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Sample records for electron donor-acceptor interactions

  1. Electron Donor Acceptor Interactions. Final Progress Report

    SciTech Connect

    2002-08-16

    The Gordon Research Conference (GRC) on Electron Donor Acceptor Interactions was held at Salve Regina University, Newport, Rhode Island, 8/11-16/02. Emphasis was placed on current unpublished research and discussion of the future target areas in this field.

  2. 2012 ELECTRON DONOR-ACCEPTOR INTERACTIONS GORDON RESEARCH CONFERENCE, AUGUST 5-10, 2012

    SciTech Connect

    McCusker, James

    2012-08-10

    The upcoming incarnation of the Gordon Research Conference on Electron Donor Acceptor Interactions will feature sessions on classic topics including proton-coupled electron transfer, dye-sensitized solar cells, and biological electron transfer, as well as emerging areas such as quantum coherence effects in donor-acceptor interactions, spintronics, and the application of donor-acceptor interactions in chemical synthesis.

  3. Photocurrent generation through electron-exciton interaction at the organic semiconductor donor/acceptor interface.

    PubMed

    Chen, Lijia; Zhang, Qiaoming; Lei, Yanlian; Zhu, Furong; Wu, Bo; Zhang, Ting; Niu, Guoxi; Xiong, Zuhong; Song, Qunliang

    2013-10-21

    In this work, we report our effort to understand the photocurrent generation that is contributed via electron-exciton interaction at the donor/acceptor interface in organic solar cells (OSCs). Donor/acceptor bi-layer heterojunction OSCs, of the indium tin oxide/copper phthalocyanine (CuPc)/fullerene (C60)/molybdenum oxide/Al type, were employed to study the mechanism of photocurrent generation due to the electron-exciton interaction, where CuPc and C60 are the donor and the acceptor, respectively. It is shown that the electron-exciton interaction and the exciton dissociation processes co-exist at the CuPc/C60 interface in OSCs. Compared to conventional donor/acceptor bi-layer OSCs, the cells with the above configuration enable holes to be extracted at the C60 side while electrons can be collected at the CuPc side, resulting in a photocurrent in the reverse direction. The photocurrent thus observed is contributed to primarily by the charge carriers that are generated by the electron-exciton interaction at the CuPc/C60 interface, while charges derived from the exciton dissociation process also exist at the same interface. The mechanism of photocurrent generation due to electron-exciton interaction in the OSCs is further investigated, and it is manifested by the transient photovoltage characteristics and the external quantum efficiency measurements. PMID:24002235

  4. 2004 Electron Donor Acceptor Interactions Gordon Conference - August 8-13, 2004

    SciTech Connect

    GUILFORD JONES BOSTON UNIVERSITY PHOTONICS CENTER 8 ST. MARY'S ST BOSTON, MA 02215

    2005-09-14

    The 2004 Gordon Conference on Donor/Acceptor Interactions will take place at Salve Regina University in Newport, Rhode Island on August 8-13, 2004. The conference will be devoted to the consequences of charge interaction and charge motion in molecular and materials systems.

  5. Remarkable Dependence of the Final Charge Separation Efficiency on the Donor-Acceptor Interaction in Photoinduced Electron Transfer.

    PubMed

    Higashino, Tomohiro; Yamada, Tomoki; Yamamoto, Masanori; Furube, Akihiro; Tkachenko, Nikolai V; Miura, Taku; Kobori, Yasuhiro; Jono, Ryota; Yamashita, Koichi; Imahori, Hiroshi

    2016-01-11

    The unprecedented dependence of final charge separation efficiency as a function of donor-acceptor interaction in covalently-linked molecules with a rectilinear rigid oligo-p-xylene bridge has been observed. Optimization of the donor-acceptor electronic coupling remarkably inhibits the undesirable rapid decay of the singlet charge-separated state to the ground state, yielding the final long-lived, triplet charge-separated state with circa 100% efficiency. This finding is extremely useful for the rational design of artificial photosynthesis and organic photovoltaic cells toward efficient solar energy conversion. PMID:26610285

  6. 2010 Electron Donor-Acceptor Interactions Gordon Research Conference, August 8 - 13, 2010.

    SciTech Connect

    Gerald Meyer

    2010-08-18

    The Gordon Research Conference on Electron Donor Acceptor Interactions (GRC EDAI) presents and advances the current frontiers in experimental and theoretical studies of Electron Transfer Processes and Energy Conversion. The fundamental concepts underpinning the field of electron transfer and charge transport phenomena are understood, but fascinating experimental discoveries and novel applications based on charge transfer processes are expanding the discipline. Simultaneously, global challenges for development of viable and economical alternative energy resources, on which many researchers in the field focus their efforts, are now the subject of daily news headlines. Enduring themes of this conference relate to photosynthesis, both natural and artificial, and solar energy conversion. More recent developments include molecular electronics, optical switches, and nanoscale charge transport structures of both natural (biological) and man-made origin. The GRC EDAI is one of the major international meetings advancing this field, and is one of the few scientific meetings where fundamental research in solar energy conversion has a leading voice. The program includes sessions on coupled electron transfers, molecular solar energy conversion, biological and biomimetic systems, spin effects, ultrafast reactions and technical frontiers as well as electron transport in single molecules and devices. In addition to disseminating the latest advances in the field of electron transfer processes, the conference is an excellent forum for scientists from different disciplines to meet and initiate new directions; for scientists from different countries to make contacts; for young scientists to network and establish personal contacts with other young scientists and with established scientists who, otherwise, might not have the time to meet young people. The EDAI GRC also features an interactive atmosphere with lively poster sessions, a few of which are selected for oral presentations.

  7. Electron donor-acceptor interaction of 3,4-dimethylaniline with 2,3-dicyano-1,4-naphthoquinone

    NASA Astrophysics Data System (ADS)

    Neelgund, Gururaj M.; Magadum, Subash R.; Budni, M. L.

    2011-01-01

    The electron donor-acceptor (EDA) interaction between 2,3-dicyano-1,4-naphthoquinone (DCNQ) and 3,4-dimethylaniline (3,4-DMA) is studied in chloroform, dichloromethane and 1:1 (v/v) mixture of chloroform and dichloromethane. The rate of formation of the product was measured as a function of time using UV-vis spectrophotometer. The formation constant ( K) and molar extinction coefficient ( ɛ) values for the formation of EDA complex were evaluated in the temperature range of 20-35 °C. The pseudo-first-order rate constant ( k1) and the second-order rate constant ( k2) for the disappearance of EDA complex and for the formation of product were evaluated. The activation parameters (Δ H#, Δ S# and Δ G#) of the reaction were determined by temperature dependence of rate constants using the Arrhenius plots. The effect of relative permittivity of the medium on the reaction is discussed. The observed results indicate that formation of final product proceeds through initial formation of EDA complex as an intermediate. The product of the reaction was purified by column chromatography method and identified as 3-( N-3,4-dimethyl-phenylamino)-2-cyano-1,4-naphthoquinone by elemental analysis, IR and NMR spectroscopy. On the basis of kinetic, analytical and spectroscopic results, a plausible mechanism for the formation of EDA complex and its transformation into product is proposed.

  8. Aromatic donor-acceptor interactions in non-polar environments.

    PubMed

    Prentice, Giles M; Pascu, Sofia I; Filip, Sorin V; West, Kevin R; Pantoş, G Dan

    2015-05-14

    We have evaluated the strength of aromatic donor-acceptor interactions between dialkyl naphthalenediimide and dialkoxynaphthalene in non-polar environments. (1)H NMR, UV-vis spectroscopy and isothermal titration calorimetry were used to characterise this interaction. We concluded that the strength of donor-acceptor interactions in heptane is sufficient to drive supramolecular assemblies in this and other aliphatic solvents. PMID:25875729

  9. 2008 Electron Donor Acceptor Interactions Gordon Research Conference-August 3-8, 2009

    SciTech Connect

    Malcolm Forbes and Nancy Ryan Gray

    2009-09-19

    The conference presents and advances the current frontiers in experimental and theoretical studies of Electron Transfer and Transport in Molecular and Nano-scale Systems. The program includes sessions on coupled electron transfers, molecular solar energy conversion, biological and biomimetic systems, spin effects, ultrafast reactions and technical frontiers as well as electron transport in single molecules and devices.

  10. Electron Transfer Rate Maxima at Large Donor-Acceptor Distances.

    PubMed

    Kuss-Petermann, Martin; Wenger, Oliver S

    2016-02-01

    Because of their low mass, electrons can transfer rapidly over long (>15 Å) distances, but usually reaction rates decrease with increasing donor-acceptor distance. We report here on electron transfer rate maxima at donor-acceptor separations of 30.6 Å, observed for thermal electron transfer between an anthraquinone radical anion and a triarylamine radical cation in three homologous series of rigid-rod-like donor-photosensitizer-acceptor triads with p-xylene bridges. Our experimental observations can be explained by a weak distance dependence of electronic donor-acceptor coupling combined with a strong increase of the (outer-sphere) reorganization energy with increasing distance, as predicted by electron transfer theory more than 30 years ago. The observed effect has important consequences for light-to-chemical energy conversion. PMID:26800279

  11. Spectral engineering in π-conjugated polymers with intramolecular donor-acceptor interactions.

    PubMed

    Beaujuge, Pierre M; Amb, Chad M; Reynolds, John R

    2010-11-16

    With the development of light-harvesting organic materials for solar cell applications and molecular systems with fine-tuned colors for nonemissive electrochromic devices (e.g., smart windows, e-papers), a number of technical challenges remain to be overcome. Over the years, the concept of "spectral engineering" (tailoring the complex interplay between molecular physics and the various optical phenomena occurring across the electromagnetic spectrum) has become increasingly relevant in the field of π-conjugated organic polymers. Within the spectral engineering toolbox, the "donor-acceptor" approach uses alternating electron-rich and electron-deficient moieties along a π-conjugated backbone. This approach has proved especially valuable in the synthesis of dual-band and broadly absorbing chromophores with useful photovoltaic and electrochromic properties. In this Account, we highlight and provide insight into a present controversy surrounding the origin of the dual band of absorption sometimes encountered in semiconducting polymers structured using the "donor-acceptor" approach. Based on empirical evidence, we provide some schematic representations to describe the possible mechanisms governing the evolution of the two-band spectral absorption observed on varying the relative composition of electron-rich and electron-deficient substituents along the π-conjugated backbone. In parallel, we draw attention to the choice of the method employed to estimate and compare the absorption coefficients of polymer chromophores exhibiting distinct repeat unit lengths, and containing various extents of solubilizing side-chains along their backbone. Finally, we discuss the common assumption that "donor-acceptor" systems should have systematically lower absorption coefficients than their "all-donor" counterparts. The proposed models point toward important theoretical parameters which could be further explored at the macromolecular level to help researchers take full advantage of the

  12. Benzo[e]pyrene skeleton dipyrylium dication with a strong donor-acceptor-donor interaction, and its two-electron reduced molecule.

    PubMed

    Rao, Koya Prabhakara; Kondo, Mio; Sakamoto, Ryota; Kusamoto, Tetsuro; Nishikawa, Michihiro; Kume, Shoko; Nihei, Masayuki; Oshio, Hiroki; Nishihara, Hiroshi

    2011-12-01

    The donor-acceptor-donor (D-A-D) conjugated molecules 1,4-bis(diarylaminophenylethynyl)anthraquinone (1,4-Am(2)Aq) and 1,4-bis(ferrocenylethynyl)anthraquinone (1,4-Fc(2)Aq), undergo a double proton cyclization reaction with bis(trifluoromethanesulfone)imide acid (TFSIH) to yield 1,4-bis(diarylaminophenyl or ferrocenyl) dipyrylium salts [1,4-R(2)Pyl(2)](TFSI)(2) (R=Am or Fc) with novel planar pentacyclic structures similar to the aromatic benzo[e]pyrene-type skeleton. [1,4-Am(2)Pyl(2)](TFSI)(2) could be reduced to give the neutral molecule [1,4-Am(2)Pyl(2)](0), which is stable and maintains the benzo[e]pyrene-type skeleton. To the best of our knowledge, this is the first oxygen-atom-containing polycyclic aromatic hydrocarbon with 22 (4n+2) π-electrons. The obtained condensed-ring benzo[e]pyrene-type skeleton compounds show physical and chemical properties that are significantly different from those of [1,5-Am(2)Pyl(2)](TFSI)(2), which has a perylene-type skeleton.

  13. Intramolecular Charge-Transfer Interaction of Donor-Acceptor-Donor Arrays Based on Anthracene Bisimide.

    PubMed

    Iwanaga, Tetsuo; Ogawa, Marina; Yamauchi, Tomokazu; Toyota, Shinji

    2016-05-20

    We designed anthracene bisimide (ABI) derivatives having two triphenylamine (TPA) groups as donor units at the 9,10-positions to form a novel π-conjugated donor-acceptor system. These compounds and their analogues with ethynylene linkers were synthesized by Suzuki-Miyaura and Sonogashira coupling reactions, respectively. In UV-vis spectra, the linker-free derivatives showed broad absorption bands arising from intramolecular charge-transfer interactions. Introducing ethynylene linkers resulted in a considerable red shift of the absorption bands. In fluorescence spectra, the ethynylene derivatives showed intense emission bands at 600-650 nm. Their photophysical and electrochemical properties were compared with those of the corresponding mono TPA derivatives on the basis of theoretical calculations and cyclic voltammetry to evaluate the intramolecular electronic interactions between the donor and acceptor units.

  14. Energy level realignment in weakly interacting donor-acceptor binary molecular networks.

    PubMed

    Zhong, Jian-Qiang; Qin, Xinming; Zhang, Jia-Lin; Kera, Satoshi; Ueno, Nobuo; Wee, Andrew Thye Shen; Yang, Jinlong; Chen, Wei

    2014-02-25

    Understanding the effect of intermolecular and molecule-substrate interactions on molecular electronic states is key to revealing the energy level alignment mechanism at organic-organic heterojunctions or organic-inorganic interfaces. In this paper, we investigate the energy level alignment mechanism in weakly interacting donor-acceptor binary molecular superstructures, comprising copper hexadecafluorophthalocyanine (F16CuPc) intermixed with copper phthalocyanine (CuPc), or manganese phthalocynine (MnPc) on graphite. The molecular electronic structures have been systematically studied by in situ ultraviolet photoelectron spectroscopy (UPS) and low-temperature scanning tunneling microscopy/spectroscopy (LT-STM/STS) experiments and corroborated by density functional theory (DFT) calculations. As demonstrated by the UPS and LT-STM/STS measurements, the observed unusual energy level realignment (i.e., a large downward shift in donor HOMO level and a corresponding small upward shift in acceptor HOMO level) in the CuPc-F16CuPc binary superstructures originates from the balance between intermolecular and molecule-substrate interactions. The enhanced intermolecular interactions through the hydrogen bonding between neighboring CuPc and F16CuPc can stabilize the binary superstructures and modify the local molecular electronic states. The obvious molecular energy level shift was explained by gap-state-mediated interfacial charge transfer. PMID:24433044

  15. Donor-acceptor graphene-based hybrid materials facilitating photo-induced electron-transfer reactions.

    PubMed

    Stergiou, Anastasios; Pagona, Georgia; Tagmatarchis, Nikos

    2014-01-01

    Graphene research and in particular the topic of chemical functionalization of graphene has exploded in the last decade. The main aim is to increase the solubility and thereby enhance the processability of the material, which is otherwise insoluble and inapplicable for technological applications when stacked in the form of graphite. To this end, initially, graphite was oxidized under harsh conditions to yield exfoliated graphene oxide sheets that are soluble in aqueous media and amenable to chemical modifications due to the presence of carboxylic acid groups at the edges of the lattice. However, it was obvious that the high-defect framework of graphene oxide cannot be readily utilized in applications that are governed by charge-transfer processes, for example, in solar cells. Alternatively, exfoliated graphene has been applied toward the realization of some donor-acceptor hybrid materials with photo- and/or electro-active components. The main body of research regarding obtaining donor-acceptor hybrid materials based on graphene to facilitate charge-transfer phenomena, which is reviewed here, concerns the incorporation of porphyrins and phthalocyanines onto graphene sheets. Through illustrative schemes, the preparation and most importantly the photophysical properties of such graphene-based ensembles will be described. Important parameters, such as the generation of the charge-separated state upon photoexcitation of the organic electron donor, the lifetimes of the charge-separation and charge-recombination as well as the incident-photon-to-current efficiency value for some donor-acceptor graphene-based hybrids, will be discussed.

  16. Donor acceptor electronic couplings in π-stacks: How many states must be accounted for?

    NASA Astrophysics Data System (ADS)

    Voityuk, Alexander A.

    2006-04-01

    Two-state model is commonly used to estimate the donor-acceptor electronic coupling Vda for electron transfer. However, in some important cases, e.g. for DNA π-stacks, this scheme fails to provide accurate values of Vda because of multistate effects. The Generalized Mulliken-Hush method enables a multistate treatment of Vda. In this Letter, we analyze the dependence of calculated electronic couplings on the number of the adiabatic states included in the model. We suggest a simple scheme to determine this number. The superexchange correction of the two-state approximation is shown to provide good estimates of the electronic coupling.

  17. Fresh look at electron-transfer mechanisms via the donor/acceptor bindings in the critical encounter complex.

    PubMed

    Rosokha, Sergiy V; Kochi, Jay K

    2008-05-01

    Seminal insights provided by the iconic R. S. Mulliken and his "charge-transfer" theory, H. Taube and his "outer/inner-sphere" mechanisms, R. A. Marcus and his "two-state non-adiabatic" theory, and N. S. Hush and his "intervalence" theory are each separately woven into the rich panoramic tapestry constituting chemical research into electron-transfer dynamics, and its mechanistic dominance for the past half century and more. In this Account, we illustrate how the simultaneous melding of all four key concepts allows sharp focus on the charge-transfer character of the critical encounter complex to evoke the latent facet of traditional electron-transfer mechanisms. To this end, we exploit the intervalence (electronic) transition that invariably accompanies the diffusive encounter of electron-rich organic donors (D) with electron-poor acceptors (A) as the experimental harbinger of the collision complex, which is then actually isolated and X-ray crystallographically established as loosely bound pi-stacked pairs of various aromatic and olefinic donor/acceptor dyads with uniform interplanar separations of r(DA) = 3.1 +/- 0.2 A. These X-ray structures, together with the spectral measurements of their intervalence transitions, lead to the pair of important electron-transfer parameters, H(DA) (electronic coupling element) versus lambdaT (reorganization energy), the ratio of which generally defines the odd-electron mobility within such an encounter complex in terms of the resonance stabilization of the donor/acceptor assembly [D, A] as opposed to the reorganization-energy penalty required for its interconversion to the electron-transfer state [D(+*), A(-*)]. We recognize the resonance-stabilization energy relative to the intrinsic activation barrier as the mechanistic binding factor, Q = 2H(DA)/lambdaT, to represent the quantitative measure of the highly variable continuum of inner-sphere/outer-sphere interactions that are possible within various types of precursor complexes

  18. Tuning the electronic coupling in a low-bandgap donor-acceptor copolymer via the placement of side-chains

    SciTech Connect

    Oberhumer, Philipp M.; Huang, Ya-Shih; Massip, Sylvain; Albert-Seifried, Sebastian; Greenham, Neil C.; Hodgkiss, Justin M.; Friend, Richard H.; James, David T.; Kim, Ji-Seon; Tu Guoli; Huck, Wilhelm T. S.; Beljonne, David; Cornil, Jerome

    2011-03-21

    We present a spectroscopic and theoretical investigation of the effect of the presence and position of hexyl side-chains in the novel low-bandgap alternating donor-acceptor copolymer poly[bis-N,N-(4-octylphenyl)-bis-N,N-phenyl-1, 4-phenylenediamine-alt-5,5'-4',7',-di-2-thienyl-2',1',3'-benzothiadiazole] (T8TBT). We use electronic absorption and Raman spectroscopic measurements supported by calculations of chain conformation, electronic transitions, and Raman modes. Using these tools, we find that sterically demanding side-chain configurations induce twisting in the electronic acceptor unit and reduce the electronic interaction with the donor. This leads to a blue-shifted and weakened (partial) charge-transfer absorption band together with a higher photoluminescence efficiency. On the other hand, sterically relaxed side-chain configurations promote coupling between donor and acceptor units and exhibit enhanced absorption at the expense of luminescence efficiency. The possibility of tuning the donor-acceptor character of conjugated polymers by varying the placement of side-chains has very important ramifications for light emitting diode, Laser, display, and photovoltaic device optimization.

  19. The effects of conformation on the noncovalent bonding interactions in a bistable donor-acceptor [3]catenane.

    PubMed

    Wang, Cheng; Cao, Dennis; Fahrenbach, Albert C; Grunder, Sergio; Dey, Sanjeev K; Sarjeant, Amy A; Stoddart, J Fraser

    2012-09-25

    A switchable donor-acceptor bistable [3]catenane, composed of a crown ether containing a pair of alternating π-electron rich tetrathiafulvalene and 1,5-dioxynaphthalene units, encircled by two π-electron deficient cyclobis(paraquat-p-phenylene) rings, has been synthesised and the redox-activated switching it undergoes investigated.

  20. Triazole bridges as versatile linkers in electron donor-acceptor conjugates

    PubMed Central

    de Miguel, Gustavo; Wielopolski, Mateusz; Schuster, David I.; Fazio, Michael A; Lee, Olivia P.; Haley, Christopher K.; Ortiz, Angy L.; Echegoyen, Luis; Clark, Timothy; Guldi, Dirk M.

    2011-01-01

    Aromatic triazoles have been frequently used as π-conjugated linkers in intramolecular electron transfer processes. To gain a deeper understanding of the electron mediating function of triazoles, we have synthesized a family of new triazole-based electron donor-acceptor conjugates. We have connected porphyrins and fullerenes through a central triazole moiety – (ZnP-Tri-C60) – each with a single change in their connection through the linker. An extensive photophysical and computational investigation reveals that the electron transfer dynamics – charge separation and charge recombination – in the different ZnP-Tri-C60 conjugates reflect a significant influence of the connectivity at the triazole linker. Except for m4m-ZnP-Tri-C60 17, the conjugates exhibit through-bond electron transfer with varying rate constants. Since the through-bond distance is nearly equal in the ZnP-Tri-C60 conjugates, the variation in charge separation and charge recombination dynamics is mainly associated with the electronic properties of the conjugates, including orbital energies, electron affinity, and the energies of the excited states. The changes of the electronic couplings are, in turn, a consequence of the different connectivity patterns at the triazole moieties. PMID:21702513

  1. Experimental investigation of donor-acceptor electron transfer and back transfer in solid solutions

    SciTech Connect

    Dorfman, R.C.; Lin, Y.; Fayer, M.D. )

    1989-08-24

    Electron transfer from an optically excited donor (rubrene) to randomly distributed acceptors (duroquinone) followed by electron back transfer in a rigid solution (sucrose octaacetate) has been studied experimentally. The forward electron-transfer process was observed by time-dependent fluorescence quenching measurements, while the electron back transfer from the radical anion to the radical cation was monitored by use of the picosecond transient grating technique. A statistical mechanics theory is used to describe the time-dependent dynamics of the system and to extract the forward- and back-transfer parameters from the data. The theory includes donor-acceptor and acceptor-acceptor excluded volume. It is found that the inclusion of excluded volume is necessary to obtain accurate transfer parameters. These parameters enable a detailed description of the electron transfer and recombination dynamics to be given. The agreement between theory and experiment is excellent. A variety of time-dependent properties of the system are calculated. These include the time-dependent ion populations and the probability that the ith acceptor is an ion as a function of time and distance. In addition, (R(t)) and ({tau}(t)), which are the average ion separation as a function of time and the average ion existence time as a function of ion separation, respectively, are calculated.

  2. Theory and computational modeling: Medium reorganization and donor/acceptor coupling in electron transfer processes

    SciTech Connect

    Newton, M.D.; Feldberg, S.W.; Smalley, J.F.

    1998-03-01

    The continuing goal is to convert the rapidly accumulating mechanistic information about electron transfer (et) kinetics (often representable in terms of simple rate constants) into precise tools for fine-tuned control of the kinetics and for design of molecular-based systems which meet specified et characteristics. The present treatment will be limited to the kinetic framework defined by the assumption of transition state theory (TST). The primary objective of this paper is to report recent advances in the theoretical formulation, calculation, and analysis of energetics and electronic coupling pertinent to et in complex molecular aggregates. The control of et kinetics (i.e., enhancing desired processes, while inhibiting others) involves, of course, both system energetics (especially reorganization energies (E{sub r}) and free energy changes ({Delta}G{sup 0})) and electronic coupling of local D and A sites, which for thermal processes is most directly relevant only after the system has reached the appropriate point (or region) along the reaction coordinate (i.e., the transition state). The authors first discuss TST rate constant models, emphasizing genetic features, but also noting some special features arising when metal electrodes are involved. They then turn to a consideration of detailed aspects of medium reorganization and donor/acceptor coupling. With these theoretical tools in hand, they examine the results of recent applications to complex molecular systems using the techniques of computational quantum chemistry and electrostatics, together with detailed analysis of the numerical results and comparison with recent electrochemical kinetic data.

  3. Phenothiazine-anthraquinone donor-acceptor molecules: synthesis, electronic properties and DFT-TDDFT computational study.

    PubMed

    Zhang, Wen-Wei; Mao, Wei-Li; Hu, Yun-Xia; Tian, Zi-Qi; Wang, Zhi-Lin; Meng, Qing-Jin

    2009-09-17

    Two donor-acceptor molecules with different pi-electron conjugative units, 1-((10-methyl-10H-phenothiazin-3-yl)ethynyl)anthracene-9,10-dione (AqMp) and 1,1'-(10-methyl-10H-phenothiazine-3,7-diyl)bis(ethyne-2,1-diyl)dianthracene-9,10-dione (Aq2Mp), have been synthesized and investigated for their photochemical and electrochemical properties. Density functional theory (DFT) calculations provide insights into their molecular geometry, electronic structures, and properties. These studies satisfactorily explain the electrochemistry of the two compounds and indicate that larger conjugative effect leads to smaller HOMO-LUMO gap (Eg) in Aq2Mp. Both compounds show ICT and pi --> pi* transitions in the UV-visible range in solution, and Aq2Mp has a bathochromic shift and shows higher oscillator strength of the absorption, which has been verified by time-dependent DFT (TDDFT) calculations. The differences between AqMp and Aq2Mp indicate that the structural and conjugative effects have great influence on the electronic properties of the molecules. PMID:19705823

  4. Femtosecond transient grating studies of electron transfer in porphyrin and chlorophyll donor-acceptor molecules

    SciTech Connect

    Wiederrecht, G.P.; Svec, W.A.; Wasielewski, M.R.

    1994-04-01

    Transient grating studies of electron transfer in artificial photosynthetic systems are described. These systems include simple donor-acceptor molecules where the donor, a chlorophyll or porphyrin, is rigidly attached to an easily reduced species such as napthoquinone or benzoquinone. We have previously synthesized acceptor molecules which have well defined absorption bands upon reduction and are well removed from the excited and cationic states of porphyrins and chlorophylls. They also possess large molar extinction coefficients that dominate the spectra and have well defined polarization characteristics. These traits are ideal for polarization sensitive transient grating experiments which enable accurate determination of the angle of the transition dipole between the initial excitation and the acceptor probe, dynamic solvation effects on the charge separated species, and any time dependent rotation of the chromophores relative to each other. An example of the type of molecule utilized for these experiments is a free base porphyrin (HP) donor and a pyromellitic diimide (PI) acceptor directly bonded to the porphyrin ring.

  5. Electrical Instability Induced by Electron Trapping in Low-Bandgap Donor-Acceptor Polymer Field-Effect Transistors.

    PubMed

    Phan, Hung; Wang, Ming; Bazan, Guillermo C; Nguyen, Thuc-Quyen

    2015-11-18

    The mechanism of electrical instability and the double slope of p-type organic field-effect transistors (OFETs) fabricated from low-bandgap donor-acceptor copolymers are resolved. Those polymers enable electron conduction in the device, which leads to electron trapping and consequent formation of -SiO(-). This causes a turn-on voltage shift, hole-mobility increase, and double-slope occurrence. These findings tremendously impact the molecular design and device engineering of OFETs. PMID:26441385

  6. Intermolecular electron transfer promoted by directional donor-acceptor attractions in self-assembled diketopyrrolopyrrole-thiophene films.

    PubMed

    Liu, Huiying; Jia, Hui; Wang, Lanfen; Wu, Yishi; Zhan, Chuanlang; Fu, Hongbing; Yao, Jiannian

    2012-11-01

    The photophysics of a symmetric triad consisting of two bithiophene (BT) units covalently linked to a central diketopyrrolopyrrole unit (DPP) has been investigated both in dichloromethane and in the thin film. The DPP-BT film exhibits a red-shifted low-energy absorption band compared to its solution, which is indicative of efficient π-π interactions in the solid-state phase. The steady-state and time-resolved fluorescence results revealed that the photoluminescence was subjected to severe emission quenching when DPP-BT changes from its solution phase to its film form. Further femtosecond transient absorption studies clarified that rapid intermolecular electron transfer accounts for the considerable fluorescence quenching event. The structural characterization of DPP-BT nanobelts, based on GIXRD and SAED patterns, suggested that the composite may be self-assembled into a slipped face-to-face configuration in the film, providing compact interlayer D-A interactions. As a result, intermolecular electron transfer is promoted by the favorable donor-acceptor attractions between the adjacent molecules. Moreover, this packing configuration provides a moderate channel for charge transportation. The hole mobility, which was measured based on a single-belt field-effect transistor, was found to be around 0.07 cm(2) V(-1) s(-1). Our observation reveals the role of spatial orientation in photophysical processes and the consequential semiconductor performance, providing guidance for the development and self-assembly of new opto-electronic molecules. PMID:22951990

  7. Donor/acceptor chromophores-decorated triazolyl unnatural nucleosides: synthesis, photophysical properties and study of interaction with BSA.

    PubMed

    Bag, Subhendu Sekhar; Talukdar, Sangita; Das, Suman Kalyan; Pradhan, Manoj Kumar; Mukherjee, Soumen

    2016-06-14

    Much effort has been put forth to develop unnatural, stable, hydrophobic base pairs with orthogonal recognition properties and study their effect on DNA duplex stabilisation. Our continuous efforts on the design of fluorescent unnatural biomolecular building blocks lead us to the synthesis of some triazolyl donor/acceptor unnatural nucleosides via an azide-alkyne 1,3-dipolar cycloaddition reaction as a key step, which we want to report herein. We have studied their photophysical properties and found interesting solvatochromic fluorescence for two of the nucleosides. Photophysical interactions among two donor-acceptor β-nucleosides as well as a pair of α/β-nucleosides have also been evaluated. Furthermore, we have exploited one of the fluorescent nucleosides in studying its interaction with BSA with the help of UV-visible and steady state fluorescence techniques. Our design concept is based on the hypothesis that a pair of such donor/acceptor nucleosides might be involved in π-stacking as well as in photophysical interactions, leading to stabilization of the DNA duplex if such nucleosides can be incorporated into short oligonucleotide sequences. Therefore, the designed bases may find application in biophysical studies in the context of DNA. PMID:27181694

  8. Charge transfer in the electron donor-acceptor complexes of a meso-phenol BODIPY dye with chloranils and fullerenes

    NASA Astrophysics Data System (ADS)

    Karmakar, Animesh; Chaudhuri, Tandrima; Mula, Soumyaditya; Chattopadhyay, Subrata

    2015-02-01

    UV-Vis spectral investigations of electron donor-acceptor complexes of laser dye 2,6-Diethyl-4,4-difluoro-1,3,5,7-tetramethyl-8-(4‧-hydroxyphenyl)-4-bora-3a,4a-diaza-s-indecene (1c) with chloranils and fullerenes are reported in toluene medium. Well defined charge transfer (CT) absorption bands have been located in the visible region. Oscillator strengths, transition dipole and resonance energies of the CT complexes have been estimated. Vertical ionization potential of 1c has been determined utilizing Mulliken's equation. A possible mechanism for the interaction between electronic subsystems of chloranils, [60]- and [70]fullerenes with three different BODIPY dyes (1a, 1b and 1c shown in Fig. 1) have been discussed in comparing the parameters like degree of charge transfer and binding constant in nonpolar toluene. Comparison of 1c complexes is done with DFT/B3LYP/6-31G optimized gas phase geometries.

  9. Strong electronic coupling and electron transfer in a Ce2@Ih-C80-H2P electron donor acceptor conjugate

    NASA Astrophysics Data System (ADS)

    Rudolf, Marc; Feng, Lai; Slanina, Zdenek; Wang, Weiwei; Nagase, Shigeru; Akasaka, Takeshi; Guldi, Dirk M.

    2016-07-01

    A newly designed electron donor-acceptor conjugate, namely Ce2@Ih-C80-H2P consisting of an endohedral dimetallofullerene Ce2@Ih-C80 and a free-base prophyrin (H2P), has been synthesized and systematically investigated. Basic characterization by means of NMR spectroscopy, steady-state absorption spectroscopy, and electrochemistry points to a folded configuration with sizeable interactions between Ce2@Ih-C80 and H2P. Complementary DFT optimization also results in the same conclusions. Time-resolved absorption spectroscopic investigations corroborate the formation of the (Ce2)&z.rad;-@Ih-C80-(H2P)&z.rad;+ radical ion pair state in non-polar as well as polar media. Overall, the modus operandi is an ultrafast through-space electron transfer enabled by the folded configuration in the ground and excited state.A newly designed electron donor-acceptor conjugate, namely Ce2@Ih-C80-H2P consisting of an endohedral dimetallofullerene Ce2@Ih-C80 and a free-base prophyrin (H2P), has been synthesized and systematically investigated. Basic characterization by means of NMR spectroscopy, steady-state absorption spectroscopy, and electrochemistry points to a folded configuration with sizeable interactions between Ce2@Ih-C80 and H2P. Complementary DFT optimization also results in the same conclusions. Time-resolved absorption spectroscopic investigations corroborate the formation of the (Ce2)&z.rad;-@Ih-C80-(H2P)&z.rad;+ radical ion pair state in non-polar as well as polar media. Overall, the modus operandi is an ultrafast through-space electron transfer enabled by the folded configuration in the ground and excited state. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr03324e

  10. ELECTRON DONOR ACCEPTOR DESCRIPTORS OF THE SINGLE AND DOUBLE BONDED SUBSTITUENT AND HETEROATOM INCORPORATION EFFECTS. A REVIEW.

    PubMed

    Mazurek, Andrzej

    2016-01-01

    The properties of the series of Electron Donor-Acceptor (EDA) descriptors of classical substituent effect (sEDA(I), pEDA(I)), double bonded substituent effect (sEDA(=), pEDA(=)), heteroatom incorporation effect in monocyclic systems (sEDA(II), pEDA(II)), and in ring-junction position (sEDA(III), pEDA(III)), are reviewed. The descriptors show the amount of electrons donated to or withdrawn from the σ-(sEDA) or π(pEDA) valence orbitals by the substituent or incorporant. The new descriptors are expected to enrich the potency of QSAR analyses in drug design and materials chemistry.

  11. Three Redox States of a Diradical Acceptor-Donor-Acceptor Triad: Gating the Magnetic Coupling and the Electron Delocalization.

    PubMed

    Souto, Manuel; Lloveras, Vega; Vela, Sergi; Fumanal, Maria; Ratera, Imma; Veciana, Jaume

    2016-06-16

    The diradical acceptor-donor-acceptor triad 1(••), based on two polychlorotriphenylmethyl (PTM) radicals connected through a tetrathiafulvalene(TTF)-vinylene bridge, has been synthesized. The generation of the mixed-valence radical anion, 1(•-), and triradical cation species, 1(•••+), obtained upon electrochemical reduction and oxidation, respectively, was monitored by optical and ESR spectroscopy. Interestingly, the modification of electron delocalization and magnetic coupling was observed when the charged species were generated and the changes have been rationalized by theoretical calculations.

  12. The separation distance distribution in electron-donor-acceptor systems and the wavelength dependence of free ion yields

    NASA Astrophysics Data System (ADS)

    Zhou, Jinwei; Findley, Bret R.; Braun, Charles L.; Sutin, Norman

    2001-06-01

    We recently reported that free radical ion quantum yields for electron-donor-acceptor (EDA) systems of alkylbenzenes-tetracyanoethylene (TCNE) exhibit a remarkable wavelength dependence in dichloromethane, a medium polarity solvent. We proposed that weak absorption by long-distance, unassociated or "random" D⋯A pairs is mainly responsible for the free radical ion yield. Here a model for the wavelength dependence of the free ion yield is developed for four systems in which differing degrees of EDA complex formation are present: 1,3,5-tri-tert-butylbenzene-TCNE in which only random pairs exist due to the bulky groups on the electron donor, and toluene—TCNE, 1,3,5-triethylbenzene-TCNE and 1,3,5-trimethylbenzene-TCNE. Mulliken-Hush theory is used to determine the excitation distance distribution of unassociated, random pairs at different wavelengths. For each absorption distribution, free radical ion yields at different wavelengths are then calculated using Onsager's result for the ion separation probability. Encouraging agreement between the calculated yields and our experimental results is obtained. As far as we are aware, this is the first time that photoexcitation of unassociated donor/acceptor pairs has been invoked as the source of separated radical ion pairs.

  13. Electronic spectra and hyperpolarizabilities of structurally similar donor-acceptor dyes. A density functional theory analysis

    NASA Astrophysics Data System (ADS)

    Sarkar, Amrita; Das, Mousumi; Bagchi, Sanjib

    2015-12-01

    Studies with density functional theory (DFT) have been done to reinforce our previous experimental findings involving the solvatochromism and the effect of protonation and for three structurally similar donor-acceptor dyes exhibiting intramolecular charge transfer transition. These dyes have similar donor (indole N/amino N) site and similar carbonyl O as the acceptor centre. The dye with an amino N donor site and indanone O as the acceptor centre has the lowest value of the energy gap between HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) and highest percentage of charge transfer from the N to the O centre. Time dependent density functional theory (TDDFT) has been used to calculate the excitation energy to the lowest singlet excited dipole-allowed states of the dyes. Effect of solvation on excitation energy has been studied by the use of polarisable continuum model (PCM). Computational results indicate that the excitation energy of these dyes is sensitive to solvent polarity and exhibits a red shift as polarity increases. The calculated excitation energies are in good agreement with the values of absorption maximum of these dyes in different solvents obtained in experiment. Studies on protonation of the dyes show that the carbonyl O to be the most favourable site of protonation for all the three dyes. Calculations of linear and first hyperpolarizabilities indicate these dyes to be suitable candidates for possible non-linear optical application.

  14. Fragment charge difference method for estimating donor-acceptor electronic coupling: Application to DNA π-stacks

    NASA Astrophysics Data System (ADS)

    Voityuk, Alexander A.; Rösch, Notker

    2002-09-01

    The purpose of this communication is two-fold. We introduce the fragment charge difference (FCD) method to estimate the electron transfer matrix element HDA between a donor D and an acceptor A, and we apply this method to several aspects of hole transfer electronic couplings in π-stacks of DNA, including systems with several donor-acceptor sites. Within the two-state model, our scheme can be simplified to recover a convenient estimate of the electron transfer matrix element HDA=(1-Δq2)1/2(E2-E1)/2 based on the vertical excitation energy E2-E1 and the charge difference Δq between donor and acceptor. For systems with strong charge separation, Δq≳0.95, one should resort to the FCD method. As favorable feature, we demonstrate the stability of the FCD approach for systems which require an approach beyond the two-state model. On the basis of ab initio calculations of various DNA related systems, we compared three approaches for estimating the electronic coupling: the minimum splitting method, the generalized Mulliken-Hush (GMH) scheme, and the FCD approach. We studied the sensitivity of FCD and GMH couplings to the donor-acceptor energy gap and found both schemes to be quite robust; they are applicable also in cases where donor and acceptor states are off resonance. In the application to π-stacks of DNA, we demonstrated for the Watson-Crick pair dimer [(GC),(GC)] how structural changes considerably affect the coupling strength of electron hole transfer. For models of three Watson-Crick pairs, we showed that the two-state model significantly overestimates the hole transfer coupling whereas simultaneous treatment of several states leads to satisfactory results.

  15. The electronic structure and second-order nonlinear optical properties of donor-acceptor acetylenes - A detailed investigation of structure-property relationships

    NASA Technical Reports Server (NTRS)

    Stiegman, A. E.; Graham, Eva; Khundkar, Lutfur R.; Perry, Joseph W.; Cheng, L.-T.; Perry, Kelly J.

    1991-01-01

    A series of donor-acceptor acetylene compounds was synthesized in which systematic changes in both the conjugation length and the donor-acceptor strength were made. The effect of these structural changes on the spectroscopic and electronic properties of the molecules and, ultimately, on the measured second-order molecular hyperpolarizabilities (beta) was investigated. It was found that increases in the donor-acceptor strength resulted in increases in the magnitude of beta. For this class of molecules, the increase is dominated by the energy of the intramolecular charge-transfer transition, while factors such as the ground to excited-state dipole moment change and the transition-moment integral are much less important. Increasing the conjugation length from one to two acetylene linkers did not result in an increase in the value of beta; however, beta increased sharply in going from two acetylenes to three. This increase is attributed to the superposition of several nearly isoenergetic excited states.

  16. Time dependence of donor-acceptor electron transfer and back transfer in solid solution

    NASA Astrophysics Data System (ADS)

    Lin, Y.; Dorfman, R. C.; Fayer, M. D.

    1989-01-01

    Electron transfer from an optically excited donor to randomly distributed acceptors followed by electron back transfer is treated theoretically for donors and acceptors in a rigid solution. The forward electron transfer process is described in terms of the excited state population probabilityPex(t) of the donor molecules, while the electron back transfer from the radical anion to the radical cation is characterized by Pct(t), the donor cation state population probability. Exact expressions for the ensemble averages and are derived. Numerical calulations are presented for the cation probabilities, the average cation-anion separation distance , and the average cation existence time <τ(R)>, using parameters which characterize the forward and back transfer distance dependent rates. Relationships among , and the intermolecular interaction parameters provide detailed insights into the distance and time dependence of the flow of electron probability in an ensemble of donors and acceptors. The theoretical expressions can be used to calculate experimental observables. In particular, picosecond transient grating experiments are analyzed, and it is shown that by combining grating experiments (or other ground state recovery experiments) with fluorescence experiments it is possible to obtain the intermolecular interaction parameters for both forward and back transfer and a detailed description of the dynamics. The calculations presented here for rigid solutions are the precursor to the inclusion of diffusive motion of donors and acceptors to describe the dynamics of coupled electron transfer and back transfer in liquid solutions.

  17. Ultrafast electron transfer in all-carbon-based SWCNT-C60 donor-acceptor nanoensembles connected by poly(phenylene-ethynylene) spacers.

    PubMed

    Barrejón, Myriam; Gobeze, Habtom B; Gómez-Escalonilla, María J; Fierro, José Luis G; Zhang, Minfang; Yudasaka, Masako; Iijima, Sumio; D'Souza, Francis; Langa, Fernando

    2016-08-21

    Building all-carbon based functional materials for light energy harvesting applications could be a solution to tackle and reduce environmental carbon output. However, development of such all-carbon based donor-acceptor hybrids and demonstration of photoinduced charge separation in such nanohybrids is a challenge since in these hybrids part of the carbon material should act as an electron donating or accepting photosensitizer while the second part should fulfil the role of an electron acceptor or donor. In the present work, we have successfully addressed this issue by synthesizing covalently linked all-carbon-based donor-acceptor nanoensembles using single-walled carbon nanotubes (SWCNTs) as the donor and C60 as the acceptor. The donor-acceptor entities in the nanoensembles were connected by phenylene-ethynylene spacer units to achieve better electronic communication and to vary the distance between the components. These novel SWCNT-C60 nanoensembles have been characterized by a number of techniques, including TGA, FT-IR, Raman, AFM, absorbance and electrochemical methods. The moderate number of fullerene addends present on the side-walls of the nanotubes largely preserved the electronic structure of the nanotubes. The thermodynamic feasibility of charge separation in these nanoensembles was established using spectral and electrochemical data. Finally, occurrence of ultrafast electron transfer from the excited nanotubes in these donor-acceptor nanohybrids has been established by femtosecond transient absorption studies, signifying their utility in building light energy harvesting devices.

  18. Ultrafast electron transfer in all-carbon-based SWCNT-C60 donor-acceptor nanoensembles connected by poly(phenylene-ethynylene) spacers.

    PubMed

    Barrejón, Myriam; Gobeze, Habtom B; Gómez-Escalonilla, María J; Fierro, José Luis G; Zhang, Minfang; Yudasaka, Masako; Iijima, Sumio; D'Souza, Francis; Langa, Fernando

    2016-08-21

    Building all-carbon based functional materials for light energy harvesting applications could be a solution to tackle and reduce environmental carbon output. However, development of such all-carbon based donor-acceptor hybrids and demonstration of photoinduced charge separation in such nanohybrids is a challenge since in these hybrids part of the carbon material should act as an electron donating or accepting photosensitizer while the second part should fulfil the role of an electron acceptor or donor. In the present work, we have successfully addressed this issue by synthesizing covalently linked all-carbon-based donor-acceptor nanoensembles using single-walled carbon nanotubes (SWCNTs) as the donor and C60 as the acceptor. The donor-acceptor entities in the nanoensembles were connected by phenylene-ethynylene spacer units to achieve better electronic communication and to vary the distance between the components. These novel SWCNT-C60 nanoensembles have been characterized by a number of techniques, including TGA, FT-IR, Raman, AFM, absorbance and electrochemical methods. The moderate number of fullerene addends present on the side-walls of the nanotubes largely preserved the electronic structure of the nanotubes. The thermodynamic feasibility of charge separation in these nanoensembles was established using spectral and electrochemical data. Finally, occurrence of ultrafast electron transfer from the excited nanotubes in these donor-acceptor nanohybrids has been established by femtosecond transient absorption studies, signifying their utility in building light energy harvesting devices. PMID:27305145

  19. Computational characterization of competing energy and electron transfer states in bimetallic donor-acceptor systems for photocatalytic conversion

    NASA Astrophysics Data System (ADS)

    Fredin, Lisa A.; Persson, Petter

    2016-09-01

    The rapidly growing interest in photocatalytic systems for direct solar fuel production such as hydrogen generation from water splitting is grounded in the unique opportunity to achieve charge separation in molecular systems provided by electron transfer processes. In general, both photoinduced and catalytic processes involve complicated dynamics that depend on both structural and electronic effects. Here the excited state landscape of metal centered light harvester-catalyst pairs is explored using density functional theory calculations. In weakly bound systems, the interplay between structural and electronic factors involved can be constructed from the various mononuclear relaxed excited states. For this study, supramolecular states of electron transfer and excitation energy transfer character have been constructed from constituent full optimizations of multiple charge/spin states for a set of three Ru-based light harvesters and nine transition metal catalysts (based on Ru, Rh, Re, Pd, and Co) in terms of energy, structure, and electronic properties. The complete set of combined charge-spin states for each donor-acceptor system provides information about the competition of excited state energy transfer states with the catalytically active electron transfer states, enabling the identification of the most promising candidates for photocatalytic applications from this perspective.

  20. Computational characterization of competing energy and electron transfer states in bimetallic donor-acceptor systems for photocatalytic conversion.

    PubMed

    Fredin, Lisa A; Persson, Petter

    2016-09-14

    The rapidly growing interest in photocatalytic systems for direct solar fuel production such as hydrogen generation from water splitting is grounded in the unique opportunity to achieve charge separation in molecular systems provided by electron transfer processes. In general, both photoinduced and catalytic processes involve complicated dynamics that depend on both structural and electronic effects. Here the excited state landscape of metal centered light harvester-catalyst pairs is explored using density functional theory calculations. In weakly bound systems, the interplay between structural and electronic factors involved can be constructed from the various mononuclear relaxed excited states. For this study, supramolecular states of electron transfer and excitation energy transfer character have been constructed from constituent full optimizations of multiple charge/spin states for a set of three Ru-based light harvesters and nine transition metal catalysts (based on Ru, Rh, Re, Pd, and Co) in terms of energy, structure, and electronic properties. The complete set of combined charge-spin states for each donor-acceptor system provides information about the competition of excited state energy transfer states with the catalytically active electron transfer states, enabling the identification of the most promising candidates for photocatalytic applications from this perspective.

  1. Computational characterization of competing energy and electron transfer states in bimetallic donor-acceptor systems for photocatalytic conversion.

    PubMed

    Fredin, Lisa A; Persson, Petter

    2016-09-14

    The rapidly growing interest in photocatalytic systems for direct solar fuel production such as hydrogen generation from water splitting is grounded in the unique opportunity to achieve charge separation in molecular systems provided by electron transfer processes. In general, both photoinduced and catalytic processes involve complicated dynamics that depend on both structural and electronic effects. Here the excited state landscape of metal centered light harvester-catalyst pairs is explored using density functional theory calculations. In weakly bound systems, the interplay between structural and electronic factors involved can be constructed from the various mononuclear relaxed excited states. For this study, supramolecular states of electron transfer and excitation energy transfer character have been constructed from constituent full optimizations of multiple charge/spin states for a set of three Ru-based light harvesters and nine transition metal catalysts (based on Ru, Rh, Re, Pd, and Co) in terms of energy, structure, and electronic properties. The complete set of combined charge-spin states for each donor-acceptor system provides information about the competition of excited state energy transfer states with the catalytically active electron transfer states, enabling the identification of the most promising candidates for photocatalytic applications from this perspective. PMID:27634263

  2. Donor-Acceptor-Type Semiconducting Polymers Consisting of Benzothiadiazole Derivatives as Electron-Acceptor Units for Organic Photovoltaic Cells.

    PubMed

    Kim, Hee Su; Park, Jong Baek; Kim, Ji-Hoon; Hwang, Do-Hoon

    2015-11-01

    We synthesized two fused pentacyclic donor-acceptor structures, where the two different outer electron rich thiophene (DTPBT) and electron poor benzene (ICTh) moieties are covalently bonded to the central electron-deficient benzothiadiazole core by two nitrogen bridges. These new electron-acceptor DTPBT and ICTh building blocks were copolymerized with fluorene, as the electron donor group, via Suzuki coupling polymerization, to produce two new alternating copolymers, PFDTPBT and PFICTh, respectively. The average molecular weights of the synthesized polymers were determined by GPC. The number-average molecular weights of PFDTPBT and PFICTh were 19,000 (PDI = 2.5) and 20,000 (PDI = 4.0), respectively. The optical bandgap energies of the polymers were measured from their absorption onsets to be 2.15 and 2.55 eV, depending on the polymer structure. The HOMO energy levels of the polymers were determined, by measuring the oxidation onsets of the polymer films by cyclic voltammetry. The measured HOMO energy levels of PFDTPBT and PFICTh were -5.10 and -5.57 eV, respectively. When the polymers were blended with PC71BM, as the active layer for bulk-heterojunction photovoltaic devices, power conversion efficiencies were 2.08% and 0.34%, respectively, under AM 1.5 G (100 mW cm(-2)) conditions.

  3. Electron and hole polaron accumulation in low-bandgap ambipolar donor-acceptor polymer transistors imaged by infrared microscopy

    NASA Astrophysics Data System (ADS)

    Khatib, O.; Mueller, A. S.; Stinson, H. T.; Yuen, J. D.; Heeger, A. J.; Basov, D. N.

    2014-12-01

    A resurgence in the use of the donor-acceptor approach in synthesizing conjugated polymers has resulted in a family of high-mobility ambipolar systems with exceptionally narrow energy bandgaps below 1 eV. The ability to transport both electrons and holes is critical for device applications such as organic light-emitting diodes and transistors. Infrared spectroscopy offers direct access to the low-energy excitations associated with injected charge carriers. Here we use a diffraction-limited IR microscope to probe the spectroscopic signatures of electron and hole injection in the conduction channel of an organic field-effect transistor based on an ambipolar DA polymer polydiketopyrrolopyrrole-benzobisthiadiazole. We observe distinct polaronic absorptions for both electrons and holes and spatially map the carrier distribution from the source to drain electrodes for both unipolar and ambipolar biasing regimes. For ambipolar device configurations, we observe the spatial evolution of hole-induced to electron-induced polaron absorptions throughout the transport path. Our work provides a platform for combined transport and infrared studies of organic semiconductors on micron length scales relevant to functional devices.

  4. Microscopic simulations of electronic excitations in donor-acceptor heterojunctions of small-molecule based solar cells

    NASA Astrophysics Data System (ADS)

    Baumeier, Bjoern

    2015-03-01

    Fundamental processes involving electronic excitations govern the functionality of molecular materials in which the dynamics of excitons and charges is determined by an interplay of molecular electronic structure and morphological order. To understand, e.g., charge separation and recombination at donor-acceptor heterojunctions in organic solar cells, knowledge about the microscopic details influencing these dynamics in the bulk and across the interface is required. For a set of prototypical heterojunctions of small-molecule donor materials with C60, we employ a hybrid QM/MM approach linking density-functional and many-body Green's functions theory and analyze the charged and neutral electronic excitations therein. We pay special attention the spatially-resolved electron/hole transport levels, as well as the relative energies of Frenkel and charge-transfer excitations at the interface. Finally, we link the molecular architecture of the donor material, its orientation on the fullerene substrate as well as mesoscale order to the solar cell performance.

  5. Influence of donor-acceptor distance variation on photoinduced electron and proton transfer in rhenium(I)-phenol dyads.

    PubMed

    Kuss-Petermann, Martin; Wolf, Hilke; Stalke, Dietmar; Wenger, Oliver S

    2012-08-01

    A homologous series of four molecules in which a phenol unit is linked covalently to a rhenium(I) tricarbonyl diimine photooxidant via a variable number of p-xylene spacers (n = 0-3) was synthesized and investigated. The species with a single p-xylene spacer was structurally characterized to get some benchmark distances. Photoexcitation of the metal complex in the shortest dyad (n = 0) triggers release of the phenolic proton to the acetonitrile/water solvent mixture; a H/D kinetic isotope effect (KIE) of 2.0 ± 0.4 is associated with this process. Thus, the shortest dyad basically acts like a photoacid. The next two longer dyads (n = 1, 2) exhibit intramolecular photoinduced phenol-to-rhenium electron transfer in the rate-determining excited-state deactivation step, and there is no significant KIE in this case. For the dyad with n = 1, transient absorption spectroscopy provided evidence for release of the phenolic proton to the solvent upon oxidation of the phenol by intramolecular photoinduced electron transfer. Subsequent thermal charge recombination is associated with a H/D KIE of 3.6 ± 0.4 and therefore is likely to involve proton motion in the rate-determining reaction step. Thus, some of the longer dyads (n = 1, 2) exhibit photoinduced proton-coupled electron transfer (PCET), albeit in a stepwise (electron transfer followed by proton transfer) rather than concerted manner. Our study demonstrates that electronically strongly coupled donor-acceptor systems may exhibit significantly different photoinduced PCET chemistry than electronically weakly coupled donor-bridge-acceptor molecules.

  6. Photoinduced electron transfer in rigidly linked dimethoxynapthalene-N-methylpyridinium donor-acceptor molecules

    NASA Astrophysics Data System (ADS)

    Clayton, Andrew H. A.; Ghiggino, Kenneth P.; Wilson, Gerard J.; Keyte, Peter J.; Paddon-Row, Michael N.

    1992-07-01

    Photoinduced electron transfer (ET) is studied in a series of novel molecules containing a dimethoxynaphthalene (DMN) donor and either a pyridine (P) or N-methylpyridinium (P-Me +) acceptor covalently linked via a rigid nonbornalogous bridge ( n sigma bonds in length). ET rates of the order of 10 10 s -1 were measured for the DMN- n-P-Me + series ( n = 4, 6), while no appreciable ET was observed for the DMN- n-P compounds. Electronic and nuclear factors are discussed and the results rationalized in terms of Marcus—Hush and non-adiabatic ET theories.

  7. 5' modification of duplex DNA with a ruthenium electron donor-acceptor pair using solid-phase DNA synthesis

    NASA Technical Reports Server (NTRS)

    Frank, Natia L.; Meade, Thomas J.

    2003-01-01

    Incorporation of metalated nucleosides into DNA through covalent modification is crucial to measurement of thermal electron-transfer rates and the dependence of these rates with structure, distance, and position. Here, we report the first synthesis of an electron donor-acceptor pair of 5' metallonucleosides and their subsequent incorporation into oligonucleotides using solid-phase DNA synthesis techniques. Large-scale syntheses of metal-containing oligonucleotides are achieved using 5' modified phosporamidites containing [Ru(acac)(2)(IMPy)](2+) (acac is acetylacetonato; IMPy is 2'-iminomethylpyridyl-2'-deoxyuridine) (3) and [Ru(bpy)(2)(IMPy)](2+) (bpy is 2,2'-bipyridine; IMPy is 2'-iminomethylpyridyl-2'-deoxyuridine) (4). Duplexes formed with the metal-containing oligonucleotides exhibit thermal stability comparable to the corresponding unmetalated duplexes (T(m) of modified duplex = 49 degrees C vs T(m) of unmodified duplex = 47 degrees C). Electrochemical (3, E(1/2) = -0.04 V vs NHE; 4, E(1/2) = 1.12 V vs NHE), absorption (3, lambda(max) = 568, 369 nm; 4, lambda(max) = 480 nm), and emission (4, lambda(max) = 720 nm, tau = 55 ns, Phi = 1.2 x 10(-)(4)) data for the ruthenium-modified nucleosides and oligonucleotides indicate that incorporation into an oligonucleotide does not perturb the electronic properties of the ruthenium complex or the DNA significantly. In addition, the absence of any change in the emission properties upon metalated duplex formation suggests that the [Ru(bpy)(2)(IMPy)](2+)[Ru(acac)(2)(IMPy)](2+) pair will provide a valuable probe for DNA-mediated electron-transfer studies.

  8. Spectral fine tuning of cyanine dyes: electron donor-acceptor substituted analogues of thiazole orange.

    PubMed

    Rastede, Elizabeth E; Tanha, Matteus; Yaron, David; Watkins, Simon C; Waggoner, Alan S; Armitage, Bruce A

    2015-09-26

    The introduction of electron donor and acceptor groups at strategic locations on a fluorogenic cyanine dye allows fine-tuning of the absorption and emission spectra while preserving the ability of the dye to bind to biomolecular hosts such as double-stranded DNA and a single-chain antibody fragment originally selected for binding to the parent unsubstituted dye, thiazole orange (TO). The observed spectral shifts are consistent with calculated HOMO-LUMO energy gaps and reflect electron density localization on the quinoline half of TO in the LUMO. A dye bearing donating methoxy and withdrawing trifluoromethyl groups on the benzothiazole and quinoline rings, respectively, shifts the absorption spectrum to sufficiently longer wavelengths to allow excitation at green wavelengths as opposed to the parent dye, which is optimally excited in the blue.

  9. Spectral Fine Tuning of Cyanine Dyes: Electron Donor-Acceptor Substituted Analogues of Thiazole Orange†

    PubMed Central

    Rastede, Elizabeth E.; Tanha, Matteus; Yaron, David; Watkins, Simon C.; Waggoner, Alan S.; Armitage, Bruce A.

    2015-01-01

    The introduction of electron donor and acceptor groups at strategic locations on a fluorogenic cyanine dye allows fine-tuning of the absorption and emission spectra while preserving the ability of the dye to bind to biomolecular hosts such as double-stranded DNA and a single-chain antibody fragment originally selected for binding to the parent unsubstituted dye, thiazole orange (TO). The observed spectral shifts are consistent with calculated HOMO-LUMO energy gaps and reflect electron density localization on the quinoline half of TO in the LUMO. A dye bearing donating methoxy and withdrawing trifluoromethyl groups on the benzothiazole and quinoline rings, respectively, shifts the absorption spectrum to sufficiently longer wavelengths to allow excitation at green wavelengths as opposed to the parent dye, which is optimally excited in the blue. PMID:26171668

  10. Ultrafast electron transfer in all-carbon-based SWCNT-C60 donor-acceptor nanoensembles connected by poly(phenylene-ethynylene) spacers

    NASA Astrophysics Data System (ADS)

    Barrejón, Myriam; Gobeze, Habtom B.; Gómez-Escalonilla, María J.; Fierro, José Luis G.; Zhang, Minfang; Yudasaka, Masako; Iijima, Sumio; D'Souza, Francis; Langa, Fernando

    2016-08-01

    Building all-carbon based functional materials for light energy harvesting applications could be a solution to tackle and reduce environmental carbon output. However, development of such all-carbon based donor-acceptor hybrids and demonstration of photoinduced charge separation in such nanohybrids is a challenge since in these hybrids part of the carbon material should act as an electron donating or accepting photosensitizer while the second part should fulfil the role of an electron acceptor or donor. In the present work, we have successfully addressed this issue by synthesizing covalently linked all-carbon-based donor-acceptor nanoensembles using single-walled carbon nanotubes (SWCNTs) as the donor and C60 as the acceptor. The donor-acceptor entities in the nanoensembles were connected by phenylene-ethynylene spacer units to achieve better electronic communication and to vary the distance between the components. These novel SWCNT-C60 nanoensembles have been characterized by a number of techniques, including TGA, FT-IR, Raman, AFM, absorbance and electrochemical methods. The moderate number of fullerene addends present on the side-walls of the nanotubes largely preserved the electronic structure of the nanotubes. The thermodynamic feasibility of charge separation in these nanoensembles was established using spectral and electrochemical data. Finally, occurrence of ultrafast electron transfer from the excited nanotubes in these donor-acceptor nanohybrids has been established by femtosecond transient absorption studies, signifying their utility in building light energy harvesting devices.Building all-carbon based functional materials for light energy harvesting applications could be a solution to tackle and reduce environmental carbon output. However, development of such all-carbon based donor-acceptor hybrids and demonstration of photoinduced charge separation in such nanohybrids is a challenge since in these hybrids part of the carbon material should act as an

  11. Three component assemblies by orthogonal H-bonding and donor-acceptor charge-transfer interaction.

    PubMed

    Kar, Haridas; Ghosh, Suhrit

    2014-02-01

    Three component supramolecular assemblies from a mixture of an aromatic donor (D), acceptor (A) and external structure directing agent (ESDA) are achieved by orthogonal noncovalent interactions involving two different types of H-bonding and alternate D-A stacking. An ESDA containing amide or urea produces a charge-transfer gel and sol, respectively, owing to their contrasting morphology. PMID:24309620

  12. Electron Transfer within Self-Assembling Cyclic Tetramers Using Chlorophyll-Based Donor-Acceptor Building Blocks

    SciTech Connect

    Gunderson, Victoria L; Smeigh, Amanda L; Kim, Chul Hoon; Co, Dick T; Wasielewski, Michael R

    2012-05-09

    The synthesis and photoinduced charge transfer properties of a series of Chl-based donor-acceptor triad building blocks that self-assemble into cyclic tetramers are reported. Chlorophyll a was converted into zinc methyl 3-ethylpyrochlorophyllide a (Chl) and then further modified at its 20-position to covalently attach a pyromellitimide (PI) acceptor bearing a pyridine ligand and one or two naphthalene-1,8:4,5-bis(dicarboximide) (NDI) secondary electron acceptors to give Chl-PI-NDI and Chl-PI-NDI2. The pyridine ligand within each ambident triad enables intermolecular Chl metal-ligand coordination in dry toluene, which results in the formation of cyclic tetramers in solution, as determined using small- and wide-angle X-ray scattering at a synchrotron source. Femtosecond and nanosecond transient absorption spectroscopy of the monomers in toluene-1% pyridine and the cyclic tetramers in toluene shows that the selective photoexcitation of Chl results in intramolecular electron transfer from 1*Chl to PI to form Chl+.-PI-.-NDI and Chl+.-PI-.-NDI2. This initial charge separation is followed by a rapid charge shift from PI-. to NDI and subsequent charge recombination of Chl+.-PI-NDI-. and Chl+.-PI-(NDI)NDI-. on a 5-30 ns time scale. Charge recombination in the Chl-PI-NDI2 cyclic tetramer (τCR = 30 ± 1 ns in toluene) is slower by a factor of 3 relative to the monomeric building blocks (τCR = 10 ± 1 ns in toluene-1% pyridine). This indicates that the self-assembly of these building blocks into the cyclic tetramers alters their structures in a way that lengthens their charge separation lifetimes, which is an advantageous strategy for artificial photosynthetic systems.

  13. Self-assembly properties of semiconducting donor-acceptor-donor bithienyl derivatives of tetrazine and thiadiazole-effect of the electron accepting central ring.

    PubMed

    Zapala, Joanna; Knor, Marek; Jaroch, Tomasz; Maranda-Niedbala, Agnieszka; Kurach, Ewa; Kotwica, Kamil; Nowakowski, Robert; Djurado, David; Pecaut, Jacques; Zagorska, Malgorzata; Pron, Adam

    2013-11-26

    Scanning tunneling microscopy was used to study the effect of the electron-accepting unit and the alkyl substituent's position on the type and extent of 2D supramolecular organization of penta-ring donor-acceptor-donor (DAD) semiconductors, consisting of either tetrazine or thiadiazole central acceptor ring symmetrically attached to two bithienyl groups. Microscopic observations of monomolecular layers on HOPG of four alkyl derivatives of the studied adsorbates indicate significant differences in their 2D organizations. Ordered monolayers of thiadiazole derivatives are relatively loose and, independent of the position of alkyl substituents, characterized by large intermolecular separation of acceptor units in the adjacent molecules located in the face-to-face configuration. The 2D supramolecular architecture in both derivatives of thiadiazole is very sensitive to the alkyl substituent's position. Significantly different behavior is observed for derivatives of tetrazine (which is a stronger electron acceptor). Stronger intermolecular DA interactions in these adsorbates generate an intermolecular shift in the monolayer, which is a dominant factor determining the 2D structural organization. As a consequence of this molecular arrangement, tetrazine groups (A segments) face thiophene rings (D segments) of the neighboring molecules. Monolayers of tetrazine derivatives are therefore much more densely packed and characterized by similar π-stacking of molecules independently of the position of alkyl substituents. Moreover, a comparative study of 3D supramolecular organization, deduced from the X-ray diffraction patterns, is also presented clearly confirming the polymorphism of the studied adsorbates.

  14. Development of imide- and imidazole-containing electron acceptors for use in donor-acceptor conjugated compounds and polymers

    NASA Astrophysics Data System (ADS)

    Li, Duo

    Conjugated organic compounds and polymers have attracted significant attention due to their potential application in electronic devices as semiconducting materials, such as organic solar cells (OSCs). In order to tune band gaps, donor-acceptor (D-A) structure is widely used, which has been proved to be one of the most effective strategies. This thesis consists of three parts: 1) design, syntheses and characterization of new weak acceptors based on imides and the systematic study of the structure-property relationship; (2) introduction of weak and strong acceptors in one polymer to achieve a broad coverage of light absorption and improve the power conversion efficiency (PCE); (3) modification of benzothiadiazole (BT) acceptor in order to increase the electron withdrawing ability. Imide-based electron acceptors, 4-(5-bromothiophen-2-y1)-2-(2-ethylhexyl)-9- phenyl- 1H-benzo[f]isoindole-1,3(2H)-dione (BIDO-1) and 4,9-bis(5-bromothiophen-2-yl)-2-(2-ethylhexyl)-benzo[f]isoindole-1,3-dione (BIDO-2), were designed and synthesized. In this design, naphthalene is selected as its main core to maintain a planar structure, and thienyl groups are able to facilitate the bromination reaction and lower the band gap. BIDO-1 and BIDO-2 were successfully coupled with different donors by both Suzuki cross-coupling and Stille cross-coupling reactions. Based on the energy levels and band gaps of the BIDO-containing compounds and polymers, BIDO-1 and BIDO-2 are proved to be weak electron acceptors. Pyromellitic diimide (PMDI) was also studied and found to be a stronger electron acceptor than BIDO . In order to obtain broad absorption coverage, both weak acceptor ( BIDO-2) and strong acceptor diketopyrrolopyrrole (DPP) were introduced in the same polymer. The resulting polymers show two absorption bands at 400 and 600 nm and two emission peaks at 500 and 680 nm. The band gaps of the polymers are around 1.6 eV, which is ideal for OSC application. The PCE of 1.17% was achieved. Finally

  15. Tailored donor-acceptor polymers with an A-D1-A-D2 structure: controlling intermolecular interactions to enable enhanced polymer photovoltaic devices.

    PubMed

    Qin, Tianshi; Zajaczkowski, Wojciech; Pisula, Wojciech; Baumgarten, Martin; Chen, Ming; Gao, Mei; Wilson, Gerry; Easton, Christopher D; Müllen, Klaus; Watkins, Scott E

    2014-04-23

    Extensive efforts have been made to develop novel conjugated polymers that give improved performance in organic photovoltaic devices. The use of polymers based on alternating electron-donating and electron-accepting units not only allows the frontier molecular orbitals to be tuned to maximize the open-circuit voltage of the devices but also controls the optical band gap to increase the number of photons absorbed and thus modifies the other critical device parameter-the short circuit current. In fact, varying the nonchromophoric components of a polymer is often secondary to the efforts to adjust the intermolecular aggregates and improve the charge-carrier mobility. Here, we introduce an approach to polymer synthesis that facilitates simultaneous control over both the structural and electronic properties of the polymers. Through the use of a tailored multicomponent acceptor-donor-acceptor (A-D-A) intermediate, polymers with the unique structure A-D1-A-D2 can be prepared. This approach enables variations in the donor fragment substituents such that control over both the polymer regiochemistry and solubility is possible. This control results in improved intermolecular π-stacking interactions and therefore enhanced charge-carrier mobility. Solar cells using the A-D1-A-D2 structural polymer show short-circuit current densities that are twice that of the simple, random analogue while still maintaining an identical open-circuit voltage. The key finding of this work is that polymers with an A-D1-A-D2 structure offer significant performance benefits over both regioregular and random A-D polymers. The chemical synthesis approach that enables the preparation of A-D1-A-D2 polymers therefore represents a promising new route to materials for high-efficiency organic photovoltaic devices.

  16. Experimental and computational studies of a multi-electron donor-acceptor ligand containing the thiazolo[5,4-d]thiazole core and its incorporation into a metal-organic framework.

    PubMed

    Rizzuto, Felix J; Faust, Thomas B; Chan, Bun; Hua, Carol; D'Alessandro, Deanna M; Kepert, Cameron J

    2014-12-22

    A ligand containing the thiazolo[5,4-d]thiazole (TzTz) core (acceptor) with terminal triarylamine moieties (donors), N,N'-(thiazolo[5,4-d]thiazole-2,5-diylbis(4,1-phenylene))bis(N-(pyridine-4-yl)pyridin-4-amine (1), was designed as a donor-acceptor system for incorporation into electronically active metal-organic frameworks (MOFs). The capacity for the ligand to undergo multiple sequential oxidation and reduction processes was examined using UV/Vis-near-infrared spectroelectrochemistry (UV/Vis-NIR SEC) in combination with DFT calculations. The delocalized nature of the highest occupied molecular orbital (HOMO) was found to inhibit charge-transfer interactions between the terminal triarylamine moieties upon oxidation, whereas radical species localized on the TzTz core were formed upon reduction. Conversion of 1 to diamagnetic 2+ and 4+ species resulted in marked changes in the emission spectra. Incorporation of this highly delocalized multi-electron donor-acceptor ligand into a new two-dimensional MOF, [Zn(NO3 )2 (1)] (2), resulted in an inhibition of the oxidation processes, but retention of the reduction capability of 1. Changes in the electrochemistry of 1 upon integration into 2 are broadly consistent with the geometric and electronic constraints enforced by ligation. PMID:25346539

  17. Photochromic and electrochromic performances of new types of donor/acceptor systems based on crosslinked polyviologen film and electron donors

    NASA Astrophysics Data System (ADS)

    Gao, Li-ping; Ding, Guo-jing; Li, Chao-long; Wang, Yue-chuan

    2011-01-01

    Viologen-functionalized copolymer COPV2+ was synthesized by copolymer graft-modified, which was crosslinked by NH3·H2O gas-fumigated at 25 °C for 4 h due to the condensation of the siloxanes of COPV2+ film. Simultaneously, different donor/acceptor systems had been prepared based on crosslinked polyviologen film (COPV2+) and N,N,N‧,N‧-tetramethyl-1,4-phenylenediamine (TMPD) or hydroxyethylferrocene (HEFc) in order to shorten the response times and improve contrast ratios in response to external photo- and potential stimuli. The evolution of structures from COPO to COPV2+ is carefully characterized. The COPV2+/TMPD and COPV2+/HEFc films exhibited both photochromic and electrochromic performances. After UV irradiations, COPV2+/TMPD and COPV2+/HEFc films changed their colors from colorless to deep blue, while optical transmissions at 610 nm decreased about 64% and 75%, respectively. When removing out from UV irradiation, the colored COPV2+/TMPD and COPV2+/HEFc films faded to the original colors within about 60 min. When COPV2+/TMPD and COPV2+/HEFc films were biased with negative voltage of -2.5 V, they changed their colors from colorless to deep blue in 4 s and 3 s, while the optical transmissions at 556 nm decreased about 81% and 75%, respectively. When electric impulse was switched off, the colored COPV2+/TMPD and COPV2+/HEFc films faded to the original colors within about 7 s and 6 s, respectively.

  18. Self-Assembly of Electron Donor-Acceptor-Based Carbazole Derivatives: Novel Fluorescent Organic Nanoprobes for Both One- and Two-Photon Cellular Imaging.

    PubMed

    Zhang, Jinfeng; Chen, Wencheng; Kalytchuk, Sergii; Li, King Fai; Chen, Rui; Adachi, Chihaya; Chen, Zhan; Rogach, Andrey L; Zhu, Guangyu; Yu, Peter K N; Zhang, Wenjun; Cheah, Kok Wai; Zhang, Xiaohong; Lee, Chun-Sing

    2016-05-11

    In this study, we report fluorescent organic nanoprobes with intense blue, green, and orange-red emissions prepared by self-assembling three carbazole derivatives into nanorods/nanoparticles. The three compounds consist of two or four electron-donating carbazole groups linked to a central dicyanobenzene electron acceptor. Steric hindrance from the carbazole groups leads to noncoplanar 3D molecular structures favorable to fluorescence in the solid state, while the donor-acceptor structures endow the molecules with good two-photon excited emission properties. The fluorescent organic nanoprobes exhibit good water dispersibility, low cytotoxicity, superior resistance against photodegradation and photobleaching. Both one- and two-photon fluorescent imaging were shown in the A549 cell line. Two-photon fluorescence imaging with the fluorescent probes was demonstrated to be more effective in visualizing and distinguishing cellular details compared to conventional one-photon fluorescence imaging.

  19. An electronic spectroscopic study of micellisation of surfactants and solvation of homomicelles formed by cationic or anionic surfactants using a solvatochromic electron donor acceptor dye

    NASA Astrophysics Data System (ADS)

    Kedia, Niraja; Sarkar, Amrita; Purkayastha, Pradipta; Bagchi, Sanjib

    2014-10-01

    Solvatochromic absorption and fluorescence bands of a donor-acceptor dye have been utilised for following the micellisation and for probing the polarity of the aqueous homomicellar phase provided separately by cationic (cetyltrimethylammonimum bromide, CTAB and dodecyltrimethylammonimum bromide, DTAB) and anionic (sodium dodecyl sulphate, SDS) surfactant. Results indicate that for a low concentration of surfactant (below cmc) the dye forms a dimer in aqueous solution. In a micellar media, however, the dye exists as monomers. A strong dye-micelle interaction, as indicated by the shift of the solvatochromic intramolecular charge transfer band of the dye, has also been indicated. The absorption and fluorescence parameters of the dye have been utilised for studying the onset of aggregation of the surfactants. An iterative procedure has been developed for the estimation of cmc and the distribution coefficient (KD) of the dye between the aqueous and the micellar phase. All the parameters provide convergent values of cmc. A high value of KD indicates that the dye exists predominantly in the micellar phase. The solvatochromic parameters characterising the dipolarity-polarisability (π*) and H-bond donation ability (α) of modes of solvation interaction in different micellar media have been estimated. The dye is found to distribute itself between two regions in a catanionic vesicle formed by surfactants SDS and DTAB, one being relatively polar than other. The distribution coefficients have been found out using the fluorescence data.

  20. An electronic spectroscopic study of micellisation of surfactants and solvation of homomicelles formed by cationic or anionic surfactants using a solvatochromic electron donor acceptor dye.

    PubMed

    Kedia, Niraja; Sarkar, Amrita; Purkayastha, Pradipta; Bagchi, Sanjib

    2014-10-15

    Solvatochromic absorption and fluorescence bands of a donor-acceptor dye have been utilised for following the micellisation and for probing the polarity of the aqueous homomicellar phase provided separately by cationic (cetyltrimethylammonimum bromide, CTAB and dodecyltrimethylammonimum bromide, DTAB) and anionic (sodium dodecyl sulphate, SDS) surfactant. Results indicate that for a low concentration of surfactant (below cmc) the dye forms a dimer in aqueous solution. In a micellar media, however, the dye exists as monomers. A strong dye-micelle interaction, as indicated by the shift of the solvatochromic intramolecular charge transfer band of the dye, has also been indicated. The absorption and fluorescence parameters of the dye have been utilised for studying the onset of aggregation of the surfactants. An iterative procedure has been developed for the estimation of cmc and the distribution coefficient (KD) of the dye between the aqueous and the micellar phase. All the parameters provide convergent values of cmc. A high value of KD indicates that the dye exists predominantly in the micellar phase. The solvatochromic parameters characterising the dipolarity-polarisability (π(*)) and H-bond donation ability (α) of modes of solvation interaction in different micellar media have been estimated. The dye is found to distribute itself between two regions in a catanionic vesicle formed by surfactants SDS and DTAB, one being relatively polar than other. The distribution coefficients have been found out using the fluorescence data.

  1. Revealing the interactions between pentagon-octagon-pentagon defect graphene and organic donor/acceptor molecules: a theoretical study.

    PubMed

    Li, Jie-Wei; Liu, Yu-Yu; Xie, Ling-Hai; Shang, Jing-Zhi; Qian, Yan; Yi, Ming-Dong; Yu, Ting; Huang, Wei

    2015-02-21

    Defect engineering and the non-covalent interaction strategy allow for dramatically tuning the optoelectronic features of graphene. Herein, we theoretically investigated the intrinsic mechanism of non-covalent interactions between pentagon-octagon-pentagon (5-8-5) defect graphene (DG) and absorbed molecules, tetrathiafulvalene (TTF), perfluoronaphthalene (FNa), tetracyanoquinodimethane (TCNQ) and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), through geometry, distance, interaction energy, Mulliken charge distribution, terahertz frequency vibration, visualization of the interactions, charge density difference, electronic transition behaviour, band structure and density of state. All the calculations were performed using density functional theory including a dispersion correction (DFT-D). The calculated results indicate that the cyano- (CN) group (electron withdraw group) in TCNQ and F4TCNQ, rather than the F group, gain the electron from DG effectively and exhibit much stronger interactions via wavefunction overlap with DG, leading to a short non-covalent interaction distance, a large interaction energy and a red-shift of out-of-plane terahertz frequency vibration, changing the bands near the Fermi level and enhancing the infrared (IR) light absorption significantly. The enhancement of such IR absorbance offering a broader absorption (from 300 to 1200 nm) will benefit light harvesting in potential applications of solar energy conversion.

  2. Revealing the interactions between pentagon-octagon-pentagon defect graphene and organic donor/acceptor molecules: a theoretical study.

    PubMed

    Li, Jie-Wei; Liu, Yu-Yu; Xie, Ling-Hai; Shang, Jing-Zhi; Qian, Yan; Yi, Ming-Dong; Yu, Ting; Huang, Wei

    2015-02-21

    Defect engineering and the non-covalent interaction strategy allow for dramatically tuning the optoelectronic features of graphene. Herein, we theoretically investigated the intrinsic mechanism of non-covalent interactions between pentagon-octagon-pentagon (5-8-5) defect graphene (DG) and absorbed molecules, tetrathiafulvalene (TTF), perfluoronaphthalene (FNa), tetracyanoquinodimethane (TCNQ) and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), through geometry, distance, interaction energy, Mulliken charge distribution, terahertz frequency vibration, visualization of the interactions, charge density difference, electronic transition behaviour, band structure and density of state. All the calculations were performed using density functional theory including a dispersion correction (DFT-D). The calculated results indicate that the cyano- (CN) group (electron withdraw group) in TCNQ and F4TCNQ, rather than the F group, gain the electron from DG effectively and exhibit much stronger interactions via wavefunction overlap with DG, leading to a short non-covalent interaction distance, a large interaction energy and a red-shift of out-of-plane terahertz frequency vibration, changing the bands near the Fermi level and enhancing the infrared (IR) light absorption significantly. The enhancement of such IR absorbance offering a broader absorption (from 300 to 1200 nm) will benefit light harvesting in potential applications of solar energy conversion. PMID:25559269

  3. Ultrafast photoinduced charge transport in Pt(II) donor-acceptor assembly bearing naphthalimide electron acceptor and phenothiazine electron donor.

    PubMed

    Sazanovich, Igor V; Best, Jonathan; Scattergood, Paul A; Towrie, Michael; Tikhomirov, Sergei A; Bouganov, Oleg V; Meijer, Anthony J H M; Weinstein, Julia A

    2014-12-21

    Visible light-induced charge transfer dynamics were investigated in a novel transition metal triad acceptor-chromophore-donor, (NDI-phen)Pt(II)(-C≡C-Ph-CH2-PTZ)2 (1), designed for photoinduced charge separation using a combination of time-resolved infrared (TRIR) and femtosecond electronic transient absorption (TA) spectroscopy. In 1, the electron acceptor is 1,4,5,8-naphthalene diimide (NDI), and the electron donor is phenothiazine (PTZ), and [(phen)Pt(-C≡C-Ph-)], where phen is 1,10-phenanthroline, represents the chromophoric core. The first excited state observed in 1 is a (3)MLCT/LL'CT, with {Pt(II)-acetylide}-to-phen character. Following that, charge transfer from the phen-anion onto the NDI subunit to form NDI(-)-phen-[Pt-(C≡C)2](+)-PTZ2 occurs with a time constant of 2.3 ps. This transition is characterised by appearance of the prominent NDI-anion features in both TRIR and TA spectra. The final step of the charge separation in 1 proceeds with a time constant of ∼15 ps during which the hole migrates from the [Pt-(C≡C)2] subunit to one of the PTZ groups. Charge recombination in 1 then occurs with two distinct time constants of 36 ns and 107 ns, corresponding to the back electron transfer to each of the two donor groups; a rather rare occurrence which manifests that the hole in the final charge-separated state is localised on one of the two donor PTZ groups. The assignment of the nature of the excited states and dynamics in 1 was assisted by TRIR investigations of the analogous previously reported ((COOEt)2bpy)Pt(C≡C-Ph-CH2-PTZ)2 (2), (J. E. McGarrah and R. Eisenberg, Inorg. Chem., 2003, 42, 4355; J. E. McGarrah, J. T. Hupp and S. N. Smirnov, J. Phys. Chem. A, 2009, 113, 6430) as well as (bpy)Pt(C≡C-Ph-C7H15)2, which represent the acceptor-free dyad, and the chromophoric core, respectively. Thus, the step-wise formation of the full charge-separated state on the picosecond time scale and charge recombination via tunnelling have been established; and

  4. Density functional study of the electronic structure of dye-functionalized fullerenes and their model donor-acceptor complexes containing P3HT.

    PubMed

    Baruah, Tunna; Garnica, Amanda; Paggen, Marina; Basurto, Luis; Zope, Rajendra R

    2016-04-14

    We study the electronic structure of C60 fullerenes functionalized with a thiophene-diketo-pyrrolopyrrole-thiophene based chromophore using density functional theory combined with large polarized basis sets. As the attached chromophore has electron donor character, the functionalization of the fullerene leads to a donor-acceptor (DA) system. We examine in detail the effect of the linker and the addition site on the electronic structure of the functionalized fullerenes. We further study the electronic structure of these DA complexes with a focus on the charge transfer excitations. Finally, we examine the interface of the functionalized fullerenes with the widely used poly(3-hexylthiophene-2,5-diyl) (P3HT) donor. Our results show that all functionalized fullerenes with an exception of the C60-pyrrolidine [6,6], where the pyrrolidine is attached at a [6,6] site, have larger electron affinities relative to the pristine C60 fullerene. We also estimate the quasi-particle gap, lowest charge transfer excitation energy, and the exciton binding energies of the functionalized fullerene-P3MT model systems. Results show that the exciton binding energies in these model complexes are slightly smaller compared to a similarly prepared phenyl-C61-butyric acid methyl ester (PCBM)-P3MT complex.

  5. Density functional study of the electronic structure of dye-functionalized fullerenes and their model donor-acceptor complexes containing P3HT

    NASA Astrophysics Data System (ADS)

    Baruah, Tunna; Garnica, Amanda; Paggen, Marina; Basurto, Luis; Zope, Rajendra R.

    2016-04-01

    We study the electronic structure of C60 fullerenes functionalized with a thiophene-diketo-pyrrolopyrrole-thiophene based chromophore using density functional theory combined with large polarized basis sets. As the attached chromophore has electron donor character, the functionalization of the fullerene leads to a donor-acceptor (DA) system. We examine in detail the effect of the linker and the addition site on the electronic structure of the functionalized fullerenes. We further study the electronic structure of these DA complexes with a focus on the charge transfer excitations. Finally, we examine the interface of the functionalized fullerenes with the widely used poly(3-hexylthiophene-2,5-diyl) (P3HT) donor. Our results show that all functionalized fullerenes with an exception of the C60-pyrrolidine [6,6], where the pyrrolidine is attached at a [6,6] site, have larger electron affinities relative to the pristine C60 fullerene. We also estimate the quasi-particle gap, lowest charge transfer excitation energy, and the exciton binding energies of the functionalized fullerene-P3MT model systems. Results show that the exciton binding energies in these model complexes are slightly smaller compared to a similarly prepared phenyl-C61-butyric acid methyl ester (PCBM)-P3MT complex.

  6. Photoinduced electron donor/acceptor processes in colloidal II-VI semiconductor quantum dots and nitroxide free radicals

    NASA Astrophysics Data System (ADS)

    Dutta, Poulami

    Electron transfer (ET) processes are one of the most researched topics for applications ranging from energy conversion to catalysis. An exciting variation is utilizing colloidal semiconductor nanostructures to explore such processes. Semiconductor quantum dots (QDs) are emerging as a novel class of light harvesting, emitting and charge-separation materials for applications such as solar energy conversion. Detailed knowledge of the quantitative dissociation of the photogenerated excitons and the interfacial charge- (electron/hole) transfer is essential for optimization of the overall efficiency of many such applications. Organic free radicals are the attractive counterparts for studying ET to/from QDs because these undergo single-electron transfer steps in reversible fashion. Nitroxides are an exciting class of stable organic free radicals, which have recently been demonstrated to be efficient as redox mediators in dye-sensitized solar cells, making them even more interesting for the aforementioned studies. This dissertation investigates the interaction between nitroxide free radicals TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl), 4-amino-TEMPO (4-amino- 2,2,6,6-tetramethylpiperidine-1-oxyl) and II-VI semiconductor (CdSe and CdTe) QDs. The nature of interaction in these hybrids has been examined through ground-state UV-Vis absorbance, steady state and time-resolved photoluminescence (PL) spectroscopy, transient absorbance, upconversion photoluminescence spectroscopy and electron paramagnetic resonance (EPR). The detailed analysis of the PL quenching indicates that the intrinsic charge transfer is ultrafast however, the overall quenching is still limited by the lower binding capacities and slower diffusion related kinetics. Careful analysis of the time resolved PL decay kinetics reveal that the decay rate constants are distributed and that the trap states are involved in the overall quenching process. The ultrafast hole transfer from CdSe QDs to 4-Amino TEMPO observed

  7. Tuning Optical and Electron Donor Properties by Peripheral Thio-Aryl Substitution of Subphthalocyanine: A New Series of Donor-Acceptor Hybrids for Photoinduced Charge Separation.

    PubMed

    Kc, Chandra B; Lim, Gary N; D'Souza, Francis

    2016-09-01

    Subphthalocyanine (SubPc), a unique ring-reduced member of the common phthalocyanines family, although known for its higher absorptivity, reveals narrow absorption with peak maxima around 570 nm thus limiting its utility in light-energy-harvesting applications. In the present study, by peripheral thio-aryl substitution of SubPc macrocycle, the spectral properties have been modulated to extend the absorption and emission well into the visible/near-IR region. Additionally, for α-ring-substituted derivatives, facile oxidation of SubPc was witnessed, thus making these derivatives better electron donors. Next, the preparation of donor-acceptor dyads containing the well-known electron acceptor C60 connected to the central boron atom of SubPc was accomplished by making use of the 1,3-dipolar cycloaddition reaction. Control experiments and free-energy calculations using the redox and spectral data suggested that the observed fluorescence quenching of SubPc in these dyads is due to electron transfer. Accordingly, transient spectral studies performed both in polar and nonpolar solvents conclusively proved electron transfer to be the quenching mechanism in these dyads. The measured rate constants by fitting kinetic data revealed efficient charge separation and charge recombination processes, suggesting that these dyads could be useful materials for the construction of light-to-electricity or light-to-fuel production devices. PMID:27515576

  8. Tuning Optical and Electron Donor Properties by Peripheral Thio-Aryl Substitution of Subphthalocyanine: A New Series of Donor-Acceptor Hybrids for Photoinduced Charge Separation.

    PubMed

    Kc, Chandra B; Lim, Gary N; D'Souza, Francis

    2016-09-01

    Subphthalocyanine (SubPc), a unique ring-reduced member of the common phthalocyanines family, although known for its higher absorptivity, reveals narrow absorption with peak maxima around 570 nm thus limiting its utility in light-energy-harvesting applications. In the present study, by peripheral thio-aryl substitution of SubPc macrocycle, the spectral properties have been modulated to extend the absorption and emission well into the visible/near-IR region. Additionally, for α-ring-substituted derivatives, facile oxidation of SubPc was witnessed, thus making these derivatives better electron donors. Next, the preparation of donor-acceptor dyads containing the well-known electron acceptor C60 connected to the central boron atom of SubPc was accomplished by making use of the 1,3-dipolar cycloaddition reaction. Control experiments and free-energy calculations using the redox and spectral data suggested that the observed fluorescence quenching of SubPc in these dyads is due to electron transfer. Accordingly, transient spectral studies performed both in polar and nonpolar solvents conclusively proved electron transfer to be the quenching mechanism in these dyads. The measured rate constants by fitting kinetic data revealed efficient charge separation and charge recombination processes, suggesting that these dyads could be useful materials for the construction of light-to-electricity or light-to-fuel production devices.

  9. Theoretical characterization of photoinduced electron transfer in rigidly linked donor-acceptor molecules: the fragment charge difference and the generalized Mulliken-Hush schemes

    NASA Astrophysics Data System (ADS)

    Lee, Sheng-Jui; Chen, Hung-Cheng; You, Zhi-Qiang; Liu, Kuan-Lin; Chow, Tahsin J.; Chen, I.-Chia; Hsu, Chao-Ping

    2010-10-01

    We calculate the electron transfer (ET) rates for a series of heptacyclo[6.6.0.02,6.03,13.014,11.05,9.010,14]-tetradecane (HCTD) linked donor-acceptor molecules. The electronic coupling factor was calculated by the fragment charge difference (FCD) [19] and the generalized Mulliken-Hush (GMH) schemes [20]. We found that the FCD is less prone to problems commonly seen in the GMH scheme, especially when the coupling values are small. For a 3-state case where the charge transfer (CT) state is coupled with two different locally excited (LE) states, we tested with the 3-state approach for the GMH scheme [30], and found that it works well with the FCD scheme. A simplified direct diagonalization based on Rust's 3-state scheme was also proposed and tested. This simplified scheme does not require a manual assignment of the states, and it yields coupling values that are largely similar to those from the full Rust's approach. The overall electron transfer (ET) coupling rates were also calculated.

  10. Electronic and optical properties of novel carbazole-based donor-acceptor compounds for applications in blue-emitting organic light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Legaspi, Christian M.; Stubbs, Regan E.; Yaron, David J.; Peteanu, Linda A.; Sfeir, Matthew Y.; Kemboi, Abraham; Picker, Jesse; Fossum, Eric

    2015-08-01

    Organic light-emitting diodes (OLEDs) have received a significant attention over the past decade due to their energy-saving potential. We have recently synthesized two novel carbazole-based donor-acceptor compounds and analyzed their optical properties to determine their suitability for use as blue emitters in OLEDs. These compounds show remarkable photo-stability and high quantum yields in the blue region of the spectrum. In addition, they have highly solvatochromic emission. In non-polar solvents, bright, blue-shifted (λmax ≈ 398 nm), and highly structured emission is seen. With increasing solvent dielectric constant, the emission becomes weaker, red-shifted (λmax ≈ 507 nm), and broad. We aim to determine the underlying cause of these changes. Electronic structure calculations indicate the presence of multiple excited states with comparable oscillator strength. These states are of interest because there are several with charge-transfer (CT) character, and others centered on the donor moiety. We theorize that CT states play a role in the observed changes in emission lineshape and may promote charge mobility for electrofluorescence in OLEDs. In the future, we plan to use Stark spectroscopy to analyze the polarity of excited states and transient absorption spectroscopy to observe the dynamics in the excited state.

  11. Encapsulation of MEH-PPV:PCBM Hybrids in the Cores of Block Copolymer Micellar Assemblies: Photoinduced Electron Transfer in a Nanoscale Donor-Acceptor System.

    PubMed

    Wang, Suxiao; Ryan, James William; Singh, Amita; Beirne, Jason Gerard; Palomares, Emilio; Redmond, Gareth

    2016-01-12

    The objective of this work is to demonstrate that conjugated polymer:fullerene hybrid nanoparticles encapsulated in the hydrophobic cores of triblock copolymer micelles may successfully act as spatially confined donor-acceptor systems capable of facilitating photoinduced charge carrier separation. To this end, aqueous dispersions of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) nanoparticles were first prepared by solubilization of the polymer in the cores of poly(oxyethylene)-poly(oxypropylene)-poly(oxyethylene) triblock copolymer, Pluronic F-127 micelles. A number of significant optical spectroscopic changes were observed on transfer of the conjugated polymer from a nonaqueous solvent to the aqueous micellar environment. These were primarily attributed to increased interchain interactions due to conjugated polymer chain collapse during encapsulation in the micellar cores. When prepared in buffer solution, the micelles exhibited good long-term collodial stability. When MEH-PPV micelles were blended by the addition of controlled amounts of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), the observed correspondence of photoluminescence emission quenching, quantum yield decreases, and emission lifetime shortening with increasing PCBM concentration indicated efficient photoinduced donor-to-acceptor charge transfer between MEH-PPV and the fullerenes in the cores of the micelles, an assignment that was confirmed by transient absorption spectroscopic monitoring of carrier photogeneration and recombination. PMID:26653672

  12. Bimolecular electron transfer reactions in coumarin amine systems: Donor acceptor orientational effect on diffusion-controlled reaction rates

    NASA Astrophysics Data System (ADS)

    Satpati, A. K.; Nath, S.; Kumbhakar, M.; Maity, D. K.; Senthilkumar, S.; Pal, H.

    2008-04-01

    Electron transfer (ET) reactions between excited coumarin dyes and different aliphatic amine (AlA) and aromatic amine (ArA) donors have been investigated in acetonitrile solution using steady-state (SS) and time-resolved (TR) fluorescence quenching measurements. No ground state complex or emissive exciplex formation has been indicated in these systems. SS and TR measurements give similar quenching constants ( kq) for each of the coumarin-amine pairs, suggesting dynamic nature of interaction in these systems. On correlating kq values with the free energy changes (Δ G0) of the ET reactions show the typical Rehm-Weller type of behavior as expected for bimolecular ET reactions under diffusive condition, where kq increases with -Δ G0 at the lower exergonicity (-Δ G0) region but ultimately saturate to a diffusion-limited value (kqDC) at the higher exergonicity region. It is, however, interestingly observed that the kqDC values vary largely depending on the type of the amines used. Thus, kqDC is much higher with ArAs than AlAs. Similarly, the kqDC for cyclic monoamine 1-azabicyclo-[2,2,2]-octane (ABCO) is distinctly lower and that for cyclic diamine 1,4-diazabicyclo-[2,2,2]-octane (DABCO) is distinctly higher than the kqDC value obtained for other noncyclic AlAs. These differences in the kqDC values have been rationalized on the basis of the differences in the orientational restrictions involved in the ET reactions with different types of amines. As understood, n-type donors (AlAs) introduce large orientational restriction and thus significantly reduces the ET efficiency in comparison to the π-type donors (ArAs). Structural constrains are inferred to be the reason for the differences in the kqDC values involving ABCO, DABCO donors in comparison to other noncyclic AlAs. Supportive evidence for the orientational restrictions involving different types of amines donors has also been obtained from DFT based quantum chemical calculations on the molecular orbitals of

  13. Long-range coupling of electron-hole pairs in spatially separated organic donor-acceptor layers.

    PubMed

    Nakanotani, Hajime; Furukawa, Taro; Morimoto, Kei; Adachi, Chihaya

    2016-02-01

    Understanding exciton behavior in organic semiconductor molecules is crucial for the development of organic semiconductor-based excitonic devices such as organic light-emitting diodes and organic solar cells, and the tightly bound electron-hole pair forming an exciton is normally assumed to be localized on an organic semiconducting molecule. We report the observation of long-range coupling of electron-hole pairs in spatially separated electron-donating and electron-accepting molecules across a 10-nanometers-thick spacer layer. We found that the exciton energy can be tuned over 100 megaelectron volts and the fraction of delayed fluorescence can be increased by adjusting the spacer-layer thickness. Furthermore, increasing the spacer-layer thickness produced an organic light-emitting diode with an electroluminescence efficiency nearly eight times higher than that of a device without a spacer layer. Our results demonstrate the first example of a long-range coupled charge-transfer state between electron-donating and electron-accepting molecules in a working device.

  14. Long-range coupling of electron-hole pairs in spatially separated organic donor-acceptor layers

    PubMed Central

    Nakanotani, Hajime; Furukawa, Taro; Morimoto, Kei; Adachi, Chihaya

    2016-01-01

    Understanding exciton behavior in organic semiconductor molecules is crucial for the development of organic semiconductor-based excitonic devices such as organic light-emitting diodes and organic solar cells, and the tightly bound electron-hole pair forming an exciton is normally assumed to be localized on an organic semiconducting molecule. We report the observation of long-range coupling of electron-hole pairs in spatially separated electron-donating and electron-accepting molecules across a 10-nanometers-thick spacer layer. We found that the exciton energy can be tuned over 100 megaelectron volts and the fraction of delayed fluorescence can be increased by adjusting the spacer-layer thickness. Furthermore, increasing the spacer-layer thickness produced an organic light-emitting diode with an electroluminescence efficiency nearly eight times higher than that of a device without a spacer layer. Our results demonstrate the first example of a long-range coupled charge-transfer state between electron-donating and electron-accepting molecules in a working device. PMID:26933691

  15. Electronic structure, molecular orientation, charge transfer dynamics and solar cells performance in donor/acceptor copolymers and fullerene: Experimental and theoretical approaches

    SciTech Connect

    Garcia-Basabe, Y.; Borges, B. G. A. L.; Rocco, M. L. M. E-mail: luiza@iq.ufrj.br; Marchiori, C. F. N.; Yamamoto, N. A. D.; Koehler, M.; Roman, L. S. E-mail: luiza@iq.ufrj.br; Macedo, A. G.

    2014-04-07

    By combining experimental and theoretical approaches, the electronic structure, molecular orientation, charge transfer dynamics and solar cell performance in donor/acceptor copolymer poly[2,7-(9,9-bis(2-ethylhexyl)-dibenzosilole)-alt-4,7-bis(thiophen-2-yl) benzo-2,1,3-thiadiazole] (PSiF-DBT) films and blended with 6,6.-phenyl-C 61-butyric acid methyl ester (PSiF-DBT:PCBM) were investigated. Good agreement between experimental and theoretical PSiF-DBT UV-Vis absorption spectrum is observed and the main molecular orbitals contributing to the spectrum were determined using DFT single point calculations. Non-coplanar configuration was determined by geometric optimization calculation in isolated PSiF-DBT pentamer and corroborated by angular variation of the sulphur 1s near-edge X-ray absorption fine structure (NEXAFS) spectra. Edge-on and plane-on molecular orientations were obtained for thiophene and benzothiadiazole units, respectively. A power conversion efficiency up to 1.58%, open circuit voltage of 0.51 V, short circuit current of 8.71 mA/cm{sup 2} and a fill factor of 35% was obtained using blended PSiF-DBT:PCBM as active layer in a bulk heterojunction solar cell. Ultrafast electron dynamics in the low-femtosecond regime was evaluated by resonant Auger spectroscopy using the core-hole clock methodology around sulphur 1s absorption edge. Electron delocalization times for PSiF-DBT and PSiF-DBT:PCBM polymeric films were derived for selected excitation energies corresponding to the main transitions in the sulphur 1s NEXAFS spectra. The mixture of PSiF-DBT with PCBM improves the charge transfer process involving the π* molecular orbital of the thiophene units.

  16. Electronic structure, molecular orientation, charge transfer dynamics and solar cells performance in donor/acceptor copolymers and fullerene: Experimental and theoretical approaches

    NASA Astrophysics Data System (ADS)

    Garcia-Basabe, Y.; Marchiori, C. F. N.; Borges, B. G. A. L.; Yamamoto, N. A. D.; Macedo, A. G.; Koehler, M.; Roman, L. S.; Rocco, M. L. M.

    2014-04-01

    By combining experimental and theoretical approaches, the electronic structure, molecular orientation, charge transfer dynamics and solar cell performance in donor/acceptor copolymer poly[2,7-(9,9-bis(2-ethylhexyl)-dibenzosilole)-alt-4,7-bis(thiophen-2-yl)benzo-2,1,3-thiadiazole] (PSiF-DBT) films and blended with 6,6.-phenyl-C 61-butyric acid methyl ester (PSiF-DBT:PCBM) were investigated. Good agreement between experimental and theoretical PSiF-DBT UV-Vis absorption spectrum is observed and the main molecular orbitals contributing to the spectrum were determined using DFT single point calculations. Non-coplanar configuration was determined by geometric optimization calculation in isolated PSiF-DBT pentamer and corroborated by angular variation of the sulphur 1s near-edge X-ray absorption fine structure (NEXAFS) spectra. Edge-on and plane-on molecular orientations were obtained for thiophene and benzothiadiazole units, respectively. A power conversion efficiency up to 1.58%, open circuit voltage of 0.51 V, short circuit current of 8.71 mA/cm2 and a fill factor of 35% was obtained using blended PSiF-DBT:PCBM as active layer in a bulk heterojunction solar cell. Ultrafast electron dynamics in the low-femtosecond regime was evaluated by resonant Auger spectroscopy using the core-hole clock methodology around sulphur 1s absorption edge. Electron delocalization times for PSiF-DBT and PSiF-DBT:PCBM polymeric films were derived for selected excitation energies corresponding to the main transitions in the sulphur 1s NEXAFS spectra. The mixture of PSiF-DBT with PCBM improves the charge transfer process involving the π* molecular orbital of the thiophene units.

  17. Magnetic field enhanced electroluminescence in organic light emitting diodes based on electron donor-acceptor exciplex blends

    NASA Astrophysics Data System (ADS)

    Baniya, Sangita; Basel, Tek; Sun, Dali; McLaughlin, Ryan; Vardeny, Zeev Valy

    2016-03-01

    A useful process for light harvesting from injected electron-hole pairs in organic light emitting diodes (OLED) is the transfer from triplet excitons (T) to singlet excitons (S) via reverse intersystem crossing (RISC). This process adds a delayed electro-luminescence (EL) emission component that is known as thermally activated delayed fluorescence (TADF). We have studied electron donor (D)/acceptor(A) blends that form an exciplex manifold in which the energy difference, ΔEST between the lowest singlet (S1) and triplet (T1) levels is relatively small (<100 meV), and thus allows RISC at ambient temperature. We found that the EL emission in OLED based on the exciplex blend is enhanced up to 40% by applying a relatively weak magnetic field of 50 mT at ambient. Moreover the MEL response is activated with activation energy similar that of the EL emission. This suggests that the large magneto-EL originates from an additional spin-mixing channel between singlet and triplet states of the generated exciplexes, which is due to TADF. We will report on the MEL dependencies on the temperature, bias voltage, and D-A materials for optimum OLED performance. Supported by SAMSUNG Global Research Outreach (GRO) program, and also by the NSF-Material Science & Engineering Center (MRSEC) program at the University of Utah (DMR-1121252).

  18. Ferrocene-dithiolene hybrids: control of strong donor-acceptor electronic communication to reverse the charge transfer direction.

    PubMed

    Kusamoto, Tetsuro; Takada, Kenji; Sakamoto, Ryota; Kume, Shoko; Nishihara, Hiroshi

    2012-11-19

    We prepared a novel class of ferrocene-dithiolene hybrid molecules, FcS4dt(Me)2 and FcS4dt[Pt((t)Bu2bpy)] (where FcS4dt indicates 2-(1,3-dithia[3]ferrocenophane-2-ylidene)-1,3-dithiole-4,5-dithiolate and (t)Bu2bpy indicates 4,4'-di-tert-butyl-2,2'-bipyridine), in which the ferrocene moiety was bound to the planar conjugated dithiolene skeleton via two sulfur atoms such that the cyclopentadienyl rings were perpendicular to the dithiolene backbone. The physical properties and electronic structures of the complexes and their oxidized species [FcS4dt(Me)2](•+) and [FcS4dt[Pt((t)Bu2bpy)

  19. An Inexpensive Co-Intercalated Layered Double Hydroxide Composite with Electron Donor-Acceptor Character for Photoelectrochemical Water Splitting.

    PubMed

    Zheng, Shufang; Lu, Jun; Yan, Dongpeng; Qin, Yumei; Li, Hailong; Evans, David G; Duan, Xue

    2015-07-15

    In this paper, the inexpensive 4,4-diaminostilbene-2,2-disulfonate (DAS) and 4,4-dinitro-stilbene-2,2- disulfonate (DNS) anions with arbitrary molar ratios were successfully co-intercalated into Zn2Al-layered double hydroxides (LDHs). The DAS(50%)-DNS/LDHs composite exhibited the broad UV-visible light absorption and fluorescence quenching, which was a direct indication of photo-induced electron transfer (PET) process between the intercalated DAS (donor) and DNS (acceptor) anions. This was confirmed by the matched HOMO/LUMO energy levels alignment of the intercalated DAS and DNS anions, which was also compatible for water splitting. The DAS(50%)-DNS/LDHs composite was fabricated as the photoanode and Pt as the cathode. Under the UV-visible light illumination, the enhanced photo-generated current (4.67 mA/cm(2) at 0.8 V vs. SCE) was generated in the external circuit, and the photoelectrochemical water split was realized. Furthermore, this photoelectrochemical water splitting performance had excellent crystalline, electrochemical and optical stability. Therefore, this novel inorganic/organic hybrid photoanode exhibited potential application prospect in photoelectrochemical water splitting.

  20. An Inexpensive Co-Intercalated Layered Double Hydroxide Composite with Electron Donor-Acceptor Character for Photoelectrochemical Water Splitting

    PubMed Central

    Zheng, Shufang; Lu, Jun; Yan, Dongpeng; Qin, Yumei; Li, Hailong; Evans, David G.; Duan, Xue

    2015-01-01

    In this paper, the inexpensive 4,4-diaminostilbene-2,2-disulfonate (DAS) and 4,4-dinitro-stilbene-2,2- disulfonate (DNS) anions with arbitrary molar ratios were successfully co-intercalated into Zn2Al-layered double hydroxides (LDHs). The DAS(50%)-DNS/LDHs composite exhibited the broad UV-visible light absorption and fluorescence quenching, which was a direct indication of photo-induced electron transfer (PET) process between the intercalated DAS (donor) and DNS (acceptor) anions. This was confirmed by the matched HOMO/LUMO energy levels alignment of the intercalated DAS and DNS anions, which was also compatible for water splitting. The DAS(50%)-DNS/LDHs composite was fabricated as the photoanode and Pt as the cathode. Under the UV-visible light illumination, the enhanced photo-generated current (4.67 mA/cm2 at 0.8 V vs. SCE) was generated in the external circuit, and the photoelectrochemical water split was realized. Furthermore, this photoelectrochemical water splitting performance had excellent crystalline, electrochemical and optical stability. Therefore, this novel inorganic/organic hybrid photoanode exhibited potential application prospect in photoelectrochemical water splitting. PMID:26174201

  1. Deep proton tunneling in the electronically adiabatic and non-adiabatic limits: comparison of the quantum and classical treatment of donor-acceptor motion in a protein environment.

    PubMed

    Benabbas, Abdelkrim; Salna, Bridget; Sage, J Timothy; Champion, Paul M

    2015-03-21

    Analytical models describing the temperature dependence of the deep tunneling rate, useful for proton, hydrogen, or hydride transfer in proteins, are developed and compared. Electronically adiabatic and non-adiabatic expressions are presented where the donor-acceptor (D-A) motion is treated either as a quantized vibration or as a classical "gating" distribution. We stress the importance of fitting experimental data on an absolute scale in the electronically adiabatic limit, which normally applies to these reactions, and find that vibrationally enhanced deep tunneling takes place on sub-ns timescales at room temperature for typical H-bonding distances. As noted previously, a small room temperature kinetic isotope effect (KIE) does not eliminate deep tunneling as a major transport channel. The quantum approach focuses on the vibrational sub-space composed of the D-A and hydrogen atom motions, where hydrogen bonding and protein restoring forces quantize the D-A vibration. A Duschinsky rotation is mandated between the normal modes of the reactant and product states and the rotation angle depends on the tunneling particle mass. This tunnel-mass dependent rotation contributes substantially to the KIE and its temperature dependence. The effect of the Duschinsky rotation is solved exactly to find the rate in the electronically non-adiabatic limit and compared to the Born-Oppenheimer (B-O) approximation approach. The B-O approximation is employed to find the rate in the electronically adiabatic limit, where we explore both harmonic and quartic double-well potentials for the hydrogen atom bound states. Both the electronically adiabatic and non-adiabatic rates are found to diverge at high temperature unless the proton coupling includes the often neglected quadratic term in the D-A displacement from equilibrium. A new expression is presented for the electronically adiabatic tunnel rate in the classical limit for D-A motion that should be useful to experimentalists working near

  2. Deep proton tunneling in the electronically adiabatic and non-adiabatic limits: Comparison of the quantum and classical treatment of donor-acceptor motion in a protein environment

    SciTech Connect

    Benabbas, Abdelkrim; Salna, Bridget; Sage, J. Timothy; Champion, Paul M.

    2015-03-21

    Analytical models describing the temperature dependence of the deep tunneling rate, useful for proton, hydrogen, or hydride transfer in proteins, are developed and compared. Electronically adiabatic and non-adiabatic expressions are presented where the donor-acceptor (D-A) motion is treated either as a quantized vibration or as a classical “gating” distribution. We stress the importance of fitting experimental data on an absolute scale in the electronically adiabatic limit, which normally applies to these reactions, and find that vibrationally enhanced deep tunneling takes place on sub-ns timescales at room temperature for typical H-bonding distances. As noted previously, a small room temperature kinetic isotope effect (KIE) does not eliminate deep tunneling as a major transport channel. The quantum approach focuses on the vibrational sub-space composed of the D-A and hydrogen atom motions, where hydrogen bonding and protein restoring forces quantize the D-A vibration. A Duschinsky rotation is mandated between the normal modes of the reactant and product states and the rotation angle depends on the tunneling particle mass. This tunnel-mass dependent rotation contributes substantially to the KIE and its temperature dependence. The effect of the Duschinsky rotation is solved exactly to find the rate in the electronically non-adiabatic limit and compared to the Born-Oppenheimer (B-O) approximation approach. The B-O approximation is employed to find the rate in the electronically adiabatic limit, where we explore both harmonic and quartic double-well potentials for the hydrogen atom bound states. Both the electronically adiabatic and non-adiabatic rates are found to diverge at high temperature unless the proton coupling includes the often neglected quadratic term in the D-A displacement from equilibrium. A new expression is presented for the electronically adiabatic tunnel rate in the classical limit for D-A motion that should be useful to experimentalists working

  3. Deep proton tunneling in the electronically adiabatic and non-adiabatic limits: comparison of the quantum and classical treatment of donor-acceptor motion in a protein environment.

    PubMed

    Benabbas, Abdelkrim; Salna, Bridget; Sage, J Timothy; Champion, Paul M

    2015-03-21

    Analytical models describing the temperature dependence of the deep tunneling rate, useful for proton, hydrogen, or hydride transfer in proteins, are developed and compared. Electronically adiabatic and non-adiabatic expressions are presented where the donor-acceptor (D-A) motion is treated either as a quantized vibration or as a classical "gating" distribution. We stress the importance of fitting experimental data on an absolute scale in the electronically adiabatic limit, which normally applies to these reactions, and find that vibrationally enhanced deep tunneling takes place on sub-ns timescales at room temperature for typical H-bonding distances. As noted previously, a small room temperature kinetic isotope effect (KIE) does not eliminate deep tunneling as a major transport channel. The quantum approach focuses on the vibrational sub-space composed of the D-A and hydrogen atom motions, where hydrogen bonding and protein restoring forces quantize the D-A vibration. A Duschinsky rotation is mandated between the normal modes of the reactant and product states and the rotation angle depends on the tunneling particle mass. This tunnel-mass dependent rotation contributes substantially to the KIE and its temperature dependence. The effect of the Duschinsky rotation is solved exactly to find the rate in the electronically non-adiabatic limit and compared to the Born-Oppenheimer (B-O) approximation approach. The B-O approximation is employed to find the rate in the electronically adiabatic limit, where we explore both harmonic and quartic double-well potentials for the hydrogen atom bound states. Both the electronically adiabatic and non-adiabatic rates are found to diverge at high temperature unless the proton coupling includes the often neglected quadratic term in the D-A displacement from equilibrium. A new expression is presented for the electronically adiabatic tunnel rate in the classical limit for D-A motion that should be useful to experimentalists working near

  4. Bright Solid-State Emission of Disilane-Bridged Donor-Acceptor-Donor and Acceptor-Donor-Acceptor Chromophores.

    PubMed

    Shimada, Masaki; Tsuchiya, Mizuho; Sakamoto, Ryota; Yamanoi, Yoshinori; Nishibori, Eiji; Sugimoto, Kunihisa; Nishihara, Hiroshi

    2016-02-24

    The development of disilane-bridged donor-acceptor-donor (D-Si-Si-A-Si-Si-D) and acceptor-donor-acceptor (A-Si-Si-D-Si-Si-A) compounds is described. Both types of compound showed strong emission (λem =ca. 500 and ca. 400 nm, respectively) in the solid state with high quantum yields (Φ: up to 0.85). Compound 4 exhibited aggregation-induced emission enhancement in solution. X-ray diffraction revealed that the crystal structures of 2, 4, and 12 had no intermolecular π-π interactions to suppress the nonradiative transition in the solid state.

  5. Electronic energy and electron transfer processes in photoexcited donor-acceptor dyad and triad molecular systems based on triphenylene and perylene diimide units.

    PubMed

    Lee, K J; Woo, J H; Kim, E; Xiao, Y; Su, X; Mazur, L M; Attias, A-J; Fages, F; Cregut, O; Barsella, A; Mathevet, F; Mager, L; Wu, J W; D'Aléo, A; Ribierre, J-C

    2016-03-21

    We investigate the photophysical properties of organic donor-acceptor dyad and triad molecular systems based on triphenylene and perylene diimide units linked by a non-conjugated flexible bridge in solution using complementary optical spectroscopy techniques. When these molecules are diluted in dichloromethane solution, energy transfer from the triphenylene to the perylene diimide excited moieties is evidenced by time-resolved fluorescence measurements resulting in a quenching of the emission from the triphenylene moieties. Simultaneously, another quenching process that affects the emission from both donor and acceptor units is observed. Solution ultrafast transient absorption measurements provide evidence of photo-induced charge transfer from either the donor or the acceptor depending upon the excitation. Overall, the analysis of the detailed time-resolved spectroscopic measurements carried out in the dyad and triad systems as well as in the triphenylene and perylene diimide units alone provides useful information both to better understand the relations between energy and charge transfer processes with molecular structures, and for the design of future functional dyad and triad architectures based on donor and acceptor moieties for organic optoelectronic applications. PMID:26911420

  6. Theory of Primary Photoexcitations in Donor-Acceptor Copolymers

    NASA Astrophysics Data System (ADS)

    Aryanpour, Karan; Dutta, Tirthankar; Huynh, Uyen N. V.; Vardeny, Zeev Valy; Mazumdar, Sumit

    2015-12-01

    We present a generic theory of primary photoexcitations in low band gap donor-acceptor conjugated copolymers. Because of the combined effects of strong electron correlations and broken symmetry, there is considerable mixing between a charge-transfer exciton and an energetically proximate triplet-triplet state with an overall spin singlet. The triplet-triplet state, optically forbidden in homopolymers, is allowed in donor-acceptor copolymers. For an intermediate difference in electron affinities of the donor and the acceptor, the triplet-triplet state can have a stronger oscillator strength than the charge-transfer exciton. We discuss the possibility of intramolecular singlet fission from the triplet-triplet state, and how such fission can be detected experimentally.

  7. Donor-acceptor heteroleptic open sandwiches.

    PubMed

    Merino, Gabriel; Beltrán, Hiram I; Vela, Alberto

    2006-02-01

    A series of donor-acceptor heteroleptic open sandwiches with formula CpM-M'Pyl (M = B, Al, Ga; M' = Li, Na; Cp = cyclopentadienyl; Pyl = pentadienyl) has been designed in silico using density functional theory. The most stable complexes are those containing boron as a donor atom. A molecular orbital analysis shows that the s character of the lone pair located at the group 13 element is mainly responsible for the complex stabilization. It is also found that the surrounding medium has a similar effect on these sandwiches such as in the "classical" donor-acceptor complexes, showing a decrement in the group 13 element-alkaline metal bond lengths.

  8. Supramolecular donor-acceptor hybrids of porphyrins/phthalocyanines with fullerenes/carbon nanotubes: electron transfer, sensing, switching, and catalytic applications.

    PubMed

    D'Souza, Francis; Ito, Osamu

    2009-09-01

    Since the three-dimensional electron-accepting fullerene has been found to be an excellent building block for self-assembled supramolecular systems, we have investigated photoinduced electron transfer processes in supramolecular fullerene systems with porphyrins and phthalocyanines as electron donors to mimic natural photosynthesis. We have successfully formed self-assembled supramolecular dyads and triads via metal-ligand coordination, crown-ether inclusion, ion pairing, hydrogen-bonding, or pi-pi stacking interactions. Although the single mode of binding gives usually flexible supramolecular structures, the newly developed strategy of multiple modes of binding results in conjugates of defined distance and orientation between the donor and acceptor entities, which influences the overall electron transfer reactions. In these conjugates, we observe the anticipated acceleration of the charge separation process and deceleration of the charge recombination process. Applications of these supramolecular systems for reversible photoswitching of inter- and intramolecular electron transfer events open up new opportunities in the area of photosensors. Extension of the self-assembly approaches to single wall carbon nanotubes (SWNT) results in SWNT-porphyrin/phthalocyanine nanohybrids capable of undergoing photoinduced electron transfer. These photochemical processes lead to photocatalytic reactions accumulating redox active substances of electron acceptor/mediator entities with the help of a sacrificial electron donor. Studies on these self-assembled supramolecular dyads, triads, tetrads, etc., are only in the beginning stages and future studies anticipate involvement of more complex systems targeted for better performances in light-driven devices. PMID:19668806

  9. Design directed self-assembly of donor-acceptor polymers.

    PubMed

    Marszalek, Tomasz; Li, Mengmeng; Pisula, Wojciech

    2016-09-21

    Donor-acceptor polymers with an alternating array of donor and acceptor moieties have gained particular attention during recent years as active components of organic electronics. By implementation of suitable subunits within the conjugated backbone, these polymers can be made either electron-deficient or -rich. Additionally, their band gap and light absorption can be precisely tuned for improved light-harvesting in solar cells. On the other hand, the polymer design can also be modified to encode the desired supramolecular self-assembly in the solid-state that is essential for an unhindered transport of charge carriers. This review focuses on three major factors playing a role in the assembly of donor-acceptor polymers on surfaces which are (1) nature, geometry and substitution position of solubilizing alkyl side chains, (2) shape of the conjugated polymer defined by the backbone curvature, and (3) molecular weight which determines the conjugation length of the polymer. These factors adjust the fine balance between attractive and repulsive forces and ensure a close polymer packing important for an efficient charge hopping between neighboring chains. On the microscopic scale, an appropriate domain formation with a low density of structural defects in the solution deposited thin film is crucial for the charge transport. The charge carrier transport through such thin films is characterized by field-effect transistors as basic electronic elements. PMID:27440174

  10. Impact of donor-acceptor geometry and metal chelation on photophysical properties and applications of triarylboranes.

    PubMed

    Hudson, Zachary M; Wang, Suning

    2009-10-20

    Three-coordinate organoboron compounds have recently found a wide range of applications in materials chemistry as nonlinear optical materials, chemical sensors, and emitters for organic light-emitting diodes (OLEDs). These compounds are excellent electron acceptors due to the empty p(pi) orbital on the boron center. When accompanied by electron donors such as amines, these molecules possess large electronic dipoles, which promote donor-acceptor charge-transfer upon excitation with light. Because of this, donor-acceptor triarylboranes are often highly luminescent both in the solid state and in solution. In this Account, we describe our research to develop donor-acceptor triarylboranes as efficient blue emitters for OLEDs. Through the use of hole-transporting donor groups such as 1-napthylphenylamines, we have prepared multifunctional triarylboranes that can act as the emissive, electron transport, or hole transport layers in OLEDs. We have also examined donor-acceptor compounds based on 2,2'-dipyridylamine or 7-azaindolyl donors, several of which have fluorescent quantum efficiencies approaching 100%. We are also investigating the chemistry of metal-containing triarylboranes. Our studies show that the electron-deficient boryl group can greatly facilitate metal-to-ligand charge-transfer transitions and phosphorescence. In addition, electronegative linker groups such as 2,2'-bipyridine can act in synergy with metal chelation to greatly improve the electron-accepting ability and Lewis acidity of triarylboranes. Donor-acceptor triarylboranes developed in our laboratory can also serve as a series of "switch-on" sensors for fluoride ions. When the donor and acceptor are linked by rigid naphthyl or nonrigid silane linkers, donor-acceptor conjugation is disrupted and charge transfer occurs primarily through space. The binding of fluoride ions to the boron center disrupts this charge transfer, activating alternative pi --> pi* transitions in the molecule and changing the

  11. Electronic structure of p-type perylene monoimide-based donor-acceptor dyes on the nickel oxide (100) surface: a DFT approach.

    PubMed

    Kontkanen, O V; Niskanen, M; Hukka, T I; Rantala, T T

    2016-05-25

    A p-type dye-sensitized solar cell, where the dye injects a hole into the semiconductor, could be combined with a typical Grätzel cell to create an efficient tandem device. However, the current p-type devices suffer from low efficiency. Here, geometries and electronic structures of four perylenemonoimide-based dyes () both as free and adsorbed on the NiO(100) semiconductor surface have been investigated to gain a better understanding of the p-type devices. In particular, the electronic transitions relevant to charge transfer between the dye and the surface have been identified. Excitations have been evaluated using the time-dependent DFT calculations, and the roles of frontier orbitals and band edges in transitions have been assessed. The adsorbed dyes can adopt either upright or slightly tilted geometries depending on the structure of the anchoring group and the binding mode of the dye. The adsorption slightly lowers the NiO band gap, from 4.06 eV to 3.90-3.96 eV, depending on the surface-adsorbate system and the band gaps of the dye molecules by 0.1-0.2 eV. Additionally, the adsorption mode of dye moves the LUMO+1 level down by 0.5 eV. The effective mass of charge carrier holes is significantly smaller at the NiO surface than in the bulk indicating the importance of surface conductivity. We also found that the potential drop, i.e. the driving force for charge transfer from NiO to the dye molecule, depends on the adsorption mode of . PMID:27224900

  12. Donor-acceptor binding interaction of 1-(naphthalene-1-yl)-2,4,5-triphenyl-1H-imidazole with semiconductor nanomaterials.

    PubMed

    Jayabharathi, J; Karunakaran, C; Kalaiarasi, V; Ramanathan, P

    2015-02-25

    The dynamics of photoinduced electron injection from 1-(naphthalene-1-yl)-2,4,5-triphenyl-1H-imidazole (NTI) to pristine ZnO, Mn-doped TiO2 and BaTiO3 nanoparticles have been studied by absorption, fluorescence and lifetime spectroscopic methods. Both the absorption and fluorescence results suggest the association between the nanoparticles and NTI. The calculated free energy change (ΔGet) confirms the electron injection from NTI to nano semiconductors. The critical energy transfer distance between NTI and the nanoparticles have been deduced. The emission of NTI is enhanced by pristine ZnO and quenched by Mn-doped TiO2 and BaTiO3 nanoparticles which are likely due to change of LUMO and HOMO levels of NTI on its association with nano semiconductors. The strong adsorption of the NTI on the surface of ZnO nanocrystals is likely due to the chemical affinity of the nitrogen atom of the NTI to the zinc ion on the surface of nanocrystals. Electron injection from photoexcited NTI to the CB(S(∗)→S(+)+eCB(-)) is likely to be the reason for the fluorescence enhancement.

  13. Donor-acceptor binding interaction of 1-(naphthalene-1-yl)-2,4,5-triphenyl-1H-imidazole with semiconductor nanomaterials

    NASA Astrophysics Data System (ADS)

    Jayabharathi, J.; Karunakaran, C.; Kalaiarasi, V.; Ramanathan, P.

    2015-02-01

    The dynamics of photoinduced electron injection from 1-(naphthalene-1-yl)-2,4,5-triphenyl-1H-imidazole (NTI) to pristine ZnO, Mn-doped TiO2 and BaTiO3 nanoparticles have been studied by absorption, fluorescence and lifetime spectroscopic methods. Both the absorption and fluorescence results suggest the association between the nanoparticles and NTI. The calculated free energy change (ΔGet) confirms the electron injection from NTI to nano semiconductors. The critical energy transfer distance between NTI and the nanoparticles have been deduced. The emission of NTI is enhanced by pristine ZnO and quenched by Mn-doped TiO2 and BaTiO3 nanoparticles which are likely due to change of LUMO and HOMO levels of NTI on its association with nano semiconductors. The strong adsorption of the NTI on the surface of ZnO nanocrystals is likely due to the chemical affinity of the nitrogen atom of the NTI to the zinc ion on the surface of nanocrystals. Electron injection from photoexcited NTI to the CB(S∗ → S+ + e-CB) is likely to be the reason for the fluorescence enhancement.

  14. Rational design of two-dimensional molecular donor-acceptor nanostructure arrays

    NASA Astrophysics Data System (ADS)

    Zhang, Jia Lin; Zhong, Shu; Zhong, Jian Qiang; Niu, Tian Chao; Hu, Wen Ping; Wee, Andrew Thye Shen; Chen, Wei

    2015-02-01

    The construction of long-range ordered organic donor-acceptor nanostructure arrays over microscopic areas supported on solid substrates is one of the most challenging tasks towards the realization of molecular nanodevices. They can also be used as ideal model systems to understand light induced charge transfer, charge separation and energy conversion processes and mechanisms at the nanometer scale. The aim of this paper is to highlight recent advances and progress in this topic. Special attention is given to two different strategies for the construction of organic donor-acceptor nanostructure arrays, namely (i) molecular self-assembly on artificially patterned or pre-defined molecular surface nanotemplates and (ii) molecular nanostructure formation steered via directional and selective intermolecular interactions. The interfacial charge transfer and the energy level alignment of these donor-acceptor nanostructures are also discussed.

  15. Donor-acceptor-donor tetrazines containing a ferrocene unit: synthesis, electrochemical and spectroscopic properties.

    PubMed

    Janowska, Izabela; Miomandre, Fabien; Clavier, Gilles; Audebert, Pierre; Zakrzewski, Janusz; Thi, Khuyen Hoang; Ledoux-Rak, Isabelle

    2006-11-30

    Donor-acceptor-donor tetrazines containing ferrocene moieties and phenyl unit as a pi-bridge have been synthesized and characterized. UV-vis spectroscopic and cyclic voltamperometric results indicate sizable intramolecular charge transfer interactions in the ground state when the ferrocene is directly bound to the tetrazine. On the other hand, the results show reduction of the electron-donor strength of ferrocene moieties when there is a phenyl linkage. Both tetrazines display a high reduction potential. The role of ferrocenyl groups appear to be detrimental to maximize the cubic hyperpolarizability gamma of tetrazines, as compared to purely organic groups such as thiophene. A possible explanation for this behavior may originate from metal-to-ligand charge transfer processes.

  16. Organic Materials in the Undergraduate Laboratory: Microscale Synthesis and Investigation of a Donor-Acceptor Molecule

    ERIC Educational Resources Information Center

    Pappenfus, Ted M.; Schliep, Karl B.; Dissanayake, Anudaththa; Ludden, Trevor; Nieto-Ortega, Belen; Lopez Navarrete, Juan T.; Ruiz Delgado, M. Carmen; Casado, Juan

    2012-01-01

    A series of experiments for undergraduate courses (e.g., organic, physical) have been developed in the area of small molecule organic materials. These experiments focus on understanding the electronic and redox properties of a donor-acceptor molecule that is prepared in a convenient one-step microscale reaction. The resulting intensely colored…

  17. An extended Foerster-Dexter model for correlated donor-acceptor placement in solid state materials

    NASA Astrophysics Data System (ADS)

    Rotman, S. R.; Hartmann, F. X.

    1987-09-01

    The current theory of donor-acceptor interactions in solid-state materials is based on a random distribution of donors and acceptors through the crystal. In this paper, we present a model to calculate the observable transfer rates for the correlated positioning of donors and acceptors in laser materials. Chemical effects leading to such correlations are discussed.

  18. Red-shifted cyanide stretching frequencies in cyanide-bridged transition metal donor-acceptor complexes. Support for vibronic coupling

    SciTech Connect

    Watzky, M.A.; Endicott, J.F.; Song, X.

    1996-06-05

    Patterns in the cyanide stretching frequencies have been examined in several series of monometal- and CN{sup {minus}} bridged transition metal complexes. Metal-to-cyanide back-bonding can be identified as a major factor contributing to red shifts of v{sub CN} in monometal complexes. This effect is complicated in cyanide-bridged complexes in two ways: (a) when both metals can back-bond to cyanide, the net interaction is repulsive and results in a blue shift of v{sub CN}: and (b) when a donor and acceptor are bridged, V{sub CN} undergoes a substantial red shift (sometimes more than 60 cm{sup {minus}1} lower in energy than the parent monometal complex). These effects can be described by simple perturbational models for the electronic interactions. Monometal cyanide complexes and CN{sup {minus}}-bridged backbonding metals can be treated in terms of their perturbations of the CN{sup {minus}} {pi} and {pi}* orbitals by using a simple, Hueckel-like, three-center perturbational treatment of electronic interactions. However, bridged donor-acceptor pairs are best described by a vibronic model in which it is assumed that the extent of electronic delocalization is in equilibrium with variations of some nuclear coordinates. Consistent with this approach, it is found that (a) the oscillator strength of the donor-acceptor charge transfer (DACT) absorption is roughly proportional to the red shift of v{sub CN} and (b) there are strong symmetry constraints on the coupling.

  19. Nonequilibrium phenomena in charge recombination of excited donor-acceptor complexes and free energy gap law.

    PubMed

    Yudanov, Vladislav V; Mikhailova, Valentina A; Ivanov, Anatoly I

    2010-12-23

    The charge recombination dynamics of excited donor-acceptor complexes in polar solvents has been investigated within the framework of the stochastic approach. The model involves the excited state formation by the pump pulse and accounts for the reorganization of a number of intramolecular high-frequency vibrational modes, for their relaxation as well as for the solvent reorganization following nonexponential relaxation. The hot transitions accelerate the charge recombination in the low exergonic region and suppress it in the region of moderate exothermicity. This straightens the dependence of the logarithm of the charge recombination rate constant on the free energy gap to the form that can be fitted to the experimental data. The free energy dependence of the charge recombination rate constant can be well fitted to the multichannel stochastic model if the donor-acceptor complexes are separated into a few groups with different values of the electronic coupling. The model provides correct description of the nonexponential charge recombination dynamics in excited donor-acceptor complexes, in particular, nearly exponential recombination in perylene-tetracyanoethylene complex in acetonitrile. It appears that majority of the initially excited donor-acceptor complexes recombines in a nonthermal (hot) stage when the nonequilibrium wave packet passes through a number of term crossings corresponding to transitions toward vibrational excited states of the electronic ground state in the area of the low and moderate exothermicity.

  20. Swift Electrofluorochromism of Donor-Acceptor Conjugated Polytriphenylamines.

    PubMed

    Sun, Jingwei; Liang, Ziqi

    2016-07-20

    Electrofluorochromic (EFC) materials, which exhibit electrochemically controllable fluorescence, hold great promise in optoelectronic devices and biological analysis. Here we design such donor-acceptor (D-A) conjugated polymers-P(TPACO) and P(TCEC)-that contain the same electron-rich and oxidizable polytriphenylamine (PTPA) as π-backbone, yet with different electron-deficient ketone and cyano units as pendant groups, respectively. They both exhibit solvatochromic effects due to intrinsic characteristics of intramolecular charge transfer (ICT). Compared to P(TPACO), P(TCEC) shows stronger ICT, which leads to higher electrochemical oxidation potential and lower ion diffusion coefficient. Moreover, both polymers present simultaneous electrochromic (EC) and EFC behaviors with multistate display and remarkably rapid fluorescence response. The response time of P(TPACO) is as short as 0.19 s, nearly 4-fold faster than that of P(TCEC) (0.92 s). Such rapid response is found to be determined by the ion diffusion coefficient which is associated with the ICT nature. Finally, the EFC display device based on P(TPACO) is successfully demonstrated, which shows green fluorescence ON/OFF switching upon applied potentials. This work has successfully demonstrated that swift EFCs can be achieved by rational modulation of the ICT effect in such D-A conjugated polymers. PMID:27347724

  1. Well-defined star-shaped donor-acceptor conjugated molecules for organic resistive memory devices.

    PubMed

    Wu, Hung-Chin; Zhang, Jicheng; Bo, Zhishan; Chen, Wen-Chang

    2015-09-28

    Solution processable star-shaped donor-acceptor (D-A) conjugated molecules (TPA-T-NI and TPA-3T-NI) with an electron-donating triphenylamine (TPA) core, three thienylene or terthienylene spacers, and three 1.8-naphthalimide (NI) electron-withdrawing end-groups are explored for the first time as charge storage materials for resistor-type memory devices owing to the efficient electric charge transfer and trapping.

  2. Well-defined star-shaped donor-acceptor conjugated molecules for organic resistive memory devices.

    PubMed

    Wu, Hung-Chin; Zhang, Jicheng; Bo, Zhishan; Chen, Wen-Chang

    2015-09-28

    Solution processable star-shaped donor-acceptor (D-A) conjugated molecules (TPA-T-NI and TPA-3T-NI) with an electron-donating triphenylamine (TPA) core, three thienylene or terthienylene spacers, and three 1.8-naphthalimide (NI) electron-withdrawing end-groups are explored for the first time as charge storage materials for resistor-type memory devices owing to the efficient electric charge transfer and trapping. PMID:26255879

  3. Curved Oligophenylenes as Donors in Shape-Persistent Donor-Acceptor Macrocycles with Solvatofluorochromic Properties.

    PubMed

    Kuwabara, Takuya; Orii, Jun; Segawa, Yasutomo; Itami, Kenichiro

    2015-08-10

    Many optoelectronic organic materials are based on donor-acceptor (D-A) systems with heteroatom-containing electron donors. Herein, we introduce a new molecular design for all-carbon curved oligoparaphenylenes as donors, which results in the generation of unique shape-persistent D-A macrocycles. Two types of acceptor-inserted cycloparaphenylenes were synthesized. These macrocycles display positive solvatofluorochromic properties owing to their D-A characteristics, which were confirmed by theoretical and electrochemical studies. PMID:26140706

  4. Benzodipyrrole-based Donor-Acceptor-type Boron Complexes as Tunable Near-infrared-Absorbing Materials.

    PubMed

    Nakamura, Tomoya; Furukawa, Shunsuke; Nakamura, Eiichi

    2016-07-20

    Benzodipyrrole-based donor-acceptor boron complexes were designed and synthesized as near-infrared-absorbing materials. The electron-rich organic framework combined with the Lewis acidic boron co-ordination enabled us to tune the LUMO energy level and the HOMO-LUMO gap (i.e.,the absorption wavelength) by changing the organic acceptor units, the number of boron atoms, and the substituents on the boron atoms.

  5. Imprinting of molecular recognition sites combined with π-donor-acceptor interactions using bis-aniline-crosslinked Au-CdSe/ZnS nanoparticles array on electrodes: Development of electrochemiluminescence sensor for the ultrasensitive and selective detection of 2-methyl-4-chlorophenoxyacetic acid.

    PubMed

    Yang, Yukun; Fang, Guozhen; Wang, Xiaomin; Liu, Guiyang; Wang, Shuo

    2016-03-15

    A novel strategy is reported for the fabrication of bis-aniline-crosslinked Au nanoparticles (NPs)-CdSe/ZnS quantum dots (QDs) array composite by facil one-step co-electropolymerization of thioaniline-functionalized AuNPs and thioaniline-functionalized CdSe/ZnS QDs onto thioaniline-functionalized Au elctrodes (AuE). Stable and enhanced cathodic electrochemiluminescence (ECL) of CdSe/ZnS QDs is observed on the modified electrode in neutral solution, suggesting promising applications in ECL sensing. An advanced ECL sensor is explored for detection of 2-methyl-4-chlorophenoxyacetic acid (MCPA) which quenches the ECL signal through electron-transfer pathway. The sensitive determination of MCPA with limit of detection (LOD) of 2.2 nmolL(-1) (S/N=3) is achieved by π-donor-acceptor interactions between MCPA and the bis-aniline bridging units. Impressively, the imprinting of molecular recognition sites into the bis-aniline-crosslinked AuNPs-CdSe/ZnS QDs array yields a functionalized electrode with an extremely sensitive response to MCPA in a linear range of 10 pmolL(-1)-50 μmolL(-1) with a LOD of 4.3 pmolL(-1 ()S/N=3). The proposed ECL sensor with high sensitivity, good selectivity, reproducibility and stability has been successfully applied for the determination of MCPA in real samples with satisfactory recoveries. In this study, ECL sensor combined the merits of QDs-ECL and molecularly imprinting technology is reported for the first time. The developed ECL sensor holds great promise for the fabrication of QDs-based ECL sensors with improved sensitivity and furthermore opens the door to wide applications of QDs-based ECL in food safety and environmental monitoring.

  6. Imprinting of molecular recognition sites combined with π-donor-acceptor interactions using bis-aniline-crosslinked Au-CdSe/ZnS nanoparticles array on electrodes: Development of electrochemiluminescence sensor for the ultrasensitive and selective detection of 2-methyl-4-chlorophenoxyacetic acid.

    PubMed

    Yang, Yukun; Fang, Guozhen; Wang, Xiaomin; Liu, Guiyang; Wang, Shuo

    2016-03-15

    A novel strategy is reported for the fabrication of bis-aniline-crosslinked Au nanoparticles (NPs)-CdSe/ZnS quantum dots (QDs) array composite by facil one-step co-electropolymerization of thioaniline-functionalized AuNPs and thioaniline-functionalized CdSe/ZnS QDs onto thioaniline-functionalized Au elctrodes (AuE). Stable and enhanced cathodic electrochemiluminescence (ECL) of CdSe/ZnS QDs is observed on the modified electrode in neutral solution, suggesting promising applications in ECL sensing. An advanced ECL sensor is explored for detection of 2-methyl-4-chlorophenoxyacetic acid (MCPA) which quenches the ECL signal through electron-transfer pathway. The sensitive determination of MCPA with limit of detection (LOD) of 2.2 nmolL(-1) (S/N=3) is achieved by π-donor-acceptor interactions between MCPA and the bis-aniline bridging units. Impressively, the imprinting of molecular recognition sites into the bis-aniline-crosslinked AuNPs-CdSe/ZnS QDs array yields a functionalized electrode with an extremely sensitive response to MCPA in a linear range of 10 pmolL(-1)-50 μmolL(-1) with a LOD of 4.3 pmolL(-1 ()S/N=3). The proposed ECL sensor with high sensitivity, good selectivity, reproducibility and stability has been successfully applied for the determination of MCPA in real samples with satisfactory recoveries. In this study, ECL sensor combined the merits of QDs-ECL and molecularly imprinting technology is reported for the first time. The developed ECL sensor holds great promise for the fabrication of QDs-based ECL sensors with improved sensitivity and furthermore opens the door to wide applications of QDs-based ECL in food safety and environmental monitoring. PMID:26569444

  7. Growth of polythiophene/perylene tetracarboxydiimide donor/acceptor shish-kebab nanostructures by coupled crystal modification.

    PubMed

    Bu, Laju; Pentzer, Emily; Bokel, Felicia A; Emrick, Todd; Hayward, Ryan C

    2012-12-21

    Self-assembled crystalline organic nanostructures containing electron donor and acceptor materials hold promise as building blocks for photovoltaic devices. We show that coupled crystallization of poly(3-hexyl thiophene) (P3HT) and perylene tetracarboxydiimide (PDI) induced by solvent evaporation, wherein both components modify crystallization of the other, gives rise to donor/acceptor "shish-kebabs" with tunable nanostructures. P3HT kinetically stabilizes supersaturated solutions of PDI and modifies the growth of PDI crystals, leading to formation of extended PDI shish nanowires that in turn serve as heterogeneous nucleation sites for fibrillar P3HT kebabs during solvent casting. The dimensions of these nanostructures can be tailored through variations in donor/acceptor ratio or solvent quality, and the method is shown to be general to several other poly(3-alkyl thiophenes) and perylene derivatives, thus providing a simple and robust route to form highly crystalline nanophase separated organic donor/acceptor assemblies.

  8. Synthesis, Properties, and Design Principles of Donor-Acceptor Nanohoops.

    PubMed

    Darzi, Evan R; Hirst, Elizabeth S; Weber, Christopher D; Zakharov, Lev N; Lonergan, Mark C; Jasti, Ramesh

    2015-09-23

    We have synthesized a series of aza[8]cycloparaphenylenes containing one, two, and three nitrogens to probe the impact of nitrogen doping on optoelectronic properties and solid state packing. Alkylation of these azananohoops afforded the first donor-acceptor nanohoops where the phenylene backbone acts as the donor and the pyridinium units act as the acceptor. The impact on the optoelectronic properties was then studied experimentally and computationally to provide new insight into the effect of functionalization on nanohoops properties. PMID:27162989

  9. Solvent-tuned intramolecular charge-recombination rates in a conjugated donor-acceptor molecule

    NASA Technical Reports Server (NTRS)

    Khundkar, Lutfur R.; Stiegman, A. E.; Perry, Joseph W.

    1990-01-01

    The nonradiative charge-recombination rates from the charge-transfer state of a new conjugated donor-acceptor molecule (p-cyano-p-prime-methylthiodiphenylacetylene) can be tuned over almost an order of magnitude by varying the polarity of the solvent. These measurements of intramolecular recombination show a turnover of rates as a function of emission energy, consistent with the 'normal' and 'inverted' behavior of Marcus theory. Steady-state spectra and time-resolved measurements make it possible to quantitatively compare thermal and optical electron-transfer rates as a function of driving force and demonstrate their correspondence.

  10. Donor-acceptor chemistry in the main group.

    PubMed

    Rivard, Eric

    2014-06-21

    This Perspective article summarizes recent progress from our laboratory in the isolation of reactive main group species using a general donor-acceptor protocol. A highlight of this program is the use of carbon-based donors in combination with suitable Lewis acidic acceptors to yield stable complexes of parent Group 14 element hydrides (e.g. GeH2 and H2SiGeH2). It is anticipated that this strategy could be extended to include new synthetic targets from throughout the Periodic Table with possible applications in bottom-up materials synthesis and main group element catalysis envisioned. PMID:24788390

  11. Vibrational properties of organic donor-acceptor molecular crystals: Anthracene-pyromellitic-dianhydride (PMDA) as a case study

    SciTech Connect

    Fonari, A.; Corbin, N. S.; Coropceanu, V. E-mail: coropceanu@gatech.edu; Vermeulen, D.; McNeil, L. E.; Goetz, K. P.; Jurchescu, O. D.; Bredas, J. L. E-mail: coropceanu@gatech.edu

    2015-12-14

    We establish a reliable quantum-mechanical approach to evaluate the vibrational properties of donor-acceptor molecular crystals. The anthracene-PMDA (PMDA = pyromellitic dianhydride) crystal, where anthracene acts as the electron donor and PMDA as the electron acceptor, is taken as a representative system for which experimental non-resonance Raman spectra are also reported. We first investigate the impact that the amount of nonlocal Hartree-Fock exchange (HFE) included in a hybrid density functional has on the geometry, normal vibrational modes, electronic coupling, and electron-vibrational (phonon) couplings. The comparison between experimental and theoretical Raman spectra indicates that the results based on the αPBE functional with 25%-35% HFE are in better agreement with the experimental results compared to those obtained with the pure PBE functional. Then, taking αPBE with 25% HFE, we assign the vibrational modes and examine their contributions to the relaxation energy related to the nonlocal electron-vibration interactions. The results show that the largest contribution (about 90%) is due to electron interactions with low-frequency vibrational modes. The relaxation energy in anthracene-PMDA is found to be about five times smaller than the electronic coupling.

  12. Quantifying charge transfer energies at donor-acceptor interfaces in small-molecule solar cells with constrained DFTB and spectroscopic methods

    NASA Astrophysics Data System (ADS)

    Scholz, Reinhard; Luschtinetz, Regina; Seifert, Gotthard; Jägeler-Hoheisel, Till; Körner, Christian; Leo, Karl; Rapacioli, Mathias

    2013-11-01

    Charge transfer states around the donor-acceptor interface in an organic solar cell determine the device performance in terms of the open circuit voltage. In the present work, we propose a computational scheme based on constrained density functional tight binding theory (c-DFTB) to assess the energy of the lowest charge transfer (CT) state in such systems. A comparison of the c-DFTB scheme with Hartree-Fock based configuration interaction of singles (CIS) and with time-dependent density functional theory (TD-DFT) using the hybrid functional B3LYP reveals that CIS and c-DFTB reproduce the correct Coulomb asymptotics between cationic donor and anionic acceptor configurations, whereas TD-DFT gives a qualitatively wrong excitation energy. Together with an embedding scheme accounting for the polarizable medium, this c-DFTB scheme is applied to several donor-acceptor combinations used in molecular solar cells. The external quantum efficiency of photovoltaic cells based on zinc phthalocyanine-C60 blends reveals a CT band remaining much narrower than the density of states of acceptor HOMO and donor LUMO, an observation which can be interpreted in a natural way in terms of Marcus transfer theory. A detailed comparison with c-DFTB calculations reveals an energy difference of 0.32 eV between calculated and observed absorption from the electronic ground state into the CT state. In a blend of a functionalized thiophene and C60, the photoluminescence spectra differ significantly from neat films, allowing again an assignment to CT states. The proposed computational scheme reproduces the observed trends of the observed open circuit voltages in photovoltaic devices relying on several donor-acceptor blends, finding an offset of 1.16 eV on average. This value is similar as in polymer-fullerene photovoltaic systems where it amounts to about 0.9 eV, indicating that the photophysics of CT states in molecular donor-acceptor blends and in polymer-fullerene blends are governed by the same

  13. Quantifying charge transfer energies at donor-acceptor interfaces in small-molecule solar cells with constrained DFTB and spectroscopic methods.

    PubMed

    Scholz, Reinhard; Luschtinetz, Regina; Seifert, Gotthard; Jägeler-Hoheisel, Till; Körner, Christian; Leo, Karl; Rapacioli, Mathias

    2013-11-27

    Charge transfer states around the donor-acceptor interface in an organic solar cell determine the device performance in terms of the open circuit voltage. In the present work, we propose a computational scheme based on constrained density functional tight binding theory (c-DFTB) to assess the energy of the lowest charge transfer (CT) state in such systems. A comparison of the c-DFTB scheme with Hartree-Fock based configuration interaction of singles (CIS) and with time-dependent density functional theory (TD-DFT) using the hybrid functional B3LYP reveals that CIS and c-DFTB reproduce the correct Coulomb asymptotics between cationic donor and anionic acceptor configurations, whereas TD-DFT gives a qualitatively wrong excitation energy. Together with an embedding scheme accounting for the polarizable medium, this c-DFTB scheme is applied to several donor-acceptor combinations used in molecular solar cells. The external quantum efficiency of photovoltaic cells based on zinc phthalocyanine-C60 blends reveals a CT band remaining much narrower than the density of states of acceptor HOMO and donor LUMO, an observation which can be interpreted in a natural way in terms of Marcus transfer theory. A detailed comparison with c-DFTB calculations reveals an energy difference of 0.32 eV between calculated and observed absorption from the electronic ground state into the CT state. In a blend of a functionalized thiophene and C60, the photoluminescence spectra differ significantly from neat films, allowing again an assignment to CT states. The proposed computational scheme reproduces the observed trends of the observed open circuit voltages in photovoltaic devices relying on several donor-acceptor blends, finding an offset of 1.16 eV on average. This value is similar as in polymer-fullerene photovoltaic systems where it amounts to about 0.9 eV, indicating that the photophysics of CT states in molecular donor-acceptor blends and in polymer-fullerene blends are governed by the

  14. The role of amino acid electron-donor/acceptor atoms in host-cell binding peptides is associated with their 3D structure and HLA-binding capacity in sterile malarial immunity induction

    SciTech Connect

    Patarroyo, Manuel E.; Almonacid, Hannia; Moreno-Vranich, Armando

    2012-01-20

    Highlights: Black-Right-Pointing-Pointer Fundamental residues located in some HABPs are associated with their 3D structure. Black-Right-Pointing-Pointer Electron-donor atoms present in {beta}-turn, random, distorted {alpha}-helix structures. Black-Right-Pointing-Pointer Electron-donor atoms bound to HLA-DR53. Black-Right-Pointing-Pointer Electron-acceptor atoms present in regular {alpha}-helix structure bound to HLA-DR52. -- Abstract: Plasmodium falciparum malaria continues being one of the parasitic diseases causing the highest worldwide mortality due to the parasite's multiple evasion mechanisms, such as immunological silence. Membrane and organelle proteins are used during invasion for interactions mediated by high binding ability peptides (HABPs); these have amino acids which establish hydrogen bonds between them in some of their critical binding residues. Immunisation assays in the Aotus model using HABPs whose critical residues had been modified have revealed a conformational change thereby enabling a protection-inducing response. This has improved fitting within HLA-DR{beta}1{sup Asterisk-Operator} molecules where amino acid electron-donor atoms present in {beta}-turn, random or distorted {alpha}-helix structures preferentially bound to HLA-DR53 molecules, whilst HABPs having amino acid electron-acceptor atoms present in regular {alpha}-helix structure bound to HLA-DR52. This data has great implications for vaccine development.

  15. Donor-acceptor complexation and dehydrogenation chemistry of aminoboranes.

    PubMed

    Malcolm, Adam C; Sabourin, Kyle J; McDonald, Robert; Ferguson, Michael J; Rivard, Eric

    2012-12-01

    A series of formal donor-acceptor adducts of aminoborane (H(2)BNH(2)) and its N-substituted analogues (H(2)BNRR') were prepared: LB-H(2)BNRR'(2)-BH(3) (LB = DMAP, IPr, IPrCH(2) and PCy(3); R and R' = H, Me or tBu; IPr = [(HCNDipp)(2)C:] and Dipp = 2,6-iPr(2)C(6)H(3)). To potentially access complexes of molecular boron nitride, LB-BN-LA (LA = Lewis acid), preliminary dehydrogenation chemistry involving the parent aminoborane adducts LB-H(2)BNH(2)-BH(3) was investigated using [Rh(COD)Cl](2), CuBr, and NiBr(2) as dehydrogenation catalysts. In place of isolating the intended dehydrogenated BN donor-acceptor complexes, the formation of borazine was noted as a major product. Attempts to prepare the fluoroarylborane-capped aminoborane complexes, LB-H(2)BNH(2)-B(C(6)F(5))(3), are also described. PMID:23153209

  16. New acceptor-donor-acceptor (A-D-A) type copolymers for efficient organic photovoltaic devices

    NASA Astrophysics Data System (ADS)

    Ghomrasni, S.; Ayachi, S.; Alimi, K.

    2015-01-01

    Three new conjugated systems alternating acceptor-donor-acceptor (A-D-A) type copolymers have been investigated by means of Density Functional Theory (DFT) and Time-Dependent DFT (TD-DFT) at the 6-31g (d) level of theory. 4,4‧-Dimethoxy-chalcone, also called the 1,3-bis(4-methoxyphenyl)prop-2-en-1-one (BMP), has been used as a common acceptor moiety. It forced intra-molecular S⋯O interactions through alternating oligo-thiophene derivatives: 4-AlkylThiophenes (4-ATP), 4-AlkylBithiophenes (4-ABTP) and 4-Thienylene Vinylene (4-TEV) as donor moieties. The band gap, HOMO and LUMO electron distributions as well as optical properties were analyzed for each molecule. The fully optimized resulting copolymers showed low band gaps (2.2-2.8 eV) and deep HOMO energy levels ranging from -4.66 to -4.86 eV. A broad absorption [300-900 nm] covering the solar spectrum and absorption maxima ranges from 486 to 604 nm. In addition, organic photovoltaic cells (OPCs) based on alternating copolymers in bulk heterojunction (BHJ) composites with the 1-(3-methoxycarbonyl) propyl-1-phenyl-[6,6]-C61 (PCBM), as an acceptor, have been optimized. Thus, the band gap decreased to 1.62 eV, the power conversion efficiencies (PCEs) were about 3-5% and the open circuit voltage Voc of the resulting molecules decreased from 1.50 to 1.27 eV.

  17. Direct view at colossal permittivity in donor-acceptor (Nb, In) co-doped rutile TiO2

    NASA Astrophysics Data System (ADS)

    Mandal, Suman; Pal, Somnath; Kundu, Asish K.; Menon, Krishnakumar S. R.; Hazarika, Abhijit; Rioult, Maxime; Belkhou, Rachid

    2016-08-01

    Topical observations of colossal permittivity (CP) with low dielectric loss in donor-acceptor cations co-doped rutile TiO2 have opened up several possibilities in microelectronics and energy-storage devices. Yet, the precise origin of the CP behavior, knowledge of which is essential to empower the device integration suitably, is highly disputed in the literature. From spectromicroscopic approach besides dielectric measurements, we explore that microscopic electronic inhomogeneities along with the nano-scale phase boundaries and the low temperature polaronic relaxation are mostly responsible for such a dielectric behavior, rather than electron-pinned defect-dipoles/grain-boundary effects as usually proposed. Donor-acceptor co-doping results in a controlled carrier-hopping inevitably influencing the dielectric loss while invariably upholding the CP value.

  18. Highly Emissive Far Red/Near-IR Fluorophores Based on Borylated Fluorene-Benzothiadiazole Donor-Acceptor Materials.

    PubMed

    Crossley, Daniel L; Vitorica-Yrezabal, Inigo; Humphries, Martin J; Turner, Michael L; Ingleson, Michael J

    2016-08-22

    Stille, Suzuki-Miyaura and Negishi cross-coupling reactions of bromine-functionalised borylated precursors enable the facile, high yielding, synthesis of borylated donor-acceptor materials that contain electron-rich aromatic units and/or extended effective conjugation lengths. These materials have large Stokes shifts, low LUMO energies, small band-gaps and significant fluorescence emission >700 nm in solution and when dispersed in a host polymer. PMID:27460768

  19. Nanostructured donor-acceptor self assembly with improved photoconductivity.

    PubMed

    Saibal, B; Ashar, A Z; Devi, R Nandini; Narayan, K S; Asha, S K

    2014-11-12

    Nanostructured supramolecular donor-acceptor assemblies were formed when an unsymmetrical N-substituted pyridine functionalized perylenebisimide (UPBI-Py) was complexed with oligo(p-phenylenevinylene) (OPVM-OH) complementarily functionalized with hydroxyl unit and polymerizable methacrylamide unit at the two termini. The resulting supramolecular complex [UPBI-Py (OPVM-OH)]1.0 upon polymerization by irradiation in the presence of photoinitiator formed well-defined supramolecular polymeric nanostructures. Self-assembly studies using fluorescence emission from thin film samples showed that subtle structural changes occurred on the OPV donor moiety following polymerization. The 1:1 supramolecular complex showed red-shifted aggregate emission from both OPV (∼500 nm) and PBI (∼640 nm) units, whereas the OPV aggregate emission was replaced by intense monomeric emission (∼430 nm) upon polymerizing the methacrylamide units on the OPVM-OH. The bulk structure was studied using wide-angle X-ray diffraction (WXRD). Complex formation resulted in distinct changes in the cell parameters of OPVM-OH. In contrast, a physical mixture of 1 mol each of OPVM-OH and UPBI-Py prepared by mixing the powdered solid samples together showed only a combination of reflections from both parent molecules. Thin film morphology of the 1:1 molecular complex as well as the supramolecular polymer complex showed uniform lamellar structures in the domain range <10 nm. The donor-acceptor supramolecular complex [UPBI-Py (OPVM-OH)]1.0 exhibited space charge limited current (SCLC) with a bulk mobility estimate of an order of magnitude higher accompanied by a higher photoconductivity yield compared to the pristine UPBI-Py. This is a very versatile method to obtain spatially defined organization of n and p-type semiconductor materials based on suitably functionalized donor and acceptor molecules resulting in improved photocurrent response using self-assembly.

  20. Nanostructured donor-acceptor self assembly with improved photoconductivity.

    PubMed

    Saibal, B; Ashar, A Z; Devi, R Nandini; Narayan, K S; Asha, S K

    2014-11-12

    Nanostructured supramolecular donor-acceptor assemblies were formed when an unsymmetrical N-substituted pyridine functionalized perylenebisimide (UPBI-Py) was complexed with oligo(p-phenylenevinylene) (OPVM-OH) complementarily functionalized with hydroxyl unit and polymerizable methacrylamide unit at the two termini. The resulting supramolecular complex [UPBI-Py (OPVM-OH)]1.0 upon polymerization by irradiation in the presence of photoinitiator formed well-defined supramolecular polymeric nanostructures. Self-assembly studies using fluorescence emission from thin film samples showed that subtle structural changes occurred on the OPV donor moiety following polymerization. The 1:1 supramolecular complex showed red-shifted aggregate emission from both OPV (∼500 nm) and PBI (∼640 nm) units, whereas the OPV aggregate emission was replaced by intense monomeric emission (∼430 nm) upon polymerizing the methacrylamide units on the OPVM-OH. The bulk structure was studied using wide-angle X-ray diffraction (WXRD). Complex formation resulted in distinct changes in the cell parameters of OPVM-OH. In contrast, a physical mixture of 1 mol each of OPVM-OH and UPBI-Py prepared by mixing the powdered solid samples together showed only a combination of reflections from both parent molecules. Thin film morphology of the 1:1 molecular complex as well as the supramolecular polymer complex showed uniform lamellar structures in the domain range <10 nm. The donor-acceptor supramolecular complex [UPBI-Py (OPVM-OH)]1.0 exhibited space charge limited current (SCLC) with a bulk mobility estimate of an order of magnitude higher accompanied by a higher photoconductivity yield compared to the pristine UPBI-Py. This is a very versatile method to obtain spatially defined organization of n and p-type semiconductor materials based on suitably functionalized donor and acceptor molecules resulting in improved photocurrent response using self-assembly. PMID:25283356

  1. Hot charge-transfer excitons set the time limit for charge separation at donor/acceptor interfaces in organic photovoltaics.

    PubMed

    Jailaubekov, Askat E; Willard, Adam P; Tritsch, John R; Chan, Wai-Lun; Sai, Na; Gearba, Raluca; Kaake, Loren G; Williams, Kenrick J; Leung, Kevin; Rossky, Peter J; Zhu, X-Y

    2013-01-01

    Photocurrent generation in organic photovoltaics (OPVs) relies on the dissociation of excitons into free electrons and holes at donor/acceptor heterointerfaces. The low dielectric constant of organic semiconductors leads to strong Coulomb interactions between electron-hole pairs that should in principle oppose the generation of free charges. The exact mechanism by which electrons and holes overcome this Coulomb trapping is still unsolved, but increasing evidence points to the critical role of hot charge-transfer (CT) excitons in assisting this process. Here we provide a real-time view of hot CT exciton formation and relaxation using femtosecond nonlinear optical spectroscopies and non-adiabatic mixed quantum mechanics/molecular mechanics simulations in the phthalocyanine-fullerene model OPV system. For initial excitation on phthalocyanine, hot CT excitons are formed in 10(-13) s, followed by relaxation to lower energies and shorter electron-hole distances on a 10(-12) s timescale. This hot CT exciton cooling process and collapse of charge separation sets the fundamental time limit for competitive charge separation channels that lead to efficient photocurrent generation.

  2. Liquid-crystalline semiconducting copolymers with intramolecular donor-acceptor building blocks for high-stability polymer transistors.

    PubMed

    Kim, Do Hwan; Lee, Bang-Lin; Moon, Hyunsik; Kang, Hee Min; Jeong, Eun Jeong; Park, Jeong-Il; Han, Kuk-Min; Lee, Sangyoon; Yoo, Byung Wook; Koo, Bon Won; Kim, Joo Young; Lee, Wi Hyoung; Cho, Kilwon; Becerril, Hector Alejandro; Bao, Zhenan

    2009-05-01

    The ability to control the molecular organization of electronically active liquid-crystalline polymer semiconductors on surfaces provides opportunities to develop easy-to-process yet highly ordered supramolecular systems and, in particular, to optimize their electrical and environmental reliability in applications in the field of large-area printed electronics and photovoltaics. Understanding the relationship between liquid-crystalline nanostructure and electrical stability on appropriate molecular surfaces is the key to enhancing the performance of organic field-effect transistors (OFETs) to a degree comparable to that of amorphous silicon (a-Si). Here, we report a novel donor-acceptor type liquid-crystalline semiconducting copolymer, poly(didodecylquaterthiophene-alt-didodecylbithiazole), which contains both electron-donating quaterthiophene and electron-accepting 5,5'-bithiazole units. This copolymer exhibits excellent electrical characteristics such as field-effect mobilities as high as 0.33 cm(2)/V.s and good bias-stress stability comparable to that of amorphous silicon (a-Si). Liquid-crystalline thin films with structural anisotropy form spontaneously through self-organization of individual polymer chains as a result of intermolecular interactions in the liquid-crystalline mesophase. These thin films adopt preferential well-ordered intermolecular pi-pi stacking parallel to the substrate surface. This bottom-up assembly of the liquid-crystalline semiconducting copolymer enables facile fabrication of highly ordered channel layers with remarkable electrical stability.

  3. Spin relaxation and donor-acceptor recombination of Se+ in 28-silicon

    NASA Astrophysics Data System (ADS)

    Lo Nardo, Roberto; Wolfowicz, Gary; Simmons, Stephanie; Tyryshkin, Alexei M.; Riemann, Helge; Abrosimov, Nikolai V.; Becker, Peter; Pohl, Hans-Joachim; Steger, Michael; Lyon, Stephen A.; Thewalt, Mike L. W.; Morton, John J. L.

    2015-10-01

    Selenium impurities in silicon are deep double donors and their optical and electronic properties have been recently investigated due to their application for infrared detection. However, a singly ionized selenium donor (Se+) possesses an electron spin which makes it a potential candidate as a silicon-based spin qubit, with significant potential advantages compared to the more commonly studied group V donors. Here we study the electron spin relaxation (T1) and coherence (T2) times of Se+ in isotopically purified 28-silicon, and find them to be up to two orders of magnitude longer than shallow group V donors at temperatures above ˜15 K . We further study the dynamics of donor-acceptor recombination between selenium and boron, demonstrating that it is possible to control the donor charge state through optical excitation of neutral Se0.

  4. Identification of photoluminescence bands in AlGaAs/InGaAs/GaAs PHEMT heterostructures with donor-acceptor-doped barriers

    SciTech Connect

    Gulyaev, D. V. Zhuravlev, K. S.; Bakarov, A. K.; Toropov, A. I.

    2015-02-15

    The photoluminescence of AlGaAs/InGaAs/GaAs pseudomorphic high-electron mobility transistor heterostructures with donor-acceptor-doped AlGaAs barriers is studied. It is found that the introduction of additional p{sup +}-doped AlGaAs layers into the design brings about the appearance of new bands in the photoluminescence spectra. These bands are identified as resulting from transitions (i) in donor-acceptor pairs in doped AlGaAs layers and (ii) between the conduction subband and acceptor levels in the undoped InGaAs quantum well.

  5. Alternative Donor--Acceptor Stacks from Crown Ethers and Naphthalene Diimide Derivatives: Rapid, Selective Formation from Solution and Solid State Grinding

    SciTech Connect

    Advanced Light Source; Liu, Yi; Klivansky, Liana; Cao, Dennis; Snauko, Marian; Teat, Simon J.; Struppe, Jochem O.; Koshkakaryan, Gayane

    2009-01-22

    Self assembling {pi}-conjugated molecules into ordered structures are of increasing interest in the field of organic electronics. One particular example is charge transfer complexes containing columnar alternative donor-acceptor (ADA) stacks, where neutral and ionic ground states can be readily tuned to modulate electrical, optical, and ferroelectrical properties. Aromatic-aromatic and charge transfer interactions have been the leading driving forces in assisting the self-assembly of ADA stacks. Various folding structures containing ADA stacks were assembled in solution with the aid of solvophobic or ion-binding interactions. Meanwhile, examples of solid ADA stacks, which are more appealing for practical use in devices, were obtained from cocrystalization of binary components or mesophase assembly of liquid crystals in bulk blends. Regardless of these examples, faster and more controllable approaches towards precise supramolecular order in the solid state are still highly desirable.

  6. Structural control of donor-acceptor mechanically interlocked molecules and supramolecular complexes

    NASA Astrophysics Data System (ADS)

    Friedman, Douglas Cary

    aided the structural analysis, are described. The final chapter describes how to control the secondary structure of donor-acceptor oligorotaxanes in which electron-poor tetracationic cyclophanes encircle electron-rich aromatic recognition sites linked by polyether chains. Design aspects, including built-in [pi···pi] stacking and [C--H···O] and [C--H···pi] interactions, are critical to ensure the discrete, extended secondary structures envisioned in the design and which are evidenced by comprehensive 1H NMR spectroscopic analyses.

  7. Proton Donor/acceptor Propensities of Ammonia: Rotational Studies of its Molecular Complexes with Organic Molecules

    NASA Astrophysics Data System (ADS)

    Giuliano, Barbara M.; Maris, Assimo; Melandri, Sonia; Favero, Laura B.; Evangelisti, Luca; Caminati, Walther

    2009-06-01

    We studied the rotational spectra of the adducts of ammonia with several organic molecules, namely tert-butanol, glycidol, ethyl alcohol, anisol and 1,4-difluorobenzene. The adducts with glycidol and ethanol have been observed for both conformers of the substrate molecule. Based on the rotational and ^{14}N quadrupole coupling constants of the various complexes, we found a considerably different behaviour of ammonia, with respect to water, in its proton donor/acceptor double role. In the interaction with the three alcohol molecules, NH_{3} acts as a proton acceptor and the OH groups as a proton donor. However, in the case of glycidol-NH_{3}, a secundary N-H\\cdotsO interaction occurrs between ammonia and the ether oxygen. This interaction generates a sizable V_{3} barrier to the internal rotation of the NH_{3} moiety, while NH_{3} undergoes a free rotation in tert-butanol-NH_{3} and in ethanol-NH_{3}. As to the anisole-NH_{3} and 1,4-difluorobenzene-NH_{3} complexes, the NH_{3} group explicits its double proton donor/acceptor role, although through two weak (C_{Me}-H\\cdotsN and N-H\\cdotsπ) H-bonds. There is, however, an important difference between the two complexes, because in the first one NH_{3} lies out of the aromatic plane, while in the second one it is in the plane of the aromatic ring. B. M. Giuliano, M. C. Castrovilli, A. Maris, S. Melandri, W. Caminati and E. A. Cohen, Chem.Phys.Lett., 2008, 463, 330 B. M. Giuliano, S. Melandri, A. Maris, L. B. Favero and W. Caminati, Angew.Chem.Int.Ed., 2009, 48, 1102

  8. A design strategy for intramolecular singlet fission mediated by charge-transfer states in donor-acceptor organic materials

    NASA Astrophysics Data System (ADS)

    Busby, Erik; Xia, Jianlong; Wu, Qin; Low, Jonathan Z.; Song, Rui; Miller, John R.; Zhu, X.-Y.; Campos, Luis M.; Sfeir, Matthew Y.

    2015-04-01

    The ability to advance our understanding of multiple exciton generation (MEG) in organic materials has been restricted by the limited number of materials capable of singlet fission. A particular challenge is the development of materials that undergo efficient intramolecular fission, such that local order and strong nearest-neighbour coupling is no longer a design constraint. Here we address these challenges by demonstrating that strong intrachain donor-acceptor interactions are a key design feature for organic materials capable of intramolecular singlet fission. By conjugating strong-acceptor and strong-donor building blocks, small molecules and polymers with charge-transfer states that mediate population transfer between singlet excitons and triplet excitons are synthesized. Using transient optical techniques, we show that triplet populations can be generated with yields up to 170%. These guidelines are widely applicable to similar families of polymers and small molecules, and can lead to the development of new fission-capable materials with tunable electronic structure, as well as a deeper fundamental understanding of MEG.

  9. Synthesis, Structure, and Optical Studies of Donor-Acceptor-Type Near-Infrared (NIR) Aza-Boron-Dipyrromethene (BODIPY) Dyes.

    PubMed

    Balsukuri, Naresh; Lone, Mohsin Y; Jha, Prakash C; Mori, Shigeki; Gupta, Iti

    2016-05-20

    Six donor-acceptor-type near-infrared (NIR) aza-boron-dipyrromethene (BODIPY) dyes and their corresponding aza-dipyrrins were designed and synthesized. The donor moieties at the 1,7-positions of the aza-BODIPY core were varied from naphthyl to N-phenylcarbazole to N-butylcarbazole. The 3,5-positions were also substituted with phenyl or thienyl groups in the aza-BODIPYs. Photophysical, electrochemical, and computational studies were carried out. The absorption and emission spectra of aza-BODIPYs were significantly redshifted (≈100 nm) relative to the parent tetraphenylaza-BODIPY. Fluorescence studies suggested effective energy transfer (up to 93 %) from donor groups to the aza-BODIPY core in all of the compounds under study. Time-dependent (TD)-DFT studies indicated effective electronic interactions between energy donor groups and aza-dipyrrin unit in all the aza-BODIPYs studied. The HOMO-LUMO gap (ΔE) calculated from cyclic voltammetry data was found to be lower for six aza-BODIPYs relative to their corresponding aza-dipyrrins. PMID:26918806

  10. News from the Periodic Table: An Introduction to "Periodicity Symbols, Tables, and Models for Higher-Order Valency and Donor-Acceptor Kinships"

    ERIC Educational Resources Information Center

    Bent, Henry A.; Weinhold, Frank

    2007-01-01

    The study presents and explains the various periodicity symbols, tables and models for the higher-order valency and donor-acceptor kinships used in chemistry. The described alternative tables are expected to improve the pedagogical consistency of the chemical periodicity patterns with better electronic behavior.

  11. Pyrimidone-based series of glucokinase activators with alternative donor-acceptor motif.

    PubMed

    Filipski, Kevin J; Guzman-Perez, Angel; Bian, Jianwei; Perreault, Christian; Aspnes, Gary E; Didiuk, Mary T; Dow, Robert L; Hank, Richard F; Jones, Christopher S; Maguire, Robert J; Tu, Meihua; Zeng, Dongxiang; Liu, Shenping; Knafels, John D; Litchfield, John; Atkinson, Karen; Derksen, David R; Bourbonais, Francis; Gajiwala, Ketan S; Hickey, Michael; Johnson, Theodore O; Humphries, Paul S; Pfefferkorn, Jeffrey A

    2013-08-15

    Glucokinase activators are a class of experimental agents under investigation as a therapy for Type 2 diabetes mellitus. An X-ray crystal structure of a modestly potent agent revealed the potential to substitute the common heterocyclic amide donor-acceptor motif for a pyridone moiety. We have successfully demonstrated that both pyridone and pyrimidone heterocycles can be used as a potent donor-acceptor substituent. Several sub-micromolar analogs that possess the desired partial activator profile were synthesized and characterized. Unfortunately, the most potent activators suffered from sub-optimal pharmacokinetic properties. Nonetheless, these donor-acceptor motifs may find utility in other glucokinase activator series or beyond.

  12. Synthesis, photophysical properties of triazolyl-donor/acceptor chromophores decorated unnatural amino acids: Incorporation of a pair into Leu-enkephalin peptide and application of triazolylperylene amino acid in sensing BSA.

    PubMed

    Bag, Subhendu Sekhar; Jana, Subhashis; Pradhan, Manoj Kumar

    2016-08-15

    The research in the field of design and synthesis of unnatural amino acids is growing at a fast space for the increasing demand of proteins of potential therapeutics and many other diversified novel functional applications. Thus, we report herein the design and synthesis of microenvironment sensitive fluorescent triazolyl unnatural amino acids (UNAA) decorated with donor and/or acceptor aromatic chromophores via click chemistry. The synthesized fluorescent amino acids show interesting solvatochromic characteristic and/or intramolecular charge transfer (ICT) feature as is revealed from the UV-visible, fluorescence photophysical properties and DFT/TDDFT calculation. HOMO-LUMO distribution shows that the emissive states of some of the amino acids are characterized with more significant electron redistribution between the triazolyl moiety and the aromatic chromophores linked to it leading to modulated emission property. A pair of donor-acceptor amino acid shows interesting photophysical interaction property indicating a FRET quenching event. Furthermore, one of the amino acid, triazolyl-perylene amino acid, has been exploited for studying interaction with BSA and found that it is able to sense BSA with an enhancement of fluorescence intensity. Finally, we incorporated a pair of donor/acceptor amino acids into a Leu-enkephalin analogue pentapeptide which was found to adopt predominantly type II β-turn conformation. We envisage that our investigation is of importance for the development of new fluorescent donor-acceptor unnatural amino acids a pair of which can be exploited for generating fluorescent peptidomimetic probe of interesting photophysical property for applications in studying peptide-protein interaction. PMID:27372839

  13. Synthesis, photophysical properties of triazolyl-donor/acceptor chromophores decorated unnatural amino acids: Incorporation of a pair into Leu-enkephalin peptide and application of triazolylperylene amino acid in sensing BSA.

    PubMed

    Bag, Subhendu Sekhar; Jana, Subhashis; Pradhan, Manoj Kumar

    2016-08-15

    The research in the field of design and synthesis of unnatural amino acids is growing at a fast space for the increasing demand of proteins of potential therapeutics and many other diversified novel functional applications. Thus, we report herein the design and synthesis of microenvironment sensitive fluorescent triazolyl unnatural amino acids (UNAA) decorated with donor and/or acceptor aromatic chromophores via click chemistry. The synthesized fluorescent amino acids show interesting solvatochromic characteristic and/or intramolecular charge transfer (ICT) feature as is revealed from the UV-visible, fluorescence photophysical properties and DFT/TDDFT calculation. HOMO-LUMO distribution shows that the emissive states of some of the amino acids are characterized with more significant electron redistribution between the triazolyl moiety and the aromatic chromophores linked to it leading to modulated emission property. A pair of donor-acceptor amino acid shows interesting photophysical interaction property indicating a FRET quenching event. Furthermore, one of the amino acid, triazolyl-perylene amino acid, has been exploited for studying interaction with BSA and found that it is able to sense BSA with an enhancement of fluorescence intensity. Finally, we incorporated a pair of donor/acceptor amino acids into a Leu-enkephalin analogue pentapeptide which was found to adopt predominantly type II β-turn conformation. We envisage that our investigation is of importance for the development of new fluorescent donor-acceptor unnatural amino acids a pair of which can be exploited for generating fluorescent peptidomimetic probe of interesting photophysical property for applications in studying peptide-protein interaction.

  14. Dinitrogen extrusion from enoldiazo compounds under thermal conditions: synthesis of donor-acceptor cyclopropenes.

    PubMed

    Deng, Yongming; Jing, Changcheng; Doyle, Michael P

    2015-08-21

    Donor-acceptor cyclopropenes are formed quantitatively or in high yield from enoldiazoacetates and enoldiazoacetamides under moderate thermal conditions. They are more versatile than their corresponding enoldiazocarbonyl compounds as carbene precursors.

  15. Experiments probing the viability of donor-acceptor norbornenes for (5 + 2)-annulation.

    PubMed

    Walker, Morgan M; Goodman, C Guy; Johnson, Jeffrey S

    2014-10-01

    This Note details experiments that probe the mechanism by which donor-acceptor norbornene systems epimerize. A number of mechanistic studies indicate that epimerization in these systems occurs via a Lewis acid catalyzed retro-Diels-Alder/Diels-Alder sequence, rather than bond rotation in an intimate ion pair. These results suggest that, under the reaction conditions examined, the ring strain present in norbornene is inadequate to induce zwitterion formation analogous to that observed with donor-acceptor cyclopropanes.

  16. Effects of size restriction on donor-acceptor recombination in AgBr

    NASA Astrophysics Data System (ADS)

    Rodney, Paul J.; Marchetti, Alfred P.; Fauchet, Philippe M.

    2000-08-01

    The behavior of donor-acceptor (DA) recombination luminescence in quantum confined AgBr has been investigated. The DA luminescence decay, after pulsed excitation, became longer lived as the nanocluster size decreased. This result differs from theoretical expectations and from observations with AgI nanoclusters. The DA lifetime increase with decreasing size is due to an increase in yield and lifetime of ``free'' excitons that slowly dissociate into ``close'' donor-acceptor pairs, giving rise to an ``exciton dribbling'' effect.

  17. Interfacial Donor-Acceptor Engineering of Nanofiber Materials To Achieve Photoconductivity and Applications.

    PubMed

    Zang, Ling

    2015-10-20

    Self-assembly of π-conjugate molecules often leads to formation of well-defined nanofibril structures dominated by the columnar π-π stacking between the molecular planes. These nanofibril materials have drawn increasing interest in the research frontiers of nanomaterials and nanotechnology, as the nanofibers demonstrate one-dimensionally enhanced exciton and charge diffusion along the long axis, and present great potential for varying optoelectronic applications, such as sensors, optics, photovoltaics, and photocatalysis. However, poor electrical conductivity remains a technical drawback for these nanomaterials. To address this problem, we have developed a series of nanofiber structures modified with different donor-acceptor (D-A) interfaces that are tunable for maximizing the photoinduced charge separation, thus leading to increase in the electrical conductivity. The D-A interface can be constructed with covalent linker or noncovalent interaction (e.g., hydrophobic interdigitation between alkyl chains). The noncovalent method is generally more flexible for molecular design and solution processing, making it more adaptable to be applied to other fibril nanomaterials such as carbon nanotubes. In this Account, we will discuss our recent discoveries in these research fields, aiming to provide deep insight into the enabling photoconductivity of nanofibril materials, and the dependence on interface structure. The photoconductivity generated with the nanofibril material is proportional to the charge carriers density, which in turn is determined by the kinetics balance of the three competitive charge transfer processes: (1) the photoinduced electron transfer from D to A (also referred to as exciton dissociation), generating majority charge carrier located in the nanofiber; (2) the back electron transfer; and (3) the charge delocalization along the nanofiber mediated by the π-π stacking interaction. The relative rates of these charge transfer processes can be tuned by

  18. Tuning the Rainbow: Systematic Modulation of Donor-Acceptor Systems through Donor Substituents and Solvent.

    PubMed

    Larsen, Christopher B; van der Salm, Holly; Shillito, Georgina E; Lucas, Nigel T; Gordon, Keith C

    2016-09-01

    A series of donor-acceptor compounds is reported in which the energy of the triarylamine donor is systematically tuned through para substitution with electron-donating methoxy and electron-withdrawing cyano groups. The acceptor units investigated are benzothiadiazole (btd), dipyridophenazine (dppz), and its [ReCl(CO)3(dppz)] complex. The effect of modulating donor energy on the electronic and photophysical properties is investigated using (1)H NMR spectroscopy, DFT calculations, electrochemistry, electronic absorption and emission spectroscopies, ground state and resonance Raman spectroscopy, and transient absorption spectroscopy. Qualitative correlations between the donor energy and the properties of interest are obtained using Hammett σ(+) constants. Methoxy and cyano groups are shown to destabilize and stabilize, respectively, the frontier molecular orbitals, with the HOMO affected more significantly than the LUMO, narrowing the HOMO-LUMO band gap as the substituent becomes more electron-donating-observable as a bathochromic shift in low-energy charge-transfer absorption bands. Charge-transfer emission bands are also dependent on the electron-donating/withdrawing nature of the substituent, and in combination with the highly solvatochromic nature of charge-transfer states, emission can be tuned to span the entire visible region. PMID:27500590

  19. Combined impact of entropy and carrier delocalization on charge transfer exciton dissociation at the donor-acceptor interface

    NASA Astrophysics Data System (ADS)

    Ono, Shota; Ohno, Kaoru

    2016-08-01

    Several models of the charge transfer exciton (CTE) have been proposed to explain its dissociation at the donor-acceptor (DA) interface. However, the underlying physics is still under debate. Here, we derive a temperature (T ) dependent tight-binding model for an electron-hole pair at the DA interface. The main finding is the existence of the localization-delocalization transition at a critical T , which can explain the CTE dissociation. The present study highlights the combined effect of entropy (finite T ) and carrier delocalization in the CTE dissociation.

  20. Cycloparaphenylene-based ionic donor-acceptor supramolecule: isolation and characterization of Li⁺@C60⊂[10]CPP.

    PubMed

    Ueno, Hiroshi; Nishihara, Taishi; Segawa, Yasutomo; Itami, Kenichiro

    2015-03-16

    The first cycloparaphenylene (CPP)-based ionic donor-acceptor supramolecule Li(+)@C60⊂[10]CPP⋅X(-) has been synthesized. X-ray crystallography not only confirmed the molecular structure of Li(+)@C60⊂[10]CPP⋅X(-) but also uncovered the formation of a unique ionic crystal. The strong charge-transfer interaction between [10]CPP and Li(+)@C60, which was confirmed by electrochemical measurement and spectroscopic analyses, caused significant delocalization of the positive charge across the entire complex. PMID:25693784

  1. Donor-acceptor bonding in novel low-coordinated compounds of boron and group-14 atoms C-Sn.

    PubMed

    Frenking, Gernot; Hermann, Markus; Andrada, Diego M; Holzmann, Nicole

    2016-02-21

    A summary of theoretical and experimental work in the area of low-coordinated compounds of boron and group-14 atoms C-Sn in the last decade is presented. The focus of the account lies on molecules EL2, E2L2 and E3L3, which possess dative bonds between one, two or three atoms E and σ-donor ligands L that stabilize the atoms E through L→E donor-acceptor interactions. The interplay between theory and experiment provides detailed insight into the bonding situation of the molecules, which serves as guideline for the synthesis of molecules that possess unusual bonding motifs.

  2. High Resolution Stark Spectroscopy of Model Donor-Acceptor Aminobenzonitriles in the Gas Phase.

    NASA Astrophysics Data System (ADS)

    Fleisher, Adam J.; Clements, Casey L.; Bird, Ryan G.; Pratt, David W.; Alvarez-Valtierra, Leonardo

    2011-06-01

    Electronic communication between donor-acceptor systems is prevalent in many chemical processes. Unfortunately, an accurate description of the changes in molecular geometry responsible for intramolecular charge transfer (ICT) is difficult to ascertain. Reported here are the S0, LA, and LB electronic state structures and dipole moments of two model ICT systems, 4-(1H-pyrrol-l-yl)benzonitrile (PBN) and 4-(1-pyrrolidinyl)benzonitrile (PDBN), as measured by rotationally resolved electronic spectroscopy. As was observed for phenylpyrrole, the unsaturted rings of PBN become collectively more planar following excitation with UV light, in support of the planar ICT model. However, in PDBN the twist/inversion angle between rings is nearly zero in both the ground and excited electronic states. The unperturbed dipole moments measured here, taken in conjunction with available solvatochromism data, provide an estimate for the polarization, dispersion, and charge transfer contributions to solvent-mediated excited state stabilization. J.A. Thomas, J.W. Young, A.J. Fleisher, L. Álvarez-Valtierra, and D.W. Pratt, J. Phys. Chem. Lett. 1, 2017 (2010).

  3. Designing novel copolymers of donor-acceptor polymers using an artificial intelligence method

    NASA Astrophysics Data System (ADS)

    Kapoor, Vinita; Bakhshi, A. K.

    2013-08-01

    Using the ab initio Hartree-Fock crystal orbital results of three donor-acceptor polymers, PFUCO ([A]x), PSIFCO ([B]x) and PSIFCH ([C]x), the electronic properties of their novel quasi-one-dimensional copolymers (AmBn)x and (AmCn)x were investigated using an artificial intelligence technique, the genetic algorithm, in combination with negative factor counting and inverse iteration method. The repeat units in PFUCO consist of bifuran bridged by electron accepting groups Y (>Cdbnd O); while in PSIFCO and PSIFCH, the repeat units consist of bicyclopentadifluorosilole bridged by electron accepting groups Y (Y is >Cdbnd O in PSIFCO, and >Cdbnd CH2 in PSIFCH). The trends in the electronic properties of the copolymers (AmBn)x and (AmCn)x as a function of block sizes m and n, and arrangement of units (periodic and random) in the copolymer chain are also discussed. The results obtained are important guidelines for molecular designing of copolymers with tailor-made conduction properties.

  4. The donor-acceptor approach allows a black-to-transmissive switching polymeric electrochrome

    NASA Astrophysics Data System (ADS)

    Beaujuge, P. M.; Ellinger, S.; Reynolds, J. R.

    2008-10-01

    In the context of the fast-growing demand for innovative high-performance display technologies, the perspective of manufacturing low-cost functional materials that can be easily processed over large areas or finely printed into individual pixels, while being mechanically deformable, has motivated the development of novel electronically active organic components fulfilling the requirements for flexible displays and portable applications. Among all technologies relying on a low-power stimulated optical change, non-emissive organic electrochromic devices (ECDs) offer the advantage of being operational under a wide range of viewing angles and lighting conditions spanning direct sunlight as desired for various applications including signage, information tags and electronic paper. Combining mechanical flexibility, high contrast ratios and fast response times, along with colour tunability through structural control, polymeric electrochromes constitute the most attractive organic electronics for tomorrow's reflective/transmissive ECDs and displays. Although red, blue and most recently green electrochromic polymers (ECPs) required for additive primary colour space were investigated, attempts to make saturated black ECPs have not been reported, probably owing to the complexity of designing materials absorbing effectively over the whole visible spectrum. Here, we report on the use of the donor-acceptor approach to make the first neutral-state black polymeric electrochrome. Processable black-to-transmissive ECPs promise to affect the development of both reflective and transmissive ECDs by providing lower fabrication and processing costs through printing, spraying and coating methods, along with good scalability when compared with their traditional inorganic counterparts.

  5. 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%.

  6. Controlling charge separation and recombination by chemical design in donor-acceptor dyads.

    PubMed

    Liu, Li; Eisenbrandt, Pierre; Roland, Thomas; Polkehn, Matthias; Schwartz, Pierre-Olivier; Bruchlos, Kirsten; Omiecienski, Beatrice; Ludwigs, Sabine; Leclerc, Nicolas; Zaborova, Elena; Léonard, Jérémie; Méry, Stéphane; Burghardt, Irene; Haacke, Stefan

    2016-07-21

    Conjugated donor-acceptor block co-oligomers that self-organize into D-A mesomorphic arrays have raised increasing interest due to their potential applications in organic solar cells. We report here a combined experimental and computational study of charge transfer (CT) state formation and recombination in isolated donor-spacer-acceptor oligomers based on bisthiophene-fluorene (D) and perylene diimide (A), which have recently shown to self-organize to give a mesomorphic lamellar structure at room temperature. Using femtosecond transient absorption spectroscopy and Time-Dependent Density Functional Theory in combination with the Marcus-Jortner formalism, the observed increase of the CT lifetimes is rationalized in terms of a reduced electronic coupling between D and A brought about by the chemical design of the donor moiety. A marked dependence of the CT lifetime on solvent polarity is observed, underscoring the importance of electrostatic effects and those of the environment at large. The present investigation therefore calls for a more comprehensive design approach including the effects of molecular packing. PMID:27341086

  7. Design of Bicontinuous Donor/Acceptor Morphologies for Use as Organic Solar Cell Active Layers

    NASA Astrophysics Data System (ADS)

    Kipp, Dylan; Mok, Jorge; Verduzco, Rafael; Ganesan, Venkat

    Two of the primary challenges limiting the marketability of organic solar cells are i) the smaller device efficiency of the organic solar cell relative to the conventional silicon-based solar cell and ii) the long term thermal instability of the device active layer. The achievement of equilibrium donor/acceptor morphologies with the characteristics believed to yield high device performance characteristics could address each of these two challenges. In this work, we present the results of a combined simulations and experiments-based approach to investigate if a conjugated BCP additive can be used to control the self-assembled morphologies taken on by conjugated polymer/PCBM mixtures. First, we use single chain in mean field Monte Carlo simulations to identify regions within the conjugated polymer/PCBM composition space in which addition of copolymers can lead to bicontinuous equilibrium morphologies with high interfacial areas and nanoscale dimensions. Second, we conduct experiments as directed by the simulations to achieve such morphologies in the PTB7 + PTB7- b-PNDI + PCBM model blend. We characterize the results of our experiments via a combination of transmission electron microscopy and X-ray scattering techniques and demonstrate that the morphologies from experiments agree with those predicted in simulations. Accordingly, these results indicate that the approach utilized represents a promising approach to intelligently design the morphologies taken on by organic solar cell active layers.

  8. Ab-initio study of donor-acceptor codoping for n-type CuO

    SciTech Connect

    Peng, Yuan; Wang, Junling; Zheng, Jianwei; Wu, Ping

    2014-10-28

    Single n-type dopant in CuO has either a deep donor level or limited solubility, inefficient in generating free electrons. We have performed ab-initio study of the donor-acceptor codoping to obtain n-type CuO. Our results show that N codoping can slightly improve the donor level of Zr and In by forming shallower n-type complexes (Zr{sub Cu}-N{sub O} and 2In{sub Cu}-N{sub O}), but their formation energies are too high to be realized in experiments. However, Li codoping with Al and Ga is found to be relatively easy to achieve. 2Al{sub Cu}-Li{sub Cu} and 2Ga{sub Cu}-Li{sub Cu} have shallower donor levels than single Al and Ga by 0.14 eV and 0.08 eV, respectively, and their formation energies are reasonably low to act as efficient codopants. Moreover, Li codoping with both Al and Ga produce an empty impurity band just below the host conduction band minimum, which may reduce the donor ionization energy at high codoping concentrations.

  9. Dynamics of exciton dissociation in donor-acceptor polymer heterojunctions.

    PubMed

    Sun, Zhen; Stafström, Sven

    2013-04-28

    Exciton dissociation in a donor-accepter polymer heterojunction has been simulated using a nonadiabatic molecular dynamics approach, which allows for the coupled evolution of the nuclear degrees of freedom and the electronic degrees of freedom described by multiconfigurational electronic wavefunctions. The simulations reveal important details of the charge separation process: the exciton in the donor polymer first dissociates into a "hot" charge transfer state, which is best described as a polaron pair. The polaron pair can be separated into free polaron charge carriers if a sufficiently strong external electric field is applied. We have also studied the effects of inter-chain interaction, temperature, and the external electric field strength. Increasing inter-chain interactions makes it easier for the exciton to dissociate into a polaron pair state, but more difficult for the polaron pair to dissociate into free charge carriers. Higher temperature and higher electric field strength both favor exciton dissociation as well as the formation of free charge carriers. PMID:23635169

  10. Benzo[c][1,2,5]thiadiazole Donor-Acceptor Dyes: A Synthetic, Spectroscopic, and Computational Study.

    PubMed

    Barnsley, Jonathan E; Shillito, Georgina E; Larsen, Christopher B; van der Salm, Holly; Wang, Lei E; Lucas, Nigel T; Gordon, Keith C

    2016-03-24

    The synthesis, optical characterization and computational modeling of seven benzo[c][1,2,5]thiadiazole (BTD) donor-acceptor dyes are reported. These dyes have been studied using electrochemical analysis, electronic absorption, emission, and Raman and resonance Raman spectroscopies coupled with various density functional theoretical approaches. Crystal structure geometries on a number of these compounds are also reported. The optical spectra are dominated by low energy charge-transfer states; this may be modulated by the coupling between donor and acceptor through variation in donor energy, variation of the donor-acceptor torsion angle, and incorporation of an insulating bridge. These modifications result in a perturbation of the excitation energy for this charge-transfer transition of up to ∼2000 cm(-1). Emission spectra exhibit significant solvatochromisim, with Lippert-Mataga analysis yielding Δμ between 8 and 33 D. Predicted λmax, ε, and Raman cross sections calculated by M06L, B3LYP, PBE0, M06, CAM-B3LYP, and ωB97XD DFT functionals were compared to experimental results and analyzed using multivariate analysis, which shows that hybrid functionals with 20-27% HF best predict ground state absorption, while long-range corrected functionals best predict molecular polarizabilities. PMID:26918584

  11. High-resolution noncontact AFM and Kelvin probe force microscopy investigations of self-assembled photovoltaic donor-acceptor dyads.

    PubMed

    Grévin, Benjamin; Schwartz, Pierre-Olivier; Biniek, Laure; Brinkmann, Martin; Leclerc, Nicolas; Zaborova, Elena; Méry, Stéphane

    2016-01-01

    Self-assembled donor-acceptor dyads are used as model nanostructured heterojunctions for local investigations by noncontact atomic force microscopy (nc-AFM) and Kelvin probe force microscopy (KPFM). With the aim to probe the photo-induced charge carrier generation, thin films deposited on transparent indium tin oxide substrates are investigated in dark conditions and upon illumination. The topographic and contact potential difference (CPD) images taken under dark conditions are analysed in view of the results of complementary transmission electron microscopy (TEM) experiments. After in situ annealing, it is shown that the dyads with longer donor blocks essentially lead to standing acceptor-donor lamellae, where the acceptor and donor groups are π-stacked in an edge-on configuration. The existence of strong CPD and surface photo-voltage (SPV) contrasts shows that structural variations occur within the bulk of the edge-on stacks. SPV images with a very high lateral resolution are achieved, which allows for the resolution of local photo-charging contrasts at the scale of single edge-on lamella. This work paves the way for local investigations of the optoelectronic properties of donor-acceptor supramolecular architectures down to the elementary building block level. PMID:27335768

  12. A compact planar low-energy-gap molecule with a donor-acceptor-donor nature based on a bimetal dithiolene complex.

    PubMed

    Hayashi, Mikihiro; Otsubo, Kazuya; Kato, Tatsuhisa; Sugimoto, Kunihisa; Fujiwara, Akihiko; Kitagawa, Hiroshi

    2015-11-11

    We present the first report of a compact, planar and low-energy-gap molecule based on a π-conjugated bimetal system comprising a tetrathiooxalate (tto) skeleton. The observed low HOMO-LUMO energy gap (1.19 eV) is attributed to its donor-acceptor-donor (D-A-D) nature because the skeleton acts as an electron acceptor as well as a tiny and noninnocent bridging moiety.

  13. Digital memory versatility of fully π-conjugated donor-acceptor hybrid polymers.

    PubMed

    Ko, Yong-Gi; Kim, Dong Min; Kim, Kyungtae; Jung, Sungmin; Wi, Dongwoo; Michinobu, Tsuyoshi; Ree, Moonhor

    2014-06-11

    The fully π-conjugated donor-acceptor hybrid polymers Fl-TPA, Fl-TPA-TCNE, and Fl-TPA-TCNQ, which are composed of fluorene (Fl), triphenylamine (TPA), dimethylphenylamine, alkyne, alkyne-tetracyanoethylene (TCNE) adduct, and alkyne-7,7,8,8-tetracyanoquinodimethane (TCNQ) adduct, were synthesized. These polymers are completely amorphous in the solid film state and thermally stable up to 291-409 °C. Their molecular orbital levels and band gaps vary with their compositions. The TCNE and TCNQ units, despite their electron-acceptor characteristics, were found to enhance the π-conjugation lengths of Fl-TPA-TCNE and Fl-TPA-TCNQ (i.e., to produce red shifts in their absorption spectra and significant reductions in their band gaps). These changes are reflected in the electrical digital memory behavior of the polymers. Moreover, the TCNE and TCNQ units were found to diversify the digital memory modes and to widen the active polymer layer thickness window. In devices with aluminum top and bottom electrodes, the Fl-TPA polymer exhibits stable unipolar permanent memory behavior with high reliability. The Fl-TPA-TCNE and Fl-TPA-TCNQ devices exhibit stable unipolar permanent memory behavior as well as dynamic random access memory behavior with excellent reliability. These polymer devices were found to operate by either hole injection or hole injection along with electron injection, depending on the polymer composition. Overall, this study demonstrated that the incorporation of π-conjugated cyano moieties, which control both the π-conjugation length and electron-accepting power, is a sound approach for the design and synthesis of high-performance digital memory polymers. The TCNE and TCNQ polymers synthesized in this study are highly suitable active materials for the low-cost mass production of high-performance, polarity-free, programmable, volatile, and permanent memory devices that can be operated with very low power consumption, high ON/OFF current ratios, and high

  14. Syntheses, electrochemistry, and photodynamics of ferrocene-azadipyrromethane donor--acceptor dyads and triads.

    PubMed

    Amin, Anu N; El-Khouly, Mohamed E; Subbaiyan, Navaneetha K; Zandler, Melvin E; Supur, Mustafa; Fukuzumi, Shunichi; D'Souza, Francis

    2011-09-01

    A near-IR-emitting sensitizer, boron-chelated tetraarylazadipyrromethane, has been utilized as an electron acceptor to synthesize a series of dyads and triads linked with a well-known electron donor, ferrocene. The structural integrity of the newly synthesized dyads and triads was established by spectroscopic, electrochemical, and computational methods. The DFT calculations revealed a 'molecular clip'-type structure for the triads wherein the donor and acceptor entities were separated by about 14 Å. Differential pulse voltammetry combined with spectroelectrochemical studies have revealed the redox states and estimated the energies of the charge-separated states. Free-energy calculations revealed the charge separation from the covalently linked ferrocene to the singlet excited ADP to yield Fc(+)-ADP(•-) to be energetically favorable. Consequently, the steady-state emission studies revealed quantitative quenching of the ADP fluorescence in all of the investigated dyads and triads. Femtosecond laser flash photolysis studies provided concrete evidence for the occurrence of photoinduced electron transfer in these donor-acceptor systems by providing spectral proof for formation of ADP radical anion (ADP(•-)) which exhibits a diagnostic absorption band in the near-IR region. The kinetics of charge separation and charge recombination measured by monitoring the rise and decay of the ADP(•-) band revealed ultrafast charge separation in these molecular systems. The charge-separation performance of the triads with two ferrocenes and a fluorophenyl-modified ADP macrocycle was found to be superior. Nanosecond transient absorption studies revealed the charge-recombination process to populate the triplet ADP as well as the ground state. PMID:21793546

  15. First-principles description of charge transfer in donor-acceptor compounds from self-consistent many-body perturbation theory

    NASA Astrophysics Data System (ADS)

    Caruso, Fabio; Atalla, Viktor; Ren, Xinguo; Rubio, Angel; Scheffler, Matthias; Rinke, Patrick

    2014-08-01

    We investigate charge transfer in prototypical molecular donor-acceptor compounds using hybrid density functional theory (DFT) and the GW approximation at the perturbative level (G0W0) and at full self-consistency (sc-GW). For the systems considered here, no charge transfer should be expected at large intermolecular separation according to photoemission experiments and accurate quantum-chemistry calculations. The capability of hybrid exchange-correlation functionals of reproducing this feature depends critically on the fraction of exact exchange α, as for small values of α spurious fractional charge transfer is observed between the donor and the acceptor. G0W0 based on hybrid DFT yields the correct alignment of the frontier orbitals for all values of α. However, G0W0 has no capacity to alter the ground-state properties of the system because of its perturbative nature. The electron density in donor-acceptor compounds thus remains incorrect for small α values. In sc-GW, where the Green's function is obtained from the iterative solution of the Dyson equation, the electron density is updated and reflects the correct description of the level alignment at the GW level, demonstrating the importance of self-consistent many-body approaches for the description of ground- and excited-state properties in donor-acceptor systems.

  16. Dominant effects of first monolayer energetics at donor/acceptor interfaces on organic photovoltaics.

    PubMed

    Izawa, Seiichiro; Nakano, Kyohei; Suzuki, Kaori; Hashimoto, Kazuhito; Tajima, Keisuke

    2015-05-20

    Energy levels of the first monolayer are manipulated at donor/acceptor interfaces in planar heterojunction organic photovoltaics by using molecular self-organization. A "cascade" energy landscape allows thermal-activation-free charge generation by photoirradiation, destabilizes the energy of the interfacial charge-transfer state, and suppresses bimolecular charge recombination, resulting in a higher open-circuit voltage and fill factor.

  17. Bonding analysis of the donor-acceptor sandwiches CpE-MCp (E = B, Al, Ga; M = Li, Na, K; Cp = η⁵-C₅H₅).

    PubMed

    Huo, Suhong; Meng, Decheng; Zhang, Xiayan; Meng, Lingpeng; Li, Xiaoyan

    2014-10-01

    The nature of E-M bonds in CpE-MCp (E = B, Al, Ga; M = Li, Na, K; Cp = η (5)-C5H5) donor-acceptor sandwiches was studied using the atoms in molecules (AIM) theory, electron localization function (ELF), energy decomposition analysis (EDA), and natural bond orbital analysis (NBO) methods. Both topological and orbital analysis show that the E atom determines the bond strength of the E-M bonds, while the M atom has little influence on it. E-M bond strength decreases in the order E = B, Al, and Ga. The EDA analysis shows that the electrostatic character decreases following the sequence E = B > Al > Ga. Not only the s orbital, but also the p orbital of the E/M atom participates in formation of the E-M bond. The interactions of E and M with Cp are different. The M-Cp interaction is purely electrostatic while the E-Cp interaction has a partly covalent character.

  18. Highly Segregated Lamello-Columnar Mesophase Organizations and Fast Charge Carrier Mobility in New Discotic Donor-Acceptor Triads.

    PubMed

    Zhao, Ke-Qing; An, Ling-Ling; Zhang, Xiao-Bo; Yu, Wen-Hao; Hu, Ping; Wang, Bi-Qin; Xu, Jing; Zeng, Qing-Dao; Monobe, Hirosato; Shimizu, Yo; Heinrich, Benoît; Donnio, Bertrand

    2015-07-13

    Four new donor-acceptor triads (D-A-D) based on discotic and arylene mesogens have been synthesized by using Sonogashira coupling and cyclization reactions. This family of triads consists of two side-on pending triphenylene mesogens, acting as the electron-donating groups (D), laterally connected through short lipophilic spacers to a central perylenediimide (PI), benzo[ghi]perylenediimide (BI), or coronenediimide (CI) molecular unit, respectively, playing the role of the electron acceptor (A). All D-A-D triads self-organize to form a lamello-columnar oblique mesophase, with a highly segregated donor-acceptor (D-A) heterojunction organization, consequent to efficient molecular self-sorting. The structure consists in the regular alternation of two disrupted rows of triphenylene columns and a continuous row of diimine species. High-resolution STM images demonstrate that PI-TP2 forms stable 2D self-assembly nanostructures with some various degrees of regularity, whereas the other triads do not self-organize into ordered architectures. The electron-transport mobility of CI-TP2, measured by time-of-flight at 200 °C in the mesophase, is one order of magnitude higher than the hole mobility. By means of this specific molecular designing idea, we realized and demonstrated for the first time the so-called p-n heterojunction at the molecular level in which the electron-rich triphenylene columns act as the hole transient pathways, and the coronenediimide stacks form the electron-transport channels. PMID:26095600

  19. Exciton dissociation at organic small molecule donor-acceptor interfaces (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Robey, Steven W.

    2015-08-01

    Exciton dissociation at organic semiconductor donor-acceptor (D-A) heterojunctions is critical for the performance of organic photovoltaic (OPV) structures. Interfacial charge separation and recombination processes control device efficiency. We have investigated these fundamental interfacial issues using time-resolved two-photon photoemission (TR-2PPE), coupled with the formation of well-controlled D-A structures by organic molecular beam epitaxy. The interfacial electronic and molecular structure of these model interfaces was well-characterized using scanning tunneling microscopy and ultraviolet photoemission. Exciton dissociation dynamics were investigated by using a sub-picosecond pump pulse to create Pc π-->π* transitions, producing a population of singlet (S1) Pc excitons. The subsequent decay dynamics of this population was monitored via photoemission with a time-delayed UV pulse. For CuPcC60 interfaces, S1 exciton population decay in the interfacial CuPc layer was much faster than decay in the bulk due to interfacial charge separation. The rate constant for exciton dissociation was found to be ≍ 7 x 10 12 sec-1 (≍ 140 fs). Excitons that lose energy via intersystem crossing (ISC) to triplet levels dissociate approximately 500 to 1000 times slower. The dependence of exciton dissociation on separation was also studied. Exciton dissociation falls of rapidly with distance from the interface. Dissociation from the 2nd, and subsequent, layers of H2Pc is reduced by at least a factor of 10 from that in the interfacial layer. Finally, investigations of the relative efficiency for interfacial exciton dissociation by alternative acceptors based on perylene cores, (perylene tetracarboxylic dianhydride, or PTCDA) compared to fullerene-based acceptors such as C60 will also be discussed.

  20. Time-dependent transition density matrix for visualizing charge-transfer excitations in photoexcited organic donor-acceptor systems

    NASA Astrophysics Data System (ADS)

    Li, Yonghui; Ullrich, Carsten

    2013-03-01

    The time-dependent transition density matrix (TDM) is a useful tool to visualize and interpret the induced charges and electron-hole coherences of excitonic processes in large molecules. Combined with time-dependent density functional theory on a real-space grid (as implemented in the octopus code), the TDM is a computationally viable visualization tool for optical excitation processes in molecules. It provides real-time maps of particles and holes which gives information on excitations, in particular those that have charge-transfer character, that cannot be obtained from the density alone. Some illustration of the TDM and comparison with standard density difference plots will be shown for photoexcited organic donor-acceptor molecules. This work is supported by NSF Grant DMR-1005651

  1. H-Bonded Donor-Acceptor Units Segregated in Coaxial Columnar Assemblies: Toward High Mobility Ambipolar Organic Semiconductors.

    PubMed

    Feringán, Beatriz; Romero, Pilar; Serrano, José Luis; Folcia, César L; Etxebarria, Jesús; Ortega, Josu; Termine, Roberto; Golemme, Attilio; Giménez, Raquel; Sierra, Teresa

    2016-09-28

    A novel approach to ambipolar semiconductors based on hydrogen-bonded complexes between a star-shaped tris(triazolyl)triazine and triphenylene-containing benzoic acids is described. The formation of 1:3 supramolecular complexes was evidenced by different techniques. Mesogenic driving forces played a decisive role in the formation of the hydrogen-bonded complexes in the bulk. All of the complexes formed by nonmesogenic components gave rise to hexagonal columnar (Colh) liquid crystal phases, which are stable at room temperature. In all cases, X-ray diffraction experiments supported by electron density distribution maps confirmed triphenylene/tris(triazolyl)triazine segregation into hexagonal sublattices and lattices, respectively, as well as remarkable intracolumnar order. These highly ordered nanostructures, obtained by the combined supramolecular H-bond/columnar liquid crystal approach, yielded donor/acceptor coaxial organization that is promising for the formation of ambipolar organic semiconductors with high mobilities, as indicated by charge transport measurements. PMID:27577722

  2. H-Bonded Donor-Acceptor Units Segregated in Coaxial Columnar Assemblies: Toward High Mobility Ambipolar Organic Semiconductors.

    PubMed

    Feringán, Beatriz; Romero, Pilar; Serrano, José Luis; Folcia, César L; Etxebarria, Jesús; Ortega, Josu; Termine, Roberto; Golemme, Attilio; Giménez, Raquel; Sierra, Teresa

    2016-09-28

    A novel approach to ambipolar semiconductors based on hydrogen-bonded complexes between a star-shaped tris(triazolyl)triazine and triphenylene-containing benzoic acids is described. The formation of 1:3 supramolecular complexes was evidenced by different techniques. Mesogenic driving forces played a decisive role in the formation of the hydrogen-bonded complexes in the bulk. All of the complexes formed by nonmesogenic components gave rise to hexagonal columnar (Colh) liquid crystal phases, which are stable at room temperature. In all cases, X-ray diffraction experiments supported by electron density distribution maps confirmed triphenylene/tris(triazolyl)triazine segregation into hexagonal sublattices and lattices, respectively, as well as remarkable intracolumnar order. These highly ordered nanostructures, obtained by the combined supramolecular H-bond/columnar liquid crystal approach, yielded donor/acceptor coaxial organization that is promising for the formation of ambipolar organic semiconductors with high mobilities, as indicated by charge transport measurements.

  3. Photoinduced Charge Transfer and Electrochemical Properties of Triphenylamine Ih-Sc3N@C80 Donor-Acceptor Conjugates

    PubMed Central

    Pinzón, Julio R.; Gasca, Diana C.; Shankara, Gayathri. S; Bottari, Giovanni; Torres, Tomás; Guldi, Dirk M.; Echegoyen, Luis

    2009-01-01

    Two isomeric [5,6]-pyrrolidine-Ih-Sc3N@C80 electron donor acceptor conjugates containing triphenylamine (TPA) as the donor system were synthesized. Electrochemical and photophysical studies of the novel conjugates were made and compared with those of their C60 analogues, in order to determine i) the effect of the linkage position (N-substituted versus 2-substituted pyrrolidine) of the donor system in the formation of photoinduced charge separated states, ii) the thermal stability towards the retro-cycloaddition reaction and iii) the effect of changing C60 for Ih-Sc3N@C80 as the electron acceptor. It was found that when the donor is connected to the pyrrolidine nitrogen atom, the resulting dyad produces a significantly longer lived radical pair than the corresponding 2-substituted isomer for both the C60 and Ih-Sc3N@C80 dyads. In addition to that, the N-substituted TPA-Ih-Sc3N@C80 dyad has much better thermal stability than the 2-subtituted one. Finally, the Ih-Sc3N@C80 dyads have considerably longer lived charge separated states than their C60 analogues, thus approving the advantage of using Ih-Sc3N@C80 instead of C60 as the acceptor for the construction of fullerene based donor acceptor conjugates. These findings are important for the design and future application of Ih-Sc3N@C80 dyads as materials for the construction of plastic organic solar cells. PMID:19445462

  4. Photoconductive and supramolecularly engineered organic field-effect transistors based on fibres from donor-acceptor dyads

    NASA Astrophysics Data System (ADS)

    Treier, Matthias; Liscio, Andrea; Mativetsky, Jeffrey M.; Kastler, Marcel; Müllen, Klaus; Palermo, Vincenzo; Samorì, Paolo

    2012-02-01

    We report on the formation of photoconductive self-assembled fibres by solvent induced precipitation of a HBC-PMI donor-acceptor dyad. Kelvin Probe Force Microscopy revealed that upon illumination with white light the surface potential of the fibres shifted to negative values due to a build-up of negative charge. When integrated in a field-effect transistor (FET) configuration, the devices can be turned `on' much more efficiently using light than conventional bias triggered field-effect, suggesting that these structures could be used for the fabrication of light sensing devices. Such a double gating represents an important step towards bi-functional organic FETs, in which the current through the junction can be modulated both optically (by photoexcitation) and electrically (by gate control).We report on the formation of photoconductive self-assembled fibres by solvent induced precipitation of a HBC-PMI donor-acceptor dyad. Kelvin Probe Force Microscopy revealed that upon illumination with white light the surface potential of the fibres shifted to negative values due to a build-up of negative charge. When integrated in a field-effect transistor (FET) configuration, the devices can be turned `on' much more efficiently using light than conventional bias triggered field-effect, suggesting that these structures could be used for the fabrication of light sensing devices. Such a double gating represents an important step towards bi-functional organic FETs, in which the current through the junction can be modulated both optically (by photoexcitation) and electrically (by gate control). Electronic supplementary information (ESI) available: Experimental details and photoresponse on spin-coated film (3 pages). See DOI: 10.1039/c2nr11635a

  5. Alteration of the Donor/Acceptor Spectrum of the (S)-Amine Transaminase from Vibrio fluvialis

    PubMed Central

    Genz, Maika; Vickers, Clare; van den Bergh, Tom; Joosten, Henk-Jan; Dörr, Mark; Höhne, Matthias; Bornscheuer, Uwe T.

    2015-01-01

    To alter the amine donor/acceptor spectrum of an (S)-selective amine transaminase (ATA), a library based on the Vibrio fluvialis ATA targeting four residues close to the active site (L56, W57, R415 and L417) was created. A 3DM-derived alignment comprising fold class I pyridoxal-5′-phosphate (PLP)-dependent enzymes allowed identification of positions, which were assumed to determine substrate specificity. These positions were targeted for mutagenesis with a focused alphabet of hydrophobic amino acids to convert an amine:α-keto acid transferase into an amine:aldehyde transferase. Screening of 1200 variants revealed three hits, which showed a shifted amine donor/acceptor spectrum towards aliphatic aldehydes (mainly pentanal), as well as an altered pH profile. Interestingly, all three hits, although found independently, contained the same mutation R415L and additional W57F and L417V substitutions. PMID:26569229

  6. Alteration of the Donor/Acceptor Spectrum of the (S)-Amine Transaminase from Vibrio fluvialis.

    PubMed

    Genz, Maika; Vickers, Clare; van den Bergh, Tom; Joosten, Henk-Jan; Dörr, Mark; Höhne, Matthias; Bornscheuer, Uwe T

    2015-01-01

    To alter the amine donor/acceptor spectrum of an (S)-selective amine transaminase (ATA), a library based on the Vibrio fluvialis ATA targeting four residues close to the active site (L56, W57, R415 and L417) was created. A 3DM-derived alignment comprising fold class I pyridoxal-5'-phosphate (PLP)-dependent enzymes allowed identification of positions, which were assumed to determine substrate specificity. These positions were targeted for mutagenesis with a focused alphabet of hydrophobic amino acids to convert an amine:α-keto acid transferase into an amine:aldehyde transferase. Screening of 1200 variants revealed three hits, which showed a shifted amine donor/acceptor spectrum towards aliphatic aldehydes (mainly pentanal), as well as an altered pH profile. Interestingly, all three hits, although found independently, contained the same mutation R415L and additional W57F and L417V substitutions. PMID:26569229

  7. Donor-Acceptor Distance Sampling Enhances the Performance of "Better than Nature" Nicotinamide Coenzyme Biomimetics.

    PubMed

    Geddes, Alexander; Paul, Caroline E; Hay, Sam; Hollmann, Frank; Scrutton, Nigel S

    2016-09-01

    Understanding the mechanisms of enzymatic hydride transfer with nicotinamide coenzyme biomimetics (NCBs) is critical to enhancing the performance of nicotinamide coenzyme-dependent biocatalysts. Here the temperature dependence of kinetic isotope effects (KIEs) for hydride transfer between "better than nature" NCBs and several ene reductase biocatalysts is used to indicate transfer by quantum mechanical tunneling. A strong correlation between rate constants and temperature dependence of the KIE (ΔΔH(⧧)) for H/D transfer implies that faster reactions with NCBs are associated with enhanced donor-acceptor distance sampling. Our analysis provides the first mechanistic insight into how NCBs can outperform their natural counterparts and emphasizes the need to optimize donor-acceptor distance sampling to obtain high catalytic performance from H-transfer enzymes. PMID:27552302

  8. Donor-Acceptor Heterojunction Configurations Based on DNA-Multichromophore Arrays.

    PubMed

    Nakamura, Mitsunobu; Tsuto, Koji; Jomura, Ayumi; Takada, Tadao; Yamana, Kazushige

    2015-08-10

    Multichromophore arrays of bis(2-thienyl)diketopyrrolopyrrole (DPP) and naphthalenediimide (NDI) with two Zn(II) -cyclens were constructed using thymidine DNA as a scaffold through the binding of the Zn(II) -cyclens with thymine bases. We demonstrate photocurrent generation in a donor-acceptor heterojunction configuration consisting of the DPP (donor) and NDI (acceptor) arrays co-immobilized on an Au electrode. The co-immobilized electrode exhibited good photocurrent responses because of the efficient charge separation between the DPP and NDI arrays. In contrast, an immobilized electrode consisting of randomly assembled DPP-NDI arrays generated no photocurrent response because DPP formed ground-state charge-transfer complexes with NDI in the randomly assembled arrays. Therefore, our approach to generate donor-acceptor heterojunctions based on DNA-multichromophore arrays is a useful method to efficiently generate photocurrent. PMID:26179473

  9. Ultra-flexible nonvolatile memory based on donor-acceptor diketopyrrolopyrrole polymer blends

    PubMed Central

    Zhou, Ye; Han, Su-Ting; Yan, Yan; Zhou, Li; Huang, Long-Biao; Zhuang, Jiaqing; Sonar, Prashant; Roy, V. A. L.

    2015-01-01

    Flexible memory cell array based on high mobility donor-acceptor diketopyrrolopyrrole polymer has been demonstrated. The memory cell exhibits low read voltage, high cell-to-cell uniformity and good mechanical flexibility, and has reliable retention and endurance memory performance. The electrical properties of the memory devices are systematically investigated and modeled. Our results suggest that the polymer blends provide an important step towards high-density flexible nonvolatile memory devices. PMID:26029856

  10. Ultra-flexible nonvolatile memory based on donor-acceptor diketopyrrolopyrrole polymer blends.

    PubMed

    Zhou, Ye; Han, Su-Ting; Yan, Yan; Zhou, Li; Huang, Long-Biao; Zhuang, Jiaqing; Sonar, Prashant; Roy, V A L

    2015-01-01

    Flexible memory cell array based on high mobility donor-acceptor diketopyrrolopyrrole polymer has been demonstrated. The memory cell exhibits low read voltage, high cell-to-cell uniformity and good mechanical flexibility, and has reliable retention and endurance memory performance. The electrical properties of the memory devices are systematically investigated and modeled. Our results suggest that the polymer blends provide an important step towards high-density flexible nonvolatile memory devices.

  11. Molecular assembly of amino acid interlinked, topologically symmetric, π-complementary donor-acceptor-donor triads.

    PubMed

    Avinash, M B; Sandeepa, K V; Govindaraju, T

    2013-01-01

    Amino acid interlinked pyrene and naphthalenediimide (NDI) based novel donor-acceptor-donor (D-A-D) triads are designed to exploit their topological symmetry and complementary π-character for facile charge-transfer complexation. Consequently, free-floating high-aspect-ratio supercoiled nanofibres and hierarchical helical bundles of triads are realized by modulating the chemical functionality of interlinking amino acids. PMID:23946856

  12. Field emission analysis of band bending in donor/acceptor heterojunction

    NASA Astrophysics Data System (ADS)

    Xing, Yingjie; Li, Shuai; Wang, Guiwei; Zhao, Tianjiao; Zhang, Gengmin

    2016-06-01

    The donor/acceptor heterojunction plays an important role in organic solar cells. An investigation of band bending in the donor/acceptor heterojunction is helpful in analysis of the charge transport behavior and for the improvement of the device performance. In this work, we report an approach for detection of band bending in a donor/acceptor heterojunction that has been prepared on a small and sharp tungsten tip. In situ field emission measurements are performed after the deposition process, and a linear Fowler-Nordheim plot is obtained from the fresh organic film surface. The thickness-dependent work function is then measured in the layer-by-layer deposited heterojunction. Several different types of heterojunction (zinc phthalocyanine (ZnPc)/C60, copper phthalocyanine (CuPc)/3,4,9,10-perylenetetracarboxylic bisbenzimidazole, and CuPc/C60) are fabricated and analyzed. The different charge transfer directions in the heterojunctions are distinguished by field emission measurements. The calculation method used to determine the band bending is then discussed in detail. A triple layer heterojunction (C60/ZnPc/CuPc) is also analyzed using this method. A small amount of band bending is measured in the outer CuPc layer. This method provides an independent reference method for determination of the band bending in an organic heterojunction that will complement photoemission spectroscopy and current-voltage measurement methods.

  13. Generalized Mulliken-Hush analysis of electronic coupling interactions in compressed pi-stacked porphyrin-bridge-quinone systems.

    PubMed

    Zheng, Jieru; Kang, Youn K; Therien, Michael J; Beratan, David N

    2005-08-17

    Donor-acceptor interactions were investigated in a series of unusually rigid, cofacially compressed pi-stacked porphyrin-bridge-quinone systems. The two-state generalized Mulliken-Hush (GMH) approach was used to compute the coupling matrix elements. The theoretical coupling values evaluated with the GMH method were obtained from configuration interaction calculations using the INDO/S method. The results of this analysis are consistent with the comparatively soft distance dependences observed for both the charge separation and charge recombination reactions. Theoretical studies of model structures indicate that the phenyl units dominate the mediation of the donor-acceptor coupling and that the relatively weak exponential decay of rate with distance arises from the compression of this pi-electron stack.

  14. Electronic structure of novel charge transfer compounds: application of Fermi orbital self-interaction corrected density functional theory

    NASA Astrophysics Data System (ADS)

    Hahn, Torsten; Rückerl, Florian; Liebing, Simon; Pederson, Mark

    We present our experimental and theoretical results on novel Picene/F4TCNQ and Manganese-Phthalocyanine/F4TCNQ donor / acceptor systems. We apply the recently developed Fermi-orbital based approach for self-interaction corrected density functional theory (FO-SIC DFT) to these materials and compare the results to standard DFT calculations and to experimental data obtained by photoemission spectroscopy. We focus our analysis on the description of the magnitude of the ground state charge transfer and on the details of the formed hybrid orbitals. Further, we show that for weakly bound donor / acceptor systems the FO-SIC approach delivers a more realistic description of the electronic structure compared to standard DFT calculations Support by DFG FOR1154 is greatly acknowledged.

  15. Large Spatially Resolved Rectification in a Donor-Acceptor Molecular Heterojunction.

    PubMed

    Smerdon, Joseph A; Giebink, Noel C; Guisinger, Nathan P; Darancet, Pierre; Guest, Jeffrey R

    2016-04-13

    We demonstrate that rectification ratios (RR) of ≳250 (≳1000) at biases of 0.5 V (1.2 V) are achievable at the two-molecule limit for donor-acceptor bilayers of pentacene on C60 on Cu using scanning tunneling spectroscopy and microscopy. Using first-principles calculations, we show that the system behaves as a molecular Schottky diode with a tunneling transport mechanism from semiconducting pentacene to Cu-hybridized metallic C60. Low-bias RRs vary by two orders-of-magnitude at the edge of these molecular heterojunctions due to increased Stark shifts and confinement effects.

  16. Thermoelectric Performance of Donor-Acceptor-Donor Conjugated Polymers Based on Benzothiadiazole Derivatives

    NASA Astrophysics Data System (ADS)

    Ming, Shouli; Zhen, Shijie; Lin, Kaiwen; Zhao, Li; Xu, Jingkun; Lu, Baoyang; Wang, Liangying; Xiong, Jinhua; Zhu, Zhengzhou

    2015-06-01

    Donor-acceptor-donor conjugated polymers are superior to other thermoelectric organic materials because it is much easier to modify their structure to reduce the bandgap between the conduction and valence bands, which is desirable for thermoelectric materials with high Seebeck coefficients. Despite this, studies of the thermoelectric performance of donor-acceptor-donor conjugated polymers are rare. In this study, four low-bandgap donor-acceptor-donor conjugated polymers, poly(4,7-bis(2,3-dihydrothieno[3,4- b][1,4] dioxin-5-yl)benzo[ c][1,2,5]thiadiazole) (PEBTE), poly(4,7-bis(2,3-dihydrothieno[3,4- b][1,4]dioxin-5-yl)benzo[ c][1,2,5]selenadiazole) (PEBSeE), poly (4,7-bis(2,3-dihydrothieno[3,4- b][1,4]dioxin-5-yl)-[1,2,5]thiadiazolo [3,4- c] pyridine) (PEPTE), and poly(4,7-bis(2,3-dihydrothieno[3,4- b][1,4]dioxin-5-yl)-[1,2,5]selenadiazolo[3,4- c]pyridine) (PEPSeE), were deposited by electrochemical polymerization of 4,7-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)benzo[c][1,2,5]thiadiazole (EBTE), 4,7-bis(2,3-dihydro-thieno[3,4-b][1,4] dioxin-5-yl)benzo[c][1,2,5]selenadiazole (EBSeE), 4,7-bis(2,3-dihydrothieno [3,4-b][1,4]dioxin-5-yl)-[1,2,5]thiadiazolo[3,4-c] pyridine (EPTE) and 4,7-bis (2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-[1,2,5] selenadiazolo[3,4-c]pyridine (EPSeE), respectively and their thermoelectric performance was investi- gated. Compared with polyselenophenes, PEBTE and PEBSeE in pressed pellets had higher electrical conductivity (10-1-101 S cm-1) but lower Seebeck coefficient (14.0 μV K-1) at room temperature. Future work may focus on treatment of these donor-acceptor-donor polymers to improve their electrical conductivity and Seebeck coefficient, and further investigation of their thermoelectric performance.

  17. CVD graphene as interfacial layer to engineer the organic donor-acceptor heterojunction interface properties.

    PubMed

    Zhong, Shu; Zhong, Jian Qiang; Mao, Hong Ying; Wang, Rui; Wang, Yu; Qi, Dong Chen; Loh, Kian Ping; Wee, Andrew Thye Shen; Chen, Zhi Kuan; Chen, Wei

    2012-06-27

    We demonstrate the use of chemical-vapor-deposited (CVD) graphene as an effective indium-tin-oxide (ITO) electrode surface modifier to engineer the organic donor-acceptor heterojunction interface properties in an inverted organic solar cell device configuration. As revealed by in situ near-edge X-ray adsorption fine structure measurement, the organic donor-acceptor heterojunction, comprising copper-hexadecafluoro-phthalocyanine (F16CuPc) and copper phthalocyanine (CuPc), undergoes an obvious orientation transition from a standing configuration (molecular π-plane nearly perpendicular to the substrate surface) on the bare ITO electrode to a less standing configuration with the molecular π-plane stacking adopting a large projection along the direction perpendicular to the electrode surface on the CVD graphene-modified ITO electrode. Such templated less-standing configuration of the organic heterojunction could significantly enhance the efficiency of charge transport along the direction perpendicular to the electrode surface in the planar heterojunction-based devices. Compared with the typical standing organic-organic heterojunction on the bare ITO electrode, our in situ ultraviolet photoelectron spectroscopy experiments reveal that the heterojunction on the CVD graphene modified ITO electrode possesses better aligned energy levels with respective electrodes, hence facilitating effective charge collection. PMID:22662875

  18. Asymmetric intramolecular α-cyclopropanation of aldehydes using a donor/acceptor carbene mimetic

    PubMed Central

    Luo, Chaosheng; Wang, Zhen; Huang, Yong

    2015-01-01

    Enantioselective α-alkylation of carbonyl is considered as one of the most important processes for asymmetric synthesis. Common alkylation agents, that is, alkyl halides, are notorious substrates for both Lewis acids and organocatalysts. Recently, olefins emerged as a benign alkylating species via photo/radical mechanisms. However, examples of enantioselective alkylation of aldehydes/ketones are scarce and direct asymmetric dialkylation remains elusive. Here we report an intramolecular α-cyclopropanation reaction of olefinic aldehydes to form chiral cyclopropane aldehydes. We demonstrate that an α-iodo aldehyde can function as a donor/acceptor carbene equivalent, which engages in a formal [2+1] annulation with a tethered double bond. Privileged bicyclo[3.1.0]hexane-type scaffolds are prepared in good optical purity using a chiral amine. The synthetic utility of the products is demonstrated by versatile transformations of the bridgehead formyl functionality. We expect the concept of using α-iodo iminium as a donor/acceptor carbene surrogate will find wide applications in chemical reaction development. PMID:26644194

  19. Solution-Processed Donor-Acceptor Polymer Nanowire Network Semiconductors For High-Performance Field-Effect Transistors

    NASA Astrophysics Data System (ADS)

    Lei, Yanlian; Deng, Ping; Li, Jun; Lin, Ming; Zhu, Furong; Ng, Tsz-Wai; Lee, Chun-Sing; Ong, Beng S.

    2016-04-01

    Organic field-effect transistors (OFETs) represent a low-cost transistor technology for creating next-generation large-area, flexible and ultra-low-cost electronics. Conjugated electron donor-acceptor (D-A) polymers have surfaced as ideal channel semiconductor candidates for OFETs. However, high-molecular weight (MW) D-A polymer semiconductors, which offer high field-effect mobility, generally suffer from processing complications due to limited solubility. Conversely, the readily soluble, low-MW D-A polymers give low mobility. We report herein a facile solution process which transformed a lower-MW, low-mobility diketopyrrolopyrrole-dithienylthieno[3,2-b]thiophene (I) into a high crystalline order and high-mobility semiconductor for OFETs applications. The process involved solution fabrication of a channel semiconductor film from a lower-MW (I) and polystyrene blends. With the help of cooperative shifting motion of polystyrene chain segments, (I) readily self-assembled and crystallized out in the polystyrene matrix as an interpenetrating, nanowire semiconductor network, providing significantly enhanced mobility (over 8 cm2V‑1s‑1), on/off ratio (107), and other desirable field-effect properties that meet impactful OFET application requirements.

  20. Solution-Processed Donor-Acceptor Polymer Nanowire Network Semiconductors For High-Performance Field-Effect Transistors.

    PubMed

    Lei, Yanlian; Deng, Ping; Li, Jun; Lin, Ming; Zhu, Furong; Ng, Tsz-Wai; Lee, Chun-Sing; Ong, Beng S

    2016-01-01

    Organic field-effect transistors (OFETs) represent a low-cost transistor technology for creating next-generation large-area, flexible and ultra-low-cost electronics. Conjugated electron donor-acceptor (D-A) polymers have surfaced as ideal channel semiconductor candidates for OFETs. However, high-molecular weight (MW) D-A polymer semiconductors, which offer high field-effect mobility, generally suffer from processing complications due to limited solubility. Conversely, the readily soluble, low-MW D-A polymers give low mobility. We report herein a facile solution process which transformed a lower-MW, low-mobility diketopyrrolopyrrole-dithienylthieno[3,2-b]thiophene (I) into a high crystalline order and high-mobility semiconductor for OFETs applications. The process involved solution fabrication of a channel semiconductor film from a lower-MW (I) and polystyrene blends. With the help of cooperative shifting motion of polystyrene chain segments, (I) readily self-assembled and crystallized out in the polystyrene matrix as an interpenetrating, nanowire semiconductor network, providing significantly enhanced mobility (over 8 cm(2)V(-1)s(-1)), on/off ratio (10(7)), and other desirable field-effect properties that meet impactful OFET application requirements. PMID:27091315

  1. Charge and energy transfer in a bithiophene perylenediimide based donor-acceptor-donor system for use in organic photovoltaics.

    PubMed

    Wenzel, Jan; Dreuw, Andreas; Burghardt, Irene

    2013-07-28

    The elementary charge and excitation energy transfer steps in a novel symmetric donor-acceptor-donor triad first described in Roland et al. Phys. Chem. Chem. Phys., 2012, 14, 273, consisting of a central perylenediimide moiety as a potential electron acceptor and two identical electron rich bithiophene compounds, have been investigated using quantum chemical methodology. These elementary processes determine the applicability of such systems in photovoltaic devices. The molecular structure, excited states and the photo-physical properties are investigated using smaller model systems and including solvation effects. The donor and acceptor π-systems are separated by an ethyl bridge such that the molecular orbitals are either located on the donor or acceptor moiety making the identification of locally excited versus charge transfer states straightforward. Using excited state geometry optimizations, the mechanism of photo-initiated charge separation could be identified. Geometry relaxation in the excited donor state leads to a near-degeneracy with the locally excited acceptor state, entailing strong excitonic coupling and resonance energy transfer. This energy transfer process is driven by planarization and bond length alternation of the donor molecule. Geometry relaxation of the locally excited acceptor state in turn reveals a crossing with the energetically lowest charge transfer excited state. The energetic position of the latter depends in a sensitive fashion on the solvent. This provides an explanation of the sequential process observed in the experiment, favoring ultrafast (∼130 fs) formation of the excited acceptor state followed by slower (∼3 ps scale) formation of the charge separated state.

  2. Solution-Processed Donor-Acceptor Polymer Nanowire Network Semiconductors For High-Performance Field-Effect Transistors

    PubMed Central

    Lei, Yanlian; Deng, Ping; Li, Jun; Lin, Ming; Zhu, Furong; Ng, Tsz-Wai; Lee, Chun-Sing; Ong, Beng S.

    2016-01-01

    Organic field-effect transistors (OFETs) represent a low-cost transistor technology for creating next-generation large-area, flexible and ultra-low-cost electronics. Conjugated electron donor-acceptor (D-A) polymers have surfaced as ideal channel semiconductor candidates for OFETs. However, high-molecular weight (MW) D-A polymer semiconductors, which offer high field-effect mobility, generally suffer from processing complications due to limited solubility. Conversely, the readily soluble, low-MW D-A polymers give low mobility. We report herein a facile solution process which transformed a lower-MW, low-mobility diketopyrrolopyrrole-dithienylthieno[3,2-b]thiophene (I) into a high crystalline order and high-mobility semiconductor for OFETs applications. The process involved solution fabrication of a channel semiconductor film from a lower-MW (I) and polystyrene blends. With the help of cooperative shifting motion of polystyrene chain segments, (I) readily self-assembled and crystallized out in the polystyrene matrix as an interpenetrating, nanowire semiconductor network, providing significantly enhanced mobility (over 8 cm2V−1s−1), on/off ratio (107), and other desirable field-effect properties that meet impactful OFET application requirements. PMID:27091315

  3. Efficient end-capping synthesis of neutral donor-acceptor [2]rotaxanes under additive-free and mild conditions.

    PubMed

    Domoto, Yuya; Sase, Shohei; Goto, Kei

    2014-11-24

    Efficient end-capping synthesis of neutral donor-acceptor (D-A) [2]rotaxanes without loading any catalysts or activating agents was achieved by utilizing high reactivity of a pentacoordinated hydrosilane toward salicylic acid derivatives. As components of [2]rotaxanes, an electron-deficient naphthalenediimide-containing axle with a salicylic acid terminus and several electron-rich bis(naphthocrown) ether macrocycles were employed. End-capping reactions with the pentacoordinated hydrosilane underwent smoothly even at low temperature to afford the corresponding [2]rotaxanes in good yields. A [2]rotaxane containing bis-1,5-(dinaphtho)-38-crown-10 ether as a wheel molecule was synthesized and isolated in 84% yield by the end-capping at -10 °C, presenting the highest yield ever reported for the end-capping synthesis of a neutral D-A [2]rotaxane. It was found that the yields of the [2]rotaxanes in the end-capping reactions were almost parallel to the formation ratios of the corresponding pseudo[2]rotaxanes estimated by utilizing model systems. These results indicate that the end-capping reaction using the pentacoordinated hydrosilane proceeded without perturbing the threading process, and most of the pseudo[2]rotaxanes underwent efficient end-capping reaction even at low temperature. PMID:25284148

  4. Two-photon absorption and spectroscopy of the lowest two-photon transition in small donor-acceptor-substituted organic molecules

    NASA Astrophysics Data System (ADS)

    Beels, Marten T.; Biaggio, Ivan; Reekie, Tristan; Chiu, Melanie; Diederich, François

    2015-04-01

    We determine the dispersion of the third-order polarizability of small donor-acceptor substituted organic molecules using wavelength-dependent degenerate four-wave mixing experiments in solutions with varying concentrations. We find that donor-acceptor-substituted molecules that are characterized by extremely efficient off-resonant nonlinearities also have a correspondingly high two-photon absorption cross section. The width and shape of the first two-photon resonance for these noncentrosymmetric molecules follows what is expected from their longest wavelength absorption peak, and the observed two-photon absorption cross sections are record high when compared to the available literature data, the size of the molecule, and the fundamental limit for two-photon absorption to the lowest excited state, which is essentially determined by the number of conjugated electrons and the excited-state energies. The two-photon absorption of the smallest molecule, which only has 16 electrons in its conjugated system, is one order of magnitude larger than for the molecule called AF-50, a reference molecule for two-photon absorption [O.-K. Kim et al., Chem. Mater. 12, 284 (2000), 10.1021/cm990662r].

  5. Exquisite 1D Assemblies Arising from Rationally Designed Asymmetric Donor-Acceptor Architectures Exhibiting Aggregation-Induced Emission as a Function of Auxiliary Acceptor Strength.

    PubMed

    Singh, Roop Shikha; Mukhopadhyay, Sujay; Biswas, Arnab; Pandey, Daya Shankar

    2016-01-11

    One-dimensional nanostructures with aggregation-induced emission (AIE) properties have been fabricated to keep the pace with growing demand from optoelectronics applications. The compounds 2-[4-(4-methylpiperazin-1-yl)benzylidene]malononitrile (PM1), 2-{4-[4-(pyridin-2-yl)piperazin-1-yl]-benzylidene}malononitrile (PM2), and 2-{4-[4-(pyrimidin-2-yl)piperazin-1-yl]benzylidene}malononitrile (PM3) have been designed and synthesized by melding piperazine and dicyanovinylene to investigate AIE in an asymmetric donor-acceptor (D-A) construct of A'-D-π-A- topology. The synthetic route has been simplified by using phenylpiperazine as a weak donor (D), dicyanovinylene as an acceptor (A), and pyridyl/pyrimidyl groups (PM2/PM3) as auxiliary acceptors (A'). It has been established that A' plays a vital role in triggering AIE in these compounds because the same D-A construct led to aggregation-caused quenching upon replacing A' with an electron-donating ethyl group (PM1). Moreover, the effect of restricted intramolecular rotation and twisted intramolecular charge transfer on the mechanism of AIE has also been investigated. Furthermore, it has been clearly shown that the optical disparities of these A'-D-π-A architectures are a direct consequence of comparative A' strength. Single-crystal X-ray analyses provided justification for role of intermolecular interactions in aggregate morphology. Electrochemical and theoretical studies affirmed the effect of the A' strength on the overall properties of the A'-D-π-A system.

  6. Energy transfer within self-assembled cyclic multichromophoric arrays based on orthogonally arranged donor-acceptor building blocks.

    PubMed

    Karakostas, Nikolaos; Kaloudi-Chantzea, Antonia; Martinou, Elisabeth; Seintis, Kostas; Pitterl, Florian; Oberacher, Herbert; Fakis, Mihalis; Kallitsis, Joannis K; Pistolis, George

    2015-01-01

    We herein present the coordination-driven supramolecular synthesis and photophysics of a [4+4] and a [2+2] assembly, built up by alternately collocated donor-acceptor chromophoric building blocks based, respectively, on the boron dipyrromethane (Bodipy) and perylene bisimide dye (PBI). In these multichromophoric scaffolds, the intensely absorbing/emitting dipoles of the Bodipy subunit are, by construction, cyclically arranged at the corners and aligned perpendicular to the plane formed by the closed polygonal chain comprising the PBI units. Steady-state and fs time-resolved spectroscopy reveal the presence of efficient energy transfer from the vertices (Bodipys) to the edges (PBIs) of the polygons. Fast excitation energy hopping - leading to a rapid excited state equilibrium among the low energy perylene-bisimide chromophores - is revealed by fluorescence anisotropy decays. The dynamics of electronic excitation energy hopping between the PBI subunits was approximated on the basis of a theoretical model within the framework of Förster energy transfer theory. All energy-transfer processes are quantitatively describable with Förster theory. The influence of structural deformations and orientational fluctuations of the dipoles in certain kinetic schemes is discussed. PMID:26396034

  7. Fluorinated arene, imide and unsaturated pyrrolidinone based donor acceptor conjugated polymers: Synthesis, structure-property and device studies

    NASA Astrophysics Data System (ADS)

    Liyanage, Arawwawala Don Thilanga

    After the discovery of doped polyacetylene, organic semiconductor materials are widely studied as high impending active components in consumer electronics. They have received substantial consideration due to their potential for structural tailoring, low cost, large area and mechanically flexible alternatives to common inorganic semiconductors. To acquire maximum use of these materials, it is essential to get a strong idea about their chemical and physical nature. Material chemist has an enormous role to play in this novel area, including development of efficient synthetic methodologies and control the molecular self-assembly and (opto)-electronic properties. The body of this thesis mainly focuses on the substituent effects: how different substituents affect the (opto)-electronic properties of the donor-acceptor (D-A) conjugated polymers. The main priority goes to understand, how different alkyl substituent effect to the polymer solubility, crystallinity, thermal properties (e.g.: glass transition temperature) and morphological order. Three classes of D-A systems were extensively studied in this work. The second chapter mainly focuses on the synthesis and structure-property study of fluorinated arene (TFB) base polymers. Here we used commercially available 1,4-dibromo-2,3,5,6-tetrafluorobenzene (TFB) as the acceptor material and prepare several polymers using 3,3'-dialkyl(3,3'-R2T2) or 3,3'-dialkoxy bithiophene (3,3'-RO2T2) units as electron donors. A detail study was done using 3,3'-bithiophene donor units incorporating branched alkoxy-functionalities by systematic variation of branching position and chain length. The study allowed disentangling the branching effects on (i) aggregation tendency, intermolecular arrangement, (iii) solid state optical energy gaps, and (iv) electronic properties in an overall consistent picture, which might guide future polymer synthesis towards optimized materials for opto-electronic applications. The third chapter mainly focused on

  8. Tetrathiafulvalene-based mixed-valence acceptor-donor-acceptor triads: a joint theoretical and experimental approach.

    PubMed

    Calbo, Joaquín; Aragó, Juan; Otón, Francisco; Lloveras, Vega; Mas-Torrent, Marta; Vidal-Gancedo, José; Veciana, Jaume; Rovira, Concepció; Ortí, Enrique

    2013-12-01

    This work presents a joint theoretical and experimental characterisation of the structural and electronic properties of two tetrathiafulvalene (TTF)-based acceptor-donor-acceptor triads (BQ-TTF-BQ and BTCNQ-TTF-BTCNQ; BQ is naphthoquinone and BTCNQ is benzotetracyano-p-quinodimethane) in their neutral and reduced states. The study is performed with the use of electrochemical, electron paramagnetic resonance (EPR), and UV/Vis/NIR spectroelectrochemical techniques guided by quantum-chemical calculations. Emphasis is placed on the mixed-valence properties of both triads in their radical anion states. The electrochemical and EPR results reveal that both BQ-TTF-BQ and BTCNQ-TTF-BTCNQ triads in their radical anion states behave as class-II mixed-valence compounds with significant electronic communication between the acceptor moieties. Density functional theory calculations (BLYP35/cc-pVTZ), taking into account the solvent effects, predict charge-localised species (BQ(.-)-TTF-BQ and BTCNQ(.-)-TTF-BTCNQ) as the most stable structures for the radical anion states of both triads. A stronger localisation is found both experimentally and theoretically for the BTCNQ-TTF-BTCNQ anion, in accordance with the more electron-withdrawing character of the BTCNQ acceptor. CASSCF/CASPT2 calculations suggest that the low-energy, broad absorption bands observed experimentally for the BQ-TTF-BQ and BTCNQ-TTF-BTCNQ radical anions are associated with the intervalence charge transfer (IV-CT) electronic transition and two nearby donor-to-acceptor CT excitations. The study highlights the molecular efficiency of the electron-donor TTF unit as a molecular wire connecting two acceptor redox centres.

  9. Very low band gap thiadiazoloquinoxaline donor-acceptor polymers as multi-tool conjugated polymers.

    PubMed

    Steckler, Timothy T; Henriksson, Patrik; Mollinger, Sonya; Lundin, Angelica; Salleo, Alberto; Andersson, Mats R

    2014-01-29

    Here we report on the synthesis of two novel very low band gap (VLG) donor-acceptor polymers (Eg ≤ 1 eV) and an oligomer based on the thiadiazoloquinoxaline acceptor. Both polymers demonstrate decent ambipolar mobilities, with P1 showing the best performance of ∼10(-2) cm(2) V(-1) s(-1) for p- and n-type operation. These polymers are among the lowest band gap polymers (≲0.7 eV) reported, with a neutral λmax = 1476 nm (P2), which is the farthest red-shifted λmax reported to date for a soluble processable polymer. Very little has been done to characterize the electrochromic aspects of VLG polymers; interestingly, these polymers actually show a bleaching of their neutral absorptions in the near-infrared region and have an electrochromic contrast up to 30% at a switching speed of 3 s.

  10. Thermally stable and efficient polymer solar cells based on a novel donor-acceptor copolymer

    NASA Astrophysics Data System (ADS)

    Synooka, O.; Eberhardt, K.-R.; Balko, J.; Thurn-Albrecht, T.; Gobsch, G.; Mitchell, W.; Berny, S.; Carrasco-Orozco, M.; Hoppe, H.

    2016-06-01

    We report high photovoltaic performance of a novel donor-acceptor (D-A) conjugated polymer poly[2,6[4,8-bis(2-ethyl-hexyl)benzo[1,2-b4,5-b‧]dithiophene-co-2,5-thiophene-co-4,7[5,6-bis-octyloxy-benzo[1,2,5]thiadiazole]-co-2,5-thiophene] (PBDTTBTZT) in bulk heterojunctions with [6,6]-phenyl-C71-butyric acid methyl ester (PC70BM). A power conversion efficiency (PCE) of more than 7% is obtained for optimized charge-extracting electrodes. Upon application of thermal stress via annealing, a superior thermal stability is demonstrated as compared to poly[N-9″-hepta-decanyl-2,7-carbazole-alt-5,5-(4‧,7‧-di-2-thienyl-2‧,1‧,3‧-benzothiadiazole)] (PCDTBT).

  11. GaCl3 -Mediated Reactions of Donor-Acceptor Cyclopropanes with Aromatic Aldehydes.

    PubMed

    Borisov, Denis D; Novikov, Roman A; Tomilov, Yury V

    2016-09-26

    A new strategy for cascade assembly of substituted indenes and polycyclic lactones based on reactions of donor-acceptor cyclopropanes and styrylmalonates with aromatic aldehydes in the presence of GaCl3 has been developed. The use of GaCl3 makes it possible to principally change the direction of the reaction known in this series of substrates and to perform the process in a multicomponent version. Generation of formal 1,2-zwitterionic intermediates owing to complexation of dicarboxylate groups with GaCl3 is the driving force of the reactions discovered. This method makes it possible to assemble indenylmalonates or indano[1',2':2,3]indano[2,1-b]furan-2-ones in one synthetic stage from readily available starting compounds with high regio- and diastereoselectivity. A mechanism of the reactions has been suggested using the (18) O label in benzaldehyde. PMID:27573178

  12. Photovoltaic enhancement of organic solar cells by a bridged donor-acceptor block copolymer approach

    NASA Astrophysics Data System (ADS)

    Sun, Sam-Shajing; Zhang, Cheng; Ledbetter, Abram; Choi, Soobum; Seo, Kang; Bonner, Carl E.; Drees, Martin; Sariciftci, Niyazi Serdar

    2007-01-01

    The authors show that a photovoltaic device composed of a -donor-bridge-acceptor-bridge- type block copolymer thin film exhibits a significant performance improvement over its corresponding donor/acceptor blend (Voc increased from 0.14to1.10V and Jsc increased from 0.017 to 0.058mA/cm2) under identical conditions, where donor is an alkyl derivatized poly-p-phenylenevinylene (PPV) conjugated block, acceptor is a sulfone-alkyl derivatized PPV conjugated block, and bridge is a nonconjugated and flexible unit. The authors attribute such improvement to the block copolymer intrinsic nanophase separation and molecular self-assembly that results in the reduction of the exciton and carrier losses.

  13. Generation of a Multicomponent Library of Disulfide Donor-Acceptor Architectures Using Dynamic Combinatorial Chemistry.

    PubMed

    Drożdż, Wojciech; Kołodziejski, Michał; Markiewicz, Grzegorz; Jenczak, Anna; Stefankiewicz, Artur R

    2015-07-17

    We describe here the generation of new donor-acceptor disulfide architectures obtained in aqueous solution at physiological pH. The application of a dynamic combinatorial chemistry approach allowed us to generate a large number of new disulfide macrocyclic architectures together with a new type of [2]catenanes consisting of four distinct components. Up to fifteen types of structurally-distinct dynamic architectures have been generated through one-pot disulfide exchange reactions between four thiol-functionalized aqueous components. The distribution of disulfide products formed was found to be strongly dependent on the structural features of the thiol components employed. This work not only constitutes a success in the synthesis of topologically- and morphologically-complex targets, but it may also open new horizons for the use of this methodology in the construction of molecular machines.

  14. Generation of a Multicomponent Library of Disulfide Donor-Acceptor Architectures Using Dynamic Combinatorial Chemistry

    PubMed Central

    Drożdż, Wojciech; Kołodziejski, Michał; Markiewicz, Grzegorz; Jenczak, Anna; Stefankiewicz, Artur R.

    2015-01-01

    We describe here the generation of new donor-acceptor disulfide architectures obtained in aqueous solution at physiological pH. The application of a dynamic combinatorial chemistry approach allowed us to generate a large number of new disulfide macrocyclic architectures together with a new type of [2]catenanes consisting of four distinct components. Up to fifteen types of structurally-distinct dynamic architectures have been generated through one-pot disulfide exchange reactions between four thiol-functionalized aqueous components. The distribution of disulfide products formed was found to be strongly dependent on the structural features of the thiol components employed. This work not only constitutes a success in the synthesis of topologically- and morphologically-complex targets, but it may also open new horizons for the use of this methodology in the construction of molecular machines. PMID:26193265

  15. Isolation by crystallization of translational isomers of a bistable donor-acceptor [2]catenane

    PubMed Central

    Wang, Cheng; Olson, Mark A.; Fang, Lei; Benítez, Diego; Tkatchouk, Ekaterina; Basu, Subhadeep; Basuray, Ashish N.; Zhang, Deqing; Zhu, Daoben; Goddard, William A.; Stoddart, J. Fraser

    2010-01-01

    The template-directed synthesis of a bistable donor-acceptor [2]catenane wherein both translational isomers—one in which a tetrathiafulvalene unit in a mechanically interlocked crown ether occupies the cavity of a cyclobis(paraquat-p-phenylene) ring and the other in which a 1,5-dioxynaphthalene unit in the crown ether resides inside the cavity of the tetracationic cyclophane—exist in equilibrium in solution, has led to the isolation and separation by hand picking of single crystals colored red and green, respectively. These two crystalline co-conformations have been characterized separately at both the molecular and supramolecular levels, and also by dynamic NMR spectroscopy in solution where there is compelling evidence that the mechanically interlocked molecules are present as a complex mixture of translational, configurational, and conformational isomers wherein the isomerization is best described as being a highly dynamic and adaptable phenomenon. PMID:20663950

  16. Donor-acceptor-pair emission in fluorescent 4H-SiC grown by PVT method

    SciTech Connect

    Liu, Xi Zhuo, Shi-Yi; Gao, Pan; Huang, Wei; Yan, Cheng-Feng; Shi, Er-Wei

    2015-04-15

    Fluorescent SiC, which contains donor and acceptor impurities with optimum concentrations, can work as a phosphor for visible light emission by donor-acceptor-pair (DAP) recombination. In this work, 3 inch N-B-Al co-doped fluorescent 4H-SiC crystals are prepared by PVT method. The p-type fluorescent 4H-SiC with low aluminum doping concentration can show intensive yellow-green fluorescence at room temperature. N-B DAP peak wavelength shifts from 578nm to 525nm and weak N-Al DAP emission occurred 403/420 nm quenches, when the temperature increases from 4K to 298K. The aluminum doping induces higher defect concentration in the fluorescent crystal and decreases optical transmissivity of the crystal in the visible light range. It triggers more non-radiative recombination and light absorption losses in the crystal.

  17. Synthesis of dithiafulvene-quinone donor-acceptor systems: isolation of a Michael adduct.

    PubMed

    Lissau, Henriette; Jevric, Martyn; Madsen, Anders Østergaard; Nielsen, Mogens Brøndsted

    2015-06-01

    π-Conjugated donor-acceptor systems based on dithiafulvene (DTF) donor units and various acceptor units have attracted attention for their linear and nonlinear optical properties. The reaction between p-benzoquinone and a 1,3-dithiole phosphonium salt, deprotonated by lithium hexamethyldisilazide (LiHMDS), gave a product mixture from which the Michael adduct [systematic name: dimethyl 2-(3-hydroxy-6-oxocyclohexa-2,4-dien-1-ylidene)-2H-1,3-dithiole-4,5-dicarboxylate], C13H10O6S2, was isolated. It is likely that one of the unidentified products obtained previously by others from related reactions could be a similar Michael adduct.

  18. Role of donor-acceptor macrocycles in sequence specific peptide recognition and their optoelectronic properties: a detailed computational insight.

    PubMed

    Bandyopadhyay, Arkamita; Pati, Swapan K

    2016-07-27

    In this study, we have considered an experimentally synthesized organic donor-acceptor (D-A) macrocycle (CPP-TCAQ) and have modified it by incorporating different acceptor groups. We have performed density functional theory and classical molecular dynamics studies on these D-A macrocycles. We have clearly shown that cyclo[10]paraphenylene-2,6-tetracyanoanthraquinodimethanylene (CPP-TCAQ) isomers interact specifically with one particular peptide sequence tyr-leu-ala, over its structural isomer, tyr-ala-leu. However, other functionalized macrocycles bind to the tyr-ala-leu peptide sequence over tyr-leu-ala. Our calculations show that the presence of hydrogen bonds as well as π-π interactions responsible for this specific selection. Interestingly, it is the additional charge transfer induced dipolar interactions that favour binding of the tripeptide with the bulky C-terminal leucine amino acid, tyr-ala-leu. We confirmed that these host-guest complexes are stable in water medium as well as at room temperature. Thus, these hosts can bind effectively to any protein fragment bearing a particular tripeptide. Interestingly, the macrocycle, which recognizes the peptide sequence with a bulky C-terminal amino acid, also shows photophysical properties. The reasons for this happen to be the same (dipolar interactions introduce dipole allowed states for optical absorption as well as attracting the oppositely oriented dipolar groups). Recognition of the peptide sequence with a bulky C-terminal group is carried out for the first time with this functionalised macrocycle, which in addition shows photophysical properties. PMID:27412849

  19. Annulation Reactions of Donor-Acceptor Cyclopropanes with (1-Azidovinyl)benzene and 3-Phenyl-2H-azirine.

    PubMed

    Curiel Tejeda, Joanne E; Irwin, Lauren C; Kerr, Michael A

    2016-09-16

    Under the influence of heat and Lewis acid, donor/acceptor cyclopropanes underwent annulation reactions with (1-azidovinyl)benzene and 3-phenyl-2H-azirine to form an unusual azabicyclic scaffold with an imbedded aziridine. The mechanism of reaction is believed to proceed via a vinyl nitrene intermediate. PMID:27598518

  20. Enhanced Visible Photovoltaic Response of TiO₂ Thin Film with an All-Inorganic Donor-Acceptor Type Polyoxometalate.

    PubMed

    Li, Jian-Sheng; Sang, Xiao-Jing; Chen, Wei-Lin; Zhang, Lan-Cui; Zhu, Zai-Ming; Ma, Teng-Ying; Su, Zhong-Min; Wang, En-Bo

    2015-06-24

    In the field of material chemistry, it is of great significance to develop abundant and sustainable materials for solar energy harvesting and management. Herein, after evaluating the energy band characteristics of 13 kinds of polyoxometalates (POMs), the trisubstituted POM compound K6H4[α-SiW9O37Co3(H2O)3]·17H2O (SiW9Co3) was first studied due to its relatively smaller band gap (2.23 eV) and higher lowest unoccupied molecular orbital (LUMO) level (-0.63 V vs NHE). Additionally, the preliminary computational modeling indicated that SiW9Co3 exhibited the donor-acceptor (D-A) structure, in which the cobalt oxygen clusters and tungsten skeletons act as the electron donor and electron acceptor, respectively. By employing SiW9Co3 to modify the TiO2 film, the visible photovoltaic and photocurrent response were both enhanced, and the light-induced photocurrent at 420 nm was improved by 7.1 times. Moreover, the highly dispersive and small sized SiW9Co3 nanoclusters loading on TiO2 were successfully achieved by fabricating the nanocomposite film of {TiO2/SiW9Co3}3 with the layer-by-layer method, which can result in the photovoltaic performance enhancement of dye-sensitized solar cells (DSSCs), of which the overall power conversion efficiency was improved by 25.6% from 6.79% to 8.53% through the synergistic effect of POMs and Ru-complex.

  1. Proficiency of acceptor-donor-acceptor organic dye with spiro-MeOTAD HTM on the photovoltaic performance of dye sensitized solar cell

    NASA Astrophysics Data System (ADS)

    Ramavenkateswari, K.; Venkatachalam, P.

    2016-08-01

    This work investigates the proficiency of acceptor-donor-acceptor (A-D-A) organic dye Diisopropyl azodicarboxylate (DIAC) as photosensitizer on the photovoltaic parameters of silver (Ag) doped TiO2 photoanode dye-sensitized solar cells (DSSCs) with quasi-solid state electrolyte/hole transport material (HTM) spiro-MeOTAD. TNSs (TiO2 nanosticks) photoanodes are prepared through sol-gel method and hydrothermal technique. X-ray powder diffraction (XRD), transmission electron microscope (TEM), scanning electron microscopy (SEM) and BET measurement were used to characterize the structure and morphology of TiO2 nanostructures. The Diisopropyl azodicarboxylate organic dye with TNPs-Ag@TNSs composite photoanode structure and spiro-MeOTAD HTM exhibited better power conversion efficiency (PCE). [Figure not available: see fulltext.

  2. Proficiency of acceptor-donor-acceptor organic dye with spiro-MeOTAD HTM on the photovoltaic performance of dye sensitized solar cell

    NASA Astrophysics Data System (ADS)

    Ramavenkateswari, K.; Venkatachalam, P.

    2016-09-01

    This work investigates the proficiency of acceptor-donor-acceptor (A-D-A) organic dye Diisopropyl azodicarboxylate (DIAC) as photosensitizer on the photovoltaic parameters of silver (Ag) doped TiO2 photoanode dye-sensitized solar cells (DSSCs) with quasi-solid state electrolyte/hole transport material (HTM) spiro-MeOTAD. TNSs (TiO2 nanosticks) photoanodes are prepared through sol-gel method and hydrothermal technique. X-ray powder diffraction (XRD), transmission electron microscope (TEM), scanning electron microscopy (SEM) and BET measurement were used to characterize the structure and morphology of TiO2 nanostructures. The Diisopropyl azodicarboxylate organic dye with TNPs-Ag@TNSs composite photoanode structure and spiro-MeOTAD HTM exhibited better power conversion efficiency (PCE).

  3. New donor-acceptor chromophores by formal [2+2] cycloaddition of donor-substituted alkynes to dicyanovinyl derivatives.

    PubMed

    Jarowski, Peter D; Wu, Yi-Lin; Boudon, Corinne; Gisselbrecht, Jean-Paul; Gross, Maurice; Schweizer, W Bernd; Diederich, François

    2009-04-01

    The efficient methodology of the cycloaddition between electron-rich alkynes and tetracyanoethylene (TCNE) or 7,7,8,8-tetracyanoquinodimethane (TCNQ), followed by retro-electrocyclisation, is extended to dicyanovinyl derivatives to produce new donor-acceptor push-pull 1,1-dicyanobutadienyl chromophores in excellent to quantitative yield (63-98%) that express strong charge-transfer (CT) absorptions from 300 to 600 nm. The scope of this reaction is established by both varying the nucleophilic and electrophilic components. Electrochemical studies show that the CT properties of these systems are readily tunable by substitution on the electrophile, which has the largest effect on the lowest unoccupied molecular orbital (LUMO). Non-reversible reduction potentials range from ca. -1.2 to -1.9 V in CH(2)Cl(2), against the ferricinium/ferrocene couple (Fc(+)/Fc) according to cyclovoltammetry (CV) and rotating disk voltammetry (RDV). The chromophores show a significant non-planarity between the N,N-dimethylanilino donor and the 1,1-dicyanovinyl acceptor moieties, with torsional angles around 40 degrees from X-ray analysis, but retain strong quinoidal character. The mechanism of this reaction has been studied computational using density functional methods in the gas-phase and using the polarizable continuum model (PCM) for addressing solvent effects. The complete reaction free-energy profile has been determined for the reaction of 1,1-dicyanoethene and 4-ethynyl-N,N-dimethylaniline. The process proceeds through formal [2+2] cycloaddition followed by retro-electrocyclisation. The formation of a zwitterionic intermediate in the cycloaddition step is shown. PMID:19300815

  4. Comparison of fluctuating potentials and donor-acceptor pair transitions in a Cu-poor Cu{sub 2}ZnSnS{sub 4} based solar cell

    SciTech Connect

    Teixeira, J. P.; Sousa, R. A.; Sousa, M. G.; Cunha, A. F. da; Leitão, J. P.; Fernandes, P. A.; Salomé, P. M. P.; González, J. C.

    2014-10-20

    The structure of the electronic energy levels of a single phase Cu{sub 2}ZnSnS{sub 4} film, as confirmed by Raman Scattering and x-ray diffraction, is investigated through a dependence on the excitation power of the photoluminescence (PL). The behavior of the observed asymmetric band, with a peak energy at ∼1.22 eV, is compared with two theoretical models: (i) fluctuating potentials and (ii) donor-acceptor pair transitions. It is shown that the radiative recombination channels in the Cu-poor film are strongly influenced by tail states in the bandgap as a consequence of a heavy doping and compensation levels. The contribution of the PL for the evaluation of secondary phases is also highlighted.

  5. Donor-acceptor-structured 1,4-diazatriphenylene derivatives exhibiting thermally activated delayed fluorescence: design and synthesis, photophysical properties and OLED characteristics

    NASA Astrophysics Data System (ADS)

    Takahashi, Takehiro; Shizu, Katsuyuki; Yasuda, Takuma; Togashi, Kazunori; Adachi, Chihaya

    2014-06-01

    A new series of luminescent 1,4-diazatriphenylene (ATP) derivatives with various peripheral donor units, including phenoxazine, 9,9-dimethylacridane and 3-(diphenylamino)carbazole, is synthesized and characterized as thermally activated delayed fluorescence (TADF) emitters. The influence of the donor substituents on the electronic and photophysical properties of the materials is investigated by theoretical calculations and experimental spectroscopic measurements. These ATP-based molecules with donor-acceptor-donor (D-A-D) structures can reduce the singlet-triplet energy gap (0.04-0.26 eV) upon chemical modification of the ATP core, and thus exhibit obvious TADF characteristics in solution and doped thin films. As a demonstration of the potential of these materials, organic light-emitting diodes containing the D-A-D-structured ATP derivatives as emitters are fabricated and tested. External electroluminescence quantum efficiencies above 12% and 8% for green- and sky-blue-emitting devices, respectively, are achieved.

  6. Oligomeric Dithienopyrrole-Thienopyrrolodione (DTP-TPD) Donor-Acceptor Copolymer for Organic Photovoltaics: Preprint

    SciTech Connect

    Hammond, S. R.; Braunecker, W.; Garcia, A.; Larsen, R.; Owczarczyk, Z.; Olson, D.; Ginley, D.

    2011-07-01

    A new donor-acceptor copolymer system based upon a dithienopyrrole (DTP) donor moiety and a thienopyrrolodione (TPD) accepting moiety has been designed and synthesized for organic photovoltaic (OPV) applications. The TPD accepting moiety has recently gained significant attention in the OPV community and is being incorporated into a number of different polymer systems. In contrast, the DTP donor moiety has received only limited attention, likely due in part to synthetic difficulties relating to the monomer. In our hands, the bis(trimethyltin)-DTP monomer was indelibly contaminated with ~5% of the mono-destannylated DTP, which limited the Stille polymerization with the dibromo-TPD monomer (>99% pure) to produce material with Mn ~ 4130 g/mol (PDI = 1.10), corresponding to around eight repeat units. Despite this limitation, UV-visible absorption spectroscopy demonstrates strong absorption for this material with a band gap of ~1.6 eV. Cyclic voltammetry indicates a highest occupied molecular orbital (HOMO) energy level of -5.3 eV, which is much lower than calculations predicted. Initial bulk heterojunction OPV devices fabricated with the fullerene acceptor phenyl C61 butyric acid methyl ester (PCBM) exhibit Voc ~ 700 mV, which supports the deep HOMO value obtained from CV. These results suggest the promise of this copolymer system.

  7. Time-dependent efficiency measurements of donor-acceptor, dye-sensitized polymer solar cells

    NASA Astrophysics Data System (ADS)

    Bandaccari, Kyle; Chesmore, Grace; Tajalli-Tehrani Valverde, Parisa; Bugaj, Mitchel; McNelis, Brian; Barber, Richard, Jr.

    The fullerene/polymer active layer pairing of PCBM/P3HT has become the model system within the field of polymer solar cell research. A large body of work concerned with reporting improved efficiencies for this system exists, but truly quantitative studies of device lifetime and long-term degradation tendencies are much rarer. Here, we report the effects of two donor-acceptor diazo dye sensitizers on efficiency and lifetime upon addition into the PCBM/P3HT active layer at varied concentrations. The electrical and efficiency measurements were supplemented by time-dependent UV-visible spectroscopy studies and morphology investigations via atomic-force microscopy (AFM). This pairing with spectroscopy offers an internal check on the data as the rate of change in absorbance of the active layer correlates almost exactly to the rate of power conversion efficiency decrease. Additionally, AFM imaging reveals different morphology patterns when dye concentrations and functionalities change. Such observations suggest that such small-molecule sensitizers exert yet undetermined effects on the organization of components within the active layer at the molecular level.

  8. Density of states determination in organic donor-acceptor blend layers enabled by molecular doping

    NASA Astrophysics Data System (ADS)

    Fischer, Janine; Ray, Debdutta; Kleemann, Hans; Pahner, Paul; Schwarze, Martin; Koerner, Christian; Vandewal, Koen; Leo, Karl

    2015-06-01

    Charge carrier transport is a key parameter determining the efficiency of organic solar cells, and is closely related to the density of free and trapped states. For trap characterization, impedance spectroscopy is a suitable, non-invasive method, applicable to complete organic semiconductor devices. In order to contribute to the capacitive signal, the traps must be filled with charge carriers. Typically, trap filling is achieved by illuminating the device or by injecting charge carriers through application of a forward bias voltage. However, in both cases, the exact number of charge carriers in the device is not known and depends strongly on the measurement conditions. Here, hole trap states of the model blend layer ZnPc:C60 are filled by weak p-doping, enabling trap characterization in a blend layer at a controlled hole density. We evaluate impedance spectra at different temperatures in order to determine the density of occupied states (DOOS) directly from the capacitance-frequency spectra by assuming a simple energy diagram. The reconstructed DOOS distribution is analyzed at different doping concentrations and device thicknesses and compared to thermally stimulated current measurements performed on the same devices. In both methods, a pronounced Gaussian peak at about 0.4 eV below the transport level is found as well as deep, exponential tail states, providing a deeper insight into the density of states distribution of this donor-acceptor blend layer. Additionally, the effect of doping-induced trap filling on the solar cell characteristics is studied in these devices.

  9. Donor/acceptor morphology control for efficient and stable photovoltaic cells by using semiconducting diblock copolymers

    NASA Astrophysics Data System (ADS)

    Tajima, Keisuke; Miyanishi, Shoji; Zhang, Yue; Hashimoto, Kazuhito

    2012-09-01

    Poly(3-alkylthiophene)-based diblock copolymers with controllable block lengths were synthesized by combining Grignard metathesis (GRIM) method, Ni-catalyzed quasi-living polymerization and a subsequent azide-alkyne click reaction to introduce a fullerene functionality into the side chains of one of the blocks. The fullerene-attached copolymers had good solubility (> 30 g L-1 in chlorobenzene) with high molecular weights (Mn > 20000). The diblock copolymer films showed the formation of clear nanostructures with the size of 20 nm in AFM phase image driven by the crystallization of poly(3-hexylthiophene) block and aggregation of the fullerene groups. The photovoltaic device based on the copolymers showed a power conversion efficiency of 2.5% with a much higher fill factor of 0.63 compared with the single component devices previously reported. These results indicate that the rational material designs enable to construct the donor-acceptor nanostructure suitable for the photovoltaic application without relying on the mixing of the materials.

  10. Analysis of degradation mechanisms in donor-acceptor copolymer based organic photovoltaic devices using impedance spectroscopy

    NASA Astrophysics Data System (ADS)

    Srivastava, S. B.; Sonar, P.; Singh, S. P.

    2016-09-01

    The stability of organic photovoltaic (OPV) devices in ambient conditions has been a serious issue which needs to be addressed and resolved timely. In order to probe the degradation mechanism in a donor-acceptor polymer PDPP-TNT: PC71BM bulk heterojunction based OPV devices, we have studied current density-voltage (J-V) behavior and impedance spectroscopy of fresh and aged devices. The current-voltage characteristic of optimized fresh devices exhibit a short circuit current density (J sc) of 8.9 mA cm-2, open circuit voltage (V oc) of 0.79 V, fill factor (FF) of 54.6%, and power conversion efficiency (PCE) of 3.8%. For aged devices, J sc, V oc, FF, and PCE were reduced to 57.3%, 89.8%, 44.3% and 23.7% of its initial value, respectively. The impedance spectra measured under illumination for these devices were successfully fitted using a CPE-based circuit model. For aged devices, the low-frequency response in impedance spectra suggests an accumulation of the photo-generated charge carriers at the interfaces which leads to a significant lowering in fill factor. Such degradation in device performance is attributed to the incorporation of oxygen and water molecules in devices. An increase in the recombination resistance indicates a deterioration of free charge carrier generation and conduction in devices.

  11. Solution-grown organic single-crystalline donor-acceptor heterojunctions for photovoltaics.

    PubMed

    Li, Hanying; Fan, Congcheng; Fu, Weifei; Xin, Huolin L; Chen, Hongzheng

    2015-01-12

    Organic single crystals are ideal candidates for high-performance photovoltaics due to their high charge mobility and long exciton diffusion length; however, they have not been largely considered for photovoltaics due to the practical difficulty in making a heterojunction between donor and acceptor single crystals. Here, we demonstrate that extended single-crystalline heterojunctions with a consistent donor-top and acceptor-bottom structure throughout the substrate can be simply obtained from a mixed solution of C60 (acceptor) and 3,6-bis(5-(4-n-butylphenyl)thiophene-2-yl)-2,5-bis(2-ethylhexyl)pyrrolo[3,4-c]pyrrole-1,4-dione (donor). 46 photovoltaic devices were studied with the power conversion efficiency of (0.255±0.095)% under 1 sun, which is significantly higher than the previously reported value for a vapor-grown organic single-crystalline donor-acceptor heterojunction (0.007%). As such, this work opens a practical avenue for the study of organic photovoltaics based on single crystals.

  12. Multiple Charge Transfer States at Ordered and Disordered Donor/Acceptor Interfaces

    NASA Astrophysics Data System (ADS)

    Fusella, Michael; Verreet, Bregt; Lin, Yunhui; Brigeman, Alyssa; Purdum, Geoffrey; Loo, Yueh-Lin; Giebink, Noel; Rand, Barry

    The presence of charge transfer (CT) states in organic solar cells is accepted, but their role in photocurrent generation is not well understood. Here we investigate solar cells based on rubrene and C60 to show that CT state properties are influenced by molecular ordering at the donor/acceptor (D/A) interface. Crystalline rubrene films are produced with domains of 100s of microns adopting the orthorhombic phase, as confirmed by grazing incidence XRD, with the (h00) planes parallel to the substrate. C60 grown atop these films adopts a highly oriented face-centered cubic phase with the (111) plane parallel to the substrate. For this highly ordered system we have discovered the presence of four CT states. Polarized external quantum efficiency (EQE) measurements assign three of these to crystalline origins with the remaining one well aligned with the disordered CT state. Varying the thickness of a disordered blend of rubrene:C60 atop the rubrene template modulates the degree of crystallinity at the D/A interface. Strikingly, this process alters the prominence of the four CT states measured via EQE, and results in a transition from single to multiple electroluminescence peaks. These results underscore the impact of molecular structure at the heterojunction on charge photogeneration.

  13. High-Resolution Kelvin Probe Force Microscopy Imaging of Interface Dipoles and Photogenerated Charges in Organic Donor-Acceptor Photovoltaic Blends.

    PubMed

    Fuchs, Franz; Caffy, Florent; Demadrille, Renaud; Mélin, Thierry; Grévin, Benjamin

    2016-01-26

    We present noncontact atomic force microscopy and Kelvin probe force microscopy studies of nanophase segregated photovoltaic blends based on an oligothiophene-fluorenone oligomer and [6,6]-phenyl C70 butyric acid methyl ester. We carried out a complete analysis of the influence of the tip-surface interaction regime on the topographic, in-dark contact potential and surface photovoltage contrasts. It is demonstrated that an optimal lateral resolution is achieved for all channels below the onset of a contrast in the damping images. With the support of electrostatic simulations, it is shown that in-dark contact potential difference contrasts above subsurface acceptor clusters are consistent with an uneven distribution of permanent charges at the donor-acceptor interfaces. A remarkable dependence of the surface photovoltage magnitude with respect to the tip-surface distance is evidenced and attributed to a local enhancement of the electromagnetic field at the tip apex.

  14. Contrasting performance of donor-acceptor copolymer pairs in ternary blend solar cells and two-acceptor copolymers in binary blend solar cells.

    PubMed

    Khlyabich, Petr P; Rudenko, Andrey E; Burkhart, Beate; Thompson, Barry C

    2015-02-01

    Here two contrasting approaches to polymer-fullerene solar cells are compared. In the first approach, two distinct semi-random donor-acceptor copolymers are blended with phenyl-C61-butyric acid methyl ester (PC61BM) to form ternary blend solar cells. The two poly(3-hexylthiophene)-based polymers contain either the acceptor thienopyrroledione (TPD) or diketopyrrolopyrrole (DPP). In the second approach, semi-random donor-acceptor copolymers containing both TPD and DPP acceptors in the same polymer backbone, termed two-acceptor polymers, are blended with PC61BM to give binary blend solar cells. The two approaches result in bulk heterojunction solar cells that have the same molecular active-layer components but differ in the manner in which these molecular components are mixed, either by physical mixing (ternary blend) or chemical "mixing" in the two-acceptor (binary blend) case. Optical properties and photon-to-electron conversion efficiencies of the binary and ternary blends were found to have similar features and were described as a linear combination of the individual components. At the same time, significant differences were observed in the open-circuit voltage (Voc) behaviors of binary and ternary blend solar cells. While in case of two-acceptor polymers, the Voc was found to be in the range of 0.495-0.552 V, ternary blend solar cells showed behavior inherent to organic alloy formation, displaying an intermediate, composition-dependent and tunable Voc in the range from 0.582 to 0.684 V, significantly exceeding the values achieved in the two-acceptor containing binary blend solar cells. Despite the differences between the physical and chemical mixing approaches, both pathways provided solar cells with similar power conversion efficiencies, highlighting the advantages of both pathways toward highly efficient organic solar cells.

  15. Boron(III)-Containing Donor-Acceptor Compound with Goldlike Reflective Behavior for Organic Resistive Memory Devices.

    PubMed

    Poon, Chun-Ting; Wu, Di; Yam, Vivian Wing-Wah

    2016-03-01

    A small-molecule-based boron(III)-containing donor-acceptor compound has been designed and synthesized. Interesting goldlike reflective behavior was observed in the neat thin-film sample from simple spin-coating preparation, which can serve as a potential organic thin-film optical reflector. The small thickness in nanometer range and the relatively smooth surface morphology, together with simple preparation and easy solution processability, are attractive features for opening up new avenues for the fabrication of reflective coatings. Moreover, this donor-acceptor compound has been employed in the fabrication of organic resistive memory device, which exhibited good performance with low turn-on voltage, small operating bias, large ON/OFF ratio, and long retention time. PMID:26879606

  16. Theoretical design of solvatochromism switching by photochromic reactions using donor-acceptor disubstituted diarylethene derivatives with oxidized thiophene rings.

    PubMed

    Okuno, Katsuki; Shigeta, Yasuteru; Kishi, Ryohei; Nakano, Masayoshi

    2015-03-01

    We have designed several diarylethene derivatives with oxidized thiophene rings and donor-acceptor substituents, which show the solvatochromism switching by photochromic reactions, using a time-dependent density functional theory (TD-DFT) method using the polarizable continuum model (PCM). It is found that in the UV-vis spectral region examined only the open-ring isomers exhibit the solvatochromism, while the closed-ring isomers do not. The mechanism of the solvatochromism behavior and its switching process are clarified from the viewpoint of the charge-transfer (CT) excitation from the donor to the acceptor substituents. We demonstrate that this CT excitation can be controlled by choosing appropriate pairs of the donor and the acceptor substituents on the basis of the orbital correlation diagram between the diarylethene derivatives and the donor-acceptor substituents, which is constructed from the topologies and the orbital energies of the molecular orbitals primarily contributing to the excitations.

  17. [3 + 3]-Cycloaddition of Donor-Acceptor Cyclopropanes with Nitrile Imines Generated in Situ: Access to Tetrahydropyridazines.

    PubMed

    Garve, Lennart K B; Petzold, Martin; Jones, Peter G; Werz, Daniel B

    2016-02-01

    Donor-acceptor cyclopropanes are reacted under the influence of a Lewis acid with hydrazonyl chlorides to afford tetrahydropyridazines. Formally, this transformation can be regarded as a [3 + 3]-cycloaddition of three-membered rings and nitrile imines generated in situ. This efficient method provides fast access to a variety of structurally diverse pyridazine derivatives. The structure of a typical product was confirmed by X-ray crystallography.

  18. Donor/Acceptor Molecular Orientation-Dependent Photovoltaic Performance in All-Polymer Solar Cells.

    PubMed

    Zhou, Ke; Zhang, Rui; Liu, Jiangang; Li, Mingguang; Yu, Xinhong; Xing, Rubo; Han, Yanchun

    2015-11-18

    The correlated donor/acceptor (D/A) molecular orientation plays a crucial role in solution-processed all-polymer solar cells in term of photovoltaic performance. For the conjugated polymers PTB7-th and P(NDI2OD-T2), the preferential molecular orientation of neat PTB7-th films kept face-on regardless of the properties of processing solvents. However, an increasing content of face-on molecular orientation in the neat P(NDI2OD-T2) films could be found by changing processing solvents from chloronaphthalene (CN) and o-dichlorobenzene (oDCB) to chlorobenzene (CB). Besides, the neat P(NDI2OD-T2) films also exhibited a transformation of preferential molecular orientation from face-on to edge-on when extending film drying time by casting in the same solution. Consequently, a distribution diagram of molecular orientation for P(NDI2OD-T2) films was depicted and the same trend could be observed for the PTB7-th/P(NDI2OD-T2) blend films. By manufacture of photovoltaic devices with blend films, the relationship between the correlated D/A molecular orientation and device performance was established. The short-circuit current (Jsc) of devices processed by CN, oDCB, and CB enhanced gradually from 1.24 to 8.86 mA/cm(2) with the correlated D/A molecular orientation changing from face-on/edge-on to face-on/face-on, which could be attributed to facile exciton dissociation at D/A interface with the same molecular orientation. Therefore, the power conversion efficiency (PCE) of devices processed by CN, oDCB, and CB improved from 0.53% to 3.52% ultimately.

  19. π-conjugated donor-acceptor porphyrin copolymers for organic photovoltaics

    NASA Astrophysics Data System (ADS)

    Peng, Xiaobin; Huang, Yuying; Li, Lisheng; Cao, Yong

    2015-01-01

    Conjugated donor-acceptor (D-A) molecular structures play a very important role in the significant progress of organic photovotaics. However, the reports on conjugated D-A porphyrin polymers for organic solar cells are very limited. In this work, five conjugated D-A porphyrin copolymers PEZPEBTA(C12), PEZPEBT, PEZPEBTff, PEZPETPD(O), and PEZPETDPPT(O) were synthesized by Sonagashira coupling of a porphyrin donor unit with five typical acceptor units 2-dodecyl-2H-benzotriazole, benzo[1,2,5]thiadiazole, 5,6-difluoro-benzo[1,2,5]thiadiazole, 5-octyl-thieno[3,4-c]pyrrole-4,6-dione, and 3,6-bis-(thiophen-2-yl)-2,5-dioctyl-2,5-dihydro-pyrrolo[3,4-c]pyrrole-1,4-dione linked by ethynylene linkages, respectively. They possess excellent thermal stability with a decomposition temperature of around 400°C. All absorption spectra of the copolymers were significantly red shifted with enhanced Q bands at the near-infrared region both in solutions and in films due to the simultaneous introduction of ethynylene linkages and acceptor units, which make the polymer main chains coplanar and π-conjugated and enhance the intramolecular charge transfer. PEZPEBT and PEZPEBTff are electrochemically active in both the oxidation and reduction regions, while PEZPEBTA(C12), PEZPETPD(O), and PEZPETDPPT(O) show only oxidation peaks. Power conversion efficiencies of 0.12%, 0.41%, 0.26%, 0.19%, and 0.41% were achieved for the polymer solar cells based on PEZPEBTA(C12), PEZPEBT, PEZPEBTff, PEZPETPD(O), and PEZPETDPPT(O), respectively, under AM 1.5, 100 mW/cm2 with methanofullerene [6,6]-phenyl C61-butyric acid methyl ester (PC61BM) (1:2, w/w) as the active layer in the presence of 3% pyridine.

  20. One pot/two donors/one diol give one differentiated trisaccharide: powerful evidence for reciprocal donor-acceptor selectivity (RDAS).

    PubMed

    Fraser-Reid, Bert; López, J Cristóbal; Radhakrishnan, K V; Nandakumar, M V; Gómez, Ana M; Uriel, Clara

    2002-09-21

    Three component, one-pot reactions involving equimolar amounts of the acceptor diol and both armed and disarmed donors presented simultaneously, produce a single double-differential glycosidation product; this phenomenon provides evidence for Reciprocal Donor Acceptor Selectivity (RDAS).

  1. Blinking fluorescence of single donor-acceptor pairs: important role of "dark'' states in resonance energy transfer via singlet levels.

    PubMed

    Osad'ko, I S; Shchukina, A L

    2012-06-01

    The influence of triplet levels on Förster resonance energy transfer via singlet levels in donor-acceptor (D-A) pairs is studied. Four types of D-A pair are considered: (i) two-level donor and two-level acceptor, (ii) three-level donor and two-level acceptor, (iii) two-level donor and three-level acceptor, and (iv) three-level donor and three-level acceptor. If singlet-triplet transitions in a three-level acceptor molecule are ineffective, the energy transfer efficiency E=I_{A}/(I_{A}+I_{D}), where I_{D} and I_{A} are the average intensities of donor and acceptor fluorescence, can be described by the simple theoretical equation E(F)=FT_{D}/(1+FT_{D}). Here F is the rate of energy transfer, and T_{D} is the donor fluorescence lifetime. In accordance with the last equation, 100% of the donor electronic energy can be transferred to an acceptor molecule at FT_{D}≫1. However, if singlet-triplet transitions in a three-level acceptor molecule are effective, the energy transfer efficiency is described by another theoretical equation, E(F)=F[over ¯](F)T_{D}/[1+F[over ¯](F)T_{D}]. Here F[over ¯](F) is a function of F depending on singlet-triplet transitions in both donor and acceptor molecules. Expressions for the functions F[over ¯](F) are derived. In this case the energy transfer efficiency will be far from 100% even at FT_{D}≫1. The character of the intensity fluctuations of donor and acceptor fluorescence indicates which of the two equations for E(F) should be used to find the value of the rate F. Therefore, random time instants of photon emission in both donor and acceptor fluorescence are calculated by the Monte Carlo method for all four types of D-A pair. Theoretical expressions for start-stop correlators (waiting time distributions) in donor and acceptor fluorescence are derived. The probabilities w_{N}^{D}(t) and w_{N}^{A}(t) of finding N photons of donor and acceptor fluorescence in the time interval t are calculated for various values of the energy

  2. Theoretical Investigation of Donor-Acceptor Copolymers Based on C-, Si-, and Ge-Bridged Thieno[3,2-b]dithiophene for Organic Solar Cell Applications

    NASA Astrophysics Data System (ADS)

    Liu, Xiaorui; Huang, Chengzhi; Shen, Wei; He, Rongxing; Li, Ming

    2016-06-01

    The aim of this work is to modify the electron-donating block in donor-acceptor (D-A) copolymers to improve their electronic and photophysical properties for organic solar cell (OSC) applications. Based on the reported polymer PCPDTTTTz (Pa1), which includes electron-rich cyclopenta[2,1-b:3,4-b']dithiophene (CPDT), electron-withdrawing tetrazine, and bridge thiophene, we substituted CPDT with electron-rich dithienocyclopentadithiophene, dithienosiloledithiophene, and dithienogermolodithiophene to design three D-A copolymers (Pa2 to Pa4). The calculation results indicate that Pa3 and Pa4 show lower highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO) energy levels and larger open-circuit voltage (V oc) than Pa1. Polymers Pa2 to Pa4 exhibit better performance with stronger and wider optical absorption and good hole transport properties in comparison with Pa1. The predicted power conversion efficiencies for the designed polymers Pa2 to Pa4 in OSC applications are ˜5.7%, ˜5.9%, and 6.0%, respectively. These results clearly indicate that modifying the electron-donating block in D-A copolymers can effectively improve their electronic and photophysical properties and OSC performance. The designed polymers Pa2 to Pa4 may be promising donor candidates for OSC applications.

  3. Theoretical Investigation of Donor-Acceptor Copolymers Based on C-, Si-, and Ge-Bridged Thieno[3,2- b]dithiophene for Organic Solar Cell Applications

    NASA Astrophysics Data System (ADS)

    Liu, Xiaorui; Huang, Chengzhi; Shen, Wei; He, Rongxing; Li, Ming

    2016-10-01

    The aim of this work is to modify the electron-donating block in donor-acceptor (D-A) copolymers to improve their electronic and photophysical properties for organic solar cell (OSC) applications. Based on the reported polymer PCPDTTTTz (Pa1), which includes electron-rich cyclopenta[2,1- b:3,4- b']dithiophene (CPDT), electron-withdrawing tetrazine, and bridge thiophene, we substituted CPDT with electron-rich dithienocyclopentadithiophene, dithienosiloledithiophene, and dithienogermolodithiophene to design three D-A copolymers (Pa2 to Pa4). The calculation results indicate that Pa3 and Pa4 show lower highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO) energy levels and larger open-circuit voltage ( V oc) than Pa1. Polymers Pa2 to Pa4 exhibit better performance with stronger and wider optical absorption and good hole transport properties in comparison with Pa1. The predicted power conversion efficiencies for the designed polymers Pa2 to Pa4 in OSC applications are ˜5.7%, ˜5.9%, and 6.0%, respectively. These results clearly indicate that modifying the electron-donating block in D-A copolymers can effectively improve their electronic and photophysical properties and OSC performance. The designed polymers Pa2 to Pa4 may be promising donor candidates for OSC applications.

  4. Tuning the opto-electronic properties of donor-acceptor polymers with molecular doping

    NASA Astrophysics Data System (ADS)

    von Hauff, Elizabeth

    2015-03-01

    Organic semiconductors offer vast potential for low cost, flexible energy production. The photocurrents in organic solar cells, however, are inherently limited by the poor electrical properties of the active layer. In this talk, strategies to increase the power conversion efficiency of polymer:fullerene solar cells by microscopically tuning the transport properties of the donor material are discussed. We observe that molecular doping the active layer of the device leads to increased charge separation efficiency and photocurrents. To investigate the influence of doping on the transport properties, impedance spectroscopy, a powerful, non-destructive technique, was applied. This allows us to probe carrier dynamics at different operational points in the current-voltage characteristics, and thereby correlate material properties with device performance.

  5. Polyimide dendrimers containing multiple electron donor-acceptor units and their unique photophysical properties.

    PubMed

    Toma, Francesca M; Puntoriero, Fausto; Pho, Toan V; La Rosa, Marcello; Jun, Young-Si; Tremolet de Villers, Bertrand J; Pavlovich, James; Stucky, Galen D; Campagna, Sebastiano; Wudl, Fred

    2015-06-01

    A high-yielding synthesis of a series of polyimide dendrimers, including decacyclene- and perylene-containing dendrimer D6, in which two types of polyimide dyes are present, is reported. In these constructs, the branching unit is represented by trisphenylamine, and the solubilizing chains by N-9-heptadecanyl-substituted perylene diimides. The photophysical properties of the dendrimers have been studied by absorption, steady-state, and time-resolved emission spectroscopy and pump-probe transient absorption spectroscopy. Photoinduced charge-separated (CS) states are formed on the femtosecond timescale upon visible excitation. In particular, in D6, two different CS states can be formed, involving different subunits that decays independently with different lifetimes (ca. 10-100 ps).

  6. Photoinduced interfacial electron transfer and lateral charge transport in molecular donor-acceptor photovoltaic systems.

    PubMed

    Punzi, Angela; Brauer, Jan C; Marchioro, Arianna; Ghadiri, Elham; de Jonghe, Jelissa; Moser, Jacques E

    2011-01-01

    Nanostructured liquid/solid and solid/solid bulk heterojunctions designed for the conversion of solar energy offer ideal models for the investigation of light-induced ET dynamics at surfaces. Despite significant study of processes leading to charge generation in third-generation solar cells, a conclusive picture of the photophysics of these photovoltaic converters is still missing. More specifically searched is the link between the molecular structure of the interface and the kinetics of surface photoredox reactions. Fundamental scientific issues in this field are addressed by the research project undertaken in the frame of the NCCR MUST endeavor, an outline of which is given here.

  7. A benzothiadiazole end capped donor-acceptor based small molecule for organic electronics.

    PubMed

    Sonar, Prashant; Williams, Evan L; Singh, Samarendra P; Manzhos, Sergei; Dodabalapur, Ananth

    2013-10-28

    A benzothiadiazole end-capped small molecule 3,6-bis(5-(benzo-[c][1,2,5]thiadiazol-4-yl)thiophen-2-yl)-2,5-bis(2-butyloctyl)pyrrolo-[3,4-c]pyrrole-1,4(2H,5H)-dione (BO-DPP-BTZ) using a fused aromatic moiety DPP (at the centre) is designed and synthesized. BO-DPP-BTZ is a donor–acceptor–donor (D–A–D) structure which possesses a band gap of 1.6 eV and exhibits a strong solid state ordering inferred from ~120 nm red shift of the absorption maxima from solution to thin film. Field-effect transistors utilizing a spin coated thin film of BO-DPP-BTZ as an active layer exhibited a hole mobility of 0.06 cm(2) V(-1) s(-1). Solution-processed bulk heterojunction organic photovoltaics employing a blend of BO-DPP-BTZ and [70]PCBM demonstrated a power conversion efficiency of 0.9%.

  8. Creation of Superheterojunction Polymers via Direct Polycondensation: Segregated and Bicontinuous Donor-Acceptor π-Columnar Arrays in Covalent Organic Frameworks for Long-Lived Charge Separation.

    PubMed

    Jin, Shangbin; Supur, Mustafa; Addicoat, Matthew; Furukawa, Ko; Chen, Long; Nakamura, Toshikazu; Fukuzumi, Shunichi; Irle, Stephan; Jiang, Donglin

    2015-06-24

    By developing metallophthalocyanines and diimides as electron-donating and -accepting building blocks, herein, we report the construction of new electron donor-acceptor covalent organic frameworks (COFs) with periodically ordered electron donor and acceptor π-columnar arrays via direct polycondensation reactions. X-ray diffraction measurements in conjunction with structural simulations resolved that the resulting frameworks consist of metallophthalocyanine and diimide columns, which are ordered in a segregated yet bicontinuous manner to form built-in periodic π-arrays. In the frameworks, each metallophthalocyanine donor and diimide acceptor units are exactly linked and interfaced, leading to the generation of superheterojunctions-a new type of heterojunction machinery, for photoinduced electron transfer and charge separation. We show that this polycondensation method is widely applicable to various metallophthalocyanines and diimides as demonstrated by the combination of copper, nickel, and zinc phthalocyanine donors with pyrommellitic diimide, naphthalene diimide, and perylene diimide acceptors. By using time-resolved transient absorption spectroscopy and electron spin resonance, we demonstrated that the COFs enable long-lived charge separation, whereas the metal species, the class of acceptors, and the local geometry between donor and acceptor units play roles in determining the photochemical dynamics. The results provide insights into photoelectric COFs and demonstrate their enormous potential for charge separation and photoenergy conversions. PMID:26030399

  9. Creation of Superheterojunction Polymers via Direct Polycondensation: Segregated and Bicontinuous Donor-Acceptor π-Columnar Arrays in Covalent Organic Frameworks for Long-Lived Charge Separation.

    PubMed

    Jin, Shangbin; Supur, Mustafa; Addicoat, Matthew; Furukawa, Ko; Chen, Long; Nakamura, Toshikazu; Fukuzumi, Shunichi; Irle, Stephan; Jiang, Donglin

    2015-06-24

    By developing metallophthalocyanines and diimides as electron-donating and -accepting building blocks, herein, we report the construction of new electron donor-acceptor covalent organic frameworks (COFs) with periodically ordered electron donor and acceptor π-columnar arrays via direct polycondensation reactions. X-ray diffraction measurements in conjunction with structural simulations resolved that the resulting frameworks consist of metallophthalocyanine and diimide columns, which are ordered in a segregated yet bicontinuous manner to form built-in periodic π-arrays. In the frameworks, each metallophthalocyanine donor and diimide acceptor units are exactly linked and interfaced, leading to the generation of superheterojunctions-a new type of heterojunction machinery, for photoinduced electron transfer and charge separation. We show that this polycondensation method is widely applicable to various metallophthalocyanines and diimides as demonstrated by the combination of copper, nickel, and zinc phthalocyanine donors with pyrommellitic diimide, naphthalene diimide, and perylene diimide acceptors. By using time-resolved transient absorption spectroscopy and electron spin resonance, we demonstrated that the COFs enable long-lived charge separation, whereas the metal species, the class of acceptors, and the local geometry between donor and acceptor units play roles in determining the photochemical dynamics. The results provide insights into photoelectric COFs and demonstrate their enormous potential for charge separation and photoenergy conversions.

  10. The effect of intermolecular donor?acceptor energy transfer on emission anisotropy in uniaxially oriented polymer films

    NASA Astrophysics Data System (ADS)

    Sadownik, M.; Bojarski, Piotr

    2004-10-01

    Excitation energy transport between donors and acceptors is studied for uniaxially stretched and unstretched poly(vinyl) alcohol films. Donor emission anisotropy courses versus acceptor concentration as well as donor-acceptor emission anisotropy spectra occurred quite different in stretched and unstretched films. Upon donor excitation the total emission anisotropy rapidly decreases when passing from the donor to the acceptor fluorescence band in disordered systems. However, such a pronounced effect has not been found in partly ordered films. Donors and acceptors exhibit highly preferential mutual orientation in strongly ordered films resulting in the preservation of acceptor emission anisotropy.

  11. Synthesis and characterization of unsymmetrical disubstituted ferrocenes possessing hydroxyl group as a new donor/acceptor of hydrogen bond

    NASA Astrophysics Data System (ADS)

    Lapić, Jasmina; Pezerović, Alma; Cetina, Mario; Djaković, Senka; Rapić, Vladimir

    2011-03-01

    The preparation and characterization of heteroannularly disubstituted ferrocene derivatives 2- 8 are described, with a special attention given on the conformation and hydrogen-bonding of compounds 3b, 7a and 8a. Compounds 3 and 8 comprise hydroxyl group as a new hydrogen bond donor/acceptor and are precursors for preparation of organometallics in asymmetric bioconjugates with natural amino acids. Newly prepared compounds are characterized by elemental analysis, FTIR and NMR spectroscopy. The structures of compounds 1, 3b and 6a were also confirmed by X-ray crystal structure analysis.

  12. Calcium-Catalyzed, Dehydrative, Ring-Opening Cyclizations of Cyclopropyl Carbinols Derived from Donor-Acceptor Cyclopropanes.

    PubMed

    Sandridge, Matthew J; France, Stefan

    2016-09-01

    A calcium-catalyzed, dehydrative, ring-opening cyclization of (hetero)aryl cyclopropyl carbinols is reported. The cyclopropyl carbinols are prepared directly from the corresponding donor-acceptor (D-A) cyclopropanes. The calcium catalyst catalyzes the formation of putative (hetero)aryl cyclopropyl carbinyl cations that undergo ring-opening to allylcarbinyl cations. Subsequent intramolecular Friedel-Crafts reaction affords (hetero)aryl-fused cyclohexa-1,3-dienes in up to 97% yield. This approach represents the first example of catalysis for this intramolecular, dehydrative ring-opening cyclization and outperforms the previous reports using stoichiometric Lewis acids. PMID:27517711

  13. Thiophene-based donor-acceptor co-oligomers by copper-catalyzed 1,3-dipolar cycloaddition.

    PubMed

    Potratz, Stefanie; Mishra, Amaresh; Bäuerle, Peter

    2012-01-01

    Herein we present a three-component one-pot procedure to synthesize co-oligomers of a donor-acceptor-donor type, in which thiophene moieties work as donor and 1,2,3-triazoles as acceptor units. In this respect, terminally ethynylated (oligo)thiophenes were coupled to halogenated (oligo)thiophenes in the presence of sodium azide and a copper catalyst. Optoelectronic properties of various thiophene-1,2,3-triazole co-oligomers were investigated by UV-vis spectroscopy and cyclic voltammetry. Several co-oligomers were electropolymerized to the corresponding conjugated polymers. PMID:23015814

  14. 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.

  15. Theoretical investigation of self-assembled donor-acceptor phthalocyanine complexes and their application in dye-sensitized solar cells.

    PubMed

    Yu, Lijuan; Lin, Li; Liu, Yuwen; Li, Renjie

    2015-06-01

    A theoretical investigation of self-assembled donor-acceptor dyads (ZnPca, ZnPcb and ZnPcc) formed by axial coordination of zinc phthalocyanines appended with 4-carboxyl pyridine has been conducted with the density functional theory (DFT) method and time-dependent DFT (TD-DFT) calculations. A comparison between the molecular structures, atomic charges, molecular orbitals, UV-vis spectra and infrared (IR) spectra has been studied. Further, as sensitizers for the TiO2-based dye-sensitized solar cells, the photovoltaic performances have been investigated. The ZnPcc-sensitized solar cell exhibits a higher conversion efficiency than the ZnPcb and ZnPca-sensitized ones under AM 1.5G solar irradiation, while the ZnPca-sensitized cell performs the poorest due to the lack of peripheral substituents (n-butyoxyl groups) which can be confirmed by the result of the theoretical research. It shows that the directionality of charge transfer in the self-assembled donor-acceptor dyads is important and benefit for the efficiency of the DSSC.

  16. Charge transport studies in donor-acceptor block copolymer PDPP-TNT and PC71BM based inverted organic photovoltaic devices processed in room conditions

    NASA Astrophysics Data System (ADS)

    Srivastava, Shashi B.; Sonar, Prashant; Singh, Samarendra P.

    2015-07-01

    Diketopyrrolopyrole-naphthalene polymer (PDPP-TNT), a donor-acceptor co-polymer, has shown versatile behavior demonstrating high performances in organic field-effect transistors (OFETs) and organic photovoltaic (OPV) devices. In this paper we report investigation of charge carrier dynamics in PDPP-TNT, and [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) bulk-heterojunction based inverted OPV devices using current density-voltage (J-V) characteristics, space charge limited current (SCLC) measurements, capacitance-voltage (C-V) characteristics, and impedance spectroscopy (IS). OPV devices in inverted architecture, ITO/ZnO/PDPP-TNT:PC71BM/MoO3/Ag, are processed and characterized at room conditions. The power conversion efficiency (PCE) of these devices are measured ˜3.8%, with reasonably good fill-factor 54.6%. The analysis of impedance spectra exhibits electron's mobility ˜2 × 10-3 cm2V-1s-1, and lifetime in the range of 0.03-0.23 ms. SCLC measurements give hole mobility of 1.12 × 10-5 cm2V-1s-1, and electron mobility of 8.7 × 10-4 cm2V-1s-1.

  17. Charge transport studies in donor-acceptor block copolymer PDPP-TNT and PC71BM based inverted organic photovoltaic devices processed in room conditions

    SciTech Connect

    Srivastava, Shashi B.; Singh, Samarendra P.; Sonar, Prashant

    2015-07-15

    Diketopyrrolopyrole-naphthalene polymer (PDPP-TNT), a donor-acceptor co-polymer, has shown versatile behavior demonstrating high performances in organic field-effect transistors (OFETs) and organic photovoltaic (OPV) devices. In this paper we report investigation of charge carrier dynamics in PDPP-TNT, and [6,6]-phenyl C{sub 71} butyric acid methyl ester (PC71BM) bulk-heterojunction based inverted OPV devices using current density-voltage (J-V) characteristics, space charge limited current (SCLC) measurements, capacitance-voltage (C-V) characteristics, and impedance spectroscopy (IS). OPV devices in inverted architecture, ITO/ZnO/PDPP-TNT:PC71BM/MoO{sub 3}/Ag, are processed and characterized at room conditions. The power conversion efficiency (PCE) of these devices are measured ∼3.8%, with reasonably good fill-factor 54.6%. The analysis of impedance spectra exhibits electron’s mobility ∼2 × 10{sup −3} cm{sup 2}V{sup −1}s{sup −1}, and lifetime in the range of 0.03-0.23 ms. SCLC measurements give hole mobility of 1.12 × 10{sup −5} cm{sup 2}V{sup −1}s{sup −1}, and electron mobility of 8.7 × 10{sup −4} cm{sup 2}V{sup −1}s{sup −1}.

  18. Donor/Acceptor Dihydroindeno[1,2-a]fluorene and Dihydroindeno[2,1-b]fluorene: Towards New Families of Organic Semiconductors.

    PubMed

    Romain, Maxime; Tondelier, Denis; Geffroy, Bernard; Jeannin, Olivier; Jacques, Emmanuel; Rault-Berthelot, Joëlle; Poriel, Cyril

    2015-06-22

    New families of donor/acceptor semiconductors based on dihydroindeno[1,2-a]fluorene and dihydroindeno[2,1-b]fluorene are reported. Due to the spiro bridges, this new generation of dihydroindenofluorenes allows a spatial separation of HOMO and LUMO, which retains the high ET value of the dihydroindenofluorene backbone and excellent physical properties. This control of the electronic and physical properties has allowed a second generation of dihydroindeno[1,2-a]fluorene to be obtained with strongly enhanced performance in green and sky-blue phosphorescent organic light-emitting diodes (PhOLEDs) relative to the first generation of materials. To date, this is the highest performance ever reported for a blue PhOLED by using a dihydroindenofluorene derivative. Through this structure-property relationship study, a remarkable difference of performance between syn and anti isomers has also been highlighted. This surprising behaviour has been attributed to the different symmetry of the two molecules, and highlights the importance of the geometry profiles in the design of host materials for PhOLEDs. PMID:26012479

  19. The Dependence of Donor:Acceptor Ratio on the Photovoltaic Performances of Blended poly (3-octylthiophene-2,5-diyl) and (6,6)-phenyl C{sub 71} butyric acid methyl ester Bulk Heterojunction Organic Solar Cells

    SciTech Connect

    Fauzia, Vivi; Umar, Akrajas Ali; Salleh, Muhamad Mat; Yahya, Muhammad

    2010-10-24

    Bulk heterojunction organic solar cells using blended poly (3-octylthiophene-2,5-diyl)(P3OT) and (6,6)-phenyl C{sub 71} butyric acid methyl ester (PC{sub 71}BM) have been fabricated. P3OT and PC{sub 71}BM were used as the electron donor (D) and acceptor (A), respectively. Both materials were mixed and dissolved in dichlorobenzene with three different D:A ratios i.e. 1:3, 1:1 and 3:1 (weight) while maintained at the concentration of 2 wt%(26 mg/ml). The blended thin films were sandwiched between the indium tin oxide (ITO) coated glass and the aluminum film. This paper reports the influence of donor:acceptor ratio on the performance of solar cell devices measured by current-voltage measurement both in the dark and under 1.5 AM solar illumination. It was found that all devices showed the photovoltaic effect with poor diode behavior and the donor:acceptor ratio significantly influenced on the performance of bulk heterojunction organic solar cells.

  20. Photoconductive and supramolecularly engineered organic field-effect transistors based on fibres from donor-acceptor dyads.

    PubMed

    Treier, Matthias; Liscio, Andrea; Mativetsky, Jeffrey M; Kastler, Marcel; Müllen, Klaus; Palermo, Vincenzo; Samorì, Paolo

    2012-03-01

    We report on the formation of photoconductive self-assembled fibres by solvent induced precipitation of a HBC-PMI donor-acceptor dyad. Kelvin Probe Force Microscopy revealed that upon illumination with white light the surface potential of the fibres shifted to negative values due to a build-up of negative charge. When integrated in a field-effect transistor (FET) configuration, the devices can be turned 'on' much more efficiently using light than conventional bias triggered field-effect, suggesting that these structures could be used for the fabrication of light sensing devices. Such a double gating represents an important step towards bi-functional organic FETs, in which the current through the junction can be modulated both optically (by photoexcitation) and electrically (by gate control).

  1. Trimethylsilane-containing donor-acceptor-donor type material for red fluorescent organic light-emitting diodes.

    PubMed

    Lee, Kum Hee; Kim, Young Kwan; Yoon, Seung Soo

    2012-05-01

    In this paper, we described a donor-acceptor-donor type red fluorescence material, which have the bulky trimethylsilane groups in the donor moieties. To explore the electroluminescence properties of these materials, multilayered OLEDs were fabricated with a device structure of ITO/2-TNATA (60 nm)/NPB (40 nm)/Red 1 (2%):rubrene (50%):Alq3 (30 nm)/Alq3 (60 nm)/Liq (3 nm)/Al (100 nm). A device using Red 1 as the dopant material showed a maximum luminance of 5138 cd/m2 at 12.0 V, maximum luminous efficiencies of 1.62 cd/A, and maximum power efficiencies of 1.04 lm/W. The Commission Internationale de L'Eclairage coordinates of this device was (0.67, 0.33) at 7.0 V, which indicated stable color chromaticity at various voltages. PMID:22852373

  2. Donor-acceptor pair recombination luminescence from monoclinic Cu{sub 2}SnS{sub 3} thin film

    SciTech Connect

    Aihara, Naoya; Tanaka, Kunihiko Uchiki, Hisao; Kanai, Ayaka; Araki, Hideaki

    2015-07-20

    The defect levels in Cu{sub 2}SnS{sub 3} (CTS) were investigated using photoluminescence (PL) spectroscopy. A CTS thin film was prepared on a soda-lime glass/molybdenum substrate by thermal co-evaporation and sulfurization. The crystal structure was determined to be monoclinic, and the compositional ratios of Cu/Sn and S/Metal were determined to be 1.8 and 1.2, respectively. The photon energy of the PL spectra observed from the CTS thin film was lower than that previously reported. All fitted PL peaks were associated with defect related luminescence. The PL peaks observed at 0.843 and 0.867 eV were assigned to donor-acceptor pair recombination luminescence, the thermal activation energies of which were determined to be 22.9 and 24.8 meV, respectively.

  3. Self-Enhanced Ultrasensitive Photoelectrochemical Biosensor Based on Nanocapsule Packaging Both Donor-Acceptor-Type Photoactive Material and Its Sensitizer.

    PubMed

    Zheng, Ying-Ning; Liang, Wen-Bin; Xiong, Cheng-Yi; Yuan, Ya-Li; Chai, Ya-Qin; Yuan, Ruo

    2016-09-01

    In this work, a self-enhanced ultrasensitive photoelectrochemical (PEC) biosensor was established based on a functionalized nanocapsule packaging both donor-acceptor-type photoactive material and its sensitizer. The functionalized nanocapsule with self-enhanced PEC responses was achieved first by packaging both the donor-acceptor-type photoactive material (poly{4,8-bis[5-(2-ethylhexyl)thiophen-2-yl]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl-alt-3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophene-4,6-diyl}, PTB7-Th) and its sensitizer (nano-C60, fullerene) in poly(ethylene glycol) (PEG) to form a nanocapsule, which significantly enhanced PEC signal and stability of the PEC biosensor. Moreover, a quadratic enzymes-assisted target recycling amplification strategy was introduced to the system for ultrasensitive determination. Compared with other established PEC biosensors, our proposed self-enhanced approach showed higher effectivity, accuracy, sensitivity, and convenience without any addition of coreactant or sensitizers into the testing electrolyte for photocurrent amplification and performed excellent analytical properties for microRNA estimation down to femtomole level with microRNA-141 as a model. Additionally, the proposed PEC biosensor was employed for estimation of microRNA in different cancer cells and pharmacodynamic evaluation in cancer cells. This self-enhanced PEC strategy has laid the foundation for fabrication of simple, effective, and ultrasensitive PEC diagnostic devices, leading to the possibility for early diagnosis, timely stage estimation, and accurate prognosis judgment of disease. PMID:27513736

  4. Self-Enhanced Ultrasensitive Photoelectrochemical Biosensor Based on Nanocapsule Packaging Both Donor-Acceptor-Type Photoactive Material and Its Sensitizer.

    PubMed

    Zheng, Ying-Ning; Liang, Wen-Bin; Xiong, Cheng-Yi; Yuan, Ya-Li; Chai, Ya-Qin; Yuan, Ruo

    2016-09-01

    In this work, a self-enhanced ultrasensitive photoelectrochemical (PEC) biosensor was established based on a functionalized nanocapsule packaging both donor-acceptor-type photoactive material and its sensitizer. The functionalized nanocapsule with self-enhanced PEC responses was achieved first by packaging both the donor-acceptor-type photoactive material (poly{4,8-bis[5-(2-ethylhexyl)thiophen-2-yl]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl-alt-3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophene-4,6-diyl}, PTB7-Th) and its sensitizer (nano-C60, fullerene) in poly(ethylene glycol) (PEG) to form a nanocapsule, which significantly enhanced PEC signal and stability of the PEC biosensor. Moreover, a quadratic enzymes-assisted target recycling amplification strategy was introduced to the system for ultrasensitive determination. Compared with other established PEC biosensors, our proposed self-enhanced approach showed higher effectivity, accuracy, sensitivity, and convenience without any addition of coreactant or sensitizers into the testing electrolyte for photocurrent amplification and performed excellent analytical properties for microRNA estimation down to femtomole level with microRNA-141 as a model. Additionally, the proposed PEC biosensor was employed for estimation of microRNA in different cancer cells and pharmacodynamic evaluation in cancer cells. This self-enhanced PEC strategy has laid the foundation for fabrication of simple, effective, and ultrasensitive PEC diagnostic devices, leading to the possibility for early diagnosis, timely stage estimation, and accurate prognosis judgment of disease.

  5. Calculation of electron transfer in ruthenium-modified derivatives of cytochrome b562

    NASA Astrophysics Data System (ADS)

    Glukhova, O. E.; Prytkova, T. R.; Shunaev, V. V.

    2016-03-01

    Quantitative theoretical studies of long-range electron transfer are still quite rare and require further development of computational methods for the analysis of such reactions. We considered the electron transfer reaction in rutenium-modified derivatives of cytochrome b562 with advanced modeling techniques. We conducted a series of ab initio calculations of the donor/acceptor interaction in protein fragments and compared the calculated electron velocity with available experimental data. Our approach takes into account the co-factor of the electronic structure and the impact of the solution on a donor-acceptor interaction. This allows us to predict the absolute values of the electron transfer rate unlike other computational methods which provide only qualitative results. Our estimates with good accuracy repeat the experimental values of electron transfer rate. It was found that the electron transfer in certain derivatives of cytochrome b562 is mainly caused by "shortcut" conformations in which the donor/acceptor interactions are mediated by the interaction of Ru-unbound ligands with groups of the protein surface. We argue that a quantitative theoretical analysis is essential for detailed understanding of electron transfer in proteins and mechanisms of biological redox reactions.

  6. Mixed donor-acceptor charge-transfer stacks formed via hierarchical self-assembly of a non-covalent amphiphilic foldamer.

    PubMed

    Jalani, Krishnendu; Kumar, Mohit; George, Subi J

    2013-06-01

    A non-covalent, amphiphilic foldamer design leads to an efficient charge-transfer complex between dipyrene (donor) and naphthalene diimide (acceptor) derivatives, which further self-assembles into one-dimensional nanofibers with an alternate (mixed) donor-acceptor arrangement. PMID:23628867

  7. Frontier orbital symmetry control of intermolecular electron transfer

    SciTech Connect

    Stevens, B.

    1991-09-01

    This report contains sections describing the selection of electron donor-acceptor systems, the synthesis and photophysical properties of linked electron-donor-acceptor systems, the estimation of photoinduced charge-separation rate constants from fluorescence quenching data, and radical ion-pair recombination by picosecond transient absorption spectroscopy. 9 refs., 1 fig., 7 tabs.

  8. An Obvious Improvement in the Performance of Ternary Organic Solar Cells with "Guest" Donor Present at the "Host" Donor/Acceptor Interface.

    PubMed

    Bi, Peng-Qing; Wu, Bo; Zheng, Fei; Xu, Wei-Long; Yang, Xiao-Yu; Feng, Lin; Zhu, Furong; Hao, Xiao-Tao

    2016-09-01

    A small-molecule material, 7,7-(4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b']dithiophene-2,6-diyl)bis(6-fluoro-4-(5'-hexyl-[2,2'-bithiophen]-5-yl)benzo-[c] [1,2,5]thiadiazole) (p-DTS(FBTTH2)2), was used to modify the morphology and electron-transport properties of the polymer blend of poly(3-hexythiophene) (P3HT) and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) bulk heterojunctions. As a result, a 24% increase in the power-conversion efficiency (PCE) of the p-DTS(FBTTH2)2:P3HT:PC71BM ternary organic solar cells (OSCs) is obtained. The improvement in the performance of OSCs is attributed to the constructive energy cascade path in the ternary system that benefits an efficient Förster resonance energy/charge transfer process between P3HT and p-DTS(FBTTH2)2, thereby improving photocurrent generation. It is shown that p-DTS(FBTTH2)2 molecules engage themselves at the P3HT/PC71BM interface. A combination of absorption enhancement, efficient energy transfer process, and ordered nanomorphology in the ternary system favors exciton dissociation and charge transportation in the polymer bulk heterojunction. The finding of this work reveals that distribution of the appropriate "guest" donor at the "host" donor/acceptor interface is an effective approach for attaining high-performance OSCs. PMID:27525544

  9. Optoelectronic properties and charge transfer in donor-acceptor all-conjugated diblock copolymers.

    SciTech Connect

    Botiz, I.; Schaller, R. D.; Verduzco, R.; Darling, S. B.

    2011-05-12

    All-conjugated block copolymers, which can self-assemble into well-ordered morphologies, provide exciting opportunities to rationally design and control the nanoscale organization of electron-donor and electron-acceptor moieties in optoelectronic active layers. Here we report on the steady-state and time-resolved optical characterization of block copolymer films and solutions containing poly(3-hexylthiophene) as the donor block and poly(9,9-dioctylfluorene) with and without copolymerization with benzothiadiazole as the acceptor block. Transient absorption measurements suggest rapid charge transfer occurs in both systems, with higher efficiency observed in the latter composition. These results indicate that this class of materials has promise in preparing highly ordered bulk heterojunction all-polymer organic photovoltaic devices.

  10. Organic Thin-Film Solar Cells Based on Donor-Acceptor Interpenetrating Nano-Interface

    SciTech Connect

    Fujii, Akihiko; Hori, Tetsuro; Moritou, Hiroki; Fukuoka, Naoki; Sakamoto, Junki; Ozaki, Masanori

    2010-12-23

    Photovoltaic cells with interpenetrating interfaces between a conducting polymer layer and a fullerene layer fabricated by a solvent corrosion method have been investigated. Using a weakly dissoluble combination of a solvent and an underlayer film, we fabricated a ''semi-layered'' structure that was maintaining a bilayer structure and furthermore interpenetrating at the interface of the conducting polymer and the fullerene layers. In these cells, high external quantum efficiencies (EQE) were obtained. The photovoltaic properties have been interpreted by the effective absorption of incident photons around the interface of conducting polymer and fullerene, the interpenetrating fullerene / conducting polymer interface involving the efficient photo-induced charge transfer, and the short distance between the electron-generation region and electrode resulting in the enhancement of the electron collection to the electrode. In these cells, both of the efficient exciton dissociations at the interpenetrating interface and the efficient carrier transports by each continuous pathway for electrons between fullerene molecules and for holes between conducting polymers occur.

  11. Roles of Energy/Charge Cascades and Intermixed Layers at Donor/Acceptor Interfaces in Organic Solar Cells

    NASA Astrophysics Data System (ADS)

    Nakano, Kyohei; Suzuki, Kaori; Chen, Yujiao; Tajima, Keisuke

    2016-07-01

    The secret to the success of mixed bulk heterojunctions (BHJs) in yielding highly efficient organic solar cells (OSCs) could reside in the molecular structures at their donor/acceptor (D/A) interfaces. In this study, we aimed to determine the effects of energy and charge cascade structures at the interfaces by using well-defined planar heterojunctions (PHJs) as a model system. The results showed that (1) the charge cascade structure enhanced VOC because it shuts down the recombination pathway through charge transfer (CT) state with a low energy, (2) the charge cascade layer having a wider energy gap than the bulk material decreased JSC because the diffusion of the excitons from the bulk to D/A interface was blocked; the energy of the cascade layers must be appropriately arranged for both the charges and the excitons, and (3) molecular intermixing in the cascade layer opened the recombination path through the low-energy CT state and decreased VOC. Based on these findings, we propose improved structures for D/A interfaces in BHJs.

  12. Roles of Energy/Charge Cascades and Intermixed Layers at Donor/Acceptor Interfaces in Organic Solar Cells

    PubMed Central

    Nakano, Kyohei; Suzuki, Kaori; Chen, Yujiao; Tajima, Keisuke

    2016-01-01

    The secret to the success of mixed bulk heterojunctions (BHJs) in yielding highly efficient organic solar cells (OSCs) could reside in the molecular structures at their donor/acceptor (D/A) interfaces. In this study, we aimed to determine the effects of energy and charge cascade structures at the interfaces by using well-defined planar heterojunctions (PHJs) as a model system. The results showed that (1) the charge cascade structure enhanced VOC because it shuts down the recombination pathway through charge transfer (CT) state with a low energy, (2) the charge cascade layer having a wider energy gap than the bulk material decreased JSC because the diffusion of the excitons from the bulk to D/A interface was blocked; the energy of the cascade layers must be appropriately arranged for both the charges and the excitons, and (3) molecular intermixing in the cascade layer opened the recombination path through the low-energy CT state and decreased VOC. Based on these findings, we propose improved structures for D/A interfaces in BHJs. PMID:27404948

  13. Roles of Energy/Charge Cascades and Intermixed Layers at Donor/Acceptor Interfaces in Organic Solar Cells.

    PubMed

    Nakano, Kyohei; Suzuki, Kaori; Chen, Yujiao; Tajima, Keisuke

    2016-07-12

    The secret to the success of mixed bulk heterojunctions (BHJs) in yielding highly efficient organic solar cells (OSCs) could reside in the molecular structures at their donor/acceptor (D/A) interfaces. In this study, we aimed to determine the effects of energy and charge cascade structures at the interfaces by using well-defined planar heterojunctions (PHJs) as a model system. The results showed that (1) the charge cascade structure enhanced VOC because it shuts down the recombination pathway through charge transfer (CT) state with a low energy, (2) the charge cascade layer having a wider energy gap than the bulk material decreased JSC because the diffusion of the excitons from the bulk to D/A interface was blocked; the energy of the cascade layers must be appropriately arranged for both the charges and the excitons, and (3) molecular intermixing in the cascade layer opened the recombination path through the low-energy CT state and decreased VOC. Based on these findings, we propose improved structures for D/A interfaces in BHJs.

  14. Roles of Energy/Charge Cascades and Intermixed Layers at Donor/Acceptor Interfaces in Organic Solar Cells.

    PubMed

    Nakano, Kyohei; Suzuki, Kaori; Chen, Yujiao; Tajima, Keisuke

    2016-01-01

    The secret to the success of mixed bulk heterojunctions (BHJs) in yielding highly efficient organic solar cells (OSCs) could reside in the molecular structures at their donor/acceptor (D/A) interfaces. In this study, we aimed to determine the effects of energy and charge cascade structures at the interfaces by using well-defined planar heterojunctions (PHJs) as a model system. The results showed that (1) the charge cascade structure enhanced VOC because it shuts down the recombination pathway through charge transfer (CT) state with a low energy, (2) the charge cascade layer having a wider energy gap than the bulk material decreased JSC because the diffusion of the excitons from the bulk to D/A interface was blocked; the energy of the cascade layers must be appropriately arranged for both the charges and the excitons, and (3) molecular intermixing in the cascade layer opened the recombination path through the low-energy CT state and decreased VOC. Based on these findings, we propose improved structures for D/A interfaces in BHJs. PMID:27404948

  15. Ultrafast Transient Absorption Spectroscopy Investigation of Photoinduced Dynamics in Novel Donor-Acceptor Core-Shell Nanostructures for Organic Photovoltaics

    NASA Astrophysics Data System (ADS)

    Strain, Jacob; Jamhawi, Abdelqader; Abeywickrama, Thulitha M.; Loomis, Wendy; Rathnayake, Hemali; Liu, Jinjun

    2016-06-01

    Novel donor-acceptor nanostructures were synthesized via covalent synthesis and/or UV cross-linking method. Their photoinduced dynamics were investigated with ultrafast transient absorption (TA) spectroscopy. These new nanostructures are made with the strategy in mind to reduce manufacturing steps in the process of fabricating an organic photovoltaic cell. By imitating the heterojunction interface within a fixed particle domain, several fabrication steps can be bypassed reducing cost and giving more applicability to other film deposition methods. Such applications include aerosol deposition and ink-jet printing. The systems that were studied by TA spectroscopy include PDIB core, PDIB-P3HT core-shell, and PDIB-PANT core-shell which range in size from 60 to 130 nm. Within the experimentally accessible spectra range there resides a region of ground state bleaching, stimulated emission, and excited-state absorption of both neutrals and anions. Control experiments have been carried out to assign these features. At high pump fluences the TA spectra of PDIB core alone also indicate an intramolecular charge separation. The TA spectroscopy results thus far suggest that the core-shells resemble the photoinduced dynamics of a standard film although the particles are dispersed in solution, which indicates the desired outcome of the work.

  16. Emission quenching and charge separation in bridged donor-acceptor block copolymers

    NASA Astrophysics Data System (ADS)

    Bonner, Carl E., Jr.; Sun, Sam-Shajing; Wang, Meina; Vick, Shameika; Winston, Kizzy M.; Ledbetter, Abram J.; Douglas, Lawrence

    2004-11-01

    The optical properties of previously synthesized sulfone and methoxy substituted block co-polymers of poly-phenlyenevinylene (PPV) have been examined. An internal space charge field is formed which has been used to quench the luminescence intensity in these materials by separating optically generated excitons and electron-hole pairs. The absorption and emission spectra and the time dependence of the emission of donor and acceptor derivatized block co-polymers was measured and the quenching of the luminescence was observed and quantified. PPV materials with this internal field have potential applications as solar energy converters and photodetectors.

  17. A Combined Study of Mesomorphism, Optical and Electronic Properties of Novel Columnar Liquid Crystals

    NASA Astrophysics Data System (ADS)

    Chen, Shuai

    Columnar mesophases of discotic liquid crystals (DLCs) are a separate class of organic semiconductors. Anisotropic charge transport, high charge carrier mobility, and self-organizing properties have been regarded as superior properties of DLCs but their performance in devices, such as organic light-emitting diodes, has been inferior to the best performing conventional organic semiconductors. Our group recently demonstrated that a DLC of donor-acceptor structure can bias electron over hole conduction if the occupied and unoccupied frontier orbitals are localized on different parts of the molecule and only the unoccupied frontier orbitals electronically interact in columnar stacks. This thesis describes the first systematic approach to different types of donor-acceptor DLCs and the investigation of their mesomorphism and optoelectronic properties. In spite of their large aspect ratios, four board-shaped donor-acceptor-donor quinoxalinophenanthrophenazine (QPP) dyes (Chapters 2 and 3) induce complex columnar mesomorphism over wide temperature ranges. These QPP derivatives also show strong fluorescence in solution and as thin films. This strong fluorescence in columnar mesophases is explained with a nonparallel orientation of the elongated donor-acceptor cores in the columnar stacks that minimizes interactions between transition dipole moments of co-facially stacked molecules. Opto-electronic properties suggest that the QPP derivatives are organic semiconductors. Inspired by the donor-acceptor concept, we generated novel ionic DLCs based on imidazole and imidazolium structures (Chapter 5). Unexpectedly, only the ionic triphenylenoimidazolium derivatives display columnar mesomorphism. Strong ionic interactions between the cores are apparently required for the formation of columnar mesophases. Overall, these compounds are rather unusual because few ionic DLCs have the charge localized on the aromatic core. Most often the charged group is attached via spacer chains. A

  18. Structures and photoelectric properties of five benzotrithiophene isomers-based donor-acceptor copolymers.

    PubMed

    Cheng, Na; Ma, Yuchen; Liu, Yongjun; Zhang, Changqiao; Liu, Chengbu

    2016-04-15

    In this paper, we have investigated the structures, electronic and optical properties of five conjugated copolymers (BTT1-BTz, BTT2-BTz, BTT3-BTz, BTT4-BTz and BTT5-BTz) featuring benzotrithiophene (BTT) isomers as donor units and benzothiadiazole (BTz) as acceptor units, linked through thiophene spacers, employing many-body perturbation theory (MBPT). We have explored the isomer effects by configuration of the sulfur atoms in BTT units, aimed to get insight into how the structural modifications to the conjugated backbone can influence the molecular structures and electronic properties of conjugated polymers. Using the trimer as the computational model, the calculated low and high energy absorption bands (660 and 413 nm) for BTT1-BTz agree well with the experimental ones (645 and 430 nm) with a small offset of ~15 nm. On the basis of our calculations, it is found that the backbones of these polymers display different coplanarities, with the dihedral angles between the two neighboring rings varying from 12.3° to 79.0°. Importantly, both BTT1-BTz and BTT2-BTz exhibit intense adsorption around 660 and 623 nm, indicating their promising application in solar cells, whereas BTT3-BTz and BTT4-BTz display the intense adsorption at 569 and 551 nm, which are also usable in the tandem solar cells. BTT5-BTz has narrow and weak adsorption in the visible and infrared region, implying it is not conducive to the sunlight absorption. The blue shift of about 150 nm from BTT1-BTz to BTT5-BTz is suggested to be originated from the shorter effective conjugation lengths.

  19. Structures and photoelectric properties of five benzotrithiophene isomers-based donor-acceptor copolymers

    NASA Astrophysics Data System (ADS)

    Cheng, Na; Ma, Yuchen; Liu, Yongjun; Zhang, Changqiao; Liu, Chengbu

    2016-04-01

    In this paper, we have investigated the structures, electronic and optical properties of five conjugated copolymers (BTT1-BTz, BTT2-BTz, BTT3-BTz, BTT4-BTz and BTT5-BTz) featuring benzotrithiophene (BTT) isomers as donor units and benzothiadiazole (BTz) as acceptor units, linked through thiophene spacers, employing many-body perturbation theory (MBPT). We have explored the isomer effects by configuration of the sulfur atoms in BTT units, aimed to get insight into how the structural modifications to the conjugated backbone can influence the molecular structures and electronic properties of conjugated polymers. Using the trimer as the computational model, the calculated low and high energy absorption bands (660 and 413 nm) for BTT1-BTz agree well with the experimental ones (645 and 430 nm) with a small offset of ~ 15 nm. On the basis of our calculations, it is found that the backbones of these polymers display different coplanarities, with the dihedral angles between the two neighboring rings varying from 12.3° to 79.0°. Importantly, both BTT1-BTz and BTT2-BTz exhibit intense adsorption around 660 and 623 nm, indicating their promising application in solar cells, whereas BTT3-BTz and BTT4-BTz display the intense adsorption at 569 and 551 nm, which are also usable in the tandem solar cells. BTT5-BTz has narrow and weak adsorption in the visible and infrared region, implying it is not conducive to the sunlight absorption. The blue shift of about 150 nm from BTT1-BTz to BTT5-BTz is suggested to be originated from the shorter effective conjugation lengths.

  20. Structures and photoelectric properties of five benzotrithiophene isomers-based donor-acceptor copolymers.

    PubMed

    Cheng, Na; Ma, Yuchen; Liu, Yongjun; Zhang, Changqiao; Liu, Chengbu

    2016-04-15

    In this paper, we have investigated the structures, electronic and optical properties of five conjugated copolymers (BTT1-BTz, BTT2-BTz, BTT3-BTz, BTT4-BTz and BTT5-BTz) featuring benzotrithiophene (BTT) isomers as donor units and benzothiadiazole (BTz) as acceptor units, linked through thiophene spacers, employing many-body perturbation theory (MBPT). We have explored the isomer effects by configuration of the sulfur atoms in BTT units, aimed to get insight into how the structural modifications to the conjugated backbone can influence the molecular structures and electronic properties of conjugated polymers. Using the trimer as the computational model, the calculated low and high energy absorption bands (660 and 413 nm) for BTT1-BTz agree well with the experimental ones (645 and 430 nm) with a small offset of ~15 nm. On the basis of our calculations, it is found that the backbones of these polymers display different coplanarities, with the dihedral angles between the two neighboring rings varying from 12.3° to 79.0°. Importantly, both BTT1-BTz and BTT2-BTz exhibit intense adsorption around 660 and 623 nm, indicating their promising application in solar cells, whereas BTT3-BTz and BTT4-BTz display the intense adsorption at 569 and 551 nm, which are also usable in the tandem solar cells. BTT5-BTz has narrow and weak adsorption in the visible and infrared region, implying it is not conducive to the sunlight absorption. The blue shift of about 150 nm from BTT1-BTz to BTT5-BTz is suggested to be originated from the shorter effective conjugation lengths. PMID:26881340

  1. Charge Transfer States in Dilute Donor-Acceptor Blend Organic Heterojunctions.

    PubMed

    Liu, Xiao; Ding, Kan; Panda, Anurag; Forrest, Stephen R

    2016-08-23

    We study the charge transfer (CT) states in small-molecule blend heterojunctions comprising the nonpolar donor, tetraphenyldibenzoperiflanthene (DBP), and the acceptor, C70, using electroluminescence and steady-state and time-resolved photoluminescence spectroscopy along with density functional theory calculations. We find that the CT exciton energy blue shifts as the C70 concentration in the blend is either decreased or increased away from 50 vol %. At 20 K, the increase in CT state lifetime is correlated with the increasing diameter of C70 nanocrystallites in the blends. A quantum confinement model is used to quantitatively describe the dependence of both CT energy and lifetime on the C70 or DBP domain size. Two discrete CT emission peaks are observed for blends whose C70 concentration is >65%, at which point C70 nanocrystallites with diameters >4 nm appear in high-resolution transmission electron micrographs. The presence of two CT states is attributed to coexistence of crystalline C70 and amorphous phases in the blends. Furthermore, analysis of CT dissociation efficiency versus photon energy suggests that the >90% dissociation efficiency of delocalized CT2 states from the crystalline phase significantly contributes to surprisingly efficient photogeneration in highly dilute (>80% C70) DBP/C70 heterojunctions. PMID:27487403

  2. Direct Uniaxial Alignment of a Donor-Acceptor Semiconducting Polymer Using Single-Step Solution Shearing.

    PubMed

    Shaw, Leo; Hayoz, Pascal; Diao, Ying; Reinspach, Julia Antonia; To, John W F; Toney, Michael F; Weitz, R Thomas; Bao, Zhenan

    2016-04-13

    The alignment of organic semiconductors (OSCs) in the active layers of electronic devices can confer desirable properties, such as enhanced charge transport properties due to better ordering, charge transport anisotropy for reduced device cross-talk, and polarized light emission or absorption. The solution-based deposition of highly aligned small molecule OSCs has been widely demonstrated, but the alignment of polymeric OSCs in thin films deposited directly from solution has typically required surface templating or complex pre- or postdeposition processing. Therefore, single-step solution processing and the charge transport enhancement afforded by alignment continue to be attractive. We report here the use of solution shearing to tune the degree of alignment in poly(diketopyrrolopyrrole-terthiophene) thin films by controlling the coating speed. A maximum dichroic ratio of ∼7 was achieved on unpatterned substrates without any additional pre- or postdeposition processing. The degree of polymer alignment was found to be a competition between the shear alignment of polymer chains in solution and the complex thin film drying process. Contrary to previous reports, no charge transport anisotropy was observed because of the small crystallite size relative to the channel length, a meshlike morphology, and the likelihood of increased grain boundaries in the direction transverse to coating. In fact, the lack of aligned morphological structures, coupled with observed anisotropy in X-ray diffraction data, suggests the alignment of polymer molecules in both the crystalline and the amorphous regions of the films. The shear speed at which maximum dichroism is achieved can be controlled by altering deposition parameters such as temperature and substrate treatment. Modest changes in molecular weight showed negligible effects on alignment, while longer polymer alkyl side chains were found to reduce the degree of alignment. This work demonstrates that solution shearing can be used

  3. Direct Uniaxial Alignment of a Donor-Acceptor Semiconducting Polymer Using Single-Step Solution Shearing.

    PubMed

    Shaw, Leo; Hayoz, Pascal; Diao, Ying; Reinspach, Julia Antonia; To, John W F; Toney, Michael F; Weitz, R Thomas; Bao, Zhenan

    2016-04-13

    The alignment of organic semiconductors (OSCs) in the active layers of electronic devices can confer desirable properties, such as enhanced charge transport properties due to better ordering, charge transport anisotropy for reduced device cross-talk, and polarized light emission or absorption. The solution-based deposition of highly aligned small molecule OSCs has been widely demonstrated, but the alignment of polymeric OSCs in thin films deposited directly from solution has typically required surface templating or complex pre- or postdeposition processing. Therefore, single-step solution processing and the charge transport enhancement afforded by alignment continue to be attractive. We report here the use of solution shearing to tune the degree of alignment in poly(diketopyrrolopyrrole-terthiophene) thin films by controlling the coating speed. A maximum dichroic ratio of ∼7 was achieved on unpatterned substrates without any additional pre- or postdeposition processing. The degree of polymer alignment was found to be a competition between the shear alignment of polymer chains in solution and the complex thin film drying process. Contrary to previous reports, no charge transport anisotropy was observed because of the small crystallite size relative to the channel length, a meshlike morphology, and the likelihood of increased grain boundaries in the direction transverse to coating. In fact, the lack of aligned morphological structures, coupled with observed anisotropy in X-ray diffraction data, suggests the alignment of polymer molecules in both the crystalline and the amorphous regions of the films. The shear speed at which maximum dichroism is achieved can be controlled by altering deposition parameters such as temperature and substrate treatment. Modest changes in molecular weight showed negligible effects on alignment, while longer polymer alkyl side chains were found to reduce the degree of alignment. This work demonstrates that solution shearing can be used

  4. Probing charge and energy transfer process at the donor-acceptor interface of semiconductor nanostructures with simultaneous photocurrent-optical microscopy

    NASA Astrophysics Data System (ADS)

    Gao, Yongqian; Acharya, Krishna; Galande, Charudatta; Ajayan, Pulickel; Mohite, Aditya; Dattelbaum, Andrew; Hollingsworth, Jennifer; Htoon, Han; Los Alamos Natioal Lab Team; Rice Univerisity Collaboration

    2013-03-01

    Understanding and control of charge and energy transfer (CT & ET) processes happening at the donor-acceptor interface of colloidal semiconductor nanostructures play a critical role in defining the performance of many exploratory photo-voltaic devices. Ultrafast dynamics of CT and ET processes in semiconductor nanostrucutres can be investigated effectively by time and energy resolved PL spectroscopy. However a full understanding on impact of these process on device performance demand direct correlation of these dynamical measurements with photocurrent measurements that probe the separation and transport of charges. To this end we develop simultaneous optical and electrical characterization approaches capable of performing scanning photocurrent microscopy and various single nanostructure optical spectroscopies (e.g. photoluminescence (PL), Raman, time resolved PL) simultaneously. We will present application of this technique on various donor/acceptor interfaces including graphene oxide/CdSe nanowire and TiO2 nanocrystals/CdSe nanowire interfaces.

  5. Modified triphenylamine-dicyanovinyl-based donor-acceptor dyes with enhanced power conversion efficiency of p-type dye-sensitized solar cells.

    PubMed

    Zhu, Linna; Yang, Hongbin; Zhong, Cheng; Li, Chang Ming

    2012-12-01

    To dye for: Two new dyes are synthesized by structural modifications of one of the best dyes for NiO p-type dye-sensitized solar cells, which is based on a triphenylamine-dicyanovinyl donor-acceptor system. An additional thiophene unit near the anchoring group can greatly retard charge recombination while enhancing the absorption coefficient to significantly improve the photoconversion efficiency by 50%.

  6. Limitations and design considerations for donor-acceptor systems in luminescent solar concentrators: the effect of coupling-induced red-edge absorption

    NASA Astrophysics Data System (ADS)

    MacQueen, Rowan W.; Tayebjee, Murad J. Y.; Webb, James E. A.; Falber, Alexander; Thordarson, Pall; Schmidt, Timothy W.

    2016-06-01

    Luminescent solar concentrators (LSCs) use luminescence and waveguiding to concentrate photons within thin dielectric slabs for use in photovoltaic, lighting, and photobioreactor applications. Donor-acceptor systems of organic chromophores are widely used in LSCs to broaden the sunlight absorption range and attempt to reduce loss-inducing reabsorption by the emitting chromophore. We use raytrace simulations across a large parameter space to model the performance of LSCs containing two novel donor-acceptor trimers based on the perylene moiety. We find that under certain conditions, trimers outperform single-dye LSCs as expected. However, at higher concentrations, a slight increase in red-edge absorption by the trimers increases reabsorption and has a deleterious effect on LSC performance. This underscores the large effect that even small changes in the red edge can have, and may discourage the use of donor-acceptor schemes with high interchromophore coupling that promotes red-edge absorption. Finally, we show that for a LSC-PV pair, selecting a PV cell that is well-matched with the LSC emission spectrum has a large effect on the flux gain of the system, and that the systems studied here are well-matched to emerging PV technologies.

  7. Energy transfer enhancement by oxygen perturbation of spin-forbidden electronic transitions in aromatic systems

    NASA Astrophysics Data System (ADS)

    Monguzzi, A.; Tubino, R.; Salamone, M. M.; Meinardi, F.

    2010-09-01

    Triplet-triplet energy transfer in multicomponent organic systems is usually entirely ascribed to a Dexter-type mechanism involving only short-range donor/acceptor interactions. We demonstrate that the presence of molecular oxygen introduces a perturbation to the electronic structure of one of the involved moieties which can induce a large increase in the spin-forbidden transition oscillator strength so that the otherwise negligible Förster contribution dominates the overall energy transfer rate.

  8. Interactions of triazine herbicides with biochar: Steric and electronic effects.

    PubMed

    Xiao, Feng; Pignatello, Joseph J

    2015-09-01

    We studied the adsorption of triazine herbicides and several reference heteroaromatic amines from water onto a temperature series of hardwood biochars (300-700 °C, labeled B300-B700). Adsorption on biochars correlated poorly with pyrolysis temperature, H/C, O/C, mean minimum fused ring size, surface area (N2 or CO2), microporosity, and mesoporosity, but correlated well with a weighted sum of microporosity and mesoporosity. Steric effects were evident by the negative influence of solute molecular volume on adsorption rate. For a given compound, adsorption rate maximized for the biochar with the greatest mesoporosity-to-total-porosity ratio, suggesting that mesopores are important for facilitating diffusion into pore networks. The cationic forms of amines adsorb more slowly than the neutral forms. To further probe steric and electronic effects, adsorption on a biochar (B400) was compared to adsorption on graphite-a nonporous reference material with an unhindered, unfunctionalized graphene surface-and in comparison with reference compounds (benzene, naphthalene, pyridine, quinoline and 1,3-triazine). Relative to benzene, the surface area-normalized adsorption of the triazine herbicides was disfavored on B400 (favored on graphite) by 11-19 kJ/mol, depending on concentration. It is estimated that steric suppression of B400 adsorption comprises 6.2 kJ/mol of this difference, the remainder being the difference in polar electronic effects. Based on the behavior of the reference amines, the difference in polar effects is dominated by π-π electron donor-acceptor (EDA) interactions with sites on polyaromatic surfaces, which are more electropositive and/or more abundant on graphite. Overall, our results show that mesoporosity is critical, that adsorption rate is a function of solute molecular size and charge, that steric bulk in the solute suppresses equilibrium adsorption, and that π-π EDA forces play a role in triazine polar interactions with biochar. PMID:26001283

  9. Interactions of triazine herbicides with biochar: Steric and electronic effects.

    PubMed

    Xiao, Feng; Pignatello, Joseph J

    2015-09-01

    We studied the adsorption of triazine herbicides and several reference heteroaromatic amines from water onto a temperature series of hardwood biochars (300-700 °C, labeled B300-B700). Adsorption on biochars correlated poorly with pyrolysis temperature, H/C, O/C, mean minimum fused ring size, surface area (N2 or CO2), microporosity, and mesoporosity, but correlated well with a weighted sum of microporosity and mesoporosity. Steric effects were evident by the negative influence of solute molecular volume on adsorption rate. For a given compound, adsorption rate maximized for the biochar with the greatest mesoporosity-to-total-porosity ratio, suggesting that mesopores are important for facilitating diffusion into pore networks. The cationic forms of amines adsorb more slowly than the neutral forms. To further probe steric and electronic effects, adsorption on a biochar (B400) was compared to adsorption on graphite-a nonporous reference material with an unhindered, unfunctionalized graphene surface-and in comparison with reference compounds (benzene, naphthalene, pyridine, quinoline and 1,3-triazine). Relative to benzene, the surface area-normalized adsorption of the triazine herbicides was disfavored on B400 (favored on graphite) by 11-19 kJ/mol, depending on concentration. It is estimated that steric suppression of B400 adsorption comprises 6.2 kJ/mol of this difference, the remainder being the difference in polar electronic effects. Based on the behavior of the reference amines, the difference in polar effects is dominated by π-π electron donor-acceptor (EDA) interactions with sites on polyaromatic surfaces, which are more electropositive and/or more abundant on graphite. Overall, our results show that mesoporosity is critical, that adsorption rate is a function of solute molecular size and charge, that steric bulk in the solute suppresses equilibrium adsorption, and that π-π EDA forces play a role in triazine polar interactions with biochar.

  10. Simultaneous control over both molecular order and long-range alignment in films of the donor-acceptor copolymer.

    PubMed

    Wang, Haiyang; Chen, Liang; Xing, Rubo; Liu, Jiangang; Han, Yanchun

    2015-01-13

    Control over both molecular order and long-range alignment order in films of the donor-acceptor copolymer of 3,6-bis(thiophen-2-yl)-N,N'-bis(2-octyl-1-dodecyl)-1,4-dioxo-pyrrolo[3,4-c]pyrrole and thieno[3,2-b]thiophene (PDBT-TT) was demonstrated via off-center spin-coating (OCSC) from its blend solution with polystyrene (PS). It was found that the dichroic ratio (DR) of OCSC blend films was dependent on both the physical process of spin-coating and the effect of PS chains. The highest DR of 2.75 was obtained via OCSC from the blend solution in oDCB at 1500 rpm. Meanwhile, both the intrachain and interchain molecular order were improved in blend films compared with neat ones, which were indicated by the red-shift of the max absorption, enhanced J-aggregation absorption, and smaller π-π stacking distance (from 3.77 to 3.70 Å). According to the results of the investigation into the macro anisotropy, micro morphology, solution rheology properties, and photophysics features of films, an overall mechanism of simultaneous control over molecular and long-range order of D-A copolymer films was proposed. On the one hand, a larger viscosity and the pseudoplastic nature of the solution tuned by choosing good solvents with high boiling points and adding PS resulted in a better chain disentanglement, better shear transfer, and a slower contact line receding velocity to induce an enhanced alignment of chains and thus fibrillar aggregates. Also, the critical contact line receding velocity for alignment dominated by the solvent evaporation rate accounted for the variation of DR with OCSC rates. A vertical phase separation accompanying the formation of aligned fibrils during OCSC was also confirmed due to the friction shear between air and solution surface. On the other hand, the negligible dependence of the blend OCSC film's photophysical and morphological features on the solvent suggested the critical role of PS in determining the better intrachain conjugation in blend films

  11. Theoretical analysis of the intermolecular interactions in naphthalene diimide and pyrene complexes.

    PubMed

    Yeh, Mei-Yu; Lin, Hsin-Chieh

    2014-11-28

    Supramolecular assembly of donor-acceptor complexes as the key component in organic functional nanomaterials is a promising approach for future electronic devices. One representative example of the donor-acceptor complexes is the naphthalene diimide-pyrene (NDI-Py) system, which shows fascinating photoelectric properties. Herein, the analysis of the π-π interactions between NDI and Py has been investigated using the DFT/M06-2X and reduced density gradient methods. According to the calculations, the attractive forces for the stabilization of the NDI-Py dimer are dependent on the rotation angles, which provide physical insight into the experimental data reported by Wilson and co-workers (Langmuir, 2011, 27, 6554). Our results not only provide computational evidence for the origin of the rotation in the crystal structure of the NDI-Py but also address the role of the charge-transfer attractions in the complexes.

  12. Magnetically modulated electroluminescence from hybrid organic/inorganic light-emitting diodes based on electron donor-acceptor exciplex blends

    NASA Astrophysics Data System (ADS)

    Pang, Zhiyong; Baniya, Sangita; Zhang, Chuang; Sun, Dali; Vardeny, Z. Valy

    2016-03-01

    We report room temperature magnetically modulated electroluminescence from a hybrid organic/inorganic light-emitting diode (h-OLED), in which an inorganic magnetic tunnel junction (MTJ) with large room temperature magnetoresistance is coupled to an N,N,N ',N '-Tetrakis(4-methoxyphenyl)benzidine (MeO-TPD): tris-[3-(3-pyridyl)mesityl]borane (3TPYMB) [D-A] based OLED that shows thermally activated delayed luminescence. The exciplex-based OLED provides two spin-mixing channels: upper energy channel of polaron pairs and lower energy channel of exciplexes. In operation, the large resistance mismatch between the MTJ and OLED components is suppressed due to the non-linear I-V characteristic of the OLED. This leads to enhanced giant magneto-electroluminescence (MEL) at room temperature. We measured MEL of ~ 75% at ambient conditions. Supported by SAMSUNG Global Research Outreach (GRO) program, and also by the NSF-Material Science & Engineering Center (MRSEC) program at the University of Utah (DMR-1121252).

  13. Tuning the reorganization energy of electron transfer in supramolecular ensembles - metalloporphyrin, oligophenylenevinylenes, and fullerene - and the impact on electron transfer kinetics

    NASA Astrophysics Data System (ADS)

    Stangel, Christina; Schubert, Christina; Kuhri, Susanne; Rotas, Georgios; Margraf, Johannes T.; Regulska, Elzbieta; Clark, Timothy; Torres, Tomás; Tagmatarchis, Nikos; Coutsolelos, Athanassios G.; Guldi, Dirk M.

    2015-01-01

    Oligo(p-phenylenevinylene) (oPPV) wires of various lengths featuring pyridyls at one terminal and C60 moieties at the other, have been used as molecular building blocks in combination with porphyrins to construct a novel class of electron donor-acceptor architectures. These architectures, which are based on non-covalent, directional interactions between the zinc centers of the porphyrins and the pyridyls, have been characterized by nuclear magnetic resonance spectroscopy and mass spectrometry. Complementary physico-chemical assays focused on the interactions between electron donors and acceptors in the ground and excited states. No appreciable electron interactions were noted in the ground state, which was being probed by electrochemistry, absorption spectroscopy, etc.; the electron acceptors are sufficiently decoupled from the electron donors. In the excited state, a different picture evolved. In particular, steady-state and time-resolved fluorescence and transient absorption measurements revealed substantial electron donor-acceptor interactions. These led, upon photoexcitation of the porphyrins, to tunable intramolecular electron-transfer processes, that is, the oxidation of porphyrin and the reduction of C60. In this regard, the largest impact stems from a rather strong distance dependence of the total reorganization energy in stark contrast to the distance independence seen for covalently linked conjugates.Oligo(p-phenylenevinylene) (oPPV) wires of various lengths featuring pyridyls at one terminal and C60 moieties at the other, have been used as molecular building blocks in combination with porphyrins to construct a novel class of electron donor-acceptor architectures. These architectures, which are based on non-covalent, directional interactions between the zinc centers of the porphyrins and the pyridyls, have been characterized by nuclear magnetic resonance spectroscopy and mass spectrometry. Complementary physico-chemical assays focused on the interactions

  14. A High-Energy Charge-Separated State of 1.70 eV from a High-Potential Donor-Acceptor Dyad: A Catalyst for Energy-Demanding Photochemical Reactions.

    PubMed

    Lim, Gary N; Obondi, Christopher O; D'Souza, Francis

    2016-09-12

    A high potential donor-acceptor dyad composed of zinc porphyrin bearing three meso-pentafluorophenyl substituents covalently linked to C60 , as a novel dyad capable of generating charge-separated states of high energy (potential) has been developed. The calculated energy of the charge-separated state was found to be 1.70 eV, the highest reported for a covalently linked porphyrin-fullerene dyad. Intramolecular photoinduced electron transfer leading to charge-separated states of appreciable lifetimes in polar and nonpolar solvents has been established from studies involving femto- to nanosecond transient absorption techniques. The high energy stored in the form of charge-separated states along with its persistence of about 50-60 ns makes this dyad a potential electron-transporting catalyst to carry out energy-demanding photochemical reactions. This type of high-energy harvesting dyad is expected to open new research in the areas of artificial photosynthesis especially producing energy (potential) demanding light-to-fuel products.

  15. Novel coronene-naphthalene dimide-based donor-acceptor pair for tunable charge-transfer nanostructures.

    PubMed

    Kumar, Mohit; George, Subi J

    2014-09-01

    Charge-transfer (CT) assemblies of aromatic donor (D) and acceptor (A) molecules have recently gained attention as a promising material for organic electronics and ferroelectrics. Two major factors which govern their functions are the strength of CT interaction and their supramolecular nanostructuring. Here we present coronene-naphthalenediimide (NDI)-based novel D-A pairs that form alternately stacked CT assemblies. Through systematic substitution of the NDI derivatives and studying their CT interactions with coronene, a clear understanding of the secondary forces responsible for controlling their association is gained. Finally, the use of CT-based supramolecular amphiphiles for their nanostructural engineering into ordered one-dimensional (1-D) assemblies is demonstrated. PMID:25045008

  16. Electron interaction in matter

    NASA Technical Reports Server (NTRS)

    Dance, W. E.; Rainwater, W. J.; Rester, D. H.

    1969-01-01

    Data on the scattering of 1-MeV electrons in aluminum for the case of non-normal incidence, electron-bremsstrahlung cross-sections in thin targets, and the production of bremstrahlung by electron interaction in thick targets, are presented both in tabular and graphic form. These results may interest physicists and radiologists.

  17. G-Tetraplex-Induced FRET within Telomeric Repeat Sequences Using (Py) A-(Per) A as Energy Donor-Acceptor Pair.

    PubMed

    Kundu, Rajen

    2016-01-01

    G-tetraplex induced fluorescence resonance energy transfer (FRET) within telomeric repeat sequences has been studied using a nucleoside-tethered FRET pair embedded in the human telomeric G-quadruplex forming sequence (5'-A GGG TT(Py) A GGG TT(Per) A GGG TTA GGG-3', Py=pyrene, Per=perylene). Conformational change from a single strand to an anti-parallel G-quadruplex leads to FRET from energy donor ((Py) A) to acceptor ((Per) A). The distance between the FRET donor/acceptor partners was controlled by changing the number of G-quartet spacer units. The FRET efficiency decreases with increase in G-quartet units. Overall findings indicate that this could be further used for the development of FRET-based sensing and measurement techniques. PMID:26490798

  18. Role of donor-acceptor domain formation and interface states in initial degradation of P3HT:PCBM-based solar cells

    NASA Astrophysics Data System (ADS)

    Arora, Swati; Rajouria, Satish Kumar; Kumar, Pankaj; Bhatnagar, P. K.; Arora, Manoj; Tandon, R. P.

    2011-03-01

    This work is devoted to identifying the degradation mechanism in various structures of a poly(3-hexylthiophene) (P3HT):6,6-phenyl C61-butyric acid methyl ester (PCBM)-based solar cell. We have tried to identify the dominant initial degradation mechanism on the basis of experimental studies carried out on different structures of an organic solar cell. It is known that many of these problems can be solved by means of the following: using proper electrodes and a suitable annealing temperature and duration, improving the morphology of the active film and maintaining a donor-acceptor phase-segregated ordered network as far as possible. The present studies have been carried out both in the dark and under illumination, and it is suggested that initial degradation plays a key role in device performance. The dominant degradation mechanism is the growth of the donor-acceptor complex with time, which not only reduces the effective surface area but also hampers the charge separation. The little change in VOC and the significant change in JSC suggest that once the LiF/Al electrode is improved, one must modify the structure either by introducing a thin layer of high-molecular-weight P3HT between PEDOT:PSS (poly(3,4-ethylenedioxythiopene) poly(styrenesulfonate)) and photoactive P3HT:PCBM layers or by introducing an optimized content of P3HT nanofibrils/nanoparticles into the P3HT:PCBM blend. The best structure was found to be ITO/PEDOT:PSS/P3HT:PCBM/LiF/Al and it can be improved by the above two methods.

  19. π-Conjugated zwitterions as paradigm of donor-acceptor building blocks in organic-based materials.

    PubMed

    Beverina, Luca; Pagani, Giorgio A

    2014-02-18

    The very peculiar characteristics of zwitterions, as well as a clearand unambiguous definition, have been overlooked in past literature. However, these compounds are particularly important in view of the impact they have had in the recent past and will likely continue to have in the future as components of performing functional organic and hybrid materials. In this Account, we primarily aim to define critically important organic concepts of zwitterions regarding both their design and nomenclature. We will particularly focus on a specific kind of zwitterions we define as π-conjugated zwitterions. These types of zwitterions are systems pertaining to the class ofdonor-acceptor (push-pull) molecules. In the ground state, they are preferentially represented in terms of an electron donor moiety bearing a negative net charge, and electron acceptor one bearing a positive net charge connected by a conjugated bridge. As such, they are possibly the most effective example of push-pull structure, possessing relevant features for applications like nonlinear optics, photovoltaics, imaging, and high capacitance dielectrics. In addition, the interaction between these dipolar compounds and the environment is highly specific and can be exploited in the construction of well-organized nanostructures, both in solution and in the solid state. According to the Gold Book of IUPAC for nomenclature, the distinction between zwitterions and the charged molecule called a betaine is subtle. The betaine is a particular class of zwitterion possessing an onium atom not bearing a hydrogen. The two terms are often considered equivalent, thus generating confusion while retrieving literature. In this Account, we define and describe π-conjugated zwitterions systems that are dipolar in the ground state, admitting resonance limiting structures that are neutral and chargeless. For the purpose of this Account and to the benefit of researchers striving to retrieve materials-related zwitterion literature

  20. A double-leg donor-acceptor molecular elevator: new insight into controlling the distance of two platforms.

    PubMed

    Zhang, Zhi-Jun; Han, Min; Zhang, Heng-Yi; Liu, Yu

    2013-04-01

    A double-leg elevator with an electron-rich anthracene moiety at the platformlike component and an electron-deficient naphthalenediimide unit in the middle of a double-leg riglike component was prepared through "click chemistry", in which the reversible elevator movement between different levels could be controlled upon the addition of base and acid. PMID:23534551

  1. Enhanced functionality for donor-acceptor oligothiophenes by means of inclusion of BODIPY: synthesis, electrochemistry, photophysics, and model chemistry.

    PubMed

    Collado, Daniel; Casado, Juan; Rodríguez González, Sandra; López Navarrete, Juan T; Suau, Rafael; Perez-Inestrosa, Ezequiel; Pappenfus, Ted M; Raposo, M Manuela M

    2011-01-10

    We have synthesized several new push-pull oligothiophenes based on the boron dipyrromethene (BODIPY) moiety as the electron acceptor and the more well-known oligothiophenes substituted with N,N-dialkylamino functions to enhance their electron-donor ability. A complete characterization of the electronic properties has been carried out; it consists of their photophysical, electrochemical, and vibrational properties. The compounds have been studied after chemical treatment with acids and after oxidation. In this regard, they can be termed as NIR dyes and amphoteric redox electroactive molecules. We have described the presence of dual fluorescence in these molecules and fluorescence quenching either by energy transfer or, in the push-pull molecules, by electron exchange. The combination of electrochemical and proton reversibility along with the interesting optical properties of the new species offer an interesting platform for sensor and material applications.

  2. Push-pull macrocycles: donor-acceptor compounds with paired linearly conjugated or cross-conjugated pathways.

    PubMed

    Leu, Wade C W; Fritz, Amanda E; Digianantonio, Katherine M; Hartley, C Scott

    2012-03-01

    Two-dimensional π-systems are of current interest in the design of functional organic molecules, exhibiting unique behavior for applications in organic electronics, single-molecule devices, and sensing. Here we describe the synthesis and characterization of "push-pull macrocycles": electron-rich and electron-poor moieties linked by a pair of (matched) conjugated bridges. We have developed a two-component macrocyclization strategy that allows these structures to be synthesized with efficiencies comparable to acyclic donor-bridge-acceptor systems. Compounds with both cross-conjugated (m-phenylene) and linearly conjugated (2,5-thiophene) bridges have been prepared. As expected, the compounds undergo excitation to locally excited states followed by fluorescence from charge-transfer states. The m-phenylene-based systems exhibit slower charge-recombination rates presumably due to reduced electronic coupling through the cross-conjugated bridges. Interestingly, pairing the linearly conjugated 2,5-thiophene bridges also slows charge recombination. DFT calculations of frontier molecular orbitals show that the direct HOMO-LUMO transition is polarized orthogonal to the axis of charge transfer for these symmetrical macrocyclic architectures, reducing the electronic coupling. We believe the push-pull macrocycle design may be useful in engineering functional frontier molecular orbital symmetries.

  3. Improved Exciton Dissociation at Semiconducting Polymer:ZnO Donor:Acceptor Interfaces via Nitrogen Doping of ZnO

    PubMed Central

    Musselman, Kevin P; Albert-Seifried, Sebastian; Hoye, Robert L Z; Sadhanala, Aditya; Muñoz-Rojas, David; MacManus-Driscoll, Judith L; Friend, Richard H

    2014-01-01

    Exciton dissociation at the zinc oxide/poly(3-hexylthiophene) (ZnO/P3HT) interface as a function of nitrogen doping of the zinc oxide, which decreases the electron concentration from approximately 1019 cm−3 to 1017 cm−3, is reported. Exciton dissociation and device photocurrent are strongly improved with nitrogen doping. This improved dissociation of excitons in the conjugated polymer is found to result from enhanced light-induced de-trapping of electrons from the surface of the nitrogen-doped ZnO. The ability to improve the surface properties of ZnO by introducing a simple nitrogen dopant has general applicability. PMID:25520604

  4. Theoretical insight on novel donor-acceptor exTTF-based dyes for dye-sensitized solar cells.

    PubMed

    Calbo, Joaquín; Viruela, Pedro M; Ortí, Enrique

    2014-04-01

    A thorough density functional theory study is performed for the three carboxyl-based derivatives of the exTTF-TCF chromophore, where the π-extended tetrathiafulvalene (exTTF) electron-donor is linked to the tricyanofuran (TCF) electron-acceptor through an ethylene bridge, as dyes for dye-sensitized solar cells. Calculations predict that the carboxyl group in the acceptor moiety adopts an adequate orientation for an efficient anchoring on the semiconductor TiO₂ surface. The carboxylic acid group holds a negative charge twice larger than the cyano moiety that favors the electron injection to the semiconductor. Time-dependent calculations allow for the assignment of the absorption bands in the UV-vis spectrum of exTTF-TCF and confirm the presence of two low-lying charge-transfer electronic transitions that account for the moderately-intense absorption in the 450-800 nm range. The striking optical absorption properties of exTTF-TCF are preserved for the carboxylic analogues. Finally, periodic calculations show relevant topological differences between the carboxylic derivatives anchored on the TiO₂ surface, which would notably influence in the power conversion efficiency of a dye-sensitized solar cell. PMID:24643466

  5. Efficiency improvement of new Tetrathienoacene-based dyes by enhancing donor, acceptor and bridge units, a theoretical study

    NASA Astrophysics Data System (ADS)

    Tavangar, Zahra; Zareie, Nazanin

    2016-10-01

    A series of metal free Tetrathienoacene-based (TTA-based) organic dyes are designed and investigated as sensitizers for application in dye sensitized solar cells (DSSCs). Density function theory and time dependent density function theory calculations were performed on these dyes at vacuum and orthodichlorobenzene as the solvent. Effects of changing π-conjugation bridges and different functional groups in acceptor and donor units were investigated. UV-Vis absorption spectra were simulated to show the wavelength shifting and absorption properties. Inserting nitro and acyl chloride functional groups in acceptor and NH2 in donor units leads to the reduction of HOMO-LUMO gap by lowering the lowest unoccupied molecular orbital (LUMO) energy level and raising the highest occupied molecular orbital (HOMO) energy level and the increase in effective parameters in DSSC' efficiency. The results show that changing spacer units from thiophene to furan has a great effect on electronic structure and absorption spectra. Investigation of the electron distributions of frontier orbitals shows the HOMO and LUMO localization in donor and acceptor, respectively. Some key parameters that were studied here include light harvesting efficiency, free energy of electron injection and open circuit photo-voltage.

  6. Synthesis and Photovoltaic Properties of a New Class of Donor-Acceptor Alternating Copolymers Containing Pechmann-Dye Derivatives

    NASA Astrophysics Data System (ADS)

    Jung, Jae Woong; Jo, Won Ho

    2011-03-01

    Over the last decade, various low bandgap copolymers that exhibit over 5% power conversion efficiency have been developed. However, the synthesis of most low-bandgap polymers is complicated with relatively long synthetic routes and low yield. In this work, a new series of novel alternating copolymers composed of thiophene and Pechmann-dye derivatives were synthesized and used as an electron donor material of bulk heterojunction polymer solar cells. Two Pechmann-dye derivatives, 5,5'-bis-(3-octyl-thiophen-2-yl)-[3,3']bifuranylidene-2,2'-dione and 3,7-bis-(3-octyl-thiophen-2-yl)-pyrano[4,3-c]pyran-1,5-dione which have high molar absorption coefficient, strong electron-deficient core, and planar structure, were easily synthesized via simple three steps with high yield. The use of the Pechmann-dye derivatives as a building block for copolymers results in promising optical, electrochemical, and photophysical properties. Morphology, charge transport, and photovoltaic characteristics of the new copolymers will be discussed.

  7. "Hot or cold": how do charge transfer states at the donor-acceptor interface of an organic solar cell dissociate?

    PubMed

    Bässler, Heinz; Köhler, Anna

    2015-11-21

    Electron transfer from an excited donor to an acceptor in an organic solar cell (OSC) is an exothermic process, determined by the difference in the electronegativities of donor and acceptor. It has been suggested that the associated excess energy facilitates the escape of the initially generated electron-hole pair from their mutual coulomb well. Recent photocurrent excitation spectroscopy on conjugated polymer/PCBM cells challenged this view. In this perspective we shall briefly outline the strengths and weaknesses of relevant experimental approaches and concepts. We shall enforce the notion that the charge separating state is a vibrationally cold charge transfer (CT) state. It can easily dissociate provided that (i) there is electrostatic screening at the interface and (ii) the charge carriers are delocalized, e.g. if the donor is a well ordered conjugated polymer. Both effects diminish the coulomb attraction and assure that the in-built electric field existing in the OSC under short current condition is already sufficient to separate most the CT states. The remaining CT excitations relax towards tail states of the disorder controlled density of states distribution, such as excimer forming states, that are more tightly bound and have longer lifetimes.

  8. Examining the effect of the dipole moment on charge separation in donor-acceptor polymers for organic photovoltaic applications.

    PubMed

    Carsten, Bridget; Szarko, Jodi M; Son, Hae Jung; Wang, Wei; Lu, Luyao; He, Feng; Rolczynski, Brian S; Lou, Sylvia J; Chen, Lin X; Yu, Luping

    2011-12-21

    A new low band gap copolymer PBB3 containing [6,6']bi[thieno[3,4-b]thiophenyl]-2,2'-dicarboxylic acid bis-(2-butyloctyl) ester (BTT) and 4,8-bis(2-butyloctyl)benzo[1,2-b:4,5-b']dithiophene (BDT) units was synthesized and tested for solar cell efficiency. PBB3 showed a broad absorbance in the near-IR region with a substantially red-shifted (by more than 100 nm) λ(max) at 790 nm as compared to the PTB series of polymers, which have been previously reported. The PBB3 polymer also showed both a favorable energy level match with PCBM (with a LUMO energy level of -3.29 eV) and a favorable film domain morphology as evidenced by TEM images. Despite these seemingly optimal parameters, a bulk heterojunction (BHJ) photovoltaic device fabricated from a blend of PBB3 and PC(71)BM showed an overall power conversion efficiency (PCE) of only 2.04% under AM 1.5G/100 mW cm(-2). The transient absorption spectra of PBB3 showed the absence of cationic and pseudo charge transfer states that were observed previously in the PTB series polymers, which were also composed of alternating thienothiophene (TT) and BDT units. We compared the spectral features and electronic density distribution of PBB3 with those of PTB2, PTB7, and PTBF2. While PTB2 and PTB7 have substantial charge transfer characteristics and also relatively large local internal dipoles through BDT to TT moieties, PTBF2 and PBB3 have minimized internal dipole moments due to the presence of two adjacent TT units (or two opposing fluorine atoms in PTBF2) with opposite orientations or internal dipoles. PBB3 showed a long-lived excitonic state and the slowest electron transfer dynamics of the series of polymers, as well as the fastest recombination rate of the charge-separated (CS) species, indicating that electrons and holes are more tightly bound in these species. Consequently, substantially lower degrees of charge separation were observed in both PBB3 and PTBF2. These results show that not only the energetics but also the

  9. Base pair sensitivity and enhanced ON/OFF ratios of DNA-binding: donor-acceptor-donor fluorophores.

    PubMed

    Wilson, James N; Wigenius, Jens; Pitter, Demar R G; Qiu, Yanhua; Abrahamsson, Maria; Westerlund, Fredrik

    2013-10-10

    The photophysical properties of two recently reported live cell compatible, DNA-binding dyes, 4,6-bis(4-(4-methylpiperazin-1-yl)phenyl)pyrimidin-2-ol, 1, and [1,3-bis[4-(4-methylpiperazin-1-yl)phenyl]-1,3-propandioato-κO, κO']difluoroboron, 2, are characterized. Both dyes are quenched in aqueous solutions, while binding to sequences containing only AT pairs enhances the emission. Binding of the dyes to sequences containing only GC pairs does not produce a significant emission enhancement, and for sequences containing both AT and GC base pairs, emission is dependent on the length of the AT pair tracts. Through emission lifetime measurements and analysis of the dye redox potentials, photoinduced electron transfer with GC pairs is implicated as a quenching mechanism. Binding of the dyes to AT-rich regions is accompanied by bathochromic shifts of 26 and 30 nm, respectively. Excitation at longer wavelengths thus increases the ON/OFF ratio of the bound probes significantly and provides improved contrast ratios in solution as well as in fluorescence microscopy of living cells. PMID:24079271

  10. Donor-acceptor systems: energy transfer from CdS quantum dots/rods to Nile Red dye.

    PubMed

    Sadhu, Suparna; Patra, Amitava

    2008-10-01

    We demonstrate strong evidence of shape-dependent efficient resonance energy transfer between CdS quantum dots (QDs) and quantum rods (QRs) (donor) to Nile Red dye (acceptor). We also report a simple solution-based method for the preparation of high quality CdS QDs and CdS QRs at relatively low temperature. The observed quenching of PL intensities are 78.8 % and 63.8 % for CdS QDs and QRs, respectively in the presence of Nile Red dye. The calculated energy-transfer efficiencies are 45 % and 19 % from QDs and QRs to dyes, respectively. The energy transfer varies with changing the shape of the nanoparticles. The estimated Förster distances (R(0)) are 37.8 and 33.8 A for CdS QDs and QRs, respectively. In the present study, the estimated distances (r) between one donor and one acceptor are 39.1 and 43.1 A for QDs and QRs, respectively, using the efficiency of Förster resonance energy transfer (FRET) which depends on the inverse sixth power of the distance of separations between one nanocrystal and one dye molecule. Considering single donor and multiple acceptors interactions, the calculated average distances (r(n)) between the donor and acceptor are 47.7 and 53.9 A for QD's and QR's, respectively. The steady-state and time-resolved spectroscopic analysis of nanoassemblies confirm the formation of one donor and multiple acceptors.

  11. Quantum-Chemical Studies on Excitation Energy Transfer Processes in BODIPY-Based Donor-Acceptor Systems.

    PubMed

    Spiegel, J Dominik; Kleinschmidt, Martin; Larbig, Alexander; Tatchen, Jörg; Marian, Christel M

    2015-09-01

    BODIPY-based excitation energy transfer (EET) cassettes are experimentally extensively studied and serve as excellent model systems for the investigation of photophysical processes, since they occur in any photosynthetic system and in organic photovoltaics. In the present work, the EET rates in five BODIPY-based EET cassettes in which anthracene serves as the donor have been determined, employing the monomer transition density approach (MTD) and the ideal dipole approximation (IDA). To this end, a new computer program has been devised that calculates the direct and exchange contributions to the excitonic coupling (EC) matrix element from transition density matrices generated by a combined density functional and multireference configuration interaction (DFT/MRCI) calculation for the monomers. EET rates have been calculated according to Fermi's Golden Rule from the EC and the spectral overlap, which was obtained from the calculated vibrationally resolved emission and absorption spectra of donor and acceptor, respectively. We find that the direct contribution to the EC matrix element is dominant in the studied EET cassettes. Furthermore, we show that the contribution of the molecular linker to the EET rate cannot be neglected. In our best fragment model, the molecular linker is attached to the donor moiety. For cassettes in which the transition dipole moments of donor and acceptor are oriented in parallel manner, our results confirm the experimental findings reported by Kim et al. [J. Phys. Chem. A 2006, 110, 20-27]. In cassettes with a perpendicular orientation of the donor and acceptor transition dipole moments, dynamic effects turn out to be important. PMID:26575926

  12. Quantum-Chemical Studies on Excitation Energy Transfer Processes in BODIPY-Based Donor-Acceptor Systems.

    PubMed

    Spiegel, J Dominik; Kleinschmidt, Martin; Larbig, Alexander; Tatchen, Jörg; Marian, Christel M

    2015-09-01

    BODIPY-based excitation energy transfer (EET) cassettes are experimentally extensively studied and serve as excellent model systems for the investigation of photophysical processes, since they occur in any photosynthetic system and in organic photovoltaics. In the present work, the EET rates in five BODIPY-based EET cassettes in which anthracene serves as the donor have been determined, employing the monomer transition density approach (MTD) and the ideal dipole approximation (IDA). To this end, a new computer program has been devised that calculates the direct and exchange contributions to the excitonic coupling (EC) matrix element from transition density matrices generated by a combined density functional and multireference configuration interaction (DFT/MRCI) calculation for the monomers. EET rates have been calculated according to Fermi's Golden Rule from the EC and the spectral overlap, which was obtained from the calculated vibrationally resolved emission and absorption spectra of donor and acceptor, respectively. We find that the direct contribution to the EC matrix element is dominant in the studied EET cassettes. Furthermore, we show that the contribution of the molecular linker to the EET rate cannot be neglected. In our best fragment model, the molecular linker is attached to the donor moiety. For cassettes in which the transition dipole moments of donor and acceptor are oriented in parallel manner, our results confirm the experimental findings reported by Kim et al. [J. Phys. Chem. A 2006, 110, 20-27]. In cassettes with a perpendicular orientation of the donor and acceptor transition dipole moments, dynamic effects turn out to be important.

  13. Crystal Structures of Aspergillus japonicus Fructosyltransferase Complex with Donor/Acceptor Substrates Reveal Complete Subsites in the Active Site for Catalysis*

    PubMed Central

    Chuankhayan, Phimonphan; Hsieh, Chih-Yu; Huang, Yen-Chieh; Hsieh, Yi-You; Guan, Hong-Hsiang; Hsieh, Yin-Cheng; Tien, Yueh-Chu; Chen, Chung-De; Chiang, Chien-Min; Chen, Chun-Jung

    2010-01-01

    Fructosyltransferases catalyze the transfer of a fructose unit from one sucrose/fructan to another and are engaged in the production of fructooligosaccharide/fructan. The enzymes belong to the glycoside hydrolase family 32 (GH32) with a retaining catalytic mechanism. Here we describe the crystal structures of recombinant fructosyltransferase (AjFT) from Aspergillus japonicus CB05 and its mutant D191A complexes with various donor/acceptor substrates, including sucrose, 1-kestose, nystose, and raffinose. This is the first structure of fructosyltransferase of the GH32 with a high transfructosylation activity. The structure of AjFT comprises two domains with an N-terminal catalytic domain containing a five-blade β-propeller fold linked to a C-terminal β-sandwich domain. Structures of various mutant AjFT-substrate complexes reveal complete four substrate-binding subsites (−1 to +3) in the catalytic pocket with shapes and characters distinct from those of clan GH-J enzymes. Residues Asp-60, Asp-191, and Glu-292 that are proposed for nucleophile, transition-state stabilizer, and general acid/base catalyst, respectively, govern the binding of the terminal fructose at the −1 subsite and the catalytic reaction. Mutants D60A, D191A, and E292A completely lost their activities. Residues Ile-143, Arg-190, Glu-292, Glu-318, and His-332 combine the hydrophobic Phe-118 and Tyr-369 to define the +1 subsite for its preference of fructosyl and glucosyl moieties. Ile-143 and Gln-327 define the +2 subsite for raffinose, whereas Tyr-404 and Glu-405 define the +2 and +3 subsites for inulin-type substrates with higher structural flexibilities. Structural geometries of 1-kestose, nystose and raffinose are different from previous data. All results shed light on the catalytic mechanism and substrate recognition of AjFT and other clan GH-J fructosyltransferases. PMID:20466731

  14. Distance distributions recovered from steady-state fluorescence measurements on thirteen donor-acceptor pairs with different Förster distances.

    PubMed

    Wiczk, W; Eis, P S; Fishman, M N; Johnson, M L; Lakowicz, J R

    1991-12-01

    The end-to-end distance distribution of a flexible molecule was recovered from steady-state fluorescence energy transfer measurements using the method suggested by Cantor and Pechukas (Proc. Natl. Acad. Sci. USA 68, 2099-2101, 1971). In this method, the Förster distance (R 0) is varied by attaching different donor-acceptor (D-A) pairs to the flexible linker of interest. Distance distributions are then recovered from energy transfer efficiency measurements on the set of D-A pairs with differentR 0 values. Thirteen D-A pair compounds were synthesized withR 0 values ranging from 6 to 32 Å. Each compound contained a tryptamine donor linked by an alkyl chain (∼10 carbons) to 1 of 13 acceptors. Using these compounds, we have experimentally confirmed the Cantor and Pechukas method for recovering distance distributions. The measured transfer efficiencies, as a function ofR 0, were fit to the transfer efficiencies predicted for both Gaussian and skewed Gaussian distance distributions. The data support the existence of a skewed Gaussian distribution, and we believe that this is the first experimental observation of an asymmetric distribution for a flexible molecule using fluorescence resonance energy transfer measurements. Finally, the experimentally recovered distance distribution was found to be in good agreement with the distribution predicted from the rotational isomeric state model of Flory (Statistical Mechanics of Chain Molecules, John Wiley & Sons, New York, 1969, Chaps. 1, 3, and 5) but not with the predicted distribution for a freely rotating or freely jointed chain. PMID:24243077

  15. Photoinduced electron transfer and geminate recombination in solution

    SciTech Connect

    Song, L.; Swallen, S.F.; Dorfman, R.C.; Weidemaier, K.; Fayer, M.D. )

    1993-02-18

    Intermolecular electron transfer and geminate recombination are explored experimentally in both solid and liquid solutions using the same donor-acceptor pair. The solvents were chosen to have similar chemical and dielectric properties, but vastly different viscosities. Systems of an electron donor, rubrene, and varying concentrations of an electron acceptor, duroquinone, were studied. The solvents used were diethyl sebacate (liquid) and sucrose octaacetate (solid). Forward electron transfer was studied using time-resolved and steady-state fluorescence measurements for a variety of acceptor concentrations. Electron back-transfer (geminate recombination) was measured using pump-probe experiments. The data were analyzed using a theoretical treatment that takes into account diffusion of the donor and acceptors, a distance-dependent (exponential) transfer rate, Coulomb interactions between the ions generated by the forward transfer, and donor-acceptor and acceptor-acceptor excluded volumes. The forward transfer data, in both the solid and liquid solutions, are in very good agreement with calculations. Virtually identical forward transfer parameters are obtained from the solid and liquid samples. The back-transfer parameters obtained from the measurements on solid solution are able to reproduce the liquid solution's back-transfer data, but only when the high-frequency dielectric constant is used. The use of this value for the dielectric constant is discussed. 48 refs., 10 figs.

  16. Density functional theory approach to gold-ligand interactions: Separating true effects from artifacts

    NASA Astrophysics Data System (ADS)

    Koppen, Jessica V.; Hapka, Michał; Modrzejewski, Marcin; Szcześniak, Małgorzata M.; Chałasiński, Grzegorz

    2014-06-01

    Donor-acceptor interactions are notoriously difficult and unpredictable for conventional density functional theory (DFT) methodologies. This work presents a reliable computational treatment of gold-ligand interactions of the donor-acceptor type within DFT. These interactions require a proper account of the ionization potential of the electron donor and electron affinity of the electron acceptor. This is accomplished in the Generalized Kohn Sham framework that allows one to relate these properties to the frontier orbitals in DFT via the tuning of range-separated functionals. A donor and an acceptor typically require different tuning schemes. This poses a problem when the binding energies are calculated using the supermolecular method. A two-parameter tuning for the monomer properties ensures that a common functional, optimal for both the donor and the acceptor, is found. A reliable DFT approach for these interactions also takes into account the dispersion contribution. The approach is validated using the water dimer and the (HAuPH3)2 aurophilic complex. Binding energies are computed for Au4 interacting with the following ligands: SCN-, benzenethiol, benzenethiolate anion, pyridine, and trimethylphosphine. The results agree for the right reasons with coupled-cluster reference values.

  17. Phase transitions and photoinduced transformations at high pressure in the molecular donor-acceptor fullerene complex (Cd(dedtc){sub 2}){sub 2} · C{sub 60}

    SciTech Connect

    Meletov, K. P.; Konarev, D. V.; Tolstikova, A. O.

    2015-06-15

    The Raman spectra of crystals of C{sub 60} fullerene-cadmium diethyldithiocarbamate molecular donor-acceptor complexes (Cd(dedtc){sub 2}){sub 2} · C{sub 60} were measured at pressures of up to 17 GPa, and the crystal lattice parameters of these complexes were determined at pressures of up to 6 GPa. An increase in pressure up to ∼2 GPa leads to changes in the Raman spectra, which are manifested by splitting of the intramolecular H{sub g}(1)-H{sub g}(8) phonon modes and by softening of the A{sub g}(2) mode of the C{sub 60} molecule. A further increase in pressure up to 17 GPa does not induce significant new changes to the Raman spectra, while a decrease is accompanied by the reverse transformation at a pressure of about 2 GPa. The pressure dependence of the lattice parameters also exhibits a reversible feature at 2 GPa related to a jumplike decrease in compressibility. All these data are indicative of a phase transition in the vicinity of 2 GPa related to the formation of covalent bonds between C{sub 60} molecules and, probably, the appearance of C{sub 120} dimers in fullerene layers. It was also found that, in the pressure interval from 2 to 6.3 GPa, the Raman spectra of complexes exhibit photoinduced transformations under prolonged exposure to laser radiation with a wavelength of λ = 532 nm and power density up to 5000 W/cm{sup 2}. These changes are manifested by splitting and softening of the A{sub g}(2) mode and resemble analogous changes accompanying the photopolymerization of C{sub 60} fullerene. The intensity of new bands exhibits exponential growth with increasing exposure time. The photopolymer yield depends on both the laser radiation power and external pressure. The A{sub g}(2) mode splitting under irradiation can be related to the formation of photo-oligomers with various numbers of intermolecular covalent bonds per C{sub 60} molecule.

  18. Electron-Electron Interactions in Artificial Graphene

    NASA Astrophysics Data System (ADS)

    Räsänen, E.; Rozzi, C. A.; Pittalis, S.; Vignale, G.

    2012-06-01

    Recent advances in the creation and modulation of graphenelike systems are introducing a science of “designer Dirac materials”. In its original definition, artificial graphene is a man-made nanostructure that consists of identical potential wells (quantum dots) arranged in an adjustable honeycomb lattice in the two-dimensional electron gas. As our ability to control the quality of artificial graphene samples improves, so grows the need for an accurate theory of its electronic properties, including the effects of electron-electron interactions. Here we determine those effects on the band structure and on the emergence of Dirac points.

  19. Electron-electron interactions in artificial graphene

    NASA Astrophysics Data System (ADS)

    Rasanen, Esa

    2013-03-01

    Recent advances in the creation and modulation of graphenelike systems are introducing a science of ``designer Dirac materials.'' In its original definition, artificial graphene is a man-made nanostructure that consists of identical potential wells (quantum dots) arranged in an adjustable honeycomb lattice in the two-dimensional electron gas. As our ability to control the quality of artificial graphene samples improves, so grows the need for an accurate theory of its electronic properties, including the effects of electron-electron interactions. Here we determine those effects on the band structure and on the emergence of Dirac points, and discuss future investigations and challenges in this field.

  20. Electron-excited molecule interactions

    SciTech Connect

    Christophorou, L.G. Tennessee Univ., Knoxville, TN . Dept. of Physics)

    1991-01-01

    In this paper the limited but significant knowledge to date on electron scattering from vibrationally/rotationally excited molecules and electron scattering from and electron impact ionization of electronically excited molecules is briefly summarized and discussed. The profound effects of the internal energy content of a molecule on its electron attachment properties are highlighted focusing in particular on electron attachment to vibrationally/rotationally and to electronically excited molecules. The limited knowledge to date on electron-excited molecule interactions clearly shows that the cross sections for certain electron-molecule collision processes can be very different from those involving ground state molecules. For example, optically enhanced electron attachment studies have shown that electron attachment to electronically excited molecules can occur with cross sections 10{sup 6} to 10{sup 7} times larger compared to ground state molecules. The study of electron-excited molecule interactions offers many experimental and theoretical challenges and opportunities and is both of fundamental and technological significance. 54 refs., 15 figs.

  1. Electron Photon Interaction Cross Sections

    2014-11-01

    Version 00 The Electron Photon Interaction Cross Sections, EPICS, provides the atomic data needed to perform coupled Electron-Photon transport calculations, to produce accurate macroscopic results, such as energy deposit and dose. Atomic data is provided for elements, Z = 1 to 100, over the energy range 10 eV to 100 GeV; note that nuclear data, such as photo-nuclear, and data for compounds, are not included. All data is in a simple computer independent text formatmore » that is standard and presented to a high precision that can be easily read by computer codes written in any computer language, e.g., C, C++, and FORTRAN. EPICS includes four separate data bases that are designed to be used in combination, these include, • The Evaluated Electron Data Library (EEDL), to describe the interaction of electrons with matter. • The Evaluated Photon Data Library (EPDL), to describe the interaction of photons with matter. • The Evaluated Atomic Data Library (EADL), to describe the emission of electrons and photons back to neutrality following an ionizing event, caused by either electron or photon interactions. • The Evaluated Excitation Data Library (EXDL), to describe the excitation of atoms due to photon interaction. All of these are available in the Extended ENDL format (ENDLX) in which the evaluations were originally performed. The first three are also available in the ENDF format; as yet ENDF does not include formats to handle excitation data (EXDL).« less

  2. Electron Photon Interaction Cross Sections

    SciTech Connect

    Cullen, D. E.

    2014-11-01

    Version 00 The Electron Photon Interaction Cross Sections, EPICS, provides the atomic data needed to perform coupled Electron-Photon transport calculations, to produce accurate macroscopic results, such as energy deposit and dose. Atomic data is provided for elements, Z = 1 to 100, over the energy range 10 eV to 100 GeV; note that nuclear data, such as photo-nuclear, and data for compounds, are not included. All data is in a simple computer independent text format that is standard and presented to a high precision that can be easily read by computer codes written in any computer language, e.g., C, C++, and FORTRAN. EPICS includes four separate data bases that are designed to be used in combination, these include, • The Evaluated Electron Data Library (EEDL), to describe the interaction of electrons with matter. • The Evaluated Photon Data Library (EPDL), to describe the interaction of photons with matter. • The Evaluated Atomic Data Library (EADL), to describe the emission of electrons and photons back to neutrality following an ionizing event, caused by either electron or photon interactions. • The Evaluated Excitation Data Library (EXDL), to describe the excitation of atoms due to photon interaction. All of these are available in the Extended ENDL format (ENDLX) in which the evaluations were originally performed. The first three are also available in the ENDF format; as yet ENDF does not include formats to handle excitation data (EXDL).

  3. Polar solvation and electron transfer

    SciTech Connect

    Not Available

    1993-04-13

    The report is divided into the following sections: completion of previous studies on solvation dynamics, dipole lattice studies, inertial components of solvation response, simple models of solvation dynamics, rotational dynamics and dielectric friction, intramolecular electron transfer reactions, and intermolecular donor-acceptor complexes.

  4. Interaction of Humic Acids with Organic Toxicants

    NASA Astrophysics Data System (ADS)

    Tchaikovskaya, O. N.; Yudina, N. V.; Maltseva, E. V.; Nechaev, L. V.; Svetlichnyi, V. A.

    2016-08-01

    Interaction of humic acids with polyaromatic hydrocarbons (PAH) (naphthalene and anthracene) and triazole series fungicides (cyproconazole (CC) and tebuconazole (TC)) is investigated by the method of fluorescence quenching depending on the concentration of substances in solutions and their structural features. Humic acids were modified by mechanochemical activation in a planetary mill. The complex character of intermolecular interactions between PAH and fungicides with humic acids, including donor-acceptor and hydrophobic binding, is established. Thermodynamically stable conformations of biocide molecules were estimated using ChemOffice CS Chem3D 8.0 by methods of molecular mechanics (MM2) and molecular dynamics. Biocide molecules with pH 7 are in energetically favorable position when the benzene and triazole rings are almost parallel to each other. After acidification of solutions to pH 4.5, the CC molecule retains the geometry for which donor-acceptor interactions are possible: the benzene ring in the molecule represents the electron donor, and triazole is the acceptor. In this case, the electron density in CC is redistributed easier, which is explained by a smaller number of carbon atoms between the triazole and benzene rings, unlike TC. As a result, the TC triazole ring is protonated to a greater degree, acquiring a positive charge, and enters into donoracceptor interactions with humic acid (HA) samples. The above-indicated bond types allow HA to participate actively in sorption processes and to provide their interaction with biocides and PAH and hence, to act as detoxifying agents for recultivation of the polluted environment.

  5. Electron-electron interaction in projectile electron loss

    SciTech Connect

    Huelskoetter, H.; Meyerhof, W.E.; Dillard, E.A.; Guardala, N.; Spooner, D.W. ); Feinberg, B. ); Belkacem, A. Sciences Division, Building 71-259, Lawrence Berkeley Laboratory, One Cyclotron Road, Berkeley, CA ); Alonso, J.R.; Krebs, G.F.; McMahan, M.A.; Rude, B.S ); Blumenfeld, L.; Gould, H. ); Rhoades-Brown, M.E. ); Schweppe, J. (Chemical Sciences Division, Building 71-259, Lawrence Berkeley Laboratory, One Cyclotron Road, Berkeley, CA (

    1991-08-01

    In ion-atom collisions where the projectile is ionized, target electrons act not only coherently by screening the target nucleus but they may also act incoherently by directly ejecting a projectile electron. This electron-electron interaction should be relatively most important for targets that have a low nuclear charge, since the cross section for a neutral target is roughly proportional to {ital Z}{sub {ital t}}{sup 2}+{ital Z}{sub {ital t}}, where {ital Z}{sub {ital t}}{sup 2} is the contribution due to the target nucleus and {ital Z}{sub {ital t}} comes from the target electrons. In order to investigate the electron-electron interaction, we have measured and calculated cross sections for Li{sup 2+}, C{sup 5+}, and O{sup 7+} on H{sub 2} and He, Au{sup 52+} on H{sub 2}, He, C, and N{sub 2}, Au{sup 75+} on H{sub 2} and N{sub 2}, U{sup 86+} on H{sub 2} and He, and U{sup 90+} on H{sub 2}. The collision energies range from 0.75 to 405 MeV/nucleon. The calculations have been performed in the plane-wave Born approximation. We demonstrate that for energies where the target electrons have sufficient kinetic energy in the projectile frame to ionize the projectile, the electron-electron interaction can lead to a significant increase in the total electron-loss cross section.

  6. Pellet interaction with runaway electrons

    SciTech Connect

    James, A. N.; Hollmann, E. M.; Yu, J.H.; Austin, M. E.; Commaux, Nicolas JC; Evans, T.E.; Humphrey, D. A.; Jernigan, T. C.; Parks, P. B.; Putvinski, S.; Strait, E. J.; Tynan, G. R.; Wesley, J. C.

    2011-01-01

    We describe results from recent experiments studying interaction of solid polystyrene pellets with a runaway electron current channel generated after cryogenic argon pellet rapid shutdown of DIII-D. Fast camera imaging shows the pellet trajectory and continuum emission from the subsequent explosion, with geometric calibration providing detailed explosion analysis and runaway energy. Electron cyclotron emission also occurs, associated with knock-on electrons broken free from the pellet by RE which then accelerate and runaway, and also with a short lived hot plasma blown off the pellet surface. In addition, we compare heating and explosion times from observations and a model of pellet heating and breakdown by runaway interaction. (C) 2011 Elsevier B.V. All rights reserved

  7. Theoretical investigations into optical and charge transfer properties of donor-acceptor 1,8-naphthalimide derivatives as possible organic light-emitting materials

    NASA Astrophysics Data System (ADS)

    Chai, Wandong; Jin, Ruifa

    2016-01-01

    A series of D-A naphthalimide-substituted fluorene derivatives have been designed to explore their optical, electronic, and charge transport properties as charge transport and/or luminescent materials for organic light-emitting diodes (OLEDs). The frontier molecular orbitals (FMOs) analysis turned out that the vertical electronic transitions of absorption and emission are characterized as intramolecular charge transfer (ICT). The calculated results show that their optical and electronic properties are affected by the substituent groups in fluorene moieties. Our results suggest that all selected candidates are promising as luminescent materials for OLEDs. In addition, all derivatives can be used as promising hole and electron transport materials while derivatives with dibenzothiophene fragment can be used as hole transport material only for OLEDs.

  8. Computational study on the effects of substituent and heteroatom on physical properties and solar cell performance in donor-acceptor conjugated polymers based on benzodithiophene.

    PubMed

    Zhang, Lvyong; Shen, Wei; He, Rongxing; Liu, Xiaorui; Fu, Zhiyong; Li, Ming

    2014-11-01

    Computationally driven material design has attracted increasing interest to accelerate the search for optimal conjugated donor materials in bulk heterojunction organic solar cells. A series of novel copolymers containing benzo[1,2-b:4,5-b']dithiophene (BDT) and thieno[3,4-c]pyrrole-4,6-dione (TPD) derivatives were simulated by density functional theory (DFT) and time-dependent density functional theory (TD-DFT). We performed a systematic study on the influences on molecular geometry parameters, electronic properties, optical properties, photovoltaic performances, and intermolecular stacking as well as hole mobility when different chalcogenophenes in TPD derivatives were used and functional groups with different electron-withdrawing abilities such as alkyl, fluorine, sufonyl, and cyano were introduced to the nitrogen positions in electron-deficient units. The substitution position of electron-withdrawing groups may cause little steric hindrance to the neighboring donor units, especially fluorine and cyano group. It was found that the incorporation of these new electron-deficient substituents and sulfur-selenium exchange can be applicable to further modify and optimize existing molecular structures. Our findings will provide valuable guidance and chemical methodologies for a judicious material design of conjugated polymers for solar cell applications with desirable photovoltaic characteristics.

  9. Effect of charge delocalization on radical ion pair electronic coupling

    NASA Astrophysics Data System (ADS)

    Sinks, Louise E.; Weiss, Emily A.; Giaimo, Jovan M.; Wasielewski, Michael R.

    2005-03-01

    Photoinduced charge separation and recombination were studied in a series of covalent donor-acceptor triads consisting of aniline, 1-aminonaphthalene, or 9-aminoanthracene donors (D) attached to a 4-aminonaphthalene-1,8-dicarboximide chromophore (ANI), which in turn is attached to a naphthalene-1,4:5,8-bis(dicarboximide) acceptor (NI) to give D-ANI-NI. The relationship between the molecular structure of D + rad and the magnitude of the electronic coupling between the radicals within D + rad -ANI-NI - rad was probed by direct measurements of the spin-spin exchange interaction, 2J, using magnetic field effects on the yield of the neutral triplet state resulting from charge recombination and by density functional theory calculations.

  10. Novel donor-acceptor polymer containing 4,7-bis(thiophen-2-yl)benzo[c][1,2,5]thiadiazole for polymer solar cells with power conversion efficiency of 6.21%.

    PubMed

    Han, Liangliang; Bao, Xichang; Hu, Tong; Du, Zhengkun; Chen, Weichao; Zhu, Dangqiang; Liu, Qian; Sun, Mingliang; Yang, Renqiang

    2014-06-01

    In order to improve the solution processability of 4,7-bis(thiophen-2-yl)benzo[c][1,2,5]thiadiazole (DTBT)-based polymers, novel donor-acceptor polymer PTOBDTDTBT containing DTBT and benzo[1,2-b:4,5-b']dithiophene (BDT) with conjugated side chain is designed and synthesized with narrow band gap 1.67 eV and low lying HOMO energy level -5.4 eV. The blend film of PTOBDTDTBT and PC71 BM exhibits uniform and smooth film with root-mean-square (RMS) surface roughness 1.15 nm because of the excellent solubility of PTOBDTDTBT when six octyloxy side chains are introduced. The hole mobility of the blend film is measured to be 4.4 × 10(-5) cm(2) V(-1) s(-1) by the space-charge-limited current (SCLC) model. The optimized polymer solar cells (PSCs) based on PTOBDTDTBT/PC71 BM exhibits an improved PCE of 6.21% with Voc = 0.80 V, Jsc = 11.94 mA cm(-2) and FF = 65.10%, one of the highest PCE in DTBT containing polymers.

  11. Adsorption geometry, molecular interaction, and charge transfer of triphenylamine-based dye on rutile TiO{sub 2}(110)

    SciTech Connect

    Yu Shun; Ahmadi, Sareh; Weissenrieder, Jonas; Goethelid, Mats; Zuleta, Marcelo; Tian Haining; Yang Xichuan; Schulte, Karina; Pietzsch, Annette; Hennies, Franz

    2010-12-14

    The fast development of new organic sensitizers leads to the need for a better understanding of the complexity and significance of their adsorption processes on TiO{sub 2} surfaces. We have investigated a prototype of the triphenylamine-cyanoacrylic acid (donor-acceptor) on rutile TiO{sub 2} (110) surface with special attention on the monolayer region. This molecule belongs to the type of dye, some of which so far has delivered the record efficiency of 10%-10.3% for pure organic sensitizers [W. Zeng, Y. Cao, Y. Bai, Y. Wang, Y. Shi, M. Zhang, F. Wang, C. Pan, and P. Wang, Chem. Mater. 22, 1915 (2010)]. The molecular configuration of this dye on the TiO{sub 2} surface was found to vary with coverage and adopt gradually an upright geometry, as determined from near edge x-ray absorption fine structure spectroscopy. Due to the molecular interaction within the increasingly dense packed layer, the molecular electronic structure changes systematically: all energy levels shift to higher binding energies, as shown by photoelectron spectroscopy. Furthermore, the investigation of charge delocalization within the molecule was carried out by means of resonant photoelectron spectroscopy. A fast delocalization ({approx}1.8 fs) occurs at the donor part while a competing process between delocalization and localization takes place at the acceptor part. This depicts the ''push-pull'' concept in donor-acceptor molecular system in time scale.

  12. Evaluating the extent of intramolecular charge transfer in the excited states of rhenium(I) donor-acceptor complexes with time-resolved vibrational spectroscopy.

    PubMed

    Yue, Yuankai; Grusenmeyer, Tod; Ma, Zheng; Zhang, Peng; Pham, Tri Tat; Mague, Joel T; Donahue, James P; Schmehl, Russell H; Beratan, David N; Rubtsov, Igor V

    2013-12-12

    Excited states in transition-metal complexes, even in those featuring ligands with strong electron donating and accepting properties, often involve only partial charge transfer between the donor and acceptor ligands. The excited-state properties of [Re(bpy)(CO)3L](+) compounds were studied, where L is 4-dimethylaminobenzonitrile (Re4DMABN), 3-dimethylaminobenzonitrile (Re3DMABN), and benzonitrile (ReBN) using time-resolved infrared (TRIR) and electronic spectroscopy methods as well as electronic structure computations. The DMABN complexes exhibit strongly solvent-dependent luminescence; the excited state lifetime decreases from microseconds in dichloromethane to several nanoseconds in mixed MeOH:DCM (1:1) solvent. Despite the similarities in the solvent dependence of the excited state dynamics and redox properties for Re3DMABN and Re4DMABN, the nature of the lowest energy excited states formed in these two compounds is drastically different. For example, the lowest energy excited state for Re4DMABN in the mixed solvent is assigned to the (4DMABN → bpy) ligand-to-ligand charge transfer (LLCT) state featuring partial charge transfer character. An equilibrium between a 3DMABN intraligand triplet ((3)IL) and a metal-ligand-to-ligand charge transfer (MLLCT) state is found for Re3DMABN in the mixed solvent with the latter at ca. 400 cm(-1) lower energy. The origin of such a drastic difference between the states involved in Re4DMABN and Re3DMABN is attributed to a difference in the energies of polarized quinoidal resonance structures in 4DMABN and 3DMABN ligands.

  13. Lowest excited states and optical absorption spectra of donor-acceptor copolymers for organic photovoltaics: a new picture emerging from tuned long-range corrected density functionals.

    PubMed

    Pandey, Laxman; Doiron, Curtis; Sears, John S; Brédas, Jean-Luc

    2012-11-01

    Polymers with low optical gaps are of importance to the organic photovoltaics community due to their potential for harnessing a large portion of the solar energy spectrum. The combination along their backbones of electron-rich and electron-deficient fragments contributes to the presence of low-lying excited states that are expected to display significant charge-transfer character. While conventional hybrid functionals are known to provide unsatisfactory results for charge-transfer excitations at the time-dependent DFT level, long-range corrected (LRC) functionals have been reported to give improved descriptions in a number of systems. Here, we use such LRC functionals, considering both tuned and default range-separation parameters, to characterize the absorption spectra of low-optical-gap systems of interest. Our results indicate that tuned LRC functionals lead to simulated optical-absorption properties in good agreement with experimental data. Importantly, the lowest-lying excited states (excitons) are shown to present a much more localized nature than initially anticipated.

  14. A Comparative PCET Study of a Donor-Acceptor Pair Linked by Ionized and Non-ionized Asymmetric Hydrogen-Bonded Interfaces

    PubMed Central

    Young, Elizabeth R.; Rosenthal, Joel; Hodgkiss, Justin M.

    2012-01-01

    A Zn(II) porphyrin-amidinium is the excited state electron donor (D) to a naphthalene diimide acceptor (A) appended with either a carboxylate or sulfonate functionality. The two-point hydrogen bond (---[H+]---) formed between the amidinium and carboxylate or sulfonate establishes a proton-coupled electron transfer (PCET) pathway for charge transfer. The two D---[H+]---A assemblies differ only by the proton configuration within the hydrogen bonding interface. Specifically, the amidinium transfers a proton to the carboxylate to form a non-ionized amidine-carboxylic acid two-point hydrogen network whereas the amidinium maintains both protons when bound to the sulfonate functionality forming an ionized amidinium-sulfonate two-point hydrogen network. These two interface configurations within the dyads thus allow for a direct comparison of PCET kinetics for the same donor and acceptor juxtaposed by an ionized and non-ionized hydrogen-bonded interface. Analysis of PCET kinetics ascertained from transient absorption and transient emission spectroscopy reveal that the ionized interface is more strongly impacted by the local solvent environment, thus establishing that the initial static configuration of the proton interface is a critical determinant to the kinetics of PCET. PMID:19489645

  15. One-Pot Synthesis, Spectroscopic and Physicochemical Studies of Quinoline Based Blue Emitting Donor-Acceptor Chromophores with Their Biological Application.

    PubMed

    Asiri, Abdullah M; Khan, Salman A; Al-Thaqafya, Saad H

    2015-09-01

    Blue emitting cyano substituted isoquinoline dyes were synthesized by one-pot multicomponent reactions (MCRs) of aldehydes, malononitrile, 6-methoxy-1,2,3,4-tetrahydro-naphthalin-1-one and ammonium acetate. Results obtained from spectroscopic (FT-IR, (1)H-NMR, (13)C-NMR, EI-MS) and elemental analysis of synthesized compounds was in good agreement with their chemical structures. UV-vis and fluorescence spectroscopy measurements proved that all compounds are good absorbent and fluorescent. Fluorescence polarity study demonstrated that these compounds were sensitive to the polarity of the microenvironment provided by different solvents. In addition, spectroscopic and physicochemical parameters, including electronic absorption, excitation coefficient, stokes shift, oscillator strength, transition dipole moment and fluorescence quantum yield were investigated in order to explore the analytical potential of synthesized compounds. The anti-bacterial activity of these compounds were first studied in vitro by the disk diffusion assay against two Gram-positive and two Gram-negative bacteria then the minimum inhibitory concentration (MIC) was determined with the reference of standard drug chloramphenicol. The results displayed that compound 3 was better inhibitors of both types of the bacteria (Gram-positive and Gram-negative) than chloramphenicol. Graphical Abstract ᅟ.

  16. Unsymmetrical Donor-Acceptor-Acceptor-π-Donor Type Benzothiadiazole-Based Small Molecule for a Solution Processed Bulk Heterojunction Organic Solar Cell.

    PubMed

    Gautam, Prabhat; Misra, Rajneesh; Siddiqui, Shahbaz A; Sharma, Ganesh D

    2015-05-20

    A D1-A-A'-π-D2 type (D = donor; A = acceptor) unsymmetrical small molecule denoted as BTD3 containing different end group donor moieties has been designed and synthesized for use as a donor in the solution processable bulk heterojunction (BHJ) solar cell. The BTD3 exhibits a low HOMO-LUMO gap of 1.68 eV and deeper HOMO energy level (-5.5 eV). Its LUMO energy level (-3.65 eV) is compatible with the LUMO level of PC71BM to facilitate the electron transfer from BTD3 to PC71BM in the BHJ solar cell. The solution processed BHJ solar cell with optimized BTD3:PC71BM active layer processed with THF solvent exhibited a PCE of 3.15% with Jsc = 7.45 mA/cm(2), Voc = 0.94 V, and FF = 0.45. Moreover, the device with optimized concentration of 3 vol. % 1-chloronaphthalene (CN) additive, i.e., CN/THF, showed significant enhancement in PCE up to 4.61% (Jsc = 9.48 mA/cm(2), Voc = 0.90 V, and FF = 0.54). The improvement in the PCE has been attributed to the appropriate nanoscale phase separation morphology, balance charge transport, and enhancement in the light harvesting ability of the active layer.

  17. Long-Range π-Conjugation in Phenothiazine-containing Donor-Acceptor Dyes for Application in Dye-Sensitized Solar Cells.

    PubMed

    Antony, Mini P; Moehl, Thomas; Wielopolski, Mateusz; Moser, Jacques-E; Nair, Shantikumar; Yu, Yong-Jae; Kim, Jong-Hyung; Kay, Kwang-Yol; Jung, Young-Sam; Yoon, Kyung Byung; Grätzel, Carole; Zakeeruddin, Shaik M; Grätzel, Michael

    2015-11-01

    Four organic donor-π-bridge-acceptor dyes containing phenothiazine as a spacer and cyanoacrylic acid as an acceptor were synthesized and tested as sensitizers in dye-sensitized solar cells (DSCs). The influence of iodide- and cobalt-based redox electrolytes on the photovoltaic device performance was investigated. In these new dyes, systematic π-conjugation was extended by inserting one or two phenothiazine moieties and investigated within the context of the resulting photoinduced charge-transfer properties. A detailed investigation, including transient absorption spectroscopy and quantum chemical methods, provided important information on the role of extended π-conjugation on the photophysical properties and photovoltaic device performance. Overall, the results showed that the extension of π-conjugation by one phenothiazine unit resulted in the best device performance owing to reduced recombination rates, whereas extension by two phenothiazine units reduced dye adsorption on TiO2 probably owing to the increase in molecular size. The performance of the dyes in DSCs was found to be a complex interaction between dye structure and size. PMID:26616683

  18. Polarization Energies at Organic-Organic Interfaces: Impact on the Charge Separation Barrier at Donor-Acceptor Interfaces in Organic Solar Cells.

    PubMed

    Ryno, Sean M; Fu, Yao-Tsung; Risko, Chad; Brédas, Jean-Luc

    2016-06-22

    We probe the energetic landscape at a model pentacene/fullerene (C60) interface to investigate the interactions between positive and negative charges, which are critical to the processes of charge separation and recombination in organic solar cells. Using a polarizable force field, we find that polarization energy, i.e., the stabilization a charge feels due to its environment, is larger at the interface than in the bulk for both a positive and a negative charge. The combination of the charge being more stabilized at the interface and the Coulomb attraction between the charges results in a barrier to charge separation at the pentacene/C60 interface that can be in excess of 0.7 eV for static configurations of the donor and acceptor locations. However, the impact of molecular motions, i.e., the dynamics, at the interface at room temperature results in a distribution of polarization energies and in charge separation barriers that can be significantly reduced. The dynamic nature of the interface is thus critical, with the polarization energy distributions indicating that sites along the interface shift in time between favorable and unfavorable configurations for charge separation.

  19. Charge separation in organic solar cells: Effects of Coulomb interaction, recombination and hole propagation

    NASA Astrophysics Data System (ADS)

    Nemati Aram, Tahereh; Asgari, Asghar; Mayou, Didier

    2016-07-01

    Bulk heterojunction (BHJ) organic photovoltaic cells are analysed within a simple efficient model that includes the important physical properties of such photovoltaic systems. In this model, in contrast with most of the previous studies, we take into account the motion of both the electron and the hole in the separation process at the donor-acceptor interface. We theoretically examine the exciton dissociation yield under the influences of charge Coulomb interaction and non-radiative recombination. We find that the electron-hole local Coulomb attraction and charge carriers' coupling parameters play an important role in the system performance and in the optimal energy conversion efficiency of the BHJ photocell. We show that the fixed-hole models tend to underestimate the yield.

  20. 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

    SciTech Connect

    Sontakke, Atul D. Katayama, Yumiko; Tanabe, Setsuhisa; Ueda, Jumpei; Dorenbos, Pieter

    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. 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.

  1. Splitting of type-I (N-B, P-Al) and type-II (N-Al, N-Ga) donor-acceptor pair spectra in 3C-SiC

    NASA Astrophysics Data System (ADS)

    Sun, J. W.; Ivanov, I. G.; Juillaguet, S.; Camassel, J.

    2011-05-01

    Discrete series of lines have been observed for many years in donor-acceptor pair (DAP) spectra in 3C-SiC. In this work, the splitting of both type-I (N-B, P-Al) and type-II (N-Al, N-Ga) DAP spectra in 3C-SiC has been systematically investigated by considering the multipole terms. For type-I spectra, in which either N or B substitutes on C sites or P and Al replace Si, the splitting energy of the substructure for a given shell is almost the same for both pairs. For type-II spectra, in which N is on the C site while Al and Ga acceptors replace Si, we find that, when compared with literature data, the splitting energy for a given shell is almost independent of the identity of the acceptor. For both type-I and type-II spectra, this splitting energy can be successfully explained by the octupole term V3 alone with k3 = -2 × 105 Å4 meV. Comparing the experimental donor and acceptor binding energies with the values calculated by the effective-mass model, this suggests that the shallow donor (N,P) ions can be treated as point charges while the charge distribution of the acceptor ions (Al,Ga,B) is distorted in accord with the Td point group symmetry, resulting in a considerable value for k3. This gives a reasonable explanation for the observed splitting energies for both type-I and type-II DAP spectra.

  2. Electronic coupling for charge transfer in donor-bridge-acceptor systems. Performance of the two-state FCD model.

    PubMed

    Voityuk, Alexander A

    2012-10-28

    Electronic coupling is a key parameter that determines the rate of electron transfer reactions and electrical conductivity of molecular wires. To examine the performance of a two-state approach based on the orthogonal transformation of adiabatic states to diabatic states, we compare the effective donor-acceptor coupling V(DA) computed with three different approaches in model donor-bridge-acceptor (D-B-A) systems. It is found that V(DA) derived with the two-state method accounts properly for both the direct and superexchange interactions. The approach becomes, however, less accurate with the increasing energy difference of the donor and acceptor states. We suggest a simple diagnostic to identify the situation when the estimated coupling might be inaccurate and consider how to improve the performance of the two-state scheme in such a case.

  3. Nonadiabatic rate constants for proton transfer and proton-coupled electron transfer reactions in solution: Effects of quadratic term in the vibronic coupling expansion.

    PubMed

    Soudackov, Alexander V; Hammes-Schiffer, Sharon

    2015-11-21

    Rate constant expressions for vibronically nonadiabatic proton transfer and proton-coupled electron transfer reactions are presented and analyzed. The regimes covered include electronically adiabatic and nonadiabatic reactions, as well as high-frequency and low-frequency proton donor-acceptor vibrational modes. These rate constants differ from previous rate constants derived with the cumulant expansion approach in that the logarithmic expansion of the vibronic coupling in terms of the proton donor-acceptor distance includes a quadratic as well as a linear term. The analysis illustrates that inclusion of this quadratic term in the framework of the cumulant expansion framework may significantly impact the rate constants at high temperatures for proton transfer interfaces with soft proton donor-acceptor modes that are associated with small force constants and weak hydrogen bonds. The effects of the quadratic term may also become significant in these regimes when using the vibronic coupling expansion in conjunction with a thermal averaging procedure for calculating the rate constant. In this case, however, the expansion of the coupling can be avoided entirely by calculating the couplings explicitly for the range of proton donor-acceptor distances sampled. The effects of the quadratic term for weak hydrogen-bonding systems are less significant for more physically realistic models that prevent the sampling of unphysical short proton donor-acceptor distances. Additionally, the rigorous relation between the cumulant expansion and thermal averaging approaches is clarified. In particular, the cumulant expansion rate constant includes effects from dynamical interference between the proton donor-acceptor and solvent motions and becomes equivalent to the thermally averaged rate constant when these dynamical effects are neglected. This analysis identifies the regimes in which each rate constant expression is valid and thus will be important for future applications to proton

  4. Nonadiabatic rate constants for proton transfer and proton-coupled electron transfer reactions in solution: Effects of quadratic term in the vibronic coupling expansion

    SciTech Connect

    Soudackov, Alexander V.; Hammes-Schiffer, Sharon

    2015-11-21

    Rate constant expressions for vibronically nonadiabatic proton transfer and proton-coupled electron transfer reactions are presented and analyzed. The regimes covered include electronically adiabatic and nonadiabatic reactions, as well as high-frequency and low-frequency proton donor-acceptor vibrational modes. These rate constants differ from previous rate constants derived with the cumulant expansion approach in that the logarithmic expansion of the vibronic coupling in terms of the proton donor-acceptor distance includes a quadratic as well as a linear term. The analysis illustrates that inclusion of this quadratic term in the framework of the cumulant expansion framework may significantly impact the rate constants at high temperatures for proton transfer interfaces with soft proton donor-acceptor modes that are associated with small force constants and weak hydrogen bonds. The effects of the quadratic term may also become significant in these regimes when using the vibronic coupling expansion in conjunction with a thermal averaging procedure for calculating the rate constant. In this case, however, the expansion of the coupling can be avoided entirely by calculating the couplings explicitly for the range of proton donor-acceptor distances sampled. The effects of the quadratic term for weak hydrogen-bonding systems are less significant for more physically realistic models that prevent the sampling of unphysical short proton donor-acceptor distances. Additionally, the rigorous relation between the cumulant expansion and thermal averaging approaches is clarified. In particular, the cumulant expansion rate constant includes effects from dynamical interference between the proton donor-acceptor and solvent motions and becomes equivalent to the thermally averaged rate constant when these dynamical effects are neglected. This analysis identifies the regimes in which each rate constant expression is valid and thus will be important for future applications to proton

  5. Nonadiabatic rate constants for proton transfer and proton-coupled electron transfer reactions in solution: Effects of quadratic term in the vibronic coupling expansion.

    PubMed

    Soudackov, Alexander V; Hammes-Schiffer, Sharon

    2015-11-21

    Rate constant expressions for vibronically nonadiabatic proton transfer and proton-coupled electron transfer reactions are presented and analyzed. The regimes covered include electronically adiabatic and nonadiabatic reactions, as well as high-frequency and low-frequency proton donor-acceptor vibrational modes. These rate constants differ from previous rate constants derived with the cumulant expansion approach in that the logarithmic expansion of the vibronic coupling in terms of the proton donor-acceptor distance includes a quadratic as well as a linear term. The analysis illustrates that inclusion of this quadratic term in the framework of the cumulant expansion framework may significantly impact the rate constants at high temperatures for proton transfer interfaces with soft proton donor-acceptor modes that are associated with small force constants and weak hydrogen bonds. The effects of the quadratic term may also become significant in these regimes when using the vibronic coupling expansion in conjunction with a thermal averaging procedure for calculating the rate constant. In this case, however, the expansion of the coupling can be avoided entirely by calculating the couplings explicitly for the range of proton donor-acceptor distances sampled. The effects of the quadratic term for weak hydrogen-bonding systems are less significant for more physically realistic models that prevent the sampling of unphysical short proton donor-acceptor distances. Additionally, the rigorous relation between the cumulant expansion and thermal averaging approaches is clarified. In particular, the cumulant expansion rate constant includes effects from dynamical interference between the proton donor-acceptor and solvent motions and becomes equivalent to the thermally averaged rate constant when these dynamical effects are neglected. This analysis identifies the regimes in which each rate constant expression is valid and thus will be important for future applications to proton

  6. Mechanisms of Bacterial Extracellular Electron Exchange.

    PubMed

    White, G F; Edwards, M J; Gomez-Perez, L; Richardson, D J; Butt, J N; Clarke, T A

    2016-01-01

    The biochemical mechanisms by which microbes interact with extracellular soluble metal ions and insoluble redox-active minerals have been the focus of intense research over the last three decades. The process presents two challenges to the microorganism. Firstly, electrons have to be transported at the cell surface, which in Gram-negative bacteria presents an additional problem of electron transfer across the ~6nm of the outer membrane. Secondly, the electrons must be transferred to or from the terminal electron acceptors or donors. This review covers the known mechanisms that bacteria use to transport electrons across the cell envelope to external electron donors/acceptors. In Gram-negative bacteria, electron transfer across the outer membrane involves the use of an outer membrane β-barrel and cytochrome. These can be in the form of a porin-cytochrome protein, such as Cyc2 of Acidithiobacillus ferrooxidans, or a multiprotein porin-cytochrome complex like MtrCAB of Shewanella oneidensis MR-1. For mineral-respiring organisms, there is the additional challenge of transferring the electrons from the cell to mineral surface. For the strict anaerobe Geobacter sulfurreducens this requires electron transfer through conductive pili to associated cytochrome OmcS that directly reduces Fe(III)oxides, while the facultative anaerobe S. oneidensis MR-1 accomplishes mineral reduction through direct membrane contact, contact through filamentous extensions and soluble flavin shuttles, all of which require the outer membrane cytochromes MtrC and OmcA in addition to secreted flavin. PMID:27134022

  7. Explorers of the Universe: Interactive Electronic Network

    NASA Technical Reports Server (NTRS)

    Alvarez, Marino C.; Burks, Geoffrey; Busby, Michael R.; Cannon, Tiffani; Sotoohi, Goli; Wade, Montanez

    2000-01-01

    This paper details how the Interactive Electronic Network is being utilized by secondary and postsecondary students, and their teachers and professors, to facilitate learning and understanding. The Interactive Electronic Network is couched within the Explorers of the Universe web site in a restricted portion entitled Gateway.

  8. Polar solvation and electron transfer. Annual progress report, July 1, 1992--June 30, 1993

    SciTech Connect

    Not Available

    1993-04-13

    The report is divided into the following sections: completion of previous studies on solvation dynamics, dipole lattice studies, inertial components of solvation response, simple models of solvation dynamics, rotational dynamics and dielectric friction, intramolecular electron transfer reactions, and intermolecular donor-acceptor complexes.

  9. Supramolecular fullerene/porphyrin charge transfer interaction studied by absorption spectrophotometric method

    NASA Astrophysics Data System (ADS)

    Mukherjee, Partha; Bhattacharya (Banerjee), Shrabanti; Nayak, Sandip K.; Chattopadhyay, Subrata; Bhattacharya, Sumanta

    2009-06-01

    A detailed UV-Vis spectrometric and thermodynamic studies were done to look insight into the nature of molecular interactions of the electron donor-acceptor complexes of C60 and C70 with 5,10,15,20-tetrakis(octadecyloxyphenyl)-21H,23H-porphyrin (1) in chloroform and toluene. Charge transfer (CT) absorption bands were located in the visible region and vertical ionization potential of 1 was determined utilizing CT transition energy. Low values of oscillator and transition dipole strengths suggested that the complexes were almost of neutral character in ground states. The high binding constant value for the C70-1 complex indicated high selectivity of 1 molecule towards C70. Experimental as well as theoretically determined of enthalpies of formation value substantiated the trend in K values for fullerene-1 complexes.

  10. Photoinduced Electron Transfer from Various Aniline Derivatives to Graphene Quantum Dots.

    PubMed

    Ghosh, Tufan; Chatterjee, Swarupa; Prasad, Edamana

    2015-12-10

    The present study utilizes the luminescence nature of the graphene quantum dots (GQDs) to analyze the mechanistic aspects of the photoinduced electron transfer (PET) processes between GQDs and aniline derivatives. A systematic investigation of PET from various aniline derivatives to GQDs has been presented. Solution-processable GQDs have been synthesized from graphene oxide (GO) at 200 °C. The as-synthesized GQDs exhibit a strong green luminescence at 510 nm, upon photoexcitation at 440 nm. Various aniline derivatives (aniline, N-methylaniline, N,N'-dimethylaniline, N-ethylaniline, N,N'-diethylaniline, and N,N'-diphenylaniline) have been utilized as electron donors to probe the PET process. Results from UV-visible absorption and steady-state and time-resolve luminescence spectroscopy suggest that the GQDs interact with the aniline derivatives in the excited state, which results in a significant luminescence quenching of the GQDs. The bimolecular rate constants of the dynamic quenching have been deduced for various donor-acceptor systems, and the values are in the range of (1.06-2.68) × 10(9) M(-1) s(-1). The negative values of the free energy change of the electron transfer process suggest that PET from aniline derivatives to GQDs is feasible and could be responsible for the luminescence quenching. The PET has been confirmed by detecting radical cations for certain aniline derivatives, using a nanosecond laser flash photolysis setup. The present study shows that among the various types of graphene systems, GQDs are better candidates for understanding the mechanism of PET in graphene-based donor-acceptor systems.

  11. Geometrically induced electron-electron interaction in semiconductor nanowires

    NASA Astrophysics Data System (ADS)

    Pinto, N.; Rezvani, S. J.; Favre, L.; Berbezier, I.; Fretto, M.; Boarino, L.

    2016-09-01

    We report the observation of a structurally induced doping compensation mechanism in doped semiconductor nanowires that results from the reduced size geometry. This kind of compensation can significantly affect the electronic transport properties of the doped nanowires. We demonstrate that in a crystalline n-type doped Ge wire, compensated by the acceptor-like localized surface states, strong electron-electron interactions occur. Variable range hopping conduction detected in these nanowires is directly generated from strong interactions, exhibiting an unusual large Coulomb gap in the density of states of wires.

  12. The Electron Transport Chain: An Interactive Simulation

    ERIC Educational Resources Information Center

    Romero, Chris; Choun, James

    2014-01-01

    This activity provides students an interactive demonstration of the electron transport chain and chemiosmosis during aerobic respiration. Students use simple, everyday objects as hydrogen ions and electrons and play the roles of the various proteins embedded in the inner mitochondrial membrane to show how this specific process in cellular…

  13. Electronic Documentation and Nurse-Patient Interaction.

    PubMed

    Gaudet, Cynthia A

    2016-01-01

    This author explored the culture of nurse-patient interactions associated with electronic bedside documentation. Data were collected through passive participant observation, audiotaping of nurse-patient interactions, and interviews with nurses. Nurses acknowledged that they need to share their attention between the patient and the computer. They stated that prioritizing patients' needs while completing the required electronic documentation was demanding. Stationary computers challenged the logistics of the exchange. Understanding the adaptation of caregiving necessitated by bedside electronic documentation will have a positive impact on developing systems that interface seamlessly with nurses' workflow and encourage patients' active participation in their care. PMID:26539694

  14. Atropisomerism about aryl-Csp(3) bonds: the electronic and steric influence of ortho-substituents on conformational exchange in cannabidiol and linderatin derivatives.

    PubMed

    Berber, Hatice; Lameiras, Pedro; Denhez, Clément; Antheaume, Cyril; Clayden, Jonathan

    2014-07-01

    Terpenylation reactions of substituted phenols were used to prepare cannabidiol and linderatin derivatives, and their structure and conformational behavior in solution were investigated by NMR and, for some representative examples, by DFT. VT-NMR spectra and DFT calculations were used to determine the activation energies of the conformational change arising from restricted rotation about the aryl-Csp(3) bond that lead to two unequally populated rotameric epimers. The NBO calculation was applied to explain the electronic stabilization of one conformer over another by donor-acceptor charge transfer interactions. Conformational control arises from a combination of stereoelectronic and steric effects between substituents in close contact with each other on the two rings of the endocyclic epoxide atropisomers. This study represents the first exploration of the stereoelectronic origins of atropisomerism around C(sp(2))-C(sp(3)) single bonds through theoretical calculations.

  15. Block copolymers for opto-electronics

    NASA Astrophysics Data System (ADS)

    Sun, Sam-Shajing; Fan, Zhen; Wang, Yiqing; Taft, Charles; Haliburton, James H.; Maaref, Shahin; Ledbetter, Abram J.; Bonner, Carl E.

    2004-05-01

    A D(donor)-B(bridge)-A(acceptor)-B(bridge)-type block copolymer system has been developed and preliminarily examined for potential opto-electronic photovoltaic functions. The unique feature of the device includes a primary DBAB-type block copolymer backbone, where D and A are conjugated donor and acceptor polymer blocks, and B is a non-conjugated and flexible chain, a π orbital stacked and conjugated chain self-assembled and ordered "secondary structure", and a donor/acceptor asymmetric layers sandwiched D/A columnar "tertiary structure". This structure is expected to improve photovoltaic power conversion efficiency significantly in comparison to most existing organic or polymeric donor/acceptor binary photovoltaic systems due to the reduction of "exciton loss", the "carrier loss", as well as the "photon loss" via three-dimensional space and energy level optimizations. Preliminary experimental results revealed better morphology and opto-electronic properties of DBAB vs. D/A blends.

  16. The effect of electron-electron interaction induced dephasing on electronic transport in graphene nanoribbons

    SciTech Connect

    Kahnoj, Sina Soleimani; Touski, Shoeib Babaee; Pourfath, Mahdi E-mail: pourfath@iue.tuwien.ac.at

    2014-09-08

    The effect of dephasing induced by electron-electron interaction on electronic transport in graphene nanoribbons is theoretically investigated. In the presence of disorder in graphene nanoribbons, wavefunction of electrons can set up standing waves along the channel and the conductance exponentially decreases with the ribbon's length. Employing the non-equilibrium Green's function formalism along with an accurate model for describing the dephasing induced by electron-electron interaction, we show that this kind of interaction prevents localization and transport of electrons remains in the diffusive regime where the conductance is inversely proportional to the ribbon's length.

  17. Variationally fitting the total electron-electron interaction

    NASA Astrophysics Data System (ADS)

    Dunlap, Brett I.; Palenik, Mark C.

    2016-05-01

    Density fitting is used throughout quantum chemistry to simplify the electron-electron interaction energy (EE). A fundamental property of quantum chemistry, and DFT in particular, is that a variational principle connects the EE to a potential. Density fitting generally does not preserve this connection. Herein we describe the construction of a robust EE that is variationally connected to fitted potentials in all electronic structure methods. For DFT, this results in fitting equations that are satisfied at an energy saddle point in multidimensional fitting space.

  18. Axial interaction free-electron laser

    DOEpatents

    Carlsten, B.E.

    1997-09-02

    Electron orbits from a helical axial wiggler in an axial guide field are absolutely unstable as power is extracted from the particles. For off-axis beams an axial FEL mechanism exists when the axial electric field in a TM mode is wiggled to interact with the axial velocity of the electrons that form the beam. The interaction strength is comparable to that for helical FELs and is insensitive to beam orbit errors. The orbits for this mechanism are extremely stable in the absence of space charge and lead to high extraction efficiencies without particle phasing incoherence or interception. This interaction mechanism is suitable for use with intense annular electron beams for high power generation at microwave frequencies. 5 figs.

  19. Axial interaction free-electron laser

    DOEpatents

    Carlsten, Bruce E.

    1997-01-01

    Electron orbits from a helical axial wiggler in an axial guide field are absolutely unstable as power is extracted from the particles. For off-axis beams an axial FEL mechanism exists when the axial electric field in a TM mode is wiggled to interact with the axial velocity of the electrons that form the beam. The interaction strength is comparable to that for helical FELs and is insensitive to beam orbit errors. The orbits for this mechanism are extremely stable in the absence of space charge and lead to high extraction efficiencies without particle phasing incoherence or interception. This interaction mechanism is suitable for use with intense annular electron beams for high power generation at microwave frequencies.

  20. Low-energy electron interactions with biomolecules

    NASA Astrophysics Data System (ADS)

    Winstead, Carl

    2012-06-01

    Low-energy electron interactions with biomolecules have been the focus of sustained attention over the past decade. The demonstration by Sanche and coworkers that even subexcitation and subionization electrons can induce strand breaks in DNA opened a new frontier in understanding radiation damage to living systems. Many studies of DNA subunits and their analogues, both experimental and theoretical, have elucidated likely mechanisms by which slow electrons attach to and disrupt DNA, although the full picture is far from clear and some elements of it remain controversial. Increasing attention is also being given to low-energy electron collisions with amino acids in order to explore possible mechanisms of electron-mediated radiation damage to proteins. In a completely different context, electron-biomolecule collisions are fundamental to spark ignition and cumbustion of biofuels such as methanol and ethanol. Not to be overlooked, either, is the simplest but most ubiquitous biomolecule of all, water, whose low-energy electron cross sections remain surprisingly ill-characterized. This talk will survery recent ab initio computational studies using the Schwinger multichannel method of DNA- and protein-related molecules, alcohols, and water. Much of the work to be presented was carried out in collaboration with experimentalists who undertook complementary measurements, allowing for useful comparisons to be made. Although the primary focus will be on electronically elastic collisions relevant to dissociative attachment and electron transport, electron-impact excitation cross sections for water will be presented and discussed.

  1. Studying electron-PAG interactions using electron-induced fluorescence

    NASA Astrophysics Data System (ADS)

    Narasimhan, Amrit; Grzeskowiak, Steven; Ostrander, Jonathan; Schad, Jonathon; Rebeyev, Eliran; Neisser, Mark; Ocola, Leonidas E.; Denbeaux, Gregory; Brainard, Robert L.

    2016-03-01

    In extreme ultraviolet (EUV) lithography, 92 eV photons are used to expose photoresists. Typical EUV resists are organic-based and chemically amplified using photoacid generators (PAGs). Upon exposure, PAGs produce acids which catalyze reactions that result in changes in solubility. In EUV lithography, photo- and secondary electrons (energies of 10- 80 eV) play a large role in PAG acid-production. Several mechanisms for electron-PAG interactions (e.g. electron trapping, and hole-initiated chemistry) have been proposed. The aim of this study is to explore another mechanism - internal excitation - in which a bound PAG electron can be excited by receiving energy from another energetic electron, causing a reaction that produces acid. This paper explores the mechanism of internal excitation through the analogous process of electron-induced fluorescence, in which an electron loses energy by transferring that energy to a molecule and that molecule emits a photon rather than decomposing. We will show and quantify electron-induced fluorescence of several fluorophores in polymer films to mimic resist materials, and use this information to refine our proposed mechanism. Relationships between the molecular structure of fluorophores and fluorescent quantum yield may aid in the development of novel PAGs for EUV lithography.

  2. Rates and energetics of intramolecular electron transfer processes in conjugated metallofullerenes.

    PubMed

    Schubert, Christina; Rudolf, Marc; Guldi, Dirk M; Takano, Yuta; Mizorogi, Naomi; Herranz, M Ángeles; Martín, Nazario; Nagase, Shigeru; Akasaka, Takeshi

    2013-09-13

    In this paper, we report on the design, redox potentials, excited state energies and radical ion pair state energies in electron donor-acceptor conjugates comprising the electron-donating π-extended tetrathiafulvalene and several electron-accepting fullerenes. To this end, we contrast an empty fullerene, that is, C₆₀, with two endohedral metallofullerenes, that is, open-shell La@C₈₂ and closed-shell La₂@C₈₀, in terms of charge separation and charge recombination dynamics.

  3. Dynamic spin susceptibility of interacting electron systems

    NASA Astrophysics Data System (ADS)

    Zyuzin, Vladimir; Maslov, Dmitrii

    2015-03-01

    We study the dynamic spin susceptibility of interacting electrons in spatial dimensions from one to three. In all cases, backscattering processes result in non-zero imaginary part of the spin susceptibility above the particle-hole continuum of non-interacting electrons. In one dimension, we employ the renormalization group to go beyond the second order and obtain a general expression for the spin susceptibility. In higher dimensions, we show that the imaginary part of the spin susceptibility arises from the same mechanism as non-analytic corrections to the Fermi-liquid theory. We relate the obtained results to the lifetime of collective spin modes. This work was supported by the National Science Foundation via Grant NSF DMR-1308972.

  4. High-field electron-photon interactions

    SciTech Connect

    Hartemann, F V

    1999-02-26

    Recent advances in novel technologies (including chirped-pulse amplification, femtosecond laser systems operating in the TW-PW range, high-gradient rf photoinjectors, and synchronized relativistic electron bunches with subpicosecond durations and THz bandwidths) allow experimentalists to study the interaction of relativistic electrons with ultrahigh-intensity photon fields. Ponderomotive scattering can accelerate these electrons with extremely high gradients in a three-dimensional vacuum laser focus. The nonlinear Doppler shift induced by relativistic radiation pressure in Compton backscattering is shown to yield complex nonlinear spectra which can be modified by using temporal laser pulse shaping techniques. Colliding laser pulses, where ponderomotive acceleration and Compton backscattering are combined, could also yield extremely short wavelength photons. Finally, one expects strong radiative corrections when the Doppler-upshifted laser wavelength approaches the Compton scale. These are discussed within the context of high-field classical electrodynamics, a new discipline borne out of the aforementioned innovations.

  5. Nonadiabatic rate constants for proton transfer and proton-coupled electron transfer reactions in solution: Effects of quadratic term in the vibronic coupling expansion

    SciTech Connect

    Soudackov, Alexander; Hammes-Schiffer, Sharon

    2015-11-17

    Rate constant expressions for vibronically nonadiabatic proton transfer and proton-coupled electron transfer reactions are presented and analyzed. The regimes covered include electronically adiabatic and nonadiabatic reactions, as well as high-frequency and low-frequency regimes for the proton donor-acceptor vibrational mode. These rate constants differ from previous rate constants derived with the cumulant expansion approach in that the logarithmic expansion of the vibronic coupling in terms of the proton donor-acceptor distance includes a quadratic as well as a linear term. The analysis illustrates that inclusion of this quadratic term does not significantly impact the rate constants derived using the cumulant expansion approach in any of the regimes studied. The effects of the quadratic term may become significant when using the vibronic coupling expansion in conjunction with a thermal averaging procedure for calculating the rate constant, however, particularly at high temperatures and for proton transfer interfaces with extremely soft proton donor-acceptor modes that are associated with extraordinarily weak hydrogen bonds. Even with the thermal averaging procedure, the effects of the quadratic term for weak hydrogen-bonding systems are less significant for more physically realistic models that prevent the sampling of unphysical short proton donor-acceptor distances, and the expansion of the coupling can be avoided entirely by calculating the couplings explicitly for the range of proton donor-acceptor distances. This analysis identifies the regimes in which each rate constant expression is valid and thus will be important for future applications to proton transfer and proton-coupled electron transfer in chemical and biological processes. We are grateful for support from National Institutes of Health Grant GM056207 (applications to enzymes) and the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy

  6. [Significance of quantum chemical interactions for medicinal science and design of β-secretase inhibitors].

    PubMed

    Hamada, Yoshio

    2013-01-01

    This review discusses the importance of quantum chemical interactions in biomolecules for medicinal science and their relevance to the author's β-secretase (BACE1) inhibitor drug discovery research. Although molecular mechanics/dynamics (MM/MD) methods are available in many in silico design tools used for drug discovery, they cannot accurately evaluate quantum effects between biomolecules and drugs. The key roles of biomolecular quantum chemical interactions in drug discovery are discussed using the arginine side chain as an example. Arginine is recognized as a charged amino acid in commonly used drug design software, unlike other amino acids with π-electron orbitals, such as phenylalanine, tyrosine, and tryptophan. Quantum chemical interactions via the arginine side chain are crucial for molecular recognition, and are found in many X-ray crystal structures, such as protein-protein, protein homodimer, RNA aptamer-protein, and enzyme-inhibitor complexes. This review describes the essential role of quantum chemical interactions via the arginine side chain in the mechanism of BACE1 inhibition, and proposes an "electron donor/acceptor bioisostere" concept for medicinal science based on quantum chemical interactions. Several potent BACE1 inhibitors, as well as the first peptides with BACE1 inhibiting activity were designed and synthesized based on studies of quantum chemical interactions via arginine side chain and the "electron donor bioisostere" concept.

  7. Site-directed deep electronic tunneling through a molecular network

    SciTech Connect

    Caspary, Maytal; Peskin, Uri

    2005-10-15

    Electronic tunneling in a complex molecular network of N(>2) donor/acceptor sites, connected by molecular bridges, is analyzed. The 'deep' tunneling dynamics is formulated using a recursive perturbation expansion, yielding a McConnell-type reduced N-level model Hamiltonian. Applications to models of molecular junctions demonstrate that the donor-bridge contact parameters can be tuned in order to control the tunneling dynamics and particularly to direct the tunneling pathway to either one of the various acceptors.

  8. Interaction of aromatic derivatives with single-walled carbon nanotubes.

    PubMed

    Hung, Wei-Chun; Elias, Gracy; Wai, Chien M

    2010-11-15

    Fluorescence of semiconducting single-walled carbon nanotubes (SWNTs) normally exhibits diameter-dependent oxidative quenching behaviour. This behaviour can be changed substantially to become an almost diameter-independent quenching phenomenon in the presence of electron-withdrawing nitroaromatic compounds, including o-nitrotoluene, 2,4-dinitrotoluene, and nitrobenzene. This change is observed for SWNTs suspended either in sodium dodecyl sulfate or in Nafion upon titration with hydrogen peroxide. Benzene, toluene, phenol, and nitromethane do not show such change. These findings suggest the possibility of forming an electron donor-acceptor complex between SWNTs and nitroaromatic compounds, resulting in leveling the redox potential of different SWNT species. The observation appears to provide a new method for modifying the electrochemical potentials of SWNTs through donor-acceptor complex formation. PMID:20878687

  9. Tuning nanoscale thermoelectricity with electron-electron interactions

    NASA Astrophysics Data System (ADS)

    Coomar, Arunima; Stafford, Charles

    2015-03-01

    The Nonequilibrium Green's Function (NEGF) formalism is a powerful tool that provides a microscopic theory for interacting quantum systems out of equilibrium. In this talk, I will be presenting a few results obtained using the NEGF approach combined with pi-electron effective field theory to study the thermoelectric transport properties such as the thermopower (S) and the dimensionless figure of merit (ZT) across single-molecule junctions with pi-conjugated molecular systems, which exhibit destructive quantum interference of the electron waves. Some interesting results showcasing the tuning of the thermoelectric properties by embedding the junctions in a dielectric medium will be presented, along with our ongoing investigations of the transmission node spectrum in these molecular junctions, and the enhanced thermoelectricity resulting from it. This work was supported by the Department of Energy, Basic Energy Sciences Grant No. DE-SC0006699.

  10. Revealing electronic open quantum systems with subsystem TDDFT.

    PubMed

    Krishtal, Alisa; Pavanello, Michele

    2016-03-28

    Open quantum systems (OQSs) are perhaps the most realistic systems one can approach through simulations. In recent years, describing OQSs with Density Functional Theory (DFT) has been a prominent avenue of research with most approaches based on a density matrix partitioning in conjunction with an ad-hoc description of system-bath interactions. We propose a different theoretical approach to OQSs based on partitioning of the electron density. Employing the machinery of subsystem DFT (and its time-dependent extension), we provide a novel way of isolating and analyzing the various terms contributing to the coupling between the system and the surrounding bath. To illustrate the theory, we provide numerical simulations on a toy system (a molecular dimer) and on a condensed phase system (solvated excimer). The simulations show that non-Markovian dynamics in the electronic system-bath interactions are important in chemical applications. For instance, we show that the superexchange mechanism of transport in donor-bridge-acceptor systems is a non-Markovian interaction between the donor-acceptor (OQS) with the bridge (bath) which is fully characterized by real-time subsystem time-dependent DFT. PMID:27036438

  11. Revealing electronic open quantum systems with subsystem TDDFT

    NASA Astrophysics Data System (ADS)

    Krishtal, Alisa; Pavanello, Michele

    2016-03-01

    Open quantum systems (OQSs) are perhaps the most realistic systems one can approach through simulations. In recent years, describing OQSs with Density Functional Theory (DFT) has been a prominent avenue of research with most approaches based on a density matrix partitioning in conjunction with an ad-hoc description of system-bath interactions. We propose a different theoretical approach to OQSs based on partitioning of the electron density. Employing the machinery of subsystem DFT (and its time-dependent extension), we provide a novel way of isolating and analyzing the various terms contributing to the coupling between the system and the surrounding bath. To illustrate the theory, we provide numerical simulations on a toy system (a molecular dimer) and on a condensed phase system (solvated excimer). The simulations show that non-Markovian dynamics in the electronic system-bath interactions are important in chemical applications. For instance, we show that the superexchange mechanism of transport in donor-bridge-acceptor systems is a non-Markovian interaction between the donor-acceptor (OQS) with the bridge (bath) which is fully characterized by real-time subsystem time-dependent DFT.

  12. Synthesis of the donor acceptor ligand 2-(4-dimethylaminobenzylidene)-4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (dbpcd) and X-ray diffraction structure of the platinum(II) compound PtCl2(dbpcd) 1.5CH2Cl2

    SciTech Connect

    Atim, Silvia; Wang, Xiaoping; Richmond, Michael G.

    2010-01-01

    The synthesis of the donor acceptor ligand 2-(4-dimethylaminobenzylidene)-4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (dbpcd) from the Knoevenagel condensation of 4-(dimethylamino)benzaldehyde with 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) is reported. This new ligand reacts with PtCl2(cod) to afford the platinum(II) complex PtCl2(dbpcd) in high yield. The dbpcd ligand and PtCl2(dbpcd) have been isolated and characterized by IR and NMR spectroscopies, cyclic voltammetry, MO calculations at the extended H ckel level, and X-ray diffraction analysis in the case of PtCl2(dbpcd).

  13. Constraining nonstandard neutrino-electron interactions

    SciTech Connect

    Barranco, J.; Miranda, O. G.; Moura, C. A.; Valle, J. W. F.

    2008-05-01

    We present a detailed analysis on nonstandard neutrino interactions (NSI) with electrons including all muon and electron (anti)-neutrino data from existing accelerators and reactors, in conjunction with the 'neutrino counting' data (e{sup +}e{sup -}{yields}{nu}{nu}{gamma}) from the four LEP collaborations. First we perform a one-parameter-at-a-time analysis, showing how most constraints improve with respect to previous results reported in the literature. We also present more robust results where the NSI parameters are allowed to vary freely in the analysis. We show the importance of combining LEP data with the other experiments in removing degeneracies in the global analysis constraining flavor-conserving NSI parameters which, at 90% and 95% C.L., must lie within unique allowed regions. Despite such improved constraints, there is still substantial room for improvement, posing a big challenge for upcoming experiments.

  14. Interaction of electron neutrino with LSD detector

    NASA Astrophysics Data System (ADS)

    Ryazhskaya, O. G.; Semenov, S. V.

    2016-06-01

    The interaction of electron neutrino flux, originating in the rotational collapse mechanism on the first stage of Supernova burst, with the LSD detector components, such as 56Fe (a large amount of this metal is included in as shielding material) and liquid scintillator barNnH2n+2, is being investigated. Both charged and neutral channels of neutrino reaction with 12barN and 56Fe are considered. Experimental data, giving the possibility to extract information for nuclear matrix elements calculation are used. The number of signals, produced in LSD by the neutrino pulse of Supernova 1987A is determined. The obtained results are in good agreement with experimental data.

  15. Electron Solvation in Liquid Ammonia: Lithium, Sodium, Magnesium, and Calcium as Electron Sources.

    PubMed

    Chaban, Vitaly V; Prezhdo, Oleg V

    2016-03-10

    A free electron in solution, known as a solvated electron, is the smallest possible anion. Alkali and alkaline earth atoms serve as electron donors in solvents that mediate outer-sphere electron transfer. We report herein ab initio molecular dynamics simulations of lithium, sodium, magnesium, and calcium in liquid ammonia at 250 K. By analyzing the electronic properties and the ionic and solvation structures and dynamics, we systematically characterize these metals as electron donors and ammonia molecules as electron acceptors. We show that the solvated metal strongly modifies the properties of its solvation shells and that the observed effect is metal-specific. Specifically, the radius and charge exhibit major impacts. The single solvated electron present in the alkali metal systems is distributed more uniformly among the solvent molecules of each metal's two solvation shells. In contrast, alkaline earth metals favor a less uniform distribution of the electron density. Alkali and alkaline earth atoms are coordinated by four and six NH3 molecules, respectively. The smaller atoms, Li and Mg, are stronger electron donors than Na and Ca. This result is surprising, as smaller atoms in a column of the periodic table have higher ionization potentials. However, it can be explained by stronger electron donor-acceptor interactions between the smaller atoms and the solvent molecules. The structure of the first solvation shell is sharpest for Mg, which has a large charge and a small radius. Solvation is weakest for Na, which has a small charge and a large radius. Weak solvation leads to rapid dynamics, as reflected in the diffusion coefficients of NH3 molecules of the first two solvation shells and the Na atom. The properties of the solvated electrons established in the present study are important for radiation chemistry, synthetic chemistry, condensed-matter charge transfer, and energy sources. PMID:26886153

  16. Electron Solvation in Liquid Ammonia: Lithium, Sodium, Magnesium, and Calcium as Electron Sources.

    PubMed

    Chaban, Vitaly V; Prezhdo, Oleg V

    2016-03-10

    A free electron in solution, known as a solvated electron, is the smallest possible anion. Alkali and alkaline earth atoms serve as electron donors in solvents that mediate outer-sphere electron transfer. We report herein ab initio molecular dynamics simulations of lithium, sodium, magnesium, and calcium in liquid ammonia at 250 K. By analyzing the electronic properties and the ionic and solvation structures and dynamics, we systematically characterize these metals as electron donors and ammonia molecules as electron acceptors. We show that the solvated metal strongly modifies the properties of its solvation shells and that the observed effect is metal-specific. Specifically, the radius and charge exhibit major impacts. The single solvated electron present in the alkali metal systems is distributed more uniformly among the solvent molecules of each metal's two solvation shells. In contrast, alkaline earth metals favor a less uniform distribution of the electron density. Alkali and alkaline earth atoms are coordinated by four and six NH3 molecules, respectively. The smaller atoms, Li and Mg, are stronger electron donors than Na and Ca. This result is surprising, as smaller atoms in a column of the periodic table have higher ionization potentials. However, it can be explained by stronger electron donor-acceptor interactions between the smaller atoms and the solvent molecules. The structure of the first solvation shell is sharpest for Mg, which has a large charge and a small radius. Solvation is weakest for Na, which has a small charge and a large radius. Weak solvation leads to rapid dynamics, as reflected in the diffusion coefficients of NH3 molecules of the first two solvation shells and the Na atom. The properties of the solvated electrons established in the present study are important for radiation chemistry, synthetic chemistry, condensed-matter charge transfer, and energy sources.

  17. The importance of chain connectivity in the formation of non-covalent interactions between polymers and single-walled carbon nanotubes and its impact on dispersion

    SciTech Connect

    Sumpter, Bobby G; Dadmun, Mark D; Driva, Paraskevi; Ivanov, Ilia N; Geohegan, David B; Linton, Dias; Feigerle, Charles S

    2010-01-01

    In this study we investigate the formation of non-covalent electron donor acceptor (EDA) interactions between polymers and single-walled carbon nanotubes (SWNTs) with the goal of optimizing interfacial adhesion and homogeneity of nanocomposites without modifying the SWNT native surface. Nanocomposites of SWNTs and three sets of polymer matrices with varying composition of electron donating 2-(dimethylamino)ethyl methacrylate (DMAEMA) or electron accepting acrylonitrile (AN) and cyanostyrene (CNSt) were prepared, quantitatively characterized by optical microscopy and Raman spectroscopy (Raman mapping, Raman D* peak shifts) and qualitatively compared through thick film composite visualization. The experimental data show that copolymers with 30 mol% DMAEMA, 45 mol% AN, 23 mol% CNSt and polyacrylonitrile homopolymer have the highest extent of intermolecular interaction, which translates to an optimum SWNT spatial dispersion among the series. These results are found to correlate very well with the intermolecular interaction energies obtained from quantum density functional theory calculations. Both experimental and computational results also illustrate that chain connectivity is critical in controlling the accessibility of the functional groups to form intermolecular interactions. This means that an adequate distance between interacting functional groups on a polymer chain is needed in order to allow efficient intermolecular contact. Thus, controlling the amount of electron donating or withdrawing moieties throughout the polymer chain will direct the extent of EDA interaction, which enables tuning the SWNT dispersion.

  18. The importance of chain connectivity in the formation of non-covalent interactions between polymers and single-walled carbon nanotubes and its impact on dispersion

    SciTech Connect

    Linton, Dias; Driva, Paraskevi; Ivanov, Ilia N; Geohegan, David B; Feigerle, Charles S; Dadmun, Mark D

    2010-05-01

    In this study we investigate the formation of non-covalent electron donor acceptor (EDA) interactions between polymers and single-walled carbon nanotubes (SWNTs) with the goal of optimizing interfacial adhesion and homogeneity of nanocomposites without modifying the SWNT native surface. Nanocomposites of SWNTs and three sets of polymer matrices with varying composition of electron donating 2-(dimethylamino)ethyl methacrylate (DMAEMA) or electron accepting acrylonitrile (AN) and cyanostyrene (CNSt) were prepared, quantitatively characterized by optical microscopy and Raman spectroscopy (Raman mapping, Raman D* peak shifts) and qualitatively compared through thick film composite visualization. The experimental data show that copolymers with 30 mol% DMAEMA, 45 mol% AN, 23 mol% CNSt and polyacrylonitrile homopolymer have the highest extent of intermolecular interaction, which translates to an optimum SWNT spatial dispersion among the series. These results are found to correlate very well with the intermolecular interaction energies obtained from quantum density functional theory calculations. Both experimental and computational results also illustrate that chain connectivity is critical in controlling the accessibility of the functional groups to form intermolecular interactions. This means that an adequate distance between interacting functional groups on a polymer chain is needed in order to allow efficient intermolecular contact. Thus, controlling the amount of electron donating or withdrawing moieties throughout the polymer chain will direct the extent of EDA interaction, which enables tuning the SWNT dispersion.

  19. Interacting Flatland Electrons Never Stop Surprising

    NASA Astrophysics Data System (ADS)

    Shayegan, Mansour

    2015-03-01

    I will present the highlights of several new magneto-transport experiments that probe the physics of interacting two-dimensional (2D) electrons (or holes) at high magnetic fields and low temperatures. These include: (1) observation of rare fractional quantum Hall states at even-denominator (1/2) filling factor in 2D hole systems at an unusual crossing of the two lowest Landau levels; (2) tuning and measuring the shape and anisotropy of the composite fermion (CF) Fermi contours, and (3) data suggesting that CFs themselves can be interacting and form their own fractional quantum Hall and Wigner solid states. I will also discuss a bilayer experiment where the CFs in one layer are used to probe an electron Wigner solid in the other layer. (Work done in collaboration with Yang Liu, D. Kamburov, M.A. Mueed, S. Hasdemir, I. Jo, H. Deng, L.N. Pfeiffer, K.W. West, and K.W. Baldwin. Supported by the NSF, DOE, Keck, and Moore Foundations.)

  20. Chiral Sensitivity in Electron-Molecule Interactions

    NASA Astrophysics Data System (ADS)

    Dreiling, Joan

    2015-09-01

    All molecular forms of life possess a chiral asymmetry, with amino acids and sugars found respectively in L- and D-enantiomers only. The primordial origin of this enantiomeric excess is unknown. One possible explanation is given by the Vester- Ulbricht hypothesis, which suggests that left-handed electrons present in beta-radiation, produced by parity-violating weak decays, interacted with biological precursors and preferentially destroyed one of the two enantiomers. Experimental tests of this idea have thus far yielded inconclusive results. We show direct evidence for chirally-dependent bond breaking through a dissociative electron attachment (DEA) reaction when spin-polarized electrons are incident on gas-phase chiral molecules. This provides unambiguous evidence for a well-defined, chirally-sensitive destructive molecular process and, as such, circumstantial evidence for the Vester-Ulbricht hypothesis. I will also present the results of our systematic study of the DEA asymmetry for different chiral halocamphor molecules. Three halocamphor molecules were investigated: 3-bromocamphor (C10H15BrO), 3-iodocamphor(C10H15IO), and 10-iodocamphor. The DEA asymmetries collected for bromocamphor and iodocamphor are qualitatively different, suggesting that the atomic number of the heaviest atom in the molecule plays a crucial role in the asymmetric interactions. The DEA asymmetry data for 3- and 10-iodocamphor have the same qualitative behavior, but the 10-iodocamphor asymmetry is about twice as large at the lowest energies investigated, so the location of the heavy atom in the camphor molecule also affects the asymmetries. This work was performed at the University of Nebraska-Lincoln. This project is funded by NSF Grant PHY-1206067.

  1. Manifestation of nonlocal electron-electron interaction in graphene

    NASA Astrophysics Data System (ADS)

    Ulstrup, Søren; Schüler, Malte; Bianchi, Marco; Fromm, Felix; Raidel, Christian; Seyller, Thomas; Wehling, Tim; Hofmann, Philip

    2016-08-01

    Graphene is an ideal platform to study many-body effects due to its semimetallic character and the possibility to dope it over a wide range. Here we study the width of graphene's occupied π band as a function of doping using angle-resolved photoemission. Upon increasing electron doping, we observe the expected shift of the band to higher binding energies. However, this shift is not rigid and the bottom of the band moves less than the Dirac point. We show that the observed shift cannot be accounted for by single-particle effects and local self-energies alone, but that nonlocal many-body effects, in particular exchange interactions, must be taken into account.

  2. Disentangling electron tunneling and protein dynamics of cytochrome c through a rationally designed surface mutation.

    PubMed

    Alvarez-Paggi, Damián; Meister, Wiebke; Kuhlmann, Uwe; Weidinger, Inez; Tenger, Katalin; Zimányi, László; Rákhely, Gábor; Hildebrandt, Peter; Murgida, Daniel H

    2013-05-23

    Nonexponential distance dependence of the apparent electron-transfer (ET) rate has been reported for a variety of redox proteins immobilized on biocompatible electrodes, thus posing a physicochemical challenge of possible physiological relevance. We have recently proposed that this behavior may arise not only from the structural and dynamical complexity of the redox proteins but also from their interplay with strong electric fields present in the experimental setups and in vivo (J. Am Chem. Soc. 2010, 132, 5769-5778). Therefore, protein dynamics are finely controlled by the energetics of both specific contacts and the interaction between the protein's dipole moment and the interfacial electric fields. In turn, protein dynamics may govern electron-transfer kinetics through reorientation from low to high donor-acceptor electronic coupling orientations. Here we present a combined computational and experimental study of WT cytochrome c and the surface mutant K87C adsorbed on electrodes coated with self-assembled monolayers (SAMs) of varying thickness (i.e., variable strength of the interfacial electric field). Replacement of the positively charged K87 by a neutral amino acid allowed us to disentangle protein dynamics and electron tunneling from the reaction kinetics and to rationalize the anomalous distance dependence in terms of (at least) two populations of distinct average electronic couplings. Thus, it was possible to recover the exponential distance dependence expected from ET theory. These results pave the way for gaining further insight into the parameters that control protein electron transfer.

  3. Electron transport mechanism of bathocuproine exciton blocking layer in organic photovoltaics.

    PubMed

    Lee, Jeihyun; Park, Soohyung; Lee, Younjoo; Kim, Hyein; Shin, Dongguen; Jeong, Junkyeong; Jeong, Kwangho; Cho, Sang Wan; Lee, Hyunbok; Yi, Yeonjin

    2016-02-21

    Efficient exciton management is a key issue to improve the power conversion efficiency of organic photovoltaics (OPVs). It is well known that the insertion of an exciton blocking layer (ExBL) having a large band gap promotes the efficient dissociation of photogenerated excitons at the donor-acceptor interface. However, the large band gap induces an energy barrier which disrupts the charge transport. Therefore, building an adequate strategy based on the knowledge of the true charge transport mechanism is necessary. In this study, the true electron transport mechanism of a bathocuproine (BCP) ExBL in OPVs is comprehensively investigated by in situ ultraviolet photoemission spectroscopy, inverse photoemission spectroscopy, density functional theory calculation, and impedance spectroscopy. The chemical interaction between deposited Al and BCP induces new states within the band gap of BCP, so that electrons can transport through these new energy levels. Localized trap states are also formed upon the Al-BCP interaction. The activation energy of these traps is estimated with temperature-dependent conductance measurements to be 0.20 eV. The Al-BCP interaction induces both transport and trap levels in the energy gap of BCP and their interplay results in the electron transport observed.

  4. Electron transport mechanism of bathocuproine exciton blocking layer in organic photovoltaics.

    PubMed

    Lee, Jeihyun; Park, Soohyung; Lee, Younjoo; Kim, Hyein; Shin, Dongguen; Jeong, Junkyeong; Jeong, Kwangho; Cho, Sang Wan; Lee, Hyunbok; Yi, Yeonjin

    2016-02-21

    Efficient exciton management is a key issue to improve the power conversion efficiency of organic photovoltaics (OPVs). It is well known that the insertion of an exciton blocking layer (ExBL) having a large band gap promotes the efficient dissociation of photogenerated excitons at the donor-acceptor interface. However, the large band gap induces an energy barrier which disrupts the charge transport. Therefore, building an adequate strategy based on the knowledge of the true charge transport mechanism is necessary. In this study, the true electron transport mechanism of a bathocuproine (BCP) ExBL in OPVs is comprehensively investigated by in situ ultraviolet photoemission spectroscopy, inverse photoemission spectroscopy, density functional theory calculation, and impedance spectroscopy. The chemical interaction between deposited Al and BCP induces new states within the band gap of BCP, so that electrons can transport through these new energy levels. Localized trap states are also formed upon the Al-BCP interaction. The activation energy of these traps is estimated with temperature-dependent conductance measurements to be 0.20 eV. The Al-BCP interaction induces both transport and trap levels in the energy gap of BCP and their interplay results in the electron transport observed. PMID:26821701

  5. Controlling Non-Covalent Interactions to Modulate the Dispersion of Fullerenes in Polymer Nanocomposites

    SciTech Connect

    Sumpter, Bobby G

    2011-01-01

    Polymer nanocomposites (PNCs) are materials based on a class of filled plastics that contain relatively small amounts of nanoparticles, which can impart improved structural, mechanical, and thermal properties relative to the neat polymer. However, the homogeneous dispersion of the nanoparticles into a polymer matrix is critical and an impeding factor for the controlled enhancement of PNC properties. In this work, we provide new insight into the importance of polymer chain connectivity and nanoparticle shape and curvature on the formation of noncovalent electron donor-acceptor (EDA) interactions between polymers and nanoparticles. This is accomplished by experimentally monitoring the dispersion of nanoparticles in copolymers containing varying amounts of functional moieties that can form noncovalent interactions with carbon nanoparticles with corroboration through density functional calculations. The results show that the presence of a minority of interacting functional groups within a polymer chain leads to an optimum interaction between the polymer and fullerene. Density functional theory calculations that identify the binding energy and geometry of the interaction between the functional monomers and fullerenes correspond very well with the experimental results. Moreover, comparison of these results to similar studies with single-walled carbon nanotubes (SWNT) indicate a distinct difference in the ability of EDA interactions to improve the dispersion of fullerenes relative to their impact on SWNT. Thus, the polymer chain connectivity, the polymer chain conformation, and size and shape of the nanoparticle modulate the formation of intermolecular interactions and directly impact the dispersion of the resultant nanocomposite.

  6. Vibrationally dependent electron-electron interactions in resonant electron transport through single-molecule junctions

    NASA Astrophysics Data System (ADS)

    Erpenbeck, A.; Härtle, R.; Bockstedte, M.; Thoss, M.

    2016-03-01

    We investigate the role of electronic-vibrational coupling in resonant electron transport through single-molecule junctions, taking into account that the corresponding coupling strengths may depend on the charge and excitation state of the molecular bridge. Within an effective-model Hamiltonian approach for a molecule with multiple electronic states, this requires to extend the commonly used model and include vibrationally dependent electron-electron interaction. We use Born-Markov master equation methods and consider selected models to exemplify the effect of the additional interaction on the transport characteristics of a single-molecule junction. In particular, we show that it has a significant influence on local cooling and heating mechanisms, it may result in negative differential resistance, and it may cause pronounced asymmetries in the conductance map of a single-molecule junction.

  7. Study of electron-positron interactions

    SciTech Connect

    Abashian, A.; Gotow, K.; Philonen, L.

    1990-09-15

    For the past seven years, this group has been interested in the study of tests of the Standard Model of Electroweak interactions. The program has centered about the AMY experiment which examines the nature of the final state products in electron-positron collisions in the center of mass energy range near 60 GeV. Results of these measurements have shown a remarkable consistency with the predictions of the minimal model of 3 quark and lepton generations and single charged and neutral intermediate bosons. No new particles or excited states have been observed nor has any evidence for departures in cross sections or angular asymmetries from expectations been observed. These conclusions have been even more firmly established by the higher energy results from the LEP and SLC colliders at center of mass energies of about 90 GeV. Our focus is shifting to the neutrino as a probe to electroweak interactions. The relative merit of attempting to observe neutrinos from point sources versus observing neutrinos generally is not easy to predict. The improved ability to interpret is offset by the probably episodic nature of the emission and irreproducibility of the results. In this phase of development, it is best to be sensitive to both sources of neutrinos. As a second phase of our program at Virginia Tech, we are studying the feasibility of detecting cosmic ray neutrinos in a proposed experiment which we have called NOVA. the results of the test setup will be instrumental in developing an optimum design. A third program we are involved in is the MEGA experiment at Los Alamos, an experiment to place a limit on the rate of muon decay to electron plus photon which is forbidden by the Standard Model.

  8. Kinetic properties of surface electrons over liquid helium under strong electron-electron interaction

    NASA Astrophysics Data System (ADS)

    Buntar, V. A.; Grigoriev, V. N.; Kirichek, O. I.; Kovdrya, Yu. Z.; Monarkha, Yu. P.; Sokolov, S. S.

    1990-06-01

    The mobility μ and lifetime of ground-level electrons τ⊥ are studied experimentally in a two-dimensional electron system at the surface of liquid helium at temperatures of 0.4 to 1.4 K and charge concentrations of (2.8 12.0) × 108 cm-2. It is shown that for fairly low temperature and high concentration where the frequency of interelectronic collisions is much higher than that of electron-ripplon ones, the so-called complete control condition is realized in the electron system, i.e., when the average drift velocity of electrons and the effective electron temperature can be introduced. This model is found to describe well the kinetic properties of surface electrons in the range of charge concentrations up to 4×108 cm-2, where the one-particle approach is no longer applicable. For the value of parameter Γ=e2(πns)1/2/T=47 that corresponds to a strong electron-electron interaction, the lifetime τ⊥ is found to increase sharply and the short-range order typical of a liquid state appears in the two-dimensional electron layer.

  9. Structure and Electronic Spectra of Purine-Methyl Viologen Charge Transfer Complexes

    PubMed Central

    Jalilov, Almaz S.; Patwardhan, Sameer; Singh, Arunoday; Simeon, Tomekia; Sarjeant, Amy A.; Schatz, George C.; Lewis, Frederick D.

    2014-01-01

    The structure and properties of the electron donor-acceptor complexes formed between methyl viologen (MV) and purine nucleosides and nucleotides in water and the solid state have been investigated using a combination of experimental and theoretical methods. Solution studies were performed using UV-vis and 1H NMR spectroscopy. Theoretical calculations were performed within the framework of density functional theory (DFT). Energy decomposition analysis indicates that dispersion and induction (charge-transfer) interactions dominate the total binding energy, whereas electrostatic interactions are largely repulsive. The appearance of charge transfer bands in the absorption spectra of the complexes are well described by time-dependent (TD) DFT and are further explained in terms of the redox properties of purine monomers and solvation effects. Crystal structures are reported for complexes of methyl viologen with the purines 2′-deoxyguanosine 3′-monophosphate GMP (DAD′DAD′ type) and 7-deazaguanosine zG (DAD′ADAD′ type). Comparison of the structures determined in the solid state and by theoretical methods in solution provides valuable insights into the nature of charge-transfer interactions involving purine bases as electron donors. PMID:24294996

  10. Structure and electronic spectra of purine-methyl viologen charge transfer complexes.

    PubMed

    Jalilov, Almaz S; Patwardhan, Sameer; Singh, Arunoday; Simeon, Tomekia; Sarjeant, Amy A; Schatz, George C; Lewis, Frederick D

    2014-01-01

    The structure and properties of the electron donor-acceptor complexes formed between methyl viologen and purine nucleosides and nucleotides in water and the solid state have been investigated using a combination of experimental and theoretical methods. Solution studies were performed using UV-vis and (1)H NMR spectroscopy. Theoretical calculations were performed within the framework of density functional theory (DFT). Energy decomposition analysis indicates that dispersion and induction (charge-transfer) interactions dominate the total binding energy, whereas electrostatic interactions are largely repulsive. The appearance of charge transfer bands in the absorption spectra of the complexes are well-described by time-dependent DFT and are further explained in terms of the redox properties of purine monomers and solvation effects. Crystal structures are reported for complexes of methyl viologen with the purines 2'-deoxyguanosine 3'-monophosphate (DAD'DAD' type) and 7-deazaguanosine (DAD'ADAD' type). Comparison of the structures determined in the solid state and by theoretical methods in solution provides valuable insights into the nature of charge-transfer interactions involving purine bases as electron donors.

  11. Effect of electron-electron interaction on thermal conductivity of disordered systems

    SciTech Connect

    Arfi, B. )

    1992-02-01

    Arfi presents a calculation of a correction to the thermal conductivity due to the inclusion of electron-electron interaction in a disordered metallic system. He finds that, to the first order in electron-electron interaction, the Wiedemann-Franz law is not satisfied.

  12. An energy decomposition analysis for intermolecular interactions from an absolutely localized molecular orbital reference at the coupled-cluster singles and doubles level

    SciTech Connect

    Azar, R. Julian; Head-Gordon, Martin

    2012-01-14

    We propose a wave function-based method for the decomposition of intermolecular interaction energies into chemically-intuitive components, isolating both mean-field- and explicit correlation-level contributions. We begin by solving the locally-projected self-consistent field for molecular interactions equations for a molecular complex, obtaining an intramolecularly polarized reference of self-consistently optimized, absolutely-localized molecular orbitals (ALMOs), determined with the constraint that each fragment MO be composed only of atomic basis functions belonging to its own fragment. As explicit inter-electronic correlation is integral to an accurate description of weak forces underlying intermolecular interaction potentials, namely, coordinated fluctuations in weakly interacting electronic densities, we add dynamical correlation to the ALMO polarized reference at the coupled-cluster singles and doubles level, accounting for explicit dispersion and charge-transfer effects, which map naturally onto the cluster operator. We demonstrate the stability of energy components with basis set extension, follow the hydrogen bond-breaking coordinate in the C{sub s}-symmetry water dimer, decompose the interaction energies of dispersion-bound rare gas dimers and other van der Waals complexes, and examine charge transfer-dominated donor-acceptor interactions in borane adducts. We compare our results with high-level calculations and experiment when possible.

  13. An energy decomposition analysis for intermolecular interactions from an absolutely localized molecular orbital reference at the coupled-cluster singles and doubles level.

    PubMed

    Azar, R Julian; Head-Gordon, Martin

    2012-01-14

    We propose a wave function-based method for the decomposition of intermolecular interaction energies into chemically-intuitive components, isolating both mean-field- and explicit correlation-level contributions. We begin by solving the locally-projected self-consistent field for molecular interactions equations for a molecular complex, obtaining an intramolecularly polarized reference of self-consistently optimized, absolutely-localized molecular orbitals (ALMOs), determined with the constraint that each fragment MO be composed only of atomic basis functions belonging to its own fragment. As explicit inter-electronic correlation is integral to an accurate description of weak forces underlying intermolecular interaction potentials, namely, coordinated fluctuations in weakly interacting electronic densities, we add dynamical correlation to the ALMO polarized reference at the coupled-cluster singles and doubles level, accounting for explicit dispersion and charge-transfer effects, which map naturally onto the cluster operator. We demonstrate the stability of energy components with basis set extension, follow the hydrogen bond-breaking coordinate in the C(s)-symmetry water dimer, decompose the interaction energies of dispersion-bound rare gas dimers and other van der Waals complexes, and examine charge transfer-dominated donor-acceptor interactions in borane adducts. We compare our results with high-level calculations and experiment when possible.

  14. Electronic structure of the sulfonyl and phosphonyl groups: a computational and crystallographic study.

    PubMed

    Denehy, Emma; White, Jonathan M; Williams, Spencer J

    2007-10-15

    A computational and X-ray crystallographic investigation of the electronic and geometric structures of a range of sulfonyl (-SO(2)-) and phosphonyl (-PO(2)--) containing species was undertaken to investigate the nature of valency and bonding in these functional groups. The traditional representation of sulfonyl and phosphonyl species is with octet-violating Lewis structures, which require d-orbital participation at the central atom. However, computational studies cast serious doubt upon this bonding model. In this work, we have employed NBO/NRT analysis to investigate hybridization, atomic formal charges, donor-acceptor interactions, and resonance structure contributions. Our results predict that within sulfonyl and phosphonyl systems, bonding interactions are highly polarized, of the form X+-Y- (X = P, S), and possess additional contributions from reciprocal n --> sigma* interactions where substituents off sulfur or phosphorus simultaneously act as donors and acceptors. Experimental evidence for the proposed bonding arrangement is provided for the sulfonyl functional group through a series of low-temperature X-ray structure correlations for sulfate monoesters, sulfamates, and methanesulfonates. Examination of changes to bond lengths and geometries upon substituent variation support the computational results. Together, our studies lend support for a bonding network in sulfonyl and phosphonyl groups composed of polar interactions augmented with reciprocal hyperconjugative bonding, which does not necessitate significant d-orbital participation nor formal octet violation at the central sulfur or phosphorus. PMID:17880060

  15. Bay-annulated indigo (BAI) as an excellent electron accepting building block for high performance organic semiconductors

    DOEpatents

    Liu, Yi; He, Bo; Pun, Andrew

    2016-04-19

    A novel electron acceptor based on bay-annulated indigo (BAI) was synthesized and used for the preparation of a series of high performance donor-acceptor small molecules and polymers. The resulting materials possess low-lying LUMO energy level and small HOMO-LUMO gaps, while their films exhibited high crystallinity upon thermal treatment, commensurate with high field effect mobilities and ambipolar transfer characteristics.

  16. Bay-annulated indigo (BAI) as an excellent electron accepting building block for high performance organic semiconductors

    SciTech Connect

    Liu, Yi; He, Bo; Pun, Andrew

    2015-11-24

    A novel electron acceptor based on bay-annulated indigo (BAI) was synthesized and used for the preparation of a series of high performance donor-acceptor small molecules and polymers. The resulting materials possess low-lying LUMO energy level and small HOMO-LUMO gaps, while their films exhibited high crystallinity upon thermal treatment, commensurate with high field effect mobilities and ambipolar transfer characteristics.

  17. Importance of direct metal-π coupling in electronic transport through conjugated single-molecule junctions.

    PubMed

    Meisner, Jeffrey S; Ahn, Seokhoon; Aradhya, Sriharsha V; Krikorian, Markrete; Parameswaran, Radha; Steigerwald, Michael; Venkataraman, Latha; Nuckolls, Colin

    2012-12-19

    We study the effects of molecular structure on the electronic transport and mechanical stability of single-molecule junctions formed with Au point contacts. Two types of linear conjugated molecular wires are compared: those functionalized with methylsulfide or amine aurophilic groups at (1) both or (2) only one of its phenyl termini. Using scanning tunneling and atomic force microscope break-junction techniques, the conductance of mono- and difunctionalized molecular wires and its dependence on junction elongation and rupture forces were studied. Charge transport through monofunctionalized wires is observed when the molecular bridge is coupled through a S-Au donor-acceptor bond on one end and a relatively weak Au-π interaction on the other end. For monofunctionalized molecular wires, junctions can be mechanically stabilized by installing a second aurophilic group at the meta position that, however, does not in itself contribute to a new conduction pathway. These results reveal the important interplay between electronic coupling through metal-π interactions and quantum mechanical effects introduced by chemical substitution on the conjugated system. This study affords a strategy to deterministically tune the electrical and mechanical properties through molecular wires.

  18. Epitaxial composite layers of electron donors and acceptors from very large polycyclic aromatic hydrocarbons.

    PubMed

    Samorí, Paolo; Severin, Nikolai; Simpson, Christopher D; Müllen, Klaus; Rabe, Jürgen P

    2002-08-14

    Large polycyclic aromatic hydrocarbons (PAHs) can be considered as nanographenes, whose electron donating or accepting properties are controlled by their size and shape as well as functionalities in their periphery. Epitaxial thin films of them are targets for optoelectronic applications; however, large PAHs are increasingly difficult to process. Here we show that epitaxial layers of very large unsubstituted PAHs (C(42)H(18) and C(132)H(34)), as well as a mixed layer of C(42)H(18) with an electron acceptor, can be obtained by self-assembly from solution. The C(132)H(34) is by far the largest nanographene that up to now has been processed into ordered thin films; due to its size it cannot be sublimed in a vacuum. Scanning tunneling microscopy (STM) studies reveal that the interaction with the substrate induces a strong perturbation of the electronic structure of the pure donor in the first epitaxial monolayer. In a second epitaxial layer with a donor acceptor stoichiometry of 2:1 the molecules are unperturbed.

  19. Convergent Flows: Humanities Scholars and Their Interactions with Electronic Texts

    ERIC Educational Resources Information Center

    Sukovic, Suzana

    2008-01-01

    This article reports research findings related to converging formats, media, practices, and ideas in the process of academics' interaction with electronic texts during a research project. The findings are part of the results of a study that explored interactions of scholars in literary and historical studies with electronic texts as primary…

  20. A new ladder-type benzodi(cyclopentadithiophene)-based donor-acceptor polymer and a modified hole-collecting PEDOT:PSS layer to achieve tandem solar cells with an open-circuit voltage of 1.62 V.

    PubMed

    Chen, Yung-Lung; Kao, Wei-Shun; Tsai, Che-En; Lai, Yu-Ying; Cheng, Yen-Ju; Hsu, Chain-Shu

    2013-09-11

    We have developed a new ladder-type conjugated polymer and a robust interconnecting layer (ICL) integrating a hole-collecting m-PEDOT:PSS layer with an electron-collecting ZnO layer. The inverted device using exhibited a high power conversion efficiency (PCE) of 5.76% with a Voc of 0.81 V, a Jsc of 12.82 mA cm(-2), and a FF of 55.5%. The inverted tandem device incorporating the and ICL achieves a Voc of 1.62 V leading to a PCE of 7.08%. PMID:23877029

  1. Minimizing Electron-Hole Recombination on TiO2 Sensitized with PbSe Quantum Dots: Time-Domain Ab Initio Analysis.

    PubMed

    Long, Run; English, Niall J; Prezhdo, Oleg V

    2014-09-01

    TiO2 sensitized with quantum dots (QDs) gives efficient photovoltaic and photocatalytic systems due to high stability and large absorption cross sections of QDs and rapid photoinduced charge separation at the interface. The yields of the light-induced processes are limited by electron-hole recombination that also occurs at the interface. We combine ab initio nonadiabatic molecular dynamics with analytic theory to investigate the experimentally studied charge recombination at the PbSe QD-TiO2 interface. The time-domain atomistic simulation directly mimics the laser experiment and generates important details of the recombination mechanism. The process occurs due to coupling of the electronic subsystem to polar optical modes of the TiO2 surface. The inelastic electron-phonon scattering happens on a picosecond time scale, while the elastic scattering takes 40 fs. Counter to expectations, the donor-acceptor bonding strengthens at an elevated temperature. An analytic theory extends the simulation results to larger QDs and longer QD-TiO2 bridges. It shows that the electron-hole recombination rate decreases significantly for longer bridges and larger dots and that the main effect arises due to reduced donor-acceptor coupling rather than changes in the donor-acceptor energy gap. The study indicates that by varying QD size or ligands one can reduce charge losses while still maintaining efficient charge separation, providing design principles for optimizing solar cell design and increasing photon-to-electron conversion efficiencies.

  2. Stimulated electromagnetic interactions in spatiotemporally gyrating relativistic electron beams

    SciTech Connect

    Davies, J.A.; Chen, C.

    1999-07-01

    One possible method to significantly widen the band-widths of present gyroklystron amplifiers is to utilize extended interaction structures in the input sections, the buncher sections and the output sections, in conjunction with stagger tuning. Through extended interactions, however, electron beams can undergo stimulated electromagnetic interactions, causing multimode excitations. In this paper, the authors investigate stimulated electromagnetic interactions in relativistic electron beams gyrating in an externally applied uniform magnetic field. The electron gyrophases are assumed to have strong spatiotemporal correlations. By applying Vlassor-Maxwell equations together with Lorentz transformations, they obtain the general dispersion relation for electromagnetic and electrostatic wave perturbations on the electron beam for this system. The dispersion relation is used to analyze a variety of stimulated electromagnetic interactions on such electron beams. Results of these analyses are discussed.

  3. Acceleration of electrons in strong beam-plasma interactions

    NASA Astrophysics Data System (ADS)

    Wilhelm, K.; Bernstein, W.; Kellogg, P. J.; Whalen, B. A.

    1984-12-01

    The effects of strong beam-plasma interactions on the electron population of the upper atmosphere have been investigated in an electron acceleration experiment performed with a sounding rocket. The rocket carried the Several Complex Experiments (SCEX) payload which included an electron accelerator, three disposable 'throwaway' detectors (TADs), and a stepped electron energy analyzer. The payload was launched in an auroral arc over the rocket at altitudes of 157 and 178 km, respectively. The performance characteristics of the instruments are discussed in detail. The data are combined with the results of laboratory measurements and show that electrons with energies of at least two and probably four times the injection energy of 2 keV were observed during strong beam-plasma interaction events. The interaction events occurred at pitch angles of 54 and 126 degrees. On the basis of the data it is proposed that the superenergization of the electrons is correlated with the length of the beam-plasma interaction region.

  4. Acceleration of electrons in strong beam-plasma interactions

    NASA Technical Reports Server (NTRS)

    Wilhelm, K.; Bernstein, W.; Kellogg, P. J.; Whalen, B. A.

    1984-01-01

    The effects of strong beam-plasma interactions on the electron population of the upper atmosphere have been investigated in an electron acceleration experiment performed with a sounding rocket. The rocket carried the Several Complex Experiments (SCEX) payload which included an electron accelerator, three disposable 'throwaway' detectors (TADs), and a stepped electron energy analyzer. The payload was launched in an auroral arc over the rocket at altitudes of 157 and 178 km, respectively. The performance characteristics of the instruments are discussed in detail. The data are combined with the results of laboratory measurements and show that electrons with energies of at least two and probably four times the injection energy of 2 keV were observed during strong beam-plasma interaction events. The interaction events occurred at pitch angles of 54 and 126 degrees. On the basis of the data it is proposed that the superenergization of the electrons is correlated with the length of the beam-plasma interaction region.

  5. The role of delocalization error in non-covalent interactions from dispersion-corrected density-functional theory

    NASA Astrophysics Data System (ADS)

    Otero de La Roza, Alberto

    2015-03-01

    Extensive benchmarking of dispersion-corrected density functional theory (dcDFT) methods has shown that it is nowadays feasible to calculate, with great accuracy, binding energies of small dimers and lattice energies of molecular crystals. However, there are many outstanding questions that can only be answered by a proper understanding of the interplay between base functional and dispersion correction. In this talk, I explore how delocalization error from the exchange-correlation functional impacts the calculation of non-covalent donor-acceptor interactions. Delocalization error arises from the failure of most functionals to model the long-range behavior of the exchange-correlation hole. Its primary consequence for non-covalent interactions is that the stability of donor-acceptor interactions is overestimated. Errors caused by delocalization error are particularly harmful in systems with strong and extensive hydrogen-bonded networks (water clusters and ice) or strong donor-acceptor interactions (halogen bonding), and can not be corrected using a pairwise dispersion correction. In addition, I present how delocalization error affects real-life applications of dcDFT, such as molecular adsorption on iron-oxide nanoparticles and surfaces.

  6. Weak localization and electron-electron interactions in few layer black phosphorus devices

    NASA Astrophysics Data System (ADS)

    Shi, Yanmeng; Gillgren, Nathaniel; Espiritu, Timothy; Tran, Son; Yang, Jiawei; Watanabe, Kenji; Taniguchi, Takahashi; Lau, Chun Ning

    2016-09-01

    Few layer phosphorene (FLP) devices are extensively studied due to their unique electronic properties and potential applications on nano-electronics. Here we present magnetotransport studies which reveal electron-electron interactions as the dominant scattering mechanism in hexagonal boron nitride-encapsulated FLP devices. From weak localization measurements, we estimate the electron dephasing length to be 30 to 100 nm at low temperatures, which exhibits a strong dependence on carrier density n and a power-law dependence on temperature (˜T -0.4). These results establish that the dominant scattering mechanism in FLP is electron-electron interactions.

  7. Interaction of electrons with light metal hydrides in the transmission electron microscope.

    PubMed

    Wang, Yongming; Wakasugi, Takenobu; Isobe, Shigehito; Hashimoto, Naoyuki; Ohnuki, Somei

    2014-12-01

    Transmission electron microscope (TEM) observation of light metal hydrides is complicated by the instability of these materials under electron irradiation. In this study, the electron kinetic energy dependences of the interactions of incident electrons with lithium, sodium and magnesium hydrides, as well as the constituting element effect on the interactions, were theoretically discussed, and electron irradiation damage to these hydrides was examined using in situ TEM. The results indicate that high incident electron kinetic energy helps alleviate the irradiation damage resulting from inelastic or elastic scattering of the incident electrons in the TEM. Therefore, observations and characterizations of these materials would benefit from increased, instead decreased, TEM operating voltage.

  8. Measurement of the magnetic interaction between two electrons

    NASA Astrophysics Data System (ADS)

    Kotler, Shlomi; Akerman, Nitzan; Navon, Nir; Glickman, Yinnon; Ozeri, Roee

    2014-03-01

    In this talk we will report on the first measurement of the magnetic interaction between two electronic spins. While the dipolar magnetic interactions between different spin systems, such as an electron and its nucleus or several multi-electron spin complexes, were experimentally studied, the magnetic interaction between two isolated electronic spins was never observed. We will explain why columb exchange forces on the one hand, and magnetic field noise on the other hand, make the electron-electron magnetic interaction measurement a challenging one. This challenge was resolved by the use of Quantum Information techniques. In our experiment, we used the ground state valence electrons of two 88 Sr+ ions, co-trapped in an electric Paul trap and separated by more than two micrometers. We measured a weak, millihertz scale, magnetic interaction between their electronic spins, in the presence of magnetic noise that was six orders of magnitude larger than the respective magnetic fields the electrons apply on each other. Spin dynamics was restricted to a Decoherence Free Subspace where a coherent evolution of 15 s led to spin-entanglement. Finally, by varying the separation between the two ions, we were able to recover the cubic distance dependence of the interaction Current position: NIST, Boulder, CO.

  9. Measurement of the Magnetic Interaction Between Two Electrons

    NASA Astrophysics Data System (ADS)

    Kotler, Shlomi; Akerman, Nitzan; Navon, Nir; Glickman, Yinnon; Ozeri, Roee

    2014-05-01

    In this talk we will report on the first measurement of the magnetic interaction between two electronic spins. While the dipolar magnetic interaction between different spin systems, such as an electron and its nucleus or several multi-electron spin complexes, were experimentally studied, the magnetic interaction between two isolated electronic spins was never observed. We will explain why the Coulomb exchange forces on the one hand, and magnetic field noise on the other hand, make the electron-electron magnetic interaction measurement a challenging one. This challenge was resolved by the use of Quantum Information techniques. In our experiment, we used the ground state valence electrons of two 88Sr+ ions, co-trapped in an electric Paul trap and separated by more than two micrometers. We measured a weak, millihertz scale, magnetic interaction between their electronic spins, in the presence of magnetic noise that was six orders of magnitude larger than the respective fields the electrons apply on each other. Spin dynamics was restricted to a Decoherence Free Subspace where a coherent evolution of 15 seconds led to spin-entanglement. Finally, by varying the separation between the ions, we were able to recover the inverse cubic distance dependence of the interaction. Current position: National Institute of Standards and Technology, Boulder, CO.

  10. Mulliken Hush elucidation of the encounter (precursor) complex in intermolecular electron transfer via self-exchange of tetracyanoethylene anion-radical

    NASA Astrophysics Data System (ADS)

    Rosokha, S. V.; Newton, M. D.; Head-Gordon, M.; Kochi, J. K.

    2006-05-01

    The paramagnetic [1:1] encounter complex (TCNE)2-rad is established as the important precursor in the kinetics and mechanism of electron-transfer for the self-exchange between tetracyanoethylene acceptor ( TCNE) and its radical-anion as the donor. Spectroscopic observation of the dimeric complex (TCNE)2-rad by its intervalence absorption band at the solvent-dependent wavelength of λIV ˜ 1500 nm facilitates the application of Mulliken-Hush theory which reveals the significant electronic interaction extant between the pair of cofacial TCNE moieties with the sizable coupling of HDA = 1000 cm -1. The transient existence of such an encounter complex provides the critical link in the electron-transfer kinetics by lowering the classical Marcus reorganization barrier by the amount of HDA in this strongly adiabatic system. Ab initio quantum-mechanical methods as applied to independent theoretical computations of both the reorganization energy ( λ) and the electronic coupling element ( HDA) confirm the essential correctness of the Mulliken-Hush formalism for fast electron transfer via strongly coupled donor/acceptor encounter complexes.

  11. Chalcogen bonding in solution: interactions of benzotelluradiazoles with anionic and uncharged Lewis bases.

    PubMed

    Garrett, Graham E; Gibson, Gregory L; Straus, Rita N; Seferos, Dwight S; Taylor, Mark S

    2015-04-01

    Chalcogen bonding is the noncovalent interaction between an electron-deficient, covalently bonded chalcogen (Te, Se, S) and a Lewis base. Although substantial evidence supports the existence of chalcogen bonding in the solid state, quantitative data regarding the strengths of the interactions in the solution phase are lacking. Herein, determinations of the association constants of benzotelluradiazoles with a variety of Lewis bases (Cl(-), Br(-), I(-), NO3(-) and quinuclidine, in organic solvent) are described. The participation of the benzotelluradiazoles in chalcogen bonding interactions was probed by UV-vis, (1)H and (19)F NMR spectroscopy as well as nano-ESI mass spectrometry. Trends in the free energy of chalcogen bonds upon variation of the donor, acceptor and solvent are evident from these data, including a linear free energy relationship between chalcogen bond donor ability and calculated electrostatic potential at the tellurium center. Calculations using the dispersion-corrected B97-D3 functional were found to give good agreement with the experimental free energies of chalcogen bonding.

  12. Chalcogen bonding interactions between reducible sulfur and selenium compounds and models of zinc finger proteins.

    PubMed

    Lutz, Patricia B; Bayse, Craig A

    2016-04-01

    Reducible sulfur and selenium (r-S/Se) compounds, defined as sulfur and selenium compounds not in the lowest -2 oxidation state (e.g., -1 to +6), release Zn(2+) from zinc-sulfur proteins such as zinc fingers (ZFs) and metallothionein. A series of density functional theory calculations was performed on donor-acceptor complexes between r-S/Se compounds and models of the Cys2His2, Cys3His and Cys4 ZF sites. These S⋯S/Se chalcogen bonding interactions consist of the donation of electron density from a S lone pair on the ZF model to a S/Se-X antibonding molecular orbital of the r-S/Se compound. The strength of the interaction was shown to be dependent upon the Lewis basicity of the ZF model (Cys4>Cys3His>Cys2His2) and the Lewis acidity of the r-S/Se compound as measured by the energy of the S/Se-X antibonding orbital. Interactions with the softer r-Se compounds were stronger than the r-S compounds, consistent with the greater reactivity of the former with ZF proteins.

  13. Annealing effect on donor-acceptor interface and its impact on the performance of organic photovoltaic devices based on PSiF-DBT copolymer and C{sub 60}

    SciTech Connect

    Marchiori, Cleber F. N.; Yamamoto, Natasha A. D.; Koehler, Marlus; Roman, Lucimara S.; Matos, Carolina F.; Zarbin, Aldo J. G.; Kujala, Jiri; Tuomisto, Filip; Macedo, Andréia G.

    2015-03-30

    In this work, poly[2,7-(9,9-bis(2-ethylhexyl)-dibenzosilole)-alt-4,7-bis(thiophen-2-yl) benzo-2,1,3-thiadiazole] (PSiF-DBT) was used as active layer in bilayer solar cell with C{sub 60} as electron acceptor. As cast devices already show reasonable power conversion efficiency (PCE) that increases to 4% upon annealing at 100 °C. Space charge limited measurements of the hole mobility (μ) in PSiF-DBT give μ ∼ 1.0 × 10{sup −4} cm{sup 2}/(V s) which does not depend on the temperature of the annealing treatment. Moreover, positron annihilation spectroscopy experiments revealed that PSiF-DBT films are well stacked even without the thermal treatment. The variations in the transport of holes upon annealing are then small. As a consequence, the PCE rise was mainly induced by the increase of the polymer surface roughness that leads to a more effective interface for exciton dissociation at the PSiF-DBT/fullerene heterojunction.

  14. Microscopic structure and interaction analysis for supercritical carbon dioxide-ethanol mixtures: a Monte Carlo simulation study.

    PubMed

    Xu, Wenhao; Yang, Jichu; Hu, Yinyu

    2009-04-01

    Configurational-bias Monte Carlo simulations in the isobaric-isothermal ensemble using the TraPPE-UA force field were performed to study the microscopic structures and molecular interactions of mixtures containing supercritical carbon dioxide (scCO(2)) and ethanol (EtOH). The binary vapor-liquid coexisting curves were calculated at 298.17, 333.2, and 353.2 K and are in excellent agreement with experimental results. For the first time, three important interactions, i.e., EtOH-EtOH hydrogen bonding, EtOH-CO(2) hydrogen bonding, and EtOH-CO(2) electron donor-acceptor (EDA) bonding, in the mixtures were fully analyzed and compared. The EtOH mole fraction, temperature, and pressure effect on the three interactions was investigated and then explained by the competition of interactions between EtOH and CO(2) molecules. Analysis of the microscopic structures indicates a strong preference for the formation of EtOH-CO(2) hydrogen-bonded tetramers and pentamers at higher EtOH compositions. The distribution of aggregation sizes and types shows that a very large EtOH-EtOH hydrogen-bonded network exists in the mixtures, while only linear EtOH-CO(2) hydrogen-bonded and EDA-bonded dimers and trimers are present. Further analysis shows that EtOH-CO(2) EDA complex is more stable than the hydrogen-bonded one.

  15. RKKY interaction for the spin-polarized electron gas

    NASA Astrophysics Data System (ADS)

    Valizadeh, Mohammad M.; Satpathy, Sashi

    2015-11-01

    We extend the original work of Ruderman, Kittel, Kasuya and Yosida (RKKY) on the interaction between two magnetic moments embedded in an electron gas to the case where the electron gas is spin-polarized. The broken symmetry of a host material introduces the Dzyaloshinsky-Moriya (DM) vector and tensor interaction terms, in addition to the standard RKKY term, so that the net interaction energy has the form ℋ = JS1 ṡS2 + D ṡS1 ×S2 + S1 ṡΓ ↔ṡS2. We find that for the spin-polarized electron gas, a nonzero tensor interaction Γ ↔ is present in addition to the scalar RKKY interaction J, while D is zero due to the presence of inversion symmetry. Explicit expressions for these are derived for the electron gas both in 2D and 3D and we show that the net magnetic interaction can be expressed as a sum of Heisenberg and Ising like terms. The RKKY interaction exhibits a beating pattern, caused by the presence of the two Fermi momenta kF↑ and kF↓, while the R-3 distance dependence of the original RKKY result for the 3D electron gas is retained. This model serves as a simple example of the magnetic interaction in systems with broken symmetry, which goes beyond the RKKY interaction.

  16. Problem Solving Interactions on Electronic Networks.

    ERIC Educational Resources Information Center

    Waugh, Michael; And Others

    Arguing that electronic networking provides a medium which is qualitatively superior to the traditional classroom for conducting certain types of problem solving exercises, this paper details the Water Problem Solving Project, which was conducted on the InterCultural Learning Network in 1985 and 1986 with students from the United States, Mexico,…

  17. Writing an Electronic Astronomy Book with Interactive Curricular Material

    NASA Astrophysics Data System (ADS)

    Thompson, Kristen L.; Belloni, Mario; Christian, Wolfgang

    2015-01-01

    With the rise of tablets, the past few years have seen an increase in the demand for quality electronic textbooks. Unfortunately, most of the current offerings do not exploit the accessibility and interactivity that electronic books can deliver. In this poster, we discuss how we are merging our curriculum development projects (Physlets, Easy Java/JavaScript Simulations, and Open Source Physics) with the EPUB electronic book format to develop an interactive textbook for use in a one-semester introductory astronomy course. The book, Astronomy: An Interactive Introduction, combines the narrative, equations, and images of a traditional astronomy text with new JavaScript simulations.

  18. Photoinitiated Charge Transport through π-Stacked Electron Conduits in Supramolecular Ordered Assemblies of Donor−Acceptor Triads

    SciTech Connect

    Bullock, Joseph E.; Carmieli, Raanan; Mickley, Sarah M.; Vura-Weis, Josh; Wasielewski, Michael R.

    2009-09-25

    Photochemical electron donor-acceptor triads having an aminopyrene primary donor (APy) and a p-diaminobenzene secondary donor (DAB) attached to either one or both imide nitrogen atoms of a perylene-3,4:9,10-bis(dicarboximide) (PDI) electron acceptor were prepared to give DAB-APy-PDI and DAB-APy-PDI-APy-DAB. In toluene, both triads are monomeric, but in methylcyclohexane, they self-assemble into ordered helical heptamers and hexamers, respectively, in which the PDI molecules are {pi}-stacked in a columnar fashion, as evidenced by small- and wide-angle X-ray scattering. Photoexcitation of these supramolecular assemblies results in rapid formation of DAB{sup +}-PDI{sup -} spin-polarized radical ion pairs having spin-spin dipolar interactions, which show that the average distance between the two radical ions is much larger in the assemblies (31 {angstrom}) than it is in their monomeric building blocks (23 {angstrom}). This work demonstrates that electron hopping through the {pi}-stacked PDI molecules is fast enough to compete effectively with charge recombination (40 ns) in these systems, making these materials of interest as photoactive assemblies for artificial photosynthesis and organic photovoltaics.

  19. Interactive Technologies in Electronic Educational Resources

    ERIC Educational Resources Information Center

    Anisimova, Tatyana Ivanovna; Krasnova, Lyubov Alekseevna

    2015-01-01

    Modern professional education in the transition to a tiered system of specialists training is focused not on the transfer of ready knowledge but on teaching to find this knowledge and to apply them in situations close to the professional conditions. The educational process, relying on use of interactive methods of teaching, which is organized with…

  20. The Electron-Phonon Interaction as Studied by Photoelectron Spectroscopy

    SciTech Connect

    D.W. Lynch

    2004-09-30

    With recent advances in energy and angle resolution, the effects of electron-phonon interactions are manifest in many valence-band photoelectron spectra (PES) for states near the Fermi level in metals.

  1. Study of electronic structures of solids with strongly interacting electrons

    NASA Astrophysics Data System (ADS)

    Su, Yen-Sheng

    This work contains studies of two classes of perovskite transition metal oxides. The first class is the layered perovskite cuprates and the related nickelate. The second class is the three dimensional perovskite manganites. Both model and ab initio calculations are carried out for the two classes of systems. The dissertation is therefore divided into the following four parts. The first part is about the 3-band Hubbard model. The model is commonly used for describing the electronic properties of the important CuO2 layers in the crystals of high-Tc superconducting cuprates, such as doped La2CuO4 and YBa2Cu3O 7. The straightforward perturbation expansion on the model taking tpd/ɛpd (~0.36 for the cuprates) as the small parameter does not converge. In this work, I show that there exist canonical transformations on the model Hamiltonian such that the perturbation expansion based on the transformed Hamiltonians converges. In the second part, crystal Hartree-Fock calculations are carried out for La2NiO4 and La2CuO4. The results predict correctly that these two materials are antiferromagnetic insulators, in contrast to the wrong predictions made by the density functional calculations using the local spin density approximation (LSDA). The spin form factors of the materials are also calculated. The results agree with previous theoretical works using an embedded cluster model. The calculated spin form factor of La2CuO4 is consistent with the few experimental data currently available, while the results for La2NiO4 show a large discrepancy between theory and experiment. We question the accuracy of the experimental results of La2NiO4 and call for more experiments to settle the issue. In the third part, crystal Hartree-Fock calculations are carried out for LaMnO3. Our main focus is on the magnetic and orbital orderings, the effect of the crystal distortion from the cubic perovskite structure, and the analysis of the projected density of states. In addition, we also find

  2. Electron acceleration via high contrast laser interacting with submicron clusters

    SciTech Connect

    Zhang Lu; Chen Liming; Wang Weiming; Yan Wenchao; Yuan Dawei; Mao Jingyi; Wang Zhaohua; Liu Cheng; Shen Zhongwei; Li Yutong; Dong Quanli; Lu Xin; Ma Jinglong; Wei Zhiyi; Faenov, Anatoly; Pikuz, Tatiana; Li Dazhang; Sheng Zhengming; Zhang Jie

    2012-01-02

    We experimentally investigated electron acceleration from submicron size argon clusters-gas target irradiated by a 100 fs, 10 TW laser pulses having a high-contrast. Electron beams are observed in the longitudinal and transverse directions to the laser propagation. The measured energy of the longitudinal electron reaches 600 MeV and the charge of the electron beam in the transverse direction is more than 3 nC. A two-dimensional particle-in-cell simulation of the interaction has been performed and it shows an enhancement of electron charge by using the cluster-gas target.

  3. Evidence for electron-electron interaction in projectile K -shell ionization

    SciTech Connect

    Hulskotter, H.; Meyerhof, W.E.; Dillard, E.; Guardala, N. )

    1989-10-30

    Cross sections for projectile {ital K}-shell ionization were measured for 0.75--3.5-MeV/{ital N} C{sup 5+} and O{sup 7+} projectiles in collisions with H{sub 2} and He targets. The experimental results agree with plane-wave Born-approximation calculations which take into account the interaction between projectile and target electrons. We demonstrate that for energies where the target electrons have sufficient kinetic energy in the projectile frame to ionize the projectile electron, the electron-electron interaction can lead to a significant increase in the total ionization cross section.

  4. Photoconductivity in donor-acceptor heterojunction organic photovoltaics

    NASA Astrophysics Data System (ADS)

    Renshaw, C. K.; Zimmerman, J. D.; Lassiter, B. E.; Forrest, S. R.

    2012-08-01

    Organic photovoltaics (OPVs) differ from ideal inorganic solar cells due to their pronounced voltage dependence under reverse bias. This feature is commonly modeled in an ad hoc fashion by including a parallel junction resistance (Rp) that bypasses the heterojunction energy barrier between donor and acceptor. The existence of a finite Rp has variously been attributed to rough interfaces, pinhole defects, or to the electric field dependence of the dissociation of polaron pairs that are bound at the heterojunction. Here we show that the voltage dependence of the photocurrent can also arise from photoconductivity resulting from exciton generation followed by dissociation into free polarons within the bulk of the donor and acceptor layers. The presence of photoconductivity of the active layers does not result in an increase in power conversion efficiency, and places a constraint on the maximum fill factor that can be achieved in an OPV cell.

  5. Recent advances in photoinduced donor/acceptor copolymerization

    NASA Astrophysics Data System (ADS)

    Jönsson, S.; Viswanathan, K.; Hoyle, C. E.; Clark, S. C.; Miller, C.; Morel, F.; Decker, C.

    1999-05-01

    Photoinitiated free radical polymerization of donor (D)/acceptor (A) type monomers has gained considerable interest due to the possibility to efficiently photopolymerize non-acrylate based systems. Furthermore, this photoinduced alternating copolymerization can be accomplished without the presence of a conventional free radical generating photoinitiator. In the past, we have shown that the structural influences in the direct photolysis of N-Alkyl and N-Arylmaleimides as well as their corresponding ground state charge transfer complexes (CTC) with suitable donors have carefully been investigated. For certain combinations of A and D type monomers, a direct photolysis of the ground state complex or the excitation of the acceptor, followed by the formation of an exciplex, has been shown to initiate the copolymerization. Herein, we show that the main route of initiation is based on inter or intra molecular H-abstraction from an excited state maleimide, whereby no exciplex formation takes place. H-abstraction will predominantly take place in systems where easily abstractable hydrogens are present. Our laser flash photolysis investigation, ESR [1] (A. Hiroshi, I. Takasi, T. Nosi, Macromol. Chem. 190 (1989) 2821) and phosphorescence emissions [2,3] (K.S. Chen, T. Foster, J.K.S. Wan, J. Phys. Chem. 84 (1980) 2473; C.J. Seliskar, S.P. McGlynn, J. Chem. Phys. 55 (1971) 4337) studies show that triplet excited states of N-alkyl substituted maleimides (RMI), which are well known strong precursors for direct H-abstractions from aliphatic ethers and secondary alcohols, are formed upon excitation. Rates of copolymerization and degrees of conversion for copolymerization of maleimide/vinyl ether pairs in air and nitrogen have been measured as a function of hydrogen abstractability of the excited triplet state MI as well as the influence of concentration and hydrogen donating effect of the hydrogen donor.

  6. Electron and pion interactions with nuclei

    NASA Astrophysics Data System (ADS)

    McCarthy, J. S.

    The analysis of high momentum transfer data on Hc-3, He-4, and A1 from the SLAC experiments is discussed. The data collection on Ca-48 isotope is completed. A high spin M8 transition was identified along with some 50 other levels. Analyses of this data is proceeding using microscopic DWBA descriptions of the nucleus The quasi-free scattering form Ca-40 and Ca-48 is completed. The preliminary results confirm earliest measurements on Fe-56; the Coulomb sum rule is substantially reduced from independent particle models. The study of Sr-88 and Y-89 continues with emphasis on the extraction of the single particle distribution of the proton and its effect upon nuclear core polarization. Inelastic electron scattering from H-1, H-2, H-3, He-3 and He-4 began at the present Bates linac and measurements at higher energies (750 GeV) are approved for the recirculated beam.

  7. Effect of Electronic Acceptor Segments on Photophysical Properties of Low-Band-Gap Ambipolar Polymers

    PubMed Central

    Li, Yuanzuo; Cui, Jingang; Zhao, Jianing; Liu, Jinglin; Song, Peng; Ma, Fengcai

    2013-01-01

    Stimulated by a recent experimental report, charge transfer and photophysical properties of donor-acceptor ambipolar polymer were studied with the quantum chemistry calculation and the developed 3D charge difference density method. The effects of electronic acceptor strength on the structure, energy levels, electron density distribution, ionization potentials, and electron affinities were also obtained to estimate the transporting ability of hole and electron. With the developed 3D charge difference density, one visualizes the charge transfer process, distinguishes the role of molecular units, and finds the relationship between the role of DPP and excitation energy for the three polymers during photo-excitation. PMID:23365549

  8. Fast photodriven electron spin coherence transfer: a quantum gate based on a spin exchange J-jump.

    PubMed

    Kobr, Lukáš; Gardner, Daniel M; Smeigh, Amanda L; Dyar, Scott M; Karlen, Steven D; Carmieli, Raanan; Wasielewski, Michael R

    2012-08-01

    Photoexcitation of the electron donor (D) within a linear, covalent donor-acceptor-acceptor molecule (D-A(1)-A(2)) in which A(1) = A(2) results in sub-nanosecond formation of a spin-coherent singlet radical ion pair state, (1)(D(+•)-A(1)(-•)-A(2)), for which the spin-spin exchange interaction is large: 2J = 79 ± 1 mT. Subsequent laser excitation of A(1)(-•) during the lifetime of (1)(D(+•)-A(1)(-•)-A(2)) rapidly produces (1)(D(+•)-A(1)-A(2)(-•)), which abruptly decreases 2J 3600-fold. Subsequent coherent spin evolution mixes (1)(D(+•)-A(1)-A(2)(-•)) with (3)(D(+•)-A(1)-A(2)(-•)), resulting in mixed states which display transient spin-polarized EPR transitions characteristic of a spin-correlated radical ion pair. These photodriven J-jump experiments show that it is possible to use fast laser pulses to transfer electron spin coherence between organic radical ion pairs and observe the results using an essentially background-free time-resolved EPR experiment. PMID:22799875

  9. Classification of interacting electronic topological insulators in three dimensions.

    PubMed

    Wang, Chong; Potter, Andrew C; Senthil, T

    2014-02-01

    A fundamental open problem in condensed-matter physics is how the dichotomy between conventional and topological band insulators is modified in the presence of strong electron interactions. We show that there are six interacting electronic topological insulators that have no noninteracting counterpart. Combined with the previously known band insulators, these produce a total of eight topologically distinct phases. Two of the six interacting topological insulators can be described as Mott insulators in which the electron spins form spin analogs of the topological band insulator. The remaining phases are obtained as combinations of these two "topological paramagnets" and the topological band insulator. We prove that these eight phases form a complete list of all possible interacting topological insulators and discuss their experimental signatures.

  10. Enthalpy (DeltaH) and entropy (DeltaS) for pi-stacking interactions in near-sandwich configurations: relative importance of electrostatic, dispersive, and charge-transfer effects.

    PubMed

    Gung, Benjamin W; Xue, Xiaowen; Zou, Yan

    2007-03-30

    Interactions between two aromatic rings with various substituents in a near-sandwich configuration have been quantitatively studied by using the triptycene derived molecular models. This model system allows a stacking arrangement of two arenes to assume a near-perfect face-to-face configuration in its ground state conformation. Comparing to our previous study of the parallel displaced configuration, repulsive interactions are predominant for most arenes currently studied. However, if one arene is strongly electron deficient (Ar2=pentafluorobenzoate), attractive interactions were observed regardless of the character of the other arene (Ar1). For stacking interactions between Me2NC6H4 and C6F5CO groups, a DeltaH of -1.84+/-0.2 kcal/mol and a DeltaS of -2.9+/-0.8 cal/(mol.K) were determined. The general trend in the attractive stacking interaction toward a pentafluorobenzoate is Me2NC6H4>Me3C6H2>Me2C6H3>MeC6H4>MeOC6H4>C6H5>O2NC6H4. The observed trend is consistent with a donor-acceptor relationship and the acceptor is a C6F5CO group.

  11. Interaction-Free Quantum Electron Microscope in Free-Space

    NASA Astrophysics Data System (ADS)

    Yang, Yujia; Kim, Chung-Soo; Hobbs, Richard; Manfrinato, Vitor; Celiker, Orhan; Kruit, Pieter; Berggren, Karl

    2015-03-01

    We propose the design and theoretical analysis of a quantum electron microscope (QEM), which utilizes interaction-free quantum measurement with electrons for nanoscale imaging. The QEM can be used to image electron-irradiation-sensitive materials, such as biological samples, with a high resolution and low radiation damage. Our QEM scheme is an electron interferometer with a storage resonator. The incoming electron beam is asymmetrically split into a strong reference beam and a weak sample beam, both of which are stored in the resonator. Only the weak sample beam transmits through the sample for multiple times. We propose to build the QEM with free-space electron optics. We develop a scattering matrix method to theoretically analyze the contrast mechanism, radiation damage, and measurement accuracy. We propose an electron-mirror-based storage resonator and we have performed electron optics simulation of electron trajectories within the resonator. We also report experimental implementation and characterization of the electron beam-splitter to be used in the QEM. Thin crystals fabricated with focused ion beam and nano-gratings fabricated with electron-beam lithography are two candidate beam-splitters, both of which are characterized by electron diffraction. This work is funded by Gordon and Betty Moore Foundation.

  12. Electromagnetic interactions between a fast electron beam and metamaterial cloaks.

    PubMed

    Xu, Jinying; Dong, Yunxia; Zhang, Xiangdong

    2008-10-01

    Relativistic energy loss and photon emission in the interaction of ideal and nonideal metamaterial cloaks with an external electron beam are studied based on the classical electrodynamics. The effects of various imperfect parameters on the efficiency of the cloak are emphasized. The energy-loss spectra and the photon emission for such structures with the different combinations of electron velocity and impact parameter are calculated. It is shown that the efficiency of nonideal electromagnetic cloaks and the effect of various nonideal parameters on the cloak invisibility can be exhibited in the electron energy loss spectroscopy. This means that the properties of cloak can be explored by scanning transmission electron microscopy.

  13. Generation of anomalously energetic suprathermal electrons by an electron beam interacting with a nonuniform plasma

    SciTech Connect

    Sydorenko, D.; Kaganovich, I. D.; Chen, L.; Ventzek, P. L. G.

    2015-12-15

    Generation of anomalously energetic suprathermal electrons was observed in simulation of a high-voltage dc discharge with electron emission from the cathode. An electron beam produced by the emission interacts with the nonuniform plasma in the discharge via a two-stream instability. The energy transfer from the beam to the plasma electrons is ensured by the plasma nonuniformity. The electron beam excites plasma waves whose wavelength and phase speed gradually decrease towards anode. The waves with short wavelength near the anode accelerate plasma bulk electrons to suprathermal energies. The sheath near the anode reflects some of the accelerated electrons back into the plasma. These electrons travel through the plasma, reflect near the cathode, and enter the accelerating area again but with a higher energy than before. Such particles are accelerated to energies much higher than after the first acceleration. This mechanism plays a role in explaining earlier experimental observations of energetic suprathermal electrons in similar discharges.

  14. Spectroscopic studies of porphyrin functionalized multiwalled carbon nanotubes and their interaction with TiO2 nanoparticles surface

    NASA Astrophysics Data System (ADS)

    Zannotti, Marco; Giovannetti, Rita; D'Amato, Chiara Anna; Rommozzi, Elena

    2016-01-01

    UV-vis and fluorescence investigations about the non-covalent interaction, in ethanolic solutions, of multi-wall carbon nanotube (MWCNT) with Coproporphyrin-I, and its Cu(II) and Zn(II) complexes (MCPIs) have been reported. Evidence of binding between MWCNTs and porphyrins was discovered from spectral adsorption decrease with respect to free porphyrins and by the exhibition of photoluminescence quenching with respect to free porphyrins demonstrating that MWCNT@MCPIs are potential donor-acceptor complexes. Equilibrium and kinetic aspects in the interactions with monolayer transparent TiO2 thin films with the obtained MWCNT@MCPIs are clarified showing their effective adsorption by porphyrin links on the TiO2 monolayer support, with respect to not only MWCNTs, according to the Langmuir model and with pseudo-first-order kinetics. Morphological description of the adsorption of MWCNT@MCPIs on TiO2 with scanning electron microscopy has been reported. The obtained experimental evidences describe therefore MWCNT@MCPIs as potential sensitizers in the DSSC (Dye-Sensitized Solar Cell) applications.

  15. The Binding Mode Prediction and Similar Ligand Potency in the Active Site of Vitamin D Receptor with QM/MM Interaction, MESP, and MD Simulation.

    PubMed

    Selvaraman, Nagamani; Selvam, Saravana Kumar; Muthusamy, Karthikeyan

    2016-08-01

    Non-secosteroidal ligands are well-known vitamin D receptor (VDR) agonists. In this study, we described a combined QM/MM to define the protein-ligand interaction energy a strong positive correlation in both QM-MM interaction energy and binding free energy against the biological activity. The molecular dynamics simulation study was performed, and specific interactions were extensively studied. The molecular docking results and surface analysis shed light on steric and electrostatic complementarities of these non-secosteroidal ligands to VDR. Finally, the drug likeness properties were also calculated and found within the acceptable range. The results show that bulky group substitutions in side chain decrease the VDR activity, whereas a small substitution increased it. Functional analyses of H393A and H301A mutations substantiate their roles in the VDR agonistic and antagonistic activities. Apart from the His393 and His301, two other amino acids in the hinge region viz. Ser233 and Arg270 acted as an electron donor/acceptor specific to the agonist in the distinct ligand potency. The results from this study disclose the binding mechanism of VDR agonists and structural modifications required to improve the selectivity.

  16. Rippled beam free-electron laser amplifier using the axial free-electron laser interaction

    SciTech Connect

    Carlsten, B.E.

    1997-05-01

    A new microwave generation mechanism involving a scalloping annular electron beam is discussed. The beam interacts with the axial electric field of a TM{sub 0n} mode in a smooth circular waveguide through the axial free-electron laser interaction, in which the beam ripple period is synchronous with the phase slippage of the rf mode relative to the electron beam. In this paper, we analyze the ripple motion of the electron beam and derive the dispersion relation describing the exponential growth of the rf mode. We calculate the gain for a nominal design and as a function of beam current and ripple amplitude, and show that power gain on the order of 30 dB/m of interaction is achievable. We additionally demonstrate that, under the right conditions, the interaction is autoresonant. {copyright} {ital 1997 American Institute of Physics.}

  17. A study of the interaction of thioindigo dye, with several inorganic host materials

    NASA Astrophysics Data System (ADS)

    Ramirez, Alejandra

    Maya Blue has been the focus of numerous studies and is believed to be a mixture of palygorskite clay and indigo dye.1,2 Several derivatives of this pigment have been developed with intriguing properties. For instance, the dye thioindigo reacts with the palygorskite clay to exhibit a broad range of colors from red to blue under UV-Vis excitation. Based on FT-Raman and computer simulation, previous work performed in our group could relate indigo and thioindigo interaction to the aluminum sites in the framework. 3,4 The work performed with other inorganic host materials such as, layer structures and zeolites have displayed reversible acid indicator properties, similar to the ones observed in concentrated sulfuric acid. Spectroscopic analyses and computer modeling of the above mentioned interactions have been evaluated. Results obtained by these techniques showed that in dehydrated materials a disturbance of thioindigo C=O at 1655 cm-1 to lower frequencies occurs, due to the C=O---Lewis acid sites (LAS) interaction. In the presence of water, a smaller C=O shift due to C=O---HO(H)LAS was observed. Moreover, displacement of the 001 plane in some layer materials confirmed the effect of water on the color changes displayed by UV-Vis spectroscopy. Based on these premises, it was concluded that weak electron donor-acceptor interactions took place between thioindigo functional groups (electron donors) and LAS of the aluminum silicate framework (electron acceptor). LAS (extra-framework aluminum and exchangeable cations) high hydration enthalpy made them extremely susceptible to water molecules (electron donors); generating a hydrogen bond between the two sites. The reversibility of these chromatic hybrid materials could have potential applications as water sensors and charge transfer photosensitizers in nanocrystalline TiO2-based solar cells.

  18. Proton-Coupled Electron Transfer in a Series of Ruthenium-Linked Tyrosines with Internal Bases: Evaluation of a Tunneling Model for Experimental Temperature-Dependent Kinetics.

    PubMed

    Markle, Todd F; Zhang, Ming-Tian; Santoni, Marie-Pierre; Johannissen, Linus O; Hammarström, Leif

    2016-09-01

    Photoinitiated proton-coupled electron transfer (PCET) kinetics has been investigated in a series of four modified tyrosines linked to a ruthenium photosensitizer in acetonitrile, with each tyrosine bearing an internal hydrogen bond to a covalently linked pyridine or benzimidazole base. After correcting for differences in driving force, it is found that the intrinsic PCET rate constant still varies by 2 orders of magnitude. The differences in rates, as well as the magnitude of the kinetic isotope effect (KIE = kH/kD), both generally correlate with DFT calculated proton donor-acceptor distances. An Arrhenius analysis of temperature dependent data shows that the difference in reactivity arises primarily from differences in activation energies. We use this kinetic data to evaluate a commonly employed theoretical model for proton tunneling which includes a harmonic distribution of proton donor-acceptor distances due to vibrational motions of the molecule. Applying this model to the experimental data yields the conclusion that donor-acceptor compression is more facile in the compounds with shorter PT distance; however, this is contrary to independent calculations for the same compounds. This discrepancy is likely because the assumption in the model of Morse-shaped proton potential energy surfaces is inappropriate for (strongly) hydrogen-bonded systems. These results question the general applicability of this model. The results also suggest that a correlation of rate vs proton tunneling distance for the series of compounds is complicated by a concomitant variation of other relevant parameters.

  19. Proton-Coupled Electron Transfer in a Series of Ruthenium-Linked Tyrosines with Internal Bases: Evaluation of a Tunneling Model for Experimental Temperature-Dependent Kinetics.

    PubMed

    Markle, Todd F; Zhang, Ming-Tian; Santoni, Marie-Pierre; Johannissen, Linus O; Hammarström, Leif

    2016-09-01

    Photoinitiated proton-coupled electron transfer (PCET) kinetics has been investigated in a series of four modified tyrosines linked to a ruthenium photosensitizer in acetonitrile, with each tyrosine bearing an internal hydrogen bond to a covalently linked pyridine or benzimidazole base. After correcting for differences in driving force, it is found that the intrinsic PCET rate constant still varies by 2 orders of magnitude. The differences in rates, as well as the magnitude of the kinetic isotope effect (KIE = kH/kD), both generally correlate with DFT calculated proton donor-acceptor distances. An Arrhenius analysis of temperature dependent data shows that the difference in reactivity arises primarily from differences in activation energies. We use this kinetic data to evaluate a commonly employed theoretical model for proton tunneling which includes a harmonic distribution of proton donor-acceptor distances due to vibrational motions of the molecule. Applying this model to the experimental data yields the conclusion that donor-acceptor compression is more facile in the compounds with shorter PT distance; however, this is contrary to independent calculations for the same compounds. This discrepancy is likely because the assumption in the model of Morse-shaped proton potential energy surfaces is inappropriate for (strongly) hydrogen-bonded systems. These results question the general applicability of this model. The results also suggest that a correlation of rate vs proton tunneling distance for the series of compounds is complicated by a concomitant variation of other relevant parameters. PMID:27490689

  20. Specific features of the effect of irradiation with electrons and neutrons on photoelectric properties of CdS single crystals nominally undoped and doped with Cu

    SciTech Connect

    Davidyuk, H. Ye.; Bozhko, V. V.; Bulatetska, L. V.

    2008-10-15

    Electrical, photoelectric, and magnetic properties of CdS single crystals undoped and doped with copper (N{sub Cu} {approx} 10{sup 18} cm{sup -3}) and irradiated with electrons (E = 1.2 MeV, {phi} = 2 x 10{sup 17} cm{sup -2}) and neutrons (E = 2 MeV, {phi} = 10{sup 18} cm{sup -2}) are studied. It is shown that the donor-acceptor pairs are responsible for extrinsic photoconductivity and paramagnetic properties; in particular, these pairs are represented by Cu{sub Cd}{sup -}-D{sup +} complexes that are destroyed during irradiation and are formed again with time (as secondary radiation defects) in irradiated samples. It is established that the majority of paramagnetic centers and donor-acceptor pairs are located in the near-surface region of the crystal. It is confirmed that large structural defects (defect clusters) formed by irradiation with neutrons are efficient sinks for copper atoms. Specific features of isochronous annealing of paramagnetic centers and donor-acceptor pairs responsible for the variation in magnetic parameters and in the photoconductivity spectra of irradiated undoped and Cu-doped CdS samples are studied.

  1. INTERACTION REGION DESIGN FOR THE ELECTRON-ION COLLIDER ERHIC.

    SciTech Connect

    MONTAG, C.; PARKER, B.; TEPIKIAN, S.; ET AL.

    2005-05-16

    To facilitate the study of collisions between 10 GeV polarized electrons and 100 GeV/u heavy ions or 250 GeV polarized protons at luminosities in the 10{sup 33} cm{sup -2} sec{sup -1} range (e-p case), adding a 10 GeV electron storage ring to the existing RHIC complex has been proposed. The interaction region of this electron-ion collider eRHIC has to provide the required low-beta focusing, while simultaneously accommodating the synchrotron radiation fan generated by beam separation close to the interaction point, which is particularly challenging. The latest design status of the eRHIC interaction region will be presented.

  2. Optimal parameters of gyrotrons with weak electron-wave interaction

    NASA Astrophysics Data System (ADS)

    Glyavin, M. Yu.; Oparina, Yu. S.; Savilov, A. V.; Sedov, A. S.

    2016-09-01

    In low-power gyrotrons with weak electron-wave interaction, there is a problem of determining the optimal length of the operating cavity, which is found as a result of a tradeoff between the enhancement of the electron efficiency and the increase in the Ohmic loss share with increasing cavity length. In fact, this is the problem of an optimal ratio between the diffraction and Ohmic Q-factors of the operating gyrotron mode, which determines the share of the radiated rf power lost in the cavity wall. In this paper, this problem is studied on the basis of a universal set of equations, which are appropriate for a wide class of electron oscillators with low efficiencies of the electron-wave interaction.

  3. Electron interactions with positively and negatively multiply charged biomolecular clusters

    NASA Astrophysics Data System (ADS)

    Feketeová, Linda

    2012-07-01

    Interactions of positively and negatively multiply charged biomolecular clusters with low-energy electrons, from ~ 0 up to 50 eV of electron energy, were investigated in a high resolution Fourier-Transform Ion Cyclotron Resonance mass spectrometer equipped with an electrospray ionisation source. Electron-induced dissociation reactions of these clusters depend on the energy of the electrons, the size and the charge state of the cluster. The positively charged clusters [Mn+2H]2+ of zwitterionic betaines, M = (CH3)2XCH2CO2 (X = NCH3 and S), do capture an electron in the low electron energy region (< 10 eV). At higher electron energies neutral evaporation from the cluster becomes competitive with Coulomb explosion. In addition, a series of singly charged fragments arise from bond cleavage reactions, including decarboxylation and CH3 group transfer, due to the access of electronic excited states of the precursor ions. These fragmentation reactions depend on the type of betaine (X = NCH3 or S). For the negative dianionic clusters of tryptophan [Trp9-2H]2-, the important channel at low electron energies is loss of a neutral. Coulomb explosion competes from 19.8 eV and dominates at high electron energies. A small amount of [Trp2-H-NH3]- is observed at 21.8 eV.

  4. Loschmidt Echo in a System of Interacting Electrons

    SciTech Connect

    Manfredi, G.; Hervieux, P.-A.

    2006-11-10

    We study the Loschmidt echo for a system of electrons interacting through mean-field Coulomb forces. The electron gas is modeled by a self-consistent set of hydrodynamic equations. It is observed that the quantum fidelity drops abruptly after a time that is proportional to the logarithm of the perturbation amplitude. The fidelity drop is related to the breakdown of the symmetry properties of the wave function.

  5. The electronic structure and charge transfer excited states of the endohedral trimetallic nitride C80 (I(h)) fullerenes-Zn-tetraphenyl porphyrin dyads.

    PubMed

    Basurto, Luis; Amerikheirabadi, Fatemeh; Zope, Rajendra; Baruah, Tunna

    2015-02-28

    Endohedral fullerenes offer the possibility of tuning their properties through a choice of the endohedral unit. The Sc3N@C80 fullerene is the most abundant fullerene after C60 and C70. Recently, Sc3N@C80 has been tested for light harvesting properties with encouraging results. In this work, we study the electronic structure of three endohedral fullerene-Zn tetraphenyl porphyrin complexes using density functional theory. The binding between the components in these complexes arises due to van der Waals interaction. A fragment orbital analysis is carried out to examine the interaction between the two components which shows that a small charge transfer occurs in the ground state from the ZnTPP to the fullerenes and that the orientation of the Sc3N plane affects the ground state charge transfer. The charge transfer excited state energies are calculated using our perturbative delta-SCF method. A comparison with earlier calculations shows that the charge transfer excitation energy increases as C60-ZnTPP < C70-ZnTPP < Sc3N@C80-ZnTPP < Y3N@C80-ZnTPP. The orientation of the endohedral unit does not influence the excitation energy in the donor-acceptor complexes.

  6. Coulomb Interactions in Hanbury Brown-Twiss Experiments with Electrons

    ERIC Educational Resources Information Center

    Shen, Kan

    2009-01-01

    This dissertation examines the effect of Coulomb interactions in Hanbury Brown-Twiss (HBT) type experiments with electrons. HBT experiments deal with intensity interference, which is related to the second-order correlation function of the particle field. This is an extension of the usual amplitude interference experiment, such as Young's…

  7. Magnetization of interacting electrons in anisotropic quantum dots with Rashba spin-orbit interaction

    NASA Astrophysics Data System (ADS)

    Avetisyan, Siranush; Chakraborty, Tapash; Pietiläinen, Pekka

    2016-07-01

    Magnetization of anisotropic quantum dots in the presence of the Rashba spin-orbit interaction has been studied for three and four interacting electrons in the dot for non-zero values of the applied magnetic field. We observe unique behaviors of magnetization that are direct reflections of the anisotropy and the spin-orbit interaction parameters independently or concurrently. In particular, there are saw-tooth structures in the magnetic field dependence of the magnetization, as caused by the electron-electron interaction, that are strongly modified in the presence of large anisotropy and high strength of the spin-orbit interactions. We also report the temperature dependence of magnetization that indicates the temperature beyond which these structures due to the interactions disappear. Additionally, we found the emergence of a weak sawtooth structure in magnetization for three electrons in the high anisotropy and large spin-orbit interaction limit that was explained as a result of merging of two low-energy curves when the level spacings evolve with increasing values of the anisotropy and the spin-orbit interaction strength.

  8. Ab initio molecular orbital-configuration interaction based quantum master equation (MOQME) approach to the dynamic first hyperpolarizabilities of asymmetric π-conjugated systems

    SciTech Connect

    Kishi, Ryohei; Fujii, Hiroaki; Minami, Takuya; Shigeta, Yasuteru; Nakano, Masayoshi

    2015-01-22

    In this study, we apply the ab initio molecular orbital - configuration interaction based quantum master equation (MOQME) approach to the calculation and analysis of the dynamic first hyperpolarizabilities (β) of asymmetric π-conjugated molecules. In this approach, we construct the excited state models by the ab initio configuration interaction singles method. Then, time evolutions of system reduced density matrix ρ(t) and system polarization p(t) are calculated by the QME approach. Dynamic β in the second harmonic generation is calculated based on the nonperturbative definition of nonlinear optical susceptibility, using the frequency domain system polarization p(ω). Spatial contributions of electrons to β are analyzed based on the dynamic hyperpolarizability density map, which visualizes the second-order response of charge density oscillating with a frequency of 2ω. We apply the present method to the calculation of the dynamic β of a series of donor/acceptor substituted polyene oligomers, and then discuss the applicability of the MOQME method to the calculation and analysis of dynamic NLO properties of molecular systems.

  9. ENERGETIC PHOTON AND ELECTRON INTERACTIONS WITH POSITIVE IONS

    SciTech Connect

    Phaneuf, Ronald A.

    2013-07-01

    The objective of this research is a deeper understanding of the complex multi-electron interactions that govern inelastic processes involving positive ions in plasma environments, such as those occurring in stellar cares and atmospheres, x-ray lasers, thermonuclear fusion reactors and materials-processing discharges. In addition to precision data on ionic structure and transition probabilities, high resolution quantitative measurements of ionization test the theoretical methods that provide critical input to computer codes used for plasma modeling and photon opacity calculations. Steadily increasing computational power and a corresponding emphasis on simulations gives heightened relevance to precise and accurate benchmark data. Photons provide a highly selective probe of the internal electronic structure of atomic and molecular systems, and a powerful means to better understand more complex electron-ion interactions.

  10. Electron interactions in graphene through an effective Coulomb potential

    NASA Astrophysics Data System (ADS)

    Rodrigues, Joao N. B.; Adam, Shaffique

    A recent numerical work [H.-K. Tang et al, PRL 115, 186602 (2015)] considering graphene's π-electrons interacting through an effective Coulomb potential that is finite at short-distances, stressed the importance of the sp2 -electrons in determining the semimetal to Mott insulator phase transition in graphene. Some years ago, I. F. Herbut [PRL 97, 146401 (2006)] studied such a transition by mapping graphene's π-electrons into a Gross-Neveu model. From a different perspective, D. T. Son [PRB 75, 235423 (2007)] put the emphasis on the long-range interactions by modelling graphene as Dirac fermions interacting through a bare Coulomb potential. Here we build on these works and explore the phase diagram of Dirac fermions interacting through an effective Coulomb-like potential screened at short-distances. The interaction potential used allows for analytic results that controllably switch between the two perspectives above. This work was supported by the Singapore National Research Foundation (NRF-NRFF2012-01 and CA2DM medium-sized centre program) and by the Singapore Ministry of Education and Yale-NUS College (R-607-265-01312).

  11. Electron Acceleration in Shock-Shock Interaction: Simulations and Observations

    NASA Astrophysics Data System (ADS)

    Nakanotani, M.; Matsukiyo, S.; Mazelle, C. X.; Hada, T.

    2015-12-01

    Collisionless shock waves play a crucial role in producing high energy particles (cosmic rays) in space. While most of the past studies about particle acceleration assume the presence of a single shock, in space two shocks frequently come close to or even collide with each other. Hietala et al. [2011] observed the collision of an interplanetary shock and the earth's bow shock and the associated acceleration of energetic ions. The kinetic natures of a shock-shock collision has not been well understood. Only the work done by using hybrid simulation was reported by Cargill et al. [1986], in which they focus on a collision of two supercritical shocks and the resultant ion acceleration. We expect similarly that electron acceleration can also occur in shock-shock collision. To investigate the electron acceleration process in a shock-shock collision, we perform one-dimensional full particle-in-cell (PIC) simulations. In the simulation energetic electrons are observed between the two approaching shocks before colliding. These energetic electrons are efficiently accelerated through multiple reflections at the two shocks (Fermi acceleration). The reflected electrons create a temperature anisotropy and excite large amplitude waves upstream via the electron fire hose instability. The large amplitude waves can scatter the energetic electrons in pitch angle so that some of them gain large pitch angles and are easily reflected when they encounter the shocks subsequently. The reflected electrons can sustain, or probably even strengthen, them. We further discuss observational results of an interaction of interplanetary shocks and the earth's bow shock by examining mainly Cluster data. We focus on whether or not electrons are accelerated in the shock-shock interaction.

  12. Effects of electron-electron interactions on the electronic Raman scattering of graphite in high magnetic fields

    NASA Astrophysics Data System (ADS)

    Ma, Y.; Kim, Y.; Kalugin, N. G.; Lombardo, A.; Ferrari, A. C.; Kono, J.; Imambekov, A.; Smirnov, D.

    2014-03-01

    We report the observation of strongly temperature (T)-dependent spectral lines in electronic Raman-scattering spectra of graphite in a high magnetic field up to 45 T applied along the c axis. The magnetic field quantizes the in-plane motion, while the out-of-plane motion remains free, effectively reducing the system dimension from 3 to 1. Optically created electron-hole pairs interact with, or shake up, the one-dimensional Fermi sea in the lowest Landau subbands. Based on the Tomonaga-Luttinger liquid theory, we show that interaction effects modify the spectral line shape from (ω-Δ)-1/2 to (ω-Δ)2α-1/2 at T = 0. At finite T, we predict a thermal broadening factor that increases linearly with T. Our model reproduces the observed T-dependent line shape, determining the electron-electron interaction parameter α to be ˜0.05 at 40 T.

  13. Radiating electron source generation in ultraintense laser-foil interactions

    NASA Astrophysics Data System (ADS)

    Capdessus, R.; King, M.; McKenna, P.

    2016-08-01

    A radiating electron source is shown to be created by a laser pulse (with intensity of 1023 W/cm2 and duration equal to 30 fs) interacting with a near-critical density plasma. It is shown that the back radiation reaction resulting from high energy synchrotron radiation tends to counteract the action of the ponderomotive force. This enhances the collective dynamics of the radiating electrons in the highest field areas, resulting in the production of a compact radiation source (containing 80% of the synchrotron radiation emission), with an energy on the order of tens of MeV over the laser pulse duration. These phenomena are investigated using a QED-particle-in-cell code, and compared with a kinetic model accounting for the radiation reaction force in the electron distribution function. The results shed new light on electron-photon sources at ultra-high laser intensities and could be tested on future laser facilities.

  14. Electron acceleration in long scale laser - plasma interactions

    NASA Astrophysics Data System (ADS)

    Kamperidis, Christos; Mangles, Stuart P. D.; Nagel, Sabrina R.; Bellei, Claudio; Krushelnick, Karl; Najmudin, Zulfikar; Bourgeois, Nicola; Marques, Jean Raphael; Kaluza, Malte C.

    2006-10-01

    Broad energy electron bunches are produced through the Self-Modulated Laser Wakefield Acceleration scheme at the 30J, 300 fsec laser, LULI, France, with long scale underdense plasmas, created in a He filled gas cell and in He gas jet nozzles of various lengths. With c.τlaser>>λplasma, electrons reached Emax ˜ 200MeV. By carefully controlling the dynamics of the interaction and by simultaneous observations of the electron energy spectra and the forward emitted optical spectrum, we found that a plasma density threshold (˜5.10^18 cm-3) exists for quasi-monoenergetic (˜30MeV) features to appear. The overall plasma channel size was inferred from the collected Thomson scattered light. 2D PIC simulations indicate that the main long laser pulse breaks up into small pulselets that eventually get compressed and tightly focused inside the first few plasma periods, leading to a bubble like acceleration of electron bunches.

  15. Dynamic docking and electron-transfer between cytochrome b5 and a suite of myoglobin surface-charge mutants. Introduction of a functional-docking algorithm for protein-protein complexes.

    PubMed

    Liang, Zhao-Xun; Kurnikov, Igor V; Nocek, Judith M; Mauk, A Grant; Beratan, David N; Hoffman, Brian M

    2004-03-10

    Horse myoglobin (Mb) provides a convenient "workbench" for probing the effects of electrostatics on binding and reactivity in the dynamic [Mb, cytochrome b(5)] electron-transfer (ET) complex. We have combined mutagenesis and heme neutralization to prepare a suite of six Mb surface-charge variants: the [S92D]Mb and [V67R]Mb mutants introduce additional charges on the "front" face, and incorporation of the heme di-ester into each of these neutralizes the charge on the heme propionates which further increases the positive charge on the "front" face. For this set of mutants, the nominal charge of Mb changes by -1 to +3 units relative to that for native Mb. For each member of this set, we have measured the bimolecular quenching rate constant (k(2)) for the photoinitiated (3)ZnDMb --> Fe(3+)b(5) ET reaction as a function of ionic strength. We find: (i) a dramatic decoupling of binding and reactivity, in which k(2) varies approximately 10(3)-fold within the suite of Mbs without a significant change in binding affinity; (ii) the ET reaction occurs within the "thermodynamic" or "rapid exchange" limit of the "Dynamic Docking" model, in which a large ensemble of weakly bound protein-protein configurations contribute to binding, but only a few are reactive, as shown by the fact that the zero-ionic-strength bimolecular rate constant varies exponentially with the net charge on Mb; (iii) Brownian dynamic docking profiles allow us to visualize the microscopic basis of dynamic docking. To describe these results we present a new theoretical approach which mathematically combines PATHWAY donor/acceptor coupling calculations with Poisson-Boltzmann-based electrostatics estimates of the docking energetics in a Monte Carlo (MC) sampling framework that is thus specially tailored to the intermolecular ET problem. This procedure is extremely efficient because it targets only the functionally active complex geometries by introducing a "reactivity filter" into the computations themselves

  16. X-Ray Free Electron Laser Interaction With Matter

    SciTech Connect

    Hau-Riege, S

    2009-05-12

    X-ray free electron lasers (XFELs) will enable studying new areas of laser-matter interaction. We summarize the current understanding of the interaction of XFEL pulses with matter and describe some of the simulation approaches that are used to design experiments on future XFEL sources. Modified versions of these models have been successful in guiding and analyzing experiments performed at the extreme-ultraviolet FEL FLASH at wavelengths of 6 nm and longer. For photon energies of several keV, no XFEL-matter interaction experiments have been performed yet but data is anticipated to become available in the near future, which will allow to test our understanding of the interaction physics in this wavelength regime.

  17. Interlayer Interaction and Electronic Screening in MultilayerGraphene

    SciTech Connect

    Ohta, Taisuke; Bostwick, Aaron; McChesney, J.L.; Seyller, Thomas; Horn, Karsten; Rotenberg, Eli

    2007-06-07

    The unusual transport properties of graphene are the direct consequence of a peculiar bandstructure near the Dirac point. We determine the shape of the {pi} bands and their characteristic splitting, and find the transition from two-dimensional to bulk character for 1 to 4 layers of graphene by angle-resolved photoemission. By detailed measurements of the {pi} bands we derive the stacking order, layer-dependent electron potential, screening length and strength of interlayer interaction by comparison with tight binding calculations, yielding a comprehensive description of multilayer graphene's electronic structure.

  18. Relativistic electron beam interaction and Ka - generation in solid targets

    SciTech Connect

    Eder, D C; Eidman, K; Fill, E; Pretzler, G; Saemann, A

    1999-06-01

    When fs laser pulses interact with solid surfaces at intensities I{lambda}{sup 2} > 10{sup 18} W/cm{sup 2} {micro}m{sup 2}, collimated relativistic electron beams are generated. These electrons can be used for producing intense X-radiation (bremsstrahlung or K{sub {alpha}}) for pumping an innershell X-ray laser. The basic concept of such a laser involves the propagation of the electron beam in a material which converts electron energy into appropriate pump photons. Using the ATLAS titanium-sapphire laser at Max-Planck-Institut fuer Quantenoptik, the authors investigate the generation of hot electrons and of characteristic radiation in copper. The laser (200 mJ/130 fs) is focused by means of an off-axis parabola to a diameter of about 10 {micro}m. By varying the position of the focus, they measure the copper K{sub {alpha}} - yield as a function of intensity in a range of 10{sup 15} to 2 x 10{sup 18} W/cm{sup 2} while keeping the laser pulse energy constant. Surprisingly, the highest emission is obtained at an intensity of about 10{sup 17} W/cm{sup 2}. However, this result is readily explained by the weak scaling of the hot-electron temperature with intensity. An efficiency of 2 x 10{sup -4} for the conversion of laser energy into copper K{sub {alpha}} is measured. Simulations of the interaction of the hot electrons with the cold target material and the conversion into X-rays are carried out by means of the TIGER/ITS code, a time-independent, coupled electron/photon Monte Carlo transport code. The code calculates the propagation of individual electrons and the generation of photons in cold material. Comparison of the code predictions with the data shows an efficiency of 15% for the generation of electrons with energies in the 100 keV range. A second experiment involves the demonstration of photopumping of an innershell transition in cobalt by the copper radiation. Comparing the emission with the one of nickel, which is not photopumped by copper K{sub {alpha}} photons

  19. Electron interactions in the two-dimensional electron-gas base of a vertical hot-electron transistor

    NASA Astrophysics Data System (ADS)

    Matthews, P.; Kelly, M. J.; Law, V. J.; Hasko, D. G.; Pepper, M.; Stobbs, W. M.; Ahmed, H.; Peacock, D. C.; Frost, J. E. F.; Ritchie, D. A.; Jones, G. A. C.

    1990-12-01

    We present results on the interaction of hot and cold electrons in a large-area two-dimensional electron-gas-base hot-electron transistor. Four-terminal magnetoresistance measurements of the cold electrons in the two-dimensional electron-gas (2DEG) base, as a function of forward-emitter bias, VEB, show significant deviations from the zero-bias condition. We identify two distinct regimes: (i) an enhanced interface scattering as the 2DEG is forced against the collector-barrier heterojunction for low biases before emitter-current injection and (ii) an electron-heating effect in the 2DEG once current injection occurs. We invoke a simple heat-exchange argument to analyze the relaxation of the injected hot carriers.

  20. Anisotropy in a high Landau level due to effective electron-electron interactions

    NASA Astrophysics Data System (ADS)

    Ciftja, Orion

    2013-05-01

    Quantization of Hall resistivity in strongly correlated two-dimensional electronic systems at high magnetic fields generally indicates the stabilization of novel electronic quantum liquid phases of matter. This is the nature of the integer and fractional quantum Hall states that stabilize at integer and fractional odd-denominator (not always, though) filling factors of the Landau level. Away from certain filling factors that represent quantum Hall liquid states, different phases, some of them with unusually high magneto-transport anisotropy have been known to stabilize specially in high Landau levels. In this work, we try to understand this anisotropic behaviour in terms of effective electron-electron interaction potentials. To this effect, we implement a full projection of the original Coulomb interaction potential in the suitable Landau level. We find out that, in high Landau levels, thus for relatively weak magnetic fields, a semi-classical description of the interaction potential between electrons appear to be an adequate choice. The features of this semi-classical interaction potential in this limit suggest ways how the energetic balance between density waves and/or liquid crystalline phases might be sensitively affected.

  1. Jensen-Feynman approach to the statistics of interacting electrons.

    PubMed

    Pain, Jean-Christophe; Gilleron, Franck; Faussurier, Gérald

    2009-08-01

    Faussurier [Phys. Rev. E 65, 016403 (2001)] proposed to use a variational principle relying on Jensen-Feynman (or Gibbs-Bogoliubov) inequality in order to optimize the accounting for two-particle interactions in the calculation of canonical partition functions. It consists of a decomposition into a reference electron system and a first-order correction. The procedure appears to be very efficient in order to evaluate the free energy and the orbital populations. In this work, we present numerical applications of the method and propose to extend it using a reference energy which includes the interaction between two electrons inside a given orbital. This is possible, thanks to our efficient recursion relation for the calculation of partition functions. We also show that a linear reference energy, however, is usually sufficient to achieve a good precision and that the most promising way to improve the approach of Faussurier is to apply Jensen's inequality to a more convenient convex function.

  2. Constraining Nonstandard Interactions in Neutrino-Electron Processes

    SciTech Connect

    Moura, C. A.

    2008-07-02

    We present a detailed analysis on nonstandard neutrino interactions with electrons including muon and electron (anti)-neutrino data from existing accelerators and reactors in conjunction with data from the four LEP collaborations. First we perform a one-parameter-at-a-time analysis, showing how most constraints improve with respect to previous results reported in the literature. We show the importance of combining LEP data with the other experiments in removing degeneracies in the global analysis constraining flavor-conserving nonstandard neutrino interactions parameters which, at 90% and 95% C.L., lie within unique allowed regions. Despite such improved constraints, there is still substantial room for improvement, posing a big challenge for upcoming experiments.

  3. Advanced Accelerating Structures and Their Interaction with Electron Beams

    SciTech Connect

    Gai Wei

    2009-01-22

    In this paper, we give a brief description of several advanced accelerating structures, such as dielectric loaded waveguides, photonic band gap, metamaterials and improved iris-loaded cavities. We describe wakefields generated by passing high current electron beams through these structures, and applications of wakefields to advanced accelerator schemes. One of the keys to success for high gradient wakefield acceleration is to develop high current drive beam sources. As an example, the high current RF photo injector at the Argonne Wakefield Accelerator, passed a {approx}80 nC electron beam through a high gradient dielectric loaded structure to achieve a 100 MV/m gradient. We will summarize recent related experiments on beam-structure interactions and also discuss high current electron beam generation and propagation and their applications to wakefield acceleration.

  4. Advanced accelerating structures and their interaction with electron beams.

    SciTech Connect

    Gai, W.; High Energy Physics

    2008-01-01

    In this paper, we give a brief description of several advanced accelerating structures, such as dielectric loaded waveguides, photonic band gap, metamaterials and improved iris-loaded cavities. We describe wakefields generated by passing high current electron beams through these structures, and applications of wakefields to advanced accelerator schemes. One of the keys to success for high gradient wakefield acceleration is to develop high current drive beam sources. As an example, the high current RF photo injector at the Argonne Wakefield Accelerator, passed a {approx}80 nC electron beam through a high gradient dielectric loaded structure to achieve a 100 MV/m gradient. We will summarize recent related experiments on beam-structure interactions and also discuss high current electron beam generation and propagation and their applications to wakefield acceleration.

  5. Strongly turbulent stabilization of electron beam-plasma interactions

    NASA Technical Reports Server (NTRS)

    Freund, H. P.; Haber, I.; Palmadesso, P.; Papadopoulos, K.

    1980-01-01

    The stabilization of electron beam interactions due to strongly turbulent nonlinearities is studied analytically and numerically for a wide range of plasma parameters. A fluid mode coupling code is described in which the effects of electron and ion Landau damping and linear growth due to the energetic electron beam are included in a phenomenological manner. Stabilization of the instability is found to occur when the amplitudes of the unstable modes exceed the threshold of the oscillating two-stream instability. The coordinate space structure of the turbulent spectrum which results clearly shows that soliton-like structures are formed by this process. Phenomenological models of both the initial stabilization and the asymptotic states are developed. Scaling laws between the beam-plasma growth rate and the fluctuations in the fields and plasma density are found in both cases, and shown to be in good agreement with the results of the simulation.

  6. Controlling Photons, Qubits and their Interactions in Superconducting Electronic Circuits

    NASA Astrophysics Data System (ADS)

    Wallraff, Andreas

    2009-03-01

    A combination of ideas from atomic physics, quantum optics and solid state physics allows us to investigate the fundamental interaction of matter and light on the level of single quanta in electronic circuits. In an approach known as circuit quantum electrodynamics, we coherently couple individual photons stored in a high quality microwave frequency resonator to a fully controllable superconducting two-level system (qubit) realized in a macroscopic electronic circuit [1]. In particular, we have recently observed the simultaneous interaction of one, two and three photons with a single qubit. In these experiments, we have probed the quantum nonlinearity of the qubit/light interaction governed by the Jaynes-Cummings hamiltonian, clearly demonstrating the quantization of the radiation field in the on-chip cavity. We have also performed quantum optics experiments with no photons at all. In this situation, i.e. in pure vacuum, we have resolved the renormalization of the qubit transition frequency - known as the Lamb shift - due to its non-resonant interaction with the cavity vacuum fluctuations [3].[4pt] [1] A. Wallraff et al., Nature (London) 431, 162 (2004)[0pt] [2] J. Fink et al., Nature (London) 454, 315 (2008)[0pt] [3] A. Fragner et al., Science 322, 1357 (2008)

  7. Terahertz electron cyclotron maser interactions with an axis-encircling electron beam

    SciTech Connect

    Li, G. D.; Kao, S. H.; Chang, P. C.; Chu, K. R.

    2015-04-15

    To generate terahertz radiation via the electron cyclotron maser instability, harmonic interactions are essential in order to reduce the required magnetic field to a practical value. Also, high-order mode operation is required to avoid excessive Ohmic losses. The weaker harmonic interaction and mode competition associated with an over-moded structure present challenging problems to overcome. The axis-encircling electron beam is a well-known recipe for both problems. It strengthens the harmonic interaction, as well as minimizing the competing modes. Here, we examine these advantages through a broad data base obtained for a low-power, step-tunable, gyrotron oscillator. Linear results indicate far more higher-harmonic modes can be excited with an axis-encircling electron beam than with an off-axis electron beam. However, multi-mode, time-dependent simulations reveal an intrinsic tendency for a higher-harmonic mode to switch over to a lower-harmonic mode at a high beam current or upon a rapid current rise. Methods are presented to identify the narrow windows in the parameter space for stable harmonic interactions.

  8. Superconducting Pairing Mechanism of Rare-Earth Effects of Electron-Electron and Electron-Phonon Interactions

    NASA Astrophysics Data System (ADS)

    Varshney, Dinesh; Jain, Rajendra K.

    Upon considering the three interactions namely, the electron-acoustic phonon, the electron-optical phonon and the Coulomb, the analytical solutions for the energy gap equation allows one to determine the electronic structure parameters to discuss the behavior of superconducting transition temperature (Tc) and isotope effect coefficient (α) for layered structure YNi2 B2C. Tc of 17 K is estimated for YNi2B2C with electron-acoustic phonon (λac) = 0.31, electron-optical phonon (λop) = 0.1 and Coulomb screening parameter (μ*) = 0.126 indicating that the YNi2B2C superconductor is in the intermediate coupling regime. To correlate the Tc with various coupling strengths as λac, λop and μ*, we present curves of Tc with them. The present approach also explains the conditions for the Boron and Carbon isotope effect. The negative pressure coefficient of Tc in this layered material is attributed to the contraction along c-axis under hydrostatic pressure. We suggest from these results that both the acoustic and optical phonons within the framework of a three-square well scheme consistently explains the effective electron-electron interaction leading to superconductivity in layered structure YNi2B2C.

  9. 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

  10. Interaction Determined Electron Energy Levels in One-Dimension

    NASA Astrophysics Data System (ADS)

    Pepper, Michael; Kumar, Sanjeev; Thomas, Kalarikad; Smith, Luke; Creeth, Graham; Farrer, Ian; Ritchie, David; Jones, Geraint; Jonathan, Griffiths; UCL Collaboration; Cavendish Laboratory Collaboration

    2015-03-01

    We have investigated electron transport in a quasi-one dimensional electron gas in the GaAs-AlGaAs heterostructure designed so that the confinement potential can be progressively weakened. This causes the energy levels to decrease in energy relative to each other, however this decrease occurs at different rates, a feature attributed to the energy being determined by both confinement and the electron-electron repulsion which varies with the shape of the wavefunction. It is found that the initial ground state crosses the higher levels so resulting in missing plateaux of quantised conductance. A change in the nature of the ground state to a more extended form causes an increase in the capacitance between the confining gates and the electrons. Both crossings and anti-crossings of the levels are found and these will be discussed along with other consequences of the form of the level interactions. The effects of level crossing on the spin dependent 0.7 structure will be presented. Supported by EPSRC (UK).

  11. Electronic interaction between nitrogen atoms in doped graphene.

    PubMed

    Tison, Yann; Lagoute, Jérôme; Repain, Vincent; Chacon, Cyril; Girard, Yann; Rousset, Sylvie; Joucken, Frédéric; Sharma, Dimpy; Henrard, Luc; Amara, Hakim; Ghedjatti, Ahmed; Ducastelle, François

    2015-01-27

    Many potential applications of graphene require either the possibility of tuning its electronic structure or the addition of reactive sites on its chemically inert basal plane. Among the various strategies proposed to reach these objectives, nitrogen doping, i.e., the incorporation of nitrogen atoms in the carbon lattice, leads in most cases to a globally n-doped material and to the presence of various types of point defects. In this context, the interactions between chemical dopants in graphene have important consequences on the electronic properties of the systems and cannot be neglected when interpreting spectroscopic data or setting up devices. In this report, the structural and electronic properties of complex doping sites in nitrogen-doped graphene have been investigated by means of scanning tunneling microscopy and spectroscopy, supported by density functional theory and tight-binding calculations. In particular, based on combined experimental and simulation works, we have systematically studied the electronic fingerprints of complex doping configurations made of pairs of substitutional nitrogen atoms. Localized bonding states are observed between the Dirac point and the Fermi level in contrast with the unoccupied state associated with single substitutional N atoms. For pyridinic nitrogen sites (i.e., the combination of N atoms with vacancies), a resonant state is observed close to the Dirac energy. This insight into the modifications of electronic structure induced by nitrogen doping in graphene provides us with a fair understanding of complex doping configurations in graphene, as it appears in real samples.

  12. Electron microscopy study of antioxidant interaction with bacterial cells

    NASA Astrophysics Data System (ADS)

    Plotnikov, Oleg P.; Novikova, Olga V.; Konnov, Nikolai P.; Korsukov, Vladimir N.; Gunkin, Ivan F.; Volkov, Uryi P.

    2000-10-01

    To maintain native microorganisms genotype and phenotype features a lyophylization technique is widely used. However in this case cells are affected by influences of vacuum and low temperature that cause a part of the cells population to be destruction. Another factor reduced microorganisms vitality is formation of reactive oxygen forms that damage certain biological targets (such as DNA, membranes etc.) Recently to raise microorganism's resistance against adverse condition natural and synthetic antioxidants are used. Antioxidant- are antagonists of free radicals. Introduction of antioxidants in protective medium for lyophylization increase bacteria storage life about 2,0-4,8 fold in comparison with reference samples. In the article the main results of our investigation of antioxidants interaction with microorganism cells is described. As bacteria cells we use vaccine strain yersinia pestis EV, that were grown for 48 h at 28 degree(s)C on the Hottinger agar (pH 7,2). Antioxidants are inserted on the agar surface in specimen under test. To investigate a localization of antioxidants for electron microscopy investigation, thallium organic antioxidants were used. The thallium organic compounds have an antioxidant features if thallium is in low concentration (about 1(mu) g/ml). The localization of the thallium organic antioxidants on bacteria Y. pestis EV is visible in electron microscopy images, thallium being heavy metal with high electron density. The negatively stained bacteria and bacteria thin sections with thallium organic compounds were investigated by means of transmission electron microscopy. The localization of the thallium organic compounds is clearly visible in electron micrographs as small dark spots with size about 10-80nm. Probably mechanisms of interaction of antioxidants with bacteria cells are discussed.

  13. Efficiency of combined cyclotron--[hacek C]erenkov interaction between electrons and electromagnetic fields

    SciTech Connect

    Nusinovich, G.S.; Vlasov, A.N. )

    1993-02-01

    A theory is presented describing the electron cyclotron interaction at frequencies near cutoff, followed by a [hacek C]erenkov interaction region. In such a case, the cyclotron interaction withdraws only the orbital component of electron momentum, while in the [hacek C]erenkov interaction the electrons lose their axial momentum. It is shown that the addition of the [hacek C]erenkov interaction significantly enhances the total electronic efficiency. Since both kinds of operation are relatively insensitive to electron velocity spread, the efficiency of the combined interaction is also rather tolerant to velocity spread. Thus, rather efficient sources of electromagnetic radiation based on poor quality electron beams may be developed.

  14. User-interactive electronic skin for instantaneous pressure visualization

    NASA Astrophysics Data System (ADS)

    Wang, Chuan; Hwang, David; Yu, Zhibin; Takei, Kuniharu; Park, Junwoo; Chen, Teresa; Ma, Biwu; Javey, Ali

    2013-10-01

    Electronic skin (e-skin) presents a network of mechanically flexible sensors that can conformally wrap irregular surfaces and spatially map and quantify various stimuli. Previous works on e-skin have focused on the optimization of pressure sensors interfaced with an electronic readout, whereas user interfaces based on a human-readable output were not explored. Here, we report the first user-interactive e-skin that not only spatially maps the applied pressure but also provides an instantaneous visual response through a built-in active-matrix organic light-emitting diode display with red, green and blue pixels. In this system, organic light-emitting diodes (OLEDs) are turned on locally where the surface is touched, and the intensity of the emitted light quantifies the magnitude of the applied pressure. This work represents a system-on-plastic demonstration where three distinct electronic components—thin-film transistor, pressure sensor and OLED arrays—are monolithically integrated over large areas on a single plastic substrate. The reported e-skin may find a wide range of applications in interactive input/control devices, smart wallpapers, robotics and medical/health monitoring devices.

  15. Vibrational Properties of Hydrogen-Bonded Systems Using the Multireference Generalization to the "On-the-Fly" Electronic Structure within Quantum Wavepacket ab Initio Molecular Dynamics (QWAIMD).

    PubMed

    Li, Junjie; Li, Xiaohu; Iyengar, Srinivasan S

    2014-06-10

    We discuss a multiconfigurational treatment of the "on-the-fly" electronic structure within the quantum wavepacket ab initio molecular dynamics (QWAIMD) method for coupled treatment of quantum nuclear effects with electronic structural effects. Here, multiple single-particle electronic density matrices are simultaneously propagated with a quantum nuclear wavepacket and other classical nuclear degrees of freedom. The multiple density matrices are coupled through a nonorthogonal configuration interaction (NOCI) procedure to construct the instantaneous potential surface. An adaptive-mesh-guided set of basis functions composed of Gaussian primitives are used to simplify the electronic structure calculations. Specifically, with the replacement of the atom-centered basis functions positioned on the centers of the quantum-mechanically treated nuclei by a mesh-guided band of basis functions, the two-electron integrals used to compute the electronic structure potential surface become independent of the quantum nuclear variable and hence reusable along the entire Cartesian grid representing the quantum nuclear coordinates. This reduces the computational complexity involved in obtaining a potential surface and facilitates the interpretation of the individual density matrices as representative diabatic states. The parametric nuclear position dependence of the diabatic states is evaluated at the initial time-step using a Shannon-entropy-based sampling function that depends on an approximation to the quantum nuclear wavepacket and the potential surface. This development is meant as a precursor to an on-the-fly fully multireference electronic structure procedure embedded, on-the-fly, within a quantum nuclear dynamics formalism. We benchmark the current development by computing structural, dynamic, and spectroscopic features for a series of bihalide hydrogen-bonded systems: FHF(-), ClHCl(-), BrHBr(-), and BrHCl(-). We find that the donor-acceptor structural features are in good

  16. Molecular orbital assistance in the design of intramolecular and photoinduced electron transfer systems

    NASA Astrophysics Data System (ADS)

    Petsalakis, Ioannis D.; Theodorakopoulos, Giannoula

    2012-02-01

    A theoretical approach is described for the design of donor-acceptor intramolecular charge transfer (ICT) systems and for photoinduced electron transfer (PET) hybrids of fullerene, based on orbital level diagrams of the separate donor and acceptor moieties. Minimization of the HOMO-LUMO (highest occupied-lowest unoccupied orbital) gap in ICT systems, translates to a requirement for near degeneracy of the HOMO of the donor and LUMO of the acceptor, determined separately for the two moieties by density functional theory calculations. Similarly, near degeneracy of the LUMO of the donor and LUMO of the acceptor moieties would indicate the possibility of PET in the combined hybrid.

  17. Magnetism and electronic structure of binuclear manganese complexes in ortho-quinone ligand and polymer environments

    NASA Astrophysics Data System (ADS)

    Rakhimov, R. R.; Arrington, S. A.; Hwang, J. S.; Prokof'ev, A. I.; Alexandrov, I. A.; Aleksandrov, A. I.

    2006-04-01

    By means of mechanochemical synthesis we obtained a coordination polymer containing binuclear manganese complexes with organic catechol/ortho-quinone ligands. The reaction system contained polystyrene, manganese acetylacetonate, and donor-acceptor mixture catechol/ortho-quinone. Electron paramagnetic resonance (EPR) and infrared spectroscopic data show that the binuclear manganese complex is covalently linked to the chain of polystyrene. Theoretical EPR spectrum analysis revealed a triplet state of the complex with two nonequivalent manganese ions coupled to each other by spin exchange. The type of magnetic coupling between manganese ions in this system is similar to the one in manganese based inorganic magnetic materials.

  18. Laser-electron Compton interaction in plasma channels

    SciTech Connect

    Pogorelsky, I.V.; Ben-Zvi, I.; Hirose, T.

    1998-10-01

    A concept of high intensity femtosecond laser synchrotron source (LSS) is based on Compton backscattering of focused electron and laser beams. The short Rayleigh length of the focused laser beam limits the length of interaction to a few picoseconds. However, the technology of the high repetition rate high-average power picosecond lasers required for high put through LSS applications is not developed yet. Another problem associated with the picosecond laser pulses is undesirable nonlinear effects occurring when the laser photons are concentrated in a short time interval. To avoid the nonlinear Compton scattering, the laser beam has to be split, and the required hard radiation flux is accumulated over a number of consecutive interactions that complicates the LSS design. In order to relieve the technological constraints and achieve a practically feasible high-power laser synchrotron source, the authors propose to confine the laser-electron interaction region in the extended plasma channel. This approach permits to use nanosecond laser pulses instead of the picosecond pulses. That helps to avoid the nonlinear Compton scattering regime and allows to utilize already existing technology of the high-repetition rate TEA CO{sub 2} lasers operating at the atmospheric pressure. They demonstrate the advantages of the channeled LSS approach by the example of the prospective polarized positron source for Japan Linear Collider.

  19. LASER-ELECTRON COMPTON INTERACTION IN PLASMA CHANNELS

    SciTech Connect

    POGORELSKY,I.V.

    1998-10-01

    A concept of high intensity femtosecond laser synchrotron source (LSS) is based on Compton backscattering of focused electron and laser beams. The short Rayleigh length of the focused laser beam limits the length of interaction to a few picoseconds. However, the technology of the high repetition rate high-average power picosecond lasers required for high put through LSS applications is not developed yet. Another problem associated with the picosecond laser pulses is undesirable nonlinear effects occurring when the laser photons are concentrated in a short time interval. To avoid the nonlinear Compton scattering, the laser beam has to be split, and the required hard radiation flux is accumulated over a number of consecutive interactions that complicates the LSS design. In order to relieve the technological constraints and achieve a practically feasible high-power laser synchrotron source, we propose to confine the laser-electron interaction region in the extended plasma channel. This approach permits to use nanosecond laser pulses instead of the picosecond pulses. That helps to avoid the nonlinear Compton scattering regime and allows to utilize already existing technology of the high-repetition rate TEA CO{sub 2} lasers operating at the atmospheric pressure. We demonstrate the advantages of the channeled LSS approach by the example of the prospective polarized positron source for Japan Linear Collider.

  20. Enhancement of charge ordering by dynamic electron-phonon interaction

    NASA Astrophysics Data System (ADS)

    Singer, Andrej; Fullerton, Eric; Shpyrko, Oleg

    Symmetry breaking and emergence of order is one of the most fascinating phenomena in condensed matter physics and leads to a plethora of intriguing ground states such as in antiferromagnets, Mott insulators, superconductors, and density-wave systems. Exploiting non-equilibrium dynamics of matter following ultrafast external excitation can provide even more striking routes to symmetry-lowered, ordered states, for instance, by accessing hidden equilibrium states in the free-energy landscape or dynamic stabilization of non-equilibrium states. This is remarkable because ultrafast excitation typically creates disorder, reduces the order parameter, and raises the symmetry. Here, we demonstrate for the case of antiferromagnetic chromium that moderate photo-excitation can transiently enhance the charge-density-wave (CDW) order by up to 30% above its equilibrium value, while strong excitation leads to an oscillating, large-amplitude CDW state that persists above the equilibrium transition temperature. Both effects result from dynamic electron-phonon interaction, which provides an efficient mechanism to selectively transform a broad excitation of the electronic order into a well defined, long-lived coherent lattice vibration. This mechanism may be exploited to transiently enhance the order parameter in other systems with coupled electronic and lattice orders. The data was collected at the x-ray free electron laser LCLS at SLAC.

  1. Restricting the ψ Torsion Angle Has Stereoelectronic Consequences on a Scissile Bond: An Electronic Structure Analysis.

    PubMed

    Strieter, Eric R; Andrew, Trisha L

    2015-09-22

    Protein motion is intimately linked to enzymatic catalysis, yet the stereoelectronic changes that accompany different conformational states of a substrate are poorly defined. Here we investigate the relationship between conformation and stereoelectronic effects of a scissile amide bond. Structural studies have revealed that the C-terminal glycine of ubiquitin and ubiquitin-like proteins adopts a syn (ψ ∼ 0°) or gauche (ψ ∼ ±60°) conformation upon interacting with deubiquitinases/ubiquitin-like proteases. We used hybrid density functional theory and natural bond orbital analysis to understand how the stereoelectronic effects of the scissile bond change as a function of φ and ψ torsion angles. This led to the discovery that when ψ is between 30° and -30° the scissile bond becomes geometrically and electronically deformed. Geometric distortion occurs through pyramidalization of the carbonyl carbon and amide nitrogen. Electronic distortion is manifested by a decrease in the strength of the donor-acceptor interaction between the amide nitrogen and antibonding orbital (π*) of the carbonyl. Concomitant with the reduction in nN → π* delocalization energy, the sp(2) hybrid orbital of the carbonyl carbon becomes richer in p-character, suggesting the syn configuration causes the carbonyl carbon hybrid orbitals to adopt a geometry reminiscent of a tetrahedral-like intermediate. Our work reveals important insights into the role of substrate conformation in activating the reactive carbonyl of a scissile bond. These findings have implications for designing potent active site inhibitors based on the concept of transition state analogues.

  2. [Electronic learning: interactive learning in medicine or Socrates in electronic guise].

    PubMed

    Wautier, J-L; Vileyn, F; Lefrère, J-J

    2005-06-01

    E-learning has been widely used for training in different fields. More recently, it was introduced during medical studies or for continuous medical education. The Canadian Universities are pioneers in e-learning creating special departments dedicated to pedagogy. Developing countries like Brazil or Central Europe have made some pilot experiments, which were successful. Several electronic companies have given a free access to the programmes and sites. The use of electronic media leads to an adaptation of teaching methods making them more interactive.

  3. Electronic and vibronic properties of a discotic liquid-crystal and its charge transfer complex

    SciTech Connect

    Haverkate, Lucas A.; Mulder, Fokko M.; Zbiri, Mohamed Johnson, Mark R.; Carter, Elizabeth; Kotlewski, Arek; Picken, S.

    2014-01-07

    Discotic liquid crystalline (DLC) charge transfer (CT) complexes combine visible light absorption and rapid charge transfer characteristics, being favorable properties for photovoltaic (PV) applications. We present a detailed study of the electronic and vibrational properties of the prototypic 1:1 mixture of discotic 2,3,6,7,10,11-hexakishexyloxytriphenylene (HAT6) and 2,4,7-trinitro-9-fluorenone (TNF). It is shown that intermolecular charge transfer occurs in the ground state of the complex: a charge delocalization of about 10{sup −2} electron from the HAT6 core to TNF is deduced from both Raman and our previous NMR measurements [L. A. Haverkate, M. Zbiri, M. R. Johnson, B. Deme, H. J. M. de Groot, F. Lefeber, A. Kotlewski, S. J. Picken, F. M. Mulder, and G. J. Kearley, J. Phys. Chem. B 116, 13098 (2012)], implying the presence of permanent dipoles at the donor-acceptor interface. A combined analysis of density functional theory calculations, resonant Raman and UV-VIS absorption measurements indicate that fast relaxation occurs in the UV region due to intramolecular vibronic coupling of HAT6 quinoidal modes with lower lying electronic states. Relatively slower relaxation in the visible region the excited CT-band of the complex is also indicated, which likely involves motions of the TNF nitro groups. The fast quinoidal relaxation process in the hot UV band of HAT6 relates to pseudo-Jahn-Teller interactions in a single benzene unit, suggesting that the underlying vibronic coupling mechanism can be generic for polyaromatic hydrocarbons. Both the presence of ground state CT dipoles and relatively slow relaxation processes in the excited CT band can be relevant concerning the design of DLC based organic PV systems.

  4. Electron-electron interaction, weak localization and spin valve effect in vertical-transport graphene devices

    SciTech Connect

    Long, Mingsheng; Gong, Youpin; Wei, Xiangfei; Zhu, Chao; Xu, Jianbao; Liu, Ping; Guo, Yufen; Li, Weiwei; Liu, Liwei; Liu, Guangtong

    2014-04-14

    We fabricated a vertical structure device, in which graphene is sandwiched between two asymmetric ferromagnetic electrodes. The measurements of electron and spin transport were performed across the combined channels containing the vertical and horizontal components. The presence of electron-electron interaction (EEI) was found not only at low temperatures but also at moderate temperatures up to ∼120 K, and EEI dominates over weak localization (WL) with and without applying magnetic fields perpendicular to the sample plane. Moreover, spin valve effect was observed when magnetic filed is swept at the direction parallel to the sample surface. We attribute the EEI and WL surviving at a relatively high temperature to the effective suppress of phonon scattering in the vertical device structure. The findings open a way for studying quantum correlation at relatively high temperature.

  5. Resonant tunneling of interacting electrons in an AC electric field

    SciTech Connect

    Elesin, V. F.

    2013-11-15

    The problem of the effect of electron-electron interaction on the static and dynamic properties of a double-barrier nanostructure (resonant tunneling diode (RTD)) is studied in terms of a coherent tunneling model, which includes a set of Schrödinger and Poisson equations with open boundary conditions. Explicit analytical expressions are derived for dc and ac potentials and reduced (active and reactive) currents in the quasi-classical approximation over a wide frequency range. These expressions are used to analyze the frequency characteristics of RTD. It is shown that the interaction can radically change the form of these expressions, especially in the case of a hysteretic I-V characteristic. In this case, the active current and the ac potentials can increase sharply at both low and high frequencies. For this increase to occur, it is necessary to meet quantum regime conditions and to choose a proper working point in the I-V characteristic of RTD. The possibility of appearance of specific plasma oscillations, which can improve the high-frequency characteristics of RTD, is predicted. It is found that the active current can be comparable with the resonant dc current of RTD.

  6. Jensen-Feynman approach to the statistics of interacting electrons

    SciTech Connect

    Pain, Jean-Christophe; Gilleron, Franck; Faussurier, Gerald

    2009-08-15

    Faussurier et al. [Phys. Rev. E 65, 016403 (2001)] proposed to use a variational principle relying on Jensen-Feynman (or Gibbs-Bogoliubov) inequality in order to optimize the accounting for two-particle interactions in the calculation of canonical partition functions. It consists of a decomposition into a reference electron system and a first-order correction. The procedure appears to be very efficient in order to evaluate the free energy and the orbital populations. In this work, we present numerical applications of the method and propose to extend it using a reference energy which includes the interaction between two electrons inside a given orbital. This is possible, thanks to our efficient recursion relation for the calculation of partition functions. We also show that a linear reference energy, however, is usually sufficient to achieve a good precision and that the most promising way to improve the approach of Faussurier et al. is to apply Jensen's inequality to a more convenient convex function.

  7. Estimation of electronic coupling in π-stacked donor-bridge-acceptor systems: Correction of the two-state model

    NASA Astrophysics Data System (ADS)

    Voityuk, Alexander A.

    2006-02-01

    Comparison of donor-acceptor electronic couplings calculated within two-state and three-state models suggests that the two-state treatment can provide unreliable estimates of Vda because of neglecting the multistate effects. We show that in most cases accurate values of the electronic coupling in a π stack, where donor and acceptor are separated by a bridging unit, can be obtained as Ṽda=(E2-E1)μ12/Rda+(2E3-E1-E2)2μ13μ23/Rda2, where E1, E2, and E3 are adiabatic energies of the ground, charge-transfer, and bridge states, respectively, μij is the transition dipole moments between the states i and j, and Rda is the distance between the planes of donor and acceptor. In this expression based on the generalized Mulliken-Hush approach, the first term corresponds to the coupling derived within a two-state model, whereas the second term is the superexchange correction accounting for the bridge effect. The formula is extended to bridges consisting of several subunits. The influence of the donor-acceptor energy mismatch on the excess charge distribution, adiabatic dipole and transition moments, and electronic couplings is examined. A diagnostic is developed to determine whether the two-state approach can be applied. Based on numerical results, we showed that the superexchange correction considerably improves estimates of the donor-acceptor coupling derived within a two-state approach. In most cases when the two-state scheme fails, the formula gives reliable results which are in good agreement (within 5%) with the data of the three-state generalized Mulliken-Hush model.

  8. Electron Interferometry in the Quantum Hall Regime: Aharonov-Bohm Effect of Interacting Electrons

    SciTech Connect

    Lin, P.V.; Camino, F.; Goldman, V.J.

    2009-09-01

    An apparent h/fe Aharonov-Bohm flux period, where f is an integer, has been reported in coherent quantum Hall devices. Such subperiod is not expected for noninteracting electrons and thus is thought to result from interelectron Coulomb interaction. Here we report experiments in a Fabry-Perot interferometer comprised of two wide constrictions enclosing an electron island. By carefully tuning the constriction front gates, we find a regime where interference oscillations with period h/2e persist throughout the transition between the integer quantum Hall plateaus 2 and 3, including half-filling. In a large quantum Hall sample, a transition between integer plateaus occurs near half-filling, where the bulk of the sample becomes delocalized and thus dissipative bulk current flows between the counterpropagating edges ('backscattering'). In a quantum Hall constriction, where conductance is due to electron tunneling, a transition between forward and backscattering is expected near the half-filling. In our experiment, neither period nor amplitude of the oscillations show a discontinuity at half-filling, indicating that only one interference path exists throughout the transition. We also present experiments and an analysis of the front-gate dependence of the phase of the oscillations. The results point to a single physical mechanism of the observed conductance oscillations: Aharonov-Bohm interference of interacting electrons in quantum Hall regime.

  9. Electron-electron interactions and lattice distortions in the perovskite titanates

    NASA Astrophysics Data System (ADS)

    Bjaalie, Lars

    A two-dimensional electron gas (2DEG) with the unprecedented high density of 3x1014 (corresponding to 1/2 electron per interface unit cell area) can be formed at the interface between SrTiO3 and a rare-earth titanate (RTiO3). The 2DEG resides in the SrTiO3, and arises from a polar discontinuity at the interface. The formation of this 2DEG has led us to study these perovskite titanates in detail. Some of these compounds are Mott insulators, where a Mott-Hubbard gap opens up between partially filled Ti 3 d bands. This talk focuses on the importance of the interplay between electron-electron interactions and lattice distortions in these complex oxides, which we study with density functional theory using a hybrid functional, capable of correctly describing electron localization and Mott-insulating behavior. These effects are crucial to understanding the metal-to-insulator transition as a function of electron density. Indeed, very thin SrTiO3 layers inserted in GdTiO3 show insulating behavior, in contrast to the metallic character of thicker layers in which the electrons form a 2DEG. The same physics is observed in bulk SrTiO3 when doped with 1/2 electron per Ti atom. Charge localization and lattice distortions also govern the formation of small hole polarons in the rare-earth titanates. We demonstrate that these polarons impact the optical absorption measurements commonly used to determine the value of the Mott-Hubbard gap. Work performed in collaboration with Anderson Janotti, Burak Himmetoglu, and Chris G. Van de Walle, and supported by NSF and ARO.

  10. Electron transfer in peptides.

    PubMed

    Shah, Afzal; Adhikari, Bimalendu; Martic, Sanela; Munir, Azeema; Shahzad, Suniya; Ahmad, Khurshid; Kraatz, Heinz-Bernhard

    2015-02-21

    In this review, we discuss the factors that influence electron transfer in peptides. We summarize experimental results from solution and surface studies and highlight the ongoing debate on the mechanistic aspects of this fundamental reaction. Here, we provide a balanced approach that remains unbiased and does not favor one mechanistic view over another. Support for a putative hopping mechanism in which an electron transfers in a stepwise manner is contrasted with experimental results that support electron tunneling or even some form of ballistic transfer or a pathway transfer for an electron between donor and acceptor sites. In some cases, experimental evidence suggests that a change in the electron transfer mechanism occurs as a result of donor-acceptor separation. However, this common understanding of the switch between tunneling and hopping as a function of chain length is not sufficient for explaining electron transfer in peptides. Apart from chain length, several other factors such as the extent of the secondary structure, backbone conformation, dipole orientation, the presence of special amino acids, hydrogen bonding, and the dynamic properties of a peptide also influence the rate and mode of electron transfer in peptides. Electron transfer plays a key role in physical, chemical and biological systems, so its control is a fundamental task in bioelectrochemical systems, the design of peptide based sensors and molecular junctions. Therefore, this topic is at the heart of a number of biological and technological processes and thus remains of vital interest.

  11. A Novel Compact Electron Spectrometer for Hot Electron Measurement in Pulsed Laser Solid Interaction

    SciTech Connect

    Chen, H; Patel, P; Price, D F; Young, B K; Springer, P T; Berry, R; Booth, R; Bruns, C; Nelson, D

    2002-07-05

    Ultra-intense laser-matter interactions provide a unique source of temporally short, broad spectrum electrons, which may be utilized in many varied applications. One such, which we are pursuing, is as part of a novel diagnostic to trace magnetic field lines in a magnetically-confined fusion device. An essential aspect of this scheme is to have a detailed characterization of the electron angular and energy distribution. To this effect we designed and constructed a compact electron spectrometer that uses permanent magnets for electron energy dispersion and over 100 scintillating fibers coupled to a 1024 x 1024 pixel CCD as the detection system. This spectrometer has electron energy coverage from 10 keV to 2 MeV. We tested the spectrometer on a high intensity (10{sup 17} to 10{sup 21} W/cm{sup 2}) short pulse (< 100 fs) laser, JanUSP, at Lawrence Livermore National laboratory using various solid targets. The details of the spectrometer and the experimental results will be reported.

  12. Interactions between Antibiotics and Graphene-Based Materials in Water: A Comparative Experimental and Theoretical Investigation.

    PubMed

    Zhang, Xuntong; Shen, Jiachun; Zhuo, Ning; Tian, Ziqi; Xu, Peiran; Yang, Zhen; Yang, Weiben

    2016-09-14

    Complex interactions between antibiotics and graphene-based materials determine both the adsorption performance of graphene-based materials and the transport behaviors of antibiotics in water. In this work, such interactions were investigated through adsorption experiments, instrumental analyses and theoretical DFT calculations. Three typical antibiotics (norfloxacin (NOR), sulfadiazine (SDZ) and tetracycline (TC)) and different graphene-based materials (divided into two groups: graphene oxides-based ones (GOs) and reduced GOs (RGOs)) were employed. Optimal adsorption pHs for NOR, SDZ, and TC are 6.2, 4.0, and 4.0, respectively. At corresponding optimal pHs, NOR favored RGOs (adsorption capability: ∼50 mg/g) while SDZ preferred GOs (∼17 mg/g); All adsorbents exhibited similar uptake of TC (∼70 mg/g). Similar amounts of edge carboxyls of both GOs and RGOs wielded electrostatic attraction with NOR and TC, but not with SDZ. According to DFT-calculated most-stable-conformations of antibiotics-adsorbents complexes, the intrinsic distinction between GOs and RGOs was the different amounts of sp(2) and sp(3) hybridization regions: π-π electron donor-acceptor effect of antibiotic-sp(2)/sp(3) and H-bonds of antibiotic-sp(3) coexisted. Binding energy (BE) of the former was larger for NOR; the latter interaction was stronger for SDZ; two species of TC at the optimal pH, i.e., TC(+) and TC(0), possessed larger BE with sp(3) and sp(2) regions, respectively. PMID:27548426

  13. Photon-Electron Interactions in Graphene-Based Heterojunctions

    NASA Astrophysics Data System (ADS)

    Liu, Fangze

    Graphene, a single layer of carbon atoms arranged in honeycomb lattice, has been one of the most attractive materials for fundamental and applied research in the past decade. Its unique electronic, optical, thermal, chemical and mechanical properties have lead to the discovery of new physics and many promising applications. In particular, research on photon-electron interaction in graphene-based heterojunctions has revealed a new route to design photoactive devices. In this thesis, I present our work on the synthesis of graphene by chemical vapor deposition (CVD) and the study of graphene-based optoelectronic devices. In addition to the conventional synthesis of graphene on copper (Cu) foils, we also present the CVD synthesis of graphene on a new substrate: palladium (Pd). Especially, we performed detailed study of the nucleation, evolution and morphology of graphene growth on Pd substrate. It helps us to understand the growth reaction mechanism and achieve controllable synthesis of graphene from single layer to multiple layers with different morphologies. We then studied the broadband and ultrasensitive photocurrent and photovoltage response of graphene/silicon (Si) Schottky diodes. For the same architecture, we identified a new photoconductive mode with ultra high photoconductive gain, namely "quantum carrier reinvestment (QCR)". A gain exceeding 107 A/W was demonstrated. The underlying physics of photon-electron interactions in these junctions were studied by a combination of optical characterization tools including Raman spectroscopy, UV-Vis spectroscopy and scanning optical microscopy. The results obtained have been discussed in the framework of the unique electronic band structure, density states, and mobility of graphene, along with the manner in witch photoexcited carrier behave under various externally tuned parameters. We also systematically studied the optimization of performance of graphene/Si and thin transparent graphite/Si junction solar cells and

  14. Steric and electronic interactions between cofacial metallocene rings

    SciTech Connect

    Arnold, R.; Foxman, B.M.; Rosenblum, M.; Euler, W.B.

    1988-06-01

    As part of a study of interactions between metallocenes, held so that two cyclopentadienyl rings are constrained to be proximate and facing one another, 1,8-diruthenocenylnaphthalene has been prepared and its crystal structure has been determined. This structure is shown to be close to that of 1,8-diferrocenylnaphthalene reported earlier, especially in respect to the dihedral angle between the substituted cyclopentadienyl and naphthalene ring planes and the splay angle between the two substituted cyclopentadienyl rings. Both of these distortions are significantly diminished in the monocation derived from 1a, suggesting that there is a significant decrease in electron density on the cyclopentadienyl rings on oxidation of ferrocene to a ferricenium cation, consistent with theoretical analyses.

  15. Electron-phonon interaction within classical molecular dynamics

    DOE PAGESBeta

    Tamm, A.; Samolyuk, G.; Correa, A. A.; Klintenberg, M.; Aabloo, A.; Caro, A.

    2016-07-14

    Here, we present a model for nonadiabatic classical molecular dynamics simulations that captures with high accuracy the wave-vector q dependence of the phonon lifetimes, in agreement with quantum mechanics calculations. It is based on a local view of the e-ph interaction where individual atom dynamics couples to electrons via a damping term that is obtained as the low-velocity limit of the stopping power of a moving ion in a host. The model is parameter free, as its components are derived from ab initio-type calculations, is readily extended to the case of alloys, and is adequate for large-scale molecular dynamics computermore » simulations. We also show how this model removes some oversimplifications of the traditional ionic damped dynamics commonly used to describe situations beyond the Born-Oppenheimer approximation.« less

  16. Electron-phonon interaction within classical molecular dynamics

    NASA Astrophysics Data System (ADS)

    Tamm, A.; Samolyuk, G.; Correa, A. A.; Klintenberg, M.; Aabloo, A.; Caro, A.

    2016-07-01

    We present a model for nonadiabatic classical molecular dynamics simulations that captures with high accuracy the wave-vector q dependence of the phonon lifetimes, in agreement with quantum mechanics calculations. It is based on a local view of the e -ph interaction where individual atom dynamics couples to electrons via a damping term that is obtained as the low-velocity limit of the stopping power of a moving ion in a host. The model is parameter free, as its components are derived from ab initio-type calculations, is readily extended to the case of alloys, and is adequate for large-scale molecular dynamics computer simulations. We also show how this model removes some oversimplifications of the traditional ionic damped dynamics commonly used to describe situations beyond the Born-Oppenheimer approximation.

  17. An interactive electronic instructional unit on substance abuse.

    PubMed

    Bonder, Bette R; Hulisz, Darrell; Marsh, Sybil; Bonaguro, John

    2006-01-01

    This paper describes an approach to instruction for allied health students in screening and brief intervention to assist children and adolescents living with adults who are abusing substances. Substance abuse is a major public health problem in the United States; among its outcomes is damage to children living in the home. Health professionals should screen child and adolescent clients to determine whether adults in the home are substance abusers, and provide help for children living with such adults. An interactive electronic instructional unit, suitable for either independent study or classroom use, was developed to provide this content to allied health students. The unit includes an introductory page, followed by pages focused on the scope of the problem, screening, and brief intervention. Evaluation by means of a pre and post-test suggested that the unit has the potential to increase occupational and physical therapy students' knowledge and modify attitudes regarding their role in providing screening, referral, and brief intervention for this population.

  18. Electron-electron interactions, topological phase, and optical properties of a charged artificial benzene ring

    NASA Astrophysics Data System (ADS)

    Ozfidan, Isil; Vladisavljevic, Milos; Korkusinski, Marek; Hawrylak, Pawel

    2015-12-01

    We present a theory of the electronic and optical properties of a charged artificial benzene ring (ABR). The ABR is described by the extended Hubbard model solved using exact diagonalization methods in both real and Fourier space as a function of the tunneling matrix element t , Hubbard on-site repulsion U , and interdot interaction V . In the strongly interacting case, we discuss exact analytical results for the spectrum of the hole in a half-filled ABR dressed by the spin excitations of the remaining electrons. The spectrum is interpreted in terms of the appearance of a topological phase associated with an effective gauge field piercing through the ring. We show that the maximally spin-polarized (S =5 /2 ) and maximally spin-depolarized (S =1 /2 ) states are the lowest energy, orbitally nondegenerate, states. We discuss the evolution of the phase diagram and level crossings as interactions are switched off and the ground state becomes spin nondegenerate but orbitally degenerate S =1 /2 . We present a theory of optical absorption spectra and show that the evolution of the ground and excited states, level crossings, and presence of artificial gauge can be detected optically.

  19. Ions interacting with planar aromatic molecules: Modeling electron transfer reactions

    SciTech Connect

    Forsberg, B. O.; Alexander, J. D.; Chen, T.; Pettersson, A. T.; Gatchell, M.; Cederquist, H.; Zettergren, H.

    2013-02-07

    We present theoretical absolute charge exchange cross sections for multiply charged cations interacting with the Polycyclic Aromatic Hydrocarbon (PAH) molecules pyrene C{sub 14}H{sub 10}, coronene C{sub 24}H{sub 12}, or circumcoronene C{sub 54}H{sub 18}. These planar, nearly circular, PAHs are modelled as conducting, infinitely thin, and perfectly circular discs, which are randomly oriented with respect to straight line ion trajectories. We present the analytical solution for the potential energy surface experienced by an electron in the field of such a charged disc and a point-charge at an arbitrary position. The location and height of the corresponding potential energy barrier from this simple model are in close agreement with those from much more computationally demanding Density Functional Theory (DFT) calculations in a number of test cases. The model results compare favourably with available experimental data on single- and multiple electron transfer reactions and we demonstrate that it is important to include the orientation dependent polarizabilities of the molecules (model discs) in particular for the larger PAHs. PAH ionization energy sequences from DFT are tabulated and used as model inputs. Absolute cross sections for the ionization of PAH molecules, and PAH ionization energies such as the ones presented here may be useful when considering the roles of PAHs and their ions in, e.g., interstellar chemistry, stellar atmospheres, and in related photoabsorption and photoemission spectroscopies.

  20. Transmission zero in a quantum dot with strong electron-electron interaction: Perturbative conductance calculations

    NASA Astrophysics Data System (ADS)

    Kim, Sejoong; Lee, Hyun-Woo

    2006-05-01

    A pioneering experiment [E. Schuster, E. Buks, M. Heiblum, D. Mahalu, V. Umansky, and Hadas Shtrikman, Nature 385, 417 (1997)] reported the measurement of the transmission phase of an electron traversing a quantum dot and found the intriguing feature of a sudden phase drop in the conductance valleys. Based on the Friedel sum rule for a spinless effective one-dimensional system, it has been previously argued [H.-W. Lee, Phys. Rev. Lett. 82, 2358 (1999)] that the sudden phase drop should be accompanied by the vanishing of the transmission amplitude, or transmission zero. Here we address roles of strong electron-electron interactions on the electron transport through a two-level quantum dot where one level couples with the leads much more strongly than the other level does [P. G. Silvestrov and Y. Imry, Phys. Rev. Lett. 85, 2565 (2000)]. We perform a perturbative conductance calculation with an explicit account of large charging energy and verify that the resulting conductance exhibits transmission zero, in agreement with the analysis based on the Friedel sum rule.

  1. Discrete Chromatic Aberrations Arising from Photoinduced Electron-Photon Interactions in Ultrafast Electron Microscopy.

    PubMed

    Plemmons, Dayne A; Flannigan, David J

    2016-05-26

    In femtosecond ultrafast electron microscopy (UEM) experiments, the initial excitation period is composed of spatiotemporal overlap of the temporally commensurate pump photon pulse and probe photoelectron packet. Generation of evanescent near-fields at the nanostructure specimens produces a dispersion relation that enables coupling of the photons (ℏω = 2.4 eV, for example) and freely propagating electrons (200 keV, for example) in the near-field. Typically, this manifests as discrete peaks occurring at integer multiples (n) of the photon energy in the low-loss/gain region of electron-energy spectra (i.e., at 200 keV ± nℏω eV). Here, we examine the UEM imaging resolution implications of the strong inelastic near-field interactions between the photons employed in optical excitation and the probe photoelectrons. We find that the additional photoinduced energy dispersion occurring when swift electrons pass through intense evanescent near-fields results in a discrete chromatic aberration that limits the spatial resolving power to several angstroms during the excitation period. PMID:27111530

  2. Weak localization and electron-electron interactions in indium-doped ZnO nanowires.

    PubMed

    Thompson, Richard S; Li, Dongdong; Witte, Christopher M; Lu, Jia G

    2009-12-01

    Single crystal ZnO nanowires doped with indium are synthesized via the laser-assisted chemical vapor deposition method. The conductivity of the nanowires is measured at low temperatures in magnetic fields with directions both perpendicular and parallel to the wire axes. A quantitative fit of our data is obtained, consistent with the theory of a quasi-one-dimensional metallic system with quantum corrections due to weak localization and electron-electron interactions. The anisotropy of the magneto-conductivity agrees with theory. The two quantum corrections are of approximately equal magnitude with respective temperature dependences of T(-1/3)and T(-1/2). The alternative model of quasi-two-dimensional surface conductivity is excluded by the absence of oscillations in the magneto-conductivity in parallel magnetic fields. PMID:19831413

  3. Local electron-electron interaction strength in ferromagnetic nickel determined by spin-polarized positron annihilation.

    PubMed

    Ceeh, Hubert; Weber, Josef Andreas; Weber, Josef Andreass; Böni, Peter; Leitner, Michael; Benea, Diana; Chioncel, Liviu; Ebert, Hubert; Minár, Jan; Vollhardt, Dieter; Hugenschmidt, Christoph

    2016-01-01

    We employ a positron annihilation technique, the spin-polarized two-dimensional angular correlation of annihilation radiation (2D-ACAR), to measure the spin-difference spectra of ferromagnetic nickel. The experimental data are compared with the theoretical results obtained within a combination of the local spin density approximation (LSDA) and the many-body dynamical mean-field theory (DMFT). We find that the self-energy defining the electronic correlations in Ni leads to anisotropic contributions to the momentum distribution. By direct comparison of the theoretical and experimental results we determine the strength of the local electronic interaction U in ferromagnetic Ni as 2.0 ± 0.1 eV. PMID:26879249

  4. Local electron-electron interaction strength in ferromagnetic nickel determined by spin-polarized positron annihilation

    PubMed Central

    Ceeh, Hubert; Weber, Josef Andreass; Böni, Peter; Leitner, Michael; Benea, Diana; Chioncel, Liviu; Ebert, Hubert; Minár, Jan; Vollhardt, Dieter; Hugenschmidt, Christoph

    2016-01-01

    We employ a positron annihilation technique, the spin-polarized two-dimensional angular correlation of annihilation radiation (2D-ACAR), to measure the spin-difference spectra of ferromagnetic nickel. The experimental data are compared with the theoretical results obtained within a combination of the local spin density approximation (LSDA) and the many-body dynamical mean-field theory (DMFT). We find that the self-energy defining the electronic correlations in Ni leads to anisotropic contributions to the momentum distribution. By direct comparison of the theoretical and experimental results we determine the strength of the local electronic interaction U in ferromagnetic Ni as 2.0 ± 0.1 eV. PMID:26879249

  5. Efficient ternary organic photovoltaics incorporating a graphene-based porphyrin molecule as a universal electron cascade material

    NASA Astrophysics Data System (ADS)

    Stylianakis, M. M.; Konios, D.; Kakavelakis, G.; Charalambidis, G.; Stratakis, E.; Coutsolelos, A. G.; Kymakis, E.; Anastasiadis, S. H.

    2015-10-01

    A graphene-based porphyrin molecule (GO-TPP) was synthesized by covalent linkage of graphene oxide (GO) with 5-(4-aminophenyl)-10,15,20-triphenyl porphyrin (TPP-NH2). The yielded graphene-based material is a donor-acceptor (D-A) molecule, exhibiting strong intermolecular interactions between the GO core (A) and the covalently anchored porphyrin molecule (D). To demonstrate the universal role of GO-TPP as an electron cascade material, ternary blend organic photovoltaics based on [6,6]-phenyl-C71-butyric-acid-methyl-ester (PC71BM) as an electron acceptor material and two different polymer donor materials, poly[N-9'-hepta-decanyl-2,7-carbazole-alt-5,5-(40,70-di-2-thienyl-20,10,30-benzothiadiazole)] (PCDTBT) and the highly efficient poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl}) (PTB7), were fabricated. The addition of GO-TPP into the active layer implies continuous percolation paths between the D-A interfaces, enhancing charge transport, reducing exciton recombination and thus improving the photovoltaic performance of the device. A simultaneous increase of short circuit current density (Jsc), open-circuit voltage (Voc) and fill factor (FF), compared to the PTB7:PC71BM reference cell, led to an improved power conversion efficiency (PCE) of 8.81% for the PTB7:GO-TPP:PC71BM-based device, owing mainly to the more efficient energy level offset between the active layer components.A graphene-based porphyrin molecule (GO-TPP) was synthesized by covalent linkage of graphene oxide (GO) with 5-(4-aminophenyl)-10,15,20-triphenyl porphyrin (TPP-NH2). The yielded graphene-based material is a donor-acceptor (D-A) molecule, exhibiting strong intermolecular interactions between the GO core (A) and the covalently anchored porphyrin molecule (D). To demonstrate the universal role of GO-TPP as an electron cascade material, ternary blend organic photovoltaics based on [6,6]-phenyl-C71-butyric

  6. Murine macrophage-lymphocyte interactions: scanning electron microscopic study.

    PubMed Central

    Albrecht, R M; Hinsdill, R D; Sandok, P L; Horowitz, S D

    1978-01-01

    Light and scanning electron microscopic observations revealed murine macrophage-lymphocyte interactions involving the initial contact of peritoneal, spleen, or thymus lymphocytes with peritoneal macrophage processes or microprocesses followed by clustering of lymphocytes over the central nuclear area of the macrophages. Lymphocyte-lymphocyte clustering was not observed in the absence of macrophages. Attachment and subsequent clustering appeared not to require the presence of serum or antigen; the attachment of allogeneic or xenogeneic lymphocytes was comparable to that seen in the syngeneic system, but central clustering of these lymphocytes failed to occur. No attachment or clustering was observed when thymic lymphocytes were cultured with thymus derived fibroblasts rather than with peritoneal macrophages. Lymphocyte attachment to immune, antigen-activated, syngeneic macrophages occurred more rapidly than that to normal unstimulated syngeneic macrophages; however, lymphocytes attached to the "activated" macrophages appeared to be killed by a nonphagocytic mechanism. A similar increase in the rate of lymphocyte attachment to macrophages occurred in the presence of migration inhibitory factor. Subsequent lymphocyte clustering on macrophages was observed in the migration inhibitory factor-stimulated cultures. In addition, lymphocyte-macrophage interactions similar to those in vitro were observed to occur in vivo on intraperitoneally implanted cover slips. Images PMID:101458

  7. Ultrafast electron transfer reactions initiated by excited CT states of push pull perylenes

    NASA Astrophysics Data System (ADS)

    Miller, Scott E.; Zhao, Yongyu; Schaller, Richard; Mulloni, Viviana; Just, Eric M.; Johnson, Robert C.; Wasielewski, Michael R.

    2002-01-01

    Two new chromophores that absorb in the visible spectrum, the 9-( N-pyrrolidinyl)- and 9-( N-piperidinyl)perylene-3,4-dicarboximides, 5PMI and 6PMI, respectively, were synthesized and shown to possess lowest excited singlet states with about 70% charge transfer (CT) character. Changing the ring size of the cyclic amine from 5 to 6 significantly changes the energies of the CT states, as well as the redox potentials of the chromophores. These chromophores were linked to pyromellitimide (PI) and 1,8:4,5-naphthalenediimide (NI) electron acceptors using a single N-N bond between their respective imides to yield the corresponding donor-acceptor dyads 5PMI-PI, 5PMI-NI, 6PMI-PI, and 6PMI-NI. The donors and acceptors in these molecules are positioned relative to one another in a rod-like arrangement at fixed distances and restricted orientations. The rates of charge separation and recombination were measured using transient absorption spectroscopy. These chromophores were also used to prepare rigid donor-acceptor triads 5PMI-PI-NI and 6PMI-PI-NI, which display one- or two-step electron transfer mechanisms that depend on solvent polarity. These compounds exhibit a broad range of structure and media driven changes in electron transfer mechanism.

  8. Electronic Structure Theory for Radicaloid Systems and Intermolecular Interactions

    NASA Astrophysics Data System (ADS)

    Kurlancheek, Westin

    associated with unrestriction. Second, the relaxed density matrix itself fails to be N-representable, with natural orbital occupation numbers less than zero and greater than one. Therefore, it is desirable to use a method that is not dependent on the inverse of the Hessian like orbital optimized MP2 (O2). Another system which requires the use of orbital optimization is a neutral soliton on a polyacetylene chain. In this system, the Hartree-Fock reference suffers from severe spin-polarization making the wavefunction physically unreasonable unless a very sophisticated treatment of electron correlation is used to correct this problem. Originally, it was found that computationally expensive methods like CCSD(T) and CASSCF could adequately describe small model chain but not the full system. The O2 method is found to be an dramatic improvement over traditional MP2 which can be feasibly applied to polyenyl chains long enough to characterize the soliton. It is also discovered that density functionals are generally inadequate in describing the half-width of the soliton. Finally, the last chapter takes a slightly different perspective and focuses on the addition of correlation energy to a successful energy decomposition analysis based on absolutely localized molecular orbitals. It is discovered that the resulting new method can adequately describe systems with dispersive intermolecular interactions and large amounts of charge transfer. This scheme is then applied to the water dimer systems and it is found that all of the intermolecular interactions similar in size with the electrostatic interaction being the largest and the dispersive interaction being the smallest. This method is also contrasted with other EDA schemes.

  9. Gypsy moth pheromone-binding protein-ligand interactions: pH profiles and simulations as tools for detecting polar interactions.

    PubMed

    Sanes, Jurgen T; Plettner, Erika

    2016-09-15

    Pheromone-binding proteins (PBPs) are believed to control diffusion of pheromones in sensory hairs of insects. The interactions of gypsy moth (Lymantria dispar) PBPs with the sex attractant pheromone, (+)-Disparlure ((7R,8S)-epoxy-2-methyloctadecane), and the enantioselectivity of recognition are not completely understood. Enantioselectivity is important for L. dispar, because (-)-disparlure cancels the attraction of (+)-disparlure, so these moths use enantiopure (+)-disparlure for communication. We performed docking simulations of the protonated homology PBP models with the enantiomers of disparlure, 5-oxadisparlure, 10-oxadisparlure, 5-thiadisparlure and 10-thiadisparlure, together with a binding assay experiment, in which the pH profiles for the PBP-ligand combinations were surveyed. The molecular simulations revealed different amino acid residues in the binding sites, movement of specific amino acid residues at certain pH values, distinct amino acid-ligand interactions (side chain donors/acceptors, H-arene bonding, backbone donors/acceptors) and differences in the conformations of each protein-ligand complex. The pKa values obtained from the binding experiment and the results from the molecular simulations served as tools for detecting polar interactions between the PBPs and ligands. The differences found between structures docked with ligand enantiomers reveal the enantioselectivity of the gypsy moth PBPs towards the pheromone and its antipode, as well as towards enantiomers of pheromone analogs with heteroatom substitutions. PMID:27431057

  10. Gypsy moth pheromone-binding protein-ligand interactions: pH profiles and simulations as tools for detecting polar interactions.

    PubMed

    Sanes, Jurgen T; Plettner, Erika

    2016-09-15

    Pheromone-binding proteins (PBPs) are believed to control diffusion of pheromones in sensory hairs of insects. The interactions of gypsy moth (Lymantria dispar) PBPs with the sex attractant pheromone, (+)-Disparlure ((7R,8S)-epoxy-2-methyloctadecane), and the enantioselectivity of recognition are not completely understood. Enantioselectivity is important for L. dispar, because (-)-disparlure cancels the attraction of (+)-disparlure, so these moths use enantiopure (+)-disparlure for communication. We performed docking simulations of the protonated homology PBP models with the enantiomers of disparlure, 5-oxadisparlure, 10-oxadisparlure, 5-thiadisparlure and 10-thiadisparlure, together with a binding assay experiment, in which the pH profiles for the PBP-ligand combinations were surveyed. The molecular simulations revealed different amino acid residues in the binding sites, movement of specific amino acid residues at certain pH values, distinct amino acid-ligand interactions (side chain donors/acceptors, H-arene bonding, backbone donors/acceptors) and differences in the conformations of each protein-ligand complex. The pKa values obtained from the binding experiment and the results from the molecular simulations served as tools for detecting polar interactions between the PBPs and ligands. The differences found between structures docked with ligand enantiomers reveal the enantioselectivity of the gypsy moth PBPs towards the pheromone and its antipode, as well as towards enantiomers of pheromone analogs with heteroatom substitutions.

  11. Theory of Auger-electron and appearance-potential spectroscopy for interacting valence-band electrons

    NASA Astrophysics Data System (ADS)

    Nolting, W.; Geipel, G.; Ertl, K.

    1991-12-01

    A theory of Auger-electron spectroscopy (AES) and appearance-potential spectroscopy (APS) is presented for interacting electrons in a nondegenerate energy band, described within the framework of the Hubbard model. Both types of spectroscopy are based on the same two-particle spectral density. A diagrammatic vertex-correction method (Matsubara formalism) is used to express this function in terms of the one-particle spectral density. The latter is approximately determined for arbitrary temperature T, arbitrary coupling strength U/W (U, the intra-atomic Coulomb matrix element; W, the width of the ``free'' Bloch band), and arbitrary band occupations n (0<=n<=2 average number of band electrons per site) by a self-consistent moment method. In weakly coupled systems the electron correlations give rise to certain deformations of the quasiparticle density of states (QDOS) in relation to the Bloch density of states (BDOS), where, however, spontaneous magnetic order is excluded, irrespective of the band filling n. The AE (AP) spectra consist of only one structure a few eV wide (``bandlike'') which is strongly n dependent, but only slightly T dependent, being rather well approximated by a simple self-convolution of the occupied (unoccupied) QDOS. For strongly correlated electrons the Bloch band splits into two quasiparticle subbands. This leads for n<1 to one line in the AE spectrum and three lines in the AP spectrum, and vice versa for n>1. For sufficiently strong correlations U/W additional satellites appear that refer to situations where the two excited quasiparticles (quasiholes) propagate as tightly bound pairs through the lattice without being scattered by other charge carriers. As soon as the satellite splits off from the bandlike part of the spectrum, it takes almost the full spectral weight, conveying the impression of an ``atomiclike'' AE (AP) line shape. The satellite has almost exactly the structure of the free BDOS. If the particle density n as well as the hole

  12. Anisotropic Electron-Photon and Electron-Phonon Interactions in Black Phosphorus.

    PubMed

    Ling, Xi; Huang, Shengxi; Hasdeo, Eddwi H; Liang, Liangbo; Parkin, William M; Tatsumi, Yuki; Nugraha, Ahmad R T; Puretzky, Alexander A; Das, Paul Masih; Sumpter, Bobby G; Geohegan, David B; Kong, Jing; Saito, Riichiro; Drndic, Marija; Meunier, Vincent; Dresselhaus, Mildred S

    2016-04-13

    Orthorhombic black phosphorus (BP) and other layered materials, such as gallium telluride (GaTe) and tin selenide (SnSe), stand out among two-dimensional (2D) materials owing to their anisotropic in-plane structure. This anisotropy adds a new dimension to the properties of 2D materials and stimulates the development of angle-resolved photonics and electronics. However, understanding the effect of anisotropy has remained unsatisfactory to date, as shown by a number of inconsistencies in the recent literature. We use angle-resolved absorption and Raman spectroscopies to investigate the role of anisotropy on the electron-photon and electron-phonon interactions in BP. We highlight, both experimentally and theoretically, a nontrivial dependence between anisotropy and flake thickness and photon and phonon energies. We show that once understood, the anisotropic optical absorption appears to be a reliable and simple way to identify the crystalline orientation of BP, which cannot be determined from Raman spectroscopy without the explicit consideration of excitation wavelength and flake thickness, as commonly used previously.

  13. Anisotropic Electron-Photon and Electron-Phonon Interactions in Black Phosphorus

    DOE PAGESBeta

    Ling, Xi; Huang, Shengxi; Hasdeo, Eddwi; Liang, Liangbo; Parkin, William; Tatsumi, Yuki; Nugraha, Ahmad; Puretzky, Alexander A; Das, Paul; Sumpter, Bobby G; et al

    2016-03-10

    Orthorhombic black phosphorus (BP) and other layered materials, such as gallium telluride (GaTe) and tin selenide (SnSe), stand out among two-dimensional (2D) materials owing to their anisotropic in-plane structure. This anisotropy adds a new dimension to the properties of 2D materials and stimulates the development of angle-resolved photonics and electronics. However, understanding the effect of anisotropy has remained unsatisfactory to-date, as shown by a number of inconsistencies in the recent literatures. We use angle-resolved absorption and Raman spectroscopies to investigate the role of anisotropy on the electron-photon and electron-phonon interactions in BP. We highlight a non-trivial dependence between anisotropies andmore » flake thickness, photon and phonon energies. We show that once understood, the anisotropic optical absorption appears to be a reliable and simple way to identify the crystalline orientation of BP, which cannot be determined from Raman spectroscopy without the explicit consideration of excitation wavelength and flake thickness, as commonly used previously.« less

  14. Ideal dipole approximation fails to predict electronic coupling between semiconducting single wall carbon nanotubes

    SciTech Connect

    Tretiak, Sergei

    2008-01-01

    Single-walled carbon nanotubes (SWNTs) are highly conjugated carbon tubes that are a few nanometers in diameter and can be up to millimeters in length. The excited electronic states of semiconductor-type SWNTs are quasi-1D excitons. It is known that these spatially-extended electronic excitations can migrate among SWNTs that are bundled together, thus quenching the fluorescence owing to the presence of metallic SWNTs. Recent advances in purification and isolation have enabled studies of electronic energy transfer (EET) between SWNTs and molecular chromophores. Here we examine the electronic coupling among SWNTs in order to understand EET involving SWNTs. There are two main difficulties that need to be addressed when studying SWNT EET. The first is to obtain the electronic coupling matrix element that promotes EET. The most common method to calculate the electronic coupling between two molecules is the point dipole approximation (PDA) method, where the electronic coupling is described as the Coulombic interaction between transition dipole moments of D and A. In this approximation, each molecule is represented by a single dipole located at the center of mass for each molecule. It is well known that the PDA method fails at small separations in molecular systems. Owing to the size of SWNTs compared to typical donor-acceptor separations, it is likely that the PDA method will fail. Even when using the PDA method, however, it is difficult to obtain the dipole strength of the transition because the radiative lifetime is obscured by thermal population of dark states in the exciton band. The second difficulty is that there are a few closely spaced states associated with the lowest bright exciton transition (E{sub 11}), and each of these states might act as energy donors or acceptors. Here we will focus on the first of these challenges: the evaluation of electronic couplings between SWNTs, overcoming the limitations of the PDA method. In the last decade, sophisticated quantum

  15. Effect of electron-electron interaction on the magnetic moment and susceptibility of a parabolic GaAs quantum dot

    NASA Astrophysics Data System (ADS)

    Boda, Aalu; Kumar, D. Sanjeev; Sankar, I. V.; Chatterjee, Ashok

    2016-11-01

    The problem of a parabolically confined two-dimensional semiconductor GaAs quantum dot with two interacting electrons in the presence of an external magnetic field and the spin-Zeeman interaction is studied using a method of numerical diagonalization. The energy spectrum is calculated as a function of the magnetic field. The magnetic moment (M) and the magnetic susceptibility (χ) show zero temperature diamagnetic peaks due to the exchange induced singlet-triplet transitions. The position and the number of these peaks depend both on the confinement strength of the quantum dot and the strength of the electron-electron interaction (β) .

  16. Experimental and theoretical analysis of photoinduced electron transfer: Including the role of liquid structure

    SciTech Connect

    Swallen, S.F.; Weidemaier, K.; Tavernier, H.L.; Fayer, M.D.

    1996-05-16

    Experimental determinations of the dynamics of photoinduced electron transfer from rubrene to duroquinone in three solvents, dibutyl phthalate, diethyl sebacate, and cyclohexanone are presented. The data are analyzed using recent theoretical developements that include important features of the solvent, i.e., the effects of finite molecular volume on local solvent structure and on the mutual donor-acceptor diffusion rates. Inclusion of the liquid radial distribution function (rdf) in the theory accounts for the significant variation of the acceptor concentration near a donor. Hydrodynamic effects, which slow the rate of donor-acceptor approach at short distance, are important and are also included in the theoretical analysis of the data. The data analysis depends on a reasonable model of the rdf. A method is presented to obtain the hard-sphere parameters needed to calculate the rdf. The Marcus form of the distance-dependent transfer rate is used. For the highest viscosity solvent (dibutylphthalate), a unique set of the Marcus transfer parameters is obtained. For lower viscosity solvents, the transfer parameters are less well defined, but information on the distance and time dependence of charge separation is still acquired. These experiments, combined with the theoretical analysis, yield the first realistic description of through-solvent photoinduced electron transfer. 102 refs., 6 figs., 1 tab.

  17. Efficient ternary organic photovoltaics incorporating a graphene-based porphyrin molecule as a universal electron cascade material.

    PubMed

    Stylianakis, M M; Konios, D; Kakavelakis, G; Charalambidis, G; Stratakis, E; Coutsolelos, A G; Kymakis, E; Anastasiadis, S H

    2015-11-14

    A graphene-based porphyrin molecule (GO-TPP) was synthesized by covalent linkage of graphene oxide (GO) with 5-(4-aminophenyl)-10,15,20-triphenyl porphyrin (TPP-NH2). The yielded graphene-based material is a donor-acceptor (D-A) molecule, exhibiting strong intermolecular interactions between the GO core (A) and the covalently anchored porphyrin molecule (D). To demonstrate the universal role of GO-TPP as an electron cascade material, ternary blend organic photovoltaics based on [6,6]-phenyl-C71-butyric-acid-methyl-ester (PC71BM) as an electron acceptor material and two different polymer donor materials, poly[N-9'-hepta-decanyl-2,7-carbazole-alt-5,5-(40,70-di-2-thienyl-20,10,30-benzothiadiazole)] (PCDTBT) and the highly efficient poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl}) (PTB7), were fabricated. The addition of GO-TPP into the active layer implies continuous percolation paths between the D-A interfaces, enhancing charge transport, reducing exciton recombination and thus improving the photovoltaic performance of the device. A simultaneous increase of short circuit current density (Jsc), open-circuit voltage (Voc) and fill factor (FF), compared to the PTB7:PC71BM reference cell, led to an improved power conversion efficiency (PCE) of 8.81% for the PTB7:GO-TPP:PC71BM-based device, owing mainly to the more efficient energy level offset between the active layer components.

  18. The interaction between two planar and nonplanar quantum electron acoustic solitary waves in dense electron-ion plasmas

    SciTech Connect

    EL-Labany, S. K.; El-Mahgoub, M. G.; EL-Shamy, E. F.

    2012-06-15

    The interaction between two planar and nonplanar (cylindrical and spherical) quantum electron acoustic solitary waves (QEASWs) in quantum dense electron-ion plasmas has been studied. The extended Poincare-Lighthill-Kuo method is used to obtain planar and nonplanar phase shifts after the interaction of the two QEASWs. The change of phase shifts and trajectories for QEASWs due to the effect of the different geometries, the quantum corrections of diffraction, and the cold electron-to-hot electron number density ratio are discussed. It is shown that the interaction of the QEASWs in planar geometry, cylindrical geometry, and spherical geometry are different. The present investigation may be beneficial to understand the interaction between two planar and nonplanar QEASWs that may occur in the quantum plasmas found in laser-produced plasmas as well as in astrophysical plasmas.

  19. The interaction between two planar and nonplanar quantum electron acoustic solitary waves in dense electron-ion plasmas

    NASA Astrophysics Data System (ADS)

    EL-Labany, S. K.; EL-Shamy, E. F.; El-Mahgoub, M. G.

    2012-06-01

    The interaction between two planar and nonplanar (cylindrical and spherical) quantum electron acoustic solitary waves (QEASWs) in quantum dense electron-ion plasmas has been studied. The extended Poincaré-Lighthill-Kuo method is used to obtain planar and nonplanar phase shifts after the interaction of the two QEASWs. The change of phase shifts and trajectories for QEASWs due to the effect of the different geometries, the quantum corrections of diffraction, and the cold electron-to-hot electron number density ratio are discussed. It is shown that the interaction of the QEASWs in planar geometry, cylindrical geometry, and spherical geometry are different. The present investigation may be beneficial to understand the interaction between two planar and nonplanar QEASWs that may occur in the quantum plasmas found in laser-produced plasmas as well as in astrophysical plasmas.

  20. A study of the interacting electron system in stressed (001) Si MOSFETs

    NASA Astrophysics Data System (ADS)

    Lutz, J.; Kuchar, F.

    1996-11-01

    The interaction of the electrons in Si MOSFETs has been studied under uniaxial stress using quantum magnetotransport experiments (Shubnikov - de Haas and quantum Hall effect). The stress allows one to vary the relative positions of the conduction band valleys where the electron - electron interaction plays a crucial role. From the evaluation of the data we obtain the phase diagram of the population of the valleys as a function of stress and carrier density. Our results are excellently described by the theory of Takada and Ando where intervalley electron - electron interaction is taken into account.