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Sample records for de-fg02-86er13504 photoinduced electron

  1. Photo-induced electron transfer method

    DOEpatents

    Wohlgemuth, Roland; Calvin, Melvin

    1984-01-01

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

  2. Photo-induced electron transfer method

    DOEpatents

    Wohlgemuth, R.; Calvin, M.

    1984-01-24

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

  3. Photoinduced electron transfer in ordered polymers

    SciTech Connect

    Jones, G. II.

    1991-12-01

    Long range photoinduced electron transfer between electron donor and acceptor groups is of considerable current interest in terms of strategies for artificial photosynthesis and studies regarding the redox properties of proteins. As part of an extensive study of long range electron transfer involving biopolymers, we have carried out this year investigations of the assembly of electron transfer agents in a system of model short peptides. Also studied is a polyelectrolyte that can adopt a helical conformation when electrostatically complexed with organic dye counter-ions. The principal interest in these systems has to do with the well ordered secondary structures adopted by peptide polymers, and the capabilities for synthetic modification of peptide side chains and end groups with chromophores or electroactive substituents. The present report gives a brief account of the following elements of work related to photochemical electron transfer themes: (1) the synthesis and photochemical characterization of chromophore-bound peptides and amino acid model compounds based on the amino acids, tryptophan and the spacer residue, alanine (Ala); (2) the study of binding of the cationic organic dye to a peptide electrolyte, for which cooperative dye loading and helix formation is important; and (3) completion of the synthesis of a new series of acridinium chromophores that have rod-like'' arrangements of inked aryl rings for assembly of electron donor-acceptor systems that will exhibit especially long lived charge separation.

  4. Photoinduced electron transfer in a porphyrin dyad

    SciTech Connect

    Gust, D.; Moore, T.A.; Moore, A.L.; Leggett, L.; Lin, S.; DeGraziano, J.M.; Hermant, R.M.; Nicodem, D.; Craig, P.; Seely, G.R.; Nieman, R.A. )

    1993-07-29

    A prophyrin dyad designed to facilitate vectorial interporphyrin electron transfer has been synthesized and studied using steady-state and time-resolved absorption and emission spectroscopies. The dyad features a zinc tetraaylporphyrin bearing electron-donating substituents linked by an amide bond to a free base porphyrin carrying electron-withdrawing groups. Excitation of the zinc porphyrin moiety in dichloromethane solution is followed by singlet energy transfer to the free base and concurrent electron transfer to the same moiety to yield a charge-separated state. The free base first excited singlet state decays by accepting an electron from the zinc porphyrin to form the same charge-separated state. Similar results are observed in butyronitrile. Transient absorption studies in butyronitrile verify the formation of a short-lived (8 ps) charge-separated state from the porphyrin first excited singlet states. The results support the suggestion that fluorescence quenching in related porphyrin dyads and carotenoid--diporphyrin triads is due to photoinduced electron transfer, rather than some other decay process. 17 refs., 8 refs.

  5. Photoinduced electron transfer in binary blends of conjugated polymers

    SciTech Connect

    Jenekhe, A.A.; Paor, L.R. de; Chen, X.L.; Tarkka, R.M.

    1996-10-01

    The authors report observations concerning the intermolecular photoinduced electron transfer through blends of n-type/p-type {pi}-conjugated organic polymers. The results of transient absorption spectroscopy, fluorescence quenching analysis, and delocalized radical ion pair generation studies imply that these materials are supramolecular materials.

  6. Photoinduced absolute negative current in a symmetric molecular electronic bridge

    SciTech Connect

    Prociuk, Alexander; Dunietz, Barry D

    2010-09-28

    The study of current induced by photoradiating a molecular-based device under bias is of fundamental importance to the improvement of photoconductors and photovoltaics. In this technology, electron pumps generate an uphill current that opposes a potential drop and thereby recharges a fuel cell. While the modeled molecular electron pump is completely symmetric, the sign of the photocurrent is solely determined by the existing bias and the nature of photoinduced electronic excitations. The photoradiation induces nonequilibrium population of the electrode-coupled system. The dependence of the photocurrent on electrode coupling, photoradiation field strength, and applied bias are studied at a basic model level.

  7. Photoinduced electron transfer in ordered polymers

    SciTech Connect

    Jones, G. II.

    1990-10-20

    Photochemical studies on organic polymers or biopolymers (particularly synthetic peptides) that have been modified by covalent attachment (or other means of binding) of organic chromophores and electron transfer agents are described. Specific projects involve are: peptide conjugates bearing electroactive residues such as tryptophan and specifically labeled at the N- or C-terminus of peptide chains; the electrostatic binding of organic dyes to poly-electrolytes (polyacrylates) for which the formation of dimeric aggregates of bound dye that display unusual photophysical and electron transfer properties is important; a study of the binding of dyes and electron transfer agents to the protein mimic,'' polyvinyl-2-pyrrolidinone (PVP), in hydrophobic domains that depend on specific H-bond interaction; and completion of an earlier study having to do with the triplet state properties of charge-transfer (CT) complexes of a high potential quinone and various electron donors (investigation of the properties of triplet (contact) radical-ion pairs). 13 refs., 5 figs., 2 tabs.

  8. Photoinduced Electron Transfer Based Ion Sensing within an Optical Fiber

    PubMed Central

    Englich, Florian V.; Foo, Tze Cheung; Richardson, Andrew C.; Ebendorff-Heidepriem, Heike; Sumby, Christopher J.; Monro, Tanya M.

    2011-01-01

    We combine suspended-core microstructured optical fibers with the photoinduced electron transfer (PET) effect to demonstrate a new type of fluorescent optical fiber-dip sensing platform for small volume ion detection. A sensor design based on a simple model PET-fluoroionophore system and small core microstructured optical fiber capable of detecting sodium ions is demonstrated. The performance of the dip sensor operating in a high sodium concentration regime (925 ppm Na+) and for lower sodium concentration environments (18.4 ppm Na+) is explored and future approaches to improving the sensor’s signal stability, sensitivity and selectivity are discussed. PMID:22163712

  9. Photoinduced Electron Transfer in Organic Solar Cells.

    PubMed

    Song, Peng; Li, Yuanzuo; Ma, Fengcai; Pullerits, Tõnu; Sun, Mengtao

    2016-04-01

    Electron transfer (ET) is the key process in light-driven charge separation reactions in organic solar cells. The current review summarizes the progress in theoretical modelling of ET in these materials. First we give an account of ET, with a description originating from Marcus theory. We systematically go through all the relevant parameters and show how they depend on different material properties, and discuss the consequences such dependencies have for the performance of the devices. Finally, we present a set of visualization methods which have proven to be very useful in analyzing the elementary processes in absorption and charge separation events. Such visualization tools help us to understand the properties of the photochemical and photobiological systems in solar cells. PMID:26853631

  10. Neutral histidine and photoinduced electron transfer in DNA photolyases.

    PubMed

    Domratcheva, Tatiana

    2011-11-16

    The two major UV-induced DNA lesions, the cyclobutane pyrimidine dimers (CPD) and (6-4) pyrimidine-pyrimidone photoproducts, can be repaired by the light-activated enzymes CPD and (6-4) photolyases, respectively. It is a long-standing question how the two classes of photolyases with alike molecular structure are capable of reversing the two chemically different DNA photoproducts. In both photolyases the repair reaction is initiated by photoinduced electron transfer from the hydroquinone-anion part of the flavin adenine dinucleotide (FADH(-)) cofactor to the photoproduct. Here, the state-of-the-art XMCQDPT2-CASSCF approach was employed to compute the excitation spectra of the respective active site models. It is found that protonation of His365 in the presence of the hydroquinone-anion electron donor causes spontaneous, as opposed to photoinduced, coupled proton and electron transfer to the (6-4) photoproduct. The resulting neutralized biradical, containing the neutral semiquinone and the N3'-protonated (6-4) photoproduct neutral radical, corresponds to the lowest energy electronic ground-state minimum. The high electron affinity of the N3'-protonated (6-4) photoproduct underlines this finding. Thus, it is anticipated that the (6-4) photoproduct repair is assisted by His365 in its neutral form, which is in contrast to the repair mechanisms proposed in the literature. The repair via hydroxyl group transfer assisted by neutral His365 is considered. The repair involves the 5'base radical anion of the (6-4) photoproduct which in terms of electronic structure is similar to the CPD radical anion. A unified model of the CPD and (6-4) photoproduct repair is proposed. PMID:21970417

  11. DNA Intercalated Psoralen Undergoes Efficient Photoinduced Electron Transfer.

    PubMed

    Fröbel, Sascha; Reiffers, Anna; Torres Ziegenbein, Christian; Gilch, Peter

    2015-04-01

    The interaction of psoralens with DNA has been used for therapeutic and research purposes for decades. Still the photoinduced behavior of psoralens in DNA has never been observed directly. Femtosecond transient absorption spectroscopy is used here to gain direct insight into the photophysics of a DNA-intercalated psoralen (4'-aminomethyl-4,5',8-trimethyl-psoralen (AMT)). Intercalation reduces the excited singlet lifetime of AMT to 4 ps compared with 1400 ps for AMT in water. This singlet quenching prohibits the population of the triplet state that is accessed in free AMT. Instead, a DNA to AMT electron transfer takes place. The resulting radical pair decays primarily via charge recombination with a time constant of 30 ps. The efficient electron transfer observed here reveals a completely new aspect of the psoralen-DNA interaction. PMID:26262984

  12. Final Report: Vibrational Dynamics in Photoinduced Electron Transfer

    SciTech Connect

    Kenneth G. Spears

    2006-04-19

    The objective of this grant was to understand how molecular vibrational states (geometry distortions) are involved in photoinduced electron transfer rates of molecules. This subject is an important component of understanding how molecular absorbers of light convert that energy into charge separation. This is important because the absorption usually excites molecular vibrations in a new electronic state prior to electron transfer to other molecules or semiconductor nanoparticles, as in some types of solar cells. The speeds of charge separation and charge recombination are key parameters that require experiments such as those in this work to test the rules governing electron transfer rates. Major progress was made on this goal. Some of the molecular structures selected for developing experimental data were bimolecular charge transfer complexes that contained metals of cobalt or vanadium. The experiments used the absorption of an ultrafast pulse of light to directly separate charges onto the two different molecular parts of the complex. The charge recombination then proceeds naturally, and one goal was to measure the speed of this recombination for different types of molecular vibrations. We used picosecond and femtosecond duration pulses with tunable colors at infrared wavelengths to directly observe vibrational states and their different rates of charge recombination (also called electron transfer). We discovered that different contact geometries in the complexes had very different electron transfer rates, and that one geometry had a significant dependence on the amount of vibration in the complex. This is the first and only measurement of such rates, and it allowed us to confirm our interpretation with a number of molecular models and test the sensitivity of electron transfer to vibrational states. This led us to develop a general theory, where we point out how molecular distortions can change the electron transfer rates to be much faster than prior theories

  13. Structural studies of photoinduced intramolecular electron transfer in cyclopentadienylnickelnitrosyl

    SciTech Connect

    Chen, L.X.; Bowman, M.K.; Wang, Zhiyu; Norris, J.R. |; Montano, P.A. |

    1994-03-01

    A structural study based on EXAFS, FTIR, and optical absorption spectroscopies has been conducted on a photogenerated, metastable state of cyclopentadienylnickelnitrosyl (CpNiNO) produced by a reversible photochemical reaction. The photogenerated, metastable state with distinctively different EXAFS, IR, and optical absorption spectra from those of the ground state molecules was created by irradiating the sample with the 365 nm line of a mercury lamp at 20K . At the same temperature, the reverse reaction was induced by irradiation with the 313 nm line from the mercury lamp. Based on the analysis of the EXAFS data, the photogenerated, metastable state of CpNiNO has undergone considerable nuclear rearrangements compared to its ground state. The nuclear movement is characterized by a 0.12{angstrom} elongation of Ni-N bond and by a bending of Ni-N-O. A shift of the N-O stretching frequency from 1824 to 1387 cm{sup {minus}1} was observed in the photoinduced reaction with 365 nm light, implying that a NO{sup {minus}} like species results from intramolecular electron transfer from Ni to NO. The changes in the absorption spectra for the same reaction showed reduced absorption of the 385 nm band and a newly generated broad band near IR region. Temperature dependence of the Debye-Waller factor of CpNiNO was in good agreement with the diatomic harmonic oscillator for the Ni-N bond, but deviated for the Ni-O and the Ni-C bonds. Based on the structures obtained from EXAFS, ZINDO calculations for both the ground state and the photogenerated, metastable state of CpNiNO reproduced the general features of the observed absorption spectra and qualitatively explained the wavelength dependence of the reaction. The calculated partial charges on each atom in the ground state and the photogenerated, metastable state of CpNiNO are consistent with intramolecular electron transfer upon photoexcitation by 365 nm light.

  14. Photoinduced electron transfer in perylene-TiO2 nanoassemblies.

    PubMed

    Llansola-Portoles, Manuel J; Bergkamp, Jesse J; Tomlin, John; Moore, Thomas A; Kodis, Gerdenis; Moore, Ana L; Cosa, Gonzalo; Palacios, Rodrigo E

    2013-01-01

    The photosensitization effect of three perylene dye derivatives on titanium dioxide nanoparticles (TiO2 NPs) has been investigated. The dyes used, 1,7-dibromoperylene-3,4,9,10-tetracarboxy dianhydride (1), 1,7-dipyrrolidinylperylene-3,4,9,10-tetracarboxy dianhydride (2) and 1,7-bis(4-tert-butylphenyloxy)perylene-3,4,9,10-tetracarboxy dianhydride (3) have in common bisanhydride groups that convert into TiO2 binding groups upon hydrolysis. The different substituents on the bay position of the dyes enable tuning of their redox properties to yield significantly different driving forces for photoinduced electron transfer (PeT). Recently developed TiO2 NPs having a small average size and a narrow distribution (4 ± 1 nm) are used in this work to prepare the dye-TiO2 systems under study. Whereas successful sensitization was obtained with 1 and 2 as evidenced by steady-state spectral shifts and transient absorption results, no evidence for the attachment of 3 to TiO2 was observed. The comparison of the rates of PeT (kPeT ) for 1- and 2-TiO2 systems studied in this work with those obtained for previously reported analogous systems, having TiO2 NPs covered by a surfactant layer (Hernandez et al. [2012] J. Phys. Chem. B., 117, 4568-4581), indicates that kPeT for the former systems is slower than that for the later. These results are interpreted in terms of the different energy values of the conduction band edge in each system. PMID:23742178

  15. Photoinduced electron transfer reaction in polymer-surfactant aggregates: Photoinduced electron transfer between N,N-dimethylaniline and 7-amino coumarin dyes

    SciTech Connect

    Chakraborty, Anjan; Seth, Debabrata; Setua, Palash; Sarkar, Nilmoni

    2008-05-28

    Photoinduced electron transfer between coumarin dyes and N,N-dimethylaniline has been investigated by using steady state and picosecond time resolved fluorescence spectroscopy in sodium dodecyl sulphate (SDS) micelles and PVP-polyvinyl pyrrolidone (SDS) polymer-surfactant aggregates. A slower rate of electron transfer is observed in PVP-SDS aggregates than in polymer-free SDS micelles. A Marcus type inversion is observed in the correlation of free energy change in comparison with the electron transfer rate. The careful investigation reveals that C-151 deviates from the normal Marcus inverted region compared to its analogs C-152 and C-481 due to slower rotational relaxation and smaller translational diffusion coefficient.

  16. Photochemistry of compounds adsorbed into cellulose: Effect on environment on photoinduced electron transfer in constringent media

    NASA Astrophysics Data System (ADS)

    Milosavljevic, B. H.; Thomas, J. K.

    1985-02-01

    Photoinduced electron transfer reactions in Ru(bpy) 32+/MV 2+ and Py/Cu(II) donor—acceptor systems have been studied in cellophane polymer film under conditions of various water content. The results obtained are discussed in terms of both the reaction exothermicity and separation between the reactants.

  17. 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.

  18. 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.

  19. Design of Polymer Networks Involving a Photoinduced Electronic Transmission Circuit toward Artificial Photosynthesis.

    PubMed

    Okeyoshi, Kosuke; Kawamura, Ryuzo; Yoshida, Ryo; Osada, Yoshihito

    2016-01-19

    Many strategies have been explored to achieve artificial photosynthesis utilizing mediums such as liposomes and supramolecules. Because the photochemical reaction is composed of multiple functional molecules, the surrounding microenvironment is expected to be rationally integrated as observed during photosynthesis in chloroplasts. In this study, photoinduced electronic transmission surrounding the microenvironment of Ru(bpy)3(2+) in a polymer network was investigated using poly(N-isopropylacrylamide-co-Ru(bpy)3), poly(acrylamide-co-Ru(bpy)3), and Ru(bpy)3-conjugated microtubules. Photoinduced energy conversion was evaluated by investigating the effects of (i) Ru(bpy)3(2+) immobilization, (ii) polymer type, (iii) thermal energy, and (iv) cross-linking. The microenvironment surrounding copolymerized Ru(bpy)3(2+) in poly(N-isopropylacrylamide) suppressed quenching and had a higher radiative process energy than others. This finding is related to the nonradiative process, i.e., photoinduced H2 generation with significantly higher overall quantum efficiency (13%) than for the bulk solution. We envision that useful molecules will be generated by photoinduced electronic transmission in polymer networks, resulting in the development of a wide range of biomimetic functions with applications for a sustainable society. PMID:26735211

  20. 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.

  1. Discrete Chromatic Aberrations Arising from Photoinduced Electron-Photon Interactions in Ultrafast Electron Microscopy.

    PubMed

    Plemmons, Dayne A; Flannigan, David J

    2016-05-26

    In femtosecond ultrafast electron microscopy (UEM) experiments, the initial excitation period is composed of spatiotemporal overlap of the temporally commensurate pump photon pulse and probe photoelectron packet. Generation of evanescent near-fields at the nanostructure specimens produces a dispersion relation that enables coupling of the photons (ℏω = 2.4 eV, for example) and freely propagating electrons (200 keV, for example) in the near-field. Typically, this manifests as discrete peaks occurring at integer multiples (n) of the photon energy in the low-loss/gain region of electron-energy spectra (i.e., at 200 keV ± nℏω eV). Here, we examine the UEM imaging resolution implications of the strong inelastic near-field interactions between the photons employed in optical excitation and the probe photoelectrons. We find that the additional photoinduced energy dispersion occurring when swift electrons pass through intense evanescent near-fields results in a discrete chromatic aberration that limits the spatial resolving power to several angstroms during the excitation period. PMID:27111530

  2. Quantum Dot–Bridge–Fullerene Heterodimers with Controlled Photoinduced Electron Transfer

    SciTech Connect

    Cotlet, M.; Xu, Z.

    2011-06-27

    A series of donor-bridge-acceptor systems in the form of core/shell CdSe/ZnS quantum dot-bridge-fullerene heterodimers (see picture) with varying bridge length and varying quantum dot size were self-assembled by a surface-based stepwise method to demonstrate control of the rate and of the magnitude of fluctuations of photoinduced electron transfer at the single-molecule level.

  3. Photoinduced hydrogen evolution using bipyridinium salts as electron carrier

    SciTech Connect

    Okura, I.; Kaji, N.; Aono, S.; Kita, T.; Yamada, A.

    1985-02-13

    Photochemical redox systems have been proposed for solar energy utilization. The systems including a photosensitizer, an electron donor, and an electron carrier, have been able to evolve hydrogen from water when a suitable catalyst can be applied. The electron carrier employed almost exclusively in these studies is methylviologen except for a few cases. It is desirable to explore other suitable electron carriers. In this paper some bipyridinium salts are described which are more suitable electron carriers than methylviologen. To clarify why hydrogen evolution rates are so high when some bipyridinium salts are used as electron carriers, kinetic studies were carried out by laser flash photolysis. 13 references, 4 figures, 1 table.

  4. Photonic switching of photoinduced electron transfer in a dihydropyrene-porphyrin-fullerene molecular triad.

    PubMed

    Liddell, Paul A; Kodis, Gerdenis; Andréasson, Joakim; de la Garza, Linda; Bandyopadhyay, Subhajit; Mitchell, Reginald H; Moore, Thomas A; Moore, Ana L; Gust, Devens

    2004-04-21

    Photonic control of photoinduced electron transfer has been demonstrated in a dimethyldihydropyrene (DHP) porphyrin (P) fullerene (C(60)) molecular triad. In the DHP-P-C(60) form of the triad, excitation of the porphyrin moiety is followed by photoinduced electron transfer to give a DHP-P(*)(+)-C(60)(*)(-) charge-separated state, which evolves by a charge shift reaction to DHP(*)(+)-P-C(60)(*)(-). This final state has a lifetime of 2 micros and is formed in an overall yield of 94%. Visible (>or=300 nm) irradiation of the triad leads to photoisomerization of the DHP moiety to the cyclophanediene (CPD). Excitation of the porphyrin moiety of CPD-P-C(60) produces a short-lived (<10 ns) CPD-P(*)(+)-C(60)(*)(-) state, but charge shift to the CPD moiety does not occur, due to the relatively high oxidation potential of the CPD group. Long-lived charge separation is not observed. Irradiation of CPD-P-C(60) with UV (254 nm) light converts the triad back to the DHP form. Thermal interconversion of the DHP and CPD forms is very slow, photochemical cycling is facile, and in the absence of oxygen, many cycles may be performed without substantial degradation. Thus, light is used to switch long-lived photoinduced charge separation on or off. The principles demonstrated by the triad may be useful for the design of molecule-based optoelectronic systems. PMID:15080684

  5. Photoinduced electron transfer processes in homogeneous and microheterogeneous solutions

    SciTech Connect

    Whitten, D.G.

    1991-10-01

    The focus of the work described in this report is on single electron transfer reactions of excited states which culminate in the formation of stable or metastable even electron species. For the most part the studies have involved even electron organic substrates which are thus converted photochemically to odd electron species and then at some stage reconvert to even electron products. These reactions generally fall into two rather different categories. In one set of studies we have examined reactions in which the metastable reagents generated by single electron transfer quenching of an excited state undergo novel fragmentation reactions, chiefly involving C-C bond cleavage. These reactions often culminate in novel and potentially useful chemical reactions and frequently have the potential for leading to new chemical products otherwise unaffordable by conventional reaction paths. In a rather different investigation we have also studied reactions in which single electron transfer quenching of an excited state is followed by subsequent reactions which lead reversibly to metastable two electron products which, often stable in themselves, can nonetheless be reacted with each other or with other reagents to regenerate the starting materials with release of energy. 66 refs., 9 figs., 1 tab.

  6. Photoinduced Electron Transfer in Ordered Macromolecular Assemblies. Final report for May 1, 1988 - June 30, 2002

    SciTech Connect

    Jones, G.

    2005-02-11

    The final report describes studies over a 13 year period having to do with photoinduced electron transfer for active chromophores and redox agents, including assembly of the components in water soluble polymers or polypeptides. The findings include observation of long range charge separation and electron transport using laser phototransient spectroscopy. The systems targeted in these studies include peptide assemblies for which helical conformations and aggregation are documented. Oligomeric peptides modified with non-native redox active groups were also selected for investigation. Highly charged polymers or peptides were investigated as host agents that resemble proteins. The overall goal of these investigations focused on the design and characterization of systems capable of artificial photosynthesis.

  7. Dynamics of photoinduced electron transfer from adsorbed molecules into solids

    NASA Astrophysics Data System (ADS)

    Gundlach, L.; Ernstorfer, R.; Willig, F.

    2007-08-01

    Ultrafast interfacial electron transfer from the donor orbital of organic chromophores into empty electronic acceptor states of a semiconductor and of a metal was investigated by two-photon photoemission spectroscopy (2PPE). Experimental tools and procedures have been developed for carrying out wet-chemistry preparation of the molecule/solid interface. The organic chromophore perylene was investigated with several different bridge/anchor groups on TiO2(110). One perylene compound was investigated for comparison on Ag(110). Angle and polarization dependent 2PPE measurements revealed the orientation of the perylene chromophore on the surface as controlled by the adsorption geometry of the respective anchor group on TiO2. UPS measurements gave the position of the HOMO level of the chromophore with respect to the Fermi level of the solid. The donor level of each molecule was found high enough to fulfill the “wide band limit” of heterogeneous electron transfer dynamics. Time constants for heterogeneous electron transfer were extracted from 2PPE transients. A difference by a factor of four was found, 13 fs against 47 fs, when a conjugated bond was exchanged for a saturated bond in the otherwise identical bridge group. The two different contributions to the 2PPE transients arising firstly from the excited state of the chromophore and secondly from the injected electrons were separated by measuring the latter contribution separately in the case of instantaneous interfacial electron transfer realized with catechol as adsorbate. The time scales measured for the electron transfer step and for the subsequent electron escape process from the surface into the bulk of TiO2 showed both good agreement with recent theoretical predictions of other groups for these systems.

  8. Cycloreversion of β-lactams via photoinduced electron transfer.

    PubMed

    Pérez-Ruiz, Raúl; Sáez, Jose A; Jiménez, M Consuelo; Miranda, Miguel A

    2014-11-14

    The radical anions of β-lactams, photogenerated in the presence of DABCO as an electron donor, undergo cycloreversion via N-C4 bond cleavage, back electron transfer and final C2-C3 bond cleavage, leading to olefins. The involved intermediates are 1,4-radical anions and 1,4-biradicals. The experimental observations are consistent with the results of DFT calculations. PMID:25223340

  9. Photoinduced electron transfer from DABCO to trans-nitrostilbenes

    NASA Astrophysics Data System (ADS)

    Görner, Helmut; Schulte-Frohlinde, Dietrich

    The anion radical of the trans isomers of 4-nitro-, 4,4'-dinitro-, and 4-nitro-4'-methoxystilbene was generated by triplet quenching with 1,4-diazabicyclo[2.2.2]octane (DABCO) in polar solvents at room temperature using laser flash photolysis. Electron transfer and trans → cis photoisomerization are competing processes. The radical ions decay by electron back-transfer yielding the initial ground states.

  10. Theory of ultrafast photoinduced heterogeneous electron transfer: Decay of vibrational coherence into a finite electronic-vibrational quasicontinuum

    NASA Astrophysics Data System (ADS)

    Ramakrishna, S.; Willig, F.; May, V.

    2001-08-01

    Photo-induced electron transfer from a surface attached dye molecule to the band levels of a semiconductor is modeled via an electronic-vibronic quasicontinuum. The description enables one to obtain a fairly accurate expression for the decay of the excited molecular state, including initial vibronic coherences. The model accounts for (a) the effect of a finite band width, (b) variations in reorganization energy and electronic coupling, (c) various energetic positions for the injecting level, (d) different initial vibrational wave packets in the excited state, and (e) two vibrational modes participating in the electron transfer process. Most cases are studied numerically and can be reasonably well understood from the obtained decay expression.

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

    PubMed

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

    2016-01-01

    Photo-induced charge transfer at molecular heterojunctions has gained particular interest due to the development of organic solar cells (OSC) based on blends of electron donating and accepting materials. While charge transfer between donor and acceptor molecules can be described by Marcus theory, additional carrier delocalization and coherent propagation might play the dominant role. Here, we describe ultrafast charge separation at the interface of a conjugated polymer and an aggregate of the fullerene derivative PCBM using the stochastic Schrödinger equation (SSE) and reveal the complex time evolution of electron transfer, mediated by electronic coherence and delocalization. By fitting the model to ultrafast charge separation experiments, we estimate the extent of electron delocalization and establish the transition from coherent electron propagation to incoherent hopping. Our results indicate that even a relatively weak coupling between PCBM molecules is sufficient to facilitate electron delocalization and efficient charge separation at organic interfaces. PMID:27605035

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

    PubMed Central

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

    2016-01-01

    Photo-induced charge transfer at molecular heterojunctions has gained particular interest due to the development of organic solar cells (OSC) based on blends of electron donating and accepting materials. While charge transfer between donor and acceptor molecules can be described by Marcus theory, additional carrier delocalization and coherent propagation might play the dominant role. Here, we describe ultrafast charge separation at the interface of a conjugated polymer and an aggregate of the fullerene derivative PCBM using the stochastic Schrödinger equation (SSE) and reveal the complex time evolution of electron transfer, mediated by electronic coherence and delocalization. By fitting the model to ultrafast charge separation experiments, we estimate the extent of electron delocalization and establish the transition from coherent electron propagation to incoherent hopping. Our results indicate that even a relatively weak coupling between PCBM molecules is sufficient to facilitate electron delocalization and efficient charge separation at organic interfaces. PMID:27605035

  13. Photoinduced Electron Transfer to Engineered Surface Traps in CdSe Nanocrystals

    NASA Astrophysics Data System (ADS)

    Califano, Marco; Zhu, Haiming; Yang, Ye; Hyeon-Deuk, Kim; Song, Nianhui; Wang, Youwei; Zhang, Wenqing; Prezhdo, Oleg; Lian, Tianquan

    2014-03-01

    Quantum confined nanomaterials, such as semiconductor nanocrystals (NCs), have emerged in the past decade as a new class of materials for solar energy conversion. An appropriate model for describing photoinduced charge transfer in these systems is, however, still lacking. Recently we observed that the rate of photoinduced electron transfer from CdSe NCs to molecular acceptors increased with decreasing NC size (and increasing driving force) exhibiting a lack of Marcus inverted regime behaviour over an apparent driving force range of 0-1.3 V. Our atomistic semiempirical pseudopotential calculations show that an Auger assisted ET mechanism, in which the transfer of the electron is coupled to the excitation of the hole, can circumvent the unfavourable Frank-Condon overlap (that is a signature of inter- or intra- molecular electron transfer) in the Marcus inverted regime, reproducing our observed ET rates with remarkable accuracy. We conclude that electron transfer from quantum dots differs from electron transfer originating from both molecules and bulk semiconductors. It proceeds via a novel Auger-assisted pathway which we believe is available to most excitonic nanomaterials. This new finding will have a major impact on the design of next generation solar energy harvesting devices.

  14. Photoinduced Electron Accumulation of Titanium Dioxide Nanoparticles Modified Electrodes

    NASA Astrophysics Data System (ADS)

    Miyoshi, Hirokazu; Sakamoto, Kensho; Kurashina, Masaru; Kanezaki, Eiji

    Titanium dioxide (TiO2) nanoparticles (Nps) were prepared by the hydrolysis of titanium tetraisopropoxide (TTIP) in 2-propanol with different water contents (0.5 vol% to 7.2 vol%) at 45 °C. The diameter of the Nps was estimated to be 1.5±0.5 nm (L-TiO2) and 3.0±0.6 nm (S-TiO2) from the onset wavelength in the absorption spectra and by transmission electron microscopy (TEM). A modified Pt electrode with a three-layered sandwich structure was prepared; the outermost and innermost layers were composed of S-TiO2 and L-TiO2, respectively, and the middle layer contained 1, 1'-dimethyl-4,4'-bipyridyl (MV2+)/Nafion®. Irradiation by a 500 W superhigh-pressure mercury lamp produced electrons in the conduction band of TiO2. An anodic current was observed after turning off the light. The mechanism by which anodic current is generated after turning off the radiation involves the reduction of MV2+ to MV+. by photogenerated electrons on the Nps and the diffusion of MV+. in the middle layer. After turning off the irradiation, MV+. transferred an electron to the Pt electrode via holes in the innermost layer or the conduction band of S-TiO2 coincidentally localized on the Pt electrode, resulting in the generation of the anodic current. The generation of MV+. was confirmed by the absorption spectra of MV+.. As a sacrificial reagent, 2-propanol (0.1 M) was used.

  15. Time-domain ab initio studies of photoinduced electron dynamics in nanoscale semiconductors

    NASA Astrophysics Data System (ADS)

    Prezhdo, Oleg

    2010-03-01

    Design of novel materials for energy harvesting and storage requires an understanding of the dynamical response on the nanometer scale. We have developed state-of-the-art non-adiabatic molecular dynamics techniques and implemented them within time-dependent density functional theory in order to model the ultrafast processes in these materials at the atomistic level and in real time. Quantum dots (QD) are quasi-zero dimensional structures with a unique combination of molecular and bulk properties. As a result, QDs exhibit new physical phenomena such as the electron-phonon relaxation bottleneck and carrier multiplication, which have the potential to greatly increase solar cell efficiencies. Photoinduced charge separation across molecular/bulk interfaces drives the dye-sensitized semiconductor solar cell. A subject of active research, it creates many challenges due to the stark differences between the quantum states of molecular and periodic systems, as well as the different sets of theories and experimental tools used by physicists and chemists. Our time-domain atomistic simulations create a detailed picture of these materials. By comparing and contrasting their properties, we provide a unifying description of quantum dynamics on the nanometer scale, resolve several highly debated issues, and generate theoretical guidelines for development of novel systems for energy harvesting and storage. [4pt] [1] O. V. Prezhdo ``Photoinduced dynamics in semiconductor quantum-dots: insights from time-domain ab initio studies'', Acc. Chem. Res., available online.[0pt] [2] O. V. Prezhdo, W. R. Duncan, V. V. Prezhdo, ``Photoinduced electron dynamics at semiconductor interfaces: a time-domain ab initio prospective'', Prog. Surf. Science, 84, 39 (2009).[0pt] [3] O. V. Prezhdo, et al., ``Dynamics of the photoexcited electron at the chromophore-semiconductor interface'', Acc. Chem. Res., 41, 339 (2008).[0pt] [4] W. R. Duncan, O. V. Prezhdo, ``Theoretical studies of photoinduced electron

  16. 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

  17. Photoinduced amplification of phonons localized in a two-dimensional electron gas

    SciTech Connect

    Epshtein, E.M.

    1995-09-01

    This paper discusses how phonons localized within a two-dimensional electron gas are affected by the presence a strong electromagnetic wave whose electric field vector lies in the plane of the two-dimensional electron gas. A dispersion relation for the phonons is derived under the assumption and the electromagnetic wave affects the phonon subsystem only via the two-dimensional electron gas. When the energy of an electromagnetic wave quantum is large compared to the electron energies, new regimes of electron-phonon interaction become possible (which are forbidden by conservation laws in the absence of the wave), including regimes in which the {open_quotes}attenuation{close_quotes} of the phonons is negative (photoinduced gain). 7 refs.

  18. Photoinduced electron transfer from phycoerythrin to colloidal metal semiconductor nanoparticles

    NASA Astrophysics Data System (ADS)

    Kathiravan, A.; Chandramohan, M.; Renganathan, R.; Sekar, S.

    2009-04-01

    Phycoerythrin is a water soluble pigment which absorbs in the visible region at 563 nm. The interaction of phycoerythrin with colloidal metal semiconductors was studied by absorption, FT-IR and fluorescence spectroscopy. Phycoerythrin adsorbed strongly on the surface of TiO 2 nanoparticles, the apparent association constant for the association between colloidal metal-TiO 2 nanoparticles and phycoerythrin was determined from fluorescence quenching data. The free energy change (Δ Get) for electron transfer process has been calculated by applying Rehm-Weller equation.

  19. Fluorescent recognition of Fe3+ ion with photoinduced electron transfer (PET) sensor

    NASA Astrophysics Data System (ADS)

    Fegade, Umesh; Attarde, Sanjay; Kuwar, Anil

    2013-10-01

    We synthesized a fluorescence receptor 2,2-(pyridine-2,6-diylbis(azanediyl))bis(methylene)diphenol (2) and report it as a photoinduced electron transfer (PET) cation sensor that is capable of indicating the presence of Fe3+ ion via a fluorescence signal. It was observed that fluorescence intensity changes and quenched. The association constant (Ka) of receptor (2) with Fe3+ ions was calculated from Benesi-Hildebrand and Scatchard Plot at 1.60 and 1.30 × 104 M-1 respectively.

  20. Measurement of Local Sodium Ion Levels near Micelle Surfaces with Fluorescent Photoinduced-Electron-Transfer Sensors.

    PubMed

    Uchiyama, Seiichi; Fukatsu, Eiko; McClean, Gareth D; de Silva, A Prasanna

    2016-01-11

    The Na(+) concentration near membranes controls our nerve signals aside from several other crucial bioprocesses. Fluorescent photoinduced electron transfer (PET) sensor molecules target Na(+) ions in nanospaces near micellar membranes with excellent selectivity against H(+). The Na(+) concentration near anionic micelles was found to be higher than that in bulk water by factors of up to 160. Sensor molecules that are not held tightly to the micelle surface only detected a Na(+) amplification factor of 8. These results were strengthened by the employment of control compounds whose PET processes are permanently "on" or "off". PMID:26503173

  1. Photoinduced melting of magnetic order in the correlated electron insulator NdNiO3

    NASA Astrophysics Data System (ADS)

    Caviglia, A. D.; Först, M.; Scherwitzl, R.; Khanna, V.; Bromberger, H.; Mankowsky, R.; Singla, R.; Chuang, Y.-D.; Lee, W. S.; Krupin, O.; Schlotter, W. F.; Turner, J. J.; Dakovski, G. L.; Minitti, M. P.; Robinson, J.; Scagnoli, V.; Wilkins, S. B.; Cavill, S. A.; Gibert, M.; Gariglio, S.; Zubko, P.; Triscone, J.-M.; Hill, J. P.; Dhesi, S. S.; Cavalleri, A.

    2013-12-01

    Using ultrafast resonant soft x-ray diffraction, we demonstrate photoinduced melting of antiferromagnetic order in the correlated electron insulator NdNiO3. Time-dependent analysis of the resonant diffraction spectra allows us to follow the temporal evolution of the charge imbalance between adjacent Ni sites. A direct correlation between the melting of magnetic order and charge rebalancing is found. Furthermore, we demonstrate that the magnetic ordering on the Ni and Nd sites, which are locked together in equilibrium, become decoupled during this nonthermal process.

  2. Photoinduced electron transfer from dialkyl nitroxides to halogenated solvents

    SciTech Connect

    Chateauneuf, J. ); Lusztyk, J.; Ingold, K.U. )

    1990-02-02

    Laser flash photolysis (LFP) at wavelengths within the charge-transfer absorption present in CCl{sub 4} solutions of 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) yields the oxoammonium chloride of TEMPO, 1 ({lambda}{sub max} = 460 nm), and the trichloromethyl radical in an essentially instantaneous ({le}18 ps) process. The primary photochemical event is an electron transfer from TEMPO to CCl{sub 4}, and this is followed by immediate decomposition of the CCl{sub 4}{sup {sm bullet}{minus}} radical anion to Cl{sup {minus}} and Cl{sub 3}C{sup {sm bullet}}. An independent synthesis of 1 confirmed that the absorption attributed to this species has been correctly assigned. The formation of Cl{sub 3}C{sup {sm bullet}} was inferred by its trapping by molecular oxygen. LFP of TEMPO in other halogenated solvents and of other nitroxides in halogenated solvents has confirmed the generality of these photoreactions.

  3. Photoinduced Electron Transfer between Anionic Corrole and DNA.

    PubMed

    Wang, Li-Li; Zhang, Lei; Wang, Hui; Zhang, Yang; Huang, Jun-Teng; Zhu, He; Ying, Xiao; Ji, Liang-Nian; Liu, Hai-Yang

    2016-02-01

    The interaction between a water-soluble anionic Ga(III) corrole [Ga(tpfc)(SO3Na)2] and calf thymus DNA (ct-DNA) has been investigated by using femtosecond transient absorption spectroscopy. A significant broadening from 570 to 585 nm of positive absorption band of the blend of Ga(tpfc)(SO3Na)2 and ct-DNA (Ga(tpfc)(SO3Na)2-ctDNA) has been observed from 0.15 to 0.50 ps after photoexcitation of Ga(tpfc)(SO3Na)2 into the Soret band. The control experiment has been performed on the model DNA ([poly(dG-dC)]2) rich in guanine bases, which exhibits a similar spectral broadening, whereas it is absent for [poly(dA-dT)]2 without guanine bases. The molecular orbital calculation shows that HOMO of Ga(tpfc)(SO3Na)2 is lower than that of guanine bases. The results of the electrochemical experiment show the reversible electron transfer (ET) between Ga(tpfc)(SO3Na)2 and guanine bases of ct-DNA is thermodynamically favorable. The dynamical analysis of the transient absorption spectra reveals that an ultrafast forward ET from the guanine bases to Ga(tpfc)(SO3Na)2 occurs within the pulse duration (156 fs), leading to the formation of an intermediate state. The following back ET to the ground state of Ga(tpfc)(SO3Na)2 may be accomplished in 520 fs. PMID:26752116

  4. Photoinduced melting and charge order in quarter-filled organic conductors: Itinerant electron systems with competing interactions

    NASA Astrophysics Data System (ADS)

    Yonemitsu, Kenji; Maeshima, Nobuya; Tanaka, Yasuhiro; Miyashita, Satoshi

    2009-02-01

    Photoinduced charge dynamics in one- and two-dimensional organic conductors are studied theoretically in extended Peierls-Hubbard models. For quasi-one-dimensional (EDO-TTF)2PF6, photoinduced change in the charge order pattern from (0110) to (1010) is accompanied by probe-energy-dependent oscillations of conductivity. This is caused by coexistence of charge order and delocalized electrons. For quasi-two-dimensional α-(BEDT-TTF)2I3 and θ-(BEDT-TTF)2RbZn(SCN)4, photoinduced melting of the horizontal-stripe charge order proceeds easier in the α-type salt than in the θ-type salt. This is because the charge order in the θ-type salt is more strongly stabilized by electron-phonon interactions.

  5. Photoinduced electron transfer in ordered polymers: Progress report, May 1, 1988--December 31, 1988

    SciTech Connect

    Jones, G. II

    1988-12-31

    Long-range photoinduced electron transfer between potential electron donors and acceptors is of considerable current interest in terms of strategies for artificial photosynthesis and studies regarding the redox properties of proteins. Electron transfer over organized arrays of significant dimension (e.g., 10 nm) may also be important for molecule-based bistable switches or rectifiers. As part of a program of study of long range electron transfer involving biopolymers, we report early investigations of the interaction of the xanthene dye, eosin (EY), with synthetic peptides constructed of the amino acid residues, lysine (Lys), tryptophan (Trp), and tyrosine (Tyr). The principal interest in these systems has to do with the well ordered secondary structures (e.g., ..cap alpha..-helices) adopted by peptide polymers and the capabilities for synthetic modification of peptide side chains and end groups with chromophores or electroactive substituents. Work which is completed or well underway includes synthesis of Trp homopolymer (20-25 Trp amino acid residues) with EY attached specifically at the N-terminus. Model compounds in which the xanthene dye is attached to one or two Trp residues have been prepared along with copolymers of Trp or Tyr and Lys with randomally labeled EY at Lys side chains. Photoinduced electron transfer between variously attached eosin pendants and co-bound Trp units has been studied using fluorescence quenching and laser flash photolysis methods. Also, as a model for events occurring for the synthetic peptides, electron transfer quenching of eosin singlet and triplet excited states by substituted phenols, representative of the pendant groups of Tyr residues has been investigated. The observation of ultra-long-lived contact radical ion pairs which result from the quenching an excited quinone molecule and the photolysis of quinone charge-transfer complexes constitute another theme of continuing research.

  6. Photoinduced 2-way electron transfer in composites of metal nanoclusters and semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

    Mondal, Navendu; Paul, Sneha; Samanta, Anunay

    2016-07-01

    In order to explore the potential of nanocomposites comprising semiconductor quantum dots (QDs) and metal nanoclusters (NCs) in photovoltaic and catalytic applications, the interaction between CdTe QDs and gold NCs, Au10 and Au25, stabilized by histidine, bovine serum albumin (BSA) and glutathione, is studied by an ultrafast transient absorption (TA) technique. Temporal and spectral studies of the transients reveal photoinduced 2-way electron transfer between the two constituents of the nanocomposites, where Au NCs, which generally act as electron donors when used as photosensitizers, perform the role of the efficient electron acceptor. Interestingly, it is found that the electron transfer dynamics in these composites is governed not by the distance of separation of the constituents but by the nature of the surface capping ligands. Despite a large separation between the QDs and NCs in a giant BSA-capped system, a higher electron transfer rate in this composite suggests that unlike other smaller capping agents, which act more like insulators, BSA allows much better electron conduction, as indicated previously.In order to explore the potential of nanocomposites comprising semiconductor quantum dots (QDs) and metal nanoclusters (NCs) in photovoltaic and catalytic applications, the interaction between CdTe QDs and gold NCs, Au10 and Au25, stabilized by histidine, bovine serum albumin (BSA) and glutathione, is studied by an ultrafast transient absorption (TA) technique. Temporal and spectral studies of the transients reveal photoinduced 2-way electron transfer between the two constituents of the nanocomposites, where Au NCs, which generally act as electron donors when used as photosensitizers, perform the role of the efficient electron acceptor. Interestingly, it is found that the electron transfer dynamics in these composites is governed not by the distance of separation of the constituents but by the nature of the surface capping ligands. Despite a large separation

  7. Optically monitoring voltage in neurons by photo-induced electron transfer through molecular wires

    PubMed Central

    Miller, Evan W.; Lin, John Y.; Frady, E. Paxon; Steinbach, Paul A.; Kristan, William B.; Tsien, Roger Y.

    2012-01-01

    Fluorescence imaging is an attractive method for monitoring neuronal activity. A key challenge for optically monitoring voltage is development of sensors that can give large and fast responses to changes in transmembrane potential. We now present fluorescent sensors that detect voltage changes in neurons by modulation of photo-induced electron transfer (PeT) from an electron donor through a synthetic molecular wire to a fluorophore. These dyes give bigger responses to voltage than electrochromic dyes, yet have much faster kinetics and much less added capacitance than existing sensors based on hydrophobic anions or voltage-sensitive ion channels. These features enable single-trial detection of synaptic and action potentials in cultured hippocampal neurons and intact leech ganglia. Voltage-dependent PeT should be amenable to much further optimization, but the existing probes are already valuable indicators of neuronal activity. PMID:22308458

  8. Two-semiconductive-component hybrid coordination polymers with controllable photo-induced electron-transfer properties.

    PubMed

    Liu, Jian-Jun; Chen, Yong; Lin, Mei-Jin; Huang, Chang-Cang; Dai, Wen-Xin

    2016-04-12

    Two semiconductive inorganic-organic hybrid coordination polymers constructed from metal iodide clusters and naphthalene diimide semiconductive components, [Cu2I2(DPNDI)]n () and [PbI2(DPNDI)]n () (DPNDI = N,N'-di-(4-pyridyl)-1,4,5,8-naphthalene diimide), have been synthesized and characterized. Although possessing similar 2D heterostructures, hybrids exhibited different photo-induced electron-transfer properties. Due to the higher HOMO energy level of the [Cu2I2]n chain than that of the [PbI2]n cluster, only hybrid can easily undergo intramolecular electron transfer to form a long-lived charge separated state, which may be applied in artificial photosynthesis. PMID:26985714

  9. Dynamics of Radical Ion Pairs following Photoinduced Electron Transfer in Solvents with Low and Intermediate Polarities.

    PubMed

    Mentel, Kamila K; Nunes, Rui M D; Serpa, Carlos; Arnaut, Luis G

    2015-06-18

    Fluorescence quenching of p-xylene, naphthalene, or pyrene by fumaronitrile in apolar solvents and in solvents of intermediate polarities leads to weakly fluorescent radical ion pairs. This emission is assigned to ion pairs in close contact on the basis of their solvent polarity dependence, kinetics, and thermodynamics. The temperature-dependence of the intensity and fluorescence emission maxima of ion pairs in methyl acetate reveals that they have decay channels competitive with their thermal equilibration. The results presented in this work are consistent with the direct formation of contact ion pairs in weakly polar solvents and in solvents of intermediate polarities as the result of bimolecular photoinduced electron transfer reactions between aromatic hydrocarbons and nitriles. The implications of these findings in free-energy relationships of electron transfer reactions are discussed. PMID:25588979

  10. Photoinduced Electron Transfer between Psoralens and DNA: Influence of DNA Sequence and Substitution.

    PubMed

    Fröbel, Sascha; Levi, Lucilla; Ulamec, Sabine M; Gilch, Peter

    2016-05-01

    Psoralens are heterocyclic compounds which are, among other uses, used to treat skin deseases in the framework of PUVA therapy. In the dark, they intercalate into DNA and can form photoadducts with thymines upon UV-A excitation, which harms the affected cells. We have recently discovered that after excitation of intercalated psoralens, an efficient photoinduced electron transfer (PET) from DNA occurs. Here, the PET is studied in detail by means of femtosecond transient absorption spectroscopy. Using DNA samples that contain either only GC or AT base pairs, we show that only guanine donates the electrons. Additionally, the substituent effects on PET are studied relying on three different psoralen derivatives. The substitution alters spectroscopic and electrochemical properties of the psoralens, which are determined by cyclic voltammetry and steady state spectroscopy. These experiments allow us to estimate the PET energetics, which are in line with the measured kinetics. Implications for the applications of psoralens are discussed. PMID:26607751

  11. Structural effects on photoinduced electron transfer in carotenoid-porphyrin-quinone triads

    SciTech Connect

    Kuciauskas, D.; Liddell, P.A.; Hung, S.C.; Lin, S.; Stone, S.; Seely, G.R.; Moore, A.L.; Moore, T.A.; Gust, D.

    1997-01-16

    meso-Polyarylporphyrins are often used as components of molecules that mimic photosynthetic reaction centers by carrying out photoinduced electron-transfer reactions. Studies of these systems have raised questions concerning the role of alkyl substituents at the `{beta}-pyrrolic` positions on the porphyrin periphery in limiting {pi}-{pi} overlap between the macrocycle and the aryl rings. The degree of overlap affects electronic coupling and, therefore, the rates of electron-transfer reactions. There is also evidence that when the linkages joining porphyrins to electron-acceptor or -donor moieties contain amide bonds, the sense of the amide linkage may strongly affect electron-transfer rate constants. In this study, three carotenoid-porphyrin-quinone molecular triads and various model compounds have been prepared, and electron-transfer has been studied using time-resolved emission and absorption techniques. The results show that steric hindrance due to methyl groups at the {beta}-pyrrolic positions reduces electron-transfer rate constants by a factor of approximately 1/5. In addition, amide-containing donor-acceptor linkages having the nitrogen atom attached to the porphyrin meso-aryl ring demonstrate electron-transfer rate constants approximately 30 times larger than those for similar linkages with the amide reversed, after correction for thermodynamic effects. 52 refs., 7 figs., 2 tabs.

  12. Photoinduced electron transfer between sulfur-containing carboxylic acids and the 4-carboxybenzophenone triplet state in aqueous solution

    SciTech Connect

    Marciniak, B. A. Mickiewicz Univ., Poznan ); Bobrowski, K.; Hug, G.L. ); Rozwadowski, J. )

    1994-05-05

    The mechanism of photoinduced electron transfer was investigated using laser flash photolysis and steady-state photolysis techniques. Bimolecular rate constants for quenching of the CB triplet state by six sulfur-containing acids, with varying numbers of COO[sup [minus

  13. Nonadiabatic dynamics of photoinduced proton-coupled electron transfer: comparison of explicit and implicit solvent simulations.

    PubMed

    Auer, Benjamin; Soudackov, Alexander V; Hammes-Schiffer, Sharon

    2012-07-01

    Theoretical approaches for simulating the ultrafast dynamics of photoinduced proton-coupled electron transfer (PCET) reactions in solution are developed and applied to a series of model systems. These processes are simulated by propagating nonadiabatic surface hopping trajectories on electron-proton vibronic surfaces that depend on the solute and solvent nuclear coordinates. The PCET system is represented by a four-state empirical valence bond model, and the solvent is treated either as explicit solvent molecules or as a dielectric continuum, in which case the solvent dynamics is described in terms of two collective solvent coordinates corresponding to the energy gaps associated with electron and proton transfer. The explicit solvent simulations reveal two distinct solvent relaxation time scales, where the faster time scale relaxation corresponds to librational motions of solvent molecules in the first solvation shell, and the slower time scale relaxation corresponds to the bulk solvent dielectric response. The charge transfer dynamics is strongly coupled to both the fast and slow time scale solvent dynamics. The dynamical multistate continuum theory is extended to include the effects of two solvent relaxation time scales, and the resulting coupled generalized Langevin equations depend on parameters that can be extracted from equilibrium molecular dynamics simulations. The implicit and explicit solvent approaches lead to qualitatively similar charge transfer and solvent dynamics for model PCET systems, suggesting that the implicit solvent treatment captures the essential elements of the nonequilibrium solvent dynamics for many systems. A combination of implicit and explicit solvent approaches will enable the investigation of photoinduced PCET processes in a variety of condensed phase systems. PMID:22651684

  14. Photoinduced 2-way electron transfer in composites of metal nanoclusters and semiconductor quantum dots.

    PubMed

    Mondal, Navendu; Paul, Sneha; Samanta, Anunay

    2016-08-01

    In order to explore the potential of nanocomposites comprising semiconductor quantum dots (QDs) and metal nanoclusters (NCs) in photovoltaic and catalytic applications, the interaction between CdTe QDs and gold NCs, Au10 and Au25, stabilized by histidine, bovine serum albumin (BSA) and glutathione, is studied by an ultrafast transient absorption (TA) technique. Temporal and spectral studies of the transients reveal photoinduced 2-way electron transfer between the two constituents of the nanocomposites, where Au NCs, which generally act as electron donors when used as photosensitizers, perform the role of the efficient electron acceptor. Interestingly, it is found that the electron transfer dynamics in these composites is governed not by the distance of separation of the constituents but by the nature of the surface capping ligands. Despite a large separation between the QDs and NCs in a giant BSA-capped system, a higher electron transfer rate in this composite suggests that unlike other smaller capping agents, which act more like insulators, BSA allows much better electron conduction, as indicated previously. PMID:27396603

  15. Thioamide quenching of fluorescent probes through photoinduced electron transfer: mechanistic studies and applications.

    PubMed

    Goldberg, Jacob M; Batjargal, Solongo; Chen, Benson S; Petersson, E James

    2013-12-11

    Previously we have shown that thioamides can be incorporated into proteins as minimally perturbing fluorescence-quenching probes to study protein dynamics, folding, and aggregation. Here, we show that the spontaneity of photoinduced electron transfer between a thioamide and an excited fluorophore is governed by the redox potentials of each moiety according to a Rehm-Weller-type model. We have used this model to predict thioamide quenching of various common fluorophores, and we rigorously tested more than a dozen examples. In each case, we found excellent agreement between our theoretical predictions and experimental observations. In this way, we have been able to expand the scope of fluorophores quenched by thioamides to include dyes suitable for microscopy and single-molecule studies, including fluorescein, Alexa Fluor 488, BODIPY FL, and rhodamine 6G. We describe the photochemistry of these systems and explore applications that demonstrate the utility of thioamide quenching of fluorescein to studying protein folding and proteolysis. PMID:24266520

  16. Thioamide Quenching of Fluorescent Probes Through Photoinduced Electron Transfer: Mechanistic Studies and Applications

    PubMed Central

    Goldberg, Jacob M.; Batjargal, Solongo; Chen, Benson S.; Petersson, E. James

    2014-01-01

    Previously we have shown that thioamides can be incorporated into proteins as minimally perturbing fluorescence- quenching probes to study protein dynamics, folding, and aggregation. Here, we show that the spontaneity of photoinduced electron transfer between a thioamide and an excited fluorophore is governed by the redox potentials of each moiety according to a Rehm-Weller-type model. We have used this model to predict thioamide quenching of various common fluorophores, and we rigorously tested more than a dozen examples. In each case, we found excellent agreement between our theoretical predictions and experimental observations. In this way, we have been able to expand the scope of fluorophores quenched by thioamides to include dyes suitable for microscopy and single molecule studies, including fluorescein, Alexa Fluor 488, BODIPY FL, and rhodamine 6G. We describe the photochemistry of these systems and explore applications that demonstrate the utility of thioamide quenching of fluorescein to studying protein folding and proteolysis. PMID:24266520

  17. Photoinduced electron transfer and fluorescence mechanisms in covalently linked polynuclear aromatic-nucleotide complexes

    SciTech Connect

    Geacintov, N.E.; Mao, Bing; Zhao, Rushen; Chen, Junxin; Liu, Tong Ming; Ya, Nai-Qi; France, L.L.; Sutherland, J.D.

    1992-04-01

    The fluorescence of polycyclic aromatic hydrocarbon-nucleic acid complexes is quenched by photoinduced electron transfer mechanisms in aqueous solutions at ambient temperatures. These effects are illustrated with the biologically important compound benzo[a]pyrene-7,8-diol-9,10-epoxide (BPDE), a mutagenic and carcinogenic metabolite of the environmental pollutant benzo[a]pyrene, which forms covalent mutagenic lesions with 2{prime}-deoxyguanosine (dG) residues in DNA. The dependence of the fluroescence yeild and fluorescence decay times of the covalent model adduct (+)-trans-BPDE-N{sup 2}-dG as a function of temperature and methanol/water composition are described. Because of the sensitivity of the fluorescence of the pyrenyl residue to the polarity of the microenvironment, the magnitude of the fluorescence yield can be used to distinguish between highly hydrophobic (e.g. intercalation) and other more solvent-exposed BPDE-nucleic acid binding sites.

  18. Photoinduced electron transfer and fluorescence mechanisms in covalently linked polynuclear aromatic-nucleotide complexes

    SciTech Connect

    Geacintov, N.E.; Mao, Bing; Zhao, Rushen; Chen, Junxin; Liu, Tong Ming; Ya, Nai-Qi . Dept. of Chemistry); France, L.L.; Sutherland, J.D. )

    1992-01-01

    The fluorescence of polycyclic aromatic hydrocarbon-nucleic acid complexes is quenched by photoinduced electron transfer mechanisms in aqueous solutions at ambient temperatures. These effects are illustrated with the biologically important compound benzo(a)pyrene-7,8-diol-9,10-epoxide (BPDE), a mutagenic and carcinogenic metabolite of the environmental pollutant benzo(a)pyrene, which forms covalent mutagenic lesions with 2{prime}-deoxyguanosine (dG) residues in DNA. The dependence of the fluroescence yeild and fluorescence decay times of the covalent model adduct (+)-trans-BPDE-N{sup 2}-dG as a function of temperature and methanol/water composition are described. Because of the sensitivity of the fluorescence of the pyrenyl residue to the polarity of the microenvironment, the magnitude of the fluorescence yield can be used to distinguish between highly hydrophobic (e.g. intercalation) and other more solvent-exposed BPDE-nucleic acid binding sites.

  19. Role of the bridge in photoinduced electron transfer in porphyrin-fullerene dyads.

    PubMed

    Pelado, Beatriz; Abou-Chahine, Fawzi; Calbo, Joaquín; Caballero, Rubén; de la Cruz, Pilar; Junquera-Hernández, José M; Ortí, Enrique; Tkachenko, Nikolai V; Langa, Fernando

    2015-04-01

    The role of π-conjugated molecular bridges in through-space and through-bond electron transfer is studied by comparing two porphyrin-fullerene donor-acceptor (D-A) dyads. One dyad, ZnP-Ph-C60 (ZnP = zinc porphyrin), incorporates a phenyl bridge between D and A and behaves very similarly to analogous dyads studied previously. The second dyad, ZnP-EDOTV-C60, introduces an additional 3,4-ethylenedioxythienylvinylene (EDOTV) unit into the conjugated bridge, which increases the distance between D and A, but, at the same time, provides increased electronic communication between them. Two essential outcomes that result from the introduction of the EDOTV unit in the bridge are as follows: 1) faster charge recombination, which indicates enhanced electronic coupling between the charge-separated and ground electronic states; and 2) the disappearance of the intramolecular exciplex, which mediates photoinduced charge separation in the ZnP-Ph-C60 dyad. The latter can be interpreted as a gradual decrease in electronic coupling between locally excited singlet states of D and A when introducing the EDOTV unit into the D-A bridge. PMID:25737468

  20. Photoinduced phase transitions in vanadium dioxide revealed by ultrafast electron diffraction and mid-infrared spectroscopy

    NASA Astrophysics Data System (ADS)

    Tiwari, Kunal; Morrison, Vance; Chatelain, Robert; Hendaoui, Ali; Bruhacs, Andrew; Chaker, Mohamed; Siwick, Bradley

    2015-03-01

    The complex interplay between strong electron-electron correlations and structural distortions is thought to determine the electronic properties of many oxides, but the respective role of these two contributions is often difficult to determine. We report combined radio-frequency compressed ultrafast electron diffraction (RF-UED) and infrared transmissivity experiments in which we directly monitor and separate the lattice and charge density reorganizations associated with the optically induced semiconductor-to-metal phase transition in vanadium dioxide. These studies have uncovered a previously unreported photoinduced transition to a metastable phase retaining the periodic lattice distortion characteristic of the insulating phase, but differing by a reorganization of charge density along the vanadium dimer chains and a transition to metal-like mid IR optical properties. These results demonstrate that UED is able to follow details of both lattice and electronic structural dynamics on the ultrafast timescale. Supported by Natural Sciences and Engineering Research Council of Canada, the Canada Foundation for Innovation, the Canada Research Chairs program, NSERC PGS-D and CGS-D fellowships, and Fonds de Récherche du Québec-Nature et Technologies.

  1. Photochemical reactions of electron-deficient olefins with N,N,N‧,N‧-tetramethylbenzidine via photoinduced electron-transfer

    NASA Astrophysics Data System (ADS)

    Pan, Yang; Zhao, Junshu; Ji, Yuanyuan; Yan, Lei; Yu, Shuqin

    2006-01-01

    Photoinduced electron transfer reactions of several electron-deficient olefins with N, N, N', N'-tetramethylbenzidine (TMB) in acetonitrile solution have been studied by using laser flash photolysis technique and steady-state fluorescence quenching method. Laser pulse excitation of TMB yields 3TMB* after rapid intersystem crossing from 1TMB*. The triplet which located at 480 nm is found to undergo fast quenching with the electron acceptors fumaronitrile (FN), dimethyl fumarate (DMF), diethyl fumarate (DEF), cinnamonitrile (CN), α-acetoxyacrylonitrile (AAN), crotononitrile (CrN) and 3-methoxyacrylonitrile (MAN). Substituents binding to olefin molecule own different electron-donating/withdrawing powers, which determine the electron-deficient property (π-cloud density) of olefin molecule as well as control the electron transfer rate constant directly. The detection of ion radical intermediates in the photolysis reactions confirms the proposed electron transfer mechanism, as expected from thermodynamics. The quenching rate constants of triplet TMB by these olefins have been determined at 510 nm to avoid the disturbance of formed TMB cation radical around 475 nm. All the kqT values approach or reach to the diffusion-controlled limit. In addition, fluorescence quenching rate constants kqS have been also obtained by calculating with Stern-Volmer equation. A correlation between experimental electron transfer rate constants and free energy changes has been explained by Marcus theory of adiabatic outer-sphere electron transfer. Disharmonic kq values for CN and CrN in endergonic region may be the disturbance of exciplexs formation.

  2. Geometries, Electronic Couplings, and Hole Dissociation Dynamics of Photoinduced Electron-Hole Pairs in Polyhexylthiophene-Fullerene Dyads Rigidly Linked by Oligophenylenes.

    PubMed

    Miura, Taku; Tao, Ran; Shibata, Sho; Umeyama, Tomokazu; Tachikawa, Takashi; Imahori, Hiroshi; Kobori, Yasuhiro

    2016-05-11

    To shed a light on fundamental molecular functions of photoinduced charge conductions by organic photovoltaic materials, it is important to directly observe molecular geometries of the intermediate charges just after the photoinduced electron-transfer reactions. However, highly inhomogeneous molecular environments at the bulk heteojunction interfaces in the photoactive layers have prevented us from understanding the mechanism of the charge conductions. We have herein investigated orbital geometries, electronic couplings, and hole-dissociation dynamics of photoinduced charge-separated (CS) states in a series of poly(3-hexylthiophene)-fullerene linked dyads bridged by rigid oligo-p-phenylene spacers by using time-resolved EPR spectroscopy. It has been revealed that one-dimensional intramolecular hole-dissociations exothermically take place from localized holes in initial CS states, following bridge-mediated, photoinduced charge-separations via triplet exciton diffusions in the conjugated polymer-backbones. This molecular wire property of the photoinduced charges in solution at room temperature demonstrates the potential utility of the covalently bridged polymer molecules applied for the molecular devices. PMID:27082279

  3. Dynamics and mechanisms of interfacial photoinduced electron transfer processes of third generation photovoltaics and photocatalysis.

    PubMed

    Bauer, Christophe; Teuscher, Joël; Brauer, Jan C; Punzi, Angela; Marchioro, Arianna; Ghadiri, Elham; De Jonghe, Jelissa; Wielopolski, Mateusz; Banerji, Natalie; Moser, Jacques E

    2011-01-01

    Photoinduced electron transfer (PET) across molecular/bulk interfaces has gained attention only recently and is still poorly understood. These interfaces offer an excellent case study, pertinent to a variety of photovoltaic systems, photo- and electrochemistry, molecular electronics, analytical detection, photography, and quantum confinement devices. They play in particular a key role in the emerging fields of third-generation photovoltaic energy converters and artificial photosynthetic systems aimed at the production of solar fuels, creating a need for a better understanding and theoretical treatment of the dynamics and mechanisms of interfacial PET processes. We aim to achieve a fundamental understanding of these phenomena by designing experiments that can be used to test and alter modern theory and computational modeling. One example illustrating recent investigations into the details of the ultrafast processes that form the basis for photoinduced charge separation at a molecular/bulk interface relevant to dye-sensitized solar cells is briefly presented here: Kinetics of interfacial PET and charge recombination processes were measured by fs and ns transient spectroscopy in a heterogeneous donor-bridge-acceptor (D-B-A) system, where D is a Ru(II)(terpyridyl-PO3)(NCS)3 complex, B an oligo-p-phenylene bridge, and A nanocrystalline TiO2. The forward ET reaction was found to be faster than vibrational relaxation of the vibronic excited state of the donor. Instead, the back ET occurred on the micros time scale and involved fully thermalized species. The D-A distance dependence of the electron transfer rate was studied by varying the number of p-phenylene units contained in the bridge moiety. The remarkably low damping factor beta = 0.16 angstroms(-1) observed for the ultrafast charge injection from the dye excited state into the conduction band of TiO2 is attributed to the coupling of electron tunneling with nonequilibrium vibrations redistributed on the bridge

  4. Transient electronic structure of the photoinduced phase of Pr0.7Ca0.3MnO3 probed with soft x-ray pulses

    SciTech Connect

    Rini, M.; Zhu, Y.; Wall, S.; Tobey, R. I.; Ehrke, H.; Garl, T.; Freeland, J. W.; Tomioka, Y.; Tokura, Y.; Cavalleri, A.; Schoenlein, R. W.

    2009-04-01

    We use time-resolved x-ray absorption near-edge structure spectroscopy to investigate the electronic dynamics associated with the photoinduced insulator-to-metal phase transition in the colossal magnetoresistive manganite Pr{sub 0.7}Ca{sub 0.3}MnO{sub 3}. Absorption changes at the O K and Mn L edges directly monitor the evolution of the density of unoccupied states in the transient photoinduced phase. We show that the electronic structure of the photoinduced phase is remarkably similar to that of the ferromagnetic metallic phase reached in related manganites upon cooling below the Curie temperature.

  5. Classical molecular dynamics simulation of the photoinduced electron transfer dynamics of plastocyanin.

    PubMed Central

    Ungar, L W; Scherer, N F; Voth, G A

    1997-01-01

    Classical molecular dynamics simulations are used to investigate the nuclear motions associated with photoinduced electron transfer in plastocyanin. The blue copper protein is modeled using a molecular mechanics potential; potential parameters for the copper-protein interactions are determined using an x-ray crystallographic structure and absorption and resonance Raman spectra. Molecular dynamics simulations yield a variety of information about the ground (oxidized) and optically excited (charge-transfer) states: 1) The probability distribution of the potential difference between the states, which is used to determine the coordinate and energy displacements, places the states well within the Marcus inverted region. 2) The two-time autocorrelation function of the difference potential in the ground state and the average of the difference potential after instantaneous excitation to the excited state are very similar (confirming linear response in this system); their decay indicates that vibrational relaxation occurs in about 1 ps in both states. 3) The spectral densities of various internal coordinates begin to identify the vibrations that affect the optical transition; the spectral density of the difference potential correlation function should also prove useful in quantum simulations of the back electron transfer. 4) Correlation functions of the protein atomic motions with the difference potential show that the nuclear motions are correlated over a distance of more than 20 A, especially along proposed electron transport paths. Images FIGURE 1 FIGURE 7 PMID:8994588

  6. Electron spectrometer in adjustable triode configuration for photo-induced field emission measurements

    SciTech Connect

    Bornmann, B.; Mingels, S.; Luetzenkirchen-Hecht, D.; Mueller, G.; Dams, F.; Prommesberger, C.; Schreiner, R.

    2012-01-15

    We have constructed a new ultrahigh vacuum apparatus with a triode configuration for the systematic investigation of photo-induced field emission (PFE) from metallic or semiconducting cathodes. These are exposed to electric fields up to 400 MV/m and laser irradiation by means of hole or mesh gates. Cathodes and gates are in situ exchangeable and adjustable with high precision to ensure a homogeneous extraction of electrons which are partially transmitted to the fixed electron spectrometer. Its hemispherical sector analyzer provides an energy resolution limit of 8 meV. The commissioning of the measurement system has been performed with a tungsten needle. Its temperature showed up in the high-energy tail of the electron spectrum, while its work function was derived from the spectral low-energy part combined with the integral current-voltage curve. First PFE measurements on B-doped Si-tip arrays yielded a small field emission current increase under green laser illumination. A shift and splitting of the energy spectra was observed which revealed different emission regimes as well as the photosensitivity of the cathode due to carrier excitation into the conduction band. For the full exploitation of the PFE system, a tunable laser over a wide eV-range is required.

  7. Rational design of signal-on biosensors by using photoinduced electron transfer between Ag nanoclusters and split G-quadruplex halves-hemin complexes.

    PubMed

    Zhang, Kai; Wang, Ke; Zhu, Xue; Gao, Yun; Xie, Minhao

    2014-11-25

    Photoinduced electron transfer (PET) between DNA-Ag nanoclusters (AgNCs) and G-quadruplex halves-hemin has been used for building a new sensing platform for the signal-on detection of adenosine and RNA. PMID:25284278

  8. Photoinduced Electron Transfer in the Strong Coupling Regime: Waveguide–Plasmon Polaritons

    NASA Astrophysics Data System (ADS)

    Zeng, Peng; Cadusch, Jasper; Chakraborty, Debadi; Smith, Trevor A.; Roberts, Ann; Sader, John E.; Davis, Timothy J.; Gómez, Daniel E.

    2016-04-01

    Reversible exchange of photons between a material and an optical cavity can lead to the formation of hybrid light--matter states where material properties such as the work function\\cite{Hutchison_AM2013a}, chemical reactivity\\cite{Hutchison_ACIE2012a}, ultra--fast energy relaxation \\cite{Salomon_ACIE2009a,Gomez_TJOPCB2012a} and electrical conductivity\\cite{Orgiu_NM2015a} of matter differ significantly to those of the same material in the absence of strong interactions with the electromagnetic fields. Here we show that strong light--matter coupling between confined photons on a semiconductor waveguide and localised plasmon resonances on metal nanowires modifies the efficiency of the photo--induced charge--transfer rate of plasmonic derived (hot) electrons into accepting states in the semiconductor material. Ultra--fast spectroscopy measurements reveal a strong correlation between the amplitude of the transient signals, attributed to electrons residing in the semiconductor, and the hybridization of waveguide and plasmon excitations.

  9. Photoinduced Electron Transfer in the Strong Coupling Regime: Waveguide-Plasmon Polaritons.

    PubMed

    Zeng, Peng; Cadusch, Jasper; Chakraborty, Debadi; Smith, Trevor A; Roberts, Ann; Sader, John E; Davis, Timothy J; Gómez, Daniel E

    2016-04-13

    Reversible exchange of photons between a material and an optical cavity can lead to the formation of hybrid light-matter states where material properties such as the work function [ Hutchison et al. Adv. Mater. 2013 , 25 , 2481 - 2485 ], chemical reactivity [ Hutchison et al. Angew. Chem., Int. Ed. 2012 , 51 , 1592 - 1596 ], ultrafast energy relaxation [ Salomon et al. Angew. Chem., Int. Ed. 2009 , 48 , 8748 - 8751 ; Gomez et al. J. Phys. Chem. B 2013 , 117 , 4340 - 4346 ], and electrical conductivity [ Orgiu et al. Nat. Mater. 2015 , 14 , 1123 - 1129 ] of matter differ significantly to those of the same material in the absence of strong interactions with the electromagnetic fields. Here we show that strong light-matter coupling between confined photons on a semiconductor waveguide and localized plasmon resonances on metal nanowires modifies the efficiency of the photoinduced charge-transfer rate of plasmonic derived (hot) electrons into accepting states in the semiconductor material. Ultrafast spectroscopy measurements reveal a strong correlation between the amplitude of the transient signals, attributed to electrons residing in the semiconductor and the hybridization of waveguide and plasmon excitations. PMID:26963038

  10. Tetramethoxybenzene is a Good Building Block for Molecular Wires: Insights from Photoinduced Electron Transfer.

    PubMed

    Heinz, Luisa G; Yushchenko, Oleksandr; Neuburger, Markus; Vauthey, Eric; Wenger, Oliver S

    2015-06-01

    Two donor bridge-acceptor molecules with terminal triarylamine and Ru(bpy)3(2+) (bpy = 2,2'-bipyridine) redox partners were synthesized and investigated by cyclic voltammetry, optical absorption, luminescence, and transient absorption spectroscopy. The two dyads differ only by the central bridging unit, which was tetramethoxybenzene (tmb) in one case and unsubstituted phenylene (ph) in the other case. Photoirradiation of the Ru(bpy)3(2+) complex of the two dyads triggers intramolecular electron transfer from the triarylamine to the (3)MLCT-excited metal complex, and this process occurs with time constants of 1.5 and 6.8 ns for the tmb- and ph-bridged dyads, respectively. Thermal electron transfer in the reverse direction then leads to disappearance of the photoproduct with a time constant of 10 ns in both dyads. The faster rate of photoinduced charge transfer in the tmb-bridged dyad can be understood in the framework of a hole-tunneling model in which the electron-rich tmb bridge imposes a more shallow barrier than the less electron-rich ph spacer. Until now tmb-based molecular wires have received very little attention, and alkoxy substituents have been mostly used for improving the solubility of oligo-p-phenylene vinylene (OPV) and oligo-p-phenylene ethynylene (OPE) wires. Our study illustrates how four alkoxy-substituents on a phenylene backbone can have a significant influence on the charge-transfer properties of a molecular wire, and this is relevant in the greater context of a future molecular electronics technology. PMID:25974891

  11. Phosphorescent quantum dots/ethidium bromide nanohybrids based on photoinduced electron transfer for DNA detection

    NASA Astrophysics Data System (ADS)

    Bi, Lin; Yu, Yuan-Hua

    2015-04-01

    Mercaptopropionic acid-capped Mn-doped ZnS quantum dots/ethidium bromide (EB) nanohybrids were constructed for photoinduced electron transfer (PIET) and then used as a room-temperature phosphorescence (RTP) probe for DNA detection. EB could quench the RTP of Mn-doped ZnS QDs by PIET, thereby forming Mn-doped ZnS QDs/EB nanohybrids and storing RTP. Meanwhile, EB could be inserted into DNA and EB could be competitively desorbed from the surface of Mn-doped ZnS QDs by DNA, thereby releasing the RTP of Mn-doped ZnS QDs. Based on this mechanism, a RTP sensor for DNA detection was developed. Under optimal conditions, the detection limit for DNA was 0.045 mg L-1, the relative standard deviation was 1.7%, and the method linear ranged from 0.2 to 20 mg L-1. The proposed method was applied to biological fluids, in which satisfactory results were obtained.

  12. Photoinduced electron transfer and geminate recombination in the group head region of micelles

    SciTech Connect

    Glusac, Ksenija; Goun, Alexei; Fayer, M. D.

    2006-08-07

    A pump-probe spectroscopic study of photoinduced forward electron transfer and geminate recombination between donors and acceptors located in the head group regions of micelles is presented. The hole donor is octadecyl-rhodamine B (ODRB) and the hole acceptor is N,N-dimethyl-aniline (DMA). The experiments are conducted as a function of the DMA concentration in the dodecyltrimethylammonium bromide and tetradecyltrimethylammonium bromide micelles. In spite of the fact that the absorptions of both the ODRB radical and ground state bleach spectrally overlap with the ODRB excited state absorption, a procedure that makes it possible to determine the geminate recombination dynamics is presented. These experiments are the first to measure the dynamics of geminate recombination in micelles, and the experiments have two orders of magnitude better time resolution than previous studies of forward transfer. The experimental data are compared to statistical mechanics theoretical calculations of both the forward transfer and the geminate recombination. The theory includes important aspects of the topology of the micelle and the diffusion of the donor-acceptors in the micelle head group region. A semiquantitative but nonquantitative agreement between theory and experiments is achieved.

  13. Thymidine radical formation via one-electron transfer oxidation photoinduced by pterin: Mechanism and products characterization.

    PubMed

    Serrano, Mariana P; Vignoni, Mariana; Lorente, Carolina; Vicendo, Patricia; Oliveros, Esther; Thomas, Andrés H

    2016-07-01

    UV-A radiation (320-400nm), recognized as a class I carcinogen, induces damage to the DNA molecule and its components through different mechanisms. Pterin derivatives are involved in various biological functions, including enzymatic processes, and it has been demonstrated that oxidized pterins may act as photosensitizers. In particular, they accumulate in the skin of patients suffering from vitiligo, a chronic depigmentation disorder. We have investigated the ability of pterin (Ptr), the parent compound of oxidized pterins, to photosensitize the degradation of the pyrimidine nucleotide thymidine 5'-monophosphate (dTMP) in aqueous solutions under UV-A irradiation. Although thymine is less reactive than purine nucleobases, our results showed that Ptr is able to photoinduce the degradation of dTMP and that the process is initiated by an electron transfer from the nucleotide to the triplet excited state of Ptr. In the presence of molecular oxygen, the photochemical process leads to the oxidation of dTMP, whereas Ptr is not consumed. In the absence of oxygen, both compounds are consumed to yield a product in which the pterin moiety is covalently linked to the thymine. This compound retains some of the spectroscopic properties of Ptr, such as absorbance in the UV-A region and fluorescence properties. PMID:27154982

  14. 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

  15. Photoinduced Electron Transfer Elicits a Change in the Static Dielectric Constant of a de Novo Designed Protein.

    PubMed

    Polizzi, Nicholas F; Eibling, Matthew J; Perez-Aguilar, Jose Manuel; Rawson, Jeff; Lanci, Christopher J; Fry, H Christopher; Beratan, David N; Saven, Jeffery G; Therien, Michael J

    2016-02-24

    We provide a direct measure of the change in effective dielectric constant (εS) within a protein matrix after a photoinduced electron transfer (ET) reaction. A linked donor-bridge-acceptor molecule, PZn-Ph-NDI, consisting of a (porphinato)Zn donor (PZn), a phenyl bridge (Ph), and a naphthalene diimide acceptor (NDI), is shown to be a "meter" to indicate protein dielectric environment. We calibrated PZn-Ph-NDI ET dynamics as a function of solvent dielectric, and computationally de novo designed a protein SCPZnI3 to bind PZn-Ph-NDI in its interior. Mapping the protein ET dynamics onto the calibrated ET catalogue shows that SCPZnI3 undergoes a switch in the effective dielectric constant following photoinduced ET, from εS ≈ 8 to εS ≈ 3. PMID:26840013

  16. Nonadiabatic dynamics of photoinduced proton-coupled electron transfer in a solvated phenol-amine complex.

    PubMed

    Goyal, Puja; Schwerdtfeger, Christine A; Soudackov, Alexander V; Hammes-Schiffer, Sharon

    2015-02-12

    Photoinduced concerted electron-proton transfer (EPT), denoted photo-EPT, is important for a wide range of energy conversion processes. Transient absorption and Raman spectroscopy experiments on the hydrogen-bonded p-nitrophenylphenol-t-butylamine complex, solvated in 1,2-dichloroethane, suggested that this complex may undergo photo-EPT. The experiments probed two excited electronic states that were interpreted as an intramolecular charge transfer (ICT) state and an EPT state. Herein mixed quantum mechanical/molecular mechanical nonadiabatic surface hopping dynamics is used to investigate the relaxation pathways following photoexcitation. The potential energy surface is generated on the fly with a semiempirical floating occupation molecular orbital complete active space configuration interaction method for the solute molecule and a molecular mechanical force field for the explicit solvent molecules. The free energy curves along the proton transfer coordinate illustrate that proton transfer is thermodynamically and kinetically favorable on the lower-energy excited state but not on the higher-energy excited state, supporting the characterization of these states as EPT and ICT, respectively. The nonadiabatic dynamics simulations indicate that the population decays from the ICT state to the EPT state in ∼100 fs and from the EPT state to the ground state on the slower time scale of ∼1 ps, qualitatively consistent with the experimental measurements. For ∼54% of the trajectories, the proton transfers from the phenol to the amine in ∼400 fs on the EPT state and then transfers back to the phenol rapidly upon decay to the ground state. Thus, these calculations augment the original interpretation of the experimental data by providing evidence of proton transfer on the EPT state prior to decay to the ground state. The fundamental insights obtained from these simulations are also relevant to other photo-EPT processes. PMID:25545667

  17. Solvent polarity effect on photoinduced electron transfer between C{sub 60} and tetramethylbenzidine studied by laser flash photolysis

    SciTech Connect

    Ito, Osamu; Yoshikawa, Yuko; Watanabe, Akira; Sasaki, Yoshiko

    1995-06-15

    The photoinduced electron transfer between C{sub 60} and N,N,N{prime},N{prime}-tetramethylbenzidine (NTMB) in polar and nonpolar solvents and their mixtures has been investigated by nanosecond laser flash photolysis/transient absorption spectroscopy in the visible and near-IR regions. The transient absorption bands of the C{sub 60} triplet state ({sup T}C{sub 60}*) and the NTMB radical cation were observed in both nonpolar and polar solvents. In polar solvents such as benzonitrile, the reaction rate constants were determined from the decay of {sup T}C{sub 60}* at 740 nm, which were consistent with the rate constants evaluated from the growth of the NTMB radical cation, suggesting that direct electron transfer occurs from ground-state NTMB to {sup T}C{sub 60}*. In nonpolar solvents such as benzene, the NTMB radical cation and C{sub 60} radical anion were produced immediately after the nanosecond laser pulse, simultaneous with the formation of {sup T}C{sub 60}*, indicating that a different electron transfer mechanism exists in nonpolar solvents. In the solvent mixtures, two simultaneous reaction routes are present for both forward and back electron transfer reactions. Pronounced solvent effects found for electron transfer reaction kinetics and rates are characteristic of the photoinduced electron transfer reactions between C{sub 60} and some kinds of aromatic amines. 25 refs., 8 figs., 2 tabs.

  18. Distance-dependent photo-induced electron transport in nanometer-sized junctions

    NASA Astrophysics Data System (ADS)

    Albee, Brian; Liu, Xuejun; Tork Ladani, Faezeh; Dutta, Rajen K.; Potma, Eric O.

    2016-05-01

    We describe photo-induced current experiments observed in nm-sized electro-migrated nano gaps, using surface plasmon polaritons (SPPs) as the source of the optical driving field. For gaps smaller than 5 nm, we observe a stable photo-induced current that is linear with the intensity of the SPP mode, whereas the photo-current in wider gaps shows a highly nonlinear dependence that is reminiscent of field emission. The results are explained by a modified Wentzel-Kramers-Brillouin tunneling model, which reproduces the observed transition from optical rectification to optically driven field emission in the nano junction.

  19. 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

  20. Highly specific fluorescence detection of T4 polynucleotide kinase activity via photo-induced electron transfer.

    PubMed

    Tao, Mangjuan; Shi, Zhilu; Cheng, Rui; Zhang, Jing; Li, Baoxin; Jin, Yan

    2015-09-15

    Sensitive and reliable study of the activity of polynucleotide kinase (PNK) and its potential inhibitors is of great importance for biochemical interaction related to DNA phosphorylation as well as development of kinase-targeted drug discovery. To achieve facile and reliable detection of PNK activity, we report here a novel fluorescence method for PNK assay based on a combination of exonuclease cleavage reaction and photo-induced electron transfer (PIET) by using T4 PNK as a model target. The fluorescence of 3'-carboxyfluorescein-labeled DNA probe (FDNA) is effectively quenched by deoxyguanosines at the 5' end of its complementary DNA (cDNA) due to an effective PIET between deoxyguanosines and fluorophore. Whereas FDNA/cDNA hybrid is phosphorylated by PNK and then immediately cleaved by lambda exonuclease (λ exo), fluorescence is greatly restored due to the break of PIET. This homogeneous PNK activity assay does not require a complex design by taking advantage of the quenching ability of deoxyguanosines, making the proposed strategy facile and cost-effective. The activity of PNK can be sensitively detected in the range of 0.005 to 10 U mL(-1) with a detection limit of 2.1×10(-3) U mL(-1). Research on inhibition efficiency of different inhibitors demonstrated that it can be explored to evaluate inhibition capacity of inhibitors. The application for detection of PNK activity in complex matrix achieved satisfactory results. Therefore, this PIET strategy opens a promising avenue for studying T4 PNK activity as well as evaluating PNK inhibitors, which is of great importance for discovering kinase-targeted drugs. PMID:26050629

  1. Experimentation and Theoretic Calculation of a BODIPY Sensor Based on Photoinduced Electron Transfer for Ions Detection

    NASA Astrophysics Data System (ADS)

    Lu, Hua; Zhang, Shushu; Liu, Hanzhuang; Wang, Yanwei; Shen, Zhen; Liu, Chungen; You, Xiaozeng

    2009-12-01

    A boron-dipyrromethene (BODIPY)-based fluorescence probe with a N,N'-(pyridine-2, 6-diylbis(methylene))-dianiline substituent (1) has been prepared by condensation of 2,6-pyridinedicarboxaldehyde with 8-(4-amino)-4,4-difluoro-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene and reduction by NaBH4. The sensing properties of compound 1 toward various metal ions are investigated via fluorometric titration in methanol, which show highly selective fluorescent turn-on response in the presence of Hg2+ over the other metal ions, such as Li+, Na+, K+, Ca2+, Mg2+, Pb2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Ag+, and Mn2+. Computational approach has been carried out to investigate the mechanism why compound 1 provides different fluorescent signal for Hg2+ and other ions. Theoretic calculations of the energy levels show that the quenching of the bright green fluorescence of boradiazaindacene fluorophore is due to the reductive photoinduced electron transfer (PET) from the aniline subunit to the excited state of BODIPY fluorophore. In metal complexes, the frontier molecular orbital energy levels changes greatly. Binding Zn2+ or Cd2+ ion leads to significant decreasing of both the HOMO and LUMO energy levels of the receptor, thus inhibit the reductive PET process, whereas an oxidative PET from the excited state fluorophore to the receptor occurs, vice versa, which also quenches the fluorescence. However, for 1-Hg2+ complex, both the reductive and oxidative PETs are prohibited; therefore, strong fluorescence emission from the fluorophore can be observed experimentally. The agreement of the experimental results and theoretic calculations suggests that our calculation method can be applicable as guidance for the design of new chemosensors for other metal ions.

  2. Enaminones in a multicomponent synthesis of 4-aryldihydropyridines for potential applications in photoinduced intramolecular electron-transfer systems

    PubMed Central

    Ibrahim, Maher R; Elnagdi, Mohamed H; John, Elizabeth; Ibrahim, Yehia A

    2012-01-01

    Summary An efficient three component reaction with enaminones, primary amines and aldehydes resulted in easy access to 1,4-dihydropyridines with different substituents at the 1-, 3-, 4- and 5-positions. Microwaves improved the reaction yield, reducing also considerably the reaction time and the amount of solvent used. Chiral primary amines gave chiral 1-substituted-1,4-dihydropyridines. The 4-(1-naphthyl) and 4-(phenanthren-9-yl)dihydropyridine derivatives exhibited an interesting photoluminescence behavior, which suggests their potential application as suitable photoinduced intramolecular electron-transfer systems. PMID:22509215

  3. Photoinduced electron and energy transfer from coumarin 153 to perylenetetracarboxylic diimide in bmimPF6/TX-100/water microemulsions.

    PubMed

    Wu, Haixia; Wang, Haixia; Xue, Lin; Li, Xiyou

    2011-01-15

    A perylenetetracarboxylic diimide (PDI) compound with an attached hydrophilic polyoxyethylene group at the imide nitrogen position was designed and synthesized. Photoinduced electron and energy transfer between coumarin 153 (C-153) and PDI in a ternary microemulsion with an ionic liquid (bmimPF(6)/TX-100/H(2)O) were investigated by steady state electronic absorption and fluorescence spectroscopy. The results revealed that both PDI and C-153 resided at the interface between the surfactant TX-100 and the ionic liquid bmimPF(6) in the ternary microemulsions. The absorption spectra suggested no interactions between C-153 and PDI in the ground states, but the fluorescence spectra revealed the presence of an efficient electron transfer and a less efficient energy transfer from C-153 to PDI. Moreover, the electron transfer was much more efficient in microemulsions than that in homogeneous conventional organic solvents due to the unique micro-environment of the microemulsion. PMID:20965513

  4. Effect of micellar environment on Marcus correlation curves for photoinduced bimolecular electron transfer reactions

    SciTech Connect

    Kumbhakar, Manoj; Nath, Sukhendu; Mukherjee, Tulsi; Pal, Haridas

    2005-07-15

    Photoinduced electron transfer (ET) between coumarin dyes and aromatic amine has been investigated in two cationic micelles, namely, cetyltrimethyl ammonium bromide (CTAB) and dodecyltrimethyl ammonium bromide (DTAB), and the results have been compared with those observed earlier in sodium dodecyl sulphate (SDS) and triton-X-100 (TX-100) micelles for similar donor-acceptor pairs. Due to a reasonably high effective concentration of the amines in the micellar Stern layer, the steady-state fluorescence results show significant static quenching. In the time-resolved (TR) measurements with subnanosecond time resolution, contribution from static quenching is avoided. Correlations of the dynamic quenching constants (k{sub q}{sup TR}), as estimated from the TR measurements, show the typical bell-shaped curves with the free-energy changes ({delta}G{sup 0}) of the ET reactions, as predicted by the Marcus outersphere ET theory. Comparing present results with those obtained earlier for similar coumarin-amine systems in SDS and TX-100 micelles, it is seen that the inversion in the present micelles occurs at an exergonicity (-{delta}G{sup 0}>{approx}1.2-1.3 eV) much higher than that observed in SDS and TX-100 micelles (-{delta}G{sup 0}>{approx}0.7 eV), which has been rationalized based on the relative propensities of the ET and solvation rates in different micelles. In CTAB and DTAB micelles, the k{sub q}{sup TR} values are lower than the solvation rates, which result in the full contribution of the solvent reorganization energy ({lambda}{sub s}) towards the activation barrier for the ET reaction. Contrary to this, in SDS and TX-100 micelles, k{sub q}{sup TR} values are either higher or comparable with the solvation rates, causing only a partial contribution of {lambda}{sub s} in these cases. Thus, Marcus inversion in present cationic micelles is inferred to be the true inversion, whereas that in the anionic SDS and neutral TX-100 micelles are understood to be the apparent

  5. 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

  6. Photoinduced melting of charge order in a quarter-filled electron system coupled with different types of phonons

    NASA Astrophysics Data System (ADS)

    Yonemitsu, Kenji; Maeshima, Nobuya

    2007-08-01

    Photoinduced melting of charge order is calculated by using the exact many-electron wave function coupled with classically treated phonons in the one-dimensional quarter-filled Hubbard model with Peierls and Holstein types of electron-phonon couplings. The model parameters are taken from recent experiments on (EDO-TTF)2PF6 (EDO-TTF=ethylenedioxy-tetrathiafulvalene) with a (0110) charge order, where transfer integrals are modulated by molecular displacements (bond-coupled phonons) and site energies by molecular deformations (charge-coupled phonons). The charge-transfer photoexcitation from (0110) to (0200) configurations and that from (0110) to (1010) configurations have different energies. The corresponding excited states have different shapes of adiabatic potentials as a function of these two phonon amplitudes. The adiabatic potentials are shown to be useful in understanding differences in the photoinduced charge dynamics and the efficiency of melting, which depend not only on the excitation energy but also on the relative phonon frequency of the bond- and charge-coupled phonons.

  7. Bimolecular photoinduced electron transfer beyond the diffusion limit: the Rehm-Weller experiment revisited with femtosecond time resolution.

    PubMed

    Rosspeintner, Arnulf; Angulo, Gonzalo; Vauthey, Eric

    2014-02-01

    To access the intrinsic, diffusion free, rate constant of bimolecular photoinduced electron transfer reactions, fluorescence quenching experiments have been performed with 14 donor/acceptor pairs, covering a driving-force range going from 0.6 to 2.4 eV, using steady-state and femtosecond time-resolved emission, and applying a diffusion-reaction model that accounts for the static and transient stages of the quenching for the analysis. The intrinsic electron transfer rate constants are up to 2 orders of magnitude larger than the diffusion rate constant in acetonitrile. Above ∼1.5 eV, a slight decrease of the rate constant is observed, pointing to a much weaker Marcus inverted region than those reported for other types of electron transfer reactions, such as charge recombination. Despite this, the driving force dependence can be rationalized in terms of Marcus theory. PMID:24400958

  8. Electrochemical control over photoinduced electron transfer and trapping in CdSe-CdTe quantum-dot solids.

    PubMed

    Boehme, Simon C; Walvis, T Ardaan; Infante, Ivan; Grozema, Ferdinand C; Vanmaekelbergh, Daniël; Siebbeles, Laurens D A; Houtepen, Arjan J

    2014-07-22

    Understanding and controlling charge transfer between different kinds of colloidal quantum dots (QDs) is important for devices such as light-emitting diodes and solar cells and for thermoelectric applications. Here we study photoinduced electron transfer between CdTe and CdSe QDs in a QD film. We find that very efficient electron trapping in CdTe QDs obstructs electron transfer to CdSe QDs under most conditions. Only the use of thiol ligands results in somewhat slower electron trapping; in this case the competition between trapping and electron transfer results in a small fraction of electrons being transferred to CdSe. However, we demonstrate that electron trapping can be controlled and even avoided altogether by using the unique combination of electrochemistry and transient absorption spectroscopy. When the Fermi level is raised electrochemically, traps are filled with electrons and electron transfer from CdTe to CdSe QDs occurs with unity efficiency. These results show the great importance of knowing and controlling the Fermi level in QD films and open up the possibility of studying the density of trap states in QD films as well as the systematic investigation of the intrinsic electron transfer rates in donor-acceptor films. PMID:24883930

  9. Steric and Electronic Factors Associated with the Photoinduced Ligand Exchange of Bidentate Ligands Coordinated to Ru(II).

    PubMed

    Albani, Bryan A; Whittemore, Tyler; Durr, Christopher B; Turro, Claudia

    2015-01-01

    In an effort to create a molecule that can absorb low energy visible or near-infrared light for photochemotherapy (PCT), the new complexes [Ru(biq)2 (dpb)](PF6 )2 (1, biq = 2,2'-biquinoline, dpb = 2,3-bis(2-pyridyl)benzoquinoxaline) and [(biq)2 Ru(dpb)Re(CO)3 Cl](PF6 )2 (2) were synthesized and characterized. Complexes 1 and 2 were compared to [Ru(bpy)2 (dpb)](PF6 )2 (3, bpy = 2,2'-bipyridine) and [Ru(biq)2 (phen)](PF6 )2 (4, phen = 1,10-phenanthroline). Distortions around the metal and biq ligands were used to explain the exchange of one biq ligand in 4 upon irradiation. Complex 1, however, undergoes photoinduced dissociation of the dpb ligand rather than biq under analogous experimental conditions. Complex 3 is not photoactive, providing evidence that the biq ligands are crucial for ligand photodissociation in 1. The crystal structures of 1 and 4 are compared to explain the difference in photochemistry between the complexes. Complex 2 absorbs lower energy light than 1, but is photochemically inert although its crystal structure displays significant distortions. These results indicate that both the excited state electronic structure and steric bulk play key roles in bidentate photoinduced ligand dissociation. The present work also shows that it is possible to stabilize sterically hindered Ru(II) complexes by the addition of another metal, a property that may be useful for other applications. PMID:25403564

  10. Photo-induced reactions from efficient molecular dynamics with electronic transitions using the FIREBALL local-orbital density functional theory formalism.

    PubMed

    Zobač, Vladimír; Lewis, James P; Abad, Enrique; Mendieta-Moreno, Jesús I; Hapala, Prokop; Jelínek, Pavel; Ortega, José

    2015-05-01

    The computational simulation of photo-induced processes in large molecular systems is a very challenging problem. Firstly, to properly simulate photo-induced reactions the potential energy surfaces corresponding to excited states must be appropriately accessed; secondly, understanding the mechanisms of these processes requires the exploration of complex configurational spaces and the localization of conical intersections; finally, photo-induced reactions are probability events, that require the simulation of hundreds of trajectories to obtain the statistical information for the analysis of the reaction profiles. Here, we present a detailed description of our implementation of a molecular dynamics with electronic transitions algorithm within the local-orbital density functional theory code FIREBALL, suitable for the computational study of these problems. As an example of the application of this approach, we also report results on the [2 + 2] cycloaddition of ethylene with maleic anhydride and on the [2 + 2] photo-induced polymerization reaction of two C60 molecules. We identify different deactivation channels of the initial electron excitation, depending on the time of the electronic transition from LUMO to HOMO, and the character of the HOMO after the transition. PMID:25791682

  11. Photo-induced reactions from efficient molecular dynamics with electronic transitions using the FIREBALL local-orbital density functional theory formalism

    NASA Astrophysics Data System (ADS)

    Zobač, Vladimír; Lewis, James P.; Abad, Enrique; Mendieta-Moreno, Jesús I.; Hapala, Prokop; Jelínek, Pavel; Ortega, José

    2015-05-01

    The computational simulation of photo-induced processes in large molecular systems is a very challenging problem. Firstly, to properly simulate photo-induced reactions the potential energy surfaces corresponding to excited states must be appropriately accessed; secondly, understanding the mechanisms of these processes requires the exploration of complex configurational spaces and the localization of conical intersections; finally, photo-induced reactions are probability events, that require the simulation of hundreds of trajectories to obtain the statistical information for the analysis of the reaction profiles. Here, we present a detailed description of our implementation of a molecular dynamics with electronic transitions algorithm within the local-orbital density functional theory code FIREBALL, suitable for the computational study of these problems. As an example of the application of this approach, we also report results on the [2 + 2] cycloaddition of ethylene with maleic anhydride and on the [2 + 2] photo-induced polymerization reaction of two C60 molecules. We identify different deactivation channels of the initial electron excitation, depending on the time of the electronic transition from LUMO to HOMO, and the character of the HOMO after the transition.

  12. Light-Activated Protein Inhibition through Photoinduced Electron Transfer of a Ruthenium(II)–Cobalt(III) Bimetallic Complex

    PubMed Central

    Holbrook, Robert J.; Weinberg, David J.; Peterson, Mark D.; Weiss, Emily A.; Meade, Thomas J.

    2015-01-01

    We describe a mechanism of light activation that initiates protein inhibitory action of a biologically inert Co(III) Schiff base (Co(III)-sb) complex. Photoinduced electron transfer (PET) occurs from a Ru(II) bipyridal complex to a covalently attached Co(III) complex and is gated by conformational changes that occur in tens of nanoseconds. Reduction of the Co(III)-sb by PET initiates displacement of the inert axial imidazole ligands, promoting coordination to active site histidines of α-thrombin. Upon exposure to 455 nm light, the rate of ligand exchange with 4-methylimidazole, a histidine mimic, increases by approximately 5-fold, as observed by NMR spectroscopy. Similarly, the rate of α-thrombin inhibition increases over 5-fold upon irradiation. These results convey a strategy for light activation of inorganic therapeutic agents through PET utilizing redox-active metal centers. PMID:25671465

  13. Effect of laser intensity on the determination of intermolecular electron transfer rate constants—Observation of Marcus inverted region in photoinduced back electron transfer reactions

    NASA Astrophysics Data System (ADS)

    Weng, Yu-Xiang; Chan, Kwok-Chu; Tzeng, Biing-Chiau; Che, Chi-Ming

    1998-10-01

    The light intensity and concentration dependence of the photoproduct yield are investigated in a monophotonic process. The relationship of the photoproduct yield with the laser intensity and the complex concentration for a monophotonic process is derived under laser flash photolysis. The relationship is confirmed experimentally in a monophotonic process, i.e., triplet-triplet transition for a Cu(I) complex Cu6(DMNSN')6 (DMNSN'=4,6-dimethylpyrimidine-2-thiolate). At low light intensity, the relationship can be approximated by a linear inverse square root dependence on the light intensity. Based on this equation, a method is proposed to determine the intrinsic back electron transfer rate constant kETb in photoinduced intermolecular electron transfer reactions, precluding the effect from the diffusional encounter pairs. The Marcus "inverted region" is observed by using the method in photoinduced back electron transfer reactions of [Au2(dppm)2](ClO4)2 (dppm=bis(diphenylphosphino)methane) with a series of substituted pyridinium acceptors.

  14. Visualizing the non-equilibrium dynamics of photoinduced intramolecular electron transfer with femtosecond X-ray pulses

    SciTech Connect

    Canton, Sophie E.; Kjær, Kasper S.; Vankó, György; van Driel, Tim B.; Adachi, Shin -ichi; Bordage, Amélie; Bressler, Christian; Chabera, Pavel; Christensen, Morten; Dohn, Asmus O.; Galler, Andreas; Gawelda, Wojciech; Gosztola, David; Haldrup, Kristoffer; Harlang, Tobias; Liu, Yizhu; Møller, Klaus B.; Németh, Zoltán; Nozawa, Shunsuke; Pápai, Mátyás; Sato, Tokushi; Sato, Takahiro; Suarez-Alcantara, Karina; Togashi, Tadashi; Tono, Kensuke; Uhlig, Jens; Vithanage, Dimali A.; Wärnmark, Kenneth; Yabashi, Makina; Zhang, Jianxin; Sundström, Villy; Nielsen, Martin M.

    2015-03-02

    Ultrafast photoinduced electron transfer preceding energy equilibration still poses many experimental and conceptual challenges to the optimization of photoconversion since an atomic-scale description has so far been beyond reach. Here we combine femtosecond transient optical absorption spectroscopy with ultrafast X-ray emission spectroscopy and diffuse X-ray scattering at the SACLA facility to track the non-equilibrated electronic and structural dynamics within a bimetallic donor–acceptor complex that contains an optically dark centre. Exploiting the 100-fold increase in temporal resolution as compared with storage ring facilities, these measurements constitute the first X-ray-based visualization of a non-equilibrated intramolecular electron transfer process over large interatomic distances. Thus experimental and theoretical results establish that mediation through electronically excited molecular states is a key mechanistic feature. The present study demonstrates the extensive potential of femtosecond X-ray techniques as diagnostics of non-adiabatic electron transfer processes in synthetic and biological systems, and some directions for future studies, are outlined.

  15. Visualizing the non-equilibrium dynamics of photoinduced intramolecular electron transfer with femtosecond X-ray pulses

    DOE PAGESBeta

    Canton, Sophie E.; Kjær, Kasper S.; Vankó, György; van Driel, Tim B.; Adachi, Shin -ichi; Bordage, Amélie; Bressler, Christian; Chabera, Pavel; Christensen, Morten; Dohn, Asmus O.; et al

    2015-03-02

    Ultrafast photoinduced electron transfer preceding energy equilibration still poses many experimental and conceptual challenges to the optimization of photoconversion since an atomic-scale description has so far been beyond reach. Here we combine femtosecond transient optical absorption spectroscopy with ultrafast X-ray emission spectroscopy and diffuse X-ray scattering at the SACLA facility to track the non-equilibrated electronic and structural dynamics within a bimetallic donor–acceptor complex that contains an optically dark centre. Exploiting the 100-fold increase in temporal resolution as compared with storage ring facilities, these measurements constitute the first X-ray-based visualization of a non-equilibrated intramolecular electron transfer process over large interatomic distances.more » Thus experimental and theoretical results establish that mediation through electronically excited molecular states is a key mechanistic feature. The present study demonstrates the extensive potential of femtosecond X-ray techniques as diagnostics of non-adiabatic electron transfer processes in synthetic and biological systems, and some directions for future studies, are outlined.« less

  16. Visualizing the non-equilibrium dynamics of photoinduced intramolecular electron transfer with femtosecond X-ray pulses

    PubMed Central

    Canton, Sophie E.; Kjær, Kasper S.; Vankó, György; van Driel, Tim B.; Adachi, Shin-ichi; Bordage, Amélie; Bressler, Christian; Chabera, Pavel; Christensen, Morten; Dohn, Asmus O.; Galler, Andreas; Gawelda, Wojciech; Gosztola, David; Haldrup, Kristoffer; Harlang, Tobias; Liu, Yizhu; Møller, Klaus B.; Németh, Zoltán; Nozawa, Shunsuke; Pápai, Mátyás; Sato, Tokushi; Sato, Takahiro; Suarez-Alcantara, Karina; Togashi, Tadashi; Tono, Kensuke; Uhlig, Jens; Vithanage, Dimali A.; Wärnmark, Kenneth; Yabashi, Makina; Zhang, Jianxin; Sundström, Villy; Nielsen, Martin M.

    2015-01-01

    Ultrafast photoinduced electron transfer preceding energy equilibration still poses many experimental and conceptual challenges to the optimization of photoconversion since an atomic-scale description has so far been beyond reach. Here we combine femtosecond transient optical absorption spectroscopy with ultrafast X-ray emission spectroscopy and diffuse X-ray scattering at the SACLA facility to track the non-equilibrated electronic and structural dynamics within a bimetallic donor–acceptor complex that contains an optically dark centre. Exploiting the 100-fold increase in temporal resolution as compared with storage ring facilities, these measurements constitute the first X-ray-based visualization of a non-equilibrated intramolecular electron transfer process over large interatomic distances. Experimental and theoretical results establish that mediation through electronically excited molecular states is a key mechanistic feature. The present study demonstrates the extensive potential of femtosecond X-ray techniques as diagnostics of non-adiabatic electron transfer processes in synthetic and biological systems, and some directions for future studies, are outlined. PMID:25727920

  17. Incorporation of Water-Oxidation Catalysts into Photoinduced Electron Transfer Systems: Toward Solar Fuel Generation via Artificial Photosynthesis

    NASA Astrophysics Data System (ADS)

    Vagnini, Michael Thomas

    A key goal of artificial photosynthesis is to mimic the photochemistry of photosystem II and oxidize water using light energy, with the ultimate aim of using the liberated electrons for reductive, fuel-forming reactions. One of the more recent challenges in the field of solar fuels chemistry is the efficient activation of molecular water-oxidation catalysts with photoinduced electron transfer, an effort that would benefit from detailed knowledge of the energetics and kinetics of each electron transfer step in a light-driven catalytic cycle. The focus of this thesis is the synthesis and photophysical characterization of covalent assemblies comprising a redox-active organic chromophore and the iridium(III)-based water-oxidation catalyst Cp*Ir(ppy)Cl (ppy = 2-phenylpyridine), and the rates and pathways for photogeneration of higher-valence states of the catalyst are determined with femtosecond transient absorption spectroscopy and other time-resolved spectroscopic techniques. In linking the photooxidant perylene-3,4:9,10-bis (dicarboximide) (PDI) to the Ir(III) catalyst, fast photoinduced electron transfer from the metal complex to PDI outcompetes heavy-atom quenching of the dye excited state, and the catalytic integrity of the complex is retained, as determined by electrocatalysis experiments. Long-lived higher-valence states of the catalyst are necessary for the accumulation of oxidizing equivalents for oxygen evolution, and the lifetime of photogenerated Ir(IV) has been extended by over two orders of magnitude by catalyst incorporation into a covalent electron acceptor--chromophore--catalyst triad, in which the dye is perylene-3,4-dicarboximide (PMI). Time resolved X-ray absorption studies of the triad confirm the photogeneration of an Ir(IV) metal center, a species that is too unstable to observe with chemical or electrochemical oxidation methods. This approach to preparing higher-valence states of water-oxidation catalysts has great promise for deducing catalytic

  18. Photoinduced electron transfer occurs between 2-aminopurine and the DNA nucleic acid monophosphates: results from cyclic voltammetry and fluorescence quenching.

    PubMed

    Narayanan, Madhavan; Kodali, Goutham; Xing, Yangjun; Stanley, Robert J

    2010-08-19

    2-Aminopurine (2AP) is a fluorescent adenine analogue that is useful in part because its substantial fluorescence quantum yield is sensitive to base stacking with native bases in ss- and ds-DNA. However, the degree of quenching is sequence dependent and the mechanism of quenching is still a matter of some debate. Here we show that the most likely quenching mechanism in aqueous solution involves photoinduced electron transfer (PET), as revealed by cyclic voltammetry (CV) performed in aprotic organic solvents. These potentials were used with spectroscopic data to obtain excited-state reduction and oxidation potentials. Stern-Volmer (S-V) experiments using the native base monophosphate nucleotides (NMPs) rGMP, rAMP, rCMP, and dTMP were performed in aqueous solution to obtain quenching rate constants kq. The results suggest that 2AP* can act as either an electron donor or an electron acceptor depending on the particular NMP but that PET proceeds for all NMPs tested. PMID:20734496

  19. Multidimensional treatment of stochastic solvent dynamics in photoinduced proton-coupled electron transfer processes: sequential, concerted, and complex branching mechanisms.

    PubMed

    Soudackov, Alexander V; Hazra, Anirban; Hammes-Schiffer, Sharon

    2011-10-14

    A theoretical approach for the multidimensional treatment of photoinduced proton-coupled electron transfer (PCET) processes in solution is presented. This methodology is based on the multistate continuum theory with an arbitrary number of diabatic electronic states representing the relevant charge distributions in a general PCET system. The active electrons and transferring proton(s) are treated quantum mechanically, and the electron-proton vibronic free energy surfaces are represented as functions of multiple scalar solvent coordinates corresponding to the single electron and proton transfer reactions involved in the PCET process. A dynamical formulation of the dielectric continuum theory is used to derive a set of coupled generalized Langevin equations of motion describing the time evolution of these collective solvent coordinates. The parameters in the Langevin equations depend on the solvent properties, such as the dielectric constants, relaxation time, and molecular moment of inertia, as well as the solute properties. The dynamics of selected intramolecular nuclear coordinates, such as the proton donor-acceptor distance or a torsional angle within the PCET complex, may also be included in this formulation. A surface hopping method in conjunction with the Langevin equations of motion is used to simulate the nonadiabatic dynamics on the multidimensional electron-proton vibronic free energy surfaces following photoexcitation. This theoretical treatment enables the description of both sequential and concerted mechanisms, as well as more complex processes involving a combination of these mechanisms. The application of this methodology to a series of model systems corresponding to collinear and orthogonal PCET illustrates fundamental aspects of these different mechanisms and elucidates the significance of proton vibrational relaxation and nonequilibrium solvent dynamics. PMID:22010706

  20. Ultrafast photoinduced electron transfer in the micelle and the gel phase of a PEO-PPO-PEO triblock copolymer

    SciTech Connect

    Mandal, Ujjwal; Ghosh, Subhadip; Dey, Shantanu; Adhikari, Aniruddha; Bhattacharyya, Kankan

    2008-04-28

    Ultrafast photoinduced electron transfer (PET) from N,N-dimethylaniline (DMA) to coumarin dyes is studied in the micelle and the gel phase of a triblock copolymer, (PEO){sub 20}-(PPO){sub 70}-(PEO){sub 20} (Pluronic P123) by picosecond and femtosecond emission spectroscopies. The rate of PET in a P123 micelle and gel is found to be nonexponential and faster than the slow components of solvation dynamics. In a P123 micelle and gel, PET occurs on multiple time scales ranging from a subpicosecond time scale to a few nanoseconds. In the gel phase, the highest rate constant (9.3x10{sup 9} M{sup -1} s{sup -1}) of ET for C152 is about two times higher than that (3.8x10{sup 9} M{sup -1} s{sup -1}) observed in micelle phase. The ultrafast components of electron transfer (ET) exhibits a bell shaped dependence with the free energy change which is similar to the Marcus inversion. Possible reasons for slower PET in P123 micelle compared to other micelles and relative to P123 gel are discussed.

  1. Self-assembly of zincporphyrin dimer and pyromellitimide using two coordination bonds and photoinduced intramolecular electron transfer.

    SciTech Connect

    Yamada, K.; Imahori, H.; Yoshizawa, E.; Gosztola, D.; Wasielewski, M. R.; Sakata, Y.; Chemistry; Osaka Univ.; Northwestern Univ.

    1999-01-01

    Zincporphyrin dimer-pyromellitimide supramolecule has been designed and assembled using two coordination bonds. Photoinduced charge separation and charge recombination in the supramolecule were observed by picosecond time-resolved transient absorption measurements.

  2. Probing the effect of electron acceptor structure and morphology on charge separation in ZnO/P3HT hybrid photovoltaics using steady-state transient photoinduced absorption.

    SciTech Connect

    Davis, Robert Jackson; Lloyd, Matthew T.; Ferreira, Summer Rhodes; Lee, Yun-Ju; Hsu, Julia W. P.

    2010-04-01

    Hybrid cells based on ZnO/P3HT heterojunctions have the advantage of better device stability, but suffer poor photovoltaic performance compared to all-organic cells which use PCBM as the electron acceptor. The photovoltaic effect in these hybrid systems is accomplished via photoinduced charge separation at the interface between the absorbing polymer (P3HT) and the electron acceptor (ZnO). Efforts to improve device performance in these hybrid systems have centered on reducing the required diffusion length for P3HT excitons by creating bulk heterojunctions from either ZnO nanoparticles and P3HT or using ZnO precursors which convert in situ to form ZnO networks inside a polymer matrix. In this study, we use transient photoinduced absorption to access the lifetimes of P3HT polarons and excitons in bulk heterojunctions constructed using P3HT and ZnO nanoparticles or ZnO precursors and compare to those in planar ZnO/P3HT devices. Steady-state photoinduced absorption spectra of ZnO/P3HT show characteristic of sub-bandgap transitions associated with the formation of long-lived (msec lifetimes) radical cations (polarons) in P3HT. Similar short-lived polarons (psec lifetimes) are observed by picosecond transient photoinduced absorption in addition to infrared absorption due to excitons. Here we examine the lifetimes of both the excitons and polarons in ZnO:P3HT bulk heterojunctions using both picosecond and millisecond techniques in an effort to understand the effect of the structure and morphology of the electron acceptor on charge separation. We will also compare the relative photoexitation lifetimes, hence charge separation efficiency, for the planar and bulk heterojunction hybrid system to an all-organic P3HT:PCBM system.

  3. Photoinduced Electron Transfer of PAMAM Dendrimer-Zinc(II) Porphyrin Associates at Polarized Liquid|Liquid Interfaces.

    PubMed

    Nagatani, Hirohisa; Sakae, Hiroki; Torikai, Taishi; Sagara, Takamasa; Imura, Hisanori

    2015-06-01

    The heterogeneous photoinduced electron-transfer reaction of the ion associates between NH2-terminated polyamidoamine (PAMAM) dendrimers and 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrinato zinc(II) (ZnTPPS(4-)) was studied at the polarized water|1,2-dichloroethane (DCE) interface. The positive photocurrent arising from the photoreduction of ZnTPPS(4-) by a lipophilic quencher, decamethylferrocene, in the interfacial region was significantly enhanced by the ion association with the PAMAM dendrimers. The photocurrent response of the dendrimer-ZnTPPS(4-) associates was dependent on the pH condition and on the generation of dendrimer. A few cationic additives such as polyallylamine and n-octyltrimethyammonium were also examined as alternatives to the PAMAM dendrimer, but the magnitude of the photocurrent enhancement was rather small. The high photoreactivity of the dendrimer-ZnTPPS(4-) associates was interpreted mainly as a result of the high interfacial concentration of photoreactive porphyrin units associated stably with the dendrimer which was preferably adsorbed at the polarized water|DCE interface. The photochemical data observed in the second and fourth generation PAMAM dendrimer systems demonstrated that the higher generation dendrimer which can incorporate a porphyrin molecule more completely in the interior is less efficient for the photocurrent enhancement at the interface. These results indicated that the photoreactivity of ionic reactant at a polarized liquid|liquid interface can readily be modified via ion association with the charged dendrimer. PMID:25989445

  4. A new fluorescence turn-on probe for biothiols based on photoinduced electron transfer and its application in living cells

    NASA Astrophysics Data System (ADS)

    Wang, Jianxi; Zhou, Cheng; Zhang, Jianjian; Zhu, Xinyue; Liu, Xiaoyan; Wang, Qin; Zhang, Haixia

    2016-09-01

    A new biothiol-selective fluorescent probe 1 based on photoinduced electron transfer (PET) mechanism was designed and synthesized. The UV-Vis absorption and fluorescent emission properties of probe 1 towards various analytes were studied in detail. The probe exhibited a large stokes shift (~ 200 nm) after reacted with biothiols and could selectively detect cysteine (Cys) in dimethyl sulfoxide (DMSO)/H2O solution (9:1, v/v, 10 mM phosphate buffer saline, pH 3.5) over glutathione (GSH), homocysteine (Hcy) and other analytes with a detection limit of 0.117 μM. In addition, probe 1 responded well to GSH, Hcy and Cys in the same above solution with pH 5.5 and got the detection limits of 0.151 μM, 0.128 μM and 0.037 μM, respectively. Probe 1 was of very low cytotoxicity and successfully applied for imaging of thiols in living cells.

  5. Significant expansion of fluorescent protein sensing ability through the genetic incorporation of superior photo-induced electron-transfer quenchers.

    PubMed

    Liu, Xiaohong; Jiang, Li; Li, Jiasong; Wang, Li; Yu, Yang; Zhou, Qing; Lv, Xiaoxuan; Gong, Weimin; Lu, Yi; Wang, Jiangyun

    2014-09-24

    Photo-induced electron transfer (PET) is ubiquitous for photosynthesis and fluorescent sensor design. However, genetically coded PET sensors are underdeveloped, due to the lack of methods to site-specifically install PET probes on proteins. Here we describe a family of acid and Mn(III) turn-on fluorescent protein (FP) sensors, named iLovU, based on PET and the genetic incorporation of superior PET quenchers in the fluorescent flavoprotein iLov. Using the iLovU PET sensors, we monitored the cytoplasmic acidification process, and achieved Mn(III) fluorescence sensing for the first time. The iLovU sensors should be applicable for studying pH changes in living cells, monitoring biogentic Mn(III) in the environment, and screening for efficient manganese peroxidase, which is highly desirable for lignin degradation and biomass conversion. Our work establishes a platform for many more protein PET sensors, facilitates the de novo design of metalloenzymes harboring redox active residues, and expands our ability to probe protein conformational dynamics. PMID:25197956

  6. A new fluorescence turn-on probe for biothiols based on photoinduced electron transfer and its application in living cells.

    PubMed

    Wang, Jianxi; Zhou, Cheng; Zhang, Jianjian; Zhu, Xinyue; Liu, Xiaoyan; Wang, Qin; Zhang, Haixia

    2016-09-01

    A new biothiol-selective fluorescent probe 1 based on photoinduced electron transfer (PET) mechanism was designed and synthesized. The UV-Vis absorption and fluorescent emission properties of probe 1 towards various analytes were studied in detail. The probe exhibited a large stokes shift (~200nm) after reacted with biothiols and could selectively detect cysteine (Cys) in dimethyl sulfoxide (DMSO)/H2O solution (9:1, v/v, 10mM phosphate buffer saline, pH3.5) over glutathione (GSH), homocysteine (Hcy) and other analytes with a detection limit of 0.117μM. In addition, probe 1 responded well to GSH, Hcy and Cys in the same above solution with pH5.5 and got the detection limits of 0.151μM, 0.128μM and 0.037μM, respectively. Probe 1 was of very low cytotoxicity and successfully applied for imaging of thiols in living cells. PMID:27203232

  7. High-frequency (95 GHz) electron paramagnetic resonance study of the photoinduced charge transfer in conjugated polymer-fullerene composites

    NASA Astrophysics Data System (ADS)

    Ceuster, J. De; Goovaerts, E.; Bouwen, A.; Hummelen, J. C.; Dyakonov, V.

    2001-11-01

    Light-induced electron paramagnetic resonance (LEPR) measurements are reported in composites of poly(2-methoxy-5-(3-,7-dimethyloctyloxy)-1,4-phenylenevinylene) (MDMO-PPV) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), a soluble derivative of C60. Under illumination of the sample, two paramagnetic species are formed due to photoinduced charge transfer between conjugated polymer and fullerene. One is the positive polaron P+ on the polymer backbone and the other is the radical anion on the methanofullerene. Using high-frequency (95 GHz) LEPR it was possible to separate these two contributions to the spectrum on the basis of their g factors, and moreover to resolve the g anisotropy for both radicals. The positive polaron on the conjugated polymer chain possesses axial symmetry with g values g||=2.0034(1) and g⊥=2.0024(1). EPR on low doped polymer gave extra proof for the assignment to the positive polaron. The negatively charged methanofullerene has a lower, rhombic symmetry with gx=2.0003(1), gy=2.0001(1), and gz=1.9982(1). Different spin-lattice relaxation of both species gives rise to a rapid passage effect for the positive polaron spectrum.

  8. Photoinduced intramolecular electron transfer in a bridged C{sub 60}. (Acceptor)-Aniline (donor) system. Photophysical properties of the first `active` fullerene diad

    SciTech Connect

    Williams, R.M.; Zwier, J.M.; Verhoeven, J.W.

    1995-04-12

    A covalently functionalized fullerene comprising an electron donating aniline group coupled to the fullerene unit by a saturated heterocyclic bridge is shown to undergo a photoinduced intramolecular electron transfer process that causes quenching of the fluorescence of the adduct and strong decrease triplet population in polar solvents. VIS-absorption, fluorescence and phosphorescence at 77 K, triplet-triplet absorption, time resolved fluorescence and redox potentials of the fullerene adduct are presented. Analysis of the solvent dependence of the energetics of the intramolecular electron transfer is given and is in good agreement with the experimental results. 17 refs., 6 figs., 3 tabs.

  9. Efficiencies of photoinduced electron-transfer reactions: Role of the Marcus inverted region in return electron transfer within geminate radical-ion pairs

    SciTech Connect

    Gould, I.R.; Ege, D.; Moser, J.E.; Farid, S. )

    1990-05-23

    In photoinduced electron-transfer processes the primary step is conversion of the electronic energy of an excited state into chemical energy retained in the form of a redox (geminate radical-ion) pair (A + D {sup hv}{yields} A{sup {sm bullet}{minus}}/D{sup {sm bullet}+}). In polar solvents, separation of the geminate pair occurs with formation of free radical ions in solution. The quantum yields of product formation, from reactions of either the free ions, or of the geminate pair, are often low, however, due to the return electron transfer reaction (A{sup {sm bullet}{minus}}/D{sup {sm bullet}+} {yields} A + D), an energy-wasting step that competes with the useful reactions of the ion pair. The present study was undertaken to investigate the parameters controlling the rates of these return electron transfer reactions. Quantum yields of free radical ion formation were measured for ion pairs formed upon electron-transfer quenching of the first excited singlet states of cyanoanthracenes by simple aromatic hydrocarbon donors in aceonitrile at room temperature. The free-ion yields are determined by the competition between the rates of separation and return electron transfer.

  10. An Evaluation of Sensor Performance for Harmful Compounds by Using Photo-Induced Electron Transfer from Photosynthetic Membranes to Electrodes.

    PubMed

    Kasuno, Megumi; Kimura, Hiroki; Yasutomo, Hisataka; Torimura, Masaki; Murakami, Daisuke; Tsukatani, Yusuke; Hanada, Satoshi; Matsushita, Takayuki; Tao, Hiroaki

    2016-01-01

    Rapid, simple, and low-cost screening procedures are necessary for the detection of harmful compounds in the effluent that flows out of point sources such as industrial outfall. The present study investigated the effects on a novel sensor of harmful compounds such as KCN, phenol, and herbicides such as 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), 2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine (atrazine), and 2-N-tert-butyl-4-N-ethyl-6-methylsulfanyl-1,3,5-triazine-2,4-diamine (terbutryn). The sensor employed an electrode system that incorporated the photocurrent of intra-cytoplasmic membranes (so-called chromatophores) prepared from photosynthetic bacteria and linked using carbon paste electrodes. The amperometric curve (photocurrent-time curve) of photo-induced electron transfer from chromatophores of the purple photosynthetic bacterium Rhodobacter sphaeroides to the electrode via an exogenous electron acceptor was composed of two characteristic phases: an abrupt increase in current immediately after illumination (I₀), and constant current over time (Ic). Compared with other redox compounds, 2,5-dichloro-1,4-benzoquinone (DCBQ) was the most useful exogenous electron acceptor in this system. Photo-reduction of DCBQ exhibited Michaelis-Menten-like kinetics, and reduction rates were dependent on the amount of DCBQ and the photon flux intensity. The Ic decreased in the presence of KCN at concentrations over 0.05 μM (=μmol·dm(-3)). The I₀ decreased following the addition of phenol at concentrations over 20 μM. The Ic was affected by terbutryn at concentrations over 10 μM. In contrast, DCMU and atrazine had no effect on either I₀ or Ic. The utility of this electrode system for the detection of harmful compounds is discussed. PMID:27023553

  11. An Evaluation of Sensor Performance for Harmful Compounds by Using Photo-Induced Electron Transfer from Photosynthetic Membranes to Electrodes

    PubMed Central

    Kasuno, Megumi; Kimura, Hiroki; Yasutomo, Hisataka; Torimura, Masaki; Murakami, Daisuke; Tsukatani, Yusuke; Hanada, Satoshi; Matsushita, Takayuki; Tao, Hiroaki

    2016-01-01

    Rapid, simple, and low-cost screening procedures are necessary for the detection of harmful compounds in the effluent that flows out of point sources such as industrial outfall. The present study investigated the effects on a novel sensor of harmful compounds such as KCN, phenol, and herbicides such as 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), 2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine (atrazine), and 2-N-tert-butyl-4-N-ethyl-6-methylsulfanyl-1,3,5-triazine-2,4-diamine (terbutryn). The sensor employed an electrode system that incorporated the photocurrent of intra-cytoplasmic membranes (so-called chromatophores) prepared from photosynthetic bacteria and linked using carbon paste electrodes. The amperometric curve (photocurrent-time curve) of photo-induced electron transfer from chromatophores of the purple photosynthetic bacterium Rhodobacter sphaeroides to the electrode via an exogenous electron acceptor was composed of two characteristic phases: an abrupt increase in current immediately after illumination (I0), and constant current over time (Ic). Compared with other redox compounds, 2,5-dichloro-1,4-benzoquinone (DCBQ) was the most useful exogenous electron acceptor in this system. Photo-reduction of DCBQ exhibited Michaelis-Menten-like kinetics, and reduction rates were dependent on the amount of DCBQ and the photon flux intensity. The Ic decreased in the presence of KCN at concentrations over 0.05 μM (=μmol·dm−3). The I0 decreased following the addition of phenol at concentrations over 20 μM. The Ic was affected by terbutryn at concentrations over 10 μM. In contrast, DCMU and atrazine had no effect on either I0 or Ic. The utility of this electrode system for the detection of harmful compounds is discussed. PMID:27023553

  12. The wavelength dependence of photoinduced hot electron dissociative attachment to methyl bromide adsorbed on gallium arsenide (110)

    SciTech Connect

    Camillone, N. III; Khan, K.A.; Lasky, P.J.; Wu, L.; Moryl, J.E.; Osgood, R.M. Jr.

    1998-11-01

    The wavelength dependence of photoinduced dissociation of CH{sub 3}Br via dissociative electron attachment (DEA) of {open_quotes}hot{close_quotes} electrons for one monolayer CH{sub 3}Br adsorbed on GaAs(110) has been measured. The cross section for dissociation is found to decrease monotonically by two orders of magnitude as the incident wavelength is varied from 308 to 550 nm. There is an apparent threshold near 490 nm (2.5 eV), well below the gas phase photodissociation threshold near 250 nm (5.0 eV), but in good agreement with a simple estimate based on expected values for the decrease in the photoemission threshold and the lowering of the molecular affinity level upon adsorption of CH{sub 3}Br on a semiconductor surface. The observed threshold is found to move to higher energy as dissociation of the monolayer proceeds. Based on the work of Hasselbrink and co-workers [F. Weik, A. de Meijere, and E. Hasselbrink, J. Chem. Phys. {bold 99}, 682 (1993)], a simple theoretical model is developed which considers the tunneling of hot electrons through the interfacial barrier between the physisorbed CH{sub 3}Br and the GaAs. The results of our theoretical model in conjunction with those of earlier {ital ab initio} calculations [S. Black, R. Friesner, P. H. Lu, and R. M. Osgood, Jr., Surf. Sci. {bold 382}, 154 (1997)] suggest that the adsorbate affinity level is centered at {approximately}0.6 eV above the (adsorbate- modified) vacuum level of the substrate. This value corresponds to a {approximately}1.8 eV stabilization of the negative ion resonance upon adsorption. {copyright} {ital 1998 American Institute of Physics.}

  13. Role of hydrogen atoms in the photoinduced formation of stable electron centers in H-doped 12CaO•7 Al2 O3

    NASA Astrophysics Data System (ADS)

    Sushko, Peter V.; Shluger, Alexander L.; Hayashi, Katsuro; Hirano, Masahiro; Hosono, Hideo

    2006-01-01

    In this work we investigate a variety of chemical and photoinduced processes in which different hydrogenous species including H2 molecules, H- ions, and H0 atoms interact with the bulk of a complex nanoporous oxide 12CaO•7Al2O3 . Our results provide a detailed and consistent explanation of the recently observed phenomenon of photoinduced conversion of the insulating H-doped 12CaO•7Al2O3 to a conductor [K. Hayashi , Nature (London) 419, 462 (2002)]. The formation of a large and thermally stable concentration of electron centers in this process is facilitated by a large concentration (up to 1020cm-3 ) of extraframework O2- naturally present in this material and homogeneously distributed in its bulk. We show that these species are able to split H2 molecules into pairs of H+ and H- ions and convert H0 atoms into H+ and e- promoting the photoinduced conversion process. The similarity of the mechanisms described in this work to those known for low-coordinated sites at MgO surfaces indicates that the formation of electronic centers in oxides interacting with hydrogenous species could be a generic feature.

  14. Vibrational dynamics in photoinduced electron transfer. Progress report, December 1, 1992--November 30, 1993

    SciTech Connect

    Spears, K.G.

    1993-09-08

    Objective is to perform a new type of measurement for optically excited electron transfer processes that can provide unique experimental insight into the molecular mechanism of electron transfer. Measurements of optically excited electron transfer are done with picosecond infrared (IR) absorption spectroscopy to monitor the vibrational motions of the molecules immediately after electron transfer. Theory and experiment suggest that molecular vibrations and distortions are important controlling elements for electron transfer, and direct information has yet to be obtained on these elements of electron transfer mechanisms. The second period of funding has been dedicated to finishing technique development and performing studies of electron transfer in ion pair systems to identify if vibrational dependent electron transfer rates are present in this system. We have succeeded in measuring, for the first time, electron transfer rates as a function of vibrational state in an ion pair complex in solution. In a different area of electron transfer research we have proposed a new mechanism of solvent gated electron transfer.

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

    PubMed Central

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

    2011-01-01

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

  16. Photoinduced diffusion molecular transport

    NASA Astrophysics Data System (ADS)

    Rozenbaum, Viktor M.; Dekhtyar, Marina L.; Lin, Sheng Hsien; Trakhtenberg, Leonid I.

    2016-08-01

    We consider a Brownian photomotor, namely, the directed motion of a nanoparticle in an asymmetric periodic potential under the action of periodic rectangular resonant laser pulses which cause charge redistribution in the particle. Based on the kinetics for the photoinduced electron redistribution between two or three energy levels of the particle, the time dependence of its potential energy is derived and the average directed velocity is calculated in the high-temperature approximation (when the spatial amplitude of potential energy fluctuations is small relative to the thermal energy). The thus developed theory of photoinduced molecular transport appears applicable not only to conventional dichotomous Brownian motors (with only two possible potential profiles) but also to a much wider variety of molecular nanomachines. The distinction between the realistic time dependence of the potential energy and that for a dichotomous process (a step function) is represented in terms of relaxation times (they can differ on the time intervals of the dichotomous process). As shown, a Brownian photomotor has the maximum average directed velocity at (i) large laser pulse intensities (resulting in short relaxation times on laser-on intervals) and (ii) excited state lifetimes long enough to permit efficient photoexcitation but still much shorter than laser-off intervals. A Brownian photomotor with optimized parameters is exemplified by a cylindrically shaped semiconductor nanocluster which moves directly along a polar substrate due to periodically photoinduced dipole moment (caused by the repetitive excited electron transitions to a non-resonant level of the nanocylinder surface impurity).

  17. Dynamics of ultrafast photoinduced heterogeneous electron transfer, implications for recent solar energy conversion scenarios

    NASA Astrophysics Data System (ADS)

    Gundlach, Lars; Burfeindt, Bernd; Mahrt, Jürgen; Willig, Frank

    2012-08-01

    The general case of a heterogeneous electron transfer reaction is realized by ultrafast electron transfer from a photo-excited molecule to a wide continuum of electronic acceptor states. Two different theoretical model calculations addressing the injection dynamics have recently been presented. The first scenario predicts a wide energy distribution for the injected electron via excitations of high-energy vibrational modes in the ionized molecule, whereas the second scenario ascribes the width to thermal fluctuations. We present experimental data at different temperatures and identify the valid injection scenario for perylene/TiO2 systems. The results are discussed in view of recent solar energy conversion scenarios.

  18. Mechanistic studies of photoinduced spin crossover and electron transfer in inorganic complexes.

    PubMed

    Zhang, Wenkai; Gaffney, Kelly J

    2015-04-21

    Electronic excited-state phenomena provide a compelling intersection of fundamental and applied research interests in the chemical sciences. This holds true for coordination chemistry, where harnessing the strong optical absorption and photocatalytic activity of compounds depends on our ability to control fundamental physical and chemical phenomena associated with the nonadiabatic dynamics of electronic excited states. The central events of excited-state chemistry can critically influence the dynamics of electronic excited states, including internal conversion (transitions between distinct electronic states) and intersystem crossing (transitions between electronic states with different spin multiplicities), events governed by nonadiabatic interactions between electronic states in close proximity to conical intersections, as well as solvation and electron transfer. The diversity of electronic and nuclear dynamics also makes the robust interpretation of experimental measurements challenging. Developments in theory, simulation, and experiment can all help address the interpretation and understanding of chemical dynamics in organometallic and coordination chemistry. Synthesis presents the opportunity to chemically engineer the strength and symmetry of the metal-ligand interactions. This chemical control can be exploited to understand the influence of electronic ground state properties on electronic excited-state dynamics. New time-resolved experimental methods and the insightful exploitation of established methods have an important role in understanding, and ideally controlling, the photophysics and photochemistry of transition metal complexes. Techniques that can disentangle the coupled motion of electrons and nuclear dynamics warrant emphasis. We present a review of electron localization dynamics in charge transfer excited states and the dynamics of photoinitiated spin crossover dynamics. Both electron localization and spin crossover have been investigated by

  19. Photo-induced regeneration of hormones by electron transfer processes: Potential biological and medical consequences

    NASA Astrophysics Data System (ADS)

    Getoff, Nikola; Hartmann, Johannes; Schittl, Heike; Gerschpacher, Marion; Quint, Ruth Maria

    2011-08-01

    Based on the previous results concerning electron transfer processes in biological substances, it was of interest to investigate if hormone transients resulting by e.g. electron emission can be regenerated. The presented results prove for the first time that the hormone transients originating by the electron emission process can be successfully regenerated by the transfer of electrons from a potent electron donor, such as vitamin C (VitC). Investigations were performed using progesterone (PRG), testosterone (TES) and estrone (E1) as representatives of hormones. By irradiation with monochromatic UV light (λ=254 nm) in a media of 40% water and 60% ethanol, the degradation as well as the regeneration of the hormones was studied with each hormone individually and in the mixture with VitC as a function of the absorbed UV dose, using HPLC. Calculated from the obtained initial yields, the determined regeneration of PRG amounted to 52.7%, for TES to 58.6% and for E1 to 90.9%. The consumption of VitC was determined in the same way. The reported results concerning the regeneration of hormones by the transfer of electrons from an electron donor offer a new, promising method for the therapy with hormones. As a consequence of the regeneration of hormones, a decreased formation of carcinogenic metabolites is expected.

  20. Photo-induced electron transfer between a dendritic zinc(II) phthalocyanine and methyl viologen

    NASA Astrophysics Data System (ADS)

    Wang, Yuhua; Chen, Jiangxu; Huang, Lishan; Xie, Shusen; Yang, Hongqin; Peng, Yiru

    2013-01-01

    The intermolecular electron transfer between the carboxylic dendritic zinc(II) phthalocyanines [G1-ZnPc( and G2-ZnPc(] and methyl viologen (MV) is studied by steady-state fluorescence and UV/Vis absorption spectroscopic method. The effect of dendron generation of this series of dendritic phthalocyanines on intermolecular electron transfer is investigated. The results show that the fluorescence emission of these dendritic phthalocyanines could be greatly quenched by MV upon excitation at 610 nm. The Stern-Volmer constant (KSV) of electron transfer is decreased with increasing dendron generations. Our study suggests that these dendritic phthalocyanines are an effective new electron donor and transmission complex and could be used as a potential artificial photosynthesis system.

  1. Efficient photoinduced orthogonal energy and electron transfer reactions via phospholipid membrane-bound donors and acceptors

    SciTech Connect

    Clapp, P.J.; Armitage, B.; Roosa, P.; O'Brien, D.F. )

    1994-10-05

    A three component, liposome-bound photochemical molecular device (PMD) consisting of energy and electron transfer reactions is described. Bilayer membrane surface-associated dyes, 5,10,15,20-tetrakis[4-(trimethylammonio)-phenyl]-21H,2 3H-porphine tetra-p-tosylate salt and N,N[prime]-bis[(3-trimethylammonio)propyl]thiadicarbocya nine tribromide, are the energy donor and acceptor, respectively, in a blue light stimulated energy transfer reaction along the vesicle surface. The electronically excited cyanine is quenched by electron transfer from the phospholipid membrane bound triphenylbenzyl borate anion, which is located in the lipid bilayer interior. The PMD exhibits sequential reactions following electronic excitation with the novel feature that the steps proceed with orthogonal orientation: energy transfer occurs parallel to the membrane surface, and electron transfer occurs perpendicular to the surface. Photobleaching and fluorescence quenching experiments verify the transfer reactions, and Stern-Volmer analysis was used to estimate the reaction rate constants. At the highest concentrations examined of energy and electron acceptor ca. 60% of the photoexcited porphyrins were quenched by energy transfer to the cyanine. 56 refs., 6 figs., 3 tabs.

  2. Photoinduced Electron Transfer in DNA: Charge Shift Dynamics Between 8-Oxo-Guanine Anion and Adenine.

    PubMed

    Zhang, Yuyuan; Dood, Jordan; Beckstead, Ashley A; Li, Xi-Bo; Nguyen, Khiem V; Burrows, Cynthia J; Improta, Roberto; Kohler, Bern

    2015-06-18

    Femtosecond time-resolved IR spectroscopy is used to investigate the excited-state dynamics of a dinucleotide containing an 8-oxoguanine anion at the 5'-end and neutral adenine at the 3'-end. UV excitation of the dinucleotide transfers an electron from deprotonated 8-oxoguanine to its π-stacked neighbor adenine in less than 1 ps, generating a neutral 8-oxoguanine radical and an adenine radical anion. These species are identified by the excellent agreement between the experimental and calculated IR difference spectra. The quantum efficiency of this ultrafast charge shift reaction approaches unity. Back electron transfer from the adenine radical anion to the 8-oxguanine neutral radical occurs in 9 ps, or approximately 6 times faster than between the adenine radical anion and the 8-oxoguanine radical cation (Zhang, Y. et al. Proc. Natl. Acad. Sci. U.S.A. 2014, 111, 11612-11617). The large asymmetry in forward and back electron transfer rates is fully rationalized by semiclassical nonadiabatic electron transfer theory. Forward electron transfer is ultrafast because the driving force is nearly equal to the reorganization energy, which is estimated to lie between 1 and 2 eV. Back electron transfer is highly exergonic and takes place much more slowly in the Marcus inverted region. PMID:25660103

  3. Photoinduced Interfacial Electron Injection Dynamics in Dye-Sensitized Solar Cells under Photovoltaic Operating Conditions.

    PubMed

    Teuscher, Joël; Décoppet, Jean-David; Punzi, Angela; Zakeeruddin, Shaik M; Moser, Jacques-E; Grätzel, Michael

    2012-12-20

    We report a pump-probe spectroscopy study of electron injection rates in dye-sensitized solar cell (DSSC) devices. We examine the case of working devices employing an N719 ruthenium sensitizer and an iodide electrolyte. Electron injection is found to occur mainly on a sub-100 fs time scale, followed by a slower component with a lifetime of 26.9 ps, in accordance with previous reports on model samples. The amplitude of this latter component varies with electrolyte composition from 25 to 9%. The appearance of slower components in the electron injection dynamics may be attributed to an aggregated or weakly bound state of the surface-adsorbed N719 sensitizer. Further measurements are reported varying the cell light bias and load conditions, revealing no influence on electron injection dynamics. No other electron injection event is found to occur up to 1 ns. These results show no evidence for a slowdown of electron injection under working conditions compared to model systems for the electrolytes examined in this study. PMID:26291112

  4. Proton Quantization and Vibrational Relaxation in Nonadiabatic Dynamics of Photoinduced Proton-Coupled Electron Transfer in a Solvated Phenol-Amine Complex.

    PubMed

    Goyal, Puja; Schwerdtfeger, Christine A; Soudackov, Alexander V; Hammes-Schiffer, Sharon

    2016-03-10

    Nonadiabatic dynamics simulations of photoinduced proton-coupled electron transfer (PCET) in a phenol-amine complex in solution were performed. The electronic potential energy surfaces were generated on-the-fly with a hybrid quantum mechanical/molecular mechanical approach that described the solute with a multiconfigurational method in a bath of explicit solvent molecules. The transferring hydrogen nucleus was represented as a quantum mechanical wave function calculated with grid-based methods, and surface hopping trajectories were propagated on the adiabatic electron-proton vibronic surfaces. Following photoexcitation to the excited S1 electronic state, the overall decay to the ground vibronic state was found to be comprised of relatively fast decay from a lower proton vibrational state of S1 to a highly excited proton vibrational state of the ground S0 electronic state, followed by vibrational relaxation within the S0 state. Proton transfer can occur either on the highly excited proton vibrational states of S0 due to small environmental fluctuations that shift the delocalized vibrational wave functions or on the low-energy proton vibrational states of S1 due to solvent reorganization that alters the asymmetry of the proton potential and reduces the proton transfer barrier. The isotope effect arising from replacing the transferring hydrogen with deuterium is predicted to be negligible because hydrogen and deuterium behave similarly in both types of proton transfer processes. Although an isotope effect could be observed for other systems, in general the absence of an isotope effect does not imply the absence of proton transfer in photoinduced PCET systems. This computational approach is applicable to a wide range of other photoinduced PCET processes. PMID:26812149

  5. Theory of ultrafast photoinduced electron transfer from a bulk semiconductor to a quantum dot

    SciTech Connect

    Rasmussen, Andrew M. Ramakrishna, S.; Weiss, Emily A.; Seideman, Tamar

    2014-04-14

    This paper describes analytical and numerical results from a model Hamiltonian method applied to electron transfer (ET) from a quasicontinuum (QC) of states to a set of discrete states, with and without a mediating bridge. Analysis of the factors that determine ET dynamics yields guidelines for achieving high-yield electron transfer in these systems, desired for instance for applications in heterogeneous catalysis. These include the choice of parameters of the laser pulse that excites the initial state into a continuum electronic wavepacket and the design of the coupling between the bridge molecule and the donor and acceptor. The vibrational mode on a bridging molecule between donor and acceptor has an influence on the yield of electron transfer via Franck-Condon factors, even in cases where excited vibrational states are only transiently populated. Laser-induced coherence of the initial state as well as energetic overlap is crucial in determining the ET yield from a QC to a discrete state, whereas the ET time is influenced by competing factors from the coupling strength and the coherence properties of the electronic wavepacket.

  6. Photoinduced Electron and Energy Transfer in a Molecular Triad Featuring a Fullerene Redox Mediator.

    PubMed

    Antoniuk-Pablant, Antaeres; Kodis, Gerdenis; Moore, Ana L; Moore, Thomas A; Gust, Devens

    2016-07-14

    In order to investigate the possibility of a fullerene acting as an electron and/or singlet energy relay between a donor chromophore and an acceptor, a triad consisting of a fullerene (C60) covalently linked to both a porphyrin energy and electron donor (P) and a β-tetracyanoporphyrin energy and electron acceptor (CyP) was synthesized. Steady state and time-resolved spectroscopic investigations show that the porphyrin first excited singlet state donates singlet excitation and an electron to the fullerene and also donates singlet excitation to the CyP. All three processes differ in rate constant by factors of ≤1.3, and all are much faster than the decay of (1)P-C60-CyP by unichromophoric processes. The fullerene excited state accepts an electron from P and donates singlet excitation energy to CyP. The P(•+)-C60(•-)-CyP charge-separated state transfers an electron to CyP to produce a final P(•+)-C60-CyP(•-) state. The same state is formed from P-C60-(1)CyP. Overall, the final charge-separated state is formed with a quantum yield of 85% in benzonitrile, and has a lifetime of 350 ps. Rate constants for formation and quantum yields of all intermediate states were estimated from results for the triad and several model compounds. Interestingly, the intermediate P(•+)-C60(•-)-CyP charge-separated state has a lifetime of 660 ps. It is longer lived than the final state in spite of stronger coupling of the radical ions. This is ascribed to the fact that recombination lies far into the inverted region of the Marcus rate constant vs thermodynamic driving force relationship. PMID:27275648

  7. Photoinduced electron transfer between Fe(III) and adenosine triphosphate-BODIPY conjugates: Application to alkaline-phosphatase-linked immunoassay.

    PubMed

    Lin, Jia-Hui; Yang, Ya-Chun; Shih, Ya-Chen; Hung, Szu-Ying; Lu, Chi-Yu; Tseng, Wei-Lung

    2016-03-15

    Fluorescent boron dipyrromethene (BODIPY) analogs are often used as sensors for detecting various species because of their relatively high extinction coefficients, outstanding fluorescence quantum yields, photostability, and pH-independent fluorescence. However, there is little-to-no information in the literature that describes the use of BODIPY analogs for detecting alkaline phosphatase (ALP) activity and inhibition. This study discovered that the fluorescence of BODIPY-conjugated adenosine triphosphate (BODIPY-ATP) was quenched by Fe(III) ions through photoinduced electron transfer. The ALP-catalyzed hydrolysis of BODIPY-ATP resulted in the formation of BODIPY-adenosine and phosphate ions. The fluorescence of the generated BODIPY-adenosine was insensitive to the change in the concentration of Fe(III) ions. Thus, the Fe(III)-induced fluorescence quenching of BODIPY-ATP can be paired with its ALP-mediated dephosphorylation to design a turn-on fluorescence probe for ALP sensing. A method detection limit at a signal-to-noise ratio of 3 for ALP was estimated to be 0.02 units/L (~6 pM; 1 ng/mL). This probe was used for the screening of ALP inhibitors, including Na3VO4, imidazole, and arginine. Because ALP is widely used in enzyme-linked immunosorbent assays, the probe was coupled to an ALP-linked immunosorbent assay for the sensitive and selective detection of immunoglobulin G (IgG). The lowest detectable concentration for IgG in this system was 5 ng/mL. Compared with the use of 3,6-fluorescein diphosphate as a signal reporter in an ALP-linked immunosorbent assay, the proposed system provided comparable sensitivity, large linear range, and high stability over temperature and pH changes. PMID:26409025

  8. The kinetic model for slow photoinduced electron transport in the reaction centers of purple bacteria.

    PubMed

    Serdenko, T V; Barabash, Y M; Knox, P P; Seifullina, N Kh

    2016-12-01

    The present work is related to the investigation of slow kinetics of electron transport in the reaction centers (RCs) of Rhodobacter sphaeroides. Experimental data on the absorption kinetics of aqueous solutions of reaction centers at different modes of photoexcitation are given. It is shown that the kinetics of oxidation and reduction of RCs are well described by the sum of three exponential functions. This allows to suggest a two-level kinetic model for electron transport in the RC as a system of four electron-conformational states which correspond to three balance differential equations combined with state equation. The solution of inverse problem made it possible to obtain the rate constant values in kinetic equations for different times and intensities of exciting light. Analysis of rate constant values in different modes of RC excitation allowed to suggest that two mechanisms of structural changes are involved in RC photo-oxidation. One mechanism leads to the increment of the rate of electron return, another one-to its drop. Structural changes were found out to occur in the RCs under incident light. After light was turned off, the reduction of RCs was determined by the second mechanism. PMID:27271854

  9. The kinetic model for slow photoinduced electron transport in the reaction centers of purple bacteria

    NASA Astrophysics Data System (ADS)

    Serdenko, T. V.; Barabash, Y. M.; Knox, P. P.; Seifullina, N. Kh.

    2016-06-01

    The present work is related to the investigation of slow kinetics of electron transport in the reaction centers (RCs) of Rhodobacter sphaeroides. Experimental data on the absorption kinetics of aqueous solutions of reaction centers at different modes of photoexcitation are given. It is shown that the kinetics of oxidation and reduction of RCs are well described by the sum of three exponential functions. This allows to suggest a two-level kinetic model for electron transport in the RC as a system of four electron-conformational states which correspond to three balance differential equations combined with state equation. The solution of inverse problem made it possible to obtain the rate constant values in kinetic equations for different times and intensities of exciting light. Analysis of rate constant values in different modes of RC excitation allowed to suggest that two mechanisms of structural changes are involved in RC photo-oxidation. One mechanism leads to the increment of the rate of electron return, another one—to its drop. Structural changes were found out to occur in the RCs under incident light. After light was turned off, the reduction of RCs was determined by the second mechanism.

  10. Photoinduced electronic transport in K1-xLixTaO3

    NASA Astrophysics Data System (ADS)

    Sangalli, P.; Giulotto, E.; Rollandi, L.; Calvi, P.; Camagni, P.; Samoggia, G.

    1998-03-01

    Photocurrent and Hall effect measurements were performed on K0.984Li0.016TaO3 and K0.966Li0.034TaO3 single crystals under illumination with 514.5-nm and UV light. The currents observed are carried by electrons, whose mobility does not undergo large variations on cooling across the dipole-glass freezing temperature Tf. The sharp increase of photocurrent occurring in the polar phase is primarily due to enhancement of carrier density. The effect is much larger after field cooling, being accompanied in this case by persistent currents. The present results lead us to conclude that hole traps with vanishing cross section for electron recombination are active below Tf.

  11. Mechanisms of photoinduced electron transfer: Final report, July 1, 1977-September 30, 1987

    SciTech Connect

    Jones, G. II

    1987-12-01

    Work which has been conducted under Department of Energy sponsorship over the past ten years at Boston University is described. A general theme for projects which are summarized involves photochemically induced electron transfer reactions for organic compounds. Early studies in the series were directed to the development of new mechanisms for driving isomerization processes which store light energy as latent heat. Other investigations were devoted to an understanding of the dynamics of charge separation for photoexcited (charge-transfer) complexes or ion-pairs. Recent studies focused on the development of charge relays such as dithioethers and viologen or pyridinium ions, the electron transfer photochemistry of high potential quinones, and the photophysical properties of organic dyes bound to water-soluble polymers. 9 figs.

  12. Photoinduced Electron and H-atom Transfer Reactions of Xanthone by Laser Flash Photolysis

    NASA Astrophysics Data System (ADS)

    Wang, Jin-ting; Pan, Yang; Zhang, Li-min; Yu, Shu-qin

    2007-08-01

    The property of the lowest excited triplet states of xanthone in acetonitrile was investigated using time-resolved laser flash photolysis at 355 nm. The transient absorption spectra and the quenching rate constants (kq) of the excited xanthone with several amines were determined. Good correlation between lgkq and the driving force of the reactions suggests the electron transfer mechanism, except aniline and 3-nitroaniline (3-NO2-A) which showed energy transfer mechanism. With the appearance of ketyl radical, hydrogen atom transfer also happened between xanthone and dimethyl-p-toluidine, 3,5,N,N-tetramethylaniline, N,N-dimethylaniline, and triethylamine. Therefore, both electron transfer and H-atom transfer occured in these systems. Great discrepancies of kq values were discovered in H-atom abstraction reactions for alcohols and phenols, which can be explained by different abstraction mechanisms. The quenching rate constants between xanthone and alcohols correlate well with the α-C-H bonding energy of alcohols.

  13. Photoinduced electron transfer in porous organic salt crystals impregnated with fullerenes.

    PubMed

    Hasegawa, Tetsuya; Ohkubo, Kei; Hisaki, Ichiro; Miyata, Mikiji; Tohnai, Norimitsu; Fukuzumi, Shunichi

    2016-06-28

    Porous organic salt (POS) crystals composed of 9-(4-sulfophenyl)anthracene (SPA) and triphenylmethylamine (TPMA) were impregnated with fullerenes (C60 and C70), which were arranged in one dimensional close contact. POS crystals of SPA and TPMA without fullerenes exhibit blue fluorescence due to SPA, whereas the fluorescence was quenched in POS with fullerenes due to electron transfer from the singlet excited state of SPA to fullerenes. PMID:27182038

  14. Photo-induced electron detachment of protein polyanions in the VUV range

    SciTech Connect

    Brunet, Claire; Antoine, Rodolphe; Dugourd, Philippe; Canon, Francis; Nahon, Laurent; Giuliani, Alexandre

    2013-02-14

    Biomolecular polyanions mainly relax by electron emission after UV excitation. Here, we study photodetachment of protein polyanions in the 6-16 eV VUV range by coupling a linear quadrupole ion trap with a synchrotron beamline. Gas-phase VUV action spectra of electrospray-produced multiply deprotonated insulin (5.6 kDa) and myoglobin (16.7 kDa) proteins are reported, which significantly increases the amount of data available on the optical response of proteins in the VUV. The influence of the protein charge and oxidation state upon the electron detachment efficiency is discussed. For small protein such as insulin, it appears that higher charge states produce higher detachment yields. Investigations on oxidized species show that the nature of the groups bearing the negative charges has an influence on the yields. For larger proteins, comparison of two forms of myoglobin clearly indicate that the three-dimensional structure does not impact much on the shape and the magnitude of the photodetachment spectra, in spite of a slight shift for the first electronic excited states.

  15. 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.

  16. Photophysical properties and photo-induced intermolecular electron transfer of a novel aryl benzyl ester dendritic axially substituted silicon (IV) phthalocyanine

    NASA Astrophysics Data System (ADS)

    Chen, Xiuqin; Ma, Dongdong; Wang, Xiongwei; Chen, Jianling; Ruan, Youhong; Qi, Yiling; Ye, Qiuhao; Peng, Yiru

    2014-11-01

    The photophysical properties of a novel dendritic phthalocyanine di-{3,5-di-(4-methoxycarbonyl group benzyloxy) benzyloxy) benzyloxy} axially substituted silicon (IV) phthalocyanine (DSiPc) were studied by UV/Vis, steady state and time-resolved spectroscopic methods. The effect of dendritic structure on the photophysical properties and photoinduced intermolecular electron transfer were investigated. The maximum absorption, fluorescence intensity, lifetime and fluorescence quantum yield of DSiPc were greatly sensitized by the dendritic structure on the axially position of silicon (IV) phthalocyanine. The photoinduced intermolecular electron transfer between this novel macromolecule and benzoquinone (BQ) was studied. The results showed that the fluorescence emission of this dendritic phthalocyanine could be quenched by BQ with KSV value of DSiPc is 52.84 dm3 mol-1. The cyclic voltammogram and square wave voltammogram of DSiPc in DMF further evidenced the electron was transfer from DSiPc to BQ from thermodynamics. Therefore, this novel dendritic phthalocyanine was an effective new electron donor and transmission complex could be used as a potential artificial photosynthesis system.

  17. Electron Source in Photoinduced Hydrogen Production on Pt-supported TiO Particles

    SciTech Connect

    Perkins, Craig L.; Henderson, Michael A.; McCready, David E.; Herman, Gregory S.

    2001-01-18

    Abe et al. illuminated an aqueous suspension of TiO/Pt with a Hg arc lamp and observed H production in the absence of O production. An unspecified elemental analysis excluded carbonaceous contaminants, and the source of the electron donor was concluded to be Ti+ cations. We can suggest at least three more likely (than Ti) sources for their mysterious electron donor: (1)an overlooked inorganic species, (2) Ti, and/or (3)organic impurities. The authors excluded the latter in their paper, but we view this conclusion as suspect given the lack of information on the limits of detection of the carbon assay, and the fact that the choice of argon(thermal conductivity= 41.33 x 10-6 cal cm-2s-1 (C cm-1)-1)3 as a carrier gas in their thermal conductivity detector4 probably precluded the observation of CO (thermal conductivity= 37.61 x 10-6 cal cm-2s-1 (C cm-1)-1)3, which is a common product of organic photochemical oxidations. No mention is made of an analysis for inorganic impurities. It is widely accepted that nanometer scale TiO particles can have significant fractions of undercoordinated Ti sites which can be easily oxidized to Ti, the highest valence of Ti observed in condensed phases. Here we point out that oxidation of Ti to Ti is much more physically realistic than oxidation of Ti to Ti. Removal of a fifth electron from titanium requires {approx}56 eV5.Ti, if it were to be generated in a solid oxide, would extract an electron from the valence band composed mainly of oxygen 2s and 2p states rather than remain in the 5 valence state. This unrealistically high oxidation state seems even more unlikely given the fact that at the room temperatures used in the authors' reactions Ti would have been generated and remained at the surface (at room temperature the diffusion of Ti cations in TiO is minimal), and the fact that the surface Madelung potential is smaller than that of the bulk6.

  18. Coherent control of long-range photoinduced electron transfer by stimulated X-ray Raman processes.

    PubMed

    Dorfman, Konstantin E; Zhang, Yu; Mukamel, Shaul

    2016-09-01

    We show that X-ray pulses resonant with selected core transitions can manipulate electron transfer (ET) in molecules with ultrafast and atomic selectivity. We present possible protocols for coherently controlling ET dynamics in donor-bridge-acceptor (DBA) systems by stimulated X-ray resonant Raman processes involving various transitions between the D, B, and A sites. Simulations presented for a Ru(II)-Co(III) model complex demonstrate how the shapes, phases and amplitudes of the X-ray pulses can be optimized to create charge on demand at selected atoms, by opening up otherwise blocked ET pathways. PMID:27559082

  19. Generation of Phosphorescent Triplet States via Photoinduced Electron Transfer: Energy and Electron Transfer Dynamics in Pt Porphyrin-Rhodamine B Dyads

    PubMed Central

    Mani, Tomoyasu; Niedzwiedzki, Dariusz M.; Vinogradov, Sergei A.

    2012-01-01

    Control over generation and dynamics of excited electronic states is fundamental to their utilization in all areas of technology. We present the first example of multichromophoric systems in which emissive triplet states are generated via a pathway involving photoinduced electron transfer (ET), as opposed to local intrachromophoric processes. In model dyads, PtP-Phn-pRhB+ (1-3, n=1-3), comprising platinum(II) meso-tetraarylporphyrin (PtP) and rhodamine B piperazine derivative (pRhB+), linked by oligo-p-phenylene bridges (Phn), upon selective excitation of pRhB+ at a frequency below that of the lowest allowed transition of PtP, room-temperature T1→S0 phosphorescence of PtP was observed. The pathway leading to the emissive PtP triplet state includes excitation of pRhB+, ET with formation of the singlet radical pair, intersystem crossing within that pair and subsequent radical recombination. Due to the close proximity of the triplet energy levels of PtP and pRhB+, reversible triplet-triplet (TT) energy transfer between these states was observed in dyads 1 and 2. As a result, the phosphorescence of PtP was extended in time by the long decay of the pRhB+ triplet. Observation of ET and TT in the same series of molecules enabled direct comparison of the distance attenuation factors β between these two closely related processes. PMID:22400988

  20. Controlling Photoinduced Electron Transfer Via Defects Self-Organization for Novel Functional Macromolecular Systems

    PubMed Central

    Campi, Gaetano; Ciasca, Gabriele; Poccia, Nicola; Ricci, Alessandro; Fratini, Michela; Bianconi, Antonio

    2014-01-01

    The electrons transfer (ET) from an atom or a molecule, donor (D), to another, acceptor (A) is the basis of many fundamental chemical and physical processes. The ET mechanism is controlled by spatial arrangements of donor and acceptors: it’s the particular spatial arrangement and thus the particular distance and the orientation between the electron donors and acceptors that controls the efficiency in charge separation processes in nature. Here, we stress the importance of this concept reviewing how spatial distribution of atomic and molecular self-assembly can determine the quality and physical features of ET process from biology to material science. In this context, we propose novel lab-on-chip techniques to be used to control spatial distribution of molecules at nanoscale. Synchrotron source brightness jointly to focusing optics fabrication allows one nowadays to monitor and visualize structures with sub-micrometric spatial resolution. This can give us a new powerful tool to set up sophisticated X-ray imaging techniques as well as spectroscopic elemental and chemical mapping to investigate the structure-function relationship controlling the spatial arrangement of the molecules at nanoscale. Finally, we report intriguing recent case studies on the possibility to manipulate and control this spatial distribution and material functionality at nanoscale by using X ray illumination.

  1. All-optical photochromic spatial light modulators based on photoinduced electron transfer in rigid matrices

    NASA Technical Reports Server (NTRS)

    Beratan, David N. (Inventor); Perry, Joseph W. (Inventor)

    1991-01-01

    A single material (not a multi-element structure) spatial light modulator may be written to, as well as read out from, using light. The device has tailorable rise and hold times dependent on the composition and concentration of the molecular species used as the active components. The spatial resolution of this device is limited only by light diffraction as in volume holograms. The device may function as a two-dimensional mask (transmission or reflection) or as a three-dimensional volume holographic medium. This device, based on optically-induced electron transfer, is able to perform incoherent to coherent image conversion or wavelength conversion over a wide spectral range (ultraviolet, visible, or near-infrared regions).

  2. ATP binding and aspartate protonation enhance photoinduced electron transfer in plant cryptochrome.

    PubMed

    Cailliez, Fabien; Müller, Pavel; Gallois, Michaël; de la Lande, Aurélien

    2014-09-17

    Cryptochromes are flavoproteins encountered in most vegetal and animal species. They play a role of blue-light receptors in plants and in invertebrates. The putative resting state of the FAD cofactor in these proteins is its fully oxidized form, FADox. Upon blue-light excitation, the isoalloxazine ring (ISO) may undergo an ultrafast reduction by a nearby tryptophan residue W400. This primary reduction triggers a cascade of electron and proton transfers, ultimately leading to the formation of the FADH° radical. A recent experimental study has shown that the yield of FADH° formation in Arabidopsis cryptochrome can be strongly modulated by ATP binding and by pH, affecting the protonation state of D396 (proton donor to FAD°(-)). Here we provide a detailed molecular analysis of these effects by means of combined classical molecular dynamics simulations and time-dependent density functional theory calculations. When ATP is present and D396 protonated, FAD remains in close contact with W400, thereby enhancing electron transfer (ET) from W400 to ISO*. In contrast, deprotonation of D396 and absence of ATP introduce flexibility to the photoactive site prior to FAD excitation, with the consequence of increased ISO-W400 distance and diminished tunneling rate by almost two orders of magnitude. We show that under these conditions, ET from the adenine moiety of FAD becomes a competitive relaxation pathway. Overall, our data suggest that the observed effects of ATP and pH on the FAD photoreduction find their roots in the earliest stage of the photoreduction process; i.e., ATP binding and the protonation state of D396 determine the preferred pathway of ISO* relaxation. PMID:25157750

  3. Photoinduced phase transitions.

    PubMed

    Bennemann, K H

    2011-02-23

    Optically induced ultrafast electronic excitations with sufficiently long lifetimes may cause strong effects on phase transitions like structural and nonmetal→metal ones and on supercooling, supersaturation, etc. Examples are the transitions diamond→graphite, graphite→graphene, non-metal→metal, solid→liquid and vapor→liquid, solid. Photoinduced formation of graphene and water condensation of saturated or supersaturated vapor due to increased bonding amongst water molecules are of particular interest. These nonequilibrium transitions are an ultrafast response, on a few hundred fs time scale, to the fast low to large energy electronic excitations. The energy of the photons is converted into electronic energy via electronic excitations changing the cohesive energy. This changes the chemical potential controlling the phase transition. In view of the advances in laser optics photon induced transitions are expected to become an active area in nonequilibrium physics and phase transition dynamics. Conservation laws like energy or angular momentum conservation control the time during which the transitions occur. Since the photon induced effects result from weakening or strengthening of the bonding between the atoms or molecules transitions like solid/liquid, etc can be shifted in both directions. Photoinduced transitions will be discussed from a unified point of view. PMID:21411879

  4. 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

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

    PubMed Central

    Stergiou, Anastasios; Pagona, Georgia

    2014-01-01

    Summary 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

  6. Photoinduced ultrafast interfacial electron transfer probed with two-photon-photoemission

    NASA Astrophysics Data System (ADS)

    Gundlach, Lars; Ernstorfer, Ralph; Willig, Frank

    2007-09-01

    Ultrafast heterogeneous electron transfer (HET) from the excited singlet state of the organic chromophore perylene into the inorganic semiconductor rutile TiO II was investigated with femtosecond time-resolved two-photon photoemission (2PPE). With 2PPE one can address adsorbates at coverages far below a monolayer on single crystal surfaces. With the same chromophore perylene fixed with different anchor and bridge groups at the surface of rutile TiO II(110) the corresponding 2PPE transients revealed the relevant parameters that characterize the contributing processes. Instantaneous optical injection on one hand and slow injection over a long distance on the other hand were realized. Direct optical charge transfer was realized with the chromophore catechol that is known to form a charge transfer complex with Ti atoms on the surface of TiO II. The slow injection cases were realized by inserting rigid molecular bridges. Comparison of the different 2PPE signals with corresponding transient absorption (TA) signals for the identical systems revealed the physical processes and time scales that control the 2PPE transients. On the surface of the single crystals only one long time constant was measured via 2PPE also in the case of a long rigid bridge/anchor group in contrast to a broad distribution of time constants observed for the same molecules anchored in the nm-size cavities of an anatase TiO II film measured via TA. The broad distribution of time constants in the latter measurements can be attributed to different microscopic environments giving rise to different distances between the chromophore and the nearest TiO II wall.

  7. Photo-Induced Phase Transition in an Electron-Lattice Correlated System —Future Role of a Time-Resolved X-ray Measurement for Materials Science—

    NASA Astrophysics Data System (ADS)

    Koshihara, Shin-ya; Adachi, Shin-ichi

    2006-01-01

    The search for materials that show a phase transition triggered by weak external stimulation of light is an important and attractive target for photonic and materials science. We review experimental evidence indicating that photo-injected local excitation can really trigger an electron-lattice coupled cooperative phenomenon called photo-induced phase transition (PIPT). We discuss the dynamical nature of electron (spin)-lattice-coupled changes in π-conjugated polymer crystals, organic transition metal complexes, and organic A2B charge transfer complexes. We also review the development of ultra-fast X-ray technology in collaboration with work in the fields of quantum electronics and synchrotron radiation, which are essential for the promotion of the future study of PIPT.

  8. Applications of photoinduced electron transfer and hydrogen abstraction reactions to chemical and electrochemical conversion processes. Progress report, September 1, 1982-August 1, 1985

    SciTech Connect

    Whitten, D.G.

    1985-01-01

    The studies carried out have focused on photoinduced electron transfer and hydrogen atom abstraction processes. The main thrust over the past three years has been on a study of light induced electron transfer reactions and in particular on fates of the energy rich radical ions formed in electron transfer quenching of excited states. In particular we have studied these reactions under conditions - light absorbing substrates, quenchers, media - where net chemical conversion is favored over the usual back electron transfer to return to starting materials. The first part of the progress report focuses on our efforts to control reactivity by the use of specific substrates or quenchers which favor net chemical conversion. The second part describes our studies using reaction media - in this case amylose which preferentially complexes hydrophobic molecules in aqueous solution - to alter the rates of primary and secondary photophysical events associated with light induced electron transfer and other photoreactions. Our most extensive investigations of electron transfer reactions have involved the photoreduction of indigo dyes by electron donors. We have found that three representative indigo dyes, thioindigo, N,N'-diacetylindigo and oxalylindigo, all undergo photobleaching reactions with a variety of potential reductance ranging from alcohols to amines, such as triethylamine and N-benzyl-1, 4-dihydronicotinamide. 25 refs.

  9. Factoring the contribution of through-space and through-bond interactions to rates of photoinduced electron transfer in donor- spacer-acceptor molecules using ultrafast transient absorption spectroscopy

    SciTech Connect

    Gosztola, D.; Wang, Bing; Wasielewski, M.R. |

    1996-06-01

    Contributions from through-space and through-bond interactions to the electronic coupling matrix elements for photoinduced charge separation and recombination in linked donor-spacer-acceptor molecules were studied. The molecules consisted of a 4-piperidinyl-naphthalene-1,8-dicarboximide electron donor and a N-(n-octyl)pyromellitimide electron acceptor attached to the 1,5- and 1,8-positions of either anthracene or dibenzobicyclo(2.2.2)octatriene spacers.

  10. Thermodynamic control over the competitive anchoring of N719 dye on nanocrystalline TiO2 for improving photoinduced electron generation.

    PubMed

    Lim, Jongchul; Kwon, Young Soo; Park, Sung-Hae; Song, In Young; Choi, Jongmin; Park, Taiho

    2011-12-01

    TiO(2) electrodes, sensitized with the N719 dye at high immersion temperatures during the sensitization process, were found to have large fractions of weakly bound N719 on the electrode surface, which resulted in dye aggregation and decreased device longevity. These disadvantages were ameliorated using a low-temperature stearic acid (SA)-assisted anchoring method described here. The activation energy (ΔE(NS)(++)) and relative fraction of strongly bound N719 were twice as large as the respective values obtained without the use of SA. Slowing of adsorption, both by thermal means and through SA-mediated processes, effectively controlled the binding mode of N719 on the surface of TiO(2). The resulting sensitized electrodes displayed enhanced device longevity and improved generation of photoinduced electrons. PMID:21988282

  11. Ligand structure, conformational dynamics, and excited-state electron delocalization for control of photoinduced electron transfer rates in synthetic donor-bridge-acceptor systems.

    PubMed

    Meylemans, Heather A; Lei, Chi-Fong; Damrauer, Niels H

    2008-05-19

    Synthesis, ground-, and excited-state properties are reported for two new electron donor-bridge-acceptor (D-B-A) molecules and two new photophysical model complexes. The D-B-A molecules are [Ru(bpy)2(bpy-phi-MV)](PF6)4 (3) and [Ru(tmb)2(bpy-phi-MV)](PF6)4 (4), where bpy is 2,2'-bipyridine, tmb is 4,4',5,5'-tetramethyl-2,2'-bipyridine, MV is methyl viologen, and phi is a phenylene spacer. Their model complexes are [Ru(bpy)2(p-tol-bpy)](PF6)2 (1) and [Ru(tmb)2(p-tol-bpy)](PF6)2 (2), where p-tolyl-bpy is 4-(p-tolyl)-2,2'-bipyridine. Photophysical characterization of 1 and 2 indicates that 2.17 eV and 2.12 eV are stored in their respective (3)MLCT (metal-to-ligand charge transfer) excited state. These values along with electrochemical measurements show that photoinduced electron transfer (D*-B-A-->D (+)-B-A(-)) is favorable in 3 and 4 with DeltaG degrees(ET)=-0.52 eV and -0.62 eV, respectively. The driving force for the reverse process (D(+)-B-A(-) --> D-B-A) is also reported: DeltaG degrees(BET)=-1.7 eV for 3 and -1.5 eV for 4. Transient absorption (TA) spectra for 3 and 4 in 298 K acetonitrile provide evidence that reduced methyl viologen is observable at 50 ps following excitation. Detailed TA kinetics confirm this, and the data are fit to a model to determine both forward (k(ET)) and back (k(BET)) electron transfer rate constants: k(ET)=2.6 x 10(10) s(-1) for 3 and 2.8 x 10(10) s(-1) for 4; k(BET)=0.62 x 10(10) s(-1) for 3 and 1.37 x 10(10) s(-1) for 4. The similar rate constants k ET for 3 and 4 despite a 100 meV driving force (DeltaG degrees(ET)) increase suggests that forward electron transfer in these molecules in room temperature acetonitrile is nearly barrierless as predicted by the Marcus theory. The reduction in electron transfer reorganization energy necessary for this barrierless reactivity is attributed to excited-state electron delocalization in the (3)MLCT excited states of 3 and 4, an effect that is made possible by excited-state conformational

  12. Time Resolved EPR Study on the Photoinduced Long-Range Charge-Separated State in Protein: Electron Tunneling Mediated by Arginine Residue in Human Serum Albumin.

    PubMed

    Fuki, Masaaki; Murai, Hisao; Tachikawa, Takashi; Kobori, Yasuhiro

    2016-05-19

    To elucidate how local molecular conformations play a role on electronic couplings for the long-range photoinduced charge-separated (CS) states in protein systems, we have analyzed time-resolved electron paramagnetic resonance (TREPR) spectra by polarized laser irradiations of 9,10-anthraquinone-1-sulfonate (AQ1S(-)) bound to human serum albumin (HSA). Analyses of the magnetophotoselection effects on the EPR spectra and a docking simulation clarified the molecular geometry and the electronic coupling of the long-range CS states of AQ1S(•2-)-tryptophan214 radical cation (W214(•+)) separated by 1.2 nm. The ligand of AQ1S(-) has been demonstrated to be bound to the drug site I in HSA. Molecular conformations of the binding region were estimated by the docking simulations, indicating that an arginine218 (R218(+)) residue bound to AQ1S(•2-) mediates the long-range electron-transfer. The energetics of triad states of AQ1S(•2-)-R218(+)-W214(•+) and AQ1S(-)-R218(•)-W214(•+) have been computed on the basis of the density functional molecular orbital calculations, providing the clear evidence for the long-range electronic couplings of the CS states in terms of the superexchange tunneling model through the arginine residue. PMID:27116363

  13. Photoinduced hydrogen-bonding dynamics.

    PubMed

    Chu, Tian-Shu; Xu, Jinmei

    2016-09-01

    Hydrogen bonding dynamics has received extensive research attention in recent years due to the significant advances in femtolaser spectroscopy experiments and quantum chemistry calculations. Usually, photoexcitation would cause changes in the hydrogen bonding formed through the interaction between hydrogen donor and acceptor molecules on their ground electronic states, and such transient strengthening or weakening of hydrogen bonding could be crucial for the photophysical transformations and the subsequent photochemical reactions that occurred on a time scale from tens of femtosecond to a few nanoseconds. In this article, we review the combined experimental and theoretical studies focusing on the ultrafast electronic and vibrational hydrogen bonding dynamics. Through these studies, new mechanisms and proposals and common rules have been put forward to advance our understanding of the hydrogen bondings dynamics in a variety of important photoinduced phenomena like photosynthesis, dual fluorescence emission, rotational reorientation, excited-state proton transfer and charge transfer processes, chemosensor fluorescence sensing, rearrangements of the hydrogen-bond network including forming and breaking hydrogen bond in water. Graphical Abstract We review the recent advances on exploring the photoinduced hydrogen bonding dynamics in solutions through a joint approach of laser spectroscopy and theoretical calculation. The reviewed studies have put forward a new mechanism, new proposal, and new rule for a variety of photoinduced phenomena such as photosynthesis, dual fluorescence emission, rotational reorientation, excited-state proton transfer and charge transfer, chemosensor fluorescence sensing, and rearrangements of the hydrogen-bond network in water. PMID:27491849

  14. Influences of acid on molecular forms of fluorescein and photoinduced electron transfer in fluorescein-dispersing sol-gel titania films.

    PubMed

    Nishikiori, Hiromasa; Setiawan, Rudi Agus; Miyashita, Kyohei; Teshima, Katsuya; Fujii, Tsuneo

    2014-01-01

    Fluorescein-dispersing titania gel films were prepared by the acid-catalyzed sol-gel reaction using a titanium alkoxide solution containing fluorescein. The molecular forms of fluorescein in the films, depending on its acid-base equilibria, and the complex formation and photoinduced electron transfer process between the dye and titania surface were investigated by fluorescence and photoelectric measurements. The titanium species were coordinated to the carboxylate and phenolate-like groups of the fluorescein species. The quantum efficiencies of the fluorescence quenching and photoelectric conversion were higher upon excitation of the dianion species interacting with the titania, i.e. the dye-titania complex. This result indicated that the dianion form was the most favorable for formation of the dye-titania complex exhibiting the highest electron transfer efficiency. Using nitric acid as the catalyst, the titania surface bonded to the fluorescein instead of the adsorbed nitrate ion during the steam treatment. The dye-titania complex formation played an important role in the electron injection from the dye to the titania conduction band. PMID:24502447

  15. 10-methylacridine derivatives acting as efficient and stable photocatalysts in reductive dehalogenation of halogenated compounds with sodium borohydride via photoinduced electron transfer

    SciTech Connect

    Ishikawa, Masashi; Fukuzumi, Shunichi )

    1990-11-21

    10-Methylacridine derivatives, 9,10-dihydro-10-methylacridine (AcrH{sub 2}) and acriflavine (AFH{sup +}), act as efficient and stable photocatalysts in reductive dechlorination of p-chlorobiphenyl (ClBP) as well as dehalogenation of other halogenated compounds with sodium borohydride (NaBH{sub 4}) in a mixture of acetonitrile and H{sub 2}O (9:1 v/v) at 298 K. The reductive dechlorination proceeds via the reduction of ClBP by the singlet excited state ({sup 1}AcrH{sub 2}*) to yield dechlorinated product (biphenyl) and 10-methylacridinium ion (AcrH{sup +}), followed by the facile reduction of AcrH{sup +} with NaBH{sub 4} to regenerate AcrH{sub 2}. The absence of the primary kinetic isotope effect as well as the comparison of the observed rate constants with those predicted by using the Marcus theory of electron transfer indicates that the reduction of halogenated compounds (RX) by the singlet excited state ({sup 1}AcrH{sub 2}*) proceeds via photoinduced electron transfer from {sup 1}AcrH{sub 2}* to RX, which results in the cleavage of C-X bonds.

  16. Sensitive fast electron spectrometer in adjustable triode configuration with pulsed tunable laser for research on photo-induced field emission cathodes

    SciTech Connect

    Mingels, S. Porshyn, V.; Bornmann, B.; Lützenkirchen-Hecht, D.; Müller, G.

    2015-04-15

    We have completed an ultra-high vacuum system for sensitive fast electron spectroscopy from cold cathodes in triode configuration under high electric fields E (<100 MV/m) and pulsed tunable laser illumination (3.5 ns, 10 Hz, hν = 0.5-5.9 eV, and 0.3-17 mJ). The cathodes are prepared and inserted under clean room conditions and can be precisely 3D-positioned, cooled or heated (77-400 K). Commissioning results with the upgraded system are presented. Field emission measurements with a W tip yielded an energy resolution of 14 meV at 4 eV pass energy and a precise determination of the emitter work function, size, and temperature. Photoemission spectroscopy of short electron bunches from a virgin and laser-ablated S-GaP crystal and quantum efficiency measurements revealed surface states, energy relaxation, and band structure effects. In conclusion, this novel system is ready now for the development and characterization of photo-induced field emission cathodes.

  17. Studies of Photoinduced Electron Transfer (PET) and Energy Migration in a Conjugated Polymer System for Fluorescence “Turn-on” Chemosensor Applications

    PubMed Central

    Fan, Li-Juan; Jones, Wayne E.

    2008-01-01

    A series of poly [p-(phenyleneethynylene)-alt-(thienyleneethynylene)] (PPETE) polymers with variable percent loadings of the N, N, N’-trimethylethylenediamino group on the polymer backbone were synthesized and fully characterized. Photophysical studies show that changes in the loading of the amino group receptor on the backbone do not affect the polymer electronic structure in either the ground or excited states. The fluorescence quantum yields were found to be directly related to the loading of the amino groups and can be modeled by a Stern-Volmer type relationship. Photophysical studies related the total quenching efficiency to the inherent rate of photoinduced electron transfer (PET), the lifetime of the exciton, the rate of excitation energy migration along the polymer backbone and the total loading of the receptor on the polymer. The role of the loading dependence on the application of these polymers as fluorescence “turn-on” sensors for toxic metal cations in dilute solution was also studied. Results showed that the fluorescence enhancement upon binding various cations was maintained even when the amino receptor loading along the polymer backbone was reduced. PMID:16610873

  18. Photoinduced reactions of both 2-formyl-2H-azirine and isoxazole: A theoretical study based on electronic structure calculations and nonadiabatic dynamics simulations.

    PubMed

    Cao, Jun

    2015-06-28

    In the present work, the combined electronic structure calculations and dynamics simulations have been performed to explore photocleavages of 2-formyl-2H-azirine and isoxazole in the gas phase and the subsequent rearrangement reactions. The carbonyl n → π(*) transition induces a cleavage of the C-N single bond of 2-formyl-2H-azirine to yield β-formylvinylnitrene in open-shell singlet state. However, the n → π(*) excitation of the imine chromophore results in a cleavage of the C-C single bond, producing a nitrile ylide intermediate through an internal conversion to the ground state. β-formylvinylnitrene and nitrile ylide with the carbonyl group are easily transformed into 2-formyl-2H-azirine and oxazole, respectively. The N-O bond cleavages on both S1((1)ππ(*)) and S2((1)nNπ(*)) of isoxazole are ultrafast processes, and they give products of 2-formyl-2H-azirine, 3-formylketenimine, HCN + CHCHO, and HCO + CHCHN. Both 2H-azirines and ketenimines were suggested to be formed from the triplet vinylnitrenes by intersystem crossing in the previous studies. However, our calculations show that the singlet β-formylvinylnitrene is responsible for the formation of 2-formyl-2H-azirine and 3-formylketenimine, and the singlet vinylnitrenes can play a key role in the photoinduced reactions of both 2H-azirines and isoxazoles. PMID:26133423

  19. Photoinduced reactions of both 2-formyl-2H-azirine and isoxazole: A theoretical study based on electronic structure calculations and nonadiabatic dynamics simulations

    SciTech Connect

    Cao, Jun

    2015-06-28

    In the present work, the combined electronic structure calculations and dynamics simulations have been performed to explore photocleavages of 2-formyl-2H-azirine and isoxazole in the gas phase and the subsequent rearrangement reactions. The carbonyl n → π{sup *} transition induces a cleavage of the C—N single bond of 2-formyl-2H-azirine to yield β-formylvinylnitrene in open-shell singlet state. However, the n → π{sup *} excitation of the imine chromophore results in a cleavage of the C—C single bond, producing a nitrile ylide intermediate through an internal conversion to the ground state. β-formylvinylnitrene and nitrile ylide with the carbonyl group are easily transformed into 2-formyl-2H-azirine and oxazole, respectively. The N—O bond cleavages on both S{sub 1}({sup 1}ππ{sup *}) and S{sub 2}({sup 1}n{sub N}π{sup *}) of isoxazole are ultrafast processes, and they give products of 2-formyl-2H-azirine, 3-formylketenimine, HCN + CHCHO, and HCO + CHCHN. Both 2H-azirines and ketenimines were suggested to be formed from the triplet vinylnitrenes by intersystem crossing in the previous studies. However, our calculations show that the singlet β-formylvinylnitrene is responsible for the formation of 2-formyl-2H-azirine and 3-formylketenimine, and the singlet vinylnitrenes can play a key role in the photoinduced reactions of both 2H-azirines and isoxazoles.

  20. Mixed Quantum-Classical Simulations of Transient Absorption Pump-Probe Signals for a Photo-Induced Electron Transfer Reaction Coupled to an Inner-Sphere Vibrational Mode.

    PubMed

    Martinez, Franz; Hanna, Gabriel

    2016-05-19

    In a previous study (Martinez, F.; Hanna, G. Chem. Phys. Lett. 2013, 573, 77-83), we demonstrated the ability of two approximate solutions of the quantum-classical Liouville equation (QCLE) for qualitatively capturing the electronic dynamics in the pump-probe transient absorption (TA) signal of a model of a condensed phase photoinduced electron transfer reaction whose ground and excited donor states have the same equilibrium geometry. However, the question remained as to the ability of these solutions to treat the more complex situation in which the electronic states are coupled to a low-frequency inner-sphere harmonic vibrational mode (representing an intramolecular mode of the donor-acceptor complex) that shifts their equilibrium geometries with respect to each other and thereby gives rise to signatures of vibrational dynamics in the TA signal. Thus, in this study, we investigated this situation by treating the vibrational mode both quantum mechanically and classically within the context of the approximate Poisson bracket mapping equation (PBME) and forward-backward trajectory solutions (FBTS) of the QCLE. Depending on the definition of the quantum subsystem, both PBME and FBTS are capable of qualitatively capturing several of the main features in the exact TA signal and quantitatively capturing the characteristic time scale of the vibrational dynamics, despite the moderately strong subsystem-bath coupling in this model. Particularly, we found that treating the vibrational mode quantum mechanically using either PBME or FBTS better captures the signatures of the vibrational dynamics, while treating it classically using FBTS better captures the decay in the signal. These findings underscore the utility of the PBME and FBTS approaches for efficiently modeling and interpreting TA signals. PMID:26766568

  1. Photoinduced tellurium precipitation in CdTe

    NASA Astrophysics Data System (ADS)

    Sugai, Shunji

    1991-06-01

    Tellurium precipitation in CdTe is found to be induced by photoirradiation with energy higher than the energy gap at 240 W/sq cm. It is suggested that this photoinduced precipitation is related with the strong electron-phonon interactions, possibly self-trapped excitons. This irreducible tellurium precipitation may cause a serious problem for the life of semiconductor devices.

  2. Polydopamine-embedded Cu(2-x)Se nanoparticles as a sensitive biosensing platform through the coupling of nanometal surface energy transfer and photo-induced electron transfer.

    PubMed

    Zou, Hong Yan; Gao, Peng Fei; Gao, Ming Xuan; Huang, Cheng Zhi

    2015-06-21

    Full understanding and easy construction of specific biosensing principles is necessary for disease diagnostics and therapeutics in the hope of creating new types of biosensors. Herein, we developed a new conceptual nanobiosensing platform by coupling nanometal surface energy transfer (NSET) and photo-induced electron transfer (PET) with polydopamine-embedded Cu(2-x)Se nanoparticles (Cu(2-x)SeNPs@pDA) and DNA-conjugated fluorescent organic dyes. The new prepared Cu(2-x)SeNPs@pDA has intense and broad localized surface plasmon resonance (LSPR) absorption over UV to near infrared (NIR) wavelengths, with different affinities toward ssDNA versus dsDNA. It also exhibits a high multiplexed fluorescence quenching ability, and thus can act as an acceptor in the energy transfer and electron transfer interactions between Cu(2-x)SeNPs@pDA and fluorescent organic dyes. As a proof of concept, a new biosensing platform has been successfully developed to target biomacromolecules such as DNA and proteins, in which the NSET and PET interactions between Cu(2-x)SeNPs@pDA and three different DNA-conjugated fluorescent dyes have been identified using steady-state and time-resolved fluorescence. A simple mathematical model was further applied to simulate the respective contributions of the coexisting NSET and PET to the total quenching observed for each DNA-conjugated dye in this sensing system. This study highlights the importance of understanding the mechanistic details of NSET and PET coupling processes, and the disclosed coupling mechanism of NSET and PET (NSET©PET) in the systems of Cu(2-x)SeNPs@pDA with wide wavelength range dyes provides new opportunities for sensitive biosensing applications. PMID:25899757

  3. Photoinduced electron transfer (PET) based label-free aptasensor for platelet-derived growth factor-BB and its logic gate application.

    PubMed

    Wang, Guangfeng; Zhu, Yanhong; Chen, Ling; Zhang, Xiaojun

    2015-01-15

    Platelet-derived growth factor-BB (PDGF-BB) is often overexpressed in human malignant tumors as an indicator for tumor angiogenesis. Here by the photoinduced electron transfer (PET) between DNA-Ag fluorescent nanoclusters (NCs) and G-quadruplex/hemin complexes, we present a sensitive label-free fluorescent sensor for PDGF-BB. In the presence of PDGF-BB, the specific conjugation with its aptamer induced the conformational change of the duplex-like DNA sequence, releasing the G-quadruplex sequence part. Then in the presence of hemin and K(+), the horseradish peroxidase mimicking DNAzyme (HRP-DNAzyme) was formed. With the electron transfer between the DNA-Ag NCs to the hemin Fe (III) center of HRP-DNAzyme, the PET occurred with a decrease in the fluorescence intensity of the DNA-Ag NCs. The detection performance such as selectivity, linear dynamic range, sensitivity, and the quenching capability of HRP-DNAzyme were estimated. The detection range for PDGF-BB is from 5×10(-13) to 1×10(-8) M and the detection limit is 1×10(-13) M. The experimental results confirmed that the novel fluorescent aptasensor possessed a good sensitivity and high selectivity for PDGF-BB. In addition, the developed probe is nontoxic, label-free only involving one-step hybridization without sophisticated fabrication process. Furthermore, based on this quenching mode occurred by PDGF-BB and hemin, using PDGF-BB and hemin as inputs and the fluorescence signal as an output, a logic gate has been fabricated. PMID:25150781

  4. Photo-induced electron transfer between dendritic zinc(II) phthalocyanine bearing carboxylic terminal groups and methyl viologen

    NASA Astrophysics Data System (ADS)

    Wang, Yuhua; Chen, Jiangxu; Huang, Lishan; Xie, Shusen; Yang, Hongqin; Peng, Yiru

    2012-12-01

    The intermolecular electron transfer between carboxylic dendritic zinc(II) phthalocyanine bearing carboxylic terminal groups(G1-ZnPc(COOH)8) and methyl viologens (MV2+) was studied by steady-state fluorescence and UV/Vis spectroscopy. The effect of different concentrations of MV2+ on intermolecular electron transfer was investigated. The results show that the fluorescence emission of this dendritic phthalocyanine could be greatly quenched with an increasing amount of MV2+ upon excitation at 610 nm. Our study suggests that this novel dendritic phthalocyanine is an effective new electron donor and transmission complex and could be used as a potential biosensor conjugated with suitable fluorescence quencher.

  5. Microwave-enhanced photocatalysis on CdS quantum dots - Evidence of acceleration of photoinduced electron transfer

    PubMed Central

    Kishimoto, Fuminao; Imai, Takashi; Fujii, Satoshi; Mochizuki, Dai; Maitani, Masato M.; Suzuki, Eiichi; Wada, Yuji

    2015-01-01

    The rate of electron transfer is critical in determining the efficiency of photoenergy conversion systems and is controlled by changing the relative energy gap of components, their geometries, or surroundings. However, the rate of electron transfer has not been controlled by the remote input of an external field without changing the geometries or materials of the systems. We demonstrate here that an applied microwave field can enhance the photocatalytic reduction of bipyridinium ion using CdS quantum dots (QDs) by accelerating electron transfer. Analysis of the time-resolved emission decay profiles of CdS quantum dots immersed in aqueous solutions of bipyridinium exhibited the shortening of their emission lifetimes, because of the accelerated electron transfer from QDs to bipyridinium under microwave irradiation. This discovery leads us to a new methodology using microwaves as an external field to enhance photocatalytic reactions. PMID:26080653

  6. Interference of electron pairs in photoinduced N4,5 - O1O2,3 Auger decay in xenon

    NASA Astrophysics Data System (ADS)

    Žitnik, M.; Bučar, K.; Lablanquie, P.; Penent, F.; Palaudoux, J.; Andric, L.; Hikosaka, Y.; Ito, K.

    2012-11-01

    We observed an interference originating from coincidence detection of two indistinguishable electron pairs emitted upon photoionization of 4d electron in Xe. At 89.9 eV photon impact the energy of photoelectron ejected from 4d5/2 orbital equals energy of Auger electron emitted in decay of 4d3/2 hole into the [5s5p1P] state, and for the same final state the energy of the 4d3/2 photoelectron equals the Auger electron energy in decay of 4d5/2 hole. An angle-integrated coincidence yield as a function of photon energy is measured with the magnetic bottle time-of-flight spectrometer and shows a peak at the expected energy position.

  7. Synthesis, Characterization and Photoinduced Electron Transfer in a Supramolecular Tetrakis(ruthenium (II) phthalocyanine)-perylenediimide Pentad

    SciTech Connect

    Jiménez, Angel J.; Grimm, Bruno; Gunderson, Victoria; Vagnini, Michael T.; Calderon, Sandra K.; Rodríguez-Morgade, M. S.; Wasielewski, Michael R.; Guldi, Dirk M.; Torres, Tomas

    2011-03-22

    Metal coordination was probed as a versatile approach for designing a novel electron donor/acceptor hybrid [PDIpy4{Ru(CO)Pc}4] (1), in which four pyridines placed at the bay region of a perylenediimides (PDIpy4) coordinate with four ruthenium phthalocyanine units [Ru(CO)Pc]. This structural motif was expected to promote strong electronic coupling between the electron donors and the electron acceptor, a hypothesis that was confirmed in a full-fledged physicochemical investigation focusing on the ground and excited state reactivities. As far as the ground state is concerned, absorption and electrochemical assays indeed reveal a notable redistribution of electron density, that is, from the electron-donating [Ru(CO)Pc] to the electron-accepting PDIpy4. The most important thing to note in this context is that both the [Ru(CO)Pc] oxidation and the PDIpy4 reduction are rendered more difficult in 1 than in the individual building blocks. Likewise, in the excited state, strong electronic communication is the inception for a rapid charge-transfer process in photoexcited 1. Regardless of exciting [Ru(CO)Pc] or PDIpy4, spectral characteristics of the [RuPc] radical cation (broad absorptive features from 425 to 600 nm with a maximum at 575 nm, as well as a band centered at 725 nm) and of the PDI radical anion (780 nm maximum) emerge. The correspondingly formed radical ion pair state lasts for up to several hundred picoseconds in toluene, for example. On the other hand, employing more polar solvents, such as dichloromethane, destabilizes the radical ion pair state.

  8. Photoinduced electron-transfer reactions of poly(pyridine)ruthenium(II) complexes with europium(III/II) cryptates

    SciTech Connect

    Sabbatini, N.; Dellonte, S.; Bonazzi, A.; Ciano, M.; Balzani, V.

    1986-05-21

    Rate constants for electron-transfer reactions between poly(pyridine)ruthenium(II) (RuL/sub 3//sup 2 +/) excited states and the europium cryptates (Eu contains 2.2.1)/sup 3 +/ and (Eu contains 2.2.1)/sup 2 +/ have been measured in aqueous solution by luminescence quenching techniques. The rate constants for a few electron-transfer back-reactions between the photogenerated RuL/sub 3//sup 3 +/ and (Eu contains 2.2.1)/sup 2 +/ or RuL/sub 3//sup +/ and (Eu contains 2.2.1)/sup 3 +/ species have also been measured by flash photolysis experiments. The results obtained have been elaborated and discussed on the basis of current electron-transfer theories. Comparison of the results obtained with those previously available for the Eu/sub aq//sup 3 +/ and Eu/sub aq//sup 2 +/ ions shows that cryptation decreases the intrinsic barrier and/or increases the adiabaticity coefficient of the electron-transfer reaction. A plot of the rate constants vs. the free energy changes of the electron-transfer processes shows that the data concerning (Eu contains 2.2.1)/sup 3 +/ reduction do not correlate with those concerning (Eu contains 2.2.1)/sup 2 +/ oxidation. Possible reasons for this asymmetric behavior include (i) different shapes of the potential energy wells for (Eu contains 2.2.1)/sup 3 +/ and (Eu contains 2.2.1)/sup 2 +/, (ii) different work terms for the formation of the precursor complex, and (iii) different distances of closest approach of (Eu contains 2.2.1)/sup 3 +/ and (Eu contains 2.2.1)/sup 2 +/ with the hydrophobic RuL/sub 3//sup n+/ reaction partners.

  9. Controlling photoinduced electron transfer from PbS@CdS core@shell quantum dots to metal oxide nanostructured thin films

    NASA Astrophysics Data System (ADS)

    Zhao, H.; Fan, Z.; Liang, H.; Selopal, G. S.; Gonfa, B. A.; Jin, L.; Soudi, A.; Cui, D.; Enrichi, F.; Natile, M. M.; Concina, I.; Ma, D.; Govorov, A. O.; Rosei, F.; Vomiero, A.

    2014-05-01

    N-type metal oxide solar cells sensitized by infrared absorbing PbS quantum dots (QDs) represent a promising alternative to traditional photovoltaic devices. However, colloidal PbS QDs capped with pure organic ligand shells suffer from surface oxidation that affects the long term stability of the cells. Application of a passivating CdS shell guarantees the increased long term stability of PbS QDs, but can negatively affect photoinduced charge transfer from the QD to the oxide and the resulting photoconversion efficiency (PCE). For this reason, the characterization of electron injection rates in these systems is very important, yet has never been reported. Here we investigate the photoelectron transfer rate from PbS@CdS core@shell QDs to wide bandgap semiconducting mesoporous films using photoluminescence (PL) lifetime spectroscopy. The different electron affinity of the oxides (SiO2, TiO2 and SnO2), the core size and the shell thickness allow us to fine tune the electron injection rate by determining the width and height of the energy barrier for tunneling from the core to the oxide. Theoretical modeling using the semi-classical approximation provides an estimate for the escape time of an electron from the QD 1S state, in good agreement with experiments. The results demonstrate the possibility of obtaining fast charge injection in near infrared (NIR) QDs stabilized by an external shell (injection rates in the range of 110-250 ns for TiO2 films and in the range of 100-170 ns for SnO2 films for PbS cores with diameters in the 3-4.2 nm range and shell thickness around 0.3 nm), with the aim of providing viable solutions to the stability issues typical of NIR QDs capped with pure organic ligand shells.N-type metal oxide solar cells sensitized by infrared absorbing PbS quantum dots (QDs) represent a promising alternative to traditional photovoltaic devices. However, colloidal PbS QDs capped with pure organic ligand shells suffer from surface oxidation that affects the

  10. Dimensionality of nanoscale TiO2 determines the mechanism of photoinduced electron injection from a CdSe nanoparticle

    DOE PAGESBeta

    Tafen, De Nyago; Long, Run; Prezhdo, Oleg V.

    2014-03-10

    Assumptions about electron transfer (ET) mechanisms guide design of catalytic, photovoltaic, and electronic systems. We demonstrate that the mechanism of ET from a CdSe quantum dot (QD) into nanoscale TiO2 depends on TiO2 dimensionality. The injection into a TiO2 QD is adiabatic due to strong donor–acceptor coupling, arising from unsaturated chemical bonds on the QD surface, and low density of acceptor states. In contrast, the injection into a TiO2 nanobelt (NB) is nonadiabatic, because the state density is high, the donor–acceptor coupling is weak, and multiple phonons accommodate changes in the electronic energy. The CdSe adsorbant breaks symmetry of delocalizedmore » TiO2 NB states, relaxing coupling selection rules, and generating more ET channels. Both mechanisms can give efficient ultrafast injection. Furthermore, the dependence on system properties is very different for the two mechanisms, demonstrating that the fundamental principles leading to efficient charge separation depend strongly on the type of nanoscale material.« less

  11. 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

  12. Photoinduced electron transfer from quantum dots to TiO2: elucidating the involvement of excitonic and surface states.

    PubMed

    Chauhan, Saurabh; Watson, David F

    2016-07-27

    Colloidal semiconductor quantum dots (QDs) exhibit excitonic and surface states, both of which may participate in charge-transfer processes relevant to solar energy conversion. To explore this inherent complexity of the charge-transfer mechanisms of QDs, we used steady-state and time-resolved emission measurements to characterize excited-state electron transfer (ET) from core-only CdSe QDs and core/shell CdSe/ZnS QDs to TiO2 nanoparticles (NPs). Core-only QDs transferred electrons from both excitonic and surface states to TiO2 with rate constants of ET (ket) of approximately (1-3) × 10(8) s(-1) and (4-7) × 10(7) s(-1), respectively. Efficiencies of ET (ηet) from excitonic and surface states were approximately 71-82% and 64-76%, respectively. Thus, trapping of electrons lowered their potential energy but did not greatly affect the efficiency of their transfer to TiO2. Photogenerated holes were transferred from core-only CdSe QDs to adsorbed 3-mercaptopropionic acid (MPA), which linked the QDs to TiO2. We characterized core/shell CdSe/ZnS QDs as alternatives to core-only QDs. The ZnS shell eliminated the undesirable trapping of electrons and transfer of photogenerated holes to MPA. We measured ket of approximately (1-3) × 10(8) s(-1) and ηet of approximately 66-85% for ET from excitonic states of core/shell CdSe/ZnS QDs to TiO2 NPs. The insensitivity of ket to the presence of the ZnS shell may have arisen from increased cross-linking of core/shell QDs to TiO2. Our results highlight the involvement of surface states in excited-state ET processes of core-only QDs and, for the heterostructures reported here, the improved performance of core/shell CdSe/ZnS QDs relative to core-only CdSe QDs. PMID:27401207

  13. Photoinduced electron transfer through peptide-based self-assembled monolayers chemisorbed on gold electrodes: directing the flow-in and flow-out of electrons through peptide helices.

    PubMed

    Venanzi, Mariano; Gatto, Emanuela; Caruso, Mario; Porchetta, Alessandro; Formaggio, Fernando; Toniolo, Claudio

    2014-08-21

    Photoinduced electron transfer (PET) experiments have been carried out on peptide self-assembled monolayers (SAM) chemisorbed on a gold substrate. The oligopeptide building block was exclusively formed by C(α)-tetrasubstituted α-aminoisobutyric residues to attain a helical conformation despite the shortness of the peptide chain. Furthermore, it was functionalized at the C-terminus by a pyrene choromophore to enhance the UV photon capture cross-section of the compound and by a lipoic group at the N-terminus for linking to gold substrates. Electron transfer across the peptide SAM has been studied by photocurrent generation experiments in an electrochemical cell employing a gold substrate modified by chemisorption of a peptide SAM as a working electrode and by steady-state and time-resolved fluorescence experiments in solution and on a gold-coated glass. The results show that the electronic flow through the peptide bridge is strongly asymmetric; i.e., PET from the C-terminus to gold is highly favored with respect to PET in the opposite direction. This effect arises from the polarity of the Au-S linkage (Au(δ+)-S(δ-), junction effect) and from the electrostatic field generated by the peptide helix. PMID:24901672

  14. A novel photoinduced electron transfer (PET) primer technique for rapid real-time PCR detection of Cryptosporidium spp

    SciTech Connect

    Jothikumar, N. Hill, Vincent R.

    2013-06-28

    Highlights: •Uses a single-labeled fluorescent primer for real-time PCR. •The detection sensitivity of PET PCR was comparable to TaqMan PCR. •Melt curve analysis can be performed to confirm target amplicon production. •Conventional PCR primers can be converted to PET PCR primers. -- Abstract: We report the development of a fluorescently labeled oligonucleotide primer that can be used to monitor real-time PCR. The primer has two parts, the 3′-end of the primer is complimentary to the target and a universal 17-mer stem loop at the 5′-end forms a hairpin structure. A fluorescent dye is attached to 5′-end of either the forward or reverse primer. The presence of guanosine residues at the first and second position of the 3′ dangling end effectively quenches the fluorescence due to the photo electron transfer (PET) mechanism. During the synthesis of nucleic acid, the hairpin structure is linearized and the fluorescence of the incorporated primer increases several-fold due to release of the fluorescently labeled tail and the absence of guanosine quenching. As amplicons are synthesized during nucleic acid amplification, the fluorescence increase in the reaction mixture can be measured with commercially available real-time PCR instruments. In addition, a melting procedure can be performed to denature the double-stranded amplicons, thereby generating fluorescence peaks that can differentiate primer dimers and other non-specific amplicons if formed during the reaction. We demonstrated the application of PET-PCR for the rapid detection and quantification of Cryptosporidium parvum DNA. Comparison with a previously published TaqMan® assay demonstrated that the two real-time PCR assays exhibited similar sensitivity for a dynamic range of detection of 6000–0.6 oocysts per reaction. PET PCR primers are simple to design and less-expensive than dual-labeled probe PCR methods, and should be of interest for use by laboratories operating in resource

  15. Photoinduced Anomalous Hall Effects in Weyl Semimetals

    NASA Astrophysics Data System (ADS)

    Chan, Ching-Kit; Lee, Patrick A.; Burch, Kenneth S.; Han, Jung Hoon; Ran, Ying

    We examine theoretically the interplay between chiral photons and chiral electrons in Weyl semimetals. Owing to its monopole nature, a three-dimensional Weyl node is topologically-robust against a circularly polarized light. A driven Weyl system exhibits node shifts in the momentum space, in sharp contrast to the gap opening in a driven two-dimensional Dirac system. We show that the node shift leads to a change of the Chern vector which gives arise to a net photoinduced anomalous Hall conductivity, in the plane perpendicular to the light propagation. We shall describe the basic idea behind this generic photoinduced Hall effect, illustrate it with a concrete microscope model, and estimate its feasibility based on current optical experimental techniques.

  16. A new signal-on method for the detection of protein based on binding-induced strategy and photoinduced electron transfer between Ag nanoclusters and split G-quadruplex-hemin complexes.

    PubMed

    Zhang, Kai; Wang, Ke; Zhu, Xue; Xie, Minhao

    2015-08-01

    Proteins play important roles in biological and cellular processes. The levels of proteins can be useful biomarkers for cellular events or disease diagnosis, thus the method for sensitive and selective detection of proteins is imperative to proteins express, study, and clinical diagnosis. Herein, we report a "signal-on" platform for the assay of protein based on binding-induced strategy and photoinduced electron transfer between Ag nanoclusters and split G-quadruplex-hemin complexes. By using biotin as the affinity ligand, this simple protocol could sensitively detect streptavidin with a detection limit down to 10 pM. With the use of an antibody as the affinity ligand, a method for homogeneous fluorescence detection of Prostate Specific Antigen (PSA) was also proposed with a detection limit of 10 pM. The one-step and wash-free assay showed good selectivity. Its high sensitivity, acceptable accuracy, and satisfactory versatility of analytes led to various applications in bioanalysis. PMID:26320806

  17. Manipulating photoinduced voltage in metasurface with circularly polarized light.

    PubMed

    Bai, Qiang

    2015-02-23

    Recently, the concept of metasurface has provided one an unprecedented opportunity and ability to control the light in the deep subwavelength scale. However, so far most efforts are devoted to exploiting the novel scattering properties and applications of metasurface in optics. Here, I theoretically and numerically demonstrate that longitudinal and transverse photoinduced voltages can be simultaneously realized in the proposed metasurface utilizing the magnetic resonance under the normal incidence of circularly polarized light, which may extend the concept and functionality of metasurface into the electronics and may provide a potential scheme to realize a nanoscale tunable voltage source through a nanophotonic roadmap. The signs of longitudinal and transverse photoin-duced voltages can be manipulated by tuning the resonant frequency and the handedness of circularly polarized light, respectively. Analytical formulae of photoinduced voltage are presented based on the theory of symmetry of field. This work may bridge nanophotonics and electronics, expands the capability of metasurface and has many potential applications. PMID:25836566

  18. Characterization of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Emim][Tf2N])∕TX-100∕cyclohexane ternary microemulsion: investigation of photoinduced electron transfer in this RTIL containing microemulsion.

    PubMed

    Sarkar, Souravi; Pramanik, Rajib; Ghatak, Chiranjib; Rao, Vishal Govind; Sarkar, Nilmoni

    2011-02-21

    In this study we have characterized a ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethyl- sulfonyl)imide containing ternary nonaqueous microemulsion ([Emim][Tf(2)N]∕∕TX-100∕cyclo- hexane). The phase behavior and dynamic light scattering study show that the [Emim][Tf(2)N]∕TX-100∕cyclohexane three component system can form microemulsion with [Emim][Tf(2)N] as polar core at suitable condition. We have investigated photoinduced electron transfer (PET) using dimethyl aniline as electron donor and several Coumarin dyes as electron acceptor molecules at two different R values (R = [ionic liquid]∕[surfactant]) to observe how the dynamics of the PET rate is affected in this type of confined microenvironment compared to that of the PET dynamics in neat ionic liquid and other pure solvent media. The plot of observed k(q) values with the free energy change (ΔG(0)) for electron transfer reaction shows an apparent inversion in the observed rate as predicted by the Marcus theory. PMID:21341859

  19. Characterization of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Emim][Tf2N])/TX-100/cyclohexane ternary microemulsion: Investigation of photoinduced electron transfer in this RTIL containing microemulsion

    NASA Astrophysics Data System (ADS)

    Sarkar, Souravi; Pramanik, Rajib; Ghatak, Chiranjib; Rao, Vishal Govind; Sarkar, Nilmoni

    2011-02-01

    In this study we have characterized a ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethyl- sulfonyl)imide containing ternary nonaqueous microemulsion ([Emim][Tf2N]//TX-100/cyclo- hexane). The phase behavior and dynamic light scattering study show that the [Emim][Tf2N]/TX-100/cyclohexane three component system can form microemulsion with [Emim][Tf2N] as polar core at suitable condition. We have investigated photoinduced electron transfer (PET) using dimethyl aniline as electron donor and several Coumarin dyes as electron acceptor molecules at two different R values (R = [ionic liquid]/[surfactant]) to observe how the dynamics of the PET rate is affected in this type of confined microenvironment compared to that of the PET dynamics in neat ionic liquid and other pure solvent media. The plot of observed kq values with the free energy change (ΔG0) for electron transfer reaction shows an apparent inversion in the observed rate as predicted by the Marcus theory.

  20. Photoinduced charge separation by polymer-bound chromophores

    SciTech Connect

    Rodgers, M.A.J.

    1991-09-01

    This project has examined the photodynamic behavior of water-soluble polymers that have covalently linked hydrophobic chromophores spaced along the chains. These polymeric systems have been examined for photoinduced charge separation with electron-accepting ions having different total charge. Focus has been on the excited singlet (S{sub 1}) state formed by laser flash absorption. The effects of pH and ionic strength -- factors that govern the conformational nature of the polymer in solution -- have been studied. A second major effort has been to study photoinduced redox processes involving excited states of water-soluble variants of anthracene and acridine. 27 refs., 16 figs., 2 tabs.

  1. Effect of humidity and temperature on photoinduced reactions in cellulose

    NASA Astrophysics Data System (ADS)

    Murtagh, James; Thomas, J. Kerry

    1988-07-01

    Pulsed laser studies and phosphorimetry have been used to investigate the reaction of O 2 and methyl viologen with the triplet excited state of tetramethylbenzidene in cellophane. Small amounts of water markedly affect the photoinduced reactions. In the case of methyl viologen, electron transfer via tunnelling is observed to give reduced methyl viologen.

  2. Photo-induced electron transfer in a diamino-substituted Ru(bpy)3[PF6]2 complex and its application as a triplet photosensitizer for nitric oxide (NO)-activated triplet-triplet annihilation upconversion.

    PubMed

    Xu, Kejing; Zhao, Jianzhang; Moore, Evan G

    2016-08-01

    A system demonstrating Nitric Oxide (NO) activated Triplet-Triplet Annihilation (TTA) upconversion has been devised, based on a substituted [Ru(II)(bpy)3](PF6)2 complex (bpy = 2,2'-dipyridine) bearing a single 1,2-diaminophenyl moiety as an NO activatable triplet photosensitizer (Ru-1), and 9,10-diphenylanthracene (DPA) as a triplet acceptor/emitter. The excited triplet state of Ru-1 is significantly quenched (ΦT∼ 22%) by a Photoinduced Electron Transfer (PET) reaction, as confirmed by steady state phosphorescence and transient absorption spectroscopy, and hence Ru-1 does not function as a TTA upconversion sensitizer. However, in the presence of NO/O2, the 1,2-diaminophenyl group of Ru-1 is transformed into a benzotriazole. This inhibits PET, and the triplet state quantum yield is increased to ca. 85%, switching on the TTA upconversion process which increases by 10-fold. These processes were studied using a combination of steady state and time-resolved luminescence together with transient absorption spectroscopy on the nanosecond and femtosecond timescales. The energy level of the charge transfer state (CTS) for Ru-1 was also obtained electrochemically, supporting the PET mechanism of triplet state quenching and hence the lack of TTA upconversion with Ru-1. PMID:27387268

  3. Photoinduced Biohydrogen Production from Biomass

    PubMed Central

    Amao, Yutaka

    2008-01-01

    Photoinduced biohydrogen production systems, coupling saccharaides biomass such as sucrose, maltose, cellobiose, cellulose, or saccharides mixture hydrolysis by enzymes and glucose dehydrogenase (GDH), and hydrogen production with platinum colloid as a catalyst using the visible light-induced photosensitization of Mg chlorophyll-a (Mg Chl-a) from higher green plant or artificial chlorophyll analog, zinc porphyrin, are introduced. PMID:19325796

  4. Photo-induced isotopic fractionation

    NASA Astrophysics Data System (ADS)

    Miller, Charles E.; Yung, Yuk L.

    2000-12-01

    This paper presents a systematic method for the analysis of photo-induced isotopic fractionation. The physical basis for this fractionation mechanism centers on the fact that isotopic substitution alters the energy levels, molecular symmetries, spin statistical weights and other fundamental molecular properties, producing spectroscopic signatures distinguishable from that of the parent isotopomer. These mass-dependent physical properties are identical to those invoked by Urey to explain stable isotope fractionation in chemical systems subject to thermodynamic equilibrium. Photo-induced isotopic fractionation is a completely general phenomenon and should be observable in virtually all gas phase photochemical systems. Water photo-induced isotopic fractionation has been examined in detail using experimental and theoretical data. These results illustrate the salient features of this fractionation mechanism for molecules possessing continuous UV absorption spectra and unit photodissociation quantum yields. Using the photo-induced isotopic fractionation methodology in conjunction with standard photochemical models, we predict substantial deuterium enrichment of water vapor in the planetary atmospheres of Earth and Mars.

  5. Nanoscale chemical imaging by photoinduced force microscopy

    PubMed Central

    Nowak, Derek; Morrison, William; Wickramasinghe, H. Kumar; Jahng, Junghoon; Potma, Eric; Wan, Lei; Ruiz, Ricardo; Albrecht, Thomas R.; Schmidt, Kristin; Frommer, Jane; Sanders, Daniel P.; Park, Sung

    2016-01-01

    Correlating spatial chemical information with the morphology of closely packed nanostructures remains a challenge for the scientific community. For example, supramolecular self-assembly, which provides a powerful and low-cost way to create nanoscale patterns and engineered nanostructures, is not easily interrogated in real space via existing nondestructive techniques based on optics or electrons. A novel scanning probe technique called infrared photoinduced force microscopy (IR PiFM) directly measures the photoinduced polarizability of the sample in the near field by detecting the time-integrated force between the tip and the sample. By imaging at multiple IR wavelengths corresponding to absorption peaks of different chemical species, PiFM has demonstrated the ability to spatially map nm-scale patterns of the individual chemical components of two different types of self-assembled block copolymer films. With chemical-specific nanometer-scale imaging, PiFM provides a powerful new analytical method for deepening our understanding of nanomaterials. PMID:27051870

  6. Nanoscale chemical imaging by photoinduced force microscopy.

    PubMed

    Nowak, Derek; Morrison, William; Wickramasinghe, H Kumar; Jahng, Junghoon; Potma, Eric; Wan, Lei; Ruiz, Ricardo; Albrecht, Thomas R; Schmidt, Kristin; Frommer, Jane; Sanders, Daniel P; Park, Sung

    2016-03-01

    Correlating spatial chemical information with the morphology of closely packed nanostructures remains a challenge for the scientific community. For example, supramolecular self-assembly, which provides a powerful and low-cost way to create nanoscale patterns and engineered nanostructures, is not easily interrogated in real space via existing nondestructive techniques based on optics or electrons. A novel scanning probe technique called infrared photoinduced force microscopy (IR PiFM) directly measures the photoinduced polarizability of the sample in the near field by detecting the time-integrated force between the tip and the sample. By imaging at multiple IR wavelengths corresponding to absorption peaks of different chemical species, PiFM has demonstrated the ability to spatially map nm-scale patterns of the individual chemical components of two different types of self-assembled block copolymer films. With chemical-specific nanometer-scale imaging, PiFM provides a powerful new analytical method for deepening our understanding of nanomaterials. PMID:27051870

  7. Photoinduced Charge Separation in Molecular Silicon.

    PubMed

    Zhou, Jiawang; Surampudi, Sravan K; Bragg, Arthur E; Klausen, Rebekka S

    2016-04-25

    Interest in molecular silicon semiconductors arises from the properties shared with bulk silicon like earth abundance and the unique architectures accessible from a structure distinctly different than rigid π-conjugated organic semiconductors. We report ultrafast spectroscopic evidence for direct, photoinduced charge separation in molecular silicon semiconductors that supports the viability of molecular silicon as donor materials in optoelectronic devices. The materials in this study are σ-π hybrids, in which electron-deficient aromatic acceptors flank a σ-conjugated silicon chain. Transient absorption and femtosecond-stimulated Raman spectroscopy (FSRS) techniques revealed signatures consistent with direct, optical charge transfer from the silane chain to the acceptor; these signatures were only observed by probing excited-state structure. Our findings suggest new opportunities for controlling charge separation in molecular electronics. PMID:26919126

  8. Micellar Effects on Photoinduced Electron Transfer in Aqueous Solutions Revisited: Dramatic Enhancement of Cage Escape Yields in Surfactant Ru(II) Diimine Complex/[Ru(NH3)6](2+) Systems.

    PubMed

    Adams, Rebecca E; Schmehl, Russell H

    2016-08-30

    The effect of cationic micelle incorporation on light induced electron transfer, charge separation and back electron transfer between an aqueous electron donor, [Ru(NH3)6](2+), and a series of Ru(II) diimine complex chromophores/acceptors, is presented. The chromophores have the general formula [(bpy)2Ru(LL)](2+) (LL = bpy; 4-R-4'-methyl-2,2'-bpy, R = pentyl (MC5), terdecyl (MC13), heptadecyl (MC17); 4,4'-di(heptadecyl)-2,2'-bpy (DC17)). Of the five chromophores, the MC13, MC17, and DC17 complexes associate with the added micelle forming surfactant, cetyltrimethylammonium bromide (CTAB). Quenching of the luminescence of the bpy and MC5 complexes by [Ru(NH3)6](2+) is unaffected by addition of surfactant, while rate constants for quenching of the MC13 and MC17 complexes are decreased. Cage escape yields following photoinduced electron transfer to generate [(bpy)2Ru(LL)](+) and [Ru(NH3)6](3+) are approximately 0.1 for all the water-soluble chromophores (excluding DC17) in the absence of added CTAB. In the presence of surfactant, the cage escape yields dramatically increase for the MC13 (0.4) and MC17 (0.6) complexes, while remaining unchanged for [Ru(bpy)3](2+) and the MC5 complex. Back electron transfer of the solvent separated ions is also strongly influenced by the presence of surfactant. For the MC13 and MC17 complexes, back electron transfer rate constants decrease by factors of 270 and 190, respectively. The MC5 complex exhibits two component back electron transfer, with the fast component having a rate constant close to that in the absence of surfactant and a slow component nearly 200 times smaller. Results are interpreted in terms of the partitioning of the 2+ and 1+ forms of the chromophores between aqueous and micellar phases. The extended lifetimes of the radical ions may prove useful in coupling the strong reductants formed to kinetically facile catalysts for reduction of water to hydrogen. PMID:27486891

  9. Dynamical properties of nucleus boundaries in photoinduced structural change

    NASA Astrophysics Data System (ADS)

    Ishida, Kunio; Nasu, Keiichiro

    2014-01-01

    Dynamics of the boundaries of photoinduced nuclei in electron-phonon systems is theoretically studied. By regarding the spatial distribution of the excited electronic state population as a geometric pattern, we applied the multifractal analysis to it and calculated the temporal behavior of the fractal dimension f(α) as a function of the Lipschitz-Hölder exponent α, which is an appropriate method for understanding the cooperative relaxation process of photoexcited states. We found that the incubation period observed in various types of photoinduced cooperative phenomena corresponds to the formation of embryonic nuclei which is driven by nonadiabatic/adiabatic transition between electronic states during the relaxation of the Franck-Condon state.

  10. Applications of photoinduced electron transfer and hydrogen abstraction reactions to chemical and electrochemical conversion processes. Final report, March 1, 1981-February 28, 1984

    SciTech Connect

    Not Available

    1984-01-01

    Goal has been to study light-driven electron transfer and hydrogen atom abstraction processes with emphasis on reactions giving rise to net chemical or electrochemical conversion. The work focused on studies using substrates excitable with visible light - ranging from metal complexes, porphyrins and metalloporphyrins to dyes and ketones - and quencher-mediators capable of acting as electron donors or acceptors by virtue of having multiple closely spaced redox levels. The work can be conveniently divided into five major areas: Generation and Reaction of Reducing and Oxidizing Radicals and Radical Ions in Photoelectrochemical Cells; Studies of Weitz-type Quenchers Having Stable One-electron Redox Products; Two-electron Oxidative and Reductive Quenching Processes with Weitz-type Systems in Solution and Organized Media; Photoredox Reactions of Indigo Dyes; and Modification of Photochemical Reactivity by Formation of Amylose Inclusion Complexes in Aqueous and Partially Aqueous Solutions.

  11. Applications of photoinduced electron transfer and hydrogen abstraction reactions to chemical and electrochemical conversion processes. Part I. Progress report, March 1, 1981-July 1, 1983

    SciTech Connect

    Whitten, D.G.

    1983-01-01

    Goal is to study light-driven electron transfer and hydrogen atom abstraction processes with emphasis on reactions giving rise to net chemical or electrochemical conversion. The original proposal focused on studies using substrates excitable with visible light - ranging from metal complexes, porphyrins and metalloporphyrins to dyes and ketones - and quencher-mediators capable of acting as electron donors or acceptors by virtue of having multiple closely spaced redox levels. During the past eighteen months results were obtained in five areas: generation and reaction of reducing and oxidizing radicals and radical ions in photoelectrochemical cells; studies of Weitz-type quenchers having stable one-electron redox products; two-electron oxidative and reductive quenching processes with Weitz-type systems in solution and organized media; photoredox reactions of indigo dyes; and modification of photochemical reactivity by formation of amylose inclusion complexes in aqueous and partially aqueous solutions.

  12. Photo-induced electron transfers to CCl{sub 4} and its degradation mechanism on TiO{sub 2} particles

    SciTech Connect

    Choi, W.; Hoffmann, M.R.

    1995-12-01

    The photoreductive degradation of CCl{sub 4} in TiO{sub 2} particulate suspensions in the presence of a variety of organic electron donors (alcohols, carboxylic acids, and benzene derivatives) has been examined. CHCl{sub 3}, C{sub 2}Cl{sub 4}, and C{sub 2}Cl{sub 6} are detected as intermediates during photolysis. The rate of CCl{sub 4} dechlorination can be enhanced significantly when alcohols and organic acids are used as electron donors. Kinetic isotope effects and structure-reactivity relationships show that hydrogen-abstraction by hydroxyl radicals plays an important role in the hole-scavenging mechanism. The pH of the TiO{sub 2} suspension influences the rate of CCl{sub 4} reduction either by altering the electrostatic interactions of electron donors on the TiO{sub 2} surface or by changing the reduction potential of the conduction band electron in a Nernstian fashion. Since dissolved oxygen is shown to be nonessential for the complete mineralization of CCl{sub 4}, a mechanism, which involves dichlorocarbene formation through a two-electron transfer, is proposed.

  13. Applications of photoinduced electron transfer and hydrogen abstraction reactions to chemical and electrochemical conversion processes. Progress report, March 1, 1981-September 1, 1982

    SciTech Connect

    Whitten, D.G.

    1982-01-01

    The major goal of this research as outlined in our proposal is to study light-driven electron transfer and hydrogen atom abstraction processes with a particular emphasis on reactions giving rise to net chemical or electrochemical conversion. During the past eighteen months we have obtained results of some significance in each of the five areas which are discussed individually in the report: (1) generation and reaction of reducing and oxidizing radicals and radical ions in photoelectrochemical cells; (2) studies of Weitz-type quenchers having stable one-electron redox products; (3) two-electron oxidative and reductive quenching processes with Weitz-type systems in solution and organized media; (4) photoredox reactions of indigo dyes; and (5) modification of photochemical reactivity by formation of amylose inclusion complexes in aqueous and partially aqueous solutions.

  14. Dual Site-Controlled and Lysosome-Targeted Intramolecular Charge Transfer-Photoinduced Electron Transfer-Fluorescence Resonance Energy Transfer Fluorescent Probe for Monitoring pH Changes in Living Cells.

    PubMed

    Dong, Baoli; Song, Xuezhen; Wang, Chao; Kong, Xiuqi; Tang, Yonghe; Lin, Weiying

    2016-04-01

    Acidic pH is a critical physiological factor for controlling the activities and functions of lysosome. Herein, we report a novel dual site-controlled and lysosome-targeted intramolecular charge transfer-photoinduced electron transfer-Fluorescence resonance energy transfer (ICT-PET-FRET) fluorescent probe (CN-pH), which was essentially the combination of a turn-on pH probe (CN-1) and a turn-off pH probe (CN-2) by a nonconjugated linker. Coumarin and naphthalimide fluorophores were selected as donor and acceptor to construct the FRET platform. Hydroxyl group and morpholine were simultaneously employed as the two pH sensing sites and controlled the fluorescence of coumarin and naphthalimide units by ICT and PET, respectively. The sensing mechanism of CN-pH to pH was essentially an integration of ICT, PET, and FRET processes. Meanwhile, the morpholine also can serve as a lysosome-targeted group. By combining the two data analysis approaches of the ratios of the two emission intensities (R) and the reverse ratio R' (R' = 1/R), the fluorescent ratio of CN-pH can show proportional relationship to pH values in a very broad range from pH 4.0 to 8.0 with high sensitivity. The probe has been successfully applied for the fluorescence imaging of the lysosomal pH values, as well as ratiometrically visualizing chloroquine-stimulated changes of intracellular pH in living cells. These features demonstrate that the probe can afford practical application in biological systems. PMID:26987045

  15. Photoinduced 1,2,3,4-tetrahydropyridine ring conversions.

    PubMed

    Turovska, Baiba; Lund, Henning; Lūsis, Viesturs; Lielpētere, Anna; Liepiņš, Edvards; Beljakovs, Sergejs; Goba, Inguna; Stradiņš, Jānis

    2015-01-01

    Stable heterocyclic hydroperoxide can be easily prepared as a product of fast oxidation of a 1,2,3,4-tetrahydropyridine by (3)O2 if the solution is exposed to sunlight. The driving force for the photoinduced electron transfer is calculated from electrochemical and spectroscopic data. The outcome of the reaction depends on the light intensity and the concentration of O2. In the solid state the heterocyclic hydroperoxide is stable; in solution it is involved in further reactions. PMID:26664638

  16. Photoinduced 1,2,3,4-tetrahydropyridine ring conversions

    PubMed Central

    Lund, Henning; Lūsis, Viesturs; Lielpētere, Anna; Liepiņš, Edvards; Beljakovs, Sergejs; Goba, Inguna; Stradiņš, Jānis

    2015-01-01

    Summary Stable heterocyclic hydroperoxide can be easily prepared as a product of fast oxidation of a 1,2,3,4-tetrahydropyridine by 3O2 if the solution is exposed to sunlight. The driving force for the photoinduced electron transfer is calculated from electrochemical and spectroscopic data. The outcome of the reaction depends on the light intensity and the concentration of O2. In the solid state the heterocyclic hydroperoxide is stable; in solution it is involved in further reactions. PMID:26664638

  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. Photoinduced electron transfer in a charge-transfer complex formed between corannulene and Li+@C60 by concave-convex π-π interactions.

    PubMed

    Yamada, Mihoko; Ohkubo, Kei; Shionoya, Mitsuhiko; Fukuzumi, Shunichi

    2014-09-24

    A charge-transfer (CT) complex was formed between corannulene (C20H10) and lithium ion-encapsulated [60]fullerene (Li(+)@C60) with the binding constant KG = 1.9 × 10 M(-1) by concave-convex π-π CT interactions in benzonitrile at 298 K, exhibiting a broad CT absorption extended to the NIR region. Femotosecond laser excitation of the C20H10/Li(+)@C60 CT complex resulted in the singlet charge-separated (CS) state, (1)(C20H10(•+)/Li(+)@C60(•-)), which decayed with the lifetime of 1.4 ns. Nanosecond laser excitation of Li(+)@C60 resulted in intermolecular electron transfer (ET) from C20H10 to the triplet excited state of Li(+)@C60 [(3)(Li(+)@C60)*] to produce the triplet CS state (3)(C20H10(•+)/Li(+)@C60(•-)). The distance between two electron spins in the triplet CS state was estimated to be 10 Å from the zero-field splitting pattern observed by EPR measurements at 4 K. The triplet CS state decayed to the ground state via intramolecular back electron transfer (BET). The CS lifetime was determined to be 240 μs in benzonitrile at 298 K. The temperature dependence of the rate constant of BET afforded the reorganization energy (λ = 1.04 eV) and the electronic coupling term (V = 0.0080 cm(-1)). The long lifetime of triplet CS state results from the spin-forbidden BET process and a small V value. PMID:25166343

  19. First-principles calculation of photo-induced electron transfer rate constants in phthalocyanine-C60 organic photovoltaic materials: Beyond Marcus theory

    NASA Astrophysics Data System (ADS)

    Lee, Myeong H.; Dunietz, Barry D.; Geva, Eitan

    2014-03-01

    Classical Marcus theory is commonly adopted in solvent-mediated charge transfer (CT) process to obtain the CT rate constant, but it can become questionable when the intramolecular vibrational modes dominate the CT process as in OPV devices because Marcus theory treats these modes classically and therefore nuclear tunneling is not accounted for. We present a computational scheme to obtain the electron transfer rate constant beyond classical Marcus theory. Within this approach, the nuclear vibrational modes are treated quantum-mechanically and a short-time approximation is avoided. Ab initio calculations are used to obtain the basic parameters needed for calculating the electron transfer rate constant. We apply our methodology to phthalocyanine(H2PC)-C60 organic photovoltaic system where one C60 acceptor and one or two H2PC donors are included to model the donor-acceptor interface configuration. We obtain the electron transfer and recombination rate constants for all accessible charge transfer (CT) states, from which the CT exciton dynamics is determined by employing a master equation. The role of higher lying excited states in CT exciton dynamics is discussed. This work is pursued as part of the Center for Solar and Thermal Energy Conversion, an Energy Frontier Research Center funded by the US Department of Energy Office of Science, Office of Basic Energy Sciences under 390 Award No. DE-SC0000957.

  20. Dimensionality of nanoscale TiO2 determines the mechanism of photoinduced electron injection from a CdSe nanoparticle

    SciTech Connect

    Tafen, De Nyago; Long, Run; Prezhdo, Oleg V.

    2014-03-10

    Assumptions about electron transfer (ET) mechanisms guide design of catalytic, photovoltaic, and electronic systems. We demonstrate that the mechanism of ET from a CdSe quantum dot (QD) into nanoscale TiO2 depends on TiO2 dimensionality. The injection into a TiO2 QD is adiabatic due to strong donor–acceptor coupling, arising from unsaturated chemical bonds on the QD surface, and low density of acceptor states. In contrast, the injection into a TiO2 nanobelt (NB) is nonadiabatic, because the state density is high, the donor–acceptor coupling is weak, and multiple phonons accommodate changes in the electronic energy. The CdSe adsorbant breaks symmetry of delocalized TiO2 NB states, relaxing coupling selection rules, and generating more ET channels. Both mechanisms can give efficient ultrafast injection. Furthermore, the dependence on system properties is very different for the two mechanisms, demonstrating that the fundamental principles leading to efficient charge separation depend strongly on the type of nanoscale material.

  1. High-potential perfluorinated phthalocyanine-fullerene dyads for generation of high-energy charge-separated states: formation and photoinduced electron-transfer studies.

    PubMed

    Das, Sushanta K; Mahler, Andrew; Wilson, Angela K; D'Souza, Francis

    2014-08-25

    High oxidation potential perfluorinated zinc phthalocyanines (ZnF(n)Pcs) are synthesised and their spectroscopic, redox, and light-induced electron-transfer properties investigated systematically by forming donor-acceptor dyads through metal-ligand axial coordination of fullerene (C60) derivatives. Absorption and fluorescence spectral studies reveal efficient binding of the pyridine- (Py) and phenylimidazole-functionalised fullerene (C60Im) derivatives to the zinc centre of the F(n)Pcs. The determined binding constants, K, in o-dichlorobenzene for the 1:1 complexes are in the order of 10(4) to 10(5) M(-1); nearly an order of magnitude higher than that observed for the dyad formed from zinc phthalocyanine (ZnPc) lacking fluorine substituents. The geometry and electronic structure of the dyads are determined by using the B3LYP/6-31G* method. The HOMO and LUMO levels are located on the Pc and C60 entities, respectively; this suggests the formation of ZnF(n)Pc(.+)-C60Im(.-) and ZnF(n)Pc(.+)-C60Py(.-) (n=0, 8 or 16) intra-supramolecular charge-separated states during electron transfer. Electrochemical studies on the ZnPc-C60 dyads enable accurate determination of their oxidation and reduction potentials and the energy of the charge-separated states. The energy of the charge-separated state for dyads composed of ZnF(n)Pc is higher than that of normal ZnPc-C60 dyads and reveals their significance in harvesting higher amounts of light energy. Evidence for charge separation in the dyads is secured from femtosecond transient absorption studies in nonpolar toluene. Kinetic evaluation of the cation and anion radical ion peaks reveals ultrafast charge separation and charge recombination in dyads composed of perfluorinated phthalocyanine and fullerene; this implies their significance in solar-energy harvesting and optoelectronic device building applications. PMID:24850373

  2. Photoinduced electron transfer double fragmentation. An oxygen-mediated radical chain process in the cofragmentation of aminopinacol donors with organic halides

    SciTech Connect

    Chen, L.; Farahat, M.S.; Gan, H.; Whitten, D.G.; Farid, S. |

    1995-06-14

    We reprot an investigation in which excited states of amino pinacols 1-3 are reacted with the halides CCl{sub 4}, benzyl bromide, and p-cyanobenzyl bromide. Interesting results from this study include the finding that low-to-moderate quantum efficiencies for reaction are observed when the reactions are carried out under degassed conditions, indicating that the halide radical anions must survive long enough within the initial ion pair formed in the quenching step to undergo considerable return electron transfer. More strikingly we find that for certain pinacol-halide combinations reaction in aerared solutions leads to much higher efficiencies, which can be attributed to a chain reaction involving oxygen capture of a primary radical product. 25 refs., 1 fig., 1 tab.

  3. Photoinduced Charge-Carrier Generation in Epitaxial MOF Thin Films: High Efficiency as a Result of an Indirect Electronic Band Gap?

    PubMed

    Liu, Jinxuan; Zhou, Wencai; Liu, Jianxi; Howard, Ian; Kilibarda, Goran; Schlabach, Sabine; Coupry, Damien; Addicoat, Matthew; Yoneda, Satoru; Tsutsui, Yusuke; Sakurai, Tsuneaki; Seki, Shu; Wang, Zhengbang; Lindemann, Peter; Redel, Engelbert; Heine, Thomas; Wöll, Christof

    2015-06-15

    For inorganic semiconductors crystalline order leads to a band structure which gives rise to drastic differences to the disordered material. An example is the presence of an indirect band gap. For organic semiconductors such effects are typically not considered, since the bands are normally flat, and the band-gap therefore is direct. Herein we show results from electronic structure calculations demonstrating that ordered arrays of porphyrins reveal a small dispersion of occupied and unoccupied bands leading to the formation of a small indirect band gap. We demonstrate herein that such ordered structures can be fabricated by liquid-phase epitaxy and that the corresponding crystalline organic semiconductors exhibit superior photophysical properties, including large charge-carrier mobility and an unusually large charge-carrier generation efficiency. We have fabricated a prototype organic photovoltaic device based on this novel material exhibiting a remarkable efficiency. PMID:25960115

  4. Photo-induced water oxidation at the aqueous GaN (101¯0) interface: Deprotonation kinetics of the first proton-coupled electron-transfer step

    DOE PAGESBeta

    Ertem, Mehmed Z.; Kharche, Neerav; Batista, Victor S.; Hybertsen, Mark S.; Tully, John C.; Muckerman, James T.

    2015-03-12

    Photoeclectrochemical water splitting plays a key role in a promising path to the carbon-neutral generation of solar fuels. Wurzite GaN and its alloys (e.g., GaN/ZnO and InGaN) are demonstrated photocatalysts for water oxidation, and they can drive the overall water splitting reaction when coupled with co-catalysts for proton reduction. In the present work, we investigate the water oxidation mechanism on the prototypical GaN (101¯0) surface using a combined ab initio molecular dynamics and molecular cluster model approach taking into account the role of water dissociation and hydrogen bonding within the first solvation shell of the hydroxylated surface. The investigation ofmore » free-energy changes for the four proton-coupled electron-transfer (PCET) steps of the water oxidation mechanism shows that the first PCET step for the conversion of –Ga-OH to –Ga-O˙⁻ requires the highest energy input. We further examine the sequential PCETs, with the proton transfer (PT) following the electron transfer (ET), and find that photo-generated holes localize on surface –NH sites is thermodynamically more favorable than –OH sites. However, proton transfer from –OH sites with subsequent localization of holes on oxygen atoms is kinetically favored owing to hydrogen bonding interactions at the GaN (101¯0)–water interface. We find that the deprotonation of surface –OH sites is the limiting factor for the generation of reactive oxyl radical ion intermediates and consequently for water oxidation.« less

  5. Photo-induced water oxidation at the aqueous GaN (101¯0) interface: Deprotonation kinetics of the first proton-coupled electron-transfer step

    SciTech Connect

    Ertem, Mehmed Z.; Kharche, Neerav; Batista, Victor S.; Hybertsen, Mark S.; Tully, John C.; Muckerman, James T.

    2015-03-12

    Photoeclectrochemical water splitting plays a key role in a promising path to the carbon-neutral generation of solar fuels. Wurzite GaN and its alloys (e.g., GaN/ZnO and InGaN) are demonstrated photocatalysts for water oxidation, and they can drive the overall water splitting reaction when coupled with co-catalysts for proton reduction. In the present work, we investigate the water oxidation mechanism on the prototypical GaN (101¯0) surface using a combined ab initio molecular dynamics and molecular cluster model approach taking into account the role of water dissociation and hydrogen bonding within the first solvation shell of the hydroxylated surface. The investigation of free-energy changes for the four proton-coupled electron-transfer (PCET) steps of the water oxidation mechanism shows that the first PCET step for the conversion of –Ga-OH to –Ga-O˙⁻ requires the highest energy input. We further examine the sequential PCETs, with the proton transfer (PT) following the electron transfer (ET), and find that photo-generated holes localize on surface –NH sites is thermodynamically more favorable than –OH sites. However, proton transfer from –OH sites with subsequent localization of holes on oxygen atoms is kinetically favored owing to hydrogen bonding interactions at the GaN (101¯0)–water interface. We find that the deprotonation of surface –OH sites is the limiting factor for the generation of reactive oxyl radical ion intermediates and consequently for water oxidation.

  6. QSARs for photo-induced toxicity of polycyclic aromatic hydrocarbons (PAHs)

    SciTech Connect

    Mekenyan, O.; Call, D.; Ankley, G.; Veith, G.

    1994-12-31

    Photo-induced toxicity of polycyclic aromatic hydrocarbons (PAHs) was found to be a result of competing internal and external factors which interact to produce a complex, multilinear relationship between toxicity and chemical structure. The relationship between molecular electronic structure and photo-dynamic effects was studied in both ground and excited states. A measure of the energy required for an electron to be elevated from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO), or HOMO-LUMO gap, provided a useful ground state index to explain the persistence, light absorption, and eventual photo-induced toxicity of PAHs to Daphnia magna. The derived QSARs clearly distinguished photo-induced toxicity differences between pairs of structurally similar PAHs, such as phenanthrene and anthracene, benzo[a]anthracene and tetracene, etc. Those PAHs exhibiting photo-induced toxicity were consistently within a specific HOMO-LUMO gap range. The relationship between the excited state electronic parameters and toxicity was also studied. Significant correlations were found with the measured energies of singlet and triplet states from spectroscopic data. An investigation of the effect of substituent additions on photo-induced acute toxicity of parent PAHs revealed that alkyl and hydroxy moieties did not significantly reduce the HOMO-LUMO gap of the parent PAHs. Nitro, alkene and chloro substituents cause gap reductions, whereby certain derivatives of parent chemicals that were close to the ``toxic region`` of the electronic gap could become phototoxic with such additions.

  7. Photoinduced molecular reorientation of absorbing liquid crystals

    NASA Astrophysics Data System (ADS)

    Marrucci, L.; Paparo, D.

    1997-08-01

    The phenomenon of photoinduced molecular reorientation of absorbing nematic liquid crystals is analyzed in a macroscopic general framework and with a specific molecular model. The photoinduced torque responsible for the reorientation is shown to describe a transfer of angular momentum from the molecule center-of-mass degrees of freedom to the rotational ones, mediated by molecular friction. As a consequence, a photoinduced stress tensor is predicted to develop together with the torque in the illuminated fluid. A molecular expression of the photoinduced torque is derived with a rigorous procedure, valid both for a pure material and for a dye-liquid-crystal mixture. This torque expression corrects those reported in previous works on the same subject. The photoinduced torque is evaluated analytically in a simple approximate limit.

  8. Photoelectric Properties Based on Electric Field Modulation of Photoinduced Electron Transfer Processes in Flavin-Porphyrin Hetero-type Langmuir-Blodgett Films

    NASA Astrophysics Data System (ADS)

    Isoda, Satoru; Hanazato, Yoshio; Ueyama, Satoshi; Nishikawa, Satoshi; Akiyama, Kouich

    2004-05-01

    Metal-insulator-meal devices composed of flavin-porphyrin hetero-type Langmuir-Blodgett films showed highly efficient photoelectric properties mainly attributable to the fast charge separation process at a molecular heterojunction (MHJ) between flavin and porphyrin. The photoelectric properties of the MHJ devices showed different characteristics depending on the redox state of the central metal of porphyrin, i.e., Ru(III) or Ru(II). The rectifying behavior of the photocurrent was observed for the Ru(III)-MHJ device, whereas the Ru(II)-MHJ device did not show the rectifying behavior. We concluded that the rectifying behavior was mainly controlled by the electric field dependence of the charge recombination process. Furthermore, a bell-shaped photocurrent-voltage curve was observed for the Ru(II)-MHJ device. The mechanism underlying the negative resistance might be based on the electric field dependence of the charge shift process in flavin monolayers controlled by the inverted region mechanism of the Marcus electron transfer theory.

  9. Photoinduced Electron-Transfer Mechanisms for Radical-Enhanced Photodynamic Therapy Mediated by Water-Soluble Decacationic C70 and C84O2 Fullerene Derivatives

    PubMed Central

    Sperandio, Felipe F.; Sharma, Sulbha K.; Wang, Min; Jeon, Seaho; Huang, Ying-Ying; Dai, Tianhong; Nayka, Suhasini; de Sousa, Suzana C.O.M.; Chiang, Long Y.; Hamblin, Michael R.

    2012-01-01

    Fullerenes are promising candidates for photodynamic therapy (PDT). Thus, C70 and novel C84O2 fullerenes were functionalized with and without an additional deca-tertiary ethyleneamino-chain as an electron source, giving rise to two distinct pairs of photosensitizers, the monoadducts LC-17, LC-19 and the bisadducts LC18 and LC-20 to perform PDT in HeLa cells with UVA, blue, green, white and red light. Shorter wavelengths gave more phototoxicity with LC-20 while LC-19 was better at longer wavelengths; the ratio between killing obtained with LC-19 and LC-20 showed an almost perfect linear correlation (R = 0.975) with wavelength. The incorporation of a deca-tertiary amine chain in the C84O2 fullerene gave more PDT killing when excited with shorter wavelengths or in presence of low ascorbate concentration through higher generation of hydroxyl radicals. Photoactivated C84O2 fullerenes induced apoptosis of HeLa cancer cells, together with mitochondrial and lysosomal damage demonstrated by acridine orange and rhodamine 123 fluorescent probes. PMID:23117043

  10. Numerical simulation on the dynamics of photoinduced cooperative phenomena in molecular crystals

    NASA Astrophysics Data System (ADS)

    Ishida, Kunio; Nasu, Keiichiro

    2009-09-01

    We develop a new simulation method to study the dynamics of initial nucleation processes of photoinduced structural change of molecular crystals. In order to describe the nonadiabatic transition in each molecule, we employ a model of localized electrons coupled with a fully quantized phonon mode, and the time-dependent Schrödinger equation for the model is numerically solved. By applying a mean-field approximation in solving the Schrödinger equation, the calculation method is quite efficient on parallel computing systems. We show that coherently driven molecular distortion plays an important role in the successive conversion of electronic states which leads to photoinduced cooperative phenomena.

  11. Photoinduced modulation and relaxation characteristics in LaAlO3/SrTiO3 heterointerface

    PubMed Central

    Jin, K. X.; Lin, W.; Luo, B. C.; Wu, T.

    2015-01-01

    We report the modulation and relaxation characteristics in the two-dimensional electron gas system at LaAlO3/SrTiO3 heterointerface induced by the ultraviolet light illumination (365 nm). The suppression of Kondo effect at the interface illuminated by the light originates from the light irradiation-induced decoherence effect of localized states. It is interesting to note that the persistent and transient photoinduced effects are simultaneously observed and the photoinduced maximum change values in resistance are 80.8% and 51.4% at T = 20 K, respectively. Moreover, the photoinduced relaxation processes after the irradiation are systematically analyzed using the double exponential model. These results provide the deeper understanding of the photoinduced effect and the experimental evidence of tunable Kondo effect in oxides-based two-dimensional electron gas systems. PMID:25739889

  12. Inactivation of tyrosinase photoinduced by pterin

    SciTech Connect

    Laura Dantola, M.; Gojanovich, Aldana D.; Thomas, Andres H.

    2012-08-03

    Highlights: Black-Right-Pointing-Pointer Under UV-A radiation, tirosinase is photoinactivated by pterin. Black-Right-Pointing-Pointer The mechanism involves an electron transfer-initiated process. Black-Right-Pointing-Pointer The photochemical process affects both activities of tyrosinase. -- Abstract: Tyrosinase catalyzes in mammals the first and rate-limiting step in the biosynthesis of the melanin, the main pigment of the skin. Pterins, heterocyclic compounds able to photoinduce oxidation of DNA and its components, accumulate in the skin of patients suffering from vitiligo, a chronic depigmentation disorder in which the protection against UV radiation fails due to the lack of melanin. Aqueous solutions of tyrosinase were exposed to UV-A irradiation (350 nm) in the presence of pterin, the parent compound of oxidized pterins, under different experimental conditions. The enzyme activity in the irradiated solutions was determined by spectrophotometry and HPLC. In this work, we present data that demonstrate unequivocally that the enzyme is photoinactivated by pterin. The mechanism of the photosensitized process involves an electron transfer from tyrosinase to the triplet excited state of pterin, formed after UV-A excitation of pterin. The biological implications of the results are discussed.

  13. Photoinduced Energy Transfer in Artificial Photosynthetic Systems

    NASA Astrophysics Data System (ADS)

    Imahori, H.; Umeyama, T.

    Artificial photosynthesis is a current topic of intensive investigations, both in order to understand the reactions that play a central role in natural photosynthesis as well as to develop highly efficient solar energy conversion systems and molecular optoelectronic devices [1-34]. Artificial photosynthesis is defined as a research field that attempts to mimic the natural process of photosynthesis. Therefore, the outline of natural photosynthesis is described briefly for the better understanding of artificial photosynthesis . Natural photosynthetic system is regarded as one of the most elaborate nanobiological machines [35,36]. It converts solar energy into electrochemical potential or chemical energy, which is prerequisite for the living organisms on the earth. The core function of photosynthesis is a cascade of photoinduced energy and electron transfer between donors and acceptors in the antenna complexes and the reaction center. For instance, in purple photosynthetic bacteria (Rhodopseudomonas acidophila and Rhodopseudomonas palustris) there are two different types of antenna complexes: a core light-harvesting antenna (LH1) and peripheral light-harvesting antenna (LH2) [37-39]. LH1 surrounds the reaction center where charge separation takes place.

  14. The photoinduced polarization in Kapton-H film

    NASA Astrophysics Data System (ADS)

    Quamara, J. K.; Bhardwaj, R. P.; Sharma, B. L.

    1984-12-01

    The photoinduced polarization in Kapton-H thin film has been studied by analysing the isothermal dark decay characteristics of photo- and dark-polarized specimens for different values of the polarizing parameters. The total polarization induced has been found to increase continuously with polarizing temperature but with polarizing field, it approaches a saturation. The behaviour of dark decay currents for photo and dark polarized identical samples changes with operating temperature. The phenomenon is explained in terms of the shift of electrons and hole demarcation levels under variation of temperature and illumination intensity.

  15. Improved Photo-Induced Stability in Amorphous Metal-Oxide Based TFTs for Transparent Displays.

    PubMed

    Koo, Sang-Mo; Ha, Tae-Jun

    2015-10-01

    In this paper, we investigate the origin of photo-induced instability in amorphous metal-oxide based thin-film transistors (oxide-TFTs) by exploring threshold voltage (Vth) shift in transfer characteristics. The combination of photo irradiation and prolonged gate bias stress enhanced the shift in Vth in amorphous hafnium-indium-zinc-oxide (a-HfIZO) TFTs. Such results stem from the extended trapped charges at the localized defect states related to oxygen vacancy which play a role in a screening effect on the electric field induced by gate voltage. We also demonstrate the chemically clean interface in oxide-TFTs by employing oxygen annealing which reduces the density of trap states, thereby resulting in improved photo-induced stability. We believe that this work stimulates the research society of transparent electronics by providing a promising approach to suppress photo-induced instability in metal-oxide TFTs. PMID:26726416

  16. Photo-induced and electrooptic properties of (Pb,La)(Zr,Ti)O{sub 3} films

    SciTech Connect

    Dimos, D.; Warren, W.L.; Tuttle, B.A.

    1993-07-01

    Photo-induced changes in the hysteresis behavior of sol-gel derived Pb(Zr,Ti)O{sub 3} (PZT) and (Pb,La)(Zr,Ti)O{sub 3} (PLZT) films have been characterized. Film photosensitivity has been evaluated with respect to magnitude of effects, time response and spectral dependence. Photo-induced hysteresis changes exhibit a stretched-exponential time dependence, which implies a dispersive mechanism. The spectral dependence is strongly peaked at the band edge ({approximately} 3.4 eV), which indicates that generation of electron-hole pairs in the material is critical. The photo-induced hysteresis changes are reproducible and stable, which indicates that the controlling charge traps are stable. However, improvements in film photosensitivity will be required to develop these materials for optical memory applications.

  17. Photoinduced Charge Transport in a BHJ Solar Cell Controlled by an External Electric Field

    PubMed Central

    Li, Yongqing; Feng, Yanting; Sun, Mengtao

    2015-01-01

    This study investigated theoretical photoinduced charge transport in a bulk heterojunction (BHJ) solar cell controlled by an external electric field. Our method for visualizing charge difference density identified the excited state properties of photoinduced charge transfer, and the charge transfer excited states were distinguished from local excited states during electronic transitions. Furthermore, the calculated rates for the charge transfer revealed that the charge transfer was strongly influenced by the external electric field. The external electric field accelerated the rate of charge transfer by up to one order when charge recombination was significantly restrained. Our research demonstrated that photoinduced charge transport controlled by an external electric field in a BHJ solar cell is efficient, and the exciton dissociation is not the limiting factor in organic solar cells.Our research should aid in the rational design of a novel conjugated system of organic solar cells. PMID:26353997

  18. Static and dynamic photoinduced magnetic effects in yttrium-iron garnet lightly doped with barium ions

    SciTech Connect

    Vorob'eva, N. V. Khalilov, R. Z.

    2012-04-15

    In yttrium-iron garnet lightly doped with barium, direct measurements of the photoinduced changes in magnetostrictive strains disagree with those in magnetostriction constants at 78-100 K. This is attributed to a considerable photoinduced modification of the initial state in this sample due to a redistribution of the charge (during illumination) between cations of the ferromagnetic octahedral sublattice. In the same sample, the temperature dependence of the photoinduced disaccomodation of magnetic permeability characterizing the initial demagnetized state is measured and calculated. A change in the electron mechanism of the phenomenon during the transition to room temperature is shown. The conclusion about the promising prospects for using such samples for remagnetization by light is advanced.

  19. Photoinduced toxicity of engineered nanomaterials

    NASA Astrophysics Data System (ADS)

    Jones, Philip Scott

    Engineered nanomaterials including metal, metal oxide and carbon based nanomaterials are extensively used in a wide variety of applications to the extent that their presence in the environment is expected to increase dramatically over the next century. These nanomaterials may be photodegraded by solar radiation and thereby release metal ions into the environment that can produce cytotoxic and genotoxic effects. Photoinduced toxicity experiments are performed exposing human lung epithelial carcinoma cells [H1650] to engineered semiconductor nanoparticles such as CdSe quantum dots and ZnO nanoparticles after exposure to 3, 6, and 9 hours of solar simulated radiation. Cytotoxicity and genotoxicity of the metal ions are evaluated using ZnSO4 and CdCl2 solutions for the MTT assay and Comet assay respectively. The objective of the dissertation is to obtain quantitative information about the environmental transformation of engineered nanomaterials and their mechanism of toxicity. This information is critical for addressing the environmental health and safety risks of engineered nanomaterials to workers, consumers and the environment.

  20. Photoinduced magnetic force between nanostructures

    NASA Astrophysics Data System (ADS)

    Guclu, Caner; Tamma, Venkata Ananth; Wickramasinghe, Hemantha Kumar; Capolino, Filippo

    2015-12-01

    Photoinduced magnetic force between nanostructures, at optical frequencies, is investigated theoretically. Till now optical magnetic effects were not used in scanning probe microscopy because of the vanishing natural magnetism with increasing frequency. On the other hand, artificial magnetism in engineered nanostructures led to the development of measurable optical magnetism. Here two examples of nanoprobes that are able to generate strong magnetic dipolar fields at optical frequency are investigated: first, an ideal magnetically polarizable nanosphere and then a circular cluster of silver nanospheres that has a looplike collective plasmonic resonance equivalent to a magnetic dipole. Magnetic forces are evaluated based on nanostructure polarizabilities, i.e., induced magnetic dipoles, and magnetic-near field evaluations. As an initial assessment on the possibility of a magnetic nanoprobe to detect magnetic forces, we consider two identical magnetically polarizable nanoprobes and observe magnetic forces on the order of piconewtons, thereby bringing it within detection limits of conventional atomic force microscopes at ambient pressure and temperature. The detection of magnetic force is a promising method in studying optical magnetic transitions that can be the basis of innovative spectroscopy applications.

  1. Photoinduced effect in Ga Ge S based thin films

    NASA Astrophysics Data System (ADS)

    Messaddeq, S. H.; Li, M. Siu; Inoue, S.; Ribeiro, S. J. L.; Messaddeq, Y.

    2006-10-01

    Glassy films of Ga 10Ge 25S 65 with 4 μm thickness were deposited on quartz substrates by electron beam evaporation. Photoexpansion (PE) (photoinduced increase in volume) and photobleaching (PB) (blue shift of the bandgap) effects have been examined. The exposed areas have been analyzed using perfilometer and an expansion of 1.7 μm (Δ V/ V ≈ 30%) is observed for composition Ga 10Ge 25S 65 exposed during 180 min and 3 mW/cm 2 power density. The optical absorption edge measured for the film Ge 25Ga 10S 65 above and below the bandgap show that the blue shift of the gap by below bandgap photon illumination is considerable higher (Δ Eg = 440 meV) than Δ Eg induced by above bandgap illumination (Δ Eg = 190 meV). The distribution of the refraction index profile showed a negative change of the refraction index in the irradiated samples (Δ n = -0.6). The morphology was examined using a scanning electron microscopy (SEM). The chemical compositions measured using an energy dispersive analyzer (EDX) indicate an increase of the oxygen atoms into the irradiated area. Using a Lloyd's mirror setup for continuous wave holography it was possible to record holographic gratings using the photoinduced effects that occur in them. Diffraction efficiency up to 25% was achieved for the recorded gratings and atomic force microscopy images are presented.

  2. Photoinduced development of antibacterial materials derived from isosorbide moiety.

    PubMed

    Lorenzini, Cedric; Haider, Adnan; Kang, Inn-Kyu; Sangermano, Marco; Abbad-Andalloussi, Samir; Mazeran, Pierre-Emmanuel; Lalevée, Jacques; Renard, Estelle; Langlois, Valérie; Versace, Davy-Louis

    2015-03-01

    A straightforward method for immobilizing in situ generated silver nanoparticles on the surface of a photoactivable isosorbide-derived monomer is developed with the objective to design a functional material having antibacterial properties. The photoinduced thiol-ene mechanism involved in these syntheses is described by the electron spin resonance/spin trapping technique. The resulting materials with or without silver nanoparticles (Ag NPs) were used as films or as coatings on glass substrate. The surface of the synthesized materials was characterized by X-ray photoelectron spectroscopy and scanning electron microscopy, and their thermal and mechanical properties were evaluated by dynamic-mechanical thermal tests, differential scanning calorimetry, thermogravimetric analyses, along with pencil hardness, nanoindentation, and scratch resistance tests. The photoinduced formation of Ag NPs is also confirmed by UV spectrophotometry. Finally, a primary investigation demonstrates the antibacterial properties of the isosorbide-derived material against Staphylococcus aureus and Escherichia coli, as well as its cytocompatibility toward NIH 3T3 fibroblastic cells. PMID:25633575

  3. NA-ESMD modeling of photoinduced dynamics in conjugated molecules

    NASA Astrophysics Data System (ADS)

    Nelson, Tammie; Fernandez-Alberti, Sebastian; Chernyak, Vladimir; Roitberg, Adrian; Tretiak, Sergei

    2011-03-01

    The evolution of electronic excitations in optically active molecules can generally be defined by non-adiabatic (NA) dynamics. A number of fundamental and complex processes are associated with NA dynamics. To treat ultrafast excited state dynamics we have developed a non-adiabatic excited state molecular dynamics (NA-ESMD) framework incorporating quantum transitions. Our calculations combine the Collective Electronic Oscillator (CEO) package with the Tully's fewest switches algorithm for surface hopping, and the actual potential energy surfaces of the excited states are used. This method is applied to model the photoinduced dynamics of distyrylbenzene. Our analysis shows intricate details of vibronic relaxation and identifies specific slow and fast nuclear motions that are strongly coupled to the electronic degrees of freedom. Non-adiabatic relaxation of the highly excited mAg state is predicted to occur on a femtosecond timescale at room temperature and on a picosecond timescale at low temperature.

  4. Direct observations of the photoinduced change in dimerization in K-TCNQ

    NASA Astrophysics Data System (ADS)

    Ishikawa, Tadahiko; Hosoda, Ryosuke; Okimoto, Yoichi; Tanaka, Sei'ichi; Onda, Ken; Koshihara, Shinya; Kumai, Reiji

    2016-05-01

    The photoinduced dynamics of a potassium-tetracyanoquinodimethane (K-TCNQ) single crystal in the generalized Peierls phase are evaluated via time-resolved vibrational spectroscopy. The transient reflectivity spectrum of the photoinduced state in the mid-IR range shows a decrease in the height and width of the reflectivity band because of the electron-molecular-vibration-coupled CN stretching mode at approximately 2180 cm-1. This spectral change suggests that the photoexcitation of the charge transfer in TCNQ molecules induces melting of the dimerization of the molecules. From detailed analysis of the spectral evolution, the relaxation time constant from the photoinduced state to the dimerized state is estimated to be approximately 0.6 ps. Even after the recovery of the dimerization, a fluctuation is still observed, probably because of a domain-wall soliton. The fluctuation gradually dissipates with a time constant of approximately 2.3 ps. Direct observation of the dimerization process reveals the true dynamics of the photoinduced cooperative phenomenon within this system.

  5. Photoinduced charge and energy transfer in molecular wires.

    PubMed

    Gilbert, Mélina; Albinsson, Bo

    2015-02-21

    Exploring charge and energy transport in donor-bridge-acceptor systems is an important research field which is essential for the fundamental knowledge necessary to develop future applications. These studies help creating valuable knowledge to respond to today's challenges to develop functionalized molecular systems for artificial photosynthesis, photovoltaics or molecular scale electronics. This tutorial review focuses on photo-induced charge/energy transfer in covalently linked donor-bridge-acceptor (D-B-A) systems. Of utmost importance in such systems is to understand how to control signal transmission, i.e. how fast electrons or excitation energy could be transferred between the donor and acceptor and the role played by the bridge (the "molecular wire"). After a brief description of the electron and energy transfer theory, we aim to give a simple yet accurate picture of the complex role played by the bridge to sustain donor-acceptor electronic communication. Special emphasis is put on understanding bridge energetics and conformational dynamics effects on the distance dependence of the donor-acceptor electronic coupling and transfer rates. Several examples of donor-bridge-acceptor systems from the literature are described as a support to the discussion. Finally, porphyrin-based molecular wires are introduced, and the relationship between their electronic structure and photophysical properties is outlined. In strongly conjugated porphyrin systems, limitations of the existing electron transfer theory to interpret the distance dependence of the transfer rates are also discussed. PMID:25212903

  6. Photoinduced Oxidative DNA Damage Revealed by an Agarose Gel Nicking Assay: A Biophysical Chemistry Laboratory Experiment

    NASA Astrophysics Data System (ADS)

    Shafirovich, Vladimir; Singh, Carolyn; Geacintov, Nicholas E.

    2003-11-01

    Oxidative damage of DNA molecules associated with electron-transfer reactions is an important phenomenon in living cells, which can lead to mutations and contribute to carcinogenesis and the aging processes. This article describes the design of several simple experiments to explore DNA damage initiated by photoinduced electron-transfer reactions sensitized by the acridine derivative, proflavine (PF). A supercoiled DNA agarose gel nicking assay is employed as a sensitive probe of DNA strand cleavage. A low-cost experimental and computer-interfaced imaging apparatus is described allowing for the digital recording and analysis of the gel electrophoresis results. The first experiment describes the formation of direct strand breaks in double-stranded DNA induced by photoexcitation of the intercalated PF molecules. The second experiment demonstrates that the addition of the well-known electron acceptor, methylviologen, gives rise to a significant enhancement of the photochemical DNA strand cleavage effect. This occurs by an electron transfer step to methylviologen that renders the inital photoinduced charge separation between photoexcited PF and DNA irreversible. The third experiment demonstrates that the action spectrum of the DNA photocleavage matches the absorption spectrum of DNA-bound, intercalated PF molecules, which differs from that of free PF molecules. This result demonstrates that the photoinduced DNA strand cleavage is initiated by intercalated rather than free PF molecules.

  7. Photoinduced mass transport in azo compounds

    NASA Astrophysics Data System (ADS)

    Klismeta, K.; Teteris, J.; Aleksejeva, J.

    2013-12-01

    The photoinduced changes of optical properties in azobenzene containing compound thin films were studied under influence of polarized and non-polarized 532 nm laser light. Under influence of light azo compounds experience trans-cis isomerisation process, that can be observed in the absorbance spectrum of the sample. If the light is linearly polarized, molecules align perpendicularly to the electric field vector and as a result photoinduced dichroism and birefringence is obtained. If a known lateral polarization modulation of the light beam is present, mass transport of the azobenzene containing compound occurs. By measuring the surface relief with a profilometer the direction of mass transport can be determined. The studies of this work show that direct holographic recording of surface relief gratings can be used in optoelectronics, telecommunications and data storage.

  8. Photoinduced Charge and Energy Transfer Processes in Molecular Aggregates

    SciTech Connect

    John F. Endicott

    2009-10-20

    This project involved the experimental probing of the electronic excited states generated by photoinduced (center-to-center) electron and energy transfer processes in several classes of transition metal donor/acceptor (D/A) complexes. Some of the general properties inferred from these studies should be useful in the design of new systems for energy conversion applications. Pursuit of the project goals has involved the determination of electron transfer efficiencies and the detailed study of variations in the electronic spectra of D/A complexes. This has resulted in the study of some very fundamental issues of photoinduced charge transfer and the identification of some of the constraints on its efficiency. The experimental studies of the competition between the degradative non-radiative unimolecular relaxation of transition metal excited states and their transfer of charge from these excited states to external acceptors have involved a range of techniques such as transient decay kinetics, photoacoustic calorimetry and transient or stationary state spectroscopy. The substrates synthesized for these studies were selected to provide model systems, or series of model systems to probe the validity of models of electronic excited states and their reactivity. The work during the last few years has focused largely, but not exclusively, on the use of emission spectral band shapes to probe the properties of charge transfer (CT) excited states. Bandshape variations are one of the very few approaches for systematically probing electronic excited states and good band shape resolution is necessary in order to gain information about the structural variations that correlate with excited state reactivity. Differences in molecular structure correlate with differences in chemical reactivity, and the variations in emission bandshapes are well known to relate to variations in the molecular structural differences between the excited and ground electronic states. However, it is has been

  9. Nature and mechanism of the photoinduced spin transition in [Fe(PM-BiA){sub 2}(NCS){sub 2}

    SciTech Connect

    Ichiyanagi, K.; Hebert, J.; Toupet, L.; Cailleau, H.; Collet, E.

    2006-02-01

    We report the investigation of a prototype cooperative photoinduced spin transition in [Fe(PM-BiA){sub 2}(NCS){sub 2}] by x-ray diffraction. The structural rearrangement accompanying the change of an electronic state between the low spin and the photoinduced out-of-equilibrium high spin phases is similar to the one occurring around the phase transition at thermal equilibrium. The cooperative behavior of the light-induced optical hysteresis and light-induced thermal hysteresis phenomena investigated here show a strong similarity with thermal hysteresis around first-order phase transitions, since they are driven by a domain nucleation process.

  10. Photoinduced reorientation phenomena in dyed liquid crystals: recent steps toward a complete understanding of the underlying mechanism

    NASA Astrophysics Data System (ADS)

    Marrucci, Lorenzo

    2002-12-01

    A survey of recent results of experiments aimed at understanding the basic mechanism of the photoinduced reorientation phenomena in dye-doped liquid crystals is presented. In particular, I shall focus on experiments based on the isotopic substitution of hydrogen atoms with deuterium in dye molecules, which have shown an unexpected enhancement of the photoinduced reorientation effect by a factor two. The isotopic substitution also changes the dye excited state lifetime and orientational diffusion times. These results are in good agreement with the model proposed for the effect, and confirm the hypothesis that the active photoexcited state in the photoinduced reorientation phenomena is simply the first-excited singlet electronic state of dye molecules.

  11. Photoinduced charge separation and recombination: The influence of medium on rates and energetics

    NASA Astrophysics Data System (ADS)

    Wasielewski, M. R.; Gaines, G. L.; Oneil, M. P.; Svec, W. A.; Niemczyk, M. P.

    Recent interest in the role of the solvent in electron transfer reactions has focused on ultrafast photoinduced electron transfers, highlighted by investigations into the primary events of bacterial photosynthesis. Rates of photoinduced charge separation proceeding from the lowest excited singlet state in 14 fixed-distance porphyrin triptycene acceptor molecules were measured in 2-methyl tetrahydrofuran glass at 77 K. Analysis of the rate data as a function of free energy of reaction reveals that the ion-pair state of the oxidized donor and reduced acceptor is destabilized in a rigid glass medium by 0.8 eV relative to the ion-pair state energy determined from the sum of the one-electron redox potentials for the donor and acceptor in polar liquids. The measured value of this destabilization energy agrees remarkably well with predictions based on the dielectric continuum model of the solvent. From the maximum of the rate vs free energy profile for photoinduced charge separation, the total reorganization energy of the reaction is 0.6 eV. Analysis of this data shows that the solvent reorganization energy is 0.3 eV, while the internal nuclear reorganization energy of the donor-acceptor molecules is 0.3 eV.

  12. Photoinduced bulk-surface dynamics: time resolved two photon photoemission signals at semiconductor surfaces

    NASA Astrophysics Data System (ADS)

    Ramakrishna, S.; Willig, F.; Knorr, A.

    2004-06-01

    A free particle theory of photoinduced bulk-surface dynamics at semiconductor surfaces is developed wherein relaxation processes arising from electron-electron and electron-phonon scattering are treated phenomenologically. The role played by bulk-surface dynamics in the thermalization and cooling processes of the bulk and the complementary issue of how bulk dynamics influences the surface state occupancy are both studied. Time resolved 2PPE spectra is analysed both in the context of pure bulk as well as combined bulk-surface dynamics and its relation to the time dependent populations in the conduction band and surface states is discussed.

  13. [Photoinduced reduction of NAD(P) in the cells of green sulfur bacteria].

    PubMed

    Ivanovskiĭ, R N

    1975-01-01

    The spectrum of a photoinduced increase in luminescence of the cells of the gree sulphur bacterium Chlorobium limicola f. thiosulfatophilum, within the range of 400 to 520 nm, was found to correspond to the spectrum of luminescence of NADH in the protein-bound form. Photoinduced reduction of NAD(P) in green bacteria, contrary to purple bacteria, is not susceptible to the action of p-chlorocarbonylcyanide phenlhydrazone which uncouples photophosphorylation. Therefore, in Chlorobium limicola f. thiosulfatophilum, NAD(P) is reduced by direct non-cyclic transport of electrons via the photosynthetic chain. NAD(P)H is utilized mainly in the system of CO2 fixation; the process is inhibited by fluoroacetate, and the inhibition is eliminated by substrates of the cycle of carboxylic acids. PMID:2843

  14. Photoinduced DNA Interstrand Cross-Link Formation by Naphthalene Boronates via a Carbocation.

    PubMed

    Wang, Yibin; Lin, Zechao; Fan, Heli; Peng, Xiaohua

    2016-07-18

    Most photoinduced DNA cross-link formation by a bifunctional aryl derivative is through a bisquinone methide. DNA cross-linking via a bisarylcarbocation remains a less explored area. We designed and synthesized a series of naphthalene boronates that produce DNA interstrand cross-links via a carbocation upon UV irradiation. A free radical was generated from the naphthalene boronates with 350 nm irradiation and further converted to a carbocation by electron transfer. The activation mechanism was determined using the orthogonal traps, 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) and methoxyamine that react with either the free radical or the carbocation but not both. This represents a novel example of photoinduced DNA cross-link formation via carbocations generated from a bisaryl derivative. This work provides information useful for the design of novel photoactivated DNA cross-linking agents. PMID:27189512

  15. Photoinduced spinodal decomposition in stratifying solutions

    NASA Astrophysics Data System (ADS)

    Bunkin, F. V.; Podgaetskii, V. I.; Semin, V. N.

    1988-01-01

    The effect of photoinduced spinodal decomposition in stratifying solutions is examined with particular reference to experimental results obtained for an aqueous solution of butyl Cellosolve of critical concentration (30.14 percent by mass). At the late stages of spinodal decomposition, the coalescence of similar microheterophase inhomogeneities leads to the formation of small-scale (up to 5 microns) grains of each of the phases, which are then grouped into larger-scale (up to 100 microns) segregations. Such multilevel self-organization of the stratifying phases leads to the formation of a granular-cellular structure. This effect can be used for the quick interruption of chemical reactions in a stratifying solution.

  16. Towards efficient photoinduced charge separation in carbon nanodots and TiO2 composites in the visible region.

    PubMed

    Sun, Mingye; Qu, Songnan; Ji, Wenyu; Jing, Pengtao; Li, Di; Qin, Li; Cao, Junsheng; Zhang, Hong; Zhao, Jialong; Shen, Dezhen

    2015-03-28

    In this work, photoinduced charge separation behaviors in non-long-chain-molecule-functionalized carbon nanodots (CDs) with visible intrinsic absorption (CDs-V) and TiO2 composites were investigated. Efficient photoinduced electron injection from CDs-V to TiO2 with a rate of 8.8 × 10(8) s(-1) and efficiency of 91% was achieved in the CDs-V/TiO2 composites. The CDs-V/TiO2 composites exhibited excellent photocatalytic activity under visible light irradiation, superior to pure TiO2 and the CDs with the main absorption band in the ultraviolet region and TiO2 composites, which indicated that visible photoinduced electrons and holes in such CDs-V/TiO2 composites could be effectively separated. The incident photon-to-current conversion efficiency (IPCE) results for the CD-sensitized TiO2 solar cells also agreed with efficient photoinduced charge separation between CDs-V and the TiO2 electrode in the visible range. These results demonstrate that non-long-chain-molecule-functionlized CDs with a visible intrinsic absorption band could be appropriate candidates for photosensitizers and offer a new possibility for the development of a well performing CD-based photovoltaic system. PMID:25721932

  17. Origin of the photo-induced changes in hydrogenated amorphous silicon

    NASA Astrophysics Data System (ADS)

    Adler, D.

    1983-07-01

    The electronic properties of hydrogenated amorphous silicon films are discussed in detail. Particular attention is paid to the changes induced by photogeneration of excess free carriers. Previous models which have been proposed to account for such effects are classified and criticized. An alternative explanation, which is based on the unique electronic structure of hydrogenated amorphous silicon, is proposed and analyzed. In this model, no new defects are created by the light, but rather the photo-induced effects follow from a metastable trapping of the excess free carriers at charged spinless defects which are present at equilibrium.

  18. Photoinduced valley-polarized current of layered MoS2 by electric tuning.

    PubMed

    Yu, Yunjin; Zhou, Yanfeng; Wan, Langhui; Wang, Bin; Xu, Fuming; Wei, Yadong; Wang, Jian

    2016-05-01

    A photoinduced current of a layered MoS2-based transistor is studied from first-principles. Under the illumination of circular polarized light, a valley-polarized current is generated, which can be tuned by the gate voltage. For monolayer MoS2, the valley-polarized spin-up (down) electron current at K ([Formula: see text]) points is induced by the right (left) circular polarized light. The valley polarization is found to reach +1.0 (-1.0) for the valley current that carried such a K ([Formula: see text]) index. For bilayer MoS2, the spin-up (down) current can be induced at both K and [Formula: see text] valleys by the right (left) circular light. In contrast to monolayer MoS2, the photoinduced valley polarization shows asymmetric behavior upon reversal of the gate voltage. Our results show that the valley polarization of the photoinduced current can be modulated by the circular polarized light and the gate voltage. All the results can be well understood using a simple kp model. PMID:27004920

  19. Combined experimental and theoretical study on photoinduced toxicity of an anthraquinone dye intermediate to Daphnia magna.

    PubMed

    Wang, Ying; Chen, Jingwen; Lin, Jing; Wang, Zhen; Bian, Haitao; Cai, Xiyun; Hao, Ce

    2009-04-01

    The toxicity of chemicals can be enhanced by light through two photochemical pathways: Photomodification to more toxic substances and photosensitization. In the present study, the reactive oxygen species (ROS) mechanism for photoinduced acute toxicity of 1-amino-2,4-dibromoanthraquinone (ADBAQ) to Daphnia magna was clarified by experiment and theoretical calculation. The results of the present study show that ADBAQ exhibited high toxicity to D. magna under simulated solar radiation (SSR), with a median effective concentration of 1.23 +/- 0.19 nM (mean +/- standard deviation). The photomodified ADBAQ (mixtures of ADBAQ and its photoproducts) was less phototoxic than the intact ADBAQ. The SSR-only or ADBAQ-only treatments did not affect the ROS level in D. magna, whereas increased ROS levels were observed in the presence of SSR and ADBAQ. The ROS in vivo were determined by measuring the fluorescence of 2',7'-dichlorofluorescein, which is a useful technique to assess toxicity of chemicals to aquatic organisms. The antioxidants, including vitamin C, vitamin E, and beta-carotene, decreased the photoinduced oxidative damage to D. magna, probably by scavenging ROS. These experimental results demonstrate that photosensitization is the potential mechanism of photoinduced toxicity of ADBAQ to D. magna. Proposed phototoxic pathways of ADBAQ were elucidated by means of time-dependent density functional theory. The theoretical calculation indicates that superoxide anion and singlet oxygen are able to be generated through electron transfer or energy transfer in the photosensitization reactions. PMID:19391687

  20. Phase diagram of the ultrafast photoinduced insulator-metal transition in vanadium dioxide

    NASA Astrophysics Data System (ADS)

    Cocker, T. L.; Titova, L. V.; Fourmaux, S.; Holloway, G.; Bandulet, H.-C.; Brassard, D.; Kieffer, J.-C.; El Khakani, M. A.; Hegmann, F. A.

    2012-04-01

    We use time-resolved terahertz spectroscopy to probe the ultrafast dynamics of the insulator-metal phase transition induced by femtosecond laser pulses in a nanogranular vanadium dioxide (VO2) film. Based on the observed thresholds for characteristic transient terahertz dynamics, a phase diagram of critical pump fluence versus temperature for the insulator-metal phase transition in VO2 is established for the first time over a broad range of temperatures down to 17 K. We find that both Mott and Peierls mechanisms are present in the insulating state and that the photoinduced transition is nonthermal. We propose a critical-threshold model for the ultrafast photoinduced transition based on a critical density of electrons and a critical density of coherently excited phonons necessary for the structural transition to the metallic state. As a result, evidence is found at low temperatures for an intermediate metallic state wherein the Mott state is melted but the Peierls distortion remains intact, consistent with recent theoretical predictions. Finally, the observed terahertz conductivity dynamics above the photoinduced transition threshold reveal nucleation and growth of metallic nanodomains over picosecond time scales.

  1. Photoinduced valley-polarized current of layered MoS2 by electric tuning

    NASA Astrophysics Data System (ADS)

    Yu, Yunjin; Zhou, Yanfeng; Wan, Langhui; Wang, Bin; Xu, Fuming; Wei, Yadong; Wang, Jian

    2016-05-01

    A photoinduced current of a layered MoS2-based transistor is studied from first-principles. Under the illumination of circular polarized light, a valley-polarized current is generated, which can be tuned by the gate voltage. For monolayer MoS2, the valley-polarized spin-up (down) electron current at K ({K}\\prime ) points is induced by the right (left) circular polarized light. The valley polarization is found to reach +1.0 (-1.0) for the valley current that carried such a K ({K}\\prime ) index. For bilayer MoS2, the spin-up (down) current can be induced at both K and {K}\\prime valleys by the right (left) circular light. In contrast to monolayer MoS2, the photoinduced valley polarization shows asymmetric behavior upon reversal of the gate voltage. Our results show that the valley polarization of the photoinduced current can be modulated by the circular polarized light and the gate voltage. All the results can be well understood using a simple kp model.

  2. Infrared-photoinduced-absorption studies in soluble trans-polyacetylene

    NASA Technical Reports Server (NTRS)

    Dorsinville, R.; Tubino, R.; Krimchansky, S.; Alfano, R. R.; Birman, J. L.

    1985-01-01

    The observation of photoinduced excitations in trans-polyacetylene in its liquid form in the frequency range from 2000 to 6000/cm is reported on. These measurements strongly suggest that transpolyacetylene is capable of supporting charged solitons even in solution.

  3. Generalized model for photoinduced surface structure in amorphous thin films.

    PubMed

    Lu, Chao; Recht, Daniel; Arnold, Craig

    2013-09-01

    We present a generalized model to explain the spatial and temporal evolution of photoinduced surface structure in photosensitive amorphous thin films. The model describes these films as an incompressible viscous fluid driven by a photoinduced pressure originating from dipole rearrangement. This derivation requires only the polarizability, viscosity and surface tension of the system. Using values of these physical parameters, we check the validity of the model by fitting to experimental data of As2S3 and demonstrating good agreement. PMID:25166680

  4. Cobalt(III) tetraaza-macrocyclic complexes as efficient catalyst for photoinduced hydrogen production in water: Theoretical investigation of the electronic structure of the reduced species and mechanistic insight.

    PubMed

    Gueret, Robin; Castillo, Carmen E; Rebarz, Mateusz; Thomas, Fabrice; Hargrove, Aaron-Albert; Pécaut, Jacques; Sliwa, Michel; Fortage, Jérôme; Collomb, Marie-Noëlle

    2015-11-01

    We recently reported a very efficient homogeneous system for visible-light driven hydrogen production in water based on the cobalt(III) tetraaza-macrocyclic complex [Co(CR)Cl2](+) (1) (CR=2,12-dimethyl-3,7,11,17-tetra-azabicyclo(11.3.1)-heptadeca-1(17),2,11,13,15-pentaene) as a noble metal-free catalyst, with [Ru(II)(bpy)3](2+) (Ru) as photosensitizer and ascorbate/ascorbic acid (HA(-)/H2A) as a sacrificial electron donor and buffer (PhysChemChemPhys 2013, 15, 17544). This catalyst presents the particularity to achieve very high turnover numbers (TONs) (up to 1000) at pH 4.0 at a relative high concentration (0.1mM) generating a large amount of hydrogen and having a long term stability. A similar activity was observed for the aquo derivative [Co(III)(CR)(H2O)2](3+) (2) due to substitution of chloro ligands by water molecule in water. In this work, the geometry and electronic structures of 2 and its analog [Zn(II)(CR)Cl](+) (3) derivative containing the redox innocent Zn(II) metal ion have been investigated by DFT calculations under various oxidation states. We also further studied the photocatalytic activity of this system and evaluated the influence of varying the relative concentration of the different components on the H2-evolving activity. Turnover numbers versus catalyst (TONCat) were found to be dependent on the catalyst concentration with the highest value of 1130 obtained at 0.05 mM. Interestingly, the analogous nickel derivative, [Ni(II)(CR)Cl2] (4), when tested under the same experimental conditions was found to be fully inactive for H2 production. Nanosecond transient absorption spectroscopy measurements have revealed that the first electron-transfer steps of the photocatalytic H2-evolution mechanism with the Ru/cobalt tetraaza/HA(-)/H2A system involve a reductive quenching of the excited state of the photosensitizer by ascorbate (kq=2.5×10(7) M(-1) s(-1)) followed by an electron transfer from the reduced photosensitizer to the catalyst (ket=1.4×10(9) M

  5. Direct laser photo-induced fluorescence determination of bisphenol A.

    PubMed

    Maroto, Alicia; Kissingou, Prosnick; Diascorn, Alexandre; Benmansour, Badr; Deschamps, Laure; Stephan, Ludovic; Cabon, Jean-Yves; Giamarchi, Philippe

    2011-11-01

    Classical photo-induced fluorescence methods are conducted in two steps: a UV irradiation step in order to form a photo-induced compound followed by its fluorimetric determination. Automated flow injection methods are frequently used for these analyses. In this work, we propose a new method of direct laser photo-induced fluorescence analysis. This new method is based on direct irradiation of the analyte in a fluorimetric cell in order to form a photo-induced fluorescent compound and its direct fluorimetric detection during a short irradiation time. Irradiation is performed with a tuneable Nd:YAG laser to select the optimal excitation wavelength and to improve the specificity. It has been applied to the determination of bisphenol A, an endocrine disrupter compound that may be a potential contaminant for food. Irradiation of bisphenol A at 230 nm produces a photo-induced compound with a much higher fluorescence quantum yield and specific excitation/emission wavelengths. In tap water, the fluorescence of bisphenol A increases linearly versus its concentration and, its determination by direct laser photo-induced fluorescence permits to obtain a low limit of detection of 17 μg L(-1). PMID:21904798

  6. Photoinduced electro-optics measurements of biosilica transformation to cristobalite

    SciTech Connect

    Fuchs, Ido; Aluma, Yaniv; Ilan, Micha; Kityk, Iwan; Mastai, Yitzhak

    2015-03-15

    In this paper we studied the photoinduced electro optics effects in the thermal transformation process of biosilica to cristobalite, at a relatively low temperature and ambient pressure. This process was characterized by a variety of standards techniques with emphasis on linear electro optic effect measurements. Overall we demonstrated that photoinduced electro optics measurements are very sensitive to the transformation from amorphous structure of silica in the natural sponge samples to laminar string morphology of cristobalite. With this technique we could probe the change in the samples chirality from achiral bio silica to chiral cristobalite structure. Furthermore it is shown that natural biosilica have photoinduced linear electro optics respond indicating the chiral natural of biosilica. - Graphical abstract: The phase transformation of biosilica from marine sponges to Cristobalite under thermal treatment was investigated using photoinduced electro optics measurements. The figure shows the changes of the electro-optic coefficient of cristobalite and biosilica. - Highlights: • We examine phase transformation of biosilica. • We report transition from amorphous biosilica to crystalline Cristobalite. • Biosilica transformation to Cristobalite at temperature of 850 °C. • Biosilica transformation is studied with photoinduced measurements. • We examine changes in the photoinduced linear electro optics properties.

  7. Photoinduced nonadiabatic decay and dissociation dynamics of dimethylnitramine.

    PubMed

    Zhuang, Xuhui; Wang, Jun; Lan, Zhenggang

    2013-06-13

    Dimethylnitramine (DMNA) is a prototype system used in the investigation of the unimolecular decomposition mechanism of the nitramine-compound family. The photoinduced excited-state nonadiabatic processes and successive unimolecular dissociation of DMNA were investigated by trajectory surface-hopping dynamics at the semiempirical OM2/MRCI level. Two S1/S0 conical intersections (CI01α and CI01β) were found to play essential roles in the nonadiabatic decay dynamics of DMNA. After the S1 → S0 decay, the excess kinetic energy finally results in the cleavage of the N-N bond in the ground electronic state. The two reaction channels through CI01α and CI01β show differences in molecular motions and decay features. The trajectories passing CI01α can hop one or several times, and the intramolecular vibrational energy transfer in the ground state takes place before dissociation, whereas trajectories following the CI01β channel mainly dissociate directly after only one S1 → S0 hop. PMID:23672370

  8. Highly Twisted Triarylamines for Photoinduced Intramoleculer ChargeTransfer

    SciTech Connect

    Chudomel, J. M.; Yang, B. Q.; Barnes, M. D.; Achermann, M.; Mague, J. T.; Lahti, P. M.

    2011-08-04

    9-(N,N-Dianisylamino)anthracene (9DAAA), 9-(N,N-dianisylamino)dinaphth([1,2-a:2'-1'-j]-anthracene (9DAAH), and 9,10-bis(N,N-dianisylamino)anthracene (910BAA) were synthesized as highly twisted triarylamines with potential for photoexcited internal charge transfer. Crystallography of 9DAAA shows its dianisylamino group to be twisted nearly perpendicular to its anthracene unit, similar to a report for 910BAA. The solution fluorescence spectra show strong bathochromic shifts for each of the three molecular systems with strongly decreased quantum efficiency in higher polarity solvents. Solution-phase (ensemble) time-resolved photoluminescence measurements show up to 4-fold decreases in fluorescence lifetime in acetonitrile compared to hexane. The combined results are consistent with photoinduced, transient intramolecular charge-transfer from the bis-anisylamine unit to the polycyclic aromatic unit. Computational modeling is in accord with intramolecular transfer of electron density from the bis-anisylamino unit to the anthracene, based on in comparisons of HOMO and LUMO.

  9. Photoinduced degradation of organic solar cells with different microstructures

    NASA Astrophysics Data System (ADS)

    Lu, Chun-Xi; Yan, Peng; Wang, Jin-Ze; Liu, Ai-Min; Song, De; Jiang, Chao

    2014-08-01

    An in situ measurement setup is established to investigate the photoinduced degradation effects in a controllable inert gas ambient environment for the two different microstructures of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyricacid methyl ester (PCBM) bulk-heterojunction organic solar cells. The two devices are fabricated with the solvent vapor drying process followed by a thermal annealing (vapor drying device) and only a normal thermal annealing process (control device), respectively. Their power conversion efficiencies (PCEs) and aging features are compared. Their different degradation behaviors in light absorption are confirmed. In addition, irradiation-induced changes in both nanostructure and surface morphology of the P3HT:PCBM blend films treated with two different fabrication processes are observed through scanning electron microscopy and atomic force microscopy. Aggregated bulbs are observed at the surfaces for control devices after light irradiation for 50 h, while the vapor drying devices exhibit smooth film surfaces, and the corresponding device features are not easy to degrade under the aging measurement. Thus the devices having solvent vapor drying and thermal annealing show better device stabilities than those having only the thermal annealing process.

  10. 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

  11. Study of photoinduced absorption by the method of modified laser photothermal radiometry

    SciTech Connect

    Skvortsov, L A; Maksimov, E M; Tuchkov, A A

    2008-10-31

    The application of the method of modified laser photothermal radiometry for studying the photoinduced absorption in thin films is considered. The sensitivity of the method is estimated. The mechanism of induced near-IR absorption in titanium dioxide films is proposed and the nature of surface defects responsible for this process is explained. It is shown that kinetic equations describing monomolecular recombination are consistent with the experimental dependences for the thermal activation energy of defects equal to 0.17{+-}0.04 eV. (laser applications and other topics in quantum electronics)

  12. Photoinduced Reconfiguration Cycle in a Molecular Adsorbate Layer Studied by Femtosecond Inner-Shell Photoelectron Spectroscopy

    SciTech Connect

    Dachraoui, H.; Michelswirth, M.; Bartz, P.; Pfeiffer, W.; Heinzmann, U.; Siffalovic, P.; Schaefer, C.; Schnatwinkel, B.; Mattay, J.; Drescher, M.

    2011-03-11

    A time-resolved study of core-level chemical shifts in a monolayer of aromatic molecules reveals complex photoinduced reaction dynamics. The combination of electron spectroscopy for chemical analysis and ultrashort pulse excitation in the extreme ultraviolet allows performing time-correlated 4d-core-level spectroscopy of iodine atoms that probe the local chemical environment in the adsorbate molecule. The selectivity of the method unveils metastable molecular configurations that appear about 50 ps after the excitation and are efficiently quenched back to the ground state.

  13. Photoinduced cytotoxicity by a platinum diimine complex employing magnetite-silica nanocomposites as delivery vehicles.

    PubMed

    Zhang, Zhigang; Li, Haisha; Dai, Ruihui; Chai, Aiyun

    2015-10-01

    Tartaric acid-modified core-shell magnetite-silica nanocomposites were prepared by a sol-gel method, and characterized by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy and dynamic light scattering. Then the nanocomposites were employed as carriers of a photoactive platinum diimine complex. Photoinduced cytotoxicity by the photosensitizer-loaded nanocomposites in different human carcinoma cells has been studied by cell viability assay. The results suggest that the as-synthesized nanocomposites have good stability in water, and the cytotoxicity induced by the platinum diimine complex in red light can be significantly enhanced when the photosensitizer is loaded with the magnetic nanocomposites. PMID:26315847

  14. Photo-induced conductance fluctuations in mesoscopic Ge/Si systems with quantum dots

    SciTech Connect

    Stepina, N. P.; Dvurechenskii, A. V.; Nikiforov, A. I.; Moers, J.; Gruetzmacher, D.

    2014-08-20

    We study the evolution of electron transport in strongly localized mesoscopic system with quantum dots under small photon flux. Exploring devices with narrow transport channels lead to the observation of giant fluctuations of the photoconductance, which is attributed to the strong dependence of hopping current on the filling of dots by holes. In our experiments, single-photon mode operation is indicated by the linear dependence of the frequency of photo-induced fluctuations on the light intensity and the step-like response of conductance on the pulse excitation. The effect of the light wavelength, measurement temperature, size of the conductive channel on the device efficiency are considered.

  15. Photoinduced stiffening and photoplastic effect of ZnS individual nanobelt in nanoindentation

    SciTech Connect

    Zheng, X. J.; Yu, G. C.; Chen, Y. Q.; Mao, S. X.; Zhang, T.

    2010-11-15

    The photoinduced stiffening (PIS) and photoplastic effect (PPE) of ZnS individual nanobelt (NB) were observed by using a nanoindenter in conjunction with an incident ultraviolet (UV) light source system. The results show that the elastic modulus and hardness of ZnS individual NB under UV illumination are at least 32% and 20% larger than those in darkness. The mechanisms of PIS and PPE are interpreted by the increase in electronic strain and Peierls barrier due to the photogeneration of free carriers in ZnS individual NB. The research may offer useful guidelines to the application of optoelectronic devices based on individual nanostructures.

  16. Photoinduced electron transfer between the cationic complexes Ru(NH3)5pz2+ and trans-RuCl([15]aneN4)NO2+ mediated by phosphate ion: visible light generation of nitric oxide for biological targets.

    PubMed

    da Silva, Roberto S; Marchesi, Mario S P; Khin, Chosu; Lunardi, Claure N; Bendhack, Lusiane M; Ford, Peter C

    2007-06-21

    The photochemical behavior of the tetraazamacrocyclic complex trans-RuCl([15]ane)(NO)2+ (RuNO2+) in a 10 mM phosphate buffer solution, pH 7.4, and in the presence of Ru(NH3)5pz2+ (Rupz2+) is reported. Irradiation (436 nm) of an aqueous solution containing both cationic complexes as PF6- salts labilizes NO from RuNO2+ with a quantum yield (phiNO) dependent on the concentration of Rupz2+ with a maximum value of phiNO (1.03(11)x10(-3) einstein mol-1) found for a solution with equimolar concentrations (5x10(-5) M) of the two complexes in phosphate buffer solution. The quantitative behavior of this system suggests that the two cations undergo preassociation such that photoexcitation of the visible absorbing Rupz2+ is followed by electron or energy transfer to RuNO2+, which does not absorb appreciably at the excitation wavelength, and this leads to NO release from the reduced nitrosyl complex. Notably, the NO release was not seen in the absence of phosphate buffer; thus, it appears that phosphate ions mediate NO generation, perhaps by facilitating formation of a supramolecular complex between the two ruthenium cations. Reexamination of the cyclic voltammetry of Rupz2+ showed that the electrochemical behavior of this species is also affected by the presence of the phosphate buffer. PMID:17439277

  17. sp3 domain in graphite by visible light and photoinduced phase transitions

    NASA Astrophysics Data System (ADS)

    Nasu, K.

    2010-06-01

    Photoinduced structural phase transition (PSPT)s are reviewed in connection with recent experimental results. There are two key concepts: the hidden multi-stability of the ground state, and the proliferations of optically excited states. Taking the ionic (I)-neutral (N) phase transition in an organic charge-transfer (CT) crystal TTF-CA, as an example, we, briefly look back the essence of its PSPT, in terms of the CT exciton and the N-domain proliferation. Next, we are concerned with the discovery of a new photoinduced phase with inter-layer σ-bonds in a graphite. We will see the mechanism of this nonequilibrium phase transition, in terms of the proliferation of photo-generated inter-layer CT excitations in the visible region. At the Franck-Condon state, the resultant electron-hole pair is quite unstable, being easily dissipated into the two-dimensional electronic continuum, as plus and minus free carriers. However, by a small probability, the electron and the hole are bound as an inter-layer CT exciton. This exciton self-localizes, contracting the inter-layer distance and buckling the six membered ring of graphite, only around it. Thus a tiny sp3 nano-domain appears.

  18. Exploring Photoinduced Excited State Evolution in Heterobimetallic Ru(II)-Co(III) Complexes.

    PubMed

    Kuhar, Korina; Fredin, Lisa A; Persson, Petter

    2015-06-18

    Quantum chemical calculations provide detailed theoretical information concerning key aspects of photoinduced electron and excitation transfer processes in supramolecular donor-acceptor systems, which are particularly relevant to fundamental charge separation in emerging molecular approaches for solar energy conversion. Here we use density functional theory (DFT) calculations to explore the excited state landscape of heterobimetallic Ru-Co systems with varying degrees of interaction between the two metal centers, unbound, weakly bound, and tightly bound systems. The interplay between structural and electronic factors involved in various excited state relaxation processes is examined through full optimizations of multiple charge/spin states of each of the investigated systems. Low-energy relaxed heterobimetallic states of energy transfer and excitation transfer character are characterized in terms of energy, structure, and electronic properties. These findings support the notion of efficient photoinduced charge separation from a Ru(II)-Co(III) ground state, via initial optical excitation of the Ru-center, to low-energy Ru(III)-Co(II) states. The strongly coupled system has significant involvement of the conjugated bridge, qualitatively distinguishing it from the other two weakly coupled systems. Finally, by constructing potential energy surfaces for the three systems where all charge/spin state combinations are projected onto relevant reaction coordinates, excited state decay pathways are explored. PMID:25719556

  19. Ultrafast dynamics during the photoinduced phase transition in VO2

    NASA Astrophysics Data System (ADS)

    Wegkamp, Daniel; Stähler, Julia

    2015-12-01

    The phase transition of VO2 from a monoclinic insulator to a rutile metal, which occurs thermally at TC = 340 K, can also be driven by strong photoexcitation. The ultrafast dynamics during this photoinduced phase transition (PIPT) have attracted great scientific attention for decades, as this approach promises to answer the question of whether the insulator-to-metal (IMT) transition is caused by electronic or crystallographic processes through disentanglement of the different contributions in the time domain. We review our recent results achieved by femtosecond time-resolved photoelectron, optical, and coherent phonon spectroscopy and discuss them within the framework of a selection of latest, complementary studies of the ultrafast PIPT in VO2. We show that the population change of electrons and holes caused by photoexcitation launches a highly non-equilibrium plasma phase characterized by enhanced screening due to quasi-free carriers and followed by two branches of non-equilibrium dynamics: (i) an instantaneous (within the time resolution) collapse of the insulating gap that precedes charge carrier relaxation and significant ionic motion and (ii) an instantaneous lattice potential symmetry change that represents the onset of the crystallographic phase transition through ionic motion on longer timescales. We discuss the interconnection between these two non-thermal pathways with particular focus on the meaning of the critical fluence of the PIPT in different types of experiments. Based on this, we conclude that the PIPT threshold identified in optical experiments is most probably determined by the excitation density required to drive the lattice potential change rather than the IMT. These considerations suggest that the IMT can be driven by weaker excitation, predicting a transiently metallic, monoclinic state of VO2 that is not stabilized by the non-thermal structural transition and, thus, decays on ultrafast timescales.

  20. Nonlinear fluorescence probe using photoinduced charge separation (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Mochizuki, Kentaro; Shi, Lanting; Mizukami, Shin; Yamanaka, Masahito; Tanabe, Mamoru; Gong, Wei-Tao; Palonpon, Almar F.; Kawano, Shogo; Kawata, Satoshi; Kikuchi, Kazuya; Fujita, Katsumasa

    2015-08-01

    Two-photon excitation microscopy (TPEM) provides spatial resolution beyond the optical diffraction limit using the nonlinear response of fluorescent molecules. One of the strong advantages of TPEM is that it can be performed using a laser-scanning microscope without a complicated excitation method or computational post-processing. However, TPEM has not been recognized as a super-resolution microscopy due to the use of near-infrared light as excitation source, which provides lower resolution than visible light. In our research, we aimed for the realization of nonlinear fluorescence response with visible light excitation to perform super-resolution imaging using a laser-scanning microscope. The nonlinear fluorescence response with visible light excitation is achieved by developing a probe which provides stepwise two-photon excitation through photoinduced charge separation. The probe named nitro-bisBODIPY consists of two fluorescent molecules (electron donor: D) and one electron acceptor (A), resulting to the structure of D-A-D. Excited by an incident photon, nitro-bisBODIPY generates a charge-separated pair between one of the fluorescent molecules and the acceptor. Fluorescence emission is obtained only when one more incident photon is used to excite the other fluorescent molecule of the probe in the charge-separated state. This stepwise two-photon excitation by nitro-bisBODIPY was confirmed by detection of the 2nd order nonlinear fluorescence response using a confocal microscope with 488 nm CW excitation. The physical model of the stepwise two-photon excitation was investigated by building the energy diagram of nitro-bisBODIPY. Finally, we obtained the improvement of spatial resolution in fluorescence imaging of HeLa cells using nitro-bisBODIPY.

  1. Photoinduced and chemical oxidation of coordinated imine to amide in isomeric osmium(II) complexes of N-arylpyridine-2-carboxaldimines. Synthesis, characterization, electron transfer properties, and structural studies.

    PubMed

    Ghosh, Amit K; Kamar, Kunal K; Paul, Parimal; Peng, Shie-Ming; Lee, Gene-Hsiang; Goswami, Sreebrata

    2002-12-01

    temperature magnetic moment of 3 corresponds to a t(2)(5) configuration for the osmium(III) center. EPR spectra of the amido complexes were recorded at 77 K in 1:1 dichloromethane-toluene glass, and they were anisotropic in nature. FAB mass spectra of 3 displayed intense peaks due to parent molecular ions. For example, the complex [OsBr(2)(HL(1))(L(1)O)], 3a, showed a strong peak at m/z 729 amu. The electronic spectrum of compound 3 consisted of a broad LMCT transition (ca. 525 nm; epsilon, 3000 M(-1) cm(-1)). The cyclic voltammogram of compound 3 consisted of two responses, one each on the positive and negative side of SCE, corresponding to Os(IV)/Os(III) (ca. 0.8V) and Os(III)/Os(II) (ca. -0.3V) couples, respectively. There has been a large cathodic shift of potential for the Os(III)/Os(II) couple in 3 in comparison to that in the parent complex, 1. The diamido compound [OsBr(2)(LO)(2)], 4, is diamagnetic and insoluble in common solvents. The X-ray structure determination of a representative sample, 4a, is reported. The molecule contains a C(2)-symmetry axis with bromide ions in relative cis positions. The Os-N(amide) bond lengths are considerably shorter than the Os-N(pyridine) lengths. All other bond lengths and angles fall within the expected range. PMID:12444777

  2. Dynamics of photoinduced cell plasma membrane injury.

    PubMed Central

    Thorpe, W P; Toner, M; Ezzell, R M; Tompkins, R G; Yarmush, M L

    1995-01-01

    We have developed a video microscopy system designed for real-time measurement of single cell damage during photolysis under well defined physicochemical and photophysical conditions. Melanoma cells cultured in vitro were treated with the photosensitizer (PS), tin chlorin e6 (SnCe6) or immunoconjugate (SnCe6 conjugated to a anti-ICAM monoclonal antibody), and illuminated with a 10 mW He/Ne laser at a 630 nm wavelength. Cell membrane integrity was assessed using the vital dye calcein-AM. In experiments in which the laser power density and PS concentration were varied, it was determined that the time lag before cell rupture was inversely proportional to the estimated singlet oxygen flux to the cell surface. Microscopic examination of the lytic event indicated that photo-induced lysis was caused by a point rupture of the plasma membrane. The on-line nature of this microscopy system offers an opportunity to monitor the dynamics of the cell damage process and to gain insights into the mechanism governing photolytic cell injury processes. Images FIGURE 2 FIGURE 3 FIGURE 6 FIGURE 7 PMID:7612864

  3. Photoinduced anchoring on a chalcogenide surface

    NASA Astrophysics Data System (ADS)

    Sheremet, N.; Kurioz, Yu.; Klebanov, M.; Lyubin, V.; Slyusarenko, K.; Reznikov, Yu.

    2012-05-01

    We present basic characteristics and a model of photoinduced anchoring of liquid crystals (LCs) on a chalcogenide surface. It was found that characteristics of the alignment strongly depend on the LC material for the same chalcogenide glass. The photoalignment is partially reversible and can be controlled by changing the light polarization direction. We propose a model in which the existence of dichroic units on the chalcogenide surface and competition between two mechanisms of the photoalignment is suggested. The first mechanism is related to the light-induced anisotropy on the chalcogenide surface and results in an easy orientation axes of a LC parallel to the polarization of the incident light. The second mechanism is attributed to an energy transfer from the dichroic units after the light absorption to the LC molecules adsorbed on the chalcogenide surface. The transferred energy causes polarization-sensitive desorption of the LC molecules from the chalcogenide surface and the light-induced easy orientation axis of a LC perpendicular to the incident light polarization. The competition between these mechanisms leads to the observed change of the direction of the easy axis with the exposure.

  4. Photoinduced carrier annihilation in silicon pn junction

    NASA Astrophysics Data System (ADS)

    Sameshima, Toshiyuki; Motoki, Takayuki; Yasuda, Keisuke; Nakamura, Tomohiko; Hasumi, Masahiko; Mizuno, Toshihisa

    2015-08-01

    We report analysis of the photo-induced minority carrier effective lifetime (τeff) in a p+n junction formed on the top surfaces of a n-type silicon substrate by ion implantation of boron and phosphorus atoms at the top and bottom surfaces followed by activation by microwave heating. Bias voltages were applied to the p+ boron-doped surface with n+ phosphorus-doped surface kept at 0 V. The values of τeff were lower than 1 × 10-5 s under the reverse-bias condition. On the other hand, τeff markedly increased to 1.4 × 10-4 s as the forward-bias voltage increased to 0.7 V and then it leveled off when continuous-wave 635 nm light was illuminated at 0.74 mW/cm2 on the p+ surface. The carrier annihilation velocity S\\text{p + } at the p+ surface region was numerically estimated from the experimental τeff. S\\text{p + } ranged from 4000 to 7200 cm/s under the reverse-bias condition when the carrier annihilation velocity S\\text{n + } at the n+ surface region was assumed to be a constant value of 100 cm/s. S\\text{p + } markedly decreased to 265 cm/s as the forward-bias voltage increased to 0.7 V.

  5. Linear and Nonlinear Optical Spectroscopy at the Nanoscale with Photoinduced Force Microscopy.

    PubMed

    Jahng, Junghoon; Fishman, Dmitry A; Park, Sung; Nowak, Derek B; Morrison, Will A; Wickramasinghe, H Kumar; Potma, Eric O

    2015-10-20

    The enormous advances made in nanotechnology have also intensified the need for tools that can characterize newly synthesized nanoaterials with high sensitivity and with high spatial resolution. Many existing tools with nanoscopic resolution or better, including scanning electron microscopy (SEM), atomic force microscopy (AFM), and scanning tunneling microscopy (STM) methods, can generate highly detailed maps of nanoscopic structures. However, while these approaches provide great views of the morphological properties of nanomaterials, it has proven more challenging to derive chemical information from the corresponding images. To address this issue, attempts have been made to dress existing nanoscopy methods with spectroscopic sensitivity. A powerful approach in this direction is the combination of scan probe techniques with optical illumination, which aims to marry the nanoscopic resolution provided by a sharp tip with the chemical selectivity provided by optical spectroscopy. Examples of this approach include existing techniques such as scattering-type scanning near-field optical microscopy and tip-enhanced Raman spectroscopy. A new and emerging technique in this direction is photoinduced force microscopy (PiFM), which enables spectroscopic probing of materials with a spatial resolution well under 10 nm. In PiFM, the sample is optically excited and the response of the material is probed directly in the near-field by reading out the time-integrated force between the tip and the sample. Because the magnitude of the force is dependent on the photoinduced polarization in the sample, PiFM exhibits spectroscopic sensitivity. The photoinduced forces measured in PiFM are spatially confined on the nanometer scale, which translates into a very high spatial resolution even under ambient conditions. The PiFM approach is compatible with a wide range optical excitation frequencies, from the visible to the mid-infrared, enabling nanoscale imaging contrast based on either

  6. Perovskites for Photovoltaics in the Spotlight: Photoinduced Physical Changes and Their Implications.

    PubMed

    Gottesman, Ronen; Zaban, Arie

    2016-02-16

    Organic-inorganic halide perovskites are in consensus to revolutionize the field of photovoltaics and optoelectronic devices due to their superior optical and electronic properties which are unprecedented in comparison to those of other solution processed semiconductors. These hybrid materials are used as light absorbers and also as charge carriers which makes them very versatile to be implemented and studied in a multitude of fields. Traditionally, the working paradigm in solar cells and optoelectronic devices' characterization has been that the properties of photovoltaic materials remain stable following illumination of varying times and intensities. However, recently there has been a growing number of reports on prolonged illumination-dependent physical changes in perovskite films and perovskite based devices. The changes are reversible and range from structural transformations and differences in optical characteristics, to an increase in optoelectronic properties and physical parameters. In this Account, we review the physical changes in three reported model systems which display changes under prolonged illumination of light intensities of ∼0.01-1 sun. The three systems are (i) a free-standing perovskite film on a glass substrate, (ii) a symmetrical system with nonselective electrical contacts, and (iii) a working perovskite solar cell (either a planar or a porous structure). We examine each model system and discuss its photoinduced physical changes and conclude with the implications on future experimentation design, data analysis, and characterization that involve organic-inorganic halide perovskites illumination. Since hybrid perovskites are considered to be mixed ionic-electronic conductors in nature, ions that migrate in the perovskite under electrical fields can influence its properties. Therefore, an important distinction is made between photoinduced effects and photo and electric field induced effects. Thus, photoinduced effects are designated as

  7. Photoinduced electro-optics measurements of biosilica transformation to cristobalite

    NASA Astrophysics Data System (ADS)

    Fuchs, Ido; Aluma, Yaniv; Ilan, Micha; Kityk, Iwan; Mastai, Yitzhak

    2015-03-01

    In this paper we studied the photoinduced electro optics effects in the thermal transformation process of biosilica to cristobalite, at a relatively low temperature and ambient pressure. This process was characterized by a variety of standards techniques with emphasis on linear electro optic effect measurements. Overall we demonstrated that photoinduced electro optics measurements are very sensitive to the transformation from amorphous structure of silica in the natural sponge samples to laminar string morphology of cristobalite. With this technique we could probe the change in the samples chirality from achiral bio silica to chiral cristobalite structure. Furthermore it is shown that natural biosilica have photoinduced linear electro optics respond indicating the chiral natural of biosilica.

  8. Dynamics of a photoinduced phase transition in polydiacetylene crystals

    NASA Astrophysics Data System (ADS)

    Koshihara, S.; Tokura, Y.; Takeda, K.; Koda, T.

    1995-09-01

    The dynamical process of the photoinduced phase transition in polydiacetylene (PDA) single crystals has been investigated by time-resolved spectroscopy with varying temperature, excitation photon energy, and intensity. The photoinduced phase transition can be driven bidirectionally between the two (A and B) phases by dichromatic irradiation of a laser pulse, when the temperature of the PDA crystal is kept around the phase transition temperature (Tc). It was found that primary process of the photoinduced phase transition is mostly completed within 50 ns. In addition, occurrence of a transient domain injection has been confirmed at temperatures far below and above Tc. Together with the time-resolved measurement of photocurrent, we have found a close correlation between the photocurrent intensity and the phase conversion efficiency. This suggests that the domain walls separating the A and B phases can carry the charge.

  9. Novel photoinduced phase transitions in transition metal oxides and diluted magnetic semiconductors

    PubMed Central

    2012-01-01

    Some transition metal oxides have frustrated electronic states under multiphase competition due to strongly correlated d electrons with spin, charge, and orbital degrees of freedom and exhibit drastic responses to external stimuli such as optical excitation. Here, we present photoemission studies on Pr0.55(Ca1 − ySry)0.45MnO3 (y = 0.25), SrTiO3, and Ti1 − xCoxO2 (x = 0.05, 0.10) under laser illumination and discuss electronic structural changes induced by optical excitation in these strongly correlated oxides. We discuss the novel photoinduced phase transitions in these transition metal oxides and diluted magnetic semiconductors on the basis of polaronic pictures such as orbital, ferromagnetic, and ferroelectric polarons. PMID:23092248

  10. Photoinduced Ag deposition on periodically poled lithium niobate: Wavelength and polarization screening dependence

    NASA Astrophysics Data System (ADS)

    Sun, Yang; Nemanich, Robert J.

    2011-05-01

    This research addresses the wavelength dependence of the fabrication of Ag nanostructures through photoinduced deposition using single crystal ferroelectric lithium niobate as a template. The photoinduced deposition involves ultraviolent light illumination of polarity patterned lithium niobate while immersed in a AgNO3 solution. The results focus on the differences of the Ag nanostructure formation process on the positive and negative domains and domain boundaries. The results indicate that for below-band-gap excitation, a very low density of nanostructures is observed. However, for all above-gap-excitation wavelengths, deposition occurs on both polarity surfaces and at the domain boundaries. The density is greatest at the domain boundaries and reduced densities of smaller nanostructures are observed to form on both the positive and negative domains. The deposition on the domain surfaces is greatest for the shortest wavelengths, whereas the domain selectivity is increased for wavelengths just above the band gap. The external screening and weak band bending of single crystal lithium niobate introduces an enhanced electric field at the domain boundary. The enhanced electric field leads to migration of electrons to the domain boundary and consequently enhanced formation of Ag nanoparticles along the boundary. The variation in the reduction rate versus illumination wavelength is attributed to the light absorption depth and the competition between the photochemical and photoelectric deposition processes. To explore the transition from surface to bulk screening of the polarization charge, oxygen implanted PPLN surfaces were prepared and used for the Ag photoinduced deposition. Consistent with the transition to internal (bulk) screening, the Ag nanoparticle formation on the oxygen implanted PPLN surfaces showed suppressed boundary nanowire formation.

  11. Computational Electronic Structure of Photoinduced Spin Transitions in Molecular Photoswithches

    NASA Astrophysics Data System (ADS)

    Chachiyo, Teepanis

    2005-03-01

    Minimum Energy Crossing Points (MECPs) are the energy barriers associated with radiationless spin-crossover. Understanding the mechanisms of such spin-forbidden processes is of great fundamental and practical interest. Methods of locating MECPs have been developed by several authors with, in general, a poor convergence behavior which increases the computational cost. We present a new method based on spin density functional theory (SDFT) that exhibits fast logarithmic convergence and is suitable for large molecular systems. Spin photo-switchable compounds are becoming a growing area of research since, in principle, it is possible to exploit their spin degrees of freedom to store bits of information. For instance, the photoswitch [Fe(ptz)6](BF4)2;(ptz=1-propyltetrazole) has a singlet (S=0) ground state and, upon optical excitation, becomes trapped in a quintet state (S=2) as long as T < 50K. We applied our MECP methodology to study its geometrical and spin dynamics during spin crossover. Our results are useful for elucidating the geometric rearrangements and microscopic mechanisms that control the lifetime and the critical temperature of the meta-stable high spin (quintet) state. For example, the MECP-SDFT calculations showed that the transition from singlet ground state to a triplet ``intermediate'' state is accompanied by an unusually large 0.3å bond length elongation of the iron axial ligands.

  12. Photoinduced charge-separation in DNA.

    PubMed

    Kawai, Kiyohiko; Majima, Tetsuro

    2015-01-01

    DNA site-specifically modified with a photosensitizer (Sens) was synthesized and the charge-separation and charge-recombination dynamics in DNA were studied. We specifically focused on the formation of the long-lived charge-separated state whose lifetime (τ) is longer than 0.1 μs. The quantum yields of the formation of the charge-separated states (Φ) upon the photoexcitation of the Sens, and the τ were measured using the laser flash photolysis technique. We utilized naphthalimide (NI), naphthaldiimide (ND), and anthraquinone (AQ) as a Sens to investigate the mechanism of the formation of the charge-separated state in DNA via rapid positive charge (hole) transfer between adenine and thymine (A-T) base-pairs. By replacing some T bases in the A-T stretch with 5-bromouracil ((br)U), the charge-separation was shown to occur via the photoinduced charge-injection into the second and further neighboring As to the Sens. On the other hand, the generation of a hole on A nearest to Sens ends up with the rapid charge-recombination within a contact ion pair. A long-lived charge-separated state was also generated in DNA when a commonly used fluorophore such asTAMRA, Alexa 532, and ATTO 655, which can only oxidize guanine-cytosine (G-C) base-pair, but not A-T, was used as a Sens. These results suggested that the charge-separation in DNA is a general phenonmenon for fluorescent dyes which fluorescence is quenched only by G-C. PMID:24577608

  13. Photoinduced structural changes to protein kinase A

    NASA Astrophysics Data System (ADS)

    Rozinek, Sarah C.; Thomas, Robert J.; Brancaleon, Lorenzo

    2014-03-01

    The importance of porphyrins in organisms is underscored by the ubiquitous biological and biochemical functions that are mediated by these compounds and by their potential biomedical and biotechnological applications. Protoporphyrin IX (PPIX) is the precursor to heme and has biomedical applications such as its use as a photosensitizer in phototherapy and photodetection of cancer. Among other applications, our group has demonstrated that low-irradiance exposure to laser irradiation of PPIX, Fe-PPIX, or meso-tetrakis (4-sulfonatophenyl) porphyrin (TSPP) non-covalently docked to a protein causes conformational changes in the polypeptide. Such approach can have remarkable consequences in the study of protein structure/function relationship and can be used to prompt non-native protein properties. Therefore we have investigated protein kinase A (PKA), a more relevant protein model towards the photo-treatment of cancer. PKA's enzymatic functions are regulated by the presence of cyclic adenosine monophosphate for intracellular signal transduction involved in, among other things, stimulation of transcription, tumorigenesis in Carney complex and migration of breast carcinoma cells. Since phosphorylation is a necessary step in some cancers and inflammatory diseases, inhibiting the protein kinase, and therefore phosphorylation, may serve to treat these diseases. Changes in absorption, steady-state fluorescence, and fluorescence lifetime indicate: 1) both TSPP and PPIX non-covalently bind to PKA where they maintain photoreactivity; 2) absorptive photoproduct formation occurs only when PKA is bound to TSPP and irradiated; and 3) PKA undergoes secondary structural changes after irradiation with either porphyrin bound. These photoinduced changes could affect the protein's enzymatic and signaling capabilities.

  14. Nonlinearity in the dynamics of photoinduced nucleation process.

    PubMed

    Ishida, Kunio; Nasu, Keiichiro

    2008-03-21

    Coherent nonlinear dynamics of photoinduced cooperative phenomena at 0 K is studied by numerical calculations on a model of molecular crystals. We found that the photoinduced nucleation process is triggered only when a certain amount of excitation energy is supplied in a narrow part of the system; i.e., there exists the smallest size of the cluster of excited molecules which makes the nucleation possible. As a result, the portion of the cooperatively converted molecules is nonlinearly dependent on the photoexcitation strength, which has been observed in various materials. PMID:18517805

  15. Photoinduced charge dissociation and transport at P3HT/ITO interfaces: studied by modulated surface spectroscopy

    NASA Astrophysics Data System (ADS)

    Rujisamphan, Nopporn; Supasai, Thidarat; Dittrich, Thomas

    2016-02-01

    Results of a temperature dependence study of photoinduced charge separation across P3HT nanocrystals at P3HT/ITO interfaces have been investigated by modulated surface photovoltage (SPV) spectroscopy in a fixed capacitor arrangement. The SPV measurements were correlated with the crystalline sizes of P3HT nanocrystals determined by grazing incidence X-ray diffraction (GIXRD). The crystalline sizes of P3HT nanocrystals were varied systematically by progressive heating/cooling cycles identical for SPV and GIXRD measurements. Photovoltage signals, indication of photoinduced charge dissociation in space, at the P3HT/ITO interface were collected, and electrons were separated across the first monolayer of P3HT nanocrystals at the P3HT/ITO interface due to band bending. The activation energies for quenching of the in-phase and phase-shifted by 90° SPV signals were 0.7 and 0.6 eV, respectively. Thermal activation of the formation of P3HT nanocrystals was of the same order as the enthalpy of fusion of ideal crystals from regioregular P3HT. A schematic drawing of photoinduced charge separation at the P3HT/ITO is proposed.

  16. Spectra of thermoprogrammed annealing of photoinduced color centers

    NASA Astrophysics Data System (ADS)

    Glazkova, N. I.; Mikhaylov, R. V.; Kuznetsov, V. N.

    2015-04-01

    The kinetics of photoinduced formation and thermoprogrammed annealing of color centers in photochromic rutile ceramics has been studied in situ with the aid of a specially designed attachment for a spectrofluorimeter. Using a regime of constant heating rate, the spectra of color center annealing have been measured and the energy depths of hole traps responsible for the annealing of these centers have been determined.

  17. Photoinduced Bending of Self-Assembled Azobenzene-Siloxane Hybrid.

    PubMed

    Guo, Sufang; Matsukawa, Kimihiro; Miyata, Takashi; Okubo, Tatsuya; Kuroda, Kazuyuki; Shimojima, Atsushi

    2015-12-16

    A novel azobenzene-siloxane hybrid material displaying photoinduced macroscopic motions has been prepared by one-step organosilane self-assembly. Two types of alkoxysilane precursors with either pendant or bridging azobenzene groups were synthesized via thiol-ene click reactions. Hybrid films with well-ordered lamellar structures were obtained by hydrolysis and polycondensation of these precursors. The film with solely pendant azobenzene groups showed reversible and rapid d-spacing variation upon UV-vis irradiation, which was induced by the trans-cis isomerization of azobenzene moieties. The flexible, free-standing film obtained by co-condensation of two types of precursors showed reversible bending-unbending motions upon UV-vis irradiation. The partial cross-linking between the siloxane layers by bridging azobenzene groups was crucial for photoinduced distortion of the film. This film possesses high elastic modulus, good thermal stability, and shows large amplitude of photoinduced bending-unbending over a wide temperature range. This is the first report on photoinduced macroscopic motions of azobenzene-containing siloxane-based materials. These materials possess great potential for applications in smart devices and energy conversion systems. PMID:26575345

  18. Measurements of Photo-induced Changes in Conjugated Polymers

    DOE R&D Accomplishments Database

    Seager, C. H.; Sinclair, M. B.; Mc Branch, D.; Heeger, A. J.; Baker, G. L.

    1991-01-01

    We have used the highly sensitive technique of Photothermal Deflection Spectroscopy (PDS) to measure changes in the infrared absorption spectra of MEHPPV, P3HT and Polydiacetylene-4BCMU induced by pumping these polymers with light above the {pi} - {pi}* transition energy. In contrast to previous chopped light transmission measurements of these effects, the PDS technique can directly measure the buildup or decay of the absorption coefficient, {alpha}, on the time scale of second to days. In the case of MEHPPV we observe that the time scale of seconds to days. In the case of MEHPPV we observe that above-gap light causes the appearance of a broad infrared peak in {alpha}, which continues to grow-in hours after the pump light is first applied. For this polymer the general shape of the absorption spectra in the unpumped state mimics the photo-induced changes, suggesting that remnant photo-induced states determine the maximum transparency observed under normal experimental conditions. For P3HT and to a lesser extent, MEHPPV, we also observe irreversible photo-induced absorption components which we tentatively identify with photo-induced oxidation of the polymer matrix.

  19. Photo-induced halide redistribution in organic–inorganic perovskite films

    PubMed Central

    deQuilettes, Dane W.; Zhang, Wei; Burlakov, Victor M.; Graham, Daniel J.; Leijtens, Tomas; Osherov, Anna; Bulović, Vladimir; Snaith, Henry J.; Ginger, David S.; Stranks, Samuel D.

    2016-01-01

    Organic–inorganic perovskites such as CH3NH3PbI3 are promising materials for a variety of optoelectronic applications, with certified power conversion efficiencies in solar cells already exceeding 21%. Nevertheless, state-of-the-art films still contain performance-limiting non-radiative recombination sites and exhibit a range of complex dynamic phenomena under illumination that remain poorly understood. Here we use a unique combination of confocal photoluminescence (PL) microscopy and chemical imaging to correlate the local changes in photophysics with composition in CH3NH3PbI3 films under illumination. We demonstrate that the photo-induced ‘brightening' of the perovskite PL can be attributed to an order-of-magnitude reduction in trap state density. By imaging the same regions with time-of-flight secondary-ion-mass spectrometry, we correlate this photobrightening with a net migration of iodine. Our work provides visual evidence for photo-induced halide migration in triiodide perovskites and reveals the complex interplay between charge carrier populations, electronic traps and mobile halides that collectively impact optoelectronic performance. PMID:27216703

  20. Photo-induced halide redistribution in organic–inorganic perovskite films

    DOE PAGESBeta

    deQuilettes, Dane W.; Zhang, Wei; Burlakov, Victor M.; Graham, Daniel J.; Leijtens, Tomas; Osherov, Anna; Bulovic, Vladimir; Snaith, Henry J.; Ginger, David S.; Stranks, Samuel D.

    2016-05-24

    Organic-inorganic perovskites such as CH3NH3PbI3 are promising materials for a variety of optoelectronic applications, with certified power conversion efficiencies in solar cells already exceeding 21%. Nevertheless, state-of-the-art films still contain performance-limiting non-radiative recombination sites and exhibit a range of complex dynamic phenomena under illumination that remain poorly understood. Here we use a unique combination of confocal photoluminescence (PL) microscopy and chemical imaging to correlate the local changes in photophysics with composition in CH3NH3PbI3 films under illumination. We demonstrate that the photo-induced 'brightening' of the perovskite PL can be attributed to an order-of-magnitude reduction in trap state density. By imaging themore » same regions with time-of-flight secondary-ion-mass spectrometry, we correlate this photobrightening with a net migration of iodine. In conclusion, our work provides visual evidence for photo-induced halide migration in triiodide perovskites and reveals the complex interplay between charge carrier populations, electronic traps and mobile halides that collectively impact optoelectronic performance.« less

  1. Photo-induced halide redistribution in organic-inorganic perovskite films

    NASA Astrophysics Data System (ADS)

    Dequilettes, Dane W.; Zhang, Wei; Burlakov, Victor M.; Graham, Daniel J.; Leijtens, Tomas; Osherov, Anna; Bulović, Vladimir; Snaith, Henry J.; Ginger, David S.; Stranks, Samuel D.

    2016-05-01

    Organic-inorganic perovskites such as CH3NH3PbI3 are promising materials for a variety of optoelectronic applications, with certified power conversion efficiencies in solar cells already exceeding 21%. Nevertheless, state-of-the-art films still contain performance-limiting non-radiative recombination sites and exhibit a range of complex dynamic phenomena under illumination that remain poorly understood. Here we use a unique combination of confocal photoluminescence (PL) microscopy and chemical imaging to correlate the local changes in photophysics with composition in CH3NH3PbI3 films under illumination. We demonstrate that the photo-induced `brightening' of the perovskite PL can be attributed to an order-of-magnitude reduction in trap state density. By imaging the same regions with time-of-flight secondary-ion-mass spectrometry, we correlate this photobrightening with a net migration of iodine. Our work provides visual evidence for photo-induced halide migration in triiodide perovskites and reveals the complex interplay between charge carrier populations, electronic traps and mobile halides that collectively impact optoelectronic performance.

  2. Anomalous photo-induced spectral changes in CdSe/ZnS quantum dots

    NASA Astrophysics Data System (ADS)

    Shcherbatyuk, G. V.; Inman, R. H.; Ghosh, S.

    2011-09-01

    We study photo-induced static and dynamic spectral changes in self-assembled CdSe/ZnS quantum dot (QD) thin films with varying QD concentrations under ambient conditions. Using spatially resolved scanning photoluminescence microscopy in conjunction with spectrally resolved time-correlated photon counting, we measure the variations in spectral intensity, emission wavelength, and recombination lifetimes as functions of photo-exposure time. We find that at low concentrations photo-darkening and photo-oxidation rates slow down with increasing QD density, but in the high concentration limit these rates are strongly enhanced. Our measurements lead us to conclude that the interplay of photo-induced surface trap discharging with preferential photo-oxidation of smaller QDs is further modulated by resonant energy transfer driven by strong inter-dot interactions in highly concentrated samples. Our results would imply that the efficiency and longevity of semiconducting nanoparticle based opto-electronic devices will be limited by the concentration of the active material

  3. Photo-induced halide redistribution in organic-inorganic perovskite films.

    PubMed

    deQuilettes, Dane W; Zhang, Wei; Burlakov, Victor M; Graham, Daniel J; Leijtens, Tomas; Osherov, Anna; Bulović, Vladimir; Snaith, Henry J; Ginger, David S; Stranks, Samuel D

    2016-01-01

    Organic-inorganic perovskites such as CH3NH3PbI3 are promising materials for a variety of optoelectronic applications, with certified power conversion efficiencies in solar cells already exceeding 21%. Nevertheless, state-of-the-art films still contain performance-limiting non-radiative recombination sites and exhibit a range of complex dynamic phenomena under illumination that remain poorly understood. Here we use a unique combination of confocal photoluminescence (PL) microscopy and chemical imaging to correlate the local changes in photophysics with composition in CH3NH3PbI3 films under illumination. We demonstrate that the photo-induced 'brightening' of the perovskite PL can be attributed to an order-of-magnitude reduction in trap state density. By imaging the same regions with time-of-flight secondary-ion-mass spectrometry, we correlate this photobrightening with a net migration of iodine. Our work provides visual evidence for photo-induced halide migration in triiodide perovskites and reveals the complex interplay between charge carrier populations, electronic traps and mobile halides that collectively impact optoelectronic performance. PMID:27216703

  4. Photoinduced enhancement in the luminescence of hydrophilic quantum dots coated with photocleavable ligands.

    PubMed

    Impellizzeri, Stefania; McCaughan, Bridgeen; Callan, John F; Raymo, Françisco M

    2012-02-01

    In search of strategies to photoactivate the luminescence of semiconductor quantum dots, we devised a synthetic approach to attach photocleavable 2-nitrobenzyl groups to CdSe-ZnS core-shell quantum dots coated with hydrophilic polymeric ligands. The emission intensity of the resulting nanostructured constructs increases by more than 60% with the photolysis of the 2-nitrobenzyl appendages. Indeed, the photoinduced separation of the organic chromophores from the inorganic nanoparticles suppresses an electron-transfer pathway from the latter to the former and is mostly responsible for the luminescence enhancement. However, the thiol groups anchoring the polymeric envelope to the ZnS shell also contribute to the photoinduced emission increase. Presumably, their photooxidation eliminates defects on the nanoparticle surface and promotes the radiative deactivation of the excited quantum dots. This effect is fully reversible but its magnitude is only a fraction of the change caused by the photocleavage of the 2-nitrobenzyl groups. In addition, these particular quantum dots can cross the membrane of model cells and their luminescence increases by ~80% after the intracellular photocleavage of the 2-nitrobenzyl quenchers. Thus, photoswitchable luminescent constructs with biocompatible character can be assembled combining the established photochemistry of the 2-nitrobenzyl photocage with the outstanding photophysical properties of semiconductor quantum dots and the hydrophilic character of appropriate polymeric ligands. PMID:22217330

  5. Reflectivity, transmission, and photoinduced infrared spectra of NdNiO{sub 3}

    SciTech Connect

    Massa, N.E.; Alonso, J.A.; Martinez-Lope, M.J.; Rasines, I.

    1997-07-01

    We report temperature-dependent infrared spectra of NdNiO{sub 3} prepared by synthesis under high oxygen pressure. Its room-temperature reflectivity is characteristic of a metal oxide with a Drude tail asymptotically extending to higher frequencies. The sharp metal-insulator transition is detected at about 200 K as phonons become unscreened. While their activity is in the frequency range for a distorted perovskite, the strength of involving the Nd ion against the NiO{sub 6} octahedra at 183cm{sup {minus}1} is remarkable. This and all phonon groups show strong antiresonances near the longitudinal optical frequencies and these are unusually close to absorptions seen in transmission measurements. We interpret this as evidence of strong electron-phonon interactions with carrier localization in a temperature-dependent regime. Low-temperature photoinduced spectra, excited with argon laser lines, support this picture by showing weak absorptions at about those frequencies as well as a relatively very strong photoinduced band at 810cm{sup {minus}1} and one very broad and weak peak at {approximately}2300cm{sup {minus}1} and tail up to 4000cm{sup {minus}1}. They are assigned to electronic transitions involving localized defects. Our measurements suggest that the metal-insulator phase transition in NdNiO{sub 3} is triggered by electron localization in a polaronic environment. We conclude that a suitable order parameter for perovskites with a metal-insulator phase transition may be identified in the coupling between those electrons and local spins {copyright} {ital 1997} {ital The American Physical Society}

  6. Photoinduced dynamics in doped Mott insulators with polaronic conduction: Ba2Ti13O22 and BaxTi8O16

    NASA Astrophysics Data System (ADS)

    Yamaguchi, N.; Furuhashi, A.; Nishihara, H.; Murata, R.; Takayama, K.; Katsufuji, T.

    2016-07-01

    To clarify the dynamics of polarons in doped Mott insulators, we performed pump-probe reflectivity measurements for two barium titanates, Ba2Ti13O22 and BaxTi8O16 , with a noninteger average number of d electrons per Ti. We found that the photoinduced dynamics in Ba2Ti13O22 with a three-dimensional electronic structure is characterized by a broadening of the polaron-excitation peak immediately after photoirradiation, whereas that in BaxTi8O16 with a one-dimensional electronic structure is characterized by a change in the intensities of the polaron-excitation peak and charge-gap-excitation peak with time. This indicates that a difference in dimensionality results in different photoinduced dynamics of polarons in doped Mott insulators.

  7. Photoinduced molecular dissociation and photoinduced recombination mediated by superfluid helium nanodroplets.

    PubMed

    Kautsch, Andreas; Koch, Markus; Ernst, Wolfgang E

    2015-05-14

    We have investigated photoinduced chemical reaction dynamics of cold, isolated Cr2 molecules in helium nanodroplets (HeN), exploiting the quantum state specific spatial separation of solvated and surface locations on the droplet. The molecules are excited to achieve dissociation to a ground state (a(7)S3) and a metastable state (a(5)S2) atom. State specific spatial separation, in combination with efficient translational cooling to avoid ejection, causes the ground state atom to be solvated inside the droplet while the metastable atom migrates to the surface. A barrier between the two reactants formed by the HeN prevents recombination. We apply a resonance-enhanced multiphoton ionization scheme including the y(5)P°(1,2,3) <-- a(5)S(2) transition of the surface atom as well as a two-laser scheme including the y(7)P°(2,3,4) <-- a(7)S(3) transition of the solvated atom in order to verify the locations and separation of the dissociation products. Furthermore, ionization of the a(5)S2 surface atom triggers solvation followed by geminate recombination with the a(7)S3 atom, which is verified by the detection of Cr2(+) molecular ions. For small Cr clusters, our results indicate that they may be composed of chromium dimers that exhibit the same dissociation behavior. PMID:25894482

  8. Photoinduced Phase Transition in Single Crystals on Urethane-Sustituted Polydiacetylenes

    NASA Astrophysics Data System (ADS)

    Tachibana, Hiroaki; Hosaka, Noriko; Osaki, Masayuki; Tokura, Yoshinori

    Thermochromic behaviors were investigated by measurements of reflectance spectra for urethane-substituted polydiacetylene crystal having side groups of R=(CH)2)6OCONHC2H5 (PDA-6UEt). The PDA-6UEt crystal shows an irreversible thermochromic A-to-B (blue-to-red) phase transition: the absorption band at 1.88 eV due to the lowest exciton shifts to higher energy (2.15 eV) in the heating run, but the reflectance spectra remain in the B phase even when cooled down to room temperature. We have demonstrated that photoinduced phase transition (PIPT) is observed by utilizing the irreversible A-to-B phase transition. The conversion shows the presence of a threshold of the light intensity and depends on photon energy, suggesting that the PIPT is mediated by the photogenerated electron-hole pairs.

  9. Photoinduced Phase Transition in Single Crystals of Urethane-Substituted Polydiacetylenes

    NASA Astrophysics Data System (ADS)

    Tachibana, Hiroaki; Hosaka, Noriko; Osaki, Masayuki; Tokura, Yoshinori

    2001-08-01

    Thermochromic behaviors were investigated by measurements of reflectance spectra for urethane-substituted polydiacetylene crystal having side groups of R=(CH2)6OCONHC2H5 (PDA-6UEt). The PDA-6UEt crystal shows an irreversible thermochromic A-to-B (blue-to-red) phase transition: the absorption band at 1.88 eV due to the lowest exciton shifts to higher energy (2.15 eV) in the heating run, but the reflectance spectra remain in the B phase even when cooled down to room temperature. We have demonstrated that photoinduced phase transition (PIPT) is observed by utilizing the irreversible A-to-B phase transition. The conversion shows the presence of a threshold of the light intensity and depends on photon energy, suggesting that the PIPT is mediated by the photogenerated electron-hole pairs.

  10. Unraveling Photoinduced Spin Dynamics in the Topological Insulator Bi(2)Se(3).

    PubMed

    Wang, M C; Qiao, S; Jiang, Z; Luo, S N; Qi, J

    2016-01-22

    We report on a time-resolved ultrafast optical spectroscopy study of the topological insulator Bi_{2}Se_{3}. We unravel that a net spin polarization cannot only be generated using circularly polarized light via interband transitions between topological surface states (SSs), but also via transitions between SSs and bulk states. Our experiment demonstrates that tuning photon energy or temperature can essentially allow for photoexcitation of spin-polarized electrons to unoccupied topological SSs with two distinct spin relaxation times (∼25 and ∼300  fs), depending on the coupling between SSs and bulk states. The intrinsic mechanism leading to such distinctive spin dynamics is the scattering in SSs and bulk states which is dominated by E_{g}^{2} and A_{1g}^{1} phonon modes, respectively. These findings are suggestive of novel ways to manipulate the photoinduced coherent spins in topological insulators. PMID:26849605

  11. Evidence for Photoinduced Insulator-to-Metal transition in B-phase vanadium dioxide.

    PubMed

    Lourembam, James; Srivastava, Amar; La-O-Vorakiat, Chan; Cheng, Liang; Venkatesan, T; Chia, Elbert E M

    2016-01-01

    Ultrafast optical studies have been performed on epitaxial films of the novel B-phase of vanadium dioxide using temperature-dependent optical pump-probe technique. Signature of temperature-driven metal-to-insulator transition was distinctly observed in the ultrafast dynamics - the insulating phase showed two characteristic electronic relaxation times while the metallic phase showed only one. Beyond a threshold value of the pump fluence, the insulating state collapses into a 'metallic-like' phase which can be further subdivided into two regimes according to the lengths of the fast characteristic time. The first regime can be explained by lattice heating due to the optical pump; the other cannot be accounted by simple lattice heating effects alone, and thus offers evidence for a true photoinduced phase transition. PMID:27157532

  12. TDDFT-MD Study on Dynamics in Photoinduced Ring Opening of Benzene

    NASA Astrophysics Data System (ADS)

    Tateyama, Yoshitaka; Miyamoto, Yoshiyuki; Oyama, Norihisa; Ohno, Takahisa

    2004-03-01

    Coupled dynamics of ions and electrons in the excited states of molecular and solid benzene is investigated on the femtosecond scale by the efficient simulation scheme recently developed for the time-dependent density functional theory. Within the π arrow π excitations, any out-of-plane motion of ions is not induced in the molecular system basically. In the solid, however, we found that large swing of the C-H bonds and subsequent twist of the carbon ring takes place, leading to sp^3-like bonding of carbon ions. This swing-to-twist motion presents a plausible mechanism underlying the photoinduced ring opening in solid benzene experimentally observed under pressure. This research is partially supported by ACT-JST, and also by FSIS and Special Coordination Funds of Ministry of Education, Culture, Sports, Science and Technology of Japanese Government.

  13. Generalized Förster-Dexter theory of photoinduced intramolecular energy transfer

    NASA Astrophysics Data System (ADS)

    Lin, S. H.; Xiao, W. Z.; Dietz, W.

    1993-05-01

    In this paper, we generalize the Förster-Dexter theory to treat photoinduced electronic energy transfer for a system in dense media and for an isolated system (i.e., a system in the collision-free condition). Instead of expressing the rate of energy transfer in terms of spectral overlap, we obtain the expression of the energy-transfer rate constant by evaluating a Fourier integral using the saddle-point method. In this way, the energy-gap dependence and the effect of temperature and the isotope effect on the energy transfer can be easily studied. The effect of bridge groups connecting between donor and acceptor on the energy transfer is also studied.

  14. Evidence for Photoinduced Insulator-to-Metal transition in B-phase vanadium dioxide

    NASA Astrophysics Data System (ADS)

    Lourembam, James; Srivastava, Amar; La-O-Vorakiat, Chan; Cheng, Liang; Venkatesan, T.; Chia, Elbert E. M.

    2016-05-01

    Ultrafast optical studies have been performed on epitaxial films of the novel B-phase of vanadium dioxide using temperature-dependent optical pump-probe technique. Signature of temperature-driven metal-to-insulator transition was distinctly observed in the ultrafast dynamics — the insulating phase showed two characteristic electronic relaxation times while the metallic phase showed only one. Beyond a threshold value of the pump fluence, the insulating state collapses into a ‘metallic-like’ phase which can be further subdivided into two regimes according to the lengths of the fast characteristic time. The first regime can be explained by lattice heating due to the optical pump; the other cannot be accounted by simple lattice heating effects alone, and thus offers evidence for a true photoinduced phase transition.

  15. Photoinduced charge-transfer dynamics simulations in noncovalently bonded molecular aggregates.

    PubMed

    Medrano, Carlos R; Oviedo, M Belén; Sánchez, Cristián G

    2016-06-01

    The rational design of new materials as prototype systems for organic solar cells remains challenging. Perylene diimide has emerged as a promising material to replace fullerene derivatives because of its synthetic flexibility, leading to the manipulation of their optical properties. As a result of their fused aromatic core that favors π-π stacking interactions, the aggregation of these molecules can reach highly ordered nanostructures as one-dimensional nanofibers, with a fast photoinduced charge transfer mechanism. In this article, we present an atomistic description of the photoexcited exciton dynamics in noncovalently bonded perylene diimides by time integration of the electron density in the presence of external time varying electric fields. We show that our approach is able to capture and explain the physics that underlies the charge transport mechanism through perylene diimide aggregates. PMID:27189740

  16. Direct visualization of photoinduced glassy dynamics on the amorphous silicon carbide surface by STM movies

    NASA Astrophysics Data System (ADS)

    Nguyen, Duc; Nienhaus, Lea; Haasch, Richard T.; Lyding, Joseph; Gruebele, Martin

    2015-03-01

    Glassy dynamics can be controlled by light irradiation. Sub- and above-bandgap irradiation cause numerous phenomena in glasses including photorelaxation, photoexpansion, photodarkening and pohtoinduced fluidity. We used scanning tunneling microscopy to study surface glassy dynamics of amorphous silicon carbide irradiated with above- bandgap 532 nm light. Surface clusters of ~ 4-5 glass forming unit in diameter hop mostly in a two-state fashion, both without and with irradiation. Upon irradiation, the average surface hopping activity increases by a factor of 3. A very long (~1 day) movie of individual clusters with varying laser power density provides direct evidence for photoinduced enhanced hopping on the glass surfaces. We propose two mechanisms: heating and electronic for the photoenhanced surface dynamics.

  17. When Chiral Photons Meet Chiral Fermions: Photoinduced Anomalous Hall Effects in Weyl Semimetals.

    PubMed

    Chan, Ching-Kit; Lee, Patrick A; Burch, Kenneth S; Han, Jung Hoon; Ran, Ying

    2016-01-15

    The Weyl semimetal is characterized by three-dimensional linear band touching points called Weyl nodes. These nodes come in pairs with opposite chiralities. We show that the coupling of circularly polarized photons with these chiral electrons generates a Hall conductivity without any applied magnetic field in the plane orthogonal to the light propagation. This phenomenon comes about because with all three Pauli matrices exhausted to form the three-dimensional linear dispersion, the Weyl nodes cannot be gapped. Rather, the net influence of chiral photons is to shift the positions of the Weyl nodes. Interestingly, the momentum shift is tightly correlated with the chirality of the node to produce a net anomalous Hall signal. Application of our proposal to the recently discovered TaAs family of Weyl semimetals leads to an order-of-magnitude estimate of the photoinduced Hall conductivity which is within the experimentally accessible range. PMID:26824561

  18. Evidence for Photoinduced Insulator-to-Metal transition in B-phase vanadium dioxide

    PubMed Central

    Lourembam, James; Srivastava, Amar; La-o-vorakiat, Chan; Cheng, Liang; Venkatesan, T.; Chia, Elbert E. M.

    2016-01-01

    Ultrafast optical studies have been performed on epitaxial films of the novel B-phase of vanadium dioxide using temperature-dependent optical pump-probe technique. Signature of temperature-driven metal-to-insulator transition was distinctly observed in the ultrafast dynamics — the insulating phase showed two characteristic electronic relaxation times while the metallic phase showed only one. Beyond a threshold value of the pump fluence, the insulating state collapses into a ‘metallic-like’ phase which can be further subdivided into two regimes according to the lengths of the fast characteristic time. The first regime can be explained by lattice heating due to the optical pump; the other cannot be accounted by simple lattice heating effects alone, and thus offers evidence for a true photoinduced phase transition. PMID:27157532

  19. Dynamics of photoinduced dichroism and birefringence in optically thick azopolymers

    SciTech Connect

    Ponomarev, Yu V; Ivanov, Yu V; Rumyantsev, Yu A; Gromchenko, A A

    2009-01-31

    Dynamics of photoinduced dichroism and birefringence have been studied experimentally and theoretically (with the help of the Dumont model) by using some comb-shaped azopolymers. It is shown that the dynamics of trans-isomer concentration and their angular distribution anisotropy can be restored from the experimentally found dichroism dynamics, with the concentration and anisotropy being averaged over the thickness for optically thick samples. At the initial stage of photoinduced anisotropy when the active role of the polymer matrix can be neglected, the experimental time dependence of dichroism is shown to comply well with the Dumont model even if the orientation memory is neglected, provided that only a part of trans-isomers participates in trans-isomerisation. (nonlinear optical phenomena)

  20. Photo-induced anisotropic photoelectric response in oriented bacteriorhodopsin films

    NASA Astrophysics Data System (ADS)

    Xu, J.; Bhattacharya, P.; Váró, G.

    2003-06-01

    The photo-induced anisotropic properties of the chromophore protein bacteriorhodopsin (bR) are of interest for possible applications in optical image processing and spatial filtering. Here we report experimental results on the photo-induced anisotropic photoelectric response of dried oriented bR films. A polarization dependent photovoltage is measured across an ITO/bR/ITO photodetector. The anisotropy is introduced by a 632.8 nm linearly polarized pump beam and is detected with a 594.1 nm polarized probe beam. The influence of the pump light intensity on the photovoltage anisotropy has also been investigated. A model, based on the polarization dependent photoselection of the bR molecules reasonably explains the behavior of the measured data. The observed effect can be used to construct a polarization sensitive bR-based bio-photoreceiver.

  1. The time of a photoinduced spin-Peierls phase transition

    SciTech Connect

    Semenov, A. L.

    2015-02-15

    The time τ of the spin-Peierls phase transition is analyzed theoretically as a function of the duration τ{sub p} of the exciting light pulse and the average number x{sub 0} of absorbed photons per magnetic ion after the transmission of the pulse. It is shown that the phase transition occurs at x{sub 0} > x{sub c}. The critical value x{sub c} is determined as a function of the duration τ{sub p} of the light pulse. A photoinduced variation in the optical reflection coefficient R is calculated as a function of time t. The results of calculation are compared with experimental data on ultrafast photoinduced melting of the low-temperature spin-Peierls phase into potassium tetracyanoquinodimethan (K-TCNQ)

  2. Photoinduced translational molecular mobility in solid nanostructured azo dye films

    SciTech Connect

    Ezhov, A A; Kozenkov, V M; Magnitskii, Sergey A; Nagorskii, Nikolay M; Panov, Vladimir I

    2011-11-30

    A new mechanism controlling the molecular motion in thin azo-containing films during a photoinduced change in the surface nanorelief is found. It is shown experimentally that exposure of a solid AD-1 azo dye, deposited on a glass substrate, to incoherent linearly polarised light leads to formation of nanostructures with a characteristic size of 200 nm, which are similar to droplets of melt of this dye on the same substrate. It is shown that photoinduced mass transport in a solid AD-1 azo dye film can be explained by the mobility of molecules related to their trans-cis-photoisomerisation, which leads to film softening with subsequent formation of spherical protrusions under surface tension forces.

  3. Silver photo-diffusion and photo-induced macroscopic surface deformation of Ge33S67/Ag/Si substrate

    NASA Astrophysics Data System (ADS)

    Sakaguchi, Y.; Asaoka, H.; Uozumi, Y.; Kondo, K.; Yamazaki, D.; Soyama, K.; Ailavajhala, M.; Mitkova, M.

    2016-08-01

    Ge-chalcogenide films show various photo-induced changes, and silver photo-diffusion is one of them which attracts lots of interest. In this paper, we report how silver and Ge-chalcogenide layers in Ge33S67/Ag/Si substrate stacks change under light exposure in the depth by measuring time-resolved neutron reflectivity. It was found from the measurement that Ag ions diffuse all over the matrix Ge33S67 layer once Ag dissolves into the layer. We also found that the surface was macroscopically deformed by the extended light exposure. Its structural origin was investigated by a scanning electron microscopy.

  4. On the mechanism of photoinduced refractive index changes in phosphosilicate glass

    SciTech Connect

    Larionov, Yu V; Sokolov, V O; Plotnichenko, V G

    2010-05-26

    The photoinduced growth of the refractive index of phosphosilicate glass during Bragg grating inscription and the thermal decay of the grating have a number of unusual features. The observed index variations are interpreted in terms of a new model for photoinduced glass network rearrangement. The model assumes the formation of photoinduced voids (nanopores) in the glass network near point defects. The nanopores may migrate through the network via bond switching when the network is in a 'soft' state. The photoinduced variations in network density lead to index variations. (fibres)

  5. Photoinduced Dynamics and Toxicity of a Cancer Drug in Proximity of Inorganic Nanoparticles under Visible Light.

    PubMed

    Chaudhuri, Siddhi; Sardar, Samim; Bagchi, Damayanti; Dutta, Shreyasi; Debnath, Sushanta; Saha, Partha; Lemmens, Peter; Pal, Samir Kumar

    2016-01-18

    Drug sensitization with various inorganic nanoparticles (NPs) has proved to be a promising and an emergent concept in the field of nanomedicine. Rose bengal (RB), a notable photosensitizer, triggers the formation of reactive oxygen species under green-light irradiation, and consequently, it induces cytotoxicity and cell death. In the present study, the effect of photoinduced dynamics of RB upon complexation with semiconductor zinc oxide NPs is explored. To accomplish this, we successfully synthesized nanohybrids of RB with ZnO NPs with a particle size of 24 nm and optically characterized them. The uniform size and integrity of the particles were confirmed by high-resolution transmission electron microscopy. UV/Vis absorption and steady-state fluorescence studies reveal the formation of the nanohybrids. ultrafast picosecond-resolved fluorescence studies of RB-ZnO nanohybrids demonstrate an efficient electron transfer from the photoexcited drug to the semiconductor NPs. Picosecond-resolved Förster resonance energy transfer from ZnO NPs to RB unravel the proximity of the drug to the semiconductor at the molecular level. The photoinduced ROS formation was monitored using a dichlorofluorescin oxidation assay, which is a conventional oxidative stress indicator. It is observed that the ROS generation under green light illumination is greater at low concentrations of RB-ZnO nanohybrids compared with free RB. Substantial photodynamic activity of the nanohybrids in bacterial and fungal cell lines validated the in vitro toxicity results. Furthermore, the cytotoxic effect of the nanohybrids in HeLa cells, which was monitored by MTT assay, is also noteworthy. PMID:26563628

  6. Direct Observation of Photoinduced Tautomerization in Single Molecules at a Metal Surface.

    PubMed

    Böckmann, H; Liu, S; Mielke, J; Gawinkowski, S; Waluk, J; Grill, L; Wolf, M; Kumagai, T

    2016-02-10

    Molecular switches are of fundamental importance in nature, and light is an important stimulus to selectively drive the switching process. However, the local dynamics of a conformational change in these molecules remain far from being completely understood at the single-molecule level. Here, we report the direct observation of photoinduced tautomerization in single porphycene molecules on a Cu(111) surface by using a combination of low-temperature scanning tunneling microscopy and laser excitation in the near-infrared to ultraviolet regime. It is found that the thermodynamically stable trans configuration of porphycene can be converted to the metastable cis configuration in a unidirectional fashion by photoirradiation. The wavelength dependence of the tautomerization cross section exhibits a steep increase around 2 eV and demonstrates that excitation of the Cu d-band electrons and the resulting hot carriers play a dominant role in the photochemical process. Additionally, a pronounced isotope effect in the cross section (∼100) is observed when the transferred hydrogen atoms are substituted with deuterium, indicating a significant contribution of zero-point energy in the reaction. Combined with the study of inelastic tunneling electron-induced tautomerization with the STM, we propose that tautomerization occurs via excitation of molecular vibrations after photoexcitation. Interestingly, the observed cross section of ∼10(-19) cm(2) in the visible-ultraviolet region is much higher than that of previously studied molecular switches on a metal surface, for example, azobenzene derivatives (10(-23)-10(-22) cm(2)). Furthermore, we examined a local environmental impact on the photoinduced tautomerization by varying molecular density on the surface and find substantial changes in the cross section and quenching of the process due to the intermolecular interaction at high density. PMID:26796945

  7. Photoinduced Hydrodefluorination Mechanisms of Perfluorooctanoic Acid by the SiC/Graphene Catalyst.

    PubMed

    Huang, Dahong; Yin, Lifeng; Niu, Junfeng

    2016-06-01

    Cleavage of the strong carbon-fluorine bonds is critical for elimination of perfluorooctanoic acid (PFOA) from the environment. In this work, we investigated the decomposition of PFOA with the SiC/graphene catalyst under UV light irradiation. The decomposition rate constant (k) with SiC/graphene was 0.096 h(-1), 2.2 times higher than that with commercial nano-TiO2. Surface fluorination on SiC/graphene was analyzed by X-ray photoelectron spectroscopy (XPS), revealing the conversions of Si-H bonds into Si-F bonds. A different route was found to generate the reactive Si-H bonds on SiC/graphene, substituting for silylium (R3Si(+)) to activate C-F bonds. During the activation process, photogenerated electrons on SiC transfer rapidly to perfluoroalkyl groups by the medium of graphene, further reducing the electron cloud density of C-F bonds to promote the activation. The hydrogen-containing hydrodefluorination intermediates including (CF3(CF2)2CFH, CF3(CF2)3CH2, CF3(CF2)4CH2, and CF3(CF2)4CFHCOOH) were detected to verify the hydrodefluorination process. The photoinduced hydrodefluorination mechanisms of PFOA can be consequently inferred as follows: (1) fluorine atoms in perfluoroalkyl groups were replaced by hydrogen atoms due to the nucleophilic substitution reaction via the Si-H/C-F redistribution, and (2) generation of CH2 carbene from the hydrogen-containing perfluoroalkyl groups and the C-C bonds scission by the Photo-Kolbe decarboxylation reaction under UV light excitation. This photoinduced hydrodefluorination provides insight into the photocatalytic decomposition of perfluorocarboxylic acids (PFCAs) in an aqueous environment. PMID:27128100

  8. Photoinduced Charge-Transfer State of 4-Carbazolyl-3-(trifluoromethyl)benzoic Acid: Photophysical Property and Application to Reduction of Carbon-Halogen Bonds as a Sensitizer.

    PubMed

    Matsubara, Ryosuke; Shimada, Toshiyuki; Kobori, Yasuhiro; Yabuta, Tatsushi; Osakai, Toshiyuki; Hayashi, Masahiko

    2016-07-20

    The photoinduced persistent intramolecular charge-transfer state of 4-carbazolyl-3-(trifluoromethyl)benzoic acid was confirmed. It showed a higher catalytic activity in terms of yield and selectivity in the photochemical reduction of alkyl halides compared to the parent carbazole. Even unactivated primary alkyl bromides could be reduced by this photocatalyst. The high catalytic activity is rationalized by considering the slower backward single-electron transfer owing to the spatial separation of the donor and acceptor subunits. PMID:27305449

  9. Plasmonic, excitonic and exciton-plasmonic photoinduced nanocomposites

    NASA Astrophysics Data System (ADS)

    Bityurin, N.; Ermolaev, N.; Smirnov, A. A.; Afanasiev, A.; Agareva, N.; Koryukina, T.; Bredikhin, V.; Kamensky, V.; Pikulin, A.; Sapogova, N.

    2016-03-01

    UV irradiation of materials consisting of a polymer matrix that possesses precursors of different kinds can result in creation of nanoparticles within the irradiated domains. Such photoinduced nanocomposites are promising for photonic applications due to the strong alteration of their optical properties compared to initial non-irradiated materials. We report our results on the synthesis and investigation of plasmonic, excitonic and exciton-plasmonic photoinduced nanocomposites. Plasmonic nanocomposites contain metal nanoparticles of noble metals with a pronounced plasmon resonance. Excitonic nanocomposites possess semiconductor nanoclusters (quantum dots). We consider the CdS-Au pair because the luminescent band of CdS nanoparticles enters the plasmon resonance band of gold nanoparticles. The obtaining of such particles within the same composite materials is promising for the creation of media with exciton-plasmon resonance. We demonstrate that it is possible to choose appropriate precursor species to obtain the initially transparent poly(methyl methacrylate) (PMMA) films containing both types of these molecules either separately or together. Proper irradiation of these materials by a light-emitting diode operating at the wavelength of 365 nm provides material alteration demonstrating light-induced optical absorption and photoluminescent properties typical for the corresponding nanoparticles. Thus, an exciton-plasmonic photoinduced nanocomposite is obtained. It is important that here we use the precursors that are different from those usually employed.

  10. Direct characterization of photoinduced lattice dynamics in BaFe2As2

    NASA Astrophysics Data System (ADS)

    Gerber, S.; Kim, K. W.; Zhang, Y.; Zhu, D.; Plonka, N.; Yi, M.; Dakovski, G. L.; Leuenberger, D.; Kirchmann, P. S.; Moore, R. G.; Chollet, M.; Glownia, J. M.; Feng, Y.; Lee, J.-S.; Mehta, A.; Kemper, A. F.; Wolf, T.; Chuang, Y.-D.; Hussain, Z.; Kao, C.-C.; Moritz, B.; Shen, Z.-X.; Devereaux, T. P.; Lee, W.-S.

    2015-06-01

    Ultrafast light pulses can modify electronic properties of quantum materials by perturbing the underlying, intertwined degrees of freedom. In particular, iron-based superconductors exhibit a strong coupling among electronic nematic fluctuations, spins and the lattice, serving as a playground for ultrafast manipulation. Here we use time-resolved X-ray scattering to measure the lattice dynamics of photoexcited BaFe2As2. On optical excitation, no signature of an ultrafast change of the crystal symmetry is observed, but the lattice oscillates rapidly in time due to the coherent excitation of an A1g mode that modulates the Fe-As-Fe bond angle. We directly quantify the coherent lattice dynamics and show that even a small photoinduced lattice distortion can induce notable changes in the electronic and magnetic properties. Our analysis implies that transient structural modification can be an effective tool for manipulating the electronic properties of multi-orbital systems, where electronic instabilities are sensitive to the orbital character of bands.

  11. Direct characterization of photoinduced lattice dynamics in BaFe2As2

    PubMed Central

    Gerber, S.; Kim, K. W.; Zhang, Y.; Zhu, D.; Plonka, N.; Yi, M.; Dakovski, G. L.; Leuenberger, D.; Kirchmann, P.S.; Moore, R. G.; Chollet, M.; Glownia, J. M.; Feng, Y.; Lee, J.-S.; Mehta, A.; Kemper, A. F.; Wolf, T.; Chuang, Y.-D.; Hussain, Z.; Kao, C.-C.; Moritz, B.; Shen, Z.-X.; Devereaux, T. P.; Lee, W.-S.

    2015-01-01

    Ultrafast light pulses can modify electronic properties of quantum materials by perturbing the underlying, intertwined degrees of freedom. In particular, iron-based superconductors exhibit a strong coupling among electronic nematic fluctuations, spins and the lattice, serving as a playground for ultrafast manipulation. Here we use time-resolved X-ray scattering to measure the lattice dynamics of photoexcited BaFe2As2. On optical excitation, no signature of an ultrafast change of the crystal symmetry is observed, but the lattice oscillates rapidly in time due to the coherent excitation of an A1g mode that modulates the Fe–As–Fe bond angle. We directly quantify the coherent lattice dynamics and show that even a small photoinduced lattice distortion can induce notable changes in the electronic and magnetic properties. Our analysis implies that transient structural modification can be an effective tool for manipulating the electronic properties of multi-orbital systems, where electronic instabilities are sensitive to the orbital character of bands. PMID:26051704

  12. Direct characterization of photoinduced lattice dynamics in BaFe2As2.

    PubMed

    Gerber, S; Kim, K W; Zhang, Y; Zhu, D; Plonka, N; Yi, M; Dakovski, G L; Leuenberger, D; Kirchmann, P S; Moore, R G; Chollet, M; Glownia, J M; Feng, Y; Lee, J-S; Mehta, A; Kemper, A F; Wolf, T; Chuang, Y-D; Hussain, Z; Kao, C-C; Moritz, B; Shen, Z-X; Devereaux, T P; Lee, W-S

    2015-01-01

    Ultrafast light pulses can modify electronic properties of quantum materials by perturbing the underlying, intertwined degrees of freedom. In particular, iron-based superconductors exhibit a strong coupling among electronic nematic fluctuations, spins and the lattice, serving as a playground for ultrafast manipulation. Here we use time-resolved X-ray scattering to measure the lattice dynamics of photoexcited BaFe2As2. On optical excitation, no signature of an ultrafast change of the crystal symmetry is observed, but the lattice oscillates rapidly in time due to the coherent excitation of an A1g mode that modulates the Fe-As-Fe bond angle. We directly quantify the coherent lattice dynamics and show that even a small photoinduced lattice distortion can induce notable changes in the electronic and magnetic properties. Our analysis implies that transient structural modification can be an effective tool for manipulating the electronic properties of multi-orbital systems, where electronic instabilities are sensitive to the orbital character of bands. PMID:26051704

  13. Photoinduced charge separation in wide-band capturing, multi-modular bis(donor styryl)BODIPY-fullerene systems.

    PubMed

    Obondi, Christopher O; Lim, Gary N; Karr, Paul A; Nesterov, Vladimir N; D'Souza, Francis

    2016-07-21

    A new series of multi-modular donor-acceptor systems capable of exhibiting photoinduced charge separation have been designed, synthesized and characterized using various techniques. In this series, the electron donor was a BF2-chelated dipyrromethene (BODIPY) appended with two styryl linkers carrying two electron rich triphenylamine or phenothiazine entities. Fulleropyrrolidine linked at the meso-position of the BODIPY ring served as an electron acceptor. As a result of extended conjugation and multiple electroactive chromophore entities, the bis-styryl BODIPY revealed absorbance and emission well-into the near-infrared region covering a 300-850 nm spectral range. Using redox, computational, absorbance and emission data, an energy level diagram was constructed that helped in envisioning the different photochemical events. Spectral evidence for photoinduced charge separation in these systems was established from femtosecond and nanosecond transient absorption studies. The measured rate constants indicated fast charge separation and relatively slow charge recombination revealing their usefulness in light energy harvesting and optoelectronic device building applications. The bis(donor styryl)BODIPY-fullerene systems populated BODIPY triplet excited states during the process of charge recombination. PMID:27333163

  14. Photoinduced charge transfer properties of bolaamphiphile membrane-gramicidrin diad composites

    NASA Astrophysics Data System (ADS)

    Thompson, David H.; Kim, Jong-Mok; Di Meglio, Ciro

    1993-04-01

    Ether-linked bolaform amphiphiles (Langmuir 1992 8, 637; J. Am. Chem. Soc. 1992, 9035) and novel gramicidin-porphyrin `diads' (MRS Symposium Series, Vol. 277, 1992, 93) have been synthesized. Protocols for vectorial insertion of the derivatized gramicidins into bolaform lipid vesicles have been developed and the photochemical behavior of these proteinaceous composite membranes probed in the presence of electron donors and acceptors. Photoinduced electron transfer properties of the gramicidin-porphyrin conjugates were compared in TRIS- buffered dihexadecyl-phosphate bilayer (DHP) and bolaform monolayer membrane vesicles containing dithiothreitol as sacrificial donor and methyl viologen as electron acceptor on both the inner and outer vesicle surfaces. Although the rates of methyl viologen photoreduction varied depending on the mode of diad orientation within DHP bilayer membranes, photoreduction rates were not orientation- dependent in bolaform membrane vesicles containing the gramicidin-porphyrin diad. The relevance of these results on vectorial electron transfer processes in lamellar systems and the design of integrated charge transfer components is discussed.

  15. Photoinduced Charge Separation in the Carbon Nano-Onion C60@C240.

    PubMed

    Voityuk, Alexander A; Solà, Miquel

    2016-07-28

    The double-shell fullerene C60@C240 formed by inclusion of C60 into C240 is the smallest stable carbon nano-onion. In this article, we analyze in detail the character of the excited states of C60@C240 in terms of exciton localization and charge transfer between the inner and outer shells. The unique structure of the buckyonion leads to a large electrostatic stabilization of charge-separated (CS) states in the C60@C240. As a result, the CS states C60(+)@C240(-) lie in the same region of the electronic spectrum (2.4-2.6 eV) as strongly absorbing locally excited states and, therefore, can be effectively populated. The CS states C60(-)@C240(+) are found to be 0.5 eV higher in energy than the CS states C60(+)@C240(-). Unlike the situation observed in donor-acceptor systems, the energies of the CS states in C60@C240 do not practically depend on the environment polarity. This leads to exceptionally small reorganization energies for electron transfer between the shells. Electronic couplings for photoinduced charge-separation and charge-recombination processes are calculated. The absolute rate of the formation of the CS state C60(+)@C240(-) is estimated at ∼4 ps(-1). The electronic features found in C60@C240 are likely to be shared by other carbon nano-onions. PMID:27383921

  16. Different shapes of spherical vaterite by photo-induced cis?trans isomerization of an azobenzene-containing polymer in a mixture of dimethyl sulfoxide and water

    NASA Astrophysics Data System (ADS)

    Keum, Dong-Ki; Na, Hai-Sub; Naka, Kensuke; Chujo, Yoshiki

    2004-10-01

    We studied the crystallization of CaCO3 by the photoisomerization of azobenzene groups in poly[1-[4-[3-carboxy-4-hydroxyphenylazobenzenesulfonamido]-1,2-ethanediyl, sodium salt] (PAZO) in a mixture of dimethyl sulfoxide and water at 30 °C. The products were characterized by scanning electron microscopy (SEM), FT-IR, and powder X-ray diffraction (XRD) analysis. We observed that the different shapes of spherical vaterite particles were produced by the changes of configuration and polarity of the azobenzene groups in the polymer which resulted from photo-induced isomerization. The results indicate that the nucleation of primary particles of CaCO3 was inhibited by in situ photo-induced cis-trans isomerization of PAZO. Therefore, we suggest that the shapes of the spherical vaterite can be effectively modified by photoisomerization of the azobenzene groups in the polymer at the initial stage of CaCO3 crystallization.

  17. Photoinduced surface reactions on TiO{sub 2} and SrTiO{sub 3} films: Photocatalytic oxidation and photoinduced hydrophilicity

    SciTech Connect

    Miyauchi, Masahiro; Nakajima, Akira; Fujishima, Akira; Hashimoto, Kazuhito; Watanabe, Toshiya

    2000-01-01

    In the present study, the authors have evaluated photocatalytic activities and photoinduced wettabilities for TiO{sub 2} and SrTiO{sub 3} films. Although both types of films had almost the same photocatalytic oxidation activity, photoinduced wettabilities of these films showed different phenomena. The photoinduced hydrophilicity peculiar to TiO{sub 2} is not caused by the photocatalytic oxidation of organic compounds adsorbed on the surface. The highly hydrophilic surface of TiO{sub 2} is ascribed to photogenerated Ti{sup 3+} defect sites that are favorable for dissociative water absorption. The yield of this photoinduced hydrophilic reaction is not clear at the present time. It is noted that this reaction involves a surface structural change, which should not require a high quantum efficiency as compared to conventional photocatalytic oxidation.

  18. Distance dependent rates of photoinduced charge separation and dark charge recombination in fixed distance porphyrin-quinone molecules

    SciTech Connect

    Wasielewski, M.R.; Niemczyk, M.P.

    1986-01-01

    Three zinc tetraphenylporphyrin-anthraquinone derivatives were prepared in which the edge-to-edge distances between the porphyrin and quinone ..pi.. systems are fixed by a rigid hydrocarbon spacer molecule. Triptycene, trans-1,2-diphenylcyclopentane, and adamantane were used to fix the porphyrin-anthraquinone distance at 2.5, 3.7, and 4.9 A, respectively. These molecules possess 1,2, and 3 saturated carbon atoms, respectively, between the porphyrin donor and the quinone acceptor. Rate constants for photoinduced electron transfer from the lowest excited singlet state of the zinc tetraphenylporphyrin donor to the anthraquinone acceptor were measured. In addition, the corresponding radical ion pair recombination rate constants for each of these molecules were also determined. The rate constants for both photoinduced charge separation and subsequent radical ion pair recombination decrease by approximately a factor of 10 for each saturated carbon atom intervening between the porphyrin donor and the quinone acceptor. These results are consistent with a model in which the rate of electron transfer is determined by weak mixing of the sigma orbitals of the saturated hydrocarbon spacer with the ..pi.. orbitals of the donor and acceptor. 22 refs., 5 figs.

  19. Photoswitchable stable charge-distributed states in a new cobalt complex exhibiting photo-induced valence tautomerism.

    PubMed

    Slota, Michael; Blankenhorn, Marian; Heintze, Eric; Vu, Minh; Hübner, Ralph; Bogani, Lapo

    2015-01-01

    We report the synthesis and magnetic and photomagnetic behaviour of a novel valence tautomeric cobalt complex, [Co(3,5-dbbq)2(μ-bpym)] (1) (3,5-dbbq = 3,5-di-tert-butyl-1,2-benzoquinone and μ-bpym = 2,2'-bipyrimidine). The synthesis is performed by reacting Co2(CO)8 and μ-bpym in the presence of the ligand 3,5-dbbq in a mixed solvent under inert atmosphere. The magnetic behavior clearly shows the presence of electron transfer from the catecholate ligand to the cobalt center, producing valence tautomers of [Co(II)(SQ)2] with a transition temperature (T1/2) of 215 K. Photomagnetic studies, performed via both SQUID magnetometry and X-band electron paramagnetic resonance, show the clear presence of photoinduced valence tautomerism, at temperatures considerably higher than previous systems. A metastable charge distribution is observed, strengthening previous investigations on the character of mixed valence ligands. Entropy-driven valence tautomeric interconversion is observed, and drives the transition to the most stable charge distribution. The complex has the ability to coordinate and can be used as a photoswitchable building block, with the photomagnetic characterisation evidencing a metastable state lifetime of the photo-induced valence tautomeric process of ca. 2.9 × 10(4) s below 20 K. The observed yields are higher than ones in similar systems, showing that tiny changes in the molecular structures may have a huge impact. PMID:26470791

  20. Photoinduced dichroism in Bacteriorhodopsin and its application to optical computing and information processing

    NASA Astrophysics Data System (ADS)

    Denis, Kevin; Aranda, Francisco J.

    1998-03-01

    The intensity dependence of the photoinduced dichroism in Bacteriorhodopsin (bR) films has potential application in optical image processing and optical computing. Under the illumination of linearly polarized actinic light of 570 nm wavelength, the photoinduced dichroism in a Bacteriorhodopsin film induces polarization rotation for a probe beam of the same wavelength. This behavior is a function of the life time of the M state in the Bacteriorhodopsin photocycle. We studied the dependence of the photoinduced dichroism on the pH environment in which the bR molecules are and on genetic mutation by replacement of the Aspartic amino acid in position 96 by Asparagine. The photoinduced probe polarization rotation can be exploited for optical Fourier processing and logic operations. The intensity dependence of the photoinduced dichroism in the different films has important implications on the applications for which they are suitable.

  1. Photoinduced "stick-slip" on superhydrophilic semiconductor surfaces.

    PubMed

    Denison, Kieth R; Boxall, Colin

    2007-04-10

    Transparent mesoporous TiO2 (M-TiO2) thin films were prepared on quartz via a reverse micelle, sol-gel, spin-coating technique. Films were characterized by atomic force microscopy (AFM) and Raman and UV-vis spectroscopies and were found to be mostly anatase with low surface roughness (Rt approximately 5 nm). The time dependence of film photoinduced superhydrophilicity (PISH) was measured by observation of the spreading of a sessile water drop using a new, continuous measurement technique wherein the drop was first applied to the semiconductor surface and then was filmed while it and the underlying substrate were illuminated by 315 nm ultraband gap light. Results obtained at 100% relative humidity (RH) at 293 K showed that drops on M-TiO2 surfaces exhibited a photoinduced "stick-slip" behavior, the first time such an effect has been observed. The thermodynamic driving force for this photoinduced stick-slip was the departure of the system from capillary equilibrium as, with increasing illumination time, the concentration of surface Ti-OH groups increased and the equilibrium contact angle of the drop, theta0, decreased. A simple theoretical description of photoinduced stick-slip is derived and is used to calculate a value of the potential energy barrier associated with surface inhomogeneities that oppose onset of movement of the triple line, U = 6.63 x 10(-6) J m(-1). This is the first time that U has been quantified for a surface with photoinduced superhydrophilicity. Triple line retreat measurements on an evaporating drop on M-TiO2 in the dark, RH = 60%, T = 293 K, gave a value of U = 9.4 x 10(-6) J m(-1), indicating that U decreases upon UV illumination and that U in the light is primarily associated with inhomogeneities that are unaffected by an increase in the surface Ti-OH population, such as the physical roughness of the surface. In the dark evaporation experiment, the drop was found to retreat with an areal velocity of 1.48 x 10(-8) m2 s(-1). However, under UV

  2. Photoinduced switching to metallic states in the two-dimensional organic Mott insulator dimethylphenazine-tetrafluorotetracyanoquinodimethane with anisotropic molecular stacks

    NASA Astrophysics Data System (ADS)

    Matsuzaki, Hiroyuki; Ohkura, Masa-aki; Ishige, Yu; Nogami, Yoshio; Okamoto, Hiroshi

    2015-06-01

    A photoinduced phase transition was investigated in an organic charge-transfer (CT) complex M2P -TCNQ F4 , [M2P : 5,10-dihydro-5,10-dimethylphenazine, donor (D) molecule; TCNQ F4 : 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane, acceptor (A) molecule] by means of femtosecond pump-probe reflection spectroscopy. This is an ionic compound and has a peculiar two-dimensional (2D) molecular arrangement; the same A (or D) molecules arrange along the [100] direction, and A and D molecules alternately arrange along the [111] direction. It results in a strongly anisotropic two-dimensional electronic structure. This compound shows a structural and magnetic phase transition at 122 K below which the two neighboring molecules are dimerized along both the [100] and [111] directions. We demonstrate that two kinds of photoinduced phase transitions occur by irradiation of a femtosecond laser pulse; in the high-temperature lattice-uniform phase, a quasi-one-dimensional (1D) metallic state along the AA(DD) stack is generated, and in the low-temperature lattice-dimerized phase, a quasi-2D metallic state is initially produced and molecular dimerizations are subsequently released. Mixed-stack CT compounds consisting of DA stacks are generally insulators or semiconductors in the ground state. Here, such a dynamical metallization in the DA stack is demonstrated. The release of the dimerizations drives several kinds of coherent oscillations which play an important role in the stabilization of the lattice-dimerized phase. The mechanisms of those photoinduced phase transitions are discussed in terms of the magnitudes of the anisotropic bandwidths and molecular dimerizations along two different directions of the molecular stacks.

  3. Polyion complex vesicles for photoinduced intracellular delivery of amphiphilic photosensitizer.

    PubMed

    Chen, Huabing; Xiao, Ling; Anraku, Yasutaka; Mi, Peng; Liu, Xueying; Cabral, Horacio; Inoue, Aki; Nomoto, Takahiro; Kishimura, Akihiro; Nishiyama, Nobuhiro; Kataoka, Kazunori

    2014-01-01

    Polymer vesicles formed by a pair of oppositely charged poly(ethylene glycol) (PEG)-based block aniomer and homocatiomer, termed "PICsomes", have tunable size, and are characterized by unique semipermeable property due to the flexible and tunable hydrophilicity of polyion complex (PIC) membranes. The PICsomes can encapsulate a variety of molecules in an inner aqueous phase just by a simple vortex mixing of solution, expecting their utility as nanocontainers of substances with biomedical interests. Here, we report on a new functionality of the PICsomes: photoinduced release of photoactive agents for intracellular drug delivery. A potent photosensitizer, Al(III) phthalocyanine chloride disulfonic acid (AlPcS2a), was efficiently incorporated into the PICsomes (11%(w/w)), and its quick release was induced by photoirradiation possibly due to the photochemical damage of the PIC membranes. The combination of a high-resolution fluorescent confocal microscopy and a lysosome membrane-specific staining method revealed that such photoinduced release of AlPcS2a occurred even in the lysosomes of living cells after endocytic internalization. Simultaneously, the released AlPcS2a photochemically affected the integrity of the lysosomal membranes, leading to the translocation of AlPcS2a and PICsomes themselves to the cytoplasm. Consequently, the AlPcS2a-encapsulated PICsomes (AlPcS2a-PICsomes) exhibited appreciably stronger photocytotoxicity compared with free AlPcS2a alone. Thus, the AlPcS2a-PICsomes have promising feasibility for the photodynamic therapy or the photoinduced cytoplasmic delivery of therapeutic molecules. PMID:24283288

  4. Design of a Molecular Memory Device: The Electron Transfer Shift Register Memory

    NASA Technical Reports Server (NTRS)

    Beratan, D.

    1993-01-01

    A molecular shift register memory at the molecular level is described. The memory elements consist of molecules can exit in either an oxidized or reduced state and the bits are shifted between the cells with photoinduced electron transfer reactions.

  5. Photo-Induced Effect on Bacterial Cells

    NASA Astrophysics Data System (ADS)

    El Batanouny, M. H.; Amin, Rehab M.; Naga, M. I.; Ibrahim, M. K.

    2010-04-01

    Bacterial resistance against antibiotics is an increasing problem in medicine. This stimulates study of other bactericidal regimens, one of which is photodynamic therapy (PDT), which involves the killing of bacterial species by low power laser light (LLL) in the presence of photosensitizing agent. It has already been shown that, various gram- negative and gram-positive bacteria can be killed by photodynamic therapy in vitro, using exogenous sensitizers. The mechanisms of laser action on bacteria are not adequately understood. Here, PDT on H. pylori, as an example of gram negative bacteria was studied. The ultra structure changes of the organism after PDT were examined under electron microscope. Neither Irradiation with laser without sensitizer nor sensitizing without laser has any lethal effect on bacterial cells. However, the successful lethal photosensitization was achieved by applying certain laser dose with the corresponding concentration of the photosensitizer. On the other hand, PDT has no significant effect on the genomic DNA of the cells.

  6. Photo-induced polymerization of polyaniline

    SciTech Connect

    Barros, R.A. de; Azevedo, W.M. de; Aguiar, F.M. de

    2003-03-15

    A straightforward route to prepare polyaniline is presented in which photons and metallic ions replace conventional oxidants to promote polymerization of aniline monomer. The photopolymerization methods yield a composite material that has been characterized by its UV, visible and Raman spectroscopic analysis and by scanning electron microscopy and X-ray microanalysis as well. Intriguing forms of silver wires embedded in polyaniline are observed, typically of 1 {mu}m wide and up to 100 {mu}m long. It is shown that the morphology of the resulting conducting polymer strongly depends on the excitation wavelength, while a globular morphology is found for the UV synthesis and a fibrillar one is found for visible light excitation.

  7. Measurements of photoinduced refractive index changes in bacteriorhodopsin films

    NASA Astrophysics Data System (ADS)

    Banyal, Ravinder Kumar; Raghavendra Prasad, B.

    2007-03-01

    We report the pump--probe measurements of nonlinear refractive index changes in photochromic bacteriorhodopsin films. The photoinduced absorption is caused by pump beam at 532 nm and the accompanying refractive index changes are studied using a probe beam at 633 nm. The proposed technique is based on a convenient and accurate determination of optical path difference using digital interferometry-based local fringe shift. The results are presented for the wild-type as well as genetically modified D96N variant of the bacteriorhodopsin.

  8. Inhomogeneity of photo-induced fat cell lipolysis

    NASA Astrophysics Data System (ADS)

    Doubrovsky, V. A.; Yanina, I. Yu.; Tuchin, V. V.

    2010-10-01

    The effect of optical properties changes of adipose tissue cells in vitro as a result of photoaction was found and investigated. The experimental study of photo-induced post action upon the cells of fat tissue by means of digital microscopy was fulfilled. The computer processing of digital photos obtained gave an opportunity to estimate quantitatively the level of photoaction upon tissue. Optical interpretation of photos obtained proves that the phenomenon observed corresponds to the lipolysis of adipose tissue cells, but without their complete destruction.

  9. Inhomogeneity of photo-induced fat cell lipolysis

    NASA Astrophysics Data System (ADS)

    Doubrovsky, V. A.; Yanina, I. Yu.; Tuchin, V. V.

    2011-03-01

    The effect of optical properties changes of adipose tissue cells in vitro as a result of photoaction was found and investigated. The experimental study of photo-induced post action upon the cells of fat tissue by means of digital microscopy was fulfilled. The computer processing of digital photos obtained gave an opportunity to estimate quantitatively the level of photoaction upon tissue. Optical interpretation of photos obtained proves that the phenomenon observed corresponds to the lipolysis of adipose tissue cells, but without their complete destruction.

  10. Time-domain ab initio modeling of photoinduced dynamics at nanoscale interfaces.

    PubMed

    Wang, Linjun; Long, Run; Prezhdo, Oleg V

    2015-04-01

    Nonequilibrium processes involving electronic and vibrational degrees of freedom in nanoscale materials are under active experimental investigation. Corresponding theoretical studies are much scarcer. The review starts with the basics of time-dependent density functional theory, recent developments in nonadiabatic molecular dynamics, and the fusion of the two techniques. Ab initio simulations of this kind allow us to directly mimic a great variety of time-resolved experiments performed with pump-probe laser spectroscopies. The focus is on the ultrafast photoinduced charge and exciton dynamics at interfaces formed by two complementary materials. We consider purely inorganic materials, inorganic-organic hybrids, and all organic interfaces, involving bulk semiconductors, metallic and semiconducting nanoclusters, graphene, carbon nanotubes, fullerenes, polymers, molecular crystals, molecules, and solvent. The detailed atomistic insights available from time-domain ab initio studies provide a unique description and a comprehensive understanding of the competition between electron transfer, thermal relaxation, energy transfer, and charge recombination processes. These advances now make it possible to directly guide the development of organic and hybrid solar cells, as well as photocatalytic, electronic, spintronic, and other devices relying on complex interfacial dynamics. PMID:25622188

  11. Photo-induced reduction of flavin mononucleotide in aqueous solutions

    NASA Astrophysics Data System (ADS)

    Song, S.-H.; Dick, B.; Penzkofer, A.

    2007-01-01

    The photo-induced reduction of flavin mononucleotide (FMN) in aqueous solutions is studied by absorption spectra measurement under aerobic and anaerobic conditions. Samples without exogenous reducing agent and with the exogenous reducing agents ethylene-diamine-tetraacetic acid (EDTA) and dithiothreitol (DTT) are investigated. Under anaerobic conditions the photo-induced reduction with and without reducing agents is irreversible. Under aerobic conditions the photo-reduction without added reducing agent is small compared to the photo-degradation, and the photo-reduction of FMN by the reducing agents is reversible (re-oxidation in the dark). During photo-excitation of FMN the dissolved oxygen is consumed by singlet oxygen formation and subsequent chemical reaction. After light switch-off slow re-oxidation (slow absorption recovery) occurs due to air in-diffusion from surface. EDTA degradation by FMN excitation leads to oxygen scavenging. The quantum efficiencies of photo-reduction under aerobic and anaerobic conditions are determined. The re-oxidation of reduced FMN under aerobic conditions and due to air injection is investigated.

  12. Photoinduced Kondo effect in CeZn3P3

    NASA Astrophysics Data System (ADS)

    Kitagawa, J.; Kitajima, D.; Shimokawa, K.; Takaki, H.

    2016-01-01

    The Kondo effect, which originates from the screening of a localized magnetic moment by a spin-spin interaction, is widely observed in nonartificial magnetic materials, artificial quantum dots, and carbon nanotubes. In devices based on quantum dots or carbon nanotubes that target quantum information applications, the Kondo effect can be tuned by a gate voltage, a magnetic field, or light. However, the manipulation of the Kondo effect in nonartificial materials has not been thoroughly studied; in particular, the artificial creation of the Kondo effect remains unexplored. Per this subject study, however, a route for the optical creation of the Kondo effect in the nonartificial material p -type semiconductor CeZn3P3 is presented. The Kondo effect emerges under visible-light illumination of the material by a continuous-wave laser diode and is ultimately revealed by photoinduced electrical resistivity, which clearly exhibits a logarithmic temperature dependency. By contrast, a La-based compound (LaZn3P3 ) displays only normal metallic behavior under similar illumination. The photoinduced Kondo effect, which occurs at higher temperatures when compared with the Kondo effect in artificial systems, provides a potential range of operation for not only quantum information/computation devices but also for operation of magneto-optic devices, thereby expanding the range of device applications based on the Kondo effect.

  13. Overview of photo-induced therapy for ATP production

    NASA Astrophysics Data System (ADS)

    Abdalla, Mohamed; Nagy, A.; Ye, W. N.; Mussivand, T.

    2012-10-01

    The purpose of this report is to provide a review of the effects of low-power photo-induced therapy using lasers of different device parameters such as intensity, wavelength, lasing mechanism (i.e., pulsed or continuous) on the production of Adenosine triphosphate (ATP) in mammalian cells. This is a very important research topic as it is suggested in literature that there might be a relationship between the ATP levels and specific diseases. It has been shown that the ATP production was enhanced at wavelengths ranging between 600 nm and 1000 nm (also known as the optical window), in particular at 600nm, 632.8nm, 635nm, 650nm, and 904nm. However, certain experiments showed that the effectiveness of the photo-induced therapy was also dependent on the dosage and the duration of the supplied light. We present the research conclusions drawn from the experiments reported within the last decade, and provide a list of potential medical treatment(s) for patients using visible and near infrared (NIR) light.

  14. Photoinduced currents in pristine and ion irradiated kapton-H polyimide

    SciTech Connect

    Sharma, Anu Sridharbabu, Y. Quamara, J. K.

    2014-10-15

    The photoinduced currents in pristine and ion irradiated kapton-H polyimide have been investigated for different applied electric fields at 200°C. Particularly the effect of illumination intensity on the maximum current obtained as a result of photoinduced polarization has been studied. Samples were irradiated by using PELLETRON facility, IUAC, New Delhi. The photo-carrier charge generation depends directly on intensity of illumination. The samples irradiated at higher fluence show a decrease in the peak current with intensity of illumination. The secondary radiation induced crystallinity (SRIC) is responsible for the increase in maximum photoinduced currents generated with intensity of illumination.

  15. The dynamics of photoinduced defect creation in amorphous chalcogenides: The origin of the stretched exponential function

    NASA Astrophysics Data System (ADS)

    Freitas, R. J.; Shimakawa, K.; Wagner, T.

    2014-01-01

    The article discusses the dynamics of photoinduced defect creations (PDC) in amorphous chalcogenides, which is described by the stretched exponential function (SEF), while the well known photodarkening (PD) and photoinduced volume expansion (PVE) are governed only by the exponential function. It is shown that the exponential distribution of the thermal activation barrier produces the SEF in PDC, suggesting that thermal energy, as well as photon energy, is incorporated in PDC mechanisms. The differences in dynamics among three major photoinduced effects (PD, PVE, and PDC) in amorphous chalcogenides are now well understood.

  16. Photoinduced in-plane switching of a photochromic nematic liquid crystal

    SciTech Connect

    Komitov, L.; Yamamoto, J.; Yokoyama, H.

    2001-06-15

    Photoinduced fast in-plane switching of the optic axis of a photochromic nematic liquid crystal is found in a sandwich cell with substrates promoting a twofold degenerate anchoring. The switching process is governed by the modification of the anchoring conditions associated with the photoisomerization of the photochromic nematic liquid crystal. Photoinduced in-plane reorientation of the sample optic axis of about 80{degree} has been found. Together with the model of photoinduced in-plane switching, some implementations of this effect are briefly discussed. {copyright} 2001 American Institute of Physics.

  17. The dynamics of photoinduced defect creation in amorphous chalcogenides: The origin of the stretched exponential function

    SciTech Connect

    Freitas, R. J.; Shimakawa, K.; Wagner, T.

    2014-01-07

    The article discusses the dynamics of photoinduced defect creations (PDC) in amorphous chalcogenides, which is described by the stretched exponential function (SEF), while the well known photodarkening (PD) and photoinduced volume expansion (PVE) are governed only by the exponential function. It is shown that the exponential distribution of the thermal activation barrier produces the SEF in PDC, suggesting that thermal energy, as well as photon energy, is incorporated in PDC mechanisms. The differences in dynamics among three major photoinduced effects (PD, PVE, and PDC) in amorphous chalcogenides are now well understood.

  18. Mechanism of Photoinduced Metal-Free Atom Transfer Radical Polymerization: Experimental and Computational Studies.

    PubMed

    Pan, Xiangcheng; Fang, Cheng; Fantin, Marco; Malhotra, Nikhil; So, Woong Young; Peteanu, Linda A; Isse, Abdirisak A; Gennaro, Armando; Liu, Peng; Matyjaszewski, Krzysztof

    2016-02-24

    Photoinduced metal-free atom transfer radical polymerization (ATRP) of methyl methacrylate was investigated using several phenothiazine derivatives and other related compounds as photoredox catalysts. The experiments show that all selected catalysts can be involved in the activation step, but not all of them participated efficiently in the deactivation step. The redox properties and the stability of radical cations derived from the catalysts were evaluated by cyclic voltammetry. Laser flash photolysis (LFP) was used to determine the lifetime and activity of photoexcited catalysts. Kinetic analysis of the activation reaction according to dissociative electron-transfer (DET) theory suggests that the activation occurs only with an excited state of catalyst. Density functional theory (DFT) calculations revealed the structures and stabilities of the radical cation intermediates as well as the reaction energy profiles of deactivation pathways with different photoredox catalysts. Both experiments and calculations suggest that the activation process undergoes a DET mechanism, while an associative electron transfer involving a termolecular encounter (the exact reverse of DET pathway) is favored in the deactivation process. This detailed study provides a deeper understanding of the chemical processes of metal-free ATRP that can aid the design of better catalytic systems. Additionally, this work elucidates several important common pathways involved in synthetically useful organic reactions catalyzed by photoredox catalysts. PMID:26820243

  19. Enhanced Rates of Photoinduced Molecular Orientation in a Series of Molecular Glassy Thin Films.

    PubMed

    Snell, Kristen E; Hou, Renjie; Ishow, Eléna; Lagugné-Labarthet, François

    2015-07-01

    Photoinduced orientation in a series of molecular glasses made of small push-pull azo derivatives is dynamically investigated for the first time. Birefringence measurements at 632.8 nm are conducted with a temporal resolution of 100 ms to probe the fast rate of the azo orientation induced under polarized light and its temporal stability over several consecutive cycles. To better evaluate the influence of the azo chemical substituents and their electronic properties on the orientation of the whole molecule, a series of push-pull azo derivatives involving a triphenylaminoazo core substituted with distinct electron-withdrawing moieties is studied. All resulting thin films are probed using polarization modulation infrared spectroscopy that yields dynamical linear dichroism measurements during a cycle of orientation followed by relaxation. We show here in particular that the orientation rates of small molecule-based azo materials are systematically increased up to 7-fold compared to those of a reference polymer counterpart. For specific compounds, the percentage of remnant orientation is also higher, which makes these materials of great interest and promising alternatives to azobenzene-containing polymers for a variety of applications requiring a fast response and absolute control over the molecular weight. PMID:26072966

  20. Role of Conical Intersections in Molecular Spectroscopy and Photoinduced Chemical Dynamics

    NASA Astrophysics Data System (ADS)

    Domcke, Wolfgang; Yarkony, David R.

    2012-05-01

    This review describes how conical intersections affect measured molecular spectra and simple photofragmentation processes. We consider excitations that result in electron ejection, that is, photoionization or photodetachment, as well as photoinduced H-atom elimination. Section 1 presents a brief overview of the history of conical intersections and their rise from an arcane theoretical concept to a major paradigm in nonadiabatic chemistry. In Section 2, the generic properties of conical intersections are discussed, as well as their characterization with modern electronic-structure methods. Section 3 briefly discusses computational tools used to compute the nuclear motion involving conical intersections. Section 4 describes how the ideas of Sections 2 and 3 are combined to simulate molecular spectra impacted by conical intersections. Section 5 describes selected recent experimental and computational studies of photoelectron, photodetachment, and photofragment spectra. Rather than providing an encyclopedic bibliography of the previous and current literature, we illustrate significant problems currently being addressed and describe what can be accomplished with current computational techniques and how these results are achieved. Section 6 suggests future directions in this field.

  1. Photoinduced Br Desorption from CsBr Thin Films Grown on Cu(100)

    SciTech Connect

    Halliday, Matthew T.; Joly, Alan G.; Hess, Wayne P.; Shluger, AL

    2015-10-22

    Thin films of CsBr deposited onto metals such as copper are potential photocathode materials for light sources and other applications. We investigate desorption dynamics of Br atoms from CsBr films grown on insulator (KBr, LiF) and metal (Cu) substrates induced by sub-bandgap 6.4 eV laser pulses. The experimental results demonstrate that the peak kinetic energy of Br atoms desorbed from CsBr/Cu films is much lower than that for the hyperthermal desorption from CsBr/LiF films. Kelvin probe measurements indicate negative charge at the surface following Br desorption from CsBr/Cu films. Our ab initio calculations of excitons at CsBr surfaces demonstrate that this behavior can be explained by an exciton model of desorption including electron trapping at the CsBr surface. Trapped negative charges reduce the energy of surface excitons available for Br desorption. We examine the electron-trapping characteristics of low-coordinated sites at the surface, in particular, divacancies and kink sites. We also provide a model of cation desorption caused by Franck-Hertz excitation of F centers at the surface in the course of irradiation of CsBr/Cu films. These results provide new insights into the mechanisms of photoinduced structural evolution of alkali halide films on metal substrates and activation of metal photocathodes coated with CsBr.

  2. Role of conical intersections in molecular spectroscopy and photoinduced chemical dynamics.

    PubMed

    Domcke, Wolfgang; Yarkony, David R

    2012-01-01

    This review describes how conical intersections affect measured molecular spectra and simple photofragmentation processes. We consider excitations that result in electron ejection, that is, photoionization or photodetachment, as well as photoinduced H-atom elimination. Section 1 presents a brief overview of the history of conical intersections and their rise from an arcane theoretical concept to a major paradigm in nonadiabatic chemistry. In Section 2, the generic properties of conical intersections are discussed, as well as their characterization with modern electronic-structure methods. Section 3 briefly discusses computational tools used to compute the nuclear motion involving conical intersections. Section 4 describes how the ideas of Sections 2 and 3 are combined to simulate molecular spectra impacted by conical intersections. Section 5 describes selected recent experimental and computational studies of photoelectron, photodetachment, and photofragment spectra. Rather than providing an encyclopedic bibliography of the previous and current literature, we illustrate significant problems currently being addressed and describe what can be accomplished with current computational techniques and how these results are achieved. Section 6 suggests future directions in this field. PMID:22475338

  3. Photoinduced charge transfer from vacuum-deposited molecules to single-layer transition metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Osada, Kazuki; Tanaka, Masatoshi; Ohno, Shinya; Suzuki, Takanori

    2016-06-01

    Variations of photoluminescence (PL) and Raman spectra of single-layer MoS2, MoSe2, WS2, and WSe2 due to the vacuum deposition of C60 or copper phthalocyanine (CuPc) molecules have been investigated. PL spectra are decomposed into two competitive components, an exciton and a charged exciton (trion), depending on carrier density. The variation of PL spectra is interpreted in terms of charge transfer across the interfaces between transition metal dichalcogenides (TMDs) and dopant molecules. We find that deposited C60 molecules inject photoexcited electrons into MoS2, MoSe2, and WS2 or holes into WSe2. CuPc molecules also inject electrons into MoS2, MoSe2, and WS2, while holes are depleted from WSe2 to CuPc. We then propose a band alignment between TMDs and dopant molecules. Peak shifts of Raman spectra and doped carrier density estimated using a three-level model also support the band alignment. We thus demonstrate photoinduced charge transfer from dopant molecules to single-layer TMDs.

  4. Nitroxides as redox probes of melanins: dark-induced and photoinduced changes in redox equilibria

    SciTech Connect

    Sarna, T.; Korytowski, W.; Sealy, R.C.

    1985-05-15

    The interaction of nitroxide free radicals and their reduced products (hydroxylamines) with synthetic and natural melanins has been studied. Electron spin resonance spectroscopy was used to measure changes in radical concentration in the dark and during irradiation with visible or uv light. Some reduction of nitroxide occurs in the dark, and is reversible: the nitroxide can be completely regenerated by the one-electron oxidant ferricyanide. The kinetics of the process depend strongly on radical charge and pH. For positively charged nitroxides the rate is much faster than for either neutral or anionic radicals. At pH 10 the rate is about 20 times faster than at pH 5. Oxidation of hydroxylamine also can occur so that a redox equilibrium is established. The equilibrium constant has been estimated for the reaction between a nitroxide and melanin from autoxidation of 3,4-dihydroxyphenylalanine. Results are also dependent upon the type of melanin used and chemical modification (oxidation or reduction) of the melanin. Redox equilibria are altered during irradiation with either visible or uv light. Rapid oxidation of hydroxylamine to nitroxide is apparent, together with a slower reduction of nitroxide. Action spectra for these processes are related to those for melanin radical production and oxygen consumption in nitroxide-free melanin systems. Reduction of nitroxide is inhibited by oxygen, suggesting a competition between nitroxide and oxygen for photoinduced reducing equivalents.

  5. Biotinylated Platinum(II) Ferrocenylterpyridine Complexes for Targeted Photoinduced Cytotoxicity.

    PubMed

    Mitra, Koushambi; Shettar, Abhijith; Kondaiah, Paturu; Chakravarty, Akhil R

    2016-06-01

    Biotinylated platinum(II) ferrocenylterpyridine (Fc-tpy) complexes [Pt(Fc-tpy)(L(1))]Cl (1) and [Pt(Fc-tpy)(L(2))]Cl (2), where HL(1) and HL(2) are biotin-containing ligands, were prepared, and their targeted photoinduced cytotoxic effect in cancer cells over normal cells was studied. A nonbiotinylated complex, [Pt(Fc-tpy)(L(3))]Cl (3), was prepared as a control to study the role of the biotin moiety in cellular uptake properties of the complexes. Three platinum(II) phenylterpyridine (Ph-tpy) complexes, viz., [Pt(Ph-tpy)(L(1))]Cl (4), [Pt(Ph-tpy)(L(2))]Cl (5), and [Pt(Ph-tpy)(L(3))]Cl (6), were synthesized and explored to understand the role of a metal-bound Fc-tpy ligand over Ph-tpy as a photoinitiator. The Fc-tpy complexes displayed an intense absorption band near 640 nm, which was absent in their Ph-tpy analogues. The Fc-tpy complexes (1 mM in 0.1 M TBAP) showed an irreversible cyclic voltammetric anodic response of the Fc/Fc(+) couple near 0.25 V. The Fc-tpy complexes displayed photodegradation in red light of 647 nm involving the formation of a ferrocenium ion (Fc(+)) and reactive oxygen species (ROS). Photoinduced release of the biotinylated ligands was observed from spectral measurements, and this possibly led to the controlled generation of an active platinum(II) species, which binds to the calf-thymus DNA used for this study. The biotinylated photoactive Fc-tpy complexes showed significant photoinduced cytotoxicity, giving a IC50 value of ∼7 μM in visible light of 400-700 nm with selective uptake in BT474 cancer cells over HBL-100 normal cells. Furthermore, ferrocenyl complexes resulted in light-induced ROS-mediated apoptosis, as indicated by DCFDA, annexin V/FITC staining, and sub-G1 DNA content determined by fluorescent activated cell sorting analysis. The phenyl analogues 4 and 5 were photostable, served as DNA intercalators, and demonstrated selective cytotoxicity in the cancer cells, giving IC50 values of ∼4 μM. PMID:27171926

  6. Photo-induced trimming of chalcogenide-assisted silicon waveguides.

    PubMed

    Canciamilla, Antonio; Morichetti, Francesco; Grillanda, Stefano; Velha, Philippe; Sorel, Marc; Singh, Vivek; Agarwal, Anu; Kimerling, Lionel C; Melloni, Andrea

    2012-07-01

    A chalcogenide-assisted silicon waveguide is realized by depositing a thin layer of A(2)S(3) glass onto a conventional silicon on insulator optical waveguide. The photosensitivity of the chalcogenide is exploited to locally change the optical properties of the waveguide through exposure to visible light radiation. Waveguide trimming is experimentally demonstrated by permanently shifting the resonant wavelength of a microring resonator by 6.7 nm, corresponding to an effective index increase of 1.6·10(-2). Saturation effects, trimming range, velocity and temporal stability of the process are discussed in details. Results demonstrate that photo-induced treatments can be exploited for a post-fabrication compensation of fabrication tolerances, as well as to set and reconfigure the circuit response. PMID:22772270

  7. Photoinduced underwater superoleophobicity of TiO2 thin films.

    PubMed

    Sawai, Yusuke; Nishimoto, Shunsuke; Kameshima, Yoshikazu; Fujii, Eiji; Miyake, Michihiro

    2013-06-11

    The photoinduced wettabilities of water, n-hexadecane, dodecane, and n-heptane on a flat TiO2 surface prepared by a sol-gel method-based coating were investigated. An amphiphilic surface produced by UV irradiation exhibited underwater superoleophobicity with an extremely high static oil contact angle (CA) of over 160°. The TiO2 surface almost completely repelled the oil droplet in water. A robust TiO2 surface with no fragile nanomicrostructure was fabricated on a Ti mesh with a pore size of approximately 150 μm. The fabricated mesh was found to be applicable as an oil/water separation filter. PMID:23701360

  8. Photo-induced reflectivity in the mid and far infrared

    SciTech Connect

    Haar, P.; Harrington, K.J.; Schwettman, H.A.

    1995-12-31

    Interest in switching FEL beams has motivated studies of photo-induced reflectivity in the mid and far infrared. We are particularly interested in Ge{sup 4}, GaAs, and Si{sup 5}, materials that can be pumped with a visible or near-IR conventional laser and which together cover the wavelengths from 3-100{mu}m. We have made quantitative measurements to determine the induced reflectivity, carrier lifetime, and transient absorption of these materials at several wavelengths across this range using a variety of pump laser wavelengths and pulse lengths. These measurements allow us to determine the feasibility of single pulse selection and cavity dumping with our FELs at high repetition rates.

  9. Photoinduced surface voltage mapping study for large perovskite single crystals

    NASA Astrophysics Data System (ADS)

    Liu, Xiaojing; Liu, Yucheng; Gao, Fei; Yang, Zhou; Liu, Shengzhong Frank

    2016-05-01

    Using a series of illumination sources, including white light (tungsten-halogen lamp), 445-nm, 532-nm, 635-nm, and 730-nm lasers, the surface photovoltage (SPV) images were mapped for centimeter-sized CH3NH3PbX3 (X = Cl, Br, I) perovskite single crystals using Kelvin probe force microscopy. The significant SPV signals were observed to be wavelength-dependent. We attribute the appreciable SPV to the built-in electric field in the space charge region. This study shines light into the understanding of photoinduced charge generation and separation processes at nanoscale to help advance the development of perovskite solar cells, optoelectronics, laser, photodetector, and light-emitting diode (LED).

  10. A Photoinduced Cobalt-Catalyzed Synthesis of Pyrroles through in Situ-Generated Acylazirines.

    PubMed

    Pusch, Stefan; Kowalczyk, Danuta; Opatz, Till

    2016-05-20

    Tetrasubstituted pyrroles can be synthesized in a one-pot procedure from isoxazoles. The process includes the photoinduced in situ formation of acylazirines combined with a subsequent cobalt(II)-catalyzed ring expansion with 1,3-diketones. PMID:27081704

  11. Modeling and experimental study of photoinduced anisotropy in hybrid solgel films

    NASA Astrophysics Data System (ADS)

    Raschellà, Raffaella; Marino, Iari-Gabriel; Razzetti, Carlo; Bersani, Danilo; Lottici, Pier P.

    2007-03-01

    The mechanism of photoinduced anisotropy through photoisomerization has been studied by measuring photoinduced dichroism and birefringence in solgel silica-based glasses containing an azo dye (Disperse Red 1) and a plasticizer (carbazole). The equations commonly adopted to describe the molecular orientation (Sekkat's theory) have been solved numerically and analytically within two different approximations. The results have been applied to photoinduced birefringence measured with expanded beams, and the dominant mechanisms driving the azo-dye molecular orientation in the investigated materials during both illumination and relaxation have been inferred. The experiments of photoinduced dichroism, performed with nonexpanded beams, suggest that the distribution of times describing the kinetics of the anisotropy formation, usually attributed to inhomogeneities in the chromophore environment, may be ascribed instead to the nonuniform profile of the beams.

  12. Unambiguous Diagnosis of Photoinduced Charge Carrier Signatures in a Stoichiometrically Controlled Semiconducting Polymer-Wrapped Carbon Nanotube Assembly.

    PubMed

    Olivier, Jean-Hubert; Park, Jaehong; Deria, Pravas; Rawson, Jeff; Bai, Yusong; Kumbhar, Amar S; Therien, Michael J

    2015-07-01

    Single-walled carbon nanotube (SWNT)-based nanohybrid compositions based on (6,5) chirality-enriched SWNTs ([(6,5) SWNTs]) and a chiral n-type polymer (S-PBN(b)-Ph4 PDI) that exploits a perylenediimide (PDI)-containing repeat unit are reported; S-PBN(b)-Ph4 PDI-[(6,5) SWNT] superstructures feature a PDI electron acceptor unit positioned at 3 nm intervals along the nanotube surface, thus controlling rigorously SWNT-electron acceptor stoichiometry and organization. Potentiometric studies and redox-titration experiments determine driving forces for photoinduced charge separation (CS) and thermal charge recombination (CR) reactions, as well as spectroscopic signatures of SWNT hole polaron and PDI radical anion (PDI(-.) ) states. Time-resolved pump-probe spectroscopic studies demonstrate that S-PBN(b)-Ph4 PDI-[(6,5) SWNT] electronic excitation generates PDI(-.) via a photoinduced CS reaction (τCS ≈0.4 ps, ΦCS ≈0.97). These experiments highlight the concomitant rise and decay of transient absorption spectroscopic signatures characteristic of the SWNT hole polaron and PDI(-.) states. Multiwavelength global analysis of these data provide two charge-recombination time constants (τCR ≈31.8 and 250 ps) that likely reflect CR dynamics involving both an intimately associated SWNT hole polaron and PDI(-.) charge-separated state, and a related charge-separated state involving PDI(-.) and a hole polaron site produced via hole migration along the SWNT backbone that occurs over this timescale. PMID:26014277

  13. Tuning the Photoinduced Motion of Glassy Azobenzene Polymers and Networks

    NASA Astrophysics Data System (ADS)

    Vaia, R. A.

    2013-03-01

    Continual innovation at the forefront of soft-matter, in areas such as liquid crystal networks, nano-composites and bio-molecules, is providing exciting opportunities to create smart materials systems that exhibit a controlled, reproducible and reversible modulation of physical properties. These material systems evoke the adaptivity of natural organisms, and inspire radical aerospace notions. A key example is photo-responsive polymers, which convert a light stimulus input into a mechanical output (work). Photoinduced conformational changes, such as within azobenzene, dictate molecular-level distortions that summate into a macroscopic strain, which often manifests as a shape change or motion. The transduction of the molecular-level response to a macroscale effect is regulated by mesoscopic features, such as chain packing, free volume, and local molecular order - factors which depend on chemical composition as well as the process history of the material. For example, physical aging increases the density of the glass, reduces local free volume, and thus decreases the minima in local conformation space which strongly influences the azobenzene photochemistry (trans-cis-trans isomerization). The subsequent change in the energy landscape of the system reduces the fraction of azobenzene able to undergo reconfiguration as well as increases the probability that those photoinduced conformations will relax back to the initial local environment. The result is a tuning of the magnitude of macroscopic strain and the ability to shift from shape fixing to shape recovery, respectively. Work done in collaboration with H. Koerner, K.M. Lee, M. Smith, D. Wang, L-S. Tan. and T. White, Air Force Research Laboratory.

  14. Luminescence and photoinduced absorption in ytterbium-doped optical fibres

    SciTech Connect

    Rybaltovsky, A A; Aleshkina, S S; Likhachev, M E; Bubnov, M M; Umnikov, A A; Yashkov, M V; Gur'yanov, Aleksei N; Dianov, Evgenii M

    2011-12-31

    Photochemical reactions induced in the glass network of an ytterbium-doped fibre core by IR laser pumping and UV irradiation have been investigated by analysing absorption and luminescence spectra. We have performed comparative studies of the photoinduced absorption and luminescence spectra of fibre preforms differing in core glass composition: Al{sub 2}O{sub 3} : SiO{sub 2}, Al{sub 2}O{sub 3} : Yb{sub 2}O{sub 3} : SiO{sub 2}, and P{sub 2}O{sub 5} : Yb{sub 2}O{sub 3} : SiO{sub 2}. The UV absorption spectra of unirradiated preform core samples show strong bands peaking at 5.1 and 6.5 eV, whose excitation plays a key role in photoinduced colour centre generation in the glass network. 'Direct' UV excitation of the 5.1- and 6.5-eV absorption bands at 244 and 193 nm leads to the reduction of some of the Yb{sup 3+} ions to Yb{sup 2+}. The photodarkening of ytterbium-doped fibres by IR pumping is shown to result from oxygen hole centre generation. A phenomenological model is proposed for the IR-pumping-induced photodarkening of ytterbium-doped fibres. The model predicts that colour centre generation in the core glass network and the associated absorption in the visible range result from a cooperative effect involving simultaneous excitation of a cluster composed of several closely spaced Yb{sup 3+} ions.

  15. Highly efficient photoinduced desorption of N{sub 2}O and CO from porous silicon

    SciTech Connect

    Toker, Gil; Sagi, Roey; Bar-Nachum, Shay; Asscher, Micha

    2013-01-28

    Photoinduced desorption (PID) of N{sub 2}O and CO from porous silicon (PSi) samples is reported. Both adsorbates exhibit unusually large cross sections for PID at 193 nm, up to 10{sup -15} cm{sup 2}, 2-3 orders of magnitude larger than the literature values for similar processes on flat Si. Under this UV irradiation, N{sub 2}O molecules undergo photodissociation (a competing process leading to surface oxidation) with a cross section that is 2 orders of magnitude smaller than photodesorption. In the case of CO desorption is the exclusive photodepletion mechanism. PID efficiency decreases with increasing CO coverage suggesting PID hindrance by interactions among the desorbing CO molecules leading to re-adsorption at higher coverage. The wavelength and fluence dependence measurements exclude the possibility of laser induced thermal desorption for both adsorbates. The proposed mechanism for this phenomenon is desorption induced by hot electron transfer from the substrate to the adsorbate. Enhanced lifetime of transient negative adsorbate due to stabilization by localized holes on PSi nanotips can explain the observed abnormally large PID efficiency on top of porous silicon.

  16. Mode of photo-induced toxic action of PAH in fish

    SciTech Connect

    Weinstein, J.E.; Oris, J.T.; Taylor, D.H.

    1995-12-31

    Juvenile fathead minnows (Pimephales promelas) were exposed to 0, 6, and 12 {micro}g/L fluoranthene in the presence of ultraviolet (US) light for 6, 12, 24, 48 and 96 hours. Ultrastructural pathology of the secondary gill lamellae was examined using transmission electron microscopy. Following 12 hours of exposure to 12 {micro}g/L fluoranthene and UV light, epithelial cells appeared highly vacuolated and swollen. Following 48 hours, additional morphological alterations in epithelial cells included multivesiculated blebbing of the plasma membrane into intercellular gaps, numerous cytolysosomes, myelinoid bodies, and enlarged lysosomes with lipid-like contents. The staining characteristics of these cytoplasmic inclusions were consistent with that of phospholipid autodigestion. In addition, an inflammatory-type reaction occurred in the secondary lamellae following 24 hours of exposure. This reaction was characterized by large areas of intercellular edema, which produced a lifting of the epithelium, and the occasional presence of macrophages and granulocytes within the edematous areas and the lamellar blood sinuses. No morphological changes were observed in chloride cells, mucous cells, or pillar cells. In those fish exposed to 6 {micro}g/L fluoranthene and UV light, a similar progression compared to 12 {micro}g/L exposure of epithelial cell damage and inflammatory-type reaction was evident beginning at 24 hours of exposure. The results of this study suggest that the mode of action of photo-induced fluoranthene toxicity in fish is respiratory stress.

  17. Unravelling the mechanism of photoinduced charge transfer processes in lead iodide perovskite solar cells

    NASA Astrophysics Data System (ADS)

    Marchioro, Arianna; Teuscher, Joël; Friedrich, Dennis; Kunst, Marinus; van de Krol, Roel; Moehl, Thomas; Grätzel, Michael; Moser, Jacques-E.

    2014-03-01

    Lead halide perovskites have recently been used as light absorbers in hybrid organic-inorganic solid-state solar cells, with efficiencies as high as 15% and open-circuit voltages of 1 V. However, a detailed explanation of the mechanisms of operation within this photovoltaic system is still lacking. Here, we investigate the photoinduced charge transfer processes at the surface of the perovskite using time-resolved techniques. Transient laser spectroscopy and microwave photoconductivity measurements were applied to TiO2 and Al2O3 mesoporous films impregnated with CH3NH3PbI3 perovskite and the organic hole-transporting material spiro-OMeTAD. We show that primary charge separation occurs at both junctions, with TiO2 and the hole-transporting material, simultaneously, with ultrafast electron and hole injection taking place from the photoexcited perovskite over similar timescales. Charge recombination is shown to be significantly slower on TiO2 than on Al2O3 films.

  18. Direct Observation of Photoinduced Charge Separation in Ruthenium Complex/Ni(OH)2 Nanoparticle Hybrid

    PubMed Central

    Tang, Yu; Pattengale, Brian; Ludwig, John; Atifi, Abderrahman; Zinovev, Alexander V.; Dong, Bin; Kong, Qingyu; Zuo, Xiaobing; Zhang, Xiaoyi; Huang, Jier

    2015-01-01

    Ni(OH)2 have emerged as important functional materials for solar fuel conversion because of their potential as cost-effective bifunctional catalysts for both hydrogen and oxygen evolution reactions. However, their roles as photocatalysts in the photoinduced charge separation (CS) reactions remain unexplored. In this paper, we investigate the CS dynamics of a newly designed hybrid catalyst by integrating a Ru complex with Ni(OH)2 nanoparticles (NPs). Using time resolved X-ray absorption spectroscopy (XTA), we directly observed the formation of the reduced Ni metal site (~60 ps), unambiguously demonstrating CS process in the hybrid through ultrafast electron transfer from Ru complex to Ni(OH)2 NPs. Compared to the ultrafast CS process, the charge recombination in the hybrid is ultraslow (≫50 ns). These results not only suggest the possibility of developing Ni(OH)2 as solar fuel catalysts, but also represent the first time direct observation of efficient CS in a hybrid catalyst using XTA. PMID:26673578

  19. Photoinduced hydroxyl radical and photocatalytic activity of samarium-doped TiO(2) nanocrystalline.

    PubMed

    Xiao, Qi; Si, Zhichun; Zhang, Jiang; Xiao, Chong; Tan, Xiaoke

    2008-01-15

    Sm(3+)-doped TiO(2) nanocrystalline has been prepared by sol-gel auto-combustion technique and characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) method, and also UV-vis diffuse reflectance spectroscopy (DRS). These Sm(3+)-doped TiO(2) samples were tested for methylene blue (MB) decomposition and *OH radical formation. The analysis of *OH radical formation on the sample surface under UV irradiation was performed by fluorescence technique with using terephthalic acid, which readily reacted with *OH radical to produce highly fluorescent product, 2-hydroxyterephthalic acid. It was observed that the presence of Sm(3+) ion as a dopant significantly enhanced the photocatalytic activity for MB degradation under UV light irradiation because both the larger specific surface area and the greater the formation rate of *OH radical were simultaneously obtained for Sm(3+)-doped TiO(2) nanocrystalline. The adsorption experimental demonstrated that Sm(3+)-TiO(2) had a higher MB adsorption capacity than undoped TiO(2) and the adsorption capacity of MB increased with the increase of samarium ion content. The results also indicated that the greater the formation rate of *OH radical was, the higher photocatalytic activity was achieved. In this study, the optimum amount of Sm(3+) doping was 0.5 mol%, at which the recombination of photo-induced electrons and holes could be effectively inhibited, the highest formation rate of *OH radicals was, and thereby the highest photocatalytic activity was achieved. PMID:17540502

  20. Direct Observation of Photoinduced Charge Separation in Ruthenium Complex/Ni(OH)2 Nanoparticle Hybrid

    DOE PAGESBeta

    Tang, Yu; Pattengale, Brian A.; Ludwig, John M.; Atifi, Abderrahman; Zinovev, Alexander V.; Dong, Bin; Kong, Qingyu; Zuo, Xiaobing; Zhang, Xiaoyi; Huang, Jier

    2015-12-17

    We report that Ni(OH)2 have emerged as important functional materials for solar fuel conversion because of their potential as cost-effective bifunctional catalysts for both hydrogen and oxygen evolution reactions. However, their roles as photocatalysts in the photoinduced charge separation (CS) reactions remain unexplored. In this paper, we investigate the CS dynamics of a newly designed hybrid catalyst by integrating a Ru complex with Ni(OH)2 nanoparticles (NPs). Using time resolved X-ray absorption spectroscopy (XTA), we directly observed the formation of the reduced Ni metal site (~60 ps), unambiguously demonstrating CS process in the hybrid through ultrafast electron transfer from Ru complexmore » to Ni(OH)2 NPs. Compared to the ultrafast CS process, the charge recombination in the hybrid is ultraslow (>>50 ns). These results not only suggest the possibility of developing Ni(OH)2 as solar fuel catalysts, but also represent the first time direct observation of efficient CS in a hybrid catalyst using XTA.« less

  1. Photophysics of Voltage Increase by Photoinduced Dipole Layers in Sensitized Solar Cells.

    PubMed

    Kazes, Miri; Buhbut, Sophia; Itzhakov, Stella; Lahad, Ohr; Zaban, Arie; Oron, Dan

    2014-08-01

    Significant overpotentials between the sensitizer and both the electron and hole conductors hamper the performance of sensitized solar cells, leading to a reduced photovoltage. We show that by using properly designed type-II quantum dots (QDs) between the sensitizer and the hole conductor in thin absorber cells, it is possible to increase the open circuit voltage (Voc) by more than 100 mV. This increase is due to the formation of a photoinduced dipole (PID) layer. Photogenerated holes in the type-II QDs are retained in the core for a relatively long time, allowing for the accumulation of a positively charged layer. Negative charges are, in turn, injected and accumulated in the TiO2 anode, creating a dipole moment, which negatively shifts the TiO2 conduction band relative to the electrolyte. We study this phenomenon using a unique TiO2/CdSe/(ZnSe:Te/CdS)/polysulfide system, where the formation of a PID depends on the color of the illumination. The PID concept thus introduces a new design strategy, where the operating parameters of the solar cell can be manipulated separately. PMID:26277969

  2. Reversible modulated mid-infrared absorption of Ag/TiO{sub 2} by photoinduced interfacial charge transfer

    SciTech Connect

    Xu, S. C. E-mail: ghli@issp.ac.cn; Li, L.; Pan, S. S.; Luo, Y. Y.; Zhang, Y. X.; Li, G. H. E-mail: ghli@issp.ac.cn

    2014-10-06

    An enhanced mid-infrared absorption in Ag nanoparticles-decorated TiO{sub 2} microflowers was reported. It was found that the mid-infrared absorption of the Ag/TiO{sub 2} complex depends strongly on the content and size of Ag nanoparticles, the higher the Ag nanoparticles content, the stronger the infrared absorption. The average reflectivity in the entire mid-infrared region of the microflowers drops from 57.6% to 10.5% after Ag nanoparticles decoration. Reversible modulated mid-infrared absorption properties were found in the Ag/TiO{sub 2} complexes upon alternative illumination of visible and UV light due to the photoinduced interfacial electron transfer between TiO{sub 2} semiconductor and Ag nanoparticles.

  3. Surface chemistry and interfacial charge-transfer mechanisms in photoinduced oxygen exchange at O2-TiO2 interfaces.

    PubMed

    Montoya, Juan Felipe; Peral, José; Salvador, Pedro

    2011-04-01

    Experimental results obtained over the last three decades on photoinduced oxygen isotopic exchange (POIE) of TiO₂ oxygen atoms with those of adsorbed water molecules and gaseous O₂ are analyzed in the light of recent information from the literature on the interaction of water and O₂ species with the TiO₂ surface (obtained by application of surface spectroscopy techniques in combination with high-resolution scanning tunnelling microscopy). The analysis emphasizes the singular role that bridging oxygen ions and bridging oxygen vacancies play in TiO₂ surface chemistry and interfacial electron transfer at the gas phase-TiO₂ interface in the absence and presence of water. The observed competition between POIE and the photo-oxidation (PO) of organic compounds is analyzed in terms of the recently developed direct-indirect (D-I) kinetic model for heterogeneous photocatalysis (D. Monllor-Satoca et al., Catal. Today, 2007, 129, 247, and references therein). PMID:21442702

  4. Long-lived excited states of zwitterionic copper(I) complexes for photoinduced cross-dehydrogenative coupling reactions.

    PubMed

    Wang, Bin; Shelar, Deepak Prakash; Han, Xian-Zhu; Li, Ting-Ting; Guan, Xiangguo; Lu, Wei; Liu, Kun; Chen, Yong; Fu, Wen-Fu; Che, Chi-Ming

    2015-01-12

    Four heteroleptic copper(I) complexes containing phenanthroline and monoanionic nido-carborane-diphosphine ligands have been prepared and structurally characterized by various spectroscopic techniques and X-ray diffraction. These complexes exhibit intense absorptions in the visible range and excited-state lifetimes on the microsecond scale. Their application in visible-light-induced cross-dehydrogenative coupling reactions was investigated. Preliminary studies showed that one of the four copper(I) complexes is an efficient catalyst for photoinduced oxidative C-H functionalization using oxygen as oxidant. Furthermore, α-functionalized tertiary amines were obtained in good-to-excellent yields by light irradiation (λ>420 nm) of a mixture of our Cu(I) complex, tertiary amines, and a variety of nucleophiles (nitroalkane, acetone, or indoles) under aerobic conditions. Electron paramagnetic resonance measurements provided evidence for the formation of superoxide radical anions (O2(-⋅)) rather than singlet oxygen ((1)O2) during these photocatalytic reactions. PMID:25413572

  5. Intramolecular photoinduced proton transfer in 2-(2‧-hydroxyphenyl)benzazole family: A TD-DFT quantum chemical study

    NASA Astrophysics Data System (ADS)

    Roohi, Hossein; Mohtamedifar, Nafiseh; Hejazi, Fahemeh

    2014-11-01

    In this work, intramolecular photoinduced proton transfer in 2-(2‧-hydroxyphenyl)benzazole family (HBO, HBI and HBT) was investigated using TD-DFT calculations at PBE1PBE/6-311++G(2d,2p) level of theory. The potential energy surfaces were employed to explore the proton transfer reactions in both states. In contrast to the ground state, photoexcitation from S0 state to S1 one encourages the operation of the excited-state intramolecular proton transfer process. Structural parameters, H-bonding energy, absorption and emission bands, vertical excitation and emission energies, oscillator strength, fluorescence rate constant, dipole moment, atomic charges and electron density at critical points were calculated. Molecular orbital analysis shows that vertical S0 → S1 transition in the studied molecules corresponds essentially to the excitation from HOMO (π) to LUMO (π∗). Our calculated results are in good agreement with the experimental observations.

  6. Frontier orbital symmetry control of intermolecular electron transfer. Final report, September 15, 1988--December 31, 1994

    SciTech Connect

    Stevens, B.

    1997-07-01

    This report discusses the following topics: the recovery of intermolecular transfer parameters from fluorescence quenching in liquids; photoinduced intramolecular electron transfer in flexible donor/space/acceptor systems containing an extended unsaturated spacer; electron transfer sensitized reaction; the recovery of solute and fractal dimensions from electron transfer quenching data; and frontier orbital symmetry control of back electron transfer.

  7. Self-assembly of semiconductor organogelator nanowires for photoinduced charge separation.

    PubMed

    Wicklein, André; Ghosh, Suhrit; Sommer, Michael; Würthner, Frank; Thelakkat, Mukundan

    2009-05-26

    We investigated an innovative concept of general validity based on an organogel/polymer system to generate donor-acceptor nanostructures suitable for charge generation and charge transport. An electron conducting (acceptor) perylene bisimide organogelator forms nanowires in suitable solvents during gelation process. This phenomenon was utilized for its self-assembly in an amorphous hole conducting (donor) polymer matrix to realize an interpenetrating donor-acceptor interface with inherent morphological stability. The self-assembly and interface generation were carried out either stepwise or in a single-step. Morphology of the donor-acceptor network in thin films obtained via both routes were studied by a combination of scanning electron microscopy and atomic force microscopy. Additionally, photoinduced charge separation and charge transport in these systems were tested in organic solar cells. Fabrication steps of multilayer organogel/polymer photovoltaic devices were optimized with respect to morphology and surface roughness by introducing additional smoothening layers and charge injection/blocking layers. An inverted cell geometry was used here in which electrons are collected at the bottom electrode and holes at the top electrode. The simultaneous preparation of the interface exhibits almost 3-fold improvement in device characteristics compared to the successive method. The device characteristics under AM1.5 spectral conditions and 100 mW/cm(2) for the simultaneous preparation route are short circuit current J(sc) = 0.28 mA cm(-2), open circuit voltage V(OC) = 390 mV, fill factor FF = 38%, and a power conversion efficiency eta = 0.041%. PMID:19408933

  8. 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.

  9. Impact of chirality on the photoinduced charge transfer in linked systems containing naproxen enantiomers.

    PubMed

    Khramtsova, E A; Sosnovsky, D V; Ageeva, A A; Nuin, E; Marin, M L; Purtov, P A; Borisevich, S S; Khursan, S L; Roth, H D; Miranda, M A; Plyusnin, V F; Leshina, T V

    2016-05-14

    The model reaction of photoinduced donor-acceptor interaction in linked systems (dyads) has been used to study the comparative reactivity of a well-known anti-inflammatory drug, (S)-naproxen (NPX) and its (R)-isomer. (R)- or (S)-NPX in these dyads is linked to (S)-N-methylpyrrolidine (Pyr) using a linear or cyclic amino acid bridge (AA or CyAA), to give (R)-/(S)-NPX-AA-(S)-Pyr flexible and (R)-/(S)-NPX-CyAA-(S)-Pyr rigid dyads. The donor-acceptor interaction is reminiscent of the binding (partial charge transfer, CT) and electron transfer (ET) processes involved in the extensively studied inhibition of the cyclooxygenase enzymes (COXs) by the NPX enantiomers. Besides that, both optical isomers undergo oxidative metabolism by enzymes from the P450 family, which also includes ET. The scheme proposed for the excitation quenching of the (R)- and (S)-NPX excited state in these dyads is based on the joint analysis of the chemically induced dynamic nuclear polarization (CIDNP) and fluorescence data. The (1)H CIDNP effects in this system appear in the back electron transfer in the biradical-zwitterion (BZ), which is formed via dyad photoirradiation. The rate constants of individual steps in the proposed scheme and the fluorescence quantum yields of the local excited (LE) states and exciplexes show stereoselectivity. It depends on the bridge's length, structure and solvent polarity. The CIDNP effects (experimental and calculated) also demonstrate stereodifferentiation. The exciplex quantum yields and the rates of formation are larger for the dyads containing (R)-NPX, which let us suggest a higher contribution from the CT processes with the (R)-optical isomer. PMID:27098151

  10. Photo-induced chemical reaction of trans-resveratrol.

    PubMed

    Zhao, Yue; Shi, Meng; Ye, Jian-Hui; Zheng, Xin-Qiang; Lu, Jian-Liang; Liang, Yue-Rong

    2015-03-15

    Photo-induced chemical reaction of trans-resveratrol has been studied. UV B, liquid state and sufficient exposure time are essential conditions to the photochemical change of trans-resveratrol. Three principal compounds, cis-resveratrol, 2,4,6-phenanthrenetriol and 2-(4-hydroxyphenyl)-5,6-benzofurandione, were successively generated in the reaction solution of trans-resveratrol (0.25 mM, 100% ethanol) under 100 μW cm(-2) UV B radiation for 4h. cis-Resveratrol, originated from isomerization of trans-resveratrol, resulted in 2,4,6-phenanthrenetriol through photocyclisation reaction meanwhile loss of 2 H. 2,4,6-Phenanthrenetriol played a role of photosensitizer producing singlet oxygen in the reaction pathway. The singlet oxygen triggered [4+2] cycloaddition reaction of trans-resveratrol, and then resulted in the generation of 2-(4-hydroxyphenyl)-5,6-benzofurandione through photorearrangement and oxidation reaction. The singlet oxygen reaction was closely related to the substrate concentration of trans-resveratrol in solution. PMID:25308653

  11. Photoinducing the hidden M2 phase in VO2

    NASA Astrophysics Data System (ADS)

    Walko, D. A.; Smith, R. K.; Wen, Haidan; Dichiara, A. D.; Jeong, Jaewoo; Samant, Mahensh G.; Parkin, Stuart S. P.

    We used time-resolved x-ray diffraction to study photoinduced structural phase transitions in a 170-nm-thick VO2 film grown on sapphire (1,0,-1,0). Heating the unstrained film from room temperature induces the well-known phase transition from the monoclinic (M1) phase directly to the high-temperature tetragonal rutile (R) phase. In contrast, upon ultrafast optical excitation, the phase transition depends strongly on the laser intensity. At low fluences, the film is partially transformed into the monoclinic M2 phase, a phase which generally is observed only in doped or strained materials. Above a threshold at higher fluences, a small portion of the film is transformed into the M2 phase, decaying on a time scale of a few nanoseconds, while the majority of the film is transformed into the R phase which can persist for tens of nanoseconds. We further discuss the effects of laser wavelength on the efficiency of producing the M2 phase. Work at the Advanced Photon Source supported by DOE Contract No. DE-AC02-06CH11357.

  12. Diel variations in photoinduced oxidation of Hg0 in freshwater.

    PubMed

    Garcia, Edenise; Poulain, Alexandre J; Amyot, Marc; Ariya, Parisa A

    2005-05-01

    Experiments have been conducted to determine diel variations in photoinduced Hg0 oxidation in lake water under natural Hg0(aq) concentrations. Pseudo-first-order rates of photooxidation (k') were calculated for water freshly collected in a Canadian Shield lake, Lake Croche (45 degrees 56' N, 74 degrees 00' W), at different periods of the day and subsequently incubated in the dark. Hg0 oxidation rates ranged from 0.02 to 0.07 h(-1), increasing from sunrise to noon and then decreasing throughout the remainder of the day. These changes paralleled those in sunlight intensity integrated over 1 h preceding water collection, and suggested that the water freshly collected in daylight was rich in photochemically produced Hg0 oxidants. It was also estimated that under intense solar radiation, even if oxidation rates reached a peak, reduction of Hg(II) was the prevalent redox process. Inversely, Hg0 oxidation overcame DGM production during the night or at periods of weaker light intensity. Overall, these findings explain the decreases in the DGM pool generally observed overnight. They also support previous reports that, during summer days, volatilization of Hg0 from water represent an important step in the Hg cycle in freshwater systems. PMID:15823331

  13. Gradient and scattering forces in photoinduced force microscopy

    NASA Astrophysics Data System (ADS)

    Jahng, Junghoon; Brocious, Jordan; Fishman, Dmitry A.; Huang, Fei; Li, Xiaowei; Tamma, Venkata Ananth; Wickramasinghe, H. Kumar; Potma, Eric Olaf

    2014-10-01

    A theoretical and experimental analysis of the dominant forces measured in photoinduced force microscopy is presented. It is shown that when operated in the noncontact and soft-contact modes, the microscope is sensitive to the optically induced gradient force (Fg) and the scattering force (Fsc). The reconstructed force-distance curve reveals a tip-dependent scattering force in the 30-60 pN range. Whereas the scattering force is virtually insensitive to the nanoscopic tip-sample distance, the gradient force shows a z-4 dependence and is manifest only for tip-sample distances of a few nm. Measurements on glass, gold nanowires, and molecular clusters of silicon naphtalocyanine confirm that the gradient force is strongly dependent on the polarizability of the sample, enabling spectroscopic imaging through force detection. The nearly constant Fsc and the spatially dependent Fg give rise to a complex force-distance curve, which varies from point to point in the specimen and dictates the image contrast observed for a given set point of the cantilevered tip.

  14. Photoinduced superhydrophilicity: a kinetic study of time dependent photoinduced contact angle changes on TiO2 surfaces.

    PubMed

    Foran, Philip S; Boxall, Colin; Denison, Kieth R

    2012-12-21

    Transparent TiO(2) thin films were prepared on quartz substrates via a reverse micelle, sol-gel, spin-coating technique. The time dependence of the TiO(2) film photoinduced superhydrophilicity (PISH) was measured by goniometric observation of the contact angle, θ, of sessile water drops at the film surfaces. In these measurements, the TiO(2) substrate was illuminated by 315 nm light and drops were sequentially applied at a range of illumination times. Using a model for the wetting of heterogeneous surfaces derived by Israelachvili and Gee, these measurements were used to calculate the time dependence of f(2), the fractional surface coverage of the TiO(2) surface by adventitious contaminating organics (Israelachvili, J. N.; Gee, M. L. Contact angles on chemically heterogeneous surfaces. Langmuir 1989, 5, 288). Extending this model to include a Langmuir-Hinshelwood based kinetic analysis of f(2) as a function of time allowed for calculation of an expected value for θ immediately prior to illumination, that is, at illumination time t = 0. Such expected values of θ at t = 0 were calculated using two possible values of θ(1), the contact angle on a pristine unilluminated homogeneous TiO(2) surface: (i) θ(1) = 4° as suggested by, inter alia, Zubkov et al. (Zubkov, T.; Stahl, D.; Thompson, T. L.; Panayotov, D.; Diwald, O.; Yates, J. T. Ultraviolet Light-Induced Hydrophilicity Effect on TiO(2)(110)(1 × 1). Dominant Role of the Photooxidation of Adsorbed Hydrocarbons Causing Wetting by Water Droplets. J. Phys. Chem. B2005, 109, 15454); and (ii) where θ(1) = 25°, as suggested by Fujishima et al., representative of a more hydrophobic homogeneous TiO(2) surface that reconstructs upon exposure to ultraband gap illumination into a hydrophilic surface where θ(1) → 0° (Fujishima, A.; Zhang, X.; Tryk, D. A. TiO(2) photocatalysis and related surface phenomena Surf. Sci. Rep.2008, 63, 515). Analysis of data from our experiments and from selected literature sources

  15. Simultaneous photoinduced generation of Fe(2+) and H2O2 in rivers: An indicator for photo-Fenton reaction.

    PubMed

    Mostofa, Khan M G; Sakugawa, Hiroshi

    2016-09-01

    The photo-Fenton reaction is a key source of the highly reactive hydroxyl radical (HO) that is produced by the reaction of simultaneous photo-induced generation of Fe(2)(+)-dissolved organic matter (DOM) with H2O2 in sunlit surface waters as well as in the treatment of organic pollutants in the advanced oxidation processes (AOPs). Concentrations of both H2O2 and Fe(2)(+)-DOM were dependent on time and total solar intensity flux, and their levels were highest in the diurnal samples collected at noon compared with the samples collected during the period before sunrise and after sunset. H2O2 and Fe(2)(+)-DOM concentrations during monthly readings were also found higher in comparison with the diurnal samples, shortly before sunrise or after sunset. A π-electron bonding system is formed between Fe and the functional groups in DOM (Fe-DOM), through electron donation from the functional groups of DOM to an empty d-orbital of Fe. The π-electron is loosely bound and is highly susceptible to a rapid excitation upon light exposure that will provide better understanding of the formation of aqueous electrons, superoxide radical anions, H2O2 and finally, photo-Fenton reactions, too. Our results imply that simultaneous generation of H2O2 and Fe(2)(+)-DOM upon sunlight exposure during the daytime is most likely to be the key photo-Fenton reaction pathway, taking place in surface waters. PMID:27593270

  16. Enhancement of Photoinduced Charge-Order Melting via Anisotropy Control by Double-Pulse Excitation in Perovskite Manganites: Pr_{0.6}Ca_{0.4}MnO_{3}.

    PubMed

    Yada, H; Ijiri, Y; Uemura, H; Tomioka, Y; Okamoto, H

    2016-02-19

    To control the efficiency of photoinduced charge-order melting in perovskite manganites, we performed femtosecond pump-probe spectroscopy using double-pulse excitation on Pr_{0.6}Ca_{0.4}MnO_{3}. The results revealed that the transfer of the spectral weight from the near-infrared to infrared region by the second pump pulse is considerably enhanced by the first pump pulse and that the suppression of crystal anisotropy, that is, the decrease of long-range lattice deformations due to the charge order by the first pump pulse is a key factor to enhance the charge-order melting. This double-pulse excitation method can be applied to various photoinduced transitions in complex materials with electronic and structural instabilities. PMID:26943548

  17. Photo-induced Doping in GaN Epilayers with Graphene Quantum Dots

    PubMed Central

    Lin, T. N.; Inciong, M. R.; Santiago, S. R. M. S.; Yeh, T. W.; Yang, W. Y.; Yuan, C. T.; Shen, J. L.; Kuo, H. C.; Chiu, C. H.

    2016-01-01

    We demonstrate a new doping scheme where photo-induced carriers from graphene quantum dots (GQDs) can be injected into GaN and greatly enhance photoluminescence (PL) in GaN epilayers. An 8.3-fold enhancement of PL in GaN is observed after the doping. On the basis of time-resolved PL studies, the PL enhancement is attributed to the carrier transfer from GQDs to GaN. Such a carrier transfer process is caused by the work function difference between GQDs and GaN, which is verified by Kelvin probe measurements. We have also observed that photocurrent in GaN can be enhanced by 23-fold due to photo-induced doping with GQDs. The improved optical and transport properties from photo-induced doping are promising for applications in GaN-based optoelectronic devices. PMID:26987403

  18. Photo-induced Doping in GaN Epilayers with Graphene Quantum Dots.

    PubMed

    Lin, T N; Inciong, M R; Santiago, S R M S; Yeh, T W; Yang, W Y; Yuan, C T; Shen, J L; Kuo, H C; Chiu, C H

    2016-01-01

    We demonstrate a new doping scheme where photo-induced carriers from graphene quantum dots (GQDs) can be injected into GaN and greatly enhance photoluminescence (PL) in GaN epilayers. An 8.3-fold enhancement of PL in GaN is observed after the doping. On the basis of time-resolved PL studies, the PL enhancement is attributed to the carrier transfer from GQDs to GaN. Such a carrier transfer process is caused by the work function difference between GQDs and GaN, which is verified by Kelvin probe measurements. We have also observed that photocurrent in GaN can be enhanced by 23-fold due to photo-induced doping with GQDs. The improved optical and transport properties from photo-induced doping are promising for applications in GaN-based optoelectronic devices. PMID:26987403

  19. Photo-induced Doping in GaN Epilayers with Graphene Quantum Dots

    NASA Astrophysics Data System (ADS)

    Lin, T. N.; Inciong, M. R.; Santiago, S. R. M. S.; Yeh, T. W.; Yang, W. Y.; Yuan, C. T.; Shen, J. L.; Kuo, H. C.; Chiu, C. H.

    2016-03-01

    We demonstrate a new doping scheme where photo-induced carriers from graphene quantum dots (GQDs) can be injected into GaN and greatly enhance photoluminescence (PL) in GaN epilayers. An 8.3-fold enhancement of PL in GaN is observed after the doping. On the basis of time-resolved PL studies, the PL enhancement is attributed to the carrier transfer from GQDs to GaN. Such a carrier transfer process is caused by the work function difference between GQDs and GaN, which is verified by Kelvin probe measurements. We have also observed that photocurrent in GaN can be enhanced by 23-fold due to photo-induced doping with GQDs. The improved optical and transport properties from photo-induced doping are promising for applications in GaN-based optoelectronic devices.

  20. Dynamic structural effects and ultrafast biomolecular kinetics in photoinduced charge transfer reactions. Three year progress report, March 15, 1991--May 14, 1994

    SciTech Connect

    Hupp, J.T.

    1994-04-01

    The reactions were primarily electron-transfer-reactivity related (ET?). Goals were to obtain complete, multimode, experimental descriptions of vibrational (Franck-Condon) barriers to intramolecular electron transfer, explore molecular generality of time-dependent scattering analysis, connect the information directly to measured rates of photoinduced ET (femtosecond, picosecond, nanosecond regime), obtain complementary information in the microsecond regime (longer-range thermal ET) via pulsed-accelrated flow, explore valence localization/delocalization via vibronic coupling (resonance Raman in extended near infrared) and via reversible external manipulation of internal electronic structure, and manipulate and accelerate bimolecular photoredox processes by using room-temperature supercritical fluids. Fe and Ru complexes with such compounds as cyano-N-methylpyridinium compounds were studied.

  1. Photoinduced extrinsic electrical conduction of nematic liquid crystal

    NASA Astrophysics Data System (ADS)

    Dedov, O. V.; Krivoschekov, V. A.

    1996-05-01

    During recent years the interest in media with strong nonlinear response is growing. These media allow the user to observe different nonlinear optic effects using small intensities of light. It is well known that liquid crystals are rather promising media for this research. This paper is devoted to the experimental research of the photoinduced conduction of a mixture of a nematic liquid crystal and a dye. Dependence of the conduction on the intensity of light was studied for different concentrations of a dye added to the nematic crystal. Also the problem of the optimum type of a dye for observing the photorefractive nonlinearity using Ar+- ion laser was considered. We made the experiments using the following available laser dyes: rhodamine '6G,' rhodamine 'G,' rhodamine 'C' and two ocsasine-type dyes also. The mixture of the nematic crystal 5CB and a dye was placed in a cell of 100 micrometer width, with the plates filmed with the transparent electrodes of SnO2. The dc voltage on the order of magnitude 1 V was applied to decrease the influence of the cell capacity on the conduction measurements of the samples. We used the light of two wavelengths: lambda1 equals 488 nm, lambda2 equals 514.5 nm. The best dyes for these wavelengths were the rhodamine- type dyes. Taking the other two dyes we observed much smaller effect of influence of the laser radiation on conduction of the samples. Maybe the reason was that the pump wavelength of ocsasine dyes is too far way from the wavelength of the radiation used. So the optimum dye must have the wavelength of the pump near to the wavelength used. Using rhodamine 'C' we obtained the dependencies of the induced conduction on laser light intensity for three different concentrations of the dye.

  2. Qsars for photoinduced toxicity: 1. acute lethality of polycyclic aromatic hydrocarbons to daphnia magna'

    SciTech Connect

    Mekenyan, O.G.; Ankley, G.T.; Veith, G.D.; Call, D.J.

    1994-01-01

    Research with a variety of aquatic species has shown that while polycyclic aromatic hydrocarbons (PAHs) are generally not acutely toxic in conventional laboratory tests, many are extremely toxic in the presence of sunlight. In an effort to develop a model for predicting which PAHs may exhibit photo-induced toxicity, Newsted and Giesy (1987) reported a parabolic relationship between the toxicity and the energy of the triplet state of a variety of PAHs. The authors have reexamined these data and propose a more mechanistic explanation for the prediction of photo-induced PAH toxicity. They sought a molecular descriptor which could be computed from structure rather than measured empirically.

  3. Photoinduced dimerization of macrocyclic complexes mediated by a metal-assisted oxidation of the macrocycle

    SciTech Connect

    Ferraudi, G.; Muralidharan, S.

    1981-12-01

    The triplet state of benzophenone oxidizes Ni((14)aneN/sub 4//sup 2 +/ to a Ni(III) intermediate which subsequently produces the dimer of the complex as a product. The nature of the product was confirmed by structural studies. (Ni(13-At))/sup +/ reacts with the triplet of fluorenone and /sup 2/Estate of Cr(bpy)/sub 3//sup 3 +/ forming also a dimer in a reaction that involves different intermediates. Intermediates in the photoinduced oxidations of the macrocycles have been investigated by flash photolysis. The mechanism of the photoinduced oxidation is discussed in terms of the reported properties of the macrocycles.

  4. The nature of photoinduced changes in the magnetostriction of yttrium-iron garnet single crystals

    SciTech Connect

    Vorob'eva, N. V.

    2011-05-15

    A model of the occurrence of photoinduced changes in linear magnetostriction is proposed based on a complex experimental study of magnetostrictive strains in yttrium-iron garnets Y{sub 3}Fe{sub 5}O{sub 12} with low contents of different impurities. Analytical expressions for calculating the magnetostriction in yttrium-iron garnet single crystals with different types of doping are presented. The correlation of the photoinduced change in the magnetostriction with the crystallographic features of the samples is demonstrated. The changes in the magnetostriction constants are analyzed quantitatively for samples prepared in different ways.

  5. Modulating Optoelectronic Properties of Two-Dimensional Transition Metal Dichalcogenide Semiconductors by Photoinduced Charge Transfer.

    PubMed

    Choi, Jungwook; Zhang, Hanyu; Choi, Jong Hyun

    2016-01-26

    Atomically thin transition metal dichalcogenides (TMDCs) have attracted great interest as a new class of two-dimensional (2D) direct band gap semiconducting materials. The controllable modulation of optical and electrical properties of TMDCs is of fundamental importance to enable a wide range of future optoelectronic devices. Here we demonstrate a modulation of the optoelectronic properties of 2D TMDCs, including MoS2, MoSe2, and WSe2, by interfacing them with two metal-centered phthalocyanine (MPc) molecules: nickel Pc (NiPc) and magnesium Pc (MgPc). We show that the photoluminescence (PL) emission can be selectively and reversibly engineered through energetically favorable electron transfer from photoexcited TMDCs to MPcs. NiPc molecules, whose reduction potential is positioned below the conduction band minima (CBM) of monolayer MoSe2 and WSe2, but is higher than that of MoS2, quench the PL signatures of MoSe2 and WSe2, but not MoS2. Similarly, MgPc quenches only WSe2, as its reduction potential is situated below the CBM of WSe2, but above those of MoS2 and MoSe2. The quenched PL emission can be fully recovered when MPc molecules are removed from the TMDC surfaces, which may be refunctionalized and recycled multiple times. We also find that photocurrents from TMDCs, probed by photoconductive atomic force microscopy, increase over 2-fold only when the PL is quenched by MPcs, further supporting the photoinduced charge transfer mechanism. Our results should benefit design strategies for 2D inorganic-organic optoelectronic devices and systems with tunable properties and improved performances. PMID:26720839

  6. Generalized quantum Fokker-Planck equation for photoinduced nonequilibrium processes with positive definiteness condition

    NASA Astrophysics Data System (ADS)

    Jang, Seogjoo

    2016-06-01

    This work provides a detailed derivation of a generalized quantum Fokker-Planck equation (GQFPE) appropriate for photo-induced quantum dynamical processes. The path integral method pioneered by Caldeira and Leggett (CL) [Physica A 121, 587 (1983)] is extended by utilizing a nonequilibrium influence functional applicable to different baths for the ground and the excited electronic states. Both nonequilibrium and non-Markovian effects are accounted for consistently by expanding the paths in the exponents of the influence functional up to the second order with respect to time. This procedure results in approximations involving only single time integrations for the exponents of the influence functional but with additional time dependent boundary terms that have been ignored in previous works. The boundary terms complicate the derivation of a time evolution equation but do not affect position dependent physical observables or the dynamics in the steady state limit. For an effective density operator with the boundary terms factored out, a time evolution equation is derived, through short time expansion of the effective action and Gaussian integration in analytically continued complex domain of space. This leads to a compact form of the GQFPE with time dependent kernels and additional terms, which renders the resulting equation to be in the Dekker form [Phys. Rep. 80, 1 (1981)]. Major terms of the equation are analyzed for the case of Ohmic spectral density with Drude cutoff, which shows that the new GQFPE satisfies the positive definiteness condition in medium to high temperature limit. Steady state limit of the GQFPE is shown to approach the well-known expression derived by CL in the high temperature and Markovian bath limit and also provides additional corrections due to quantum and non-Markovian effects of the bath.

  7. Generalized quantum Fokker-Planck equation for photoinduced nonequilibrium processes with positive definiteness condition.

    PubMed

    Jang, Seogjoo

    2016-06-01

    This work provides a detailed derivation of a generalized quantum Fokker-Planck equation (GQFPE) appropriate for photo-induced quantum dynamical processes. The path integral method pioneered by Caldeira and Leggett (CL) [Physica A 121, 587 (1983)] is extended by utilizing a nonequilibrium influence functional applicable to different baths for the ground and the excited electronic states. Both nonequilibrium and non-Markovian effects are accounted for consistently by expanding the paths in the exponents of the influence functional up to the second order with respect to time. This procedure results in approximations involving only single time integrations for the exponents of the influence functional but with additional time dependent boundary terms that have been ignored in previous works. The boundary terms complicate the derivation of a time evolution equation but do not affect position dependent physical observables or the dynamics in the steady state limit. For an effective density operator with the boundary terms factored out, a time evolution equation is derived, through short time expansion of the effective action and Gaussian integration in analytically continued complex domain of space. This leads to a compact form of the GQFPE with time dependent kernels and additional terms, which renders the resulting equation to be in the Dekker form [Phys. Rep. 80, 1 (1981)]. Major terms of the equation are analyzed for the case of Ohmic spectral density with Drude cutoff, which shows that the new GQFPE satisfies the positive definiteness condition in medium to high temperature limit. Steady state limit of the GQFPE is shown to approach the well-known expression derived by CL in the high temperature and Markovian bath limit and also provides additional corrections due to quantum and non-Markovian effects of the bath. PMID:27276940

  8. Fullerene-Assisted Photoinduced Charge Transfer of Single-Walled Carbon Nanotubes through a Flavin Helix.

    PubMed

    Mollahosseini, Mehdi; Karunaratne, Erandika; Gibson, George N; Gascón, Jose A; Papadimitrakopoulos, Fotios

    2016-05-11

    One of the greatest challenges with single-walled carbon nanotube (SWNT) photovoltaics and nanostructured devices is maintaining the nanotubes in their pristine state (i.e., devoid of aggregation and inhomogeneous doping) so that their unique spectroscopic and transport characteristics are preserved. To this effect, we report on the synthesis and self-assembly of a C60-functionalized flavin (FC60), composed of PCBM and isoalloxazine moieties attached on either ends of a linear, C-12 aliphatic spacer. Small amounts of FC60 (up to 3 molar %) were shown to coassembly with an organic soluble derivative of flavin (FC12) around SWNTs and impart effective dispersion and individualization. A key annealing step was necessary to perfect the isoalloxazine helix and expel the C60 moiety away from the nanotubes. Steady-state and transient absorption spectroscopy illustrate that 1% or higher incorporation of FC60 allows for an effective photoinduced charge transfer quenching of the encased SWNTs through the seamless helical encase. This is enabled via the direct π-π overlap between the graphene sidewalls, isoalloxazine helix, and the C60 cage that facilitates SWNT exciton dissociation and electron transfer to the PCBM moiety. Atomistic molecular simulations indicate that the stability of the complex originates from enhanced van der Waals interactions of the flexible spacer wrapped around the fullerene that brings the C60 in π-π overlap with the isoalloxazine helix. The remarkable spectral purity (in terms of narrow E(S)ii line widths) for the resulting ground-state complex signals a new class of highly organized supramolecular nanotube architecture with profound importance for advanced nanostructured devices. PMID:27127896

  9. Coherent orbital waves during an Ultrafast Photo-induced Isulator-metal Transition in a magnetoresistive manganite

    SciTech Connect

    ULTRAS-INFM-CNR Dipartimento di Fisica, Politecnico di Milano, Italy; Department of Physics - Cavalleri Group, Clarendon Laboratory, University of Oxford, U.K.; Correlated Electron Research Center, Tsukuba, Japan; Schoenlein, Robert William; Polli, D.; Rini, M.; Wall, S.; Schoenlein, R.W.; Tomioka, Y.; Tokura, Y.; Cerullo, G.; Cavalleri, A.

    2007-06-01

    Photo-excitation can drive strongly correlated electron insulators into competing conducting phases1,2, resulting in giant and ultrafast changes of their electronic and magnetic properties. The underlying non-equilibrium dynamics involve many degrees of freedom at once, whereby sufficiently short optical pulses can trigger the corresponding collective modes of the solid along temporally coherent pathways. The characteristic frequencies of these modes range between the few GHz of acoustic vibrations3 to the tens or even hundreds of THz for purely electronic excitations. Virtually all experiments so far have used 100 fs or longer pulses, detecting only comparatively slow lattice dynamics4,5. Here, we use sub-10-fs optical pulses to study the photo-induced insulator-metal transition in the magneto-resistive manganite Pr0.7Ca0.3MnO3. At room temperature, we find that the time-dependent pathway towards the metallic phase is accompanied by coherent 31 THz oscillations of the optical reflectivity, significantly faster than all lattice vibrations. These high-frequency oscillations are suggestive of coherent orbital waves6,7, crystal-field excitations triggered here by impulsive stimulated Raman scattering. Orbital waves are likely to be initially localized to the small polarons of this room-temperature manganite, coupling to other degrees of freedom at longer times, as photo-domains coalesce into a metallic phase.

  10. Hierarchical Sheet-on-Sheet ZnIn2S4/g-C3N4 Heterostructure with Highly Efficient Photocatalytic H2 production Based on Photoinduced Interfacial Charge Transfer

    PubMed Central

    Zhang, Zhenyi; Liu, Kuichao; Feng, Zhiqing; Bao, Yanan; Dong, Bin

    2016-01-01

    We have realized in-situ growth of ultrathin ZnIn2S4 nanosheets on the sheet-like g-C3N4 surfaces to construct a “sheet-on-sheet” hierarchical heterostructure. The as-synthesized ZnIn2S4/g-C3N4 heterojunction nanosheets exhibit remarkably enhancement on the photocatalytic activity for H2 production. This enhanced photoactivity is mainly attributed to the efficient interfacial transfer of photoinduced electrons and holes from g-C3N4 to ZnIn2S4 nanosheets, resulting in the decreased charge recombination on g-C3N4 nanosheets and the increased amount of photoinduced charge carriers in ZnIn2S4 nanosheets. Meanwhile, the increased surface-active-sites and extended light absorption of g-C3N4 nanosheets after the decoration of ZnIn2S4 nanosheets may also play a certain role for the enhancement of photocatalytic activity. Further investigations by the surface photovoltage spectroscopy and transient photoluminescence spectroscopy demonstrate that ZnIn2S4/g-C3N4 heterojunction nanosheets considerable boost the charge transfer efficiency, therefore improve the probability of photoinduced charge carriers to reach the photocatalysts surfaces for highly efficient H2 production. PMID:26753795

  11. Hierarchical Sheet-on-Sheet ZnIn2S4/g-C3N4 Heterostructure with Highly Efficient Photocatalytic H2 production Based on Photoinduced Interfacial Charge Transfer.

    PubMed

    Zhang, Zhenyi; Liu, Kuichao; Feng, Zhiqing; Bao, Yanan; Dong, Bin

    2016-01-01

    We have realized in-situ growth of ultrathin ZnIn2S4 nanosheets on the sheet-like g-C3N4 surfaces to construct a "sheet-on-sheet" hierarchical heterostructure. The as-synthesized ZnIn2S4/g-C3N4 heterojunction nanosheets exhibit remarkably enhancement on the photocatalytic activity for H2 production. This enhanced photoactivity is mainly attributed to the efficient interfacial transfer of photoinduced electrons and holes from g-C3N4 to ZnIn2S4 nanosheets, resulting in the decreased charge recombination on g-C3N4 nanosheets and the increased amount of photoinduced charge carriers in ZnIn2S4 nanosheets. Meanwhile, the increased surface-active-sites and extended light absorption of g-C3N4 nanosheets after the decoration of ZnIn2S4 nanosheets may also play a certain role for the enhancement of photocatalytic activity. Further investigations by the surface photovoltage spectroscopy and transient photoluminescence spectroscopy demonstrate that ZnIn2S4/g-C3N4 heterojunction nanosheets considerable boost the charge transfer efficiency, therefore improve the probability of photoinduced charge carriers to reach the photocatalysts surfaces for highly efficient H2 production. PMID:26753795

  12. Optical logic operations using photoinduced anisotropy in bacteriorhodopsin films

    NASA Astrophysics Data System (ADS)

    Joseph, Joby; Aranda, Francisco J.; Rao, Devulapalli V. G. L. N.; Akkara, Joseph A.; DeCristofano, Barry S.

    1997-10-01

    We constructed an optical system for performing 2D logic operations. We demonstrated the logic operations of OR, NOR, XOR, AND. The photoinduced dichroism of Bacteriorhodopsin (bR) is the physical mechanism exploited in the optical system. In its normal state with no light illumination a bR doped polymer film is isotropic with random distribution of bR molecules. When excited by linearly polarized light, only those bR molecules whose transition dipole moments for absorption lie in or near the direction of the electric field ar bleached at the actinic light wavelength due to the B to M transition. If a probe beam is incident in the regions illuminated by the actinic light it will no longer be interacting with an isotropic film. The film is now anisotropic and dichroic. Due to dichroism the actinic light illumination produces an angular rotation of the plane of polarization of the probe beam. In the experiments the bR film is kept between two crossed polarizers to get zero output from the probe beam at a screen when no actinic light is incident on the bR film. The two polarizers and the screen are kept in the path of the probe beam. There are two actinic light beams that induce dichroism and they are made orthogonally polarized with respect to each other by the use of a polarization rotator. The polarization rotator can be arranged so that their polarizations are made parallel for some of the logic operations. The plane of polarization of these two actinic beams are at 45 degrees to the pane of polarization of the probe beam. The combination of rotation of the analyzer and the polarization rotation of one of the actinic beams allows for many logic operations to be performed. No interference recordings are involved in the experiments and hence vibration isolation systems are not required. A coherent source is not a requirement either since a white light source with an appropriate wavelength filter can induce photoanisotropy in the bR film.

  13. Humic acids reduce the bioaccumulation and photoinduced toxicity of fluoranthene to fish

    SciTech Connect

    Weinstein, J.E.; Oris, J.T.

    1999-09-01

    The effects of dissolved humic materials (DHM) on the photoinduced toxicity of fluoranthene to juvenile fathead minnows (Pimephales promelas) were studied in single-treatment evaluations in a laboratory system under simulated sunlight (UV-A = 140.2 {+-} 2.6 {micro}W/cm{sup 2}, UV-B = 6.40 {+-} 0.21 {micro}W/cm{sup 2})(mean {+-} SE). Five concentrations of fluoranthene and five concentrations of DHM were achieved. The presence of DHM reduced the acute photoinduced toxicity of fluoranthene. Regression analysis revealed that median lethal times (LT50) were directly related to DHM concentration and inversely related to fluoranthene water concentration. The presence of DHM also reduced fluoranthene bioaccumulation, and LT50 values were inversely related to fluoranthene body residues. These findings demonstrate that (1) the photoinduced toxicity of fluoranthene is dependent on body residue and (2) site-specific environmental parameters that affect uptake and/or elimination can determine the rates of mortality due to photoinduced toxicity.

  14. Photo-induced reversible structural transition of cationic diphenylalanine peptide self-assembly.

    PubMed

    Ma, Hongchao; Fei, Jinbo; Li, Qi; Li, Junbai

    2015-04-17

    The photo-induced self-assembly of a cationic diphenylalanine peptide (CDP) is investigated using a photoswitchable sulfonic azobenzene as the manipulating unit. A reversible structural transition between a branched structure and a vesicle-like structure is observed by alternating between UV and visible light irradiation. PMID:25405602

  15. Water-soluble fullerene materials for bioapplications: photoinduced reactive oxygen species generation

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The photoinduced reactive oxygen species (ROS) generation from several water-soluble fullerenes was examined. Macromolecular or small molecular water-soluble fullerene complexes/derivatives were prepared and their 1O2 and O2•- generation abilities were evaluated by EPR spin-trapping methods. As a r...

  16. EFFECT OF IRRADIANCE SPECTRA ON THE PHOTOINDUCED TOXICITY OF THREE POLYCYCLIC AROMATIC HYDROCARBONS

    EPA Science Inventory

    Photoinduced toxicity of polycyclic aromatic hydrocarbons (PAHs) is dependent on the concentration of compounds present and the dose of light received. Of the light present, only those wavelengths absorbed by the compound have the potential to initiate the photochemical events un...

  17. Photoinduced refractive index change and absorption bleaching in poly(methylphenylsilane) under varied atmospheres.

    SciTech Connect

    Potter, Barrett George, Jr.; Simmons-Potter, Kelly; Chandra, Haripin; Thomes, William Joseph, Jr.; Jamison, Gregory Marks

    2005-06-01

    Polysilane materials exhibit large photo-induced refractive index changes under low incident optical fluences, making them attractive candidates for applications in which rapid patterning of photonic device structures is desired immediately prior to their use. This agile fabrication strategy for integrated photonics inherently requires that optical exposure, and associated material response, occurs in nonlaboratory environments, motivating the study of environmental conditions on the photoinduced response of the material. The present work examines the impact of atmosphere on the photosensitive response of poly(methylphenylsilane) (PMPS) thin films in terms of both photoinduced absorption change and refractive index modification. Material was subjected to UV light exposure resonant with the lowest energy optical transition associated with the conjugated Si-Si backbone. Exposures were performed in both aerobic and anaerobic atmospheres (oxygen, air, nitrogen, and 5% H{sub 2}/95% N{sub 2}). The results clearly demonstrate that the photosensitive response of this model polysilane material was dramatically affected by local environment, exhibiting a photoinduced refractive index change, when exposed under an oxygen containing atmosphere, that was twice that observed under anaerobic conditions. This effect is discussed in terms of photo-oxidation processes within the polysilane structure and in the context of the need for predictable photosensitive refractive index change in varied photoimprinting environments.

  18. Photo-induced oxidation and amorphization of trigonal tellurium: A means to engineer hybrid nanostructures and explore glass structure under spatial confinement

    SciTech Connect

    Vasileiadis, Thomas; Yannopoulos, Spyros N.

    2014-09-14

    Controlled photo-induced oxidation and amorphization of elemental trigonal tellurium are achieved by laser irradiation at optical wavelengths. These processes are monitored in situ by time-resolved Raman scattering and ex situ by electron microscopies. Ultrathin TeO₂ films form on Te surfaces, as a result of irradiation, with an interface layer of amorphous Te intervening between them. It is shown that irradiation, apart from enabling the controllable transformation of bulk Te to one-dimensional nanostructures, such as Te nanotubes and hybrid core-Te/sheath-TeO₂ nanowires, causes also a series of light-driven (athermal) phase transitions involving the crystallization of the amorphous TeO₂ layers and its transformation to a multiplicity of crystalline phases including the γ-, β-, and α-TeO₂ crystalline phases. The kinetics of the above photo-induced processes is investigated by Raman scattering at various laser fluences revealing exponential and non-exponential kinetics at low and high fluence, respectively. In addition, the formation of ultrathin (less than 10 nm) layers of amorphous TeO₂ offers the possibility to explore structural transitions in 2D glasses by observing changes in the short- and medium-range structural order induced by spatial confinement.

  19. Photoinduced, Copper-Catalyzed Carbon-Carbon Bond Formation with Alkyl Electrophiles: Cyanation of Unactivated Secondary Alkyl Chlorides at Room Temperature.

    PubMed

    Ratani, Tanvi S; Bachman, Shoshana; Fu, Gregory C; Peters, Jonas C

    2015-11-01

    We have recently reported that, in the presence of light and a copper catalyst, nitrogen nucleophiles such as carbazoles and primary amides undergo C-N coupling with alkyl halides under mild conditions. In the present study, we establish that photoinduced, copper-catalyzed alkylation can also be applied to C-C bond formation, specifically, that the cyanation of unactivated secondary alkyl chlorides can be achieved at room temperature to afford nitriles, an important class of target molecules. Thus, in the presence of an inexpensive copper catalyst (CuI; no ligand coadditive) and a readily available light source (UVC compact fluorescent light bulb), a wide array of alkyl halides undergo cyanation in good yield. Our initial mechanistic studies are consistent with the hypothesis that an excited state of [Cu(CN)2](-) may play a role, via single electron transfer, in this process. This investigation provides a rare example of a transition metal-catalyzed cyanation of an alkyl halide, as well as the first illustrations of photoinduced, copper-catalyzed alkylation with either a carbon nucleophile or a secondary alkyl chloride. PMID:26491957

  20. Kinetics of a photoinduced NH tautomerism of free-base porphyrins in crystalline matrices at low temperatures: Computer simulations and experiment

    NASA Astrophysics Data System (ADS)

    Stanishevsky, I. V.; Solovyov, K. N.

    2004-03-01

    Photoinduced NH tautomerism, along with the reaction pathways of phototautomerization in tetrabenzoporphin and porphin free bases in n-octane polycrystalline matrices at 77 K, is studied by simulation of kinetic processes and their experimental observation. The simulation of the processes is performed by the numerical solution of the system of kinetic equations describing the populations of electronic levels and transitions between them. Kinetic dependences are obtained by measuring the perturbation of stationary fluorescence of one component of the 0-0 doublet origin upon pulsed selective photoexcitation of the other component. For two tautomeric forms related by the reversibility of the photochemical reaction, under the assumption of synchronism of the NH rearrangement, (i) analytical solutions governing the reaction rate are found, (ii) a method of measuring the rate constants of the proton rearrangement is suggested and the constants themselves are estimated, and (iii) direct evidence of the participation of T 1 levels in the photochemical reaction is obtained. With the aid of numerical simulations, the specific features of kinetic manifestation of an asynchronous mechanism of the photoinduced NH rearrangement are studied.

  1. Improved solar-driven photocatalytic performance of BiOI decorated TiO2 benefiting from the separation properties of photo-induced charge carriers

    NASA Astrophysics Data System (ADS)

    Li, Jianzhang; Zhong, Junbo; Si, Yujun; Huang, Shengtian; Dou, Lin; Li, Minjiao; Liu, Yinping; Ding, Jie

    2016-02-01

    In this work, BiOI decorated TiO2 photocatalysts were prepared in-situ by a facile hydrothermal method and characterized by X-ray diffraction (XRD), UV/Vis diffuse reflectance spectroscopy, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and surface photovoltage (SPV) spectroscopy. The reactive radicals during the photocatalytic reaction were detected by scavenger experiments. BiOI/TiO2 composites exhibit higher performance than the pure TiO2 towards photocatalytic decolorization of methyl orange (MO) aqueous solution, when the molar ratio of Bi/Ti is 2%, the sample has the highest photocatalytic activity. The enhanced photocatalytic performance of BiOI/TiO2 could be ascribed to the separation properties of photo-induced charge carriers and strong interaction between BiOI and TiO2. Based on the observations, a Z-scheme charge separation mechanism was proposed.

  2. CORRELATING ELECTRONIC AND VIBRATIONAL MOTIONS IN CHARGE TRANSFER SYSTEMS

    SciTech Connect

    Khalil, Munira

    2014-06-27

    The goal of this research program was to measure coupled electronic and nuclear motions during photoinduced charge transfer processes in transition metal complexes by developing and using novel femtosecond spectroscopies. The scientific highlights and the resulting scientific publications from the DOE supported work are outlined in the technical report.

  3. Bridge mediated ultrafast heterogeneous electron transfer

    NASA Astrophysics Data System (ADS)

    Ramakrishna, S.; Willig, F.; May, V.

    2002-01-01

    Bridge mediated photoinduced ultrafast heterogeneous electron transfer (ET) from a molecularly anchored chromophore to a semiconductor surface is modelled theoretically. The continuum levels of the semiconductor substrate are taken into account in the numerical calculations via a polynomial expansion. Electron transfer for the direct injection case in the strong coupling limit is studied and compared with cases where intermediate bridging states are successively introduced to weaken the effective electronic coupling. The role of vibronic coherences in the strong electronic coupling limit as well as in off-resonant bridge mediated electron transfer is also discussed.

  4. Temperature-dependent photoinduced third-harmonic-generation variation in azo-homopolymer and azo-doped polymer thin films

    NASA Astrophysics Data System (ADS)

    Hsu, Chia-Chen; Lin, Jian-Hung; Huang, Tzer-Hsiang; Harada, Kenji

    2003-04-01

    The temperature effect on the variation of photoinduced third-harmonic generation (THG) of an azo-polyurethane homopolymer and an azo guest-host polymer is studied at several different temperatures. At higher temperatures, both angular hole burning and molecule angular redistribution motions weaken, due to the decreases of cis-to-trans thermal relaxation time and the cis population and the increase of orientational diffusion coefficient. Smaller photoinduced THG variation is observed in both samples at higher temperatures. Results from the THG recovery experiment show that polyurethane homopolymer thin films pumped at a high temperature have the best photoinduced THG variation stability after turning off the pump beam.

  5. Direct photofabrication of focal-length-controlled microlens array using photoinduced migration mechanisms of photosensitive sol-gel hybrid materials

    NASA Astrophysics Data System (ADS)

    Kang, Dong Jun; Jeong, Jong-Pil; Bae, Byeong-Soo

    2006-09-01

    Photosensitive sol-gel hybrid (SGH) materials exhibited the peculiar photoinduced migration behavior of unreacted molecules from unexposed areas to exposed areas by selective UV exposure. Using the photoinduced migration mechanism of the photosensitive SGH materials, the microlens array (MLA) with a smooth surface was directly photofabricated, and the focal length was controlled by changing the photoinduced migration parameters. The higher photoactive monomer content and the thicker film creating a higher curvature produced a smaller focal length of the MLA. Thus, a simple fabrication and easy control of the focal length can be applicable to a fabrication of an efficient MLA.

  6. Chemical Detection Based on Adsorption-Induced and Photo-Induced Stresses in MEMS Devices

    SciTech Connect

    Datskos, P.G.

    1999-04-05

    Recently there has been an increasing demand to perform real-time in-situ chemical detection of hazardous materials, contraband chemicals, and explosive chemicals. Currently, real-time chemical detection requires rather large analytical instrumentation that are expensive and complicated to use. The advent of inexpensive mass produced MEMS (micro-electromechanical systems) devices opened-up new possibilities for chemical detection. For example, microcantilevers were found to respond to chemical stimuli by undergoing changes in their bending and resonance frequency even when a small number of molecules adsorb on their surface. In our present studies, we extended this concept by studying changes in both the adsorption-induced stress and photo-induced stress as target chemicals adsorb on the surface of microcantilevers. For example, microcantilevers that have adsorbed molecules will undergo photo-induced bending that depends on the number of absorbed molecules on the surface. However, microcantilevers that have undergone photo-induced bending will adsorb molecules on their surfaces in a distinctly different way. Depending on the photon wavelength and microcantilever material, the microcantilever can be made to bend by expanding or contracting the irradiated surface. This is important in cases where the photo-induced stresses can be used to counter any adsorption-induced stresses and increase the dynamic range. Coating the surface of the microstructure with a different material can provide chemical specificity for the target chemicals. However, by selecting appropriate photon wavelengths we can change the chemical selectivity due to the introduction of new surface states in the MEMS device. We will present and discuss our results on the use of adsorption-induced and photo-induced bending of microcantilevers for chemical detection.

  7. Final Report on project Photoinduced Dipoles and Charge Pairs in Condensed Media

    SciTech Connect

    Braun, Charles L.

    2006-09-27

    Most of our work involves photogenerated donor (D+) and acceptor (A-) radical ion pairs and their escape and recombination. The geminate radical ions are produced by inter or intramolecular electron transfer quenching of photoexcited acceptors. We made great progress in understanding the effect of charge separation distance and other factors on free ion formation. For geminate radical ion pairs formed by intermolecular electron transfer quenching, we found that, at least in a medium polarity solvent lilce dichloromethane, free radical ions are mainly formed from solvent separated radical ion pairs (SSRIPs). Contact radical ion pairs (CRIPs) make a very small contribution to free radical ion formation. It is observed that CRIPs and SSRIPs are kinetically distinguishable species. There is a potential barrier between CRIPs and SSRIPs that prevents a fast equilibrium between the two during the recombination of radical ion pairs and free radical ion formation. We confirmed for the first time that, for the recombination of both CRIPs and SSRIPs that are in the Marcus inverted region, rate constants of SSRIPs are larger than those of CRIPs. Our study indicates that initial charge separation distance and the potential barrier between CRIPs and SSRIPs play a more important role than recombination rate on free ion formation. Temperature dependence experiments reveal that through-tunneling back electron transfer is the dominant approach for the SSRIP recombination process. We believe that our discovery of the roles played by the initial charge separation distance and the potential barrier between radical ion pairs of different separation have very important implications for the development of new concepts for the design of organic photovoltaic (OPV) cells. Photoinduced transient dipole experiments are used to probe the effective charge separation distance of flexible electron donor/acceptor systems, D-(CH2)n-A, where D is 4-N-N-dimethylaniline, A is 9-anthryl and n=3, 4. We

  8. Study of electrons photoemitted from field-emission tips. Progress report, July 1, 1980-January 1, 1981

    SciTech Connect

    Reifenberger, R.

    1981-01-01

    Photo-induced field emission is a technique which studies electrons that have been photoemitted from a field emission tip. This new experimental method promises to combine the proven utility of both field emission and photoemission for investigating the electronic states near a metal surface. The primary objective of the research being performed is to investigate photo-induced field emitted electrons using a tuneable cw dye laser. To fully exploit this continuously tuneable photon source, a differential energy analyzer has been constructed to allow energy resolved measurements of the photo-field emitted electrons. This report describes the progress made in implementing experiments on photo-induced field emission from July 1980 to January 1981.

  9. Photoinduced interaction between riboflavin and TiO 2 colloid

    NASA Astrophysics Data System (ADS)

    Kathiravan, A.; Renganathan, R.

    2008-12-01

    The adsorption of riboflavin on the surface of TiO 2 colloidal particles and the electron transfer process from its singlet excited state to the conduction band of TiO 2 were examined by absorption and fluorescence quenching measurements. The apparent association constants ( Kapp) were determined. The quenching mechanism is discussed involving electron transfer from riboflavin to TiO 2.

  10. Direct Observation of Cascade of Photoinduced Ultrafast Intramolecular Charge Transfer Dynamics in Diphenyl Acetylene Derivatives: Via Solvation and Intramolecular Relaxation.

    PubMed

    Karunakaran, Venugopal; Das, Suresh

    2016-07-21

    Interaction of light with electron donor-acceptor π-conjugated systems leading to intramolecular charge transfer (ICT) plays an essential role in transformation of light energy. Here the cascade of photoinduced ICT processes is directly observed by investigating the excited state relaxation dynamics of cyano and mono/di methoxy substituted diphenyl acetylene derivatives using femtosecond pump-probe spectroscopy and nanosecond laser flash photolysis. The femtosecond transient absorption spectra of the chromophores upon ultrafast excitation reveal the dynamics of intermediates involved in transition from initially populated Frank-Condon state to local excited state (LE). It also provides the dynamic details of the transition from the LE to the charge transfer state yielding the formation of the radical ions. Finally, the charge transfer state decays to the triplet state by geminate charge recombination. The latter dynamics are observed in the nanosecond transient absorption spectra. It is found that excited state relaxation pathways are controlled by different stages of solvation and intramolecular relaxation depending on the solvent polarity. The twisted ICT state is more stabilized (978 ps) in acetonitrile than cyclohexane where major components of transient absorption originate from the S1 state. PMID:27347705

  11. Direct Observation of Photoinduced Charge Separation in Ruthenium Complex/Ni(OH)2 nanoparticle Hybrid

    SciTech Connect

    Tang, Yu; Pattengale, Brian A.; Ludwig, John M.; Atifi, Abderrahman; Zinovev, Alexander V.; Dong, Bin; Kong, Qingyu; Zuo, Xiaobing; Zhang, Xiaoyi; Huang, Jier

    2015-12-17

    Ni(OH)2 have emerged as important functional materials for solar fuel conversion because of their potential as cost-effective bifunctional catalysts for both hydrogen and oxygen evolution reactions. However, their roles as photocatalysts in the photoinduced charge separation (CS) reactions remain unexplored. In this paper, we investigate the CS dynamics of a newly designed hybrid catalyst by integrating a Ru complex with Ni(OH)2 nanoparticles (NPs). Using time resolved X-ray absorption spectroscopy (XTA), we directly observed the formation of the reduced Ni metal site (~60 ps), unambiguously demonstrating CS process in the hybrid through ultrafast electron transfer from Ru complex to Ni(OH)2 NPs. Compared to the ultrafast CS process, the charge recombination in the hybrid is ultraslow (>>50 ns). These results not only suggest the possibility of developing Ni(OH)2 as solar fuel catalysts, but also represent the first time direct observation of efficient CS in a hybrid catalyst using XTA.

  12. Photoinduced interactions of supramolecular ruthenium(II) complexes with plasmid DNA: synthesis and spectroscopic, electrochemical, and DNA photocleavage studies.

    PubMed

    Swavey, Shawn; DeBeer, Madeleine; Li, Kaiyu

    2015-04-01

    Two new bridging ligands have been synthesized by combining substituted benzaldehydes with phenanthrolinopyrrole (php), resulting in new polyazine bridging ligands. The ligands have been characterized by (1)H NMR, mass spectroscopy, and elemental analysis. These new ligands display π-π* transitions above 500 nm with modest molar absorptivities. Upon excitation at the ligand-centered charge-transfer transition, weak emission with a maximum wavelength of 612 nm is observed. When coordinated to two ruthenium(II) bis(bipyridyl) groups, the new bimetallic complexes generated give an overall 4+ charge. The electronic transitions of the bimetallic ruthenium(II) complexes display traditional π-π* transitions at 287 nm and metal-to-ligand charge-transfer transitions at 452 nm with molar absorptivities greater than 30000 M(-1) cm(-1). Oxidation of the ruthenium(II) metal centers to ruthenium(III) occurs at potentials above 1.4 V versus the Ag/AgCl reference electrode. Spectroscopic and electrochemical measurements indicate that the ruthenium(II) moieties behave independently. Both complexes are water-soluble and show the ability to photonick plasmid DNA when irradiated with low-energy light above 550 nm. In addition, one of the complexes, [Ru(bpy)2php]2Van(4+), shows the ability to linearize plasmid DNA and gives evidence, by gel electrophoresis, of photoinduced binding to plasmid DNA. PMID:25798576

  13. Synthesis of decacationic [60]fullerene decaiodides giving photoinduced production of superoxide radicals and effective PDT-mediation on antimicrobial photoinactivation

    PubMed Central

    Wang, Min; Maragani, Satyanarayana; Huang, Liyi; Jeon, Seaho; Canteenwala, Taizoon; Hamblin, Michael R.; Chiang, Long Y.

    2013-01-01

    We report a novel class of highly water-soluble decacationic methano[60]fullerene decaiodides C60[>M(C3N6+C3)2]-(I−)10[1-(I−)10] capable of co-producing singlet oxygen (Type-II) and highly reactive hydroxyl radicals, formed from superoxide radicals in Type-I photosensitizing reactions, upon illumination at both UVA and white light wavelengths. The O2-·-production efficiency of 1-(I−)10 was confirmed by using an O2-·-reactive bis(2,4-dinitrobenzenesulfonyl)tetrafluorofluorescein probe and correlated to the photoinduced electron-transfer event going from iodide anions to C360∗[>M(C3N6+C3)2] leading to C60-·[>M(C3N6+C3)2]. Incorporation of a defined number (ten) of quaternary ammonium cationic charges per C60 in 1 was aimed to enhance its ability to target pathogenic Gram-positive and Gram-negative bacterial cells. We used the well-characterized malonato[60]fullerene diester mono-adduct C60[>M(t-Bu)2] as the starting fullerene derivative to provide a better synthetic route to C60[>M(C3N6+C3)2] via transesterification reaction under trifluoroacetic acid catalyzed conditions. These compounds may be used as effective photosensitizers and nano-PDT drugs for photoinactivation of pathogens. PMID:23474903

  14. A Mechanism of Photo-Induced Desorption of Oxygen Atoms From MgO Nano-Crystals

    SciTech Connect

    Trevisanutto, P. E.; Sushko, Petr V.; Shluger, Alexander L.; Beck, Kenneth M.; Henyk, Matthias; Joly, Alan G.; Hess, Wayne P.

    2005-11-20

    In a series of recent experimental and theoretical papers we reported the results of our studies of photo-induced hyper-thermal halogen atom desorption from alkali halide surfaces. There we demonstrated that the yield, electronic state and velocity distributions of desorbed atoms can be controlled by carefully choosing parameters of photo-irradiation such as laser photon energy and pulse power [ ]. To achieve laser control over desorption process one must have clear understanding of possible desorption mechanisms and parameters responsible for their selective excitation. For alkali halides, as it has been shown through a combination of theory and experiment, such selectively is observed if the laser energy is tuned to preferentially excite surface excitons. If similar mechanisms could be demonstrated for a wider variety of materials, this approach could become a new method for controlling surface processes and hence modifying surface structures on an atomic scale. In this paper we report the first experimental observation of the hyper-thermal oxygen atom emission from an of MgO nano-clusters and thin films using frequency selected laser pulses oxide surface and investigate theoretically the mechanisms of this process. On this way we demonstrate a new concept that can be applied to studying surface reactions and desorption of binary oxides.

  15. Photo-induced H2 production from a CH3OH-H2O solution at insulator surface

    PubMed Central

    Li, Rengui; Wang, Xiuli; Jin, Shaoqing; Zhou, Xin; Feng, Zhaochi; Li, Zheng; Shi, Jingying; Zhang, Qiao; Li, Can

    2015-01-01

    In a conventional photocatalytic or photochemical process, either a photocatalyst or a molecule is excited by irradiation light that has energy greater than the forbidden band (i.e., the band gap) of the semiconductor or the transition energy of an excited state of the molecule, respectively, for a reaction to occur. However, in this work, we found that a considerable amount of H2 can be generated from a CH3OH-H2O solution at a quartz surface using light with energy far outside the electronic absorbance range of the CH3OH-H2O solution; this process should not occur in principle via either conventional photocatalysis or a photochemical process. The H2 production was further confirmed using 266 nm and 355 nm lasers as light sources. Our work demonstrates that photo-induced H2 production can occur on insulator surfaces (e.g., quartz), which were commonly believed to be inert, and will shed light on the surface nature of insulators. PMID:26315657

  16. Photo-induced H2 production from a CH3OH-H2O solution at insulator surface.

    PubMed

    Li, Rengui; Wang, Xiuli; Jin, Shaoqing; Zhou, Xin; Feng, Zhaochi; Li, Zheng; Shi, Jingying; Zhang, Qiao; Li, Can

    2015-01-01

    In a conventional photocatalytic or photochemical process, either a photocatalyst or a molecule is excited by irradiation light that has energy greater than the forbidden band (i.e., the band gap) of the semiconductor or the transition energy of an excited state of the molecule, respectively, for a reaction to occur. However, in this work, we found that a considerable amount of H2 can be generated from a CH3OH-H2O solution at a quartz surface using light with energy far outside the electronic absorbance range of the CH3OH-H2O solution; this process should not occur in principle via either conventional photocatalysis or a photochemical process. The H2 production was further confirmed using 266 nm and 355 nm lasers as light sources. Our work demonstrates that photo-induced H2 production can occur on insulator surfaces (e.g., quartz), which were commonly believed to be inert, and will shed light on the surface nature of insulators. PMID:26315657

  17. Direct Observation of Photoinduced Charge Separation in Ruthenium Complex/Ni(OH)2 Nanoparticle Hybrid

    SciTech Connect

    Tang, Yu; Pattengale, Brian A.; Ludwig, John M.; Atifi, Abderrahman; Zinovev, Alexander V.; Dong, Bin; Kong, Qingyu; Zuo, Xiaobing; Zhang, Xiaoyi; Huang, Jier

    2015-12-17

    We report that Ni(OH)2 have emerged as important functional materials for solar fuel conversion because of their potential as cost-effective bifunctional catalysts for both hydrogen and oxygen evolution reactions. However, their roles as photocatalysts in the photoinduced charge separation (CS) reactions remain unexplored. In this paper, we investigate the CS dynamics of a newly designed hybrid catalyst by integrating a Ru complex with Ni(OH)2 nanoparticles (NPs). Using time resolved X-ray absorption spectroscopy (XTA), we directly observed the formation of the reduced Ni metal site (~60 ps), unambiguously demonstrating CS process in the hybrid through ultrafast electron transfer from Ru complex to Ni(OH)2 NPs. Compared to the ultrafast CS process, the charge recombination in the hybrid is ultraslow (>>50 ns). These results not only suggest the possibility of developing Ni(OH)2 as solar fuel catalysts, but also represent the first time direct observation of efficient CS in a hybrid catalyst using XTA.

  18. Improving the photoinduced charge separation parameters in corrole-perylene carboximide dyads by tuning the redox and spectroscopic properties of the components.

    PubMed

    Flamigni, Lucia; Ciuciu, Adina I; Langhals, Heinz; Böck, Bernd; Gryko, Daniel T

    2012-03-01

    A couple of corrole-perylene carboximide dyads (C2-PIa and C2-PIx) have been synthesized and their photoreactivity has been evaluated. We aimed at obtaining better performances for photoinduced charge separation, both in terms of efficiency and in terms of lifetime, with respect to formerly studied systems. The energy level of the charge-separated state was tuned by selecting perylene and corrole components with diverse redox and spectroscopic properties. High spectroscopic energy levels of the perylene carboximide derivatives (PIs) allow a fast charge separation to be maintained in competition with an energy-transfer process from the PI to the corrole unit. Yields and lifetimes of charge separation in toluene are, respectively, 75% and 2.5 μs for C2-PIa and 65% and 24 ns for C2-PIx. The results and the effect of solvent polarity are discussed in the framework of current energy- and electron-transfer theories. PMID:22234895

  19. Polarization holograms in a bifunctional amorphous polymer exhibiting equal values of photoinduced linear and circular birefringences.

    PubMed

    Provenzano, Clementina; Pagliusi, Pasquale; Cipparrone, Gabriella; Royes, Jorge; Piñol, Milagros; Oriol, Luis

    2014-10-01

    Light-controlled molecular alignment is a flexible and useful strategy introducing novelty in the fields of mechanics, self-organized structuring, mass transport, optics, and photonics and addressing the development of smart optical devices. Azobenzene-containing polymers are well-known photocontrollable materials with large and reversible photoinduced optical anisotropies. The vectorial holography applied to these materials enables peculiar optical devices whose properties strongly depend on the relative values of the photoinduced birefringences. Here is reported a polarization holographic recording based on the interference of two waves with orthogonal linear polarization on a bifunctional amorphous polymer that, exceptionally, exhibits equal values of linear and circular birefringence. The peculiar photoresponse of the material coupled with the holographic technique demonstrates an optical device capable of decomposing the light into a set of orthogonally polarized linear components. The holographic structures are theoretically described by the Jones matrices method and experimentally investigated. PMID:25187982

  20. A bifunctional amorphous polymer exhibiting equal linear and circular photoinduced birefringences.

    PubMed

    Royes, Jorge; Provenzano, Clementina; Pagliusi, Pasquale; Tejedor, Rosa M; Piñol, Milagros; Oriol, Luis

    2014-11-01

    The large and reversible photoinduced linear and circular birefringences in azo-compounds are at the basis of the interest in these materials, which are potentially useful for several applications. Since the onset of the linear and circular anisotropies relies on orientational processes, which typically occur on the molecular and supramolecular length scale, respectively, a circular birefringence at least one order of magnitude lower than the linear one is usually observed. Here, the synthesis and characterization of an amorphous polymer with a dimeric repeating unit containing a cyanoazobenzene and a cyanobiphenyl moiety are reported, in which identical optical linear and circular birefringences are induced for proper light dose and ellipticity. A pump-probe technique and an analytical method based on the Stokes-Mueller formalism are used to investigate the photoinduced effects and to evaluate the anisotropies. The peculiar photoresponse of the polymer makes it a good candidate for applications in smart functional devices. PMID:25257542

  1. Photoinduced transformation of UVR8 monitored by vibrational and fluorescence spectroscopy.

    PubMed

    Heilmann, Monika; Christie, John M; Kennis, John T M; Jenkins, Gareth I; Mathes, Tilo

    2015-02-01

    Tryptophan residues at the dimer interface of the plant photoreceptor UVR8 promote monomerisation after UV-B absorption via a so far unknown mechanism. Using FTIR spectroscopy we assign light-induced structural transitions of UVR8 mainly to amino acid side chains without major transformations of the secondary structure of the physiologically relevant C-terminal extension. Additionally, we assign the monomerisation associated increase and red shift of the UVR8 tryptophan emission to a photoinduced rearrangement of tryptophan side chains and a relocation of the aspartic acid residues D96 and D107, respectively. By illumination dependent emission spectroscopy we furthermore determined the quantum yield of photoinduced monomerisation to 20 ± 8%. PMID:25274012

  2. Broadband optical limiter based on nonlinear photoinduced anisotropy in bacteriorhodopsin film

    NASA Astrophysics Data System (ADS)

    Huang, Yuhua; Siganakis, Georgios; Moharam, M. G.; Wu, Shin-Tson

    2004-11-01

    Nonlinear photoinduced anisotropy in a bacteriorhodopsin film was theoretically and experimentally investigated and a broadband active optical limiter was demonstrated in the visible spectral range. A diode-pumped second harmonic yttrium aluminum garnet laser was used as a pumping beam and three different wavelengths at λ =442, 532, and 655nm from different lasers were used as probing beams. The pump and probe beams overlap at the sample. When the pumping beam is absent, the probing beam cannot transmit the crossed polarizers. With the presence of the pumping beam, a portion of the probing light is detected owing to the photoinduced anisotropy. Due to the optical nonlinearity, the transmitted probing beam intensity is clamped at a certain value, which depends on the wavelength, when the pumping beam intensity exceeds 5mW/mm2. Good agreement between theory and experiment is found.

  3. Evidence for photo-induced charge separation between dye molecules adsorbed to aluminium oxide surfaces

    PubMed Central

    Cappel, Ute B.; Moia, Davide; Bruno, Annalisa; Vaissier, Valerie; Haque, Saif A.; Barnes, Piers R. F.

    2016-01-01

    Excited state dynamics and photo-induced charge transfer of dye molecules have been widely studied due to their relevance for organic and dye-sensitised solar cells. Herein, we present a femtosecond transient absorption spectroscopy study of the indolene dye D131 when adsorbed to inert Al2O3 substrates for different surface concentration of the dye. Surprisingly, we find that at high surface concentrations, the first singlet excited state of the dye is converted into a new state with an efficiency of about 80%. We assign the absorption features of this state to the oxidised dye and discuss the possibility of photo-induced charge separation between neighboring dye molecules. Our study is the first to show that this process can be highly efficient without the use of donor and acceptor molecules of different chemical structures. PMID:26891851

  4. Synthesis and photo-induced birefringence of pyrazoline substituted azo-dyes in PMMA films

    NASA Astrophysics Data System (ADS)

    Jin, Ming; Xin Yang, Qing; Lu, Ran; Yun Pan, Ling; Chong Xue, Peng; Zhao, YingYing

    2003-12-01

    Three push-pull type azo dyes, 4 '-{[(2-hydroxylethyl)methyl]amino}-4-nitroazobenzene (compound I), 1-[4-(4 '-nitrophenyl)-azophenyl]-3,5-biphenyl-2-pyrazoline (compound II) and 1-[4-(4 '-nitrophenyl)-azophenyl]-3-(3 '-trifluoromethyl)-phenyl-5-phenyl-2-pyrazoline (compound III) were synthesized. The cis- trans isomerization process and polarized photoinduced birefringence of those azo dyes doped PMMA films were investigated. It was found that the rise and relaxation process of birefringence signals were fit with biexponential functions and the molecular structures have effects on their photo-induced birefringence. This suggests that the three films have similar storage speed when the laser intensity is high enough. Compound III, which has the biggest substituent, has the largest long-term storage ability and can even keep 90% of its saturated birefringence.

  5. Photoinduced transformations of oxygen-deficient centers in Silica and Germanosilicate glasses

    SciTech Connect

    Marchenko, V.M.

    1995-07-01

    The methods for producing the oxygen-deficient centers and the experimental findings on the photoinduced processes in silica and germanosilicate glasses as well as in such optical waveguides manufactured from these glasses that underlie the development of promising integrated-optical and optical fiber devices and instruments are considered. the discrepancy in the photochromic process interpretation made on the ground of the structural models proposed for the oxygen-deficient centers in the glasses under consideration is discussed. The observable photoinduced transformations of the oxygen-deficient centers and associated changes in the physical properties of the glasses are explained on the assumption that photoexcitation initiates not internal ionization, but solid-phase chemical reactions accompanied by the breaking and switching of valence bonds.

  6. Probing ultrafast photo-induced dynamics of the exchange energy in a Heisenberg antiferromagnet

    NASA Astrophysics Data System (ADS)

    Batignani, G.; Bossini, D.; di Palo, N.; Ferrante, C.; Pontecorvo, E.; Cerullo, G.; Kimel, A.; Scopigno, T.

    2015-08-01

    Manipulating the macroscopic phases of solids using ultrashort light pulses has resulted in spectacular phenomena, including metal-insulator transitions, superconductivity and subpicosecond modification of magnetic order. The development of this research area strongly depends on the understanding and optical control of fundamental interactions in condensed matter, in particular the exchange interaction. However, disentangling the timescales relevant for the contributions of the exchange interaction and spin dynamics to the exchange energy, Eex, is a challenge. Here, we introduce femtosecond stimulated Raman scattering to unravel the ultrafast photo-induced dynamics of magnetic excitations at the edge of the Brillouin zone. We find that femtosecond laser excitation of the antiferromagnet KNiF3 triggers a spectral shift of the two-magnon line, the energy of which is proportional to Eex. By unravelling the photo-induced modification of the two-magnon line frequency from a dominating nonlinear optical effect, we find that Eex is increased by the electromagnetic stimulus.

  7. Photolabile Amphiphiles with Fluorogenic Thioxanthone-Dithiane Functionality: Synthesis and Photoinduced Fragmentation in Micelles

    PubMed Central

    Ezhov, Roman N.; Rozhkov, Vladimir V.; Majjigapu, Janaki R. R.

    2014-01-01

    Novel photolabile amphiphiles containing thioxanthone-based fluorogenic caging groups are developed. Photoinduced fragmentation in dithiane-thioxanthone adducts was demonstrated to occur with 100% quantum efficiency at λ ~ 320 nm and more than 50% at λ ~ 360 nm. A plausible mechanism involves homolytic fission of a carbon-carbon single bond in the excited thioxanthone followed by disproportionation via hydrogen transfer. The critical feature of the system is that fluorescence of a substituted thioxanthone is recovered as a result of photofragmentation, making dithiane-thioxanthone adducts efficient fluorogenic caging groups. Photolabile amphiphiles containing these fluorogens are synthesized and their photoinduced disassembly is probed while following the fluorescence recovery. This methodology allows for destabilizing supramolecular assemblies of amphiphiles and at the same time offers a feedback mechanism for monitoring the process by fluorescence. PMID:24436724

  8. Photoinduced Directional and Bidirectional Phase Transitions in Bistable Linear Polycyclic Aromatic Compounds

    NASA Astrophysics Data System (ADS)

    Zhang, Longlong; Yamamoto, Shoji

    2014-06-01

    We study photoinduced phase transitions in linear homocyclic and heterocyclic aromatic polymers, numerically solving the time-dependent Schrödinger equation and observing the photoinduced optical conductivity spectra along the way. All the polycyclic compounds of our interest have bistable cis-trans isomers, which are degenerate in energetics but distinct in optics, and therefore exhibit corresponding photochromism. We reveal that the molecular symmetry is decisive of the photoexchangeability of these bistable configurations, which is directional in molecules of the D2h geometry such as polyacene and paracyanogen but is bidirectional in those of the C2v geometry such as polypyridinopyridine and B, N-substituted acenes. We propose a series of polycyclic compounds for designing tunable photochromism of geometric origin.

  9. Photo-induced Modulation Doping in Graphene/Boron nitride Heterostructures

    NASA Astrophysics Data System (ADS)

    Velasco, Jairo, Jr.; Ju, Long; Hwang, Edwin; Kahn, Salman; Nosiglia, Casey; Tsai, Hsin-Zon; Yang, Wei; Zhang, Guangyu; Taniguchi, Takashi; Watanabe, Kenji; Zhang, Yuanbo; Crommie, Michael; Zettl, Alex; Wang, Feng

    2014-03-01

    Van der Waals heterostructures (VDH) provide an exciting new platform for materials engineering, where a variety of layered materials with different electrical, optical and mechanical responses can be stacked together to enable new physics and novel functionalities. We report an emerging optoelectronic phenomenon (i.e. photo-induced modulation doping) in the graphene-boron nitride VDH (G/BN heterostructure). We find it enables flexible and repeatable writing and erasing of charge doping in graphene with optical light. We show that the photo-induced modulation doping maintains the remarkable carrier mobility of the G/BN heterostructure, and it can be used to generate spatially varying doping profiles like pn junctions. Our work contributes towards understanding light matter interactions in VDHs, and introduces a simple technique for creating inhomogeneous doping in high mobility graphene devices. J. Velasco Jr. acknowledges support from UC President's Postdoctoral Fellowship.

  10. Photoinduced piezooptics effect in TeO2-Ga2O3 glasses

    NASA Astrophysics Data System (ADS)

    Ozga, K.; Fedorchuk, A. O.; Armand, P.

    2015-08-01

    We have found that during the bicolor illumination by two boicolor coherent wavelengths 1540 nm/770 nm there occurred substantial changes of the elastooptical non-diagonal coefficients at 1150 nm cw laser wavelength. They are maximal at power densities 400 … 500 MW/cm2. The studies have shown that the maximal effect exists for ultra-fast quenching glasses and occurs after the 1-2 min of the treatment. The switching off of the optical treatment leads to the disappearance of the photoinduced piezooptics at about 100 ms. The observed changes are explained within the photoinduced changes of the charge density distribution for the principal structural clusters within a framework of the DFT approach. The studies were done both for diagonal as well as off-diagonal piezooptical effect (POE) tensor components.

  11. Photo-induced changes in a hybrid amorphous chalcogenide/silica photonic crystal fiber

    SciTech Connect

    Markos, Christos

    2014-01-06

    Photostructural changes in a hybrid photonic crystal fiber with chalcogenide nanofilms inside the inner surface of the cladding holes are experimentally demonstrated. The deposition of the amorphous chalcogenide glass films inside the silica capillaries of the fiber was made by infiltrating the nanocolloidal solution-based As{sub 25}S{sub 75}, while the photoinduced changes were performed by side illuminating the fiber near the bandgap edge of the formed glass nanofilms. The photoinduced effect of the chalcogenide glass directly red-shifts the transmission bandgap position of the fiber as high as ∼20.6 nm at around 1600 nm wavelength, while the maximum bandgap intensity change at ∼1270 nm was −3 dB.

  12. Evidence for photo-induced charge separation between dye molecules adsorbed to aluminium oxide surfaces

    NASA Astrophysics Data System (ADS)

    Cappel, Ute B.; Moia, Davide; Bruno, Annalisa; Vaissier, Valerie; Haque, Saif A.; Barnes, Piers R. F.

    2016-02-01

    Excited state dynamics and photo-induced charge transfer of dye molecules have been widely studied due to their relevance for organic and dye-sensitised solar cells. Herein, we present a femtosecond transient absorption spectroscopy study of the indolene dye D131 when adsorbed to inert Al2O3 substrates for different surface concentration of the dye. Surprisingly, we find that at high surface concentrations, the first singlet excited state of the dye is converted into a new state with an efficiency of about 80%. We assign the absorption features of this state to the oxidised dye and discuss the possibility of photo-induced charge separation between neighboring dye molecules. Our study is the first to show that this process can be highly efficient without the use of donor and acceptor molecules of different chemical structures.

  13. Photo-induced isomerization and chemical reaction dynamics in superfluid helium droplets

    NASA Astrophysics Data System (ADS)

    Merritt, Jeremy; Douberly, Gary; Miller, Roger

    2008-03-01

    Near threshold photo-induced isomerization and photo-induced chemical reactions have long been sough after as sensitive probes of the underlying potential energy surface. One of the most important questions asked is how the initially bright quantum state couples to the reaction coordinate, and thus relates to energy transfer in general. Helium droplets have now allowed us to stabilize entrance channel clusters behind very small reaction barriers such that vibrational excitation may result in reaction. Through two examples, namely the isomerization of the 2 binary complexes of HF-HCN Douberly et al. PCCP 2005, 7,463, and the induced reaction of the gallium-HCN complex Merritt et al. JPCA 2007, DOI:10.1021/jp074981e we will show how the branching ratios for reaction and predissociation can determined and the influence of the superfluid He solvent.

  14. Surface Grafting via Photo-Induced Copper-Mediated Radical Polymerization at Extremely Low Catalyst Concentrations.

    PubMed

    Laun, Joachim; Vorobii, Mariia; de los Santos Pereira, Andres; Pop-Georgievski, Ognen; Trouillet, Vanessa; Welle, Alexander; Barner-Kowollik, Christopher; Rodriguez-Emmenegger, Cesar; Junkers, Thomas

    2015-09-01

    Surface-initiated photo-induced copper-mediated radical polymerization is employed to graft a wide range of polyacrylate brushes from silicon substrates at extremely low catalyst concentrations. This is the first time that the controlled nature of the reported process is demonstrated via block copolymer formation and re-initiation experiments. In addition to unmatched copper catalyst concentrations in the range of few ppb, film thicknesses up to almost 1 μm are achieved within only 1 h. PMID:26149622

  15. Instability of photoinduced optical absorption of Bi12SiO20: Al crystals

    NASA Astrophysics Data System (ADS)

    Panchenko, T. V.; Dyachenko, A. A.; Khmelenko, O. V.

    2015-04-01

    The results of the experimental investigation of the instability of the establishment and relaxation of a photochromic effect in aluminum-doped Bi12SiO20 crystals have been presented. The oscillating and nonmonotonic kinetic dependences of the photoinduced optical absorption have been observed. The absorption oscillations are associated with the competition of the formation and destruction of [AlSiO4]0 photochromic centers.

  16. Procedure for quantitative determination of effectiveness of photoinduced destruction of malignant tumors

    NASA Astrophysics Data System (ADS)

    Bizyuk, S. A.; Istomin, Yu. P.; Dzhagarov, B. M.

    2006-07-01

    We have developed a procedure for analysis of the functional status of blood vessels in tumor tissues using computer-assisted color scanning of tumor slices and also for a quantitative assessment of the effectiveness of photoinduced destruction of tumor tissues in animal experiments. Its major advantage is direct determination of the size of the tumor necrosis zone. The procedure has been tested in an experiment on three strains of malignant tumors with different morphologies.

  17. Dark spatial solitons in bulk azo-dye-doped polymer using photoinduced molecular reorientation

    SciTech Connect

    Bian Shaoping; Kuzyk, Mark G.

    2004-08-16

    We report the generation of dark spatial solitons in bulk Disperse Red 1 doped poly(methyl methacrylate) using photoinduced reorientation of azo-dye molecules. Planar solitions are formed when illuminated with a continuous-wave laser at intensities of the order of hundreds of miliwatts per square centimeter. The width of the soliton saturates to a minimum value at high intensity; and when the width of the initial dark notch is reduced, the equilibrium minimum width is unchanged.

  18. Ultrafast photoinduced mechanical strain in epitaxial BiFeO3 thin films

    NASA Astrophysics Data System (ADS)

    Chen, L. Y.; Yang, J. C.; Luo, C. W.; Laing, C. W.; Wu, K. H.; Lin, J.-Y.; Uen, T. M.; Juang, J. Y.; Chu, Y. H.; Kobayashi, T.

    2012-07-01

    We studied ultrafast dynamics and photoinduced mechanical strain of BiFeO3 thin films by dual-color transient reflectivity measurements (ΔR/R). Anisotropic photostriction in BiFeO3 is found to be mainly driven by the optical rectification effect. Results of the photostriction at various thicknesses show that the estimated sound velocity along [110] direction of BiFeO3 is 4.76 km/s.

  19. Capturing ultrafast photoinduced local structural distortions of BiFeO3

    DOE PAGESBeta

    Wen, Haidan; Sassi, Michel JPC; Luo, Zhenlin; Adamo, Carolina; Schlom, Darrell; Rosso, Kevin M.; Zhang, Xiaoyi

    2015-10-14

    The interaction of light with materials is an intensively studied research forefront, in which the coupling of radiation energy to selective degrees of freedom offers contact-free tuning of functionalities on ultrafast time scales. Capturing the fundamental processes and understanding the mechanism of photoinduced structural rearrangement are essential to applications such as photo-active actuators and efficient photovoltaic devices. Using ultrafast x-ray absorption spectroscopy aided by density functional theory calculations, we reveal the local structural arrangement around the transition metal atom in a unit cell of the photoferroelectric archetype BiFeO3 film. The out-of-plane elongation of the unit cell is accompanied by themore » in-plane shrinkage with minimal change of interaxial lattice angles upon photoexcitation. This uniaxial elastic deformation of the unit cell is driven by localized electric field as a result of photoinduced charge separation, in contrast to a global lattice constant increase and lattice angle variations as a result of heating. The finding of a photoinduced elastic unit cell deformation elucidates a microscopic picture of photocarrier-mediated nonequilibrium processes in polar materials.« less

  20. Capturing ultrafast photoinduced local structural distortions of BiFeO3

    SciTech Connect

    Wen, Haidan; Sassi, Michel JPC; Luo, Zhenlin; Adamo, Carolina; Schlom, Darrell; Rosso, Kevin M.; Zhang, Xiaoyi

    2015-10-14

    The interaction of light with materials is an intensively studied research forefront, in which the coupling of radiation energy to selective degrees of freedom offers contact-free tuning of functionalities on ultrafast time scales. Capturing the fundamental processes and understanding the mechanism of photoinduced structural rearrangement are essential to applications such as photo-active actuators and efficient photovoltaic devices. Using ultrafast x-ray absorption spectroscopy aided by density functional theory calculations, we reveal the local structural arrangement around the transition metal atom in a unit cell of the photoferroelectric archetype BiFeO3 film. The out-of-plane elongation of the unit cell is accompanied by the in-plane shrinkage with minimal change of interaxial lattice angles upon photoexcitation. This uniaxial elastic deformation of the unit cell is driven by localized electric field as a result of photoinduced charge separation, in contrast to a global lattice constant increase and lattice angle variations as a result of heating. The finding of a photoinduced elastic unit cell deformation elucidates a microscopic picture of photocarrier-mediated nonequilibrium processes in polar materials.

  1. Capturing ultrafast photoinduced local structural distortions of BiFeO3

    PubMed Central

    Wen, Haidan; Sassi, Michel; Luo, Zhenlin; Adamo, Carolina; Schlom, Darrell G.; Rosso, Kevin M.; Zhang, Xiaoyi

    2015-01-01

    The interaction of light with materials is an intensively studied research forefront, in which the coupling of radiation energy to selective degrees of freedom offers contact-free tuning of functionalities on ultrafast time scales. Capturing the fundamental processes and understanding the mechanism of photoinduced structural rearrangement are essential to applications such as photo-active actuators and efficient photovoltaic devices. Using ultrafast x-ray absorption spectroscopy aided by density functional theory calculations, we reveal the local structural arrangement around the transition metal atom in a unit cell of the photoferroelectric archetype BiFeO3 film. The out-of-plane elongation of the unit cell is accompanied by the in-plane shrinkage with minimal change of interaxial lattice angles upon photoexcitation. This anisotropic elastic deformation of the unit cell is driven by localized electric field as a result of photoinduced charge separation, in contrast to a global lattice constant increase and lattice angle variations as a result of heating. The finding of a photoinduced elastic unit cell deformation elucidates a microscopic picture of photocarrier-mediated non-equilibrium processes in polar materials. PMID:26463128

  2. Capturing ultrafast photoinduced local structural distortions of BiFeO3

    NASA Astrophysics Data System (ADS)

    Wen, Haidan; Sassi, Michel; Luo, Zhenlin; Adamo, Carolina; Schlom, Darrell G.; Rosso, Kevin M.; Zhang, Xiaoyi

    2015-10-01

    The interaction of light with materials is an intensively studied research forefront, in which the coupling of radiation energy to selective degrees of freedom offers contact-free tuning of functionalities on ultrafast time scales. Capturing the fundamental processes and understanding the mechanism of photoinduced structural rearrangement are essential to applications such as photo-active actuators and efficient photovoltaic devices. Using ultrafast x-ray absorption spectroscopy aided by density functional theory calculations, we reveal the local structural arrangement around the transition metal atom in a unit cell of the photoferroelectric archetype BiFeO3 film. The out-of-plane elongation of the unit cell is accompanied by the in-plane shrinkage with minimal change of interaxial lattice angles upon photoexcitation. This anisotropic elastic deformation of the unit cell is driven by localized electric field as a result of photoinduced charge separation, in contrast to a global lattice constant increase and lattice angle variations as a result of heating. The finding of a photoinduced elastic unit cell deformation elucidates a microscopic picture of photocarrier-mediated non-equilibrium processes in polar materials.

  3. Photo-induced toxicity of Deepwater Horizon slick oil to blue crab (Callinectes sapidus) larvae.

    PubMed

    Alloy, Matthew M; Boube, Idrissa; Griffitt, Robert J; Oris, James T; Roberts, Aaron P

    2015-09-01

    The 2010 Deepwater Horizon oil spill resulted in the accidental release of approximately 700 million L of crude oil into the Gulf of Mexico. Photo-induced toxicity after co-exposure to ultraviolet (UV) radiation is 1 mechanism by which polycyclic aromatic hydrocarbons (PAHs) from oil spills may exert toxicity. Blue crab are an important commercial and ecological resource in the Gulf of Mexico, and their largely transparent larvae may make them sensitive to PAH photo-induced toxicity. The goal of the present study was to examine the sensitivity of early lifestage blue crab (Callinectes sapidus) zoea to slick oil collected during the Deepwater Horizon spill. Blue crab zoea were exposed to 1 of several dilutions of water accommodated fractions from 1 of 2 sources of oil and gradations of natural sunlight in a factorial design. Two 7-h solar exposures were carried out with a recovery period (dark) in between. Survival was found to be UV- and PAH-dependent. Toxicity was observed within the range of surface PAH concentrations reported in the Gulf of Mexico during the Deepwater Horizon spill. These findings indicate that early lifestage blue crab are sensitive to photo-induced toxicity from Deepwater Horizon slick oil. PMID:26198885

  4. Capturing ultrafast photoinduced local structural distortions of BiFeO3.

    PubMed

    Wen, Haidan; Sassi, Michel; Luo, Zhenlin; Adamo, Carolina; Schlom, Darrell G; Rosso, Kevin M; Zhang, Xiaoyi

    2015-01-01

    The interaction of light with materials is an intensively studied research forefront, in which the coupling of radiation energy to selective degrees of freedom offers contact-free tuning of functionalities on ultrafast time scales. Capturing the fundamental processes and understanding the mechanism of photoinduced structural rearrangement are essential to applications such as photo-active actuators and efficient photovoltaic devices. Using ultrafast x-ray absorption spectroscopy aided by density functional theory calculations, we reveal the local structural arrangement around the transition metal atom in a unit cell of the photoferroelectric archetype BiFeO3 film. The out-of-plane elongation of the unit cell is accompanied by the in-plane shrinkage with minimal change of interaxial lattice angles upon photoexcitation. This anisotropic elastic deformation of the unit cell is driven by localized electric field as a result of photoinduced charge separation, in contrast to a global lattice constant increase and lattice angle variations as a result of heating. The finding of a photoinduced elastic unit cell deformation elucidates a microscopic picture of photocarrier-mediated non-equilibrium processes in polar materials. PMID:26463128

  5. Three-centered model of ultrafast photoinduced charge transfer: Continuum dielectric approach

    SciTech Connect

    Khohlova, Svetlana S.; Mikhailova, Valentina A.; Ivanov, Anatoly I.

    2006-03-21

    A theoretical description of photoinduced charge transfer involves explicit treating both the optical formation of the nuclear wave packet on the excited free energy surface and its ensuing dynamics. The reaction pathway constitutes two-stage charge transfer between three centers. Manifestations of fractional charge transfer at first stage are explored. An expression for time dependent rate constant of photoinduced charge transfer is found in the framework of the linear dielectric continuum model of the medium. The model involves both the intramolecular vibrational reorganization and the Coulombic interaction of the transferred charge with the medium polarization fluctuations and allows to express the rate in terms of intramolecular reorganization parameters and complex dielectric permittivity. The influence of the vibrational coherent motion in the locally excited state on the charge transfer dynamics has been explored. The dependence of the ultrafast photoinduced charge transfer dynamics on the excitation pulse carrier frequency (spectral effect) has been investigated. The spectral effect has been shown to depend on quantity of the fractional charge.

  6. Highly active ppm level organic copper catalyzed photo-induced ICAR ATRP of methyl methacrylate.

    PubMed

    Jiang, Xiaowu; Wu, Jian; Zhang, Lifen; Cheng, Zhenping; Zhu, Xiulin

    2014-11-01

    A novel photo-induced homogeneous atom transfer radical polymerization (ATRP) system is constructed using an organic copper salt (Cu(SC(S)N(C2 H5 )2 )2 ) as a photo-induced catalyst at 30 °C. Herein, N,N,N',N'',N''-pentamethyldiethylenetriamine (PMDETA) is used as a ligand, ethyl 2-bromophenylacetate (EBPA) as an ATRP initiator, and (2,4,6-trimethylbenzoyl) diphenylphosphine oxide (TPO) as a photo-induced radical initiator to establish an ICAR (initiators for continuous activator regeneration) ATRP using methyl methacrylate (MMA) as a modal monomer. The effect of the concentration of the organic copper on the polymerization is investigated in detail. It is found that well-controlled polymerization can be obtained even with the amount of (Cu(SC(S)N(C2 H5 )2 )2 decreasing to a 1.56 ppm level, with the molecular weight of the resultant polymers increasing linearly with monomer conversion while maintaining a narrow molecular weight distribution (M¯w/M¯n < 1.3). PMID:25250767

  7. Photoinduced interactions of two dirhodium complexes with d(GTCGAC)2 probed by 2D NOESY

    PubMed Central

    Palmer, Alycia M.; Knoll, Jessica D.; Turro, Claudia

    2015-01-01

    The interactions between the 6-mer duplex oligonucleotide d(GTCGAC)2 and the photoactive dirhodium complexes cis-H,H-[Rh2(HNOCCH3)2(L)(CH3CN)4]2+, where L represents bpy (1, 2,2´-bipyridine) and dppz (2, dipyrido[3,2-a:2′,3′-c]phenazine), were probed using 2D 1H–1H NOESY NMR spectroscopy. Complex 1 does not interact with the duplex in the dark, but binds covalently to the terminal guanine following irradiation with visible light. Similar behavior was observed for 2, but in addition to the photoinduced covalent DNA binding, the planar dppz ligand of the complex shields the terminal cytosine protons after irradiation. The results are consistent with photoinduced guanine coordination and end-capping of the duplex through π-stacking interactions with the terminal GC base pair. These data show that in the presence of the 6-mer duplex oligonucleotide, 1 and 2 exhibit photoinduced covalent binding to DNA. In addition, the π-stacking interactions of 2 with the duplex are enhanced upon irradiation. PMID:25557067

  8. Photoinduced Disaggregation of TiO2 Nanoparticles Enables Transdermal Penetration

    PubMed Central

    Bennett, Samuel W.; Zhou, Dongxu; Mielke, Randall; Keller, Arturo A.

    2012-01-01

    Under many aqueous conditions, metal oxide nanoparticles attract other nanoparticles and grow into fractal aggregates as the result of a balance between electrostatic and Van Der Waals interactions. Although particle coagulation has been studied for over a century, the effect of light on the state of aggregation is not well understood. Since nanoparticle mobility and toxicity have been shown to be a function of aggregate size, and generally increase as size decreases, photo-induced disaggregation may have significant effects. We show that ambient light and other light sources can partially disaggregate nanoparticles from the aggregates and increase the dermal transport of nanoparticles, such that small nanoparticle clusters can readily diffuse into and through the dermal profile, likely via the interstitial spaces. The discovery of photoinduced disaggregation presents a new phenomenon that has not been previously reported or considered in coagulation theory or transdermal toxicological paradigms. Our results show that after just a few minutes of light, the hydrodynamic diameter of TiO2 aggregates is reduced from ∼280 nm to ∼230 nm. We exposed pigskin to the nanoparticle suspension and found 200 mg kg−1 of TiO2 for skin that was exposed to nanoparticles in the presence of natural sunlight and only 75 mg kg−1 for skin exposed to dark conditions, indicating the influence of light on NP penetration. These results suggest that photoinduced disaggregation may have important health implications. PMID:23155401

  9. Capturing ultrafast photoinduced local structural distortion of BiFeO3

    SciTech Connect

    Wen, Haidan; Sassi, Michel; Luo, Zhenlin; Adamo, Carolina; Schlom, Darrell G.; Rosso, Kevin M.; Zhang, Xiaoyi

    2015-10-14

    The interaction of light with materials is an intensively studied research forefront, in which the coupling of radiation energy to selective degrees of freedom offers contact-free tuning of functionalities on ultrafast time scales. Capturing the fundamental processes and understanding the mechanism of photoinduced structural rearrangement are essential to applications such as photo-active actuators and efficient photovoltaic devices. Using ultrafast x-ray absorption spectroscopy aided by density functional theory calculations, we reveal the local structural arrangement around the transition metal atom in a unit cell of the photoferroelectric archetype BiFeO3 film. The out-of-plane elongation of the unit cell is accompanied by the in-plane shrinkage with minimal change of interaxial lattice angles upon photoexcitation. This anisotropic elastic deformation of the unit cell is driven by localized electric field as a result of photoinduced charge separation, in contrast to a global lattice constant increase and lattice angle variations as a result of heating. The finding of a photoinduced elastic unit cell deformation elucidates a microscopic picture of photocarrier-mediated non-equilibrium processes in polar materials.

  10. Copper catalyst activation driven by photoinduced electron transfer: a prototype photolatent click catalyst.

    PubMed

    Harmand, Lydie; Cadet, Sarah; Kauffmann, Brice; Scarpantonio, Luca; Batat, Pinar; Jonusauskas, Gediminas; McClenaghan, Nathan D; Lastécouères, Dominique; Vincent, Jean-Marc

    2012-07-16

    PET cat. While the copper(II) tren ketoprofenate precatalyst 1 (see picture) is inactive at room temperature in methanol, it is quantitatively and rapidly reduced to its cuprous state upon light irradiation to provide a highly reactive click catalyst. By simply introducing air into the reaction medium the catalysis can be switched off and then switched on again by bubbling argon followed by irradiation. PMID:22777953

  11. Photo-induced alternating copolymerization of N-substituted maleimides and electron donor olefins

    NASA Astrophysics Data System (ADS)

    Jönsson, S.; Sundell, P. E.; Shimose, M.; Clark, S.; Miller, C.; Morel, F.; Decker, C.; Hoyle, C. E.

    1997-08-01

    Photo-initiated free radical polymerization of donor/acceptor type monomers have gained considerable interest due to the possibility of formulating UV curable non-acrylate systems. Recently, we described a photoinitiator free system based on donor/acceptor combinations [1-7]. Photoinitiator free nonacrylate based compositions will of course attain an enhanced interest and importance because of a broader selection of raw materials and combinations thereof, potential outdoor use, lower costs of formulations, improved odour, no formation of benzaldehyde, less extractables and so on. Recent developments of the direct photolysis of these acceptors and complexes, and their potential use in practical "UV curing" will be outlined. By a selective combination of A and D type monomers, a direct photolysis of the ground state complex (CTC) or the excitation of the acceptor, followed by the formation of an exciplex, will initiate a free radical copolymerization. A second route of direct initiation is based on inter- or intra-molecular H-abstraction from an excited state acceptor or exciplex. This paper will focus on the photochemistry as it relates to initiation of polymerization depending on acceptor and donor strength of the monomer system. Inherently different reactivities in air and nitrogen of donors and acceptors are compared to photoinitiator containing acrylates. Furthermore, the ratio of homo and alternating copolymerization as well as the 2 + 2 cycloaddition will be discussed.

  12. Two new isomerous fluorescent chemosensors for Al3+ based on photoinduced electron transfer

    NASA Astrophysics Data System (ADS)

    Jiang, Xiu-Juan; Tang, Hao; Li, Xiao-Yuan; Zang, Shuang-Quan; Hou, Hong-Wei; Mak, Thomas C. W.

    2013-11-01

    Two new isomerous PET fluorescent chemosensors (L and L‧) for Al3+ have been designed, synthesized and characterized. The two chemosensors exhibited fluorescence enhancement upon binding Al3+ in CH3CN by PET inhibition processes from both the sulfur and the nitrogen donors to anthracene. The job's plot, Benesi-Hildebrand plot and 1H NMR titration experiments indicate that both chemosensors form a 1:1 complex with Al3+. The binding constants were calculated to be (1.432 ± 0.186) × 105 and (1.427 ± 0.970) × 105, respectively. Furthermore, the lowest detection limit for Al3+ in CH3CN was determined to be 4.8 × 10-7 M and 2.2 × 10-7 M, respectively.

  13. Photo-induced changes in arsenic selenide films

    NASA Astrophysics Data System (ADS)

    Moharram, A. H.; Mansour, S. A.; Al-Marzouki, F.; Hendi, Asma. A.; Rashad, M.

    2013-01-01

    The spectral dependence of the transmittance and reflectance of thermally-evaporated amorphous As x Se100- x (where x = 20 and 40 at.%) films was measured in the wavelength range of 190-900 nm. A procedure was given for accurate determination of the film thickness using a standard method of numerical differences from the experimental data. The process of indirect electronic transitions was found to be responsible for the photon absorption. The variation of the energy band gap with the exposure time was investigated. Amorphous-crystalline transformations occurring as a result of photoexposure have been confirmed by the structural studies of the As20Se80 specimens using the scanning electron microscope and transmission electron microscope. Photodarkening relaxation under light exposure of the well annealed films was studied and the relaxation process has been described by the stretched exponential function (SEF).

  14. Photoinduced Processes of Supramolecular Nanoarrays Composed of Porphyrin and Benzo[ghi]perylenetriimide Units through Triple Hydrogen Bonds with One-Dimensional Columnar Phases.

    PubMed

    Sakai, Hayato; Ohkubo, Kei; Fukuzumi, Shunichi; Hasobe, Taku

    2016-02-18

    One-dimensional supramolecular columnar phases composed of porphyrins (electron donor: D) and benzo[ghi]perylenetriimides (electron acceptor: A) through triple hydrogen bonds have been successfully constructed to perform sequential light-harvesting and electron-transfer processes. A series of benzo[ghi]peryleneimide derivatives have been synthesized to examine the substituent effects such as imide and nitrile groups on the spectroscopic and electrochemical properties. Then, formation of the 1:1 supramolecular complex between zinc porphyrin and benzo[ghi]perylenetriimide derivatives through triple hydrogen bonds was confirmed by Job's plot of (1) H NMR titration. Next, the one-dimensional supramolecular nanoarrays were successfully prepared in a mixed solvent. X-ray diffraction (XRD) measurement suggested that these nanoarrays contained one-dimensional columnar phases composed of stacked donor and acceptor layers. Finally, femtosecond transient absorption and electron spin resonance (ESR) measurements clearly indicated that photoinduced electron transfer occurred via the singlet excited states in the supramolecular columns. PMID:26766519

  15. 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

  16. Photoinduced Enhancement of the Charge Density Wave Amplitude.

    PubMed

    Singer, A; Patel, S K K; Kukreja, R; Uhlíř, V; Wingert, J; Festersen, S; Zhu, D; Glownia, J M; Lemke, H T; Nelson, S; Kozina, M; Rossnagel, K; Bauer, M; Murphy, B M; Magnussen, O M; Fullerton, E E; Shpyrko, O G

    2016-07-29

    Symmetry breaking and the emergence of order is one of the most fascinating phenomena in condensed matter physics. It leads to a plethora of intriguing ground states found in antiferromagnets, Mott insulators, superconductors, and density-wave systems. Exploiting states of matter far from equilibrium can provide even more striking routes to symmetry-lowered, ordered states. Here, we demonstrate for the case of elemental chromium that moderate ultrafast photoexcitation can transiently enhance the charge-density-wave (CDW) amplitude by up to 30% above its equilibrium value, while strong excitations lead to an oscillating, large-amplitude CDW state that persists above the equilibrium transition temperature. Both effects result from dynamic electron-phonon interactions, providing 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 order parameters in other systems with coupled degrees of freedom. PMID:27517781

  17. Photoinduced currents in metal-barrier-metal junctions

    NASA Technical Reports Server (NTRS)

    Guedes, M. P.; Gustafson, T. K.; Heiblum, M.; Siu, D. P.; Slayman, C. W.; Whinnery, J. R.; Yasuoka, Y.

    1978-01-01

    The fabrication and application of metal-barrier-metal tunneling junctions for radiative interactions are discussed. Particular attention is given to the photolithographic fabrication of small area devices and the coupling to such devices via surface plasmon waves which play an important role at infrared and optical frequencies. It has been shown that the junction electron tunneling currents can be strongly coupled to surface plasmon junction modes, and spontaneous and stimulated emission of the latter are possible as well as nonlinear interactions. Finally, results demonstrating the photo-excitation of electrons with subsequent tunneling induced by ultraviolet radiation are presented. It is estimated that quantum efficiencies of the order of 5% and higher are possible in the ultraviolet region.

  18. Photoinduced Enhancement of the Charge Density Wave Amplitude

    NASA Astrophysics Data System (ADS)

    Singer, A.; Patel, S. K. K.; Kukreja, R.; Uhlíř, V.; Wingert, J.; Festersen, S.; Zhu, D.; Glownia, J. M.; Lemke, H. T.; Nelson, S.; Kozina, M.; Rossnagel, K.; Bauer, M.; Murphy, B. M.; Magnussen, O. M.; Fullerton, E. E.; Shpyrko, O. G.

    2016-07-01

    Symmetry breaking and the emergence of order is one of the most fascinating phenomena in condensed matter physics. It leads to a plethora of intriguing ground states found in antiferromagnets, Mott insulators, superconductors, and density-wave systems. Exploiting states of matter far from equilibrium can provide even more striking routes to symmetry-lowered, ordered states. Here, we demonstrate for the case of elemental chromium that moderate ultrafast photoexcitation can transiently enhance the charge-density-wave (CDW) amplitude by up to 30% above its equilibrium value, while strong excitations lead to an oscillating, large-amplitude CDW state that persists above the equilibrium transition temperature. Both effects result from dynamic electron-phonon interactions, providing 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 order parameters in other systems with coupled degrees of freedom.

  19. Photoinduced Charge Transfer at Metal Oxide/Oxide Interfaces Prepared with Plasma Enhanced Atomic Layer Deposition

    NASA Astrophysics Data System (ADS)

    Kaur, Manpuneet

    LiNbO3 and ZnO have shown great potential for photochemical surface reactions and specific photocatalytic processes. However, the efficiency of LiNbO3 is limited due to recombination or back reactions and ZnO exhibits a chemical instability in a liquid cell. In this dissertation, both materials were coated with precise thickness of metal oxide layers to passivate the surfaces and to enhance their photocatalytic efficiency. LiNbO 3 was coated with plasma enhanced atomic layer deposited (PEALD) ZnO and Al2O3, and molecular beam deposited TiO2 and VO2. On the other hand, PEALD ZnO and single crystal ZnO were passivated with PEALD SiO2 and Al2O3. Metal oxide/LiNbO3 heterostructures were immersed in aqueous AgNO3 solutions and illuminated with ultraviolet (UV) light to form Ag nanoparticle patterns. Alternatively, Al2O3 and SiO2/ZnO heterostructures were immersed in K3PO 4 buffer solutions and studied for photoelectrochemical reactions. A fundamental aspect of the heterostructures is the band alignment and band bending, which was deduced from in situ photoemission measurements. This research has provided insight to three aspects of the heterostructures. First, the band alignment at the interface of metal oxides/LiNbO 3, and Al2O3 or SiO2/ZnO were used to explain the possible charge transfer processes and the direction of carrier flow in the heterostructures. Second, the effect of metal oxide coatings on the LiNbO3 with different internal carrier concentrations was related to the surface photochemical reactions. Third is the surface passivation and degradation mechanism of Al2O 3 and SiO2 on ZnO was established. The heterostructures were characterized after stability tests using atomic force microscopy (AFM), scanning electron microscopy (SEM), and cross-section transmission electron microscopy (TEM). The results indicate that limited thicknesses of ZnO or TiO2 on polarity patterned LiNbO3 (PPLN) enhances the Ag+ photoinduced reduction process. ZnO seems more efficient

  20. Ultrafast photoinduced charge separation in metal-semiconductor nanohybrids.

    PubMed

    Mongin, Denis; Shaviv, Ehud; Maioli, Paolo; Crut, Aurélien; Banin, Uri; Del Fatti, Natalia; Vallée, Fabrice

    2012-08-28

    Hybrid nano-objects formed by two or more disparate materials are among the most promising and versatile nanosystems. A key parameter in their properties is interaction between their components. In this context we have investigated ultrafast charge separation in semiconductor-metal nanohybrids using a model system of gold-tipped CdS nanorods in a matchstick architecture. Experiments are performed using an optical time-resolved pump-probe technique, exciting either the semiconductor or the metal component of the particles, and probing the light-induced change of their optical response. Electron-hole pairs photoexcited in the semiconductor part of the nanohybrids are shown to undergo rapid charge separation with the electron transferred to the metal part on a sub-20 fs time scale. This ultrafast gold charging leads to a transient red-shift and broadening of the metal surface plasmon resonance, in agreement with results for free clusters but in contrast to observation for static charging of gold nanoparticles in liquid environments. Quantitative comparison with a theoretical model is in excellent agreement with the experimental results, confirming photoexcitation of one electron-hole pair per nanohybrid followed by ultrafast charge separation. The results also point to the utilization of such metal-semiconductor nanohybrids in light-harvesting applications and in photocatalysis. PMID:22792998

  1. Photoinduced water splitting via benzoquinone and semiquinone sensitisation.

    PubMed

    Karsili, Tolga N V; Tuna, Deniz; Ehrmaier, Johannes; Domcke, Wolfgang

    2015-12-28

    The splitting of water into H˙ and OH˙ radicals by sensitisation of a redox-active chromophore with sunlight may eventually become a viable way of producing unlimited, clean and sustainable energy. In this work, we explore the possibility of photo-oxidation of water via sensitisation of benzoquinone with ultraviolet (UV) light in the hydrogen-bonded complex of benzoquinone with a single water molecule. Using state-of-the-art quantum chemical calculations, the mechanisms of electron/proton transfer reactions between photoexcited benzoquinone and water are characterised. In the benzoquinone-H2O complex, photoexcitation of the chromophore leads to the population of locally excited ππ* and nπ* singlet states, which are coupled to hitherto unknown charge-transfer states. In the latter, an electron is transferred from the oxygen atom of the water molecule to the lowest π* orbital of benzoquinone. These charge-separated states drive the transfer of a proton from the water molecule to the carbonyl acceptor site, yielding the semiquinone-OH˙ biradical. Upon absorption of a second UV photon, the semiquinone radical may undergo O-H bond fission, which generates an H˙ radical and restores the benzoquinone photocatalyst. Our computational results shed light on long-standing questions regarding the nature of the photoreactive electronic states in the aqueous photochemistry of benzoquinone. PMID:26488227

  2. Near-Infrared Photoelectrochemical Conversion via Photoinduced Charge Separation in Supramolecular Complexes of Anionic Phthalocyanines with Li(+)@C60.

    PubMed

    Kawashima, Yuki; Ohkubo, Kei; Blas-Ferrando, Vicente Manuel; Sakai, Hayato; Font-Sanchis, Enrique; Ortíz, Javier; Fernández-Lázaro, Fernando; Hasobe, Taku; Sastre-Santos, Ángela; Fukuzumi, Shunichi

    2015-06-18

    Two phthalocyanines possessing carboxylate groups ((TBA)4H2Pc·1 and (TBA)4H2Pc·2) form 1:2 supramolecular complexes with lithium cation-encapsulated C60 (Li(+)@C60) [H2Pc·1(4-)/(Li(+)@C60)2 and H2Pc·2(4-)/(Li(+)@C60)2] in a polar mixed solvent. From the UV-vis spectral changes, the binding constants (K) were estimated as ca. 10(12) M(-2). Upon the photoexcitation of constructed supramolecular complexes, photoinduced electron transfer occurred to form the charge-separated (CS) state. The lifetime of the CS state was determined to be 1.2 ms for H2Pc·2(4-)/(Li(+)@C60)2, which is the longest CS lifetime among the porphyrinoid/fullerene supramolecular complexes. H2Pc·1(4-)/(Li(+)@C60)2 also afforded the long-lived CS state of 1.0 ms. The spin state of the long-lived CS states was determined to be a triplet, as indicated by the EPR signal at g = 4. The reorganization energy (λ) and the electronic coupling term were determined to be λ = 1.70 eV, V = 0.15 cm(-1) from the temperature dependence of the rate constant for the charge recombination of the CS state of H2Pc·1(4-)/(Li(+)@C60)2. The energy of the CS state (0.49 eV) is much smaller than the reorganization energy, indicating that the back-electron-transfer process is located in the Marcus normal region. The small electronic coupling term results from the spin-forbidden back electron transfer due to the triplet CS state. Supramolecular complexes of anionic zinc phthalocyanines with Li(+)@C60 were also prepared and investigated. The ZnPc·4(4-)/Li(+)@C60 supramolecular nanoclusters were assembled on the optically transparent electrode (OTE) of nanostructured SnO2 (OTE/SnO2) to construct the dye-sensitized solar cell. The IPCE (incident photon-to-photocurrent efficiency) values of OTE/SnO2/(ZnPc·4(4-)/Li(+)@C60)n were much higher than the sum of the two IPCE values of the individual systems OTE/SnO2/(Li(+)@C60)n and OTE/SnO2/(ZnPc·4(4-))n, covering the near-infrared region. PMID:25615010

  3. Efficient photoinduced charge accumulation in reduced graphene oxide coupled with titania nanosheets to show highly enhanced and persistent conductance.

    PubMed

    Cai, Xingke; Sakai, Nobuyuki; Ozawa, Tadashi C; Funatsu, Asami; Ma, Renzhi; Ebina, Yasuo; Sasaki, Takayoshi

    2015-06-01

    Tuning of the electrical properties of graphene via photoexcitation of a heteroassembled material has started to attract attention for electronic and optoelectronic applications. Actually photoinduced carrier doping from the hexagonal boron nitride (h-BN) substrate greatly modulated the transport property of the top layer graphene, showing promising potential for this approach. However, for practical applications, the large scale production of this two-dimensional heterostructure is needed. Here, a superlattice film constructed from reduced graphene oxide (rGO) and photoactive titania nanosheets (Ti0.87O2(0.52-)) was employed as a channel to construct a field effect transistor (FET) device, and its UV light response on the electrical transport property was examined. The UV light illumination induced significant improvement of the electrical conductance by ∼7 times on the basis of simultaneous enhancements of the electron carrier concentration and its mobility in rGO. Furthermore, the polarity of the FET response changed from ambipolar to n-type unipolar. Such modulated properties persisted in vacuum even after the UV light was turned off. These interesting behaviors may be explained in terms of photomodulation effects from Ti0.87O2(0.52-) nanosheets. The photoexcited electrons in Ti0.87O2(0.52-) are injected into rGO to increase the electron carrier concentration as high as 7.6×10(13) cm(-2). On the other hand, the holes are likely trapped in the Ti0.87O2(0.52-) nanosheets. These photocarriers undergo reduction and oxidation of oxygen and water molecules adsorbed in the film, respectively, which act as carrier scattering centers, contributing to the enhancement of the carrier mobility. Since the film likely contains more water molecules than oxygen, upon extinction of UV light, a major portion of electrons (∼80% of the concentration at the UV off) survives in rGO, showing the highly enhanced conductance for days. This surpassing photomodulated FET response and

  4. Electron accumulation on metal nanoparticles in plasmon-enhanced organic solar cells.

    PubMed

    Salvador, Michael; MacLeod, Bradley A; Hess, Angela; Kulkarni, Abhishek P; Munechika, Keiko; Chen, Jennifer I L; Ginger, David S

    2012-11-27

    Plasmonic metal nanoparticles have been used to enhance the performance of thin-film devices such as organic photovoltaics based on polymer/fullerene blends. We show that silver nanoprisms accumulate long-lived negative charges when they are in contact with a photoexcited bulk heterojunction blend composed of poly(3-hexylthiophene)/phenyl-C61-butyric acid methyl ester (P3HT/PCBM). We report both the charge modulation and electroabsorption spectra of silver nanoprisms in solid-state devices and compare these spectra with the photoinduced absorption spectra of P3HT/PCBM blends containing silver nanoprisms. We assign a previously unidentified peak in the photoinduced absorption spectra to the presence of photoinduced electrons on the silver nanoprisms. We show that coating the nanoprisms with a 2.5 nm thick insulating layer can completely inhibit this charging. These results may inform methods for limiting metal-mediated losses in plasmonic solar cells. PMID:23062171

  5. Thermally and photoinduced polymerization of ultrathin sexithiophene films

    SciTech Connect

    Sander, Anke; Hammer, Rene; Duncker, Klaus; Förster, Stefan; Widdra, Wolf

    2014-09-14

    The thermally-induced polymerization of α-sexithiophene (6T) molecules on Ag(001) and Au(001) gives rise to long unbranched polymer chains or branched polymer networks depending on the annealing parameters. There, the onset temperature for polymerization depends on the strength of interaction with the underlying substrate. Similar polymerization processes are also induced by ultraviolet radiation with photon energies between 3.0 and 4.2 eV. Radical formation by an electronic excitation in the 6T molecule is proposed as the driving mechanism that necessitates the interplay with the metallic substrate.

  6. Photo-induced free radicals on a simulated Martian surface

    NASA Technical Reports Server (NTRS)

    Tseng, S.-S.; Chang, S.

    1974-01-01

    Results of an electron spin resonance study of free radicals in the ultraviolet irradiation of a simulated Martian surface suggest that the ultraviolet photolysis of CO or CO2, or a mixture of both, adsorbed on silica gel at minus 170 C involves the formation of OH radicals and possibly of H atoms as the primary process, followed by the formation of CO2H radicals. It is concluded that the photochemical synthesis of organic compounds could occur on Mars if the siliceous surface dust contains enough silanol groups and/or adsorbed H2O in the form of bound water.

  7. Novel photon detection based on electronically-induced stress in silicon

    SciTech Connect

    Datskos, P.G. |; Rajic, S.; Egert, C.M.; Datskou, I.

    1998-04-01

    The feasibility of microcantilever-based optical detection is demonstrated. Specifically, the authors report here on an evaluation of laboratory prototypes that are based on commercially available microcantilevers. In this work, optical transduction techniques were used to measure microcantilever response to photons and study the electronic stress in silicon microcantilevers, and their temporal and photometric response. The photo-generation of free charge carriers (electrons, holes) in a semiconductor gives rise to photo-induced (electronic) mechanical strain. The excess charge carriers responsible for the photo-induced stress, were produced via photon irradiation from a diode laser with wavelength {lambda} = 780 nm. The authors found that for silicon, the photo-induced stress results in a contraction of the crystal lattice due to the presence of excess electron-hole-pairs. In addition, the photo-induced stress is of opposite direction and about four times larger than the stress resulting from direct thermal excitation. When charge carriers are generated in a short time, a very rapid deflection of the microcantilever is observed (response time {approximately} {micro}s).

  8. A molecular shift register based on electron transfer

    NASA Technical Reports Server (NTRS)

    Hopfield, J. J.; Onuchic, Josenelson; Beratan, David N.

    1988-01-01

    An electronic shift-register memory at the molecular level is described. The memory elements are based on a chain of electron-transfer molecules and the information is shifted by photoinduced electron-transfer reactions. This device integrates designed electronic molecules onto a very large scale integrated (silicon microelectronic) substrate, providing an example of a 'molecular electronic device' that could actually be made. The design requirements for such a device and possible synthetic strategies are discussed. Devices along these lines should have lower energy usage and enhanced storage density.

  9. Photoinduced reduction of surface states in Fe:ZnO

    SciTech Connect

    Knut, R. Palmgren, P.; Karis, O.; Lagerqvist, U.; Pohl, A.; Pal, P.; Svedlindh, P.

    2015-05-28

    We report on the electronic structure of nano-crystalline Fe:ZnO, which has recently been found to be an efficient photocatalyst. Using resonant photoemission spectroscopy, we determine the binding energy of Fe 3d states corresponding to different valencies and coordination of the Fe atoms. The photo-activity of ZnO reduces Fe from 3+ to 2+ in the surface region of the nano-crystalline material due to the formation of oxygen vacancies. Electronic states corresponding to low-spin Fe{sup 2+} are observed and attributed to crystal field modification at the surface. These states are potentially important for the photocatalytic sensitivity to visible light due to their location deep in the ZnO bandgap. X-ray absorption and x-ray photoemission spectroscopy suggest that Fe is only homogeneously distributed for concentrations up to 3%. Increased concentrations does not result in a higher concentration of Fe ions in the surface region. This is limiting the photocatalytic functionality of ZnO, where the most efficient Fe doping concentration has been shown to be 1%-4%.

  10. Phototoxicity identification by solid phase extraction and photoinduced toxicity to Daphnia magna.

    PubMed

    Wernersson, A; Dave, G

    1997-04-01

    The photoinduced toxicity of several environmental pollutants (some Polycyclic Aromatic Hydrocarbons [PAHs]) is a potential threat to aquatic organisms. To identify the cause/s of photoinduced toxicity of a sample, it is not sufficient to simply analyze the content of some known phototoxic compounds; so far too few substances of environmental concern have ever been tested for their photoinduced toxicity. The PAHs as well as other known phototoxic compounds are hydrophobic and are expected to bind to C18 columns. The use of Solid Phase Extraction (SPE) is typically part of the procedure identifying any primary nonpolar toxicant/s, and adding phototoxicity tests to these manipulations would not substantially increase the workload. In this study, therefore, the difference in acute toxicity to Daphnia magna before and after 2 h of UV irradiation was determined for six PAHs. The ratio between EC50 values before and after UV irradiation ranged from 4.6 (for benzo-a-pyrene) to >244 (for 3, 4-benzofluoranthene), demonstrating that the UV enhances the PAH-toxicity. A further characterization technique using binding to Sep-Pak SPE C18 columns and recovery with methanol as an eluting agent was then tested in combination with UV irradiation. The mean recovered UV induced toxicity after binding and elution of the six PAHs was 119% according to the phototoxicity tests made. A linear relationship, between the log10 Kow values for the PAHs and the log10 for the concentration of methanol at peak elution was found. The combined use of C18 column separation and UV activation may, therefore, be used in toxicity identification evaluations (TIE) of organic phototoxic compounds. PMID:9096075

  11. Photoinduced charge-transfer materials for nonlinear optical applications

    DOEpatents

    McBranch, Duncan W.

    2006-10-24

    A method using polyelectrolyte self-assembly for preparing multi-layered organic molecular materials having individual layers which exhibit ultrafast electron and/or energy transfer in a controlled direction occurring over the entire structure. Using a high molecular weight, water-soluble, anionic form of poly-phenylene vinylene, self-assembled films can be formed which show high photoluminescence quantum efficiency (QE). The highest emission QE is achieved using poly(propylene-imine) (PPI) dendrimers as cationic binders. Self-quenching of the luminescence is observed as the solid polymer film thickness is increased and can be reversed by inserting additional spacer layers of transparent polyelectrolytes between each active conjugated layer, such that the QE grows with thickness. A red shift of the luminescence is also observed as additional PPV layers are added. This effect persists as self-quenching is eliminated. Charge transfer superlattices can be formed by additionally incorporating C.sub.60 acceptor layers.

  12. Development of ultrafast photochromic organometallics and photoinduced linkage isomerization of arene chromium carbonyl derivatives.

    PubMed

    To, Tung T; Heilweil, Edwin J; Duke, Charles B; Ruddick, Kristie R; Webster, Charles Edwin; Burkey, Theodore J

    2009-03-26

    We review recent studies of processes relevant to photoinduced linkage isomerization of organometallic systems with the goal of preparing organometallics with an efficient and ultrafast photochromic response. The organometallic system thus corresponds to two linkage isomers with different electronic environments that are responsible for different optical properties. Much of this work has focused on examining processes following irradiation of cyclopentadienyl manganese tricarbonyl derivatives (compounds 3-21) including solvent coordination, thermal relaxation, solvent displacement by tethered functional groups (chelation), dissociation of tethered functional groups, and linkage isomerization. A new platform is investigated for obtaining a photochromic response in new experiments with arene chromium dicarbonyl complexes. A photochromic response is observed for arene chromium dicarbonyl complexes with tethered pyridine and olefin functional groups based on light-driven linkage isomerization on the nanosecond time scale. Irradiation at 532 nm of 23 ([Cr{eta(6)-C(6)H(5)CH(2-Py-kappaN)CH(2)CH=CH(2)}(CO)(2)]) (Py = pyridine) results in the isomerization to 22 ([Cr{eta(6)-C(6)H(5)CH(2-Py)CH(2)-eta(2)-CH=CH(2)}(CO)(2)]), and 355 nm irradiation isomerizes 22 to 23. The ultrafast linkage isomerization has been investigated at room temperature in n-heptane solution on the picosecond to microsecond time scale with UV- or visible-pump and IR-probe transient absorption spectroscopy by comparing the dynamics with model compounds containing only a tethered pyridine. Irradiation of 24 ([Cr{eta(6)-C(6)H(5)(CH(2))(3)(2-Py)}(CO)(3)]) and 25 ([Cr{eta(6)-C(6)H(5)(CH(2))(2)(2-Py)}(CO)(3)]) at 289 nm induces CO loss to immediately yield a Cr-heptane solvent coordinated intermediate of the unsaturated Cr fragment, which then converts to the kappaN(1)-pyridine chelate within 200 and 100 ns, respectively. Irradiation of 26 ([Cr{eta(6)-C(6)H(5)CH(2)(2-Py)}(CO)(3)]) also induces CO loss to

  13. Photoinduced Charge Transfer from Titania to Surface Doping Site

    PubMed Central

    Inerbaev, Talgat; Hoefelmeyer, James D.; Kilin, Dmitri S.

    2013-01-01

    We evaluate a theoretical model in which Ru is substituting for Ti at the (100) surface of anatase TiO2. Charge transfer from the photo-excited TiO2 substrate to the catalytic site triggers the photo-catalytic event (such as water oxidation or reduction half-reaction). We perform ab-initio computational modeling of the charge transfer dynamics on the interface of TiO2 nanorod and catalytic site. A slab of TiO2 represents a fragment of TiO2 nanorod in the anatase phase. Titanium to ruthenium replacement is performed in a way to match the symmetry of TiO2 substrate. One molecular layer of adsorbed water is taken into consideration to mimic the experimental conditions. It is found that these adsorbed water molecules saturate dangling surface bonds and drastically affect the electronic properties of systems investigated. The modeling is performed by reduced density matrix method in the basis of Kohn-Sham orbitals. A nano-catalyst modeled through replacement defect contributes energy levels near the bottom of the conduction band of TiO2 nano-structure. An exciton in the nano-rod is dissipating due to interaction with lattice vibrations, treated through non-adiabatic coupling. The electron relaxes to conduction band edge and then to the Ru cite with faster rate than hole relaxes to the Ru cite. These results are of the importance for an optimal design of nano-materials for photo-catalytic water splitting and solar energy harvesting. PMID:23795229

  14. Photoinduced Charge Transfer from Titania to Surface Doping Site.

    PubMed

    Inerbaev, Talgat; Hoefelmeyer, James D; Kilin, Dmitri S

    2013-05-16

    We evaluate a theoretical model in which Ru is substituting for Ti at the (100) surface of anatase TiO2. Charge transfer from the photo-excited TiO2 substrate to the catalytic site triggers the photo-catalytic event (such as water oxidation or reduction half-reaction). We perform ab-initio computational modeling of the charge transfer dynamics on the interface of TiO2 nanorod and catalytic site. A slab of TiO2 represents a fragment of TiO2 nanorod in the anatase phase. Titanium to ruthenium replacement is performed in a way to match the symmetry of TiO2 substrate. One molecular layer of adsorbed water is taken into consideration to mimic the experimental conditions. It is found that these adsorbed water molecules saturate dangling surface bonds and drastically affect the electronic properties of systems investigated. The modeling is performed by reduced density matrix method in the basis of Kohn-Sham orbitals. A nano-catalyst modeled through replacement defect contributes energy levels near the bottom of the conduction band of TiO2 nano-structure. An exciton in the nano-rod is dissipating due to interaction with lattice vibrations, treated through non-adiabatic coupling. The electron relaxes to conduction band edge and then to the Ru cite with faster rate than hole relaxes to the Ru cite. These results are of the importance for an optimal design of nano-materials for photo-catalytic water splitting and solar energy harvesting. PMID:23795229

  15. Collapse and revival of photoinduced oscillations in the optical reflectivity of bismuth

    NASA Astrophysics Data System (ADS)

    Semenov, A. L.

    2016-02-01

    The average optical reflectivity of bismuth as a function of time t after irradiation by a short laser pulse has been calculated. The amplitude A of photoinduced oscillations in the average optical reflectivity is shown to have extrema under certain conditions. The time τ j ( j is a natural number) at which the amplitude A reaches the jth extremum has been calculated. The calculated dependences of the times τ1 and τ2 at which, respectively, the first and second extrema (the first minimum and the first maximum) of the amplitude A are reached on the maximum laser pulse energy density Q are consistent with the experimental data from [8].

  16. Deuterium enrichment by selective photoinduced dissociation of a multihalogenated organic compound

    DOEpatents

    Marling, John B.; Herman, Irving P.

    1981-01-01

    A method for deuterium enrichment by photoinduced dissociation which uses as the deuterium source a multihalogenated organic compound selected from the group consisting of a dihalomethane, a trihalomethane, a 1,2-dihaloethene, a trihaloethene, a tetrahaloethane and a pentahaloethane. The multihalogenated organic compound is subjected to intense infrared radiation at a preselected wavelength to selectively excite and thereby induce dissociation of substantially only those molecules containing deuterium to provide a deuterium enriched dissociation product. The deuterium enriched product may be combusted with oxygen to provide deuterium enriched water. The deuterium depleted undissociated molecules may be redeuterated by treatment with a deuterium source such as water.

  17. Photo-induced fractionation of water isotopomers in the Martian atmosphere

    NASA Astrophysics Data System (ADS)

    Cheng, Bing-Ming; Chew, Eh Piew; Liu, Chin-Ping; Bahou, Mohammed; Lee, Yuan-Pern; Yung, Yuk L.; Gerstell, M. F.

    The history and size of the water reservoirs on early Mars can be constrained using isotopic ratios of deuterium to hydrogen. We present new laboratory measurements of the ultraviolet cross-sections of H2O and its isotopomers, and modeling calculations in support of a photo-induced fractionation effect (PHIFE), that reconciles a discrepancy between past theoretical modeling and recent observations. This supports the hypothesis that Mars had an early warm atmosphere and has lost at least a 50-m global layer of water. Likely applications of PHIFE to other planetary atmospheres are sketched.

  18. Photo-induced fractionation of water isotopomers in the Martian atmosphere.

    PubMed

    Cheng, B M; Chew, E P; Liu, C P; Bahou, M; Lee, Y P; Yung, Y L; Gerstell, M F

    1999-12-15

    The history and size of the water reservoirs on early Mars can be constrained using isotopic ratios of deuterium to hydrogen. We present new laboratory measurements of the ultraviolet cross-sections of H2O and its isotopomers, and modeling calculations in support of a photo-induced fractionation effect (PHIFE), that reconciles a discrepancy between past theoretical modeling and recent observations. This supports the hypothesis that Mars had an early warm atmosphere and has lost at least a 50-m global layer of water. Likely applications of PHIFE to other planetary atmospheres are sketched. PMID:11543402

  19. Nonlinear photoinduced anisotropy and modifiable optical image display in a bacteriorhodopsin/polymer composite film

    NASA Astrophysics Data System (ADS)

    Wei, Lai; Luo, Jia; Zhu, Jiang; Lu, Ming; Zhao, You-yuan; Ma, De-wang; Ding, Jian-dong

    2007-04-01

    The nonlinear photoinduced anisotropy with large birefringence in a bacteriorhodopsin/polymer composite (bR/PC) film was observed. The contrast ratio, a ratio of the maximum to the minimum intensity of transmitted probe light through the bR/PC film within the linear gray scale range could reach ˜350:1. An all-optical image display in different colors was performed. The intensity of the transmitted signal could be modulated by adjusting the multibeam polarization states and intensities. Therefore, the positive image, negative image, and image erasure in display were demonstrated.

  20. Spatial light modulation based on photoinduced change in the complex refractive index of bacteriorhodopsin

    NASA Astrophysics Data System (ADS)

    Takei, Hiroyuki; Shimizu, Norio

    1996-04-01

    Bacteriorhodopsin exhibits photoinduced changes in both absorption and refractive index at 633 nm. To explore the possibility of exploiting this property in constructing a photoaddressed spatial light modulator, we investigated the transmission property of a Fabry-Perot interferometer containing a bacteriorhodopsin thin film. Film was formed that had a phase shift of pi /4 and sufficient interference fringe contrast for spatial light modulation. This establishes the possibility of constructing a spatial light modulator that features nonlinear input-output characteristics and can operate at moderate light intensities of the order of tens of milliwatts per centimeter square. spatial light modulation, complex refractive index.

  1. Photoinduced phase transition in VO2 nanocrystals: ultrafast control of surface-plasmon resonance

    SciTech Connect

    Rini, Matteo; Cavalleri, Andrea; Schoenlein, Robert

    2005-01-01

    We study the ultrafast insulator-to-metal transition in nanoparticles of VO2 , obtained by ion implantation and self-assembly in silica. The nonmagnetic, strongly correlated compound VO2 undergoes a reversible phase transition, which can be photoinduced on an ultrafast time scale. In the nanoparticles, prompt formation of the metallic state results in the appearance of surface-plasmon resonance. We achieve large, ultrafast enhancement of optical absorption in the near-infrared spectral region that encompasses the wavelength range for optical-fiber communications. One can further tailor the response of the nanoparticles by controlling their shape.

  2. Optimal ultrafast laser pulse-shaping to direct photo-induced phase transitions

    NASA Astrophysics Data System (ADS)

    Hwang, Bin; Portman, Jenni; Duxbury, Phillip

    Photo-induced phase transitions (PIPT) in quantum and/or complex materials are the epitome of challenging non-equilibrium many-body phenomena, that also have a wide range of potential applications. We present a computational approach to finding optimal ultrafast laser pulse shapes to control the outcome of pump-probe PIPT experiments. The Krotov approach for optimal control is combined with a Keldysh Green's function calculation to describe experimental outcomes such as photoemission, transient single particle density of states and optical responses. Results for a simple model charge density wave system will be presented. main author.

  3. Deuterium enrichment by selective photo-induced dissociation of an organic carbonyl compound

    DOEpatents

    Marling, John B.

    1981-01-01

    A method for producing a deuterium enriched material by photoinduced dissociation which uses as the working material a gas phase photolytically dissociable organic carbonyl compound containing at least one hydrogen atom bonded to an atom which is adjacent to a carbonyl group and consisting of molecules wherein said hydrogen atom is present as deuterium and molecules wherein said hydrogen atom is present as another isotope of hydrogen. The organic carbonyl compound is subjected to intense infrared radiation at a preselected wavelength to selectively excite and thereby induce dissociation of the deuterium containing species to yield a deuterium enriched stable molecular product. Undissociated carbonyl compound, depleted in deuterium, is preferably redeuterated for reuse.

  4. [Photoinduced charge separation in solid state and molecular systems]. Final report

    SciTech Connect

    Not Available

    1993-10-01

    A critical theme has been to understand the role of intrinsic cyanometalate overlayers in modulating interfacial photoinduced charge transfer processes occurring at the Cd chalconide/aqueous ferri-ferrocyanide interface. Structural and charge transfer studies of [CdFe(CN){sub 6}]{sup 2-/1-} overlayers have been undertaken. It is reiterated that the focus of attention on the Cd ferrocyanide overlayer as a critical element in II-VI semiconductor based photoelectrochemical cells, is correct. A new project on metallization of solid supports, using photodeposition of Pt, has been initiated. A project has also been started in the area of visible light, molecular, charge transfer photochemistry.

  5. Time-resolved photoinduced thermoelectric and transport currents in GaAs nanowires.

    PubMed

    Prechtel, Leonhard; Padilla, Milan; Erhard, Nadine; Karl, Helmut; Abstreiter, Gerhard; Fontcuberta I Morral, Anna; Holleitner, Alexander W

    2012-05-01

    In order to clarify the temporal interplay of the different photocurrent mechanisms occurring in single GaAs nanowire based circuits, we introduce an on-chip photocurrent pump-probe spectroscopy with a picosecond time resolution. We identify photoinduced thermoelectric, displacement, and carrier lifetime limited currents as well as the transport of photogenerated holes to the electrodes. Moreover, we show that the time-resolved photocurrent spectroscopy can be used to investigate the drift velocity of photogenerated carriers in semiconducting nanowires. Hereby, our results are relevant for nanowire-based optoelectronic and photovoltaic applications. PMID:22494021

  6. Decay of photoinduced oscillations of the optical reflection coefficient of bismuth

    SciTech Connect

    Semenov, A. L.

    2013-07-15

    A model describing the decay of photoinduced oscillations of the optical reflection coefficient R of bismuth is constructed, taking the crystal lattice anharmonicity into account. The decay time of oscillations of R is calculated as a function of the energy density of a laser pulse. The results of calculations explain the experimental data on the anomalously strong decay of oscillations of the optical reflection coefficient of bismuth (the decay time decreases by more than an order of magnitude with an increase in the laser pulse energy density from 0 to 4 mJ/cm{sup 2})

  7. Large photoinduced refractive index changes of a polymer containing photochromic norbornadiene groups

    SciTech Connect

    Kinoshita, K.; Horie, K.; Morino, S.; Nishikubo, T.

    1997-06-01

    We prepared a polymer containing pendant norbornadiene (NBD) moieties, P(MMA{sub 0.43}-co-GMA{sub 0.57}-PNCA), and measured absorbance and refractive index spectra before and after photoisomerization of norbornadiene moieties. Large photoinduced refractive index changes of {approximately}0.01 were obtained at 632.8 nm, the region far from the absorption band. A quantum yield of 0.50 was obtained for the photoisomerization of NBD moieties in this polymer. These values are sufficient to make efficient channel waveguides by photoisomerization. {copyright} {ital 1997 American Institute of Physics.}

  8. Control of the Ultrafast Photoinduced Magnetization across the Morin Transition in DyFeO_{3}.

    PubMed

    Afanasiev, D; Ivanov, B A; Kirilyuk, A; Rasing, Th; Pisarev, R V; Kimel, A V

    2016-03-01

    Excitation of the collinear compensated antiferromagnet DyFeO_{3} with a single 60 fs laser pulse triggers a phase transition across the Morin point into a noncollinear spin state with a net magnetization. Time-resolved imaging of the magnetization dynamics of this process reveals that the pulse first excites the spin oscillations upon damping of which the noncollinear spin state emerges. The sign of the photoinduced magnetization is defined by the relative orientation of the pump polarization and the direction of the antiferromagnetic vector in the initial collinear spin state. PMID:26991201

  9. Graphene/CdTe heterostructure solar cell and its enhancement with photo-induced doping

    SciTech Connect

    Lin, Shisheng Chen, Hongsheng; Li, Xiaoqiang; Zhang, Shengjiao; Wang, Peng; Xu, Zhijuan; Zhong, Huikai; Wu, Zhiqian

    2015-11-09

    We report a type of solar cell based on graphene/CdTe Schottky heterostructure, which can be improved by surface engineering as graphene is atomic thin. By coating a layer of ultrathin CdSe quantum dots onto graphene/CdTe heterostructure, the power conversion efficiency is increased from 2.08% to 3.10%. Photo-induced doping is mainly accounted for this enhancement, as evidenced by field effect transport, Raman, photoluminescence, and quantum efficiency measurements. This work demonstrates a feasible way of improving the performance of graphene/semiconductor heterostructure solar cells by combining one dimensional with two dimensional materials.

  10. Mode tuning of photonic crystal nanocavities by photoinduced non-thermal oxidation

    NASA Astrophysics Data System (ADS)

    Intonti, Francesca; Caselli, Niccolò; Vignolini, Silvia; Riboli, Francesco; Kumar, Santosh; Rastelli, Armando; Schmidt, Oliver G.; Francardi, Marco; Gerardino, Annamaria; Balet, Laurent; Li, Lianhe H.; Fiore, Andrea; Gurioli, Massimo

    2012-01-01

    A method to achieve photoinduced tuning of PhC nanocavity modes is discussed and implemented. It is based on light induced oxidation in air atmosphere with very low thermal budget which produces a local reduction of the GaAs membrane effective thickness and a large blueshift of the nanocavity modes. It is also shown that green light is much more efficient in inducing the micro-oxidation with respect to near infrared light. The observed behaviour is attributed to oxide growth promoted by photoenhanced reactivity.

  11. Photoinduced magnetization enhancement in two-dimensional weakly anisotropic Heisenberg magnets

    NASA Astrophysics Data System (ADS)

    Caretta, Antonio; Donker, Michiel C.; Polyakov, Alexey O.; Palstra, Thomas T. M.; van Loosdrecht, Paul H. M.

    2015-01-01

    By comparing the photoinduced magnetization dynamics in simple layered systems we show how light-induced modifications of the magnetic anisotropy directly enhance the magnetization. It is observed that the spin precession in (CH3NH3) 2CuCl4 , initiated by a light pulse, increases in amplitude at the critical temperature TC. The phenomenon is related to the dependence of the critical temperature on the axial magnetic anisotropy. The present results underline the possibility and the importance of the optical modifications of the anisotropy, opening different paths toward the control of the magnetization state for ultrafast memories.

  12. Control of the Ultrafast Photoinduced Magnetization across the Morin Transition in DyFeO3

    NASA Astrophysics Data System (ADS)

    Afanasiev, D.; Ivanov, B. A.; Kirilyuk, A.; Rasing, Th.; Pisarev, R. V.; Kimel, A. V.

    2016-03-01

    Excitation of the collinear compensated antiferromagnet DyFeO3 with a single 60 fs laser pulse triggers a phase transition across the Morin point into a noncollinear spin state with a net magnetization. Time-resolved imaging of the magnetization dynamics of this process reveals that the pulse first excites the spin oscillations upon damping of which the noncollinear spin state emerges. The sign of the photoinduced magnetization is defined by the relative orientation of the pump polarization and the direction of the antiferromagnetic vector in the initial collinear spin state.

  13. Control of photo-induced drug release by the use of conformational change of DNA.

    PubMed

    Tanabe, Kazuhito; Inasaki, Takeshi; Okamoto, Akimitsu; Nishimoto, Sei-ichi; Saito, Isao

    2002-01-01

    Photo-induced drug release system which was controlled by triplet quenching using the molecular beacon strategy of photoreactive oligodeoxynucleotides (P-ODN) was developed. The strand ends of P-ODN were modified with a phenacyl ester of biotin and naphthalene as photoreactive group and triplet quencher, respectively. Photoirradiation to P-ODN in the presence of complementary DNA caused an efficient release of biotin. In contrast, the biotin release was suppressed in the absence of complementary DNA by the intramolecular triplet quenching in the stem-and-loop structure of P-ODN. PMID:12903158

  14. Photoinduced GRIN lens formation in chalcogenide Ge-As-S thin films

    NASA Astrophysics Data System (ADS)

    Palanjyan, K.; Vallée, R.; Galstian, T.

    2014-09-01

    We describe the photo induced formation of gradient index (GRIN) lenses in thin films of chalcogenide glass (ChG) of Ge25As30S45 composition. We examine the changes of thickness of these samples by DekTak profilometry, as well as the optical performance and wave front distortions of the obtained lenses by using a Shack Hartmann sensor. The GRIN formation is related to the photo induced shift of the band gap towards shorter wavelengths (so-called photo-bleaching effect). The corresponding photo-induced birefringence of this material is in the origin of anisotropic GRIN lenses formed [1].

  15. Spontaneous photoinduced patterning of azo-dye polymer films: the facts

    SciTech Connect

    Hubert, Christophe

    2007-08-15

    We describe the spontaneous photoinduced patterning of azo-dye polymer films. We have observed that the illumination of an azo-dye polymer film by a uniform single laser beam with normal incidence leads to a self-structurization process that results in the formation of well-ordered submicrometer-sized structures whose organization depends on the light polarization direction. A modulation depth as high as 100 nm can be achieved. The influence of several experimental parameters on the structure formation is studied. Results are discussed and confronted to different models and phenomena already investigated in the literature. A physical origin to this peculiar photopatterning process is proposed.

  16. Dielectric characteristic of photoinduced isomerization in azo-dye doped polymeric matrices

    SciTech Connect

    Luo Duanbin; Deng Li

    2006-05-01

    The dielectric permittivities and losses of poly(methyl methacrylate) doped with different concentrations of azo dye are investigated under the irradiation of 532 nm light for the first time. The dielectric permittivities increase with the concentration of chromophores increasing, and the dielectric relaxation is mainly influenced by the doped azo-dye chromophores. Given the dye concentration, the dielectric permittivities depend on the pump power of 532 nm light. With the increase of pumping light power, the low frequency dielectric losses increase while the high frequency dielectric losses decrease. The results are explained based on the photoinduced isomerization of chromophores and the interaction between the chromophores and polymer matrices.

  17. Graphene/CdTe heterostructure solar cell and its enhancement with photo-induced doping

    NASA Astrophysics Data System (ADS)

    Lin, Shisheng; Li, Xiaoqiang; Zhang, Shengjiao; Wang, Peng; Xu, Zhijuan; Zhong, Huikai; Wu, Zhiqian; Chen, Hongsheng

    2015-11-01

    We report a type of solar cell based on graphene/CdTe Schottky heterostructure, which can be improved by surface engineering as graphene is atomic thin. By coating a layer of ultrathin CdSe quantum dots onto graphene/CdTe heterostructure, the power conversion efficiency is increased from 2.08% to 3.10%. Photo-induced doping is mainly accounted for this enhancement, as evidenced by field effect transport, Raman, photoluminescence, and quantum efficiency measurements. This work demonstrates a feasible way of improving the performance of graphene/semiconductor heterostructure solar cells by combining one dimensional with two dimensional materials.

  18. Raman and infrared spectroscopy of organic electronic devices

    NASA Astrophysics Data System (ADS)

    Furukawa, Y.

    2010-09-01

    We present Raman and infrared studies on the structures of organic semiconductor thin films used for electronic devices. The Raman spectra of crystalline and amorphous states of an organic semiconductor, N,N'-di-1-naphthaleyl-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (NPD), were measured. These states give rise to slightly different peak positions and widths of each Raman band. Raman images were observed for polycrystalline pentacene films evaporated on a silicon substrate. The structural defects were found in the images of the intensity ratio I1596/I1533, which reflects the orientation of molecules i.e., crystalline domains. Photoinduced infrared absorption from the composite of regioregular poly(3-dodecylthiphene) and C60 was measured by the difference FT-IR method. The observed absorption is attributable to photogenerated carriers. The action spectra of photoinduced infrared absorption are explained by electron transfer from photogenerated excited states on a polymer chain to C60.

  19. Simultaneous Photoinduced ATRP and CuAAC Reactions for the Synthesis of Block Copolymers.

    PubMed

    Murtezi, Eljesa; Yagci, Yusuf

    2014-09-01

    Atom transfer radical polymerization (ATRP) and copper-catalyzed azide-alkyne cycloaddition (CuAAC) reactions, both utilizing copper(I) (Cu(I)) complexes, make a tremendous progress in synthetic polymer chemistry. Independently or in combination with other polymerization processes, they give access to the synthesis of polymers with well-defined structures, desired molecular architectures, and a wide variety of functionalities. Here, a novel in situ photoinduced formation of block copolymers is described by simultaneous ATRP and CuAAC processes. This approach relies on the direct reduction of initially charged copper(II) complexes to Cu(I) complexes to trigger both ATRP and CuAAC reactions coinciding under UV light at ambient temperature in one pot. Its synthetic utility is demonstrated on a model block copolymerization process by photoinduced ATRP of methyl methacrylate (MMA) using an initiator possessing acetylene functionality and concomitant click reaction between thus formed α-acetylene-poly(methyl methacrylate) (Ac-PMMA) and independently prepared azide functional polystyrene (PS-N3 ). Successful formation of PS-b-PMMA block copolymer is confirmed by FT-IR and (1) H NMR spectral analysis and gel permeation chromatography (GPC) measurements. PMID:25200624

  20. Reaction Mechanisms of a Photo-Induced [1,3] Sigmatropic Rearrangement via a Nonadiabatic Pathway

    NASA Astrophysics Data System (ADS)

    Wu, Weiqiang; Liu, Kunhui; Yang, Chunfan; Zhao, Hongmei; Wang, Huan; Yu, Youqing; Su, Hongmei

    2009-11-01

    Time-resolved Fourier transform infrared absorption spectroscopy measurements and B3LYP/cc-pVDZ calculations have been conducted to characterize the reaction dynamics of a remarkable photoinduced 1,3-Cl sigmatropic rearrangement reaction upon 193 or 266 nm excitation of the model systems acryloyl chloride (CH2CHCOCl) and crotonyl chloride (CH3CHCHCOCl) in solution. The reaction is elucidated to follow nonadiabatic pathways via two rapid ISC processes, S1 → T1 and T1 → S0, and the S1/T1 and T1/S0 surface intersections are found to play significant roles leading to the nonadiabatic pathways. The S1 → T1 → S0 reaction pathway involving the key participation of the T1 state is the most favorable, corresponding to the lowest energy path. It is also suggested that the photoinduced 1,3-Cl migration reaction of RCHCHCOCl (R = H, CH3) proceeds through a stepwise mechanism involving radical dissociation-recombination, which is quite different from the generally assumed one-step concerted process for pericyclic reactions.