WorldWideScience

Sample records for singlet excitation transfer

  1. 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.

  2. Photo-excitation of carotenoids causes cytotoxicity via singlet oxygen production

    International Nuclear Information System (INIS)

    Yoshii, Hiroshi; Yoshii, Yukie; Asai, Tatsuya; Furukawa, Takako; Takaichi, Shinichi; Fujibayashi, Yasuhisa

    2012-01-01

    Highlights: ► Some photo-excited carotenoids have photosensitizing ability. ► They are able to produce ROS. ► Photo-excited fucoxanthin can produce singlet oxygen through energy transfer. -- Abstract: Carotenoids, natural pigments widely distributed in algae and plants, have a conjugated double bond system. Their excitation energies are correlated with conjugation length. We hypothesized that carotenoids whose energy states are above the singlet excited state of oxygen (singlet oxygen) would possess photosensitizing properties. Here, we demonstrated that human skin melanoma (A375) cells are damaged through the photo-excitation of several carotenoids (neoxanthin, fucoxanthin and siphonaxanthin). In contrast, photo-excitation of carotenoids that possess energy states below that of singlet oxygen, such as β-carotene, lutein, loroxanthin and violaxanthin, did not enhance cell death. Production of reactive oxygen species (ROS) by photo-excited fucoxanthin or neoxanthin was confirmed using a reporter assay for ROS production with HeLa Hyper cells, which express a fluorescent indicator protein for intracellular ROS. Fucoxanthin and neoxanthin also showed high cellular penetration and retention. Electron spin resonance spectra using 2,2,6,6-tetramethil-4-piperidone as a singlet oxygen trapping agent demonstrated that singlet oxygen was produced via energy transfer from photo-excited fucoxanthin to oxygen molecules. These results suggest that carotenoids such as fucoxanthin, which are capable of singlet oxygen production through photo-excitation and show good penetration and retention in target cells, are useful as photosensitizers in photodynamic therapy for skin disease.

  3. Study of photo-activated electron transfer reactions in the first excited singlet state by picosecond and nanosecond laser spectroscopy

    International Nuclear Information System (INIS)

    Doizi, Denis

    1983-01-01

    Picosecond laser spectroscopy has been used to study two photo-activated electron transfer reactions: - a bimolecular electron transfer reaction between a sensitizer, DODCI, and an electron acceptor, methylviologen. The two radical ions created with an electron transfer efficiency γ ≅ 0.07 have been identified in picosecond and nanosecond laser absorption spectroscopy by adding selective solutes such as para-benzoquinone (an electron acceptor) or L(+) ascorbic acid (an electron donor). - an intramolecular electron transfer reaction in a triad molecule consisting of a tetra-aryl-porphyrin covalently linked to both a carotenoid and a quinone. The photoinduced charge separation occurs within 30 ps and leads, with a yield of 25 pc, to the formation of a zwitterion whose half-life is 2.5 μs. The experimental results obtained in these two studies show an effective decrease in the recombination rate of the two radical ions created in the encounter pair. (author) [fr

  4. 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.

  5. Photo-excitation of carotenoids causes cytotoxicity via singlet oxygen production

    Energy Technology Data Exchange (ETDEWEB)

    Yoshii, Hiroshi, E-mail: yoshii@nirs.go.jp [Research Center for Radiation Emergency Medicine, National Institute of Radiological Science, Chiba 263-8555 (Japan); Faculty of Medical Sciences, University of Fukui, Eiheiji, Fukui 910-1193 (Japan); Yoshii, Yukie, E-mail: yukiey@nirs.go.jp [Molecular Imaging Center, National Institute of Radiological Science, Chiba 263-8555 (Japan); Biomedical Imaging Research Center, University of Fukui, Eiheiji, Fukui 910-1193 (Japan); Asai, Tatsuya [Biomedical Imaging Research Center, University of Fukui, Eiheiji, Fukui 910-1193 (Japan); Faculty of Engineering, University of Fukui, Fukui 910-8507 (Japan); Furukawa, Takako [Molecular Imaging Center, National Institute of Radiological Science, Chiba 263-8555 (Japan); Biomedical Imaging Research Center, University of Fukui, Eiheiji, Fukui 910-1193 (Japan); Takaichi, Shinichi [Department of Biology, Nippon Medical School, Kawasaki, Kanagawa 211-0063 (Japan); Fujibayashi, Yasuhisa [Molecular Imaging Center, National Institute of Radiological Science, Chiba 263-8555 (Japan); Biomedical Imaging Research Center, University of Fukui, Eiheiji, Fukui 910-1193 (Japan)

    2012-01-06

    Highlights: Black-Right-Pointing-Pointer Some photo-excited carotenoids have photosensitizing ability. Black-Right-Pointing-Pointer They are able to produce ROS. Black-Right-Pointing-Pointer Photo-excited fucoxanthin can produce singlet oxygen through energy transfer. -- Abstract: Carotenoids, natural pigments widely distributed in algae and plants, have a conjugated double bond system. Their excitation energies are correlated with conjugation length. We hypothesized that carotenoids whose energy states are above the singlet excited state of oxygen (singlet oxygen) would possess photosensitizing properties. Here, we demonstrated that human skin melanoma (A375) cells are damaged through the photo-excitation of several carotenoids (neoxanthin, fucoxanthin and siphonaxanthin). In contrast, photo-excitation of carotenoids that possess energy states below that of singlet oxygen, such as {beta}-carotene, lutein, loroxanthin and violaxanthin, did not enhance cell death. Production of reactive oxygen species (ROS) by photo-excited fucoxanthin or neoxanthin was confirmed using a reporter assay for ROS production with HeLa Hyper cells, which express a fluorescent indicator protein for intracellular ROS. Fucoxanthin and neoxanthin also showed high cellular penetration and retention. Electron spin resonance spectra using 2,2,6,6-tetramethil-4-piperidone as a singlet oxygen trapping agent demonstrated that singlet oxygen was produced via energy transfer from photo-excited fucoxanthin to oxygen molecules. These results suggest that carotenoids such as fucoxanthin, which are capable of singlet oxygen production through photo-excitation and show good penetration and retention in target cells, are useful as photosensitizers in photodynamic therapy for skin disease.

  6. Delayed fluorescence from upper excited singlet states of aromatic ketones

    International Nuclear Information System (INIS)

    Nickel, B.; Roden, G.

    1980-01-01

    With liquid solutions of the aromatic ketones anthraquinone and xanthone, a P-type delayed fluorescence from upper excited singlet states, resulting from triplet-triplet annihilation, has been observed. Some peculiarities of the triplet-triplet annihilation of aromatic ketones are discussed. (orig.)

  7. Nature of the singlet and triplet excitations mediating thermally activated delayed fluorescence

    Science.gov (United States)

    Olivier, Y.; Yurash, B.; Muccioli, L.; D'Avino, G.; Mikhnenko, O.; Sancho-García, J. C.; Adachi, C.; Nguyen, T.-Q.; Beljonne, D.

    2017-12-01

    Despite significant efforts, a complete mechanistic understanding of thermally activated delayed fluorescence (TADF) materials has not yet been fully uncovered. Part of the complexity arises from the apparent dichotomy between the need for close energy resonance and for a significant spin-orbit coupling between alike charge-transfer singlet and triplet excitations. Here we show, in the case of reference carbazole derivatives, that this dichotomy can be resolved in a fully atomistic model accounting for thermal fluctuations of the molecular conformations and microscopic electronic polarization effects in amorphous films. These effects yield electronic excitations with a dynamically mixed charge-transfer and localized character, resulting in thermally averaged singlet-triplet energy differences and interconversion rates in excellent agreement with careful spectroscopic studies.

  8. Influence of an intermolecular charge-transfer state on excited-state relaxation dynamics: solvent effect on the methylnaphthalene-oxygen system and its significance for singlet oxygen production.

    Science.gov (United States)

    Jensen, Poul-Gudmund; Arnbjerg, Jacob; Tolbod, Lars Poulsen; Toftegaard, Rasmus; Ogilby, Peter R

    2009-09-17

    The extent to which an intermolecular charge-transfer (CT) state can influence excited-state relaxation dynamics is examined for the system wherein 1-methylnaphthalene (MN) interacts with molecular oxygen. The MN-O2 system is ideally suited for such a study because excited states can be independently accessed by (i) irradiation into the discrete MN-O2 CT absorption band, (ii) direct irradiation of MN, and (iii) the photosensitized production of triplet state MN. Changing the solvent in which the MN-O2 system is dissolved influences the MN-dependent photoinduced production of singlet oxygen, O2(a1Delta(g)), which, in turn, yields information about fundamental concepts of state mixing. Results of experiments conducted in the polar solvent acetonitrile differ substantially from those obtained from the nonpolar solvent cyclohexane. The data reflect differences in the energy and behavior of the solvent-equilibrated MN-O2 CT state, CT(SE), and the extent to which this state couples to other states of the MN-O2 system. In particular, the data are consistent with a model where both the MN triplet state and the MN-O2 CT(SE) state are immediate precursors of O2(a1Delta(g)). Although the work reported herein is of direct and practical significance for the wide variety of systems in which O2(a1Delta(g)) can be produced upon irradiation, it also serves as an accessible model for a study of general issues pertinent to state mixing and the solvent-dependent dynamics of CT-mediated excited-state relaxation.

  9. Photophysics of trioxatriangulenium ion. Electrophilic reactivity in the ground state and excited singlet state

    DEFF Research Database (Denmark)

    Reynisson, J.; Wilbrandt, R.; Brinck, V.

    2002-01-01

    . The physical and chemical properties of the excited singlet state of the trioxatriangulenium (TOTA(+)) carbenium ion are investigated by experimental and Computational means. The degeneracy of the lowest excited states is counteracted by Jahn-Teller-type distortion, which leads to vibronic broadening...... of the long wavelength absorption band. A strong fluorescence is observed at 520 nm (tau(n) = 14.6 ns, phi(n) = 0.12 in deaerated acetonitrile). The fluorescence is quenched by 10 aromatic electron donors predominantly via a dynamic charge transfer mechanism, but ground state complexation is shown...... triphenylenes is studied separately. Phosphorescence spectra, triplet lifetimes, and triplet-triplet absorption spectra are provided. In the discussion, TOTA(+) is compared to the unsubstituted xanthenium ion and its 9-phenyl derivative with respect to the excited state properties....

  10. Is π-Stacking Prone To Accelerate Singlet-Singlet Energy Transfers?

    Science.gov (United States)

    Gao, Di; Aly, Shawkat M; Karsenti, Paul-Ludovic; Harvey, Pierre D

    2018-03-23

    π-Stacking is the most common structural feature that dictates the optical and electronic properties of chromophores in the solid state. Herein, a unidirectional singlet-singlet energy-transfer dyad has been designed to test the effect of π-stacking of zinc(II) porphyrin, [Zn 2 ], as a slipped dimer acceptor using a BODIPY unit, [bod], as the donor, bridged by the linker C 6 H 4 C≡CC 6 H 4 . The rate of singlet energy transfer, k ET (S 1 ), at 298 K ( k ET (S 1 ) = 4.5 × 10 10 s -1 ) extracted through the change in fluorescence lifetime, τ F , of [bod] in the presence (27.1 ps) and the absence of [Zn 2 ] (4.61 ns) from Streak camera measurements, and the rise time of the acceptor signal in femtosecond transient absorption spectra (22.0 ps), is faster than most literature cases where no π-stacking effect exists (i.e., monoporphyrin units). At 77 K, the τ F of [bod] increases to 45.3 ps, indicating that k ET (S 1 ) decreases by 2-fold (2.2 × 10 10 s -1 ), a value similar to most values reported in the literature, thus suggesting that the higher value at 298 K is thermally promoted at a higher temperature.

  11. Singlet-triplet splittings from the virial theorem and single-particle excitation energies

    Science.gov (United States)

    Becke, Axel D.

    2018-01-01

    The zeroth-order (uncorrelated) singlet-triplet energy difference in single-particle excited configurations is 2Kif, where Kif is the Coulomb self-energy of the product of the transition orbitals. Here we present a non-empirical, virial-theorem argument that the correlated singlet-triplet energy difference should be half of this, namely, Kif. This incredibly simple result gives vertical HOMO-LUMO excitation energies in small-molecule benchmarks as good as the popular TD-B3LYP time-dependent approach to excited states. For linear acenes and nonlinear polycyclic aromatic hydrocarbons, the performance is significantly better than TD-B3LYP. In addition to the virial theorem, the derivation borrows intuitive pair-density concepts from density-functional theory.

  12. Singlet and Triplet Excitation Management in a Bichromophoric Near-Infrared-Phosphorescent BODIPY-Benzoporphyrin Platinum Complex

    KAUST Repository

    Whited, Matthew T.

    2011-01-12

    Multichromophoric arrays provide one strategy for assembling molecules with intense absorptions across the visible spectrum but are generally focused on systems that efficiently produce and manipulate singlet excitations and therefore are burdened by the restrictions of (a) unidirectional energy transfer and (b) limited tunability of the lowest molecular excited state. In contrast, we present here a multichromophoric array based on four boron dipyrrins (BODIPY) bound to a platinum benzoporphyrin scaffold that exhibits intense panchromatic absorption and efficiently generates triplets. The spectral complementarity of the BODIPY and porphryin units allows the direct observation of fast bidirectional singlet and triplet energy transfer processes (k ST(1BDP→1Por) = 7.8×1011 s-1, kTT(3Por→3BDP) = 1.0×1010 s-1, kTT(3BDP→ 3Por) = 1.6×1010 s-1), leading to a long-lived equilibrated [3BDP][Por]=[BDP][3Por] state. This equilibrated state contains approximately isoenergetic porphyrin and BODIPY triplets and exhibits efficient near-infrared phosphorescence (λem = 772 nm, φ = 0.26). Taken together, these studies show that appropriately designed triplet-utilizing arrays may overcome fundamental limitations typically associated with core-shell chromophores by tunable redistribution of energy from the core back onto the antennae. © 2010 American Chemical Society.

  13. Theoretical rationalization of the singlet-triplet gap in OLEDs materials: impact of charge-transfer character.

    Science.gov (United States)

    Moral, M; Muccioli, L; Son, W-J; Olivier, Y; Sancho-García, J C

    2015-01-13

    New materials for OLED applications with low singlet-triplet energy splitting have been recently synthesized in order to allow for the conversion of triplet into singlet excitons (emitting light) via a Thermally Activated Delayed Fluorescence (TADF) process, which involves excited-states with a non-negligible amount of Charge-Transfer (CT). The accurate modeling of these states with Time-Dependent Density Functional Theory (TD-DFT), the most used method so far because of the favorable trade-off between accuracy and computational cost, is however particularly challenging. We carefully address this issue here by considering materials with small (high) singlet-triplet gap acting as emitter (host) in OLEDs and by comparing the accuracy of TD-DFT and the corresponding Tamm-Dancoff Approximation (TDA), which is found to greatly reduce error bars with respect to experiments thanks to better estimates for the lowest singlet-triplet transition. Finally, we quantitatively correlate the singlet-triplet splitting values with the extent of CT, using for it a simple metric extracted from calculations with double-hybrid functionals, that might be applied in further molecular engineering studies.

  14. Intermolecular Singlet and Triplet Exciton Transfer Integrals from Many-Body Green's Functions Theory.

    Science.gov (United States)

    Wehner, Jens; Baumeier, Björn

    2017-04-11

    A general approach to determine orientation and distance-dependent effective intermolecular exciton transfer integrals from many-body Green's functions theory is presented. On the basis of the GW approximation and the Bethe-Salpeter equation (BSE), a projection technique is employed to obtain the excitonic coupling by forming the expectation value of a supramolecular BSE Hamiltonian with electron-hole wave functions for excitations localized on two separated chromophores. Within this approach, accounting for the effects of coupling mediated by intermolecular charge transfer (CT) excitations is possible via perturbation theory or a reduction technique. Application to model configurations of pyrene dimers shows an accurate description of short-range exchange and long-range Coulomb interactions for the coupling of singlet and triplet excitons. Computational parameters, such as the choice of the exchange-correlation functional in the density-functional theory (DFT) calculations that underly the GW-BSE steps and the convergence with the number of included CT excitations, are scrutinized. Finally, an optimal strategy is derived for simulations of full large-scale morphologies by benchmarking various approximations using pairs of dicyanovinyl end-capped oligothiophenes (DCV5T), which are used as donor material in state-of-the-art organic solar cells.

  15. Efficient singlet-singlet energy transfer in a novel host-guest assembly composed of an organic cavitand, aromatic molecules, and a clay nanosheet.

    Science.gov (United States)

    Ishida, Yohei; Kulasekharan, Revathy; Shimada, Tetsuya; Takagi, Shinsuke; Ramamurthy, V

    2013-02-12

    A supramolecular host-guest assembly composed of a cationic organic cavitand (host), neutral aromatic molecules (guests), and an anionic clay nanosheet has been prepared and demonstrated that in this arrangement efficient singlet-singlet energy transfer could take place. The novelty of this system is the use of a cationic organic cavitand that enabled neutral organic molecules to be placed on an anionic saponite nanosheet. Efficient singlet-singlet energy transfer between neutral pyrene and 2-acetylanthracene enclosed within a cationic organic cavitand (octa amine) arranged on a saponite nanosheet was demonstrated through steady-state and time-resolved emission studies. The high efficiency was realized from the suppression of aggregation, segregation, and self-fluorescence quenching. We believe that the studies presented here using a novel supramolecular assembly have expanded the types of molecules that could serve as candidates for efficient energy-transfer systems, such as in an artificial light-harvesting system.

  16. Vibrational dynamics of aniline (N2)1 clusters in their first excited singlet state

    Science.gov (United States)

    Hineman, M. F.; Kim, S. K.; Bernstein, E. R.; Kelley, D. F.

    1992-04-01

    The first excited singlet state S1 vibrational dynamics of aniline(N2)1 clusters are studied and compared to previous results on aniline(CH4)1 and aniline(Ar)1. Intramolecular vibrational energy redistribution (IVR) and vibrational predissociation (VP) rates fall between the two extremes of the CH4 (fast IVR, slow VP) and Ar (slow IVR, fast VP) cluster results as is predicted by a serial IVR/VP model using Fermi's golden rule to describe IVR processes and a restricted Rice-Ramsperger-Kassel-Marcus (RRKM) theory to describe unimolecular VP rates. The density of states is the most important factor determining the rates. Two product states, 00 and 10b1, of bare aniline and one intermediate state ˜(00) in the overall IVR/VP process are observed and time resolved measurements are obtained for the 000 and ˜(000) transitions. The results are modeled with the serial mechanism described above.

  17. Energy transfer within Zn-porphyrin dendrimers: Study of the singlet-singlet annihilation kinetics

    Czech Academy of Sciences Publication Activity Database

    Larsen, J.; Brüggemann, B.; Polívka, Tomáš; Sundström, V.; Akesson, E.; Sly, J.; Crossley, M.J.

    2005-01-01

    Roč. 109, č. 47 (2005), s. 10654-10662 ISSN 1089-5639 Institutional research plan: CEZ:AV0Z50510513 Keywords : Energy transfer * Zn-porphyrin Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.898, year: 2005

  18. 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 unusually large fluorescence Stokes shift of 10500 cm−1. The emission appears as a broad band with a maximum at 17500 cm−1 and is characterized by a low and nearly temperature-independent quantum yield. The results are interpreted as an indication of a large equilibrium geometry change upon excitation...

  19. Enhanced red emission of 808 nm excited upconversion nanoparticles by optimizing the composition of shell for efficient generation of singlet oxygen

    Science.gov (United States)

    Liu, Jinxue; Zhang, Tingbin; Song, Xiaoyan; Xing, Jinfeng

    2018-01-01

    With the aim to enhance the upconversion luminescence (UCL) intensity, much attention was paid to reduce the energy-back transfer from Er3+ ions to Nd3+ ions by constructing various kinds of multilayer upconversion nanoparticles (UCNPs). However, the energy-back transfer was difficult to be completely eliminated. Also, the thick shell of multilayer UCNPs is not favourable for effective Förster resonance energy transfer (FRET) in photodynamic therapy (PDT) system. Herein, an effective and facile method was applied to prepare UCNPs by optimizing the composition to largely enhance the red emission (at 660 nm) for efficient generation of singlet oxygen (1O2). In detail, the concentrations of Nd3+ ions and Yb3+ ions doped in the sensitizing shell were systematically researched to balance the energy back-transfer and the light harvest ability. The optimal emission and a relatively high Red/Green (R/G) ratio of NaYF4:Yb,Er,Nd@NaYF4:Yb0.1Nd0.2 UCNPs were obtained simultaneously. Furthermore, the emission under 980 nm excitation demonstrated the energy back-transfer from Er3+ to Yb3+ ions was also notable which was largely ignored previously. Then, UCNPs were encapsulated into mesoporous silica shell, and the photosensitizer Chlorin e6 (Ce6) was covalently conjugated to form a non-leaking nanoplatform. The efficiency of 1O2 generation obviously increased with the enhanced emission of UCNPs.

  20. Energy traps of excited energy transfer processes in polymer solids

    International Nuclear Information System (INIS)

    Masahide Yamamoto; Kenji Hisada; Shinzaburo Ito

    1999-01-01

    In this report, the singlet and triplet exciton behaviors of the polymers containing carbazole (Cz) or phenanthrene (Ph) chromophores as the side group were studied in the solid state. The role of electronic energy traps in energy transfer process will be discussed and controlling factors of energy transfer processes will be given

  1. Absence of Intramolecular Singlet Fission in Pentacene-Perylenediimide Heterodimers: The Role of Charge Transfer State.

    Science.gov (United States)

    Wang, Long; Wu, Yishi; Chen, Jianwei; Wang, Lanfen; Liu, Yanping; Yu, Zhenyi; Yao, Jiannian; Fu, Hongbing

    2017-11-16

    A new class of donor-acceptor heterodimers based on two singlet fission (SF)-active chromophores, i.e., pentacene (Pc) and perylenediimide (PDI), was developed to investigate the role of charge transfer (CT) state on the excitonic dynamics. The CT state is efficiently generated upon photoexcitation. However, the resulting CT state decays to different energy states depending on the energy levels of the CT state. It undergoes extremely rapid deactivation to the ground state in polar CH 2 Cl 2 , whereas it undergoes transformation to a Pc triplet in nonpolar toluene. The efficient triplet generation in toluene is not due to SF but CT-mediated intersystem crossing. In light of the energy landscape, it is suggested that the deep energy level of the CT state relative to that of the triplet pair state makes the CT state actually serve as a trap state that cannot undergoes an intramolecular singlet fission process. These results provide guidance for the design of SF materials and highlight the requisite for more widely applicable design principles.

  2. 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 *.

  3. Singlet oxygen generation in O2 flow excited by RF discharge: I. Homogeneous discharge mode: α-mode

    International Nuclear Information System (INIS)

    Braginskiy, O V; Vasilieva, A N; Klopovskiy, K S; Kovalev, A S; Lopaev, D V; Proshina, O V; Rakhimova, T V; Rakhimov, A T

    2005-01-01

    The production and transport dynamics of O 2 (a 1 Δ g ) and O 2 (b 1 Σ g + ) molecules as well as O( 3 P) atoms has been studied in an O 2 flow excited by a 13.56 MHz RF discharge in a quartz tube at pressures of 1-20 Torr. It has been shown that the densities of O 2 (a 1 Δ g ) and O( 3 P) are saturated with increasing energy input into the discharge. The maximum yield of singlet oxygen (SO) and the O 2 dissociation degree drops with pressure. It is demonstrated that depending on the energy input the RF discharge can exist in three modes: I-in the spatially homogeneous mode or α-mode; III-in the substantially inhomogeneous mode, when plasma jets are present outside the discharge; and II-in the transient mode between modes I and III. In this paper only the homogeneous mode of RF discharge in the O 2 flow is considered in detail. A self-consistent model of the α-mode is developed, that allows us to analyse elementary processes responsible for the production and loss of O 2 (a 1 Δ g ) and O 2 (b 1 Σ g + ) molecules as well as O( 3 P) atoms in detail. To verify both the kinetic scheme of the model and the conclusions, some experiments have been carried out at lower flow velocities and higher pressures (≥10 Torr), when the stationary densities of O 2 (a 1 Δ g ), O 2 (b 1 Σ g + ) and O( 3 P) in the discharge area were established not by the escape of particles but by the losses due to the volumetric and surface reactions. The O 2 (b 1 Σ g + ) density under these conditions is determined by the balance of O 2 (b 1 Σ g + ) production by both direct electron impact and electronic excitation transfer from metastable O( 1 D) atoms and deactivation by oxygen atoms and tube walls, including quenching by ozone in the afterglow. The O( 3 P) density is determined by the balance between the production through O 2 dissociation by electron impact and heterogeneous loss at the wall recombination. The stationary density of O 2 (a 1 Δ g ) is provided by the processes of O

  4. Charge transfer state induced from locally excited state by polar solvent

    Science.gov (United States)

    Sun, Mengtao

    2005-06-01

    The photophysical properties of the novel perylene imide (Pi) and oligo-pentaphenyl bisfluorene (pPh) containing molecule have been investigated by quantum chemical methods. It is concluded that the first excited singlet state in the gas is the locally excited state; while the lowest excited state in polar solvents is the intramolecular charge transfer (ICT) state, which corresponds to the ICT from pPh to Pi. This excited state in the polar solvent adopts a planar geometry, in marked contrast to the twisted geometry in the gas phase. The planar geometry in the polar solvent significantly delocalized densities of HOMOs, compared to those in the gas phase, but the influence of the planar geometry to densities of LUMO is very small. Overall, the computed results remain in good agreement with the relevant experimental data.

  5. The lowest excited singlet state of isolated 1-phenyl-butadiene and 1-phenyl-hexatriene

    NARCIS (Netherlands)

    Kohler, B.E.; Shaler, T.A.; Buma, W.J.; Song, K.; Nuss, J.M.

    1992-01-01

    We report vibrationally resolved S0S1 excitation spectra and vibronic level decay times for the phenyl-substituted polyenes 1-phenylbutadiene and 1-phenylhexatriene seeded in supersonic He expansions. This information was obtained using one- and two-color resonance-enhanced multiphoton ionization

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

    Science.gov (United States)

    Osad'ko, I S; Shchukina, A L

    2012-06-01

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

  7. Spin-Transfer Excitations in Permalloy Nanomagnets

    Science.gov (United States)

    Myers, E. B.; Ralph, D. C.; Albert, F. J.; Buhrman, R. A.

    2001-03-01

    Recent experiments have shown that large (> 10^7 A/cm^2) spin-polarized currents in magnetic nanostructures can, through local exchange interactions, induce controllable magnetic excitations such as spin-waves and hysteretic domain reversal(E. B. Myers et al., Science )285, 867 (1999); J. A. Katine et al., Phys. Rev. Lett. 84, 3149 (2000).. We present new data on this effect, called spin-transfer, in Permalloy (Ni_81Fe_19) / Copper / Cobalt trilayer pillars. The near-absence of crystalline anisotropy in Permalloy allows us to tailor the magnetic anisotropy by varying the shape of the pillar(F. J. Albert et al., submitted to Appl. Phys. Lett. )., thus providing a more detailed quantitative exploration of the effect. Data demonstrating the behavior of the pillars as a function of perpendicular current and in-plane magnetic field will be presented and compared with numerical and analytical predictions of magnetic dynamics in the presence of spin-transfer(J. Z. Sun, Phys. Rev. B ) 62, 570 (2000). .

  8. The effect of the silver nanoparticles on the dynamics of singlet-singlet energy transfer of luminophores in thin films of polyvinyl alcohol

    International Nuclear Information System (INIS)

    Bryukhanov, V.V.; Samusev, I.G.; Slezhkin, V.A.; Tsibul'nikova, A.V.

    2014-01-01

    The effect of ablated silver nanoparticles (ANP) on the dynamics of non-radiative inductance-resonance energy transfer and phosphorescence in the donor-acceptor pair of molecules of eosin and methylene blue (MB) luminophores embedded in thin films of polyvinyl alcohol have been investigated. Increased fluorescence intensity of donor (eosin) and acceptor (MB) molecules, as well as a growth of the dipole-dipole transfer efficiency have been obtained under the resonant excitation of the silver ANP surface plasmons in the absorption band of the donor energy. The luminescence quantum yields and the fluorescence lifetimes have been measured. The energy transfer constants, degree of polarization and fluorescence anisotropy have been determined. (authors)

  9. 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

  10. 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.

  11. Excitation energies and properties of open-shell singlet molecules applications to a new class of molecules for nonlinear optics and singlet fission

    CERN Document Server

    Nakano, Masayoshi

    2014-01-01

    This brief investigates the diradical character, which is one of the ground-state chemical indices for 'bond weakness' or 'electron correlation' and which allows researchers to explore the origins of the electron-correlation-driven physico-chemical phenomena concerned with electronic, optical and magnetic properties as well as to control them in the broad fields of physics and chemistry. It then provides the theoretical fundamentals of ground and excited electronic structures of symmetric and asymmetric open-shell molecular systems by using model molecular systems. Moreover, it presents the th

  12. Excitation energy transfer from dye molecules to doped graphene

    Indian Academy of Sciences (India)

    Recently, we have reported theoretical studies on the rate of energy transfer from an electronically excited molecule to graphene. It was found that graphene is a very efficient quencher of the electronically excited states and that the rate -4. The process was found to be effective up to 30 which is well beyond the ...

  13. 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.

  14. Time-resolved studies on the photoisomerization of a phenylene-silylene-vinylene type compound in its first singlet excited state

    International Nuclear Information System (INIS)

    Burdzinski, G.; Bayda, M.; Hug, G.L.; Majchrzak, M.; Marciniec, B.; Marciniak, B.

    2011-01-01

    In femtosecond laser-flash photolysis experiments, the first singlet excited state of trans-ST, ((E,E)-{1,4-bis(2-dimethylphenylsilyl)ethenyl}benzene) showed a strong S1(π,π * )-Sn absorption band at 540 nm in acetonitrile and at 550 nm in hexane. The lifetime of this state was determined to be 13.2±2.0 and 11.1±1.5 ps, respectively. Intersystem crossing was shown not to be a principal route for the deactivation of this S1 state of trans-ST. Evidence for this conclusion involved two complementary nanosecond laser-flash photolysis experiments. In one experiment involving direct excitation, no transient absorption spectrum was detected in the 350-650 nm spectral range. Yet, in the second experiment, on triplet sensitization, using xanthone, a transient absorption at 400 nm was tentatively assigned to the triplet state absorption of trans-ST. Photoisomerization was monitored in nanosecond time-resolved bleaching experiments. From these experiments the trans-cis photoisomerization quantum yield was determined to be 0.23 on direct trans-ST excitation. In a xanthone-sensitized stationary-state excitation experiment, the trans-cis isomerization quantum yield was determined to be 0.32. The main deactivation route of trans-ST in its S1 state is repopulation of the ground state directly through internal conversion or with the intermediacy of conformers with twisted geometry.

  15. S1←S0 vibronic spectra and structure of cyclopropanecarboxaldehyde molecule in the S1 lowest excited singlet electronic state

    International Nuclear Information System (INIS)

    Godunov, I.A.; Yakovlev, N.N.; Terentiev, R.V.; Maslov, D.V.; Bataev, V.A.; Abramenkov, A.V.

    2016-01-01

    The S 1 ←S 0 vibronic spectra of gas-phase absorption at room temperature and fluorescence excitation of jet-cooled cyclopropanecarboxaldehyde (CPCA, c-C 3 H 5 CHO)were obtained and analyzed. In addition, the quantum chemical calculation (CASPT2/cc-pVTZ)was carried out for CPCA in the ground (S 0 ) and lowest excited singlet (S 1 ) electronic states. As a result, it was proved that the S 1 ←S 0 electronic excitation of the CPCA conformers (syn and anti) causes (after geometrical relaxation) significant structural changes, namely, the carbonyl fragments become non-planar and the cyclopropyl groups rotate around the central C–C bond. As a consequence, the potential energy surface of CPCA in the S 1 state has six minima, 1ab, 2ab, and 3ab, corresponding to three pairs of mirror symmetry conformers: a and b. It was shown that vibronic bands of experimental spectra can be assigned to the 2(S 1 )←syn(S 0 ) electronic transition with the origin at 30,481 cm −1 . A number of fundamental vibrational frequencies for the 2 conformer of CPCA were assigned. In addition, several inversional energy levels for the 2 conformer were found and the 2a↔2b potential function of inversion was determined. The experimental barrier to inversion and the equilibrium angle between the CH bond and the CCO plane were calculated as 570 cm −1 and 28°, respectively. - Highlights: • S 1 ←S 0 vibronic gas-phase absorption spectrum of cyclopropanecarboxaldehyde (CPCA). • S 1 ←S 0 fluorescence excitation spectrum of CPCA. • Ab initio calculation for CPCA in S 0 and S 1 electronic states. • Structural changes of the CPCA at S 1 ←S 0 electronic excitation.

  16. Excitation energy transfer from the bacteriochlorophyll Soret band to carotenoids in the LH2 light-harvesting complex from Ectothiorhodospira haloalkaliphila is negligible.

    Science.gov (United States)

    Razjivin, A P; Lukashev, E P; Kompanets, V O; Kozlovsky, V S; Ashikhmin, A A; Chekalin, S V; Moskalenko, A A; Paschenko, V Z

    2017-09-01

    Pathways of intramolecular conversion and intermolecular electronic excitation energy transfer (EET) in the photosynthetic apparatus of purple bacteria remain subject to debate. Here we experimentally tested the possibility of EET from the bacteriochlorophyll (BChl) Soret band to the singlet S 2 level of carotenoids using femtosecond pump-probe measurements and steady-state fluorescence excitation and absorption measurements in the near-ultraviolet and visible spectral ranges. The efficiency of EET from the Soret band of BChl to S 2 of the carotenoids in light-harvesting complex LH2 from the purple bacterium Ectothiorhodospira haloalkaliphila appeared not to exceed a few percent.

  17. Phonons and charge-transfer excitations in HTS superconductors

    International Nuclear Information System (INIS)

    Bishop, A.R.

    1989-01-01

    Some of the experimental and theoretical evidence implicating phonons and charge-transfer excitations in HTS superconductors is reviewed. It is suggested that superconductivity may be driven by a synergistic interplay of (anharmonic) phonons and electronic degrees of freedom (e.g., charge fluctuations, excitons). 47 refs., 5 figs

  18. Anomalous temperature dependence of excitation transfer between quantum dots

    Czech Academy of Sciences Publication Activity Database

    Král, Karel; Menšík, Miroslav

    2015-01-01

    Roč. 7, č. 4 (2015), 325-330 ISSN 2164-6627 R&D Projects: GA MŠk(CZ) LD14011; GA MŠk LH12236; GA MŠk LH12186 Institutional support: RVO:68378271 ; RVO:61389013 Keywords : excitation transfer * quantum dots * temperature dependence * electron-phonon interaction Subject RIV: BM - Solid Matter Physics ; Magnetism

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

    Indian Academy of Sciences (India)

    Administrator

    Abstract. Excited state intramolecular charge transfer reaction of 4-(1-azetidinyl) benzonitrile (P4C) in deuterated and normal methanol, ethanol and acetonitrile has been studied in order to investigate the solvent isotope effects on reaction rates and yields. These quantities (reaction rates and yields) along with several.

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

    Indian Academy of Sciences (India)

    Excited state intramolecular charge transfer reaction of 4-(1-azetidinyl) benzonitrile (P4C) in deuterated and normal methanol, ethanol and acetonitrile has been studied in order to investigate the solvent isotope effects on reaction rates and yields. These quantities (reaction rates and yields) along with several other ...

  1. Photochemical hydrogen-deuterium exchange reaction of tryptophan: the role in nonradiative decay of singlet tryptophan

    International Nuclear Information System (INIS)

    Saito, I.; Sugiyama, H.; Yamamoto, A.; Muramatsu, S.; Matsuura, T.

    1984-01-01

    The mechanism of nonradiative decay of singlet excited tryptophan (Trp) in aqueous solution was investigated by a highly selective photosubstitution of the C-4 hydrogen of Trp with deuterium of solvent D 2 O. It was concluded that intramolecular proton transfer from the α-ammonia group giving rise to formation of a protonated species plays an important role in the nonradiative decay of singlet Trp at neutral pH. 11 references, 1 figure

  2. Singlet Fission in Rubrene Derivatives: Impact of Molecular Packing

    KAUST Repository

    Sutton, Christopher

    2017-03-13

    We examine the properties of six recently synthesized rubrene derivatives (with substitutions on the side phenyl rings) that show vastly different crystal structures. In order to understand how packing in the solid state affects the excited states and couplings relevant for singlet fission, the lowest excited singlet (S), triplet (T), multiexciton (TT), and charge-transfer (CT) states of the rubrene derivatives are compared to known singlet fission materials [tetracene, pentacene, 5,12-diphenyltetracene (DPT), and rubrene itself]. While a small difference of less than 0.2 eV is calculated for the S and TT energies, a range of 0.50 to 1.2 eV in the CT energies and nearly 3 orders of magnitude in the electronic couplings are computed for the rubrene derivatives in their crystalline packings, which strongly affects the role of the CT state in facilitating SF. To rationalize experimental observations of singlet fission occurring in amorphous phases of rubrene, DPT, and tetracene, we use molecular dynamics (MD) simulations to assess the impact of molecular packing and orientations and to gain a better understanding of the parameters that control singlet fission in amorphous films compared to crystalline packings. The MD simulations point to a crystalline-like packing for thin films of tetracene; on the other hand, DPT, rubrene, and the rubrene derivatives all show various degrees of disorder with a number of sites that have larger electronic couplings than in the crystal, which can facilitate singlet fission in such thin films. Our analysis underlines the potential of these materials as promising candidates for singlet fission and helps understand how various structural motifs affect the critical parameters that control the ability of a system to undergo singlet fission.

  3. Study of excited states in liquid organic systems with the use of pulse radiolysis

    International Nuclear Information System (INIS)

    Ramanan, G.

    1979-01-01

    Application of electron pulse radiolysis of liquid organic systems in the investigations of excited singlet and triplet states has been illustrated with ethyl acetate and hexafluorobenzene. The fluorescence spectrum and lifetime of singlet excited hexafluorobenzene ( 1 HFB*) in cyclohexane medium have been obtained using nanosecond electron pulses. The possible formation of excimer in this case has been investigated. Energy transfer reactions from excited benzene singlet to HFB in benzene and cyclohexane media have been studied and their transfer constants were evaluated. Pulse radiolysis of ethyl acetate in presence of different concentrations of anthracene or biphenyl were used in the study of solute triplets. An upper limit for the yield of excited singlet anthracene was estimated to be approximately 0.1. The contribution of ethyl acetate cations in forming the excited singlet states of anthracene has been discussed. (auth.)

  4. Ultrafast intramolecular charge transfer in tetrapyrazinoporphyrazines controls the quantum yields of fluorescence and singlet oxygen

    Czech Academy of Sciences Publication Activity Database

    Nováková, V.; Zimčík, P.; Miletín, M.; Váchová, L.; Kopecký, K.; Lang, Kamil; Chábera, P.; Polívka, T.

    2010-01-01

    Roč. 12, č. 11 (2010), s. 2555-2563 ISSN 1463-9076 R&D Projects: GA ČR GA203/07/1424 Institutional research plan: CEZ:AV0Z40320502 Keywords : photoinduced electron-transfer * phthalocyanine -fullerene ensembles * nonlinear-optical properties Subject RIV: CA - Inorganic Chemistry Impact factor: 3.454, year: 2010

  5. Collective spin excitations in the singlet-correlated band model: a comparison with resonant inelastic x-ray scattering

    International Nuclear Information System (INIS)

    Eremin, M V; Shigapov, I M; Thuy, Ho Thi Duyen

    2013-01-01

    We analyse the spin excitations near the optimal doping of superconducting layered cuprates taking into account both the local and the itinerant spin components self-consistently. The obtained expression allows us to reproduce well the basic features of the resonant inelastic x-ray scattering and neutron scattering data experiments using a reasonable set of tight-binding parameters corresponding to the angle-resolved photoemission spectroscopy data. We also find that the spin excitation branch along the (0,0) − (0,π) symmetry direction in the first Brillouin zone shows a splitting at T c . Possible experiments for verification of that prediction are briefly discussed. (paper)

  6. Quenching Enhancement of the Singlet Excited State of Pheophorbide-a by DNA in the Presence of the Quinone Carboquone

    OpenAIRE

    Díaz-Espinosa, Yisaira; Crespo-Hernández, Carlos E.; Alegría, Antonio E.; García, Carmelo; Arce, Rafael

    2011-01-01

    Changes in the emission fluorescence intensity of pheophorbide-a (PHEO) in the presence of carboquone (CARBOQ) were used to obtain the association constant, the number of CARBOQ molecules interacting with PHEO, and the fluorescence quantum yield of the complex. Excitation spectra of mixtures of PHEO and CARBOQ in ethanol (EtOH) show an unresolved doublet in the red-most excitation band of PHEO, indicating the formation of a loose ground-state complex. The 1:1 CARBOQ–PHEO complex shows a highe...

  7. Calibration transfer for excitation-emission fluorescence measurements.

    Science.gov (United States)

    Thygesen, Jonas; van den Berg, Frans

    2011-10-31

    The main part of the wide array of different calibration transfer methods found in literature is dedicated to two-way data arrangements (m×n matrices). Less work has been done within the area of calibration transfer for three-way data structures (m×n×l tensors) such as calibrations made for excitation-emission-matrix (EEM) fluorescence spectra. There are two possible ways to attack the problem for EEM transfer. Either the tensors are unfolded to two-way data, whereby the existing methods can be applied, or new methods dedicated to three-way calibration transfer have to be developed. This paper presents and compares both. It was possible to make a local linear pixel-based model that could be used for transfer of EEM's. This new method has a similar performance to the classical methods found in literature, direct- and piecewise direct standardization. The three-way advantages made it possible to use as few as four samples to build useable transfer models. Care has to be taken though when choosing the samples. When subset recalibration of the systems is compared to calibration transfer, better performance is seen for the transferred calibrations. Overall the three-way calibration transfer methods have a slightly better performance than the two-way methods. Copyright © 2011 Elsevier B.V. All rights reserved.

  8. 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

  9. 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.

  10. 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.

  11. Search for Singlet Fission Chromophores

    Energy Technology Data Exchange (ETDEWEB)

    Havlas, Z.; Akdag, A.; Smith, M. B.; Dron, P.; Johnson, J. C.; Nozik, A. J.; Michl, J.

    2012-01-01

    Singlet fission, in which a singlet excited chromophore shares its energy with a ground-state neighbor and both end up in their triplet states, is of potential interest for solar cells. Only a handful of compounds, mostly alternant hydrocarbons, are known to perform efficiently. In view of the large number of conditions that a successful candidate for a practical cell has to meet, it appears desirable to extend the present list of high performers to additional classes of compounds. We have (i) identified design rules for new singlet fission chromophores and for their coupling to covalent dimers, (ii) synthesized them, and (iii) evaluated their performance as neat solids or covalent dimers.

  12. Singlet and triplet energy transfer dynamics in self-assembled axial porphyrin-anthracene complexes: towards supra-molecular structures for photon upconversion.

    Science.gov (United States)

    Gray, Victor; Küçüköz, Betül; Edhborg, Fredrik; Abrahamsson, Maria; Moth-Poulsen, Kasper; Albinsson, Bo

    2018-03-14

    Energy and electron transfer reactions are central to many different processes and research fields, from photosynthesis and solar energy harvesting to biological and medical applications. Herein we report a comprehensive study of the singlet and triplet energy transfer dynamics in porphyrin-anthracene coordination complexes. Seven newly synthesized pyridine functionalized anthracene ligands, five with various bridge lengths and two dendrimer structures containing three and seven anthracene units, were prepared. We found that triplet energy transfer from ruthenium octaethylporphyrin to an axially coordinated anthracene is possible, and is in some cases followed by back triplet energy transfer to the porphyrin. The triplet energy transfer follows an exponential distance dependence with an attenuation factor, β, of 0.64 Å -1 . Further, singlet energy transfer from anthracene to the ruthenium porphyrin appears to follow a R 6 Förster distance dependence. Porphyrin-anthracene complexes are also used as triplet sensitizers for triplet-triplet annihilation (TTA) based photon upconversion, demonstrating their potential for photophysical and photochemical applications. The triplet lifetime of the complex is extended by the anthracene ligands, resulting in a threefold increase in the upconversion efficiency, Φ UC to 4.5%, compared to the corresponding ruthenium porphyrin-pyridine complex. Based on the results herein we discuss the future design of supra-molecular structures for TTA upconversion.

  13. Roles of singlet oxygen and triplet excited state of dissolved organic matter formed by different organic matters in bacteriophage MS2 inactivation

    KAUST Repository

    Rosado-Lausell, Sahid L.

    2013-09-01

    Inactivation of bacteriophage MS2 by reactive oxygen species (ROS) and triplet excited state of dissolved organic matter (3DOM*) produced by irradiation of natural and synthetic sensitizers with simulated sunlight of wavelengths greater than 320nm was investigated. Natural sensitizers included purified DOM isolates obtained from wastewater and river waters, and water samples collected from Singapore River, Stamford Canal, and Marina Bay Reservoir in Singapore. Linear correlations were found between MS2 inactivation rate constants (kobs) and the photo-induced reaction rate constants of 2,4,6-trimethylphenol (TMP), a probe compound shown to react mainly with 3DOM*. Linear correlations between MS2 kobs and singlet oxygen (1O2) concentrations were also found for both purified DOM isolates and natural water samples. These correlations, along with data from quenching experiments and experiments with synthetic sensitizers, Rose Bengal (RB), 3\\'-methoxyacetophenone (3\\'-MAP), and nitrite (NO2-), suggest that 1O2, 3DOM*, and hydroxyl radicals (•OH) could inactivate bacteriophage MS2. Linear correlations between MS2 kobs and Specific Ultraviolet Absorption determined at 254nm (SUVA254) were also found for both purified DOM isolates and natural samples. These results suggest the potential use of TMP as a chemical probe and SUVA254 as an indicator for virus inactivation in natural and purified DOM water samples. © 2013 Elsevier Ltd.

  14. Luminescence property and lowest excited singlet state level of various carotenes; Shuju no karochinrui no hako tokusei to saitei reiki -juko jotai jun'i

    Energy Technology Data Exchange (ETDEWEB)

    Ito, T. [Miyagi Midical Univ., Miyagi (Japan)

    2000-01-01

    Specification of the lowest excited singlet state (S{sub l}) of the butadiene which is the simplest {pi} electron conjugated system molecule has not sufficiently clarified at present. Recently, Andersson et al. found the weak light emission which was considered to be the S{sub 1} fluorescence in a near infrared region in a room temperature solution of {beta}- carotene (n=11), and specified the S{sub 1} level in 14,200{+-}500cm {sup -1}. And, Fujii et al. reported the S{sub 1} fluorescence of spheroidine (n=10). In very recent, Christensen et al. measured the comparatively clear fluorescence spectrum of carotenes n=5 to 11 separated by HPLC in EPA glass at 77K, and systematically examined the unique luminescence property observed in polyene. Christensen et al. issued the warning for the rough conventional method that the S{sub 1} level was estimated from the S{sub 1} fluorescence lifetime of the polyene molecule using the comprehensive energy gap law, because the ratio of quantum yield of the S{sub 1} and S{sub 2} fluorescence is different by the substituent type of the polyene end even if n is same. (NEDO)

  15. Singlet Fission

    Czech Academy of Sciences Publication Activity Database

    Smith, M. B.; Michl, Josef

    2010-01-01

    Roč. 110, č. 11 (2010), s. 6891-6936 ISSN 0009-2665 Grant - others:Department of Energy(US) DE- FG36 -08GO18017 Institutional research plan: CEZ:AV0Z40550506 Keywords : solar energy conversion * photovoltaics * singlet fission Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 33.033, year: 2010

  16. Excited state intramolecular proton transfer (ESIPT) in dihydroxyphenyl anthracenes.

    Science.gov (United States)

    Wang, Yu-Hsuan; Wan, Peter

    2011-12-01

    The photochemistry of three 9-(dihydroxyphenyl)anthracenes 6-8 was studied in neat CH(3)CN and selected organic solvents, to investigate excited state intramolecular proton transfer (ESIPT) from the phenol to the anthracene moiety. In D(2)O-CH(3)CN mixtures, the observed deuterium exchange of 6-8 is consistent with water-mediated (formal) ESIPT process from the ortho phenolic OH to the 10'-position of the anthracene ring, giving rise to quinone methide (QM) intermediates 12-14. There is no ESIPT for the corresponding methoxy-substituted compounds. Introduction of an extra hydroxyl group onto the phenol ring at different positions led to a range of deuterium exchange quantum yields (Φ = 0.03 to 0.15). In addition to the anticipated ESIPT process to the 10'-position, in neat CH(3)CN and other organic solvents, 6 (but not 7 or 8) undergoes a clean photocyclization to give bridged product 19 in quantitative yield. The mechanism of this unique photocyclization may involve a direct ESIPT or a 1,4-hydrogen transfer from the ortho phenolic OH to the 9'-position of the anthracene ring, generating a zwitterion (20) or diradical (21) intermediate, respectively, followed by ring closure. Fluorescence studies of 6 in various solvents show the existence of both local excited and intramolecular charge transfer states whereas only the former was present for 7 and 8, offering a possible rationalization for the photocyclization pathway.

  17. 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.

  18. 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.

  19. 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 th...

  20. Solvent-free one-step photochemical hydroxylation of benzene derivatives by the singlet excited state of 2,3-Dichloro-5,6-dicyano-p-benzoquinone acting as a super oxidant.

    Science.gov (United States)

    Ohkubo, Kei; Hirose, Kensaku; Fukuzumi, Shunichi

    2015-02-09

    Photoinduced hydroxylation of neat deaerated benzene to phenol occurred under visible-light irradiation of 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), which acts as a super photooxidant in the presence of water. Photocatalytic solvent-free hydroxylation of benzene derivatives with electron-withdrawing substituents such as benzonitrile, nitrobenzene, and trifluoromethylbenzene used as neat solvents has been achieved for the first time by using DDQ as a super photooxidant to yield the corresponding phenol derivatives and 2,3-dichloro-5,6-dicyanohydroquinone (DDQH2 ) in the presence of water under deaerated conditions. In the presence of dioxygen and tert-butyl nitrite, the photocatalytic hydroxylation of neat benzene occurred with DDQ as a photocatalyst to produce phenol. The photocatalytic reactions are initiated by oxidation of benzene derivatives with the singlet and triplet excited states of DDQ to form the corresponding radical cations, which associate with benzene derivatives to produce the dimer radical cations, which were detected by the femto- and nanosecond laser flash photolysis measurements to clarify the photocatalytic reaction mechanisms. Radical cations of benzene derivatives react with water to yield the OH-adduct radicals. On the other hand, DDQ(.) (-) produced by the photoinduced electron transfer from benzene derivatives reacts with the OH-adduct radicals to yield the corresponding phenol derivatives and DDQH2 . DDQ is recovered by the reaction of DDQH2 with tert-butyl nitrite when DDQ acts as a photocatalyst for the hydroxylation of benzene derivatives by dioxygen. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Electron transfer mechanism and photochemistry of ferrioxalate induced by excitation in the charge transfer band.

    Science.gov (United States)

    Chen, Jie; Zhang, Hua; Tomov, Ivan V; Rentzepis, Peter M

    2008-03-17

    The photoredox reaction of ferrioxalate after 266/267 nm excitation in the charge transfer band has been studied by means of ultrafast extended X-ray absorption fine structure (EXAFS) analysis, optical transient spectroscopy, and quantum chemistry calculations. The Fe-O bond length changes combined with the transient spectra and kinetics have been measured and in combination with ultrahigh frequency density functional theory (UHF/DFT) calculations are used to determine the photochemical mechanism for the Fe(III) to Fe(II) redox reaction. The present data and the results obtained with 266/267 nm excitations strongly suggest that the primary reaction is the dissociation of the Fe-O bond before intramolecular electron transfer occurs. Low quantum yield electron photodetachment from ferrioxalate has also been observed.

  2. Up-Conversion Intersystem Crossing Rates in Organic Emitters for Thermally Activated Delayed Fluorescence: Impact of the Nature of Singlet vs Triplet Excited States

    KAUST Repository

    Samanta, Pralok Kumar

    2017-02-28

    The rates for up-conversion intersystem crossing (UISC) from the T1 state to the S1 state are calculated for a series of organic emitters with an emphasis on thermally activated delayed fluorescence (TADF) materials. Both the spin-orbit coupling and the energy difference between the S1 and T1 states (ΔEST) are evaluated, at the density functional theory (DFT) and time-dependent DFT levels. The calculated UISC rates and ΔEST values are found to be in good agreement with available experimental data. Our results underline that small ΔEST values and sizable spin-orbit coupling matrix elements have to be simultaneously realized in order to facilitate UISC and ultimately TADF. Importantly, the spatial separation of the highest occupied and lowest unoccupied molecular orbitals of the emitter, a widely accepted strategy for the design of TADF molecules, does not necessarily lead to a sufficient reduction in ΔEST; in fact, either a significant charge-transfer (CT) contribution to the T1 state or a minimal energy difference between the local-excitation and charge-transfer triplet states is required to achieve a small ΔEST. Also, having S1 and T1 states of a different nature is found to strongly enhance spin-orbit coupling, which is consistent with the El-Sayed rule for ISC rates. Overall, our results indicate that having either similar energies for the local-excitation and charge-transfer triplet states or the right balance between a substantial CT contribution to T1 and somewhat different natures of the S1 and T1 states, paves the way toward UISC enhancement and thus TADF efficiency improvement.

  3. Two-Photon Irradiation of an Intracellular Singlet Oxygen Photosensitizer: Achieving Localized Sub-Cellular Excitation in Spatially-Resolved Experiments

    DEFF Research Database (Denmark)

    Pedersen, Brian Wett; Breitenbach, Thomas; Redmond, Robert W.

    2010-01-01

    The response of a given cell to spatially-resolved sub-cellular irradiation of a singlet oxygen photosensitizer (protoporphyrin IX, PpIX) using a focused laser was assessed. In these experiments, incident light was scattered over a volume greater than that defi ned by the dimensions of the laser...

  4. Cold transfer between deformed, Coulomb excited nuclei; Kalter Transfer zwischen deformierten, Coulomb-angeregten Kernen

    Energy Technology Data Exchange (ETDEWEB)

    Bauer, H.

    1998-12-31

    The scattering system {sup 162}Dy {yields} {sup 116}Sn has been examined at energies in the vicinity of the Coulomb barrier using the Heidelberg-Darmstadt Crystal Ball spectrometer combined with 5 Germanium-CLUSTER detectors. In order to study pairing correlations as a function of angular momentum cold events were selected in the 2n stripping channel by identifying and suppressing the dominant hot part of the transfer with the Crystal Ball. The CLUSTER detectors with their high {gamma}-efficiency were used to identify the transfer channel and to resolve individual final states. Cross sections for the population of individual yrast states in a cold transfer reaction have been measured for the first time indicating the strong influence of higher transfer multipolarities. At small surface distances Coulomb-nuclear interferences were found to be responsible for the stronger decline of the population of higher yrast states in the transfer channel as compared to the Coulex channel. As a preparatory study for 2n transfer measurements between high spin yrast states in the backbending region of deformed nuclei the Coulomb excitation process in the crossing region of two bands in {sup 162}Dy has been analyzed. The gross properties of the measured population probabilities could be interpreted in a simple band mixing model. (orig.)

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

    Energy Technology Data Exchange (ETDEWEB)

    Fayed, Tarek A. [Chemistry Department, Faculty of Science, Tanta University, 31527-Tanta (Egypt)], E-mail: tfayed2003@yahoo.co.uk

    2006-05-31

    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 ({delta}{mu} {sub 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{sup 2+}, Cd{sup 2+} and Hg{sup 2+}. This was concluded from the high acidochromic and metallochromic behaviour of DMAC on adding such cations to its acetonitrile solutions.

  6. Excitation of Terahertz Charge Transfer Plasmons in Metallic Fractal Structures

    Science.gov (United States)

    Ahmadivand, Arash; Gerislioglu, Burak; Sinha, Raju; Vabbina, Phani Kiran; Karabiyik, Mustafa; Pala, Nezih

    2017-08-01

    There have been extensive researches on terahertz (THz) plasmonic structures supporting resonant modes to demonstrate nano and microscale devices with high efficiency and responsivity as well as frequency selectivity. Here, using antisymmetric plasmonic fractal Y-shaped (FYS) structures as building blocks, we introduce a highly tunable four-member fractal assembly to support charge transfer plasmons (CTPs) and classical dipolar resonant modes with significant absorption cross section in the THz domain. We first present that the unique geometrical nature of the FYS system and corresponding spectral response allow for supporting intensified dipolar plasmonic modes under polarised light exposure in a standalone structure. In addition to classical dipolar mode, for the very first time, we demonstrated CTPs in the THz domain due to the direct shuttling of the charges across the metallic fractal microantenna which led to sharp resonant absorption peaks. Using both numerical and experimental studies, we have investigated and confirmed the excitation of the CTP modes and highly tunable spectral response of the proposed plasmonic fractal structure. This understanding opens new and promising horizons for tightly integrated THz devices with high efficiency and functionality.

  7. Low-energy charge transfer excitations in NiO

    International Nuclear Information System (INIS)

    Sokolov, V I; Yermakov, A Ye; Uimin, M A; Gruzdev, N B; Pustovarov, V A; Churmanov, V N; Ivanov, V Yu; Sokolov, P S; Baranov, A N; Moskvin, A S

    2012-01-01

    Comparative analysis of photoluminescence (PL) and photoluminescence excitation (PLE) spectra of NiO poly- and nanocrystals in the spectral range 2-5.5 eV reveals two PLE bands peaked near 3.7 and 4.6 eV with a dramatic rise in the low-temperature PLE spectral weight of the 3.7 eV PLE band in the nanocrystalline NiO as compared with its polycrystalline counterpart. In frames of a cluster model approach we assign the 3.7 eV PLE band to the low-energy bulk-forbidden p-d (t 1g (π)-e g ) charge transfer (CT) transition which becomes the allowed one in the nanocrystalline state while the 4.6 eV PLE band is related to a bulk allowed d-d (e g -e g ) CT transition scarcely susceptible to the nanocrystallization. The PLE spectroscopy of the nanocrystalline materials appears to be a novel informative technique for inspection of different CT transitions.

  8. Singlet oxygen reactions with flavonoids. A theoretical-experimental study.

    Directory of Open Access Journals (Sweden)

    Javier Morales

    Full Text Available Detection of singlet oxygen emission, λ(max = 1270 nm, following laser excitation and steady-state methods were employed to measure the total reaction rate constant, k(T, and the reactive reaction rate constant, k(r, for the reaction between singlet oxygen and several flavonoids. Values of k(T determined in deuterated water, ranging from 2.4×10(7 M(-1 s(-1 to 13.4×10(7 M(-1 s(-1, for rutin and morin, respectively, and the values measured for k(r, ranging from 2.8×10(5 M(-1 s(-1 to 65.7×10(5 M(-1 s(-1 for kaempferol and morin, respectively, being epicatechin and catechin chemically unreactive. These results indicate that all the studied flavonoids are good quenchers of singlet oxygen and could be valuable antioxidants in systems under oxidative stress, in particular if a flavonoid-rich diet was previously consumed. Analysis of the dependence of rate constant values with molecular structure in terms of global descriptors and condensed Fukui functions, resulting from electronic structure calculations, supports the formation of a charge transfer exciplex in all studied reactions. The fraction of exciplex giving reaction products evolves through a hydroperoxide and/or an endoperoxide intermediate produced by singlet oxygen attack on the double bond of the ring C of the flavonoid.

  9. Singlet oxygen reactions with flavonoids. A theoretical-experimental study.

    Science.gov (United States)

    Morales, Javier; Günther, Germán; Zanocco, Antonio L; Lemp, Else

    2012-01-01

    Detection of singlet oxygen emission, λ(max) = 1270 nm, following laser excitation and steady-state methods were employed to measure the total reaction rate constant, k(T), and the reactive reaction rate constant, k(r), for the reaction between singlet oxygen and several flavonoids. Values of k(T) determined in deuterated water, ranging from 2.4×10(7) M(-1) s(-1) to 13.4×10(7) M(-1) s(-1), for rutin and morin, respectively, and the values measured for k(r), ranging from 2.8×10(5) M(-1) s(-1) to 65.7×10(5) M(-1) s(-1) for kaempferol and morin, respectively, being epicatechin and catechin chemically unreactive. These results indicate that all the studied flavonoids are good quenchers of singlet oxygen and could be valuable antioxidants in systems under oxidative stress, in particular if a flavonoid-rich diet was previously consumed. Analysis of the dependence of rate constant values with molecular structure in terms of global descriptors and condensed Fukui functions, resulting from electronic structure calculations, supports the formation of a charge transfer exciplex in all studied reactions. The fraction of exciplex giving reaction products evolves through a hydroperoxide and/or an endoperoxide intermediate produced by singlet oxygen attack on the double bond of the ring C of the flavonoid.

  10. 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

  11. Vibrational energy transfer in selectively excited diatomic molecules

    International Nuclear Information System (INIS)

    Dasch, C.J.

    1978-09-01

    Single rovibrational states of HCl(v=2), HBr(v=2), DCl(v=2), and CO(v=2) were excited with a pulsed optical parametric oscillator (OPO). Total vibrational relaxation rates near - resonance quenchers were measured at 295 0 K using time resolved infrared fluorescence. These rates are attributed primarily to V - V energy transfer, and they generally conform to a simple energy gap law. A small deviation was found for the CO(v) + DCl(v') relaxation rates. Upper limits for the self relaxation by V - R,T of HCl(v=2) and HBr(v=2) and for the two quantum exchange between HCl and HBr were determined. The HF dimer was detected at 295 0 K and 30 torr HF pressure with an optoacoustic spectrometer using the OPO. Pulsed and chopped, resonant and non-resonant spectrophones are analyzed in detail. From experiments and first order perturbation theory, these V - V exchange rates appear to behave as a first order perturbation in the vibrational coordinates. The rotational dynamics are known to be complicated however, and the coupled rotational - vibrational dynamics were investigated theoreticaly in infinite order by the Dillon and Stephenson and the first Magnus approximations. Large ΔJ transitions appear to be important, but these calculations differ by orders of magnitude on specific rovibrational transition rates. Integration of the time dependent semiclassical equations by a modified Gordon method and a rotationally distorted wave approximation are discussed as methods which would treat the rotational motion more accurately. 225 references

  12. Effects of Intermolecular Coupling on Excimer Formation and Singlet Fission

    Science.gov (United States)

    Mauck, Catherine McKay

    The development of organic photovoltaic devices benefits from understanding the fundamental processes underlying charge generation in thin films of organic semiconductors. This dissertation exploits model systems of pi-stacked chromophores such as perylene-3,4:9,10-bis(dicarboximide) (PDI) and 3,6-bis(aryl)diketopyrrolopyrrole (DPP) to study these processes using ultrafast electronic and vibrational spectroscopy. In particular, the characterization of covalent molecular dimers, thin films, and solution aggregates can reveal how supramolecular order affects photophysical properties. PDI and DPP are organic semiconductors that have been widely studied in organic photovoltaics, due to their strong visible absorption and excellent chemical stability. As solution-phase monomers, they are highly fluorescent, but in the thin film environment of photovoltaic devices these planar aromatic molecules couple to one another, stacking largely through pi-pi interactions. In self-assembled stacks of PDI, strong interchromophore coupling may disrupt charge separation through the formation of excimer states, preventing the generation of free carriers. By studying molecular dimers of PDI with different pi-stacked geometry, femtosecond visible pump mid-infrared probe spectroscopy allows direct observation of the structural dynamics associated with excimer state relaxation, showing that this low-energy state is primarily coupled to the core modes that shift as planarization and rotation lead to the most stable excimer geometry. PDI is also able to undergo singlet fission in thin films and aggregates. Singlet fission is the process in which a singlet excited state is downconverted into two triplet excitons, when the energy of its first singlet excited state is at least twice the energy of the lowest triplet state in an appropriately coupled molecular system. This spin-allowed, ultrafast process enables a theoretical yield of two charge carriers per incident photon, making it a

  13. 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.

  14. Singlet oxygen quenching by oxygen in tetraphenyl-porphyrin solutions

    International Nuclear Information System (INIS)

    Dedic, Roman; Korinek, Miloslav; Molnar, Alexander; Svoboda, Antonin; Hala, Jan

    2006-01-01

    Time-resolved measurement of singlet oxygen infrared phosphorescence is a powerful tool for determination of quantum yields and kinetics of its photosensitization. This technique was employed to investigate in detail the previously observed effect of singlet oxygen quenching by oxygen. The question whether the singlet oxygen is quenched by oxygen in ground or in excited state was addressed by study of two complementary dependencies of singlet oxygen lifetimes: on dissolved oxygen concentration and on excitation intensity. Oxygen concentration dependence study of meso-tetra(4-sulphonato)phenylporphyrin (TPPS 4 ) phosphorescence kinetics showed linearity of the dependence of TPPS 4 triplet state rate-constant. Corresponding bimolecular quenching constant of (1.5±0.1)x10 9 l/mol s was obtained. On the other hand, rate constants of singlet oxygen depopulation exhibit nonlinear dependence on oxygen concentration. Comparison of zero oxygen concentration-extrapolated value of singlet oxygen lifetime of (6.5±0.4) μs to (3.7±0.1) μs observed under air-saturated conditions indicates importance of the effect of quenching of singlet oxygen by oxygen. Upward-sloping dependencies of singlet oxygen depopulation rate-constant on excitation intensity evidence that singlet oxygen is predominantly quenched by oxygen in excited singlet state

  15. Optogalvanic monitoring of collisional transfer of laser excitation energy in a neon RF plasma

    International Nuclear Information System (INIS)

    Armstrong, T.D.

    1994-01-01

    The optogalvanic signals produced by pulsed laser excitation of 1s5--2p8 and 1s5-2p9 (Paschen notation) transition by a ∼29 MHz radiofrequency (rf) discharge at ∼5 torr have been investigated. The optogalvanic signal produced by 1s5-2p9 excitations indicates that there is transfer of energy from the 2p9 state to some other state. The state to which this energy is transferred is believed to be mainly the 2p8 state because of the very small energy gap between the 2p9 and 2p8 states. To verify this transfer, the 1s5-2p8 transition was investigated. The similarity of the temporal profiles of the optogalvanic signals in both excitations confirms the collisional transfer of laser excitation energy from 2p9 to 2p8

  16. Dependence of the energy transfer to graphene on the excitation energy

    Energy Technology Data Exchange (ETDEWEB)

    Mackowski, Sebastian, E-mail: mackowski@fizyka.umk.pl; Kamińska, Izabela [Institute of Physics, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziadzka 5, 87-100 Torun (Poland)

    2015-07-13

    Fluorescence studies of natural photosynthetic complexes on a graphene layer demonstrate pronounced influence of the excitation wavelength on the energy transfer efficiency to graphene. Ultraviolet light yields much faster decay of fluorescence, with average efficiencies of the energy transfer equal to 87% and 65% for excitation at 405 nm and 640 nm, respectively. This implies that focused light changes locally the properties of graphene affecting the energy transfer dynamics, in an analogous way as in the case of metallic nanostructures. Demonstrating optical control of the energy transfer is important for exploiting unique properties of graphene in photonic and sensing architectures.

  17. Vibration transfers to measure the performance of vibration isolated platforms on site using background noise excitation

    NARCIS (Netherlands)

    Segerink, Franciscus B.; Korterik, Jeroen P.; Offerhaus, Herman L.

    2011-01-01

    This article demonstrates a quick and easy way of quantifying the performance of a vibration-isolated platform. We measure the vibration transfer from floor to table using background noise excitation from the floor. As no excitation device is needed, our setup only requires two identical sensors (in

  18. Intramolecular Singlet Fission in Quinoidal Bi- and Tetrathiophenes: A Comparative Study of Low-Lying Excited Electronic States and Potential Energy Surfaces.

    Science.gov (United States)

    Momeni, Mohammad R

    2016-10-11

    Quinoidal bithiophene has recently been introduced ( Varnavski, O. et al. J. Phys. Chem. Lett. 2015 , 6 , 1375 - 1384 ) as a very promising isolated organic compound for intramolecular singlet fission (iSF) with an outstanding SF quantum yield of ≈180%. In contrast, another recent study ( Ren, L. et al. J. Am. Chem. Soc. 2015 , 137 , 11294 - 11302 ) revealed that quinoidal tetrathiophenes have no activity in the iSF process and are strong fluorophores instead, with measured fluorescent quantum yields up to 53.1%. Using DFT and TD-DFT methods, the authors of the second contribution attributed the marked differences between these compounds to faster reverse T 2 → S 1 intersystem crossing processes in the tetrathiophenes. To address this unprecedented discrepancy, quinoidal bithiophene and tetrathiophene compounds and their derivatives are carefully examined using the CASPT2 technique. Theoretical evidence is provided through detailed investigation of CASPT2 potential energy surfaces of different singlet and triplet states involved in the iSF process. Through comparison of the CASPT2 results with the CASSCF and RAS-2SF data, it is found that the dynamic electron correlation present in the CASPT2 method plays a crucial role for correct description of the multiexciton nature of the triplet pair 1 [TT] state in quinoidal bi- and tetrathiophenes. Effects of substitution and structural modification on iSF activity of these compounds are also examined using the CASPT2 method where the obtained results are in accordance with previous experimental predictions. These results contribute to a better understanding of the iSF mechanism in quinoidal systems which could be relevant for designing new iSF active compounds.

  19. Variety in excitation energy transfer processes from phycobilisomes to photosystems I and II.

    Science.gov (United States)

    Ueno, Yoshifumi; Aikawa, Shimpei; Niwa, Kyosuke; Abe, Tomoko; Murakami, Akio; Kondo, Akihiko; Akimoto, Seiji

    2017-09-01

    The light-harvesting antennas of oxygenic photosynthetic organisms capture light energy and transfer it to the reaction centers of their photosystems. The light-harvesting antennas of cyanobacteria and red algae, called phycobilisomes (PBSs), supply light energy to both photosystem I (PSI) and photosystem II (PSII). However, the excitation energy transfer processes from PBS to PSI and PSII are not understood in detail. In the present study, the energy transfer processes from PBS to PSs in various cyanobacteria and red algae were examined in vivo by selectively exciting their PSs or PBSs, and measuring the resulting picosecond to nanosecond time-resolved fluorescences. By observing the delayed fluorescence spectrum of PBS-selective excitation in Arthrospira platensis, we demonstrated that energy transfer from PBS to PSI via PSII (PBS→PSII→PSI transfer) occurs even for PSI trimers. The contribution of PBS→PSII→PSI transfer was species dependent, being largest in the wild-type of red alga Pyropia yezoensis (formerly Porphyra yezoensis) and smallest in Synechococcus sp. PCC 7002. Comparing the time-resolved fluorescence after PSs- and PBS-selective excitation, we revealed that light energy flows from CP43 to CP47 by energy transfer between the neighboring PSII monomers in PBS-PSII supercomplexes. We also suggest two pathways of energy transfer: direct energy transfer from PBS to PSI (PBS→PSI transfer) and indirect transfer through PSII (PBS→PSII→PSI transfer). We also infer that PBS→PSI transfer conveys light energy to a lower-energy red chlorophyll than PBS→PSII→PSI transfer.

  20. Photosensitized, energy transfer-mediated organometallic catalysis through electronically excited nickel(II).

    Science.gov (United States)

    Welin, Eric R; Le, Chip; Arias-Rotondo, Daniela M; McCusker, James K; MacMillan, David W C

    2017-01-27

    Transition metal catalysis has traditionally relied on organometallic complexes that can cycle through a series of ground-state oxidation levels to achieve a series of discrete yet fundamental fragment-coupling steps. The viability of excited-state organometallic catalysis via direct photoexcitation has been demonstrated. Although the utility of triplet sensitization by energy transfer has long been known as a powerful activation mode in organic photochemistry, it is surprising to recognize that photosensitization mechanisms to access excited-state organometallic catalysts have lagged far behind. Here, we demonstrate excited-state organometallic catalysis via such an activation pathway: Energy transfer from an iridium sensitizer produces an excited-state nickel complex that couples aryl halides with carboxylic acids. Detailed mechanistic studies confirm the role of photosensitization via energy transfer. Copyright © 2017, American Association for the Advancement of Science.

  1. Linker proteins enable ultrafast excitation energy transfer in the phycobilisome antenna system of Thermosynechococcus vulcanus.

    Science.gov (United States)

    Nganou, C; David, L; Adir, N; Mkandawire, M

    2016-01-01

    We applied a femtosecond flash method, using induced transient absorption changes, to obtain a time-resolved view of excitation energy transfer in intact phycobilisomes of Thermosynechococcus vulcanus at room temperature. Our measurement of an excitation energy transfer rate of 888 fs in phycobilisomes shows the existence of ultrafast kinetics along the phycocyanin rod subcomplex to the allophycocyanin core that is faster than expected for previous excitation energy transfer based on Förster theory in phycobilisomes. Allophycocyanin in the core further transfers energy to the terminal emitter(s) in 17 ps. In the phycobilisome, rod doublets composed of hexameric phycocyanin discs and internal linker proteins are arranged in a parallel fashion, facilitating direct rod-rod interactions. Excitonic splitting likely drives rod absorption at 635 nm as a result of strong coupling between β84 chromophores (20 ± 1 Å) in adjacent hexamers. In comparison to the absorbance of the phycobilisome antenna system of the cyanobacterium Acaryochloris marina, which possesses a single rod structure, the linkers in T. vulcanus rods induce a 17 nm red shift in the absorbance spectrum. Furthermore, the kinetics of 888 fs indicates that the presence of the linker protein induces ultrafast excitation energy transfer between phycocyanin and allophycocyanin inside the phycobilisome, which is faster than all previous excitation energy transfer in phycobilisome subunits or sub-complexes reported to date.

  2. Effect resonance radiation transfer of excitation porous silicon to I sub 2 molecules sorbed in pores

    CERN Document Server

    Zakharchenko, K V; Kuznetsov, M B; Chistyakov, A A; Karavanskij, V A

    2001-01-01

    One studies the effect of resonance radiation-free transfer of electronic excitation between silicon nanocrystals and iodine molecules sorbed in pores. The experiment procedure includes laser-induced luminescence and laser desorption mass spectrometry. One analyzes photoluminescence spectra prior to and upon iodine sorption. Excitation of iodine through the mechanism of resonance transfer is determined to result in desorption of the iodine sorbed molecules with relatively high kinetic energies (3-1 eV). One evaluated the peculiar distance of resonance transfer the approximate value of which was equal to 2 nm

  3. Collisional excitation transfer between Rb(5P) states in 50–3000 Torr of 4He

    International Nuclear Information System (INIS)

    Sell, J F; Gearba, M A; Patterson, B M; Byrne, D; Jemo, G; Meeter, R; Knize, R J; Lilly, T C

    2012-01-01

    Measurements of the mixing rates and cross sections for collisional excitation transfer between the 5P 1/2 and 5P 3/2 states of rubidium (Rb) in the presence of 4 He buffer gas are presented. Selected pulses from a high repetition rate, mode-locked femtosecond laser are used to excite either Rb state with the fluorescence due to collisional excitation transfer observed by time-correlated single-photon counting. The time dependence of this fluorescence is fitted to the solution of rate equations which include the mixing rate, atomic lifetimes and any quenching processes. The variation in the mixing rate over a large range of buffer gas densities allows the determination of both the binary collisional transfer cross section and a three-body collisional transfer rate. We do not observe any collisional quenching effects at 4 He pressures up to 6 atm and discuss in detail other systematic effects considered in the experiment. (paper)

  4. Excitation energy transfer from dye molecules to doped graphene

    Indian Academy of Sciences (India)

    to graphene. Recent experiments that have been per- formed after our theoretical studies have infact found efficient energy transfer to graphene and the process was found to be useful in identifying graphene flakes both on substrates and in solution.4 Quenching by graphene was also found to be useful in obtaining good.

  5. Excitation energy transfer from dye molecules to doped graphene

    Indian Academy of Sciences (India)

    of energy transfer to graphene.15,16 We imagine that the. Fermi level is shifted into the conduction band to a level with magnitude of wave vector, kF . To keep the calcu- lations simple, we use the Dirac cone approximation, which allows us to get analytical expressions for the rate at large distances. We note that as we are ...

  6. Excited state intramolecular charge transfer reaction of 4 ...

    Indian Academy of Sciences (India)

    An intramolecular charge transfer (ICT) molecule with an extra hetero atom in its donor moiety has been synthesized in order to investigate how ICT reaction is affected by hetero atom replacement. Photo-physical and photo-dynamical properties of this molecule, 4-(morpholenyl)benzonitrile (M6C), have been studied in 20 ...

  7. Resonant and nonresonant transfer and excitation in Si11+ + He collisions

    International Nuclear Information System (INIS)

    Clark, M.W.

    1988-01-01

    For many years now, dielectronic recombination (DR) has been discussed as a possible energy loss mechanism in high temperature plasmas (e.g. stars). The process is basically the inverse Auger process and involves the capture of a free electron by an ion and the simultaneous excitation of an inner shell electron of the ion producing a doubly excited state. The DR process also includes the radiative deexcitation of the ion and hence represents an energy loss from the plasma since the plasma is essentially transparent to the photons. If, instead of a free electron, an electron that is weakly bound to an atom is captured and an inner shell electron of the ion is excited, the same excited states are produced as in DR. Because the bound electrons have a momentum distribution (Compton profile), individual doubly excited states cannot, in general, be observed in this case. This new process has been called Resonant Transfer and Excitation (RTE). There is also a competing mechanism for RTE in which excitation occurs via the interaction between a projectile ion electron and a target nucleus and the capture occurs because of the interaction of the projectile nucleus and a target electron. This competing mechanism has been termed Nonresonant Transfer and Excitation (NTE) Measurements have been performed to measure RTE and NTE cross sections. A discussion of the theory, methods, and results is included

  8. 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

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

    Indian Academy of Sciences (India)

    to the relatively more polar charge transfer (CT) state with a forward reaction rate constant, kf . Note that the. LE→CT conversion reaction in P4C is associated with an activation barrier21 of ∼ 6kB T. Subsequently, the CT state either regenerates the LE state by participating in the reverse reaction with a rate constant, kr, or, ...

  10. Optical detection of singlet oxygen from single cells

    DEFF Research Database (Denmark)

    Snyder, John; Skovsen, Esben; Lambert, John D. C.

    2006-01-01

    The lowest excited electronic state of molecular oxygen, singlet molecular oxygen, O2(a 1g), is a reactive species involved in many chemical and biological processes. To better understand the roles played by singlet oxygen in biological systems, particularly at the sub-cellular level, optical tools...

  11. Regulation of excitation energy transfer in diatom PSII dimer: How does it change the destination of excitation energy?

    Science.gov (United States)

    Yokono, Makio; Nagao, Ryo; Tomo, Tatsuya; Akimoto, Seiji

    2015-10-01

    Energy transfer dynamics in dimeric photosystem II (PSII) complexes isolated from four diatoms, Chaetoceros gracilis, Cyclotella meneghiniana, Thalassiosira pseudonana, and Phaeodactylum tricornutum, are examined. Time-resolved fluorescence measurements were conducted in the range of 0-80ns. Delayed fluorescence spectra showed a clear difference between PSII monomer and PSII dimer isolated from the four diatoms. The difference can be interpreted as reflecting suppressed energy transfer between PSII monomers in the PSII dimer for efficient energy trapping at the reaction center. The observation was especially prominent in C. gracilis and T. pseudonana. The pathways seem to be suppressed under a low pH condition in isolated PSII complexes from C. gracilis, and excitation energy may be quenched with fucoxanthin chlorophyll a/c-binding protein (FCP) that was closely associated with PSII in C. gracilis. The energy transfer between PSII monomers in the PSII dimer may play a role in excitation energy regulation in diatoms. Copyright © 2015 Elsevier B.V. All rights reserved.

  12. Posture-Dependent Corticomotor Excitability Differs Between the Transferred Biceps in Individuals With Tetraplegia and the Biceps of Nonimpaired Individuals.

    Science.gov (United States)

    Peterson, Carrie L; Rogers, Lynn M; Bednar, Michael S; Bryden, Anne M; Keith, Michael W; Perreault, Eric J; Murray, Wendy M

    2017-04-01

    Following biceps transfer to enable elbow extension in individuals with tetraplegia, motor re-education may be facilitated by greater corticomotor excitability. Arm posture modulates corticomotor excitability of the nonimpaired biceps. If arm posture also modulates excitability of the transferred biceps, posture may aid in motor re-education. Our objective was to determine whether multi-joint arm posture affects corticomotor excitability of the transferred biceps similar to the nonimpaired biceps. We also aimed to determine whether corticomotor excitability of the transferred biceps is related to elbow extension strength and muscle length. Corticomotor excitability was assessed in 7 arms of individuals with tetraplegia and biceps transfer using transcranial magnetic stimulation and compared to biceps excitability of nonimpaired individuals. Single-pulse transcranial magnetic stimulation was delivered to the motor cortex with the arm in functional postures at rest. Motor-evoked potential amplitude was recorded via surface electromyography. Elbow moment was recorded during maximum isometric extension trials, and muscle length was estimated using a biomechanical model. Arm posture modulated corticomotor excitability of the transferred biceps differently than the nonimpaired biceps. Elbow extension strength was positively related and muscle length was unrelated, respectively, to motor-evoked potential amplitude across the arms with biceps transfer. Corticomotor excitability of the transferred biceps is modulated by arm posture and may contribute to strength outcomes after tendon transfer. Future work should determine whether modulating corticomotor excitability via posture promotes motor re-education during the rehabilitative period following surgery.

  13. Decision making based on optical excitation transfer via near-field interactions between quantum dots

    International Nuclear Information System (INIS)

    Naruse, Makoto; Nomura, Wataru; Ohtsu, Motoichi; Aono, Masashi; Sonnefraud, Yannick; Drezet, Aurélien; Huant, Serge; Kim, Song-Ju

    2014-01-01

    Optical near-field interactions between nanostructured matters, such as quantum dots, result in unidirectional optical excitation transfer when energy dissipation is induced. This results in versatile spatiotemporal dynamics of the optical excitation, which can be controlled by engineering the dissipation processes and exploited to realize intelligent capabilities such as solution searching and decision making. Here, we experimentally demonstrate the ability to solve a decision making problem on the basis of optical excitation transfer via near-field interactions by using colloidal quantum dots of different sizes, formed on a geometry-controlled substrate. We characterize the energy transfer behavior due to multiple control light patterns and experimentally demonstrate the ability to solve the multi-armed bandit problem. Our work makes a decisive step towards the practical design of nanophotonic systems capable of efficient decision making, one of the most important intellectual attributes of the human brain.

  14. Separating annihilation and excitation energy transfer dynamics in light harvesting systems.

    Science.gov (United States)

    Vengris, Mikas; Larsen, Delmar S; Valkunas, Leonas; Kodis, Gerdenis; Herrero, Christian; Gust, Devens; Moore, Thomas; Moore, Ana; van Grondelle, Rienk

    2013-09-26

    The dependence of excitation energy transfer kinetics on the electronic state of the acceptor (ground vs excited) has been resolved with a novel multipulse prePump-Pump-Probe spectroscopy. The primary energy transfer and annihilation dynamics in two model light-harvesting systems were explored: an artificially synthesized carotenoid-zinc-phthalocyanine dyad and a naturally occurring light-harvesting peridinin-chlorophyll protein complex from Amphidinium carterae. Both systems use carotenoid as the primary excitation energy donor with porphyrin chromophores as the acceptor molecules. The prePump-Pump-Probe transient signals were analyzed with Monte Carlo modeling to explicitly address the underlying step-by-step kinetics involved in both excitation migration and annihilation processes. Both energy transfer and annihilation dynamics were demonstrated to occur with approximately the same rate in both systems, regardless of the excitation status of the acceptor pigments. The possible reasons for these observations are discussed in the framework of the Förster energy transfer model.

  15. Photochemistry and electron-transfer mechanism of transition metal oxalato complexes excited in the charge transfer band.

    Science.gov (United States)

    Chen, Jie; Zhang, Hua; Tomov, Ivan V; Ding, Xunliang; Rentzepis, Peter M

    2008-10-07

    The photoredox reaction of trisoxalato cobaltate (III) has been studied by means of ultrafast extended x-ray absorption fine structure and optical transient spectroscopy after excitation in the charge-transfer band with 267-nm femtosecond pulses. The Co-O transient bond length changes and the optical spectra and kinetics have been measured and compared with those of ferrioxalate. Data presented here strongly suggest that both of these metal oxalato complexes operate under similar photoredox reaction mechanisms where the primary reaction involves the dissociation of a metal-oxygen bond. These results also indicate that excitation in the charge-transfer band is not a sufficient condition for the intramolecular electron transfer to be the dominant photochemistry reaction mechanism.

  16. Vibration excitation and energy transfer during ultrasonically assisted drilling

    Science.gov (United States)

    Babitsky, V. I.; Astashev, V. K.; Meadows, A.

    2007-12-01

    Successful application of ultrasonically assisted drilling needs dynamic matching of the transducer with the drill bit considered as a continuous system loaded by the nonlinear processing load. When using standard tools this leads to the compatible choice of the transducer and accurate matching of the transducer and tool. The principal dynamical features of this matching are considered. Optimal position of excitation cross section of the drill bit, which depends on the relationship between elasto-dissipative characteristics of the transducer, the drill bit and the work load, is found in general analytical form. The optimal matching preserves the resonant tuning of the transducer and compensates the additional energy losses in the drill bit and processing. This produces also an amplification of vibration amplitude. The effect is achieved through the generation and maintenance of a nonlinear resonant mode of vibration and by active matching of the oscillating system with the dynamic loads imposed by the cutting process with the help of the intelligent electronic feedback circuitry. A prototype of an ultrasonic drilling system has been designed, manufactured. and tested. Improvements of machining characteristics due to superposition of ultrasonic vibration are demonstrated. Substantial improvements in the cutting performance of drill bits lead to benefits in drilling performance, which include faster penetration rates, reduction of tool wear, improvements in the surface finish, roundness and straightness of holes and, in ductile materials, the reduction or even complete elimination of burrs on both the entrance and exit faces of plates. The reduction in the reactive force experienced also causes greatly reduced deformation when drilling through thin, flexible plates and helps to alleviate delamination hazard.

  17. 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.

  18. Comparison of excitation energy transfer in cyanobacterial photosystem I in solution and immobilized on conducting glass.

    Science.gov (United States)

    Szewczyk, Sebastian; Giera, Wojciech; D'Haene, Sandrine; van Grondelle, Rienk; Gibasiewicz, Krzysztof

    2017-05-01

    Excitation energy transfer in monomeric and trimeric forms of photosystem I (PSI) from the cyanobacterium Synechocystis sp. PCC 6803 in solution or immobilized on FTO conducting glass was compared using time-resolved fluorescence. Deposition of PSI on glass preserves bi-exponential excitation decay of ~4-7 and ~21-25 ps lifetimes characteristic of PSI in solution. The faster phase was assigned in part to photochemical quenching (charge separation) of excited bulk chlorophylls and in part to energy transfer from bulk to low-energy (red) chlorophylls. The slower phase was assigned to photochemical quenching of the excitation equilibrated over bulk and red chlorophylls. The main differences between dissolved and immobilized PSI (iPSI) are: (1) the average excitation decay in iPSI is about 11 ps, which is faster by a few ps than for PSI in solution due to significantly faster excitation quenching of bulk chlorophylls by charge separation (~10 ps instead of ~15 ps) accompanied by slightly weaker coupling of bulk and red chlorophylls; (2) the number of red chlorophylls in monomeric PSI increases twice-from 3 in solution to 6 after immobilization-as a result of interaction with neighboring monomers and conducting glass; despite the increased number of red chlorophylls, the excitation decay accelerates in iPSI; (3) the number of red chlorophylls in trimeric PSI is 4 (per monomer) and remains unchanged after immobilization; (4) in all the samples under study, the free energy gap between mean red (emission at ~710 nm) and mean bulk (emission at ~686 nm) emitting states of chlorophylls was estimated at a similar level of 17-27 meV. All these observations indicate that despite slight modifications, dried PSI complexes adsorbed on the FTO surface remain fully functional in terms of excitation energy transfer and primary charge separation that is particularly important in the view of photovoltaic applications of this photosystem.

  19. The development of efficient two-photon singlet oxygen sensitizers

    DEFF Research Database (Denmark)

    Nielsen, Christian Benedikt

    the singlet oxygen yield and the two-photon absorption cross section, where it was revealed that a careful balancing of the amount of charge transfer present in theexcited state of the sensitizer is necessary to obtain both a high singlet oxygen quantum yield and a high two-photon cross section. An increasing...... amount of charge-transfer is beneficial for high two-photon absorption cross sections but iscounter-productive for singlet oxygen generation. The design principles obtained from the studies in lipophilic solvents were applied to synthesize water-soluble twophoton singlet oxygen sensitizers......The development of efficient two-photon singlet oxygen sensitizers is addressed focusing on organic synthesis. Photophysical measurements were carried out on new lipophilic molecules, where two-photon absorption cross sections and singlet oxygen quantumyields were measured. Design principles...

  20. 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)

  1. Synthesis, spectral behaviour and photophysics of donor-acceptor kind of chalcones: Excited state intramolecular charge transfer and fluorescence quenching studies

    Science.gov (United States)

    Pannipara, Mehboobali; Asiri, Abdullah M.; Alamry, Khalid A.; Arshad, Muhammad N.; El-Daly, Samy A.

    2015-02-01

    The spectral and photophysical properties of two chalcones containing electron donating and accepting groups with intramolecular charge transfer characteristics were synthesized and characterized by 1H NMR, 13C NMR and X-ray crystallography. Both compounds show very strong solvent polarity dependent changes in their photophysical characteristics, namely, remarkable red shift in the emission spectra with increasing solvent polarity, large change in Stokes shift, significant reduction in the fluorescence quantum yield; indicating that the fluorescence states of these compounds are of intramolecular charge transfer (ICT) character. The solvent effect on the photophysical parameters such as singlet absorption, molar absorptivity, oscillator strength, dipole moment, fluorescence spectra, and fluorescence quantum yield of both compounds have been investigated comprehensively. For both dyes, Lippert-Mataga and Reichardt's correlations were used to estimate the difference between the excited and ground state dipole moments (Δμ). The interactions of dyes with colloidal silver nanoparticles (Ag NPs) were also studied in ethanol using steady state fluorescence quenching measurements. The fluorescence quenching data reveal that dynamic quenching and energy transfer play a major role in the fluorescence quenching of dyes by Ag NPs.

  2. Theoretical characterization of excitation energy transfer in chlorosome light-harvesting antennae from green sulfur bacteria.

    Science.gov (United States)

    Fujita, Takatoshi; Huh, Joonsuk; Saikin, Semion K; Brookes, Jennifer C; Aspuru-Guzik, Alán

    2014-06-01

    We present a theoretical study of excitation dynamics in the chlorosome antenna complex of green photosynthetic bacteria based on a recently proposed model for the molecular assembly. Our model for the excitation energy transfer (EET) throughout the antenna combines a stochastic time propagation of the excitonic wave function with molecular dynamics simulations of the supramolecular structure and electronic structure calculations of the excited states. We characterized the optical properties of the chlorosome with absorption, circular dichroism and fluorescence polarization anisotropy decay spectra. The simulation results for the excitation dynamics reveal a detailed picture of the EET in the chlorosome. Coherent energy transfer is significant only for the first 50 fs after the initial excitation, and the wavelike motion of the exciton is completely damped at 100 fs. Characteristic time constants of incoherent energy transfer, subsequently, vary from 1 ps to several tens of ps. We assign the time scales of the EET to specific physical processes by comparing our results with the data obtained from time-resolved spectroscopy experiments.

  3. Dynamics of excited state proton transfer in nitro substituted 10-hydroxybenzo[h] quinolines

    DEFF Research Database (Denmark)

    Marciniak, 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...... occurs with a time constant of 0.89 ps and 0.68 ps, respectively. In both cases a mixture of the enol and proton transfer forms is optically excited. The enol form exhibits then the ESIPT and subsequently both fractions take the same relaxation path. We propose that in 2 and 3 the ESIPT path exhibits...... a potential energy barrier resulting in an incoherent rate governed process while in HBQ the ESIPT proceeds as a ballistic wavepacket motion along a path without significant barriers. The theoretical calculations (M06-2X/TZVP) confirm the existence of a barrier in the ground and excited states as result...

  4. Effect of antenna-depletion in photosystem II on excitation energy transfer in Arabidopsis thaliana

    NARCIS (Netherlands)

    Van Oort, Bart; Alberts, Marieke; De Bianchi, Silvia; Dall'Osto, Luca; Bassi, Roberto; Trinkunas, Gediminas; Croce, Roberta; van Amerongen, Herbert

    2010-01-01

    The role of individual photosynthetic antenna complexes of Photosystem II (PSII) both in membrane organization and excitation energy transfer have been investigated. Thylakoid membranes from wild-type Arabidopsis thaliana, and three mutants lacking light-harvesting complexes CP24, CP26, or CP29,

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

    KAUST Repository

    Whited, Matthew T.

    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.

  6. Evidence for resonance electron transfer in photon excited X-ray ...

    Indian Academy of Sciences (India)

    is also measured. The measured relative intensities are compared with the theoretical estimates of Aberg. Keywords. X-ray satellites; resonance electron transfer; crystal spectrometer. PACS Nos 32.30.Rj; 32.80.Hd; 78.70.En. 1. Introduction. When an atom ionized simultaneously in different shells de-excites, X-ray satellites.

  7. Evidence for resonance electron transfer in photon excited X-ray ...

    Indian Academy of Sciences (India)

    Evidence for resonance electron transfer in photon excited X-ray satellite spectra of fluorine compounds. K Ram Narayana B Seetharami Reddy S S Raju T Seshi Reddy S Lakshmi Narayana K Premachand B M Rao M V R Murti L S Mombasawala. Research Articles Volume 65 Issue 2 August 2005 pp 285-290 ...

  8. Generating Excitement: Build Your Own Generator to Study the Transfer of Energy

    Science.gov (United States)

    Fletcher, Kurt; Rommel-Esham, Katie; Farthing, Dori; Sheldon, Amy

    2011-01-01

    The transfer of energy from one form to another can be difficult to understand. The electrical energy that turns on a lamp may come from the burning of coal, water falling at a hydroelectric plant, nuclear reactions, or gusts of wind caused by the uneven heating of the Earth. The authors have developed and tested an exciting hands-on activity to…

  9. BODIPY-pyrene and perylene dyads as heavy atom-free singlet oxygen sensitizers

    KAUST Repository

    Filatov, Mikhail A.

    2018-02-23

    Dyads combining BODIPY as an electron acceptor and pyrene or perylene as electron donor subunits were prepared and studied their photophysical properties studied by steady-state and transient spectroscopy. Depending on the structure of the subunits and polarity of the media, the dyads show either bright fluorescence or photo-induced electron transfer (PeT) in solution. Charge-transfer (CT) states formed as a result of PeT and were found to yield triplet excited states of the BODIPY. In the presence of molecular oxygen, the dyads sensitize singlet oxygen (1O2) with quantum yields of up to 0.75.

  10. Photophysics of Singlet and Triplet Intraligand Excited States in [ReCl(CO)(3)(1-(2-pyridyl)-imidazo[1,5-alpha]pyridine)] Complexes

    Czech Academy of Sciences Publication Activity Database

    Blanco-Rodríguez, A. M.; Kvapilová, Hana; Sýkora, Jan; Towrie, M.; Nervi, C.; Volpi, G.; Záliš, Stanislav; Vlček, Antonín

    2014-01-01

    Roč. 136, č. 16 (2014), s. 5963-5973 ISSN 0002-7863 R&D Projects: GA ČR GBP208/12/G016; GA MŠk LD11086 Institutional support: RVO:61388955 Keywords : CARBONYL-BIPYRIDINE COMPLEXES * RESOLVED INFRARED-SPECTROSCOPY * CHARGE-TRANSFER STATES Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 12.113, year: 2014

  11. Probing nuclear shell structure beyond the N=40 subshell using multiple Coulomb excitation and transfer experiments

    Energy Technology Data Exchange (ETDEWEB)

    Hellgartner, Stefanie Christine

    2015-11-13

    In this work, the N=40 subshell closure is investigated with two complementary methods using a radioactive {sup 72}Zn ISOLDE beam: One- and two-neutron transfer reactions and multiple Coulomb excitation. In the one-neutron transfer reaction, two new levels of {sup 73}Zn were discovered. The two-neutron transfer channel allowed to study the differential cross section of the ground state and the 2{sup +}{sub 1} state of {sup 74}Zn. In the Coulomb excitation experiment, the measured B(E2) values and quadrupole moments of {sup 72}Zn showed that the yrast states 0{sup +}{sub 1}, 2{sup +}{sub 1} and 4{sup +}{sub 1} are moderately collective. Contrary, the 0{sup +}{sub 2} state has a different structure, since it features a stronger closed N=40 configuration compared to the ground state.

  12. Transient negative photoconductance in a charge transfer double quantum well under optical intersubband excitation

    Science.gov (United States)

    Rüfenacht, M.; Tsujino, S.; Sakaki, H.

    1998-06-01

    Recently, it was shown that an electron-hole radiative recombination is induced by a mid-infrared light exciting an intersubband transition in a charge transfer double quantum well (CTDQW). This recombination was attributed to an upstream transfer of electrons from an electron-rich well to a hole-rich well. In this study, we investigated the electrical response of a CTDQW under intersubband optical excitation, and found that a positive photocurrent, opposite in sign and proportional to the applied electric field, accompanies the intersubband-transition-induced luminescence (ITIL) signal. A negative photocurrent component was also observed and attributed to heating processes. This work brings a further evidence of the ITIL process and shows that an important proportion of the carriers are consumed by the transfer of electrons.

  13. Novel foamy origin for singlet fermion masses

    Science.gov (United States)

    Ellis, John; Mavromatos, Nick E.; Nanopoulos, Dimitri V.

    2017-10-01

    We show how masses for singlet fermions can be generated by interactions with a D-particle model of space-time foam inspired by brane theory. It has been shown previously by one of the authors (N. E. M.) that such interactions may generate dynamically small masses for charged fermions via the recoils of D-particle defects interacting with photons. In this work we consider the direct interactions of D-particle with uncharged singlet fermions such as right-handed neutrinos. Quantum fluctuations of the lattice of D-particles have massless vector (spin-one) excitations that are analogues of phonons. These mediate forces with the singlet fermions, generating large dynamical masses that may be communicated to light neutrinos via the seesaw mechanism.

  14. Optimized excitation energy transfer in a three-dye luminescent solar concentrator

    Energy Technology Data Exchange (ETDEWEB)

    Bailey, Sheldon T.; Lokey, Gretchen E.; Hanes, Melinda S.; McLafferty, Jason B.; Beaumont, Gregg T.; Wittmershaus, Bruce P. [School of Science, Pennsylvania State University: Erie, The Behrend College, Erie, PA 16563-0203 (United States); Shearer, John D.M.; Baseler, Timothy T.; Layhue, Joshua M.; Broussard, Dustin R. [School of Engineering, Pennsylvania State University: Erie, The Behrend College, Erie, PA 16563-1701 (United States); Zhang, Yu-Zhong [Molecular Probes Inc., 4849 Pitchford Ave., Eugene, OR 97402-9165 (United States)

    2007-01-05

    The spectral range of sunlight absorbed by a luminescent solar concentrator (LSC) is increased by using multiple dyes. Absorption, fluorescence, and fluorescence excitation spectra, and relative light output are reported for LSCs made with one, two, or three BODIPY dyes in a thin polymer layer on glass. Losses caused by multiple emission and reabsorption events are minimized by optimizing resonance excitation energy transfer between dyes. Increases in the outputs from the multiple-dye LSCs are directly proportional to increases in the number of photons absorbed. The output of the three-dye LSC is 45-170% higher than those of the single-dye LSCs. (author)

  15. Comparison of modified driver circuit and capacitor-transfer circuit in longitudinally excited N2 laser.

    Science.gov (United States)

    Uno, Kazuyuki; Akitsu, Tetsuya; Nakamura, Kenshi; Jitsuno, Takahisa

    2013-04-01

    We developed a modified driver circuit composed of a capacitance and a spark gap, called a direct-drive circuit, for a longitudinally excited gas laser. The direct-drive circuit uses a large discharge impedance caused by a long discharge length of the longitudinal excitation scheme and eliminates the buffer capacitance used in the traditional capacitor-transfer circuit. We compared the direct-drive circuit and the capacitor-transfer circuit in a longitudinally excited N2 laser (wavelength: 337 nm). Producing high output energy with the capacitor-transfer circuit requires a large storage capacitance and a discharge tube with optimum dimensions (an inner diameter of 4 mm and a length of 10 cm in this work); in contrast, the direct-drive circuit requires a high breakdown voltage, achieved with a small storage capacitance and a large discharge tube. Additionally, for the same input energy of 792 mJ, the maximum output energy of the capacitor-transfer circuit was 174.2 μJ, and that of the direct-drive circuit was 344.7 μJ.

  16. 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.

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

    Science.gov (United States)

    Lee, Mi Kyung; Coker, David F

    2016-08-18

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

  18. 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.

  19. Excitation functions for quasi-elastic transfer reactions induced with heavy ions in bismuth

    International Nuclear Information System (INIS)

    Gardes, D.; Bimbot, R.; Maison, J.; Reilhac, L. de; Rivet, M.F.; Fleury, A.; Hubert, F.; Llabador, Y.

    1977-01-01

    The excitation functions for the production of 210 Bi, 210 Po, sup(207-211)At and 211 Rn through quasi-elastic transfer reactions induced with heavy ions in 209 Bi have been measured. The corresponding reactions involved the transfer of one neutron, one proton, two and three charges from projectile to target. The projectiles used were 12 C, 14 N, 16 O, 19 F, 20 Ne, 40 Ca, 56 Fe and 63 Cu. The experimental techniques involved target irradiations and off-line α and γ activity measurements. Chemical separations were used to solve specific problems. Careful measurements of incident energies and cross sections were performed close to the reaction thresholds

  20. Excitation and charge transfer in low-energy hydrogen atom collisions with neutral oxygen

    Science.gov (United States)

    Barklem, P. S.

    2018-02-01

    Excitation and charge transfer in low-energy O+H collisions is studied; it is a problem of importance for modelling stellar spectra and obtaining accurate oxygen abundances in late-type stars including the Sun. The collisions have been studied theoretically using a previously presented method based on an asymptotic two-electron linear combination of atomic orbitals (LCAO) model of ionic-covalent interactions in the neutral atom-hydrogen-atom system, together with the multichannel Landau-Zener model. The method has been extended to include configurations involving excited states of hydrogen using an estimate for the two-electron transition coupling, but this extension was found to not lead to any remarkably high rates. Rate coefficients are calculated for temperatures in the range 1000-20 000 K, and charge transfer and (de)excitation processes involving the first excited S-states, 4s.5So and 4s.3So, are found to have the highest rates. Data are available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/vizbin/qcat?J/A+A/610/A57. The data are also available at http://https://github.com/barklem/public-data

  1. 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.

  2. Vibration transfers to measure the performance of vibration isolated platforms on site using background noise excitation

    Science.gov (United States)

    Segerink, F. B.; Korterik, J. P.; Offerhaus, H. L.

    2011-06-01

    This article demonstrates a quick and easy way of quantifying the performance of a vibration-isolated platform. We measure the vibration transfer from floor to table using background noise excitation from the floor. As no excitation device is needed, our setup only requires two identical sensors (in our case, low noise accelerometers), a data acquisition system, and processing software. Background noise excitation from the floor has the additional advantage that any non-linearity in the suspension system relevant to the actual vibration amplitudes will be taken into account. Measurement time is typically a few minutes, depending on the amount of background noise. The (coherent) transfer of the vibrations in the floor to the platform, as well as the (non-coherent) acoustical noise pick-up by the platform are measured. Since we use calibrated sensors, the absolute value of the vibration levels is established and can be expressed in vibration criterion curves. Transfer measurements are shown and discussed for two pneumatic isolated optical tables, a spring suspension system, and a simple foam suspension system.

  3. Energy transfer in anisotropic systems: A. Excitation migration in substitutionally disordered one-dimensional solids. B. The spectroscopy of molecules adsorbed on metal surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Zwemer, D.A.

    1978-11-01

    The energy and dynamics of excited states in a variety of anisotropic environments, including isotopically and chemically mixed crystals and molecular overlayers adsorbed on a nickel (111) surface, are investigated. The relationship between local and long-range structure and spectroscopic properties is explored. A theory for energy transfer in substitutionally disordered solids is presented. Explicit expressions for the ''diffusion'' coefficients and the energy partitioning ratios in binary systems are derived. Energy transfer between localized states is found to be facilitated by concurrent tunnelling and thermal promotion. Experimental results for triplet energy partitioning between mobile and stationary trap states as a function of mobile trap concentration in the ternary d/sub 2/-1,2,4,5-tetrachlorobenzene--h/sub 2/-1,2,4,5-tetrachlorobenzene--pyrazine system are analyzed. It is shown that both tunnelling and thermal detrapping contribute to triplet exciton mobility below 4.2 K. Singlet exciton migration makes an important contribution to trap equilibration before intersystem crossing to the triplet manifold. Spin coherence experiments are used to determine the energy level structure, physical geometry, and exciton dynamics of a series of impurity-induced traps in 1,2,4,5-tetrachlorobenzene. The uv spectra of pyrazine, pyridine, and naphthalene adsorbed on a nickel single crystal (111) surface are measured by spectroscopic ellipsometry at low temperatures. The excited electronic and vibronic energy levels measured are similar to bulk molecular crystal values, but pyrazine and pyridine show small, but significant deviations. The ordering of molecular overlays is observed spectroscopically and information about overlayer crystal structure is deduced. 148 references, 48 figures, 5 tables.

  4. Excited-state intramolecular proton transfer in 3-hyroxyflavone isolated in solid argon: fluorescence and fluorescence-excitation spectra and tautomer fluorescence rise time

    Energy Technology Data Exchange (ETDEWEB)

    Dick, B.; Ernsting, N.P.

    1987-07-30

    The fluorescence properties of 3-hydroxyflavone isolated in solid argon at 15 K have been investigated. Upon electronic excitation the molecules undergo rapid intramolecular proton transfer. No fluorescence from the excited state of the normal form of the molecule could be detected. Perturbations due to hydrogen-bonding impurities which produce serious experimental problems in hydrocarbon glasses are largely suppressed in argon matrices. The rise of the green fluorescence of the tautomer was studied with excitation pulses of 230-fs duration and streak camera detection. An apparent tautomer fluorescence rise time of 2.7 ps was obtained by deconvolution. A comparative measurement of the dye coumarine 6 yielded an apparent fluorescence rise time of 2.5 ps, which can be entirely attributed to the group velocity dispersion of the streak camera optics. This indicates a rate constant for excited-state intramolecular proton transfer in 3-hydroxyflavone of greater than 10/sup 12/ s/sup -1/.

  5. Machine learning for quantum dynamics: deep learning of excitation energy transfer properties.

    Science.gov (United States)

    Häse, Florian; Kreisbeck, Christoph; Aspuru-Guzik, Alán

    2017-12-01

    Understanding the relationship between the structure of light-harvesting systems and their excitation energy transfer properties is of fundamental importance in many applications including the development of next generation photovoltaics. Natural light harvesting in photosynthesis shows remarkable excitation energy transfer properties, which suggests that pigment-protein complexes could serve as blueprints for the design of nature inspired devices. Mechanistic insights into energy transport dynamics can be gained by leveraging numerically involved propagation schemes such as the hierarchical equations of motion (HEOM). Solving these equations, however, is computationally costly due to the adverse scaling with the number of pigments. Therefore virtual high-throughput screening, which has become a powerful tool in material discovery, is less readily applicable for the search of novel excitonic devices. We propose the use of artificial neural networks to bypass the computational limitations of established techniques for exploring the structure-dynamics relation in excitonic systems. Once trained, our neural networks reduce computational costs by several orders of magnitudes. Our predicted transfer times and transfer efficiencies exhibit similar or even higher accuracies than frequently used approximate methods such as secular Redfield theory.

  6. Energy transfer from excited cyclobutane-t chemically activated by nuclear recoil reaction

    International Nuclear Information System (INIS)

    Nogar, N.S.

    1976-01-01

    Relative energy transfer efficiencies were determined for collisions between highly excited cyclobutane-t and a number of thermal bath gases, including nitrogen, tetrafluoromethane, the noble gases, and cyclobutane. The excited cyclobutane-t was produced with a broad spectrum of energies about a mean energy of 5 eV by replacement of hydrogen with nuclear recoil tritium. The distribution of cyclobutane-t included a fraction produced at such low energies that it was not subjected to unimolecular decomposition, a fraction always found as the decomposition product, ethylene-t, and a fraction subject to competitive stabilization-decomposition reactions. The fraction of cyclobutane-t produced at such extreme energies that it was not subject to competitive unimolecular reaction was determined by curve-fitting the pressure dependence of ratio of cyclobutane-t to ethylene-t. Subsequent examination of the composition dependence of the ratio of competitive cyclobutane-t and ethylene-t yields gave energy transfer efficiencies for C 4 H 8 , CF 4 , N 2 , He, Ne, Ar, Kr, and Xe of 1.00:1.05:0.40, 0.12, 0.23, 0.24, 0.31, 0.39. The relative efficiencies found in this system are similar to those found in high energy conventional chemical activation systems, supporting this method for determination of energy transfer efficiencies following nuclear recoil activation. Cascade deactivation is demonstrated for this system and discussed with respect to energy transfer in hot atom activated systems

  7. Excited-state proton transfer in methanol-doped ice in the presence of KF.

    Science.gov (United States)

    Uritski, Anna; Huppert, Dan

    2008-05-15

    Steady-state and time-resolved emission techniques were employed to study the photoprotolytic cycle of an excited photoacid in ice in the presence of a low concentration of a weak base-like F(-). In previous studies we found that the photoprotolytic cycle in methanol-doped ice (1% mol fraction) is too slow to be observed at temperatures below 190 K. In this study we found that at temperatures below 240 K an additional proton-transfer process occurs in ice doped with 10 mM KF. We attributed this reaction to the creation of a mobile L-defect by F(-) ions. We used a diffusion-assisted reaction model, based on the Debye-Smoluchowski equation, to account for the direct reaction of the L-defect with the excited photoacid at temperatures below T < 240 K. Below 160 K the spectroscopic properties as well as the photoprotolytic cycle change dramatically. We propose that below 160 K the sample enters a new phase. The excited-state proton-transfer (ESPT) process was observed and followed down to a liquid nitrogen temperature of approximately 78 K. In the low-temperature phase the ESPT rate is almost twice as much as at 180 K and the temperature dependence of the rate is very small. The kinetic isotope effect of the ESPT at the low-temperature phase is small of about 1.3.

  8. Studies on bacterial chromatophores I. Reversible disturbance of transfer of electronic excitation energy between bacteriochlorophyll-types in chromatium

    NARCIS (Netherlands)

    Bril, C.

    1960-01-01

    Desocycholate affects the transfer of excitation energy between bacteriochlorophyll-types in Chromatium chromatophores. It is suggested, that the detergent fragments the chromatophore into subunits and subsequenyly disturbs the spatial arrangement of these bacteriochlorophyll-types.

  9. Investigation of collisional excitation-transfer processes in a plasma by laser perturbation method

    International Nuclear Information System (INIS)

    Sakurai, Takeki

    1983-01-01

    The theoretical background and the experimental method of the laser perturbation method applied to the study of collisional excitation transfer process in plasma are explained. The atomic density at some specified level can be evaluated theoretically. By using the theoretical results and the experimentally obtained data, the total attenuation probability, the collisional transfer probability and natural emission probability were estimated. For the experiments, continuous wave laser (cw) and pulse laser are employed. It is possible by using pulse dye laser to observe the attenuation curve directly, and to bring in resonance to any atomic spectra. At the beginning, the experimental studies were made on He-Ne discharge. The pulse dye laser has been used for the excitation of alkali atoms. The first application of pulse laser to the study of plasma physics was the study on He. The cross section of disalignment has also been studied by the laser perturbation. The alignment of atoms, step and cascade transfer, the confinement of radiation and optogalvanic effect are discussed in this paper. (Kato, T.)

  10. Prototropic studies in vitreous and in solid phases: Pyranine and 2-naphthol excited state proton transfer

    Energy Technology Data Exchange (ETDEWEB)

    Silva, Fátima Aparecida das Chagas [Departamento de Química Fundamental, Faculdade de Ciências Farmacêuticas, Universidade de São Paulo, SP (Brazil); Rezende, Eduardo Triboni [Universidade Nove de Julho, São Paulo, SP (Brazil); Filho, Décio Briotto [Departamento de Bioquímica Instituto de Química, Faculdade de Ciências Farmacêuticas, Universidade de São Paulo, SP (Brazil); Brito Rezende, Daisy de [Departamento de Química Fundamental, Faculdade de Ciências Farmacêuticas, Universidade de São Paulo, SP (Brazil); Cuccovia, Iolanda Midea [Departamento de Bioquímica Instituto de Química, Faculdade de Ciências Farmacêuticas, Universidade de São Paulo, SP (Brazil); Gome, Ligia Ferreira [Departamento de Análises Clínicas, Faculdade de Ciências Farmacêuticas, Universidade de São Paulo, SP (Brazil); Silva, Mauro Francisco Pinheiro da [Departamento de Química Fundamental, Faculdade de Ciências Farmacêuticas, Universidade de São Paulo, SP (Brazil); and others

    2014-02-15

    Excited state proton transfer processes in vitreous glasses and in solid mixtures are investigated by steady state fluorimetry and laser flash photolysis kinetic studies with the photoacids pyranine and 2-naphthol. Glasses were derived from TEOS by the sol–gel condensation process and hydrated solid mixtures from NaCl or KH{sub 2}PO{sub 4}/K{sub 2}HPO{sub 4} crystals. The extent of the water content necessary for the reaction is determined. Shrinkage of TEOS derived monoliths from water loss leads to an increase in proton transfer extent due to the increase in local concentrations of accepting and donor buffer species, but the concomitant increase in the ionic strength actuates in an opposite direction. Furthermore, water losses by aging of air-exposed gel goes to a critical 20% weight fraction, beyond it proton transfer reactions are hindered. Similar studies with solid NaCl or solid phosphate buffer mixtures demonstrated the same critical water level indicating that free water molecules are crucial for the proton to escape from the original cage where the geminate ion pair [–||RO{sup −⁎}H{sup +}||–] is formed and can undergo coupled proton transfer reactions. -- Highlights: • Pyranine and 2-naphthol excited state proton transfer in SiO{sub 2} gel, solid phosphate buffer and NaCl. • Sol–gel formation leads to contraction and concentration of donor and accepting species. • 20% weight fraction water is required for the ESPT to go forward.

  11. Picosecond excitation energy transfer of allophycocyanin studied in solution and in crystals.

    Science.gov (United States)

    Ranjbar Choubeh, Reza; Sonani, Ravi R; Madamwar, Datta; Struik, Paul C; Bader, Arjen N; Robert, Bruno; van Amerongen, Herbert

    2018-03-01

    Cyanobacteria perform photosynthesis with the use of large light-harvesting antennae called phycobilisomes (PBSs). These hemispherical PBSs contain hundreds of open-chain tetrapyrrole chromophores bound to different peptides, providing an arrangement in which excitation energy is funnelled towards the PBS core from where it can be transferred to photosystem I and/or photosystem II. In the PBS core, many allophycocyanin (APC) trimers are present, red-light-absorbing phycobiliproteins that covalently bind phycocyanobilin (PCB) chromophores. APC trimers were amongst the first light-harvesting complexes to be crystallized. APC trimers have two spectrally different PCBs per monomer, a high- and a low-energy pigment. The crystal structure of the APC trimer reveals the close distance (~21 Å) between those two chromophores (the distance within one monomer is ~51 Å) and this explains the ultrafast (~1 ps) excitation energy transfer (EET) between them. Both chromophores adopt a somewhat different structure, which is held responsible for their spectral difference. Here we used spectrally resolved picosecond fluorescence to study EET in these APC trimers both in crystallized and in solubilized form. We found that not all closely spaced pigment couples consist of a low- and a high-energy pigment. In ~10% of the cases, a couple consists of two high-energy pigments. EET to a low-energy pigment, which can spectrally be resolved, occurs on a time scale of tens of picoseconds. This transfer turns out to be three times faster in the crystal than in the solution. The spectral characteristics and the time scale of this transfer component are similar to what have been observed in the whole cells of Synechocystis sp. PCC 6803, for which it was ascribed to EET from C-phycocyanin to APC. The present results thus demonstrate that part of this transfer should probably also be ascribed to EET within APC trimers.

  12. 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

  13. 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.

  14. Non-typical fluorescence studies of excited and ground state proton and hydrogen transfer

    KAUST Repository

    Gil, Michał

    2017-02-03

    Fluorescence studies of tautomerization have been carried out for various systems that exhibit single and double proton or hydrogen translocation in various environments, such as liquid and solid condensed phases, ultracold supersonic jets, and finally, polymer matrices with single emitters.We focus on less explored areas of application of fluorescence for tautomerization studies, using porphycene, a porphyrin isomer, as an example. Fluorescence anisotropy techniques allow investigations of self-exchange reactions, where the reactant and product are formally identical. Excitation with polarized light makes it possible to monitor tautomerization in single molecules and to detect their three-dimensional orientation. Analysis of fluorescence from single vibronic levels of jet-isolated porphycene not only demonstrates coherent tunneling of two internal protons, but also indicates that the process is vibrational mode-specific. Next, we present bifunctional proton donoracceptor systems, molecules that are able, depending on the environment, to undergo excited state single intramolecular or double intermolecular proton transfer. For molecules that have donor and acceptor groups located in separate moieties linked by a single bond, excited state tautomerization can be coupled to mutual twisting of the two subunits.

  15. NO-γ emissions from streamer discharges: direct electron impact excitation versus resonant energy transfer

    International Nuclear Information System (INIS)

    Liu Ningyu; Pasko, Victor P

    2010-01-01

    It has been established that production of NO-γ emission in pulsed corona discharges is dominated by the energy transfer from N 2 (A 3 Σ u + ) to the NO ground state NO(X 2 Π r ) while direct excitation by electron impact is negligible. However, recent studies suggest that the electron impact excitation plays a more important role. In this work, we report modelling results of NO-γ emission associated with streamer discharges using two cross section data sets available in the literature. The first set was originally reported by Mojarrabi et al (1996 Phys. Rev. A 54 2977-82) and later updated by Brunger et al (2000 J. Phys. B: At. Mol. Opt. Phys. 33 809-19); the second set was published by Hayashi (1990 Nonequilibrium Processes in Partially Ionized Gases (NATO Advanced Science Institutes Series, Series B, Physics vol 220) ed M Capitelli and J N Bardsley (New York: Plenum) pp 333-40). According to the results, the role played by the electron impact excitation in the production of NO-γ is drastically different when different cross sections are used. The results indicate that the first data set leads to better agreement with experimental measurements. (fast track communication)

  16. New strategies to produce and detect singlet oxygen in a cell

    DEFF Research Database (Denmark)

    Gollmer, Anita

    2012-01-01

    product of the reaction between SOSG and singlet oxygen is itself an efficient singlet oxygen sensitizer and, second, that despite published claims to the contrary, SOSG can, in fact, be incorporated into living mammalian cells. Further, a new fluorescent probe for singlet oxygen called “Aarhus Green...... to achieve a reproducible assessment of cell response to a controlled dose of singlet oxygen produced in a spatially-localized two-photon sensitized experiment. Different assays were used to visualize cell response. In this dissertation, various aspects of fluorescence imaging and two-photon excitation......Singlet oxygen, the first excited electronic state of molecular oxygen, plays a major role in oxygen-dependent photo-induced cell death. In such systems, singlet oxygen is generally produced in a photosensitized process wherein light is absorbed by a molecule (the so-called sensitizer) which...

  17. 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.

  18. Theory of Excitation Transfer between Two-Dimensional Semiconductor and Molecular Layers

    Science.gov (United States)

    Specht, Judith F.; Verdenhalven, Eike; Bieniek, Björn; Rinke, Patrick; Knorr, Andreas; Richter, Marten

    2018-04-01

    The geometry-dependent energy transfer rate from an electrically pumped inorganic semiconductor quantum well into an organic molecular layer is studied theoretically. We focus on Förster-type nonradiative excitation transfer between the organic and inorganic layers and include quasimomentum conservation and intermolecular coupling between the molecules in the organic film. (Transition) partial charges calculated from density-functional theory are used to calculate the coupling elements. The partial charges describe the spatial charge distribution and go beyond the common dipole-dipole interaction. We find that the transfer rates are highly sensitive to variations in the geometry of the hybrid inorganic-organic system. For instance, the transfer efficiency is improved by up to 2 orders of magnitude by tuning the spatial arrangement of the molecules on the surface: Parameters of importance are the molecular packing density along the effective molecular dipole axis and the distance between the molecules and the surface. We also observe that the device performance strongly depends on the orientation of the molecular dipole moments relative to the substrate dipole moments determined by the inorganic crystal structure. Moreover, the operating regime is identified where inscattering dominates over unwanted backscattering from the molecular layer into the substrate.

  19. Strategy of ring-shaped aggregates in excitation energy transfer for removing disorder-induced shielding

    Science.gov (United States)

    Tei, Go; Nakatani, Masatoshi; Ishihara, Hajime

    2013-06-01

    Peripheral light harvesting complex (LH2), which is found in photosynthetic antenna systems of purple photosynthetic bacteria, has important functions in the photosynthetic process, such as harvesting sunlight and transferring its energy to the photosynthetic reaction center. The key component in excitation energy transfer (EET) between LH2s is B850, which is a characteristic ring-shaped aggregate of pigments usually formed by 18 or 16 bacteriochlorophylls in LH2. We theoretically study the strategy of the ring-shaped aggregate structure, which maximizes EET efficiency, by using the standard Frenkel exciton model and the self-consistent calculation method for the Markovian quantum master equation and Maxwell equation. As a result, we have revealed a simple but ingenious strategy of the ring-shaped aggregate structure. The combination of three key properties of the ring unit system maximizes the EET efficiency, namely the large dipole moment of aggregates causes the basic improvement of EET efficiency, and the isotropic nature and the large occupying area are critically effective to remove the disorder-induced shielding that inhibits EET in the presence of the randomness of orientation and alignment of carriers of excitation energy.

  20. Strategy of ring-shaped aggregates in excitation energy transfer for removing disorder-induced shielding

    International Nuclear Information System (INIS)

    Tei, Go; Nakatani, Masatoshi; Ishihara, Hajime

    2013-01-01

    Peripheral light harvesting complex (LH2), which is found in photosynthetic antenna systems of purple photosynthetic bacteria, has important functions in the photosynthetic process, such as harvesting sunlight and transferring its energy to the photosynthetic reaction center. The key component in excitation energy transfer (EET) between LH2s is B850, which is a characteristic ring-shaped aggregate of pigments usually formed by 18 or 16 bacteriochlorophylls in LH2. We theoretically study the strategy of the ring-shaped aggregate structure, which maximizes EET efficiency, by using the standard Frenkel exciton model and the self-consistent calculation method for the Markovian quantum master equation and Maxwell equation. As a result, we have revealed a simple but ingenious strategy of the ring-shaped aggregate structure. The combination of three key properties of the ring unit system maximizes the EET efficiency, namely the large dipole moment of aggregates causes the basic improvement of EET efficiency, and the isotropic nature and the large occupying area are critically effective to remove the disorder-induced shielding that inhibits EET in the presence of the randomness of orientation and alignment of carriers of excitation energy. (paper)

  1. Excited-state annihilation reduces power dependence of single-molecule FRET experiments.

    Science.gov (United States)

    Nettels, Daniel; Haenni, Dominik; Maillot, Sacha; Gueye, Moussa; Barth, Anders; Hirschfeld, Verena; Hübner, Christian G; Léonard, Jérémie; Schuler, Benjamin

    2015-12-28

    Single-molecule Förster resonance energy transfer (FRET) experiments are an important method for probing biomolecular structure and dynamics. The results from such experiments appear to be surprisingly independent of the excitation power used, in contradiction to the simple photophysical mechanism usually invoked for FRET. Here we show that excited-state annihilation processes are an essential cause of this behavior. Singlet-singlet annihilation (SSA) is a mechanism of fluorescence quenching induced by Förster-type energy transfer between two fluorophores while they are both in their first excited singlet states (S1S1), which is usually neglected in the interpretation of FRET experiments. However, this approximation is only justified in the limit of low excitation rates. We demonstrate that SSA is evident in fluorescence correlation measurements for the commonly used FRET pair Alexa 488/Alexa 594, with a rate comparable to the rate of energy transfer between the donor excited state and the acceptor ground state (S1S0) that is exploited in FRET experiments. Transient absorption spectroscopy shows that SSA occurs exclusively via energy transfer from Alexa 488 to Alexa 594. Excitation-power dependent microsecond correlation experiments support the conclusion based on previously reported absorption spectra of triplet states that singlet-triplet annihilation (STA) analogously mediates energy transfer if the acceptor is in the triplet state. The results indicate that both SSA and STA have a pronounced effect on the overall FRET process and reduce the power dependence of the observed FRET efficiencies. The existence of annihilation processes thus seems to be essential for using FRET as a reliable spectroscopic ruler at the high excitation rates commonly employed in single-molecule spectroscopy.

  2. Singlet and triplet instability theorems

    Energy Technology Data Exchange (ETDEWEB)

    Yamada, Tomonori; Hirata, So, E-mail: sohirata@illinois.edu [Department of Chemistry, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801 (United States); CREST, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan)

    2015-09-21

    A useful definition of orbital degeneracy—form-degeneracy—is introduced, which is distinct from the usual energy-degeneracy: Two canonical spatial orbitals are form-degenerate when the energy expectation value in the restricted Hartree–Fock (RHF) wave function is unaltered upon a two-electron excitation from one of these orbitals to the other. Form-degenerate orbitals tend to have isomorphic electron densities and occur in the highest-occupied and lowest-unoccupied molecular orbitals (HOMOs and LUMOs) of strongly correlated systems. Here, we present a mathematical proof of the existence of a triplet instability in a real or complex RHF wave function of a finite system in the space of real or complex unrestricted Hartree–Fock wave functions when HOMO and LUMO are energy- or form-degenerate. We also show that a singlet instability always exists in a real RHF wave function of a finite system in the space of complex RHF wave functions, when HOMO and LUMO are form-degenerate, but have nonidentical electron densities, or are energy-degenerate. These theorems provide Hartree–Fock-theory-based explanations of Hund’s rule, a singlet instability in Jahn–Teller systems, biradicaloid electronic structures, and a triplet instability during some covalent bond breaking. They also suggest (but not guarantee) the spontaneous formation of a spin density wave (SDW) in a metallic solid. The stability theory underlying these theorems extended to a continuous orbital-energy spectrum proves the existence of an oscillating (nonspiral) SDW instability in one- and three-dimensional homogeneous electron gases, but only at low densities or for strong interactions.

  3. Conditional Lyapunov exponents and transfer entropy in coupled bursting neurons under excitation and coupling mismatch

    Science.gov (United States)

    Soriano, Diogo C.; Santos, Odair V. dos; Suyama, Ricardo; Fazanaro, Filipe I.; Attux, Romis

    2018-03-01

    This work has a twofold aim: (a) to analyze an alternative approach for computing the conditional Lyapunov exponent (λcmax) aiming to evaluate the synchronization stability between nonlinear oscillators without solving the classical variational equations for the synchronization error dynamical system. In this first framework, an analytic reference value for λcmax is also provided in the context of Duffing master-slave scenario and precisely evaluated by the proposed numerical approach; (b) to apply this technique to the study of synchronization stability in chaotic Hindmarsh-Rose (HR) neuronal models under uni- and bi-directional resistive coupling and different excitation bias, which also considered the root mean square synchronization error, information theoretic measures and asymmetric transfer entropy in order to offer a better insight of the synchronization phenomenon. In particular, statistical and information theoretical measures were able to capture similarity increase between the neuronal oscillators just after a critical coupling value in accordance to the largest conditional Lyapunov exponent behavior. On the other hand, transfer entropy was able to detect neuronal emitter influence even in a weak coupling condition, i.e. under the increase of conditional Lyapunov exponent and apparently desynchronization tendency. In the performed set of numerical simulations, the synchronization measures were also evaluated for a two-dimensional parameter space defined by the neuronal coupling (emitter to a receiver neuron) and the (receiver) excitation current. Such analysis is repeated for different feedback couplings as well for different (emitter) excitation currents, revealing interesting characteristics of the attained synchronization region and conditions that facilitate the emergence of the synchronous behavior. These results provide a more detailed numerical insight of the underlying behavior of a HR in the excitation and coupling space, being in accordance

  4. Correlated Pair States Formed by Singlet Fission and Exciton-Exciton Annihilation.

    Science.gov (United States)

    Scholes, Gregory D

    2015-12-24

    Singlet fission to form a pair of triplet excitations on two neighboring molecules and the reverse process, triplet-triplet annihilation to upconvert excitation, have been extensively studied. Comparatively little work has sought to examine the properties of the intermediate state in both of these processes-the bimolecular pair state. Here, the eigenstates constituting the manifold of 16 bimolecular pair excitations and their relative energies in the weak-coupling regime are reported. The lowest-energy states obtained from the branching diagram method are the triplet pairs with overall singlet spin |X1⟩ ≈ (1)[TT] and quintet spin |Q⟩ ≈ (5)[TT]. It is shown that triplet pair states can be separated by a triplet-triplet energy-transfer mechanism to give a separated, yet entangled triplet pair (1)[T···T]. Independent triplets are produced by decoherence of the separated triplet pair. Recombination of independent triplets by exciton-exciton annihilation to form the correlated triplet pair (i.e., nongeminate recombination) happens with 1/3 of the rate of either triplet migration or recombination of the separated correlated triplet pair (geminate recombination).

  5. The role of hydrogen bonding in excited state intramolecular charge transfer.

    Science.gov (United States)

    Chipem, Francis A S; Mishra, Anasuya; Krishnamoorthy, G

    2012-07-07

    Intramolecular charge transfer (ICT) that occurs upon photoexcitation of molecules is a vital process in nature and it has ample applications in chemistry and biology. The ICT process of the excited molecules is affected by several environmental factors including polarity, viscosity and hydrogen bonding. The effect of polarity and viscosity on the ICT processes is well understood. But, despite the fact that hydrogen bonding significantly influences the ICT process, the specific role of hydrogen bonding in the formation and stabilization of the ICT state is not unambiguously established. Some literature reports predicted that the hydrogen bonding of the solvent with a donor promotes the formation of a twisted intramolecular charge transfer (TICT) state. Some other reports stated that it inhibits the formation of the TICT state. Alternatively, it was proposed that the hydrogen bonding of the solvent with an acceptor favors the TICT state. It is also observed that a dynamic equilibrium is established between the free and the hydrogen bonded ICT states. This perspective focuses on the specific role played by hydrogen bonding of the solvent with the donor and the acceptor, and by proton transfer in the ICT process. The utility of such influence in molecular recognition and anion sensing is discussed with a few recent literature examples in the end.

  6. Dynamics and quantumness of excitation energy transfer through a complex quantum network

    Science.gov (United States)

    Qin, M.; Shen, H. Z.; Zhao, X. L.; Yi, X. X.

    2014-10-01

    Understanding the mechanisms of efficient and robust energy transfer in organic systems provides us with insights for the optimal design of artificial systems. In this paper, we explore the dynamics of excitation energy transfer (EET) through a complex quantum network by a toy model consisting of three sites coupled to environments. We study how the coherent evolution and the noise-induced decoherence work together to reach efficient EET and illustrate the role of the phase factor attached to the coupling constant in the EET. By comparing the differences between the Markovian and non-Markovian dynamics, we discuss the effect of environment and the spatial structure of system on the dynamics and the efficiency of EET. A intuitive picture is given to show how the exciton is transferred through the system. Employing the simple model, we show the robustness of EET efficiency under the influence of the environment and elucidate the important role of quantum coherence in EET. We go further to study the quantum feature of the EET dynamics by quantumness and show the importance of quantum coherence from a different perspective. We calculate the energy current in the EET and its quantumness, and results for different system parameters are presented and discussed.

  7. 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.

  8. Spectral and electrooptical absorption and emission studies on internally hydrogen bonded benzoxazole 'double' derivatives: 2,5-bis(benzoxazolyl)hydroquinone (BBHQ) and 3,6-bis(benzoxazolyl)pyrocatechol (BBPC). Single versus double proton transfer in the excited BBPC revisited

    Energy Technology Data Exchange (ETDEWEB)

    Wortmann, R.; Lebus, S.; Reis, H. [Institute of Physical Chemistry, University of Mainz, Jakob-Welder-Weg 11, 55099 Mainz (Germany); Grabowska, A.; Kownacki, K. [Institute of Physical Chemistry, Polish Academy of Sciences, 44/52 Kasprzaka, 01-224 Warsaw (Poland); Jarosz, S. [Institute of Organic Chemistry, Polish Academy of Sciences, 44/52 Kasprzaka, 01-224 Warsaw (Poland)

    1999-05-15

    Ground and excited state dipole moments and polarizabilities of 2,5-bis(benzoxazolyl)hydroquinone (BBHQ) and 3,6-bis(benzoxazolyl)pyrocatechol (BBPC) are determined by means of electrooptical absorption and emission measurements. BBHQ is found to exhibit a small, while BBPC a large increase of the static polarizability in the Franck-Condon (FC) excited singlet state. The change of the dipole moments upon excitation to the FC state is zero within experimental error. However, both molecules show dipole moments in the fluorescent states of their phototautomers, of about 5 D, the major component being parallel to the long molecular axis. The experimental and theoretical results strongly suggest that the fluorescent species of BBHQ and BBPC are monoketo-tautomers created by single proton transfer in the course of the excited state relaxation. For BBPC this was confirmed by a comparative photophysical study with its monomethoxy-derivative (MeBBPC), in which one active proton is replaced by the CH{sub 3} group. These results lead to the revision of previous conclusions [Grabowska et al., Chem. Phys. Lett. 177 (1991) 17] stating that BBPC undergoes a double proton transfer in the excited state. For BBHQ the previously found single proton transfer mechanism of tautomerization is fully confirmed. (Copyright (c) 1999 Elsevier Science B.V., Amsterdam. All rights reserved.)

  9. Photophysical Model of 10-Hydroxybenzo[h]quinoline: Internal Conversion and Excited State Intramolecular Proton Transfer

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Junghwa; Joo, Taiha [Pohang Univ. of Science and Technology, Pohang (Korea, Republic of)

    2014-03-15

    Photophysics of 10-hydroxybenzo[h]quinoline (HBQ) has been in controversy, in particular, on the nature of the electronic states before and after the excited state intramolecular proton transfer (ESIPT), even though the dynamics and mechanism of the ESIPT have been well established. We report highly time resolved fluorescence spectra over the full emission frequency regions of the enol and keto isomers and the anisotropy in time domain to determine the accurate rates of the population decay, spectral relaxation and anisotropy decay of the keto isomer. We have shown that the ∼300 fs component observed frequently in ESIPT dynamics arises from the S{sub 2}→S{sub 1} internal conversion in the reaction product keto isomer and that the ESIPT occurs from the enol isomer in S{sub 1} state to the keto isomer in S{sub 2} state.

  10. High Excitation Transfer Efficiency from Energy Relay Dyes in Dye-Sensitized Solar Cells

    KAUST Repository

    Hardin, Brian E.

    2010-08-11

    The energy relay dye, 4-(Dicyanomethylene)-2-methyl-6-(4- dimethylaminostyryl)-4H-pyran (DCM), was used with a near-infrared sensitizing dye, TT1, to increase the overall power conversion efficiency of a dye-sensitized solar cell (DSC) from 3.5% to 4.5%. The unattached DCM dyes exhibit an average excitation transfer efficiency (EÌ?TE) of 96% inside TT1-covered, mesostructured TiO2 films. Further performance increases were limited by the solubility of DCM in an acetonitrile based electrolyte. This demonstration shows that energy relay dyes can be efficiently implemented in optimized dye-sensitized solar cells, but also highlights the need to design highly soluble energy relay dyes with high molar extinction coefficients. © 2010 American Chemical Society.

  11. 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.

  12. Role of inelastic excitation and nucleon transfer in quasielastic reactions between 86Kr and 208Pb

    International Nuclear Information System (INIS)

    Sohlbach, H.; Freiesleben, H.; Schneider, W.F.W.; Schuell, D.; Braun-Munzinger, P.; Kohlmeyer, B.; Marinescu, M.; Puehlhofer, F.

    1986-01-01

    In order to get detailed information about the interplay between inelastic excitation and nucleon transfer the authors studied the system 86 Kr + 208 Pb at 10, 13, and 18.2 MeV/u at GSI. The GSI-magnetic spectrometer was used to determine atomic number Z, mass number A, and kinetic energies of projectile-like reaction products. The measured momentum spectra were carefully checked and were found to be free of contaminations from target impurities and slit scattering tails. The experimental energy spectra of various reaction products exhibit in addition to the quasielastic peak very distinct structures, the centroids of which shift to higher TKEL as the bombarding energy increases. A Monte Carlo simulation of sequential 1- and 2-neutron emission was performed and all the structures observed, in particular their dependence on bombarding energy, were consistently reproduced. Two main conclusions can be drawn: firstly, all structures observed in the energy spectra are accounted for by sequential decay, secondly, the centroids of these structures can only be reproduced if the excitation energy sharing is adjusted separately for each reaction channel considered

  13. A non-adiabatic quantum-classical dynamics study of the intramolecular excited state hydrogen transfer in ortho-nitrobenzaldehyde.

    Science.gov (United States)

    Leyva, Verónica; Corral, Inés; Feixas, Ferran; Migani, Annapaola; Blancafort, Lluís; González-Vázquez, Jesús; González, Leticia

    2011-08-28

    Ab initio surface-hopping dynamics calculations have been performed to simulate the intramolecular excited state hydrogen transfer dynamics of ortho-nitrobenzaldehyde (o-NBA) in the gas phase from the electronic S(1) excited state. Upon UV excitation, the hydrogen is transferred from the aldehyde substituent to the nitro group, generating o-nitrosobenzoic acid through a ketene intermediate. The semiclassical propagations show that the deactivation from the S(1) is ultrafast, in agreement with the experimental measurements, which detect the ketene in less than 400 fs. The trajectories show that the deactivation mechanism involves two different conical intersections. The first one, a planar configuration with the hydrogen partially transferred, is responsible for the branching between the formation of a biradical intermediate and the regeneration of the starting material. The conversion of the biradical to the ketene corresponds to the passage through a second intersection region in which the ketene group is formed.

  14. Excited-state properties of a photochromic spirooxazine: double pathways for both fluorescence emission and camphorquinone-sensitized reaction.

    Science.gov (United States)

    di Nunzio, Maria Rosaria; Romani, Aldo; Favaro, Gianna

    2009-08-27

    In this article, we report a study on the singlet and triplet excited-state properties of a spirooxazine (1,3-dihydro-3,3-dimethyl-1-isobutyl-6'-(2,3-dihydro-1H-indol-1-yl)spiro[2H-indole-2,3'-3H-naphtho[2,1-b][1,4]oxazine]). The singlet state of this molecule is photoreactive: upon UV light stimulation, it produces a colored merocyanine that thermally reverts to the starting compound. A double-way radiative relaxation path was found for singlet-state excitation. Experimental observations on the absorption and fluorescence spectra were in excellent agreement with TD-DFT calculations for the singlet state. The triplet state, which could not be directly populated by intersystem crossing from the singlet, when reached by energy transfer from a suitable sensitizer (camphorquinone), yielded the colored merocyanine with quantum yield close to unity. However, the donor/acceptor interaction also originated a new photochromic system as a consequence of the competition of hydrogen abstraction with energy transfer in the interplay of the sensitizer with the substrate. The newly produced photochrome was structurally, spectrally, and photochemically characterized. It exhibited excellent colorability in both directly excited and triplet-sensitized photoreactions by virtue of high photoreaction quantum yield and rather slow bleaching rate of the colored form but also underwent significant degradation in the presence of oxygen that led to the destruction of the photochromic functionality.

  15. Singlet Ground State Magnetism:

    DEFF Research Database (Denmark)

    Loidl, A.; Knorr, K.; Kjems, Jørgen

    1979-01-01

    The magneticGamma 1 –Gamma 4 exciton of the singlet ground state system TbP has been studied by inelastic neutron scattering above the antiferromagnetic ordering temperature. Considerable dispersion and a pronounced splitting was found in the [100] and [110] directions. Both the band width...... and the splitting increased rapidly as the transition temperature was approached in accordance with the predictions of the RPA-theory. The dispersion is analysed in terms of a phenomenological model using interactions up to the fourth nearest neighbour....

  16. Strategies to enhance the excitation energy-transfer efficiency in a light-harvesting system using the intra-molecular charge transfer character of carotenoids

    Energy Technology Data Exchange (ETDEWEB)

    Yukihira, Nao [Department of Applied Chemistry for Environment; School of Science and Technology; Kwansei Gakuin University; Sanda; Japan; Sugai, Yuko [Department of Applied Chemistry for Environment; School of Science and Technology; Kwansei Gakuin University; Sanda; Japan; Fujiwara, Masazumi [Department of Applied Chemistry for Environment; School of Science and Technology; Kwansei Gakuin University; Sanda; Japan; Kosumi, Daisuke [Institute of Pulsed Power Science; Kumamoto University; Kumamoto; Japan; Iha, Masahiko [South Product Co. Ltd.; Uruma-shi; Japan; Sakaguchi, Kazuhiko [Department of Chemistry; Graduate School of Science; Osaka City University; Osaka 558-8585; Japan; Katsumura, Shigeo [Department of Chemistry; Graduate School of Science; Osaka City University; Osaka 558-8585; Japan; Gardiner, Alastair T. [Glasgow Biomedical Research Centre; University of Glasgow; 126 University Place; Glasgow, G12 8QQ; UK; Cogdell, Richard J. [Glasgow Biomedical Research Centre; University of Glasgow; 126 University Place; Glasgow, G12 8QQ; UK; Hashimoto, Hideki [Department of Applied Chemistry for Environment; School of Science and Technology; Kwansei Gakuin University; Sanda; Japan

    2017-01-01

    Fucoxanthin is a carotenoid that is mainly found in light-harvesting complexes from brown algae and diatoms. Due to the presence of a carbonyl group attached to polyene chains in polar environments, excitation produces an excited intra-molecular charge transfer. This intra-molecular charge transfer state plays a key role in the highly efficient (~95%) energy-transfer from fucoxanthin to chlorophyllain the light-harvesting complexes from brown algae. In purple bacterial light-harvesting systems the efficiency of excitation energy-transfer from carotenoids to bacteriochlorophylls depends on the extent of conjugation of the carotenoids. In this study we were successful, for the first time, in incorporating fucoxanthin into a light-harvesting complex 1 from the purple photosynthetic bacterium,Rhodospirillum rubrumG9+ (a carotenoidless strain). Femtosecond pump-probe spectroscopy was applied to this reconstituted light-harvesting complex in order to determine the efficiency of excitation energy-transfer from fucoxanthin to bacteriochlorophyllawhen they are bound to the light-harvesting 1 apo-proteins.

  17. Ultrafast spin exchange-coupling torque via photo-excited charge-transfer processes

    Science.gov (United States)

    Ma, X.; Fang, F.; Li, Q.; Zhu, J.; Yang, Y.; Wu, Y. Z.; Zhao, H. B.; Lüpke, G.

    2015-10-01

    Optical control of spin is of central importance in the research of ultrafast spintronic devices utilizing spin dynamics at short time scales. Recently developed optical approaches such as ultrafast demagnetization, spin-transfer and spin-orbit torques open new pathways to manipulate spin through its interaction with photon, orbit, charge or phonon. However, these processes are limited by either the long thermal recovery time or the low-temperature requirement. Here we experimentally demonstrate ultrafast coherent spin precession via optical charge-transfer processes in the exchange-coupled Fe/CoO system at room temperature. The efficiency of spin precession excitation is significantly higher and the recovery time of the exchange-coupling torque is much shorter than for the demagnetization procedure, which is desirable for fast switching. The exchange coupling is a key issue in spin valves and tunnelling junctions, and hence our findings will help promote the development of exchange-coupled device concepts for ultrafast coherent spin manipulation.

  18. A coherent modified Redfield theory for excitation energy transfer in molecular aggregates

    Energy Technology Data Exchange (ETDEWEB)

    Hwang-Fu, Yu-Hsien; Chen, Wei; Cheng, Yuan-Chung, E-mail: yuanchung@ntu.edu.tw

    2015-02-02

    Highlights: • A CMRT method for coherent energy transfer in molecular aggregates was developed. • Applicability of the method was verified in two-site systems with various parameters. • CMRT accurately describes population dynamics in the FMO-complex. • The method is accurate in a large parameter space and computationally efficient. - Abstract: Excitation energy transfer (EET) is crucial in photosynthetic light harvesting, and quantum coherence has been recently proven to be a ubiquitous phenomenon in photosynthetic EET. In this work, we derive a coherent modified Redfield theory (CMRT) that generalizes the modified Redfield theory to treat coherence dynamics. We apply the CMRT method to simulate the EET in a dimer system and compare the results with those obtained from numerically exact path integral calculations. The comparison shows that CMRT provides excellent computational efficiency and accuracy within a large EET parameter space. Furthermore, we simulate the EET dynamics in the FMO complex at 77 K using CMRT. The results show pronounced non-Markovian effects and long-lasting coherences in the ultrafast EET, in excellent agreement with calculations using the hierarchy equation of motion approach. In summary, we have successfully developed a simple yet powerful framework for coherent EET dynamics in photosynthetic systems and organic materials.

  19. Ultrafast spin exchange-coupling torque via photo-excited charge-transfer processes.

    Science.gov (United States)

    Ma, X; Fang, F; Li, Q; Zhu, J; Yang, Y; Wu, Y Z; Zhao, H B; Lüpke, G

    2015-10-28

    Optical control of spin is of central importance in the research of ultrafast spintronic devices utilizing spin dynamics at short time scales. Recently developed optical approaches such as ultrafast demagnetization, spin-transfer and spin-orbit torques open new pathways to manipulate spin through its interaction with photon, orbit, charge or phonon. However, these processes are limited by either the long thermal recovery time or the low-temperature requirement. Here we experimentally demonstrate ultrafast coherent spin precession via optical charge-transfer processes in the exchange-coupled Fe/CoO system at room temperature. The efficiency of spin precession excitation is significantly higher and the recovery time of the exchange-coupling torque is much shorter than for the demagnetization procedure, which is desirable for fast switching. The exchange coupling is a key issue in spin valves and tunnelling junctions, and hence our findings will help promote the development of exchange-coupled device concepts for ultrafast coherent spin manipulation.

  20. Impact of Dielectric Constant on the Singlet-Triplet Gap in Thermally Activated Delayed Fluorescence (TADF) Materials

    KAUST Repository

    Sun, Haitao

    2017-04-28

    Thermally activated delayed fluorescence (TADF) relies on the presence of a very small energy gap, ΔEST, between the lowest singlet and triplet excited states. ΔEST is thus a key factor in the molecular design of more efficient materials. However, its accurate theoretical estimation remains challenging, especially in the solid state due to the influence of polarization effects. We have quantitatively studied ΔEST as a function of dielectric constant, ε, for four representative organic molecules using the methodology we recently proposed at the Tamm-Dancoff approximation ωB97X level of theory, where the range-separation parameter ω is optimized with the polarizable continuum model. The results are found to be in very good agreement with experimental data. Importantly, the polarization effects can lead to a marked reduction in the ΔEST value, which is favorable for TADF applications. This ΔEST decrease in the solid state is related to the hybrid characters of the lowest singlet and triplet excited states, whose dominant contribution switches to charge-transfer-like with increasing ε. The present work provides a theoretical understanding on the influence of polarization effect on the singlet-triplet gap and confirms our methodology to be a reliable tool for the prediction and development of novel TADF materials.

  1. Singlet oxygen: photosensitized generation, detection and reaction with organic molecules

    International Nuclear Information System (INIS)

    Barik, Atanu; Indira Priyadarsini, K.; Hari Mohan; Bajaj, P.N.; Sapre, A.V.; Mittal, J.P.; Mukherjee, T.

    2006-10-01

    Singlet molecular oxygen ( 1 O 2 ) is an excited state of molecular oxygen, having antiparallel spin in the same π antibonding orbital. The study of singlet oxygen production and reactivity has emerged as a rich and diverse area, with implication in diverse fields, such as synthetic chemistry, polymer chemistry, photodynamic therapy, etc. There are several known methods to produce singlet oxygen, and also various techniques employed to detect it. Out of these, photosensitization method is the most popular one. In this article, photosensitized production of singlet oxygen from triplet oxygen and photosensitizers in presence of light, and its detection by the infrared luminescence at 1270 nm have been presented. Further, some results using different types of photosensitizers, effect of solvent on singlet oxygen quantum yields and lifetime have been discussed. The quenching rate constants of singlet oxygen have been determined with different types of organic molecules such as derivatives of thiourea and its analogues, hydroxy indoles and antioxidants and the results have been presented. (author)

  2. Singlets of fermionic gauge symmetries

    NARCIS (Netherlands)

    Bergshoeff, E.A.; Kallosh, R.E.; Rahmanov, M.A.

    1989-01-01

    We investigate under which conditions singlets of fermionic gauge symmetries which are "square roots of gravity" can exist. Their existence is non-trivial because there are no fields neutral in gravity. We tabulate several examples of singlets of global and local supersymmetry and κ-symmetry and

  3. Locally-excited (LE) versus charge-transfer (CT) excited state competition in a series of para-substituted neutral green fluorescent protein (GFP) chromophore models.

    Science.gov (United States)

    Olsen, Seth

    2015-02-12

    In this paper, I provide a characterization of the low-energy electronic structure of a series of para-substituted neutral green fluorescent protein (GFP) chromophore models using a theoretical approach that blends linear free energy relationships (LFERs) with state-averaged complete-active-space self-consistent field (SA-CASSCF) theory. The substituents are chosen to sample the Hammett σ(p) scale from R = F to NH2, and a model of the neutral GFP chromophore structure (R = OH) is included. I analyze the electronic structure for different members of the series in a common complete-active-space valence-bond (CASVB) representation, exploiting an isolobal analogy between active-space orbitals for different members of the series. I find that the electronic structure of the lowest adiabatic excited state is a strong mixture of weakly coupled states with charge-transfer (CT) or locally excited (LE) character and that the dominant character changes as the series is traversed. Chromophores with strongly electron-donating substituents have a CT-like excited state such as expected for a push-pull polyene or asymmetric cyanine. Chromophores with weakly electron-donating (or electron-withdrawing) substituents have an LE-like excited state with an ionic biradicaloid structure localized to the ground-state bridge π bond.

  4. Failures of TDDFT in describing the lowest intramolecular charge-transfer excitation in para-nitroaniline

    DEFF Research Database (Denmark)

    Eriksen, Janus J.; Sauer, Stephan P. A.; Mikkelsen, Kurt Valentin

    2013-01-01

    We investigate the failure of Time{Dependent Density Functional Theory (TDDFT) with the CAM{B3LYP exchange{correlation (xc) functional coupled to the Polarizable Embedding (PE) scheme (PE-CAM-B3LYP) in reproducing the solvatochromic shift of the lowest intense charge{transfer excitation in para{n...

  5. 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

  6. ANISOTROPY EFFECTS IN SINGLE-ELECTRON TRANSFER BETWEEN LASER-EXCITED ATOMS AND HIGHLY-CHARGED IONS

    NARCIS (Netherlands)

    Recent collision experiments are reviewed in which one-electron transfer between laser excited target atoms and (highly charged) keV-ions has been studied. Especially results showing a dependence of the charge exchange on the initial target orbital alignment are discussed. The question to what

  7. 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

  8. Gaugino Mass without Singlets

    CERN Document Server

    Giudice, Gian Francesco; Murayama, H; Rattazzi, Riccardo; Giudice, Gian F.; Luty, Markus A.; Murayama, Hitoshi; Rattazzi, Riccardo

    1998-01-01

    In models with dynamical supersymmetry breaking in the hidden sector, the gaugino masses in the observable sector have been believed to be extremely suppressed (below 1 keV), unless there is a gauge singlet in the hidden sector with specific couplings to the observable sector gauge multiplets. We point out that there is a pure supergravity contribution to gaugino masses at the quantum level arising from the superconformal anomaly. Our results are valid to all orders in perturbation theory and are related to the `exact' beta functions for soft terms. There is also an anomaly contribution to the A terms proportional to the beta function of the corresponding Yukawa coupling. The gaugino masses are proportional to the corresponding gauge beta functions, and so do not satisfy the usual GUT relations.

  9. Stepwise vs concerted excited state tautomerization of 2-hydroxypyridine: Ammonia dimer wire mediated hydrogen/proton transfer

    Energy Technology Data Exchange (ETDEWEB)

    Esboui, Mounir, E-mail: mounir.esboui@fst.rnu.tn [Laboratoire de Spectroscopie Atomique, Moléculaire et Applications, Département de Physique, Faculté des Sciences de Tunis, 2092 Tunis (Tunisia); Technical and Vocational Training Corporation, Hail College of Technology, P.O. Box 1960, Hail 81441 (Saudi Arabia)

    2015-07-21

    The stepwise and concerted excited state intermolecular proton transfer (PT) and hydrogen transfer (HT) reactions in 2-hydroxypyridine-(NH{sub 3}){sub 2} complex in the gas phase under Cs symmetry constraint and without any symmetry constraints were performed using quantum chemical calculations. It shows that upon excitation, the hydrogen bonded in 2HP-(NH{sub 3}){sub 2} cluster facilitates the releasing of both hydrogen and proton transfer reactions along ammonia wire leading to the formation of the 2-pyridone tautomer. For the stepwise mechanism, it has been found that the proton and the hydrogen may transfer consecutively. These processes are distinguished from each other through charge translocation analysis and the coupling between the motion of the proton and the electron density distribution along ammonia wire. For the complex under Cs symmetry, the excited state HT occurs on the A″({sup 1}πσ{sup ∗}) and A′({sup 1}nσ{sup ∗}) states over two accessible energy barriers along reaction coordinates, and excited state PT proceeds mainly through the A′({sup 1}ππ{sup ∗}) and A″({sup 1}nπ{sup ∗}) potential energy surfaces. For the unconstrained complex, potential energy profiles show two {sup 1}ππ{sup ∗}-{sup 1}πσ{sup ∗} conical intersections along enol → keto reaction path indicating that proton and H atom are localized, respectively, on the first and second ammonia of the wire. Moreover, the concerted excited state PT is competitive to take place with the stepwise process, because it proceeds over low barriers of 0.14 eV and 0.11 eV with respect to the Franck-Condon excitation of enol tautomer, respectively, under Cs symmetry and without any symmetry constraints. These barriers can be probably overcome through tunneling effect.

  10. Singlet-triplet annihilation in single LHCII complexes.

    Science.gov (United States)

    Gruber, J Michael; Chmeliov, Jevgenij; Krüger, Tjaart P J; Valkunas, Leonas; van Grondelle, Rienk

    2015-08-14

    In light harvesting complex II (LHCII) of higher plants and green algae, carotenoids (Cars) have an important function to quench chlorophyll (Chl) triplet states and therefore avoid the production of harmful singlet oxygen. The resulting Car triplet states lead to a non-linear self-quenching mechanism called singlet-triplet (S-T) annihilation that strongly depends on the excitation density. In this work we investigated the fluorescence decay kinetics of single immobilized LHCIIs at room temperature and found a two-exponential decay with a slow (3.5 ns) and a fast (35 ps) component. The relative amplitude fraction of the fast component increases with increasing excitation intensity, and the resulting decrease in the fluorescence quantum yield suggests annihilation effects. Modulation of the excitation pattern by means of an acousto-optic modulator (AOM) furthermore allowed us to resolve the time-dependent accumulation and decay rate (∼7 μs) of the quenching species. Inspired by singlet-singlet (S-S) annihilation studies, we developed a stochastic model and then successfully applied it to describe and explain all the experimentally observed steady-state and time-dependent kinetics. That allowed us to distinctively identify the quenching mechanism as S-T annihilation. Quantitative fitting resulted in a conclusive set of parameters validating our interpretation of the experimental results. The obtained stochastic model can be generalized to describe S-T annihilation in small molecular aggregates where the equilibration time of excitations is much faster than the annihilation-free singlet excited state lifetime.

  11. Quantitative Förster resonance energy transfer efficiency measurements using simultaneous spectral unmixing of excitation and emission spectra.

    Science.gov (United States)

    Mustafa, Sanam; Hannagan, John; Rigby, Paul; Pfleger, Kevin; Corry, Ben

    2013-02-01

    Accurate quantification of Förster resonance energy transfer (FRET) using intensity-based methods is difficult due to the overlap of fluorophore excitation and emission spectra. Consequently, mechanisms are required to remove bleedthrough of the donor emission into the acceptor channel and direct excitation of the acceptor when aiming to excite only the donor fluorophores. Methods to circumvent donor bleedthrough using the unmixing of emission spectra have been reported, but these require additional corrections to account for direct excitation of the acceptor. Here we present an alternative method for robust quantification of FRET efficiencies based upon the simultaneous spectral unmixing of both excitation and emission spectra. This has the benefit over existing methodologies in circumventing the issue of donor bleedthrough and acceptor cross excitation without the need for additional corrections. Furthermore, we show that it is applicable with as few as two excitation wavelengths and so can be used for quantifying FRET efficiency in microscope images as easily as for data collected on a spectrofluorometer. We demonstrate the accuracy of the approach by reproducing efficiency values in well characterized FRET standards: HEK cells expressing a variety of linked cerulean and venus fluorescent proteins. Finally we describe simple ImageJ plugins that can be used to calculate and create images of FRET efficiencies from microscope images.

  12. Luminescence and excitation energy transfer in new fluoride crystals containing rare earth ions

    Energy Technology Data Exchange (ETDEWEB)

    Ryba-Romanowski, W. [Institute of Low Temperature and Structure Research Polish Academy of Sciences, ul. Okolna 2, PL-50422, Wroclaw (Poland)], E-mail: W.Ryba-Romanowski@int.pan.wroc.pl; Solarz, P.; Gusowski, M.; Dominiak-Dzik, G. [Institute of Low Temperature and Structure Research Polish Academy of Sciences, ul. Okolna 2, PL-50422, Wroclaw (Poland)

    2007-04-15

    Spectroscopic characteristics of Pr{sup 3+} and Eu{sup 3+} in K{sub 2}Na{sub 2}GdF{sub 7}, K{sub 5}Li{sub 2}GdF{sub 10} and K{sub 3}GdF{sub 6} fluoride matrices are considered. Crystal structures of these compounds have been ascertained based on X-ray measurement on single crystal samples. Energies of lattice vibrations have been derived from IR and Raman spectra. Spectroscopic features of crystals in the VUV region were studied using experimental facilities of the Superlumi station at HASYLAB in Hamburg. High-resolution spectra and decay curves of luminescence in the visible were used to determine the energy levels and excited state relaxation dynamics of luminescent ions. Relevance of energy transfer processes, which feed the {sup 5}D{sub J} levels of Eu{sup 3+} and the {sup 3}P{sub 0} level of Pr{sup 3+}, is discussed.

  13. General theory of excitation energy transfer in donor-mediator-acceptor systems.

    Science.gov (United States)

    Kimura, Akihiro

    2009-04-21

    General theory of the excitation energy transfer (EET) in the case of donor-mediator-acceptor system was constructed by using generalized master equation (GME). In this theory, we consider the direct and indirect transitions in the EET consistently. Hence, our theory includes the quantum mechanical interference between the direct and indirect transitions automatically. Memory functions in the GME were expressed by the overlap integrals among the time-dependent emission spectrum of the donor, the absorption spectrum of the mediator, the time-dependent emission spectrum of the mediator, and the absorption spectrum of the acceptor. In the Markov limit of the memory functions, we obtained the rate of EET which consists of three terms due to the direct transition, the indirect transition, and the interference between them. We found that the interference works effectively in the limit of slow thermalization at the intermediate state. The formula of EET rate in this limit was expressed by the convolution of the EET interaction and optical spectra. The interference effect strongly depends on the width of the absorption spectrum of mediator molecule and the energy gap between the donor and the mediator molecules.

  14. 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.

  15. Assessment of charge-transfer excitations with time-dependent, range-separated density functional theory based on long-range MP2 and multiconfigurational self- consistent field wave functions

    DEFF Research Database (Denmark)

    Hedegård, Erik D.; Jensen, Hans Jørgen Aagaard; Knecht, Stefan

    2013-01-01

    TD-MC-srDFT and performs slightly better against the reference data for this small subset. Beyond the proof-of-principle calculations comprising the first part of this contribution, we additionally studied the low-lying singlet excited states (S1 and S2) of the retinal chromophore. The chromophore...

  16. High resolution IR diode laser study of collisional energy transfer between highly vibrationally excited monofluorobenzene and CO2: the effect of donor fluorination on strong collision energy transfer.

    Science.gov (United States)

    Kim, Kilyoung; Johnson, Alan M; Powell, Amber L; Mitchell, Deborah G; Sevy, Eric T

    2014-12-21

    Collisional energy transfer between vibrational ground state CO2 and highly vibrationally excited monofluorobenzene (MFB) was studied using narrow bandwidth (0.0003 cm(-1)) IR diode laser absorption spectroscopy. Highly vibrationally excited MFB with E' = ∼41,000 cm(-1) was prepared by 248 nm UV excitation followed by rapid radiationless internal conversion to the electronic ground state (S1→S0*). The amount of vibrational energy transferred from hot MFB into rotations and translations of CO2 via collisions was measured by probing the scattered CO2 using the IR diode laser. The absolute state specific energy transfer rate constants and scattering probabilities for single collisions between hot MFB and CO2 were measured and used to determine the energy transfer probability distribution function, P(E,E'), in the large ΔE region. P(E,E') was then fit to a bi-exponential function and extrapolated to the low ΔE region. P(E,E') and the biexponential fit data were used to determine the partitioning between weak and strong collisions as well as investigate molecular properties responsible for large collisional energy transfer events. Fermi's Golden rule was used to model the shape of P(E,E') and identify which donor vibrational motions are primarily responsible for energy transfer. In general, the results suggest that low-frequency MFB vibrational modes are primarily responsible for strong collisions, and govern the shape and magnitude of P(E,E'). Where deviations from this general trend occur, vibrational modes with large negative anharmonicity constants are more efficient energy gateways than modes with similar frequency, while vibrational modes with large positive anharmonicity constants are less efficient at energy transfer than modes of similar frequency.

  17. Photophysical Parameters, Excitation Energy Transfer, and Photoreactivity of 1,4-Bis(5-phenyl-2-oxazolylbenzene (POPOP Laser Dye

    Directory of Open Access Journals (Sweden)

    Samy A. El-Daly

    2012-01-01

    Full Text Available The effect of solvents on the absorption and emission spectra of 1,4-bis(5-phenyl-2-oxazolylbenzene (POPOP laser dye has been studied in various solvents at 298 K. A bathochromic shift was observed in absorption and fluorescence spectra upon increase of solvent polarity, which indicates that this transition is π-∗. The ground and excited state dipole moments were calculated as 2.23 and 6.34 Debye, respectively. The dye solution in MeOH, n-heptane, and methyl isobutyl ketone gives laser emission in the blue region upon excitation by a 337.1 nm nitrogen pulse; the gain coefficient and emission cross section as well as normalized photostability have been determined. Excitation energy transfer from POPOP to rhodamine B and fluorescine was studied to improve the laser emission from these dyes. Such an energy transfer dye laser system (ETDL obeys a long range columbic energy transfer mechanism with a critical transfer distance, R0, of 25 and 33 Å and kq equal to 10.4×1012 and 26.2×1012M−1s−1 for the POPOP/RB and POPOP/fluorescine pair, respectively. The POPOP dye is highly photostable in polar protic and polar aprotic solvents, while it displays photodecomposition in chloromethane solvent via formation of a contact ion pair. The photochemical quantum yield and rate of photodecomposition depend on the electron affinity of solvent.

  18. Exciton description of chlorosome to baseplate excitation energy transfer in filamentous anoxygenic phototrophs and green sulfur bacteria.

    Science.gov (United States)

    Linnanto, Juha M; Korppi-Tommola, Jouko E I

    2013-09-26

    A description of intra-chlorosome and from chlorosome to baseplate excitation energy transfer in green sulfur bacteria and in filamentous anoxygenic phototrophs is presented. Various shapes and sizes, single and multiwalled tubes, cylindrical spirals and lamellae of the antenna elements mimicking pigment organization in chlorosomes were generated by using molecular mechanics calculations, and the absorption, LD, and CD spectra of these were predicted by using exciton theory. Calculated absorption and LD spectra were similar for all modeled antenna structures; on the contrary, CD spectra turned out to be sensitive to the size and pigment orientations in the antenna. It was observed that, bringing two tubular antennae at close enough interaction distance, the exciton density of the lowest energy state became localized on pigments facing each other in the antenna dimer. Calculations predicted for stacked tubular antenna elements extremely fast, faster than 500 fs, intra-chlorosome energy transfer toward the baseplates in the direction perpendicular to the chlorosome long axis. Downhill excitation energy transfer according to our model is driven by interactions of the antennae with their immediate surroundings. Energy transfer from the chlorosome to the baseplate, consisting of 2D lattices of monomeric and dimeric bacteriochlorophyll a molecules, was predicted to occur in 5-15 ps, in agreement with experimental findings. Advancement of excitation through a double tube antenna stack, a model for antenna element organization in chlorosomes of green sulfur bacteria, to a monomeric baseplate was visualized in space and in time.

  19. Bond Shortening (1.4 Å) in the Singlet and Triplet Excited States of [Ir2(dimen)4]2+ in Solution Determined by Time-Resolved X-ray Scattering

    DEFF Research Database (Denmark)

    Haldrup, Martin Kristoffer; Harlang, Tobias; Christensen, Morten

    2011-01-01

    Ground- and excited-state structures of the bimetallic, ligand-bridged compound Ir2(dimen)42+ are investigated in acetonitrile by means of time-resolved X-ray scattering. Following excitation by 2 ps laser pulses at 390 nm, analysis of difference scattering patterns obtained at eight different ti...

  20. 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......) Kβ hard X-ray fluorescence spectroscopy with femtosecond time-resolved UV-visible absorption spectroscopy to characterize the electronic excited state dynamics initiated by MLCT excitation of [Fe(CN)4(bpy)]2-. The two experimental techniques are highly complementary; the time-resolved UV...

  1. Vibrational energy transfer in selectively excited diatomic molecules. [Relaxation rates, self-relaxation, upper limits

    Energy Technology Data Exchange (ETDEWEB)

    Dasch, C.J.

    1978-09-01

    Single rovibrational states of HCl(v=2), HBr(v=2), DCl(v=2), and CO(v=2) were excited with a pulsed optical parametric oscillator (OPO). Total vibrational relaxation rates near - resonance quenchers were measured at 295/sup 0/K using time resolved infrared fluorescence. These rates are attributed primarily to V - V energy transfer, and they generally conform to a simple energy gap law. A small deviation was found for the CO(v) + DCl(v') relaxation rates. Upper limits for the self relaxation by V - R,T of HCl(v=2) and HBr(v=2) and for the two quantum exchange between HCl and HBr were determined. The HF dimer was detected at 295/sup 0/K and 30 torr HF pressure with an optoacoustic spectrometer using the OPO. Pulsed and chopped, resonant and non-resonant spectrophones are analyzed in detail. From experiments and first order perturbation theory, these V - V exchange rates appear to behave as a first order perturbation in the vibrational coordinates. The rotational dynamics are known to be complicated however, and the coupled rotational - vibrational dynamics were investigated theoreticaly in infinite order by the Dillon and Stephenson and the first Magnus approximations. Large ..delta..J transitions appear to be important, but these calculations differ by orders of magnitude on specific rovibrational transition rates. Integration of the time dependent semiclassical equations by a modified Gordon method and a rotationally distorted wave approximation are discussed as methods which would treat the rotational motion more accurately. 225 references.

  2. Excited state intramolecular charge transfer reaction in nonaqueous electrolyte solutions: temperature dependence.

    Science.gov (United States)

    Pradhan, Tuhin; Gazi, Harun Al Rasid; Biswas, Ranjit

    2009-08-07

    Temperature dependence of the excited state intramolecular charge transfer reaction of 4-(1-azetidinyl)benzonitrile (P4C) in ethyl acetate (EA), acetonitrile (ACN), and ethanol at several concentrations of lithium perchlorate (LiClO(4)) has been investigated by using the steady state and time resolved fluorescence spectroscopic techniques. The temperature range considered is 267-343 K. The temperature dependent spectral peak shifts and reaction driving force (-DeltaG(r)) in electrolyte solutions of these solvents can be explained qualitatively in terms of interaction between the reactant molecule and ion-atmosphere. Time resolved studies indicate that the decay kinetics of P4C is biexponential, regardless of solvents, LiClO(4) concentrations, and temperatures considered. Except at higher electrolyte concentrations in EA, reaction rates in solutions follow the Arrhenius-type temperature dependence where the estimated activation energy exhibits substantial electrolyte concentration dependence. The average of the experimentally measured activation energies in these three neat solvents is found to be in very good agreement with the predicted value based on data in room temperature solvents. While the rate constant in EA shows a electrolyte concentration induced parabolic dependence on reaction driving force (-DeltaG(r)), the former in ethanol and ACN increases only linearly with the increase in driving force (-DeltaG(r)). The data presented here also indicate that the step-wise increase in solvent reorganization energy via sequential addition of electrolyte induces the ICT reaction in weakly polar solvents to crossover from the Marcus inverted region to the normal region.

  3. Does excited-state proton-transfer reaction contribute to the emission behaviour of 4-aminophthalimide in aqueous media?

    Science.gov (United States)

    Khara, Dinesh Chandra; Banerjee, Sanghamitra; Samanta, Anunay

    2014-06-23

    4-Aminophthalimide (AP) is an extensively used molecule both for fundamental studies and applications primarily due to its highly solvent-sensitive fluorescence properties. The fluorescence spectrum of AP in aqueous media was recently shown to be dependent on the excitation wavelength. A time-dependent blue shift of its emission spectrum is also reported. On the basis of these findings, the excited-state solvent-mediated proton-transfer reaction of the molecule, which was proposed once but discarded at a later stage, is reintroduced. We report on the fluorescence behaviour of AP and its imide-H protected derivative, N-BuAP, to prove that a solvent-assisted excited-state keto-enol transformation does not contribute to the steady-state and time-resolved emission behaviour of AP in aqueous media. Our results also reveal that the fluorescence of AP in aqueous media arises from two distinct hydrogen-bonded species. The deuterium isotope effect on the fluorescence quantum yield and lifetime of AP, which was thought to be a reflection of the excited-state proton-transfer reaction in the system, is explained by considering the difference in the influence of H(2)O and D(2)O on the nonradiative rates and ground-state exchange of the proton with the solvent. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Evidence for resonance electron transfer in photon excited X-ray ...

    Indian Academy of Sciences (India)

    with the experimental values and (3) to compare the experimental values obtained by photon excitation with those measured by electron excitation in the available cases. 2. Experimental details. In the present investigations, a Philips 1410 wavelength dispersive plane crystal spectrometer was used. The principle involved ...

  5. 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

  6. The nature of singlet excitons in oligoacene molecular crystals

    KAUST Repository

    Yamagata, H.

    2011-01-01

    A theory for polarized absorption in crystalline oligoacenes is presented, which includes Frenkel exciton coupling, the coupling between Frenkel and charge-transfer (CT) excitons, and the coupling of all neutral and ionic excited states to the dominant ring-breathing vibrational mode. For tetracene, spectra calculated using all Frenkel couplings among the five lowest energy molecular singlet states predict a Davydov splitting (DS) of the lowest energy (0-0) vibronic band of only -32cm-1, far smaller than the measured value of 631cm-1 and of the wrong sign-a negative sign indicating that the polarizations of the lower and upper Davydov components are reversed from experiment. Inclusion of Frenkel-CT coupling dramatically improves the agreement with experiment, yielding a 0-0 DS of 601cm-1 and a nearly quantitative reproduction of the relative spectral intensities of the 0-n vibronic components. Our analysis also shows that CT mixing increases with the size of the oligoacenes. We discuss the implications of these results on exciton dissociation and transport. © 2011 American Institute of Physics.

  7. Electronic energy transfer involving carotenoid pigments in chlorosomes of two green bacteria: Chlorobium tepidum and Chloroflexus aurantiacus

    DEFF Research Database (Denmark)

    Melø, T B; Frigaard, N-U; Matsuura, K

    2000-01-01

    S) spectra, recorded at ambient temperature and under non-reducing or reducing conditions, are reported. The carotenoid (Car) pigments in both species transfer their singlet excitation to bacteriochlorophyll c (BChlc) with an efficiency which is high (between 0.5 and 0.8) but smaller than unity; BChlc...

  8. Guidance for Mutual Disposition of Chromophores for Singlet Fission

    Czech Academy of Sciences Publication Activity Database

    Havlas, Zdeněk; Michl, Josef

    2016-01-01

    Roč. 56, č. 1 (2016), s. 96-106 ISSN 0021-2148 R&D Projects: GA ČR GA15-19143S Institutional support: RVO:61388963 Keywords : chromophores * energy transfer * photophysics * singlet fission * theory Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.455, year: 2016

  9. Study of a Quantum Dot in an Excited State

    Science.gov (United States)

    Slamet, Marlina; Sahni, Viraht

    We have studied the first excited singlet state of a quantum dot via quantal density functional theory (QDFT). The quantum dot is represented by a 2D Hooke's atom in an external magnetostatic field. The QDFT mapping is from an excited singlet state of this interacting system to one of noninteracting fermions in a singlet ground state. The results of the study will be compared to (a) the corresponding mapping from a ground state of the quantum dot and (b) to the similar mapping from an excited singlet state of the 3D Hooke's atom.

  10. Singlet oxygen-mediated damage to proteins and its consequences

    DEFF Research Database (Denmark)

    Davies, Michael Jonathan

    2003-01-01

    as radical termination reactions. This paper reviews the data available on singlet oxygen-mediated protein oxidation and concentrates primarily on the mechanisms by which this excited state species brings about changes to both the side-chains and backbone of amino acids, peptides, and proteins. Recent work...... to other biological targets, and may play a significant role in bystander damage, or dark reactions, in systems where proteins are subjected to oxidation....

  11. Role of thermal excitation in ultrafast energy transfer in chlorosomes revealed by two-dimensional electronic spectroscopy.

    Science.gov (United States)

    Jun, Sunhong; Yang, Cheolhee; Kim, Tae Wu; Isaji, Megumi; Tamiaki, Hitoshi; Ihee, Hyotcherl; Kim, Jeongho

    2015-07-21

    Chlorosomes are the largest light harvesting complexes in nature and consist of many bacteriochlorophyll pigments forming self-assembled J-aggregates. In this work, we use two-dimensional electronic spectroscopy (2D-ES) to investigate ultrafast dynamics of excitation energy transfer (EET) in chlorosomes and their temperature dependence. From time evolution of the measured 2D electronic spectra of chlorosomes, we directly map out the distribution of the EET rate among the manifold of exciton states in a 2D energy space. In particular, it is found that the EET rate varies gradually depending on the energies of energy-donor and energy-acceptor states. In addition, from comparative 2D-ES measurements at 77 K and room temperature, we show that the EET rate exhibits subtle dependence on both the exciton energy and temperature, demonstrating the effect of thermal excitation on the EET rate. This observation suggests that active thermal excitation at room temperature prevents the excitation trapping at low-energy states and thus promotes efficient exciton diffusion in chlorosomes at ambient temperature.

  12. Local Control Theory in Trajectory Surface Hopping Dynamics Applied to the Excited-State Proton Transfer of 4-Hydroxyacridine.

    Science.gov (United States)

    Curchod, Basile F E; Penfold, Thomas J; Rothlisberger, Ursula; Tavernelli, Ivano

    2015-07-20

    The application of local control theory combined with nonadiabatic ab initio molecular dynamics to study the photoinduced intramolecular proton transfer reaction in 4-hydroxyacridine was investigated. All calculations were performed within the framework of linear-response time-dependent density functional theory. The computed pulses revealed important information about the underlying excited-state nuclear dynamics highlighting the involvement of collective vibrational modes that would normally be neglected in a study performed on model systems constrained to a subset of the full configuration space. This study emphasizes the strengths of local control theory for the design of pulses that can trigger chemical reactions associated with the population of a given molecular excited state. In addition, analysis of the generated pulses can help to shed new light on the photophysics and photochemistry of complex molecular systems. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Observation of Electronic Excitation Transfer Through Light Harvesting Complex II Using Two-Dimensional Electronic-Vibrational Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Lewis, NHC; Gruenke, NL; Oliver, TAA; Ballottari, M; Bassi, R; Fleming, GR

    2016-10-05

    Light-harvesting complex II (LHCII) serves a central role in light harvesting for oxygenic photosynthesis and is arguably the most important photosynthetic antenna complex. In this article, we present two-dimensional electronic–vibrational (2DEV) spectra of LHCII isolated from spinach, demonstrating the possibility of using this technique to track the transfer of electronic excitation energy between specific pigments within the complex. We assign the spectral bands via comparison with the 2DEV spectra of the isolated chromophores, chlorophyll a and b, and present evidence that excitation energy between the pigments of the complex are observed in these spectra. Lastly, we analyze the essential components of the 2DEV spectra using singular value decomposition, which makes it possible to reveal the relaxation pathways within this complex.

  14. Excitation relaxation dynamics and energy transfer in pigment-protein complexes of a dinoflagellate, revealed by ultrafast fluorescence spectroscopy.

    Science.gov (United States)

    Tanaka, Kazunori; Iida, Satoko; Takaichi, Shinichi; Mimuro, Mamoru; Murakami, Akio; Akimoto, Seiji

    2016-12-01

    Photosynthetic light-harvesting complexes, found in aquatic photosynthetic organisms, contain a variety of carotenoids and chlorophylls. Most of the photosynthetic dinoflagellates possess two types of light-harvesting antenna complexes: peridinin (Peri)-chlorophyll (Chl) a/c-protein, as an intrinsic thylakoid membrane complex protein (iPCP), and water-soluble Peri-Chl a-protein, as an extrinsic membrane protein (sPCP) on the inner surface of the thylakoid. Peri is a unique carotenoid that has eight C=C bonds and one C=O bond, which results in a characteristic absorption band in the green wavelength region. In the present study, excitation relaxation dynamics of Peri in solution and excitation energy transfer processes of sPCP and the thylakoid membranes, prepared from the photosynthetic dinoflagellate, Symbiodinium sp., are investigated by ultrafast time-resolved fluorescence spectroscopy. We found that Peri-to-Chl a energy transfer occurs via the Peri S 1 state with a time constant of 1.5 ps or 400 fs in sPCP or iPCP, respectively, and that Chl c-to-Chl a energy transfer occurs in the time regions of 350-400 fs and 1.8-2.6 ps.

  15. Oxygen auroral transition laser system excited by collisional and photolytic energy transfer

    International Nuclear Information System (INIS)

    Murray, J.R.; Powell, H.T.; Rhodes, C.K.

    1975-06-01

    The properties of laser media involving the auroral transition of atomic oxygen and analogous systems are examined. A discussion of the atomic properties, collisional mechanisms, excitation processes, and collisionally induced radiative phenomena is given. Crossing phenomena play a particularly important role in governing the dynamics of the medium

  16. Electron and excitation energy transfers in covalently linked donor-acceptor dyads: mechanisms and dynamics revealed using quantum chemistry.

    Science.gov (United States)

    Cupellini, Lorenzo; Giannini, Samuele; Mennucci, Benedetta

    2017-12-20

    Photoinduced electron transfer (ET), hole transfer (HT), charge recombination (CR) and energy transfer (EET) are fundamental mechanisms, which occur in both natural and artificial light harvesting systems. Here, we present a computational strategy which determines ET, HT, CR and EET rates in a consistent way and merges them in a kinetic model to reproduce the net excited state dynamics. The effects of the solvent are included in all steps of the calculations making the present strategy a useful tool for a rational design of charge and energy transfer processes in complex systems. An application to covalently linked zinc and free-base porphyrin-naphthalenediimide dyads is presented. For each of the two systems, ultrafast optical spectroscopy experiments have shown a specific photophysics with different processes taking place simultaneously. The model reveals that such a diversity is mainly due to the different relative stability of the charge-separated state, while the electronic couplings for charge and energy transfer processes are quite similar in the two dyads.

  17. LIME - a flexible, non-LTE line excitation and radiation transfer method for millimeter and far-infrared wavelengths

    DEFF Research Database (Denmark)

    Brinch, Christian; Hogerheijde, Michiel

    2010-01-01

    We present a new code for solving the molecular and atomic excitation and radiation transfer problem in a molecular gas and predicting emergent spectra. This code works in arbitrary three dimensional geometry using unstructured Delaunay latices for the transport of photons. Various physical models...... that can readily be compared to observations. Because of the high dynamic range in scales that can be resolved using this type of grid, our code is particularly well suited for modeling of ALMA data. Our code can furthermore deal with overlapping lines of multiple molecular and atomic species....

  18. 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

  19. Conservative modelling of the moisture and heat transfer in building components under atmospheric excitation

    DEFF Research Database (Denmark)

    Janssen, Hans; Blocken, Bert; Carmeliet, Jan

    2007-01-01

    While the transfer equations for moisture and heat in building components are currently undergoing standardisation, atmospheric boundary conditions, conservative modelling and numerical efficiency are not addressed. In a first part, this paper adds a comprehensive description of those boundary...

  20. Transfer reactions and multiple Coulomb excitation in the $^{100}$Sn Region

    CERN Multimedia

    It is proposed to continue our REX-ISOLDE program in the $^{100}$Sn region at HIE-ISOLDE at ~5 MeV/u. Earlier measurements, with a precision of 10-20%, at 3 MeV/u with REX-ISOLDE point to a deviation between the measured B(E2) values for the first excited 2$^{+}$ states in $^{110,108,106}$Sn compared to theoretical predictions. In addition, the trend of B(E2) values for the lighter isotopes, in particular $^{106}$Sn, appear to differ between low- and high-energy measurements. In line with our letter-of-intent we aim in a first step to address the electromagnetic properties of the first 2$^{+}$and 4$^{+}$ states in $^{110,108,106}$Sn using Coulomb excitation. In these measurements we will directly access the lifetimes of the first excited 4$^{+}$ states in $^{110,108,106}$Sn for the first time. The yield of $^{104}$Sn from the LaC$_{x}$ target will be revisited to clarify if the new solid state RILIS gives sufficient yield to expand the measurements to this isotope. Following this proposal we plan similar meas...

  1. Photoexcitation of iodide ion-pyrimidine clusters above the electron detachment threshold: Intracluster electron transfer versus nucleobase-centred excitations

    Science.gov (United States)

    Matthews, Edward; Cercola, Rosaria; Mensa-Bonsu, Golda; Neumark, Daniel M.; Dessent, Caroline E. H.

    2018-02-01

    Laser photodissociation spectroscopy of the I-.thymine (I-.T) and I-.cytosine (I-.C) nucleobase clusters has been conducted for the first time across the regions above the electron detachment thresholds to explore the excited states and photodissociation channels. Although photodepletion is strong, only weak ionic photofragment signals are observed, indicating that the clusters decay predominantly by electron detachment. The photodepletion spectra of the I-.T and I-.C clusters display a prominent dipole-bound excited state (I) in the vicinity of the vertical detachment energy (˜4.0 eV). Like the previously studied I-.uracil (I-.U) cluster [W. L. Li et al., J. Chem. Phys. 145, 044319 (2016)], the I-.T cluster also displays a second excited state (II) centred at 4.8 eV, which we similarly assign to a π-π* nucleobase-localized transition. However, no distinct higher-energy absorption bands are evident in the spectra of the I-.C. Time-dependent density functional theory (TDDFT) calculations are presented, showing that while each of the I-.T and I-.U clusters displays a single dominant π-π* nucleobase-localized transition, the corresponding π-π* nucleobase transitions for I-.C are split across three separate weaker electronic excitations. I- and deprotonated nucleobase anion photofragments are observed upon photoexcitation of both I-.U and I-.T, with the action spectra showing bands (at 4.0 and 4.8 eV) for both the I- and deprotonated nucleobase anion production. The photofragmentation behaviour of the I-.C cluster is distinctive as its I- photofragment displays a relatively flat profile above the expected vertical detachment energy. We discuss the observed photofragmentation profiles of the I-.pyrimidine clusters, in the context of the previous time-resolved measurements, and conclude that the observed photoexcitations are primarily consistent with intracluster electron transfer dominating in the near-threshold region, while nucleobase-centred excitations

  2. Comparative study on contribution of charge-transfer collision to excitations of iron ion between argon radio-frequency inductively-coupled plasma and nitrogen microwave induced plasma

    Energy Technology Data Exchange (ETDEWEB)

    Satoh, Kozue; Wagatsuma, Kazuaki, E-mail: wagatuma@imr.tohoku.ac.jp

    2015-06-01

    This paper describes an ionization/excitation phenomenon of singly-ionized iron occurring in an Okamoto-cavity microwave induced plasma (MIP) as well as an argon radio-frequency inductively-coupled plasma (ICP), by comparing the Boltzmann distribution among iron ionic lines (Fe II) having a wide range of the excitation energy from 4.76 to 9.01 eV. It indicated in both the plasmas that plots of Fe II lines having lower excitation energies (4.76 to 5.88 eV) were fitted on each linear relationship, implying that their excitations were caused by a dominant thermal process such as collision with energetic electron. However, Fe II lines having higher excitation energies (more than 7.55 eV) had a different behavior from each other. In the ICP, Boltzmann plots of Fe II lines assigned to the higher excited levels also followed the normal Boltzmann relationship among the low-lying excited levels, even including a deviation from it in particular excited levels having an excitation energy of ca. 7.8 eV. This deviation can be attributed to a charge-transfer collision with argon ion, which results in the overpopulation of these excited levels, but the contribution is small. On the other hand, the distribution of the high-lying excited levels was non-thermal in the Okamoto-cavity MIP, which did not follow the normal Boltzmann relationship among the low-lying excited levels. A probable reason for the non-thermal characteristics in the MIP is that a charge-transfer collision with nitrogen molecule ion having many vibrational/rotational levels could work for populating the 3d{sup 6}4p (3d{sup 5}4s4p) excited levels of iron ion broadly over an energy range of 7.6–9.0 eV, while collisional excitation by energetic electron would occur insufficiently to excite these high-energy levels. - Highlights: • This paper describes the excitation mechanism of iron ion in Okamoto-cavity MIP in comparison with conventional ICP. • Boltzmann distribution is studied among iron ionic lines of

  3. Excited state and ground state proton transfer rates of 3-hydroxyflavone and its derivatives studied by shpol'skii spectroscopy: The influence of redistribution of electron density

    NARCIS (Netherlands)

    Bader, A.N.; Pivovarenko, V.; Demchenko, A.P.; Ariese, F.; Gooijer, C.

    2004-01-01

    We studied the mechanisms of excited-state intramolecular proton transfer (ESIPT) and ground-state back proton transfer (BPT) in 3-hydroxyflavone (3HF) at cryogenic temperatures. The focus was on substituents that change the distribution of electronic density on the chromophore and their influence

  4. Singlet-to-triplet intermediates and triplet exciton dynamics in pentacene thinfilms

    Science.gov (United States)

    Thorsmolle, Verner; Korber, Michael; Obergfell, Emanuel; Kuhlman, Thomas; Campbell, Ian; Crone, Brian; Taylor, Antoinette; Averitt, Richard; Demsar, Jure

    Singlet-to-triplet fission in organic semiconductors is a spin-conserving multiexciton process in which one spin-zero singlet excitation is converted into two spin-one triplet excitations on an ultrafast timescale. Current scientific interest into this carrier multiplication process is largely driven by prospects of enhancing the efficiency in photovoltaic applications by generating two long-lived triplet excitons by one photon. The fission process is known to involve intermediate states, known as correlated triplet pairs, with an overall singlet character, before being interchanged into uncorrelated triplets. Here we use broadband femtosecond real-time spectroscopy to study the excited state dynamics in pentacene thin films, elucidating the fission process and the role of intermediate triplet states. VKT and AJT acknowledge support by the LDRD program at Los Alamos National Laboratory and the Department of Energy, Grant No. DE-FG02-04ER118. MK, MO and JD acknowledge support by the Alexander von Humboldt Foundation.

  5. The role of quantum coherence in dimer and trimer excitation energy transfer

    Science.gov (United States)

    Bengtson, Charlotta; Sjöqvist, Erik

    2017-11-01

    Recent progress in resource theory of quantum coherence has resulted in measures to quantify coherence in quantum systems. Especially, the l 1-norm and relative entropy of coherence have been shown to be proper quantifiers of coherence and have been used to investigate coherence properties in different operational tasks. Since long-lasting quantum coherence has been experimentally confirmed in a number of photosynthetic complexes, it has been debated if and how coherence is connected to the known efficiency of population transfer in such systems. In this study, we investigate quantitatively the relationship between coherence, as quantified by l 1-norm and relative entropy of coherence, and efficiency, as quantified by fidelity, for population transfer between end-sites in a network of two-level quantum systems. In particular, we use the coherence averaged over the duration of the population transfer in order to carry out a quantitative comparison between coherence and fidelity. Our results show that although coherence is a necessary requirement for population transfer, there is no unique relation between coherence and the efficiency of the transfer process.

  6. Collisional and radiative relaxation of the first excited states of rare gases. Energy transfer from argon excited atoms to different molecules and fluorescence of molecular xenon excited by synchrotron radiation

    International Nuclear Information System (INIS)

    Dutuit-Fleischmann, Odile

    1978-01-01

    In the first section, the measurement of total deexcitation cross sections of the 3P 2,1,0 and 1 P 1 argon states by N 2 , H 2 , CO and SF 6 using a pulsed gas radiolysis technique and 600 keV electrons is discussed. The energy transfer from the resonant states 3 P 1 and 1 P 1 of argon (as excited selectively by synchrotron radiation) to the C 3 π u state of nitrogen has been studied in more detail. On the basis of these results, the different theoretical models for these reactions have been discussed. In the second section, the fluorescence of the second continuum of molecular xenon at around 1700 A, as excited by synchrotron radiation in the region of the 3P 1 1 S 0 resonance line at 1470 A, is considered. A short lived component of the fluorescence decay has been observed; this is attributed to emission at short interatomic distances from the high vibrational levels of Xe 2 + (O u + ). The emissions at the left turning point of the potential curve of the O u + state has been observed at λ > 2000 A. From these results, the potential curves for the states Xe 2 (O g + ) and Xe 2 * (O u + ) have been estimated and the Franck-Condon factors have also been calculated as a function of the wavelength of the fluorescence. (author) [fr

  7. Excited-state proton transfer from pyranine to acetate in methanol

    Indian Academy of Sciences (India)

    TECS

    -trisulphonate,. HPTS) to acetate in methanol has been studied by steady-state and time-resolved fluorescence spectros- copy. The rate constant of direct proton transfer from pyranine to acetate (k1) is calculated to be. ~1 × 10. 9. M. –1 s. –1.

  8. Excited-state proton transfer from pyranine to acetate in methanol

    Indian Academy of Sciences (India)

    trisulphonate, HPTS) to acetate in methanol has been studied by steady-state and time-resolved fluorescence spectroscopy. The rate constant of direct proton transfer from pyranine to acetate (1) is calculated to be ∼ 1 × 109 M-1 s-1. This is slower by ...

  9. Glow discharge in singlet oxygen

    International Nuclear Information System (INIS)

    Vagin, N.P.; Ionin, A.A.; Klimachev, Yu.M.; Sinitsyn, D.V.; Yuryshev, N.N.; Kochetov, I.V.; Napartovich, A.P.

    2003-01-01

    Currently, there is no experimental data on the plasma balance in gas mixtures with a high content of singlet delta oxygen O 2 ( 1 Δ g ). These data can be obtained by studying the parameters of an electric discharge in singlet oxygen produced by a chemical generator. The O 2 ( 1 Δ g ) molecules significantly change the kinetics of electrons and negative ions in plasma. Hence, the discharge conditions at low and high O 2 ( 1 Δ g ) concentrations are very different. Here, the parameters of the positive column of a glow discharge in a gas flow from a chemical singlet-oxygen generator are studied. It is experimentally shown that, at an O 2 ( 1 Δ g ) concentration of 50% and at pressures of 1.5 and 2 torr, the electric field required to sustain the discharge is considerably lower than in the case when all of the oxygen molecules are in the ground state. A theoretical model of the glow discharge is proposed whose predictions are in good agreement with the experimental data

  10. Confinement sensitivity in quantum dot singlet-triplet relaxation

    Science.gov (United States)

    Wesslén, C. J.; Lindroth, E.

    2017-11-01

    Spin-orbit mediated phonon relaxation in a two-dimensional quantum dot is investigated using different confining potentials. Elliptical harmonic oscillator and cylindrical well results are compared to each other in the case of a two-electron GaAs quantum dot subjected to a tilted magnetic field. The lowest energy set of two-body singlet and triplet states are calculated including spin-orbit and magnetic effects. These are used to calculate the phonon induced transition rate from the excited triplet to the ground state singlet for magnetic fields up to where the states cross. The roll of the cubic Dresselhaus effect, which is found to be much more important than previously assumed, and the positioning of ‘spin hot-spots’ are discussed and relaxation rates for a few different systems are exhibited.

  11. Spin-singlet quantum Hall states and Jack polynomials with a prescribed symmetry

    International Nuclear Information System (INIS)

    Estienne, Benoit; Bernevig, B. Andrei

    2012-01-01

    We show that a large class of bosonic spin-singlet Fractional Quantum Hall model wavefunctions and their quasihole excitations can be written in terms of Jack polynomials with a prescribed symmetry. Our approach describes new spin-singlet quantum Hall states at filling fraction ν=(2k)/(2r-1) and generalizes the (k,r) spin-polarized Jack polynomial states. The NASS and Halperin spin-singlet states emerge as specific cases of our construction. The polynomials express many-body states which contain configurations obtained from a root partition through a generalized squeezing procedure involving spin and orbital degrees of freedom. The corresponding generalized Pauli principle for root partitions is obtained, allowing for counting of the quasihole states. We also extract the central charge and quasihole scaling dimension, and propose a conjecture for the underlying CFT of the (k,r) spin-singlet Jack states.

  12. Theoretical study on the excited-state intramolecular proton-transfer reaction of 10-hydroxybenzo[h]quinoline in methanol and cyclohexane

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Meng [Department of Chemistry, Liaoning University, Shenyang 110036 (China); State Key Lab of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023 (China); Zhao, Jinfeng [Department of Physics, Liaoning University, Shenyang 110036 (China); State Key Lab of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023 (China); Cui, Yanling; Wang, Qianyu [Department of Physics, Liaoning University, Shenyang 110036 (China); Dai, Yumei [Normal College, Shenyang University, Shenyang 110044 (China); Song, Peng, E-mail: songpeng@lnu.edu.cn [Department of Physics, Liaoning University, Shenyang 110036 (China); Xia, Lixin, E-mail: lixinxia@lnu.edu.cn [Department of Chemistry, Liaoning University, Shenyang 110036 (China)

    2015-05-15

    The dynamics of the excited-state intramolecular proton-transfer (ESIPT) reaction of 10-hydroxybenzoquinoline (HBQ) in different solvents, have been investigated based on the time-dependent density functional theory (TD-DFT) in detail. Upon excitation, the intramolecular hydrogen bond between the hydroxyl and phenanthrene functionality is significantly strengthened in the S{sub 1} state, which can be used as a reasonable tendency for facilitating the ESIPT process. In addition, the calculated vertical excitation energies in the S{sub 0} state and S{sub 1} state reproduce the experimental UV–vis absorbance and fluorescence emission spectra well. Through calculating the fluorescence spectra of the HBQ chromophore, two outcomes for this chromophore were found in the S{sub 1} state, which demonstrates that the ESIPT process occurs. The potential energy curves have been calculated to account for the mechanism of the proton-transfer process in the excited-state. As a result, the barrierless ESIPT process can occur in the S{sub 1} state with proton transfer from the O atom to the N atom. And maybe the ESIPT process is easier in methanol solvent due to the higher potential energy difference. - Highlights: • The hydrogen bond between the hydroxyl and phenanthrene is strengthened. • The hydrogen bond facilitates the proton transfer from the hydroxyl group to the N atom. • The spontaneous excited-state intramolecular proton transfer reaction can be observed.

  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. Multi-step excitation energy transfer engineered in genetic fusions of natural and synthetic light-harvesting proteins.

    Science.gov (United States)

    Mancini, Joshua A; Kodali, Goutham; Jiang, Jianbing; Reddy, Kanumuri Ramesh; Lindsey, Jonathan S; Bryant, Donald A; Dutton, P Leslie; Moser, Christopher C

    2017-02-01

    Synthetic proteins designed and constructed from first principles with minimal reference to the sequence of any natural protein have proven robust and extraordinarily adaptable for engineering a range of functions. Here for the first time we describe the expression and genetic fusion of a natural photosynthetic light-harvesting subunit with a synthetic protein designed for light energy capture and multi-step transfer. We demonstrate excitation energy transfer from the bilin of the CpcA subunit (phycocyanin α subunit) of the cyanobacterial photosynthetic light-harvesting phycobilisome to synthetic four-helix-bundle proteins accommodating sites that specifically bind a variety of selected photoactive tetrapyrroles positioned to enhance energy transfer by relay. The examination of combinations of different bilin, chlorin and bacteriochlorin cofactors has led to identification of the preconditions for directing energy from the bilin light-harvesting antenna into synthetic protein-cofactor constructs that can be customized for light-activated chemistry in the cell. © 2017 The Author(s).

  15. Tunable luminescence mediated by energy transfer in Tm3+/Dy3+ co-doped phosphate glasses under UV excitation

    Science.gov (United States)

    Chen, Yong; Chen, Guohua; Liu, Xiangyu; Yuan, Changlai; Zhou, Changrong

    2017-11-01

    Tm3+/Dy3+ co-doped phosphate glasses for white light-emitting diodes were synthesized by a conventional melting-quenching method. A spectroscopic research based on optical, photoluminescence spectrum and decay time curves in Tm3+/Dy3+ co-doped phosphate glasses was carried out. The color of luminescence could be tuned by altering the concentrations of Tm3+ ions. Under UV light excitation, the CIE chromaticity coordinates (0.3471, 0.3374) and color correlate temperature (CCT = 4866.21 K) close to the standard white-light illumination (0.333, 0.333 and CCT = 5454.12 K) could be achieved in 0.4 Tm3+/0.6 Dy3+ (mol %) co-doped glass sample. The decrease of the Dy3+ emission decay time in existence of Tm3+ ascertained that non-radiative energy transfer from Dy3+ to Tm3+ occurred. Moreover, the research of energy transfers between Dy3+ and Tm3+ based on the Inokuti-Hirayama model revealed that an electric quadrupole-quadrupole interaction might be the predominant mechanism participated in the energy transfer. This finding suggests that the as-prepared Tm3+/Dy3+ co-doped phosphate glasses may be promising candidate for white LEDs and other display devices.

  16. Distance dependence of intrahelix Ru(II)* to Os(II) polypyridyl excited-state energy transfer in oligoproline assemblies.

    Science.gov (United States)

    Brennaman, M Kyle; Fleming, Cavan N; Slate, Cheryl A; Serron, Scafford A; Bettis, Stephanie E; Erickson, Bruce W; Papanikolas, John M; Meyer, Thomas J

    2013-05-30

    Energy transfer between the metal-to-ligand charge transfer (MLCT) excited states of [Pra [M(II)(bpy)2(4-Me-4'(-N(H)CO)bpy)](PF6)2 units ([Pra(M(II)bpy2(mbpy)](2+): M(II) = Ru(II) or Os(II), bpy = 2,2'-bipyridine, mbpy = 4'-methyl-2,2'-bipyridine-4-carboxamido, Pra = 4-M(II)-L-proline) linked covalently to oligoproline assemblies in room temperature acetonitrile occurs on the picosecond-nanosecond time scale and has been time-resolved by transient emission measurements. Three derivatized oligoprolines, [CH3-CO-Pro6-Pra[Os(II)(bpy)2(mbpy)](2+)-Pro2-Pra[Ru(II)(bpy)2(mbpy)](2+)-Pro2-Pra[Ru(II)(bpy)2(mbpy)](2+)-Pro6-Glu-NH2](6+) (ORR-2, Pro = L-proline and Glu = glutamic acid); [CH3-CO-Pro6-Pra[Os(II)(bpy)2(mbpy)](2+)-Pro3-Pra[Ru(II)(bpy)2(mbpy)](2+)-Pro3-Pra[Ru(II)(bpy)2(mbpy)](2+)-Pro6-Glu-NH2](6+) (ORR-3); and CH3-CO-Pro6-Pra[Os(II)(bpy)2(mbpy)](2+)-Pro5-Pra[Ru(II)(bpy)2(mbpy)](2+)-Pro5-Pra[Ru(II)(bpy)2(mbpy)](2+)Pro6-Glu2-NH2](6+) (ORR-5), were prepared by using solid-phase peptide synthesis. Given the helical nature of the resulting assemblies and the nature of the synthesis, composition, length, and loading pattern are precisely controlled in the assemblies. In acetonitrile, they adopt a proline I helical secondary structure, confirmed by circular dichroism, in which the appended chromophores are ordered in well-defined orientations and internuclear separation distances although helix formation for ORR-2 is incomplete. Quantitative comparison of oligoproline ground-state absorption and steady-state emission spectra to those for the constituents, [Boc-Pra[M(II)(bpy)2(mbpy)](2+)-OH](PF6)2 (Boc = N(α)-(1,1-dimethylethoxycarbonyl), shows that following Ru(II) light absorption, Ru(II)* undergoes facile energy transfer resulting in sensitization of Os(II). Sensitization efficiencies are 93% for ORR-2, 77% for ORR-3, and 73% for ORR-5. Picosecond-resolved emission measurements reveal complex, coupled dynamics that arise from excited-state decay and kinetically

  17. Excited baryon form-factors at high momentum transfer at CEBAF at higher energies

    Energy Technology Data Exchange (ETDEWEB)

    Stoler, P. [Rensselaer Polytechnic Inst., Troy, NY (United States)

    1994-04-01

    The possibilities of measuring the properties of excited nucleons at high Q{sup 2} by means of exclusive single meson production at CEBAF with an electron energy of 8 GeV is considered. The motivation is to access short range phenomena in baryon structure, and to investigate the transition from the low Q{sup 2} non-perturbative QCD regime, where constituent quark models are valid, to higher Q{sup 2} where it is believed perturbative QCD plays an increasingly important role. It is found that high quality baryon decay angular distributions can be obtained for the most prominent states up to Q{sup 2} {approximately} 12 GeV{sup 2}/c{sup 2} using a set of moderate resolution, large solid angle magnetic spectrometers.

  18. Testing two-nucleon transfer reaction mechanism with elementary modes of excitation in exotic nuclei

    CERN Document Server

    Broglia, R A; Idini, A; Barranco, F; Vigezzi, E

    2015-01-01

    Nuclear Field Theory of structure and reactions is confronted with observations made on neutron halo dripline nuclei, resulting in the prediction of a novel (symbiotic) mode of nuclear excitation, and on the observation of the virtual effect of the halo phenomenon in the apparently non-halo nucleus $^7$Li. This effect is forced to become real by intervening the virtual process with an external (t,p) field which, combined with accurate predictive abilities concerning the absolute differential cross section, reveals an increase of a factor 2 in the cross section due to the presence of halo ground state correlations, and is essential to reproduce the value of the observed $d \\sigma(^7$Li(t,p)$^9$Li)/d$\\Omega$.

  19. Excited baryon form-factors at high momentum transfer at CEBAF at higher energies

    International Nuclear Information System (INIS)

    Stoler, P.

    1994-01-01

    The possibilities of measuring the properties of excited nucleons at high Q 2 by means of exclusive single meson production at CEBAF with an electron energy of 8 GeV is considered. The motivation is to access short range phenomena in baryon structure, and to investigate the transition from the low Q 2 non-perturbative QCD regime, where constituent quark models are valid, to higher Q 2 where it is believed perturbative QCD plays an increasingly important role. It is found that high quality baryon decay angular distributions can be obtained for the most prominent states up to Q 2 ∼ 12 GeV 2 /c 2 using a set of moderate resolution, large solid angle magnetic spectrometers

  20. Modeling energy transfer in molecular collisions: Statistical theory versus experiment for highly excited toluene and azulene

    Science.gov (United States)

    Nilsson, Daniel; Nordholm, Sture

    2003-12-01

    The recent development and application of the method of kinetically controlled selective ionization has produced detailed and reliable data on the collisional energy transfer kernel P(E',E) entering master equation theories of unimolecular reaction rates. Here we test the ability of our partially ergodic collision theory (PECT) to predict the functional form of the observed kernel leaving only one parameter, the first moment of the distribution , to be input from other sources. The data explored here include two reactant molecules, toluene and azulene, in collisions with 18 and 8 medium molecules, respectively, ranging from inert gas atoms to n-heptane. The initial energy of the reactant molecule is varied from 10 000 cm-1 to 49 000 cm-1 and 30 000 cm-1, respectively. The energy transfer efficiency βE is about one-tenth of its ergodic collision limit of unity. The PECT is found to fit the monoexponential form of the kernel determined from the experimental data over a broad range of initial energies E including tail regions of very low probability. A minor but systematic deviation is observed for nearly elastic collisions of large medium molecules. The functional fit is good enough to effectively allow the three parameters of the monoexponential experimental kernel to be replaced by a single parameter representing energy transfer efficiency.

  1. Excitation energy transfer in Chlamydomonas reinhardtii deficient in the PSI core or the PSII core under conditions mimicking state transitions.

    Science.gov (United States)

    Wlodarczyk, Lucyna M; Dinc, Emine; Croce, Roberta; Dekker, Jan P

    2016-06-01

    The efficient use of excitation energy in photosynthetic membranes is achieved by a dense network of pigment-protein complexes. These complexes fulfill specific functions and interact dynamically with each other in response to rapidly changing environmental conditions. Here, we studied how in the intact cells of Chlamydomonas reinhardtii (C.r.) the lack of the photosystem I (PSI) core or the photosystem II (PSII) core affects these interactions. To that end the mutants F15 and M18 (both PSI-deficient) and FUD7 (PSII-deficient) were incubated under conditions known to promote state transitions in wild-type. The intact cells were then instantly frozen to 77K and the full-spectrum time-resolved fluorescence emission of the cells was measured by means of streak camera. In the PSI-deficient mutants excitation energy transfer (EET) towards light-harvesting complexes of PSI (Lhca) occurs in less than 0.5 ns, and fluorescence from Lhca decays in 3.1 ns. Decreased trapping by PSII and increased fluorescence of Lhca upon state 1 (S1)→state 2 (S2) transition appears in the F15 and less in the M18 mutant. In the PSII-deficient mutant FUD7, quenched (0.5 ns) and unquenched (2 ns) light-harvesting complexes of PSII (LHCII) are present in both states, with the quenched form more abundant in S2 than in S1. Moreover, EET of 0.4 ns from the remaining LHCII to PSI increases upon S1→S2 transition. We relate the excitation energy kinetics observed in F15, M18 and FUD7 to the remodeling of the photosynthetic apparatus in these mutants under S1 and S2 conditions. Copyright © 2016 Elsevier B.V. All rights reserved.

  2. Investigation of the charge-transfer in photo-excited nanoparticles for CO2 reduction in non-aqueous media

    Directory of Open Access Journals (Sweden)

    Dimitrijević Nada M.

    2013-01-01

    Full Text Available Photoinduced charge separation in TiO2 and Cu2O semiconductor nanoparticles was examined using Electron Paramagnetic Resonance spectroscopy in order to get insight into the photocatalytic reduction of CO2 in nonaqueous media. For dissolution/grafting of CO2 we have used carboxy-PEG4-amine, and as a solvent poly(ethylene glycol 200. We have found that, in this system, reduction of CO2 starts at potential of -0.5 V vs Ag/AgCl, which is significantly more positive than the potential for electrochemical reduction of CO2 in most organic solvents and water (-2.0 V vs. Ag/AgCl. The electron transfer from excited nanoparticles to CO2 is governed both by thermodynamic and kinetic parameters, namely by the redox potential of conduction band electrons and adsorption/binding of CO2 on the surface of nanoparticles.

  3. LIME - a flexible, non-LTE line excitation and radiation transfer method for millimeter and far-infrared wavelengths

    DEFF Research Database (Denmark)

    Brinch, Christian; Hogerheijde, Michiel

    2010-01-01

    We present a new code for solving the molecular and atomic excitation and radiation transfer problem in a molecular gas and predicting emergent spectra. This code works in arbitrary three dimensional geometry using unstructured Delaunay latices for the transport of photons. Various physical models...... can be used as input, ranging from analytical descriptions over tabulated models to SPH simulations. To generate the Delaunay grid we sample the input model randomly, but weigh the sample probability with the molecular density and other parameters, and thereby we obtain an average grid point...... separation that scales with the local opacity. Our code does photon very efficiently so that the slow convergence of opaque models becomes traceable. When convergence between the level populations, the radiation field, and the point separation has been obtained, the grid is ray-traced to produced images...

  4. The Effect of Substituent Position on Excited State Intramolecular Proton Transfer in Benzoxazinone Derivatives: Experiment and DFT Calculation.

    Science.gov (United States)

    Bian, Gao-Feng; Guo, Yun; Lv, Xiao-Jing; Zhang, Cheng

    2017-01-01

    The preparation and the photophysical behaviour of two benzoxazinone derivatives isomers 2-(1-hydroxynaphthalen-2-yl)-4H-benzo[e][1, 3]oxazin-4-one(1) and 2-(3-hydroxynaphthalen-2-yl)-4H-benzo[e][1, 3]oxazin-4-one(2) designed for displaying were reported. The effect of substituent position and solvent effect on the excited state intramolecular proton transfer (ESIPT) dynamics and the spectroscopic properties were investigated using a combined theoretical (i.e., time-dependent density function theory (DFT)) and experimental (i.e., steady-state absorption and emission spectra and time-resolved fluorescence spectra) study. The results showed that compound 1 would facilitate ESIPT process and favored the keto tautomer emission, while compound 2 suppressed the ESIPT process and favored the enol emission.

  5. Effect of NaCl Salts on the Activation Energy of Excited-State Proton Transfer Reaction of Coumarin 183.

    Science.gov (United States)

    Joung, Joonyoung F; Kim, Sangin; Park, Sungnam

    2015-12-17

    Coumarin 183 (C183) was used as a photoacid to study excited-state proton transfer (ESPT) reactions. Here, we studied the effect of ions on the ESPT of C183 in aqueous NaCl solutions using a steady-state fluorescence spectroscopy and time-correlated single photon counting (TCSPC) method. The acid dissociation equilibrium of excited-state C183 and the activation energy for the ESPT of C183 were determined as a function of NaCl concentration. The change in the equilibrium constant was found to be correlated with the solvation energy of deprotonated C183. Frequency-resolved TCSPC signals measured at several temperatures were analyzed by using a global fitting analysis method which enabled us to extract all the rate constants involving the ESPT reaction and the spectra of individual species. The activation energy for the ESPT reaction of C183 was highly dependent on NaCl concentration. Quantum chemical calculations were used to calculate the local hydrogen-bond (H-bond) configurations around C183 in aqueous NaCl solutions. It was found that the activation energy for the ESPT was determined by the local H-bond configurations around C183 which were significantly influenced by the dissolved ions.

  6. Investigation of excited 0+ states in 160Er populated via the (p , t) two-neutron transfer reaction

    Science.gov (United States)

    Burbadge, C.

    2017-09-01

    The interpretation of low-lying 0+ states in rare-earth nuclei remains a highly-debated topic in nuclear structure. Resolving the nature of these states is particularly difficult due to the presence of shape coexistence which can increase the number of low-lying states, as well as the paucity of data for excited 0+ states. Two-neutron transfer reactions are ideal tools for probing 0+ -> 0+ transitions in deformed nuclei. In the present work, excited 0+ states are studied via a series of (p , t) reactions on 162 , 164 , 166 , 168Er targets at the Maier-Leibnitz Laboratory in Garching, Germany. Reaction products were momentum-analyzed with a Q3D magnetic spectrograph. The results confirm strong population of the 02+state of 18% of the ground state strength in 160Er consistent with the strength observed in other N = 92 isotones, suggesting a special character for this state which is inconsistent with a β-vibration interpretation. Preliminary results of the 0+ strength in the aforementioned (p , t) experiments will be presented and placed into context with similar experiments in the N = 90 region, underlining the potential role of the 112- [ 505 ] ν orbital in the observed 02+ state strength.

  7. Effective targeting of proton transfer at ground and excited states of ortho-(2'-imidazolyl)naphthol constitutional isomers.

    Science.gov (United States)

    Oliveira, Thaís C F; Carmo, Luiz F V; Murta, Bárbara; Duarte, Luís G T A; Nome, Rene A; Rocha, Willian R; Brandão, Tiago A S

    2015-01-28

    Steady-state and time-resolved spectroscopy and quantum chemical computational studies were employed to investigate ground and excited state proton transfer of a novel series of ortho-(1H-imidazol-2-yl)naphthol constitutional isomers: 1-(1H-imidazol-2-yl)naphthalen-2-ol (1NI2OH), 2-(1H-imidazol-2-yl)naphthalen-1-ol (2NI1OH) and 3-(1H-imidazol-2-yl)naphthalen-2-ol (3NI2OH). Proper Near Attack Conformations (NACs) involving a strong intramolecular hydrogen bond between the naphthol moiety and the ortho-imidazole group account for the highest ground state acidity of 2NI1OH compared with 1NI2OH and 3NI2OH. Moreover, ESIPT for 2NI1OH and 3NI2OH is further associated with planar chelate H-ring formation whereas 1NI2OH shows the highest ESIPT barrier and a noncoplanar imidazole group. In addition to energetic and structural requirements, the final state also depends on electronic configuration of the ESIPT product with the neutral 3NI2OH showing an ICT effect that correlates with the excited state pKa of the cationic species.

  8. 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.

  9. 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

  10. Supersymmetric singlet majorons and cosmology

    International Nuclear Information System (INIS)

    Chun, E.J.; Kim, H.B.; Lukas, A.

    1994-02-01

    We examine cosmological constraints on the lepton number breaking scale in super-symmetric singlet majoron models. Special attention is drawn to the model dependence arising from the particular choice of a certain majoron extension and a cosmological scenario. We find that the bounds on the symmetry breaking scale can vary substantially. Large values of this scale can be allowed if the decoupling temperature of majoron and majorino exceeds the reheating temperature of inflation. In the opposite case an upper bound depending on the majoron model can be obtained which, however, is unlikely to be much larger than 10 10 GeV. (author). 13 refs, 2 figs

  11. Flavor-singlet hidden charm pentaquark

    Science.gov (United States)

    Irie, Yoya; Oka, Makoto; Yasui, Shigehiro

    2018-02-01

    One type of hidden charm pentaquark Pc s with quark content c c ¯u d s in light-flavor singlet state is studied in the quark model. This state is analogous to the Pc with c c ¯u u d in light-flavor octet, which was observed in LHC in 2015. Considering various combinations of color, spin, and light flavor as internal quantum numbers in Pc s, we investigate the mass ordering of the Pc s's by adopting both the one-gluon exchange interaction and the instanton-induced interaction in the quark model. The most stable configuration of Pc s is identified to be total spin 1 /2 in which the c c ¯ is combined to be color octet and spin 1, while the u d s cluster is in a color octet state. The other color octet configurations, the total spin 1 /2 state with the c c ¯ spin 0, and the state with total spin 3 /2 and c c ¯ spin 1, are found as excited states. We also discuss possible decay modes of these hidden charm pentaquarks.

  12. Singlet-paired coupled cluster theory for open shells

    International Nuclear Information System (INIS)

    Gomez, John A.; Henderson, Thomas M.; Scuseria, Gustavo E.

    2016-01-01

    Restricted single-reference coupled cluster theory truncated to single and double excitations accurately describes weakly correlated systems, but often breaks down in the presence of static or strong correlation. Good coupled cluster energies in the presence of degeneracies can be obtained by using a symmetry-broken reference, such as unrestricted Hartree-Fock, but at the cost of good quantum numbers. A large body of work has shown that modifying the coupled cluster ansatz allows for the treatment of strong correlation within a single-reference, symmetry-adapted framework. The recently introduced singlet-paired coupled cluster doubles (CCD0) method is one such model, which recovers correct behavior for strong correlation without requiring symmetry breaking in the reference. Here, we extend singlet-paired coupled cluster for application to open shells via restricted open-shell singlet-paired coupled cluster singles and doubles (ROCCSD0). The ROCCSD0 approach retains the benefits of standard coupled cluster theory and recovers correct behavior for strongly correlated, open-shell systems using a spin-preserving ROHF reference.

  13. Excited-State Dynamics in Folic Acid and 6-CARBOXYPTERIN upon Uva Excitation

    Science.gov (United States)

    Huang, Huijuan; Vogt, R. Aaron; Crespo-Hernandez, Carlos E.

    2013-06-01

    The excited-state dynamics of folic acid (FA) and 6-carboxypterin (6CP) are poorly understood and work is needed to uncover the relaxation pathways that ultimately lead to their oxidative damage of DNA. In our approach, broad-band transient absorption spectroscopy was used to monitor the evolution of the excited states in FA and 6CP in basic aqueous solution upon excitation at 350 nm. In addition, quantum-chemical calculations were performed to assist in the interpretation of the experimental results and in the postulation of kinetic mechanisms. The combined experimental and computational results support a kinetic model where excitation of FA results in ultrafast charge separation (τ = 0.6 ps), which decays back to the ground state primarily by charge recombination with a lifetime of 2.2 ps. A small fraction of the charge transfer state undergoes intersystem crossing to populate the lowest-energy triplet state with a lifetime of 200 ps. On the other hand, a large fraction of the initially excited singlet state in 6CP decays by fluorescence emission with a lifetime of 100 ps, while intersystem crossing to the triplet state occurs with a lifetime of 4.4 ns. The potential implications of these results to the oxidative damage of DNA by FA and 6CP will be discussed. Funding from the National Science Foundation is gratefully acknowledged (CHE-1255084).

  14. Photosensitized production of singlet oxygen: spatially-resolved optical studies in single cells

    DEFF Research Database (Denmark)

    Breitenbach, Thomas; Kuimova, Marina; Gbur, Peter

    2009-01-01

    be monitored using viability assays. Time- and spatially-resolved optical measurements of both singlet oxygen and its precursor, the excited state sensitizer, reflect the complex and dynamic morphology of the cell. These experiments help elucidate photoinduced, oxygen-dependent events that compromise cell...

  15. Phosphorescence dynamics of singlet oxygen and Radachlorin photosensitizer in aqueous solution

    Science.gov (United States)

    Belik, V. P.; Beltukova, D. M.; Gadzhiev, I. M.; Semenova, I. V.; Vasyutinskii, O. S.

    2017-07-01

    The luminescence spectrum of aqueous solution of Radachlorin photosensitizer in the near IR spectral range (950-1350 nm) has been determined at the excitation in both the Soret and Q absorption bands. Major sources of the recorded luminescence were analyzed. Kinetics of photosensitizer and singlet oxygen phosphorescence signals were studied by means of time-resolved spectroscopy. The corresponding characteristic lifetimes were determined.

  16. Singlet Ground State Magnetism: III Magnetic Excitons in Antiferromagnetic TbP

    DEFF Research Database (Denmark)

    Knorr, K.; Loidl, A.; Kjems, Jørgen

    1981-01-01

    The dispersion of the lowest magnetic excitations of the singlet ground state system TbP has been studied in the antiferromagnetic phase by inelastic neutron scattering. The magnetic exchange interaction and the magnetic and the rhombohedral molecular fields have been determined....

  17. Dynamics of Singlet Fission and Electron Injection in Self-Assembled Acene Monolayers on Titanium Dioxide

    Energy Technology Data Exchange (ETDEWEB)

    Johnson, Justin C [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Pace, Natalie A [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Arias, Dylan H [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Christensen, Steven T [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Granger, Devin B. [University of Kentucky; Anthony, John E. [University of Kentucky

    2018-02-26

    We employ a combination of linear spectroscopy, electrochemistry, and transient absorption spectroscopy to characterize the interplay between electron transfer and singlet fission dynamics in polyacene-based dyes attached to nanostructured TiO2. For triisopropyl silylethynyl (TIPS)-pentacene, we find that the singlet fission time constant increases to 6.5 ps on a nanostructured TiO2 surface relative to a thin film time constant of 150 fs, and that triplets do not dissociate after they are formed. In contrast, TIPS-tetracene singlets quickly dissociate in 2 ps at the molecule/TiO2 interface, and this dissociation outcompetes the relatively slow singlet fission process. The addition of an alumina layer slows down electron injection, allowing the formation of triplets from singlet fission in 40 ps. However, the triplets do not inject electrons, which is likely due to a lack of sufficient driving force for triplet dissociation. These results point to the critical balance required between efficient singlet fission and appropriate energetics for interfacial charge transfer.

  18. Exposure of vitamins to UVB and UVA radiation generates singlet oxygen.

    Science.gov (United States)

    Knak, Alena; Regensburger, Johannes; Maisch, Tim; Bäumler, Wolfgang

    2014-05-01

    Deleterious effects of UV radiation in tissue are usually attributed to different mechanisms. Absorption of UVB radiation in cell constituents like DNA causes photochemical reactions. Absorption of UVA radiation in endogenous photosensitizers like vitamins generates singlet oxygen via photosensitized reactions. We investigated two further mechanisms that might be involved in UV mediated cell tissue damage. Firstly, UVB radiation and vitamins also generate singlet oxygen. Secondly, UVB radiation may change the chemical structure of vitamins that may change the role of such endogenous photosensitizers in UVA mediated mechanisms. Vitamins were irradiated in solution using monochromatic UVB (308 nm) or UVA (330, 355, or 370 nm) radiation. Singlet oxygen was directly detected and quantified by its luminescence at 1270 nm. All investigated molecules generated singlet oxygen with a quantum yield ranging from 0.007 (vitamin D3) to 0.64 (nicotinamide) independent of the excitation wavelength. Moreover, pre-irradiation of vitamins with UVB changed their absorption in the UVB and UVA spectral range. Subsequently, molecules such as vitamin E and vitamin K1, which normally exhibit no singlet oxygen generation in the UVA, now produce singlet oxygen when exposed to UVA at 355 nm. This interplay of different UV sources is inevitable when applying serial or parallel irradiation with UVA and UVB in experiments in vitro. These results should be of particular importance for parallel irradiation with UVA and UVB in vivo, e.g. when exposing the skin to solar radiation.

  19. 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.

  20. State-selective electron transfer and ionization in collisions of highly charged ions with ground-state Na(3s) and laser-excited Na*(3p)

    NARCIS (Netherlands)

    Blank, I.; Otranto, S.; Meinema, C.; Olson, R. E.; Hoekstra, R.

    2012-01-01

    Single electron transfer and ionization in collisions of N5+ and Ne8+ with ground state Na(3s) and laser excited Na*(3p) are investigated both experimentally and theoretically at collision energies from 1 to 10 keV/amu, which includes the classical orbital velocity of the valence electron.

  1. 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.

  2. 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

  3. 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.

  4. Colour singlets in perturbative QCD

    International Nuclear Information System (INIS)

    Bassetto, A.

    1979-01-01

    In the axial gauge and at the leading log level, a definite and consistent picture seems to emerge of a parton decay into states in which many partons are found just before confinement should take place. They are grouped into colourless clusters in a number sufficient to exhaust the ''final'' state, still possessing a finite average mass. This result is peculiar of QCD, in particular of its non-abelian nature. Large transverse momenta or more generally average invariant quantities of partons are mainly due to the multiplicities involved in the branching processes. If eventually confinement would convert these clusters into hadrons (and this is of course the main issue which has still to be proven) without a large rearrangement of the colour lines, the picture we have found for colour singlets could apply to the real hadronic world. (author)

  5. On the Lowest Excited Singlet State of Osmium Tetroxide.

    Science.gov (United States)

    1981-03-10

    aqreemert indicates that N, is involved in the proqression in the lower T2 state. Thee conclusions are consistent with those reached throuqh MCD studies of...Diemann, Chem. Phys. Let.. 20, 540 tI973). P~ ~~ -MIR... a 12 19. P. Day, L. Disiplo, and L. Oleari , Chem. Phys. Lett. 5, 533 (1970). 20. L.W. Johnson...E. Hughes, Jr., and S.P. McGlynn, J. Chem. Phys. 55, 4476 (1971), 21. J.C. Collingwood, P. Day, R.G. Denning, D.J. Robbins, L. Disiplo, and L. Oleari

  6. A novel construction of complex-valued Gaussian processes with arbitrary spectral densities and its application to excitation energy transfer.

    Science.gov (United States)

    Chen, Xin; Cao, Jianshu; Silbey, Robert J

    2013-06-14

    The recent experimental discoveries about excitation energy transfer (EET) in light harvesting antenna (LHA) attract a lot of interest. As an open non-equilibrium quantum system, the EET demands more rigorous theoretical framework to understand the interaction between system and environment and therein the evolution of reduced density matrix. A phonon is often used to model the fluctuating environment and convolutes the reduced quantum system temporarily. In this paper, we propose a novel way to construct complex-valued Gaussian processes to describe thermal quantum phonon bath exactly by converting the convolution of influence functional into the time correlation of complex Gaussian random field. Based on the construction, we propose a rigorous and efficient computational method, the covariance decomposition and conditional propagation scheme, to simulate the temporarily entangled reduced system. The new method allows us to study the non-Markovian effect without perturbation under the influence of different spectral densities of the linear system-phonon coupling coefficients. Its application in the study of EET in the Fenna-Matthews-Olson model Hamiltonian under four different spectral densities is discussed. Since the scaling of our algorithm is linear due to its Monte Carlo nature, the future application of the method for large LHA systems is attractive. In addition, this method can be used to study the effect of correlated initial condition on the reduced dynamics in the future.

  7. Modeling of fluorescence line-narrowed spectra in weakly coupled dimers in the presence of excitation energy transfer

    Science.gov (United States)

    Lin, Chen; Reppert, Mike; Feng, Ximao; Jankowiak, Ryszard

    2014-07-01

    This work describes simple analytical formulas to describe the fluorescence line-narrowed (FLN) spectra of weakly coupled chromophores in the presence of excitation energy transfer (EET). Modeling studies for dimer systems (assuming low fluence and weak coupling) show that the FLN spectra (including absorption and emission spectra) calculated for various dimers using our model are in good agreement with spectra calculated by: (i) the simple convolution method and (ii) the more rigorous treatment using the Redfield approach [T. Renger and R. A. Marcus, J. Chem. Phys. 116, 9997 (2002)]. The calculated FLN spectra in the presence of EET of all three approaches are very similar. We argue that our approach provides a simplified and computationally more efficient description of FLN spectra in the presence of EET. This method also has been applied to FLN spectra obtained for the CP47 antenna complex of Photosystem II reported by Neupane et al. [J. Am. Chem. Soc. 132, 4214 (2010)], which indicated the presence of uncorrelated EET between pigments contributing to the two lowest energy (overlapping) exciton states, each mostly localized on a single chromophore. Calculated and experimental FLN spectra for CP47 complex show very good qualitative agreement.

  8. 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.

  9. X-ray Inducible Luminescence and Singlet Oxygen Sensitization by an Octahedral Molybdenum Cluster Compound: A New Class of Nanoscintillators.

    Science.gov (United States)

    Kirakci, Kaplan; Kubát, Pavel; Fejfarová, Karla; Martinčík, Jiří; Nikl, Martin; Lang, Kamil

    2016-01-19

    Newly synthesized octahedral molybdenum cluster compound (n-Bu4N)2[Mo6I8(OOC-1-adamantane)6] revealed uncharted features applicable for the development of X-ray inducible luminescent materials and sensitizers of singlet oxygen, O2((1)Δg). The compound exhibits a red-NIR luminescence in the solid state and in solution (e.g., quantum yield of 0.76 in tetrahydrofuran) upon excitation by UV-vis light. The luminescence originating from the excited triplet states is quenched by molecular oxygen to produce O2((1)Δg) with a high quantum yield. Irradiation of the compound by X-rays generated a radioluminescence with the same emission spectrum as that obtained by UV-vis excitation. It proves the formation of the same excited triplet states regardless of the excitation source. By virtue of the described behavior, the compound is suggested as an efficient sensitizer of O2((1)Δg) upon X-ray excitation. The luminescence and radioluminescence properties were maintained upon embedding the compound in polystyrene films. In addition, polystyrene induced an enhancement of the radioluminescence intensity via energy transfer from the scintillating polymeric matrix. Sulfonated polystyrene nanofibers were used for the preparation of nanoparticles which form stable dispersions in water, while keeping intact the luminescence properties of the embedded compound over a long time period. Due to their small size and high oxygen diffusivity, these nanoparticles are suitable carriers of sensitizers of O2((1)Δg). The presented results define a new class of nanoscintillators with promising properties for X-ray inducible photodynamic therapy.

  10. Excitation relaxation dynamics and energy transfer in fucoxanthin-chlorophyll a/c-protein complexes, probed by time-resolved fluorescence.

    Science.gov (United States)

    Akimoto, Seiji; Teshigahara, Ayaka; Yokono, Makio; Mimuro, Mamoru; Nagao, Ryo; Tomo, Tatsuya

    2014-09-01

    In algae, light-harvesting complexes contain specific chlorophylls (Chls) and keto-carotenoids; Chl a, Chl c, and fucoxanthin (Fx) in diatoms and brown algae; Chl a, Chl c, and peridinin in photosynthetic dinoflagellates; and Chl a, Chl b, and siphonaxanthin in green algae. The Fx-Chl a/c-protein (FCP) complex from the diatom Chaetoceros gracilis contains Chl c1, Chl c2, and the keto-carotenoid, Fx, as antenna pigments, in addition to Chl a. In the present study, we investigated energy transfer in the FCP complex associated with photosystem II (FCPII) of C. gracilis. For these investigations, we analyzed time-resolved fluorescence spectra, fluorescence rise and decay curves, and time-resolved fluorescence anisotropy data. Chl a exhibited different energy forms with fluorescence peaks ranging from 677 nm to 688 nm. Fx transferred excitation energy to lower-energy Chl a with a time constant of 300fs. Chl c transferred excitation energy to Chl a with time constants of 500-600fs (intra-complex transfer), 600-700fs (intra-complex transfer), and 4-6ps (inter-complex transfer). The latter process made a greater contribution to total Chl c-to-Chl a transfer in intact cells of C. gracilis than in the isolated FCPII complexes. The lower-energy Chl a received excitation energy from Fx and transferred the energy to higher-energy Chl a. This article is part of a special issue entitled: photosynthesis research for sustainability: keys to produce clean energy. Copyright © 2014. Published by Elsevier B.V.

  11. Mechanism of singlet oxygen deactivation in an electric discharge oxygen - iodine laser

    Science.gov (United States)

    Azyazov, V. N.; Mikheyev, P. A.; Pershin, A. A.; Torbin, A. P.; Heaven, M. C.

    2014-12-01

    We have determined the influence of the reaction of molecular singlet oxygen with a vibrationally excited ozone molecule O2(a 1Δ) + O3(ν) → 2O2 + O on the removal rate of O2(a 1Δ) in an electric-discharge-driven oxygen - iodine laser. This reaction has been shown to be a major channel of O2(a 1Δ) loss at the output of an electric-discharge singlet oxygen generator. In addition, it can also contribute significantly to the loss of O2(a 1Δ) in the discharge region of the generator.

  12. Excited state decay of cyclometalated polypyridine ruthenium complexes: insight from theory and experiment.

    Science.gov (United States)

    Kreitner, Christoph; Heinze, Katja

    2016-09-21

    Deactivation pathways of the triplet metal-to-ligand charge transfer ((3)MLCT) excited state of cyclometalated polypyridine ruthenium complexes with [RuN5C](+) coordination are discussed on the basis of the available experimental data and a series of density functional theory calculations. Three different complex classes are considered, namely with [Ru(N^N)2(N^C)](+), [Ru(N^N^N)(N^C^N)](+) and [Ru(N^N^N)(N^N^C)](+) coordination modes. Excited state deactivation in these complex types proceeds via five distinct decay channels. Vibronic coupling of the (3)MLCT state to high-energy oscillators of the singlet ground state ((1)GS) allows tunneling to the ground state followed by vibrational relaxation (path A). A ligand field excited state ((3)MC) is thermally accessible via a (3)MLCT →(3)MC transition state with the (3)MC state being strongly coupled to the (1)GS surface via a low-energy minimum energy crossing point (path B). Furthermore, a (3)MLCT →(1)GS surface crossing point directly couples the triplet and singlet potential energy surfaces (path C). Charge transfer states either with higher singlet character or with different orbital parentage and intrinsic symmetry restrictions are thermally populated which promote non-radiative decay via tunneling to the (1)GS state (path D). Finally, the excited state can decay via phosphorescence (path E). The dominant deactivation pathways differ for the three individual complex classes. The implications of these findings for isoelectronic iridium(iii) or iron(ii) complexes are discussed. Ultimately, strategies for optimizing the emission efficiencies of cyclometalated polypyridine complexes of d(6)-metal ions, especially Ru(II), are suggested.

  13. Interaction of plasmalogens and their diacyl analogs with singlet oxygen in selected model systems

    Science.gov (United States)

    Broniec, Agnieszka; Klosinski, Radoslaw; Pawlak, Anna; Wrona-Krol, Marta; Thompson, David; Sarna, Tadeusz

    2011-01-01

    Plasmalogens (Plg) are phospholipids containing vinyl ether linkage at the sn-1 position of the glycerophospholipid backbone. In spite of being quite abundant in humans, the biological role of plasmalogens remains speculative. It has been postulated that plasmalogens are physiological antioxidants with the vinyl ether functionality serving as sacrificial trap for free radicals and singlet oxygen. However, no quantitative data on the efficiency of plasmalogens to scavenge these reactive species are available. In this study, rate constants of quenching of singlet oxygen, generated by photosensitized energy transfer, by several plasmalogens and, for comparison, by their diacyl analogs, were determined by time-resolved detection of phosphorescence at 1270 nm. Relative rates of the interaction of singlet oxygen, with plasmalogens and other lipids in solution and liposomal membranes were measured by electron paramagnetic resonance oximetry and product analysis, employing HPLC-EC detection of cholesterol hydroperoxides and iodometric assay of lipid hydroperoxides. Results show that singlet oxygen interacts with plasmalogens significantly faster than with the other lipids, with he corresponding rate constants being by one-two orders of magnitude greater. The quenching of singlet oxygen by plasmalogens is mostly reactive in nature and results from its preferential interaction with the vinyl ether bond. The data suggest that plasmalogens could protect unsaturated membrane lipids against oxidation induced by singlet oxygen, providing that the oxidation products are not excessively cytotoxic. PMID:21236336

  14. 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

    -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(bpy)2(CN)2] undergoes ultrafast spin crossover to a metal-centered quintet excited state through a short lived metal-centered triplet transient species. These measurements of [Fe(bpy)2(CN)2] complement prior measurement performed on [Fe(bpy)3]2+ and [Fe(bpy)(CN)4]2− in dimethylsulfoxide solution......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...

  15. Excited state dynamics and energy transfer rates in Sr3Tb0.90Eu0.10(PO4)3

    International Nuclear Information System (INIS)

    Bettinelli, Marco; Piccinelli, Fabio; Speghini, Adolfo; Ueda, Jumpei; Tanabe, Setsuhisa

    2012-01-01

    The emission spectrum of neat Sr 3 Tb(PO 4 ) 3 upon excitation at 337 nm in the levels above 5 D 3 is dominated by 5 D 4 emission and no significant emission from 5 D 3 is observed due to efficient cross relaxation involving the Tb 3+ levels. On the other hand, the emission spectrum of the same host containing 10 mol% Eu 3+ upon excitation at the same wavelength (in the Tb 3+ levels) is dominated by strong emission bands from the 5 D 0 level of Eu 3+ . This clearly indicates that Tb 3+ →Eu 3+ energy transfer is present. The excitation spectrum of the Eu 3+5 D 0 emission is dominated by Tb 3+ bands extending in the UV region. The presence of 10 mol% Eu 3+ in Sr 3 Tb(PO 4 ) 3 very strongly shortens the 5 D 4 decay time. The decay curve is not far from exponential, indicating that the energy transfer to Eu 3+ is accompanied by fast energy migration. The transfer regimes are identified and the donor-donor and donor-acceptor transfer microparameters are quantified under the assumption of electric dipole-electric dipole interactions. - Highlights: → Tb 3+ →Eu 3+ energy transfer in Sr 3 Tb 0.90 Eu 0.10 (PO 4 ) 3 is evidenced and investigated. → The energy migration in the 5 D 4 level of Tb 3+ is faster than the transfer to the Eu 3+ ion. → The fast migration among the Tb 3+ ions greatly enhances the transfer efficiency.

  16. Effects of ligand substitution on the excited state dynamics of the Ru(dcbpy)(CO){sub 2}I{sub 2} complex

    Energy Technology Data Exchange (ETDEWEB)

    Lehtovuori, Viivi; Kallioinen, Jani; Myllyperkioe, Pasi; Haukka, Matti; Korppi-Tommola, Jouko

    2003-11-15

    Spectroscopic evidence suggest [PCCP 3 (2001) 1992] that illumination with visible light of the [trans-I-Ru(dcbpy)(CO){sub 2}I{sub 2}] (dcbpy4,4{sup '}-dicarboxy-2,2{sup '}-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{sub 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{sup -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.

  17. Transient photocurrent in molecular junctions: singlet switching on and triplet blocking.

    Science.gov (United States)

    Petrov, E G; Leonov, V O; Snitsarev, V

    2013-05-14

    The kinetic approach adapted to describe charge transmission in molecular junctions, is used for the analysis of the photocurrent under conditions of moderate light intensity of the photochromic molecule. In the framework of the HOMO-LUMO model for the single electron molecular states, the analytic expressions describing the temporary behavior of the transient and steady state sequential (hopping) as well as direct (tunnel) current components have been derived. The conditions at which the current components achieve their maximal values are indicated. It is shown that if the rates of charge transmission in the unbiased molecular diode are much lower than the intramolecular singlet-singlet excitation/de-excitation rate, and the threefold degenerated triplet excited state of the molecule behaves like a trap blocking the charge transmission, a possibility of a large peak-like transient switch-on photocurrent arises.

  18. 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.

  19. Holographic monitoring of spatial distributions of singlet oxygen in water

    Science.gov (United States)

    Belashov, A. V.; Bel'tyukova, D. M.; Vasyutinskii, O. S.; Petrov, N. V.; Semenova, I. V.; Chupov, A. S.

    2014-12-01

    A method for monitoring spatial distributions of singlet oxygen in biological media has been developed. Singlet oxygen was generated using Radachlorin® photosensitizer, while thermal disturbances caused by nonradiative deactivation of singlet oxygen were detected by the holographic interferometry technique. Processing of interferograms yields temperature maps that characterize the deactivation process and show the distribution of singlet oxygen species.

  20. Charge-transfer excitations in low-gap systems under the influence of solvation and conformational disorder: Exploring range-separation tuning

    Energy Technology Data Exchange (ETDEWEB)

    Queiroz, Thiago B. de, E-mail: thiago.branquinho-de-queiroz@uni-bayreuth.de; Kümmel, Stephan [Theoretical Physics IV, University of Bayreuth, D-95440 Bayreuth (Germany)

    2014-08-28

    Charge transfer excitations play a prominent role in the fields of molecular electronics and light harvesting. At the same time they have developed a reputation for being hard to predict with time-dependent density functional theory, which is the otherwise predominant method for calculating molecular structure and excitations. Recently, it has been demonstrated that range-separated hybrid functionals, in particular with an “optimally tuned” range separation parameter, describe charge-transfer excitations reliably for different molecules. Many of these studies focused on molecules in vacuum. Here we investigate the influence of solvation on the electronic excitations of thiophene oligomers, i.e., paradigm low gap systems. We take into account bulk solvation using a continuum solvation model and geometrical distortions from molecular dynamics. From our study, three main findings emerge. First, geometrical distortions increase absorption energies by about 0.5 eV for the longer thiophene oligomers. Second, combining optimal tuning of the range separation parameter with a continuum solvation method is not straightforward and has to be approached with great care. Third, optimally tuned range-separated hybrids without a short-range exchange component tend to inherit undesirable characteristics of semi-local functionals: with increasing system size the range separation parameter takes a smaller value, leading to a functional of effectively more semi-local nature and thus not accurately capturing, e.g., the saturation of the optical gap with increasing system size.

  1. Charge-transfer excitations in low-gap systems under the influence of solvation and conformational disorder: Exploring range-separation tuning

    International Nuclear Information System (INIS)

    Queiroz, Thiago B. de; Kümmel, Stephan

    2014-01-01

    Charge transfer excitations play a prominent role in the fields of molecular electronics and light harvesting. At the same time they have developed a reputation for being hard to predict with time-dependent density functional theory, which is the otherwise predominant method for calculating molecular structure and excitations. Recently, it has been demonstrated that range-separated hybrid functionals, in particular with an “optimally tuned” range separation parameter, describe charge-transfer excitations reliably for different molecules. Many of these studies focused on molecules in vacuum. Here we investigate the influence of solvation on the electronic excitations of thiophene oligomers, i.e., paradigm low gap systems. We take into account bulk solvation using a continuum solvation model and geometrical distortions from molecular dynamics. From our study, three main findings emerge. First, geometrical distortions increase absorption energies by about 0.5 eV for the longer thiophene oligomers. Second, combining optimal tuning of the range separation parameter with a continuum solvation method is not straightforward and has to be approached with great care. Third, optimally tuned range-separated hybrids without a short-range exchange component tend to inherit undesirable characteristics of semi-local functionals: with increasing system size the range separation parameter takes a smaller value, leading to a functional of effectively more semi-local nature and thus not accurately capturing, e.g., the saturation of the optical gap with increasing system size

  2. Magnetic Excitations in Weakly Coupled Spin Dimers and Chains Material Cu2Fe2Ge4O13

    International Nuclear Information System (INIS)

    Masuda, Takatsugu; Zheludev, Andrey I.; Sales, Brian C.; Imai, S.; Uchinokura, K.; Park, S.

    2005-01-01

    Magnetic excitations in a weakly coupled spin dimers and chains compound Cu 2 Fe 2 Ge 4 O 13 are measured by inelastic neutron scattering. Both structure factors and dipsersion of low-energy excitations up to 10 meV energy transfer are well described by a semiclassical spin wave theory involving interacting Fe 3+ (S=5/2) chains. Additional dispersionsless excitations are observed at higher energies, at ℎω=24 meV, and associated with singlet-triplet transitions within Cu 2+ dimers. Both types of excitations can be understood by treating weak interactions between the Cu 2+ and Fe 3+ subsystems at the level of the mean-field random phase approximation. However, this simple model fails to account for the measured temperature dependence of the 24 meV mode.

  3. 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.

  4. Efficient singlet exciton fission in pentacene prepared from a soluble precursor

    Directory of Open Access Journals (Sweden)

    Maxim Tabachnyk

    2016-11-01

    Full Text Available Carrier multiplication using singlet exciton fission (SF to generate a pair of spin-triplet excitons from a single optical excitation has been highlighted as a promising approach to boost the photocurrent in photovoltaics (PVs thereby allowing PV operation beyond the Shockley-Queisser limit. The applicability of many efficient fission materials, however, is limited due to their poor solubility. For instance, while acene-based organics such as pentacene (Pc show high SF yields (up to200%, the plain acene backbone renders the organic molecule insoluble in common organic solvents. Previous approaches adding solubilizing side groups such as bis(tri-iso-propylsilylethynyl to the Pc core resulted in low vertical carrier mobilities due to reduction of the transfer integrals via steric hindrance, which prevented high efficiencies in PVs. Here we show how to achieve good solubility while retaining the advantages of molecular Pc by using a soluble precursor route. The precursor fully converts into molecular Pc through thermal removal of the solubilizing side groups upon annealing above 150 °C in the solid state. The annealed precursor shows small differences in the crystallinity compared to evaporated thin films of Pc, indicating that the Pc adopts the bulk rather than surface polytype. Furthermore, we identify identical SF properties such as sub-100 fs fission time and equally long triplet lifetimes in both samples.

  5. Photophysical characterization and time-resolved spectroscopy of a anthradithiophene dimer: exploring the role of conformation in singlet fission

    KAUST Repository

    Dean, Jacob C.

    2017-08-18

    Quantitative singlet fission has been observed for a variety of acene derivatives such as tetracene and pentacene, and efforts to extend the library of singlet fission compounds is of current interest. Preliminary calculations suggest anthradithiophenes exhibit significant exothermicity between the first optically-allowed singlet state, S1, and 2 × T1 with an energy difference of >5000 cm−1. Given the fulfillment of this ingredient for singlet fission, here we investigate the singlet fission capability of a difluorinated anthradithiophene dimer (2ADT) covalently linked by a (dimethylsilyl)ethane bridge and derivatized by triisobutylsilylethynyl (TIBS) groups. Photophysical characterization of 2ADT and the single functionalized ADT monomer were carried out in toluene and acetone solution via absorption and fluorescence spectroscopy, and their photo-initiated dynamics were investigated with time-resolved fluorescence (TRF) and transient absorption (TA) spectroscopy. In accordance with computational predictions, two conformers of 2ADT were observed via fluorescence spectroscopy and were assigned to structures with the ADT cores trans or cis to one another about the covalent bridge. The two conformers exhibited markedly different excited state deactivation mechanisms, with the minor trans population being representative of the ADT monomer showing primarily radiative decay, while the dominant cis population underwent relaxation into an excimer geometry before internally converting to the ground state. The excimer formation kinetics were found to be solvent dependent, yielding time constants of ∼1.75 ns in toluene, and ∼600 ps in acetone. While the difference in rates elicits a role for the solvent in stabilizing the excimer structure, the rate is still decidedly long compared to most singlet fission rates of analogous dimers, suggesting that the excimer is neither a kinetic nor a thermodynamic trap, yet singlet fission was still not observed. The result

  6. Photocurrent Enhanced by Singlet Fission in a Dye-Sensitized Solar Cell

    Czech Academy of Sciences Publication Activity Database

    Schrauben, J. N.; Zhao, Y.; Mercado, C.; Dron, P. I.; Ryerson, J. L.; Michl, Josef; Zhu, K.; Johnson, J. C.

    2015-01-01

    Roč. 7, č. 4 (2015), s. 2286-2293 ISSN 1944-8244 Institutional support: RVO:61388963 Keywords : photovoltaics * singlet fission * triplet * spectroscopy * charge transfer * photocurrent Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 7.145, year: 2015

  7. Development of the Fragment Molecular Orbital Method for Calculating Nonlocal Excitations in Large Molecular Systems.

    Science.gov (United States)

    Fujita, Takatoshi; Mochizuki, Yuji

    2018-04-19

    We developed the fragment-based method for calculating nonlocal excitations in large molecular systems. This method is based on the multilayer fragment molecular orbital method and the configuration interaction single (CIS) wave function using localized molecular orbitals. The excited-state wave function for the whole system is described as a superposition of configuration state functions (CSFs) for intrafragment excitations and for interfragment charge-transfer excitations. The formulation and calculations of singlet excited-state Hamiltonian matrix elements in the fragment CSFs are presented in detail. The efficient approximation schemes for calculating the matrix elements are also presented. The computational efficiency and the accuracy were evaluated using the molecular dimers and molecular aggregates. We confirmed that absolute errors of 50 meV (relative to the conventional calculations) are achievable for the molecular systems in their equilibrium geometries. The perturbative electron correlation correction to the CIS excitation energies is also demonstrated. The present theory can compute a large number of excited states in large molecular systems; in addition, it allows for the systematic derivation of a model exciton Hamiltonian. These features are useful for studying excited-state dynamics in condensed molecular systems based on the ab initio electronic structure theory.

  8. Coherent dynamics of singlet fission controlled by nonlocal electron-phonon coupling

    Science.gov (United States)

    Yao, Yao

    2016-03-01

    Based on the Frenkel and charge transfer mixing model of singlet fission (SF), we incorporate both the local and nonlocal phonon baths into the Hamiltonian and adopt the algorithm of the time-dependent density matrix renormalization group to simulate the SF process in tetracene and pentacene. The endergonic SF is found to be facilitated by the robust quantum coherence, which concurrently gives rise to a notable quantum beating effect. Being controlled by the nonlocal electron-phonon coupling, the SF process is accelerated and the triplet yield manifests a nonlinear relationship with the singlet density.

  9. Kinetics of oxygen species in an electrically driven singlet oxygen generator

    Science.gov (United States)

    Azyazov, V. N.; Torbin, A. P.; Pershin, A. A.; Mikheyev, P. A.; Heaven, M. C.

    2015-12-01

    The kinetics of oxygen species in the gaseous medium of a discharge singlet oxygen generator has been revisited. Vibrationally excited ozone O3(υ) formed in O + O2 recombination is thought to be a significant agent in the deactivation of singlet oxygen O2(a1Δ), oxygen atom removal and ozone formation. It is shown that the process O3(υ ⩾ 2) + O2(a1Δ) → 2O2 + O is the main O2(a1Δ) deactivation channel in the post-discharge zone. If no measures are taken to decrease the oxygen atom concentration, the contribution of this process to the overall O2(a1Δ) removal is significant, even in the discharge zone. A simplified model for the kinetics of vibrationally excited ozone is proposed. Calculations based on this model yield results that are in good agreement with the experimental data.

  10. Singlet Fission and Excimer Formation in Disordered Solids of Alkyl-Substituted 1,3-Diphenylisobenzofurans.

    Science.gov (United States)

    Dron, Paul I; Michl, Josef; Johnson, Justin C

    2017-11-16

    We describe the preparation and excited state dynamics of three alkyl derivatives of 1,3-diphenylisobenzofuran (1) in both solutions and thin films. The substitutions are intended to disrupt the slip-stacked packing observed in crystals of 1 while maintaining the favorable energies of singlet and triplet for singlet fission (SF). All substitutions result in films that are largely amorphous as judged by the absence of strong X-ray diffraction peaks. The films of 1 carrying a methyl in the para position of one phenyl ring undergo SF relatively efficiently (≥75% triplet yield, Φ T ) but more slowly than thin films of 1. When the methyl is replaced with a t-butyl, kinetic competition in the excited state favors excimer formation rather than SF (Φ T = 55%). When t-Bu groups are placed in both meta positions of the phenyl substituent, SF is slowed further and Φ T = 35%.

  11. 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.

  12. Photofragment Coincidence Imaging of Small I- (H2O)n Clusters Excited to the Charge-transfer-to-solvent State

    Energy Technology Data Exchange (ETDEWEB)

    Neumark, D. E. Szpunar, K. E. Kautzman, A. E. Faulhaber, and D. M.; Kautzman, K.E.; Faulhaber, A.E.; Faulhaber, A.E.

    2005-11-09

    The photodissociation dynamics of small I{sup -}(H{sub 2}O){sub n} (n = 2-5) clusters excited to their charge-transfer-to-solvent (CTTS) states have been studied using photofragment coincidence imaging. Upon excitation to the CTTS state, two photodissociation channels were observed. The major channel ({approx}90%) is a 2-body process forming neutral I + (H{sub 2}O){sub n} photofragments, and the minor channel is a 3-body process forming I + (H{sub 2}O){sub n-1} + H{sub 2}O fragments. Both process display translational energy (P(E{sub T})) distributions peaking at E{sub T} = 0 with little available energy partitioned into translation. Clusters excited to the detachment continuum rather than to the CTTS state display the same two channels with similar P(E{sub T}) distributions. The observation of similar P(E{sub T}) distributions from the two sets of experiments suggests that in the CTTS experiments, I atom loss occurs after autodetachment of the excited (I(H{sub 2}O){sub n}{sup -})* cluster, or, less probably, that the presence of the excess electron has little effect on the departing I atom.

  13. Seeking small molecules for singlet fission: a heteroatom substitution strategy.

    Science.gov (United States)

    Zeng, Tao; Ananth, Nandini; Hoffmann, Roald

    2014-09-10

    We design theoretically small molecule candidates for singlet fission chromophores, aiming to achieve a balance between sufficient diradical character and kinetic persistence. We develop a perturbation strategy based on the captodative effect to introduce diradical character into small π-systems. Specifically, this can be accomplished by replacing pairs of not necessarily adjacent C atoms with isoelectronic and isosteric pairs of B and N atoms. Three rules of thumb emerge from our studies to aid further design: (i) Lewis structures provide insight into likely diradical character; (ii) formal radical centers of the diradical must be well-separated; (iii) stabilization of radical centers by a donor (N) and an acceptor (B) is essential. Following the rules, we propose candidate molecules. Employing reliable multireference calculations for excited states, we identify three likely candidate molecules for SF chromophores. These include a benzene, a napthalene, and an azulene, where four C atoms are replaced by a pair of B and a pair of N atoms.

  14. Application of time-resolved near-infrared spectroscopy (TRNIR) to the metal-to-ligand charge transfer (MLCT) excited state(s) of Os(phen)32+

    International Nuclear Information System (INIS)

    Dattelbaum, Dana M.; Kober, Edward M.; Papanikolas, John M.; Meyer, Thomas J.

    2006-01-01

    Application of time-resolved near-infrared spectroscopy (TRNIR) to Os(phen) 3 2+ in CD 3 CN, following visible (450nm) laser flash excitation, reveals an absorption feature at ν-bar max =5460cm -1 (ε max >=5000M -1 cm -1 , Δν-bar 1/2 =1840cm -1 ) for the MLCT excited state Os(phen) 3 2+ *. Based on an electronic structure model, including spin-orbit coupling, the absorption is tentatively assigned to three overlapping ligand-to-ligand charge transfer (LLCT) bands two of which have dπ->dπ interconfigurational character. This assignment is consistent with the results of a solvent dependence study and an analysis of predicted band energies

  15. Coherent population transfer and superposition of atomic states via stimulated Raman adiabatic passage using an excited-doublet four-level atom

    International Nuclear Information System (INIS)

    Jin Shiqi; Gong Shangqing; Li Ruxin; Xu Zhizhan

    2004-01-01

    Coherent population transfer and superposition of atomic states via a technique of stimulated Raman adiabatic passage in an excited-doublet four-level atomic system have been analyzed. It is shown that the behavior of adiabatic passage in this system depends crucially on the detunings between the laser frequencies and the corresponding atomic transition frequencies. Particularly, if both the fields are tuned to the center of the two upper levels, the four-level system has two degenerate dark states, although one of them contains the contribution from the excited atomic states. The nonadiabatic coupling of the two degenerate dark states is intrinsic, it originates from the energy difference of the two upper levels. An arbitrary superposition of atomic states can be prepared due to such nonadiabatic coupling effect

  16. Non-diagonal processes of singlet and ordinary quark production

    International Nuclear Information System (INIS)

    Bejlin, V.A.; Vereshkov, G.M.; Kuksa, V.I.

    1995-01-01

    Non-diagonal processes of singlet and ordinary quark production are analyzed in the model where the down singlet quark mixes with the ordinary ones. The possibility of experimental selection of h-quark effects is demonstrated

  17. Excited-state intramolecular proton transfer (ESIPT) emission of hydroxyphenylimidazopyridine: computational study on enhanced and polymorph-dependent luminescence in the solid state.

    Science.gov (United States)

    Shigemitsu, Yasuhiro; Mutai, Toshiki; Houjou, Hirohiko; Araki, Koji

    2012-12-13

    Although 2-(2'-hydroxyphenyl)imidazo[1,2-a]pyridine (HPIP) is only weakly fluorescent in solution, two of its crystal polymorphs in which molecules are packed as stacked pairs and in nearly coplanar conformation exhibit bright excited-state intramolecular proton transfer (ESIPT) luminescence of different colors (blue-green and yellow). In order to clarify the enhanced and polymorph-dependent luminescence of HPIP in the solid state, the potential energy surfaces (PESs) of HPIP in the ground (S(0)) and excited (S(1)) states were analyzed computationally by means of ab initio quantum chemical calculations. The calculations reproduced the experimental photophysical properties of HPIP in solution, indicating that the coplanar keto form in the first excited (S(1)) state smoothly approaches the S(0)/S(1) conical intersection (CI) coupled with the twisting motion of the central C-C bond. The S(1)-S(0) energy gap of the keto form became sufficiently small at the torsion angle of 60°, and the corresponding CI point was found at 90°. Since a minor role of the proximity effect was indicated experimentally and theoretically, the observed emission enhancement of the HPIP crystals was ascribed to the following two factors: (1) suppression of efficient radiationless decay via the CI by fixing the torsion angle at the nearly coplanar conformation of the molecules in the crystals and (2) inhibition of excimer formation resulting from the lower excited level of the S(1)-keto state compared to the S(0)-S(1) excitation energy in the enol form. However, the fluorescence color difference between the two crystal polymorphs having slightly different torsion angles was not successfully reproduced, even at the MS-CASPT2 level of theory.

  18. L X-ray emission from fast highly charged Cu ions in collisions with gaseous targets: Saturation effect in excitation and transfer

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Ajay [Tata Institute of Fundamental Research, Colaba, Mumbai-400 005 (India); Misra, D. [Tata Institute of Fundamental Research, Colaba, Mumbai-400 005 (India); Kadhane, U. [Tata Institute of Fundamental Research, Colaba, Mumbai-400 005 (India); Kelkar, A.H. [Tata Institute of Fundamental Research, Colaba, Mumbai-400 005 (India); Dhal, B.B. [School of Physics, University of Melbourne, Victoria 3010 (Australia); Tribedi, L.C. [Tata Institute of Fundamental Research, Colaba, Mumbai-400 005 (India)]. E-mail: lokesh@tifr.res.in

    2006-11-15

    We have measured L X-ray production cross sections for highly charged 156 MeV Be-like Cu ions in collisions with gaseous targets of H{sub 2}, Ne, Ar, Kr and Xe. In the present collision systems, measured projectile L X-ray intensity is contributed by the excitation as well as electron transfer processes. The projectile L X-ray production cross sections are found to increase initially and then saturate with increasing target atomic number. The charge state dependence of projectile L X-ray production cross sections have been measured with Kr target.

  19. Reliable Prediction with Tuned Range-Separated Functionals of the Singlet-Triplet Gap in Organic Emitters for Thermally Activated Delayed Fluorescence (TADF)

    KAUST Repository

    Sun, Haitao

    2015-07-09

    The thermally activated delayed fluorescence (TADF) mechanism has recently attracted much interest in the field of organic light-emitting diodes (OLEDs). TADF relies on the presence of a very small energy gap between the lowest singlet and triplet excited states. Here, we demonstrate that time-dependent density functional theory (TD-DFT) in the Tamm-Dancoff Approximation can be very successful in the calculations of the lowest singlet and triplet excitation energies and the corresponding singlet-triplet gap when using nonempirically tuned range-separated functionals. Such functionals provide very good estimates in a series of 17 molecules used in TADF-based OLED devices, with mean absolute deviations of 0.15 eV for the vertical singlet excitation energies and 0.09 eV [0.07 eV] for the adiabatic [vertical] singlet-triplet energy gaps as well as low relative errors and high correlation coefficients compared to the corresponding experimental values. They significantly outperform conventional functionals, a feature which is rationalized on the basis of the amount of exact-exchange included and the delocalization error. The present work provides a reliable theoretical tool for the prediction and development of novel TADF-based materials with low singlet-triplet energetic splittings.

  20. 10-hydroxybenzo[h]quinoline: Switching between single and double-well proton transfer through structural modifications

    DEFF Research Database (Denmark)

    Hristova, S; Dobrikov, G; Kamounah, F. S.

    2015-01-01

    and excited singlet state. We observed that the incorporation of electron acceptor substituents on position 7 of the HBQ backbone led to appearance of a keto tautomer in ground state and changes in the excited state potential energy surface. Both processes were strongly solvent dependent. In the ground state...... the equilibrium could be driven from the enol to the keto form by change of solvent. The theoretical calculations explain the substitution-determined transition from a single- to a double-well proton transfer mechanism...

  1. Singlet oxygen-mediated protein oxidation

    DEFF Research Database (Denmark)

    Wright, Adam; Bubb, William A; Hawkins, Clare Louise

    2002-01-01

    Singlet oxygen (1O2) is generated by a number of enzymes as well as by UV or visible light in the presence of a sensitizer and has been proposed as a damaging agent in a number of pathologies including cataract, sunburn, and skin cancers. Proteins, and Cys, Met, Trp, Tyr and His side chains in pa...

  2. Recycling and imaging of nuclear singlet hyperpolarization

    DEFF Research Database (Denmark)

    Pileio, Giuseppe; Bowen, Sean; Laustsen, Christoffer

    2013-01-01

    observation of the same batch of polarized nuclei over a period of 30 min and more. We report a recycling protocol in which the enhanced nuclear polarization achieved by dissolution-DNP is observed with full intensity and then returned to singlet order. MRI experiments may be run on a portion of the available...

  3. 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.

  4. Graphene oxide functionalized with methylene blue and its performance in singlet oxygen generation

    Energy Technology Data Exchange (ETDEWEB)

    Wojtoniszak, M., E-mail: mwojtoniszak@zut.edu.pl [West Pomeranian University of Technology in Szczecin, Institute of Chemical and Environment Engineering, Pulaskiego 10, 70-322 Szczecin (Poland); Rogińska, D.; Machaliński, B. [Pomeranian Medical University, Department of General Pathology, Powstańców Wlkp. 72, 70-111 Szczecin (Poland); Drozdzik, M. [Pomeranian Medical University, Department of Pharmacology, Powstańców Wlkp. 72, 70-111 Szczecin (Poland); Mijowska, E. [West Pomeranian University of Technology in Szczecin, Institute of Chemical and Environment Engineering, Pulaskiego 10, 70-322 Szczecin (Poland)

    2013-07-15

    Graphical abstract: - Highlights: • Adsorption of methylene blue (MB) on graphene oxide (GO). • Characterization of graphene oxide–methylene blue nanocomposite (MB–GO). • Examination of MB–GO efficiency in singlet oxygen generation (SOG). • MB–GO performs higher SOG efficiency than pristine MB. - Abstract: Due to unique electronic, mechanical, optical and structural properties, graphene has shown promising applications in many fields, including biomedicine. One of them is noninvasive anticancer therapy – photodynamic therapy (PDT), where singlet oxygen (SO), generated under the irradiation of light with appropriate wavelengths, kills cancer cells. In this study, authors report graphene oxide (GO) noncovalent functionalization with methylene blue (MB). MB molecules underwent adsorption on the surface of GO. Detailed characterization of the obtained material was carried out with UV–vis spectroscopy, Raman spectroscopy, FT-IR spectroscopy, and confocal laser scanning microscopy. Furthermore, its performance in singlet oxygen generation (SOG) under irradiation of laser with excitation wavelengths of 785 nm was investigated. Interestingly, GO functionalized with MB (MB–GO) showed enhanced efficiency in singlet oxygen generation compared to pristine MB. The efficiency in SOG was detected by photobleaching of 9,10-anthracenediyl-bis(methylene)dimalonic acid (ABMDMA). These results indicate the material is promising in PDT anticancer therapy and further in vitro and in vivo studies are required.

  5. Singlet fission/silicon solar cell exceeding 100% EQE (Conference Presentation)

    Science.gov (United States)

    Pazos, Luis M.; Lee, Jumin; Kirch, Anton; Tabachnyk, Maxim; Friend, Richard H.; Ehrler, Bruno

    2016-09-01

    Current matching limits the commercialization of tandem solar cells due to their instability over spectral changes, leading to the need of using solar concentrators and trackers to keep the spectrum stable. We demonstrate that voltage-matched systems show far higher performance over spectral changes; caused by clouds, dust and other variations in atmospheric conditions. Singlet fission is a process in organic semiconductors which has shown very efficient, 200%, down-conversion yield and the generated excitations are long-lived, ideal for solar cells. As a result, the number of publications has grown exponentially in the past 5 years. Yet, so far no one has achieved to combine singlet fission with most low bandgap semiconductors, including crystalline silicon, the dominating solar cell material with a 90% share of the PV Market. Here we show that singlet fission can facilitate the fabrication of voltage-matched systems, opening a simple design route for the effective implementation of down-conversion in commercially available photovoltaic technologies, with no modification of the electronic circuitry of such. The implemention of singlet fission is achieved simply by decoupling the fabrication of the individual subcells. For this demonstration we used an ITO/PEDOT/P3HT/Pentacene/C60/Ag wide-bandgap subcell, and a commercial silicon solar cell as the low-bandgap component. We show that the combination of the two leads to the first tandem silicon solar cell which exceeds 100% external quantum efficiency.

  6. Singlet Exciton Lifetimes in Conjugated Polymer Films for Organic Solar Cells

    KAUST Repository

    Dimitrov, Stoichko

    2016-01-13

    The lifetime of singlet excitons in conjugated polymer films is a key factor taken into account during organic solar cell device optimization. It determines the singlet exciton diffusion lengths in polymer films and has a direct impact on the photocurrent generation by organic solar cell devices. However, very little is known about the material properties controlling the lifetimes of singlet excitons, with most of our knowledge originating from studies of small organic molecules. Herein, we provide a brief summary of the nature of the excited states in conjugated polymer films and then present an analysis of the singlet exciton lifetimes of 16 semiconducting polymers. The exciton lifetimes of seven of the studied polymers were measured using ultrafast transient absorption spectroscopy and compared to the lifetimes of seven of the most common photoactive polymers found in the literature. A plot of the logarithm of the rate of exciton decay vs. the polymer optical bandgap reveals a medium correlation between lifetime and bandgap, thus suggesting that the Energy Gap Law may be valid for these systems. This therefore suggests that small bandgap polymers can suffer from short exciton lifetimes, which may limit their performance in organic solar cell devices. In addition, the impact of film crystallinity on the exciton lifetime was assessed for a small bandgap diketopyrrolopyrrole co-polymer. It is observed that the increase of polymer film crystallinity leads to reduction in exciton lifetime and optical bandgap again in agreement with the Energy Gap Law.

  7. Förster resonance energy transfer and excited state life time reduction of rhodamine 6G with NiO nanorods in PVP films.

    Science.gov (United States)

    Karthikeyan, B

    2017-02-15

    In the present study, we report the preparation of NiO nanorods (NNR) and its Förster resonant energy transfer (FRET) behaviour with rhodamine 6G (R6G) in a Polyvinyl pyrrolidone (PVP) polymer matrix. The prepared nanocomposite polymer (NCP) films contain PVP and R6G whose concentrations are kept constant and different concentrations of NNR. Spectral overlap between the absorption and fluorescence spectrum of R6G and NNR shows the possibility of FRET phenomena to be occurring in the prepared NCP films. Steady state and time resolved fluorescence measurements are carried out at two excitation wavelengths (330 and 510nm) to study the energy transfer process between R6G and NNR in the PVP host. The obtained results show that the energy transfer is from R6G (serves as a donor) to NNR (functions as an acceptor). Calculated radiative efficiencies, donor-acceptor distances and average lifetime also confirm the energy transfer from R6G to NNR. Copyright © 2016 Elsevier B.V. All rights reserved.

  8. Kinetics of oxygen species in an electrically driven singlet oxygen generator

    International Nuclear Information System (INIS)

    Azyazov, V.N.; Torbin, A.P.; Pershin, A.A.; Mikheyev, P.A.; Heaven, M.C.

    2015-01-01

    Highlights: • Vibrational excitation of O 3 increases the rate constant for O 3 + O 2 (a) → 2O 2 (X) + O. • Vibrationally excited O 3 is produced by the O + O 2 (X) + M → O 3 + M reaction. • Ozone concentrations are impacted by the reactions of vibrationally excited O 3 . • Relevant to ozone concentrations in oxygen discharges and the upper atmosphere. - Abstract: The kinetics of oxygen species in the gaseous medium of a discharge singlet oxygen generator has been revisited. Vibrationally excited ozone O 3 (υ) formed in O + O 2 recombination is thought to be a significant agent in the deactivation of singlet oxygen O 2 (a 1 Δ), oxygen atom removal and ozone formation. It is shown that the process O 3 (υ ⩾ 2) + O 2 (a 1 Δ) → 2O 2 + O is the main O 2 (a 1 Δ) deactivation channel in the post-discharge zone. If no measures are taken to decrease the oxygen atom concentration, the contribution of this process to the overall O 2 (a 1 Δ) removal is significant, even in the discharge zone. A simplified model for the kinetics of vibrationally excited ozone is proposed. Calculations based on this model yield results that are in good agreement with the experimental data.

  9. In situ simultaneous profiling of phosphorylation and ubiquitination by single excitation-duplexed luminescence resonance energy transfer.

    Science.gov (United States)

    Ma, Fengjiao; Zhang, Lei; Wong, Bernardino J Córdova; Lei, Jianping

    2018-03-26

    A dual luminescence resonance energy transfer system is developed based on aptamer-functionalized upconversion nanoparticles as the energy donor and a synthetic dye derivative as the acceptor, which can be applied in the simultaneous profiling and relative quantification of phosphorylation and ubiquitination on a specific protein, even at low levels of protein expression.

  10. 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.

  11. Direct Detection of the Open-Shell Singlet Phenyloxenium Ion: An Atom-Centered Diradical Reacts as an Electrophile.

    Science.gov (United States)

    Du, Lili; Qiu, Yunfan; Lan, Xin; Zhu, Ruixue; Phillips, David Lee; Li, Ming-De; Dutton, Andrew S; Winter, Arthur H

    2017-10-25

    A new photoprecursor to the phenyloxenium ion, 4-methoxyphenoxypyridinium tetrafluoroborate, was investigated using trapping studies, product analysis, computational investigations, and laser flash photolysis experiments ranging from the femtosecond to the millisecond time scale. These experiments allowed us to trace the complete arc of the photophysics and photochemistry of this photoprecursor beginning with the initially populated excited states to its sequential formation of transient intermediates and ultimate formation of stable photoproducts. We find that the excited state of the photoprecursor undergoes heterolysis to generate the phenyloxenium ion in ∼2 ps but surprisingly generates the ion in its open-shell singlet diradical configuration ( 1 A 2 ), permitting an unexpected look at the reactivity of an atom-centered open-shell singlet diradical. The open-shell phenyloxenium ion ( 1 A 2 ) has a much shorter lifetime (τ ∼ 0.2 ns) in acetonitrile than the previously observed closed-shell singlet ( 1 A 1 ) phenyloxenium ion (τ ∼ 5 ns). Remarkably, despite possessing no empty valence orbitals, this open-shell singlet oxenium ion behaves as an even more powerful electrophile than the closed-shell singlet oxenium ion, undergoing solvent trapping by weakly nucleophilic solvents such as water and acetonitrile or externally added nucleophiles (e.g., azide) rather than engaging in typical diradical chemistry, such as H atom abstraction, which we have previously observed for a triplet oxenium ion. In acetonitrile, the open-shell singlet oxenium ion is trapped to generate ortho and para Ritter intermediates, one of which (para) is directly observed as a longer-lived species (τ ∼ 0.1 ms) in time-resolved resonance Raman experiments. The Ritter intermediates are ultimately trapped by either the 4-methoxypyridine leaving group (in the case of para addition) or trapped internally via an essentially barrierless rearrangement (in the case of ortho addition) to

  12. Singlet Glueballs In Klebanov-Strassler Theory

    Science.gov (United States)

    Gordeli, Ivan

    In this thesis we complete the singlet glueball sector analysis of the N = 1 super-symmetric Klebanov-Strassler gauge theory. Employing the string theory holographic approach we come up with a prediction of the spectrum of lightest glueballs in SU(N) N = 1 supersymmetric Yang-Mills theory at large N. Interestingly the spectrum of some of the glueballs is consistent with the lattice results for QCD glueballs.

  13. Magnetic properties of singlet ground state systems

    International Nuclear Information System (INIS)

    Diederix, K.M.

    1979-01-01

    Experiments are described determining the properties of a magnetic system consisting of a singlet ground state. Cu(NO 3 ) 2 .2 1/2H 2 O has been studied which is a system of S = 1/2 alternating antiferromagnetic Heisenberg chains. The static properties, spin lattice relaxation time and field-induced antiferromagnetically ordered state measurements are presented. Susceptibility and magnetic cooling measurements of other compounds are summarised. (Auth.)

  14. Singlet - oxygen therapy. 'MIT-S' apparatus

    International Nuclear Information System (INIS)

    Samosyuk, I.Z.; Chukhraev, N.V.; Pisanko, O.I.

    2003-01-01

    The described method is based on using singlet-oxygen mixture with antioxiding properties. This mixture is produced by photochemical sensibilization of air or water vapour in MIT-S apparatus. Technical parameters of MIT-S are presented. The method is used for therapy of different organs, for prophylactics, treatment and rehabilitation of a series of diseases (bronchial asthma, cardio-vascular, neurologic, sugar diabet, immune diseases)

  15. High-power generator of singlet oxygen

    Czech Academy of Sciences Publication Activity Database

    Jirásek, Vít; Čenský, Miroslav; Špalek, Otomar; Kodymová, Jarmila

    2013-01-01

    Roč. 36, č. 10 (2013), s. 1755-1763 ISSN 0930-7516 Grant - others:Laser Science and Technology Centre(IN) LASTEC/FE/RKT/54/10-11 Institutional research plan: CEZ:AV0Z10100523 Keywords : high-pressure singlet oxygen generator * spray generator * centrifugal separation Subject RIV: BH - Optics, Masers, Lasers Impact factor: 2.175, year: 2013

  16. Theory of singlet-ground-state magnetism. Application to field-induced transitions in CsFeCl3 and CsFeBr3

    DEFF Research Database (Denmark)

    Lindgård, P.-A.; Schmid, B.

    1993-01-01

    In the singlet ground-state systems CsFeCl3 and CsFeBr3 a large single-ion anisotropy causes a singlet ground state and a doubly degenerate doublet as the first excited states of the Fe2+ ion. In addition the magneteic interaction is anisotropic being much larger along the z axis than perpendicular...... to it. Therefore, these quasi-one-dimensional magnetic model systems are ideal to demonstrate unique correlation effects. Within the framework of the correlation theory we derive the expressions for the excitation spectrum. When a magnetic field is applied parallel to the z axis both substances have...

  17. Excitonic singlet-triplet ratios in molecular and polymeric organic materials

    Science.gov (United States)

    Baldo, Marc; Agashe, Shashank; Forrest, Stephen

    2002-03-01

    A simple technique is described for the determination of the internal efficiency and excitonic singlet-triplet formation statistics of electroluminescent organic thin films. The internal efficiency is measured by optically exciting a luminescent film within an electroluminescent device under reverse bias. This gives minimum singlet fractions of (0.20+/-0.03) and (0.19+/-0.04) for tris(8-hydroxyquinoline) aluminum (Alq3) and poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), respectively. These results are discussed in terms of the current understanding of exciton formation within organic materials. We also present measurements of the out-coupling fraction, or the fraction of photons emitted in the forward direction, as a function of the position of the emitting layer within a microcavity.

  18. The Contribution of Singlet Oxygen to Insulin Resistance

    Directory of Open Access Journals (Sweden)

    Arnold N. Onyango

    2017-01-01

    Full Text Available Insulin resistance contributes to the development of diabetes and cardiovascular dysfunctions. Recent studies showed that elevated singlet oxygen-mediated lipid peroxidation precedes and predicts diet-induced insulin resistance (IR, and neutrophils were suggested to be responsible for such singlet oxygen production. This review highlights literature suggesting that insulin-responsive cells such as endothelial cells, hepatocytes, adipocytes, and myocytes also produce singlet oxygen, which contributes to insulin resistance, for example, by generating bioactive aldehydes, inducing endoplasmic reticulum (ER stress, and modifying mitochondrial DNA. In these cells, nutrient overload leads to the activation of Toll-like receptor 4 and other receptors, leading to the production of both peroxynitrite and hydrogen peroxide, which react to produce singlet oxygen. Cytochrome P450 2E1 and cytochrome c also contribute to singlet oxygen formation in the ER and mitochondria, respectively. Endothelial cell-derived singlet oxygen is suggested to mediate the formation of oxidized low-density lipoprotein which perpetuates IR, partly through neutrophil recruitment to adipose tissue. New singlet oxygen-involving pathways for the formation of IR-inducing bioactive aldehydes such as 4-hydroperoxy-(or hydroxy or oxo-2-nonenal, malondialdehyde, and cholesterol secosterol A are proposed. Strategies against IR should target the singlet oxygen-producing pathways, singlet oxygen quenching, and singlet oxygen-induced cellular responses.

  19. Coherent dynamics of singlet fission controlled by nonlocal electron-phonon coupling

    OpenAIRE

    Yao, Yao

    2015-01-01

    Based on the Frenkel-charge transfer (CT) mixing model of singlet fission (SF), we incorporate both the local and nonlocal phonon baths in the Hamiltonian and adopt the algorithm of time-dependent density matrix renormalization group to simulate the fission process in tetracene. The endergonic SF is found to be facilitated by the robust quantum coherence, which concurrently gives rise to a notable quantum beating effect. Controlled by the nonlocal electron-phonon coupling, the density of trip...

  20. Effects of alignment and interference in resonant transfer and excitation for F6+ and O5+ collisions with H2 in 0 degree Auger measurements

    International Nuclear Information System (INIS)

    Zouros, T.J.M.; Bhalla, C.P.; Lee, D.H.; Richard, P.

    1990-01-01

    We have renormalized our previously reported 0 degree cross sections for zero resonant transfer and excitation calculation using high-resolution Auger spectroscopy (RTEA), dσ RTEA (0 degree)/dΩ, obtained in 0.25--2-MeV/u collisions of F 6+ and O 5+ ions with H 2 by normalizing to calculated binary-encounter electron yields rather than the usual Ne K Auger yields. The renormalized data are found to be in good agreement with recent angular-dependent impulse-approximation calculations of RTE, showing the importance of alignment and the small influence of interference between RTEA and elastic electron scattering for a 0 degree observation

  1. Time-resolved resonance Raman study of proton transferring systems in the excited triplet state: 2,2'-bipyridine and 2,2'-bipyridine-3,3'-diol

    DEFF Research Database (Denmark)

    Langkilde, F.W.; Mordzinski, A.; Wilbrandt, R.

    1992-01-01

    Time-resolved resonance Raman (RR) spectra of the excited triplet state T1 of 2,2'-bipyridine (BP), 2,2'-bipyridine-3,3'-diol BP(OH)2, and 5,5'-dimethyl-2,2'-bipyridine-3,3'-diol Me2BP(OH)2 are obtained. and interpreted by comparison with their ground-state Raman spectra and the T1 spectrum...... of biphenyl. The BP T1 RR spectrum is assigned assuming C2h molecular symmetry. The T1 RR spectra of BP(OH)2 and Me2BP(OH)2 are ascribed to diketo tautomers that are products of double proton transfer in the S1 state....

  2. Real-space investigation of energy transfer in heterogeneous molecular dimers.

    Science.gov (United States)

    Imada, Hiroshi; Miwa, Kuniyuki; Imai-Imada, Miyabi; Kawahara, Shota; Kimura, Kensuke; Kim, Yousoo

    2016-10-20

    Given its central role in photosynthesis and artificial energy-harvesting devices, energy transfer has been widely studied using optical spectroscopy to monitor excitation dynamics and probe the molecular-level control of energy transfer between coupled molecules. However, the spatial resolution of conventional optical spectroscopy is limited to a few hundred nanometres and thus cannot reveal the nanoscale spatial features associated with such processes. In contrast, scanning tunnelling luminescence spectroscopy has revealed the energy dynamics associated with phenomena ranging from single-molecule electroluminescence, absorption of localized plasmons and quantum interference effects to energy delocalization and intervalley electron scattering with submolecular spatial resolution in real space. Here we apply this technique to individual molecular dimers that comprise a magnesium phthalocyanine and a free-base phthalocyanine (MgPc and H 2 Pc) and find that locally exciting MgPc with the tunnelling current of the scanning tunnelling microscope generates a luminescence signal from a nearby H 2 Pc molecule as a result of resonance energy transfer from the former to the latter. A reciprocating resonance energy transfer is observed when exciting the second singlet state (S 2 ) of H 2 Pc, which results in energy transfer to the first singlet state (S 1 ) of MgPc and final funnelling to the S 1 state of H 2 Pc. We also show that tautomerization of H 2 Pc changes the energy transfer characteristics within the dimer system, which essentially makes H 2 Pc a single-molecule energy transfer valve device that manifests itself by blinking resonance energy transfer behaviour.

  3. Improved spectrometer-microscope for quantitative fluorescence resonance energy transfer measurement based on simultaneous spectral unmixing of excitation and emission spectra.

    Science.gov (United States)

    Lin, Fangrui; Du, Mengyan; Yang, Fangfang; Wei, Lichun; Chen, Tongsheng

    2018-01-01

    Based on our recently developed quantitative fluorescence resonance energy transfer (FRET) measurement method using simultaneous spectral unmixing of excitation and emission spectra (ExEm-spFRET), we here set up an improved spectrometer-microscope (SM) for implementing modified ExEm-spFRET (mExEm-spFRET), in which a system correction factor (fsc) is introduced. Our SM system is very stable for at least six months. Implementation of mExEm-spFRET with four or two excitation wavelengths on SM for single living cells expressing different FRET constructs obtained consistent FRET efficiency (E) and acceptor-donor concentration ratio (Rc) values. We also performed mExEm-spFRET measurement for single living cells coexpressing cyan fluorescent protein (CFP)-Bax and yellow fluorescent protein (YFP)-Bax and found that the E values between CFP-Bax and YFP-Bax were very low (2.2%) and independent of Rc for control cells, indicating that Bax did not exist as homooligomer in healthy cells, but positively proportional to Rc in the case of Rc1 for staurosporine (STS)-treated cells, demonstrating that all Bax formed homooligomer after STS treatment for 6 h. (2018) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE).

  4. Collisional energy transfer between highly excited vibrational levels of K2 (11Σu+, V=46∼61) and H2

    International Nuclear Information System (INIS)

    Zhang Liping; Cai Qin; Luan Nannan; Dai Kang; Shen Yifan

    2011-01-01

    Using the CARS (Coherent Anti-stokes Raman Spectroscopy) detection technique, the electronic-to-rovibrational levels energy transfer between electronically excited K 2 (which is in the state of 1 1 ∑ u + , V=46∼61) and H 2 has been investigated. The scanned CARS spectra reveals that H 2 molecules are produced only at the V=1, J=2 and V=2, J=0, 1, 2 rovibrational levels during energy transfer processes. From scanned CARS spectral peaks the population ratios are obtained. The n 1 /n 4 9 n 2 /n 4 , and n 3 /n 4 are 3.3±0.5, 2.2±0.3 and 2.0±0.3, respectively, where n 1 , n 2 , n 3 and n 4 represent the number densities of H 2 at rovibrational levels (2, 0), (2, 1), (2, 2) and (1, 2), respectively. The population ratios indicate that the H 2 molecules produced by the energy transfer process are 88% populated at the V=2 level and 12% at V=1. The relative fractions (, , ) of average energy disposal are derived as (0.53, 0.01, 0.46), having major vibrational and translational energy release. Through simple kinetic model at the experimental conditions of T=573 K and P(H 2 ) =5 X 10 3 Pa, collisional transfer rate coefficients k 12 =(3.3±0.7) X 10 -14 and k 2 =(1.4±0.3) X 10 -14 cm 3 s -1 have been obtained. (authors)

  5. Protonation effect on the excited state behaviour of EE-1-(n-pyridyl)-4-phenylbutadienes (n = 2, 3 and 4).

    Science.gov (United States)

    Mazzucato, Ugo; Spalletti, Anna

    2003-03-01

    The acid-base equilibria of three aza-derivatives of EE-1,4-diphenylbutadiene and the excited state properties of their neutral and protonated forms have been studied in aqueous solutions. The prevalent relaxation of the neutral molecules is photoisomerization by a diabatic singlet mechanism accompanied by substantial internal conversion while the quantum yield of the radiative pathway is very small, particularly for the ortho- and para-substituted pyridines. Protonation affects only slightly the isomerization yield of these two compounds while drastically decreasing that of the meta-substituted analogue. Molecular orbital calculations and comparison with the corresponding azastilbenes indicate that the first excited singlet state of the protonated meta compound has a net charge transfer character, which leads to an increase of the torsional barrier in S1. Application of the Forster cycle to the three compounds showed that they become much stronger bases in S1. The 3-pyridyl derivative proved to be peculiar also in this respect since its equilibration with the proton occurs during the S1 lifetime thus allowing the acid-base equilibration in the excited state to be directly monitored by fluorimetric titration.

  6. Probing color-singlet exchange at D0

    International Nuclear Information System (INIS)

    Abbott, B.; Abolins, M.; Acharya, B.S.

    1997-07-01

    We present latest preliminary results on hard color-singlet exchange in proton-antiproton collisions. The fraction of dijet events produced via color-singlet exchange is measured as a function of jet transverse energy, dijet pseudorapidity separation, and proton-antiproton center-of-mass energy. These results are qualitatively consistent with a color-singlet fraction that increases with increasing quark-initiated processes

  7. Tunable excited-state intramolecular proton transfer reactions with Nsbnd H or Osbnd H as a proton donor: A theoretical investigation

    Science.gov (United States)

    Li, Yuanyuan; Wen, Keke; Feng, Songyan; Yuan, Huijuan; An, Beibei; Zhu, Qiuling; Guo, Xugeng; Zhang, Jinglai

    2017-12-01

    Excited-state intramolecular proton transfer (ESIPT) reactions occurring in the S1 state for five molecules, which possess five/six-membered ring intramolecular Nsbnd H···N or Osbnd H···N hydrogen bonds bearing quinoline or 2-phenylpyridine moiety, have been described in detail by the time-dependent density functional theory (TD-DFT) approach using the B3LYP hybrid functional. For the five molecules, the constrained potential energy profiles along the ESIPT reactions show that proton transfer is barrierless in molecules possessing six-membered ring intramolecular H-bonds, which is smoother than that with certain barriers in five-membered ring H-bonding systems. For the latter, chemical modification by a more strong acid group can lower the ESIPT barrier significantly, which harnesses the ESIPT reaction from a difficult type to a fast one. The energy barrier of the ESIPT reaction depends on the intensity of the intramolecular H-bond, which can be measured with the topological descriptors by topology analysis of the bond critical point (BCP) of the intramolecular H-bond. It is found that when the value of electron density ρ(r) at BCP is bigger than 0.025 a.u., the corresponding molecule might go through an ultrafast and barrierless ESIPT process, which opens a new scenario to explore the ESIPT reactions.

  8. Faster photoinduced electron transfer in a diluted mixture than in a neat donor solvent: effect of excited-state H-bonding.

    Science.gov (United States)

    Barman, Nabajeet; Singha, Debabrata; Sahu, Kalyanasis

    2014-04-07

    In a neat electron-donating solvent (in this case aniline), photoinduced electron transfer (PET) from the solvent to an excited acceptor (e.g. a coumarin fluorophore) may be anticipated to be the most efficient because of the close contact of the acceptor with many donors. Addition of an inert component would most likely retard the PET process by replacing some donors from the neighbourhood of the acceptors. Surprisingly, we found dramatic acceleration of PET (6-10 fold enhancement compared to neat aniline), for coumarin 102 (C102) dissolved in a binary mixture of aniline and an inert solvent (cyclohexane or toluene). The PET induced fluorescence follows an anomalous trend against the mole fraction of aniline (XAN); first quenches up to certain XAN (0.075 for cyclohexane; 0.13 for toluene), thereafter, enhances with increase in XAN. Although the non-interacting component cannot directly participate in the PET process, it may modulate C102-aniline H-bonding association by changing the polarity of the medium or by disrupting the aniline-aniline H-bond. The study clearly illustrates the dominant role of hydrogen bonding in activating the electron transfer rate where standard thermodynamics predicts very weak donor-acceptor interaction.

  9. Energy transfer dynamics in trimers and aggregates of light-harvesting complex II probed by 2D electronic spectroscopy.

    Science.gov (United States)

    Enriquez, Miriam M; Akhtar, Parveen; Zhang, Cheng; Garab, Győző; Lambrev, Petar H; Tan, Howe-Siang

    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 Qy 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.

  10. 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.

  11. Storage of magnetization as singlet order by optimal control designed pulses

    DEFF Research Database (Denmark)

    Laustsen, Christoffer; Bowen, Sean; Vinding, Mads Sloth

    2014-01-01

    . With this aim, optimal control theory was applied to create pulses that for near‐equivalent spins accomplish transfers in and out of the singlet state with maximum efficiency while ensuring robustness toward variations in the nuclear spin system Hamiltonian (chemical shift, J‐couplings, B1 and B magnetic field...... inhomogeneity). The pulses are designed to accomplish efficient transfer with low B1 amplitude, essential for applications on preclinical and clinical MR scanners. It is demonstrated that significantly improved efficiency and robustness can be obtained within the limitations of typical MR scanner performance...

  12. Excitonic singlet-triplet ratio in a semiconducting organic thin film

    Science.gov (United States)

    Baldo, M. A.; O'brien, D. F.; Thompson, M. E.; Forrest, S. R.

    1999-11-01

    A technique is presented to determine the spin statistics of excitons formed by electrical injection in a semiconducting organic thin film. With the aid of selective addition of luminescent dyes, we generate either fluorescence or phosphorescence from the archetype organic host material aluminum tris (8-hydroxyquinoline) (Alq3). Spin statistics are calculated from the ratio of fluorescence to phosphorescence in the films under electrical excitation. After accounting for varying photoluminescent efficiencies, we find a singlet fraction of excitons in Alq3 of (22+/-3)%.

  13. An accurate full-dimensional potential energy surface for H-Au(111): Importance of nonadiabatic electronic excitation in energy transfer and adsorption.

    Science.gov (United States)

    Janke, Svenja M; Auerbach, Daniel J; Wodtke, Alec M; Kandratsenka, Alexander

    2015-09-28

    We have constructed a potential energy surface (PES) for H-atoms interacting with fcc Au(111) based on fitting the analytic form of the energy from Effective Medium Theory (EMT) to ab initio energy values calculated with density functional theory. The fit used input from configurations of the H-Au system with Au atoms at their lattice positions as well as configurations with the Au atoms displaced from their lattice positions. It reproduces the energy, in full dimension, not only for the configurations used as input but also for a large number of additional configurations derived from ab initio molecular dynamics (AIMD) trajectories at finite temperature. Adiabatic molecular dynamics simulations on this PES reproduce the energy loss behavior of AIMD. EMT also provides expressions for the embedding electron density, which enabled us to develop a self-consistent approach to simulate nonadiabatic electron-hole pair excitation and their effect on the motion of the incident H-atoms. For H atoms with an energy of 2.7 eV colliding with Au, electron-hole pair excitation is by far the most important energy loss pathway, giving an average energy loss ≈3 times that of the adiabatic case. This increased energy loss enhances the probability of the H-atom remaining on or in the Au slab by a factor of 2. The most likely outcome for H-atoms that are not scattered also depends prodigiously on the energy transfer mechanism; for the nonadiabatic case, more than 50% of the H-atoms which do not scatter are adsorbed on the surface, while for the adiabatic case more than 50% pass entirely through the 4 layer simulation slab.

  14. 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

  15. High-efficiency fluorescent organic light-emitting devices using sensitizing hosts with a small singlet-triplet exchange energy.

    Science.gov (United States)

    Zhang, Dongdong; Duan, Lian; Li, Chen; Li, Yilang; Li, Haoyuan; Zhang, Deqiang; Qiu, Yong

    2014-08-06

    Materials with small singlet-triplet splits (ΔEST s) are introduced as sensitizing hosts to excite fluorescent dopants, breaking the trade-off between small ΔEST and high radiative decay rates. A highly efficient orange-fluorescent organic light-emitting diode (OLED) is prepared, showing a maximum external quantum efficiency of 12.2%. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Production of Singlet Oxygen in a Non-Self-Sustained Discharge

    International Nuclear Information System (INIS)

    Vasil'eva, A.N.; Klopovskii, K.S.; Kovalev, A.S.; Lopaev, D.V.; Mankelevich, Yu.A.; Popov, N.A.; Rakhimov, A.T.; Rakhimova, T.V.

    2005-01-01

    The production of O 2 (a 1 Δ g ) singlet oxygen in non-self-sustained discharges in pure oxygen and mixtures of oxygen with noble gases (Ar or He) was studied experimentally. It is shown that the energy efficiency of O 2 (a 1 Δ g ) production can be optimized with respect to the reduced electric field E/N. It is shown that the optimal E/N values correspond to electron temperatures of 1.2-1.4 eV. At these E/N values, a decrease in the oxygen percentage in the mixture leads to an increase in the excitation rate of singlet oxygen because of the increase in the specific energy deposition per O 2 molecule. The onset of discharge instabilities not only greatly reduces the energy efficiency of singlet oxygen production but also makes it impossible to achieve high energy deposition in a non-self-sustained discharge. A model of a non-self-sustained discharge in pure oxygen is developed. It is shown that good agreement between the experimental and computed results for a discharge in oxygen over a wide range of reduced electric fields can be achieved only by taking into account the ion component of the discharge current. The cross section for the electron-impact excitation of O 2 (a 1 Δ g ) and the kinetic scheme of the discharge processes with the participation of singlet oxygen are verified by comparing the experimental and computed data on the energy efficiency of the production of O 2 (a 1 Δ g ) and the dynamics of its concentration. It is shown that, in the dynamics of O 2 (a 1 Δ g ) molecules in the discharge afterglow, an important role is played by their deexcitation in a three-body reaction with the participation of O( 3 P) atoms. At high energy depositions in a non-self-sustained discharge, this reaction can reduce the maximal attainable concentration of singlet oxygen. The effect of a hydrogen additive to an Ar : O 2 mixture is analyzed based on the results obtained using the model developed. It is shown that, for actual electron beam current densities, a

  17. Stability of singlet and triplet trions in carbon nanotubes

    International Nuclear Information System (INIS)

    Ronnow, Troels F.; Pedersen, Thomas G.; Cornean, Horia D.

    2009-01-01

    We investigate singlet and triplet trion states in semiconducting carbon nanotubes using a one-dimensional model. It is concluded that singlet trion states in bind up to 13.6% stronger than exciton states, and that they lower the optical transition energy with up to 50% of the tight binding band gap energy.

  18. Stability of singlet and triplet trions in carbon nanotubes

    DEFF Research Database (Denmark)

    Rønnow, Troels Frimodt; Pedersen, Thomas Garm; Cornean, Horia

    2009-01-01

    We investigate singlet and triplet trion states in semiconducting carbon nanotubes using a one-dimensional model. It is concluded that singlet trion states in bind up to 13.5% stronger than exciton states, and that they lower the optical transition energy with up to 50% of the tight binding band...

  19. External quantum efficiency exceeding 100% in a singlet-exciton-fission-based solar cell

    Science.gov (United States)

    Baldo, Marc

    2013-03-01

    Singlet exciton fission can be used to split a molecular excited state in two. In solar cells, it promises to double the photocurrent from high energy photons, thereby breaking the single junction efficiency limit. We demonstrate organic solar cells that exploit singlet exciton fission in pentacene to generate more than one electron per incident photon in the visible spectrum. Using a fullerene acceptor, a poly(3-hexylthiophene) exciton confinement layer, and a conventional optical trapping scheme, the peak external quantum efficiency is (109 +/-1)% at λ = 670 nm for a 15-nm-thick pentacene film. The corresponding internal quantum efficiency is (160 +/-10)%. Independent confirmation of the high internal efficiency is obtained by analysis of the magnetic field effect on photocurrent, which determines that the triplet yield approaches 200% for pentacene films thicker than 5 nm. To our knowledge, this is the first solar cell to generate quantum efficiencies above 100% in the visible spectrum. Alternative multiple exciton generation approaches have been demonstrated previously in the ultraviolet, where there is relatively little sunlight. Singlet exciton fission differs from these other mechanisms because spin conservation disallows the usual dominant loss process: a thermal relaxation of the high-energy exciton into a single low-energy exciton. Consequently, pentacene is efficient in the visible spectrum at λ = 670 nm because only the collapse of the singlet exciton into twotriplets is spin-allowed. Supported as part of the Center for Excitonics, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001088.

  20. Supramolecular Surface Photochemistry: Cascade Energy Transfer between Encapsulated Dyes Aligned on a Clay Nanosheet Surface.

    Science.gov (United States)

    Tsukamoto, Takamasa; Ramasamy, Elamparuthi; Shimada, Tetsuya; Takagi, Shinsuke; Ramamurthy, V

    2016-03-29

    Three coumarin derivatives (7-propoxy coumarin, coumarin-480, and coumarin-540a, 2, 3, and 4, respectively) having different absorption and emission spectra were encapsulated within a water-soluble organic capsule formed by the two positively charged ammonium-functionalized cavitand octaamine (OAm, 1). Guests 2, 3, and 4 absorb in ultraviolet, violet, and blue regions and emit in violet, blue, and green regions, respectively. Energy transfer between the above three coumarin@(OAm)2 complexes assembled on the surface of a saponite clay nanosheet was investigated by steady-state and time-resolved emission techniques. Judging from their emission and excitation spectra, we concluded that the singlet-singlet energy transfer proceeded from 2 to 3, from 2 to 4, and from 3 to 4 when OAm-encapsulated 2, 3, and 4 were aligned on a clay surface as two-component systems. Under such conditions, the energy transfer efficiencies for the paths 2* to 3, 2* to 4, and 3* to 4 were calculated to be 33, 36, and 50% in two-component systems. When all three coumarins were assembled on the surface and 2 was excited, the energy transfer efficiencies for the paths 2* to 3, 2* to 4, and 3* to 4 were estimated to be 32, 34, and 33%. A comparison of energy transfer efficiencies of the two-component and three-component systems revealed that excitation of 2 leads to emission from 4. Successful merging of supramolecular chemistry and surface chemistry by demonstrating novel multi-step energy transfer in a three-component dye encapsulated system on a clay surface opens up newer opportunities for exploring such systems in an artificial light-harvesting phenomenon.

  1. Excitation functions of inelastic and transfer channels in {sup 12} C+{sup 12} C around E{sub c.m.} = 32.5 MeV

    Energy Technology Data Exchange (ETDEWEB)

    Szilner, S.; Basrak, Z.; Freeman, R.M.; Haas, F.; Beck, C. [Strasbourg-1 Univ., 67 (France). Centre de Recherches Nucleaires]|[Strasbourg-1 Univ., 67 (France); Morsad, A. [Universite Hassan II, Casablanca (Morocco). Faculte des Sciences

    1996-12-31

    A prominent and wide resonance centered at E{sub c.m.} = 32.5 MeV has recently been found in the (0{sub 2}{sup +}, 0{sub 2}{sup +}) inelastic channel of the {sup 12}C+{sup 12}C reaction. It has been suggested that it corresponds to a 6{alpha}-particle-chain state in {sup 24}Mg. In the present work we study {sup 12}C+{sup 12}C excitation functions between center-of-mass energies of 30 and 35 MeV in steps of 250 keV for weakly populated outgoing channels. We present the inelastic channels to the states above the {alpha}-particle decay threshold, (0{sub 1}{sup +},0{sub 2}{sup +}), (0{sub 1}{sup +},3{sub 1}{sup -}), and (0{sub 1}{sup +},4{sub 1}{sup 4}), and the one- and two-nucleon transfer channels. In the inelastic and the transfer channels we observe correlated intermediate-width structures at E{sub c.m.} = 31, 32.5, and 33.5 MeV, whose widths are appreciably smaller than the width measured in the (0{sub 2}{sup +},0{sub 2}{sup +}) channel. Our E{sub c.m.} = 31, 32.5, and 33.5 MeV, whose widths are appreciably smaller than the width measured in the (0{sub 2}{sup +},0{sub 2}{sup +}) channel. Our E{sub c.m.} = 32.5 MeV angular distribution of the (0{sub 1}{sup +},0{sub 2}{sup +})channel exhibits oscillatory behavior and, unlike that of the (0{sup +}{sub 2}, 0{sup +}{sub 2}) channel, does not display enhancement around {Theta}{sub c.m.} = 90 deg. Data were collected via the kinematic coincidence technique. For data reduction we use a novel approach allowing for the extraction of results on non-binary channels. (authors). 39 refs.

  2. A comprehensive spectroscopic and computational investigation of intramolecular proton transfer in the excited states of 2-(2′-hydroxyphenyl) benzoxazole and its derivatives

    Energy Technology Data Exchange (ETDEWEB)

    Padalkar, Vikas S. [Tinctorial Chemistry Group, Institute of Chemical Technology, Matunga, Mumbai 400019 (India); Ramasami, Ponnadurai, E-mail: ramchemi@intnet.mu [Computational Chemistry Group, Department of Chemistry, Faculty of Science, University of Mauritius, Réduit (Mauritius); Sekar, Nagaiyan, E-mail: n.sekar@ictmumbai.edu.in [Tinctorial Chemistry Group, Institute of Chemical Technology, Matunga, Mumbai 400019 (India)

    2014-02-15

    The excited-state intramolecular proton transfer (ESIPT) fluorescence of the 2-(2′ hydroxyphenyl) benzoxazole (HBO) and its derivatives with NO{sub 2} as electron acceptor and NH{sub 2} as electron donor at the 4 and 5 position of benzoxazole ring was studied by spectroscopic and computational methods. The changes in the electronic transition, energy levels, and orbital diagrams of the HBO derivatives were investigated using the DFT computations and they were correlated with the experimental spectral emission. The benzoxazole derivatives are fluorescent under UV-light in solution. Photophysical properties of the compounds were also studied in solvents of different polarities. Experimental absorption and emission wavelengths are in agreement with those computed with a deviation ranging between 0 and 50%. The computational methods have been useful for molecular understanding of the transitions responsible for the fluorescent spectra. -- Highlights: • Experimental photophysical properties of 2-substituted benzoxazoles in different solvents have been studied and compared with the computational data. • Compounds show dual emission due to ESIPT process and was supported by DFT and TD-DFT computations. • Experimental results and computational results are in good agreements.

  3. Obstruction of photoinduced electron transfer from excited porphyrin to graphene oxide: a fluorescence turn-on sensing platform for iron (III ions.

    Directory of Open Access Journals (Sweden)

    Zhong De Liu

    Full Text Available A comparative research of the assembly of different porphyrin molecules on graphene oxide (GO and reduced graphene oxide (RGO was carried out, respectively. Despite the cationic porphyrin molecules can be assembled onto the surfaces of graphene sheets, including GO and RGO, to form complexes through electrostatic and π-π stacking interactions, the more obvious fluorescence quenching and the larger red-shift of the Soret band of porphyrin molecule in RGO-bound states were observed than those in GO-bound states, due to the difference of molecular flattening in degree. Further, more interesting finding was that the complexes formed between cationic porphyrin and GO, rather than RGO sheets, can facilitate the incorporation of iron (III ions into the porphyrin moieties, due to the presence of the oxygen-contained groups at the basal plane of GO sheets served as auxiliary coordination units, which can high-efficiently obstruct the electron transfer from excited porphyrin to GO sheets and result in the occurrence of fluorescence restoration. Thus, a fluorescence sensing platform has been developed for iron (III ions detection in this contribution by using the porphyrin/GO nanohybrids as an optical probe, and our present one exhibited rapid and sensitive responses and high selectivity toward iron (III ions.

  4. Magnetism of singlet - singlet ions interacting with an electron gas: application to PrAl2

    International Nuclear Information System (INIS)

    Palermo, L.

    1986-01-01

    Various magnetic quantities are investigated for a system consisting of singlet-singlet ions interacting with an electron gas. In obtaining the magnetic state equations, the molecular field approximation is used. At T=0, an onset magnetic order condition in function of crystal field and exchange parameters and eletronic density of states at Fermi level is derived. A parametric study of the model is performed numerically. Main results are shown on diagrams. From the experimental data existent in the literature for magnetisation, susceptibility and magnetic specific heat of the PrAl 2 , a fitting with the model predictions is obtained using the following parameters: exchange interaction: 611meV; crystal field parameters: 2,5 meV; band with: 10 eV (of a rectangular density of states with 0,8 el/atom). (author) [pt

  5. Quantum mechanical modeling of excited electronic states and their relationship to cathodoluminescence of BaZrO3

    OpenAIRE

    Moreira, Mario L.; Andrés Bort, Juan; Gracia Edo, Lourdes; Beltrán Flors, Armando; Montoro, Luciano A.; Varela, José A.; Longo, E.

    2013-01-01

    First-principles calculations set the comprehension over performance of novel cathodoluminescence (CL) properties of BaZrO3 prepared through microwave-assisted hydrothermal. Ground (singlet, s*) and excited (singlet s** and triplet t** ) electronic states were built from zirconium displacement of 0.2 Å in {001} direction. Each ground and excited states were characterized by the correlation of their corresponding geometry with electronic structures and Raman vibrational frequencies which were ...

  6. Complex singlet extension of the standard model

    International Nuclear Information System (INIS)

    Barger, V.; Langacker, P.; McCaskey, M.; Ramsey-Musolf, M.; Shaughnessy, G.

    2009-01-01

    We analyze a simple extension of the standard model (SM) obtained by adding a complex singlet to the scalar sector (cxSM). We show that the cxSM can contain one or two viable cold dark matter candidates and analyze the conditions on the parameters of the scalar potential that yield the observed relic density. When the cxSM potential contains a global U(1) symmetry that is both softly and spontaneously broken, it contains both a viable dark matter candidate and the ingredients necessary for a strong first order electroweak phase transition as needed for electroweak baryogenesis. We also study the implications of the model for discovery of a Higgs boson at the Large Hadron Collider

  7. Electronic energy transfer involving carotenoid pigments in chlorosomes of two green bacteria: Chlorobium tepidum and Chloroflexus aurantiacus

    Science.gov (United States)

    Melø, T. B.; Frigaard, N.-U.; Matsuura, K.; Razi Naqvi, K.

    2000-09-01

    Electronic energy transfer processes in chlorosomes isolated from the green sulphur bacterium Chlorobium tepidum and from the green filamentous bacterium Chloroflexus aurantiacus have been investigated. Steady-state fluorescence excitation spectra and time-resolved triplet-minus-singlet (TmS) spectra, recorded at ambient temperature and under non-reducing or reducing conditions, are reported. The carotenoid (Car) pigments in both species transfer their singlet excitation to bacteriochlorophyll c (BChl c) with an efficiency which is high (between 0.5 and 0.8) but smaller than unity; BChl c and bacteriochlorophyll a (BChl a) transfer their triplet excitation to the Car's with nearly 100% efficiency. The lifetime of the Car triplet states is approximately 3 μs, appreciably shorter than that of the Car triplets in the light-harvesting complex II (LHCII) in green plants and in other antenna systems. In both types of chlorosomes the yield of BChl c triplets (as judged from the yield of the Car triplets) remains insensitive to the redox conditions. In notable contrast the yield of BChl c singlet emission falls, upon a change from reducing to non-reducing conditions, by factors of 4 and 35 in Cfx. aurantiacus and Cb. tepidum, respectively. It is possible to account for these observations if one postulates that the bulk of the BChl c triplets originate either from a large BChl c pool which is essentially non-fluorescent and non-responsive to changes in the redox conditions, or as a result of a process which quenches BChl c singlet excitation and becomes more efficient under non-reducing conditions. In chlorosomes from Cfx. aurantiacus whose Car content is lowered, by hexane extraction, to 10% of the original value, nearly one-third of the photogenerated BChl c triplets still end up on the residual Car pigments, which is taken as evidence of BChl c-to-BChl c migration of triplet excitation; the BChl c triplets which escape rapid static quenching contribute a depletion

  8. Nuclear magnetic resonance in high magnetic fields: Study of singlet-ground-state due to 1-D quantum spin effect

    Science.gov (United States)

    Chiba, Meiro; Ajiro, Yoshitami; Satoh, Eiji; Kubo, Takeji

    1996-02-01

    In one-dimensional (1-D) magnets the singlet-ground-state (SGS) due to the quantum spin effect is one of the most interesting phenomena. The temperature and the field dependences of the proton spin-lattice relaxation under magnetic fields up to 15 T have been observed for SGS materials, namely, NENP (Haldane system) and CuCI 2(γ-picoline) 2 (alternating antiferromagnetic chain). The results clearly show the excitation of SGS with a characteristic energy gap in the magnetic excited state. The observed relaxation rate is discussed in terms of the number of magnetic excitons in focussing on the dissimilarity between two systems.

  9. Field-dependent molecular ionization and excitation energies: Implications for electrically insulating liquids

    Directory of Open Access Journals (Sweden)

    N. Davari

    2014-03-01

    Full Text Available The molecular ionization potential has a relatively strong electric-field dependence as compared to the excitation energies which has implications for electrical insulation since the excited states work as an energy sink emitting light in the UV/VIS region. At some threshold field, all the excited states of the molecule have vanished and the molecule is a two-state system with the ground state and the ionized state, which has been hypothesized as a possible origin of different streamer propagation modes. Constrained density-functional theory is used to calculate the field-dependent ionization potential of different types of molecules relevant for electrically insulating liquids. The low singlet-singlet excitation energies of each molecule have also been calculated using time-dependent density functional theory. It is shown that low-energy singlet-singlet excitation of the type n → π* (lone pair to unoccupied π* orbital has the ability to survive at higher fields. This type of excitation can for example be found in esters, diketones and many color dyes. For alkanes (as for example n-tridecane and cyclohexane on the other hand, all the excited states, in particular the σ → σ* excitations vanish in electric fields higher than 10 MV/cm. Further implications for the design of electrically insulating dielectric liquids based on the molecular ionization potential and excitation energies are discussed.

  10. The electroweak phase transition in models with gauge singlets

    International Nuclear Information System (INIS)

    Ahriche, A.

    2007-01-01

    A strong first order phase transition is needed for generating the baryon asymmetry; and also to save it during the electroweak phase transition (EWPT). However this condition is not fulfilled within the Standard Model (SM), but in its extensions. It is widely believed that the existence of singlet scalars in some Standard Model extensions can easily make the EWPT strongly first order. In this work, we will examine the strength of the EWPT in the simplest extension of the SM with a real gauge singlet using the sphaleron energy at the critical temperature. We find that the phase transition is stronger by adding a singlet; and also that the criterion for a strong phase transition Ω(T c )/T c >or similar 1, where Ω = (v 2 + (x - x 0 ) 2 ) ( 1)/(2) and x(x 0 ) is the singlet vacuum expectation value in the broken (symmetric) phase, is not valid for models containing singlets, even though often used in the literature. The usual condition v c /T c >or similar 1 is more meaningful, and it is satisfied for the major part of the parameter space for physically allowed Higgs masses. Then it is convenient to study the EWPT in models with singlets that couple only to the Higgs doublets, by replacing the singlets by their vevs. (orig.)

  11. The electroweak phase transition in models with gauge singlets

    Energy Technology Data Exchange (ETDEWEB)

    Ahriche, A.

    2007-04-18

    A strong first order phase transition is needed for generating the baryon asymmetry; and also to save it during the electroweak phase transition (EWPT). However this condition is not fulfilled within the Standard Model (SM), but in its extensions. It is widely believed that the existence of singlet scalars in some Standard Model extensions can easily make the EWPT strongly first order. In this work, we will examine the strength of the EWPT in the simplest extension of the SM with a real gauge singlet using the sphaleron energy at the critical temperature. We find that the phase transition is stronger by adding a singlet; and also that the criterion for a strong phase transition {omega}(T{sub c})/T{sub c} >or similar 1, where {omega} = (v{sup 2} + (x - x{sub 0}){sup 2}){sup (}1)/(2) and x(x{sub 0}) is the singlet vacuum expectation value in the broken (symmetric) phase, is not valid for models containing singlets, even though often used in the literature. The usual condition v{sub c}/T{sub c} >or similar 1 is more meaningful, and it is satisfied for the major part of the parameter space for physically allowed Higgs masses. Then it is convenient to study the EWPT in models with singlets that couple only to the Higgs doublets, by replacing the singlets by their vevs. (orig.)

  12. Relaxation of the excited -(2-hydroxy benzylidene) aniline ...

    Indian Academy of Sciences (India)

    The geometry optimizations and the subsequent frequency calculations of the excited singlet electronic states of the various tautomeric forms of SA molecule were performed with the CIS level of theory. A detail theoretical investigation on the relaxation dynamics of the SA molecule has been presented. Possible explanation ...

  13. Zethrenes, Extended p -Quinodimethanes, and Periacenes with a Singlet Biradical Ground State

    KAUST Repository

    Sun, Zhe

    2014-08-19

    , transient absorption spectroscopy, electrochemistry, and spectroelectrochemistry.These systematic studies revealed that aromaticity played a very important role in determining their singlet biradical character, which is critically related to both their physical properties and their chemical reactivity. In particular, we found that Clars aromatic sextet rule, which is useful for the closed-shell PAHs, can also predict the relative biradical character of benzenoid PH-based singlet biradicaloids. Other factors, such as structural flexibility of the biradical and quinoid resonance forms and the participation of the substitution in the π-conjugation, also influence the biradical character. These molecular materials demonstrate a number of unique properties such as near-infrared absorption, redox amphotericity, large two-photon absorption cross section, short excited state lifetime, stimuli-responsive magnetic activity, and singlet fission, which suggests promise for future applications. © 2014 American Chemical Society.

  14. Performance of SOPPA-based methods in the calculation of vertical excitation energies and oscillator strengths

    DEFF Research Database (Denmark)

    Sauer, Stephan P. A.; Pitzner-Frydendahl, Henrik Frank; Buse, Mogens

    2015-01-01

    methods, the original SOPPA method as well as SOPPA(CCSD) and RPA(D) in the calculation of vertical electronic excitation energies and oscillator strengths is investigated for a large benchmark set of 28 medium-size molecules with 139 singlet and 71 triplet excited states. The results are compared...

  15. SHORT COMMUNICATION SINGLET-TRIPLET GAP STUDIES ON ...

    African Journals Online (AJOL)

    Preferred Customer

    2009-02-10

    yahoo.com. SHORT COMMUNICATION. SINGLET-TRIPLET GAP STUDIES ON ARYL-CYCLOPENTADIENYLIDENES: INDIRECT ELECTRONIC EFFECTS. E. Vessally*. Payame Noor University (PNU), Zanjan, Iran. (Received February 10, 2009; ...

  16. Excitation of lowest electronic states of thymine by slow electrons

    Science.gov (United States)

    Chernyshova, I. V.; Kontros, E. J.; Markush, P. P.; Shpenik, O. B.

    2013-11-01

    Excitation of lowest electronic states of the thymine molecules in the gas phase is studied by elec- tron energy loss spectroscopy. In addition to dipole-allowed transitions to singlet states, transitions to the lowest triplet states were observed. The low-energy features of the spectrum at 3.66 and 4.61 eV are identified with the excitation of the first triplet states 13 A' (π → π*) and 13 A″ ( n → π*). The higher-lying features at 4.96, 5.75, 6.17, and 7.35 eV are assigned mainly to the excitation of the π → π* transitions to the singlet states of the molecule. The excitation dynamics of the lowest states is studied. It is found that the first triplet state 13 A'(π → π*) is most efficiently excited at a residual energy close to zero, while the singlet 21 A'(π → π*) state is excited with almost identical efficiency at different residual energies.

  17. Singlet oxygen-mediated protein oxidation

    DEFF Research Database (Denmark)

    Wright, Adam; Bubb, William A; Hawkins, Clare Louise

    2002-01-01

    Singlet oxygen (1O2) is generated by a number of enzymes as well as by UV or visible light in the presence of a sensitizer and has been proposed as a damaging agent in a number of pathologies including cataract, sunburn, and skin cancers. Proteins, and Cys, Met, Trp, Tyr and His side chains...... methods. The yield of these species is significantly enhanced in D2O and decreased by azide. Nuclear magnetic resonance and mass spectroscopic analysis of reaction mixtures, or materials separated by high-performance liquid chromatography, are consistent with the initial formation of an (undetected......-hydroxy-6-oxo-2,3,3a,6,7,7a-hexahydro-1H-indole-2-carboxylic acid. Hydroperoxides that lack a free alpha-amino group (e.g. those formed on 3-(4-hydroxyphenyl)propionic acid, N-Ac-Tyr and Tyr-containing peptides) are longer-lived, with half-lives of hours to days. These species undergo slow decay at low...

  18. Singlet-oxygen therapy. Scientific and methodological materials

    OpenAIRE

    Chukhraiev, N.; Chukhraieva, E.; Gun'ko, M.; Kurik, L.; Lomeiko, S.; Marushko, Y.; Samosyuk, N.; Tkalina, A.; Vladimirov, A.; Unichenko, A.; Zavorotnaya, R.; Zukow, W.

    2018-01-01

    Radomska Szkoła Wyższa w Radomiu MEDICAL INNOVATIVE TECHNOLOGIES SINGLET-OXYGEN THERAPY Scientific and methodological materials 2018 This edition had extended and translated from ukrainian Edited by Chukhraiev N., Vladimirov A., Zukow W. Radom, Kyiv Radomska Szkoła Wyższa w Radomiu MEDICAL INNOVATIVE TECHNOLOGIES SINGLET-OXYGEN THERAPY Scientific and methodological materials 2018 This edition had extended and translated from ukrainian Edited by ...

  19. Excited State s-cis Rotamers Produced by Extreme Red Edge Excitation of all-trans-1,4-Diphenyl-1,3-butadiene

    DEFF Research Database (Denmark)

    Wallace-Williams, Stacie E.; Møller, Søren; Goldbeck, Robert A.

    1993-01-01

    The shapes of the fluorescence emission and lowest excited singlet-state absorption spectra of all-trans-1,4- diphenylbutadiene (DPB) in hydrocarbon solvents vary with excitation wavelength when exciting on the extreme red edge of the ground-state absorption spectrum. This contrasts...... changes in DPB can be explained in terms of an excitation wavelength-dependent production of s-cis and s-trans rotamer populations in the excited state. The DPB fluorescence emission spectrum was resolved into s-cis and s-trans components. The vibronic structure of the s-cis fluorescence spectrum...... with the wavelength independence observed for the excited singlet-state absorption and fluorescence emission spectra of 1,5-diphenyl-2,3,4,6,7,8- hexahydronaphthalene and for the fluorescence emission spectra of 1,4diphenyl-1,3-cyclopentadiene, s-trans and s-cis structural analogs of DPB, respectively. The spectral...

  20. Combined two-photon excitation and d → f energy-transfer in Ir/lanthanide dyads with time-gated selection from a two-component emission spectrum.

    Science.gov (United States)

    Edkins, Robert M; Sykes, Daniel; Beeby, Andrew; Ward, Michael D

    2012-10-14

    In a pair of Ir/Eu and Ir/Tb dyads, two-photon excitation of the Ir-phenylpyridine chromophore at 780 nm is followed by partial d → f energy-transfer to give a combination of short-lived Ir-based (blue) and long-lived lanthanide-based (red or green) emission; these components can be selected separately by time-gated detection.

  1. Singlet Oxygen Photophysics in Liquid Solvents: Converging on a Unified Picture.

    Science.gov (United States)

    Bregnhøj, Mikkel; Westberg, Michael; Minaev, Boris F; Ogilby, Peter R

    2017-08-15

    Singlet oxygen, O 2 (a 1 Δ g ), the lowest excited electronic state of molecular oxygen, is an omnipresent part of life on earth. It is readily formed through a variety of chemical and photochemical processes, and its unique reactions are important not just as a tool in chemical syntheses but also in processes that range from polymer degradation to signaling in biological cells. For these reasons, O 2 (a 1 Δ g ) has been the subject of intense activity in a broad distribution of scientific fields for the past ∼50 years. The characteristic reactions of O 2 (a 1 Δ g ) kinetically compete with processes that deactivate this excited state to the ground state of oxygen, O 2 (X 3 Σ g - ). Moreover, O 2 (a 1 Δ g ) is ideally monitored using one of these deactivation channels: O 2 (a 1 Δ g ) → O 2 (X 3 Σ g - ) phosphorescence at 1270 nm. Thus, there is ample justification to study and control these competing processes, including those mediated by solvents, and the chemistry community has likewise actively tackled this issue. In themselves, the solvent-mediated radiative and nonradiative transitions between the three lowest-lying electronic states of oxygen [O 2 (X 3 Σ g - ), O 2 (a 1 Δ g ), and O 2 (b 1 Σ g + )] are relevant to issues at the core of modern chemistry. In the isolated oxygen molecule, these transitions are forbidden by quantum-mechanical selection rules. However, solvent molecules perturb oxygen in such a way as to make these transitions more probable. Most interestingly, the effect of a series of solvents on the O 2 (X 3 Σ g - )-O 2 (b 1 Σ g + ) transition, for example, can be totally different from the effect of the same series of solvents on the O 2 (X 3 Σ g - )-O 2 (a 1 Δ g ) transition. Moreover, a given solvent that appreciably increases the probability of a radiative transition generally does not provide a correspondingly viable pathway for nonradiative energy loss, and vice versa. The ∼50 years of experimental work leading to

  2. Efficiencies of singlet oxygen production and rate constants for oxygen quenching in the S1 state of dicyanonaphthalenes and related compounds.

    Science.gov (United States)

    Tanaka, Fujio; Tsumura, Kazuyuki; Furuta, Tomoaki; Iwamoto, Kenichi; Okamoto, Masami

    2008-01-01

    The quantum yield of singlet oxygen ((1)O(2) ((1)Delta(g))) production (Phi(Delta)) in the oxygen quenching of photoexcited states for 1,2-dicyanonaphthalene (1,2-DCNN), 1,4-dicyanonaphthalene (1,4-DCNN) and 2,3-dicyanonaphthalene (2,3-DCNN) in cyclohexane, benzene, and acetonitrile was measured using a time-resolved thermal lens (TRTL) technique, in order to determine the efficiency of singlet oxygen ((1)Delta(g)) production in the first excited singlet state (S(1)), (f(Delta)(S)). The efficiencies of singlet oxygen ((1)Delta(g)) production from the lowest triplet state (T(1)), (f(Delta)(T)), were nearly unity for all DCNNs in all the solvents. The values of f(Delta)(S) were fairly large for 1,2-DCNN (0.33-0.57) and 1,4-DCNN (0.33-0.66), but were close to zero for 2,3-DCNN. Rate constants for oxygen quenching in the S(1) state (k(q)(S)) obtained for these compounds were significantly smaller than diffusion-controlled rate constants. The kinetics for processes leading to production and no production of singlet oxygen is discussed on the basis of the values of f(Delta)(S) and k(q)(S). The results obtained regarding phenanthrene (PH), 9-cyanophenanthrene (9-CNPH), pyrene (PY) and 1-cyanopyrene (1-CNPY) are also discussed.

  3. Modulation of Energy Transfer into Sequential Electron Transfer upon Axial Coordination of Tetrathiafulvalene in an Aluminum(III) Porphyrin-Free-Base Porphyrin Dyad.

    Science.gov (United States)

    Poddutoori, Prashanth K; Bregles, Lucas P; Lim, Gary N; Boland, Patricia; Kerr, Russ G; D'Souza, Francis

    2015-09-08

    Axially assembled aluminum(III) porphyrin based dyads and triads have been constructed to investigate the factors that govern the energy and electron transfer processes in a perpendicular direction to the porphyrin plane. In the aluminum(III) porphyrin-free-base porphyrin (AlPor-Ph-H2Por) dyad, the AlPor occupies the basal plane, while the free-base porphyrin (H2Por) with electron withdrawing groups resides in the axial position through a benzoate spacer. The NMR, UV-visible absorption, and steady-state fluorescence studies confirm that the coordination of pyridine appended tetrathiafulvalene (TTF) derivative (TTF-py or TTF-Ph-py) to the dyad in noncoordinating solvents afford vertically arranged supramolecular self-assembled triads (TTF-py→AlPor-Ph-H2Por and TTF-Ph-py→AlPor-Ph-H2Por). Time-resolved studies revealed that the AlPor in dyad and triads undergoes photoinduced energy and/or electron transfer processes. Interestingly, the energy and electron donating/accepting nature of AlPor can be modulated by changing the solvent polarity or by stimulating a new competing process using a TTF molecule. In modest polar solvents (dichloromethane and o-dichlorobenzene), excitation of AlPor leads singlet-singlet energy transfer from the excited singlet state of AlPor ((1)AlPor*) to H2Por with a moderate rate constant (k(EnT)) of 1.78 × 10(8) s(-1). In contrast, excitation of AlPor in the triad results in ultrafast electron transfer from TTF to (1)AlPor* with a rate constant (k(ET)) of 8.33 × 10(9)-1.25 × 10(10) s(-1), which outcompetes the energy transfer from (1)AlPor* to H2Por and yields the primary radical pair TTF(+•)-AlPor(-•)-H2Por. A subsequent electron shift to H2Por generates a spatially well-separated TTF(+•)-AlPor-H2Por(-•) radical pair.

  4. Optical Energy Transfer Mechanisms: From Naphthalene to Biacetyl in Liquids and from Pyrazine to Biacetyl

    Directory of Open Access Journals (Sweden)

    Fuat Bayrakceken

    2012-01-01

    Full Text Available Optical energy transfer from naphthalene to biacetyl in liquids at room temperature is studied. Electronically excited naphthalene with 200–260 nm ultraviolet (UV light emits photons in its emission band and the emitted photons are absorbed by biacetyl, which, in turn, excites biacetyl phosphorescence. The resulting phosphorescence is very stable with emission peak at 545 nm for different excitation wavelengths from 200 to 260 nm. Similar optical energy transfer is also observed from pyrazine to biacetyl. The sensitization of biacetyl by several aromatic donors has been investigated in detail. An aromatic donor, pyrazine, is raised to its first excited singlet state by absorption of ultraviolet radiation. Excitation wavelengths were selected in the first - band of pyrazine. Intersystem crossing in pyrazine is sufficiently fast to give a triplet yield of almost unity as determined by the biacetyl method. The optical excess energy in the biacetyl will be released as light, which is sensitized fluorescence. Biacetyl is the simplest molecule among a wide range of -dicarbonyl compounds, which is important for photophysics and photochemistry applications.

  5. Focal point analysis of the singlet-triplet energy gap of octacene and larger acenes.

    Science.gov (United States)

    Hajgató, Balázs; Huzak, Matija; Deleuze, Michael S

    2011-08-25

    A benchmark theoretical study of the electronic ground state and of the vertical and adiabatic singlet-triplet (ST) excitation energies of n-acenes (C(4n+2)H(2n+4)) ranging from octacene (n = 8) to undecacene (n = 11) is presented. The T1 diagnostics of coupled cluster theory and further energy-based criteria demonstrate that all investigated systems exhibit predominantly a (1)A(g) singlet closed-shell electronic ground state. Singlet-triplet (S(0)-T(1)) energy gaps can therefore be very accurately determined by applying the principle of a focal point analysis (FPA) onto the results of a series of single-point and symmetry-restricted calculations employing correlation consistent cc-pVXZ basis sets (X = D, T, Q, 5) and single-reference methods [HF, MP2, MP3, MP4SDQ, CCSD, and CCSD(T)] of improving quality. According to our best estimates, which amount to a dual extrapolation of energy differences to the level of coupled cluster theory including single, double, and perturbative estimates of connected triple excitations [CCSD(T)] in the limit of an asymptotically complete basis set (cc-pV∞Z), the S(0)-T(1) vertical (adiabatic) excitation energies of these compounds amount to 13.40 (8.21), 10.72 (6.05), 8.05 (3.67), and 7.10 (2.58) kcal/mol, respectively. In line with the absence of Peierls distortions (bond length alternations), extrapolations of results obtained at this level for benzene (n = 1) and all studied n-acenes so far (n = 2-11) indicate a vanishing S(0)-T(1) energy gap, in the limit of an infinitely large polyacene, within an uncertainty of 1.5 kcal/mol (0.06 eV). Lacking experimental values for the S(0)-T(1) energy gaps of n-acenes larger than hexacene, comparison is made with recent optical and electrochemical determinations of the HOMO-LUMO band gap. Further issues such as scalar relativistic, core correlation, and diagonal Born-Oppenheimer corrections (DBOCs) are tentatively examined. © 2011 American Chemical Society

  6. Molecular reorganization of selected quinoline derivatives in the ground and excited states—Investigations via static DFT

    Energy Technology Data Exchange (ETDEWEB)

    Błaziak, Kacper; Panek, Jarosław J.; Jezierska, Aneta, E-mail: aneta.jezierska@chem.uni.wroc.pl [Faculty of Chemistry, University of Wrocław, ul. F. Joliot-Curie 14, 50-383 Wrocław (Poland)

    2015-07-21

    Quinoline derivatives are interesting objects to study internal reorganizations due to the observed excited-state-induced intramolecular proton transfer (ESIPT). Here, we report on computations for selected 12 quinoline derivatives possessing three kinds of intramolecular hydrogen bonds. Density functional theory was employed for the current investigations. The metric and electronic structure simulations were performed for the ground state and first excited singlet and triplet states. The computed potential energy profiles do not show a spontaneous proton transfer in the ground state, whereas excited states exhibit this phenomenon. Atoms in Molecules (AIM) theory was applied to study the nature of hydrogen bonding, whereas Harmonic Oscillator Model of aromaticity index (HOMA) provided data of aromaticity evolution as a derivative of the bridge proton position. The AIM-based topological analysis confirmed the presence of the intramolecular hydrogen bonding. In addition, using the theory, we were able to provide a quantitative illustration of bonding transformation: from covalent to the hydrogen. On the basis of HOMA analysis, we showed that the aromaticity of both rings is dependent on the location of the bridge proton. Further, the computed results were compared with experimental data available. Finally, ESIPT occurrence was compared for the three investigated kinds of hydrogen bridges, and competition between two bridges in one molecule was studied.

  7. Molecular reorganization of selected quinoline derivatives in the ground and excited states—Investigations via static DFT

    Science.gov (United States)

    Błaziak, Kacper; Panek, Jarosław J.; Jezierska, Aneta

    2015-07-01

    Quinoline derivatives are interesting objects to study internal reorganizations due to the observed excited-state-induced intramolecular proton transfer (ESIPT). Here, we report on computations for selected 12 quinoline derivatives possessing three kinds of intramolecular hydrogen bonds. Density functional theory was employed for the current investigations. The metric and electronic structure simulations were performed for the ground state and first excited singlet and triplet states. The computed potential energy profiles do not show a spontaneous proton transfer in the ground state, whereas excited states exhibit this phenomenon. Atoms in Molecules (AIM) theory was applied to study the nature of hydrogen bonding, whereas Harmonic Oscillator Model of aromaticity index (HOMA) provided data of aromaticity evolution as a derivative of the bridge proton position. The AIM-based topological analysis confirmed the presence of the intramolecular hydrogen bonding. In addition, using the theory, we were able to provide a quantitative illustration of bonding transformation: from covalent to the hydrogen. On the basis of HOMA analysis, we showed that the aromaticity of both rings is dependent on the location of the bridge proton. Further, the computed results were compared with experimental data available. Finally, ESIPT occurrence was compared for the three investigated kinds of hydrogen bridges, and competition between two bridges in one molecule was studied.

  8. Molecular reorganization of selected quinoline derivatives in the ground and excited states—Investigations via static DFT

    International Nuclear Information System (INIS)

    Błaziak, Kacper; Panek, Jarosław J.; Jezierska, Aneta

    2015-01-01

    Quinoline derivatives are interesting objects to study internal reorganizations due to the observed excited-state-induced intramolecular proton transfer (ESIPT). Here, we report on computations for selected 12 quinoline derivatives possessing three kinds of intramolecular hydrogen bonds. Density functional theory was employed for the current investigations. The metric and electronic structure simulations were performed for the ground state and first excited singlet and triplet states. The computed potential energy profiles do not show a spontaneous proton transfer in the ground state, whereas excited states exhibit this phenomenon. Atoms in Molecules (AIM) theory was applied to study the nature of hydrogen bonding, whereas Harmonic Oscillator Model of aromaticity index (HOMA) provided data of aromaticity evolution as a derivative of the bridge proton position. The AIM-based topological analysis confirmed the presence of the intramolecular hydrogen bonding. In addition, using the theory, we were able to provide a quantitative illustration of bonding transformation: from covalent to the hydrogen. On the basis of HOMA analysis, we showed that the aromaticity of both rings is dependent on the location of the bridge proton. Further, the computed results were compared with experimental data available. Finally, ESIPT occurrence was compared for the three investigated kinds of hydrogen bridges, and competition between two bridges in one molecule was studied

  9. Recoil detection of the lightest neutralino in MSSM singlet extensions

    International Nuclear Information System (INIS)

    Barger, Vernon; Lewis, Ian; McCaskey, Mat; Shaughnessy, Gabe; Yencho, Brian; Langacker, Paul

    2007-01-01

    We investigate the correlated predictions of singlet extended MSSM models for direct detection and the cosmological relic density of the lightest neutralino. To illustrate the general effects of the singlet, we take heavy sleptons and squarks. We apply CERN LEP (g-2) μ , and perturbativity constraints. We find that the WMAP upper bound on the cold dark matter density limits much of the parameter space to regions where the lightest neutralino can be discovered in recoil experiments. The results for the next-to-minimal supersymmetric standard model and U(1) ' -extended minimal supersymmetric standard model are typically similar to the MSSM since their light neutralinos have similar compositions and masses. In the nearly minimal supersymmetric standard model the neutralino is often very light and its recoil detection is within the reach of the CDMS II experiment. In general, most points in the parameter spaces of the singlet models we consider are accessible to the WARP experiment

  10. Impurities near an antiferromagnetic-singlet quantum critical point

    International Nuclear Information System (INIS)

    Mendes-Santos, T.; Costa, N. C.; Batrouni, G.

    2017-01-01

    Heavy-fermion systems and other strongly correlated electron materials often exhibit a competition between antiferromagnetic (AF) and singlet ground states. We examine the effect of impurities in the vicinity of such an AF-singlet quantum critical point (QCP), through an appropriately defined “impurity susceptibility” χimp, using exact quantum Monte Carlo simulations. Our key finding is a connection within a single calculational framework between AF domains induced on the singlet side of the transition and the behavior of the nuclear magnetic resonance (NMR) relaxation rate 1/T1. Furthermore, we show that local NMR measurements provide a diagnostic for the location of the QCP, which agrees remarkably well with the vanishing of the AF order parameter and large values of χimp.

  11. Gamma rays from the annihilation of singlet scalar dark matter

    Science.gov (United States)

    Yaguna, Carlos E.

    2009-03-01

    We consider an extension of the Standard Model by a singlet scalar that accounts for the dark matter of the Universe. Within this model we compute the expected gamma ray flux from the annihilation of dark matter particles in a consistent way. To do so, an updated analysis of the parameter space of the model is first presented. By enforcing the relic density constraint from the very beginning, the viable parameter space gets reduced to just two variables: the singlet mass and the higgs mass. Current direct detection constraints are then found to require a singlet mass larger than 50 GeV. Finally, we compute the gamma ray flux and annihilation cross section and show that a large fraction of the viable parameter space lies within the sensitivity of Fermi-GLAST.

  12. Gamma rays from the annihilation of singlet scalar dark matter

    International Nuclear Information System (INIS)

    Yaguna, Carlos E.

    2009-01-01

    We consider an extension of the Standard Model by a singlet scalar that accounts for the dark matter of the Universe. Within this model we compute the expected gamma ray flux from the annihilation of dark matter particles in a consistent way. To do so, an updated analysis of the parameter space of the model is first presented. By enforcing the relic density constraint from the very beginning, the viable parameter space gets reduced to just two variables: the singlet mass and the higgs mass. Current direct detection constraints are then found to require a singlet mass larger than 50 GeV. Finally, we compute the gamma ray flux and annihilation cross section and show that a large fraction of the viable parameter space lies within the sensitivity of Fermi-GLAST

  13. Singlet fission efficiency in tetracene-based organic solar cells

    International Nuclear Information System (INIS)

    Wu, Tony C.; Thompson, Nicholas J.; Congreve, Daniel N.; Hontz, Eric; Yost, Shane R.; Van Voorhis, Troy; Baldo, Marc A.

    2014-01-01

    Singlet exciton fission splits one singlet exciton into two triplet excitons. Using a joint analysis of photocurrent and fluorescence modulation under a magnetic field, we determine that the triplet yield within optimized tetracene organic photovoltaic devices is 153% ± 5% for a tetracene film thickness of 20 nm. The corresponding internal quantum efficiency is 127% ± 18%. These results are used to prove the effectiveness of a simplified triplet yield measurement that relies only on the magnetic field modulation of fluorescence. Despite its relatively slow rate of singlet fission, the measured triplet yields confirm that tetracene is presently the best candidate for use with silicon solar cells

  14. A Comparison of Singlet Oxygen Explicit Dosimetry (SOED and Singlet Oxygen Luminescence Dosimetry (SOLD for Photofrin-Mediated Photodynamic Therapy

    Directory of Open Access Journals (Sweden)

    Michele M. Kim

    2016-12-01

    Full Text Available Accurate photodynamic therapy (PDT dosimetry is critical for the use of PDT in the treatment of malignant and nonmalignant localized diseases. A singlet oxygen explicit dosimetry (SOED model has been developed for in vivo purposes. It involves the measurement of the key components in PDT—light fluence (rate, photosensitizer concentration, and ground-state oxygen concentration ([3O2]—to calculate the amount of reacted singlet oxygen ([1O2]rx, the main cytotoxic component in type II PDT. Experiments were performed in phantoms with the photosensitizer Photofrin and in solution using phosphorescence-based singlet oxygen luminescence dosimetry (SOLD to validate the SOED model. Oxygen concentration and photosensitizer photobleaching versus time were measured during PDT, along with direct SOLD measurements of singlet oxygen and triplet state lifetime (τΔ and τt, for various photosensitizer concentrations to determine necessary photophysical parameters. SOLD-determined cumulative [1O2]rx was compared to SOED-calculated [1O2]rx for various photosensitizer concentrations to show a clear correlation between the two methods. This illustrates that explicit dosimetry can be used when phosphorescence-based dosimetry is not feasible. Using SOED modeling, we have also shown evidence that SOLD-measured [1O2]rx using a 523 nm pulsed laser can be used to correlate to singlet oxygen generated by a 630 nm laser during a clinical malignant pleural mesothelioma (MPM PDT protocol by using a conversion formula.

  15. Efficient energy transfer and luminescence properties of Ca3Y(GaO)3(BO3)4:Tb3+,Eu3+as a green-to-red colour tunable phosphor under near-UV excitation.

    Science.gov (United States)

    Khan, Wasim Ullah; Li, Junhao; Li, Xiaohui; Wu, Qili; Yan, Jing; Xu, Yiqin; Xie, Feiyan; Shi, Jianxin; Wu, Mingmei

    2017-02-14

    A series of Ca 3 Y(GaO) 3 (BO 3 ) 4 :Tb 3+ ,Eu 3+ phosphors were prepared by a high-temperature solid-state reaction. Their phase structures were confirmed by powder X-ray diffraction and the element distribution was measured using transmission electron microscopy elemental mapping. The photoluminescence emission and excitation spectra and fluorescence lifetime were studied and discussed in detail. The results revealed that Eu 3+ ions can be efficiently sensitized by Tb 3+ ions under near-UV excitation. In addition, the energy transfer efficiency can be controlled by adjusting the ratio of Eu 3+ and Tb 3+ to realize colour tunable emission from green to red. For Ca 3 Y(GaO) 3 (BO 3 ) 4 :0.50Tb 3+ ,0.10Eu 3+ , the emission intensity at 425 K is 78.11% of that at 300 K, being available to near-UV LEDs.

  16. 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

  17. 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.)

  18. Voiced Excitations

    National Research Council Canada - National Science Library

    Holzricher, John

    2004-01-01

    To more easily obtain a voiced excitation function for speech characterization, measurements of skin motion, tracheal tube, and vocal fold, motions were made and compared to EM sensor-glottal derived...

  19. Induced quadrupolar singlet ground state of praseodymium in a modulated pyrochlore

    Science.gov (United States)

    van Duijn, J.; Kim, K. H.; Hur, N.; Ruiz-Bustos, R.; Adroja, D. T.; Bridges, F.; Daoud-Aladine, A.; Fernandez-Alonso, F.; Wen, J. J.; Kearney, V.; Huang, Q. Z.; Cheong, S.-W.; Perring, T. G.; Broholm, C.

    2017-09-01

    The complex structure and magnetism of Pr2 -xBixRu2O7 was investigated by neutron scattering and extended x-ray absorption fine structure. Pr has an approximate doublet ground state and the first excited state is a singlet. While the B -site (Ru) is well ordered throughout, this is not the case for the A -site (Pr/Bi). A broadened distribution for the Pr-O2 bond length at low temperature indicates the Pr environment varies from site to site even for x =0 . The environment about the Bi site is highly disordered ostensibly due to the 6 s lone pairs on Bi3 +. Correspondingly, we find that the non-Kramers doublet ground-state degeneracy, otherwise anticipated for Pr in the pyrochlore structure, is lifted so as to produce a quadrupolar singlet ground state with a spatially varying energy gap. For x =0 , below TN, the Ru sublattice orders antiferromagnetically, with propagation vector k =(0 ,0 ,0 ) as for Y2Ru2O7 . No ordering associated with the Pr sublattice is observed down to 100 mK. The low-energy magnetic response of Pr2 -xBixRu2O7 features a broad spectrum of magnetic excitations associated with inhomogeneous splitting of the Pr quasidoublet ground state. For x =0 (x =0.97 ), the spectrum is temperature dependent (independent). It appears disorder associated with Bi alloying enhances the inhomogeneous Pr crystal-field level splitting so that intersite interactions become irrelevant for x =0.97 . The structural complexity for the A -site may be reflected in the hysteretic uniform magnetization of B -site ruthenium in the Néel phase.

  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. Calculation of the ground and excited states of the Ne2 molecule by the variational cellular method

    International Nuclear Information System (INIS)

    Dias, A.M.; Rosato, A.

    1981-07-01

    The potential curves for the ground state 1 Σ + sub(g) and for the first singlet excited state 1 Σ + sub (u) of the Ne 2 molecule are determined by the Variational Cellular Method. From these curves some spectroscopical constants are obtained. Ionization energies of the excited state 1 Σ + sub (u) are calculated. (Author) [pt

  2. Excited State Studies of Polyacenes Using the All-Order Constricted Variational Density Functional Theory with Orbital Relaxation.

    Science.gov (United States)

    Senn, Florian; Krykunov, Mykhaylo

    2015-10-22

    For the polyacenes series from naphthalene to hexacene, we present the vertical singlet excitation energies 1 (1)La and 1 (1)Lb, as well as the first triplet excitation energies obtained by the all-order constricted variational density functional theory with orbital relaxation (R-CV(∞)-DFT). R-CV(∞)-DFT is a further development of variational density functional theory (CV(∞)-DFT), which has already been successfully applied for the calculation of the vertical singlet excitation energies (1)La and (1)Lb for polyacenes,15 and we show that one obtains consistent excitation energies using the local density approximation as a functional for singlet as well as for triplet excitations when going beyond the linear response theory. Furthermore, we apply self-consistent field density functional theory (ΔSCF-DFT) and compare the obtained excitation energies for the first triplet excitations T1, where, due to the character of the transition, ΔSCF-DFT and R-CV(∞)-DFT become numerically equivalent, and for the singlet excitations 1 (1)La and 1 (1)Lb, where the two methods differ.

  3. Calculation of the ground and excited states of the Ne2 molecule by the Variational Cellular Method

    International Nuclear Information System (INIS)

    Dias, A.M.; Rosato, A.

    1982-01-01

    The potential curves for the ground 1 μ + sub(g) and for the first singlet excited state 1 μ + sub(u) of the Ne 2 molecule are determined by the Variational Cellular Method. From these curves some spectroscopical constants are obtained. Ionization energies of the excited state 1 μ + sub(u) are calculated. (Author) [pt

  4. Intramolecular proton-transfer processes starting at higher excited states: a fluorescence study on 2-butylamino-6-methyl-4-nitropyridine N-oxide in nonpolar solutions

    NARCIS (Netherlands)

    de Klerk, J.S.; Szemik-Hojniak, A.; Ariese, F.; Gooijer, C.

    2007-01-01

    This article describes the exceptional photophysics of 2-butylamino-6- methyl-4-nitropyridine N-oxide (2B6M). It is known from the literature that this compound may undergo excited-state intra- or intermolecular protontransfer reactions. In nonpolar solvents, 2B6M exhibits an unusual fluorescence

  5. Reversible Photochemical Control of Singlet Oxygen Generation Using Diarylethene Photochromic Switches

    NARCIS (Netherlands)

    Hou, Lili; Zhang, Xiaoyan; Pijper, Thomas C.; Browne, Wesley R.; Feringa, Bernard

    2014-01-01

    Reversible noninvasive control over the generation of singlet oxygen is demonstrated in a bicomponent system comprising a diarylethene photochromic switch and a porphyrin photosensitizer by selective irradiation at distinct wavelengths. The efficient generation of singlet oxygen by the

  6. Excited state dynamics and isomerization in ruthenium sulfoxide complexes.

    Science.gov (United States)

    King, Albert W; Wang, Lei; Rack, Jeffrey J

    2015-04-21

    Molecular photochromic compounds are those that interconvert between two isomeric forms with light. The two isomeric forms display distinct electronic and molecular structures and must not be in equilibrium with one another. These light-activated molecular switch compounds have found wide application in areas of study ranging from chemical biology to materials science, where conversion from one isomeric form to another by light prompts a response in the environment (e.g., protein or polymeric material). Certain ruthenium and osmium polypyridine sulfoxide complexes are photochromic. The mode of action is a phototriggered isomerization of the sulfoxide from S- to O-bonded. The change in ligation drastically alters both the spectroscopic and electrochemical properties of the metal complex. Our laboratory has pioneered the preparation and study of these complexes. In particular, we have applied femtosecond pump-probe spectroscopy to reveal excited state details of the isomerization mechanism. The data from numerous complexes allowed us to predict that the isomerization was nonadiabatic in nature, defined as occurring from a S-bonded triplet excited state (primarily metal-to-ligand charge transfer in character) to an O-bonded singlet ground state potential energy surface. This prediction was corroborated by high-level density functional theory calculations. An intriguing aspect of this reactivity is the coupling of nuclear motion to the electronic wave function and how this coupling affects motions productive for isomerization. In an effort to learn more about this coupling, we designed a project to examine phototriggered isomerization in bis-sulfoxide complexes. The goal of these studies was to determine whether certain complexes could be designed in which a single photon excitation event would prompt two sulfoxide isomerizations. We employed chelating sulfoxides in this study and found that both the nature of the chelate ring and the R group on the sulfoxide affect

  7. Influence of donor-donor transport on excitation energy transfer in binary system C102-C6 doped in Poly (methylmethacrylate)

    Science.gov (United States)

    Singh, Khushboo; Joshi, G. C.; Gairola, R. P.

    2018-03-01

    Energy transfer and migration from Coumarin102 to Coumarin6 in Poly (methylmethacrylate) have been investigated using steady-state and time domain fluorescence spectroscopy. It is found that the influence of energy migration in energy transfer can be described quite convincingly on the basis of theories of Loring, Anderson and Fayer (LAF) and Huber. At higher acceptor concentrations direct donor-acceptor transfer occurs through Förster mechanism. It is suggested to use a mixture of these two dyes in the LSCs.

  8. Competitive Energy and Electron Transfer in β-Functionalized Free-Base Porphyrin-Zinc Porphyrin Dimer Axially Coordinated to C60: Synthesis, Supramolecular Formation and Excited-State Processes.

    Science.gov (United States)

    Hu, Yi; Thomas, Michael B; Jinadasa, R G Waruna; Wang, Hong; D'Souza, Francis

    2017-09-18

    Simultaneous occurrence of energy and electron transfer events involving different acceptor sites in a newly assembled supramolecular triad comprised of covalently linked free-base porphyrin-zinc porphyrin dyad, H 2 P-ZnP axially coordinated to electron acceptor fullerene, has been successfully demonstrated. The dyad was connected through the β-pyrrole positions of the porphyrin macrocycle instead of the traditionally used meso-positions for better electronic communication. Interestingly, the β-pyrrole functionalization modulated the optical properties to such an extent that it was possible to almost exclusively excite the zinc porphyrin entity in the supramolecular triad. The measured binding constant for the complex with 1:1 molecular stoichiometry was in the order of 10 4  m -1 revealing moderately stable complex formation. An energy level diagram constructed using optical, electrochemical and computational results suggested that both the anticipated energy and electron events are thermodynamically feasible in the triad. Consequently, it was possible to demonstrate occurrence of excited state energy transfer to the covalently linked H 2 P, and electron transfer to the coordinated ImC 60 from studies involving steady-state and time-resolved emission, and femto- and nanosecond transient absorption studies. The estimated energy transfer was around 67 % in the dyad with a rate constant of 1.1×10 9  s -1 . In the supramolecular triad, the charge separated state was rather long-lived although it was difficult to arrive the exact lifetime of charge separated state from nanosecond transient spectral studies due to overlap of strong triplet excited signals of porphyrin in the monitoring wavelength window. Nevertheless, simultaneous occurrence of energy and electron transfer in the appropriately positioned energy and electron acceptor entities in a supramolecular triad was possible to demonstrate in the present study, a step forward to unraveling the complex

  9. Flavor-singlet spectrum in multi-flavor QCD

    Energy Technology Data Exchange (ETDEWEB)

    Aoki, Yasamichi; Rinaldi, Enrico

    2017-06-18

    Studying SU(3) gauge theories with increasing number of light fermions is relevant both for understanding the strong dynamics of QCD and for constructing strongly interacting extensions of the Standard Model (e.g. UV completions of composite Higgs models). In order to contrast these many-flavors strongly interacting theories with QCD, we study the flavor-singlet spectrum as an interesting probe. In fact, some composite Higgs models require the Higgs boson to be the lightest flavor-singlet scalar in the spectrum of a strongly interacting new sector with a well defined hierarchy with the rest of the states. Moreover, introducing many light flavors at fixed number of colors can influence the dynamics of the lightest flavor-singlet pseudoscalar. We present the on-going study of these flavor-singlet channels using multiple interpolating operators on high-statistics ensembles generated by the LatKMI collaboration and we compare results with available data obtained by the Lattice Strong Dynamics collaboration. For the theory with 8 flavors, the two collaborations have generated configurations that complement each others with the aim to tackle the massless limit using the largest possible volumes.

  10. Status of the scalar singlet dark matter model

    Science.gov (United States)

    Athron, Peter; Balázs, Csaba; Bringmann, Torsten; Buckley, Andy; Chrząszcz, Marcin; Conrad, Jan; Cornell, Jonathan M.; Dal, Lars A.; Edsjö, Joakim; Farmer, Ben; Jackson, Paul; Kahlhoefer, Felix; Krislock, Abram; Kvellestad, Anders; McKay, James; Mahmoudi, Farvah; Martinez, Gregory D.; Putze, Antje; Raklev, Are; Rogan, Christopher; Saavedra, Aldo; Savage, Christopher; Scott, Pat; Serra, Nicola; Weniger, Christoph; White, Martin

    2017-08-01

    One of the simplest viable models for dark matter is an additional neutral scalar, stabilised by a Z_2 symmetry. Using the GAMBIT package and combining results from four independent samplers, we present Bayesian and frequentist global fits of this model. We vary the singlet mass and coupling along with 13 nuisance parameters, including nuclear uncertainties relevant for direct detection, the local dark matter density, and selected quark masses and couplings. We include the dark matter relic density measured by Planck, direct searches with LUX, PandaX, SuperCDMS and XENON100, limits on invisible Higgs decays from the Large Hadron Collider, searches for high-energy neutrinos from dark matter annihilation in the Sun with IceCube, and searches for gamma rays from annihilation in dwarf galaxies with the Fermi-LAT. Viable solutions remain at couplings of order unity, for singlet masses between the Higgs mass and about 300 GeV, and at masses above ˜ 1 TeV. Only in the latter case can the scalar singlet constitute all of dark matter. Frequentist analysis shows that the low-mass resonance region, where the singlet is about half the mass of the Higgs, can also account for all of dark matter, and remains viable. However, Bayesian considerations show this region to be rather fine-tuned.

  11. Atmospheric and Solar Neutrinos with a Heavy Singlet

    CERN Document Server

    King, S F

    1998-01-01

    We follow a minimalistic approach to neutrino masses, by introducing a single heavy singlet $N$ into the standard model (or supersymmetric standard model) with a heavy Majorana mass $M$, which couples as a single right-handed neutrino in a Dirac fashion to leptons, and induces a single light see-saw mass $m_{\

  12. Bounds on neutrino mixing with exotic singlet neutrinos E

    Indian Academy of Sciences (India)

    This allows us to neglect the masses of light (known) neutrinos. In the SM the process occurs at tree level via light neutrino exchange in t- and u-channels. The neu- trino mixing in special cases (e.g. mixing of exotic and/or singlets), induces non-diagonal light–heavy neutrino neutral currents and additional contribution to the ...

  13. Singlet Oxygen Generation Mediated By Silicon Nanocrystal Assemblies

    Science.gov (United States)

    2011-01-01

    efficient red-orange emission under illumination by ultraviolet light appeared. Increase of the etching time results in significant increase of the...in the singlet oxygen-mediated oxidation of organic compounds K. Loponov, B. Goller, A. Moskalenko, D. Kovalev, A. Lapkin Journal of Photochemistry

  14. Real gauge singlet scalar extension of the Standard Model: A ...

    Indian Academy of Sciences (India)

    2013-03-05

    Mar 5, 2013 ... Abstract. The simplest extension of Standard Model (SM) is considered in which a real SM gauge singlet scalar with an additional discrete symmetry Z2 is introduced to SM. This additional scalar can be a viable candidate of cold dark matter (CDM) since the stability of S is achieved by the application of Z2 ...

  15. Explorative computational study of the singlet fission process

    NARCIS (Netherlands)

    Havenith, Remco W. A.; de Gier, Hilde D.; Broer, Ria

    2012-01-01

    Different ab initio methods, namely multi-reference and nonorthogonal configuration interaction techniques, are explored for their applicability in studying the singlet fission problem. It has been shown for 2-methyl-1,5-hexadiene that the (TT)-T-1 state can be identified using multi-reference

  16. 1,3-Diphenylisobenzofuran: a Model Chromophore for Singlet Fission

    Czech Academy of Sciences Publication Activity Database

    Johnson, J. C.; Michl, Josef

    2017-01-01

    Roč. 375, č. 5 (2017), č. článku 80. ISSN 2365-0869 R&D Projects: GA ČR GA15-19143S Institutional support: RVO:61388963 Keywords : 1,3-diphenylisobenzofuran * photophysics * solar energy * singlet fission * covalent dimers Subject RIV: CF - Physical ; Theoretical Chemistry OBOR OECD: Physical chemistry Impact factor: 4.033, year: 2016

  17. Status of the scalar singlet dark matter model

    Energy Technology Data Exchange (ETDEWEB)

    Athron, Peter; Balazs, Csaba [Monash University, School of Physics and Astronomy, Melbourne, VIC (Australia); Australian Research Council Centre of Excellence for Particle Physics at the Tera-scale (Australia); Bringmann, Torsten; Dal, Lars A.; Krislock, Abram; Raklev, Are [University of Oslo, Department of Physics, Oslo (Norway); Buckley, Andy [University of Glasgow, SUPA, School of Physics and Astronomy, Glasgow (United Kingdom); Chrzaszcz, Marcin [Universitaet Zuerich, Physik-Institut, Zurich (Switzerland); Polish Academy of Sciences, H. Niewodniczanski Institute of Nuclear Physics, Krakow (Poland); Conrad, Jan; Edsjoe, Joakim; Farmer, Ben [AlbaNova University Centre, Oskar Klein Centre for Cosmoparticle Physics, Stockholm (Sweden); Stockholm University, Department of Physics, Stockholm (Sweden); Cornell, Jonathan M. [McGill University, Department of Physics, Montreal, QC (Canada); Jackson, Paul; White, Martin [Australian Research Council Centre of Excellence for Particle Physics at the Tera-scale (Australia); University of Adelaide, Department of Physics, Adelaide, SA (Australia); Kahlhoefer, Felix [DESY, Hamburg (Germany); Kvellestad, Anders; Savage, Christopher [NORDITA, Stockholm (Sweden); McKay, James; Scott, Pat [Imperial College London, Department of Physics, Blackett Laboratory, London (United Kingdom); Mahmoudi, Farvah [Univ. Lyon, Univ. Lyon 1, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, Saint-Genis-Laval (France); CERN, Theoretical Physics Department, Geneva (Switzerland); Martinez, Gregory D. [University of California, Physics and Astronomy Department, Los Angeles, CA (United States); Putze, Antje [LAPTh, Universite de Savoie, CNRS, Annecy-le-Vieux (France); Rogan, Christopher [Harvard University, Department of Physics, Cambridge, MA (United States); Saavedra, Aldo [Australian Research Council Centre of Excellence for Particle Physics at the Tera-scale (Australia); The University of Sydney, Centre for Translational Data Science, Faculty of Engineering and Information Technologies, School of Physics, Sydney, NSW (Australia); Serra, Nicola [Universitaet Zuerich, Physik-Institut, Zurich (Switzerland); Weniger, Christoph [University of Amsterdam, GRAPPA, Institute of Physics, Amsterdam (Netherlands); Collaboration: The GAMBIT Collaboration

    2017-08-15

    One of the simplest viable models for dark matter is an additional neutral scalar, stabilised by a Z{sub 2} symmetry. Using the GAMBIT package and combining results from four independent samplers, we present Bayesian and frequentist global fits of this model. We vary the singlet mass and coupling along with 13 nuisance parameters, including nuclear uncertainties relevant for direct detection, the local dark matter density, and selected quark masses and couplings. We include the dark matter relic density measured by Planck, direct searches with LUX, PandaX, SuperCDMS and XENON100, limits on invisible Higgs decays from the Large Hadron Collider, searches for high-energy neutrinos from dark matter annihilation in the Sun with IceCube, and searches for gamma rays from annihilation in dwarf galaxies with the Fermi-LAT. Viable solutions remain at couplings of order unity, for singlet masses between the Higgs mass and about 300 GeV, and at masses above ∝ 1 TeV. Only in the latter case can the scalar singlet constitute all of dark matter. Frequentist analysis shows that the low-mass resonance region, where the singlet is about half the mass of the Higgs, can also account for all of dark matter, and remains viable. However, Bayesian considerations show this region to be rather fine-tuned. (orig.)

  18. Status of the scalar singlet dark matter model

    International Nuclear Information System (INIS)

    Athron, Peter; Balazs, Csaba; Bringmann, Torsten; Dal, Lars A.; Krislock, Abram; Raklev, Are; Buckley, Andy; Chrzaszcz, Marcin; Conrad, Jan; Edsjoe, Joakim; Farmer, Ben; Cornell, Jonathan M.; Jackson, Paul; White, Martin; Kahlhoefer, Felix; Kvellestad, Anders; Savage, Christopher; McKay, James; Scott, Pat; Mahmoudi, Farvah; Martinez, Gregory D.; Putze, Antje; Rogan, Christopher; Saavedra, Aldo; Serra, Nicola; Weniger, Christoph

    2017-01-01

    One of the simplest viable models for dark matter is an additional neutral scalar, stabilised by a Z 2 symmetry. Using the GAMBIT package and combining results from four independent samplers, we present Bayesian and frequentist global fits of this model. We vary the singlet mass and coupling along with 13 nuisance parameters, including nuclear uncertainties relevant for direct detection, the local dark matter density, and selected quark masses and couplings. We include the dark matter relic density measured by Planck, direct searches with LUX, PandaX, SuperCDMS and XENON100, limits on invisible Higgs decays from the Large Hadron Collider, searches for high-energy neutrinos from dark matter annihilation in the Sun with IceCube, and searches for gamma rays from annihilation in dwarf galaxies with the Fermi-LAT. Viable solutions remain at couplings of order unity, for singlet masses between the Higgs mass and about 300 GeV, and at masses above ∝ 1 TeV. Only in the latter case can the scalar singlet constitute all of dark matter. Frequentist analysis shows that the low-mass resonance region, where the singlet is about half the mass of the Higgs, can also account for all of dark matter, and remains viable. However, Bayesian considerations show this region to be rather fine-tuned. (orig.)

  19. Flavor-singlet spectrum in multi-flavor QCD

    Science.gov (United States)

    Aoki, Yasumichi; Aoyama, Tatsumi; Bennett, Ed; Kurachi, Masafumi; Maskawa, Toshihide; Miura, Kohtaroh; Nagai, Kei-ichi; Ohki, Hiroshi; Rinaldi, Enrico; Shibata, Akihiro; Yamawaki, Koichi; Yamazaki, Takeshi

    2018-03-01

    Studying SU(3) gauge theories with increasing number of light fermions is relevant both for understanding the strong dynamics of QCD and for constructing strongly interacting extensions of the Standard Model (e.g. UV completions of composite Higgs models). In order to contrast these many-flavors strongly interacting theories with QCD, we study the flavor-singlet spectrum as an interesting probe. In fact, some composite Higgs models require the Higgs boson to be the lightest flavor-singlet scalar in the spectrum of a strongly interacting new sector with a well defined hierarchy with the rest of the states. Moreover, introducing many light flavors at fixed number of colors can influence the dynamics of the lightest flavor-singlet pseudoscalar. We present the on-going study of these flavor-singlet channels using multiple interpolating operators on high-statistics ensembles generated by the LatKMI collaboration and we compare results with available data obtained by the Lattice Strong Dynamics collaboration. For the theory with 8 flavors, the two collaborations have generated configurations that complement each others with the aim to tackle the massless limit using the largest possible volumes.

  20. Label-free electrochemical detection of singlet oxygen protein damage

    Czech Academy of Sciences Publication Activity Database

    Vargová, Veronika; Gimenez, R.E.; Černocká, Hana; Trujillo, D.C.; Tulli, F.; Zanini, V.I.P.; Paleček, Emil; Borsarelli, C.D.; Ostatná, Veronika

    2016-01-01

    Roč. 187, JAN 2016 (2016), s. 662-669 ISSN 0013-4686 R&D Projects: GA ČR GA13-00956S Institutional support: RVO:68081707 Keywords : singlet oxygen protein damage * surface-attached protein stability * mercury and carbon electrodes Subject RIV: BO - Biophysics Impact factor: 4.798, year: 2016

  1. Observation of the energy transfer sequence in an organic host–guest system of a luminescent polymer and a phosphorescent molecule

    Energy Technology Data Exchange (ETDEWEB)

    Basel, Tek; Sun, Dali; Gautam, Bhoj; Valy Vardeny, Z., E-mail: val@physics.utah.edu

    2014-11-15

    We used steady state optical spectroscopies such as photoluminescence and photoinduced absorption (PA), and magnetic-field PA (MPA) for studying the energy transfer dynamics in films and organic light emitting diodes (OLED) based on host–guest blends with different guest concentrations of the fluorescent polymer poly-[2-methoxy, 5-(2′-ethyl-hexyloxy)phenylene vinylene] (MEHPPV-host), and phosphorescent molecule PtII-tetraphenyltetrabenzoporphyrin [Pt(tpbp); guest]. We show that the energy transfer process between the excited states of the host polymer and guest molecule takes a ‘ping-pong’ type sequence, because the lowest guest triplet exciton energy, E{sub T}(guest), lies higher than that of the host, E{sub T}(host). Upon photon excitation the photogenerated singlet excitons in the host polymer chains first undergo a Förster resonant energy transfer process to the guest singlet manifold, which subsequently reaches E{sub T}(guest) by intersystem crossing. Because E{sub T}(guest)>E{sub T}(host) there is a subsequent Dexter type energy transfer from E{sub T}(guest) to E{sub T}(host). This energy transfer sequence has profound influence on the photoluminescence and electroluminescence emission spectra in both films and OLED devices based on the MEHPPV-Pt(tpbp) system. - Highlights: • We studied electroluminescence of OLEDs based on host–guest blends. • The emission efficiency decreases with the guest concentration. • We found a dominant Dexter energy transfer from the triplet(guest) to triplet(host). • Energy transfer occurs from the host to guest and back to the host again.

  2. Spectral variations and energy transfer processes on both Er 3+ ion concentration and excitation densities in Yb 3+-Er 3+ codoped LaF3 materials

    International Nuclear Information System (INIS)

    Zhang Jisen; Qin Weiping; Zhao Dan; Degejihu; Zhang Jishuang; Wang Yan; Cao Chunyan

    2007-01-01

    In comparison with the up-conversion spectra of Yb 3+ -Er 3+ codopded systems reported previously, the interesting intensity changes of up-conversion luminescence between the violet, the blue, the green and the red on the both Er 3+ ion concentration and excitation density with 978 nm laser diodes as an excitation source were observed in Yb 3+ -Er 3+ codopded LaF 3 powders. In order to clarify the change mechanisms, the up-conversion spectra of LaF 3 : 10 mol% Yb 3+ , 0.5 mol% Er 3+ and LaF 3 : 10 mol% Yb 3+ , 1 mol% Er 3+ were investigated and the results indicated that the cross-relaxation processes between Er 3+ ions and the thermal population of the 2 H 11/2 level play significant roles

  3. Relaxed structure of typical nitro explosives in the excited state: Observation, implication and application

    Science.gov (United States)

    Chu, Genbai; Yang, Zuhua; Xi, Tao; Xin, Jianting; Zhao, Yongqiang; He, Weihua; Shui, Min; Gu, Yuqiu; Xiong, Ying; Xu, Tao

    2018-04-01

    Understanding the structural, geometrical, and chemical changes that occur after an electronic excitation is essential to elucidate the inherent mechanism of nitro explosives. Herein, relaxed structures of typical nitro explosives in the lowest singlet excited state are investigated using time-dependent density functional theory. During the excitation process, the nitro group is activated and relaxes via geometrical change. The five explosives RDX, HMX, CL-20, PETN, and LLM-105 exhibit similar relaxed structures, and the impact sensitivity is related to their excitation energy. High-sensitivity δ-HMX has a lower excitation energy for relaxed structure than β-HMX. This study offers novel insight into energetic materials.

  4. Morphological Tuning of the Energetics in Singlet Fission Organic Solar Cells

    NARCIS (Netherlands)

    Lin, Yun Hui L; Fusella, Michael A.; Kozlov, Oleg V.; Lin, Xin; Kahn, Antoine; Pshenichnikov, Maxim S.; Rand, Barry P.

    2016-01-01

    Effective singlet fission solar cells require both fast and efficient singlet fission as well as favorable energetics for harvesting the resulting triplet excitons. Notable progress has been made to engineer materials with rapid and efficient singlet fission, but the ability to control the

  5. Sea quark matrix elements and flavor singlet spectroscopy on the lattice

    International Nuclear Information System (INIS)

    Lagae, J.F.

    1996-01-01

    I summarize the results of three recent lattice studies which use stochastic estimator techniques in order to investigate the flavor singlet dynamics in QCD. These include a measurement of the pion-nucleon σ-term, the computation of the flavor singlet axial coupling constant of the nucleon and a determination of flavor singlet meson screening lengths in finite temperature QCD

  6. Singlet molecular oxygen on natural snow and ice

    Science.gov (United States)

    Bower, J. P.; Anastasio, C.

    2010-12-01

    Singlet molecular oxygen (1O2*) is a reactive intermediate formed when a chromophore absorbs light and subsequently transfers energy to dissolved oxygen. As an oxidant, 1O2* reacts rapidly with a number of electron-rich environmental pollutants. In our work, we show enhanced kinetics for 1O2* in frozen solutions, where its rate of formation (Rf) and steady state concentration ([1O2*]) can be many orders of magnitude higher than found in the same unfrozen solution. Our goal here is to identify the contribution of 1O2* to the decay of pollutants on snow and ice. We conducted experiments in laboratory solutions made to simulate the concentrations and characteristics of natural snow, as well as in natural snow collected in the Sierra Nevada mountains of California and at Summit, Greenland. Natural snow contains a mixture of inorganic salts and organic species that can function as sources and/or sinks for oxidants, as well as contribute colligative control on the volume of quasi-liquid layers that occur at the surface and grain boundaries of ice. In our experiments, solutions typically contained up to five components: (1) Furfuryl alcohol (FFA), a commonly used probe for 1O2*, (2) Rose Bengal (RB), a 1O2* sensitizer, (3) HOOH, a photochemical precursor for hydroxyl radical (●OH), (4) glycerol to simulate unknown, naturally occurring sinks for ●OH, and (5) sodium sulfate to control the total concentration of solutes. We illuminated samples in a temperature-controlled solar simulator and subsequently measured the loss of FFA using high performance liquid chromatography. To differentiate reactions of 1O2* from other sinks (e.g. ●OH), selective sink species were added to determine the fraction of FFA loss due to direct photolysis, reaction with 1O2*, and reaction with ●OH. We verified reactions of 1O2* with FFA by two methods. First, we utilized the kinetic solvent isotope effect, where an enhancement of FFA loss in a mixture of D2O/water is indicative 1O2* since [1

  7. Approximate inclusion of triple excitations in combined coupled cluster/molecular mechanics: Calculations of electronic excitation energies in solution for acrolein, water, formamide, and n-methylacetamide

    DEFF Research Database (Denmark)

    Sneskov, Kristian; Gras, Eduard Matito; Kongsted, Jacob

    2010-01-01

    as being applicable for averaging over many solvent configurations derived from, for example, molecular simulations. We test the proposed model using as a benchmark the two lowest-lying valence singlet excitations (n → π* and π → π*) of acrolein, formamide, and N-methylacetamide in aqueous solution as well...

  8. Pulsed electron-beam-sustained discharge in oxygen-containing gas mixtures: electrical characteristics, spectroscopy,and singlet oxygen yield

    International Nuclear Information System (INIS)

    Vagin, Nikolai P; Ionin, Andrei A; Klimachev, Yu M; Kotkov, A A; Podmar'kov, Yu P; Seleznev, L V; Sinitsyn, D V; Frolov, M P; Yuryshev, Nikolai N; Kochetov, Igor' V; Napartovich, A P; Hager, G D

    2004-01-01

    The electrical and spectroscopic characteristics of electron-beam-sustained discharge (EBSD) in oxygen and oxygen-containing gas mixtures are studied experimentally under gas pressures up to 100 Torr in a large excitation volume (∼18 L). It is shown that the EBSD in pure oxygen and its mixtures with inert gases is unstable and is characterised by a small specific energy contribution. The addition of small amounts (∼1%-10%) of carbon monoxide or hydrogen to oxygen or its mixtures with inert gases considerably improves the stability of the discharge, while the specific energy contribution W increases by more then an order of magnitude, achieving ∼6.5 kJ L -1 atm -1 per molecular component of the gas mixture. A part of the energy supplied to the EBSD is spent to excite vibrational levels of molecular additives. This was demonstrated experimentally by the initiation of a CO laser based on the O 2 : Ar : CO = 1 : 1 : 0.1 mixture. Experimental results on spectroscopy of the excited electronic states O 2 (a 1 Δ g ) and O 2 (b 1 Σ g + ), of oxygen formed in the EBSD are presented. A technique was worked out for measuring the concentration of singlet oxygen in the O 2 (a 1 Δ g ) state in the afterglow of the pulsed EBSD by comparing with the radiation intensity of singlet oxygen of a given concentration produced in a chemical generator. Preliminary measurements of the singlet-oxygen yield in the EBSD show that its value ∼3% for W ∼ 1.0 kJ L -1 atm -1 is in agreement with the theoretical estimate. Theoretical calculations performed for W ∼ 6.5 kJ L -1 atm -1 at a fixed temperature show that the singlet-oxygen yield may be ∼20%, which is higher than the value required to achieve the lasing threshold in an oxygen-iodine laser at room temperature. (laser applications and other topics in quantum electronics)

  9. Energy transfer upon collision of selectively excited CO2 molecules: State-to-state cross sections and probabilities for modeling of atmospheres and gaseous flows.

    Science.gov (United States)

    Lombardi, A; Faginas-Lago, N; Pacifici, L; Grossi, G

    2015-07-21

    Carbon dioxide molecules can store and release tens of kcal/mol upon collisions, and such an energy transfer strongly influences the energy disposal and the chemical processes in gases under the extreme conditions typical of plasmas and hypersonic flows. Moreover, the energy transfer involving CO2 characterizes the global dynamics of the Earth-atmosphere system and the energy balance of other planetary atmospheres. Contemporary developments in kinetic modeling of gaseous mixtures are connected to progress in the description of the energy transfer, and, in particular, the attempts to include non-equilibrium effects require to consider state-specific energy exchanges. A systematic study of the state-to-state vibrational energy transfer in CO2 + CO2 collisions is the focus of the present work, aided by a theoretical and computational tool based on quasiclassical trajectory simulations and an accurate full-dimension model of the intermolecular interactions. In this model, the accuracy of the description of the intermolecular forces (that determine the probability of energy transfer in molecular collisions) is enhanced by explicit account of the specific effects of the distortion of the CO2 structure due to vibrations. Results show that these effects are important for the energy transfer probabilities. Moreover, the role of rotational and vibrational degrees of freedom is found to be dominant in the energy exchange, while the average contribution of translations, under the temperature and energy conditions considered, is negligible. Remarkable is the fact that the intramolecular energy transfer only involves stretching and bending, unless one of the colliding molecules has an initial symmetric stretching quantum number greater than a threshold value estimated to be equal to 7.

  10. 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...

  11. Multiconfiguration pair-density functional theory for doublet excitation energies and excited state geometries: the excited states of CN.

    Science.gov (United States)

    Bao, Jie J; Gagliardi, Laura; Truhlar, Donald G

    2017-11-15

    Multiconfiguration pair-density functional theory (MC-PDFT) is a post multiconfiguration self-consistent field (MCSCF) method with similar performance to complete active space second-order perturbation theory (CASPT2) but with greater computational efficiency. Cyano radical (CN) is a molecule whose spectrum is well established from experiments and whose excitation energies have been used as a testing ground for theoretical methods to treat excited states of open-shell systems, which are harder and much less studied than excitation energies of closed-shell singlets. In the present work, we studied the adiabatic excitation energies of CN with MC-PDFT. Then we compared this multireference (MR) method to some single-reference (SR) methods, including time-dependent density functional theory (TDDFT) and completely renormalized equation-of-motion coupled-cluster theory with singles, doubles and noniterative triples [CR-EOM-CCSD(T)]; we also compared to some other MR methods, including configuration interaction singles and doubles (MR-CISD) and multistate CASPT2 (MS-CASPT2). Through a comparison between SR and MR methods, we achieved a better appreciation of the need to use MR methods to accurately describe higher excited states, and we found that among the MR methods, MC-PDFT stands out for its accuracy for the first four states out of the five doublet states studied this paper; this shows its efficiency for calculating doublet excited states.

  12. Roles of binding energy and diffusion length of singlet and triplet excitons in organic heterojunction solar cells

    International Nuclear Information System (INIS)

    Narayan, Monishka Rita; Singh, Jai

    2012-01-01

    The influence of binding energy and diffusion length on the dissociation of excitons in organic solids is studied. The binding energy and excitonic Bohr radius of singlet and triplet excitons are calculated and compared using the dissociation energy of 0.3 eV, which is provided by the lowest unoccupied molecular orbital offset in heterojunction organic solar cells. A relation between the diffusion coefficient and diffusion length of singlet and triplet excitons is derived using the Foerster and Dexter transfer processes and are plotted as a function of the donor-acceptor separation. The diffusion length reduces nearly to a zero if the distance between donor and acceptor is increased to more than 1.5 nm. It is found that the donor-acceptor separation needs to be ≤ 1.5 nm for easy dissociation on singlet excitons leading to better conversion efficiency in heterojunction organic solar cells. (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  13. Roles of binding energy and diffusion length of singlet and triplet excitons in organic heterojunction solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Narayan, Monishka Rita [Centre for Renewable Energy and Low Emission Technology, Charles Darwin University, Darwin, NT 0909 (Australia); Singh, Jai [School of Engineering and IT, Charles Darwin University, Darwin, NT 0909 (Australia)

    2012-12-15

    The influence of binding energy and diffusion length on the dissociation of excitons in organic solids is studied. The binding energy and excitonic Bohr radius of singlet and triplet excitons are calculated and compared using the dissociation energy of 0.3 eV, which is provided by the lowest unoccupied molecular orbital offset in heterojunction organic solar cells. A relation between the diffusion coefficient and diffusion length of singlet and triplet excitons is derived using the Foerster and Dexter transfer processes and are plotted as a function of the donor-acceptor separation. The diffusion length reduces nearly to a zero if the distance between donor and acceptor is increased to more than 1.5 nm. It is found that the donor-acceptor separation needs to be {<=} 1.5 nm for easy dissociation on singlet excitons leading to better conversion efficiency in heterojunction organic solar cells. (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  14. Collision-Induced Transfer Rates Connecting Fine-Structure Levels in Diatomic Sulfur in an Excited Vibrational Level Where V’=4.

    Science.gov (United States)

    1980-08-01

    State-to-State Transfer X& A§STNACT (C’m=t = mvinee N " ney md Idenclfy y block nube ) Ct) Rates for collision-induced transfer between a single rotational...0D rn ii CD n -4r-*I- LA ’ I I I I I Q 0 -- 0 D - -4 0 ~ I t r) nrf d 13 IV. RATE CONSTANTS Prior to a consideration of the quantitative...Copies Organization 1 University of California, San Diego Ames Department ATTN: F. WYilliamus P. 0. Box 109 La Jolla, CA 92037 1 University of Illinois

  15. Fifth Stereoactive Orbital on Silicon: Relaxation of the Lowest Singlet Excited State of Octamethyltrisilane

    Czech Academy of Sciences Publication Activity Database

    MacLeod, M. K.; Kobr, L.; Michl, Josef

    2012-01-01

    Roč. 116, č. 43 (2012), s. 10507-10517 ISSN 1089-5639 Grant - others:NSF(US) CHE0848477 Institutional support: RVO:61388963 Keywords : density-functional theory * polysilane high polymers * zeta valence quality * Gaussian-basis sets * electronic-structure Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.771, year: 2012

  16. Tetrapyrrole singlet excited state quenching by carotenoids in an artificial photosynthetic antenna

    NARCIS (Netherlands)

    Palacios, R.E.; Kodis, G.; Herrero, C.; Ochoa, E.M.; Gervaldo, M.; Gould, S.L.; Kennis, J.T.M.; Gust, D.; Moore, T.A.; Moore, A.L.

    2006-01-01

    Two artificial photosynthetic antenna models consisting of a Si phthalocyanine (Pc) bearing two axially attached carotenoid moieties having either 9 or 10 conjugated double bonds are used to illustrate some of the function of carotenoids in photosynthetic membranes. Both models studied in toluene,

  17. Extracting the cross section angular distributions for 15C high-energy resonance excited via the (18O,16O two-neutron transfer reaction

    Directory of Open Access Journals (Sweden)

    Carbone D.

    2016-01-01

    Full Text Available The 13C(18O,16O15C reaction has been studied at 84 MeV incident energy. The ejectiles have been momentum analized by the MAGNEX spectrometer and 15C excitation energy spectra have been obtained up to about 20 MeV. In the region above the two-neutron separation energy, a bump has been observed at 13.7 MeV. The extracted cross section angular distribution for this structure, obtained by using different models for background, displays a clear oscillating pattern, typical of resonant state of the residual nucleus.

  18. Surface hopping dynamics using a locally diabatic formalism: Charge transfer in the ethylene dimer cation and excited state dynamics in the 2- pyridone dimer

    Czech Academy of Sciences Publication Activity Database

    Plasser, F.; Granucci, G.; Pittner, Jiří; Barbatti, M.; Persico, M.; Lischka, H.

    2012-01-01

    Roč. 137, č. 22 (2012), 22A514 ISSN 0021-9606 R&D Projects: GA ČR(CZ) GAP208/12/0559 Institutional support: RVO:61388955 Keywords : surface hopping dynamics * molecular dynamics * electron transfer Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.164, year: 2012

  19. Theoretical study of intermolecular energy transfer involving electronically excited molecules: He(1S) + H2(B 1Σ/sub u/+)

    International Nuclear Information System (INIS)

    Grimes, R.M.

    1986-11-01

    To further understanding of gas phase collision dynamics involving electronically-excited molecules, a fully quantum mechanical study of He + H 2 (B 1 Σ/sub u/ + ) was undertaken. Iterative natural orbital configuration interaction (CI) calculations were performed to obtain the interaction potential between He and H 2 (B 1 Σ/sub u/ + ). The potential energy surface (PES) is highly anisotropic and has a van der Waals well of about 0.03 eV for C/sub 2v/ approach. Avoided PES crossings occur with He + H 2 (E,F 1 Σ/sub g/ + ) and with He + H 2 (X 1 Σ/sub g/ + ) and cause a local maximum and a deep minimum in the He + H 2 (B 1 Σ/sub u/ + ) PES, respectively. The crossing with He + H 2 (X 1 Σ/sub g/ + ) provides a mechanism for fluorescence quenching. The computed CI energies were combined with previous multi-reference double excitation CI calculations and fit with analytic functions for convenience in scattering calculations. Accurate dipole polarizabilities and quadrupole moment of H 2 (B 1 Σ/sub u/ + ) were computed for use in the multipole expansion, which is the analytic form of the long-range PES. 129 refs., 28 figs., 35 tabs

  20. Single Cell Responses to Spatially Controlled Photosensitized Production of Extracellular Singlet Oxygen

    DEFF Research Database (Denmark)

    Pedersen, Brian Wett; Sinks, Louise E.; Breitenbach, Thomas

    2011-01-01

    The response of individual HeLa cells to extracellularly produced singlet oxygen was examined. The spatial domain of singlet oxygen production was controlled using the combination of a membrane-impermeable Pd porphyrin-dendrimer, which served as a photosensitizer, and a focused laser, which served...... to localize the sensitized production of singlet oxygen. Cells in close proximity to the domain of singlet oxygen production showed morphological changes commonly associated with necrotic cell death. The elapsed post-irradiation “waiting period” before necrosis became apparent depended on (a) the distance...... between the cell membrane and the domain irradiated, (b) the incident laser fluence and, as such, the initial concentration of singlet oxygen produced, and (c) the lifetime of singlet oxygen. The data imply that singlet oxygen plays a key role in this process of light-induced cell death. The approach...

  1. Toward designed singlet fission: Solution photophysics of two indirectly coupled covalent dimers of 1,3-diphenylisobenzofuran

    Czech Academy of Sciences Publication Activity Database

    Johnson, J. C.; Akdag, A.; Zamadar, M.; Chen, X.; Schwerin, A. F.; Paci, I.; Smith, M. B.; Havlas, Zdeněk; Miller, J. R.; Ratner, M. A.; Nozik, A. J.; Michl, Josef

    2013-01-01

    Roč. 117, č. 16 (2013), s. 4680-4695 ISSN 1520-6106 R&D Projects: GA ČR GBP208/12/G016 Institutional support: RVO:61388963 Keywords : density-functional theory * intramolecular charge-transfer * electron-transfer * transfer excitations * exciton fission Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.377, year: 2013

  2. Large-Scale Quantum Many-Body Perturbation on Spin and Charge Separation in the Excited States of the Synthesized Donor-Acceptor Hybrid PBI-Macrocycle Complex.

    Science.gov (United States)

    Ziaei, Vafa; Bredow, Thomas

    2017-03-17

    The reliable calculation of the excited states of charge-transfer (CT) compounds poses a major challenge to the ab initio community because the frequently employed method, time-dependent density functional theory (TD-DFT), massively relies on the underlying density functional, resulting in heavily Hartree-Fock (HF) exchange-dependent excited-state energies. By applying the highly sophisticated many-body perturbation approach, we address the encountered unreliabilities and inconsistencies of not optimally tuned (standard) TD-DFT regarding photo-excited CT phenomena, and present results concerning accurate vertical transition energies and the correct energetic ordering of the CT and the first visible singlet state of a recently synthesized thermodynamically stable large hybrid perylene bisimide-macrocycle complex. This is a large-scale application of the quantum many-body perturbation approach to a chemically relevant CT system, demonstrating the system-size independence of the quality of the many-body-based excitation energies. Furthermore, an optimal tuning of the ωB97X hybrid functional can well reproduce the many-body results, making TD-DFT a suitable choice but at the expense of introducing a range-separation parameter, which needs to be optimally tuned. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. A Possible Role for Singlet Oxygen in the Degradation of Various Antioxidants. A Meta-Analysis and Review of Literature Data.

    Science.gov (United States)

    Petrou, Athinoula L; Petrou, Petros L; Ntanos, Theodoros; Liapis, Antonis

    2018-02-27

    The thermodynamic parameters E act , ΔH ≠ , ΔS ≠ , and ΔG ≠ for various processes involving antioxidants were calculated using literature kinetic data (k, T). The ΔG ≠ values of the antioxidants' processes vary in the range 91.27-116.46 kJmol -1 at 310 K. The similarity of the ΔG ≠ values (for all of the antioxidants studied) is supported to be an indication that a common mechanism in the above antioxidant processes may be taking place. A value of about 10-30 kJmol -1 is the activation energy for the diffusion of reactants depending on the reaction and the medium. The energy 92 kJmol -1 is needed for the excitation of O₂ from the ground to the first excited state (¹Δ g , singlet oxygen). We suggest the same role of the oxidative stress and specifically of singlet oxygen to the processes of antioxidants as in the processes of proteinaceous diseases. We therefore suggest a competition between the various antioxidants and the proteins of proteinaceous diseases in capturing singlet oxygen's empty π* orbital. The concentration of the antioxidants could be a crucial factor for the competition. Also, the structures of the antioxidant molecules play a significant role since the various structures have a different number of regions of high electron density.

  4. A Possible Role for Singlet Oxygen in the Degradation of Various Antioxidants. A Meta-Analysis and Review of Literature Data

    Science.gov (United States)

    Petrou, Athinoula L.; Petrou, Petros L.; Ntanos, Theodoros; Liapis, Antonis

    2018-01-01

    The thermodynamic parameters Eact, ΔH≠, ΔS≠, and ΔG≠ for various processes involving antioxidants were calculated using literature kinetic data (k, T). The ΔG≠ values of the antioxidants’ processes vary in the range 91.27–116.46 kJmol−1 at 310 K. The similarity of the ΔG≠ values (for all of the antioxidants studied) is supported to be an indication that a common mechanism in the above antioxidant processes may be taking place. A value of about 10–30 kJmol−1 is the activation energy for the diffusion of reactants depending on the reaction and the medium. The energy 92 kJmol−1 is needed for the excitation of O2 from the ground to the first excited state (1Δg, singlet oxygen). We suggest the same role of the oxidative stress and specifically of singlet oxygen to the processes of antioxidants as in the processes of proteinaceous diseases. We therefore suggest a competition between the various antioxidants and the proteins of proteinaceous diseases in capturing singlet oxygen’s empty π* orbital. The concentration of the antioxidants could be a crucial factor for the competition. Also, the structures of the antioxidant molecules play a significant role since the various structures have a different number of regions of high electron density. PMID:29495515

  5. Zethrene biradicals: How pro-aromaticity is expressed in the ground electronic state and in the lowest energy singlet, triplet, and ionic states

    Science.gov (United States)

    Zafra, José Luis; González Cano, Rafael C.; Ruiz Delgado, M. Carmen; Sun, Zhe; Li, Yuan; López Navarrete, Juan T.; Wu, Jishan; Casado, Juan

    2014-02-01

    A analysis of the electronic and molecular structures of new molecular materials based on zethrene is presented with particular attention to those systems having a central benzo-quinoidal core able to generate Kekulé biradicals whose stability is provided by the aromaticity recovery in this central unit. These Kekulé biradicals display singlet ground electronic states thanks to double spin polarization and have low-energy lying triplet excited states also featured by the aromaticity gain. Pro-aromatization is also the driving force for the stabilization of the ionized species. Moreover, the low energy lying singlet excited states also display a profound biradical fingerprint allowing to singlet exciton fission. These properties are discussed in the context of the size of the zethrene core and of its substitution. The work encompasses all known long zethrenes and makes use of a variety of experimental techniques, such as Raman, UV-Vis-NIR absorption, transient absorption, in situ spectroelectrochemistry and quantum chemical calculations. This study reveals how the insertion of suitable molecular modules (i.e., quinoidal) opens the door to new intriguing molecular properties exploitable in organic electronics.

  6. Excited baryons

    Energy Technology Data Exchange (ETDEWEB)

    Mukhopadhyay, N.C.

    1986-01-01

    The status of the theory of the low-energy approach to hadron structure is reviewed briefly by surveying a few relevant models. A few examples of tests needed to sort out the predictions of different models pertaining to the quark-gluon structure of hadrons are discussed, and given the resulting physics objectives, a few experimental options for excited baryon research at CFBAF are suggested. (LEW)

  7. Excited baryons

    International Nuclear Information System (INIS)

    Mukhopadhyay, N.C.

    1986-01-01

    The status of the theory of the low-energy approach to hadron structure is reviewed briefly by surveying a few relevant models. A few examples of tests needed to sort out the predictions of different models pertaining to the quark-gluon structure of hadrons are discussed, and given the resulting physics objectives, a few experimental options for excited baryon research at CFBAF are suggested

  8. 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

  9. Magnetic Dimer Excitations in Cs3Cr2CI9 Studied by Neutron Scattering

    DEFF Research Database (Denmark)

    Leuenberger, Bruno; Güdel, Hans U.; Kjems, Jørgen

    1985-01-01

    The energy dispersion of the singlet-triplet dimer excitation in Cs3Cr2CI9h as been studied by inelastic neutron scattering (INS) at temperatures down to 1.3 K. The results can be accounted for by using a completely isotropic Heisenberg Hamiltonian in the random phase approximation (RPA). Only...

  10. Electroweak baryogenesis and dark matter from a singlet Higgs

    Energy Technology Data Exchange (ETDEWEB)

    Cline, James M. [Department of Physics, McGill University, 3600 Rue University, Montréal, Québec, H3A 2T8 Canada (Canada); Kainulainen, Kimmo, E-mail: jcline@physics.mcgill.ca, E-mail: kimmo.kainulainen@jyu.fi [Department of Physics, University of Jyväskylä, P.O. Box 35 (YFL), FI-40014 Jyväskylä (Finland)

    2013-01-01

    If the Higgs boson H couples to a singlet scalar S via λ{sub m}|H|{sup 2}S{sup 2}, a strong electroweak phase transition can be induced through a large potential barrier that exists already at zero temperature. In this case properties of the phase transition can be computed analytically. We show that electroweak baryogenesis can be achieved using CP violation from a dimension-6 operator that couples S to the top-quark mass, suppressed by a new physics scale that can be well above 1 TeV. Moreover the singlet is a dark matter candidate whose relic density is ∼<3% of the total dark matter density, but which nevertheless interacts strongly enough with nuclei (through Higgs exchange) to be just below the current XENON100 limits. The DM mass is predicted to be in the range 80–160 GeV.

  11. Mixing of Singlet and Triplet Pairing for Surface Superconductivity

    Science.gov (United States)

    Gor'kov, L. P.; Rashba, E. I.

    2002-07-01

    We consider structure of the Cooper wave function for superconductivity in a surface layer. Broken space inversion at the surface results in lifted spin degeneracy and in two branches of the gapped energy spectrum as caused by the spin-orbit interaction. The pair wave function consists of a mixture of both singlet and triplet components. Anisotropy of the Knight shift measurable in the NMR experiments is calculated in the whole temperature regime. Implications for a few known experimental situations is briefly discussed.

  12. Photorelease of triplet and singlet oxygen from dioxygen complexes

    Czech Academy of Sciences Publication Activity Database

    Wagnerová, Dana Marie; Lang, Kamil

    2011-01-01

    Roč. 255, 23-24 (2011), s. 2904-2911 ISSN 0010-8545 R&D Projects: GA ČR GAP207/10/1447; GA ČR GAP208/10/1678 Institutional research plan: CEZ:AV0Z40320502 Keywords : singlet oxygen * triplet oxygen * photochemical elimination * photorelease * Dioxygen complex Subject RIV: CA - Inorganic Chemistry Impact factor: 12.110, year: 2011

  13. Generation of deviation parameters for amino acid singlets, doublets ...

    Indian Academy of Sciences (India)

    consecutive amino acids (ABC) for triplets in the selected dataset, Ni (X) = number of counts for X in the ith protein, Yi. = Ti for singlets, Ti-1 for doublets, Ti-2 for triplets where Ti is the total number of amino acids in the ith protein, i varies from 1 to n and n = total number of proteins considered (in this case, 408). Based on the ...

  14. Multiflavour excited mesons from the fifth dimension

    Energy Technology Data Exchange (ETDEWEB)

    Paredes, Angel [Centre de Physique Theorique, Ecole Polytechnique, 91128 Palaiseau (France)]. E-mail: angel.paredes@cpht.polytechnique.fr; Talavera, Pere [Departament de Fisica i Enginyeria Nuclear, Universitat Politecnica de Catalunya, Jordi Girona 1-3, E-08034 Barcelona (Spain)]. E-mail: pere.talavera@upc.es

    2005-05-02

    We study the Regge trajectories and the quark-antiquark energy in excited hadrons composed by different dynamical mass constituents via the gauge/string correspondence. First we exemplify the procedure in a supersymmetric system, D3-D7, in the extremal case. Afterwards we discuss the model dual to large-N{sub c} QCD, D4-D6 system. In the latter case we find the field theory expected gross features of vector like theories: the spectrum resembles that of heavy quarkonia and the Chew-Frautschi plot of the singlet and first excited states is in qualitative agreement with those of lattice QCD. We stress the salient points of including different constituents masses.

  15. Multiflavour excited mesons from the fifth dimension

    International Nuclear Information System (INIS)

    Paredes, Angel; Talavera, Pere

    2005-01-01

    We study the Regge trajectories and the quark-antiquark energy in excited hadrons composed by different dynamical mass constituents via the gauge/string correspondence. First we exemplify the procedure in a supersymmetric system, D3-D7, in the extremal case. Afterwards we discuss the model dual to large-N c QCD, D4-D6 system. In the latter case we find the field theory expected gross features of vector like theories: the spectrum resembles that of heavy quarkonia and the Chew-Frautschi plot of the singlet and first excited states is in qualitative agreement with those of lattice QCD. We stress the salient points of including different constituents masses

  16. IDMS: inert dark matter model with a complex singlet

    Science.gov (United States)

    Bonilla, Cesar; Sokolowska, Dorota; Darvishi, Neda; Diaz-Cruz, J. Lorenzo; Krawczyk, Maria

    2016-06-01

    We study an extension of the inert doublet model (IDM) that includes an extra complex singlet of the scalars fields, which we call the IDMS. In this model there are three Higgs particles, among them a SM-like Higgs particle, and the lightest neutral scalar, from the inert sector, remains a viable dark matter (DM) candidate. We assume a non-zero complex vacuum expectation value for the singlet, so that the visible sector can introduce extra sources of CP violation. We construct the scalar potential of IDMS, assuming an exact Z 2 symmetry, with the new singlet being Z 2-even, as well as a softly broken U(1) symmetry, which allows a reduced number of free parameters in the potential. In this paper we explore the foundations of the model, in particular the masses and interactions of scalar particles for a few benchmark scenarios. Constraints from collider physics, in particular from the Higgs signal observed at the Large Hadron Collider with {M}h≈ 125 {{GeV}}, as well as constraints from the DM experiments, such as relic density measurements and direct detection limits, are included in the analysis. We observe significant differences with respect to the IDM in relic density values from additional annihilation channels, interference and resonance effects due to the extended Higgs sector.

  17. NLO electroweak corrections in general scalar singlet models

    Science.gov (United States)

    Costa, Raul; Sampaio, Marco O. P.; Santos, Rui

    2017-07-01

    If no new physics signals are found, in the coming years, at the Large Hadron Collider Run-2, an increase in precision of the Higgs couplings measurements will shift the discussion to the effects of higher order corrections. In Beyond the Standard Model (BSM) theories this may become the only tool to probe new physics. Extensions of the Standard Model (SM) with several scalar singlets may address several of its problems, namely to explain dark matter, the matter-antimatter asymmetry, or to improve the stability of the SM up to the Planck scale. In this work we propose a general framework to calculate one loop-corrections to the propagators and to the scalar field vacuum expectation values of BSM models with an arbitrary number of scalar singlets. We then apply our method to a real and to a complex scalar singlet models. We assess the importance of the one-loop radiative corrections first by computing them for a tree level mixing sum constraint, and then for the main Higgs production process gg → H. We conclude that, for the currently allowed parameter space of these models, the corrections can be at most a few percent. Notably, a non-zero correction can survive when dark matter is present, in the SM-like limit of the Higgs couplings to other SM particles.

  18. Critical Assessment of TD-DFT for Excited States of Open-Shell Systems: I. Doublet-Doublet Transitions.

    Science.gov (United States)

    Li, Zhendong; Liu, Wenjian

    2016-01-12

    A benchmark set of 11 small radicals is set up to assess the performance of time-dependent density functional theory (TD-DFT) for the excited states of open-shell systems. Both the unrestricted (U-TD-DFT) and spin-adapted (X-TD-DFT) formulations of TD-DFT are considered. For comparison, the well-established EOM-CCSD (equation-of-motion coupled-cluster with singles and doubles) is also used. In total, 111 low-lying singly excited doublet states are accessed by all the three approaches. Taking the MRCISD+Q (multireference configuration interaction with singles and doubles plus the Davidson correction) results as the benchmark, it is found that both U-TD-DFT and EOM-CCSD perform well for those states dominated by singlet-coupled single excitations (SCSE) from closed-shell to open-shell, open-shell to vacant-shell, or closed-shell to vacant-shell orbitals. However, for those states dominated by triplet-coupled single excitations (TCSE) from closed-shell to vacant-shell orbitals, both U-TD-DFT and EOM-CCSD fail miserably due to severe spin contaminations. In contrast, X-TD-DFT provides balanced descriptions of both SCSE and TCSE. As far as the functional dependence is concerned, it is found that, when the Hartree-Fock ground state does not suffer from the instability problem, both global hybrid (GH) and range-separated hybrid (RSH) functionals perform grossly better than pure density functionals, especially for Rydberg and charge-transfer excitations. However, if the Hartree-Fock ground state is instable or nearly instable, GH and RSH tend to underestimate severely the excitation energies. The SAOP (statistically averaging of model orbital potentials) performs more uniformly than any other density functionals, although it generally overestimates the excitation energies of valence excitations. Not surprisingly, both EOM-CCSD and adiabatic TD-DFT are incapable of describing excited states with substantial double excitation characters.

  19. Singlet oxygen treatment of tumor cells triggers extracellular singlet oxygen generation, catalase inactivation and reactivation of intercellular apoptosis-inducing signaling.

    Science.gov (United States)

    Riethmüller, Michaela; Burger, Nils; Bauer, Georg

    2015-12-01

    Intracellular singlet oxygen generation in photofrin-loaded cells caused cell death without discrimination between nonmalignant and malignant cells. In contrast, extracellular singlet oxygen generation caused apoptosis induction selectively in tumor cells through singlet oxygen-mediated inactivation of tumor cell protective catalase and subsequent reactivation of intercellular ROS-mediated apoptosis signaling through the HOCl and the NO/peroxynitrite signaling pathway. Singlet oxygen generation by extracellular photofrin alone was, however, not sufficient for optimal direct inactivation of catalase, but needed to trigger the generation of cell-derived extracellular singlet oxygen through the interaction between H2O2 and peroxynitrite. Thereby, formation of peroxynitrous acid, generation of hydroxyl radicals and formation of perhydroxyl radicals (HO2(.)) through hydroxyl radical/H2O2 interaction seemed to be required as intermediate steps. This amplificatory mechanism led to the formation of singlet oxygen at a sufficiently high concentration for optimal inactivation of membrane-associated catalase. At low initial concentrations of singlet oxygen, an additional amplification step needed to be activated. It depended on singlet oxygen-dependent activation of the FAS receptor and caspase-8, followed by caspase-8-mediated enhancement of NOX activity. The biochemical mechanisms described here might be considered as promising principle for the development of novel approaches in tumor therapy that specifically direct membrane-associated catalase of tumor cells and thus utilize tumor cell-specific apoptosis-inducing ROS signaling. Copyright © 2015 The Authors. Published by Elsevier B.V. All rights reserved.

  20. Singlet oxygen treatment of tumor cells triggers extracellular singlet oxygen generation, catalase inactivation and reactivation of intercellular apoptosis-inducing signaling☆

    Science.gov (United States)

    Riethmüller, Michaela; Burger, Nils; Bauer, Georg

    2015-01-01

    Intracellular singlet oxygen generation in photofrin-loaded cells caused cell death without discrimination between nonmalignant and malignant cells. In contrast, extracellular singlet oxygen generation caused apoptosis induction selectively in tumor cells through singlet oxygen-mediated inactivation of tumor cell protective catalase and subsequent reactivation of intercellular ROS-mediated apoptosis signaling through the HOCl and the NO/peroxynitrite signaling pathway. Singlet oxygen generation by extracellular photofrin alone was, however, not sufficient for optimal direct inactivation of catalase, but needed to trigger the generation of cell-derived extracellular singlet oxygen through the interaction between H2O2 and peroxynitrite. Thereby, formation of peroxynitrous acid, generation of hydroxyl radicals and formation of perhydroxyl radicals (HO2.) through hydroxyl radical/H2O2 interaction seemed to be required as intermediate steps. This amplificatory mechanism led to the formation of singlet oxygen at a sufficiently high concentration for optimal inactivation of membrane-associated catalase. At low initial concentrations of singlet oxygen, an additional amplification step needed to be activated. It depended on singlet oxygen-dependent activation of the FAS receptor and caspase-8, followed by caspase-8-mediated enhancement of NOX activity. The biochemical mechanisms described here might be considered as promising principle for the development of novel approaches in tumor therapy that specifically direct membrane-associated catalase of tumor cells and thus utilize tumor cell-specific apoptosis-inducing ROS signaling. PMID:26225731

  1. Spectral characterization and excited-state interactions between rare earth ions doped in borosilicate and sol-gel glasses. Energy transfer up-conversion in the Pr-Sm system

    International Nuclear Information System (INIS)

    Assefa, Z.; Haire, R.G.; Stump, N.A.

    1996-01-01

    Spectroscopic properties of selected 4f-elements in a sol-gel and two high temperature silicate based glasses are reported. In particular, the spectral properties of the Eu[sup 3+] ion have been used to probe the local coordination environment of the f-elements in these glass matrices. Luminescence studies of the high temperature glasses indicated that the electric dipole allowed f-f transitions dominate the spectra which suggests that the local symmetry around the 4f-ions is low. Temperature-dependent spectroscopic studies of the sol-gel glasses indicated that the f-elements retain a 'solution-like' environment prior to thermal processing. After heat treatment, an increase in the emission intensities of the electric-dipole transitions is accompanied by a concomitant decrease in the magnetic- dipole allowed transitions. Moreover, excited state interactions has also been observed in the high temperature glasses that contain certain multiple f-elements. In Pr-Sm systems, exclusive excitation of the Sm[sup 3+] ion with a 514 nm argon ion laser line provides a higher- energy emission band ( ca. 490 mn ) from the PR[sup 3+] ion ([sup 3]P[sub 0] -> '[sup 3]H[sub 4]) transition. This energy up- conversion is attributed to energy transfer from the [sup 6]H[sub 13/2] level of the Se[sup 3+] ion to the [sup 3]H[sub 6] state of the PR[sup 3+] ion. Following a second photon absorption, the PR[sup 3+] ion is excited to the emitting [sup 3]P[sub O] level

  2. Structural factors influencing the intramolecular charge transfer and photoinduced electron transfer in tetrapyrazinoporphyrazines.

    Science.gov (United States)

    Novakova, Veronika; Hladík, Petr; Filandrová, Tereza; Zajícová, Ivana; Krepsová, Veronika; Miletin, Miroslav; Lenčo, Juraj; Zimcik, Petr

    2014-03-21

    A series of unsymmetrical tetrapyrazinoporphyrazines (TPyzPzs) from the group of azaphthalocyanines with one peripherally attached amino substituent (donor) were synthesized, and their photophysical properties (fluorescence quantum yield and singlet oxygen quantum yield) were determined. The synthesized TPyzPzs were expected to undergo intramolecular charge transfer (ICT) as the main pathway for deactivating their excited states. Several structural factors were found to play a critical role in ICT efficiency. The substituent in the ortho position to the donor center significantly influences the ICT, with tert-butylsulfanyl and butoxy substituents inducing the strongest ICTs, whereas chloro, methyl, phenyl, and hydrogen substituents in this position reduce the efficiency. The strength of the donor positively influences the ICT efficiency and correlates well with the oxidation potential of the amines used as the substituents on the TPyzPz as follows: n-butylamine ICT (with conjugated donors and acceptors) in the TPyzPz also proved to be much stronger than a photoinduced electron transfer in which the donor and the acceptor are connected through an aliphatic linker.

  3. Synthetic system mimicking the energy transfer and charge separation of natural photosynthesis

    Energy Technology Data Exchange (ETDEWEB)

    Gust, D.; Moore, T.A.

    1985-05-01

    A synthetic molecular triad consisting of a porphyrin P linked to both a quinone Q and a carotenoid polyene C has been prepared as a mimic of natural photosynthesis for solar energy conversion purposes. Laser flash excitation of the porphyrin moiety yields a charge-separated state Csup(+.)-P-Qsup(-.) within 100 ps with a quantum yield of more than 0.25. This charge-separated state has a lifetime on the microsecond time scale in suitable solvents. The triad also models photosynthetic antenna function and photoprotection from singlet oxygen damge. The successful biomimicry of photosynthetic charge separation is in part the result of multistep electron transfers which rapidly separate the charges and leave the system at high potential, but with a considerable barrier to recombination.

  4. Singlet oxygen generation in a high pressure non-self-sustained electric discharge

    International Nuclear Information System (INIS)

    Hicks, Adam; Norberg, Seth; Shawcross, Paul; Lempert, Walter R; Rich, J William; Adamovich, Igor V

    2005-01-01

    This paper presents results of singlet oxygen generation experiments in a high-pressure, non-self-sustained crossed discharge. The discharge consists of a high-voltage, short pulse duration, high repetition rate pulsed discharge, which produces ionization in the flow, and a low-voltage dc discharge which sustains current in a decaying plasma between the pulses. The sustainer voltage can be independently varied to maximize the energy input into electron impact excitation of singlet delta oxygen (SDO). The results demonstrate operation of a stable and diffuse crossed discharge in O 2 -He mixtures at static pressures of at least up to P 0 = 380 Torr and sustainer discharge powers of at least up to 1200 W, achieved at P 0 = 120 Torr. The reduced electric field in the positive column of the sustainer discharge varies from E/N = 0.3 x 10 -16 to 0.65 X 10 -16 V cm 2 , which is significantly lower than E/N in self-sustained discharges and close to the theoretically predicted optimum value for O 2 (a 1 Δ) excitation. Measurements of visible emission spectra O 2 (b 1 Σ → X 3 Σ) in the discharge afterglow show the O 2 (b 1 Σ) concentration to increase with the sustainer discharge power and to decrease as the O 2 fraction in the flow is increased. Rotational temperatures inferred from these spectra in 10% O 2 -90% He flows at P 0 = 120 Torr and mass flow rates of m-dot = 2.2 are 365-465 K. SDO yield at these conditions, 1.7% to 4.4%, was inferred from the integrated intensity of the (0, 0) band of the O 2 (a 1 Δ → X 3 Σ) infrared emission spectra calibrated using a blackbody source. The yield remains nearly constant in the discharge afterglow, up to at least 15 cm distance from the discharge. Kinetic modelling calculations using a quasi-one-dimensional nonequilibrium pulser-sustainer discharge model coupled with the Boltzmann equation for plasma electrons predict gas temperature rise in the discharge in satisfactory agreement with the experimental measurements

  5. Multicomponent Molecular Puzzles for Photofunction Design: Emission Color Variation in Lewis Acid-Base Pair Crystals Coupled with Guest-to-Host Charge Transfer Excitation.

    Science.gov (United States)

    Ono, Toshikazu; Sugimoto, Manabu; Hisaeda, Yoshio

    2015-08-05

    Simple yet ubiquitous multimolecular assembly systems with color-tunable emissions are realized by cooperative electron donor-acceptor interactions, such as the boron-nitrogen (B-N) dative bond as a Lewis acid-base pair and charge transfer (CT) interactions. These are ternary-component systems consisting of a naphthalenediimide derivative (NDI), tris(pentafluorophenyl)borane (TPFB), and aromatic molecules (guest) with an NDI:TPFB:guest ratio of 1:2:2. The crystal shows guest-dependent color-tunable emissions such as deep blue to orange when a guest molecule of benzene is replaced with other π-conjugated systems. A good correlation between the emission wavelength and ionization potential of the guest and electronic structure calculations indicated that the emission is due to the CT transition from the guest to the NDI. The present study suggests that a rational solution of multcomponent molecular puzzles would be useful for obtaining novel photofunctional solid-state systems.

  6. Effects of pulse width and repetition rate of pulsed laser on kinetics and production of singlet oxygen luminescence

    Directory of Open Access Journals (Sweden)

    Defu Chen

    2016-11-01

    Full Text Available Pulsed and continuous-wave (CW lasers have been widely used as the light sources for photodynamic therapy (PDT treatment. Singlet oxygen (1O2 is known to be a major cytotoxic agent in type-II PDT and can be directly detected by its near-infrared luminescence at 1270nm. As compared to CW laser excitation, the effects of pulse width and repetition rate of pulsed laser on the kinetics and production of 1O2 luminescence were quantitatively studied during photosensitization of Rose Bengal. Significant difference in kinetics of 1O2 luminescence was found under the excitation with various pulse widths of nanosecond, microsecond and CW irradiation with power of 20mW. The peak intensity and duration of 1O2 production varied with the pulse widths for pulsed laser excitation, while the 1O2 was generated continuously and its production reached a steady state with CW excitation. However, no significant difference (P>0.05 in integral 1O2 production was observed. The results suggest that the PDT efficacy using pulsed laser may be identical to the CW laser with the same wavelength and the same average fluence rate below a threshold in solution.

  7. Direct spectroscopic observation of singlet oxygen quenching and kinetic studies of physical and chemical singlet oxygen quenching rate constants of synthetic antioxidants (BHA, BHT, and TBHQ) in methanol.

    Science.gov (United States)

    Lee, Jun Hyun; Jung, Mun Yhung

    2010-08-01

    Singlet oxygen quenching by synthetic antioxidants (BHA, BHT, and TBHQ) was directly observed by spectroscopic monitoring of luminescence at 1268 nm. The luminescence data showed unambiguous evidence of singlet oxygen quenching by synthetic phenolic antioxidants with the highest activity for TBHQ, followed by BHA and BHT. The protective activities of these synthetic antioxidants on alpha-terpinene oxidation with chemically-induced singlet oxygen under dark further confirmed their singlet oxygen quenching abilities. Total singlet oxygen quenching rate constants (k(r) + k(q)) of BHA, BHT, and TBHQ were determined in a system containing alpha-terpinene (as a singlet oxygen trap) and methylene blue (as a sensitizer) during light irradiation, and the values were 5.14 x 10(7), 3.41 x 10(6), and 1.99 x 10(8) M(-1)s(-1), respectively. After the k(r) value of alpha-terpinene was first determined, the k(r) values of the synthetic antioxidants were calculated by measuring their relative reaction rates with singlet oxygen to that of alpha-terpinene under the identical conditions. The k(r) values of the BHA, BHT, and TBHQ were 3.90 x 10(5), 1.23 x 10(5), and 2.93 x 10(6), M(-1)s(-1). The percent partition of chemical quenching over total singlet oxygen quenching (k(r) x 100)/(k(r) + k(q)) for BHA, BHT, and TBHQ were 0.76%, 3.61%, and 1.47%, respectively. The results showed that the synthetic antioxidants quench singlet oxygen almost exclusively through the mechanism of physical quenching. This represents the first report on the singlet oxygen quenching mechanism of these synthetic antioxidants. Practical Application: The synthetic antioxidants, especially TBHQ, have been found to have a strong singlet oxygen quenching ability. This article also clearly showed that singlet oxygen quenching by synthetic antioxidants was mainly by the physical quenching mechanism. The results suggested that these synthetic antioxidants, especially TBHQ, could be used practically for the protection

  8. A novel tunable blue-green-emitting CaGdGaAl2O7:Ce(3+),Tb(3+) phosphor via energy transfer for UV-excited white LEDs.

    Science.gov (United States)

    Liang, Chao; You, Hongpeng; Fu, Yibing; Teng, Xiaoming; Liu, Kai; He, Jinhua

    2015-05-07

    CaGdGaAl2O7 and CaGdGaAl2O7:Ce(3+),Tb(3+) have been synthesized by a traditional solid state reaction for the first time. The Rietveld refinement confirmed that CaGdGaAl2O7 has a tetragonal crystal system with the space group P4[combining macron]21m. The photoluminescence properties show that the obtained phosphors can be efficiently excited in the range from 330 to 400 nm, which matches perfectly with commercial UV LED chips. A tunable blue-green emitting CaGdGaAl2O7:Ce(3+),Tb(3+) phosphor has been obtained, by codoping Ce(3+) and Tb(3+) ions into the host and varying their relative ratios, and may be a good candidate for blue-green components in UV white LEDs. The luminescence properties and lifetimes reveal an efficient energy transfer from the Ce(3+) to Tb(3+) ions. The energy transfer is demonstrated to be a dipole-quadrupole mechanism, and the critical distance for Ce(3+) to Tb(3+) calculated by the concentration quenching is 12.25 Å.

  9. Relationship between symmetry of porphyrinic pi-conjugated systems and singlet oxygen (1Delta g) yields: low-symmetry tetraazaporphyrin derivatives.

    Science.gov (United States)

    Ishii, Kazuyuki; Itoya, Hatsumi; Miwa, Hideya; Fujitsuka, Mamoru; Ito, Osamu; Kobayashi, Nagao

    2005-07-07

    We have investigated the excited-state properties and singlet oxygen ((1)Delta(g)) generation mechanism in phthalocyanines (4M; M = H(2), Mg, or Zn) and in low-symmetry metal-free, magnesium, and zinc tetraazaporphyrins (TAPs), that is, monobenzo-substituted (1M), adjacently dibenzo-substituted (2AdM), oppositely dibenzo-substituted (2OpM), and tribenzo-substituted (3M) TAP derivatives, whose pi conjugated systems were altered by fusing benzo rings. The S(1)(x) and S(1)(y) states (these lowest excited singlet states are degenerate in D(4)(h) symmetry) split in the low-symmetry TAP derivatives. The excited-state energies were quantitatively determined from the electronic absorption spectra. The lowest excited triplet (T(1)(x)) energies were also determined from phosphorescence spectra, while the second lowest excited triplet (T(1)(y)) states were evaluated by using the energy splitting between the T(1)(x) and T(1)(y) states previously reported (Miwa, H.; Ishii, K.; Kobayashi, N. Chem. Eur. J. 2004, 10, 4422-4435). The singlet oxygen quantum yields (Phi(Delta)) are strongly dependent on the pi conjugated system. In particular, while the Phi(Delta) value of 2AdH(2) is smallest in our system, that of 2OpH(2), an isomer of 2AdH(2), is larger than that of 4Zn, in contrast to the heavy atom effect. The relationship between the molecular structure and Phi(Delta) values can be transformed into a relationship between the S(1)(x) --> T(1)(y) intersystem crossing rate constant (k(ISC)) and the energy difference between the S(1)(x) and T(1)(y) states (DeltaE(S)(x)(T)(y)). In each of the Zn, Mg, and metal-free compounds, the Phi(Delta)/tau(F) values (tau(F): fluorescence lifetime), which are related to the k(ISC) values, are proportional to exp(-DeltaE(S)(x)(T)(y)), indicating that singlet oxygen ((1)Delta(g)) is produced via the T(1)(y) state and that the S(1)(x) --> T(1)(y) ISC process follows the energy-gap law. From the viewpoint of photodynamic therapy, our methodology

  10. Intramolecular proton transfer and tunnelling reactions of hydroxyphenylbenzoxazole derivatives in Xenon at 15 K

    Energy Technology Data Exchange (ETDEWEB)

    Walla, Peter J. [Max-Planck-Institute for Biophysical Chemistry, Department 010, Spectroscopy and Photochemical Kinetics, Am Fassberg 11, D-37077 Goettingen (Germany) and Department for Biophysical Chemistry, Technical University of Brunswick, Institute for Physical and Theoretical Chemistry, Hans-Sommerstr. 10, D-38106 Braunschweig (Germany)]. E-mail: pwalla@gwdg.de; Nickel, Bernhard [Max-Planck-Institute for Biophysical Chemistry, Department 010, Spectroscopy and Photochemical Kinetics, Am Fassberg 11, D-37077 Goettingen (Germany)

    2005-06-06

    We investigated the site dependence and the tunnelling processes of the intramolecular proton and deuteron transfer in the triplet state of the compounds 2-(2'-hydroxy-4'-methylphenyl)benzoxazole (m-MeHBO) and 2-(2'-hydroxy-3'-methylphenyl)benzoxazoles (o-MeHBO) and their deuterio-oxy analogues in a solid xenon matrix. After singlet excitation there occurs an ultrafast intramolecular enol {yields} keto proton transfer and subsequent intersystem crossing mainly to the keto triplet state. In the triplet state of m-MeHBO, the proton transfer back to the lower enol triplet state is governed by tunnelling processes. In o-MeHBO, however, the enol triplet state is higher and therefore normally no tunnel reaction can be observed. Because of the external heavy atom-effect in a xenon matrix, we were able to investigate the reverse enol-keto-tunnelling after exciting directly the enol triplet state of deuterated o-MeHBO. The time constants of the reverse enol-keto tautomerization are similar to those of the normal keto-enol tautomerization. In a xenon matrix, the observed site-selective phosphorescence spectra are very well-resolved vibrationally. This allowed the study of the tunnel rates in different well-defined sites. The vibrational energies obtained in the spectra are in good agreement with vibrational energies found in resonant Raman and IR spectra of 2-(2'-hydroxyphenyl)benzoxazole (HBO)

  11. Singlet Fission of Non-polycyclic Aromatic Molecules in Organic Photovoltaics.

    Science.gov (United States)

    Kawata, So; Pu, Yong-Jin; Saito, Ayaka; Kurashige, Yuki; Beppu, Teruo; Katagiri, Hiroshi; Hada, Masaki; Kido, Junji

    2016-02-24

    Singlet fission of thienoquinoid compounds in organic photovoltaics is demonstrated. The escalation of the thienoquinoid length of the compounds realizes a suitable packing structure and energy levels for singlet fission. The magnetic-field dependence of the photocurrent and the external quantum efficiency of the devices reveal singlet fission of the compounds and dissociation of triplet excitons into charges. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Hydrogen Bonding in the Electronic Excited State

    Science.gov (United States)

    Zhao, Guang-Jiu; Han, Ke-Li; DICP1101 Group Team

    2013-03-01

    Here, I will give a talk on our recent advances in electronic excited-state hydrogen-bonding dynamics and the significant role of excited-state hydrogen bonding on internal conversion (IC), electronic spectral shifts (ESS), photoinduced electron transfer (PET), fluorescence quenching (FQ), intramolecular charge transfer (ICT), and metal-to-ligand charge transfer (MLCT). The combination of various spectroscopic experiments with theoretical calculations has led to tremendous progress in excited-state hydrogen-bonding research. We first demonstrated that intermolecular hydrogen bond in excited state can be greatly strengthened or weakened for many chromophores. We have also clarified that intermolecular hydrogen-bond strengthening and weakening correspond to red-shifts and blue-shifts, respectively, in the electronic spectra. Moreover, radiationless deactivations (via IC, PET, ICT, MLCT, and so on) can be dramatically influenced by excited-state hydrogen bonding. GJZ and KLH thank the NSFC (Nos: 20903094 and 20833008) for financial support.

  13. Toward Singlet-Triplet Bistable Nonalternant Kekulé Hydrocarbons: Azulene-to-Naphthalene Rearrangement.

    Science.gov (United States)

    Das, Soumyajit; Wu, Jishan

    2015-12-04

    Recent developments of open-shell singlet diradicaloids motivated the search for stable singlet-triplet bistable nonalternant polycyclic hydrocarbons. During the synthesis of this type of molecule, such as the dibenzo-cyclohepta[def]fluorene 3, an unexpected azulene-to-naphthalene rearrangement was observed at room temperature, which resulted in new nonalternant hydrocarbons 8a/8b with a closed-shell singlet ground state. These studies provided insight into the unique chemistry of azulene and challenges for the synthesis of singlet-triplet bistable polycyclic hydrocarbons.

  14. Singlet Oxygen Sensor Green: Photochemical Behavior in Solution and in a Mammalian Cell

    DEFF Research Database (Denmark)

    Gollmer, Anita; Arnbjerg, Jacob; Blaikie, Frances Helen

    2011-01-01

    The development of efficient and selective luminescent probes for reactive oxygen species, particularly for singlet molecular oxygen, is currently of great importance. In this study, the photochemical behavior of Singlet Oxygen Sensor Green® (SOSG), a commercially available fluorescent probe...... of the reaction between SOSG and singlet oxygen is, itself, an efficient singlet oxygen photosensitizer. Second, SOSG appears to efficiently bind to proteins which, in turn, can influence uptake by a cell as well as behavior in the cell. As such, incorrect use of SOSG can yield misleading data on yields...

  15. Ultraweak bioluminescence dynamics and singlet oxygen correlations during injury repair in sweet potato

    Science.gov (United States)

    Hossu, Marius; Ma, Lun; Chen, Wei

    2011-03-01

    Ultraweak bioluminescence at the level of hundreds of photons per second per square centimeter after cutting injury of sweet potato was investigated. A small emission peak immediate after cutting and a later and higher peak were observed. Selective singlet oxygen inhibitors and sensors have been use to study the contribution of singlet oxygen during the curing process, demonstrating increased presence of singlet oxygen during and after the late bioemission peak. It was confirmed that singlet oxygen has direct contribution to ultraweak bioluminescence but also induces the formation of other exited luminescent species that are responsible for the recorded bioluminescence.

  16. Singlet oxygen-mediated formation of protein peroxides within cells

    International Nuclear Information System (INIS)

    Wright, A.; Policarpio, V.

    2003-01-01

    Full text: Singlet oxygen is generated by a number of cellular, enzymatic and chemical reactions as well as by exposure to UV, or visible light in the presence of a sensitizer; as a consequence this oxidant has been proposed as a damaging agent in a number of pathologies including photo-aging and skin cancer. Proteins are major targets for singlet oxygen as a result of their abundance and high rate constants for reaction. In this study it is shown that illumination of viable, sensitizer-loaded, THP-1 (human monocyte-like) cells with visible light gives rise to intra-cellular protein-derived peroxides. The peroxide yield increases with illumination time, requires the presence of the sensitizer, is enhanced in D 2 O, and decreased by azide; these data are consistent with the mediation of singlet oxygen. The concentration of peroxides detected, which is not affected by glucose or ascorbate loading of the cells, corresponds to ca. 1.5 nmoles peroxide per 10 6 cells using rose bengal as sensitizer, or 10 nmoles per mg cell protein and account for up to ca. 15% of the O 2 consumed by the cells. Similar peroxides have been detected on isolated cellular proteins exposed to light in the presence of rose bengal and oxygen. After cessation of illumination, the cellular protein peroxide levels decreases with t 1/2 ca. 4 hrs at 37 deg C, and this is associated with increased cell lysis. Decomposition of protein peroxides formed within cells, or on isolated cellular proteins, by metal ions, gives rise to radicals as detected by EPR spin trapping. These protein peroxides, and radicals derived from them, can inactivate key cellular enzymes (including caspases, GAPDH and glutathione reductase) and induce DNA base oxidation, strand breaks and DNA-protein cross-links. These studies demonstrate that exposure of intact cells to visible light in the presence of a sensitizer gives rise to novel long-lived, but reactive, intra-cellular protein peroxides via singlet oxygen

  17. Entanglement and Metrology with Singlet-Triplet Qubits

    Science.gov (United States)

    Shulman, Michael Dean

    Electron spins confined in semiconductor quantum dots are emerging as a promising system to study quantum information science and to perform sensitive metrology. Their weak interaction with the environment leads to long coherence times and robust storage for quantum information, and the intrinsic tunability of semiconductors allows for controllable operations, initialization, and readout of their quantum state. These spin qubits are also promising candidates for the building block for a scalable quantum information processor due to their prospects for scalability and miniaturization. However, several obstacles limit the performance of quantum information experiments in these systems. For example, the weak coupling to the environment makes inter-qubit operations challenging, and a fluctuating nuclear magnetic field limits the performance of single-qubit operations. The focus of this thesis will be several experiments which address some of the outstanding problems in semiconductor spin qubits, in particular, singlet-triplet (S-T0) qubits. We use these qubits to probe both the electric field and magnetic field noise that limit the performance of these qubits. The magnetic noise bath is probed with high bandwidth and precision using novel techniques borrowed from the field of Hamiltonian learning, which are effective due to the rapid control and readout available in S-T 0 qubits. These findings allow us to effectively undo the undesired effects of the fluctuating nuclear magnetic field by tracking them in real-time, and we demonstrate a 30-fold improvement in the coherence time T2*. We probe the voltage noise environment of the qubit using coherent qubit oscillations, which is partially enabled by control of the nuclear magnetic field. We find that the voltage noise bath is frequency-dependent, even at frequencies as high as 1MHz, and it shows surprising and, as of yet, unexplained temperature dependence. We leverage this knowledge of the voltage noise environment, the

  18. Color-singlet instantaneous potential in the coulomb gauge QCD

    International Nuclear Information System (INIS)

    Nakagawa, Yoshiyuki; Toki, Hiroshi; Nakamura, Atsushi; Saito, Takuya

    2007-01-01

    We study the Coulomb gauge confinement mechanism in the quenched lattice QCD simulations. It is found that the color-Coulomb instantaneous potential in the color-singlet channel between two quarks grows linearly at large distances; namely, the color-Coulomb interaction is a source of color confinement. However, the linearity of this potential remains even in the quark-gluon plasma phase. We discuss the relation between this thermal Coulomb-string tension and a magnetic scaling introduced as an infrared cutoff of the thermal QCD theory. (author)

  19. Relative and absolute level populations in beam-foil--excited neutral helium

    International Nuclear Information System (INIS)

    Davidson, J.

    1975-01-01

    Relative and absolute populations of 19 levels in beam-foil--excited neutral helium at 0.275 MeV have been measured. The singlet angular-momentum sequences show dependences on principal quantum number consistent with n -3 , but the triplet sequences do not. Singlet and triplet angular-momentum sequences show similar dependences on level excitation energy. Excitation functions for six representative levels were measured in the range 0.160 to 0.500 MeV. The absolute level populations increase with energy, whereas the neutral fraction of the beam decreases with energy. Further, the P angular-momentum levels are found to be overpopulated with respect to the S and D levels. The overpopulation decreases with increasing principal quantum number

  20. Relative and absolute level populations in beam-foil-excited neutral helium

    Science.gov (United States)

    Davidson, J.

    1975-01-01

    Relative and absolute populations of 19 levels in beam-foil-excited neutral helium at 0.275 MeV have been measured. The singlet angular-momentum sequences show dependences on principal quantum number consistent with n to the -3rd power, but the triplet sequences do not. Singlet and triplet angular-momentum sequences show similar dependences on level excitation energy. Excitation functions for six representative levels were measured in the range from 0.160 to 0.500 MeV. The absolute level populations increase with energy, whereas the neutral fraction of the beam decreases with energy. Further, the P angular-momentum levels are found to be overpopulated with respect to the S and D levels. The overpopulation decreases with increasing principal quantum number.

  1. 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)

  2. 808 nm-excited upconversion nanoprobes with low heating effect for targeted magnetic resonance imaging and high-efficacy photodynamic therapy in HER2-overexpressed breast cancer.

    Science.gov (United States)

    Zeng, Leyong; Pan, Yuanwei; Zou, Ruifen; Zhang, Jinchao; Tian, Ying; Teng, Zhaogang; Wang, Shouju; Ren, Wenzhi; Xiao, Xueshan; Zhang, Jichao; Zhang, Lili; Li, Aiguo; Lu, Guangming; Wu, Aiguo

    2016-10-01

    To avoid the overheating effect of excitation light and improve the efficacy of photodynamic therapy (PDT) of upconversion nanoplatform, a novel nanoprobe based on 808 nm-excited upconversion nanocomposites (T-UCNPs@Ce6@mSiO2) with low heating effect and deep penetration has been successfully constructed for targeted upconversion luminescence, magnetic resonance imaging (MRI) and high-efficacy PDT in HER2-overexpressed breast cancer. In this nanocomposite, photosensitizers (Ce6) were covalently conjugated inside of mesoporous silica to enhance the PDT efficacy by shortening the distance of fluorescence resonance energy transfer and to decrease the cytotoxicity by preventing the undesired leakage of Ce6. Compared with UCNPs@mSiO2@Ce6, UCNPs@Ce6@mSiO2 greatly promoted the singlet oxygen generation and amplified the PDT efficacy under the excitation of 808 nm laser. Importantly, the designed nanoprobe can greatly improve the uptake of HER2-positive cells and tumors by modifying the site-specific peptide, and the in vivo experiments showed excellent MRI and PDT via intravenous injection by modeling MDA-MB-435 tumor-bearing nude mice. Our strategy may provide an effective solution for overcoming the heating effect and improving the PDT efficacy of upconversion nanoprobes, and has potential application in visualized theranostics of HER2-overexpressed breast cancer. Copyright © 2016 Elsevier Ltd. All rights reserved.

  3. Influence of nitrogen oxides NO and NO2 on singlet delta oxygen production in pulsed discharge

    International Nuclear Information System (INIS)

    Ionin, A A; Klimachev, Yu M; Kozlov, A Yu; Kotkov, A A; Rulev, O A; Seleznev, L V; Sinitsyn, D V; Vagin, N P; Yuryshev, N N; Kochetov, I V; Napartovich, A P

    2009-01-01

    The influence of nitrogen oxides NO and NO 2 on the specific input energy (SIE) and the time behaviour of singlet delta oxygen (SDO) luminescence excited by a pulsed e-beam sustained discharge in oxygen were experimentally and theoretically studied. NO and NO 2 addition into oxygen results in a small increase and decrease in the SIE, respectively, the latter being connected with a large energy of electron affinity to NO 2 . The addition of 0.1-0.3% nitrogen oxides was experimentally and theoretically demonstrated to result in a notable enhancement of the SDO lifetime, which is related to a decrease in the atomic oxygen concentration in afterglow. It was experimentally demonstrated that to get a high SDO concentration at the gas pressure 30-60 Torr for a time interval of less than ∼0.5 s one needs to add not less than 0.2% nitrogen oxides into oxygen. The temperature dependence of the relaxation constant for SDO quenching by unexcited oxygen was estimated by using experimental data on the time behaviour of SDO luminescence.

  4. Correlation-enhanced odd-parity inter-orbital singlet pairing in LiFeAs

    Science.gov (United States)

    Nourafkan, Reza; Kotliar, Gabi; Tremblay, A.-M. S.

    The rich variety of iron-based superconductors and their complex electronic structure lead to a wide range of possibilities for gap symmetry and pairing components. We solved, in the two-Fe Brillouin zone, the full frequency-dependent linearized Eliashberg equations to investigate spin-fluctuations mediated Cooper pairing for LiFeAs . The magnetic excitations were calculated with the random phase approximation on a correlated electronic structure obtained with density functional theory and dynamical mean field theory. The interaction between electrons through Hund's coupling promotes both the intra-orbital dxz (yz) and the inter-orbital magnetic susceptibility. As a consequence, the leading pairing channel, conventional s+-, acquires sizeable inter-orbital dxy -dxz (yz) singlet pairing with odd parity under glide-plane symmetry. The combination of intra- and inter-orbital components makes the results consistent with available experiments on the angular dependence of the gaps observed on the different Fermi surfaces. We also explain the difference in pairing symmetry between LiFeAs and LiFeP.

  5. Preorganized Chromophores Facilitate Triplet Energy Migration, Annihilation and Upconverted Singlet Energy Collection.

    Science.gov (United States)

    Mahato, Prasenjit; Yanai, Nobuhiro; Sindoro, Melinda; Granick, Steve; Kimizuka, Nobuo

    2016-05-25

    Photon upconversion (UC) based on triplet-triplet annihilation (TTA) has the potential to enhance significantly photovoltaic and photocatalytic efficiencies by harnessing sub-bandgap photons, but the progress of this field is held back by the chemistry problem of how to preorganize multiple chromophores for efficient UC under weak solar irradiance. Recently, the first maximization of UC quantum yield at solar irradiance was achieved using fast triplet energy migration (TEM) in metal-organic frameworks (MOFs) with ordered acceptor arrays, but at the same time, a trade-off between fast TEM and high fluorescence efficiency was also found. Here, we provide a solution for this trade-off issue by developing a new strategy, triplet energy migration, annihilation and upconverted singlet energy collection (TEM-UPCON). The porous structure of acceptor-based MOF crystals allows triplet donor molecules to be accommodated without aggregation. The surface of donor-doped MOF nanocrystals is modified with highly fluorescent energy collectors through coordination bond formation. Thanks to the higher fluorescence quantum yield of surface-bound collectors than parent MOFs, the implementation of the energy collector greatly improves the total UC quantum yield. The UC quantum yield maximization behavior at ultralow excitation intensity was retained because the TTA events take place only in the MOF acceptors. The TEM-UPCON concept may be generalized to collectors with various functions and would lead to quantitative harvesting of upconverted energy, which is difficult to achieve in common molecular diffusion-based systems.

  6. Singlet Oxygen Detection Using Red Wine Extracts as Photosensitizers.

    Science.gov (United States)

    Lagunes, Irene; Vázquez-Ortega, Fernanda; Trigos, Ángel

    2017-09-01

    Moderate consumption of red wine provides beneficial effects to health. This is attributed to polyphenol compounds present in wine such as resveratrol, quercetin, gallic acid, rutin, and vanillic acid. The amount of these antioxidants is variable; nevertheless, the main beneficial effects of red wine are attributed to resveratrol. However, it has been found that resveratrol and quercetin are able to photosensitize singlet oxygen generation and conversely, gallic acid acts as quencher. Therefore, and since resveratrol and quercetin are some of the most important antioxidants reported in red wines, the aim of this research was to evaluate the photosensitizing ability of 12 red wine extracts through photo-oxidation of ergosterol. The presence of 1 O 2 was detected by ergosterol conversion into peroxide of ergosterol through 1 H NMR analysis. Our results showed that 10 wine extracts were able to act as photosensitizers in the generation of singlet oxygen. The presence of 1 O 2 can damage other compounds of red wine and cause possible organoleptic alterations. Finally, although the reaction conditions employed in this research do not resemble the inherent conditions in wine making processing or storing, or even during its consumption, this knowledge could be useful to prevent possible pro-oxidant effects and avoid detrimental effects in red wines. © 2017 Institute of Food Technologists®.

  7. Natural NMSSM with a light singlet Higgs and singlino LSP

    International Nuclear Information System (INIS)

    Potter, C.T.

    2016-01-01

    Supersymmetry (SUSY) is an attractive extension of the Standard Model (SM) of particle physics which solves the SM hierarchy problem. Motivated by the theoretical μ-term problem of the Minimal Supersymmetric Model (MSSM), the Next-to MSSM (NMSSM) can also account for experimental deviations from the SM like the anomalous muon magnetic moment and the dark matter relic density. Natural SUSY, motivated by naturalness considerations, exhibits small fine tuning and a characteristic phenomenology with light higgsinos, stops, and gluinos. We describe a scan in NMSSM parameter space motivated by Natural SUSY and guided by the phenomenology of an NMSSM with a slightly broken Peccei-Quinn symmetry and a lightly coupled singlet. We identify a scenario which survives experimental constraints with a light singlet Higgs and a singlino lightest SUSY particle. We then discuss how the scenario is not presently excluded by searches at the Large Hadron Collider (LHC) and which channels are promising for discovery at the LHC and International Linear Collider. (orig.)

  8. An XML file format for exchanging singlet lens specifications

    Science.gov (United States)

    Gay, Shawn C.; Gangadhara, Sanjay

    2015-10-01

    Zemax has developed an XML schema for the distribution of singlet lens specifications based on the ISO 10110 standard. In OpticStudio 15, this kind of XML data can be exported from the ISO Element Drawing analysis. The data file is then used in a feature that automates exchange of lens data between designer and manufacturer, the Cost Estimator. This Cost Estimator feature submits the XML data to various manufacturers to obtain cost estimates for prototype lens production. The workflow centered on the XML data exchange facilitates rapid cost estimate retrieval and eliminates the need for redundant manual data entry. The XML Schema Definition (XSD) for the XML format can be used with Microsoft developer tools to automatically create .NET classes to serialize and deserialize the singlet lens data to/from XML files. The format provides flexible unit specification for most parameters. Choosing XML as the basis for the file format has provided several benefits, such as the above mentioned automated serialization capabilities in .NET, a human-readable text-based format, and ready support for consumption by web services.

  9. Discrete R symmetries for the MSSM and its singlet extensions

    CERN Document Server

    Lee, Hyun Min; Ratz, Michael; Ross, Graham G; Schieren, Roland; Schmidt-Hoberg, Kai; Vaudrevange, Patrick K S

    2011-01-01

    We determine the anomaly free discrete R symmetries, consistent with the MSSM, that commute with SU(5) and suppress the $\\mu$ parameter and nucleon decay. We show that the order M of such $Z_M^R$ symmetries has to divide 24 and identify 5 viable symmetries. The simplest possibility is a $Z_4^R$ symmetry which commutes with SO(10). We present a string-derived model with this $Z_4^R$ symmetry and the exact MSSM spectrum below the GUT scale; in this model $Z_4^R$ originates from the Lorentz symmetry of compactified dimensions. We extend the discussion to include the singlet extensions of the MSSM and find $Z_4^R$ and $Z_8^R$ are the only possible symmetries capable of solving the $\\mu$ problem in the NMSSM. We also show that a singlet extension of the MSSM based on a $Z_{24}^R$ symmetry can provide a simultaneous solution to the $\\mu$ and strong CP problem with the axion coupling in the favoured window.

  10. Correlation-Enhanced Odd-Parity Interorbital Singlet Pairing in the Iron-Pnictide Superconductor LiFeAs.

    Science.gov (United States)

    Nourafkan, R; Kotliar, G; Tremblay, A-M S

    2016-09-23

    The rich variety of iron-based superconductors and their complex electronic structure lead to a wide range of possibilities for gap symmetry and pairing components. Here we solve in the two-Fe Brillouin zone the full frequency-dependent linearized Eliashberg equations to investigate spin-fluctuations mediated Cooper pairing for LiFeAs. The magnetic excitations are calculated with the random phase approximation on a correlated electronic structure obtained with density functional theory and dynamical mean field theory. The interaction between electrons through Hund's coupling promotes both the intraorbital d_{xz(yz)} and the interorbital magnetic susceptibility. As a consequence, the leading pairing channel, conventional s^{+-}, acquires sizable interorbital d_{xy}-d_{xz(yz)} singlet pairing with odd parity under glide-plane symmetry. The combination of intra- and interorbital components makes the results consistent with available experiments on the angular dependence of the gaps observed on the different Fermi surfaces.

  11. Localized excitations and the geometry of the 1nπ* excited states of pyrazine

    International Nuclear Information System (INIS)

    Kleier, D.A.; Martin, R.L.; Wadt, W.R.; Moomaw, W.R.

    1982-01-01

    Previous theoretical work has shown that the lowest excited singlet state of pyrazine, the π* 1 B 3 u state, is best described in terms of interacting excitations localized on each nitrogen. The present work refines the localized excitation model and considers its implications for the geometry of the 1 B 3 u state. Hartree-Fock calculations show that the best single configuration description of the nπ* state has broken ( 1 B 1 ) symmetry with the excitation strongly localized at one end of the molcule. If the symmetry-restricted hf result is used for reference, this localization describes an important correlation effect. The excited-state geometry was probed using configuration interaction wave functions based on the symmetry-restricted orbitals, as well as properly symmetrized ''valance-bond'' wave functions based on the broken symmetry solutions. Both descriptions lead to a very flat potential for a b/sub 1u/ vibrational mode. This mode reduces the molecular geometry from D/sub 2h/ to C/sub 2v/. We present spectroscopic evidence of our own and of other workers which is consistent with such a flat potential

  12. Magnitude and direction of the change in dipole moment associated with excitation of the primary electron donor in Rhodopseudomonas sphaeroides reaction centers

    Energy Technology Data Exchange (ETDEWEB)

    Lockhart, D.J.; Boxer, S.G.

    1987-02-10

    The magnitude and direction of the change in dipole moment, ..delta mu.., associated with the Q/sub y/ transition of the dimeric primary electron donor (special pair or P870) in Rhodopseudomonas sphaeroides reaction centers have been measured by Stark spectroscopy at 20 /sup 0/C. The magnitude of ..delta mu.. is found to be f/sup -1/ (10.3 +/- 0.7) D, where f is a correction factor for the local dielectric properties of the protein matrix. With the spherical cavity approximation and an effective local dielectric constant of 2, f = 1.2, and absolute value of ..delta mu.. is 8.6 +/- 0.6 D. Absolute value of ..delta mu.. for the Q/sub y/ transition of the special pair is approximately a factor of 3.4 and 2 greater than for the monomeric bacteriochlorophylls and bacteriopheophytins, respectively, in the reaction center. The angle between ..delta mu.. and the transition dipole moment for excitation of the first singlet electron state of the special pair was found to be 24 +/- 2/sup 0/. The measured values are combined to suggest a physical model in which the lowest excited singlet state of the special pair has substantial charge-transfer character and where charge is separated between the two monomers comprising the dimeric special pair. This leads to the hypothesis that the first charge-separated state in bacterial photosynthesis is formed directly upon photoexcitation. These data provide stringent values for comparison with theoretical calculations of the electronic structure of the chromophores in the reaction center.

  13. In-vitro singlet oxygen threshold dose at PDT with Radachlorin photosensitizer

    Science.gov (United States)

    Klimenko, V. V.; Shmakov, S. V.; Kaydanov, N. E.; Knyazev, N. A.; Kazakov, N. V.; Rusanov, A. A.; Bogdanov, A. A.; Dubina, M. V.

    2017-07-01

    In this present study we investigate the Radachlorin photosensitizer accumulation in K562 cells and Hela cells and determined the cell viability after PDT. Using the macroscopic singlet oxygen modeling and cellular photosensitizer concentration the singlet oxygen threshold doses for K562 cells and Hela cells were calculated.

  14. Search for Colour Singlet and Colour Reconnection Effects in Hadronic Z Decays at LEP

    CERN Document Server

    Achard, P; Aguilar-Benítez, M; Alcaraz, J; Alemanni, G; Allaby, James V; Aloisio, A; Alviggi, M G; Anderhub, H; Andreev, V P; Anselmo, F; Arefev, A; Azemoon, T; Aziz, T; Bagnaia, P; Bajo, A; Baksay, G; Baksay, L; Baldew, S V; Banerjee, S; Banerjee, Sw; Barczyk, A; Barillère, R; Bartalini, P; Basile, M; Batalova, N; Battiston, R; Bay, A; Becattini, F; Becker, U; Behner, F; Bellucci, L; Berbeco, R; Berdugo, J; Berges, P; Bertucci, B; Betev, B L; Biasini, M; Biglietti, M; Biland, A; Blaising, J J; Blyth, S C; Bobbink, Gerjan J; Böhm, A; Boldizsar, L; Borgia, B; Bottai, S; Bourilkov, D; Bourquin, Maurice; Braccini, S; Branson, J G; Brochu, F; Burger, J D; Burger, W J; Cai, X D; Capell, M; Cara Romeo, G; Carlino, G; Cartacci, A M; Casaus, J; Cavallari, F; Cavallo, N; Cecchi, C; Cerrada, M; Chamizo-Llatas, M; Chang, Y H; Chemarin, M; Chen, A; Chen, G; Chen, G M; Chen, H F; Chen, H S; Chiefari, G; Cifarelli, Luisa; Cindolo, F; Clare, I; Clare, R; Coignet, G; Colino, N; Costantini, S; de la Cruz, B; Cucciarelli, S; van Dalen, J A; De Asmundis, R; Déglon, P L; Debreczeni, J; Degré, A; Dehmelt, K; Deiters, K; Della Volpe, D; Delmeire, E; Denes, P; De Notaristefani, F; De Salvo, A; Diemoz, M; Dierckxsens, M; Dionisi, C; Dittmar, M; Doria, A; Dova, M T; Duchesneau, D; Duda, M; Echenard, B; Eline, A; El-Hage, A; El-Mamouni, H; Engler, A; Eppling, F J; Extermann, P; Falagán, M A; Falciano, S; Favara, A; Fay, J; Fedin, O; Felcini, M; Ferguson, T; Fesefeldt, H S; Fiandrini, E; Field, J H; Filthaut, F; Fisher, P H; Fisher, W; Fisk, I; Forconi, G; Freudenreich, Klaus; Furetta, C; Galaktionov, Yu; Ganguli, S N; García-Abia, P; Gataullin, M; Gentile, S; Giagu, S; Gong, Z F; Grenier, G; Grimm, O; Grünewald, M W; Guida, M; van Gulik, R; Gupta, V K; Gurtu, A; Gutay, L J; Haas, D; Hatzifotiadou, D; Hebbeker, T; Hervé, A; Hirschfelder, J; Hofer, H; Hohlmann, M; Holzner, G; Hou, S R; Hu, Y; Jin, B N; Jones, L W; de Jong, P; Josa-Mutuberria, I; Käfer, D; Kaur, M; Kienzle-Focacci, M N; Kim, J K; Kirkby, Jasper; Kittel, E W; Klimentov, A; König, A C; Kopal, M; Koutsenko, V F; Kräber, M H; Krämer, R W; Krüger, A; Kunin, A; Ladrón de Guevara, P; Laktineh, I; Landi, G; Lebeau, M; Lebedev, A; Lebrun, P; Lecomte, P; Lecoq, P; Le Coultre, P; Le Goff, J M; Leiste, R; Levtchenko, M; Levchenko, P M; Li, C; Likhoded, S; Lin, C H; Lin, W T; Linde, Frank L; Lista, L; Liu, Z A; Lohmann, W; Longo, E; Lü, Y S; Luci, C; Luminari, L; Lustermann, W; Ma Wen Gan; Malgeri, L; Malinin, A; Maña, C; Mans, J; Martin, J P; Marzano, F; Mazumdar, K; McNeil, R R; Mele, S; Merola, L; Meschini, M; Metzger, W J; Mihul, A; Milcent, H; Mirabelli, G; Mnich, J; Mohanty, G B; Muanza, G S; Muijs, A J M; Musicar, B; Musy, M; Nagy, S; Natale, S; Napolitano, M; Nessi-Tedaldi, F; Newman, H; Nisati, A; Novák, T; Nowak, H; Ofierzynski, R A; Organtini, G; Pal, I; Palomares, C; Paolucci, P; Paramatti, R; Passaleva, G; Patricelli, S; Paul, T; Pauluzzi, M; Paus, C; Pauss, Felicitas; Pedace, M; Pensotti, S; Perret-Gallix, D; Petersen, B; Piccolo, D; Pierella, F; Pioppi, M; Piroué, P A; Pistolesi, E; Plyaskin, V; Pohl, M; Pozhidaev, V; Pothier, J; Prokofev, D; Prokofiev, D O; Quartieri, J; Rahal-Callot, G; Rahaman, M A; Raics, P; Raja, N; Ramelli, R; Rancoita, P G; Ranieri, R; Raspereza, A V; Razis, P A; Ren, D; Rescigno, M; Reucroft, S; Riemann, S; Riles, K; Roe, B P; Romero, L; Rosca, A; Rosier-Lees, S; Roth, S; Rosenbleck, C; Rubio, J A; Ruggiero, G; Rykaczewski, H; Sakharov, A; Saremi, S; Sarkar, S; Salicio, J; Sánchez, E; Schäfer, C; Shchegelskii, V; Schopper, Herwig Franz; Schotanus, D J; Sciacca, C; Servoli, L; Shevchenko, S; Shivarov, N; Shoutko, V; Shumilov, E; Shvorob, A V; Son, D; Souga, C; Spillantini, P; Steuer, M; Stickland, D P; Stoyanov, B; Strässner, A; Sudhakar, K; Sultanov, G G; Sun, L Z; Sushkov, S; Suter, H; Swain, J D; Szillási, Z; Tang, X W; Tarjan, P; Tauscher, Ludwig; Taylor, L; Tellili, B; Teyssier, D; Timmermans, C; Ting, Samuel C C; Ting, S M; Tonwar, S C; Tóth, J; Tully, C; Tung, K L; Ulbricht, J; Valente, E; Van de Walle, R T; Vásquez, R; Veszpremi, V; Vesztergombi, G; Vetlitskii, I; Vicinanza, D; Viertel, Gert M; Villa, S; Vivargent, M; Vlachos, S; Vodopyanov, I; Vogel, H; Vogt, H; Vorobev, I; Vorobyov, A A; Wadhwa, M; Wang, Q; Wang, X L; Wang, Z M; Weber, M; Wienemann, P; Wilkens, H; Wynhoff, S; Xia, L; Xu, Z Z; Yamamoto, J; Yang, B Z; Yang, C G; Yang, H J; Yang, M; Yeh, S C; Zalite, A; Zalite, Yu; Zhang, Z P; Zhao, J; Zhu, G Y; Zhu, R Y; Zhuang, H L; Zichichi, A; Zimmermann, B; Zöller, M

    2004-01-01

    A search is performed in symmetric 3-jet hadronic Z decay events for evidence of colour singlet production or colour reconnection effects. Asymmetries in the angular separation of particles are found to be sensitive indicators of such effects. Upper limits on the level of colour singlet production and colour reconnection effects are established for a variety of models.

  15. Recent development of organic light-emitting diode utilizing energy transfer from exciplex to phosphorescent emitter

    Science.gov (United States)

    Seo, Satoshi; Shitagaki, Satoko; Ohsawa, Nobuharu; Inoue, Hideko; Suzuki, Kunihiko; Nowatari, Hiromi; Takahashi, Tatsuyoshi; Hamada, Takao; Watabe, Takeyoshi; Yamada, Yui; Mitsumori, Satomi

    2016-09-01

    This study investigates an organic light-emitting diode (OLED) utilizing energy transfer from an excited complex (exciplex) comprising donor and acceptor molecules to a phosphorescent dopant. An exciplex has a very small energy gap between the lowest singlet and triplet excited states (S1 and T1). Thus, both S1 and T1 energies of the exciplex can be directly transferred to the T1 of the phosphorescent dopant by adjusting the emission energy of the exciplex to the absorption-edge energy of the dopant. Such an exciplex‒triplet energy transfer (ExTET) achieves high efficiency at low drive voltage because the electrical excitation energy of the exciplex approximates the T1 energy of the dopant. Furthermore, the efficiency of the reverse intersystem crossing (RISC) of the exciplex does not affect the external quantum efficiency (EQE) of the ExTET OLED. The RISC of the exciplex is inhibited when the T1 energy of either donor or acceptor molecules is close to or lower than that of the exciplex itself. Even in this case, however, the ExTET OLED maintains its high efficiency because the T1 energy of each component of the exciplex or the T1 energy of the exciplex itself can be transferred to the dopant. We also varied the emission colors of ExTET OLEDs from sky-blue to red by introducing various phosphorescent dopants. These devices achieved high EQEs (≍30%), low drive voltages (≍3 V), and extremely long lifetimes (e.g., 1 million hours for the orange OLED) at a luminance of 1,000 cd/m2.

  16. Controlling Long-Lived Triplet Generation from Intramolecular Singlet Fission in the Solid State

    KAUST Repository

    Pace, Natalie A.

    2017-11-30

    The conjugated polymer poly(benzothiophene dioxide) (PBTDO1) has recently been shown to exhibit efficient intramolecular singlet fission in solution. In this paper, we investigate the role of intermolecular interactions in triplet separation dynamics after singlet fission. We use transient absorption spectroscopy to determine the singlet fission rate and triplet yield in two polymers differing only by side chain motif in both solution and the solid state. Whereas solid-state films show singlet fission rates identical to those measured in solution, the average lifetime of the triplet population increases dramatically, and is strongly dependent on side-chain identity. These results show that it may be necessary to carefully engineer the solid-state microstructure of these “singlet fission polymers” in order to produce the long-lived triplets needed to realize efficient photovoltaic devices.

  17. Singlet oxygen in the low-temperature plasma of an electron-beam-sustained discharge

    International Nuclear Information System (INIS)

    Vagin, N. P.; Ionin, A. A.; Klimachev, Yu. M.; Kotkov, A. A.; Kochetov, I. V.; Napartovich, A. P.; Podmar'kov, Yu. P.; Rulev, O. A.; Seleznev, L. V.; Sinitsyn, D. V.; Frolov, M. P.; Yuryshev, N. N.

    2006-01-01

    Results are presented from experimental and theoretical studies of the production of singlet delta oxygen in a pulsed electron-beam-sustained discharge ignited in a large (∼18-1) volume at a total gas mixture pressure of up to 210 Torr. The measured yield of singlet oxygen reaches 10.5%. It is found that varying the reduced electric field from ∼2 to ∼11 kV/(cm atm) slightly affects singlet oxygen production. It is shown experimentally that an increase in the gas mixture pressure or the specific input energy reduces the duration of singlet oxygen luminescence. The calculated time evolution of the singlet oxygen concentration is compared with experimental results

  18. Photoinduced symmetry-breaking intramolecular charge transfer in a quadrupolar pyridinium derivative.

    Science.gov (United States)

    Carlotti, Benedetta; Benassi, Enrico; Spalletti, Anna; Fortuna, Cosimo G; Elisei, Fausto; Barone, Vincenzo

    2014-07-21

    We report here a joint experimental and theoretical study of a quadrupolar, two-branched pyridinium derivative of interest as a potential non-linear optical material. The spectral and photophysical behaviour of this symmetric system is greatly affected by the polarity of the medium. A very efficient photoinduced intramolecular charge transfer, surprisingly more efficient than in the dipolar asymmetric analogue, is found to occur by femtosecond resolved transient absorption spectroscopy. TD-DFT calculations are in excellent agreement with these experimental findings and predict large charge displacements in the molecular orbitals describing the ground state and the lowest excited singlet state. The theoretical study also revealed that in highly polar media the symmetry of the excited state is broken giving a possible explanation to the fluorescence and transient absorption spectra resembling those of the one-branched analogous compound in the same solvents. The present study may give an important insight into the excited state deactivation mechanism of cationic (donor-π-acceptor-π-donor)(+) quadrupolar compounds characterised by negative solvatochromism, which are expected to show significant two-photon absorption (TPA). Moreover, the water solubility of the investigated quadrupolar system may represent an added value in view of the most promising applications of TPA materials in biology and medicine.

  19. Singlet-triplet interaction in linear triatomic molecules

    Science.gov (United States)

    Osherov, V. I.; Osherov, M. V.; Poluyanov, L. V.

    2018-01-01

    We present here two-electronic model, which describes singlet-triplet interaction 1 π -3Σ+ in linear triatomic molecules. The analysis takes into account spin-orbital coupling terms in electronic Hamiltonian, as well as its symmetry properties. We give the symmetry operators of electronic Hamiltonian including space operators (acting on electronic coordinates) and matrix operators (acting on electronic spin). We consider only deformation π -modes and our resulting 5 × 5 vibronic matrix describes actual relativistic pseudo-Renner effect (1 π -3 Σ) × π . The eigenvalues of vibronic matrix (i.e. potential energy surfaces) have axial symmetry and represented by analytical expressions, include five electrostatic and three spin-orbital parameters.

  20. Evolution of truncated moments of singlet parton distributions

    International Nuclear Information System (INIS)

    Forte, S.; Magnea, L.; Piccione, A.; Ridolfi, G.

    2001-01-01

    We define truncated Mellin moments of parton distributions by restricting the integration range over the Bjorken variable to the experimentally accessible subset x 0 ≤x≤1 of the allowed kinematic range 0≤x≤1. We derive the evolution equations satisfied by truncated moments in the general (singlet) case in terms of an infinite triangular matrix of anomalous dimensions which couple each truncated moment to all higher moments with orders differing by integers. We show that the evolution of any moment can be determined to arbitrarily good accuracy by truncating the system of coupled moments to a sufficiently large but finite size, and show how the equations can be solved in a way suitable for numerical applications. We discuss in detail the accuracy of the method in view of applications to precision phenomenology

  1. Generation of macroscopic singlet states in atomic ensembles

    Science.gov (United States)

    Tóth, Géza; Mitchell, Morgan W.

    2010-05-01

    We study squeezing of the spin uncertainties by quantum non-demolition (QND) measurement in non-polarized spin ensembles. Unlike the case of polarized ensembles, the QND measurements can be performed with negligible back-action, which allows, in principle, perfect spin squeezing as quantified by Tóth et al (2007 Phys. Rev. Lett. 99 250405). The generated spin states approach many-body singlet states and contain a macroscopic number of entangled particles even when individual spin is large. We introduce the Gaussian treatment of unpolarized spin states and use it to estimate the achievable spin squeezing for realistic experimental parameters. Our proposal might have applications for magnetometry with a high spatial resolution or quantum memories storing information in decoherence free subspaces.

  2. Singlet oxygen-based electrosensing by molecular photosensitizers

    Science.gov (United States)

    Trashin, Stanislav; Rahemi, Vanoushe; Ramji, Karpagavalli; Neven, Liselotte; Gorun, Sergiu M.; de Wael, Karolien

    2017-07-01

    Enzyme-based electrochemical biosensors are an inspiration for the development of (bio)analytical techniques. However, the instability and reproducibility of the reactivity of enzymes, combined with the need for chemical reagents for sensing remain challenges for the construction of useful devices. Here we present a sensing strategy inspired by the advantages of enzymes and photoelectrochemical sensing, namely the integration of aerobic photocatalysis and electrochemical analysis. The photosensitizer, a bioinspired perfluorinated Zn phthalocyanine, generates singlet-oxygen from air under visible light illumination and oxidizes analytes, yielding electrochemically-detectable products while resisting the oxidizing species it produces. Compared with enzymatic detection methods, the proposed strategy uses air instead of internally added reactive reagents, features intrinsic baseline correction via on/off light switching and shows C-F bonds-type enhanced stability. It also affords selectivity imparted by the catalytic process and nano-level detection, such as 20 nM amoxicillin in μl sample volumes.

  3. Two-singlet model for light cold dark matter

    International Nuclear Information System (INIS)

    Abada, Abdessamad; Ghaffor, Djamal; Nasri, Salah

    2011-01-01

    We extend the standard model by adding two gauge-singlet Z 2 -symmetric scalar fields that interact with visible matter only through the Higgs particle. One is a stable dark matter WIMP, and the other one undergoes a spontaneous breaking of the symmetry that opens new channels for the dark matter annihilation, hence lowering the mass of the WIMP. We study the effects of the observed dark matter relic abundance on the WIMP annihilation cross section and find that in most regions of the parameters' space, light dark matter is viable. We also compare the elastic-scattering cross section of our dark matter candidate off a nucleus with existing (CDMSII and XENON100) and projected (SuperCDMS and XENON1T) experimental exclusion bounds. We find that most of the allowed mass range for light dark matter will be probed by the projected sensitivity of the XENON1T experiment.

  4. Signal for a light singlet scalar at the LHC

    Science.gov (United States)

    Chang, We-Fu; Modak, Tanmoy; Ng, John N.

    2018-03-01

    In the general Higgs portal-like models, the extra neutral scalar, S , can mix with the Standard Model (SM) Higgs boson, H . We perform an exploratory study focusing on the direct search for such a light singlet S at the Large Hadron Collider (LHC). After careful study of the SM background, we find the process p p →t t ¯ S followed by S →b b ¯ can be used to investigate S with mass in the 20 Higgs factories. With similar luminosity, the current Large Electron-Positron Collider (LEP) limits on the mixing between S and H can be improved by at least one or two order of magnitudes.

  5. Resummation of singlet parton evolution at small x

    CERN Document Server

    Altarelli, Guido; Forte, Stefano; Altarelli, Guido; Ball, Richard D.; Forte, Stefano

    2000-01-01

    We propose an improvement of the splitting functions at small x which overcomes the apparent problems encountered by the BFKL approach. We obtain a stable expansion for the x-evolution function chi(M) near M=0 by including in it a sequence of terms derived from the one- and two-loop anomalous dimension gamma. The requirement of momentum conservation is always satisfied. The residual ambiguity on the splitting functions is effectively parameterized in terms of the value of lambda, which fixes the small x asymptotic behaviour x^-lambda of the singlet parton distributions. We derive from this improved evolution function an expansion of the splitting function which leads to good apparent convergence, and to a description of scaling violations valid both at large and small x.

  6. CINE: Comet INfrared Excitation

    Science.gov (United States)

    de Val-Borro, Miguel; Cordiner, Martin A.; Milam, Stefanie N.; Charnley, Steven B.

    2017-08-01

    CINE calculates infrared pumping efficiencies that can be applied to the most common molecules found in cometary comae such as water, hydrogen cyanide or methanol. One of the main mechanisms for molecular excitation in comets is the fluorescence by the solar radiation followed by radiative decay to the ground vibrational state. This command-line tool calculates the effective pumping rates for rotational levels in the ground vibrational state scaled by the heliocentric distance of the comet. Fluorescence coefficients are useful for modeling rotational emission lines observed in cometary spectra at sub-millimeter wavelengths. Combined with computational methods to solve the radiative transfer equations based, e.g., on the Monte Carlo algorithm, this model can retrieve production rates and rotational temperatures from the observed emission spectrum.

  7. Excitation energy transfer pathways in Lhca4

    NARCIS (Netherlands)

    Gibasiewicz, K; Croce, R; Morosinotto, T.; Ihalainen, J A; van Stokkum, I H M; Dekker, J P; Bassi, R.; van Grondelle, R

    EET in reconstituted Lhca4, a peripheral light-harvesting complex from Photosystem I of Arabidopsis thaliana, containing 10 chlorophylls and 2 carotenoids, was studied at room temperature by femtosecond transient absorption spectroscopy. Two spectral forms of Lut were observed in the sites L1 and

  8. Excitation energy transfer pathways in Lhca4

    NARCIS (Netherlands)

    Gibasiewicz, K.; Croce, R.; Morosinotto, T.; Ihalainen, J.A.; van Stokkum, I.H.M.; Dekker, J.P.; Bassi, R.; van Grondelle, R.

    2005-01-01

    EET in reconstituted Lhca4, a peripheral light-harvesting complex from Photosystem I of Arabidopsis thaliana, containing 10 chlorophylls and 2 carotenoids, was studied at room temperature by femtosecond transient absorption spectroscopy. Two spectral forms of Lut were observed in the sites L1 and

  9. Volume 1: The Solid-Gas Singlet Delta Oxygen Generator

    National Research Council Canada - National Science Library

    Alfano, Angelo

    2004-01-01

    ...: a) construction of a Raman diagnostic system for the simultaneous measurement of excited and ground state oxygen in gas-solid reactions between solid peroxides and hydrogen halides or chlorine gas, b...

  10. Unique photophysical behavior of 2,2'-bipyridine-3,3'-diol in DMSO-water binary mixtures: potential application for fluorescence sensing of Zn2+ based on the inhibition of excited-state intramolecular double proton transfer.

    Science.gov (United States)

    Mandal, Sarthak; Ghosh, Surajit; Banerjee, Chiranjib; Kuchlyan, Jagannath; Sarkar, Nilmoni

    2013-10-10

    In this work we have investigated the anomalous behavior of DMSO-water binary mixtures using 2,2'-bipyridine-3,3'-diol (BP(OH)2) as a microenvironment-sensitive excited-state-intramolecular-double-proton-transfer (ESIDPT) probe. Here we present results on the UV-vis absorption and fluorescence properties of BP(OH)2 in the binary solutions. DMSO-water binary mixtures at various compositions are an intriguing hydrogen bonded system, where DMSO acts to diminish the hydrogen bonding ability of water with the dissolved solutes. As a result, we observe unusual changes in the photophysical properties of BP(OH)2 with increasing DMSO content in complete correlation with the prior simulation and experimental results on the solvent structures and dynamics. The fluorescence quantum yield and fluorescence lifetime of BP(OH)2 depend strongly on the DMSO content and become maximum at very low mole fraction (∼0.12) of DMSO. The anomalous behavior at this particular region likely arises from the enhanced pair hydrophobicity of the medium as demonstrated by Bagchi and co-workers (Banerjee, S.; Roy, S.; Bagchi, B. J. Phys. Chem. B 2010, 114, 12875-12882). In addition we have also shown the utilization of BP(OH)2 as a potential Zn(2+)-selective fluorescent sensor in a 1:1 DMSO-water binary mixture useful for biological applications. We observed highly enhanced fluorescence emission of BP(OH)2 selectively for binding with the Zn(2+) metal ion. Moreover, the fluorescence emission maximum of BP(OH)2-Zn(2+) is significantly blue-shifted with a reduced Stokes shift due to the inhibition of the ESIDPT process of BP(OH)2 through strong coordination.

  11. Enhancement of second hyperpolarizabilities in open-shell singlet slipped-stack dimers composed of square planar nickel complexes involving o-semiquinonato type ligands.

    Science.gov (United States)

    Fukui, Hitoshi; Shigeta, Yasuteru; Nakano, Masayoshi; Kubo, Takashi; Kamada, Kenji; Ohta, Koji; Champagne, Benoît; Botek, Edith

    2011-02-17

    Using the spin-unrestricted hybrid density functional theory method, we have investigated the intermolecular interaction effects on the longitudinal static second hyperpolarizability (γ) of open-shell singlet slipped-stack dimers composed of singlet diradical square planar nickel complexes involving o-semiquinonato type ligands, Ni(o-C(6)H(4)X(2))(2) (where X = O, NH, S, Se, PH). For comparison, we have also examined the γ values of a closed-shell singlet slipped-stack dimer composed of closed-shell monomers Ni[o-C(6)H(4)S(NH(2))](2). It is found that for interplanar distance ranging between 3.0 and 5.0 Å the slipped-stack dimers with intermediate monomer diradical characters exhibit larger γ values per monomer (γ(dimer)/2) than those with large monomer diradical characters or than the closed-shell dimer. These results extend the domain of validity of the relationship found between γ and the diradical character for individual molecules. It also turns out that the ratio R = (γ(dimer)/2)/γ(monomer) increases upon decreasing the interplanar distance and that this increase is larger for intermediate diradical character than for the other cases. These phenomena have been analyzed by considering the γ density distributions of the dimers, demonstrating a significant field-induced third-order charge transfer between the monomers in the case of intermediate diradical character. The present results indicate that open-shell singlet slipped-stack aggregates composed of monomers with intermediate diradical characters constitute another mean for achieving highly efficient and tunable third-order nonlinear optical materials.

  12. Can we Predict Quantum Yields Using Excited State Density Functional Theory for New Families of Fluorescent Dyes?

    Science.gov (United States)

    Kohn, Alexander W.; Lin, Zhou; Shepherd, James J.; Van Voorhis, Troy

    2016-06-01

    For a fluorescent dye, the quantum yield characterizes the efficiency of energy transfer from the absorbed light to the emitted fluorescence. In the screening among potential families of dyes, those with higher quantum yields are expected to have more advantages. From the perspective of theoreticians, an efficient prediction of the quantum yield using a universal excited state electronic structure theory is in demand but still challenging. The most representative examples for such excited state theory include time-dependent density functional theory (TDDFT) and restricted open-shell Kohn-Sham (ROKS). In the present study, we explore the possibility of predicting the quantum yields for conventional and new families of organic dyes using a combination of TDDFT and ROKS. We focus on radiative (kr) and nonradiative (knr) rates for the decay of the first singlet excited state (S_1) into the ground state (S_0) in accordance with Kasha's rule. M. Kasha, Discuss. Faraday Soc., 9, 14 (1950). For each dye compound, kr is calculated with the S_1-S_0 energy gap and transition dipole moment obtained using ROKS and TDDFT respectively at the relaxed S_1 geometry. Our predicted kr agrees well with the experimental value, so long as the order of energy levels is correctly predicted. Evaluation of knr is less straightforward as multiple processes are involved. Our study focuses on the S_1-T_1 intersystem crossing (ISC) and the S_1-S_0 internal conversion (IC): we investigate the properties that allow us to model the knr value using a Marcus-like expression, such as the Stokes shift, the reorganization energy, and the S_1-T_1 and S_1-S_0 energy gaps. Taking these factors into consideration, we compare our results with those obtained using the actual Marcus theory and provide explanation for discrepancy. T. Kowalczyk, T. Tsuchimochi, L. Top, P.-T. Chen, and T. Van Voorhis, J. Chem. Phys., 138, 164101 (2013). M. Kasha, Discuss. Faraday Soc., 9, 14 (1950).

  13. Diurnal Variations of Emissions of O2 singlet Delta Near Mars' Northern Summer Solstice

    Science.gov (United States)

    Nosowitz, Jonathon; Ziobron, Elijah; Novak, Robert E.

    2017-10-01

    We are presenting results of O2 singlet Delta emission, a tracer for ozone, in the Martian atmosphere for observations taken before Mars’ Northern summer solstice (Ls = 88o, February 10, 2014 ). The data were taken using CSHELL on the NASA-IRTF telescope located on Mauna Kea in Hawaii. The slit was positioned east-west on Mars and we observed diurnal variations at 20o N and 60o N. Spectral/spatial images were taken with a spectral resolution above 38,000. Mars’ relative velocity of -16 km/s enabled us to separate the Martian emission lines from the telluric absorption lines. Raw images were cleaned by removing dead and hot pixels. The images were then adjusted so that the spatial dimension was perpendicular to the spectral dimension. Extracts at 0.6 arcsec spatial resolution were taken which allowed us to measure Martian emission peaks. The Martian data were calibrated by taking similar observations from a standard star (HR4689) using the temperature, wavelength, and intensity of the star to calibrate the flux density. A Boltzmann analysis was performed on the observed emission peaks to obtain the rotational temperature of the excited O2. From this, the total emission rates were obtained. We found that at both latitudinal locations, the greatest emissions occured between 12:00- 13:00 local time on Mars. The emission intensity increases during the morning hours and then decreases towards sunset. We thank the administration and staff of the NASA-IRTF for observation time and for their assistance during operations of the telescope. We also thank Drs. M. Mumma and G. Villanueva of the NASA Goddard Space Flight Center with whom we collaborate.

  14. Generation and suppression of singlet oxygen in hair by photosensitization of melanin.

    Science.gov (United States)

    Chiarelli-Neto, Orlando; Pavani, Christiane; Ferreira, Alan S; Uchoa, Adjaci F; Severino, Divinomar; Baptista, Maurício S

    2011-09-15

    We have studied the spectroscopic properties of hair (white, blond, red, brown, and black) under illumination with visible light, giving special emphasis to the photoinduced generation of singlet oxygen ((1)O(2)). Irradiation of hair shafts (λ(ex)>400 nm) changed their properties by degrading the melanin. Formation of C3 hydroperoxides in the melanin indol groups was proven by (1)H NMR. After 532-nm excitation, all hair shafts presented the characteristic (1)O(2) emission (λ(em)=1270 nm), whose intensity varied inversely with the melanin content. (1)O(2) lifetime was also shown to vary with hair type, being five times shorter in black hair than in blond hair, indicating the role of melanin as a (1)O(2) suppressor. Lifetime ranged from tenths of a nanosecond to a few microseconds, which is much shorter than the lifetime expected for (1)O(2) in the solvents in which the hair shafts were suspended, indicating that (1)O(2) is generated and suppressed inside the hair structure. Both eumelanin and pheomelanin were shown to produce and to suppress (1)O(2), with similar efficiencies. The higher amount of (1)O(2) generated in blond hair and its longer lifetime is compatible with the stronger damage that light exposure causes in blond hair. We propose a model to explain the formation and suppression of (1)O(2) in hair by photosensitization of melanin with visible light and the deleterious effects that an excess of visible light may cause in hair and skin. Copyright © 2011. Published by Elsevier Inc.

  15. Indolo[2,3-b]carbazoles with tunable ground states: How Clar's aromatic sextet determines the singlet biradical character

    KAUST Repository

    Luo, Ding

    2014-01-01

    Polycyclic hydrocarbons (PHs) with a singlet biradical ground state have recently attracted extensive interest in physical organic chemistry and materials science. Replacing the carbon radical center in the open-shell PHs with a more electronegative nitrogen atom is expected to result in the more stable aminyl radical. In this work, two kinetically blocked stable/persistent derivatives (1 and 2) of indolo[2,3-b]carbazole, an isoelectronic structure of the known indeno[2,1-b]fluorene, were synthesized and showed different ground states. Based on variable-temperature NMR/ESR measurements and density functional theory calculations, it was found that the indolo[2,3-b]carbazole derivative 1 is a persistent singlet biradical in the ground state with a moderate biradical character (y0 = 0.269) and a small singlet-triplet energy gap (ΔES-T ≅ -1.78 kcal mol-1), while the more extended dibenzo-indolo[2,3-b]carbazole 2 exhibits a quinoidal closed-shell ground state. The difference can be explained by considering the number of aromatic sextet rings gained from the closed-shell to the open-shell biradical resonance form, that is to say, two for compound 1 and one for compound 2, which determines their different biradical characters. The optical and electronic properties of 2 and the corresponding aromatic precursors were investigated by one-photon absorption, transient absorption and two-photon absorption (TPA) spectroscopies and electrochemistry. Amphoteric redox behaviour, a short excited lifetime and a moderate TPA cross section were observed for 2, which can be correlated to its antiaromaticity and small biradical character. Compound 2 showed high reactivity to protic solvents due to its extremely low-lying LUMO energy level. Unusual oxidative dimerization was also observed for the unblocked dihydro-indolo[2,3-b]carbazole precursors 6 and 11. Our studies shed light on the rational design of persistent aminyl biradicals with tunable properties in the future. This journal

  16. Theory of the magnetic excitations in the Cu-O superconductors

    International Nuclear Information System (INIS)

    Hedegard, P.; Brix Pedersen, M.

    1989-01-01

    We show that all the features of the recent neutron scattering data by Shirane et al. on large, superconducting single crystals can be explained in a model with singlet pairing of bosonic spins. The temperature dependence of the integrated intensity seen experimentally is due to the creation of two spin excitations out of the pair condensate in one scattering event. The Goldstone modes of the theory are identified, and suggestions for experimental tests are given. (orig.)

  17. Excited state dependent electron transfer of a rhenium-dipyridophenazine complex intercalated between the base pairs of DNA: a time-resolved UV-visible and IR absorption investigation into the photophysics of fac-[Re(CO)3(F2dppz)(py)]+ bound to either [poly(dA-dT)]2 or [poly(dG-dC)]2.

    Science.gov (United States)

    Cao, Qian; Creely, Caitriona M; Davies, E Stephen; Dyer, Joanne; Easun, Timothy L; Grills, David C; McGovern, David A; McMaster, Jonathan; Pitchford, Jonathan; Smith, Jayden A; Sun, Xue-Zhong; Kelly, John M; George, Michael W

    2011-08-01

    The transient species formed following excitation of fac-[Re(CO)(3)(F(2)dppz)(py)](+) (F(2)dppz = 11,12-difluorodipyrido[3,2-a:2',3'-c]phenazine) bound to double-stranded polynucleotides [poly(dA-dT)](2) or [poly(dG-dC)](2) have been studied by transient visible and infra-red spectroscopy in both the picosecond and nanosecond time domains. The latter technique has been used to monitor both the metal complex and the DNA by monitoring the regions 1900-2100 and 1500-1750 cm(-1) respectively. These data provide direct evidence for electron transfer from guanine to the excited state of the metal complex, which proceeds both on a sub-picosecond time scale and with a lifetime of 35 ps, possibly due to the involvement of two excited states. No electron transfer is found for the [poly(dA-dT)](2) complex, although characteristic changes are seen in the DNA-region TRIR consistent with changes in the binding of the bases in the intercalation site upon excitation of the dppz-complex. This journal is © The Royal Society of Chemistry and Owner Societies 2011

  18. Charge Transfer and Triplet States in High Efficiency OPV Materials and Devices

    Science.gov (United States)

    Dyakonov, Vladimir

    2013-03-01

    The advantage of using polymers and molecules in electronic devices, such as light-emitting diodes (LED), field-effect transistors (FET) and, more recently, solar cells (SC) is justified by the unique combination of high device performance and processing of the semiconductors used. Power conversion efficiency of nanostructured polymer SC is in the range of 10% on lab scale, making them ready for up-scaling. Efficient charge carrier generation and recombination in SC are strongly related to dissociation of the primary singlet excitons. The dissociation (or charge transfer) process should be very efficient in photovoltaics. The mechanisms governing charge carrier generation, recombination and transport in SC based on the so-called bulk-heterojunctions, i.e. blends of two or more semiconductors with different electron affinities, appear to be very complex, as they imply the presence of the intermediate excited states, neutral and charged ones. Charge transfer states, or polaron pairs, are the intermediate states between free electrons/holes and strongly bound excitons. Interestingly, the mostly efficient OLEDs to date are based on the so-called triplet emitters, which utilize the triplet-triplet annihilation process. In SC, recent investigations indicated that on illumination of the device active layer, not only mobile charges but also triplet states were formed. With respect to triplets, it is unclear how these excited states are generated, via inter-system crossing or via back transfer of the electron from acceptor to donor. Triplet formation may be considered as charge carrier loss channel; however, the fusion of two triplets may lead to a formation of singlet excitons instead. In such case, a generation of charges by utilizing of the so far unused photons will be possible. The fundamental understanding of the processes involving the charge transfer and triplet states and their relation to nanoscale morphology and/or energetics of blends is essential for the

  19. Pallidol, a resveratrol dimer from red wine, is a selective singlet oxygen quencher

    International Nuclear Information System (INIS)

    He Shan; Jiang Liyan; Wu Bin; Pan Yuanjiang; Sun Cuirong

    2009-01-01

    Pallidol is a naturally occurring resveratrol dimer from red wine with antioxidant and antifungal activities. In this report, with the use of the EPR spin-trapping technique, the scavenging and quenching effects of pallidol on reactive oxygen species (ROS) were investigated. The results demonstrated that pallidol showed strong quenching effects on singlet oxygen at very low concentrations, but it was ineffective to scavenge hydroxyl radicals or superoxide anions. Further kinetic study revealed that the reaction of pallidol with singlet oxygen had an extremely high rate constant (k a = 1.71 x 10 10 ). Therefore, pallidol is a potent and selective singlet oxygen quencher in aqueous systems. It may be used in singlet oxygen-mediated diseases as a pharmacological agent, which may contribute to the health beneficial effects of red wine.

  20. A two-component dark matter model with real singlet scalars ...

    Indian Academy of Sciences (India)

    2016-01-05

    component dark matter model with real singlet scalars confronting GeV -ray excess from galactic centre and Fermi bubble. Debasish Majumdar Kamakshya Prasad Modak Subhendu Rakshit. Special: Cosmology Volume 86 Issue ...

  1. Singlet Delta Oxygen: A Quantitative Analysis Using Off-Axis Integrated-Cavity-Output-Spectroscopy (ICOS)

    National Research Council Canada - National Science Library

    Gallagher, Jeffrey E

    2006-01-01

    .... The method is based on off-axis integrated-cavity-output spectroscopy (ICOS). The primary goal for this research effort is to utilize the ICOS technique and demonstrate its ability to provide quantitative data of singlet delta oxygen...

  2. Effect of oxygen concentration on singlet oxygen luminescence detection

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Longchao; Lin, Lisheng; Li, Yirong; Lin, Huiyun; Qiu, Zhihai [MOE Key Laboratory of OptoElectronic Science and Technology for Medicine, Fujian Provincial Key Laboratory for Photonics Technology, Fujian Normal University, Fuzhou 350007 (China); Gu, Ying [Department of Laser Medicine, Chinese PLA General Hospital, Beijing 100853 (China); Li, Buhong, E-mail: bhli@fjnu.edu.cn [MOE Key Laboratory of OptoElectronic Science and Technology for Medicine, Fujian Provincial Key Laboratory for Photonics Technology, Fujian Normal University, Fuzhou 350007 (China)

    2014-08-01

    Singlet oxygen ({sup 1}O{sub 2}) is a major phototoxic component in photodynamic therapy (PDT) and its generation is dependent on the availability of tissue oxygen. To examine the effect of oxygen concentration on {sup 1}O{sub 2} detection, two hydrophilic photosensitizer (PS), rose bengal (RB) and meso-metra (N-methyl-4-pyridyl) porphine tetra tosylate (TMPyP) were used as model PS. Irradiation was carried out using 523 nm under hypoxic (2%, 13%), normoxic (21%) and hyperoxic (65%) conditions. The spectral and spatial resolved {sup 1}O{sub 2} luminescence was measured by near-infrared (NIR) photomultiplier tube (PMT) and camera, respectively. Upon the irradiation, the emission signal mainly consisted of background scattering light, PS fluorescence and phosphorescence, and {sup 1}O{sub 2} luminescence. The PS phosphorescence was evidently dependent on the oxygen concentration and PS type, which resulted in the change of emission profile of {sup 1}O{sub 2} luminescence. This change was further demonstrated on {sup 1}O{sub 2} luminescence image. The present study suggests that the low oxygen concentration could affect {sup 1}O{sub 2} luminescence detection. - Highlights: • Both spectral and spatial resolved {sup 1}O{sub 2} luminescence measurements were performed. • Effect of oxygen concentration on {sup 1}O{sub 2} generation was quantitatively evaluated. • Low oxygen concentration could affect {sup 1}O{sub 2} luminescence detection.

  3. Towards photodynamic therapy with ionizing radiation: nanoparticle-mediated singlet oxygen generation (Conference Presentation)

    Science.gov (United States)

    Clement, Sandhya; Deng, Wei; Camilleri, Elizabeth; Wilson, Brian; Goldys, Ewa

    2016-03-01

    Photodynamic therapy (PDT) is a clinically approved method for the treatment of cancer by using singlet oxygen, a highly reactive oxygen generated from a photosensitizer drug upon photoactivation. Limited light penetration depth into to the tissue means that PDT is unsuitable for deep tissue cancer treatments. This can be overcome by using X-ray /gamma rays activated nanoparticles able to trigger the photosensitizer drug and generate singlet oxygen. Additionally, inorganic nanoparticles interact more strongly with X and/or gamma rays than the tissue, allowing to concentrate the effects of radiation near nanoparticle surface and they can also be molecularly targeted to cancer cells. In this work we synthesized and characterized CeF3 nanoparticles, a well-known scintillator material. The nanoparticles were conjugated with Verteporfin, a photosensitizer drug by electrostatic interaction. We assessed the performance of CeF3 and the conjugates to generate singlet oxygen exposed to X-ray radiation. The X-ray singlet oxygen quantum yield of the nanoparticle-photosensitizer system was accurately quantified for the first time. This provided realistic estimates of the singlet oxygen dose taking into consideration the dose partition of the radiation between CeF3 and the tissue. Furthermore, we investigated gold nanoparticle-photosensitizer systems. We confirmed that pure gold nanoparticles itself generate singlet oxygen which is attributed to plasmonic effects. We found enhanced singlet oxygen generation from gold-Rose Bengal conjugates and gold nanorod-verteporfin conjugates. These singlet-oxygen-generating nanomaterials add a new dimension to radiation-assisted PDT.

  4. Singlet oxygen mediated DNA degradation by copper nanoparticles: potential towards cytotoxic effect on cancer cells

    OpenAIRE

    Sengupta Tapas K; Mandal Swadhin K; Santra Subhankar; Jose Gregor P

    2011-01-01

    Abstract The DNA degradation potential and anti-cancer activities of copper nanoparticles of 4-5 nm size are reported. A dose dependent degradation of isolated DNA molecules by copper nanoparticles through generation of singlet oxygen was observed. Singlet oxygen scavengers such as sodium azide and Tris [hydroxyl methyl] amino methane were able to prevent the DNA degradation action of copper nanoparticles confirming the involvement of activated oxygen species in the degradation process. Addit...

  5. Spray generator of singlet oxygen for a chemical oxygen-iodine laser

    Czech Academy of Sciences Publication Activity Database

    Jirásek, Vít; Hrubý, Jan; Špalek, Otomar; Čenský, Miroslav; Kodymová, Jarmila

    2010-01-01

    Roč. 100, č. 4 (2010), s. 779-791 ISSN 0946-2171 Grant - others:European Office of Aerospace R&D(US) FA8655-09-1-3091 Institutional research plan: CEZ:AV0Z10100523; CEZ:AV0Z20760514 Keywords : spray generator of singlet oxygen * singlet oxygen * chemical oxygen-iodine laser Subject RIV: BH - Optics, Masers, Lasers Impact factor: 2.239, year: 2010

  6. Synthesis of Pyridylanthracenes and Their Reversible Reaction with Singlet Oxygen to Endoperoxides.

    Science.gov (United States)

    Fudickar, Werner; Linker, Torsten

    2017-09-01

    The ortho, meta, and para isomers of 9,10-dipyridylanthracene 1 have been synthesized and converted into their endoperoxides 1-O 2 upon oxidation with singlet oxygen. The kinetics of this reaction can be controlled by the substitution pattern and the solvent: in highly polar solvents, the meta isomer is the most reactive, whereas the ortho isomer is oxidized fastest in nonpolar solvents. Heating of the endoperoxides affords the parent anthracenes by release of singlet oxygen.

  7. Nuclear spin singlet states as a contrast mechanism for NMR spectroscopy.

    Science.gov (United States)

    Devience, Stephen J; Walsworth, Ronald L; Rosen, Matthew S

    2013-10-01

    Nuclear magnetic resonance (NMR) spectra of complex chemical mixtures often contain unresolved or hidden spectral components, especially when strong background signals overlap weaker peaks. In this article we demonstrate a quantum filter utilizing nuclear spin singlet states, which allows undesired NMR spectral background to be removed and target spectral peaks to be uncovered. The quantum filter is implemented by creating a nuclear spin singlet state with spin quantum numbers j = 0, mz  = 0 in a target molecule, applying a continuous RF field to both preserve the singlet state and saturate the magnetization of undesired molecules and then mapping the target molecule singlet state back into an NMR observable state so that its spectrum can be read out unambiguously. The preparation of the target singlet state can be carefully controlled with pulse sequence parameters, so that spectral contrast can be achieved between molecules with very similar structures. We name this NMR contrast mechanism 'Suppression of Undesired Chemicals using Contrast-Enhancing Singlet States' (SUCCESS) and we demonstrate it in vitro for three target molecules relevant to neuroscience: aspartate, threonine and glutamine. Copyright © 2013 John Wiley & Sons, Ltd.

  8. On Emulation of Flueric Devices in Excitable Chemical Medium.

    Directory of Open Access Journals (Sweden)

    Andrew Adamatzky

    Full Text Available Flueric devices are fluidic devices without moving parts. Fluidic devices use fluid as a medium for information transfer and computation. A Belousov-Zhabotinsky (BZ medium is a thin-layer spatially extended excitable chemical medium which exhibits travelling excitation wave-fronts. The excitation wave-fronts transfer information. Flueric devices compute via jets interaction. BZ devices compute via excitation wave-fronts interaction. In numerical model of BZ medium we show that functions of key flueric devices are implemented in the excitable chemical system: signal generator, and, xor, not and nor Boolean gates, delay elements, diodes and sensors. Flueric devices have been widely used in industry since late 1960s and are still employed in automotive and aircraft technologies. Implementation of analog of the flueric devices in the excitable chemical systems opens doors to further applications of excitation wave-based unconventional computing in soft robotics, embedded organic electronics and living technologies.

  9. Excited charmed mesons

    International Nuclear Information System (INIS)

    Butler, J.N.; Shukla, S.

    1995-05-01

    The experimental status of excited charmed mesons is reviewed and is compared to theoretical expectations. Six states have been observed and their properties are consistent with those predicted for excited charmed states with orbital angular momentum equal to one

  10. Photoinduced singlet and triplet energy transfer in fullerene-oligothiophene-fullerene triads

    NARCIS (Netherlands)

    Hal, Paul A. van; Knol, Joop; Langeveld-Voss, Bea M.W.; Meskers, Stefan C.J.; Hummelen, J.C.; Janssen, René A.J.

    2001-01-01

    Photophysical properties of fullerene-oligothiophene-fullerene (C60-nT-C60) triads with n = 3, 6, or 9 thiophene units have been investigated using photoinduced absorption (PIA) and (time-resolved) fluorescence spectroscopy in toluene and compared to mixtures of oligothiophenes (nT) with

  11. Electron Transfer Mechanism of Substituted Benzimidazoles: Dimer Switching, Oscillations, and Search for Singlet Fission Properties

    Czech Academy of Sciences Publication Activity Database

    Plutnar, Jan; Hromadová, Magdaléna; Fanelli, N.; Ramešová, Šárka; Havlas, Zdeněk; Pospíšil, Lubomír

    2017-01-01

    Roč. 121, č. 18 (2017), s. 9963-9969 ISSN 1932-7447 R&D Projects: GA ČR(CZ) GA16-03085S; GA ČR GA15-19143S Institutional support: RVO:61388963 ; RVO:61388955 Keywords : correlated molecular calculations * Gaussian basis sets * reduction Subject RIV: CF - Physical ; Theoretical Chemistry; CG - Electrochemistry (UFCH-W) OBOR OECD: Physical chemistry Impact factor: 4.536, year: 2016

  12. Critically assessed electron-impact excitation cross sections for He(11S)

    International Nuclear Information System (INIS)

    Heer, F.J. de

    1998-11-01

    In this paper we reconsider the previous assessment of collision strengths, now mostly presented as cross sections, for excitation of He(1 1 S) to He(n 1,3 L) states (n=2-4, L=0-3). Due to the appearance of additional theoretical results the assessment can now be often given within smaller error limits than before for the singlet levels, as well as for the lower triplet levels (n=2). For the higher excited triplet states more studies are desirable to reduce the possible errors. (author)

  13. Topological spin-singlet superconductors with underlying sublattice structure

    Science.gov (United States)

    Dutreix, C.

    2017-07-01

    Majorana boundary quasiparticles may naturally emerge in a spin-singlet superconductor with Rashba spin-orbit interactions when a Zeeman magnetic field breaks time-reversal symmetry. Their existence and robustness against adiabatic changes is deeply related, via a bulk-edge correspondence, to topological properties of the band structure. The present paper shows that the spin-orbit may be responsible for topological transitions when the superconducting system has an underlying sublattice structure, as it appears in a dimerized Peierls chain, graphene, and phosphorene. These systems, which belong to the Bogoliubov-de Gennes class D, are found to have an extra symmetry that plays the role of the parity. It enables the characterization of the topology of the particle-hole symmetric band structure in terms of band inversions. The topological phase diagrams this leads to are then obtained analytically and exactly. They reveal that, because of the underlying sublattice structure, the existence of topological superconducting phases requires a minimum doping fixed by the strength of the Rashba spin orbit. Majorana boundary quasiparticles are finally predicted to emerge when the Fermi level lies in the vicinity of the bottom (top) of the conduction (valence) band in semiconductors such as the dimerized Peierls chain and phosphorene. In a two-dimensional topological superconductor based on (stretched) graphene, which is semimetallic, Majorana quasiparticles cannot emerge at zero and low doping, that is, when the Fermi level is close to the Dirac points. Nevertheless, they are likely to appear in the vicinity of the van Hove singularities.

  14. Targeted oxidation of Torpedo californica acetylcholinesterase by singlet oxygen.

    Science.gov (United States)

    Weiner, Lev; Roth, Esther; Silman, Israel

    2011-01-01

    The photosensitizer, methylene blue (MB), is a strong reversible inhibitor of Torpedo californica acetylcholinesterase (AChE) in the dark. Under illumination it causes irreversible inactivation. Loss of fluorescence of the singlet oxygen ((1)O(2)) trap, 9,10-dimethylanthracene, was retarded in the presence of AChE, and the rate of photo-inactivation was increased in the presence of D(2)O, indicating that inactivation was due to (1)O(2) generated by the photosensitizer. CD revealed slightly reduced far-UV ellipticity, and slightly enhanced binding of an amphiphilic probe, indicating limited unfolding of the photo-oxidized AChE. However, both near-UV ellipticity and intrinsic fluorescence were markedly reduced, suggesting photo-oxidative damage to tryptophans, (Trp) supported by appearance of novel emission peaks ascribed to N'-formylkynurenine and/or kynurenine. Like other partially unfolded forms, the photo-oxidized AChE was sensitive to proteolysis. Photosensitized inactivation produced exclusively chemically cross-linked dimers, whereas irradiation of a partially unfolded state generated higher-order oligomers. The active-site gorge of AChE contains Trp in inhibitor-binding sites that might be targets for photo-oxidation. Indeed, reversible inhibitors retard photo-inactivation, and photo-inactivation destroys their binding sites. An excess of AChE protects paraoxonase from photo-inactivation by sequestering the photosensitizer. Affinity photo-oxidation of AChE by MB thus provides a valuable model for studying site-specific photo-inactivation of enzymes in both fundamental and clinical contexts. © 2010 The Authors. Photochemistry and Photobiology © 2010 The American Society of Photobiology.

  15. Excited S 1 state dipole moments of nitrobenzene and p-nitroaniline from thermochromic effect on electronic absorption spectra

    Science.gov (United States)

    Kawski, A.; Kukliński, B.; Bojarski, P.

    2006-11-01

    The effect of temperature on the absorption spectra of nitrobenzene (NB) and p-nitroaniline (NA) in 1,2-dichloroethane was studied for temperature ranging from 295 K to 378 K and from 296 K to 408 K, respectively. With temperature increase the absorption bands of both compounds are blue shifted, which is caused by the decrease of permittivity ɛ and refractive index n. From the band shifts and by using the Bilot and Kawski theory [ L. Bilot, A. Kawski, Z. Naturforsch. 17a (1962) 621] the dipole moments in the excited singlet state μe = 6.59 D of NB and μe = 13.35 D of NA were determined. The influence of polarizability α, the Onsager cavity radius a and dipole moment in the ground state μg on the determined values of μe are discussed. A comparison of the obtained μe values with those of other authors is given. In the case of p-NA a strong intramolecular charge transfer (ICT) was confirmed.

  16. Endogenous Generation of Singlet Oxygen and Ozone in Human and Animal Tissues: Mechanisms, Biological Significance, and Influence of Dietary Components

    Directory of Open Access Journals (Sweden)

    Arnold N. Onyango

    2016-01-01

    Full Text Available Recent studies have shown that exposing antibodies or amino acids to singlet oxygen results in the formation of ozone (or an ozone-like oxidant and hydrogen peroxide and that human neutrophils produce both singlet oxygen and ozone during bacterial killing. There is also mounting evidence that endogenous singlet oxygen production may be a common occurrence in cells through various mechanisms. Thus, the ozone-producing combination of singlet oxygen and amino acids might be a common cellular occurrence. This paper reviews the potential pathways of formation of singlet oxygen and ozone in vivo and also proposes some new pathways for singlet oxygen formation. Physiological consequences of the endogenous formation of these oxidants in human tissues are discussed, as well as examples of how dietary factors may promote or inhibit their generation and activity.

  17. The excited state antiaromatic benzene ring: a molecular Mr Hyde?

    Science.gov (United States)

    Papadakis, Raffaello; Ottosson, Henrik

    2015-09-21

    The antiaromatic character of benzene in its first ππ* excited triplet state (T1) was deduced more than four decades ago by Baird using perturbation molecular orbital (PMO) theory [J. Am. Chem. Soc. 1972, 94, 4941], and since then it has been confirmed through a range of high-level quantum chemical calculations. With focus on benzene we now first review theoretical and computational studies that examine and confirm Baird's rule on reversal in the electron count for aromaticity and antiaromaticity of annulenes in their lowest triplet states as compared to Hückel's rule for the ground state (S0). We also note that the rule according to quantum chemical calculations can be extended to the lowest singlet excited state (S1) of benzene. Importantly, Baird, as well as Aihara [Bull. Chem. Soc. Jpn. 1978, 51, 1788], early put forth that the destabilization and excited state antiaromaticity of the benzene ring should be reflected in its photochemical reactivity, yet, today these conclusions are often overlooked. Thus, in the second part of the article we review photochemical reactions of a series of benzene derivatives that to various extents should stem from the excited state antiaromatic character of the benzene ring. We argue that benzene can be viewed as a molecular "Dr Jekyll and Mr Hyde" with its largely unknown excited state antiaromaticity representing its "Mr Hyde" character. The recognition of the "Jekyll and Hyde" split personality feature of the benzene ring can likely be useful in a range of different areas.

  18. Reduced-cost second-order algebraic-diagrammatic construction method for excitation energies and transition moments

    Science.gov (United States)

    Mester, Dávid; Nagy, Péter R.; Kállay, Mihály

    2018-03-01

    A reduced-cost implementation of the second-order algebraic-diagrammatic construction [ADC(2)] method is presented. We introduce approximations by restricting virtual natural orbitals and natural auxiliary functions, which results, on average, in more than an order of magnitude speedup compared to conventional, density-fitting ADC(2) algorithms. The present scheme is the successor of our previous approach [D. Mester, P. R. Nagy, and M. Kállay, J. Chem. Phys. 146, 194102 (2017)], which has been successfully applied to obtain singlet excitation energies with the linear-response second-order coupled-cluster singles and doubles model. Here we report further methodological improvements and the extension of the method to compute singlet and triplet ADC(2) excitation energies and transition moments. The various approximations are carefully benchmarked, and conservative truncation thresholds are selected which guarantee errors much smaller than the intrinsic error of the ADC(2) method. Using the canonical values as reference, we find that the mean absolute error for both singlet and triplet ADC(2) excitation energies is 0.02 eV, while that for oscillator strengths is 0.001 a.u. The rigorous cutoff parameters together with the significantly reduced operation count and storage requirements allow us to obtain accurate ADC(2) excitation energies and transition properties using triple-ζ basis sets for systems of up to one hundred atoms.

  19. Determination of ground and excited state dipole moments via electronic Stark spectroscopy: 5-methoxyindole

    Energy Technology Data Exchange (ETDEWEB)

    Wilke, Josefin; Wilke, Martin; Schmitt, Michael, E-mail: mschmitt@uni-duesseldorf.de [Institut für Physikalische Chemie, Heinrich-Heine-Universität, D-40225 Düsseldorf (Germany); Meerts, W. Leo, E-mail: leo.meerts@science.ru.nl [Institute for Molecules and Materials, Radboud University, NL-6525 AS Nijmegen (Netherlands)

    2016-01-28

    The dipole moments of the ground and lowest electronically excited singlet state of 5-methoxyindole have been determined by means of optical Stark spectroscopy in a molecular beam. The resulting spectra arise from a superposition of different field configurations, one with the static electric field almost parallel to the polarization of the exciting laser radiation, the other nearly perpendicular. Each field configuration leads to different intensities in the rovibronic spectrum. With an automated evolutionary algorithm approach, the spectra can be fit and the ratio of both field configurations can be determined. A simultaneous fit of two spectra with both field configurations improved the precision of the dipole moment determination by a factor of two. We find a reduction of the absolute dipole moment from 1.59(3) D to 1.14(6) D upon electronic excitation to the lowest electronically excited singlet state. At the same time, the dipole moment orientation rotates by 54{sup ∘} showing the importance of the determination of the dipole moment components. The dipole moment in the electronic ground state can approximately be obtained from a vector addition of the indole and the methoxy group dipole moments. However, in the electronically excited state, vector addition completely fails to describe the observed dipole moment. Several reasons for this behavior are discussed.

  20. Multi-frequency excitation

    KAUST Repository

    Younis, Mohammad I.

    2016-03-10

    Embodiments of multi-frequency excitation are described. In various embodiments, a natural frequency of a device may be determined. In turn, a first voltage amplitude and first fixed frequency of a first source of excitation can be selected for the device based on the natural frequency. Additionally, a second voltage amplitude of a second source of excitation can be selected for the device, and the first and second sources of excitation can be applied to the device. After applying the first and second sources of excitation, a frequency of the second source of excitation can be swept. Using the methods of multi- frequency excitation described herein, new operating frequencies, operating frequency ranges, resonance frequencies, resonance frequency ranges, and/or resonance responses can be achieved for devices and systems.