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Sample records for lowest singlet excitation

  1. Lowest singlet excited state and spectroscopy of α-carotene

    NASA Astrophysics Data System (ADS)

    Itoh, Takao

    2011-03-01

    Emission, excitation and absorption spectra of α-carotene have been measured in solvents with different polarizabilities. It is shown that in highly-polarized solvents α-carotene emits weak fluorescence from the S 1( π, π∗) state with the fluorescence origin observed at 14 800 ± 200 cm -1. The relative S 1/S 2 fluorescence intensity ratio tends to increase with increasing solvent polarizability or decreasing the S 1-S 2 energy separation. The obtained spectroscopic data include the Raman spectrum of α-carotene along with the vibrational analyses of the Raman spectrum based on the DFT calculation at the B3LYP/6-31G(d,p) level.

  2. The Ground and Two Lowest-lying Singlet Excited Electronic States of Copper Hydroxide (CuOH)

    SciTech Connect

    Wang, Suyun; Paul, Ankan; DeYonker, Nathan John; Yamaguchi, Yukio; Schaefer, Henry F

    2005-07-12

    The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. Various ab initio methods, including self-consistent field (SCF), configuration interaction, coupled cluster (CC), and complete-active-space SCF (CASSCF), have been employed to study the electronic structure of copper hydroxide (CuOH). Geometries, total energies, dipole moments, harmonic vibrational frequencies, and zero-point vibrational energies are reported for the linear 1Σ+ and 1Π stationary points, and for the bent ground-state X˜ 1A', and excited-states 2 1A" and 1 1A". Six different basis sets have been used in the study, Wachters/DZP being the smallest and QZVPP being the largest. The ground- and excited-state bending modes present imaginary frequencies for the linear stationary points, indicating that bent structures are more favorable. The effects of relativity for CuOH are important and have been considered using the Douglas–Kroll approach with cc-pVTZ/cc-pVTZ_DK and cc-pVQZ/cc-pVQZ_DK basis sets. The bent ground and two lowest-lying singlet excited states of the CuOH molecule are indeed energetically more stable than the corresponding linear structures. The optimized geometrical parameters for the X˜ 1A' and 1 1A" states agree fairly well with available experimental values. However, the 2 1A' structure and rotational constants are in poor agreement with experiment, and we suggest that the latter are in error. The predicted adiabatic excitation energies are also inconsistent with the experimental values of 45.5 kcal mol-1 for the 2 1A' state and 52.6 kcal mol-1 for the 1 1A" state. The theoretical CC and CASSCF methods show lower

  3. Experimental and theoretical dipole moments of purines in their ground and lowest excited singlet states

    NASA Astrophysics Data System (ADS)

    Aaron, Jean-Jacques; Diabou Gaye, Mame; Párkányi, Cyril; Cho, Nam Sook; Von Szentpály, László

    1987-01-01

    The ground-state dipole moments of seven biologically important purines (purine, 6-chloropurine, 6-mercaptopurine, hypoxanthine, theobromine, theophylline and caffeine) were determined at 25°C in acetic acid (all the above compounds with the exception of purine) and in ethyl acetate (purine, theophylline and caffeine). Because of its low solubility, it was not possible to measure the dipole moment of uric acid. The first excited singlet-state dipole moments were obtained on the basis of the Bakhshiev and Chamma—Viallet equations using the variation of the Stokes shift with the solvent dielectric constant-refractive index term. The theoretical dipole moments for all the purines listed above and including uric acid were calculated by combining the use of the PPP (π-LCI-SCF-MO) method for the π-contribution to the overall dipole moment with the σ-contribution obtained as a vector sum of the σbond moments and group moments. The experimental and theoretical values were compared with the data available in the literature for some of the purines under study. For several purines, the calculations were carried out for different tautomeric forms. Excited singlet-state dipole moments are smaller than the ground-state values by 0.8 to 2.2 Debye units for all purines under study with the exception of 6-chloropurine. The effects of the structure upon the ground- and excited-state dipole moments of the purines are discussed.

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

    NASA Astrophysics Data System (ADS)

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

    2016-11-01

    The S1←S0 vibronic spectra of gas-phase absorption at room temperature and fluorescence excitation of jet-cooled cyclopropanecarboxaldehyde (CPCA, c-C3H5CHO)were obtained and analyzed. In addition, the quantum chemical calculation (CASPT2/cc-pVTZ)was carried out for CPCA in the ground (S0) and lowest excited singlet (S1) electronic states. As a result, it was proved that the S1←S0 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 S1 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(S1)←syn(S0) 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.

  5. Charge-Transfer Excitations Steer the Davydov Splitting and Mediate Singlet Exciton Fission in Pentacene

    NASA Astrophysics Data System (ADS)

    Beljonne, D.; Yamagata, H.; Brédas, J. L.; Spano, F. C.; Olivier, Y.

    2013-05-01

    Quantum-chemical calculations are combined to a model Frenkel-Holstein Hamiltonian to assess the nature of the lowest electronic excitations in the pentacene crystal. We show that an admixture of charge-transfer excitations into the lowest singlet excited states form the origin of the Davydov splitting and mediate instantaneous singlet exciton fission by direct optical excitation of coherently coupled single and double exciton states, in agreement with recent experiments.

  6. Ab Initio Calculations of Singlet and Triplet Excited States of Chlorine Nitrate and Nitric Acid

    NASA Technical Reports Server (NTRS)

    Grana, Ana M.; Lee, Timothy J.; Head-Gordon, Martin; Langhoff, Stephen R. (Technical Monitor)

    1994-01-01

    Ab initio calculations of vertical excitations to singlet and triplet excited states of chlorine nitrate and nitric acid are reported. The nature of the electronic transitions are examined by decomposing the difference density into the sum of detachment and attachment densities. Counterparts for the three lowest singlet excited states of nitric acid survive relatively unperturbed in chlorine nitrate, while other low-lying singlet states of chlorine nitrate appear to be directly dissociative in the ClO chromophore. These results suggest an assignment of the two main peaks in the experimental chlorine nitrate absorption spectrum. In addition, triplet vertical excitations and the lowest optimized triplet geometries of both molecules are studied.

  7. Testing quantum electrodynamics in the lowest singlet state of neutral beryllium-9

    NASA Astrophysics Data System (ADS)

    Williams, Will; Cao, Melody; Kaplan, Emily

    2016-05-01

    We present high precision spectroscopic results on the 2s2p J = 1 singlet state in neutral beryllium-9. Combined with theoretical predictions this measurement serves as a test of quantum electrodynamics and various theoretical methods for predicting the energy of this state. Our experimental setup consists of an oven at 1200C that produces a beam of beryllium atoms. The singlet state is probed transverse to the atomic beam with 235nm light from a frequency quadrupled titanium sapphire laser, where the frequency doubled light at 470nm is stabilized to an ultra low expansion cavity. We also present our progress on spectroscopy on the lowest triplet states and the ionization threshold.

  8. Multiple magnetic singlet-singlet excitations in intermetallic PrNiSn

    NASA Astrophysics Data System (ADS)

    McEwen, K. A.; Jensen, J.; Beirne, E. D.; Allen, J. P.; Habicht, K.; Adroja, D. T.; Bewley, R. I.; Fort, D.

    2006-01-01

    Inelastic neutron-scattering experiments have been carried out on a polycrystalline sample of PrNiSn, and seven of the eight excited crystal-field singlets of the Pr ions were detected. The system stays paramagnetic, at least down to 0.9K , and the three principal susceptibility components have been measured on a PrNiSn single crystal between room temperature and 1.7K . The crystal-field excitations of the single crystal at low temperatures have been studied by triple-axis neutron spectroscopy. Dispersive effects are observed for three different levels of singlet-singlet excitations. The results are analyzed in terms of a mean-field/random phase approximation model, and it is concluded that the exchange interaction is highly anisotropic and of long range. The critical ratio between the maximum of the exchange interaction and that required for inducing a magnetic ordering of the singlet ground-state system is derived to be 0.48, leading to a predicted ordering temperature of 6mK for the combined electron-nuclear magnetic system.

  9. Conical intersections and diabatic potential energy surfaces for the three lowest electronic singlet states of H{sub 3}{sup +}

    SciTech Connect

    Mukherjee, Saikat; Adhikari, Satrajit; Mukhopadhyay, Debasis

    2014-11-28

    We calculate the adiabatic Potential Energy Surfaces (PESs) and the Non-Adiabatic Coupling Terms (NACTs) for the three lowest singlet states of H{sub 3}{sup +} in hyperspherical coordinates as functions of hyperangles (θ and ϕ) for a grid of fixed values of hyperradius (1.5 ⩽ ρ ⩽ 20 bohrs) using the MRCI level of methodology employing ab initio quantum chemistry package (MOLPRO). The NACT between the ground and the first excited state translates along the seams on the θ − ϕ space, i.e., there are six Conical Intersections (CIs) at each θ (60° ⩽ θ ⩽ 90°) within the domain, 0 ⩽ ϕ ⩽ 2π. While transforming the adiabatic PESs to the diabatic ones, such surfaces show up six crossings along those seams. Our beyond Born-Oppenheimer approach could incorporate the effect of NACTs accurately and construct single-valued, continuous, smooth, and symmetric diabatic PESs. Since the location of CIs and the spatial amplitudes of NACTs are most prominent around ρ = 10 bohrs, generally only those results are depicted.

  10. Inter- and intramolecular quenching of the singlet excited state of porphyrins by ferrocene

    SciTech Connect

    Giasson, R.; Lee, E.J.; Xiaohong Zhao; Wrighton, M.S. )

    1993-03-18

    Inter- and intramolecular quenching of the lowest singlet excited state of three porphyrins by ferrocene derivatives is reported. 5,15-Bis(4-tolyl)-2,3,7,8,12,13,17,18-octamethylporphyrin (1) and two derivatives of 1 where one of the tolyl methyl groups was replaced by a ferrocenylvinyl group, 2, or by a ferrocenylethyl group, 3, were prepared. Porphyrin 2 was isolated as a mixture of cis (73%) and trans (27%) isomers. Singlet excited state properties were studied by steady-state emission spectroscopy and by emission lifetime measurements. The relative quantum yields of fluorescence for 2 and 3 compared to 1 are 0.38 and 0.84, respectively. Fluorescence decay lifetimes of 1 and 3 are 15 and 14 ns, respectively. Fluorescence of 2 is revealed to be due to the emission of two species (cis and trans isomers) with lifetimes of 4 and 13 ns. The shorter fluorescence lifetimes and smaller fluorescence quantum yields for 2 and 3 compared to 1 are attributed to quenching of the singlet excited state of the porphyrin by the ferrocenyl centers. However, the fraction of quenching by electron transfer and energy transfer could not be quantitatively measured. The rate constant for quenching is no more than 10[sup 8] s[sup [minus]1], consistent with electron-transfer quenching. Intermolecular quenching rate constants for the quenching of the porphyrin singlet excited state by ferrocene derivatives were also found to be consistent with an electron transfer quenching mechanism. 28 refs., 3 figs., 1 tab.

  11. Calculating singlet excited states: Comparison with fast time-resolved infrared spectroscopy of coumarins

    NASA Astrophysics Data System (ADS)

    Hanson-Heine, Magnus W. D.; Wriglesworth, Alisdair; Uroos, Maliha; Calladine, James A.; Murphy, Thomas S.; Hamilton, Michelle; Clark, Ian P.; Towrie, Michael; Dowden, James; Besley, Nicholas A.; George, Michael W.

    2015-04-01

    In contrast to the ground state, the calculation of the infrared (IR) spectroscopy of molecular singlet excited states represents a substantial challenge. Here, we use the structural IR fingerprint of the singlet excited states of a range of coumarin dyes to assess the accuracy of density functional theory based methods for the calculation of excited state IR spectroscopy. It is shown that excited state Kohn-Sham density functional theory provides a high level of accuracy and represents an alternative approach to time-dependent density functional theory for simulating the IR spectroscopy of singlet excited states.

  12. Calculating singlet excited states: Comparison with fast time-resolved infrared spectroscopy of coumarins.

    PubMed

    Hanson-Heine, Magnus W D; Wriglesworth, Alisdair; Uroos, Maliha; Calladine, James A; Murphy, Thomas S; Hamilton, Michelle; Clark, Ian P; Towrie, Michael; Dowden, James; Besley, Nicholas A; George, Michael W

    2015-04-21

    In contrast to the ground state, the calculation of the infrared (IR) spectroscopy of molecular singlet excited states represents a substantial challenge. Here, we use the structural IR fingerprint of the singlet excited states of a range of coumarin dyes to assess the accuracy of density functional theory based methods for the calculation of excited state IR spectroscopy. It is shown that excited state Kohn-Sham density functional theory provides a high level of accuracy and represents an alternative approach to time-dependent density functional theory for simulating the IR spectroscopy of singlet excited states.

  13. Origin of the Red Shift for the Lowest Singlet π → π* Charge-Transfer Absorption of p-Nitroaniline in Supercritical CO2.

    PubMed

    Hidalgo, Marcelo; Rivelino, Roberto; Canuto, Sylvio

    2014-04-01

    The origin of the unusual solvatochromic shift of p-nitroaniline (PNA) in supercritical carbon dioxide (SCCO2) is theoretically investigated on the basis of experimental data. Ab initio quantum chemistry calculations have been employed to unveil the interaction of CO2 with this archetypical molecule. It is demonstrated that the nitro group of PNA works as an electron-donating site binding to the electron-deficient carbon atom of CO2, most probably via a Lewis acid-base interaction. Moreover, a cooperative C-H···O hydrogen bond seems to act as an additional stabilizing source during the solvation process of PNA in SCCO2. To support the influence of solute-solvent specific interactions on the lowest singlet π → π* charge-transfer excitation, we perform a sequential Monte Carlo time-dependent density functional theory simulation to evaluate the excited states of PNA in SCCO2 (T = 315 K, ρ = 0.81 g/cm(3)). A critical assessment of this simulation, compared to calculations carried out within the polarized continuum model, gives strong evidence that our proposed complexes are important in describing the solvatochromic shift of PNA in SCCO2. The calculated red shift from the gas phase accounts for 66% to 80% (depending on the degree of complexation) of the experimental data. Finally, these results also alleviate possible failures commonly attributed to long-range corrected functionals in reproducing the solvatochromism of PNA.

  14. Origin of the Red Shift for the Lowest Singlet π → π* Charge-Transfer Absorption of p-Nitroaniline in Supercritical CO2.

    PubMed

    Hidalgo, Marcelo; Rivelino, Roberto; Canuto, Sylvio

    2014-04-01

    The origin of the unusual solvatochromic shift of p-nitroaniline (PNA) in supercritical carbon dioxide (SCCO2) is theoretically investigated on the basis of experimental data. Ab initio quantum chemistry calculations have been employed to unveil the interaction of CO2 with this archetypical molecule. It is demonstrated that the nitro group of PNA works as an electron-donating site binding to the electron-deficient carbon atom of CO2, most probably via a Lewis acid-base interaction. Moreover, a cooperative C-H···O hydrogen bond seems to act as an additional stabilizing source during the solvation process of PNA in SCCO2. To support the influence of solute-solvent specific interactions on the lowest singlet π → π* charge-transfer excitation, we perform a sequential Monte Carlo time-dependent density functional theory simulation to evaluate the excited states of PNA in SCCO2 (T = 315 K, ρ = 0.81 g/cm(3)). A critical assessment of this simulation, compared to calculations carried out within the polarized continuum model, gives strong evidence that our proposed complexes are important in describing the solvatochromic shift of PNA in SCCO2. The calculated red shift from the gas phase accounts for 66% to 80% (depending on the degree of complexation) of the experimental data. Finally, these results also alleviate possible failures commonly attributed to long-range corrected functionals in reproducing the solvatochromism of PNA. PMID:26580369

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

    SciTech Connect

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

    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.

  16. The influence of excitation radiation parameters on photosensitized generation of singlet oxygen in water

    NASA Astrophysics Data System (ADS)

    Il'ina, A. D.; Glazov, A. L.; Semenova, I. V.; Vasyutinskii, O. S.

    2016-06-01

    Photosensitized generation of singlet oxygen with the aid of Radahlorin® photosensitizer has been investigated. The dependences of the intensity of singlet oxygen phosphorescence and photosensitizer fluorescence on the excitation radiation wavelength in the range of 350-440 nm and on the irradiation dose have been obtained. The dependence of the ratio of the sensitizer fluorescence intensity at about 670 nm to the singlet oxygen phosphorescence intensity at a wavelength of 1270 nm on the excitation radiation wavelength is found to be nonmonotonic and have a minimum near the center of the absorption band on its red wing. The results obtained can be used to monitor the singlet oxygen concentration in solutions.

  17. Singlet-to-Triplet Excitations in the Unconventional Spin-Peierls System TiOBr

    SciTech Connect

    Clancy, James P; Gaulin, Bruce D.; Adams, Carl P; Granroth, Garrett E; Kolesnikov, Alexander I; Sherline, Todd E; Chou, F. C.

    2011-01-01

    We have performed time-of-flight neutron scattering measurements on powder samples of the unconventional spin-Peierls compound TiOBr using the fine-resolution Fermi chopper spectrometer (SEQUOIA) at the SNS. These measurements reveal two branches of magnetic excitations within the commensurate and incommensurate spin-Peierls phases, which we associate with n = 1 and n = 2 triplet excitations out of the singlet ground state. These measurements represent the first direct measure of the singlet-triplet energy gap in TiOBr, which is found to have a value of Eg 21 meV.

  18. Accurate ab initio potential energy curves and spectroscopic properties of the four lowest singlet states of C2

    SciTech Connect

    Boschen, Jeffery S.; Theis, Daniel; Ruedenberg, Klaus; Windus, Theresa L.

    2013-12-07

    The diatomic carbon molecule has a complex electronic structure with a large number of low-lying electronic excited states. In this work, the potential energy curves (PECs) of the four lowest lying singlet states (X-1 Sigma(+)(g), A(1)Pi(u), B-1 Delta(g), and B'(1)Sigma(+)(g)) were obtained by high-level ab initio calculations. Valence electron correlation was accounted for by the correlation energy extrapolation by intrinsic scaling (CEEIS) method. Additional corrections to the PECs included core-valence correlation and relativistic effects. Spin-orbit corrections were found to be insignificant. The impact of using dynamically weighted reference wave functions in conjunction with CEEIS was examined and found to give indistinguishable results from the even weighted method. The PECs showed multiple curve crossings due to the B-1 Delta(g) state as well as an avoided crossing between the two (1)Sigma(+)(g) states. Vibrational energy levels were computed for each of the four electronic states, as well as rotational constants and spectroscopic parameters. Comparison between the theoretical and experimental results showed excellent agreement overall. Equilibrium bond distances are reproduced to within 0.05 %. The dissociation energies of the states agree with experiment to within similar to 0.5 kcal/mol, achieving "chemical accuracy." Vibrational energy levels show average deviations of similar to 20 cm(-1) or less. The B-1 Delta(g) state shows the best agreement with a mean absolute deviation of 2.41 cm(-1). Calculated rotational constants exhibit very good agreement with experiment, as do the spectroscopic constants.

  19. A theoretical analysis of the lowest excited states in HNO/NOH and HPO/POH

    NASA Astrophysics Data System (ADS)

    Luna, Alberto; Merchán, Manuela; Ross, Björn O.

    1995-07-01

    A theoretical study has been performed on the ground and two lowest excited states of the HNO/NOH and HPO/POH systems. Full geometry optimization was made for all states using the CASSCF method with dynamic correlation effects accounted for by second order perturbation theory (CASPT2). The computed vertical and adiabatic transition energies are in agreement with available experimental data.

  20. Excitation of singlet levels of a singly charged scandium ion in e-Sc collisions

    NASA Astrophysics Data System (ADS)

    Smirnov, Yu. M.

    2011-09-01

    The excitation of singlet levels of the singly charged scandium ion is experimentally studied in collisions of slow electrons with scandium atoms. At the exciting electron energy of 30 eV, 59 excitation cross sections are measured. In the electron energy range of 0-200 eV, seven optical excitation functions are recorded. On the basis of these data the total excitation cross sections are calculated for 11 even and 9 odd levels of Sc II, as well as the contribution of cascade population to 8 even and 7 odd levels.

  1. Zethrene biradicals: How pro-aromaticity is expressed in the ground electronic state and in the lowest energy singlet, triplet, and ionic states

    SciTech Connect

    Zafra, José Luis; González Cano, Rafael C.; Ruiz Delgado, M. Carmen; López Navarrete, Juan T.; Casado, Juan

    2014-02-07

    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.

  2. Low-energy singlet excitations in spin-1/2 Heisenberg antiferromagnet on square lattice

    NASA Astrophysics Data System (ADS)

    Aktersky, A. Yu.; Syromyatnikov, A. V.

    2016-05-01

    We present an approach based on a dimer expansion which describes low-energy singlet excitations (singlons) in spin-1/2 Heisenberg antiferromagnet on simple square lattice. An operator ("effective Hamiltonian") is constructed whose eigenvalues give the singlon spectrum. The "effective Hamiltonian" looks like a Hamiltonian of a spin-1/2 magnet in strong external magnetic field and it has a gapped spectrum. It is found that singlet states lie above triplet ones (magnons) in the whole Brillouin zone except in the vicinity of the point (π , 0), where their energies are slightly smaller. Based on this finding, we suggest that a magnon decay is possible near (π , 0) into another magnon and a singlon which may contribute to the dip of the magnon spectrum near (π , 0) and reduce the magnon lifetime. It is pointed out that the singlon-magnon continuum may contribute to the continuum of excitations observed recently near (π , 0).

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

    NASA Astrophysics Data System (ADS)

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

    2013-07-01

    We investigate the failure of time-dependent density functional theory (TDDFT) with the CAM-B3LYP exchange-correlation (xc) functional coupled to the polarisable embedding (PE) scheme (PE-CAM-B3LYP) in reproducing the solvatochromic shift of the lowest intense charge-transfer excitation in para-nitroaniline (pNA) in water by comparing with results obtained with the coupled cluster singles and doubles (CCSD) model also coupled to the polarisable embedding scheme (PE-CCSD). We determine the amount of charge separation in the ground and excited charge-transfer state with both methods by calculating the electric dipole moments in the gas phase and for 100 solvent configurations. We find that CAM-B3LYP overestimates the amount of charge separation inherent in the ground state and TDDFT/CAM-B3LYP drastically underestimates this amount in the excited charge-transfer state. As the errors in the solvatochromatic shift are found to be inverse proportional to the change in dipole moment upon excitation, we conclude that the flaws in the description of the solvatochromic shift of this excitation are related to TDDFT itself and how it responds to the solvent effects modelled by the PE scheme. We recommend therefore to benchmark results of TDDFT calculations with CAM-B3LYP for intramolecular charge-transfer excitations in molecular systems similar to pNA against higher level ab initio wave function methods, like, e.g. CCSD, prior to their use. Using the calculated change in dipole moment upon excitation as a measure for charge-transfer character, we furthermore confirm that the difference between excitation energies calculated with TDDFT and with the Tamm-Dancoff approximation (TDA) to TDDFT is indeed correlated with the charge-transfer character of a given electronic transition both in vacuo and in solution. This is supported by a corresponding correlation between the change in dipole moment and the size of the Λ index diagnostic for the investigated CT excitation.

  4. Reverse intersystem crossing from upper triplet levels to excited singlet: a 'hot excition' path for organic light-emitting diodes.

    PubMed

    Hu, Dehua; Yao, Liang; Yang, Bing; Ma, Yuguang

    2015-06-28

    Since researches on the fate of highly excited triplet states demonstrated the existence of reverse intersystem crossing (RISC) from upper triplet levels to singlet manifold in naphthalene, quinoline, isoquinoline, etc. in the 1960s, this unique photophysical process was then found and identified in some other aromatic materials. However, the early investigations mainly focus on exploring the mechanism of this photophysical process; no incorporation of specific application was implemented. Until recently, our group innovatively used this 'sleeping' photophysical process to enhance the efficiency of fluorescent organic light-emitting diodes by simultaneously harvesting singlet and triplet excitons. Efforts are devoted to developing materials with high photoluminescence efficiency and effective RISC through appropriate molecular design in a series of donor-acceptor material systems. The experimental and theoretical results indicate that these materials exhibit hybridized local and charge-transfer excited state, which achieve a combination of the high radiation from local excited state and the high T(m)→S(n) (m≥2, n≥1) conversion along charge-transfer excited state. As expected, the devices exhibited favourable external quantum efficiency and low roll-off, and especially an exciton utilization efficiency exceeding the limit of 25%. Considering the significant progress made in organic light-emitting diodes with this photophysical process, we review the relevant mechanism and material systems, as well as our design principle in materials and device application.

  5. Spectroscopy and intramolecular relaxation of methyl salicylate in its first excited singlet state

    NASA Astrophysics Data System (ADS)

    Kuper, Jerry W.; Perry, David S.

    1984-05-01

    High resolution fluorescence excitation experiments are reported for the blue emitting rotamer of methyl salicylate in its first excited singlet state. These experiments employ moderate expansions of methyl salicylate seeded in argon ( P0D=5-8 Torr cm) to achieve rotational and vibrational cooling in a pulsed supersonic jet. The rotational contour of the electronic origin at 30 055.3 cm-1 is shown to be consistent with a geometrically distorted π-π* excited state, partially polarized along the A axis and with a rotational temperature of 5-7 K. A noticeable broadening of the spectral features beyond the rotational contour begins at 500 cm-1 above the origin and then increases rapidly above 900 cm-1 reaching a width of 12 cm-1 near 1200 cm-1. The constancy of fluorescence decay lifetimes in this region indicate that intramolecular vibrational relaxation in the S1 manifold is the broadening mechanism.

  6. The holographic recording in photopolymer by excitation forbidden singlet-triplet transitions

    NASA Astrophysics Data System (ADS)

    Shelkovnikov, V. V.; Pen, E. F.; Russkich, V. V.; Vasiliev, E. V.; Kovalevsky, V. I.

    2006-05-01

    The possibility and features of the holographic recording by excitation of the forbidden singlet-triplet transitions are considered in the report. The experimental demonstration of the hologram recording on forbidden transition is carried out in thick photopolymer material sensitized by Erithrozine dye. The single hologram with diffraction efficiency DE=50% and 16 angle multiplexing hologram were recorded by irradiation of the low intensity He-Ne laser (632 nm) at high concentration of the sensitizing dye and at high optical density in allowed absorption band of dye. The growth of DE of transition hologram depending on the Kr+(647 nm) laser irradiation intensity of was studied. The observed linear dependence of the maximal rate of DE growth on the intensity of recording irradiation was explained by two steps-two photon excitation (T I<--S 0, T II<--T I) of the dye in the photopolymer samples.

  7. The electronic origin and vibrational levels of the first excited singlet state of isocyanic acid (HNCO)

    SciTech Connect

    Berghout, H. Laine; Crim, F. Fleming; Zyrianov, Mikhail; Reisler, Hanna

    2000-04-15

    The combination of vibrationally mediated photofragment yield spectroscopy, which excites molecules prepared in single vibrational states, and multiphoton fluorescence spectroscopy, which excites molecules cooled in a supersonic expansion, provides detailed information on the energetics and vibrational structure of the first excited singlet state (S{sub 1}) of isocyanic acid (HNCO). Dissociation of molecules prepared in individual vibrational states by stimulated Raman excitation probes vibrational levels near the origin of the electronically excited state. Detection of fluorescence from dissociation products formed by multiphoton excitation through S{sub 1} of molecules cooled in a supersonic expansion reveals the vibrational structure at higher energies. Both types of spectra show long, prominent progressions in the N-C-O bending vibration built on states with different amounts of N-C stretching excitation and H-N-C bending excitation. Analyzing the spectra locates the origin of the S{sub 1} state at 32 449{+-}20 cm{sup -1} and determines the harmonic vibrational frequencies of the N-C stretch ({omega}{sub 3}=1034{+-}20 cm{sup -1}), the H-N-C bend ({omega}{sub 4}=1192{+-}19 cm{sup -1}), and the N-C-O bend ({omega}{sub 5}=599{+-}7 cm{sup -1}), values that are consistent with several ab initio calculations. The assigned spectra strongly suggest that the N-C stretching vibration is a promoting mode for internal conversion from S{sub 1} to S{sub 0}. (c) 2000 American Institute of Physics.

  8. Long-Lived Triplet Excited States of Bent-Shaped Pentacene Dimers by Intramolecular Singlet Fission.

    PubMed

    Sakuma, Takao; Sakai, Hayato; Araki, Yasuyuki; Mori, Tadashi; Wada, Takehiko; Tkachenko, Nikolai V; Hasobe, Taku

    2016-03-24

    Intramolecular singlet fission (ISF) is a promising photophysical process to construct more efficient light energy conversion systems as one excited singlet state converts into two excited triplet states. Herein we synthesized and evaluated bent-shaped pentacene dimers as a prototype of ISF to reveal intrinsic characters of triplet states (e.g., lifetimes of triplet excited states). In this study, meta-phenylene-bridged TIPS-pentacene dimer (PcD-3Ph) and 2,2'-bipheynyl bridged TIPS-pentacene dimer (PcD-Biph) were newly synthesized as bent-shaped dimers. In the steady-state spectroscopy, absorption and emission bands of these dimers were fully characterized, suggesting the appropriate degree of electronic coupling between pentacene moieties in these dimers. In addition, the electrochemical measurements were also performed to check the electronic interaction between two pentacene moieties. Whereas the successive two oxidation peaks owing to the delocalization were observed in a directly linked-pentacene dimer (PcD) by a single bond, the cyclic voltammograms in PcD-Biph and PcD-3Ph implied the weaker interaction compared to that of p-phenylene-bridged TIPS-pentacene dimer (PcD-4Ph) and PcD. The femtosecond and nanosecond transient absorption spectra clearly revealed the slower ISF process in bent-shaped pentacene dimers (PcD-Biph and PcD-3Ph), more notably, the slower relaxation of the excited triplet states in PcD-Biph and PcD-3Ph. Namely, the quantum yields of triplet states (ΦT) by ISF approximately remain constant (ca. 180-200%) in all dimer systems, whereas the lifetimes of the triplet excited states became much longer (up to 360 ns) in PcD-Biph as compared to PcD-4Ph (15 ns). Additionally, the lifetimes of the corresponding triplet states in PcD-Biph and PcD-3Ph were sufficiently affected by solvent viscosity. In particular, the lifetimes of PcD-Biph triplet state in THF/paraffin (1.0 μs) increased up to approximately three times as compared to that in THF

  9. Long-Lived Triplet Excited States of Bent-Shaped Pentacene Dimers by Intramolecular Singlet Fission.

    PubMed

    Sakuma, Takao; Sakai, Hayato; Araki, Yasuyuki; Mori, Tadashi; Wada, Takehiko; Tkachenko, Nikolai V; Hasobe, Taku

    2016-03-24

    Intramolecular singlet fission (ISF) is a promising photophysical process to construct more efficient light energy conversion systems as one excited singlet state converts into two excited triplet states. Herein we synthesized and evaluated bent-shaped pentacene dimers as a prototype of ISF to reveal intrinsic characters of triplet states (e.g., lifetimes of triplet excited states). In this study, meta-phenylene-bridged TIPS-pentacene dimer (PcD-3Ph) and 2,2'-bipheynyl bridged TIPS-pentacene dimer (PcD-Biph) were newly synthesized as bent-shaped dimers. In the steady-state spectroscopy, absorption and emission bands of these dimers were fully characterized, suggesting the appropriate degree of electronic coupling between pentacene moieties in these dimers. In addition, the electrochemical measurements were also performed to check the electronic interaction between two pentacene moieties. Whereas the successive two oxidation peaks owing to the delocalization were observed in a directly linked-pentacene dimer (PcD) by a single bond, the cyclic voltammograms in PcD-Biph and PcD-3Ph implied the weaker interaction compared to that of p-phenylene-bridged TIPS-pentacene dimer (PcD-4Ph) and PcD. The femtosecond and nanosecond transient absorption spectra clearly revealed the slower ISF process in bent-shaped pentacene dimers (PcD-Biph and PcD-3Ph), more notably, the slower relaxation of the excited triplet states in PcD-Biph and PcD-3Ph. Namely, the quantum yields of triplet states (ΦT) by ISF approximately remain constant (ca. 180-200%) in all dimer systems, whereas the lifetimes of the triplet excited states became much longer (up to 360 ns) in PcD-Biph as compared to PcD-4Ph (15 ns). Additionally, the lifetimes of the corresponding triplet states in PcD-Biph and PcD-3Ph were sufficiently affected by solvent viscosity. In particular, the lifetimes of PcD-Biph triplet state in THF/paraffin (1.0 μs) increased up to approximately three times as compared to that in THF

  10. Singlet and triplet excited state properties of natural chlorophylls and bacteriochlorophylls

    SciTech Connect

    Niedzwiedzki, Dariusz; Blankenship, R. E.

    2010-11-18

    Ten naturally occurring chlorophylls (a, b, c{sub 2}, d) and bacteriochlorophylls (a, b, c, d, e, g) were purified and studied using the optical spectroscopic techniques of both steady state and time-resolved absorption and fluorescence. The studies were carried out at room temperature in nucleophilic solvents in which the central Mg is hexacoordinated. The comprehensive studies of singlet excited state lifetimes show a clear dependency on the structural features of the macrocycle and terminal substituents. The wide-ranging studies of triplet state lifetime demonstrate the existence of an energy gap law for these molecules. The knowledge of the dynamics and the energies of the triplet state that were obtained in other studies allowed us to construct an energy gap law expression that can be used to estimate the triplet state energies of any (B)chlorophyll molecule from its triplet lifetime obtained in a liquid environment.

  11. Excited singlet molecular O2 (1Δg) is generated enzymatically from excited carbonyls in the dark

    PubMed Central

    Mano, Camila M.; Prado, Fernanda M.; Massari, Júlio; Ronsein, Graziella E.; Martinez, Glaucia R.; Miyamoto, Sayuri; Cadet, Jean; Sies, Helmut; Medeiros, Marisa H. G.; Bechara, Etelvino J. H.; Di Mascio, Paolo

    2014-01-01

    In mammalian tissues, ultraweak chemiluminescence arising from biomolecule oxidation has been attributed to the radiative deactivation of singlet molecular oxygen [O2 (1Δg)] and electronically excited triplet carbonyl products involving dioxetane intermediates. Herein, we describe evidence of the generation of O2 (1Δg) in aqueous solution via energy transfer from excited triplet acetone. This involves thermolysis of 3,3,4,4-tetramethyl-1,2-dioxetane, a chemical source, and horseradish peroxidase-catalyzed oxidation of 2-methylpropanal, as an enzymatic source. Both sources of excited carbonyls showed characteristic light emission at 1,270 nm, directly indicative of the monomolecular decay of O2 (1Δg). Indirect analysis of O2 (1Δg) by electron paramagnetic resonance using the chemical trap 2,2,6,6-tetramethylpiperidine showed the formation of 2,2,6,6-tetramethylpiperidine-1-oxyl. Using [18O]-labeled triplet, ground state molecular oxygen [18O2 (3Σg-)], chemical trapping of 18O2 (1Δg) with disodium salt of anthracene-9,10-diyldiethane-2,1-diyl disulfate yielding the corresponding double-[18O]-labeled 9,10-endoperoxide, was detected through mass spectrometry. This corroborates formation of O2 (1Δg). Altogether, photoemission and chemical trapping studies clearly demonstrate that chemically and enzymatically nascent excited carbonyl generates 18O2 (1Δg) by triplet-triplet energy transfer to ground state oxygen O2 (3Σg−), and supports the long formulated hypothesis of O2 (1Δg) involvement in physiological and pathophysiological events that might take place in tissues in the absence of light. PMID:25087485

  12. Switching between Aromatic and Antiaromatic 1,3-Phenylene-Strapped [26]- and [28]Hexaphyrins upon Passage to the Singlet Excited State.

    PubMed

    Sung, Young Mo; Oh, Juwon; Kim, Woojae; Mori, Hirotaka; Osuka, Atsuhiro; Kim, Dongho

    2015-09-23

    We have demonstrated aromaticity reversal in the singlet excited states of internally 1,3-phenylene-strapped [26]- and [28]hexaphyrins (P26H and P28H). P26H displays a broad and reduced singlet-excited-state absorption spectrum, whereas P28H exhibits a sharp and intense singlet-excited-state absorption spectrum; both are in contrast to the ground-state absorption spectra, strongly indicating aromaticity reversal in the singlet excited state. Furthermore, magnetic and topological indices of aromaticity such as nucleus-independent chemical shift and harmonic oscillator model of aromaticity values for P26H and P28H also suggest that their singlet excited states become antiaromatic and aromatic, respectively.

  13. Two-photon excitation microscopy using the second singlet state of fluorescent agents within the ``tissue optical window''

    NASA Astrophysics Data System (ADS)

    Pu, Yang; Shi, Lingyan; Pratavieira, Sebastião; Alfano, R. R.

    2013-10-01

    Two-photon (2P) excitation of the second singlet (S2) state of a group of fluorescent agents with near infrared emission was used to extend the optical excitation and imaging regime of 2P microscope into "tissue optical window" (650-1100 nm). As the first step to achieve deeper optical imaging, Chlorophyll a and Indocyanine green are investigated and demonstrated as imaging agents using 2P S2 excitation at 800 nm for microscope imaging at 685 nm. The salient feature is to drive both the 2P excitation and emission wavelengths of the imaging agents to fall into the "tissue optical window."

  14. Theoretical prediction of the vibrational spectrum of naphthalene in the first excited singlet state

    NASA Astrophysics Data System (ADS)

    Swiderek, Petra; Hohlneicher, Georg; Maluendes, Sergio A.; Dupuis, Michel

    1993-01-01

    Complete harmonic force fields have been calculated for the ground state (S0) and the first excited singlet state (S1) of naphthalene using the multiconfiguration self-consistent field (MCSCF) approach. Identical calculations were performed for benzene to test the methodology with already available theoretical and empirical force fields. Two different basis sets were applied (STO-3G and near double-zeta) and all π-orbitals included in the active space. The geometries of ground and excited states were separately optimized. Following the ideas of Pulay, the force constants were scaled before calculating frequencies and normal modes. For the ground states the influence of correlation is discussed by comparison with Pulay's results. Except for special vibrations where correlation effects turn out to be important, the use of Pulay's scaling factors leads to a satisfactory description of the in-plane-vibrations. In the case of benzene the calculated frequency shifts between S0 and S1 are in complete qualitative agreement with experimental observations. In the case of naphthalene the new theoretical results suggest several revisions of earlier empirical assignments.

  15. Excitation of the lowest electronic transitions in ethanol by low-energy electrons

    NASA Astrophysics Data System (ADS)

    Hargreaves, L. R.; Khakoo, M. A.; Winstead, C.; McKoy, V.

    2016-09-01

    We report absolute differential and integral cross sections for electronic excitation of ethanol, by low-energy electron impact. Cross sections for low-lying excited states were measured at incident electron energies from 9 to 20 eV and at scattering angles from {5}\\circ through {130}\\circ . Our results include cross sections for excitation of the 1{}3A\\prime \\prime and 1{}1A\\prime \\prime states as well as for the 2{}3A\\prime \\prime + 1{}3A\\prime and 2{}1A\\prime \\prime + 2{}1A\\prime cross section sums. Corresponding calculations were also performed using the Schwinger multichannel method, within an 11-channel close-coupling scheme.

  16. Theoretical description of electronically excited vinylidene up to 10 eV: first high level ab initio study of singlet valence and Rydberg states.

    PubMed

    Boyé-Péronne, Séverine; Gauyacq, Dolores; Liévin, Jacques

    2014-11-01

    The first quantitative description of the Rydberg and valence singlet electronic states of vinylidene lying in the 0-10 eV region is performed by using large scale ab initio calculations. A deep analysis of Rydberg-valence interactions has been achieved thanks to the comprehensive information contained in the accurate Multi-Reference Configuration Interaction wavefunctions and an original population analysis highlighting the respective role played by orbital and state mixing in such interactions. The present theoretical approach is thus adequate for dealing with larger than diatomic Rydberg systems. The nine lowest singlet valence states have been optimized. Among them, some are involved in strong Rydberg-valence interactions in the region of the Rydberg state equilibrium geometry. The Rydberg states of vinylidene present a great similarity with the acetylene isomer, concerning their quantum defects and Rydberg molecular orbital character. As in acetylene, strong s-d mixing is revealed in the n = 3 s-d supercomplex. Nevertheless, unlike in acetylene, the close-energy of the two vinylidene ionic cores (2)A1 and (2)B1 results into two overlapped Rydberg series. These Rydberg series exhibit local perturbations when an accidental degeneracy occurs between them and results in avoided crossings. In addition, some Δl = 1 (s-p and p-d) mixings arise for some Rydberg states and are rationalized in term of electrostatic interaction from the electric dipole moment of the ionic core. The strongest dipole moment of the (2)B1 cationic state also stabilizes the lowest members of the n = 3 Rydberg series converging to this excited state, as compared to the adjacent series converging toward the (2)A1 ionic ground state. The overall energies of vinylidene Rydberg states lie above their acetylene counterpart. Finally, predictions for optical transitions in singlet vinylidene are suggested for further experimental spectroscopic characterization of vinylidene.

  17. Nonradiative deactivation of the lowest excited triplet state of the dibenzo- p-dioxin molecule

    NASA Astrophysics Data System (ADS)

    Gastilovich, E. A.; Klimenko, V. G.; Volkova, L. V.; Nurmukhametov, R. N.

    2011-11-01

    In the nonadiabatic approximation, we study how intramolecular interactions affect the nonradiative energy degradation T {1/ s } ↝ S 0 of triplet sublevels s of the lowest triplet state of the dibenzo- p-dioxin molecule. We consider the role played in the degradation by the shape of promoting high- and low-frequency vibrational modes and by spin-orbit interactions separately in the carbon backbone of the molecule and in heteroatoms (oxygen). We find that σ-electrons of oxygen that correspond to the lone pair and to valence electrons play different roles in the nonadiabatic interaction.

  18. Observations and theoretical analysis of highly excited singlet and triplet states of cadmium

    NASA Astrophysics Data System (ADS)

    Vidolova-Angelova, E.; Baharis, C.; Roupakas, G.; Kompitsas, M.

    1996-06-01

    We have recorded the 0953-4075/29/12/010/img7 - 50) bound Rydberg spectrum of cadmium. We have fully resolved the multiplet up to n = 19 and partially up to n = 24. Furthermore, we have observed the odd singlet and triplet 5sn f Rydberg series for n = 10 - 22 and n = 4 - 21, respectively. We have applied two- and three-step laser schemes to excite Cd vapour in a heat pipe-like oven which was operated as a thermionic diode for detection. Theoretical calculations were performed for the energies of the 5sn p and 5sn f series using perturbation theory with a zero-order model approximation. There is a good agreement between theoretical and experimental results for the 5sn p series, the deviation decreasing with n and being 1 - 2 0953-4075/29/12/010/img8 for n = 50. The agreement for the 5sn f is satisfactory. From the quantum defect of the 5sn f series we approximate a value of the effective dipole polarizability of the 0953-4075/29/12/010/img9 ion of 0953-4075/29/12/010/img10 in units of the Bohr radius.

  19. Isotope effects and Born-Oppenheimer breakdown in excited singlet states of the lithium dimer.

    PubMed

    Adohi-Krou, A; Martin, F; Ross, A J; Linton, C; Le Roy, R J

    2004-10-01

    Observation of infrared electronic transitions involving the 1 (1)Deltag state of 7Li2 has instigated an investigation of Born-Oppenheimer breakdown in four singlet electronic states correlating with (2s+2s), (2s+2p), and (2p+2p) lithium atoms. The 1 (1)Deltag state, which correlates at long range with (2p+2p) atoms, has been observed in emission from the (5p) (1)Piu Rydberg state and in 1 (1)Deltag-B (1)Piu bands, in both instances following optical-optical double-resonance excitation. The latter transition was observed previously for the lighter isotopomer, 6Li2 [C. Linton, F. Martin, P. Crozet, A. J. Ross, and R. Bacis, J. Mol. Spectrosc. 158, 445 (1993)]. By analyzing multiple-isotopomer data for several electronic systems simultaneously, we have determined the electronic isotope shifts and the leading vibrational and/or rotational Born-Oppenheimer breakdown terms for the X (1)Sigmag+, A (1)Sigmau+, B (1)Piu, and 1 (1)Deltag states of the lithium dimer. This paper also reports Fourier transform measurements of the B-X absorption spectra of 6Li2 and 7Li2, which were required to better define the bottom portion of the B (1)Piu state potential.

  20. Aromaticity Reversal in the Lowest Excited Triplet State of Archetypical Möbius Heteroannulenic Systems.

    PubMed

    Oh, Juwon; Sung, Young Mo; Kim, Woojae; Mori, Shigeki; Osuka, Atsuhiro; Kim, Dongho

    2016-05-23

    The aromaticity reversal in the lowest triplet state (T1 ) of a comparable set of Hückel/Möbius aromatic metalated expanded porphyrins was explored by optical spectroscopy and quantum calculations. In the absorption spectra, the T1 states of the Möbius aromatic species showed broad, weak, and ill-defined spectral features with small extinction coefficients, which is in line with typical antiaromatic expanded porphyrins. In combination with quantum calculations, these results indicate that the Möbius aromatic nature of the S0 state is reversed to Möbius antiaromaticity in the T1 state. This is the first experimental observation of aromaticity reversal in the T1 state of Möbius aromatic molecules. PMID:27079620

  1. Singlet fission in rubrene single crystal: direct observation by femtosecond pump-probe spectroscopy.

    PubMed

    Ma, Lin; Zhang, Keke; Kloc, Christian; Sun, Handong; Michel-Beyerle, Maria E; Gurzadyan, Gagik G

    2012-06-21

    The excited state dynamics of rubrene in solution and in the single crystal were studied by femtosecond pump-probe spectroscopy under various excitation conditions. Singlet fission was demonstrated to play a predominant role in the excited state relaxation of the rubrene crystal in contrast to rubrene in solution. Upon 500 nm excitation, triplet excitons form on the picosecond time scale via fission from the lowest excited singlet state. Upon 250 nm excitation, fission from upper excited singlet states is observed within 200 fs. PMID:22510785

  2. Generating Light from Upper Excited Triplet States: A Contribution to the Indirect Singlet Yield of a Polymer OLED, Helping to Exceed the 25% Singlet Exciton Limit

    PubMed Central

    Jankus, Vygintas; Aydemir, Murat; Dias, Fernando B.

    2016-01-01

    The mechanisms by which light is generated in an organic light emitting diode have slowly been elucidated over the last ten years. The role of triplet annihilation has demonstrated how the “spin statistical limit” can be surpassed, but it cannot account for all light produced in the most efficient devices. Here, a further mechanism is demonstrated by which upper excited triplet states can also contribute to indirect singlet production and delayed fluorescence. Since in a device the population of these TN states is large, this indirect radiative decay channel can contribute a sizeable fraction of the total emission measured from a device. The role of intra‐ and interchain charge transfer states is critical in underpinning this mechanism. PMID:27610333

  3. Generating Light from Upper Excited Triplet States: A Contribution to the Indirect Singlet Yield of a Polymer OLED, Helping to Exceed the 25% Singlet Exciton Limit

    PubMed Central

    Jankus, Vygintas; Aydemir, Murat; Dias, Fernando B.

    2016-01-01

    The mechanisms by which light is generated in an organic light emitting diode have slowly been elucidated over the last ten years. The role of triplet annihilation has demonstrated how the “spin statistical limit” can be surpassed, but it cannot account for all light produced in the most efficient devices. Here, a further mechanism is demonstrated by which upper excited triplet states can also contribute to indirect singlet production and delayed fluorescence. Since in a device the population of these TN states is large, this indirect radiative decay channel can contribute a sizeable fraction of the total emission measured from a device. The role of intra‐ and interchain charge transfer states is critical in underpinning this mechanism.

  4. Generation of singlet oxygen with the use of optically excited fullerenes and fullerene-like nanoparticles

    NASA Astrophysics Data System (ADS)

    Danilov, O. B.; Belousova, I. M.; Mak, A. A.; Belousov, V. P.; Grenishin, A. S.; Kiselev, V. M.; Kris'ko, A. V.; Ponomarev, A. N.; Sosnov, E. N.

    2003-12-01

    Experimental results and a kinetic model of generation of singlet oxygen during the interaction of oxygen molecules with optically pumped (lamp or laser radiation) fullerenes or fullerene-like nanoclusters in solutions, suspensions, and the form of various solid-phase membranes (surfaces) are presented. The experimental data on the photoluminescence of singlet oxygen in solutions of fullerenes are compared with the results of numerical simulation on the basis of the kinetic model with specified constants of photochemical processes. On the basis of the experimental results, it is shown that evaporation of a solution caused by pumping radiation yields long-lived gas-phase singlet oxygen. Release of gas-phase singlet oxygen from solid-phase fullerene-containing membranes (surfaces) is also demonstrated; however, this process is hindered by adsorption of singlet oxygen on the membrane surface. The prospects for creation of a singlet-oxygen generator on the basis of photoexcited fullerene molecules and fullerene-like nanoclusters are discussed.

  5. Bright fission: singlet fission into a pair of emitting states.

    PubMed

    Casanova, David

    2015-06-01

    This paper reintroduces and explores the generation of two bright states from a single photon via a singlet fission mechanism in organic materials. This particular photophysical process is labeled here as bright fission (BF). The central part of the study is devoted to set the theoretical foundations of BF by discussing possible electronic mechanisms, the role of different excited states with various physical nature, the presence of competing deactivation channels, and the possible requirements for the BF viability. In a second part, some of the properties related to BF are computationally explored in anthracene. The analysis of computed high-lying excited states identifies several optical transitions as good candidates to trigger BF in anthracene. The approximation of excitonic couplings of these high energy levels to other electronic states within the same energy range suggests possible paths to populate electronic configurations potentially able to split in two independent spin singlets, i.e. singlet-singlet states. The study also explores the electronic structure of the energetically lowest singlet-singlet states in anthracene dimers and discusses the presence of charge transfer configurations and their relation to the singlet-singlet manifold. The computational results suggest fast relaxation to the lowest singlet-singlet state, from which the excitonic fission may occur. All in all, the present work aims at motivating to pursue further efforts in the study of the BF process in organic materials.

  6. Zero-field splitting of the lowest excited triplet states of C(60) and C(70) and benzene.

    PubMed

    van Gastel, Maurice

    2010-10-14

    The electronic structure of the lowest excited triplet states of C(60) and C(70) are characterized by a magnetic interaction between the unpaired electrons for which the zero-field-splitting parameter D is negative for the former and positive for the latter molecule. The sign of D has so far been qualitatively understood, and its magnitude has been found to critically depend on the degree of delocalization of the singly occupied molecular orbitals. In this contribution, the effect of spin polarization to the zero-field-splitting parameters of the fullerenes is evaluated, the inclusion of which results in quantitative agreement between the experimental and calculated D values. The direct spin-spin contribution is found to be dominant for both molecules. For C(60), a significant contribution of 20% of the total zero-field splitting has been found to derive from spin polarization. The physical reason for the sign difference of D for C(60) and C(70) is traced back to the relative phases of the local p(z) orbitals of adjacent carbon atoms near the equatorial plane in both singly occupied molecular orbitals. These relative phases differ for C(60) and C(70), because C(70) has an additional set of ten carbon atoms in its equatorial plane as compared to C(60). Additionally, the triplet wave function of C(70) is found to contain significant multireference character. In order to evaluate the effect of spin polarization in multireference systems, the zero-field-splitting parameters of the lowest triplet state of benzene have been evaluated in an illustrative and insightful calculation as well. Though this prototypical molecule is much smaller than C(60) and C(70), the electronic structure of its lowest excited triplet state is also of multireference character. For benzene, 18% of the total zero-field splitting arises from spin polarization.

  7. Assignments of Lowest Triplet State in Ir Complexes by Observation of Phosphorescence Excitation Spectra at 6 K

    NASA Astrophysics Data System (ADS)

    Kodate, Satoshi; Suzuka, Isamu

    2006-01-01

    We tried the assignment of the origin of phosphorescent bands in Ir complexes. It is important to elucidate the luminescent mechanism in order to design organic light-emitting devices (OLEDs) besed on new materials. The Stokes shift between the phosphorescence and phosphorescence excitation spectra of Ir complexes such as fac-tris(2-phenylpyridine) iridium(III) [Ir(ppy)3], fac-tris(2-(2-thienyl)pyridine) iridium(III) [Ir(thpy)3], bis(2-phenylpyridine) iridium(III)benzo[h]quinoline [Ir(ppy)2bzq], fac-tris(benzo[h]quinoline) iridium(III) [Ir(bzq)3] and bis[(4,6-difluorophenyl)pyridinato](picolinato) iridium(III) [FIrpic] was measured in a solution and (phenyl)4Sn at 6 K. The amount of Stokes shift corresponds to the nature of the lowest triplet state. We discovered that the amount of Stokes shift clearly differs depending on whether the lowest triplet state of each Ir complex is triplet metal-to-ligand charge transfer (3MLCT) or 3π-π*. Namely, the case of 3MLCT shows a large shift, while the case of 3π-π* shows a small shift. We also present the resolved phosphorescence and phosphorescence excitation spectra of Ir complexes in (phenyl)4Sn. The sharp bands were assigned to the 3π-π* transition, and the broad bands were assigned to the 3MLCT state. The nature of the lowest triplet state is also discussed on the basis of resolved spectra.

  8. Double excitations and state-to-state transition dipoles in π-π∗ excited singlet states of linear polyenes: Time-dependent density-functional theory versus multiconfigurational methods

    NASA Astrophysics Data System (ADS)

    Mikhailov, Ivan A.; Tafur, Sergio; Masunov, Artëm E.

    2008-01-01

    The effect of static and dynamic electron correlation on the nature of excited states and state-to-state transition dipole moments is studied with a multideterminant wave function approach on the example of all-trans linear polyenes ( C4H6 , C6H8 , and C8H10 ). Symmetry-forbidden singlet nAg states were found to separate into three groups: purely single, mostly single, and mostly double excitations. The excited-state absorption spectrum is dominated by two bright transitions: 1Bu-2Ag and 1Bu-mAg , where mAg is the state, corresponding to two-electron excitation from the highest occupied to lowest unoccupied molecular orbital. The richness of the excited-state absorption spectra and strong mixing of the doubly excited determinants into lower- nAg states, reported previously at the complete active space self-consistent field level of theory, were found to be an artifact of the smaller active space, limited to π orbitals. When dynamic σ-π correlation is taken into account, single- and double-excited states become relatively well separated at least at the equilibrium geometry of the ground state. This electronic structure is closely reproduced within time-dependent density-functional theory (TD DFT), where double excitations appear in a second-order coupled electronic oscillator formalism and do not mix with the single excitations obtained within the linear response. An extension of TD DFT is proposed, where the Tamm-Dancoff approximation (TDA) is invoked after the linear response equations are solved (a posteriori TDA). The numerical performance of this extension is validated against multideterminant-wave-function and quadratic-response TD DFT results. It is recommended for use with a sum-over-states approach to predict the nonlinear optical properties of conjugated molecules.

  9. Enhancing the depth of tissue microscope imaging using two-photon excitation of the second singlet state of fluorescent agents

    NASA Astrophysics Data System (ADS)

    Pu, Yang; Shi, Lingyan; Pratavieira, Sebastião.; Alfano, R. R.

    2014-03-01

    Increasing the depth to image inside tissue is critical in biomedicine. Two-photon (2P) excitation of the second singlet (S2) state of a group of fluorescent agents with near infrared emission, Chlorophyll a (Chl a) and Indocyanine green (ICG), is used to extend the optical imaging regime of 2PM into "tissue optical window" for deep tissue penetration. The fast nonradiative from S2 to S1 yields both emission and absorption wavelengths in the therapeutic window. The salient feature is to place both the 2P excitation and emission wavelengths of the imaging agents falling into the "tissue optical window". As a first step to achieve deeper optical imaging, Chl a and ICG are investigated and demonstrated as imaging agents for 2P S2 excitation microscope image.

  10. The effect of gold nanoparticles on exchange processes in collision complexes of triplet and singlet oxygen molecules with excited eosin molecules

    NASA Astrophysics Data System (ADS)

    Bryukhanov, V. V.; Minaev, B. M.; Tsibul'nikova, A. V.; Slezhkin, V. A.

    2015-07-01

    We have studied exchange processes in contact complexes of triplet eosin molecules with oxygen molecules in the triplet (3Σ{/g -}) and singlet (1Δ g ) states in thin polyvinylbutyral films in the presence of gold nanoparticles. Upon resonant excitation of surface plasmons in gold nanoparticles into the absorption band of eosin molecules-singlet oxygen sensitizers-we have obtained an increase in the intensity of the delayed fluorescence and an increase in the lifetime of the dye with simultaneous quenching of the luminescence of singlet oxygen. The kinetics of the delayed fluorescence of the dye as a result of singlet-triplet annihilation of triplet eosin molecules with singlet oxygen molecules has been investigated. To compare theoretical and experimental data, we have numerically simulated energy transfer processes. Rate constants of energy transfer and of singlet-triplet annihilation, as well as quenching constants of triplet states of the dye by molecular oxygen, have been calculated. Luminescence quantum yield 1Δ g of polyvinylbutyral has been estimated. We have analyzed quantum-chemically electronic mechanisms of singlet-triplet annihilation of oxygen and eosin.

  11. Vibronic and magnetic coupling in the radiative deactivation of the lowest excited state of (Os(bpy) sub 3 ) sup 2+ doped into (Ru(bpy) sub 3 )(PF sub 6 ) sub 2

    SciTech Connect

    Braun, D.; Hensler, G.; Gallhuber, E.; Yersin, H. )

    1991-02-07

    Small amounts of (Os(bpy){sub 3}){sup 2+} doped into single-crystal (Ru(bpy){sub 3})(PF{sub 6}){sub 2} exhibit highly resolved MLCT spectra corresponding to the transitions between the ground state and the lowest excited states. The electronic origins as well as the vibronic satellites appear as sharp lines with half-widths of {approx}2 cm{sup {minus}1}. Three distinct spectroscopic sites are identified. For the lowest energy site the lowest excited state {vert bar}I> is located at 14,423 cm{sup {minus}1} and the second excited state {vert bar}II> lies 72 cm{sup {minus}1} above {vert bar}>. Due to the polarization properties of the origins both states are assigned to be doubly degenerate (E representations in the D{sub 3} double group). The emission from {vert bar}I> shows a very weak origin line compared to the intense vibronic satellites which mostly correspond to IR-active vibrations. It is proposed that the vibronic intensity is induced by spin-vibronic and/or spin-orbit-vibronic coupling. The electronic state(s) supplying allowedness to the radiative decay from {vert bar}I> are assigned to doubly degenerate E state(s) of singlet parentage. Further, magnetic fields induce a mixing of the wave functions of {vert bar}I> and {vert bar}II>, which results in an intensity increase of the electronic origin of the perturbed state {vert bar}I{prime}>{sub B} by a factor of about 1,000.

  12. Difluorodiazirine (CF2N2): A comparative quantum mechanical study of the first triplet and first singlet excited states

    NASA Astrophysics Data System (ADS)

    Terrabuio, Luiz Alberto; Haiduke, Roberto Luiz Andrade; Matta, Chérif F.

    2016-07-01

    3,3‧-Difluorodiazirine is a precursor of difluorocarbene radical (:CF2) which is used in organic synthesis and photo affinity labelling. This molecule possesses no dipole moment in the ground electronic state (S0) but has a significant dipole moment (of magnitude ~0.97 D) in both its first (triplet, T1) and second (singlet S1) excited states. These equal dipole moments are shown to originate from widely differing atomic polarization and inter-atomic charge transfer terms (defined by the Quantum Theory of Atoms in Molecules (QTAIM)). The calculated vertical/adiabatic excitation energies for the T1 and S1 states are 2.81/2.63 and 3.99/3.78 eV, respectively. Geometries, vibrational frequencies, atomic charges and spin populations, and the localization-delocalization matrices (LDMs) (Matta, J. Comput. Chem. 35 (2014) 1165) of the excited states are compared with those of the ground state. All calculations have been conducted at the (U)QCISD/aug-cc-pVTZ level of theory.

  13. Estimation of first excited singlet-state dipole moments of aminoanthraquinones by solvatochromic method.

    PubMed

    Siddlingeshwar, B; Hanagodimath, S M

    2009-04-01

    The ground state (micro(g)) and the excited state (micro(e)) dipole moments of three substituted anthraquinones, namely 1-aminoanthracene-9,10-dione (AAQ), 1-(methylamino)anthracence-9,10-dione (MAQ) and 1,5-diaminoanthracene-9,10-dione (DAQ) were estimated in various solvents. The dipole moments (micro(g) and micro(e)) were estimated from Lippert, Bakhshiev, Kawski-Chamma-Viallet, McRae and Suppan equations by using the variation of Stokes shift with the solvent dielectric constant and refractive index. The excited state dipole moments were also calculated by using the variation of Stokes shift with microscopic solvent polarity parameter (Epsilon(T)(N)). It was observed that dipole moment values of excited states (micro(e)) were higher than corresponding ground state values (micro(g)), indicating a substantial redistribution of the pi-electron densities in a more polar excited state for all the molecules investigated.

  14. Vertical Singlet Excitations on Adenine Dimer: A Time Dependent Density Functional Study

    NASA Astrophysics Data System (ADS)

    Crespo-Hernández, Carlos E.; Marai, Christopher N. J.

    2007-12-01

    The condense phase, excited state dynamics of the adenylyl(3'→5')adenine (ApA) dinucleotide has been previously studied using transient absorption spectroscopy with femtosecond time resolution (Crespo-Hernández et al. Chem. Rev. 104, 1977-2019 (2004)). An ultrafast and a long-lived component were observed with time constants of <1 ps and 60±16 ps, respectively. Comparison of the time constants measured for the dinucleotide with that for the adenine nucleotide suggested that the fast component observed in ApA could be assigned to monomer dynamics. The long-lived component observed in ApA was assigned to an excimer state that originates from a fraction of base stacked conformations present at the time of excitation. In this contribution, supermolecule calculations using the time dependent implementation of density functional theory is used to provide more insights on the origin of the initial Franck-Condon excitations. Monomer-like, localized excitations are observed for conformations having negligible base stacking interactions, whereas delocalized excitations are predicted for conformations with significant vertical base-base overlap.

  15. Photosensitized Singlet Oxygen Production upon Two-Photon Excitation of Single-Walled Carbon Nanotubes and Their Functionalized Analogs

    PubMed Central

    Gandra, Naveen; Chiu, Pui Lam; Li, Wenbing; Anderson, Yolanda R.; Mitra, Somenath; He, Huixin; Gao, Ruomei

    2009-01-01

    Single-walled carbon nanotubes (SWNTs) functionalized with -COOH (along with some sulphonation and nitration), and/or modified with chitosan were prepared and tested for their singlet oxygen (1O2) production. The emission from 1O2 observed upon SWNT irradiation at 532 nm was due to a two-photon process, while 1O2 production via excitation at 355 nm occurred through a conventional one-photon pathway. The relative quantum yield of 1O2 production at excitation wavelength of 532 nm was found to be 0.00, 0.07-0.13 and 0.24-0.54 for highly-functionalized, partially-functionalized and non-functionalized SWNT samples respectively. The nanotube-mediated generation of 1O2 may find applications in both targeted destruction of tumor cells and selective degradation of drug molecules. Our research provides a practical approach to modulate the production of reactive oxygen species from SWNTs via surface functionalization/modification. PMID:20046942

  16. Photophysical properties of some methylindoles and studies on quenching reactions in their excited singlet and triplet states in presence of the electron acceptor 2-nitrofluorene at 296 K as well as at 77 K

    NASA Astrophysics Data System (ADS)

    Sinha, S.; De, R.; Ganguly, T.

    1998-01-01

    Electronic absorption, steady state and time resolved, in the domain of nanosecond order, luminescence techniques were employed to study the photophysical properties of some electron donors methylindoles, e.g. 1-methylindole (1MI), 2-methylindole (2MI), 3-methylindole (3MI) and 5-methylindole (5MI) in nonpolar and polar environments at 296 K and in ethanol (EtOH) rigid glassy matrix at 77 K in the presence of electron acceptor 2-nitrofluorene (2NF). It has been proposed that at room temperature and in polar acetonitrile (ACN) solvent, MI (1, 2 or 3) emission originates mainly from the closely lying lowest excited states S 1 ( 1L b), S 2 ( 1L a) and the charge transfer (CT) exciplex state which is formed due to solute-highly polar solvent ACN interaction. This CT state has its origin in 1L a. The room temperature fluorescence quenchings of the MI donors in presence of acceptor 2NF are found to be mainly due to photoinduced electron transfer (ET), excitational energy transfer and transient quenching processes. Out of the three processes Förster's long range energy transfer seems to be the most dominant one. At 77 K singlet-singlet and triplet-triplet energy transfer processes seem to be responsible for the observed quenching in fluorescence and phosphorescence spectra of the donor molecules in presence of the acceptor 2NF.

  17. Polymer characterization using the time-resolved phosphorescence of singlet oxygen as a spectroscopic probe

    SciTech Connect

    Ogilby, P.R.; Kristiansen, M.; Dillon, M.P. . Dept. of Chemistry); Taylor, V.L.; Clough, R.L. )

    1990-01-01

    The lowest excited electronic state of molecular oxygen, singlet oxygen ({sup 1}{Delta}{sub g}0{sub 2}), can be produced in solid organic polymers by a variety of different methods. Once produced, singlet oxygen will return to the ground triplet state by two pathways, radiative (phosphorescence) and non-radiative decay. Although the quantum efficiency of phosphorescence is small ({minus}10{sup {minus}5}), singlet oxygen can be detected by its emission at 1270 mn in both steady-state and time-resolved experiments. The phosphorescence of singlet oxygen can be used to characterize many properties of a solid organic polymer. 2 refs., 5 figs.

  18. From Model Hamiltonians to ab Initio Hamiltonians and Back Again: Using Single Excitation Quantum Chemistry Methods To Find Multiexciton States in Singlet Fission Materials.

    PubMed

    Mayhall, Nicholas J

    2016-09-13

    Due to the promise of significantly enhanced photovoltaic efficiencies, significant effort has been directed toward understanding and controlling the singlet fission mechanism. Although accurate quantum chemical calculations would provide a detail-rich view of the singlet fission mechanism, this is complicated by the multiexcitonic nature of one of the key intermediates, the (1)(TT) state. Being described as two simultaneous and singlet-coupled triplet excitations on a pair of nearest neighbor monomers, the (1)(TT) state is inherently a multielectronic excitation. This fact renders most single-reference ab initio quantum chemical methods incapable of providing accurate results. This paper serves two purposes: (1) to demonstrate that the multiexciton states in singlet fission materials can be described using a spin-only Hamiltonian and with each monomer treated as a biradical and (2) to propose a very simple procedure for extracting the values for this Hamiltonian from single-reference calculations. Numerical examples are included for a number of different systems, including dimers, trimers, tetramers, and a cluster comprised of seven chromophores. PMID:27472260

  19. Time-resolved photoelectron spectroscopy of a dinuclear Pt(II) complex: Tunneling autodetachment from both singlet and triplet excited states of a molecular dianion.

    PubMed

    Winghart, Marc-Oliver; Yang, Ji-Ping; Vonderach, Matthias; Unterreiner, Andreas-Neil; Huang, Dao-Ling; Wang, Lai-Sheng; Kruppa, Sebastian; Riehn, Christoph; Kappes, Manfred M

    2016-02-01

    Time-resolved pump-probe photoelectron spectroscopy has been used to study the relaxation dynamics of gaseous [Pt2(μ-P2O5H2)4 + 2H](2-) after population of its first singlet excited state by 388 nm femtosecond laser irradiation. In contrast to the fluorescence and phosphorescence observed in condensed phase, a significant fraction of the photoexcited isolated dianions decays by electron loss to form the corresponding monoanions. Our transient photoelectron data reveal an ultrafast decay of the initially excited singlet (1)A2u state and concomitant rise in population of the triplet (3)A2u state, via sub-picosecond intersystem crossing (ISC). We find that both of the electronically excited states are metastably bound behind a repulsive Coulomb barrier and can decay via delayed autodetachment to yield electrons with characteristic kinetic energies. While excited state tunneling detachment (ESETD) from the singlet (1)A2u state takes only a few picoseconds, ESETD from the triplet (3)A2u state is much slower and proceeds on a time scale of hundreds of nanoseconds. The ISC rate in the gas phase is significantly higher than in solution, which can be rationalized in terms of changes to the energy dissipation mechanism in the absence of solvent molecules. [Pt2(μ-P2O5H2)4 + 2H](2-) is the first example of a photoexcited multianion for which ESETD has been observed following ISC.

  20. Time-resolved photoelectron spectroscopy of a dinuclear Pt(II) complex: Tunneling autodetachment from both singlet and triplet excited states of a molecular dianion

    NASA Astrophysics Data System (ADS)

    Winghart, Marc-Oliver; Yang, Ji-Ping; Vonderach, Matthias; Unterreiner, Andreas-Neil; Huang, Dao-Ling; Wang, Lai-Sheng; Kruppa, Sebastian; Riehn, Christoph; Kappes, Manfred M.

    2016-02-01

    Time-resolved pump-probe photoelectron spectroscopy has been used to study the relaxation dynamics of gaseous [Pt2(μ-P2O5H2)4 + 2H]2- after population of its first singlet excited state by 388 nm femtosecond laser irradiation. In contrast to the fluorescence and phosphorescence observed in condensed phase, a significant fraction of the photoexcited isolated dianions decays by electron loss to form the corresponding monoanions. Our transient photoelectron data reveal an ultrafast decay of the initially excited singlet 1A2u state and concomitant rise in population of the triplet 3A2u state, via sub-picosecond intersystem crossing (ISC). We find that both of the electronically excited states are metastably bound behind a repulsive Coulomb barrier and can decay via delayed autodetachment to yield electrons with characteristic kinetic energies. While excited state tunneling detachment (ESETD) from the singlet 1A2u state takes only a few picoseconds, ESETD from the triplet 3A2u state is much slower and proceeds on a time scale of hundreds of nanoseconds. The ISC rate in the gas phase is significantly higher than in solution, which can be rationalized in terms of changes to the energy dissipation mechanism in the absence of solvent molecules. [Pt2(μ-P2O5H2)4 + 2H]2- is the first example of a photoexcited multianion for which ESETD has been observed following ISC.

  1. Multiple Decay Mechanisms and 2D-UV Spectroscopic Fingerprints of Singlet Excited Solvated Adenine-Uracil Monophosphate.

    PubMed

    Li, Quansong; Giussani, Angelo; Segarra-Martí, Javier; Nenov, Artur; Rivalta, Ivan; Voityuk, Alexander A; Mukamel, Shaul; Roca-Sanjuán, Daniel; Garavelli, Marco; Blancafort, Lluís

    2016-05-23

    The decay channels of singlet excited adenine uracil monophosphate (ApU) in water are studied with CASPT2//CASSCF:MM potential energy calculations and simulation of the 2D-UV spectroscopic fingerprints with the aim of elucidating the role of the different electronic states of the stacked conformer in the excited state dynamics. The adenine (1) La state can decay without a barrier to a conical intersection with the ground state. In contrast, the adenine (1) Lb and uracil S(U) states have minima that are separated from the intersections by sizeable barriers. Depending on the backbone conformation, the CT state can undergo inter-base hydrogen transfer and decay to the ground state through a conical intersection, or it can yield a long-lived minimum stabilized by a hydrogen bond between the two ribose rings. This suggests that the (1) Lb , S(U) and CT states of the stacked conformer may all contribute to the experimental lifetimes of 18 and 240 ps. We have also simulated the time evolution of the 2D-UV spectra and provide the specific fingerprint of each species in a recommended probe window between 25 000 and 38 000 cm(-1) in which decongested, clearly distinguishable spectra can be obtained. This is expected to allow the mechanistic scenarios to be discerned in the near future with the help of the corresponding experiments. Our results reveal the complexity of the photophysics of the relatively small ApU system, and the potential of 2D-UV spectroscopy to disentangle the photophysics of multichromophoric systems. PMID:27113273

  2. Multiple Decay Mechanisms and 2D-UV Spectroscopic Fingerprints of Singlet Excited Solvated Adenine-Uracil Monophosphate.

    PubMed

    Li, Quansong; Giussani, Angelo; Segarra-Martí, Javier; Nenov, Artur; Rivalta, Ivan; Voityuk, Alexander A; Mukamel, Shaul; Roca-Sanjuán, Daniel; Garavelli, Marco; Blancafort, Lluís

    2016-05-23

    The decay channels of singlet excited adenine uracil monophosphate (ApU) in water are studied with CASPT2//CASSCF:MM potential energy calculations and simulation of the 2D-UV spectroscopic fingerprints with the aim of elucidating the role of the different electronic states of the stacked conformer in the excited state dynamics. The adenine (1) La state can decay without a barrier to a conical intersection with the ground state. In contrast, the adenine (1) Lb and uracil S(U) states have minima that are separated from the intersections by sizeable barriers. Depending on the backbone conformation, the CT state can undergo inter-base hydrogen transfer and decay to the ground state through a conical intersection, or it can yield a long-lived minimum stabilized by a hydrogen bond between the two ribose rings. This suggests that the (1) Lb , S(U) and CT states of the stacked conformer may all contribute to the experimental lifetimes of 18 and 240 ps. We have also simulated the time evolution of the 2D-UV spectra and provide the specific fingerprint of each species in a recommended probe window between 25 000 and 38 000 cm(-1) in which decongested, clearly distinguishable spectra can be obtained. This is expected to allow the mechanistic scenarios to be discerned in the near future with the help of the corresponding experiments. Our results reveal the complexity of the photophysics of the relatively small ApU system, and the potential of 2D-UV spectroscopy to disentangle the photophysics of multichromophoric systems.

  3. Multiple Decay Mechanisms and 2D‐UV Spectroscopic Fingerprints of Singlet Excited Solvated Adenine‐Uracil Monophosphate

    PubMed Central

    Li, Quansong; Giussani, Angelo; Segarra‐Martí, Javier; Nenov, Artur; Rivalta, Ivan; Voityuk, Alexander A.; Mukamel, Shaul; Roca‐Sanjuán, Daniel

    2016-01-01

    Abstract The decay channels of singlet excited adenine uracil monophosphate (ApU) in water are studied with CASPT2//CASSCF:MM potential energy calculations and simulation of the 2D‐UV spectroscopic fingerprints with the aim of elucidating the role of the different electronic states of the stacked conformer in the excited state dynamics. The adenine 1La state can decay without a barrier to a conical intersection with the ground state. In contrast, the adenine 1Lb and uracil S(U) states have minima that are separated from the intersections by sizeable barriers. Depending on the backbone conformation, the CT state can undergo inter‐base hydrogen transfer and decay to the ground state through a conical intersection, or it can yield a long‐lived minimum stabilized by a hydrogen bond between the two ribose rings. This suggests that the 1Lb, S(U) and CT states of the stacked conformer may all contribute to the experimental lifetimes of 18 and 240 ps. We have also simulated the time evolution of the 2D‐UV spectra and provide the specific fingerprint of each species in a recommended probe window between 25 000 and 38 000 cm−1 in which decongested, clearly distinguishable spectra can be obtained. This is expected to allow the mechanistic scenarios to be discerned in the near future with the help of the corresponding experiments. Our results reveal the complexity of the photophysics of the relatively small ApU system, and the potential of 2D‐UV spectroscopy to disentangle the photophysics of multichromophoric systems. PMID:27113273

  4. Time-resolved spectroscopy of the singlet excited state of betanin in aqueous and alcoholic solutions.

    PubMed

    Wendel, Monika; Nizinski, Stanislaw; Tuwalska, Dorota; Starzak, Karolina; Szot, Dominika; Prukala, Dorota; Sikorski, Marek; Wybraniec, Slawomir; Burdzinski, Gotard

    2015-07-21

    The photophysical properties of betanin in aqueous and alcoholic solutions were determined at room temperature using ultrafast UV-vis-NIR transient absorption spectroscopy (λexc = 535 nm). Its S1 → Sn (n > 1) absorption bands appear with maxima at about λ ∼ 450 and 1220 nm. The short betanin S1 state lifetime (6.4 ps in water) is mainly determined by the efficient S1 → S0 radiationless relaxation, probably requiring a strong change in geometry, since the S1 lifetime grows to 27 ps in the more viscous ethylene glycol. The fluorescence quantum yield is very low (Φf ∼ 0.0007 in water), therefore this deactivation path is of minor importance. Other processes, such as S1 → T1 intersystem crossing or photoproduct formation, are virtually absent, since full S0 ← S1 ground state recovery is observed within tens of picoseconds after photoexcitation. The observed fast light-to-heat conversion in the absence of triplet excited state formation supports the idea that betanin is a photoprotector in vivo.

  5. Measurement of the autoionization lifetime of the energetically lowest doubly excited Q_1\\,^1\\Sigma ^+_{u} state in H2 using electron ejection asymmetry

    NASA Astrophysics Data System (ADS)

    Fischer, Andreas; Sperl, Alexander; Cörlin, Philipp; Schönwald, Michael; Meuren, Sebastian; Ullrich, Joachim; Pfeifer, Thomas; Moshammer, Robert; Senftleben, Arne

    2014-01-01

    The autoionization lifetime of doubly excited H2 created by single photon absorption has been measured by means of a kinematically complete study. For dissociative ionization the experimentally observed asymmetry in the electron ejection direction with respect to the emitted proton is used to disentangle the two interfering pathways, direct ionization and autoionization. This allows us to determine the autoionization lifetime of the energetically lowest doubly excited Q_1\\,^1\\Sigma _{u}^+(1) state for a large range of internuclear distances, including the previously inaccessible small values. Excellent agreement with available ab initio calculations is obtained.

  6. Lowest excited states and optical absorption spectra of donor-acceptor copolymers for organic photovoltaics: a new picture emerging from tuned long-range corrected density functionals.

    PubMed

    Pandey, Laxman; Doiron, Curtis; Sears, John S; Brédas, Jean-Luc

    2012-11-01

    Polymers with low optical gaps are of importance to the organic photovoltaics community due to their potential for harnessing a large portion of the solar energy spectrum. The combination along their backbones of electron-rich and electron-deficient fragments contributes to the presence of low-lying excited states that are expected to display significant charge-transfer character. While conventional hybrid functionals are known to provide unsatisfactory results for charge-transfer excitations at the time-dependent DFT level, long-range corrected (LRC) functionals have been reported to give improved descriptions in a number of systems. Here, we use such LRC functionals, considering both tuned and default range-separation parameters, to characterize the absorption spectra of low-optical-gap systems of interest. Our results indicate that tuned LRC functionals lead to simulated optical-absorption properties in good agreement with experimental data. Importantly, the lowest-lying excited states (excitons) are shown to present a much more localized nature than initially anticipated.

  7. Transient resonance Raman spectra of benzophenone and its four isotopic analogues in the lowest excited triplet state

    SciTech Connect

    Tahara, T.; Hamaguchi, H.; Tasumi, M.

    1987-11-05

    Transient resonance Raman spectra of T/sub 1/ benzophenone (T/sub 1/BP) and its four isotopic analogues in carbon tetrachloride solutions were measured. Vibrational assignments of eight T/sub 1/ bands have been made on the basis of the observed isotopic frequency shifts. The assignments clarified the following three points concerning the structure of T/sub 1/ BP in solution. (1) The CO bond order in T/sub 1/ BP is much lower than that in the ground-state benzophenone (S/sub 0/ BP). The CO stretching frequency in T/sub 1/ is found to be 1222 cm/sup -1/, whereas the corresponding value in S/sub 0/ is 1665 cm/sup -1/. The former frequency indicates a single-bond-like character of the CO bonding in the T/sub 1/ state. (2) Vibrational frequencies of several ring modes show marked downshifts in going from S/sub 0/ to T/sub 1/. This suggests the delocalization of the ..pi..* electron into the ring part. (3) The assignment (1302 cm/sup -1/) of the symmetric C-phenyl stretch mode in the T/sub 1/ withdraws S/sub 0/ absorption spectrum is questioned. According to the present assignment, the frequency of this mode (approx. 1100 cm/sup -1/) is slightly lower than that in the ground state (1150 cm/sup -1/). The simple quantum chemical picture of T/sub 1/ BP, which predicted the increase of the C-phenyl bond order with the ..pi..* withdraws n excitation, should therefore be reconsidered.

  8. Application of recent double-hybrid density functionals to low-lying singlet-singlet excitation energies of large organic compounds

    NASA Astrophysics Data System (ADS)

    Meo, F. Di; Trouillas, P.; Adamo, C.; Sancho-García, J. C.

    2013-10-01

    The present work assesses some recently developed double-hybrid density functionals (B2π-PLYP, PBE0-DH, and PBE0-2) using linear-response Tamm-Dancoff Time-Dependent Density Functional Theory. This assessment is achieved against experimentally derived low-lying excitation energies of large organic dyes of recent interest, including some excitations dominated by charge-transfer transitions. Comparisons are made with some of the best-performing methods established from the literature, such as PBE0 or B3LYP hybrid or the recently proposed B2-PLYP and B2GP-PLYP double-hybrid models, to ascertain their quality and robustness on equal footing. The accuracy of parameter-free or empirical forms of double-hybrid functionals is also briefly discussed. Generally speaking, it turns out that double-hybrid expressions always provide more accurate estimates than corresponding hybrid methods. Double-hybrid functionals actually reach averaged accuracies of 0.2 eV, that can be admittedly considered close to any intended accuracy limit within the present theoretical framework.

  9. Tuning of the stability and energy levels of singlet exciton fission relevant excited states of pentacenes by site-specific substitution.

    PubMed

    Shen, Li; Chen, Yuhan; Li, Xiyou; Li, Chungang

    2016-05-01

    Pentacene crystals or oligomers undergo efficient singlet exciton fission (SF) after photo-excitation, which is expected to be useful in overcoming the Shockley-Queisser theoretical limit of solar cells. However, pentacenes are extremely unstable in air due to oxidation by oxygen. In this work, we designed a group of pentacene compounds with different substituents at different positions. The energy levels of HOMO and LUMO, which are believed to be closely related to the stability of pentacene, were calculated. The relationship between the molecular structure and the stability was discussed. The driving force for SF was estimated from the difference between the energy of first singlet excited state (E(S1)) and the energy of two triplet excited state (2×E(T1)) following equation E(S1)-2E(T1). Strong electron-withdrawing groups can stabilize pentacene compounds significantly, but induce a decrease on the driving force of SF slightly. Electron-donating groups destabilize the pentacene compounds dramatically and hence the introduction of electron donating groups to pentacene is not recommended. TIPS is an ideal group to improve the stability of pentacene compounds. TIPS does not change the driving force of SF significantly. Sulfur containing groups are also efficient on stabilizing pentacene compounds. These groups increase the driving force of SF at ɑ position, and recued the driving force of SF at other positions. The results of this work provide a theoretical ground for rational design of new SF molecules based on pentacenes. PMID:27131283

  10. Tuning of the stability and energy levels of singlet exciton fission relevant excited states of pentacenes by site-specific substitution.

    PubMed

    Shen, Li; Chen, Yuhan; Li, Xiyou; Li, Chungang

    2016-05-01

    Pentacene crystals or oligomers undergo efficient singlet exciton fission (SF) after photo-excitation, which is expected to be useful in overcoming the Shockley-Queisser theoretical limit of solar cells. However, pentacenes are extremely unstable in air due to oxidation by oxygen. In this work, we designed a group of pentacene compounds with different substituents at different positions. The energy levels of HOMO and LUMO, which are believed to be closely related to the stability of pentacene, were calculated. The relationship between the molecular structure and the stability was discussed. The driving force for SF was estimated from the difference between the energy of first singlet excited state (E(S1)) and the energy of two triplet excited state (2×E(T1)) following equation E(S1)-2E(T1). Strong electron-withdrawing groups can stabilize pentacene compounds significantly, but induce a decrease on the driving force of SF slightly. Electron-donating groups destabilize the pentacene compounds dramatically and hence the introduction of electron donating groups to pentacene is not recommended. TIPS is an ideal group to improve the stability of pentacene compounds. TIPS does not change the driving force of SF significantly. Sulfur containing groups are also efficient on stabilizing pentacene compounds. These groups increase the driving force of SF at ɑ position, and recued the driving force of SF at other positions. The results of this work provide a theoretical ground for rational design of new SF molecules based on pentacenes.

  11. Fine-Tuning of β-Substitution to Modulate the Lowest Triplet Excited States: A Bioinspired Approach to Design Phosphorescent Metalloporphyrinoids.

    PubMed

    Ke, Xian-Sheng; Zhao, Hongmei; Zou, Xiaoran; Ning, Yingying; Cheng, Xin; Su, Hongmei; Zhang, Jun-Long

    2015-08-26

    Learning nature's approach to modulate photophysical properties of NIR porphyrinoids by fine-tuning β-substituents including the number and position, in a manner similar to naturally occurring chlorophylls, has the potential to circumvent the disadvantages of traditional "extended π-conjugation" strategy such as stability, molecular size, solubility, and undesirable π-π stacking. Here we show that such subtle structural changes in Pt(II) or Pd(II) cis/trans-porphodilactones (termed by cis/trans-Pt/Pd) influence photophysical properties of the lowest triplet excited states including phosphorescence, Stokes shifts, and even photosensitization ability in triplet-triplet annihilation reactions with rubrene. Prominently, the overall upconversion capability (η, η = ε·Φ(UC)) of Pd or Pt trans-complex is 10(4) times higher than that of cis-analogue. Nanosecond time-resolved infrared (TR-IR) spectroscopy experiments showed larger frequency shift of ν(C═O) bands (ca. 10 cm(-1)) of cis-complexes than those of trans-complexes in the triplet excited states. These spectral features, combining with TD-DFT calculations, suggest the strong electronic coupling between the lactone moieties and the main porphyrin chromophores and thus the importance of precisely positioning β-substituents by mimicking chlorophylls, as an alternative to "extended π-conjugation", in designing NIR active porphyrinoids. PMID:26247480

  12. Singlet-triplet excitations and long range entanglement in the spin-orbital liquid candidate FeSc2S4

    NASA Astrophysics Data System (ADS)

    Laurita, N. J.; Deisenhofer, J.; Pan, Lidong; Morris, C. M.; Schmidt, M.; Johnsson, M.; Tsurkan, V.,; Loidl, A.; Armitage, N. P.

    2015-03-01

    Theoretical models of the spin-orbital liquid (SOL) FeSc2S4 have predicted it to be in close proximity to a quantum critical point separating a spin-orbital liquid phase from a long-range ordered magnetic phase. Here, we examine the magnetic excitations of FeSc2S4 through time-domain terahertz spectroscopy under an applied magnetic field. At low temperatures an excitation emerges that we attribute to a singlet-triplet excitation from the SOL ground state. A three-fold splitting of this excitation is observed as a function of applied magnetic field. Using experimentally obtained parameters we compare to existing theoretical models to determine FeSc2S4's proximity to the quantum critical point and establish FeSc2S4 as a SOL with long-range entanglement. Work at Johns Hopkins was supported by the Gordon and Betty Moore Foundation through Grant GBMF2628, the DOE-BES through DE-FG02-08ER46544, and the ARCS Foundation.

  13. LASERS IN MEDICINE: Quantum efficiency of the laser-excited singlet-oxygen-sensitised delayed fluorescence of the zinc complex of tetra(4-tert-butyl)phthalocyanine

    NASA Astrophysics Data System (ADS)

    Bashtanov, M. E.; Drozdova, N. N.; Krasnovskii, A. A.

    1999-12-01

    An investigation was made of the ratios of the intensity Idf of the singlet-oxygen(1O2)-sensitised delayed fluorescence of the zinc complex of tetra(4-tert-butyl)phthalocyanine (ZnTBPc), with the maximum at λ = 685 nm, to the intensity I1270 of the photosensitised phosphorescence of 1O2 with the maximum at λ = 1270 nm in deuterated benzene when excited with λ = 337 nm nitrogen-laser pulses. Depending on the energy density of the laser radiation (0.25 — 0.7 mJ cm-2) and on the concentration of ZnTBPc (0.06 — 3.4 μM), the ratio of the zero-time intensities of the delayed fluorescence of ZnTBPc and of the singlet-oxygen phosphorescence Idf0/I12700 varied from 0.01 to 0.2 in air-saturated solutions of ZnTBPc. The intensity Idf0 decreased fivefold as a result of saturation with oxygen of air-saturated solutions. The quantum efficiency of the delayed fluorescence was represented by the coefficient α =(Idf0/I12700)kr/(γf[1O2]0[ZnTBPc]), where [1O2]0 is the zero-time concentration of 1O2 after a laser shot; kr is the rate constant of radiative deactivation of 1O2 in the investigated solvent; γf is the quantum yield of the ZnTBPc fluorescence. It was established that in the case of air-saturated solutions of ZnTBPc this coefficient was approximately 200 times less than for metal-free tetra(4-tert-butyl)phthalocyanine and its absolute value was ~2 × 1011 M-2 s-1.

  14. Two-Photon Study on the Electronic Interactions between the First Excited Singlet States in Carotenoid-Tetrapyrrole Dyads

    SciTech Connect

    Liao, Pen-Nan; Pillai, Smitha; Gust, Devens; Moore, Thomas A.; Moore, Ana L.; Walla, Peter J.

    2011-03-22

    Electronic interactions between the first excited states (S1) of carotenoids (Car) of different conjugation lengths (8-11 double bonds) and phthalocyanines (Pc) in different Car-Pc dyad molecules were investigated by two-photon spectroscopy and compared with Car S1-chlorophyll (Chl) interactions in photosynthetic light harvesting complexes (LHCs). The observation of Chl/Pc fluorescence after selective two-photon excitation of the Car S1 state allowed sensitive monitoring of the flow of energy between Car S1 and Pc or Chl. It is found that two-photon excitation excites to about 80% to 100% exclusively the carotenoid state Car S1 and that only a small fraction of direct tetrapyrrole two-photon excitation occurs. Amide-linked Car-Pc dyads in tetrahydrofuran demonstrate a molecular gear shift mechanism in that effective Car S1 → Pc energy transfer is observed in a dyad with 9 double bonds in the carotenoid, whereas in similar dyads with 11 double bonds in the carotenoid, the Pc fluorescence is strongly quenched by Pc → Car S1 energy transfer. In phenylamino-linked Car-Pc dyads in toluene extremely large electronic interactions between the Car S1 state and Pc were observed, particularly in the case of a dyad in which the carotenoid contained 10 double bonds. This observation together with previous findings in the same system provides strong evidence for excitonic Car S1-Pc Qy interactions. Very similar results were observed with photosynthetic LHC II complexes in the past, supporting an important role of such interactions in photosynthetic down-regulation.

  15. π-Conjugated Organometallic Isoindigo Oligomer and Polymer Chromophores: Singlet and Triplet Excited State Dynamics and Application in Polymer Solar Cells.

    PubMed

    Goswami, Subhadip; Gish, Melissa K; Wang, Jiliang; Winkel, Russell W; Papanikolas, John M; Schanze, Kirk S

    2015-12-01

    An isoindigo based π-conjugated oligomer and polymer that contain cyclometalated platinum(II) "auxochrome" units were subjected to photophysical characterization, and application of the polymer in bulk heterojunction polymer solar cells with PCBM acceptor was examined. The objective of the study was to explore the effect of the heavy metal centers on the excited state properties, in particular, intersystem crossing to a triplet (exciton) state, and further how this would influence the performance of the organometallic polymer in solar cells. The materials were characterized by electrochemistry, ground state absorption, emission, and picosecond-nanosecond transient absorption spectroscopy. Electrochemical measurements indicate that the cyclometalated units have a significant impact on the HOMO energy level of the chromophores, but little effect on the LUMO, which is consistent with localization of the LUMO on the isoindigo acceptor unit. Picosecond-nanosecond transient absorption spectroscopy reveals a transient with ∼100 ns lifetime that is assigned to a triplet excited state that is produced by intersystem crossing from a singlet state on a time scale of ∼130 ps. This is the first time that a triplet state has been observed for isoindigo π-conjugated chromophores. The performance of the polymer in bulk heterojunction solar cells was explored with PC61BM as an acceptor. The performance of the cells was optimum at a relatively high PCBM loading (1:6, polymer:PCBM), but the overall efficiency was relatively low with power conversion efficiency (PCE) of 0.22%. Atomic force microscopy of blend films reveals that the length scale of the phase separation decreases with increasing PCBM content, suggesting a reason for the increase in PCE with acceptor loading. Energetic considerations show that the triplet state in the polymer is too low in energy to undergo charge separation with PCBM. Further, due to the relatively low LUMO energy of the polymer, charge transfer

  16. Electronic Structure Study of Singlet Fission in Tetracene Derivatives.

    PubMed

    Casanova, David

    2014-01-14

    A detailed theoretical study of the singlet fission process in tetracene and two of its derivatives, that is 5,12-diphenyltetracene (DPT) and rubrene, is presented. This work aims to unravel the intricacies and the differences of their singlet fission mechanism by means of electronic structure calculations using molecular and cluster models and a variety of computational tools. Although the electronic structure at the molecular level is very similar for the three compounds, their different crystal packing has important consequences in their ability to produce two triplet states from a single exciton. The results obtained indicate that the lowest singlet is found to delocalize at least over seven molecules. Computed relative energies rule out the presence of charge transfer (CT) states as intermediates in a two-step mechanism in all cases. On the other hand, CT states do play a role as mediators, specially in tetracene. They decisively participate in the coupling between single and multiexcitonic states through second-order contributions. Finally, the present study pinpoints that the transition from the optically allowed exciton to the dark multiexciton state might be facilitated by intramolecular motion toward the lowest excited singlet geometry. PMID:26579913

  17. Degradation of organic pollutants in/on snow and ice by singlet molecular oxygen (¹O₂*) and an organic triplet excited state.

    PubMed

    Bower, Jonathan P; Anastasio, Cort

    2014-04-01

    Singlet molecular oxygen (¹O₂*) can be a significant sink for a variety of electron-rich pollutants in surface waters and atmospheric drops. We recently found that ¹O₂* concentrations are enhanced by up to a factor of 10(4) on illuminated ice compared to in the equivalent liquid solution, suggesting that ¹O₂* could be an important oxidant for pollutants in snow. To examine this, here we study the degradation of three model organic pollutants: furfuryl alcohol (to represent furans), tryptophan (for aromatic amino acids), and bisphenol A (for phenols). Each compound was studied in illuminated aqueous solution and ice containing Rose Bengal (RB, a sensitizer for ¹O₂*) and sodium chloride (to adjust the concentration of total solutes). The RB-mediated loss of each organic compound is enhanced on illuminated ice compared to in solution, by factors of 6400 for furfuryl alcohol, 8300 for tryptophan, and 50 for bisphenol A for ice containing 0.065 mM total solutes. Rates of loss of furfuryl alcohol and tryptophan decrease at a higher total solute concentration, in qualitative agreement with predictions from freezing-point depression. In contrast, the loss of bisphenol A on ice is independent of total solute concentration. Relative to liquid tests, the enhanced loss of tryptophan on ice during control experiments made with deoxygenated solutions and solutions in D₂O show that the triplet excited state of Rose Bengal may also contribute to loss of pollutants on ice. PMID:24487942

  18. Degradation of organic pollutants in/on snow and ice by singlet molecular oxygen (¹O₂*) and an organic triplet excited state.

    PubMed

    Bower, Jonathan P; Anastasio, Cort

    2014-04-01

    Singlet molecular oxygen (¹O₂*) can be a significant sink for a variety of electron-rich pollutants in surface waters and atmospheric drops. We recently found that ¹O₂* concentrations are enhanced by up to a factor of 10(4) on illuminated ice compared to in the equivalent liquid solution, suggesting that ¹O₂* could be an important oxidant for pollutants in snow. To examine this, here we study the degradation of three model organic pollutants: furfuryl alcohol (to represent furans), tryptophan (for aromatic amino acids), and bisphenol A (for phenols). Each compound was studied in illuminated aqueous solution and ice containing Rose Bengal (RB, a sensitizer for ¹O₂*) and sodium chloride (to adjust the concentration of total solutes). The RB-mediated loss of each organic compound is enhanced on illuminated ice compared to in solution, by factors of 6400 for furfuryl alcohol, 8300 for tryptophan, and 50 for bisphenol A for ice containing 0.065 mM total solutes. Rates of loss of furfuryl alcohol and tryptophan decrease at a higher total solute concentration, in qualitative agreement with predictions from freezing-point depression. In contrast, the loss of bisphenol A on ice is independent of total solute concentration. Relative to liquid tests, the enhanced loss of tryptophan on ice during control experiments made with deoxygenated solutions and solutions in D₂O show that the triplet excited state of Rose Bengal may also contribute to loss of pollutants on ice.

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

    PubMed

    Rosado-Lausell, Sahid L; Wang, Hanting; Gutiérrez, Leonardo; Romero-Maraccini, Ofelia C; Niu, Xi-Zhi; Gin, Karina Y H; Croué, Jean-Philippe; Nguyen, Thanh H

    2013-09-15

    Inactivation of bacteriophage MS2 by reactive oxygen species (ROS) and triplet excited state of dissolved organic matter ((3)DOM*) produced by irradiation of natural and synthetic sensitizers with simulated sunlight of wavelengths greater than 320 nm 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 (3)DOM*. Linear correlations between MS2 kobs and singlet oxygen ((1)O2) 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 [Formula: see text] , suggest that (1)O2, (3)DOM*, and hydroxyl radicals ((•)OH) could inactivate bacteriophage MS2. Linear correlations between MS2 kobs and Specific Ultraviolet Absorption determined at 254 nm (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. PMID:23866126

  20. Excitation Localization/Delocalization Isomerism in a Strongly Coupled Covalent Dimer of 1,3-Diphenylisobenzofuran.

    PubMed

    Schrauben, Joel N; Akdag, Akin; Wen, Jin; Havlas, Zdenek; Ryerson, Joseph L; Smith, Millie B; Michl, Josef; Johnson, Justin C

    2016-05-26

    Two isomers of both the lowest excited singlet (S1) and triplet (T1) states of the directly para, para'-connected covalent dimer of the singlet-fission chromophore 1,3-diphenylisobenzofuran have been observed. In one isomer, excitation is delocalized over both halves of the dimer, and in the other, it is localized on one or the other half. For a covalent dimer in solution, such "excitation isomerism" is extremely rare. The vibrationally relaxed isomers do not interconvert, and their photophysical properties, including singlet fission, differ significantly.

  1. Water-soluble naphthalene diimides as singlet oxygen sensitizers.

    PubMed

    Doria, Filippo; Manet, Ilse; Grande, Vincenzo; Monti, Sandra; Freccero, Mauro

    2013-08-16

    Bromo- and/or alkylamino-substituted and hydrosoluble naphthalene diimides (NDIs) were synthesized to study their multimodal photophysical and photochemical properties. Bromine-containing NDIs (i.e., 11) behaved as both singlet oxygen ((1)O2) photosensitizers and fluorescent molecules upon irradiation at 532 nm. Among the NDIs not containing Br, only 12 exhibited photophysical properties similar to those of Br-NDIs, by irradiation above 610 nm, suggesting that for these NDIs both singlet and triplet excited-state properties are strongly affected by length, structure of the solubilizing moieties, and pH of the solution. Laser flash photolysis confirmed that the NDI lowest triplet excited state was efficiently populated, upon excitation at both 355 and 532 nm, and that free amine moieties quenched both the singlet and triplet excited states by intramolecular electron transfer, with generation of detectable radical anions. Time-resolved experiments, monitoring the 1270 nm (1)O2 phosphorescence decay generated upon laser irradiation at 532 nm, allowed a ranking of the NDIs as sensitizers, based on their (1)O2 quantum yields (ΦΔ). The tetrafunctionalized 12, exhibiting a long-lived triplet state (τ ~ 32 μs) and the most promising absorptivity for photodynamic therapy application, was tested as efficient photosensitizers in the photo-oxidations of 1,5-dihydroxynaphthalene and 9,10-anthracenedipropionic acid in acetonitrile and water. PMID:23869544

  2. Pigment-pigment interactions in thylakoids and LHCII of chlorophyll a/ c containing alga Pleurochloris meiringensis: analysis of fluorescence-excitation and triplet-minus-singlet spectra

    NASA Astrophysics Data System (ADS)

    Büchel, C.; Razi Naqvi, K.; Melø, T. B.

    1998-05-01

    Time-resolved triplet-minus-singlet (TmS) difference spectra, Δ A( λ; t), fluorescence excitation spectra, X( λ), and absorption spectra, A( λ), are used for probing pigment-pigment interactions in the thylakoids (Chl a/ c-Thyl) and isolated light-harvesting complexes associated with photosystem II (Chl a/ c-LHCII) of the alga Pleurochloris meiringensis, whose chromophores comprise chlorophyll a (Chl a), chlorophyll c (Chl c), and several carotenoids. The data provide information about interactions between Car*-and-Chl a0, Chl a†-and-Car 0, Car †-and-Chl a0 (where the abbreviation Car stands for carotenoid, an asterisk and a dagger denote singlet and triplet excitation, respectively, and the superscript 0 denotes a molecule in the ground state). In Chl a/c-Thyl, the efficiency of Car*→Chl a* transfer ( φLH), determined by comparing A( λ) and X( λ), is slightly less than unity (ca. 0.85), whereas the efficiency of Chl a†→Car † transfer of triplet energy ( φTT) must be much closer to unity, since no long-lived Chl a† could be detected; an interaction between Car † and Chl a0, already familiar from investigations concerning the TmS spectra of the trimers and aggregates of Chl a/ b-LHCII (the light-harvesting complex associated with the photosystem II of higher plants), which manifests itself through a depletion signal (in the Qy region of Chl a) decaying at the same rate as the Car TmS signal, is observed, and explained likewise. In Chl a/ c-LHCII, both efficiencies are found to be much lower; the drastic reduction in the two yields is attributed to the perturbation of the native molecular architecture of the complex by the detergent used in the isolation procedure. The overall TmS signal from Chl a/ c-LHCII can be decomposed into two contributions, Δ A( λ; t)=Δ 1A( λ; t)+Δ 2A( λ; t), where Δ 1A( λ; t) with a lifetime of about 8 μs; Δ 2A( λ; t), which persists for several hundred microseconds, is contributed by those Chl a

  3. Singlet and triplet instability theorems

    SciTech Connect

    Yamada, Tomonori; Hirata, So

    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.

  4. Singlet and triplet instability theorems

    NASA Astrophysics Data System (ADS)

    Yamada, Tomonori; Hirata, So

    2015-09-01

    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.

  5. Singlet and triplet instability theorems.

    PubMed

    Yamada, Tomonori; Hirata, So

    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. PMID:26395692

  6. Theoretical investigation on properties of the ground and lowest excited states of a red emitter with donor-π-acceptor structure

    NASA Astrophysics Data System (ADS)

    Liu, Xiaojun; Zhang, Xiao; Hou, Yanbing; Teng, Feng; Lou, Zhidong

    2011-03-01

    The ground and excited state properties of DCDPC, particularly designed as a red emitter for organic light emitting diodes applications have been studied by means of density functional theory (DFT) and time-dependent (TD)DFT. The electronic and geometrical structures of DCDPC in acetone, tetrahydrofuran and benzene solvents are reported for the first time. The experimental absorption and fluorescence spectra are reproduced by calculations. By comparison with experimental data, insight on the performance of 10 exchange correlation functionals is also given. M06 in the frame of DFT and TDDFT with a polarizable continuum model and a medium sized basis set emerges as the most effective strategy. Beside the good agreement between the calculational and experimental spectra proving the accuracy of the strategy, the calculations allow further insights into the electronic structure for the family of isophorone-based light emitting materials with D-π-A structure, especially the electronic and geometrical structures for the excited states.

  7. Metal-to-Ligand Charge-Transfer Emissions of Ruthenium(II) Pentaammine Complexes with Monodentate Aromatic Acceptor Ligands and Distortion Patterns of their Lowest Energy Triplet Excited States.

    PubMed

    Tsai, Chia Nung; Mazumder, Shivnath; Zhang, Xiu Zhu; Schlegel, H Bernhard; Chen, Yuan Jang; Endicott, John F

    2015-09-01

    This is the first report of the 77 K triplet metal-to-ligand charge-transfer ((3)MLCT) emission spectra of pentaammine-MDA-ruthenium(II) ([Ru(NH3)5(MDA)](2+)) complexes, where MDA is a monodentate aromatic ligand. The emission spectra of these complexes and of the related trans-[Ru(NH3)4(MDA) (MDA')](2+) complexes are closely related, and their emission intensities are very weak. Density functional theory (DFT) calculations indicate that the energies of the lowest (3)MLCT excited states of Ru-MDA complexes are either similar to or lower than those of the lowest energy metal-centered excited states ((3)MC(X(Y))), that the barrier to internal conversion at 77 K is large compared to kBT, and that the (3)MC(X(Y)) excited states are weakly bound. The [Ru(NH3)5py](2+) complex is an exception to the general pattern: emission has been observed for the [Ru(ND3)5(d5-py)](2+) complex, but its lifetime is apparently very short. DFT modeling indicates that the excited state distortions of the different (3)MC excited states are very large and are in both Ru-ligand bonds along a single Cartesian axis for each different (3)MC excited state, nominally resulting in (3)MC(X(Y)), (3)MC((X)Y), and (3)MC(Z) lowest energy metal-centered states. The (3)MC(X(Y)) and (3)MC((X)Y) states appear to be the pseudo-Jahn-Teller distorted components of a (3)MC((XY)) state. The (3)MC(X(Y)) states are distorted up to 0.5 Å in each H3N-Ru-NH3 bond along a single Cartesian axis in the pentaammine and trans-tetraammine complexes, whereas the (3)MC(Z) states are found to be dissociative. DFT modeling of the (3)MLCT excited state of [Ru(NH3)5(py)](2+) indicates that the Ru center has a spin density of 1.24 at the (3)MLCT energy minimum and that the (3)MLCT → (3)MC(Z) crossing is smooth with a very small barrier (<0.5 kcal/mol) along the D3N-Ru-py distortion coordinate, implying strong (3)MLCT/(3)MC excited state configurational mixing. Furthermore, the DFT modeling indicates that the long

  8. Time-resolved EPR and optical studies of intermoiety interactions in the lowest triplet state of L-shaped dimers of naphthalene: Conformation dependence of excitation exchange interaction

    SciTech Connect

    Terazima, Masahide; Cai, Jianjian; Lim, E.C.

    2000-03-02

    Time-resolved EPR (TREPR), transient absorption, and phosphorescence spectra have been measured in solid matrixes at 77 K for the covalently linked L-shaped dimers of naphthalene, in which the in-plane long axes of the two naphthalene moieties are parallel and the in-plane short axes make an angle. The zero-field splitting (ZFS) parameters obtained by simulation of the TREPR spectra are consistent with the dimer geometries, if it is assumed that excitation exchange interaction is responsible for the small D values of the dimers relative to the monomer. The tilt angle in the triplet state is significantly smaller for the dimers exhibiting excimeric phosphorescence than those exhibiting monomeric emissions. Comparison of the spectral position and lifetime of phosphorescence from the L-shaped dimers with those from the sandwich dimers indicates that the excitation exchange interaction is substantially greater for the L-shaped dimers as compared to the sandwich dimers. The proposal that the preferred conformation of the triplet excimer of naphthalene is L-shaped, rather than sandwich, is supported by the measurements.

  9. A theoretical study of the ground state and lowest excited states of PuO0/+/+2 and PuO20/+/+2

    SciTech Connect

    Gibson, John K.; La Macchia, Giovanni; Infante, Ivan; Gagliardi, Laura; Raab, Juraj

    2008-12-08

    The ground and excited states of neutral and cationic PuO and PuO2 have been studied with multiconfigurational quantum chemical methods followed by second order perturbation theory, the CASSCF/CASPT2 method. Scalar relativistic effects and spin-orbit coupling have been included in the treatment. As literature values for the ionization energy of PuO2 are in the wide range of ~;;6.6 eV to ~;;10.1 eV, a central goal of the computations was to resolve these discrepancies; the theoretical results indicate that the ionization energy is near the lower end of this range. The calculated ionization energies for PuO, PuO+ and PuO2+ are in good agreement with the experimental values.

  10. Low-lying excited states in armchair polyacene within Pariser-Parr-Pople model: A density matrix renormalization group study

    SciTech Connect

    Das, Mousumi

    2014-03-28

    We studied the nature of the ground state and low-lying excited states of armchair polyacene oligomers (Polyphenanthrene) within long-range Pariser-Parr-Pople model Hamiltonian with up to 14 monomers using symmetrized density matrix renormalization group technique. The ground state of all armchair polyacenes studied is found to be singlet. The results show that lowest singlet dipole allowed excited state has higher energy for armchair polyacenes as compared to linear fused polyacenes. Moreover, unlike linear fused polyacenes, the lowest singlet excited state of these oligomers is always found to lie below the lowest dipole forbidden two-photon state indicating that these armchair polyacene oligomers strongly fluoresce. The calculations of low-lying excitations on singly and triply electron doped armchair polyacene oligomers show a low energy band with strong transition dipole moment that coupled to charge conductivity. This implies armchair polyacene posses novel field-effect transistor properties.

  11. An Analysis of the Torsion-Rotation-Vibration Rotational Spectrum of the Lowest In-Plane Bend and First Excited Torsional State of the C(3V) Internal Rotor C2H5CN

    NASA Technical Reports Server (NTRS)

    Pearson, J. C.; Pickett, Herbert M.; Sastry, K. V. L. N.

    2000-01-01

    C2H5CN (Propionitrile or ethyl cyanide) is a well known interstellar species abundantly observed in hot cores during the onset of star formation. The onset of star formation generally results in elevated temperature, which thermally populates may low lying vibrational states such as the 206/cm in-plane bend and the 212/cm first excited torsional state in C2H5CN. Unfortunately, these two states are strongly coupled through a complex series of torsion-vibration-rotation interactions, which dominate the spectrum. In order to understand the details of these interactions and develop models capable of predicting unmeasured transitions for astronomical observations in C2H5CN and similar molecules, several thousand rotational transitions in the lowest excited in-plane bend and first excited torsional state have been recorded, assigned and analyzed. The analysis reveals very strong a- and b-type Coriolis interactions and a number of other smaller interactions and has a number of important implications for other C3V torsion-rotation-vibration systems. The relative importance and the physical origins of the coupling among the rotational, vibrational and torsional motions will be presented along with a full spectroscopic analysis and supporting astronomical observations.

  12. Triplet-singlet conversion in ultracold Cs{sub 2} and production of ground-state molecules

    SciTech Connect

    Bouloufa, Nadia; Aymar, Mireille; Dulieu, Olivier; Pichler, Marin

    2011-02-15

    We propose a process to convert ultracold metastable Cs{sub 2} molecules in their lowest triplet state into (singlet) ground-state molecules in their lowest vibrational levels. Molecules are first pumped into an excited triplet state, and the triplet-singlet conversion is facilitated by a two-step spontaneous decay through the coupled A {sup 1{Sigma}}{sub u}{sup +}-b {sup 3{Pi}}{sub u} states. Using spectroscopic data and accurate quantum chemistry calculations for Cs{sub 2} potential curves and transition dipole moments, we show that this process competes favorably with the single-photon decay back to the lowest triplet state. In addition, we demonstrate that this conversion process represents a loss channel for vibrational cooling of metastable triplet molecules, preventing an efficient optical pumping cycle down to low vibrational levels.

  13. Singlet molecular oxygen generated by biological hydroperoxides.

    PubMed

    Miyamoto, Sayuri; Martinez, Glaucia R; Medeiros, Marisa H G; Di Mascio, Paolo

    2014-10-01

    The chemistry behind the phenomenon of ultra-weak photon emission has been subject of considerable interest for decades. Great progress has been made on the understanding of the chemical generation of electronically excited states that are involved in these processes. Proposed mechanisms implicated the production of excited carbonyl species and singlet molecular oxygen in the mechanism of generation of chemiluminescence in biological system. In particular, attention has been focused on the potential generation of singlet molecular oxygen in the recombination reaction of peroxyl radicals by the Russell mechanism. In the last ten years, our group has demonstrated the generation of singlet molecular oxygen from reactions involving the decomposition of biologically relevant hydroperoxides, especially from lipid hydroperoxides in the presence of metal ions, peroxynitrite, HOCl and cytochrome c. In this review we will discuss details on the chemical aspects related to the mechanism of singlet molecular oxygen generation from different biological hydroperoxides.

  14. The transition from the open minimum to the ring minimum on the ground state and on the lowest excited state of like symmetry in ozone: A configuration interaction study.

    PubMed

    Theis, Daniel; Ivanic, Joseph; Windus, Theresa L; Ruedenberg, Klaus

    2016-03-14

    The metastable ring structure of the ozone 1(1)A1 ground state, which theoretical calculations have shown to exist, has so far eluded experimental detection. An accurate prediction for the energy difference between this isomer and the lower open structure is therefore of interest, as is a prediction for the isomerization barrier between them, which results from interactions between the lowest two (1)A1 states. In the present work, valence correlated energies of the 1(1)A1 state and the 2(1)A1 state were calculated at the 1(1)A1 open minimum, the 1(1)A1 ring minimum, the transition state between these two minima, the minimum of the 2(1)A1 state, and the conical intersection between the two states. The geometries were determined at the full-valence multi-configuration self-consistent-field level. Configuration interaction (CI) expansions up to quadruple excitations were calculated with triple-zeta atomic basis sets. The CI expansions based on eight different reference configuration spaces were explored. To obtain some of the quadruple excitation energies, the method of Correlation Energy Extrapolation by Intrinsic Scaling was generalized to the simultaneous extrapolation for two states. This extrapolation method was shown to be very accurate. On the other hand, none of the CI expansions were found to have converged to millihartree (mh) accuracy at the quadruple excitation level. The data suggest that convergence to mh accuracy is probably attained at the sextuple excitation level. On the 1(1)A1 state, the present calculations yield the estimates of (ring minimum-open minimum) ∼45-50 mh and (transition state-open minimum) ∼85-90 mh. For the (2(1)A1-(1)A1) excitation energy, the estimate of ∼130-170 mh is found at the open minimum and 270-310 mh at the ring minimum. At the transition state, the difference (2(1)A1-(1)A1) is found to be between 1 and 10 mh. The geometry of the transition state on the 1(1)A1 surface and that of the minimum on the 2(1)A1 surface

  15. The transition from the open minimum to the ring minimum on the ground state and on the lowest excited state of like symmetry in ozone: A configuration interaction study.

    PubMed

    Theis, Daniel; Ivanic, Joseph; Windus, Theresa L; Ruedenberg, Klaus

    2016-03-14

    The metastable ring structure of the ozone 1(1)A1 ground state, which theoretical calculations have shown to exist, has so far eluded experimental detection. An accurate prediction for the energy difference between this isomer and the lower open structure is therefore of interest, as is a prediction for the isomerization barrier between them, which results from interactions between the lowest two (1)A1 states. In the present work, valence correlated energies of the 1(1)A1 state and the 2(1)A1 state were calculated at the 1(1)A1 open minimum, the 1(1)A1 ring minimum, the transition state between these two minima, the minimum of the 2(1)A1 state, and the conical intersection between the two states. The geometries were determined at the full-valence multi-configuration self-consistent-field level. Configuration interaction (CI) expansions up to quadruple excitations were calculated with triple-zeta atomic basis sets. The CI expansions based on eight different reference configuration spaces were explored. To obtain some of the quadruple excitation energies, the method of Correlation Energy Extrapolation by Intrinsic Scaling was generalized to the simultaneous extrapolation for two states. This extrapolation method was shown to be very accurate. On the other hand, none of the CI expansions were found to have converged to millihartree (mh) accuracy at the quadruple excitation level. The data suggest that convergence to mh accuracy is probably attained at the sextuple excitation level. On the 1(1)A1 state, the present calculations yield the estimates of (ring minimum-open minimum) ∼45-50 mh and (transition state-open minimum) ∼85-90 mh. For the (2(1)A1-(1)A1) excitation energy, the estimate of ∼130-170 mh is found at the open minimum and 270-310 mh at the ring minimum. At the transition state, the difference (2(1)A1-(1)A1) is found to be between 1 and 10 mh. The geometry of the transition state on the 1(1)A1 surface and that of the minimum on the 2(1)A1 surface

  16. The transition from the open minimum to the ring minimum on the ground state and on the lowest excited state of like symmetry in ozone: A configuration interaction study

    DOE PAGESBeta

    Theis, Daniel; Ivanic, Joseph; Windus, Theresa L.; Ruedenberg, Klaus

    2016-03-10

    The metastable ring structure of the ozone 11A1 ground state, which theoretical calculations have shown to exist, has so far eluded experimental detection. An accurate prediction for the energy difference between this isomer and the lower open structure is therefore of interest, as is a prediction for the isomerization barrier between them, which results from interactions between the lowest two 1A1 states. In the present work, valence correlated energies of the 11A1 state and the 21A1 state were calculated at the 11A1 open minimum, the 11A1 ring minimum, the transition state between these two minima, the minimum of the 21A1more » state, and the conical intersection between the two states. The geometries were determined at the full-valence multi-configuration self-consistent-field level. Configuration interaction (CI) expansions up to quadruple excitations were calculated with triple-zeta atomic basis sets. The CI expansions based on eight different reference configuration spaces were explored. To obtain some of the quadruple excitation energies, the method of CorrelationEnergy Extrapolation by Intrinsic Scaling was generalized to the simultaneous extrapolation for two states. This extrapolation method was shown to be very accurate. On the other hand, none of the CI expansions were found to have converged to millihartree (mh) accuracy at the quadruple excitation level. The data suggest that convergence to mh accuracy is probably attained at the sextuple excitation level. On the 11A1 state, the present calculations yield the estimates of (ring minimum—open minimum) ~45–50 mh and (transition state—open minimum) ~85–90 mh. For the (21A1–1A1) excitation energy, the estimate of ~130–170 mh is found at the open minimum and 270–310 mh at the ring minimum. At the transition state, the difference (21A1–1A1) is found to be between 1 and 10 mh. The geometry of the transition state on the 11A1 surface and that of the minimum on the 21A1 surface nearly coincide

  17. The transition from the open minimum to the ring minimum on the ground state and on the lowest excited state of like symmetry in ozone: A configuration interaction study

    NASA Astrophysics Data System (ADS)

    Theis, Daniel; Ivanic, Joseph; Windus, Theresa L.; Ruedenberg, Klaus

    2016-03-01

    The metastable ring structure of the ozone 11A1 ground state, which theoretical calculations have shown to exist, has so far eluded experimental detection. An accurate prediction for the energy difference between this isomer and the lower open structure is therefore of interest, as is a prediction for the isomerization barrier between them, which results from interactions between the lowest two 1A1 states. In the present work, valence correlated energies of the 11A1 state and the 21A1 state were calculated at the 11A1 open minimum, the 11A1 ring minimum, the transition state between these two minima, the minimum of the 21A1 state, and the conical intersection between the two states. The geometries were determined at the full-valence multi-configuration self-consistent-field level. Configuration interaction (CI) expansions up to quadruple excitations were calculated with triple-zeta atomic basis sets. The CI expansions based on eight different reference configuration spaces were explored. To obtain some of the quadruple excitation energies, the method of Correlation Energy Extrapolation by Intrinsic Scaling was generalized to the simultaneous extrapolation for two states. This extrapolation method was shown to be very accurate. On the other hand, none of the CI expansions were found to have converged to millihartree (mh) accuracy at the quadruple excitation level. The data suggest that convergence to mh accuracy is probably attained at the sextuple excitation level. On the 11A1 state, the present calculations yield the estimates of (ring minimum—open minimum) ˜45-50 mh and (transition state—open minimum) ˜85-90 mh. For the (21A1-1A1) excitation energy, the estimate of ˜130-170 mh is found at the open minimum and 270-310 mh at the ring minimum. At the transition state, the difference (21A1-1A1) is found to be between 1 and 10 mh. The geometry of the transition state on the 11A1 surface and that of the minimum on the 21A1 surface nearly coincide. More accurate

  18. Singlet oxygen production in Chlamydomonas reinhardtii under heat stress.

    PubMed

    Prasad, Ankush; Ferretti, Ursula; Sedlářová, Michaela; Pospíšil, Pavel

    2016-01-01

    In the current study, singlet oxygen formation by lipid peroxidation induced by heat stress (40 °C) was studied in vivo in unicellular green alga Chlamydomonas reinhardtii. Primary and secondary oxidation products of lipid peroxidation, hydroperoxide and malondialdehyde, were generated under heat stress as detected using swallow-tailed perylene derivative fluorescence monitored by confocal laser scanning microscopy and high performance liquid chromatography, respectively. Lipid peroxidation was initiated by enzymatic reaction as inhibition of lipoxygenase by catechol and caffeic acid prevented hydroperoxide formation. Ultra-weak photon emission showed formation of electronically excited species such as triplet excited carbonyl, which, upon transfer of excitation energy, leads to the formation of either singlet excited chlorophyll or singlet oxygen. Alternatively, singlet oxygen is formed by direct decomposition of hydroperoxide via Russell mechanisms. Formation of singlet oxygen was evidenced by the nitroxyl radical 2,2,6,6-tetramethylpiperidine-1-oxyl detected by electron paramagnetic resonance spin-trapping spectroscopy and the imaging of green fluorescence of singlet oxygen sensor green detected by confocal laser scanning microscopy. Suppression of singlet oxygen formation by lipoxygenase inhibitors indicates that singlet oxygen may be formed via enzymatic lipid peroxidation initiated by lipoxygenase. PMID:26831215

  19. Singlet oxygen production in Chlamydomonas reinhardtii under heat stress

    PubMed Central

    Prasad, Ankush; Ferretti, Ursula; Sedlářová, Michaela; Pospíšil, Pavel

    2016-01-01

    In the current study, singlet oxygen formation by lipid peroxidation induced by heat stress (40 °C) was studied in vivo in unicellular green alga Chlamydomonas reinhardtii. Primary and secondary oxidation products of lipid peroxidation, hydroperoxide and malondialdehyde, were generated under heat stress as detected using swallow-tailed perylene derivative fluorescence monitored by confocal laser scanning microscopy and high performance liquid chromatography, respectively. Lipid peroxidation was initiated by enzymatic reaction as inhibition of lipoxygenase by catechol and caffeic acid prevented hydroperoxide formation. Ultra-weak photon emission showed formation of electronically excited species such as triplet excited carbonyl, which, upon transfer of excitation energy, leads to the formation of either singlet excited chlorophyll or singlet oxygen. Alternatively, singlet oxygen is formed by direct decomposition of hydroperoxide via Russell mechanisms. Formation of singlet oxygen was evidenced by the nitroxyl radical 2,2,6,6-tetramethylpiperidine-1-oxyl detected by electron paramagnetic resonance spin-trapping spectroscopy and the imaging of green fluorescence of singlet oxygen sensor green detected by confocal laser scanning microscopy. Suppression of singlet oxygen formation by lipoxygenase inhibitors indicates that singlet oxygen may be formed via enzymatic lipid peroxidation initiated by lipoxygenase. PMID:26831215

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

    PubMed

    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. PMID:26574215

  1. Estimation of the ground and the first excited singlet-state dipole moments of 1,4-disubstituted anthraquinone dyes by the solvatochromic method.

    PubMed

    Siddlingeshwar, B; Hanagodimath, S M

    2010-04-01

    The both, ground-state (mu(g)) and the excited-state (mu(e)) dipole moments of three 1,4-disubstituted anthraquinones, namely 1,4-diaminoanthracene-9,10-dione (1,4-DAAQ), 1-amino-4-hydroxyanthracene-9,10-dione (1,4-AHAQ), and 1,4-dihydroxyanthracene-9,10-dione (1,4-DHAQ) were estimated in binary solvent mixtures (methylcyclohexane-ethyl acetate and ethyl acetate-acetonitrile). The dipole moments (mu(g) and mu(e)) were estimated from Lippert-Mataga, Bakhshiev, Kawski-Chamma-Viallet, McRae, and Suppan equations by using the variation of Stokes shift with the solvent's relative permittivity and refractive index. The ground-state dipole moments were also calculated theoretically by Gaussian 03 software using B3LYP/6-31 G* level of theory. Further, the change in dipole moment values Deltamu were also calculated by using the variation of Stokes shift with the molecular-microscopic empirical solvent polarity parameter (E(T)(N)). The excited-state dipole moments observed are larger than their ground-state counterparts, indicating a substantial redistribution of the pi-electron densities in a more polar excited state for all the molecules investigated.

  2. Singlet fission of hot excitons in π-conjugated polymers

    PubMed Central

    Zhai, Yaxin; Sheng, Chuanxiang; Vardeny, Z. Valy

    2015-01-01

    We used steady-state photoinduced absorption (PA), excitation dependence (EXPA(ω)) spectrum of the triplet exciton PA band, and its magneto-PA (MPA(B)) response to investigate singlet fission (SF) of hot excitons into two separated triplet excitons, in two luminescent and non-luminescent π-conjugated polymers. From the high energy step in the triplet EXPA(ω) spectrum of the luminescent polymer poly(dioctyloxy)phenylenevinylene (DOO-PPV) films, we identified a hot-exciton SF (HE-SF) process having threshold energy at E≈2ET (=2.8 eV, where ET is the energy of the lowest lying triplet exciton), which is about 0.8 eV above the lowest singlet exciton energy. The HE-SF process was confirmed by the triplet MPA(B) response for excitation at E>2ET, which shows typical SF response. This process is missing in DOO-PPV solution, showing that it is predominantly interchain in nature. By contrast, the triplet EXPA(ω) spectrum in the non-luminescent polymer polydiacetylene (PDA) is flat with an onset at E=Eg (≈2.25 eV). From this, we infer that intrachain SF that involves a triplet–triplet pair state, also known as the ‘dark’ 2Ag exciton, dominates the triplet photogeneration in PDA polymer as Eg>2ET. The intrachain SF process was also identified from the MPA(B) response of the triplet PA band in PDA. Our work shows that the SF process in π-conjugated polymers is a much more general process than thought previously. PMID:25987576

  3. 1,1-Dilithioethylene: Toward Spectroscopic Identification of the Definitive Singlet Ground Electronic State of a Peculiar Structure.

    PubMed

    Liu, Yameng; Wang, Xiao; Liu, Yongdong; Zhong, Rugang; Xie, Yaoming; Schaefer, Henry F

    2016-06-01

    1,1-Dilithioethylene is a prototypical carbon-lithium compound that is not known experimentally. All low-lying singlet and triplet structures of interest were investigated by using high-level theoretical methods with correlation-consistent basis sets up to pentuple ζ. The coupled cluster methods adopted included up to full triple excitations and perturbative quadruples. In contrast to earlier studies that predicted the twisted C2v triplet to be the ground state, we found a peculiar planar Cs singlet ground state in the present research. The lowest excited electronic state of 1,1-dilithioethylene, the twisted Cs triplet, was found to lie 9.0 kcal mol(-1) above the ground state by using energy extrapolation to the complete basis set limit. For the planar Cs singlet and twisted Cs triplet states of 1,1-dilithioethylene, anharmonic vibrational frequencies were reported on the basis of second-order vibrational perturbation theory. The remarkably low (2050 cm(-1) ) C-H stretching fundamental (the C-H bond near the bridging lithium) of the singlet state was found to have very strong infrared intensity. These highly reliable theoretical findings may assist in the long-sought experimental identification of 1,1-dilithioethylene. Using natural bond orbital analysis, we found that lithium bridging structures were strongly influenced by electrostatic effects. All carbon-carbon linkages corresponded to conventional double bonds. PMID:27038425

  4. Is Nitrate Anion Photodissociation Mediated by Singlet-Triplet Absorption?

    PubMed

    Svoboda, Ondřej; Slavíček, Petr

    2014-06-01

    Photolysis of the nitrate anion is involved in the oxidation processes in the hydrosphere, cryosphere, and stratosphere. While it is known that the nitrate photolysis in the long-wavelength region proceeds with a very low quantum yield, the mechanism of the photodissociation remains elusive. Here, we present the quantitative modeling of singlet-singlet and singlet-triplet absorption spectra in the atmospherically relevant region around 300 nm, and we argue that a spin-forbidden transition between the singlet ground state and the first triplet state contributes non-negligibly to the nitrate anion photolysis. We further propose that the nitrate anion excited into the first singlet excited state relaxes nonradiatively into its ground state. The full understanding of the nitrate anion photolysis can improve modeling of the asymmetric solvation in the atmospheric processes, e.g., photolysis on the surfaces of ice or snow. PMID:26273880

  5. Trapping on demand: External regulation of excitation energy transfer in a photoswitchable smart matrix

    NASA Astrophysics Data System (ADS)

    Schmidt, R.; Pärs, M.; Weller, T.; Thelakkat, M.; Köhler, J.

    2014-01-01

    A thin film of polystyrene has been doped with small amounts of dithienylcyclopentene (DCP) based molecular switches and perylene bisimide (PBI) chromophores to obtain a photoswitchable smart matrix. The photochromic DCP can be converted by light between two bistable conformations and thereby changes the energetic position of its lowest excited singlet state. We exploit this feature to regulate the transfer of excitation energy between PBI and DCP as a function of the externally controllable illumination conditions in such a blend.

  6. Four-electron model for singlet and triplet excitation energy transfers with inclusion of coherence memory, inelastic tunneling and nuclear quantum effects

    NASA Astrophysics Data System (ADS)

    Suzuki, Yosuke; Ebina, Kuniyoshi; Tanaka, Shigenori

    2016-08-01

    A computational scheme to describe the coherent dynamics of excitation energy transfer (EET) in molecular systems is proposed on the basis of generalized master equations with memory kernels. This formalism takes into account those physical effects in electron-bath coupling system such as the spin symmetry of excitons, the inelastic electron tunneling and the quantum features of nuclear motions, thus providing a theoretical framework to perform an ab initio description of EET through molecular simulations for evaluating the spectral density and the temporal correlation function of electronic coupling. Some test calculations have then been carried out to investigate the dependence of exciton population dynamics on coherence memory, inelastic tunneling correlation time, magnitude of electronic coupling, quantum correction to temporal correlation function, reorganization energy and energy gap.

  7. Singlet exciton fission photovoltaics.

    PubMed

    Lee, Jiye; Jadhav, Priya; Reusswig, Philip D; Yost, Shane R; Thompson, Nicholas J; Congreve, Daniel N; Hontz, Eric; Van Voorhis, Troy; Baldo, Marc A

    2013-06-18

    Singlet exciton fission, a process that generates two excitons from a single photon, is perhaps the most efficient of the various multiexciton-generation processes studied to date, offering the potential to increase the efficiency of solar devices. But its unique characteristic, splitting a photogenerated singlet exciton into two dark triplet states, means that the empty absorption region between the singlet and triplet excitons must be filled by adding another material that captures low-energy photons. This has required the development of specialized device architectures. In this Account, we review work to develop devices that harness the theoretical benefits of singlet exciton fission. First, we discuss singlet fission in the archetypal material, pentacene. Pentacene-based photovoltaic devices typically show high external and internal quantum efficiencies. They have enabled researchers to characterize fission, including yield and the impact of competing loss processes, within functional devices. We review in situ probes of singlet fission that modulate the photocurrent using a magnetic field. We also summarize studies of the dissociation of triplet excitons into charge at the pentacene-buckyball (C60) donor-acceptor interface. Multiple independent measurements confirm that pentacene triplet excitons can dissociate at the C60 interface despite their relatively low energy. Because triplet excitons produced by singlet fission each have no more than half the energy of the original photoexcitation, they limit the potential open circuit voltage within a solar cell. Thus, if singlet fission is to increase the overall efficiency of a solar cell and not just double the photocurrent at the cost of halving the voltage, it is necessary to also harvest photons in the absorption gap between the singlet and triplet energies of the singlet fission material. We review two device architectures that attempt this using long-wavelength materials: a three-layer structure that uses

  8. Reaction of singlet-excited 2,3-diazabicyclo[2.2.2]oct-2-ene and tert-butoxyl radicals with aryl-substituted benzofuranones.

    PubMed

    Lundgren, Cecilia Vannesjö; Koner, Apurba L; Tinkl, Michael; Pischel, Uwe; Nau, Werner M

    2006-03-01

    5,7-Di-tert-butyl-3-aryl-3H-benzofuran-2-ones are lactones with potential antioxidant activity, owing to their abstractable benzylic C-H hydrogens. The fluorescence quenching of the azoalkane 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO), an established probe for the hydrogen-donor propensity of chain-breaking antioxidants, was investigated for 16 aryl-substituted benzofuranone derivatives [m,m-(CF3)2, p-CN, m-CN, p-CF3, p-COOCH3, m-CF3, p-Cl, p-F, H, m-CH3, p-CH3, m,p-(CH3)2, p-OCH3, o-CH3, o-CF3, o,m-(CH3)2]. Analysis of the rate data in terms of a linear free energy relationship yielded a reaction constant of rho = +0.35. This implies that n,pi*-excited DBO acts as nucleophilic species. In contrast, hydrogen abstraction of tert-butoxyl radicals from the benzofuranones was accelerated by electron-donating substituents (rho = -0.23), in conformity with the electrophilic character of oxygen-centered alkoxyl radicals. Possible implications for the optimization of the hydrogen-donor propensity of antioxidants through structural variation are discussed.

  9. Impact of ground- and excited-state aromaticity on cyclopentadiene and silole excitation energies and excited-state polarities.

    PubMed

    Jorner, Kjell; Emanuelsson, Rikard; Dahlstrand, Christian; Tong, Hui; Denisova, Aleksandra V; Ottosson, Henrik

    2014-07-21

    A new qualitative model for estimating the properties of substituted cyclopentadienes and siloles in their lowest ππ* excited states is introduced and confirmed through quantum chemical calculations, and then applied to explain earlier reported experimental excitation energies. According to our model, which is based on excited-state aromaticity and antiaromaticity, siloles and cyclopentadienes are cross-hyperconjugated "aromatic chameleons" that adapt their electronic structures to conform to the various aromaticity rules in different electronic states (Hückel's rule in the π(2) electronic ground state (S0) and Baird's rule in the lowest ππ* excited singlet and triplet states (S1 and T1)). By using pen-and-paper arguments, one can explain polarity changes upon excitation of substituted cyclopentadienes and siloles, and one can tune their lowest excitation energies by combined considerations of ground- and excited-state aromaticity/antiaromaticity effects. Finally, the "aromatic chameleon" model can be extended to other monocyclic compound classes of potential use in organic electronics, thereby providing a unified view of the S0, T1, and S1 states of a range of different cyclic cross-π-conjugated and cross-hyperconjugated compound classes. PMID:25043523

  10. Biradical vs singlet oxygen photogeneration in suprofen-cholesterol systems.

    PubMed

    Palumbo, Fabrizio; Bosca, Francisco; Morera, Isabel Maria; Andreu, Inmaculada; Miranda, Miguel A

    2016-01-01

    Cholesterol (Ch) is an important lipidic building block and a target for oxidative degradation, which can be induced via free radicals or singlet oxygen ((1)O2). Suprofen (SP) is a nonsteroidal anti-inflammatory drug that contains the 2-benzoylthiophene (BZT) chromophore and has a π,π* lowest triplet excited state. In the present work, dyads (S)- and (R)-SP-α-Ch (1 and 2), as well as (S)-SP-β-Ch (3) have been prepared from β- or α-Ch and SP to investigate the possible competition between photogeneration of biradicals and (1)O2, the key mechanistic steps in Ch photooxidation. Steady-state irradiation of 1 and 2 was performed in dichloromethane, under nitrogen, through Pyrex, using a 400 W medium pressure mercury lamp. The spectral analysis of the separated fractions revealed formation of two photoproducts 4 and 5, respectively. By contrast, under the same conditions, 3 did not give rise to any isolable Ch-derived product. These results point to an intramolecular hydrogen abstraction in 1 and 2 from the C7 position of Ch and subsequent C-C coupling of the generated biradicals. Interestingly, 2 was significantly more photoreactive than 1 indicating a clear stereodifferentiation in the photochemical behavior. Transient absorption spectra obtained for 1-3 were very similar and matched that described for the SP triplet excited state (typical bands with maxima at ca. 350 nm and 600 nm). Direct kinetic analysis of the decay traces at 620 nm led to determination of triplet lifetimes that were ca. 4.1 μs for 1 and 2 and 5.8 μs for 3. From these data, the intramolecular quenching rate constants in 1 and 2 were determined as 0.78 × 10(5) s(-1). The capability of dyads 1-3 to photosensitize the production of singlet oxygen was assessed by time-resolved near infrared emission studies in dichloromethane using perinaphthenone as standard. The quantum yields (ΦΔ) were 0.52 for 1 and 2 and 0.56 for 3. In conclusion, SP-α-Ch dyads are unique in the sense that they can be

  11. Biradical vs singlet oxygen photogeneration in suprofen-cholesterol systems.

    PubMed

    Palumbo, Fabrizio; Bosca, Francisco; Morera, Isabel Maria; Andreu, Inmaculada; Miranda, Miguel A

    2016-01-01

    Cholesterol (Ch) is an important lipidic building block and a target for oxidative degradation, which can be induced via free radicals or singlet oxygen ((1)O2). Suprofen (SP) is a nonsteroidal anti-inflammatory drug that contains the 2-benzoylthiophene (BZT) chromophore and has a π,π* lowest triplet excited state. In the present work, dyads (S)- and (R)-SP-α-Ch (1 and 2), as well as (S)-SP-β-Ch (3) have been prepared from β- or α-Ch and SP to investigate the possible competition between photogeneration of biradicals and (1)O2, the key mechanistic steps in Ch photooxidation. Steady-state irradiation of 1 and 2 was performed in dichloromethane, under nitrogen, through Pyrex, using a 400 W medium pressure mercury lamp. The spectral analysis of the separated fractions revealed formation of two photoproducts 4 and 5, respectively. By contrast, under the same conditions, 3 did not give rise to any isolable Ch-derived product. These results point to an intramolecular hydrogen abstraction in 1 and 2 from the C7 position of Ch and subsequent C-C coupling of the generated biradicals. Interestingly, 2 was significantly more photoreactive than 1 indicating a clear stereodifferentiation in the photochemical behavior. Transient absorption spectra obtained for 1-3 were very similar and matched that described for the SP triplet excited state (typical bands with maxima at ca. 350 nm and 600 nm). Direct kinetic analysis of the decay traces at 620 nm led to determination of triplet lifetimes that were ca. 4.1 μs for 1 and 2 and 5.8 μs for 3. From these data, the intramolecular quenching rate constants in 1 and 2 were determined as 0.78 × 10(5) s(-1). The capability of dyads 1-3 to photosensitize the production of singlet oxygen was assessed by time-resolved near infrared emission studies in dichloromethane using perinaphthenone as standard. The quantum yields (ΦΔ) were 0.52 for 1 and 2 and 0.56 for 3. In conclusion, SP-α-Ch dyads are unique in the sense that they can be

  12. Biradical vs singlet oxygen photogeneration in suprofen–cholesterol systems

    PubMed Central

    Palumbo, Fabrizio; Bosca, Francisco; Morera, Isabel Maria

    2016-01-01

    Summary Cholesterol (Ch) is an important lipidic building block and a target for oxidative degradation, which can be induced via free radicals or singlet oxygen (1O2). Suprofen (SP) is a nonsteroidal anti-inflammatory drug that contains the 2-benzoylthiophene (BZT) chromophore and has a π,π* lowest triplet excited state. In the present work, dyads (S)- and (R)-SP-α-Ch (1 and 2), as well as (S)-SP-β-Ch (3) have been prepared from β- or α-Ch and SP to investigate the possible competition between photogeneration of biradicals and 1O2, the key mechanistic steps in Ch photooxidation. Steady-state irradiation of 1 and 2 was performed in dichloromethane, under nitrogen, through Pyrex, using a 400 W medium pressure mercury lamp. The spectral analysis of the separated fractions revealed formation of two photoproducts 4 and 5, respectively. By contrast, under the same conditions, 3 did not give rise to any isolable Ch-derived product. These results point to an intramolecular hydrogen abstraction in 1 and 2 from the C7 position of Ch and subsequent C–C coupling of the generated biradicals. Interestingly, 2 was significantly more photoreactive than 1 indicating a clear stereodifferentiation in the photochemical behavior. Transient absorption spectra obtained for 1–3 were very similar and matched that described for the SP triplet excited state (typical bands with maxima at ca. 350 nm and 600 nm). Direct kinetic analysis of the decay traces at 620 nm led to determination of triplet lifetimes that were ca. 4.1 μs for 1 and 2 and 5.8 μs for 3. From these data, the intramolecular quenching rate constants in 1 and 2 were determined as 0.78 × 105 s−1. The capability of dyads 1–3 to photosensitize the production of singlet oxygen was assessed by time-resolved near infrared emission studies in dichloromethane using perinaphthenone as standard. The quantum yields (ΦΔ) were 0.52 for 1 and 2 and 0.56 for 3. In conclusion, SP-α-Ch dyads are unique in the sense that they

  13. Time-resolved infrared spectroscopy of the lowest triplet state of thymine and thymidine

    NASA Astrophysics Data System (ADS)

    Hare, Patrick M.; Middleton, Chris T.; Mertel, Kristin I.; Herbert, John M.; Kohler, Bern

    2008-05-01

    Vibrational spectra of the lowest energy triplet states of thymine and its 2'-deoxyribonucleoside, thymidine, are reported for the first time. Time-resolved infrared (TRIR) difference spectra were recorded over seven decades of time from 300 fs to 3 μs using femtosecond and nanosecond pump-probe techniques. The carbonyl stretch bands in the triplet state are seen at 1603 and ˜1700 cm -1 in room-temperature acetonitrile- d3 solution. These bands and additional ones observed between 1300 and 1450 cm -1 are quenched by dissolved oxygen on a nanosecond time scale. Density-functional calculations accurately predict the difference spectrum between triplet and singlet IR absorption cross sections, confirming the peak assignments and elucidating the nature of the vibrational modes. In the triplet state, the C4 dbnd O carbonyl exhibits substantial single-bond character, explaining the large (˜70 cm -1) red shift in this vibration, relative to the singlet ground state. Femtosecond TRIR measurements unambiguously demonstrate that the triplet state is fully formed within the first 10 ps after excitation, ruling out a relaxed 1nπ ∗ state as the triplet precursor.

  14. LHC phenomenology of lowest massive Regge recurrences in the Randall-Sundrum orbifold

    SciTech Connect

    Anchordoqui, Luis A.; Huang Xing; Goldberg, Haim; Taylor, Tomasz R.

    2010-11-15

    We consider string realizations of the Randall-Sundrum effective theory for electroweak symmetry breaking and explore the search for the lowest massive Regge excitation of the gluon and of the extra (color singlet) gauge boson inherent in D-brane constructions. In these curved backgrounds, the higher-spin Regge recurrences of standard model fields localized near the IR brane are warped down to close to the TeV range and hence can be produced at collider experiments. Assuming that the theory is weakly coupled, we make use of four gauge boson amplitudes evaluated near the first Regge pole to determine the discovery potential of LHC. We study the inclusive dijet mass spectrum in the central rapidity region |y{sub jet}|<1.0 for dijet masses M{>=}2.5 TeV. We find that with an integrated luminosity of 100 fb{sup -1}, the 5{sigma} discovery reach can be as high as 4.7 TeV. Observations of resonant structures in pp{yields}direct{gamma}+jet can provide interesting corroboration for string physics up to 3.0 TeV. We also study the ratio of dijet mass spectra at small and large scattering angles. We show that with the first fb{sup -1} such a ratio can probe lowest-lying Regge states for masses {approx}2.5 TeV.

  15. Singlet Mott state simulating the bosonic Laughlin wave function

    NASA Astrophysics Data System (ADS)

    Lian, Biao; Zhang, Shoucheng

    2014-01-01

    We study properties of a class of spin-singlet Mott states for arbitrary spin S bosons on a lattice, with particle number per cite n =S/l+1, where l is a positive integer. We show that such a singlet Mott state can be mapped to a bosonic Laughlin wave function on a sphere with a finite number of particles at filling ν =1/2l. Spin, particle, and hole excitations in the Mott state are discussed, among which the hole excitation can be mapped to the quasihole of the bosonic Laughlin wave function. We show that this singlet Mott state can be realized in a cold-atom system on an optical lattice and can be identified using Bragg spectroscopy and Stern-Gerlach techniques. This class of singlet Mott states may be generalized to map to bosonic Laughlin states with filling ν =q/2l.

  16. Singlet Mott State Simulating the Bosonic Laughlin Wave Function

    NASA Astrophysics Data System (ADS)

    Lian, Biao; Zhang, Shou-Cheng

    2014-03-01

    We study properties of a class of spin singlet Mott states for arbitrary spin S bosons on a lattice, with particle number per cite n = S / l + 1 , where l is a positive integer. We show that such a singlet Mott state can be mapped to a bosonic Laughlin wave function on the sphere with a finite number of particles at filling ν = 1 / 2 l . Bosonic spinons, particle and hole excitations in the Mott state are discussed, among which the hole excitation can be mapped to the quasi-hole of the bosonic Laughlin wave function. We show that this singlet Mott state can be realized in a cold atom system on optical lattice, and can be identified using Bragg spectroscopy and Stern-Gerlach techniques. This class of singlet Mott states may be generalized to simulate bosonic Laughlin states with filling ν = q / 2 l .

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

    ERIC Educational Resources Information Center

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

    2014-01-01

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

  18. Aroylnitrenes with singlet ground states: photochemistry of acetyl-substituted aroyl and aryloxycarbonyl azides

    SciTech Connect

    Sigman, M.E.; Autrey, T.; Schuster, G.B.

    1988-06-22

    The photochemistry of 4-acetylbenzoyl azide (ABA), 4-acetyl-4'-biphenoyl azide (ADA), and 4-acetylphenoxycarbonyl azide (APA) shows unusual wavelength and structural effects. Irradiation of ABA or ADA into their ..pi..-..pi..* bands with deep-UV light leads to formation of 4-acetylbenzoylnitrene (ABN) and 4-acetyl-4'-biphenoylnitrene (ADN), respectively, in competition with photo-Curtius rearrangement to form isocyanates. Irradiation of these azides into their n-..pi..* bands with near-UV light gives only the aroylnitrenes. The triplet excited states of the azides were detected chemically and by transient spectroscopic techniques. Nitrogen loss following near-UV irradiation occurs exclusively from the excited triplet azides. However, the chemical properties of ABN and ADN are consistent only with reactions originating from their singlet states. An ESR spectrum is observed at 8 K for ((4-acetylphenoxy)carbonyl) nitrene (APN) but not for 4-acetylbenzoylnitrene (ABN) or 4-acetyl-4'-biphenylcarbonylnitrene (ADN). The chemical properties of APN in tert-butyl alcohol show that its triplet is no more than 5 kcal/mol below its lowest single state. In contrast, the chemical properties of ABN and ADN indicate that these nitrenes have singlet ground states.

  19. The {ital T}{sub 1}({ital n}{pi}{asterisk}){l_arrow}{ital S}{sub 0} laser induced phosphorescence excitation spectrum of acetaldehyde in a supersonic free jet: Torsion and wagging potentials in the lowest triplet state

    SciTech Connect

    Liu, H.; Lim, E.C.; Munoz-Caro, C.; Nino, A.; Judge, R.H.; Moule, D.C.

    1996-08-01

    The laser induced {ital T}{sub 1}({ital n}{pi}{asterisk}){l_arrow}{ital S}{sub 0} phosphorescence excitation spectrum of jet-cooled acetaldehyde has been observed for the first time with a rotating slit nozzle excitation system. The vibronic origins were fitted to a set of levels that were obtained from a Hamiltonian that employed flexible torsion-wagging large amplitude coordinates. The potential surface extracted from the fitting procedure yielded barriers to torsion and inversion of 609.68 and 869.02 cm{sup {minus}1}, respectively. Minima in the potential hypersurface at {theta}=61.7{degree} and {alpha}=42.2{degree} defined the equilibrium positions for the torsion and wagging coordinates. A comparison to the corresponding {ital S}{sub 1}-state parameters showed that the torsion barrier (in cm{sup {minus}1}) does not greatly change, {ital S}{sub 1}/{ital T}{sub 1}=710.8/609.7, whereas the barrier height for the wagging-inversion barrier increases dramatically, 574.4/869.0. {copyright} {ital 1996 American Institute of Physics.}

  20. Two-photon-induced singlet fission in rubrene single crystal.

    PubMed

    Ma, Lin; Galstyan, Gegham; Zhang, Keke; Kloc, Christian; Sun, Handong; Soci, Cesare; Michel-Beyerle, Maria E; Gurzadyan, Gagik G

    2013-05-14

    The two-photon-induced singlet fission was observed in rubrene single crystal and studied by use of femtosecond pump-probe spectroscopy. The location of two-photon excited states was obtained from the nondegenerate two-photon absorption (TPA) spectrum. Time evolution of the two-photon-induced transient absorption spectra reveals the direct singlet fission from the two-photon excited states. The TPA absorption coefficient of rubrene single crystal is 52 cm∕GW at 740 nm, as obtained from Z-scan measurements. Quantum chemical calculations based on time-dependent density functional theory support our experimental data. PMID:23676057

  1. Singlet Oxygen Generation by Laser Irradiation of Gold Nanoparticles

    PubMed Central

    2016-01-01

    The formation of singlet oxygen by irradiation of gold nanoparticles in their plasmon resonance band with continuous or pulsed laser light has been investigated. Citrate-stabilized nanoparticles were found to facilitate the photogeneration of singlet oxygen, albeit with low quantum yield. The reaction caused by pulsed laser irradiation makes use of the equilibrated hot electrons that can reach temperatures of several thousand degrees during the laser pulse. Although less efficient, continuous irradiation, which acts via the short-lived directly excited primary “hot” electrons only, can produce enough singlet oxygen for photodynamic cancer therapy and has significant advantages for practical applications. However, careful design of the nanoparticles is needed, since even a moderately thick capping layer can completely inhibit singlet oxygen formation. Moreover, the efficiency of the process also depends on the nanoparticle size. PMID:27239247

  2. Theoretical Study of Tautomerization Reactions for the Ground and First Excited Electronic States of Adenine

    NASA Technical Reports Server (NTRS)

    Salter, Latasha M.; Chaban, Galina M.; Kwak, Dochan (Technical Monitor)

    2002-01-01

    Geometrical structures and energetic properties for different tautomers of adenine are calculated in this study, using multi-configurational wave functions. Both the ground and the lowest singlet excited state potential energy surfaces are studied. Four tautomeric forms are considered, and their energetic order is found to be different on the ground and the excited state potential energy surfaces. Minimum energy reaction paths are obtained for hydrogen atom transfer (tautomerization) reactions in the ground and the lowest excited electronic states. It is found that the barrier heights and the shapes of the reaction paths are different for the ground and the excited electronic states, suggesting that the probability of such tautomerization reaction is higher on the excited state potential energy surface. This tautomerization process should become possible in the presence of water or other polar solvent molecules and should play an important role in the photochemistry of adenine.

  3. Excited State Dynamics of 7-AZAINDOLE Homodimer in Frozen Nitrogen Matrix

    NASA Astrophysics Data System (ADS)

    Mukherjee, Moitrayee; Bandyopadhyay, Biman; Karmakar, Shreetama; Chakraborty, Tapas

    2011-06-01

    In a fluid medium (liquid or gas), the doubly hydrogen bonded dimer of 7-azaindole (7AI) undergoes tautomerization via simultaneous exchange of two H-atoms/protons between the two moieties upon UV excitation to lowest excited singlet state. The excited dimer emits exclusively visible fluorescence from tautomeric configuration, and no UV fluorescence is detected from the locally excited state. We show here for the first time that this generic excited state dynamics of 7AI dimer is totally altered if the species is synthesized and confined in frozen nitrogen at 8 K. The dimer has been found to emit only from the locally excited state, and the photophysical channel leading to excited state tautomerization is completely blocked. The formation of the centrosymmetric dimer in nitrogen matrix is ensured by recording the FTIR spectrum of the dimer before initiating the photophysical measurements. The details of our findings and interpretation of the measured data will be presented in the talk.

  4. UV-vis spectra of singlet state cationic polycyclic aromatic hydrocarbons: Time-dependent density functional theory study

    SciTech Connect

    Dominikowska, Justyna Domagala, Malgorzata; Palusiak, Marcin

    2014-01-28

    A theoretical study of singlet state cations of polycyclic aromatic hydrocarbons is performed. Appropriate symmetry suitable for further calculations is chosen for each of the systems studied. The excitation states of such species are obtained by the time dependent density functional theory (TD-DFT) method. The computations are performed using both Pople and electronic response properties basis sets. The results obtained with the use of different basis sets are compared. The electronic transitions are described and the relationships for the lowest-lying transitions states of different species are found. The properties of in-plane and out-of-plane transitions are also delineated. The TD-DFT results are compared with the experimental data available.

  5. Nature of ground and electronic excited states of higher acenes.

    PubMed

    Yang, Yang; Davidson, Ernest R; Yang, Weitao

    2016-08-30

    Higher acenes have drawn much attention as promising organic semiconductors with versatile electronic properties. However, the nature of their ground state and electronic excited states is still not fully clear. Their unusual chemical reactivity and instability are the main obstacles for experimental studies, and the potentially prominent diradical character, which might require a multireference description in such large systems, hinders theoretical investigations. Here, we provide a detailed answer with the particle-particle random-phase approximation calculation. The (1)Ag ground states of acenes up to decacene are on the closed-shell side of the diradical continuum, whereas the ground state of undecacene and dodecacene tilts more to the open-shell side with a growing polyradical character. The ground state of all acenes has covalent nature with respect to both short and long axes. The lowest triplet state (3)B2u is always above the singlet ground state even though the energy gap could be vanishingly small in the polyacene limit. The bright singlet excited state (1)B2u is a zwitterionic state to the short axis. The excited (1)Ag state gradually switches from a double-excitation state to another zwitterionic state to the short axis, but always keeps its covalent nature to the long axis. An energy crossing between the (1)B2u and excited (1)Ag states happens between hexacene and heptacene. Further energetic consideration suggests that higher acenes are likely to undergo singlet fission with a low photovoltaic efficiency; however, the efficiency might be improved if a singlet fission into multiple triplets could be achieved. PMID:27528690

  6. Nature of ground and electronic excited states of higher acenes.

    PubMed

    Yang, Yang; Davidson, Ernest R; Yang, Weitao

    2016-08-30

    Higher acenes have drawn much attention as promising organic semiconductors with versatile electronic properties. However, the nature of their ground state and electronic excited states is still not fully clear. Their unusual chemical reactivity and instability are the main obstacles for experimental studies, and the potentially prominent diradical character, which might require a multireference description in such large systems, hinders theoretical investigations. Here, we provide a detailed answer with the particle-particle random-phase approximation calculation. The (1)Ag ground states of acenes up to decacene are on the closed-shell side of the diradical continuum, whereas the ground state of undecacene and dodecacene tilts more to the open-shell side with a growing polyradical character. The ground state of all acenes has covalent nature with respect to both short and long axes. The lowest triplet state (3)B2u is always above the singlet ground state even though the energy gap could be vanishingly small in the polyacene limit. The bright singlet excited state (1)B2u is a zwitterionic state to the short axis. The excited (1)Ag state gradually switches from a double-excitation state to another zwitterionic state to the short axis, but always keeps its covalent nature to the long axis. An energy crossing between the (1)B2u and excited (1)Ag states happens between hexacene and heptacene. Further energetic consideration suggests that higher acenes are likely to undergo singlet fission with a low photovoltaic efficiency; however, the efficiency might be improved if a singlet fission into multiple triplets could be achieved.

  7. Intramolecular singlet-singlet energy transfer in antenna-substituted azoalkanes.

    PubMed

    Pischel, Uwe; Huang, Fang; Nau, Werner M

    2004-03-01

    Two novel azoalkane bichromophores and related model compounds have been synthesised and photophysically characterised. Dimethylphenylsiloxy (DPSO) or dimethylnaphthylsiloxy (DNSO) serve as aromatic donor groups (antenna) and the azoalkane 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) as the acceptor. The UV spectral window of DBO (250-300 nm) allows selective excitation of the donor. Intramolecular singlet-singlet energy transfer to DBO is highly efficient and proceeds with quantum yields of 0.76 with DPSO and 0.99 with DNSO. The photophysical and spectral properties of the bichromophoric systems suggest that energy transfer occurs through diffusional approach of the donor and acceptor within a van der Waals contact at which the exchange mechanism is presumed to dominate. Furthermore, akin to the behaviour of electron-transfer systems in the Marcus inverted region, a rate of energy transfer 2.5 times slower was observed for the system with the more favourable energetics, i.e. singlet-singlet energy transfer from DPSO proceeded slower than from DNSO, although the process is more exergonic for DPSO (-142 kJ mol(-1) for DPSO versus-67 kJ mol(-1) for DNSO).

  8. Combined phosphorescence-holographic approach for singlet oxygen detection in biological media

    NASA Astrophysics Data System (ADS)

    Semenova, I. V.; Belashov, A. V.; Beltukova, D. M.; Petrov, N. V.; Vasyutinskii, O. S.

    2015-06-01

    The paper presents a novel combined approach aimed to detect and monitor singlet oxygen molecules in biological specimens by means of the simultaneous recording and monitoring of their deactivation dynamics in the two complementary channels: radiative and nonradiative. The approach involves both the direct registration of phosphorescence at the wavelength of about 1270 nm caused by radiative relaxation of excited singlet oxygen molecules and holographic recording of thermal disturbances in the medium produced by their nonradiative relaxation. The data provides a complete set of information on singlet oxygen location and dynamics in the medium. The approach was validated in the case study of photosensitized generation of singlet oxygen in onion cell structures.

  9. Gaugino mass without singlets

    SciTech Connect

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

    1998-12-21

    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.

  10. Singlet-triplet annihilation in single LHCII complexes.

    PubMed

    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. PMID:26156159

  11. Observation of Two Triplet-Pair Intermediates in Singlet Exciton Fission.

    PubMed

    Pensack, Ryan D; Ostroumov, Evgeny E; Tilley, Andrew J; Mazza, Samuel; Grieco, Christopher; Thorley, Karl J; Asbury, John B; Seferos, Dwight S; Anthony, John E; Scholes, Gregory D

    2016-07-01

    Singlet fission is an excitation multiplication process in molecular systems that can circumvent energy losses and significantly boost solar cell efficiencies; however, the nature of a critical intermediate that enables singlet fission and details of its evolution into multiple product excitations remain obscure. We resolve the initial sequence of events comprising the fission of a singlet exciton in solids of pentacene derivatives using femtosecond transient absorption spectroscopy. We propose a three-step model of singlet fission that includes two triplet-pair intermediates and show how transient spectroscopy can distinguish initially interacting triplet pairs from those that are spatially separated and noninteracting. We find that the interconversion of these two triplet-pair intermediates is limited by the rate of triplet transfer. These results clearly highlight the classical kinetic model of singlet fission and expose subtle details that promise to aid in resolving problems associated with triplet extraction. PMID:27281713

  12. Photochemistry of singlet oxygen sensor green.

    PubMed

    Kim, Sooyeon; Fujitsuka, Mamoru; Majima, Tetsuro

    2013-11-14

    To detect singlet oxygen ((1)O2), the commercially available fluorescent sensor named Singlet Oxygen Sensor Green (SOSG) has been the most widely used from material studies to medical applications, for example, photodynamic therapy. In light of the previous studies, SOSG is a dyad composed of fluorescein and anthracene moieties. In the present study, we carried out quantitative studies on photochemical dynamics of SOSG for the first time, such as the occurrence of intramolecular photoinduced electron transfer (PET), (1)O2 generation, and two-photon ionization. It was revealed that these relaxation pathways strongly depend on the irradiation conditions. The visible-light excitation (ex. 532 nm) of SOSG induced intramolecular PET as a major deactivation process (kPET = 9.7 × 10(11) s(-1)), resulting in fluorescence quenching. In addition, intersystem crossing occurred as a minor deactivation process that gave rise to (1)O2 generation via the bimolecular triplet-triplet energy transfer (kq = 1.2 × 10(9) M(-1) s(-1)). Meanwhile, ultraviolet-light excitation (355 nm) of SOSG caused the two-photon ionization to give a SOSG cation (Φion = 0.003 at 24 mJ cm(-2)), leading to SOSG decomposition to the final products. Our results clearly demonstrate the problems of SOSG, such as photodecomposition and (1)O2 generation. In fact, these are not special for SOSG but common drawbacks for most of the fluorescein-based sensors.

  13. Yields of excited states of solutes in irradiated benzene and cyclohexane

    SciTech Connect

    Choi, H.T.; Hirayama, F.; Lipsky, S.

    1984-09-13

    The yields of lowest excited singlet states of diphenyloxazole and p-terphenyl in benzene and of diphenyloxazole, p-terphenyl, and biphenyl in cyclohexane have been measured for excitation by using /sup 85/Kr ..beta.. particles. The dependence of the yield on solute concentration for benzene solutions is shown to be accurately represented by a Stern-Volmer function from 5 x 10/sup -4/ to 10/sup -2/ M and to extrapolate at infinite solute concentration to the yield of excited singlet states of neat liquid benzene. The presence of oxygen in the solution does not affect the extrapolation. The absolute efficiencies of energy transfer from irradiated benzene to the solutes are in good agreement with previous measurements made by using optical excitation below the ionization threshold. These results provide additional confirmation that the mechanism of formation of excited solute states in fast-electron-irradiated benzene does not significantly involve electron or hole capture by the solute. They also demonstrate that the inhomogeneity of energy deposition does not affect the ratio of probabilities of the decay of excited benzene by photon emission to its decay by nonradiative energy transfer to the solute. For cyclohexane solutions, it is confirmed that the yields of excited solute states are lower than in benzene solutions at comparable concentration, but larger than would be expected were the same nonionic mechanism to apply as it does in benzene. The consequences of these conclusions are discussed.

  14. Magnetic field dependence of singlet oxygen generation by nanoporous silicon

    NASA Astrophysics Data System (ADS)

    Amonkosolpan, Jamaree; Aliev, Gazi N.; Wolverson, Daniel; Snow, Paul A.; Davies, James John

    2014-07-01

    Energy transfer from photoexcited excitons localized in silicon nanoparticles to adsorbed oxygen molecules excites them to the reactive singlet spin state. This process has been studied experimentally as a function of nanoparticle size and applied external magnetic field as a test of the accepted understanding of this process in terms of the exchange coupling between the nano-Si exciton and the adsorbed O2 molecules.

  15. Competition between polaron pair formation and singlet fission observed in amorphous rubrene films

    NASA Astrophysics Data System (ADS)

    Jankus, Vygintas; Snedden, Edward W.; Bright, Daniel W.; Arac, Erhan; Dai, DeChang; Monkman, Andrew P.

    2013-06-01

    In this paper, we investigate excited state dynamics in amorphous rubrene vacuum sublimed films. We report the direct observation of singlet fission in amorphous rubrene films. We have determined the fission rate to be >2.5×1012 s-1. Simultaneously, we observe strong polaron pair absorption and propose that polaron pair formation could be competing with singlet fission. Another possible conclusion from our experiments could be that two triplets from singlet fission might arise via polaron pairs. In either case, polaron pairs play an important role in singlet fission in an amorphous rubrene film. We also observe that triplets created by singlet fission fuse to regenerate a singlet, giving delayed fluorescence (DF) scaling linearly with initial laser energy (i.e., one singlet gives two triplets and two triplets give back one singlet). This is a strong evidence of S1n→2T1. We did not observe substantial temperature dependence of DF decay curve shape, indicating that triplet migration in amorphous rubrene films is not hopping limited and that triplets undergo fusion before their migration.

  16. Singlet Oxygen at the Laundromat

    NASA Astrophysics Data System (ADS)

    Keeports, David

    1995-09-01

    Singlet molecular oxygen is an interesting molecule both visually and theoretically, since its red chemiluminescence can be analyzed by the application of simple molecular orbital theory. It can be produced from the reaction of hydrogen peroxide from either chlorine gas or hypochlorite ion from household bleach. Here we demostrate how to produce it using simple laundry cleansers.

  17. New ab initio adiabatic potential energy surfaces and bound state calculations for the singlet ground X˜ 1A1 and excited C˜ 1B2(21A') states of SO2

    NASA Astrophysics Data System (ADS)

    Kłos, Jacek; Alexander, Millard H.; Kumar, Praveen; Poirier, Bill; Jiang, Bin; Guo, Hua

    2016-05-01

    We report new and more accurate adiabatic potential energy surfaces (PESs) for the ground X˜ 1A1 and electronically excited C˜ 1B2(21A') states of the SO2 molecule. Ab initio points are calculated using the explicitly correlated internally contracted multi-reference configuration interaction (icMRCI-F12) method. A second less accurate PES for the ground X ˜ state is also calculated using an explicitly correlated single-reference coupled-cluster method with single, double, and non-iterative triple excitations [CCSD(T)-F12]. With these new three-dimensional PESs, we determine energies of the vibrational bound states and compare these values to existing literature data and experiment.

  18. Nonadiabatic effects in the photodissociation of vibrationally excited HNCO: The branching between singlet (athinsp{sup 1}{Delta}) and triplet (Xthinsp{sup 3}{Sigma}{sup {minus}}) NH

    SciTech Connect

    Berghout, H.L.; Brown, S.S.; Delgado, R.; Fleming Crim, F.

    1998-08-01

    Initial vibrational excitation of a state containing three quanta of N{endash}H stretch (3{nu}{sub 1}) decreases the fractional photolysis yield of NH (athinsp{sup 1}{Delta}) relative to NH (Xthinsp{sup 3}{Sigma}{sup {minus}}) by a factor of approximately two compared to the isoenergetic photodissociation of a 300 K thermal sample of HNCO. At a total energy of 43thinsp480thinspcm{sup {minus}1}, NH (athinsp{sup 1}{Delta}) accounts for 24{percent} of the total NH yield in the direct photolysis but only 10{percent} in the photodissociation of 3{nu}{sub 1}. At 44thinsp440thinspcm{sup {minus}1}, the NH (athinsp{sup 1}{Delta}) yields are 65{percent} and 32{percent} in the single photon and two-step photodissociations, respectively. The variation in branching ratio may arise from dynamical behavior that is closely related to the preferential production of NCO in the photolysis of vibrationally excited HNCO. The initial vibrational excitation has no influence on the rotational and vibrational distributions of NH (Xthinsp{sup 3}{Sigma}{sup {minus}}), but it significantly increases the amount of energy in rotation of NH (athinsp{sup 1}{Delta}). These results, along with several recent experimental and theoretical studies, suggest the participation of at least three different potential energy surfaces in the photodissociation of isocyanic acid. {copyright} {ital 1998 American Institute of Physics.}

  19. Photoexcited singlet and triplet states of a UV absorber ethylhexyl methoxycrylene.

    PubMed

    Kikuchi, Azusa; Hata, Yuki; Kumasaka, Ryo; Nanbu, Yuichi; Yagi, Mikio

    2013-01-01

    The excited states of UV absorber, ethylhexyl methoxycrylene (EHMCR) have been studied through measurements of UV absorption, fluorescence, phosphorescence and electron paramagnetic resonance (EPR) spectra in ethanol. The energy levels of the lowest excited singlet (S1) and triplet (T1) states of EHMCR were determined. The energy levels of the S1 and T1 states of EHMCR are much lower than those of photolabile 4-tert-butyl-4'-methoxydibenzoylmethane. The energy levels of the S1 and T1 states of EHMCR are lower than those of octyl methoxycinnamate. The weak phosphorescence and EPR B(min) signals were observed and the lifetime was estimated to be 93 ms. These facts suggest that the significant proportion of the S1 molecules undergoes intersystem crossing to the T1 state, and the deactivation process from the T1 state is predominantly radiationless. The photostability of EHMCR arises from the (3)ππ* character in the T1 state. The zero-field splitting (ZFS) parameter in the T1 state is D** = 0.113 cm(-1). PMID:23136952

  20. The quantum coherent mechanism for singlet fission: experiment and theory.

    PubMed

    Chan, Wai-Lun; Berkelbach, Timothy C; Provorse, Makenzie R; Monahan, Nicholas R; Tritsch, John R; Hybertsen, Mark S; Reichman, David R; Gao, Jiali; Zhu, X-Y

    2013-06-18

    The absorption of one photon by a semiconductor material usually creates one electron-hole pair. However, this general rule breaks down in a few organic semiconductors, such as pentacene and tetracene, where one photon absorption may result in two electron-hole pairs. This process, where a singlet exciton transforms to two triplet excitons, can have quantum yields as high as 200%. Singlet fission may be useful to solar cell technologies to increase the power conversion efficiency beyond the so-called Shockley-Queisser limit. Through time-resolved two-photon photoemission (TR-2PPE) spectroscopy in crystalline pentacene and tetracene, our lab has recently provided the first spectroscopic signatures in singlet fission of a critical intermediate known as the multiexciton state (also called a correlated triplet pair). More importantly, we found that population of the multiexciton state rises at the same time as the singlet state on the ultrafast time scale upon photoexcitation. This observation does not fit with the traditional view of singlet fission involving the incoherent conversion of a singlet to a triplet pair. However, it provides an experimental foundation for a quantum coherent mechanism in which the electronic coupling creates a quantum superposition of the singlet and the multiexciton state immediately after optical excitation. In this Account, we review key experimental findings from TR-2PPE experiments and present a theoretical analysis of the quantum coherent mechanism based on electronic structural and density matrix calculations for crystalline tetracene lattices. Using multistate density functional theory, we find that the direct electronic coupling between singlet and multiexciton states is too weak to explain the experimental observation. Instead, indirect coupling via charge transfer intermediate states is two orders of magnitude stronger, and dominates the dynamics for ultrafast multiexciton formation. Density matrix calculation for the crystalline

  1. The quantum coherent mechanism for singlet fission: experiment and theory.

    PubMed

    Chan, Wai-Lun; Berkelbach, Timothy C; Provorse, Makenzie R; Monahan, Nicholas R; Tritsch, John R; Hybertsen, Mark S; Reichman, David R; Gao, Jiali; Zhu, X-Y

    2013-06-18

    The absorption of one photon by a semiconductor material usually creates one electron-hole pair. However, this general rule breaks down in a few organic semiconductors, such as pentacene and tetracene, where one photon absorption may result in two electron-hole pairs. This process, where a singlet exciton transforms to two triplet excitons, can have quantum yields as high as 200%. Singlet fission may be useful to solar cell technologies to increase the power conversion efficiency beyond the so-called Shockley-Queisser limit. Through time-resolved two-photon photoemission (TR-2PPE) spectroscopy in crystalline pentacene and tetracene, our lab has recently provided the first spectroscopic signatures in singlet fission of a critical intermediate known as the multiexciton state (also called a correlated triplet pair). More importantly, we found that population of the multiexciton state rises at the same time as the singlet state on the ultrafast time scale upon photoexcitation. This observation does not fit with the traditional view of singlet fission involving the incoherent conversion of a singlet to a triplet pair. However, it provides an experimental foundation for a quantum coherent mechanism in which the electronic coupling creates a quantum superposition of the singlet and the multiexciton state immediately after optical excitation. In this Account, we review key experimental findings from TR-2PPE experiments and present a theoretical analysis of the quantum coherent mechanism based on electronic structural and density matrix calculations for crystalline tetracene lattices. Using multistate density functional theory, we find that the direct electronic coupling between singlet and multiexciton states is too weak to explain the experimental observation. Instead, indirect coupling via charge transfer intermediate states is two orders of magnitude stronger, and dominates the dynamics for ultrafast multiexciton formation. Density matrix calculation for the crystalline

  2. Effect of substitution on the ultrafast deactivation of the excited state of benzo[b]thiophene-arylamines.

    PubMed

    Pina, J; Queiroz, M-J R P; Seixas de Melo, J

    2016-08-01

    A complete and systematic study of the spectroscopic and photophysical properties of five novel diarylamines in the benzo[b]thiophene series (oligoanilines) was performed in solution at room (293 K) and low (77 K) temperature. The title compounds resulting from the link between one aniline unit with a benzo[b]thiophene unit (with two different methyl and methoxy substitution) were characterized using steady-state absorption, fluorescence and phosphorescence spectroscopy, as well as femto- to nano-second time resolved spectroscopies. The study involved the determination of the absorption, emission and triplet-triplet absorption together with all relevant quantum yields (fluorescence, phosphorescence, intersystem crossing, internal conversion and singlet oxygen yields), excited state lifetimes and the overall set of deactivation rate constants (kF, kIC and kISC). This study was further complemented with theoretical calculations, namely with the determination of the optimized ground-state molecular geometries for the diarylamines together with the prediction of the lowest vertical one-electron excitation energy and the relevant molecular orbital contours using DFT calculations. The DFT results were found to corroborate the observed charge-transfer character of the singlet excited state. The experimental results showed that the radiationless decay processes (internal conversion and intersystem-crossing) constitute the main excited state deactivation pathways and that substitution with methyl and methoxy groups induces significant changes in the spectroscopic and photophysical behaviour of these compounds. This was also corroborated by the femtosecond transient absorption study, where it was found that the ultrafast dynamics of the diarylamines was best described by a sequential model featuring fast solvent relaxation followed by conformational relaxation to a more planar excited state, from where singlet excited state deactivation occurs through internal conversion and

  3. Effect of substitution on the ultrafast deactivation of the excited state of benzo[b]thiophene-arylamines.

    PubMed

    Pina, J; Queiroz, M-J R P; Seixas de Melo, J

    2016-08-01

    A complete and systematic study of the spectroscopic and photophysical properties of five novel diarylamines in the benzo[b]thiophene series (oligoanilines) was performed in solution at room (293 K) and low (77 K) temperature. The title compounds resulting from the link between one aniline unit with a benzo[b]thiophene unit (with two different methyl and methoxy substitution) were characterized using steady-state absorption, fluorescence and phosphorescence spectroscopy, as well as femto- to nano-second time resolved spectroscopies. The study involved the determination of the absorption, emission and triplet-triplet absorption together with all relevant quantum yields (fluorescence, phosphorescence, intersystem crossing, internal conversion and singlet oxygen yields), excited state lifetimes and the overall set of deactivation rate constants (kF, kIC and kISC). This study was further complemented with theoretical calculations, namely with the determination of the optimized ground-state molecular geometries for the diarylamines together with the prediction of the lowest vertical one-electron excitation energy and the relevant molecular orbital contours using DFT calculations. The DFT results were found to corroborate the observed charge-transfer character of the singlet excited state. The experimental results showed that the radiationless decay processes (internal conversion and intersystem-crossing) constitute the main excited state deactivation pathways and that substitution with methyl and methoxy groups induces significant changes in the spectroscopic and photophysical behaviour of these compounds. This was also corroborated by the femtosecond transient absorption study, where it was found that the ultrafast dynamics of the diarylamines was best described by a sequential model featuring fast solvent relaxation followed by conformational relaxation to a more planar excited state, from where singlet excited state deactivation occurs through internal conversion and

  4. Singlet Fission via an Excimer-Like Intermediate in 3,6-Bis(thiophen-2-yl)diketopyrrolopyrrole Derivatives.

    PubMed

    Mauck, Catherine M; Hartnett, Patrick E; Margulies, Eric A; Ma, Lin; Miller, Claire E; Schatz, George C; Marks, Tobin J; Wasielewski, Michael R

    2016-09-14

    Singlet fission (SF) in polycrystalline thin films of four 3,6-bis(thiophen-2-yl)diketopyrrolopyrrole (TDPP) chromophores with methyl (Me), n-hexyl (C6), triethylene glycol (TEG), and 2-ethylhexyl (EH) substituents at the 2,5-positions is found to involve an intermediate excimer-like state. The four different substituents yield four distinct intermolecular packing geometries, resulting in variable intermolecular charge transfer (CT) interactions in the solid. SF from the excimer state of Me, C6, TEG, and EH takes place in τSF = 22, 336, 195, and 1200 ps, respectively, to give triplet yields of 200%, 110%, 110%, and 70%, respectively. The transient spectra of the excimer-like state and its energetic proximity to the lowest excited singlet state in these derivatives suggests that this state may be the multiexciton (1)(T1T1) state that precedes formation of the uncorrelated triplet excitons. The excimer decay rates correlate well with the SF efficiencies and the degree of intermolecular donor-acceptor interactions resulting from π-stacking of the thiophene donor of one molecule with the DPP core acceptor in another molecule as observed in the crystal structures. Such interactions are found to also increase with the SF coupling energies, as calculated for each derivative. These structural and spectroscopic studies afford a better understanding of the electronic interactions that enhance SF in chromophores having strong intra- and intermolecular CT character. PMID:27547986

  5. Singlet Fission via an Excimer-Like Intermediate in 3,6-Bis(thiophen-2-yl)diketopyrrolopyrrole Derivatives.

    PubMed

    Mauck, Catherine M; Hartnett, Patrick E; Margulies, Eric A; Ma, Lin; Miller, Claire E; Schatz, George C; Marks, Tobin J; Wasielewski, Michael R

    2016-09-14

    Singlet fission (SF) in polycrystalline thin films of four 3,6-bis(thiophen-2-yl)diketopyrrolopyrrole (TDPP) chromophores with methyl (Me), n-hexyl (C6), triethylene glycol (TEG), and 2-ethylhexyl (EH) substituents at the 2,5-positions is found to involve an intermediate excimer-like state. The four different substituents yield four distinct intermolecular packing geometries, resulting in variable intermolecular charge transfer (CT) interactions in the solid. SF from the excimer state of Me, C6, TEG, and EH takes place in τSF = 22, 336, 195, and 1200 ps, respectively, to give triplet yields of 200%, 110%, 110%, and 70%, respectively. The transient spectra of the excimer-like state and its energetic proximity to the lowest excited singlet state in these derivatives suggests that this state may be the multiexciton (1)(T1T1) state that precedes formation of the uncorrelated triplet excitons. The excimer decay rates correlate well with the SF efficiencies and the degree of intermolecular donor-acceptor interactions resulting from π-stacking of the thiophene donor of one molecule with the DPP core acceptor in another molecule as observed in the crystal structures. Such interactions are found to also increase with the SF coupling energies, as calculated for each derivative. These structural and spectroscopic studies afford a better understanding of the electronic interactions that enhance SF in chromophores having strong intra- and intermolecular CT character.

  6. The excited state antiaromatic benzene ring: a molecular Mr Hyde?

    PubMed

    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. PMID:25960203

  7. The excited state antiaromatic benzene ring: a molecular Mr Hyde?

    PubMed

    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.

  8. Singlet Oxygen Reactions with Flavonoids. A Theoretical – Experimental Study

    PubMed Central

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

    2012-01-01

    Detection of singlet oxygen emission, λmax = 1270 nm, following laser excitation and steady-state methods were employed to measure the total reaction rate constant, kT, and the reactive reaction rate constant, kr, for the reaction between singlet oxygen and several flavonoids. Values of kT determined in deuterated water, ranging from 2.4×107 M−1s−1 to 13.4×107 M−1s−1, for rutin and morin, respectively, and the values measured for kr, ranging from 2.8×105 M−1s−1 to 65.7×105 M−1s−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. PMID:22802966

  9. Collective aspects of singlet fission in molecular crystals

    SciTech Connect

    Teichen, Paul E.; Eaves, Joel D.

    2015-07-28

    We present a model to describe collective features of singlet fission in molecular crystals and analyze it using many-body theory. The model we develop allows excitonic states to delocalize over several chromophores which is consistent with the character of the excited states in many molecular crystals, such as the acenes, where singlet fission occurs. As singlet states become more delocalized and triplet states more localized, the rate of singlet fission increases. We also determine the conditions under which the two triplets resulting from fission are correlated. Using the Bethe Ansatz and an entanglement measure for indistinguishable bipartite systems, we calculate the triplet-triplet entanglement as a function of the biexciton interaction strength. The biexciton interaction can produce bound biexciton states and provides a source of entanglement between the two triplets even when the triplets are spatially well separated. Significant entanglement between the triplet pair occurs well below the threshold for bound pair formation. Our results paint a dynamical picture that helps to explain why fission has been observed to be more efficient in molecular crystals than in their covalent dimer analogues and have consequences for photovoltaic efficiency models that assume that the two triplets can be extracted independently.

  10. Photogeneration and recombination processes of neutral and charged excitations in films of a ladder-type poly(para-phenylene)

    NASA Astrophysics Data System (ADS)

    Wohlgenannt, M.; Graupner, W.; Leising, G.; Vardeny, Z. V.

    1999-08-01

    We introduce a version of the cw photomodulation technique, measured far from the steady state, for obtaining the quantum efficiency, η, of long-lived photoexcitations in π-conjugated polymers. We apply this technique to films of a ladder-type poly(para-phenylene) [mLPPP] for studying the photogeneration action spectra, η(E), and recombination kinetics of photogenerated neutral and charged excitations such as singlet and triplet excitons and charged polarons. Whereas the η(E) spectrum for singlet excitons shows a step function increase at a photon energy, E, close to the optical gap (~=2.6 eV), both triplet and polaron η(E) spectra show, in addition, a monotonous rise at higher E. The rise for triplets is explained by singlet exciton fission into triplet pairs, and from a model fit we get the triplet exciton energy (~=1.6 eV). For polarons this rise is modeled by an electron intersegment tunneling process. The electroabsorption spectrum is also measured and analyzed in terms of Stark shift of the lowest lying exciton, 1Bu, and enhanced oscillator strength of the important mAg exciton. A consistent picture for the lowest excited state energy levels and optical transitions in the neutral (singlet and triplet) and charged manifolds is presented. From both the exciton binding energy of ~=0.6 eV and the singlet-triplet energy splitting of ~=1 eV, we conclude that the e-e interaction in mLPPP is relatively strong. Our results are in good agreement with recent ab initio band structure calculations for several π-conjugated polymers.

  11. Interaction of triplet sensitizers with chlorophyll: Formation of singlet chlorophyll

    SciTech Connect

    Bohne, C.; Scaiano, J.C. )

    1989-03-29

    The interaction of several triplet sensitizers with chlorophyll a (Chla) has been examined using laser techniques. For the carbonyl sensitizers (with triplet energies > 53 kcal/mol) it was possible to measure the quenching rate constants; these were systematically {>=} 10{sup 10} M{sup {minus}1} s{sup {minus}1}. In the cases of acetone, benzophenone, and p-methoxyacetophenone the quenching process leads to the formation of the fluorescent singlet state of Chla. For benzophenone (k{sub q} = 2.4 {times} 10{sup 10} M{sup {minus}1} s{sup {minus}1}) approximately 3% of the quenching events lead to the formation of excited Chla. Several sensitizers (decafluorobenzophenone, benzil, and fluorenone) do not induce Chla fluorescence (or do it very inefficiently) in spite of having triplet energies above the S{sub 1} level of Chla. In light of their results the most probable mechanism involves energy transfer from the triplet sensitizer to an upper triple state of Chla ({sup 3}Chla**) which can undergo reverse intersystem crossing to the singlet manifold of Chla and thus induce fluorescence. The inefficient sensitizers are those where electron transfer between the excited singlet of Chla or {sup 3}Chla** and ground-state sensitizers is energetically favorable, leading to rapid in-cage quenching of the initially formed excited states of Chla. Formation of radical-ion pair between the triplet sensitizer and Chla followed by the generation of singlet Chla in the recombination of the radical ions could not be completely discarded.

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

    NASA Astrophysics Data System (ADS)

    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).

  13. Merging Active-Space and Renormalized Coupled-Cluster Methods via the CC(P;Q) Formalism, with Benchmark Calculations for Singlet-Triplet Gaps in Biradical Systems.

    PubMed

    Shen, Jun; Piecuch, Piotr

    2012-12-11

    We have recently developed a flexible form of the method of moments of coupled-cluster (CC) equations and the CC(P;Q) hierarchy, which enable one to correct the CC and equation-of-motion CC energies obtained with unconventional truncations in the cluster and excitation operators [Shen, J.; Piecuch, P. Chem. Phys.2012, 401, 180; J. Chem. Phys.2012, 136, 144104]. One of the CC(P;Q) methods is a novel hybrid scheme, abbreviated as CC(t;3), in which the results of CC calculations with singles, doubles, and active-space triples, termed CCSDt, are corrected for the triple excitations missing in CCSDt using the expressions that are reminiscent of the completely renormalized (CR) CC approach known as CR-CC(2,3). We demonstrate that the total electronic energies of the lowest singlet and triplet states, and the singlet-triplet gaps in biradical systems, including methylene, (HFH)(-), and trimethylenemethane, resulting from the CC(t;3) calculations agree with those obtained with the full CC approach with singles, doubles, and triples to within fractions of a millihartree, improving the results of the noniterative triples CCSD(T), CCSD(2)T, and CR-CC(2,3) and hybrid CCSD(T)-h calculations, and competing with the best multireference CC data.

  14. External quantum efficiency above 100% in a singlet-exciton-fission-based organic photovoltaic cell.

    PubMed

    Congreve, Daniel N; Lee, Jiye; Thompson, Nicholas J; Hontz, Eric; Yost, Shane R; Reusswig, Philip D; Bahlke, Matthias E; Reineke, Sebastian; Van Voorhis, Troy; Baldo, Marc A

    2013-04-19

    Singlet exciton fission transforms a molecular singlet excited state into two triplet states, each with half the energy of the original singlet. In solar cells, it could potentially double the photocurrent from high-energy photons. We demonstrate organic solar cells that exploit singlet exciton fission in pentacene to generate more than one electron per incident photon in a portion of the visible spectrum. Using a fullerene acceptor, a poly(3-hexylthiophene) exciton confinement layer, and a conventional optical trapping scheme, we show a peak external quantum efficiency of (109 ± 1)% at wavelength λ = 670 nanometers for a 15-nanometer-thick pentacene film. The corresponding internal quantum efficiency is (160 ± 10)%. Analysis of the magnetic field effect on photocurrent suggests that the triplet yield approaches 200% for pentacene films thicker than 5 nanometers. PMID:23599489

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

    NASA Astrophysics Data System (ADS)

    Estienne, Benoit; Bernevig, B. Andrei

    2012-04-01

    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.

  16. Short-range photoassociation from the inner wall of the lowest triplet potential of 85Rb2

    NASA Astrophysics Data System (ADS)

    Carollo, R. A.; Carini, J. L.; Eyler, E. E.; Gould, P. L.; Stwalley, W. C.

    2016-10-01

    Ultracold photoassociation is typically performed at large internuclear separations, where the scattering wavefunction amplitude is large and Franck–Condon overlap is maximized. Recently, work by this group and others on alkali-metal diatomics has shown that photoassociation can efficiently form molecules at short internuclear distance in both homonuclear and heteronuclear dimers. We propose that this short-range photoassociation is due to excitation near the wavefunction amplitude maximum at the inner wall of the lowest triplet potential. We show that Franck–Condon factors (FCFs) from the highest-energy bound state can almost precisely reproduce FCFs from a low-energy scattering state, and that both calculations match experimental data from the near-zero positive-energy scattering state with reasonable accuracy. We also show that the corresponding photoassociation from the inner wall of the ground-state singlet potential at much shorter internuclear distance is weaker and undetectable under our current experimental conditions. We predict from FCFs that the strongest of these weaker short-range photoassociation transitions are one order of magnitude below our current sensitivity.

  17. Excited States and photodebromination of selected polybrominated diphenyl ethers: computational and quantitative structure--property relationship studies.

    PubMed

    Luo, Jin; Hu, Jiwei; Wei, Xionghui; Li, Lingyun; Huang, Xianfei

    2015-01-01

    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. PMID:25569092

  18. Intramolecular triplet energy transfer via higher triplet excited state during stepwise two-color two-laser irradiation.

    PubMed

    Oseki, Yosuke; Fujitsuka, Mamoru; Sakamoto, Masanori; Majima, Tetsuro

    2007-10-01

    We studied the energy transfer processes in the molecular array consisting of pyrene (Py), biphenyl (Ph2), and bisphthalimidethiophene (ImT), (Py-Ph2)2-ImT, during two-color two-laser flash photolysis (2-LFP). The first laser irradiation predominantly generates ImT in the lowest triplet excited state (ImT(T1)) because of the efficient singlet energy transfer from Py in the lowest singlet excited state to ImT and, then, intersystem crossing of ImT. ImT(T1) was excited to the higher triplet excited state (Tn) with the second laser irradiation. Then, the triplet energy was rapidly transferred to Py via a two-step triplet energy transfer (TET) process through Ph2. The efficient generation of Py(T1) was suggested from the nanosecond-picosecond 2-LFP. The back-TET from Py(T1) to ImT was observed for several tens of microseconds after the second laser irradiation. The estimated intramolecular TET rate from Py(T1) to ImT was as slow as 3.1 x 104 s-1. Hence, long-lived Py(T1) was selectively and efficiently produced during the 2-LFP.

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

    PubMed Central

    Luo, Jin; Hu, Jiwei; Wei, Xionghui; Li, Lingyun; Huang, Xianfei

    2015-01-01

    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. PMID:25569092

  20. Standard Model with a real singlet scalar and inflation

    SciTech Connect

    Enqvist, Kari; Nurmi, Sami; Tenkanen, Tommi; Tuominen, Kimmo E-mail: sami.nurmi@helsinki.fi E-mail: kimmo.i.tuominen@helsinki.fi

    2014-08-01

    We study the post-inflationary dynamics of the Standard Model Higgs and a real singlet scalar s, coupled together through a renormalizable coupling λ{sub sh}h{sup 2}s{sup 2}, in a Z{sub 2} symmetric model that may explain the observed dark matter abundance and/or the origin of baryon asymmetry. The initial values for the Higgs and s condensates are given by inflationary fluctuations, and we follow their dissipation and relaxation to the low energy vacua. We find that both the lowest order perturbative and the non-perturbative decays are blocked by thermal effects and large background fields and that the condensates decay by two-loop thermal effects. Assuming instant reheating at T=10{sup 16} GeV, the characteristic temperature for the Higgs condensate thermalization is found to be T{sub h} ∼ 10{sup 14} GeV, whereas s thermalizes typically around T{sub s} ∼ 10{sup 6} GeV. By that time, the amplitude of the singlet is driven very close to the vacuum value by the expansion of the universe, unless the portal coupling takes a value λ{sub sh}∼< 10{sup -7} and the singlet s never thermalizes. With these values of the coupling, it is possible to slowly produce a sizeable fraction of the observed dark matter abundance via singlet condensate fragmentation and thermal Higgs scattering. Physics also below the electroweak scale can therefore be affected by the non-vacuum initial conditions generated by inflation.

  1. Intensity dependence of the excited state lifetimes and triplet conversion yield in the Fenna-Matthews-Olson antenna protein.

    PubMed

    Orf, Gregory S; Niedzwiedzki, Dariusz M; Blankenship, Robert E

    2014-02-27

    The Fenna-Matthews-Olson (FMO) protein is a soluble light-harvesting, bacteriochlorophyll a (BChl a) containing antenna complex found in green sulfur bacteria. We have measured time-resolved fluorescence and transient absorption at variable laser intensities at 298 and 77 K using FMO protein from Chlorobaculum tepidum prepared in both oxidizing and reducing environments. Fitting of the spectroscopic data shows that high laser intensities (i.e., above 10(13) photons × cm(-2) delivered per laser pulse) distort the intrinsic decay processes in this complex. At high laser intensities, both oxidized and reduced FMO samples behave similarly, exhibiting high levels of singlet-singlet annihilation. At lower laser intensities, the reduced protein mainly displays a singlet excited state lifetime of 2 ns, although upon oxidation, a 60 ps lifetime dominates. We also demonstrate that the apparent quantum yield of singlet-triplet intersystem crossing in the reduced FMO complex is ∼11% in the most favorable low laser intensities, with this yield decreasing and the probability of singlet-singlet annihilation yield increasing as laser intensity increases. After correcting for stimulated emission effects in the experiments, the actual maximum triplet yield is calculated to be ∼27%. Experiments at 77 K demonstrate that BChl a triplet states in FMO are localized on pigments no. 4 or 3, the lowest energy pigments in the complex. This study allows for a discussion of how BChl triplets form and evolve on the picosecond-to-nanosecond time scale, as well as whether triplet conversion is a physiologically relevant process.

  2. Singlet-paired coupled cluster theory for open shells.

    PubMed

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

    2016-06-28

    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. PMID:27369507

  3. Diphotons from electroweak triplet-singlet mixing

    NASA Astrophysics Data System (ADS)

    Howe, Kiel; Knapen, Simon; Robinson, Dean J.

    2016-08-01

    The neutral component of a real pseudoscalar electroweak (EW) triplet can produce a diphoton excess at 750 GeV, if it is somewhat mixed with an EW singlet pseudoscalar. This triplet-singlet mixing allows for greater freedom in the diboson branching ratios than the singlet-only case, but it is still possible to probe the parameter space extensively with 300 fb-1 . The charged component of the triplet is pair produced at the LHC, which results in a striking signal in the form of a pair of W γ resonances with an irreducible rate of 0.27 fb. Other signatures include multiboson final states from cascade decays of the triplet-singlet neutral states. A large class of composite models feature both EW singlet and triplet pseudo-Nambu-Goldstone bosons in their spectrum, with the diboson couplings generated by axial anomalies.

  4. First-Principles Quantum Dynamics of Singlet Fission: Coherent versus Thermally Activated Mechanisms Governed by Molecular π Stacking.

    PubMed

    Tamura, Hiroyuki; Huix-Rotllant, Miquel; Burghardt, Irene; Olivier, Yoann; Beljonne, David

    2015-09-01

    Singlet excitons in π-stacked molecular crystals can split into two triplet excitons in a process called singlet fission that opens a route to carrier multiplication in photovoltaics. To resolve controversies about the mechanism of singlet fission, we have developed a first principles nonadiabatic quantum dynamical model that reveals the critical role of molecular stacking symmetry and provides a unified picture of coherent versus thermally activated singlet fission mechanisms in different acenes. The slip-stacked equilibrium packing structure of pentacene derivatives is found to enhance ultrafast singlet fission mediated by a coherent superexchange mechanism via higher-lying charge transfer states. By contrast, the electronic couplings for singlet fission strictly vanish at the C(2h) symmetric equilibrium π stacking of rubrene. In this case, singlet fission is driven by excitations of symmetry-breaking intermolecular vibrations, rationalizing the experimentally observed temperature dependence. Design rules for optimal singlet fission materials therefore need to account for the interplay of molecular π-stacking symmetry and phonon-induced coherent or thermally activated mechanisms. PMID:26382701

  5. First-Principles Quantum Dynamics of Singlet Fission: Coherent versus Thermally Activated Mechanisms Governed by Molecular π Stacking

    NASA Astrophysics Data System (ADS)

    Tamura, Hiroyuki; Huix-Rotllant, Miquel; Burghardt, Irene; Olivier, Yoann; Beljonne, David

    2015-09-01

    Singlet excitons in π -stacked molecular crystals can split into two triplet excitons in a process called singlet fission that opens a route to carrier multiplication in photovoltaics. To resolve controversies about the mechanism of singlet fission, we have developed a first principles nonadiabatic quantum dynamical model that reveals the critical role of molecular stacking symmetry and provides a unified picture of coherent versus thermally activated singlet fission mechanisms in different acenes. The slip-stacked equilibrium packing structure of pentacene derivatives is found to enhance ultrafast singlet fission mediated by a coherent superexchange mechanism via higher-lying charge transfer states. By contrast, the electronic couplings for singlet fission strictly vanish at the C2 h symmetric equilibrium π stacking of rubrene. In this case, singlet fission is driven by excitations of symmetry-breaking intermolecular vibrations, rationalizing the experimentally observed temperature dependence. Design rules for optimal singlet fission materials therefore need to account for the interplay of molecular π -stacking symmetry and phonon-induced coherent or thermally activated mechanisms.

  6. Singlet Fission in a Covalently Linked Cofacial Alkynyltetracene Dimer.

    PubMed

    Korovina, Nadezhda V; Das, Saptaparna; Nett, Zachary; Feng, Xintian; Joy, Jimmy; Haiges, Ralf; Krylov, Anna I; Bradforth, Stephen E; Thompson, Mark E

    2016-01-20

    Singlet fission is a process in which a singlet exciton converts into two triplet excitons. To investigate this phenomenon, we synthesized two covalently linked 5-ethynyl-tetracene (ET) dimers with differing degrees of intertetracene overlap: BET-X, with large, cofacial overlap of tetracene π-orbitals, and BET-B, with twisted arrangement between tetracenes exhibits less overlap between the tetracene π-orbitals. The two compounds were crystallographically characterized and studied by absorption and emission spectroscopy in solution, in PMMA and neat thin films. The results show that singlet fission occurs within 1 ps in an amorphous thin film of BET-B with high efficiency (triplet yield: 154%). In solution and the PMMA matrix the S1 of BET-B relaxes to a correlated triplet pair (1)(T1T1) on a time scale of 2 ps, which decays to the ground state without forming separated triplets, suggesting that triplet energy transfer from (1)(T1T1) to a nearby chromophore is essential for producing free triplets. In support of this hypothesis, selective excitation of BET-B doped into a thin film of diphenyltetracene (DPT) leads to formation of the (1)(T1T1) state of BET-B, followed by generation of both DPT and BET-B triplets. For the structurally cofacial BET-X, an intermediate forms in <180 fs and returns to the ground state more rapidly than BET-B. First-principles calculations predict a 2 orders of magnitude faster rate of singlet fission to the (1)(T1T1) state in BET-B relative to that of crystalline tetracene, attributing the rate increase to greater coupling between the S1 and (1)(T1T1) states and favorable energetics for formation of the separated triplets. PMID:26693957

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

    PubMed

    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. PMID:24691875

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

    PubMed

    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.

  9. Singlet-Doublet Dark Matter

    SciTech Connect

    Cohen, Timothy; Kearney, John; Pierce, Aaron; Tucker-Smith, David; /Williams Coll.

    2012-02-15

    In light of recent data from direct detection experiments and the Large Hadron Collider, we explore models of dark matter in which an SU(2){sub L} doublet is mixed with a Standard Model singlet. We impose a thermal history. If the new particles are fermions, this model is already constrained due to null results from XENON100. We comment on remaining regions of parameter space and assess prospects for future discovery. We do the same for the model where the new particles are scalars, which at present is less constrained. Much of the remaining parameter space for both models will be probed by the next generation of direct detection experiments. For the fermion model, DeepCore may also play an important role.

  10. Orbital rotation in the lowest triplet state of benzophenone

    SciTech Connect

    Dinse, K.P.; Pratt, D.W.

    1982-04-07

    Optically detected magnetic resonance (ODMR) and electron-nuclear double resonance (ODENDOR) spectroscopy at both zero and high magnetic fields were used to examine single crystals of 4,4'-dibromodiphenyl ether (DOE) containing 0.1 mol % of an enriched perdeuterio (/sup 17/O) benzophenone (/sup 17/O-BP-d/sub 10/) guest. Representative spectra are presented and explanations are offered for the electron spin transitions. The summarized results indicate the currently used atomic orbital functions do not provide an accurate description of the lowest excited states of many aromatic carbonyls. (BLM)

  11. Photo-assisted intersystem crossing: The predominant triplet formation mechanism in some isolated polycyclic aromatic molecules excited with pulsed lasers

    SciTech Connect

    Johnson, Philip M.; Sears, Trevor J.

    2015-07-28

    Naphthalene, anthracene, and phenanthrene are shown to have very long-lived triplet lifetimes when the isolated molecules are excited with nanosecond pulsed lasers resonant with the lowest singlet state. For naphthalene, triplet state populations are created only during the laser pulse, excluding the possibility of normal intersystem crossing at the one photon level, and all molecules have triplet lifetimes greater than hundreds of microseconds, similar to the behavior previously reported for phenylacetylene. Although containing 7–12 thousand cm{sup −1} of vibrational energy, the triplet molecules have ionization thresholds appropriate to vibrationless T{sub 1} states. The laser power dependences (slopes of log-log power plots) of the excited singlet and triplet populations are about 0.7 for naphthalene and about 0.5 for anthracene. Kinetic modeling of the power dependences successfully reproduces the experimental results and suggests that the triplet formation mechanism involves an enhanced spin orbit coupling caused by sigma character in states at the 2-photon level. Symmetry adapted cluster-configuration interaction calculations produced excited state absorption spectra to provide guidance for estimating kinetic rates and the sigma character present in higher electronic states. It is concluded that higher excited state populations are significant when larger molecules are excited with pulsed lasers and need to be taken into account whenever discussing the molecular photodynamics.

  12. Photo-assisted intersystem crossing: The predominant triplet formation mechanism in some isolated polycyclic aromatic molecules excited with pulsed lasers

    NASA Astrophysics Data System (ADS)

    Johnson, Philip M.; Sears, Trevor J.

    2015-07-01

    Naphthalene, anthracene, and phenanthrene are shown to have very long-lived triplet lifetimes when the isolated molecules are excited with nanosecond pulsed lasers resonant with the lowest singlet state. For naphthalene, triplet state populations are created only during the laser pulse, excluding the possibility of normal intersystem crossing at the one photon level, and all molecules have triplet lifetimes greater than hundreds of microseconds, similar to the behavior previously reported for phenylacetylene. Although containing 7-12 thousand cm-1 of vibrational energy, the triplet molecules have ionization thresholds appropriate to vibrationless T1 states. The laser power dependences (slopes of log-log power plots) of the excited singlet and triplet populations are about 0.7 for naphthalene and about 0.5 for anthracene. Kinetic modeling of the power dependences successfully reproduces the experimental results and suggests that the triplet formation mechanism involves an enhanced spin orbit coupling caused by sigma character in states at the 2-photon level. Symmetry adapted cluster-configuration interaction calculations produced excited state absorption spectra to provide guidance for estimating kinetic rates and the sigma character present in higher electronic states. It is concluded that higher excited state populations are significant when larger molecules are excited with pulsed lasers and need to be taken into account whenever discussing the molecular photodynamics.

  13. Photo-assisted intersystem crossing: The predominant triplet formation mechanism in some isolated polycyclic aromatic molecules excited with pulsed lasers

    DOE PAGESBeta

    Johnson, Philip M.; Sears, Trevor J.

    2015-07-28

    Naphthalene, anthracene, and phenanthrene are shown to have very long-lived triplet lifetimes when the isolated molecules are excited with nanosecond pulsed lasers resonant with the lowest singlet state. For naphthalene, triplet state populations are created only during the laser pulse, excluding the possibility of normal intersystem crossing at the one photon level, and all molecules have triplet lifetimes greater than hundreds of microseconds, similar to the behavior previously reported for phenylacetylene. Although containing 7–12 thousand cm⁻¹ of vibrational energy, the triplet molecules have ionization thresholds appropriate to vibrationless T₁ states. The laser power dependences (slopes of log-log power plots) ofmore » the excited singlet and triplet populations are about 0.7 for naphthalene and about 0.5 for anthracene. Kinetic modeling of the power dependences successfully reproduces the experimental results and suggests that the triplet formation mechanism involves an enhanced spin orbit coupling caused by sigma character in states at the 2-photon level. Symmetry Adapted Cluster-Configuration Interaction calculations produced excited state absorption spectra to provide guidance for estimating kinetic rates and the sigma character present in higher electronic states. It is concluded that higher excited state populations are significant when larger molecules are excited with pulsed lasers and need to be taken into account whenever discussing the molecular photodynamics.« less

  14. Photo-assisted intersystem crossing: The predominant triplet formation mechanism in some isolated polycyclic aromatic molecules excited with pulsed lasers

    SciTech Connect

    Johnson, Philip M.; Sears, Trevor J.

    2015-07-28

    Naphthalene, anthracene, and phenanthrene are shown to have very long-lived triplet lifetimes when the isolated molecules are excited with nanosecond pulsed lasers resonant with the lowest singlet state. For naphthalene, triplet state populations are created only during the laser pulse, excluding the possibility of normal intersystem crossing at the one photon level, and all molecules have triplet lifetimes greater than hundreds of microseconds, similar to the behavior previously reported for phenylacetylene. Although containing 7–12 thousand cm⁻¹ of vibrational energy, the triplet molecules have ionization thresholds appropriate to vibrationless T₁ states. The laser power dependences (slopes of log-log power plots) of the excited singlet and triplet populations are about 0.7 for naphthalene and about 0.5 for anthracene. Kinetic modeling of the power dependences successfully reproduces the experimental results and suggests that the triplet formation mechanism involves an enhanced spin orbit coupling caused by sigma character in states at the 2-photon level. Symmetry Adapted Cluster-Configuration Interaction calculations produced excited state absorption spectra to provide guidance for estimating kinetic rates and the sigma character present in higher electronic states. It is concluded that higher excited state populations are significant when larger molecules are excited with pulsed lasers and need to be taken into account whenever discussing the molecular photodynamics.

  15. Photo-assisted intersystem crossing: The predominant triplet formation mechanism in some isolated polycyclic aromatic molecules excited with pulsed lasers.

    PubMed

    Johnson, Philip M; Sears, Trevor J

    2015-07-28

    Naphthalene, anthracene, and phenanthrene are shown to have very long-lived triplet lifetimes when the isolated molecules are excited with nanosecond pulsed lasers resonant with the lowest singlet state. For naphthalene, triplet state populations are created only during the laser pulse, excluding the possibility of normal intersystem crossing at the one photon level, and all molecules have triplet lifetimes greater than hundreds of microseconds, similar to the behavior previously reported for phenylacetylene. Although containing 7-12 thousand cm(-1) of vibrational energy, the triplet molecules have ionization thresholds appropriate to vibrationless T1 states. The laser power dependences (slopes of log-log power plots) of the excited singlet and triplet populations are about 0.7 for naphthalene and about 0.5 for anthracene. Kinetic modeling of the power dependences successfully reproduces the experimental results and suggests that the triplet formation mechanism involves an enhanced spin orbit coupling caused by sigma character in states at the 2-photon level. Symmetry adapted cluster-configuration interaction calculations produced excited state absorption spectra to provide guidance for estimating kinetic rates and the sigma character present in higher electronic states. It is concluded that higher excited state populations are significant when larger molecules are excited with pulsed lasers and need to be taken into account whenever discussing the molecular photodynamics.

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

    PubMed

    Kowalczyk, Tim; Le, Khoa; Irle, Stephan

    2016-01-12

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

  17. Sigma meson and lowest possible glueball candidate in an extended linear {sigma} model

    SciTech Connect

    Mukherjee, Tamal K.; Huang Mei; Yan Qishu

    2012-10-23

    We formulate an extended linear {sigma} model of a quarkonia nonet and a tetraquark nonet as well as a complex iso-singlet (glueball) field to study the low-lying scalar meson. Chiral symmetry and U{sub A}(1) symmetry and their breaking play important role to shape the scalar meson spectrum in our work. Based on our study we will comment on what may be the mass of the lowest possible scalar and pseudoscalar glueball states. We will also discuss on what may be the nature of the sigma or f{sub 0}(600) meson.

  18. a Quantum Chemical Study of Familiar and Exotic Low-Lying Singlet and Triplet States of CH2, CF2, and Chf

    NASA Astrophysics Data System (ADS)

    Xu, Lu; Woon, D. E.; Dunning, T. H., Jr.

    2010-06-01

    High level MRCI and RCCSD(T) calculations using triple and quadruple zeta quality correlation consistent basis sets were used to study the low-lying singlet and triplet states of CH2, CF2, and CHF. The bonding in carbon was found to be very similar to that of sulfur, where there is also a competition between states that form through normal covalent bonding and recoupled pair bonding. The recoupled pair bonding model was used to investigate these states systematically to see how closely they resemble the behavior of SF2, which has a 1A1 ground state and 3B1 and 3A2 excited states. In addition to accounting for the separations and ordering of the lowest singlet and triplet states of each species, the less-studied 3A2 states of CH2 and CF2 and the 3A^" state of CHF were investigated and compared to gain insight into the underlying reasons for the energetic and bonding differences between these species. Interestingly, the 3A2 state of CH2 is a cyclic structure, the 3A2 state of CF2 is bent but not cyclic (resembling the same state of SF_2), and the analogous minimum structure on the 3A^" surface of CHF is a C---HF complex.

  19. Photosensitized reactions initiated by 6-carboxypterin: singlet and triplet reactivity.

    PubMed

    Tinel, L; Rossignol, S; Ciuraru, R; Dumas, S; George, C

    2016-06-22

    Pterins, derivatives of 2-aminopteridin-4(3H)-one, are natural photosensitizers, common to many biological systems. Indications that these photosensitizers are also present in the sea-surface microlayer motivated the study of the photophysical and photochemical properties of 6-carboxypterin (CPT), which was chosen as a model for this group of photoactive compounds. The kinetics of excited CPT in the singlet and triplet state in the presence of halides and organics were studied in aqueous solutions at neutral pH by means of steady-state fluorescence and laser-flash photolysis. The fluorescence of CPT was efficiently quenched by two halides (iodide and bromide) and by four carboxylic acids (lactic, malonic, propionic and citric acid) with reaction rates close to the diffusion-controlled limit. In the triplet state, the triplet absorption spectrum was measured and its pH dependence was studied. The triplet state of CPT showed relatively high reactivity towards iodide, but no reaction with bromide or chloride could be observed. No singlet or triplet state quenching in the presence of limonene could be measured. A reaction mechanism is proposed, initiated by electron transfer from the quencher to the excited photosensitizer. This type of photo-induced reaction in the sea-surface microlayer has the potential to trigger the production of many oxidized species, including halogen atoms, in the bulk and gaseous phases. PMID:27296228

  20. Hydrodynamics on the lowest Landau level

    NASA Astrophysics Data System (ADS)

    Geracie, Michael; Son, Dam Thanh

    2015-06-01

    Using the recently developed approach to quantum Hall physics based on Newton-Cartan geometry, we consider the hydrodynamics of an interacting system on the lowest Landau level. We rephrase the non-relativistic fluid equations of motion in a manner that manifests the spacetime diffeomorphism invariance of the underlying theory. In the massless (or lowest Landau level) limit, the fluid obeys a force-free constraint which fixes the charge current. An entropy current analysis further constrains the energy response, determining four transverse response functions in terms of only two: an energy magnetization and a thermal Hall conductivity. Kubo formulas are presented for all transport coefficients and constraints from Weyl invariance derived. We also present a number of Středa-type formulas for the equilibrium response to external electric, magnetic and gravitational fields.

  1. Phonon coupling in optical transitions for singlet-triplet pairs of bound excitons in semiconductors

    NASA Astrophysics Data System (ADS)

    Pistol, M. E.; Monemar, B.

    1986-05-01

    A model is presented for the observed strong difference in selection rules for coupling of phonons in the one-phonon sideband of optical spectra related to bound excitons in semiconductors. The present treatment is specialized to the case of a closely spaced pair of singlet-triplet character as the lowest electronic states, as is common for bound excitons associated with neutral complexes in materials like GaP and Si. The optical transition for the singlet bound-exciton state is found to couple strongly only to symmetric A1 modes. The triplet state has a similar coupling strength to A1 modes, but in addition strong contributions are found for replicas corresponding to high-density-of-states phonons TAX, LAX, and TOX. This can be explained by a treatment of particle-phonon coupling beyond the ordinary adiabatic approximation. A weak mixing between the singlet and triplet states is mediated by the phonon coupling, as described in first-order perturbation theory. The model derived in this work, for such phonon-induced mixing of closely spaced electronic states, is shown to explain the observed phonon coupling for several bound-exciton systems of singlet-triplet character in GaP. In addition, the observed oscillator strength of the forbidden triplet state may be explained as partly derived from phonon-induced mixing with the singlet state, which has a much larger oscillator strength.

  2. Intramolecular Singlet Fission in Oligoacene Heterodimers.

    PubMed

    Sanders, Samuel N; Kumarasamy, Elango; Pun, Andrew B; Steigerwald, Michael L; Sfeir, Matthew Y; Campos, Luis M

    2016-03-01

    We investigate singlet fission (SF) in heterodimers comprising a pentacene unit covalently bonded to another acene as we systematically vary the singlet and triplet pair energies. We find that these energies control the SF process, where dimers undergo SF provided that the resulting triplet pair energy is similar or lower in energy than the singlet state. In these systems the singlet energy is determined by the lower-energy chromophore, and the rate of SF is found to be relatively independent of the driving force. However, triplet pair recombination in these heterodimers follows the energy gap law. The ability to tune the energies of these materials provides a key strategy to study and design new SF materials-an important process for third-generation photovoltaics. PMID:26836223

  3. Solution-processable singlet fission photovoltaic devices.

    PubMed

    Yang, Le; Tabachnyk, Maxim; Bayliss, Sam L; Böhm, Marcus L; Broch, Katharina; Greenham, Neil C; Friend, Richard H; Ehrler, Bruno

    2015-01-14

    We demonstrate the successful incorporation of a solution-processable singlet fission material, 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene), into photovoltaic devices. TIPS-pentacene rapidly converts high-energy singlet excitons into pairs of triplet excitons via singlet fission, potentially doubling the photocurrent from high-energy photons. Low-energy photons are captured by small-bandgap electron-accepting lead chalcogenide nanocrystals. This is the first solution-processable singlet fission system that performs with substantial efficiency with maximum power conversion efficiencies exceeding 4.8%, and external quantum efficiencies of up to 60% in the TIPS-pentacene absorption range. With PbSe nanocrystal of suitable bandgap, its internal quantum efficiency reaches 170 ± 30%.

  4. Intramolecular Singlet Fission in Oligoacene Heterodimers

    DOE PAGESBeta

    Sanders, Samuel N.; Kumarasamy, Elango; Pun, Andrew B.; Steigerwald, Michael L.; Sfeir, Matthew L.; Campos, Luis M.

    2016-02-02

    In this Communication we investigate singlet fission (SF) in heterodimers comprising a pentacene unit covalently bonded to another acene as we systematically vary the singlet and triplet pair energies. We find that these energies control the SF process, where dimers undergo SF provided that the resulting triplet pair energy is similar or lower in energy than the singlet state. In these systems the singlet energy is determined by the lower energy chromophore, and the rate of SF is found to be relatively independent of the driving force. However, triplet pair recombination in these heterodimers follows the energy gap law. Themore » ability to tune the energies of these materials provides a key strategy to study and design new SF materials – an important process for third generation photovoltaics.« less

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

    PubMed

    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.

  6. The lowest ionization potentials of Al2

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Barnes, Leslie A.; Taylor, Peter R.

    1988-01-01

    Potential curves for the lowest two electronic states (X 2 sigma g + and A 2 pi u) of Al2(+) were computed using complete active space SCF/multireference CI wave functions and large Gaussian basis sets. The lowest observable vertical ionization potential (to Al2(+) X 2 sigma g +) of the Al2 X 3 pi u ground state is calculated to occur around 6.1 eV, in excellent agreement with the experimental range of 6.0 to 6.42 eV obtained in recent cluster ionization studies by Cox and co-workers. The second vertical ionization potential (to Al2(+) A 2 pi u) occurs near 6.4 eV, also within the experimental range. The adiabatic IP of 5.90 eV is in good agreement with the value of 5.8 to 6.1 eV deduced by Hanley and co-workers from the difference in thresholds between collision induced dissociation processes of Al3(+). The computed IP values are somewhat larger than those deduced from branching ratios in cluster fragmentation experiments by Jarrold and co-workers. The observation of an ionization threshold below 6.42 eV is shown to be incompatible with an Al2 ground electronic state assignment of 3 sigma g -, but the separation between the two lowest states of Al2 is so small that it is likely that both are populated in the experiments, so that this does not provide unambiguous support for the recent theoretical assignment of the ground state as 3 pi u.

  7. Scope and limitations of the TEMPO/EPR method for singlet oxygen detection: the misleading role of electron transfer.

    PubMed

    Nardi, Giacomo; Manet, Ilse; Monti, Sandra; Miranda, Miguel A; Lhiaubet-Vallet, Virginie

    2014-12-01

    For many biological and biomedical studies, it is essential to detect the production of (1)O2 and quantify its production yield. Among the available methods, detection of the characteristic 1270-nm phosphorescence of singlet oxygen by time-resolved near-infrared (TRNIR) emission constitutes the most direct and unambiguous approach. An alternative indirect method is electron paramagnetic resonance (EPR) in combination with a singlet oxygen probe. This is based on the detection of the TEMPO free radical formed after oxidation of TEMP (2,2,6,6-tetramethylpiperidine) by singlet oxygen. Although the TEMPO/EPR method has been widely employed, it can produce misleading data. This is demonstrated by the present study, in which the quantum yields of singlet oxygen formation obtained by TRNIR emission and by the TEMPO/EPR method are compared for a set of well-known photosensitizers. The results reveal that the TEMPO/EPR method leads to significant overestimation of singlet oxygen yield when the singlet or triplet excited state of the photosensitizer is efficiently quenched by TEMP, acting as electron donor. In such case, generation of the TEMP(+) radical cation, followed by deprotonation and reaction with molecular oxygen, gives rise to an EPR-detectable TEMPO signal that is not associated with singlet oxygen production. This knowledge is essential for an appropriate and error-free application of the TEMPO/EPR method in chemical, biological, and medical studies.

  8. A helpful technology--the luminescence detection of singlet oxygen to investigate photodynamic inactivation of bacteria (PDIB).

    PubMed

    Regensburger, Johannes; Maisch, Tim; Felgenträger, Ariane; Santarelli, Francesco; Bäumler, Wolfgang

    2010-06-01

    Photodynamic inactivation of bacteria (PDIB) is considered a new approach for the struggle against multiresistant bacteria. To achieve a sufficient level of bacteria killing, the photosensitizer must attach to and/or penetrate the bacteria and generate a sufficiently high amount of singlet oxygen. To optimize PDIB, the direct detection and quantification of singlet oxygen in bacteria is a helpful tool. Singlet-oxygen luminescence is a very weak signal, in particular in living bacteria. We first performed experiments in aqueous photosensitizer solution to optimize the luminescence system. We eliminated non-singlet-oxygen photons, which is important for the quantification of singlet oxygen and its rise and decay rates. This procedure is even more important when the laser excitation beam is scattered by bacteria (diameter 1 microm). In suspensions with both Gram-positive and Gram-negative bacteria we then clearly detected singlet oxygen by its luminescence and determined the respective rise and decay times. The decay times should provide an indication of localization of singlet oxygen and hence of the photosensitizer even in small bacteria.

  9. Supramolecular nanoreactors for intracellular singlet-oxygen sensitization

    NASA Astrophysics Data System (ADS)

    Swaminathan, Subramani; Fowley, Colin; Thapaliya, Ek Raj; McCaughan, Bridgeen; Tang, Sicheng; Fraix, Aurore; Burjor, Captain; Sortino, Salvatore; Callan, John F.; Raymo, Françisco M.

    2015-08-01

    An amphiphilic polymer with multiple decyl and oligo(ethylene glycol) chains attached to a common poly(methacrylate) backbone assembles into nanoscaled particles in aqueous environments. Hydrophobic anthracene and borondipyrromethene (BODIPY) chromophores can be co-encapsulated within the self-assembling nanoparticles and transported across hydrophilic media. The reversible character of the noncovalent bonds, holding the supramolecular containers together, permits the exchange of their components with fast kinetics in aqueous solution. Incubation of cervical cancer (HeLA) cells with a mixture of two sets of nanoparticles, pre-loaded independently with anthracene or BODIPY chromophores, results in guest scrambling first and then transport of co-entrapped species to the intracellular space. Alternatively, incubation of cells with the two sets of nanocarriers in consecutive steps permits the sequential transport of the anthracene and BODIPY chromophores across the plasma membrane and only then allows their co-encapsulation within the same supramolecular containers. Both mechanisms position the two sets of chromophores with complementary spectral overlap in close proximity to enable the efficient transfer of energy intracellularly from the anthracene donors to the BODIPY acceptors. In the presence of iodine substituents on the BODIPY platform, intersystem crossing follows energy transfer. The resulting triplet state can transfer energy further to molecular oxygen with the concomitant production of singlet oxygen to induce cell mortality. Furthermore, the donor can be excited with two near-infrared photons simultaneously to permit the photoinduced generation of singlet oxygen intracellularly under illumination conditions compatible with applications in vivo. Thus, these supramolecular strategies to control the excitation dynamics of multichromophoric assemblies in the intracellular environment can evolve into valuable protocols for photodynamic therapy.An amphiphilic

  10. TDDFT study on the excited-state proton transfer of 8-hydroxyquinoline: Key role of the excited-state hydrogen-bond strengthening

    NASA Astrophysics Data System (ADS)

    Lan, Sheng-Cheng; Liu, Yu-Hui

    2015-03-01

    Density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations have been employed to study the excited-state intramolecular proton transfer (ESIPT) reaction of 8-hydroxyquinoline (8HQ). Infrared spectra of 8HQ in both the ground and the lowest singlet excited states have been calculated, revealing a red-shift of the hydroxyl group (-OH) stretching band in the excited state. Hence, the intramolecular hydrogen bond (O-H···N) in 8HQ would be significantly strengthened upon photo-excitation to the S1 state. As the intramolecular proton-transfer reaction occurs through hydrogen bonding, the ESIPT reaction of 8HQ is effectively facilitated by strengthening of the electronic excited-state hydrogen bond (O-H···N). As a result, the intramolecular proton-transfer reaction would occur on an ultrafast timescale with a negligible barrier in the calculated potential energy curve for the ESIPT reaction. Therefore, although the intramolecular proton-transfer reaction is not favorable in the ground state, the ESIPT process is feasible in the excited state. Finally, we have identified that radiationless deactivation via internal conversion (IC) becomes the main dissipative channel for 8HQ by analyzing the energy gaps between the S1 and S0 states for the enol and keto forms.

  11. TDDFT study on the excited-state proton transfer of 8-hydroxyquinoline: key role of the excited-state hydrogen-bond strengthening.

    PubMed

    Lan, Sheng-Cheng; Liu, Yu-Hui

    2015-03-15

    Density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations have been employed to study the excited-state intramolecular proton transfer (ESIPT) reaction of 8-hydroxyquinoline (8HQ). Infrared spectra of 8HQ in both the ground and the lowest singlet excited states have been calculated, revealing a red-shift of the hydroxyl group (-OH) stretching band in the excited state. Hence, the intramolecular hydrogen bond (O-H···N) in 8HQ would be significantly strengthened upon photo-excitation to the S1 state. As the intramolecular proton-transfer reaction occurs through hydrogen bonding, the ESIPT reaction of 8HQ is effectively facilitated by strengthening of the electronic excited-state hydrogen bond (O-H···N). As a result, the intramolecular proton-transfer reaction would occur on an ultrafast timescale with a negligible barrier in the calculated potential energy curve for the ESIPT reaction. Therefore, although the intramolecular proton-transfer reaction is not favorable in the ground state, the ESIPT process is feasible in the excited state. Finally, we have identified that radiationless deactivation via internal conversion (IC) becomes the main dissipative channel for 8HQ by analyzing the energy gaps between the S1 and S0 states for the enol and keto forms.

  12. Protoporphyrin IX nanoparticle carrier: preparation, optical properties, and singlet oxygen generation.

    PubMed

    Rossi, Liane M; Silva, Paulo R; Vono, Lucas L R; Fernandes, Adjaci U; Tada, Dayane B; Baptista, Maurício S

    2008-11-01

    The present study is focused on developing a nanoparticle carrier for the photosensitizer protoporphyrin IX for use in photodynamic therapy. The entrapment of protoporphyrin IX (Pp IX) in silica spheres was achieved by modification of Pp IX molecules with an organosilane reagent. The immobilized drug preserved its optical properties and the capacity to generate singlet oxygen, which was detected by a direct method from its characteristic phosphorescence decay curve at near-infrared and by a chemical method using 1,3-diphenylisobenzofuran to trap singlet oxygen. The lifetime of singlet oxygen when a suspension of Pp IX-loaded particles in acetonitrile was excited at 532 nm was determined as 52 micros, which is in good agreement with the value determined for methylene blue in acetonitrile solution under the same conditions. The Pp IX-loaded silica particles have an efficiency of singlet oxygen generation (eta Delta) higher than the quantum yield of free porphyrins. This high efficiency of singlet oxygen generation was attributed to changes on the monomer-dimer equilibrium after photosentisizer immobilization. PMID:18834155

  13. A Description of Vibrational Modes in Hexaphyrins: Understanding the Aromaticity Reversal in the Lowest Triplet State.

    PubMed

    Sung, Young Mo; Oh, Juwon; Naoda, Koji; Lee, Taegon; Kim, Woojae; Lim, Manho; Osuka, Atsuhiro; Kim, Dongho

    2016-09-19

    Aromaticity reversal in the lowest triplet state, or Baird's rule, has been postulated for the past few decades. Despite numerous theoretical works on aromaticity reversal, experimental study is still at a rudimentary stage. Herein, we investigate the aromaticity reversal in the lowest excited triplet state using a comparable set of [26]- and [28]hexaphyrins by femtosecond time-resolved infrared (IR) spectroscopy. Compared to the relatively simple IR spectra of [26]bis(rhodium) hexaphyrin (R26H), those of [28]bis(rhodium) hexaphyrin (R28H) show complex IR spectra the region for the stretching modes of conjugated rings. Whereas time-resolved IR spectra of R26H in the excited triplet state are dominated by excited state IR absorption peaks, while those of R28H largely show ground state IR bleaching peaks, reflecting the aromaticity reversal in the lowest triplet state. These contrasting IR spectral features serve as new experimental aromaticity indices for Baird's rule. PMID:27510963

  14. Optical and time-resolved electron paramagnetic resonance studies of the excited states of a UV-B absorber (4-methylbenzylidene)camphor.

    PubMed

    Kikuchi, Azusa; Shibata, Kenji; Kumasaka, Ryo; Yagi, Mikio

    2013-02-21

    The excited states of UV-B absorber (4-methylbenzylidene)camphor (MBC) have been studied through measurements of UV absorption, phosphorescence, triplet-triplet (T-T) absorption, and steady-state and time-resolved electron paramagnetic resonance spectra in ethanol. The energy level and lifetime of the lowest excited triplet (T(1)) state of MBC were determined. The energy level of the T(1) state of MBC is much lower than that of photolabile 4-tert-butyl-4'-methoxydibenzoylmethane. The weak phosphorescence and strong time-resolved EPR signals, and T-T absorption band of MBC were observed. These facts suggest that the significant proportion of the lowest excited singlet (S(1)) molecules undergoes intersystem crossing to the T(1) state and the deactivation process from the T(1) state is predominantly radiationless. The quantum yields of singlet oxygen production by MBC determined by time-resolved near-IR luminescence measurements are 0.05 ± 0.01 and 0.06 ± 0.01 in ethanol and in acetonitrile, respectively. The photostability of MBC arises from the (3)ππ* character in the T(1) state. The zero-field splitting parameters in the T(1) state are D = 0.0901 cm(-1) and E = -0.0498 cm(-1). The sublevel preferentially populated by intersystem crossing is T(y) (y close to in-plane short axis and to the C═O direction). PMID:23320917

  15. Exciton Correlations in Intramolecular Singlet Fission.

    PubMed

    Sanders, Samuel N; Kumarasamy, Elango; Pun, Andrew B; Appavoo, Kannatassen; Steigerwald, Michael L; Campos, Luis M; Sfeir, Matthew Y

    2016-06-15

    We have synthesized a series of asymmetric pentacene-tetracene heterodimers with a variable-length conjugated bridge that undergo fast and efficient intramolecular singlet fission (iSF). These compounds have distinct singlet and triplet energies, which allow us to study the spatial dynamics of excitons during the iSF process, including the significant role of exciton correlations in promoting triplet pair generation and recombination. We demonstrate that the primary photoexcitations in conjugated dimers are delocalized singlets that enable fast and efficient iSF. However, in these asymmetric dimers, the singlet becomes more localized on the lower energy unit as the length of the bridge is increased, slowing down iSF relative to analogous symmetric dimers. We resolve the recombination kinetics of the inequivalent triplets produced via iSF, and find that they primarily decay via concerted processes. By identifying different decay channels, including delayed fluorescence via triplet-triplet annihilation, we can separate transient species corresponding to both correlated triplet pairs and uncorrelated triplets. Recombination of the triplet pair proceeds rapidly despite our experimental and theoretical demonstration that individual triplets are highly localized and unable to be transported across the conjugated linker. In this class of compounds, the rate of formation and yield of uncorrelated triplets increases with bridge length. Overall, these constrained, asymmetric systems provide a unique platform to isolate and study transient species essential for singlet fission, which are otherwise difficult to observe in symmetric dimers or condensed phases. PMID:27183040

  16. Exciton Correlations in Intramolecular Singlet Fission

    DOE PAGESBeta

    Sanders, Samuel N.; Kumarasamy, Elango; Pun, Andrew B.; Appavoo, Kannatassen; Steigerwald, Michael L.; Campos, Luis M.; Sfeir, Matthew Y.

    2016-05-16

    We have synthesized a series of asymmetric pentacene-tetracene heterodimers with a variable-length conjugated bridge that undergo fast and efficient intramolecular singlet fission (iSF). These compounds have distinct singlet and triplet energies, which allow us to study the spatial dynamics of excitons during the iSF process, including the significant role of exciton correlations in promoting triplet pair generation and recombination. We demonstrate that the primary photoexcitations in conjugated dimers are delocalized singlets that enable fast and efficient iSF. However, in these asymmetric dimers, the singlet becomes more localized on the lower energy unit as the length of the bridge is increased,more » slowing down iSF relative to analogous symmetric dimers. We resolve the recombination kinetics of the inequivalent triplets produced via iSF, and find that they primarily decay via concerted processes. By identifying different decay channels, including delayed fluorescence via triplet-triplet annihilation, we can separate transient species corresponding to both correlated triplet pairs and uncorrelated triplets. Recombination of the triplet pair proceeds rapidly despite our experimental and theoretical demonstration that individual triplets are highly localized and unable to be transported across the conjugated linker. In this class of compounds, the rate of formation and yield of uncorrelated triplets increases with bridge length. Overall, these constrained, asymmetric systems provide a unique platform to isolate and study transient species essential for singlet fission, which are otherwise difficult to observe in symmetric dimers or condensed phases.« less

  17. Tetrahydrobenzenes: Singlet-triplet separations and vibrational frequencies

    SciTech Connect

    Bettinger, H.F.; Schleyer, P.V.R.; Schaefer, H.F. III

    1999-03-31

    The energies and structures of the three tetradehydrobenzene (C{sub 6}H{sub 2}) isomers (ortho, meta, and para) were studied employing density functional theory (BLYP and B3LYP), complete active space SCF (CASSCF), and the coupled-cluster method with single, double (CCSD), and perturbative triple excitations [CCSD(T)] in conjunction with basis sets of up to triple-{zeta} plus double polarization quality. The meta isomer, 1,2,3,5-tetradehydrobenzene, is the most favorable cyclic isomer, but is 38 kcal mol{sup {minus}1} less stable than the hexatriyne C{sub 6}H{sub 2} global minimum. All of the cyclic isomers have singlet ground states, but these are less stable for the ortho and para isomers; hence, the singlet-triplet energy splittings for 1,2,4,5- and 1,2,3,4-tetradehydrobenzene are smaller than for ortho-benzyne. Harmonic vibrational frequency analyses [up to CCSD(T)/TZ2P] suggest that the {nu}{sub as}(C{triple{underscore}bond}C) vibration should be observable in the IR spectra of 1,2,4,5-tetradehydrobenzene at ca. 1,675 cm{sup {minus}1} but that this vibration might be too weak to be seen for 1,4-bis(trifluoromethyl)-2,3,5,6-tetradehydrobenzene.

  18. Mass loss at the lowest stellar masses

    NASA Astrophysics Data System (ADS)

    Fernández, M.; Comerón, F.

    2005-09-01

    We report the discovery of a jet in a [SII] image of Par-Lup3-4, a remarkable M 5-type pre-main sequence object in the Lupus 3 star-forming cloud. The spectrum of this star is dominated by the emission lines commonly interpreted as tracers of accretion and outflows. Par-Lup3-4 is therefore at the very low-mass end of the exciting sources of jets. High resolution spectroscopy shows that the [SII] line profile is double-peaked, implying that the low excitation jet is seen at a small angle (probably ⪆8circ) with respect to the plane of the sky. The width of the Hα line suggests a dominating contribution from the accretion columns and from the shocks on the stellar surface. Unresolved Hα emission coming from an object located at 4farcs2 from Par-Lup3-4 is detected at a position angle 30circ or 210circ, with no counterpart seen either in visible or infrared images. We also confirm previous evidence of strong mass loss from the very low mass star LS-RCrA 1, with spectral type M 6.5 or later. All its forbidden lines are blueshifted with respect to the local standard of rest (LSR) of the molecular cloud at a position very close to the object and the line profile of the [OI] lines is clearly asymmetric. Thus, the receding jet could be hidden by a disk which is not seen edge-on. If an edge-on disk does not surround Par-Lup3-4 or LS-RCrA 1, an alternative explanation, possibly based on the effects of mass accretion, is required to account for their unusually low luminosities.

  19. Pseudoscalar flavor-singlets and staggered fermions

    NASA Astrophysics Data System (ADS)

    Gregory, Eric

    2006-12-01

    The Asqtad improved staggered fermion formalism has been a valuable tool in successfully cal- culating the non-singlet parts of the hadronic spectrum. We are engaged in a project to calculate the spectrum of the pseudoscalar singlet mesons with 2 + 1-flavor Asqtad staggered gauge con- figurations. Propagators of flavor-singlet states incorporate contributions from both disconnected and connected diagrams, and hence are sensitive to any differences in the actions governing the sea and valence fermions on the lattice. As such, they also present the possibility of a probe of the validity of the "fourth-root trick" in the staggered fermion formulation. We present an update on our progress toward measuring the η mass on 2 + 1-flavor Asqtad staggered gauge configura- tions, including a review of methods and preliminary results. We also show a strong correlation between Tr(γ5 ⊗ 1) and the topological charge in these configurations, as predicted by the index theorem.

  20. Ab initio reaction pathways for photodissociation and isomerization of nitromethane on four singlet potential energy surfaces with three roaming paths

    SciTech Connect

    Isegawa, Miho; Liu, Fengyi; Morokuma, Keiji; Maeda, Satoshi

    2014-06-28

    Photodissociation pathways of nitromethane following π → π{sup *} electronic excitation are reported. The potential energy surfaces for four lowest singlet states are explored, and structures of many intermediates, dissociation limits, transition states, and minimum energy conical intersections were determined using the automated searching algorism called the global reaction route mapping strategy. Geometries are finally optimized at CASSCF(14e,11o) level and energies are computed at CAS(14o,11e)PT2 level. The calculated preferable pathways and important products qualitatively explain experimental observations. The major photodissociation product CH{sub 3} and NO{sub 2} ({sup 2}B{sub 2}) is formed by direct dissociation from the S{sub 1} state. Important pathways involving S{sub 1} and S{sub 0} states for production of various dissociation products CH{sub 3}NO + O ({sup 1}D), CH{sub 3}O(X{sup 2}E) + NO (X{sup 2}Π), CH{sub 2}NO + OH, and CH{sub 2}O + HNO, as well as various isomerization pathways have been identified. Three roaming processes also have been identified: the O atom roaming in O dissociation from CH{sub 3}NO{sub 2}, the OH radical roaming in OH dissociation from CH{sub 2}N(O)(OH), and the NO roaming in NO dissociation from CH{sub 3}ONO.

  1. Reactions of singlet oxygen with pine pollen.

    NASA Technical Reports Server (NTRS)

    Dowty, B.; Laseter, J. L.; Griffin, G. W.; Politzer, I. R.; Walkinshaw, C. H.

    1973-01-01

    A study was initiated to determine whether viable atmospheric particles such as plant pollens and fungal spores containing unsaturated lipids can interact with singlet oxygen to give oxygenated products that are potentially toxic. The results obtained confirm that surface and near surface components of common viable particulate matter in the atmosphere may be subject to rapid oxidation by singlet oxygen, leading to products which are probably allylic hydroperoxides. In connection with increasing atmospheric pollution, it is important to note that materials toxic to mammalian lung tissue may be oxidatively produced on the surfaces of viable particulate matter.

  2. Supramolecular nanoreactors for intracellular singlet-oxygen sensitization

    NASA Astrophysics Data System (ADS)

    Swaminathan, Subramani; Fowley, Colin; Thapaliya, Ek Raj; McCaughan, Bridgeen; Tang, Sicheng; Fraix, Aurore; Burjor, Captain; Sortino, Salvatore; Callan, John F.; Raymo, Françisco M.

    2015-08-01

    An amphiphilic polymer with multiple decyl and oligo(ethylene glycol) chains attached to a common poly(methacrylate) backbone assembles into nanoscaled particles in aqueous environments. Hydrophobic anthracene and borondipyrromethene (BODIPY) chromophores can be co-encapsulated within the self-assembling nanoparticles and transported across hydrophilic media. The reversible character of the noncovalent bonds, holding the supramolecular containers together, permits the exchange of their components with fast kinetics in aqueous solution. Incubation of cervical cancer (HeLA) cells with a mixture of two sets of nanoparticles, pre-loaded independently with anthracene or BODIPY chromophores, results in guest scrambling first and then transport of co-entrapped species to the intracellular space. Alternatively, incubation of cells with the two sets of nanocarriers in consecutive steps permits the sequential transport of the anthracene and BODIPY chromophores across the plasma membrane and only then allows their co-encapsulation within the same supramolecular containers. Both mechanisms position the two sets of chromophores with complementary spectral overlap in close proximity to enable the efficient transfer of energy intracellularly from the anthracene donors to the BODIPY acceptors. In the presence of iodine substituents on the BODIPY platform, intersystem crossing follows energy transfer. The resulting triplet state can transfer energy further to molecular oxygen with the concomitant production of singlet oxygen to induce cell mortality. Furthermore, the donor can be excited with two near-infrared photons simultaneously to permit the photoinduced generation of singlet oxygen intracellularly under illumination conditions compatible with applications in vivo. Thus, these supramolecular strategies to control the excitation dynamics of multichromophoric assemblies in the intracellular environment can evolve into valuable protocols for photodynamic therapy.An amphiphilic

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

    NASA Astrophysics Data System (ADS)

    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.

  4. Singlet-triplet annihilation limits exciton yield in poly(3-hexylthiophene).

    PubMed

    Steiner, Florian; Vogelsang, Jan; Lupton, John M

    2014-04-01

    Control of chain length and morphology in combination with single-molecule spectroscopy techniques provides a comprehensive photophysical picture of excited-state losses in the prototypical conjugated polymer poly(3-hexylthiophene) (P3HT). Our examination reveals a universal self-quenching mechanism, based on singlet-triplet exciton annihilation, which accounts for the dramatic loss in fluorescence quantum yield of a single P3HT chain between its solution (unfolded) and bulklike (folded) state. Triplet excitons fundamentally limit the fluorescence of organic photovoltaic materials, which impacts the conversion of singlet excitons to separated charge carriers, decreasing the efficiency of energy harvested at high excitation densities. Interexcitonic interactions are so effective that a single P3HT chain of order 100  kDa weight behaves like a 2-level system, exhibiting perfect photon antibunching. PMID:24745453

  5. Supramolecular nanoreactors for intracellular singlet-oxygen sensitization.

    PubMed

    Swaminathan, Subramani; Fowley, Colin; Thapaliya, Ek Raj; McCaughan, Bridgeen; Tang, Sicheng; Fraix, Aurore; Captain, Burjor; Sortino, Salvatore; Callan, John F; Raymo, Françisco M

    2015-09-01

    An amphiphilic polymer with multiple decyl and oligo(ethylene glycol) chains attached to a common poly(methacrylate) backbone assembles into nanoscaled particles in aqueous environments. Hydrophobic anthracene and borondipyrromethene (BODIPY) chromophores can be co-encapsulated within the self-assembling nanoparticles and transported across hydrophilic media. The reversible character of the noncovalent bonds, holding the supramolecular containers together, permits the exchange of their components with fast kinetics in aqueous solution. Incubation of cervical cancer (HeLA) cells with a mixture of two sets of nanoparticles, pre-loaded independently with anthracene or BODIPY chromophores, results in guest scrambling first and then transport of co-entrapped species to the intracellular space. Alternatively, incubation of cells with the two sets of nanocarriers in consecutive steps permits the sequential transport of the anthracene and BODIPY chromophores across the plasma membrane and only then allows their co-encapsulation within the same supramolecular containers. Both mechanisms position the two sets of chromophores with complementary spectral overlap in close proximity to enable the efficient transfer of energy intracellularly from the anthracene donors to the BODIPY acceptors. In the presence of iodine substituents on the BODIPY platform, intersystem crossing follows energy transfer. The resulting triplet state can transfer energy further to molecular oxygen with the concomitant production of singlet oxygen to induce cell mortality. Furthermore, the donor can be excited with two near-infrared photons simultaneously to permit the photoinduced generation of singlet oxygen intracellularly under illumination conditions compatible with applications in vivo. Thus, these supramolecular strategies to control the excitation dynamics of multichromophoric assemblies in the intracellular environment can evolve into valuable protocols for photodynamic therapy.

  6. Energy Dependence of the Ruthenium(II)-Bipyridine Metal-to-Ligand-Charge-Transfer Excited State Radiative Lifetimes: Effects of ππ*(bipyridine) Mixing.

    PubMed

    Thomas, Ryan A; Tsai, Chia Nung; Mazumder, Shivnath; Lu, I Chen; Lord, Richard L; Schlegel, H Bernhard; Chen, Yuan Jang; Endicott, John F

    2015-06-18

    The variations in band shape with excited state energy found for the triplet metal to ligand charge transfer ((3)MLCT) emission spectra of ruthenium-bipyridine (Ru-bpy) chromophores at 77 K have been postulated to arise from excited state/excited state configurational mixing. This issue is more critically examined through the determination of the excited state energy dependence of the radiative rate constants (kRAD) for these emissions. Experimental values for kRAD were determined relative to known literature references for Ru-bpy complexes. When the lowest energy excited states are metal centered, kRAD can be anomalously small and such complexes have been identified using density functional theory (DFT) modeling. When such complexes are removed from the energy correlation, there is a strong (3)MLCT energy-dependent contribution to kRAD in addition to the expected classical energy cubed factor for complexes with excited state energies greater than 10 000 cm(-1). This correlates with the DFT calculations which show significant excited state electronic delocalization between a π(bpy-orbital) and a half-filled dπ*-(Ru(III)-orbital) for Ru-bpy complexes with (3)MLCT excited state energies greater than about 16 000 cm(-1). Overall, this work implicates the "stealing" of emission bandshapes as well as intensity from the higher energy, strongly allowed bpy-centered singlet ππ* excited state.

  7. Solution-based intramolecular singlet fission in cross-conjugated pentacene dimers

    NASA Astrophysics Data System (ADS)

    Zirzlmeier, Johannes; Casillas, Rubén; Reddy, S. Rajagopala; Coto, Pedro B.; Lehnherr, Dan; Chernick, Erin T.; Papadopoulos, Ilias; Thoss, Michael; Tykwinski, Rik R.; Guldi, Dirk M.

    2016-05-01

    We show unambiguous and compelling evidence by means of pump-probe experiments, which are complemented by calculations using ab initio multireference perturbation theory, for intramolecular singlet fission (SF) within two synthetically tailored pentacene dimers with cross-conjugation, namely XC1 and XC2. The two pentacene dimers differ in terms of electronic interactions as evidenced by perturbation of the ground state absorption spectra stemming from stronger through-bond contributions in XC1 as confirmed by theory. Multiwavelength analysis, on one hand, and global analysis, on the other hand, confirm that the rapid singlet excited state decay and triplet excited state growth relate to SF. SF rate constants and quantum yields increase with solvent polarity. For example, XC2 reveals triplet quantum yields and rate constants as high as 162 +/- 10% and (0.7 +/- 0.1) × 1012 s-1, respectively, in room temperature solutions.We show unambiguous and compelling evidence by means of pump-probe experiments, which are complemented by calculations using ab initio multireference perturbation theory, for intramolecular singlet fission (SF) within two synthetically tailored pentacene dimers with cross-conjugation, namely XC1 and XC2. The two pentacene dimers differ in terms of electronic interactions as evidenced by perturbation of the ground state absorption spectra stemming from stronger through-bond contributions in XC1 as confirmed by theory. Multiwavelength analysis, on one hand, and global analysis, on the other hand, confirm that the rapid singlet excited state decay and triplet excited state growth relate to SF. SF rate constants and quantum yields increase with solvent polarity. For example, XC2 reveals triplet quantum yields and rate constants as high as 162 +/- 10% and (0.7 +/- 0.1) × 1012 s-1, respectively, in room temperature solutions. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr02493a

  8. Time-Resolved Insight into the Photosensitized Generation of Singlet Oxygen in Endoperoxides

    PubMed Central

    2014-01-01

    A synergistic approach combining high-level multiconfigurational static calculations and full-dimensional ab initio surface hopping dynamics has been employed to gain insight into the photochemistry of endoperoxides. Electronic excitation of endoperoxides triggers two competing pathways, cycloreversion and O–O homolysis, that result in the generation of singlet oxygen and oxygen diradical rearrangement products. Our results reveal that cycloreversion or the rupture of the two C–O bonds occurs via an asynchronous mechanism that can lead to the population of a ground-state intermediate showing a single C–O bond. Furthermore, singlet oxygen is directly generated in its most stable excited electronic state 1Δg. The triplet states do not intervene in this mechanism, as opposed to the O–O homolysis where the exchange of population between the singlet and triplet manifolds is remarkable. In line with recent experiments performed on the larger anthracene-9,10-endoperoxide, upon excitation to the spectroscopic ππ* electronic states, the primary photoreactive pathway that governs deactivation of endoperoxides is O–O homolysis with a quantum yield of 65%. PMID:25688180

  9. Metal bacteriochlorins which act as dual singlet oxygen and superoxide generators.

    PubMed

    Fukuzumi, Shunichi; Ohkubo, Kei; Zheng, Xiang; Chen, Yihui; Pandey, Ravindra K; Zhan, Riqiang; Kadish, Karl M

    2008-03-01

    A series of stable free-base, Zn(II) and Pd(II) bacteriochlorins containing a fused six- or five-member diketo- or imide ring have been synthesized as good candidates for photodynamic therapy sensitizers, and their electrochemical, photophysical, and photochemical properties were examined. Photoexcitation of the palladium bacteriochlorin affords the triplet excited state without fluorescence emission, resulting in formation of singlet oxygen with a high quantum yield due to the heavy atom effect of palladium. Electrochemical studies revealed that the zinc bacteriochlorin has the smallest HOMO-LUMO gap of the investigated compounds, and this value is significantly lower than the triplet excited-state energy of the compound in benzonitrile. Such a small HOMO-LUMO gap of the zinc bacteriochlorin enables intermolecular photoinduced electron transfer from the triplet excited state to the ground state to produce both the radical cation and the radical anion. The radical anion thus produced can transfer an electron to molecular oxygen to produce superoxide anion which was detected by electron spin resonance. The same photosensitizer can also act as an efficient singlet oxygen generator. Thus, the same zinc bacteriochlorin can function as a sensitizer with a dual role in that it produces both singlet oxygen and superoxide anion in an aprotic solvent (benzonitrile). PMID:18254618

  10. The Predicted Spectrum and Singlet-Triplet Interaction of the Hypermetallic Molecule SrOSr

    NASA Astrophysics Data System (ADS)

    Ostojić, B.; Jensen, Per; Schwerdtfeger, P.; Bunker, P. R.

    2013-10-01

    In accordance with previous studies in our group on Be, Mg, and Ca hypermetallic oxides, we find that SrOSr has a linear X-1Σg+ ground electronic state and a very low lying first excited -3Σu+ triplet electronic state. No gas-phase spectrum of this molecule has been assigned yet, and to encourage and assist in its discovery we present a complete ab initio simulation, with absolute intensities, of the infrared absorption spectrum for both electronic states. The three-dimensional potential energy surfaces and the electric dipole moment surfaces of the X-1Σg+ and -3Σu+ electronic states are calculated using a multireference configuration interaction (MRCISD) approach in combination with internally contracted multireference perturbation theory (RS2C) based on complete active space self-consistent field (CASSCF) wave functions applying a Sadlej pVTZ basis set for both O and Sr and the Stuttgart relativistic small-core effective core potential for Sr. The infrared spectra are simulated using the MORBID program system. We also calculate vertical excitation energies and transition moments for several excited singlet and triplet electronic states in order to predict the positions and intensities of the most prominent singlet and triplet electronic absorption bands. Finally, for this heavy molecule, we calculate the singlet-triplet interaction matrix elements between close-lying vibronic levels of the X- and - electronic states and find them to be very small.

  11. The low-energy, charge-transfer excited states of 4-amino-4-prime-nitrodiphenyl sulfide

    NASA Technical Reports Server (NTRS)

    O'Connor, Donald B.; Scott, Gary W.; Tran, Kim; Coulter, Daniel R.; Miskowski, Vincent M.; Stiegman, Albert E.; Wnek, Gary E.

    1992-01-01

    Absorption and emission spectra of 4-amino-4-prime-nitrodiphenyl sulfide in polar and nonpolar solvents were used to characterize and assign the low-energy excited states of the molecule. Fluorescence-excitation anisotropy spectra and fluorescence quantum yields were also used to characterize the photophysics of these states. The lowest-energy fluorescent singlet state was determined to be an intramolecular charge transfer (ICT) state involving transfer of a full electron charge from the amino to the nitro group yielding a dipole moment of about 50 D. A low-energy, intense absorption band is assigned as a transition to a different ICT state involving a partial electron charge transfer from sulfur to the nitro group.

  12. Determination of the geometry change of benzimidazole upon electronic excitation from a combined Franck-Condon/rotational constants fit

    NASA Astrophysics Data System (ADS)

    Stuhlmann, Benjamin; Gmerek, Felix; Krügler, Daniel; Schmitt, Michael

    2014-08-01

    Single vibronic level fluorescence spectra of the electronic origin and of seven vibronic bands between 0,0 and 0,0 + 1265 cm-1 have been measured and analyzed by means of a combined Franck-Condon/rotational constants fit. The rotational constants in ground and lowest electronically excited singlet state of four different isotopologues have been taken from previous rotationally resolved measurements of Schmitt et al. (2006). The intensities of 182 vibronic emission bands and of 8 rotational constants have been used for a fit of the complete heavy atom geometry changes upon electronic excitation. Vibronic modes, about 1000 cm-1 above the electronic origin, show strong deviations from Franck-Condon behavior in emission. Herzberg-Teller coupling contributes to this effect. 1300 cm-1 above the origin, we observe the onset of intramolecular vibrational redistribution in the emission spectra.

  13. Quasi-classical trajectory study of the adiabatic reactions occurring on the two lowest-lying electronic states of the LiH2+ system.

    PubMed

    Pino, Ilaria; Martinazzo, Rocco; Tantardini, Gian Franco

    2008-09-28

    Quasi-classical trajectory calculations have been performed on the adiabatically allowed reactions taking place on the two lowest-lying electronic states of the LiH2+ system, using the ab initio potential energy surfaces of Martinazzo et al. (J. Chem. Phys., 2003, 119, 11 241). These reactions comprise: (i) the exoergic H2 and H2+ formation occurring through LiH+ + H and LiH + H+ collisions in the ground and in the first electronically excited state, respectively; (ii) the endoergic (ground state) LiH+ dissociation induced by collisions with H atoms; and (iii) the endoergic (excited state) Li + H2+ --> LiH + H+ reaction. The topic is of relevance for a better understanding of the lithium chemistry in the early universe. Thermal rate constants for the above reactions have been computed in the temperature range 10-5000 K and found in reasonably good agreement with estimates based on the capture model.

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

    SciTech Connect

    Wojtoniszak, M.; Rogińska, D.; Machaliński, B.; Drozdzik, M.; Mijowska, E.

    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.

  15. Singlet molecular oxygen production in the reaction of peroxynitrite with hydrogen peroxide.

    PubMed

    Di Mascio, P; Bechara, E J; Medeiros, M H; Briviba, K; Sies, H

    1994-12-01

    Peroxynitrite and hydrogen peroxide are mediators of cytotoxicity. This study shows that the peroxynitrite anion reacts with hydrogen peroxide to release oxygen accompanied by emission of chemiluminescence (CL). Direct characterization of this light emission attributes it to the transition of singlet molecular oxygen to the triplet ground state. Chemiluminescence was monitored: (i) by dimol light emission in the red spectral region (> 610 nm) using a red-sensitive photomultiplier; and (ii) by monomol light emission in the infrared (1270 nm) with a liquid nitrogen-cooled germanium diode. These properties of photoemission and the enhancing effect of deuterium oxide on CL intensity as well as the quenching effect of sodium azide are diagnostic of molecular oxygen in the excited singlet state. For comparison, singlet molecular oxygen arising from the thermolysis of the water-soluble endoperoxide of 3,3'-(1,4-naphthylidene)dipropionate or from the hypochlorite/H2O2 system was also monitored. These novel observations identify a potential singlet oxygen-dependent mechanism contributing to cytotoxicity mediated by peroxynitrite and hydrogen peroxide.

  16. Magnetic dipolar interaction between correlated triplets created by singlet fission in tetracene crystals

    PubMed Central

    Wang, Rui; Zhang, Chunfeng; Zhang, Bo; Liu, Yunlong; Wang, Xiaoyong; Xiao, Min

    2015-01-01

    Singlet fission can potentially break the Shockley–Queisser efficiency limit in single-junction solar cells by splitting one photoexcited singlet exciton (S1) into two triplets (2T1) in organic semiconductors. A dark multiexciton state has been proposed as the intermediate connecting S1 to 2T1. However, the exact nature of this multiexciton state, especially how the doubly excited triplets interact, remains elusive. Here we report a quantitative study on the magnetic dipolar interaction between singlet-fission-induced correlated triplets in tetracene crystals by monitoring quantum beats relevant to the multiexciton sublevels at room temperature. The resonances of multiexciton sublevels approached by tuning an external magnetic field are observed to be avoided, which agrees well with the theoretical predictions considering a magnetic dipolar interaction of ∼0.008 GHz. Our work quantifies the magnetic dipolar interaction in certain organic materials and marks an important step towards understanding the underlying physics of the multiexciton state in singlet fission. PMID:26456368

  17. Nonlinear Density Dependence of Singlet Fission Rate in Tetracene Films.

    PubMed

    Zhang, Bo; Zhang, Chunfeng; Wang, Rui; Tan, Zhanao; Liu, Yunlong; Guo, Wei; Zhai, Xiaoling; Cao, Yi; Wang, Xiaoyong; Xiao, Min

    2014-10-16

    Singlet fission holds the potential to dramatically improve the efficiency of solar energy conversion by creating two triplet excitons from one photoexcited singlet exciton in organic semiconductors. It is generally assumed that the singlet-fission rate is linearly dependent on the exciton density. Here we experimentally show that the rate of singlet fission has a nonlinear dependence on the density of photoexcited singlet excitons in tetracene films with small crystalline grains. We disentangle the spectrotemporal features of singlet and triplet dynamics from ultrafast spectroscopic data with the algorithm of singular value decomposition. The correlation between their temporal dynamics indicates a superlinear dependence of fission rate on the density of singlet excitons, which may arise from excitonic interactions. PMID:26278594

  18. Singlet molecular oxygen generated in dark biological process.

    PubMed

    Di Mascio, Paolo; Medeiros, Marisa H G

    2014-10-01

    Ultraweak chemiluminescence arising from biomolecules oxidation has been attributed to the radiative deactivation of singlet molecular oxygen [(1)O2] and electronically excited triplet carbonyl products involving dioxetane intermediates. As examples, we will discuss the generation of (1)O2 from lipid hydroperoxides, which involves a cyclic mechanism from a linear tetraoxide intermediate. The generation of (1)O2 in aqueous solution via energy transfer from the excited triplet acetone arising from the thermodecomposition of dioxetane a chemical source, and horseradish peroxidase-catalyzed oxidation of 2-methylpropanal, as an enzymatic source, will also be discussed. The approach used to unequivocally demonstrate the generation of (1)O2 in these reactions is the use of (18)O-labeled hydroperoxide / triplet dioxygen ((18)[(3)O2]), the detection of labeled compounds by HPLC coupled to tandem mass spectrometry (HPLC-MS/MS) and the direct spectroscopic detection and characterization of (1)O2 light emission. Characteristic light emission at 1,270nm, corresponding to the singlet delta state monomolecular decay was observed. Using(18)[(3)O2], we observed the formation of (18)O-labeled (1)O2 ((18)[(1)O2]) by the chemical trapping of (18)[(1)O2]with the anthracene-9,10-diyldiethane-2,1-diyl disulfate disodium salt (EAS) and detected the corresponding (18)O-labeled EAS endoperoxide usingHPLC-MS/MS. The combined use of the thermolysis of a water-soluble naphthalene endoperoxide as a generator of (18)O labeled (1)O2 and the sensitivity of HPLC-MS/MS allowed the study of (1)O2reactivity toward biomolecules. Photoemission properties and chemical trapping clearly demonstrate that the production of hydroperoxide and excited carbonyls generates (18)[(1)O2], and points to the involvement of (1)O2 in physiological and pathophysiological mechanism. Supported by FAPESP (2012/12663-1), CAPES, INCT Redoxoma (FAPESP/CNPq/CAPES; 573530/2008-4), NAP Redoxoma (PRPUSP; 2011.1.9352.1.8), CEPID

  19. Single-molecule spectroscopy unmasks the lowest exciton state of the B850 assembly in LH2 from Rps. acidophila.

    PubMed

    Kunz, Ralf; Timpmann, Kõu; Southall, June; Cogdell, Richard J; Freiberg, Arvi; Köhler, Jürgen

    2014-05-01

    We have recorded fluorescence-excitation and emission spectra from single LH2 complexes from Rhodopseudomonas (Rps.) acidophila. Both types of spectra show strong temporal spectral fluctuations that can be visualized as spectral diffusion plots. Comparison of the excitation and emission spectra reveals that for most of the complexes the lowest exciton transition is not observable in the excitation spectra due to the cutoff of the detection filter characteristics. However, from the spectral diffusion plots we have the full spectral and temporal information at hand and can select those complexes for which the excitation spectra are complete. Correlating the red most spectral feature of the excitation spectrum with the blue most spectral feature of the emission spectrum allows an unambiguous assignment of the lowest exciton state. Hence, application of fluorescence-excitation and emission spectroscopy on the same individual LH2 complex allows us to decipher spectral subtleties that are usually hidden in traditional ensemble spectroscopy.

  20. Single-Molecule Spectroscopy Unmasks the Lowest Exciton State of the B850 Assembly in LH2 from Rps. acidophila

    PubMed Central

    Kunz, Ralf; Timpmann, Kõu; Southall, June; Cogdell, Richard J.; Freiberg, Arvi; Köhler, Jürgen

    2014-01-01

    We have recorded fluorescence-excitation and emission spectra from single LH2 complexes from Rhodopseudomonas (Rps.) acidophila. Both types of spectra show strong temporal spectral fluctuations that can be visualized as spectral diffusion plots. Comparison of the excitation and emission spectra reveals that for most of the complexes the lowest exciton transition is not observable in the excitation spectra due to the cutoff of the detection filter characteristics. However, from the spectral diffusion plots we have the full spectral and temporal information at hand and can select those complexes for which the excitation spectra are complete. Correlating the red most spectral feature of the excitation spectrum with the blue most spectral feature of the emission spectrum allows an unambiguous assignment of the lowest exciton state. Hence, application of fluorescence-excitation and emission spectroscopy on the same individual LH2 complex allows us to decipher spectral subtleties that are usually hidden in traditional ensemble spectroscopy. PMID:24806933

  1. Role of Geometric Distortion and Polarization in Localizing Electronic Excitations in Conjugated Polymers.

    PubMed

    Nayyar, Iffat H; Batista, Enrique R; Tretiak, Sergei; Saxena, Avadh; Smith, Darryl L; Martin, Richard L

    2013-02-12

    Five different Density Functional Theory (DFT) models (ranging from pure GGA to long-range-corrected hybrid functionals) were used to study computationally the nature of the self-trapped electronic states in oligophenylene vinylenes. The electronic excitations in question include the lowest singlet (S1) and triplet (T1(†)) excitons (calculated using Time Dependent DFT (TD-DFT) method), positive (P(+)) and negative (P(-)) polarons, and the lowest triplet (T1) states (computed with the Self-Consistent Field (SCF) scheme). The polaron formation (spatial localization of excitations) is observed only with the use of range-corrected hybrid DFT models including long-range electronic exchange interactions. The extent of localization for all studied excitations is found to be invariant with respect to the size of the oligomer chain in their corresponding optimal geometries. We have analyzed the interdependence between the extent of the geometrical distortion and the localization of the orbital and spin density, and have observed that the localization of the P(+) and P(-) charged species is quite sensitive to solvent polarization effects and the character of the DFT functional used, rather than the structural deformations. In contrast, the localization of neutral states, S1 and T1(†), is found to follow the structural distortions. Notably, T1 excitation obtained with the mean field SCF approach is always strongly localized in range-corrected hybrid DFT models. The molecular orbital energetics of these excitations was further investigated to identify the relationship between state localization and the corresponding orbital structure. A characteristic stabilization (destabilization) of occupied (virtual) orbitals is observed in hybrid DFT models, compared to tight-binding model-like orbital filling in semilocal GGA functionals. The molecular and natural orbital representation allows visualization of the spatial extent of the underlying electronic states. In terms of

  2. Electromagnetic structure of the lowest-lying decuplet resonances in covariant chiral perturbation theory

    SciTech Connect

    Geng, L. S.; Camalich, J. Martin; Vacas, M. J. Vicente

    2009-08-01

    We present a calculation of the leading SU(3)-breaking O(p{sup 3}) corrections to the electromagnetic moments and charge radius of the lowest-lying decuplet resonances in covariant chiral perturbation theory. In particular, the magnetic dipole moment of the members of the decuplet is predicted fixing the only low-energy constant (LEC) present up to this order with the well-measured magnetic dipole moment of the {omega}{sup -}. We predict {mu}{sub {delta}}{sup ++}=6.04(13) and {mu}{sub {delta}}{sup +}=2.84(2), which agree well with the current experimental information. For the electric quadrupole moment and the charge radius, we use state-of-the-art lattice QCD results to determine the corresponding LECs, whereas for the magnetic octupole moment there is no unknown LEC up to the order considered here, and we obtain a pure prediction. We compare our results with those reported in large N{sub c}, lattice QCD, heavy-baryon chiral perturbation theory, and other models.

  3. Singlet fission: Towards efficient solar cells

    SciTech Connect

    Havlas, Zdeněk; Wen, Jin; Michl, Josef

    2015-12-31

    Singlet fission (SF) offers an opportunity to improve solar cell efficiency, but its practical use is hindered by the limited number of known efficient materials, limited knowledge of SF mechanism, mainly the relation between the dimer structure and SF efficiency and diffusion of the triplet states allowing injection of electrons into the solar cell semiconductor band. Here we report on our attempt to design new classes of chromophores and to study the relation between the structure and SF efficiency.

  4. Martensitic transformation of CsFeS/sub 2/ driven by the singlet to Neel state transition

    SciTech Connect

    Ito, Y.; Nishi, M.; Passell, L.; Majkrzak, C.F.; Shirane, G.

    1985-01-01

    CsFeS/sub 2/ is regarded as an example of the quasi one-dimensional alternating antiferromagnetic Heisenberg chain above about 70K. In accordance with this picture, an energy gap of 10MeV was observed for the singlet to triplet excitation at a zone center near the transition temperature by our neutron measurements. Large excitation width implies a strong coupling of excitons to phonons, and LA phonons along <001> direction become ill-defined for q greater than 0.3. At about 70K, the first order transition occurs, whereby the singlet ground state changes to a Neel state and the simultaneous structural transformation takes place, which is a martensitic transformation. Mechanism for such martensitic transformation is discussed based on the similarity of the magnetic excitation and phonon behaviors between the present compound and the ..gamma.. Mn alloys with Fe and Cu, which are itinerant electron magnetic systems. 10 refs., 3 figs.

  5. Probing ground and low-lying excited states for HIO2 isomers

    NASA Astrophysics Data System (ADS)

    de Souza, Gabriel L. C.; Brown, Alex

    2014-12-01

    We present a computational study on HIO2 molecules. Ground state properties such as equilibrium structures, relative energetics, vibrational frequencies, and infrared intensities were obtained for all the isomers at the coupled-cluster with single and double excitations as well as perturbative inclusion of triples (CCSD(T)) level of theory with the aug-cc-pVTZ-PP basis set and ECP-28-PP effective core potential for iodine and the aug-cc-pVTZ basis set for hydrogen and oxygen atoms. The HOIO structure is confirmed as the lowest energy isomer. The relative energies are shown to be HOIO < HOOI < HI(O)O. The HO(O)I isomer is only stable at the density functional theory (DFT) level of theory. The transition states determined show interconversion of the isomers is possible. In order to facilitate future experimental identification, vibrational frequencies are also determined for all corresponding deuterated species. Vertical excitation energies for the three lowest-lying singlet and triplet excited states were determined using the configuration interaction singles, time-dependent density functional theory (TD-DFT)/B3LYP, TD-DFT/G96PW91, and equation of motion-CCSD approaches with the LANL2DZ basis set plus effective core potential for iodine and the aug-cc-pVTZ basis set for hydrogen and oxygen atoms. It is shown that HOIO and HOOI isomers have excited states accessible at solar wavelengths (<4.0 eV) but these states have very small oscillator strengths (<2 × 10-3).

  6. Probing ground and low-lying excited states for HIO2 isomers.

    PubMed

    de Souza, Gabriel L C; Brown, Alex

    2014-12-21

    We present a computational study on HIO2 molecules. Ground state properties such as equilibrium structures, relative energetics, vibrational frequencies, and infrared intensities were obtained for all the isomers at the coupled-cluster with single and double excitations as well as perturbative inclusion of triples (CCSD(T)) level of theory with the aug-cc-pVTZ-PP basis set and ECP-28-PP effective core potential for iodine and the aug-cc-pVTZ basis set for hydrogen and oxygen atoms. The HOIO structure is confirmed as the lowest energy isomer. The relative energies are shown to be HOIO < HOOI < HI(O)O. The HO(O)I isomer is only stable at the density functional theory (DFT) level of theory. The transition states determined show interconversion of the isomers is possible. In order to facilitate future experimental identification, vibrational frequencies are also determined for all corresponding deuterated species. Vertical excitation energies for the three lowest-lying singlet and triplet excited states were determined using the configuration interaction singles, time-dependent density functional theory (TD-DFT)/B3LYP, TD-DFT/G96PW91, and equation of motion-CCSD approaches with the LANL2DZ basis set plus effective core potential for iodine and the aug-cc-pVTZ basis set for hydrogen and oxygen atoms. It is shown that HOIO and HOOI isomers have excited states accessible at solar wavelengths (<4.0 eV) but these states have very small oscillator strengths (<2 × 10(-3)). PMID:25527931

  7. Probing ground and low-lying excited states for HIO{sub 2} isomers

    SciTech Connect

    Souza, Gabriel L. C. de; Brown, Alex

    2014-12-21

    We present a computational study on HIO{sub 2} molecules. Ground state properties such as equilibrium structures, relative energetics, vibrational frequencies, and infrared intensities were obtained for all the isomers at the coupled-cluster with single and double excitations as well as perturbative inclusion of triples (CCSD(T)) level of theory with the aug-cc-pVTZ-PP basis set and ECP-28-PP effective core potential for iodine and the aug-cc-pVTZ basis set for hydrogen and oxygen atoms. The HOIO structure is confirmed as the lowest energy isomer. The relative energies are shown to be HOIO < HOOI < HI(O)O. The HO(O)I isomer is only stable at the density functional theory (DFT) level of theory. The transition states determined show interconversion of the isomers is possible. In order to facilitate future experimental identification, vibrational frequencies are also determined for all corresponding deuterated species. Vertical excitation energies for the three lowest-lying singlet and triplet excited states were determined using the configuration interaction singles, time-dependent density functional theory (TD-DFT)/B3LYP, TD-DFT/G96PW91, and equation of motion-CCSD approaches with the LANL2DZ basis set plus effective core potential for iodine and the aug-cc-pVTZ basis set for hydrogen and oxygen atoms. It is shown that HOIO and HOOI isomers have excited states accessible at solar wavelengths (<4.0 eV) but these states have very small oscillator strengths (<2 × 10{sup −3})

  8. Mechanism of singlet oxygen deactivation in an electric discharge oxygen – iodine laser

    SciTech Connect

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

    2014-12-31

    We have determined the influence of the reaction of molecular singlet oxygen with a vibrationally excited ozone molecule O{sub 2}(a {sup 1}Δ) + O{sub 3}(ν) → 2O{sub 2} + O on the removal rate of O{sub 2}(a {sup 1}Δ) in an electric-discharge-driven oxygen – iodine laser. This reaction has been shown to be a major channel of O{sub 2}(a {sup 1}Δ) loss at the output of an electric-discharge singlet oxygen generator. In addition, it can also contribute significantly to the loss of O{sub 2}(a {sup 1}Δ) in the discharge region of the generator. (lasers)

  9. Effects of Ferromagnetic Nanowires on Singlet and Triplet Exciton Fractions in Fluorescent and Phosphorescent Organic Semiconductors

    SciTech Connect

    Hu, Bin; Wu, Yue; Zhang, Zongtao; Dai, Sheng; Shen, Jian

    2006-01-01

    We report a magnetic field-dependent electroluminescence (EL) induced by ferromagnetic Co{sub 53}Pt{sub 47} nanowires in fluorescent conjugated polymer poly[2-methoxy-5-(2{prime}-ethylhexyloxy)-1,4-phenylenevinylene] and phosphorescent iridium-complex Ir(ppy){sub 3} molecules. The photoluminescence and EL studies indicate that the dispersed CoPt nanowires increase the singlet-to-triplet exciton ratio in organic semiconductors, suggesting that the spin-polarized holes were injected into the organic molecules from the CoPt nanowires under electrical excitation. Therefore, the use of ferromagnetic nanomaterials demonstrates a pathway to tune the optoelectronic properties that are related to singlet and triplet states in organic semiconducting materials.

  10. Collisional excitation of interstellar water

    NASA Technical Reports Server (NTRS)

    Palma, Amedeo; Green, Sheldon; Defrees, D. J.; Mclean, A. D.

    1988-01-01

    Rates for rotational excitation of water molecules in collisions with He atoms have been obtained from a new, accurate theoretical interaction potential. Rates among the lowest 40 ortho levels are given for kinetic temperatures to 1400 K and among the lowest 29 para levels for kinetic temperatures to 800 K.

  11. Real-time observation of multiexcitonic states in ultrafast singlet fission using coherent 2D electronic spectroscopy.

    PubMed

    Bakulin, Artem A; Morgan, Sarah E; Kehoe, Tom B; Wilson, Mark W B; Chin, Alex W; Zigmantas, Donatas; Egorova, Dassia; Rao, Akshay

    2016-01-01

    Singlet fission is the spin-allowed conversion of a spin-singlet exciton into a pair of spin-triplet excitons residing on neighbouring molecules. To rationalize this phenomenon, a multiexcitonic spin-zero triplet-pair state has been hypothesized as an intermediate in singlet fission. However, the nature of the intermediate states and the underlying mechanism of ultrafast fission have not been elucidated experimentally. Here, we study a series of pentacene derivatives using ultrafast two-dimensional electronic spectroscopy and unravel the origin of the states involved in fission. Our data reveal the crucial role of vibrational degrees of freedom coupled to electronic excitations that facilitate the mixing of multiexcitonic states with singlet excitons. The resulting manifold of vibronic states drives sub-100 fs fission with unity efficiency. Our results provide a framework for understanding singlet fission and show how the formation of vibronic manifolds with a high density of states facilitates fast and efficient electronic processes in molecular systems.

  12. Real-time observation of multiexcitonic states in ultrafast singlet fission using coherent 2D electronic spectroscopy

    NASA Astrophysics Data System (ADS)

    Bakulin, Artem A.; Morgan, Sarah E.; Kehoe, Tom B.; Wilson, Mark W. B.; Chin, Alex W.; Zigmantas, Donatas; Egorova, Dassia; Rao, Akshay

    2016-01-01

    Singlet fission is the spin-allowed conversion of a spin-singlet exciton into a pair of spin-triplet excitons residing on neighbouring molecules. To rationalize this phenomenon, a multiexcitonic spin-zero triplet-pair state has been hypothesized as an intermediate in singlet fission. However, the nature of the intermediate states and the underlying mechanism of ultrafast fission have not been elucidated experimentally. Here, we study a series of pentacene derivatives using ultrafast two-dimensional electronic spectroscopy and unravel the origin of the states involved in fission. Our data reveal the crucial role of vibrational degrees of freedom coupled to electronic excitations that facilitate the mixing of multiexcitonic states with singlet excitons. The resulting manifold of vibronic states drives sub-100 fs fission with unity efficiency. Our results provide a framework for understanding singlet fission and show how the formation of vibronic manifolds with a high density of states facilitates fast and efficient electronic processes in molecular systems.

  13. Intracellular singlet oxygen photosensitizers: on the road to solving the problems of sensitizer degradation, bleaching and relocalization.

    PubMed

    da Silva, Elsa F F; Pimenta, Frederico M; Pedersen, Brian W; Blaikie, Frances H; Bosio, Gabriela N; Breitenbach, Thomas; Westberg, Michael; Bregnhøj, Mikkel; Etzerodt, Michael; Arnaut, Luis G; Ogilby, Peter R

    2016-02-01

    Selected singlet oxygen photosensitizers have been examined from the perspective of obtaining a molecule that is sufficiently stable under conditions currently employed to study singlet oxygen behavior in single mammalian cells. Reasonable predictions about intracellular sensitizer stability can be made based on solution phase experiments that approximate the intracellular environment (e.g., solutions containing proteins). Nevertheless, attempts to construct a stable sensitizer based solely on the expected reactivity of a given functional group with singlet oxygen are generally not sufficient for experiments in cells; it is difficult to construct a suitable chromophore that is impervious to all of the secondary and/or competing degradative processes that are present in the intracellular environment. On the other hand, prospects are reasonably positive when one considers the use of a sensitizer encapsulated in a specific protein; the local environment of the chromophore is controlled, degradation as a consequence of bimolecular reactions can be mitigated, and genetic engineering can be used to localize the encapsulated sensitizer in a given cellular domain. Also, the option of directly exciting oxygen in sensitizer-free experiments provides a useful complementary tool. These latter systems bode well with respect to obtaining more accurate control of the "dose" of singlet oxygen used to perturb a cell; a parameter that currently limits mechanistic studies of singlet-oxygen-mediated cell signaling. PMID:26878203

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

    NASA Astrophysics Data System (ADS)

    Closser, Kristina Danielle

    superpositions of atomic states with surface states appearing close to the atomic excitation energies and interior states being blue shifted by up to ≈2 eV. The dynamics resulting from excitation of He_7 were subsequently explored using ab initio molecular dynamics (AIMD). These simulations were performed with classical adiabatic dynamics coupled to a new state-following algorithm on CIS potential energy surfaces. Most clusters were found to completely dissociate and resulted in a single excited atomic state (90%), however, some trajectories formed bound, He*2 (3%), and a few yielded excited trimers (<0.5%). Comparisons were made with available experimental information on much larger clusters. Various applications of this state following algorithm are also presented. In addition to AIMD, these include excited-state geometry optimization and minimal energy path finding via the growing string method. When using state following we demonstrate that more physical results can be obtained with AIMD calculations. Also, the optimized geometries of three excited states of cytosine, two of which were not found without state following, and the minimal energy path between the lowest two singlet excited states of protonated formaldimine are offered as example applications. Finally, to address large clusters, a local variation of CIS was developed. This method exploits the properties of absolutely localized molecular orbitals (ALMOs) to limit the total number of excitations to scaling only linearly with cluster size, which results in formal scaling with the third power of the system size. The derivation of the equations and design of the algorithm are discussed in detail, and computational timings as well as a pilot application to the size dependence of the helium cluster spectrum are presented.

  15. Surface plasmon excitation of porphyrin self-assembly monolayers on an Au surface

    NASA Astrophysics Data System (ADS)

    Ishida, Akito; Majima, Tetsuro

    1999-09-01

    Surface plasmon (SP) enhanced fluorescence spectroscopy has been employed to elucidate the molecular orientation, molecular exchange process, and photoelectrochemical properties of photofunctional self-assembly monolayers (SAMs) for the first time. A 48 nm Au film on a BK-7 right-angle prism was treated with a porphyrin disulfide ((-S(CH2)10CONH-Por)2, Por = p-(tris(p-tolyl)porphyrinyl)phenyl) (1) giving a porphyrin SAM (2). SP excitation of 2 using p-polarized 425 nm light at an incident angle of 55° gave a strongly p-polarized fluorescence of the porphyrin. This indicates selective excitation of the porphyrins having transition moments effectively overlap with the SP field vectors and the suppressed molecular motions in 2. The Q bands in the fluorescence excitation spectrum were considerably enhanced attributable to the field enhancement of SP. The molecular exchange process of a decanethiol SAM with 1 has been elucidated based on changes in the fluorescence properties. The photoelectrochemical measurement using 632.8 nm light gave a much more intense photocurrent (18.6 µA cm-2) than that provided by conventional direct photoexcitation (2.7 µA cm-2). Moreover, the photocurrent was observed using near-IR light while the energy is considerably lower than the lowest singlet excited state of the porphyrin.

  16. Statistical equilibrium in cometary C2. III - Triplet-singlet, Phillips, Ballik-Ramsay, and Mulliken bands

    NASA Technical Reports Server (NTRS)

    Swamy, K. S. K.; Odell, C. R.

    1981-01-01

    A new series of vibrational bands is predicted which arises from transitions between the lowest electron states of the triplet and singlet states of homonuclear C2. The predictions are useful for C2 identifications and for disentangling congested low resolution spectra that characterize new observations. Predictions are also made for Mulliken, Phillips, and Ballik-Ramsay band sequences, and all calculations are made with the assumed molecular constants and computational methods of KSO-II.

  17. Contribution of electronically excited states to the radiation chemistry of organic systems. Informal technical progress report, December 1, 1981-January 31, 1983

    SciTech Connect

    Lipsky, S.

    1983-01-01

    Summaries are presented for the research projects in progress and for the following three completed projects: (1) comparision of the quenching of the fluorescence of saturated hydrocarbons excited below and above the ionization threshold; (2) dependence on scavenger concentration of the efficiency of quenching genunate-ion recombination fluorescence of saturated hydrocarbon liquids; (3) positive charge transfer from saturated non-polar liquids to N,N,N'-tetramethyl-p-phenylenediamine. In addition to these projects the following investigations have been completed and published during the past two years: effect of perfluorocarbons on ultraviolet absorption and fluorescence characteristics of some saturated hydrocarbon liquids; note on the G value for the production of the lowest excited singlet state of cyclohexane; effect of electron scavengers to reduce the ionization current of photoexcited N,N,N',N'-tetramethyl-p-phenylediamine in non-polar organic fluids; polystyren fluorescence-effects of molecular weight in various solvents.

  18. Doublet-singlet model and unitarity

    NASA Astrophysics Data System (ADS)

    Cynolter, G.; Kovács, J.; Lendvai, E.

    2016-12-01

    We study the renormalizable singlet-doublet fermionic extension of the Standard Model (SM). In this model, the new vector-like fermions couple to the gauge bosons and to the Higgs via new Yukawa couplings that allow for nontrivial mixing in the new sector, providing a stable, neutral dark matter candidate. Approximate analytic formulae are given for the mass spectrum around the blind spots, where the dark matter candidate coupling to h or Z vanishes. We calculate the two particle scattering amplitudes in the model, impose the perturbative unitarity constraints and establish bounds on the Yukawa couplings.

  19. Decamethylytterbocene Complexes of Bipyridines and Diazabutadienes: Multiconfigurational Ground States and Open-Shell Singlet Formation

    SciTech Connect

    Booth, Corwin H.; Walter, Marc D.; Kazhdan, Daniel; Hu, Yung-Jin; Lukens, Wayne W.; Bauer, Eric D.; Maron, Laurent; Eisenstein, Odile; Andersen, Richard A.

    2009-04-22

    Partial ytterbium f-orbital occupancy (i.e., intermediate valence) and open-shell singlet formation are established for a variety of bipyridine and diazabutadiene adducts with decamethylytterbocene, (C5Me5)2Yb, abbreviated as Cp*2Yb. Data used to support this claim include ytterbium valence measurements using Yb LIII-edge X-ray absorption near-edge structure spectroscopy, magnetic susceptibility, and complete active space self-consistent field (CASSCF) multiconfigurational calculations, as well as structural measurements compared to density functional theory calculations. The CASSCF calculations indicate that the intermediate valence is the result of a multiconfigurational ground-state wave function that has both an open-shell singlet f13(?*)1, where pi* is the lowest unoccupied molecular orbital of the bipyridine or dpiazabutadiene ligands, and a closed-shell singlet f14 component. A number of other competing theories for the unusual magnetism in these materials are ruled out by the lack of temperature dependence of the measured intermediate valence. These results have implications for understanding chemical bonding not only in organolanthanide complexes but also for f-element chemistry in general, as well as understanding magnetic interactions in nanoparticles and devices.

  20. The nature of singlet exciton fission in carotenoid aggregates.

    PubMed

    Musser, Andrew J; Maiuri, Margherita; Brida, Daniele; Cerullo, Giulio; Friend, Richard H; Clark, Jenny

    2015-04-22

    Singlet exciton fission allows the fast and efficient generation of two spin triplet states from one photoexcited singlet. It has the potential to improve organic photovoltaics, enabling efficient coupling to the blue to ultraviolet region of the solar spectrum to capture the energy generally lost as waste heat. However, many questions remain about the underlying fission mechanism. The relation between intermolecular geometry and singlet fission rate and yield is poorly understood and remains one of the most significant barriers to the design of new singlet fission sensitizers. Here we explore the structure-property relationship and examine the mechanism of singlet fission in aggregates of astaxanthin, a small polyene. We isolate five distinct supramolecular structures of astaxanthin generated through self-assembly in solution. Each is capable of undergoing intermolecular singlet fission, with rates of triplet generation and annihilation that can be correlated with intermolecular coupling strength. In contrast with the conventional model of singlet fission in linear molecules, we demonstrate that no intermediate states are involved in the triplet formation: instead, singlet fission occurs directly from the initial 1B(u) photoexcited state on ultrafast time scales. This result demands a re-evaluation of current theories of polyene photophysics and highlights the robustness of carotenoid singlet fission. PMID:25825939

  1. Excitations and benchmark ensemble density functional theory for two electrons

    SciTech Connect

    Pribram-Jones, Aurora; Burke, Kieron; Yang, Zeng-hui; Ullrich, Carsten A.; Trail, John R.; Needs, Richard J.

    2014-05-14

    A new method for extracting ensemble Kohn-Sham potentials from accurate excited state densities is applied to a variety of two-electron systems, exploring the behavior of exact ensemble density functional theory. The issue of separating the Hartree energy and the choice of degenerate eigenstates is explored. A new approximation, spin eigenstate Hartree-exchange, is derived. Exact conditions that are proven include the signs of the correlation energy components and the asymptotic behavior of the potential for small weights of the excited states. Many energy components are given as a function of the weights for two electrons in a one-dimensional flat box, in a box with a large barrier to create charge transfer excitations, in a three-dimensional harmonic well (Hooke's atom), and for the He atom singlet-triplet ensemble, singlet-triplet-singlet ensemble, and triplet bi-ensemble.

  2. Polymorphism influences singlet fission rates in tetracene thin films

    SciTech Connect

    Arias, Dylan H.; Ryerson, Joseph L.; Cook, Jasper D.; Damrauer, Niels H.; Johnson, Justin C.

    2015-11-06

    Here, we report the effect of crystal structure and crystallite grain size on singlet fission (SF) in polycrystalline tetracene, one of the most widely studied SF and organic semiconductor materials. SF has been comprehensively studied in one polymoprh (Tc I), but not in the other, less stable polymorph (Tc II). Using carefully controlled thermal evaporation deposition conditions and high sensitivity ultrafast transient absorption spectroscopy, we found that for large crystallite size samples, SF in nearly pure Tc II films is significantly faster than SF in Tc I films. We also discovered that crystallite size has a minimal impact on the SF rate in Tc II films, but a significant influence in Tc I films. Large crystallites exhibit SF times of 125 ps and 22 ps in Tc I and Tc II, respectively, whereas small crystallites have SF times of 31 ps and 33 ps. Our results demonstrate first, that attention must be paid to polymorphism in obtaining a self-consistent rate picture for SF in tetracene and second, that control of polymorphism can play a significant role towards achieving a mechanistic understanding of SF in polycrystalline systems. In this latter context we show that conventional theory based on non-covalent tetracene couplings is insufficient, thus highlighting the need for models that capture the delocalized and highly mobile nature of excited states in elucidating the full photophysical picture.

  3. Polymorphism influences singlet fission rates in tetracene thin films

    DOE PAGESBeta

    Arias, Dylan H.; Ryerson, Joseph L.; Cook, Jasper D.; Damrauer, Niels H.; Johnson, Justin C.

    2015-11-06

    Here, we report the effect of crystal structure and crystallite grain size on singlet fission (SF) in polycrystalline tetracene, one of the most widely studied SF and organic semiconductor materials. SF has been comprehensively studied in one polymoprh (Tc I), but not in the other, less stable polymorph (Tc II). Using carefully controlled thermal evaporation deposition conditions and high sensitivity ultrafast transient absorption spectroscopy, we found that for large crystallite size samples, SF in nearly pure Tc II films is significantly faster than SF in Tc I films. We also discovered that crystallite size has a minimal impact on themore » SF rate in Tc II films, but a significant influence in Tc I films. Large crystallites exhibit SF times of 125 ps and 22 ps in Tc I and Tc II, respectively, whereas small crystallites have SF times of 31 ps and 33 ps. Our results demonstrate first, that attention must be paid to polymorphism in obtaining a self-consistent rate picture for SF in tetracene and second, that control of polymorphism can play a significant role towards achieving a mechanistic understanding of SF in polycrystalline systems. In this latter context we show that conventional theory based on non-covalent tetracene couplings is insufficient, thus highlighting the need for models that capture the delocalized and highly mobile nature of excited states in elucidating the full photophysical picture.« less

  4. A theoretical study of the isotope effects on the fluorescence excitation spectrum of 5-aminotropolone

    NASA Astrophysics Data System (ADS)

    Paz, Juan J.; Moreno, Miquel; Lluch, José M.

    1998-05-01

    A combined ab initio+nuclear dynamics study is performed to theoretically analyze the intramolecular H-atom transfer process in 5-aminotropolone in both the ground (S0) and first excited (S1) singlet electronic states. A complete active space self-consistent field (CASSCF) method is used to optimize the geometries. Energies are then corrected through the second order Møller-Plesset perturbation theory. These results are used to build up reduced bidimensional energy surfaces so that the nuclear wave functions for the nuclear motions in both electronic states are obtained. In particular we have analyzed the six isotopomers that result from deuteration of the amino and hydroxy groups of 5-aminotropolone. It is found that for symmetric structures (-OH/-NH2, -OH/-ND2, -OD/-NH2, and -OD/-ND2), the two lowest vibrational levels in both S0 and S1 appear as a quasidegenerated tunneling doublet. The tunneling splitting in S0 is much lower so that the doublet at the origin, seen in the fluorescence excitation spectra of 5-aminotropolone, can be entirely assigned to the S1 state. In agreement with the experimental findings, this splitting greatly diminishes when the transferring hydrogen is substituted by a deuterium, whereas deuteration of the amino group produces only a modest decrease of such a splitting. A quite different result is found for the nonsymmetric isotopically substituted structures (-OH/-NHD and -OD/-NHD), as the isotope induced asymmetry, combined with the high energy barrier in the S0 potential energy surface, leads to a complete localization of the two lowest vibrational wave functions in S0. On the other hand, for S1 the asymmetry and energy barriers are low enough so that an important degree of delocalization of the two lowest vibrational wave functions is found. These results are again in agreement with the presence of an isotope induced quartet in the fluorescence excitation spectra of these species.

  5. Electron, Hole, Singlet, and Triplet Energy Transfer in Photoexcited Porphyrin-Naphthalenediimide Dyads.

    PubMed

    Yushchenko, Oleksandr; Hangarge, Rahul V; Mosquera-Vazquez, Sandra; Boshale, Sheshanath V; Vauthey, Eric

    2015-06-18

    The excited-state dynamics of two molecular dyads, consisting of zinc (1) and free-base (2) porphyrin connected via a peptide linker to a core-substituted naphthalenediimide (NDI) have been investigated using optical spectroscopy. These dyads exhibit rich photophysics because of the large number of electronic excited states below 3 eV. In the case of 1 in apolar solvents, excitation energy transfer from the vibrationally hot singlet excited porphyrin to the NDI takes place with a 500 fs time constant. Electronic energy ends up in the NDI-localized triplet state, which decays to the ground state on a microsecond timescale. In polar solvents, ground-state recovery is faster by 5 orders of magnitude because of the occurrence of charge separation followed by recombination. On the other hand, excitation energy transfer in 2 takes place in the opposite direction, namely from the NDI to the porphyrin, which then undergoes intersystem crossing to the triplet state, followed by triplet energy transfer back to the NDI. Therefore, four distinct local electronic excited states are consecutively populated after excitation of the NDI unit of 2, with the energy shuttling between the two ends of the dyad. PMID:25418961

  6. Ground- and excited-state diatomic bond lengths, vibrational levels, and potential-energy curves from conventional and localized Hartree-Fock-based density-functional theory

    NASA Astrophysics Data System (ADS)

    Teale, Andrew M.; Tozer, David J.

    2005-01-01

    Ground- and excited-state diatomic bond lengths, vibrational levels, and potential-energy curves are determined using conventional and localized Hartree-Fock (LHF)-based density-functional theory. Exchange only and hybrid functionals (with various fractions of exchange) are considered, together with a standard generalized gradient approximation (GGA). Ground-state bond lengths and vibrational wave numbers are relatively insensitive to whether orbital exchange is treated using the conventional or LHF approach. Excited-state calculations are much more sensitive. For a standard fraction of orbital exchange, N2 and CO vertical excitation energies at experimental bond lengths are accurately described by both conventional and LHF-based approaches, providing an asymptotic correction is present. Excited-state bond lengths and vibrational levels are more accurate with the conventional approach. The best quality, however, is obtained with an asymptotically corrected GGA functional. For the ground and lowest four singlet excited states, the GGA mean absolute errors in bond lengths are 0.006 Å (0.5%) and 0.011 Å (0.8%) for N2 and CO, respectively. Mean absolute errors in fundamental vibrational wavenumbers are 49 cm-1 (2.7%) and 68 cm-1 (5.0%), respectively. The GGA potential-energy curves are compared with near-exact Rydberg-Klein-Rees curves. Agreement is very good for the ground and first excited state, but deteriorates for the higher states.

  7. Singlet oxygen detection in water by means of digital holography and digital holographic tomography

    NASA Astrophysics Data System (ADS)

    Belashov, A. V.; Petrov, N. V.; Semenova, I. V.; Vasyutinskii, O. S.

    2016-04-01

    The paper presents results on singlet oxygen detection in aqueous solutions of a photosensitizer based on the reconstruction of 3D temperature gradients resulting from nonradiative deactivation of excited oxygen molecules. 3D temperature distributions were reconstructed by means of the inverse Abel transformation from a single digital hologram in the case of cylindrically symmetric distribution of the temperature gradient and using holographic tomography algorithm with filtered back projection in the case of nonsymmetrical distribution. Major features of the applied techniques are discussed and results obtained by the two methods are compared.

  8. Supersymmetric Higgs singlet effects on FCNC observables

    SciTech Connect

    Hodgkinson, Robert N.

    2008-11-23

    Higgs singlet superflelds, usually present in extensions of the Minimal Supersymmetric Standard Model (MSSM) which address the {mu}-problem, such as the Next-to-Minimal Supersymmetric Standard Model (NMSSM) and the Minimal Nonminimal Supersymmetric Standard Model (mnSSM), can have significant contributions to B-meson flavour-changing neutral current observables for large values of tan{beta} > or approx. 50. Illustrative results are presented including effects on the B{sub s} and on the rare decay B{sub s}{yields}{mu}{sup +}{mu}{sup -}. In particular, we find that in the NMSSM, the branching ratio for B{sub s}{yields}{mu}{sup +}{mu}{sup -} can be enhanced or even suppressed with respect to the Standard Model prediction by more than one order of magnitude.

  9. Molecular dynamics of excited state intramolecular proton transfer: 3-hydroxyflavone in solution

    SciTech Connect

    Bellucci, Michael A.; Coker, David F.

    2012-05-21

    The ultrafast enol-keto photoisomerization in the lowest singlet excited state of 3-hydroxyflavone is investigated using classical molecular dynamics in conjunction with empirical valence bond (EVB) potentials for the description of intramolecular interactions, and a molecular mechanics and variable partial charge model, dependent on transferring proton position, for the description of solute-solvent interactions. A parallel multi-level genetic program was used to accurately fit the EVB potential energy surfaces to high level ab initio data. We have studied the excited state intramolecular proton transfer (ESIPT) reaction in three different solvent environments: methylcyclohexane, acetonitrile, and methanol. The effects of the environment on the proton transfer time and the underlying mechanisms responsible for the varied time scales of the ESIPT reaction rates are analyzed. We find that simulations with our EVB potential energy surfaces accurately reproduce experimentally determined reaction rates, fluorescence spectra, and vibrational frequency spectra in all three solvents. Furthermore, we find that the ultrafast ESIPT process results from a combination of ballistic transfer, and intramolecular vibrational redistribution, which leads to the excitation of a set of low frequency promoting vibrational modes. From this set of promoting modes, we find that an O-O in plane bend and a C-H out of plane bend are present in all three solvents, indicating that they are fundamental to the ultrafast proton transfer. Analysis of the slow proton transfer trajectories reveals a solvent mediated proton transfer mechanism, which is diffusion limited.

  10. Vertical and adiabatic electronic excitations in biphenylene: A theoretical study

    NASA Astrophysics Data System (ADS)

    Beck, M. E.; Rebentisch, R.; Hohlneicher, G.; Fülscher, M. P.; Serrano-Andrés, L.; Roos, B. O.

    1997-12-01

    The low-lying singlet states of biphenylene have been studied using ab initio methods. Vertical excitation energies were calculated by multiconfigurational perturbation theory (CASPT2), starting from a complete active space self-consistent field (CASSCF) reference. The geometries of the most important low-lying excited states were individually optimized at the CASSCF level to study the difference between vertical and adiabatic excitations. Extended atomic natural orbital (ANO)-type basis sets were used to calculate state energies. Geometry optimizations were done with smaller ANO-type basis sets. Excitations from the ground state to the 1 1B3g and 1 1B2u excited singlet states lead to pronounced geometry changes which alter the bond alternation pattern. The theoretical results provide a solid basis for the assignment and interpretation of experimental spectra.

  11. Excitation of {sup 1}S and {sup 3}S Metastable Helium Atoms to Doubly Excited States

    SciTech Connect

    Alagia, M.; Coreno, M.; Farrokhpour, H.; Omidyan, R.; Tabrizchi, M.; Franceschi, P.; Mihelic, A.; Zitnik, M.; Moise, A.; Prince, K. C.; Richter, R.; Soederstroem, J.; Stranges, S.

    2009-04-17

    We present spectra of triplet and singlet metastable helium atoms resonantly photoexcited to doubly excited states. The first members of three dipole-allowed {sup 1,3}P{sup o} series have been observed and their relative photoionization cross sections determined, both in the triplet (from 1s2s {sup 3}S{sup e}) and singlet (from 1s2s {sup 1}S{sup e}) manifolds. The intensity ratios are drastically different with respect to transitions from the ground state. When radiation damping is included the results for the singlets are in agreement with theory, while for triplets spin-orbit interaction must also be taken into account.

  12. Excited state properties of naphtho-homologated xxDNA bases and effect of methanol solution, deoxyribose, and base pairing.

    PubMed

    Zhang, Laibin; Ren, Tingqi; Tian, Jianxiang; Yang, Xiuqin; Zhou, Liuzhu; Li, Xiaoming

    2013-04-18

    Design and synthesis of fluorescent nucleobase analogues for studying structures and dynamics of nucleic acids have attracted much attention in recent years. In the present work, a comprehensive theoretical study of electronic transitions of naphtho-homologated base analogues, namely, xxC, xxT, xxA, and xxG, was performed. The nature of the low-lying excited states was discussed, and the results were compared with those of x-bases. Geometrical characteristics of the lowest excited singlet ππ* states were explored using the CIS method. The calculated excitation maxima are 423, 397, 383, and 357 nm for xxA, xxG, xxC, and xxT, respectively, and they are greatly red-shifted compared with x-bases and natural bases, allowing them to be selectively excited in the presence of the natural bases. In the gas phase, the fluorescence from them would be expected to occur around 497, 461, 457, and 417 nm, respectively. The effects of methanol solution, deoxyribose, and base paring with their complementary natural bases on the relevant absorption and emission spectra of these modified bases were also examined.

  13. Singlet Oxygen Generation by Cyclometalated Complexes and Applications†

    PubMed Central

    Ashen-Garry, David; Selke, Matthias

    2014-01-01

    While cyclometalated complexes have been extensively studied for optoelectronic applications, these compounds also represent a relatively new class of photosensitizers for the production of singlet oxygen. Thus far, singlet oxygen generation from cyclometalated Ir and Pt complexes has been studied in detail. In this review, photophysical data for singlet oxygen generation from these complexes is presented, and the mechanism of 1O2 generation is discussed, including evidence for singlet oxygen generation via an electron transfer mechanism for some of cyclometalated Ir complexes. The period from the first report of singlet oxygen generation by a cyclometalated Ir complex in 2002 through August 2013 is covered in this review. This new class of singlet oxygen photosensitizers may prove to be rather versatile due to the ease of substitution of ancillary ligands without loss of activity. Several cyclometalated complexes have been tethered to zeolites, polystyrene, or quantum dots. Applications for photooxygenation of organic molecules, including “traditional” singlet oxygen reactions (ene reaction, [4+2] and [2+2] cycloadditions) as well as oxidative coupling of amines are presented. Potential biomedical applications are also reviewed. PMID:24344628

  14. Fluctuations in Electronic Energy Affecting Singlet Fission Dynamics and Mixing with Charge-Transfer State: Quantum Dynamics Study.

    PubMed

    Fujihashi, Yuta; Ishizaki, Akihito

    2016-02-01

    Singlet fission is a spin-allowed process by which a singlet excited state is converted to two triplet states. To understand mechanisms of the ultrafast fission via a charge transfer (CT) state, one has investigated the dynamics through quantum-dynamical calculations with the uncorrelated fluctuation model; however, the electronic states are expected to experience the same fluctuations induced by the surrounding molecules because the electronic structure of the triplet pair state is similar to that of the singlet state except for the spin configuration. Therefore, the fluctuations in the electronic energies could be correlated, and the 1D reaction coordinate model may adequately describe the fission dynamics. In this work we develop a model for describing the fission dynamics to explain the experimentally observed behaviors. We also explore impacts of fluctuations in the energy of the CT state on the fission dynamics and the mixing with the CT state. The overall behavior of the dynamics is insensitive to values of the reorganization energy associated with the transition from the singlet state to the CT state, although the coherent oscillation is affected by the fluctuations. This result indicates that the mixing with the CT state is rather robust under the fluctuations in the energy of the CT state as well as the high-lying CT state. PMID:26732701

  15. An ab initio investigation of the ground and low-lying singlet and triplet electronic states of XNO{sub 2} and XONO (X = Cl, Br, and I)

    SciTech Connect

    Peterson, Kirk A.; Francisco, Joseph S.

    2014-01-28

    A systematic ab initio treatment of the nitryl halides (XNO{sub 2}) and the cis- and trans- conformers of the halide nitrites (XONO), where X = Cl, Br, and I, have been carried out using highly correlated methods with sequences of correlation consistent basis sets. Equilibrium geometries and harmonic frequencies have been accurately calculated in all cases at the explicitly correlated CCSD(T)-F12b level of theory, including the effects of core-valence correlation for the former. Where experimental values are available for the equilibrium structures (ClNO{sub 2} and BrNO{sub 2}), the present calculations are in excellent agreement; however, the X-O distances are slightly too long by about 0.01 Å due to missing multireference effects. Accurate predictions for the iodine species are made for the first time. The vertical electronic excitation spectra have been calculated using equation-of-motion coupled cluster methods for the low-lying singlet states and multireference configuration interaction for both singlet and triplet states. The latter also included the effects of spin-orbit coupling to provide oscillator strengths for the ground state singlet to excited triplet transitions. While for ClNO{sub 2} the transitions to excited singlet states all occur at wavelengths shorter than 310 nm, there is one longer wavelength singlet transition in BrNO{sub 2} and two in the case of INO{sub 2}. The long wavelength tail in the XNO{sub 2} species is predicted to be dominated by transitions to triplet states. In addition to red-shifting from X = Cl to I, the triplet transitions also increase in oscillator strength, becoming comparable to many of the singlet transitions in the case of INO{sub 2}. Hence in particular, the latter species should be very photolabile. Similar trends are observed and reported for the halogen nitrites, many of which for the first time.

  16. Triple-Singlet Mixing in Si_3: the 1^3A_{1}^{''} - {a}{^3}A{^{'}_2} Transition

    NASA Astrophysics Data System (ADS)

    Zhang, Ruohan; Steimle, Timothy C.

    2013-06-01

    The electronic spectrum of the triplet states of the D_{3h} isomer of Si_3 recorded using both mass selected REMPI and LIF spectroscopy was recently reported. In that same study the dispersed laser induced fluorescence (DLIF) spectra resulting from excitation of various bands in the visible range were recorded. The DLIF spectra exhibited a progression with a 505 cm^{-1} spacing, which was assign to the breathing mode of the D_{3h}, equilateral triangle, Si_{3} molecule. In addition, and quite unexpectedly, the DLIF spectra exhibited a progression having a spacing of 173 cm^{-1}. This progression was tentatively assigned to transition involving the bending mode of the ^1A_1 state of the C_{2v} isomer. A possible explanation for the observation of transitions in the singlet manifold is that upon laser excitation in the D_{3h} triplet manifold there is rapid intersystem crossing to the singlet manifold followed by fluorescence to the ground state of C_{2v} isomer. Here we address the issue of possible intersystem crossing by recording the excitation on DLIF spectra in the present of a static magnetic field. Magnetic fields are known to enhance the singlet-triple mixing. Si_{3} was produced using a supersonic pulsed discharge source (900 V, 20 μs, 6kΩ) with a 1% SiH_{4} in argon mixture. Magnetic fields of approximately 500 and 950 Gauss were applied. We will report the interpretation of the magnetic field induced changes to the LIF and DLIF spectra and the implications for the singlet-triple mixing process. N. J. Reilly, X. Zhuang, V. Gupta, R. Nagarajan, R. C. Fortenberry, J. P. Maier, T. C. Steimle, J. F. Stanton, M. C. McCarthy; {J. Chem. Phys., {136(19)}, 194307, (2004). V. I. Makarov, I. V. Khmelinskii; {Advances in Chemical Phisics, {Volume 118}, 45-98, (2001). thanks

  17. Excited-state relaxation in π-conjugated polymers

    NASA Astrophysics Data System (ADS)

    Frolov, S. V.; Bao, Z.; Wohlgenannt, M.; Vardeny, Z. V.

    2002-05-01

    We study ultrafast relaxation processes of odd- (Bu) and even-parity (Ag) exciton states in poly(p-phenylene vinylene) derivatives. The Bu states are studied using a regular two-beam pump-and-probe spectroscopy, which can monitor vibronic relaxation and exciton diffusion. In order to observe the Ag states, a three-beam femtosecond transient spectroscopy is developed, in which two different excitation pulses successively generate odd-parity (1Bu) excitons at 2.2 eV and then reexcite them to higher Ag states. We are able to distinguish two different classes of Ag states: one class (mAg) experiences ultrafast internal conversion back to the lowest singlet exciton, whereas the other class (kAg) in violation of the Vavilov-Kasha's rule undergoes a different relaxation pathway. The excitons subsequently dissociate into long-lived polaron pairs, which results in emission quenching with the action spectrum similar to that of the intrinsic photoconductivity. We conclude that the Ag states above 3.3 eV (kAg) are charge-transfer states, that mediate carrier photogeneration.

  18. Excited-State Dynamics in 6-THIOGUANOSINE from Femtosecond to Microsecond Time Scale

    NASA Astrophysics Data System (ADS)

    Guo, Cao; Reichardt, Christian; Crespo-Hernández, Carlos E.

    2011-06-01

    6-thioguanine is a widely used pro-drug in which the oxygen atom in the carbonyl group of guanine is replaced by a sulfur atom. Previous studies have shown that patients treated with 6-thioguanine can metabolize and incorporate it in DNA as 6-thioguanosine (6tGuo). These patients show a high incidence of skin cancer when they are exposed to extended periods of sunlight irradiation. In this work, the photodynamics of 6tGuo is investigated by broad band time resolved transient spectroscopy. Similar to previously studied 4-thiothymidine, our results show that excitation of 6tGuo with UVA light at 340 nm results in efficient and ultrafast intersystem crossing to the triplet manifold (τ = 0.31±0.05 ps) and a high triplet quantum yield (φ = 0.8±0.2). The triplet state has a lifetime of 720±10 ns in N2-saturated vs. 460±10 ns in air-saturated aqueous solution. In addition, a minor picosecond deactivation channel (80±15 ps) is observed, which is tentatively assigned to internal conversion from the lowest-energy excited singlet state to the ground state. Quantum chemical calculations support the proposed kinetic model. Based on the high triplet quantum yield measured, it is proposed that the phototoxicity of 6tGuo is due to its ability to photosensitized singlet oxygen, which can result in oxidative damage to DNA. P. O'Donovan, C. M. Perrett, X. Zhang, B. Montaner, Y.-Z. Xu, C. A. Harwood, J. M. McGregor, S. L. Walker, F. Hanaoka, P. Karran, Science 309, 1871 (2005). C. Reichardt, C. Guo, C. E. Crespo-Hernández, J. Phys. Chem. B. in press (2011). C. Reichardt, C. E. Crespo-Hernández, J. Phys. Chem. Lett. 1, 2239 (2010) C. Reichardt, C. E. Crespo-Hernández, Chem. Comm. 46, 5963 (2010).

  19. Light-Harvesting Photosensitizers for Photodynamic Inactivation of Bacteria under Both Visible and Near-Infrared Excitations.

    PubMed

    Hu, Bo; Cao, Xian; Ahmadov, Ms Tevhide Ozkaya; Ding, Rui; Tang, Hong; Zhang, Peng

    2016-04-01

    We report a hybrid singlet oxygen production system, where strong resonance coupling between plasmonic nanoparticles and photosensitizing molecules results in exceptionally high singlet oxygen production under both visible light and near-infrared light excitation, even for the photosensitizing molecules without near-infrared absorption. The light-harvesting property of the plasmon-photosensitizer hybrids leads to an enhanced, broad-spectrum photodynamic inactivation of bacteria under a wide range of excitations, including that with near-infrared light.

  20. Cryogenic exciter

    SciTech Connect

    Bray, James William; Garces, Luis Jose

    2012-03-13

    The disclosed technology is a cryogenic static exciter. The cryogenic static exciter is connected to a synchronous electric machine that has a field winding. The synchronous electric machine is cooled via a refrigerator or cryogen like liquid nitrogen. The static exciter is in communication with the field winding and is operating at ambient temperature. The static exciter receives cooling from a refrigerator or cryogen source, which may also service the synchronous machine, to selected areas of the static exciter and the cooling selectively reduces the operating temperature of the selected areas of the static exciter.

  1. Oxygen pressure measurement using singlet oxygen emission

    SciTech Connect

    Khalil, Gamal E.; Chang, Alvin; Gouterman, Martin; Callis, James B.; Dalton, Larry R.; Turro, Nicholas J.; Jockusch, Steffen

    2005-05-15

    Pressure sensitive paint (PSP) provides a visualization of two-dimensional pressure distributions on airfoil and model automobile surfaces. One type of PSP utilizes platinum tetra(pentafluorophenyl)porphine (PtTFPP) dissolved in a fluoro-polymer film. Since the intense 650 nm triplet emission of PtTFPP is quenched by ground state oxygen, it is possible to measure two-dimensional oxygen concentration from the 650 nm emission intensity using a Stern-Volmer-type relationship. This article reports an alternative luminescence method to measure oxygen concentration based on the porphyrin-sensitized 1270 nm singlet oxygen emission, which can be imaged with an InGaAs near infrared camera. This direct measurement of oxygen emission complements and further validates the oxygen measurement based on PtTFPP phosphorescence quenching. Initial success at obtaining a negative correlation between the 650 nm PtTFPP emission and the 1270 nm O{sub 2} emission in solution led us to additional two-dimensional film studies using surfaces coated with PtTFPP, MgTFPP, and H{sub 2}TFPP in polymers in a pressure and temperature controlled chamber.

  2. Oxygen pressure measurement using singlet oxygen emission

    NASA Astrophysics Data System (ADS)

    Khalil, Gamal E.; Chang, Alvin; Gouterman, Martin; Callis, James B.; Dalton, Larry R.; Turro, Nicholas J.; Jockusch, Steffen

    2005-05-01

    Pressure sensitive paint (PSP) provides a visualization of two-dimensional pressure distributions on airfoil and model automobile surfaces. One type of PSP utilizes platinum tetra(pentafluorophenyl)porphine (PtTFPP) dissolved in a fluoro-polymer film. Since the intense 650nm triplet emission of PtTFPP is quenched by ground state oxygen, it is possible to measure two-dimensional oxygen concentration from the 650nm emission intensity using a Stern-Volmer-type relationship. This article reports an alternative luminescence method to measure oxygen concentration based on the porphyrin-sensitized 1270nm singlet oxygen emission, which can be imaged with an InGaAs near infrared camera. This direct measurement of oxygen emission complements and further validates the oxygen measurement based on PtTFPP phosphorescence quenching. Initial success at obtaining a negative correlation between the 650nm PtTFPP emission and the 1270nm O2 emission in solution led us to additional two-dimensional film studies using surfaces coated with PtTFPP, MgTFPP, and H2TFPP in polymers in a pressure and temperature controlled chamber.

  3. Pulsed diode laser-based monitor for singlet molecular oxygen

    PubMed Central

    Lee, Seonkyung; Zhu, Leyun; Minhaj, Ahmed M.; Hinds, Michael F.; Vu, Danthu H.; Rosen, David I.; Davis, Steven J.; Hasan, Tayyaba

    2010-01-01

    Photodynamic therapy (PDT) is a promising cancer treatment. PDT uses the affinity of photosensitizers to be selectively retained in malignant tumors. When tumors, pretreated with the photosensitizer, are irradiated with visible light, a photochemical reaction occurs and tumor cells are destroyed. Oxygen molecules in the metastable singlet delta state O2(1Δ) are believed to be the species that destroys cancerous cells during PDT. Monitoring singlet oxygen produced by PDT may lead to more precise and effective PDT treatments. Our approach uses a pulsed diode laser-based monitor with optical fibers and a fast data acquisition system to monitor singlet oxygen during PDT. We present results of in vitro singlet oxygen detection in solutions and in a rat prostate cancer cell line as well as PDT mechanism modeling. PMID:18601555

  4. Pulsed diode laser-based monitor for singlet molecular oxygen.

    PubMed

    Lee, Seonkyung; Zhu, Leyun; Minhaj, Ahmed M; Hinds, Michael F; Vu, Danthu H; Rosen, David I; Davis, Steven J; Hasan, Tayyaba

    2008-01-01

    Photodynamic therapy (PDT) is a promising cancer treatment. PDT uses the affinity of photosensitizers to be selectively retained in malignant tumors. When tumors, pretreated with the photosensitizer, are irradiated with visible light, a photochemical reaction occurs and tumor cells are destroyed. Oxygen molecules in the metastable singlet delta state O2(1Delta) are believed to be the species that destroys cancerous cells during PDT. Monitoring singlet oxygen produced by PDT may lead to more precise and effective PDT treatments. Our approach uses a pulsed diode laser-based monitor with optical fibers and a fast data acquisition system to monitor singlet oxygen during PDT. We present results of in vitro singlet oxygen detection in solutions and in a rat prostate cancer cell line as well as PDT mechanism modeling.

  5. A tandem mass spectrometric method for singlet oxygen measurement.

    PubMed

    Karonen, Maarit; Mattila, Heta; Huang, Ping; Mamedov, Fikret; Styring, Stenbjörn; Tyystjärvi, Esa

    2014-01-01

    Singlet oxygen, a harmful reactive oxygen species, can be quantified with the substance 2,2,6,6-tetramethylpiperidine (TEMP) that reacts with singlet oxygen, forming a stable nitroxyl radical (TEMPO). TEMPO has earlier been quantified with electron paramagnetic resonance (EPR) spectroscopy. In this study, we designed an ultra-high-performance liquid chromatographic-tandem mass spectrometric (UHPLC-ESI-MS/MS) quantification method for TEMPO and showed that the method based on multiple reaction monitoring (MRM) can be used for the measurements of singlet oxygen from both nonbiological and biological samples. Results obtained with both UHPLC-ESI-MS/MS and EPR methods suggest that plant thylakoid membranes produce 3.7 × 10(-7) molecules of singlet oxygen per chlorophyll molecule in a second when illuminated with the photosynthetic photon flux density of 2000 μmol m(-2 ) s(-1). PMID:24849296

  6. Singlet Exciton Fission in Nanostructured Organic Solar Cells

    SciTech Connect

    Jadhav, P. J.; Mohanty, A.; Sussman, J.; Baldo, Marc

    2011-04-13

    Singlet exciton fission is an efficient multiexciton generation process in organic molecules. But two concerns must be satisfied before it can be exploited in low-cost solution-processed organic solar cells. Fission must be combined with longer wavelength absorption in a structure that can potentially surpass the single junction limit, and its efficiency must be demonstrated in nanoscale domains within blended devices. Here, we report organic solar cells comprised of tetracene, copper phthalocyanine, and the buckyball C{sub 6}0. Short wavelength light generates singlet excitons in tetracene. These are subsequently split into two triplet excitons and transported through the phthalocyanine. In addition, the phthalocyanine absorbs photons below the singlet exciton energy of tetracene. To test tetracene in nanostructured blends, we fabricate coevaporated bulk heterojunctions and multilayer heterojunctions of tetracene and C{sub 60}. We measure a singlet fission efficiency of (71 ± 18)%, demonstrating that exciton fission can efficiently compete with exciton dissociation on the nanoscale.

  7. Singlet Oxygen in Aqueous Solution: A Lecture Demonstration

    ERIC Educational Resources Information Center

    Shakhashiri, Bassam Z.; Williams, Lloyd G.

    1976-01-01

    Describes a demonstration that illustrates the red chemiluminescence due to singlet molecular oxygen that can be observed when aqueous solutions of hypochlorite ion and hydrogen peroxide are mixed. (MLH)

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

    NASA Astrophysics Data System (ADS)

    Davari, N.; Åstrand, P.-O.; Unge, M.; Lundgaard, L. E.; Linhjell, D.

    2014-03-01

    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.

  9. Nanostructured singlet fission photovoltaics subject to triplet-charge annihilation.

    PubMed

    Thompson, Nicholas J; Hontz, Eric; Congreve, Daniel N; Bahlke, Matthias E; Reineke, Sebastian; Van Voorhis, Troy; Baldo, Marc A

    2014-03-01

    Singlet exciton fission is an efficient multiple-exciton generation process that is vulnerable to a characteristic loss process: triplet-charge annihilation. This loss process is characterized in singlet-fission photovoltaics and losses as high as 40% are observed in poorly designed devices. Techniques are demonstrated to improve charge extraction and reduce triplet-charge annihilation to negligible levels at short-circuit conditions. PMID:24281738

  10. [Decrease of singlet oxygen chemiluminescence by the presence of carnosine].

    PubMed

    Svachko, A G; Formaziuk, V E; Sergienko, V I

    1990-08-01

    To test antiradical medicines effect the chemical production of singlet oxygen (NaClO + H2O2) was investigated. The quantity singlet oxygen chemiluminescence was decreased in the presence of Japanese Catalin and Chine Baineiting, antirheumatic Voltaren and less strong Finish Catachrome and Carnosine. American Quinax does not possess such an effect. One of the possible starting mechanisms causing different diseases (atherosclerosis, cataract etc.) is destruction of biomembranes by active forms of oxygen.

  11. Computational Evidence of Inversion of (1)La and (1)Lb-Derived Excited States in Naphthalene Excimer Formation from ab Initio Multireference Theory with Large Active Space: DMRG-CASPT2 Study.

    PubMed

    Shirai, Soichi; Kurashige, Yuki; Yanai, Takeshi

    2016-05-10

    The naphthalene molecule has two important lowest-lying singlet excited states, denoted (1)La and (1)Lb. Association of the excited and ground state monomers yields a metastable excited dimer (excimer), which emits characteristic fluorescence. Here, we report a first computational result based on ab initio theory to corroborate that the naphthalene excimer fluorescence is (1)La parentage, resulting from inversion of (1)La and (1)Lb-derived dimer states. This inversion was hypothesized by earlier experimental studies; however, it has not been confirmed rigorously. In this study, the advanced multireference (MR) theory based on the density matrix renormalization group that enables using unprecedented large-size active space for describing significant electron correlation effects is used to provide accurate potential energy curves (PECs) of the excited states. The results evidenced the inversion of the PECs and accurately predicted transition energies for excimer fluorescence and monomer absorption. Traditional MR calculations with smaller active spaces and single-reference theory calculations exhibit serious inconsistencies with experimental observations.

  12. Charge separated states and singlet oxygen generation of mono and bis adducts of C60 and C70

    NASA Astrophysics Data System (ADS)

    Dallas, Panagiotis; Rogers, Gregory; Reid, Ben; Taylor, Robert A.; Shinohara, Hisanori; Briggs, G. Andrew D.; Porfyrakis, Kyriakos

    2016-02-01

    We present a series of fullerene derivatives and a study on their photoluminescence properties, complete with their efficiency as singlet oxygen generation photosensitizers. We demonstrate the intramolecular charge transfer between pyrene donor and fullerene acceptor. The opposite effect in decay lifetime measurements is observed for the mono and bis adducts of C60 and C70 for the first time, indicating an interplay between charge-separation and locally excited states. A monoexponential decay was observed for the mono adduct of C60 and the bis adduct of C70, while a biexponential decay was observed for the bis adduct of C60 and the mono adduct of C70. The effect of these molecules as sensitizers of the singlet oxygen radical was tested using detailed 3D excitation photoluminescence maps. A quenching of the singlet oxygen for the C60-mono and C70-bis adducts was observed while a strong photosensitizing effect was observed for the C60-bis and C70-mono adducts.

  13. Guanidine and guanidinium cation in the excited state—theoretical investigation

    SciTech Connect

    Antol, Ivana Glasovac, Zoran; Crespo-Otero, Rachel; Barbatti, Mario

    2014-08-21

    Diverse ab initio and density-functional-theory methods were used to investigate geometries, energies, and electronic absorption spectra of guanidine and its protonated form, as well as their photo-deactivation processes. It was shown that the guanidine is a weakly absorbing species with the excitation spectrum consisting mostly of transitions to the Rydberg excited states and one valence n-π{sub 4} state. The lowest energy band has a maximum at ca. 6.9 eV (∼180 nm). The protonation of guanidine affects its excitation spectrum substantially. A major shift of the Rydberg states to higher energies is clearly visible and strongly absorbing transitions from the ground state to the π{sub 3}-π{sub 4} and π{sub 2}-π{sub 4} states appears at 7.8 eV (∼160 nm). Three low-lying conical intersections (two for guanidine and one for protonated guanidine) between the ground state and the first excited singlet state were located. They are accessible from the Franck–Condon region through amino N–H stretching and out-of-plane deformations in guanidine and protonated guanidine, respectively. The relaxation of the π{sub 3}-3s Rydberg state via amino N–H bond stretching was hindered by a barrier. The nondissociated conical intersection in protonated guanidine mediates the radiationless deactivation of the compound after excitation into the π{sub 3}-π{sub 4} state. This fact is detrimental for the photostability of guanidine, since its conjugate acid is stable in aqueous solution over a wide pH range and in protein environment, where guanidinium moiety in arginine is expected to be in a protonated form.

  14. Guanidine and guanidinium cation in the excited state—theoretical investigation

    NASA Astrophysics Data System (ADS)

    Antol, Ivana; Glasovac, Zoran; Crespo-Otero, Rachel; Barbatti, Mario

    2014-08-01

    Diverse ab initio and density-functional-theory methods were used to investigate geometries, energies, and electronic absorption spectra of guanidine and its protonated form, as well as their photo-deactivation processes. It was shown that the guanidine is a weakly absorbing species with the excitation spectrum consisting mostly of transitions to the Rydberg excited states and one valence n-π4 state. The lowest energy band has a maximum at ca. 6.9 eV (˜180 nm). The protonation of guanidine affects its excitation spectrum substantially. A major shift of the Rydberg states to higher energies is clearly visible and strongly absorbing transitions from the ground state to the π3-π4 and π2-π4 states appears at 7.8 eV (˜160 nm). Three low-lying conical intersections (two for guanidine and one for protonated guanidine) between the ground state and the first excited singlet state were located. They are accessible from the Franck-Condon region through amino N-H stretching and out-of-plane deformations in guanidine and protonated guanidine, respectively. The relaxation of the π3-3s Rydberg state via amino N-H bond stretching was hindered by a barrier. The nondissociated conical intersection in protonated guanidine mediates the radiationless deactivation of the compound after excitation into the π3-π4 state. This fact is detrimental for the photostability of guanidine, since its conjugate acid is stable in aqueous solution over a wide pH range and in protein environment, where guanidinium moiety in arginine is expected to be in a protonated form.

  15. Singlet oxygen-sensitized delayed fluorescence of common water-soluble photosensitizers.

    PubMed

    Scholz, Marek; Dědic, Roman; Breitenbach, Thomas; Hála, Jan

    2013-10-01

    Six common water-soluble singlet oxygen ((1)O2) photosensitizers - 5,10,15,20-tetrakis(1-methyl-4-pyridinio) porphine (TMPyP), meso-tetrakis(4-sulfonathophenyl)porphine (TPPS4), Al(III) phthalocyanine chloride tetrasulfonic acid (AlPcS4), eosin Y, rose bengal, and methylene blue - were investigated in terms of their ability to produce delayed fluorescence (DF) in solutions at room temperature. All the photosensitizers dissolved in air-saturated phosphate buffered saline (PBS, pH 7.4) exhibit easily detectable DF, which can be nearly completely quenched by 10 mM NaN3, a specific (1)O2 quencher. The DF kinetics has a biexponential rise-decay character in a microsecond time domain. Therefore, we propose that singlet oxygen-sensitized delayed fluorescence (SOSDF), where the triplet state of a photosensitizer reacts with (1)O2 giving rise to an excited singlet state of the photosensitizer, is the prevailing mechanism. It was confirmed by additional evidence, such as a monoexponential decay of triplet-triplet transient absorption kinetics, dependence of SOSDF kinetics on oxygen concentration, absence of SOSDF in a nitrogen-saturated sample, or the effect of isotopic exchange H2O-D2O. Eosin Y and AlPcS4 show the largest SOSDF quantum yield among the selected photosensitizers, whereas rose bengal possesses the highest ratio of SOSDF intensity to prompt fluorescence intensity. The rate constant for the reaction of triplet state with (1)O2 giving rise to the excited singlet state of photosensitizer was estimated to be ~/>1 × 10(9) M(-1) s(-1). SOSDF kinetics contains information about both triplet and (1)O2 lifetimes and concentrations, which makes it a very useful alternative tool for monitoring photosensitizing and (1)O2 quenching processes, allowing its detection in the visible spectral region, utilizing the photosensitizer itself as a (1)O2 probe. Under our experimental conditions, SOSDF was up to three orders of magnitude more intense than the infrared (1)O2

  16. Higher Order π-Conjugated Polycyclic Hydrocarbons with Open-Shell Singlet Ground State: Nonazethrene versus Nonacene.

    PubMed

    Huang, Rui; Phan, Hoa; Herng, Tun Seng; Hu, Pan; Zeng, Wangdong; Dong, Shao-Qiang; Das, Soumyajit; Shen, Yongjia; Ding, Jun; Casanova, David; Wu, Jishan

    2016-08-17

    Higher order acenes (i.e., acenes longer than pentacene) and extended zethrenes (i.e., zethrenes longer than zethrene) are theoretically predicted to have an open-shell singlet ground state, and the radical character is supposed to increase with extension of molecular size. The increasing radical character makes the synthesis of long zethrenes and acenes very challenging, and so far, the longest reported zethrene and acene derivatives are octazethrene and nonacene, respectively. In addition, there is a lack of fundamental understanding of the differences between these two closely related open-shell singlet systems. In this work, we report the first synthesis of a challenging nonazethrene derivative, HR-NZ, and its full structural and physical characterizations including variable temperature NMR, ESR, SQUID, UV-vis-NIR absorption and electrochemical measurements. Compound HR-NZ has an open-shell singlet ground state with a moderate diradical character (y0 = 0.48 based on UCAM-B3LYP calculation) and a small singlet-triplet gap (ΔES-T = -5.2 kcal/mol based on SQUID data), thus showing magnetic activity at room temperature. It also shows amphoteric redox behavior, with a small electrochemical energy gap (1.33 eV). Its electronic structure and physical properties are compared with those of Anthony's nonacene derivative JA-NA and other zethrene derivatives. A more general comparison between higher order acenes and extended zethrenes was also conducted on the basis of ab initio electronic structure calculations, and it was found that zethrenes and acenes have very different spatial localization of the unpaired electrons. As a result, a faster decrease of singlet-triplet energy gap and a faster increase of radical character with increase of the number of benzenoid rings were observed in zethrene series. Our studies reveal that spatial localization of the frontier molecular orbitals play a very important role on the nature of radical character as well as the excitation

  17. Accurate adiabatic singlet-triplet gaps in atoms and molecules employing the third-order spin-flip algebraic diagrammatic construction scheme for the polarization propagator

    NASA Astrophysics Data System (ADS)

    Lefrancois, Daniel; Rehn, Dirk R.; Dreuw, Andreas

    2016-08-01

    For the calculation of adiabatic singlet-triplet gaps (STG) in diradicaloid systems the spin-flip (SF) variant of the algebraic diagrammatic construction (ADC) scheme for the polarization propagator in third order perturbation theory (SF-ADC(3)) has been applied. Due to the methodology of the SF approach the singlet and triplet states are treated on an equal footing since they are part of the same determinant subspace. This leads to a systematically more accurate description of, e.g., diradicaloid systems than with the corresponding non-SF single-reference methods. Furthermore, using analytical excited state gradients at ADC(3) level, geometry optimizations of the singlet and triplet states were performed leading to a fully consistent description of the systems, leading to only small errors in the calculated STGs ranging between 0.6 and 2.4 kcal/mol with respect to experimental references.

  18. Accurate adiabatic singlet-triplet gaps in atoms and molecules employing the third-order spin-flip algebraic diagrammatic construction scheme for the polarization propagator.

    PubMed

    Lefrancois, Daniel; Rehn, Dirk R; Dreuw, Andreas

    2016-08-28

    For the calculation of adiabatic singlet-triplet gaps (STG) in diradicaloid systems the spin-flip (SF) variant of the algebraic diagrammatic construction (ADC) scheme for the polarization propagator in third order perturbation theory (SF-ADC(3)) has been applied. Due to the methodology of the SF approach the singlet and triplet states are treated on an equal footing since they are part of the same determinant subspace. This leads to a systematically more accurate description of, e.g., diradicaloid systems than with the corresponding non-SF single-reference methods. Furthermore, using analytical excited state gradients at ADC(3) level, geometry optimizations of the singlet and triplet states were performed leading to a fully consistent description of the systems, leading to only small errors in the calculated STGs ranging between 0.6 and 2.4 kcal/mol with respect to experimental references. PMID:27586899

  19. 48 CFR 47.306-2 - Lowest overall transportation costs.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... transportation costs. 47.306-2 Section 47.306-2 Federal Acquisition Regulations System FEDERAL ACQUISITION REGULATION CONTRACT MANAGEMENT TRANSPORTATION Transportation in Supply Contracts 47.306-2 Lowest overall transportation costs. (a) For the evaluation of offers, the transportation officer shall give to the...

  20. 48 CFR 47.306-2 - Lowest overall transportation costs.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... transportation costs. 47.306-2 Section 47.306-2 Federal Acquisition Regulations System FEDERAL ACQUISITION REGULATION CONTRACT MANAGEMENT TRANSPORTATION Transportation in Supply Contracts 47.306-2 Lowest overall transportation costs. (a) For the evaluation of offers, the transportation officer shall give to the...

  1. 48 CFR 47.306-2 - Lowest overall transportation costs.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... transportation costs. 47.306-2 Section 47.306-2 Federal Acquisition Regulations System FEDERAL ACQUISITION REGULATION CONTRACT MANAGEMENT TRANSPORTATION Transportation in Supply Contracts 47.306-2 Lowest overall transportation costs. (a) For the evaluation of offers, the transportation officer shall give to the...

  2. 48 CFR 47.306-2 - Lowest overall transportation costs.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... transportation costs. 47.306-2 Section 47.306-2 Federal Acquisition Regulations System FEDERAL ACQUISITION REGULATION CONTRACT MANAGEMENT TRANSPORTATION Transportation in Supply Contracts 47.306-2 Lowest overall transportation costs. (a) For the evaluation of offers, the transportation officer shall give to the...

  3. 48 CFR 47.306-2 - Lowest overall transportation costs.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... transportation costs. 47.306-2 Section 47.306-2 Federal Acquisition Regulations System FEDERAL ACQUISITION REGULATION CONTRACT MANAGEMENT TRANSPORTATION Transportation in Supply Contracts 47.306-2 Lowest overall transportation costs. (a) For the evaluation of offers, the transportation officer shall give to the...

  4. Singlet photochemistry in model photosynthesis: Identification of charge separated intermediates by Fourier transform and CW-EPR spectroscopies

    SciTech Connect

    Hasharoni, K.; Levanon, H. Hebrew Univ. of Jerusalem ); Tang, Jau; Bowman, M.K.; Norris, J.R. ); Gust, D.; Moore, T.A.; Moore, A.L. )

    1990-08-29

    Intramolecular electron transfer from the photoexcited state of a carotenoid-porphyrin-diquinone tetrad was studied by selective laser excitation with both Fourier transform and CW EPR spectroscopies. It is shown that the electron transfer occurs from the singlet state of the porphyrin constituent to produce the terminal benzoquinone radical anion and the carotenoid radical cation. This tetrad molecule can maintain the charge-separated state for a substantial period of time ({approximately} 1 {mu}s), allowing the characterization of the short-lived radicals. The derivative-like spectrum of the quinone radical anion and its dependence on the turning angle of the microwave pulse indicates that electron transfer proceeds via the singlet state.

  5. Direct measurement of singlet oxygen by using a photomultiplier tube-based detection system.

    PubMed

    Kim, In-Wook; Park, Jae Myung; Roh, Yoon Jin; Kim, Ju Hee; Choi, Myung-Gyu; Hasan, Tayyaba

    2016-06-01

    The effective dosimetry for photodynamic therapy (PDT) can be specified by direct measurement of singlet oxygen ((1)O2) production. The purpose of this study was to investigate the feasibility of a newly developed photomultiplier tube (PMT)-based singlet oxygen detection (SOD) system. The lowest and highest (1)O2 concentrations detectable by the PMT-SOD system were 15nM and 10μM, respectively. Dose-dependent quenching, by NaN3, of the fluorogenic reaction was observed, which was negatively correlated with the (1)O2 level measured by the PMT-SOD system. The lifetime of (1)O2, as measured by the PMT-SOD system, was found to be lengthened when H2O was replaced with deuterium oxide. (1)O2 photon counts were significantly and dose-dependently correlated with intracellular fluorescence intensity after photosensitizer treatments. In vitro cell viability test and in vivo xenografted-tumor mass shrinkage showed a positive association between PDT-induced cytotoxicity and (1)O2 production concomitantly measured by the PMT-SOD system. It was concluded that the PMT-SOD system is capable of measuring (1)O2 production directly and accurately, demonstrating that this system can be useful in the determination of dosimetry for PDT. PMID:26995671

  6. The Nature of the Singlet and Triplet States of Cyclobutadiene as Revealed by Quantum Interference.

    PubMed

    Fantuzzi, Felipe; Cardozo, Thiago M; Nascimento, Marco A C

    2016-01-18

    The generalized product function energy partitioning (GPF-EP) method is applied to the description of the cyclobutadiene molecule. The GPF wave function was built to reproduce generalized valence bond (GVB) and spin-coupled (SC) wave functions. The influence of quasiclassical and quantum interference contributions to each chemical bond of the system are analyzed along the automerization reaction coordinate for the lowest singlet and triplet states. The results show that the interference effect on the π space reduces the electronic energy of the singlet cyclobutadiene relative to the second-order Jahn-Teller distortion, which takes the molecule from a D4h to a D2h structure. Our results also suggest that the π space of the (1) B1g state of the square cyclobutadiene is composed of a weak four center-four electron bond, whereas the (3) A2g state has a four center-two electron π bond. Finally, we also show that, although strain effects are nonnegligible, the thermodynamics of the main decomposition pathway of cyclobutadiene in the gas phase is dominated by the π space interference.

  7. Interactions of dietary carotenoids with activated (singlet) oxygen and free radicals: potential effects for human health.

    PubMed

    Böhm, Fritz; Edge, Ruth; Truscott, George

    2012-02-01

    Molecular mechanisms associated with the anti-/pro-oxidative properties of carotenoids (CARs) are described in organic solvents, micro-heterogeneous environments and model lipid membranes and in cellular suspensions. Singlet oxygen is important in the skin and eye and CARs are efficient singlet oxygen (SO) quenchers with corresponding rate constants near diffusion controlled (typically app. 10¹⁰ M⁻¹ s⁻¹) with lycopene (LYC) exhibiting the most efficient quenching in organic solvents. However, in membrane environments there is little or no difference in the quenching efficiency between the dietary CARs. Furthermore, aggregation of CARs, particularly those in the macula (lutein and zeaxanthin), markedly reduces SO quenching efficiency. Free radical interactions with CARs leads to at least three processes, electron and hydrogen atom transfer and adduct formation. The most studied is electron transfer where the CAR loses an electron to become a radical cation. The reactivity/lifetime of such CAR radicals may lead to a switch from anti- to pro-oxidant behaviour of CARs. These reactions are related to CAR redox potentials with LYC being the lowest (most easily oxidised) allowing LYC to reduce/repair all other CAR radical cations and LYC 'sacrificed' where mixtures of CARs are present in oxidative environments. Such redox-controlled reactions may lead to deleterious as well as beneficial health effects.

  8. Collisionally-Mediated Singlet-Triplet Crossing in ˜{a}1A1 CH_2 Revisited: (010) Coupling

    NASA Astrophysics Data System (ADS)

    Le, Anh T.; Hall, Gregory; Sears, Trevor

    2014-06-01

    Methylene, CH2, possesses a ground ˜{X}3B1 ground electronic state and an excited ˜{a}1A1 state only 3150cm-1 higher in energy. The collision-induced singlet-triplet crossing in the gaseous mixtures is important in determining overall reaction rates and chemical behavior. Accidental near-degeneracies between rotational levels of the singlet state and the vibrationally excited triplet state result in a few gateway rotational levels that mediate collision-induced intersystem crossing. The mixed states can be recognized and quantified by deperturbation, knowing the zero-order singlet and triplet energy levels. Hyperfine structure can be used as alternative indicator of singlet-triplet mixing. Non-zero mixing will induce hyperfine splittings intermediate between the unresolved hyperfine structure of pure singlet and the resolvable (≈50MHz) splittings of pure triplet, arising from the (I\\cdotS) interaction in the ortho states, where nuclear spin I=1. Collision-induced intersystem crossing rates from the (010) state are comparable to those for (000), yet the identities and characters of the presumed gateway states are unknown. A new spectrometer is under construction to investigate triplet mixing rotational levels of ˜{a}1A1(010) by sub-Doppler measurements of perturbation-induced hyperfine splittings. Their observation will permit the identification of gateway states and quantification of the degree of triplet contamination of the singlet wavefunction. Progress in the measurements and the analysis of rotational energy transfer in (010) will be reported. Acknowledgments: Work at Brookhaven National Laboratory was carried out under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy and supported by its Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences. C.-H. Chang, G. E. Hall, T. J. Sears, J. Chem. Phys 133, 144310(2010) G. E. Hall, A. V. Komissarov, and T. J. Sears, J. Phys. Chem. A 108 7922-7927 (2004)

  9. A new analytical potential energy surface for the singlet state of He2H+

    NASA Astrophysics Data System (ADS)

    Liang, Jing-Juan; Yang, Chuan-Lu; Wang, Li-Zhi; Zhang, Qing-Gang

    2012-03-01

    The analytic potential energy surface (APES) for the exchange reaction of HeH+ (X1Σ+) + He at the lowest singlet state 11A/ has been built. The APES is expressed as Aguado-Paniagua function based on the many-body expansion. Using the adaptive non-linear least-squares algorithm, the APES is fitted from 15 682 ab initio energy points calculated with the multireference configuration interaction calculation with a large d-aug-cc-pV5Z basis set. To testify the new APES, we calculate the integral cross sections for He + H+He (v = 0, 1, 2, j = 0) → HeH+ + He by means of quasi-classical trajectory and compare them with the previous result in literature.

  10. Conformational analysis of N-methylformamide in ground S0 and excited S1 and T1 electronic states

    NASA Astrophysics Data System (ADS)

    Tukachev, N. V.; Bataev, V. A.; Godunov, I. A.

    2016-07-01

    For conformers of the N-methylformamide (HCONHCH3) molecule, calculations of equilibrium geometry parameters, harmonic vibration frequencies, energy differences and potential barriers to conformational transitions were performed in the ground (S0) and lowest excited singlet (S1) and triplet (T1) electronic states. In the S0 state, the molecule exists in trans and cis stable conformations (having Cs symmetry). Our calculations show that the electronic excitations T1←S0 and S1←S0 cause changes in the structure of conformers: both HCON and HNCC fragments become pyramidal and rotate around the CN bond. As a result, in each excited electronic state under consideration, there are 12 minima forming six pairs of equivalent conformers separated by relatively small potential barriers. One- and two-dimensional potential energy surface sections corresponding to different intramolecular large-amplitude motions were calculated using the MP2/aug-cc-pVTZ (S0) and CASPT2/cc-pVTZ (S1 and T1) methods. Anharmonic vibrational problems for large-amplitude motions were solved, and the corresponding frequencies were estimated.

  11. Multidirectional Angular Electronic Flux during Adiabatic Attosecond Charge Migration in Excited Benzene.

    PubMed

    Hermann, Gunter; Liu, ChunMei; Manz, Jörn; Paulus, Beate; Pérez-Torres, Jhon Fredy; Pohl, Vincent; Tremblay, Jean Christophe

    2016-07-14

    Recently, adiabatic attosecond charge migration (AACM) has been monitored and simulated for the first time, with application to the oriented iodoacetylene cation where AACM starts from the initial superposition of the ground state (φ0) and an electronic excited state (φ1). Here, we develop the theory for electronic fluxes during AACM in ring-shaped molecules, with application to oriented benzene prepared in the superposition of the ground and first excited singlet states. The initial state and its time evolution are analogous to coherent tunneling where φ0 and φ1 have different meanings; however, they denote the wave functions of the lowest tunneling doublet. This analogy suggests to transfer the theory of electronic fluxes during coherent tunneling to AACM, with suitable modifications which account for (i) the different time scales and (ii) the different electronic states, and which make use of (iii) the preparation of the initial state for AACM by a linearly polarized laser pulse. Application to benzene yields the multidirectional angular electronic flux with a pincer-motion type pattern during AACM: this unequivocal result confirms a previous working hypothesis. Moreover, the theory of AACM allows quantification of the electronic flux; that is, the maximum number of electrons (out of 42) which flow concertedly during AACM in benzene is 6 × 0.08 = 0.48.

  12. Theoretical Studies of Possible Synthetic Routes for the High Energy Density Material Td N4: Excited Electronic States

    NASA Technical Reports Server (NTRS)

    Lee, Timothy J.; Dateo, Christopher E.

    2001-01-01

    Vertical electronic excitation energies for single states have been computed for the high energy density material (HEDM) Td N4 in order to assess possible synthetic routes that originate from excited electronic states of N2 molecules. Several ab initio theoretical approaches have been used, including complete active space self-consistent field (CASSCF), state averaged CASSCF (SA-CASSCF), singles configuration interaction (CIS), CIS with second-order and third-order correlation corrections [CIS(D)) and CIS(3)], and linear response singles and doubles coupled-cluster (LRCCSD), which is the highest level of theory employed. Standard double zeta polarized (DZP) and triple zeta double polarized (TZ2P) one-particle basis sets were used. The CASSCF calculations are found to overestimate the excitation energies, while the SA-CASSCF approach rectifies this error to some extent, but not completely. The accuracy of the CIS calculations varied depending on the particular state, while the CIS(D), CIS(3), and LRCCSD results are in generally good agreement. Based on the LRCCSD calculations, the lowest six excited singlet states are 9.35(l(sup)T1), 10.01(l(sup)T2), 10.04(1(sup)A2), 10.07(1(sup)E), 10.12(2(sup)T1), and 10.42(2(sup)T2) eV above the ground state, respectively. Comparison of these excited state energies with the energies of possible excited states of N2+N2 fragments, leads us to propose that the most likely synthetic route for Td N4 involving this mechanism arises from combination of two bound quintet states of N2.

  13. Singlet and triplet excitons and charge polarons in cycloparaphenylenes: a density functional theory study.

    PubMed

    Liu, Jin; Adamska, Lyudmyla; Doorn, Stephen K; Tretiak, Sergei

    2015-06-14

    The conformational structure and the electronic properties of various electronic excitations in cycloparaphenylenes (CPPs) are calculated using hybrid density functional theory (DFT). The results demonstrate that wavefunctions of singlet and triplet excitons as well as the positive and negative polarons remain fully delocalized in CPPs. In contrast, these excitations in larger CPP molecules become localized on several phenyl rings, which are locally planarized, while the undeformed ground state geometry is preserved on the rest of the hoop. As evidenced by the measurements of bond-length alternation and dihedral angles, localized regions show stronger hybridization between neighboring bonds and thus enhanced electronic communication. This effect is even more significant in the smaller hoops, where phenyl rings have strong quinoid character in the ground state. Thus, upon excitation, electron-phonon coupling leads to the self-trapping of the electronic wavefunction and release of energy from fractions of an eV up to two eVs, depending on the type of excitation and the size of the hoop. The impact of such localization on electronic and optical properties of CPPs is systematically investigated and compared with the available experimental measurements. PMID:25971627

  14. Singlet and triplet excitons and charge polarons in cycloparaphenylenes. A density functional theory study

    DOE PAGESBeta

    Liu, Jin; Adamska, Lyudmyla; Doorn, Stephen K.; Tretiak, Sergei

    2015-05-14

    Conformational structure and the electronic properties of various electronic excitations in cycloparaphenylenes (CPPs) are calculated using hybrid Density Functional Theory (DFT). The results demonstrate that wavefunctions of singlet and triplet excitons as well as the positive and negative polarons remain fully delocalized in CPPs. In contrast, these excitations in larger CPP molecules become localized on several phenyl rings, which are locally planarized, while the undeformed ground state geometry is preserved on the rest of the hoop. As evidenced by the measurements of bond-length alternation and dihedral angles, localized regions show stronger hybridization between neighboring bonds and thus enhanced electronic communication.more » This effect is even more significant in the smaller hoops, where phenyl rings have strong quinoid character in the ground state. Thus, upon excitation, electron–phonon coupling leads to the self-trapping of the electronic wavefunction and release of energy from fractions of an eV up to two eVs, depending on the type of excitation and the size of the hoop. The impact of such localization on electronic and optical properties of CPPs is systematically investigated and compared with the available experimental measurements.« less

  15. Singlet and triplet excitons and charge polarons in cycloparaphenylenes. A density functional theory study

    SciTech Connect

    Liu, Jin; Adamska, Lyudmyla; Doorn, Stephen K.; Tretiak, Sergei

    2015-05-14

    Conformational structure and the electronic properties of various electronic excitations in cycloparaphenylenes (CPPs) are calculated using hybrid Density Functional Theory (DFT). The results demonstrate that wavefunctions of singlet and triplet excitons as well as the positive and negative polarons remain fully delocalized in CPPs. In contrast, these excitations in larger CPP molecules become localized on several phenyl rings, which are locally planarized, while the undeformed ground state geometry is preserved on the rest of the hoop. As evidenced by the measurements of bond-length alternation and dihedral angles, localized regions show stronger hybridization between neighboring bonds and thus enhanced electronic communication. This effect is even more significant in the smaller hoops, where phenyl rings have strong quinoid character in the ground state. Thus, upon excitation, electron–phonon coupling leads to the self-trapping of the electronic wavefunction and release of energy from fractions of an eV up to two eVs, depending on the type of excitation and the size of the hoop. The impact of such localization on electronic and optical properties of CPPs is systematically investigated and compared with the available experimental measurements.

  16. Singlet and triplet energy transfer in the peridinin-chlorophyll a-protein from Amphidinium carterae

    SciTech Connect

    Bautista, J.A.; Frank, H.A.; Hiller, R.G.; Sharples, F.P.; Gosztola, D.; Wasielewski, M. |

    1999-04-08

    The spectroscopic properties of peridinin in solution, and the efficiency and dynamics of energy transfer from peridinin to chlorophyll a in the peridinin-chlorophyll-protein (PCP) from Amphidinium carterae, were studied by steady-state absorption, fluorescence, fluorescence excitation, and fast transient optical spectroscopy. Steady-state measurements of singlet energy transfer from peridinin to chlorophyll revealed an 88 {+-} 2% efficiency. Fast-transient absorption experiments showed that the excited S{sub 1} state of peridinin decayed in 13.4 {+-} 0.6 ps in methanol and 3.1 {+-} 0.4 ps in the PCP complex after direct excitation of the carotenoid. The onset of the bleaching of the chlorophyll absorption band at 672 nm, signifying the arrival of the excitation from the carotenoid, occurred in 3.2 {+-} 0.3 ps. These data show that the primary route of energy transfer from peridinin to chlorophyll in the PCP complex is through the S{sub 1} state of peridinin. Nanosecond time-resolved transient optical spectroscopy revealed that chlorophyll triplet states are efficiently quenched by peridinin whose triplet state subsequently decays with a lifetime of 10 {+-} 1 {micro}s in the PCP complex. Close association between the peridinins and chlorophyll, which is clearly evident in the 3-D structure of the PCP complex, along with proper alignment of pigments and energy state matching are responsible for the high efficiencies of the photochemical processes.

  17. On the influence of singlet oxygen molecules on characteristics of HCCI combustion: A numerical study

    NASA Astrophysics Data System (ADS)

    Starik, A. M.; Kozlov, V. E.; Titova, N. S.

    2013-08-01

    Mechanisms of homogeneous charge compression ignition (HCCI) combustion enhancement are investigated numerically when excited O2(a 1Δg) molecules are produced at different points in the compression stroke. The analysis is conducted with the use of an extended kinetic model involving the submechanism of nitric oxide formation in the presence of singlet oxygen O2(a 1Δg) or O2(b 1Σg +) molecules in the methane-air mixture. It is demonstrated that the abundance of excited O2(a 1Δg) molecules in the mixture even in a small amounts intensifies the ignition and combustion and allows one to control the ignition event in the HCCI engine. Such a method of energy supply in the HCCI engine is much more effective in advancement of combustion timing than mere heating of the mixture, because it leads to acceleration of the chain-branching mechanism. The excitation of O2 molecules to the a 1Δg electronic state makes it possible to organise the successful combustion in the cylinder at diminished initial temperature of the mixture and increase the effective energy released during HCCI combustion. The advance in the value of this energy is much higher than the energy needed for the excitation of oxygen molecules. Moreover, in this case, the output concentration of NO and CO can be reduced significantly.

  18. Triplet-triplet energy transfer and protection mechanisms against singlet oxygen in photosynthesis

    NASA Astrophysics Data System (ADS)

    Kihara, Shigeharu

    In photosynthesis, (bacterio)chlorophylls ((B)Chl) play a crucial role in light harvesting and electron transport. (B)Chls, however, are known to be potentially dangerous due to the formation of the triplet excited state which forms the singlet oxygen (1O2*) when exposed to the sunlight. Singlet oxygen is highly reactive and all modern organisms incorporate special protective mechanisms to minimize the oxidative damage. One of the conventional photoprotective mechanisms used by photosynthetic organisms is by the nearby carotenoids quenching the excess energy and releasing it by heat. In this dissertation, two major aspects of this process are studied. First, based on experimental data and model calculations, the oxygen content in a functioning oxygenic photosynthetic oxygen cell was determined. These organisms perform water splitting and as a result significant amount of oxygen can be formed within the organism itself. It was found, that contrary to some published estimates, the excess oxygen concentration generated within an individual cell is extremely low -- 0.025 ... 0.25 microM, i.e. about 103-104 times lower than the oxygen concentration in air saturated water. Such low concentrations imply that the first oxygenic photosynthetic cells that evolved in oxygen-free atmosphere of the Earth ~2.8 billion years ago might have invented the water splitting machinery (photosystem II) without the need for special oxygen-protective mechanisms, and the latter mechanisms could have evolved in the next 500 million years during slow rise of oxygen in the atmosphere. This result also suggests that proteins within photosynthetic membranes are not exposed to significant O2 levels and thus can be studied in vitro under the usual O2 levels. Second, the fate of triplet excited states in the Fenna Matthew Olson (FMO) pigment-protein complex is studied by means of time-resolved nanosecond spectroscopy and exciton model simulations. For the first time, the properties of several

  19. Singlet levels of the NV- centre in diamond

    NASA Astrophysics Data System (ADS)

    Rogers, L. J.; Doherty, M. W.; Barson, M. S. J.; Onoda, S.; Ohshima, T.; Manson, N. B.

    2015-01-01

    The characteristic transition of the N{{V}-} centre at 637 nm is between 3{{A}2} and 3E triplet states. There are also intermediate 1{{A}1} and 1E singlet states, and the infrared transition at 1042 nm between these singlets is studied here using uniaxial stress. The stress shift and splitting parameters are determined, and the physical interaction giving rise to the parameters is considered within the accepted electronic model of the centre. It is established that this interaction for the infrared transition is due to a modification of electron-electron Coulomb repulsion interaction. This is in contrast to the visible 637 nm transition where shifts and splittings arise from modification to the one-electron Coulomb interaction. It is also established that a dynamic Jahn-Teller interaction is associated with the singlet 1E state, which gives rise to a vibronic level 115 cm-1 above the 1E electronic state. Arguments associated with this level are used to provide experimental confirmation that the 1{{A}1} is the upper singlet level and 1E is the lower singlet level.

  20. Identifying the lowest electronic states of the chlorophylls in the CP47 core antenna protein of photosystem II.

    PubMed

    De Weerd, Frank L; Palacios, Miguel A; Andrizhiyevskaya, Elena G; Dekker, Jan P; Van Grondelle, Rienk

    2002-12-24

    CP47 is a pigment-protein complex in the core of photosystem II that tranfers excitation energy to the reaction center. Here we report on a spectroscopic investigation of the isolated CP47 complex. By deconvoluting the 77 K absorption and linear dichroism, red-most states at 683 and 690 nm have been identified with oscillator strengths corresponding to approximately 3 and approximately 1 chlorophyll, respectively. Both states contribute to the 4 K emission, and the Stark spectrum shows that they have a large value for the difference polarizability between their ground and excited states. From site-selective polarized triplet-minus-singlet spectra, an excitonic origin for the 683 nm state was found. The red shift of the 690 nm state is most probably due to strong hydrogen bonding to a protein ligand, as follows from the position of the stretch frequency of the chlorophyll 13(1) keto group (1633 cm(-)(1)) in the fluorescence line narrowing spectrum at 4 K upon red-most excitation. We discuss how the 683 and 690 nm states may be linked to specific chlorophylls in the crystal structure [Zouni, A., Witt, H.-T., Kern, J., Fromme, P., Krauss, N., Saenger, W., and Orth, P. (2001) Nature 409, 739-743].

  1. The relativistic polarization propagator for the calculation of electronic excitations in heavy systems

    SciTech Connect

    Pernpointner, Markus

    2014-02-28

    In this work, we present a new four-component implementation of the polarization propagator for accurate calculations of excited states in heavy systems. Differences to existing nonrelativistic realizations are detailed and the energetically lowest final states of the ns{sup 2}np{sup 6} → ns{sup 2}np{sup 5}(n + 1)s{sup 1} and ns{sup 2}np{sup 6} → ns{sup 2}np{sup 5}(n + 1)p{sup 1} transitions in noble gases are calculated and compared with experimental data. Already for the light atoms Ne and Ar spin-orbit coupling leads to noticeable zero field splitting that gradually increases in the heavier homologues and eventually invalidates the LS-based description of singlet and triplet excited states. For all four noble gases Ne through Xe, we observe a very good agreement with experimental transition energies in the considered energetic range where the extended version of the propagator implementation in general yields better excitation energy differences than the strict variant. In the extended version, off-diagonal first-order contributions in the two-particle-two-hole block are included that are not present in the strict variant. In case of Kr and Xe, nonrelativistic approaches already exhibit unacceptable deviations in the reproduction of transition energies and the spectral structure. The obtained excited final states are analyzed in terms of atomic contributions to the donor and acceptor orbitals constituting the corresponding wave functions. The relativistic polarization propagator provides a consistent description of electron correlation and relativistic effects especially relevant for the heavier systems where these two contributions are no longer separable.

  2. Reinvestigation of the triplet-minus-singlet spectrum of chloroplasts.

    PubMed

    Jávorfi, T; Garab, G; Naqvi, K R

    2000-01-01

    A comparison of the triplet-minus-singlet (TmS) absorption spectrum of spinach chloroplasts, recorded some thirty years ago, with the more recently published TmS spectrum of isolated Chla/b LHCII (light-harvesting complexes associated with photosystem II of higher plants) shows that the two spectra are very similar, which is to be expected, since only the carotenoid pigments contribute to each spectrum. Be that as it may, the comparison also reveals a dissimilarity: photoexcitation of the sample does, or does not, affect the absorbance in the Qy region (650-700 nm), depending on whether the sample is a suspension of chloroplasts or of isolated LHCII. The Qy-signal in the TmS spectrum of LHCII decays, it should be noted, at the same rate as the rest of the difference spectrum, and its most prominent feature is a negative peak. As the carotenoids do not absorb in the Qy region, the presence of a signal in this region calls for an explanation: van der Vos, Carbonera and Hoff, the first to find as well as fathom the phenomenon, attributed the Qy-signal to a change, in the absorption spectrum of a chlorophyll a (Chla) molecule, brought about by the presence of triplet excitation on a neighbouring carotenoid (Car). The difference in the behaviours of chloroplasts and LHCII, if reproducible, would imply that the Car triplets which give rise to the TmS spectrum of chloroplasts do not influence the absorption spectra of their Chla neighbours. With a view to reaching a firm conclusion about this vexed issue, spinach chloroplasts and thylakoids have been examined with the aid of the same kinetic spectrometer as that used for investigating LHCII; the TmS spectra of both chloroplasts and thylakoids contain prominent bleaching signals centred at 680 nm, and the triplet decay time in each case is comparable to that of the Chla/b LHCII triplets. Results pertaining to other closely related systems are recalled, and it is concluded that, so far as the overall appearance of the Tm

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

    SciTech Connect

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

    2014-05-12

    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.

  4. Ground state of naphthyl cation: Singlet or triplet?

    SciTech Connect

    Dutta, Achintya Kumar; Vaval, Nayana Pal, Sourav; Manohar, Prashant U.

    2014-03-21

    We present a benchmark theoretical investigation on the electronic structure and singlet-triplet(S-T) gap of 1- and 2-naphthyl cations using the CCSD(T) method. Our calculations reveal that the ground states of both the naphthyl cations are singlet, contrary to the results obtained by DFT/B3LYP calculations reported in previous theoretical studies. However, the triplet states obtained in the two structural isomers of naphthyl cation are completely different. The triplet state in 1-naphthyl cation is (π,σ) type, whereas in 2-naphthyl cation it is (σ,σ{sup ′}) type. The S-T gaps in naphthyl cations and the relative stability ordering of the singlet and the triplet states are highly sensitive to the basis-set quality as well as level of correlation, and demand for inclusion of perturbative triples in the coupled-cluster ansatz.

  5. Ultrathin Black Phosphorus Nanosheets for Efficient Singlet Oxygen Generation.

    PubMed

    Wang, Hui; Yang, Xianzhu; Shao, Wei; Chen, Shichuan; Xie, Junfeng; Zhang, Xiaodong; Wang, Jun; Xie, Yi

    2015-09-01

    Benefiting from its strong oxidizing properties, the singlet oxygen has garnered serious attentions in physical, chemical, as well as biological studies. However, the photosensitizers for the generation of singlet oxygen bear in low quantum yields, lack of long wavelength absorption band, poor biocompatibility, undegradable in living tissues, and so on. Here we first demonstrate the exfoliated black phosphorus nanosheets to be effective photosensitizers for the generation of singlet oxygen with a high quantum yield of about 0.91, rendering their attractive applications in catalysis and photodynamic therapy. Through in vitro and in vivo studies, the water dispersible black phosphorus nanosheets show notable cancer therapy ability. In addition, the photodegradable character of black phosphorus from element to biocompatible phosphorus oxides further highlights its therapeutic potential against cancer. This study will not only expand the breadth of study in black phosphorus but also offer an efficient catalyst and photodynamic therapy agent.

  6. Probing scalar coupling differences via long-lived singlet states

    NASA Astrophysics Data System (ADS)

    DeVience, Stephen J.; Walsworth, Ronald L.; Rosen, Matthew S.

    2016-01-01

    We probe small scalar coupling differences via the coherent interactions between two nuclear spin singlet states in organic molecules. We show that the spin-lock induced crossing (SLIC) technique enables the coherent transfer of singlet order between one spin pair and another. The transfer is mediated by the difference in syn and anti vicinal or long-range J couplings among the spins. By measuring the transfer rate, we calculate a J coupling difference of 8 ± 2 mHz in phenylalanine-glycine-glycine and 2.57 ± 0.04 Hz in glutamate. We also characterize a coherence between two singlet states in glutamate, which may enable the creation of a long-lived quantum memory.

  7. Current perspectives of singlet oxygen detection in biological environments.

    PubMed

    Gorman, A A; Rodgers, M A

    1992-07-15

    There is widespread acceptance that singlet oxygen is a key intermediate on one of the pathways leading to the phenomenon of photodynamic action. However, the identification of this moiety within a particular biological system and the determination of a direct link between its presence and a particular photodynamic effect is a goal which photobiologists have hitherto failed to achieve. The aim of this review is to assess the problems associated with such a goal and methods whereby they might be overcome. Initially the general photochemical and environmental factors which govern the ability of a photosensitizer to promote photodynamic action via the intermediacy of singlet oxygen are introduced and the fundamental parameters defining the formation, decay and reactivity of this species summarized. The experimental requirements for relating a particular photodynamic effect to singlet oxygen intermediacy are then analysed and the intrinsic properties of singlet oxygen which will influence this goal are discussed. Having concluded that the singlet oxygen detection method of choice for this purpose is that in which the IR emission at 1269 nm of this molecule is monitored, the advantages and disadvantages of pulsed and continuous wave photoexcitation of cellular systems are analysed. It becomes evident that, no matter what the future improvements in instrumentation are likely to be, the inherent natures of singlet oxygen and the biological system lead to a kinetic situation which will preclude a successful time-resolved solution to this problem. In contrast, experimentation with continuous wave systems holds out significant hope for the future. In particular, the use of phase modulation techniques to overcome background emission problems, the enhancement of photosensitizer optical densities as a consequence of higher extinction coefficients and/or improved photosensitizer delivery systems and the use of high power lasers and/or improved light delivery systems can, at

  8. Dynamics of momentum entanglement in lowest-order QED

    SciTech Connect

    Lamata, L.; Leon, J.; Solano, E.

    2006-01-15

    We study the dynamics of momentum entanglement generated in the lowest-order QED interaction between two massive spin-(1/2) charged particles, which grows in time as the two fermions exchange virtual photons. We observe that the degree of generated entanglement between interacting particles with initial well-defined momentum can be infinite. We explain this divergence in the context of entanglement theory for continuous variables, and show how to circumvent this apparent paradox. Finally, we discuss two different possibilities of transforming momentum into spin entanglement, through dynamical operations or through Lorentz boosts.

  9. Electron number dependence of spin triplet-singlet relaxation time

    NASA Astrophysics Data System (ADS)

    Li, H. O.; Xiao, M.; Cao, G.; You, J.; Guo, G. P.

    2014-02-01

    In a GaAs single quantum dot, the relaxation time T1 between spin triplet and singlet states has been measured for the last few even electron numbers. The singlet-triplet energy separation EST is tuned as a control parameter for the comparison of T1 between different electron numbers. T1 steadily decreases with increasing electron numbers from 2-electrons to 6-electrons. This implies an enhancement of the spin-orbit coupling strength due to multi-electron interaction in a quantum dot.

  10. Highly efficient spin-conversion effect leading to energy up-converted electroluminescence in singlet fission photovoltaics

    NASA Astrophysics Data System (ADS)

    Pandey, Ajay K.

    2015-01-01

    Free charge generation in donor-acceptor (D-A) based organic photovoltaic diodes (OPV) progresses through formation of charge-transfer (CT) and charge-separated (CS) states and excitation decay to the triplet level is considered as a terminal loss. On the other hand a direct excitation decay to the triplet state is beneficial for multiexciton harvesting in singlet fission photovoltaics (SF-PV) and the formation of CT-state is considered as a limiting factor for multiple triplet harvesting. These two extremes when present in a D-A system are expected to provide important insights into the mechanism of free charge generation and spin-character of bimolecular recombination in OPVs. Herein, we present the complete cycle of events linked to spin conversion in the model OPV system of rubrene/C60. By tracking the spectral evolution of photocurrent generation at short-circuit and close to open-circuit conditions we are able to capture spectral changes to photocurrent that reveal the triplet character of CT-state. Furthermore, we unveil an energy up-conversion effect that sets in as a consequence of triplet population build-up where triplet-triplet annihilation (TTA) process effectively regenerates the singlet excitation. This detailed balance is shown to enable a rare event of photon emission just above the open-circuit voltage (VOC) in OPVs.

  11. Highly efficient spin-conversion effect leading to energy up-converted electroluminescence in singlet fission photovoltaics.

    PubMed

    Pandey, Ajay K

    2015-01-01

    Free charge generation in donor-acceptor (D-A) based organic photovoltaic diodes (OPV) progresses through formation of charge-transfer (CT) and charge-separated (CS) states and excitation decay to the triplet level is considered as a terminal loss. On the other hand a direct excitation decay to the triplet state is beneficial for multiexciton harvesting in singlet fission photovoltaics (SF-PV) and the formation of CT-state is considered as a limiting factor for multiple triplet harvesting. These two extremes when present in a D-A system are expected to provide important insights into the mechanism of free charge generation and spin-character of bimolecular recombination in OPVs. Herein, we present the complete cycle of events linked to spin conversion in the model OPV system of rubrene/C60. By tracking the spectral evolution of photocurrent generation at short-circuit and close to open-circuit conditions we are able to capture spectral changes to photocurrent that reveal the triplet character of CT-state. Furthermore, we unveil an energy up-conversion effect that sets in as a consequence of triplet population build-up where triplet-triplet annihilation (TTA) process effectively regenerates the singlet excitation. This detailed balance is shown to enable a rare event of photon emission just above the open-circuit voltage (V(OC)) in OPVs. PMID:25585937

  12. Highly efficient spin-conversion effect leading to energy up-converted electroluminescence in singlet fission photovoltaics

    PubMed Central

    Pandey, Ajay K.

    2015-01-01

    Free charge generation in donor-acceptor (D-A) based organic photovoltaic diodes (OPV) progresses through formation of charge-transfer (CT) and charge-separated (CS) states and excitation decay to the triplet level is considered as a terminal loss. On the other hand a direct excitation decay to the triplet state is beneficial for multiexciton harvesting in singlet fission photovoltaics (SF-PV) and the formation of CT-state is considered as a limiting factor for multiple triplet harvesting. These two extremes when present in a D-A system are expected to provide important insights into the mechanism of free charge generation and spin-character of bimolecular recombination in OPVs. Herein, we present the complete cycle of events linked to spin conversion in the model OPV system of rubrene/C60. By tracking the spectral evolution of photocurrent generation at short-circuit and close to open-circuit conditions we are able to capture spectral changes to photocurrent that reveal the triplet character of CT-state. Furthermore, we unveil an energy up-conversion effect that sets in as a consequence of triplet population build-up where triplet-triplet annihilation (TTA) process effectively regenerates the singlet excitation. This detailed balance is shown to enable a rare event of photon emission just above the open-circuit voltage (VOC) in OPVs. PMID:25585937

  13. Generation of Three-Qutrit Singlet States with Two-Level Trapped Ions

    NASA Astrophysics Data System (ADS)

    Yang, Rong-Can; Ye, Li-Xiang; Lin, Xiu; Chen, Xiang

    2015-10-01

    We propose an adiabatic-passage scheme for the generation of three-qutrit singlet states with two-level trapped ions. Distinctly different from previous proposals, we encode qutrits in Dicke states with two-level ions and use the adiabatic-evolution techniques in order not to exactly control the laser pulses, making the realization of the scheme much easier. Furthermore, the phonon is only virtually excited in the procedure, so the effect of the phonon losses can be reduced. Supported by National Natural Science Foundation of China under Grant Nos. 61308012 and 61275215, by the Fujian Natural Science Foundation under Grant Nos. 2013J01008 and 2012J01004 and by the Fund from Fujian Educational Department under Grant Nos. JA14075, JB13021, and JB12014

  14. Rationality, irrationality and escalating behavior in lowest unique bid auctions.

    PubMed

    Radicchi, Filippo; Baronchelli, Andrea; Amaral, Luís A N

    2012-01-01

    Information technology has revolutionized the traditional structure of markets. The removal of geographical and time constraints has fostered the growth of online auction markets, which now include millions of economic agents worldwide and annual transaction volumes in the billions of dollars. Here, we analyze bid histories of a little studied type of online auctions--lowest unique bid auctions. Similarly to what has been reported for foraging animals searching for scarce food, we find that agents adopt Lévy flight search strategies in their exploration of "bid space". The Lévy regime, which is characterized by a power-law decaying probability distribution of step lengths, holds over nearly three orders of magnitude. We develop a quantitative model for lowest unique bid online auctions that reveals that agents use nearly optimal bidding strategies. However, agents participating in these auctions do not optimize their financial gain. Indeed, as long as there are many auction participants, a rational profit optimizing agent would choose not to participate in these auction markets.

  15. Near infrared photo-induced DNA damage in the presence of copper-dppz complex: Evidence for the involvement of singlet oxygen

    NASA Astrophysics Data System (ADS)

    Fortner, Angela; Wang, Shuguang; Darbha, Gopala Krishna; Ray, Anandhi; Yu, Hongtao; Ray, Paresh Chandra; Kalluru, Rajamohan R.; Kim, Chan Kyu; Rai, Vinita; Singh, Jagdish P.

    2007-01-01

    We present the effect of the DNA damage efficiency by excitation wavelengths above 700 nm within d-d transition bands of ( L-lysine) (dppz) Cu(II) complexes. Our results show significant DNA cleavage between 700 and 755 nm. The efficiency of photosensitized DNA cleavage and quantum yield of singlet oxygen production at different excitation wavelengths have been determined to gain insight into the involvement of the d-d band in the DNA damage process. Time-dependent density functional (TD-DFT) calculations were performed to understand the influence of the metal to L-lysine transition on the d-d bands of the Cu(II) complex-DNA moiety. It is found that the involvement of d-d transition in the reaction pathway of singlet oxygen formation seems to play an important role in the DNA cleavage efficiency using light of wavelength above 700 nm.

  16. Identification of singlet oxygen photosensitizes in lambs drinking water in an alveld risk area in West Norway.

    PubMed

    Tønnesen, Hanne Hjorth; Mysterud, Ivar; Karlsen, Jan; Skulberg, Olav M; Laane, Carl M M; Schumacher, Trond

    2013-02-01

    Alveld is a hepatogenous photosensitivity disorder in lambs. Although alveld has been known in Norway for more than 100years, there are still questions related to the cause of the disease. Phytoporphyrin has long been incriminated as the photosensitizer in hepatogenous photosensitivity diseases but previous findings suggest that the photosensitizing mechanism in alveld is more complex, possibly involving other co-factors. The current work investigates the presence of non-hepatogenous photosensitizers originating in lamb's drinking water from various sources. In addition samples of two of the predominent cyanobacteria found in a representative biofilm (i.e. aggregates of microbes) were identified and isolated in axenic (i.e. pure) cultures. Information from the absorption-, fluorescence emission-, and -excitation spectra and the action spectrum for the formation of singlet oxygen was combined in order to identify the chromophores responsible for the formation of singlet oxygen, e.g. phycocyanins from the cyanobacteria. The highest level of singlet oxygen formation was detected in lotic (i.e. flowing) water in the period consistent with the outbreak of the alveld disease in the area. Meteorological data indicate a warm and wet May with a high radiation exposure leading up to a colder and wet June with an even higher solar irradiance. The seasonal variation in the amount of photosensitizers in lamb's drinking water combined meteorological data can be important to predict the outbreak of alveld.

  17. Lowest l=0 proton resonance in {sup 26}Si and implications for nucleosynthesis of {sup 26}Al

    SciTech Connect

    Peplowski, P. N.; Baby, L. T.; Wiedenhoever, I.; Diffenderfer, E.; Hoeflich, P.; Rojas, A.; Volya, A.; Dekat, S. E.; Gay, D. L.; Grubor-Urosevic, O.; Kaye, R. A.; Keeley, N.

    2009-03-15

    Using a beam of the radioactive isotope {sup 25}Al, produced with the new RESOLUT facility, we measured the direct (d,n) proton-transfer reaction leading to low-lying proton resonances in {sup 26}Si. We observed the lowest l=0 proton resonance, identified with the 3{sup +} state at 5.914-MeV excitation energy. This result eliminates the largest uncertainty in astrophysical reaction rates involved in the nucleosynthesis of {sup 26}Al.

  18. Negative Ion Photoelectron Spectroscopy Confirms the Prediction that D-3h Carbontrioxide (CO3) Has a Singlet Ground State

    DOE PAGESBeta

    Hrovat, David; Hou, Gao-Lei; Chen, Bo; Wang, Xue B.; Borden, Weston

    2015-11-13

    The CO3 radical anion (CO3•–) has been formed by electrospraying carbonate dianion (CO32–) into the gas phase. The negative ion photoelectron (NIPE) spectrum of CO3•– shows that, unlike trimethylenemethane [C(CH2)3], carbontrioxide (CO3) has a singlet ground state. From the NIPE spectrum, the electron affinity of CO3 was determined to be EA = 4.06 ± 0.03 eV, and the singlet-triplet energy difference was found to be ΔEST = - 17.8 ± 0.9 kcal/mol. B3LYP, CCSD(T), and CASPT2 calculations all find that the two lowest triplet states of CO3 are very close in energy, a prediction that is confirmed by the relativemore » intensities of the bands in the NIPE spectrum of CO3•–. The 560 cm-1 vibrational progression, seen in the low energy region of the triplet band, enables the identification of the lowest, Jahn-Teller-distorted, triplet state as 3A1, in which both unpaired electrons reside in σ MOs, rather than 3A2, in which one unpaired electron occupies the b2 σ MO, and the other occupies the b1 π MO.« less

  19. Fast Triplet Formation via Singlet Exciton Fission in a Covalent Perylenediimide-β-apocarotene Dyad Aggregate.

    PubMed

    Mauck, Catherine M; Brown, Kristen E; Horwitz, Noah E; Wasielewski, Michael R

    2015-06-01

    A covalent dyad was synthesized in which perylene-3,4,:9:10-bis(dicarboximide) (PDI) is linked to β-apocarotene (Car) using a biphenyl spacer. The dyad is monomeric in toluene and forms a solution aggregate in methylcyclohexane (MCH). Using femtosecond transient absorption (fsTA) spectroscopy, the monomeric dyad and its aggregates were studied both in solution and in thin films. In toluene, photoexcitation at 530 nm preferentially excites PDI, and the dyad undergoes charge separation in τ = 1.7 ps and recombination in τ = 1.6 ns. In MCH and in thin solid films, 530 nm excitation of the PDI-Car aggregate also results in charge transfer that competes with energy transfer from (1)*PDI to Car and with an additional process, rapid Car triplet formation in <50 ps. Car triplet formation is only observed in the aggregated PDI-Car dyad and is attributed to singlet exciton fission (SF) within the aggregated PDI, followed by rapid triplet energy transfer from (3)*PDI to the carotenoid. SF from β-apocarotene aggregation is ruled out by direct excitation of Car films at 414 nm, where no triplet formation is observed. Time-resolved electron paramagnetic resonance measurements on aggregated PDI-Car show the formation of (3)*Car with a spin-polarization pattern that rules out radical-pair intersystem crossing as the mechanism of triplet formation as well. PMID:25961130

  20. Calculation of singlet oxygen formation from one photon absorbing photosensitizers used in PDT

    NASA Astrophysics Data System (ADS)

    Potasek, M.; Parilov, Evgueni; Beeson, K.

    2013-03-01

    Advances in biophotonic medicine require new information on photodynamic mechanisms. In photodynamic therapy (PDT), a photosensitizer (PS) is injected into the body and accumulates at higher concentrations in diseased tissue compared to normal tissue. The PS absorbs light from a light source and generates excited-state triplet states of the PS. The excited triplet states of the PS can then react with ground state molecular oxygen to form excited singlet - state oxygen or form other highly reactive species. The reactive species react with living cells, resulting in cel l death. This treatment is used in many forms of cancer including those in the prostrate, head and neck, lungs, bladder, esophagus and certain skin cancers. We developed a novel numerical method to model the photophysical and photochemical processes in the PS and the subsequent energy transfer to O2, improving the understanding of these processes at a molecular level. Our numerical method simulates light propagation and photo-physics in PS using methods that build on techniques previously developed for optical communications and nonlinear optics applications.

  1. Preparation of nuclear spin singlet states using spin-lock induced crossing.

    PubMed

    DeVience, Stephen J; Walsworth, Ronald L; Rosen, Matthew S

    2013-10-25

    We introduce a broadly applicable technique to create nuclear spin singlet states in organic molecules and other many-atom systems. We employ a novel pulse sequence to produce a spin-lock induced crossing (SLIC) of the spin singlet and triplet energy levels, which enables triplet-singlet polarization transfer and singlet-state preparation. We demonstrate the utility of the SLIC method by producing a long-lived nuclear spin singlet state on two strongly coupled proton pairs in the tripeptide molecule phenylalanine-glycine-glycine dissolved in D(2)O and by using SLIC to measure the J couplings, chemical shift differences, and singlet lifetimes of the proton pairs. We show that SLIC is more efficient at creating nearly equivalent nuclear spin singlet states than previous pulse sequence techniques, especially when triplet-singlet polarization transfer occurs on the same time scale as spin-lattice relaxation.

  2. Cooperative Singlet and Triplet Exciton Transport in Tetracene Crystals Visualized by Ultrafast Microscopys

    SciTech Connect

    Wan, Yan; Guo, Zhi; Zhu, Tong; Yan, Suxia; Johnson, Justin; Huang, Libai

    2015-09-14

    Singlet fission presents an attractive solution to overcome the Shockley–Queisser limit by generating two triplet excitons from one singlet exciton. Although triplet excitons are long-lived, their transport occurs through a Dexter transfer, making them slower than singlet excitons, which travel by means of a Förster mechanism. A thorough understanding of the interplay between singlet fission and exciton transport is therefore necessary to assess the potential and challenges of singlet-fission utilization. We report a direct visualization of exciton transport in single tetracene crystals using transient absorption microscopy with 200 fs time resolution and 50 nm spatial precision. Moreover, these measurements reveal a new singlet-mediated transport mechanism for triplets, which leads to an enhancement in effective triplet exciton diffusion of more than one order of magnitude on picosecond to nanosecond timescales. These results establish that there are optimal energetics of singlet and triplet excitons that benefit both singlet fission and exciton diffusion.

  3. Stabilization of secondary diesel fuels by singlet-oxygen quenchers

    SciTech Connect

    Rat`kova, M.Y.; Danilov, A.M.

    1993-05-10

    A study was carried out on the effect of singlet-oxygen quenchers on the stability of light catalytic gas oil not subjected to hydrogen treatment. Compositions based on {alpha}-tocopherol with Ionol and a dispersing agent (Dneprol additive) have a stabilizing effect.

  4. Photoactivatable protein labeling by singlet oxygen mediated reactions.

    PubMed

    To, Tsz-Leung; Medzihradszky, Katalin F; Burlingame, Alma L; DeGrado, William F; Jo, Hyunil; Shu, Xiaokun

    2016-07-15

    Protein-protein interactions regulate many biological processes. Identification of interacting proteins is thus an important step toward molecular understanding of cell signaling. The aim of this study was to investigate the use of photo-generated singlet oxygen and a small molecule for proximity labeling of interacting proteins in cellular environment. The protein of interest (POI) was fused with a small singlet oxygen photosensitizer (miniSOG), which generates singlet oxygen ((1)O2) upon irradiation. The locally generated singlet oxygen then activated a biotin-conjugated thiol molecule to form a covalent bond with the proteins nearby. The labeled proteins can then be separated and subsequently identified by mass spectrometry. To demonstrate the applicability of this labeling technology, we fused the miniSOG to Skp2, an F-box protein of the SCF ubiquitin ligase, and expressed the fusion protein in mammalian cells and identified that the surface cysteine of its interacting partner Skp1 was labeled by the biotin-thiol molecule. This photoactivatable protein labeling method may find important applications including identification of weak and transient protein-protein interactions in the native cellular context, as well as spatial and temporal control of protein labeling.

  5. Singlet oxygen is essential for neutrophil extracellular trap formation.

    PubMed

    Nishinaka, Yoko; Arai, Toshiyuki; Adachi, Souichi; Takaori-Kondo, Akifumi; Yamashita, Kouhei

    2011-09-16

    Neutrophil extracellular traps (NETs) that bind invading microbes are pivotal for innate host defense. There is a growing body of evidence for the significance of NETs in the pathogenesis of infectious and inflammatory diseases, but the mechanism of NET formation remains unclear. Previous observation in neutrophils of chronic granulomatous disease (CGD) patients, which defect NADPH oxidase (Nox) and fail to produce reactive oxygen species (ROS), revealed that ROS contributed to the formation of NETs. However, the active species were not identified. In this study, we discovered that singlet oxygen, one of the ROS, mediated Nox-dependent NET formation upon stimulation with phorbol myristate acetate. We also revealed that singlet oxygen itself could induce NET formation by a distinct system generating singlet oxygen with porfimer sodium (Photofrin) in CGD neutrophils, as well as healthy neutrophils. This was independent of Nox activation. These results show that singlet oxygen is essential for NET formation, and provide novel insights into the pathogenesis of infectious and inflammatory diseases.

  6. Temperature-independent singlet exciton fission in tetracene.

    PubMed

    Wilson, Mark W B; Rao, Akshay; Johnson, Kerr; Gélinas, Simon; di Pietro, Riccardo; Clark, Jenny; Friend, Richard H

    2013-11-01

    We use transient absorption spectroscopy to demonstrate that the dynamics of singlet exciton fission in tetracene are independent of temperature (10–270 K). Low-intensity, broad-band measurements allow the identification of spectral features while minimizing bimolecular recombination. Hence, by directly observing both species, we find that the time constant for the conversion of singlets to triplet pairs is ~90 ps. However, in contrast to pentacene, where fission is effectively unidirectional, we confirm that the emissive singlet in tetracene is readily regenerated from spin-correlated "geminate" triplets following fission, leading to equilibrium dynamics. Although free triplets are efficiently generated at room temperature, the interplay of superradiance and frustrated triplet diffusion contributes to a nearly 20-fold increase in the steady-state fluorescence as the sample is cooled. Together, these results require that singlets and triplet pairs in tetracene are effectively degenerate in energy, and begin to reconcile the temperature dependence of many macroscopic observables with a fission process which does not require thermal activation.

  7. Singlet oxygen and organic light-emitting diodes

    SciTech Connect

    Jacobs, S.J.; Sinclair, M.B.; Valencia, V.S.; Kepler, R.G.; Clough, R.L.; Scurlock, R.D.; Ogilby, P.R.

    1995-07-01

    The preparation of light emitting diodes employing a new class of materials, 5,10-dihetera 5,10-dihydro-indeno[3,2b]indenes, as hole transport agents is described. These materials have been found to be more resistant to degradation by singlet oxygen than a poly(p-phenylene vinylene) (PPV) derivative.

  8. Singlet-based photon upconversion in multichromophore organic thin films (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Weingarten, Daniel H.; LaCount, Michael; Rumbles, Garry; van de Lagemaat, Jao; Lusk, Mark T.; Shaheen, Sean E.

    2015-10-01

    Solid-state energy upconversion has many potential applications, from nonlinear photonics and biophotonics to expanding the spectrum available for solar energy harvest. In organic molecular systems, upconversion is frequently done in solution to mitigate aggregation-induced photoluminescence quenching or to facilitate the diffusion of triplet donors in Triplet-Triplet Annihilation (TTA) systems. Here we demonstrate an organic thin film upconversion system utilizing two-photon absorption (TPA) properties to improve upconversion efficiency. In blend films of Stilbene-420 and Rhodamine 6G we observe a tenfold increase in up-converted fluorescence compared to the fluorescence yield of TPA in pristine stilbene films. While TPA normally has quadratic dependence on excitation intensity, these blend films exhibit sub-quadratic intensity dependence, indicating a combination of linear and quadratic upconversion processes and dramatically improving upconversion efficiency at lower excitation intensities. This improvement in intensity dependence allows for relatively efficient upconversion upon excitation by a nanosecond laser pulse, in contrast to the more expensive femtosecond lasers generally required for excitation in TPA microscopy and similar systems. Time-resolved photoluminescence decay measurements reveal that all excited states involved in this upconversion process are singlets, which indicates the potential for reduced energy losses when compared to TTA upconversion systems and their inherent intersystem-crossing energy losses. We observe emission from both the Rhodamine 6G donor molecules and Stilbene-420 acceptor molecules, indicating the presence of prompt fluorescence from the donor as well as upconversion to the acceptor, and FRET losses from acceptor back to donor. By fitting to a kinetic model we extract rates for these competing processes.

  9. Singlet Fission of Non-polycyclic Aromatic Molecules in Organic Photovoltaics.

    PubMed

    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.

  10. Excited-state dynamics in diketopyrrolopyrrole-based copolymer for organic photovoltaics investigated by transient optical spectroscopy

    NASA Astrophysics Data System (ADS)

    Matsuzaki, Hiroyuki; Furube, Akihiro; Katoh, Ryuzi; Pratap Singh, Samarendra; Sonar, Prashant; Williams, Evan Laurence; Vijila, Chellappan; Sandhya Subramanian, Gomathy; Gorelik, Sergey; Hobley, Jonathan

    2014-01-01

    We investigate the photoexcited state dynamics in a donor-acceptor copolymer, poly{3,6-dithiophene-2-yl-2,5-di(2-octyldodecyl)-pyrrolo[3,4-c]pyrrole-1,4-dione-alt-naphthalene} (pDPP-TNT), by picosecond fluorescence and femtosecond transient absorption spectroscopies. Time-resolved fluorescence lifetime measurements of pDPP-TNT thin films reveal that the lifetime of the singlet excited state is 185 ± 5 ps and that singlet-singlet annihilation occurs at excitation photon densities above 6 × 1017 photons/cm3. From the results of singlet-singlet annihilation analysis, we estimate that the single-singlet annihilation rate constant is (6.0 ± 0.2) × 10-9 cm3 s-1 and the singlet diffusion length is ~7 nm. From the comparison of femtosecond transient absorption measurements and picosecond fluorescence measurements, it is found that the time profile of the photobleaching signal in the charge-transfer (CT) absorption band coincides with that of the fluorescence intensity and there is no indication of long-lived species, which clearly suggests that charged species, such as polaron pairs and triplet excitons, are not effectively photogenerated in the neat pDPP-TNT polymer.

  11. Valence and Ionic Lowest-Lying Electronic States of Isobutyl Formate Studied by High-Resolution Vacuum Ultraviolet Photoabsorption, Photoelectron Spectroscopy, and Ab Initio Calculations.

    PubMed

    Śmiałek, M A; Łabuda, M; Guthmuller, J; Hoffmann, S V; Jones, N C; MacDonald, M A; Zuin, L; Mason, N J; Limão-Vieira, P

    2015-08-13

    The highest resolution vacuum ultraviolet photoabsorption spectrum of isobutyl formate, C5H10O2, yet reported is presented over the energy range 4.5-10.7 eV (275.5-118.0 nm) revealing several new spectral features. Valence and Rydberg transitions and their associated vibronic series observed in the photoabsorption spectrum have been assigned in accordance with new ab initio calculations of the vertical excitation energies and oscillator strengths. Calculations have also been carried out to determine the ionization energies and fine structure of the lowest ionic state of isobutyl formate and are compared with a newly recorded photoelectron spectrum (from 9.0 to 27.0 eV). The value of the first ionization energy was determined to be 10.508 eV (adiabatic) and 10.837 eV (vertical). New vibrational structure is observed in the first photoelectron band, predominantly resulting from C-O and C═O stretches of the molecule. The photoabsorption cross sections have been used to calculate the photolysis lifetime of isobutyl formate in the upper stratosphere (20-50 km), indicating that the hydroxyl radical processes will be the main loss process for isobutyl formate.

  12. Valence and Ionic Lowest-Lying Electronic States of Isobutyl Formate Studied by High-Resolution Vacuum Ultraviolet Photoabsorption, Photoelectron Spectroscopy, and Ab Initio Calculations.

    PubMed

    Śmiałek, M A; Łabuda, M; Guthmuller, J; Hoffmann, S V; Jones, N C; MacDonald, M A; Zuin, L; Mason, N J; Limão-Vieira, P

    2015-08-13

    The highest resolution vacuum ultraviolet photoabsorption spectrum of isobutyl formate, C5H10O2, yet reported is presented over the energy range 4.5-10.7 eV (275.5-118.0 nm) revealing several new spectral features. Valence and Rydberg transitions and their associated vibronic series observed in the photoabsorption spectrum have been assigned in accordance with new ab initio calculations of the vertical excitation energies and oscillator strengths. Calculations have also been carried out to determine the ionization energies and fine structure of the lowest ionic state of isobutyl formate and are compared with a newly recorded photoelectron spectrum (from 9.0 to 27.0 eV). The value of the first ionization energy was determined to be 10.508 eV (adiabatic) and 10.837 eV (vertical). New vibrational structure is observed in the first photoelectron band, predominantly resulting from C-O and C═O stretches of the molecule. The photoabsorption cross sections have been used to calculate the photolysis lifetime of isobutyl formate in the upper stratosphere (20-50 km), indicating that the hydroxyl radical processes will be the main loss process for isobutyl formate. PMID:26176891

  13. Direct Oxygen Abundances for the Lowest Luminosity LVL Galaxies

    NASA Astrophysics Data System (ADS)

    Berg, Danielle; Skillman, E. D.; Marble, A. R.; van Zee, L.; Engelbracht, C. W.

    2012-01-01

    We present new MMT spectroscopic observations of HII regions in 42 of the lowest luminosity galaxies in the Spitzer Local Volume Legacy (LVL) survey. For 31 of the galaxies in our sample we were able to measure the [OIII] ? auroral line at a strength of 4σ or greater, and thus determine oxygen abundances using the direct method. Direct oxygen abundances were compared to B-band luminosity, 4.5 μm luminosity, and stellar mass to characterize the luminosity-metallicity (L-Z) and mass-metallicity (M-Z) relationships at low-luminosity. We examined a "Combined Select” sample composed of 38 objects, from the present sample and the literature, with direct oxygen abundances and reliable distance determinations (based on the tip of the red giant branch or Cepheid variables). The B-band and 4.5 μm L-Z relationships were found to be 12+log(O/H) = (6.19±0.07) + (-0.12±0.01)MB and 12+log(O/H) = (5.93±0.11) + (-0.11±0.01)M[4.5] with dispersions of σ = 0.17 and σ = 0.14 respectively. Since the slope of the L-Z relationship doesn't seem to vary from the optical to the near-IR, as has been observed in studies of more luminous galaxies, we propose that less extinction due to dust is created in the lowest luminosity galaxies. We subsequently derived a M-Z relationship of 12+log(O/H) = (5.49±0.23) + (0.31±0.03)log M*, with a dispersion of σ = 0.16. None of the relationships seem to hold an advantage with respect to dispersion, supporting the idea of minimized dust. Additionally, the trend of N/O abundance with respect to B-V color and oxygen abundance was examined. Similar to the conclusions of van Zee & Haynes (2006), we find a positive correlation between N/O ratio and B-V color: log(N/O) = 0.92 (B-V) - 1.83. Furthermore, there are no objects with high N/O ratio below 12+log(O/H)=7.9.

  14. Proton release from Stentor photoreceptors in the excited states.

    PubMed Central

    Song, P S; Walker, E B; Auerbach, R A; Robinson, G W

    1981-01-01

    Steady-state and picosecond pulse excitations of the photophobic-phototactic receptors isolated from Stentor coeruleus produced anionic species predominantly in the excited singlet state, although neutral photoreceptors in the ground state were exclusively excited. The same photoreceptor in vivo also emits fluorescence from the excited state of its anionic species, with an excitation spectrum identical to the absorption spectrum of the neutral species in the ground state. The excited state dissociation of protons from the photoreceptor chromophore (stentorin; hypericin covalently linked to protein) efficiently occurs in less than 10 ps. A possible role of the transient-proton release from the photoreceptor, in the signal transduction photoresponse of Stentor, is briefly discussed. PMID:6791722

  15. Coherent quantum control of internal conversion: {S}_{2}\\;\\leftrightarrow \\;{S}_{1} in pyrazine via {S}_{0}\\;\\to \\;{S}_{2}/{S}_{1} weak field excitation

    NASA Astrophysics Data System (ADS)

    Grinev, Timur; Shapiro, Moshe; Brumer, Paul

    2015-09-01

    Coherent control of internal conversion (IC) between the first (S1) and second (S2) singlet excited electronic states in pyrazine, where the S2 state is populated from the ground singlet electronic state S0 by weak field excitation, is examined. Control is implemented by shaping the laser which excites S2. Excitation and IC are considered simultaneously, using the recently introduced resonance-based control approach. Highly successful control is achieved by optimizing both the amplitude and phase profiles of the laser spectrum. The dependence of control on the properties of resonances in S2 is demonstrated.

  16. Lowest adverse effects concentrations (LOAECs) for formaldehyde exposure.

    PubMed

    Gelbke, Heinz-Peter; Gröters, Sibylle; Morfeld, Peter

    2014-10-01

    In 2012 the Committee for Risk Assessment (RAC) of the European Chemicals Agency concluded that 2ppm formaldehyde represent a Lowest Observed Adverse Effect Concentration (LOAEC) for polypoid adenomas, histopathological lesions and cell proliferation. An analysis of all data shows that a LOAEC of 2ppm it is not justified for cell proliferation and polypoid adenomas. Higher values are also supported by a new statistical analysis. For histopathological lesions a NOAEC of 1ppm may be defined but the lesions at 2ppm cannot be regarded as pre-stages for tumour development. One major uncertainty exists: the description of polypoid adenomas and the lesions at 2ppm often is insufficient and diagnostic uncertainties can only be resolved by a re-evaluation according to modern histomorphological standards. Although the discrepancy between our assessment and that of RAC may seem rather small we feel the LOAECs proposed by RAC must be challenged taking into consideration the broad data base for formaldehyde and the potential impact of any published RAC opinion on the present discussions about appropriate occupational and indoor exposure limits.

  17. Smarter than Others? Conjectures in Lowest Unique Bid Auctions

    PubMed Central

    Hu, Rui; Chen, Qinghua

    2015-01-01

    Research concerning various types of auctions, such as English auctions, Dutch auctions, highest-price sealed-bid auctions, and second-price sealed-bid auctions, is always a topic of considerable interest in interdisciplinary fields. The type of auction, known as a lowest unique bid auction (LUBA), has also attracted significant attention. Various models have been proposed, but they often fail to explain satisfactorily the real bid-distribution characteristics. This paper discusses LUBA bid-distribution characteristics, including the inverted-J shape and the exponential decrease in the upper region. The authors note that this type of distribution, which initially increases and later decreases, cannot be derived from the symmetric Nash equilibrium framework based on perfect information that has previously been used. A novel optimization model based on non-perfect information is presented. The kernel of this model is the premise that agents make decisions to achieve maximum profit based on imaginary information or assumptions regarding the behavior of others. PMID:25849631

  18. Deep two-photon microscopic imaging through brain tissue using the second singlet state from fluorescent agent chlorophyll α in spinach leaf

    NASA Astrophysics Data System (ADS)

    Shi, Lingyan; Rodríguez-Contreras, Adrián; Budansky, Yury; Pu, Yang; An Nguyen, Thien; Alfano, Robert R.

    2014-06-01

    Two-photon (2P) excitation of the second singlet (S) state was studied to achieve deep optical microscopic imaging in brain tissue when both the excitation (800 nm) and emission (685 nm) wavelengths lie in the "tissue optical window" (650 to 950 nm). S2 state technique was used to investigate chlorophyll α (Chl α) fluorescence inside a spinach leaf under a thick layer of freshly sliced rat brain tissue in combination with 2P microscopic imaging. Strong emission at the peak wavelength of 685 nm under the 2P S state of Chl α enabled the imaging depth up to 450 μm through rat brain tissue.

  19. Carbon dioxide photolysis from 150 to 210 nm: Singlet and triplet channel dynamics, UV-spectrum, and isotope effects

    PubMed Central

    Schmidt, Johan A.; Johnson, Matthew S.; Schinke, Reinhard

    2013-01-01

    We present a first principles study of the carbon dioxide (CO2) photodissociation process in the 150- to 210-nm wavelength range, with emphasis on photolysis below the carbon monoxide + singlet channel threshold at ∼167 nm. The calculations reproduce experimental absorption cross-sections at a resolution of ∼0.5 nm without scaling the intensity. The observed structure in the 150- to 210-nm range is caused by excitation of bending motion supported by the deep wells at bent geometries in the and potential energy surfaces. Predissociation below the singlet channel threshold occurs via spin-orbit coupling to nearby repulsive triplet states. Carbon monoxide vibrational and rotational state distributions in the singlet channel as well as the triplet channel for excitation at 157 nm satisfactorily reproduce experimental data. The cross-sections of individual CO2 isotopologues (12C16O2, 12C17O16O, 12C18O16O, 13C16O2, and 13C18O16O) are calculated, demonstrating that strong isotopic fractionation will occur as a function of wavelength. The calculations provide accurate, detailed insight into CO2 photoabsorption and dissociation dynamics, and greatly extend knowledge of the temperature dependence of the cross-section to cover the range from 0 to 400 K that is useful for calculations of propagation of stellar light in planetary atmospheres. The model is also relevant for the interpretation of laboratory experiments on mass-independent isotopic fractionation. Finally, the model shows that the mass-independent fractionation observed in a series of Hg lamp experiments is not a result of hyperfine interactions making predissociation of 17O containing CO2 more efficient. PMID:23776249

  20. Carbon dioxide photolysis from 150 to 210 nm: singlet and triplet channel dynamics, UV-spectrum, and isotope effects.

    PubMed

    Schmidt, Johan A; Johnson, Matthew S; Schinke, Reinhard

    2013-10-29

    We present a first principles study of the carbon dioxide (CO2) photodissociation process in the 150- to 210-nm wavelength range, with emphasis on photolysis below the carbon monoxide + singlet channel threshold at ~167 nm. The calculations reproduce experimental absorption cross-sections at a resolution of ~0.5 nm without scaling the intensity. The observed structure in the 150- to 210-nm range is caused by excitation of bending motion supported by the deep wells at bent geometries in the and potential energy surfaces. Predissociation below the singlet channel threshold occurs via spin-orbit coupling to nearby repulsive triplet states. Carbon monoxide vibrational and rotational state distributions in the singlet channel as well as the triplet channel for excitation at 157 nm satisfactorily reproduce experimental data. The cross-sections of individual CO2 isotopologues ((12)C(16)O2, (12)C(17)O(16)O, (12)C(18)O(16)O, (13)C(16)O2, and (13)C(18)O(16)O) are calculated, demonstrating that strong isotopic fractionation will occur as a function of wavelength. The calculations provide accurate, detailed insight into CO2 photoabsorption and dissociation dynamics, and greatly extend knowledge of the temperature dependence of the cross-section to cover the range from 0 to 400 K that is useful for calculations of propagation of stellar light in planetary atmospheres. The model is also relevant for the interpretation of laboratory experiments on mass-independent isotopic fractionation. Finally, the model shows that the mass-independent fractionation observed in a series of Hg lamp experiments is not a result of hyperfine interactions making predissociation of (17)O containing CO2 more efficient.

  1. Charge-Transfer Versus Charge-Transfer-Like Excitations Revisited

    SciTech Connect

    Moore, Barry; Sun, Haitao; Govind, Niranjan; Kowalski, Karol; Autschbach, Jochen

    2015-07-14

    Criteria to assess charge-transfer (CT) and `CT-like' character of electronic excitations are examined. Time-dependent density functional theory (TDDFT) with non-hybrid, hybrid, and tuned long-range corrected (LC) functionals is compared with with coupled-cluster (CC) benchmarks. The test set includes an organic CT complex, two `push-pull' donor-acceptor chromophores, a cyanine dye, and several polycyclic aromatic hydrocarbons. Proper CT is easily identified. Excitations with significant density changes upon excitation within regions of close spatial proximity can also be diagnosed. For such excitations, the use of LC functionals in TDDFT sometimes leads to dramatic improvements of the singlet energies, similar to proper CT, which has led to the concept of `CT-like' excitations. However, `CT-like' excitations are not like charge transfer, and the improvements are not obtained for the right reasons. The triplet excitation energies are underestimated for all systems, often severely. For the `CT-like' candidates, when going from a non-hybrid to an LC functional the error in the singlet-triplet (S/T) separation changes from negative to positive, providing error compensation. For the cyanine, the S/T separation is too large with all functionals, leading to the best error compensation for non-hybrid functionals.

  2. Up-converted fluorescence from photosynthetic light-harvesting complexes linearly dependent on excitation intensity.

    PubMed

    Leiger, Kristjan; Freiberg, Arvi

    2016-01-01

    Weak up-converted fluorescence related to bacteriochlorophyll a was recorded from various detergent-isolated and membrane-embedded light-harvesting pigment-protein complexes as well as from the functional membranes of photosynthetic purple bacteria under continuous-wave infrared laser excitation at 1064 nm, far outside the optically allowed singlet absorption bands of the chromophore. The fluorescence increases linearly with the excitation power, distinguishing it from the previously observed two-photon excited fluorescence upon femtosecond pulse excitation. Possible mechanisms of this excitation are discussed.

  3. Singlet-triplet electron scattering admixture due to fine- and hyper-fine interactions in Cs Rydberg molecules

    NASA Astrophysics Data System (ADS)

    Markson, Samuel; Rittenhouse, Seth; Sadeghpour, Hossein

    2016-05-01

    We will present the admixture of singlet electron scattering into the more dominant triplet scattering in the formation of ultracold Cs Rydberg molecules excited into non-zero electronic angular momentum states. This admixture comes about due to both spin-orbit (SO) coupling in the Rydberg atom as well as the hyperfine (HF) coupling in the ground state atom. In Cs, the Rydberg SO and ground HF interactions are on par. The interaction between the Rydberg electron and the ground state atom includes both s-wave and p-wave scattering components which can cause additional mixing of electronic Rydberg states in the bound molecules. We intend to apply the formalism to Rydberg excitation in Cs in p and d states and will give a progress report at the meeting.

  4. Singlet fermion dark matter within left-right model

    NASA Astrophysics Data System (ADS)

    Patra, Sudhanwa; Rao, Soumya

    2016-08-01

    We discuss singlet fermion dark matter within a left-right symmetric model promoting baryon and lepton numbers as separate gauge symmetries. We add a simple Dirac fermionic dark matter singlet under SU(2) L , R with nonzero and equal baryon and lepton number which ensures electric charge neutrality. Such a dark matter candidate interacts with SM particles through the extra ZB,ℓ gauge bosons. This can give rise to a dark matter particle of a few hundred GeV that couples to ∼TeV scale gauge bosons to give the correct relic density. This model thus accommodates TeV scale ZB,ℓ gauge bosons and other low scale BSM particles, which can be easily probed at LHC.

  5. A transferable model for singlet-fission kinetics.

    PubMed

    Yost, Shane R; Lee, Jiye; Wilson, Mark W B; Wu, Tony; McMahon, David P; Parkhurst, Rebecca R; Thompson, Nicholas J; Congreve, Daniel N; Rao, Akshay; Johnson, Kerr; Sfeir, Matthew Y; Bawendi, Moungi G; Swager, Timothy M; Friend, Richard H; Baldo, Marc A; Van Voorhis, Troy

    2014-06-01

    Exciton fission is a process that occurs in certain organic materials whereby one singlet exciton splits into two independent triplets. In photovoltaic devices these two triplet excitons can each generate an electron, producing quantum yields per photon of >100% and potentially enabling single-junction power efficiencies above 40%. Here, we measure fission dynamics using ultrafast photoinduced absorption and present a first-principles expression that successfully reproduces the fission rate in materials with vastly different structures. Fission is non-adiabatic and Marcus-like in weakly interacting systems, becoming adiabatic and coupling-independent at larger interaction strengths. In neat films, we demonstrate fission yields near unity even when monomers are separated by >5 Å. For efficient solar cells, however, we show that fission must outcompete charge generation from the singlet exciton. This work lays the foundation for tailoring molecular properties like solubility and energy level alignment while maintaining the high fission yield required for photovoltaic applications. PMID:24848234

  6. A transferable model for singlet-fission kinetics

    NASA Astrophysics Data System (ADS)

    Yost, Shane R.; Lee, Jiye; Wilson, Mark W. B.; Wu, Tony; McMahon, David P.; Parkhurst, Rebecca R.; Thompson, Nicholas J.; Congreve, Daniel N.; Rao, Akshay; Johnson, Kerr; Sfeir, Matthew Y.; Bawendi, Moungi G.; Swager, Timothy M.; Friend, Richard H.; Baldo, Marc A.; van Voorhis, Troy

    2014-06-01

    Exciton fission is a process that occurs in certain organic materials whereby one singlet exciton splits into two independent triplets. In photovoltaic devices these two triplet excitons can each generate an electron, producing quantum yields per photon of >100% and potentially enabling single-junction power efficiencies above 40%. Here, we measure fission dynamics using ultrafast photoinduced absorption and present a first-principles expression that successfully reproduces the fission rate in materials with vastly different structures. Fission is non-adiabatic and Marcus-like in weakly interacting systems, becoming adiabatic and coupling-independent at larger interaction strengths. In neat films, we demonstrate fission yields near unity even when monomers are separated by >5 Å. For efficient solar cells, however, we show that fission must outcompete charge generation from the singlet exciton. This work lays the foundation for tailoring molecular properties like solubility and energy level alignment while maintaining the high fission yield required for photovoltaic applications.

  7. A flippon related singlet at the LHC II

    NASA Astrophysics Data System (ADS)

    Li, Tianjun; Maxin, James A.; Mayes, Van E.; Nanopoulos, Dimitri V.

    2016-06-01

    We consider the 750 GeV diphoton resonance at the 13 TeV LHC in the ℱ-SU(5) model with a Standard Model (SM) singlet field which couples to TeV-scale vector-like particles, dubbed flippons. This singlet field assumes the role of the 750 GeV resonance, with production via gluon fusion and subsequent decay to a diphoton via the vector-like particle loops. We present a numerical analysis showing that the observed 8 TeV and 13 TeV diphoton production cross-sections can be generated in the model space with realistic electric charges and Yukawa couplings for light vector-like masses. We further discuss the experimental viability of light vector-like masses in a General No-Scale ℱ-SU(5) model, offering a few benchmark scenarios in this consistent GUT that can satisfy all experimental constraints imposed by the LHC and other essential experiments.

  8. Trap-induced photoconductivity in singlet fission pentacene diodes

    SciTech Connect

    Qiao, Xianfeng Zhao, Chen; Chen, Bingbing; Luan, Lin

    2014-07-21

    This paper reports a trap-induced photoconductivity in ITO/pentacene/Al diodes by using current-voltage and magneto-conductance measurements. The comparison of photoconductivity between pentacene diodes with and without trap clearly shows that the traps play a critical role in generating photoconductivity. It shows that no observable photoconductivity is detected for trap-free pentacene diodes, while significant photoconductivity is observed in diodes with trap. This is because the initial photogenerated singlet excitons in pentacene can rapidly split into triplet excitons with higher binding energy prior to dissociating into free charge carriers. The generated triplet excitons react with trapped charges to release charge-carriers from traps, leading to a trap-induced photoconductivity in the single-layer pentacene diodes. Our studies elucidated the formation mechanisms of photoconductivity in pentacene diodes with extremely fast singlet fission rate.

  9. Fast Singlet Exciton Decay in Push-Pull Molecules Containing Oxidized Thiophenes.

    PubMed

    Busby, Erik; Xia, Jianlong; Low, Jonathan Z; Wu, Qin; Hoy, Jessica; Campos, Luis M; Sfeir, Matthew Y

    2015-06-18

    A common synthetic strategy used to design low-bandgap organic semiconductors employs the use of "push-pull" building blocks, where electron -rich and electron-deficient monomers are alternated along the π-conjugated backbone of a molecule or polymer. Incorporating strong "pull" units with high electron affinity is a means to further decrease the optical gap for infrared optoelectronics or to develop n-type semiconducting materials. Here we show that the use of thiophene-1,1-dioxide as a strong acceptor in "push-pull" oligomers affects the electronic structure and carrier dynamics in unexpected ways. Critically, the overall excited-state lifetime is reduced by several orders of magnitude relative to unoxidized analogs due to the introduction of low-energy optically dark states and low-energy triplet states that allow for fast internal conversion and intramolecular singlet fission. We found that the electronic structure and excited-state lifetime are strongly dependent on the number of sequential thiophene-1,1-dioxide units. These results suggest that both the static and dynamical optical properties are highly tunable via small changes in chemical structure that have drastic effects on the optoelectronic properties, which can impact the types of applications that involve these materials.

  10. A systematic approach to vertically excited states of ethylene using configuration interaction and coupled cluster techniques

    SciTech Connect

    Feller, David Peterson, Kirk A.; Davidson, Ernest R.

    2014-09-14

    A systematic sequence of configuration interaction and coupled cluster calculations were used to describe selected low-lying singlet and triplet vertically excited states of ethylene with the goal of approaching the all electron, full configuration interaction/complete basis set limit. Included among these is the notoriously difficult, mixed valence/Rydberg {sup 1}B{sub 1u} V state. Techniques included complete active space and iterative natural orbital configuration interaction with large reference spaces which led to variational spaces of 1.8 × 10{sup 9} parameters. Care was taken to avoid unintentionally biasing the results due to the widely recognized sensitivity of the V state to the details of the calculation. The lowest vertical and adiabatic ionization potentials to the {sup 2}B{sub 3u} and {sup 2}B{sub 3} states were also determined. In addition, the heat of formation of twisted ethylene {sup 3}A{sub 1} was obtained from large basis set coupled cluster theory calculations including corrections for core/valence, scalar relativistic and higher order correlation recovery.

  11. Ultrafast electron transfer reactions initiated by excited CT states of push pull perylenes

    NASA Astrophysics Data System (ADS)

    Miller, Scott E.; Zhao, Yongyu; Schaller, Richard; Mulloni, Viviana; Just, Eric M.; Johnson, Robert C.; Wasielewski, Michael R.

    2002-01-01

    Two new chromophores that absorb in the visible spectrum, the 9-( N-pyrrolidinyl)- and 9-( N-piperidinyl)perylene-3,4-dicarboximides, 5PMI and 6PMI, respectively, were synthesized and shown to possess lowest excited singlet states with about 70% charge transfer (CT) character. Changing the ring size of the cyclic amine from 5 to 6 significantly changes the energies of the CT states, as well as the redox potentials of the chromophores. These chromophores were linked to pyromellitimide (PI) and 1,8:4,5-naphthalenediimide (NI) electron acceptors using a single N-N bond between their respective imides to yield the corresponding donor-acceptor dyads 5PMI-PI, 5PMI-NI, 6PMI-PI, and 6PMI-NI. The donors and acceptors in these molecules are positioned relative to one another in a rod-like arrangement at fixed distances and restricted orientations. The rates of charge separation and recombination were measured using transient absorption spectroscopy. These chromophores were also used to prepare rigid donor-acceptor triads 5PMI-PI-NI and 6PMI-PI-NI, which display one- or two-step electron transfer mechanisms that depend on solvent polarity. These compounds exhibit a broad range of structure and media driven changes in electron transfer mechanism.

  12. IDMS: inert dark matter model with a complex singlet

    NASA Astrophysics Data System (ADS)

    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.

  13. Combining Ruthenium(II) Complexes with Metal-Organic Frameworks to Realize Effective Two-Photon Absorption for Singlet Oxygen Generation.

    PubMed

    Zhang, Wenxiang; Li, Bin; Ma, Heping; Zhang, Liming; Guan, Yunlong; Zhang, Yihe; Zhang, Xindan; Jing, Pengtao; Yue, Shumei

    2016-08-24

    Singlet oxygen ((1)O2), as a reactive oxygen species, has garnered serious attention in physical, chemical, and biological studies. In this paper, we designed and synthesized a new type of singlet-oxygen generation system by exchanging cationic ruthenium complexes (RCs) into anionic bio-MOF-1. The resulting bio-MOF-1&RCs can be used as effective photocatalysts for generation of singlet oxygen under both single-photon and two-photon excitation. Especially, the excellent two-photon absorption (TPA) behavior of bio-MOF-1&RCs aroused our interest greatly because their two-photon absorption band lies in the optical window of biological tissue. Here, we measured the ability of bio-MOF-1&RCs to generate (1)O2 by irradiation under both 490 and 800 nm wavelength light in DMF. 1,3-Diphenylisobenzofuran (DPBF) and 2',7'-dichlorofluorescein (DCFH) were used as typical (1)O2 traps to detect and evaluate the efficiency of generation of (1)O2 under single-photon and two-photon excitation, respectively. Results indicated that bio-MOF-1&[Ru(phen)3](2+) was able to effectively generate (1)O2 under both conditions. Our work creates a novel synergistic TPA system with the excellent photophysical properties of RCs and the unique microporous structure benefit of MOFs, which may open a new avenue for creation of a cancer treatment system with both photodynamic therapy and chemotherapy. PMID:27483010

  14. Singlet oxygen treatment of tumor cells triggers extracellular singlet oxygen generation, catalase inactivation and reactivation of intercellular apoptosis-inducing signaling.

    PubMed

    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.

  15. Singlet oxygen treatment of tumor cells triggers extracellular singlet oxygen generation, catalase inactivation and reactivation of intercellular apoptosis-inducing signaling☆

    PubMed Central

    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

  16. Excited Delirium

    PubMed Central

    Takeuchi, Asia; Ahern, Terence L.; Henderson, Sean O.

    2011-01-01

    Excited (or agitated) delirium is characterized by agitation, aggression, acute distress and sudden death, often in the pre-hospital care setting. It is typically associated with the use of drugs that alter dopamine processing, hyperthermia, and, most notably, sometimes with death of the affected person in the custody of law enforcement. Subjects typically die from cardiopulmonary arrest, although the cause is debated. Unfortunately an adequate treatment plan has yet to be established, in part due to the fact that most patients die before hospital arrival. While there is still much to be discovered about the pathophysiology and treatment, it is hoped that this extensive review will provide both police and medical personnel with the information necessary to recognize and respond appropriately to excited delirium. PMID:21691475

  17. Excited baryons

    SciTech Connect

    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)

  18. Singlet oxygen signatures are detected independent of light or chloroplasts in response to multiple stresses.

    PubMed

    Mor, Avishai; Koh, Eugene; Weiner, Lev; Rosenwasser, Shilo; Sibony-Benyamini, Hadas; Fluhr, Robert

    2014-05-01

    The production of singlet oxygen is typically associated with inefficient dissipation of photosynthetic energy or can arise from light reactions as a result of accumulation of chlorophyll precursors as observed in fluorescent (flu)-like mutants. Such photodynamic production of singlet oxygen is thought to be involved in stress signaling and programmed cell death. Here we show that transcriptomes of multiple stresses, whether from light or dark treatments, were correlated with the transcriptome of the flu mutant. A core gene set of 118 genes, common to singlet oxygen, biotic and abiotic stresses was defined and confirmed to be activated photodynamically by the photosensitizer Rose Bengal. In addition, induction of the core gene set by abiotic and biotic selected stresses was shown to occur in the dark and in nonphotosynthetic tissue. Furthermore, when subjected to various biotic and abiotic stresses in the dark, the singlet oxygen-specific probe Singlet Oxygen Sensor Green detected rapid production of singlet oxygen in the Arabidopsis (Arabidopsis thaliana) root. Subcellular localization of Singlet Oxygen Sensor Green fluorescence showed its accumulation in mitochondria, peroxisomes, and the nucleus, suggesting several compartments as the possible origins or targets for singlet oxygen. Collectively, the results show that singlet oxygen can be produced by multiple stress pathways and can emanate from compartments other than the chloroplast in a light-independent manner. The results imply that the role of singlet oxygen in plant stress regulation and response is more ubiquitous than previously thought.

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

    PubMed

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

    2015-12-21

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

  20. Determination of the singlet-triplet energy separation for C{sub 60}{sup 2+} in DMSO by electron paramagnetic resonance

    SciTech Connect

    Trulove, P.C.; Carlin, R.T.; Eaton, G.R.; Eaton, S.S.

    1995-06-14

    In situ near-IR (NIR) spectra for C{sub 60}{sup 2-} generated electrochemically in DMSO (dimethyl sulfoxide) indicate 87 {+-} 10% conversion to C{sub 60}{sup 2-}. In the EPR spectra at 106 K a single line with 2-G peak-to-peak linewidth is superimposed on signals with splittings of 11 and 30 G, which is similar to spectra reported in the literature. The low intensity of the sharp EPR signals is inconsistent with assignment to the ground state of C{sub 60}{sup 2-} or to an excited state with ground-excited state separation less than kT between 4.5 and 200 K. A broad signal that has not been reported previously and increased in intensity with increasing temperature above 135 K is assigned to an excited triplet state with a singlet-triplet splitting of 600 {+-} 100 cm{sup -1}. The absolute intensity of the signal is consistent with the proposed singlet-triplet splitting. The 30-G line width of this signal corresponds to a lifetime of 2 ns, which is tentatively assigned as the lifetime of the triplet excited state. 48 refs., 7 figs.

  1. The phototoxicity of polycyclic aromatic hydrocarbons: a theoretical study of excited states and correlation to experiment.

    PubMed

    Betowski, Leon D; Enlow, Mark; Riddick, Lee

    2002-06-01

    Investigators using models to determine the phototoxic effects of sunlight on polycyclic aromatic hydrocarbons (PAHs) have invoked the excited states of the molecule as important in elucidating the mechanism of these reactions. Energies of actual excited states were calculated for ten PAHs by several ab initio methods. The main method used for these calculations was the Configuration Interaction approach, modeling excited states as combinations of single substitutions out of the Hartree-Fock ground state. These calculations correlate well with both experimentally measured singlet and triplet state energies and also previous HOMO-LUMO gap energies that approximate the singlet state energies. The excited state calculations then correlate well with general models of photo-induced toxicity based for the PAHs.

  2. Decreasing the singlet-triplet gap for thermally activated delayed fluorescence molecules by structural modification on the donor fragment: First-principles study

    NASA Astrophysics Data System (ADS)

    Fan, Jian-zhong; Lin, Li-li; Wang, Chuan-kui

    2016-05-01

    The small energy gap between singlet excitons (S) and triplet excitons (T) of organic molecules is a dominant condition for high efficient thermally activated delayed fluorescence (TADF). In this study, influence of modification in donor groups of a series of molecules on their geometries, S-T energy gaps, and photophysical properties, is investigated based on first-principles calculations. Investigation shows that, as the electron donating ability is increased, both S-T energy gap and overlap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are decreased. This work provides strategy for designing high efficient and multi-color TADF devices.

  3. 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.

    PubMed

    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

  4. Electron scattering by laser-excited barium atoms

    NASA Technical Reports Server (NTRS)

    Register, D. F.; Trajmar, S.; Jensen, S. W.; Poe, R. T.

    1978-01-01

    Inelastic and superelastic scattering of 30- and 100-eV electrons by laser-excited 6s 6p 1P and subsequent cascade-populated 6s 6p 3P, 6s 5d 1D, and 6s 5d 3D Ba atoms have been observed. Absolute differential cross sections for the singlet and relative scattering intensities for the triplet species have been determined in the 5 to 20 deg angular region. Under the present conditions excitations dominate over deexcitations.

  5. A new analytical potential energy surface for the singlet state of He{sub 2}H{sup +}

    SciTech Connect

    Liang Jingjuan; Zhang Qinggang; Yang Chuanlu; Wang Lizhi

    2012-03-07

    The analytic potential energy surface (APES) for the exchange reaction of HeH{sup +} (X{sup 1}{Sigma}{sup +}) + He at the lowest singlet state 1{sup 1}A{sup /} has been built. The APES is expressed as Aguado-Paniagua function based on the many-body expansion. Using the adaptive non-linear least-squares algorithm, the APES is fitted from 15 682 ab initio energy points calculated with the multireference configuration interaction calculation with a large d-aug-cc-pV5Z basis set. To testify the new APES, we calculate the integral cross sections for He + H{sup +}He (v= 0, 1, 2, j= 0) {yields} HeH{sup +}+ He by means of quasi-classical trajectory and compare them with the previous result in literature.

  6. Photosensitized production of singlet oxygen by merocyanine 540 bound to liposomes.

    PubMed

    Hoebeke, M; Piette, J; van de Vorst, A

    1991-06-01

    The production of singlet oxygen by merocyanine 540 was studied in dimyristoyl-phosphatidylcholine liposomes using two singlet oxygen probes: 9,10-anthracenedipropionic acid (water soluble) and 9,10-dimethylanthracene (liposoluble). Upper and lower limits of singlet oxygen quantum yield for bound merocyanine 540 were determined to be 0.055 and 0.015 respectively. The diffusion characteristics of singlet oxygen were examined using the isotropic enhancement effect of D2O and the inhibitory effect of sodium azide. It was shown that 1O2 spent more than 87% of its lifetime in a vesicle environment. When the singlet-reacting substrate and the dye were both located in the bilayer, approximately 40% of the singlet oxygen remained in the liposomes where it was originally generated.

  7. Long-Lived Heteronuclear Spin-Singlet States in Liquids at a Zero Magnetic field

    NASA Astrophysics Data System (ADS)

    Emondts, M.; Ledbetter, M. P.; Pustelny, S.; Theis, T.; Patton, B.; Blanchard, J. W.; Butler, M. C.; Budker, D.; Pines, A.

    2014-02-01

    We report an observation of long-lived spin-singlet states in a C-H113 spin pair in a zero magnetic field. In C13-labeled formic acid, we observe spin-singlet lifetimes as long as 37 s, about a factor of 3 longer than the T1 lifetime of dipole polarization in the triplet state. In contrast to common high-field experiments, the observed coherence is a singlet-triplet coherence with a lifetime T2 longer than the T1 lifetime of dipole polarization in the triplet manifold. Moreover, we demonstrate that heteronuclear singlet states formed between a H1 and a C13 nucleus can exhibit longer lifetimes than the respective triplet states even in the presence of additional spins that couple to the spin pair of interest. Although long-lived homonuclear spin-singlet states have been extensively studied, this is the first experimental observation of analogous singlet states in heteronuclear spin pairs.

  8. Singlet exciton fission for solar cell applications: energy aspects of interchromophore coupling.

    PubMed

    Greyson, Eric C; Stepp, Brian R; Chen, Xudong; Schwerin, Andrew F; Paci, Irina; Smith, Millicent B; Akdag, Akin; Johnson, Justin C; Nozik, Arthur J; Michl, Josef; Ratner, Mark A

    2010-11-18

    Singlet exciton fission, a process that converts one singlet exciton to a pair of triplet excitons, has the potential to enhance the efficiency of both bulk heterojunction and dye-sensitized solar cells and is understood in crystals but not well understood in molecules. Previous studies have identified promising building blocks for singlet fission in molecular systems, but little work has investigated how these individual chromophores should be combined to maximize triplet yield. We consider the effects of chemically connecting two chromophores to create a coupled chromophore pair and compute how various structural choices alter the thermodynamic and kinetic parameters likely to control singlet fission yield. We use density functional theory to compute the electron transfer matrix element and the thermodynamics of fission for several promising chromophore pairs and find a trade-off between the desire to maximize this element and the desire to keep the singlet fission process exoergic. We identify promising molecular systems for singlet fission and suggest future experiments.

  9. Singlet oxygen as a reactive intermediate in the photodegradation of an electroluminescent polymer

    SciTech Connect

    Scurlock, R.D.; Wang, B.; Ogilby, P.R.; Sheats, J.R.; Clough, R.L.

    1995-10-18

    Singlet molecular oxygen (a{sup 1}{Delta}{sub g}) is shown to be a reactive intermediate in the photoinduced oxidative decomposition of the electroluminescent material poly(2,5-bis(5,6-dihydrocholestanoxy)-1,4-phenylenevinylene) [BCHA-PPV] in both liquid solutions and solid films. Upon irradiation of this polymer in CS{sub 2}, singlet oxygen is produced by energy transfer from the BCHA-PPV triplet state to ground state oxygen with a quantum yield of nearly 0.025. Singlet oxygen reacts with BCHA-PPV, resulting in extensive chain scission of the macromolecule. The reaction with singlet oxygen is unique to the polymer; the monomeric analog of this system, stilbene, does not appreciably react with singlet oxygen. Polymer degradation is proposed to proceed via addition of singlet oxygen in a{sub {pi}} 2+{sub {pi}}2 cycloaddition reaction to the double bond that connects phenylene groups in the macromolecule. 60 refs., 6 figs.

  10. Interplay between Kondo screening and local singlets in SU (N) -symmetric cold atoms

    NASA Astrophysics Data System (ADS)

    Isaev, Leonid; Rey, Ana Maria

    2015-03-01

    We study collective phenomena in strongly interacting fermionic alkaline-earth atoms (AEAs) loaded in an optical lattice. Owing to the strong decoupling between electronic orbital and nuclear-spin degrees of freedom, AEAs prepared in the two lowest electronic states are predicted to obey an accurate SU (N > 2 I + 1) symmetry in their two-body collisions (I is the nuclear spin). The SU (N) symmetric models offer a great opportunity to generate exotic many-body behavior emerging from the increased degeneracy and strict conservation laws. We focus on a parameter regime that realizes an SU (N > 2) (Coqblin-Schrieffer) generalization of the usual Kondo lattice model, and show that for band fillings above one atom per site, the system exhibits a peculiar interplay between Kondo screening and formation of singlets between localized atoms. In the limit of large Kondo coupling, we derive an effective Hamiltonian and determine its phase diagram. Our results can be tested in experiments with ultracold 173 Yb or 87 Sr atoms and are relevant for the physics of heavy-fermion materials with magnetic frustration. Supported by AFOSR, MURI-AFOSR and NSF.

  11. Sexual excitement.

    PubMed

    Stoller, R J

    1976-08-01

    Sexual excitement depends on a scenario the person to be aroused has been writing since childhood. The story is an adventure, an autobiography disguised as fiction, in which the hero/heroine hides crucial intrapsychic conflicts, mysteries, screen memories of actual traumatic events and the resolution of these elements into a happy ending, best celebrated by orgasm. The function of the fantasy is to take these painful experiences and convert them to pleasure-triumph. In order to sharpen excitement-the vibration between the fear of original traumas repeating and the hope of a pleasurable conclusion this time-one introduces into the story elements of risk (approximations of the trauma) meant to prevent boredom and safety factors (sub-limnal signals to the storyteller that the risk are not truly dangerous). Sexual fantasy can be studied by means of a person's daydreams (including those chosen in magazines, books, plays, television, movies, and outright pornography), masturbatory behavior, object choice, foreplay, techniques of intercourse, or postcoital behavior. PMID:949223

  12. Sexual excitement.

    PubMed

    Stoller, R J

    1976-08-01

    Sexual excitement depends on a scenario the person to be aroused has been writing since childhood. The story is an adventure, an autobiography disguised as fiction, in which the hero/heroine hides crucial intrapsychic conflicts, mysteries, screen memories of actual traumatic events and the resolution of these elements into a happy ending, best celebrated by orgasm. The function of the fantasy is to take these painful experiences and convert them to pleasure-triumph. In order to sharpen excitement-the vibration between the fear of original traumas repeating and the hope of a pleasurable conclusion this time-one introduces into the story elements of risk (approximations of the trauma) meant to prevent boredom and safety factors (sub-limnal signals to the storyteller that the risk are not truly dangerous). Sexual fantasy can be studied by means of a person's daydreams (including those chosen in magazines, books, plays, television, movies, and outright pornography), masturbatory behavior, object choice, foreplay, techniques of intercourse, or postcoital behavior.

  13. Deactivation of singlet oxygen by single-wall carbon nanohorns

    NASA Astrophysics Data System (ADS)

    Yanagi, Kazuhiro; Okazaki, Toshiya; Miyata, Yasumitsu; Kataura, Hiromichi

    2006-11-01

    The deactivation rate constant of singlet oxygen 1O 2 by single-wall carbon nanohorns (SWNHs) was determined. The estimated rate constant by SWNHs, 8 × 10 4 L g -1 s -1, was significantly larger than the physical quenching rate constant by α-Tocopherol, 0.9 × 10 4 L g -1 s -1. The origin of this remarkable efficiency of SWNHs for 1O 2 deactivation is ascribed to the unique curvature of the graphitic tube in their horn shaped structure.

  14. Singlet-assisted supersymmetry breaking for Sp(2N) theories

    NASA Astrophysics Data System (ADS)

    Zhu, Bin; Meng, Kun; Ding, Ran; Li, Qiyi

    2013-07-01

    We investigate local supersymmetry-breaking vacua in s-confining theories with gauge group Sp(2N). By adapting the general recipe developed by Shadmi and Shirman, we construct a realistic model based on dynamics of SQCD coupled with singlets which allows a spontaneously broken supersymmetry. Since the chiral superfields in model have R-charges R = 0 and R = 2 only, the tedious computations of Coleman-Weinberg potential can be greatly alleviated from the lesson of David Shih. We observe that the pseudomoduli fields are stabilized at the origin of moduli space at one-loop order with calculability being preserved.

  15. Localization length scales of triplet excitons in singlet fission materials

    NASA Astrophysics Data System (ADS)

    Bayliss, Sam L.; Thorley, Karl J.; Anthony, John E.; Bouchiat, Hélène; Greenham, Neil C.; Chepelianskii, Alexei D.

    2015-09-01

    We measure the dielectric confinement length scales of triplet excitons in organic semiconductors by jointly measuring their microwave-domain electric and magnetic susceptibilities. We apply this technique to characterize triplet excitons in two singlet fission materials with distinct solid-state packing and correlate the extracted localization length scales with the role of the excitonic environment. By using the magnetic susceptibility simultaneously determined through our experiments, we compare the independently extracted dielectric and spin-spin localization length scales, highlighting the role of local anisotropy on the properties of excitonic triplet states.

  16. The entanglement structure of the Kondo singlet in energy space

    NASA Astrophysics Data System (ADS)

    Yang, Chun; Feiguin, Adrian

    We unveil the entanglement structure of the Kondo singlet in energy space by studying the contribution of each individual free electron eigenstate. This is a problem of two spins coupled to a bath, where the bath is formed by the remaining conduction electrons. Being a mixed state, we resort to the ''concurrence'' as a good measure of entanglement. Using the density matrix renormalization group and analytical variational calculations with the Yoshida wave-function, and slave bosons, we find a distinct transition between weak and strong coupling regimes characterized by very different entanglement distributions. We discuss implications to the theory of the Kondo cloud.

  17. Detection techniques for singlet oxygen production during photodynamic therapy (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Li, Buhong

    2016-03-01

    Singlet oxygen is widely considered to be the major cytotoxic reactive oxygen species (ROS) generated during photodynamic therapy (PDT). This talk summarizes recent advances and future perspectives in detection techniques for singlet oxygen production, and the advantages and limitations of each technique will be presented. In addition, our custom developed novel configuration of a near-infrared sensitive camera and adaptive optics for in vivo fast imaging of singlet oxygen luminescence around 1270 nm will be highlighted. For clinical PDT application, the challenges for direct measrement of singlet oxygen luminescence will be discussed.

  18. Ultraweak bioluminescence dynamics and singlet oxygen correlations during injury repair in sweet potato

    NASA Astrophysics Data System (ADS)

    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.

  19. Toward Singlet-Triplet Bistable Nonalternant Kekulé Hydrocarbons: Azulene-to-Naphthalene Rearrangement.

    PubMed

    Das, Soumyajit; Wu, Jishan

    2015-12-01

    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. PMID:26569547

  20. Excited nucleon spectrum with two flavors of dynamical fermions

    SciTech Connect

    M. Bulava, John; Edward, Robert; Engelson, Eric; Joo, Balint; Lichtl, Adam; Lin, Huey-Wen; Mathur, Nilmani; Morningstar, Colin; Richards, David; Wallace, Stephen

    2009-01-01

    We compute the spectrum of excited nucleons using the anisotropic Wilson lattice with two flavors of dynamical fermions. Using optimized sets of operators which transform irreducibly under the octahedral group, matrices of correlation functions are computed. We apply the variational method to these matrices to extract excited energy eigenstates. We obtain several states for each irrep and identify the continuum spin for the lowest-lying states, including a $J^P={5/2}^-$ state.

  1. Singlet-triplet energy splitting between 1D and 3D (1s2 2s nd), n = 3, 4, 5, and 6, Rydberg states of the beryllium atom (9Be) calculated with all-electron explicitly correlated Gaussian functions

    NASA Astrophysics Data System (ADS)

    Sharkey, Keeper L.; Bubin, Sergiy; Adamowicz, Ludwik

    2014-11-01

    Accurate variational nonrelativistic quantum-mechanical calculations are performed for the five lowest 1D and four lowest 3D states of the 9Be isotope of the beryllium atom. All-electron explicitly correlated Gaussian (ECG) functions are used in the calculations and their nonlinear parameters are optimized with the aid of the analytical energy gradient determined with respect to these parameters. The effect of the finite nuclear mass is directly included in the Hamiltonian used in the calculations. The singlet-triplet energy gaps between the corresponding 1D and 3D states, are reported.

  2. Zeaxanthin and Echinenone Protect the Repair of Photosystem II from Inhibition by Singlet Oxygen in Synechocystis sp. PCC 6803.

    PubMed

    Kusama, Yuri; Inoue, Shuhei; Jimbo, Haruhiko; Takaichi, Shinichi; Sonoike, Kintake; Hihara, Yukako; Nishiyama, Yoshitaka

    2015-05-01

    Carotenoids are important components of antioxidative systems in photosynthetic organisms. We investigated the roles of zeaxanthin and echinenone in the protection of PSII from photoinhibition in Synechocystis sp. PCC 6803, using mutants of the cyanobacterium that lack these carotenoids. The activity of PSII in mutant cells deficient in either zeaxanthin or echinenone was more sensitive to strong light than the activity in wild-type cells, and the activity in mutant cells deficient in both carotenoids was hypersensitive to strong light, indicating that the absence of these carotenoids increased the extent of photoinhibition. Nonetheless, the rate of photodamage to PSII, as measured in the presence of chloramphenicol, which blocks the repair of PSII, was unaffected by the absence of either carotenoid, suggesting that these carotenoids might act by protecting the repair of PSII. Knockout of the gene for the so-called orange carotenoid protein (OCP), in which the 3'-hydroxyechinenone cofactor, a derivative of echinenone, is responsible for the thermal dissipation of excitation energy, increased the extent of photoinhibition but did not affect photodamage, suggesting that thermal dissipation also protects the repair of PSII. In mutant cells lacking OCP, as well as those lacking zeaxanthin and echinenone, the production of singlet oxygen was stimulated and the synthesis de novo of various proteins, including the D1 protein, was markedly suppressed under strong light. These observations suggest that the carotenoids and thermal dissipation might protect the repair of photodamaged PSII by depressing the levels of singlet oxygen that inhibits protein synthesis.

  3. Intersystem Crossing Pathway in Quinoline-Pyrazole Isomerism: A Time-Dependent Density Functional Theory Study on Excited-State Intramolecular Proton Transfer.

    PubMed

    Liu, Yu-Hui; Lan, Sheng-Cheng; Zhu, Chaoyuan; Lin, Sheng-Hsien

    2015-06-18

    The dynamics of the excited-state intramolecular proton-transfer (ESIPT) reaction of quinoline-pyrazole (QP) isomers, designated as QP-I and QP-II, has been investigated by means of time-dependent density functional theory (TDDFT). A lower barrier has been found in the potential energy curve for the lowest singlet excited state (S1) along the proton-transfer coordinate of QP-II compared with that of QP-I; however, this is at variance with a recent experimental report [J. Phys. Chem. A 2010, 114, 7886-7891], in which the authors proposed that the ESIPT reaction would only proceed in QP-I due to the absence of a PT emission for QP-II. Therefore, several deactivating pathways have been investigated to determine whether fluorescence quenching occurs in the PT form of QP-II (PT-II). The S1 state of PT-II has nπ* character, which is a well-known dark state. Moreover, the energy gap between the S1 and T2 states is only 0.29 eV, implying that an intersystem crossing (ISC) process would occur rapidly following the ESIPT reaction. Therefore, it is demonstrated that the ESIPT could successfully proceed in QP-II and that the PT emission would be quenched by the ISC process.

  4. Athermalization of polymer radial gradient-index singlets

    NASA Astrophysics Data System (ADS)

    Corsetti, James A.; Gardner, Leo R.; Schmidt, Greg R.; Moore, Duncan T.

    2013-11-01

    The article explores the possibility of athermalizing a gradient-index (GRIN) lens so that the effective focal length (EFL) of the element remains constant over a change in temperature. This is accomplished by designing the lens so that the surface curvatures and index profile compensate for one another over a change in temperature to maintain constant optical power. The means to determine how the lens geometry and index profile change with temperature for both a homogeneous and radial GRIN are explained. An analytic model for the purpose of identifying athermalized GRIN singlets is described and validated against the previous work in this field. The model is used to identify an athermalized polymer radial GRIN element and compare it with four other polymer elements of the same focal length but different index profiles, including a homogeneous one. Comparison of these singlets in CODE V optical design software shows that the athermalized GRIN element maintains its nominal EFL over a temperature change the best of the five in the group while the homogeneous element (having no GRIN profile to counteract the effect of temperature on the surface curvatures) has the poorest performance. A numerical model to analyze more complicated GRIN systems is discussed.

  5. Singlet-triplet donor-quantum-dot qubit in silicon

    NASA Astrophysics Data System (ADS)

    Harvey-Collard, Patrick; Ten Eyck, Gregory A.; Wendt, Joel R.; Pluym, Tammy; Lilly, Michael P.; Carroll, Malcolm S.; Pioro-Ladrière, Michel

    2015-03-01

    Electron spins bound to phosphorus (P) donors in silicon (Si) are promising qubits due to their high fidelities, but donor-donor coupling is challenging. We propose an alternative two-electron singlet-triplet quantum-dot (QD) and donor (D) hybrid qubit. A QD is formed at a MOS 28-Si interface and is tunnel-coupled to implanted P. The proposed two-axis system is defined by the exchange and contact hyperfine interactions. We demonstrate that a few electron QD can be formed and tuned to interact with a donor. We investigate the spin filling of the QD-D system through charge-sensed (CS) magnetospectroscopy and identify spin-up loading consistent with a singlet-triplet splitting of ~100 μeV near a QD-D anti-crossing. We also demonstrate an enhanced CS readout contrast and time window due to the restricted relaxation path of the D through the QD. This work was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. DOE's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  6. An XML file format for exchanging singlet lens specifications

    NASA Astrophysics Data System (ADS)

    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.

  7. Unimolecular photodissociation dynamics of ketene (CH{sub 2}CO): The singlet/triplet branching ratio and experimental observation of the vibrational level thresholds of the transition-state

    SciTech Connect

    Kim, S.K.

    1993-05-01

    The rotational distributions of CO products from the dissociation of ketene at photolysis energies 10 cm{sup {minus}1} below, 56, 110, 200, 325, 425, 1,107, 1,435, 1,720, and 2,500 cm{sup {minus}1} above the singlet threshold, are measured in a supersonic free jet of ketene. The CO(v{double_prime} = 0) rotational distributions at 56, 110, 200, 325, and 425 cm{sup {minus}1} are bimodal. The peaks at low J`s, which are due to CO from the singlet channel, show that the product rotational distribution of CO product from ketene dissociation on the singlet surface is well described by phase space theory (PST). For CO(v{double_prime} = 0) rotational distributions at higher excess energies, the singlet and triplet contributions are not clearly resolved, and the singlet/triplet branching ratios are estimated by assuming that PST accurately predicts the CO rotational distribution from the singlet channel and that the distribution from the triplet channel changes little from that at 10 cm{sup {minus}1} below the singlet threshold. At 2,500 cm{sup {minus}1} excess energy, the CO(v{double_prime} = 1) rotational distribution is obtained, and the ratio of CO(v{double_prime} = 1) to CO(v{double_prime} = 0) products for the singlet channel is close to the variational RRKM calculation, 0.038, and the separate statistical ensembles (SSE) prediction, 0.041, but much greater than the PST prediction, 0.016. Rate constants for the dissociation of ketene (CH{sub 2}CO) and deuterated ketene (CD{sub 2}CO) have been measured at the threshold for the production of the CH(D){sub 2} and CO. Sharp peaks observed in photofragment excitation (PHOFEX) spectra probing CO (v = 0, J = 2) product are identified with the C-C-O bending mode of the transition state. RRKM calculations are carried out for two limiting cases for the dynamics of K-mixing in highly vibrationally excited reactant states.

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

    PubMed

    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.

  9. Solvent dependent photosensitized singlet oxygen production from an Ir(III) complex: pointing to problems in studies of singlet-oxygen-mediated cell death.

    PubMed

    Takizawa, Shin-ya; Breitenbach, Thomas; Westberg, Michael; Holmegaard, Lotte; Gollmer, Anita; Jensen, Rasmus L; Murata, Shigeru; Ogilby, Peter R

    2015-10-01

    A cationic cyclometallated Ir(III) complex with 1,10-phenanthroline and 2-phenylpyridine ligands photosensitizes the production of singlet oxygen, O2(a(1)Δ(g)), with yields that depend appreciably on the solvent. In water, the quantum yield of photosensitized O2(a(1)Δ(g)) production is small (ϕ(Δ) = 0.036 ± 0.008), whereas in less polar solvents, the quantum yield is much larger (ϕ(Δ) = 0.54 ± 0.05 in octan-1-ol). A solvent effect on ϕ(Δ) of this magnitude is rarely observed and, in this case, is attributed to charge-transfer-mediated processes of non-radiative excited state deactivation that are more pronounced in polar solvents and that kinetically compete with energy transfer to produce O2(a(1)Δ(g)). A key component of this non-radiative deactivation process, electronic-to-vibrational energy transfer, is also manifested in pronounced H2O/D2O isotope effects that indicate appreciable coupling between the Ir(III) complex and water. This Ir(III) complex is readily incorporated into HeLa cells and, upon irradiation, is cytotoxic as a consequence of the O2(a(1)Δ(g)) thus produced. The data reported herein point to a pervasive problem in mechanistic studies of photosensitized O2(a(1)Δ(g))-mediated cell death: care must be exercised when interpreting the effective cytotoxicity of O2(a(1)Δ(g)) photosensitizers whose photophysical properties depend strongly on the local environment. Specifically, the photophysics of the sensitizer in bulk solutions may not accurately reflect its intracellular behavior, and the control and quantification of the O2(a(1)Δ(g)) "dose" can be difficult in vivo.

  10. Cold atmospheric pressure plasma jets as sources of singlet delta oxygen for biomedical applications

    SciTech Connect

    Sousa, J. S.; Niemi, K.; Cox, L. J.; Algwari, Q. Th.; Gans, T.; O'Connell, D.

    2011-06-15

    Absolute densities of singlet delta oxygen (SDO) molecules were measured using infrared optical emission spectroscopy in the flowing effluents of two different atmospheric-pressure plasma jets (APPJs): a capacitively coupled radio-frequency-driven jet (rf-APPJ) and a lower frequency kilohertz-driven dielectric barrier discharge jet. The plasma jets were operated in helium, with small admixtures of molecular oxygen (O{sub 2} < 2%). High absolute SDO densities of up to 6.2 x 10{sup 15} cm{sup -3} were measured at approximately 10 cm downstream. The rf-APPJ seems to be much more efficient in producing SDO. The influence of different parameters, such as gas flows and mixtures and power coupled to the plasmas, on the production of SDO by the two APPJs has been investigated. Despite the considerable differences between the two plasma jets (excitation frequency, electric field direction, inter-electrode distance, plasma propagation), similar dependencies on the oxygen admixture and on the dissipated power were found in both APPJs. However, opposite trends were observed for the gas flow dependence. The results presented in this paper show that the control of the external operating conditions of each APPJ enables the tailoring of the SDO composition of both plasma effluents. This provides scope to tune the plasma jets for desired applications, e.g., in biomedicine.

  11. Preorganized Chromophores Facilitate Triplet Energy Migration, Annihilation and Upconverted Singlet Energy Collection.

    PubMed

    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.

  12. Singlet molecular oxygen-quenching activity of carotenoids: relevance to protection of the skin from photoaging

    PubMed Central

    Terao, Junji; Minami, Yuko; Bando, Noriko

    2011-01-01

    Carotenoids are known to be potent quenchers of singlet molecular oxygen [O2 (1Δg)]. Solar light-induced photooxidative stress causes skin photoaging by accelerating the generation of reactive oxygen species via photodynamic actions in which O2 (1Δg) can be generated by energy transfer from excited sensitizers. Thus, dietary carotenoids seem to participate in the prevention of photooxidative stress by accumulating as antioxidants in the skin. An in vivo study using hairless mice clarified that a O2 (1Δg) oxygenation-specific peroxidation product of cholesterol, cholesterol 5α-hydroperoxide, accumulates in skin lipids due to ultraviolet-A exposure. Matrix metalloproteinase-9, a metalloproteinase family enzyme responsible for the formation of wrinkles and sagging, was enhanced in the skin of ultraviolet-A -irradiated hairless mice. The activation of metalloproteinase-9 and the accumulation of 5α-hydroperoxide, as well as formation of wrinkles and sagging, were lowered in mice fed a β-carotene diet. These results strongly suggest that dietary β-carotene prevents the expression of metalloproteinase-9 (at least in part), by inhibiting the photodynamic action involving the formation of 5α-hydroperoxide in the skin. Intake of β-Carotene therefore appears to be helpful in slowing down ultraviolet-A -induced photoaging in human skin by acting as a O2 (1Δg) quencher. PMID:21297913

  13. Preorganized Chromophores Facilitate Triplet Energy Migration, Annihilation and Upconverted Singlet Energy Collection.

    PubMed

    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. PMID:27163784

  14. Ensemble density functional theory method correctly describes bond dissociation, excited state electron transfer, and double excitations

    SciTech Connect

    Filatov, Michael; Huix-Rotllant, Miquel; Burghardt, Irene

    2015-05-14

    State-averaged (SA) variants of the spin-restricted ensemble-referenced Kohn-Sham (REKS) method, SA-REKS and state-interaction (SI)-SA-REKS, implement ensemble density functional theory for variationally obtaining excitation energies of molecular systems. In this work, the currently existing version of the SA-REKS method, which included only one excited state into the ensemble averaging, is extended by adding more excited states to the averaged energy functional. A general strategy for extension of the REKS-type methods to larger ensembles of ground and excited states is outlined and implemented in extended versions of the SA-REKS and SI-SA-REKS methods. The newly developed methods are tested in the calculation of several excited states of ground-state multi-reference systems, such as dissociating hydrogen molecule, and excited states of donor–acceptor molecular systems. For hydrogen molecule, the new method correctly reproduces the distance dependence of the lowest excited state energies and describes an avoided crossing between the doubly excited and singly excited states. For bithiophene–perylenediimide stacked complex, the SI-SA-REKS method correctly describes crossing between the locally excited state and the charge transfer excited state and yields vertical excitation energies in good agreement with the ab initio wavefunction methods.

  15. Ensemble density functional theory method correctly describes bond dissociation, excited state electron transfer, and double excitations.

    PubMed

    Filatov, Michael; Huix-Rotllant, Miquel; Burghardt, Irene

    2015-05-14

    State-averaged (SA) variants of the spin-restricted ensemble-referenced Kohn-Sham (REKS) method, SA-REKS and state-interaction (SI)-SA-REKS, implement ensemble density functional theory for variationally obtaining excitation energies of molecular systems. In this work, the currently existing version of the SA-REKS method, which included only one excited state into the ensemble averaging, is extended by adding more excited states to the averaged energy functional. A general strategy for extension of the REKS-type methods to larger ensembles of ground and excited states is outlined and implemented in extended versions of the SA-REKS and SI-SA-REKS methods. The newly developed methods are tested in the calculation of several excited states of ground-state multi-reference systems, such as dissociating hydrogen molecule, and excited states of donor-acceptor molecular systems. For hydrogen molecule, the new method correctly reproduces the distance dependence of the lowest excited state energies and describes an avoided crossing between the doubly excited and singly excited states. For bithiophene-perylenediimide stacked complex, the SI-SA-REKS method correctly describes crossing between the locally excited state and the charge transfer excited state and yields vertical excitation energies in good agreement with the ab initio wavefunction methods.

  16. Decay pathways for excitations in a conjugated oligofluorene

    NASA Astrophysics Data System (ADS)

    Wesely, Elizabeth Jane

    Oligofluorenes are promising candidates for light emitting applications due to their efficient blue emission, solubility, and chemical purity. The decay routes for some excitations in the fluorescent oligofluorene F(MB)10F(EH)2 are investigated. Geminate recombination of photogenerated charge pairs to form luminescent singlet excitons represents a significant contribution (> 10%) to the overall fluorescence quantum yield. This suggests a substantial yield of charge pair generation in spite of a large exciton binding energy. I propose that the unusual decay dynamics of the delayed fluorescence is the result of the interconversion between singlet and triplet polaron pairs on the submicrosecond timescale (˜500 ns). A model that includes activated recombination from singlet polaron pairs with a distribution of barriers centered 0.2 eV below the excited state produces a fit to the decay of the delayed fluorescence. Results from the model suggest that a large (90% at 296 K) fraction of photoexcited polaron pairs return to form singlet excitons so that this pathway cannot account for the dramatic reduction of fluorescence yields in thin films relative to those in dilute solution. The model also predicts that the ratio of singlet to triplet excitons formed from the recombination of spin randomized charge pairs is greater than that predicted by spin statistics at 296 K, and increases with temperature. The quenching of photoluminescence in F(MB)10F(EH)2 by fluorenone-like defects is also studied through deliberate incorporation of the defects into a solid sample. The results are consistent with a mechanism responsible for part of the quenching of the fluorescence in the oligofluorene samples being exciton migration to defects followed by the trapping of a charge from the exciton on the defect. The defects emit weak, delayed luminescence. The mechanism for the excitation of the defects is similar to that of delayed fluorescence in a pristine sample, which includes the

  17. Singlet oxygen-sensitized delayed emissions from hydrogen peroxide/gallic acid/potassium ferricyanide systems containing organic solvents

    NASA Astrophysics Data System (ADS)

    Ishii, Hiroshi; Tsukino, Kazuo; Sekine, Masahiko; Nakata, Munetaka

    2009-06-01

    Fourier-transform chemiluminescence spectra of H 2O 2/gallic acid/K 3[Fe(CN) 6] systems containing organic solvents were measured. Emission bands with peaks around 530 and 700 nm were observed in systems containing solvents with a carbonyl group such as N, N-dimethylformamide, and those with a hydroxyl group such as methanol, respectively. The relative band intensities depended strongly on the concentration of these organic solvents. The emission species are attributed to gallic acid-ferricyanide complexes excited by energy transfer from singlet oxygen dimol, ( 1O 2) 2. The effects of organic solvents are interpreted in terms of intermolecular interactions of gallic acid-ferricyanide complexes, water molecules and organic solvents.

  18. Correlation-Enhanced Odd-Parity Interorbital Singlet Pairing in the Iron-Pnictide Superconductor LiFeAs

    NASA Astrophysics Data System (ADS)

    Nourafkan, R.; Kotliar, G.; Tremblay, A.-M. S.

    2016-09-01

    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 dx z (y z ) and the interorbital magnetic susceptibility. As a consequence, the leading pairing channel, conventional s+- , acquires sizable interorbital dx y-dx z (y z ) 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.

  19. Computing electronic structures: A new multiconfiguration approach for excited states

    SciTech Connect

    Cances, Eric . E-mail: cances@cermics.enpc.fr; Galicher, Herve . E-mail: galicher@cermics.enpc.fr; Lewin, Mathieu . E-mail: lewin@cermic.enpc.fr

    2006-02-10

    We present a new method for the computation of electronic excited states of molecular systems. This method is based upon a recent theoretical definition of multiconfiguration excited states [due to one of us, see M. Lewin, Solutions of the multiconfiguration equations in quantum chemistry, Arch. Rat. Mech. Anal. 171 (2004) 83-114]. Our algorithm, dedicated to the computation of the first excited state, always converges to a stationary state of the multiconfiguration model, which can be interpreted as an approximate excited state of the molecule. The definition of this approximate excited state is variational. An interesting feature is that it satisfies a non-linear Hylleraas-Undheim-MacDonald type principle: the energy of the approximate excited state is an upper bound to the true excited state energy of the N-body Hamiltonian. To compute the first excited state, one has to deform paths on a manifold, like this is usually done in the search for transition states between reactants and products on potential energy surfaces. We propose here a general method for the deformation of paths which could also be useful in other settings. We also compare our method to other approaches used in Quantum Chemistry and give some explanation of the unsatisfactory behaviours which are sometimes observed when using the latter. Numerical results for the special case of two-electron systems are provided: we compute the first singlet excited state potential energy surface of the H {sub 2} molecule.

  20. Coulomb excitation of 107Sn

    NASA Astrophysics Data System (ADS)

    DiJulio, D. D.; Cederkall, J.; Fahlander, C.; Ekström, A.; Hjorth-Jensen, M.; Albers, M.; Bildstein, V.; Blazhev, A.; Darby, I.; Davinson, T.; De Witte, H.; Diriken, J.; Fransen, Ch.; Geibel, K.; Gernhäuser, R.; Görgen, A.; Hess, H.; Iwanicki, J.; Lutter, R.; Reiter, P.; Scheck, M.; Seidlitz, M.; Siem, S.; Taprogge, J.; Tveten, G. M.; Van de Walle, J.; Voulot, D.; Warr, N.; Wenander, F.; Wimmer, K.

    2012-07-01

    The radioactive isotope 107Sn was studied using Coulomb excitation at the REX-ISOLDE facility at CERN. This is the lightest odd-Sn nucleus examined using this technique. The reduced transition probability of the lowest-lying 3/2+ state was measured and is compared to shell-model predictions based on several sets of single-neutron energies relative to 100Sn . Similar to the transition probabilities for the 2+ states in the neutron-deficient even-even Sn nuclei, the measured value is underestimated by shell-model calculations. Part of the strength may be recovered by considering the ordering of the d_{5/2} and g_{7/2} single-neutron states.

  1. Detection of singlet oxygen in photoexcited porous silicon nanocrystals by photoluminescence measurements

    SciTech Connect

    Gongalsky, M. B. Konstantinova, E. A.; Osminkina, L. A.; Timoshenko, V. Yu.

    2010-01-15

    Luminescence of gas-phase singlet oxygen optically sensitized by microporous silicon at room temperature is detected for the first time. At the same time, a photoinduced increase in the photoluminescence intensity of defects at the sample surface in oxygen atmosphere is observed. It is shown that mechanical grinding of porous silicon layers yields a decrease in the amount of photogenerated singlet oxygen.

  2. Two Birds with One Stone: Tailoring Singlet Fission for Both Triplet Yield and Exciton Diffusion Length.

    PubMed

    Zhu, Tong; Wan, Yan; Guo, Zhi; Johnson, Justin; Huang, Libai

    2016-09-01

    By direct imaging of singlet and triplet populations with ultrafast microscopy, it is shown that the triplet diffusion length and singlet fission yield can be simultaneously optimized for tetracene and its derivatives, making them ideal structures for application in bilayer solar cells. PMID:27348847

  3. Cooperative singlet and triplet exciton transport in tetracene crystals visualized by ultrafast microscopy

    NASA Astrophysics Data System (ADS)

    Wan, Yan; Guo, Zhi; Zhu, Tong; Yan, Suxia; Johnson, Justin; Huang, Libai

    2015-10-01

    Singlet fission presents an attractive solution to overcome the Shockley-Queisser limit by generating two triplet excitons from one singlet exciton. However, although triplet excitons are long-lived, their transport occurs through a Dexter transfer, making them slower than singlet excitons, which travel by means of a Förster mechanism. A thorough understanding of the interplay between singlet fission and exciton transport is therefore necessary to assess the potential and challenges of singlet-fission utilization. Here, we report a direct visualization of exciton transport in single tetracene crystals using transient absorption microscopy with 200 fs time resolution and 50 nm spatial precision. These measurements reveal a new singlet-mediated transport mechanism for triplets, which leads to an enhancement in effective triplet exciton diffusion of more than one order of magnitude on picosecond to nanosecond timescales. These results establish that there are optimal energetics of singlet and triplet excitons that benefit both singlet fission and exciton diffusion.

  4. Acetylene bridged porphyrin-monophthalocyaninato ytterbium(III) hybrids with strong two-photon absorption and high singlet oxygen quantum yield.

    PubMed

    Ke, Hanzhong; Li, Wenbin; Zhang, Tao; Zhu, Xunjin; Tam, Hoi-Lam; Hou, Anxin; Kwong, Daniel W J; Wong, Wai-Kwok

    2012-04-21

    Several acetylene bridged porphyrin-monophthalocyaninato ytterbium(III) hybrids, PZn-PcYb, PH(2)-PcYb and PPd-PcYb, have been prepared and characterized by (1)H and (31)P NMR, mass spectrometry, and UV-vis spectroscopy. Their photophysical and photochemical properties, especially the relative singlet oxygen ((1)O(2)) quantum yields and the two-photon absorption cross-section (σ(2)), were investigated. These three newly synthesized compounds exhibited very large σ(2) values and substantial (1)O(2) quantum yields upon photo-excitation, making them potential candidates as one- and two-photon photodynamic therapeutic agents.

  5. Photonics of laser-excited symmetric cationic polymethine dyes

    SciTech Connect

    Svetlichnyi, Valerii A; Maier, G V; Lapin, I N; Kopylova, T N; Derevyanko, Nadezhda A; Ishchenko, Aleksandr A

    2007-02-28

    Efficient lasing is obtained in the visible and near-IR spectral regions in solutions of symmetric polymethine dyes of the indolenine series (indocyanines) pumped by the second harmonic of a Nd{sup 3+}:YAG laser at 532 nm and an exciplex XeCl* laser at 308 nm into the first (long-wavelength) and higher-lying electronic absorption bands. The quantum lasing efficiency upon UV excitation achieves 37%. It is shown that these dyes can also limit the radiation power of these lasers. Polymethine dyes limit especially efficiently the second-harmonic power, their attenuation factor for the radiation power density of 100 MW cm{sup -2} achieving 14. The nanosecond flash-photolysis study of transient absorption spectra showed that the radiation power is limited by the mechanism of reverse saturated singlet-singlet absorption. It is established that the limiting ability of polymethines strongly depends on their structure. (active media)

  6. Magnetic Excitations from the Exotic Ground State of the Quantum FCC Antiferromagnet Ba2YMoO6

    SciTech Connect

    Carlo, Jeremy P; Clancy, James P; Aharen, T.; Yamani, Zahra; Ruff, Jacob; Wagman, J.; Van Gastel, G. J.; Noad, H. M.; Granroth, Garrett E; Greedan, John E; Dabkowska, H. A.; Gaulin, Bruce D.

    2011-01-01

    The geometrically frustrated double perovskite Ba{sub 2}YMoO{sub 6} is characterized by quantum s = 1/2 spins at the Mo{sup 5+} sites of an undistorted fcc lattice. Previous low-temperature characterization revealed an absence of static long-range magnetic order and suggested a nonmagnetic spin-singlet ground state. We report unique time-of-flight and triple-axis neutron spectroscopy of Ba{sub 2}YMoO{sub 6} that shows a 28 meV spin excitation with a bandwidth of {approx}4 meV, which vanishes above {approx}125 K. We identify this as the singlet-triplet excitation that arises out of a singlet ground state, and further identify a weaker continuum of magnetic states within the gap, reminiscent of spin-polaron states arising due to weak disorder.

  7. Photo-ionization and photo-excitation of curcumin investigated by laser flash photolysis

    NASA Astrophysics Data System (ADS)

    Qian, Tingting; Kun, Li; Gao, Bo; Zhu, Rongrong; Wu, Xianzheng; Wang, ShiLong

    2013-12-01

    Curcumin (Cur) has putative antitumor properties. In the current study, we examined photophysical and photochemical properties of Cur using laser flash photolysis. The results demonstrated that Cur could be photo-ionized at 355 nm laser pulse to produce radical cation (Currad +) and solvated electron esol- in 7:3 ethanol-water mixtures. The quantum yield of Cur photo-ionization and the ratio of photo-ionization to photo-excitation were also determined. Currad + could be transferred into neutral radical of Cur (Currad ) via deprotonation with the pKa 4.13. The excited singlet of Cur (1Cur*) could be transferred into excited triplet (3Cur*), which could be quenched by oxygen to produce singlet oxygen 1O2∗. Reaction of 3Cur* with tryptophan was confirmed. The results encourage developing curcumin as a photosensitive antitumor agent.

  8. Plasmonic Nanoparticle-based Hybrid Photosensitizers with Broadened Excitation Profile for Photodynamic Therapy of Cancer Cells

    PubMed Central

    Wang, Peng; Tang, Hong; Zhang, Peng

    2016-01-01

    Photodynamic therapy combining nanotechnology has shown great potential with improved therapeutic efficacy and fewer side effects. Ideal photosensitizers for cancer treatment should both have good singlet oxygen production capability and be excitable by light illuminations with deep tissue penetration. Here we report a type of hybrid photosensitizers consisting of plasmonic silver nanoparticles and photosensitizing molecules, where strong resonance coupling between the two leads to a broadened excitation profile and exceptionally high singlet oxygen production under both visible light and infrared light excitations. Our results indicate that the hybrid photosensitizers display low cytotoxicity without light illumination yet highly enhanced photodynamic inhibition efficacy against Hela cells under a broad spectrum of light illuminations including the near-infrared light, which has great implication in photodynamic therapy of deep-tissue cancers. PMID:27725746

  9. Relative and absolute level populations in beam-foil-excited neutral helium

    NASA Technical Reports Server (NTRS)

    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.

  10. Plasmonic Nanoparticle-based Hybrid Photosensitizers with Broadened Excitation Profile for Photodynamic Therapy of Cancer Cells

    NASA Astrophysics Data System (ADS)

    Wang, Peng; Tang, Hong; Zhang, Peng

    2016-10-01

    Photodynamic therapy combining nanotechnology has shown great potential with improved therapeutic efficacy and fewer side effects. Ideal photosensitizers for cancer treatment should both have good singlet oxygen production capability and be excitable by light illuminations with deep tissue penetration. Here we report a type of hybrid photosensitizers consisting of plasmonic silver nanoparticles and photosensitizing molecules, where strong resonance coupling between the two leads to a broadened excitation profile and exceptionally high singlet oxygen production under both visible light and infrared light excitations. Our results indicate that the hybrid photosensitizers display low cytotoxicity without light illumination yet highly enhanced photodynamic inhibition efficacy against Hela cells under a broad spectrum of light illuminations including the near-infrared light, which has great implication in photodynamic therapy of deep-tissue cancers.

  11. WIMP dark matter and unitarity-conserving inflation via a gauge singlet scalar

    SciTech Connect

    Kahlhoefer, Felix; McDonald, John E-mail: j.mcdonald@lancaster.ac.uk

    2015-11-01

    A gauge singlet scalar with non-minimal coupling to gravity can drive inflation and later freeze out to become cold dark matter. We explore this idea by revisiting inflation in the singlet direction (S-inflation) and Higgs Portal Dark Matter in light of the Higgs discovery, limits from LUX and observations by Planck. We show that large regions of parameter space remain viable, so that successful inflation is possible and the dark matter relic abundance can be reproduced. Moreover, the scalar singlet can stabilise the electroweak vacuum and at the same time overcome the problem of unitarity-violation during inflation encountered by Higgs Inflation, provided the singlet is a real scalar. The 2-σ Planck upper bound on n{sub s} imposes that the singlet mass is below 2 TeV, so that almost the entire allowed parameter range can be probed by XENON1T.

  12. New two-photon excitation chromophores for cellular imaging

    NASA Astrophysics Data System (ADS)

    D'Alfonso, Laura; Chirico, Giuseppe; Collini, Maddalena; Baldini, Giancarlo; Diaspro, Alberto; Ramoino, Paola; Abbotto, Alessandro; Beverina, Luca; Pagani, Giorgio A.

    2003-10-01

    The one photon and two photon excitation spectral properties (absorption, emission spectra, singlet lifetime) of a very efficient two photon absorber, dimethyl-pepep, have been measured in solution. The one photon excitation peak lye near 525 nm and the emission falls at 600 nm, where autofluorescence of cells is weak. The value of the singlet-triplet conversion rate, obtained by two-photon excitation fluorescence correlation spectroscopy, has a quadratic dependence on the excitation power and is comparable to that shown by the dye rhodamine. Preliminary results on stained cells from yeast Saccaromices cerevisiae and Paramecium primaurelia show that the dye preferentially stains DNA in the cell. A direct comparison with a DNA stainer, Dapi, is also performed. Some measurements of the dye functionalized to react with lysine and n-terminal residues of protein are presented. Moreover, this dye can be employed in order to follow in detail some cellular processes such as nuclei division. In vitro fluorescence titration of dimethyl-pepep with calf thymus DNA allowed to estimate the values of the dye-DNA association constant versus ionic strength, and an affinity close to that of ethidium bromide is found.

  13. Locally Broken Crystal Symmetry Facilitates Singlet Exciton Fission.

    PubMed

    Petelenz, Piotr; Snamina, Mateusz

    2016-05-19

    Photovoltaic yield is normally limited to at most two charge carriers per photon. In solid pentacene this limit may be potentially bypassed owing to singlet exciton fission into a pair of triplets. The process occurs via a superexchange mechanism mediated by charge-transfer (CT) configurations and is sensitive to their energies. As demonstrated recently, these strongly depend on the local environment of the two molecules on which the charges reside. Using a multiscale model, here we show that in the crystal bulk approximate local symmetry affects CT state energetics in a way unfavorable for fission, so that at the places where this symmetry is broken the fission probability is enhanced by up to an order of magnitude. These fission-favorable locations entail the vicinity of vacancies, specific impurities, and interfaces, such as crystallite boundaries. Hence, photovoltaic yield might be substantially increased by using nanoscopically disordered pentacene rather than highly ordered specimens. PMID:27152577

  14. Two-singlet model for light cold dark matter

    SciTech Connect

    Abada, Abdessamad; Ghaffor, Djamal; Nasri, Salah

    2011-05-01

    We extend the standard model by adding two gauge-singlet Z{sub 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.

  15. Possible singlet and triplet superconductivity on honeycomb lattice

    NASA Astrophysics Data System (ADS)

    Xiao, Long-Yun; Yu, Shun-Li; Wang, Wei; Yao, Zi-Jian; Li, Jian-Xin

    2016-07-01

    We study the possible superconducting pairing symmetry mediated by spin and charge fluctuations on the honeycomb lattice using the extended Hubbard model and the random-phase-approximation method. From 2% to 20% doping levels, a spin-singlet dx2-y2+idxy -wave is shown to be the leading superconducting pairing symmetry when only the on-site Coulomb interaction U is considered, with the gap function being a mixture of the nearest-neighbor and next-nearest-neighbor pairings. When the offset of the energy level between the two sublattices exceeds a critical value, the most favorable pairing is a spin-triplet f-wave which is mainly composed of the next-nearest-neighbor pairing. We show that the next-nearest-neighbor Coulomb interaction V is also in favor of the spin-triplet f-wave pairing.

  16. Singlet oxygen production in a microcathode sustained discharge

    NASA Astrophysics Data System (ADS)

    Bauville, G.; Lacour, B.; Magne, L.; Puech, V.; Boeuf, J. P.; Munoz-Serrano, E.; Pitchford, L. C.

    2007-01-01

    The authors report experimental results showing that high yields of singlet oxygen O2(aΔg1) can be generated in a three-electrode microcathode sustained discharge (MCSD) configuration. This configuration consists of a microhollow cathode discharge (MHCD) acting as a plasma cathode to sustain a stable glow discharge between the MHCD and a third, planar electrode placed at a distance of 8mm. Experiments were performed in pure oxygen and in mixtures of oxygen with rare gases (He or Ar) at pressures up to 130Torr. O2(aΔg1) relative yields of 7.6% were measured 23cm downstream in the afterglow of the MCSD discharge.

  17. Intercepts of the non-singlet structure functions

    NASA Astrophysics Data System (ADS)

    Ermolaev, B. I.; Greco, M.; Troyan, S. I.

    2001-01-01

    Infrared evolution equations for small- x behaviour of the non-singlet structure functions f 1NS and g 1NS are obtained and solved in the next-to-leading approximation, to all orders in α s, and including running α s effects. The intercepts of these structure functions, i.e., the exponents of the power-like small- x behaviour, are calculated. A detailed comparison with the leading logarithmic approximation (LLA) and DGLAP is made. We explain why the LLA predictions for the small- x dependence of the structure functions may be more reliable than the prediction for the Q 2 dependence in the range of Q 2 explored at HERA.

  18. Staggered fermions, zero modes, and flavor-singlet mesons

    SciTech Connect

    Donald, Gordon C; Davies, Christine T.H.; Follana, Eduardo; Kronfeld, Andreas S.

    2011-09-12

    We examine the taste structure of eigenvectors of the staggered-fermion Dirac operator. We derive a set of conditions on the eigenvectors of modes with small eigenvalues (near-zero modes), such that staggered fermions reproduce the 't Hooft vertex in the continuum limit. We also show that, assuming these conditions, the correlators of flavor-singlet mesons are free of contributions singular in 1/m, where m is the quark mass. This conclusion holds also when a single flavor of sea quark is represented by the fourth root of the staggered-fermion determinant. We then test numerically, using the HISQ action, whether these conditions hold on realistic lattice gauge fields. We find that the needed structure does indeed emerge.

  19. Staggered fermions, zero modes, and flavor-singlet mesons

    DOE PAGESBeta

    Donald, Gordon C; Davies, Christine T.H.; Follana, Eduardo; Kronfeld, Andreas S.

    2011-09-12

    We examine the taste structure of eigenvectors of the staggered-fermion Dirac operator. We derive a set of conditions on the eigenvectors of modes with small eigenvalues (near-zero modes), such that staggered fermions reproduce the 't Hooft vertex in the continuum limit. We also show that, assuming these conditions, the correlators of flavor-singlet mesons are free of contributions singular in 1/m, where m is the quark mass. This conclusion holds also when a single flavor of sea quark is represented by the fourth root of the staggered-fermion determinant. We then test numerically, using the HISQ action, whether these conditions hold onmore » realistic lattice gauge fields. We find that the needed structure does indeed emerge.« less

  20. Light sparticles from a light singlet in gauge mediation

    NASA Astrophysics Data System (ADS)

    Allanach, Ben; Badziak, Marcin; Hugonie, Cyril; Ziegler, Robert

    2015-07-01

    We revisit a simple model that combines minimal gauge mediation and the next-to-minimal supersymmetric standard model. We show that one can obtain a 125 GeV Standard Model-like Higgs boson with top squarks as light as 1.1 TeV, thanks to the mixing of the Higgs with a singlet state at O (90 - 100 ) GeV . Sparticle searches at the LHC may come with additional b jets or taus and may involve displaced vertices. The sparticle production cross section at the 13 TeV LHC can be O (10 - 100 ) fb , leading to great prospects for discovery in the early phase of LHC run II.

  1. Device-independent parallel self-testing of two singlets

    NASA Astrophysics Data System (ADS)

    Wu, Xingyao; Bancal, Jean-Daniel; McKague, Matthew; Scarani, Valerio

    2016-06-01

    Device-independent self-testing offers the possibility of certifying the quantum state and measurements, up to local isometries, using only the statistics observed by querying uncharacterized local devices. In this paper we study parallel self-testing of two maximally entangled pairs of qubits; in particular, the local tensor product structure is not assumed but derived. We prove two criteria that achieve the desired result: a double use of the Clauser-Horne-Shimony-Holt inequality and the 3 ×3 magic square game. This demonstrate that the magic square game can only be perfectly won by measuring a two-singlet state. The tolerance to noise is well within reach of state-of-the-art experiments.

  2. The scalar singlet-triplet dark matter model

    SciTech Connect

    Fischer, O.; Van der Bij, J.J. E-mail: vdbij@physik.uni-freiburg.de

    2014-01-01

    We consider a model for cold dark matter, which combines a real scalar singlet and a real scalar SU(2){sub L} triplet field, both of which are residing in the odd representation of a global Z{sub 2} symmetry. The parameter space of the model is constrained by the inferred dark matter abundance from the WMAP and Planck data, the most recent results from the direct dark matter search experiment LUX, the Z boson decay width from LEP-I and perturbativity of the coupling parameters. The phenomenology of the remaining parameter space is studied. We find that the model allows for DM masses near the electroweak scale and a variety of decay scenarios.

  3. Theoretical Insights into the Photo-Deactivation of Emitting Triplet Excited State of (C^N)Pt(O^O) Complexes: Radiative and Nonradiative Decay Processes.

    PubMed

    Xu, Yanyan; Luo, Yafei; Li, Ming; He, Rongxing; Shen, Wei

    2016-09-01

    In this study, density functional theory (DFT) and time-dependent DFT were employed to elucidate the photo-deactivation mechanisms of (C^N)Pt(O^O) complexes 1-4 (where C^N = 2-phenylpyridine derivatives, O^O = dipivolylmethanoate). To make thorough understanding of the radiative decay, the singlet-triplet splitting energies ΔE(Sn-T1) (n = 1, 2, 3, 4, ...), transition dipole moment μ(Sn) for S0-Sn transitions and the spin-orbit coupling (SOC) matrix elements ⟨T1|HSOC|Sn⟩ were all calculated. Moreover, the spin-orbit coupling between T1 and S0 ⟨T1|HSOC|S0⟩ and Huang-Rhys factors were calculated to estimate the temperature-independent nonradiative decay processes. Meanwhile, the thermal deactivation via metal-centered (3)MC was described to analyze the temperature-dependent nonradiative decay processes. As a result, the effective SOC interaction between the lowest triplet and singlet excited states successfully rationalize why complexes 1 and 3 have higher radiative decay rate constant than that of complex 2, while the larger ⟨T1|HSOC|S0⟩ and lower energy barrier for thermal deactivation in 3 reasonably explains why 3 has larger nonradiative rate than that of 1 and 2. Consequently, it can be concluded that it is the ⟨T1|HSOC|S0⟩ and thermal population of (3)MC that account for the nonemissive behavior of (C^N)Pt(O^O) complexes, and controlling π-conjugation is an efficient method for tuning phosphorescence properties of transition-metal complexes. PMID:27517617

  4. Singlet-Oxygen Generation in Alkaline Periodate Solution.

    PubMed

    Bokare, Alok D; Choi, Wonyong

    2015-12-15

    A nonphotochemical generation of singlet oxygen ((1)O2) using potassium periodate (KIO4) in alkaline condition (pH > 8) was investigated for selective oxidation of aqueous organic pollutants. The generation of (1)O2 was initiated by the spontaneous reaction between IO4(-) and hydroxyl ions, along with a stoichiometric conversion of IO4(-) to iodate (IO3(-)). The reactivity of in-situ-generated (1)O2 was monitored by using furfuryl alcohol (FFA) as a model substrate. The formation of (1)O2 in the KIO4/KOH system was experimentally confirmed using electron spin resonance (ESR) measurements in corroboration with quenching studies using azide as a selective (1)O2 scavenger. The reaction in the KIO4/KOH solution in both oxic and anoxic conditions initiated the generation of superoxide ion as a precursor of the singlet oxygen (confirmed by using superoxide scavengers), and the presence of molecular oxygen was not required as a precursor of (1)O2. Although hydrogen peroxide had no direct influence on the FFA oxidation process, the presence of natural organic matter, such as humic and fulvic acids, enhanced the oxidation efficiency. Using the oxidation of simple organic diols as model compounds, the enhanced (1)O2 formation is attributed to periodate-mediated oxidation of vicinal hydroxyl groups present in humic and fulvic constituent moieties. The efficient and simple generation of (1)O2 using the KIO4/KOH system without any light irradiation can be employed for the selective oxidation of aqueous organic compounds under neutral and near-alkaline conditions.

  5. Valence and ionic lowest-lying electronic states of ethyl formate as studied by high-resolution vacuum ultraviolet photoabsorption, He(I) photoelectron spectroscopy, and ab initio calculations.

    PubMed

    Śmiałek, M A; Łabuda, M; Guthmuller, J; Hubin-Franskin, M-J; Delwiche, J; Duflot, D; Mason, N J; Hoffmann, S V; Jones, N C; Limão-Vieira, P

    2014-09-14

    The highest resolution vacuum ultraviolet photoabsorption spectrum of ethyl formate, C2H5OCHO, yet reported is presented over the wavelength range 115.0-275.5 nm (10.75-4.5 eV) revealing several new spectral features. Valence and Rydberg transitions and their associated vibronic series, observed in the photoabsorption spectrum, have been assigned in accordance with new ab initio calculations of the vertical excitation energies and oscillator strengths. Calculations have also been carried out to determine the ionization energies and fine structure of the lowest ionic state of ethyl formate and are compared with a newly recorded He(I) photoelectron spectrum (from 10.1 to 16.1 eV). New vibrational structure is observed in the first photoelectron band. The photoabsorption cross sections have been used to calculate the photolysis lifetime of ethyl formate in the upper stratosphere (20-50 km).

  6. Valence and ionic lowest-lying electronic states of ethyl formate as studied by high-resolution vacuum ultraviolet photoabsorption, He(I) photoelectron spectroscopy, and ab initio calculations.

    PubMed

    Śmiałek, M A; Łabuda, M; Guthmuller, J; Hubin-Franskin, M-J; Delwiche, J; Duflot, D; Mason, N J; Hoffmann, S V; Jones, N C; Limão-Vieira, P

    2014-09-14

    The highest resolution vacuum ultraviolet photoabsorption spectrum of ethyl formate, C2H5OCHO, yet reported is presented over the wavelength range 115.0-275.5 nm (10.75-4.5 eV) revealing several new spectral features. Valence and Rydberg transitions and their associated vibronic series, observed in the photoabsorption spectrum, have been assigned in accordance with new ab initio calculations of the vertical excitation energies and oscillator strengths. Calculations have also been carried out to determine the ionization energies and fine structure of the lowest ionic state of ethyl formate and are compared with a newly recorded He(I) photoelectron spectrum (from 10.1 to 16.1 eV). New vibrational structure is observed in the first photoelectron band. The photoabsorption cross sections have been used to calculate the photolysis lifetime of ethyl formate in the upper stratosphere (20-50 km). PMID:25217920

  7. Valence and ionic lowest-lying electronic states of ethyl formate as studied by high-resolution vacuum ultraviolet photoabsorption, He(I) photoelectron spectroscopy, and ab initio calculations

    SciTech Connect

    Śmiałek, M. A.; Duflot, D.; Mason, N. J.; Hoffmann, S. V.; Jones, N. C.; Limão-Vieira, P.

    2014-09-14

    The highest resolution vacuum ultraviolet photoabsorption spectrum of ethyl formate, C{sub 2}H{sub 5}OCHO, yet reported is presented over the wavelength range 115.0–275.5 nm (10.75–4.5 eV) revealing several new spectral features. Valence and Rydberg transitions and their associated vibronic series, observed in the photoabsorption spectrum, have been assigned in accordance with new ab initio calculations of the vertical excitation energies and oscillator strengths. Calculations have also been carried out to determine the ionization energies and fine structure of the lowest ionic state of ethyl formate and are compared with a newly recorded He(I) photoelectron spectrum (from 10.1 to 16.1 eV). New vibrational structure is observed in the first photoelectron band. The photoabsorption cross sections have been used to calculate the photolysis lifetime of ethyl formate in the upper stratosphere (20–50 km)

  8. Ultrafast excited-state dynamics of rhenium(I) photosensitizers [Re(Cl)(CO)3(N,N)] and [Re(imidazole)(CO)3(N,N)]+: diimine effects.

    PubMed

    El Nahhas, Amal; Consani, Cristina; Blanco-Rodríguez, Ana María; Lancaster, Kyle M; Braem, Olivier; Cannizzo, Andrea; Towrie, Michael; Clark, Ian P; Zális, Stanislav; Chergui, Majed; Vlcek, Antonín

    2011-04-01

    Femto- to picosecond excited-state dynamics of the complexes [Re(L)(CO)(3)(N,N)](n) (N,N = bpy, phen, 4,7-dimethyl-phen (dmp); L = Cl, n = 0; L = imidazole, n = 1+) were investigated using fluorescence up-conversion, transient absorption in the 650-285 nm range (using broad-band UV probe pulses around 300 nm) and picosecond time-resolved IR (TRIR) spectroscopy in the region of CO stretching vibrations. Optically populated singlet charge-transfer (CT) state(s) undergo femtosecond intersystem crossing to at least two hot triplet states with a rate that is faster in Cl (∼100 fs)(-1) than in imidazole (∼150 fs)(-1) complexes but essentially independent of the N,N ligand. TRIR spectra indicate the presence of two long-lived triplet states that are populated simultaneously and equilibrate in a few picoseconds. The minor state accounts for less than 20% of the relaxed excited population. UV-vis transient spectra were assigned using open-shell time-dependent density functional theory calculations on the lowest triplet CT state. Visible excited-state absorption originates mostly from mixed L;N,N(•-) → Re(II) ligand-to-metal CT transitions. Excited bpy complexes show the characteristic sharp near-UV band (Cl, 373 nm; imH, 365 nm) due to two predominantly ππ*(bpy(•-)) transitions. For phen and dmp, the UV excited-state absorption occurs at ∼305 nm, originating from a series of mixed ππ* and Re → CO;N,N(•-) MLCT transitions. UV-vis transient absorption features exhibit small intensity- and band-shape changes occurring with several lifetimes in the 1-5 ps range, while TRIR bands show small intensity changes (≤5 ps) and shifts (∼1 and 6-10 ps) to higher wavenumbers. These spectral changes are attributable to convoluted electronic and vibrational relaxation steps and equilibration between the two lowest triplets. Still slower changes (≥15 ps), manifested mostly by the excited-state UV band, probably involve local-solvent restructuring. Implications of

  9. Two-dimensional singlet oxygen imaging with its near-infrared luminescence during photosensitization

    PubMed Central

    Hu, Bolin; Zeng, Nan; Liu, Zhiyi; Ji, Yanhong; Xie, Weidong; Peng, Qing; Zhou, Yong; He, Yonghong; Ma, Hui

    2011-01-01

    Photodynamic therapy is a promising cancer treatment that involves activation of photosensitizer by visible light to create singlet oxygen. This highly reactive oxygen species is believed to induce cell death and tissue destruction in PDT. Our approach used a near-infrared area CCD with high quantum efficiency to detect singlet oxygen by its 1270-nm luminescence. Two-dimensional singlet oxygen images with its near-infrared luminescence during photosensitization could be obtained with a CCD integration time of 1 s, without scanning. Thus this system can produce singlet oxygen luminescence images faster and achieve more accurate measurements in comparison to raster-scanning methods. The experimental data show a linear relationship between the singlet oxygen luminescence intensity and sample concentration. This method provides a detection sensitivity of 0.0181 μg/ml (benzoporphyrin derivative monoacid ring A dissolved in ethanol) and a spatial resolution better than 50 μm. A pilot study was conducted on a total of six female Kunming mice. The results from this study demonstrate the system's potential for in vivo measurements. Further experiments were carried out on two tumor-bearing nude mice. Singlet oxygen luminescence images were acquired from the tumor-bearing nude mouse with intravenous injection of BPD-MA, and the experimental results showed real-time singlet oxygen signal depletion as a function of the light exposure. PMID:21280909

  10. Direct detection of singlet oxygen generated by UVA irradiation in human cells and skin.

    PubMed

    Baier, Jürgen; Maisch, Tim; Maier, Max; Landthaler, Michael; Bäumler, Wolfgang

    2007-06-01

    UVA light produces deleterious biological effects in which singlet oxygen plays a major role. These effects comprise a significant risk of carcinogenesis in the skin and cataract formation of the eye lens. Singlet oxygen is generated by UVA light absorption in endogenous molecules present in the cells. To elucidate the primary processes and sources of singlet oxygen in tissue, it is a major goal to uncover the hidden process of singlet oxygen generation, in particular in living tissue. When exposing keratinocytes or human skin in vivo to UVA laser light (355 nm) at 6 J/cm2, we measured the luminescence of singlet oxygen at 1,270 nm. This is a positive and direct proof of singlet oxygen generation in cells and skin by UVA light. Moreover, a clear signal of singlet oxygen luminescence was detected in phosphatidylcholine suspensions (water or ethanol) irradiated by UVA. Oxidized products of phosphatidylcholine are the likely chromophores because phosphatidylcholine itself does not absorb at 355 nm. The signal intensity was reduced by mannitol or super oxide dismutase. Additionally, the monochromatic UVA irradiation at 355 nm leads to upregulation of the key cytokine IL-12. This affects the balance of UV radiation on the immune system, which is comparable to effects of broadband UVA irradiation. PMID:17363921

  11. Phosphoprotein SAK1 is a regulator of acclimation to singlet oxygen in Chlamydomonas reinhardtii

    PubMed Central

    Wakao, Setsuko; Chin, Brian L; Ledford, Heidi K; Dent, Rachel M; Casero, David; Pellegrini, Matteo; Merchant, Sabeeha S; Niyogi, Krishna K

    2014-01-01

    Singlet oxygen is a highly toxic and inevitable byproduct of oxygenic photosynthesis. The unicellular green alga Chlamydomonas reinhardtii is capable of acclimating specifically to singlet oxygen stress, but the retrograde signaling pathway from the chloroplast to the nucleus mediating this response is unknown. Here we describe a mutant, singlet oxygen acclimation knocked-out 1 (sak1), that lacks the acclimation response to singlet oxygen. Analysis of genome-wide changes in RNA abundance during acclimation to singlet oxygen revealed that SAK1 is a key regulator of the gene expression response during acclimation. The SAK1 gene encodes an uncharacterized protein with a domain conserved among chlorophytes and present in some bZIP transcription factors. The SAK1 protein is located in the cytosol, and it is induced and phosphorylated upon exposure to singlet oxygen, suggesting that it is a critical intermediate component of the retrograde signal transduction pathway leading to singlet oxygen acclimation. DOI: http://dx.doi.org/10.7554/eLife.02286.001 PMID:24859755

  12. Nonlinear optical spectra having characteristics of Fano interferences in coherently coupled lowest exciton biexciton states in semiconductor quantum dots

    SciTech Connect

    Gotoh, Hideki Sanada, Haruki; Yamaguchi, Hiroshi; Sogawa, Tetsuomi

    2014-10-15

    Optical nonlinear effects are examined using a two-color micro-photoluminescence (micro-PL) method in a coherently coupled exciton-biexciton system in a single quantum dot (QD). PL and photoluminescence excitation spectroscopy (PLE) are employed to measure the absorption spectra of the exciton and biexciton states. PLE for Stokes and anti-Stokes PL enables us to clarify the nonlinear optical absorption properties in the lowest exciton and biexciton states. The nonlinear absorption spectra for excitons exhibit asymmetric shapes with peak and dip structures, and provide a distinct contrast to the symmetric dip structures of conventional nonlinear spectra. Theoretical analyses with a density matrix method indicate that the nonlinear spectra are caused not by a simple coherent interaction between the exciton and biexciton states but by coupling effects among exciton, biexciton and continuum states. These results indicate that Fano quantum interference effects appear in exciton-biexciton systems at QDs and offer important insights into their physics.

  13. Solid-phase fullerene-like nanostructures as singlet oxygen photosensitizers in liquid media

    NASA Astrophysics Data System (ADS)

    Belousova, I. M.; Danilov, O. B.; Kiselev, V. M.; Kislyakov, I. M.; Kris'ko, T. K.; Murav'eva, T. D.; Videnichev, D. A.

    2007-04-01

    Singlet oxygen generation by fullerene and astralen containing surfaces and powders under visible irradiation was studied in water and organic liquids by means of 1Δ g state luminescence and chemical scavenger transmittance measurements. The chemical method, pioneered for solid photosensitizers of 10 II, allowed to measure the singlet oxygen concentration in the aqueous medium down to 10 8 cm -3. The singlet oxygen sensitizing by the solid-phase fullerene-containing systems was found to be 100 times less effective then by fullerene in solution. The results obtained confirm the applicability of these structures in biology and medicine.

  14. Singlet oxygen generation from [bis(trifluoroacetoxy)iodo]benzene and hydrogen peroxide.

    PubMed

    Catir, Mustafa; Kilic, Hamdullah; Nardello-Rataj, Véronique; Aubry, Jean-Marie; Kazaz, Cavit

    2009-06-19

    Decomposition of hydrogen peroxide with a hypervalent iodine compound was examined. The results indicate that treatment of a hypervalent iodine compound with hydrogen peroxide produces singlet molecular oxygen ((1)O(2)). Convergent evidence for the production of singlet molecular oxygen ((1)O(2)) by decomposition of hydrogen peroxide with a hypervalent iodine compound comes from chemical trapping experiments and the specific chemiluminescence detection of (1)O(2) at 1270 nm. Substantial evidence demonstrates that hydroperoxyl radical produced from hydrogen peroxide with hypervalent iodine reacts via a tetraoxidane intermediate, decomposing to give singlet molecular oxygen. PMID:19449850

  15. Cytotoxicity But No Mutagenicity In Bacteria With Externally Generated Singlet Oxygen

    NASA Astrophysics Data System (ADS)

    Midden, W. Robert; Dahl, Thomas A.; Hartman, Philip E.

    1988-02-01

    Singlet oxygen is believed to be an important intermediate responsible for the cytotoxicity of HpD phototherapy. It has been recognized as a possible intermediate in photosensitization for more than 20 years. However, it has been difficult to obtain conclusive evidence of its biological characteristics in the past because most of the methods available for its generation that are compatible with biological systems also generate other reactive intermediates whose effects are difficult to distinguish from singlet oxygen. We have used a recently devised separated-surface-sensi-tizer (S-S-S) system for singlet oxygen generation' to measure the cytotoxicity and mutagenicity of singlet oxygen in bacteria. The S-S-S system employs rose bengal as a sensitizer immobilized on one surface of a glass plate. The glass plate is placed sensitizer-side down a small distance (< 1.5 mm) above a microscopically flat membrane (MilliporeTM or NucleoporeTM) that carries a monocellular layer of bacteria. The sensi-tizer-coated plate is illuminated from above to generate singlet oxygen at the surface of the sensitizer. The singlet oxygen thus generated can diffuse the short dis-tance to the surface of the membrane to react with the bacteria. Because of the short lifetime of singlet oxygen in air, increasing the distance between the sensitizer and the membrane causes a decline in the amount of singlet oxygen reaching the membrane according to a function derived from the Einstein-Smoluchowski equation for net displacement by diffusion. Plotting the log of the effect measured (e.g., cytotoxicity) vs. the square of the distance gives a straight line. The slope of this line can be used to calculate the gas phase half life of the intermediate responsible for the observed effects. We have found that bacteria are rapidly killed in the illuminated S-S-S system and that the gas phase half life of the agent responsible for cell killing is the same as that of singlet oxygen. This observation and other

  16. 2D gasdynamic simulation of the kinetics of an oxygen-iodine laser with electric-discharge generation of singlet oxygen

    SciTech Connect

    Chukalovsky, A. A.; Rakhimova, T. V.; Klopovsky, K. S.; Mankelevich, Yu. A.; Proshina, O. V.

    2011-03-15

    The kinetic processes occurring in an electric-discharge oxygen-iodine laser are analyzed with the help of a 2D (r, z) gasdynamic model taking into account transport of excited oxygen, singlet oxygen, and radicals from the electric discharge and their mixing with the iodine-containing gas. The main processes affecting the dynamics of the gas temperature and gain are revealed. The simulation results obtained using the 2D model agree well with the experimental data on the mixture gain. A subsonic oxygen-iodine laser in which singlet oxygen is generated by a 350 W transverse RF discharge excited in an oxygen flow at a pressure P = 10 Torr and the discharge tube wall is covered with mercury oxide is simulated. The simulated mixing system is optimized in terms of the flow rate and the degree of preliminary dissociation of the iodine flow. The optimal regime of continuous operation of a subsonic electric-discharge oxygen-iodine laser is found.

  17. Photosensitized damage inflicted on plasma membranes of live cells by an extracellular generator of singlet oxygen--a linear dependence of a lethal dose on light intensity.

    PubMed

    Zarębski, Mirosław; Kordon, Magdalena; Dobrucki, Jurek W

    2014-01-01

    We describe a study of the influence of a dose rate, i.e. light intensity or photon flux, on the efficiency of induction of a loss of integrity of plasma membranes of live cells in culture. The influence of a photon flux on the size of the light dose, which was capable of causing lethal effects, was measured in an experimental system where singlet oxygen was generated exclusively outside of live cells by ruthenium(II) phenantroline complex. Instantaneous, sensitive detection of a loss of integrity of a plasma membrane was achieved by fluorescence confocal imaging of the entry of this complex into a cell interior. We demonstrate that the size of the lethal dose of light is directly proportional to the intensity of the exciting light. Thus, the probability of a photon of the exciting light inflicting photosensitized damage on plasma membranes diminishes with increasing density of the incident photons.

  18. Doubly excited states in some light atoms

    SciTech Connect

    Berry, H.G.; Brooks, R.L.; Hardis, J.E.; Ray, W.J.

    1981-01-01

    We have identified a singlet transition in doubly excited helium: 2p/sup 2/ /sup 1/D - 2p3d /sup 1/D, at 3298 +- 2A with a full width of 54A or 0.061 +- 0.005 eV. This width is in good agreement with a previous measurement and theory for the width of the 2p/sup 2/ /sup 1/D/sub 2/ state. We have remeasured the decay rate of 1s/sup 2/2p/sup 2/P - 1s2p/sup 2/ /sup 2/P in Li I and find it is in good agreement with theory. Several transitions in doubly excited Li II have been identified in the 1000A region. No evidence was found for doubly excited quartet transitions in Li I in the vacuum ultraviolet. We present measurements of wavelengths and fine structure of the 1s2s2p/sup 2/ /sup 5/P - 1s2p/sup 3/ /sup 5/S transitions in C III, N IV and O V.

  19. Inner-shell excitation of acetylene by electron impact

    SciTech Connect

    Michelin, S.E.; Pessoa, O.; Oliveira, H.L.; Veiteinheimer, E.; Santos, A.M.S.; Fujimoto, M.M.; Iga, I.; Lee, M.-T.

    2005-08-15

    The distorted-wave approximation (DWA) is applied to study K-shell excitation in C{sub 2}H{sub 2} by electron impact. More specifically, calculated differential and integral cross sections for the X {sup 1}{sigma}{sub g}{sup +}{yields}{sup 1,3}{pi}{sub g}(1s{sigma}{sub g}{yields}1p{pi}{sub g}) and X {sup 1}{sigma}{sub g}{sup +}{yields}{sup 1,3}{pi}{sub u}(1s{sigma}{sub u}{yields}1p{pi}{sub g}) transitions in this target in the 300-800 eV incident energy range are reported. The triplet-to-singlet ratios of respective integral cross sections, namely, RI(3:1), calculated by dividing the integral cross sections for transitions leading to the triplet core-excited states by those leading to the corresponding singlet states, are also reported as a function of incident energies. In general, our calculated sums of the generalized oscillator strength for transitions leading to the {sup 1}{pi}{sub g} and {sup 1}{pi}{sub u} excited states are in good agreement with the available experimental data. On the other hand, the present calculated integral cross sections and the corresponding data for its isoelectronic species CO are significantly different. Possible physical origins for this difference are discussed.

  20. Enhanced Singlet Oxygen Production by Photodynamic Therapy and a Novel Method for Its Intracellular Measurement

    PubMed Central

    Marin, Gustavo Horacio; Aviles, Kevin; Acuña, Ricardo Cruz; Roque, Gustavo; Nieto, Felipe Rodríguez; Sanchez, Francisco; Tarditi, Adrián; Rivera, Luis; Mansilla, Eduardo

    2014-01-01

    Abstract The generation of singlet oxygen (SO) in the presence of specific photosensitizers (PSs) or semiconductor quantum dots (QDs) and its application in photodynamic therapy (PDT) is of great interest to develop cancer therapies with no need of surgery, chemotherapy, and/or radiotherapy. This work was focused on the identification of the main factors leading to the enhancement of SO production using Rose Bengal (RB), and Methylene Blue (MB) as PS species in organic and aqueous mediums. Subsequently, the capacity of zinc oxide (ZnO), zinc sulfide (ZnS), and ZnO/ZnS core-shell QDs as well as manganese (Mn+2) doped ZnO and ZnS nanoparticles (NPs) as potential PS was also investigated. Many variable parameters such as type of quencher, PSs, NPs, as well as its different concentrations, light source, excitation wavelength, reaction time, distance from light source, and nature of solvent were used. The degradation kinetics of the quenchers generated by SO species and the corresponding quantum yields were determined by monitoring the photo-oxidation of the chemical quencher and measuring its disappearance by fluorometry and spectrophotometry in the presence of NPs. Small intracellular changes of SO induced by these metal Zn (zinc) NPs and PDT could execute and accelerate deadly programs in these leukemic cells, providing in this way an innovative modality of treatment. In order to perform further more specific in vitro cytotoxic studies on B-chronic lymphocytic leukemia cells exposed to Zn NPs and PDT, we needed first to measure and ascertain those possible intracellular SO variations generated by this type of treatment; for this purpose, we have also developed and tested a novel method first described by us. PMID:25490599

  1. On the origin of regio- and stereoselectivity in singlet oxygen addition to enecarbamates.

    PubMed

    Rajeev, Ramanan; Sunoj, Raghavan B

    2012-03-01

    The reactions of excited state singlet molecular oxygen ((1)Δ(g),(1)O(2)) continue to witness interesting new developments. In the most recent manifestation, (1)O(2) is tamed to react with enecarbamates in a stereoselective manner, which is remarkable, in view of its inherently high reactivity (Acc. Chem. Res. 2008, 41, 387). Herein, we employed the CAS-MP2(8,7)/6-31G* as well as the CAS-MP2(10,8)/6-31G* computations to unravel the origin of (i) diastereoselectivities in dioxetane or hydroperoxide formation and (ii) regioselectivity leading to a [2 + 2] cycloadduct or an ene product when (1)O(2) reacts with an oxazolidinone tethered 2-phenyl-1-propenyl system. The computed Gibbs free energy profiles for E- and Z-isomers when (1)O(2) approaches through the hindered and nonhindered diastereotopic faces (by virtue of chiral oxazolidinone) of the enecarbamates exhibit distinct differences. In the case of E-isomer, the relative energies of the transition structures responsible for hydroperoxide (ene product) are lower than that for dioxetane formation. On the other hand, the ene pathway is predicted to involve higher barriers as compared to the corresponding dioxetane pathway for Z-isomer. The energy difference between the rate-determining diastereomeric transition structures involved in the most favored ene reaction for E-enecarbamate suggests high diastereoselectivity. In contrast, the corresponding energy difference for Z-enecarbamate in the ene pathway is found to be diminishingly close, implying low diastereoselectivity. However, the dioxetane formation from Z-enecarbamate is predicted to exhibit high diastereoselectivity. The application of activation strain model as well as the differences in stereoelectronic effects in the stereocontrolling transition structures is found to be effective toward rationalizing the origin of selectivities reported herein. These predictions are found to be in excellent agreement with the experimental observations.

  2. Approaches to Future Generation Photovoltaics and Solar Fuels: Multiple Exciton Generation in Quantum Dots, Quantum Dot Arrays, Molecular Singlet Fission, and Quantum Dot Solar Cells

    SciTech Connect

    Nozik, A. J.; Beard, M. C.; Johnson, J. C.; Hanna, M. C.; Luther, J. M.; Midgett, A.; Semonin, O.; Michel, J.

    2012-01-01

    One potential, long-term approach to more efficient future generation solar cells is to utilize the unique properties of quantum dots (QDs) and unique molecular chromophores to control the relaxation pathways of excited states to produce enhanced conversion efficiency through efficient multiple electron-hole pair generation from single photons . We have observed efficient multiple exciton generation (MEG) in PbSe, PbS, PbTe, and Si QDs and efficient singlet fission (SF) in molecules that satisfy specific requirements for their excited state energy level structure to achieve carrier multiplication. We have studied MEG in close-packed QD arrays where the QDs are electronically coupled in the films and thus exhibit good transport while still maintaining quantization and MEG. We have developed simple, all-inorganic QD solar cells that produce large short-circuit photocurrents and power conversion efficiencies in the 3-5% range via both nanocrystalline Schottky junctions and nanocrystalline p-n junctions. These solar cells also show QYs for photocurrent that exceed 100% in the photon energy regions where MEG is possible; the photocurrent MEG QYs as a function of photon energy match those determined via time-resolved spectroscopy. We have also observed very efficient SF in thin films of molecular crystals of 1,3 diphenylisobenzofuran with quantum yields of 200% at the optimum SF threshold of 2Eg (HOMO-LUMO for S{sub 0}-S{sub 1}), reflecting the creation of two excited triplet states from the first excited singlet state. Various possible configurations for novel solar cells based on MEG in QDs and SF in molecules that could produce high conversion efficiencies will be presented, along with progress in developing such new types of solar cells. Recent analyses of the effect of MEG or SF combined with solar concentration on the conversion efficiency of solar cells will be discussed.

  3. Naturalness and Higgs Decays in the MSSM with a Singlet

    SciTech Connect

    Chang, Spencer; Fox, Patrick J.; Weiner, Neal

    2005-11-21

    The simplest extension of the supersymmetric standard model--the addition of one singlet superfield--can have a profound impact on the Higgs and its decays. We perform a general operator analysis of this scenario, focusing on the phenomenologically distinct scenarios that can arise, and not restricting the scope to the narrow framework of the NMSSM. We reexamine decays to four b quarks and four {tau}'s, finding that they are still generally viable, but at the edge of LEP limits. We find a broad set of Higgs decay modes, some new, including those with four gluon final states, as well as more general six and eight parton final states. We find the phenomenology of these scenarios is dramatically impacted by operators typically ignored, specifically those arising from D-terms in the hidden sector, and those arising from weak-scale colored fields. In addition to sensitivity of m{sub z}, there are potential tunings of other aspects of the spectrum. In spite of this, these models can be very natural, with light stops and a Higgs as light as 82 GeV. These scenarios motivate further analyses of LEP data as well as studies of the detection capabilities of future colliders to the new decay channels presented.

  4. Noise filtering of composite pulses for singlet-triplet qubits

    PubMed Central

    Yang, Xu-Chen; Wang, Xin

    2016-01-01

    Semiconductor quantum dot spin qubits are promising candidates for quantum computing. In these systems, the dynamically corrected gates offer considerable reduction of gate errors and are therefore of great interest both theoretically and experimentally. They are, however, designed under the static-noise model and may be considered as low-frequency filters. In this work, we perform a comprehensive theoretical study of the response of a type of dynamically corrected gates, namely the supcode for singlet-triplet qubits, to realistic 1/f noises with frequency spectra 1/ωα. Through randomized benchmarking, we have found that supcode offers improvement of the gate fidelity for α  1 and the improvement becomes exponentially more pronounced with the increase of the noise exponent in the range 1  α ≤ 3 studied. On the other hand, for small α, supcode will not offer any improvement. The δJ-supcode, specifically designed for systems where the nuclear noise is absent, is found to offer additional error reduction than the full supcode for charge noises. The computed filter transfer functions of the supcode gates are also presented. PMID:27383129

  5. TPP and singlet oxygen quenching by carotene in solution

    NASA Astrophysics Data System (ADS)

    Scholz, Marek; Dědic, Roman; Svoboda, Antonín; Hála, Jan

    2011-05-01

    Antioxidant properties of naturally occurring species, β-carotene, are investigated by examining its ability to quench singlet oxygen ( 1O 2) and triplet states of photosensitizer 5,10,15,20-tetraphenyl-porphin (TPP) in tetrahydrofuran solutions. Concentrations of all species are biologically relevant. The quenching is evaluated using direct spectral- and temporal-resolved detection of weak near-infrared phosphorescence of both triplet TPP ( 3TPP) and 1O 2. Dependencies of lifetimes of 3TPP and 1O 2 on concentration of β-carotene were established as well as quenching rate constants for β-carotene. Hypothesis of multi-component 3TPP is proposed and investigated. Quenching constant of (10.9 ± 0.5) × 10 9 M -1 s -1 for bimolecular quenching of 1O 2 by β-carotene and quenching constant of (8 ± 3) × 10 9 M -1 s -1 for bimolecular quenching of 3TPP longer lived component were determined.

  6. Micro-plasmas as efficient generators of singlet delta oxygen

    NASA Astrophysics Data System (ADS)

    Puech, Vincent; Bauville, Gerard; Lacour, Bernard; Santos Sousa, Joao; Pitchford, Leanne C.; Touzeau, Michel

    2008-05-01

    This paper discusses the possibility of producing high concentrations of O2(a1Δg) states at pressures up to atmospheric in rare-gas/oxygen/NO mixtures by using micro-plasmas. Micro-plasmas refer to electric discharges created in very small geometries which have been proven able to operate in DC mode at high pressure and high power loading without undergoing any glow to arc transition. The so-called Micro Cathode Sustained Discharge (MCSD), which is a three-electrode configuration using a Micro Hollow Cathode Discharge (MHCD) as a plasma cathode, can be operated as a non-self-sustained discharge with low values of the reduced electric field and of the gas temperature. As a result, these MCSDs can efficiently generate large amounts of singlet delta oxygen. In Ar/O2/NO mixtures, at an oxygen partial pressure of 10 mbar, high values of O2(a1Δg) number density (1.5 1016 cm-3) and of the production yield (6.7 %) can be simultaneously obtained. For lower O2 partial pressure, yields higher than 10 % have been measured. In He/O2/NO mixtures, O2(a1Δg) number densities around 1016 cm-3 were achieved at atmospheric pressure for flow rates in the range 5-30 ln/mn, which could give rise to new applications.

  7. Noise filtering of composite pulses for singlet-triplet qubits.

    PubMed

    Yang, Xu-Chen; Wang, Xin

    2016-01-01

    Semiconductor quantum dot spin qubits are promising candidates for quantum computing. In these systems, the dynamically corrected gates offer considerable reduction of gate errors and are therefore of great interest both theoretically and experimentally. They are, however, designed under the static-noise model and may be considered as low-frequency filters. In this work, we perform a comprehensive theoretical study of the response of a type of dynamically corrected gates, namely the supcode for singlet-triplet qubits, to realistic 1/f noises with frequency spectra 1/ω(α). Through randomized benchmarking, we have found that supcode offers improvement of the gate fidelity for α  1 and the improvement becomes exponentially more pronounced with the increase of the noise exponent in the range 1  α ≤ 3 studied. On the other hand, for small α, supcode will not offer any improvement. The δJ-supcode, specifically designed for systems where the nuclear noise is absent, is found to offer additional error reduction than the full supcode for charge noises. The computed filter transfer functions of the supcode gates are also presented. PMID:27383129

  8. Quantification of photosensitized singlet oxygen production by a fluorescent protein.

    PubMed

    Ragàs, Xavier; Cooper, Laurie P; White, John H; Nonell, Santi; Flors, Cristina

    2011-01-17

    Fluorescent proteins are increasingly becoming actuators in a range of cell biology techniques. One of those techniques is chromophore-assisted laser inactivation (CALI), which is employed to specifically inactivate the function of target proteins or organelles by producing photochemical damage. CALI is achieved by the irradiation of dyes that are able to produce reactive oxygen species (ROS). The combination of CALI and the labelling specificity that fluorescent proteins provide is useful to avoid uncontrolled photodamage, although the inactivation mechanisms by ROS are dependent on the fluorescent protein and are not fully understood. Herein, we present a quantitative study of the ability of the red fluorescent protein TagRFP to produce ROS, in particular singlet oxygen ((1)O(2)). TagRFP is able to photosensitize (1)O(2) with an estimated quantum yield of 0.004. This is the first estimation of a quantum yield of (1)O(2) production value for a GFP-like protein. We also find that TagRFP has a short triplet lifetime compared to EGFP, which reflects relatively high oxygen accessibility to the chromophore. The insight into the structural and photophysical properties of TagRFP has implications in improving fluorescent proteins for fluorescence microscopy and CALI. PMID:21226197

  9. Noise filtering of composite pulses for singlet-triplet qubits

    NASA Astrophysics Data System (ADS)

    Wang, Xin; Yang, Xu-Chen

    Dynamically corrected gates are useful measures to combat decoherence in spin qubit systems. They are, however, mostly designed assuming the static-noise model and may thus be considered low-frequency noise filters. In this talk we carefully examine the applicability of a particular type of dynamically corrected gates, namely the supcode designed for singlet-triplet qubits, under realistic 1 /fα noises. Through randomized benchmarking, we have found that supcode offers improvement of the gate fidelity for α > 1 and the improvement becomes exponentially more pronounced with the increase of the noise exponent α up to 3. On the other hand, for small α supcode will not offer any improvement. We also present the computed filter transfer functions for the supcode gates for nuclear and charge noise respectively and have found that they are consistent with the finding from the benchmarking. The work is supported by Grants from City University of Hong Kong (Projects No. 9610335 and No. 7200456).

  10. Collective spin 1 singlet phase in high-pressure oxygen

    PubMed Central

    Crespo, Yanier; Fabrizio, Michele; Scandolo, Sandro; Tosatti, Erio

    2014-01-01

    Oxygen, one of the most common and important elements in nature, has an exceedingly well-explored phase diagram under pressure, up to and beyond 100 GPa. At low temperatures, the low-pressure antiferromagnetic phases below 8 GPa where O2 molecules have spin S = 1 are followed by the broad apparently nonmagnetic ε phase from about 8 to 96 GPa. In this phase, which is our focus, molecules group structurally together to form quartets while switching, as believed by most, to spin S = 0. Here we present theoretical results strongly connecting with existing vibrational and optical evidence, showing that this is true only above 20 GPa, whereas the S = 1 molecular state survives up to about 20 GPa. The ε phase thus breaks up into two: a spinless ε0 (20−96 GPa), and another ε1 (8−20 GPa) where the molecules have S = 1 but possess only short-range antiferromagnetic correlations. A local spin liquid-like singlet ground state akin to some earlier proposals, and whose optical signature we identify in existing data, is proposed for this phase. Our proposed phase diagram thus has a first-order phase transition just above 20 GPa, extending at finite temperature and most likely terminating into a crossover with a critical point near 30 GPa and 200 K. PMID:25002513

  11. Simulation of Singlet Exciton Diffusion in Bulk Organic Materials.

    PubMed

    Kranz, Julian J; Elstner, Marcus

    2016-09-13

    We present a scheme for nonadiabatic direct dynamics simulation of Frenkel exciton diffusion in bulk molecular systems. The fluctuations of exciton couplings caused by the molecular motion can crucially influence exciton transport in such materials. This effect can be conveniently taken into account by computing the exciton couplings along molecular dynamics trajectories, as shown recently. In this work, we combine Molecular Dynamics simulations with a Frenkel Hamiltonian into a combined quantum-mechanical/molecular mechanics approach in order to allow for a simultaneous propagation of nuclear and electronic degrees of freedom using nonadiabatic dynamics propagation schemes. To reach the necessary time and length scales, we use classical force-fields and the semiempirical time-dependent density functional tight-binding method in combination with a fragmentation of the electronic structure. Fewest-switches surface-hopping, with adaptions to handle trivial crossings, and the Boltzmann-corrected Ehrenfest method are used to follow the excitonic quantum dynamics according to the classical evolution of the nuclei. As an application, we present the simulation of singlet exciton diffusion in crystalline anthracene, which allows us to address strengths and shortcomings of the presented methodology in detail. PMID:27434173

  12. Noise filtering of composite pulses for singlet-triplet qubits

    NASA Astrophysics Data System (ADS)

    Yang, Xu-Chen; Wang, Xin

    2016-07-01

    Semiconductor quantum dot spin qubits are promising candidates for quantum computing. In these systems, the dynamically corrected gates offer considerable reduction of gate errors and are therefore of great interest both theoretically and experimentally. They are, however, designed under the static-noise model and may be considered as low-frequency filters. In this work, we perform a comprehensive theoretical study of the response of a type of dynamically corrected gates, namely the SUPCODE for singlet-triplet qubits, to realistic 1/f noises with frequency spectra 1/ωα. Through randomized benchmarking, we have found that SUPCODE offers improvement of the gate fidelity for α  1 and the improvement becomes exponentially more pronounced with the increase of the noise exponent in the range 1  α ≤ 3 studied. On the other hand, for small α, SUPCODE will not offer any improvement. The δJ-SUPCODE, specifically designed for systems where the nuclear noise is absent, is found to offer additional error reduction than the full SUPCODE for charge noises. The computed filter transfer functions of the supcode gates are also presented.

  13. Excitation migration, quenching, and regulation of photosynthetic light harvesting in photosystem II.

    PubMed

    Valkunas, Leonas; Chmeliov, Jevgenij; Trinkunas, Gediminas; Duffy, Christopher D P; van Grondelle, Rienk; Ruban, Alexander V

    2011-07-28

    Excitation energy transfer and quenching in LHCII aggregates is considered in terms of a coarse-grained model. The model assumes that the excitation energy transfer within a pigment-protein complex is much faster than the intercomplex excitation energy transfer, whereas the quenching ability is attributed to a specific pigment-protein complex responsible for the nonphotochemical quenching (NPQ). It is demonstrated that the pump-probe experimental data obtained at low excitation intensities for LHCII aggregates under NPQ conditions can be equally well explained at two limiting cases, either describing the excitation kinetics in the migration-limited or in the trap-limited regime. Thus, it is concluded that low excitation conditions do not allow one to unambiguously define the relationship between the mean times of excitation migration and trapping. However, this could be achieved by using high excitation conditions when exciton-exciton annihilation is dominant. In this case it was found that in the trap-limited regime the excitation kinetics in the aggregate should be almost insensitive to the excitation density, meaning that singlet-singlet annihilation has little effect on the NPQ decay kinetics, whereas in the migration-limited case there is a clear intensity dependence. In order to account for the random distribution of the NPQ-traps within the LHCII aggregates, excitation diffusion in a continuous medium with random static traps was considered. This description demonstrates a very good correspondence to the experimental fluorescence kinetics assuming a lamellar (quasi-3D) structure of the antenna characterized by the dimension d=2.4 and therefore justifying the diffusion-limited approach on which the model is based. Using the coarse-grained model to describe the aggregate we estimate one NPQ-trap per 100 monomeric LHCII complexes. Finally we discuss the origin of the traps responsible for excitation quenching under NPQ conditions.

  14. Validation of local hybrid functionals for TDDFT calculations of electronic excitation energies

    NASA Astrophysics Data System (ADS)

    Maier, Toni M.; Bahmann, Hilke; Arbuznikov, Alexei V.; Kaupp, Martin

    2016-02-01

    The first systematic evaluation of local hybrid functionals for the calculation of electronic excitation energies within linear-response time-dependent density functional theory (TDDFT) is reported. Using our recent efficient semi-numerical TDDFT implementation [T. M. Maier et al., J. Chem. Theory Comput. 11, 4226 (2015)], four simple, thermochemically optimized one-parameter local hybrid functionals based on local spin-density exchange are evaluated against a database of singlet and triplet valence excitations of organic molecules, and against a mixed database including also Rydberg, intramolecular charge-transfer (CT) and core excitations. The four local hybrids exhibit comparable performance to standard global or range-separated hybrid functionals for common singlet valence excitations, but several local hybrids outperform all other functionals tested for the triplet excitations of the first test set, as well as for relative energies of excited states. Evaluation for the combined second test set shows that local hybrids can also provide excellent Rydberg and core excitations, in the latter case rivaling specialized functionals optimized specifically for such excitations. This good performance of local hybrids for different excitation types could be traced to relatively large exact-exchange (EXX) admixtures in a spatial region intermediate between valence and asymptotics, as well as close to the nucleus, and lower EXX admixtures in the valence region. In contrast, the tested local hybrids cannot compete with the best range-separated hybrids for intra- and intermolecular CT excitation energies. Possible directions for improvement in the latter category are discussed. As the used efficient TDDFT implementation requires essentially the same computational effort for global and local hybrids, applications of local hybrid functionals to excited-state problems appear promising in a wide range of fields. Influences of current-density dependence of local kinetic

  15. X-ray induced singlet oxygen generation by nanoparticle-photosensitizer conjugates for photodynamic therapy: determination of singlet oxygen quantum yield.

    PubMed

    Clement, Sandhya; Deng, Wei; Camilleri, Elizabeth; Wilson, Brian C; Goldys, Ewa M

    2016-01-01

    Singlet oxygen is a primary cytotoxic agent in photodynamic therapy. We show that CeF3 nanoparticles, pure as well as conjugated through electrostatic interaction with the photosensitizer verteporfin, are able to generate singlet oxygen as a result of UV light and 8 keV X-ray irradiation. The X-ray stimulated singlet oxygen quantum yield was determined to be 0.79 ± 0.05 for the conjugate with 31 verteporfin molecules per CeF3 nanoparticle, the highest conjugation level used. From this result we estimate the singlet oxygen dose generated from CeF3-verteporfin conjugates for a therapeutic dose of 60 Gy of ionizing radiation at energies of 6 MeV and 30 keV to be (1.2 ± 0.7) × 10(8) and (2.0 ± 0.1) × 10(9) singlet oxygen molecules per cell, respectively. These are comparable with cytotoxic doses of 5 × 10(7)-2 × 10(9) singlet oxygen molecules per cell reported in the literature for photodynamic therapy using light activation. We confirmed that the CeF3-VP conjugates enhanced cell killing with 6 MeV radiation. This work confirms the feasibility of using X- or γ- ray activated nanoparticle-photosensitizer conjugates, either to supplement the radiation treatment of cancer, or as an independent treatment modality.

  16. X-ray induced singlet oxygen generation by nanoparticle-photosensitizer conjugates for photodynamic therapy: determination of singlet oxygen quantum yield

    NASA Astrophysics Data System (ADS)

    Clement, Sandhya; Deng, Wei; Camilleri, Elizabeth; Wilson, Brian C.; Goldys, Ewa M.

    2016-01-01

    Singlet oxygen is a primary cytotoxic agent in photodynamic therapy. We show that CeF3 nanoparticles, pure as well as conjugated through electrostatic interaction with the photosensitizer verteporfin, are able to generate singlet oxygen as a result of UV light and 8 keV X-ray irradiation. The X-ray stimulated singlet oxygen quantum yield was determined to be 0.79 ± 0.05 for the conjugate with 31 verteporfin molecules per CeF3 nanoparticle, the highest conjugation level used. From this result we estimate the singlet oxygen dose generated from CeF3-verteporfin conjugates for a therapeutic dose of 60 Gy of ionizing radiation at energies of 6 MeV and 30 keV to be (1.2 ± 0.7) × 108 and (2.0 ± 0.1) × 109 singlet oxygen molecules per cell, respectively. These are comparable with cytotoxic doses of 5 × 107-2 × 109 singlet oxygen molecules per cell reported in the literature for photodynamic therapy using light activation. We confirmed that the CeF3-VP conjugates enhanced cell killing with 6 MeV radiation. This work confirms the feasibility of using X- or γ- ray activated nanoparticle-photosensitizer conjugates, either to supplement the radiation treatment of cancer, or as an independent treatment modality.

  17. X-ray induced singlet oxygen generation by nanoparticle-photosensitizer conjugates for photodynamic therapy: determination of singlet oxygen quantum yield

    PubMed Central

    Clement, Sandhya; Deng, Wei; Camilleri, Elizabeth; Wilson, Brian C.; Goldys, Ewa M.

    2016-01-01

    Singlet oxygen is a primary cytotoxic agent in photodynamic therapy. We show that CeF3 nanoparticles, pure as well as conjugated through electrostatic interaction with the photosensitizer verteporfin, are able to generate singlet oxygen as a result of UV light and 8 keV X-ray irradiation. The X-ray stimulated singlet oxygen quantum yield was determined to be 0.79 ± 0.05 for the conjugate with 31 verteporfin molecules per CeF3 nanoparticle, the highest conjugation level used. From this result we estimate the singlet oxygen dose generated from CeF3-verteporfin conjugates for a therapeutic dose of 60 Gy of ionizing radiation at energies of 6 MeV and 30 keV to be (1.2 ± 0.7) × 108 and (2.0 ± 0.1) × 109 singlet oxygen molecules per cell, respectively. These are comparable with cytotoxic doses of 5 × 107–2 × 109 singlet oxygen molecules per cell reported in the literature for photodynamic therapy using light activation. We confirmed that the CeF3-VP conjugates enhanced cell killing with 6 MeV radiation. This work confirms the feasibility of using X- or γ- ray activated nanoparticle-photosensitizer conjugates, either to supplement the radiation treatment of cancer, or as an independent treatment modality. PMID:26818819

  18. Isotope effects of ground and lowest lying vibrational states of H 3 - x D x O2 - complexes

    NASA Astrophysics Data System (ADS)

    Ansari, Narjes; Meyer, Hans-Dieter

    2016-02-01

    Isotope effects of the H 3 O2 - anion are investigated. For this, the 24 lowest excited vibrational states of the H 3 - x D x O2 - complexes, with x = 0-3, are computed using two different Hamiltonians, namely, a 7D reduced-dimensionality one with a numerical representation of the kinetic energy operator (KEO) and a 9D full-dimensionality Hamiltonian with an exact analytic KEO. The computations are carried out with the multiconfiguration time-dependent Hartree method. The obtained results show that bridge and terminal H-D exchange cause a variation in energy with or without a rearrangement of states. A clear rearrangement of fundamental modes is observed in bridge H-D exchange of the H 3 O2 - complex, where the frequency of bridge hydrogen stretching (z) is strongly lowered by substitution. The isotope effects show that rotation (ϕ), rocking (u1 + u2), wagging (u1 - u2), and O-O stretch (R) modes are sensitive to terminal H-D exchange, while the bridge-atom bending (x,y) and stretch (z) modes are sensitive to bridge H-D exchange. An influence coefficient, which measures the influence of an excitation of one mode on the various 1D reduced densities, is defined and analyzed in detail. It is shown that the D 3 O2 - complex is more strongly correlated or coupled than the other isotopologues.

  19. Accessing long-lived nuclear singlet states between chemically equivalent spins without breaking symmetry

    PubMed Central

    Feng, Yesu; Davis, Ryan M.; Warren, Warren S.

    2013-01-01

    Long-lived nuclear spin states could greatly enhance the applicability of hyperpolarized nuclear magnetic resonance. Using singlet states between inequivalent spin pairs has been shown to extend the signal lifetime by more than an order of magnitude compared to the spin lattice relaxation time (T1), but they have to be prevented from evolving into other states. In the most interesting case the singlet is between chemically equivalent spins, as it can then be inherently an eigenstate. However this presents major challenges in the conversion from bulk magnetization to singlet. In the only case demonstrated so far, a reversible chemical reaction to break symmetry was required. Here we present a pulse sequence technique that interconverts between singlet spin order and bulk magnetization without breaking the symmetry of the spin system. This technique is independent of field strength and is applicable to a broad range of molecules. PMID:23505397

  20. Determination of the low concentration correction in the macroscopic singlet oxygen model for PDT

    NASA Astrophysics Data System (ADS)

    Kim, Michele M.; Penjweini, Rozhin; Finlay, Jarod C.; Zhu, Timothy C.

    2016-03-01

    The macroscopic singlet oxygen model has been used for singlet oxygen explicit dosimetry in photodynamic therapy (PDT). The photophysical parameters for commonly used sensitizers, HPPH and BPD, have been investigated in pre-clinical studies using mouse models. So far, studies have involved optimizing fitting algorithms to obtain the some of the photophysical parameters (ξ, σ, g) and the threshold singlet oxygen dose ([1O2]rx,sh), while other parameters such as the low concentration correction, δ, has been kept as a constant. In this study, using photobleaching measurements of mice in vivo, the value of δ was also optimized and fit to better describe experimental data. Furthermore, the value of the specific photobleaching ratio (σ) was also fine-tuned using the photobleaching results. Based on literature values of δ, σ for photosensitizers can be uniquely determined using the additional photobleaching measurements. This routine will further improve the macroscopic model of singlet oxygen production for use in explicit dosimetry.

  1. Pallidol, a resveratrol dimer from red wine, is a selective singlet oxygen quencher

    SciTech Connect

    He Shan; Jiang Liyan; Wu Bin; Pan Yuanjiang; Sun Cuirong

    2009-02-06

    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{sub a} = 1.71 x 10{sup 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.

  2. Towards photodynamic therapy with ionizing radiation: nanoparticle-mediated singlet oxygen generation (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    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.

  3. Photochemical inactivation of viruses by antibody conjugates of compounds generating singlet oxygen

    NASA Astrophysics Data System (ADS)

    Savitsky, Alexander P.; Tourkin, Andrey I.; Tourkina, Elena V.; Cherednikova, Tatyana V.; Ponomarev, Gely V.; Poglazov, Boris F.

    1994-03-01

    For the first time a method is proposed for targeted destruction of viral particles with a photoimmuno-toxin. The photoinununotoxin is a conjugate of antibodies and dimethoxy haematoporphyrin (a potent singlet oxygen generator), binding with the viral particle and upon illumination with visible light inactivating the virus by singlet oxygen. The method can be used to combat viral infection in humans and to prevent lysis of industrial micro-organisms by lysogenic bacteriophage strains.

  4. RESONANT CAVITY EXCITATION SYSTEM

    DOEpatents

    Baker, W.R.; Kerns, Q.A.; Riedel, J.

    1959-01-13

    An apparatus is presented for exciting a cavity resonator with a minimum of difficulty and, more specifically describes a sub-exciter and an amplifier type pre-exciter for the high-frequency cxcitation of large cavities. Instead of applying full voltage to the main oscillator, a sub-excitation voltage is initially used to establish a base level of oscillation in the cavity. A portion of the cavity encrgy is coupled to the input of the pre-exciter where it is amplified and fed back into the cavity when the pre-exciter is energized. After the voltage in the cavity resonator has reached maximum value under excitation by the pre-exciter, full voltage is applied to the oscillator and the pre-exciter is tunned off. The cavity is then excited to the maximum high voltage value of radio frequency by the oscillator.

  5. Temperature dependence of the lowest excitonic transition for an InAs ultrathin quantum well

    NASA Astrophysics Data System (ADS)

    Singh, S. D.; Porwal, S.; Sharma, T. K.; Rustagi, K. C.

    2006-03-01

    Temperature dependent photoluminescence and photoreflectance techniques are used to investigate the lowest excitonic transition of InAs ultrathin quantum well. It is shown that the temperature dependence of the lowest energy transition follows the band gap variation of GaAs barrier, which is well reproduced by calculated results based on the envelope function approximation with significant corrections due to strain and temperature dependences of the confinement potential. A redshift in photoluminescence peak energy compared to photoreflectance is observed at low temperatures. This is interpreted to show that the photoluminescence signal originates from the recombination of carriers occupying the band-tail states below the lowest critical point.

  6. Comparison of killing of gram-negative and gram-positive bacteria by pure singlet oxygen.

    PubMed Central

    Dahl, T A; Midden, W R; Hartman, P E

    1989-01-01

    Gram-negative and gram-positive bacteria were found to display different sensitivities to pure singlet oxygen generated outside of cells. Killing curves for Salmonella typhimurium and Escherichia coli strains were indicative of multihit killing, whereas curves for Sarcina lutea, Staphylococcus aureus, Streptococcus lactis, and Streptococcus faecalis exhibited single-hit kinetics. The S. typhimurium deep rough strain TA1975, which lacks nearly all of the cell wall lipopolysaccharide coat and manifests concomitant enhancement of penetration by some exogenous substances, responded to singlet oxygen with initially faster inactivation than did the S. typhimurium wild-type strain, although the maximum rates of killing appeared to be quite similar. The structure of the cell wall thus plays an important role in susceptibility to singlet oxygen. The outer membrane-lipopolysaccharide portion of the gram-negative cell wall initially protects the bacteria from extracellular singlet oxygen, although it may also serve as a source for secondary reaction products which accentuate the rates of cell killing. S. typhimurium and E. coli strains lacking the cellular antioxidant, glutathione, showed no difference from strains containing glutathione in response to the toxic effects of singlet oxygen. Strains of Sarcina lutea and Staphylococcus aureus that contained carotenoids, however, were far more resistant to singlet oxygen lethality than were both carotenoidless mutants of the same species and other gram-positive species lacking high levels of protective carotenoids. PMID:2703469

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

    PubMed Central

    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

  8. Singlet oxygen scavenging activity and cytotoxicity of essential oils from rutaceae.

    PubMed

    Ao, Yoko; Satoh, Kazue; Shibano, Katsushige; Kawahito, Yukari; Shioda, Seiji

    2008-07-01

    Since we have been exposed to excessive amounts of stressors, aromatherapy for the relaxation has recently become very popular recently. However, there is a problem which responds to light with the essential oil used by aromatherapy. It is generally believed that singlet oxygen is implicated in the pathogenesis of various diseases such as light-induced skin disorders and inflammatory responses. Here we studied whether essential oils can effectively scavenge singlet oxygen upon irradiation, using the electron spin resonance (ESR) method. Green light was used to irradiate twelve essential oils from rutaceae. Among these twelve essential oils, eight were prepared by the expression (or the compression) method (referred to as E oil), and four samples were prepared by the steam distillation method (referred to as SD oil). Five E oils enhanced singlet oxygen production. As these essential oils may be phototoxic, it should be used for their use whit light. Two E oils and three SD oils showed singlet oxygen scavenging activity. These results may suggest that the antioxidant activity of essential oils are judged from their radical scavenging activity. Essential oils, which enhance the singlet oxygen production and show higher cytotoxicity, may contain much of limonene. These results suggest that limonene is involved not only in the enhancement of singlet oxygen production but also in the expression of cytotoxic activity, and that attention has to be necessary for use of blended essential oils.

  9. Synergism between Airborne Singlet Oxygen and a Trisubstituted Olefin Sulfonate for the Inactivation of Bacteria

    PubMed Central

    2015-01-01

    The reactivity of a trisubstituted alkene surfactant (8-methylnon-7-ene-1 sulfonate, 1) to airborne singlet oxygen in a solution containing E. coli was examined. Surfactant 1 was prepared by a Strecker-type reaction of 9-bromo-2-methylnon-2-ene with sodium sulfite. Submicellar concentrations of 1 were used that reacted with singlet oxygen by an “ene” reaction to yield two hydroperoxides (7-hydroperoxy-8-methylnon-8-ene-1 sulfonate and (E)-8-hydroperoxy-8-methylnon-6-ene-1 sulfonate) in a 4:1 ratio. Exchanging the H2O solution for D2O where the lifetime of solution-phase singlet oxygen increases by 20-fold led to an ∼2-fold increase in the yield of hydroperoxides pointing to surface activity of singlet oxygen with the surfactant in a partially solvated state. In this airborne singlet oxygen reaction, E. coli inactivation was monitored in the presence and absence of 1 and by a LIVE/DEAD cell permeabilization assay. It was shown that the surfactant has low dark toxicity with respect to the bacteria, but in the presence of airborne singlet oxygen, it produces a synergistic enhancement of the bacterial inactivation. How the ene-derived surfactant hydroperoxides can provoke 1O2 toxicity and be of general utility is discussed. PMID:24611688

  10. Solvent-dependent singlet oxygen lifetimes: temperature effects implicate tunneling and charge-transfer interactions.

    PubMed

    Bregnhøj, Mikkel; Westberg, Michael; Jensen, Frank; Ogilby, Peter R

    2016-08-17

    The effect of solvent on the lifetime of singlet oxygen, O2(a(1)Δg), particularly the pronounced H/D solvent isotope effect, has drawn the attention of chemists for almost 50 years. The currently accepted model for this phenomenon is built on a foundation in which the electronic excitation energy of O2(a(1)Δg) is transferred to vibrational modes in a solvent molecule, with oxygen returning to its ground electronic state, O2(X(3)Σg(-)). This model of electronic-to-vibrational (e-to-v) energy transfer specifically focusses on the solvent as a "sink" for the excitation energy of O2(a(1)Δg). On the basis of temperature-dependent changes in the solvent-mediated O2(a(1)Δg) lifetime, we demonstrate that this energy-sink-based model has limitations and needs to be re-formulated. We now show that the effect of solvent on the O2(a(1)Δg) lifetime is more reasonably interpreted by considering an activation barrier that reflects the extent to which a solvent molecule perturbs the forbidden O2(a(1)Δg) → O2(X(3)Σg(-)) transition. For a given solvent molecule, this barrier reflects contributions from (a) the oxygen-solvent charge transfer state that mediates nonradiative coupling between the O2(a(1)Δg) and O2(X(3)Σg(-)) states, and (b) vibrations of specific bonds in the solvent molecule. The latter establishes connectivity to the desirable features of the energy-sink-based model. Moreover, temperature-dependent H/D solvent isotope effects imply that tunneling through this barrier plays a role in the mechanism for O2(a(1)Δg) deactivation, even at room temperature. Although we focus on a long-standing problem involving O2(a(1)Δg), our results and interpretation touch fundamental issues of interest to chemists at large. PMID:27484979

  11. A cyclometallated fluorenyl Ir(iii) complex as a potential sensitiser for two-photon excited photodynamic therapy (2PE-PDT).

    PubMed

    Boreham, Elizabeth M; Jones, Lucy; Swinburne, Adam N; Blanchard-Desce, Mireille; Hugues, Vincent; Terryn, Christine; Miomandre, Fabien; Lemercier, Gilles; Natrajan, Louise S

    2015-09-28

    A new Ir(iii) cyclometallated complex bearing a fluorenyl 5-substituted-1,10-phenanthroline ligand ([Ir(ppy)2()][PF6], ppy = 2-phenylpyridine) is presented which exhibits enhanced triplet oxygen sensing properties. The efficacy of this complex to act as a photosensitiser for altering the morphology of C6 Glioma cells that represent malignant nervous tumours has been evaluated. The increased heavy metal effect and related spin-orbit coupling parameters on the photophysical properties of this complex are evidenced by comparison with Ru(ii) analogues. The complex [Ir(ppy)2()][PF6] is shown to exhibit relatively high two-photon absorption efficiencies for the lowest energy MLCT electronic transitions with two-photon absorption cross sections that range from 50 to 80 Goeppert-Mayer units between 750 to 800 nm. Quantum yields for the complex were measured up to 23% and the Stern-Volmer quenching constant, KSV was determined to be 40 bar(-1) in acetonitrile solution, confirming the high efficiency of the complex as a triplet oxygen sensitiser. Preliminary in vitro experiments with C6 Glioma cells treated with [Ir(ppy)2()][PF6], show that the complex is an efficient sensitizer for triplet oxygen, producing cytotoxic singlet oxygen ((1)O2) by two-photon excitation at 740 nm resulting in photodynamic effects that lead to localised cell damage and death.

  12. A cyclometallated fluorenyl Ir(iii) complex as a potential sensitiser for two-photon excited photodynamic therapy (2PE-PDT).

    PubMed

    Boreham, Elizabeth M; Jones, Lucy; Swinburne, Adam N; Blanchard-Desce, Mireille; Hugues, Vincent; Terryn, Christine; Miomandre, Fabien; Lemercier, Gilles; Natrajan, Louise S

    2015-09-28

    A new Ir(iii) cyclometallated complex bearing a fluorenyl 5-substituted-1,10-phenanthroline ligand ([Ir(ppy)2()][PF6], ppy = 2-phenylpyridine) is presented which exhibits enhanced triplet oxygen sensing properties. The efficacy of this complex to act as a photosensitiser for altering the morphology of C6 Glioma cells that represent malignant nervous tumours has been evaluated. The increased heavy metal effect and related spin-orbit coupling parameters on the photophysical properties of this complex are evidenced by comparison with Ru(ii) analogues. The complex [Ir(ppy)2()][PF6] is shown to exhibit relatively high two-photon absorption efficiencies for the lowest energy MLCT electronic transitions with two-photon absorption cross sections that range from 50 to 80 Goeppert-Mayer units between 750 to 800 nm. Quantum yields for the complex were measured up to 23% and the Stern-Volmer quenching constant, KSV was determined to be 40 bar(-1) in acetonitrile solution, confirming the high efficiency of the complex as a triplet oxygen sensitiser. Preliminary in vitro experiments with C6 Glioma cells treated with [Ir(ppy)2()][PF6], show that the complex is an efficient sensitizer for triplet oxygen, producing cytotoxic singlet oxygen ((1)O2) by two-photon excitation at 740 nm resulting in photodynamic effects that lead to localised cell damage and death. PMID:26289593

  13. Effects of quantum confinement on excited state properties of SrTiO3 from ab initio many-body perturbation theory

    NASA Astrophysics Data System (ADS)

    Reyes-Lillo, Sebastian E.; Rangel, Tonatiuh; Bruneval, Fabien; Neaton, Jeffrey B.

    2016-07-01

    The Ruddlesden-Popper (RP) homologous series Srn +1TinO3 n +1 provides a useful template for the study and control of the effects of dimensionality and quantum confinement on the excited state properties of the complex oxide SrTiO3. We use ab initio many-body perturbation theory within the G W approximation and the Bethe-Salpeter equation approach to calculate quasiparticle energies and absorption spectra of Srn +1TinO3 n +1 for n =1 -5 and ∞ . Our computed direct and indirect optical gaps are in excellent agreement with spectroscopic measurements. The calculated optical spectra reproduce the main experimental features and reveal excitonic structure near the gap edge. We find that electron-hole interactions are important across the series, leading to significant exciton binding energies that increase for small n and reach a value of 330 meV for n =1 , a trend attributed to increased quantum confinement. We find that the lowest-energy singlet exciton of Sr2TiO4 (n =1 ) localizes in the two-dimensional plane defined by the TiO2 layer, and we explain the origin of its localization.

  14. Singlet Oxygen Signatures Are Detected Independent of Light or Chloroplasts in Response to Multiple Stresses1[C][W

    PubMed Central

    Mor, Avishai; Koh, Eugene; Weiner, Lev; Rosenwasser, Shilo; Sibony-Benyamini, Hadas; Fluhr, Robert

    2014-01-01

    The production of singlet oxygen is typically associated with inefficient dissipation of photosynthetic energy or can arise from light reactions as a result of accumulation of chlorophyll precursors as observed in fluorescent (flu)-like mutants. Such photodynamic production of singlet oxygen is thought to be involved in stress signaling and programmed cell death. Here we show that transcriptomes of multiple stresses, whether from light or dark treatments, were correlated with the transcriptome of the flu mutant. A core gene set of 118 genes, common to singlet oxygen, biotic and abiotic stresses was defined and confirmed to be activated photodynamically by the photosensitizer Rose Bengal. In addition, induction of the core gene set by abiotic and biotic selected stresses was shown to occur in the dark and in nonphotosynthetic tissue. Furthermore, when subjected to various biotic and abiotic stresses in the dark, the singlet oxygen-specific probe Singlet Oxygen Sensor Green detected rapid production of singlet oxygen in the Arabidopsis (Arabidopsis thaliana) root. Subcellular localization of Singlet Oxygen Sensor Green fluorescence showed its accumulation in mitochondria, peroxisomes, and the nucleus, suggesting several compartments as the possible origins or targets for singlet oxygen. Collectively, the results show that singlet oxygen can be produced by multiple stress pathways and can emanate from compartments other than the chloroplast in a light-independent manner. The results imply that the role of singlet oxygen in plant stress regulation and response is more ubiquitous than previously thought. PMID:24599491

  15. An optical-optical double resonance probe of the lowest triplet state of jet-cooled thiophosgene: Rovibronic structures and electronic relaxation

    NASA Astrophysics Data System (ADS)

    Fujiwara, Takashige; Lim, Edward C.; Judge, Richard H.; Moule, David C.

    2006-03-01

    The vibrational structure, rotational structure, and electronic relaxation of the "dark" T1A23(n,π*) state of jet-cooled thiophosgene have been investigated by two-color S2←T1←S0 optical-optical double resonance (OODR) spectroscopy, which monitors the S2→S0 fluorescence generated by S2←T1 excitation. This method is capable of isolating the T1 vibrational structure into a1, b1, and b2 symmetry blocks. The fluorescence-detected vibrational structure of the Tz spin state of T1 shows that the CS stretching frequency as well as the barrier height for pyramidal deformation are significantly greater in the A23(n,π*) state than in the corresponding A21(n,π*) state. The differing vibrational parameters of the T1 thiophosgene relative to the S1 thiophosgene can be attributed to the motions of unpaired electrons that are better correlated when they are in the excited singlet state than when they are in the triplet state of same electron configuration. A set of T1 structural parameters and the information concerning the T1 spin states have been obtained from least-square fittings of the rotationally resolved T1←S0 excitation spectrum. The nearly degenerate ∣x⟩ and ∣y⟩ spin states are well removed from ∣z⟩ spin component, indicating that T1 thiophosgene is a good example of case (ab) coupling. The decay of the ∣z⟩ spin state of T1 thiophosgene, obtained from time-resolved S2←T1←S0 OODR experiment, is characteristic of strong-coupling intermediate-case decay in which an initial rapid decay is followed by recurrences and/or a long-lived quasiexponential decay.

  16. Search for lowest-energy fullerenes: C98 to C110.

    PubMed

    Shao, Nan; Gao, Yi; Yoo, Soohaeng; An, Wei; Zeng, Xiao Cheng

    2006-06-22

    By combining the semiempirical density-functional based tight-binding optimization with density-functional theory single-point energy calculation at the PBE1PBE/6-311G level, we propose an efficient computational approach to determine lowest-energy structures of large-sized carbon fullerenes. Our studies show that C(92) (D(3): 28) and C(94) (C(2): 43) are the new leading candidates for the lowest-energy structures of C(92) and C(94). Moreover, for the first time, the lowest-energy structures of C(98)-C(110) are identified on the basis of the density-functional theory calculation. The lowest-energy isomers C(102) (C(1): 603) and C(108) (D(2): 1771) are readily isolated experimentally because they are much lower in energy than their other low-lying IPR isomers.

  17. Polarized pump--probe spectroscopy of electronic excitation transport in photosynthetic antennas

    SciTech Connect

    Struve, W.S. )

    1990-08-01

    Polarized pump--probe spectroscopy was performed with 1.5--2 psec resolution on the bacteriochlorophyll a protein antenna complex from the green sulfur bacterium Prosthecochloris aestuarii and on native and enriched photosystem I particles from spinach. The resulting photobleaching profiles reflect the details of singlet electronic-excitation transport in these photosynthetic antennas, in which the pigments are complexed by proteins into clusters of five or more chromophores.

  18. The role of vasoactive intestinal peptide in scavenging singlet oxygen

    SciTech Connect

    Misra, B.R.; Misra, H.P. )

    1990-02-26

    The neuropeptide vasoactive intestinal peptide (VIP), a highly basic 28 amino acid peptide, has a widespread distribution in the body. The functional specificity of this peptide not only includes its potent vasodilatory activity, but also its role in protecting lungs against acute injury, in preventing T-lymphocyte proliferation and in modulating immune function. The purpose of this study was to examine the possible antioxidant properties of VIP. The authors found that VIP up to 50 {mu}g/ml had no inhibitory effect on its reduction of cytochrome C by xanthine and xanthine oxidase, indicating that the peptide does not have significant O{sub 2} scavenging ability. However, VIP was found to inhibit, in a dose-dependent manner, the {sup 1}O{sub 2} dependent 2, 2, 6, 6 tetramethyl piperidine oxide (TEMPO) formation. {sup 1}O{sub 2} was produced by rose benzal photosensitizing system and was detected as TEMP-{sup 1}O{sub 2} adduct (TEMPO) by electron paramagnetic resonance (EPR) spectroscopic technique. The formation of TEMPO signal was strongly inhibited by {beta}-carotene, histidine as well as azide, but not by superoxide dismutase (48 {mu}g/ml), catalase (20 {mu}g/ml) and mannitol (6mM), indicating that TEMPO signal was a TEMP-{sup 1}O{sub 2} adduct. These results indicate that VIP has potent antioxidant activity and may serve as a singlet O{sub 2} scavenger, thus it may modulate the oxidative tissue injury caused by this reactive oxygen species.

  19. Photochemical production of singlet oxygen from particulate organic matter.

    PubMed

    Appiani, Elena; McNeill, Kristopher

    2015-03-17

    Dissolved organic matter is established as one of the most relevant photosensitizers in aquatic environments, producing singlet oxygen (1O2) alongside other photochemically produced reactive intermediates. While the production of 1O2 from DOM has been well studied, the relative importance of particulate organic matter (POM) to the overall 1O2 production is less well understood. POM is known to play an important role in pollutant fate through the sorption and transport of hydrophobic pollutants. If POM is directly involved in 1O2 production, sorbed molecules would be expected to undergo enhanced photodegradation. In this work, synthetic POM was prepared by coating silica particles with commercial humic acid. The photochemical behavior of these POM samples was compared to dissolved commercial humic acids (DOM). Suspended natural sediment was also studied to test the environmental relevance of the synthetic POM model. Synthetic POM particles appear to simulate well the 1O2-production of suspended sediment. The 1O2 concentrations experienced by POM-sorbed probe molecules was up to 30% higher than experienced by DOM-sorbed ones, even though the aqueous concentration of 1O2 in irradiated POM suspensions was much lower than the analogous DOM solutions. These results were interpreted with a reaction-diffusion model, which suggested that the production rate of 1O2 by POM is lower than DOM, but the loss of 1O2 from the POM-phase is also lower than DOM. Based on the experimental results of this study, calculations were conducted to estimate the impact of removing POM on 1O2-mediated processes. These calculations indicate that compounds with a log Koc value near 4 will be most affected by removal of POM and that the magnitude of the effect is proportional to the fraction of the total organic matter represented by POM. This study demonstrates that particles can play an important role in the degradation of organic compounds via aquatic photochemistry.

  20. Diboson excess in the Higgs singlet and vectorlike quark models

    NASA Astrophysics Data System (ADS)

    Chen, Chuan-Hung; Nomura, Takaaki

    2015-12-01

    Diboson resonance with mass of 1.8-2 TeV is reported successively by CMS and ATLAS experiments in proton-proton collisions at √{s }=8 TeV . We investigate the potentiality of Higgs singlet as the TeV resonance. The challenges of low production cross section and high width for a fundamental scalar could be got over by three factors: (1) larger Yukawa couplings, (2) larger number of heavy quarks and (3) smaller mixing angle with standard model Higgs. We find that the required factors could be realized in the framework of two vectorlike triplet quarks (VLTQs) and the resulting production cross section and decay fraction of heavy Higgs σ (p p →H )×BR (H →W+W-+Z Z ) can be of O (10 ) fb when masses of new heavy quarks are 1 TeV, the values of Yukawa couplings are around 3 and the mixing angle is sin θ ˜0.11 . We also find that the SM Higgs production and its decay in the process p p →h →γ γ could be still consistent with current data when a color-triplet scalar (3 ,3 )1 /3 is considered. Furthermore, we study the product of VLTQ-pair production cross section and the BRs of VLTQ decays, and find that the cross sections in the decay channels, such as u4 ,5→b W+ , d5→t W- and d4→b h (Z ) could be 7-17 fb at 13 TeV LHC.

  1. Investigation of polar and stereoelectronic effects on pure excited-state hydrogen atom abstractions from phenols and alkylbenzenes.

    PubMed

    Pischel, Uwe; Patra, Digambara; Koner, Apurba L; Nau, Werner M

    2006-01-01

    The fluorescence quenching of singlet-excited 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) by 22 phenols and 12 alkylbenzenes has been investigated. Quenching rate constants in acetonitrile are in the range of 10(8)-10(9) M(-1)s(-1) for phenols and 10(5)-10(6) M(-1)s(-1) for alkylbenzenes. In contrast to the quenching of triplet-excited benzophenone, no exciplexes are involved, so that a pure hydrogen atom transfer is proposed as quenching mechanism. This is supported by (1) pronounced deuterium isotope effects (kH/kD ca 4-6), which were observed for phenols and alkylbenzenes, and (2) a strongly endergonic thermodynamics for charge transfer processes (electron transfer, exciplex formation). In the case of phenols, linear free energy relationships applied, which led to a reaction constant of rho = -0.40, suggesting a lower electrophilicity of singlet-excited DBO than that of triplet-excited ketones and alkoxyl radicals. The reactivity of singlet-excited DBO exposes statistical, steric, polar and stereoelectronic effects on the hydrogen atom abstraction process in the absence of complications because of competitive exciplex formation.

  2. Transient F-H Center Pairs Produced from Self-Trapped Excitons at the Lowest Triplet State in Alkali Chloride Crystals

    NASA Astrophysics Data System (ADS)

    Suzuki, Yoshiro; Abe, Hidetoshi; Hirai, Masamitsu

    1992-08-01

    Time delayed double excitation spectroscopy in the picosecond range has revealed transient F bands due to the F center perturbed by an H center at the next nearest site, [F-H]nnn, in RbCl, KCl and NaCl single crystals after excitation of the self-trapped exciton (STE) from the lowest triplet state to higher excited states. The F band consists of a doublet peaking at 1.99 and 2.11 eV (RbCl), at 2.25 and 2.38 eV (KCl) and at 2.70 and 2.86 eV (NaCl) with the ratio of 2:1 in height in every crystal at 108 ps after the excitation. The peak positions and relative height of the doublets are understood qualitatively by the theory for the off-center type STE. No dichroism of the doublet observed by the light polarized in the [100] or [010] direction suggests rotation of the [F-H] axis during relaxation from the electronic b1u state, but not necessarily from the hole excited πg state.

  3. Using the singlet oxygen scavenging property of carotenoid in photodynamic molecular beacons to minimize photodamage to non-targeted cells.

    PubMed

    Chen, Juan; Jarvi, Mark; Lo, Pui-Chi; Stefflova, Klara; Wilson, Brian C; Zheng, Gang

    2007-12-01

    We recently introduced the concept of photodynamic molecular beacons (PMB) for selective control of photodynamic therapy (PDT). The PMB consists of a peptide linker that is sequence specific to a cancer-associated protease. A photosensitizer (PS) and a singlet oxygen (1O2) quencher are conjugated to the opposite ends of this linker. Proximity of the PS and quencher can efficiently inhibit 1O2 generation. In the presence of a targeted protease, the substrate sequence is cleaved and the PS and quencher will separate so that the PS can be photo-activated. There are two ways to optimize the PMB selectivity to cancer cells. The first is to increase the protease specificity to targeted cells and the second is to minimize the phototoxicity of intact (uncleaved) PMBs in non-targeted (normal) cells. Carotenoids (CARs) are well known in nature for their role in quenching excited states of PS and in directly scavenging 1O2. The purpose of this study is to evaluate whether the CAR with dual quenching modes (PS excited states deactivation and 1O2 scavenging) can be used to minimize the photodamage of intact PMBs to non-targeted cells. Thus, we synthesized a beacon (PPC) with a caspase-3 cleavable peptide linking a PS and a CAR quencher. It was confirmed that CAR deactivates the PS excited states and also directly scavenges 1O2. Moreover, the in vitro PDT response showed that CAR completely shuts off the photodynamic effect in non-targeted HepG(2) cells, while PS without CAR (control) remains highly potent even at a much lower (30-fold) dose.

  4. A Doubles Correction to Electronic Excited States from Configuration Interaction in the Space of Single Substitutions

    NASA Technical Reports Server (NTRS)

    Head-Gordon, Martin; Rico, Rudolph J.; Lee, Timothy J.; Oumi, Manabu

    1994-01-01

    A perturbative correction to the method of configuration interaction with single substitutions (CIS) is presented. This CIS(D) correction approximately introduces the effect of double substitutions which are absent in CIS excited states. CIS(D) is a second-order perturbation expansion of the coupled-cluster excited state method, restricted to single and double substitutions, in a series in which CIS is zeroth order, and the first-order correction vanishes. CIS (D) excitation energies are size consistent and the calculational complexity scales with the fifth power of molecular size, akin to second-order Moller-Plesset theory for the ground state. Calculations on singlet excited states of ethylene, formaldehyde, acetaldehyde, butadiene and benzene show that CIS (D) is a uniform improvement over CIS. CIS(D) appears to be a promising method for examining excited states of large molecules, where more accurate methods are not feasible.

  5. Excitation energies and Stokes shifts from a restricted open-shell Kohn-Sham approach

    NASA Astrophysics Data System (ADS)

    Kowalczyk, Tim; Tsuchimochi, Takashi; Chen, Po-Ta; Top, Laken; Van Voorhis, Troy

    2013-04-01

    Restricted open-shell Kohn-Sham (ROKS) theory provides a powerful computational tool for calculating singlet excited state energies and dynamics. However, the possibility of multiple solutions to the ROKS equations — with the associated difficulty of automatically selecting the physically meaningful solution — limits its usefulness for intensive applications such as long-time Born-Oppenheimer molecular dynamics. We present an implementation of ROKS for excited states which prescribes the physically correct solution from an overlap criterion and guarantees that this solution is stationary, allowing for straightforward evaluation of nuclear gradients. The method is used to benchmark ROKS for vertical excitation energies of small and large organic dyes and for the calculation of Stokes shifts. With common density functional approximations, ROKS vertical excitation energies, and Stokes shifts show similar accuracy to those from time-dependent density functional theory and Δ-self-consistent-field approaches. Advantages of the ROKS approach for excited state structure and molecular dynamics are discussed.

  6. Walking Down the Chalcogenic Group of the Periodic Table: From Singlet to Triplet Organic Emitters.

    PubMed

    Kremer, Adrian; Aurisicchio, Claudia; De Leo, Federica; Ventura, Barbara; Wouters, Johan; Armaroli, Nicola; Barbieri, Andrea; Bonifazi, Davide

    2015-10-19

    The synthesis, X-ray crystal structures, ground- and excited-state UV/Vis absorption spectra, and luminescence properties of chalcogen-doped organic emitters equipped on both extremities with benzoxa-, benzothia-, benzoselena- and benzotellurazole (1X and 2X ) moieties have been reported for the first time. The insertion of the four different chalcogen atoms within the same molecular skeleton enables the investigation of only the chalcogenic effect on the organisation and photophysical properties of the material. Detailed crystal-structure analyses provide evidence of similar packing for 2O -2Se , in which the benzoazoles are engaged in π-π stacking and, for the heavier atoms, in secondary X⋅⋅⋅X and X⋅⋅⋅N bonding interactions. Detailed computational analysis shows that the arrangement is essentially governed by the interplay of van der Waals and secondary bonding interactions. Progressive quenching of the fluorescence and concomitant onset of phosphorescence features with gradually shorter lifetimes are detected as the atomic weight of the chalcogen heteroatom increases, with the tellurium-doped derivatives exhibiting only emission from the lowest triplet excited state. Notably, the phosphorescence spectra of the selenium and tellurium derivatives can be recorded even at room temperature; this is a very rare finding for fully organic emitters. PMID:26471446

  7. Walking Down the Chalcogenic Group of the Periodic Table: From Singlet to Triplet Organic Emitters.

    PubMed

    Kremer, Adrian; Aurisicchio, Claudia; De Leo, Federica; Ventura, Barbara; Wouters, Johan; Armaroli, Nicola; Barbieri, Andrea; Bonifazi, Davide

    2015-10-19

    The synthesis, X-ray crystal structures, ground- and excited-state UV/Vis absorption spectra, and luminescence properties of chalcogen-doped organic emitters equipped on both extremities with benzoxa-, benzothia-, benzoselena- and benzotellurazole (1X and 2X ) moieties have been reported for the first time. The insertion of the four different chalcogen atoms within the same molecular skeleton enables the investigation of only the chalcogenic effect on the organisation and photophysical properties of the material. Detailed crystal-structure analyses provide evidence of similar packing for 2O -2Se , in which the benzoazoles are engaged in π-π stacking and, for the heavier atoms, in secondary X⋅⋅⋅X and X⋅⋅⋅N bonding interactions. Detailed computational analysis shows that the arrangement is essentially governed by the interplay of van der Waals and secondary bonding interactions. Progressive quenching of the fluorescence and concomitant onset of phosphorescence features with gradually shorter lifetimes are detected as the atomic weight of the chalcogen heteroatom increases, with the tellurium-doped derivatives exhibiting only emission from the lowest triplet excited state. Notably, the phosphorescence spectra of the selenium and tellurium derivatives can be recorded even at room temperature; this is a very rare finding for fully organic emitters.

  8. Inactivation of viruses by chemically and photochemically generated singlet molecular oxygen.

    PubMed

    Müller-Breitkreutz, K; Mohr, H; Briviba, K; Sies, H

    1995-09-01

    Inactivation of viruses in blood plasma can be achieved by photodynamic procedures using methylene blue (MB) or other photoactive dyes. Singlet molecular oxygen (1O2) probably contributes to the virucidal effects of photosensitization. We report the inactivation of herpes simplex virus type 1 (HSV-1) and suid herpes virus type 1 (SHV-1) by chemically generated singlet oxygen, produced by thermal decomposition of the endoperoxide of 3,3'-(1,4-naphthylidene)dipropionate (NDPO2). We demonstrate that viruses can be inactivated by 1O2 generated by chemiexcitation in a reaction in the dark, even in the presence of human plasma. Virus inactivation in phosphate-buffered saline (PBS) was enhanced when water was replaced by deuterium oxide (D2O) and diminished when human plasma or quenchers (imidazole or histidine) were added. The singlet oxygen quenching activities of plasma, imidazole and histidine correlated with their inhibitory effects on virus inactivation. The production of 1O2 was assessed by an indicator reaction: the bleaching of p-nitrosodimethylaniline (RNO) with imidazole as 1O2 acceptor. Virus inactivation and singlet oxygen generation of NDPO2 were compared with those of MB/light-mediated photosensitization. Based on similar amounts of 1O2 generated by either procedure, virus inactivation by MB/light was more effective. Virus inactivation by MB/light was not affected by type I quenchers (e.g. mannitol), but was inhibited by human plasma or singlet oxygen quenchers. Furthermore, in D2O-based PBS, virus inactivation was more effective than that in H2O. These observations confirm that singlet oxygen is involved in virus inactivation by MB/light. Taken together, the results demonstrate that singlet oxygen produced by either procedure is virucidal. The enhanced effect of the photochemical procedure suggests that, in addition to type II, type I reactions and/or the binding affinity of the dye for the virus contribute to virus killing by MB/light.

  9. Effect of sensitizer protonation on singlet oxygen production in aqueous and nonaqueous media.

    PubMed

    Arnbjerg, Jacob; Johnsen, Mette; Nielsen, Christian B; Jørgensen, Mikkel; Ogilby, Peter R

    2007-05-31

    The yield of singlet molecular oxygen, O2(a(1)Delta(g)), produced in a photosensitized process can be very susceptible to environmental perturbations. In the present study, protonation of photosensitizers whose chromophores contain amine functional groups is shown to adversely affect the singlet oxygen yield. Specifically, for bis(amino) phenylene vinylenes dissolved both in water and in toluene, addition of a protic acid to the solution alters properties of the system that, in turn, result in a decrease in the efficiency of singlet oxygen production. In light of previous studies on other molecules where protonation-dependent changes in the yield of photosensitized singlet oxygen production have been ascribed to changes in the quantum yield of the sensitizer triplet state, Phi(T), and to possible changes in the triplet state energy, E(T), our results demonstrate that this photosystem can respond to protonation in other ways. Although protonation-dependent changes in the amount of charge-transfer character in the sensitizer-oxygen complex may influence the singlet oxygen yield, it is likely that other processes also play a role. These include (a) protonation-dependent changes in sensitizer aggregation and (b) nonradiative channels for sensitizer deactivation that are enhanced as a consequence of the reversible protonation/deprotonation of the chromophore. The data obtained, although complicated, are relevant for understanding and ultimately controlling the behavior of photosensitizers in systems with microheterogeneous domains that have appreciable pH gradients. These data are particularly important given the use of such bi-basic chromophores as two-photon singlet oxygen sensitizers, with applications in spatially resolved singlet oxygen experiments (e.g., imaging experiments).

  10. Two-photon, /sup 13/C and two-dimensional /sup 1/H NMR spectroscopic studies of retinyl Schiff bases, protonated Schiff bases, and Schiff base salts: evidence for a protonation induced. pi pi. * excited state level ordering reversal

    SciTech Connect

    Birge, R.R.; Murray, L.P.; Zidovetzki, R.; Knapp, H.M.

    1987-04-01

    The ..pi pi..* excited singlet state manifolds of the visual chromophores, all-trans-retinylpyrrolidiniminium perchlorate (ATRSBS) and all-trans-N-retinylidene-n-butylimine:HCl (ATRPSB) are studied by using one-photon and two-photon laser spectroscopy. The goal is a better understanding of how protonation and counterion location affect level ordering in retinyl Schiff bases. Ambient temperature two-photon thermal lensing spectra indicate that ATRSBS has a lowest lying /sup 1/A/sub g/*/sup -/-like state as was observed previously for all-trans-retinal and the Schiff base of all-trans-retinal. In contrast, two-photon spectra of ATRPSB indicate that the protonated Schiff base has a lowest lying /sup 1/B/sub u/*/sup +/-like state. The origin of this level ordering reversal is analyzed by using molecular orbital theory as well as /sup 13/C and two-dimensional /sup 1/H NMR. They conclude that the relative level ordering of the low-lying covalent and ionic ..pi pi..* excited states of protonated Schiff bases and Schiff base salts is highly sensitive to counterion location (diffuseness). INDO-PSDCI molecular orbital theory is shown to be a reliable theoretical method of predicting the effect of counterion location on the one-photon and two-photon properties of retinyl protonated Schiff bases and Schiff base salts. This study provides further experimental support for the conclusions of a previous two-photon investigation of the rhodopsin binding site which demonstrated that the protein bound 11-cis-retinyl chromophore is protonated and occupies a neutral binding site.

  11. Phenomenological model of photoluminescence degradation and photoinduced defect formation in silicon nanocrystal ensembles under singlet oxygen generation

    SciTech Connect

    Gongalsky, Maxim B. Timoshenko, Victor Yu.

    2014-12-28

    We propose a phenomenological model to explain photoluminescence degradation of silicon nanocrystals under singlet oxygen generation in gaseous and liquid systems. The model considers coupled rate equations, which take into account the exciton radiative recombination in silicon nanocrystals, photosensitization of singlet oxygen generation, defect formation on the surface of silicon nanocrystals as well as quenching processes for both excitons and singlet oxygen molecules. The model describes well the experimentally observed power law dependences of the photoluminescence intensity, singlet oxygen concentration, and lifetime versus photoexcitation time. The defect concentration in silicon nanocrystals increases by power law with a fractional exponent, which depends on the singlet oxygen concentration and ambient conditions. The obtained results are discussed in a view of optimization of the photosensitized singlet oxygen generation for biomedical applications.

  12. Endogenous Generation of Singlet Oxygen and Ozone in Human and Animal Tissues: Mechanisms, Biological Significance, and Influence of Dietary Components

    PubMed Central

    2016-01-01

    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. PMID:27042259

  13. Studies on singlet oxygen formation and UVA light-mediated photobleaching of the yellow chromophores in human lenses.

    PubMed

    Ortwerth, Beryl J; Chemoganskiy, Vitaliy; Olesen, P R

    2002-02-01

    The protein-bound chromophores, which increase with aging in the human lens, act as UVA sensitizers, producing almost exclusively singlet oxygen in vitro. Direct irradiation of whole, aged human lenses with high intensity UVA light (200 mW cm(-2) for 24 hr), however, failed to produce singlet oxygen damage, as evidenced by the lack of either His or Trp photodestruction. Total homogenates of human lenses prepared in a cuvette under air did show destruction of His and Trp residues by UVA light, but no destruction was seen when equivalent homogenates were prepared under argon. These data are consistent with the idea that the low oxygen levels in the lens prevent singlet oxygen damage in vivo.UVA irradiation of aged human lenses in culture caused an extensive photobleaching of the yellow chromophores. A time course indicated that the photobleaching increased with time, with significant color loss apparent after 6 hr. Homogenization of the irradiated and dark control lenses in 6 M guanidine-HCl, followed by determination of the difference spectrum, showed approximately 50% bleaching of compounds with a lambda(max) at 355 nm. Similarly, fluorophores with a lambda(max) for excitation of 355 nm and for emission of 420 nm were 50% destroyed by the UVA light. Similar results were obtained in vitro by the anaerobic irradiation of a sonication-solubilized WI fraction from type II brunescent cataracts and from aged human lenses. In this system, there was an initial bleaching of 15% after 30 min of irradiation, followed by a slow increase over the next 6 hr to a final bleaching of 30%. The addition of 1.0 m M ascorbic acid, but not 1.0 m M glutathione (GSH), increased the photobleaching to 60% under argon, and the loss of ascorbate could be detected under these anaerobic conditions. In the presence of air, UVA light produced no photobleaching, but rather caused a three-fold increase in absorbance at 345 nm, which was prevented by the inclusion of 1.0 m M ascorbic acid and almost

  14. Optically detected magnetic resonance studies of photoexcited /sup 17/O-benzophenone. Orbital rotation in the lowest triplet state

    SciTech Connect

    Waeckerle, G.; Baer, M.; Zimmermann, H.; Dinse, K.H.; Yamauchi, S.; Kashmar, R.J.; Pratt, D.W.

    1982-03-01

    The magnetically active isotope of oxygen /sup 17/O has been used to probe the changes in the electron charge and spin density distributions in oxygen valence orbitals which occur when benzophenone is excited to its lowest triplet state. The data obtained include the optically detected magnetic resonance (ODMR) and electron-nuclear double resonance spectra at both zero and high magnetic fields. New methods of analysis of zero-field ODMR spectra, appropriate when the second-order hyperfine splitting exceeds the quadrupole coupling, are described. This analysis yields the principal values of the electron fine-structure (D), oxygen hyperfine (A), and oxygen quadrupole (Q) tensors, and the orientation of their principal axes with respect to the molecular frame. It is found, consistent with expectations for an n..pi..( state, that the direction of the largest component of Q is different from that of the ground state. It is also found, by two independent methods, that the principal transverse axes of A and Q do not conform to the local C/sub 2v/ symmetry axes of the carbonyl group. This result is interpreted to mean that the axis of the n-type oxygen 2p orbital is rotated out of the carbonyl plane, a rotation which appears to be direct consequence of n..pi..(/..pi pi..( configurational mixing. In agreement with this, the principal values of D, A, and Q are different from those expected for a ''pure'' n..pi..( state. Other consequences of n..pi..(/..pi pi..( mixing, not only in benzophenone but also in the lowest triplet states of other aromatic carbonyls, are discussed briefly.

  15. Understanding the charge-transfer state and singlet exciton emission from solution-processed small-molecule organic solar cells.

    PubMed

    Ran, Niva A; Kuik, Martijn; Love, John A; Proctor, Christopher M; Nagao, Ikuhiro; Bazan, Guillermo C; Nguyen, Thuc-Quyen

    2014-11-19

    Electroluminescence (EL) from the charge-transfer state and singlet excitons is observed at low applied voltages from high-performing small-molecule bulk-heterojunction solar cells. Singlet emission from the blends emerges upon altering the processing conditions, such as thermal annealing and processing with a solvent additive, and correlates with improved photovoltaic performance. Low-temperature EL measurements are utilized to access the physics behind the singlet emission.

  16. Negative Ion Photoelectron Spectroscopy Confirms the Prediction that D-3h Carbontrioxide (CO3) Has a Singlet Ground State

    SciTech Connect

    Hrovat, David; Hou, Gao-Lei; Chen, Bo; Wang, Xue B.; Borden, Weston

    2015-11-13

    The CO3 radical anion (CO3•–) has been formed by electrospraying carbonate dianion (CO32–) into the gas phase. The negative ion photoelectron (NIPE) spectrum of CO3•– shows that, unlike trimethylenemethane [C(CH2)3], carbontrioxide (CO3) has a singlet ground state. From the NIPE spectrum, the electron affinity of CO3 was determined to be EA = 4.06 ± 0.03 eV, and the singlet-triplet energy difference was found to be ΔEST = - 17.8 ± 0.9 kcal/mol. B3LYP, CCSD(T), and CASPT2 calculations all find that the two lowest triplet states of CO3 are very close in energy, a prediction that is confirmed by the relative intensities of the bands in the NIPE spectrum of CO3•–. The 560 cm-1 vibrational progression, seen in the low energy region of the triplet band, enables the identification of the lowest, Jahn-Teller-distorted, triplet state as 3A1, in which both unpaired electrons reside in σ MOs, rather than 3A2, in which one unpaired electron occupies the b2 σ MO, and the other occupies the b1 π MO.

  17. Singlet molecular oxygen on natural snow and ice

    NASA Astrophysics Data System (ADS)

    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

  18. Oxidation of Flame Retardant Tetrabromobisphenol A by Singlet Oxygen

    PubMed Central

    Han, S.-K.; Bilski, P.; Karriker, B.; Sik, R.H.; Chignell, C.F.

    2008-01-01

    Wide use of flame retardants can pose an environmental hazard and it is of interest to investigate how they may degrade. We report here that 3,3′,5,5′-tetrabromobisphenol A (TBBPA) is subject to photosensitized oxidation involving singlet molecular oxygen (1O2). By using visible light and Rose Bengal or Methylene Blue as 1O2 photosensitizers, we have found that TBBPA is a 1O2 quencher. The quenching rate constant, kq, depends on TBBPA ionization (pK=7.4). In acetonitrile, where TBBPA is undissociated, the kq value is 6.1×105 M-1s-1 for a TBBPA monomer and decreasing to kq=2.9×104M-1s-1 for TBBPA dimers/aggregates. TBBPA dissociates in aqueous solutions, and its kq value is 1.44×109 M-1s-1 in alkaline solution, decreasing to kq=3.9×108 M-1s-1 at pH 7.2. The strong 1O2 quenching by TBBPA anion initiates an efficient oxidation of TBBPA, which results in oxygen consumption in aqueous micellar (e.g. Triton-X 100) solutions containing photosensitizer. This oxygen consumption is mediated by transient radical species, which we detected by using EPR spectroscopy. We observed two major radicals and one minor radical generated from TBBPA by reaction with 1O2 at pH 10. One was identified as the 2,6-dibromo-p-benzosemiquinone radical (a2H = 2.36 G, g = 2.0056). A second radical (aH = 2.10 G, g = 2.0055) could not be identified but was probably a 2,6-dibromo-p-benzosemiquinone radical containing an EPR silent substituent in the 3-position. Spin trapping with 5,5,-dimethyl-1-pyrroline N-oxide (DPMO) showed that other minor radicals (hydroxyl, carbon centered) are also generated during the reaction of TBBPA with 1O2. The photosensitized production of radicals and oxygen consumption were completely inhibited by the azide anion, an efficient physical 1O2 quencher. Because TBBPA is a stable compound that at neutral pH does not absorb much of the atmosphere-filtered solar radiation, its photosensitized oxidation by 1O2 may be the key reaction initiating/mediating TBBPA

  19. Two-Photon Excitation of trans-Stilbene: Spectroscopy and Dynamics of Electronically Excited States above S1.

    PubMed

    Houk, Amanda L; Zheldakov, Igor L; Tommey, Tyler A; Elles, Christopher G

    2015-07-23

    The photoisomerization dynamics of trans-stilbene have been well studied in the lowest excited state, but much less is known about the behavior following excitation to higher-lying electronically excited states. This contribution reports a combined study of the spectroscopy and dynamics of two-photon accessible states above S1. Two-photon absorption (2PA) measurements using a broadband pump-probe technique reveal distinct bands near 5.1 and 6.4 eV. The 2PA bands have absolute cross sections of 40 ± 16 and 270 ± 110 GM, respectively, and a pump-probe polarization dependence that suggests both of the transitions access Ag-symmetry excited states. Separate transient absorption measurements probe the excited-state dynamics following two-photon excitation into each of the bands using intense pulses of 475 and 380 nm light, respectively. The initially excited states rapidly relax via internal conversion, leading to the formation of an S1 excited-state absorption band that is centered near 585 nm and evolves on a time scale of 1-2 ps due to intramolecular vibrational relaxation. The subsequent evolution of the S1 excited-state absorption is identical to the behavior following direct one-photon excitation of the lowest excited state at 4.0 eV. The complementary spectroscopy and dynamics measurements provide new benchmarks for computational studies of the electronic structure and dynamics of this model system on excited states above S1. Probing the dynamics of molecules in their higher-lying excited states is an important frontier in chemical reaction dynamics.

  20. Excited-State Properties of Molecular Solids from First Principles.

    PubMed

    Kronik, Leeor; Neaton, Jeffrey B

    2016-05-27

    Molecular solids have attracted attention recently in the context of organic (opto)electronics. These materials exhibit unique charge carrier generation and transport phenomena that are distinct from those of conventional semiconductors. Understanding these phenomena is fundamental to optoelectronics and requires a detailed description of the excited-state properties of molecular solids. Recent advances in many-body perturbation theory (MBPT) and density functional theory (DFT) have made such description possible and have revealed many surprising electronic and optical properties of molecular crystals. Here, we review this progress. We summarize the salient aspects of MBPT and DFT as well as various properties that can be described by these methods. These properties include the fundamental gap and its renormalization, hybridization and band dispersion, singlet and triplet excitations, optical spectra, and excitonic properties. For each, we present concrete examples, a comparison to experiments, and a critical discussion.