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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 Emphasis was placed on current unpublished research and discussion of the future target areas in this field.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. DONOR-ACCEPTOR INTERACTIONS OF NITROGEN*

    PubMed Central

    Kimura, J. E.; Szent-Györgyi, A.

    1969-01-01

    The nitrogen atoms of organic molecules readily enter into donor-acceptor interactions, giving off an electron from their lone pair. Under favorable conditions the acceptor can form free radicals. S and O atoms behave likewise but less intensely. PMID:4306047

  5. 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.

  6. 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

  7. 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.

  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. 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.

  10. 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.

  11. Donor-acceptor electron transport mediated by solitons.

    PubMed

    Brizhik, L S; Piette, B M A G; Zakrzewski, W J

    2014-11-01

    We study the long-range electron and energy transfer mediated by solitons in a quasi-one-dimensional molecular chain (conjugated polymer, alpha-helical macromolecule, etc.) weakly bound to a donor and an acceptor. We show that for certain sets of parameter values in such systems an electron, initially located at the donor molecule, can tunnel to the molecular chain, where it becomes self-trapped in a soliton state, and propagates to the opposite end of the chain practically without energy dissipation. Upon reaching the end, the electron can either bounce back and move in the opposite direction or, for suitable parameter values of the system, tunnel to the acceptor. We estimate the energy efficiency of the donor-acceptor electron transport depending on the parameter values. Our calculations show that the soliton mechanism works for the parameter values of polypeptide macromolecules and conjugated polymers. We also investigate the donor-acceptor electron transport in thermalized molecular chains. PMID:25493866

  12. Donor-acceptor electron transport mediated by solitons

    NASA Astrophysics Data System (ADS)

    Brizhik, L. S.; Piette, B. M. A. G.; Zakrzewski, W. J.

    2014-11-01

    We study the long-range electron and energy transfer mediated by solitons in a quasi-one-dimensional molecular chain (conjugated polymer, alpha-helical macromolecule, etc.) weakly bound to a donor and an acceptor. We show that for certain sets of parameter values in such systems an electron, initially located at the donor molecule, can tunnel to the molecular chain, where it becomes self-trapped in a soliton state, and propagates to the opposite end of the chain practically without energy dissipation. Upon reaching the end, the electron can either bounce back and move in the opposite direction or, for suitable parameter values of the system, tunnel to the acceptor. We estimate the energy efficiency of the donor-acceptor electron transport depending on the parameter values. Our calculations show that the soliton mechanism works for the parameter values of polypeptide macromolecules and conjugated polymers. We also investigate the donor-acceptor electron transport in thermalized molecular chains.

  13. Rational design of aggregation-induced emission luminogen with weak electron donor-acceptor interaction to achieve highly efficient undoped bilayer OLEDs.

    PubMed

    Chen, Long; Jiang, Yibin; Nie, Han; Hu, Rongrong; Kwok, Hoi Sing; Huang, Fei; Qin, Anjun; Zhao, Zujin; Tang, Ben Zhong

    2014-10-01

    In this work, two tailored luminogens (TPE-NB and TPE-PNPB) consisting of tetraphenylethene (TPE), diphenylamino, and dimesitylboryl as a π-conjugated linkage, electron donor, and electron acceptor, respectively, are synthesized and characterized. Their thermal stabilities, photophysical properties, solvachromism, fluorescence decays, electronic structures, electrochemical behaviors, and electroluminescence (EL) properties are investigated systematically, and the impacts of electron donor-acceptor (D-A) interaction on optoelectronic properties are discussed. Due to the presence of a TPE unit, both luminogens show aggregation-induced emission, but strong D-A interaction causes a decrease in emission efficiency and red-shifts in photoluminescence and EL emissions. The luminogen, TPE-PNPB, with a weak D-A interaction fluoresces strongly in solid film with a high fluorescence quantum yield of 94%. The trilayer OLED [ITO/NPB (60 nm)/TPE-PNPB (20 nm)/TPBi (40 nm)/LiF (1 nm)/Al (100 nm)] utilizing TPE-PNPB as a light emitter shows a peak luminance of 49 993 cd m(-2) and high EL efficiencies up to 15.7 cd A(-1), 12.9 lm W(-1), and 5.12%. The bilayer OLED [ITO/TPE-PNPB (80 nm)/TPBi (40 nm)/LiF (1 nm)/Al (100 nm)] adopting TPE-PNPB as a light emitter and hole transporter simultaneously affords even better EL efficiencies of 16.2 cd A(-1), 14.4 lm W(-1), and 5.35% in ambient air, revealing that TPE-PNPB is an eximious p-type light emitter. PMID:25254940

  14. 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

  15. Electronic and Chemical Properties of Donor, Acceptor Centers in Graphene.

    PubMed

    Telychko, Mykola; Mutombo, Pingo; Merino, Pablo; Hapala, Prokop; Ondráček, Martin; Bocquet, François C; Sforzini, Jessica; Stetsovych, Oleksandr; Vondráček, Martin; Jelínek, Pavel; Švec, Martin

    2015-09-22

    Chemical doping is one of the most suitable ways of tuning the electronic properties of graphene and a promising candidate for a band gap opening. In this work we report a reliable and tunable method for preparation of high-quality boron and nitrogen co-doped graphene on silicon carbide substrate. We combine experimental (dAFM, STM, XPS, NEXAFS) and theoretical (total energy DFT and simulated STM) studies to analyze the structural, chemical, and electronic properties of the single-atom substitutional dopants in graphene. We show that chemical identification of boron and nitrogen substitutional defects can be achieved in the STM channel due to the quantum interference effect, arising due to the specific electronic structure of nitrogen dopant sites. Chemical reactivity of single boron and nitrogen dopants is analyzed using force-distance spectroscopy by means of dAFM. PMID:26256407

  16. 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

  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 Electron Acceptor in Phthalocyanine-Based Electron Donor-Acceptor Conjugates.

    PubMed

    Sekita, Michael; Jiménez, Ángel J; Marcos, M Luisa; Caballero, Esmeralda; Rodríguez-Morgade, M Salomé; Guldi, Dirk M; Torres, Tomás

    2015-12-21

    Zinc phthalocyanines (ZnPc) have been attached to the peri-position of a perylenemonoimide (PMI) and a perylenemonoanhydride (PMA), affording electron donor-acceptor conjugates 1 and 2, respectively. In addition, a perylene-monoimide-monoanhydride (PMIMA) has been connected to a ZnPc through its imido position to yield the ZnPc-PMIMA conjugate 10. The three conjugates have been studied for photoinduced electron transfer. For ZnPc-PMIMA 10, electron transfer occurs upon both ZnPc and PMIMA excitation, giving rise to a long-lived (340 ps) charge-separated state. For ZnPc-PMI 1 and ZnPc-PMA 2, stabilization of the radical ion pair states by using polar media is necessary. In THF, photoexcitation of either ZnPc or PMI/PMA produces charge-separated states with lifetimes of 375 and 163 ps, respectively. PMID:26593778

  19. 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. PMID:25247140

  20. 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.

  1. 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

  2. High performance weak donor-acceptor polymers in thin film transistors: effect of the acceptor on electronic properties, ambipolar conductivity, mobility, and thermal stability.

    PubMed

    Yuen, Jonathan D; Fan, Jian; Seifter, Jason; Lim, Bogyu; Hufschmid, Ryan; Heeger, Alan J; Wudl, Fred

    2011-12-28

    We have studied the electronic, physical, and transistor properties of a family of donor-acceptor polymers consisting of diketopyrrolopyrrole (DPP) coupled with different accepting companion units in order to determine the effects of donor-acceptor interaction. Using the electronically neutral benzene (B), the weakly accepting benzothiadiazole (BT), and the strongly accepting benzobisthiadiazole (BBT), the accepting strength of the companion unit was systematically modulated. All polymers exhibited excellent transistor performance, with mobilities above 0.1 cm(2)V(-1)s(-1), even exceeding 1 cm(2)V(-1)s(-1) for one of the BBT-containing polymers. We find that the BBT is the strongest acceptor, enabling the BBT-containing polymers to be strongly ambipolar. The BBT moiety also strengthens interchain interactions, which provides higher thermal stability and performance for transistors with BBT-containing polymers as the active layer. PMID:22043809

  3. Triggering Gel Formation and Luminescence through Donor-Acceptor Interactions in a C3 -Symmetric Tris(pyrene) System.

    PubMed

    Lai, Thanh-Loan; Pop, Flavia; Melan, Caroline; Canevet, David; Sallé, Marc; Avarvari, Narcis

    2016-04-18

    Straightforward modulation of the gelation, absorption and luminescent properties of a tris(pyrene) organogelator containing a C3 -symmetric benzene-1,3,5-tricarboxamide central unit functionalized by three 3,3'-diamino-2,2'-bipyridine fragments is achieved through donor-acceptor interactions in the presence of tetracyanoquinodimethane. PMID:26864120

  4. 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.

  5. Photoinduced electron transfer across fixed distances in chlorophyll donor-acceptor molecules

    SciTech Connect

    Wasielewski, M.R.; Johnson, D.G.; Svec, W.A.

    1987-06-01

    The primary events of photosynthesis are a series of rapid, unidirectional electron transfer events between donors and acceptors that are positioned in the reaction center protein at precise spatial orientations and distances relative to one another. Recent work suggests that electron transfer rates depend on distance and free energy of reaction in porphyrin-quinone models in which the distance and orientation of the donor relative to the acceptor is highly restricted. Spacer molecules were developed which were used to link chlorophyll donors with either chlorophyll or quinone acceptors to produce models in which the donor-acceptor distance is well-defined. Recent theoretical studies and photochemical hole-burning experiments have suggested that the actual primary event of photosynthesis is the production of an intramolecular charge transfer state involving the two bacteriochlorophyll molecules of the special pair dimer. This possibility was explored with symmetric, fixed distance chlorophyll dimer. The chlorophyll macrocycles share a common vinyl group at the 2-position. This linkage serves to increase the degree of electronic coupling between the macrocycles. This dimer exhibits a remarkable decrease in fluorescence quantum yield as the dielectric constant of the medium in which it is dissolved increases. This decrease is accompanied by a proportional decrease in the lowest excited singlet state lifetime as measured by picosecond fluorescence and absorption. 11 refs., 2 figs.

  6. Relationship Between the Structure Parameters of a Solid Body and the Kinetics of Donor-Acceptor Interaction in Heterogeneous Systems

    NASA Astrophysics Data System (ADS)

    Khentov, V. Ya.; Khussein, Kh. Kh.

    2016-05-01

    Interaction of an organic ligand molecule with the surface of a d-metal or of disperse particles of chemical compounds containing covalent bonds in a nonaqueous solvent (direct synthesis of complex compounds) is determined by the structure parameters of the solid body. The relationships of the rate and energy of activation of the donor-acceptor interaction of the metal with the Grüneisen coefficient and the Debye temperature of the metal have been established.

  7. Relationship Between the Structure Parameters of a Solid Body and the Kinetics of Donor-Acceptor Interaction in Heterogeneous Systems

    NASA Astrophysics Data System (ADS)

    Khentov, V. Ya.; Khussein, Kh. Kh.

    2016-06-01

    Interaction of an organic ligand molecule with the surface of a d-metal or of disperse particles of chemical compounds containing covalent bonds in a nonaqueous solvent (direct synthesis of complex compounds) is determined by the structure parameters of the solid body. The relationships of the rate and energy of activation of the donor-acceptor interaction of the metal with the Grüneisen coefficient and the Debye temperature of the metal have been established.

  8. 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

  9. Bipyridinium Polymers That Dock Tetrathiafulvalene Guests in Water Driven by Donor-Acceptor and Ion Pair Interactions.

    PubMed

    Zhang, Yun-Chang; Qin, Ying; Wang, Hui; Zhang, Dan-Wei; Yang, Guanyu; Li, Zhan-Ting

    2016-04-01

    Two water-soluble para-xylylene-connected 4,4'-bipyridinium (BIPY(2+) ) polymers have been prepared. UV-Vis absorption, (1) H NMR spectroscopy, and cyclic voltammetry experiments support that in water the BIPY(2+) units in the polymers form stable 1:1 charge-transfer complexes with tetrathiafulvalene (TTF) guests that bear two or four carboxylate groups. These charge-transfer complexes are stabilized by the donor-acceptor interaction between electron-rich TTF and electron-deficient BIPY(2+) units and electrostatic attraction between the dicationic BIPY(2+) units and the anionic carboxylate groups attached to the TTF core. On the basis of UV-Vis experiments, a lower limit to the apparent association constant of the TTF⋅BIPY(2+) complexes of the mixtures, 1.8×10(6)  m(-1) , has been estimated in water. Control experiments reveal substantially reduced binding ability of the neutral TTF di- and tetracarboxylic acids to the BIPY(2+) molecules and polymers. Moreover, the stability of the charge-transfer complexes formed by the BIPY(2+) units of the polymers are considerably higher than that of the complexes formed between two monomeric BIPY(2+) controls and the dicarboxylate-TTF donor; this has been attributed to the mutually strengthened electron-deficient nature of the BIPY(2+) units of the polymers due to the electron-withdrawing effect of the BIPY(2+) units. PMID:26833904

  10. 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.

  11. Modulation of electronic and self-assembly properties of a donor-acceptor-donor-based molecular materials via atomistic approach.

    PubMed

    Dhar, Joydeep; Swathi, K; Karothu, Durga Prasad; Narayan, K S; Patil, Satish

    2015-01-14

    The performance of molecular materials in optoelectronic devices critically depends upon their electronic properties and solid-state structure. In this report, we have synthesized sulfur and selenium based (T4BT and T4BSe) donor-acceptor-donor (D-A-D) organic derivatives in order to understand the structure-property correlation in organic semiconductors by selectively tuning the chalcogen atom. The photophysical properties exhibit a significant alteration upon varying a single atom in the molecular structure. A joint theoretical and experimental investigation suggests that replacing sulfur with selenium significantly reduces the band gap and molar absorption coefficient because of lower electronegativity and ionization potential of selenium. Single-crystal X-ray diffraction analysis showed differences in their solid-state packing and intermolecular interactions. Subsequently, difference in the solid-state packing results variation in self-assembly. Micorstructural changes within these materials are correlated to their electrical resistance variation, investigated by conducting probe atomic force microscopy (CP-AFM) measurements. These results provide useful guidelines to understand the fundamental properties of D-A-D materials prepared by atomistic modulation. PMID:25532139

  12. 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. PMID:27231856

  13. 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.

  14. Tuning the Electronic Coupling and Electron Transfer in Mo2 Donor-Acceptor Systems by Variation of the Bridge Conformation.

    PubMed

    Kang, Mei Ting; Meng, Miao; Tan, Ying Ning; Cheng, Tao; Liu, Chun Y

    2016-02-24

    Assembling two quadruply bonded dimolybdenum units [Mo2 (DAniF)3 ](+) (DAniF=N,N'-di(p-anisyl)formamidinate) with 1,4-naphthalenedicarboxylate and its thiolated derivatives produced three complexes [{Mo2 (DAniF)3 }2 (μ-1,4-O2 CC10 H6 CO2 )], [{Mo2 (DAniF)3 }2 (μ-1,4-OSCC10 H6 COS)], and [{Mo2 (DAniF)3 }2 (μ-1,4-S2 CC10 H6 CS2 )]. In the X-ray structures, the naphthalene bridge deviates from the plane defined by the two Mo-Mo bond vectors with the torsion angle increasing as the chelating atoms of the bridging ligand vary from O to S. The mixed-valent species exhibit intervalence transition absorption bands with high energy and very low intensity. In comparison with the data for the phenylene analogues, the optically determined electronic coupling matrix elements (Hab =258-345 cm(-1) ) are lowered by a factor of two or more, and the electron-transfer rate constants (ket ≈10(11)  s(-1) ) are reduced by about one order of magnitude. These results show that, when the electron-transporting ability of the bridge and electron-donating (electron-accepting) ability of the donor (acceptor) are both variable, the former plays a dominant role in controlling the intramolecular electron transfer. DFT calculations revealed that increasing the torsion angle enlarges the HOMO-LUMO energy gap by elevating the (bridging) ligand-based LUMO energy. Therefore, our experimental results and theoretical analyses verify the superexchange mechanism for electronic coupling and electron transfer. PMID:26807909

  15. 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

  16. Ab initio MO based lattice energy for molecular crystals: packing structure of electron donor-acceptor (EDA) complex H 3N-BF 3

    NASA Astrophysics Data System (ADS)

    Ikeda, Tohru; Nagayoshi, Kanade; Kitaura, Kazuo

    2003-03-01

    A computational procedure is proposed for calculating the lattice energy of molecular crystals using the ab initio MO method. Our method does not require any adjustable parameters and provides a general description for various molecular crystals including electron donor-acceptor (EDA) complexes. Using the method, the packing structure of H 3N-BF 3 crystal was optimized at the HF/3-21 + G level and the lattice energy was calculated at the MP2/6-311 + G * level. The calculation reproduced the experimental lattice constants with reasonable accuracy. Moreover, the structural feature of the H 3N-BF 3 crystal was discussed based on the molecular interactions in the crystal.

  17. Electron-Donor-Acceptor (EDA) Complexes Of Aromatic Hydrocarbons With Organic Acceptors In Solution And In The Solid State. A Quantitative FT-IR Investigation.

    NASA Astrophysics Data System (ADS)

    Bruni, Paolo; Giorgini, Elisabetta; Tosi, Giorgio; Zampini, Angela

    1989-12-01

    Liquid phase FT-IR investigation on π-π Electron-Donor-Acceptor (EDA) complexes between arenes and organic acceptors leads to values of formation constants that are in good agreement with the ones from other techniques (UV-Vis and NMR). In addition solid state FT-IR and UV-Vis determinations on the complexes are also reported and discussed.

  18. 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. PMID:26726610

  19. Rationally designed donor-acceptor scheme based molecules for applications in opto-electronic devices.

    PubMed

    Subash Sundar, T; Sen, R; Johari, P

    2016-04-01

    Several donor (D)-acceptor (A) based molecules are rationally designed by adopting three different schemes in which the conjugation length, strength of the donor and acceptor moieties, and planarity of the molecules are varied. These variations are made by introducing a π-conjugated linkage unit, terminating the ends of the moieties by different electron donating and accepting functional groups, and fusing the donor and acceptor moieties, respectively. Our DFT and TDDFT based calculations reveal that using the above-mentioned design schemes, the electronic and optical properties of the D-A based molecules can be largely tuned. While introduction of a linkage and fusing of moieties enhance the π-π interaction, addition of electron donating groups (-CH3, -OH, and -NH2) and electron accepting groups (-CF3, -CN, -NO2, and -NH3(+)) varies the strength of the donor and acceptor moieties. These factors lead to modulation of the HOMO and LUMO energy levels and facilitate the engineering of the HOMO-LUMO gap and the optical gap over a wide range of ∼0.7-3.7 eV. Moreover, on the basis of calculated ionization potential and reorganization energy, most of the investigated molecules are predicted to be air stable and to exhibit high electron mobility, with the possibility of the presence of ambipolar characteristics in a few of them. The results of our calculations not only demonstrate the examined molecules to be the potential materials for organic opto-electronic devices, but also establish an understanding of the composition-structure-property correlation, which will provide guidelines for designing and synthesizing new materials of choice. PMID:26972386

  20. 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.

  1. 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.

  2. Photo-initiated multi-step electron transfer in donor-acceptor systems using a novel bi-functionalized perylene chromophore

    NASA Astrophysics Data System (ADS)

    Dyar, Scott M.; Smeigh, Amanda L.; Karlen, Steven D.; Young, Ryan M.; Wasielewski, Michael R.

    2015-06-01

    The excited state and redox properties of a new bi-functional perylene redox chromophore, 2,3-dihydro-1-azabenzo[cd]perylene (DABP), are described. Perylene has been widely used in electron donor-acceptor molecules in fields ranging from artificial photosynthesis to molecular spintronics. However, attaching multiple redox components to perylene to carry out multi-step electron transfer reactions often produces hard to separate regioisomers, which complicate data analysis. The use of DABP provides a strategy to retain the electronic properties of perylene, yet eliminate regioisomers. Ultrafast photo-initiated single- and two-step electron transfer reactions in three linear electron donor-acceptor systems incorporating DABP are described to illustrate its utility.

  3. 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.

  4. The Tetrathiafulvalene-based Donor-acceptor Diads for Molecular Electronics

    NASA Astrophysics Data System (ADS)

    Perepichka, Dmitrii F.; Bryce, Martin R.; Ho, Gregory; Heath, James R.; Pearson, Christopher; Petty, Michael C.

    2004-03-01

    The challenge of covalent linking a strong electron donor (as tetrathiafulvalene, TTF) to a strong acceptor (as tetracyanoquinodimethane, TCNQ) was laid down by Aviram and Ratner, who proposed that a single donor-sigma-acceptor molecule could rectify an electric current. Although numerous organic compounds have been tested in metal-molecule-metal junctions, they had substantially higher HOMO-LUMO gap (Eg >0.5 eV) and, in most cases, high dipole moment due to conjugated character of the linker. Those molecules re-orient in the electric field limiting the device stability. Recently, we have pioneered the synthesis of DsigmaA molecules with the HOMO-LUMO gap 0.17-0.3 eV, including the original TTF-TCNQ.* We will present the intriguing electronic properties of these compounds, including the conformational control of the Eg and the thermoexcited electron transfer. The compounds form high-quality LB films, suitable for molecular electronics applications. In Si-molecule-Ti junctions, the rectification ratio increases as molecules align perpendicularly to the surface, and the device stability override significantly the related system based on D-pi-A molecules. * Perepichka, et al., Angew. Chem. Int. Ed. 2003, 42, 4635.

  5. 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

  6. 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

  7. 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. PMID:26171668

  8. 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

  9. 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.

  10. 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. PMID:24228736

  11. 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

  12. Synthesis and photophysical properties of new catenated electron donor-acceptor materials with magnesium and free base porphyrins as donors and C60 as the acceptor

    NASA Astrophysics Data System (ADS)

    Kirner, Sabrina V.; Guldi, Dirk M.; Megiatto, Jackson D., Jr.; Schuster, David I.

    2014-12-01

    A new series of nanoscale electron donor-acceptor systems with [2]catenane architectures has been synthesized, incorporating magnesium porphyrin (MgP) or free base porphyrin (H2P) as electron donor and C60 as electron acceptor, surrounding a central tetrahedral Cu(i)-1,10-phenanthroline (phen) complex. Model catenated compounds incorporating only one or none of these photoactive moieties were also prepared. The synthesis involved the use of Sauvage's metal template protocol in combination with the 1,3-dipolar cycloaddition of azides and alkynes (``click chemistry''), as in other recent reports from our laboratories. Ground state electron interactions between the individual constituents was probed using electrochemistry and UV-vis absorption spectroscopy, while events occurring following photoexcitation in tetrahydrofuran (under both aerobic and anaerobic conditions) at various wavelengths were followed by means of time-resolved transient absorption and emission spectroscopies on the femtosecond and nanosecond time scales, respectively, complemented by measurements of quantum yields for generation of singlet oxygen. From similar studies with model catenates containing one or neither of the chromophores, the events following photoexcitation could be elucidated. The results were compared with those previously reported for analogous catenates based on zinc porphyrin (ZnP). It was determined that a series of energy transfer (EnT) and electron transfer (ET) processes take place in the present catenates, ultimately generating long-distance charge separated (CS) states involving oxidized porphyrin and reduced C60 moieties, with lifetimes ranging from 400 to 1060 nanoseconds. Shorter lived short-distance CS states possessing oxidized copper complexes and reduced C60, with lifetimes ranging from 15 to 60 ns, were formed en route to the long-distance CS states. The dynamics of the ET processes were analyzed in terms of their thermodynamic driving forces. It was clear that

  13. 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. PMID:27097920

  14. 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

  15. 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. PMID:27083718

  16. 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.

  17. 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

  18. Easy Access to NO2 -Containing Donor-Acceptor-Acceptor Electron Donors for High Efficiency Small-Molecule Organic Solar Cells.

    PubMed

    Ting, Hao-Chun; Yang, Ya-Ting; Chen, Chia-Hsun; Lee, Jiun-Haw; Chang, Jung-Hung; Wu, Chih-I; Chiu, Tien-Lung; Lin, Chi-Feng; Chung, Chin-Lung; Wong, Ken-Tsung

    2016-06-22

    Two donor-acceptor-acceptor (D-A-A)-type molecules incorporating nitrobenzoxadiazole (NBO) as the A-A block and ditolylamine as the D block bridged through a phenylene (PNBO) and a thiophene (TNBO) spacer were synthesized in a one-step coupling reaction. Their electronic, photophysical, and thermal properties; crystallographic analysis; and theoretical calculations were studied to establish a clear structure-property relationship. The results indicate that the quinoidal character of the thiophene bridge strongly governs the structural features and crystal packings (herringbone vs. brickwork) and thus the physical properties of the compounds. PNBO and TNBO were utilized as electron donors combined with C70 as the electron acceptor in the active layer of vacuum-processed bulk heterojunction small-molecule organic solar cells (SMOSCs). The power conversion efficiency of both PNBO- and TNBO-based OSCs exceeded 5 %. The ease of accessibility of PNBO and TNBO demonstrates the potential for simple and economical synthesis of electron donors in vacuum-processed SMOSCs. PMID:27213296

  19. Photobehavior of the geometrical isomers of two 1,4-distyrylbenzene analogues with side groups of different electron donor/acceptor character.

    PubMed

    Ciorba, S; Galiazzo, G; Mazzucato, U; Spalletti, A

    2010-10-14

    The photobehavior of two 1,4-distyrylbenzene analogues where the central benzene ring is asymmetrically substituted with a pyrid-4-ylethenyl group at one side and thien-2-ylethenyl or a p-nitrostyryl group at the other side, has been studied in two solvents at room temperature. The four geometrical isomers (EE, ZE, EZ, and ZZ) of each compound were separated by the combined use of HPLC and spectrophotometric techniques. The radiative/reactive competition in their excited state relaxation was particularly examined: the diabatic/adiabatic contributions were estimated and a reasonable interpretation of the photoisomerization mechanism was proposed. The role of the conformational isomers was also investigated by measured and computed spectral data. Since the different electron donor/acceptor character of the side groups of these molecules can induce charge transfer phenomena that can affect the relaxation pathways of their excited states, the photobehavior was compared in inert and polar solvents to clarify the role of the intramolecular charge transfer. The latter was found to affect markedly the relaxation properties and to induce interesting fluorosolvatochromic effects, particularly in the p-nitro derivative. The participation of the triplet state in the reaction mechanism of the latter was also investigated by flash photolysis and sensitized experiments. PMID:20857985

  20. 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.

  1. 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

  2. Efficient Synthesis and Photosensitizer Performance of Nonplanar Organic Donor-Acceptor Molecules.

    PubMed

    Yuan, Yuping; Michinobu, Tsuyoshi; Satoh, Norifusa; Ashizawa, Minoru; Han, Liyuan

    2015-08-01

    Nonplanar organic donor-acceptor molecules bearing a carboxylic acid group were synthesized by the formal [2+2] cycloaddition-retroelectrocyclization reaction between aniline-substituted alkynes and tetracyanoethylene (TCNE) or 7,7,8,8-tetracyanoquinodimethane (TCNQ). This reaction offers an atom-economic one-step approach to donor-acceptor chromophores in satisfactory high yields. The resulting donor-acceptor molecules were characterized by conventional analytical techniques. In addition, the nonplanarity and intermolecular interactions were investigated by X-ray crystallography. The energy levels and intramolecular charge-transfer (CT), evaluated by UV-Vis-near IR spectroscopy and electrochemistry, suggested that there is a linear correlation between the optical and electrochemical band gaps. Based on these structural and electronic analyses, the photosensitizer performances of the donor-acceptor molecules in dye-sensitized solar cells (DSSCs) were initially investigated using TiO2 or SnO2 electrodes. Although the power conversion efficiencies were limited, the incident-photon-to-current-conversion efficiency (IPCE) spectra indicated a better photocurrent generation for the devices on SnO2 as compared to those on TiO2. PMID:26369162

  3. 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

  4. Ultrafast Photoinduced Electron Transfer and Charge Stabilization in Donor-Acceptor Dyads Capable of Harvesting Near-Infrared Light.

    PubMed

    Bandi, Venugopal; Gobeze, Habtom B; D'Souza, Francis

    2015-08-01

    To harvest energy from the near-infrared (near-IR) and infrared (IR) regions of the electromagnetic spectrum, which constitutes nearly 70 % of the solar radiation, there is a great demand for near-IR and IR light-absorbing sensitizers that are capable of undergoing ultrafast photoinduced electron transfer when connected to a suitable electron acceptor. Towards achieving this goal, in the present study, we report multistep syntheses of dyads derived from structurally modified BF2-chelated azadipyrromethene (ADP; to extend absorption and emission into the near-IR region) and fullerene as electron-donor and electron-acceptor entities, respectively. The newly synthesized dyads were fully characterized based on optical absorbance, fluorescence, geometry optimization, and electrochemical studies. The established energy level diagram revealed the possibility of electron transfer either from the singlet excited near-IR sensitizer or singlet excited fullerene. Femtosecond and nanosecond transient absorption studies were performed to gather evidence of excited state electron transfer and to evaluate the kinetics of charge separation and charge recombination processes. These studies revealed the occurrence of ultrafast photoinduced electron transfer leading to charge stabilization in the dyads, and populating the triplet states of ADP, benzanulated-ADP and benzanulated thiophene-ADP in the respective dyads, and triplet state of C60 in the case of BF2 -chelated dipyrromethene derived dyad during charge recombination. The present findings reveal that these sensitizers are suitable for harvesting light energy from the near-IR region of the solar spectrum and for building fast-responding optoelectronic devices operating under near-IR radiation input. PMID:26130432

  5. A photon-working on/off switch for intramolecular donor-acceptor interactions and invisible modulation of the fluorescence.

    PubMed

    Takeuchi, Sakiko; Nakagawa, Tetsuya; Yokoyama, Yasushi

    2016-03-01

    An on/off switching for charge-transfer interactions between the side chains of a diarylethene based on photochromic reactions has been proved by the disappearance and appearance of an additional fluorescence band. PMID:26906945

  6. 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.

  7. 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).

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

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

    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.

  9. 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

  10. 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

  11. 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

  12. 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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

    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

  13. 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

    2016-02-01

    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. PMID:26822564

  14. 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

    2016-03-01

    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

  15. 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.

  16. Theory of Primary Photoexcitations in Donor-Acceptor Copolymers.

    PubMed

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

    2015-12-31

    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. PMID:26765027

  17. Photoelectric covalent organic frameworks: converting open lattices into ordered donor-acceptor heterojunctions.

    PubMed

    Chen, Long; Furukawa, Ko; Gao, Jia; Nagai, Atsushi; Nakamura, Toshikazu; Dong, Yuping; Jiang, Donglin

    2014-07-16

    Ordered one-dimensional open channels represent the typical porous structure of two-dimensional covalent organic frameworks (COFs). Here we report a general synthetic strategy for converting these open lattice structures into ordered donor-acceptor heterojunctions. A three-component topological design scheme was explored to prepare electron-donating intermediate COFs, which upon click reaction were transformed to photoelectric COFs with segregated donor-acceptor alignments, whereas electron-accepting buckyballs were spatially confined within the nanochannels via covalent anchoring on the channel walls. The donor-acceptor heterojunctions trigger photoinduced electron transfer and allow charge separation with radical species delocalized in the π-arrays, whereas the charge separation efficiency was dependent on the buckyball content. This new donor-acceptor strategy explores both skeletons and pores of COFs for charge separation and photoenergy conversion. PMID:24963896

  18. Evaluating the Performance of DFT Functionals in Assessing the Interaction Energy and Ground-State Charge Transfer of Donor/Acceptor Complexes: Tetrathiafulvalene-Tetracyanoquinodimethane (TTF-TCNQ) as a Model Case.

    PubMed

    Sini, Gjergji; Sears, John S; Brédas, Jean-Luc

    2011-03-01

    We have evaluated the performance of several density functional theory (DFT) functionals for the description of the ground-state electronic structure and charge transfer in donor/acceptor complexes. The tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) complex has been considered as a model test case. Hybrid functionals have been chosen together with recently proposed long-range corrected functionals (ωB97X, ωB97X-D, LRC-ωPBEh, and LC-ωPBE) in order to assess the sensitivity of the results to the treatment and magnitude of exact exchange. The results show an approximately linear dependence of the ground-state charge transfer with the HOMOTTF-LUMOTCNQ energy gap, which in turn depends linearly on the percentage of exact exchange in the functional. The reliability of ground-state charge transfer values calculated in the framework of a monodeterminantal DFT approach was also examined. PMID:26596294

  19. Optically tunable spin-exchange energy at donor:acceptor interfaces in organic solar cells

    SciTech Connect

    Li, Mingxing; Wang, Hongfeng; He, Lei; Zang, Huidong; Xu, Hengxing; Hu, Bin

    2014-07-14

    Spin-exchange energy is a critical parameter in controlling spin-dependent optic, electronic, and magnetic properties in organic materials. This article reports optically tunable spin-exchange energy by studying the line-shape characteristics in magnetic field effect of photocurrent developed from intermolecular charge-transfer states based on donor:acceptor (P3HT:PCBM) system. Specifically, we divide magnetic field effect of photocurrent into hyperfine (at low field < 10 mT) and spin-exchange (at high field > 10 mT) regimes. We observe that increasing photoexcitation intensity can lead to a significant line-shape narrowing in magnetic field effect of photocurrent occurring at the spin-exchange regime. We analyze that the line-shape characteristics is essentially determined by the changing rate of magnetic field-dependent singlet/triplet ratio when a magnetic field perturbs the singlet-triplet transition through spin mixing. Based on our analysis, the line-shape narrowing results indicate that the spin-exchange energy at D:A interfaces can be optically changed by changing photoexcitation intensity through the interactions between intermolecular charge-transfer states. Therefore, our experimental results demonstrate an optical approach to change the spin-exchange energy through the interactions between intermolecular charge-transfer states at donor:acceptor interface in organic materials.

  20. 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

  1. Synthesis of dithienosilole-based highly photoluminescent donor-acceptor type compounds.

    PubMed

    Ohshita, Joji; Tominaga, Yuta; Tanaka, Daiki; Ooyama, Yousuke; Mizumo, Tomonobu; Kobayashi, Norifumi; Higashimura, Hideyuki

    2013-03-14

    Highly photoluminescent acceptor-donor-acceptor (A-D-A) and donor-acceptor (D-A) type compounds with a dithienosilole unit as the donor and perfluorotolyl or dimesitylboryl group(s) as the acceptor were prepared by the reaction of lithiated dithienosilole derivatives with perfluorotoluene or fluorodimesitylborane, respectively. The resulting A-D-A and D-A type compounds showed red-shifted UV absorption and PL bands compared to those of simple dithienosiloles having no acceptor units, reported previously, and were highly photoluminescent in the solid state as well as in solution. Solvatochromic behaviour that would arise from the intramolecular donor-acceptor interaction were observed for the D-A type compounds with respect to the UV absorption and PL spectra. In addition, it was found that bis(dimesitylboryl)dithienosilole and (dimesitylboryl)(methylthio)dithienosilole responded to coexisting fluoride anions, leading to clear UV absorption and PL spectral changes in solutions. PMID:23295388

  2. 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

  3. Donor-acceptor conjugated polymers based on multifused ladder-type arenes for organic solar cells.

    PubMed

    Wu, Jhong-Sian; Cheng, Sheng-Wen; Cheng, Yen-Ju; Hsu, Chain-Shu

    2015-03-01

    Harvesting solar energy from sunlight to generate electricity is considered as one of the most important technologies to address the future sustainability of humans. Polymer solar cells (PSCs) have attracted tremendous interest and attention over the past two decades due to their potential advantage to be fabricated onto large area and light-weight flexible substrates by solution processing at a lower cost. PSCs based on the concept of bulk heterojunction (BHJ) configuration where an active layer comprises a composite of a p-type (donor) and an n-type (acceptor) material represents the most useful strategy to maximize the internal donor-acceptor interfacial area allowing for efficient charge separation. Fullerene derivatives such as [6,6]-phenyl-C61 or 71-butyric acid methyl ester (PCBM) are the ideal n-type materials ubiquitously used for BHJ solar cells. The major effort to develop photoactive materials is numerously focused on the p-type conjugated polymers which are generally synthesized by polymerization of electron-rich donor and electron-deficient acceptor monomers. Compared to the development of electron-deficient comonomers (acceptor segments), the development of electron-rich donor materials is considerably flourishing. Forced planarization by covalently fastening adjacent aromatic and heteroaromatic subunits leads to the formation of ladder-type conjugated structures which are capable of elongating effective conjugation, reducing the optical bandgap, promoting intermolecular π-π interactions and enhancing intrinsic charge mobility. In this review, we will summarize the recent progress on the development of various well-defined new ladder-type conjugated materials. These materials serve as the superb donor monomers to prepare a range of donor-acceptor semi-ladder copolymers with sufficient solution-processability for solar cell applications. PMID:25322211

  4. 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…

  5. 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.

  6. Synthesis and characterization of a highly strained donor-acceptor nanohoop.

    PubMed

    Van Raden, J M; Darzi, E R; Zakharov, L N; Jasti, R

    2016-06-15

    A highly-strained, nitrogen-doped cycloparaphenylene (CPP), aza[6]CPP, was synthesized and then converted to a donor-acceptor nanohoop, N-methylaza[6]CPP, via alkylation of the nitrogen center. The energy levels of the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) for both molecules were then probed by cyclic voltammetry (CV), which revealed that the donor-acceptor nanohoop had a significantly lower LUMO energy relative to [6]CPP and aza[6]CPP. Density functional theory (DFT) revealed that the donor-acceptor nanohoop underwent a redistribution of the frontier molecular orbital (FMO) density such that a significant portion of the LUMO density resided upon the electron-deficient nitrogen-containing ring. This localization of LUMO density caused a large lowering in the LUMO energy of nearly a full electron volt, while the HOMO energy was less affected due to a large centralization of the FMO on the electron-rich phenylene backbone. This ultimately resulted in a net lowering of the HOMO-LUMO energy gap which was observed both experimentally and computationally. In addition, N-methylaza[6]CPP has a significantly lower energy LUMO than N-methylaza[8]CPP, illustrating that the FMO levels of donor-acceptor nanohoops can be tuned by adjusting the hoop size. PMID:26881906

  7. 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.

  8. 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

  9. 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. PMID:27311060

  10. Donor-Acceptor Complexes between Ammonia and Sulfur Trioxide: An FTIR and Computational Study.

    PubMed

    Haupa, Karolina; Bil, Andrzej; Mielke, Zofia

    2015-10-29

    The complexes of ammonia with sulfur trioxide have been studied using FTIR matrix isolation spectroscopy and DFT/B3LYP calculations with the aug-cc-pVTZ basis set. The NH3/SO3/Ar matrixes were prepared in two different ways. In one set of experiments the matrix was prepared by the simultaneous deposition of the NH3/Ar mixture and SO3 vapor from the thermal decomposition of K2S2O7. In the second set of experiments thermolysis products of sulfamic acid were trapped in an argon matrix. Both methods of matrix preparation led to the formation of the H3N·SO3 electron donor-acceptor complex that was characterized earlier. In the matrixes comprising thermolysis products of sulfamic acid, in addition to H3N·SO3, the H3N-SO3···NH3 complex (II(D)) was also identified. The identity of the complex was confirmed by comparison of the experimental and theoretical spectra of H3N-SO3···NH3 and D3N-SO3···ND3. The performed calculations show that in H3N-SO3···NH3 the two N atoms and the S atom are collinear; the two S-N bonds are nonequivalent, one is much shorter (2.230 Å) than the other one (2.852 Å). In the AIM topological analysis, the interaction energy decomposition and topological properties of the electron localizability indicator (ELI-D) allowed us to categorize the stronger N-S bond in the II(D) complex as a dative bond and to assume that the fragile N-S bond is a consequence of a weak electron-donor-acceptor interaction. The calculations indicate that the identified II(D) complex corresponds to a local minimum on the PES of the NH3/SO3 system of 2:1 stoichiometry. The (NH3)2SO3 complex, II(HB), corresponding to a global minimum is 7.95 kcal mol(-1) more stable than the II(D) complex. The reason that the II(D) complex is present in the matrix but not the II(HB) complex is discussed. PMID:26447490

  11. Efficient ambipolar transport properties in alternate stacking donor-acceptor complexes: from experiment to theory.

    PubMed

    Qin, Yunke; Cheng, Changli; Geng, Hua; Wang, Chao; Hu, Wenping; Xu, Wei; Shuai, Zhigang; Zhu, Daoben

    2016-05-18

    Comprehensive investigations of crystal structures, electrical transport properties and theoretical simulations have been performed over a series of sulfur-bridged annulene-based donor-acceptor complexes with an alternate stacking motif. A remarkably high mobility, up to 1.57 cm(2) V(-1) s(-1) for holes and 0.47 cm(2) V(-1) s(-1) for electrons, was obtained using organic single crystal field-effect transistor devices, demonstrating the efficient ambipolar transport properties. These ambipolar properties arise from the fact that the electronic couplings for both holes and electrons have the same super-exchange nature along the alternate stacking direction. The magnitude of super-exchange coupling depends not only on the intermolecular stacking distance and pattern, but also the energy level alignments between the adjacent donor-acceptor moieties. The concluded transport mechanism and structure-property relationship from this research will provide an important guideline for the future design of organic semiconductors based on donor-acceptor complexes. PMID:27157854

  12. Donor-acceptor type co-crystals of arylthio-substituted tetrathiafulvalenes and fullerenes.

    PubMed

    Lu, Xiaofeng; Sun, Jibin; Zhang, Shangxi; Ma, Longfei; Liu, Lei; Qi, Hui; Shao, Yongliang; Shao, Xiangfeng

    2015-01-01

    A series of donor-acceptor type co-crystals of fullerene (as the acceptor) and arylthio-substituted tetrathiafulvalene derivatives (Ar-S-TTF, as the donor) were prepared and their structural features were thoroughly investigated. The formation of co-crystals relies on the flexibility of Ar-S-TTF and the size matches between Ar-S-TTF and fullerene. Regarding their compositions, the studied co-crystals can be divided into two types, where types I and II have donor:acceptor ratios of 1:1 and 1:2, respectively. Multiple intermolecular interactions are observed between the donor and acceptor, which act to stabilize the structures of the resulting co-crystals. In the type I co-crystals, the fullerene molecule is surrounded by four Ar-S-TTF molecules, that is, two Ar-S-TTF molecules form a sandwich structure with one fullerene molecule and the other two Ar-S-TTF molecules interact with the fullerene molecule along their lateral axes. In the type II co-crystals, one fullerene molecule has the donor-acceptor mode similar to that in type I, whereas the other fullerene molecule is substantially surrounded by the aryl groups on Ar-S-TTF molecules and the solvent molecules. PMID:26199659

  13. How intermolecular geometrical disorder affects the molecular doping of donor-acceptor copolymers

    NASA Astrophysics Data System (ADS)

    di Nuzzo, Daniele; Fontanesi, Claudio; Jones, Rebecca; Allard, Sybille; Dumsch, Ines; Scherf, Ullrich; von Hauff, Elizabeth; Schumacher, Stefan; da Como, Enrico

    2015-03-01

    Molecular doping of conjugated polymers represents an important strategy for improving organic electronic devices. However, the widely reported low efficiency of doping remains a crucial limitation to obtain high performance. Here we investigate how charge transfer between dopant and donor-acceptor copolymers is affected by the spatial arrangement of the dopant molecule with respect to the copolymer repeat unit. We p-dope a donor-acceptor copolymer and probe its charge-sensitive molecular vibrations in films by infrared spectroscopy. We find that, compared with a related homopolymer, a four times higher dopant/polymer molar ratio is needed to observe signatures of charges. By DFT methods, we simulate the vibrational spectra, moving the dopant along the copolymer backbone and finding that efficient charge transfer occurs only when the dopant is close to the donor moiety. Our results show that the donor-acceptor structure poses an obstacle to efficient doping, with the acceptor moiety being inactive for p-type doping.

  14. Enhanced Charge Mobility in Polymer Nanocomposites Incorporating Donor-Acceptor Interfaces

    NASA Astrophysics Data System (ADS)

    Tameev, Alexey R.; Nikitenko, Vladimir R.; Vannikov, Anatoly V.

    2011-01-01

    Charge carrier transport in donor-acceptor (D-A) composites based on either poly(N-vinyl carbazole) or polyimide derivative incorporating either carbon single-walled nanotubes or nanocrystals of J-aggregated cyanine dyes is shown to exhibit a similar behavior. In the composite films, polymer/nanomaterial interface provides pathways of the high conductivity. Charge-transfer states (CTS) formed at the D-A interface are involved in the transport. The charge transport along the interface is suggested to arise due to the D-A integer charge transfer and strong interaction between adjacent opposite charges located on the donor and acceptor molecules. The approach based on the concept of sequence of charge carrier transfers through charge transfer states describes the increased electron and hole mobility in the composites. The approach predicts enhanced conductivity with reduced activation energy. Moreover, once the density of electron-hole pairs at the interface is rather high, significant part of the charge carriers can avoid hopping transport resulting in conductivity of metal type. The value of two-dimensional conductivity is estimated by numerical modeling.

  15. Synthesis and optoelectronic properties of Janus-dendrimer-type multivalent donor-acceptor systems.

    PubMed

    Dengiz, Cagatay; Breiten, Benjamin; Gisselbrecht, Jean-Paul; Boudon, Corinne; Trapp, Nils; Schweizer, W Bernd; Diederich, François

    2015-01-16

    A convergent, multistep protocol was employed for the synthesis of a Janus-type multivalent donor-acceptor system. The synthetic approach is based on a Sonogashira cross-coupling of two differently ferrocene-(Fc) substituted dendrons and a final sixfold [2 + 2] cycloaddition-retroelectrocyclization (CA-RE) reaction with tetracyanoethene, which occurs regioselectively at only one of the rigidly linked dendrons. The structural and optoelectronic properties of the compounds were investigated by X-ray analysis, UV/vis spectroscopy, and electrochemistry. The target Janus-system displays redox-amphoteric behavior. The nonalkynylated Fc end groups in one dendron are readily and reversibly oxidized. The second dendron, in which the terminal Fc-activated alkynes underwent the CA-RE reaction to give tetracyanobuta-1,3-dienes in the final step of the synthesis, undergoes four reversible 3-e(-) reductions in the very narrow potential range of 1 V. A spontaneous intramolecular charge transfer from the donor into the acceptor hemisphere was not observed. Furthermore, the oxidation potential of the Fc donors in one hemisphere is hardly perturbed by the push-pull acceptors in the other, which suggests that electronic communication along the π-system, with several meta-connectivities, is not efficient. Therefore, the charge-transfer bands seen in the Janus-type system originate from the interaction of the Fc donors with the directly connected tetracyanobuta-1,3-diene acceptors in the same hemisphere. PMID:25489964

  16. 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.

  17. Vacancy compensation and related donor-acceptor pair recombination in bulk AlN

    SciTech Connect

    Gaddy, BE; Bryan, Z; Bryan, I; Kirste, R; Xie, JQ; Dalmau, R; Moody, B; Kumagai, Y; Nagashima, T; Kubota, Y; Kinoshita, T; Koukitu, A; Sitar, Z; Collazo, R; Irving, DL

    2013-10-14

    A prominent 2.8 eV emission peak is identified in bulk AlN substrates grown by physical vapor transport. This peak is shown to be related to the carbon concentration in the samples. Density functional theory calculations predict that this emission is caused by a donor-acceptor pair (DAP) recombination between substitutional carbon on the nitrogen site and a nitrogen vacancy. Photoluminescence and photoluminescence-excitation spectroscopy are used to confirm the model and indicate the DAP character of the emission. The interaction between defects provides a pathway to creating ultraviolet-transparent AlN substrates for optoelectronics applications. (C) 2013 AIP Publishing LLC.

  18. Unraveling the Photoswitching Mechanism in Donor-Acceptor Stenhouse Adducts.

    PubMed

    Lerch, Michael M; Wezenberg, Sander J; Szymanski, Wiktor; Feringa, Ben L

    2016-05-25

    Molecular photoswitches have opened up a myriad of opportunities in applications ranging from responsive materials and control of biological function to molecular logics. Here, we show that the photoswitching mechanism of donor-acceptor Stenhouse adducts (DASA), a recently reported class of photoswitches, proceeds by photoinduced Z-E isomerization, followed by a thermal, conrotatory 4π-electrocyclization. The photogenerated intermediate is manifested by a bathochromically shifted band in the visible absorption spectrum of the DASA. The identification of the role of this intermediate reveals a key step in the photoswitching mechanism that is essential to the rational design of switching properties via structural modification. PMID:27152878

  19. 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

  20. Intramolecular charge transfer in donor-acceptor molecules

    SciTech Connect

    Slama-Schwok, A.; Blanchard-Desce, M.; Lehn, J.M. )

    1990-05-17

    The photophysical properties of donor-acceptor molecules, push-pull polyenes and carotenoids, have been studied by absorption and fluorescence spectroscopy. The compounds bear various acceptor and donor groups, linked together by chains of different length and structure. The position of the absorption and fluorescence maxima and their variation in solvents of increasing polarity are in agreement with long-distance intramolecular charge-transfer processes, the linker acting as a molecular wire. The effects of the linker length and structure and of the nature of acceptor and donor are presented.

  1. 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

  2. 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

  3. 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.

  4. 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

  5. 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.

  6. 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

  7. 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.

  8. 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.

  9. Design, synthesis and study of supramolecular donor-acceptor systems mimicking natural photosynthesis processes

    NASA Astrophysics Data System (ADS)

    Bikram, Chandra

    This dissertation investigates the chemical ingenuity into the development of various photoactive supramolecular donor -- acceptor systems to produce clean and carbon free energy for the next generation. The process is inspired by the principles learned from nature's approach where the solar energy is converted into the chemical energy through the natural photosynthesis process. Owing to the importance and complexity of natural photosynthesis process, we have designed ideal donor-acceptor systems to investigate their light energy harvesting properties. This process involves two major steps: the first step is the absorption of light energy by antenna or donor systems to promote them to an excited electronic state. The second step involves, the transfer of excitation energy to the reaction center, which triggers an electron transfer process within the system. Based on this principle, the research is focused into the development of artificial photosynthesis systems to investigate dynamics of photo induced energy and electron transfer events. The derivatives of Porphyrins, Phthalocyanines, BODIPY, and SubPhthalocyanines etc have been widely used as the primary building blocks for designing photoactive and electroactive ensembles in this area because of their excellent and unique photophysical and photochemical properties. Meanwhile, the fullerene, mainly its readily available version C60 is typically used as an electron acceptor component because of its unique redox potential, symmetrical shape and low reorganization energy appropriate for improved charge separation behavior. The primary research motivation of the study is to achieve fast charge separation and slow charge recombination of the system by stabilizing the radical ion pairs which are formed from photo excitation, for maximum utility of solar energy. Besides Fullerene C60, this dissertation has also investigated the potential application of carbon nanomaterials (Carbon nanotubes and graphene) as primary

  10. 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.

  11. 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

  12. Stimuli-Responsive Reversible Fluorescence Switching in a Crystalline Donor-Acceptor Mixture Film: Mixed Stack Charge-Transfer Emission versus Segregated Stack Monomer Emission.

    PubMed

    Park, Sang Kyu; Cho, Illhun; Gierschner, Johannes; Kim, Jin Hong; Kim, Jong H; Kwon, Ji Eon; Kwon, Oh Kyu; Whang, Dong Ryeol; Park, Jung-Hwa; An, Byeong-Kwan; Park, Soo Young

    2016-01-01

    We report on a molecularly tailored 1:1 donor-acceptor (D-A) charge-transfer (CT) cocrystal that manifests strongly red-shifted CT luminescence characteristics, as well as noteworthy reconfigurable self-assembling behaviors. A loosely packed molecular organization is obtained as a consequence of the noncentrosymmetric chemical structure of molecule A1, which gives rise to considerable free volume and weak intermolecular interactions. The stacking features of the CT complex result in an external stimuli-responsive molecular stacking reorganization between the mixed and demixed phases of the D-A pair. Accordingly, high-contrast fluorescence switching (red↔blue) is realized on the basis of the strong alternation of the electronic properties between the mixed and demixed phases. A combination of structural, spectroscopic, and computational studies reveal the underlying mechanism of this stimuli-responsive behavior. PMID:26585755

  13. 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.

  14. 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.

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

    PubMed

    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. PMID:25581625

  16. 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

  17. The effect of memory in the stochastic master equation analyzed using the stochastic Liouville equation of motion. Electronic energy migration transfer between reorienting donor-donor, donor-acceptor chromophores

    NASA Astrophysics Data System (ADS)

    Håkansson, Pär; Westlund, Per-Olof

    2005-01-01

    This paper discusses the process of energy migration transfer within reorientating chromophores using the stochastic master equation (SME) and the stochastic Liouville equation (SLE) of motion. We have found that the SME over-estimates the rate of the energy migration compared to the SLE solution for a case of weakly interacting chromophores. This discrepancy between SME and SLE is caused by a memory effect occurring when fluctuations in the dipole-dipole Hamiltonian ( H( t)) are on the same timescale as the intrinsic fast transverse relaxation rate characterized by (1/ T2). Thus the timescale critical for energy-transfer experiments is T2≈10 -13 s. An extended SME is constructed, accounting for the memory effect of the dipole-dipole Hamiltonian dynamics. The influence of memory on the interpretation of experiments is discussed.

  18. The effect of memory in the stochastic master equation analyzed using the stochastic Liouville equation of motion. Electronic energy migration transfer between reorienting donor-donor, donor-acceptor chromophores.

    PubMed

    Håkansson, Pär; Westlund, Per-Olof

    2005-01-01

    This paper discusses the process of energy migration transfer within reorientating chromophores using the stochastic master equation (SME) and the stochastic Liouville equation (SLE) of motion. We have found that the SME over-estimates the rate of the energy migration compared to the SLE solution for a case of weakly interacting chromophores. This discrepancy between SME and SLE is caused by a memory effect occurring when fluctuations in the dipole-dipole Hamiltonian (H(t)) are on the same timescale as the intrinsic fast transverse relaxation rate characterized by (1/T(2)). Thus the timescale critical for energy-transfer experiments is T(2) approximately 10(-13) s. An extended SME is constructed, accounting for the memory effect of the dipole-dipole Hamiltonian dynamics. The influence of memory on the interpretation of experiments is discussed. PMID:15556453

  19. 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

  20. Donor-acceptor star-shaped conjugated macroelectrolytes: synthesis, light-harvesting properties, and self-assembly-induced Förster resonance energy transfer.

    PubMed

    Zhao, Li; Liu, Cheng-Fang; Xu, Wei-Dong; Jiang, Yi; Lai, Wen-Yong; Huang, Wei

    2015-06-01

    A novel series of donor-acceptor star-shaped conjugated macroelectrolytes (CMEs), denoted as 4FTs, including anionic carboxylic acid sodium groups (4FNaT), neutral diethanolamine groups (4FNOHT), and cationic ammonium groups (4FNBrT), were designed, synthesized, and explored as an excellent platform to investigate the impact of various polar pendent groups on self-assembly behaviors. The resulting CMEs with donor-acceptor star-shaped architectures exhibited distinct light-harvesting properties. The interactions between 4FTs and TrNBr, a star-shaped monodisperse CME grafted with cationic quaternary ammonium side chains, were investigated in H2O and CH3OH using steady-state, time-resolved fluorescence, dynamic light scattering (DLS), and transmission electron microscopy (TEM). Highly favored energy transfer has been proven by the excellent spectral overlap between TrNBr fluorescence and 4FTs absorptions which can be tuned by adjusting the pendent polar groups and solvents. It is suggested that self-assembled structures are formed between TrNBr and 4FNaT, while there is no obvious change for TrNBr/4FNOHT and TrNBr/4FNBrT in both H2O and CH3OH at low concentrations (<10(-6) M). This result is confirmed by the change of the TrNBr and 4FTs fluorescence properties and the time-resolved fluorescence data. The overall results manifest that at low concentrations the self-assembly between TrNBr and 4FTs is dominated by the electrostatic interactions. This study suggests that the functionalization of pendent polar groups of star-shaped CMEs has proven to be effective to modulate the self-assembly behaviors in dilute solutions and thus provide a strategy to further manage the optoelectronic properties. PMID:25981514

  1. 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

  2. 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

  3. 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.

  4. 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).

  5. Infrared spectroscopy of narrow gap donor-acceptor polymer-based ambipolar transistors

    NASA Astrophysics Data System (ADS)

    Khatib, Omar; Yuen, Jonathan; Wilson, Jim; Kumar, Rajeev; di Ventra, Massimiliano; Heeger, Alan; Basov, Dimitri

    2013-03-01

    Donor-acceptor (D-A) copolymers have recently emerged as versatile materials for use in a large variety of device applications. Specifically, these systems possess extremely narrow band gaps, enabling ambipolar charge transport when integrated in solution-processed organic field-effect transistors (OFETs). However, the fundamentals of electronic transport in this class of materials remain unexplored. We present a systematic investigation of ambipolar charge injection in a family of narrow-gap D-A conjugated polymers based on benzobisthiadiazole (BBT) using infrared (IR) spectroscopy. We observe a significant modification of the absorption edge in polymer-based OFETs under the applied electric field. The absorption edge reveals hardening under electron injection and softening under hole injection. Additionally, we register localized vibrational resonances associated with injected charges. Our findings indicate a significant self-doping of holes that is modified by charge injection. Observations of both electron and hole transport with relatively high carrier mobility strongly suggest an inhomogeneous, phase-separated conducting polymer.

  6. Part I. The fire properties of polymer clay nanocomposites. Part II. Thermal rearrangement of donor-acceptor substituted cyclopropanes

    NASA Astrophysics Data System (ADS)

    Su, Shengpei

    2003-08-01

    This work consists of two parts. Part I, which includes chapter 1--5, is focused on the fire properties of nanocomposites while part II deals with thermal rearrangement of the donor-acceptor cyclopropanes. In chapter 1 of the first part an introduction to the preparation of polymer-clay nanocomposites is provided along with their application to fire retardancy. Chapter 2 details the exfoliation process of clay using in situ polymerization; the results show that the exfoliation process is related to the monomer, the modified clay and the initiator. Chapter 3 concentrates on the preparation of nanocomposites by melt blending with polymer modified clays. Three different polymer modified clays (PS, PMMA and PBD modified clay) and six polymers (PS, HIPS, ABS, PMMA, PP and PE) are reported. The morphology, thermal stability, fire behavior and mechanical properties were studied. This research shows that the exfoliation process by melt blending is controlled by the types of interactions between the various polymers, the silicate surfaces and the organic modifier. The combination of polar polymer matrix and non-polar polymer modified clay with large d-spacing will be more likely to give the exfoliated nanocomposites. TGA-FTIR results show that the mechanism of degradation of polystyrene is changed in the presence of the clay. In order to better understand the effects of the organic modifier, PS surfactants with five different pendant groups, dimethylhexadecylamine, trimethylamine, dimethylbenzylamine, 1,2-dimethylimidizole and triphenylphosphine, were used and the results show that the degradation depends upon the pendant. Chapter 5 provides some suggestions for future work based upon this work. The synthesis of several new and previously reported donor-acceptor cyclopropanes is reported in part II. The study shows that the facility of the donor-acceptor cyclopropane ring cleavage is strongly influenced by the kind of activating substitutes on the cyclopropane ring, and the

  7. Photophysics and charge transfer in donor-acceptor triblock copolymer photovoltaic materials

    NASA Astrophysics Data System (ADS)

    Schwarz, Kyra N.; Jones, David J.; Smith, Trevor A.; Ghiggino, Kenneth P.

    2014-10-01

    Efficient conversion of solar energy to electricity in low-cost organic photovoltaic (OPV) devices requires the complex interplay between multiple processes and components over various length and time scales. Optimizing device morphology to ensure efficient exciton diffusion and charge transport as well as ensuring efficient charge photogeneration is necessary to achieve optimum performance in new materials. The conjugated polymer electron donor PFM (poly(9,9-diocetyluorene-co-bis-N,N-(4-methylphenyl)-bis-N,N-phenyl-1,4-phenylenediamine)) and electron acceptor F8BT (poly[(9,9-di-n-octyluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,8-diyl)), comprise the novel triblock copolymer PFM-F8BT-PFM. This copolymer is designed to phase separate on the 20-30 nm scale, a domain size ideal for maximizing exciton collection at the donor-acceptor interface. Using steady-state and ultrafast spectroscopic characterization including high repetition rate transient absorption spectroscopy, the dynamics of charge and energy transfer of the component polymers and the triblock co-polymer have been investigated. The results demonstrate that for the homopolymers solvent dependent exciton transport processes dominate, while in the triblock copolymer solutions transient spectroscopy provides evidence for interfacial charge separation.

  8. Giant spatially-resolved self-assembled donor-acceptor molecular heterojunctions

    NASA Astrophysics Data System (ADS)

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

    Despite theoretical models predicting that rectification ratios (RR) >1000 should be achievable in molecular rectifiers, demonstrations of this have been rare. It has also been extremely challenging to unravel the structure-function relationships on the nanometer length scales that determine their behavior. Using scanning tunneling microscopy (STM) and spectroscopy (STS), we show that RRs >1000 at biases <500 mV are realized in the two-molecule limit for self-assembled donor-acceptor bilayers of pentacene on C60 on Cu. We show that the system behaves as a molecular analog to a Schottky diode due to strong electronic coupling of C60 to the metallic substrate, and electronic transport is dominated by sequential tunneling from semiconducting pentacene to metallic C60. Furthermore, we demonstrate the extreme sensitivity of the low-bias I (V) characteristics to the molecularly-resolved structure of the heterojunction (HJ), which leads to negative differential resistance and ~ 100 × variation in the rectification ratio within 2 nm of the edge of the molecular HJ. Support was provided by the Department of Energy Office of Basic Energy Sciences (SISGR Grant DE-FG02-09ER16109).

  9. A systematic study of thermochromic aromatic donor-acceptor materials.

    PubMed

    Alvey, Paul M; Reczek, Joseph J; Lynch, Vincent; Iverson, Brent L

    2010-11-19

    Molar mixtures (1:1) of electron-rich dialkoxynapthalene (Dan) and electron-deficient 1,4,5,8-napthalenetetracarboxylic diimide (Ndi) derivatives form highly tunable, columnar mesophases with a dark red color due to a charge transfer absorbance derived from alternating face-centered stacking. Certain Dan-Ndi mixtures undergo a dramatic color change from dark red to an almost colorless material upon crystallizing from the mesophase. Macroscopic morphology of the solid is not changed during this process. In order to investigate the origins of this interesting thermochromic behavior, Dan and Ndi side chains were systematically altered and their 1:1 mixtures were studied. We have previously speculated that the presence or absence of steric interactions due to side chain branching on the aromatic units controlled the level of color change associated with crystallization. Results from the present study further refine this conclusion including a key crystal structure that provides a structural rationale for the observed results. PMID:20973470

  10. A Systematic Study of Thermochromic Aromatic Donor-Acceptor Materials

    PubMed Central

    Alvey, Paul M.; Reczek, Joseph J.; Lynch, Vincent; Iverson, Brent L.

    2010-01-01

    1:1 molar mixtures of electron rich dialkoxynapthalene (Dan) and electron deficient 1,4,5,8-napthalenetetracarboxylic diimide (Ndi) derivatives form highly tunable, columnar mesophases with a dark red color due to a charge transfer absorbance derived from alternating face-centered stacking. Certain Dan-Ndi mixtures undergo a dramatic color change from dark red to an almost colorless material upon crystallizing from the mesophase. Macroscopic morphology of the solid is not changed during this process. In order to investigate the origins of this interesting thermochromic behavior, Dan and Ndi side chains were systematically altered and their 1:1 mixtures studied. We have previously speculated that the presence or absence of steric interactions due to side chain branching on the aromatic units controlled the level of color change associated with crystallization. Results from the present study further refine this conclusion including a key crystal structure that provides a structural rationale for the observed results. PMID:20973470

  11. 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.

  12. A charge carrier transport model for donor-acceptor blend layers

    NASA Astrophysics Data System (ADS)

    Fischer, Janine; Widmer, Johannes; Kleemann, Hans; Tress, Wolfgang; Koerner, Christian; Riede, Moritz; Vandewal, Koen; Leo, Karl

    2015-01-01

    Highly efficient organic solar cells typically comprise donor-acceptor blend layers facilitating effective splitting of excitons. However, the charge carrier mobility in the blends can be substantially smaller than in neat materials, hampering the device performance. Currently, available mobility models do not describe the transport in blend layers entirely. Here, we investigate hole transport in a model blend system consisting of the small molecule donor zinc phthalocyanine (ZnPc) and the acceptor fullerene C60 in different mixing ratios. The blend layer is sandwiched between p-doped organic injection layers, which prevent minority charge carrier injection and enable exploiting diffusion currents for the characterization of exponential tail states from a thickness variation of the blend layer using numerical drift-diffusion simulations. Trap-assisted recombination must be considered to correctly model the conductivity behavior of the devices, which are influenced by local electron currents in the active layer, even though the active layer is sandwiched in between p-doped contacts. We find that the density of deep tail states is largest in the devices with 1:1 mixing ratio (Et = 0.14 eV, Nt = 1.2 × 1018 cm-3) directing towards lattice disorder as the transport limiting process. A combined field and charge carrier density dependent mobility model are developed for this blend layer.

  13. A charge carrier transport model for donor-acceptor blend layers

    SciTech Connect

    Fischer, Janine Widmer, Johannes; Koerner, Christian; Vandewal, Koen; Leo, Karl; Kleemann, Hans; Tress, Wolfgang; Riede, Moritz

    2015-01-28

    Highly efficient organic solar cells typically comprise donor-acceptor blend layers facilitating effective splitting of excitons. However, the charge carrier mobility in the blends can be substantially smaller than in neat materials, hampering the device performance. Currently, available mobility models do not describe the transport in blend layers entirely. Here, we investigate hole transport in a model blend system consisting of the small molecule donor zinc phthalocyanine (ZnPc) and the acceptor fullerene C{sub 60} in different mixing ratios. The blend layer is sandwiched between p-doped organic injection layers, which prevent minority charge carrier injection and enable exploiting diffusion currents for the characterization of exponential tail states from a thickness variation of the blend layer using numerical drift-diffusion simulations. Trap-assisted recombination must be considered to correctly model the conductivity behavior of the devices, which are influenced by local electron currents in the active layer, even though the active layer is sandwiched in between p-doped contacts. We find that the density of deep tail states is largest in the devices with 1:1 mixing ratio (E{sub t} = 0.14 eV, N{sub t} = 1.2 × 10{sup 18 }cm{sup −3}) directing towards lattice disorder as the transport limiting process. A combined field and charge carrier density dependent mobility model are developed for this blend layer.

  14. Photophysical Properties and Efficient, Stable, Electrogenerated Chemiluminescence of Donor-Acceptor Molecules Exhibiting Thermal Spin Upconversion.

    PubMed

    Ishimatsu, Ryoichi; Edura, Tomohiko; Adachi, Chihaya; Nakano, Koji; Imato, Toshihiko

    2016-03-24

    The photophysical properties and electrogenerated chemiluminescence (ECL) of three donor-acceptor molecules composed of dicyanobenzene and methyl-, tert-butyl-, and phenyl-substituted carbazolyl groups, 1,2,3,5-tetrakis(3,6-disubstituted-carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN-Me, 4CzIPN-tBu, and 4CzIPN-Ph, respectively) are described. These molecules show delayed fluorescence as a result of thermal spin upconversion from the lowest triplet state to the lowest singlet state at room temperature. The three molecules showed yellow to yellowish-red ECL. Remarkably, the ECL efficiencies of 4CzIPN-tBu in dichloromethane reached almost 40 %. Moreover, stable ECL was emitted from 4CzIPN-tBu and 4CzIPN-Ph. In case of 4CzIPN-Me, the ECL intensity decreased during voltage cycles because of polymerization. Quantum chemical calculations revealed that polymerization was inhibited by the steric hindrance of the bulky tert-butyl and phenyl groups on the carbazolyl moieties and lowered the spin density on the carbazolyl groups through electron conjugation for 4CzIPN-Ph. PMID:26916843

  15. 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.

  16. 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

  17. 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

  18. 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

  19. 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

  20. Acceptor-donor-acceptor-based small molecules with varied crystallinity: processing additive-induced nanofibril in blend film for photovoltaic applications

    NASA Astrophysics Data System (ADS)

    Li, Chao; Chen, Yujin; Zhao, Yue; Wang, Huifang; Zhang, Wei; Li, Yaowen; Yang, Xiaoming; Ma, Changqi; Chen, Liwei; Zhu, Xiulin; Tu, Yingfeng

    2013-09-01

    A series of acceptor-donor-acceptor-based small molecules (SMs) with varied crystallinity were successfully synthesized. The processing additive can induce the SMs to self-organize as nanofibrils with higher crystallinity and controlled scales of nanofibrils, which have significant influence on the photovoltaic performance.A series of acceptor-donor-acceptor-based small molecules (SMs) with varied crystallinity were successfully synthesized. The processing additive can induce the SMs to self-organize as nanofibrils with higher crystallinity and controlled scales of nanofibrils, which have significant influence on the photovoltaic performance. Electronic supplementary information (ESI) available: Synthetic process and characterizations of SMs; TGA, electrochemical properties, molecular orbital surfaces of SMs; AFM images of SM:PC71BM blend films; EQE curves; optical, electrochemical properties and photovoltaic parameters. See DOI: 10.1039/c3nr03048b

  1. 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

  2. Theoretical estimation of the rate of photoinduced charge transfer reactions in triphenylamine C60 donor-acceptor conjugate.

    PubMed

    Martínez, Juan Pablo; Solà, Miquel; Voityuk, Alexander A

    2016-06-01

    Fullerene-based molecular heterojunctions such as the [6,6]-pyrrolidine-C60 donor-acceptor conjugate containing triphenylamine (TPA) are potential materials for high-efficient dye-sensitized solar cells. In this work, we estimate the rate constants for the photoinduced charge separation and charge recombination processes in TPA-C60 using the unrestricted and time-dependent DFT methods. Different schemes are applied to evaluate excited state properties and electron transfer parameters (reorganization energies, electronic couplings, and Gibbs energies). The use of open-shell singlet or triplet states, several density functionals, and continuum solvation models is discussed. Strengths and limitations of the computational approaches are highlighted. The present benchmark study provides an overview of the expected performance of DFT-based methodologies in the description of photoinduced charge transfer reactions in fullerene heterojunctions. © 2016 Wiley Periodicals, Inc. PMID:26992355

  3. 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.

  4. Direct Correlation of Charge Transfer Absorption with Molecular Donor:Acceptor Interfacial Area via Photothermal Deflection Spectroscopy.

    PubMed

    Buchaca-Domingo, Ester; Vandewal, Koen; Fei, Zhuping; Watkins, Scott E; Scholes, Fiona H; Bannock, James H; de Mello, John C; Richter, Lee J; DeLongchamp, Dean M; Amassian, Aram; Heeney, Martin; Salleo, Alberto; Stingelin, Natalie

    2015-04-29

    Here we show that the charge transfer (CT) absorption signal in bulk-heterojunction solar cell blends, measured by photothermal deflection spectroscopy, is directly proportional to the density of molecular donor:acceptor interfaces. Since the optical transitions from the ground state to the interfacial CT state are weakly allowed at photon energies below the optical gap of both the donor and acceptor, we can exploit the use of this sensitive linear absorption spectroscopy for such quantification. Moreover, we determine the absolute molar extinction coefficient of the CT transition for an archetypical polymer:fullerene interface. The latter is ∼100 times lower than the extinction coefficient of the donor chromophore involved, allowing us to experimentally estimate the transition dipole moment as 0.3 D and the electronic coupling between the ground and CT states to be on the order of 30 meV. PMID:25856143

  5. Optical properties of disilane-bridged donor-acceptor architectures: strong effect of substituents on fluorescence and nonlinear optical properties.

    PubMed

    Shimada, Masaki; Yamanoi, Yoshinori; Matsushita, Tomonori; Kondo, Takashi; Nishibori, Eiji; Hatakeyama, Akari; Sugimoto, Kunihisa; Nishihara, Hiroshi

    2015-01-28

    A series of disilane-bridged donor-acceptor architectures 1-9 containing strong electron-donating and -withdrawing substituents were designed and synthesized in acceptable yields. The substituents substantially affected the fluorescence and nonlinear optical properties of the compounds. In the solid state, the compounds showed purple-blue fluorescence (λ(em) = 360-420 nm) with high quantum yields (up to 0.81). Compound 3, which had p-N,N-dimethylamino and o-cyano substituents, exhibited optical second harmonic generation (activity 2.9 times that of urea, calculated molecular hyperpolarizability β = 1.6 × 10(-30) esu) in the powder state. Density functional theory calculations for the ground and excited states indicated that both the locally excited state and the intramolecular charge transfer excited state make important contributions to the luminescence behavior. PMID:25565361

  6. 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

  7. Tuning of Stepwise Neutral-Ionic Transitions by Acceptor Site Doping in Alternating Donor/Acceptor Chains.

    PubMed

    Nakabayashi, Keita; Nishio, Masaki; Miyasaka, Hitoshi

    2016-03-01

    The stepwise neutral-ionic (N-I) phase transition found in the alternating donor/acceptor (DA) chain [Ru2(2,3,5,6-F4PhCO2)4(DMDCNQI)]·2(p-xylene) (0; 2,3,5,6-F4PhCO2(-) = 2,3,5,6-tetrafluorobenzoate; DMDCNQI = 2,5-dimethyl-N,N'-dicyanoquinonediimine) was tuned by partly substituting the acceptor DMDCNQI with 2,5-dimethoxy-N,N'-dicyanoquinonediimine (DMeODCNQI), which displays a poorer electron affinity in an isostructural series. The site-doped series comprised [Ru2(2,3,5,6-F4PhCO2)4(DMDCNQI)1-x(DMeODCNQI)x]·2(p-xylene) for doping rates (x) = 0.05 (0.05-MeO), 0.10 (0.10-MeO), 0.15 (0.15-MeO), and 0.20 (0.20-MeO). The neutral chain [Ru2(2,3,5,6-F4PhCO2)4(DMeODCNQI)]·4(p-xylene) (1), which only contained DMeODCNQI, was also characterized. All site-doped compounds were isostructural to 0 except 1 despite their identical DA chain motif. Except at an x value of 0.20, they displayed a two-step N-I transition involving an intermediate phase. This transition occurred at high temperatures in 0 but shifted to lower temperatures in a parallel manner with increasing doping rate. Simultaneously, each transition broadened with increasing doping rate, leading to a convergence of two transitions at an x value approximating 0.2. Donor/acceptor-site-doping techniques present somewhat different impacts in terms of interchain Coulomb effects. PMID:26878151

  8. 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

  9. Ultrafast Energy Transfer in Ultrathin Organic Donor/Acceptor Blend

    PubMed Central

    Kandada, Ajay Ram Srimath; Grancini, Giulia; Petrozza, Annamaria; Perissinotto, Stefano; Fazzi, Daniele; Raavi, Sai Santosh Kumar; Lanzani, Guglielmo

    2013-01-01

    It is common knowledge that poly(3-hexylthiophene) (P3HT)/[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) blend, a prototype system for bulk heterojunction (BHJ) solar cells, consists of a network of tens of nanometers-large donor-rich and acceptor-rich phases separated by extended finely intermixed border regions where PCBM diffuse into P3HT. Here we specifically address the photo-induced dynamics in a 10 nm thin P3HT/PCBM blend that consists of the intermixed region only. Using the multi-pass transient absorption technique (TrAMP) that enables us to perform ultra high sensitive measurements, we find that the primary process upon photoexcitation is ultrafast energy transfer from P3HT to PCBM. The expected charge separation due to hole transfer from PCBM to P3HT occurs in the 100 ps timescale. The derived picture is much different from the accepted view of ultra-fast electron transfer at the polymer/PCBM interface and provides new directions for the development of efficient devices. PMID:23797845

  10. Ultrafast Energy Transfer in Ultrathin Organic Donor/Acceptor Blend

    NASA Astrophysics Data System (ADS)

    Kandada, Ajay Ram Srimath; Grancini, Giulia; Petrozza, Annamaria; Perissinotto, Stefano; Fazzi, Daniele; Raavi, Sai Santosh Kumar; Lanzani, Guglielmo

    2013-06-01

    It is common knowledge that poly(3-hexylthiophene) (P3HT)/[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) blend, a prototype system for bulk heterojunction (BHJ) solar cells, consists of a network of tens of nanometers-large donor-rich and acceptor-rich phases separated by extended finely intermixed border regions where PCBM diffuse into P3HT. Here we specifically address the photo-induced dynamics in a 10 nm thin P3HT/PCBM blend that consists of the intermixed region only. Using the multi-pass transient absorption technique (TrAMP) that enables us to perform ultra high sensitive measurements, we find that the primary process upon photoexcitation is ultrafast energy transfer from P3HT to PCBM. The expected charge separation due to hole transfer from PCBM to P3HT occurs in the 100 ps timescale. The derived picture is much different from the accepted view of ultra-fast electron transfer at the polymer/PCBM interface and provides new directions for the development of efficient devices.

  11. Seeded on-surface supramolecular growth for large area conductive donor-acceptor assembly.

    PubMed

    Goudappagouda; Chithiravel, Sundaresan; Krishnamoorthy, Kothandam; Gosavi, Suresh W; Babu, Sukumaran Santhosh

    2015-07-01

    Charge transport features of organic semiconductor assemblies are of paramount importance. However, large-area extended supramolecular structures of donor-acceptor combinations with controlled self-assembly pathways are hardly accessible. In this context, as a representative example, seeded on-surface supramolecular growth of tetrathiafulvalene and tetracyano-p-quinodimethane (TTF-TCNQ) using active termini of solution-formed sheaves has been introduced to form an extended assembly. We demonstrate for the first time, the creation of a large-area donor-acceptor assembly on the surface, which is practically very tedious, using a seeded, evaporation-assisted growth process. The excellent molecular ordering in this assembly is substantiated by its good electrical conductivity (~10⁻² S cm⁻¹). The on-surface assembly via both internally formed and externally added sheaf-like seeds open new pathways in supramolecular chemistry and device applications. PMID:26036616

  12. 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

  13. 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

  14. Thermally Activated Delayed Fluorescence Materials Based on Homoconjugation Effect of Donor-Acceptor Triptycenes.

    PubMed

    Kawasumi, Katsuaki; Wu, Tony; Zhu, Tianyu; Chae, Hyun Sik; Van Voorhis, Troy; Baldo, Marc A; Swager, Timothy M

    2015-09-23

    Donor-acceptor triptycences, TPA-QNX(CN)2 and TPA-PRZ(CN)2, were synthesized and their emissive properties were studied. They exhibited a blue-green fluorescence with emission lifetimes on the order of a microsecond in cyclohexane at room temperature. The long lifetime emission is quenched by O2 and is attributed to thermally activated delayed florescence (TADF). Unimolecular TADF is made possible by the separation and weak coupling due to homoconjugation of the HOMO and LUMO on different arms of the three-dimensional donor-acceptor triptycene. Organic light emitting devices (OLEDs) were fabricated using TPA-QNX(CN)2 and TPA-PRZ(CN)2 as emitters which displayed electroluminescence with efficiencies as high as 9.4% EQE. PMID:26367852

  15. 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

  16. Synthesis and mesomorphic behavior of a donor-acceptor-type hexaazatriphenylene.

    PubMed

    Chang, Tsu-Hsin; Wu, Bi-Ru; Chiang, Michael Y; Liao, Su-Chih; Ong, Chi Wi; Hsu, Hsiu-Fu; Lin, Shu-Yu

    2005-09-15

    [structure: see text] A new donor-acceptor, 1,4,5,8,9,12-hexaazatriphenylene HATCNOR(n), is described. The synthesis of HATCNOR1 and HATCNOR6 is achieved by the regioselective displacement of 1,4,5,8,9,12-hexaazatriphenylene hexacarbonitrile (HATCN) with an alkoxy group. The X-ray analysis revealed self-assembly of HATCNOR1 in the solid state. HATCNOR6 is the new difunctionalized hexaazatriphenylene discotic liquid crystal. PMID:16146355

  17. 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

  18. 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

  19. 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.

  20. Spectral and intramolecular charge transfer properties in terminal donor/acceptor-substituted all-trans-α,ω-diphenylpolyenes and α,ω-diphenylpolyynes.

    PubMed

    Ma, Xiaonan; Yan, Linyin; Wang, Xuefei; Guo, Qianjin; Xia, Andong

    2011-10-14

    The absorption spectra and intramolecular charge transfer (CT) properties of terminal donor/acceptor-substituted all-trans-α,ω-diphenylpolyenes (DPE) and α,ω-diphenylpolyynes (DPY) molecules with different conjugated bridge length and substitution modes were investigated by using quantum chemical calculations. We calculated the ground state structures and energy of two series of terminal donor/acceptor DPE and DPY by DFT method. The dependence of conjugation length and substitution modes of the electronic absorption spectra was obtained by TDDFT calculation. The hybrid-GGA XC-functional PBE0 employed in this work was selected from several functionals by comparing the calculated electronic spectral data with experimental value. The CIS-based generalized Mulliken-Hush (GMH) approach was further used to calculate coupling values H(AD) of the CT process. The calculation shows that both the HOMO-LUMO energy gaps and average bond length alternations between unsaturated multiple (C≡C and C=C) and saturated single bonds (C-C) decrease regularly with the extension of conjugation. The effective conjugated length (ECL) of DPE and DPY with the same order MM > MP/PM > PP is found together with the regular red shift of the electronic absorption spectra with the extension of conjugation, resulting from the different π-electron delocalization and conjugation efficiency. The GMH analysis further suggests that the CT process in both DPE and DPY is predominated by the through-bond mechanism. The remarkable difference of the conjugated length dependence of squared CT coupling between substituted DPE and DPY is the result of the energetic matching degree of the frontier molecular orbitals between donor/acceptor and the conjugated bridge. PMID:21879052

  1. Cascade Reaction of Donor-Acceptor Cyclopropanes: Mechanistic Studies on Cycloadditions with Nitrosoarenes and cis-Diazenes.

    PubMed

    Chidley, Tristan; Vemula, Naresh; Carson, Cheryl A; Kerr, Michael A; Pagenkopf, Brian L

    2016-06-17

    Tandem ring opening, elimination, and cycloaddition of donor-acceptor cyclopropanes were observed in Yb(OTf)3-catalyzed cycloaddition with nitrosoarenes. The reaction results in formation of tetrahydro-1,2-oxazine instead of the normal cycloadduct isoxazolidine via in situ nitrone formation. A similar cascade sequence was observed with cis-diazines. Mechanistic studies on this unique transformation offer an entirely new approach for reaction design with donor-acceptor cyclopropanes. PMID:27267360

  2. Spectroscopic and dynamical differences between exciplex and electronically excited EDA complex

    NASA Astrophysics Data System (ADS)

    Lim, B. T.; Okajima, S.; Lim, E. C.

    1986-02-01

    We demonstrate here that the electronically excited electron donor-acceptor (EDA) complex can be different from the corresponding exciplex even in the absence of viscosity constraints that prevent the attainment of preferred donor-acceptor orientation.

  3. Density-functional Theory and Beyond for Donor-Acceptor Complexes: The Example of TTF/TCNQ

    NASA Astrophysics Data System (ADS)

    Atalla, Viktor; Yoon, Mina; Scheffler, Matthias

    2012-02-01

    We study the performance of density-functional theory (DFT) with various exchange-correlation (XC) functionals in describing electronic and structural properties of the prototypical donor/acceptor complex TTF/TCNQ. We find that the binding energetics and the amount of electron transfer between TTF and TCNQ depends strongly on the functional. In particular, all semilocal functionals give rise to significant, aritificial electron transfer due to a wrong ordering of Kohn-Sham (KS) levels. We consider the HSE [1] ``family'' of XC functionals using the fraction of exact exchange (α) as adjustable parameter. The optimum XC functional is then identified as that for which the G0W0 quasiparticle correction to the energy gap of the KS LUMO of the acceptor and the HOMO of the donor is minimized. We obtain α˜0.8 which gives an electronic level alignment that is consistent with experiment and free from spurious asymptotic charge transfer. We conclude that the proposed scheme improves the KS spectrum, and that the investigated TTF-TCNQ dimer exhibits intra-molecular electron-density rearrangement rather than electron transfer. [4pt] [1] A.V. Krukau, et al., J. Chem. Phys. 125, 224106 (2006)

  4. A predictive theoretical model for electron tunneling pathways in proteins

    NASA Technical Reports Server (NTRS)

    Onuchic, Jose Nelson; Beratan, David N.

    1990-01-01

    A practical method is presented for calculating the dependence of electron transfer rates on details of the protein medium intervening between donor and acceptor. The method takes proper account of the relative energetics and mutual interactions of the donor, acceptor, and peptide groups. It also provides a quantitative search scheme for determining the important tunneling pathways (specific sequences of localized bonding and antibonding orbitals of the protein which dominate the donor-acceptor electronic coupling) in native and tailored proteins, a tool for designing new proteins with prescribed electron transfer rates, and a consistent description of observed electron transfer rates in existing redox labeled metalloproteins and small molecule model compounds.

  5. 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. PMID:26964012

  6. Molecular Packing Determines Charge Separation in a Liquid Crystalline Bisthiophene-Perylene Diimide Donor-Acceptor Material.

    PubMed

    Polkehn, Matthias; Tamura, Hiroyuki; Eisenbrandt, Pierre; Haacke, Stefan; Méry, Stéphane; Burghardt, Irene

    2016-04-01

    Combined electronic structure and quantum dynamical calculations are employed to investigate charge separation in a novel class of covalently bound bisthiophene-perylene diimide type donor-acceptor (DA) co-oligomer aggregates. In an earlier spectroscopic study of this DA system in a smectic liquid crystalline (LC) film, efficient and ultrafast (subpicosecond) initial charge separation was found to be followed by rapid recombination. By comparison, the same DA system in solution exhibits ultrafast resonant energy transfer followed by slower (picosecond scale) charge separation. The present first-principles study explains these contrasting observations, highlighting the role of an efficient intermolecular charge-transfer pathway that results from the molecular packing in the LC phase. Despite the efficiency of this primary charge-transfer step, long-range charge separation is impeded by a comparatively high Coulomb barrier in conjunction with small electron- and hole-transfer integrals. Quantum dynamical calculations are carried out for a fragment-based model Hamiltonian, parametrized by ab initio second-order Algebraic Diagrammatic Construction (ADC(2)) and Time-Dependent Density Functional Theory (TDDFT) electronic structure calculations. Simulations of coherent vibronic quantum dynamics for up to 156 electronic states and 48 modes are performed using the Multi-Layer Multi-Configuration Time-Dependent Hartree (ML-MCTDH) method. Excellent agreement with experimentally determined charge separation time scales is obtained, and the spatially coherent nature of the dynamics is analyzed. PMID:26987362

  7. 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.

  8. 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

  9. 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

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

    PubMed

    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

  11. Effect of Oligomer Length on Photophysical Properties of Platinum Acetylide Donor-Acceptor-Donor Oligomers.

    PubMed

    Cekli, Seda; Winkel, Russell W; Schanze, Kirk S

    2016-07-21

    We report a systematic study that explores how the triplet excited state is influenced by conjugation length in a series of benzothiadiazole units containing donor-acceptor-donor (DAD)-type platinum acetylide oligomers and polymer. The singlet and triplet excited states for the series were characterized by an array of photophysical methods including steady-state luminescence spectroscopy and femtosecond-nanosecond transient absorption spectroscopy. In addition to the experimental work, a computational study using density functional theory was conducted to gain more information about the structure, composition, and energies of the frontier molecular orbitals. It is observed that both the singlet and triplet excited states are mainly localized on a single donor-acceptor-donor unit in the oligomers. Interestingly, it is discovered that the intersystem crossing efficiency increases dramatically in the longer oligomers. The effect is attributed to an enhanced contribution of the heavy metal platinum in the frontier orbitals (HOMO and LUMO), an effect that leads to enhanced spin-orbit coupling. PMID:27291712

  12. Study of the potential energy conversion efficiency of organic solar cells based on donor/acceptor heterojunctions

    NASA Astrophysics Data System (ADS)

    Geens, Wim

    2002-01-01

    Organic solar cells can offer an appealing alternative for bulk silicon solar cells due to their attractive properties such as flexibility and possibility to apply low-cost manufacturing techniques. The different types of existing organic solar cells reported in the literature have been critically assessed in terms of performance and processability, based on which it was concluded that the concept of the donor/acceptor bulk heterojunction sandwiched between a transparent and a metal electrode has the most potential. In order to gain more insight into the charge transport properties of spin-cast photovoltaic conjugated polymer/fullerene blends, these films were incorporated into field-effect transistors to derive values for the electron and hole mobilities. Model calculations showed that increasing these mobility values in combination with the use of thicker active layers could significantly enhance the short-circuit current density of the bulk heterojunction solar cells. Optimisation of the charge transport is required and was realised in this study by choosing PPV-oligomers and C60 as well-defined building blocks to construct the donor/acceptor networks. First, these materials were spin-cast in single-layer diodes to allow full electrical characterisation, which was then compared with simulation of the devices in dark as well as under illumination. The photovoltaic performance of blended PPV-oligomer/C60 devices remained rather low due to C60-induced shunting paths and high molecular disorder. In a second part, more morphological order was obtained by using vacuum evaporation to deposit the organic materials. Besides structural characterisation of the evaporated films, the electrical behaviour of single-layer devices was investigated and the influence of interfacial layers was addressed. Photovoltaic devices based on evaporated planar heterojunctions reaching a conversion efficiency of 1.9% and exhibiting an open-circuit voltage of over 1 V were realised

  13. 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

  14. 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.

  15. 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

  16. Construction of an Artificial Ferrimagnetic Lattice by Lithium Ion Insertion into a Neutral Donor/Acceptor Metal-Organic Framework.

    PubMed

    Taniguchi, Kouji; Narushima, Keisuke; Mahin, Julien; Kosaka, Wataru; Miyasaka, Hitoshi

    2016-04-18

    Construction of a molecular system in which the magnetic lattice exhibits long-range order is one of the fundamental goals in materials science. In this study, we demonstrate the artificial construction of a ferrimagnetic lattice by doping electrons into acceptor sites of a neutral donor/acceptor metal-organic framework (D/A-MOF). This doping was achieved by the insertion of Li-ions into the D/A-MOF, which was used as the cathode of a Li-ion battery cell. The neutral D/A-MOF is a layered system composed of a carboxylate-bridged paddlewheel-type diruthenium(II,II) complex as the donor and a TCNQ derivative as the acceptor. The ground state of the neutral form was a magnetically disordered paramagnetic state. Upon discharge of the cell, spontaneous magnetization was induced; the transition temperature was variable. The stability of the magnetically ordered lattice depended on the equilibrium electric potential of the D/A-MOF cathode, which reflected the electron-filling level. PMID:26990927

  17. 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

  18. Photochemical activity of a key donor-acceptor complex can drive stereoselective catalytic α-alkylation of aldehydes

    NASA Astrophysics Data System (ADS)

    Arceo, Elena; Jurberg, Igor D.; Álvarez-Fernández, Ana; Melchiorre, Paolo

    2013-09-01

    Asymmetric catalytic variants of sunlight-driven photochemical processes hold extraordinary potential for the sustainable preparation of chiral molecules. However, the involvement of short-lived electronically excited states inherent to any photochemical reaction makes it challenging for a chiral catalyst to dictate the stereochemistry of the products. Here, we report that readily available chiral organic catalysts, with well-known utility in thermal asymmetric processes, can also confer a high level of stereocontrol in synthetically relevant intermolecular carbon-carbon bond-forming reactions driven by visible light. A unique mechanism of catalysis is proposed, wherein the catalyst is involved actively in both the photochemical activation of the substrates (by inducing the transient formation of chiral electron donor-acceptor complexes) and the stereoselectivity-defining event. We use this approach to enable transformations that are extremely difficult under thermal conditions, such as the asymmetric α-alkylation of aldehydes with alkyl halides, the formation of all-carbon quaternary stereocentres and the control of remote stereochemistry.

  19. 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].

  20. Thiadiazolo[3,4-c]pyridine as an Acceptor toward Fast-Switching Green Donor-Acceptor-Type Electrochromic Polymer with Low Bandgap.

    PubMed

    Ming, Shouli; Zhen, Shijie; Lin, Kaiwen; Zhao, Li; Xu, Jingkun; Lu, Baoyang

    2015-06-01

    Thiadiazolo[3,4-c]pyridine (PT), an important analog of benzothiadiazole (BT), has most recently been explored as a novel electron acceptor. It exhibits more electron-accepting ability and other unique properties and potential advantages over BT, thus inspiring us to investigate PT-based donor-acceptor-type (D-A) conjugated polymer in electrochromics. Herein, PT was employed for the rational design of novel donor-acceptor-type systems to yield a neutral green electrochromic polymer poly(4,7-di(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-[1,2,5] thiadiazolo[3,4-c]pyridine) (PEPTE). PEPTE revealed a lower bandgap (Eg,ele=0.85 eV, Eg,opt=1.12 eV) than its BT analog and also favorable redox activity and stability. Furthermore, electrochromic kinetic studies demonstrated that PEPTE displayed higher coloration efficiency than BT analog, good optical memory, and very fast switching time (0.3 s at all three wavelengths), indicating that PT would probably be a promising choice for developing novel neutral green electrochromic polymers by matching with various donor units. PMID:25955881

  1. 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. PMID:26615814

  2. 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

  3. A Donor-Acceptor Conjugated Polymer with Alternating Isoindigo Derivative and Bithiophene Units for Near-Infrared Modulated Cancer Thermo-Chemotherapy.

    PubMed

    Li, Dong-Dong; Wang, Jun-Xia; Ma, Yan; Qian, Hai-Sheng; Wang, Dong; Wang, Li; Zhang, Guobing; Qiu, Longzhen; Wang, Yu-Cai; Yang, Xian-Zhu

    2016-08-01

    Conjugated polymers containing alternating donor/acceptor units have strong and sharp absorbance peaks in near-infrared (NIR) region, which could be suitable for photothermal therapy. However, these polymers as photothermal transducers are rarely reported because of their water insolubility, which limits their applications for cancer therapy. Herein, we report the donor-acceptor conjugated polymer PBIBDF-BT with alternating isoindigo derivative (BIBDF) and bithiophene (BT) units as a novel photothermal transducer, which exhibited strong near-infrared (NIR) absorbance due to its low band gap (1.52 eV). To stabilize the conjugated polymer physiological environments, we utilized an amphiphilic copolymer, poly(ethylene glycol)-block-poly(hexyl ethylene phosphate) (mPEG-b-PHEP), to stabilize PBIBDF-BT-based nanoparticles (PBIBDF-BT@NPPPE) through a single emulsion method. The obtained nanoparticles PBIBDF-BT@NPPPE showed great stability in physiological environments and excellent photostability. Moreover, the PBIBDF-BT@NPPPE exhibited high photothermal conversion efficiency, reaching 46.7%, which is relatively high compared with those of commonly used materials for photothermal therapy. Accordingly, in vivo and in vitro experiments demonstrated that PBIBDF-BT@NPPPE exhibits efficient photothermal anticancer efficacy. More importantly, PBIBDF-BT@NPPPE could simultaneously encapsulate other types of therapeutic agents though hydrophobic interactions with the PHEP core and achieve NIR-triggered intracellular drug release and a synergistic combination therapy of thermo-chemotherapy for the treatment of cancer. PMID:27404741

  4. 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

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

    PubMed

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

    2016-06-24

    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-b;4,5-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). PMID:27242024

  6. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    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.

  8. 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

  9. Donor-acceptor pair recombination luminescence from monoclinic Cu2SnS3 thin film

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

    The defect levels in Cu2SnS3 (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.

  10. Characterization of the donor-acceptor-pair transition in Nitrogen-implanted zinc oxide

    SciTech Connect

    Stichtenoth, D.; Duerr, J.; Ronning, C.; Wischmeier, L.; Voss, T.

    2008-04-15

    Zinc oxide bulk crystals were doped with nitrogen by ion beam implantation. After postimplantation annealing, a luminescent transition appears at 3.230 eV. Power-dependent photoluminescence studies and time-resolved measurements at several spectral positions within this band can be described by a model for donor-acceptor-pair (DAP) transitions. By tracing the luminescence in a temperature-dependent study, a connection to phonon replicas could be excluded. Based on these results, this luminescence line could be clearly assigned to a DAP transition. In order to increase the doping efficiency, various approaches are considered and discussed. A slight increase could be obtained by high-temperature implantation without postimplantation annealing.

  11. Complexes due to donor-acceptor-type transitions in GaAs

    SciTech Connect

    Reynolds, D.C.; Litton, C.W.; Almassy, R.J.; McCoy, G.L.; Nam, S.B.

    1980-09-01

    A sharp line transition at 1.51385 eV has been observed in the photoluminescence spectra of an epitaxially grown crystal of GaAs. A Si/sub 3/N/sub 4/ cap was applied by plasma deposition and the crystal was then annealed at 850 /sup 0/C for 15 min. The sharp emission line was observed after annealing. This transition was analyzed in perturbing magnetic and strain fields and is shown to result from a donor-acceptor-type complex. Three additional sharp line transitions are reported and the behavior of all of these transitions is compared with the behavior of similar transitions reported in the literature. Models for the complexes involved are re-examined and components of the complexes are suggested. All of the sharp line transitions were introduced in the growing process with the exception of the 1.51385-eV line which was introduced in the capping and annealing process.

  12. 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).

  13. Rapid Energy Transfer Enabling Control of Emission Polarization in Perylene Bisimide Donor-Acceptor Triads.

    PubMed

    Menelaou, Christopher; ter Schiphorst, Jeroen; Kendhale, Amol M; Parkinson, Patrick; Debije, Michael G; Schenning, Albertus P H J; Herz, Laura M

    2015-04-01

    Materials showing rapid intramolecular energy transfer and polarization switching are of interest for both their fundamental photophysics and potential for use in real-world applications. Here, we report two donor-acceptor-donor triad dyes based on perylene-bisimide subunits, with the long axis of the donors arranged either parallel or perpendicular to that of the central acceptor. We observe rapid energy transfer (<2 ps) and effective polarization control in both dye molecules in solution. A distributed-dipole Förster model predicts the excitation energy transfer rate for the linearly arranged triad but severely underestimates it for the orthogonal case. We show that the rapid energy transfer arises from a combination of through-bond coupling and through-space transfer between donor and acceptor units. As they allow energy cascading to an excited state with controllable polarization, these triad dyes show high potential for use in luminescent solar concentrator devices. PMID:26262968

  14. Design and synthesis of donor-acceptor Stenhouse adducts: a visible light photoswitch derived from furfural.

    PubMed

    Helmy, Sameh; Oh, Saemi; Leibfarth, Frank A; Hawker, Craig J; Read de Alaniz, Javier

    2014-12-01

    The development of an easily synthesized, modular, and tunable organic photoswitch that responds to visible light has been a long-standing pursuit. Herein we provide a detailed account of the design and synthesis of a new class of photochromes based on furfural, termed donor-acceptor Stenhouse adducts (DASAs). A wide variety of these derivatives are easily prepared from commercially available starting materials, and their photophysical properties are shown to be dependent on the substituents of the push-pull system. Analysis of the switching behavior provides conditions to access the two structural isomers of the DASAs, reversibly switch between them, and use their unique solubility behavior to provide dynamic phase-transfer materials. Overall, these negative photochromes respond to visible light and heat and display an unprecedented level of structural modularity and tunabilty. PMID:25390619

  15. Ultrafast Photoinduced Charge Separation Leading to High-Energy Radical Ion-Pairs in Directly Linked Corrole-C60 and Triphenylamine-Corrole-C60 Donor-Acceptor Conjugates.

    PubMed

    Sudhakar, Kolanu; Gokulnath, Sabapathi; Giribabu, Lingamallu; Lim, Gary N; Trâm, Tạ; D'Souza, Francis

    2015-12-01

    Closely positioned donor-acceptor pairs facilitate electron- and energy-transfer events, relevant to light energy conversion. Here, a triad system TPACor-C60 , possessing a free-base corrole as central unit that linked the energy donor triphenylamine (TPA) at the meso position and an electron acceptor fullerene (C60) at the β-pyrrole position was newly synthesized, as were the component dyads TPA-Cor and Cor-C60. Spectroscopic, electrochemical, and DFT studies confirmed the molecular integrity and existence of a moderate level of intramolecular interactions between the components. Steady-state fluorescence studies showed efficient energy transfer from (1) TPA* to the corrole and subsequent electron transfer from (1) corrole* to fullerene. Further studies involving femtosecond and nanosecond laser flash photolysis confirmed electron transfer to be the quenching mechanism of corrole emission, in which the electron-transfer products, the corrole radical cation (Cor(⋅+) in Cor-C60 and TPA-Cor(⋅+) in TPACor-C60) and fullerene radical anion (C60(⋅-)), could be spectrally characterized. Owing to the close proximity of the donor and acceptor entities in the dyad and triad, the rate of charge separation, kCS , was found to be about 10(11)  s(-1), suggesting the occurrence of an ultrafast charge-separation process. Interestingly, although an order of magnitude slower than kCS , the rate of charge recombination, kCR , was also found to be rapid (kCR ≈10(10)  s(-1)), and both processes followed the solvent polarity trend DMF>benzonitrile>THF>toluene. The charge-separated species relaxed directly to the ground state in polar solvents while in toluene, formation of (3) corrole* was observed, thus implying that the energy of the charge-separated state in a nonpolar solvent is higher than the energy of (3) corrole* being about 1.52 eV. That is, ultrafast formation of a high-energy charge-separated state in toluene has been achieved in these closely spaced corrole

  16. Fundamental Studies on Donor-acceptor Conjugated Polymers Containing 'Heavy' Group 14 and Group 16 Elements

    NASA Astrophysics Data System (ADS)

    Gibson, Gregory Laird

    One advantage of conjugated polymers as organic materials is that their properties may be readily tuned through covalent modifications. This thesis presents studies on the structure-property relationships resulting from single- and double-atom substitutions on an alternating donor-acceptor conjugated polymer. Specifically, single selenium and tellurium atoms have been incorporated into the acceptor monomer in place of sulfur; silicon and germanium atoms have been substituted in place of carbon at the donor monomer bridge position. The carbon-donor/ tellurium-acceptor polymer was synthesized by a post-polymerization reaction sequence and demonstrated the utility of heavy group 16 atoms to red shift a polymer absorption spectrum. Density functional theory calculations point to a new explanation for this result invoking the lower heavy atom ionization energy and reduced aromaticity of acceptor monomers containing selenium and tellurium compared to sulfur. Absorption and emission experiments demonstrate that both silicon and germanium substitutions in the donor slightly blue shift the polymer absorption spectrum. Polymers containing sulfur in the acceptor are the strongest light absorbers of all polymers studied here. Molecular weight and phenyl end capping studies show that molecular weight appears to affect polymer absorption to the greatest degree in a medium molecular weight regime and that these effects have a significant aggregation component. Solar cell devices containing either the silicon- or germanium-donor/selenium-acceptor polymer display improved red light harvesting or hole mobility relative to their structural analogues. Overall, these results clarify the effects of single atom substitution on donor-acceptor polymers and aid in the future design of polymers containing heavy atoms.

  17. 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

  18. Electrochromism of a fused acceptor-donor-acceptor triad covering entire UV-vis and near-infrared regions.

    PubMed

    Yao, Bin; Ye, Xichong; Zhang, Jie; Wan, Xinhua

    2014-10-17

    A novel fused acceptor-donor-acceptor (A-D-A) type panchromatically electrochromic compound was synthesized. It exhibited intensive absorption bands covering entire UV-vis and near-infrared regions upon reduction to the radical anionic state, owing to the simultaneous presence of π*-π* transitions and intervalence charge transfer. PMID:25268224

  19. 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. PMID:26030670

  20. 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.

  1. Achieving near-infrared emission in platinum(ii) complexes by using an extended donor-acceptor-type ligand.

    PubMed

    Zhang, You-Ming; Meng, Fanyuan; Tang, Jian-Hong; Wang, Yafei; You, Caifa; Tan, Hua; Liu, Yu; Zhong, Yu-Wu; Su, Shijian; Zhu, Weiguo

    2016-03-15

    A series of C^N ligands with donor-acceptor (D-A) frameworks, i.e. TPA-BTPy, TPA-BTPy-Fl and Fl(TPA-BTPy)2, as well as their mono- and di-nuclear platinum(ii) complexes of (TPA-BTPy)Pt(pic), (TPA-BTPy-Fl)Pt(pic) and [Fl(TPA-BTPy)2]Pt2(pic)2 are respectively designed and synthesized, in which triphenylamine (TPA) and fluorene (Fl) are used as the D units, 4-(pyrid-2-yl)benzothiadiazole (BTPy) as the A unit, and the picolinate anion (pic) as the auxiliary ligand. Their thermal, photophysical and electrochemical characteristics were investigated. Compared to mono-nuclear platinum complexes and their free ligands, this dinuclear one of [Fl(TPA-BTPy)2]Pt2(pic)2 shows an obvious interaction from the platinum atom to ligand and dual emission peaks at 828 and 601 nm in thin films. Upon oxidation with antimony pentachloride in dichloromethane, charge transfer transitions between the platinum and ligand are observed for the three complexes. The single-emissive-layer polymer light-emitting devices doped with [Fl(TPA-BTPy)2]Pt2(pic)2 display a strong electroluminescence with dual emission peaks at 780 and 600 nm at a dopant concentration over 4 wt%. A maximum external quantum efficiency of 0.02% with a radiance of 59 μW cm(-2) is obtained in the device at 30 wt% dopant concentration. This work indicates that the use of an extended D-A-type ligand is an effective strategy to achieve NIR emission for platinum complexes in PLEDs. PMID:26880278

  2. 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.

  3. 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.

  4. 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. PMID:26750993

  5. Organic donor-acceptor assemblies form coaxial p-n heterojunctions with high photoconductivity.

    PubMed

    Prasanthkumar, Seelam; Ghosh, Samrat; Nair, Vijayakumar C; Saeki, Akinori; Seki, Shu; Ajayaghosh, Ayyappanpillai

    2015-01-12

    The formation of coaxial p-n heterojunctions by mesoscale alignment of self-sorted donor and acceptor molecules, important to achieve high photocurrent generation in organic semiconductor-based assemblies, remains a challenging topic. Herein, we show that mixing a p-type π gelator (TTV) with an n-type semiconductor (PBI) results in the formation of self-sorted fibers which are coaxially aligned to form interfacial p-n heterojunctions. UV/Vis absorption spectroscopy, powder X-ray diffraction studies, atomic force microscopy, and Kelvin-probe force microscopy revealed an initial self-sorting at the molecular level and a subsequent mesoscale self-assembly of the resulted supramolecular fibers leading to coaxially aligned p-n heterojunctions. A flash photolysis time-resolved microwave conductivity (FP-TRMC) study revealed a 12-fold enhancement in the anisotropic photoconductivity of TTV/PBI coaxial fibers when compared to the individual assemblies of the donor/acceptor molecules. PMID:25430809

  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. 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.

  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. 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

  10. 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. PMID:25655363

  11. Charge carrier dynamics in organic semiconductors and their donor-acceptor composites: Numerical modeling of time-resolved photocurrent

    NASA Astrophysics Data System (ADS)

    Johnson, Brian; Kendrick, Mark J.; Ostroverkhova, Oksana

    2013-09-01

    We present a model that describes nanosecond (ns) time-scale photocurrent dynamics in functionalized anthradithiophene (ADT) films and ADT-based donor-acceptor (D/A) composites. By fitting numerically simulated photocurrents to experimental data, we quantify contributions of multiple pathways of charge carrier photogeneration to the photocurrent, as well as extract parameters that characterize charge transport (CT) in organic films including charge carrier mobilities, trap densities, hole trap depth, and trapping and recombination rates. In pristine ADT films, simulations revealed two competing charge photogeneration pathways: fast, occurring on picosecond (ps) or sub-ps time scales with efficiencies below 10%, and slow, which proceeds at the time scale of tens of nanoseconds, with efficiencies of about 11%-12%, at the applied electric fields of 40-80 kV/cm. The relative contribution of these pathways to the photocurrent was electric field dependent, with the contribution of the fast process increasing with applied electric field. However, the total charge photogeneration efficiency was weakly electric field dependent exhibiting values of 14%-20% of the absorbed photons. The remaining 80%-86% of the photoexcitation did not contribute to charge carrier generation at these time scales. In ADT-based D/A composites with 2 wt.% acceptor concentration, an additional pathway of charge photogeneration that proceeds via CT exciton dissociation contributed to the total charge photogeneration. In the composite with the functionalized pentacene (Pn) acceptor, which exhibits strong exciplex emission from a tightly bound D/A CT exciton, the contribution of the CT state to charge generation was small, ˜8%-12% of the total number of photogenerated charge carriers, dependent on the electric field. In contrast, in the composite with PCBM acceptor, the CT state contributed about a half of all photogenerated charge carriers. In both D/A composites, the charge carrier mobilities were

  12. Blinking fluorescence of single donor-acceptor pairs: Important role of ``dark'' states in resonance energy transfer via singlet levels

    NASA Astrophysics Data System (ADS)

    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=IA/(IA+ID), where ID and IA are the average intensities of donor and acceptor fluorescence, can be described by the simple theoretical equation E(F)=FTD/(1+FTD). Here F is the rate of energy transfer, and TD 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 FTD≫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¯(F)TD/[1+F¯(F)TD]. Here F¯(F) is a function of F depending on singlet-triplet transitions in both donor and acceptor molecules. Expressions for the functions F¯(F) are derived. In this case the energy transfer efficiency will be far from 100% even at FTD≫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 wND(t) and wNA(t) of finding N photons of donor and acceptor fluorescence in the time interval t are calculated for various values of the energy transfer rate F and for all four types of D-A pair. Comparison of the calculated D

  13. Donor-acceptor interchange tunneling in HDO-DOH and the higher energy HDO-HOD isotopomer

    NASA Astrophysics Data System (ADS)

    Karyakin, E. N.; Fraser, G. T.; Lovas, F. J.; Suenram, R. D.; Fujitake, M.

    1995-01-01

    The microwave and submillimeter spectra of the a-type K=0←0 and K=1←1, c-type K=1←0, and isotopically allowed b-type K=1←0 bands of the O-D bonded HDO-DOH water dimer isotopomer and the higher energy O-H bonded HDO-HOD isotopomer have been measured using molecular-beam electric resonance optothermal and pulsed-nozzle Fourier-transform microwave spectrometers. The present results obtained in He and He/Ne seeded molecular beams give the first evidence for the presence of the higher energy O-H bonded mixed protonated-deuterated water dimers. These species were not reported previously in studies using seeded Ar molecular beams. The donor-acceptor interchange tunneling splittings are found to be 1322.1019(43) and 5004.059(20) MHz for the HDO-DOH and the metastable HDO-HOD dimers, respectively. For both isotopomers, the donor-accepter interchange tunneling-state selections rules for the b- and c-type bands are consistent with tunneling pathways corresponding to geared partial internal rotation of the two subunits in double-minima potentials. The larger tunneling splitting in HDO-HOD is primarily the consequence of the smaller effective reduced mass for tunneling in this system compared to that in HDO-DOH. The presence of both b- and c-type K=1←0 bands allows the direct measurement of the largest tunneling splitting, that associated with the internal rotation about the O-H-O or O-D-O bond of the nonbonded proton/deuteron on the proton donating unit. For the K=0 state of HDO-DOH this splitting is 214 208.38(23) MHz, while for the K=0 state of HDO-HOD it is 117 440.97(17) MHz. A strong b-type Coriolis interaction is observed between the upper K=0 and lower K=1 states in HDO-DOH, similar to that observed previously in (H2O)2.

  14. 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.

  15. 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

  16. Thermally activated delayed fluorescence evidence in non-bonding transition electron donor-acceptor molecules

    NASA Astrophysics Data System (ADS)

    Marghad, Ikbal; Clochard, M. C.; Ollier, N.; Wade, Travis L.; Aymes-Chodur, C.; Renaud, C.; Zissis, G.

    2015-09-01

    The exhibition of thermally activated delayed fluorescence on triazine derivative by the introduction of a nonbonding part is demonstrated. Two molecules containing triazine core as acceptor and carbazole part as donor has been synthesized and characterized. One of these molecules bears an additional nonbonding part by the means of a phenoxy group. The results indicated that the molecule bearing the nonbonding molecular part (phenoxy) exhibit thermally activated delayed fluorescence while not on molecule free of non-bonding group. The results are supported by, photoluminescence, spectral analysis time-resolved fluorescence and time-dependent density functional estimation

  17. Triflic Acid-Catalyzed Cycloisomerization Reactions of Donor-Acceptor Cyclopropanes: Access to Alkyl 5-Arylfuran-2-carboxylates.

    PubMed

    Zhu, Yuequan; Xu, Panpan; Gong, Yuefa

    2016-06-01

    A direct synthetic strategy starting from alkyl 1-alkoxy-2-aroylcyclopropanecarboxylates was developed for the construction of alkyl 5-arylfuran-2-carboxylates. These donor-acceptor cyclopropanes smoothly undergo a simple ring-opening reaction or/and cycloisomerization reaction in the presence of acid at room temperature, which greatly depends on the properties of the acid used in the experiment. Alkyl 5-arylfuran-2-carboxylates were afforded in high yields in triflic acid, whereas alkyl 2,5-dioxo-5-phenylpentanoate became the major product in other protic acids and Lewis acids. PMID:27156857

  18. 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

  19. New organic donor-acceptor-π-acceptor sensitizers for efficient dye-sensitized solar cells and photocatalytic hydrogen evolution under visible-light irradiation.

    PubMed

    Li, Xing; Cui, Shicong; Wang, Dan; Zhou, Ying; Zhou, Hao; Hu, Yue; Liu, Jin-Gang; Long, Yitao; Wu, Wenjun; Hua, Jianli; Tian, He

    2014-10-01

    Two organic donor-acceptor-π-acceptor (D-A-π-A) sensitizers (AQ and AP), containing quinoxaline/pyrido[3,4-b]pyrazine as the auxiliary acceptor, have been. Through fine-tuning of the auxiliary acceptor, a higher designed and synthesized photoelectric conversion efficiency of 6.02% for the AQ-based dye-sensitized solar cells under standard global AM1.5 solar conditions was achieved. Also, it was found that AQ-Pt/TiO2 photocatalysts displayed a better rate of H2 evolution under visible-light irradiation (420 nm<λ<780 nm) because of the stability of the oxidized states and the lower rates of electron recombination. Importantly, sensitizers AQ and AP-Pt/TiO2 showed strong photocatalytic activity during continuous light soaking for 10 h with methanol as the sacrificial electron donor. Additionally, the processes of their intermolecular electron transfer were further investigated theoretically by using time-dependent DFT. The calculated results indicate that the auxiliary acceptor plays the role of an electron trap and results in broad spectral responses. PMID:25154958

  20. Acceptor and Excitation Density Dependence of the Ultrafast Polaron Absorption Signal in Donor-Acceptor Organic Solar Cell Blends.

    PubMed

    Zarrabi, Nasim; Burn, Paul L; Meredith, Paul; Shaw, Paul E

    2016-07-21

    Transient absorption spectroscopy on organic semiconductor blends for solar cells typically shows efficient charge generation within ∼100 fs, accounting for the majority of the charge carriers. In this Letter, we show using transient absorption spectroscopy on blends containing a broad range of acceptor content (0.01-50% by weight) that the rise of the polaron signal is dependent on the acceptor concentration. For low acceptor content (<10% by weight), the polaron signal rises gradually over ∼1 ps with most polarons generated after 200 fs, while for higher acceptor concentrations (>10%) most polarons are generated within 200 fs. The rise time in blends with low acceptor content was also found to be sensitive to the pump fluence, decreasing with increasing excitation density. These results indicate that the sub-100 fs rise of the polaron signal is a natural consequence of both the high acceptor concentrations in many donor-acceptor blends and the high excitation densities needed for transient absorption spectroscopy, which results in a short average distance between the exciton and the donor-acceptor interface. PMID:27355877

  1. 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. PMID:25917246

  2. 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.

  3. 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

  4. 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}.

  5. Light-triggered assembly-disassembly of an ordered donor-acceptor π-stack using a photoresponsive dimethyldihydropyrene π-switch.

    PubMed

    Krishna, V Siva Rama; Samanta, Mousumi; Pal, Suman; Anurag, N P; Bandyopadhyay, Subhajit

    2016-06-28

    Self-organization of donor and acceptor π-systems forms alternate D-A stacks of the donor and acceptor molecules. Using a photochromic π-switch as a donor and an electron deficient acceptor dye such stacks were formed. Photomodulation of the donor unit with visible light led to a photoisomerized state having a non-planar structure with reduced donor ability, thereby causing destruction of the alternate D-A π-stacks. The formation and destruction of the stacks were studied by various spectroscopy methods. Both the stacks and the depleted stacks were studied by DLS and SEM experiments. The regeneration of the stacks occurred in solution with the reversal of the photoisomerization process with ultraviolet light. Computational and differential scanning calorimetric studies validated the thermodynamics of the formation of the stacks. This work presents a reversible assembly-disassembly of a donor-acceptor π system devoid of additional auxiliary non-covalent bonding motifs in the donor and acceptor molecules. PMID:26899505

  6. Controlled energy transfer between isolated donor-acceptor molecules intercalated in thermally self-ensemble two-dimensional hydrogen bonding cages

    NASA Astrophysics Data System (ADS)

    Al Attar, Hameed A.; Monkman, Andrew P.

    2012-12-01

    Thermally assembled hydrogen bonding cages which are neither size nor guest specific have been developed using a poly (vinyl alcohol) (PVA) host. A water-soluble conjugated polymer poly(2,5-bis(3-sulfonatopropoxy)-1,4-phenylene, disodium salt-alt-1,4-phenylene) (PPP-OPSO3) as a donor and tris(2,2-bipyridyl)- ruthenium(II) [Ru(bpy)32+] as an acceptor have been isolated and trapped in such a PVA matrix network. This is a unique system that shows negligible exciton diffusion and the donor and acceptor predominantly interact by a direct single step excitation transfer process (DSSET). Singlet and triplet exciton quenching have been studied. Time-resolved fluorescence lifetime measurement at different acceptor concentrations has enabled us to determine the dimensionality of the energy-transfer process within the PVA scaffold. Our results reveal that the PVA hydrogen bonding network effectively isolates the donor-acceptor molecules in a two-dimensional layer structure (lamella) leading to the condition where a precise control of the energy and charge transfer is possible.

  7. 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.

  8. The Dependence of Donor:Acceptor Ratio on the Photovoltaic Performances of Blended poly (3-octylthiophene-2,5-diyl) and (6,6)-phenyl C71 butyric acid methyl ester Bulk Heterojunction Organic Solar Cells

    NASA Astrophysics Data System (ADS)

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

    2010-10-01

    Bulk heterojunction organic solar cells using blended poly (3-octylthiophene-2,5-diyl)(P3OT) and (6,6)-phenyl C71 butyric acid methyl ester (PC71BM) have been fabricated. P3OT and PC71BM 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.

  9. Uniaxially oriented polycrystalline thin films and air-stable n-type transistors based on donor-acceptor semiconductor (diC8BTBT)(FnTCNQ) [n = 0, 2, 4

    NASA Astrophysics Data System (ADS)

    Shibata, Yosei; Tsutsumi, Jun'ya; Matsuoka, Satoshi; Matsubara, Koji; Yoshida, Yuji; Chikamatsu, Masayuki; Hasegawa, Tatsuo

    2015-04-01

    We report the fabrication of high quality thin films for semiconducting organic donor-acceptor charge-transfer (CT) compounds, (diC8BTBT)(FnTCNQ) (diC8BTBT = 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene and FnTCNQ [n = 0,2,4] = fluorinated derivatives of 7,7,8,8,-tetracyanoquinodimethane), which have a high degree of layered crystallinity. Single-phase and uniaxially oriented polycrystalline thin films of the compounds were obtained by co-evaporation of the component donor and acceptor molecules. Organic thin-film transistors (OTFTs) fabricated with the compound films exhibited n-type field-effect characteristics, showing a mobility of 6.9 × 10-2 cm2/V s, an on/off ratio of 106, a sub-threshold swing of 0.8 V/dec, and an excellent stability in air. We discuss the suitability of strong intermolecular donor-acceptor interaction and the narrow CT gap nature in compounds for stable n-type OTFT operation.

  10. 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.

  11. Donor-Acceptor-Donor Thienopyrazines via Pd-Catalyzed C-H Activation as NIR Fluorescent Materials.

    PubMed

    McNamara, Louis E; Liyanage, Nalaka; Peddapuram, Adithya; Murphy, J Scott; Delcamp, Jared H; Hammer, Nathan I

    2016-01-01

    A series of thienopyrazine-based donor-acceptor-donor (D-A-D) near-infrared (NIR) fluorescent compounds were synthesized through a rapid, palladium-catalyzed C-H activation route. The dyes were studied through computational analysis, electrochemical properties analysis, and characterization of their photophysical properties. Large Stokes shifts of approximately 175 nm were observed, which led to near-infrared emission. Computational evaluation shows that the origin of this large Stokes shift is a significant molecular reorganization particularly about the D-A bond. The series exhibits quantum yields of up to φ = >4%, with emission maxima ranging from 725 to 820 nm. The emission is strong in solution, in thin films, and also in isolation at the single-molecule level. Their stable emission at the single-molecule level makes these compounds good candidates for single-molecule photon sources in the near-infrared. PMID:26599501

  12. 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

  13. 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

  14. The interplay of thermally activated delayed fluorescence (TADF) and room temperature organic phosphorescence in sterically-constrained donor-acceptor charge-transfer molecules.

    PubMed

    Ward, Jonathan S; Nobuyasu, Roberto S; Batsanov, Andrei S; Data, Przemyslaw; Monkman, Andrew P; Dias, Fernando B; Bryce, Martin R

    2016-02-11

    A series of phenothiazine-dibenzothiophene-S,S-dioxide charge-transfer molecules have been synthesized. Increasing steric restriction around the donor-acceptor bond significantly alters contributions from TADF and phosphorescence. Bulky substituents on the 1-(and 9) position(s) of the phenothiazine result in no TADF in the solid state; instead strong phosphorescence is observed at ambient temperature. PMID:26750426

  15. 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.

  16. Unified electronic charge transport model for organic solar cells

    NASA Astrophysics Data System (ADS)

    Mottaghian, Seyyed Sadegh; Biesecker, Matt; Bayat, Khadijeh; Farrokh Baroughi, Mahdi

    2013-07-01

    This paper provides a comprehensive modeling approach for simulation of electronic charge transport in excitonic solar cells with organic and organic/inorganic structures. Interaction of energy carrying particles (electrons, holes, singlet excitons, and triplet excitons) with each other and their transformation in the bulk of the donor and acceptor media as well as the donor/acceptor interfaces are incorporated in form of coupling matrices into the continuity equations and interface boundary conditions. As a case study, the model is applied to simulate an organic bilayer photovoltaic (PV) device to quantify the effects of photo generation, recombination coefficient, carrier mobility, and electrode work function on its PV characteristics. The study proves that electron-hole recombination at the donor/acceptor interface is the dominant mechanism that limits open circuit voltage of the device.

  17. 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.

  18. 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

  19. Modulation of Intracellular Quantum Dot to Fluorescent Protein Förster Resonance Energy Transfer via Customized Ligands and Spatial Control of Donor-Acceptor Assembly.

    PubMed

    Field, Lauren D; Walper, Scott A; Susumu, Kimihiro; Oh, Eunkeu; Medintz, Igor L; Delehanty, James B

    2015-01-01

    Understanding how to controllably modulate the efficiency of energy transfer in Förster resonance energy transfer (FRET)-based assemblies is critical to their implementation as sensing modalities. This is particularly true for sensing assemblies that are to be used as the basis for real time intracellular sensing of intracellular processes and events. We use a quantum dot (QD) donor -mCherry acceptor platform that is engineered to self-assemble in situ wherein the protein acceptor is expressed via transient transfection and the QD donor is microinjected into the cell. QD-protein assembly is driven by metal-affinity interactions where a terminal polyhistidine tag on the protein binds to the QD surface. Using this system, we show the ability to modulate the efficiency of the donor-acceptor energy transfer process by controllably altering either the ligand coating on the QD surface or the precise location where the QD-protein assembly process occurs. Intracellularly, a short, zwitterionic ligand mediates more efficient FRET relative to longer ligand species that are based on the solubilizing polymer, poly(ethylene glycol). We further show that a greater FRET efficiency is achieved when the QD-protein assembly occurs free in the cytosol compared to when the mCherry acceptor is expressed tethered to the inner leaflet of the plasma membrane. In the latter case, the lower FRET efficiency is likely attributable to a lower expression level of the mCherry acceptor at the membrane combined with steric hindrance. Our work points to some of the design considerations that one must be mindful of when developing FRET-based sensing schemes for use in intracellular sensing. PMID:26690153

  20. Charge separation and photovoltaic conversion in polymer composites with internal donor/acceptor heterojunctions

    SciTech Connect

    Yu, G.; Heeger, A.J.

    1995-10-01

    The photosensitivity of semiconducting polymers can be enhanced by blending donor and acceptor polymers to optimize photoinduced charge separation. We describe a novel phase-separated polymer blend (composite) made with poly[2-methoxy-5-(2{prime}-ethyl-hexyloxy)-1,4-phenylene vinylene], MEH-PPV, as donor and cyano-PPV, CN-PPV, as acceptor. The photoluminescence and electroluminescence of both component polymers are quenched in the blend, indicative of rapid and efficient separation of photogenerated electron-hole pairs with electrons on the acceptor and holes on the donor. Diodes made with such a composite semiconducting polymer as the photosensitive medium show promising photovoltaic characteristics with carrier collection efficiency of 5% electrons/photon and energy conversion efficiency of 0.9%, {similar_to}20 times larger than in diodes made with pure MEH-PPV and {similar_to}100 times larger than in diodes made with CN-PPV. The photosensitivity and the quantum yield increase with reverse bias voltage, to 0.3 A/W and 80% electrons/photon respectively at {minus}10 V, comparable to results obtained from photodiodes made with inorganic semiconductors. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

  1. 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

  2. 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.

  3. 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

  4. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

    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.

  6. Light-Induced Charge Separation in Densely Packed Donor-Acceptor Coordination Cages.

    PubMed

    Frank, Marina; Ahrens, Jennifer; Bejenke, Isabel; Krick, Marcel; Schwarzer, Dirk; Clever, Guido H

    2016-07-01

    Photon-powered charge separation is achieved in a supramolecular architecture based on the dense packing of functional building blocks. Therefore, self-assembled dimers of interpenetrated coordination cages consisting of redoxactive chromophors were synthesized in a single assembly step starting from easily accessible ligands and Pd(II) cations. Two backbones consisting of electron rich phenothiazine (PTZ) and electron deficient anthraquinone (ANQ) were used to assemble either homo-octameric or mixed-ligand double cages. The electrochemical and spectroscopic properties of the pure cages, mixtures of donor and acceptor cages and the mixed-ligand cages were compared by steady-state UV-vis and transient absorption spectroscopy, supported by cyclic voltammetry and spectroelectrochemistry. Only the mixed-ligand cages, allowing close intra-assembly communication between the donors and acceptors, showed the evolution of characteristic PTZ radical cation and ANQ radical anion features upon excitation in the transient spectra. In contrast, excitation of the mixtures of the homo-octameric donor and acceptor cages in solution did not lead to any signs of electron transfer. Densely packed photo- and redox-functional self-assemblies promise molecular-level control over the morphology of the charge separation layer in future photovoltaic applications. PMID:27258549

  7. 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.

  8. 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.

  9. 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

  10. 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

  11. Highly efficient donor-acceptor hydrazone dyes-inorganic Si/TiO₂ hybrid solar cells.

    PubMed

    Al-Sehemi, Abdullah G; Irfan, Ahmad; Al-Melfi, Mohrah Abdullah M

    2015-06-15

    We have synthesized the two donor-bridge-acceptor organic dyes (hydrazone dye 1 (HD1) and hydrazone dye 2 (HD2)) with the aim to enhance intra-molecular charge transfer then characterized by FTIR and NMR. The ground state geometries have been optimized at three different levels of theories, i.e., B3LYP/6-31G, B3LYP/6-31G and Hartee-Fock HF/6-31G. The absorption spectra and oscillator strengths in different solvents have been computed and compared with the experimental data. The vibrational spectral assignments have been performed on the recorded FTIR spectra based on the theoretical predicted wavenumbers at three different levels of theories. The effect of different solvents (CHCl3, CH3CN and C2H5OH) has been studied on the absorption wavelengths. Furthermore, we have computed the ionization potentials, electron affinities and reorganization energies of studied compounds and shed light on the charge transport properties. The hetero-junction solar cell devices were fabricated by organic-inorganic hetero-junction (Si/TiO2/dye) then the efficiency has been measured by applying the incident power 30, 50 and 70 mW/cm(2). The maximum efficiency 3.12% has been observed for HD1. PMID:25766477

  12. Synthesis and investigation of intra-molecular charge transfer state properties of novel donor-acceptor-donor pyridine derivatives: the effects of temperature and environment on molecular configurations and the origin of delayed fluorescence.

    PubMed

    Aydemir, Murat; Haykır, Gülçin; Türksoy, Figen; Gümüş, Selçuk; Dias, Fernando B; Monkman, Andy P

    2015-10-14

    A novel series of donor-acceptor-donor (D-A-D) structured pyridine derivatives were synthesised and detailed photo-physical investigations were made using mainly steady-state and time-resolved spectroscopy techniques at varying temperatures. The investigations showed that the molecules have solvent polarity and temperature dependent excited-state configurations, confirmed in two different polarity solvents (295-90 K), i.e. methyl cyclohexane (MCH) and 2-methyltetrahdrofurane (2-MeTHF). In MCH, the investigations revealed dual fluorescence over the temperature range of 295-90 K. At 295 K, the ground-state configuration of the molecules has a partially twisted geometry as determined by DFT calculation, yet the emission originates totally from a locally excited (LE) state, however once the temperature is lowered to 90 K, the twisted molecular configuration is stabilised, and the emission originates from a fully-relaxed intramolecular charge transfer state (ICT), this is contrary to the systems where structural reorganisation stabilises ICT and this is frozen out at low temperatures. The DFT calculations revealed different ground state molecular configurations due to the presence of different electron-donating groups, e.g. the molecule including anthracene groups has a near 90° twisted geometry whereas the triphenylamine including molecule has a pyramidal geometrical folding, therefore, the decrease in temperature restricts the donor degree of rotational freedom. In 2-MeTHF solution, the fluorescence spectrum of both molecules is always of ICT character, but gradually red-shifts through the fluid to glass transition temperature (∼135 K), in this case, the fluorescence occurs after structural and solvent-shell relaxations, however, upon cooling below 135 K, the spectra dramatically shift back to blue giving rise to strong emission from an ICT excited-state (but not the LE state) where the molecules have unrelaxed geometries. This significant change in the nature of

  13. Donor-acceptor small molecules for organic photovoltaics: single-atom substitution (Se or S).

    PubMed

    He, Xiaoming; Cao, Bing; Hauger, Tate C; Kang, Minkyu; Gusarov, Sergey; Luber, Erik J; Buriak, Jillian M

    2015-04-22

    Two isostructural low-band-gap small molecules that contain a one-atom substitution, S for Se, were designed and synthesized. The molecule 7,7'-[4,8-bis(2-ethylhexyloxy)benzo[1,2-b:4,5-b']dithiophene]bis[6-fluoro-4-(5'-hexyl-2,2'-bithiophen-5-yl)benzo[c][1,2,5]thiadiazole] (1) and its selenium analogue 7,7'-[4,8-bis(2-ethylhexyloxy)benzo[1,2-b:4,5-b']dithiophene]bis[6-fluoro-4-(5'-hexyl-2,2'-bithiophen-5-yl)benzo[c][1,2,5]selenodiazole] (2) are both based on the electron-rich central unit benzo[1,2-b:4,5-b']dithiophene. The aim of this work was to investigate the effect of one-atom substitution on the optoelectronic properties and photovoltaic performance of devices. Theoretical calculations revealed that this one-atom variation has a small but measurable effect on the energy of frontier molecular orbital (HOMO and LUMO), which, in turn, can affect the absorption profile of the molecules, both neat and when mixed in a bulk heterojunction (BHJ) with PC71BM. The Se-containing variant 2 led to higher efficiencies [highest power conversion efficiency (PCE) of 2.6%] in a standard organic photovoltaic architecture, when combined with PC71BM after a brief thermal annealing, than the S-containing molecule 1 (highest PCE of 1.0%). Studies of the resulting morphologies of BHJs based on 1 and 2 showed that one-atom substitution could engender important differences in the solubilities, which then influenced the crystal orientations of the small molecules within this thin layer. Brief thermal annealing resulted in rotation of the crystalline grains of both molecules to more energetically favorable configurations. PMID:25808481

  14. 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

  15. Interchain electron-electron scattering in a one-dimensional charge-transfer conductor

    SciTech Connect

    Lyo, S.K.

    1982-02-15

    The contribution of donor-acceptor interchain electron-electron scattering to the dc resistivity is calculated for one-dimensional charge-transfer metallic conductors. The interchain electron-electron interaction is due to Coulombic or phonon-exchange interactions. The resistivity arises from U processes when the relative signs of the slopes of the donor and acceptor bands are the same and from N processes when they are opposite. The results predict an upper bound for the strength of interchain and possibly on-site Coulomb interactions. Application of the model to TTF-TCNQ (tetrathiafulvalenium tetracyanoquinodimethanide) is discussed.

  16. 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.

  17. Photophysics and Nonlinear Absorption of Gold(I) and Platinum(II) Donor-Acceptor-Donor Chromophores.

    PubMed

    Goswami, Subhadip; Winkel, Russell W; Schanze, Kirk S

    2015-10-19

    A series of Au(I) and Pt(II) acetylide complexes of a π-conjugated donor-acceptor-donor (D-A-D) chromophore were studied to develop quantitative structure-property relationships for their photophysical and nonlinear optical properties. The D-A-D chromophore consists of a "TBT" unit, where T = 3-hexyl-2,5-thienylene and BTD = 2,1,3-benzothiadiazole, capped with ethynylene groups. The D-A-D chromophore is functionalized with Au(I)PR3 (R = -Me and -Ph) and trans-Pt(II)(PR3)2-CCPh (R = -Me and -Bu) "auxochromes". All of the metal complexes were characterized by ground-state absorption, photoluminescence, nanosecond transient absorption, and two-photon absorption (2PA) spectroscopy. The experiments provided quantitative values of the photophysical parameters, including rates for radiative decay and intersystem crossing (ISC), triplet yields, and two-photon absorption cross sections. Pronounced solvatochromism in the fluorescence spectra suggests an enhanced dipole moment in the excited state of the complexes compared to the unmetalated TBT chromophore. The gold complexes feature larger fluorescence quantum yields and longer emission lifetimes compared to platinum. The Pt(II) complexes exhibit enhanced triplet-triplet absorption, reduced triplet-state lifetimes, and larger singlet oxygen quantum yields, consistent with more efficient ISC compared to the Au(I) complexes. When excited by 100 fs pulses, all of the D-A-D chromophores exhibit moderate two-photon absorption in the near-infrared between 700 and 900 nm. The 2PA cross section for the Au(I) complexes is almost the same as the unmetalated D-A-D chromophore (∼100 GM). The Pt(II) complexes exhibit significantly enhanced 2PA compared to the other chromophores, reaching 1000 GM at 750 nm. Taken together, the results indicate that the Pt(II) center is considerably more effective in inducing singlet-triplet ISC and in enhancing the 2PA cross section. This result reveals the greater promise for Pt(II) acetylides in

  18. 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

  19. Experimental Demonstration of the Dependence of the First Hyperpolarizability of Donor-Acceptor Substituted Polyenes on the Ground-State Polarization and Bond Length Alternation

    NASA Technical Reports Server (NTRS)

    Bourhill, G.; Bredas, J-L.; Cheng, L-T.; Marder, S. R.; Meyers, F.; Perry, J. W.; Tiemann, B. G.

    1993-01-01

    The dependence of the product of the first hyperpolarizability, beta, and the ground-state dipole moment, mu, for a series of donor-acceptor polyenes with a large range of ground-state polarization, was measured in a variety of solvents by electric field induced second harmonic generation. The observed behavior of mu times beta as a function of ground-state polarization agrees well with theoretical predictions. In particular, as a function of increasing polarization, mu times beta was found to first increase, peak in a positive sense, decrease, pass through zero, become large and negative, and eventually peak in a negative sense.

  20. Ag(I)-Catalyzed Indolization/C3-Functionalization Cascade of 2-Ethynylanilines via Ring Opening of Donor-Acceptor Cyclopropanes.

    PubMed

    Karmakar, Raju; Suneja, Arun; Singh, Vinod K

    2016-06-01

    A AgSbF6-catalyzed cascade involving the ring opening of donor-acceptor cyclopropanes (DACs) preceded by the cyclization of N-protected 2-ethynylaniline is described. The method discloses a step-economy route to 2,3-disubstituted indole, where a Ag catalyst is found to trigger the cascade by activating both alkyne and DACs. Various functionalities at different ends of both substrates offer rapid access to 2,3-disubstituted indole derivatives in one pot in good to excellent yields. Elaboration of the cascade product to useful intermediates is also depicted. PMID:27186903

  1. 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).

  2. Electron tunneling through covalent and noncovalent pathways in proteins

    NASA Technical Reports Server (NTRS)

    Beratan, David N.; Onuchic, Jose Nelson; Hopfield, J. J.

    1987-01-01

    A model is presented for electron tunneling in proteins which allows the donor-acceptor interaction to be mediated by the covalent bonds between amino acids and noncovalent contacts between amino acid chains. The important tunneling pathways are predicted to include mostly bonded groups with less favorable nonbonded interactions being important when the through bond pathway is prohibitively long. In some cases, vibrational motion of nonbonded groups along the tunneling pathway strongly influences the temperature dependence of the rate. Quantitative estimates for the sizes of these noncovalent interactions are made and their role in protein mediated electron transport is discussed.

  3. Molecular Engineering of Pyrido[3,4-b]pyrazine-Based Donor-Acceptor-π-Acceptor Organic Sensitizers: Effect of Auxiliary Acceptor in Cobalt- and Iodine-Based Electrolytes.

    PubMed

    Liu, Bo; Giordano, Fabrizio; Pei, Kai; Decoppet, Jean-David; Zhu, Wei-Hong; Zakeeruddin, Shaik M; Grätzel, Michael

    2015-12-14

    Due to the ease of tuning its redox potential, the cobalt-based redox couple has been extensively applied for highly efficient dye-sensitized solar cells (DSSCs) with extraordinarily high photovoltages. However, a cobalt electrolyte needs particular structural changes in the organic dye components to obtain such high photovoltages. To achieve high device performance, specific requirements in the molecular tailoring of organic sensitizers still need to be met. Besides the need for large electron donors, studies of the auxiliary acceptor segment of donor-acceptor-π-acceptor (D-A-π-A) organic sensitizers are still rare in molecular optimization in the context of cobalt electrolytes. In this work, two novel organic D-A-π-A-type sensitizers (IQ13 and IQ17) have been developed and exploited in cobalt- and iodine-based redox electrolyte DSSCs, specifically to provide insight into the effect of π-bridge modification in different electrolytes. The investigation has been focused on the additional electron-withdrawing acceptor capability with grafted long alkoxy chains. Optoelectronic transient measurements have indicated that IQ17 containing a pyrido[3,4-b]pyrazine moiety bearing long alkoxyphenyl chains is more suitable for application in cobalt-based DSSCs. PMID:26548926

  4. 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

  5. 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

  6. Synthesis and photophysics of a 2,7-disubstituted donor-acceptor pyrene derivative: an example of the application of sequential Ir-catalyzed C-H borylation and substitution chemistry.

    PubMed

    Ji, Lei; Lorbach, Andreas; Edkins, Robert M; Marder, Todd B

    2015-06-01

    We report a general and selective method to synthesize 2,7-disubstituted pyrene derivatives containing two different substituents by sequential Ir-catalyzed borylation and substitution chemistry. To demonstrate the utility of our approach, we synthesized 2-cyano-7-(N,N-diethylamino)pyrene (3), a pyrene analogue of the widely studied chromophore 4-(N,N-dimethylamino)benzonitrile (DMABN). Compound 3 and the monosubstituted compounds 2-(N,N-diethylamino)pyrene (1) and 2-cyanopyrene (2) have been structurally characterized. Their electronic and optical properties have been studied by a combination of absorption and emission spectroscopies, lifetime and quantum yield measurements, and modeling by DFT and TD-DFT. The photophysical properties of 3 are compared to those of DMABN and 2-cyano-7-(N,N-dimethylamino)-4,5,9,10-tetrahydropyrene, and we show that 2,7-disubstituted pyrene is a moderately effective π-bridge for the construction of donor-acceptor compounds. It is also shown that donor or acceptor groups are only effective at the 2,7-positions of pyrene if they are suitably strong, leading to a switch in the energetic ordering of the HOMO-1 and HOMO or the LUMO and LUMO+1 of pyrene, respectively. PMID:25927248

  7. Photon upconversion in supramolecular gel matrixes: spontaneous accumulation of light-harvesting donor-acceptor arrays in nanofibers and acquired air stability.

    PubMed

    Duan, Pengfei; Yanai, Nobuhiro; Nagatomi, Hisanori; Kimizuka, Nobuo

    2015-02-11

    Efficient triplet-triplet annihilation (TTA)-based photon upconversion (UC) is achieved in supramolecular organogel matrixes. Intense UC emission was observed from donor (sensitizer)-acceptor (emitter) pairs in organogels even under air-saturated condition, which solved a major problem: deactivation of excited triplet states and TTA-UC by molecular oxygen. These unique TTA-UC molecular systems were formed by spontaneous accumulation of donor and acceptor molecules in the gel nanofibers which are stabilized by developed hydrogen bond networks. These molecules preorganized in nanofibers showed efficient transfer and migration of triplet energy, as revealed by a series of spectroscopic, microscopic, and rheological characterizations. Surprisingly, the donor and acceptor molecules incorporated in nanofibers are significantly protected from the quenching action of dissolved molecular oxygen, indicating very low solubility of oxygen to nanofibers. In addition, efficient TTA-UC is achieved even under excitation power lower than the solar irradiance. These observations clearly unveil the adaptive feature of host gel nanofiber networks that allows efficient and cooperative inclusion of donor-acceptor molecules while maintaining their structural integrity. As evidence, thermally induced reversible assembly/disassembly of supramolecular gel networks lead to reversible modulation of the UC emission intensity. Moreover, the air-stable TTA-UC in supramolecular gel nanofibers was generally observed for a wide combination of donor-acceptor pairs which enabled near IR-to-yellow, red-to-cyan, green-to-blue, and blue-to-UV wavelength conversions. These findings provide a new perspective of air-stable TTA-UC molecular systems; spontaneous and adaptive accumulation of donor and acceptor molecules in oxygen-blocking, self-assembled nanomatrixes. The oxygen-barrier property of l-glutamate-derived organogel nanofibers has been unveiled for the first time, which could find many

  8. 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.

  9. 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

  10. 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

  11. Unveiling NO2π···Cdbnd C π-hole interactions: A combined computational and crystallographic study

    NASA Astrophysics Data System (ADS)

    Bauzá, Antonio; Frontera, Antonio

    2015-07-01

    A series of π-hole complexes involving the NO2 group and several isolated π systems have been evaluated at the BP86-D3/def2-TZVP level of theory. We have used ethene, ethyne and but-2-yne as electron donor moieties and nitrobenzene and 1,2,3,4,5-pentafluoro-6-nitrobenzene as electron acceptors. The SAPT and NBO analyses show that the dispersion term is the major contributor to the binding while π(Csbnd C) → π*(Csbnd N) donor-acceptor interactions also contribute to the overall stabilization. Finally several experimental examples were retrieved from the CSD highlighting the importance of this interaction.

  12. 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

  13. Electron: Cluster interactions

    SciTech Connect

    Scheidemann, A.A.; Kresin, V.V.; Knight, W.D.

    1994-02-01

    Beam depletion spectroscopy has been used to measure absolute total inelastic electron-sodium cluster collision cross sections in the energy range from E {approximately} 0.1 to E {approximately} 6 eV. The investigation focused on the closed shell clusters Na{sub 8}, Na{sub 20}, Na{sub 40}. The measured cross sections show an increase for the lowest collision energies where electron attachment is the primary scattering channel. The electron attachment cross section can be understood in terms of Langevin scattering, connecting this measurement with the polarizability of the cluster. For energies above the dissociation energy the measured electron-cluster cross section is energy independent, thus defining an electron-cluster interaction range. This interaction range increases with the cluster size.

  14. A p-Type Quantum Dot/Organic Donor:Acceptor Solar-Cell Structure for Extended Spectral Response

    SciTech Connect

    Chen, Hsiang-Yu; Hou, Jianhui; Dayal, Smita; Huo, Lijun; Kopidakis, Nikos; Beard, Matthew C.; Luther, Joseph M.

    2011-06-21

    A coupled PbS quantum dot film and a PSBTBT:PCBM bulk heterojunction layer contribute comparable photocurrent in a new stacked solar-cell architecture with sensitivity in the near infrared and an efficiency >4%. With a focus on the energy level alignment between components, time-resolved microwave photoconductivity is used to elucidate the charge transport pathways for electrons and holes.

  15. 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

  16. Aggregation-Induced Delayed Fluorescence Based on Donor/Acceptor-Tethered Janus Carborane Triads: Unique Photophysical Properties of Nondoped OLEDs.

    PubMed

    Furue, Ryuhei; Nishimoto, Takuro; Park, In Seob; Lee, Jiyoung; Yasuda, Takuma

    2016-06-13

    Luminescent materials consisting of boron clusters, such as carboranes, have attracted immense interest in recent years. In this study, luminescent organic-inorganic conjugated systems based on o-carboranes directly bonded to electron-donating and electron-accepting π-conjugated units were elaborated as novel optoelectronic materials. These o-carborane derivatives simultaneously possessed aggregation-induced emission (AIE) and thermally activated delayed fluorescence (TADF) capabilities, and showed strong yellow-to-red emissions with high photoluminescence quantum efficiencies of up to 97 % in their aggregated states or in solid neat films. Organic light-emitting diodes utilizing these o-carborane derivatives as a nondoped emission layer exhibited maximum external electroluminescence quantum efficiencies as high as 11 %, originating from TADF. PMID:27145481

  17. A donor-acceptor triptycene-coumarin hybrid dye featuring a charge separated excited state and AIE properties.

    PubMed

    Qian, Rui; Tong, Hongjuan; Huang, Cui; Li, Junhao; Tang, Yun; Wang, Rui; Lou, Kaiyan; Wang, Wei

    2016-06-14

    A triptycene-coumarin hybrid dye DCT-1 with a 1,4-dimethoxybenzene group as the electron donor and a coumarin fluorophore as the acceptor on the separated fins of a triptycene was synthesized. DCT-1 features a charge separated excited state with emissions sensitive to solvent polarities. Moreover, DCT-1 also exhibits aggregation-induced emission properties in water with excellent photostability and pH-stability for potential cell imaging applications. PMID:27186970

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

    PubMed

    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. PMID:27258685

  19. Highly efficient donor-acceptor hydrazone dyes-inorganic Si/TiO2 hybrid solar cells

    NASA Astrophysics Data System (ADS)

    Al-Sehemi, Abdullah G.; Irfan, Ahmad; Al-Melfi, Mohrah Abdullah M.

    2015-06-01

    We have synthesized the two donor-bridge-acceptor organic dyes (hydrazone dye 1 (HD1) and hydrazone dye 2 (HD2)) with the aim to enhance intra-molecular charge transfer then characterized by FTIR and NMR. The ground state geometries have been optimized at three different levels of theories, i.e., B3LYP/6-31G∗, B3LYP/6-31G∗∗ and Hartee-Fock HF/6-31G∗∗. The absorption spectra and oscillator strengths in different solvents have been computed and compared with the experimental data. The vibrational spectral assignments have been performed on the recorded FTIR spectra based on the theoretical predicted wavenumbers at three different levels of theories. The effect of different solvents (CHCl3, CH3CN and C2H5OH) has been studied on the absorption wavelengths. Furthermore, we have computed the ionization potentials, electron affinities and reorganization energies of studied compounds and shed light on the charge transport properties. The hetero-junction solar cell devices were fabricated by organic-inorganic hetero-junction (Si/TiO2/dye) then the efficiency has been measured by applying the incident power 30, 50 and 70 mW/cm2. The maximum efficiency 3.12% has been observed for HD1.

  20. Electronically Enhanced Classroom Interaction.

    ERIC Educational Resources Information Center

    Draper, Stephen; Cargill, Julie; Cutts, Quintin

    A design rationale for introducing electronic equipment (a group response system) for student interaction in lecture theaters is presented, linking the instructional design to theory. The effectiveness of the equipment for learning depends mostly on what pedagogic method is employed. Various alternative types are introduced, including: assessment;…

  1. Effect of Donor-Acceptor Coupling on TICT Dynamics in the Excited States of Two Dimethylamine Substituted Chalcones.

    PubMed

    Ghosh, Rajib; Palit, Dipak K

    2015-11-12

    Significant effect of coupling between the electron donor and acceptor groups in intramolecular charge transfer (ICT) dynamics has been demonstrated by comparing the photophysical properties of two isomeric N,N-dimethylaminochalcone derivatives (namely, DMAC-A and DMAC-B). In the case of the DMAC-B molecule, the distance between the donor (N,N-dimethylaniline or DMA) and the acceptor (carbonyl) groups is larger by one ethylene unit as compared to that in the case of DMAC-A. The excited singlet (S1) states of both the isomers have strong ICT character but their photophysical properties are remarkably different. In polar solvents, fluorescence quantum yields (and the lifetimes of the S1 state) of DMAC-A are more than 2 orders of magnitude lower (and shorter) than those of DMAC-B. Remarkable differences in the photophysical properties of these two isomers arise due to occurrence of the ultrafast twisting of the DMA group (or the TICT process) during the course of deactivation of the S1 state of the DMAC-A molecule, but not in the case of DMAC-B. In the later case, because of the presence of a large energy barrier along the twisting coordinate(s), TICT is not a feasible process, and hence, the S1 state of DMAC-B has the planar ICT structure. In the DMAC-A molecule, the strength of coupling between the donor and acceptor groups is relatively stronger because of a shorter distance between these groups. Femtosecond transient absorption spectroscopic measurements and DFT/TDDFT calculations have been adopted to establish the above aspects of the relaxation dynamics of the S1 states of these two isomeric chalcones. PMID:26480238

  2. 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

  3. Enhanced near-infrared photoresponse of organic phototransistors based on single-component donor-acceptor conjugated polymer nanowires

    NASA Astrophysics Data System (ADS)

    Zhu, Min; Lv, Shenchen; Wang, Qinghe; Zhang, Guobing; Lu, Hongbo; Qiu, Longzhen

    2016-03-01

    Single-component near-infrared phototransistors based on ambipolar organic semiconductor nanowires have been investigated and compared with their corresponding thin-film counterparts. The nanowire organic phototransistors (NW-OPTs) showed photocurrent/dark-current ratios and photoresponsivities as high as 1.3 × 104 and 440 mA W-1 for the p-type channel, and 3.3 × 104 and 70 mA W-1 for the n-type channel, respectively, upon near-infrared illumination with an intensity of 47.1 mW cm-2. These were much higher values compared to their thin-film counterparts. The enhancement of the near-infrared photoresponse could be attributed to the larger trap density originating from the semiconductor/insulator interface and the semiconductor/air interface. The performance of NW-OPTs was demonstrated to open up new possibilities to improve the near-infrared photoresponse of single-component devices.Single-component near-infrared phototransistors based on ambipolar organic semiconductor nanowires have been investigated and compared with their corresponding thin-film counterparts. The nanowire organic phototransistors (NW-OPTs) showed photocurrent/dark-current ratios and photoresponsivities as high as 1.3 × 104 and 440 mA W-1 for the p-type channel, and 3.3 × 104 and 70 mA W-1 for the n-type channel, respectively, upon near-infrared illumination with an intensity of 47.1 mW cm-2. These were much higher values compared to their thin-film counterparts. The enhancement of the near-infrared photoresponse could be attributed to the larger trap density originating from the semiconductor/insulator interface and the semiconductor/air interface. The performance of NW-OPTs was demonstrated to open up new possibilities to improve the near-infrared photoresponse of single-component devices. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr09003b

  4. Phase transitions and photoinduced transformations at high pressure in the molecular donor-acceptor fullerene complex {Cd(dedtc)2}2 · C60

    NASA Astrophysics Data System (ADS)

    Meletov, K. P.; Konarev, D. V.; Tolstikova, A. O.

    2015-06-01

    The Raman spectra of crystals of C60 fullerene-cadmium diethyldithiocarbamate molecular donor-acceptor complexes {Cd(dedtc)2}2 · C60 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 g (1)- H g (8) phonon modes and by softening of the A g (2) mode of the C60 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 C60 molecules and, probably, the appearance of C120 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/cm2. These changes are manifested by splitting and softening of the A g (2) mode and resemble analogous changes accompanying the photopolymerization of C60 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 g (2) mode splitting under irradiation can be related to the formation of photo-oligomers with various numbers of intermolecular covalent bonds per C60 molecule.

  5. Density functional theory approach to gold-ligand interactions: Separating true effects from artifacts

    SciTech Connect

    Koppen, Jessica V.; Szczęśniak, Małgorzata M.; Hapka, Michał; Modrzejewski, Marcin; Chałasiński, Grzegorz

    2014-06-28

    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 (HAuPH{sub 3}){sub 2} aurophilic complex. Binding energies are computed for Au{sub 4} interacting with the following ligands: SCN{sup −}, benzenethiol, benzenethiolate anion, pyridine, and trimethylphosphine. The results agree for the right reasons with coupled-cluster reference values.

  6. 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.

  7. 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.

  8. Understanding the charge-transfer phenomena between prototypical electron-donors and acceptors: TTF-TCNQ as an example

    NASA Astrophysics Data System (ADS)

    Park, Changwon; Atalla, Viktor; Smith, Sean; Yoon, Mina

    2014-03-01

    It is widely accepted that the charge transfer between the conventional electron donor and acceptor molecules is independent of their relative configurations and electrons are always transferred from the molecule with the lower ionization potential, the electron-donor, to the high electron affinity molecule, the electron-acceptor. Conventional first-principles density functional theory (DFT) supports this conclusion. However, the computational results are dominated by a term in the DFT exchange-correlation functional, which often results in qualitatively and quantitatively wrong conclusion due to an artifact. In our study of prototypical electron donor-acceptor molecules, TTF-TCNQ, we show that the conventional electronic picture is not valid and the relative orientation between TTF and TCNQ is equally important as the electronic structure of the individual molecules. Our results show that the current understanding of the donor-acceptor interaction and charge transfer mechanism has to be modified. This research was conducted at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Office of Basic Energy Sciences, U.S. Department of Energy.

  9. Electron-electron interactions in artificial graphene.

    PubMed

    Räsänen, E; Rozzi, C A; Pittalis, S; Vignale, G

    2012-06-15

    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. PMID:23004308

  10. 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.

  11. 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.

  12. UV-Vis spectral investigation of photophysical properties of a solvatochromic electron donor/acceptor dye within a reverse micelle domain

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

    The optical response of a solvatochromic dye, [(E)-3-(1-methyl-1H-indol-3-yl)-1-phenylprop-2-en-1-one], N1, has been studied in the AOT/n-heptane/water reverse micellar media using steady-state and time-resolved techniques. To this end variation in the photophysical properties of N1 have been systematically studied as a function of water pool size (w0). Micropolarity, microviscosity, and relative permittivity of the immediate microenvironment surrounding the probe has been estimated from the limiting values of the photophysical parameters of N1 at high w0. Information about the location of the dye in the reverse micellar media has been obtained using the observed results.

  13. An ab initio study of specific solvent effects on the electronic coupling element in electron transfer reactions

    NASA Astrophysics Data System (ADS)

    Henderson, Thomas M.; Cave, Robert J.

    1998-11-01

    Specific solvent effects on the electronic coupling element for electron transfer are examined using two model donor-acceptor systems (Zn2+ and Li2+) and several model "solvent" species (He, Ne, H2O, and NH3). The effects are evaluated relative to the given donor-acceptor pair without solvent present. The electronic coupling element (Hab) is found to depend strongly on the identity of the intervening solvent, with He atoms decreasing Hab, whereas H2O and NH3 significantly increase Hab. The distance dependence (essentially exponential decay) is weakly affected by a single intervening solvent atom-molecule. However, when the donor-acceptor distance increases in concert with addition of successively greater numbers of solvent species, the decay with distance of Hab is altered appreciably. Effects due to varying the orientation of molecular solvent are found, somewhat surprisingly, to be quite modest.

  14. 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.

  15. Importance of Chain Connectivity in the Formation of Non-covalent Interactions between Polymers and Single-Walled Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Linton, Dias; Miller, Brad C.; Li, Huimin; Feigerle, Charles; Sumpter, Bobby G.; Dadmun, Mark D.

    2009-03-01

    Our work is focused on understanding and utilizing non-covalent electron donor-acceptor (EDA) interactions between polymers and SWNT to optimize interfacial adhesion and homogeneity of nanocomposites without modifying the SWNT native surface. Nanocomposites with polymer bound electron donating 2-(dimethylamino)ethyl methacrylate or electron accepting acrylonitrile and cyanostyrene moieties leads to improved SWNT dispersion if the interacting functional group is a minor component of a copolymer matrix. Correlation of experimental (Raman mapping, Raman D* band peak shifts, and optical microscopy) and computational results indicates that chain connectivity is critical in controlling the accessibility of the functional groups to form EDA interactions. Thus, controlling the amount of e^- donating or withdrawing moieties throughout the polymer chain will direct the extent of EDA interaction, which enables tuning the SWNT dispersion.

  16. Electron Photon Interaction Cross Sections

    Energy Science and Technology Software Center (ESTSC)

    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

  17. 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).

  18. Solvent dynamical effects in electron transfer: Predicted influences of electronic coupling upon the rate-dielectric friction dependence

    NASA Astrophysics Data System (ADS)

    Gochev, Alexander; McManis, George E.; Weaver, Michael J.

    1989-07-01

    The predicted dependence of the bimolecular rate constant for outer-sphere electron exchange kex upon the longitudinal relaxation time τL for Debye solvents is examined numerically on the basis of a suitably combined rate formulation in order to examine the manner and extent to which the rate-solvent friction dependence, of particular experimental significance, should be sensitive to the degree of donor-acceptor electronic coupling and related factors. The treatment accounts for the contributions to kex from a spatial distribution of reactant pairs as well as for the effects of donor-acceptor interactions upon the unimolecular rate constant, ket (s-1), for each encounter geometry. The latter include the influence of electronic interactions as prescribed by the matrix coupling element H12 upon the effective frequency for adiabatic barrier crossing νn, as well as upon the electronic transmission coefficient κel (i.e., the degree of reaction nonadiabaticity). The anticipated dependence of the free-energy barrier, as well as νn and κel, upon the donor-acceptor separation is accounted for in the kex calculations. The form of the resulting log kex -log τ-1L plots exhibit, as expected, a marked dependence on the value of H12 for reactant contact, H○12. Over the τ-1L range appropriate for common solvents at ambient temperatures, ˜1×1011 to 5×1012 s-1, the log kex -log τ-1L slopes, x, are significantly (or substantially) below unity for H○12≲0.5 kcal mol-1; x decreases markedly with increasing τ-1L and/or for decreasing H○12. The approach to the solvent inertial limit (for large τ-1L) also tends to decrease x further. Numerical comparisons are made with corresponding log kex -log τ-1L plots obtained using the simple ``encounter preequilibrium'' treatment which presumes that only a fixed narrow range of encounter-pair geometries contribute to kex. While the form of the plots are not greatly different, former more sophisticated treatment generally yields

  19. 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

  20. Electron spin from self interaction

    SciTech Connect

    Spavieri, G. |

    1992-06-01

    The author explores the possibility that the electron self-interaction is the origin of the spin and of the radiative effects of QED. The electron is conceived as a charged, massless, point particle with a quantum or stochastic, internal motion about its center of mass and bound by a self-interaction potential. The hydrodynamic equations of motion describing the electron in its center of mass frame are related to non-Markovian stochastic equations recently used to derive the Schroedinger equation. By averaging over this stochastic internal motion and identifying the energy with the rest mass energy, the angular momentum exhibits properties characteristic of spin. The electromagnetic self-interactions added to the Hamiltonian of the particle correct the g factor to yield the anomalous value (g{minus}2)/2 {approx} 1159.7(2.3) X 10{sup {minus}6} in agreement with experiment. Calculations of other {open_quotes}radiative{close_quotes} effects including the Lamb shift are presented. The results obtained are finite and suggest that the QED corrections attributed to radiative effects could be obtained classically, i.e., without second quantization and renormalization, by complementing the Dirac theory with this self-interaction mechanism. The g factor dependence on the external magnetic field of this and other spin models is compared with that of QED, showing that these theories can be tested by the present precision measurements of the g factor. 33 refs., 2 tabs.

  1. 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.

  2. Ferrocenyl-ended thieno-vinylene oligomers: donor-acceptor polarization and mixed-valence properties with emphasis on the raman mapping of localized-to-delocalized transitions.

    PubMed

    Casado, Juan; Rodríguez González, Sandra; Ruiz Delgado, M Carmen; Moreno Oliva, María; López Navarrete, Juan T; Caballero, Ruben; de la Cruz, Pilar; Langa, Fernando

    2009-03-01

    What's your role? New oligothiophene-vinylene compounds have been synthesized to study the role of the conjugated chain in two different cases (see scheme; MV=mixed valence). The electronic and molecular structures were analyzed by means of electronic, X-ray photoelectron, and Raman spectroscopy, together with thermo spectroscopy, electrochemistry, and DFT calculations.New oligothiophene-vinylene compounds have been synthesized in order to study the role of the conjugated chain in two different cases: 1) when push-pull action operates between an electron-donor and an electron-acceptor group at the ends of the thiophene-vinylene conjugated chain, and 2) when mixed-valence action is induced by single oxidation of the same chain functionalized at both terminal positions with ferrocene groups leading to competition between the donor groups. The electronic and molecular structures are analyzed by means of electronic, X-ray photoelectron and Raman spectroscopies, together with thermospectroscopy, electrochemistry and density functional theory calculations. The cyclic voltammetry processes have been followed by spectrochemistry. It is shown that the radical cation of the diferrocenyl derivative is a class III mixed-valence system (i.e., fully delocalized) according to its Raman spectrum. Moreover, by Raman thermo-spectroscopy the thermal transition of this radical cation from a delocalized (class III, room temperature) to a localized (class II, -160 degrees C) state is scanned. In all cases the Raman study is paralleled by an electronic absorption spectroscopic analysis. Structure-property relationships are proposed for molecules of two important fields of very active research as that of the non-linear optics (i.e., organic optoelectronic) and that of the mixed-valence systems (i.e., charge-transfer processes). PMID:19165843

  3. Novel zinc phthalocyanine-benzoquinone rigid dyad and its photoinduced electron transfer properties.

    SciTech Connect

    Lee, C.-H.; Guo, J.; Chen, L. X.; Mandal, B. K.; Chemical Sciences and Engineering Division; Illinois Inst. of Tech.; Northwestern Univ.

    2008-10-10

    While preparing the first structurally rigid zinc phthalocyanine-benzoquinone (ZnPc-BQ) dyad as a model for photoinduced charge separation mimicking natural photosynthesis, a convenient method is developed for in situ generation of a benzoquinone chromophore in the dyad using an iso-butyryl mask. The dyad has no rotamers and possesses a fixed distance between ZnPc and BQ moieties (center-to-center and edge-to-edge distances are 9.40 and 2.14 {angstrom}, respectively). The dyad displays unusual electronic perturbation in the ground state, resulting from the interactions between Pc and BQ, and exhibits photoinduced electron transfer with a lifetime of 40 ps of the charged separated states. The steady-state fluorescence and electrochemical behavior of the dyad are evaluated. This study opens a route to subsequent dyads, triads, and complex architectures of electron donor-acceptor arrays with rigid structures and long charge separation states.

  4. 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.

  5. Photoinduced Charge and Energy Transfer within meta- and para-Linked Chlorophyll a-Perylene-3,4:9,10-bis(dicarboximide) Donor-Acceptor Dyads.

    PubMed

    Huang, Guan-Jhih; Harris, Michelle A; Krzyaniak, Matthew D; Margulies, Eric A; Dyar, Scott M; Lindquist, Rebecca J; Wu, Yilei; Roznyatovskiy, Vladimir V; Wu, Yi-Lin; Young, Ryan M; Wasielewski, Michael R

    2016-02-01

    Connecting electron donors and acceptors to a benzene ring in a meta or para relationship results in quantum interference effects that can strongly influence charge separation (CS) and charge recombination (CR) processes in these systems. We report on the energy and electron transfer behavior of chlorophyll-based para- and meta-linked donor-bridge-acceptor (D-B-A) dyads, where the semisynthetic chlorophyll a derivative, zinc methyl 3-ethyl-pyrochlorophyllide a (D), is covalently attached at its 20-position to the para position of one phenyl of diphenylacetylene (B). The meta or para position of the phenyl in B distal to the donor is in turn attached to perylene-3,4:9,10-bis(dicarboximide) (PDI) (A). Photoexcitation of the D-B-A dyads produces long-lived radical ion pairs D(•+)-B-A(•-), which recombine to the ground state and to both (3*)D-B-A and D-B-(3*)A. Time-resolved optical and electron paramagnetic resonance spectroscopies were used to monitor the charge transfer and triplet energy transfer (TEnT) processes. At longer times, TEnT occurs from (3*)D-B-A to D-B-(3*)A. Surprisingly, the D-B-A molecules linked via the meta linkage exhibit faster CS, CR, and TEnT rates than do those with the para linkage in contrast to most other meta/para-linked D-B-A molecules previously examined. PMID:26731377

  6. Characterization and investigation of benzyl carbenium ion and carbanion ion-diradical intermediates with 3,5-disubstiuted pi--donors/acceptors

    NASA Astrophysics Data System (ADS)

    Perrotta, Raffaele Romano

    High-spin magnetic materials have been based on monomeric units that contain metals. Far less research has been done to develop and characterize alternative high-spin building blocks consisting of mostly organic subunits. To date, there exists a small class of known high-spin organomagnetic building blocks. These organic building blocks are comprised of neutral intermediates such as diradicals, nitrenes, and carbenes. The work presented in this text will show that a novel class of high-spin intermediates also exists that derives from ionic rather than neutral intermediates. Previous density functional theory (DFT) computations by Winter and Falvey identified a number of ion-diradicals that have favorable triplet ground states. For instance, the 3,5-bis(dimethylamino)benzyl carbenium ion, and 2-(3,5-dinitrophenyl)-1,3-dithiane carbanion, have singlet-triplet energy gaps (DeltaESTs) of +1.9 and +0.3 kcal/mol, respectively. Ion-diradicals are based on a general framework whereby either an electron deficient or electron rich exocyclic center is attached to a benzene ring that contains two pi-electron withdrawing or donating groups meta with respects to this site. The objective of chapter 2 is to identify the electronic spin state of the 3,5-bis(dimethylamino)benzyl carbenium ion. We have shown that this carbenium ion can be generated from C-O bond heterolysis of 3,5-bis(dimethylamino)benzyl esters and alcohols when photolyzed in polar protic solvents (e.g. methanol, 2-propanol, 2,2,2-trifluoroethanol). Our product studies show that indeed the 3,5-bis(dimethylamino)benzyl ethers are formed from this process, however an unexpected reduction product (3,5-bis(dimethylamino)toluene) is also observed. The reduction product here aptly demonstrates how an ion-diradical could be generated. Formal one electron transfer from a NMe 2 group to the exocyclic benzylic carbenium ion center, creates a triplet cation diradical (ion-diradical) intermediate, which eventually leads to the

  7. 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

  8. Complexation of Donor-Acceptor Substituted Aza-Crowns with Alkali and Alkaline Earth Metal Cations. Charge Transfer and Recoordination in Excited State.

    PubMed

    Volchkov, Valery V; Gostev, Fedor E; Shelaev, Ivan V; Nadtochenko, Viktor A; Dmitrieva, Svetlana N; Gromov, Sergey P; Alfimov, Mikhail V; Melnikov, Mikhail Ya

    2016-03-01

    Complexation between two aza-15-crown-5 ethers bearing electron donor and acceptor fragments and alkali and alkaline earth perchlorates has been studied using absorption, steady-state fluorescence and femtosecond transient absorption spectroscopy. The spectral-luminescent parameters, the stability and dissociation constants of the complexes were calculated. The intramolecular charge transfer reaction takes place both in the excited state of the crowns and their complexes 1:1; the latter is subjected to photorecoordination resulting in a weakening or a complete disruption of coordination bond between nitrogen atom and metal cation, disposed within a cavity of the crown. The compounds investigated can be viewed as novel optical molecular sensors for alkali and alkaline-earth metal cations. The photoejection of a metal cation into the bulk was not observed. PMID:26670689

  9. Efficiency and stability of spectral sensitization of boron-doped-diamond electrodes through covalent anchoring of a donor-acceptor organic chromophore (P1).

    PubMed

    Krysova, Hana; Barton, Jan; Petrak, Vaclav; Jurok, Radek; Kuchar, Martin; Cigler, Petr; Kavan, Ladislav

    2016-06-28

    A novel procedure is developed for chemical modification of H-terminated B-doped diamond surfaces with a donor-π-bridge-acceptor molecule (P1). A cathodic photocurrent near 1 μA cm(-2) flows under 1 Sun (AM 1.5) illumination at the interface between the diamond electrode and aqueous electrolyte solution containing dimethylviologen (electron mediator). The efficiency of this new electrode outperforms that of the non-covalently modified diamond with the same dye. The found external quantum efficiency of the P1-sensitized diamond is not far from that of the flat titania electrode sensitized by a standard organometallic dye used in solar cells. However, the P1 dye, both pure and diamond-anchored, shows significant instability during illumination by solar light. The degradation is a two-stage process in which the initially photo-generated products further decompose in complicated dark reactions. These findings need to be taken into account for optimization of organic chromophores for solar cells in general. PMID:27264474

  10. 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. PMID:27244215

  11. 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.

  12. 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.

  13. 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.

  14. 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

  15. Electron Interactions with SF_6

    NASA Astrophysics Data System (ADS)

    Christophorou, Loucas; Olthoff, James; Siegel, Ralph; Hayashi, Makoto; Nakamura, Yoshiharu

    1999-10-01

    Experimental data on electron collisions with SF6 have been reviewed and assessed. Recommended or suggested data will be presented for the cross sections for total, elastic, and differential electron scattering, for total and partial ionization, and for electron attachment. Similarly, recommended or suggested data will be presented as a function of E/N for the electron drift velocity, and the coefficients for electron diffusion, ionization, and attachment. Assessed data will be presented also on the electron attachment rate constant as a function of E/N in the pure gas and in mixtures with rare gases and N_2, and as a function of the mean electron energy and gas temperature.

  16. 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.

  17. REFLECTIONS ON THE TWO-STATE ELECTRON TRANSFER MODEL.

    SciTech Connect

    Brunschwig, B.S.

    2000-01-12

    There is general agreement that the two most important factors determining electron transfer rates in solution are the degree of electronic interaction between the donor and acceptor sites, and the changes in the nuclear configurations of the donor, acceptor, and surrounding medium that occur upon the gain or loss of an electron Ll-51. The electronic interaction of the sites will be very weak, and the electron transfer slow, when the sites are far apart or their interaction is symmetry or spin forbidden. Since electron motion is much faster than nuclear motion, energy conservation requires that, prior to the actual electron transfer, the nuclear configurations of the reactants and the surrounding medium adjust from their equilibrium values to a configuration (generally) intermediate between that of the reactants and products. In the case of electron transfer between , two metal complexes in a polar solvent, the nuclear configuration changes involve adjustments in the metal-ligand and intraligand bond lengths and angles, and changes in the orientations of the surrounding solvent molecules. In common with ordinary chemical reactions, an electron transfer reaction can then be described in terms of the motion of the system on an energy surface from the reactant equilibrium configuration (initial state) to the product equilibrium configuration (final state) via the activated complex (transition state) configuration.

  18. 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

  19. Electron-electron interactions in fast neutral-neutral collisions

    SciTech Connect

    DuBois, R.D. ); Manson, S.T. . Dept. of Physics and Astronomy)

    1992-11-01

    Differential electron emission is studied for 50--500 keV H[sup +] and H atom impact on helium. Using the first Born formulation, it is shown that projectile electron-target electron interactions are expected to dominate the differential cross sections for low energy target electron emission induced by fast neutral projectile impact on any target. Measurements of the 15[degrees] electron emission were made in order to investigate this prediction. For low impact energies, a constant ratio between the hydrogen atom and proton impact cross sections was found for emitted electron velocities less than half the projectile velocity, V[sub p] But as the collision energy increased, for electron velocities less than 0.25 V[sub p], the cross section ratio increased as the emitted electron velocity decreased. This is interpreted as a signature of projectile electron-target electron interactions becoming dominant for distant collisions between neutral particles.

  20. Electron-electron interactions in fast neutral-neutral collisions

    SciTech Connect

    DuBois, R.D.; Manson, S.T.

    1992-11-01

    Differential electron emission is studied for 50--500 keV H{sup +} and H atom impact on helium. Using the first Born formulation, it is shown that projectile electron-target electron interactions are expected to dominate the differential cross sections for low energy target electron emission induced by fast neutral projectile impact on any target. Measurements of the 15{degrees} electron emission were made in order to investigate this prediction. For low impact energies, a constant ratio between the hydrogen atom and proton impact cross sections was found for emitted electron velocities less than half the projectile velocity, V{sub p} But as the collision energy increased, for electron velocities less than 0.25 V{sub p}, the cross section ratio increased as the emitted electron velocity decreased. This is interpreted as a signature of projectile electron-target electron interactions becoming dominant for distant collisions between neutral particles.

  1. 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. PMID:26580460

  2. Electron-wall Interaction in Hall Thrusters

    SciTech Connect

    Y. Raitses; D. Staack; M. Keidar; N.J. Fisch

    2005-02-11

    Electron-wall interaction effects in Hall thrusters are studied through measurements of the plasma response to variations of the thruster channel width and the discharge voltage. The discharge voltage threshold is shown to separate two thruster regimes. Below this threshold, the electron energy gain is constant in the acceleration region and therefore, secondary electron emission (SEE) from the channel walls is insufficient to enhance electron energy losses at the channel walls. Above this voltage threshold, the maximum electron temperature saturates.

  3. Direct probing of the structure and electron transfer of fullerene/ferrocene hybrid on Au(111) electrodes by in situ electrochemical STM.

    PubMed

    Chen, Ting; Wang, Dong; Gan, Li-Hua; Matsuo, Yutaka; Gu, Jing-Ying; Yan, Hui-Juan; Nakamura, Eiichi; Wan, Li-Jun

    2014-02-26

    The electron donor-acceptor dyads are an emerging class of materials showing important applications in nonlinear optics, dye-sensitized solar cells, and molecular electronics. Investigation of their structure and electron transfer at the molecular level provides insights into the structure-property relationship and can benefit the design and preparation of electron donor-acceptor dyad materials. Herein, the interface adstructure and electron transfer of buckyferrocene Fe(C60Me5)Cp, a typical electron donor-acceptor dyad, is directly probed using in situ electrochemical scanning tunneling microscopy (STM) combined with theoretical simulations. It is found that the adsorption geometry and assembled structure of Fe(C60Me5)Cp is significantly affected by the electrochemical environments. In 0.1 M HClO4 solution, Fe(C60Me5)Cp forms well-ordered monolayers and multilayers on Au(111) surfaces with molecular dimer as the building block. In 0.1 M NaClO4 solution, typical six-fold symmetric close-packed monolayer with vertically adsorbed Fe(C60Me5)Cp is formed. Upon electrochemical oxidation, the oxidized Fe(C60Me5)Cp shows higher brightness in an STM image, which facilitates the direct visualization of the interfacial electrochemical electron transfer process. Theoretical simulation indicates that the electrode potential-activated, one-electron transfer from Fe(C60Me5)Cp to the electrode leads to the change of the delocalization character of the frontier orbital in the molecule, which is responsible for the STM image contrast change. This result is beneficial for understanding the structure and property of single electron donor-acceptor dyads. It also provides a direct approach to study the electron transfer of electron donor-acceptor compounds at the molecular level. PMID:24483295

  4. Deciphering Noncovalent Interactions Accompanying 7,7,8,8-Tetracyanoquinodimethane Encapsulation within Biphene[n]arenes: Nucleus-Independent Chemical Shifts Approach.

    PubMed

    Lande, Dipali N; Rao, Soniya S; Gejji, Shridhar P

    2016-07-18

    Binding of novel biphene[n]arene hosts to antiaromatic 7,7,8,8-tetracyanoquinodimethane (TCNQ) are investigated by DFT. Biphene[4]arene favors the inclusion complex through noncovalent interactions, such as hydrogen bonding, π-π stacking, C-H⋅⋅⋅π, and C-H⋅⋅⋅H-C dihydrogen bonding. Donor-acceptor complexation renders aromatic character to the guest through charge transfer. The formation of TCNQ anionic radicals through supramolecular π stacking significantly influences its chemical and photophysical behavior. Electron density reorganization consequent to encapsulation of TCNQ reflects in the shift of characteristic vibrations in the IR spectra. The accompanying aromaticities arising from the induced ring currents are analyzed by employing nucleus-independent chemical shifts based profiles. PMID:27028656

  5. Photon-Electron Interaction and Condense Beams

    SciTech Connect

    Chattopadhyay, S.

    1998-11-01

    We discuss beams of charged particles and radiation from multiple perspectives. These include fundamental acceleration and radiation mechanisms, underlying electron-photon interaction, various classical and quantum phase-space concepts and fluctuational interpretations.

  6. Unusual distance dependences of electron transfer rates.

    PubMed

    Kuss-Petermann, Martin; Wenger, Oliver S

    2016-07-28

    Usually the rates for electron transfer (kET) decrease with increasing donor-acceptor distance, but Marcus theory predicts a regime in which kET is expected to increase when the transfer distance gets longer. Until recently, experimental evidence for such counter-intuitive behavior had been very limited, and consequently this effect is much less well-known than the Gaussian free energy dependence of electron transfer rates leading to the so-called inverted driving-force effect. This article presents the theoretical concepts that lead to the prediction of electron transfer rate maxima at large donor-acceptor distances, and it discusses conditions that are expected to favor experimental observations of such behavior. It continues with a consideration of specific recent examples in which electron transfer rates were observed to increase with increasing donor-acceptor distance, and it closes with a discussion of the importance of this effect in the context of light-to-chemical energy conversion. PMID:27353891

  7. Electron-transfer reactions in polymer matrices

    NASA Astrophysics Data System (ADS)

    Vannikov, Anatolii V.; Grishina, Antonina D.

    1989-12-01

    This paper discusses the dark reactions and photoreactions that occur with transfer of an electron from a donor to an acceptor in polymer matrices under electron tunnelling conditions and when forming change-transfer complexes. The main emphasis is on an analysis of the factors that determine the rate of electron transfer, which, in accordance with the advanced theory of electron transfer, are the magnitude of the exchange interaction, the free energy of the process, and the reorganisation energies of the medium and the reacting donor and acceptor molecules. The existing models for the movement of charge carriers between single-type transport sites are discussed. The limits of applicability of the different models have been determined. The reorganisation energy of a polymer matrix is shown to have a considerable effect on the rate of movement of charge carriers on introduced transport molecules. The effect of the dielectric properties and free volume of polymer matrices on the characteristics of electron phototransfer in donor-acceptor complexes is discussed. The bibliography includes 126 references.

  8. 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…

  9. Electron-Electron Interaction in the Non-Relativistic Limit

    NASA Astrophysics Data System (ADS)

    Malik, F. Bary

    The electron-electron potential in the one-photon exchange approximation with the omission of the spin-spin interaction, leads to the classical Coulomb interaction, but the inclusion of the latter results in the Møller interaction. Bethe and Fermi showed that the latter interaction leads to the Breit potential, if a few of the terms in the expansion of the retardation effect are considered. In this article, it is shown that the higher order terms omitted in the Bethe-Fermi treatment reduces to terms of the same order in Dirac's alpha-matrices considered by Bethe and Fermi. This raises questions whether the Breit interaction is the appropriate first order correction to the Coulomb potential in the non-relativistic limit. It is pointed out that the nature of the interaction between two bound (1s) electron derived by Brown using the Schwinger formalism of the quantum electrodynamics but proposed empirically in 1929 by Gaunt could be a better correction to the Coulomb potential for bound electrons in atoms. The calculated energies using these matrix elements plus the vacuum polarization energies are in reasonable agreement with the data. For comparison, calculated energies using the Breit interaction plus vacuum polarization energies are also presented.

  10. Electron-Electron Interaction in the Non-Relativistic Limit

    NASA Astrophysics Data System (ADS)

    Malik, F. Bary

    2011-03-01

    The electron-electron potential in the one-photon exchange approximation with the omission of the spin-spin interaction, leads to the classical Coulomb interaction, but the inclusion of the latter results in the Møller interaction. Bethe and Fermi showed that the latter interaction leads to the Breit potential, if a few of the terms in the expansion of the retardation effect are considered. In this article, it is shown that the higher order terms omitted in the Bethe-Fermi treatment reduces to terms of the same order in Dirac's alpha-matrices considered by Bethe and Fermi. This raises questions whether the Breit interaction is the appropriate first order correction to the Coulomb potential in the non-relativistic limit. It is pointed out that the nature of the interaction between two bound (1s) electron derived by Brown using the Schwinger formalism of the quantum electrodynamics but proposed empirically in 1929 by Gaunt could be a better correction to the Coulomb potential for bound electrons in atoms. The calculated energies using these matrix elements plus the vacuum polarization energies are in reasonable agreement with the data. For comparison, calculated energies using the Breit interaction plus vacuum polarization energies are also presented.

  11. Catalyst-support interactions: Electronic perturbations

    NASA Astrophysics Data System (ADS)

    Campbell, Charles T.

    2012-08-01

    Oxide materials typically used as supports for the active metal nanoparticles of heterogeneous catalysts are known to influence catalytic activity through strong metal-support interactions. Researchers have now revealed electronic interactions between platinum and ceria that go well beyond known effects and lead to excellent catalytic activity.

  12. Analysis of kinetic isotope effects for proton-coupled electron transfer reactions.

    PubMed

    Edwards, Sarah J; Soudackov, Alexander V; Hammes-Schiffer, Sharon

    2009-03-12

    A series of rate constant expressions for nonadiabatic proton-coupled electron transfer (PCET) reactions are analyzed and compared. The approximations underlying each expression are enumerated, and the regimes of validity for each expression are illustrated by calculations on model systems. In addition, the kinetic isotope effects (KIEs) for a series of model PCET reactions are analyzed to elucidate the fundamental physical principles dictating the magnitude of the KIE and the dependence of the KIE on the physical properties of the system, including temperature, reorganization energy, driving force, equilibrium proton donor-acceptor distance, and effective frequency of the proton donor-acceptor mode. These calculations lead to three physical insights that are directly relevant to experimental data. First, these calculations provide an explanation for a decrease in the KIE as the proton donor-acceptor distance increases, even though typically the KIE will increase with increasing equilibrium proton donor-acceptor distance if all other parameters remain fixed. Often the proton donor-acceptor frequency decreases as the proton donor-acceptor distance increases, and these two effects impact the KIE in opposite directions, so either trend could be observed. Second, these calculations provide an explanation for an increase in the KIE as the temperature increases, even though typically the KIE will decrease with increasing temperature if all other parameters remain fixed. The combination of a rigid hydrogen bond, which corresponds to a high proton donor-acceptor frequency, and low solvent polarity, which corresponds to small solvent reorganization energy, allows the KIE to either increase or decrease with temperature, depending on the other properties of the system. Third, these calculations provide insight into the dependence of the rate constant and KIE on the driving force, which has been studied experimentally for a wide range of PCET systems. The rate constant

  13. Electron-electron Interaction and Thermoelectricity in Graphene

    NASA Astrophysics Data System (ADS)

    Ghahari, Fereshte; Zuev, Yuri; Forsythe, Carlos; Watanabe, Kenji; Taniguchi, Takashi; Kim, Philip

    2013-03-01

    In this presentation, we report thermoelectric power (TEP) measurements on graphene samples deposited on hexagonal boron nitride substrates where drastic suppression of disorder is achieved. Our results show that at high temperatures where the inelastic scattering rate due to electron-electron (e-e) interactions is higher than the disorder induced elastic scattering rate, the measured TEP deviates from the Mott relation, and can be explained by a non-relativistic hydrodynamic flow of electrons. We also investigated TEP in the quantum Hall regime at a high magnetic fields, where we observed symmetry broken integer quantum Hall due to the strong e-e interactions. The field dependence of TEP at these states reveals the important role that exchange interactions play.

  14. 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.

  15. 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.

  16. 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.

  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. Photoinduced electron tunneling between randomly dispersed donors and acceptors in frozen glasses and other rigid matrices.

    PubMed

    Wenger, Oliver S

    2013-07-14

    In fluid solution un-tethered donors and acceptors can diffuse freely, and consequently the donor-acceptor distance is usually not fixed on the timescale of an electron transfer event. When attempting to investigate the influence of driving-force changes or donor-acceptor distance variations on electron transfer rates this can be a problem. In rigid matrices diffusion is suppressed, and it becomes possible to investigate fixed-distance electron transfer. This method represents an attractive alternative to investigate rigid rod-like donor-bridge-acceptor molecules which have to be made in elaborate syntheses. This perspective focuses specifically on the distance dependence of photoinduced electron transfer which occurs via tunneling of charge carriers through rigid matrices over distances between 1 and 33 Å. Some key aspects of the theoretical models commonly used for analyzing kinetic data of electron tunneling through rigid matrices are recapitulated. New findings from this rather mature field of research are emphasized. PMID:23722299

  19. 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

  20. Electron-wall interaction in Hall thrusters

    SciTech Connect

    Raitses, Y.; Staack, D.; Keidar, M.; Fisch, N.J.

    2005-05-15

    Electron-wall interaction effects in Hall thrusters are studied through measurements of the plasma response to variations of the thruster channel width and the discharge voltage. The discharge voltage threshold is shown to separate two thruster regimes. Below this threshold, the electron energy gain is constant in the acceleration region and therefore, secondary electron emission (SEE) from the channel walls is insufficient to enhance electron energy losses at the channel walls. Above this voltage threshold, the maximum electron temperature saturates. This result seemingly agrees with predictions of the temperature saturation, which recent Hall thruster models explain as a transition to space-charge saturated regime of the near-wall sheath. However, in the experiment, the maximum saturation temperature exceeds by almost three times the critical value estimated under the assumption of a Maxwellian electron energy distribution function. The channel narrowing, which should also enhance electron-wall collisions, causes unexpectedly larger changes of the plasma potential distribution than does the increase of the electron temperature with the discharge voltage. An enhanced anomalous crossed-field mobility (near wall or Bohm-type) is suggested by a hydrodynamic model as an explanation to the reduced electric field measured inside a narrow channel. We found, however, no experimental evidence of a coupling between the maximum electron temperature and the location of the accelerating voltage drop, which might have been expected due to the SEE-induced near-wall conductivity.

  1. Characterization of noncovalent interactions between 6-propionyl-2-dimethylaminonaphthalene (PRODAN) and dissolved fulvic and humic acids.

    PubMed

    Gadad, Praveen; Lei, Hongxia; Nanny, Mark A

    2007-11-01

    Noncovalent interactions between the fluorescent probe 6-propionyl-2-dimethylaminonaphthalene (PRODAN) and dissolved Norman Landfill leachate fulvic acid, Suwannee River fulvic acid, Suwannee River humic acid, and Leonardite humic acid were examined as a function of pH, fulvic and humic acid (FA and HA) concentration, and solvent polarity using steady-state fluorescence spectroscopy. Static quenching processes, as indicated by linear Stern-Volmer plots and high K(d) values, were positively correlated with the % aromaticity of the FA and HAs, as well as with solution pH. Results illustrate that for FA molecules with relatively low % aromaticity values, solvophobic interactions between PRODAN and FA are the primary interaction mode. For HA molecules with higher % aromaticity, PRODAN engages in both solvophobic interactions and pi-pi interactions, in particular electron donor-acceptor interactions, via condensed aromatic, electron-accepting moieties inherent within HA molecules. Experiments modifying solvent polarity demonstrated that protonation of carboxylic acid functional groups at low pH ( approximately 4) increased the hydrophobicity of the dissolved FA and HA molecules, thereby enhancing noncovalent interactions with PRODAN through increased solvophobic forces. PMID:17632208

  2. 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.

  3. 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).

  4. 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

  5. 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.

  6. Electron-phonon interaction effects in tantalum

    SciTech Connect

    Al-Lehaibi, A.; Swihart, J.C.; Butler, W.H.; Pinski, F.J.

    1987-09-15

    The results of calculations for a number of electron-phonon interaction effects for tantalum are presented. The calculations are based on Korringa-Kohn-Rostoker energy bands, Born--von Karman phonons, and the rigid-muffin-tin approximation for the electron-phonon matrix element. The calculated Eliashberg spectral function ..cap alpha../sup 2/F is compared with the earlier tunneling data of Shen and the proximity tunneling data of Wolf et al. The calculated and tunneling transverse-phonon peaks agree well, but the height of the tunneling longitudinal-phonon peak is smaller than the calculated results. The calculated electron-phonon coupling parameter lambda is 0.88, which is larger than the lambda determined from superconducting tunneling and superconducting T/sub c/ measurements, but is slightly smaller than the lambda determined from electronic specific-heat measurements. Calculated phonon linewidths along various symmetry directions are presented. The temperature dependence of the electrical resistivity due to phonon scattering is calculated in the lowest-order variational approximation and it agrees with experiment. The point-contact spectral function of Kulik, G(..omega..), is determined and compared with ..cap alpha../sup 2/F(..omega..). The agreement between calculated and measured electronic specific heat and high-temperature electrical resistivity gives strong support to the validity of the rigid-muffin-tin approximation for electron-phonon matrix elements.

  7. 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.

  8. 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.

  9. 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

  10. Energetic electron observations of Rhea's magnetospheric interaction

    NASA Astrophysics Data System (ADS)

    Roussos, E.; Krupp, N.; Kollmann, P.; Paranicas, C.; Mitchell, D. G.; Krimigis, S. M.

    2011-10-01

    More specifically, we show results of a phase-space density analysis, looking for evidence of energetic electron transport processes in the vicinity of Rhea's wake. We also perform energetic electron trajectory tracings in order to map regions where access of energetic electrons in Rhea's interaction region is forbidden. Such regions form because of complex energetic particle magnetic drifts downstream of Rhea, where the magnetospheric electric and magnetic fields are disturbed. We show that while our approach provides some qualitative explanation for some of the observations of electrons with energies above 100 keV, the lowest energy features in the MIMI/LEMMS dataset (20-100 keV) cannot be explained, especially those that extend upstream of Rhea and in a region that a plasma absorbing moon should, in theory, have no effect on the magnetospheric populations. Given that, in addition to the fact that Rhea orbits in a region of the magnetosphere that is thought be unstable against centrifugal interchange, we propose that the formation of Rhea's wake acts as a disturbance that helps enhance local magnetospheric interchange. Interchange driven disturbances, may then actually be the source of some of the unusual energetic electron observations. We also discuss this scenario in the context of additional published observations by the Cassini's cold plasma detector.

  11. 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.

  12. 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. PMID:23611698

  13. 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

  14. Energetic electron interaction with broadband ULF waves

    NASA Astrophysics Data System (ADS)

    Vassiliadis, D.; Tornquist, M.; Koepke, M. E.; Shao, X.

    2014-12-01

    Electron energization in Earth's radiation belts is frequently explained in terms of an internal process whose effects can be enhanced by radial diffusion. Both types of energization include resonant interactions of the electrons with low-frequency waves. Spectra of such waves are often assumed to be broadband and to have a typical range of negative spectral indices (similar to 1/f), however recent studies show that power spectra of ground geomagnetic pulsations are significantly more complex. We use particle tracing simulations in a realistic magnetospheric field configuration to determine the effects of the spectral parameters. The low-frequency wave contribution to the radial diffusion coefficient is found to vary as a function of the spectral index magnitude. Research was supported by NSF/AGS 0741841.

  15. Electronic structure theory of weakly interacting bilayers

    NASA Astrophysics Data System (ADS)

    Fang, Shiang; Kaxiras, Efthimios

    2016-06-01

    We derive electronic structure models for weakly interacting bilayers such as graphene-graphene and graphene-hexagonal boron nitride, based on density functional theory calculations followed by Wannier transformation of electronic states. These transferable interlayer coupling models can be applied to investigate the physics of bilayers with arbitrary translations and twists. The functional form, in addition to the dependence on the distance, includes the angular dependence that results from higher angular momentum components in the Wannier pz orbitals. We demonstrate the capabilities of the method by applying it to a rotated graphene bilayer, which produces the analytically predicted renormalization of the Fermi velocity, Van Hove singularities in the density of states, and moiré pattern of the electronic localization at small twist angles. We further extend the theory to obtain the effective couplings by integrating out neighboring layers. This approach is instrumental for the design of van der Walls heterostructures with desirable electronic features and transport properties and for the derivation of low-energy theories for graphene stacks, including proximity effects from other layers.

  16. Interactive electronic whiteboards in the medical classroom.

    PubMed Central

    Jain, N. L.; Murphy, J. F.; Hassan, S. W.; Cunnius, E. L.; Metcalfe, E. S.; Schnase, J. L.; Schoening, P. A.; Spooner, S. A.; Frisse, M. E.

    1994-01-01

    Most research on computer-assisted instruction has concentrated on developing systems to be used outside the teaching environment to supplement or complement in-class teaching. We believe that interactive large-screen computers can be used effectively in the classroom as electronic whiteboards to more effectively teach select medical school courses. We describe our experience with one such device, the Xerox LiveBoard, to teach a course on computer-assisted clinical decision analysis to a group of first-year medical students. Images Figure 1 PMID:7949986

  17. Bridge-mediated excitation energy transfer pathways through protein media: a Slater determinant-based electronic coupling calculation combined with localized molecular orbitals.

    PubMed

    Kawatsu, Tsutomu; Matsuda, Kenji; Hasegawa, Jun-ya

    2011-10-01

    A computational method for calculating electronic coupling and pathway of electron transfer (ET) has been extended to that for excitation energy transfer (EET). A molecular orbital (MO)-based description has been generalized to one based on Slater determinants. This approach reduces the approximations used for the Green's function method from the perturbation of chemical-bond interactions to the perturbation of the configuration interactions. It is, therefore, reasonable to apply this method to EET, which involves the transfer of an electron-hole pair. To represent EET donor, acceptor, and bridge states, we adopted recently developed localized molecular orbitals (LMOs) for constructing locally excited determinants. The LMO approach provides a chemically meaningful interpretation of how each local excitation on the bridge contributes to the total electronic coupling of the EET. We applied the method to six model peptides and calculated their electronic couplings as well as the direct and through-peptide terms. Although the through-peptide term is usually negligibly small compared with the direct term, it can dominate the EET reaction in appropriate situations. The direct term dominates in long-range interactions because the indirect term decays in shorter distances. PMID:21861486

  18. 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.

  19. 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. PMID:24294996

  20. 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.

  1. 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.

  2. 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.

  3. Bay-annulated indigo (BAI) as an excellent electron accepting building block for high performance organic semiconductors

    DOEpatents

    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.

  4. 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.

  5. 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.

  6. Electron tunneling in lithium-ammonia solutions probed by frequency-dependent electron spin relaxation studies.

    PubMed

    Maeda, Kiminori; Lodge, Matthew T J; Harmer, Jeffrey; Freed, Jack H; Edwards, Peter P

    2012-06-01

    Electron transfer or quantum tunneling dynamics for excess or solvated electrons in dilute lithium-ammonia solutions have been studied by pulse electron paramagnetic resonance (EPR) spectroscopy at both X- (9.7 GHz) and W-band (94 GHz) frequencies. The electron spin-lattice (T(1)) and spin-spin (T(2)) relaxation data indicate an extremely fast transfer or quantum tunneling rate of the solvated electron in these solutions which serves to modulate the hyperfine (Fermi-contact) interaction with nitrogen nuclei in the solvation shells of ammonia molecules surrounding the localized, solvated electron. The donor and acceptor states of the solvated electron in these solutions are the initial and final electron solvation sites found before, and after, the transfer or tunneling process. To interpret and model our electron spin relaxation data from the two observation EPR frequencies requires a consideration of a multiexponential correlation function. The electron transfer or tunneling process that we monitor through the correlation time of the nitrogen Fermi-contact interaction has a time scale of (1-10) × 10(-12) s over a temperature range 230-290 K in our most dilute solution of lithium in ammonia. Two types of electron-solvent interaction mechanisms are proposed to account for our experimental findings. The dominant electron spin relaxation mechanism results from an electron tunneling process characterized by a variable donor-acceptor distance or range (consistent with such a rapidly fluctuating liquid structure) in which the solvent shell that ultimately accepts the transferring electron is formed from random, thermal fluctuations of the liquid structure in, and around, a natural hole or Bjerrum-like defect vacancy in the liquid. Following transfer and capture of the tunneling electron, further solvent-cage relaxation with a time scale of ∼10(-13) s results in a minor contribution to the electron spin relaxation times. This investigation illustrates the great

  7. Limits to Electron Beam Emittance from Stochastic Coulomb Interactions

    SciTech Connect

    Coleman-Smith, Christopher; Padmore, Howard A.; Wan, Weishi

    2008-08-22

    Dense electron beams can now be generated on an ultrafast timescale using laser driven photo-cathodes and these are used for a range of applications from ultrafast electron defraction to free electron lasers. Here we determine a lower bound to the emittance of an electron beam limited by fundamental stochastic Coulomb interactions.

  8. 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. PMID:26877152

  9. 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.

  10. Visualization of electron transfer interactions of membrane proteins

    NASA Astrophysics Data System (ADS)

    Kawato, Suguru

    1991-08-01

    To visualize electron transfer interactions of proteins in the cellular nieinbrane, we have developed a polarized laser flash-induced anisotropy decay imaging. The time-resolved anisotropy is particularly sensitive to protein-protein interactions. This technique has been successfully applied to examine formation and dissociation of electron transfer complex in adrenal cortex and liver. Electron transfer plays a significant role for steroid hormone synthesis from cholesterol in adrenalcortex and for drug metabolism in liver such as detoxification of chemical compounds. Several redox partners perticipate in dynamic electron transfer interactions. The terminal enzyme cytochrome P-450 receives electrons to activate molecular oxygen, resulting in hydroxylation of various substrates.

  11. Aharonov-Bohm oscillations in disordered nanorings with quantum dots: Effect of electron-electron interactions

    NASA Astrophysics Data System (ADS)

    Semenov, Andrew G.; Zaikin, Andrei D.

    2010-01-01

    We investigate the effect of electron-electron interactions on Aharonov-Bohm (AB) current oscillations in nanorings formed by a chain of metallic quantum dots. We demonstrate that electron-electron interactions cause electron dephasing thereby suppressing the amplitude of AB oscillations at all temperatures down to T=0. The crossover between thermal and quantum dephasing is found to be controlled by the ring perimeter. Our predictions can be directly tested in future experiments.

  12. Extraction of photogenerated electrons and holes from a covalent organic framework integrated heterojunction.

    PubMed

    Calik, Mona; Auras, Florian; Salonen, Laura M; Bader, Kathrin; Grill, Irene; Handloser, Matthias; Medina, Dana D; Dogru, Mirjam; Löbermann, Florian; Trauner, Dirk; Hartschuh, Achim; Bein, Thomas

    2014-12-24

    Covalent organic frameworks (COFs) offer a strategy to position molecular semiconductors within a rigid network in a highly controlled and predictable manner. The π-stacked columns of layered two-dimensional COFs enable electronic interactions between the COF sheets, thereby providing a path for exciton and charge carrier migration. Frameworks comprising two electronically separated subunits can form highly defined interdigitated donor-acceptor heterojunctions, which can drive the photogeneration of free charge carriers. Here we report the first example of a photovoltaic device that utilizes exclusively a crystalline organic framework with an inherent type II heterojunction as the active layer. The newly developed triphenylene-porphyrin COF was grown as an oriented thin film with the donor and acceptor units forming one-dimensional stacks that extend along the substrate normal, thus providing an optimal geometry for charge carrier transport. As a result of the degree of morphological precision that can be achieved with COFs and the enormous diversity of functional molecular building blocks that can be used to construct the frameworks, these materials show great potential as model systems for organic heterojunctions and might ultimately provide an alternative to the current disordered bulk heterojunctions. PMID:25412210

  13. 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.

  14. 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…

  15. Spectrophotometric investigation of interaction between iodine and pentadentate Schiff base ligands

    NASA Astrophysics Data System (ADS)

    Khouba, Z.; Benabdallah, T.; Maschke, U.

    The interaction between iodine as an electron acceptor (A), and three pentadentate Schiff bases, 1,3-bis(salicylideneamino)-2-propanol (SB1), 1,3-bis(2-hydroxy-1-naphthylideneamino)-2-propanol (SB2), and 1,3-bis[1-(pyridine-2-yl)methylideneamino]-2-propanol (SB3), as electron donor systems (D), was studied spectrophotometrically in methanol at 28 °C. Equilibrium constants KAD and molar extinction coefficients ɛAD of the donor-acceptor complexes (AD) were determined using the modified Benesi-Hildebrand equation in conjunction with the non linear fit analysis. The method shows the formation of 1:1 type complexes as major species in solution. The free energy changes ΔG° and the energy of the charge transfer band ECT were also calculated for all complexes. The iodine complex derived from SB2 seems to be more stable than those derived from SB3 and SB1. On the other hand, the ionization potential ID of each Schiff base was estimated from the corresponding complex band energy, using an empirical equation. An inverse relationship between ID and KAD values was found. Blue and red shift observed for the 445 nm band of iodine were also discussed on the basis of theoretical considerations.

  16. 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.

  17. Electron dynamics controlled via self-interaction.

    PubMed

    Tamburini, Matteo; Keitel, Christoph H; Di Piazza, Antonino

    2014-02-01

    The dynamics of an electron in a strong laser field can be significantly altered by radiation reaction. This usually results in a strongly damped motion, with the electron losing a large fraction of its initial energy. Here we show that the electron dynamics in a bichromatic laser pulse can be indirectly controlled by a comparatively small radiation reaction force through its interplay with the Lorentz force. By changing the relative phase between the two frequency components of the bichromatic laser field, an ultrarelativistic electron bunch colliding head-on with the laser pulse can be deflected in a controlled way, with the deflection angle being independent of the initial electron energy. The effect is predicted to be observable with laser powers and intensities close to those of current state-of-the-art petawatt laser systems. PMID:25353414

  18. Electron-phonon interaction on optical spectra of nanoelectronic devices

    NASA Technical Reports Server (NTRS)

    Kim, Q.

    2002-01-01

    Information obtained on the solid-state lattice dynamics by electron-phonon interaction between lattice phonons and electrons could open up to learn more about lattice dynamics and to apply it in nanoelectronic devices including software reliability, nano-size capacitors, master clock sources, as well as non-contact temperature probes on nano-electronic and photonicdevices.

  19. Photoelectric effect in aspect of electron waves interaction

    NASA Astrophysics Data System (ADS)

    Chrzanowski, Janusz

    2003-11-01

    The interaction of electromagnetic waves with metal surface is analyzed in terms of electrons waves and quasiparticles theory. Work function for any metal is presented in dependence on electrons density and Fourier transform of potential due to single electron. Influence of different factors on change of work function value is considered.

  20. 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.

  1. 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.

  2. The long-lived electron transfer state of the 2-phenyl-4-(1-naphthyl)quinolinium ion incorporated into nanosized mesoporous silica-alumina acting as a robust photocatalyst in water.

    PubMed

    Yamada, Yusuke; Nomura, Akifumi; Ohkubo, Kei; Suenobu, Tomoyoshi; Fukuzumi, Shunichi

    2013-06-01

    A simple electron donor-acceptor linked dyad, the 2-phenyl-4-(1-naphthyl)quinolinium ion (QuPh(+)-NA), was incorporated into nanosized mesoporous silica-alumina to form a composite, which is highly dispersed in water and acts as an efficient and robust photocatalyst for the reduction of O2 by oxalate to produce hydrogen peroxide with a quantum yield of 10%. PMID:23536036

  3. Boltzmann equation and Monte Carlo analysis of electron-electron interactions on electron distributions in nonthermal cold plasmas

    SciTech Connect

    Yousfi, M.; Himoudi, A.; Gaouar, A. )

    1992-12-15

    Electron distribution functions in nonthermal cold plasmas generated by classical electrical discharges have been calculated from a powerful Boltzmann equation solution and an original Monte Carlo simulation. In these two methods both classical (i.e., elastic, inelastic, and superelastic) electron-atom (or molecule) collisions and electron-electron interactions are taken into account. The approximations considered to include long-range (electron-electron) and short-range (electron-atom) interactions in the same Monte Carlo algorithm are first validated by comparing with Boltzmann equation results. Then, the influence of electron-electron interactions on electron distribution functions, swarm parameters, and reaction rates under nonthermal cold plasma conditions are analyzed and discussed as a function of reduced electric field [ital E]/[ital N] and ionization degree [ital n][sub [ital e

  4. 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.

  5. 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.

  6. 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,…

  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. 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…

  9. 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.

  10. Chromophore/DNA interactions: femto- to nanosecond spectroscopy, NMR structure, and electron transfer theory.

    PubMed

    von Feilitzsch, Till; Tuma, Jennifer; Neubauer, Heike; Verdier, Laurent; Haselsberger, Reinhard; Feick, Reiner; Gurzadyan, Gagik; Voityuk, Alexander A; Griesinger, Christian; Michel-Beyerle, Maria E

    2008-01-24

    The mechanism of photoinduced hole injection into DNA has been studied using an integrated approach that combines NMR structural analysis, time-resolved spectroscopy, and quantum-chemical calculations. A covalently linked acridinium derivative, the protonated 9-amino-6-chloro-2-methoxyacridine (X+), is replacing a thymine and separated from either guanine (G) or the easier to oxidize 7-deazaguanine (Z) by one adenine.thymine (A.T) base pair. The key features of this donor/acceptor system are the following: (i) In more than 95% of the duplexes, X+ is located in a central, coplanar position between the neighboring A.T base pairs with its long axis in parallel showing minimal twist and tilt angles (<15 degrees). The complementary adenine base is turned out into the extrahelical space. In a minority of less than 5%, X+ is found to be still attached to the duplex. X+ is most probably associated with one of the phosphates, since it is neither intercalated between more remote base pairs nor bound to sugars or grooves. This minority characterized by an excited state lifetime >10 ns gives rise to a small background signal in time-resolved measurements and contributes predominantly to steady-state fluorescence spectra. (ii) Although the intercalation mode of X+ is well defined, the NMR structure reveals that there are two conformations of X+ with respect to the arrangement of its methoxy substituent. In one conformation, the methoxy group is in the plane of the chromophore, while, in the other extraplanar conformation, the methoxy group forms an angle of 70 degrees with the acridinium ring. The fluorescence decay of 5'-ZAX and 5'-GAX tracts can be fitted to a biexponential function with similar amplitudes, reflecting the oxidation dynamics of G and Z, with the slower rate being determined by larger thermal activation energy. The attribution of biexponential electron transfer (ET) dynamics to the bimodal orientation of the methoxy group at the acridinium is supported by

  11. 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. PMID:26945790

  12. 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.

  13. How light modifies the electron-electron interaction under extreme conditions

    NASA Astrophysics Data System (ADS)

    Hinschberger, Y.; Hervieux, P.-A.

    2015-10-01

    In the domain of extreme light-matter interactions, we show that the electron-electron interaction can be modified coherently by the electric field of the light. The latter play the role of a third partner not only acting on the electrons individually but also on their mutual interaction. By using an original formalism based on the Foldy-Wouthuysen transformation and applied to the Dirac-Breit Hamiltonian in the presence of a time-dependent electromagnetic field, we obtain analytical expressions of new three-body light-matter interactions.

  14. 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.

  15. 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

  16. Compton interaction of free electrons with intense low frequency radiation

    NASA Technical Reports Server (NTRS)

    Illarionov, A. F.; Kompaneyets, D. A.

    1978-01-01

    Electron behavior in an intense low frequency radiation field, with induced Compton scattering as the primary mechanism of interaction, is investigated. Evolution of the electron energy spectrum is studied, and the equilibrium spectrum of relativistic electrons in a radiation field with high brightness temperature is found. The induced radiation pressure and heating rate of an electron gas are calculated. The direction of the induced pressure depends on the radiation spectrum. The form of spectrum, under the induced force can accelerate electrons to superrelativistic energies is found.

  17. 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.

  18. Electronic metal-support interactions in single-atom catalysts.

    PubMed

    Hu, Pingping; Huang, Zhiwei; Amghouz, Zakariae; Makkee, Michiel; Xu, Fei; Kapteijn, Freek; Dikhtiarenko, Alla; Chen, Yaxin; Gu, Xiao; Tang, Xingfu

    2014-03-24

    The synthesis of single-atom catalysts and the control of the electronic properties of catalytic sites to arrive at superior catalysts is a major challenge in heterogeneous catalysis. A stable supported single-atom silver catalyst with a controllable electronic state was obtained by anti-Ostwald ripening. An electronic perturbation of the catalytic sites that is induced by a subtle change in the structure of the support has a strong influence on the intrinsic reactivity. The higher depletion of the 4d electronic state of the silver atoms causes stronger electronic metal-support interactions, which leads to easier reducibility and higher catalytic activity. These results may improve our understanding of the nature of electronic metal-support interactions and lead to structure-activity correlations. PMID:24599751

  19. THE PARITY NON-CONSERVING ELECTRON-NUCLEON INTERACTION

    SciTech Connect

    Commins, E.D.; Bucksbaum, P.H.

    1980-01-01

    We present general ideas concerning the neutral weak eq interaction. Then we describe the salient features of the Weinberg-Salam model, discuss in detail the principles and methods of the SLAC polarized electron scattering experiment and atomic physics experiments, and summarize neutral weak interaction results and their implications.

  20. Interaction between electron-affinic sensitizers.

    PubMed Central

    McNally, J. N.; de Ronde, J.

    1978-01-01

    Measurements of effect of pairs of the sensitizers PNAP, misonidazole and oxygen have shown that if one sensitizer is giving an enhancement ratio (ER) of about 1.6 or less and the other is giving a larger ER, the combination behaves as if only the latter is present. There is only an additive effect of the two if they both give ERs less than 1.6 or greater than 1.6. These results show that at low concentrations sensitizers only act on damage associated with the "fast component" of the oxygen effect. This could result from interaction with two distinct species, or there could be only one critical species formed initially but more than one step by which it could be converted to a lethal form. PMID:277264

  1. Electronic Structure, Donor and Acceptor Transitions, and Magnetism of 3d Impurities in In2O3 and ZnO

    SciTech Connect

    Raebiger, H.; Lany, S,; Zunger, A.

    2009-01-01

    3d transition impurities in wide-gap oxides may function as donor/acceptor defects to modify carrier concentrations, and as magnetic elements to induce collective magnetism. Previous first-principles calculations have been crippled by the LDA error, where the occupation of the 3d-induced levels is incorrect due to spurious charge spilling into the misrepresented host conduction band, and have only considered magnetism and carrier doping separately. We employ a band-structure-corrected theory, and present simultaneously the chemical trends for electronic properties, carrier doping, and magnetism along the series of 3d{sup 1}-3d{sup 8} transition-metal impurities in the representative wide-gap oxide hosts In{sub 2}O{sub 3} and ZnO. We find that most 3d impurities in In{sub 2}O{sub 3} are amphoteric, whereas in ZnO, the early 3d's (Sc, Ti, and V) are shallow donors, and only the late 3d's (Co and Ni) have acceptor transitions. Long-range ferromagnetic interactions emerge due to partial filling of 3d resonances inside the conduction band and, in general, require electron doping from additional sources.

  2. Hybrid [5]Radialenes with Bispyrroloheteroles: New Electron-Donating Units.

    PubMed

    Higashino, Tomohiro; Imahori, Hiroshi

    2015-09-14

    Bispyrroloheteroles have been synthesized to address their intrinsic structural, optical, and electrochemical properties. The X-ray crystal structures and calculated natural bond orbital (NBO) bond orders unambiguously demonstrated the existence of a two pyrrole-fused five-membered ring with short exocyclic C-C double bonds and long endocyclic C-C single bonds, supporting that the bispyrroloheteroles are rare examples of structurally characterized hybrid [5]radialenes. The bispyrroloheteroles were found to act as an electron-donating unit, which would be fascinating for the rational design of new charge-transporting and donor-acceptor photovoltaic materials as well as versatile charge-transfer complexes. PMID:26242481

  3. 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.

  4. 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.

  5. Theoretical study of H 3AXH 3 and H 3AYH 2 (A = B, Al, Ga; X = N, P, As and Y = O, S, and Se), electrostatic and hyperconjugative interactions roles

    NASA Astrophysics Data System (ADS)

    El Guerraze, Abdelaâli; El-Nahas, Ahmed M.; Jarid, Abdellah; Serrar, Chafiq; Anane, Hafid; Esseffar, M.'hamed

    2005-06-01

    H 3AXH n (A = B, Al, and Ga; XH n = NH 3, PH 3, AsH 3, H 2O, SH 2 and SeH 2) donor-acceptor complexes are studied from conformational and coordination-mode points of view at B3LYP/6-311+G(3df,2p) and CCSD(T)/6-311+G(3df,2p) levels of theory. The metallic character of gallium atom is responsible of the irregular structural and coordination mode trends in free and complexed gallane (GaH 3). The intuitive staggered conformation is not adopted by all compounds because there is, in some cases, competition between H(donor)-H(acceptor) electrostatic interaction and hyperconjugative electronic delocalisation. All H 3AXH 3 (X = N, P, and As) complexes are staggered. In accordance with Pophristic-Goodman's study (V. Pophristic, L. Goodman, Nature 411 (2001) 565), hyperconjugation is behind this geometrical preference. For the H 3AYH 2 series, the H 3BOH 2 staggered conformation is also favoured by this interaction. Nevertheless, H 3AlOH 2 and H 3GaOH 2 are curiously eclipsed and not favoured by the hyperconjugation. This paradox is clarified by both electrostatic and energetic delocalisation interactions analysis. The coordination mode is horizontally and vertically discussed in N and O groups of the periodic table within these complex sets.

  6. Measurement and control of electron-phonon interactions in graphene

    NASA Astrophysics Data System (ADS)

    Remi, Sebastian

    Despite the weak interaction between electrons and atomic vibrations (phonons) in the one-atom thick crystal of carbon called graphene, the scattering of electrons off phonons limits coherent electron transport in pristine devices over mesoscopic length scales. The future of graphene as a replacement to silicon and other materials in advanced electronic devices will depend on the success of controlling and optimizing electronic transport. In this dissertation, we explore the electron-phonon interaction via Raman scattering, elucidating the effects of filling and emptying charge states on the phonons in both the metallic state and when levels are quantized by an applied perpendicular magnetic field. In zero magnetic field, the phonon energy shifts due to electronic screening by charge carriers. Previously, a logarithmic divergence of the phonon energy was predicted as a function of the charge carrier density. For the first time, we observe signatures of this logarithmic divergence at liquid He temperatures after vacuum annealing on single layers. We also measure the electron-phonon coupling strength, Fermi velocity, and broadening of electronic quantum levels from Raman scattering and correlate these parameters to electronic transport. In a strong perpendicular magnetic field, the energy bands split into discrete Landau levels. Here, we observe kinks and splitting of the optical phonon energy, even when the Landau level transitions are far from resonant with the phonons. We discover that the kinks are attributed to charge filling of Landau levels, as understood from a linearized model based on electron-phonon interactions. Moreover, we show that material parameters determined without magnetic fields also describe phonon behavior in high magnetic fields.

  7. Vibronic interactions in hole-transporting molecules: An interplay with electron-hole interactions

    NASA Astrophysics Data System (ADS)

    Sato, Tohru; Shizu, Katsuyuki; Uegaito, Keisuke; Iwahara, Naoya; Tanaka, Kazuyoshi; Kaji, Hironori

    2011-04-01

    Vibronic coupling constants of hole-transporting molecules, TPF and CBP, are estimated. Despite the planar structure of TPF, the calculated vibronic coupling constants are close to those of nonplanar TPD. The origin of the vibronic couplings in TPF is investigated employing the vibronic coupling density analysis. Based on a Hubbard Hamiltonian, electron-hole interactions are found to be crucial in the vibronic couplings. A large difference of on-site Coulomb interactions, or electron-hole interactions gives rise to a localization of the electron-density difference on a site which can lead to small vibronic couplings.

  8. 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.

  9. Trapped electron losses by interactions with coherent VLF waves

    SciTech Connect

    Walt, M.; Inan, U.S.; Voss, H.D.

    1996-07-01

    VLF whistler waves from lightning enter the magnetosphere and cause the precipitation of energetic trapped electrons by pitch angle scattering. These events, known as Lightning-induced Electron Precipitation (LEP) have been detected by satellite and rocket instruments and by perturbations of VLF waves traveling in the earth-ionosphere waveguide. Detailed comparison of precipitating electron energy spectra and time dependence are in general agreement with calculations of trapped electron interactions with ducted whistler waves. In particular the temporal structure of the precipitation and the dynamic energy spectra of the electrons confirm this interpretation of the phenomena. There are discrepancies between observed and measured electron flux intensities and pitch angle distributions, but these quantities are sensitive to unknown wave intensities and trapped particle fluxes near the loss cone angle. The overall effect of lightning generated VLF waves on the lifetime of trapped electrons is still uncertain. The flux of electrons deflected into the bounce loss cone by a discrete whistler wave has been measured in a few cases. However, the area of the precipitation region is not known, and thus the total number of electrons lost in an LEP event can only be estimated. While the LEP events are dramatic, more important effects on trapped electrons may arise from the small but numerous deflections which increase the pitch angle diffusion rate of the electron population. {copyright} {ital 1996 American Institute of Physics.}

  10. Trapped electron losses by interactions with coherent VLF waves

    NASA Astrophysics Data System (ADS)

    Walt, M.; Inan, U. S.; Voss, H. D.

    1996-07-01

    VLF whistler waves from lightning enter the magnetosphere and cause the precipitation of energetic trapped electrons by pitch angle scattering. These events, known as Lightning-induced Electron Precipitation (LEP) have been detected by satellite and rocket instruments and by perturbations of VLF waves traveling in the earth-ionosphere waveguide. Detailed comparison of precipitating electron energy spectra and time dependence are in general agreement with calculations of trapped electron interactions with ducted whistler waves. In particular the temporal structure of the precipitation and the dynamic energy spectra of the electrons confirm this interpretation of the phenomena. There are discrepancies between observed and measured electron flux intensities and pitch angle distributions, but these quantities are sensitive to unknown wave intensities and trapped particle fluxes near the loss cone angle. The overall effect of lightning generated VLF waves on the lifetime of trapped electrons is still uncertain. The flux of electrons deflected into the bounce loss cone by a discrete whistler wave has been measured in a few cases. However, the area of the precipitation region is not known, and thus the total number of electrons lost in an LEP event can only be estimated. While the LEP events are dramatic, more important effects on trapped electrons may arise from the small but numerous deflections which increase the pitch angle diffusion rate of the electron population.

  11. 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.

  12. 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.}

  13. Cooling of cryogenic electron bilayers via the Coulomb interaction

    NASA Astrophysics Data System (ADS)

    Gamble, John King; Friesen, Mark; Joynt, Robert; Coppersmith, S. N.

    2011-09-01

    Heat dissipation in current-carrying cryogenic nanostructures is problematic because the phonon density of states decreases strongly as energy decreases. We show that the Coulomb interaction can prove a valuable resource for carrier cooling via coupling to a nearby cold electron reservoir. Specifically, we consider the geometry of an electron bilayer in a silicon-based heterostructure and analyze the power transfer. We show that, across a range of temperatures, separations, and sheet densities, the electron-electron interaction dominates the phonon heat-dissipation modes as the main cooling mechanism. Coulomb cooling is most effective at low densities, when phonon cooling is least effective in silicon, making it especially relevant for experiments attempting to perform coherent manipulations of single spins.

  14. 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.

  15. 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.

  16. Particle Simulations for Electron Beam-Plasma Interactions

    NASA Astrophysics Data System (ADS)

    Zhou, Guo-cheng; G, Zhou C.; Li, Yang; Cao, Jin-bin; J, Cao B.; Wang, Xue-yi; X, Wang Y.

    1998-12-01

    The computer simulations of high-frequency instabilities excited by the high density electron beam and their nonlinear effect are presented. One-dimensional electromagnetic particle simulations are performed with different values of the electron beam-to-plasma density ratio. The results show that for the high electron beam-to-background plasma density ratio, all the Langmuir waves and two electromagnetic waves with left-hand and right-hand circular polarizations (i.e., the "L-O mode" and the "R-X mode") propagating parallel to the magnetic field can be generated and the maximum values of wave electric fields are nearly the same. The electron beam and background plasma are diffused and a part of energetic background electrons are obviously accelerated by the wave-particle interactions. The heating of the beam and background plasma is mainly due to the electrostatic (Langmuir) wave-particle interactions, but the accelerations of a part of energetic background electrons may be mainly due to the electromagnetic wave-particle interactions.

  17. 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.

  18. Theoretical analysis of proton relays in electrochemical proton-coupled electron transfer.

    PubMed

    Auer, Benjamin; Fernandez, Laura E; Hammes-Schiffer, Sharon

    2011-06-01

    The coupling of long-range electron transfer to proton transport over multiple sites plays a vital role in many biological and chemical processes. Recently the concerted proton-coupled electron transfer (PCET) reaction in a molecule with a hydrogen-bond relay inserted between the proton donor and acceptor sites was studied electrochemically. The standard rate constants and kinetic isotope effects (KIEs) were measured experimentally for this double proton transfer system and a related single proton transfer system. In the present paper, these systems are studied theoretically using vibronically nonadiabatic rate constant expressions for electrochemical PCET. Application of this approach to proton relays requires the calculation of multidimensional proton vibrational wave functions and the incorporation of multiple proton donor-acceptor motions. The decrease in proton donor-acceptor distances due to thermal fluctuations and the contributions from excited electron-proton vibronic states play important roles in these systems. The calculated KIEs and the ratio of the standard rate constants for the single and double proton transfer systems are in agreement with the experimental data. The calculations indicate that the standard PCET rate constant is lower for the double proton transfer system because of the smaller overlap integral between the ground state reduced and oxidized proton vibrational wave functions, resulting in greater contributions from excited electron-proton vibronic states with higher free energy barriers. The theory predicts that this rate constant may be increased by modifying the molecule in a manner that decreases the equilibrium proton donor-acceptor distances or alters the molecular thermal motions to facilitate the concurrent decrease of these distances. These insights may guide the design of more efficient catalysts for energy conversion devices. PMID:21524104

  19. 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…

  20. Interactivity Between Proteges and Scientists in an Electronic Mentoring Program

    ERIC Educational Resources Information Center

    Bonnett, Cara; Wildemuth, Barbara M.; Sonnenwald, Diane H.

    2006-01-01

    Interactivity is defined by Henri (1992) as a three-step process involving communication of information, a response to this information, and a reply to that first response. It is a key dimension of computer-mediated communication, particularly in the one-on-one communication involved in an electronic mentoring program. This report analyzes the…

  1. 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).

  2. 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.

  3. Inelastic electron interaction (attachment/ionization) with deoxyribose

    NASA Astrophysics Data System (ADS)

    Ptasińska, S.; Denifl, S.; Scheier, P.; Märk, T. D.

    2004-05-01

    We have investigated experimentally the formation of anions and cations of deoxyribose sugar (C5H10O4) via inelastic electron interaction (attachment/ionization) using a monochromatic electron beam in combination with a quadrupole mass spectrometer. The ion yields were measured as a function of the incident electron energy between about 0 and 20 eV. As in the case of other biomolecules (nucleobases and amino acids), low energy electron attachment leads to destruction of the molecule via dissociative electron attachment reactions. In contrast to the previously investigated biomolecules dehydrogenation is not the predominant reaction channel for deoxyribose; the anion with the highest dissociative electron attachment (DEA) cross section of deoxyribose is formed by the release of neutral particles equal to two water molecules. Moreover, several of the DEA reactions proceed already with "zero energy" incident electrons. In addition, the fragmentation pattern of positively charged ions of deoxyribose also indicates strong decomposition of the molecule by incident electrons. For sugar the relative amount of fragment ions compared to that of the parent cation is about an order of magnitude larger than in the case of nucleobases. We determined an ionization energy value for C5H10O4+ of 10.51±0.11 eV, which is in good agreement with ab initio calculations. For the fragment ion C5H6O2+ we obtained a threshold energy lower than the ionization energy of the parent molecular ion. All of these results have important bearing for the question of what happens in exposure of living tissue to ionizing radiation. Energy deposition into irradiated cells produces electrons as the dominant secondary species. At an early time after irradiation these electrons exist as ballistic electrons with an initial energy distribution up to several tens of electron volts. It is just this energy regime for which we find in the present study rather characteristic differences in the outcome of electron

  4. The electronic structure engineering of organic dye sensitizers for solar cells: The case of JK derivatives.

    PubMed

    Zhang, Cai-Rong; Ma, Jin-Gang; Zhe, Jian-Wu; Jin, Neng-Zhi; Shen, Yu-Lin; Wu, You-Zhi; Chen, Yu-Hong; Liu, Zi-Jiang; Chen, Hong-Shan

    2015-11-01

    The design and development of novel dye sensitizers are effective method to improve the performance of dye-sensitized solar cells (DSSCs) because dye sensitizers have significant influence on photo-to-current conversion efficiency. In the procedure of dye sensitizer design, it is very important to understand how to tune their electronic structures and related properties through the substitution of electronic donors, acceptors, and conjugated bridges in dye sensitizers. Here, the electronic structures and excited-state properties of organic JK dye sensitizers are calculated by using density functional theory (DFT) and time dependent DFT methods. Based upon the calculated results, we investigated the role of different electronic donors, acceptors, and π-conjugated bridges in the modification of electronic structures, absorption properties, as well as the free energy variations for electron injection and dye regeneration. In terms of the analysis of transition configurations and molecular orbitals, the effective chromophores which are favorable for electron injection in DSSCs are addressed. Meanwhile, considering the absorption spectra and free energy variation, the promising electronic donors, π-conjugated bridges, and acceptors are presented to design dye sensitizers. PMID:26116996

  5. Spin Relaxation in III-V Semiconductors in various systems: Contribution of Electron-Electron Interaction

    NASA Astrophysics Data System (ADS)

    Dogan, Fatih; Kesserwan, Hasan; Manchon, Aurelien

    2015-03-01

    In spintronics, most of the phenomena that we are interested happen at very fast time scales and are rich in structure in time domain. Our understanding, on the other hand, is mostly based on energy domain calculations. Many of the theoretical tools use approximations and simplifications that can be perceived as oversimplifications. We compare the structure, material, carrier density and temperature dependence of spin relaxation time in n-doped III-V semiconductors using Elliot-Yafet (EY) and D'yakanov-Perel'(DP) with real time analysis using kinetic spin Bloch equations (KSBE). The EY and DP theories fail to capture details as the system investigated is varied. KSBE, on the other hand, incorporates all relaxation sources as well as electron-electron interaction which modifies the spin relaxation time in a non-linear way. Since el-el interaction is very fast (~ fs) and spin-conserving, it is usually ignored in the analysis of spin relaxation. Our results indicate that electron-electron interaction cannot be neglected and its interplay with the other (spin and momentum) relaxation mechanisms (electron-impurity and electron-phonon scattering) dramatically alters the resulting spin dynamics. We use each interaction explicitly to investigate how, in the presence of others, each relaxation source behaves. We use GaAs and GaN for zinc-blend structure, and GaN and AlN for the wurtzite structure.

  6. 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.

  7. Simulation of Coulomb interaction effects in electron sources

    NASA Astrophysics Data System (ADS)

    Rouse, John; Zhu, Xieqing; Liu, Haoning; Munro, Eric

    2011-07-01

    Over many years, we have developed electron source simulation software that has been used widely in the electron optics community to aid the development of rotationally symmetric electron and ion guns. The simulation includes the modelling of cathode emission and the effects of volumetric space charge. In the present paper we describe the existing software and explain how we have extended this software to include the effects of discrete Coulomb interactions between the electrons as they travel from the cathode surface to the exit of the gun. In the paper, we will describe the numerical models we have employed, the techniques we have used to maximize the speed of the Coulomb force computation and present several illustrative examples of cases analyzed using the new software, including thermal field emitters, LaB 6 guns and flat dispenser-type cathodes.

  8. Electron-Phonon Coupling and CT-Character in the lowest Triplet Excited State of Anthracene EDA-Complex Crystals

    NASA Astrophysics Data System (ADS)

    Maier, S.; Port, H.

    1987-11-01

    Photoexcitation spectra of triplet (T1← S0) zero-phonon lines and phonon sidebands in different anthracene electron donor-acceptor (EDA) complex crystals (A-PMDA, A-TCNB, A-TCPA) have been analyzed between 1.3 K and 50 K at high spectral resolution. From the electron-phonon coupling strength at T = 0 K values of the charge-transfer (CT) character in the range between 6% and 10% are calculated. The differences in these values are found to be correlated with the energetic positions of the triplet state, which are explained within the framework of the Mulliken theory.

  9. 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.

  10. Electron correlation in organic crystals and polymers

    SciTech Connect

    Ukrainskii, I.I.; Shramko, O.V.

    1996-12-31

    Theoretical studies of the electronic structure of molecules and crystals are connected usually with the search of extremes in the space of variational parameters explicitly introduced to many electron wave functions. Again, there are exist variational degrees of freedom connected with the form of the wave function - more complicated functions involve more parameters. So, the restrictions of the approach for wave functions can lead to the restriction of problem under consideration. Thus the problem of bond-length calculations in conducting polymers like polyacetylenes can not be solved correctly with one-determinant functions. We must use more general functions. e.g.. geminals approach. The similar situation that occurs in studies of electron properties of new conducting and superconducting materials based on molecular electron donor-acceptor pairs (organic conducting salts TTF-TCNQ, HTS cuprates. fullerides, polymer materials) is discussed.

  11. 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

  12. 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

  13. Huge electron-hole exchange interaction in aluminum nitride

    NASA Astrophysics Data System (ADS)

    Ishii, Ryota; Funato, Mitsuru; Kawakami, Yoichi

    2013-04-01

    Optical spectroscopy is performed for c-plane homoepitaxial aluminum nitride (AlN) films. The temperature dependence of the polarization-resolved photoluminescence spectra reveals the exciton fine structure. The experimental results demonstrate that the electron-hole exchange interaction energy (j) in AlN is j=6.8meV, which is the largest value for typical III-V and II-VI compound semiconductors. We propose the effective interatomic distance as the criterion of the electron-hole exchange interaction energy, revealing a universal rule. This study should encourage potential applications of excitonic optoelectronic devices in nitride semiconductors similar to those using II-VI compound semiconductors.

  14. Nature of electron-lattice interaction in superconducting oxides

    SciTech Connect

    Egami, T.; Dmowski, W.; McQueeney, R.J.

    1994-12-31

    Various experimental results show that in high temperature superconducting oxides the lattice responds rather anomalously to the onset of superconductivity. This suggests that some unconventional electron-lattice interaction may be at work in these solids which could be important to the mechanism of high temperature superconductivity. The authors describe their recent experimental observations by neutron and X-ray scattering as well as some theoretical results which support this view, and discuss their implications.

  15. Topological phase transition driven by electron-phonon interaction

    NASA Astrophysics Data System (ADS)

    Saha, Kush; Garate, Ion

    2014-03-01

    We study the effect of electron-phonon interactions in the band topology of Dirac insulators, both at zero and finite temperature. Elaborating on recent theoretical work, we determine how and when phonons can drive a trivial insulator into a topological insulating phase. As an application, we evaluate the temperature-dependence of the critical thickness for the topological transition in CdTe/HgTe quantum wells.

  16. 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.

  17. 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.

  18. 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.

  19. Dislocation-electron interactions in metals. Final report

    SciTech Connect

    Galligan, J.M.

    1984-01-01

    In the period covering this contract major advances have been made in understanding how dislocations interact with the electrons and phonons of a metal crystal: the first observations of the influence of noble metal interstitial solutes on the mechanical properties of face-centered metals; the first observations of the influence of magnetic fields on dislocation drag processes in normal state metals; a new way of distinguishing between phonon drag processes and electron drag processes; the establishment that dislocations, at low temperature, obey a flutter mechanism. The first measurement of mobile dislocation density, measured in an instantaneous manner, as a function of plastic strain; and a demonstration of the relationship of the plastic properties of crystals to the Fermi surface parameters of the metal. This latter finding is not only the first demonstration of such a long sought connection between mechanical properties of crystals and their electronic properties, but provides a bridge between metallurgy and the basic principles of solid state physics.

  20. Heavy ion beam-ionosphere interactions - Electron acceleration

    NASA Technical Reports Server (NTRS)

    Kaufmann, R. L.; Arnoldy, R. L.; Moore, T. E.; Kintner, P. M.; Cahill, L. J., Jr.

    1985-01-01

    Moore et al. (1982) described a number of unexpected effects which were observed during the first Argon Release Controlled Study (ARCS 1, or rocket flight 29:014). The present paper provides a description of detailed analyses of the interaction of the argon beam with the ionosphere. An important feature of the considered test was that all detectors and the Ar(+) gun remained attached to the rocket throughout the flight. It is pointed out that the most dramatic effect of ion gun operation on ARCS 1 involved large changes in the fluxes of electrons with energies below about 600 eV. The observations are discussed, taking into account the distribution functions, azimuth dependence, and electron and ion trajectories. Attention is given to the perpendicular ion beam, the parallel ion beam, the acceleration of downgoing and upgoing electrons, and aspects of wave generation.

  1. Heavy ion beam-ionosphere interactions - Electron acceleration

    NASA Astrophysics Data System (ADS)

    Kaufmann, R. L.; Arnoldy, R. L.; Moore, T. E.; Kintner, P. M.; Cahill, L. J., Jr.

    1985-10-01

    Moore et al. (1982) described a number of unexpected effects which were observed during the first Argon Release Controlled Study (ARCS 1, or rocket flight 29:014). The present paper provides a description of detailed analyses of the interaction of the argon beam with the ionosphere. An important feature of the considered test was that all detectors and the Ar(+) gun remained attached to the rocket throughout the flight. It is pointed out that the most dramatic effect of ion gun operation on ARCS 1 involved large changes in the fluxes of electrons with energies below about 600 eV. The observations are discussed, taking into account the distribution functions, azimuth dependence, and electron and ion trajectories. Attention is given to the perpendicular ion beam, the parallel ion beam, the acceleration of downgoing and upgoing electrons, and aspects of wave generation.

  2. 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.

  3. 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.

  4. Terahertz electron cyclotron maser interactions with an axis-encircling electron beam

    NASA Astrophysics Data System (ADS)

    Li, G. D.; Kao, S. H.; Chang, P. C.; Chu, K. R.

    2015-04-01

    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.

  5. Experimental Studies of Interacting Electronic States in NaCs

    NASA Astrophysics Data System (ADS)

    Faust, Carl E.

    This dissertation describes methods and results of spectroscopic studies of the NaCs molecule. NaCs is of particular interest in many labs where experimental studies of ultra-cold molecules are being conducted. Data obtained in the present work will also be useful as benchmarks for various theoretical calculations. Our goals in studying this molecule were to map out high lying electronic states and to understand how these states interact with one another. Sodium and cesium metal were heated in a heat-pipe oven to form a vapor of NaCs molecules. These molecules were excited using narrow band, continuous wave (cw), tunable lasers. We employed the optical-optical double resonance (OODR) technique to obtain Doppler-free spectra of transitions to rotational and vibrational levels of high lying electronic states. One state of particular interest was the 12(0+) electronic state. Rovibrational level energies corresponding to this state were measured and used to generate a potential energy curve using computer programs to implement both the Rydberg-Klein-Rees (RKR) method and the inverted perturbation approach (IPA). By observing fluorescence from the 12(0+) state resolved as a function of wavelength, we determined that this state interacts with the nearby 11(0+) electronic state, which was previously mapped out by Ashman et al. A two-stage coupling model was devised to describe the resolved fluorescence originating from these two interacting states. The electronic states interact via spin-orbit coupling, while the individual rovibrational levels interact via a second mechanism, likely nonadiabatic coupling. This two-stage coupling between the levels of these states causes quantum interference between fluorescence pathways associated with different components of the wavefunctions describing these levels. This interference results in more complicated resolved fluorescence spectra. The model was used to fit parameters describing these interactions so that the resolved

  6. 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.

  7. 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).

  8. Novel effects of spin-orbit interaction in interacting electronic systems

    NASA Astrophysics Data System (ADS)

    Sun, Jianmin

    Over the last several years there has been a remarkable growth in research activity in the physical properties of mesoscopic systems. Significant results, which were obtained by both theoretical and experimental studies, together with the enormous promise of nano-technology applications, contribute to this interest. In mesoscopic systems, there are 1023 or so electrons with strong Coulomb interaction. The length scale governing the electrons motion is small enough to cause quantization of the energy levels. In this work we study such quantum systems: quantum wires, quantum dots. During the last decade several experimental techniques have been developed for manufacturing both kinds of devices, which are currently an important tool for understanding low dimensions physics. The finite spin-orbit coupling is very natural, and, strictly speaking, unavoidable, in semiconducting quantum wires due to pronounced structural asymmetry inherent in the fabrication process. Thus the interplay between Coulomb interaction and spin-orbit coupling is important to investigate. The magnetic field also plays an important role which breaks the time-reversal symmetry of the Hamiltonian and splits the band of free electrons into two, corresponding to up-spin and down-spin electrons, reducing spin-rotational symmetry of the system from SU(2) to U(1). The dissertation takes account of the effect of the spin-orbit coupling interactions in the properties of mesoscopic systems. The manuscript is divided in four Chapters. In Chapter 1, the field theory in mesoscopic system is introduced. I present the relations between bosonic and fermionic operators in one dimension. These relations are used to bosonize spin 1/2 interaction fermion system. I show how to derive the RG equations around a fixed-point from the Operator Product Expansion (OPE). In Chapter 2, I present analysis of the interacting quantum wire problem in the presence of magnetic field and spin-orbital interaction. I show that an

  9. Design of the large hadron electron collider interaction region

    NASA Astrophysics Data System (ADS)

    Cruz-Alaniz, E.; Newton, D.; Tomás, R.; Korostelev, M.

    2015-11-01

    The large hadron electron collider (LHeC) is a proposed upgrade of the Large Hadron Collider (LHC) within the high luminosity LHC (HL-LHC) project, to provide electron-nucleon collisions and explore a new regime of energy and luminosity for deep inelastic scattering. The design of an interaction region for any collider is always a challenging task given that the beams are brought into crossing with the smallest beam sizes in a region where there are tight detector constraints. In this case integrating the LHeC into the existing HL-LHC lattice, to allow simultaneous proton-proton and electron-proton collisions, increases the difficulty of the task. A nominal design was presented in the the LHeC conceptual design report in 2012 featuring an optical configuration that focuses one of the proton beams of the LHC to β*=10 cm in the LHeC interaction point to reach the desired luminosity of L =1033 cm-2 s-1 . This value is achieved with the aid of a new inner triplet of quadrupoles at a distance L*=10 m from the interaction point. However the chromatic beta beating was found intolerable regarding machine protection issues. An advanced chromatic correction scheme was required. This paper explores the feasibility of the extension of a novel optical technique called the achromatic telescopic squeezing scheme and the flexibility of the interaction region design, in order to find the optimal solution that would produce the highest luminosity while controlling the chromaticity, minimizing the synchrotron radiation power and maintaining the dynamic aperture required for stability.

  10. 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.

  11. 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.

  12. Mechanistic basis of electron transfer to cytochromes p450 by natural redox partners and artificial donor constructs.

    PubMed

    Hlavica, Peter

    2015-01-01

    Cytochromes P450 (P450s) are hemoproteins catalyzing oxidative biotransformation of a vast array of natural and xenobiotic compounds. Reducing equivalents required for dioxygen cleavage and substrate hydroxylation originate from different redox partners including diflavin reductases, flavodoxins, ferredoxins and phthalate dioxygenase reductase (PDR)-type proteins. Accordingly, circumstantial analysis of structural and physicochemical features governing donor-acceptor recognition and electron transfer poses an intriguing challenge. Thus, conformational flexibility reflected by togging between closed and open states of solvent exposed patches on the redox components was shown to be instrumental to steered electron transmission. Here, the membrane-interactive tails of the P450 enzymes and donor proteins were recognized to be crucial to proper orientation toward each other of surface sites on the redox modules steering functional coupling. Also, mobile electron shuttling may come into play. While charge-pairing mechanisms are of primary importance in attraction and complexation of the redox partners, hydrophobic and van der Waals cohesion forces play a minor role in docking events. Due to catalytic plasticity of P450 enzymes, there is considerable promise in biotechnological applications. Here, deeper insight into the mechanistic basis of the redox machinery will permit optimization of redox processes via directed evolution and DNA shuffling. Thus, creation of hybrid systems by fusion of the modified heme domain of P450s with proteinaceous electron carriers helps obviate the tedious reconstitution procedure and induces novel activities. Also, P450-based amperometric biosensors may open new vistas in pharmaceutical and clinical implementation and environmental monitoring. PMID:26002739

  13. Electron transfer rates in bridged molecular systems. 2. A steady-state analysis of coherent tunneling and thermal transitions

    SciTech Connect

    Segal, D.; Nitzan, A.; Davis, W.B.; Wasielewski, M.R.; Ratner, M.A.

    2000-04-27

    The effect of dephasing and relaxation on electron transfer in bridged molecular systems is investigated using a simple molecular model. The interaction between the molecular system and the thermal environment is described on the level of the Redfield theory, modified when needed for the description of steady-state situations. Noting that transient as well as steady-state measurements are possible in such system, the authors discuss the relationship between the rates obtained from these different types of experiments and, in particular, the conditions under which these rates are the same. Also, a formal relation between the steady-state rate for electron transfer across a molecular bridge and the conductance of this bridge when placed between two metal contacts is established. The effect of dephasing and relaxation on the electron transfer is investigated, and new observations are made with regard to the transition from the superexchange to the thermal (hopping through bridge) regime of the transfer process. In particular, the rate is temperature-independent in the superexchange regime, and its dependence on the bridge length (N) is exponential, exp({minus}{beta}N). The rate behaves like ({alpha}{sub 1} + {alpha}{sub 2}N){sup {minus}1} exp({minus}{Delta}E/{kappa}{sub B}T) beyond a crossover value of N, where {Delta}E is the energy gap between the donor/acceptor and the bridge levels, and where {alpha}{sub 1} and {alpha}{sub 2} are characteristic times for activation onto the bridge and diffusion in the bridge, respectively. The authors find that, in typical cases, {alpha}{sub 1} {much_gt} {alpha}{sub 2}, and therefore, a region of very weak N dependence is expected before the Ohmic behavior, N{sup {minus}1}, is established for large enough N. In addition, a relatively weak exponential dependence, exp({minus}{alpha}N), is expected for long bridges if competing processes capture electrons away from the bridge sites.

  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. 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.

  16. Effects of electron-phonon interaction in metals

    NASA Astrophysics Data System (ADS)

    Yang, Xiaodong

    Phonons and electrons are two types of excitations which are responsible for many properties of condensed matter materials. The interaction between them plays an important role in condensed matter physics. In this thesis we present some theoretical investigations of the effects due to the interactions between phonons and electrons interactions. We show evidence that a structural martensitic transition is related to significant changes in the electronic structure, as revealed in thermodynamic measurements made in high magnetic fields. The effect of the magnetic field is considered unusual, as many influential investigations of martensitic transitions have emphasized that the structural transitions are primarily lattice dynamical and are driven by the entropy due to the phonons. We provide a theoretical frame-work which can be used to describe the effect of a magnetic field on the lattice dynamics in which the field dependence originates from the dielectric constant. The temperature-dependence of the phonon spectrum of alpha-uranium has recently been measured by Manley et al. using inelastic neutron scattering and x-ray scattering techniques. Although there is scant evidence of anharmonic interactions, the phonons were reported to show some softening of the optic modes at the zone boundary. The same group of authors later reported that an extra vibrational mode was observed to form at a temperature above 450 K. The existence of the proposed new mode is inconsistent with the usual theory of harmonic phonons, as applied to a structure composed of a monoclinic Bravais lattice with a two-atom basis. We investigate the effect that the f electron-phonon interaction has on the phonon spectrum and its role on the possible formation of a breathing mode of mixed electronic and phonon character. We examine the model by using Green's function techniques to obtain the phonon spectral density. Some materials undergo phase transitions from a high temperature state with periodic

  17. Instability of Interaction of a Coherent Electron Beam and Plasma

    NASA Astrophysics Data System (ADS)

    Matveev, A. I.

    2015-12-01

    Nonlinear interaction of a beam with finite density of electrons, whose velocity is greater than the phase velocity of a plasma wave, with homogeneous collisionless plasma is described. It is shown that a positive feedback arises between plasma oscillations and the wave of longitudinal electron density of the beam if the phase of this wave is 90° ahead of the phase of plasma oscillations. An increase in the energies of plasma and beam oscillations is accompanied by a decrease in the kinetic beam energy until the moment when the beam velocity becomes equal to the plasma wave phase velocity. Since the beam velocity can be greater than the plasma wave phase velocity, such energy conversion is very efficient.

  18. Intrashell Electron Interaction Mediated Photoformation of Hollow Atoms near Threshold

    SciTech Connect

    Houtari, S.; Kao, C.; Hamalainen, K.; Diamant, R.; Sharon, R.; Deutsch, M.

    2008-07-25

    Double photoionization (DPI) of an atom by a single photon is a direct consequence of electron-electron interactions within the atom. We have measured the evolution of the K-shell DPI from threshold up in transition metals by high-resolution x-ray emission spectroscopy of the K{sup h}a hypersatellites, photoexcited by monochromatized synchrotron radiation. The measured evolution of the single-to-double photoionization cross-section ratio with excitation energy was found to be universal. Theoretical fits suggest that near threshold DPI is predominantly a semiclassical knockout effect, rather than the purely quantum-mechanical shake-off observed at the infinite photon energy limit.

  19. Relativistic collision rate calculations for electron-air interactions

    SciTech Connect

    Graham, G.; Roussel-Dupre, R.

    1993-12-01

    The most recent data available on differential cross sections for electron-air interactions are used to calculate the avalanche, momentum transfer, and energy loss rates that enter into the fluid equations. Data for the important elastic, inelastic, and ionizing processes are generally available out to electron energies of 1--10 keV. Prescriptions for extending these cross sections to the relativistic regime are presented. The angular dependence of the cross sections is included where data are available as is the doubly differential cross section for ionizing collisions. The collision rates are computed by taking moments of the Boltzmann collision integrals with the assumption that the electron momentum distribution function is given by the Juettner distribution function which satisfies the relativistic H- theorem and which reduces to the familiar Maxwellian velocity distribution in the nonrelativistic regime. The distribution function is parameterized in terms of the electron density, mean momentum, and thermal energy and the rates are therefore computed on a two dimensional grid as a function of mean kinetic energy and thermal energy.

  20. Relativistic collision rate calculations for electron-air interactions

    SciTech Connect

    Graham, G.; Roussel-Dupre, R.

    1992-12-16

    The most recent data available on differential cross sections for electron-air interactions are used to calculate the avalanche, momentum transfer, and energy loss rates that enter into the fluid equations. Data for the important elastic, inelastic, and ionizing processes are generally available out to electron energies of 1--10 kev. Prescriptions for extending these cross sections to the relativistic regime are presented. The angular dependence of the cross sections is included where data is available as is the doubly differential cross section for ionizing collisions. The collision rates are computed by taking moments of the Boltzmann collision integrals with the assumption that the electron momentum distribution function is given by the Juettner distribution function which satisfies the relativistic H- theorem and which reduces to the familiar Maxwellian velocity distribution in the nonrelativistic regime. The distribution function is parameterized in terms of the electron density, mean momentum, and thermal energy and the rates are therefore computed on a two-dimensional grid as a function of mean kinetic energy and thermal energy.

  1. Global wave modeling of electron interactions with fast magnetosonic waves

    NASA Astrophysics Data System (ADS)

    Jaeger, E. F.; Batchelor, D. B.; Murakami, M.

    Electron interactions with fast magnetosonic waves are of interest for both direct electron heating and fast-wave current drive (FWCD) in tokamaks. Here the authors apply the full-wave ICRF code PICES to examples of both of these applications. To realistically account for the actual D-shaped magnetic geometry of present-day tokamaks, PICES is interfaced with the 3-D MHD equilibrium code VMEC. Likewise, to correctly model the real toroidal structure of both source and image currents in ICRF current drive antennas, PICES is interfaced with the 2-D recessed antenna impedance code RANT. Both current drive and electron heating by fast waves can be strongly altered through modification of the kappa(sub (parallel))-spectrum by the poloidal magnetic field. A poloidal mode expansion in PICES allows such variations in kappa(sub (parallel)) to be included correctly. In this paper, comparisons are made to observations of the direct electron heating profile on TFTR and to the FWCD efficiency on DIII-D. They also extrapolate to make predictions for future tokamaks such as TPX and ITER.

  2. 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.

  3. Electronic structure and charge transfer excited states of endohedral fullerene containing electron donoracceptor complexes utilized in organic photovoltaics

    NASA Astrophysics Data System (ADS)

    Amerikheirabadi, Fatemeh

    Organic Donor-Acceptor complexes form the main component of the organic photovoltaic devices (OPVs). The open circuit voltage of OPVs is directly related to the charge transfer excited state energies of these complexes. Currently a large number of different molecular complexes are being tested for their efficiency in photovoltaic devices. In this work, density functional theory as implemented in the NRLMOL code is used to investigate the electronic structure and related properties of these donor-acceptor complexes. The charge transfer excitation energies are calculated using the perturbative delta self-consistent field method recently developed in our group as the standard time dependent density functional approaches fail to accurately provide them. The model photovoltaics systems analyzed are as follows: Sc3N C 80--ZnTPP, Y3 N C80-- ZnTPP and Sc3 N C80-- ZnPc. In addition, a thorough analysis of the isolated donor and acceptor molecules is also provided. The studied acceptors are chosen from a class of fullerenes named trimetallic nitride endohedral fullerenes. These molecules have shown to possess advantages as acceptors such as long lifetimes of the charge-separated states.

  4. Controllable electron interactions in quantum dots coupled to nanowires

    NASA Astrophysics Data System (ADS)

    Tacla, Alexandre; Cheng, Guanglei; Tomczyk, Michelle; Levy, Jeremy; Daley, Andrew; Pekker, David

    We theoretically study transport properties in quantum dot devices proximity coupled to superconducting nanowires. In particular, we investigate the controllable transition from resonant pair tunneling to Andreev bound states, which has been recently observed in nanodevices fabricated at the interface of the oxide heterostructure LaAlO3/SrTiO3. We show that such a transition in transport features can signify a Lifshitz transition, at which electron interactions change from attractive to repulsive. We also discuss an alternate description in terms of magnetic impurities.

  5. Ultrafast photoinduced electron transfer reactions in supramolecular arrays: Studies of electronic coupling and solvation

    SciTech Connect

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

    1993-05-01

    Research in our laboratory focuses on developing supramolecular arrays that produce long-lived charge separation by limiting the electronic coupling between the separated charges, and on the role of solvation in determining the rates and energetics of photoinitiated electron transfer reactions. Arrays have been developed that closely mimic the electronic coupling that was observed only for long-lived radical pairs produced in photosynthetic glassy solids. A series of 36 fixed-distance donor-acceptor molecules using porphyrin donors, triptycene spacers, and 9 different acceptors has been prepared; these are used to probe the dependence of photoinduced charge separation rates on free energy of reaction as a function of solvent both in liquid and solid solution. Data were obtained on rates of charge separation in dioxane, MTHF, butyronitrile, toluene, chlorobenzene, and benzonitrile.

  6. Ultrafast photoinduced electron transfer reactions in supramolecular arrays: Studies of electronic coupling and solvation

    SciTech Connect

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

    1993-01-01

    Research in our laboratory focuses on developing supramolecular arrays that produce long-lived charge separation by limiting the electronic coupling between the separated charges, and on the role of solvation in determining the rates and energetics of photoinitiated electron transfer reactions. Arrays have been developed that closely mimic the electronic coupling that was observed only for long-lived radical pairs produced in photosynthetic glassy solids. A series of 36 fixed-distance donor-acceptor molecules using porphyrin donors, triptycene spacers, and 9 different acceptors has been prepared; these are used to probe the dependence of photoinduced charge separation rates on free energy of reaction as a function of solvent both in liquid and solid solution. Data were obtained on rates of charge separation in dioxane, MTHF, butyronitrile, toluene, chlorobenzene, and benzonitrile.

  7. Topological Phase Transition between s+- and s++ Superconducting Phases from Competing Electron--Electron and Electron--Phonon Interactions

    NASA Astrophysics Data System (ADS)

    Kim, Ki-Seok; Gammag, Rayda

    2013-06-01

    We discover a topological phase transition between conventional s+- and s++ superconducting phases by tuning the ratio of electron--electron and electron--phonon coupling constants in an FeAs-type two-band structure. Proving the existence of this unexpected quantum criticality within the mean-field theory, we propose that the quantum critical point be identified with a critical spin liquid state of an ``extended'' Dirac spectrum, where critical superconducting fluctuations cause screening of charge degrees of freedom for electronic excitations, which allows spinon excitations to carry only the spin quantum number 1/2. The emergence of the critical spin liquid state at the s+--s++ superconducting quantum critical point leads us to predict a metal--insulator--metal crossover behavior in electrical resistivity above the superconducting transition temperatures as the ratio of the electron--electron and electron--phonon coupling constants is increased. In addition, we uncover that the competition between electron--electron repulsion and electron--phonon attraction gives rise to a huge enhancement of the superconducting transition temperature near the quantum critical point which is several hundreds percent larger than that of the case when only one of the two is taken into account. Our renormalization group analysis claims that this mechanism for the enhancement of the critical temperature is not limited to superconductivity but can be applied to various Fermi surface instabilities, proposing an underlying universal structure, which turns out to be essentially identical to that of a recent study [Phys. Rev. Lett. 108 (2012) 046601] on the enhancement of the Kondo temperature in the presence of Rashba spin--orbit interaction. We speculate that the existence of this possible ``deconfined'' quantum criticality can be verified not only theoretically but also experimentally, particularly, in Li2(Pd1-xPtx)3B superconductors, varying x from 0 to 1.

  8. 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

  9. 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.

  10. 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.

  11. Interactive, Collaborative, Electronic Learning Logs in the Physics Classroom

    NASA Astrophysics Data System (ADS)

    Gosling, Chris

    2006-12-01

    I describe my experiences using Hickman's Interactive Collaborative Electronic Learning Logs teaching HS Physics. ICE Learning Logs are written in student groups to answer questions posed by the instructor, who then in turn responds to each group’s entry before the next class. These logs were used with non-physics majors in both algebra and calculus-based introductory physics courses, and also at the high school level. I found ICE Learning Logs were found to be a clear improvement over traditional student journals. Excerpts from group entries will be presented to demonstrate the group identities that formed as well as the utility of the journals to probe for conceptual understanding. In addition, the ICE Learning Logs served as an excellent resource for students to review before exams and also to examine for critical moments to reflect on in formal essays. Hickman, P. (2000). Assessing student understanding with interactive-electronic-collaborative learning logs. ENC Focus, 7(2), 24-27. Sponsored by the National Science Foundation DUE0302097 and SUNY-Buffalo State Physics

  12. 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

  13. 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.

  14. 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.

  15. Screening of the electron-phonon interaction in STO

    NASA Astrophysics Data System (ADS)

    Edelman, Alexander; Littlewood, Peter

    Strontium titanate is a bulk insulator that becomes superconducting at remarkably low carrier densities. Even more enigmatic properties become apparent at the strontium titanate/lanthanum aluminate (STO/LAO) interface and it is important to disentangle the effects of reduced dimensionality from the poorly-understood pairing mechanism. Recent experiments measuring the electronic structure of the analogous strontium titanate surface have found a cross-over as a function of carrier density from a series well-resolved phonon replica bands to a single quasiparticle dispersion, with the crossover occuring at densities that correspond to the disappearance of superconductivity in the STO/LAO system. We interpret these results in a simple analytical model that extends an Engelsberg-Schrieffer theory of electrons coupled to a single longitudinal optic phonon mode to include the effects of electronic screening. As the carrier density increases, the effective dielectric function cuts off the long-range phonon interaction beyond the Thomas-Fermi screening length, eventually leaving only a uniform short-range coupling to the phonon bath. We additionally incorporate the effects of carrier density on the static dielectric properties of the interface.

  16. 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.

  17. 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

  18. 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.

  19. 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

  20. Ab initio nonadiabatic molecular dynamics of the ultrafast electron injection from a PbSe quantum dot into the TiO2 surface.

    PubMed

    Long, Run; Prezhdo, Oleg V

    2011-11-30

    Following recent experiments [Science 2010, 328, 1543; PNAS 2011, 108, 965], we report an ab initio nonadiabatic molecular dynamics (NAMD) simulation of the ultrafast photoinduced electron transfer (ET) from a PbSe quantum dot (QD) into the rutile TiO(2) (110) surface. The system forms the basis for QD-sensitized semiconductor solar cells and demonstrates that ultrafast interfacial ET is instrumental for achieving high efficiencies in solar-to-electrical energy conversion. The simulation supports the observation that the ET successfully competes with energy losses due to electron-phonon relaxation. The ET proceeds by the adiabatic mechanism because of strong donor-acceptor coupling. High frequency polar vibrations of both QD and TiO(2) promote the ET, since these modes can rapidly influence the donor-acceptor state energies and coupling. Low frequency vibrations generate a distribution of initial conditions for ET, which shows a broad variety of scenarios at the single-molecule level. Compared to the molecule-TiO(2) interfaces, the QD-TiO(2) system exhibits pronounced differences that arise due to the larger size and higher rigidity of QDs relative to molecules. Both donor and acceptor states are more delocalized in the QD system, and the ET is promoted by optical phonons, which have relatively low frequencies in the QD materials composed of heavy elements. In contrast, in molecular systems, optical phonons are not thermally accessible under ambient conditions. Meanwhile, TiO(2) acceptor states resemble surface impurities due to the local influence of molecular chromophores. At the same time, the photoinduced ET at both QD-TiO(2) and molecule-TiO(2) interfaces is ultrafast and occurs by the adiabatic mechanism, as a result of strong donor-acceptor coupling. The reported state-of-the-art simulation generates a detailed time-domain atomistic description of the interfacial ET process that is fundamental to a wide variety of applications. PMID:22007727

  1. Multielectron transitions resulting from interactions between target and projectile electrons in ionizing collisions

    SciTech Connect

    Manson, S.T. ); DuBois, R.D. )

    1992-12-01

    Interactions between target and projectile electrons leading to ionization of one of the collision partners and simultaneous excitation of the other are investigated for fast clothed-particle--clothed-particle collisions. For H-atom impact, the first Born approximation is used to demonstrate that the low-energy-electron emission is dominated by electron-electron rather than by electron-nucleus interaction processes. For a broad class of structured particle collision systems, the electron-electron interaction is shown to play an important, non-neglibible, role. Doubly differential cross sections for energetic H-He collisions illustrate this point.

  2. Structure and Properties of Precursor/Successor Complex and Transition State of the FeCl(2+)/Fe(2+) Electron Self-Exchange Reaction via the Inner-Sphere Pathway.

    PubMed

    Rotzinger, François P

    2015-11-01

    The electron self-exchange reaction FeCl(OH2)5(2+) + Fe(OH2)6(2+) → Fe(OH2)6(2+) + FeCl(OH2)5(2+), proceeding via the inner-sphere pathway, was investigated with quantum chemical methods. Geometry and vibrational frequencies of the precursor/successor complex, (H2O)5Fe(III)ClFe(II)(OH2)5(4+)/(H2O)5Fe(II)ClFe(III)(OH2)5(4+) (P/S), and the transition state, (H2O)5FeClFe(OH2)5(4+⧧) (TS), were computed with the LC-BOP functional and CPCM hydration. Bent and linear structures were computed for the TS and P/S. The electronic coupling matrix element (Hab) and the electronic energies were calculated with multistate extended general multiconfiguration quasi-degenerate second-order perturbation theory (XGMC-QDPT2) and spin-orbit configuration interaction (SO-CI). Since the Fe···Fe distance changes considerably along the electron transfer step, the transformation P → TS → S, equations based on the hypothesis of a fixed donor-acceptor distance cannot be applied. Hence, the rate constant for the electron transfer step (ket) was calculated as described previously (Rotzinger, F. P. Inorg. Chem. 2014, 53, 9923). ket is very fast, ∼9.4 × 10(8)-6.6 × 10(9) s(-1) at 0 °C. The experimental rate constant of the title reaction (k) is much slower and controlled by the formation of the precursor complex. The substitution of a water ligand by FeCl(OH2)5(2+) at Fe(OH2)6(2+) is rate-determining. PMID:26479082

  3. 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.

  4. 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

  5. Local electron-electron interaction strength in ferromagnetic nickel determined by spin-polarized positron annihilation

    NASA Astrophysics Data System (ADS)

    Ceeh, Hubert; Weber, Josef Andreass; Böni, Peter; Leitner, Michael; Benea, Diana; Chioncel, Liviu; Ebert, Hubert; Minár, Jan; Vollhardt, Dieter; Hugenschmidt, Christoph

    2016-02-01

    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.

  6. 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

  7. Local electron-electron interaction strength in ferromagnetic nickel determined by spin-polarized positron annihilation.

    PubMed

    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

  8. Photoinduced intramolecular charge transfer in an electronically modified flavin derivative: roseoflavin.

    PubMed

    Karasulu, Bora; Thiel, Walter

    2015-01-22

    The photophysical properties of a push-pull flavin derivative, roseoflavin (RoF), are investigated in different surroundings at the molecular level, with focus on intramolecular charge transfer (ICT). Time-dependent density functional theory (TD-DFT, CAM-B3LYP functional) and DFT-based multireference configuration interaction (DFT/MRCI) are used to compute excited-state energies and one-electron properties of a truncated RoF model, roseolumiflavin (RoLF). Solvent effects are taken into account implicitly by the conductor-like polarizable continuum model and explicitly through a microsolvation scheme. In the gas phase, the calculations predict no crossing between the lowest locally excited (LE) and charge-transfer (CT) states upon twisting the dimethylamine donor group relative to the plane of the isoalloxazine acceptor moiety, whereas this crossing is found to be facile in solution (i.e., in water or benzene). Crossing of the LE and CT states facilitates ICT, which is the main cause of the fluorescence quenching and dual fluorescence character experimentally observed for roseoflavin in solution. The barrier for the ICT process is computed to be lower in water than in benzene, consistent with the enhanced ICT rates observed in more polar solvents. We present a detailed study of the molecular mechanism of the photoinduced ICT process in RoLF. For a typical donor-acceptor chromophore, three such mechanisms are discussed in the literature, which differ in the alignment of the donor and acceptor planes, namely, planar ICT (PICT), perpendicular-twisted ICT (TICT), and wagging ICT (WICT). Our theoretical results suggest that the TICT mechanism is favored in RoLF. PMID:25214319

  9. 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

  10. Steering electrons on moving pathways.

    PubMed

    Beratan, David N; Skourtis, Spiros S; Balabin, Ilya A; Balaeff, Alexander; Keinan, Shahar; Venkatramani, Ravindra; Xiao, Dequan

    2009-10-20

    Electron transfer (ET) reactions provide a nexus among chemistry, biochemistry, and physics. These reactions underpin the "power plants" and "power grids" of bioenergetics, and they challenge us to understand how evolution manipulates structure to control ET kinetics. Ball-and-stick models for the machinery of electron transfer, however, fail to capture the rich electronic and nuclear dynamics of ET molecules: these static representations disguise, for example, the range of thermally accessible molecular conformations. The influence of structural fluctuations on electron-transfer kinetics is amplified by the exponential decay of electron tunneling probabilities with distance, as well as the delicate interference among coupling pathways. Fluctuations in the surrounding medium can also switch transport between coherent and incoherent ET mechanisms--and may gate ET so that its kinetics is limited by conformational interconversion times, rather than by the intrinsic ET time scale. Moreover, preparation of a charge-polarized donor state or of a donor state with linear or angular momentum can have profound dynamical and kinetic consequences. In this Account, we establish a vocabulary to describe how the conformational ensemble and the prepared donor state influence ET kinetics in macromolecules. This framework is helping to unravel the richness of functional biological ET pathways, which have evolved within fluctuating macromolecular structures. The conceptual framework for describing nonadiabatic ET seems disarmingly simple: compute the ensemble-averaged (mean-squared) donor-acceptor (DA) tunneling interaction, , and the Franck-Condon weighted density of states, rho(FC), to describe the rate, (2pi/variant Planck's over 2pi)rho(FC). Modern descriptions of the thermally averaged electronic coupling and of the Franck-Condon factor establish a useful predictive framework in biology, chemistry, and nanoscience. Describing the influence of geometric and

  11. Full-dimensional multilayer multiconfigurational time-dependent Hartree study of electron transfer dynamics in the anthracene/C60 complex

    SciTech Connect

    Xie, Yu; Zheng, Jie; Lan, Zhenggang

    2015-02-28

    Electron transfer at the donor-acceptor heterojunctions plays a critical role in the photoinduced process during the solar energy conversion in organic photovoltaic materials. We theoretically investigate the electron transfer process in the anthracene/C60 donor-acceptor complex by using quantum dynamics calculations. The electron-transfer model Hamiltonian with full dimensionality was built by quantum-chemical calculations. The quantum dynamics calculations were performed using the multiconfigurational time-dependent Hartree (MCTDH) theory and multilayer (ML) MCTDH methods. The latter approach (ML-MCTDH) allows us to conduct the comprehensive study on the quantum evolution of the full-dimensional electron-transfer model including 4 electronic states and 246 vibrational degrees of freedom. Our quantum dynamics calculations exhibit the ultrafast anthracene → C60 charge transfer process because of the strong coupling between excitonic and charge transfer states. This work demonstrates that the ML-MCTDH is a very powerful method to treat the quantum evolution of complex systems.

  12. Electron beam electromagnetic field interaction in one-dimensional coaxial vircator

    NASA Astrophysics Data System (ADS)

    Shao, H.; Liu, G. Z.; Yang, Z. F.

    2005-10-01

    A one-dimensional model of the interaction between an injected electron beam and an electromagnetic (EM) field inside a coaxial vircator is presented. The effects of the injected electron beam energy spread, anode absorption rate, feedback and injected current premodulation are analyzed. The EM-gains of interaction between the electron beam and TM01, TE11 modes are derived and discussed.

  13. Organic pi-stacked materials for electronic applications: Synthesis, characterizations, modeling and devices

    NASA Astrophysics Data System (ADS)

    Cao, Jie

    Structure-property relationships of organic pi-stacked materials were systematically studied in this work for potential electronic applications. Alkylbithiazole-EDOT co-oligomers were synthesized to develop high-mobility materials. The co-oligomers, 5,5'-bis(4,4' -dialkyl-2,2'-bithiazol-5-yl)-(3,4,3' ,4'-bis(ethylenedioxy)-2,2'-dithienyl) (AT2A) form pi-stacks in the solid-state. They can be reduced at potentials near -2.3 V vs. Fc/Fc+, and oxidized stepwise to mono- and di-cations at potentials near 0.2 and 0.6 V vs. Fc/Fc +. The oxidative behavior of several types of bithiazole-EDOT co-oligomers was investigated by UV-vis-NIR, CV and ESR experiments. The acceptor-donor-acceptor type of molecules, AT2A form cation radicals, pi-dimers and di-cations in solution, depending on the conditions. However, oxidation of donor-acceptor-donor type of co-oligomers (TnATn, n = 1,2) gave stable di-cations in solution. The spectra of the AT2A pi-dimers were interpreted in the context of molecular exciton theory to give a direct measure of the inter-chain transfer integral, beta ˜ 0.1 eV. OTFT devices were fabricated using one of AT2A oligomers (BT 2B with butyl sidechains) as the active material. Preliminary results show that high hole mobility is achievable at R.T. in a polycrystalline film made by vacuum deposition. Mobility as high as 6.1 cm-2V -1s-1 was measured. The crystal structures of a series of alkylbithiazole oligomers (EBTz, EBTz-COOH, (EBTz)2 and BT2B) were determined. The pi-stacking structures were compared in the framework of structural parameters: pi-stacking distance, pitch and roll angles that measure the orientation of the molecules in a given stack with respect to the stack axis, and the yaw angle that measures the orientation of neighboring stacks. Typically, molecules of bithiazole oligomers within a given pi-stack are tilted a considerable angle about the short axis (pitch angle), but a very small angle about the long axis (roll angle). In such a

  14. Anisotropic Electron-Photon and Electron-Phonon Interactions in Black Phosphorus

    SciTech Connect

    Ling, Xi; Huang, Shengxi; Hasdeo, Eddwi; Parkin, William; Gracio, Jose; Tatsumi, Yuki; Nugraha, Ahmad; Puretzky, Alexander A; Das, Paul; Sumpter, Bobby G; Geohegan, David B; Kong, Jing; Saito, Riichiro; Drndic, Marija; Meunier, Vincent; Dresselhaus, M

    2016-01-01

    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 and 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.

  15. 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

  16. 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. PMID:26963685

  17. Exact solution of the PPP model for correlated electronic states of tetracene and substituted tetracene.

    PubMed

    Pati, Y Anusooya; Ramasesha, S

    2014-06-12

    Tetracene is an important conjugated molecule for device applications. We have used the diagrammatic valence bond method to obtain the desired states, in a Hilbert space of about 450 million singlets and 902 million triplets. We have also studied the donor/acceptor (D/A)-substituted tetracenes with D and A groups placed symmetrically about the long axis of the molecule. In these cases, by exploiting a new symmetry, which is a combination of C2 symmetry and electron-hole symmetry, we are able to obtain their low-lying states. In the case of substituted tetracene, we find that optically allowed one-photon excitation gaps reduce with increasing D/A strength, while the lowest singlet-triplet gap is only weakly affected. In all the systems we have studied, the excited singlet state, S1, is at more than twice the energy of the lowest triplet state and the second triplet is very close to the S1 state. Thus, donor-acceptor-substituted tetracene could be a good candidate in photovoltaic device application as it satisfies energy criteria for singlet fission. We have also obtained the model exact second harmonic generation (SHG) coefficients using the correction vector method, and we find that the SHG responses increase with the increase in D/A strength. PMID:24842608

  18. Protein dynamics modulated electron transfer kinetics in early stage photosynthesis

    NASA Astrophysics Data System (ADS)

    Kundu, Prasanta; Dua, Arti

    2013-01-01

    A recent experiment has probed the electron transfer kinetics in the early stage of photosynthesis in Rhodobacter sphaeroides for the reaction center of wild type and different mutants [Science 316, 747 (2007)]. By monitoring the changes in the transient absorption of the donor-acceptor pair at 280 and 930 nm, both of which show non-exponential temporal decay, the experiment has provided a strong evidence that the initial electron transfer kinetics is modulated by the dynamics of protein backbone. In this work, we present a model where the electron transfer kinetics of the donor-acceptor pair is described along the reaction coordinate associated with the distance fluctuations in a protein backbone. The stochastic evolution of the reaction coordinate is described in terms of a non-Markovian generalized Langevin equation with a memory kernel and Gaussian colored noise, both of which are completely described in terms of the microscopics of the protein normal modes. This model provides excellent fits to the transient absorption signals at 280 and 930 nm associated with protein distance fluctuations and protein dynamics modulated electron transfer reaction, respectively. In contrast to previous models, the present work explains the microscopic origins of the non-exponential decay of the transient absorption curve at 280 nm in terms of multiple time scales of relaxation of the protein normal modes. Dynamic disorder in the reaction pathway due to protein conformational fluctuations which occur on time scales slower than or comparable to the electron transfer kinetics explains the microscopic origin of the non-exponential nature of the transient absorption decay at 930 nm. The theoretical estimates for the relative driving force for five different mutants are in close agreement with the experimental estimates obtained using electrochemical measurements.

  19. Protein dynamics modulated electron transfer kinetics in early stage photosynthesis.

    PubMed

    Kundu, Prasanta; Dua, Arti

    2013-01-28

    A recent experiment has probed the electron transfer kinetics in the early stage of photosynthesis in Rhodobacter sphaeroides for the reaction center of wild type and different mutants [Science 316, 747 (2007)]. By monitoring the changes in the transient absorption of the donor-acceptor pair at 280 and 930 nm, both of which show non-exponential temporal decay, the experiment has provided a strong evidence that the initial electron transfer kinetics is modulated by the dynamics of protein backbone. In this work, we present a model where the electron transfer kinetics of the donor-acceptor pair is described along the reaction coordinate associated with the distance fluctuations in a protein backbone. The stochastic evolution of the reaction coordinate is described in terms of a non-Markovian generalized Langevin equation with a memory kernel and Gaussian colored noise, both of which are completely described in terms of the microscopics of the protein normal modes. This model provides excellent fits to the transient absorption signals at 280 and 930 nm associated with protein distance fluctuations and protein dynamics modulated electron transfer reaction, respectively. In contrast to previous models, the present work explains the microscopic origins of the non-exponential decay of the transient absorption curve at 280 nm in terms of multiple time scales of relaxation of the protein normal modes. Dynamic disorder in the reaction pathway due to protein conformational fluctuations which occur on time scales slower than or comparable to the electron transfer kinetics explains the microscopic origin of the non-exponential nature of the transient absorption decay at 930 nm. The theoretical estimates for the relative driving force for five different mutants are in close agreement with the experimental estimates obtained using electrochemical measurements. PMID:23387626

  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.