documented that under monochromatic far red light illumination growth continues with rather high efficiency. The data show that the uphill-energy transfer to PS II reduces the quantum yield under white light significantly. It is discussed that this strategy of energy conversion might play a role in special environments where far red light is the predominant energy source.

Estimation of optimum density and temperature for maximum efficiency of tin ions in Z discharge extreme ultraviolet sources

DOE Office of Scientific and Technical Information (OSTI.GOV)

Masnavi, Majid; Nakajima, Mitsuo; Hotta, Eiki

Extreme ultraviolet (EUV) discharge-based lamps for EUV lithography need to generate extremely high power in the narrow spectrum band of 13.5{+-}0.135 nm. A simplified collisional-radiative model and radiative transfer solution for an isotropic medium were utilized to investigate the wavelength-integrated light outputs in tin (Sn) plasma. Detailed calculations using the Hebrew University-Lawrence Livermore atomic code were employed for determination of necessary atomic data of the Sn{sup 4+} to Sn{sup 13+} charge states. The result of model is compared with experimental spectra from a Sn-based discharge-produced plasma. The analysis reveals that considerably larger efficiency compared to the so-called efficiency of amore » black-body radiator is formed for the electron density {approx_equal}10{sup 18} cm{sup -3}. For higher electron density, the spectral efficiency of Sn plasma reduces due to the saturation of resonance transitions.« less

Theoretical Study of Electron Transfer Properties of Squaraine Dyes for Dye Sensitized Solar Cell

NASA Astrophysics Data System (ADS)

Juwita, Ratna; Tsai, Hui-Hsu Gavin

2018-01-01

The environmental issues and high cost of Ru create many scientists to explore cheaper and safer sensitizer as alternative for dye sensitized solar cells (DSCs). Dyes play an important role in solar energy conversion efficiency. The squaraine (SQ) dyes has good spectral match with the solar spectra, therefore, SQ dyes have great potential for the applications in DSCs. SQ01_CA is an unsymmetrical SQ dye, reported by Grätzel and colleagues in 2007, featuring a D-π-spacer-A framework and has a carboxylic acid anchoring group. The electron donating ability of indolium in SQ01_CA and SQ01_CAA dyes is relatively weak, better performance may be achieved by introducing an additional donor moiety into indolium [1]. In this study, we investigate six unsymmetrical SQ dyes adsorbed on a (TiO2)38 cluster [2] using density functional theory (DFT) and time-dependent DFT to study electron transfer properties of squaraine dyes on their photophysical. SQ01_CA, WH-SQ01_CA, and WH-SQ02_CA use a carboxylic acid group as its electron acceptor. Furthermore, SQ01_CAA, WH-SQ01_CAA, and WH-SQ02_CAA use a cyanoacrylic acid group as its electron acceptor. WH-SQ01_CA and WH-SQ01_CAA have an alkyl, while WH-SQ02_CA and WH-SQ02_CAA have alkoxyl substituted diarylamines to the indolium donor of sensitizer SQ01_CA. Our calculations show with additional diarylamines in donor tail of WH-SQ02_CAA, the SQ dyes have red-shifted absorption and have slightly larger probability of electron density transferred to TiO2 moiety. Furthermore, an additional -CN group as electron a withdrawing group in the acceptor exhibits red-shifted absorption and enhances the electron density transferred to TiO2 and anchoring moiety after photo-excitation. The tendency of calculated probabilities of electron density being delocalized into TiO2 and driving force for excited-state electron injection of these studied SQ dyes is compatible with their experimentally observed.

Blue Light Emitting Polyphenylene Dendrimers with Bipolar Charge Transport Moieties.

PubMed

Zhang, Guang; Auer-Berger, Manuel; Gehrig, Dominik W; Blom, Paul W M; Baumgarten, Martin; Schollmeyer, Dieter; List-Kratochvil, E J W; Müllen, Klaus

2016-10-20

Two light-emitting polyphenylene dendrimers with both hole and electron transporting moieties were synthesized and characterized. Both molecules exhibited pure blue emission solely from the pyrene core and efficient surface-to-core energy transfers when characterized in a nonpolar environment. In particular, the carbazole- and oxadiazole-functionalized dendrimer ( D1 ) manifested a pure blue emission from the pyrene core without showing intramolecular charge transfer (ICT) in environments with increasing polarity. On the other hand, the triphenylamine- and oxadiazole-functionalized one ( D2 ) displayed notable ICT with dual emission from both the core and an ICT state in highly polar solvents. D1 , in a three-layer organic light emitting diode (OLED) by solution processing gave a pure blue emission with Commission Internationale de l'Éclairage 1931 CIE xy = (0.16, 0.12), a peak current efficiency of 0.21 cd/A and a peak luminance of 2700 cd/m². This represents the first reported pure blue dendrimer emitter with bipolar charge transport and surface-to-core energy transfer in OLEDs.

Phonon-Assisted Ultrafast Charge Transfer at van der Waals Heterostructure Interface.

PubMed

Zheng, Qijing; Saidi, Wissam A; Xie, Yu; Lan, Zhenggang; Prezhdo, Oleg V; Petek, Hrvoje; Zhao, Jin

2017-10-11

The van der Waals (vdW) interfaces of two-dimensional (2D) semiconductor are central to new device concepts and emerging technologies in light-electricity transduction where the efficient charge separation is a key factor. Contrary to general expectation, efficient electron-hole separation can occur in vertically stacked transition-metal dichalcogenide heterostructure bilayers through ultrafast charge transfer between the neighboring layers despite their weak vdW bonding. In this report, we show by ab initio nonadiabatic molecular dynamics calculations, that instead of direct tunneling, the ultrafast interlayer hole transfer is strongly promoted by an adiabatic mechanism through phonon excitation occurring on 20 fs, which is in good agreement with the experiment. The atomic level picture of the phonon-assisted ultrafast mechanism revealed in our study is valuable both for the fundamental understanding of ultrafast charge carrier dynamics at vdW heterointerfaces as well as for the design of novel quasi-2D devices for optoelectronic and photovoltaic applications.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Imani, Mohammadreza F., E-mail: mohamad.imani@gmail.com; Grbic, Anthony

One of the obstacles preventing wireless power transfer from becoming ubiquitous is their leakage of power: high-amplitude electromagnetic fields that can interfere with other electronic devices, increase health concerns, or hinder power metering. In this paper, we present near-field plates (NFPs) as a novel method to tailor the electromagnetic fields generated by a wireless power transfer system while maintaining high efficiency. NFPs are modulated arrays or surfaces designed to form prescribed near-field patterns. The NFP proposed in this paper consists of an array of loaded loops that are designed to confine the electromagnetic fields of a resonant transmitting loop tomore » the desired direction (receiving loop) while suppressing fields in other directions. The step-by-step design procedure for this device is outlined. Two NFPs are designed and examined in full-wave simulation. Their performance is shown to be in close agreement with the design predictions, thereby verifying the proposed design and operation. A NFP is also fabricated and experimentally shown to form a unidirectional wireless power transfer link with high efficiency.« less

Engineering live cell surfaces with functional polymers via cytocompatible controlled radical polymerization

NASA Astrophysics Data System (ADS)

Niu, Jia; Lunn, David J.; Pusuluri, Anusha; Yoo, Justin I.; O'Malley, Michelle A.; Mitragotri, Samir; Soh, H. Tom; Hawker, Craig J.

2017-06-01

The capability to graft synthetic polymers onto the surfaces of live cells offers the potential to manipulate and control their phenotype and underlying cellular processes. Conventional grafting-to strategies for conjugating preformed polymers to cell surfaces are limited by low polymer grafting efficiency. Here we report an alternative grafting-from strategy for directly engineering the surfaces of live yeast and mammalian cells through cell surface-initiated controlled radical polymerization. By developing cytocompatible PET-RAFT (photoinduced electron transfer-reversible addition-fragmentation chain-transfer polymerization), synthetic polymers with narrow polydispersity (Mw/Mn < 1.3) could be obtained at room temperature in 5 minutes. This polymerization strategy enables chain growth to be initiated directly from chain-transfer agents anchored on the surface of live cells using either covalent attachment or non-covalent insertion, while maintaining high cell viability. Compared with conventional grafting-to approaches, these methods significantly improve the efficiency of grafting polymer chains and enable the active manipulation of cellular phenotypes.

Inverted organic electronic and optoelectronic devices

NASA Astrophysics Data System (ADS)

Small, Cephas E.

The research and development of organic electronics for commercial application has received much attention due to the unique properties of organic semiconductors and the potential for low-cost high-throughput manufacturing. For improved large-scale processing compatibility and enhanced device stability, an inverted geometry has been employed for devices such as organic light emitting diodes and organic photovoltaic cells. These improvements are attributed to the added flexibility to incorporate more air-stable materials into the inverted device geometry. However, early work on organic electronic devices with an inverted geometry typically showed reduced device performance compared to devices with a conventional structure. In the case of organic light emitting diodes, inverted devices typically show high operating voltages due to insufficient carrier injection. Here, a method for enhancing hole injection in inverted organic electronic devices is presented. By incorporating an electron accepting interlayer into the inverted device, a substantial enhancement in hole injection efficiency was observed as compared to conventional devices. Through a detailed carrier injection study, it is determined that the injection efficiency enhancements in the inverted devices are due to enhanced charge transfer at the electron acceptor/organic semiconductor interface. A similar situation is observed for organic photovoltaic cells, in which devices with an inverted geometry show limited carrier extraction in early studies. In this work, enhanced carrier extraction is demonstrated for inverted polymer solar cells using a surface-modified ZnO-polymer composite electron-transporting layer. The insulating polymer in the composite layer inhibited aggregation of the ZnO nanoparticles, while the surface-modification of the composite interlayer improved the electronic coupling with the photoactive layer. As a result, inverted polymer solar cells with power conversion efficiencies of over 8% were obtained. To further study carrier extraction in inverted polymer solar cells, the active layer thickness dependence of the efficiency was investigated. For devices with active layer thickness < 200 nm, power conversion efficiencies over 8% was obtained. This result is important for demonstrating improved large-scale processing compatibility. Above 200 nm, significant reduction in cell efficiency were observed. A detailed study of the loss processes that contributed to the reduction in efficiency for thick-film devices are presented.

Catalytic two-electron reduction of dioxygen by ferrocene derivatives with manganese(V) corroles.

PubMed

Jung, Jieun; Liu, Shuo; Ohkubo, Kei; Abu-Omar, Mahdi M; Fukuzumi, Shunichi

2015-05-04

Electron transfer from octamethylferrocene (Me8Fc) to the manganese(V) imidocorrole complex (tpfc)Mn(V)(NAr) [tpfc = 5,10,15-tris(pentafluorophenyl)corrole; Ar = 2,6-Cl2C6H3] proceeds efficiently to give an octamethylferrocenium ion (Me8Fc(+)) and [(tpfc)Mn(IV)(NAr)](-) in acetonitrile (MeCN) at 298 K. Upon the addition of trifluoroacetic acid (TFA), further reduction of [(tpfc)Mn(IV)(NAr)](-) by Me8Fc gives (tpfc)Mn(III) and ArNH2 in deaerated MeCN. TFA also results in hydrolysis of (tpfc)Mn(V)(NAr) with residual water to produce a protonated manganese(V) oxocorrole complex ([(tpfc)Mn(V)(OH)](+)) in deaerated MeCN. [(tpfc)Mn(V)(OH)](+) is rapidly reduced by 2 equiv of Me8Fc in the presence of TFA to give (tpfc)Mn(III) in deaerated MeCN. In the presence of dioxygen (O2), (tpfc)Mn(III) catalyzes the two-electron reduction of O2 by Me8Fc with TFA in MeCN to produce H2O2 and Me8Fc(+). The rate of formation of Me8Fc(+) in the catalytic reduction of O2 follows zeroth-order kinetics with respect to the concentrations of Me8Fc and TFA, whereas the rate increases linearly with increasing concentrations of (tpfc)Mn(V)(NAr) and O2. These kinetic dependencies are consistent with the rate-determining step being electron transfer from (tpfc)Mn(III) to O2, followed by further proton-coupled electron transfer from Me8Fc to produce H2O2 and [(tpfc)Mn(IV)](+). Rapid electron transfer from Me8Fc to [(tpfc)Mn(IV)](+) regenerates (tpfc)Mn(III), completing the catalytic cycle. Thus, catalytic two-electron reduction of O2 by Me8Fc with (tpfc)Mn(V)(NAr) as a catalyst precursor proceeds via a Mn(III)/Mn(IV) redox cycle.

Dynamics of Singlet Fission and Electron Injection in Self-Assembled Acene Monolayers on Titanium Dioxide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, Justin C; Pace, Natalie A; Arias, Dylan H

We employ a combination of linear spectroscopy, electrochemistry, and transient absorption spectroscopy to characterize the interplay between electron transfer and singlet fission dynamics in polyacene-based dyes attached to nanostructured TiO2. For triisopropyl silylethynyl (TIPS)-pentacene, we find that the singlet fission time constant increases to 6.5 ps on a nanostructured TiO2 surface relative to a thin film time constant of 150 fs, and that triplets do not dissociate after they are formed. In contrast, TIPS-tetracene singlets quickly dissociate in 2 ps at the molecule/TiO2 interface, and this dissociation outcompetes the relatively slow singlet fission process. The addition of an alumina layermore » slows down electron injection, allowing the formation of triplets from singlet fission in 40 ps. However, the triplets do not inject electrons, which is likely due to a lack of sufficient driving force for triplet dissociation. These results point to the critical balance required between efficient singlet fission and appropriate energetics for interfacial charge transfer.« less

Mechanically Controlled Electron Transfer in a Single-Polypeptide Transistor

NASA Astrophysics Data System (ADS)

Sheu, Sheh-Yi; Yang, Dah-Yen

2017-01-01

Proteins are of interest in nano-bio electronic devices due to their versatile structures, exquisite functionality and specificity. However, quantum transport measurements produce conflicting results due to technical limitations whereby it is difficult to precisely determine molecular orientation, the nature of the moieties, the presence of the surroundings and the temperature; in such circumstances a better understanding of the protein electron transfer (ET) pathway and the mechanism remains a considerable challenge. Here, we report an approach to mechanically drive polypeptide flip-flop motion to achieve a logic gate with ON and OFF states during protein ET. We have calculated the transmission spectra of the peptide-based molecular junctions and observed the hallmarks of electrical current and conductance. The results indicate that peptide ET follows an NC asymmetric process and depends on the amino acid chirality and α-helical handedness. Electron transmission decreases as the number of water molecules increases, and the ET efficiency and its pathway depend on the type of water-bridged H-bonds. Our results provide a rational mechanism for peptide ET and new perspectives on polypeptides as potential candidates in logic nano devices.

Stimulated Raman adiabatic passage preparation of a coherent superposition of ThO H3Δ1 states for an improved electron electric-dipole-moment measurement

NASA Astrophysics Data System (ADS)

Panda, C. D.; O'Leary, B. R.; West, A. D.; Baron, J.; Hess, P. W.; Hoffman, C.; Kirilov, E.; Overstreet, C. B.; West, E. P.; DeMille, D.; Doyle, J. M.; Gabrielse, G.

2016-05-01

Experimental searches for the electron electric-dipole moment (EDM) probe new physics beyond the standard model. The current best EDM limit was set by the ACME Collaboration [Science 343, 269 (2014), 10.1126/science.1248213], constraining time-reversal symmetry (T ) violating physics at the TeV energy scale. ACME used optical pumping to prepare a coherent superposition of ThO H3Δ1 states that have aligned electron spins. Spin precession due to the molecule's internal electric field was measured to extract the EDM. We report here on an improved method for preparing this spin-aligned state of the electron by using stimulated Raman adiabatic passage (STIRAP). We demonstrate a transfer efficiency of 75 %±5 % , representing a significant gain in signal for a next-generation EDM experiment. We discuss the particularities of implementing STIRAP in systems such as ours, where molecular ensembles with large phase-space distributions are transferred via weak molecular transitions with limited laser power and limited optical access.

Differential Electrochemical Conductance Imaging at the Nanoscale.

PubMed

López-Martínez, Montserrat; Artés, Juan Manuel; Sarasso, Veronica; Carminati, Marco; Díez-Pérez, Ismael; Sanz, Fausto; Gorostiza, Pau

2017-09-01

Electron transfer in proteins is essential in crucial biological processes. Although the fundamental aspects of biological electron transfer are well characterized, currently there are no experimental tools to determine the atomic-scale electronic pathways in redox proteins, and thus to fully understand their outstanding efficiency and environmental adaptability. This knowledge is also required to design and optimize biomolecular electronic devices. In order to measure the local conductance of an electrode surface immersed in an electrolyte, this study builds upon the current-potential spectroscopic capacity of electrochemical scanning tunneling microscopy, by adding an alternating current modulation technique. With this setup, spatially resolved, differential electrochemical conductance images under bipotentiostatic control are recorded. Differential electrochemical conductance imaging allows visualizing the reversible oxidation of an iron electrode in borate buffer and individual azurin proteins immobilized on atomically flat gold surfaces. In particular, this method reveals submolecular regions with high conductance within the protein. The direct observation of nanoscale conduction pathways in redox proteins and complexes enables important advances in biochemistry and bionanotechnology. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effects of p-(Trifluoromethoxy)benzyl and p-(Trifluoromethoxy)phenyl Molecular Architecture on the Performance of Naphthalene Tetracarboxylic Diimide-Based Air-Stable n-Type Semiconductors.

PubMed

Zhang, Dongwei; Zhao, Liang; Zhu, Yanan; Li, Aiyuan; He, Chao; Yu, Hongtao; He, Yaowu; Yan, Chaoyi; Goto, Osamu; Meng, Hong

2016-07-20

N,N'-Bis(4-trifluoromethoxyphenyl) naphthalene-1,4,5,8-tetracarboxylic acid diimide (NDI-POCF3) and N,N'-bis(4-trifluoromethoxybenzyl) naphthalene-1,4,5,8-tetracarboxylic acid diimide (NDI-BOCF3) have similar optical and electrochemical properties with a deep LUMO level of approximately 4.2 eV, but exhibit significant differences in electron mobility and molecular packing. NDI-POCF3 exhibits nondetectable charge mobility. Interestingly, NDI-BOCF3 shows air-stable electron transfer performance with enhanced mobility by increasing the deposition temperature onto the octadecyltrichlorosilane (OTS)-modified SiO2/Si substrates and achieves electron mobility as high as 0.7 cm(2) V(-1) s(-1) in air. The different mobilities of those two materials can be explained by several factors including thin-film morphology and crystallinity. In contrast to the poor thin-film morphology and crystallinity of NDI-POCF3, NDI-BOCF3 exhibits larger grain sizes and improved crystallinities due to the higher deposition temperature. In addition, the theoretical calculated transfer integrals of the intermolecular lowest unoccupied molecular orbital (LUMO) of the two materials further show that a large intermolecular orbital overlap of NDI-BOCF3 can transfer electron more efficiently than NDI-POCF3 in thin-film transistors. On the basis of fact that the theoretical calculations are consistent with the experimental results, it can be concluded that the p-(trifluoromethoxy) benzyl (BOCF3) molecular architecture on the former position of the naphthalene tetracarboxylic diimides (NDI) core provides a more effective way to enhance the intermolecular electron transfer property than the p-(trifluoromethoxy) phenyl (POCF3) group for the future design of NDI-related air-stable n-channel semiconductor.

Experimental analysis of R134a flow boiling inside a 5 PPI copper foam

NASA Astrophysics Data System (ADS)

Diani, A.; Mancin, S.; Rossetto, L.

2014-04-01

Heat dissipation is one of the most important issues for the reliability of electronic equipment. Boiling can be a very efficient heat transfer mechanism when used to face with the electronic technology needs of efficient and compact heat sinks. Recently, cellular structured materials both stochastic and periodic, particularly open cell metal foams, have been proposed as possible enhanced surfaces to lower the junction temperatures at high heat fluxes. Up today, most of the research on metal foams only regards single phase flow, whereas the two phase flow is still almost unexplored. This paper presents an experimental study on the heat transfer of R134a during flow boiling inside a 5 PPI (Pores Per linear Inch) copper foam, which is 5 mm high, 10 mm wide and 200 mm long, and it is brazed on a 10 mm thick copper plate. The experimental measurements were carried out by imposing three different heat fluxes (50, 75, and 100 kW m-2) and by varying the refrigerant mass velocity between 50 and 200 kg m-2 s-1 and the vapour quality from 0.2 to 0.90, at constant saturation temperature (30°C). The effects of the refrigerant mass flow rate, heat flux and vapour quality on the heat transfer coefficient, dry out phenomenon, and pressure drop are studied.

Design of hybrid nanoheterostructure systems for enhanced quantum and solar conversion efficiencies in dye-sensitized solar cells

NASA Astrophysics Data System (ADS)

Kılıç, Bayram; Telli, Hakan; Tüzemen, Sebahattin; Başaran, Ali; Pirge, Gursev

2015-04-01

Dye sensitized solar cells (DSSCs) with an innovative design involving controlled-morphology vertically aligned (VA) ZnO nanowires within mesoporous TiO2 structures with ultrahigh surface area for implementation as photoanodes are herein reported. Although TiO2 nanostructures exhibit excellent power conversion efficiency, the electron transport rate is low owing to low electron mobility. To overcome this, ZnO nanowires with high electron mobility have been investigated as potential candidates for photoanodes. However, the power conversion efficiency of ZnO nanowires is still lower than that of TiO2 owing to their low internal surface area. Consequently, in this work, vertical growth of ZnO nanowires within mesoporous TiO2 structures is carried out to increase their solar power conversion efficiency. The photovoltaic performance of solar cells using ZnO nanowires, mesoporous TiO2, and TiO2/ZnO hybrid structures are compared. The VA TiO2/ZnO hybrid structures are found to provide direct electron transfer compared with the tortuous pathway of zero-dimensional nanostructures, resulting in an increased conversion efficiency. It is demonstrated that the light scattering of the photoanode film is increased and electron recombination is decreased when an appropriate amount of mesoporous TiO2 is used as a substrate for ZnO nanowires. The DSSC fabricated with the TiO2/ZnO hybrid photoanode prepared with 15.8 wt. % TiO2 showed the highest conversion efficiency of 7.30%, approximately 5%, 18%, and 40% higher than that of DSSCs fabricated with 3.99 wt. % TiO2, pure TiO2, and pure ZnO photoanodes, respectively.

Old metal oxide clusters in new applications: spontaneous reduction of Keggin and Dawson polyoxometalate layers by a metallic electrode for improving efficiency in organic optoelectronics.

PubMed

Vasilopoulou, Maria; Douvas, Antonios M; Palilis, Leonidas C; Kennou, Stella; Argitis, Panagiotis

2015-06-03

The present study is aimed at investigating the solid state reduction of a representative series of Keggin and Dawson polyoxometalate (POM) films in contact with a metallic (aluminum) electrode and at introducing them as highly efficient cathode interlayers in organic optoelectronics. We show that, upon reduction, up to four electrons are transferred from the metallic electrode to the POM clusters of the Keggin series dependent on addenda substitution, whereas a six electron reduction was observed in the case of the Dawson type clusters. The high degree of their reduction by Al was found to be of vital importance in obtaining effective electron transport through the cathode interface. A large improvement in the operational characteristics of organic light emitting devices and organic photovoltaics based on a wide range of different organic semiconducting materials and incorporating reduced POM/Al cathode interfaces was achieved as a result of the large decrease of the electron injection/extraction barrier, the enhanced electron transport and the reduced recombination losses in our reduced POM modified devices.

Electron, proton and hydrogen-atom transfers in photosynthetic water oxidation.

PubMed Central

Tommos, Cecilia

2002-01-01

When photosynthetic organisms developed so that they could use water as an electron source to reduce carbon dioxide, the stage was set for efficient proliferation. Algae and plants spread globally and provided the foundation for our atmosphere and for O(2)-based chemistry in biological systems. Light-driven water oxidation is catalysed by photosystem II, the active site of which contains a redox-active tyrosine denoted Y(Z), a tetramanganese cluster, calcium and chloride. In 1995, Gerald Babcock and co-workers presented the hypothesis that photosynthetic water oxidation occurs as a metallo-radical catalysed process. In this model, the oxidized tyrosine radical is generated by coupled proton/electron transfer and re-reduced by abstracting hydrogen atoms from substrate water or hydroxide-ligated to the manganese cluster. The proposed function of Y(Z) requires proton transfer from the tyrosine site upon oxidation. The oxidation mechanism of Y(Z) in an inhibited and O(2)-evolving photosystem II is discussed. Domino-deprotonation from Y(Z) to the bulk solution is shown to be consistent with a variety of data obtained on metal-depleted samples. Experimental data that suggest that the oxidation of Y(Z) in O(2)-evolving samples is coupled to proton transfer in a hydrogen-bonding network are described. Finally, a dielectric-dependent model for the proton release that is associated with the catalytic cycle of photosystem II is discussed. PMID:12437877

A synthetic microbial consortium of Shewanella and Bacillus for enhanced generation of bioelectricity.

PubMed

Liu, Ting; Yu, Yang-Yang; Chen, Tao; Chen, Wei Ning

2017-03-01

In this study, a synthetic microbial consortium containing exoelectrogen Shewanella oneidensis MR-1 and riboflavin-producing strain, Bacillus subtilis RH33, was rationally designed and successfully constructed, enabling a stable, multiple cycles of microbial fuel cells (MFCs) operation for more than 500 h. The maximum power density of MFCs with this synthetic microbial consortium was 277.4 mW/m 2 , which was 4.9 times of that with MR-1 (56.9 mW/m 2 ) and 40.2 times of RH33 (6.9 mW/m 2 ), separately. At the same time, the Coulombic efficiency of the synthetic microbial consortium (5.6%) was higher than MR-1 (4.1%) and RH33 (2.3%). Regardless the high concentration of riboflavin produced by RH33, the power density of RH33 was rather low. The low bioelectricity generation can be ascribed to the low efficiency of RH33 in utilizing riboflavin for extracellular electron transfer (EET). In the synthetic microbial consortium of MR-1 and RH33, it was found that both mediated and direct electron transfer efficiencies were enhanced. By exchanging the anolyte of MR-1 and RH33, it was confirmed that the improved MFC performance with the synthetic microbial consortium was because MR-1 could efficiently utilize the high concentration of riboflavin produced by RH33. Biotechnol. Bioeng. 2017;114: 526-532. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

Communication: Broad manifold of excitonic states in light-harvesting complex 1 promotes efficient unidirectional energy transfer in vivo

NASA Astrophysics Data System (ADS)

Sohail, Sara H.; Dahlberg, Peter D.; Allodi, Marco A.; Massey, Sara C.; Ting, Po-Chieh; Martin, Elizabeth C.; Hunter, C. Neil; Engel, Gregory S.

2017-10-01

In photosynthetic organisms, the pigment-protein complexes that comprise the light-harvesting antenna exhibit complex electronic structures and ultrafast dynamics due to the coupling among the chromophores. Here, we present absorptive two-dimensional (2D) electronic spectra from living cultures of the purple bacterium, Rhodobacter sphaeroides, acquired using gradient assisted photon echo spectroscopy. Diagonal slices through the 2D lineshape of the LH1 stimulated emission/ground state bleach feature reveal a resolvable higher energy population within the B875 manifold. The waiting time evolution of diagonal, horizontal, and vertical slices through the 2D lineshape shows a sub-100 fs intra-complex relaxation as this higher energy population red shifts. The absorption (855 nm) of this higher lying sub-population of B875 before it has red shifted optimizes spectral overlap between the LH1 B875 band and the B850 band of LH2. Access to an energetically broad distribution of excitonic states within B875 offers a mechanism for efficient energy transfer from LH2 to LH1 during photosynthesis while limiting back transfer. Two-dimensional lineshapes reveal a rapid decay in the ground-state bleach/stimulated emission of B875. This signal, identified as a decrease in the dipole strength of a strong transition in LH1 on the red side of the B875 band, is assigned to the rapid localization of an initially delocalized exciton state, a dephasing process that frustrates back transfer from LH1 to LH2.

Development of highly accurate approximate scheme for computing the charge transfer integral

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pershin, Anton; Szalay, Péter G.

The charge transfer integral is a key parameter required by various theoretical models to describe charge transport properties, e.g., in organic semiconductors. The accuracy of this important property depends on several factors, which include the level of electronic structure theory and internal simplifications of the applied formalism. The goal of this paper is to identify the performance of various approximate approaches of the latter category, while using the high level equation-of-motion coupled cluster theory for the electronic structure. The calculations have been performed on the ethylene dimer as one of the simplest model systems. By studying different spatial perturbations, itmore » was shown that while both energy split in dimer and fragment charge difference methods are equivalent with the exact formulation for symmetrical displacements, they are less efficient when describing transfer integral along the asymmetric alteration coordinate. Since the “exact” scheme was found computationally expensive, we examine the possibility to obtain the asymmetric fluctuation of the transfer integral by a Taylor expansion along the coordinate space. By exploring the efficiency of this novel approach, we show that the Taylor expansion scheme represents an attractive alternative to the “exact” calculations due to a substantial reduction of computational costs, when a considerably large region of the potential energy surface is of interest. Moreover, we show that the Taylor expansion scheme, irrespective of the dimer symmetry, is very accurate for the entire range of geometry fluctuations that cover the space the molecule accesses at room temperature.« less

Full PIC simulations of solar radio emission

NASA Astrophysics Data System (ADS)

Sgattoni, A.; Henri, P.; Briand, C.; Amiranoff, F.; Riconda, C.

2017-12-01

Solar radio emissions are electromagnetic (EM) waves emitted in the solar wind plasma as a consequence of electron beams accelerated during solar flares or interplanetary shocks such as ICMEs. To describe their origin, a multi-stage model has been proposed in the 60s which considers a succession of non-linear three-wave interaction processes. A good understanding of the process would allow to infer the kinetic energy transfered from the electron beam to EM waves, so that the radio waves recorded by spacecraft can be used as a diagnostic for the electron beam.Even if the electrostatic problem has been extensively studied, full electromagnetic simulations were attempted only recently. Our large scale 2D-3V electromagnetic PIC simulations allow to identify the generation of both electrostatic and EM waves originated by the succession of plasma instabilities. We tested several configurations varying the electron beam density and velocity considering a background plasma of uniform density. For all the tested configurations approximately 105 of the electron-beam kinetic energy is transfered into EM waves emitted in all direction nearly isotropically. With this work we aim to design experiments of laboratory astrophysics to reproduce the electromagnetic emission process and test its efficiency.

Modification of graphene electronic properties via controllable gas-phase doping with copper chloride

NASA Astrophysics Data System (ADS)

Rybin, Maxim G.; Islamova, Vera R.; Obraztsova, Ekaterina A.; Obraztsova, Elena D.

2018-01-01

Molecular doping is an efficient, non-destructive, and simple method for changing the electronic structure of materials. Here, we present a simple air ambient vapor deposition method for functionalization of pristine graphene with a strong electron acceptor: copper chloride. The doped graphene was characterized by Raman spectroscopy, UV-vis-NIR optical absorption spectroscopy, scanning electron microscopy, and electro-physical measurements performed using the 4-probe method. The effect of charge transfer from graphene to a dopant results in shifting the Fermi level in doped graphene. The change of the electronic structure of doped graphene was confirmed by the tangential Raman peak (G-peak) shift and by the appearance of the gap in the UV-vis-NIR spectrum after doping. Moreover, the charge transfer resulted in a substantial decrease in electrical sheet resistance depending on the doping level. At the highest concentration of copper chloride, a Fermi level shift into the valence band up to 0.64 eV and a decrease in the sheet resistance value by 2.36 times were observed (from 888 Ω/sq to 376 Ω/sq for a single graphene layer with 97% of transparency).

Accuracy and Transferability of Ab Initio Electronic Band Structure Calculations for Doped BiFeO3

NASA Astrophysics Data System (ADS)

Gebhardt, Julian; Rappe, Andrew M.

2017-11-01

BiFeO3 is a multiferroic material and, therefore, highly interesting with respect to future oxide electronics. In order to realize such devices, pn junctions need to be fabricated, which are currently impeded by the lack of successful p-type doping in this material. In order to guide the numerous research efforts in this field, we recently finished a comprehensive computational study, investigating the influence of many dopants onto the electronic structure of BiFeO3. In order to allow for this large scale ab initio study, the computational setup had to be accurate and efficient. Here we discuss the details of this assessment, showing that standard density-functional theory (DFT) yields good structural properties. The obtained electronic structure, however, suffers from well-known shortcomings. By comparing the conventional DFT results for alkali and alkaline-earth metal doping with more accurate hybrid-DFT calculations, we show that, in this case, the problems of standard DFT go beyond a simple systematic error. Conventional DFT shows bad transferability and the more reliable hybrid-DFT has to be chosen for a qualitatively correct prediction of doping induced changes in the electronic structure of BiFeO3.

Photosynthetic water oxidation in Synechocystis sp. PCC6803: mutations D1-E189K, R and Q are without influence on electron transfer at the donor side of photosystem II.

PubMed

Clausen, J; Winkler, S; Hays, A M; Hundelt, M; Debus, R J; Junge, W

2001-11-01

The oxygen-evolving manganese cluster (OEC) of photosynthesis is oxidised by the photochemically generated primary oxidant (P(+*)(680)) of photosystem II via a tyrosine residue (Y(Z), Tyr161 on the D1 subunit of Synechocystis sp. PCC6803). The redox span between these components is rather small and probably tuned by protonic equilibria. The very efficient electron transfer from Y(Z) to P(+*)(680) in nanoseconds requires the intactness of a hydrogen bonded network involving Y(Z), D1-His190, and presumably D1-Glu189. We studied photosystem II core particles from photoautotrophic mutants where the residue D1-E189 was replaced by glutamine, arginine and lysine which were expected to electrostatically differ from the glutamate in the wild-type (WT). Surprisingly, the rates of electron transfer from Y(Z) to P(+*)(680) as well as from the OEC to Y(ox)(Z) were the same as in the WT. With the generally assumed proximity between D1-His190 (and thus D1-Glu189) and Y(Z), the lack of any influence on the electron transfer around Y(Z) straightforwardly implies a strongly hydrophobic environment forcing Glu (acid) and Lys, Arg (basic) at position D1-189 into electro-neutrality. As one alternative, D1-Glu189 could be located at such a large distance from the OEC, Y(Z) and P(+*)(680) that a charge on D1-189X does not influence the electron transfer. This seems less likely in the light of the drastic influence of its direct neighbour, D1-His190, on Y(Z) function. Another alternative is that D1-Glu189 is negatively charged, but is located in a cluster of acid/base groups that compensates for an alteration of charge at position 189, leaving the overall net charge unchanged in the Gln, Lys, and Arg mutants.

Investigation of excited state, reductive quenching, and intramolecular electron transfer of Ru(II)–Re(I) supramolecular photocatalysts for CO 2 reduction using time-resolved IR measurements

DOE PAGES

Koike, Kazuhide; Grills, David C.; Tamaki, Yusuke; ...

2018-02-14

Supramolecular photocatalysts in which Ru(II) photosensitizer and Re(I) catalyst units are connected to each other by an ethylene linker are among the best known, most effective and durable photocatalytic systems for CO 2 reduction. In this paper we report, for the first time, time-resolved infrared (TRIR) spectra of three of these binuclear complexes to uncover why the catalysts function so efficiently. Selective excitation of the Ru unit with a 532 nm laser pulse induces slow intramolecular electron transfer from the 3MLCT excited state of the Ru unit to the Re unit, with rate constants of (1.0–1.1) × 10 4 smore » -1 as a major component and (3.5–4.3) × 10 6 s -1 as a minor component, in acetonitrile. The produced charge-separated state has a long lifetime, with charge recombination rate constants of only (6.5–8.4) × 10 4 s -1. Thus, although it has a large driving force (-ΔG 0 CR ~ 2.6 eV), this process is in the Marcus inverted region. On the other hand, in the presence of 1-benzyl-1,4-dihydronicotinamide (BNAH), reductive quenching of the excited Ru unit proceeds much faster (k q[BNAH (0.2 M)] = (3.5–3.8) × 10 6 s -1) than the abovementioned intramolecular oxidative quenching, producing the one-electron-reduced species (OERS) of the Ru unit. Nanosecond TRIR data clearly show that intramolecular electron transfer from the OERS of the Ru unit to the Re unit (k ET > 2 × 10 7 s -1) is much faster than from the excited state of the Ru unit, and that it is also faster than the reductive quenching process of the excited Ru unit by BNAH. To measure the exact value of k ET, picosecond TRIR spectroscopy and a stronger reductant were used. Thus, in the case of the binuclear complex with tri(p-fluorophenyl)phosphine ligands (RuRe(FPh)), for which intramolecular electron transfer is expected to be the fastest among the three binuclear complexes, in the presence of 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH), k ET was measured as k ET = (1.4 ± 0.1) × 10 9 s -1. This clearly shows that intramolecular electron transfer in these RuRe binuclear supramolecular photocatalysts is not the rate-determining process in the photocatalytic reduction of CO 2, which is one of the main reasons why they work so efficiently.« less

Investigation of excited state, reductive quenching, and intramolecular electron transfer of Ru(II)–Re(I) supramolecular photocatalysts for CO 2 reduction using time-resolved IR measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Koike, Kazuhide; Grills, David C.; Tamaki, Yusuke

Supramolecular photocatalysts in which Ru(II) photosensitizer and Re(I) catalyst units are connected to each other by an ethylene linker are among the best known, most effective and durable photocatalytic systems for CO 2 reduction. In this paper we report, for the first time, time-resolved infrared (TRIR) spectra of three of these binuclear complexes to uncover why the catalysts function so efficiently. Selective excitation of the Ru unit with a 532 nm laser pulse induces slow intramolecular electron transfer from the 3MLCT excited state of the Ru unit to the Re unit, with rate constants of (1.0–1.1) × 10 4 smore » -1 as a major component and (3.5–4.3) × 10 6 s -1 as a minor component, in acetonitrile. The produced charge-separated state has a long lifetime, with charge recombination rate constants of only (6.5–8.4) × 10 4 s -1. Thus, although it has a large driving force (-ΔG 0 CR ~ 2.6 eV), this process is in the Marcus inverted region. On the other hand, in the presence of 1-benzyl-1,4-dihydronicotinamide (BNAH), reductive quenching of the excited Ru unit proceeds much faster (k q[BNAH (0.2 M)] = (3.5–3.8) × 10 6 s -1) than the abovementioned intramolecular oxidative quenching, producing the one-electron-reduced species (OERS) of the Ru unit. Nanosecond TRIR data clearly show that intramolecular electron transfer from the OERS of the Ru unit to the Re unit (k ET > 2 × 10 7 s -1) is much faster than from the excited state of the Ru unit, and that it is also faster than the reductive quenching process of the excited Ru unit by BNAH. To measure the exact value of k ET, picosecond TRIR spectroscopy and a stronger reductant were used. Thus, in the case of the binuclear complex with tri(p-fluorophenyl)phosphine ligands (RuRe(FPh)), for which intramolecular electron transfer is expected to be the fastest among the three binuclear complexes, in the presence of 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH), k ET was measured as k ET = (1.4 ± 0.1) × 10 9 s -1. This clearly shows that intramolecular electron transfer in these RuRe binuclear supramolecular photocatalysts is not the rate-determining process in the photocatalytic reduction of CO 2, which is one of the main reasons why they work so efficiently.« less

Study on Synergistic Mechanism of Inhibitor Mixture Based on Electron Transfer Behavior

PubMed Central

Han, Peng; He, Yang; Chen, Changfeng; Yu, Haobo; Liu, Feng; Yang, Hong; Ma, Yue; Zheng, Yanjun

2016-01-01

Mixing is an important method to improve the performance of surfactants due to their synergistic effect. The changes in bonding interaction and adsorption structure of IM and OP molecules before and after co-adsorbed on Fe(001) surface is calculated by DFTB+ method. It is found that mixture enable the inhibitor molecules with higher EHOMO donate more electrons while the inhibitor molecules with lower ELUMO accept more electrons, which strengthens the bonding interaction of both inhibitor agent and inhibitor additive with metal surface. Meanwhile, water molecules in the compact layer of double electric layer are repulsed and the charge transfer resistance during the corrosion process increases. Accordingly, the correlation between the frontier orbital (EHOMO and ELUMO of inhibitor molecules and the Fermi level of metal) and inhibition efficiency is determined. Finally, we propose a frontier orbital matching principle for the synergistic effect of inhibitors, which is verified by electrochemical experiments. This frontier orbital matching principle provides an effective quantum chemistry calculation method for the optimal selection of inhibitor mixture. PMID:27671332

Molecular dynamics simulations of the orientation properties of cytochrome c on the surface of single-walled carbon nanotubes.

PubMed

Zhang, Bing; Xu, Jia; Mo, Shu-Fan; Yao, Jian-Xi; Dai, Song-Yuan

2016-12-01

Electron transfer between cytochrome c (Cytc) and electrodes can be influenced greatly by the orientation of protein on the surface of the electrodes. In the present study, different initial orientations of Cytc on the surface of five types of single-walled carbon nanotubes (SWNTs), with different diameters and chirality, were constructed. Properties of the orientations of proteins on the surface of these tubes were first investigated through molecular dynamics simulations. It was shown that variations in SWNT diameter do not significantly affect the orientation; however, the chirality of the SWNTs is crucial to the orientation of the heme embedded in Cytc, and the orientation of the protein can consequently be influenced by the heme orientation. A new electron pathway between Cytc and SWNT, which hopefully benefits electron transfer efficiency, has also been proposed. This study promises to provide theoretical guidance for the rational design of bio-sensors or bio-fuel cells by using Cytc-decorated carbon nanotube electrodes.

Photoinduced Electron Transfer between Psoralens and DNA: Influence of DNA Sequence and Substitution.

PubMed

Fröbel, Sascha; Levi, Lucilla; Ulamec, Sabine M; Gilch, Peter

2016-05-04

Psoralens are heterocyclic compounds which are, among other uses, used to treat skin deseases in the framework of PUVA therapy. In the dark, they intercalate into DNA and can form photoadducts with thymines upon UV-A excitation, which harms the affected cells. We have recently discovered that after excitation of intercalated psoralens, an efficient photoinduced electron transfer (PET) from DNA occurs. Here, the PET is studied in detail by means of femtosecond transient absorption spectroscopy. Using DNA samples that contain either only GC or AT base pairs, we show that only guanine donates the electrons. Additionally, the substituent effects on PET are studied relying on three different psoralen derivatives. The substitution alters spectroscopic and electrochemical properties of the psoralens, which are determined by cyclic voltammetry and steady state spectroscopy. These experiments allow us to estimate the PET energetics, which are in line with the measured kinetics. Implications for the applications of psoralens are discussed. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electron transport limitation in P3HT:CdSe nanorods hybrid solar cells.

PubMed

Lek, Jun Yan; Xing, Guichuan; Sum, Tze Chien; Lam, Yeng Ming

2014-01-22

Hybrid solar cells have the potential to be efficient solar-energy-harvesting devices that can combine the benefits of solution-processable organic materials and the extended absorption offered by inorganic materials. In this work, an understanding of the factors limiting the performance of hybrid solar cells is explored. Through photovoltaic-device characterization correlated with transient absorption spectroscopy measurements, it was found that the interfacial charge transfer between the organic (P3HT) and inorganic (CdSe nanorods) components is not the factor limiting the performance of these solar cells. The insulating original ligands retard the charge recombination between the charge-transfer states across the CdSe-P3HT interface, and this is actually beneficial for charge collection. These cells are, in fact, limited by the subsequent electron collection via CdSe nanoparticles to the electrodes. Hence, the design of a more continuous electron-transport pathway should greatly improve the performance of hybrid solar cells in the future.

n l -> n' l' transition rates in electron and proton - Rydberg atom collision

NASA Astrophysics Data System (ADS)

Vrinceanu, Daniel

2017-04-01

Electrons and protons drive the recombination dynamics of highly excited Rydberg atoms in cold rarefied plasmas found in astrophysical conditions such as primordial recombination or star formation in H-II clouds. It has been recognized that collisions induce both energy and angular momentum transitions in Rydberg atoms, although in different proportions, depending on the initial state, temperature and the given species considered in the collision (electron or proton). Most studies focused on one collision type at a time, under the assumption that collision types are independent or their effects are not competing. The classical Monte-Carlo trajectory simulations presented in this work calculate the rates for both energy and angular momentum transfers and show their interdependence. For example, energy transfer with small angular momentum change are more efficient for target states with initial large angular momentum. The author acknowledges support received from the National Science Foundation through a Grant for the Center for Research on Complex Networks (HRD-1137732).