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Sample records for excited-state electron transfer

  1. Construction of Vibronic Diabatic Hamiltonian for Excited-State Electron and Energy Transfer Processes.

    Science.gov (United States)

    Xie, Yu; Jiang, Shengshi; Zheng, Jie; Lan, Zhenggang

    2017-12-21

    Photoinduced excited-state electron and energy transfer processes are crucial in biological photoharvesting systems and organic photovoltaic devices. We discuss the construction of a diabatic vibronic Hamiltonian for the proper treatment of these processes involving the projection approach acting on both electronic wave functions and vibrational modes. In the electronic part, the wave function projection approach is used to construct the diabatic Hamiltonian in which both local excited states and charge-transfer states are included on the same footing. For the vibrational degrees of freedom, the vibronic couplings in the diabatic Hamiltonian are obtained in the basis of the pseudonormal modes localized on each monomer site by applying delocalized-to-localized mode projection. This systematic approach allows us to construct the vibronic diabatic Hamiltonian in molecular aggregates.

  2. Electron transfer from electronic excited states to sub-vacuum electron traps in amorphous ice

    International Nuclear Information System (INIS)

    Vichnevetski, E.; Bass, A.D.; Sanche, L.

    2000-01-01

    We investigate the electron stimulated yield of electronically excited argon atoms (Ar * ) from monolayer quantities of Ar deposited onto thin films of amorphous ice. Two peaks of narrow width ( - electron-exciton complex into exciton states, by the transfer of an electron into a sub-vacuum electron state within the ice film. However, the 10.7 eV feature is shifted to lower energy since electron attachment to Ar occurs within small pores of amorphous ice. In this case, the excess electron is transferred into an electron trap below the conduction band of the ice layer

  3. Photo- and radiation chemical studies of intermediates involved in excited-state electron-transfer reactions

    International Nuclear Information System (INIS)

    Hoffman, M.Z.

    1985-01-01

    Excited-state inter- and intramolecular electron-transfer reactions lie at the heart of the most photochemical solar energy conversion schemes. The authors research, which has utilized the techniques of continuous and pulsed photolysis and radiolysis, has focused on three general aspects of these reactions involving transition metal coordination complexes and electron donor-acceptor complexes: i) the effect of solution medium on the properties and quenching of the excited states; ii) the control of the quantum yields of formation of redox products; iii) the mechanism by which reduced species interact with water to yield H 2 homogeneously and heterogeneously. EDTA is among the most popular sacrificial electron donors used in model systems. Its role is to scavenge the oxidized form of the photosensitizer in order to prevent its rapid reaction with the reduced form of the electron relay species that results from the electron-transfer quenching of the excited photosensitizer. In systems involving MV 2+ , the radicals resulting from the oxidation of EDTA can eventually lead to the generation of a second equivalent of MV + ; the reducing agent is believed to be a radical localized on the carbon atom alpha to the carboxylate group. The reaction of radiolytically-generated OH/H with EDTA produces this radical directly via H-abstraction or indirectly via deprotonation of the carbon atom adjacent to the nitrogen radical site in the oxidized amine moiety; it reduces MV 2+ with rate constants of 2.8 x 10 9 , 7.6 x 10 9 , and 8.5 x 10 6 M -1 s -1 at pH 12.5, 8.3, and 4.7, respectively. Degradative decarboxylation of EDTA-radicals and their back electron-transfer reactions are enhanced in acidic solution causing the yield of MV + to be severely diminished

  4. Bimolecular Excited-State Electron Transfer with Surprisingly Long-Lived Radical Ions

    KAUST Repository

    Alsam, Amani Abdu

    2015-09-02

    We explored the excited-state interactions of bimolecular, non-covalent systems consisting of cationic poly[(9,9-di(3,3’-N,N’-trimethyl-ammonium) propyl fluorenyl-2,7-diyl)-alt-co-(9,9-dioctyl-fluorenyl-2,7-diyl)] diiodide salt (PFN) and 1,4-dicyanobenzene (DCB) using steady-state and time-resolved techniques, including femto- and nanosecond transient absorption and femtosecond infrared spectroscopies with broadband capabilities. The experimental results demonstrated that photo-induced electron transfer from PFN to DCB occurs on the picosecond time scale, leading to the formation of PFN+• and DCB-• radical ions. Interestingly, real-time observations of the vibrational marker modes on the acceptor side provided direct evidence and insight into the electron transfer process indirectly inferred from UV-Vis experiments. The band narrowing on the picosecond time scale observed on the antisymmetric C-N stretching vibration of the DCB radical anion provides clear experimental evidence that a substantial part of the excess energy is channeled into vibrational modes of the electron transfer product and that the geminate ion pairs dissociate. More importantly, our nanosecond time-resolved data indicate that the charge-separated state is very long lived ( 30 ns) due to the dissociation of the contact radical ion pair into free ions. Finally, the fast electron transfer and slow charge recombination anticipate the current donor−acceptor system with potential applications in organic solar cells.

  5. Bimolecular Excited-State Electron Transfer with Surprisingly Long-Lived Radical Ions

    KAUST Repository

    Alsam, Amani Abdu; Aly, Shawkat Mohammede; Usman, Anwar; Parida, Manas R.; Del Gobbo, Silvano; Alarousu, Erkki; Mohammed, Omar F.

    2015-01-01

    We explored the excited-state interactions of bimolecular, non-covalent systems consisting of cationic poly[(9,9-di(3,3’-N,N’-trimethyl-ammonium) propyl fluorenyl-2,7-diyl)-alt-co-(9,9-dioctyl-fluorenyl-2,7-diyl)] diiodide salt (PFN) and 1,4-dicyanobenzene (DCB) using steady-state and time-resolved techniques, including femto- and nanosecond transient absorption and femtosecond infrared spectroscopies with broadband capabilities. The experimental results demonstrated that photo-induced electron transfer from PFN to DCB occurs on the picosecond time scale, leading to the formation of PFN+• and DCB-• radical ions. Interestingly, real-time observations of the vibrational marker modes on the acceptor side provided direct evidence and insight into the electron transfer process indirectly inferred from UV-Vis experiments. The band narrowing on the picosecond time scale observed on the antisymmetric C-N stretching vibration of the DCB radical anion provides clear experimental evidence that a substantial part of the excess energy is channeled into vibrational modes of the electron transfer product and that the geminate ion pairs dissociate. More importantly, our nanosecond time-resolved data indicate that the charge-separated state is very long lived ( 30 ns) due to the dissociation of the contact radical ion pair into free ions. Finally, the fast electron transfer and slow charge recombination anticipate the current donor−acceptor system with potential applications in organic solar cells.

  6. Coherence, energy and charge transfers in de-excitation pathways of electronic excited state of biomolecules in photosynthesis

    DEFF Research Database (Denmark)

    Bohr, Henrik; Malik, F. Bary

    2013-01-01

    The observed multiple de-excitation pathways of photo-absorbed electronic excited state in the peridinin–chlorophyll complex, involving both energy and charge transfers among its constituents, are analyzed using the bio-Auger (B-A) theory. It is also shown that the usually used F¨orster–Dexter...

  7. Ab initio study of the excited-state coupled electron-proton-transfer process in the 2-aminopyridine dimer

    International Nuclear Information System (INIS)

    Sobolewski, Andrzej L.; Domcke, Wolfgang

    2003-01-01

    The low-lying 1 ππ* excited states of the 2-aminopyridine dimer have been investigated with multi-reference ab initio methods (CASSCF and MRMP2). The 2-aminopyridine dimer can be considered as a mimetic model of Watson-Crick DNA base pairs. The reaction path and the energy profile for single proton transfer in the lowest 1 ππ* inter-monomer charge-transfer state have been obtained. A weakly avoided crossing of the 1 ππ* surface with the electronic ground-state surface has been found near the single-proton-transfer minimum of the 1 ππ* surface. From the splitting of the adiabatic surfaces at the avoided crossing, an internal-conversion lifetime of the excited state of <100 ps has been estimated. The potential relevance of these results for the rationalization of radiation-induced mutations and the photostability of the genetic code is briefly discussed

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

    Science.gov (United States)

    Amerikheirabadi, Fatemeh

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

  9. Dynamics of electron solvation in methanol: Excited state relaxation and generation by charge-transfer-to-solvent

    International Nuclear Information System (INIS)

    Elkins, Madeline H.; Williams, Holly L.; Neumark, Daniel M.

    2015-01-01

    The charge-transfer-to-solvent dynamics (CTTS) and excited state relaxation mechanism of the solvated electron in methanol are studied by time-resolved photoelectron spectroscopy on a liquid methanol microjet by means of two-pulse and three-pulse experiments. In the two-pulse experiment, CTTS excitation is followed by a probe photoejection pulse. The resulting time-evolving photoelectron spectrum reveals multiple time scales characteristic of relaxation and geminate recombination of the initially generated electron which are consistent with prior results from transient absorption. In the three-pulse experiment, the relaxation dynamics of the solvated electron following electronic excitation are measured. The internal conversion lifetime of the excited electron is found to be 130 ± 40 fs, in agreement with extrapolated results from clusters and the non-adiabatic relaxation mechanism

  10. Dynamics of electron solvation in methanol: Excited state relaxation and generation by charge-transfer-to-solvent

    Science.gov (United States)

    Elkins, Madeline H.; Williams, Holly L.; Neumark, Daniel M.

    2015-06-01

    The charge-transfer-to-solvent dynamics (CTTS) and excited state relaxation mechanism of the solvated electron in methanol are studied by time-resolved photoelectron spectroscopy on a liquid methanol microjet by means of two-pulse and three-pulse experiments. In the two-pulse experiment, CTTS excitation is followed by a probe photoejection pulse. The resulting time-evolving photoelectron spectrum reveals multiple time scales characteristic of relaxation and geminate recombination of the initially generated electron which are consistent with prior results from transient absorption. In the three-pulse experiment, the relaxation dynamics of the solvated electron following electronic excitation are measured. The internal conversion lifetime of the excited electron is found to be 130 ± 40 fs, in agreement with extrapolated results from clusters and the non-adiabatic relaxation mechanism.

  11. Dynamics of electron solvation in methanol: Excited state relaxation and generation by charge-transfer-to-solvent

    Energy Technology Data Exchange (ETDEWEB)

    Elkins, Madeline H.; Williams, Holly L. [Department of Chemistry, University of California, Berkeley, California 94720 (United States); Neumark, Daniel M. [Department of Chemistry, University of California, Berkeley, California 94720 (United States); Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

    2015-06-21

    The charge-transfer-to-solvent dynamics (CTTS) and excited state relaxation mechanism of the solvated electron in methanol are studied by time-resolved photoelectron spectroscopy on a liquid methanol microjet by means of two-pulse and three-pulse experiments. In the two-pulse experiment, CTTS excitation is followed by a probe photoejection pulse. The resulting time-evolving photoelectron spectrum reveals multiple time scales characteristic of relaxation and geminate recombination of the initially generated electron which are consistent with prior results from transient absorption. In the three-pulse experiment, the relaxation dynamics of the solvated electron following electronic excitation are measured. The internal conversion lifetime of the excited electron is found to be 130 ± 40 fs, in agreement with extrapolated results from clusters and the non-adiabatic relaxation mechanism.

  12. Excited state Intramolecular Proton Transfer in Anthralin

    DEFF Research Database (Denmark)

    Møller, Søren; Andersen, Kristine B.; Spanget-Larsen, Jens

    1998-01-01

    Quantum chemical calculations performed on anthralin (1,8-dihydroxy-9(10H)-anthracenone) predict the possibility of an excited-state intramolecular proton transfer process. Fluorescence excitation and emission spectra of the compound dissolved in n-hexane at ambient temperature results in an unus......Quantum chemical calculations performed on anthralin (1,8-dihydroxy-9(10H)-anthracenone) predict the possibility of an excited-state intramolecular proton transfer process. Fluorescence excitation and emission spectra of the compound dissolved in n-hexane at ambient temperature results......, associated with an excited-state intramolecular proton transfer process....

  13. Inelastic scattering of high transfer moment electrons to the first excited state (Jsup(π)=3-) of 208Pb

    International Nuclear Information System (INIS)

    Goutte, Dominique.

    1979-10-01

    A determination was made of an angular distribution of the inelastic scattering cross-sections of electrons by the first excited state (Jsup(π)=3 - , E*=2.615 MeV) of 208 Pb. The statistical accuracy of previous data was improved between 2 and 2.7 fm -1 and the area of transfer of moment was extended up to qsub(max)=3.4 fm -1 . Cross-sections up to 10 -37 cm 2 /sr were determined whereas the limit reached before was 7x10 -35 cm 2 /sr. In order to determine the transition charge density, it was put into parametric form by a Fourier-Bessel development using 12 coefficients and an 11 fm cut-off radius. The model error inherent in this method is reduced to an insignificant contribution by the sufficiently high transfer of moment. The experimental transition charge density was compared with the theoretical predictions [fr

  14. Ultrafast Excited-State Dynamics of Diketopyrrolopyrrole (DPP)-Based Materials: Static versus Diffusion-Controlled Electron Transfer Process

    KAUST Repository

    Alsulami, Qana

    2015-06-25

    Singlet-to-triplet intersystem crossing (ISC) and photoinduced electron transfer (PET) of platinum(II) containing diketopyrrolopyrrole (DPP) oligomer in the absence and presence of strong electron-acceptor tetracyanoethylene (TCNE) were investigated using femtosecond and nanosecond transient absorption spectroscopy with broadband capabilities. The role of platinum(II) incorporation in those photophysical properties was evaluated by comparing the excited-state dynamics of DPP with and without the metal centers. The steady-state measurements reveal that platinum(II) incorporation facilitates dramatically the interactions between DPP-Pt(acac) and TCNE, resulting in charge transfer (CT) complex formation. The transient absorption spectra in the absence of TCNE reveal ultrafast ISC of DPP-Pt(acac) followed by their long-lived triplet state. In the presence of TCNE, PET from the excited DPP-Pt(acac) and DPP to TCNE, forming the radical ion pairs. The ultrafast PET which occurs statically from DPP-Pt(acac) to TCNE in picosecond regime, is much faster than that from DPP to TCNE (nanosecond time scale) which is diffusion-controlled process, providing clear evidence that PET rate is eventually controlled by the platinum(II) incorporation.

  15. Ultrafast Excited-State Dynamics of Diketopyrrolopyrrole (DPP)-Based Materials: Static versus Diffusion-Controlled Electron Transfer Process

    KAUST Repository

    Alsulami, Qana; Aly, Shawkat Mohammede; Goswami, Subhadip; Alarousu, Erkki; Usman, Anwar; Schanze, Kirk S.; Mohammed, Omar F.

    2015-01-01

    Singlet-to-triplet intersystem crossing (ISC) and photoinduced electron transfer (PET) of platinum(II) containing diketopyrrolopyrrole (DPP) oligomer in the absence and presence of strong electron-acceptor tetracyanoethylene (TCNE) were investigated using femtosecond and nanosecond transient absorption spectroscopy with broadband capabilities. The role of platinum(II) incorporation in those photophysical properties was evaluated by comparing the excited-state dynamics of DPP with and without the metal centers. The steady-state measurements reveal that platinum(II) incorporation facilitates dramatically the interactions between DPP-Pt(acac) and TCNE, resulting in charge transfer (CT) complex formation. The transient absorption spectra in the absence of TCNE reveal ultrafast ISC of DPP-Pt(acac) followed by their long-lived triplet state. In the presence of TCNE, PET from the excited DPP-Pt(acac) and DPP to TCNE, forming the radical ion pairs. The ultrafast PET which occurs statically from DPP-Pt(acac) to TCNE in picosecond regime, is much faster than that from DPP to TCNE (nanosecond time scale) which is diffusion-controlled process, providing clear evidence that PET rate is eventually controlled by the platinum(II) incorporation.

  16. Excited-state intramolecular hydrogen transfer (ESIHT) of 1,8-Dihydroxy-9,10-anthraquinone (DHAQ) characterized by ultrafast electronic and vibrational spectroscopy and computational modeling

    KAUST Repository

    Mohammed, Omar F.; Xiao, Dequan; Batista, Victor S.; Nibbering, Erik Theodorus Johannes

    2014-01-01

    of femtosecond UV/vis and UV/IR pump-probe spectroscopic data. Upon photoabsorption at 400 nm, the S 2 electronic excited state is initially populated, followed by a rapid equilibration within 150 fs through population transfer to the S 1 state where DHAQ

  17. Excited-state intramolecular hydrogen transfer (ESIHT) of 1,8-Dihydroxy-9,10-anthraquinone (DHAQ) characterized by ultrafast electronic and vibrational spectroscopy and computational modeling

    KAUST Repository

    Mohammed, Omar F.

    2014-05-01

    We combine ultrafast electronic and vibrational spectroscopy and computational modeling to investigate the photoinduced excited-state intramolecular hydrogen-transfer dynamics in 1,8-dihydroxy-9,10-anthraquinone (DHAQ) in tetrachloroethene, acetonitrile, dimethyl sulfoxide, and methanol. We analyze the electronic excited states of DHAQ with various possible hydrogen-bonding schemes and provide a general description of the electronic excited-state dynamics based on a systematic analysis of femtosecond UV/vis and UV/IR pump-probe spectroscopic data. Upon photoabsorption at 400 nm, the S 2 electronic excited state is initially populated, followed by a rapid equilibration within 150 fs through population transfer to the S 1 state where DHAQ exhibits ESIHT dynamics. In this equilibration process, the excited-state population is distributed between the 9,10-quinone (S2) and 1,10-quinone (S1) states while undergoing vibrational energy redistribution, vibrational cooling, and solvation dynamics on the 0.1-50 ps time scale. Transient UV/vis pump-probe data in methanol also suggest additional relaxation dynamics on the subnanosecond time scale, which we tentatively ascribe to hydrogen bond dynamics of DHAQ with the protic solvent, affecting the equilibrium population dynamics within the S2 and S1 electronic excited states. Ultimately, the two excited singlet states decay with a solvent-dependent time constant ranging from 139 to 210 ps. The concomitant electronic ground-state recovery is, however, only partial because a large fraction of the population relaxes to the first triplet state. From the similarity of the time scales involved, we conjecture that the solvent plays a crucial role in breaking the intramolecular hydrogen bond of DHAQ during the S2/S1 relaxation to either the ground or triplet state. © 2014 American Chemical Society.

  18. Excited state redox properties of phthalocyanines: influence of the axial ligand on the rates of relaxation and electron-transfer quenching of the lowest /sup 3/. pi pi. /sup */ excited state

    Energy Technology Data Exchange (ETDEWEB)

    Ferraudi, G J; Prasad, D R

    1874-01-01

    Laser flash excitations at 640 nm have been used to generate the transient spectra of the lowest-lying /sup 3/..pi pi../sup */ state of phthalocyaninatoruthenium(II) complexes. The properties of this excited state such as the properties of the maxima, lambda/sub max/ = 500 +/- 30 nm, and lifetimes, t/sub 1/2/ = 70-4500 ns, exhibit a large dependence on the electron-accepting and electron-withdrawing tendencies of the axial ligands. A similar influence was observed upon the rate of electron-transfer quenching of the /sup 3/..pi pi../sup */ state. Values between 10/sup 6/ and 10/sup 7/ dm/sup 3/ mol/sup -1/ s/sup -1/ for the self-exchange rate constant have been obtained, according to Marcus-Hush theoretical treatments, for (Ru(pc.)LL')/sup +//(/sup 3/..pi pi../sup */)(Ru(pc)LL') (L and L' = neutral axial ligands; pc = phthalocyaninate (2-)) and isoelectronic cobalt(III) and rhodium(III) couples. The redox properties of the ground and excited states are correlated with axial ligand-induced perturbations of the electronic structure.

  19. Excited state electron affinity calculations for aluminum

    Science.gov (United States)

    Hussein, Adnan Yousif

    2017-08-01

    Excited states of negative aluminum ion are reviewed, and calculations of electron affinities of the states (3s^23p^2)^1D and (3s3p^3){^5}{S}° relative to the (3s^23p)^2P° and (3s3p^2)^4P respectively of the neutral aluminum atom are reported in the framework of nonrelativistic configuration interaction (CI) method. A priori selected CI (SCI) with truncation energy error (Bunge in J Chem Phys 125:014107, 2006) and CI by parts (Bunge and Carbó-Dorca in J Chem Phys 125:014108, 2006) are used to approximate the valence nonrelativistic energy. Systematic studies of convergence of electron affinity with respect to the CI excitation level are reported. The calculated value of the electron affinity for ^1D state is 78.675(3) meV. Detailed Calculations on the ^5S°c state reveals that is 1216.8166(3) meV below the ^4P state.

  20. Optimal initiation of electronic excited state mediated intramolecular H-transfer in malonaldehyde by UV-laser pulses

    Science.gov (United States)

    Nandipati, K. R.; Singh, H.; Nagaprasad Reddy, S.; Kumar, K. A.; Mahapatra, S.

    2014-12-01

    Optimally controlled initiation of intramolecular H-transfer in malonaldehyde is accomplished by designing a sequence of ultrashort (~80 fs) down-chirped pump-dump ultra violet (UV)-laser pulses through an optically bright electronic excited [ S 2 ( π π ∗)] state as a mediator. The sequence of such laser pulses is theoretically synthesized within the framework of optimal control theory (OCT) and employing the well-known pump-dump scheme of Tannor and Rice [D.J. Tannor, S.A. Rice, J. Chem. Phys. 83, 5013 (1985)]. In the OCT, the control task is framed as the maximization of cost functional defined in terms of an objective function along with the constraints on the field intensity and system dynamics. The latter is monitored by solving the time-dependent Schrödinger equation. The initial guess, laser driven dynamics and the optimized pulse structure (i.e., the spectral content and temporal profile) followed by associated mechanism involved in fulfilling the control task are examined in detail and discussed. A comparative account of the dynamical outcomes within the Condon approximation for the transition dipole moment versus its more realistic value calculated ab initio is also presented.

  1. Electronic excited states and relaxation dynamics in polymer heterojunction systems

    Science.gov (United States)

    Ramon, John Glenn Santos

    , we examine the effect of the nanoscale interfacial morphology and solvation on the electronic excited states of TFB/F8BT. Here, we employ time-dependent density functional theory (TD-DFT) to investigate the relevant excited states of two stacking configurations. We show that the calculated states agree with the excited states responsible for the experimentally observed emission peaks and that these states are blue shifted relative to those of the isolated chain. Furthermore, slight lateral shifts in the stacking orientation not only shift the excited state energies; more importantly, they alter the nature of these states altogether. Lastly, we see that solvation greatly stabilizes the charge-transfer states.

  2. Electron affinity and excited states of methylglyoxal

    Science.gov (United States)

    Dauletyarov, Yerbolat; Dixon, Andrew R.; Wallace, Adam A.; Sanov, Andrei

    2017-07-01

    Using photoelectron imaging spectroscopy, we characterized the anion of methylglyoxal (X2A″ electronic state) and three lowest electronic states of the neutral methylglyoxal molecule: the closed-shell singlet ground state (X1A'), the lowest triplet state (a3A″), and the open-shell singlet state (A1A″). The adiabatic electron affinity (EA) of the ground state, EA(X1A') = 0.87(1) eV, spectroscopically determined for the first time, compares to 1.10(2) eV for unsubstituted glyoxal. The EAs (adiabatic attachment energies) of two excited states of methylglyoxal were also determined: EA(a3A″) = 3.27(2) eV and EA(A1A″) = 3.614(9) eV. The photodetachment of the anion to each of these two states produces the neutral species near the respective structural equilibria; hence, the a3A″ ← X2A″ and A1A″ ← X2A″ photodetachment transitions are dominated by intense peaks at their respective origins. The lowest-energy photodetachment transition, on the other hand, involves significant geometry relaxation in the X1A' state, which corresponds to a 60° internal rotation of the methyl group, compared to the anion structure. Accordingly, the X1A' ← X2A″ transition is characterized as a broad, congested band, whose vertical detachment energy, VDE = 1.20(4) eV, significantly exceeds the adiabatic EA. The experimental results are in excellent agreement with the ab initio predictions using several equation-of-motion methodologies, combined with coupled-cluster theory.

  3. Photo-driven electron transfer from the highly reducing excited state of naphthalene diimide radical anion to a CO 2 reduction catalyst within a molecular triad

    Energy Technology Data Exchange (ETDEWEB)

    Martinez, Jose F. [Department of Chemistry and Argonne-Northwestern Solar Energy Research (ANSER) Center; Northwestern University; Evanston; USA; La Porte, Nathan T. [Department of Chemistry and Argonne-Northwestern Solar Energy Research (ANSER) Center; Northwestern University; Evanston; USA; Mauck, Catherine M. [Department of Chemistry and Argonne-Northwestern Solar Energy Research (ANSER) Center; Northwestern University; Evanston; USA; Wasielewski, Michael R. [Department of Chemistry and Argonne-Northwestern Solar Energy Research (ANSER) Center; Northwestern University; Evanston; USA

    2017-01-01

    The naphthalene-1,4:5,8-bis(dicarboximide) radical anion (NDI-˙), which is easily produced by mild chemical or electrochemical reduction (-0.5 Vvs.SCE), can be photoexcited at wavelengths as long as 785 nm, and has an excited state (NDI-˙*) oxidation potential of -2.1 Vvs.SCE, making it a very attractive choice for artificial photosynthetic systems that require powerful photoreductants, such as CO2 reduction catalysts. However, once an electron is transferred from NDI-˙* to an acceptor directly bound to it, a combination of strong electronic coupling and favorable free energy change frequently make the back electron transfer rapid. To mitigate this effect, we have designed a molecular triad system comprising an NDI-˙ chromophoric donor, a 9,10-diphenylanthracene (DPA) intermediate acceptor, and a Re(dmb)(CO)3carbon dioxide reduction catalyst, where dmb is 4,4'-dimethyl-2,2'-bipyridine, as the terminal acceptor. Photoexcitation of NDI-˙ to NDI-˙* is followed by ultrafast reduction of DPA to DPA-˙, which then rapidly reduces the metal complex. The overall time constant for the forward electron transfer to reduce the metal complex is τ = 20.8 ps, while the time constant for back-electron transfer is six orders of magnitude longer, τ = 43.4 μs. Achieving long-lived, highly reduced states of these metal complexes is a necessary condition for their use as catalysts. The extremely long lifetime of the reduced metal complex is attributed to careful tuning of the redox potentials of the chromophore and intermediate acceptor. The NDI-˙–DPA fragment presents many attractive features for incorporation into other photoinduced electron transfer assemblies directed at the long-lived photosensitization of difficult-to-reduce catalytic centers.

  4. Theoretical and experimental study of the relaxation of excited states of the DCM laser dye. Intra-molecular electron transfer and photo-isomerization. Solvent effects

    International Nuclear Information System (INIS)

    Marguet, Sylvie

    1992-01-01

    This research thesis reports the study of a styrenic laser dye, the 4-(dicyanomethylene)-2-methyl-6-[p-(dimethylamino) styryl]-4H-pyrane or DCM for the characterization of the first electronic states and of the influence of the solvent on efficiencies of different relaxation processes of the first excited state S1 of the DCM. Due to the presence of a combination of a donor group and acceptor group, this compound has interesting properties of intra-molecular charge transfer and of photo-isomerization which highly depend on solvent polarity. Two approaches have been adopted to study these complementary processes: an experimental approach (determination of rate constants of the different deactivation ways of the S1 state by measuring fluorescence quantum efficiencies, photo-isomerization quantum efficiencies, and fluorescence lifetimes of DCM in about twenty solvent of increasing polarity), and a computational approach (a CS-INDO-MRI type quantum chemistry calculation to obtain potential energy curves, charge distributions, and dipolar moments of DCM first electronic states) [fr

  5. Direct conversion of graphite into diamond through electronic excited states

    CERN Document Server

    Nakayama, H

    2003-01-01

    An ab initio total energy calculation has been performed for electronic excited states in diamond and rhombohedral graphite by the full-potential linearized augmented plane wave method within the framework of the local density approximation (LDA). First, calculations for the core-excited state in diamond have been performed to show that the ab initio calculations based on the LDA describe the wavefunctions in the electronic excited states as well as in the ground state quite well. Fairly good coincidence with both experimental data and theoretical prediction has been obtained for the lattice relaxation of the core exciton state. The results of the core exciton state are compared with nitrogen-doped diamond. Next, the structural stability of rhombohedral graphite has been investigated to examine the possibility of the transition into the diamond structure through electronic excited states. While maintaining the rhombohedral symmetry, rhombohedral graphite can be spontaneously transformed to cubic diamond. Tota...

  6. Electronic Excited States of Tungsten(0) Arylisocyanides

    Czech Academy of Sciences Publication Activity Database

    Kvapilová, Hana; Sattler, W.; Sattler, A.; Sazanovich, I.; Clark, I. P.; Towrie, M.; Gray, H. B.; Záliš, Stanislav; Vlček, Antonín

    2015-01-01

    Roč. 54, č. 17 (2015), s. 8518-8528 ISSN 0020-1669 R&D Projects: GA MŠk LH13015 Grant - others:COST(XE) CM1202 Institutional support: RVO:61388955 Keywords : TRANSITION-METAL-COMPLEXES * FEMTOSECOND FLUORESCENCE * CHARGE-TRANSFER Subject RIV: CG - Electrochemistry Impact factor: 4.820, year: 2015

  7. Chemical modulation of electronic structure at the excited state

    Science.gov (United States)

    Li, F.; Song, C.; Gu, Y. D.; Saleem, M. S.; Pan, F.

    2017-12-01

    Spin-polarized electronic structures are the cornerstone of spintronics, and have thus attracted a significant amount of interest; in particular, researchers are looking into how to modulate the electronic structure to enable multifunctional spintronics applications, especially in half-metallic systems. However, the control of the spin polarization has only been predicted in limited two-dimensional systems with spin-polarized Dirac structures and is difficult to achieve experimentally. Here, we report the modulation of the electronic structure in the light-induced excited state in a typical half-metal, L a1 /2S r1 /2Mn O3 -δ . According to the spin-transport measurements, there appears a light-induced increase in magnetoresistance due to the enhanced spin scattering, which is closely associated with the excited spin polarization. Strikingly, the light-induced variation can be enhanced via alcohol processing and reduced by oxygen annealing. X-ray photoelectron spectroscopy measurements show that in the chemical process, a redox reaction occurs with a change in the valence of Mn. Furthermore, first-principles calculations reveal that the change in the valence of Mn alters the electronic structure and consequently modulates the spin polarization in the excited state. Our findings thus report a chemically tunable electronic structure, demonstrating interesting physics and the potential for multifunctional applications and ultrafast spintronics.

  8. Ultrafast electronic relaxation of excited state vitamin B12 in the gas phase

    International Nuclear Information System (INIS)

    Shafizadeh, Niloufar; Poisson, Lionel; Soep, Benoit

    2008-01-01

    The time evolution of electronically excited vitamin B 12 (cyanocobalamin) has been observed for the first time in the gas phase. It reveals an ultrafast decay to a state corresponding to metal excitation. This decay is interpreted as resulting from a ring to metal electron transfer. This opens the observation of the excited state of other complex biomimetic systems in the gas phase, the key to the characterisation of their complex evolution through excited electronic states

  9. Excited State Structural Dynamics of Carotenoids and Charge Transfer Systems

    International Nuclear Information System (INIS)

    Van Tassle, Aaron Justin

    2006-01-01

    This dissertation describes the development and implementation of a visible/near infrared pump/mid-infrared probe apparatus. Chapter 1 describes the background and motivation of investigating optically induced structural dynamics, paying specific attention to solvation and the excitation selection rules of highly symmetric molecules such as carotenoids. Chapter 2 describes the development and construction of the experimental apparatus used throughout the remainder of this dissertation. Chapter 3 will discuss the investigation of DCM, a laser dye with a fluorescence signal resulting from a charge transfer state. By studying the dynamics of DCM and of its methyl deuterated isotopomer (an otherwise identical molecule), we are able to investigate the origins of the charge transfer state and provide evidence that it is of the controversial twisted intramolecular (TICT) type. Chapter 4 introduces the use of two-photon excitation to the S1 state, combined with one-photon excitation to the S2 state of the carotenoid beta-apo-8'-carotenal. These 2 investigations show evidence for the formation of solitons, previously unobserved in molecular systems and found only in conducting polymers Chapter 5 presents an investigation of the excited state dynamics of peridinin, the carotenoid responsible for the light harvesting of dinoflagellates. This investigation allows for a more detailed understanding of the importance of structural dynamics of carotenoids in light harvesting

  10. Generation of Triplet Excited States via Photoinduced Electron Transfer in meso-anthra-BODIPY: Fluorogenic Response toward Singlet Oxygen in Solution and in Vitro

    KAUST Repository

    Filatov, Mikhail A.; Karuthedath, Safakath; Polestshuk, Pavel M.; Savoie, Huguette; Flanagan, Keith J.; Sy, Cindy; Sitte, Elisabeth; Telitchko, Maxime; Laquai, Fré dé ric; Boyle, Ross W.; Senge, Mathias O.

    2017-01-01

    Heavy atom-free BODIPY-anthracene dyads (BADs) generate locally excited triplet states by way of photoinduced electron transfer (PeT), followed by recombination of the resulting charge-separated states (CSS). Subsequent quenching of the triplet states by molecular oxygen produces singlet oxygen (1O2), which reacts with the anthracene moiety yielding highly fluorescent species. The steric demand of the alkyl substituents in the BODIPY subunit defines the site of 1O2 addition. Novel bis- and tetraepoxides and bicyclic acetal products, arising from rearrangements of anthracene endoperoxides were isolated and characterized. 1O2 generation by BADs in living cells enables visualization of the dyads distribution, promising new imaging applications.

  11. Generation of Triplet Excited States via Photoinduced Electron Transfer in meso-anthra-BODIPY: Fluorogenic Response toward Singlet Oxygen in Solution and in Vitro

    KAUST Repository

    Filatov, Mikhail A.

    2017-04-14

    Heavy atom-free BODIPY-anthracene dyads (BADs) generate locally excited triplet states by way of photoinduced electron transfer (PeT), followed by recombination of the resulting charge-separated states (CSS). Subsequent quenching of the triplet states by molecular oxygen produces singlet oxygen (1O2), which reacts with the anthracene moiety yielding highly fluorescent species. The steric demand of the alkyl substituents in the BODIPY subunit defines the site of 1O2 addition. Novel bis- and tetraepoxides and bicyclic acetal products, arising from rearrangements of anthracene endoperoxides were isolated and characterized. 1O2 generation by BADs in living cells enables visualization of the dyads distribution, promising new imaging applications.

  12. Excited state intramolecular charge transfer reaction in non-aqueous ...

    Indian Academy of Sciences (India)

    polar phase and thus leading to less swelling of reverse .... ues were restricted up to the limit at which no phase separation was ..... The lower panel of figure 1 also indicates that the slopes of ... probe in its ground and excited states.55.

  13. Dynamics of the excited state intramolecular charge transfer

    International Nuclear Information System (INIS)

    Joo, T.; Kim, C.H.

    2006-01-01

    The 6-dodecanoyl-2-dimethylaminonaphtalene (laurdan), a derivative of 6-propanoyl- 2-dimethylaminonaphthalene (prodan), has been used as a fluorescent probe in cell imaging, especially in visualizing the lipid rafts by the generalized polarization (GP) images, where GP=(I 440 -I 490 )/(I 440 +I 490 ) with I being the fluorescence intensity. The fluorescence spectrum of laurdan is sensitive to its dipolar environment due to the intramolecular charge transfer (ICT) process in S 1 state, which results in a dual emission from the locally excited (LE) and the ICT states. The ICT process and the solvation of the ICT state are very sensitive to the dipolar nature of the environment. In this work, the ICT of laurdan in ethanol has been studied by femtosecond time resolved fluorescence (TRF), especially TRF spectra measurement without the conventional spectral reconstruction method. TRF probes the excited states exclusively, a unique advantage over the pump/probe transient absorption technique, although time resolution of the TRF is generally lower than transient absorption and the TRF spectra measurement was possible only though the spectral reconstruction. Over the years, critical advances in TRF technique have been made in our group to achieve <50 fs time resolution with direct full spectra measurement capability. Detailed ICT and the subsequent solvation processes can be visualized unambiguously from the TRF spectra. Fig. 1 shows the TRF spectra of laurdan in ethanol at several time delays. Surprisingly, two bands at 433 and 476 nm are clearly visible in the TRF spectra of laurdan even at T = 0 fs. As time increases, the band at 476 nm shifts to the red while its intensity increases. The band at 433 nm also shifts slightly to the red, but loses intensity as time increases. The intensity of the 476 nm band reaches maximum at around 5 ps, where it is roughly twice as intense as that at 0 fs, and stays constant until lifetime decay is noticeable. The spectra were fit by

  14. Manipulating charge transfer excited state relaxation and spin crossover in iron coordination complexes with ligand substitution

    DEFF Research Database (Denmark)

    Zhang, Wenkai; Kjær, Kasper Skov; Alonso-Mori, Roberto

    2017-01-01

    iron complexes with four cyanide (CN-;) ligands and one 2,2′-bipyridine (bpy) ligand. This enables MLCT excited state and metal-centered excited state energies to be manipulated with partial independence and provides a path to suppressing spin crossover. We have combined X-ray Free-Electron Laser (XFEL...... state lifetime of iron based complexes due to spin crossover-the extremely fast intersystem crossing and internal conversion to high spin metal-centered excited states. We revitalize a 30 year old synthetic strategy for extending the MLCT excited state lifetimes of iron complexes by making mixed ligand...

  15. Electron capture into excited states of multi-charged ions

    International Nuclear Information System (INIS)

    Dijkkamp, D.

    1985-01-01

    This thesis deals with charge exchange reactions in slow collisions of multi-charged ions with neutral atoms or molecules. These reactions proceed very efficiently via a curve crossing mechanism, which leads to preferential population of excited states of the ion. The subsequent decay of these states leads to the emission of characteristic radiation. From wavelength resolved measurements of the absolute intensity of this radiation, cross sections for selective population of the excited (n,l-) states of the ion were determined. In addition, for some systems the total capture cross section was measured directly by means of charge state analysis of the secondary projectile ions. The role of charge exchange processes in fusion plasmas and in astrophysical plasmas is indicated. An experimental set-up is described with emphasis on the Electron Cyclotron Resonance Ion Source that was used in the experiments. Results for collisions of C 6+ , N 6+ , O 6+ and Ne 6+ with He, H 2 and Ar are presented as well as for electron capture from Li atoms by C 4+ and He 2+ . The interaction of the iso-electronic sequence C 4+ , N 5+ , O 6+ with atomic hydrogen, molecular hydrogen and helium is studied. First results for partial and total cross sections in collisions of fully stripped carbon, nitrogen and oxygen ions with atomic hydrogen are presented. These data are of particular importance for applications in fusion diagnostics. The data indicate that calculations of both molecular and atomic orbital type yield correct results, if an extended basis set is used. (Auth.)

  16. Benzonitrile: Electron affinity, excited states, and anion solvation

    Science.gov (United States)

    Dixon, Andrew R.; Khuseynov, Dmitry; Sanov, Andrei

    2015-10-01

    We report a negative-ion photoelectron imaging study of benzonitrile and several of its hydrated, oxygenated, and homo-molecularly solvated cluster anions. The photodetachment from the unsolvated benzonitrile anion to the X ˜ 1 A 1 state of the neutral peaks at 58 ± 5 meV. This value is assigned as the vertical detachment energy (VDE) of the valence anion and the upper bound of adiabatic electron affinity (EA) of benzonitrile. The EA of the lowest excited electronic state of benzonitrile, a ˜ 3 A 1 , is determined as 3.41 ± 0.01 eV, corresponding to a 3.35 eV lower bound for the singlet-triplet splitting. The next excited state, the open-shell singlet A ˜ 1 A 1 , is found about an electron-volt above the triplet, with a VDE of 4.45 ± 0.01 eV. These results are in good agreement with ab initio calculations for neutral benzonitrile and its valence anion but do not preclude the existence of a dipole-bound state of similar energy and geometry. The step-wise and cumulative solvation energies of benzonitrile anions by several types of species were determined, including homo-molecular solvation by benzonitrile, hydration by 1-3 waters, oxygenation by 1-3 oxygen molecules, and mixed solvation by various combinations of O2, H2O, and benzonitrile. The plausible structures of the dimer anion of benzonitrile were examined using density functional theory and compared to the experimental observations. It is predicted that the dimer anion favors a stacked geometry capitalizing on the π-π interactions between the two partially charged benzonitrile moieties.

  17. Charge-Transfer Dynamics in the Lowest Excited State of a Pentacene–Fullerene Complex: Implications for Organic Solar Cells

    KAUST Repository

    Joseph, Saju

    2017-10-02

    We characterize the dynamic nature of the lowest excited state in a pentacene/C60 complex on the femtosecond time scale, via a combination of ab initio molecular dynamics and time-dependent density functional theory. We analyze the correlations between the molecular vibrations of the complex and the oscillations in the electron-transfer character of its lowest excited state, which point to vibration-induced coherences between the (pentacene-based) local-excitation (LE) state and the complex charge-transfer (CT) state. We discuss the implications of our results on this model system for the exciton-dissociation process in organic solar cells.

  18. Ligand manipulation of charge transfer excited state relaxation and spin crossover in [Fe(2,2′-bipyridine)2(CN)2

    DEFF Research Database (Denmark)

    Kjær, Kasper Skov; Zhang, Wenkai; Alonso-Mori, Roberto

    2017-01-01

    We have used femtosecond resolution UV-visible and Kβ x-ray emission spectroscopy to characterize the electronic excited state dynamics of [Fe(bpy)2(CN)2], where bpy=2,2′-bipyridine, initiated by metal-to-ligand charge transfer (MLCT) excitation. The excited-state absorption in the transient UV-visible...

  19. Excited state conformational dynamics in carotenoids: dark intermediates and excitation energy transfer.

    Science.gov (United States)

    Beck, Warren F; Bishop, Michael M; Roscioli, Jerome D; Ghosh, Soumen; Frank, Harry A

    2015-04-15

    A consideration of the excited state potential energy surfaces of carotenoids develops a new hypothesis for the nature of the conformational motions that follow optical preparation of the S2 (1(1)Bu(+)) state. After an initial displacement from the Franck-Condon geometry along bond length alternation coordinates, it is suggested that carotenoids pass over a transition-state barrier leading to twisted conformations. This hypothesis leads to assignments for several dark intermediate states encountered in femtosecond spectroscopic studies. The Sx state is assigned to the structure reached upon the onset of torsional motions near the transition state barrier that divides planar and twisted structures on the S2 state potential energy surface. The X state, detected recently in two-dimensional electronic spectra, corresponds to a twisted structure well past the barrier and approaching the S2 state torsional minimum. Lastly, the S(∗) state is assigned to a low lying S1 state structure with intramolecular charge transfer character (ICT) and a pyramidal conformation. It follows that the bent and twisted structures of carotenoids that are found in photosynthetic light-harvesting proteins yield excited-state structures that favor the development of an ICT character and optimized energy transfer yields to (bacterio)chlorophyll acceptors. Copyright © 2015 Elsevier Inc. All rights reserved.

  20. Excited states

    CERN Document Server

    Lim, Edward C

    1974-01-01

    Excited States, Volume I reviews radiationless transitions, phosphorescence microwave double resonance through optical spectra in molecular solids, dipole moments in excited states, luminescence of polar molecules, and the problem of interstate interaction in aromatic carbonyl compounds. The book discusses the molecular electronic radiationless transitions; the double resonance techniques and the relaxation mechanisms involving the lowest triplet state of aromatic compounds; as well as the optical spectra and relaxation in molecular solids. The text also describes dipole moments and polarizab

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

    Science.gov (United States)

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

    2018-06-01

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

  2. "Inverted" Solvent Effect on Charge Transfer in the Excited State.

    Science.gov (United States)

    Nau; Pischel

    1999-10-04

    Faster in cyclohexane than in acetonitrile is the fluorescence quenching of the azoalkane 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) by amines and sulfides. Although this photoreaction is induced by charge transfer (CT; see picture) and exciplexes are formed, the increase in the dipole moment of the exciplex is not large enough to offset the solvent stabilization of the excited reactants, and an "inverted" solvent effect results.

  3. Solvent control of charge transfer excited state relaxation pathways in [Fe(2,2 '-bipyridine)(CN)4]2-

    DEFF Research Database (Denmark)

    Kjær, Kasper Skov; Kunnus, Kristjan; Harlang, Tobias C. B.

    2018-01-01

    The excited state dynamics of solvated [Fe(bpy)(CN)4]2-, where bpy = 2,2'-bipyridine, show significant sensitivity to the solvent Lewis acidity. Using a combination of optical absorption and X-ray emission transient spectroscopies, we have previously shown that the metal to ligand charge transfer...... the MLCT excited state relaxation dynamics of [Fe(bpy)(CN)4]2- in water, a strong Lewis acid solvent. The charge-transfer excited state is now found to decay in less than 100 femtoseconds, forming a quasi-stable metal centered excited state with a 13 picosecond lifetime. We find that this MC excited state...... developed for solar applications....

  4. Excited-state intramolecular proton transfer of 2-acetylindan-1,3-dione studied by ultrafast absorption and fluorescence spectroscopy

    Directory of Open Access Journals (Sweden)

    Pramod Kumar Verma

    2016-03-01

    Full Text Available We employ transient absorption from the deep-UV to the visible region and fluorescence upconversion to investigate the photoinduced excited-state intramolecular proton-transfer dynamics in a biologically relevant drug molecule, 2-acetylindan-1,3-dione. The molecule is a ß-diketone which in the electronic ground state exists as exocyclic enol with an intramolecular H-bond. Upon electronic excitation at 300 nm, the first excited state of the exocyclic enol is initially populated, followed by ultrafast proton transfer (≈160 fs to form the vibrationally hot endocyclic enol. Subsequently, solvent-induced vibrational relaxation takes place (≈10 ps followed by decay (≈390 ps to the corresponding ground state.

  5. Spectroscopic Diagnosis of Excited-State Aromaticity: Capturing Electronic Structures and Conformations upon Aromaticity Reversal.

    Science.gov (United States)

    Oh, Juwon; Sung, Young Mo; Hong, Yongseok; Kim, Dongho

    2018-03-06

    Aromaticity, the special energetic stability derived from cyclic [4 n + 2]π-conjugated electronic structures, has been the topic of intense interest in chemistry because it plays a critical role in rationalizing molecular stability, reactivity, and physical/chemical properties. Recently, the pioneering work by Colin Baird on aromaticity reversal, postulating that aromatic (antiaromatic) character in the ground state reverses to antiaromatic (aromatic) character in the lowest excited triplet state, has attracted much scientific attention. The completely reversed aromaticity in the excited state provides direct insight into understanding the photophysical/chemical properties of photoactive materials. In turn, the application of aromatic molecules to photoactive materials has led to numerous studies revealing this aromaticity reversal. However, most studies of excited-state aromaticity have been based on the theoretical point of view. The experimental evaluation of aromaticity in the excited state is still challenging and strenuous because the assessment of (anti)aromaticity with conventional magnetic, energetic, and geometric indices is difficult in the excited state, which practically restricts the extension and application of the concept of excited-state aromaticity. Time-resolved optical spectroscopies can provide a new and alternative avenue to evaluate excited-state aromaticity experimentally while observing changes in the molecular features in the excited states. Time-resolved optical spectroscopies take advantage of ultrafast laser pulses to achieve high time resolution, making them suitable for monitoring ultrafast changes in the excited states of molecular systems. This can provide valuable information for understanding the aromaticity reversal. This Account presents recent breakthroughs in the experimental assessment of excited-state aromaticity and the verification of aromaticity reversal with time-resolved optical spectroscopic measurements. To

  6. Dynamics of Excited State Proton Transfer in Nitro Substituted 10-Hydroxybenzo[h]quinolines

    DEFF Research Database (Denmark)

    Marciak, H; Hristova, S.; Deneva, V

    2017-01-01

    The ground state tautomerism and excited state intramolecular proton transfer (ESIPT) of 10-hydroxybenzo[h]quinoline (HBQ) and its nitro derivatives, 7-nitrobenzo[h]quinolin-10-ol (2) and 7,9-dinitrobenzo[h]quinolin-10-ol (3), have been studied in acetonitrile using steady state as well as time d...

  7. Symmetry-breaking intramolecular charge transfer in the excited state of meso-linked BODIPY dyads

    KAUST Repository

    Whited, Matthew T.; Patel, Niral M.; Roberts, Sean T.; Allen, Kathryn; Djurovich, Peter I.; Bradforth, Stephen E.; Thompson, Mark E.

    2012-01-01

    We report the synthesis and characterization of symmetric BODIPY dyads where the chromophores are attached at the meso position, using either a phenylene bridge or direct linkage. Both molecules undergo symmetry-breaking intramolecular charge transfer in the excited state, and the directly linked dyad serves as a visible-light-absorbing analogue of 9,9′-bianthryl.

  8. Evidence for excited state intramolecular charge transfer in benzazole-based pseudo-stilbenes.

    Science.gov (United States)

    Santos, Fabiano da Silveira; Descalzo, Rodrigo Roceti; Gonçalves, Paulo Fernando Bruno; Benvenutti, Edilson Valmir; Rodembusch, Fabiano Severo

    2012-08-21

    Two azo compounds were obtained through the diazotization reaction of aminobenzazole derivatives and N,N-dimethylaniline using clay montmorillonite KSF as catalyst. The synthesized dyes were characterized using elemental analysis, Fourier transform infrared spectroscopy, and (13)C and (1)H NMR spectroscopy in solution. Their photophysical behavior was studied using UV-vis and steady-state fluorescence in solution. These dyes present intense absorption in the blue region. The spectral features of the azo compounds can be related to the pseudo-stilbene type as well as the E isomer of the dyes. Excitation at the absorption maxima does not produce emissive species in the excited state. However, excitation around 350 nm allowed dual emission of fluorescence, from both a locally excited (LE, short wavelength) and an intramolecular charge transfer (ICT, long wavelength) state, which was corroborated by a linear relation of the fluorescence maximum (ν(max)) versus the solvent polarity function (Δf) from the Lippert-Mataga correlation. Evidence of TICT in these dyes was discussed from the viscosity dependence of the fluorescence intensity in the ICT emission band. Theoretical calculations were also performed in order to study the geometry and charge distribution of the dyes in their ground and excited electronic states. Using DFT methods at the theoretical levels BLYP/Aug-cc-pVDZ, for geometry optimizations and frequency calculations, and B3LYP/6-311+G(2d), for single-point energy evaluations, the calculations revealed that the least energetic and most intense photon absorption leads to a very polar excited state that relaxes non-radioactively, which can be associated with photochemical isomerization.

  9. Charge transfer excitations from excited state Hartree-Fock subsequent minimization scheme

    International Nuclear Information System (INIS)

    Theophilou, Iris; Tassi, M.; Thanos, S.

    2014-01-01

    Photoinduced charge-transfer processes play a key role for novel photovoltaic phenomena and devices. Thus, the development of ab initio methods that allow for an accurate and computationally inexpensive treatment of charge-transfer excitations is a topic that nowadays attracts a lot of scientific attention. In this paper we extend an approach recently introduced for the description of single and double excitations [M. Tassi, I. Theophilou, and S. Thanos, Int. J. Quantum Chem. 113, 690 (2013); M. Tassi, I. Theophilou, and S. Thanos, J. Chem. Phys. 138, 124107 (2013)] to allow for the description of intermolecular charge-transfer excitations. We describe an excitation where an electron is transferred from a donor system to an acceptor one, keeping the excited state orthogonal to the ground state and avoiding variational collapse. These conditions are achieved by decomposing the space spanned by the Hartree-Fock (HF) ground state orbitals into four subspaces: The subspace spanned by the occupied orbitals that are localized in the region of the donor molecule, the corresponding for the acceptor ones and two more subspaces containing the virtual orbitals that are localized in the neighborhood of the donor and the acceptor, respectively. Next, we create a Slater determinant with a hole in the subspace of occupied orbitals of the donor and a particle in the virtual subspace of the acceptor. Subsequently we optimize both the hole and the particle by minimizing the HF energy functional in the corresponding subspaces. Finally, we test our approach by calculating the lowest charge-transfer excitation energies for a set of tetracyanoethylene-hydrocarbon complexes that have been used earlier as a test set for such kind of excitations

  10. An exciton approach to the excited states of two electron atoms. I Formalism and interpretation

    International Nuclear Information System (INIS)

    Schipper, P.E.

    1985-01-01

    The exciton model is formally applied to a description of the excited states of two electron atoms with the explicit inclusion of exchange. The model leads to a conceptually simple framework for the discussion of the electronic properties of the archetypical atomic electron pair

  11. Structural, photophysical, and theoretical studies of imidazole-based excited-state intramolecular proton transfer molecules

    Science.gov (United States)

    Somasundaram, Sivaraman; Kamaraj, Eswaran; Hwang, Su Jin; Park, Sanghyuk

    2018-02-01

    Imidazole-based excited state intramolecular proton transfer (ESIPT) blue fluorescent molecules, 2-(1-(4-chlorophenyl)-4,5-diphenyl-1H-imidazol-2-yl)phenol (BHPI-Cl) and 2-(1-(4-bromophenyl)-4,5-diphenyl-1H-imidazol-2-yl)phenol (BHPI-Br) were designed and synthesized by Debus-Radziszewski method through a one-pot multicomponent reaction in high yield. The synthesized compounds were fully characterized by 1H NMR, 13C NMR, FT-IR, FT-Raman, GC-Mass, and elemental analysis. The molecular structures in single crystal lattice were studied by X-ray crystallographic analysis. Because of the intramolecular hydrogen bonding, hydroxyphenyl group is planar to the central imidazole ring, while the other phenyl rings gave distorted conformations to the central heterocyclic ring. BHPI-Cl and BHPI-Br molecules showed intense ESIPT fluorescence at 480 nm, because the two twisted phenyl rings on 4- and 5-positions have reduced intermolecular interaction between adjacent molecules in each crystal through a head-to-tail packing manner. Quantum chemical calculations of energies were carried out by (TD-)DFT using B3LYP/6-31G(d, p) basis set to predict the electronic absorption spectra of the compounds, and they showed good agreement between the computational and the experimental values. The thermal analyses of the synthesized molecules were also carried out by TGA/DSC method.

  12. Excited-state intramolecular proton transfer and photoswitching in hydroxyphenyl-imidazopyridine derivatives: A theoretical study

    Science.gov (United States)

    Omidyan, Reza; Iravani, Maryam

    2016-11-01

    The MP2/CC2 and CASSCF theoretical approaches have been employed to determine the excited state proton transfer and photophysical nature of the four organic compounds, having the main frame of hydroxyphenyl-imidzaopyridine (HPIP). The nitrogen insertion effect, in addition to amine (-NH2) substitution has been investigated extensively by following the transition energies and deactivation pathways of resulted HPIP derivatives. It has been predicted that the excited state intramolecular proton transfer with or without small barrier is the most important feature of these compounds. Also, for all of the considered HPIP derivatives, a conical intersection (CI) between ground and the S1 excited state has been predicted. The strong non-adiabatic coupling in the CI (S1/S0), drives the system back to the ground state in which the proton may either return to the phenoxy unit and thus close the photocycle, or the system can continue the twisting motion that results in formation of a γ-photochromic species. This latter species can be responsible for photochromism of HPIP derivative systems.

  13. Lifetime and g-factor measurements of excited states using Coulomb excitation and alpha transfer reactions

    Energy Technology Data Exchange (ETDEWEB)

    Guevara, Z. E., E-mail: zjguevaram@unal.edu.co; Torres, D. A., E-mail: datorresg@unal.edu.co [Physics Department, Universidad Nacional de Colombia, Bogotá D.C. (Colombia)

    2016-07-07

    In this contribution the challenges in the use of a setup to simultaneously measure lifetimes and g-factor values will be presented. The simultaneous use of the transient field technique and the Doppler Shift Attenuation Method, to measure magnetic moments and lifetimes respectively, allows to obtain a complete characterization of the currents of nucleons and the deformation in excited states close to the ground state. The technique is at the moment limited to Coulomb excitation and alpha-transfer reactions, what opens an interesting perspective to consider this type of experiments with radioactive beams. The use of deep-inelastic and fusion-evaporation reactions will be discussed. An example of a setup that makes use of a beam of {sup 106}Cd to study excited states of {sup 110}Sn and the beam nuclei itself will be presented.

  14. Electronic and photophysical properties of 2-(2′-hydroxyphenyl)benzoxazole and its derivatives enhancing in the excited-state intramolecular proton transfer processes: A TD-DFT study on substitution effect

    Energy Technology Data Exchange (ETDEWEB)

    Daengngern, Rathawat; Kungwan, Nawee, E-mail: naweekung@gmail.com

    2015-11-15

    The effect of electron donating and withdrawing substituents on the enol absorption and keto emission spectra of 2-(2′-hydroxyphenyl)benzoxazole (HBO) and its derivatives has been systematically investigated by means of density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. The enol absorption spectra of HBO were simulated by using five different DFTs with various exchange-correlation functions to validate a suitable functional prior to being further used as a method of choice to study the effect of substituents on the spectral characteristics of HBO derivatives. The popular B3LYP (Becke, three-parameter, Lee–Yang–Parr) exchange-correlation functional is found to provide the best desirable result in predicting the absorption spectrum close to experimental data. In the ground state, enol forms of HBO and its derivatives are more stable than those of keto forms, while in the first lowest excited state, keto forms are found to be more stable than their enol forms. Overall, simulated absorption and emission spectra of HBO and its derivatives from TD-B3LYP calculations are in good agreement with the experimental data. For enol, absorption maxima of HBO derivatives having electron-withdrawing groups are red-shift corresponding to their lower HOMO–LUMO energy gaps compared to that of HBO. For keto emission, HBO having electron donating groups (m-MeHBO and MHBO) and withdrawing group (CNHBO) at 4′-position on the phenol fragment as well as electron donating groups (HBOMe and HBOM) at 6-position on the benzoxazole fragment make the position of keto emission peak shift to shorter wavelength (blue-shift). However, HBO derivatives with electron withdrawing groups (HBOF, HBOCl, HBOA and HBOE) at 6-position give redshifted emission compared to the parent compound (HBO). The type of substituent on both 4′- and 6-positions certainly has a pronounced effect on the absorption and emission spectra of HBO derivatives. - Highlights: • Simulated spectra

  15. Electronic and photophysical properties of 2-(2′-hydroxyphenyl)benzoxazole and its derivatives enhancing in the excited-state intramolecular proton transfer processes: A TD-DFT study on substitution effect

    International Nuclear Information System (INIS)

    Daengngern, Rathawat; Kungwan, Nawee

    2015-01-01

    The effect of electron donating and withdrawing substituents on the enol absorption and keto emission spectra of 2-(2′-hydroxyphenyl)benzoxazole (HBO) and its derivatives has been systematically investigated by means of density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. The enol absorption spectra of HBO were simulated by using five different DFTs with various exchange-correlation functions to validate a suitable functional prior to being further used as a method of choice to study the effect of substituents on the spectral characteristics of HBO derivatives. The popular B3LYP (Becke, three-parameter, Lee–Yang–Parr) exchange-correlation functional is found to provide the best desirable result in predicting the absorption spectrum close to experimental data. In the ground state, enol forms of HBO and its derivatives are more stable than those of keto forms, while in the first lowest excited state, keto forms are found to be more stable than their enol forms. Overall, simulated absorption and emission spectra of HBO and its derivatives from TD-B3LYP calculations are in good agreement with the experimental data. For enol, absorption maxima of HBO derivatives having electron-withdrawing groups are red-shift corresponding to their lower HOMO–LUMO energy gaps compared to that of HBO. For keto emission, HBO having electron donating groups (m-MeHBO and MHBO) and withdrawing group (CNHBO) at 4′-position on the phenol fragment as well as electron donating groups (HBOMe and HBOM) at 6-position on the benzoxazole fragment make the position of keto emission peak shift to shorter wavelength (blue-shift). However, HBO derivatives with electron withdrawing groups (HBOF, HBOCl, HBOA and HBOE) at 6-position give redshifted emission compared to the parent compound (HBO). The type of substituent on both 4′- and 6-positions certainly has a pronounced effect on the absorption and emission spectra of HBO derivatives. - Highlights: • Simulated spectra

  16. Calculation of Vibrational and Electronic Excited-State Absorption Spectra of Arsenic-Water Complexes Using Density Functional Theory

    Science.gov (United States)

    2016-06-03

    Naval Research Laboratory Washington, DC 20375-5320 NRL/MR/6390--16-9681 Calculation of Vibrational and Electronic Excited -State Absorption Spectra...NUMBER OF PAGES 17. LIMITATION OF ABSTRACT Calculation of Vibrational and Electronic Excited -State Absorption Spectra of Arsenic-Water Complexes Using...Unclassified Unlimited Unclassified Unlimited 59 Samuel G. Lambrakos (202) 767-2601 Calculations are presented of vibrational and electronic excited -state

  17. Implications of electron attachment to highly-excited states in pulsed-power discharges

    International Nuclear Information System (INIS)

    Pinnaduwage, L.A.; Univ. of Tennessee, Knoxville, TN

    1997-01-01

    The author points out the possible implications of electron attachment to highly-excited states of molecules in two pulsed power technologies. One involves the pulsed H 2 discharges used for the generation of H ion beams for magnetic fusion energy and particle accelerators. The other is the power modulated plasma discharges used for material processing

  18. Ligand manipulation of charge transfer excited state relaxation and spin crossover in [Fe(2,2′-bipyridine2(CN2

    Directory of Open Access Journals (Sweden)

    Kasper S. Kjær

    2017-07-01

    Full Text Available We have used femtosecond resolution UV-visible and Kβ x-ray emission spectroscopy to characterize the electronic excited state dynamics of [Fe(bpy2(CN2], where bpy=2,2′-bipyridine, initiated by metal-to-ligand charge transfer (MLCT excitation. The excited-state absorption in the transient UV-visible spectra, associated with the 2,2′-bipyridine radical anion, provides a robust marker for the MLCT excited state, while the transient Kβ x-ray emission spectra provide a clear measure of intermediate and high spin metal-centered excited states. From these measurements, we conclude that the MLCT state of [Fe(bpy2(CN2] undergoes ultrafast spin crossover to a metal-centered quintet excited state through a short lived metal-centered triplet transient species. These measurements of [Fe(bpy2(CN2] complement prior measurement performed on [Fe(bpy3]2+ and [Fe(bpy(CN4]2− in dimethylsulfoxide solution and help complete the chemical series [Fe(bpyN(CN6–2N]2N-4, where N = 1–3. The measurements confirm that simple ligand modifications can significantly change the relaxation pathways and excited state lifetimes and support the further investigation of light harvesting and photocatalytic applications of 3d transition metal complexes.

  19. Mechanism for the Excited-State Multiple Proton Transfer Process of Dihydroxyanthraquinone Chromophores.

    Science.gov (United States)

    Zhou, Qiao; Du, Can; Yang, Li; Zhao, Meiyu; Dai, Yumei; Song, Peng

    2017-06-22

    The single and dual cooperated proton transfer dynamic process in the excited state of 1,5-dihydroxyanthraquinone (1,5-DHAQ) was theoretically investigated, taking solvent effects (ethanol) into account. The absorption and fluorescence spectra were simulated, and dual fluorescence exhibited, which is consistent with previous experiments. Analysis of the calculated IR and Raman vibration spectra reveals that the intramolecular hydrogen bonding interactions (O 20 -H 21 ···O 24 and O 22 -H 23 ···O 25 ) are strengthened following the excited proton transfer process. Finally, by constructing the potential energy surfaces of the ground state, first excited singlet state, and triplet state, the mechanism of the intramolecular proton transfer of 1,5-DHAQ can be revealed.

  20. Observation of excited state charge transfer with fs/ps-CARS

    Energy Technology Data Exchange (ETDEWEB)

    Blom, Alex Jason [Iowa State Univ., Ames, IA (United States)

    2009-01-01

    Excited state charge transfer processes are studied using the fs/ps-CARS probe technique. This probe allows for multiplexed detection of Raman active vibrational modes. Systems studied include Michler's Ketone, Coumarin 120, 4-dimethylamino-4'-nitrostilbene, and several others. The vibrational spectrum of the para di-substituted benzophenone Michler's Ketone in the first excited singlet state is studied for the first time. It is found that there are several vibrational modes indicative of structural changes of the excited molecule. A combined experimental and theoretical approach is used to study the simplest 7-amino-4-methylcoumarin, Coumarin 120. Vibrations observed in FTIR and spontaneous Raman spectra are assigned using density functional calculations and a continuum solvation model is used to predict how observed modes are affected upon inclusion of a solvent. The low frequency modes of the excited state charge transfer species 4-dimethylamino-4{prime}-nitrostilbene are studied in acetonitrile. Results are compared to previous work on this molecule in the fingerprint region. Finally, several partially completed projects and their implications are discussed. These include the two photon absorption of Coumarin 120, nanoconfinement in cyclodextrin cavities and sensitization of titania nanoparticles.

  1. Theoretical Insights Into the Excited State Double Proton Transfer Mechanism of Deep Red Pigment Alkannin.

    Science.gov (United States)

    Zhao, Jinfeng; Dong, Hao; Zheng, Yujun

    2018-02-08

    As the most important component of deep red pigments, alkannin is investigated theoretically in detail based on time-dependent density functional theory (TDDFT) method. Exploring the dual intramolecular hydrogen bonds (O1-H2···O3 and O4-H5···O6) of alkannin, we confirm the O1-H2···O3 may play a more important role in the first excited state than the O4-H5···O6 one. Infrared (IR) vibrational analyses and subsequent charge redistribution also support this viewpoint. Via constructing the S 1 -state potential energy surface (PES) and searching transition state (TS) structures, we illuminate the excited state double proton transfer (ESDPT) mechanism of alkannin is the stepwise process that can be first launched by the O1-H2···O3 hydrogen bond wire in gas state, acetonitrile (CH 3 CN) and cyclohexane (CYH) solvents. We present a novel mechanism that polar aprotic solvents can contribute to the first-step proton transfer (PT) process in the S 1 state, and nonpolar solvents play important roles in lowering the potential energy barrier of the second-step PT reaction.

  2. Observation of excited state charge transfer with fs/ps-CARS

    International Nuclear Information System (INIS)

    Blom, Alex Jason

    2009-01-01

    Excited state charge transfer processes are studied using the fs/ps-CARS probe technique. This probe allows for multiplexed detection of Raman active vibrational modes. Systems studied include Michler's Ketone, Coumarin 120, 4-dimethylamino-4(prime)-nitrostilbene, and several others. The vibrational spectrum of the para di-substituted benzophenone Michler's Ketone in the first excited singlet state is studied for the first time. It is found that there are several vibrational modes indicative of structural changes of the excited molecule. A combined experimental and theoretical approach is used to study the simplest 7-amino-4-methylcoumarin, Coumarin 120. Vibrations observed in FTIR and spontaneous Raman spectra are assigned using density functional calculations and a continuum solvation model is used to predict how observed modes are affected upon inclusion of a solvent. The low frequency modes of the excited state charge transfer species 4-dimethylamino-4(prime)-nitrostilbene are studied in acetonitrile. Results are compared to previous work on this molecule in the fingerprint region. Finally, several partially completed projects and their implications are discussed. These include the two photon absorption of Coumarin 120, nanoconfinement in cyclodextrin cavities and sensitization of titania nanoparticles

  3. A benchmark study of electronic excitation energies, transition moments, and excited-state energy gradients on the nicotine molecule

    Energy Technology Data Exchange (ETDEWEB)

    Egidi, Franco, E-mail: franco.egidi@sns.it; Segado, Mireia; Barone, Vincenzo, E-mail: vincenzo.barone@sns.it [Scuola Normale Superiore, Piazza dei Cavalieri, 7 I-56126 Pisa (Italy); Koch, Henrik [Department of Chemistry, Norwegian University of Science and Technology, 7491 Trondheim (Norway); Cappelli, Chiara [Dipartimento di Chimica e Chimica Industriale, Università di Pisa, via G. Moruzzi, 3 I-56124 Pisa (Italy)

    2014-12-14

    In this work, we report a comparative study of computed excitation energies, oscillator strengths, and excited-state energy gradients of (S)-nicotine, chosen as a test case, using multireference methods, coupled cluster singles and doubles, and methods based on time-dependent density functional theory. This system was chosen because its apparent simplicity hides a complex electronic structure, as several different types of valence excitations are possible, including n-π{sup *}, π-π{sup *}, and charge-transfer states, and in order to simulate its spectrum it is necessary to describe all of them consistently well by the chosen method.

  4. Electronically excited states of chloroethylenes: Experiment and DFT calculations in comparison

    International Nuclear Information System (INIS)

    Khvostenko, O.G.

    2014-01-01

    Highlights: • B3LYP/6-311 + G(d,p) calculations of chloroethylenes molecules were performed. • Calculations were correlated with experiment on the molecules ground and excited states. • The general pattern of electron structure of chloroethylenes was obtained. • Necessity of this data for chloroethylenes negative ions study was noted. - Abstract: B3LYP/6-311 + G(d,p) calculations of ground and electronically excited states of ethylene, chloroethylene, 1,1-dichloroethylene, 1,2-dichloroethylene-cis, 1,2-dichloroethylene-trans trichloroethylene and tetrachloroethylene molecules have been performed. Molecular orbitals images and orbital correlation diagram are given. The calculation results for chloroethylenes electronically excited states were compared with experimental data from the energy-loss spectra obtained and generally considered previously by C.F. Koerting, K.N. Walzl and A. Kupperman. Several new additional triplet and singlet transitions were pointed out in these spectra considering the calculation results. The finding of the additional transitions was supported by the UV absorption spectrum of trichloroethylene recorded in big cuvette (10 cm), where the first three triplet and two low-intensive forbidden singlet transitions were registered. The first triplet of this compound was recorded to be at the same energy as was found with the energy-loss spectroscopy

  5. Electronically excited states of chloroethylenes: Experiment and DFT calculations in comparison

    Energy Technology Data Exchange (ETDEWEB)

    Khvostenko, O.G., E-mail: khv@mail.ru

    2014-08-15

    Highlights: • B3LYP/6-311 + G(d,p) calculations of chloroethylenes molecules were performed. • Calculations were correlated with experiment on the molecules ground and excited states. • The general pattern of electron structure of chloroethylenes was obtained. • Necessity of this data for chloroethylenes negative ions study was noted. - Abstract: B3LYP/6-311 + G(d,p) calculations of ground and electronically excited states of ethylene, chloroethylene, 1,1-dichloroethylene, 1,2-dichloroethylene-cis, 1,2-dichloroethylene-trans trichloroethylene and tetrachloroethylene molecules have been performed. Molecular orbitals images and orbital correlation diagram are given. The calculation results for chloroethylenes electronically excited states were compared with experimental data from the energy-loss spectra obtained and generally considered previously by C.F. Koerting, K.N. Walzl and A. Kupperman. Several new additional triplet and singlet transitions were pointed out in these spectra considering the calculation results. The finding of the additional transitions was supported by the UV absorption spectrum of trichloroethylene recorded in big cuvette (10 cm), where the first three triplet and two low-intensive forbidden singlet transitions were registered. The first triplet of this compound was recorded to be at the same energy as was found with the energy-loss spectroscopy.

  6. Excited state proton transfer in 9-aminoacridine carboxamides in water and in DNA

    Energy Technology Data Exchange (ETDEWEB)

    Smith, Charles A. [Iowa State Univ., Ames, IA (United States)

    1995-09-26

    The 9-aminoacridine molecule is important in several different fields of chemistry. The absorption and fluorescence spectra of this compound are pH sensitive and it is this property that allowed it to be used as a pH probe in different chemical environments. The compound exhibits proton transfer reactions which are among the most fundamental of chemical reactions. The planarity of 9-aminoacridine allows it to intercalate into DNA. Intercalation is a process in which the aromatic flat surface of the intercalator inserts between adjacent base pairs of DNA. The large surface area of 9-aminoacridine`s fused tricyclic ring system allows strong intercalative binding through van der Waals attractions. 9-aminoacridine and many of its derivatives have been tried as possible antitumor drugs. The cytotoxicity of an antitumor agent can be dramatically increased through the addition of one or two cationic side chains. This increase in cytotoxicity using the 9-aminoacridine compound as a parent molecule has been investigated through various derivatives with cationic side chains consisting of different number of carbon atoms between the proximal and distal N atoms. Similar derivatives varied the position of the carboxamide side chain on the aromatic ring system. The objective of this work is to first create a baseline study of the excited state kinetics of the 9-aminoacridine carboxamides in the absence of DNA. The baseline study will allow the excited state kinetics of these antitumor drugs when placed in DNA to be more fully understood.

  7. Influence of different environments on the excited-state proton transfer and dual fluorescence of fisetin

    Science.gov (United States)

    Guharay, Jayanti; Dennison, S. Moses; Sengupta, Pradeep K.

    1999-05-01

    The influence of different protic and aprotic solvent environments on the excited-state intramolecular proton transfer (ESIPT) leading to a dual fluorescence behaviour of a biologically important, naturally occurring, polyhydroxyflavone, fisetin (3,3',4',7-tetrahydroxyflavone), has been investigated. The normal fluorescence band, in particular, is extremely sensitive to solvent polarity with νmax shifting from 24 510 cm -1 in dioxane ( ET(30)=36.0) to 20 790 cm -1 in methanol ( ET(30)=55.5). This is rationalized in terms of solvent dipolar relaxation process, which also accounts for the red edge excitation shifts (REES) observed in viscous environments such as glycerol at low temperatures. Significant solvent dependence of the tautomer fluorescence properties ( νmax, yield and decay kinetics) reveals the influence of external hydrogen bonding perturbation on the internal hydrogen bond of the molecule. These excited-state relaxation phenomena and their relevant parameters have been used to probe the microenvironment of fisetin in a membrane mimetic system, namely AOT reverse micelles in n-heptane at different water/surfactant molar ratio ( w0).

  8. Radiative charge-transfer lifetime of the excited state of (NaCa)+

    International Nuclear Information System (INIS)

    Makarov, Oleg P.; Cote, R.; Michels, H.; Smith, W.W.

    2003-01-01

    New experiments were proposed recently to investigate the regime of cold atomic and molecular ion-atom collision processes in a special hybrid neutral-atom-ion trap under high-vacuum conditions. We study the collisional cooling of laser precooled Ca + ions by ultracold Na atoms. Modeling this process requires knowledge of the radiative lifetime of the excited singlet A 1 Σ + state of the (NaCa) + molecular system. We calculate the rate coefficient for radiative charge transfer using a semiclassical approach. The dipole radial matrix elements between the ground and the excited states, and the potential curves were calculated using complete active space self-consistent field and Moeller-Plesset second-order perturbation theory with an extended Gaussian basis, 6-311+G (3df). The semiclassical charge-transfer rate coefficient was averaged over a thermal Maxwellian distribution. In addition, we also present elastic collision cross sections and the spin-exchange cross section. The rate coefficient for charge transfer was found to be 2.3x10 -16 cm 3 /sec, while those for the elastic and spin-exchange cross sections were found to be several orders of magnitude higher (1.1x10 -8 cm 3 /sec and 2.3x10 -9 cm 3 /sec, respectively). This confirms our assumption that the milli-Kelvin regime of collisional cooling of calcium ions by sodium atoms is favorable with the respect to low loss of calcium ions due to the charge transfer

  9. External Electric Field Effects on Excited-State Intramolecular Proton Transfer in 4'-N,N-Dimethylamino-3-hydroxyflavone in Poly(methyl methacrylate) Films.

    Science.gov (United States)

    Furukawa, Kazuki; Hino, Kazuyuki; Yamamoto, Norifumi; Awasthi, Kamlesh; Nakabayashi, Takakazu; Ohta, Nobuhiro; Sekiya, Hiroshi

    2015-09-17

    The external electric field effects on the steady-state electronic spectra and excited-state dynamics were investigated for 4'-N,N-(dimethylamino)-3-hydroxyflavone (DMHF) in a poly(methyl methacrylate) (PMMA) film. In the steady-state spectrum, dual emission was observed from the excited states of the normal (N*) and tautomer (T*) forms. Application of an external electric field of 1.0 MV·cm(-1) enhanced the N* emission and reduced the T* emission, indicating that the external electric field suppressed the excited-state intramolecular proton transfer (ESIPT). The fluorescence decay profiles were measured for the N* and T* forms. The change in the emission intensity ratio N*/T* induced by the external electric field is dominated by ESIPT from the Franck-Condon excited state of the N* form and vibrational cooling in potential wells of the N* and T* forms occurring within tens of picoseconds. Three manifolds of fluorescent states were identified for both the N* and T* forms. The excited-state dynamics of DMHF in PMMA films has been found to be very different from that in solution due to intermolecular interactions in a rigid environment.

  10. Electronic structure and the mechanism of autoionization for doubly excited states

    International Nuclear Information System (INIS)

    Komninos, Y.; Makri, N.; Nicolaides, C.A.

    1986-01-01

    Apart from pure phenomenology, the rigorous and quantitative study of many-electron autoionizing states presents intriguing questions as regards their structure and dynamics. In this paper we present an analysis of such states within a state specific theory with application to five low-lying doubly excited states (DES) of He. The zeroth order description is multiconfigurational and is obtained numerically at the MCHF level. In this way, major radial and angular correlations are accounted for accurately, and reliable predictions can be made without the requirement of large computations. The additional localized correlation is obtained by optimizing variationally analytic virtual orbitals. (orig./WL)

  11. Electron-tunneling observation of localized excited states in superconducting manganese-doped lead

    International Nuclear Information System (INIS)

    Tsang, J.; Ginsberg, D.M.

    1980-01-01

    We have made electron-tunneling measurements on a dilute, superconducting lead-manganese alloy. A well-defined structure was observed in the ac-conductance--voltage curves, indicating excited states within the BCS energy gap. These states were partially accounted for by Shiba theory when spin-dependent s-, p-, and d-wave scattering were included. The phase shifts used in doing that were the results of band calculations. The experimental data also show the existence of a broad background density of states in the energy gap, which cannot be accounted for by the theory

  12. Excited State Structural Dynamics of Carotenoids and ChargeTransfer Systems

    Energy Technology Data Exchange (ETDEWEB)

    Van Tassle, Aaron Justin [Univ. of California, Berkeley, CA (United States)

    2006-01-01

    This dissertation describes the development andimplementation of a visible/near infrared pump/mid-infrared probeapparatus. Chapter 1 describes the background and motivation ofinvestigating optically induced structural dynamics, paying specificattention to solvation and the excitation selection rules of highlysymmetric molecules such as carotenoids. Chapter 2 describes thedevelopment and construction of the experimental apparatus usedthroughout the remainder of this dissertation. Chapter 3 will discuss theinvestigation of DCM, a laser dye with a fluorescence signal resultingfrom a charge transfer state. By studying the dynamics of DCM and of itsmethyl deuterated isotopomer (an otherwise identical molecule), we areable to investigate the origins of the charge transfer state and provideevidence that it is of the controversial twisted intramolecular (TICT)type. Chapter 4 introduces the use of two-photon excitation to the S1state, combined with one-photon excitation to the S2 state of thecarotenoid beta-apo-8'-carotenal. These 2 investigations show evidencefor the formation of solitons, previously unobserved in molecular systemsand found only in conducting polymers Chapter 5 presents an investigationof the excited state dynamics of peridinin, the carotenoid responsiblefor the light harvesting of dinoflagellates. This investigation allowsfor a more detailed understanding of the importance of structuraldynamics of carotenoids in light harvesting.

  13. Mechanistic photodecarboxylation of pyruvic acid: Excited-state proton transfer and three-state intersection

    Science.gov (United States)

    Chang, Xue-Ping; Fang, Qiu; Cui, Ganglong

    2014-10-01

    Photodissociation dynamics of pyruvic acid experimentally differs from that of commonly known ketones. We have employed the complete active space self-consistent field and its multi-state second-order perturbation methods to study its photodissociation mechanism in the S0, T1, and S1 states. We have uncovered four nonadiabatic photodecarboxylation paths. (i) The S1 system relaxes via an excited-state intramolecular proton transfer (ESIPT) to a hydrogen-transferred tautomer, near which an S1/S0 conical intersection funnels the S1 to S0 state. Then, some trajectories continue completing the decarboxylation reaction in the S0 state; the remaining trajectories via a reverse hydrogen transfer return to the S0 minimum, from which a thermal decarboxylation reaction occurs. (ii) Due to a small S1 -T1 energy gap and a large S1/T1 spin-orbit coupling, an efficient S1 → T1 intersystem crossing process happens again near this S1/S0 conical intersection. When decaying to T1 state, a direct photodecarboxylation proceeds. (iii) Prior to ESIPT, the S1 system first decays to the T1 state via an S1 → T1 intersystem crossing; then, the T1 system evolves to a hydrogen-transferred tautomer. Therefrom, an adiabatic T1 decarboxylation takes place due to a small barrier of 7.7 kcal/mol. (iv) Besides the aforementioned T1 ESIPT process, there also exists a comparable Norrish type I reaction in the T1 state, which forms the ground-state products of CH3CO and COOH. Finally, we have found that ESIPT plays an important role. It closes the S1-T1 and S1-S0 energy gaps, effecting an S1/T1/S0 three-state intersection region, and mediating nonadiabatic photodecarboxylation reactions of pyruvic acid.

  14. Fine structures of atomic excited states: precision atomic spectroscopy and electron-ion collision process

    International Nuclear Information System (INIS)

    Gao Xiang; Cheng Cheng; Li Jiaming

    2011-01-01

    Scientific research fields for future energies such as inertial confinement fusion researches and astrophysics studies especially with satellite observatories advance into stages of precision physics. The relevant atomic data are not only enormous but also of accuracy according to requirements, especially for both energy levels and the collision data. The fine structure of high excited states of atoms and ions can be measured by precision spectroscopy. Such precision measurements can provide not only knowledge about detailed dynamics of electron-ion interactions but also a bench mark examination of the accuracy of electron-ion collision data, especially incorporating theoretical computations. We illustrate that by using theoretical calculation methods which can treat the bound states and the adjacent continua on equal footing. The precision spectroscopic measurements of excited fine structures can be served as stringent tests of electron-ion collision data. (authors)

  15. An excited-state intramolecular photon transfer fluorescence probe for localizable live cell imaging of cysteine

    Science.gov (United States)

    Liu, Wei; Chen, Wen; Liu, Si-Jia; Jiang, Jian-Hui

    2017-03-01

    Small molecule probes suitable for selective and specific fluorescence imaging of some important but low-concentration intracellular reactive sulfur species such as cysteine (Cys) pose a challenge in chemical biology. We present a readily available, fast-response fluorescence probe CHCQ-Ac, with 2-(5‧-chloro-2-hydroxyl-phenyl)-6-chloro-4(3 H)-quinazolinone (CHCQ) as the fluorophore and acrylate group as the functional moiety, that enables high-selectivity and high-sensitivity for detecting Cys in both solution and biological system. After specifically reacted with Cys, the probe undergoes a seven-membered intramolecular cyclization and released the fluorophore CHCQ with excited-state intramolecular photon transfer effect. A highly fluorescent, insoluble aggregate was then formed to facilitate high-sensitivity and high-resolution imaging. The results showed that probe CHCQ-Ac affords a remarkably large Stokes shift and can detect Cys under physiological pH condition with no interference from other analytes. Moreover, this probe was proved to have excellent chemical stability, low cytotoxicity and good cell permeability. Our design of this probe provides a novel potential tool to visualize and localize cysteine in bioimaging of live cells that would greatly help to explore various Cys-related physiological and pathological cellular processes in cell biology and diagnostics.

  16. Environment-sensitive quinolone demonstrating long-lived fluorescence and unusually slow excited-state intramolecular proton transfer kinetics

    Czech Academy of Sciences Publication Activity Database

    Zamotaiev, O. M.; Shvadchak, Volodymyr; Sych, T. P.; Melnychuk, N. A.; Yushchenko, Dmytro A.; Mely, Y.; Pivovarenko, V. G.

    2016-01-01

    Roč. 4, č. 3 (2016), č. článku 034004. ISSN 2050-6120 Institutional support: RVO:61388963 Keywords : quinolone * fluorescent probes * local polarity * hydration * excited-state intramolecular proton transfer * kinetics Subject RIV: CC - Organic Chemistry Impact factor: 2.656, year: 2016

  17. An intramolecular charge transfer state of carbonyl carotenoids: implications for excited state dynamics of apo-carotenals and retinal

    Czech Academy of Sciences Publication Activity Database

    Polívka, Tomáš; Kaligotla, S.; Chábera, P.; Frank, H.A.

    2011-01-01

    Roč. 13, č. 22 (2011), s. 1463-9076 ISSN 1463-9076 Institutional research plan: CEZ:AV0Z50510513 Keywords : carotenoid * retinal * excited-state dynamics * charge-transfer state Subject RIV: BO - Biophysics Impact factor: 3.573, year: 2011

  18. Scientific Computation Application Partnerships in Materials and Chemical Sciences, Charge Transfer and Charge Transport in Photoactivated Systems, Developing Electron-Correlated Methods for Excited State Structure and Dynamics in the NWChem Software Suite

    Energy Technology Data Exchange (ETDEWEB)

    Cramer, Christopher J. [Univ. of Minnesota, Minneapolis, MN (United States)

    2017-11-12

    Charge transfer and charge transport in photoactivated systems are fundamental processes that underlie solar energy capture, solar energy conversion, and photoactivated catalysis, both organometallic and enzymatic. We developed methods, algorithms, and software tools needed for reliable treatment of the underlying physics for charge transfer and charge transport, an undertaking with broad applicability to the goals of the fundamental-interaction component of the Department of Energy Office of Basic Energy Sciences and the exascale initiative of the Office of Advanced Scientific Computing Research.

  19. Electron impact excitation of xenon from the metastable state to the excited states

    Energy Technology Data Exchange (ETDEWEB)

    Jiang Jun; Dong Chenzhong; Xie Luyou; Zhou Xiaoxin [College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou 730070 (China); Wang Jianguo [Institute of Applied Physics and Computational Mathematic, Beijing 100088 (China)], E-mail: dongcz@nwnu.edu.cn

    2008-12-28

    The electron impact excitation cross sections from the lowest metastable state 5p{sup 5}6sJ = 2 to the six lowest excited states of the 5p{sup 5}6p configuration of xenon are calculated systematically by using the fully relativistic distorted wave method. In order to discuss the effects of target state descriptions on the electron impact excitation cross sections, two correlation models are used to describe the target states based on the multiconfiguration Dirac-Fock (MCDF) method. It is found that the correlation effects play a very important role in low energy impact. For high energy impact, however, the cross sections are not sensitive to the description of the target states, but many more partial waves must be included.

  20. Electron-tunneling observation of local excited states in manganese-doped indium

    International Nuclear Information System (INIS)

    Tsang, J.; Ginsberg, D.M.

    1980-01-01

    We have measured the electron-tunneling characteristics of a dilute indium-manganese alloy. Well-defined structure was observed, corresponding to a band of local excited states within the energy gap. The measurements were made on two samples, and were quantitatively compared with the theory of Shiba and of Rusinov. We obtained good agreement of the tunneling data with the theory by taking into account only s-wave scattering of conduction electrons from the magnetic-impurity atoms. Even better agreement was obtained by including p- and d-wave scattering. Only by including these higher partial waves could we account for the magnitude of the observed depression of the transition temperature. The phase shifts used are in good agreement with band-theory values calculated recently

  1. Excited states in biological systems

    International Nuclear Information System (INIS)

    Cilento, G.; Zinner, K.; Bechara, E.J.H.; Duran, N.; Baptista, R.C. de; Shimizu, Y.; Augusto, O.; Faljoni-Alario, A.; Vidigal, C.C.C.; Oliveira, O.M.M.F.; Haun, M.

    1979-01-01

    Some aspects of bioluminescence related to bioenergetics are discussed: 1. chemical generation of excited species, by means of two general processes: electron transference and cyclic - and linear peroxide cleavage; 2. biological systems capable of generating excited states and 3. biological functions of these states, specially the non-emissive ones (tripletes). The production and the role of non-emissive excited states in biological systems are analysed, the main purpose of the study being the search for non-emissive states. Experiences carried out in biological systems are described; results and conclusions are given. (M.A.) [pt

  2. Electronic properties of excited states in single InAs quantum dots

    International Nuclear Information System (INIS)

    Warming, Till

    2009-01-01

    The application of quantum-mechanical effects in semiconductor nanostructures enables the realization of novel opto-electronic devices. Examples are given by single-photon emitters and emitters of entangled photon pairs, both being essential for quantum cryptography, or for qubit systems as needed for quantum computing. InAs/GaAs quantum dots are one of the most promising candidates for such applications. A detailed knowledge of the electronic properties of quantum dots is a prerequisite for this development. The aim of this work is an experimental access to the detailed electronic structure of the excited states in single InAs/GaAs quantum dots including few-particle effects and in particular exchange interaction. The experimental approach is micro photoluminescence excitation spectroscopy (μPLE). One of the main difficulties using μPLE to probe single QDs is the unambiguous assignment of the observed resonances in the spectrum to specific transitions. By comparing micro photoluminescence (μPL) and μPLE spectra, the identification of the main resonances becomes possible. The key is given by the fine structure of the hot trion. Excitation spectroscopy on single charged QDs enables for the first time the complete observation of a non-trivial fine structure of an excitonic complex in a QD, the hot trion. Modelling based on eight-band k.p theory in combination with a configuration interaction scheme is in excellent agreement. Therewith the simulation also enables realistic predictions on the fine structure of the ground-state exciton which is of large importance for single quantum dot devices. Theory concludes from the observed transitions that the structural symmetry of the QDs is broken. Micro photoluminescence excitation spectroscopy combined with resonantly excited micro photoluminescence enables an optical access to the single particle states of the hole without the influence of few-particle coulomb interactions. Based on this knowledge the exciton binding

  3. Influence of the excited states on the electron-energy distribution function in low-pressure microwave argon plasmas

    International Nuclear Information System (INIS)

    Yanguas-Gil, A.; Cotrino, J.; Gonzalez-Elipe, A.R.

    2005-01-01

    In this work the influence of the excited states on the electron-energy distribution function has been determined for an argon microwave discharge at low pressure. A collisional-radiative model of argon has been developed taking into account the most recent experimental and theoretical values of argon-electron-impact excitation cross sections. The model has been solved along with the electron Boltzmann equation in order to study the influence of the inelastic collisions from the argon excited states on the electron-energy distribution function. Results show that under certain conditions the excited states can play an important role in determining the shape of the distribution function and the mean kinetic energy of the electrons, deplecting the high-energy tail due to inelastic processes from the excited states, especially from the 4s excited configuration. It has been found that from the populations of the excited states an excitation temperature can be defined. This excitation temperature, which can be experimentally determined by optical emission spectroscopy, is lower than the electron kinetic temperature obtained from the electron-energy distribution function

  4. Mechanistic photodecarboxylation of pyruvic acid: Excited-state proton transfer and three-state intersection

    Energy Technology Data Exchange (ETDEWEB)

    Chang, Xue-Ping; Fang, Qiu, E-mail: fangqiu917@bnu.edu.cn; Cui, Ganglong, E-mail: ganglong.cui@bnu.edu.cn [Key Laboratory of Theoretical and Computational Photochemistry, Ministry of Education, College of Chemistry, Beijing Normal University, Beijing 100875 (China)

    2014-10-21

    Photodissociation dynamics of pyruvic acid experimentally differs from that of commonly known ketones. We have employed the complete active space self-consistent field and its multi-state second-order perturbation methods to study its photodissociation mechanism in the S{sub 0}, T{sub 1}, and S{sub 1} states. We have uncovered four nonadiabatic photodecarboxylation paths. (i) The S{sub 1} system relaxes via an excited-state intramolecular proton transfer (ESIPT) to a hydrogen-transferred tautomer, near which an S{sub 1}/S{sub 0} conical intersection funnels the S{sub 1} to S{sub 0} state. Then, some trajectories continue completing the decarboxylation reaction in the S{sub 0} state; the remaining trajectories via a reverse hydrogen transfer return to the S{sub 0} minimum, from which a thermal decarboxylation reaction occurs. (ii) Due to a small S{sub 1} −T{sub 1} energy gap and a large S{sub 1}/T{sub 1} spin-orbit coupling, an efficient S{sub 1} → T{sub 1} intersystem crossing process happens again near this S{sub 1}/S{sub 0} conical intersection. When decaying to T{sub 1} state, a direct photodecarboxylation proceeds. (iii) Prior to ESIPT, the S{sub 1} system first decays to the T{sub 1} state via an S{sub 1} → T{sub 1} intersystem crossing; then, the T{sub 1} system evolves to a hydrogen-transferred tautomer. Therefrom, an adiabatic T{sub 1} decarboxylation takes place due to a small barrier of 7.7 kcal/mol. (iv) Besides the aforementioned T{sub 1} ESIPT process, there also exists a comparable Norrish type I reaction in the T{sub 1} state, which forms the ground-state products of CH{sub 3}CO and COOH. Finally, we have found that ESIPT plays an important role. It closes the S{sub 1}-T{sub 1} and S{sub 1}-S{sub 0} energy gaps, effecting an S{sub 1}/T{sub 1}/S{sub 0} three-state intersection region, and mediating nonadiabatic photodecarboxylation reactions of pyruvic acid.

  5. Excited-state dynamics of oxazole: A combined electronic structure calculations and dynamic simulations study

    International Nuclear Information System (INIS)

    Cao, Jun; Xie, Zhi-Zhong; Yu, Xiaodong

    2016-01-01

    In the present work, the combined electronic structure calculations and surface hopping simulations have been performed to investigate the excited-state decay of the parent oxazole in the gas phase. Our calculations show that the S_2 state decay of oxazole is an ultrafast process characterized by the ring-opening and ring-closure of the five-membered oxazole ring, in which the triplet contribution is minor. The ring-opening involves the O−C bond cleavage affording the nitrile ylide and airine intermediates, while the ring-closure gives rise to a bicyclic species through a 2−5 bond formation. The azirine and bicyclic intermediates in the S_0 state are very likely involved in the phototranspositions of oxazoles. This is different from the previous mechanism in which these intermediates in the T_1 state have been proposed for these phototranspositions.

  6. Excited-state dynamics of oxazole: A combined electronic structure calculations and dynamic simulations study

    Energy Technology Data Exchange (ETDEWEB)

    Cao, Jun [Guizhou Provincial Key Laboratory of Computational Nano-material Science, Guizhou Education University, Guiyang, Guizhou 550018 (China); Guizhou Synergetic Innovation Center of Scientific Big Data for Advanced Manufacturing Technology, Guizhou Education University, Guiyang 550018 (China); Key Laboratory of Theoretical and Computational Photochemistry, Ministry of Education, College of Chemistry, Beijing Normal University, Beijing 100875 (China); Xie, Zhi-Zhong [Department of Chemistry, School of Chemistry, Chemical Engineering and Life Sciences, Wuhan University of Technology, Wuhan 430070 (China); Yu, Xiaodong, E-mail: yuxdhy@163.com [Department of Architecture and Chemical Engineering, Tangshan Polytechnic College, Tangshan 063020 (China)

    2016-08-02

    In the present work, the combined electronic structure calculations and surface hopping simulations have been performed to investigate the excited-state decay of the parent oxazole in the gas phase. Our calculations show that the S{sub 2} state decay of oxazole is an ultrafast process characterized by the ring-opening and ring-closure of the five-membered oxazole ring, in which the triplet contribution is minor. The ring-opening involves the O−C bond cleavage affording the nitrile ylide and airine intermediates, while the ring-closure gives rise to a bicyclic species through a 2−5 bond formation. The azirine and bicyclic intermediates in the S{sub 0} state are very likely involved in the phototranspositions of oxazoles. This is different from the previous mechanism in which these intermediates in the T{sub 1} state have been proposed for these phototranspositions.

  7. Dual fluorescence of excited state intra-molecular proton transfer of HBFO: mechanistic understanding, substituent and solvent effects.

    Science.gov (United States)

    Yang, Wenjing; Chen, Xuebo

    2014-03-07

    A combined approach of the multiconfigurational perturbation theory with the Rice-Ramsperger-Kassel-Marcus methodology has been employed to calculate the minimum potential energy profiles and the rates of excited state intra-molecular proton transfer (ESIPT) for the WOLED material molecule of HBFO and its four meta- or para-substituted compounds in gas phase, acetonitrile and cyclohexane solvents. The kinetic control for these reactions is quantitatively determined and extensively studied on the basis of the accurate potential energy surfaces when the thermodynamic factor associated with the free energy change becomes negligible in the case of the existence of a significant barrier in the ESIPT process. These computational efforts contribute to a deep understanding of the ESIPT mechanism, dual emission characteristics, kinetic controlling factor, substituent and solvent effects for these material molecules. The white light emission is generated by the establishment of dynamic equilibrium between enol and keto forms in the charge transfer excited SCT((1)ππ*) state. The performance of white light emission is quantitatively demonstrated to be mainly sensitive to the molecular tailoring approach of the electronic properties of meta- or para- substituents by the modulation of the forward/backward ESIPT rate ratio. The quality of white light emission is slightly tunable through its surrounding solvent environment. These computational results will provide a useful strategy for the molecular design of OLED and WOLED materials.

  8. Excited states v.6

    CERN Document Server

    Lim, Edward C

    1982-01-01

    Excited States, Volume 6 is a collection of papers that discusses the excited states of molecules. The first paper discusses the linear polyene electronic structure and potential surfaces, considering both the theoretical and experimental approaches in such electronic states. This paper also reviews the theory of electronic structure and cites some experimental techniques on polyene excitations, polyene spectroscopic phenomenology, and those involving higher states of polyenes and their triplet states. Examples of these experimental studies of excited states involve the high-resolution one-pho

  9. New Theoretical Developments in Exploring Electronically Excited States: Including Localized Configuration Interaction Singles and Application to Large Helium Clusters

    Science.gov (United States)

    Closser, Kristina Danielle

    This thesis presents new developments in excited state electronic structure theory. Contrasted with the ground state, the electronically excited states of atoms and molecules often are unstable and have short lifetimes, exhibit a greater diversity of character and are generally less well understood. The very unusual excited states of helium clusters motivated much of this work. These clusters consist of large numbers of atoms (experimentally 103--109 atoms) and bands of nearly degenerate excited states. For an isolated atom the lowest energy excitation energies are from 1s → 2s and 1s → 2 p transitions, and in clusters describing the lowest energy band minimally requires four states per atom. In the ground state the clusters are weakly bound by van der Waals interactions, however in the excited state they can form well-defined covalent bonds. The computational cost of quantum chemical calculations rapidly becomes prohibitive as the size of the systems increase. Standard excited-state methods such as configuration interaction singles (CIS) and time-dependent density functional theory (TD-DFT) can be used with ≈100 atoms, and are optimized to treat only a few states. Thus, one of our primary aims is to develop a method which can treat these large systems with large numbers of nearly degenerate excited states. Additionally, excited states are generally formed far from their equilibrium structures. Vertical excitations from the ground state induce dynamics in the excited states. Thus, another focus of this work is to explore the results of these forces and the fate of the excited states. Very little was known about helium cluster excited states when this work began, thus we first investigated the excitations in small helium clusters consisting of 7 or 25 atoms using CIS. The character of these excited states was determined using attachment/detachment density analysis and we found that in the n = 2 manifold the excitations could generally be interpreted as

  10. Modeling of charge-transfer transitions and excited states in d6 transition metal complexes by DFT techniques

    Czech Academy of Sciences Publication Activity Database

    Vlček, Antonín; Záliš, Stanislav

    2007-01-01

    Roč. 251, 3-4 (2007), s. 258-287 ISSN 0010-8545 R&D Projects: GA MŠk 1P05OC068; GA MŠk OC 139 Institutional research plan: CEZ:AV0Z40400503 Keywords : charge-transfer transition * DFT technique * excited states * spectroscopy Subject RIV: CG - Electrochemistry Impact factor: 8.568, year: 2007

  11. Excited-state structure and electronic dephasing time of Nile blue from absolute resonance Raman intensities

    Science.gov (United States)

    Lawless, Mary K.; Mathies, Richard A.

    1992-06-01

    Absolute resonance Raman cross sections are measured for Nile blue 690 perchlorate dissolved in ethylene glycol with excitation at 514, 531, and 568 nm. These values and the absorption spectrum are modeled using a time-dependent wave packet formalism. The excited-state equilibrium geometry changes are quantitated for 40 resonance Raman active modes, seven of which (590, 1141, 1351, 1429, 1492, 1544, and 1640 cm-1 ) carry 70% of the total resonance Raman intensity. This demonstrates that in addition to the prominent 590 and 1640 cm-1 modes, a large number of vibrational degrees of freedom are Franck-Condon coupled to the electronic transition. After exposure of the explicit vibrational progressions, the residual absorption linewidth is separated into its homogeneous [350 cm-1 half-width at half-maximum (HWHM)] and inhomogeneous (313 cm-1 HWHM) components through an analysis of the absolute Raman cross sections. The value of the electronic dephasing time derived from this study (25 fs) compares well to previously published results. These data should be valuable in multimode modeling of femtosecond experiments on Nile blue.

  12. Vibrational spectroscopy of the electronically excited state. 4. Nanosecond and picosecond time-resolved resonance Raman spectroscopy of carotenoid excited states

    International Nuclear Information System (INIS)

    Dallinger, R.F.; Farquharson, S.; Woodruff, W.H.; Rodgers, M.A.J.

    1981-01-01

    Resonance Raman and electronic absorption spectra are reported for the S 0 and T 1 states of the carotenoids β-carotene, zeaxanthin, echinenone, canthaxanthin, dihydroxylycopene, astaxanthin, decapreno(C 50 )-β-carotene, β-apo-8'-carotenal, and ethyl β-apo-8'-carotenoate. The results reveal qualitatively similar ground-state spectra and similar frequency shifts in all observed resonance Raman modes between S 0 and T 1 , regardless of carotenoid structure. Examinations of the relationship of the putative C--C and C==C frequencies in S 0 and T 1 reveals anomalous shifts to lower frequency in the ''single-bond'' mode upon electronic excitation. These shifts may be due to molecular distortions in the excited state which force changes in molecular motions comprising the observed modes. However, another possibility requiring no distortion is that the interaction (off-diagonal) force constants connecting the C--C and C==C modes change sign upon electronic excitation. This latter phenomenon may provide a unitary explanation for the ''anomalous'' frequency shifts in the C--C and C==C modes, both in the T 1 states of carotenoids and in the S 1 states of simpler polyenes, without postulating large, unpredicted structural changes upon excitation or general errors in existing vibrational or theoretical analyses. Resonance Raman and absorbance studies with 35-ps time resolution suggest that S 1 lifetime (of the 1 B/sub u/ and/or the 1 A/sub g/* states) of β-carotene in benzene is less than 1 ps

  13. Excited states 2

    CERN Document Server

    Lim, Edward C

    2013-01-01

    Excited States, Volume 2 is a collection of papers that deals with molecules in the excited states. The book describes the geometries of molecules in the excited electronic states. One paper describes the geometries of a diatomic molecule and of polyatomic molecules; it also discusses the determination of the many excited state geometries of molecules with two, three, or four atoms by techniques similar to diatomic spectroscopy. Another paper introduces an ordered theory related to excitons in pure and mixed molecular crystals. This paper also presents some experimental data such as those invo

  14. On the importance of excited state dynamic response electron correlation in polarizable embedding methods.

    Science.gov (United States)

    Eriksen, Janus J; Sauer, Stephan P A; Mikkelsen, Kurt V; Jensen, Hans J Aa; Kongsted, Jacob

    2012-09-30

    We investigate the effect of including a dynamic reaction field at the lowest possible ab inito wave function level of theory, namely the Hartree-Fock (HF) self-consistent field level within the polarizable embedding (PE) formalism. We formulate HF based PE within the linear response theory picture leading to the PE-random-phase approximation (PE-RPA) and bridge the expressions to a second-order polarization propagator approximation (SOPPA) frame such that dynamic reaction field contributions are included at the RPA level in addition to the static response described at the SOPPA level but with HF induced dipole moments. We conduct calculations on para-nitro-aniline and para-nitro-phenolate using said model in addition to dynamic PE-RPA and PE-CAM-B3LYP. We compare the results to recently published PE-CCSD data and demonstrate how the cost effective SOPPA-based model successfully recovers a great portion of the inherent PE-RPA error when the observable is the solvatochromic shift. We furthermore demonstrate that whenever the change in density resulting from the ground state-excited state electronic transition in the solute is not associated with a significant change in the electric field, dynamic response contributions formulated at the HF level of theory manage to capture the majority of the system response originating from derivative densities. Copyright © 2012 Wiley Periodicals, Inc.

  15. Development and implementation of theoretical methods for the description of electronically core-excited states

    Energy Technology Data Exchange (ETDEWEB)

    Wenzel, Jan

    2016-03-23

    -cc-series, a mean error of -0.23% ±0.12% for core-excitation energies can be identified at the CVS-ADC(2)-x level for carbon, nitrogen and oxygen K-edge excitations, whereas CVS-ADC(3) exhibits errors of 0.61% ± 0.32%. This is due to fortuitous error compensation of basis set truncation, electron correlation, orbital relaxation and neglect of relativistic effects at the CVS-ADC(2)-x level. Transition moments and spectral features, as well as static dipole moments, are excellently described with both CVS-ADC(2)-x and CVS-ADC(3). Especially the 6-311++G** basis set provides an excellent ratio of accuracy to computational time. Another important topic is the description of orbital relaxation effects. In the scope of this thesis, I show, how these effects are included indirectly within the CVS-ADC approaches. For this purpose, two different descriptors are used, i.e. electron promotion numbers and the amount of doubly excited amplitudes. Furthermore, with the help of detachment/attachment (D/A) densities, which can be constructed via the CVS-ISR approach, relaxation effects can be visualized. For this purpose, the (D/A) densities are compared with hole/electron (h/e) densities based on the transition density matrix. With this knowledge, the X-ray absorption spectra of medium-sized molecules and radicals from the fields of organic electronics and biology are investigated and analyzed. On the basis of these studies, the restricted and unrestricted versions of CVS-ADC(2)-x in combination with the 6-311++G** basis set exhibit mean errors of core-excitation energies around 0.1%, compared to experimental values. Additionally, core-excited state characters are analyzed with the help of state densities obtained via the CVS-ISR approach or the transition density matrix. To demonstrate the computational savings as a function of the size of the core space, several systems are investigated. CVS-ADC(3) calculations take about 8-10 times longer than CVS-ADC(2)-x calculations and since the

  16. Solvent-dependent excited-state hydrogen transfer and intersystem crossing in 2-(2′-hydroxyphenyl)-benzothiazole

    KAUST Repository

    Aly, Shawkat Mohammede

    2015-02-12

    The excited-state intramolecular hydrogen transfer (ESIHT) of 2-(2′-hydroxyphenyl) benzothiazole (HBT) has been investigated in a series of nonpolar, polar aprotic, and polar protic solvents. A variety of state-of-the-art experimental methods were employed, including femto- and nanosecond transient absorption and fluorescence upconversion spectroscopy with broadband capabilities. We show that the dynamics and mechanism of ESIHT of the singlet excited HBT are strongly solvent-dependent. In nonpolar solvents, the data demonstrate that HBT molecules adopt a closed form stabilized by O-H⋯N chelated hydrogen bonds with no twisting angle, and the photoinduced H transfer occurs within 120 fs, leading to the formation of a keto tautomer. In polar solvents, owing to dipole-dipole cross talk and hydrogen bonding interactions, the H transfer process is followed by ultrafast nonradiative deactivation channels, including ultrafast internal conversion (IC) and intersystem crossing (ISC). This is likely to be driven by the twisting motion around the C-C bond between the hydroxyphenyl and thiazole moieties, facilitating the IC back to the enol ground state or to the keto triplet state. In addition, our femtosecond time-resolved fluorescence experiments indicate, for the first time, that the lifetime of the enol form in ACN is approximately 280 fs. This observation indicates that the solvent plays a crucial role in breaking the H bond and deactivating the excited state of the HBT. Interestingly, the broadband transient absorption and fluorescence up-conversion data clearly demonstrate that the intermolecular proton transfer from the excited HBT to the DMSO solvent is about 190 fs, forming the HBT anion excited state.

  17. Solvent-dependent excited-state hydrogen transfer and intersystem crossing in 2-(2′-hydroxyphenyl)-benzothiazole

    KAUST Repository

    Aly, Shawkat Mohammede; Usman, Anwar; Alzayer, Maytham; Hamdi, Ghada A.; Alarousu, Erkki; Mohammed, Omar F.

    2015-01-01

    The excited-state intramolecular hydrogen transfer (ESIHT) of 2-(2′-hydroxyphenyl) benzothiazole (HBT) has been investigated in a series of nonpolar, polar aprotic, and polar protic solvents. A variety of state-of-the-art experimental methods were employed, including femto- and nanosecond transient absorption and fluorescence upconversion spectroscopy with broadband capabilities. We show that the dynamics and mechanism of ESIHT of the singlet excited HBT are strongly solvent-dependent. In nonpolar solvents, the data demonstrate that HBT molecules adopt a closed form stabilized by O-H⋯N chelated hydrogen bonds with no twisting angle, and the photoinduced H transfer occurs within 120 fs, leading to the formation of a keto tautomer. In polar solvents, owing to dipole-dipole cross talk and hydrogen bonding interactions, the H transfer process is followed by ultrafast nonradiative deactivation channels, including ultrafast internal conversion (IC) and intersystem crossing (ISC). This is likely to be driven by the twisting motion around the C-C bond between the hydroxyphenyl and thiazole moieties, facilitating the IC back to the enol ground state or to the keto triplet state. In addition, our femtosecond time-resolved fluorescence experiments indicate, for the first time, that the lifetime of the enol form in ACN is approximately 280 fs. This observation indicates that the solvent plays a crucial role in breaking the H bond and deactivating the excited state of the HBT. Interestingly, the broadband transient absorption and fluorescence up-conversion data clearly demonstrate that the intermolecular proton transfer from the excited HBT to the DMSO solvent is about 190 fs, forming the HBT anion excited state.

  18. Single-electron capture into Ar+ excited states in Ar2 + Na collision below 12 keV, 1

    International Nuclear Information System (INIS)

    Matsumoto, Atsushi; Tsurubuchi, Seiji; Okuno, Kazuhiko; Ohtani, Shunsuke; Iwai, Tsuruji.

    1979-08-01

    Emission spectra between 2800 and 6000 A have been observed at the ionic energies from 0.2 to 12 keV. Absolute measurements of emission cross-sections have been made for the emission lines coming from ArII excited states at 4 and 8 keV with a crossed-beam technique. Processes of single-electron capture into the ArII 4p- and 4p'-states, with exothermicity of a few eV, take place dominantly (--10 15 cm 2 ), while the endothermic processes producing ArII in the 4d- and 5s-states occur with small cross-sections. Sum of the cross-sections for electron capture into the excited states observed is comparable with the total single-electron capture cross-section estimated from attenuation measurements of ion currents. Possible errors and uncertainties are discussed. (author)

  19. Single-electron capture into Ar+ excited states in Ar2++Na collision below 12 keV, 1

    International Nuclear Information System (INIS)

    Matsumoto, Atsushi; Tsurubuchi, Seiji; Iwai, Tsuruji; Ohtani, Shunsuke; Okuno, Kazuhiko

    1980-01-01

    Emission spectra between 2800 and 6000 A have been observed at the ionic energies from 0.2 to 12 keV. Absolute measurements of emission cross-sections have been made for the emission lines coming from ArII excited states at 4 and 8 keV with a crossed-beam technique. Processes of single-electron capture into the ArII 4p- and 4p'-states, with exothermicity of a few eV, take place dominantly (--10 -15 cm 2 ), while the endothermic processes producing ArII in the 4d- and 5s-states occur with small cross-sections. Sum of the cross-sections for electron capture into the excited states observed is comparable with the total single-electron capture cross-section estimated from attenuation measurements of ion currents. Possible errors and uncertainties are discussed. (author)

  20. Excited state kinetics of anthracene-bridge-aniline intramolecular exciplexes

    DEFF Research Database (Denmark)

    Thyrhaug, Erling; Hammershøj, Peter; Kjær, Kasper Skov

    2014-01-01

    excited anthracene state (LE) and an excited state complex (exciplex, EP) in non-polar solvents. The kinetics of the excited state processes were established in decalin from the time-resolved emission, and was shown to be strongly influenced by an electron-transfer state (ET). For quantitative studies...

  1. The electronic structure of VO in its ground and electronically excited states: A combined matrix isolation and quantum chemical (MRCI) study

    International Nuclear Information System (INIS)

    Hübner, Olaf; Hornung, Julius; Himmel, Hans-Jörg

    2015-01-01

    The electronic ground and excited states of the vanadium monoxide (VO) molecule were studied in detail. Electronic absorption spectra for the molecule isolated in Ne matrices complement the previous gas-phase spectra. A thorough quantum chemical (multi-reference configuration interaction) study essentially confirms the assignment and characterization of the electronic excitations observed for VO in the gas-phase and in Ne matrices and allows the clarification of open issues. It provides a complete overview over the electronically excited states up to about 3 eV of this archetypical compound

  2. From fusion hierarchy to excited state TBA

    International Nuclear Information System (INIS)

    Juettner, G.; Kluemper, A.

    1998-01-01

    Functional relations among the fusion hierarchy of quantum transfer matrices give a novel derivation of the TBA equations, namely without string hypothesis. This is demonstrated for two important models of 1D highly correlated electron systems, the supersymmetric t-J model and the supersymmetric extended Hubbard model. As a consequence, ''the excited state TBA'' equations, which characterize correlation lengths, are explicitly derived for the t-J model. To the authors' knowledge, this is the first explicit derivation of excited state TBA equations for 1D lattice electron systems. (orig.)

  3. Excited state proton transfer in strongly enhanced GFP (sGFP2)

    NARCIS (Netherlands)

    van Oort, B.F.; ter Veer, M.J.T.; Groot, M.L.; van Stokkum, I.H.M.

    2012-01-01

    Proton transfer is an elementary process in biology. Green fluorescent protein (GFP) has served as an important model system to elucidate the mechanistic details of this reaction, because in GFP proton transfer can be induced by light absorption. We have used pump-dump-probe spectroscopy to study

  4. Excited state proton transfer in strongly enhanced GFP (sGFP2).

    Science.gov (United States)

    van Oort, Bart; ter Veer, Mirelle J T; Groot, Marie Louise; van Stokkum, Ivo H M

    2012-07-07

    Proton transfer is an elementary process in biology. Green fluorescent protein (GFP) has served as an important model system to elucidate the mechanistic details of this reaction, because in GFP proton transfer can be induced by light absorption. We have used pump-dump-probe spectroscopy to study how proton transfer through the 'proton-wire' around the chromophore is affected by a combination of mutations in a modern GFP variety (sGFP2). The results indicate that in H(2)O, after absorption of a photon, a proton is transferred (A* → I*) in 5 ps, and back-transferred from a ground state intermediate (I → A) in 0.3 ns, similar to time constants found with GFPuv, although sGFP2 shows less heterogeneous proton transfer. This suggests that the mutations left the proton-transfer largely unchanged, indicating the robustness of the proton-wire. We used pump-dump-probe spectroscopy in combination with target analysis to probe suitability of the sGFP2 fluorophore for super-resolution microscopy.

  5. The population transfer of high excited states of Rydberg lithium atoms in a microwave field

    International Nuclear Information System (INIS)

    Jiang Lijuan; Zhang Xianzhou; Ma Huanqiang; Jia Guangrui; Zhang Yonghui; Xia Lihua

    2012-01-01

    Using the time-dependent multilevel approach (TDMA), the properties of high excited Rydberg lithium atom have been obtained in the microwave field. The population transfer of lithium atom are studied on numerical calculation, quantum states are controlled and manipulated by microwave field. It shows that the population can be completely transferred to the target state by changing the chirped rate and field amplitude. (authors)

  6. Experimental test of a four-level kinetic model for excited-state intramolecular proton transfer dye lasers

    Energy Technology Data Exchange (ETDEWEB)

    Costela, A; Munnoz, J M; Douhal, A; Figuera, J M; Acuna, A U [Inst. de Quimica Fisica ' ' Rocasolano' ' , C.S.I.C., Madrid (Spain)

    1989-11-01

    The nanosecond pulses of a dye laser oscillator based on the excited-state intramolecular proton-transfer reaction (IPT) of salicylamide and 2'-hydroxylphenyl benzimidazole dyes have been studied as a function of several experimental parameters. To explain the operation of this laser a numerical four-level kinetic model was developed until the lasing properties of these dyes, in the presence of a variable oxygen concentration and pumped with a double pulse technique, could be reproduced. This was possible only by assuming that the efficiency of the laser is controlled by the absorption cross-section of a transient state with a lifetime in the nanosecond-picosecond range, which was tentatively identified as a ground state tautomeric species. (orig.).

  7. Dynamics of excited-state intramolecular proton transfer reactions in piroxicam. Role of triplet states

    Science.gov (United States)

    Cho, Dae Won; Kim, Yong Hee; Yoon, Minjoong; Jeoung, Sae Chae; Kim, Dongho

    1994-08-01

    The picosecond time-resolved fluorescence and transient absorption behavior of piroxicam at room temperature are reported. The keto tautomer in the excited singlet state ( 1K*) formed via the fast intramolecular proton transfer (≈ 20 ps) is observed. The short-lived (7.5 ns) triplet state of keto tauomer ( 3K*) is generated from 1K * in toluene whereas it is hardly observed in ethanol. Consequently, rapid reverse proton transfer takes place from 3K * to the enol triplet state ( 3E *.

  8. Correlation among Singlet-Oxygen Quenching, Free-Radical Scavenging, and Excited-State Intramolecular-Proton-Transfer Activities in Hydroxyflavones, Anthocyanidins, and 1-Hydroxyanthraquinones.

    Science.gov (United States)

    Nagaoka, Shin-Ichi; Bandoh, Yuki; Nagashima, Umpei; Ohara, Keishi

    2017-10-26

    Singlet-oxygen ( 1 O 2 ) quenching, free-radical scavenging, and excited-state intramolecular proton-transfer (ESIPT) activities of hydroxyflavones, anthocyanidins, and 1-hydroxyanthraquinones were studied by means of laser, stopped-flow, and steady-state spectroscopies. In hydroxyflavones and anthocyanidins, the 1 O 2 quenching activity positively correlates to the free-radical scavenging activity. The reason for this correlation can be understood by considering that an early step of each reaction involves electron transfer from the unfused phenyl ring (B-ring), which is singly bonded to the bicyclic chromen or chromenylium moiety (A- and C-rings). Substitution of an electron-donating OH group at B-ring enhances the electron transfer leading to activation of the 1 O 2 quenching and free-radical scavenging. In 3-hydroxyflavones, the OH substitution at B-ring reduces the activity of ESIPT within C-ring, which can be explained in terms of the nodal-plane model. As a result, the 1 O 2 quenching and free-radical scavenging activities negatively correlate to the ESIPT activity. A catechol structure at B-ring is another factor that enhances the free-radical scavenging in hydroxyflavones. In contrast to these hydroxyflavones, 1-hydroxyanthraquinones having an electron-donating OH substituent adjacent to the O-H---O═C moiety susceptible to ESIPT do not show a simple correlation between their 1 O 2 quenching and ESIPT activities, because the OH substitution modulates these reactions.

  9. Simulations of the dissociation of small helium clusters with ab initio molecular dynamics in electronically excited states

    International Nuclear Information System (INIS)

    Closser, Kristina D.; Head-Gordon, Martin; Gessner, Oliver

    2014-01-01

    The dynamics resulting from electronic excitations of helium clusters were explored using ab initio molecular dynamics. The simulations were performed with configuration interaction singles and adiabatic classical dynamics coupled to a state-following algorithm. 100 different configurations of He 7 were excited into the 2s and 2p manifold for a total of 2800 trajectories. While the most common outcome (90%) was complete fragmentation to 6 ground state atoms and 1 excited state atom, 3% of trajectories yielded bound, He 2 * , and <0.5% yielded an excited helium trimer. The nature of the dynamics, kinetic energy release, and connections to experiments are discussed

  10. Participation of electronic excited states in the positronium formation mechanism in the Gd(III) pentakis (picrate) complexes with imidazolium countercations

    Energy Technology Data Exchange (ETDEWEB)

    Fulgêncio, F., E-mail: fefulgencio@gmail.com [Departam ento de Química – ICEx Universidade Federal de Minas Gerais – UFMG, Belo Horizonte, MG (Brazil); Borges, A.S. [Coordenadoria de Química e Biologia – Instituto Federal do Espírito Santos – IFES, Campus Vitória, ES (Brazil); Araújo, M.H. [Departam ento de Química – ICEx Universidade Federal de Minas Gerais – UFMG, Belo Horizonte, MG (Brazil); Brito, H.F. [Instituto de Química, Departamento de Química Fundamental, Universidade de São Paulo, São Paulo (Brazil); Oliveira, F.C. [Departamento de Metalurgia e Química, Centro Federal de Educação Tecnológica de Minas Gerais – CEFET-MG, Campus Timóteo, MG (Brazil); Ribeiro, T.; Windmöller, D. [Departam ento de Química – ICEx Universidade Federal de Minas Gerais – UFMG, Belo Horizonte, MG (Brazil); Magalhães, W.F., E-mail: welmag@ufmg.br [Departam ento de Química – ICEx Universidade Federal de Minas Gerais – UFMG, Belo Horizonte, MG (Brazil)

    2016-02-15

    In this work, positron annihilation lifetime (PALS) and optical spectroscopies measurements were performed on [Gd(pic){sub 2}(H{sub 2}O){sub 6}](pic)·6H{sub 2}O and on complexes of general formula C{sub 2}[Gd(pic){sub 5}], where pic corresponds to picrate ligands and C to the countercations butyl-methyl, hexyl-methyl, butyl-ethyl and butyl-butyl imidazoles. Since all of these complexes have high energy ligand-to-metal charge transfer states (LMCTS) but form low amounts of Positronium (Ps), the LMCTS do not act here as a mechanism that suppress luminescence nor prevents Ps formation. This result suggests that, besides LMCTS, other effects should also contribute to prevent Ps formation. The results indicate that the electron withdrawing –NO{sub 2} groups in the picrate ligand are responsible by the effect that prevents Ps formation. Also, a rough correlation between the ligands' triplet states lifetimes and Ps formation was observed. The insertion of electron donor groups (the imidazolium countercations) increased the ligands' first triplet excited states ({sup 3}π{sup ⁎}) lifetimes and Ps formation, indicating that these two spectroscopic parameters are correlated. Also, it is demonstrated that there is no clear correlation between Ps formation probability and the excitation energy of the ligands' first triplet excited states. The results were discussed in terms of the recently proposed Ps formation mechanism, named cybotactic correlated system kinetic mechanism (CCSKM), showing that the Ps formation process involves molecular excited states and is kinetically controlled. - Highlights: • PALS and optical spectroscopies measurements performed on Gd{sup 3+} complexes. • A correlation was obtained between the ligands' {sup 3}π{sup ⁎} lifetimes and Ps formation. • Electronegative groups increased the ligands' {sup 3}π{sup ⁎} lifetimes and Ps formation. • Results discussed in terms of a new Ps formation mechanism (ccskm).

  11. Advances in electron transfer chemistry

    CERN Document Server

    Mariano, Patrick S

    1995-01-01

    Advances in Electron Transfer Chemistry, Volume 4 presents the reaction mechanisms involving the movement of single electrons. This book discusses the electron transfer reactions in organic, biochemical, organometallic, and excited state systems. Organized into four chapters, this volume begins with an overview of the photochemical behavior of two classes of sulfonium salt derivatives. This text then examines the parameters that control the efficiencies for radical ion pair formation. Other chapters consider the progress in the development of parameters that control the dynamics and reaction p

  12. Encapsulation of 3-hydroxyflavone and fisetin in β-cyclodextrins: Excited state proton transfer fluorescence and molecular mechanics studies

    Science.gov (United States)

    Banerjee, Anwesha; Sengupta, Pradeep K.

    2006-06-01

    Excited-state intramolecular proton-transfer (ESIPT) and dual emission properties (emission profile, anisotropy and decay kinetics) of 3-hydroxyflavone (a synthetic, model flavonol) and fisetin (3,7,3',4'-OH-flavone, a therapeutically active plant flavonol) have been exploited to study their encapsulation in nano-cavities comprising of natural and chemically modified β-cyclodextrins. In the presence of β-CDs, both the flavonols show significantly enhanced relative yields (along with changes in other emission parameters) of the tautomer emission. In addition, for fisetin, large blue shifts are observed for the normal emission (which has significant charge transfer character). From these we infer that the flavonols are encaged in predominantly hydrophobic micro-environments, where external hydrogen bonding perturbations (interfering with the intrinsic ESIPT), and dipolar relaxation effects, are minimized. This is further explained from results of molecular mechanics calculations which indicate selectivity in orientation of the encapsulated flavonols. Moreover, chemical modification of the β-CDs is found to profoundly influence the binding affinities of the guest flavonols.

  13. Multiconfiguration Pair-Density Functional Theory Outperforms Kohn-Sham Density Functional Theory and Multireference Perturbation Theory for Ground-State and Excited-State Charge Transfer.

    Science.gov (United States)

    Ghosh, Soumen; Sonnenberger, Andrew L; Hoyer, Chad E; Truhlar, Donald G; Gagliardi, Laura

    2015-08-11

    The correct description of charge transfer in ground and excited states is very important for molecular interactions, photochemistry, electrochemistry, and charge transport, but it is very challenging for Kohn-Sham (KS) density functional theory (DFT). KS-DFT exchange-correlation functionals without nonlocal exchange fail to describe both ground- and excited-state charge transfer properly. We have recently proposed a theory called multiconfiguration pair-density functional theory (MC-PDFT), which is based on a combination of multiconfiguration wave function theory with a new type of density functional called an on-top density functional. Here we have used MC-PDFT to study challenging ground- and excited-state charge-transfer processes by using on-top density functionals obtained by translating KS exchange-correlation functionals. For ground-state charge transfer, MC-PDFT performs better than either the PBE exchange-correlation functional or CASPT2 wave function theory. For excited-state charge transfer, MC-PDFT (unlike KS-DFT) shows qualitatively correct behavior at long-range with great improvement in predicted excitation energies.

  14. Lie algebraic approach to valence bond theory of π-electron systems: a preliminary study of excited states

    Science.gov (United States)

    Paldus, J.; Li, X.

    1992-10-01

    Following a brief outline of various developments and exploitations of the unitary group approach (UGA), and its extension referred to as Clifford algebra UGA (CAUGA), in molecular electronic structure calculations, we present a summary of a recently introduced implementation of CAUGA for the valence bond (VB) method based on the Pariser-Parr-Pople (PPP)-type Hamiltonian. The existing applications of this PPP-VB approach have been limited to groundstates of various π-electron systems or, at any rate, to the lowest states of a given multiplicity. In this paper the method is applied to the low-lying excited states of several archetypal models, namely cyclobutadiene and benzene, representing antiaromatic and aromatic systems, hexatriene, representing linear polyenic systems and, finally, naphthalene, representing polyacenes.

  15. Molecular structures and excited states of CpM(CO)(2) (Cp = eta(5)-C(5)H(5); M = Rh, Ir) and [Cl(2)Rh(CO)(2)](-). Theoretical evidence for a competitive charge transfer mechanism.

    Science.gov (United States)

    Hu, Zhenming; Boyd, Russell J; Nakatsuji, Hiroshi

    2002-03-20

    Molecular structures and excited states of CpM(CO)(2) (Cp = eta(5)-C(5)H(5); M = Rh, Ir) and [Cl(2)Rh(CO)(2)](-) complexes have been investigated using the B3LYP and the symmetry-adapted cluster (SAC)/SAC-configuration interaction (SAC-CI) theoretical methods. All the dicarbonyl complexes have singlet ground electronic states with large singlet-triplet separations. Thermal dissociations of CO from the parent dicarbonyls are energetically unfavorable. CO thermal dissociation is an activation process for [Cl(2)Rh(CO)(2)](-) while it is a repulsive potential for CpM(CO)(2). The natures of the main excited states of CpM(CO)(2) and [Cl(2)Rh(CO)(2)](-) are found to be quite different. For [Cl(2)Rh(CO)(2)](-), all the strong transitions are identified to be metal to ligand CO charge transfer (MLCT) excitations. A significant feature of the excited states of CpM(CO)(2) is that both MLCT excitation and a ligand Cp to metal and CO charge transfer excitation are strongly mixed in the higher energy states with the latter having the largest oscillator strength. A competitive charge transfer excited state has therefore been identified theoretically for CpRh(CO)(2) and CpIr(CO)(2). The wavelength dependence of the quantum efficiencies for the photoreactions of CpM(CO)(2) reported by Lees et al. can be explained by the existence of two different types of excited states. The origin of the low quantum efficiencies for the C-H/S-H bond activations of CpM(CO)(2) can be attributed to the smaller proportion of the MLCT excitation in the higher energy states.

  16. Excited-state proton transfer of 4-hydroxyl-1, 8-naphthalimide derivatives: A combined experimental and theoretical investigation

    Energy Technology Data Exchange (ETDEWEB)

    Qu, Zongjin; Li, Peng; Zhang, Xuexiang; Wang, Endong; Wang, Yanni; Zhou, Panwang, E-mail: pwzhou@dicp.ac.cn

    2016-09-15

    The photophysical properties of N-butyl-4-hydroxyl-1, 8-naphthalimide (BOH) and N-(morpholinoethyl)−4-hydroxy-1, 8-naphthalimide (MOH) in various solvents are presented and the density functional theory (DFT)/time-dependent density functional theory (TDDFT) methods at the B3LYP/TZVP theoretical level are adopted to investigate the UV–visible absorption and emission data. An efficient intermolecular excited-state proton transfer (ESPT) reaction occurs for both compounds in DMSO, methanol and water. In aqueous solution, both BOH and MOH can be used as ratiometric pH probes and perform as strong photoacids with pKa*=−2.2, −2.4, respectively. Most interestingly, in the steady-state fluorescence spectra of BOH and MOH in concentrated HCl, an unexpected blue-shifted band is observed and assumed to originate from the contact ion pair (CIP) formed by hydronium ion and the anionic form of the photoacid resulted from ESPT. Theoretical calculations are used to simulate the CIP in the case of BOH, which afford reasonable results compared with the experimental data.

  17. A Ratio-Analysis Method to the Dynamics of Excited State Proton Transfer: Pyranine in Water and Micelles.

    Science.gov (United States)

    Sahu, Kalyanasis; Nandi, Nilanjana; Dolai, Suman; Bera, Avisek

    2018-06-05

    Emission spectrum of a fluorophore undergoing excited state proton transfer (ESPT) often exhibits two distinct bands each representing emissions from protonated and deprotonated forms. The relative contribution of the two bands, best represented by an emission intensity ratio (R) (intensity maximum of the protonated band / intensity maximum of the deprotonated band), is an important parameter which usually denotes feasibility or promptness of the ESPT process. However, the use of ratio is only limited to the interpretation of steady-state fluorescence spectra. Here, for the first time, we exploit the time-dependence of the ratio (R(t)), calculated from time-resolved emission spectra (TRES) at different times, to analyze ESPT dynamics. TRES at different times were fitted with a sum of two lognormal-functions representing each peaks and then, the peak intensity ratio, R(t) was calculated and further fitted with an analytical function. Recently, a time-resolved area-normalized emission spectra (TRANES)-based analysis was presented where the decay of protonated emission or the rise of deprotonated emission intensity conveniently accounts for the ESPT dynamics. We show that these two methods are equivalent but the new method provides more insights on the nature of the ESPT process.

  18. CALCULATION OF THE PROTON-TRANSFER RATE USING DENSITY-MATRIX EVOLUTION AND MOLECULAR-DYNAMICS SIMULATIONS - INCLUSION OF THE PROTON EXCITED-STATES

    NARCIS (Netherlands)

    MAVRI, J; BERENDSEN, HJC

    1995-01-01

    The methodology for treatment of proton transfer processes by density matrix evolution (DME) with inclusion of many excited states is presented. The DME method (Berendsen, H. J. C.; Mavri, J. J. Phys. Chem. 1993, 97, 13464) that simulates the dynamics of quantum systems embedded in a classical

  19. Excited-state kinetics of the carotenoid S//1 state in LHC II and two-photon excitation spectra of lutein and beta-carotene in solution Efficient Car S//1 yields Chl electronic energy transfer via hot S//1 states?

    CERN Document Server

    Walla, P J; Linden, Patricia A; Ohta, Kaoru

    2002-01-01

    The excited-state dynamics of the carotenoids (Car) in light- harvesting complex II (LHC II) of Chlamydomonas reinhardtii were studied by transient absorption measurements. The decay of the Car S //1 population ranges from similar to 200 fs to over 7 ps, depending on the excitation and detection wavelengths. In contrast, a 200 fs Car S//1 yields Chlorophyll (Chl) energy transfer component was the dominant time constant for our earlier two-photon fluorescence up- conversion measurements (Walla, P.J. ; et al. J. Phys. Chem. B 2000, 104, 4799-4806). We also present the two-photon excitation (TPE) spectra of lutein and beta-carotene in solution and compare them with the TPE spectrum of LHC II. The TPE-spectrum of LHC II has an onset much further to the blue and a width that is narrower than expected from comparison to the S//1 fluorescence of lutein and beta-carotene in solution. Different environments may affect the shape of the S//1 spectrum significantly. To explain the blue shift of the TPE spectrum and the d...

  20. The triplet excited state of Bodipy: formation, modulation and application.

    Science.gov (United States)

    Zhao, Jianzhang; Xu, Kejing; Yang, Wenbo; Wang, Zhijia; Zhong, Fangfang

    2015-12-21

    Boron dipyrromethene (Bodipy) is one of the most extensively investigated organic chromophores. Most of the investigations are focused on the singlet excited state of Bodipy, such as fluorescence. In stark contrast, the study of the triplet excited state of Bodipy is limited, but it is an emerging area, since the triplet state of Bodipy is tremendously important for several areas, such as the fundamental photochemistry study, photodynamic therapy (PDT), photocatalysis and triplet-triplet annihilation (TTA) upconversion. The recent developments in the study of the production, modulation and application of the triplet excited state of Bodipy are discussed in this review article. The formation of the triplet state of Bodipy upon photoexcitation, via the well known approach such as the heavy atom effect (including I, Br, Ru, Ir, etc.), and the new methods, such as using a spin converter (e.g. C60), charge recombination, exciton coupling and the doubly substituted excited state, are summarized. All the Bodipy-based triplet photosensitizers show strong absorption of visible or near IR light and the long-lived triplet excited state, which are important for the application of the triplet excited state in PDT or photocatalysis. Moreover, the methods for switching (or modulation) of the triplet excited state of Bodipy were discussed, such as those based on the photo-induced electron transfer (PET), by controlling the competing Förster-resonance-energy-transfer (FRET), or the intermolecular charge transfer (ICT). Controlling the triplet excited state will give functional molecules such as activatable PDT reagents or molecular devices. It is worth noting that switching of the singlet excited state and the triplet state of Bodipy may follow different principles. Application of the triplet excited state of Bodipy in PDT, hydrogen (H2) production, photoredox catalytic organic reactions and TTA upconversion were discussed. The challenges and the opportunities in these areas were

  1. Excited state intramolecular charge transfer reaction in binary mixtures of water and tertiary butanol (TBA): alcohol mole fraction dependence.

    Science.gov (United States)

    Pradhan, Tuhin; Ghoshal, Piue; Biswas, Ranjit

    2008-02-07

    The excited state intramolecular charge transfer reaction of 4-(1-azetidinyl)benzonitrile (P4C) has been studied in water-tertiary butanol (TBA) mixtures at different alcohol mole fractions by using steady state and time-resolved fluorescence spectroscopy. The ratio between the areas under the locally excited (LE) and charge transferred (CT) emission bands is found to exhibit a sharp rise at alcohol mole fraction approximately 0.04, a value at which several thermodynamic properties of this mixture is known to show anomalous change due to the enhancement of H-bonding network. The radiative rate associated with the LE emission also shows a maximum at this TBA mole fraction. Although the structural transition from the water-like tetrahedral network to the alcohol-like chain is reflected in the red shift of the absorption spectrum up to TBA mole fraction approximately 0.10, the emission bands (both LE and CT) show the typical nonideal alcohol mole fraction dependence at all TBA mole fractions. Quantum yield, CT radiative rate as well as transition moments also exhibit a nonideal alcohol mole fraction dependence. The time-resolved emission decay of P4C has been found to be biexponential at all TBA mole fractions, regardless of emission collection around either the LE or the CT bands. The time constant associated with the slow component (tau(slow)) shows a minimum at TBA mole fraction approximately 0.04, whereas such a minimum for the fast time constant, tau(fast) (representing the rate of LE --> CT conversion reaction) is not observed. The nonobservation of the minimum in tau(fast) might be due to the limited time resolution employed in our experiments.

  2. Transient Exciplex Formation Electron Transfer Mechanism

    OpenAIRE

    Michael G. Kuzmin; Irina V. Soboleva; Elena V. Dolotova

    2011-01-01

    Transient exciplex formation mechanism of excited-state electron transfer reactions is analyzed in terms of experimental data on thermodynamics and kinetics of exciplex formation and decay. Experimental profiles of free energy, enthalpy, and entropy for transient exciplex formation and decay are considered for several electron transfer reactions in various solvents. Strong electronic coupling in contact pairs of reactants causes substantial decrease of activation energy relative to that for c...

  3. Ab initio structural and electronic properties of hydrogenated silicon nanoclusters in the ground and excited state

    International Nuclear Information System (INIS)

    Degoli, Elena; Bisi, O.; Ossicini, Stefano; Cantele, G.; Ninno, D.; Luppi, Eleonora; Magri, Rita

    2004-01-01

    Electronic and structural properties of small hydrogenated silicon nanoclusters as a function of dimension are calculated from ab initio technique. The effects induced by the creation of an electron-hole pair are discussed in detail, showing the strong interplay between the structural and optical properties of the system. The distortion induced on the structure after an electronic excitation of the cluster is analyzed together with the role of the symmetry constraint during the relaxation. We point out how the overall effect is that of significantly changing the electronic spectrum if no symmetry constraint is imposed to the system. Such distortion can account for the Stokes shift and provides a possible structural model to be linked to the four-level scheme invoked in the literature to explain recent results for the optical gain in silicon nanoclusters. Finally, formation energies for clusters with increasing dimension are calculated and their relative stability discussed

  4. The Role of Electronically Excited States and Free Radicals in Ultraviolet-Induced Lens Opacification.

    Science.gov (United States)

    1980-12-01

    of a noncrystallin protein. It has a molecular weight of 14,400 ± 100 and is found in tears, nasal mucus , milk , saliva, and blood serum and is known...electron spin resonance (EPR) can be found in an article by Yamanashi et al. (33). This recent paper describes the EPR-monitored wavelength depen- dence of

  5. Hot-electron-mediated desorption rates calculated from excited-state potential energy surfaces

    DEFF Research Database (Denmark)

    Olsen, Thomas; Gavnholt, Jeppe; Schiøtz, Jakob

    2009-01-01

    We present a model for desorption induced by (multiple) electronic transitions [DIET (DIMET)] based on potential energy surfaces calculated with the delta self-consistent field extension of density-functional theory. We calculate potential energy surfaces of CO and NO molecules adsorbed on variou...

  6. Electronically excited states of vitamin B12 and methylcobalamin: theoretical analysis of absorption, CD, and MCD data.

    Science.gov (United States)

    Solheim, Harald; Kornobis, Karina; Ruud, Kenneth; Kozlowski, Pawel M

    2011-02-03

    Linear and quadratic response time-dependent density functional theory (TD-DFT) has been applied to investigate absorption (Abs), circular dichroism (CD), and magnetic CD (MCD) spectra of cyanocobalamin (CNCbl) and methylcobalamin (MeCbl). Although electronically excited states of both cobalamins have been probed by applying different experimental techniques, their exact nature remains poorly understood from an electronic structure point of view. Recent theoretical studies have revealed a lot of relevant information about their properties but also left some unresolved issues related to the nature of individual transitions. In this contribution, not only Abs but also CD and MCD spectra of both cobalamins were computed for direct comparison with experiment. The results were evaluated with respect to the choice of exchange-correlation functional, basis set, and the environment (gas phase or solvent) used in the calculation. Taking into account the complexity of the CNCbl and MeCbl systems, reliable agreement between theory and experiment was achieved based on calculations employing the BP86 functional, particularly for the low-energy α/β bands. This spectral range has been traditionally interpreted as a vibrational progression associated with a single electronic excitation, but according to the present analysis for both cobalamins, these bands are best interpreted as consisting of multiple electronic transitions.

  7. Numerology, hydrogenic levels, and the ordering of excited states in one-electron atoms

    Science.gov (United States)

    Armstrong, Lloyd, Jr.

    1982-03-01

    We show that the observed ordering of Rydberg states of one-electron atoms can be understood by assuming that these states are basically hydrogenic in nature. Much of the confusion concerning this point is shown to arise from the failure to differentiate between hydrogenic ordering as the nuclear charge approaches infinity, and hydrogenic ordering for an effective charge of one. The origin of κ ordering of Rydberg levels suggested by Sternheimer is considered within this picture, and the predictions of κ ordering are compared with those obtained by assuming hydrogenic ordering.

  8. Electronic excited states as a probe of surface adsorbate structure and dynamics in liquid xenon

    Energy Technology Data Exchange (ETDEWEB)

    Peterson, E.S.

    1992-08-01

    A combination of second harmonic generation (SHG) and a simple dipole-dipole interaction model is presented as a new technique for determining adsorbate geometries on surfaces. The polarization dependence of SHG is used to define possible geometries of the adsorbate about the surface normal. Absorption band shifts using geometry constraints imposed by SHG data are derived for a dimer constructed from two arbitrarily placed monomers on the surface using the dipole-dipole interaction potential. These formulae can be used to determine the orientation of the two monomers relative to each other. A simplified version of this formalism is used to interpret absorption band shifts for rhodamine B adsorbed on fused silica. A brief history of the exciton is given with particular detail to Xe. Data are presented for transient absorption at RT in liquid xenon on the picosecond time scale. These are observations of both tunneling through the barrier that separates the free and trapped exciton states and the subsequent trapping of the exciton. In high densities both of these processes are found to occur within 2 to 6 picoseconds in agreement with theories of Kmiecik and Schreiber and of Martin. A threshold density is observed that separates relaxation via single binary collisions and relaxation that proceeds via Martin's resonant energy transfer hopping mechanism.

  9. Electronic excited states as a probe of surface adsorbate structure and dynamics in liquid xenon

    Energy Technology Data Exchange (ETDEWEB)

    Peterson, Eric Scott [Univ. of California, Berkeley, CA (United States)

    1992-08-01

    A combination of second harmonic generation (SHG) and a simple dipole-dipole interaction model is presented as a new technique for determining adsorbate geometries on surfaces. The polarization dependence of SHG is used to define possible geometries of the adsorbate about the surface normal. Absorption band shifts using geometry constraints imposed by SHG data are derived for a dimer constructed from two arbitrarily placed monomers on the surface using the dipole-dipole interaction potential. These formulae can be used to determine the orientation of the two monomers relative to each other. A simplified version of this formalism is used to interpret absorption band shifts for rhodamine B adsorbed on fused silica. A brief history of the exciton is given with particular detail to Xe. Data are presented for transient absorption at RT in liquid xenon on the picosecond time scale. These are observations of both tunneling through the barrier that separates the free and trapped exciton states and the subsequent trapping of the exciton. In high densities both of these processes are found to occur within 2 to 6 picoseconds in agreement with theories of Kmiecik and Schreiber and of Martin. A threshold density is observed that separates relaxation via single binary collisions and relaxation that proceeds via Martin`s resonant energy transfer hopping mechanism.

  10. Photoinduced Ultrafast Intramolecular Excited-State Energy Transfer in the Silylene-Bridged Biphenyl and Stilbene (SBS) System: A Nonadiabatic Dynamics Point of View.

    Science.gov (United States)

    Wang, Jun; Huang, Jing; Du, Likai; Lan, Zhenggang

    2015-07-09

    The photoinduced intramolecular excited-state energy-transfer (EET) process in conjugated polymers has received a great deal of research interest because of its important role in the light harvesting and energy transport of organic photovoltaic materials in photoelectric devices. In this work, the silylene-bridged biphenyl and stilbene (SBS) system was chosen as a simplified model system to obtain physical insight into the photoinduced intramolecular energy transfer between the different building units of the SBS copolymer. In the SBS system, the vinylbiphenyl and vinylstilbene moieties serve as the donor (D) unit and the acceptor (A) unit, respectively. The ultrafast excited-state dynamics of the SBS system was investigated from the point of view of nonadiabatic dynamics with the surface-hopping method at the TDDFT level. The first two excited states (S1 and S2) are characterized by local excitations at the acceptor (vinylstilbene) and donor (vinylbiphenyl) units, respectively. Ultrafast S2-S1 decay is responsible for the intramolecular D-A excitonic energy transfer. The geometric distortion of the D moiety play an essential role in this EET process, whereas the A moiety remains unchanged during the nonadiabatic dynamics simulation. The present work provides a direct dynamical approach to understand the ultrafast intramolecular energy-transfer dynamics in SBS copolymers and other similar organic photovoltaic copolymers.

  11. Excited State Charge Transfer reaction with dual emission from 5-(4-dimethylamino-phenyl)-penta-2,4-dienenitrile: Spectral measurement and theoretical density functional theory calculation

    Science.gov (United States)

    Jana, Sankar; Dalapati, Sasanka; Ghosh, Shalini; Kar, Samiran; Guchhait, Nikhil

    2011-07-01

    The excited state intramolecular charge transfer process in donor-chromophore-acceptor system 5-(4-dimethylamino-phenyl)-penta-2,4-dienenitrile (DMAPPDN) has been investigated by steady state absorption and emission spectroscopy in combination with Density Functional Theory (DFT) calculations. This flexible donor acceptor molecule DMAPPDN shows dual fluorescence corresponding to emission from locally excited and charge transfer state in polar solvent. Large solvatochromic emission shift, effect of variation of pH and HOMO-LUMO molecular orbital pictures support excited state intramolecular charge transfer process. The experimental findings have been correlated with the calculated structure and potential energy surfaces based on the Twisted Intramolecular Charge Transfer (TICT) model obtained at DFT level using B3LYP functional and 6-31+G( d, p) basis set. The theoretical potential energy surfaces for the excited states have been generated in vacuo and acetonitrile solvent using Time Dependent Density Functional Theory (TDDFT) and Time Dependent Density Functional Theory Polarized Continuum Model (TDDFT-PCM) method, respectively. All the theoretical results show well agreement with the experimental observations.

  12. Unveiling the excited state energy transfer pathways in peridinin-chlorophyll a-protein by ultrafast multi-pulse transient absorption spectroscopy.

    Science.gov (United States)

    Redeckas, Kipras; Voiciuk, Vladislava; Zigmantas, Donatas; Hiller, Roger G; Vengris, Mikas

    2017-04-01

    Time-resolved multi-pulse methods were applied to investigate the excited state dynamics, the interstate couplings, and the excited state energy transfer pathways between the light-harvesting pigments in peridinin-chlorophyll a-protein (PCP). The utilized pump-dump-probe techniques are based on perturbation of the regular PCP energy transfer pathway. The PCP complexes were initially excited with an ultrashort pulse, resonant to the S 0 →S 2 transition of the carotenoid peridinin. A portion of the peridinin-based emissive intramolecular charge transfer (ICT) state was then depopulated by applying an ultrashort NIR pulse that perturbed the interaction between S 1 and ICT states and the energy flow from the carotenoids to the chlorophylls. The presented data indicate that the peridinin S 1 and ICT states are spectrally distinct and coexist in an excited state equilibrium in the PCP complex. Moreover, numeric analysis of the experimental data asserts ICT→Chl-a as the main energy transfer pathway in the photoexcited PCP systems. Copyright © 2017 Elsevier B.V. All rights reserved.

  13. Cluster expansion of the wavefunction. Calculation of electron correlations in ground and excited states by SAC and SAC CI theories

    International Nuclear Information System (INIS)

    Nakatsuji, H.

    1979-01-01

    The SAC and SAC CI theories are formulated for actual calculations of singlet ground states and their excited states of arbitrary spin multiplicity. Approximations are considered for the variational methods since time-consuming terms are involved. The results of test calculations for singlet states have shown, with much smaller numbers of variables (sizes of the matrices involved), excellent agreement with the full CI and close-to-full CI results. This shows the utility of the SAC theory for ground states and especially of the SAC CI theory for excited states, since the slow convergence of the CI theory is much more critical for excited states than for ground states. (Auth.)

  14. Excited state electron and energy relays in supramolecular dinuclear complexes revealed by ultrafast optical and X-ray transient absorption spectroscopy.

    Science.gov (United States)

    Hayes, Dugan; Kohler, Lars; Hadt, Ryan G; Zhang, Xiaoyi; Liu, Cunming; Mulfort, Karen L; Chen, Lin X

    2018-01-28

    The kinetics of photoinduced electron and energy transfer in a family of tetrapyridophenazine-bridged heteroleptic homo- and heterodinuclear copper(i) bis(phenanthroline)/ruthenium(ii) polypyridyl complexes were studied using ultrafast optical and multi-edge X-ray transient absorption spectroscopies. This work combines the synthesis of heterodinuclear Cu(i)-Ru(ii) analogs of the homodinuclear Cu(i)-Cu(i) targets with spectroscopic analysis and electronic structure calculations to first disentangle the dynamics at individual metal sites by taking advantage of the element and site specificity of X-ray absorption and theoretical methods. The excited state dynamical models developed for the heterodinuclear complexes are then applied to model the more challenging homodinuclear complexes. These results suggest that both intermetallic charge and energy transfer can be observed in an asymmetric dinuclear copper complex in which the ground state redox potentials of the copper sites are offset by only 310 meV. We also demonstrate the ability of several of these complexes to effectively and unidirectionally shuttle energy between different metal centers, a property that could be of great use in the design of broadly absorbing and multifunctional multimetallic photocatalysts. This work provides an important step toward developing both a fundamental conceptual picture and a practical experimental handle with which synthetic chemists, spectroscopists, and theoreticians may collaborate to engineer cheap and efficient photocatalytic materials capable of performing coulombically demanding chemical transformations.

  15. Transient Exciplex Formation Electron Transfer Mechanism

    Directory of Open Access Journals (Sweden)

    Michael G. Kuzmin

    2011-01-01

    Full Text Available Transient exciplex formation mechanism of excited-state electron transfer reactions is analyzed in terms of experimental data on thermodynamics and kinetics of exciplex formation and decay. Experimental profiles of free energy, enthalpy, and entropy for transient exciplex formation and decay are considered for several electron transfer reactions in various solvents. Strong electronic coupling in contact pairs of reactants causes substantial decrease of activation energy relative to that for conventional long-range ET mechanism, especially for endergonic reactions, and provides the possibility for medium reorganization concatenated to gradual charge shift in contrast to conventional preliminary medium and reactants reorganization. Experimental criteria for transient exciplex formation (concatenated mechanism of excited-state electron transfer are considered. Available experimental data show that this mechanism dominates for endergonic ET reactions and provides a natural explanation for a lot of known paradoxes of ET reactions.

  16. [Nature of the electron-excited state in redox reactions of pigments. I. Photooxidation of chlorophyll a by n-benzoquine].

    Science.gov (United States)

    Andreeva, N E; Barashkov, B I; Zakharova, G V; Shubin, V V; Chibisov, A K

    1977-01-01

    A method for studying the nature of electronic excited state under photooxidation is proposed. It is shown by an example of the oxidation of chlorophyll a with p-benzoquinone that the formation of cation-radicals of pigments proceeds only through the triplet state. On the basis of experimental data the values of the rate constants of formation of chlorophyll cation-radicals through the singlet-excited state (K2(1)--10(7) M-1 s-1) and triplet state (Kr=10(9) M-1 s-1) of the pigment are evaluated.

  17. The Raman effect and its application to electronic spectroscopies in metal-centered species : Techniques and investigations in ground and excited states

    NARCIS (Netherlands)

    Browne, W.R.; J. McGarvey, J.

    In the decades since its discovery and somewhat limited early applications, Raman scattering has become the basis for the development of a variety of methods for probing molecular structure both in ground and electronically excited states. In this review, following a brief look at the underlying

  18. Photophysical properties of 1-acetoxy-8-hydroxy-1,4,4a,9a-tetrahydroanthraquinone: Evidence for excited state proton transfer reaction

    International Nuclear Information System (INIS)

    Singh, Rupashree Balia; Mahanta, Subrata; Guchhait, Nikhil

    2007-01-01

    The photophysical properties of 1-acetoxy-8-hydroxy-1,4,4a,9a-tetrahydroanthraquinone (HTHQ) have been investigated by steady state and time resolved spectroscopy in combination with quantum chemical calculations. The effects of various parameters such as the nature of solvent and pH of the medium on the spectral properties confirm the existence of different neutral and ionic species in the ground and excited states. In the ground state, HTHQ exists as intramolecularly hydrogen bonded closed conformer in non-polar and polar aprotic solvents. Apart from the closed conformer, the intermolecular hydrogen bonded solvated species and the anion of HTHQ are present in hydroxylic solvents. The closed conformer shows excited state intramolecular proton transfer in all solvents and the solvent polarity independent red shifted emission indicates only keto-enol tautomerism. Evaluation of the potential energy surfaces by quantum chemical calculation using density functional theory point towards the possibility of proton transfer reaction in the first excited state but not in the ground state

  19. Characterising excited states in and around the semi-magic nucleus $^{68}$ Ni using Coulomb excitation and one-neutron transfer

    CERN Multimedia

    It is proposed to investigate the structure of excited states in $^{68, 70}$Ni(Z =28, N=40, 42) via the measurement of electromagnetic matrix elements in a Coulomb excitation experiment in order to study the N = 40 harmonic-oscillator shell and the Z = 28 proton shell closures. The measured B(E2) values connecting low-lying 0$^{+}$ and 2$^{+}$ can be compared to shell-model predictions. It is also proposed to perform the one-neutron transfer reaction ${d}$($^{68}$Ni,$^{69}$Ni)${p}$, with the aim of populating excited states in $^{69}$Ni. Comparisons with the states populated in the recently performed ${d}$($^{66}$Ni,$^{67}$Ni)${p}$ reaction will be useful in determining the role of the neutron $d_{5/2}$ orbital in the semi-magic properties of $^{68}$Ni.

  20. A Series of Supramolecular Complexes for Solar Energy Conversion via Water Reduction to Produce Hydrogen: An Excited State Kinetic Analysis of Ru(II,Rh(III,Ru(II Photoinitiated Electron Collectors

    Directory of Open Access Journals (Sweden)

    Shamindri M. Arachchige

    2011-12-01

    Full Text Available Mixed-metal supramolecular complexes have been designed that photochemically absorb solar light, undergo photoinitiated electron collection and reduce water to produce hydrogen fuel using low energy visible light. This manuscript describes these systems with an analysis of the photophysics of a series of six supramolecular complexes, [{(TL2Ru(dpp}2RhX2](PF65 with TL = bpy, phen or Ph2phen with X = Cl or Br. The process of light conversion to a fuel requires a system to perform a number of complicated steps including the absorption of light, the generation of charge separation on a molecular level, the reduction by one and then two electrons and the interaction with the water substrate to produce hydrogen. The manuscript explores the rate of intramolecular electron transfer, rate of quenching of the supramolecules by the DMA electron donor, rate of reduction of the complex by DMA from the 3MLCT excited state, as well as overall rate of reduction of the complex via visible light excitation. Probing a series of complexes in detail exploring the variation of rates of important reactions as a function of sub-unit modification provides insight into the role of each process in the overall efficiency of water reduction to produce hydrogen. The kinetic analysis shows that the complexes display different rates of excited state reactions that vary with TL and halide. The role of the MLCT excited state is elucidated by this kinetic study which shows that the 3MLCT state and not the 3MMCT is likely that key contributor to the photoreduction of these complexes. The kinetic analysis of the excited state dynamics and reactions of the complexes are important as this class of supramolecules behaves as photoinitiated electron collectors and photocatalysts for the reduction of water to hydrogen.

  1. Electronic spectra of azaindole and its excited state mixing: A symmetry-adapted cluster configuration interaction study

    Energy Technology Data Exchange (ETDEWEB)

    Arulmozhiraja, Sundaram, E-mail: raja@cat.hokudai.ac.jp; Coote, Michelle L. [ARC Centre of Excellence for Electromaterials Science, Research School of Chemistry, The Australian National University, Canberra, 2601 ACT (Australia); Hasegawa, Jun-ya [Institute for Catalysis, Hokkaido University, Kita 21, Nishi 10, Kita-Ku, Sapporo 001-0021 (Japan)

    2015-11-28

    Electronic structures of azaindole were studied using symmetry-adapted cluster configuration interaction theory utilizing Dunning’s cc-pVTZ basis set augmented with appropriate Rydberg spd functions on carbon and nitrogen atoms. The results obtained in the present study show good agreement with the available experimental values. Importantly, and contrary to previous theoretical studies, the excitation energy calculated for the important n–π{sup ∗} state agrees well with the experimental value. A recent study by Pratt and co-workers concluded that significant mixing of π-π{sup ∗} and n-π{sup ∗} states leads to major change in the magnitude and direction of the dipole moment of the upper state vibrational level in the 0,0 + 280 cm{sup −1} band in the S{sub 1}←S{sub 0} transition when compared to that of the zero-point level of the S{sub 1} state. The present study, however, shows that all the four lowest lying excited states, {sup 1}L{sub b} π-π{sup ∗}, {sup 1}L{sub a} π-π{sup ∗}, n-π{sup ∗}, and π-σ{sup ∗}, cross each other in one way or another, and hence, significant state mixing between them is likely. The upper state vibrational level in the 0,0 + 280 cm{sup −1} band in the S{sub 1}←S{sub 0} transition benefits from this four-state mixing and this can explain the change in magnitude and direction of the dipole moment of the S{sub 1} excited vibrational level. This multistate mixing, and especially the involvement of π-σ{sup ∗} state in mixing, could also provide a route for hydrogen atom detachment reactions. The electronic spectra of benzimidazole, a closely related system, were also investigated in the present study.

  2. Cob(I)alamin: insight into the nature of electronically excited states elucidated via quantum chemical computations and analysis of absorption, CD and MCD data.

    Science.gov (United States)

    Kornobis, Karina; Ruud, Kenneth; Kozlowski, Pawel M

    2013-02-07

    The nature of electronically excited states of the super-reduced form of vitamin B(12) (i.e., cob(I)alamin or B(12s)), a ubiquitous B(12) intermediate, was investigated by performing quantum-chemical calculations within the time-dependent density functional theory (TD-DFT) framework and by establishing their correspondence to experimental data. Using response theory, the electronic absorption (Abs), circular dichroism (CD) and magnetic CD (MCD) spectra of cob(I)alamin were simulated and directly compared with experiment. Several issues have been taken into considerations while performing the TD-DFT calculations, such as strong dependence on the applied exchange-correlation (XC) functional or structural simplification imposed on the cob(I)alamin. In addition, the low-lying transitions were also validated by performing CASSCF/MC-XQDPT2 calculations. By comparing computational results with existing experimental data a new level of understanding of electronic excitations has been established at the molecular level. The present study extends and confirms conclusions reached for other cobalamins. In particular, the better performance of the BP86 functional, rather than hybrid-type, was observed in terms of the excitations associated with both Co d and corrin π localized transitions. In addition, the lowest energy band was associated with multiple metal-to-ligand charge transfer excitations as opposed to the commonly assumed view of a single π → π* transition followed by vibrational progression. Finally, the use of the full cob(I)alamin structure, instead of simplified molecular models, shed new light on the spectral analyses of cobalamin systems and revealed new challenges of this approach related to long-range charge transfer excitations involving side chains.

  3. On the intramolecular proton transfer of 3-hydroxyflavone in the first singlet excited state: A theoretical study

    International Nuclear Information System (INIS)

    Casadesus, Ricard; Vendrell, Oriol; Moreno, Miquel; Lluch, Jose M.; Morokuma, Keiji

    2006-01-01

    The intramolecular proton-transfer reaction in 3-hydroxyflavone (3HF) is theoretically studied both in the ground (S 0 ) and first singlet excited (S 1 ) electronic states. In S 0 the proton-transfer reaction is shown to be quite unfavorable at the DFT (B3LYP) level. However, the back proton transfer is found to be a feasible process with a small energy barrier, both results being in qualitative agreement with known experimental facts. Different theoretical levels are considered and compared for S 1 . The ab initio configuration interaction singles (CIS) method overestimates the energy of S 1 and give too high energy barriers for the proton-transfer reaction. The complete active space SCF (CASSCF) method gives a more reasonable value but the inclusion of the dynamical correlation through second-order perturbation theory (CASPT2) upon CASSCF geometries or the use of the time-dependent DFT (TDDFT) method upon CIS geometries gives a barrierless process. Optimization of geometries (minima and transition-state structures) at the TDDFT level leads to a small but non-negligible energy barrier for the proton-transfer reaction in S 1 and global energies that fit quite well with the known experimental (spectroscopic and femtochemistry) data. Finally the effect of a polar environment is analyzed through a continuum model, which gives only a small difference from the previous gas-phase results. This points out that the remarkable changes in the photochemistry of 3HF observed experimentally are not to be solely attributed to the polarity of the surrounding media

  4. On the intramolecular proton transfer of 3-hydroxyflavone in the first singlet excited state: A theoretical study

    Energy Technology Data Exchange (ETDEWEB)

    Casadesus, Ricard [Departament de Quimica, Universitat Autonoma de Barcelona, 08193 Bellaterra, Barcelona (Spain); Cherry L. Emerson Center for Scientific Computation and Department of Chemistry, Emory University, Atlanta, GA 30322 (United States); Vendrell, Oriol [Departament de Quimica, Universitat Autonoma de Barcelona, 08193 Bellaterra, Barcelona (Spain); Moreno, Miquel [Departament de Quimica, Universitat Autonoma de Barcelona, 08193 Bellaterra, Barcelona (Spain)], E-mail: mmf@klingon.uab.es; Lluch, Jose M. [Departament de Quimica, Universitat Autonoma de Barcelona, 08193 Bellaterra, Barcelona (Spain); Morokuma, Keiji [Cherry L. Emerson Center for Scientific Computation and Department of Chemistry, Emory University, Atlanta, GA 30322 (United States)

    2006-06-20

    The intramolecular proton-transfer reaction in 3-hydroxyflavone (3HF) is theoretically studied both in the ground (S{sub 0}) and first singlet excited (S{sub 1}) electronic states. In S{sub 0} the proton-transfer reaction is shown to be quite unfavorable at the DFT (B3LYP) level. However, the back proton transfer is found to be a feasible process with a small energy barrier, both results being in qualitative agreement with known experimental facts. Different theoretical levels are considered and compared for S{sub 1}. The ab initio configuration interaction singles (CIS) method overestimates the energy of S{sub 1} and give too high energy barriers for the proton-transfer reaction. The complete active space SCF (CASSCF) method gives a more reasonable value but the inclusion of the dynamical correlation through second-order perturbation theory (CASPT2) upon CASSCF geometries or the use of the time-dependent DFT (TDDFT) method upon CIS geometries gives a barrierless process. Optimization of geometries (minima and transition-state structures) at the TDDFT level leads to a small but non-negligible energy barrier for the proton-transfer reaction in S{sub 1} and global energies that fit quite well with the known experimental (spectroscopic and femtochemistry) data. Finally the effect of a polar environment is analyzed through a continuum model, which gives only a small difference from the previous gas-phase results. This points out that the remarkable changes in the photochemistry of 3HF observed experimentally are not to be solely attributed to the polarity of the surrounding media.

  5. Benchmarks for electronically excited states: Time-dependent density functional theory and density functional theory based multireference configuration interaction

    DEFF Research Database (Denmark)

    Silva-Junior, Mario R.; Schreiber, Marko; Sauer, Stephan P. A.

    2008-01-01

    Time-dependent density functional theory (TD-DFT) and DFT-based multireference configuration interaction (DFT/MRCI) calculations are reported for a recently proposed benchmark set of 28 medium-sized organic molecules. Vertical excitation energies, oscillator strengths, and excited-state dipole...

  6. Light induced electron transfer reactions of metal complexes

    International Nuclear Information System (INIS)

    Sutin, N.; Creutz, C.

    1980-01-01

    Properties of the excited states of tris(2,2'-bipyridine) and tris(1,10-phenanthroline) complexes of chromium(III), iron(II), ruthenium(II), osmium(II), rhodium(III), and iridium(III) are described. The electron transfer reactions of the ground and excited states are discussed and interpreted in terms of the driving force for the reaction and the distortions of the excited states relative to the corresponding ground states. General considerations relevant to the conversion of light into chemical energy are presented and progress in the use of polypyridine complexes to effect the light decomposition of water into hydrogen and oxygen is reviewed

  7. The mechanisms of Excited states in enzymes

    DEFF Research Database (Denmark)

    Petersen, Frederic Nicolas Rønne; Bohr, Henrik

    2010-01-01

    Enzyme catalysis is studied on the basis of excited state processes, which are of electronic, vibrational and thermal nature. The ways of achieving the excited state, such as photo-absorption and ligand binding, are discussed and exemplified by various cases of enzymes.......Enzyme catalysis is studied on the basis of excited state processes, which are of electronic, vibrational and thermal nature. The ways of achieving the excited state, such as photo-absorption and ligand binding, are discussed and exemplified by various cases of enzymes....

  8. Separating Bulk and Surface Contributions to Electronic Excited-State Processes in Hybrid Mixed Perovskite Thin Films via Multimodal All-Optical Imaging.

    Science.gov (United States)

    Simpson, Mary Jane; Doughty, Benjamin; Das, Sanjib; Xiao, Kai; Ma, Ying-Zhong

    2017-07-20

    A comprehensive understanding of electronic excited-state phenomena underlying the impressive performance of solution-processed hybrid halide perovskite solar cells requires access to both spatially resolved electronic processes and corresponding sample morphological characteristics. Here, we demonstrate an all-optical multimodal imaging approach that enables us to obtain both electronic excited-state and morphological information on a single optical microscope platform with simultaneous high temporal and spatial resolution. Specifically, images were acquired for the same region of interest in thin films of chloride containing mixed lead halide perovskites (CH 3 NH 3 PbI 3-x Cl x ) using femtosecond transient absorption, time-integrated photoluminescence, confocal reflectance, and transmission microscopies. Comprehensive image analysis revealed the presence of surface- and bulk-dominated contributions to the various images, which describe either spatially dependent electronic excited-state properties or morphological variations across the probed region of the thin films. These results show that PL probes effectively the species near or at the film surface.

  9. Solvent effects on the excited-state double proton transfer mechanism in the 7-azaindole dimer: a TDDFT study with the polarizable continuum model.

    Science.gov (United States)

    Yu, Xue-Fang; Yamazaki, Shohei; Taketsugu, Tetsuya

    2017-08-30

    Solvent effects on the excited-state double proton transfer (ESDPT) mechanism in the 7-azaindole (7AI) dimer were investigated using the time-dependent density functional theory (TDDFT) method. Excited-state potential energy profiles along the reaction paths in a locally excited (LE) state and a charge transfer (CT) state were calculated using the polarizable continuum model (PCM) to include the solvent effect. A series of non-polar and polar solvents with different dielectric constants were used to examine the polarity effect on the ESDPT mechanism. The present results suggest that in a non-polar solvent and a polar solvent with a small dielectric constant, ESDPT follows a concerted mechanism, similar to the case in the gas phase. In a polar solvent with a relatively large dielectric constant, however, ESDPT is likely to follow a stepwise mechanism via a stable zwitterionic intermediate in the LE state on the adiabatic potential energy surface, although inclusion of zero-point vibrational energy (ZPE) corrections again suggests the concerted mechanism. In the meantime, the stepwise reaction path involving the CT state with neutral intermediates is also examined, and is found to be less competitive than the concerted or stepwise path in the LE state in both non-polar and polar solvents. The present study provides a new insight into the experimental controversy of the ESDPT mechanism of the 7AI dimer in a solution.

  10. Two-Electron Transfer Pathways.

    Science.gov (United States)

    Lin, Jiaxing; Balamurugan, D; Zhang, Peng; Skourtis, Spiros S; Beratan, David N

    2015-06-18

    electrons in condensed-phase redox systems, including multiple-electron redox species, multimetallic/multielectron redox catalysts, and multiexciton excited states.

  11. General active space commutator-based coupled cluster theory of general excitation rank for electronically excited states: implementation and application to ScH.

    Science.gov (United States)

    Hubert, Mickaël; Olsen, Jeppe; Loras, Jessica; Fleig, Timo

    2013-11-21

    We present a new implementation of general excitation rank coupled cluster theory for electronically excited states based on the single-reference multi-reference formalism. The method may include active-space selected and/or general higher excitations by means of the general active space concept. It may employ molecular integrals over the four-component Lévy-Leblond Hamiltonian or the relativistic spin-orbit-free four-component Hamiltonian of Dyall. In an initial application to ground- and excited states of the scandium monohydride molecule we report spectroscopic constants using basis sets of up to quadruple-zeta quality and up to full iterative triple excitations in the cluster operators. Effects due to spin-orbit interaction are evaluated using two-component multi-reference configuration interaction for assessing the accuracy of the coupled cluster results.

  12. Silver colloidal effects on excited-state structure and intramolecular charge transfer of p-N, N-dimethylaminobenzoic acid in aqueous cyclodextrin solutions

    International Nuclear Information System (INIS)

    Choi, Jung Kwon; Kim, Yang Hee; Yoon, Min Joong; Lee, Seung Joon; Kim, Kwan; Jeoung, Sae Chae

    2001-01-01

    The silver colloidal effects on the excited-state structure and intramolecular charge transfer (ICT) of p-N,N-dimethylaminobenzoic acid (DMABA) in aqueous cyclodextrin (CD) solutions have been investigated by UV-VIS absorption, steady-state and time-resolved fluorescence, and transient Raman spectroscopy. As the concentration of silver colloids increases, the ratio of the ICT emission to the normal emission (I a /I b ) of DMABA in the aqueous α-CD solutions are greatly decreased while the I a /I b values in the aqueous β-CD solutions are significantly enhanced. It is also noteworthy that the ICT emission maxima are red-shifted by 15-40 nm upon addition of silver colloids, implying that DMABA encapsulated in α-CD or β-CD cavity is exposed to more polar environment. The transient resonance Raman spectra of DMABA in silver colloidal solutions demonstrate that DMABA in the excited-state is desorbed from silver colloidal surfaces as demonstrated by the disappearance of v s (CO 2 - )(1380 cm -1 ) with appearance of v (C-OH)(1280 cm -1 ) band, respectively. Thus, in the aqueous β-CD solutions the carboxylic acid group of DMABA in the excited-state can be readily hydrogen bonded with the secondary hydroxyl group of β-CD while in aqueous and α-CD solutions the carboxylic acid group of DMABA has the hydrogen-bonding interaction with water. Consequently, in the aqueous β-CD solutions the enhancement of the I a /I b value arises from the intermolecular hydrogen-bonding interaction between DMABA and the secondary hydroxyl group of β-CD as well as the lower polarity of the rim of the β-CD cavity compared to bulk water. This is also supported by the increase of the association constant for DMABA/β-CD complex in the presence of silver colloids

  13. Excited-state proton transfer in confined medium. 4-methyl-7-hydroxyflavylium and β-naphthol incorporated in cucurbit[7]uril.

    Science.gov (United States)

    Basílio, Nuno; Laia, César A T; Pina, Fernando

    2015-02-12

    Excited-state proton transfer (ESPT) was studied by fluorescent emission using a mathematical model recast from the Weller theory. The titration curves can be fitted with three parameters: pK(a) (acidity constant of the ground sate), pK(ap)* (apparent acidity constant of the excited state), and η(A*), the efficiency of excited base formation from the excited acid. β-Naphthol and 4-metyhl-7-hydroxyflavylium were studied in aqueous solution and upon incorporation in cucurbit[7]uril. For all the compounds studied the interaction with the host leads to 1:1 adducts and the ground-state pK(a) increases upon incorporation. Whereas the ESPT of 4-methyl-7-hydroxyflavylium practically does not change in the presence of the host, in the case of β-naphthol it is prevented and the fluorescence emission titration curves are coincident with those taken by absorption. The position of the guest inside the host was investigated by NMR experiments and seems to determine the efficiency of the ESPT. The ESPT decreases for the guest, exhibiting a great protection of the phenol to the bulk water interaction.

  14. Organic electronic materials: Recent advances in the dft description of the ground and excited states using tuned range-separated hybrid functionals

    KAUST Repository

    Körzdörfer, Thomas

    2014-11-18

    Density functional theory (DFT) and its time-dependent extension (TD-DFT) are powerful tools enabling the theoretical prediction of the ground- and excited-state properties of organic electronic materials with reasonable accuracy at affordable computational costs. Due to their excellent accuracy-to-numerical-costs ratio, semilocal and global hybrid functionals such as B3LYP have become the workhorse for geometry optimizations and the prediction of vibrational spectra in modern theoretical organic chemistry. Despite the overwhelming success of these out-of-the-box functionals for such applications, the computational treatment of electronic and structural properties that are of particular interest in organic electronic materials sometimes reveals severe and qualitative failures of such functionals. Important examples include the overestimation of conjugation, torsional barriers, and electronic coupling as well as the underestimation of bond-length alternations or excited-state energies in low-band-gap polymers.In this Account, we highlight how these failures can be traced back to the delocalization error inherent to semilocal and global hybrid functionals, which leads to the spurious delocalization of electron densities and an overestimation of conjugation. The delocalization error for systems and functionals of interest can be quantified by allowing for fractional occupation of the highest occupied molecular orbital. It can be minimized by using long-range corrected hybrid functionals and a nonempirical tuning procedure for the range-separation parameter.We then review the benefits and drawbacks of using tuned long-range corrected hybrid functionals for the description of the ground and excited states of π-conjugated systems. In particular, we show that this approach provides for robust and efficient means of characterizing the electronic couplings in organic mixed-valence systems, for the calculation of accurate torsional barriers at the polymer limit, and for the

  15. Benzothiazole-Based AIEgen with Tunable Excited-State Intramolecular Proton Transfer and Restricted Intramolecular Rotation Processes for Highly Sensitive Physiological pH Sensing.

    Science.gov (United States)

    Li, Kai; Feng, Qi; Niu, Guangle; Zhang, Weijie; Li, Yuanyuan; Kang, Miaomiao; Xu, Kui; He, Juan; Hou, Hongwei; Tang, Ben Zhong

    2018-04-23

    In this work, a benzothiazole-based aggregation-induced emission luminogen (AIEgen) of 2-(5-(4-carboxyphenyl)-2-hydroxyphenyl)benzothiazole (3) was designed and synthesized, which exhibited multifluorescence emissions in different dispersed or aggregated states based on tunable excited-state intramolecular proton transfer (ESIPT) and restricted intramolecular rotation (RIR) processes. 3 was successfully used as a ratiometric fluorescent chemosensor for the detection of pH, which exhibited reversible acid/base-switched yellow/cyan emission transition. More importantly, the pH jump of 3 was very precipitous from 7.0 to 8.0 with a midpoint of 7.5, which was well matched with the physiological pH. This feature makes 3 very suitable for the highly sensitive detection of pH fluctuation in biosamples and neutral water samples. 3 was also successfully used as a ratiometric fluorescence chemosensor for the detection of acidic and basic organic vapors in test papers.

  16. Electronic Structure and Excited-State Dynamics of an Arduengo-Type Carbene and its Imidazolone Oxidation Product.

    Science.gov (United States)

    Schmitt, Hans-Christian; Flock, Marco; Welz, Eileen; Engels, Bernd; Schneider, Heidi; Radius, Udo; Fischer, Ingo

    2017-03-02

    We describe an investigation of the excited-state dynamics of isolated 1,3-di-tert-butyl-imidazoline-2-ylidene (tBu 2 Im, C 11 H 20 N 2 , m/z=180), an Arduengo-type carbene, by time- and frequency-resolved photoionization using a picosecond laser system. The energies of several singlet and triplet excited states were calculated by time-dependent density functional theory (TD-DFT). The S 1 state of the carbene deactivates on a 100 ps time scale possibly by intersystem crossing. In the experiments we observed an additional signal at m/z=196, that was assigned to the oxidation product 1,3-di-tert-butyl-imidazolone, tBu 2 ImO. It shows a well-resolved resonance-enhanced multiphoton ionization (REMPI) spectrum with an origin located at 36951 cm -1 . Several low-lying vibrational bands could be assigned, with a lifetime that depends strongly on the excitation energy. At the origin the lifetime is longer than 3 ns, but drops to 49 ps at higher excess energies. To confirm formation of the imidazolone we also performed experiments on benzimidazolone (BzImO) for comparison. Apart from a redshift for BzImO the spectra of the two compounds are very similar. The TD-DFT values display a very good agreement with the experimental data. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Nuclear reorganization barriers to electron transfer

    International Nuclear Information System (INIS)

    Sutin, N.; Brunschwig, B.S.; Creutz, C.; Winkler, J.R.

    1988-01-01

    The nuclear barrier to electron transfer arises from the need for reorganization of intramolecular and solvent internuclear distances prior to electron transfer. For reactions with relatively small driving force (''normal'' free-energy region) the nuclear factors and rates increase as intrinsic inner-shell and outer-shell barriers decrease; this is illustrated by data for transition metal complexes in their ground electronic states. By contrast, in the inverted free-energy region, rates and nuclear factors decrease with decreasing ''intrinsic'' barriers; this is illustrated by data for the decay of charge-transfer excited states. Several approaches to the evaluation of the outer-shell barrier are explored in an investigation of the distance dependence of the nuclear factor in intramolecular electron-transfer processes. 39 refs., 14 figs., 3 tabs

  18. TDDFT study on excited state intramolecular proton transfer mechanism in 2-amino-3-(2‧-benzazolyl)-quinolines

    Science.gov (United States)

    Jia, Xueli; Li, Chaozheng; Li, Donglin; Liu, Yufang

    2018-03-01

    The intramolecular proton transfer reaction of the 2-amino-3-(2‧-benzoxazolyl)-quinoline (ABO) and 2-amino-3-(2‧-benzothiazolyl)-quinoline (ABT) molecules in both S0 and S1 states at B3LYP/6-311 ++G(d,p) level in ethanol solvent have been studied to reveal the deactivation mechanism of the tautomers of the two molecules from the S1 state to the S0 state. The results show that the tautomers of ABO and ABT molecules may return to the S0 state by emitting fluorescence. In addition, the bond lengths, angles and infrared spectra are analyzed to confirm the hydrogen bonds strengthened upon photoexcitation, which can facilitate the proton transfer process. The frontier molecular orbitals (MOs) and natural bond orbital (NBO) are also calculated to indicate the intramolecular charge transfer which can be used to explore the tendency of ESIPT reaction. The potential energy surfaces of the ABO and ABT molecules in the S0 and S1 states have been constructed. According to the energy potential barrier of 9.12 kcal/mol for ABO molecule and 5.96 kcal/mol for ABT molecule, it can be indicated that the proton transfer may occur in the S1 state.

  19. Electron transfer and decay processes of highly charged iodine ions

    International Nuclear Information System (INIS)

    Sakaue, Hiroyuki A.; Danjo, Atsunori; Hosaka, Kazumoto

    2005-01-01

    In the present experimental work we have investigated multi-electron transfer processes in I q+ (q=10, 15, 20 and 25) + Ne, Ar, Kr and Xe collisions at 1.5q keV energy. The branching ratios between Auger and radiative decay channels have been measured in decay processes of multiply excited states formed by multi-electron transfer collisions. It has been shown that, in all the multi-electron transfer processes investigated, the Auger decays are far dominant over the radiative decay processes and the branching ratios are clearly characterized by the average principal quantum number of the initial excited states of projectile ions. We could express the branching ratios in high Rydberg states formed in multi-electron transfer processes by using the decay probability of one Auger electron emission. (author)

  20. Charge transfer in low-energy collisions of H with He+ and H+ with He in excited states

    Science.gov (United States)

    Loreau, J.; Ryabchenko, S.; Muñoz Burgos, J. M.; Vaeck, N.

    2018-04-01

    The charge transfer process in collisions of excited (n = 2, 3) hydrogen atoms with He+ and in collisions of excited helium atoms with H+ is studied theoretically. A combination of a fully quantum-mechanical method and a semi-classical approach is employed to calculate the charge-exchange cross sections at collision energies from 0.1 eV u‑1 up to 1 keV u‑1. These methods are based on accurate ab initio potential energy curves and non-adiabatic couplings for the molecular ion HeH+. Charge transfer can occur either in singlet or in triplet states, and the differences between the singlet and triplet spin manifolds are discussed. The dependence of the cross section on the quantum numbers n and l of the initial state is demonstrated. The isotope effect on the charge transfer cross sections, arising at low collision energy when H is substituted by D or T, is investigated. Rate coefficients are calculated for all isotopes up to 106 K. Finally, the impact of the present calculations on models of laboratory plasmas is discussed.

  1. Ab initio calculation of the electronic structures of the 7∑+ ground and A 7Π and a 5∑+ excited states of MnH

    Science.gov (United States)

    Tomonari, Mutsumi; Nagashima, Umpei; Hirano, Tsuneo

    2009-04-01

    Electronic structures and molecular constants of the ground ∑7+ and low-lying A 7Π and a ∑5+ electronic excited states of the MnH molecule were studied by multireference single and double excitation configuration interaction (MR-SDCI) with Davidson's correction (+Q) calculations under exact C∞v symmetry using Slater-type basis sets. To correctly describe the ∑7+ electronic ground state, X ∑7+, at the MR-SDCI+Q calculation, we employed a large number of reference configurations in terms of the state-averaged complete active space self-consistent field (CASSCF) orbitals, taking into account the contribution from the B ∑7+ excited state. The A 7Π and a ∑5+ states can well be described by the MR-SDCI wave functions based on the CASSCF orbitals obtained for the lowest state only. In the MR-SDCI+Q, calculations of the X ∑7+, A 7Π, and a ∑5+ states required 16, 7, and 17 reference configurations, respectively. Molecular constants, i.e., re and ωe of these states and excitation energy from the X ∑7+ state, obtained at the MR-SDCI+Q level, showed a good agreement with experimental values. The small remaining differences may be accounted for by taking relativistic effects into account.

  2. Ab initio calculation of the electronic structures of the (7)Sigma+ ground and A (7)Pi and a (5)Sigma+ excited states of MnH.

    Science.gov (United States)

    Tomonari, Mutsumi; Nagashima, Umpei; Hirano, Tsuneo

    2009-04-21

    Electronic structures and molecular constants of the ground (7)Sigma(+) and low-lying A (7)Pi and a (5)Sigma(+) electronic excited states of the MnH molecule were studied by multireference single and double excitation configuration interaction (MR-SDCI) with Davidson's correction (+Q) calculations under exact C(infinity v) symmetry using Slater-type basis sets. To correctly describe the (7)Sigma(+) electronic ground state, X (7)Sigma(+), at the MR-SDCI+Q calculation, we employed a large number of reference configurations in terms of the state-averaged complete active space self-consistent field (CASSCF) orbitals, taking into account the contribution from the B (7)Sigma(+) excited state. The A (7)Pi and a (5)Sigma(+) states can well be described by the MR-SDCI wave functions based on the CASSCF orbitals obtained for the lowest state only. In the MR-SDCI+Q, calculations of the X (7)Sigma(+), A (7)Pi, and a (5)Sigma(+) states required 16, 7, and 17 reference configurations, respectively. Molecular constants, i.e., r(e) and omega(e) of these states and excitation energy from the X (7)Sigma(+) state, obtained at the MR-SDCI+Q level, showed a good agreement with experimental values. The small remaining differences may be accounted for by taking relativistic effects into account.

  3. Electron transfer reactions

    CERN Document Server

    Cannon, R D

    2013-01-01

    Electron Transfer Reactions deals with the mechanisms of electron transfer reactions between metal ions in solution, as well as the electron exchange between atoms or molecules in either the gaseous or solid state. The book is divided into three parts. Part 1 covers the electron transfer between atoms and molecules in the gas state. Part 2 tackles the reaction paths of oxidation states and binuclear intermediates, as well as the mechanisms of electron transfer. Part 3 discusses the theories and models of the electron transfer process; theories and experiments involving bridged electron transfe

  4. Electron transfer by excited benzoquinone anions: slow rates for two-electron transitions.

    Science.gov (United States)

    Zamadar, Matibur; Cook, Andrew R; Lewandowska-Andralojc, Anna; Holroyd, Richard; Jiang, Yan; Bikalis, Jin; Miller, John R

    2013-09-05

    Electron transfer (ET) rate constants from the lowest excited state of the radical anion of benzoquinone, BQ(-•)*, were measured in THF solution. Rate constants for bimolecular electron transfer reactions typically reach the diffusion-controlled limit when the free-energy change, ΔG°, reaches -0.3 eV. The rate constants for ET from BQ(-•)* are one-to-two decades smaller at this energy and do not reach the diffusion-controlled limit until -ΔG° is 1.5-2.0 eV. The rates are so slow probably because a second electron must also undergo a transition to make use of the energy of the excited state. Similarly, ET, from solvated electrons to neutral BQ to form the lowest excited state, is slow, while fast ET is observed at a higher excited state, which can be populated in a transition involving only one electron. A simple picture based on perturbation theory can roughly account for the control of electron transfer by the need for transition of a second electron. The picture also explains how extra driving force (-ΔG°) can restore fast rates of electron transfer.

  5. Investigation of triply excited states of Li-like ions in fast ion-atom collisions by zero-degree Auger projectile electron spectroscopy

    International Nuclear Information System (INIS)

    Zouros, T.J.M.; Benis, E.P.; Zamkov, M.; Lin, C.D.; Lee, T.G.; Richard, P.; Gorczyca, T.W.; Morishita, T.

    2005-01-01

    The production of triply excited states of Li-like systems has recently been extended beyond the lithium atom using two different ion-atom collisional techniques: (a) Triple-electron capture into 2s2p 2 and 2p 3 states of F 6+ formed in fast collisions of bare F 9+ ions with Ar and Kr atoms and (b) 180 deg. resonant scattering of quasi-free electrons of H 2 from the 1s2s 3 S metastable state of He-like B, C, N, O and F ions via the 2s2p 2 2 D resonance. Autoionization energies, decay branching ratios and production cross sections for these states were measured using zero-degree Auger projectile electron spectroscopy and compared to theoretical calculations using hyperspherical close coupling (HSCC) and R-matrix methods

  6. A novel chalcone-analogue as an optical sensor based on ground and excited states intramolecular charge transfer: A combined experimental and theoretical study

    International Nuclear Information System (INIS)

    Fayed, Tarek A.

    2006-01-01

    Steady-state absorption and emission spectroscopic techniques as well as semiempirical quantum calculations at the AM1 and ZINDO/S levels have been used to investigate the intramolecular charge transfer (ICT) behaviour of a novel chalcone namely; 1-(2-pyridyl)-5-(4-dimethylaminophenyl)-penta-2,4-diene-1-one, DMAC. The ground state DMAC has a significant ICT character and a great sensitivity to the hydrogen bond donating ability of the medium as reflected from the change of the absorption spectra in pure and mixed organic solvents. On the other hand, its excited singlet state exhibits high ICT characters as manifested by the drastic solvatochromic effects. These results are consistent with the data of charge density calculations in both the ground and excited state, which indicates enhancement of the charge transfer from the dimethyl-amino group to the carbonyl oxygen upon excitation. Also, the dipole moment calculations indicates a highly dipolar excited singlet state (Δμ eg = 15.5 D). The solvent dependence of the fluorescence quantum yield of DMAC was interpreted on the basis of positive and negative solvatokinetic as well as the hydrogen bonding effects. Incorporation of the 2-pyridyl group in the chemical structure of the present DMAC led to design of a potential optical sensor for probing acidity of the medium and metal cations such as Zn 2+ , Cd 2+ and Hg 2+ . This was concluded from the high acidochromic and metallochromic behaviour of DMAC on adding such cations to its acetonitrile solutions

  7. Evidence for excited-state intramolecular proton transfer in 4-chlorosalicylic acid from combined experimental and computational studies: Quantum chemical treatment of the intramolecular hydrogen bonding interaction

    Energy Technology Data Exchange (ETDEWEB)

    Paul, Bijan Kumar [Department of Chemistry, University of Calcutta, 92 Acharya Prafulla Chandra Road, Calcutta 700009 (India); Guchhait, Nikhil, E-mail: nikhil.guchhait@rediffmail.com [Department of Chemistry, University of Calcutta, 92 Acharya Prafulla Chandra Road, Calcutta 700009 (India)

    2012-07-25

    Highlights: Black-Right-Pointing-Pointer Experimental and computational studies on the photophysics of 4-chlorosalicylic acid. Black-Right-Pointing-Pointer Spectroscopically established ESIPT reaction substantiated by theoretical calculation. Black-Right-Pointing-Pointer Quantum chemical treatment of IMHB unveils strength, nature and directional nature. Black-Right-Pointing-Pointer Superiority of quantum chemical treatment of H-bond over geometric criteria. Black-Right-Pointing-Pointer Role of H-bond as a modulator of aromaticity. -- Abstract: The photophysical study of a pharmaceutically important chlorine substituted derivative of salicylic acid viz., 4-chlorosalicylic acid (4ClSA) has been carried out by steady-state absorption, emission and time-resolved emission spectroscopy. A large Stokes shifted emission band with negligible solvent polarity dependence marks the spectroscopic signature of excited-state intramolecular proton transfer (ESIPT) reaction in 4ClSA. Theoretical calculation by ab initio and Density Functional Theory methods yields results consistent with experimental findings. Theoretical potential energy surfaces predict the occurrence of proton transfer in S{sub 1}-state. Geometrical and energetic criteria, Atoms-In-Molecule topological parameters, Natural Bond Orbital population analysis have been exploited to evaluate the intramolecular hydrogen bond (IMHB) interaction and to explore its directional nature. The inter-correlation between aromaticity and resonance assisted H-bond is also discussed in this context. Our results unveil that the quantum chemical treatment is a more accurate tool to assess hydrogen bonding interaction in comparison to geometrical criteria.

  8. Pressure-induced emission band separation of the hybridized local and charge transfer excited state in a TPE-based crystal.

    Science.gov (United States)

    Liu, Xuedan; Li, Aisen; Xu, Weiqing; Ma, Zhiyong; Jia, Xinru

    2018-05-08

    We herein report a newly synthesized simple molecule, named TPE[double bond, length as m-dash]C4, with twisted D-A structure. TPE[double bond, length as m-dash]C4 showed two intrinsic emission bands ascribed to the locally excited (LE) state and the intramolecular charge transfer (ICT) state, respectively. In the crystal state, the LE emission band is usually observed. However, by applying hydrostatic pressure to the powder sample and the single crystal sample of TPE[double bond, length as m-dash]C4, dual-fluorescence (445 nm and 532 nm) was emerged under high pressure, owing to the pressure-induced emission band separation of the hybridized local and charge transfer excited state (HLCT). It is found that the emission of TPE[double bond, length as m-dash]C4 is generally determined by the ratio of the LE state to the ICT state. The ICT emission band is much more sensitive to the external pressure than the LE emission band. The HLCT state leads to a sample with different responsiveness to grinding and hydrostatic pressure. This study is of significance in the molecular design of such D-A type molecules and in the control of photoluminescence features by molecular structure. Such results are expected to pave a new way to further understand the relationship between the D-A molecular structure and stimuli-responsive properties.

  9. Excited State Spectra and Dynamics of Phenyl-Substituted Butadienes

    DEFF Research Database (Denmark)

    Wallace-Williams, Stacie E.; Schwartz, Benjamin J.; Møller, Søren

    1994-01-01

    indicate that phenyl torsional motion is not important to the excited-state dynamics and reveal alternative excited-state reaction pathways. The results demonstrate how molecular systems that are structually similar can exhibit different electronic properties and excited-state dynamics....

  10. Emission Spectroscopy as a Probe into Photoinduced Intramolecular Electron Transfer in Polyazine Bridged Ru(II,Rh(III Supramolecular Complexes

    Directory of Open Access Journals (Sweden)

    Karen J. Brewer

    2010-08-01

    Full Text Available Steady-state and time-resolved emission spectroscopy are valuable tools to probe photochemical processes of metal-ligand, coordination complexes. Ru(II polyazine light absorbers are efficient light harvesters absorbing in the UV and visible with emissive 3MLCT excited states known to undergo excited state energy and electron transfer. Changes in emission intensity, energy or band-shape, as well as excited state lifetime, provide insight into excited state dynamics. Photophysical processes such as intramolecular electron transfer between electron donor and electron acceptor sub-units may be investigated using these methods. This review investigates the use of steady-state and time-resolved emission spectroscopy to measure excited state intramolecular electron transfer in polyazine bridged Ru(II,Rh(III supramolecular complexes. Intramolecular electron transfer in these systems provides for conversion of the emissive 3MLCT (metal-to-ligand charge transfer excited state to a non-emissive, but potentially photoreactive, 3MMCT (metal-to-metal charge transfer excited state. The details of the photophysics of Ru(II,Rh(III and Ru(II,Rh(III,Ru(II systems as probed by steady-state and time-resolved emission spectroscopy will be highlighted.

  11. Quantum analysis in the transition process to excited state of an oxygen molecule induced by electron collisions; Denshi shototsu ni tomonau sanso bunshi ni okeru reiki jotai sen`i no ryoshironteki kaiseki

    Energy Technology Data Exchange (ETDEWEB)

    Ishimaru, K. [Gifu National College of Technology, Gifu (Japan); Okazaki, K. [Tokyo Inst. of Technology, Tokyo (Japan)

    1996-06-25

    For understanding of fundamental chemical reactions under a highly non equilibrium condition which is quite often used in plasma processing, the relevant atomic and molecular processes must be clarified. In this study, an analysis of the transition process to the excited state of an oxygen molecule induced by electron collisions in the oxygen plasma has been carried out. First, the electron density distribution in an oxygen molecule has been calculated using the extended Huckel molecular orbital method. Then, the electron potential energy distribution in the transition process to the excited state has been estimated. The electron behavior has been calculated using the estimated unidimensional electron potential energy distribution and unsteady quantum mechanics. As a result, the transition process to the excited state of an oxygen molecule induced by electron collisions and its conditions have been clarified qualitatively. 9 refs., 9 figs.

  12. Electronic properties of excited states in single InAs quantum dots; Elektronische Struktur angeregter Zustaende einzelner InAs-Quantenpunkte

    Energy Technology Data Exchange (ETDEWEB)

    Warming, Till

    2009-02-20

    The application of quantum-mechanical effects in semiconductor nanostructures enables the realization of novel opto-electronic devices. Examples are given by single-photon emitters and emitters of entangled photon pairs, both being essential for quantum cryptography, or for qubit systems as needed for quantum computing. InAs/GaAs quantum dots are one of the most promising candidates for such applications. A detailed knowledge of the electronic properties of quantum dots is a prerequisite for this development. The aim of this work is an experimental access to the detailed electronic structure of the excited states in single InAs/GaAs quantum dots including few-particle effects and in particular exchange interaction. The experimental approach is micro photoluminescence excitation spectroscopy ({mu}PLE). One of the main difficulties using {mu}PLE to probe single QDs is the unambiguous assignment of the observed resonances in the spectrum to specific transitions. By comparing micro photoluminescence ({mu}PL) and {mu}PLE spectra, the identification of the main resonances becomes possible. The key is given by the fine structure of the hot trion. Excitation spectroscopy on single charged QDs enables for the first time the complete observation of a non-trivial fine structure of an excitonic complex in a QD, the hot trion. Modelling based on eight-band k.p theory in combination with a configuration interaction scheme is in excellent agreement. Therewith the simulation also enables realistic predictions on the fine structure of the ground-state exciton which is of large importance for single quantum dot devices. Theory concludes from the observed transitions that the structural symmetry of the QDs is broken. Micro photoluminescence excitation spectroscopy combined with resonantly excited micro photoluminescence enables an optical access to the single particle states of the hole without the influence of few-particle coulomb interactions. Based on this knowledge the exciton

  13. Excited-state inter- and intramolecular proton transfer in methyl 3-hydroxy-2-quinoxalinate: effects of solvent and acid or base concentrations

    International Nuclear Information System (INIS)

    Dogra, S.K.

    2005-01-01

    Absorption, fluorescence excitation and fluorescence spectroscopy, combined with time-dependent spectroscopy and semi-empirical (AM1) and density functional theory using Gaussian 98 program calculations have been used to study the effects of solvent and acid or base concentration on the spectral characteristics of methyl 3-hydroxy-2-quinoxalinate (M3HQ). M3HQ is present as enol in less polar solvents and as keto in polar media. In non-polar solvents, large Stokes shifted fluorescence band is assigned to the phototautomer, formed by the excited-state intramolecular proton transfer, whereas fluorescence is only observed from keto in the polar solvents. In aqueous and polar solvents the monocation (MC5/MC6) is formed by protonating the carbonyl oxygen atom in the ground (S 0 ) and the first excited singlet states (S 1 ). Dication is formed by protonating one of ?N- atom of MC5/MC6. Monoanion is formed by deprotonating the phenolic proton of enol in the basic solution. pK a values for different prototropic equilibriums were determined in S 0 and S 1 states and discussed

  14. Fluorescence ratiometric sensing of polyols by phenylboronic acid complexes with ligands exhibiting excited-state intramolecular proton transfer in aqueous micellar media

    Energy Technology Data Exchange (ETDEWEB)

    Trejo-Huizar, Karla Elisa; Jiménez-Sánchez, Arturo; Martínez-Aguirre, Mayte A.; Yatsimirsky, Anatoly K., E-mail: anatoli@unam.mx

    2016-11-15

    2-Phenyl-3-hydroxy-4(1H)-quinolone possessing dual fluorescence due to excited-state intramolecular proton transfer (ESIPT) forms stable complex with phenylboronic acid with blue shifted emission maximum in micellar medium of a cationic surfactant even though the compound lacks required for complexation with boronic acids cis-diol structure. No complexation is observed in the presence of neutral or anionic surfactants. Titrations of this complex with polyols including sugars and nucleotides at pH 8 displace free quinolone showing ratiometric response, which allows determination of polyols with detection limits 0.05–1 mM and unusually wide linear dynamic ranges. Another ESIPT dye 2-(2′-hydroxyphenyl)−1H-benzimidazole also lacking cis-diol structure forms equally stable complex with phenylboronic acid and allows ratiometric determination of polyols with similar characteristics. The results of this study demonstrate that blocking ESIPT of signaling molecule by complexation of the receptor with the proton donor group eliminates the low energy emission from tautomeric form but strongly enhances the high energy emission typical for “normal” form of signaling molecule creating a possibility of ratiometric sensing.

  15. Photoinduced energy and electron transfer in rubrene-benzoquinone and rubrene-porphyrin systems

    KAUST Repository

    Khan, Jafar Iqbal

    2014-11-01

    Excited-state electron and energy transfer from singlet excited rubrene (Ru) to benzoquinone (BQ) and tetra-(4-aminophenyl) porphyrin (TAPP) were investigated by steady-state absorption and emission, time-resolved transient absorption, and femtosecond (fs)-nanosecond (ns) fluorescence spectroscopy. The low reduction potential of BQ provides the high probability of electron transfer from the excited Ru to BQ. Steady-state and time-resolved results confirm such an excited electron transfer scenario. On the other hand, strong spectral overlap between the emission of Ru and absorption of TAPP suggests that energy transfer is a possible deactivation pathway of the Ru excited state.

  16. Variational predictions of transition energies and electron affinities: He and Li ground states and Li, Be, and Mg core-excited states

    International Nuclear Information System (INIS)

    Fischer, C.F.

    1990-01-01

    Variational procedures for predicting energy differences of many-electron systems are investigated. Several different calculations for few-electron systems are considered that illustrate the problems encountered when a many-electron system is modeled as a core plus outer electrons. It is shown that sequences of increasingly more accurate calculations for outer correlation may converge yielding wrong transition energies. At the same time, accurate core-polarization calculations overestimate the binding energy, requiring a core-valence correction. For the high-spin, core-excited states of Li, it was found that outer correlation only predicted electron affinities as accurately as full-correlation studies. This observation suggested a prediction of the core-excited 4 P endash 4 S transition in Be - , based on observed 3 P 0 endash 3 P transition energies of the neutral species, predicted electron affinities including only outer correlation, and a core-valence correction, that is shown to be in good agreement with experiment. A similar calculation for Mg - predicts a wavelength of 2895.1 A for this transition

  17. Tight-binding approximations to time-dependent density functional theory — A fast approach for the calculation of electronically excited states

    Energy Technology Data Exchange (ETDEWEB)

    Rüger, Robert, E-mail: rueger@scm.com [Scientific Computing & Modelling NV, De Boelelaan 1083, 1081 HV Amsterdam (Netherlands); Department of Theoretical Chemistry, Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam (Netherlands); Wilhelm-Ostwald-Institut für Physikalische und Theoretische Chemie, Linnéstr. 2, 04103 Leipzig (Germany); Lenthe, Erik van [Scientific Computing & Modelling NV, De Boelelaan 1083, 1081 HV Amsterdam (Netherlands); Heine, Thomas [Wilhelm-Ostwald-Institut für Physikalische und Theoretische Chemie, Linnéstr. 2, 04103 Leipzig (Germany); Visscher, Lucas [Department of Theoretical Chemistry, Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam (Netherlands)

    2016-05-14

    We propose a new method of calculating electronically excited states that combines a density functional theory based ground state calculation with a linear response treatment that employs approximations used in the time-dependent density functional based tight binding (TD-DFTB) approach. The new method termed time-dependent density functional theory TD-DFT+TB does not rely on the DFTB parametrization and is therefore applicable to systems involving all combinations of elements. We show that the new method yields UV/Vis absorption spectra that are in excellent agreement with computationally much more expensive TD-DFT calculations. Errors in vertical excitation energies are reduced by a factor of two compared to TD-DFTB.

  18. TD-DFT investigation of the potential energy surface for Excited-State Intramolecular Proton Transfer (ESIPT) reaction of 10-hydroxybenzo[h]quinoline: Topological (AIM) and population (NBO) analysis of the intramolecular hydrogen bonding interaction

    International Nuclear Information System (INIS)

    Paul, Bijan Kumar; Guchhait, Nikhil

    2011-01-01

    Here, we report a Density Functional Theoretical (DFT) study on the photophysics of a potent Excited-State Intramolecular Proton Transfer (ESIPT) molecular system, viz., 10-hydroxybenzo[h]quinoline (HBQ). Particular emphasis has been rendered on the assessment of the proton transfer reaction in HBQ in the ground and excited-states through elucidation and a careful perusal of the potential energy surfaces (PES). The non-viability of Ground-State Intramolecular Proton Transfer (GSIPT) process is dictated by a high-energy barrier coupled with no energy minimum for the proton transferred (K-form) form at the ground-state (S 0 ) PES. Remarkable reduction of the barrier along with thermodynamic stability inversion between the enol (E-form) and the keto forms (K-form) of HBQ upon photoexcitation from S 0 to the S 1 -state advocate for the operation of ESIPT process. These findings have been cross-validated on the lexicon of analysis of optimized geometry parameters, Mulliken's charge distribution on the heavy atoms, and molecular orbitals (MO) of the E- and the K-forms of HBQ. Our computational results also corroborate to experimental observations. From the modulations in optimized geometry parameters in course of the PT process a critical assessment has been endeavoured to delve into the movement of the proton during the process. Additional stress has been placed on the analysis of the intramolecular hydrogen bonding (IMHB) interaction in HBQ. The IMHB interaction has been explored by calculation of electron density ρ(r) and the Laplacian ∇ 2 ρ(r) at the bond critical point (BCP) using Atoms-In-Molecule (AIM) method and by calculation of interaction between σ* of OH with the lone pair of the nitrogen atom using Natural Bond Orbital (NBO) analysis. - Highlights: → Theoretical modelling of the photophysics of an ESIPT probe 10-hydroxybenzo[h]quinoline (HBQ). → Calculation of intramolecular hydrogen bond (IMHB) energy. → Role of hyperconjugative charge transfer

  19. Giant resonances on excited states

    International Nuclear Information System (INIS)

    Besold, W.; Reinhard, P.G.; Toepffer, C.

    1984-01-01

    We derive modified RPA equations for small vibrations about excited states. The temperature dependence of collective excitations is examined. The formalism is applied to the ground state and the first excited state of 90 Zr in order to confirm a hypothesis which states that not only the ground state but every excited state of a nucleus has a giant resonance built upon it. (orig.)

  20. Electronic spectral study of interaction of electron donor – acceptor dyes in the ground and excited state with a metal ion. Effect of molecular structure of the dye

    International Nuclear Information System (INIS)

    Sardar, Sanjib Kr; Mandal, Prasun K.; Bagchi, Sanjib

    2014-01-01

    Interaction of manganese (II) ion with electron donor (D)–acceptor (A) dyes having symmetric D–A–D configuration of chromophores (ketocyanine dye) and the corresponding parent merocyanines (D–A configuration) in acetonitrile has been compared by monitoring the electronic absorption, and steady state and time resolved fluorescence characteristics of the dyes. Absorption spectral studies point to the formation of a 1:1 metal ion–dye (S 0 -state) complex. Equilibrium constant (K 0 ) and other thermodynamic parameters for complex formation have been determined for all the systems. Symmetric ketocyanine dyes (D–A–D) form stronger complex than the corresponding dye with D–A configuration. Quenching of fluorescence is caused due to complex formation with the cation. However, for very low concentration of salts, where complex formation is insignificant, an enhancement of fluorescence intensity takes place due to addition of salt. The absorption band of the dye undergoes a slight blue shift in the same concentration range of the metal ion. Fluorescence life time of the excited state also increases with an increase in salt concentration in that concentration range. Results have been explained in terms of formation of a weak association complex where one or more cations replace equivalent solvent molecules in the cybotatic region around the dye. The binding constant of the association complex involving cation and the dye (S 1 -state) has been determined. While the value of the binding constant is higher for a symmetric D–A–D dye relative to that for the corresponding dye with D–A configuration, the extent of fluorescence enhancement for the latter is larger. Values of decay constant for the different photophysical processes have been calculated. Formation of association complex in the S 1 -state is characterised by a slower nonradiative decay of S 1 -state of the dyes. -- Highlights: • A ketocyanine dye forms 1:1 complex with metal ions. • Slight

  1. Symmetry-adapted-cluster configuration-interaction and equation-of-motion coupled-cluster studies of electronically excited states of copper tetrachloride and copper tetrabromide dianions

    International Nuclear Information System (INIS)

    Ehara, Masahiro; Piecuch, Piotr; Lutz, Jesse J.; Gour, Jeffrey R.

    2012-01-01

    Graphical abstract: Electronically excited states of CuCl 4 2- and CuBr 4 2- are determined using the scalar relativistic symmetry-adapted-cluster configuration-interaction and equation-of-motion coupled-cluster calculations. The results are compared with experimental spectra. Highlights: ► Electronic spectra of CuCl 4 2- and CuBr 4 2- are examined by SAC-CI and EOMCC methods. ► Relativistic SAC-CI and EOMCC results are compared with experimental spectra. ► An assignment of bands in the CuCl 4 2- and CuBr 4 2- absorption spectra is obtained. ► Relativistic effects affect excitation energies and ground-state geometries. ► The effect of relativity on the oscillator strengths is generally small. - Abstract: The valence excitation spectra of the copper tetrachloride and copper tetrabromide open-shell dianions, CuCl 4 2- and CuBr 4 2- , respectively, are investigated by a variety of symmetry-adapted-cluster configuration-interaction (SAC-CI) and equation-of-motion coupled-cluster (EOMCC) methods. The valence excited states of the CuCl 4 2- and CuBr 4 2- species that correspond to transitions from doubly occupied molecular orbitals (MOs) to a singly occupied MO (SOMO), for which experimental spectra are available, are examined with the ionized (IP) variants of the SAC-CI and EOMCC methods. The higher-energy excited states of CuCl 4 2- and CuBr 4 2- that correspond to transitions from SOMO to unoccupied MOs, which have not been characterized experimentally, are determined using the electron-attached (EA) SAC-CI and EOMCC approaches. An emphasis is placed on the scalar relativistic SAC-CI and EOMCC calculations based on the spin-free part of the second-order Douglass–Kroll–Hess Hamiltonian (DKH2) and on a comparison of the results of the IP and EA SAC-CI and EOMCC calculations with up to 2-hole-1-particle (2h-1p) and 2-particle-1-hole (2p-1h) excitations, referred to as the IP-SAC-CI SD-R and IP-EOMCCSD(2h-1p) methods in the IP case and EA-SAC-CI SD-R and EA

  2. Basis set effects on coupled cluster benchmarks of electronically excited states: CC3, CCSDR(3) and CC2

    DEFF Research Database (Denmark)

    Silva-Junior, Mario R.; Sauer, Stephan P. A.; Schreiber, Marko

    2010-01-01

    Vertical electronic excitation energies and one-electron properties of 28 medium-sized molecules from a previously proposed benchmark set are revisited using the augmented correlation-consistent triple-zeta aug-cc-pVTZ basis set in CC2, CCSDR(3), and CC3 calculations. The results are compared...... to those obtained previously with the smaller TZVP basis set. For each of the three coupled cluster methods, a correlation coefficient greater than 0.994 is found between the vertical excitation energies computed with the two basis sets. The deviations of the CC2 and CCSDR(3) results from the CC3 reference...... values are very similar for both basis sets, thus confirming previous conclusions on the intrinsic accuracy of CC2 and CCSDR(3). This similarity justifies the use of CC2- or CCSDR(3)-based corrections to account for basis set incompleteness in CC3 studies of vertical excitation energies. For oscillator...

  3. Production of the Q2 doubly excited states of the hydrogen molecule by electron impact in a single step

    Science.gov (United States)

    Santos, Leonardo O.; Rocha, Alexandre B.; Faria, Nelson Velho de Castro; Jalbert, Ginette

    2017-03-01

    We calculate the single step cross sections for excitation of Q 2 states of H2 and its subsequent dissociation. The cross section calculations were performed within the first Born approximation and the electronic wave functions were obtained via State-Averaged Multiconfigurational Self-Consistent Field followed by Configuration Interaction. We have assumed autoionization is the only important process competing with dissociation into neutral atoms. We have estimated its probability through a semi classical approach and compared with results of literature. Special attention was given to the Q 2 1Σg +(1) state which, as has been shown in a previous work, may dissociate into H(2 sσ) + H(2 sσ) fragments (some figures in this article are in colour only in the electronic version).

  4. Photophysical properties and excited state intramolecular proton transfer in 2-hydroxy-5-[(E)-(4-methoxyphenyl)diazenyl]benzoic acid in homogeneous solvents and micro-heterogeneous environments

    Energy Technology Data Exchange (ETDEWEB)

    Gashnga, Pynsakhiat Miki [Centre for Advanced Studies, Department of Chemistry, North-Eastern Hill University, Shillong 793022, Meghalaya (India); Singh, T. Sanjoy [Department of Chemistry, Assam University, Silchar 788011, Assam (India); Baul, Tushar S. Basu [Centre for Advanced Studies, Department of Chemistry, North-Eastern Hill University, Shillong 793022, Meghalaya (India); Mitra, Sivaprasad, E-mail: smitra@nehu.ac.in [Centre for Advanced Studies, Department of Chemistry, North-Eastern Hill University, Shillong 793022, Meghalaya (India)

    2014-04-15

    A systematic study on the photophysical properties and excited state intramolecular proton transfer (ESIPT) behavior of 2-hydroxy-5-[(E)-(4-methoxyphenyl)diazenyl]benzoic acid, is reported using steady-state and time-resolved fluorescence spectroscopy in homogeneous solvents as well as in different micro-heterogeneous environments. Depending on the nature of intramolecular hydrogen bond (IHB), the salicylic acid derivative may exist in two different ground state conformers (I and II). Structure I having IHB between the carbonyl oxygen and phenolic hydrogen can undergo ESIPT upon excitation as evidenced by largely Stokes-shifted fluorescence at ∼455 nm; whereas, normal fluorescence in the blue side of the spectrum (∼410 nm) is due to the spontaneous emission from conformer II. The results in homogeneous solvents were compared with those in bio-mimicking environments of β-cyclodextrin (CD) and surfactants. The intensity of the ESIPT fluorescence increases substantially upon encapsulation of the probe into the cyclodextrin as well as micellar nano-cavities. Detailed analysis of the spectroscopic data indicates that the probe forms 1:1 complex with CD in aqueous medium. Binding constant of the probe with the micelles as well as critical micelle concentration was obtained from the variation of fluorescence intensity on increasing concentration of different surfactants in aqueous medium. -- Highlights: • Steady state and time resolved fluorescence study on ESIPT in HMBA. • Dual fluorescence corresponding to the pro- and non-ESIPT structures. • Modulation of ESIPT fluorescence in micro-heterogeneous environments. • 1:1 stoichiometry for interaction with cyclodextrin. • Calculation of binding constant and other physico-chemical properties from fluorescence titration data in surfactants.

  5. Photophysical properties and excited state intramolecular proton transfer in 2-hydroxy-5-[(E)-(4-methoxyphenyl)diazenyl]benzoic acid in homogeneous solvents and micro-heterogeneous environments

    International Nuclear Information System (INIS)

    Gashnga, Pynsakhiat Miki; Singh, T. Sanjoy; Baul, Tushar S. Basu; Mitra, Sivaprasad

    2014-01-01

    A systematic study on the photophysical properties and excited state intramolecular proton transfer (ESIPT) behavior of 2-hydroxy-5-[(E)-(4-methoxyphenyl)diazenyl]benzoic acid, is reported using steady-state and time-resolved fluorescence spectroscopy in homogeneous solvents as well as in different micro-heterogeneous environments. Depending on the nature of intramolecular hydrogen bond (IHB), the salicylic acid derivative may exist in two different ground state conformers (I and II). Structure I having IHB between the carbonyl oxygen and phenolic hydrogen can undergo ESIPT upon excitation as evidenced by largely Stokes-shifted fluorescence at ∼455 nm; whereas, normal fluorescence in the blue side of the spectrum (∼410 nm) is due to the spontaneous emission from conformer II. The results in homogeneous solvents were compared with those in bio-mimicking environments of β-cyclodextrin (CD) and surfactants. The intensity of the ESIPT fluorescence increases substantially upon encapsulation of the probe into the cyclodextrin as well as micellar nano-cavities. Detailed analysis of the spectroscopic data indicates that the probe forms 1:1 complex with CD in aqueous medium. Binding constant of the probe with the micelles as well as critical micelle concentration was obtained from the variation of fluorescence intensity on increasing concentration of different surfactants in aqueous medium. -- Highlights: • Steady state and time resolved fluorescence study on ESIPT in HMBA. • Dual fluorescence corresponding to the pro- and non-ESIPT structures. • Modulation of ESIPT fluorescence in micro-heterogeneous environments. • 1:1 stoichiometry for interaction with cyclodextrin. • Calculation of binding constant and other physico-chemical properties from fluorescence titration data in surfactants

  6. Electron correlation effect on radiative decay processes of the core-excited states of Be-like ions

    Energy Technology Data Exchange (ETDEWEB)

    Sang, Cuicui, E-mail: sangcc@126.com [Department of Physics, Qinghai Normal University, Xining 810001 (China); Li, Kaikai [College of Forensic Science, People' s Public Security University of China, Beijing 100038 (China); Sun, Yan; Hu, Feng [School of Mathematic and Physical Science, Xuzhou Institute of Technology, Xuzhou 221400, Jiangsu (China)

    2016-07-15

    Highlights: • Radiative rates of the states 1s2s{sup 2}2p and 1s2p{sup 3} with Z = 8–54 are studied. • Electron correlation effect on the radiative transition rates is studied. • Forbidden transitions are explored. - Abstract: Energy levels and the radiative decay processes of the core-excited configurations 1s2s{sup 2}2p and 1s2p{sup 3} of Be-like ions with Z = 8–54 are studied. Electron correlation effect on the energy levels and the radiative transition rates are studied in detail. Except for E1 radiative transition rates, the E2, M1 and M2 forbidden transitions are also explored. Further relativistic corrections from the Breit interaction, quantum electrodynamics and the finite nuclear size are included in the calculations to make the results more precise. Good agreement is found between our results and other theoretical data.

  7. Electron transfer in proteins

    DEFF Research Database (Denmark)

    Farver, O; Pecht, I

    1991-01-01

    Electron migration between and within proteins is one of the most prevalent forms of biological energy conversion processes. Electron transfer reactions take place between active centers such as transition metal ions or organic cofactors over considerable distances at fast rates and with remarkable...... specificity. The electron transfer is attained through weak electronic interaction between the active sites, so that considerable research efforts are centered on resolving the factors that control the rates of long-distance electron transfer reactions in proteins. These factors include (in addition......-containing proteins. These proteins serve almost exclusively in electron transfer reactions, and as it turns out, their metal coordination sites are endowed with properties uniquely optimized for their function....

  8. Temperature dependence of the hydrated electron's excited-state relaxation. I. Simulation predictions of resonance Raman and pump-probe transient absorption spectra of cavity and non-cavity models

    Science.gov (United States)

    Zho, Chen-Chen; Farr, Erik P.; Glover, William J.; Schwartz, Benjamin J.

    2017-08-01

    We use one-electron non-adiabatic mixed quantum/classical simulations to explore the temperature dependence of both the ground-state structure and the excited-state relaxation dynamics of the hydrated electron. We compare the results for both the traditional cavity picture and a more recent non-cavity model of the hydrated electron and make definite predictions for distinguishing between the different possible structural models in future experiments. We find that the traditional cavity model shows no temperature-dependent change in structure at constant density, leading to a predicted resonance Raman spectrum that is essentially temperature-independent. In contrast, the non-cavity model predicts a blue-shift in the hydrated electron's resonance Raman O-H stretch with increasing temperature. The lack of a temperature-dependent ground-state structural change of the cavity model also leads to a prediction of little change with temperature of both the excited-state lifetime and hot ground-state cooling time of the hydrated electron following photoexcitation. This is in sharp contrast to the predictions of the non-cavity model, where both the excited-state lifetime and hot ground-state cooling time are expected to decrease significantly with increasing temperature. These simulation-based predictions should be directly testable by the results of future time-resolved photoelectron spectroscopy experiments. Finally, the temperature-dependent differences in predicted excited-state lifetime and hot ground-state cooling time of the two models also lead to different predicted pump-probe transient absorption spectroscopy of the hydrated electron as a function of temperature. We perform such experiments and describe them in Paper II [E. P. Farr et al., J. Chem. Phys. 147, 074504 (2017)], and find changes in the excited-state lifetime and hot ground-state cooling time with temperature that match well with the predictions of the non-cavity model. In particular, the experiments

  9. Evidence for excited state intramolecular charge transfer reaction in donor-acceptor molecule 5-(4-dimethylamino-phenyl)-penta-2,4-dienoic acid methyl ester: Experimental and quantum chemical approach

    International Nuclear Information System (INIS)

    Kumar Paul, Bijan; Samanta, Anuva; Kar, Samiran; Guchhait, Nikhil

    2010-01-01

    Intramolecular charge transfer (ICT) reaction has been investigated in 5-(4-dimethylamino-phenyl)-penta-2,4-dienoic acid methyl ester (DPDAME) using spectroscopic techniques. The molecule DPDAME shows local emission in non-polar solvent and dual emission in polar solvents. Solvatochromic effects on the Stokes shifted emission band clearly demonstrate the charge transfer character of the excited state. Quantum chemical calculations have been performed at Hartree-Fock (HF) and density functional theoretical (DFT) levels to correlate the experimental findings. Potential energy curves (PECs) for the ICT reaction have been evaluated along the donor twist angle at DFT and time dependent density functional theory (TDDFT) levels for the ground and excited states, respectively, using B3LYP hybrid functional and 6-31G** basis set. The solvent effects on the spectral properties have been explored theoretically at the same level with time dependent density functional theory-polarized continuum model (TDDFT-PCM) and the theoretical results are found to well substantiate the solvent polarity dependent Stokes shifted emission of DPDAME. Huge enhancement of dipole moment (Δμ=16.42 D) of the molecule following photoexcitation dictates the highly polar character of the excited state. Although elucidation of PECs does not exactly predict the operation of ICT according to twisted intramolecular charge transfer (TICT) model in DPDAME, lowering of vertical transition energy as a function of the donor twist coordinate scripts the occurrence of red shifted emission as observed experimentally.

  10. Using a Spreadsheet to Solve the Schro¨dinger Equations for the Energies of the Ground Electronic State and the Two Lowest Excited States of H[subscript2

    Science.gov (United States)

    Ge, Yingbin; Rittenhouse, Robert C.; Buchanan, Jacob C.; Livingston, Benjamin

    2014-01-01

    We have designed an exercise suitable for a lab or project in an undergraduate physical chemistry course that creates a Microsoft Excel spreadsheet to calculate the energy of the S[subscript 0] ground electronic state and the S[subscript 1] and T[subscript 1] excited states of H[subscript 2]. The spreadsheet calculations circumvent the…

  11. Probes of the metal-to-ligand charge-transfer excited states in ruthenium-Am(m)ine-bipyridine complexes: the effects of NH/ND and CH/CD isotopic substitution on the 77 K luminescence.

    Science.gov (United States)

    Chen, Yuan-Jang; Xie, Puhui; Endicott, John F; Odongo, Onduru S

    2006-06-29

    The effects of ligand perdeuteration on the metal-to-ligand charge-transfer (MLCT) excited-state emission properties at 77 K are described for several [Ru(L)(4)bpy](2+) complexes in which the emission process is nominally [uIII,bpy-] --> [RuII,bpy]. The perdeuteration of the 2,2'-bipyridine (bpy) ligand is found to increase the zero-point energy differences between the ground states and MLCT excited states by amounts that vary from 0 +/- 10 to 70 +/- 10 cm(-1) depending on the ligands L. This indicates that there are some vibrational modes with smaller force constants in the excited states than in the ground states for most of these complexes. These blue shifts increase approximately as the energy difference between the excited and ground states decreases, but they are otherwise not strongly correlated with the number of bipyridine ligands in the complex. Careful comparisons of the [Ru(L)(4)(d(8)-bpy)](2+) and [Ru(L)(4)(h(8)-bpy](2+) emission spectra are used to resolve the very weak vibronic contributions of the C-H stretching modes as the composite contributions of the corresponding vibrational reorganizational energies. The largest of these, 25 +/- 10 cm(-1), is found for the complexes with L = py or bpy/2 and smaller when L = NH(3). Perdeuteration of the am(m)ine ligands (NH(3), en, or [14]aneN(4)) has no significant effect on the zero-point energy difference, and the contributions of the NH stretching vibrational modes to the emission band shape are too weak to resolve. Ligand perdeuteration does increase the excited-state lifetimes by a factor that is roughly proportional to the excited-state-ground-state energy difference, even though the CH and NH vibrational reorganizational energies are too small for nuclear tunneling involving these modes to dominate the relaxation process. It is proposed that metal-ligand skeletal vibrational modes and configurational mixing between metal-centered, bpy-ligand-centered, and MLCT excited states are important in

  12. Optical studies of multiply excited states

    International Nuclear Information System (INIS)

    Mannervik, S.

    1989-01-01

    Optical studies of multiply-excited states are reviewed with emphasis on emission spectroscopy. From optical measurements, properties such as excitation energies, lifetimes and autoionization widths can be determined with high accuracy, which constitutes a challenge for modern computational methods. This article mainly covers work on two-, three- and four-electron systems, but also sodium-like quartet systems. Furthermore, some comments are given on bound multiply-excited states in negative ions. Fine structure effects on transition wavelengths and lifetimes (autoionization) are discussed. In particular, the most recent experimental and theoretical studies of multiply-excited states are covered. Some remaining problems, which require further attention, are discussed in more detail. (orig.) With 228 refs

  13. Manipulating the Electronic Excited State Energies of Pyrimidine-Based Thermally Activated Delayed Fluorescence Emitters To Realize Efficient Deep-Blue Emission.

    Science.gov (United States)

    Komatsu, Ryutaro; Ohsawa, Tatsuya; Sasabe, Hisahiro; Nakao, Kohei; Hayasaka, Yuya; Kido, Junji

    2017-02-08

    The development of efficient and robust deep-blue emitters is one of the key issues in organic light-emitting devices (OLEDs) for environmentally friendly, large-area displays or general lighting. As a promising technology that realizes 100% conversion from electrons to photons, thermally activated delayed fluorescence (TADF) emitters have attracted considerable attention. However, only a handful of examples of deep-blue TADF emitters have been reported to date, and the emitters generally show large efficiency roll-off at practical luminance over several hundreds to thousands of cd m -2 , most likely because of the long delayed fluorescent lifetime (τ d ). To overcome this problem, we molecularly manipulated the electronic excited state energies of pyrimidine-based TADF emitters to realize deep-blue emission and reduced τ d . We then systematically investigated the relationships among the chemical structure, properties, and device performances. The resultant novel pyrimidine emitters, called Ac-XMHPMs (X = 1, 2, and 3), contain different numbers of bulky methyl substituents at acceptor moieties, increasing the excited singlet (E S ) and triplet state (E T ) energies. Among them, Ac-3MHPM, with a high E T of 2.95 eV, exhibited a high external quantum efficiency (η ext,max ) of 18% and an η ext of 10% at 100 cd m -2 with Commission Internationale de l'Eclairage chromaticity coordinates of (0.16, 0.15). These efficiencies are among the highest values to date for deep-blue TADF OLEDs. Our molecular design strategy provides fundamental guidance to design novel deep-blue TADF emitters.

  14. Molecular and excited state properties of isomeric scarlet disperse dyes

    Science.gov (United States)

    Lim, Jihye; Szymczyk, Malgorzata; Mehraban, Nahid; Ding, Yi; Parrillo-Chapman, Lisa; El-Shafei, Ahmed; Freeman, Harold S.

    2018-06-01

    This work was part of an investigation aimed at characterizing the molecular and excited state properties of currently available disperse dyes developed to provide stability to extensive sunlight exposures when adsorbed on poly(ethylene terephthalate) (PET) fibers. Having completed the characterization of yellow, magenta, and cyan disperse dyes for PET-based fabrics used outdoors, our attention turned to the colors designed to enhance the color gamut of a standard 4-member (cyan/yellow/magenta/black) color set. The present study pertained specifically to the characterization of commercially available scarlet dyes. In this regard, HPLC analysis showed that a scarlet product used for PET coloration was mainly a 70/30 mixture of dyes, and the use of HRMS and single crystal X-ray diffraction analyses indicated that these two dyes were azo compounds derived from isomeric pyridine-based couplers which differed in the location of the primary amino (sbnd NH2) and anilino (sbnd NHPh) groups attached to the pyridine ring. One dye structure has the sbnd NHPh group para to the azo group (Sc2), while the other has that group in the ortho position (Sc3). The presence of either ortho substituent provides photostabilization through intramolecular H-bonding with the azo moiety. Further, results from molecular modeling studies showed that the lower excited state oxidation potential of Sc3 relative to that of Sc2 allows Sc3 to function as an energy quencher for the excited state of Sc2 - through thermodynamically favorable electron transfer.

  15. Photoinduced electron transfer between benzyloxy dendrimer phthalocyanine and benzoquinone

    Science.gov (United States)

    Zhang, Tiantian; Ma, Dongdong; Pan, Sujuan; Wu, Shijun; Jiang, Yufeng; Zeng, Di; Yang, Hongqin; Peng, Yiru

    2016-10-01

    Photo-induced electron transfer (PET) is an important and fundamental process in natural photosynthesis. To mimic such interesting PET process, a suitable donor and acceptor couple were properly chosen. Dendrimer phthalocyanines and their derivatives have emerged as promising materials for artificial photosynthesis systems. In this paper, the electron transfer between the light harvest dendrimer phthalocyanine (donor) and the 1,4-benzoquinone (acceptor) was studied by UV/Vis and fluorescence spectroscopic methods. It was found that fluorescence of phthalocyanine was quenched by benzoquinone (BQ) via excited state electron transfer, from the phthalocyanine to the BQ upon excitation at 610 nm. The Stern-Volmer constant (KSV) of electron transfer was calculated. Our study suggests that this dendritic phthalocyanine is an effective new electron donor and transmission complex and could be used as a potential artificial photosynthesis system.

  16. Electronic energy transfer through non-adiabatic vibrational-electronic resonance. I. Theory for a dimer

    Science.gov (United States)

    Tiwari, Vivek; Peters, William K.; Jonas, David M.

    2017-10-01

    Non-adiabatic vibrational-electronic resonance in the excited electronic states of natural photosynthetic antennas drastically alters the adiabatic framework, in which electronic energy transfer has been conventionally studied, and suggests the possibility of exploiting non-adiabatic dynamics for directed energy transfer. Here, a generalized dimer model incorporates asymmetries between pigments, coupling to the environment, and the doubly excited state relevant for nonlinear spectroscopy. For this generalized dimer model, the vibrational tuning vector that drives energy transfer is derived and connected to decoherence between singly excited states. A correlation vector is connected to decoherence between the ground state and the doubly excited state. Optical decoherence between the ground and singly excited states involves linear combinations of the correlation and tuning vectors. Excitonic coupling modifies the tuning vector. The correlation and tuning vectors are not always orthogonal, and both can be asymmetric under pigment exchange, which affects energy transfer. For equal pigment vibrational frequencies, the nonadiabatic tuning vector becomes an anti-correlated delocalized linear combination of intramolecular vibrations of the two pigments, and the nonadiabatic energy transfer dynamics become separable. With exchange symmetry, the correlation and tuning vectors become delocalized intramolecular vibrations that are symmetric and antisymmetric under pigment exchange. Diabatic criteria for vibrational-excitonic resonance demonstrate that anti-correlated vibrations increase the range and speed of vibronically resonant energy transfer (the Golden Rule rate is a factor of 2 faster). A partial trace analysis shows that vibronic decoherence for a vibrational-excitonic resonance between two excitons is slower than their purely excitonic decoherence.

  17. Excited-State Conformational/Electronic Responses of Saddle-Shaped N,N'-Disubstituted-Dihydrodibenzo[a,c]phenazines: Wide-Tuning Emission from Red to Deep Blue and White Light Combination.

    Science.gov (United States)

    Zhang, Zhiyun; Wu, Yu-Sin; Tang, Kuo-Chun; Chen, Chi-Lin; Ho, Jr-Wei; Su, Jianhua; Tian, He; Chou, Pi-Tai

    2015-07-08

    A tailored strategy is utilized to modify 5,10-dimethylphenazine (DMP) to donor-acceptor type N,N'-disubstituted-dihydrodibenzo[a,c]phenazines. The representative compounds DMAC (N,N'-dimethyl), DPAC (N,N'-diphenyl), and FlPAC (N-phenyl-N'-fluorenyl) reveal significant nonplanar distortions (i.e., a saddle shape) and remarkably large Stokes-shifted emission independent of the solvent polarity. For DPAC and FlPAC with higher steric hindrance on the N,N'-substituents, normal Stokes-shifted emission also appears, for which the peak wavelength reveals solvent-polarity dependence. These unique photophysical behaviors are rationalized by electronic configuration coupled conformation changes en route to the geometry planarization in the excited state. This proposed mechanism is different from the symmetry rule imposed to explain the anomalously long-wavelength emission for DMP and is firmly supported by polarity-, viscosity-, and temperature-dependent steady-state and nanosecond time-resolved spectroscopy. Together with femtosecond early dynamics and computational simulation of the reaction energy surfaces, the results lead us to establish a sequential, three-step kinetics. Upon electronic excitation of N,N'-disubstituted-dihydrodibenzo[a,c]phenazines, intramolecular charge-transfer takes place, followed by the combination of polarization stabilization and skeletal motion toward the planarization, i.e., elongation of the π-delocalization over the benzo[a,c]phenazines moiety. Along the planarization, DPAC and FlPAC encounter steric hindrance raised by the N,N'-disubstitutes, resulting in a local minimum state, i.e., the intermediate. The combination of initial charge-transfer state, intermediate, and the final planarization state renders the full spectrum of interest and significance in their anomalous photophysics. Depending on rigidity, the N,N'-disubstituted-dihydrodibenzo[a,c]phenazines exhibit multiple emissions, which can be widely tuned from red to deep blue and

  18. Vibronic coupling in the excited-states of carotenoids

    Energy Technology Data Exchange (ETDEWEB)

    Miki, Takeshi [Physikalisch-Chemisches Institut; Ruprecht-Karls-Universität Heidelberg; D-69120 Heidelberg; Germany; Buckup, Tiago [Physikalisch-Chemisches Institut; Ruprecht-Karls-Universität Heidelberg; D-69120 Heidelberg; Germany; Krause, Marie S. [Physikalisch-Chemisches Institut; Ruprecht-Karls-Universität Heidelberg; D-69120 Heidelberg; Germany; Southall, June [College of Medical; Veterinary, and Life Science; University of Glasgow; G12 8QQ Glasgow; UK; Cogdell, Richard J. [College of Medical; Veterinary, and Life Science; University of Glasgow; G12 8QQ Glasgow; UK; Motzkus, Marcus [Physikalisch-Chemisches Institut; Ruprecht-Karls-Universität Heidelberg; D-69120 Heidelberg; Germany

    2016-01-01

    The ultrafast femtochemistry of carotenoids is governed by the interaction between electronic excited states, which has been explained by the relaxation dynamics within a few hundred femtoseconds from the lowest optically allowed excited state S2to the optically dark state S1.

  19. Extended Lagrangian Excited State Molecular Dynamics.

    Science.gov (United States)

    Bjorgaard, J A; Sheppard, D; Tretiak, S; Niklasson, A M N

    2018-02-13

    An extended Lagrangian framework for excited state molecular dynamics (XL-ESMD) using time-dependent self-consistent field theory is proposed. The formulation is a generalization of the extended Lagrangian formulations for ground state Born-Oppenheimer molecular dynamics [Phys. Rev. Lett. 2008 100, 123004]. The theory is implemented, demonstrated, and evaluated using a time-dependent semiempirical model, though it should be generally applicable to ab initio theory. The simulations show enhanced energy stability and a significantly reduced computational cost associated with the iterative solutions of both the ground state and the electronically excited states. Relaxed convergence criteria can therefore be used both for the self-consistent ground state optimization and for the iterative subspace diagonalization of the random phase approximation matrix used to calculate the excited state transitions. The XL-ESMD approach is expected to enable numerically efficient excited state molecular dynamics for such methods as time-dependent Hartree-Fock (TD-HF), Configuration Interactions Singles (CIS), and time-dependent density functional theory (TD-DFT).

  20. Electron transfer to sulfides:

    International Nuclear Information System (INIS)

    Meneses, Ana Belen; Antonello, Sabrina; Arevalo, Maria Carmen; Maran, Flavio

    2005-01-01

    The problem of characterizing the steps associated with the dissociative reduction of sulfides has been addressed. The electrochemical reduction of diphenylmethyl para-methoxyphenyl sulfide in N,N-dimethylformamide, on both glassy carbon and mercury electrodes, was chosen as a test system. The electrode process involves the slow heterogeneous outer-sphere electron transfer to the sulfide, the fast cleavage of the C-S bond, the reduction of the ensuing carbon radical, and the self-protonation triggered by the generation of the strong base Ph 2 CH - . The latter reaction is rather slow, in agreement with the large intrinsic barriers characterizing proton transfers between CH-acids and carbon bases. The dissociative reduction was studied in the presence of an exogenous acid. The results, obtained by convolution analysis, point to a stepwise DET mechanism in which the ET step is accompanied by rather large reorganization energy. Similar results were obtained on both electrode materials. Analysis of the heterogeneous electron transfer and associated C-S bond cleavage indicate that the reduction of this and other sulfides lies between the stepwise dissociative electron transfers leading to the formation of stiff π* radical anions and those going through the intermediacy of loose σ* radical anions

  1. Nonadiabatic anharmonic electron transfer

    Energy Technology Data Exchange (ETDEWEB)

    Schmidt, P. P. [Molecular Physics Research, 6547 Kristina Ursula Court, Falls Church, Virginia 22044 (United States)

    2013-03-28

    The effect of an inner sphere, local mode vibration on an electron transfer is modeled using the nonadiabatic transition probability (rate) expression together with both the anharmonic Morse and the harmonic oscillator potential. For an anharmonic inner sphere mode, a variational analysis uses harmonic oscillator basis functions to overcome the difficulties evaluating Morse-model Franck-Condon overlap factors. Individual matrix elements are computed with the use of new, fast, robust, and flexible recurrence relations. The analysis therefore readily addresses changes in frequency and/or displacement of oscillator minimums in the different electron transfer states. Direct summation of the individual Boltzmann weighted Franck-Condon contributions avoids the limitations inherent in the use of the familiar high-temperature, Gaussian form of the rate constant. The effect of harmonic versus anharmonic inner sphere modes on the electron transfer is readily seen, especially in the exoergic, inverted region. The behavior of the transition probability can also be displayed as a surface for all temperatures and values of the driving force/exoergicity {Delta}=-{Delta}G. The temperature insensitivity of the transfer rate is clearly seen when the exoergicity equals the collective reorganization energy ({Delta}={Lambda}{sub s}) along a maximum ln (w) vs. {Delta} ridge of the surface. The surface also reveals additional regions for {Delta} where ln (w) appears to be insensitive to temperature, or effectively activationless, for some kinds of inner sphere contributions.

  2. A new pathway for transmembrane electron transfer in photosynthetic reaction centers of Rhodobacter sphaeroides not involving the excited special pair.

    NARCIS (Netherlands)

    van Brederode, M.E.; Jones, M.R.; van Mourik, F.; van Stokkum, I.H.M.; van Grondelle, R.

    1997-01-01

    It is generally accepted that electron transfer in bacterial photosynthesis is driven by the first singlet excited state of a special pair of bacteriochlorophylls (P*). We have examined the first steps of electron transfer in a mutant of the Rhodobacter sphaeroides reaction center in which charge

  3. A new pathway for transmembrane electron transfer in photosyntetic reaction centers of Rhodobacter sphaeroides not involving the excited special pair.

    NARCIS (Netherlands)

    van Brederode, M.E.; Jones, M.R.; van Mourik, F.; van Stokkum, I.H.M.; van Grondelle, R.

    1997-01-01

    It is generally accepted that electron transfer in bacterial photosynthesis is driven by the first singlet excited state of a special pair of bacteriochlorophylls (P*). We have examined the first steps of electron transfer in a mutant of the Rhodobacter sphaeroides reaction center in which charge

  4. Probing the Locality of Excited States with Linear Algebra.

    Science.gov (United States)

    Etienne, Thibaud

    2015-04-14

    This article reports a novel theoretical approach related to the analysis of molecular excited states. The strategy introduced here involves gathering two pieces of physical information, coming from Hilbert and direct space operations, into a general, unique quantum mechanical descriptor of electronic transitions' locality. Moreover, the projection of Hilbert and direct space-derived indices in an Argand plane delivers a straightforward way to visually probe the ability of a dye to undergo a long- or short-range charge-transfer. This information can be applied, for instance, to the analysis of the electronic response of families of dyes to light absorption by unveiling the trend of a given push-pull chromophore to increase the electronic cloud polarization magnitude of its main transition with respect to the size extension of its conjugated spacer. We finally demonstrate that all the quantities reported in this article can be reliably approximated by a linear algebraic derivation, based on the contraction of detachment/attachment density matrices from canonical to atomic space. This alternative derivation has the remarkable advantage of a very low computational cost with respect to the previously used numerical integrations, making fast and accurate characterization of large molecular systems' excited states easily affordable.

  5. Electronic correlation studies. III. Self-correlated field method. Application to 2S ground state and 2P excited state of three-electron atomic systems

    International Nuclear Information System (INIS)

    Lissillour, R.; Guerillot, C.R.

    1975-01-01

    The self-correlated field method is based on the insertion in the group product wave function of pair functions built upon a set of correlated ''local'' functions and of ''nonlocal'' functions. This work is an application to three-electron systems. The effects of the outer electron on the inner pair are studied. The total electronic energy and some intermediary results such as pair energies, Coulomb and exchange ''correlated'' integrals, are given. The results are always better than those given by conventional SCF computations and reach the same level of accuracy as those given by more laborious methods used in correlation studies. (auth)

  6. The excited states of 79Kr

    International Nuclear Information System (INIS)

    Liptak, J.; Kristiak, J.; Kristiakova, K.

    1977-01-01

    The β + -decay of 79 Rb has been studied with Ge(Li) detectors in single and coincidence modes. The half-life of the 147.06 keV level in 79 Kr has been determined to be (78+-6) ns. The relative electron intensities of seventeen transitions have been measured with a magnetic Si(Li) spectrometer. The internal conversion coefficients have been determined. The transition multipolarities have been deduced. The spin-parity assignments have been made for excited states of 79 Kr and a β-decaying sta 79 Rb(5/2 + ). The structure of excited states in 79 Kr is discussed in the framework of the Alaga and Coriolis coupling models. It is shown that the properties of some levels in 79 Kr can be explained by the existence of relatively pure rotational bands

  7. Free electrons and ionic liquids: study of excited states by means of electron-energy loss spectroscopy and the density functional theory multireference configuration interaction method.

    Science.gov (United States)

    Regeta, Khrystyna; Bannwarth, Christoph; Grimme, Stefan; Allan, Michael

    2015-06-28

    The technique of low energy (0-30 eV) electron impact spectroscopy, originally developed for gas phase molecules, is applied to room temperature ionic liquids (IL). Electron energy loss (EEL) spectra recorded near threshold, by collecting 0-2 eV electrons, are largely continuous, assigned to excitation of a quasi-continuum of high overtones and combination vibrations of low-frequency modes. EEL spectra recorded by collecting 10 eV electrons show predominantly discrete vibrational and electronic bands. The vibrational energy-loss spectra correspond well to IR spectra except for a broadening (∼0.04 eV) caused by the liquid surroundings, and enhanced overtone activity indicating a contribution from resonant excitation mechanism. The spectra of four representative ILs were recorded in the energy range of electronic excitations and compared to density functional theory multireference configuration interaction (DFT/MRCI) calculations, with good agreement. The spectra up to about 8 eV are dominated by π-π* transitions of the aromatic cations. The lowest bands were identified as triplet states. The spectral region 2-8 eV was empty in the case of a cation without π orbitals. The EEL spectrum of a saturated solution of methylene green in an IL band showed the methylene green EEL band at 2 eV, indicating that ILs may be used as a host to study nonvolatile compounds by this technique in the future.

  8. Can Excited State Electronic Coherence Be Tuned via Molecular Structural Modification? A First-Principles Quantum Electronic Dynamics Study of Pyrazolate-Bridged Pt(II) Dimers

    Energy Technology Data Exchange (ETDEWEB)

    Lingerfelt, David B.; Lestrange, Patrick J.; Radler, Joseph J.; Brown-Xu, Samantha E.; Kim, Pyosang; Castellano, Felix N.; Chen, Lin X.; Li, Xiaosong

    2017-02-24

    Materials and molecular systems exhibiting long-lived electronic coherence can facilitate coherent transport, opening the door to efficient charge and energy transport beyond traditional methods. Recently, signatures of a possible coherent, recurrent electronic motion were identified in femtosecond pump-probe spectroscopy experiments on a binuclear platinum complex, where a persistent periodic beating in the transient absorption signal’s anisotropy was observed. In this study, we investigate the excitonic dynamics that underlie the suspected electronic coherence for a series of binuclear platinum complexes exhibiting a range of interplatinum distances. Results suggest that the long-lived coherence can only result when competitive electronic couplings are in balance. At longer Pt-Pt distances, the electronic couplings between the two halves of the binuclear system weaken, and exciton localization and recombination is favored on short time scales. For short Pt-Pt distances, electronic couplings between the states in the coherent superposition are stronger than the coupling with other excitonic states, leading to long-lived coherence.

  9. Interplay between singlet and triplet excited states in a conformationally locked donor–acceptor dyad

    KAUST Repository

    Filatov, Mikhail A.

    2015-10-13

    The synthesis and photophysical characterization of a palladium(II) porphyrin – anthracene dyad bridged via short and conformationally rigid bicyclo[2.2.2]octadiene spacer were achieved. A spectroscopic investigation of the prepared molecule in solution has been undertaken to study electronic energy transfer in excited singlet and triplet states between the anthracene and porphyrin units. By using steady-state and time-resolved photoluminescence spectroscopy it was shown that excitation of the singlet excited state of the anthracene leads to energy transfer to the lower-lying singlet state of porphyrin. Alternatively, excitation of the porphyrin followed by intersystem crossing to the triplet state leads to very fast energy transfer to the triplet state of anthracene. The rate of this energy transfer has been determined by transient absorption spectroscopy. Comparative studies of the dynamics of triplet excited states of the dyad and reference palladium octaethylporphyrin (PdOEP) have been performed.

  10. Interplay between singlet and triplet excited states in a conformationally locked donor–acceptor dyad

    KAUST Repository

    Filatov, Mikhail A.; Etzold, Fabian; Gehrig, Dominik; Laquai, Fré dé ric; Busko, Dmitri; Landfester, Katharina; Baluschev, Stanislav

    2015-01-01

    The synthesis and photophysical characterization of a palladium(II) porphyrin – anthracene dyad bridged via short and conformationally rigid bicyclo[2.2.2]octadiene spacer were achieved. A spectroscopic investigation of the prepared molecule in solution has been undertaken to study electronic energy transfer in excited singlet and triplet states between the anthracene and porphyrin units. By using steady-state and time-resolved photoluminescence spectroscopy it was shown that excitation of the singlet excited state of the anthracene leads to energy transfer to the lower-lying singlet state of porphyrin. Alternatively, excitation of the porphyrin followed by intersystem crossing to the triplet state leads to very fast energy transfer to the triplet state of anthracene. The rate of this energy transfer has been determined by transient absorption spectroscopy. Comparative studies of the dynamics of triplet excited states of the dyad and reference palladium octaethylporphyrin (PdOEP) have been performed.

  11. Advances in electron transfer chemistry

    CERN Document Server

    Mariano, Patrick S

    1993-01-01

    Advances in Electron Transfer Chemistry, Volume 3 presents studies that discuss findings in the various aspects of electron chemistry. The book is comprised of four chapters; each chapter reviews a work that tackles an issue in electron transfer chemistry. Chapter 1 discusses the photoinduced electron transfer in flexible biaryl donor-acceptor molecules. Chapter 2 tackles light-induced electron transfer in inorganic systems in homogeneous and heterogeneous phases. The book also covers internal geometry relaxation effects on electron transfer rates of amino-centered systems. The sequential elec

  12. Process to produce excited states of atomic nuclei

    International Nuclear Information System (INIS)

    Morita, M.; Morita, R.

    The claims of a patented process which relates to the production of excited states of atomic nuclei are outlined. Among these are (1) production of nuclear excited states by bombarding the atoms with x rays or electrons under given conditions, (2) production of radioactive substances by nuclear excitation with x rays or electrons, (3) separation of specific isotopes from a mixture of isotopes of the same element by means of nuclear excitation followed by chemical treatment. The invention allows production of excited states of atomic nuclei in a relatively simple manner without the need of large apparatus and equipment

  13. Application of spectroscopy and super-resolution microscopy: Excited state

    Energy Technology Data Exchange (ETDEWEB)

    Bhattacharjee, Ujjal [Iowa State Univ., Ames, IA (United States)

    2016-02-19

    Photophysics of inorganic materials and organic molecules in complex systems have been extensively studied with absorption and emission spectroscopy.1-4 Steady-state and time-resolved fluorescence studies are commonly carried out to characterize excited-state properties of fluorophores. Although steady-state fluorescence measurements are widely used for analytical applications, time-resolved fluorescence measurements provide more detailed information about excited-state properties and the environment in the vicinity of the fluorophore. Many photophysical processes, such as photoinduced electron transfer (PET), rotational reorientation, solvent relaxation, and energy transfer, occur on a nanosecond (10-9 s) timescale, thus affecting the lifetime of the fluorophores. Moreover, time-resolved microscopy methods, such as lifetimeimaging, combine the benefits of the microscopic measurement and information-rich, timeresolved data. Thus, time-resolved fluorescence spectroscopy combined with microscopy can be used to quantify these processes and to obtain a deeper understanding of the chemical surroundings of the fluorophore in a small area under investigation. This thesis discusses various photophysical and super-resolution microscopic studies of organic and inorganic materials, which have been outlined below.

  14. Doubly and triply excited states for different plasma sources

    International Nuclear Information System (INIS)

    More, R.M.; Safronova, U.I.

    2000-01-01

    Autoionizing rates of doubly excited states as nln'l' configurations with n=2-9 and n'=2-9 are calculated. Analytical expressions of decay amplitude for two-electron system are derived. Expressions for autoionizing rates with averaging over LS are obtained for many-electron systems. The n and l dependence of doubly excited states as nln'l' configurations are investigated. (author)

  15. Electron Excitation Rate Coefficients for Transitions from the IS21S Ground State to the 1S2S1,3S and 1S2P1,3P0 Excited States of Helium

    Science.gov (United States)

    Aggarwal, K. M.; Kingston, A. E.; McDowell, M. R. C.

    1984-03-01

    The available experimental and theoretical electron impact excitation cross section data for the transitions from the 1s2 1S ground state to the 1s2s 1,3S and 1s2p 1,3P0 excited states of helium are assessed. Based on this assessed data, excitation rate coefficients are calculated over a wide electron temperature range below 3.0×106K. A comparison with other published results suggests that the rates used should be lower by a factor of 2 or more.

  16. The properties of 4'-N,N-dimethylaminoflavonol in the ground and excited states

    Science.gov (United States)

    Moroz, V. V.; Chalyi, A. G.; Roshal, A. D.

    2008-09-01

    The mechanism of protonation of 4-N,N-dimethylaminoflavonol and the structure of its protolytic forms in the ground and excited states were studied by electron absorption and fluorescence (steady-state and time-resolved) spectroscopy and with the use of the RM1 quantum-chemical method. A comparison of equilibrium constants and the theoretical enthalpies of formation showed that excitation should be accompanied by the inversion of the basicity of the electron acceptor groups of this compound and, as a consequence, changes in the structure of its monocationic form. An analysis of the spectral parameters of the protolytic 4-N,N-dimethylaminoflavonol forms, however, showed that their structure and the sequence of protonation in the excited state were the same as in the ground state. Changes in the structure of the monocation in the excited state were not observed because of the fast radiationless deactivation of this form and the occurrence of excited state intramolecular proton transfer in aprotic solvents.

  17. Excited states in stochastic electrodynamics

    International Nuclear Information System (INIS)

    Franca, H.M.; Marshall, T.W.

    1987-12-01

    It is shown that the set of Wigner functions associated with the excited states of the harmonic oscillator constitute a complete set of functions over the phase space. An arbitraty distribution can be expanded in terms of these Wigner functions. By studying the time evolution, according to Stochastic Electrodynamics, of the expansion coefficients, becomes feasible to separate explicity the contributionsof the radiative reaction and the vaccuum field to the Einsten. A coefficients for this system. A simple semiclassical explanation of the Weisskopf-Heitler phenomenon in resonance fluorescence is also supplied. (author) [pt

  18. Entanglement entropy of excited states

    International Nuclear Information System (INIS)

    Alba, Vincenzo; Fagotti, Maurizio; Calabrese, Pasquale

    2009-01-01

    We study the entanglement entropy of a block of contiguous spins in excited states of spin chains. We consider the XY model in a transverse field and the XXZ Heisenberg spin chain. For the latter, we developed a numerical application of the algebraic Bethe ansatz. We find two main classes of states with logarithmic and extensive behavior in the dimension of the block, characterized by the properties of excitations of the state. This behavior can be related to the locality properties of the Hamiltonian having a given state as the ground state. We also provide several details of the finite size scaling

  19. The impact of dihydrogen phosphate anions on the excited-state proton transfer of harmane. Effect of β-cyclodextrin on these photoreactions.

    Science.gov (United States)

    Reyman, Dolores; Viñas, Montserrat H; Tardajos, Gloria; Mazario, Eva

    2012-01-12

    Photoinduced proton transfer reactions of harmane (1-methyl-9H-pyrido[3,4-b]indole) (HAR) in the presence of a proton donor/acceptor such as dihydrogen phosphate anions in aqueous solution have been studied by stationary and time-resolved fluorescence spectroscopy. The presence of high amounts of dihydrogen phosphate ions modifies the acid/base properties of this alkaloid. Thus, by keeping the pH constant at pH 8.8 and by increasing the amount of NaH(2)PO(4) in the solution, it is possible to reproduce the same spectral profiles as those obtained in high alkaline solutions (pH >12) in the absence of NaH(2)PO(4). Under these conditions, a new fluorescence profile appears at around 520 nm. This result could be related to the results of a recent investigation which suggests that a high intake of phosphates may promote skin tumorigenesis. The presence of β-cyclodextrin (β-CD) avoids the proton transfer reactions in this alkaloid by means the formation of an inclusion complex between β-CD and HAR. The formation of this complex originates a remarkable enhancement of the emission intensity from the neutral form in contrast to the cationic and zwitterionic forms. A new lifetime was obtained at 360 nm (2.5 ns), which was associated with the emission of this inclusion complex. At this wavelength, the fluorescence intensity decay of HAR can be described by a linear combination of two exponentials. From the ratio between the pre-exponential factors, we have obtained a value of K = 501 M for the equilibrium of formation of this complex.

  20. Excited-State N2 Dissociation Pathway on Fe-Functionalized Au.

    Science.gov (United States)

    Martirez, John Mark P; Carter, Emily A

    2017-03-29

    Localized surface plasmon resonances (LSPRs) offer the possibility of light-activated chemical catalysis on surfaces of strongly plasmonic metal nanoparticles. This technology relies on lower-barrier bond formation and/or dissociation routes made available through energy transfer following the eventual decay of LSPRs. The coupling between these decay processes and a chemical trajectory (nuclear motion, charge-transfer, intersystem crossing, etc.) dictates the availability of these alternative (possibly lower barrier) excited-state channels. The Haber-Bosch method of NH 3 synthesis from N 2 and H 2 is notoriously energy intensive. This is due to the difficulty of N 2 dissociation despite the overall reaction being thermodynamically favorable at ambient temperatures and pressures. LSPRs may provide means to improve the kinetics of N 2 dissociation via induced resonance electronic excitation. In this work, we calculate, via embedded n-electron valence second-order perturbation theory within the density functional embedding theory, the excited-state potential energy surfaces for dissociation of N 2 on an Fe-doped Au(111) surface. This metal alloy may take advantage simultaneously of the strong LSPR of Au and the catalytic activity of Fe toward N 2 dissociation. We find the ground-state dissociation activation energy to be 4.74 eV/N 2 , with Fe as the active site on the surface. Consecutive resonance energy transfers (RETs) may be accessed due to the availability of many electronically excited states with intermediate energies arising from the metal surface that may couple to states induced by the Fe-dopant and the adsorbate molecule, and crossing between excited states may effectively lower the dissociation barrier to 1.33 eV. Our work illustrates that large energetic barriers, prohibitive toward chemical reaction, may be overcome through multiple RETs facilitating an otherwise difficult chemical process.

  1. Excited state luminescence of multi-(5-phenyl-1,3,4-oxadiazo-2-yl)benzenes in an electron-donating matrix: exciplex or electroplex?

    Science.gov (United States)

    Yang, Chih-Chiang; Hsu, Chia-Jung; Chou, Pi-Tai; Cheng, Hsu Chun; Su, Yuhlong Oliver; Leung, Man-kit

    2010-01-21

    Multi-(5-phenyl-1,3,4-oxadiazo-2-yl)benzenes show emission in organic solvents from ultraviolet to blue (339-447 nm). The reduction potentials E(1/2)(red) cover a large range of -2.11 V for 2,5-diphenyl-1,3,4-oxadiazole to -0.76 V for 1,2,3,4,5,6-hexa(5-phenyl-1,3,4-oxadiazo-2-yl)benzene. An unexpectedly wide spectral range of the oxadiazole (OXD) exciplex emissions in PVK is observed, ranging from 406 to 603 nm. The OXDs also exhibit similar electroluminescence (EL) when blended into polyvinylcarbazole (PVK). A linear correlation between the lambda(max) of the electroluminescence and photoluminescence is observed, implying that the emission mechanisms in both processes are similar. In addition, the linear correlation between the E(1/2)(red) versus lambda(max) of EL (eV) reflected that the term of the charge-transfer configuration of the contact electron-hole pair plays a major role in the exciplex emission. The exciplex EL of 1,2,5-tri(5-phenyl-1,3,4-oxadiazo-2-yl)benzene (5) could be as high as 1.0 cd/A. Since the exciplex emission usually has a large Stokes shift, this provides a window for us to generate duo emissions for near white light EL with high efficiency. Among the devices we tried, the device of PVK/2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole/5/2,5,8,11-tetra-tert-butylperylene (100:40:40:4) gave EL with good current efficiency of 1.63 cd/A.

  2. Specificity and kinetics of alpha-synuclein binding to model membranes determined with fluorescent excited state intramolecular proton transfer (ESIPT) probe.

    Science.gov (United States)

    Shvadchak, Volodymyr V; Falomir-Lockhart, Lisandro J; Yushchenko, Dmytro A; Jovin, Thomas M

    2011-04-15

    Parkinson disease is characterized cytopathologically by the deposition in the midbrain of aggregates composed primarily of the presynaptic neuronal protein α-synuclein (AS). Neurotoxicity is currently attributed to oligomeric microaggregates subjected to oxidative modification and promoting mitochondrial and proteasomal dysfunction. Unphysiological binding to membranes of these and other organelles is presumably involved. In this study, we performed a systematic determination of the influence of charge, phase, curvature, defects, and lipid unsaturation on AS binding to model membranes using a new sensitive solvatochromic fluorescent probe. The interaction of AS with vesicular membranes is fast and reversible. The protein dissociates from neutral membranes upon thermal transition to the liquid disordered phase and transfers to vesicles with higher affinity. The binding of AS to neutral and negatively charged membranes occurs by apparently different mechanisms. Interaction with neutral bilayers requires the presence of membrane defects; binding increases with membrane curvature and rigidity and decreases in the presence of cholesterol. The association with negatively charged membranes is much stronger and much less sensitive to membrane curvature, phase, and cholesterol content. The presence of unsaturated lipids increases binding in all cases. These findings provide insight into the relation between membrane physical properties and AS binding affinity and dynamics that presumably define protein localization in vivo and, thereby, the role of AS in the physiopathology of Parkinson disease.

  3. Infrared photoexcitation spectroscopy of conducting polymer and C60 composites: direct evidence of photo-induced electron transfer

    NARCIS (Netherlands)

    Lee, Kwanghee; Janssen, R.A.J.; Sariciftci, N.S.; Heeger, A.J.

    1994-01-01

    We report direct spectral evidence of photoinduced electron transfer from the excited state of conducting polymer onto C60 by infrared photoexcitation spectroscopy, from 0.01 eV (100 cm-1) to 1.3 eV (11,000 cm-1). The photoinduced absorption spectra of poly(3-octylthiophene) (P30T) and

  4. Imaging ultrafast excited state pathways in transition metal complexes by X-ray transient absorption and scattering using X-ray free electron laser source

    DEFF Research Database (Denmark)

    Chen, Lin X; Shelby, Megan L; Lestrange, Patrick J

    2016-01-01

    This report will describe our recent studies of transition metal complex structural dynamics on the fs and ps time scales using an X-ray free electron laser source, Linac Coherent Light Source (LCLS). Ultrafast XANES spectra at the Ni K-edge of nickel(ii) tetramesitylporphyrin (NiTMP) were measured...... on the low-energy shoulder of the edge, which is aided by the computation of X-ray transitions for postulated excited electronic states. The observed and computed inner shell to valence orbital transition energies demonstrate and quantify the influence of the electronic configuration on specific metal...

  5. Organic electronic materials: Recent advances in the dft description of the ground and excited states using tuned range-separated hybrid functionals

    KAUST Repository

    Kö rzdö rfer, Thomas; Bredas, Jean-Luc

    2014-01-01

    -band-gap polymers.In this Account, we highlight how these failures can be traced back to the delocalization error inherent to semilocal and global hybrid functionals, which leads to the spurious delocalization of electron densities and an overestimation

  6. Tracking excited-state charge and spin dynamics in iron coordination complexes

    DEFF Research Database (Denmark)

    Zhang, Wenkai; Alonso-Mori, Roberto; Bergmann, Uwe

    2014-01-01

    to spin state, can elucidate the spin crossover dynamics of [Fe(2,2'-bipyridine)(3)](2+) on photoinduced metal-to-ligand charge transfer excitation. We are able to track the charge and spin dynamics, and establish the critical role of intermediate spin states in the crossover mechanism. We anticipate......Crucial to many light-driven processes in transition metal complexes is the absorption and dissipation of energy by 3d electrons(1-4). But a detailed understanding of such non-equilibrium excited-state dynamics and their interplay with structural changes is challenging: a multitude of excited...... states and possible transitions result in phenomena too complex to unravel when faced with the indirect sensitivity of optical spectroscopy to spin dynamics(5) and the flux limitations of ultrafast X-ray sources(6,7). Such a situation exists for archetypal poly-pyridyl iron complexes, such as [Fe(2...

  7. Excited states rotational effects on the behavior of excited molecules

    CERN Document Server

    Lim, Edward C

    2013-01-01

    Excited States, Volume 7 is a collection of papers that discusses the excited states of molecules. The first paper reviews the rotational involvement in intra-molecular in vibrational redistribution. This paper analyzes the vibrational Hamiltonian as to its efficacy in detecting the manifestations of intra-molecular state-mixing in time-resolved and time-averaged spectroscopic measurements. The next paper examines the temporal behavior of intra-molecular vibration-rotation energy transfer (IVRET) and the effects of IVRET on collision, reaction, and the decomposition processes. This paper also

  8. Excited-state density functional theory

    International Nuclear Information System (INIS)

    Harbola, Manoj K; Hemanadhan, M; Shamim, Md; Samal, P

    2012-01-01

    Starting with a brief introduction to excited-state density functional theory, we present our method of constructing modified local density approximated (MLDA) energy functionals for the excited states. We show that these functionals give accurate results for kinetic energy and exchange energy compared to the ground state LDA functionals. Further, with the inclusion of GGA correction, highly accurate total energies for excited states are obtained. We conclude with a brief discussion on the further direction of research that include the construction of correlation energy functional and exchange potential for excited states.

  9. Genealogical electronic coupling procedure incorporating the Hartree--Fock interacting space and suitable for degenerate point groups. Application to excited states of BH3

    International Nuclear Information System (INIS)

    Swope, W.C.; Schaefer, H.F. III; Yarkony, D.R.

    1980-01-01

    The use of Clebsch--Gordan-type coupling coefficients for finite point groups is applied to the problem of constructing symmetrized N-electron wave functions (configurations) for use by the Hartree--Fock SCF and CI methods of determining electronic wave functions for molecular systems. The configurations are eigenfunctions of electronic spin operators, and transform according to a particular irreducible representation of the relevant group of spatial operations which leave the Born--Oppenheimer Hamiltonian invariant. The method proposed for constructing the configurations involves a genealogical coupling procedure. It is particularly useful for studies of molecules which belong to a group which has multiply degenerate irreducible representations. The advantage of the method is that it results in configurations which are real linear combinations of determinants of real symmetry orbitals. This procedure for constructing configurations also allows for the identification of configurations which have no matrix element of the Hamiltonian with a reference configuration. It is therefore possible to construct a Hartree--Fock interacting space of configurations which can speed the convergence of a CI wave function. The coupling method is applied to a study of the ground and two excited electronic states of BH 3 in its D/sub 3h/ geometry. The theoretical approach involved Hartree--Fock SCF calculations followed by single and double substitution CI calculations, both of which employed double-zeta plus polarization quality basis sets

  10. The contribution of electronically excited states to the radiation chemistry of organic systems: Progress report, June 30, 1985-December 30, 1987

    International Nuclear Information System (INIS)

    Lipsky, S.

    1987-01-01

    Research progress is reported on the following topics: effects of electron scavengers on the escape probabilities of geminate ion pairs, mechanism of liquid scintillation counter, photoionization of solutes in nonpolar liquids, kinetics of recombination of geminate ion pairs, and fluorescence of saturated hydrocarbons

  11. Excited state electron and energy relays in supramolecular dinuclear complexes revealed by ultrafast optical and X-ray transient absorption spectroscopy† †Electronic supplementary information (ESI) available: Synthesis schemes, experimental methods, NMR spectra, X-ray crystallographic information, emission spectra, cyclic voltammetry, electronic structure calculations, data analysis and numerical methods, and other additional figures. CCDC 1561879. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c7sc04055e

    Science.gov (United States)

    Kohler, Lars; Hadt, Ryan G.; Zhang, Xiaoyi; Liu, Cunming

    2017-01-01

    The kinetics of photoinduced electron and energy transfer in a family of tetrapyridophenazine-bridged heteroleptic homo- and heterodinuclear copper(i) bis(phenanthroline)/ruthenium(ii) polypyridyl complexes were studied using ultrafast optical and multi-edge X-ray transient absorption spectroscopies. This work combines the synthesis of heterodinuclear Cu(i)–Ru(ii) analogs of the homodinuclear Cu(i)–Cu(i) targets with spectroscopic analysis and electronic structure calculations to first disentangle the dynamics at individual metal sites by taking advantage of the element and site specificity of X-ray absorption and theoretical methods. The excited state dynamical models developed for the heterodinuclear complexes are then applied to model the more challenging homodinuclear complexes. These results suggest that both intermetallic charge and energy transfer can be observed in an asymmetric dinuclear copper complex in which the ground state redox potentials of the copper sites are offset by only 310 meV. We also demonstrate the ability of several of these complexes to effectively and unidirectionally shuttle energy between different metal centers, a property that could be of great use in the design of broadly absorbing and multifunctional multimetallic photocatalysts. This work provides an important step toward developing both a fundamental conceptual picture and a practical experimental handle with which synthetic chemists, spectroscopists, and theoreticians may collaborate to engineer cheap and efficient photocatalytic materials capable of performing coulombically demanding chemical transformations. PMID:29629153

  12. Ethylene glycol modified 2-(2′-aminophenyl)benzothiazoles at the amino site: the excited-state N-H proton transfer reactions in aqueous solution, micelles and potential application in live-cell imaging

    International Nuclear Information System (INIS)

    Liu, Bo-Qing; Tsai, Yi-Hsuan; Li, Yi-Jhen; Chao, Chi-Min; Liu, Kuan-Miao; Chen, Yi-Ting; Chen, Yu-Wei; Chung, Kun-You; Tseng, Huan-Wei; Chou, Pi-Tai

    2016-01-01

    Triethylene glycol monomethyl ether and poly(ethylene glycol) monomethyl ether modified 2-(2′-aminophenyl)benzothiazoles, namely ABT-P3EG, ABT-P7EG and ABT-P12EG varied by different chain length of poly(ethylene glycol) at the amino site, were synthesized to probe their photophysical and bio-imaging properties. In polar, aprotic solvents such as CH 2 Cl 2 ultrafast excited-state intramolecular proton transfer (ESIPT) takes place, resulting in a large Stokes shifted tautomer emission in the green-yellow (550 nm) region. In neutral water, ABT-P12EG forms micelles with diameters of 15  ±  3 nm under a critical micelle concentration (CMC) of ∼80 μM, in which the tautomer emission is greatly enhanced free from water perturbation. Cytotoxicity experiments showed that all ABT-PnEGs have negligible cytotoxicity against HeLa cells even at doses as high as 1 mM. Live-cell imaging experiments were also performed, the results indicate that all ABT-PnEGs are able to enter HeLa cells. While the two-photon excitation emission of ABT-P3EG in cells cytoplasm shows concentration independence and is dominated by the anion blue fluorescence, ABT-P7EG and ABT-P12EG exhibit prominent green tautomer emission at  >  CMC and in part penetrate to the nuclei, adding an additional advantage for the cell imaging. (paper)

  13. Excited-state molecular photoionization dynamics

    International Nuclear Information System (INIS)

    Pratt, S.T.

    1995-01-01

    This review presents a survey of work using resonance-enhanced multiphoton ionization and double-resonance techniques to study excited-state photoionization dynamics in molecules. These techniques routinely provide detail and precision that are difficult to achieve in single-photon ionization from the ground state. The review not only emphasizes new aspects of photoionization revealed in the excited-state experiments but also shows how the excited-state techniques can provide textbook illustrations of some fundamental mechanisms in molecular photoionization dynamics. Most of the examples are confined to diatomic molecules. (author)

  14. Electron transfer reactions of ruthenium(II) complexes with polyphenolic acids in micelles

    Energy Technology Data Exchange (ETDEWEB)

    Rajeswari, Angusamy [School of Chemistry, Madurai Kamaraj University, Madurai 625 021 (India); Department of Chemistry, Fatima College, Madurai 625 018 (India); Ramdass, Arumugam [School of Chemistry, Madurai Kamaraj University, Madurai 625 021 (India); Research Department of Chemistry, Aditanar College of Arts and Science, Tiruchendur 628 216 (India); Muthu Mareeswaran, Paulpandian [School of Chemistry, Madurai Kamaraj University, Madurai 625 021 (India); Department of Industrial Chemistry, Alagappa University, Karaikudi 630 003 (India); Rajagopal, Seenivasan, E-mail: rajagopalseenivasan@yahoo.com [School of Chemistry, Madurai Kamaraj University, Madurai 625 021 (India)

    2016-02-15

    The electron transfer in a microhetrogeneous system is a perfect mimic of biological electron transfer. The electron transfer between biologically important phenolic acids and ruthenium (II) complexes is systematically studied in the presence of anionic and cationic micelles. The photophysical properties of these ruthenium (II) complexes with anionic and cationic micelles and their binding abilities with these two type of micelles are also studies using absorption, emission and excited state lifetime spectral techniques. Pseudophase Ion Exchange (PIE) Model is applied to derive mechanism of electron transfer in two types of micelles. - Highlights: • Effect of microhetrogeneous system is studied using ruthenium (II) complexes and gallic acid is studied. • Pseudophase Ion exchange model is applied to derive the mechanism. • Binding constants are in the range of 10{sup 2}–10{sup 4} M{sup −1}.

  15. Ultrafast electron and energy transfer in dye-sensitized iron oxide and oxyhydroxide nanoparticles

    DEFF Research Database (Denmark)

    Gilbert, Benjamin; Katz, Jordan E.; Huse, Nils

    2013-01-01

    photo-initiated interfacial electron transfer. This approach enables time-resolved study of the fate and mobility of electrons within the solid phase. However, complete analysis of the ultrafast processes following dye photoexcitation of the sensitized iron(iii) oxide nanoparticles has not been reported....... We addressed this topic by performing femtosecond transient absorption (TA) measurements of aqueous suspensions of uncoated and DCF-sensitized iron oxide and oxyhydroxide nanoparticles, and an aqueous iron(iii)–dye complex. Following light absorption, excited state relaxation times of the dye of 115...... a four-state model of the dye-sensitized system, finding electron and energy transfer to occur on the same ultrafast timescale. The interfacial electron transfer rates for iron oxides are very close to those previously reported for DCF-sensitized titanium dioxide (for which dye–oxide energy transfer...

  16. Application of Degenerately Doped Metal Oxides in the Study of Photoinduced Interfacial Electron Transfer.

    Science.gov (United States)

    Farnum, Byron H; Morseth, Zachary A; Brennaman, M Kyle; Papanikolas, John M; Meyer, Thomas J

    2015-06-18

    Degenerately doped In2O3:Sn semiconductor nanoparticles (nanoITO) have been used to study the photoinduced interfacial electron-transfer reactivity of surface-bound [Ru(II)(bpy)2(4,4'-(PO3H2)2-bpy)](2+) (RuP(2+)) molecules as a function of driving force over a range of 1.8 eV. The metallic properties of the ITO nanoparticles, present within an interconnected mesoporous film, allowed for the driving force to be tuned by controlling their Fermi level with an external bias while their optical transparency allowed for transient absorption spectroscopy to be used to monitor electron-transfer kinetics. Photoinduced electron transfer from excited-state -RuP(2+*) molecules to nanoITO was found to be dependent on applied bias and competitive with nonradiative energy transfer to nanoITO. Back electron transfer from nanoITO to oxidized -RuP(3+) was also dependent on the applied bias but without complication from inter- or intraparticle electron diffusion in the oxide nanoparticles. Analysis of the electron injection kinetics as a function of driving force using Marcus-Gerischer theory resulted in an experimental estimate of the reorganization energy for the excited-state -RuP(3+/2+*) redox couple of λ* = 0.83 eV and an electronic coupling matrix element, arising from electronic wave function overlap between the donor orbital in the molecule and the acceptor orbital(s) in the nanoITO electrode, of Hab = 20-45 cm(-1). Similar analysis of the back electron-transfer kinetics yielded λ = 0.56 eV for the ground-state -RuP(3+/2+) redox couple and Hab = 2-4 cm(-1). The use of these wide band gap, degenerately doped materials provides a unique experimental approach for investigating single-site electron transfer at the surface of oxide nanoparticles.

  17. Rearrangements in ground and excited states

    CERN Document Server

    de Mayo, Paul

    1980-01-01

    Rearrangements in Ground and Excited States, Volume 3 presents essays on the chemical generation of excited states; the cis-trans isomerization of olefins; and the photochemical rearrangements in trienes. The book also includes essays on the zimmerman rearrangements; the photochemical rearrangements of enones; the photochemical rearrangements of conjugated cyclic dienones; and the rearrangements of the benzene ring. Essays on the photo rearrangements via biradicals of simple carbonyl compounds; the photochemical rearrangements involving three-membered rings or five-membered ring heterocycles;

  18. Low-lying excited states by constrained DFT

    Science.gov (United States)

    Ramos, Pablo; Pavanello, Michele

    2018-04-01

    Exploiting the machinery of Constrained Density Functional Theory (CDFT), we propose a variational method for calculating low-lying excited states of molecular systems. We dub this method eXcited CDFT (XCDFT). Excited states are obtained by self-consistently constraining a user-defined population of electrons, Nc, in the virtual space of a reference set of occupied orbitals. By imposing this population to be Nc = 1.0, we computed the first excited state of 15 molecules from a test set. Our results show that XCDFT achieves an accuracy in the predicted excitation energy only slightly worse than linear-response time-dependent DFT (TDDFT), but without incurring into problems of variational collapse typical of the more commonly adopted ΔSCF method. In addition, we selected a few challenging processes to test the limits of applicability of XCDFT. We find that in contrast to TDDFT, XCDFT is capable of reproducing energy surfaces featuring conical intersections (azobenzene and H3) with correct topology and correct overall energetics also away from the intersection. Venturing to condensed-phase systems, XCDFT reproduces the TDDFT solvatochromic shift of benzaldehyde when it is embedded by a cluster of water molecules. Thus, we find XCDFT to be a competitive method among single-reference methods for computations of excited states in terms of time to solution, rate of convergence, and accuracy of the result.

  19. Electron transfer in silicon-bridged adjacent chromophores: the source for blue-green emission.

    Science.gov (United States)

    Bayda, Malgorzata; Angulo, Gonzalo; Hug, Gordon L; Ludwiczak, Monika; Karolczak, Jerzy; Koput, Jacek; Dobkowski, Jacek; Marciniak, Bronislaw

    2017-05-10

    Si-Bridged chromophores have been proposed as sources for blue-green emission in several technological applications. The origin of this dual emission is to be found in an internal charge transfer reaction. The current work is an attempt to describe the details of these processes in these kinds of substances, and to design a molecular architecture to improve their performance. Nuclear motions essential for intramolecular charge transfer (ICT) can involve processes from twisted internal moieties to dielectric relaxation of the solvent. To address these issues, we studied ICT between adjacent chromophores in a molecular compound containing N-isopropylcarbazole (CBL) and 1,4-divinylbenzene (DVB) linked by a dimethylsilylene bridge. In nonpolar solvents emission arises from the local excited state (LE) of carbazole whereas in solvents of higher polarity dual emission was detected (LE + ICT). The CT character of the additional emission band was concluded from the linear dependence of the fluorescence maxima on solvent polarity. Electron transfer from CBL to DVB resulted in a large excited-state dipole moment (37.3 D) as determined from a solvatochromic plot and DFT calculations. Steady-state and picosecond time-resolved fluorescence experiments in butyronitrile (293-173 K) showed that the ICT excited state arises from the LE state of carbazole. These results were analyzed and found to be in accordance with an adiabatic version of Marcus theory including solvent relaxation.

  20. Ground and excited states of the [Fe(H2O)6]2+ and [Fe(H2O)6]3+ clusters: Insight into the electronic structure of the [Fe(H2O)6]2+ – [Fe(H2O)6]3+ complex

    Energy Technology Data Exchange (ETDEWEB)

    Miliordos, Evangelos; Xantheas, Sotiris S.

    2015-04-14

    We report the ground and low lying electronically excited states of the [Fe(H2O)6]2+ and [Fe(H2O)6]3+ clusters using multi-configuration electronic structure theory. In particular, we have constructed the Potential Energy Curves (PECs) with respect to the iron-oxygen distance when removing all water ligands at the same time from the cluster minima and established their correlation to the long range dissociation channels. Due to the fact that both the second and third ionization potentials of iron are larger than the one for water, the ground state products asymptotically correlate with dissociation channels that are repulsive in nature at large separations as they contain at least one H2O+ fragment and a positive metal center. The most stable equilibrium structures emanate – via intersections and/or avoided crossings – from the channels consisting of the lowest electronic states of Fe2+(5D; 3d6) or Fe3+(6S; 3d5) and six neutral water molecules. Upon hydration, the ground state of Fe2+(H2O)6 is a triply (5Tg) degenerate one with the doubly (5Eg) degenerate state lying slightly higher in energy. Similarly, Fe3+(H2O)6 has a ground state of 6Ag symmetry under Th symmetry. We furthermore examine a multitude of electronically excited states of many possible spin multiplicities, and report the optimized geometries for several selected states. The PECs for those cases are characterized by a high density of states. Focusing on the ground and the first few excited states of the [Fe(H2O)6]2+ and [Fe(H2O)6]3+ clusters, we studied their mutual interaction in the gas phase. We obtained the optimal geometries of the Fe2+(H2O)6 – Fe3+(H2O)6 gas phase complex for different Fe–Fe distances. For distances shorter than 6.0 Å, the water molecules in the respective first solvation shells located between the two metal centers were found to interact via weak hydrogen bonds. We examined a total of ten electronic states for this complex, including those corresponding to the

  1. Excited-state lifetime measurements: Linearization of the Foerster equation by the phase-plane method

    International Nuclear Information System (INIS)

    Love, J.C.; Demas, J.N.

    1983-01-01

    The Foerster equation describes excited-state decay curves involving resonance intermolecular energy transfer. A linearized solution based on the phase-plane method has been developed. The new method is quick, insensitive to the fitting region, accurate, and precise

  2. Non-adiabatic Excited State Molecule Dynamics Modeling of Photochemistry and Photophysics of Materials

    Energy Technology Data Exchange (ETDEWEB)

    Nelson, Tammie Renee [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Tretiak, Sergei [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2017-01-06

    Understanding and controlling excited state dynamics lies at the heart of all our efforts to design photoactive materials with desired functionality. This tailor-design approach has become the standard for many technological applications (e.g., solar energy harvesting) including the design of organic conjugated electronic materials with applications in photovoltaic and light-emitting devices. Over the years, our team has developed efficient LANL-based codes to model the relevant photophysical processes following photoexcitation (spatial energy transfer, excitation localization/delocalization, and/or charge separation). The developed approach allows the non-radiative relaxation to be followed on up to ~10 ps timescales for large realistic molecules (hundreds of atoms in size) in the realistic solvent dielectric environment. The Collective Electronic Oscillator (CEO) code is used to compute electronic excited states, and the Non-adiabatic Excited State Molecular Dynamics (NA-ESMD) code is used to follow the non-adiabatic dynamics on multiple coupled Born-Oppenheimer potential energy surfaces. Our preliminary NA-ESMD simulations have revealed key photoinduced mechanisms controlling competing interactions and relaxation pathways in complex materials, including organic conjugated polymer materials, and have provided a detailed understanding of photochemical products and intermediates and the internal conversion process during the initiation of energetic materials. This project will be using LANL-based CEO and NA-ESMD codes to model nonradiative relaxation in organic and energetic materials. The NA-ESMD and CEO codes belong to a class of electronic structure/quantum chemistry codes that require large memory, “long-queue-few-core” distribution of resources in order to make useful progress. The NA-ESMD simulations are trivially parallelizable requiring ~300 processors for up to one week runtime to reach a meaningful restart point.

  3. Ultrafast static and diffusion-controlled electron transfer at Ag 29 nanocluster/molecular acceptor interfaces

    KAUST Repository

    Aly, Shawkat Mohammede; AbdulHalim, Lina G.; Besong, Tabot M.D.; Soldan, Giada; Bakr, Osman; Mohammed, Omar F.

    2015-01-01

    Efficient absorption of visible light and a long-lived excited state lifetime of silver nanoclusters (Ag29 NCs) are integral properties for these new clusters to serve as light-harvesting materials. Upon optical excitation, electron injection at Ag29 NC/methyl viologen (MV2+) interfaces is very efficient and ultrafast. Interestingly, our femto- and nanosecond time-resolved results demonstrate clearly that both dynamic and static electron transfer mechanisms are involved in photoluminescence quenching of Ag29 NCs. © 2016 The Royal Society of Chemistry.

  4. Ultrafast static and diffusion-controlled electron transfer at Ag 29 nanocluster/molecular acceptor interfaces

    KAUST Repository

    Aly, Shawkat Mohammede

    2015-10-29

    Efficient absorption of visible light and a long-lived excited state lifetime of silver nanoclusters (Ag29 NCs) are integral properties for these new clusters to serve as light-harvesting materials. Upon optical excitation, electron injection at Ag29 NC/methyl viologen (MV2+) interfaces is very efficient and ultrafast. Interestingly, our femto- and nanosecond time-resolved results demonstrate clearly that both dynamic and static electron transfer mechanisms are involved in photoluminescence quenching of Ag29 NCs. © 2016 The Royal Society of Chemistry.

  5. 75 FR 9120 - Electronic Fund Transfers

    Science.gov (United States)

    2010-03-01

    ... FEDERAL RESERVE SYSTEM 12 CFR Part 205 [Regulation E; Docket No. R-1343] Electronic Fund Transfers... implements the Electronic Fund Transfer Act, and the official staff commentary to the regulation. The final..., the Board adopted a final rule under Regulation E, which implements the Electronic Fund Transfer Act...

  6. An exciton approach to the excited states of two electron atoms. II Determination of spectroscopic parameters, polarizabilites and dispersion coefficients of H-, He, Li+, Be2+ and Ne8+

    International Nuclear Information System (INIS)

    Schipper, P.E.; Martire, B.

    1985-01-01

    The exciton model is applied quantitatively to a description of the excited states of representative members of the helium isoelectronic series; viz. H + , He, Li + , Be 2+ and Ne 8+ . The energies of the eight lowest excited states are in good agreement with experiment, for a relatively small (1s-4p) hydrogenic basis; the ground state is obtained with slightly less precision. Response properties including oscillator strengths, polarizabilites and dispersion interaction coefficients are also calculated. The method leads to particularly simple interpretations of the wave functions and the energies

  7. Computing correct truncated excited state wavefunctions

    Science.gov (United States)

    Bacalis, N. C.; Xiong, Z.; Zang, J.; Karaoulanis, D.

    2016-12-01

    We demonstrate that, if a wave function's truncated expansion is small, then the standard excited states computational method, of optimizing one "root" of a secular equation, may lead to an incorrect wave function - despite the correct energy according to the theorem of Hylleraas, Undheim and McDonald - whereas our proposed method [J. Comput. Meth. Sci. Eng. 8, 277 (2008)] (independent of orthogonality to lower lying approximants) leads to correct reliable small truncated wave functions. The demonstration is done in He excited states, using truncated series expansions in Hylleraas coordinates, as well as standard configuration-interaction truncated expansions.

  8. Interference between radiative emission and autoionization in the decay of excited states of atoms

    International Nuclear Information System (INIS)

    Armstrong, L. Jr.; Theodosiou, C.E.; Wall, M.J.

    1978-01-01

    An excited state of an atom which can autoionize can also undergo radiative decay. We consider the interaction between the final states resulting from these two modes of decay, and its effects on such quantities as the fluorescence yield of the excited state, excitation profile of the excited state, and the spectra of the emitted photons and electrons. It is shown that the fraction of decays of the excited state resulting in a photon (fluorescence yield) is particularly sensitive to the details of the final-state interaction. In lowest order in the final-state interaction, the fluorescence yield is increased by a factor (1 + 1/q 2 ) from the traditional value, where q is the Fano q parameter relating to the excited state and the final atomic state

  9. Nonlinear phenomena in the highly excited state of C60

    International Nuclear Information System (INIS)

    Byrne, H.J.; Maser, W.K.; Kaiser, M.; Akselrod, L.; Anders, J.; Ruehle, W.W.; Zhou, X.Q.; Mittelbach, A.; Roth, S.

    1993-01-01

    Under high intensity illumination, the optical and electronic properties of fullerenes are seen to undergo dramatic, nonlinear changes. The photoluminescence emission is seen to increase with approximately the third power of the input intensity above an apparent threshold intensity. Associated with this nonlinear increase is the emergence of a long lifetime emission component and a redshifting of the emission spectrum. Above the threshold intensity the photoconductive response increases with approximately the cube of the input power. In the highly excited state, the photoconductive response becomes relatively temperature independent compared to the thermally activated behaviour observed at low intensities. The characteristics of the temperature dependence are associated with a metallic-like phase in the highly excited state and therefore an optically driven insulator to metal transition is proposed as a description of the observed phenomena. (orig.)

  10. Excited-state imaging of cold atoms

    NARCIS (Netherlands)

    Sheludko, D.V.; Bell, S.C.; Vredenbregt, E.J.D.; Scholten, R.E.; Deshmukh, P.C.; Chakraborty, P.; Williams, J.F.

    2007-01-01

    We have investigated state-selective diffraction contrast imaging (DCI) of cold 85Rb atoms in the first excited (52P3/2) state. Excited-state DCI requires knowledge of the complex refractive index of the atom cloud, which was calculated numerically using a semi-classical model. The Autler-Townes

  11. Excited state properties of aryl carotenoids

    Czech Academy of Sciences Publication Activity Database

    Fuciman, M.; Chábera, P.; Župčanová, Anita; Hříbek, P.; Arellano, J.B.; Vácha, František; Pšenčík, J.; Polívka, Tomáš

    2010-01-01

    Roč. 12, č. 13 (2010), s. 3112-3120 ISSN 1463-9076 R&D Projects: GA AV ČR IAA608170604 Institutional research plan: CEZ:AV0Z50510513 Keywords : carotenoids * excited-states * femtosecond spectroscopy Subject RIV: BO - Biophysics Impact factor: 3.454, year: 2010

  12. Ab initio study on electron excitation and electron transfer in tryptophan-tyrosine system

    International Nuclear Information System (INIS)

    Tong Jing; Li Xiangyuan

    2002-01-01

    In this article, ab initio calculation has been performed to evaluate the transition energy of electronic excitation in tryptophan and tyrosine by using semiempirical molecular orbital method AM1 and complete active space self-consistent field method. The solvent effect has been considered by means of the conductor-like screening model. After geometric optimizations of isolated tryptophan and tyrosine, and their corresponding radicals and cations, reaction heat of these electron transfer reactions have been obtained by the means of complete active space self-consistent field method. The transition energies from the ground state, respectively, to the lowest excited state and to the lowest triplet state of these two amino acids are also calculated and compared with the experimentally observed values. The ionization potential and electron affinity are also calculated for tryptophan and tyrosine employing Koopmans' theorem and ab initio calculation. Compared with the experimental measurements, the theoretical results are found satisfactory. Theoretical results give good explanations on the experimental phenomena that N 3 · can preferably oxide the side chain of tryptophan residue and then the electron transfer from tyrosine residue to tryptophan residue follows in peptides involving tryptophan and tyrosine

  13. Quenching reactions of electronically excited atoms

    International Nuclear Information System (INIS)

    Setser, D.W.

    2001-01-01

    The two-body, thermal quenching reactions of electronically excited atoms are reviewed using excited states of Ar, Kr, and Xe atoms as examples. State-specific interstate relaxation and excitation-transfer reactions with atomic colliders are discussed first. These results then are used to discuss quenching reactions of excited-state atoms with diatomic and polyatomic molecules, the latter have large cross sections, and the reactions can proceed by excitation transfer and by reactive quenching. Excited states of molecules are not considered; however, a table of quenching rate constants is given for six excited-state molecules in an appendix

  14. Method of producing excited states of atomic nuclei

    International Nuclear Information System (INIS)

    Morita, M.; Morita, R.

    1976-01-01

    A method is claimed of producing excited states of atomic nuclei which comprises bombarding atoms with x rays or electrons, characterized in that (1) in the atoms selected to be produced in the excited state of their nuclei, (a) the difference between the nuclear excitation energy and the difference between the binding energies of adequately selected two electron orbits is small enough to introduce the nuclear excitation by electron transition, and (b) the system of the nucleus and the electrons in the case of ionizing an orbital electron in said atoms should satisfy the spin and parity conservation laws; and (2) the energy of the bombarding x rays or electrons should be larger than the binding energy of one of the said two electron orbits which is located at shorter distance from the atomic nucleus. According to the present invention, atomic nuclei can be excited in a relatively simple manner without requiring the use of large scale apparatus, equipment and production facilities, e.g., factories. It is also possible to produce radioactive substances or separate a particular isotope with an extremely high purity from a mixture of isotopes by utilizing nuclear excitation

  15. Exocellular electron transfer in anaerobic microbial communities

    NARCIS (Netherlands)

    Stams, A.J.M.; Bok, de F.A.M.; Plugge, C.M.; Eekert, van M.H.A.; Dolfing, J.; Schraa, G.

    2006-01-01

    Exocellular electron transfer plays an important role in anaerobic microbial communities that degrade organic matter. Interspecies hydrogen transfer between microorganisms is the driving force for complete biodegradation in methanogenic environments. Many organic compounds are degraded by obligatory

  16. Excited-state relaxation of some aminoquinolines

    Directory of Open Access Journals (Sweden)

    2006-01-01

    Full Text Available The absorption and fluorescence spectra, fluorescence quantum yields and lifetimes, and fluorescence rate constants ( k f of 2-amino-3-( 2 ′ -benzoxazolylquinoline (I, 2-amino-3-( 2 ′ -benzothiazolylquinoline (II, 2-amino-3-( 2 ′ -methoxybenzothiazolyl-quinoline (III, 2-amino-3-( 2 ′ -benzothiazolylbenzoquinoline (IV at different temperatures have been measured. The shortwavelength shift of fluorescence spectra of compounds studied (23–49 nm in ethanol as the temperature decreases (the solvent viscosity increases points out that the excited-state relaxation process takes place. The rate of this process depends essentially on the solvent viscosity, but not the solvent polarity. The essential increasing of fluorescence rate constant k f (up to about 7 times as the solvent viscosity increases proves the existence of excited-state structural relaxation consisting in the mutual internal rotation of molecular fragments of aminoquinolines studied, followed by the solvent orientational relaxation.

  17. [Nature of the electron excited state in pigment redox reactions. II. Analysis of the scheme of primary processes in the photooxidation reaction of chlorophylls a and b and pheophytin a ].

    Science.gov (United States)

    Andreeva, N E; Barashkov, B I; Zakharova, G V; Shubin, V V; Chibisov, A K

    1978-01-01

    A scheme of primary reactions in photooxidation of pigments was considered assuming that electron transfer processes can occur via singlet excited as well as triplet states. The results of analysis are compared with the experimental data on relative yield values of chlorophylls a, b, and pheophytin a cation-radicals, as well as with the data on fluorescence quenching. A conclusion has been drawn that photooxidation of pigments proceeds exclusively via the triplet state. The dependence of rate constant quenching values of chlorophyll a triplet state by certain electron acceptors on values of half cell potentials was given.

  18. Probability of collective excited state decay

    International Nuclear Information System (INIS)

    Manykin, Eh.A.; Ozhovan, M.I.; Poluehktov, P.P.

    1987-01-01

    Decay mechanisms of condensed excited state formed of highly excited (Rydberg) atoms are considered, i.e. stability of so-called Rydberg substance is analyzed. It is shown that Auger recombination and radiation transitions are the basic processes. The corresponding probabilities are calculated and compared. It is ascertained that the ''Rydberg substance'' possesses macroscopic lifetime (several seconds) and in a sense it is metastable

  19. Rearrangements in ground and excited states

    CERN Document Server

    de Mayo, Paul

    1980-01-01

    Rearrangements in Ground and Excited States, Volume 2 covers essays on the theoretical approach of rearrangements; the rearrangements involving boron; and the molecular rearrangements of organosilicon compounds. The book also includes essays on the polytopal rearrangement at phosphorus; the rearrangement in coordination complexes; and the reversible thermal intramolecular rearrangements of metal carbonyls. Chemists and people involved in the study of rearrangements will find the book invaluable.

  20. Hierarchical control of electron-transfer

    DEFF Research Database (Denmark)

    Westerhoff, Hans V.; Jensen, Peter Ruhdal; Egger, Louis

    1997-01-01

    In this chapter the role of electron transfer in determining the behaviour of the ATP synthesising enzyme in E. coli is analysed. It is concluded that the latter enzyme lacks control because of special properties of the electron transfer components. These properties range from absence of a strong...... back pressure by the protonmotive force on the rate of electron transfer to hierarchical regulation of the expression of the gens that encode the electron transfer proteins as a response to changes in the bioenergetic properties of the cell.The discussion uses Hierarchical Control Analysis...

  1. Nonadiabatic excited-state molecular dynamics: On-the-fly limiting of essential excited states

    Energy Technology Data Exchange (ETDEWEB)

    Nelson, Tammie [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Naumov, Artem [Skolkovo Institute of Science and Technology, Moscow 143026 (Russian Federation); Fernandez-Alberti, Sebastian [Universidad Nacional de Quilmes, Roque Saenz Pea 352, B1876BXD Bernal (Argentina); Tretiak, Sergei, E-mail: serg@lanl.gov [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)

    2016-12-20

    The simulation of nonadiabatic dynamics in extended molecular systems involving hundreds of atoms and large densities of states is particularly challenging. Nonadiabatic coupling terms (NACTs) represent a significant numerical bottleneck in surface hopping approaches. Rather than using unreliable NACT cutting schemes, here we develop “on-the-fly” state limiting methods to eliminate states that are no longer essential for the non-radiative relaxation dynamics as a trajectory proceeds. We propose a state number criteria and an energy-based state limit. The latter is more physically relevant by requiring a user-imposed energy threshold. For this purpose, we introduce a local kinetic energy gauge by summing contributions from atoms within the spatial localization of the electronic wavefunction to define the energy available for upward hops. The proposed state limiting schemes are implemented within the nonadiabatic excited-state molecular dynamics framework to simulate photoinduced relaxation in poly-phenylene vinylene (PPV) and branched poly-phenylene ethynylene (PPE) oligomers for benchmark evaluation.

  2. Ultrafast charge transfer and radiationless relaxations from higher excited state (S2) of directly linked Zn-porphyrin (ZP)-acceptor dyads: investigations into fundamental problems of exciplex chemistry

    International Nuclear Information System (INIS)

    Mataga, Noboru; Taniguchi, Seiji; Chosrowjan, Haik; Osuka, Atsuhiro; Yoshida, Naoya

    2003-01-01

    We have investigated photoinduced electron transfer and related processes from the higher excited electronic state (S 2 ) of Zn-porphyrin-imide acceptor directly linked supramolecular systems (ZP-I) designed especially for the critical studies of the energy gap law (EGL) of the charge separation (CS) from the S 2 state and solvent effects upon EGL. We have confirmed the modification of the EGL by change of solvent polarity from acetonitrile (ACN), tetrahydrofuran (THF) to toluene (Tol) and methyl-cyclohexane (MCH), from rather typical bell-shaped one in ACN to that with less prominent normal region and prominent inverted region with moderate slope extending over wider range of -ΔG CS values in nonpolar solvent MCH. We have demonstrated that these solvent effects upon EGL affect delicately various radiationless relaxation processes from S 2 state. We have examined also effects of the hydrogen bonding solvent ethanol (EtOH) on the EGL for CS and found very specific effect controlling the CS reaction and related processes

  3. Excited state populations and charge-exchange of fast ions in solids

    International Nuclear Information System (INIS)

    Miller, P.D.; Sofield, C.J.; Woods, C.J.

    1984-01-01

    Excited state populations and charge state fractions of 445 MeV Cl ions have been measured for a range of thicknesses of solid C targets. Cross sections for electron capture, loss, excitation and excited state quenching have been determined and these data are found to predict a quantitative difference between equilibrium charge state distributions from gases and solids for a special case of the Bohr-Lindhard density effect model. 8 references, 1 figure, 1 table

  4. Splitting of the luminescent excited state of the uranyl ion

    International Nuclear Information System (INIS)

    Flint, C.D.; Sharma, P.; Tanner, P.A.

    1982-01-01

    The luminescence spectra of some uranyl compounds has been studied. It has been proposed that the splitting of the luminescent excited state of the uranyl ion is due to a descent in symmetry experienced by the uranyl ion when it is placed in a crystal field. In recent years there has been developed a highly successful model of the electronic structure of the uranyl ion. In this paper the authors use this model to interpret the luminescence spectra of a variety of uranyl compounds

  5. Calculations of core-excited states in Li

    International Nuclear Information System (INIS)

    Verbockhaven, G.; Hansen, J.E.

    1999-01-01

    We report on progress in the calculation of three-electron states making use of B-spline basis sets. In particular we discuss the advantages and disadvantages of using a Hartree-Fock basis (expanded in B-splines) compared to the use of hydrogenic basis states. Preliminary results are presented for the 2 S terms in Li below the 1s2s 3 S limit at 64.4 eV. The 2 S terms have been studied less extensively than other core-excited states in Li. In this particular case the choice of basis has a large influence on the quality of the results. (orig.)

  6. Photoinduced electron transfer and persistent spectral hole-burning in natural emerald.

    Science.gov (United States)

    Riesen, Hans

    2011-06-02

    Wavelength-selective excited-state lifetime measurements and absorption, luminescence, and hole-burning spectra of a natural African emerald crystal are reported. The (2)E excited-state lifetime displays an extreme wavelength dependence, varying from 190 to 37 μs within 1.8 nm of the R(1)-line. Overall, the excited state is strongly quenched, in comparison to laboratory-created emerald (τ=1.3 ms), with an average quenching rate of ∼6 × 10(3) s(-1) at 2.5 K. This quenching is attributed to photoinduced electron transfer caused by a relatively high concentration of Fe(2+) ions. The forward electron-transfer rate, k(f), from the nearest possible Fe(2+) sites at around 5 Å is estimated to be ∼20 × 10(3) s(-1) at 2.5 K. The photoreductive quenching of the excited Cr(3+) ions by Fe(2+) is followed by rapid electron back-transfer in the ground state upon deactivation. The exchange interaction based quenching can be modeled by assuming a random quencher distribution within the possible Fe(2+) sites with the forward electron-transfer rate, k(f), given as a function of acceptor-donor separation R by exp[(R(f)-R)/a(f)]; R(f) and a(f) values of 13.5 and 2.7 Å are obtained at 2.5 K. The electron transfer/back-transfer reorganizes the local crystal lattice, occasionally leading to a minor variation of the short-range structure around the Cr(3+) ions. This provides a mechanism for spectral hole-burning for which a moderately high quantum efficiency of about ∼0.005% is observed. Spectral holes are subject to spontaneous hole-filling and spectral diffusion, and both effects can be quantified within the standard two-level systems for non-photochemical hole-burning. Importantly, the absorbance increases on both sides of broad spectral holes, and isosbestic points are observed, in accord with the expected distribution of the "photoproduct" in a non-photochemical hole-burning process. © 2011 American Chemical Society

  7. Tunneling induced electron transfer between separated protons

    Science.gov (United States)

    Vindel-Zandbergen, Patricia; Meier, Christoph; Sola, Ignacio R.

    2018-04-01

    We study electron transfer between two separated protons using local control theory. In this symmetric system one can favour a slow transfer by biasing the algorithm, achieving high efficiencies for fixed nuclei. The solution can be parametrized using a sequence of a pump followed by a dump pulse that lead to tunneling-induced electron transfer. Finally, we study the effect of the nuclear kinetic energy on the efficiency. Even in the absence of relative motion between the protons, the spreading of the nuclear wave function is enough to reduce the yield of electronic transfer to less than one half.

  8. Exocellular electron transfer in anaerobic microbial communities.

    Science.gov (United States)

    Stams, Alfons J M; de Bok, Frank A M; Plugge, Caroline M; van Eekert, Miriam H A; Dolfing, Jan; Schraa, Gosse

    2006-03-01

    Exocellular electron transfer plays an important role in anaerobic microbial communities that degrade organic matter. Interspecies hydrogen transfer between microorganisms is the driving force for complete biodegradation in methanogenic environments. Many organic compounds are degraded by obligatory syntrophic consortia of proton-reducing acetogenic bacteria and hydrogen-consuming methanogenic archaea. Anaerobic microorganisms that use insoluble electron acceptors for growth, such as iron- and manganese-oxide as well as inert graphite electrodes in microbial fuel cells, also transfer electrons exocellularly. Soluble compounds, like humic substances, quinones, phenazines and riboflavin, can function as exocellular electron mediators enhancing this type of anaerobic respiration. However, direct electron transfer by cell-cell contact is important as well. This review addresses the mechanisms of exocellular electron transfer in anaerobic microbial communities. There are fundamental differences but also similarities between electron transfer to another microorganism or to an insoluble electron acceptor. The physical separation of the electron donor and electron acceptor metabolism allows energy conservation in compounds as methane and hydrogen or as electricity. Furthermore, this separation is essential in the donation or acceptance of electrons in some environmental technological processes, e.g. soil remediation, wastewater purification and corrosion.

  9. Protein structural deformation induced lifetime shortening of photosynthetic bacteria light-harvesting complex LH2 excited state.

    Science.gov (United States)

    Chen, Xing-Hai; Zhang, Lei; Weng, Yu-Xiang; Du, Lu-Chao; Ye, Man-Ping; Yang, Guo-Zhen; Fujii, Ritsuko; Rondonuwu, Ferdy S; Koyama, Yasushi; Wu, Yi-Shi; Zhang, J P

    2005-06-01

    Photosynthetic bacterial light-harvesting antenna complex LH2 was immobilized on the surface of TiO(2) nanoparticles in the colloidal solution. The LH2/TiO(2) assembly was investigated by the time-resolved spectroscopic methods. The excited-state lifetimes for carotenoid-containing and carotenoidless LH2 have been measured, showing a decrease in the excited-state lifetime of B850 when LH2 was immobilized on TiO(2). The possibility that the decrease of the LH2 excited-state lifetime being caused by an interfacial electron transfer reaction between B850 and the TiO(2) nanoparticle was precluded experimentally. We proposed that the observed change in the photophysical properties of LH2 when assembled onto TiO(2) nanoparticles is arising from the interfacial-interaction-induced structural deformation of the LH2 complex deviating from an ellipse of less eccentric to a more eccentric ellipse, and the observed phenomenon can be accounted by an elliptical exciton model. Experiment by using photoinactive SiO(2) nanoparticle in place of TiO(2) and core complex LH1 instead of LH2 provide further evidence to the proposed mechanism.

  10. Excited States and Photodebromination of Selected Polybrominated Diphenyl Ethers: Computational and Quantitative Structure—Property Relationship Studies

    Directory of Open Access Journals (Sweden)

    Jin Luo

    2015-01-01

    Full Text Available This paper presents a density functional theory (DFT/time-dependent DFT (TD-DFT study on the lowest lying singlet and triplet excited states of 20 selected polybrominateddiphenyl ether (PBDE congeners, with the solvation effect included in the calculations using the polarized continuum model (PCM. The results obtained showed that for most of the brominated diphenyl ether (BDE congeners, the lowest singlet excited state was initiated by the electron transfer from HOMO to LUMO, involving a π–σ* excitation. In triplet excited states, structure of the BDE congeners differed notably from that of the BDE ground states with one of the specific C–Br bonds bending off the aromatic plane. In addition, the partial least squares regression (PLSR, principal component analysis-multiple linear regression analysis (PCA-MLR, and back propagation artificial neural network (BP-ANN approaches were employed for a quantitative structure-property relationship (QSPR study. Based on the previously reported kinetic data for the debromination by ultraviolet (UV and sunlight, obtained QSPR models exhibited a reasonable evaluation of the photodebromination reactivity even when the BDE congeners had same degree of bromination, albeit different patterns of bromination.

  11. The structure of 83Sr excited states

    International Nuclear Information System (INIS)

    Liptak, J.; Kristiak, J.; Kristiakova, K.

    1976-01-01

    The β-decay of 83 Y isomers (7.06 min and 2.85 min) have been studied by means of Ge(Li) detectors. The proposed level scheme of the 83 Sr nucleus is based on the coincidence measurement and the analysis of energy sums. The intensity balance requirement leads to αsub(T)(35.5keV)=3.2 which is consistent with M1 multipolarity of this transition. A probable structure of some of the excited states in the 83 Sr nucleus is discussed in the frame work of Alaga's model and Kuriyama's model

  12. Excited state dynamics of DNA bases

    Czech Academy of Sciences Publication Activity Database

    Kleinermanns, K.; Nachtigallová, Dana; de Vries, M. S.

    2013-01-01

    Roč. 32, č. 2 (2013), s. 308-342 ISSN 0144-235X R&D Projects: GA ČR GAP208/12/1318 Grant - others:National Science Foundation(US) CHE-0911564; NASA (US) NNX12AG77G; Deutsche Forschungsgemeinschaft(DE) SFB 663; Deutsche Forschungsgemeinschaft(DE) KI 531-29 Institutional support: RVO:61388963 Keywords : DNA bases * nucleobases * excited state * dynamics * computations * gas phase * conical intersections Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 4.920, year: 2013

  13. Charge transfer dynamics from adsorbates to surfaces with single active electron and configuration interaction based approaches

    Energy Technology Data Exchange (ETDEWEB)

    Ramakrishnan, Raghunathan, E-mail: r.ramakrishnan@unibas.ch [Institute of Physical Chemistry, National Center for Computational Design and Discovery of Novel Materials (MARVEL), Department of Chemistry, University of Basel, Klingelbergstrasse 80, CH-4056 Basel (Switzerland); Nest, Mathias [Theoretische Chemie, Technische Universität München, Lichtenbergstr. 4, 85747 Garching (Germany)

    2015-01-13

    Highlights: • We model electron dynamics across cyano alkanethiolates attached to gold cluster. • We present electron transfer time scales from TD-DFT and TD-CI based simulations. • Both DFT and CI methods qualitatively predict the trend in time scales. • TD-CI predicts the experimental relative time scale very accurately. - Abstract: We employ wavepacket simulations based on many-body time-dependent configuration interaction (TD-CI), and single active electron theories, to predict the ultrafast molecule/metal electron transfer time scales, in cyano alkanethiolates bonded to model gold clusters. The initial states represent two excited states where a valence electron is promoted to one of the two virtual π{sup ∗} molecular orbitals localized on the cyanide fragment. The ratio of the two time scales indicate the efficiency of one charge transfer channel over the other. In both our one-and many-electron simulations, this ratio agree qualitatively with each other as well as with the previously reported experimental time scales (Blobner et al., 2012), measured for a macroscopic metal surface. We study the effect of cluster size and the description of electron correlation on the charge transfer process.

  14. Diameter dependent electron transfer kinetics in semiconductor-enzyme complexes.

    Science.gov (United States)

    Brown, Katherine A; Song, Qing; Mulder, David W; King, Paul W

    2014-10-28

    Excited state electron transfer (ET) is a fundamental step for the catalytic conversion of solar energy into chemical energy. To understand the properties controlling ET between photoexcited nanoparticles and catalysts, the ET kinetics were measured for solution-phase complexes of CdTe quantum dots and Clostridium acetobutylicum [FeFe]-hydrogenase I (CaI) using time-resolved photoluminescence spectroscopy. Over a 2.0-3.5 nm diameter range of CdTe nanoparticles, the observed ET rate (kET) was sensitive to CaI concentration. To account for diameter effects on CaI binding, a Langmuir isotherm and two geometric binding models were created to estimate maximal CaI affinities and coverages at saturating concentrations. Normalizing the ET kinetics to CaI surface coverage for each CdTe diameter led to k(ET) values that were insensitive to diameter, despite a decrease in the free energy for photoexcited ET (ΔGET) with increasing diameter. The turnover frequency (TOF) of CaI in CdTe-CaI complexes was measured at several molar ratios. Normalization for diameter-dependent changes in CaI coverage showed an increase in TOF with diameter. These results suggest that k(ET) and H2 production for CdTe-CaI complexes are not strictly controlled by ΔG(ET) and that other factors must be considered.

  15. Linear-scaling quantum mechanical methods for excited states.

    Science.gov (United States)

    Yam, ChiYung; Zhang, Qing; Wang, Fan; Chen, GuanHua

    2012-05-21

    The poor scaling of many existing quantum mechanical methods with respect to the system size hinders their applications to large systems. In this tutorial review, we focus on latest research on linear-scaling or O(N) quantum mechanical methods for excited states. Based on the locality of quantum mechanical systems, O(N) quantum mechanical methods for excited states are comprised of two categories, the time-domain and frequency-domain methods. The former solves the dynamics of the electronic systems in real time while the latter involves direct evaluation of electronic response in the frequency-domain. The localized density matrix (LDM) method is the first and most mature linear-scaling quantum mechanical method for excited states. It has been implemented in time- and frequency-domains. The O(N) time-domain methods also include the approach that solves the time-dependent Kohn-Sham (TDKS) equation using the non-orthogonal localized molecular orbitals (NOLMOs). Besides the frequency-domain LDM method, other O(N) frequency-domain methods have been proposed and implemented at the first-principles level. Except one-dimensional or quasi-one-dimensional systems, the O(N) frequency-domain methods are often not applicable to resonant responses because of the convergence problem. For linear response, the most efficient O(N) first-principles method is found to be the LDM method with Chebyshev expansion for time integration. For off-resonant response (including nonlinear properties) at a specific frequency, the frequency-domain methods with iterative solvers are quite efficient and thus practical. For nonlinear response, both on-resonance and off-resonance, the time-domain methods can be used, however, as the time-domain first-principles methods are quite expensive, time-domain O(N) semi-empirical methods are often the practical choice. Compared to the O(N) frequency-domain methods, the O(N) time-domain methods for excited states are much more mature and numerically stable, and

  16. Theoretical description of excited state dynamics in nanostructures

    Science.gov (United States)

    Rubio, Angel

    2009-03-01

    There has been much progress in the synthesis and characterization of nanostructures however, there remain immense challenges in understanding their properties and interactions with external probes in order to realize their tremendous potential for applications (molecular electronics, nanoscale opto-electronic devices, light harvesting and emitting nanostructures). We will review the recent implementations of TDDFT to study the optical absorption of biological chromophores, one-dimensional polymers and layered materials. In particular we will show the effect of electron-hole attraction in those systems. Applications to the optical properties of solvated nanostructures as well as excited state dynamics in some organic molecules will be used as text cases to illustrate the performance of the approach. Work done in collaboration with A. Castro, M. Marques, X. Andrade, J.L Alonso, Pablo Echenique, L. Wirtz, A. Marini, M. Gruning, C. Rozzi, D. Varsano and E.K.U. Gross.

  17. Electron-electron Thomas peak in fast transfer ionization

    International Nuclear Information System (INIS)

    Tolmanov, S. G.; McGuire, J. H.

    2000-01-01

    ''Thomas process'' is a name used for a family of singular two-step processes that can lead to electron transfer. The Thomas process of the ''second kind,'' occurring in reactions with both transfer and ionization, utilizes the e-e scattering in the second step, so this Thomas process requires the dynamics of the electron-electron interaction. We calculate numerically the second order element of an S matrix and corresponding cross sections for the transfer ionization process. We find that the position and shape of the Thomas peak depend on both electron-electron and the electron-nucleus interaction. Also the direct and exchange amplitudes are equal at the peak position. We test the peaking approximation used for transfer ionization. Our results can be compared to experimental results for p + +He→H+He 2+ +e - . (c) 2000 The American Physical Society

  18. The triplet excited state of bilirubin

    International Nuclear Information System (INIS)

    Land, E.J.

    1976-01-01

    Pulse radiolysis of benzene solutions of 40 μM bilirubin alone or with 0.1 M biphenyl has yielded evidence for the formation of the triplet excited state of bilirubin. Measurements were made of a number of properties, including the absorption spectrum (lambdasub(max)500nm), lifetime 9μs), extinction coefficient (8800 M -1 cm -1 ), energy level (approximately 150 kJ mol -1 ) and the rate of quenching by oxygen (rate constant, 8.2 x 10 8 M -1 s -1 ). An upper limit of 0.1 has also been obtained for the singlet to triplet crossover efficiency of bilirubin following excitation by 353 nm radiation. Consideration is given to the relevance of these data to the mechanism of bilirubin photo-destruction, both in vivo and in vitro. (U.K.)

  19. First 3- excited state of 56Fe

    International Nuclear Information System (INIS)

    Fotiades, N.; Nelson, R. O.; Devlin, M.

    2010-01-01

    There is no reliable evidence for the existence of the 3.076 MeV (3 - ) level adopted in the ENSDF evaluation for 56 Fe although it has been reported in a few experiments. Previous reports of the observation of this level appear to be based on an incorrect assignment in early (e,e ' ) work. Recent neutron inelastic scattering measurements by Demidov et al. [Phys. At. Nucl. 67, 1884, (2004)] show that the assigned γ-ray decay of this state does not occur at a level consistent with known properties of inelastic scattering. In the present work the 56 Fe(n,n ' γ) reaction was used to populate excited states in 56 Fe. Neutrons in the energy range from 1 to 250 MeV were provided by the pulsed neutron source of the Los Alamos Neutron Science Center's WNR facility. Deexciting γ rays were detected with the GEANIE spectrometer, a Compton suppressed array of 26 Ge detectors. The γ-γ data obtained with GEANIE were used to establish coincidence relations between transitions. All previously reported levels up to E x =3.6 MeV excitation energy were observed except for the 3.076 MeV (3 - ) level. The 991- and 2229-keV transitions, previously reported to deexcite this level, were not observed in the γ-γ coincidence data obtained in the present experiment. The present work supports the assignment of the 4509.6 keV level as the first 3 - excited state in 56 Fe by observation of two previously known transitions deexciting this state.

  20. Self-Consistent Optimization of Excited States within Density-Functional Tight-Binding.

    Science.gov (United States)

    Kowalczyk, Tim; Le, Khoa; Irle, Stephan

    2016-01-12

    We present an implementation of energies and gradients for the ΔDFTB method, an analogue of Δ-self-consistent-field density functional theory (ΔSCF) within density-functional tight-binding, for the lowest singlet excited state of closed-shell molecules. Benchmarks of ΔDFTB excitation energies, optimized geometries, Stokes shifts, and vibrational frequencies reveal that ΔDFTB provides a qualitatively correct description of changes in molecular geometries and vibrational frequencies due to excited-state relaxation. The accuracy of ΔDFTB Stokes shifts is comparable to that of ΔSCF-DFT, and ΔDFTB performs similarly to ΔSCF with the PBE functional for vertical excitation energies of larger chromophores where the need for efficient excited-state methods is most urgent. We provide some justification for the use of an excited-state reference density in the DFTB expansion of the electronic energy and demonstrate that ΔDFTB preserves many of the properties of its parent ΔSCF approach. This implementation fills an important gap in the extended framework of DFTB, where access to excited states has been limited to the time-dependent linear-response approach, and affords access to rapid exploration of a valuable class of excited-state potential energy surfaces.

  1. Advances in electron transfer chemistry, v.6

    CERN Document Server

    Mariano, PS

    1999-01-01

    It is clear that electron transfer chemisty is now one of the most active areas of chemical study. Advances in Electron Transfer Chemistry has been designed to allow scientists who are developing new knowledge in this rapidly expanding area to describe their most recent research findings. This volume will serve those interested in learning about current breakthroughs in this rapidly expanding area of chemical research.

  2. Excited state mass spectra of singly charmed baryons

    Energy Technology Data Exchange (ETDEWEB)

    Shah, Zalak; Kumar Rai, Ajay [Sardar Vallabhbhai National Institute of Technology, Department of Applied Physics, Surat, Gujarat (India); Thakkar, Kaushal [GIDC Degree Engineering College, Department of Applied Sciences and Humanities, Abrama (India); Vinodkumar, P.C. [Sardar Patel University, Department of Physics, V.V. Nagar (India)

    2016-10-15

    Mass spectra of excited states of the singly charmed baryons are calculated using the hypercentral description of the three-body system. The baryons consist of a charm quark and light quarks (u, d and s) are studied in the framework of QCD motivated constituent quark model. The form of the confinement potential is hyper-Coloumb plus power potential with potential index ν, varying from 0.5 to 2.0. The first-order correction to the confinement potential is also incorporated in this approach. The radial as well as orbital excited state masses of Σ{sub c}{sup ++}, Σ{sub c}{sup +}, Σ{sub c}{sup 0}, Ξ{sub c}{sup +}, Ξ{sub c}{sup 0}, Λ{sub c}{sup +}, Ω{sub c}{sup 0} baryons, are reported in this paper. We have incorporated spin-spin, spin-orbit and tensor interactions perturbatively in the present study. The semi-electronic decay of Ω{sub c} and Ξ{sub c} are also calculated using the spectroscopic parameters of these baryons. The computed results are compared with other theoretical predictions as well as with the available experimental observations. We also construct the Regge trajectory in (n{sub r},M{sup 2}) and (J,M{sup 2}) planes for these baryons. (orig.)

  3. Dynamic study of excited state hydrogen-bonded complexes of harmane in cyclohexane-toluene mixtures.

    Science.gov (United States)

    Carmona, Carmen; Balón, Manuel; Galán, Manuel; Guardado, Pilar; Muñoz, María A

    2002-09-01

    Photoinduced proton transfer reactions of harmane or 1-methyl-9H-pyrido[3,4-b]indole (HN) in the presence of the proton donor hexafluoroisopropanol (HFIP) in cyclohexane-toluene mixtures (CY-TL; 10% vol/vol of TL) have been studied. Three excited state species have been identified: a 1:2 hydrogen-bonded proton transfer complex (PTC), between the pyridinic nitrogen of the substrate and the proton donor, a hydrogen-bonded cation-like exciplex (CL*) with a stoichiometry of at least 1:3 and a zwitterionic exciplex (Z*). Time-resolved fluorescence measurements evidence that upon excitation of ground state PTC, an excited state equilibrium is established between PTC* and the cationlike exciplex, CL*, lambdaem approximately/= 390 nm. This excited state reaction is assisted by another proton donor molecule. Further reaction of CL* with an additional HFIP molecule produces the zwitterionic species, Z*, lambda(em) approximately/= 500 nm. From the analysis of the multiexponential decays, measured at different emission wavelengths and as a function of HFIP concentration, the mechanism of these excited state reactions has been established. Thus, three rate constants and three reciprocal lifetimes have been determined. The simultaneous study of 1,9-dimethyl-9H-pyrido[3,4-b]indole (MHN) under the same experimental conditions has helped to understand the excited state kinetics of these processes.

  4. Psoralen phototherapy and the possible involvement of triplet excited states

    International Nuclear Information System (INIS)

    Bensasson, R.V.; Salet, E.J.; Land, E.J.

    1979-01-01

    Psoralens are important drugs used in the phototherapy of psoriasis and vitiligo. It has been predicted that the triplet excited state of psoralen is photoactive. The authors have employed pulse radiolysis and laser flash photolysis to determine the quantum yields of formation of the triplet states of psoralens and related molecules including 4'5' dihydropsoralen, a model for 4'5' psoralenpyrimidine mono-adducts. The triplet spectra were used to follow the reactions of the triplets with thymine and tryptophan. Such reactions may take place via a charge transfer mechanism. For 8-methoxy psoralen, in addition to triplet formation, photoionization was detected using high laser intensities. Although significant yields of psoralen triplets are formed, and some such triplets react with thymine, it is too early yet to say definitely whether or not the therapeutic action of psoralens is mediated via such triplet states. (Auth.)

  5. Single-Molecule Interfacial Electron Transfer

    Energy Technology Data Exchange (ETDEWEB)

    Lu, H. Peter [Bowling Green State Univ., Bowling Green, OH (United States). Dept. of Chemistry and Center for Photochemical Sciences

    2017-11-28

    This project is focused on the use of single-molecule high spatial and temporal resolved techniques to study molecular dynamics in condensed phase and at interfaces, especially, the complex reaction dynamics associated with electron and energy transfer rate processes. The complexity and inhomogeneity of the interfacial ET dynamics often present a major challenge for a molecular level comprehension of the intrinsically complex systems, which calls for both higher spatial and temporal resolutions at ultimate single-molecule and single-particle sensitivities. Combined single-molecule spectroscopy and electrochemical atomic force microscopy approaches are unique for heterogeneous and complex interfacial electron transfer systems because the static and dynamic inhomogeneities can be identified and characterized by studying one molecule at a specific nanoscale surface site at a time. The goal of our project is to integrate and apply these spectroscopic imaging and topographic scanning techniques to measure the energy flow and electron flow between molecules and substrate surfaces as a function of surface site geometry and molecular structure. We have been primarily focusing on studying interfacial electron transfer under ambient condition and electrolyte solution involving both single crystal and colloidal TiO2 and related substrates. The resulting molecular level understanding of the fundamental interfacial electron transfer processes will be important for developing efficient light harvesting systems and broadly applicable to problems in fundamental chemistry and physics. We have made significant advancement on deciphering the underlying mechanism of the complex and inhomogeneous interfacial electron transfer dynamics in dyesensitized TiO2 nanoparticle systems that strongly involves with and regulated by molecule-surface interactions. We have studied interfacial electron transfer on TiO2 nanoparticle surfaces by using ultrafast single

  6. Measurement of the electromagnetic lifetimes of the first four excited states of /sup 192/Pt

    Energy Technology Data Exchange (ETDEWEB)

    Butt, D K; Raoof, M A; Raoof, S A [Birkbeck Coll., London (UK)

    1976-11-01

    Measurements of the electromagnetic lifetimes of the first four excited states of /sup 192/Pt have been made by the self-comparison method using electron-electron coincidences. The partial lifetimes of the gamma transitions involved have been interpreted in terms of the pairing-plus-quadrupole model of Kumar and Baranger.

  7. Two-photon-induced hot-electron transfer to a single molecule in a scanning tunneling microscope

    International Nuclear Information System (INIS)

    Wu, S. W.; Ho, W.

    2010-01-01

    The junction of a scanning tunneling microscope (STM) operating in the tunneling regime was irradiated with femtosecond laser pulses. A photoexcited hot electron in the STM tip resonantly tunnels into an excited state of a single molecule on the surface, converting it from the neutral to the anion. The electron-transfer rate depends quadratically on the incident laser power, suggesting a two-photon excitation process. This nonlinear optical process is further confirmed by the polarization measurement. Spatial dependence of the electron-transfer rate exhibits atomic-scale variations. A two-pulse correlation experiment reveals the ultrafast dynamic nature of photoinduced charging process in the STM junction. Results from these experiments are important for understanding photoinduced interfacial charge transfer in many nanoscale inorganic-organic structures.

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

    Science.gov (United States)

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

    2017-06-14

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

  9. Effect of charged and excited states on the decomposition of 1,1-diamino-2,2-dinitroethylene molecules

    International Nuclear Information System (INIS)

    Kimmel, Anna V.; Sushko, Peter V.; Shluger, Alexander L.; Kuklja, Maija M.

    2007-01-01

    The authors have calculated the electronic structure of individual 1,1-diamino-2,2-dinitroethylene molecules (FOX-7) in the gas phase by means of density functional theory with the hybrid B3LYP functional and 6-31+G(d,p) basis set and considered their dissociation pathways. Positively and negatively charged states as well as the lowest excited states of the molecule were simulated. They found that charging and excitation can not only reduce the activation barriers for decomposition reactions but also change the dominating chemistry from endo- to exothermic type. In particular, they found that there are two competing primary initiation mechanisms of FOX-7 decomposition: C-NO 2 bond fission and C-NO 2 to CONO isomerization. Electronic excitation or charging of FOX-7 disfavors CONO formation and, thus, terminates this channel of decomposition. However, if CONO is formed from the neutral FOX-7 molecule, charge trapping and/or excitation results in spontaneous splitting of an NO group accompanied by the energy release. Intramolecular hydrogen transfer is found to be a rare event in FOX-7 unless free electrons are available in the vicinity of the molecule, in which case HONO formation is a feasible exothermic reaction with a relatively low energy barrier. The effect of charged and excited states on other possible reactions is also studied. Implications of the obtained results to FOX-7 decomposition in condensed state are discussed

  10. Photoinduced electron-transfer from imidazole derivative to nano-semiconductors.

    Science.gov (United States)

    Karunakaran, C; Jayabharathi, J; Jayamoorthy, K; Devi, K Brindha

    2012-04-01

    Bioactive imidazole derivative absorbs in the UV region at 305 nm. The interaction of imidazole derivative with nanoparticulate WO3, Fe2O3, Fe3O4, CuO, ZrO2 and Al2O3 has been studied by UV-visible absorption, FT-IR and fluorescence spectroscopies. The imidazole derivative adsorbs strongly on the surfaces of nanosemiconductor, the apparent binding constants for the association between nanomaterials and imidazole derivative have been determined from the fluorescence quenching. In the case of nanocrystalline insulator, fluorescence quenching through electron transfer from the excited state of the imidazole derivative to alumina is not possible. However, a possible mechanism for the quenching of fluorescence by the insulator is energy transfer, that is, energy transferred from the organic molecule to the alumina lattice. Based on Forster's non-radiation energy transfer theory, the distance between the imidazole derivative and nanoparticles (r0∼2.00 nm) as well as the critical energy transfer distance (R0∼1.70 nm) has been calculated. The interaction between the imidazole derivative and nanosurfaces occurs through static quenching mechanism. The free energy change (ΔGet) for electron transfer process has been calculated by applying Rehm-Weller equation. Copyright © 2012 Elsevier B.V. All rights reserved.

  11. Single Molecule Spectroscopy of Electron Transfer

    International Nuclear Information System (INIS)

    Holman, Michael; Zang, Ling; Liu, Ruchuan; Adams, David M.

    2009-01-01

    The objectives of this research are threefold: (1) to develop methods for the study electron transfer processes at the single molecule level, (2) to develop a series of modifiable and structurally well defined molecular and nanoparticle systems suitable for detailed single molecule/particle and bulk spectroscopic investigation, (3) to relate experiment to theory in order to elucidate the dependence of electron transfer processes on molecular and electronic structure, coupling and reorganization energies. We have begun the systematic development of single molecule spectroscopy (SMS) of electron transfer and summaries of recent studies are shown. There is a tremendous need for experiments designed to probe the discrete electronic and molecular dynamic fluctuations of single molecules near electrodes and at nanoparticle surfaces. Single molecule spectroscopy (SMS) has emerged as a powerful method to measure properties of individual molecules which would normally be obscured in ensemble-averaged measurement. Fluctuations in the fluorescence time trajectories contain detailed molecular level statistical and dynamical information of the system. The full distribution of a molecular property is revealed in the stochastic fluctuations, giving information about the range of possible behaviors that lead to the ensemble average. In the case of electron transfer, this level of understanding is particularly important to the field of molecular and nanoscale electronics: from a device-design standpoint, understanding and controlling this picture of the overall range of possible behaviors will likely prove to be as important as designing ia the ideal behavior of any given molecule.

  12. Ultrafast excited state processes in Roseobacter denitrificans antennae: comparison of isolated complexes and native membranes

    NARCIS (Netherlands)

    Ferretti, M.; Duquesne, K.; Sturgis, J.N.; van Grondelle, R.

    2014-01-01

    Roseobacter (Rsb.) denitrificans is a marine aerobic anoxygenic photosynthetic purple bacterium with an unusually high-800 nm absorption band. Ultrafast excited state processes have been intensively studied in the past in order to understand why the energy transfer efficiency between photosynthetic

  13. Efficient Predictions of Excited State for Nanomaterials Using Aces 3 and 4

    Science.gov (United States)

    2017-12-20

    energetics of the various isomers of the materials, obtained from computed heats of reactions that provide the enthalpy and free energy for the species... modeling , excited states, optical properties, structure, stability, activation barriers first principle methods, parallel computing 16. SECURITY...6 Figure 7. Charge- transfer from ethylene to tetrafluro ethylene

  14. Multipulse spectroscopy on the wild-type and YM210W Bacterial Reaction Centre uncovers a new intermediate state in the special pair excited state

    Science.gov (United States)

    Cohen Stuart, T. A.; van Grondelle, R.

    2009-06-01

    The Bacterial Reaction Centre (BRC) has a complex electronic excited state, P ∗, that evolves into subsequent charge separated product states P +H - and P +B -. Pump-dump-probe spectroscopy on the wild-type BRC and on YM210W, a mutant with a stabilized, long-lived P ∗ excited state, has uncovered a new charge-separated state in both BRC's. When P ∗ is dumped, a fraction of its population is transferred to this state that has a strong Stark shift in the accessory bacteriochlorophyll (B M) region which serves as a signature for P + and a lifetime highly comparable to the slow phase of P ∗ decay. This lead us propose this intermediate to be P +/P -.

  15. Some features of excited states density matrix calculation and their pairing relations in conjugated systems

    International Nuclear Information System (INIS)

    Giambiagi, M.S. de; Giambiagi, M.

    1982-01-01

    Direct PPP-type calculations of self-consistent (SC) density matrices for excited states are described and the corresponding 'thawn' molecular orbitals (MO) are discussed. Special attention is addressed to particular solutions arising in conjugated systems of a certain symmetry, and to their chemical implications. The U(2) and U(3) algebras are applied respectively to the 4-electron and 6-electron cases: a natural separation of excited states in different cases follows. A simple approach to the convergence problem for excited states is given. The complementarity relations, an alternative formulation of the pairing theorem valid for heteromolecules and non-alternant systems, allow some fruitful experimental applications. Together with the extended pairing relations shown here, they may help to rationalize general trends. (Author) [pt

  16. Excited states in 146Sm and 147Sm

    International Nuclear Information System (INIS)

    Kownacki, J.; Sujkowski, Z.; Hammaren, E.; Liukkonen, E.; Piiparinen, M.; Lindblad, Th.; Ryde, H.

    1979-10-01

    The sup(144,146)Nd(α,xn) and sup(146,148)Nd( 3 He,xn) reactions with Esub(α) = 20 - 43 MeV and E 3 sub(He) = 19 - 27 MeV are used to investigate excited states in the isotopes 146 Sm and 147 Sm. The experiments involve measurements of singles γ-ray spectra and conversion electron spectra, γ-ray angular distributions and three parameter (E sub(γ)E sub(γ) time) coincidences. From these experiments information is obtained for states with spin up to I = 13 + and I = 27/2 - , respectively, These states are interpeted within the framework of the cluster-vibration model (CVM) as well as the shell model. (author)

  17. Detection of Intramolecular Charge Transfer and Dynamic Solvation in Eosin B by Femtosecond Two-Dimensional Electronic Spectroscopy

    Science.gov (United States)

    Ghosh, Soumen; Roscioli, Jerome D.; Beck, Warren F.

    2014-06-01

    We have employed 2D electronic photon echo spectroscopy to study intramolecular charge-transfer dynamics in eosin B. After preparation of the first excited singlet state (S_1) with 40-fs excitation pulses at 520 nm, the nitro group (--NO_2) in eosin B undergoes excited state torsional motion towards a twisted intramolecular charge transfer (TICT) state. As the viscosity of the surrounding solvent increases, the charge-transfer rate decreases because the twisting of the --NO_2 group is hindered. These conclusions are supported by the time evolution of the 2D spectrum, which provides a direct measure of the the ground-to-excited-state energy gap time-correlation function, M(t). In comparison to the inertial and diffusive solvation time scales exhibited by eosin Y, which lacks the nitro group, the M(t) function for eosin B exhibits under the same conditions an additional component on the 150-fs timescale that arises from quenching of the S_1 state by crossing to the TICT state. These results indicate that 2D electronic spectroscopy can be used as a sensitive probe of the rate of charge transfer in a molecular system and of the coupling to the motions of the surrounding solvent. (Supported by grant DE-SC0010847 from the Department of Energy, Office of Basic Energy Sciences, Photosynthetic Systems program.)

  18. Electronic energy transfer through non-adiabatic vibrational-electronic resonance. II. 1D spectra for a dimer

    Science.gov (United States)

    Tiwari, Vivek; Jonas, David M.

    2018-02-01

    Vibrational-electronic resonance in photosynthetic pigment-protein complexes invalidates Förster's adiabatic framework for interpreting spectra and energy transfer, thus complicating determination of how the surrounding protein affects pigment properties. This paper considers the combined effects of vibrational-electronic resonance and inhomogeneous variations in the electronic excitation energies of pigments at different sites on absorption, emission, circular dichroism, and hole-burning spectra for a non-degenerate homodimer. The non-degenerate homodimer has identical pigments in different sites that generate differences in electronic energies, with parameters loosely based on bacteriochlorophyll a pigments in the Fenna-Matthews-Olson antenna protein. To explain the intensity borrowing, the excited state vibrational-electronic eigenvectors are discussed in terms of the vibrational basis localized on the individual pigments, as well as the correlated/anti-correlated vibrational basis delocalized over both pigments. Compared to those in the isolated pigment, vibrational satellites for the correlated vibration have the same frequency and precisely a factor of 2 intensity reduction through vibrational delocalization in both absorption and emission. Vibrational satellites for anti-correlated vibrations have their relaxed emission intensity reduced by over a factor 2 through vibrational and excitonic delocalization. In absorption, anti-correlated vibrational satellites borrow excitonic intensity but can be broadened away by the combination of vibronic resonance and site inhomogeneity; in parallel, their vibronically resonant excitonic partners are also broadened away. These considerations are consistent with photosynthetic antenna hole-burning spectra, where sharp vibrational and excitonic satellites are absent. Vibrational-excitonic resonance barely alters the inhomogeneously broadened linear absorption, emission, and circular dichroism spectra from those for a

  19. Legal Risk Associated with Electronic Funds Transfer

    OpenAIRE

    Abdulah, Samahir

    2014-01-01

    The past thirty years have seen rapid advances in the technological component of banking services and as a consequence new legal issues have come to the fore, especially with regard to Electronic Fund Transfers (EFTs) which are now used to transfer money around the world, and have made fund transactions between payers and payees easier, faster and more secure. The method involves risks for both banks and customers, due to the possibility of unauthorized payments risks, credit and insolvency p...

  20. σ-SCF: A direct energy-targeting method to mean-field excited states.

    Science.gov (United States)

    Ye, Hong-Zhou; Welborn, Matthew; Ricke, Nathan D; Van Voorhis, Troy

    2017-12-07

    The mean-field solutions of electronic excited states are much less accessible than ground state (e.g., Hartree-Fock) solutions. Energy-based optimization methods for excited states, like Δ-SCF (self-consistent field), tend to fall into the lowest solution consistent with a given symmetry-a problem known as "variational collapse." In this work, we combine the ideas of direct energy-targeting and variance-based optimization in order to describe excited states at the mean-field level. The resulting method, σ-SCF, has several advantages. First, it allows one to target any desired excited state by specifying a single parameter: a guess of the energy of that state. It can therefore, in principle, find all excited states. Second, it avoids variational collapse by using a variance-based, unconstrained local minimization. As a consequence, all states-ground or excited-are treated on an equal footing. Third, it provides an alternate approach to locate Δ-SCF solutions that are otherwise hardly accessible by the usual non-aufbau configuration initial guess. We present results for this new method for small atoms (He, Be) and molecules (H 2 , HF). We find that σ-SCF is very effective at locating excited states, including individual, high energy excitations within a dense manifold of excited states. Like all single determinant methods, σ-SCF shows prominent spin-symmetry breaking for open shell states and our results suggest that this method could be further improved with spin projection.

  1. σ-SCF: A direct energy-targeting method to mean-field excited states

    Science.gov (United States)

    Ye, Hong-Zhou; Welborn, Matthew; Ricke, Nathan D.; Van Voorhis, Troy

    2017-12-01

    The mean-field solutions of electronic excited states are much less accessible than ground state (e.g., Hartree-Fock) solutions. Energy-based optimization methods for excited states, like Δ-SCF (self-consistent field), tend to fall into the lowest solution consistent with a given symmetry—a problem known as "variational collapse." In this work, we combine the ideas of direct energy-targeting and variance-based optimization in order to describe excited states at the mean-field level. The resulting method, σ-SCF, has several advantages. First, it allows one to target any desired excited state by specifying a single parameter: a guess of the energy of that state. It can therefore, in principle, find all excited states. Second, it avoids variational collapse by using a variance-based, unconstrained local minimization. As a consequence, all states—ground or excited—are treated on an equal footing. Third, it provides an alternate approach to locate Δ-SCF solutions that are otherwise hardly accessible by the usual non-aufbau configuration initial guess. We present results for this new method for small atoms (He, Be) and molecules (H2, HF). We find that σ-SCF is very effective at locating excited states, including individual, high energy excitations within a dense manifold of excited states. Like all single determinant methods, σ-SCF shows prominent spin-symmetry breaking for open shell states and our results suggest that this method could be further improved with spin projection.

  2. Laser photoelectron spectroscopy of MnH - and FeH - : Electronic structures of the metal hydrides, identification of a low-spin excited state of MnH, and evidence for a low-spin ground state of FeH

    Science.gov (United States)

    Stevens, Amy E.; Feigerle, C. S.; Lineberger, W. C.

    1983-05-01

    The laser photoelectron spectra of MnH- and MnD-, and FeH- and FeD- are reported. A qualitative description of the electronic structure of the low-spin and high-spin states of the metal hydrides is developed, and used to interpret the spectra. A diagonal transition in the photodetachment to the known high-spin, 7Σ+, ground state of MnH is observed. An intense off-diagonal transition to a state of MnH, at 1725±50 cm-1 excitation energy, is attributed to loss of an antibonding electron from MnH-, to yield a low-spin quintet state of MnH. For FeH- the photodetachment to the ground state is an off-diagonal transition, attributed to loss of the antibonding electron from FeH-, to yield a low-spin quartet ground state of FeH. A diagonal transition results in an FeH state at 1945±55 cm-1; this state of FeH is assigned as the lowest-lying high-spin sextet state of FeH. An additional excited state of MnH and two other excited states of FeH are observed. Excitation energies for all the states are reported; vibrational frequencies and bond lengths for the ions and several states of the neutrals are also determined from the spectra. The electron affinity of MnH is found to be 0.869±0.010 eV; and the electron affinity of FeH is determined to be 0.934±0.011 eV. Spectroscopic constants for the various deuterides are also reported.

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

    Science.gov (United States)

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

    2011-10-27

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

  4. Facile Interfacial Electron Transfer of Hemoglobin

    Directory of Open Access Journals (Sweden)

    Chunhai Fan

    2005-12-01

    Full Text Available Abstract: We herein describe a method of depositing hemoglobin (Hb and sulfonated polyaniline (SPAN on GC electrodes that facilitate interfacial protein electron transfer. Well-defined, reproducible, chemically reversible peaks of Hb and SPAN can be obtained in our experiments. We also observed enhanced peroxidase activity of Hb in SPAN films. These results clearly showed that SPAN worked as molecular wires and effectively exchanged electrons between Hb and electrodes.Mediated by Conjugated Polymers

  5. Partial radiative recombination cross sections for excited states of hydrogen

    International Nuclear Information System (INIS)

    Fazio, P.M.

    1984-01-01

    In calculating the radiative recombination cross sections for interstellar H II regions, usually only the electric dipole term in the expansion of the interaction Hamiltonian is kept. The dipole and quadrupole transition strengths in closed analytical form are calculated here using the Coulomb wave functions because results for any electron energy and for recombination into any angular momentum state of hydrogen are needed. Several interesting effects are found. First, the transition probabilities are maximum for recombination into specific intermediate angular momentum states at low energies (w < 2eV) and where the free state angular momentum is greater than that of the bound state. Further, that specific intermediate angular momentum state depends on the kinetic energy of the free electron. This behavior is in contrast to the normal behavior of the transition strengths where recombination into s states is greatest and decreases with increasing angular momentum. Second, the quadrupole matrix elements vanish for certain velocities of the free electron. This leads to minima in the corresponding quadrupole cross sections when plotted as a function of the free electron's kinetic energy. Finally, the partial cross sections for highly excited states are greater than previously calculated because of the additional effects of the quadrupole transitions

  6. Elastic electron scattering at large momentum transfer

    International Nuclear Information System (INIS)

    Arnold, R.G.

    1979-05-01

    A review is given of elastic electron scattering at large momentum transfer (Q 2 > 20 fm -2 ) from nuclei with A less than or equal to 4. Recent experimental results are reviewed and the current problems in interpretation of these results are pointed out. Some questions for future experiments are posed, and a preview of possible future measurements is presented. 28 references

  7. Promoting interspecies electron transfer with biochar

    DEFF Research Database (Denmark)

    Chen, Shanshan; Rotaru, Amelia-Elena; Shrestha, Pravin Malla

    2014-01-01

    Biochar, a charcoal-like product of the incomplete combustion of organic materials, is an increasingly popular soil amendment designed to improve soil fertility. We investigated the possibility that biochar could promote direct interspecies electron transfer (DIET) in a manner similar...... biochar may enhance methane production from organic wastes under anaerobic conditions....

  8. Quantum effects in biological electron transfer

    Czech Academy of Sciences Publication Activity Database

    de la Lande, A.; Babcock, N. S.; Řezáč, Jan; Levy, B.; Sanders, B. C.; Salahub, D.

    2012-01-01

    Roč. 14, č. 17 (2012), s. 5902-5918 ISSN 1463-9076 Institutional research plan: CEZ:AV0Z40550506 Keywords : electron transfer * tunnelling * decoherence * semi-classical molecular dynamics * density functional theory Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.829, year: 2012

  9. Ponderomotive dressing of doubly-excited states with intensity-controlled laser light

    Directory of Open Access Journals (Sweden)

    Ding Thomas

    2013-03-01

    Full Text Available We laser-dress several doubly-excited states in helium. Tuning the coupling-laser intensity from perturbative to the strong-coupling regime, we are able to measure phases imprinted on the two-electron wavefunctions, and observe a new continuum coupling mechanism.

  10. Excited-State Dynamics of Oxyluciferin in Firefly Luciferase

    KAUST Repository

    Snellenburg, Joris J.

    2016-11-23

    The color variations of light emitted by some natural and mutant luciferases are normally attributed to collective factors referred to as microenvironment effects; however, the exact nature of these interactions between the emitting molecule (oxyluciferin) and the active site remains elusive. Although model studies of noncomplexed oxyluciferin and its variants have greatly advanced the understanding of its photochemistry, extrapolation of the conclusions to the real system requires assumptions about the polarity and proticity of the active site. To decipher the intricate excited-state dynamics, global and target analysis is performed here for the first time on the steady-state and time-resolved spectra of firefly oxyluciferin complexed with luciferase from the Japanese firefly (Luciola cruciata). The experimental steady-state and time resolved luminescence spectra of the oxyluciferin/luciferase complex in solution are compared with the broadband time-resolved firefly bioluminescence recorded in vivo. The results demonstrate that de-excitation of the luminophore results in a complex cascade of photoinduced proton transfer processes and can be interpreted by the pH dependence of the emitted light. It is confirmed that proton transfer is the central event in the spectrochemistry of this system for which any assignment of the pH dependent emission to a single chemical species would be an oversimplification.

  11. Excited-State Dynamics of Oxyluciferin in Firefly Luciferase

    KAUST Repository

    Snellenburg, Joris J.; Laptenok, Sergey P.; DeSa, Richard J.; Naumov, Pance; Solntsev, Kyril M.

    2016-01-01

    The color variations of light emitted by some natural and mutant luciferases are normally attributed to collective factors referred to as microenvironment effects; however, the exact nature of these interactions between the emitting molecule (oxyluciferin) and the active site remains elusive. Although model studies of noncomplexed oxyluciferin and its variants have greatly advanced the understanding of its photochemistry, extrapolation of the conclusions to the real system requires assumptions about the polarity and proticity of the active site. To decipher the intricate excited-state dynamics, global and target analysis is performed here for the first time on the steady-state and time-resolved spectra of firefly oxyluciferin complexed with luciferase from the Japanese firefly (Luciola cruciata). The experimental steady-state and time resolved luminescence spectra of the oxyluciferin/luciferase complex in solution are compared with the broadband time-resolved firefly bioluminescence recorded in vivo. The results demonstrate that de-excitation of the luminophore results in a complex cascade of photoinduced proton transfer processes and can be interpreted by the pH dependence of the emitted light. It is confirmed that proton transfer is the central event in the spectrochemistry of this system for which any assignment of the pH dependent emission to a single chemical species would be an oversimplification.

  12. Excited state fluorescence quenching of the U O2++ ion by monovalent anions

    International Nuclear Information System (INIS)

    Santarine, G.A.

    1987-01-01

    The reactions of the Uranyl ion U O 2 ++ in the excited state with the monovalent inorganic ions N O 3 - and I O 3 - in aqueous solutions at normal temperature were studied, using three techniques: Fluorescence in the steady state - Flash photolysis - Fluorescence decay after excitation. With increasing concentration of these ions it was observed a decrease in the normalized intensity and a decrease in the decay time of the fluorescence of the Uranyl ion in the solution and a corresponding appearance of the radicals N O 3 . or I O 3 . . In each case the radical was identified by its optical absorption spectrum. These results suggest that the quenching of fluorescence of the Uranyl ion in each case is owing to an electron transfer reaction. In the case of the Nitrate ion the transfer may occur after the formation of an ionic par (U O 2 + ...N O 3 ) in the ground state. Evidence for static quenching in the system Uranyl iodate was not forthcoming. A mechanism for the determination of the velocity constant (probability per ion pair per unit time) is proposed for each of the systems. (author)

  13. Photoinduced electron transfer and solvation in iodide-doped acetonitrile clusters.

    Science.gov (United States)

    Ehrler, Oli T; Griffin, Graham B; Young, Ryan M; Neumark, Daniel M

    2009-04-02

    We have used ultrafast time-resolved photoelectron imaging to measure charge transfer dynamics in iodide-doped acetonitrile clusters I(-)(CH(3)CN)(n) with n = 5-10. Strong modulations of vertical detachment energies were observed following charge transfer from the halide, allowing interpretation of the ongoing dynamics. We observe a sharp drop in the vertical detachment energy (VDE) within 300-400 fs, followed by a biexponential increase that is complete by approximately 10 ps. Comparison to theory suggests that the iodide is internally solvated and that photodetachment results in formation of a diffuse electron cloud in a confined cavity. We interpret the initial drop in VDE as a combination of expansion of the cavity and localization of the excess electron on one or two solvent molecules. The subsequent increase in VDE is attributed to a combination of the I atom leaving the cavity and rearrangement of the acetonitrile molecules to solvate the electron. The n = 5-8 clusters then show a drop in VDE of around 50 meV on a much longer time scale. The long-time VDEs are consistent with those of (CH(3)CN)(n)(-) clusters with internally solvated electrons. Although the excited-state created by the pump pulse decays by emission of a slow electron, no such decay is seen by 200 ps.

  14. Elucidation of the relationships between H-bonding patterns and excited state dynamics in cyclovalone.

    Science.gov (United States)

    Lamperti, Marco; Maspero, Angelo; Tønnesen, Hanne H; Bondani, Maria; Nardo, Luca

    2014-08-28

    Cyclovalone is a synthetic curcumin derivative in which the keto-enolic system is replaced by a cyclohexanone ring. This modification of the chemical structure might in principle result in an excited state that is more stable than that of curcumin, which in turn should produce an enhanced phototoxicity. Indeed, although curcumin exhibits photosensitized antibacterial activity, this compound is characterized by very fast excited-state dynamics which limit its efficacy as a photosensitizer. In previous works we showed that the main non-radiative decay pathway of keto-enolic curcuminoids is through excited-state transfer of the enolic proton to the keto-oxygen. Another effective deactivation pathway involves an intermolecular charge transfer mechanism occurring at the phenyl rings, made possible by intramolecular H-bonding between the methoxy and the hydroxyl substituent. In this paper we present UV-Vis and IR absorption spectra data with the aim of elucidating the intramolecular charge distribution of this compound and its solvation patterns in different environments, with particular focus on solute-solvent H-bonding features. Moreover, we discuss steady state and time-resolved fluorescence data that aim at characterizing the excited-state dynamics of cyclovalone, and we compare its decay photophysics to that of curcumin. Finally, because during the characterization procedures we found evidence of very fast photodegradation of cyclovalone, its photostability in four organic solvents was studied by HPLC and the corresponding relative degradation rates were calculated.

  15. Elucidation of the Relationships between H-Bonding Patterns and Excited State Dynamics in Cyclovalone

    Directory of Open Access Journals (Sweden)

    Marco Lamperti

    2014-08-01

    Full Text Available Cyclovalone is a synthetic curcumin derivative in which the keto-enolic system is replaced by a cyclohexanone ring. This modification of the chemical structure might in principle result in an excited state that is more stable than that of curcumin, which in turn should produce an enhanced phototoxicity. Indeed, although curcumin exhibits photosensitized antibacterial activity, this compound is characterized by very fast excited-state dynamics which limit its efficacy as a photosensitizer. In previous works we showed that the main non-radiative decay pathway of keto-enolic curcuminoids is through excited-state transfer of the enolic proton to the keto-oxygen. Another effective deactivation pathway involves an intermolecular charge transfer mechanism occurring at the phenyl rings, made possible by intramolecular H-bonding between the methoxy and the hydroxyl substituent. In this paper we present UV-Vis and IR absorption spectra data with the aim of elucidating the intramolecular charge distribution of this compound and its solvation patterns in different environments, with particular focus on solute-solvent H-bonding features. Moreover, we discuss steady state and time-resolved fluorescence data that aim at characterizing the excited-state dynamics of cyclovalone, and we compare its decay photophysics to that of curcumin. Finally, because during the characterization procedures we found evidence of very fast photodegradation of cyclovalone, its photostability in four organic solvents was studied by HPLC and the corresponding relative degradation rates were calculated.

  16. Defining Electron Bifurcation in the Electron-Transferring Flavoprotein Family.

    Science.gov (United States)

    Garcia Costas, Amaya M; Poudel, Saroj; Miller, Anne-Frances; Schut, Gerrit J; Ledbetter, Rhesa N; Fixen, Kathryn R; Seefeldt, Lance C; Adams, Michael W W; Harwood, Caroline S; Boyd, Eric S; Peters, John W

    2017-11-01

    Electron bifurcation is the coupling of exergonic and endergonic redox reactions to simultaneously generate (or utilize) low- and high-potential electrons. It is the third recognized form of energy conservation in biology and was recently described for select electron-transferring flavoproteins (Etfs). Etfs are flavin-containing heterodimers best known for donating electrons derived from fatty acid and amino acid oxidation to an electron transfer respiratory chain via Etf-quinone oxidoreductase. Canonical examples contain a flavin adenine dinucleotide (FAD) that is involved in electron transfer, as well as a non-redox-active AMP. However, Etfs demonstrated to bifurcate electrons contain a second FAD in place of the AMP. To expand our understanding of the functional variety and metabolic significance of Etfs and to identify amino acid sequence motifs that potentially enable electron bifurcation, we compiled 1,314 Etf protein sequences from genome sequence databases and subjected them to informatic and structural analyses. Etfs were identified in diverse archaea and bacteria, and they clustered into five distinct well-supported groups, based on their amino acid sequences. Gene neighborhood analyses indicated that these Etf group designations largely correspond to putative differences in functionality. Etfs with the demonstrated ability to bifurcate were found to form one group, suggesting that distinct conserved amino acid sequence motifs enable this capability. Indeed, structural modeling and sequence alignments revealed that identifying residues occur in the NADH- and FAD-binding regions of bifurcating Etfs. Collectively, a new classification scheme for Etf proteins that delineates putative bifurcating versus nonbifurcating members is presented and suggests that Etf-mediated bifurcation is associated with surprisingly diverse enzymes. IMPORTANCE Electron bifurcation has recently been recognized as an electron transfer mechanism used by microorganisms to maximize

  17. Watson-Crick base pairing controls excited-state decay in natural DNA.

    Science.gov (United States)

    Bucher, Dominik B; Schlueter, Alexander; Carell, Thomas; Zinth, Wolfgang

    2014-10-13

    Excited-state dynamics are essential to understanding the formation of DNA lesions induced by UV light. By using femtosecond IR spectroscopy, it was possible to determine the lifetimes of the excited states of all four bases in the double-stranded environment of natural DNA. After UV excitation of the DNA duplex, we detected a concerted decay of base pairs connected by Watson-Crick hydrogen bonds. A comparison of single- and double-stranded DNA showed that the reactive charge-transfer states formed in the single strands are suppressed by base pairing in the duplex. The strong influence of the Watson-Crick hydrogen bonds indicates that proton transfer opens an efficient decay path in the duplex that prohibits the formation or reduces the lifetime of reactive charge-transfer states. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Use of a 3-MV proton accelerator for study of noble gases, including laser ionization of excited states

    International Nuclear Information System (INIS)

    Hurst, G.S.; Judish, J.P.; Nayfeh, M.H.; Parks, J.E.; Payne, M.G.; Wagner, E.B.

    1974-01-01

    The use of a pulsed 3-MV accelerator to study energy pathways in the noble gases is described. The objectives of pathways research are to obtain (1) information on the spectrum of excited states produced by a charged particle in a noble gas, (2) the rate of decay of the various states through various channels as a function of gas pressure, and (3) the modification of the decay channels due to the introduction of foreign species. A new energy pathways model is presented for helium as a general illustration. A method for the study of excited states, using a laser ionization technique is reported. Use is made of a laser which is tuned to a resonance transition between the desired excited state and some higher excited state. Photons in the same pulse photoionize the higher excited state; thus the ionization current vs photon wavelength has a resonance structure. Absolute yields of selected excited states can be obtained whenever the photon fluence per pulse is large enough to saturate the ionization current. A general summary is given of experimental facilities which include a 3-MV Van de Graaff accelerator, electronics for measuring radiation lifetimes, vacuum ultraviolet spectrometers, and a pulsed laser facility for direct study of excited states. Finally, the relevance of pathways research to (1) the interaction of radiation with matter, (2) the development of gas lasers, and (3) methods of ultrasensitive elemental analysis is pointed out

  19. Highly solvatochromic emission of electron donor-acceptor compounds containing propanedioato boron electron acceptors

    NARCIS (Netherlands)

    Brouwer, A.M.; Bakker, N.A.C.; Wiering, P.G.; Verhoeven, J.W.

    1991-01-01

    Light-induced electron transfer occurs in bifunctional compounds consisting of 1,3-diphenylpropanedioato boron oxalate or fluoride electron acceptors and simple aromatic electron-donor groups, linked by a methylene bridge; fluorescence from the highly polar charge-transfer excited state is

  20. Absence of quantum oscillations in electronic excitation transfer in the Fenna-Matthews-Olson complex

    Science.gov (United States)

    Eisfeld, Alexander; Ritschel, Gerhard; Roden, Jan; Strunz, Walter; Aspuru-Guzik, Alan

    2012-02-01

    Energy transfer in the photosynthetic Fenna-Matthews-Olson (FMO) complex of the Green Sulfur Bacteria is studied theoretically taking all three subunits (monomers) of the FMO trimer and the recently found eighth bacteriochlorophyll (BChl) molecule into account. For the calculations we use the efficient Non-Markovian Quantum State diffusion approach. Since it is believed that the eighth BChl is located near the main light harvesting antenna we look at the differences in transfer between the situation when BChl 8 is initially excited and the usually considered case when BChl 1 or 6 is initially excited. We find strong differences in the transfer dynamics, both qualitatively and quantitatively. When the excited state dynamics is initialized at site eight of the FMO complex, we see a slow exponential-like decay of the excitation. This is in contrast to the oscillations and a relatively fast transfer that occurs when only seven sites or initialization at sites 1 and 6 is considered. Additionally we show that differences in the values of the electronic transition energies found in the literature lead to a large difference in the transfer dynamics.

  1. Embedding potentials for excited states of embedded species

    International Nuclear Information System (INIS)

    Wesolowski, Tomasz A.

    2014-01-01

    Frozen-Density-Embedding Theory (FDET) is a formalism to obtain the upper bound of the ground-state energy of the total system and the corresponding embedded wavefunction by means of Euler-Lagrange equations [T. A. Wesolowski, Phys. Rev. A 77(1), 012504 (2008)]. FDET provides the expression for the embedding potential as a functional of the electron density of the embedded species, electron density of the environment, and the field generated by other charges in the environment. Under certain conditions, FDET leads to the exact ground-state energy and density of the whole system. Following Perdew-Levy theorem on stationary states of the ground-state energy functional, the other-than-ground-state stationary states of the FDET energy functional correspond to excited states. In the present work, we analyze such use of other-than-ground-state embedded wavefunctions obtained in practical calculations, i.e., when the FDET embedding potential is approximated. Three computational approaches based on FDET, that assure self-consistent excitation energy and embedded wavefunction dealing with the issue of orthogonality of embedded wavefunctions for different states in a different manner, are proposed and discussed

  2. Biotechnological Aspects of Microbial Extracellular Electron Transfer

    Science.gov (United States)

    Kato, Souichiro

    2015-01-01

    Extracellular electron transfer (EET) is a type of microbial respiration that enables electron transfer between microbial cells and extracellular solid materials, including naturally-occurring metal compounds and artificial electrodes. Microorganisms harboring EET abilities have received considerable attention for their various biotechnological applications, in addition to their contribution to global energy and material cycles. In this review, current knowledge on microbial EET and its application to diverse biotechnologies, including the bioremediation of toxic metals, recovery of useful metals, biocorrosion, and microbial electrochemical systems (microbial fuel cells and microbial electrosynthesis), were introduced. Two potential biotechnologies based on microbial EET, namely the electrochemical control of microbial metabolism and electrochemical stimulation of microbial symbiotic reactions (electric syntrophy), were also discussed. PMID:26004795

  3. Dynamics in electron transfer protein complexes

    OpenAIRE

    Bashir, Qamar

    2010-01-01

    Recent studies have provided experimental evidence for the existence of an encounter complex, a transient intermediate in the formation of protein complexes. We have used paramagnetic relaxation enhancement NMR spectroscopy in combination with Monte Carlo simulations to characterize and visualize the ensemble of encounter orientations in the short-lived electron transfer complex of yeast Cc and CcP. The complete conformational space sampled by the protein molecules during the dynamic part of ...

  4. An excited state underlies gene regulation of a transcriptional riboswitch

    Science.gov (United States)

    Zhao, Bo; Guffy, Sharon L.; Williams, Benfeard; Zhang, Qi

    2017-01-01

    Riboswitches control gene expression through ligand-dependent structural rearrangements of the sensing aptamer domain. However, we found that the Bacillus cereus fluoride riboswitch aptamer adopts identical tertiary structures in solution with and without ligand. Using chemical exchange saturation transfer (CEST) NMR spectroscopy, we revealed that the structured ligand-free aptamer transiently accesses a low-populated (~1%) and short-lived (~3 ms) excited conformational state that unravels a conserved ‘linchpin’ base pair to signal transcription termination. Upon fluoride binding, this highly localized fleeting process is allosterically suppressed to activate transcription. We demonstrated that this mechanism confers effective fluoride-dependent gene activation over a wide range of transcription rates, which is essential for robust toxicity response across diverse cellular conditions. These results unveil a novel switching mechanism that employs ligand-dependent suppression of an aptamer excited state to coordinate regulatory conformational transitions rather than adopting distinct aptamer ground-state tertiary architectures, exemplifying a new mode of ligand-dependent RNA regulation. PMID:28719589

  5. Excited-state dynamics of the medicinal pigment curcumin in a hydrogel.

    Science.gov (United States)

    Harada, Takaaki; Lincoln, Stephen F; Kee, Tak W

    2016-10-12

    Curcumin is a yellow polyphenol with multiple medicinal effects. These effects, however, are limited due to its poor aqueous stability and solubility. A hydrogel of 3% octadecyl randomly substituted polyacrylate (PAAC18) has been shown to provide high aqueous stability for curcumin under physiological conditions, offering a route for photodynamic therapy. In this study, the excited-state photophysics of curcumin in the PAAC18 hydrogel is investigated using a combination of femtosecond transient absorption and fluorescence upconversion spectroscopy. The transient absorption results reveal a multiexponential decay in the excited-state kinetics with fast (1 ps & 15 ps) and slow (110 ps & ≈5 ns) components. The fast decay component exhibits a deuterium isotope effect with D 2 O in the hydrogel, indicating that the 15 ps decay component is attributable to excited-state intramolecular hydrogen atom transfer of curcumin in the PAAC18 hydrogel. In addition, solvent reorganisation of excited-state curcumin is investigated using multiwavelength femtosecond fluorescence upconversion spectroscopy. The results show that the dominant solvation response (τ = 0.08 ps) is a fast inertial motion owing to the presence of bulk-like water in the vicinity of the hydrophobic octadecyl substituents of the PAAC18 hydrogel. The results also show an additional response with longer time constants of 1 and 6 ps, which is attributable to translational diffusion of confined water molecules in the three-dimensional, cross-linking network of the octadecyl substituents of PAAC18. Overall, we show that excited-state intramolecular hydrogen atom transfer and solvent reorganisation are major photophysical events for curcumin in the PAAC18 hydrogel.

  6. Formation of excited states in high-Z helium-like systems

    International Nuclear Information System (INIS)

    Fritzsche, S.; Fricke, B.; Brinzanescu, O.

    1999-12-01

    High-Z helium-like ions represent the simplest multi-electron systems for studying the interplay between electron-electron correlations, relativistic as well as quantum electrodynamical effects in strong fields. In contrast to the adjacent lithium-like ions, however, almost no experimental information is available about the excited states in the high-Z domain of the helium sequence. Here, we present a theoretical analysis of the X-ray production and decay dynamics of the excited states in helium-like uranium. Emphasize has been paid particularly to the formation of the 3 P 0 and 3 P 2 levels by using electron capture into hydrogen-like U 91+ . Both states are of interest for precise measurements on high-Z helium-like ions in the future. (orig.)

  7. Excited state intramolecular charge transfer reaction in 4-(1 ...

    Indian Academy of Sciences (India)

    Administrator

    cal reactions to the determination of paleotempera- tures from isotopic ... ordered liquid than H2O due to stronger H-bond in- teractions in the deuterated water ... layer chromatography and monitoring the excitation wavelength dependence of ...

  8. Excited state charge transfer reaction in (mixed solvent + electrolyte ...

    Indian Academy of Sciences (India)

    vent characteristics summarized in table 1 indicate that these mixed ... polarity scale,35,36 on the other hand, seems to sug- ... electrolyte than the specified ones become insoluble in ... kinetics of P4C eventhough alternative models40,41 are ...... Maurer G 1983 Fluid Phase Equilib. ... Yoon B J and Ohr Y G 2000 J. Chem.

  9. Cathodoluminescence imaging and spectroscopy of excited states in InAs self-assembled quantum dots

    International Nuclear Information System (INIS)

    Khatsevich, S.; Rich, D.H.; Kim, Eui-Tae; Madhukar, A.

    2005-01-01

    We have examined state filling and thermal activation of carriers in buried InAs self-assembled quantum dots (SAQDs) with excitation-dependent cathodoluminescence (CL) imaging and spectroscopy. The InAs SAQDs were formed during molecular-beam epitaxial growth of InAs on undoped planar GaAs (001). The intensities of the ground- and excited-state transitions were analyzed as a function of temperature and excitation density to study the thermal activation and reemission of carriers. The thermal activation energies associated with the thermal quenching of the luminescence were measured for ground- and excited-state transitions of the SAQDs, as a function of excitation density. By comparing these activation energies with the ground- and excited-state transition energies, we have considered various processes that describe the reemission of carriers. Thermal quenching of the intensity of the QD ground- and first excited-state transitions at low excitations in the ∼230-300-K temperature range is attributed to dissociation of excitons from the QD states into the InAs wetting layer. At high excitations, much lower activation energies of the ground and excited states are obtained, suggesting that thermal reemission of single holes from QD states into the GaAs matrix is responsible for the observed temperature dependence of the QD luminescence in the ∼230-300-K temperature range. The dependence of the CL intensity of the ground-and first excited-state transition on excitation density was shown to be linear at all temperatures at low-excitation density. This result can be understood by considering that carriers escape and are recaptured as excitons or correlated electron-hole pairs. At sufficiently high excitations, state-filling and spatial smearing effects are observed together with a sublinear dependence of the CL intensity on excitation. Successive filling of the ground and excited states in adjacent groups of QDs that possess different size distributions is assumed to

  10. Transfer coating by electron initiated polymerization

    International Nuclear Information System (INIS)

    Nablo, S.V.

    1984-01-01

    The high speed and depth of cure possible with electron initiated monomer/oligomer coating systems provide many new opportunities for approaches to product finishing. Moreover, the use of transfer or cast coating using films or metallic surfaces offers the ability to precisely control the surface topology of liquid film surfaces during polymerization. Transfer coating such as with textiles has been a commercial process for many years and the synergistic addition of EB technology permits the manufacture of unusual new products. One of these, the casting paper used in the manufacture of vinyl and urethane fabrics, is the first EB application to use a drum surface for pattern replication in the coating. In this case the coated paper is cured against, and then released from, an engraved drum surface. Recent developments in the use of plastic films for transfer have been applied to the manufacture of transfer metallized and coated paper and paperboard products for packaging. Details of these and related processes are presented as well as a discussion of the typical product areas (e.g. photographic papers, release papers, magnetic media) using this high speed transfer technology

  11. Transfer coating by electron initiated polymerization

    International Nuclear Information System (INIS)

    Nablo, S.V.

    1985-01-01

    The high speed and depth of cure possible with electron initiated monomer/oligomer coating systems provide many new opportunities for approaches to product finishing. Moreover, the use of transfer or cast coating using films or metallic surfaces offers the ability to precisely control the surface topology of liquid film surfaces during polymerization. Transfer coating such as with textiles has been a commercial process for many years and the synergistic addition of EB technology permits the manufacture of unusual new products. One of these, the casting paper used in the manufacture of vinyl and urethane fabrics, is the first EB application to use a drum surface for pattern replication in the coating. In this case the coated paper is cured against, and then released from, an engraved drum surface. Recent developments in the use of plastic films for transfer have been applied to the manufacture of transfer metallized and coated paper and paperboard products for packaging. Details of these and related processes will be presented as well as a discussion of the typical product areas using this high speed transfer technology. (author)

  12. Dynamics of transfer of electron excitation in a donor-acceptor system with a carbon chain and ways of its relaxation

    Directory of Open Access Journals (Sweden)

    M.M. Sevryukova

    2017-12-01

    Full Text Available The optical properties and dynamics of transport of electron excitation and the ways of its relaxation in the supramolecular D–π–A complex on the basis of merocyanines have been investigated. There have been found two components in the transfer of charge: fast and slow, which correspond to different conformational states of the carbon chain in merocyanines. It was found that the main photoluminescence of the studied molecular solutions of merocyanines by its nature is similar to the exciplex luminescence, as a manifestation of resonant and charge transfer interaction in an excited state. The lifetime in this state is about 2000 ps.

  13. The electronically excited states of LH2 complexes from Rhodopseudomonas acidophila strain 10050 studied by time-resolved spectroscopy and dynamic Monte Carlo simulations. II. Homo-arrays of LH2 complexes reconstituted into phospholipid model membranes.

    Science.gov (United States)

    Pflock, Tobias J; Oellerich, Silke; Krapf, Lisa; Southall, June; Cogdell, Richard J; Ullmann, G Matthias; Köhler, Jürgen

    2011-07-21

    We performed time-resolved spectroscopy on homoarrays of LH2 complexes from the photosynthetic purple bacterium Rhodopseudomonas acidophila. Variations of the fluorescence transients were monitored as a function of the excitation fluence and the repetition rate of the excitation. These parameters are directly related to the excitation density within the array and to the number of LH2 complexes that still carry a triplet state prior to the next excitation. Comparison of the experimental observations with results from dynamic Monte Carlo simulations for a model cluster of LH2 complexes yields qualitative agreement without the need for any free parameter and reveals the mutual relationship between energy transfer and annihilation processes.

  14. Does the excited state of the 3He nucleus exist?

    International Nuclear Information System (INIS)

    Barabanov, A.L.

    1994-01-01

    The suggestion is made that the excited state of the 3 He nucleus found out recently in the reaction has spin and parity 1/2 + and the same configuration that the ground open of 6 He. It is shown that in an elastic nd-scattering a resonance associated with the excited state may be absent due to destructive interference of potential and resonant scattering phases

  15. Promoting Interspecies Electron Transfer with Biochar

    Science.gov (United States)

    Chen, Shanshan; Rotaru, Amelia-Elena; Shrestha, Pravin Malla; Malvankar, Nikhil S.; Liu, Fanghua; Fan, Wei; Nevin, Kelly P.; Lovley, Derek R.

    2014-01-01

    Biochar, a charcoal-like product of the incomplete combustion of organic materials, is an increasingly popular soil amendment designed to improve soil fertility. We investigated the possibility that biochar could promote direct interspecies electron transfer (DIET) in a manner similar to that previously reported for granular activated carbon (GAC). Although the biochars investigated were 1000 times less conductive than GAC, they stimulated DIET in co-cultures of Geobacter metallireducens with Geobacter sulfurreducens or Methanosarcina barkeri in which ethanol was the electron donor. Cells were attached to the biochar, yet not in close contact, suggesting that electrons were likely conducted through the biochar, rather than biological electrical connections. The finding that biochar can stimulate DIET may be an important consideration when amending soils with biochar and can help explain why biochar may enhance methane production from organic wastes under anaerobic conditions. PMID:24846283

  16. A note on calm excited states of inflation

    International Nuclear Information System (INIS)

    Ashoorioon, Amjad; Shiu, Gary

    2011-01-01

    We identify a two-parameter family of excited states within slow-roll inflation for which either the corrections to the two-point function or the characteristic signatures of excited states in the three-point function — i.e. the enhancement for the flattened momenta configurations– are absent. These excited states may nonetheless violate the adiabaticity condition maximally. We dub these initial states of inflation calm excited states. We show that these two sets do not intersect, i.e., those that leave the power-spectrum invariant can be distinguished from their bispectra, and vice versa. The same set of calm excited states that leave the two-point function invariant for slow-roll inflation, do the same task for DBI inflation. However, at the level of three-point function, the calm excited states whose flattened configuration signature is absent for slow-roll inflation, will lead to an enhancement for DBI inflation generally, although the signature is smaller than what suggested by earlier analysis. This example also illustrates that imposing the Wronskian condition is important for obtaining a correct estimate of the non-Gaussian signatures

  17. Hertzian spectroscopy application to excited states in accelerated ion beams

    Energy Technology Data Exchange (ETDEWEB)

    Gaillard, M L

    1974-01-01

    Accelerated ion beams enables the application of optical hertzian spectrometry methods to be extended to research on the excited states of free ionic systems. The photon beat method has proved especially simple to apply in beam foil geometry because of the unidirectional beam velocity while the beam gas device is suitable for experiments of the energy level crossing type. Only the resonance technique involving direct application of high-frequency magnetic fields poses serious problems because of the high HF powers necessary. So far structure intervals have been measured in ions carrying up to three charges (seven in the special case of Lamb shift measurements) with a precision of a few percent. Study of hydrogen-like or helium-like ions of high Z allows the fundamental calculations of quantum electrodynamics to be checked with regard to the Lamb shift or the spontaneous emission theory. In more complex electronic systems, optical spectroscopy of accelerated ion beams gives wavelengths with a resolution reaching 10/sup -5/, lifetimes with an accuracy better than 10% when the cascade effects are properly studied, and Lande factors with a precision of several % under present technical conditions. The photon beat method concerns hyperfine nuclear effects in light atoms of Z < = 20. (FR)

  18. Excited states in 22Mg via the 12C(12C,2n)22Mg reaction

    International Nuclear Information System (INIS)

    Jewett, Cybele; Baktash, Cyrus; Bardayan, Daniel W.; Blackmon, Jeff C.; Chipps, K.; Galindo-Uribarri, Alfredo; Greife, U.; Gross, Carl J.; Jones, K. L.; Liang, Junjien; Livesay, Jake; Kozub, R. L.; Nesaraja, Caroline D; Radford, David C.; Sarazin, F.; Smith, Michael Scott; Thomas, J. S.; Yu, Chang-Hong

    2007-01-01

    The 12C(12C, 2n)22Mg reaction was measured with the CLARION array and the RMS separator at the Holifield Facility of Oak Ridge National Laboratory. This experiment was performed to gather more information on the excited states in 22Mg, which might be of relevance to recent radioactive ion beam measurements of the astrophysically important 21Na(p,γ)22Mg reaction. The results are compared to direct measurements, transfer experiments and a competing experiment performed with Gammasphere

  19. Solvent control of intramolecular proton transfer

    DEFF Research Database (Denmark)

    Manolova, Y.; Marciniak, Heinz; Tschierlei, S.

    2017-01-01

    of molecules in the enol and zwitterionic proton transfer (PT) form exists in the ground state. However, the zwitterion is the energetically favored one in the electronically excited state. Optical excitation of the enol form results in intramolecular proton transfer and formation of the PT form within 1.4 ps...

  20. Molecular excited states from the SCAN functional

    Science.gov (United States)

    Tozer, David J.; Peach, Michael J. G.

    2018-06-01

    The performance of the strongly constrained and appropriately normed (SCAN) meta-generalised gradient approximation exchange-correlation functional is investigated for the calculation of time-dependent density-functional theory molecular excitation energies of local, charge-transfer and Rydberg character, together with the excited ? potential energy curve in H2. The SCAN results frequently resemble those obtained using a global hybrid functional, with either a standard or increased fraction of exact orbital exchange. For local excitations, SCAN can exhibit significant triplet instability problems, resulting in imaginary triplet excitation energies for a number of cases. The Tamm-Dancoff approximation offers a simple approach to improve the situation, but the excitation energies are still significantly underestimated. Understanding the origin of these (near)-triplet instabilities may provide useful insight into future functional development.

  1. Excited-State Dynamics of Melamine and Its Lysine Derivative Investigated by Femtosecond Transient Absorption Spectroscopy

    Directory of Open Access Journals (Sweden)

    Yuyuan Zhang

    2016-11-01

    Full Text Available Melamine may have been an important prebiotic information carrier, but its excited-state dynamics, which determine its stability under UV radiation, have never been characterized. The ability of melamine to withstand the strong UV radiation present on the surface of the early Earth is likely to have affected its abundance in the primordial soup. Here, we studied the excited-state dynamics of melamine (a proto-nucleobase and its lysine derivative (a proto-nucleoside using the transient absorption technique with a UV pump, and UV and infrared probe pulses. For melamine, the excited-state population decays by internal conversion with a lifetime of 13 ps without coupling significantly to any photochemical channels. The excited-state lifetime of the lysine derivative is slightly longer (18 ps, but the dominant deactivation pathway is otherwise the same as for melamine. In both cases, the vast majority of excited molecules return to the electronic ground state on the aforementioned time scales, but a minor population is trapped in a long-lived triplet state.

  2. 14 CFR 1260.69 - Electronic funds transfer payment methods.

    Science.gov (United States)

    2010-01-01

    ... Government by electronic funds transfer through the Treasury Fedline Payment System (FEDLINE) or the... 14 Aeronautics and Space 5 2010-01-01 2010-01-01 false Electronic funds transfer payment methods... COOPERATIVE AGREEMENTS General Special Conditions § 1260.69 Electronic funds transfer payment methods...

  3. The separation of vibrational coherence from ground- and excited-electronic states in P3HT film

    KAUST Repository

    Song, Yin; Hellmann, Christoph; Stingelin, Natalie; Scholes, Gregory D.

    2015-01-01

    © 2015 AIP Publishing LLC. Concurrence of the vibrational coherence and ultrafast electron transfer has been observed in polymer/fullerene blends. However, it is difficult to experimentally investigate the role that the excited-state vibrational

  4. Triplet excited state properties in variable gap π-conjugated donor–acceptor–donor chromophores

    KAUST Repository

    Cekli, Seda; Winkel, Russell W.; Alarousu, Erkki; Mohammed, Omar F.; Schanze, Kirk S.

    2016-01-01

    A series of variable band-gap donor–acceptor–donor (DAD) chromophores capped with platinum(II) acetylide units has been synthesized and fully characterized by electrochemical and photophysical methods, with particular emphasis placed on probing triplet excited state properties. A counter-intuitive trend of increasing fluorescence quantum efficiency and lifetime with decreasing excited state energy (optical gap) is observed across the series of DAD chromophores. Careful study of the excited state dynamics, including triplet yields (as inferred from singlet oxygen sensitization), reveals that the underlying origin of the unusual trend in the fluorescence parameters is that the singlet–triplet intersystem crossing rate and yield decrease with decreasing optical gap. It is concluded that the rate of intersystem crossing decreases as the LUMO is increasingly localized on the acceptor unit in the DAD chromophore, and this result is interpreted as arising because the extent of spin–orbit coupling induced by the platinum heavy metal centers decreases as the LUMO is more localized on the acceptor. In addition to the trend in intersystem crossing, the results show that the triplet decay rates follow the Energy Gap Law correlation over a 1.8 eV range of triplet energy and 1000-fold range of triplet decay rates. Finally, femtosecond transient absorption studies for the DAD chromophores reveals a strong absorption in the near-infrared region which is attributed to the singlet excited state. This spectral band appears to be general for DAD chromophores, and may be a signature of the charge transfer (CT) singlet excited state.

  5. Triplet excited state properties in variable gap π-conjugated donor–acceptor–donor chromophores

    KAUST Repository

    Cekli, Seda

    2016-02-12

    A series of variable band-gap donor–acceptor–donor (DAD) chromophores capped with platinum(II) acetylide units has been synthesized and fully characterized by electrochemical and photophysical methods, with particular emphasis placed on probing triplet excited state properties. A counter-intuitive trend of increasing fluorescence quantum efficiency and lifetime with decreasing excited state energy (optical gap) is observed across the series of DAD chromophores. Careful study of the excited state dynamics, including triplet yields (as inferred from singlet oxygen sensitization), reveals that the underlying origin of the unusual trend in the fluorescence parameters is that the singlet–triplet intersystem crossing rate and yield decrease with decreasing optical gap. It is concluded that the rate of intersystem crossing decreases as the LUMO is increasingly localized on the acceptor unit in the DAD chromophore, and this result is interpreted as arising because the extent of spin–orbit coupling induced by the platinum heavy metal centers decreases as the LUMO is more localized on the acceptor. In addition to the trend in intersystem crossing, the results show that the triplet decay rates follow the Energy Gap Law correlation over a 1.8 eV range of triplet energy and 1000-fold range of triplet decay rates. Finally, femtosecond transient absorption studies for the DAD chromophores reveals a strong absorption in the near-infrared region which is attributed to the singlet excited state. This spectral band appears to be general for DAD chromophores, and may be a signature of the charge transfer (CT) singlet excited state.

  6. Trapping Dynamics in Photosystem I-Light Harvesting Complex I of Higher Plants Is Governed by the Competition Between Excited State Diffusion from Low Energy States and Photochemical Charge Separation.

    Science.gov (United States)

    Molotokaite, Egle; Remelli, William; Casazza, Anna Paola; Zucchelli, Giuseppe; Polli, Dario; Cerullo, Giulio; Santabarbara, Stefano

    2017-10-26

    The dynamics of excited state equilibration and primary photochemical trapping have been investigated in the photosystem I-light harvesting complex I isolated from spinach, by the complementary time-resolved fluorescence and transient absorption approaches. The combined analysis of the experimental data indicates that the excited state decay is described by lifetimes in the ranges of 12-16 ps, 32-36 ps, and 64-77 ps, for both detection methods, whereas faster components, having lifetimes of 550-780 fs and 4.2-5.2 ps, are resolved only by transient absorption. A unified model capable of describing both the fluorescence and the absorption dynamics has been developed. From this model it appears that the majority of excited state equilibration between the bulk of the antenna pigments and the reaction center occurs in less than 2 ps, that the primary charge separated state is populated in ∼4 ps, and that the charge stabilization by electron transfer is completed in ∼70 ps. Energy equilibration dynamics associated with the long wavelength absorbing/emitting forms harbored by the PSI external antenna are also characterized by a time mean lifetime of ∼75 ps, thus overlapping with radical pair charge stabilization reactions. Even in the presence of a kinetic bottleneck for energy equilibration, the excited state dynamics are shown to be principally trap-limited. However, direct excitation of the low energy chlorophyll forms is predicted to lengthen significantly (∼2-folds) the average trapping time.

  7. Single-Molecule Interfacial Electron Transfer

    Energy Technology Data Exchange (ETDEWEB)

    Ho, Wilson [Univ. of California, Irvine, CA (United States)

    2018-02-03

    Interfacial electron transfer (ET) plays an important role in many chemical and biological processes. Specifically, interfacial ET in TiO2-based systems is important to solar energy technology, catalysis, and environmental remediation technology. However, the microscopic mechanism of interfacial ET is not well understood with regard to atomic surface structure, molecular structure, bonding, orientation, and motion. In this project, we used two complementary methodologies; single-molecule fluorescence spectroscopy, and scanning-tunneling microscopy and spectroscopy (STM and STS) to address this scientific need. The goal of this project was to integrate these techniques and measure the molecular dependence of ET between adsorbed molecules and TiO2 semiconductor surfaces and the ET induced reactions such as the splitting of water. The scanning probe techniques, STM and STS, are capable of providing the highest spatial resolution but not easily time-resolved data. Single-molecule fluorescence spectroscopy is capable of good time resolution but requires further development to match the spatial resolution of the STM. The integrated approach involving Peter Lu at Bowling Green State University (BGSU) and Wilson Ho at the University of California, Irvine (UC Irvine) produced methods for time and spatially resolved chemical imaging of interfacial electron transfer dynamics and photocatalytic reactions. An integral aspect of the joint research was a significant exchange of graduate students to work at the two institutions. This project bridged complementary approaches to investigate a set of common problems by working with the same molecules on a variety of solid surfaces, but using appropriate techniques to probe under ambient (BGSU) and ultrahigh vacuum (UCI) conditions. The molecular level understanding of the fundamental interfacial electron transfer processes obtained in this joint project will be important for developing efficient light harvesting

  8. Double electron transfer in H- + H+ collisions

    International Nuclear Information System (INIS)

    Braeuning, H; Helm, H; Briggs, J S; Salzborn, E

    2007-01-01

    Absolute cross sections for double electron transfer in H - + H + collisions have been measured for center-of-mass energies from 0.5 keV to 12 keV. Clear oscillations in the cross section are observed which are in excellent agreement with earlier measurements at lower energies by Brouillard et al (1979) as well as Peart and Dolder (1979). After an oscillation maximum at 3 keV center-of-mass energy the cross section decreases for increasing energy with no indication of further oscillations

  9. Analysis of 165Er excited state properties

    International Nuclear Information System (INIS)

    Morozov, V.A.; Budzynski, M.

    1982-01-01

    It is shown by the analysis of 165 Tm decay that the precision measurements of γ-ray and internal conversion electron intensities together with the measurements o.f angular correlation coefficients provide more data for the determination of γ-ray multipole composition and intensities of γ-transitions with small enerqy difference. The spin of the 589.868 ke tate is found to be I=1/2 - . Doublet transitions of different parity from the states 1103.495, 920.645 and 745.968 keV to the levels of the 590 keV region with energy difference ΔE=(108+-22) eV are identified

  10. The behavior of exciplex decay processes and interplay of radiationless transition and preliminary reorganization mechanisms of electron transfer in loose and tight pairs of reactants.

    Science.gov (United States)

    Kuzmin, Michael G; Soboleva, Irina V; Dolotova, Elena V

    2007-01-18

    Exciplex emission spectra and rate constants of their decay via internal conversion and intersystem crossing are studied and discussed in terms of conventional radiationless transition approach. Exciplexes of 9-cyanophenanthrene with 1,2,3-trimethoxybenzene and 1,3,5-trimethoxybenzene were studied in heptane, toluene, butyl acetate, dichloromethane, butyronitrile, and acetonitrile. A better description of spectra and rate constants is obtained using 0-0 transition energy and Gauss broadening of vibrational bands rather than the free energy of electron transfer and reorganization energy. The coincidence of parameters describing exciplex emission spectra and dependence of exciplex decay rate constants on energy gap gives the evidence of radiationless quantum transition mechanism rather than thermally activated medium reorganization mechanism of charge recombination in exciplexes and excited charge transfer complexes (contact radical ion pairs) as well as in solvent separated radical ion pairs. Radiationless quantum transition mechanism is shown to provide an appropriate description also for the main features of exergonic excited-state charge separation reactions if fast mutual transformations of loose and tight pairs of reactants are considered. In particular, very fast electron transfer (ET) in tight pairs of reactants with strong electronic coupling of locally excited and charge transfer states can prevent the observation of an inverted region in bimolecular excited-state charge separation even for highly exergonic reactions.

  11. Reaction Path Averaging: Characterizing the Structural Response of the DNA Double Helix to Electron Transfer

    Czech Academy of Sciences Publication Activity Database

    Kolář, Michal H.; Kubař, T.

    2017-01-01

    Roč. 121, č. 7 (2017), s. 1520-1532 ISSN 1520-6106 Institutional support: RVO:61388963 Keywords : excited-state dynamics * excitation energy transfer * solvation dynamics Subject RIV: CF - Physical ; Theoretical Chemistry OBOR OECD: Physical chemistry Impact factor: 3.177, year: 2016

  12. Water-chromophore electron transfer determines the photochemistry of cytosine and cytidine

    Czech Academy of Sciences Publication Activity Database

    Szabla, Rafal; Kruse, Holger; Šponer, Jiří; Gora, R.W.

    2017-01-01

    Roč. 19, č. 27 (2017), s. 17531-17537 ISSN 1463-9076 Institutional support: RVO:68081707 Keywords : driven proton-transfer * excited-state dynamics * potentially prebiotic synthesis Subject RIV: CF - Physical ; Theoretical Chemistry OBOR OECD: Physical chemistry Impact factor: 4.123, year: 2016

  13. Photorelaxation of imidazole and adenine via electron-driven proton transfer along H2O wires

    Czech Academy of Sciences Publication Activity Database

    Szabla, Rafal; Gora, R.W.; Janicki, M.; Šponer, Jiří

    2016-01-01

    Roč. 195, č. 2016 (2016), s. 237-251 E-ISSN 1364-5498 R&D Projects: GA ČR(CZ) GA14-12010S Institutional support: RVO:68081707 Keywords : excited-state deactivation * induced charge-transfer Subject RIV: BO - Biophysics

  14. Obtaining Hartree-Fock and density functional theory doubly excited states with Car-Parrinello density matrix search

    Science.gov (United States)

    Liang, Wenkel; Isborn, Christine M.; Li, Xiaosong

    2009-11-01

    The calculation of doubly excited states is one of the major problems plaguing the modern day excited state workhorse methodology of linear response time dependent Hartree-Fock (TDHF) and density function theory (TDDFT). We have previously shown that the use of a resonantly tuned field within real-time TDHF and TDDFT is able to simultaneously excite both the α and β electrons to achieve the two-electron excited states of minimal basis H2 and HeH+ [C. M. Isborn and X. Li, J. Chem. Phys. 129, 204107 (2008)]. We now extend this method to many electron systems with the use of our Car-Parrinello density matrix search (CP-DMS) with a first-principles fictitious mass method for wave function optimization [X. Li, C. L. Moss, W. Liang, and Y. Feng, J. Chem. Phys. 130, 234115 (2009)]. Real-time TDHF/TDDFT is used during the application of the laser field perturbation, driving the electron density toward the doubly excited state. The CP-DMS method then converges the density to the nearest stationary state. We present these stationary state doubly excited state energies and properties at the HF and DFT levels for H2, HeH+, lithium hydride, ethylene, and butadiene.

  15. Electron transfer pathways in microbial oxygen biocathodes

    Energy Technology Data Exchange (ETDEWEB)

    Freguia, Stefano, E-mail: stefano@kais.kyoto-u.ac.j [Bio-analytical and Physical Chemistry Laboratory, Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8205 (Japan); Tsujimura, Seiya, E-mail: seiya@kais.kyoto-u.ac.j [Bio-analytical and Physical Chemistry Laboratory, Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8205 (Japan); Kano, Kenji, E-mail: kkano@kais.kyoto-u.ac.j [Bio-analytical and Physical Chemistry Laboratory, Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8205 (Japan)

    2010-01-01

    The ability of some bacteria to enhance the rate of cathodic oxygen reduction to water has been recently discovered, opening the way to an entirely renewable and environmentally friendly concept of biocathode. In this study we reveal that several mechanisms may induce catalytic effects by bacteria. These comprise mechanisms that are putatively beneficial to the bacteria as well as mechanisms which are merely side effects, including quinone autoxidation and direct O{sub 2} reduction by heme compounds. Here we showed that 1 muM of ACNQ is able to generate a significant catalytic wave for oxygen reduction, with onset at approximately 0 V vs. SHE. Similarly, adsorption of hemin on a carbon surface catalyses O{sub 2} reduction to H{sub 2}O{sub 2} with an onset of +0.2 V vs. SHE. To evaluate the catalytic pathways of live cells on cathodic oxygen reduction, two species of electrochemically active bacteria were selected as pure cultures, namely Acinetobacter calcoaceticus and Shewanella putrefaciens. The former appears to exploit a self-excreted redox compound with redox characteristics matching those of pyrroloquinoline quinone (PQQ) for extracellular electron transfer. The latter appears to utilise outer membrane-bound redox compounds. Interaction of quinones and cytochromes with the membrane-bound electron transfer chain is yet to be proven.

  16. Efficient Long - Range Electron Transfer Processes in Polyfluorene – Perylene Diimide Blends

    KAUST Repository

    Isakova, Anna

    2018-05-17

    In bulk heterojunction donor-acceptor (D-A) blends, high photovoltaic yields require charge carrier separation to outcompete geminate recombination. Recently, evidence for long-range electron transfer mechanisms has been presented, avoiding strongly-bound interfacial charge transfer (CT) states. However, due to the lack of specific optical probes at the D-A interface, a detailed quantification of the long-range processes has not been feasible, until now. Here, we present a transient absorption study of long-range processes in a unique phase consisting of perylene diimide (PDI) crystals intercalated with polyfluorene (PFO), as widely used non-fullerene electron acceptor and donor, respectively. The intercalated PDI:PFO phase possesses specific well-separated spectral features for the excited states at the D-A interface. By use of femtosecond spectroscopy we reveal the excitation dynamics in this blend. PDI excitons undergo a clear symmetry-breaking charge separation in the PDI bulk, which occurs within several hundred femtoseconds, thus outcompeting excimer formation, known to limit charge separation yields when PDI is used as an acceptor. In contrast, PFO excitons are dissociated with very high yields in a one-step long-range process, enabled by large delocalization of the PFO exciton wavefunction. Moreover, both scenarios circumvent the formation of strongly-bound interfacial CT states and enable a targeted interfacial design for bulk heterojunction blends with near unity charge separation yields.

  17. Efficient Long - Range Electron Transfer Processes in Polyfluorene – Perylene Diimide Blends

    KAUST Repository

    Isakova, Anna; Karuthedath, Safakath; Arnold, Thomas; Howse, Jonathan; Topham, Paul D.; Toolan, Daniel Thomas William; Laquai, Fré dé ric; Lü er, Larry

    2018-01-01

    In bulk heterojunction donor-acceptor (D-A) blends, high photovoltaic yields require charge carrier separation to outcompete geminate recombination. Recently, evidence for long-range electron transfer mechanisms has been presented, avoiding strongly-bound interfacial charge transfer (CT) states. However, due to the lack of specific optical probes at the D-A interface, a detailed quantification of the long-range processes has not been feasible, until now. Here, we present a transient absorption study of long-range processes in a unique phase consisting of perylene diimide (PDI) crystals intercalated with polyfluorene (PFO), as widely used non-fullerene electron acceptor and donor, respectively. The intercalated PDI:PFO phase possesses specific well-separated spectral features for the excited states at the D-A interface. By use of femtosecond spectroscopy we reveal the excitation dynamics in this blend. PDI excitons undergo a clear symmetry-breaking charge separation in the PDI bulk, which occurs within several hundred femtoseconds, thus outcompeting excimer formation, known to limit charge separation yields when PDI is used as an acceptor. In contrast, PFO excitons are dissociated with very high yields in a one-step long-range process, enabled by large delocalization of the PFO exciton wavefunction. Moreover, both scenarios circumvent the formation of strongly-bound interfacial CT states and enable a targeted interfacial design for bulk heterojunction blends with near unity charge separation yields.

  18. Lowest excited states and optical absorption spectra of donor–acceptor copolymers for organic photovoltaics: a new picture emerging from tuned long-range corrected density functionals

    KAUST Repository

    Pandey, Laxman; Doiron, Curtis; Sears, John S.; Bré das, Jean-Luc

    2012-01-01

    Polymers with low optical gaps are of importance to the organic photovoltaics community due to their potential for harnessing a large portion of the solar energy spectrum. The combination along their backbones of electron-rich and electron-deficient fragments contributes to the presence of low-lying excited states that are expected to display significant charge-transfer character. While conventional hybrid functionals are known to provide unsatisfactory results for charge-transfer excitations at the time-dependent DFT level, long-range corrected (LRC) functionals have been reported to give improved descriptions in a number of systems. Here, we use such LRC functionals, considering both tuned and default range-separation parameters, to characterize the absorption spectra of low-optical-gap systems of interest. Our results indicate that tuned LRC functionals lead to simulated optical-absorption properties in good agreement with experimental data. Importantly, the lowest-lying excited states (excitons) are shown to present a much more localized nature than initially anticipated. © 2012 the Owner Societies.

  19. INVERSE ELECTRON TRANSFER IN PEROXYOXALATE CHEMIEXCITATION USING EASILY REDUCIBLE ACTIVATORS

    NARCIS (Netherlands)

    Bartoloni, Fernando Heering; Monteiro Leite Ciscato, Luiz Francisco; Augusto, Felipe Alberto; Baader, Wilhelm Josef

    2010-01-01

    INVERSE ELECTRON TRANSFER IN PEROXYOXALATE CHEMIEXCITATION USING EASILY REDUCIBLE ACTIVATORS. Chemiluminescence properties of the peroxyoxalate reaction in the presence of activators bearing electron withdrawing substituents were studied, to evaluate the possible occurrence of an inverse electron

  20. Ultrafast excited state relaxation in long-chain polyenes

    International Nuclear Information System (INIS)

    Antognazza, Maria Rosa; Lueer, Larry; Polli, Dario; Christensen, Ronald L.; Schrock, Richard R.; Lanzani, Guglielmo; Cerullo, Giulio

    2010-01-01

    Graphical abstract: Excited state dynamics of a long-chain polyene studied by femtosecond pump-probe spectroscopy. - Abstract: We present a comprehensive study, by femtosecond pump-probe spectroscopy, of excited state dynamics in a polyene that approaches the infinite chain limit. By excitation with sub-10-fs pulses resonant with the 0-0 S 0 → S 2 transition, we observe rapid loss of stimulated emission from the bright excited state S 2 , followed by population of the hot S 1 state within 150 fs. Vibrational cooling of S 1 takes place within 500 fs and is followed by decay back to S 0 with 1 ps time constant. By excitation with excess vibrational energy we also observe the ultrafast formation of a long-living absorption, that is assigned to the triplet state generated by singlet fission.

  1. Reaction of electron-transfer flavoprotein with electron-transfer flavoprotein-ubiquinone oxidoreductase

    International Nuclear Information System (INIS)

    Beckmann, J.D.; Frerman, F.E.

    1985-01-01

    The oxidative half-reaction of electron-transfer flavoprotein (ETF), electron transfer from ETF to electron-transfer flavoprotein-ubiquinone oxidoreductase (ETF-QO), is dependent on complementary surface charges on the two proteins. ETF is the positively charged member of the redox pair. The evidence is based on the pH and ionic strength dependencies of the comproportionation of oxidized ETF and ETF hydroquinone catalyzed by ETF-QO and on the effects of chemical modification of ETF on the comproportionation reaction. Acetylation of one and five epsilon-amino groups of lysyl residues results in 3- and 13-fold increases, respectively, in the K/sub m/ of ETF-QO for ETF but no change in V/sub max/. Amidination, which maintains positive charge at modified loci, has no effect on steady-state kinetic constants. These chemical modifications have no effect on the equilibrium constant for equilibration of ETF redox states. The K/sub m/ of ETF-QO for ETF is pH dependent above pH 8.5, suggesting titration of lysyl residues. The ionic strength dependence of TN/KmETF for the reaction follows the limiting Bronsted equation. The ETF-QO-catalyzed comproportionation reaction exhibits a primary deuterium isotope effect in D 2 O, perhaps indicating the participation of solvent water in the electron-transfer reaction

  2. Electron transfer in gas surface collisions

    International Nuclear Information System (INIS)

    Wunnik, J.N.M. van.

    1983-01-01

    In this thesis electron transfer between atoms and metal surfaces in general is discussed and the negative ionization of hydrogen by scattering protons at a cesiated crystalline tungsten (110) surface in particular. Experimental results and a novel theoretical analysis are presented. In Chapter I a theoretical overview of resonant electron transitions between atoms and metals is given. In the first part of chapter II atom-metal electron transitions at a fixed atom-metal distance are described on the basis of a model developed by Gadzuk. In the second part the influence of the motion of the atom on the atomic charge state is incorporated. Measurements presented in chapter III show a strong dependence of the fraction of negatively charged H atoms scattered at cesiated tungsten, on the normal as well as the parallel velocity component. In chapter IV the proposed mechanism for the parallel velocity effect is incorporated in the amplitude method. The scattering process of protons incident under grazing angles on a cesium covered surface is studied in chapter V. (Auth.)

  3. Quantum tunneling resonant electron transfer process in Lorentzian plasmas

    International Nuclear Information System (INIS)

    Hong, Woo-Pyo; Jung, Young-Dae

    2014-01-01

    The quantum tunneling resonant electron transfer process between a positive ion and a neutral atom collision is investigated in nonthermal generalized Lorentzian plasmas. The result shows that the nonthermal effect enhances the resonant electron transfer cross section in Lorentzian plasmas. It is found that the nonthermal effect on the classical resonant electron transfer cross section is more significant than that on the quantum tunneling resonant charge transfer cross section. It is shown that the nonthermal effect on the resonant electron transfer cross section decreases with an increase of the Debye length. In addition, the nonthermal effect on the quantum tunneling resonant electron transfer cross section decreases with increasing collision energy. The variation of nonthermal and plasma shielding effects on the quantum tunneling resonant electron transfer process is also discussed

  4. Study of the electron transfer in analog compounds of the Prussia blue

    International Nuclear Information System (INIS)

    Romero V, S.; Damaso C, L.F.; Reguera R, E.; Yee M, H.T.

    2006-01-01

    As answer to the necessity of the search of new nano structured materials, the present work was carried out that it studies the electron transfer in compound similar of the Prussia blue (CAAP), which are representative molecular materials, because its chromophore, magnetic, and electric properties, depend mainly on the processes that are made in their levels or orbital energy. It is known that these made up with octahedra symmetry that its are presented in form of powders, suffer processes of electron transfer when its are exposed to external stimulation by means of light (embracing the regions from the ultraviolet one until the infrared in the electromagnetic spectrum), because they are made up of mixed valency. To know that types of electronic transfers are those that are made in the study materials, 4 series of CAAP its were synthesized by the method of mixtures of aqueous solutions: M[Fe +3 CN) 6 ] 2 nH 2 O, M[Cr +3 (CN) 6 ] 2 nH 2 O, M[Mn +3 (CN) 6 ] 3 nH 2 O y M[Co +3 (CN) 6 ] 3 nH 2 O, and later on studied by means of the electron spectroscopy technique with a UV-SENSE spectrophotometer (Perkin-Elmer) in or n range of work of 250 to 1100 nm. Because to discuss the electronic structures of any compound, it is required the calculation of the energy levels, they took like reference the data tabulated by John Alexander and Harry Gray calculated by the modified theoretical approach of Wolfsberg-Helmhoz. When comparing the obtained spectra with the theoretical data, it was concludes that in the CAAP, its are carried out electronic transfers among orbital molecular metallic of the type d → d, and load transfer (TC) among orbital molecular of the ligand and metal. When being carried out a load transfer in the CAAP that initially are made up of under-spin these its are photoinduced to an excited state of high spin. In consequence it is possible to vary the interactions among the metals of transition of the CAAP and the ligands, allowing the extension of coordinated

  5. Plexciton quenching by resonant electron transfer from quantum emitter to metallic nanoantenna.

    Science.gov (United States)

    Marinica, D C; Lourenço-Martins, H; Aizpurua, J; Borisov, A G

    2013-01-01

    Coupling molecular excitons and localized surface plasmons in hybrid nanostructures leads to appealing, tunable optical properties. In this respect, the knowledge about the excitation dynamics of a quantum emitter close to a plasmonic nanoantenna is of importance from fundamental and practical points of view. We address here the effect of the excited electron tunneling from the emitter into a metallic nanoparticle(s) in the optical response. When close to a plasmonic nanoparticle, the excited state localized on a quantum emitter becomes short-lived because of the electronic coupling with metal conduction band states. We show that as a consequence, the characteristic features associated with the quantum emitter disappear from the optical absorption spectrum. Thus, for the hybrid nanostructure studied here and comprising quantum emitter in the narrow gap of a plasmonic dimer nanoantenna, the quantum tunneling might quench the plexcitonic states. Under certain conditions the optical response of the system approaches that of the individual plasmonic dimer. Excitation decay via resonant electron transfer can play an important role in many situations of interest such as in surface-enhanced spectroscopies, photovoltaics, catalysis, or quantum information, among others.

  6. GPU-accelerated computation of electron transfer.

    Science.gov (United States)

    Höfinger, Siegfried; Acocella, Angela; Pop, Sergiu C; Narumi, Tetsu; Yasuoka, Kenji; Beu, Titus; Zerbetto, Francesco

    2012-11-05

    Electron transfer is a fundamental process that can be studied with the help of computer simulation. The underlying quantum mechanical description renders the problem a computationally intensive application. In this study, we probe the graphics processing unit (GPU) for suitability to this type of problem. Time-critical components are identified via profiling of an existing implementation and several different variants are tested involving the GPU at increasing levels of abstraction. A publicly available library supporting basic linear algebra operations on the GPU turns out to accelerate the computation approximately 50-fold with minor dependence on actual problem size. The performance gain does not compromise numerical accuracy and is of significant value for practical purposes. Copyright © 2012 Wiley Periodicals, Inc.

  7. Charge transfer in gas electron multipliers

    Energy Technology Data Exchange (ETDEWEB)

    Ottnad, Jonathan; Ball, Markus; Ketzer, Bernhard; Ratza, Viktor; Razzaghi, Cina [HISKP, Bonn University, Nussallee 14-16, D-53115 Bonn (Germany)

    2015-07-01

    In order to efficiently employ a Time Projection Chamber (TPC) at interaction rates higher than ∝1 kHz, as foreseen e.g. in the ALICE experiment (CERN) and at CB-ELSA (Bonn), a continuous operation and readout mode is required. A necessary prerequisite is to minimize the space charge coming from the amplification system and to maintain an excellent spatial and energy resolution. Unfortunately these two goals can be in conflict to each other. Gas Electron Multipliers (GEM) are one candidate to fulfill these requirements. It is necessary to understand the processes within the amplification structure to find optimal operation conditions. To do so, we measure the charge transfer processes in and between GEM foils with different geometries and field configurations, and use an analytical model to describe the results. This model can then be used to predict and optimize the performance. The talk gives the present status of the measurements and describes the model.

  8. Direct electron transfer based enzymatic fuel cells

    International Nuclear Information System (INIS)

    Falk, Magnus; Blum, Zoltan; Shleev, Sergey

    2012-01-01

    In this mini-review we briefly describe some historical developments made in the field of enzymatic fuel cells (FCs), discussing important design considerations taken when constructing mediator-, cofactor-, and membrane-less biological FCs (BFCs). Since the topic is rather extensive, only BFCs utilizing direct electron transfer (DET) reactions on both the anodic and cathodic sides are considered. Moreover, the performance of mostly glucose/oxygen biodevices is analyzed and compared. We also present some unpublished results on mediator-, cofactor-, and membrane-less glucose/oxygen BFCs recently designed in our group and tested in different human physiological fluids, such as blood, plasma, saliva, and tears. Finally, further perspectives for BFC applications are highlighted.

  9. Formation of Bonded Exciplex in the Excited States of Dicyanoanthracene-Pyridine System : Time Dependent Density Functional Theory Study

    NARCIS (Netherlands)

    Setiawan, D.; Sethio, D.; Martoprawiro, M.A.; Filatov, M.; Gaol, FL; Nguyen, QV

    2012-01-01

    Strong quenching of fluorescence was recently observed in pyridine solutions of 9,10-dicyanoanthracene chromophore. It was hypothesized that quenching may be attributed to the formation of bound charge transfer complexes in the excited states of the molecules. In this work, using time-dependent

  10. Ultrafast dynamics of hydrophilic carbonyl carotenoids - Relation between structure and excited-state properties in polar solvents

    Czech Academy of Sciences Publication Activity Database

    Chábera, P.; Fuciman, M.; Naqvi, K.R.; Polívka, Tomáš

    2010-01-01

    Roč. 373, 1-2 (2010), s. 56-64 ISSN 0301-0104 Institutional research plan: CEZ:AV0Z50510513 Keywords : hydrophilic carotenoids * excited-state dynamics * charge-transfer state Subject RIV: BO - Biophysics Impact factor: 2.017, year: 2010

  11. 14 CFR 1274.931 - Electronic funds transfer payment methods.

    Science.gov (United States)

    2010-01-01

    ... cooperative agreement will be made by the Government by electronic funds transfer through the Treasury Fedline... 14 Aeronautics and Space 5 2010-01-01 2010-01-01 false Electronic funds transfer payment methods... COOPERATIVE AGREEMENTS WITH COMMERCIAL FIRMS Other Provisions and Special Conditions § 1274.931 Electronic...

  12. Dielectronic recombination rate coefficients to the excited states of CII from CIII

    International Nuclear Information System (INIS)

    Kato, Takako; Safronova, U.; Ohira, Mituhiko.

    1996-02-01

    Energy levels, radiative transition probabilities and autoionization rates for CII including 1s 2 2l2l'nl'' (n=2-6, l'≤(n-1)) states were calculated by using multi-configurational Hartree-Fock (Cowan code) method. Autoionizing levels above three thresholds: 1s 2 2s 2 ( 1 S), 1s 2 2s2p( 3 P), 1s 2 2s2p( 1 P) were considered. Branching ratios related to the first threshold and the intensity factor were calculated for satellite lines of CII ion. The dielectronic recombination rate coefficients to the excited states for n=2-6 are calculated with these atomic data. The rate coefficients are fitted to an analytical formula and the fit parameters are given. The values for higher excited states than n=6 are extrapolated and the total dielectronic recombination rate coefficients are derived. The effective recombination rate coefficient for different electron densities are also derived. (author)

  13. A new methodology for measuring time correlations and excite states of atoms and nuclei

    International Nuclear Information System (INIS)

    Cavalcante, M.A.

    1989-01-01

    A system for measuring time correlation of physical phenomena events in the range of 10 -7 to 10 5 sec is proposed, and his results presented. This system, is based on a sequential time scale which is controlled by a precision quartz oscillator; the zero time of observation is set by means of a JK Flip-Flop, which is operated by a negative transition of pulse in coincidence with the pulse from a detector which marks the time zero of the event (precedent pulse). This electronic system (named digital chronoanalizer) was used in the measurement of excited states of nuclei as well as for the determination of time fluctuations in physical phenomena, such as the time lag in a halogen Geiger counter and is the measurement of the 60 KeV excited state of N P 237 . (author)

  14. Excitation transfer and trapping kinetics in plant photosystem I probed by two-dimensional electronic spectroscopy.

    Science.gov (United States)

    Akhtar, Parveen; Zhang, Cheng; Liu, Zhengtang; Tan, Howe-Siang; Lambrev, Petar H

    2018-03-01

    Photosystem I is a robust and highly efficient biological solar engine. Its capacity to utilize virtually every absorbed photon's energy in a photochemical reaction generates great interest in the kinetics and mechanisms of excitation energy transfer and charge separation. In this work, we have employed room-temperature coherent two-dimensional electronic spectroscopy and time-resolved fluorescence spectroscopy to follow exciton equilibration and excitation trapping in intact Photosystem I complexes as well as core complexes isolated from Pisum sativum. We performed two-dimensional electronic spectroscopy measurements with low excitation pulse energies to record excited-state kinetics free from singlet-singlet annihilation. Global lifetime analysis resolved energy transfer and trapping lifetimes closely matches the time-correlated single-photon counting data. Exciton energy equilibration in the core antenna occurred on a timescale of 0.5 ps. We further observed spectral equilibration component in the core complex with a 3-4 ps lifetime between the bulk Chl states and a state absorbing at 700 nm. Trapping in the core complex occurred with a 20 ps lifetime, which in the supercomplex split into two lifetimes, 16 ps and 67-75 ps. The experimental data could be modelled with two alternative models resulting in equally good fits-a transfer-to-trap-limited model and a trap-limited model. However, the former model is only possible if the 3-4 ps component is ascribed to equilibration with a "red" core antenna pool absorbing at 700 nm. Conversely, if these low-energy states are identified with the P 700 reaction centre, the transfer-to-trap-model is ruled out in favour of a trap-limited model.

  15. On satellite lines anomalies in OH excited states

    International Nuclear Information System (INIS)

    Elitzur, M.

    1976-01-01

    It is argued that different pumps produce similar distributions of populations in the first two excited states of OH. The pattern observed recently in G 219.3 - 07 by Whiteoak and Gardner can be due either to radiative or collisional pump. (author)

  16. Size dependent deactivation of the excited state of DHICA

    DEFF Research Database (Denmark)

    Gauden, Magdalena; Pezzella, Alessandro; Panzella, Lucia

    2008-01-01

    Melanin is a natural pigment mainly responsible for the protection of skin and eyes from UV damage. 5,6- dihydroxyindole- 2 carboxylic acid (DHICA) is a key melanin building block. We have investigated the excited state dynamics of DHICA as well as its derivatives and oligomeric units using...

  17. Optimal control of peridinin excited-state dynamics

    Czech Academy of Sciences Publication Activity Database

    Dietzek, B.; Chábera, P.; Hanf, R.; Tschierlei, S.; Popp, J.; Pascher, T.; Yartsev, A.; Polívka, Tomáš

    2010-01-01

    Roč. 373, 1-2 (2010), s. 129-136 ISSN 0301-0104 Institutional research plan: CEZ:AV0Z50510513 Keywords : peridin * excited-state dynamics * coherent control Subject RIV: BO - Biophysics Impact factor: 2.017, year: 2010

  18. Dark excited states of carotenoids: Consensus and controversy

    Czech Academy of Sciences Publication Activity Database

    Polívka, Tomáš; Sundström, V.

    2009-01-01

    Roč. 477, 1-3 (2009), s. 1-11 ISSN 0009-2614 Institutional research plan: CEZ:AV0Z50510513 Keywords : carotenoids * excited states * relaxation pathways * femtosecond spectroscopy Subject RIV: BO - Biophysics Impact factor: 2.291, year: 2009

  19. Catalytic alkylation of remote C-H bonds enabled by proton-coupled electron transfer.

    Science.gov (United States)

    Choi, Gilbert J; Zhu, Qilei; Miller, David C; Gu, Carol J; Knowles, Robert R

    2016-11-10

    Despite advances in hydrogen atom transfer (HAT) catalysis, there are currently no molecular HAT catalysts that are capable of homolysing the strong nitrogen-hydrogen (N-H) bonds of N-alkyl amides. The motivation to develop amide homolysis protocols stems from the utility of the resultant amidyl radicals, which are involved in various synthetically useful transformations, including olefin amination and directed carbon-hydrogen (C-H) bond functionalization. In the latter process-a subset of the classical Hofmann-Löffler-Freytag reaction-amidyl radicals remove hydrogen atoms from unactivated aliphatic C-H bonds. Although powerful, these transformations typically require oxidative N-prefunctionalization of the amide starting materials to achieve efficient amidyl generation. Moreover, because these N-activating groups are often incorporated into the final products, these methods are generally not amenable to the direct construction of carbon-carbon (C-C) bonds. Here we report an approach that overcomes these limitations by homolysing the N-H bonds of N-alkyl amides via proton-coupled electron transfer. In this protocol, an excited-state iridium photocatalyst and a weak phosphate base cooperatively serve to remove both a proton and an electron from an amide substrate in a concerted elementary step. The resultant amidyl radical intermediates are shown to promote subsequent C-H abstraction and radical alkylation steps. This C-H alkylation represents a catalytic variant of the Hofmann-Löffler-Freytag reaction, using simple, unfunctionalized amides to direct the formation of new C-C bonds. Given the prevalence of amides in pharmaceuticals and natural products, we anticipate that this method will simplify the synthesis and structural elaboration of amine-containing targets. Moreover, this study demonstrates that concerted proton-coupled electron transfer can enable homolytic activation of common organic functional groups that are energetically inaccessible using

  20. Photoinduced intermolecular electron transfer and off-resonance Raman characteristics of Rhodamine 101/N,N-diethylaniline

    International Nuclear Information System (INIS)

    Jiang, Li-lin; Liu, Wei-long; Song, Yun-fei; He, Xing; Wang, Yang; Wang, Chang; Wu, Hong-lin; Yang, Fang; Yang, Yan-qiang

    2014-01-01

    Highlights: • Mechanism of PIET reaction process for the Rh101 + /DEA system is investigated. • The significant geometrical changes of the charge–transfer complex are explained. • Forward Electron transfer from DEA to Rh101 +∗ occurs with lifetime of 425–560 fs. • Backward electron transfer occurs with a time constant of 46.16–51.40 ps. • Intramolecular vibrational relaxation occurs with lifetime of 2.77–5.39 ps. - Abstract: The ultrafast photoinduced intermolecular electron transfer (PIET) reaction of Rhodamine 101 (Rh101 + ) in N,N-diethylaniline (DEA) was investigated using off-resonance Raman, femtosecond time-resolved multiplex transient grating (TG) and transient absorption (TA) spectroscopies. The Raman spectra indicate that the C=C stretching vibration of the chromophore aromatic ring is more sensitive to ET compared with the C-C stretching mode. The ultrafast photoinduced intermolecular forward ET (FET) from DEA to Rh101 +∗ occurs on a time scale of τ FET = 425–560 fs. The backward ET (BET) occurs in the inverted region with a time constant of τ BET = 46.16–51.40 ps. The intramolecular vibrational relaxation (IVR) process occurs on the excited state potential energy surface with the time constant of τ IVR = 2.77–5.39 ps

  1. Photoinduced intermolecular electron transfer and off-resonance Raman characteristics of Rhodamine 101/N,N-diethylaniline

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Li-lin [Department of Physics, Harbin Institute of Technology, Harbin 150001 (China); School of Mechanical and Electronic Engineering, Hezhou University, Hezhou 542800 (China); Liu, Wei-long; Song, Yun-fei; He, Xing; Wang, Yang; Wang, Chang; Wu, Hong-lin [Department of Physics, Harbin Institute of Technology, Harbin 150001 (China); Yang, Fang [National Key Laboratory of Science and Technology on Tunable Laser, Department of Optoelectronics Information Science Technology, Harbin Institute of Technology, Harbin 150001 (China); Yang, Yan-qiang, E-mail: yqyang@hit.edu.cn [Department of Physics, Harbin Institute of Technology, Harbin 150001 (China); National Key Laboratory of Shock Wave and Detonation Physics, Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang 621900, Sichuan (China)

    2014-01-31

    Highlights: • Mechanism of PIET reaction process for the Rh101{sup +}/DEA system is investigated. • The significant geometrical changes of the charge–transfer complex are explained. • Forward Electron transfer from DEA to Rh101{sup +∗} occurs with lifetime of 425–560 fs. • Backward electron transfer occurs with a time constant of 46.16–51.40 ps. • Intramolecular vibrational relaxation occurs with lifetime of 2.77–5.39 ps. - Abstract: The ultrafast photoinduced intermolecular electron transfer (PIET) reaction of Rhodamine 101 (Rh101{sup +}) in N,N-diethylaniline (DEA) was investigated using off-resonance Raman, femtosecond time-resolved multiplex transient grating (TG) and transient absorption (TA) spectroscopies. The Raman spectra indicate that the C=C stretching vibration of the chromophore aromatic ring is more sensitive to ET compared with the C-C stretching mode. The ultrafast photoinduced intermolecular forward ET (FET) from DEA to Rh101{sup +∗} occurs on a time scale of τ{sub FET} = 425–560 fs. The backward ET (BET) occurs in the inverted region with a time constant of τ{sub BET} = 46.16–51.40 ps. The intramolecular vibrational relaxation (IVR) process occurs on the excited state potential energy surface with the time constant of τ{sub IVR} = 2.77–5.39 ps.

  2. Fluorescent molecular probes based on excited state prototropism in lipid bilayer membrane

    Science.gov (United States)

    Mohapatra, Monalisa; Mishra, Ashok K.

    2012-03-01

    Excited state prototropism (ESPT) is observed in molecules having one or more ionizable protons, whose proton transfer efficiency is different in ground and excited states. The interaction of various ESPT molecules like naphthols and intramolecular ESPT (ESIPT) molecules like hydroxyflavones etc. with different microheterogeneous media have been studied in detail and excited state prototropism as a probe concept has been gaining ground. The fluorescence of different prototropic forms of such molecules, on partitioning to an organized medium like lipid bilayer membrane, often show sensitive response to the local environment with respect to the local structure, physical properties and dynamics. Our recent work using 1-naphthol as an ESPT fluorescent molecular probe has shown that the incorporation of monomeric bile salt molecules into lipid bilayer membranes composed from dipalmitoylphosphatidylcholine (DPPC, a lung surfactant) and dimyristoylphosphatidylcholine (DMPC), in solid gel and liquid crystalline phases, induce appreciable wetting of the bilayer up to the hydrocarbon core region, even at very low (fisetin, an ESIPT molecule having antioxidant properties, in lipid bilayer membrane has been sensitively monitored from its intrinsic fluorescence behaviour.

  3. Rydberg energies using excited state density functional theory

    International Nuclear Information System (INIS)

    Cheng, C.-L.; Wu Qin; Van Voorhis, Troy

    2008-01-01

    We utilize excited state density functional theory (eDFT) to study Rydberg states in atoms. We show both analytically and numerically that semilocal functionals can give quite reasonable Rydberg energies from eDFT, even in cases where time dependent density functional theory (TDDFT) fails catastrophically. We trace these findings to the fact that in eDFT the Kohn-Sham potential for each state is computed using the appropriate excited state density. Unlike the ground state potential, which typically falls off exponentially, the sequence of excited state potentials has a component that falls off polynomially with distance, leading to a Rydberg-type series. We also address the rigorous basis of eDFT for these systems. Perdew and Levy have shown using the constrained search formalism that every stationary density corresponds, in principle, to an exact stationary state of the full many-body Hamiltonian. In the present context, this means that the excited state DFT solutions are rigorous as long as they deliver the minimum noninteracting kinetic energy for the given density. We use optimized effective potential techniques to show that, in some cases, the eDFT Rydberg solutions appear to deliver the minimum kinetic energy because the associated density is not pure state v-representable. We thus find that eDFT plays a complementary role to constrained DFT: The former works only if the excited state density is not the ground state of some potential while the latter applies only when the density is a ground state density.

  4. Describing excited state relaxation and localization in TiO2 nanoparticles using TD-DFT

    International Nuclear Information System (INIS)

    Berardo, Enrico; Hu, Han-Shi; Van Dam, Hubertus J. J.; Shevlin, Stephen A.; Woodley, Scott M.; Kowalski, Karol; Zwijnenburg, Martijn A.

    2014-01-01

    We have investigated the description of excited state relaxation in naked and hydrated TiO 2 nanoparticles using Time-Dependent Density Functional Theory (TD-DFT) with three common hybrid exchange-correlation (XC) potentials; B3LYP, CAM-B3LYP and BHLYP. Use of TD-CAM-B3LYP and TD-BHLYP yields qualitatively similar results for all structures, which are also consistent with predictions of coupled cluster theory for small particles. TD-B3LYP, in contrast, is found to make rather different predictions; including apparent conical intersections for certain particles that are not observed with TD-CAM-B3LYP nor with TD-BHLYP. In line with our previous observations for vertical excitations, the issue with TD-B3LYP appears to be the inherent tendency of TD-B3LYP, and other XC potentials with no or a low percentage of Hartree-Fock Like Exchange, to spuriously stabilize the energy of charge-transfer (CT) states. Even in the case of hydrated particles, for which vertical excitations are generally well described with all XC potentials, the use of TD-B3LYP appears to result in CT-problems for certain particles. We hypothesize that the spurious stabilization of CT-states by TD-B3LYP even may drive the excited state optimizations to different excited state geometries than those obtained using TD-CAM-B3LYP or TD-BHLYP. In conclusion, focusing on the TD-CAM-B3LYP and TD-BHLYP results, excited state relaxation in naked and hydrated TiO 2 nanoparticles is predicted to be associated with a large Stokes' shift

  5. Electron transfer reactions of metal complexes in solution

    International Nuclear Information System (INIS)

    Sutin, N.

    1977-01-01

    A few representative electron-transfer reactions are selected and their kinetic parameters compared with the predictions of activated complex models. Since Taube has presented an elegant treatment of intramolecular electron-transfer reactions, emphasis is on bimolecular reactions. The latter electron-transfer reactions are more complicated to treat theoretically since the geometries of their activated complexes are not as well known as for the intramolecular case. In addition in biomolecular reactions, the work required to bring the two reactants together needs to be calculated. Since both reactants generally carry charges this presents a non-trivial problem at the ionic strengths usually used to study bimolecular electron transfer

  6. Ultrafast Photoinduced Electron Transfer in a π-Conjugated Oligomer/Porphyrin Complex

    KAUST Repository

    Aly, Shawkat Mohammede

    2014-10-02

    Controlling charge transfer (CT), charge separation (CS), and charge recombination (CR) at the donor-acceptor interface is extremely important to optimize the conversion efficiency in solar cell devices. In general, ultrafast CT and slow CR are desirable for optimal device performance. In this Letter, the ultrafast excited-state CT between platinum oligomer (DPP-Pt(acac)) as a new electron donor and porphyrin as an electron acceptor is monitored for the first time using femtosecond (fs) transient absorption (TA) spectroscopy with broad-band capability and 120 fs temporal resolution. Turning the CT on/off has been shown to be possible either by switching from an organometallic oligomer to a metal-free oligomer or by controlling the charge density on the nitrogen atom of the porphyrin meso unit. Our time-resolved data show that the CT and CS between DPP-Pt(acac) and cationic porphyrin are ultrafast (approximately 1.5 ps), and the CR is slow (ns time scale), as inferred from the formation and the decay of the cationic and anionic species. We also found that the metallic center in the DPP-Pt(acac) oligomer and the positive charge on the porphyrin are the keys to switching on/off the ultrafast CT process.

  7. Ioniclike energy structure of neutral core-excited states in free Kr clusters

    International Nuclear Information System (INIS)

    Peredkov, S.; Sorensen, S.L.; Kivimaeki, A.; Schulz, J.; Maartensson, N.; Oehrwall, G.; Lundwall, M.; Rander, T.; Lindblad, A.; Bergersen, H.; Svensson, S.; Bjoerneholm, O.; Tchaplyguine, M.

    2005-01-01

    The development of electronic states in krypton clusters is investigated by high-resolution core-level electron spectroscopy. The energy ordering of bulk versus surface 3d -1 np(n>5) core-excited states in neutral clusters is demonstrated to be reversed to the 3d -1 5p level situation. The cluster 3d -1 6p,7p states are proven to be at a lower energy than the corresponding atomic levels. These findings reveal the ioniclike energy structure of the neutral cluster core-excited levels. The phenomenon is explained by a spatial spread of the excited orbitals over the cluster lattice

  8. Bottom-up excited state dynamics of two cinnamate-based sunscreen filter molecules.

    Science.gov (United States)

    Peperstraete, Yoann; Staniforth, Michael; Baker, Lewis A; Rodrigues, Natércia D N; Cole-Filipiak, Neil C; Quan, Wen-Dong; Stavros, Vasilios G

    2016-10-12

    Methyl-E-4-methoxycinnamate (E-MMC) is a model chromophore of the commonly used commercial sunscreen agent, 2-ethylhexyl-E-4-methoxycinnamate (E-EHMC). In an effort to garner a molecular-level understanding of the photoprotection mechanisms in operation with E-EHMC, we have used time-resolved pump-probe spectroscopy to explore E-MMC's and E-EHMC's excited state dynamics upon UV-B photoexcitation to the S 1 (1 1 ππ*) state in both the gas- and solution-phase. In the gas-phase, our studies suggest that the excited state dynamics are driven by non-radiative decay from the 1 1 ππ* to the S 3 (1 1 nπ*) state, followed by de-excitation from the 1 1 nπ* to the ground electronic state (S 0 ). Using both a non-polar-aprotic solvent, cyclohexane, and a polar-protic solvent, methanol, we investigated E-MMC and E-EHMC's photochemistry in a more realistic, 'closer-to-shelf' environment. A stark change to the excited state dynamics in the gas-phase is observed in the solution-phase suggesting that the dynamics are now driven by efficient E/Z isomerisation from the initially photoexcited 1 1 ππ* state to S 0 .

  9. Pressure dependence of excited-state charge-carrier dynamics in organolead tribromide perovskites

    Science.gov (United States)

    Liu, X. C.; Han, J. H.; Zhao, H. F.; Yan, H. C.; Shi, Y.; Jin, M. X.; Liu, C. L.; Ding, D. J.

    2018-05-01

    Excited-state charge-carrier dynamics governs the performance of organometal trihalide perovskites (OTPs) and is strongly influenced by the crystal structure. Characterizing the excited-state charge-carrier dynamics in OTPs under high pressure is imperative for providing crucial insights into structure-property relations. Here, we conduct in situ high-pressure femtosecond transient absorption spectroscopy experiments to study the excited-state carrier dynamics of CH3NH3PbBr3 (MAPbBr3) under hydrostatic pressure. The results indicate that compression is an effective approach to modulate the carrier dynamics of MAPbBr3. Across each pressure-induced phase, carrier relaxation, phonon scattering, and Auger recombination present different pressure-dependent properties under compression. Responsiveness is attributed to the pressure-induced variation in the lattice structure, which also changes the electronic band structure. Specifically, simultaneous prolongation of carrier relaxation and Auger recombination is achieved in the ambient phase, which is very valuable for excess energy harvesting. Our discussion provides clues for optimizing the photovoltaic performance of OTPs.

  10. Energy cascades, excited state dynamics, and photochemistry in cob(III)alamins and ferric porphyrins.

    Science.gov (United States)

    Rury, Aaron S; Wiley, Theodore E; Sension, Roseanne J

    2015-03-17

    Porphyrins and the related chlorins and corrins contain a cyclic tetrapyrrole with the ability to coordinate an active metal center and to perform a variety of functions exploiting the oxidation state, reactivity, and axial ligation of the metal center. These compounds are used in optically activated applications ranging from light harvesting and energy conversion to medical therapeutics and photodynamic therapy to molecular electronics, spintronics, optoelectronic thin films, and optomagnetics. Cobalt containing corrin rings extend the range of applications through photolytic cleavage of a unique axial carbon-cobalt bond, permitting spatiotemporal control of drug delivery. The photochemistry and photophysics of cyclic tetrapyrroles are controlled by electronic relaxation dynamics including internal conversion and intersystem crossing. Typically the electronic excitation cascades through ring centered ππ* states, ligand to metal charge transfer (LMCT) states, metal to ligand charge transfer (MLCT) states, and metal centered states. Ultrafast transient absorption spectroscopy provides a powerful tool for the investigation of the electronic state dynamics in metal containing tetrapyrroles. The UV-visible spectrum is sensitive to the oxidation state, electronic configuration, spin state, and axial ligation of the central metal atom. Ultrashort broadband white light probes spanning the range from 270 to 800 nm, combined with tunable excitation pulses, permit the detailed unravelling of the time scales involved in the electronic energy cascade. State-of-the-art theoretical calculations provide additional insight required for precise assignment of the states. In this Account, we focus on recent ultrafast transient absorption studies of ferric porphyrins and corrin containing cob(III)alamins elucidating the electronic states responsible for ultrafast energy cascades, excited state dynamics, and the resulting photoreactivity or photostability of these compounds. Iron

  11. Mechanism of Intermolecular Electron Transfer in Bionanostructures

    Science.gov (United States)

    Gruodis, A.; Galikova, N.; Šarka, K.; Saulė, R.; Batiuškaitė, D.; Saulis, G.

    Hepatocellular carcinoma (HCC) is one of the most common malignant tumors worldwide. Most patients are inoperable and hepatoma cells are resistant to conventional chemotherapies. Thus, the development of novel therapies for HCC treatment is of paramount importance. Amongst different alimentary factors, vitamin C and vitamin K3 In the present work, it has been shown that the treatment of mouse hepatoma MH-22A cells by vitamin C and vitamin K3 at the ratio of 100:1 greatly enhanced their cytotoxicity. When cells were subjected to vitamin C at 200 μM or to vitamin K3 at 2 μM separately, their viability reduced by only about 10%. However, when vitamins C and K3 were combined at the same concentrations, they killed more than 90% of cells. To elucidate the mechanism of the synergistic cytotoxicity of the C&K3 mixture, theoretical quantum-chemical analysis of the dynamics of intermolecular electron transfer (IET) processes within the complexes containing C (five forms) and K3 (one form) has been carried out. Optimization of the ground state complex geometry has been provided by means of GAUSSIAN03 package. Simulation of the IET has been carried out using NUVOLA package, in the framework of molecular orbitals (MO). The rate of IET has been calculated using Fermi Golden rule. The results of simulations allow us to create the preliminary model of the reaction pathway.

  12. Electronic transfer of sensitive patient data.

    Science.gov (United States)

    Detterbeck, A M W; Kaiser, J; Hirschfelder, U

    2015-01-01

    The purpose of this study was to develop decision-making aids and recommendations for dental practitioners regarding the utilization and sharing of sensitive digital patient data. In the current environment of growing digitization, healthcare professionals need detailed knowledge of secure data management to maximize confidentiality and minimize the risks involved in both archiving patient data and sharing it through electronic channels. Despite well-defined legal requirements, an all-inclusive technological solution does not currently exist. The need for a preliminary review and critical appraisal of common practices of data transfer prompted a search of the literature and the Web to identify viable methods of secure data exchange and to develop a flowchart. A strong focus was placed on the transmission of datasets both smaller than and larger than 10 MB, and on secure communication by smartphone. Although encryption of patient-related data should be routine, it is often difficult to implement. Pretty Good Privacy (PGP) and Secure/Multipurpose Internet Mail Extensions (S/MIME) are viable standards for secure e-mail encryption. Sharing of high-volume data should be accomplished with the help of file encryption. Careful handling of sensitive patient data is mandatory, and it is the end-user's responsibility to meet any requirements for encryption, preferably by using free, open-source (and hence transparent) software.

  13. Calculation of neutral beam deposition accounting for excited states

    International Nuclear Information System (INIS)

    Gianakon, T.A.

    1992-09-01

    Large-scale neutral-beam auxillary heating of plasmas has led to new plasma operational regimes which are often dominated by fast ions injected via the absorption of an energetic beam of hydrogen neutrals. An accurate simulation of the slowing down and transport of these fast ions requires an intimate knowledge of the hydrogenic neutral deposition on each flux surface of the plasma. As a refinement to the present generation of transport codes, which base their beam deposition on ground-state reaction rates, a new set of routines, based on the excited states of hydrogen, is presented as mechanism for computing the attenuation and deposition of a beam of energetic neutrals. Additionally, the numerical formulations for the underlying atomic physics for hydrogen impacting on the constiuent plasma species is developed and compiled as a numerical database. Sample results based on this excited state model are compared with the ground-state model for simple plasma configurations

  14. Quantum entanglement of localized excited states at finite temperature

    Energy Technology Data Exchange (ETDEWEB)

    Caputa, Paweł [Yukawa Institute for Theoretical Physics (YITP), Kyoto University,Kyoto 606-8502 (Japan); Nordita, KTH Royal Institute of Technology and Stockholm University,Roslagstullsbacken 23, SE-106 91 Stockholm (Sweden); Simón, Joan; Štikonas, Andrius [School of Mathematics and Maxwell Institute for Mathematical Sciences,University of Edinburgh,King’s Buildings, Edinburgh EH9 3FD (United Kingdom); Takayanagi, Tadashi [Yukawa Institute for Theoretical Physics (YITP), Kyoto University,Kyoto 606-8502 (Japan); Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU),University of Tokyo,Kashiwa, Chiba 277-8582 (Japan)

    2015-01-20

    In this work we study the time evolutions of (Renyi) entanglement entropy of locally excited states in two dimensional conformal field theories (CFTs) at finite temperature. We consider excited states created by acting with local operators on thermal states and give both field theoretic and holographic calculations. In free field CFTs, we find that the growth of Renyi entanglement entropy at finite temperature is reduced compared to the zero temperature result by a small quantity proportional to the width of the localized excitations. On the other hand, in finite temperature CFTs with classical gravity duals, we find that the entanglement entropy approaches a characteristic value at late time. This behaviour does not occur at zero temperature. We also study the mutual information between the two CFTs in the thermofield double (TFD) formulation and give physical interpretations of our results.

  15. Energies and lifetimes of excited states in copperlike Kr VIII

    International Nuclear Information System (INIS)

    Livingston, A.E.; Curtis, L.J.; Schectman, R.M.; Berry, H.G.

    1980-01-01

    The spectrum of Kr VIII has been observed between 180 and 2000 A by using foil excitation of 2.5--3.5-MeV krypton ions. Twenty new transitions have been classified and eleven new excited-state energies have been determined within the n=4 --7 shells. The ionization potential is derived to be 1 015 800 +- 200 cm -1 . The excited-state energies and fine structures are compared with recent relativistic Hartree-Fock calculations. The 4p-state lifetime has been measured by performing a simultaneous analysis of decay data for the 4p level and for its dominant cascade-repopulating levels. The 4p lifetime is found to be 30% shorter than previously measured values and is in excellent agreement with the result of a recent multiconfiguration Hartree-Fock calculation. The source of the discrepancy between this result and earlier measurements is discussed

  16. Can $\\beta$-decay probe excited state halos?

    CERN Multimedia

    2002-01-01

    In the first experiment at the newly constructed ISOLDE Facility the first-forbidden $\\beta$-decay of $^{17}$Ne into the first excited state of $^{17}$F has been measured. It is a factor two faster than the corresponding mirror decay and thus gives one of the largest recorded asymmetries for $\\beta$-decays feeding bound final states. Shell-model calculations can only reproduce the asymmetry if the halo structure of the $^{17}$F state is taken into account.

  17. 76 FR 709 - Electronic Funds Transfer of Depository Taxes; Correction

    Science.gov (United States)

    2011-01-06

    ... DEPARTMENT OF THE TREASURY Internal Revenue Service 26 CFR Parts 40 and 301 [TD 9507] RIN 1545-BJ13 Electronic Funds Transfer of Depository Taxes; Correction AGENCY: Internal Revenue Service (IRS...) providing guidance relating to Federal tax deposits (FTDs) by Electronic Funds Transfer (EFT). The temporary...

  18. 76 FR 708 - Electronic Funds Transfer of Depository Taxes; Correction

    Science.gov (United States)

    2011-01-06

    ... DEPARTMENT OF THE TREASURY Internal Revenue Service 26 CFR Parts 1, 31, 40, and 301 [TD 9507] RIN 1545-BJ13 Electronic Funds Transfer of Depository Taxes; Correction AGENCY: Internal Revenue Service... Electronic Funds Transfer (EFT). The temporary and final regulations provide rules under which depositors...

  19. 78 FR 66251 - Electronic Fund Transfers(Regulation E)

    Science.gov (United States)

    2013-11-05

    ... Electronic Fund Transfers (Regulation E) AGENCY: Bureau of Consumer Financial Protection. ACTION: Notice of... subpart B of Regulation E, which implements the Electronic Fund Transfer Act, and published this list on...-rule-amendment-to-regulation-e/ . SUPPLEMENTARY INFORMATION: The Bureau published its remittance rule...

  20. 78 FR 49365 - Electronic Fund Transfers (Regulation E); Correction

    Science.gov (United States)

    2013-08-14

    ... BUREAU OF CONSUMER FINANCIAL PROTECTION 12 CFR Part 1005 [Docket No. CFPB-2012-0050] RIN 3170-AA33 Electronic Fund Transfers (Regulation E); Correction AGENCY: Bureau of Consumer Financial Protection. ACTION... 2013 Final Rule, which along with three other final rules \\1\\ implements the Electronic Fund Transfer...

  1. THE ELECTRONIC COURSE OF HEAT AND MASS TRANSFER

    Directory of Open Access Journals (Sweden)

    Alexander P. Solodov

    2013-01-01

    Full Text Available The Electronic course of heat and mass transfer in power engineering is presented containing the full Electronic book as the structured hypertext document, the full set of Mathcad-documents with the whole set of educative computer models of heat and mass transfer, the computer labs, and selected educational presentations. 

  2. Photoinduced electron transfer in covalent ruthenium-anthraquinone dyads: relative importance of driving-force, solvent polarity, and donor-bridge energy gap.

    Science.gov (United States)

    Hankache, Jihane; Wenger, Oliver S

    2012-02-28

    Four rigid rod-like molecules comprised of a Ru(bpy)(3)(2+) (bpy = 2,2'-bipyridine) photosensitizer, a 9,10-anthraquinone electron acceptor, and a molecular bridge connecting the two redox partners were synthesized and investigated by optical spectroscopic and electrochemical means. An attempt was made to assess the relative importance of driving-force, solvent polarity, and bridge variation on the rates of photoinduced electron transfer in these molecules. Expectedly, introduction of tert-butyl substituents in the bipyridine ligands of the ruthenium complex and a change in solvent from dichloromethane to acetonitrile lead to a significant acceleration of charge transfer rates. In dichloromethane, photoinduced electron transfer is not competitive with the inherent excited-state deactivation processes of the photosensitizer. In acetonitrile, an increase in driving-force by 0.2 eV through attachment of tert-butyl substituents to the bpy ancillary ligands causes an increase in electron transfer rates by an order of magnitude. Replacement of a p-xylene bridge by a p-dimethoxybenzene spacer entails an acceleration of charge transfer rates by a factor of 3.5. In the dyads from this study, the relative order of importance of individual influences on electron transfer rates is therefore as follows: solvent polarity ≥ driving-force > donor-bridge energy gap.

  3. Deciphering excited state evolution in halorhodopsin with stimulated emission pumping.

    Science.gov (United States)

    Bismuth, Oshrat; Komm, Pavel; Friedman, Noga; Eliash, Tamar; Sheves, Mordechai; Ruhman, Sanford

    2010-03-04

    The primary photochemical dynamics of Hb. pharaonis Halorhodopsin (pHR) are investigated by femtosecond visible pump-near IR dump-hyperspectral probe spectroscopy. The efficiency of excited state depletion is deduced from transient changes in absorption, recorded with and without stimulated emission pumping (SEP), as a function of the dump delay. The concomitant reduction of photocycle population is assessed by probing the "K" intermediate difference spectrum. Results show that the cross section for stimulating emission is nearly constant throughout the fluorescent state lifetime. Probing "K" demonstrates that dumping produces a proportionate reduction in photocycle yields. We conclude that, despite its nonexponential internal conversion (IC) kinetics, the fluorescent state in pHR constitutes a single intermediate in the photocycle. This contrasts with conclusions drawn from the study of primary events in the related chloride pump from Hb. salinarum (sHR), believed to produce the "K" intermediate from a distinct short-lived subpopulation in the excited state. Our discoveries concerning internal conversion dynamics in pHR are discussed in light of recent expectations for similar excited state dynamics in both proteins.

  4. The Sommerfeld enhancement for dark matter with an excited state

    International Nuclear Information System (INIS)

    Slatyer, Tracy R.

    2010-01-01

    We present an analysis of the Sommerfeld enhancement to dark matter annihilation in the presence of an excited state, where the interaction inducing the enhancement is purely off-diagonal, such as in models of exciting or inelastic dark matter. We derive a simple and accurate semi-analytic approximation for the s-wave enhancement, which is valid provided the mass splitting between the ground and excited states is not too large, and discuss the cutoff of the enhancement for large mass splittings. We reproduce previously derived results in the appropriate limits, and demonstrate excellent agreement with numerical calculations of the enhancement. We show that the presence of an excited state leads to generically larger values of the Sommerfeld enhancement, larger resonances, and shifting of the resonances to lower mediator masses. Furthermore, in the presence of a mass splitting the enhancement is no longer a monotonic function of velocity: the enhancement where the kinetic energy is close to that required to excite the higher state can be up to twice as large as the enhancement at zero velocity

  5. Controlling excited-state contamination in nucleon matrix elements

    Energy Technology Data Exchange (ETDEWEB)

    Yoon, Boram; Gupta, Rajan; Bhattacharya, Tanmoy; Engelhardt, Michael; Green, Jeremy; Joó, Bálint; Lin, Huey-Wen; Negele, John; Orginos, Kostas; Pochinsky, Andrew; Richards, David; Syritsyn, Sergey; Winter, Frank

    2016-06-01

    We present a detailed analysis of methods to reduce statistical errors and excited-state contamination in the calculation of matrix elements of quark bilinear operators in nucleon states. All the calculations were done on a 2+1 flavor ensemble with lattices of size $32^3 \\times 64$ generated using the rational hybrid Monte Carlo algorithm at $a=0.081$~fm and with $M_\\pi=312$~MeV. The statistical precision of the data is improved using the all-mode-averaging method. We compare two methods for reducing excited-state contamination: a variational analysis and a two-state fit to data at multiple values of the source-sink separation $t_{\\rm sep}$. We show that both methods can be tuned to significantly reduce excited-state contamination and discuss their relative advantages and cost-effectiveness. A detailed analysis of the size of source smearing used in the calculation of quark propagators and the range of values of $t_{\\rm sep}$ needed to demonstrate convergence of the isovector charges of the nucleon to the $t_{\\rm sep} \\to \\infty $ estimates is presented.

  6. Inelastic electron scattering at low momentum transfer

    International Nuclear Information System (INIS)

    Richter, A.

    1979-01-01

    Recent advances of high energy resolution (ΔE approx. 30 keV FWHM) inelastic electron scattering at low momentum transfer (q -1 ) using selected experimental data from the Darmstadt electron linear accelerator are discussed. Strong emphasis is given to a comparison of the data with theoretical nuclear model predictions. Of the low multipolarity electric transitions investigated, as examples only E1 transitions to unnatural parity states in 11 B and E2 transitions of the very fragmented isoscalar quadrupole giant resonance in 208 Pb are considered. In 11 B the role of the Os hole in the configuration of the 1/2 + , 3/2 + and 5/2 + states is quantitatively determined via an interference mechanism in the transition probability. By comparison of the high resolution data with RPA calculations the E2 EWSR in 208 Pb is found to be much less exhausted than anticipated from previous medium energy resolution (e,e) and hadron scattering experiments. In the case of M1 transitions it is shown that the simplest idealized independent particle shell-model prediction breaks down badly. In 28 Si, ground-state correlations influence largely the detected M1 strength and such ground-state correlations are also responsible for the occurence of a strong M1 transition to a state at Ex = 10.319 MeV in 40 Ca. In 90 Zr only about 10% of the theoretically expected M1 strength is seen in (e,e) and in 140 Ce and 208 Pb none (detection limit 1-2 μ 2 K). In the case of 208 Pb high resolution spectra exist now up to an excitation energy of Ex = approx. 12MeV. The continuous decrease of the M1 strength with mass number is corroborated by the behaviour of strong but very fragmented M2 transitions which are detected in 28 Si, 90 Zr, 140 Ce and 208 Pb concentrated at an excitation energy E x approx. 44A -1 / 3 MeV. In 90 Zr, the distribution of spacings and widths of the many Jπ = 2 states are consistent with a Wigner and Porter-Thomas distribution, respectively. (orig.) 891 KBE/orig. 892 ARA

  7. Molecular Insights into Variable Electron Transfer in Amphibian Cryptochrome

    DEFF Research Database (Denmark)

    Sjulstok, Emil; Lüdemann, Gesa; Kubař, Tomáš

    2018-01-01

    are mutated, radical-pair formation is still observed. In this study, we computationally investigate electron-transfer pathways in the X. laevis cryptochrome DASH by extensively equilibrating a previously established homology model using molecular dynamics simulations and then mutating key amino acids......Cryptochrome proteins are activated by the absorption of blue light, leading to the formation of radical pairs through electron transfer in the active site. Recent experimental studies have shown that once some of the amino acid residues in the active site of Xenopus laevis cryptochrome DASH...... involved in the electron transfer. The electron-transfer pathways are then probed by using tight-binding density-functional theory. We report the alternative electron-transfer pathways resolved at the molecular level and, through comparison of amino acid sequences for cryptochromes from different species...

  8. Transcriptomic and genetic analysis of direct interspecies electron transfer

    DEFF Research Database (Denmark)

    Shrestha, Pravin Malla; Rotaru, Amelia-Elena; Summers, Zarath M

    2013-01-01

    The possibility that metatranscriptomic analysis could distinguish between direct interspecies electron transfer (DIET) and H2 interspecies transfer (HIT) in anaerobic communities was investigated by comparing gene transcript abundance in cocultures in which Geobacter sulfurreducens....... These results demonstrate that there are unique gene expression patterns that distinguish DIET from HIT and suggest that metatranscriptomics may be a promising route to investigate interspecies electron transfer pathways in more-complex environments....

  9. Photoinduced electron transfer between the dendritic zinc phthalocyanines and anthraquinone

    Science.gov (United States)

    Chen, Kuizhi; Wen, Junri; Liu, Jiangsheng; Chen, Zhenzhen; Pan, Sujuan; Huang, Zheng; Peng, Yiru

    2015-03-01

    The intermolecular electron transfer between the novel dendritic zinc (II) phthalocyanines (G1-DPcB and G2-DPcB) and anthraquinone (AQ) was studied by steady-state fluorescence and UV/Vis absorption spectroscopic methods. The effect of dendron generation on intermolecular electron transfer was investigated. The results showed that the fluorescence emission of these dendritic phthalocyanines could be greatly quenched by AQ upon excitation at 610 nm. The Stern- Volmer constant (KSV) of electron transfer was decreased with increasing the dendron generations. Our study suggested that these novel dendritic phthalocyanines were effective new electron donors and transmission complexes and could be used as a potential artifical photosysthesis system.

  10. Electron transfer in organic glass. Distance and energy dependence

    International Nuclear Information System (INIS)

    Krongauz, V.V.

    1992-01-01

    The authors have investigated the distance and energy dependence of electron transfer in rigid organic glasses containing randomly dispersed electron donor and electron acceptor molecules. Pulsed radiolysis by an electron beam from a linear accelerator was used for ionization resulting in charge deposition on donor molecules. The disappearance kinetics of donor radical anions due to electron transfer to acceptor was monitored spectroscopically by the change in optical density at the wavelength corresponding to that of donor radical anion absorbance. It was found that the rate of the electron transfer observed experimentally was higher than that computed using the Marcus-Levich theory assuming that the electron-transfer activation barrier is equal to the binding energy of electron on the donor molecule. This discrepancy between the experimental and computed results suggests that the open-quotes inertclose quotes media in which electron-transfer reaction takes place may be participating in the process, resulting in experimentally observed higher electron-transfer rates. 32 refs., 3 figs., 2 tabs

  11. Characterization of excited-state reactions with instant spectra of fluorescence kinetics

    International Nuclear Information System (INIS)

    Tomin, Vladimir I.; Ushakou, Dzmitryi V.

    2015-01-01

    Comprehensible knowledge of the excited-state proton transfer processes in organic compounds is overwhelmingly important not only for physics, but also chemistry and Life Sciences, since they play a key role in main processes of photosynthesis and functioning of biological organisms. Moreover compounds with Excited-State Intramolecular Proton Transfer (ESIPT) are in the focus of the interest of scientists throughout the world, because dual fluorescence spectra of such objects corresponding to two forms of molecular structure (normal and photoproduct) are very sensitive to characteristics of molecular microenvironment. This property allows to use such substances as fluorescent probes for diverse applications in chemistry and Life Sciences. But at the same time studying of proton transfer processes is not simple, because this process is characterized by extremely fast times (on picoseconds time scale and less order) and very often contribution of reverse reactions is essentially complicates an interpretation of observed properties of dual fluorescence. Hence, understanding of a role of reversible reactions is crucial for a comprehensive description of all processes accompanying excited state reactions. We discuss new approach for treatment ESIPT reaction on the basis of experimentally measured instant spectra of dual fluorescence and temporal behavior of ratiometric signal of normal to tautomer form intensities. Simple analytical expressions show in transparent way how to distinguish a degree of reverse reaction contribution to ratiometric signal. A validation of the approach under consideration is fulfilled with two different flavonols – 3-hydroxyflavone and 4′-(Dimethylamino)-3-hydroxyflavone – representing two extreme cases in affecting reversible reaction on dual emission. A comparing of new approach and traditional method when we analyze kinetics of separate the N* and T* fluorescence bands decays, has been carried out. - Highlights: • The excited-state

  12. Characterization of excited-state reactions with instant spectra of fluorescence kinetics

    Energy Technology Data Exchange (ETDEWEB)

    Tomin, Vladimir I., E-mail: tomin@apsl.edu.pl; Ushakou, Dzmitryi V.

    2015-10-15

    Comprehensible knowledge of the excited-state proton transfer processes in organic compounds is overwhelmingly important not only for physics, but also chemistry and Life Sciences, since they play a key role in main processes of photosynthesis and functioning of biological organisms. Moreover compounds with Excited-State Intramolecular Proton Transfer (ESIPT) are in the focus of the interest of scientists throughout the world, because dual fluorescence spectra of such objects corresponding to two forms of molecular structure (normal and photoproduct) are very sensitive to characteristics of molecular microenvironment. This property allows to use such substances as fluorescent probes for diverse applications in chemistry and Life Sciences. But at the same time studying of proton transfer processes is not simple, because this process is characterized by extremely fast times (on picoseconds time scale and less order) and very often contribution of reverse reactions is essentially complicates an interpretation of observed properties of dual fluorescence. Hence, understanding of a role of reversible reactions is crucial for a comprehensive description of all processes accompanying excited state reactions. We discuss new approach for treatment ESIPT reaction on the basis of experimentally measured instant spectra of dual fluorescence and temporal behavior of ratiometric signal of normal to tautomer form intensities. Simple analytical expressions show in transparent way how to distinguish a degree of reverse reaction contribution to ratiometric signal. A validation of the approach under consideration is fulfilled with two different flavonols – 3-hydroxyflavone and 4′-(Dimethylamino)-3-hydroxyflavone – representing two extreme cases in affecting reversible reaction on dual emission. A comparing of new approach and traditional method when we analyze kinetics of separate the N* and T* fluorescence bands decays, has been carried out. - Highlights: • The excited-state

  13. Photoemission from excited states in rare gas solids by combining synchrotronradiation with a laser

    International Nuclear Information System (INIS)

    Bernstorff, S.

    1984-09-01

    A new spectroscopic method has been developed to study excited states in rare gas solids: Excitons and conductionband-states are populated by synchrotron radiation (photon energy hw SR =5 - 30 eV). Subsequently electrons from these bound or conduction band-states are excited above the vacuum level of the solid by a pulsed dye laser (hw L =1.9 - 3.7 eV). This experimental technique was applied to solid Xe, Kr, Ar and Ne. (orig./GSCH)

  14. A molecular shift register based on electron transfer

    Science.gov (United States)

    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.

  15. Photoinduced electron transfer involving eosin-tryptophan conjugates. Long-lived radical pair states for systems incorporating aromatic amino acid side chains

    Energy Technology Data Exchange (ETDEWEB)

    Jones, G. II; Farahat, C.W.; Oh, C. (Boston Univ., MA (United States))

    1994-07-14

    The electron-transfer photochemistry of the covalent derivatives of the dye eosin, in which the xanthene dye is covalently attached to the amino acid L-tryptophan via the thiohydantoin derivative, the tryptophan dipeptide, and an ethyl ester derivative, has been investigated. The singlet excited state of the dye is significantly quenched on attachment of the aromatic amino acid residue. Dye triplet states are also intercepted through intramolecular interaction of excited dye and amino acid pendants. Flash photolysis experiments verify that this interaction involves electron transfer from the indole side chains of tryptophan. Rate constants for electron transfer are discussed in terms of the distance relationships for the eosin chromophore and aromatic redox sites on peptide derivatives, the pathway for [sigma]-[pi] through-bond interaction between redox sites, and the multiplicity and state of protonation for electron-transfer intermediates. Selected electron-transfer photoreactions were studied under conditions of binding of the peptide derivatives in a high molecular weight, water-soluble, globular polymer, poly(vinyl-2-pyrrolidinone). 28 refs., 4 figs., 1 tab.

  16. Dissociative electron attachment and charge transfer in condensed matter

    International Nuclear Information System (INIS)

    Bass, A.D.; Sanche, L.

    2003-01-01

    Experiments using energy-selected beams of electrons incident from vacuum upon thin vapour deposited solids show that, as in the gas-phase, scattering cross sections at low energies are dominated by the formation of temporary negative ions (or resonances) and that molecular damage may be effected via dissociative electron attachment (DEA). Recent results also show that charge transfer between anionic states of target molecules and their environment is often crucial in determining cross sections for electron driven processes. Here, we review recent work from our laboratory, in which charge transfer is observed. For rare gas solids, electron exchange between the electron-exciton complex and either a metal substrate or co-adsorbed molecule enhances the desorption of metastable atoms and/or molecular dissociation. We discuss how transient electron capture by surface electron states of a substrate and subsequent electron transfer to a molecular adsorbate enhances the effective cross sections for DEA. We also consider the case of DEA to CF 2 Cl 2 condensed on water and ammonia ices, where electron exchange between pre-solvated electron states of ice and transient molecular anions can also increase DEA cross sections. Electron transfer from molecular resonances into pre-solvated electron states of ice is also discussed

  17. Lifetime measurements of excited states in 196Pt

    International Nuclear Information System (INIS)

    Bolotin, H.H.; Katayama, Ichiro; Sakai, Hideyuki; Fujita, Yoshitaka; Fujiwara, Mamoru

    1979-01-01

    The lifetimes of six excited states in 196 Pt up to an excitation energy of 1525 keV were measured by the recoil-distance method (RDM). These levels were populated by Coulomb excitation using both 90 MeV 20 Ne and 220 MeV 58 Ni ion beams. The measured lifetimes of the 2 1 + , 4 1 + , 6 1 + , 2 2 + , 4 2 + and 0 2 + states and the B(E2) values inferred for the depopulating transitions from these levels are presented. With the exception of the 2 1 + state, the meanlives of all other levels are the first such direct experimental determinations to be reported. (author)

  18. Rotational Spectra in 29 Vibrationally Excited States of Interstellar Aminoacetonitrile

    Energy Technology Data Exchange (ETDEWEB)

    Kolesniková, L.; Alonso, E. R.; Mata, S.; Alonso, J. L. [Grupo de Espectroscopia Molecular (GEM), Edificio Quifima, Área de Química-Física, Laboratorios de Espectroscopia y Bioespectroscopia, Parque Científico UVa, Unidad Asociada CSIC, Universidad de Valladolid, E-47011 Valladolid (Spain)

    2017-04-01

    We report a detailed spectroscopic investigation of the interstellar aminoacetonitrile, a possible precursor molecule of glycine. Using a combination of Stark and frequency-modulation microwave and millimeter wave spectroscopies, we observed and analyzed the room-temperature rotational spectra of 29 excited states with energies up to 1000 cm{sup −1}. We also observed the {sup 13}C isotopologues in the ground vibrational state in natural abundance (1.1%). The extensive data set of more than 2000 new rotational transitions will support further identifications of aminoacetonitrile in the interstellar medium.

  19. Excited states of open strings from N=4 SYM

    International Nuclear Information System (INIS)

    Dzienkowski, Eric

    2015-01-01

    We continue the analysis of building open strings stretched between giant gravitons from N=4 SYM by going to second order in perturbation theory using the three-loop dilatation generator from the field theory. In the process we build a Fock-like space of states using Cuntz oscillators which can be used to access the excited open string states. We find a remarkable cancellation among the excited states that shows the ground state energy is consistent with a fully relativistic dispersion relation.

  20. Formation and role of excited states in radiolysis - a foreword

    International Nuclear Information System (INIS)

    Singh, A.

    1976-01-01

    It is stated that the choice of contributions to the special issue of this Journal has been limited to those which bear on the details of the mechanisms of excited state formation and are likely to be useful to radiation chemists. Since more than half the energy deposited in radiolysis goes into excitation, studies on the fate of the excited species formed are very important. A brief reference is made to the subject matter of each of the fifteen contributions, and its significance to the development of the technique of radiolysis is outlined. (U.K.)

  1. Excited states by analytic continuation of TBA equations

    International Nuclear Information System (INIS)

    Dorey, P.; Tateo, R.

    1996-01-01

    We suggest an approach to the problem of finding integral equations for the excited states of an integrable model, starting from the thermodynamic Bethe ansatz equations for its ground state. The idea relies on analytic continuation through complex values of the coupling constant, and an analysis of the monodromies that the equations and their solutions undergo. For the scaling Lee-Yang model, we find equations in this way for the one- and two-particle states in the spin-zero sector, and suggest various generalisations. Numerical results show excellent agreement with the truncated conformal space approach, and we also treat some of the ultraviolet and infrared asymptotics analytically. (orig.)

  2. Study of the first excited state in 5Li

    International Nuclear Information System (INIS)

    Gagne, R.M.; Fou, C.M.; Ward, S.

    1975-01-01

    The reaction 6 Li( 3 He,α) 5 Li(α)p was studied with a 1.8MeV incident 3 He beam. Coincidence spectra (α-α) were measured at theta 1 =25 deg, 35 deg, 40 deg and theta 2 =-150 deg. The purpose was to locate the first excited state of 5 Li. The analysis yields E(x)=3.2+0.2MeV and GAMMA=1.5+-0.5MeV

  3. Supersymmetric quantum mechanics and higher excited states of a non-polynomial potential

    International Nuclear Information System (INIS)

    Drigo Filho, E.; Ricotta, R.M.

    1989-03-01

    Supersymmetric quantum mechanics is used to evaluate new excited states of a non-polynomial potential. This illustrates a method of evaluating higher excited states of quantum mechanical potentials. (A.C.A.S.) [pt

  4. Fundamental studies of energy-and hole/electron- transfer in hydroporphyrin architectures

    Energy Technology Data Exchange (ETDEWEB)

    Bocian, David F. [University of California, Riverside, CA (United States)

    2014-08-20

    The long-term objective of the Bocian/Holten/Lindsey research program is to design, synthesize, and characterize tetrapyrrole-based molecular architectures that absorb sunlight, funnel energy, and separate charge with high efficiency and in a manner compatible with current and future solar-energy conversion schemes. The synthetic tetrapyrroles include porphyrins and hydroporphyrins; the latter classes of molecules encompass analogues of the naturally occurring chlorophylls and bacteriochlorophylls (e.g., chlorins, bacteriochlorins, and their derivatives). The attainment of the goals of the research program requires the close interplay of molecular design and synthesis (Lindsey group), static and time-resolved optical spectroscopic measurements (Holten group), and electrochemical, electron paramagnetic resonance, and resonance Raman studies, as well as density functional theory calculations (Bocian Group). The proposed research encompasses four interrelated themes: (1) Determination of the rates of ground-state hole/electron transfer between (hydro)porphyrins in multipigment arrays as a function of array size, distance between components, linker type, site of linker connection, and frontier molecular orbital composition. (2) Examination of excited-state energy transfer among hydroporphyrins in multipigment arrrays, including both pairwise and non-adjacent transfer, with a chief aim to identify the relative contributions of through-space (Förster) and through-bond (Dexter) mechanisms of energy transfer, including the roles of site of linker connection and frontier molecular orbital composition. (3) Elucidation of the role of substituents in tuning the spectral and electronic properties of bacteriochlorins, with a primary aim of learning how to shift the long-wavelength absorption band deeper into the near-infrared region. (4) Continued development of the software package PhotochemCAD for spectral manipulations and calculations through the compilation of a database

  5. Singlet versus Triplet Excited State Mediated Photoinduced Dehalogenation Reactions of Itraconazole in Acetonitrile and Aqueous Solutions.

    Science.gov (United States)

    Zhu, Ruixue; Li, Ming-de; Du, Lili; Phillips, David Lee

    2017-04-06

    Photoinduced dehalogenation of the antifungal drug itraconazole (ITR) in acetonitrile (ACN) and ACN/water mixed solutions was investigated using femtosecond and nanosecond time-resolved transient absorption (fs-TA and ns-TA, respectively) and nanosecond time-resolved resonance Raman spectroscopy (ns-TR 3 ) experiments. An excited resonance energy transfer is found to take place from the 4-phenyl-4,5-dihydro-3H-1,2,4-triazol-3-one part of the molecule to the 1,3-dichlorobenzene part of the molecule when ITR is excited by ultraviolet light. This photoexcitation is followed by a fast carbon-halogen bond cleavage that leads to the generation of radical intermediates via either triplet and/or singlet excited states. It is found that the singlet excited state-mediated carbon-halogen cleavage is the predominant dehalogenation process in ACN solvent, whereas a triplet state-mediated carbon-halogen cleavage prefers to occur in the ACN/water mixed solutions. The singlet-to-triplet energy gap is decreased in the ACN/water mixed solvents and this helps facilitate an intersystem crossing process, and thus, the carbon-halogen bond cleavage happens mostly through an excited triplet state in the aqueous solutions examined. The ns-TA and ns-TR 3 results also provide some evidence that radical intermediates are generated through a homolytic carbon-halogen bond cleavage via predominantly the singlet excited state pathway in ACN but via mainly the triplet state pathway in the aqueous solutions. In strong acidic solutions, protonation at the oxygen and/or nitrogen atoms of the 1,2,4-triazole-3-one group appears to hinder the dehalogenation reactions. This may offer the possibility that the phototoxicity of ITR due to the generation of aryl or halogen radicals can be reduced by protonation of certain moieties in suitably designed ITR halogen-containing derivatives.

  6. Extracellular electron transfer mechanisms between microorganisms and minerals

    Energy Technology Data Exchange (ETDEWEB)

    Shi, Liang; Dong, Hailiang; Reguera, Gemma; Beyenal, Haluk; Lu, Anhuai; Liu, Juan; Yu, Han-Qing; Fredrickson, James K.

    2016-08-30

    Electrons can be transferred from microorganisms to multivalent metal ions that are associated with minerals and vice versa. As the microbial cell envelope is neither physically permeable to minerals nor electrically conductive, microorganisms have evolved strategies to exchange electrons with extracellular minerals. In this Review, we discuss the molecular mechanisms that underlie the ability of microorganisms to exchange electrons, such as c-type cytochromes and microbial nanowires, with extracellular minerals and with microorganisms of the same or different species. Microorganisms that have extracellular electron transfer capability can be used for biotechnological applications, including bioremediation, biomining and the production of biofuels and nanomaterials.

  7. On the Electronic Structure of [Cu(H2O)6]2+

    DEFF Research Database (Denmark)

    Tanaka, Kiyoshi; Johansen, Helge

    1997-01-01

    The electronic structure of the ground state and doublet excited states due to d-d transitions and charge transfer transitions from ligand to copper of [Cu(H2O)6]2+ are investigated by ab initio calculations. The excited states corresponding to the the d-d transitions are calculated to be 1.1 - 1...... on the description of these excited states. The chargetransfer excitations are predicted to start around 6.5 eV for [Cu(H2O)6]2+....

  8. Excited states above the proton threshold in {sup 26}Si

    Energy Technology Data Exchange (ETDEWEB)

    Komatsubara, T. [Institute for Basic Science (IBS), Rare Isotope Science Project, Yuseong-gu Daejeon (Korea, Republic of); Kubono, S.; Ito, Y. [RIKEN, Saitama (Japan); Hayakawa, T.; Shizuma, T. [Japan Atomic Energy Agency, Tokai, Ibaraki (Japan); Ozawa, A.; Ishibashi, Y. [University of Tsukuba, Institute of Physics, Tsukuba, Ibaraki (Japan); Moriguchi, T. [National Cerebral and Cardiovascular Center Research Institute, Suita, Osaka (Japan); Yamaguchi, H.; Kahl, D. [University of Tokyo, Wako Branch, Center for Nuclear Study (CNS), Wako, Saitama (Japan); Hayakawa, S. [Laboratori Nazionali del Sud-INFN, Catania (Italy); Nguyen Binh, Dam [Vietnamese Academy for Science and Technology, Institute of Physics, Hanoi (Viet Nam); Chen, A.A.; Chen, J. [McMaster University, Hamilton, Ontario (Canada); Setoodehnia, K. [University of Notre Dame, Department of Physics, Notre Dame, Indiana (United States); Kajino, T. [National Astronomical Observatory, Tokyo (Japan); University of Tokyo, Department of Astronomy, Graduate School of Science, Tokyo (Japan)

    2014-09-15

    The level scheme above the proton threshold in {sup 26}Si is crucial for evaluating the {sup 25}Al(p, γ){sup 26}Si stellar reaction, which is important for understanding the astrophysical origin of the long-lived cosmic radioactivity {sup 26}Al(T{sub 1/2} = 7.17 x 10{sup 5} y) in the Galaxy. The excited states in {sup 26}Si have been studied using an in-beam γ-ray spectroscopy technique with the {sup 24}Mg({sup 3}He, nγ){sup 26}Si reaction. γ-rays with energies up to 4.6 MeV emitted from excited states in {sup 26}Si have been measured using large volume HPGe detectors. The spin-parity of one of the most important states reported recently at 5890.0keV has been assigned as 0{sup +} by γ-γ angular correlation measurements in this work. (orig.)

  9. Excited states configurations of the quantum Toda lattice

    International Nuclear Information System (INIS)

    Matsuyama, A.

    2001-01-01

    Excited states configurations of the quantum Toda lattice are studied by the direct diagonalization of the Hamiltonian. The most probable configurations of one-hole and one-particle excitations are shown to be similar to the profiles of classical phonon and soliton excitations, respectively. One-hole excitation states, which are always ground states of definite E m -symmetry of the dihedral group D N , change those structures abruptly with the potential range varied. One-particle excitations, which are buried in complicated excitation spectra, have well-defined configurations similar to the conoidal profile of the classical periodic Toda lattice. The relationship that the hole (particle) excitations in quantum mechanics correspond to the phonon (soliton) excitations in classical mechanics, which has been suggested based on the similarity of dispersion relations, is confirmed in a geometrically understandable way. Based on the study of one-soliton and two-soliton states, the structure of multi-soliton states in quantum mechanics can be conjectured

  10. Gamma decays, lifetimes and spins of 47V excited states

    International Nuclear Information System (INIS)

    Thompson, J.V.; Bell, R.A.I.; Carlson, E.; Najam, M.R.

    1974-11-01

    The nucleus 47 V has been studied using the 47 Ti(p,nγ) 47 V reaction, with isotopically enriched 47 Ti targets, incident proton energies from 4.7 to 5.4 MeV, and Ge(Li) gamma-ray detectors. The previously unreported gamma decay of the second excited state was observed. Energies of the first seven excited states were deduced to be 87.5 +- 0.1, 145.7 +- 0.2, 259.6 +-0.4, 660.1 +- 0.3, 1138.3 +- 0.4, 1272.2 +- 0.4 and 1295.1 +- 0.4 keV. Their gamma-decay branching ratios were measured. The lifetimes of the last four mentioned states were deduced from attenuated Doppler shifts to be [680-340, 680+1400], [960-440, 960+1700], [390-150, 390+390], and > 750 fs respectively. Angular distribution measurements resulted in the assignment of Jsup(π) = 9/2 - to the 1272 keV level and J = 9/2 or 11/2 to the 1295 keV level. The results are discussed in the light of the Coriolis coupling model. (author)

  11. Ultrafast excited-state dynamics of 2,5-dimethylpyrrole.

    Science.gov (United States)

    Yang, Dongyuan; Min, Yanjun; Chen, Zhichao; He, Zhigang; Yuan, Kaijun; Dai, Dongxu; Yang, Xueming; Wu, Guorong

    2018-04-17

    The ultrafast excited-state dynamics of 2,5-dimethylpyrrole following excitation at wavelengths in the range of 265.7-216.7 nm is studied using the time-resolved photoelectron imaging method. It is found that excitation at longer wavelengths (265.7-250.2 nm) results in the population of the S1(1πσ*) state, which decays out of the photoionization window in about 90 fs. At shorter pump wavelengths (242.1-216.7 nm), the assignments are less clear-cut. We tentatively assign the initially photoexcited state(s) to the 1π3p Rydberg state(s) which has lifetimes of 159 ± 20, 125 ± 15, 102 ± 10 and 88 ± 10 fs for the pump wavelengths of 242.1, 238.1, 232.6 and 216.7 nm, respectively. Internal conversion to the S1(1πσ*) state represents at most a minor decay channel. The methyl substitution effects on the decay dynamics of the excited states of pyrrole are also discussed. Methyl substitution on the pyrrole ring seems to enhance the direct internal conversion from the 1π3p Rydberg state to the ground state, while methyl substitution on the N atom has less influence and the internal conversion to the S1(πσ*) state represents a main channel.

  12. Photoinduced electron transfer in some photosensitive molecules ...

    Indian Academy of Sciences (India)

    Unknown

    redox reactions of substrates like biological molecules,11,12 dyes,13,14 alcohols15,16 etc. Colloidal ... state which is characterised by a phenomenon of dual fluorescence. In the present ... The dried solid was transferred to quartz cell under vacuum ... Recently Grätzel et al34 have developed the dye-sensitized meso-.

  13. The MSINDO-sCIS and MSINDO-UCIS methods. Procedures for the calculation of properties of excited states in molecules and periodic systems by a semiempirical approach

    International Nuclear Information System (INIS)

    Gadaczek, Immanuel Patrick

    2013-01-01

    Theoretical background, parameterization and performance of the newly developed semiempirical configuration interaction singles (CIS) method MSINDO-sCIS (scaled configuration interaction singles) are presented. The CIS Hamiltonian is modified by scaling of the Coulomb and exchange integrals and a semiempirical correction of the diagonal elements. For a recently proposed benchmark set of 28 medium-sized organic molecules, vertical excitation energies for singlet and triplet states have been calculated and statistically evaluated. A full reparameterization of the MSINDO method for both ground and excited state properties was performed. The results of the reparameterized MSINDO-sCIS method are compared to the currently best semiempirical method for excited states, OM3-CISDTQ by Thiel et al., and to other standard methods, such as time-dependent density- functional theory. The mean absolute deviation with respect to the theoretical best estimates (TBEs) for MSINDO-sCIS is 0.44 eV, comparable to the OM3 method but significantly smaller than for Zerner's INDO/S. The computational effort is strongly reduced compared to OM3-CISDTQ and OM3-MRCISD, since only single excitations are taken into account. Higher excitations are implicitly included by parameterization and the empirical correction term. By application of the Davidson-Liu block diagonalization method high computational efficiency is achieved. Furthermore it is demonstrated, that the MSINDO-sCIS method correctly describes charge-transfer (CT) states, that represent a crucial problem for time-dependent density functional theory (TD-DFT) methods. Additionally this method is extended to open-shell systems by the UCIS (unrestricted CIS) approach. MSINDO allows the calculation of periodic systems via the cyclic cluster model (CCM) which is a direct-space approach and therefore can be in principle combined with all molecular quantum-chemical techniques. The sCIS/UCIS equations are solved for a cluster with periodic

  14. Theoretical aspects of electron transfer reactions of complex molecules

    DEFF Research Database (Denmark)

    Kuznetsov, A. M.; Ulstrup, Jens

    2001-01-01

    Features of electron transfer involving complex molecules are discussed. This notion presently refers to molecular reactants where charge transfer is accompanied by large molecular reorganization, and commonly used displaced harmonic oscillator models do not apply. It is shown that comprehensive...... theory of charge transfer in polar media offers convenient tools for the treatment of experimental data for such systems, with due account of large-amplitude strongly anharmonic intramolecular reorganization. Equations for the activation barrier and free energy relationships are provided, incorporating...

  15. Stark-like electron transfer between quantum wells

    International Nuclear Information System (INIS)

    Dubovis, S.A.; Voronko, A.N.; Basharov, A.M.

    2008-01-01

    The Stark-like mechanism of electron transfer between two energy subband localized in remote quantum wells is examined theoretically. Estimations of major parameters of the problem in case of delta-function-wells model are adduced. Schematic model allowing experimental study of Stark-like transfer is proposed

  16. Effect of carbazole-oxadiazole excited-state complexes on the efficiency of dye-doped light-emitting diodes

    Science.gov (United States)

    Jiang, Xuezhong; Register, Richard A.; Killeen, Kelly A.; Thompson, Mark E.; Pschenitzka, Florian; Hebner, Thomas R.; Sturm, James C.

    2002-05-01

    Interactions between hole-transporting carbazole groups and electron-transporting 1,3,4-oxadiazole groups were studied by photoluminescence and electroluminescence (EL) spectroscopy, in blends of poly(N-vinylcarbazole) with 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PVK:PBD) and in random copolymers with carbazole and oxadiazole groups attached as side chains. Different excited-state complexes form in the blends, which exhibit exciplexes, and in the copolymers, which manifest electroplexes, due to topological constraints on the position of carbazole and oxadiazole units in the polymer. Both types of complex red-shift the EL spectra of the matrices compared with pure PVK homopolymer, although the shift is significantly greater for the electroplex. The presence of these complexes has a profound effect on the external quantum efficiency of dye-doped organic light-emitting diodes employing the blends or copolymers as matrices, as it strongly affects the efficiency of Förster energy transfer from the matrix to the dye. Single-layer devices doped with either coumarin 47 (C47), coumarin 6 (C6), or nile red (NR) were compared. Among the three dye-doped PVK:PBD devices, C6 doping yields the highest efficiency, while NR doping produced the most efficient copolymer devices, consistent with the degree of overlap between the EL spectrum of the matrix material and the absorption spectrum of the dye.

  17. Distorted wave calculations for double electron transfer

    International Nuclear Information System (INIS)

    Martinez, A.E.; Rivarola, R.D.; Gayet, R.; Hanssen, J.

    1992-01-01

    The resonant double electron capture by alpha particles in helium targets is studied, at intermediate and high collision energies, using the Continuum Distorted Wave - Eikonal Initial State (CDW-EIS) model. Differential and total cross sections for capture into the He (1 s 2 ) final state are calculated in the framework of an Independent Electron Approximation (IEA). Theoretical results are compared with the experimental data available at present for capture into any final state of helium. (author)

  18. Laser pulse control of bridge mediated heterogeneous electron transfer

    International Nuclear Information System (INIS)

    Wang Luxia; May, Volkhard

    2009-01-01

    Ultrafast heterogeneous electron transfer from surface attached dye molecules into semiconductor band states is analyzed. The focus is on systems where the dye is separated from the surface by different bridge anchor groups. To simulate the full quantum dynamics of the transfer process a model of reduced dimensionality is used. It comprises the electronic levels of the dye, the bridge anchor group electronic levels and the continuum of semiconductor band states, all defined versus a single intramolecular vibrational coordinate. The effect of the bridge states is demonstrated, firstly, in studying the injection dynamics following an impulsive excitation of the dye. Then, by discussing different control tasks it is demonstrate in which way the charge injection process can be influenced by tailored laser pulses. To highlight the importance of electron wave function interference emphasis is put on asymmetric two-bridge molecule systems which are also characterized by different and complex valued electronic transfer matrix elements.

  19. Ultrafast excited state deactivation of doped porous anodic alumina membranes

    International Nuclear Information System (INIS)

    Makhal, Abhinandan; Sarkar, Soumik; Pal, Samir Kumar; Yan, Hongdan; Wulferding, Dirk; Cetin, Fatih; Lemmens, Peter

    2012-01-01

    Free-standing, bi-directionally permeable and ultra-thin anodic aluminum oxide (AAO) membranes establish attractive templates (host) for the synthesis of nano-dots and rods of various materials (guest). This is due to their chemical and structural integrity and high periodicity on length scales of 5–150 nm which are often used to host photoactive nano-materials for various device applications including dye-sensitized solar cells. In the present study, AAO membranes are synthesized by using electrochemical methods and a detailed structural characterization using FEG-SEM, XRD and TGA confirms the porosity and purity of the material. Defect-mediated photoluminescence quenching of the porous AAO membrane in the presence of an electron accepting guest organic molecule (benzoquinone) is studied by means of steady-state and picosecond/femtosecond-resolved luminescence measurements. Using time-resolved luminescence transients, we have also revealed light harvesting of complexes of porous alumina impregnated with inorganic quantum dots (Maple Red) or gold nanowires. Both the Förster resonance energy transfer and the nano-surface energy transfer techniques are employed to examine the observed quenching behavior as a function of the characteristic donor–acceptor distances. The experimental results will find their relevance in light harvesting devices based on AAOs combined with other materials involving a decisive energy/charge transfer dynamics. (paper)

  20. Ultrafast excited state deactivation of doped porous anodic alumina membranes

    Science.gov (United States)

    Makhal, Abhinandan; Sarkar, Soumik; Pal, Samir Kumar; Yan, Hongdan; Wulferding, Dirk; Cetin, Fatih; Lemmens, Peter

    2012-08-01

    Free-standing, bi-directionally permeable and ultra-thin anodic aluminum oxide (AAO) membranes establish attractive templates (host) for the synthesis of nano-dots and rods of various materials (guest). This is due to their chemical and structural integrity and high periodicity on length scales of 5-150 nm which are often used to host photoactive nano-materials for various device applications including dye-sensitized solar cells. In the present study, AAO membranes are synthesized by using electrochemical methods and a detailed structural characterization using FEG-SEM, XRD and TGA confirms the porosity and purity of the material. Defect-mediated photoluminescence quenching of the porous AAO membrane in the presence of an electron accepting guest organic molecule (benzoquinone) is studied by means of steady-state and picosecond/femtosecond-resolved luminescence measurements. Using time-resolved luminescence transients, we have also revealed light harvesting of complexes of porous alumina impregnated with inorganic quantum dots (Maple Red) or gold nanowires. Both the Förster resonance energy transfer and the nano-surface energy transfer techniques are employed to examine the observed quenching behavior as a function of the characteristic donor-acceptor distances. The experimental results will find their relevance in light harvesting devices based on AAOs combined with other materials involving a decisive energy/charge transfer dynamics.

  1. Ultrafast excited state deactivation of doped porous anodic alumina membranes

    Energy Technology Data Exchange (ETDEWEB)

    Makhal, Abhinandan; Sarkar, Soumik; Pal, Samir Kumar [Department of Chemical, Biological and Macromolecular Sciences, S N Bose National Centre for Basic Sciences, Block JD, Sector III, Salt Lake, Kolkata 700 098 (India); Yan, Hongdan; Wulferding, Dirk; Cetin, Fatih; Lemmens, Peter [Institute for Condensed Matter Physics, TU Braunschweig, Mendelssohnstrasse 3, 38106 Braunschweig (Germany)

    2012-08-03

    Free-standing, bi-directionally permeable and ultra-thin anodic aluminum oxide (AAO) membranes establish attractive templates (host) for the synthesis of nano-dots and rods of various materials (guest). This is due to their chemical and structural integrity and high periodicity on length scales of 5-150 nm which are often used to host photoactive nano-materials for various device applications including dye-sensitized solar cells. In the present study, AAO membranes are synthesized by using electrochemical methods and a detailed structural characterization using FEG-SEM, XRD and TGA confirms the porosity and purity of the material. Defect-mediated photoluminescence quenching of the porous AAO membrane in the presence of an electron accepting guest organic molecule (benzoquinone) is studied by means of steady-state and picosecond/femtosecond-resolved luminescence measurements. Using time-resolved luminescence transients, we have also revealed light harvesting of complexes of porous alumina impregnated with inorganic quantum dots (Maple Red) or gold nanowires. Both the Foerster resonance energy transfer and the nano-surface energy transfer techniques are employed to examine the observed quenching behavior as a function of the characteristic donor-acceptor distances. The experimental results will find their relevance in light harvesting devices based on AAOs combined with other materials involving a decisive energy/charge transfer dynamics. (paper)

  2. Fluorescence and picosecond induced absorption from the lowest singlet excited states of quercetin in solutions and polymer films

    Science.gov (United States)

    Bondarev, S. L.; Tikhomirov, S. A.; Buganov, O. V.; Knyukshto, V. N.; Raichenok, T. F.

    2017-03-01

    The spectroscopic and photophysical properties of the biologically important plant antioxidant quercetin in organic solvents, polymer films of polyvinyl alcohol, and a buffer solution at pH 7.0 are studied by stationary luminescence and femtosecond laser spectroscopy at room temperature and 77 K. The large magnitude of the dipole moment of the quercetin molecule in the excited Franck-Condon state μ e FC = 52.8 C m indicates the dipolar nature of quercetin in this excited state. The transient induced absorption spectra S 1→ S n in all solvents are characterized by a short-wave band at λ abs max = 460 nm with exponential decay times in the range of 10.0-20.0 ps. In the entire spectral range at times of >100 ps, no residual induced absorption was observed that could be attributed to the triplet-triplet transitions T 1 → T k in quercetin. In polar solvents, two-band fluorescence was also recorded at room temperature, which is due to the luminescence of the initial enol form of quercetin ( 415 nm) and its keto form with a transferred proton (550 nm). The short-wave band is absent in nonpolar 2-methyltetrahydrofuran (2-MTHF). The spectra of fluorescence and fluorescence excitation exhibit a low dependence on the wavelength of excitation and detection, which may be related to the solvation and conformational changes in the quercetin molecule. Decreasing the temperature of a glassy-like freezing quercetin solution in ethanol and 2-MTHF to 77 K leads to a strong increase in the intensity (by a factor of 100) of both bands. The energy circuits for the proton transfer process are proposed depending on the polarity of the medium. The main channel for the exchange of electronic excitation energy in the quercetin molecule at room temperature is the internal conversion S 1 ⇝ S 0, induced by the state with a proton transfer.

  3. Computational Approach to Electron Charge Transfer Reactions

    DEFF Research Database (Denmark)

    Jónsson, Elvar Örn

    -molecular mechanics scheme, and tools to analyse statistical data and generate relative free energies and free energy surfaces. The methodology is applied to several charge transfer species and reactions in chemical environments - chemical in the sense that solvent, counter ions and substrate surfaces are taken...... in to account - which directly influence the reactants and resulting reaction through both physical and chemical interactions. All methods are though general and can be applied to different types of chemistry. First, the basis of the various theoretical tools is presented and applied to several test systems...... and asymmetric charge transfer reactions between several first-row transition metals in water. The results are compared to experiments and rationalised with classical analytic expressions. Shortcomings of the methods are accounted for with clear steps towards improved accuracy. Later the analysis is extended...

  4. Excited-state absorption and fluorescence dynamics of Er3+:KY3F10

    Science.gov (United States)

    Labbé, C.; Doualan, J. L.; Moncorgé, R.; Braud, A.; Camy, P.

    2018-05-01

    We report here on a complete investigation of the excited-state absorption and fluorescence dynamics of Er3+ doped KY3F10 single crystals versus dopant concentrations and optical excitation conditions. Radiative and effective (including non-radiative relaxations) emission lifetimes and branching ratios are determined from a Judd-Ofelt analysis of the absorption spectra and via specific fluorescence experiments using wavelength selective laser excitations. Excited-state absorption and emission spectra are registered within seven spectral domains, i.e. 560 nm, 650 nm, 710 nm, 810 nm, 970 nm, 1550 nm and 2750 nm. A maximum gain cross-section of 0.93 × 10-21 cm2 is determined at the potential laser wavelength of 2.801 μm for a population ratio of 0.48. Saturation of fluorescence intensities and variations of population ratios versus pumping rates are registered and confronted with a rate equation model to derive the rates of the most important up-conversion and cross-relaxation energy transfers occurring at high dopant concentrations.

  5. Intramolecular photoinduced electron-transfer in azobenzene-perylene diimide

    International Nuclear Information System (INIS)

    Feng Wen-Ke; Wang Shu-Feng; Gong Qi-Huang; Feng Yi-Yu; Feng Wei; Yi Wen-Hui

    2010-01-01

    This paper studies the intramolecular photoinduced electron-transfer (PET) of covalent bonded azobenzene-perylene diimide (AZO-PDI) in solvents by using steady-state and time-resolved fluorescence spectroscopy together with ultrafast transient absorption spectroscopic techniques. Fast fluorescence quenching is observed when AZO-PDI is excited at characteristic wavelengths of AZO and perylene moieties. Reductive electron-transfer with transfer rate faster than 10 11 s −1 is found. This PET process is also consolidated by femtosecond transient absorption spectra

  6. Energy transfer dynamics in trimers and aggregates of light-harvesting complex II probed by 2D electronic spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Enriquez, Miriam M.; Zhang, Cheng; Tan, Howe-Siang, E-mail: howesiang@ntu.edu.sg [Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371 (Singapore); Akhtar, Parveen; Garab, Győző; Lambrev, Petar H., E-mail: lambrev@brc.hu [Institute of Plant Biology, Biological Research Centre, Hungarian Academy of Sciences, P.O. Box 521, H-6701 Szeged (Hungary)

    2015-06-07

    The pathways and dynamics of excitation energy transfer between the chlorophyll (Chl) domains in solubilized trimeric and aggregated light-harvesting complex II (LHCII) are examined using two-dimensional electronic spectroscopy (2DES). The LHCII trimers and aggregates exhibit the unquenched and quenched excitonic states of Chl a, respectively. 2DES allows direct correlation of excitation and emission energies of coupled states over population time delays, hence enabling mapping of the energy flow between Chls. By the excitation of the entire Chl b Q{sub y} band, energy transfer from Chl b to Chl a states is monitored in the LHCII trimers and aggregates. Global analysis of the two-dimensional (2D) spectra reveals that energy transfer from Chl b to Chl a occurs on fast and slow time scales of 240–270 fs and 2.8 ps for both forms of LHCII. 2D decay-associated spectra resulting from the global analysis identify the correlation between Chl states involved in the energy transfer and decay at a given lifetime. The contribution of singlet–singlet annihilation on the kinetics of Chl energy transfer and decay is also modelled and discussed. The results show a marked change in the energy transfer kinetics in the time range of a few picoseconds. Owing to slow energy equilibration processes, long-lived intermediate Chl a states are present in solubilized trimers, while in aggregates, the population decay of these excited states is significantly accelerated, suggesting that, overall, the energy transfer within the LHCII complexes is faster in the aggregated state.

  7. Electron transfer reactions in microporous solids

    Energy Technology Data Exchange (ETDEWEB)

    Mallouk, T.E.

    1993-01-01

    Basic thrust the research program involves use of microporous solids (zeolites, clays, layered and tunnel structure oxide semiconductors) as organizing media for artificial photosynthetic systems. Purpose of the microporous solid is twofold. First, it induces spatial organization of photoactive and electroactive components (sensitizers, semiconductor particles, electron relays, and catalysts) at the solid-solution interface, enhancing the quantum efficiency of charge separation and separating physically the ultimate electron donor and acceptor in the electron transport chain. Second, since the microcrystalline solid admits only molecules of a certain charge and size, it is possible to achieve permanent charge separation by sieving chemical photoproducts (e.g., H[sub 2] and I[sub 3][sup [minus

  8. Some studies on the formation of excited states of aromatic solutes in hydrocarbons and other solvents

    Energy Technology Data Exchange (ETDEWEB)

    Salmon, G A [Leeds Univ. (UK). Cookridge High Energy Radiation Research Centre

    1976-01-01

    This paper reviews the work of the author and his co-workers on the radiation-induced formation of excited states of aromatic compounds in solution. The experimental methods used are surveyed and in particular the method of measuring the yields of triplet and singlet excited states of the solute are described. The problems discussed are: (1) the effect of solvent on the yields of excited states, (2) formation of excited states in cyclohexane and other alicyclic hydrocarbons, (3) the formation of excited states in benzene and (4) the identification of T-T absorption spectra.

  9. Studies on electron transfer reactions of Keggin-type mixed ...

    Indian Academy of Sciences (India)

    Administrator

    (PV2) in aqueous phosphate buffer of pH 6 at ambient temperature. Electrochemical and optical studies show that the stoichiometry of the reaction is 1: 2 (NADH : HPA). EPR and optical studies show that HPA act as one electron acceptor and the products of electron transfer reactions are one elec- tron reduced heteropoly ...

  10. Quantum electron transfer processes induced by thermo-coherent ...

    Indian Academy of Sciences (India)

    WINTEC

    Thermo-coherent state; electron transfer; quantum rate. 1. Introduction. The study ... two surfaces,16 namely, one electron two-centered exchange problem,7–10 many ... temperature classical regime for the single and the two-mode cases have ...

  11. Toddlers' word learning and transfer from electronic and print books.

    Science.gov (United States)

    Strouse, Gabrielle A; Ganea, Patricia A

    2017-04-01

    Transfer from symbolic media to the real world can be difficult for young children. A sample of 73 toddlers aged 17 to 23months were read either an electronic book displayed on a touchscreen device or a traditional print book in which a novel object was paired with a novel label. Toddlers in both conditions learned the label within the context of the book. However, only those who read the traditional format book generalized and transferred the label to other contexts. An older group of 28 toddlers aged 24 to 30months did generalize and transfer from the electronic book. Across ages, those children who primarily used screens to watch prerecorded video at home transferred less from the electronic book than those with more diverse home media experiences. Copyright © 2016 Elsevier Inc. All rights reserved.

  12. Heat transfer between adsorbate and laser-heated hot electrons

    International Nuclear Information System (INIS)

    Ueba, H; Persson, B N J

    2008-01-01

    Strong short laser pulses can give rise to a strong increase in the electronic temperature at metal surfaces. Energy transfer from the hot electrons to adsorbed molecules may result in adsorbate reactions, e.g. desorption or diffusion. We point out the limitations of an often used equation to describe the heat transfer process in terms of a friction coupling. We propose a simple theory for the energy transfer between the adsorbate and hot electrons using a newly introduced heat transfer coefficient, which depends on the adsorbate temperature. We calculate the transient adsorbate temperature and the reaction yield for a Morse potential as a function of the laser fluency. The results are compared to those obtained using a conventional heat transfer equation with temperature-independent friction. It is found that our equation of energy (heat) transfer gives a significantly lower adsorbate peak temperature, which results in a large modification of the reaction yield. We also consider the heat transfer between different vibrational modes excited by hot electrons. This mode coupling provides indirect heating of the vibrational temperature in addition to the direct heating by hot electrons. The formula of heat transfer through linear mode-mode coupling of two harmonic oscillators is applied to the recent time-resolved study of carbon monoxide and atomic oxygen hopping on an ultrafast laser-heated Pt(111) surface. It is found that the maximum temperature of the frustrated translation mode can reach high temperatures for hopping, even when direct friction coupling to the hot electrons is not strong enough

  13. Excited state mass spectra of doubly heavy Ξ baryons

    Energy Technology Data Exchange (ETDEWEB)

    Shah, Zalak; Rai, Ajay Kumar [Sardar Vallabhbhai National Institute of Technology, Department of Applied Physics, Surat, Gujarat (India)

    2017-02-15

    In this paper, the mass spectra are obtained for doubly heavy Ξ baryons, namely, Ξ{sub cc}{sup +}, Ξ{sub cc}{sup ++}, Ξ{sub bb}{sup -}, Ξ{sub bb}{sup 0}, Ξ{sub bc}{sup 0} and Ξ{sub bc}{sup +}. These baryons consist of two heavy quarks (cc, bb, and bc) with a light (d or u) quark. The ground, radial, and orbital states are calculated in the framework of the hypercentral constituent quark model with Coulomb plus linear potential. Our results are also compared with other predictions, thus, the average possible range of excited states masses of these Ξ baryons can be determined. The study of the Regge trajectories is performed in (n, M{sup 2}) and (J, M{sup 2}) planes and their slopes and intercepts are also determined. Lastly, the ground state magnetic moments of these doubly heavy baryons are also calculated. (orig.)

  14. Excited state dynamics & optical control of molecular motors

    Science.gov (United States)

    Wiley, Ted; Sension, Roseanne

    2014-03-01

    Chiral overcrowded alkenes are likely candidates for light driven rotary molecular motors. At their core, these molecular motors are based on the chromophore stilbene, undergoing ultrafast cis/trans photoisomerization about their central double bond. Unlike stilbene, the photochemistry of molecular motors proceeds in one direction only. This unidirectional rotation is a result of helicity in the molecule induced by steric hindrance. However, the steric hindrance which ensures unidirectional excited state rotation, has the unfortunate consequence of producing large ground state barriers which dramatically decrease the overall rate of rotation. These molecular scale ultrafast motors have only recently been studied by ultrafast spectroscopy. Our lab has studied the photochemistry and photophysics of a ``first generation'' molecular motor with UV-visible transient absorption spectroscopy. We hope to use optical pulse shaping to enhance the efficiency and turnover rate of these molecular motors.

  15. Lifetime measurements of excited states in 73As

    International Nuclear Information System (INIS)

    Singh, K.P.; Kavakand, T.; Hajivaliei, M.

    2004-01-01

    The excited states of 73 As have been investigated via the 73 Ge(p, nγ) 73 As reaction with proton beam energies from 2.5–4.3 MeV. The lifetimes of the levels at 769.6, 860.5, 1177.8, 1188.7, 1274.9, 1344.1, 1557.1 and 1975.2 keV excitation energies have been measured for the first time using the Doppler shift attenuation method. The angular distributions have been used to assign the spins and the multipole mixing ratios using statistical theory for compound nuclear reactions. The ambiguity in the spin values for the various levels has been removed. The multipole mixing ratios for eight γ-transitions have been newly measured. (author)

  16. 2He decay from excited states: the 18Ne case

    International Nuclear Information System (INIS)

    Raciti, G.; Sfienti, C.; De Napoli, M.; Rapisarda, E.; Cardella, G.; Giacoppo, F.

    2011-01-01

    Two-proton radioactivity studies have been performed on excited states of 18 Ne produced by 20 Ne fragmentation at the FRIBs facility of the Laboratori Nazionali del Sud. The study of the relative-momentum correlations of the two protons allowed to disentangle the diproton, democratic and sequential decay contributions to the 2p emission. In order to extend the study on two-proton decay to other light-masses nuclei, an upgrade of the FRIBs facility is planned. A new configuration of the Fragment Separator would be able to increase the acceptance of the beam line and therefore the yield of the produced radioactive beams. Also the present tagging setup will be modified in view of the gain intensity, in order to sustain the higher foreseen incoming rate. Status and perspectives of the facility will be presented. (author)

  17. A new energy transfer channel from carotenoids to chlorophylls in purple bacteria.

    Science.gov (United States)

    Feng, Jin; Tseng, Chi-Wei; Chen, Tingwei; Leng, Xia; Yin, Huabing; Cheng, Yuan-Chung; Rohlfing, Michael; Ma, Yuchen

    2017-07-10

    It is unclear whether there is an intermediate dark state between the S 2 and S 1 states of carotenoids. Previous two-dimensional electronic spectroscopy measurements support its existence and its involvement in the energy transfer from carotenoids to chlorophylls, but there is still considerable debate on the origin of this dark state and how it regulates the energy transfer process. Here we use ab initio calculations on excited-state dynamics and simulated two-dimensional electronic spectrum of carotenoids from purple bacteria to provide evidence supporting that the dark state may be assigned to a new A g + state. Our calculations also indicate that groups on the conjugation backbone of carotenoids may substantially affect the excited-state levels and the energy transfer process. These results contribute to a better understanding of carotenoid excited states.Carotenoids harvest energy from light and transfer it to chlorophylls during photosynthesis. Here, Feng et al. perform ab initio calculations on excited-state dynamics and simulated 2D electronic spectrum of carotenoids, supporting the existence of a new excited state in carotenoids.

  18. Lifetime measurements of the excited states in {sup 145} Sm

    Energy Technology Data Exchange (ETDEWEB)

    El-Badry, A M; Abdel Samie, Sh; Ahmad, A A [Depatment of Physics, Faculty of Science, ElMinia University, ElMinia, (Egypt); Kuroyanagi, T; Odahara, A; Gono, Y; Morinobu, S [Tandem Accelerator Laboratory, Department of Physics, Kyushu University, (Japan)

    1997-12-31

    Lifetime of the excited levels in {sup 145} Sm has been measured through the {sup 139} La ({sup 10} B, 4 n){sup 145} Sm nuclear reaction. The optimal beam energy of 49 MeV was determined from the measurements of the excitation function and Cascade program. With the possibility of studying lifetime of this nucleus a conventional plunger system have been designed and constructed at kyushu University tandem accelerator laboratory. A La target of 0.22 mg/cm{sup 2} thickness which was evaporated onto a Au foil of 2 mg/cm{sup 2} thickness was used. Since the recoil velocity was estimated to be 1.76 mm/ns (beta 0.00585), the measurable time range resulted in the range from 5 Ps to 5 ns. The single spectra measurements were performed at the 20 plunger positions in the range from 10 {mu} to 10 mm. Analyses of the data were carried using hypermet and/or GF2 program to obtain the lifetimes. A new list of lifetimes for 12 excited states up to 3.922 MeV excitations for {sup 145} Sm were determined for the first time. Decay curves of the these transitions are discussed. The new lifetimes of excited states in {sup 145} Sm enabled us to understand the electromagnetic properties. The deduced transition probabilities were established and compared with that of N = 83 isotones and the closed shell nucleus {sup 144} Sm. In addition, a nuclear structure of {sup 145} Sm have been discussed and proposed in framework of the shell model. 4 figs., 1 tab.

  19. Electron transfer, ionization, and excitation atomic collisions

    International Nuclear Information System (INIS)

    Winter, T.G.; Alston, S.G.

    1990-01-01

    Basic atomic-collision processes at intermediate and high energies are being studied theoretically at Penn State by Alston and Winter. In the high velocity regime, single-electron capture is treated using a high order multiple-scattering approach; extensive comparison with experiment and analysis of mechanisms have been made. Fitting the calculated amplitude with a simple analytic form, the asymptotic velocity dependence of the cross section is obtained. The effect on the capture amplitude of altering the inner part of the internuclear potential has also been explored. In the intermediate velocity regime, earlier work on collisions between protons and hydrogenic-ion targets using a coupled-state approach is being extended to the two-electron helium target. 29 refs

  20. Electronic Energy Transfer in Polarizable Heterogeneous Environments

    DEFF Research Database (Denmark)

    Svendsen, Casper Steinmann; Kongsted, Jacob

    2015-01-01

    such couplings provide important insight into the strength of interaction between photo-active pigments in protein-pigment complexes. Recently, attention has been payed to how the environment modifies or even controls the electronic couplings. To enable such theoretical predictions, a fully polarizable embedding......-order multipole moments. We use this extended model to systematically examine three different ways of obtaining EET couplings in a heterogeneous medium ranging from use of the exact transition density to a point-dipole approximation. Several interesting observations are made including that explicit use...... of transition densities in the calculation of the electronic couplings - also when including the explicit environment contribution - can be replaced by a much simpler transition point charge description without comprising the quality of the model predictions....

  1. Monitoring sequential electron transfer with EPR

    International Nuclear Information System (INIS)

    Thurnauer, M.C.; Feezel, L.L.; Snyder, S.W.; Tang, J.; Norris, J.R.; Morris, A.L.; Rustandi, R.R.

    1989-01-01

    A completely general model which treats electron spin polarization (ESP) found in a system in which radical pairs with different magnetic interactions are formed sequentially has been described. This treatment has been applied specifically to the ESP found in the bacterial reaction center. Test cases show clearly how parameters such as structure, lifetime, and magnetic interactions within the successive radical pairs affect the ESP, and demonstrate that previous treatments of this problem have been incomplete. The photosynthetic bacterial reaction center protein is an ideal system for testing the general model of ESP. The radical pair which exhibits ESP, P 870 + Q - (P 870 + is the oxidized, primary electron donor, a bacteriochlorophyll special pair and Q - is the reduced, primary quinone acceptor) is formed via sequential electron transport through the intermediary radical pair P 870 + I - (I - is the reduced, intermediary electron acceptor, a bacteriopheophytin). In addition, it is possible to experimentally vary most of the important parameters, such as the lifetime of the intermediary radical pair and the magnetic interactions in each pair. It has been shown how selective isotopic substitution ( 1 H or 2 H) on P 870 , I and Q affects the ESP of the EPR spectrum of P 870 + Q - , observed at two different microwave frequencies, in Fe 2+ -depleted bacterial reaction centers of Rhodobacter sphaeroides R26. Thus, the relative magnitudes of the magnetic properties (nuclear hyperfine and g-factor differences) which influence ESP development were varied. The results support the general model of ESP in that they suggest that the P 870 + Q - radical pair interactions are the dominant source of ESP production in 2 H bacterial reaction centers

  2. Excited states of ethylene interpreted in terms of perturbed Rydberg series

    International Nuclear Information System (INIS)

    Yamamoto, Shigeyoshi; Tatewaki, Hiroshi

    2003-01-01

    We have investigated the excited states of the ethylene molecule by the multireference configuration interaction (MRCI) method. In particular, the nature of the V state (1 1 B 1u π→π*) was interpreted in terms of perturbed Rydberg series. To clarify the role of the perturbers, we use pseudo-restricted Hartree-Fock natural orbitals (PRHFNO), which would be the most suitable molecular orbital set to describe Rydberg series. It is well known that the expectation value of x 2 for the V state is reduced from 44a 0 2 (RHF) to around 17a 0 2 by considering electron correlation effects, where x is the direction out of the molecular plane. In the present study, a reasonable 2 > value was obtained from small multireference configuration interaction with single excitations (MRCIS), where the π→π* configurations and a few perturbers were assigned as the reference configurations. The major perturbers were found to be five configurations represented by 3a g → 3b 1u , 1b 3g → 3b 2u , 2b 1u → 4a g , 2a g → 3b 1u , and 1b 2u → 2b 3g with respect to the ground state configuration. The V state can therefore be described as a scattering process of the π→π* state by these perturbers. Other low-lying excited states are also investigated by the MRCI method

  3. Proton-coupled electron transfer versus hydrogen atom transfer: generation of charge-localized diabatic states.

    Science.gov (United States)

    Sirjoosingh, Andrew; Hammes-Schiffer, Sharon

    2011-03-24

    The distinction between proton-coupled electron transfer (PCET) and hydrogen atom transfer (HAT) mechanisms is important for the characterization of many chemical and biological processes. PCET and HAT mechanisms can be differentiated in terms of electronically nonadiabatic and adiabatic proton transfer, respectively. In this paper, quantitative diagnostics to evaluate the degree of electron-proton nonadiabaticity are presented. Moreover, the connection between the degree of electron-proton nonadiabaticity and the physical characteristics distinguishing PCET from HAT, namely, the extent of electronic charge redistribution, is clarified. In addition, a rigorous diabatization scheme for transforming the adiabatic electronic states into charge-localized diabatic states for PCET reactions is presented. These diabatic states are constructed to ensure that the first-order nonadiabatic couplings with respect to the one-dimensional transferring hydrogen coordinate vanish exactly. Application of these approaches to the phenoxyl-phenol and benzyl-toluene systems characterizes the former as PCET and the latter as HAT. The diabatic states generated for the phenoxyl-phenol system possess physically meaningful, localized electronic charge distributions that are relatively invariant along the hydrogen coordinate. These diabatic electronic states can be combined with the associated proton vibrational states to generate the reactant and product electron-proton vibronic states that form the basis of nonadiabatic PCET theories. Furthermore, these vibronic states and the corresponding vibronic couplings may be used to calculate rate constants and kinetic isotope effects of PCET reactions.

  4. Dielectronic recombination rate coefficients to excited states of Be-like oxygen

    Energy Technology Data Exchange (ETDEWEB)

    Murakami, Izumi; Safronova, Ulyana I.; Kato, Takako

    2001-05-01

    We have calculated energy levels, radiative transition probabilities, and autoionization rates for Be-like oxygen (O{sup 4+}) including ls{sup 2}2lnl' (n=2 - 8, l {<=} n - 1) and 1s{sup 2}3l'nl (n=3 - 6, l {<=} n - l) states by multi-configurational Hartree-Fock method (Cowan code) and perturbation theory Z-expansion method (MZ code). The state selective dielectronic recombination rate coefficients to excited states of Be-like O ions are obtained. Configuration mixing plays an important role for the principal quantum number n distribution of the dielectronic recombination rate coefficients for 2snl (n {<=} 5) levels at low electron temperature. The orbital angular momentum quantum number l distribution of the rate coefficients shows a peak at l = 4. The total dielectronic recombination rate coefficient is derived as a function of electron temperature. (author)

  5. Effect of proton transfer on the electronic coupling in DNA

    International Nuclear Information System (INIS)

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

    2006-01-01

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

  6. [Electron transfer, ionization, and excitation in atomic collisions

    International Nuclear Information System (INIS)

    1992-01-01

    Fundamental processes of electron transfer, ionization, and excitation in ion-atom and ion-ion collisions are studied. Attention is focussed on one- and two-electron systems and, more recently, quasi-one-electron systems whose electron-target-ion core can be accurately modeled by one-electron potentials. The basic computational approaches can then be taken with few, if any, approximations, and the underlying collisional mechanisms can be more clearly revealed. At intermediate collision energies (e.g., proton energies for p-He + collisions on the order of 100 kilo-electron volts), many electronic states are strongly coupled during the collision, a coupled-state approach, such as a coupled-Sturmian-pseudostate approach, is appropriate. At higher collision energies (million electron-volt energies) the coupling is weaker with, however, many more states being coupled together, so that high-order perturbation theory is essential

  7. Effects of ligand substitution on the excited state dynamics of the Ru(dcbpy)(CO) 2I 2 complex

    Science.gov (United States)

    Lehtovuori, Viivi; Kallioinen, Jani; Myllyperkiö, Pasi; Haukka, Matti; Korppi-Tommola, Jouko

    2003-11-01

    Spectroscopic evidence suggest [PCCP 3 (2001) 1992] that illumination with visible light of the [ trans-I-Ru(dcbpy)(CO) 2I 2] (dcbpy= 4,4 '-dicarboxy-2,2 '-bipyridine) complex in solution induces dissociation of a CO group followed by reorganization of the ligands and attachment of a solvent molecule. In the present study, we report results on excited state dynamics of this ruthenium complex and its photoproduct. Femtosecond transient absorption measurements reveal dominance of excited state absorption of the reactant and the photoproduct [ cis-I-Ru(dcbpy)(CO)(Sol)I 2] (Sol=ethanol or acetonitrile) in the visible spectral region. The time-resolved measurements for the reactant at 77 K indicate interligand charge transfer from mixed Ru-I states to empty dcbpy orbitals. For the photoproduct, no such transfer was observed. In both complexes recovery from the lowest energy excited triplet state to the ground state occurs via two channels: radiative relaxation and a parallel barrier controlled non-radiative relaxation. The barrier is much higher in the reactant (about 850 cm -1) than in the product. A combination of DFT and ZINDO/CI calculations was used to estimate excited singlet and triplet spectra of the reactant and the product molecules. Calculated singlet-triplet difference spectra qualitatively match the observed transient spectra 500 fs after excitation supporting the idea that observed excited state relaxation occurs from the triplet states in both complexes.

  8. Effects of ligand substitution on the excited state dynamics of the Ru(dcbpy)(CO)2I2 complex

    International Nuclear Information System (INIS)

    Lehtovuori, Viivi; Kallioinen, Jani; Myllyperkioe, Pasi; Haukka, Matti; Korppi-Tommola, Jouko

    2003-01-01

    Spectroscopic evidence suggest [PCCP 3 (2001) 1992] that illumination with visible light of the [trans-I-Ru(dcbpy)(CO) 2 I 2 ] (dcbpy4,4 ' -dicarboxy-2,2 ' -bipyridine) complex in solution induces dissociation of a CO group followed by reorganization of the ligands and attachment of a solvent molecule. In the present study, we report results on excited state dynamics of this ruthenium complex and its photoproduct. Femtosecond transient absorption measurements reveal dominance of excited state absorption of the reactant and the photoproduct [cis-I-Ru(dcbpy)(CO)(Sol)I 2 ] (Sol=ethanol or acetonitrile) in the visible spectral region. The time-resolved measurements for the reactant at 77 K indicate interligand charge transfer from mixed Ru-I states to empty dcbpy orbitals. For the photoproduct, no such transfer was observed. In both complexes recovery from the lowest energy excited triplet state to the ground state occurs via two channels: radiative relaxation and a parallel barrier controlled non-radiative relaxation. The barrier is much higher in the reactant (about 850 cm -1 ) than in the product. A combination of DFT and ZINDO/CI calculations was used to estimate excited singlet and triplet spectra of the reactant and the product molecules. Calculated singlet-triplet difference spectra qualitatively match the observed transient spectra 500 fs after excitation supporting the idea that observed excited state relaxation occurs from the triplet states in both complexes

  9. Excited-state Raman spectroscopy with and without actinic excitation: S1 Raman spectra of trans-azobenzene

    International Nuclear Information System (INIS)

    Dobryakov, A. L.; Quick, M.; Ioffe, I. N.; Granovsky, A. A.; Ernsting, N. P.; Kovalenko, S. A.

    2014-01-01

    We show that femtosecond stimulated Raman spectroscopy can record excited-state spectra in the absence of actinic excitation, if the Raman pump is in resonance with an electronic transition. The approach is illustrated by recording S 1 and S 0 spectra of trans-azobenzene in n-hexane. The S 1 spectra were also measured conventionally, upon nπ* (S 0 → S 1 ) actinic excitation. The results are discussed and compared to earlier reports

  10. Ab initio interaction potentials for X and B excited states of He-I2 for studying dynamics

    International Nuclear Information System (INIS)

    Prosmiti, Rita; Garcia-Gutierrez, Leonor; Delgado-Tellez, Laura; Valdes, Alvaro; Villarreal, Pablo; Delgado-Barrio, Gerardo

    2009-01-01

    Ab initio CCSD(T) and MRCI approaches were employed to construct potential energy surfaces of the ground and the B electronic excited states of He-I 2 complex, while full quantum mechanical methods were applied to study its spectroscopy and dynamics. A description of the approach adopted, together with the results obtained and their comparison with recent experimental data, as well as further improvements are presented.

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

    Science.gov (United States)

    Kuzmin, Michael G; Soboleva, Irina V

    2014-05-01

    Representation of the experimental reaction kinetics in the form of rate distribution is shown to be an effective method for the analysis of the mechanisms of these reactions and for comparisons of the kinetics with QC calculations, as well as with the experimental data on the medium mobility. The rate constant distribution function P(k) can be obtained directly from the experimental kinetics N(t) by an inverse Laplace transform. The application of this approach to kinetic data for several excited-state electron transfer reactions reveals the transformations of their rate control factors in the time domain of 1-1000 ps. In neat electron donating solvents two components are observed. The fastest component (k > 1 ps(-1)) was found to be controlled by the fluctuations of the overall electronic coupling matrix element, involving all the reactant molecules, located inside the interior of the solvent shell, rather than for specific pairs of reactant molecules. The slower component (1 > k > 0.1 ps(-1)) is controlled by the medium reorganization (longitudinal relaxation times, τL). A substantial contribution from the non-stationary diffusion controlled reaction is observed in diluted solutions ([Q] transformation of the rate control factors in the course of the reactions.

  12. Ground and excited state properties of high performance anthocyanidin dyes-sensitized solar cells in the basic solutions

    Energy Technology Data Exchange (ETDEWEB)

    Prima, Eka Cahya [Advanced Functional Material Laboratory, Engineering Physics, Institut Teknologi Bandung (Indonesia); Computational Material Design and Quantum Engineering Laboratory, Engineering Physics, Institut Teknologi Bandung (Indonesia); International Program on Science Education, Universitas Pendidikan Indonesia (Indonesia); Yuliarto, Brian; Suyatman, E-mail: yatman@tf.itb.ac.id [Advanced Functional Material Laboratory, Engineering Physics, Institut Teknologi Bandung (Indonesia); Dipojono, Hermawan Kresno [Computational Material Design and Quantum Engineering Laboratory, Engineering Physics, Institut Teknologi Bandung (Indonesia)

    2015-09-30

    The aglycones of anthocyanidin dyes were previously reported to form carbinol pseudobase, cis-chalcone, and trans-chalcone due to the basic levels. The further investigations of ground and excited state properties of the dyes were characterized using density functional theory with PCM(UFF)/B3LYP/6-31+G(d,p) level in the basic solutions. However, to the best of our knowledge, the theoretical investigation of their potential photosensitizers has never been reported before. In this paper, the theoretical photovoltaic properties sensitized by dyes have been successfully investigated including the electron injections, the ground and excited state oxidation potentials, the estimated open circuit voltages, and the light harvesting efficiencies. The results prove that the electronic properties represented by dyes’ LUMO-HOMO levels will affect to the photovoltaic performances. Cis-chalcone dye is the best anthocyanidin aglycone dye with the electron injection spontaneity of −1.208 eV, the theoretical open circuit voltage of 1.781 V, and light harvesting efficiency of 56.55% due to the best HOMO-LUMO levels. Moreover, the ethanol solvent slightly contributes to the better cell performance than the water solvent dye because of the better oxidation potential stabilization in the ground state as well as in the excited state. These results are in good agreement with the known experimental report that the aglycones of anthocyanidin dyes in basic solvent are the high potential photosensitizers for dye-sensitized solar cell.

  13. Intramolecular electron transfer in single-site-mutated azurins

    DEFF Research Database (Denmark)

    Farver, O; Skov, L K; Pascher, T

    1993-01-01

    . Natl. Acad. Sci. U.S.A. 86, 6968-6972]. The RSSR- radical produced in the above reaction was reoxidized in a slower intramolecular electron-transfer process (30-70 s-1 at 298 K) concomitant with a further reduction of the Cu(II) ion. The temperature dependence of the latter rates was determined......, lambda = 135 kJ mol-1 for the reorganization energy was derived. When Trp48, situated midway between the donor and the acceptor, was replaced by Leu or Met, only a small change in the rate of intramolecular electron transfer was observed, indicating that the aromatic residue in this position...... is apparently only marginally involved in electron transfer in wild-type azurin. Pathway calculations also suggest that a longer, through-backbone path is more efficient than the shorter one involving Trp48. The former pathway yields an exponential decay factor, beta, of 6.6 nm-1. Another mutation, raising...

  14. Electron transfer dynamics: Zusman equation versus exact theory

    International Nuclear Information System (INIS)

    Shi Qiang; Chen Liping; Nan Guangjun; Xu Ruixue; Yan Yijing

    2009-01-01

    The Zusman equation has been widely used to study the effect of solvent dynamics on electron transfer reactions. However, application of this equation is limited by the classical treatment of the nuclear degrees of freedom. In this paper, we revisit the Zusman equation in the framework of the exact hierarchical equations of motion formalism, and show that a high temperature approximation of the hierarchical theory is equivalent to the Zusman equation in describing electron transfer dynamics. Thus the exact hierarchical formalism naturally extends the Zusman equation to include quantum nuclear dynamics at low temperatures. This new finding has also inspired us to rescale the original hierarchical equations and incorporate a filtering algorithm to efficiently propagate the hierarchical equations. Numerical exact results are also presented for the electron transfer reaction dynamics and rate constant calculations.

  15. Screening of exciplex formation by distant electron transfer.

    Science.gov (United States)

    Fedorenko, S G; Khokhlova, S S; Burshtein, A I

    2012-01-12

    The excitation quenching by reversible exciplex formation, combined with irreversible but distant electron transfer, is considered by means of the integral encounter theory (IET). Assuming that the quenchers are in great excess, the set of IET equations for the excitations, free ions, and exciplexes is derived. Solving these equations gives the Laplace images of all these populations, and these are used to specify the quantum yields of the corresponding reaction products. It appears that diffusion facilitates the exciplex production and the electron transfer. On the other hand the stronger the electron transfer is, the weaker is the exciplex production. At slow diffusion the distant quenching of excitations by ionization prevents their reaching the contact where they can turn into exciplexes. This is a screening effect that is most pronounced when the ionization rate is large.

  16. Numerical Simulation of Transient Moisture Transfer into an Electronic Enclosure

    DEFF Research Database (Denmark)

    Shojaee Nasirabadi, Parizad; Jabbaribehnam, Mirmasoud; Hattel, Jesper Henri

    2016-01-01

    Electronic systems are sometimes exposed to harsh environmental conditions of temperature and humidity. Moisturetransfer into electronic enclosures and condensation can cause several problems such as corrosion and alteration in thermalstresses. It is therefore essential to study the local climate...... inside the enclosures to be able to protect the electronic systems.In this work, moisture transfer into a typical electronic enclosure is numerically studied using CFD. In order to reduce theCPU-time and make a way for subsequent factorial design analysis, a simplifying modification is applied in which...

  17. Realisation and crossed molecular beams study of H2/O chemical reactions at several excited states

    International Nuclear Information System (INIS)

    Marx, Jacqueline

    1986-01-01

    This work is devoted to the study of the reactive collision O + H 2 OH + H in a crossed beam experiment. This process including several channels taken a part in the chemistry of the upper atmosphere as well as in the combustion of hydrogen. According to the electronic or vibrational state of the reactants, the OH radical is produced in its ground electronic state OH (X 2 π) or in its first excited state OH (A 2 Σ + ). When the reactants are in their ground state, the reaction is endothermic in the conditions of the experiment (center of mass kinetic energy ≅ 0.12 eV). The following reactions have been obtained: O( 1 D) +H 2 (v=O) → OH (X 2 π) +H( 2 S) and O( 1 D) +H 2 (v≥5) → OH (A 2 Σ + ) +H( 2 S). The atomic oxygen is produced in its excited state O( 1 D) in a radio-frequency discharge which dissociates the molecular oxygen seeded in a carrier gas (He or Ar) and the hydrogen molecules are excited vibrationally by electron bombardment. The first reaction is studied by time-of-flight measurements. In this way, it has been possible to observe the different vibrational levels on which the OH radical is produced. The analysis of this vibrational distribution shows the competition between the abstraction and insertion-dissociation mechanisms. In the second reaction, the analysis of the spontaneous fluorescence of OH (A 2 Σ + ) reveals a very hot and non-Boltzmann rotational excitation. (author) [fr

  18. Electron Transfer Strategies Regulate Carbonate Mineral and Micropore Formation.

    Science.gov (United States)

    Zeng, Zhirui; Tice, Michael M

    2018-01-01

    Some microbial carbonates are robust biosignatures due to their distinct morphologies and compositions. However, whether carbonates induced by microbial iron reduction have such features is unknown. Iron-reducing bacteria use various strategies to transfer electrons to iron oxide minerals (e.g., membrane-bound enzymes, soluble electron shuttles, nanowires, as well as different mechanisms for moving over or attaching to mineral surfaces). This diversity has the potential to create mineral biosignatures through manipulating the microenvironments in which carbonate precipitation occurs. We used Shewanella oneidensis MR-1, Geothrix fermentans, and Geobacter metallireducens GS-15, representing three different strategies, to reduce solid ferric hydroxide in order to evaluate their influence on carbonate and micropore formation (micro-size porosity in mineral rocks). Our results indicate that electron transfer strategies determined the morphology (rhombohedral, spherical, or long-chained) of precipitated calcium-rich siderite by controlling the level of carbonate saturation and the location of carbonate formation. Remarkably, electron transfer strategies also produced distinctive cell-shaped micropores in both carbonate and hydroxide minerals, thus producing suites of features that could potentially serve as biosignatures recording information about the sizes, shapes, and physiologies of iron-reducing organisms. Key Words: Microbial iron reduction-Micropore-Electron transfer strategies-Microbial carbonate. Astrobiology 18, 28-36.

  19. Long-distance photoinitiated electron transfer through polyene molecular wires

    International Nuclear Information System (INIS)

    Wasielewski, M.R.; Johnson, D.G.; Svec, W.A.; Kersey, K.M.; Cragg, D.E.; Minsek, D.W.

    1989-01-01

    Long-chain polyenes can be used as molecular wires to facilitate electron transfer between a photo-excited donor and an acceptor in an artificial photosynthetic system. The authors present data here on two Zn-porphyrin-polyene-anthraquinone molecules possessing either 5 or 9 all trans double bonds between the donor and acceptor, 1 and 2. The center-to-center distances between the porphyrin and the quinone in these relatively rigid molecules are 25 angstrom for 1 and 35 angstrom for 2. Selective picosecond laser excitation of the Zn-porphyrin and 1 and 2 results in the very rapid transfer of an electron to the anthraquinone in <2 ps and 10 ps, respectively. The resultant radical ion pairs recombine with τ = 10 ps for 1 and τ = 25 ps for 2. The electron transfer rates remain remarkably rapid over these long distances. The involvement of polyene radical cations in the mechanism of the radical ion pair recombination reaction is clear from the transient absorption spectra of 1 and 2, which show strong absorbances in the near-infrared. The strong electronic coupling between the Zn-porphyrin n the anthraquinone provided by low-lying states of the polyene make it possible to transfer an electron rapidly over very long distances

  20. Numerical simulation of transient moisture transfer into an electronic enclosure

    International Nuclear Information System (INIS)

    Nasirabadi, P. Shojaee; Jabbari, M.; Hattel, J. H.

    2016-01-01

    Electronic systems are sometimes exposed to harsh environmental conditions of temperature and humidity. Moisture transfer into electronic enclosures and condensation can cause several problems such as corrosion and alteration in thermal stresses. It is therefore essential to study the local climate inside the enclosures to be able to protect the electronic systems. In this work, moisture transfer into a typical electronic enclosure is numerically studied using CFD. In order to reduce the CPU-time and make a way for subsequent factorial design analysis, a simplifying modification is applied in which the real 3D geometry is approximated by a 2D axial symmetry one. The results for 2D and 3D models were compared in order to calibrate the 2D representation. Furthermore, simulation results were compared with experimental data and good agreement was found.

  1. Numerical simulation of transient moisture transfer into an electronic enclosure

    Energy Technology Data Exchange (ETDEWEB)

    Nasirabadi, P. Shojaee; Jabbari, M.; Hattel, J. H. [Process Modelling Group, Department of Mechanical Engineering, Technical University of Denmark, Nils Koppels Allé, 2800 Kgs. Lyngby (Denmark)

    2016-06-08

    Electronic systems are sometimes exposed to harsh environmental conditions of temperature and humidity. Moisture transfer into electronic enclosures and condensation can cause several problems such as corrosion and alteration in thermal stresses. It is therefore essential to study the local climate inside the enclosures to be able to protect the electronic systems. In this work, moisture transfer into a typical electronic enclosure is numerically studied using CFD. In order to reduce the CPU-time and make a way for subsequent factorial design analysis, a simplifying modification is applied in which the real 3D geometry is approximated by a 2D axial symmetry one. The results for 2D and 3D models were compared in order to calibrate the 2D representation. Furthermore, simulation results were compared with experimental data and good agreement was found.

  2. Conduction mechanism studies on electron transfer of disordered system

    Institute of Scientific and Technical Information of China (English)

    徐慧; 宋祎璞; 李新梅

    2002-01-01

    Using the negative eigenvalue theory and the infinite order perturbation theory, a new method was developed to solve the eigenvectors of disordered systems. The result shows that eigenvectors change from the extended state to the localized state with the increase of the site points and the disordered degree of the system. When electric field is exerted, the electrons transfer from one localized state to another one. The conductivity is induced by the electron transfer. The authors derive the formula of electron conductivity and find the electron hops between localized states whose energies are close to each other, whereas localized positions differ from each other greatly. At low temperature the disordered system has the character of the negative differential dependence of resistivity and temperature.

  3. Inelastic electron photon scattering at moderate four momentum transfers

    International Nuclear Information System (INIS)

    Berger, C.; Genzel, H.; Grigull, R.; Lackas, W.; Raupach, F.; Klovning, A.; Lillestoel, E.; Skard, J.A.; Ackermann, H.; Buerger, J.

    1980-10-01

    We present new high statistics data on hadron production in photon photon reactions. The data are analyzed in terms of an electron photon scattering formalism. The dependence of the total cross section on Q 2 , the four momentum transfer squared of the scattered electron, and on the mass W of the hadronic system is investigated. The data are compared to predictions from Vector Dominance and the quark model. (orig.)

  4. Quality assurance and data collection -- Electronic Data Transfer

    International Nuclear Information System (INIS)

    Tomczak, L.M.; Lohner, W.G.; Ray, E.C.; Salesky, J.A.; Spitz, H.B.

    1993-05-01

    The Radiological Environmental Monitoring (REM) group at the Fernald Environmental Management Project is involved in an Electronic Data Transfer practice that will result in the improved quality assurance of collected data. This practice focuses on electronic data transfer from the recording instrument to reduce the manpower normally required for manual data entry and improve the quality of the data transferred. The application of this practice can enhance any data collection program where instruments with electronic memories and a signal output are utilized. Organizations employing this practice can strengthen the quality and efficiency of their data collection program. The use of these practices can assist in complying with Quality Assurance requirements under ASME NQA-1, RCRA, CERCLA, and DOE Order activities. Data from Pylon AB-5 instrumentation is typically configured to print data to a tape. The REM group has developed a process to electronically transfer stored data. The data are sent from the Pylon AB-5 field instrument to a HewlettPackard portable hand computer, model HP95LX. Data are recorded and stored on a 128 K-byte RAN card and later transferred to a PC database as an electronic file for analysis. The advantage of this system is twofold: (1) Data entry errors are eliminated and (2) considerable data collection and entry time is eliminated. Checks can then be conducted for data validity between recorded intervals due to light leaks etc. and the detection of outliers. This paper will discuss the interface and connector components that allow this transfer of data from the Pylon to the PC to take place and the process to perform that activity

  5. Excited states of ReO4-: A comprehensive time-dependent relativistic density functional theory study

    Science.gov (United States)

    Xu, Wenhua; Ma, Jianyi; Peng, Daoling; Zou, Wenli; Liu, Wenjian; Staemmler, Volker

    2009-02-01

    The perrhenate anion, ReO4-, is taken as a showcase of heavy transition metal complexes, to examine the performance of time-dependent relativistic density functional linear response theory for electronic excitations, which is based on a newly proposed exact two-component Hamiltonian resulting from the symmetrized elimination of the small component. In total 30 scalar and 63 spinor excited states are investigated and the results are grossly in good agreement with those by the singles and doubles coupled-cluster linear response theory. It is found that only a few scalar states of 3T1 and 3T2 symmetries are split significantly by the spin-orbit coupling, whereas only those excited states involving the Rydberg-type virtual orbital are affected by the solvent effects. The nature of the optical absorption spectra is also highlighted.

  6. Excited states of ReO4-: A comprehensive time-dependent relativistic density functional theory study

    International Nuclear Information System (INIS)

    Xu Wenhua; Ma Jianyi; Peng Daoling; Zou Wenli; Liu Wenjian; Staemmler, Volker

    2009-01-01

    The perrhenate anion, ReO 4 - , is taken as a showcase of heavy transition metal complexes, to examine the performance of time-dependent relativistic density functional linear response theory for electronic excitations, which is based on a newly proposed exact two-component Hamiltonian resulting from the symmetrized elimination of the small component. In total 30 scalar and 63 spinor excited states are investigated and the results are grossly in good agreement with those by the singles and doubles coupled-cluster linear response theory. It is found that only a few scalar states of 3 T 1 and 3 T 2 symmetries are split significantly by the spin-orbit coupling, whereas only those excited states involving the Rydberg-type virtual orbital are affected by the solvent effects. The nature of the optical absorption spectra is also highlighted

  7. Jahn-Teller distortion in the phosphorescent excited state of three-coordinate Au(I) phosphine complexes.

    Science.gov (United States)

    Barakat, Khaldoon A; Cundari, Thomas R; Omary, Mohammad A

    2003-11-26

    DFT calculations were used to optimize the phosphorescent excited state of three-coordinate [Au(PR3)3]+ complexes. The results indicate that the complexes rearrange from their singlet ground-state trigonal planar geometry to a T-shape in the lowest triplet luminescent excited state. The optimized structure of the exciton contradicts the structure predicted based on the AuP bonding properties of the ground-state HOMO and LUMO. The rearrangement to T-shape is a Jahn-Teller distortion because an electron is taken from the degenerate e' (5dxy, 5dx2-y2) orbital upon photoexcitation of the ground-state D3h complex. The calculated UV absorption and visible emission energies are consistent with the experimental data and explain the large Stokes' shifts while such correlations are not possible in optimized models that constrained the exciton to the ground-state trigonal geometry.

  8. Dielectronic recombination rate coefficients to the excited states of CI from CII

    International Nuclear Information System (INIS)

    Dubau, J.; Kato, T.; Safronova, U.I.

    1998-01-01

    The dielectronic recombination rate coefficients to the excited states for n=2-6 are calculated including 1s 2 2l 1 2l 2 2l 3 nl (n=2-6, l≤(n-1)) states. The values for the excited states higher than n=6 are extrapolated and the total dielectronic recombination rate coefficients are derived. The rate coefficients to the excited states are fitted to an analytical formula and the fit parameters are given. (author)

  9. Examination of excited state populations in sputtering using Multiphoton Resonance Ionization

    International Nuclear Information System (INIS)

    Kimock, F.M.; Baxter, J.P.; Pappas, D.L.; Kobrin, P.H.; Winograd, N.

    1984-01-01

    Multiphoton Resonance Ionization has been employed to study the populations of excited state atoms ejected from ion bombarded metal surfaces. Preliminary investigations have focused on three model systems: aluminum, indium and cobalt. In this paper the authors examine the effect of primary ion energy (2 to 12 keV Ar + ) on excited state yields for these three systems. The influence of the sample matrix on excited state populations of sputtered atoms is also discussed

  10. Examination of excited state populations in sputtering using multiphoton resonance ionization

    International Nuclear Information System (INIS)

    Kimock, F.M.; Baxter, J.P.; Pappas, D.L.; Kobrin, P.H.; Winograd, N.

    1984-01-01

    Multiphoton Resonance Ionization has been employed to study the populations of excited state atoms ejected from ion bombarded metal surfaces. Preliminary investigations have focused on three model systems: aluminum, indium and cobalt. In this paper we examine the effect of primary ion energy (2 to 12 keV Ar + ) on excited state yields for these three systems. The influence of the sample matrix on excited state populations of sputtered atoms is also discussed. 8 refs., 4 figs

  11. Spectral properties of chlorines and electron transfer with their participation in the photosynthetic reaction center of photosystem II

    Science.gov (United States)

    Shchupak, E. E.; Ivashin, N. V.

    2014-02-01

    Structural factors that provide localization of excited states and determine the properties of primary donor and acceptor of electron in the reaction center of photosystem II (PSII RC) are studied. The results of calculations using stationary and time-dependent density functional theory indicate an important role of protein environments of chlorophylls PA, PB, BA, and BB and pheophytins HA and HB in the area with a radius of no greater than ≤10 Å in the formation of excitonic states of PSII RC. When the neighboring elements are taken into account, the wavelength of long-wavelength Q y transition of chlorophyll molecules is varied by about 10 nm. The effect is less developed for pheophytin molecules (Δλ ≅ 2 nm). The following elements strongly affect energy of the transition: HisA198 and HisD197 amino-acid residues that serve as ligands of magnesium atoms affect PA and PB, respectively; MetA183 affects PA; MetA172 and MetD198 affect BA; water molecules that are located above the planes of the BA and BB macrocycles form H bonds with carbonyl groups; and phytol chains of PA and PB affect BA, BB, HA, and HB. The analysis of excitonic states, mutual positions of molecular orbitals of electron donors and acceptors, and matrix elements of electron transfer reaction shows that (i) charge separation between BA and HA and PB and BA is possible in the active A branch of cofactors of PSII RC and (ii) electron transfer is blocked at the BB - HB fragment in inactive B branch of PSII RC.

  12. Hybrid lead halide perovskites for light energy conversion: Excited state properties and photovoltaic applications

    Science.gov (United States)

    Manser, Joseph S.

    The burgeoning class of metal halide perovskites constitutes a paradigm shift in the study and application of solution-processed semiconductors. Advancements in thin film processing and our understanding of the underlying structural, photophysical, and electronic properties of these materials over the past five years have led to development of perovskite solar cells with power conversion efficiencies that rival much more mature first and second-generation commercial technologies. It seems only a matter of time before the real-world impact of these compounds is put to the test. Like oxide perovskites, metal halide perovskites have ABX3 stoichiometry, where typically A is a monovalent cation, B a bivalent post-transition metal, and X a halide anion. Characterizing the behavior of photogenerated charges in metal halide perovskites is integral for understanding the operating principles and fundamental limitations of perovskite optoelectronics. The majority of studies outlined in this dissertation involve fundamental study of the prototypical organic-inorganic compound methylammonium lead iodide (CH3NH3PbI 3). Time-resolved pump-probe spectroscopy serves as a principle tool in these investigations. Excitation of a semiconductor can lead to formation of a number different excited state species and electronic complexes. Through analysis of excited state decay kinetics and optical nonlinearities in perovskite thin films, we identify spontaneous formation of a large fraction of free electrons and holes, whose presence is requisite for efficient photovoltaic operation. Following photogeneration of charge carriers in a semiconductor absorber, these species must travel large distances across the thickness of the material to realize large external quantum efficiencies and efficient carrier extraction. Using a powerful technique known as transient absorption microscopy, we directly image long-range carrier diffusion in a CH3NH3PbI 3 thin film. Charges are unambiguously shown to

  13. Analysis of correlation effects in autoionizing doubly excited states of barium using Coulomb Green's function

    International Nuclear Information System (INIS)

    Poirier, M.

    1997-01-01

    Though one would expect that large-angular momentum doubly excited states exhibit weak electronic correlations, it is shown in this paper that a first-order perturbation theory ignoring such correlations may completely fail in predicting correct autoionization probabilities: quadrupolar transitions are poorly described by lowest-order perturbation theory, except for very large angular momenta. Inclusion of second-order dipole-dipole term considerably improves the accuracy of the method. This effect is computed using Coulomb Green's function in its analytical form, probably applied here for the first time to autoionization processes. Examples are given in barium for 5d j 5g [k[ states (j=3/2, 5/2) and for 5d 5/2 nl [k[ states with l > 4. (orig.)

  14. Electronic Coupling Dependence of Ultrafast Interfacial Electron Transfer on Nanocrystalline Thin Films and Single Crystal

    Energy Technology Data Exchange (ETDEWEB)

    Lian, Tianquan

    2014-04-22

    The long-term goal of the proposed research is to understand electron transfer dynamics in nanoparticle/liquid interface. This knowledge is essential to many semiconductor nanoparticle based devices, including photocatalytic waste degradation and dye sensitized solar cells.

  15. Electron transfer from nucleobase electron adducts to 5-bromouracil. Is guanine an ultimate sink for the electron in irradiated DNA?

    International Nuclear Information System (INIS)

    Nese, C.; Yuan, Z.; Schuchmann, M.N.; Sonntag, C. von

    1992-01-01

    Electron transfer to 5-bromouracil (5-BrU) from nucleobase (N) electron adducts (and their protonated forms) has been studied by product analysis and pulse radiolysis. When an electron is transferred to 5-BrU, the ensuing 5-BrU radical anion rapidly loses a bromide ion; the uracilyl radical thus formed reacts with added t-butanol, yielding uracil. From the uracil yields measured as the function of [N]/[5-BrU] after γ-radiolysis of Ar-saturated solutions it is concluded that thymine and adenine electron adducts and their heteroatom-protonated forms transfer electrons quantitatively to 5-BrU. The data raise the question whether in DNA the guanine moiety may act as the ultimate sink of the electron in competition with other processes such as protonation at C(6) of the thymine electron adduct. (Author)

  16. Synthesis and photoinduced electron transfer in platinum(II) bis(N-(4-ethynylphenyl)carbazole)bipyridine fullerene complexes.

    Science.gov (United States)

    Lee, Sai-Ho; Chan, Chris Tsz-Leung; Wong, Keith Man-Chung; Lam, Wai Han; Kwok, Wai-Ming; Yam, Vivian Wing-Wah

    2014-12-21

    Platinum(ii) bis(N-(4-ethynylphenyl)carbazole)bipyridine fullerene complexes, (Cbz)2-Pt(bpy)-C60 and ((t)BuCbz)2-Pt(bpy)-C60, were synthesized. Their photophysical properties were studied by electronic absorption and emission spectroscopy and the origin of the transitions was supported by computational studies. The electrochemical properties were also studied and the free energies for charge-separation and charge-recombination processes were evaluated. The photoinduced electron transfer reactions in the triads were investigated by femtosecond and nanosecond transient absorption spectroscopy. In dichloromethane, both triads undergo ultrafast charge separation from the (3)MLCT/LLCT excited state within 300 fs to yield their respective triplet charge-separated (CS) states, namely (Cbz)2˙(+)-Pt(bpy)-C60˙(-) and ((t)BuCbz)2˙(+)-Pt(bpy)-C60˙(-), and the CS states would undergo charge recombination to give the (3)C60* state, which subsequently decays to the ground state in 22-28 μs.

  17. Combining UV photodissociation with electron transfer for peptide structure analysis

    Czech Academy of Sciences Publication Activity Database

    Shaffer, C. J.; Marek, Aleš; Pepin, R.; Slováková, K.; Tureček, F.

    2015-01-01

    Roč. 50, č. 3 (2015), s. 470-475 ISSN 1076-5174 Institutional support: RVO:61388963 Keywords : electron transfer dissociation * laser photodissociation * peptide ions * cation radical * chromophores * isomer distinction Subject RIV: CE - Biochemistry Impact factor: 2.541, year: 2015

  18. Electron Transfer in Chemistry and Biology - The Primary Events in ...

    Indian Academy of Sciences (India)

    transfers, occurs in a cascade in many biological processes, including photosynthesis. ... the model reactions of photosynthetic ... biological relevance. GENERAL I ARTICLE of electrons, respectively. This has entirely changed the earlier framework of interpreting reactions in chemistry and biology. This shift in emphasis ...

  19. Electron Transfer in Chemistry and Biology – The Primary Events

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 2; Issue 12. Electron Transfer in Chemistry and Biology – The Primary Events in Photosynthesis. V Krishnan. General Article Volume 2 Issue 12 December 1997 pp 77-86. Fulltext. Click here to view fulltext PDF. Permanent link:

  20. Adsorption and Interfacial Electron Transfer of Saccharomyces Cerevisiae

    DEFF Research Database (Denmark)

    Hansen, Allan Glargaard; Boisen, Anja; Nielsen, Jens Ulrik

    2003-01-01

    We have studied the adsorption and electron-transfer dynamics of Saccharomyces cerevisiae (yeast) iso-l-cytochrome c adsorbed on Au(lll) electrodes in aqueous phosphate buffer media. This cytochrome possesses a thiol group dos e to the protein surface (Cysl02) suitable for linking the protein...