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Sample records for triplet state spectra

  1. On the triplet lifetime and triplet-triplet absorption spectra of naphthaldehydes

    NASA Astrophysics Data System (ADS)

    Samanta, Anunay; Fessenden, Richard W.

    1988-12-01

    Triplet-triplet absorption spectra of 1- and 2-naphthaldehyde have been studied in laser flash photolysis experiments. Triplet lifetimes are found to vary with laser intensity and concentration of the solution. Sensitization of naphthaldehyde triplets with thioxanthone and biphenyl in flash photolysis and pulse radiolysis experiments lead to the same spectra as produced by direct excitation. It has been concluded that only the lowest 3?-?* state is responsible for the observed triplet-triplet absorption spectra.

  2. The Triplet State

    NASA Astrophysics Data System (ADS)

    Zahlan, A. B.

    2010-01-01

    Preface; List of participants; Part I. Spin-orbit Coupling and Intersystem Crossing: 1. Spin-orbit interactions in organic molecules; 2. Singlet-triplet transitions in organic molecules; 3. Triplet decay and intersystem crossing in aromatic hydrocarbons; 4. Statistical aspects of resonance energy transfer; Discussion; Part II. Magnetic Resonance and Magnetic Interactions: 5. Magnetic resonance spectra of organic molecules in triplet states in single crystals; 6. Magnetic interactions related to phosphorescence; 7. ESR investigations of naphthalene-d8:Naphthalene-h8 mixed crystals; 8. Biradicals and polyradicals in the nitroxide series; 9. Changes induced in the phosphorescent radiation of aromatic molecules by paramagnetic resonance in their metastable triplet states; 10. Paramagnetic resonance of the triplet state of tetramethylpyrazine; 11. On magnetic dipole contributions to the intrinsic S0 = T1 transition in simple aromatics; Discussion; Part III. Photochemistry: 12. The kinetics of energy transfer from the triplet state in rigid solutions; 13. Triplet states in gas-phase photochemistry; 14. Biphotonic photochemistry, involving the triplet state: polarisation of the effective T-T transition and solvent effects; 15. Direct and sensitised photo-oxidation of aromatic hydrocarbons in boric acid glass; Discussion; Part IV. Radiationless Transitions: 16. Radiationless transitions in gaseous benzene; 17. Low-lying excited triplet states and intersystem crossing in aromatic hydrocarbons; 18. De-excitation rates of triplet states in condensed media; 19. Lifetimes of the triplet state of aromatic hydrocarbons in the vapour phase; Discussion; Part V. Triplet Excitons: 20. Some comments on the properties of triplet excitons in molecular crystals; 21. Exact treatment of coherent and incoherent triplet exciton migration; 22. Magnetic susceptibility of a system of triplet excitons: Wrster's Blue Perchlorate; 23. A study of triplet excitons in anthracene crystals under laser excitation; 24. The electronic states in crystaline anthracene; Discussion; Part VI. Delayed Fluorescent and Phosphorescence: 25. Delayed fluorescence of solutions; 26. The kinetics of the excited states of anthracene and phenanthrene vapor; 27. Optical investigations of the triplet states of naphthalene in different crystalline environments; 28. Excitation of the triplet states of organic molecules; 29. The delayed luminescence and triplet quantum yields of pyrene solutions; 30. Triplet state studies of some polyphenyls in rigid glasses; 31. Decay time of delayed fluorescence of anthracene as a function of temperature (2-30K); 32. Energy transfer between benzene and biacetyl and the lifetime of triplet benzene in the gas phase; 33. Charge transfer triplet state of molecular complexes. 34. Flash-photolytic detection of triplet acridine formed by energy transfer from biacetyl; 35. Extinction coefficients of triplet-triplet transitions between 3000 and 8800 A in anthracene; 36. Anthracene triplet-triplet annihilation rate constant; Discussion; Part VII. Triplet State Related to Biology: 37. ESR and optical studies of some triplet states of biological interest; 38. The triplet state of DNA; 39. Some characteristics of the triplet states of the nucleic bases; Discussion; Indexes.

  3. Singlet and triplet state spectra and dynamics of structurally modified peridinins.

    PubMed

    Fuciman, Marcel; Enriquez, Miriam M; Kaligotla, Shanti; Niedzwiedzki, Dariusz M; Kajikawa, Takayuki; Aoki, Kazuyoshi; Katsumura, Shigeo; Frank, Harry A

    2011-04-21

    The peridinin-chlorophyll a-protein (PCP) is a light-harvesting pigment-protein complex found in many species of marine algae. It contains the highly substituted carotenoid peridinin and chlorophyll a, which together facilitate the transfer of absorbed solar energy to the photosynthetic reaction center. Photoexcited peridinin exhibits unorthodox spectroscopic and kinetic behavior for a carotenoid, including a strong dependence of the S(1) excited singlet state lifetime on solvent environment. This effect has been attributed to the presence of an intramolecular charge transfer (ICT) state in the molecule. The present work explores the effect of changing the extent of ?-electron conjugation and attached functional groups on the nature of the ICT state of peridinin and how these factors affect the excited singlet and triplet state spectra and kinetics of the carotenoid. In this investigation three peridinin analogues denoted C-1-R-peridinin, C-1-peridinin, and D-1-peridinin were synthesized and studied using steady-state absorption and fluorescence techniques and ultrafast time-resolved transient absorption spectroscopy. The study explores the effect on the singlet and triplet state spectra and dynamics of removing the allene group from the peridinin structure and either replacing it with a rigid furanoid ring, replacing it with an epoxide group, or extending the polyene chain into the ?-ionylidine ring. PMID:21452802

  4. 13C isotope shifts of anthracene and naphthalene isomers in triplet state optical spectra

    NASA Astrophysics Data System (ADS)

    Doberer, U.; Port, H.; Rund, D.; Tuffentsammer, W.

    Position-specific 13C isotope shifts in the T1?S0 photoexcitation spectra of anthracene and naphthalene crystals containing 13C substituted molecules in natural abundance and of material enriched with various synthesized 13C isomers are compared. From the spectra of matrix isolated A-h10 in A-d10 and N-h8 in N-d8 the individual isotope shifts U0 of all the 13C monosubstituted isomers are determined (with values U0 between 07 and 35 cm-1). An additivity rule is established for the U0 of the twofold substituted 13C 13C isomers similar to that found for multiple deuteration. Applying these results also the 13C substructure of the excitonic Davydov components in anthracene and naphthalene crystals is understood quantitatively. A correlation between the specific 13C isotope shifts and the triplet state spin density distribution is discussed.

  5. Resonance Raman spectra of a perylene bis(dicarboximide) chromophore in ground and lowest triplet states.

    PubMed

    Angelella, Maria; Wang, Chen; Tauber, Michael J

    2013-09-26

    Resonance Raman spectroscopy is employed to probe the ground (S0) and lowest triplet (T1) excited states of a perylene bis(dicarboximide) (PDI) dimer. Four bands at ~1324, 1507, ~1535, and 1597 cm(-1) are signatures of the T1 excited state; a fifth band at ~1160 cm(-1) is tentatively assigned. Density functional calculations of an asymmetrically substituted PDI monomer match the experimental bands of the PDI dimer in both S0 and T1 states. The match supports a T1 excited state that is localized on a single PDI moiety of the dimer. The normal modes of the asymmetrically substituted PDI are correlated with ones calculated for the unsubstituted PDI in the D2h point group. Patterns in the Raman intensities are consistent with an A-term mechanism of enhancement. The positions of six bands are predicted for the resonance Raman spectrum of unsubstituted PDI in its T1 excited state. The spectra and normal-mode analysis reported here are expected to facilitate future studies of singlet fission in PDI crystals or other assemblies. PMID:24070416

  6. Triplet excited state spectra and dynamics of carotenoids from the thermophilic purple photosynthetic bacterium Thermochromatium tepidum

    SciTech Connect

    Niedzwiedzki, Dariusz; Kobayashi, Masayuki; Blankenship, R. E.

    2011-01-13

    Light-harvesting complex 2 from the anoxygenic phototrophic purple bacterium Thermochromatium tepidum was purified and studied by steady-state absorption, fluorescence and flash photolysis spectroscopy. Steady-state absorption and fluorescence measurements show that carotenoids play a negligible role as supportive energy donors and transfer excitation to bacteriochlorophyll-a with low energy transfer efficiency of ~30%. HPLC analysis determined that the dominant carotenoids in the complex are rhodopin and spirilloxanthin. Carotenoid excited triplet state formation upon direct (carotenoid) or indirect (bacteriochlorophyll-a Q{sub x} band) excitation shows that carotenoid triplets are mostly localized on spirilloxanthin. In addition, no triplet excitation transfer between carotenoids was observed. Such specific carotenoid composition and spectroscopic results strongly suggest that this organism optimized carotenoid composition in the light-harvesting complex 2 in order to maximize photoprotective capabilities of carotenoids but subsequently drastically suppressed their supporting role in light-harvesting process.

  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 3?-?*. Namely, the case of 3MLCT shows a large shift, while the case of 3?-?* 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 3?-?* 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. Excited-state triplet-triplet absorption in. cap alpha. NPO

    SciTech Connect

    Dharamsi, A.N.; Hassam, A.B.

    1987-11-01

    Time-resolved excited-state triplet-triplet absorption measurements in ..cap alpha..NPO solutions were performed. A concentration quenching effect on the excited absorption and fluorescence spectra, due to excimer formation, was seen. A numerical analysis of the results yielded the rate constants for intersystem crossing, triplet quenching by O/sub 2/, triplet self-quenching, and excimer formation.

  9. Triplet (S = 1) Ground State Aminyl Diradical

    SciTech Connect

    Rajca, Andrzej; Shiraishi, Kouichi; Pink, Maren; Rajca, Suchada

    2008-04-02

    Aminyl diradical, which is stable in solution at low temperatures, is prepared. EPR spectra and SQUID magnetometry indicate that the diradical is planar and it possesses triplet ground state, with strong ferromagnetic coupling.

  10. Triplet state photoassociation of LiNa

    NASA Astrophysics Data System (ADS)

    Rvachov, Timur; Jamison, Alan; Jing, Li; Jiang, Yijun; Zwierlein, Martin; Ketterle, Wolfgang

    2015-05-01

    Ultracold molecules have promise to become a useful tool for studies in quantum simulation and ultracold chemistry. We aim to produce ultracold fermionic 6Li23Na molecules in the triplet ground state. Due to the small mass, small spin-orbit coupling, and fermionic character of LiNa, the triplet ground state is expected to be long lived. We report on photoassociation spectra of LiNa to its triplet excited states from an ultracold mixture. This is the first observation of these excited triplet potentials, which have been previously difficult to observe in heat-pipe experiments due to the small spin-orbit coupling in the system. Determining the excited state potentials is a key milestone towards forming triplet ground state LiNa via two-photon STIRAP. Work supported by the NSF, AFOSR-MURI, ARO-MURI, and NSERC.

  11. Accessing the triplet excited state in perylenediimides.

    PubMed

    Rachford, Aaron A; Goeb, Sbastien; Castellano, Felix N

    2008-03-01

    Here, we present a strategy designed to permit access to the PDI triplet manifold that preserves the desirable colorfastness and visible light-absorption properties associated with these dyes. To this end, three new Pt(II) complexes each bearing two PDI moieties tethered to the metal center via acetylide linkages emanating from one of the PDI bay positions have been synthesized, structurally characterized, and thoroughly examined by nanosecond laser flash photolysis. Upon ligation, the bright singlet-state fluorescence of the PDI chromophore is quantitatively quenched, and no long wavelength photoluminescence is observed from the Pt(II)-PDI complexes in deaerated solutions. In each of the Pt-PDI chromophores, quantitatively similar transient absorption difference spectra were obtained; the only distinguishing characteristic is in their single-exponential lifetimes (tau = 246 ns, 1.0 micros, and 710 ns). Triplet-state sensitization experiments of "free" PDI-CCH using thioxanthone confirmed the PDI triplet state assignments in each of the Pt-PDI structures. PMID:18269285

  12. Electron paramagnetic resonance detection of carotenoid triplet states

    SciTech Connect

    Frank, H.A.; Bolt, J.D.; de B. Costa, S.M.; Sauer, K.

    1980-07-16

    Triplet states of carotenoids have been detected by X-band electron paramagnetic resonance (EPR) and are reported here for the first time. The systems in which carotenoid triplets are observed include cells of photosynthetic bacteria, isolated bacteriochlorophyll-protein complexes, and detergent micelles which contain ..beta..-carotene. It is well known that if electron transfer is blocked following the initial acceptor in the bacterial photochemical reaction center, back reaction of the primary radical pair produces a bacteriochlorophyll dimer triplet. Previous optical studies have shown that in reaction centers containing carotenoids the bacteriochlorophyll dimer triplet sensitizes the carotenoid triplet. We have observed this carotenoid triplet state by EPR in reaction centers of Rhodopseudomonas sphaeroides, strain 2.4.1 (wild type), which contain the carotenoid spheroidene. The zero-field splitting parameters of the triplet spectrum are /D/ = 0.0290 +- 0.0005 cm/sup -1/ and /E/ = 0.0044 +-0.0006 cm/sup -1/, in contrast with the parameters of the bacteriochlorophyll dimer triplet, which are /D/ = 0.0189 +- 0.0004 cm/sup -1/ and /E/ = 0.0032 +- 0.004 cm/sup -1/. Bacteriochlorophyll in a light harvesting protein complex from Rps. sphaeroides, wild type, also sensitizes carotenoid triplet formation. In whole cells the EPR spectra vary with temperature between 100 and 10 K. Carotenoid triplets also have been observed by EPR in whole cells of Rps. sphaeroides and cells of Rhodospirillum rubrum which contain the carotenoid spirilloxanthin. Attempts to observe the triplet state EPR spectrum of ..beta..-carotene in numerous organic solvents failed. However, in nonionic detergent micelles and in phospholipid bilayer vesicles ..beta..-carotene gives a triplet state spectrum with /D/ = 0.0333 +- 0.0010 cm/sup -1/ and /E/ = 0.0037 +- 0.0010 cm/sup -1/. 6 figures, 1 table.

  13. Triplet-state optical spectra of highly concentrated isotopically mixed crystals of anthracene A- h10: A- d10

    NASA Astrophysics Data System (ADS)

    Rund, D.; Port, H.

    1983-08-01

    Photoexcitation spectroscopy with a dye laser is applied to study highly concentrated isotopically mixed crystals of anthracene A- h10: A- d10 in the region of the T 1 ? S v 0-0 transition. The spectra of the separated A- h10 and A- d10 subbands are measured in polarized light at 6 K. The concentration-dependent intensities and energetic positions of the subbands are described quantitatively using the moment-expansion method of the mixed-crystal Green's function.

  14. Fluorescence-detected chlorophyll triplet states in chlorophyll-proteins

    NASA Astrophysics Data System (ADS)

    Schaafsma, T. J.; Searle, G. F. W.; Koehorst, R. B. M.

    Chlorophyll (chl) occurs bound Co protein as discrete, well-defined complexes in photosynthetic membranes. Chlorophyll-proteins have been isolated from barley chloroplasts and chl triplet states observed at 4.2 K under continuous illumination using a fluorescence-detected zero field magnetic resonance technique. It will be shown chat chlorophyll proteins containing chl-? , give zero field splitting parameters characteristic of monomeric as wall as dimeric chi-?; proteins containing both chl-? and b, show chl-? and - b resonances. The spectra obtained are also characterised by their sign (increase or decrease in fluorescence intensity) and their linewidth. In some chlorophyll-proteins, two or more triplets could be observed by monitoring fluorescence at different wavelengths. The decay rates of the triplet state spin levels will also be discussed. We conclude that light-induced chl triplet states can be used to probe the magnetic environment and structure within chlorophyll-proteins.

  15. Properties of the Triplet State of Coumarin Substituted Compounds

    NASA Astrophysics Data System (ADS)

    Bryantseva, N. G.; Gadirov, R. M.; Nikonov, S. Yu.; Sokolova, I. V.

    2015-03-01

    The absorption spectra of the triplet excited state of coumarin sensitizers are investigated both theoretically and experimentally. The most intense triplet-triplet (TT) absorption bands are determined. The experimental spectra of the T-T absorption are compared with the theoretical T-T transitions. The phosphorescence spectra of five compounds are measured at a temperature of 77 K. The quantum phosphorescence yield is determined by the method of comparison with an etalon (8-methoxypsoralen). The phosphorescence lifetime is determined for the examined molecules at a temperature of 77 K. For 3,4-phenyl-4',5'-cyclohexylpsoralen, 4'-methyl-3,4-cycloheptylpsoralen, and 4'5'-dimethyl-3,4-cyclohexylpsoralen compounds, this time is equal to 1.1, 1.25, and 2.5 s, respectively. The main energy deactivation channel for all examined compounds is the phosphorescence. The positions of the lower excited triplet states, calculated by the quantum-chemical method of intermediate neglect of differential overlap with spectroscopic parameterization (INDO/S), are confirmed by the available experimental data.

  16. Resonance Raman Spectroscopy of the T1 Triplet Excited State of Oligothiophenes.

    PubMed

    Wang, Chen; Angelella, Maria; Doyle, Samantha J; Lytwak, Lauren A; Rossky, Peter J; Holliday, Bradley J; Tauber, Michael J

    2015-09-17

    The characterization of triplet excited states is essential for research on organic photovoltaics and singlet fission. We report resonance Raman spectra of two triplet oligothiophenes with n-alkyl substituents, a tetramer and hexamer. The spectra of the triplets are more complex than the ground state, and we find that density functional theory calculations are a useful starting point for characterizing the bands. The spectra of triplet tetrathiophene and hexathiophene differ significantly from one another. This observation is consistent with a T1 excitation that is delocalized over at least five rings in long oligomers. Bands in the 500-800 cm(-1) region are greatly diminished for an aggregated sample of hexathiophene, likely caused by fast electronic dephasing. These experiments highlight the potential of resonance Raman spectroscopy to unequivocally detect and characterize triplets in thiophene materials. The vibrational spectra can also serve as rigorous standards for evaluating computational methods for excited-state molecules. PMID:26291623

  17. Raman spectra of triplet superconductivity in Sr2RuO4

    NASA Astrophysics Data System (ADS)

    Kee, Hae-Young; Maki, K.; Chung, C. H.

    2003-05-01

    We study the Raman spectra of spin-triplet superconductors in Sr2RuO4. The p-wave and f-wave symmetries are considered. We show that there is the clapping mode with frequency of (2)?(T) and ?(T) for p-wave and f-wave superconductors, respectively. This mode is visible as a huge resonance in the B1g and B2g modes of Raman spectra. We discuss the details of the Raman spectra in these superconducting states.

  18. Toward Triplet Ground State LiNa Molecules

    NASA Astrophysics Data System (ADS)

    Jamison, Alan; Rvachov, Timur; Jing, Li; Jiang, Yijun; Zwierlein, Martin; Ketterle, Wolfgang

    2015-05-01

    We present progress toward creation of ultracold ground-state triplet LiNa molecules. This molecule is expected to have a long lifetime in the triplet ground state due to its fermionic nature, large rotational constant, and weak spin-orbit coupling. The triplet state has both electric and magnetic dipole moments, affording unique opportunities in quantum simulation and ultracold chemistry. Our progress includes the first observation of triplet excited states in this molecule, achieved through photoassociation of ultracold mixtures of 6-Li and Na. We compare experimental results to a variety of near-dissociation expansions as well as ab initio potentials.

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

    PubMed Central

    Hare, Patrick M.; Middleton, Chris T.; Mertel, Kristin I.

    2008-01-01

    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 3 s 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=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 1n?* state as the triplet precursor. PMID:19936322

  20. 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.

  1. Photocyclization Reactions of Diarylethenes via the Excited Triplet State.

    PubMed

    Murata, Ryutaro; Yago, Tomoaki; Wakasa, Masanobu

    2015-11-12

    Cyclization reactions of three diarylethene derivatives, 1,2-bis(2-methyl-3-benzothienyl)perfluorocyclopentene (BT), 1,2-bis(2-hexyl-3-benzothienyl)perfluorocyclopentene (BTHex), and 1,2-bis(2-isopropyl-3-benzothienyl)perfluorocyclopentene (BTiPr), via their excited triplet states were studied by means of steady-state and nanosecond transient absorption spectroscopy. The excited triplet states of BT, BTHex, and BTiPr were generated by energy transfer from the photoexcited triplet states of sensitizers such as xanthone, phenanthrene, and pyrene. The single-step quantum yields of the cyclization reactions from the excited triplet states of BT, BTHex, and BTiPr were determined to be 0.34, 0.53, and 0.65, respectively. The triplet energies of these three BTs were estimated to be 190-200 kJ mol(-1). PMID:26490486

  2. Observation of triplet-state electron spin resonance in oxidized C{sub 60}

    SciTech Connect

    Thomann, H.; Bernardo, M.; Miller, G.P.

    1992-07-29

    The formation, electronic structure, stability, and reactivity of both the reduced and the oxidized C{sub 60} fullerene molecules are of intense current interest. Triplet-state ESR spectra have been observed for reduced C{sub 60} produced by electrochemical and photochemical methods. ESR spectra of S = 1/2 radicals have been reported for C{sub 60} dissolved in concentrated and fuming sulfuric acids and in Magic Acid. We now report the observation of triplet-state ESR for C{sub 60} chemically oxidized in fuming sulfuric acid. 19 refs., 2 figs.

  3. Triplet excitons: Bringing dark states to light

    NASA Astrophysics Data System (ADS)

    Bardeen, Christopher J.

    2014-11-01

    Semiconducting quantum dots have been used to harvest triplet excitons produced through singlet fission in organic semiconductors. These hybrid organic-inorganic materials may boost the efficiency of solar cells.

  4. The triplet state of fac-Ir(ppy)3.

    PubMed

    Hofbeck, Thomas; Yersin, Hartmut

    2010-10-18

    The emitting triplet state of fac-Ir(ppy)(3) (fac-tris(2-phenylpyridine)iridium) is studied for the first time on the basis of highly resolved optical spectra in the range of the electronic 0-0 transitions. For the compound dissolved in CH(2)Cl(2) and cooled to cryogenic temperatures, three 0-0 transitions corresponding to the triplet substates I, II, and III are identified. They lie at 19,693 cm(-1) (507.79 nm, I ? 0), 19,712 cm(-1) (507.31 nm, II ? 0), and 19,863 cm(-1) (503.45 nm, III ? 0). From the large total zero-field splitting (ZFS) of 170 cm(-1), the assignment of the emitting triplet term as a (3)MLCT state (metal-to-ligand charge transfer state) is substantiated, and it is seen that spin-orbit couplings to higher lying (1,3)MLCT states are very effective. Moreover, the studies provide emission decay times for the three individual substates of ?(I) = 116 ?s, ?(II) = 6.4 ?s, and ?(III) = 200 ns. Further, group-theoretical considerations and investigations under application of high magnetic fields up to B = 12 T allow us to conclude that all three substates are nondegenerate and that the symmetry of the complex in the CH(2)Cl(2) matrix cage is lower than C(3). It follows that the triplet parent term is of (3)A character. Studies of the emission decay time and photoluminescence quantum yield, ?(PL), of Ir(ppy)(3) in poly(methylmethacrylate) (PMMA) in the temperature range of 1.5 ? T ? 370 K reveal average and individual radiative and nonradiative decay rates and quantum yields of the substates. In the range 80 ? T ? 370 K, ?(PL) is as high as almost 100%. The quantum yield ?(PL) drops to ?88% when cooled to T = 1.5 K. The investigations show further that the emission properties of Ir(ppy)(3) depend distinctly on the complex's environment or the matrix cage according to distinct changes of spin-orbit coupling effectiveness. These issues also have consequences for optimizations of the material's properties if applied as an organic light-emitting diode (OLED) emitter. PMID:20853860

  5. Positronium quenching via collisions with triplet states of photomagnetic molecules

    NASA Astrophysics Data System (ADS)

    Eom, C. I.; Naidu, S. V.; Sharma, S. C.; Kowalski, J. M.

    1991-04-01

    We have studied positronium quenching resulting from collisions with the triplet states of benzaldehyde, oxygen, benzophenone, and bromonaphthalene. Positronium pick-off decay rates are presented as functions of triplet populations via uv irradiation of benzaldehyde-ethane, benzaldehyde-helium, and oxgyen-ethane gaseous mixtures and of benzophenone and bromonaphthalene adsorbed porous silicas. Our results show that the cross sections for positronium quenching in collisions with excited triplet states are not as high as reported previously. The oxygen data suggest reactions between ``hot'' (nonthermal) positronium and oxygen molecules.

  6. 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 (?,?) type, whereas in 2-naphthyl cation it is (?,?{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.

  7. Time resolved EPR of [70]fullerene monoadducts in the photoexcited triplet state.

    PubMed

    Franco, Lorenzo; Toffoletti, Antonio; Maggini, Michele

    2012-11-01

    Triplet excited states of isomers ?, ? and ? of N-methyl-[70]fulleropyrrolidine in glassy toluene (T = 120 K) are investigated with Time Resolved EPR (TR-EPR) spectroscopy using pulsed laser photoexcitation. Both the zero field splitting (ZFS) parameters D, E and the anisotropic triplet population rates are measured. Results reveal a strong dependence of the triplet state wavefunction on the position (?, ? or ?) of the pyrrolidine addend with respect to the pole of the [70]fullerene unit. The relevant molecular orbitals have been calculated giving support to this finding. The dipolar tensor principal axes are located at the molecular reference frame from the inspection of the EPR spectra in a frozen liquid crystal (E7). Time evolution of the triplet EPR signals is different among the isomers, suggesting different triplet lifetimes and/or spin relaxation properties. The spin-density distribution in the first triplet state for N-methyl-[70]fulleropyrrolidine is compared with that previously observed for pristine C(70). PMID:23011179

  8. Ultracold triplet molecules in the rovibrational ground state.

    PubMed

    Lang, F; Winkler, K; Strauss, C; Grimm, R; Denschlag, J Hecker

    2008-09-26

    We report here on the production of an ultracold gas of tightly bound Rb2 triplet molecules in the rovibrational ground state, close to quantum degeneracy. This is achieved by optically transferring weakly bound Rb2 molecules to the absolute lowest level of the ground triplet potential with a transfer efficiency of about 90%. The transfer takes place in a 3D optical lattice which traps a sizeable fraction of the tightly bound molecules with a lifetime exceeding 200 ms. PMID:18851446

  9. Calculations of N 2 triplet states vibrational populations and band emissions in venusian dayglow

    NASA Astrophysics Data System (ADS)

    Bhardwaj, Anil; Jain, Sonal Kumar

    2012-02-01

    A model for N 2 triplet states band emissions in the venusian dayglow has been developed for low and high solar activity conditions. Steady state photoelectron fluxes and volume excitation rates for N 2 triplet states have been calculated using the Analytical Yield Spectra (AYS) technique. Model calculated photoelectron flux is in good agreement with Pioneer Venus Orbiter-observed electron flux. Since inter-state cascading is important for the triplet states of N 2, populations of different levels of N 2 triplet states are calculated under statistical equilibrium considering direct electron impact excitation, and cascading and quenching effects. Densities of all vibrational levels of each triplet state are calculated in the model. Height-integrated overhead intensities of N 2 triplet band emissions are calculated, the values for Vegard-Kaplan (A3?u+-X1?g+), First Positive (B3?g-A3?u+), Second Positive ( C3? u - B3? g), and Wu-Benesch ( W3? u - B3? g) bands of N 2, are 1.9 (3.2), 3 (6), 0.4 (0.8), and 0.5 (1.1) kR, respectively, for solar minimum (maximum) conditions. The intensities of the three strong Vegard-Kaplan bands (0, 5), (0, 6), and (0, 7) are 94 (160), 120 (204), and 114 (194) R, respectively, for solar minimum (maximum) conditions. Limb profiles are calculated for VK (0, 4), (0, 5), (0, 6) and (0, 7) bands. The calculated intensities on Venus are about a factor 10 higher than those on Mars. The present study provides a motivation for a search of N 2 triplet band emissions in the dayglow of Venus.

  10. Bacteriochlorophyll protein structure - studies with polarized light and triplet state electron paramagnetic resonance

    SciTech Connect

    Bolt, J.D.

    1980-02-01

    Light harverting bacteriochlorophyll-protein complexes from Rhodopseudomonas sphaeroides 2.4.1 (B800 + 850) and R-26 (LH-R26) mutant are solubiliized in SDS and imbedded in polyvinyl alcohol. Stretching induces orientation, and the linear dichroism of visible and near infrared absorption is analyzed. Based on a simple model, angles between the particle axis system and the transition dipole moments are found. Reaction centers of the photosynthetic bacterium Rhodopseudomonas sphaeroides R-26, give rise to large triplet state EPR signals upon illumination at low temperature (11 K). Utilizing monochromatic polarized light to generate the EPR spectra (magnetophotoselection), it is shown that the intensities of the observed triplet signals are strongly dependent upon the wavelength and polarization direction of the excitation. Triplet states of carotenoids have been detected by EPR and are reported here for the first time. The systems in which carotenoid triplets are observed include cells of photosynthetic bacteria, isolated bacteriochlorophyll-protein complexes, and detergent micelles which contain ..beta..-carotene. The carotenoid triplet state is detected in reaction centers of Rhodopseudomonas sphaeroides 2.4.1 (wild type), which contain the carotenoid spheroidene.

  11. Photosystem II single crystals studied by transient EPR: the light-induced triplet state.

    PubMed

    Kammel, Michael; Kern, Jan; Lubitz, Wolfgang; Bittl, Robert

    2003-08-18

    Transient electron paramagnetic resonance (TR EPR) at 9.8 GHz has been used to study the light-induced triplet state in single crystals of Photosystem II (PS II). The crystals were grown from a solution of PS II core complexes from the thermophilic cyanobacterium Synechococcus elongatus. The core complexes contain at least 17 subunits, including the water-oxidizing complex, and 32 chlorophyll a molecules per PS II complex. The PS II complexes are active in light-induced electron transfer and water oxidation. The crystals belong to the orthorhombic space group P2(1)2(1)2(1), with four dimers of PS II complexes per unit cell. Laser excitation was used to generate the recombination triplet state in PS II which was then studied by EPR at low temperatures (10 K). The crystal spectra show the same magnitude of the zero-field splitting (ZFS) values D, E as spectra obtained earlier for the triplet state of PS II in frozen solution. The orientation of the ZFS tensor D of the triplet state with respect to the crystallographic axes has been deduced from the analysis of angular-dependent EPR spectra. Knowledge of the orientation of the D tensor component perpendicular to the plane of the chlorophyll (D(Z)) allows an assignment on which chlorophyll of the reaction centre the triplet state is localized at low temperatures. Furthermore, the orientation of the D(X) and D(Y) components of the D tensor yielded the in-plane orientation of the respective chlorophyll in the reaction centre providing first experimental evidence for the orientation of this molecule in the PS II. PMID:12907300

  12. Direct Spectroscopic Detection and EPR Investigation of a Ground State Triplet Phenyl Oxenium Ion.

    PubMed

    Li, Ming-De; Albright, Toshia R; Hanway, Patrick J; Liu, Mingyue; Lan, Xin; Li, Songbo; Peterson, Julie; Winter, Arthur H; Phillips, David Lee

    2015-08-19

    Oxenium ions are important reactive intermediates in synthetic chemistry and enzymology, but little is known of the reactivity, lifetimes, spectroscopic signatures, and electronic configurations of these unstable species. Recent advances have allowed these short-lived ions to be directly detected in solution from laser flash photolysis of suitable photochemical precursors, but all of the studies to date have focused on aryloxenium ions having closed-shell singlet ground state configurations. To study alternative spin configurations, we synthesized a photoprecursor to the m-dimethylamino phenyloxenium ion, which is predicted by both density functional theory and MRMP2 computations to have a triplet ground state electronic configuration. A combination of femtosecond and nanosecond transient absorption spectroscopy, nanosecond time-resolved Resonance Raman spectroscopy (ns-TR(3)), cryogenic matrix EPR spectroscopy, computational analysis, and photoproduct studies allowed us to trace essentially the complete arc of the photophysics and photochemistry of this photoprecursor and permitted a first look at a triplet oxenium ion. Ultraviolet photoexcitation of this precursor populates higher singlet excited states, which after internal conversion to S1 over 800 fs are followed by bond heterolysis in ∼1 ps, generating a hot closed-shell singlet oxenium ion that undergoes vibrational cooling in ∼50 ps followed by intersystem crossing in ∼300 ps to generate the triplet ground state oxenium ion. In contrast to the rapid trapping of singlet phenyloxenium ions by nucleophiles seen in prior studies, the triplet oxenium ion reacts via sequential H atom abstractions on the microsecond time domain to ultimately yield the reduced m-dimethylaminophenol as the only detectable stable photoproduct. Band assignments were made by comparisons to computed spectra of candidate intermediates and comparisons to related known species. The triplet oxenium ion was also detected in the ns-TR(3) experiments, permitting a more clear assignment and identifying the triplet state as the π,π* triplet configuration. The triplet ground state of this ion was further supported by photolysis of the photoprecursor in an ethanol glass at ∼4 K and observing a triplet species by cryogenic EPR spectroscopy. PMID:26198984

  13. 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 (360 ns), whereas those of PcD-4Ph were quite similar in both solvent. PMID:26930127

  14. Photoexcited triplet states of UV-B absorbers: ethylhexyl triazone and diethylhexylbutamido triazone.

    PubMed

    Tsuchiya, Takumi; Kikuchi, Azusa; Oguchi-Fujiyama, Nozomi; Miyazawa, Kazuyuki; Yagi, Mikio

    2015-04-01

    The excited states of UV-B absorbers, ethylhexyl triazone (EHT) and diethylhexylbutamido triazone (DBT), have been studied through measurements of UV absorption, fluorescence, phosphorescence, triplet-triplet absorption and electron paramagnetic resonance spectra in ethanol. The energy levels of the lowest excited singlet (S1) and triplet (T1) states and quantum yields of fluorescence and phosphorescence of EHT and DBT were determined. In ethanol at 77 K, the deactivation process of EHT and DBT is predominantly fluorescence, however, a significant portion of the S1 molecules undergoes intersystem crossing to the T1 state. The observed phosphorescence spectra, T1 lifetimes and zero-field splitting parameters suggest that the T1 state of EHT can be assigned to a locally excited (3)??* state within p-(N-methylamino)benzoic acid, while the T1 state of DBT can be assigned to a locally excited (3)??* state within p-(N-methylamino)benzoic acid or p-amino-N-methylbenzamide. The quantum yields of singlet oxygen generation by EHT and DBT were determined by time-resolved near-IR phosphorescence measurements in ethanol at room temperature. EHT and DBT did not exhibit significantly antioxidative properties by quenching singlet oxygen, in contrast to the study by Lhiaubet-Vallet et al. PMID:25653197

  15. Direct Observation of Triplet-State Population Dynamics in the RNA Uracil Derivative 1-Cyclohexyluracil.

    PubMed

    Brister, Matthew M; Crespo-Hernández, Carlos E

    2015-11-01

    Investigation of the excited-state dynamics in nucleic acid monomers is an area of active research due to the crucial role these early events play in DNA and RNA photodamage. The dynamics and rate at which the triplet state is populated are key mechanistic pathways yet to be fully elucidated. Direct spectroscopic evidence is presented in this contribution for intersystem crossing dynamics in a uracil derivative, 1-cyclohexyluracil. It is shown that intersystem crossing to the triplet manifold occurs in one picosecond or less in acetonitrile solution-at least an order of magnitude faster than previously estimated experimentally. Broadband transient absorption measurements also reveal the primary electronic relaxation pathways of the uracil chromophore, including the absorption spectra of the (1)ππ*, (1)nπ*, and (3)ππ* states and the rates of vibrational cooling in the ground and (3)ππ* states. The experimental results are supported by density functional calculations. PMID:26538051

  16. On-chip generation of photon-triplet states.

    PubMed

    Krapick, Stephan; Brecht, Benjamin; Herrmann, Harald; Quiring, Viktor; Silberhorn, Christine

    2016-02-01

    Efficient sources of many-partite non-classical states are key for the advancement of quantum technologies and for the fundamental testing of quantum mechanics. We demonstrate the generation of time-correlated photon triplets at telecom wavelengths via pulsed cascaded parametric down-conversion in a monolithically integrated source. By detecting the generated states with success probabilities of (6.25 ± 1.09) × 10-11 per pump pulse at injected powers as low as 10 μW, we benchmark the efficiency of the complete system and deduce its high potential for scalability. Our source is unprecedentedly long-term stable, it overcomes interface losses intrinsically due to its monolithic architecture, and the photon-triplet states dominate uncorrelated noise significantly. These results mark crucial progress towards the proliferation of robust, scalable, synchronized and miniaturized quantum technology. PMID:26906852

  17. Determining Oxygen Abundances in Metal Poor Subdwarfs from Medium Resolution Spectra of the OI Triplet

    NASA Astrophysics Data System (ADS)

    James, C. R.; Pilachowski, C. A.; Beers, T.; Sneden, C.; Cavallo, R. M.

    2002-12-01

    In the determination of oxygen abundances in unevolved metal-poor stars, the OI triplet remains the most accessible feature, but is still quite weak in the most metal-poor (oldest) stars. Pilachowski & Armandroff (1996) have explored a technique to determine oxygen and iron abundances in faint evolved stars using low-dispersion spectroscopy of the oxygen triplet. At moderate resolution, the triplet lines are blended into a single feature that can be measured and analyzed as a spectroscopic blend. Because the lines are separated by only 3.4 , the blended feature is more easily detected than the individual features; thus reliable oxygen measurements can be made in much fainter stars. Also, the immediate vicinity of the oxygen triplet is free of atmospheric absorption line contamination, and the feature is unblended with other stellar lines from additional elements. In this work, we have attempted to apply the Pilachowski and Armandroff (1996) methods to a sample of unevolved stars. Approximately half of the sample has been previously studied, allowing for a thorough assessment of the feasibility of applying the Pilachowski-Armandroff method to this population of stars. We find that the employing spectrum synthesis analysis to these low-dispersion spectra does sometimes yield meaningful results, and those results are consistent with high-resolution studies. However, in many cases, the weakness of the triplet allows for only determinations of upper limits, most of which are unenlightening. We explore the advantages and disadvantages of this method. Support from NOAO and SHSU is gratefully acknowledged.

  18. Triplet state delocalization in a conjugated porphyrin dimer probed by transient electron paramagnetic resonance techniques.

    PubMed

    Tait, Claudia E; Neuhaus, Patrik; Anderson, Harry L; Timmel, Christiane R

    2015-05-27

    The delocalization of the photoexcited triplet state in a linear butadiyne-linked porphyrin dimer is investigated by time-resolved and pulse electron paramagnetic resonance (EPR) with laser excitation. The transient EPR spectra of the photoexcited triplet states of the porphyrin monomer and dimer are characterized by significantly different spin polarizations and an increase of the zero-field splitting parameter D from monomer to dimer. The proton and nitrogen hyperfine couplings, determined using electron nuclear double resonance (ENDOR) and X- and Q-band HYSCORE, are reduced to about half in the porphyrin dimer. These data unequivocally prove the delocalization of the triplet state over both porphyrin units, in contrast to the conclusions from previous studies on the triplet states of closely related porphyrin dimers. The results presented here demonstrate that the most accurate estimate of the extent of triplet state delocalization can be obtained from the hyperfine couplings, while interpretation of the zero-field splitting parameter D can lead to underestimation of the delocalization length, unless combined with quantum chemical calculations. Furthermore, orientation-selective ENDOR and HYSCORE results, in combination with the results of density functional theory (DFT) calculations, allowed determination of the orientations of the zero-field splitting tensors with respect to the molecular frame in both porphyrin monomer and dimer. The results provide evidence for a reorientation of the zero-field splitting tensor and a change in the sign of the zero-field splitting D value. The direction of maximum dipolar coupling shifts from the out-of-plane direction in the porphyrin monomer to the vector connecting the two porphyrin units in the dimer. This reorientation, leading to an alignment of the principal optical transition moment and the axis of maximum dipolar coupling, is also confirmed by magnetophotoselection experiments. PMID:25914154

  19. Transient EPR Reveals Triplet State Delocalization in a Series of Cyclic and Linear ?-Conjugated Porphyrin Oligomers.

    PubMed

    Tait, Claudia E; Neuhaus, Patrik; Peeks, Martin D; Anderson, Harry L; Timmel, Christiane R

    2015-07-01

    The photoexcited triplet states of a series of linear and cyclic butadiyne-linked porphyrin oligomers were investigated by transient Electron Paramagnetic Resonance (EPR) and Electron Nuclear DOuble Resonance (ENDOR). The spatial delocalization of the triplet state wave function in systems with different numbers of porphyrin units and different geometries was analyzed in terms of zero-field splitting parameters and proton hyperfine couplings. Even though no significant change in the zero-field splitting parameters (D and E) is observed for linear oligomers with two to six porphyrin units, the spin polarization of the transient EPR spectra is particularly sensitive to the number of porphyrin units, implying a change of the mechanism of intersystem crossing. Analysis of the proton hyperfine couplings in linear oligomers with more than two porphyrin units, in combination with density functional theory calculations, indicates that the spin density is localized mainly on two to three porphyrin units rather than being distributed evenly over the whole ?-system. The sensitivity of the zero-field splitting parameters to changes in geometry was investigated by comparing free linear oligomers with oligomers bound to a hexapyridyl template. Significant changes in the zero-field splitting parameter D were observed, while the proton hyperfine couplings show no change in the extent of triplet state delocalization. The triplet state of the cyclic porphyrin hexamer has a much decreased zero-field splitting parameter D and much smaller proton hyperfine couplings with respect to the monomeric unit, indicating complete delocalization over six porphyrin units in this symmetric system. This surprising result provides the first evidence for extensive triplet state delocalization in an artificial supramolecular assembly of porphyrins. PMID:26035477

  20. Triplet State Delocalization in a Conjugated Porphyrin Dimer Probed by Transient Electron Paramagnetic Resonance Techniques

    PubMed Central

    2015-01-01

    The delocalization of the photoexcited triplet state in a linear butadiyne-linked porphyrin dimer is investigated by time-resolved and pulse electron paramagnetic resonance (EPR) with laser excitation. The transient EPR spectra of the photoexcited triplet states of the porphyrin monomer and dimer are characterized by significantly different spin polarizations and an increase of the zero-field splitting parameter D from monomer to dimer. The proton and nitrogen hyperfine couplings, determined using electron nuclear double resonance (ENDOR) and X- and Q-band HYSCORE, are reduced to about half in the porphyrin dimer. These data unequivocally prove the delocalization of the triplet state over both porphyrin units, in contrast to the conclusions from previous studies on the triplet states of closely related porphyrin dimers. The results presented here demonstrate that the most accurate estimate of the extent of triplet state delocalization can be obtained from the hyperfine couplings, while interpretation of the zero-field splitting parameter D can lead to underestimation of the delocalization length, unless combined with quantum chemical calculations. Furthermore, orientation-selective ENDOR and HYSCORE results, in combination with the results of density functional theory (DFT) calculations, allowed determination of the orientations of the zero-field splitting tensors with respect to the molecular frame in both porphyrin monomer and dimer. The results provide evidence for a reorientation of the zero-field splitting tensor and a change in the sign of the zero-field splitting D value. The direction of maximum dipolar coupling shifts from the out-of-plane direction in the porphyrin monomer to the vector connecting the two porphyrin units in the dimer. This reorientation, leading to an alignment of the principal optical transition moment and the axis of maximum dipolar coupling, is also confirmed by magnetophotoselection experiments. PMID:25914154

  1. Triplet emission from poly(3,6-dibromo-N-vinylcarbazole): Spectra and kinetics

    SciTech Connect

    Starzyk, F.; Burkhart, R.D. )

    1989-01-01

    The triplet delayed emission of poly(3,6-dibromo-N-vinylcarbazole) (PdBVK) in a 2-methyltetrahydrofuran (MTHF) frozen solution at 77K was examined within the spectral and time regimes of 400-570 nm and 0.2-50 ms, respectively. The influence on optical absorption of bromine substitution into the carbazole ring (3- and 6-positions) of poly(N-vinylcarbazole), as well as delayed triplet emission spectra and the kinetic decays, was monitored. The phosphorescence spectra were recorded at different delay times after excitation. The phosphorescence decays were found to be essentially exponential in the wings of the phosphorescence band but showed unusual, definitely nonexponential, behavior in the range 460-475 nm, which is the range of maximum phosphorescence intensity. A resolution of the phosphorescence band into Gaussian components yielded excellent fits by using three components at delay times less than 2 ms and two components for spectra taken at longer delay times. Based upon an average of 12 different spectra recorded at various times after excitation, the calculated wavelengths at maximum intensity for these Gaussian components were found to be 448{plus minus}2 nm, 473{plus minus}4 nm, and 501{plus minus}8 nm.

  2. Photosensitized Thymine Dimerization via Delocalized Triplet Excited States.

    PubMed

    Miro, Paula; Lhiaubet-Vallet, Virginie; Marin, M Luisa; Miranda, Miguel A

    2015-11-16

    A new mechanism of photosensitized formation of thymine (Thy) dimers is proposed, which involves generation of a delocalized triplet excited state as the key step. This is supported by chemical evidence obtained by combining one benzophenone and two Thy units with different degrees of freedom, whereby the photoreactivity is switched from a clean Paternò-Büchi reaction to a fully chemo-, regio-, and stereoselective [2+2] cycloaddition. PMID:26462463

  3. The lowest triplet states of bridged cis-2,2'-bithiophenes - theory vs. experiment.

    PubMed

    Andrzejak, Marcin; Szczepanik, Dariusz W; Orzeł, Łukasz

    2015-02-21

    Theoretical methods that were previously used to give a good quantitative description of the 3(1)Bu state of trans-2,2'-bithiophene are applied to characterize the lowest triplet states of three bridged cis-2,2'-bithiophenes: 3,3'-cyclopentadithiophene (CPDT), 3,3'-dithienylpyrrole (DTP), and 3,3'-dithienylthiophene (DTT). By obtaining highly accurate reproductions of the phosphorescence spectra of all three compounds, we rationalize the observed vibronic activity, further explore the performance of the applied theoretical methods, and address the quality of the reported experimental spectra. Over the course of this study we have, first, characterized the changes in the electronic structures between the ground state and the lowest triplet state and, second, expressed the related geometrical differences in terms of the Huang-Rhys factors. The Huang-Rhys factors have then been used to generate theoretical emission spectra with vibronic resolution. The applied procedure has yielded quantitative reproductions of the previously reported experimental phosphorescence spectra of DTT and DTP. The experimental spectrum of CPDT, on the other hand, turned out to be considerably narrower and intensity-deficient in its low energy region when compared with the theoretical results. Our experimental reinvestigation of the CPDT phosphorescence has given a refined spectrum that is significantly wider than the previously reported one, and is in nearly quantitative agreement with the theoretical prediction. This enabled us to attribute the observed discrepancy to an experimental artifact associated with the sensitivity characteristics of the commonly used photomultipliers. PMID:25609244

  4. Electron-energy-loss spectroscopy of solid phenanthrene and biphenylene: Search for the low-lying triplet states

    NASA Astrophysics Data System (ADS)

    Swiderek, Petra; Michaud, M.; Hohlneicher, G.; Sanche, L.

    1991-03-01

    Electron-energy-loss spectra of phenanthrene and biphenylene deposited on a thin film of solid argon have been measured at a temperature of 20 K and an incident energy of 10.5 eV. The second triplet state of phenanthrene (1 3A 1) and biphenylene (1 3B 2u) could be detected at 3.45 and 3.20 eV, respectively. For biphenylene, a further triplet state is tentatively assigned at 3.92 eV.

  5. The triplet state of tanshinone I and its synergic effect on the phototherapy of cancer cells with curcumin.

    PubMed

    Zhang, Chenchen; Jiang, Shan; Li, Kun; Wang, Mei; Zhu, Rongrong; Sun, Xiaoyu; Wang, Qingxiu; Wang, ShiLong

    2015-11-01

    The excited triplet state of tanshinone I (Tan I) extracted from the traditional Chinese medicine Salvia miltiorrhiza Bunge was characterized by laser flash photolysis. The synergic effect of Tan I on the phototherapy of cancer cells with curcumin (Cur) was also investigated by MTT assay because the excited energy transfer from the triplet state of Tan I ((3)Tan I(?)) to Cur occurred. At the same time, the characteristic absorption spectra of (3)Tan I(?) were recorded, and its molar absorption coefficient and rate constants for several excited energy transfers were obtained. The photo-therapeutic effect of Cur is enhanced by combination with Tan I. PMID:26046496

  6. Room temperature triplet state spectroscopy of organic semiconductors

    PubMed Central

    Reineke, Sebastian; Baldo, Marc A.

    2014-01-01

    Organic light-emitting devices and solar cells are devices that create, manipulate, and convert excited states in organic semiconductors. It is crucial to characterize these excited states, or excitons, to optimize device performance in applications like displays and solar energy harvesting. This is complicated if the excited state is a triplet because the electronic transition is dark with a vanishing oscillator strength. As a consequence, triplet state spectroscopy must usually be performed at cryogenic temperatures to reduce competition from non-radiative rates. Here, we control non-radiative rates by engineering a solid-state host matrix containing the target molecule, allowing the observation of phosphorescence at room temperature and alleviating constraints of cryogenic experiments. We test these techniques on a wide range of materials with functionalities spanning multi-exciton generation (singlet exciton fission), organic light emitting device host materials, and thermally activated delayed fluorescence type emitters. Control of non-radiative modes in the matrix surrounding a target molecule may also have broader applications in light-emitting and photovoltaic devices. PMID:24445870

  7. Room temperature triplet state spectroscopy of organic semiconductors.

    PubMed

    Reineke, Sebastian; Baldo, Marc A

    2014-01-01

    Organic light-emitting devices and solar cells are devices that create, manipulate, and convert excited states in organic semiconductors. It is crucial to characterize these excited states, or excitons, to optimize device performance in applications like displays and solar energy harvesting. This is complicated if the excited state is a triplet because the electronic transition is 'dark' with a vanishing oscillator strength. As a consequence, triplet state spectroscopy must usually be performed at cryogenic temperatures to reduce competition from non-radiative rates. Here, we control non-radiative rates by engineering a solid-state host matrix containing the target molecule, allowing the observation of phosphorescence at room temperature and alleviating constraints of cryogenic experiments. We test these techniques on a wide range of materials with functionalities spanning multi-exciton generation (singlet exciton fission), organic light emitting device host materials, and thermally activated delayed fluorescence type emitters. Control of non-radiative modes in the matrix surrounding a target molecule may also have broader applications in light-emitting and photovoltaic devices. PMID:24445870

  8. Room temperature triplet state spectroscopy of organic semiconductors

    NASA Astrophysics Data System (ADS)

    Reineke, Sebastian; Baldo, Marc A.

    2014-01-01

    Organic light-emitting devices and solar cells are devices that create, manipulate, and convert excited states in organic semiconductors. It is crucial to characterize these excited states, or excitons, to optimize device performance in applications like displays and solar energy harvesting. This is complicated if the excited state is a triplet because the electronic transition is `dark' with a vanishing oscillator strength. As a consequence, triplet state spectroscopy must usually be performed at cryogenic temperatures to reduce competition from non-radiative rates. Here, we control non-radiative rates by engineering a solid-state host matrix containing the target molecule, allowing the observation of phosphorescence at room temperature and alleviating constraints of cryogenic experiments. We test these techniques on a wide range of materials with functionalities spanning multi-exciton generation (singlet exciton fission), organic light emitting device host materials, and thermally activated delayed fluorescence type emitters. Control of non-radiative modes in the matrix surrounding a target molecule may also have broader applications in light-emitting and photovoltaic devices.

  9. Dark state experiments with ultracold, deeply-bound triplet molecules.

    PubMed

    Lang, Florian; Strauss, Christoph; Winkler, Klaus; Takekoshi, Tetsu; Grimm, Rudolf; Denschlag, Johannes Hecker

    2009-01-01

    We examine dark quantum superposition states of weakly bound Rb2 Feshbach molecules and tightly bound triplet Rb2 molecules in the rovibrational ground state, created by subjecting a pure sample of Feshbach molecules in an optical lattice to a bichromatic Raman laser field. We analyze, both experimentally and theoretically, the creation and dynamics of these dark states. Coherent wavepacket oscillations of deeply bound molecules in lattice sites, as previously observed by Lang et al. (Phys. Rev. Lett., 2008, 101, 133005), are suppressed due to laser-induced phase locking of molecular levels. This can be understood as the appearance of a novel multilevel dark state. In addition, the experimental methods developed help to determine important properties of our coupled atom/ laser system. PMID:20151548

  10. Pulse ESR of triplet states of large molecular π systems

    NASA Astrophysics Data System (ADS)

    Knorr, S.; Grupp, A.; Mehring, M.; Wehmeier, M.; Herwig, P.; Iyer, V. S.; Müllen, K.

    1998-08-01

    We report on the electronic properties of flat, disc-type molecules with extended π systems, which are designed as well-defined graphite subunit molecules by a new synthetic route. In our contribution, we have investigated the excited states of three benzenoid hydrocarbons—namely hexa-peri-hexabenzocoronene and two higher homologues—with time-resolved electron spin resonance (ESR) and optical techniques. After applying a laser flash to shock-frozen solutions of these molecules, we find excited states with lifetimes in the range of seconds. We have examined the fine-structure parameters of the triplet states in two molecules and furthermore observed the luminescence in the third one.

  11. Excited triplet states as photooxidants in surface waters

    NASA Astrophysics Data System (ADS)

    Canonica, S.

    2012-12-01

    The chromophoric components of dissolved organic matter (DOM) are generally the main absorbers of sunlight in surface waters and therefore a source of transient reactants under irradiation. Such short-lived species can be relevant for the fate of various classes of chemical contaminants in the aquatic environment. The present contribution focuses on the role of excited triplet states of chromophoric DOM, 3CDOM*, as transient photooxidants initiating the transformation and degradation of organic chemical contaminants. An early study [1] indicated that 3CDOM* may play a dominant role in the photo-induced transformation of electron-rich phenols, a conclusion which was later fortified by the results of transient absorption investigations using aromatic ketones as model photosensitizers [2] and by a recent careful analysis of the effect of oxygen concentration on transformation rates [3]. The variety of aquatic contaminants shown to be affected by triplet-induced oxidation has kept increasing, phenylurea herbicides [4], sulfonamide antibiotics [5] and some phytoestrogens [6] being prominent examples. Recent research has shown that the triplet-induced transformation of specific contaminants, especially aromatic nitrogen compounds, could be inhibited by the presence of DOM, very probably due to its antioxidant moieties [7]. While such moieties are not relevant for the quenching of 3CDOM*, they are expected to react with it in a similar way as the studied contaminants. Analogous reactions can be postulated to occur in liquid or solid phases of the atmospheric environment, as demonstrated in the case of HONO formation [8]. References 1. Canonica, S.; Jans, U.; Stemmler, K.; Hoigné, J. Transformation kinetics of phenols in water: Photosensitization by dissolved natural organic material and aromatic ketones. Environ. Sci. Technol. 1995, 29 (7), 1822-1831. 2. Canonica, S.; Hellrung, B.; Wirz, J. Oxidation of phenols by triplet aromatic ketones in aqueous solution. J. Phys. Chem. A 2000, 104 (6), 1226-1232. 3. Golanoski, K. S.; Fang, S.; Del Vecchio, R.; Blough, N. V. Investigating the mechanism of phenol photooxidation by humic substances. Environ. Sci. Technol. 2012, 46 (7), 3912-3920. 4. Gerecke, A. C.; Canonica, S.; Müller, S. R.; Schärer, M.; Schwarzenbach, R. P. Quantification of dissolved natural organic matter (DOM) mediated phototransformation of phenylurea herbicides in lakes. Environ. Sci. Technol. 2001, 35 (19), 3915-3923. 5. Boreen, A. L.; Arnold, W. A.; McNeill, K. Triplet-sensitized photodegradation of sulfa drugs containing six-membered heterocyclic groups: Identification of an SO2 extrusion photoproduct. Environ. Sci. Technol. 2005, 39 (10), 3630-3638. 6. Felcyn, J. R.; Davis, J. C. C.; Tran, L. H.; Berude, J. C.; Latch, D. E. Aquatic photochemistry of isoflavone phytoestrogens: Degradation kinetics and pathways. Environ. Sci. Technol. 2012, 46 (12), 6698-6704. 7. Wenk, J.; Canonica, S. Phenolic antioxidants inhibit the triplet-induced transformation of anilines and sulfonamide antibiotics in aqueous solution. Environ. Sci. Technol. 2012, 46 (10), 5455-5462. 8. George, C.; Strekowski, R. S.; Kleffmann, J.; Stemmler, K.; Ammann, M. Photoenhanced uptake of gaseous NO2 on solid-organic compounds: a photochemical source of HONO? Faraday Discuss. 2005, 130, 195-210.

  12. Synthesis of Aza-m-Xylylene diradicals with large singlet-triplet energy gap and statistical analyses of their EPR spectra

    SciTech Connect

    Olankitwanit, Arnon; Pink, Maren; Rajca, Suchada; Rajca, Andrzej

    2014-10-08

    We describe synthesis and characterization of a derivative of aza-m-xylylene, diradical 2, that is persistent in solution at room temperature with the half-life measured in minutes (~80–250 s) and in which the triplet ground state is below the lowest singlet state by >10 kcal mol⁻¹. The triplet ground states and ΔEST of 2 in glassy solvent matrix are determined by a new approach based on statistical analyses of their EPR spectra. Characterization and analysis of the analogous diradical 1 are carried out for comparison. Statistical analyses of their EPR spectra reliably provide improved lower bounds for ΔEST (from >0.4 to >0.6 kcal mol⁻¹) and are compatible with a wide range of relative contents of diradical vs monoradical, including samples in which the diradical and monoradical are minor and major components, respectively. This demonstrates a new powerful method for the determination of the triplet ground states and ΔEST applicable to moderately pure diradicals in matrices.

  13. Molecular Adaptation of Photoprotection: Triplet States in Light-Harvesting Proteins

    PubMed Central

    Gall, Andrew; Berera, Rudi; Alexandre, MaximeT.A.; Pascal, AndrewA.; Bordes, Luc; Mendes-Pinto, MariaM.; Andrianambinintsoa, Sandra; Stoitchkova, KaterinaV.; Marin, Alessandro; Valkunas, Leonas; Horton, Peter; Kennis, JohnT.M.; vanGrondelle, Rienk; Ruban, Alexander; Robert, Bruno

    2011-01-01

    The photosynthetic light-harvesting systems of purple bacteria and plants both utilize specific carotenoids as quenchers of the harmful (bacterio)chlorophyll triplet states via triplet-triplet energy transfer. Here, we explore how the binding of carotenoids to the different types of light-harvesting proteins found in plants and purple bacteria provides adaptation in this vital photoprotective function. We show that the creation of the carotenoid triplet states in the light-harvesting complexes may occur without detectable conformational changes, in contrast to that found for carotenoids in solution. However, in plant light-harvesting complexes, the triplet wavefunction is shared between the carotenoids and their adjacent chlorophylls. This is not observed for the antenna proteins of purple bacteria, where the triplet is virtually fully located on the carotenoid molecule. These results explain the faster triplet-triplet transfer times in plant light-harvesting complexes. We show that this molecular mechanism, which spreads the location of the triplet wavefunction through the pigments of plant light-harvesting complexes, results in the absence of any detectable chlorophyll triplet in these complexes upon excitation, and we propose that it emerged as a photoprotective adaptation during the evolution of oxygenic photosynthesis. PMID:21843485

  14. Triplet state properties of a red light emitting [Pt(s-thpy)(acac)] compound

    NASA Astrophysics Data System (ADS)

    Fischer, Tobias; Czerwieniec, Rafa?; Hofbeck, Thomas; Osminina, Maria M.; Yersin, Hartmut

    2010-02-01

    A photophysical characterization based on optical high-resolution spectra and emission decay properties at low temperatures and at high magnetic fields is carried out for [Pt(s-thpy)(acac)] (s-thpy = 5,2-bis(2-thienyl)pyridinate and acac = acetylacetonate). The electronic 0-0 transition between the lowest triplet state and the ground state lies at 16 150 cm -1 (619 nm). The zero-field splitting (ZFS) of T 1 is smaller than 1 cm -1. Thus, the emitting excited state is mainly of ligand-centered 3LC ( 3???) character and experiences only weak spin-orbit couplings to higher lying singlet states. The compound does not fulfill important requirements for OLED applications, but strategies for improvements are pointed out.

  15. Stabilizing triplet excited states for ultralong organic phosphorescence.

    PubMed

    An, Zhongfu; Zheng, Chao; Tao, Ye; Chen, Runfeng; Shi, Huifang; Chen, Ting; Wang, Zhixiang; Li, Huanhuan; Deng, Renren; Liu, Xiaogang; Huang, Wei

    2015-07-01

    The control of the emission properties of synthetic organic molecules through molecular design has led to the development of high-performance optoelectronic devices with tunable emission colours, high quantum efficiencies and efficient energy/charge transfer processes. However, the task of generating excited states with long lifetimes has been met with limited success, owing to the ultrafast deactivation of the highly active excited states. Here, we present a design rule that can be used to tune the emission lifetime of a wide range of luminescent organic molecules, based on effective stabilization of triplet excited states through strong coupling in H-aggregated molecules. Our experimental data revealed that luminescence lifetimes up to 1.35 s, which are several orders of magnitude longer than those of conventional organic fluorophores, can be realized under ambient conditions. These results outline a fundamental principle to design organic molecules with extended lifetimes of excited states, providing a major step forward in expanding the scope of organic phosphorescenceapplications. PMID:25849370

  16. EPR Evidence for Thermally Excited Triplet States in Exinite, Vitrinite and Inertinite Separated from Bituminous Coal

    NASA Astrophysics Data System (ADS)

    S?owik, G. P.; Wojtowicz, W.; Wi?ckowski, A. B.

    2006-07-01

    In this work we have made an electron spin resonance (EPR) study of macerals obtained from the lithotype clarain separated from Polish medium-rank coal (85.6 wt.% C). For three macerals: exinite, vitrinite, and inertinite, the temperature dependence of intensity of EPR spectra in the temperature range of 100-373 K was investigated. The experimentally obtained EPR spectra of macerals were fitted by curves of the derivatives of the Gaussian and Lorentzian functions. The best fitting was obtained, when the experimental EPR spectra were assumed to be a superposition of three lines, for exinite and vitrinite - a broad Gaussian (G), a broad Lorentzian (L1) and a narrow Lorentzian (L3) line, but for inertinite of two lines --- a narrow Lorentzian (L2) and a narrow Lorentzian (L3) line. The computer-assisted fitting has shown that each individual component line has similar values of resonance field, but different linewidths and amplitudes. The temperature dependence of line intensity I of the broad Gaussian (G) and narrow Lorentzian (L2 and L3) lines fulfils the Curie law in the form I=C/T or IT=C, whereas the broad Lorentzian (L1) line does not fulfil the Curie law. In the last case the temperature dependence of the Lorentzian (L1) component was fitted by the relation I=C/T+B/[T(3+exp(J/kT))] or IT=C+B/[3+exp(J/kT))], valid for thermally excited triplet states (S=1). For exinite and vitrinite the curves presenting the temperature dependence of the product IT versus temperature T were resolved into two curves, one for paramagnetic centres in the doublet state (S=1/2), and the other for paramagnetic centres in the thermally excited triplet state (S=1).

  17. Carotenoid triplet states in photosystem II: coupling with low-energy states of the core complex.

    PubMed

    Santabarbara, Stefano; Agostini, Alessandro; Casazza, Anna Paola; Zucchelli, Giuseppe; Carbonera, Donatella

    2015-02-01

    The photo-excited triplet states of carotenoids, sensitised by triplet-triplet energy transfer from the chlorophyll triplet states, have been investigated in the isolated Photosystem II (PSII) core complex and PSII-LHCII (Light Harvesting Complex II) supercomplex by Optically Detected Magnetic Resonance techniques, using both fluorescence (FDMR) and absorption (ADMR) detection. The absence of Photosystem I allows us to reach the full assignment of the carotenoid triplet states populated in PSII under steady state illumination at low temperature. Five carotenoid triplet ((3)Car) populations were identified in PSII-LHCII, and four in the PSII core complex. Thus, four (3)Car populations are attributed to ?-carotene molecules bound to the core complex. All of them show associated fluorescence emission maxima which are relatively red-shifted with respect to the bulk emission of both the PSII-LHCII and the isolated core complexes. In particular the two populations characterised by Zero Field Splitting parameters |D|=0.0370-0.0373 cm(-1)/|E|=0.00373-0.00375 cm(-1) and |D|=0.0381-0.0385 cm(-1)/|E|=0.00393-0.00389 cm(-1), are coupled by singlet energy transfer with chlorophylls which have a red-shifted emission peaking at 705 nm. This observation supports previous suggestions that pointed towards the presence of long-wavelength chlorophyll spectral forms in the PSII core complex. The fifth (3)Car component is observed only in the PSII-LHCII supercomplex and is then assigned to the peripheral light harvesting system. PMID:25481107

  18. Theoretical studies of highly excited triplet states of sodium-potassium

    NASA Astrophysics Data System (ADS)

    Wilkins, Angela D.

    Calculations have been performed to investigate the fine and hyperfine structure of highly excited triplet states of the NaK molecule. Prof. Huennekens' AMO group observed high-resolution spectra of numerous ro-vibrational levels (v, N) of various triplet states of the NaK molecule. The experimental measurements of the fine and hyperfine structure of the 1 3Delta and 33pi states were analyzed to determine the values of the spin-orbit constant Av and the Fermi constant bF. The fine and hyperfine structure of the 43Sigma+ state was analyzed to determine the values of the Fermi contact constant bF and the spin-rotation constant gamma. A theoretical model was formed to treat the intermediate angular momentum coupling in these electronic states. The model Hamiltonian developed to fit the experimental data, agreed well with the data. The 33pi state is a special case since it is a double well state. The spin-orbit constant Av and the hyperfine constant bF were determined for each region of the 33pi potential curve. The 4 3Sigma+ state was unique since there was no spin-orbit coupling (? = 0). The spin-rotation interaction (gammaR S) had to be considered to understand the ro-vibrational levels. In the case of the 1 3Delta state, the measured fine and hyperfine structure for large v exhibits anomalous behavior due to the mixing with the 1 1Delta states. The highest levels measured (v = 59) lie within 4 cm-1 of the dissociation limit. The theoretical method was extended to treat the 1 3Delta-1 1Delta interaction, and the results provide an accurate representation of the complicated patterns that arise for v ? 50. The 1 3Delta levels in the range v = 46-49 show clear effects of the 1 3Delta-1 1Delta coupling. Ab initio calculations of the spin-orbit coupling for excited triplet states of NaK were performed using the GAMESS electronic structure codes. The spin-orbit coupling constants were determined as a function of the internuclear separation R. These coupling constants were convoluted with vibrational wave functions for comparison with experimental spin-orbit constants, which depend on v. The theoretical results compare well with the experimental spin-orbit values.

  19. Direct Observation of Thermal Equilibrium of Excited Triplet States of 9,10-Phenanthrenequinone. A Time-Resolved Resonance Raman Study.

    PubMed

    Kumar, Venkatraman Ravi; Rajkumar, Nagappan; Ariese, Freek; Umapathy, Siva

    2015-10-01

    The photochemistry of aromatic ketones plays a key role in various physicochemical and biological processes, and solvent polarity can be used to tune their triplet state properties. Therefore, a comprehensive analysis of the conformational structure and the solvent polarity induced energy level reordering of the two lowest triplet states of 9,10-phenanthrenequinone (PQ) was carried out using nanosecond-time-resolved absorption (ns-TRA), time-resolved resonance Raman (TR(3)) spectroscopy, and time dependent-density functional theory (TD-DFT) studies. The ns-TRA of PQ in acetonitrile displays two bands in the visible range, and these two bands decay with similar lifetime at least at longer time scales (?s). Interestingly, TR(3) spectra of these two bands indicate that the kinetics are different at shorter time scales (ns), while at longer time scales they followed the kinetics of ns-TRA spectra. Therefore, we report a real-time observation of the thermal equilibrium between the two lowest triplet excited states of PQ, assigned to n?* and ??* of which the ??* triplet state is formed first through intersystem crossing. Despite the fact that these two states are energetically close and have a similar conformational structure supported by TD-DFT studies, the slow internal conversion (?2 ns) between the T(2)(1(3)n?*) and T(1)(1(3)??*) triplet states indicates a barrier. Insights from the singlet excited states of PQ in protic solvents [ J. Chem. Phys. 2015 , 142 , 24305 ] suggest that the lowest n?* and ??* triplet states should undergo hydrogen bond weakening and strengthening, respectively, relative to the ground state, and these mechanisms are substantiated by TD-DFT calculations. We also hypothesize that the different hydrogen bonding mechanisms exhibited by the two lowest singlet and triplet excited states of PQ could influence its ISC mechanism. PMID:26381591

  20. ADMR of carotenoid triplet states in bacterial photosynthetic antenna and reaction center complexes

    NASA Astrophysics Data System (ADS)

    Aust, V.; Angerhofer, A.; Ullrich, J.; von Schtz, J. U.; Wolf, H. C.; Cogdell, R. J.

    1991-06-01

    Using absorption detected magnetic resonance (ADMR) the triplet states of carotenoids have been detected in B880RC complexes of the purple photosynthetic bacteria Rhodocyclus gelatinosus 149, Rhodopseudomonas acidophila 7050, Rhodopseudomonas palustris 8252, and Rhodospirillum rubrum S1, and in reaction center (RC) complexes of Rhodospirillum rubrum S1. The triplet states were identified as belonging to antenna carotenois in the all-trans conformation with conjugated chain lengths ranging from 10 to 13 double bonds, and to the RC carotenoid 15,15'-cis spirilloxanthin. Carotenoids with different numbers of conjugated double bonds have similar ability to quench the triplet states of the bacteriochlorophylls.

  1. 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.

  2. Transient EPR Reveals Triplet State Delocalization in a Series of Cyclic and Linear π-Conjugated Porphyrin Oligomers

    PubMed Central

    2015-01-01

    The photoexcited triplet states of a series of linear and cyclic butadiyne-linked porphyrin oligomers were investigated by transient Electron Paramagnetic Resonance (EPR) and Electron Nuclear DOuble Resonance (ENDOR). The spatial delocalization of the triplet state wave function in systems with different numbers of porphyrin units and different geometries was analyzed in terms of zero-field splitting parameters and proton hyperfine couplings. Even though no significant change in the zero-field splitting parameters (D and E) is observed for linear oligomers with two to six porphyrin units, the spin polarization of the transient EPR spectra is particularly sensitive to the number of porphyrin units, implying a change of the mechanism of intersystem crossing. Analysis of the proton hyperfine couplings in linear oligomers with more than two porphyrin units, in combination with density functional theory calculations, indicates that the spin density is localized mainly on two to three porphyrin units rather than being distributed evenly over the whole π-system. The sensitivity of the zero-field splitting parameters to changes in geometry was investigated by comparing free linear oligomers with oligomers bound to a hexapyridyl template. Significant changes in the zero-field splitting parameter D were observed, while the proton hyperfine couplings show no change in the extent of triplet state delocalization. The triplet state of the cyclic porphyrin hexamer has a much decreased zero-field splitting parameter D and much smaller proton hyperfine couplings with respect to the monomeric unit, indicating complete delocalization over six porphyrin units in this symmetric system. This surprising result provides the first evidence for extensive triplet state delocalization in an artificial supramolecular assembly of porphyrins. PMID:26035477

  3. Higher triplet state of fullerene C70 revealed by electron spin relaxation

    NASA Astrophysics Data System (ADS)

    Uvarov, Mikhail N.; Behrends, Jan; Kulik, Leonid V.

    2015-12-01

    Spin-lattice relaxation times T1 of photoexcited triplets 3C70 in glassy decalin were obtained from electron spin echo inversion recovery dependences. In the range 30-100 K, the temperature dependence of T1 was fitted by the Arrhenius law with an activation energy of 172 cm-1. This indicates that the dominant relaxation process of 3C70 is described by an Orbach-Aminov mechanism involving the higher triplet state t2 which lies 172 cm-1 above the lowest triplet state t1. Chemical modification of C70 fullerene not only decreases the intrinsic triplet lifetime by about ten times but also increases T1 by several orders of magnitude. The reason for this is the presence of a low-lying excited triplet state in 3C70 and its absence in triplet C70 derivatives. The presence of the higher triplet state in C70 is in good agreement with the previous results from phosphorescence spectroscopy.

  4. Higher triplet state of fullerene C70 revealed by electron spin relaxation.

    PubMed

    Uvarov, Mikhail N; Behrends, Jan; Kulik, Leonid V

    2015-12-28

    Spin-lattice relaxation times T1 of photoexcited triplets (3)C70 in glassy decalin were obtained from electron spin echo inversion recovery dependences. In the range 30-100 K, the temperature dependence of T1 was fitted by the Arrhenius law with an activation energy of 172 cm(-1). This indicates that the dominant relaxation process of (3)C70 is described by an Orbach-Aminov mechanism involving the higher triplet state t2 which lies 172 cm(-1) above the lowest triplet state t1. Chemical modification of C70 fullerene not only decreases the intrinsic triplet lifetime by about ten times but also increases T1 by several orders of magnitude. The reason for this is the presence of a low-lying excited triplet state in (3)C70 and its absence in triplet C70 derivatives. The presence of the higher triplet state in C70 is in good agreement with the previous results from phosphorescence spectroscopy. PMID:26723678

  5. 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.

  6. Quenching of aromatic hydrocarbon triplet states by stable carbon free radicals

    NASA Astrophysics Data System (ADS)

    Watkins, A. R.

    1980-10-01

    Quenching of the triplet states of a series of polynuclear aromatic hydrocarbons in solution by three members of the bis-biphenylene allyl radical family has been studied. Bimolecular rate constants for the quenching process have values corresponding to a diffusion controlled process; in contrast to quenching by nitroxide radicals, there is no clear dependence of quenching rate constant on the triplet energy of the hydrocarbon being quenched. It is proposed that the mechanism leading to quenching is based on an exchange interaction between the tree radical and the triplet state.

  7. Spectroscopy of triplet states of Rb{sub 2} by femtosecond pump-probe photoionization of doped helium nanodroplets

    SciTech Connect

    Mudrich, M.; Heister, Ph.; Hippler, T.; Giese, Ch.; Stienkemeier, F.; Dulieu, O.

    2009-10-15

    The dynamics of vibrational wave packets in triplet states of rubidium dimers (Rb{sub 2}) formed on helium nanodroplets are studied using femtosecond pump-probe photoionization spectroscopy. Due to fast desorption of the excited Rb{sub 2} molecules off the droplets and due to their low internal temperature, wave-packet oscillations can be followed up to very long pump-probe delay times > or approx. 1.5 ns. In the first-excited triplet state (1){sup 3}{sigma}{sub g}{sup +}, full and fractional revivals are observed with high contrast. Fourier analysis provides high-resolution vibrational spectra which are in excellent agreement with ab initio calculations.

  8. 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)??* character in the T1 state. The zero-field splitting (ZFS) parameter in the T1 state is D** = 0.113 cm(-1). PMID:23136952

  9. Quantum chemistry-based interpretations on the lowest triplet state of luminescent lanthanides complexes. Part 1. Relation between the triplet state energy of hydroxamate complexes and their luminescence properties.

    PubMed

    Gutierrez, Fabien; Tedeschi, Christine; Maron, Laurent; Daudey, Jean-Pierre; Poteau, Romuald; Azema, Jolle; Tisns, Pierre; Picard, Claude

    2004-05-01

    In this paper, we evaluate the potential use of theoretical calculations to obtain an energy scale of the lowest ligand-centred triplet excited state in luminescent terbium(III) complexes. In these complexes, non-radiative deactivation of the terbium emitting state via a back-energy transfer process (T1<--Tb(5D4)) is a common quenching process. Consequently the prediction of the energy gap between these two excited states should be useful for programming highly luminescent Tb(III) systems. We report on a strategy based upon experimental and theoretical investigations of the excited state properties of a series of four simple aromatic hydroxamate ligands coordinated to Tb(III) and Gd(III) ions. By using previously reported crystallographic data, the structural and energies properties of these systems were investigated in the ground and first excited triplet states at the density functional theory (DFT) level of calculations. Our theoretical results are consistent with a triplet excited state T1 which is localised on one ligand only and whose the energy level is independent of the lanthanide ion nature (Tb(III), Gd(III)). A good agreement between the calculated adiabatic transition energies and experimental data derived from emission spectra is obtained when a corrective term is considered. These satisfactory results are an indication that this type of modelling can lead to discriminate in terms of the position of the lowest ligand triplet energy level the best antenna among a family of chromophoric compounds. In addition this theoretical approach has provided indications that the difference between the adiabatic transition energies of all the investigated complexes can be mainly explained by metal-ligand electrostatic interactions. The influence of the number of antennae on the quantum yield and the luminescence lifetime is discussed. PMID:15252626

  10. Quenching of triplet states of phenazine and its mono-, di-,and tetrabenzo derivatives and of their triplet exciplexes with dimethylaniline by oxygen

    SciTech Connect

    Osipov, V.V.; Dilung, I.I.; Usacheva, M.N.

    1986-05-01

    This paper studies the quenching of triplet states of phenazine and its benzo derivatives, as well as of their triplet exciplexes with dimethylaniline, by oxygen. A method which permits the quantitative evaluation of the concentration of the dissolved oxygen has been described. The calculated values of the rate constants of the quenching of the T states of the azines studied and their exiplexes have been presented. The role of donor-acceptor interactions in the quenching mechanism has been discussed.

  11. Electronic structures and dynamics of the excited triplet states of ?,?-diphenylpolyynes

    NASA Astrophysics Data System (ADS)

    Nagano, Yasutomo; Ikoma, Tadaaki; Akiyama, Kimio; Tero-Kubota, Shozo

    2001-01-01

    The lowest excited triplet (T1) states of diphenylacetylene and several ?,?-diphenylpolyynes (DPY) having two, three, four and six triple bonds were studied using continuous wave time-resolved electron paramagnetic resonance (CW-TREPR), pulsed EPR, and phosphorescence spectroscopy. Linear and planar molecular structures in the T1 states of DPY were suggested from the magnetophotoselection experiments and observation of a strong 0-0 band in the well-resolved phosphorescence spectra. The spin density distributions, which were obtained by electron spin echo envelope modulation measurements and semi-empirical molecular orbital calculations, and the phosphorescence polarization normal to the long axis of molecule for the 0-0 bands suggested that the T1 states of DPY have a 3B1u(?x?x*) electronic configuration. DPY showed an abnormally large |D| value of the zero-field splitting parameters that increased with increasing molecular size. Such an unusual behavior of the D values is interpreted in terms of the spin-orbit interaction between the T1 and 3Au(?x?y*) states mainly due to their energy proximity which is probably characteristic of the excited states for the polyynes. The estimated energy gap between the 3?x?y* and 3?x?x* states for DPY ranges from 2900 cm-1 to 1400 cm-1. There existed a good correlation between the acceleration of the nonradiative decay rate constant from the T1 state and appearance of a ring twisting vibronic band with b1g symmetry in the phosphorescence spectra for DPY. Therefore, we concluded that the vibronic interaction between the 3?x?y* and 3?x?x* states promoted by the b1g vibration leads to a broadening of the potential surface of the T1 state which results in the fast radiationless decay to the ground state.

  12. Valley spin-orbit interaction for the triplet and doublet 1sground states of lithium donor center in monoisotopic {sup 28}Si

    SciTech Connect

    Ezhevskii, Alexander A.; Popkov, Sergey A.; Soukhorukov, Andrey V.; Guseinov, Davud V.; Konakov, Anton A.; Abrosimov, Nikolai V.; Riemann, Helge

    2013-12-04

    Valley spin-orbit interaction for the triplet and doublet 1s-ground states of lithium donor center in monoisotopic {sup 28}Si was studied in order to determine its contribution to the electron spin relaxation rate. We observed new electron paramagnetic resonance spectra of lithium in monoisotopic silicon with g<2.000 and found the spin Hamiltonian parameters for it. Using our experimental results and taking into account spin-orbit coupling between the triplet states and the triplet and doublet states we found that the lithium donor electron spectrum and g-factors for its states strongly depend on both the internal strains in the crystal and the intervalley spin-orbit interactions.

  13. Photodissociation and radiative association of HeH+ in the metastable triplet state.

    PubMed

    Loreau, J; Vranckx, S; Desouter-Lecomte, M; Vaeck, N; Dalgarno, A

    2013-10-01

    We investigate the photodissociation of HeH(+) in the metastable triplet state as well as its formation through the inverse process, radiative association. In models of astrophysical plasmas, HeH(+) is assumed to be present only in the ground state, and the influence of the triplet state has not been explored. It may be formed by radiative association during collisions between a proton and metastable helium, which are present in significant concentrations in nebulae. The triplet state can also be formed by association of He(+) and H, although this process is less likely to occur. We compute the cross sections and rate coefficients corresponding to the photodissociation of the triplet state by UV photons from a central star using a wave packet method. We show that the photodissociation cross sections depend strongly on the initial vibrational state and that the effects of excited electronic states and nonadiabatic couplings cannot be neglected. We then calculate the cross section and rate coefficient for the radiative association of HeH(+) in the metastable triplet state. PMID:23437906

  14. Temperature-dependent Mollow triplet spectra from a single quantum dot: Rabi frequency renormalization and sideband linewidth insensitivity.

    PubMed

    Wei, Yu-Jia; He, Yu; He, Yu-Ming; Lu, Chao-Yang; Pan, Jian-Wei; Schneider, Christian; Kamp, Martin; Hfling, Sven; McCutcheon, Dara P S; Nazir, Ahsan

    2014-08-29

    We investigate temperature-dependent resonance fluorescence spectra obtained from a single self-assembled quantum dot. A decrease of the Mollow triplet sideband splitting is observed with increasing temperature, an effect we attribute to a phonon-induced renormalization of the driven dot Rabi frequency. We also present first evidence for a nonperturbative regime of phonon coupling, in which the expected linear increase in sideband linewidth as a function of temperature is canceled by the corresponding reduction in Rabi frequency. These results indicate that dephasing in semiconductor quantum dots may be less sensitive to changes in temperature than expected from a standard weak-coupling analysis of phonon effects. PMID:25216004

  15. Spectroscopy and photophysics of self-organized zinc porphyrin nanolayers. 3. Fluorescence detected magnetic resonance of triplet States.

    PubMed

    Schaafsma, Tjeerd; Dag, Inbar; Sitters, Rolf; Glasbeek, Max; Lifshitz, Efrat

    2005-09-15

    Fluorescence detected magnetic resonance (FDMR) has been applied to approximately 25-nm-thick porphyrin films, containing ordered domains of zinc tetra-(p-octylphenyl)-porphyrin (ZnTOPP) spin-coated onto quartz slides. Illuminating the films at 1.4 K with 457.9-nm light from a continuous wave Ar(+) laser produces at least two different, Jahn-Teller-distorted, ZnTOPP triplet species, labeled i and ii. Microwave-induced magnetic resonance of i and ii in the absence or presence of an externally applied magnetic field affects the fluorescence intensity of ZnTOPP, thus allowing FDMR. For triplet species i, formed in films spin-coated from toluene solution, the zero-field splitting (ZFS) parameters were determined as |D| = (316.9 +/- 0.1) x 10(-4) cm(-1) and |E| = (32.0 +/- 0.5) x 10(-4) cm(-1). By exposure of the spin-coated films to chloroform vapor at room temperature, triplet i is converted into species ii, with |D| = (295 +/- 3) x 10(-4) cm(-1) and |E| = (121 +/- 3) x 10(-4) cm(-1). For the excited triplet state of ZnTOPP in a toluene glass, ZFS parameters with values of |D| = (295 +/- 1) x 10(-4) cm(-1) and |E| = (91 +/- 1) x 10(-4) cm(-1) are found. From a combined study of the FDMR- and microwave-induced fluorescence spectra, i and ii are identified as unligated and ligated ZnTOPP triplet species, respectively. From the asymmetrically shaped zero-field FDMR signals of i, we conclude that the local crystal field perturbations of the stacked molecules are anisotropic. The FDMR results of the ZnTOPP films are compared with those for a film of zinc tetraphenylporphyrin (ZnTPP), which lacks the octyl substituents, and therefore is nonordered. Upon illumination, the ZnTPP films contain only a single, ligated, triplet species with ZFS parameters very similar to those of ligated ZnTOPP. At approximately 5 K, the lifetime of triplet i is considerably shortened compared to that of ZnTOPP in a glass at the same temperature. PMID:16853173

  16. Triplet state formation in photovoltaic blends of DPP-type copolymers and PC71 BM.

    PubMed

    Ochsmann, Julian R; Chandran, Deepak; Gehrig, Dominik W; Anwar, Husna; Madathil, Pramod Kandoth; Lee, Kwang-Sup; Laquai, Frdric

    2015-06-01

    The exciton dynamics in pristine films of two structurally related low-bandgap diketopyrrolopyrrole (DPP)-based donor-acceptor copolymers and the photophysical processes in bulk heterojunction solar cells using DPP copolymer:PC71 BM blends are investigated by broadband transient absorption (TA) pump-probe experiments covering the vis-near-infrared spectral and fs-?s dynamic range. The experiments reveal surprisingly short exciton lifetimes in the pristine poly-mer films in conjunction with fast triplet state formation. An in-depth analysis of the TA data by multivariate curve resolution analysis shows that in blends with fullerene as acceptor ultrafast exciton dissociation creates charge carriers, which then rapidly recombine on the sub-ns timescale. Furthermore, at the carrier densities created by pulsed laser excitation the charge carrier recombination leads to a substantial population of the polymer triplet state. In fact, virtually quantitative formation of triplet states is observed on the sub-ns timescale. However, the quantitative triplet formation on the sub-ns timescale is not in line with the power conversion efficiencies of devices indicating that triplet state formation is an intensity-dependent process in these blends and is reduced under solar illumination conditions, as free charge carriers can be extracted from the photoactive layer in devices. PMID:25923668

  17. Triplet excited States as a source of relevant (bio)chemical information.

    PubMed

    Jimnez, M Consuelo; Miranda, Miguel A

    2014-01-01

    The properties of triplet excited states are markedly medium-dependent, which turns this species into valuable tools for investigating the microenvironments existing in protein binding pockets. Monitoring of the triplet excited state behavior of drugs within transport proteins (serum albumins and ?1-acid glycoproteins) by laser flash photolysis constitutes a valuable source of information on the strength of interaction, conformational freedom and protection from oxygen or other external quenchers. With proteins, formation of spatially confined triplet excited states is favored over competitive processes affording ionic species. Remarkably, under aerobic atmosphere, the triplet decay of drug@protein complexes is dramatically longer than in bulk solution. This offers a convenient dynamic range for assignment of different triplet populations or for stereochemical discrimination. In this review, selected examples of the application of the laser flash photolysis technique are described, including drug distribution between the bulk solution and the protein cavities, or between two types of proteins, detection of drug-drug interactions inside proteins, and enzyme-like activity processes mediated by proteins. Finally, protein encapsulation can also modify the photoreactivity of the guest. This is illustrated by presenting an example of retarded photooxidation. PMID:25515745

  18. Investigation of the triplet state of chlorophylls. Technical progress report, May 1, 1979-April 30, 1980

    SciTech Connect

    Clarke, R.H.

    1980-01-01

    The triplet state of chlorophyll has been utilized as a nondestructive probe into the structural and dynamical nature of the photosynthetic apparatus, both in vitro and in isolated in vivo subunits. During the past year, using zero-field triplet state optically detected magnetic resonance spectroscopy, the research program has examined triplet energy transfer between photosynthetic pigments in solution; has isolated and studied subchloroplast particles enriched with photo-system I and the light harvesting chlorophyll protein (antenna) system; and has examined model chlorophyll-protein systems, specifically chlorophyll protein 668 and the reconstituted myoglobins. The overall aim of the research program has been to detail the physical features and interactions of the photosynthetic pigment systems through examination of structural subunits of the photosynthetic apparatus and model systems which represent them.

  19. Solid state photon upconversion utilizing thermally activated delayed fluorescence molecules as triplet sensitizer

    NASA Astrophysics Data System (ADS)

    Wu, Tony C.; Congreve, Daniel N.; Baldo, Marc A.

    2015-07-01

    The ability to upconvert light is useful for a range of applications, from biological imaging to solar cells. But modern technologies have struggled to upconvert incoherent incident light at low intensities. Here, we report solid state photon upconversion employing triplet-triplet exciton annihilation in an organic semiconductor, sensitized by a thermally activated-delayed fluorescence (TADF) dye. Compared to conventional phosphorescent sensitizers, the TADF dye maximizes the wavelength shift in upconversion due to its small singlet-triplet splitting. The efficiency of energy transfer from the TADF dye is 9.1%, and the conversion yield of sensitizer exciton pairs to singlet excitons in the annihilator is 1.1%. Our results demonstrate upconversion in solid state geometries and with non-heavy metal-based sensitizer materials.

  20. Charge Transfer and Triplet States in High Efficiency OPV Materials and Devices

    NASA Astrophysics Data System (ADS)

    Dyakonov, Vladimir

    2013-03-01

    The advantage of using polymers and molecules in electronic devices, such as light-emitting diodes (LED), field-effect transistors (FET) and, more recently, solar cells (SC) is justified by the unique combination of high device performance and processing of the semiconductors used. Power conversion efficiency of nanostructured polymer SC is in the range of 10% on lab scale, making them ready for up-scaling. Efficient charge carrier generation and recombination in SC are strongly related to dissociation of the primary singlet excitons. The dissociation (or charge transfer) process should be very efficient in photovoltaics. The mechanisms governing charge carrier generation, recombination and transport in SC based on the so-called bulk-heterojunctions, i.e. blends of two or more semiconductors with different electron affinities, appear to be very complex, as they imply the presence of the intermediate excited states, neutral and charged ones. Charge transfer states, or polaron pairs, are the intermediate states between free electrons/holes and strongly bound excitons. Interestingly, the mostly efficient OLEDs to date are based on the so-called triplet emitters, which utilize the triplet-triplet annihilation process. In SC, recent investigations indicated that on illumination of the device active layer, not only mobile charges but also triplet states were formed. With respect to triplets, it is unclear how these excited states are generated, via inter-system crossing or via back transfer of the electron from acceptor to donor. Triplet formation may be considered as charge carrier loss channel; however, the fusion of two triplets may lead to a formation of singlet excitons instead. In such case, a generation of charges by utilizing of the so far unused photons will be possible. The fundamental understanding of the processes involving the charge transfer and triplet states and their relation to nanoscale morphology and/or energetics of blends is essential for the optimization of the performance of molecular photovoltaic devices. I will present the state of the art in this field and discuss the mechanisms of polaron pair generation and recombination in the novel low band gap polymer-fullerene blends as well as in high-efficiency SC. This work was financially supported by the German Research Council (DFG) within the SPP1355 Project ``Elementary processes in organic photovoltaics'' under contract DY18/6.

  1. 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.

  2. Observation of a thermally accessible triplet state resulting from rotation around a main-group ??bond.

    PubMed

    Kostenko, Arseni; Tumanskii, Boris; Karni, Miriam; Inoue, Shigeyoshi; Ichinohe, Masaaki; Sekiguchi, Akira; Apeloig, Yitzhak

    2015-10-01

    We report the first direct spectroscopic observation by electron paramagnetic resonance (EPR) spectroscopy of a triplet diradical that is formed in a thermally induced rotation around a main-group ??bond, that is, the Si?Si double bond of tetrakis(di-tert-butylmethylsilyl)disilene (1). The highly twisted ground-state geometry of singlet 1 allows access to the perpendicular triplet diradical?2 at moderate temperatures of 350-410?K. DFT-calculated zero-field splitting (ZFS) parameters of 2 accurately reproduce the experimentally observed half-field transition. Experiment and theory suggest a thermal equilibrium between 1 and 2 with a very low singlet-triplet energy gap of only 7.3?kcal?mol(-1) . PMID:26297814

  3. Triplet state photochemistry and the three-state crossing of acetophenone within time-dependent density-functional theory

    SciTech Connect

    Huix-Rotllant, Miquel Ferré, Nicolas

    2014-04-07

    Even though time-dependent density-functional theory (TDDFT) works generally well for describing excited states energies and properties in the Franck-Condon region, it can dramatically fail in predicting photochemistry, notably when electronic state crossings occur. Here, we assess the ability of TDDFT to describe the photochemistry of an important class of triplet sensitizers, namely, aromatic ketones. We take acetophenone as a test molecule, for which accurate ab initio results exist in the literature. Triplet acetophenone is generated thanks to an exotic three-state crossing involving one singlet and two triplets states (i.e., a simultaneous intersystem crossing and triplet conical intersection), thus being a stringent test for approximate TDDFT. We show that most exchange-correlation functionals can only give a semi-qualitative picture of the overall photochemistry, in which the three-state crossing is rather represented as a triplet conical intersection separated from the intersystem crossing. The best result overall is given by the double hybrid functional mPW2PLYP, which is even able to reproduce quantitatively the three-state crossing region. We rationalize this results by noting that double hybrid functionals include a larger portion of double excitation character to the excited states.

  4. Photosensitized triplet state of 1,3-cyclodienes detected by a time-resolved ESR method

    NASA Astrophysics Data System (ADS)

    Hanazaki, Akiko; Murai, Hisao; Kuwata, Keiji

    1992-09-01

    The excited triplet states of 1,3-cyclodienes produced by photosensitization are studied by time-resolved ESR at 77 K. The zero-field splitting (ZFS) constants of 1,3-cyclodienes are influenced by the change of the molecular framework. Simple Hckel MO calculation provides qualitative aspects of ZFS constants against the twisting in conjugated parts of dienes.

  5. All-optical control of quantum state singlet-triplet character by Autler-Townes splitting.

    NASA Astrophysics Data System (ADS)

    Salihoglu, Omer; Qi, Peng; Ingram, Sonja; Ahmed, Ergin; Lyyra, Marjatta

    2008-05-01

    Using a four level extended Lambda excitation scheme [1] in ^7Li2, we have demonstrated that Autler --Townes splitting can be used to modify the mixing coefficients and thus the amount of singlet or triplet character of a pair of rovibrational A^1?u^+ and b^3?u states perturbed by the spin-orbit interaction. The singlet triplet pair of levels is naturally separated by an energy gap of 600 MHz. As indicated earlier [2] such control of molecular valence electron spin polarization can be used to create new gateway levels to the dark manifold of triplet states in molecular systems with a singlet ground state in which the spin orbit interaction is very weak and only a few gateway levels to triplet states exist naturally. In addition, a direct measurement of the spin-orbit interaction strength is possible from the observed AT splitting lineshape [2]. *E. Ahmed et al., J. Chem. Phys. 124, 084308 --1 to 13 (2006). *T. Kirova and F. C. Spano, Phys. Rev. A, 71, 063816 (2005).

  6. The evolution of spin distribution in the photoexcited triplet state of ethyne-elaborated porphyrins.

    PubMed

    Angiolillo, Paul J; Rawson, Jeff; Frail, Paul R; Therien, Michael J

    2013-10-28

    Ethyne elaboration of a (porphinato)Zn(II) (PZn) chromophoric core renders fine control over the zero-field splitting (ZFS) parameters of the lowest energy photoexcited triplet state (T1), resulting in the ability to manipulate the spin distribution and establish highly symmetrical coincident optical and magnetic principal axes. PMID:23982224

  7. Theoretical study of long oligothiophene dications: bipolaron vs polaron pair vs triplet state.

    PubMed

    Zade, Sanjio S; Bendikov, Michael

    2006-08-17

    A series of oligothiophene dications (from the sexithiophene dication to the 50-mer oligothiophene dication, nT2+, n = 6-50) were studied. Density functional theory (DFT) at the B3LYP/6-31G(d) level and, in some cases, also at BLYP/6-31Gd, was applied to study the singlet and triplet states of the whole series. We found that the singlet state is the ground state for all oligothiophene dications up to the 20-mer, and that the singlet and triplet states are degenerate for longer oligomers. Thus, the triplet state is never a pure ground state for these dications. We found that, for short oligothiophenes dication (e.g., 6T2+), the bipolaron state is the more important state, with only a small contribution made by the polaron pair state. For medium size oligothiophene dications (e.g., 14T2+), both the bipolaron state and the polaron-pair state contribute to the electronic structure. Finally, in long oligothiophene dications, such as 30T2+ and 50T2+, the contribution from the polaron pair state becomes dominant, and these molecules can be considered as consisting of two independent cation radicals or a polaron pair. Results from isodesmic reactions show that the stability of oligothiophene cation radicals over dications is inversely proportional to chain length. Small oligothiophene dications (n = 6-12) were studied at the CASSCF(m,m)/6-31G(d) (m = 4, 6, and 10) level. The major conclusions of this paper regarding the relative energy of the singlet state versus the triplet state and regarding the relative stability of the bipolaron versus the polaron pair were also supported by CASSCF calculations. PMID:16898734

  8. 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.

  9. Measurements and Analysis of Helium-Like Triplet Ratios in the X-Ray Spectra of O-Type Stars

    SciTech Connect

    Leutenegger, Maurice A.; Paerels, Frits B.S.; Kahn, Steven M.; Cohen, David H.; /Swarthmore Coll.

    2006-06-19

    We discuss new methods of measuring and interpreting the forbidden-to-intercombination line ratios of helium-like triplets in the X-ray spectra of O-type stars, including accounting for the spatial distribution of the X-ray emitting plasma and using the detailed photospheric UV spectrum. Measurements are made for four O stars using archival Chandra HETGS data. We assume an X-ray emitting plasma spatially distributed in the wind above some minimum radius R{sub 0}. We find minimum radii of formation typically in the range of 1.25 < R{sub 0}/R{sub *} < 1.67, which is consistent with results obtained independently from line profile fits. We find no evidence for anomalously low f/i ratios and we do not require the existence of X-ray emitting plasmas at radii that are too small to generate sufficiently strong shocks.

  10. Formation of Triplet Positron-helium Bound State by Stripping of Positronium Atoms in Collision with Ground State Helium

    NASA Technical Reports Server (NTRS)

    Drachman, Richard J.

    2006-01-01

    Formation of triplet positron-helium bound state by stripping of positronium atoms in collision with ground state helium JOSEPH DI RlENZI, College of Notre Dame of Maryland, RICHARD J. DRACHMAN, NASA/Goddard Space Flight Center - The system consisting of a positron and a helium atom in the triplet state e(+)He(S-3)(sup e) was conjectured long ago to be stable [1]. Its stability has recently been established rigorously [2], and the values of the energies of dissociation into the ground states of Ps and He(+) have also been reported [3] and [4]. We have evaluated the cross-section for this system formed by radiative attachment of a positron in triplet He state and found it to be small [5]. The mechanism of production suggested here should result in a larger cross-section (of atomic size) which we are determining using the Born approximation with simplified initial and final wave functions.

  11. Aqueous secondary organic aerosol (SOA) production from the oxidation of phenols by triplet excited state organics

    NASA Astrophysics Data System (ADS)

    Smith, J.; Yu, L.; Zhang, Q.; Anastasio, C.

    2011-12-01

    Recent literature has shown that atmospheric condensed-phase chemistry can play a significant role in the evolution of organic aerosols, including the formation of secondary organic aerosol (SOA). SOA formation from the oxidation of volatile organic compounds (VOCs) in the aqueous phase has largely focused on oxidations involving the hydroxyl radical and other oxidants, such as photochemically created triplet excited states, have not been fully investigated. Phenolic compounds are one of the primary carbon emission classes from biomass and wood combustion and have significant water solubility. Once in the aqueous phase, phenolic compounds can react with the triplet excited states of non-phenolic aromatic carbonyls (NPCs), particle-bound organics that are also emitted in large quantities from wood combustion. The oxidation of phenolic species in the condensed phase by triplet excited states can result in the production of SOA. A main goal of this study was to investigate bulk solution reaction kinetics under atmospherically relevant conditions in order to ascertain how these reactions can impact aqueous-phase SOA production. In our experiments, we studied the reactions of five phenols (phenol, guaiacol, syringol, catechol, and resorcinol) with the triplet state of 3,4-dimethoxybenzaldehyde (34-DMB) during simulated solar radiation. We have characterized the impacts of pH, ionic strength and reactant concentrations on the reaction behavior of this system. In addition, we analyzed the SOA formed using high-resolution aerosol mass spectrometry, ion chromatography, and liquid chromatography-mass spectrometry to infer the reaction mechanisms. Our evidence suggests that under atmospherically relevant conditions, triplet excited states can be the dominant oxidant of phenolics and contribute significantly to the total SOA budget.

  12. Dual phosphorescence from 2-(2?-hydroxyphenyl)benzoxazole due to keto-enol tautomerism in the metastable triplet state

    NASA Astrophysics Data System (ADS)

    Prieto, M. Flor Rodrguez; Nickel, Bernhard; Grellmann, Karl H.; Mordzi?ski, Andrzej

    1988-05-01

    The photoexcitation of liquid solutions of 2-(2'-hydroxyphenyl)benzoxazole (HBO) in alkanes leads to a dual phosphorescence which can be assigned to the keto and enol forms of HBO. The keto-enol tautomerism in the metastable triplet state of HBO is practically independent of temperature. The keto and enol bands of the phosphorescence from HBO decay monoexponentially with the same rate constant. The experimental data on the phosphorescence from HBO are consistent with those on the transient absorption of HBO. At high triplet concentration and low solvent viscosity, a delayed fluorescence from HBO due to triplet-triplet annihilation is also observed.

  13. Highly efficient multifluorenyl host materials with unsymmetrical molecular configurations and localized triplet States for green and red phosphorescent devices.

    PubMed

    Han, Chunmiao; Zhu, Liping; Li, Jing; Zhao, Fangchao; Zhang, Zhen; Xu, Hui; Deng, Zhaopeng; Ma, Dongge; Yan, Pengfei

    2014-11-01

    Highly efficient green and red electro-phosphorescence is achieved in devices with the host material DPESPODEF3. The multiple fluorenyl moieties of the host material are arranged such that it has an unsymmetrical molecular configuration, and its triplet-state location is tuned such that it has independent energy (ET) and charge transfer (CT) channels. As a result, DPESPODEF3 can suppress triplet-triplet annihilation and triplet-polaron quenching. In the resulting green and red phosphorescent devices, impressive external quantum efficiencies of ca. 20% and 16% and power efficiencies of ca. 75 and 20 lm W(-1) , respectively, are observed. PMID:25212516

  14. Triplet excited state distortions in a pyrazolate bridged platinum dimer measured by X-ray transient absorption spectroscopy.

    PubMed

    Lockard, Jenny V; Rachford, Aaron A; Smolentsev, Grigory; Stickrath, Andrew B; Wang, Xianghuai; Zhang, Xiaoyi; Atenkoffer, Klaus; Jennings, Guy; Soldatov, Alexander; Rheingold, Arnold L; Castellano, Felix N; Chen, Lin X

    2010-12-01

    The excited-state structure of a dinuclear platinum(II) complex with tert-butyl substituted pyrazolate bridging units, [Pt(ppy)(?-(t)Bu(2)pz)](2) (ppy = 2-phenylpyridine; (t)Bu(2)pz = 3,5-di-tert-butylpyrazolate) is studied by X-ray transient absorption (XTA) spectroscopy to reveal the transient electronic and nuclear geometry. DFT calculations predict that the lowest energy triplet excited state, assigned to a metal-metal-to-ligand charge transfer (MMLCT) transition, has a contraction in the Pt-Pt distance. The Pt-Pt bond length and other structural parameters extracted from fitting the experimental XTA difference spectra from full multiple scattering (FMS) and multidimensional interpolation calculations indicates a metal-metal distance decrease by approximately 0.2 in the triplet excited state. The advantages and challenges of this approach in resolving dynamic transient structures of nonbonding or weak-bonding dinuclear metal complexes in solution are discussed. PMID:21067164

  15. Triplet state quenching of phenosafranine dye by indolic compounds studied by transient absorption spectroscopy.

    PubMed

    Broglia, Martn F; Previtali, Carlos M; Bertolotti, Sonia G

    2015-02-01

    The interaction of the triplet state of the synthetic dye phenosafranine (3,7-diamino-5-phenylphenazinium chloride) with indolic compounds of biological relevance was investigated in water by means of laser flash photolysis. The rate constants for the triplet quenching were determined. The quenching process may be explained by an electron transfer from the indole to the dye in its triplet state. The rate constants present a typical dependence of an electron transfer process with the one-electron oxidation potential of the indole. Indole-3-acetic acid and its homologous indole propionic and indole butyric acids are the most effective quenchers with rate constants reaching the diffusion limit. Rate constants for indole itself, tryptophan and indole-3 carboxylic acid are one order of magnitude lower. The electron transfer nature of the quenching reaction is further confirmed by the detection of the semi-reduced form of the dye by its transient absorption. The absorption coefficients of the transient species were estimated, and the quantum yield of the charge separation process was determined. The efficiency of formation of radical species is between 60 and 90% of the triplets intercepted. PMID:25428794

  16. High-resolution spectroscopy and quantum-defect model for the gerade triplet np and nf Rydberg states of He{sub 2}

    SciTech Connect

    Sprecher, D.; Liu, J.; Krhenmann, T.; Schfer, M.; Merkt, F.

    2014-02-14

    Photoionization spectra and Rydberg-state-resolved threshold-ionization spectra of the gerade triplet np Rydberg states of {sup 4}He{sub 2} located in the vicinity of the X{sup +2}?{sub u}{sup +}(?{sup +} =0) ionization threshold were recorded from the 2s?a{sup 3}?{sub u}{sup +} metastable state. An accuracy of 0.01?cm{sup ?1} was achieved for the experimental term values of the observed Rydberg states. The data were combined with spectroscopic data on low-lying triplet np and nf Rydberg states from the literature to derive energy- and internuclear-distance-dependent eigenquantum-defect parameters of multichannel quantum-defect theory (MQDT). The MQDT calculations reproduce the experimental data within their experimental uncertainties and enabled the derivation of potential-energy curves for the lowest triplet p Rydberg states (n = 25) of He{sub 2}. The eigenquantum-defect parameters describing the p?-f interaction were found to be larger than 0.002 at the energies corresponding to the high-n Rydberg states, so that the p?-f interaction plays an important role in the autoionization dynamics of np Rydberg states with ?{sup +} = 0. By extrapolating the experimental term values of triplet np Rydberg states of {sup 4}He{sub 2} in the range of principal quantum number n between 87 and 110, the positions of the (?{sup +} = 0, N{sup +} = 3) and (?{sup +} = 0, N{sup +} = 5) levels of the ground state of {sup 4}He{sub 2}{sup +} were determined to lie 70.937(3)?cm{sup ?1} and 198.369(6)?cm{sup ?1}, respectively, above the (?{sup +} = 0, N{sup +} = 1) ground rotational level.

  17. Triplet ground state of the neutral oxygen-vacancy donor in rutile TiO2

    NASA Astrophysics Data System (ADS)

    Brant, A. T.; Golden, E. M.; Giles, N. C.; Yang, Shan; Sarker, M. A. R.; Watauchi, S.; Nagao, M.; Tanaka, I.; Tryk, D. A.; Manivannan, A.; Halliburton, L. E.

    2014-03-01

    Electron paramagnetic resonance (EPR) is used to investigate the triplet (S = 1) ground state of the neutral oxygen vacancy in bulk rutile TiO2 crystals. This shallow donor consists of an oxygen vacancy with two nearest-neighbor, exchange-coupled Ti3+ ions located along the [001] direction and equidistant from the vacancy. The spins of the two trapped electrons, one at each Ti3+ ion, align parallel to give the S = 1 state. These neutral oxygen vacancies are formed near 25 K in as-grown oxidized TiO2 crystals by illuminating with sub-band-gap 442 nm laser light. The angular dependence of the EPR spectra provides the principal values and axes for the g and D matrices. Observations of the 47Ti and 49Ti hyperfine lines when the magnetic field is along high-symmetry directions show that the two Ti3+ ions are equivalent; i.e., they have equal hyperfine A matrices. The A matrix for each Ti3+ ion in the neutral S = 1 oxygen vacancy is approximately half of the A matrix reported earlier for the one Ti3+ ion in the singly ionized S = 1/2 oxygen vacancy [Brant et al., J. Appl. Phys. 114, 113702 (2013), 10.1063/1.4819805]. The neutral oxygen vacancies are thermally unstable above 25 K. They release an electron to the conduction band with an activation energy near 63 meV and convert to singly ionized S = 1/2 oxygen vacancies. When undoped TiO2 is sufficiently oxygen deficient (i.e., reduced), this combination of conduction band electrons and singly ionized oxygen vacancies may result in carrier-mediated ferromagnetism at room temperature.

  18. Inter-and intraspecific variation in excited-state triplet energy transfer rates in reaction centers of photosynthetic bacteria.

    SciTech Connect

    Laible, P. D.; Morris, Z. S.; Thurnauer, M. C.; Schiffer, M.; Hanson, D. K.

    2003-08-01

    In protein-cofactor reaction center (RC) complexes of purple photosynthetic bacteria, the major role of the bound carotenoid (C) is to quench the triplet state formed on the primary electron donor (P) before its sensitization of the excited singlet state of molecular oxygen from its ground triplet state. This triplet energy is transferred from P to C via the bacteriochlorophyll monomer B{sub B}. Using time-resolved electron paramagnetic resonance (TREPR), we have examined the temperature dependence of the rates of this triplet energy transfer reaction in the RC of three wild-type species of purple nonsulfur bacteria. Species-specific differences in the rate of transfer were observed. Wild-type Rhodobacter capsulatus RCs were less efficient at the triplet transfer reaction than Rhodobacter sphaeroides RCs, but were more efficient than Rhodospirillum rubrum RCs. In addition, RCs from three mutant strains of R. capsulatus carrying substitutions of amino acids near P and B{sub B} were examined. Two of the mutant RCs showed decreased triplet transfer rates compared with wild-type RCs, whereas one of the mutant RCs demonstrated a slight increase in triplet transfer rate at low temperatures. The results show that site-specific changes within the RC of R. capsulatus can mimic interspecies differences in the rates of triplet energy transfer. This application of TREPR was instrumental in defining critical energetic and coupling factors that dictate the efficiency of this photoprotective process.

  19. Kinetic Parameters of Photo-Excited Triplet State of Pentacene Determined by Dynamic Nuclear Polarization

    NASA Astrophysics Data System (ADS)

    Kawahara, Tomomi; Sakaguchi, Satoshi; Tateishi, Kenichiro; Tang, Tsz Leung; Uesaka, Tomohiro

    2015-04-01

    The lifetimes and spin-lattice relaxation time of photo-excited triplet electron of pentacene doped in p-terphenyl at room temperature have been investigated. Values of spin-lattice relaxation time previously reported in ESR studies are inconsistent with each other. In this paper, we determined these time constants based on proton signals enhanced by dynamic nuclear polarization using the electrons (Triplet-DNP). The combined analysis of dependences of proton signal intensities on the delay time of polarization transfer and laser pulse structure allows us to disentangle contributions of the lifetimes and spin-lattice relaxation time. The lifetimes of triplet sublevels with ms = 0 and 1 were determined to be 22.3 and 88 s, respectively. The spin-lattice relaxation time was found to be longer than 300 s, hence the time evolution of the electron population in the triplet state is governed by the lifetimes. It was also found that the proton signal enhancement is limited at a high repetition rate by the partial cancellation of the electron spin polarization by the remaining population produced by the preceding laser pulses.

  20. Time-resolved resonance Raman spectroscopic studies on the triplet excited state of thioxanthone.

    PubMed

    Pandey, Rishikesh; Umapathy, Siva

    2011-07-01

    Thioxanthone has been investigated extensively owing to its unique photochemical and photophysical applications and its solvatochromic behavior. Here, we report the time-resolved resonance Raman studies on the structure of the lowest triplet excited state of thioxanthone in carbon tetrachloride. In addition, FT-IR and FT-Raman techniques have been used to study the vibrational structure in the ground state. To corroborate the experimental findings, density functional theory calculations have been carried out. Isotopic calculations and normal coordinate analysis have been used to help in assigning the observed bands to Raman vibrational modes. Structural information derived from this study is expected to help in better understanding the triplet state photochemistry of thioxanthone. PMID:21612295

  1. DERIVING METALLICITIES FROM THE INTEGRATED SPECTRA OF EXTRAGALACTIC GLOBULAR CLUSTERS USING THE NEAR-INFRARED CALCIUM TRIPLET

    SciTech Connect

    Foster, Caroline; Forbes, Duncan A.; Proctor, Robert N.; Spitler, Lee R.; Strader, Jay; Brodie, Jean P.

    2010-04-15

    The Ca II triplet (CaT) feature in the near-infrared has been employed as a metallicity indicator for individual stars as well as integrated light of Galactic globular clusters (GCs) and galaxies with varying degrees of success, and sometimes puzzling results. Using the DEIMOS multi-object spectrograph on Keck we obtain a sample of 144 integrated light spectra of GCs around the brightest group galaxy NGC 1407 to test whether the CaT index can be used as a metallicity indicator for extragalactic GCs. Different sets of single stellar population models make different predictions for the behavior of the CaT as a function of metallicity. In this work, the metallicities of the GCs around NGC 1407 are obtained from CaT index values using an empirical conversion. The measured CaT/metallicity distributions show unexpected features, the most remarkable being that the brightest red and blue GCs have similar CaT values despite their large difference in mean color. Suggested explanations for this behavior in the NGC 1407 GC system are (1) the CaT may be affected by a population of hot blue stars, (2) the CaT may saturate earlier than predicted by the models, and/or (3) color may not trace metallicity linearly. Until these possibilities are understood, the use of the CaT as a metallicity indicator for the integrated spectra of extragalactic GCs will remain problematic.

  2. Phosphorescence spectra of bacteriochlorophylls

    SciTech Connect

    Takiff, L.; Boxer, S.G.

    1988-06-22

    The authors wish to report phosphorescence spectra of the lowest triplet state of a number of bacteriochlorophylls (BChls) which provide the first accurate values for the triplet state energies of these chromophores. There have been many previous attempts to estimate the triplet state energies of bacteriochlorins motivated by the possible importance of triplet states in photosynthesis, the utility of these chromophores as sensitizers and quenchers of singlet oxygen, model studies of electron transfer, and intrinsic theoretical interest in the excited state energies of extended conjugated macrocycles.

  3. Triplet state spectroscopy and photofragment dynamics of N2 + 2

    NASA Astrophysics Data System (ADS)

    Mullin, Amy S.; Szaflarski, Diane M.; Yokoyama, Kazushige; Gerber, G.; Lineberger, W. C.

    1992-03-01

    The photofragment spectrum of N2+2?N+(3Pg)+N+(3Pg) has been studied using a coaxial laser-ion beam spectrometer. Transitions from the excited 3?+u(v=0,1) state of N2+2 to the predissociative 3?g(v=0) state result in two bands with dense rotational structure at 15 300 and 13 100 cm-1. A complete analysis of the 27 rotational branches associated with the 3?g(v=0)?3?+u(v=0) transition provides bond lengths and spectroscopic constants for both states. A perturbation is observed in the (0,0) band, caused by the interaction of 3?+u(v=0) with 3?u(v?10). From a deperturbation analysis, the coupling constants and the energy difference between the 3?u(v?10) and 3?+u(v=0) states are determined?=1.50.1 cm-1, ?=0.2200.003 cm-1, and Tpert=36525 cm-1. A broad unstructured band at 16 400 cm-1 arises from a transition out of v=0 in the 3?+u state into a very short-lived v=1 level of the 3?g state. Vibrational spacings between v=0 and v=1 in both electronic states are determined3?+u?0=221020 cm-1 and 3?g ?0?1100 cm-1. The fragmentation of N2+2 is explored by measuring the dependence of predissociation lifetimes on the rotational quantum number of the 3?g(v=0) state. Experimentally determined lifetimes of 50-70 ps for N'=2-17 are almost independent of N' and indicate that the predissociation occurs by the interaction of 3?g(v=0) with the 3?-g continuum rather than by tunneling through the 3?g barrier.

  4. First-Principles Study of Muon Trapping in Singlet and Triplet States of Oxyhemoglobin

    NASA Astrophysics Data System (ADS)

    Pink, Roger; Badu, S. R.; Das, T. P.; Sahoo, N.; Chow, Lee; Scheicher, R. H.; Nagamine, K.

    2012-02-01

    There is great current interest in the possibility of magnetic character in oxyhemoglobin (OxyHb) due to the detection [1] of muon spin-lattice relaxation in OxyHb. First-Principles variational Hartree-Fock Many Body Perturbation Theory (VHFMBPT) technique investigations on the singlet and triplet states of pure OxyHb have shown^2 that the triplet state is considerably higher than the singlet state ruling out magnetic character. However the charge distribution obtained by the VHFMBPT procedure in both states show a number of sites that have negative charges where the trapping of muon is being investigated to examine if the energy gap in the ordering of singlet and triplet states can be reduced or reversed leading to magnetic effects. Other possible sources of magnetism in Oxyhemoglobin will also be discussed. 1. K. Nagamine et al. Proc. Japan. Acad. B-Physics 83, 120 (2007); 2. S.R. Badu et al. Reported at Third Joint HFI-NQI International Conference, CERN, Geneva, September 2010.

  5. Conformational analysis of singlet-triplet state mixing in Patern-Bchi diradicals.

    PubMed

    Kutateladze, A G

    2001-09-26

    Conformational dependence of spin-orbit coupling (SOC) in flexible Patern-Bchi (PB) diradicals has been studied with high-level ab initio methods using both (i) one-electron spin-orbit Hamiltonian with parametrized (effective) nuclear charges in conjunction with a state-averaged MCSCF wave function as implemented by Robb in Gaussian 98 and (ii) complete one- and two-electron SOC with a fully optimized MCSCF triplet wave function and frozen core singlet as implemented by Furlani in the GAMESS computational package. The ab initio results revealed two distinct areas of elevated SOC values, one corresponding to the region whereby a cisoid conformation in the C-C-O-C fragment brings the two odd-electron orbitals closer to each other, and the other area corresponding to the partially eclipsed conformation lacking direct overlap between the spin centers. In this second region the 1,4-electronic communication is mediated by the oxygen's 2p-lone pair, which is suitably oriented to play the role of a "relay-antenna". The other critical factor affecting the rate of intersystem crossing (ISC)--singlet-triplet energy separation--was computed utilizing a multireference CASSCF-MP2 method to include dynamic correlation effects. The largest singlet-triplet energy gap, approximately 2 kcal/mol, was found for a gauche conformer (also a minimum SOC conformation). Rotation about the central C-O bond either toward the fully eclipsed (0 degrees ) or the partially eclipsed (120 degrees ) conformations decreases the singlet-triplet gap while increasing the value of the SOC matrix element. These computational findings support the Griesbeck model for stereochemistry of triplet PB reactions and provide a rigorous basis for predicting the probability of ISC in diradicals separated by a partially conjugated spacer. PMID:11562209

  6. Investigation of the triplet state of chlorophylls. Progress report, May 1, 1980-April 30, 1981

    SciTech Connect

    Clarke, R.H.

    1980-12-22

    The triplet state of chlorophyll has been utilized as a nondestructive probe into the structural and dynamical nature of the photosynthetic apparatus. During the past year, using zero-field triplet state optically detected magnetic resonance spectroscopy, chlorophyll aggregates were examined in both their natural environment in vivo and in model complexes in vitro. Research efforts have focused on subchloroplast particles extracted from green plants, on chlorophyll monolayers, and on isolated chlorophyll molecules bound to both simple ligands and to complete proteins. The overall aim of the research program is to detail the physical features and interactions of the photosynthetic pigment systems through examination of structural subunits of the photosynthetic apparatus and model systems which represent them.

  7. New views of collisional vibrational relaxation: Energy removal rates and energy distributions of triplet state pyrazine

    NASA Astrophysics Data System (ADS)

    McDowell, Derek Ray

    1997-09-01

    Collisional energy removal rates from vibrationally excited T1 pyrazine are measured using the refined and validated Competitive Radiationless Decay (CRD) method. Optical excitation followed by intersystem crossing prepares a vibrationally excited vapor sample of T1 pyrazine. Tn/gets T1 transient absorption kinetics, measured with a S/N ratio of ca. 1000, provides the collisional dependence of the average triplet radiationless decay rate constant. Using a calibration between this decay constant and the triplet vibrational energy, the collisional history of the sample's vibrational energy content is deduced. This leads to the rate of collisional energy removal as a function of the triplet pyrazine's vibrational energy content. Results with a variety of small relaxers comprise the most useful database to date on collisional vibrational relaxation of a triplet state polyatomic. We find the following order of relaxer effectiveness per collision: He[<]H2[<]Ne[<]D2[<]Ar[<]N2[<]Kr[<]Xe[<]CO[<]CH4[<]CO2[<]H2OThese triplet state energy removal rates exceed those recently reported for vibrationally excited ground state pyrazine by a factor of ca. 7. In addition, a new method for determining the distribution of vibrational energy contents in an excited polyatomic sample is applied to vibrationally excited T1 pyrazine. The T1 population decays with a distribution of rate constants corresponding to the underlying distribution of vibrational energies. This rate constant distribution is extracted from decay kinetics through the use of a multi-Gaussian distribution model. The calibration between decay constant and triplet vibrational energy is used to deduce the molecular vibrational energy distribution, providing the first experimental view of an excited sample's vibrational energy distribution. Relatively narrow nascent vibrational energy distributions are progressively broadened during the early collisional encounters with a relaxer. These new vibrational energy distributions and the collisional energy removal results suggests a threshold for enhanced relaxation near 2000 cm-1 of donor vibrational energy. These intriguing results should stimulate further theoretical and experimental research into the collisional relaxation of electronically excited molecules.

  8. The impact of solvents on the singlet and triplet states of selected fluorine corroles - absorption, fluorescence, and optoacoustic studies.

    PubMed

    Bursa, Bartosz; Wrbel, Danuta; Barszcz, Boles?aw; Kotkowiak, Micha?; Vakuliuk, Olena; Gryko, Daniel T; Kolanowski, ?ukasz; Baraniak, Marek; Lota, Grzegorz

    2016-03-01

    This paper examines the influence of aprotic solvents on the spectroscopic properties as well as the energy deactivation of two free-base corrole dyes substituted with C6F5 and/or 4-NO2C6H4 groups. Absorption, fluorescence and laser-induced optoacoustic spectroscopy have been used to follow the singlet and triplet states of fluorine corroles belonging to the A2B and A3 type in toluene (TL), chloroform (CL), dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and also in solvent mixtures. Changes in the absorption and fluorescence spectra are influenced by the type of solvent mixture. The fluorescence behaviors of the two investigated corroles were extremely different - fluorescence of the nitro-corrole in TL is dramatically quenched in the presence of DMF. In contrast, fluorescence quenching of fluorine corroles in DMF-TL mixtures is substantially weakened. Absorption, fluorescence, triplet population as well as singlet oxygen generation parameters are evaluated. The spectral experimental data are supported by quantum chemical calculations - time-dependent density functional theory (TD-DFT) and cyclic voltammetry experiments. The presented results are discussed from a viewpoint of aggregation, tautomerization, and deprotonation effects occurring in the corroles. PMID:26890961

  9. Theoretical study on reactions of triplet excited state thioxanthone with indole.

    PubMed

    Shen, Liang; Ji, Hong-Fang

    2009-10-01

    In the present work, a theoretical study on the deactivation of triplet excited (T(1)) state thioxanthone (TX) by indole (INH) was performed, based on density functional theory calculations. Three feasible pathways, namely direct electron transfer from INH to T(1) state TX, electron transfer followed by proton transfer from INH(.+) to TX(.-), and H-atom transfer from nitrogen of INH to keto oxygen of T(1) state TX, were proposed theoretically to be involved in T(1) state TX deactivation by INH. PMID:20057945

  10. Theoretical Study on Reactions of Triplet Excited State Thioxanthone with Indole

    PubMed Central

    Shen, Liang; Ji, Hong-Fang

    2009-01-01

    In the present work, a theoretical study on the deactivation of triplet excited (T1) state thioxanthone (TX) by indole (INH) was performed, based on density functional theory calculations. Three feasible pathways, namely direct electron transfer from INH to T1 state TX, electron transfer followed by proton transfer from INH.+ to TX.?, and H-atom transfer from nitrogen of INH to keto oxygen of T1 state TX, were proposed theoretically to be involved in T1 state TX deactivation by INH. PMID:20057945

  11. Spectrum and polarization of helium doubly excited triplet states

    NASA Astrophysics Data System (ADS)

    Brooks, Robert L.; Pinnington, Eric H.

    1980-08-01

    The beam-foil spectrum of helium from 2050 to 3600 has been acquired at 160-keV incident ion energy using a multiple-scan, computerized system. Eleven doubly-excited-state transitions, including two not previously observed, have been assigned, and the agreement between experimental and theoretical energy levels is excellent. The Stokes parameters as a function of foil-tilt angle have been measured for the two strongest transitions (2578 and 3013 ) from 0 to 80 in 10 increments and for two weaker transitions (2562 and 2818 ) at 0, 20, 40, and 60. The polarization patterns are quite different from those of the helium singlets and include the first measurement of negative MI (a Stokes parameter) at 0 foil tilt for helium at this energy. The lifetime of the 2578- transition has been investigated in detail. The present result, 0.109+/-0.004 ns, agrees with previous measurements and yields an upper limit to the autoionization width of the 2p3p 3D levels of 610-6 eV.

  12. Quenching of the triplet state of certain porphyrins by cyanocobalamin and co-phthalocyanine

    NASA Astrophysics Data System (ADS)

    Sapunov, V. V.

    1992-10-01

    The bimolecular exchange-resonance energy transfer efficiency from the triplet level of a number of Pd porphyrins to cyanocobalamin (vitamin B-12) is much lower in ethanol than in aqueous solutions. This is explained by a change in a cyanocobalamin-molecule geometry in ethanol from that in aqueous solutions. This change can be the detachment of the nucleotide from the cobalt ion or a change in the cyanocobalamin-molecule conformation. As a result, stearic hindrance of intermolecular energy transfer arises, or the mobility of the cyanocobalamin molecules decreases. No quenching of the triplet state of tetraphenyl tetrahydroporphin by cyanocobalamine is detected, whereas quenching of Co-phthalocyanine occurs with a high rate constant.

  13. Signature of the long range triplet proximity effect in the density of states

    NASA Astrophysics Data System (ADS)

    Kneevi?, Milo; Trifunovic, Luka; Radovi?, Zoran

    2012-03-01

    We study the impact of the long range spin-triplet proximity effect on the density of states (DOS) in planar SF1F2S Josephson junctions that consist of conventional superconductors (S) connected by two metallic monodomain ferromagnets (F1 and F2) with transparent interfaces. We determine the electronic DOS in F layers for arbitrary orientation of the magnetizations using the solutions of Eilenberger equations in the clean limit and for a moderate concentration of impurities in ferromagnets. We find that a fully developed long range proximity effect occurs in Josephson junctions with a highly asymmetric ferromagnetic bilayer. For orthogonal magnetizations, the effect manifests itself as an enhancement in DOS and as a dominant second harmonic in the Josephson current-phase relation. Distinctive variation of DOS in ferromagnets with the angle between magnetizations is experimentally observable by tunneling spectroscopy. This can provide an unambiguous signature of the long range spin-triplet proximity effect.

  14. Transport signatures of superconducting hybrids with mixed singlet and chiral triplet states

    NASA Astrophysics Data System (ADS)

    Burset, Pablo; Keidel, Felix; Tanaka, Yukio; Nagaosa, Naoto; Trauzettel, Bjrn

    2014-08-01

    We propose a model for a superconductor where both spin-singlet and chiral triplet pairing amplitudes can coexist. By solving the Bogoliubov-de Gennes equations with a general pair potential that accounts for both spin states we study experimental signatures of normal metal and superconductor hybrids. The interplay between the spin-singlet and triplet correlations manifests in the appearance of two effective gaps. When the amplitude of the spin-triplet component is stronger than that of the spin singlet, a topological phase transition into a nontrivial regime occurs. As a result, the normal metal-superconductor conductance evolves from a conventional gap profile onto an unconventional zero-bias peak. Additionally, in the topologically nontrivial phase, Andreev bound states formed at Josephson junctions present zero-energy modes; the number of those modes depends on the relative chirality of the junction. Finally, we present results for the current-phase relation and the temperature dependence of the Josephson critical current within both topological phases for several system parameters.

  15. Charge transfer and triplet states in OPV materials and devices (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Dyakonov, Vladimir

    2015-10-01

    Electron back transfer (EBT), potentially occurring after electron transfer from donor to acceptor may populate the lower lying donor or acceptor triplet state and serve as recombination channel.[1] Here we report on studies of charge transfer and triplet states in blends of highly efficient benzodithiophene PTB7 polymer in combination with the fullerene-derivative PC71BM using the spin sensitive optically detected magnetic resonance (ODMR) technique and compare the results with those obtained in P3HT (poly(3- hexylthiophene):PC61BM blends. Although PTB7:PC71BM absorbers yield much higher power conversion efficiencies in solar cells exceeding 7%, we found a significant increase of triplet exciton generation, which was absent in the P3HT based blends. We discuss this observation within the EBT scenario with the emphasis on the influence of morphology, fullerene load, HOMO/LUMO energy and presence of additives (DIO). Suppressing the EBT process by morphology and/or energetics of polymer and molecules is important to achieve the full potential of highly efficient OPV materials. [1] M. Liedtke, et al., JACS 133, 9088 (2011).

  16. Triplet state relaxation processes of the OLED emitter Pt(4,6-dFppy)(acac)

    NASA Astrophysics Data System (ADS)

    Rausch, Andreas F.; Thompson, Mark E.; Yersin, Hartmut

    2009-01-01

    The emitting triplet state of Pt(4,6-dFppy)(acac) doped into n-octane is studied at cryogenic temperatures by site-selective high-resolution optical spectroscopy. The investigations reveal a very specific zero-field splitting (ZFS) pattern of the emitting T 1 state and the individual deactivation times of the substates to the singlet ground state S 0. Spin-lattice relaxation (SLR) processes occurring between the T 1 substates are ascribed to a combination of the direct and the Raman process. Due to the relatively long SLR time at low temperature, a Boltzmann distribution is not established directly after the excitation pulse below ?2 K.

  17. Phase control of the spin-triplet state in S/F/S Josephson junctions

    NASA Astrophysics Data System (ADS)

    Gingrich, Eric C.

    For decades, the proximity effect in superconductor/ferromagnetic (S/F) hybrid systems was thought to be very short-ranged, with coherence lengths on the order of a nanometer. That changed in 2003 when Bergeret et al. suggested systems involving s-wave superconductors and ferromagnets with non-collinear magnetizations could generate spin-triplet supercurrent. This was a significant prediction that radically changed the outlook for these systems, with the possibility of bringing the ferromagnetic coherence length up to ranges similar to the normal metal coherence length. With the experimental confirmation of the spin-triplet state in S/F/S Josephson junctions in 2010, the flood-gates opened into a range of interesting studies. We have performed measurements on the magnetic and superconducting properties of the multilayer Ni/[Co/Ni]n. This arrangement of ferromagnetic materials, when grown with thicknesses of 0.4 nm Ni and 0.2 nm Co, demonstrate a magnetization that lies perpendicular to the plane of the films. Because it will, in the virgin state, possess a non-collinear magnetization with ferromagnets which have magnetizations that lie within the plane, it is a convenient multilayer for the generation of spin-triplet supercurrent. Our measurements of S/F'/F/F'/S Josephson junctions, where F' is a hard ferromagnet and F is the Co/Ni multilayer, confirmed the presence of the spin-triplet state, and demonstrated the viability of the Co/Ni multilayer as a triplet generating ferromagnet. We have also performed studies on the characteristics of a number of soft ferromagnetic alloys. These alloys are important for their potential as a soft ferromagnetic switching layer for application in our triplet control devices. To that end, we have created sputtering targets for four different ferromagnetic alloys: Molybdenum-doped Permalloy, Niobium-doped Permalloy, Copper-doped Permalloy, and Palladium Iron. These studies have included: atomic concentration measurements using EDS, magnetic measurements using a commercial MPMS measurement system and GMR, and superconducting studies done by fabricating S/F'/F/F''/S Josephson junctions with F'' the soft ferromagnet of interest. Lastly, we have performed measurements to study the relative phase of two S/F'/F/F''/S Josephson junctions patterned into a Superconducting Quantum Interference Device (SQUID). The phase of the junctions is determined by the relative rotation of the magnetizations through the junction. By applying an external field to the junctions, and utilizing shape anisotropy to control the switching fields, the F'' layer can be switched in a single junction. The switch in the state can be observed by measuring the interference in the current driven through the SQUID, which responds to the relative phase of the two junctions in the loop. These measurements have yielded promising early results for the prospect of controlling the spin-triplet state.

  18. Conformationally Constrained, Stable, Triplet Ground State (S = 1) Nitroxide Diradicals. Antiferromagnetic Chains of S = 1 Diradicals

    SciTech Connect

    Rajca, Andrzej; Takahashi, Masahiro; Pink, Maren; Spagnol, Gaelle; Rajca, Suchada

    2008-06-30

    Nitroxide diradicals, in which nitroxides are annelated to m-phenylene forming tricyclic benzobisoxazine-like structures, have been synthesized and characterized by X-ray crystallography, magnetic resonance (EPR and {sup 1}H NMR) spectroscopy, as well as magnetic studies in solution and in solid state. For the octamethyl derivative of benzobisoxazine nitroxide diradical, the conformationally constrained nitroxide moieties are coplanar with the m-phenylene, leading to large values of 2J (2J/k > 200 K in solution and 2J/k >> 300 K in the solid state). For the diradical, in which all ortho and para positions of the m-phenylene are sterically shielded, distortion of the nitroxide moieties from coplanarity is moderate, such that the singlet-triplet gaps remain large in both solution (2J/k > 200 K) and the solid state (2J/k {approx} 400-800 K), though an onset of thermal depopulation of the triplet ground state is detectable near room temperature. These diradicals have robust triplet ground states with strong ferromagnetic coupling and good stability at ambient conditions. Magnetic behavior of the nitroxide diradicals at low temperature is best fit to the model of one-dimensional S = 1 Heisenberg chains with intrachain antiferromagnetic coupling. The antiferromagnetic coupling between the S = 1 diradicals may be associated with the methyl nitroxide C-H {hor_ellipsis} O contacts, including nonclassical hydrogen bonds. These unprecedented organic S = 1 antiferromagnetic chains are highly isotropic, compared to those of the extensively studied Ni(II)-based chains.

  19. Optical and electron paramagnetic resonance studies of the excited triplet states of UV-B absorbers: 2-ethylhexyl salicylate and homomenthyl salicylate.

    PubMed

    Sugiyama, Kazuto; Tsuchiya, Takumi; Kikuchi, Azusa; Yagi, Mikio

    2015-09-26

    The energy levels and lifetimes of the lowest excited triplet (T1) states of UV-B absorbers, 2-ethylhexyl salicylate (EHS) and homomenthyl salicylate (HMS), and their deprotonated anions (EHS(-) and HMS(-)) were determined through measurements of phosphorescence and electron paramagnetic resonance (EPR) spectra in rigid solutions at 77 K. The observed T1 energies of EHS and HMS are higher than those of butylmethoxydibenzoylmethane, the most widely used UV-A absorber, and octyl methoxycinnamate, the most widely used UV-B absorber. The T1 states of EHS, HMS, EHS(-) and HMS(-) were assigned to almost pure (3)??* state from the observed T1 lifetimes and zero-field splitting parameters. EHS and HMS with an intramolecular hydrogen bond show a photoinduced phosphorescence enhancement in ethanol at 77 K. The EPR signals of the T1 states of EHS and HMS also increase in intensity with UV-irradiation time (photoinduced EPR enhancement). The T1 lifetimes of EHS and HMS at room temperature were determined through triplet-triplet absorption measurements in ethanol. The quantum yields of singlet oxygen production by EHS and HMS were determined by using time-resolved near-IR phosphorescence. PMID:26135028

  20. Triplet states in isotopically mixed anthracene crystals: High resolution optical spectroscopy

    NASA Astrophysics Data System (ADS)

    Port, H.; Rund, D.; Wolf, H. C.

    1981-08-01

    The triplet O,O transitions of guest and host in isotopically mixed anthracene crystals of various compositions (A- h10, 13C-monosubstituted A- h10, A- d1h9, A- d2hg in A- d10 and A- d10 in A- h10) have been investigated using high resolution laser excitation spectroscopy. The guest aggregate spectra have been studied in polarized light as a function of guest concentration up to 15%. The analyses allow us to identify the monomer, dimer and trimer lines. From the dimer splittings the dominant resonance pair interactions are dedu The comparison of different mixed crystal systems with guest levels below and above the host exciton band reveals that quasiresonance and superexchange corrections are of minor importance. The experimental resonance pair interactions are used to calculate the triplet exciton band structure of anthracen and the observed guest polarization behaviour is interpreted quantitatively by the Rashba effect. Finally, the lower Davydov component of the host is s and broadened with increasing guest concentration. The shift is discussed using a theoretical model of Lifshitz.

  1. Prediction of a neutral noble gas compound in the triplet state.

    PubMed

    Manna, Debashree; Ghosh, Ayan; Ghanty, Tapan K

    2015-05-26

    Discovery of the HArF molecule associated with H-Ar covalent bonding [Nature, 2000, 406, 874-876] has revolutionized the field of noble gas chemistry. In general, this class of noble gas compound involving conventional chemical bonds exists as closed-shell species in a singlet electronic state. For the first time, in a bid to predict neutral noble gas chemical compounds in their triplet electronic state, we have carried out a systematic investigation of xenon inserted FN and FP species by using quantum chemical calculations with density functional theory and various post-Hartree-Fock-based correlated methods, including the multireference configuration interaction technique. The FXeP and FXeN species are predicted to be stable by all the computational methods employed in the present work, such as density functional theory (DFT), second-order Møller-Plesset perturbation theory (MP2), coupled-cluster theory (CCSD(T)), and multireference configuration interaction (MRCI). For the purpose of comparison we have also included the Kr-inserted compounds of FN and FP species. Geometrical parameters, dissociation energies, transition-state barrier heights, atomic charge distributions, vibrational frequency data, and atoms-in-molecules properties clearly indicate that it is possible to experimentally realize the most stable state of FXeP and FXeN molecules, which is triplet in nature, through the matrix isolation technique under cryogenic conditions. PMID:25891838

  2. A diffusion quantum Monte Carlo study on the lowest singlet and triplet electronic states of BN molecule.

    PubMed

    Lu, Shih-I

    2005-11-01

    Ab initio calculation of both the lowest singlet and triplet electronic states of BN has been performed by the fixed-node Ornstein-Uhlenbeck diffusion quantum Monte Carlo method with the floating spherical Gaussian orbitals and spherical Gaussian geminals. The Monte Carlo calculation gives equilibrium bond lengths and equilibrium harmonic frequencies of 1.3317(7) A and 1529(7) cm(-1), respectively, for the lowest triplet state and 1.2751(7) A and 1709(8) cm(-1), respectively, for the lowest singlet state. Also, the Monte Carlo calculation reports an energy separation of 178(83) cm(-1) between the two electronic states and recommends the ground state is the lowest triplet state. PMID:16375534

  3. Photofunctional triplet excited states of cyclometalated Ir(III) complexes: beyond electroluminescence.

    PubMed

    You, Youngmin; Nam, Wonwoo

    2012-11-01

    The development of cyclometalated Ir(III) complexes has enabled important breakthroughs in electroluminescence because such complexes permit the efficient population of triplet excited states that give rise to luminescent transitions. The triplet states of Ir(III) complexes are advantageous over those of other transition metal complexes in that their electronic transitions and charge-transfer characteristics are tunable over wide ranges. These favorable properties suggest that Ir(III) complexes have significant potential in a variety of photofunctions other than electroluminescence. In this critical review, we describe recent photonic applications of novel Ir(III) complexes. Ir(III) complexes have been shown to affect the exciton statistics in the active layers of organic photovoltaic cells, thereby improving the photon-to-current conversion efficiencies. Nonlinear optical applications that take advantage of the strong charge-transfer properties of triplet transitions are also discussed. The tunability of the electrochemical potentials facilitates the development of efficient photocatalysis in the context of water photolysis or organic syntheses. The photoredox reactivities of Ir(III) complexes have been employed in studies of charge migration along DNA chains. The photoinduced cytotoxicity of Ir(III) complexes on live cells suggests that the complexes may be useful in photodynamic therapy. Potential biological applications of the complexes include phosphorescence labeling and sensing. Intriguing platforms based on cyclometalated Ir(III) complexes potentially provide novel protein tagging and ratiometric detection. We envision that future research into the photofunctionality of Ir(III) complexes will provide important breakthroughs in a variety of photonic applications. PMID:22797418

  4. Photophysical processes of triplet states and radical ions in pure and molecularly doped polymers. Final report

    SciTech Connect

    Burkhart, R.D.

    1998-01-01

    Both the past and current objectives are to learn how to control the rate and direction of triplet exciton migration in both pure and molecularly doped polymer systems. Since triplet excimers are efficient traps for migrating excitons, a secondary objective has been to characterize these excimers with a view toward their use as rate modifiers or excited state quenchers. Further objectives included those stated above as past and current objectives but with an additional goal. The authors learned that fluid solutions of many of the nitrogen containing chromophores with which they work produce both radical cations and anions upon excimer laser excitation. They also learned that a phosphorus analogue behaves similarly. At this time the mechanism of charge generation in these systems is not well established but they do know that the electronically excited states and radical ions can potentially interconvert. They wanted to find out whether or not the pure or molecularly doped polymer systems could be used in a step-wise sequence involving light absorption followed by charge generation. All of their activities are oriented toward the potential end use of polymeric systems in the conversion of light energy to perform various types of useful work.

  5. Photoformation of Triplet Excited States and Other Oxidants in Fog Waters and Their Impact on Fog Processing of Organic Compounds

    NASA Astrophysics Data System (ADS)

    Kaur, R.; Anastasio, C.; Valsaraj, K. T.; Vempati, H. S.; Vaitilingom, M.

    2014-12-01

    Reactions in fog and cloud drops are important for a number of processes, such as formation of secondary organic aerosol (SOA), cycling of organic carbon and nitrogen, and determining the lifetimes of pollutants. The rates of these processes depend upon the steady-state concentrations of the major photooxidants, namely, hydroxyl radical (.OH), singlet molecular oxygen (1O2*) and triplet excited states of organic compounds (3C*). While there are some past measurements of .OH and 1O2* concentrations in fog and cloud drops, there are no data for the concentrations of triplet excited states. However, there is increasing evidence that triplets might be important for the processing of organics in a cloudy or foggy atmosphere. To address this question, we collected fog water samples from Davis, CA and Baton Rouge, LA, illuminated them with simulated sunlight, and measured the steady-state concentrations of .OH , 1O2* and 3C* . To understand the relative importance of these photooxidants, we also measured the photochemical loss of two added model organic compounds in the illuminated fog waters - syringol (a biomass burning phenol) and methyl jasmonate (a green leaf volatile). Our results show that triplet excited states can play a major role in oxidizing the model compounds, typically accounting for 30 - 90% of the loss of both model compounds. Given that atmospheric triplets are relatively less understood, our results highlight the importance of deeper investigation into their nature.

  6. The role of triplet state keto-enol tautomerism in the photodeamination of metamitron.

    PubMed

    Kouras-Hadef, Sofia; de Sainte-Claire, Pascal; ter Halle, Alexandra; Amine-Khodja, Amina; Richard, Claire

    2011-12-22

    Substituted 4-amino-1,2,4-triazin-5-ones undergo photodeamination through cleavage of the N-NH(2) bond in the presence of oxygen and water. To elucidate the mechanism of this reaction, we investigated the photolysis of metamitron (4-amino-6-phenyl-3-methyl-1,2,4-triazin-5-one) by nanosecond laser flash photolysis, steady-state irradiation, and ab initio calculations. Upon pulsed laser excitation of deoxygenated aqueous metamitron, two transient species are clearly detected. The predictions of ab initio results are consistent with experimental results: (i) it is proposed here that the transient species are, respectively, the keto and diradical forms of the metamitron keto-enol tautomerism in the triplet state, and (ii) in water, the activation free energy barrier of enolization is drastically decreased. Thus, the formation of the diradical triplet is enabled in aqueous solvent. A detailed analysis of the intermediate structures that lead to the final products (HNO(2) and deaminometamitron) is provided. PMID:22047469

  7. Characterization of the triplet state of tanshinone IIA and its reactivity by laser flash photolysis.

    PubMed

    Li, Kun; Zhang, Qin; Wang, Mei; Zhu, Rongrong; Sun, Xiaoyu; Wu, Xianzheng; Wang, Shi-Long

    2014-01-01

    Tanshinone IIA (Tan IIA) has the properties of cardiovascular protection, anti-inflammation, antioxidation and anticancer. Its light-induced instability has drawn our interests in its photochemistry. Therefore, laser flash photolysis herein was used to investigate the transient photochemistry of Tan IIA. Our results show that direct photoexcitation by 355 nm laser pulses or photosensitization by energy transfer can lead to the formation of the triplet state of Tan IIA ((3)Tan IIA*). The triplet absorption spectrum and molar absorption coefficient, and ISC quantum yield were determined. Self-quenching of (3)Tan IIA* by its ground state was identified as an autooxidation reaction. (3)Tan IIA* was proved to react quickly with N, N-dimethylaniline, tert-butylhydroquinone and propyl gallate via electron transfer with the diffusion-controlled rate constants. One of the products with maximum absorption around 390 nm was assigned to the radical anion of Tan IIA. Our results indicate that (3)Tan IIA* is a reactive transient species and can be generated by photosensitization or direct photoexcitation. According to our results, the possible role of Tan IIA as a photosensitizer to induce potential phototoxicity via Type-II pathway in the presence of O2 can be predicted. PMID:24325277

  8. Identification and reactivity of the triplet excited state of 5-hydroxytryptophan.

    PubMed

    Dad, S; Bisby, R H; Clark, I P; Parker, A W

    2005-03-01

    Both the neurotransmitter serotonin and the unnatural amino acid 5-hydroxytryptophan (5HT), contain the 5-hydroxyindole chromophore. The photochemistry of 5HT is being investigated in relation to the multiphoton excitation of this chromophore to produce a characteristic photoproduct with green fluorescence ('hyperluminescence'). Laser flash photolysis (308 nm) of 5HT in aqueous solution at neutral pH produces both the neutral 5-indoloxyl radical (lambda(max) 400-420 nm) and another transient absorption with lambda(max) 480 nm and lifetime of 2 micros in deaerated solutions. Based on quenching by oxygen and beta-carotene, the species at 480 nm is identified as the triplet excited state of 5HT. In acidic solution a new oxygen-insensitive intermediate with lambda(max) 460 is assigned to the radical cation of 5HT. Time-resolved measurements of luminescence at 1270 nm have shown that the triplet state of 5HT is able to react with oxygen to form singlet excited oxygen (1O2*) with a quantum yield of approximately 0.1. However, 5HT has also been found to be an effective quencher of singlet oxygen with a second order rate constant of 1.3 x 10(8) dm3 mol(-1) s(-1). The results are discussed in the light of recent observations on the multiphoton-excited photochemistry of serotonin. PMID:15708522

  9. Identification and Reactivity of the Triplet Excited State of 5-Hydroxytryptophan

    PubMed Central

    Dad, S.; Bisby, R.H.; Clark, I.P.; Parker, A.W.

    2007-01-01

    Both the neurotransmitter serotonin and the unnatural amino acid 5-hydroxytryptophan (5HT), contain the 5-hydroxyindole chromophore. The photochemistry of 5HT is being investigated in relation to the multiphoton excitation of this chromophore to produce a characteristic photoproduct with green fluorescence (‘hyperluminescence’). Laser flash photolysis (308 nm) of 5HT in aqueous solution at neutral pH produces both the neutral 5-indoloxyl radical (λmax 400-420 nm) and another transient absorption with λmax 480 nm and lifetime of 2 μs in deaerated solutions. Based on quenching by oxygen and β-carotene, the species at 480 nm is identified as the triplet excited state of 5HT. In acidic solution a new oxygen-insensitive intermediate with λmax 460 is assigned to the radical cation of 5HT. Time-resolved measurements of luminescence at 1270 nm have shown that the triplet state of 5HT is able to react with oxygen to form singlet excited oxygen (1O2*) with a quantum yield of ∼0.1. However, 5HT has also been found to be an effective quencher of singlet oxygen with a second order rate constant of 1.3 × 108 dm3 mol-1 s-1. The results are discussed in the light of recent observations on the multiphoton-excited photochemistry of serotonin. PMID:15708522

  10. Accessing the Triplet State in Heavy-Atom-Free Perylene Diimides.

    PubMed

    Yu, Zhenyi; Wu, Yishi; Peng, Qian; Sun, Chunlin; Chen, Jianwei; Yao, Jiannian; Fu, Hongbing

    2016-03-24

    Previous studies of perylenediimides (PDIs) mostly utilized the lowest singlet excited state S1 . Generation of a triplet excited state (T1 ) in PDIs is important for applications ranging from photodynamic therapy to photovoltaics; however, it remains a formidable task. Herein, we developed a heavy-atom-free strategy to prompt the T1 ←S1 intersystem crossing (ISC) by introducing electron-donating aryl (Ar) groups at the head positions of an electron-deficient perylenediimide (PDI) core. We found that the ISC efficiency increases from 8 to 54 % and then to 86 % by increasing the electron-donating ability of head-substituted aryl groups from phenyl (p-PDI) to methoxyphenyl (MeO-PDI) and then to methylthioxyphenyl (MeS-PDI). By enhancing the intramolecular charge-transfer (ICT) interaction from p-PDI to MeO-PDI, and then to MeS-PDI, singlet oxygen generation via energy-transfer reactions from T1 of PDIs to (3) O2 was demonstrated with the highest yield of up to 80 %. These results provide guidelines for developing new triplet-generating PDIs and related rylene diimides for optoelectronic applications. PMID:26853213

  11. Effect of Triplet T 1-State Population on Fluorescence Polarization Kinetics of Organic Fluorophores

    NASA Astrophysics Data System (ADS)

    Stanishevsky, I. V.; Chernyavskii, V. A.

    2015-11-01

    The fluorescence polarization kinetics of fluorescent organic molecules and molecules with two interconverting photoisomeric forms and fixed molecular skeletons were investigated by numerical methods based on the solution of population balance equations. The depolarizing effect of the lowest triplet T 1 state and the polarization time dependence for quasi-continuous-wave (cw) and pulsed photoexcitation were studied using model compounds. The fluorescence depolarization with cw excitation was characterized by times that were shorter than the T 1-state lifetime; for the isomers, also by times that correlated with the photoisomerization times. Intense pulsed photoexcitation distorted significantly the initial oscillator orientation distribution in the singlet S 0 and S 1 states and could lead to sign reversal of the polarization.

  12. Theoretical radiative properties between states of the triplet manifold of NH radical

    SciTech Connect

    Owono Owono, L. C.; Ben Abdallah, D.; Jaidane, N.; Ben Lakhdar, Z.

    2008-02-28

    Ab initio transition dipole moments between states of the triplet manifold of NH radical are determined at the complete active space self-consistent field, followed by the internally contracted multireference singles plus doubles configuration interaction level of theory with a modified aug-cc-pVTZ basis set that accounts for valence-Rydberg interactions. This enables the computation of various radiative characteristics such as Einstein coefficients, radiative lifetimes, and oscillator strengths. These properties concern as well valence and Rydberg states. For the valence states, only the (0, 0) band of the A {sup 3}{pi}-X {sup 3}{sigma}{sup -} transition has received some important amount of attention. Data for the other transitions are rather scarce and sometimes inexistent. The results obtained in this work show good agreement with the available experimental data in comparison to other theoretical numbers reported in the literature.

  13. Laser-induced reduction of a dye characterised by a high triplet-state yield and dissolved in a polymer

    SciTech Connect

    Sizykh, A G; Tarakanova, E A; Tatarinova, L L

    2000-01-31

    An investigation was made of the photoreduction kinetics of a dye in a solid polymer solution under the influence of laser radiation corresponding to the band of the first singlet - singlet transition. Participation of higher triplet states was considered in a model of the photoreduction of a dye characterised by a high intersystem crossing yield. An analytic solution was obtained for a system of kinetic equations. This solution takes into account the difference between the photoprocess rates. It is shown that a linear dependence of the effective dye-photoreduction rate on the laser radiation intensity can serve as a test of the participation of higher triplet states in the reaction. A comparison of the theoretical and experimental results obtained in the present study is used to determine the ratio of the photoreduction and deactivation rate constants of the higher triplet state of eosin K. (interaction of laser radiation with matter. laser plasma)

  14. Local CC2 response method for triplet states based on Laplace transform: Excitation energies and first-order properties

    NASA Astrophysics Data System (ADS)

    Freundorfer, Katrin; Kats, Daniel; Korona, Tatiana; Schtz, Martin

    2010-12-01

    A new multistate local CC2 response method for calculating excitation energies and first-order properties of excited triplet states in extended molecular systems is presented. The Laplace transform technique is employed to partition the left/right local CC2 eigenvalue problems as well as the linear equations determining the Lagrange multipliers needed for the properties. The doubles part in the equations can then be inverted on-the-fly and only effective equations for the singles part must be solved iteratively. The local approximation presented here is adaptive and state-specific. The density-fitting method is utilized to approximate the electron-repulsion integrals. The accuracy of the new method is tested by comparison to canonical reference values for a set of 12 test molecules and 62 excited triplet states. As an illustrative application example, the lowest four triplet states of 3-(5-(5-(4-(bis(4-(hexyloxy)phenyl)amino)phenyl)thiophene-2-yl)thiophene-2-yl)-2-cyanoacrylic acid, an organic sensitizer for solar-cell applications, are computed in the present work. No triplet charge-transfer states are detected among these states. This situation contrasts with the singlet states of this molecule, where the lowest singlet state has been recently found to correspond to an excited state with a pronounced charge-transfer character having a large transition strength.

  15. Optical and magnetic properties of the lowest triplet state of pyrido(2,3-b)pyrazine. An example of /sup 3/n. pi. * azanaphthalene

    SciTech Connect

    Yamauchi, S.; Hirota, N.

    1987-03-26

    The lowest excited triplet (T/sub 1/) states of pyrido(2,3-b)pyrazine(2,3-b)pyrazine (PP; 1,4,5-triazanaphthalene) in the three kinds of environments have been studied by using various spectroscopic and magnetic resonance techniques. The authors obtained phosphorescence emission and excitation spectra, triplet lifetimes, zero field splittings (zfs), and triplet sublevel properties. From the analysis of the results the authors conclude that T/sub 1/ is /sup 3/n..pi..* in character in a single crystal of durene and in ethanol, but it is /sup 3/..pi pi..* in trifluoroethanol. Observation of the /sup 3/n..pi..* phosphoresence was made for the first time in azanaphthalenes, which provides direct information about /sup 3/n..pi..* azanaphthalene. The 0-0 band and vibronic bands involving a' vibrations are dominant in the phosphorescence spectrum. Large zfs and negative D (identical with -3/2X; -3.1 GHz) were obtained. As for the sublevel properties T/sub z/ is the most active and T/sub x/ is inactive in both radiative and nonradiative processes, whereas T/sub y/ is moderately active in the T/sub 1/ approx...-->.. S/sub 0/ nonradiative decay process. These /sup 3/n..pi..* properties were discussed in comparison with those of /sup 3/..pi pi..* PP and azanaphtalenes and numbern..pi..* azabenzenes. Possible mechanisms to explain the radiative and nonradiative properties are given.

  16. Self-homodyne measurement of a dynamic Mollow triplet in the solid state

    NASA Astrophysics Data System (ADS)

    Fischer, Kevin A.; Müller, Kai; Rundquist, Armand; Sarmiento, Tomas; Piggott, Alexander Y.; Kelaita, Yousif; Dory, Constantin; Lagoudakis, Konstantinos G.; Vučković, Jelena

    2016-03-01

    The study of the light–matter interaction at the quantum scale has been enabled by the cavity quantum electrodynamics (CQED) architecture, in which a quantum two-level system strongly couples to a single cavity mode. Originally implemented with atoms in optical cavities, CQED effects are now also observed with artificial atoms in solid-state environments. Such realizations of these systems exhibit fast dynamics, making them attractive candidates for devices including modulators and sources in high-throughput communications. However, these systems possess large photon out-coupling rates that obscure any quantum behaviour at large excitation powers. Here, we have used a self-homodyning interferometric technique that fully employs the complex mode structure of our nanofabricated cavity to observe a quantum phenomenon known as the dynamic Mollow triplet. We expect this interference to facilitate the development of arbitrary on-chip quantum state generators, thereby strongly influencing quantum lithography, metrology and imaging.

  17. Dynamics of C[sub 70] in the lowest excited triplet state at low temperatures

    SciTech Connect

    Terazima, Masahide; Sakurada, Keita; Hirota, Noboru ); Shinohara, Hisanori; Saito, Yahachi )

    1993-05-27

    The dynamic behavior of C[sub 70] in the lowest excited triplet state is investigated by the time-resolved EPR (TREPR) method in methylcyclohexane at low temperatures. From the line width of the TREPR spectrum, the distributions of the shortest and middle radii of the distorted rugby ball shape are revealed to be inhomogeneously broadened although the longest radius is relatively constant. The observing time dependence of the spectrum after the laser excitation is examined on the basis of the model involving pseudorotation and molecular rotation. The time dependence calculated based on the pseudorotation around the longest axis fits the observed one well. The activation energy of the dynamic deformation is determined. 16 refs., 4 figs.

  18. Quasiparticle density of states in triplet quasi-one-dimensional organic superconductors

    NASA Astrophysics Data System (ADS)

    Duncan, R. D.; Vaccarella, C. D.; de Melo, C. A. R. Sa

    2001-03-01

    The growing experimental evidence that some quasi-one-dimensional organic systems may be triplet superconductors [1,2] leads us to study the quasiparticle density of states for several candidate order parameter symmetries. Analytical results as well as plots from numerical calculations of symmetry specific features (such as power law behaviors) are presented and discussed. These predicted qualitative features can be tested in either scanning tunnelling microscopy (STM) or photoemission experiments. [We would like to thank the Georgia Institute of Technology, NSF (Grant No. DMR-9803111), and NATO (Grant No. CRG-972261) for financial support.] [1] I. J. Lee, M. J. Naughton, G. M. Danner, and P. M. Chaikin, Phys. Rev. Lett. 78, 3555 (1997). [2] I. J. Lee, D. S. Chow, W. G. Clark, J. Strouse, M. J. Naughton, P. M. Chaikin and S. E. Brown (preprint) cond-mat/0001332.

  19. Complete basis set extrapolations for low-lying triplet electronic states of acetylene and vinylidene

    NASA Astrophysics Data System (ADS)

    Sherrill, C. David; Byrd, Edward F. C.; Head-Gordon, Martin

    2000-07-01

    A recent study by Ahmed, Peterka, and Suits [J. Chem. Phys. 110, 4248 (1999)] has presented the first experimentally derived estimate of the singlet-triplet gap in the simplest alkyne, acetylene. Their value, T0(3B2)=28 900 cm-1, does not agree with previous theoretical predictions using the coupled-cluster singles, doubles, and perturbative triples [CCSD(T)] method and a triple-? plus double polarization plus f-function basis set (TZ2P f ), which yields 30 5001000 cm-1. This discrepancy has prompted us to investigate possible deficiencies in this usually-accurate theoretical approach. Employing extrapolations to the complete basis set limit along with corrections for full connected triple excitations, core correlation, and even relativistic effects, we obtain a value of 30 900 cm-1 (estimated uncertainty 230 cm-1), demonstrating that the experimental value is underestimated. To assist in the interpretation of anticipated future experiments, we also present highly accurate excitation energies for the other three low-lying triplet states of acetylene, 3Bu(33 570230 cm-1), b 3Au(36 040260 cm-1), and b 3A2(38 380260 cm-1), and the three lowest-lying states of vinylidene, X 1A1(15 150230 cm-1), 3B2(31 870230 cm-1), and b 3A2(36 840350 cm-1). Finally, we assess the ability of density functional theory (DFT) and the Gaussian-3 method to match our benchmark results for adiabatic excitation energies of C2H2.

  20. The Ca II triplet in red giant spectra: [Fe/H] determinations and the role of [Ca/Fe

    NASA Astrophysics Data System (ADS)

    Da Costa, G. S.

    2016-01-01

    Measurements are presented and analysed of the strength of the Ca II triplet lines in red giants in Galactic globular and open clusters, and in a sample of red giants in the LMC disc that have significantly different [Ca/Fe] abundance ratios to the Galactic objects. The Galactic objects are used to generate a calibration between Ca II triplet line strength and [Fe/H], which is then used to estimate [Fe/H]CaT for the LMC stars. The values are then compared with the [Fe/H]spec determinations from high-dispersion spectroscopy. After allowance for a small systematic offset, the two abundance determinations are in excellent agreement. Further, as found in earlier studies, the difference is only a very weak function of the [Ca/Fe] ratio. For example, changing [Ca/Fe] from +0.3 to -0.2 causes the Ca II-based abundance to underestimate [Fe/H]spec by only ˜0.15 dex, assuming a Galactic calibration. Consequently, the Ca II triplet approach to metallicity determinations can be used without significant bias to study stellar systems that have substantially different chemical evolution histories.

  1. Further evidence for dissipative energy migration via triplet states in photosynthesis. The protective mechanism of carotenoids in Rhodopseudomonas spheroides chromatophores.

    PubMed

    Renger, G; Wolff, C

    1977-04-11

    The protection action of carotenoids against irreversible photodestruction was discovered in photosynthetic bacteria by Stanieda and coworkers. In green plant material it was found by Wolff and Witt (1969) Z. Naturforsch, 24b, 1031-1037 and (1972) Proc. 2nd. Int. Congr. Photosynthesis Res. Stresa (Forti, G., Avron, M. and Melandri, A., eds.), Vol. 2, pp. 931-936, Dr. W. Junk, N. V. Publ. The Hague) that the formation of special carotenoid triplet states (via very rapid energy transfer from excited chlorophylls) and their fast radiationless decay in tau1/2 approximately 3 microns is at least one mechanism for the protective action of carotenoids to irreversible photooxidation of the chlorophylls. Hence, it is anticipated that the same mechanism might be realized also in bacteria. The present study gives evidence for such a "triplet valve" to be established also in bacteria. This conclusion was derived from the following observations: 1. The light-induced difference spectrum shows a bleaching of a carotenoid at three characteristic wavelength between 400 and 500 nm. A positive peak around 533 nm indicates the formation of a carotenoid triplet state. 2. The absorption changes can be induced by red light which excites only bacteriochlorophyll. This indicates an energy transfer from bacteriochlorophyll to carotenoids. 3. The light-induced carotenoid triplets decay radiationless in 3 microns in air-saturated aqueous suspensions of the chromatophores. 4. The carotenoid triplet formation occurs only at actinic flash intensities where the photosynthesis becomes saturated. 5. Addition of dithionite, which blocks photosynthesis, markedly increases the extent of carotenoid triplet formation. The different types of exciton migration within the photosynthetic unit are discussed, especially the routes leading to the dissipation of excess excitation energy. PMID:300630

  2. Di-neutral pion production in the triplet P-wave states of charmonium

    NASA Astrophysics Data System (ADS)

    Vidnovic, Theodore, III

    Fermilab experiment E835 has used proton-antiproton annihilations to perform a search for charmonium in the pi0pi0 final state in the triplet P-wave region (3340--3570 MeV). States with even total angular momentum and positive Parity and C-parity have access to the pi0pi0 final state. An enhancement in the pp ? pi0pi0 cross section was observed at the chic 0 resonance. The enhancement was found to be a factor of 20 larger than the expected resonant cross section and was attributed to interference between the chic0 and the large non-resonant continuum. The general helicity structure of the pi0pi 0 differential cross section was studied and the product of the branching fractions, Br(pp ? chi c0) x Br(chi c0 ? pi0pi0) = (5.09 +/- 0.81stat +/- 0.25 sys) x 10-7 was measured.

  3. Triplet state properties of the OLED emitter Ir(btp)2(acac): characterization by site-selective spectroscopy and application of high magnetic fields.

    PubMed

    Finkenzeller, Walter J; Hofbeck, Thomas; Thompson, Mark E; Yersin, Hartmut

    2007-06-11

    The well-known red emitting complex Ir(btp)2(acac) (bis(2-(2'-benzothienyl)-pyridinato-N,C3')iridium(acetylacetonate)), frequently used as emitter material in OLEDs, has been investigated in a polycrystalline CH2Cl2 matrix. The studies were carried out under variation of temperature down to 1.2 K and at magnetic fields up to B=10 T. Highly resolved emission and excitation spectra of several specific sites are obtained by site-selective spectroscopy. For the preferentially investigated site (I-->0 at 16268 cm-1), the three substates I, II, and III of the T1 triplet state are separated by DeltaEII-I=2.9 cm-1 and DeltaEIII-I=25.0 cm-1, respectively. DeltaEIII-I represents the total zero-field splitting (ZFS). The individual decay times of these substates are tauI=150 micros, tauII=58 micros, and tauIII=2 micros, respectively. The long decay time of the lowest substate I indicates its almost pure triplet character. The time for relaxation from state II to state I (spin-lattice relaxation, SLR) is as long as 22 micros at T=1.5 K, while the thermalization between the two lower lying substates and substate III is fast. Application of a magnetic field induces Zeeman mixing of the substates of T1, resulting in an increased splitting between the two lower lying substates from 2.9 cm-1 at zero field to, for example, 6.8 cm-1 at B=10 T. Further, the decay time of the B-field perturbed lowest substate IB decreases by a factor of about 7 up to 10 T. The magnetic field properties clearly show that the three investigated states belong to the same triplet parent term of one single site. Other sites show a similar behavior, though the values of ZFS vary between 15 and 27 cm-1. Since the amount of ZFS reflects the extent of MLCT (metal-to-ligand charge transfer) parentage, it can be concluded that the emitting state T1 is a 3LC (ligand centered) state with significant admixtures of 1,3MLCT (metal-to-ligand charge transfer) character. Interestingly, the results show that the MLCT perturbation is different for the various sites. An empirical correlation between the amount of ZFS and the compound's potential for its use as emitter material in an OLED is presented. As a rule of thumb, a triplet emitter is considered promising for application in OLEDs, if it has a ZFS larger than about 10 cm-1. PMID:17488070

  4. Triplet-Charge Annihilation versus Triplet-Triplet Annihilation in Organic Semiconductors

    SciTech Connect

    Shao, Ming; Yan, Liang; Li, Mingxing; Ivanov, Ilia N; Hu, Bin

    2013-01-01

    A triplet can annihilate with a charge or a triplet, generating triplet-charge annihilation (TCA) or triplet-triplet annihilation (TTA) in organic semiconductors. On one hand, the TCA and TTA are critical issues to improve optoelectronic responses by using triplet states. On the other hand, the TCA and TTA are important spin-dependent processes to generate magneto-optoelectronic responses. Our experimental studies find that the TCA is a dominant process over TTA in organic semiconductors. Specifically, we separately confine triplets with charges or with triplets towards the generation of TCA and TTA by adjusting triplet density, charge confinement, and charge/exciton ratio based on organic light-emitting diodes. We then use magnetic field effects of electroluminescence (MFEEL), as an experimental tool, to study the generation of TCA and TTA. We observe that the electroluminescence can show negative response to applied magnetic field, generating a negative MFEEL, when triplets and charges are simultaneously confined within close proximity by using interfacial confinement with unbalanced charge/exciton ratio. On contrast, the electroluminescence only exhibits a positive MFEEL when triplets are confined within close proximity by using interfacial confinement without unbalanced charge/exciton ratio. Therefore, it can be concluded from our MFEEL results that the TCA is a major process to annihilate triplets over than TTA. Clearly, this experimental finding provides a new understanding on controlling triplets-related optoelectronic and magneto-optoelectronic processes in organic semiconductors.

  5. Solvent Viscosity Effect on Triplet-Triplet Pair in Triplet Fusion.

    PubMed

    Yokoyama, Kana; Wakikawa, Yusuke; Miura, Tomoaki; Fujimori, Jun-Ichi; Ito, Fuyuki; Ikoma, Tadaaki

    2015-12-31

    The effect of the solvent viscosity dependence of time-resolved magnetoluminescence (ML) on the delayed fluorescence of 9,10-diphenylanthracene (DPA) sensitized by platinum octaethylporphyrin has clarified the structure and dynamics of the triplet-triplet pair (TT), i.e., the transition state of triplet fusion. Phase inversion of the ML effect with time provides evidence for the recycle dynamics of the excited triplet state for DPA in triplet fusion. The electron spin-relaxation by random molecular rotation causes intersystem crossing among the different spin states of the triplet-triplet pair and allows the (3,5)TT to engage in triplet fusion. Therefore, slow-down of the molecular diffusion by an increase in the solvent viscosity can enhance the triplet fusion yield. However, the reduction of the ML effect observed in quite high viscosity solvents suggests that the substantially slow rotational motion decreases the triplet fusion yield due to steric factors in electron exchange from the triplet-triplet pair. PMID:26683847

  6. Suppressed Andreev reflection and helical Andreev bound states in triplet superconductor three-dimensional topological insulator

    NASA Astrophysics Data System (ADS)

    Khezerlou, M.; Goudarzi, H.

    2015-11-01

    Effect of proximity-induced unconventional p-wave superconductivity in a three-dimensional topological insulator-based S/F/S structure on the Andreev bound states (ABSs) and Josephson supercurrent is studied. We investigate, in detail, the suppression of Andreev reflection and helical ABSs in the presence of three types of triplet superconducting gap. The magnetization of ferromagnetic section is perpendicular to the surface of junction. The influence of such features on the supercurrent flow on the surface of the topological insulator is studied. We carry out our goal by introducing a relevant form of Dirac spinors for gapless renormalized by chemical potential μ excitation states. Therefore, it enables us to consider the virtual Andreev process, simultaneously, and we propose to investigate it in a tunneling conductance junction. It is shown that the results obtained in this case are completely different from those in conventional superconductivity, as s- or d-waves, for example, the magnetization is found to decrease the gap for px and px+ipy case, whereas increase it for py order. Strongly suppressed Andreev reflection is demonstrated.

  7. Light Absorption by Secondary Organic Aerosol Produced from Aqueous Reaction of Phenols with an Organic Excited Triplet State and Hydroxyl Radical

    NASA Astrophysics Data System (ADS)

    Smith, J.; Yu, L.; George, K.; Ruthenburg, T. C.; Dillner, A. M.; Zhang, Q.; Anastasio, C.

    2012-12-01

    Although reactions in atmospheric condensed phases can form and transform secondary organic aerosol (SOA), these reactions are not well represented in many air quality models. Previous experiments have focused on hydroxyl radical-mediated oxidation of low molecular weight precursors such as gyloxal and methylglyoxal. In our work we are examining aqueous SOA formed from phenols, which are emitted from biomass burning and formed from the oxidation of anthropogenic aromatics such as benzene and toluene. In this work we examine aqueous SOA production from oxidation of three phenols (phenol, guaiacol, syringol) and three benzene-diols (catechol, resorcinol, 1,4-hydroquinone) by hydroxyl radical (OH) and the triplet excited state of 3,4-dimethoxybenzaldehyde (DMB). Our focus is on light absorption by the reaction products, which we characterized by measuring UV-Vis spectra and calculating mass absorption coefficients. To understand the elemental and molecular composition of the SOA, we also analyzed the samples with high resolution mass spectrometry and infrared spectroscopy. Our results indicate that aqueous oxidation of phenols and benzene-diols via OH and triplet excited states efficiently produce SOA that is highly absorbing in the UV-A wavelengths, consists of both small and large molecular weight products, and is highly oxidized.

  8. ?-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 ?-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 ?-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 from the singlet to PCBM is only weakly exothermic, which is believed to be the reason that the photocurrent efficiency is relatively low. PMID:26561718

  9. Intramolecular photostabilization via triplet-state quenching: design principles to make organic fluorophores "self-healing".

    PubMed

    van der Velde, Jasper H M; Uusitalo, Jaakko J; Ugen, Lourens-Jan; Warszawik, Eliza M; Herrmann, Andreas; Marrink, Siewert J; Cordes, Thorben

    2015-12-12

    Covalent linkage of fluorophores and photostabilizers was recently revived as a strategy to make organic fluorophores "self-healing"via triplet-state quenching. Although Lttke and co-workers pioneered this strategy already in the 1980s, the general design principles still remain elusive. In this contribution, we combine experiments and theory to understand what determines the photostabilization efficiency in dye-photostabilizer conjugates. Our results from single-molecule microscopy and molecular dynamics simulations of different Cy5-derivatives suggest that the distance and relative geometry between the fluorophore and photostabilizer are more important than the chemical nature of the photostabilizer, e.g. its redox potential, which is known to influence electron-transfer rates. We hypothesize that the efficiency of photostabilization scales directly with the contact rate of the fluorophore and photostabilizer. This study represents an important step in the understanding of the molecular mechanism of intramolecular photostabilization and can pave the way for further development of stable emitters for various applications. PMID:26449795

  10. Photoreduction of Pt(IV) chloro complexes: substrate chlorination by a triplet excited state.

    PubMed

    Perera, Tharushi A; Masjedi, Mehdi; Sharp, Paul R

    2014-07-21

    The Pt(IV) complexes trans-Pt(PEt3)2(Cl)3(R) 2 (R = Cl, Ph, 9-phenanthryl, 2-trifluoromethylphenyl, 4-trifluoromethylphenyl, 3-perylenyl) were prepared by chlorination of the Pt(II) complexes trans-Pt(PEt3)2(R)(Cl) 1 with Cl2(g) or PhICl2. Mixed bromo-chloro complexes trans,trans-Pt(PEt3)2(Cl)2(Br)(R) (R = 9-phenanthryl, 4-trifluoromethylphenyl), trans,cis-Pt(PEt3)2(Cl)2(Br)(4-trifluoromethylphenyl), trans,trans-Pt(PEt3)2(Br)2(Cl)(R) (R = 9-phenanthryl), and trans,cis-Pt(PEt3)2(Br)2(Cl)(4-trifluoromethylphenyl) were obtained by halide exchange or by oxidative addition of Br2 to 1 or Cl2 to trans-Pt(PEt3)2(R)(Br). Except for 2 (R = Ph, 4-trifluoromethylphenyl), all of the Pt(IV) complexes are photosensitive to UV light and undergo net halogen reductive elimination to give Pt(II) products, trans-Pt(PEt3)2(R)(X) (X = Cl, Br). Chlorine trapping experiments with alkenes indicate a reductive-elimination mechanism that does not involve molecular chlorine and is sensitive to steric effects at the Pt center. DFT calculations suggest a radical pathway involving (3)LMCT excited states. Emission from a triplet is observed in glassy 2-methyltetrahydrofuran at 77 K where photoreductive elimination is markedly slowed. PMID:24971643

  11. Transient IR Spectroscopic Observation of Singlet and Triplet States of 2-Nitrofluorene: Revisiting the Photophysics of Nitroaromatics.

    PubMed

    Larsen, Martin A B; Thgersen, Jan; Stephansen, Anne B; Peon, Jorge; Slling, Theis I; Keiding, Sren R

    2016-01-14

    The dynamics of 2-nitrofluorene (2-NF) in deuterated acetonitrile is studied using UV pump, IR probe femtosecond transient absorption spectroscopy. Upon excitation to the vibrationally excited S1 state, the excited-state population of 2-NF branches into two different relaxation pathways. One route leads to intersystem crossing (ISC) to the triplet manifold within a few hundred femtoseconds and the other to internal conversion (IC) to the ground state. The experiments indicate that after relaxation to the energetic minimum on S1, 2-NF undergoes internal conversion to the ground state in about 15 ps. IC within the triplet manifold is also observed as the initially populated triplet state relaxes to T1 in about 6 ps. Rotational anisotropy measurements corroborate the assignment of the transient IR frequencies and indicate a rotational diffusion time of 2-NF in the solvent of about 14 ps. The combined set of results provides a unified picture of the dynamics in photoexcited 2-NF. This to our knowledge is the first example using femtosecond vibrational spectroscopy for the study of the fundamental photoinduced processes in nitroaromatic compounds. PMID:26669456

  12. Excited states of homo- and heteronuclear-bridged bimetallic complexes of rhodium(I), iridium(I), platinum(II), and gold(I). Triplet manifold splittings, state assignments, and symmetry correlations

    SciTech Connect

    Striplin, D.R.; Crosby, G.A.

    1995-05-18

    Special information on bimetallic complexes of rhodium(I), iridium(I), platinum(II), and gold(I) is reported. We report spectra, polarization characteristics of the principal bands splittings of the triplet manifolds, and the response of the phosphorescence lifetimes to an external magnetic field. Our intent is to arrive at descriptions of the low-lying excited states that not only harmonize all the facts but also expose the reasons for the remarkable spectral similarities among species containing different metals and possessing diverse geometries. 26 refs., 6 figs., 5 tabs.

  13. Triplet states with unusual spin polarization resulting from radical ion pair recombination at short distances

    SciTech Connect

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

    1999-08-25

    Covalently bound electron donor-acceptor, [D-A], molecules that undergo photoinduced charge separation from a photoexcited singlet state to form radical ion pairs that subsequently undergo back electron transfer to yield a triplet state are very rare. Apart from their importance in the general context of electro-transfer reactions, these molecules provide insights into the primary photochemistry of photosynthetic reaction centers. Photoexcitation of [D-A] produces {sup 1}*[D-A], which undergoes rapid charge separation to yield {sup 1}[D{sup {sm{underscore}bullet}{plus}}-A{sup {sm{underscore}bullet}{minus}}]. At [D{sup {sm{underscore}bullet}{plus}}-A{sup {sm{underscore}bullet}(minus)}] distances {ge}20 A, the exchange integral, J, between the two radicals is generally {le}10{sup {minus}4} cm{sup {minus}1}. This weak interaction allows radical pair intersystem crossing (RP-ISC) within {sup 1}[D{sup {sm{underscore}bullet}{plus}}-A{sup {sm{underscore}bullet}(minus)}] to occur, which leads to the formation of a spin-correlated radical pair {sup 3}[D{sup {sm{underscore}bullet}{plus}}-A{sup {sm{underscore}bullet}{minus}}]. Radical ion pair recombination within {sub 3}[D{sup {sm{underscore}bullet}{plus}}-A{sup {sm{underscore}bullet}{minus}}]. In all of these reactions the spins remain correlated, which results in non-Boltzmann populations of the spin states within each intermediate. The authors report here the first example of a covalently bound [D-A] molecule in which a single electron-transfer step produces a [D{sup {sm{underscore}bullet}{plus}}-A{sup {sm{underscore}bullet}{minus}}] pair at a short 11 {angstrom} distance with a large J value that leads to efficient {sup 3}*[D-A] formation.

  14. The Photochemical Reaction Between Phenol and an Excited Triplet State is Enhanced in/on Ice Compared to in Solution

    NASA Astrophysics Data System (ADS)

    Chen, Z.; Anastasio, C.

    2014-12-01

    Photochemical reactions appear to play an important role in the processing of organic compounds in/on snow and ice. These reactions likely control the fate and lifetimes of organic compounds and influence the emissions of volatile organic compounds (VOC) from snow and ice. Triplet excited states of organic compounds (3C*) can be important aqueous oxidants in atmospheric drops and in surface waters, but little is known of this class of oxidants in frozen samples. When exposed to light, 3, 4-dimethoxybenzaldehyde (DMB), a product from biomass combustion, is excited to its triplet state (3DMB*), which can either return to the ground state, react with oxygen to form singlet oxygen, or oxidize organics, such as phenol. In this study, we examine the photochemical loss of phenol due to reaction with 3DMB* in laboratory ice samples as a function of pH, temperature, total solute, and oxygen concentration. Our results show that the rate of phenol loss due to 3DMB* is significantly enhanced in ice compared to the equivalent liquid sample at the same photon flux. This suggests that reactions of triplet excited states in ice can be significant sinks for organics, and perhaps reactive inorganic species, in snow and ice.

  15. A new graphical version of STROTAB: The analysis and fitting of singlet triplet spectra of asymmetric top molecules in the prolate or oblate limits

    NASA Astrophysics Data System (ADS)

    Kodet, John; Judge, Richard H.

    2007-05-01

    The original version of STROTAB has been modified to run under Microsoft Windows using the C++ programming language. The new version takes full advantage of the Microsoft Foundation Classes available within the Microsoft Visual C++ Version 6 development environment. Specifically, windows can be created that edit the input file, summarize the results of the least-squares fit, display the calculated and observed spectra, display whole or partial sections of the calculated spectra as a stick or Gaussian de-convoluted spectrum. A listing of the rotational quantum numbers in the cases (a) and (b) limits for each of the displayed lines is provided. A branch annotating routine provides a quick visual guide to the assignment of the spectrum. A new eigenvalue sorting method has been added as an option that complements the existing method based on the eigenvector coefficients. The new sorting method has eliminated some difficulties that may arise using the existing "Least Ambiguous Method". The program has been extended to handle near-oblate asymmetric tops using a type III r representation. New version summaryTitle of program: STROTAB Version number: 2 Catalogue identifier:ADCA_v2_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADCA_v2_0 Program obtainable from:CPC Program Library, Queen's University of Belfast, N. Ireland Reference in CPC to previous version: 93 (1996) 241-264 Catalog identifier of previous version: ADCA Authors of previous version: R.H. Judge, E.D. Womeldorf, R.A. Morris, D.E. Shimp, D.J. Clouthier, D.L. Joo, D.C. Moule Does the new version supersede the original program: Yes Computers for which the program is designed and others on which it has been tested: Pentium Xenon, Pentium Pro and Later Operating systems or monitors under which program has been tested: Windows 98, Windows 2000, Windows XP Programming language used in the new version: ANSI C, C++, Microsoft Foundation Class (MFC) No. of lines in distributed program, including test data, etc.:11 913 No. of bytes in distributed program, including test data, etc.: 2 816 652 Memory required to execute with typical data: 7 Meg No of bits in a word: 16 No of processors used: 1 Has the code been vectorized or parallelized?: No No. of bytes in distributed program, including test data, etc.: ˜3.2 MB (compressed) Distribution format: zip file Additional keywords:near oblate top, bootstrap eigenvalue sorting, graphical environment, band contour Nature of physical problem: The least-squares/band contour fitting of the singlet-triplet spectra of asymmetric tops of orthorhombic symmetry using a basis set appropriate to the symmetric top limit (prolate or oblate) of the molecule in either Hund's case (a) or case (b) coupling situations. Method of solution: The calculation of the eigenvectors and eigenvalues remains unchanged from the earlier version. An option to sort the eigenvalues of the current J by fitting them to regular progressions formed from earlier J values (bootstrap method) can be used as an option in place of the existing method based on eigenvector coefficients. Reasons for the new version: The earlier version can only handle oblate tops by diagonalizing using the prolate limit. This has turned out to be unacceptable. An improved method of sorting eigenvalues under certain conditions is also needed. A graphical interface has been added to ease the use of the program. Summary of revisions: The Hamiltonian can now be constructed in a limit appropriate the representation for of the molecule. Sorting by an alternate method is now offered. Numerous graphical features have been added. Restrictions on complexity of the problem: The rotational quantum number restrictions are J⩽255 and K (or P) ⩽127. The allowed transition frequency minus the band origin frequency must be in the range of ±10 000 cm -1. Up to five decimal places may be reported. The number of observed lines is limited by the dynamic memory and the amount of disk space available. Only molecules of symmetry D 2h, D 2 and C 2v can be accommodated in this version. Only constants of the excited triplet state may be varied.

  16. Monte Carlo simulations of triplet-state photophysics for super-resolution imaging of fluorophore-labeled gold nanorods

    NASA Astrophysics Data System (ADS)

    Titus, Eric J.; Blythe, Karole L.; Willets, Katherine A.

    2015-08-01

    Super-resolution imaging has previously been used to identify the position of individual fluorescently-labeled DNA molecules bound to the surface of gold nanorods. In order to isolate and fit emission from individual fluorophores, a stochastic photoswitching technique based on shelving the fluorophores into triplet states is used. However, the reconstructed super-resolution images of the fluorescently-labeled gold nanorods are consistently smaller than the expected size of the gold nanorod supports. Here, Monte Carlo simulations are used to probe how smaller-than-expected reconstructed images may be obtained by simultaneous emission events based on short triplet state lifetimes and/or a high density of fluorescently-labeled DNA on the gold nanorod surface.

  17. Excitation wavelength-dependent EPR study on the influence of the conformation of multiporphyrin arrays on triplet state delocalization.

    PubMed

    Tait, Claudia E; Neuhaus, Patrik; Peeks, Martin D; Anderson, Harry L; Timmel, Christiane R

    2016-02-21

    The optoelectronic properties of conjugated porphyrin arrays render them excellent candidates for use in a variety of molecular electronic devices. Understanding the factors controlling the electron delocalization in these systems is important for further developments in this field. Here, we use transient EPR and ENDOR (Electron Nuclear Double Resonance) to study the extent of electronic delocalization in the photoexcited triplet states of a series of butadiyne-linked porphyrin oligomers. We are able to distinguish between planar and twisted arrangements of adjacent porphyrin units, as the different conformations are preferentially excited at different wavelengths in the visible range. We show that the extent of triplet state delocalization is modulated by the torsional angle between the porphyrins and therefore by the excitation wavelength. These results have implications for the design of supramolecular systems with fine-tuned excitonic interactions and for the control of charge transport. PMID:26814427

  18. The role played by some factors of intramolecular interaction in nonradiative deactivation of the lowest triplet state of octachlorodibenzo- p-dioxin

    NASA Astrophysics Data System (ADS)

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

    2012-11-01

    We have studied how intramolecular interactions, such as vibronically induced spin-orbit (VISO) and nonadiabatic interactions, which are governed by different structural elements of the octachlorodibenzo- p-dioxin (OCDD) molecule, affect the deactivation of its lowest triplet state. In the nonadiabatic approximation, taking into account out-of-plane vibrational modes as promoting ones, we have estimated the values of rate constant K {dg/s} of the nonradiative energy deactivation of in-plane triplet sublevels ( s = z, y) of the triplet state of the OCDD molecule.

  19. Nonradiative deactivation of the lowest triplet state of tetrachlorodibenzo- p-dioxin

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

    In the nonadiabatic approximation, we have studied how the shape of promoting out-of-plane vibrational modes and vibronically induced spin-orbit interactions in structural elements of the 2,3,7,8-tetrachlorodibenzo- p-dioxin molecule affect the energy degradation rate constants K {dg/ s } of triplet T {1/ s } sublevels.

  20. Triplet-state conformational changes in 15-cis-spheroidene bound to the reaction center from Rhodobacter sphaeroides 2.4.1 as revealed by time-resolved EPR spectroscopy: strengthened hypothetical mechanism of triplet-energy dissipation.

    PubMed

    Kakitani, Yoshinori; Fujii, Ritsuko; Koyama, Yasushi; Nagae, Hiroyoshi; Walker, Lee; Salter, Bruce; Angerhofer, Alexander

    2006-02-21

    Time-resolved EPR spectra of 15-cis-spheroidene bound to the reaction center from Rhodobacter sphaeroides 2.4.1 were recorded at low temperatures. (1) A three-component analysis of the spectral-data matrices by singular-value decomposition followed by global fitting identified the transformation of the triplet carotenoid, (3)Car(I) --> (3)Car(II); during this process, the leak of the triplet population was suggested. A four-component analysis suggested the presence of a representative intermediate, (3)Car(R), that forms a leak channel of the triplet population. (2) A theoretical calculation of the zero-field splitting parameters, |D| and |E|, by the use of a polyene model, showed that the transformation, (3)Car(I) --> (3)Car(R) --> (3)Car(II), accompanies the conformational changes of (0 degrees , 0 degrees , 0 degrees ) --> (+20 degrees , -20 degrees , +20 degrees ) --> (+45 degrees , -40 degrees , +40 degrees ) around the central cis C15=C15', trans C13=C14, and trans C11=C12 bonds, respectively. (3) The initial, rapid decrease followed by the inversion of spin polarization along the z axis of (3)Car was observed, which was correlated with a change in the spin angular momentum. (4) In reference to the binding pocket of the Car, determined by X-ray crystallography, the conformational changes were ascribed to the intrinsic isomerization property of 15-cis (3)Car as well as the Car-peptide intermolecular interaction; a detailed picture was proposed. All of the above results support the mechanism of triplet-energy dissipation proposed previously: the rotational motions around the central double bonds cause a change in the orbital angular momentum and, through the spin-orbit coupling, a change in the spin angular momentum, which enhances the T(1) --> S(0) intersystem crossing dissipating the triplet energy. PMID:16475794

  1. Triplet state magnetic resonance and fluorescence spectroscopy of metal-substituted hemoglobins.

    PubMed

    Polm, M W; Schaafsma, T J

    1997-01-01

    Fluorescence detected magnetic resonance (FDMR) spectra detected at 596 nm of zinc-substituted hemoglobins at 4.2 K show a split D-E transition, which is not observed for zinc protoporphyrins ligated by methylimidazole in glasses. Incorporation of the zinc heme into the globin pocket is also accompanied by a blue shift of the fluorescence of 20 nm at 4.2 K. FDMR spectra recorded at 576 nm do not show the D-E splitting. The D-E splitting and the huge blue shift are not observed for the magnesium-substituted hemoglobins. Fluorescence measurements at 4.2 K and 77 K, and EPR measurements at 110 K, were carried out to obtain information about the ligation states of the zinc and magnesium protoporphyrins in glasses and in hemoglobin. The results are explained by considering ligation effects and distortion of the porphyrin plane. PMID:8994622

  2. Hyperfine structure of the photoexcited triplet state 3P680 in plant PS II reaction centres as determined by pulse ENDOR spectroscopy.

    PubMed

    Lendzian, Friedhelm; Bittl, Robert; Telfer, Alison; Lubitz, Wolfgang

    2003-08-18

    The triplet states in plant photosystem II (PS II), 3P680, and from chlorophyll a, 3Chl a, in organic solution have been investigated using pulse ENDOR combined with repetitive laser excitation at cryogenic temperature with the aim to obtain their hyperfine (hf) structure. The large zero field splitting (ZFS) tensor of 3P680 enabled orientation selection via the electron spin resonance (EPR) field setting along the ZFS tensor axes. ENDOR spectra have been obtained for the first time also for the in-plane X- and Y-orientations of the ZFS tensor. This allowed a full determination of the hf-tensors of the three methine protons and one methyl group of 3P680. Based on the orientations of the axes of these hf-tensors, a unique orientation of the axes of the ZFS tensor of 3P680 in the Chl a molecular frame was obtained. These data serve as a structural basis for determining the orientation of 3P680 in the PS II protein complex by EPR on single crystals (see M. Kammel et al. in this issue). The data obtained represent the first complete set of the larger hf-tensors of the triplet state 3P680. They reflect the spin density distribution both in the highest occupied (HOMO) and lowest unoccupied (LUMO) orbitals. The data clearly confirm that 3P680 is a monomeric Chl a species at low temperature (T=10 K) used, as has been proposed earlier based on D- and E-values obtained from EPR and optically detected magnetic resonance (ODMR) studies. Comparison with the hf data for the cation and anion radicals of Chl a indicates a redistribution of spin densities in particular for the LUMO orbital of the triplet states. The electron spin distribution in the LUMO orbital is of special interest since it harbours the excited electron in the excited P680 singlet state, from which light-induced electron transfer proceeds. Observed shifts of hf couplings from individual nuclei of 3P680 as compared with 3Chl a in organic solution are of special interest, since they indicate specific protein interactions, e.g. hydrogen bonding, which might be used in future studies for assigning 3P680 to a particular chlorophyll molecule in PS II. PMID:12907299

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

    PubMed Central

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

    2012-01-01

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

  4. Energy transport: Singlet to triplet and back again

    NASA Astrophysics Data System (ADS)

    Roberts, Sean T.

    2015-10-01

    Spin-triplet excitations commonly migrate through direct electron exchange between neighbouring molecules. Now, experiments show that back-and-forth interconversion between spin-triplet and spin-singlet states can significantly speed up triplet migration in organic crystals.

  5. Kinetic and spectroscopic study of triplet state and ionic pathways in the laser-induced photoexcitation of N-ethylcarbazole in fluid solutions

    SciTech Connect

    Haggquist, G.W.; Burkhart, R.D. ); Naqvi, K.R. )

    1991-10-03

    When fluid solutions of N-ethylcarbazole (NEC) are irradiated by 308-nm pulses from an excimer laser, transient triplets and ions may be observed in the microsecond time regime. The formation of ions is favored in more polar solvents such as acetonitrile (AcN) and that of triplets in nonpolar solvents such as paraffin oil. The quantum yield of triplet formation from initial excitation is 0.23. Triplet states decay through concurrent first- and second-order channels: the second-order process, triplet-triplet annihilation, leads to formation of excited singlet states with an efficiency of 0.12. Transient carbazolyl cations and anions display double-exponential decays. To account for this behavior, a mechanism involving initial electron donation by the multiply excited chromophore to a nearby NEC molecule or solvent molecule is proposed; subsequent decay occurs primarily by germinate recombination of the resulting ion pair. The quantum yield for cation production is 0.037. Delayed fluorescence is AcN also decays by a double-exponential decay curve with rate constants, suggesting that the emission arises mainly from ion recombination.

  6. Direct observation of the solvent effects on the low-lying n?* and ??* excited triplet states of acetophenone derivatives in thermal equilibrium.

    PubMed

    Narra, Sudhakar; Shigeto, Shinsuke

    2015-03-01

    Low-lying excited triplet states of aromatic carbonyl compounds exhibit diverse photophysical and photochemical properties of fundamental importance. Despite tremendous effort in studying those triplet states, the effects of substituents and solvents on the energetics of the triplet manifold and on photoreactivity remain to be fully understood. We have recently studied the ordering of the low-lying n?* and ??* excited triplet states and its substituent dependence in acetophenone derivatives using nanosecond time-resolved near-IR (NIR) spectroscopy. Here we address the other important issue, the solvent effects, by directly observing the electronic bands in the NIR that originate from the lowest n?* and ??* states of acetophenone derivatives in four solvents of different polarity (n-heptane, benzene, acetonitrile, and methanol). The two transient NIR bands decay synchronously in all the solvents, indicating that the lowest n?* and ??* states are in thermal equilibrium irrespective of the solvent polarity studied here. We found that the ??* band increases in intensity relative to the n?* band as solvent polarity increases. These results are compared with the photoreduction rate constant for the acetophenone derivatives in the solvents to which 2-propanol was added as a hydrogen-atom donor. Based on the present findings, we present a comprehensive, solvent- and substituent-dependent energy level diagram of the low-lying n?* and ??* excited triplet states. PMID:25686256

  7. Bound Triplet Pairs in the Highest Spin States of Coinage Metal Clusters.

    PubMed

    Danovich, David; Shaik, Sason

    2010-05-11

    The work discusses bonding in coinage metal clusters, (n+1)Mn (M = Cu, Ag, Au), that have maximum spin without a single electron pair. It is shown that the bonding energy per atom, De/n, exhibits a strong nonadditive behavior; it grows rapidly with the cluster size and converges to values as large as 16-19 kcal/mol for Au and Cu. A valence bond (VB) analysis shows that this no-pair ferromagnetic bonding arises from bound triplet electron pairs that spread over all the close neighbors of a given atom in the clusters. The bound triplet pair owes its stabilization to the resonance energy provided by the mixing of the local ionic configurations, (3)M(??)(-?)M(+) and M(+?3)M(??)(-), and by the various excited covalent configurations (involving pz and dz(2) atomic orbitals) into the fundamental covalent structure (3)(M??M) with a s(1)s(1) electronic configuration. The VB model shows that a weak interaction in the dimer can become a remarkably strong binding force that holds together monovalent atoms without a single electron pair. PMID:26615685

  8. Laser flash photolysis study of (2-anthryl)ethylenes. Triplet-related photophysical behaviors

    SciTech Connect

    Wismontski-Knittel, T.; Das, P.K.

    1984-03-15

    The triplet-state photophysical behaviors of three trans-1,2-diarylethylenes with a phenyl, 2-naphtyl, or 2-thienyl group as one substituent and a 2-anthryl as the other have been studied by laser flash photolysis and pulse radiolysis. The triplets have been generated by energy transfer under sensitized conditions, direct intersystem crossing (in bromobenzene), and assisted intersystem crossing in the presence of such singlet quenchers as oxygen, ethyl iodide (EtI), di-tert-butyl nitroxide (DTBN), and N,N-dimethylaniline (DMA). The absorption spectra of the triplets are sharp, intense, and well resolved and display two major band systems at 400-500 and 550-650 nm, respectively. The observed triplet lifetimes (tau/sub T/) are in the range 15-120 ..mu..s. On the basis of the data concerning triplet-triplet (T-T) spectra, tau/sub T/'s, triplet quenching by azulene and di-tert-butyl nitroxide, and Stern-Volmer behavior for triplet formation via exciplexes with N,N-dimethylaniline, the triplets are assignable to predominantly one conformeric species, or multiple species with indistinguishable spectral and kinetic behaviors, with the excitation energy in either case being localized primarily on the anthracene moiety. In the case of 1-(2-thienyl)-2-(2-anthryl)ethylene, triplet-related formation and decay processes with associated lifetimes 100-120 ns are observed at the initial stage following the laser excitation; these are tentatively attributed to intramolecular relaxation in the initially formed triplet conformers in the form of rotation of aryl groups about quasi-single bonds. 5 figures, 3 tables.

  9. Geminate and Nongeminate Recombination of Triplet Excitons Formed by Singlet Fission

    NASA Astrophysics Data System (ADS)

    Bayliss, Sam L.; Chepelianskii, Alexei D.; Sepe, Alessandro; Walker, Brian J.; Ehrler, Bruno; Bruzek, Matthew J.; Anthony, John E.; Greenham, Neil C.

    2014-06-01

    We report the simultaneous observation of geminate and nongeminate triplet-triplet annihilation in a solution-processable small molecule TIPS-tetracene undergoing singlet exciton fission. Using optically detected magnetic resonance, we identify recombination of triplet pairs directly following singlet fission, as well as recombination of triplet excitons undergoing bimolecular triplet-triplet annihilation. We show that the two processes give rise to distinct magnetic resonance spectra, and estimate the interaction between geminate triplet excitons to be 60 neV.

  10. Triplet states as non-radiative traps in multichromophoric entities: single molecule spectroscopy of an artificial and natural antenna system.

    PubMed

    Hofkens, J; Schroeyers, W; Loos, D; Cotlet, M; Khn, F; Vosch, T; Maus, M; Herrmann, A; Mllen, K; Gensch, T; De Schryver, F C

    2001-09-14

    Energy transfer in antenna systems, ordered arrays of chromophores, is one of the key steps in the photosynthetic process. The photophysical processes taking place in such multichromophoric systems, even at the single molecule level, are complicated and not yet fully understood. Instead of directly studying individual antenna systems, we have chosen to focus first on systems for which the amount of chromophores and the interactions among the chromophores can be varied in a systematic way. Dendrimers with a controlled number of chromophores at the rim fulfill those requirements perfectly. A detailed photophysical study of a second-generation dendrimer, containing eight peryleneimide chromophores at the rim, was performed 'J. Am. Chem. Soc., 122 (2000) 9278'. One of the most intriguing findings was the presence of collective on/off jumps in the fluorescence intensity traces of the dendrimers. This phenomenon can be explained by assuming a simultaneous presence of both a radiative trap (energetically lowest chromophoric site) and a non-radiative trap (triplet state of one chromophore) within one individual dendrimer. It was shown that an analogue scheme could explain the collective on/off jumps in the fluorescence intensity traces of the photosynthetic pigment B-phycoerythrin (B-PE) (Porphyridium cruentum). The different values of the triplet lifetime that could be recovered for a fluorescence intensity trace of B-PE were correlated with different intensity levels in the trace, suggesting different chromophores acting as a trap as function of time. PMID:11603833

  11. Triplet states as non-radiative traps in multichromophoric entities: single molecule spectroscopy of an artificial and natural antenna system

    NASA Astrophysics Data System (ADS)

    Hofkens, Johan; Schroeyers, Wouter; Loos, Davey; Cotlet, Mircea; Khn, Fabian; Vosch, Tom; Maus, Michael; Herrmann, A.; Mllen, K.; Gensch, Thomas; De Schryver, F. C.

    2001-09-01

    Energy transfer in antenna systems, ordered arrays of chromophores, is one of the key steps in the photosynthetic process. The photophysical processes taking place in such multichromophoric systems, even at the single molecule level, are complicated and not yet fully understood. Instead of directly studying individual antenna systems, we have chosen to focus first on systems for which the amount of chromophores and the interactions among the chromophores can be varied in a systematic way. Dendrimers with a controlled number of chromophores at the rim fulfill those requirements perfectly. A detailed photophysical study of a second-generation dendrimer, containing eight peryleneimide chromophores at the rim, was performed 'J. Am. Chem. Soc., 122 (2000) 9278'. One of the most intriguing findings was the presence of collective on/off jumps in the fluorescence intensity traces of the dendrimers. This phenomenon can be explained by assuming a simultaneous presence of both a radiative trap (energetically lowest chromophoric site) and a non-radiative trap (triplet state of one chromophore) within one individual dendrimer. It was shown that an analogue scheme could explain the collective on/off jumps in the fluorescence intensity traces of the photosynthetic pigment B-phycoerythrin (B-PE) ( Porphyridium cruentum). The different values of the triplet lifetime that could be recovered for a fluorescence intensity trace of B-PE were correlated with different intensity levels in the trace, suggesting different chromophores acting as a trap as function of time.

  12. Laser photolysis studies on the electron-transfer reaction from the photoexcited triplet state of chloroindium(III) tetraphenylporphyrin to methylviologen in methanol solutions

    SciTech Connect

    Hoshino, M.; Seki, H.; Shizuka, H.

    1985-01-31

    Laser photolysis studies were carried out for chloroindium (III) tetraphenylporphyrin, C1In/sup III/TPP, in methanol solutions. The triplet states of (In/sup III/)/sup +/TPP and methylviologen, MV/sup 2 +/, were found to form a triplet exciplex with an association constant of 6.5 x 10/sup 2/M/sup -1/. The triplet exciplex partly dissociates to the cation radical of (In/sup III/)/sup +/TPP, (In/sup III/)/sup +/TPP/sup +/), and methylviologen cation radical, MV/sup +/, followed by the back electron transfer from MV/sup +/ to ((In/sup III/)/sup +/TPP/sup +/) to regenerate MV/sup 2 +/ and (In/sup III/)/sup +/TPP. The triplet exciplex reacts with triethanolamine, TEA, presumably to produce a new triplet exciplex, /sup 3/((In/sup III/)/sup +/TPP(TEA)(MV/sup 2 +/)), in which a TEA molecule is considered to occupy the axial position. No ionic dissociation from this triplet exciplex was observed. Photolysis of the methanol solution of C1In/sup III/TPP containing 0.5 M TEA and 10-/sup 3/ M MV/sup 2 +/ gives rise to the formation of MV/sup +/ as a final product. The absorption spectroscopy study revealed that C1In/sup III/TPP in a methanol solution at 0.5 M TEA is transformed to (In/sup III/TPP(TEA)/sub 2/)/sup +/(C1/sup -/), in which two TEA molecules are located in the axial positions. On the basis of the laser photolysis study the triplet state of (In/sup III/TPP(TEA)/sub 2/)/sup +/ is confirmed to undergo efficient electron transfer toward MV/sup 2 +/, resulting in the formation of MV/sup 2 +/. 29 refs., 6 figs.

  13. Comparative ENDOR study at 34 GHz of the triplet state of the primary donor in bacterial reaction centers of Rb. sphaeroides and Bl. viridis.

    PubMed

    Marchanka, Aliaksandr; Lubitz, Wolfgang; Plato, Martin; van Gastel, Maurice

    2014-05-01

    The primary electron donor (P) in the photosynthetic bacterial reaction center of Rhodobacter sphaeroides and Blastochloris viridis consists of a dimer of bacteriochlorophyll a and b cofactors, respectively. Its photoexcited triplet state in frozen solution has been investigated by time resolved ENDOR spectroscopy at 34 GHz. The observed ENDOR spectra for (3)P865 and (3)P960 are essentially the same, indicating very similar spin density distributions. Exceptions are the ethylidene groups unique to the bacteriochlorophyll b dimer in (3)P960. Strikingly, the observed hyperfine coupling constants of the ethylidene groups are larger than in the monomer, which speaks for an asymmetrically delocalized wave function over both monomer halves in the dimer. The latter observation corroborates previous findings of the spin density in the radical cation states P 865 (+) (Lendzian et al. in Biochim Biophys Acta 1183:139-160, 1993) and P 960 (+) (Lendzian et al. in Chem Phys Lett 148:377-385, 1988). As compared to the bacteriochlorophyll monomer, the hyperfine coupling constants of the methyl groups 2(1) and 12(1) are reduced by at least a factor of two, and quantitative analysis of these couplings gives rise to a ratio of approximately 3:1 for the spin density on the halves PL:PM. Our findings are discussed in light of the large difference in photosynthetic activity of the two branches of cofactors present in the bacterial reaction center proteins. PMID:23184403

  14. Effect of concentration on the formation of rose bengal triplet state on microcrystalline cellulose: a combined laser-induced optoacoustic spectroscopy, diffuse reflectance flash photolysis, and luminescence study.

    PubMed

    Litman, Yair; Voss, Matthew G; Rodrguez, Hernn B; San Romn, Enrique

    2014-11-13

    Laser-induced optoacoustic spectroscopy (LIOAS), diffuse reflectance laser flash photolysis (DRLFP), and laser-induced luminescence (LIL) have been applied in conjunction to the determination of triplet state quantum yields of Rose Bengal (RB) supported on microcrystalline cellulose, a strongly light-scattering solid. Among the three used methods, the only one capable of providing absolute triplet quantum yields is LIOAS, but DRLFP and LIL aid in demonstrating that the LIOAS signal arises in fact from the triplet state and confirm the trend found with RB concentration. The coherence found for the three techniques demonstrates the usefulness of the approach. Observed triplet quantum yields are nearly constant within a limited concentration range, after which they decay strongly due to the generation of inactive dye aggregates or energy trapping centers. When quantum yields are divided by the fraction of absorbed light exciting the dye, the quotient falls off steadily with concentration, following the same trend as the observed fluorescence quantum yield. The conditions that maximize triplet formation are determined as a compromise between the rising light absorption and the decrease of quantum yield with RB concentration. PMID:25112797

  15. Matrix effects on the triplet state of the OLED emitter Ir(4,6-dFppy)2(pic) (FIrpic): investigations by high-resolution optical spectroscopy.

    PubMed

    Rausch, Andreas F; Thompson, Mark E; Yersin, Hartmut

    2009-03-01

    The sky-blue emitting compound Ir(4,6-dFppy)(2)(pic) (iridium(III)bis[2-(4',6'-difluorophenyl)pyridinato-N,C(2')]-picolinate), commonly referred to as FIrpic and representing a well-known emitter material for organic light emitting diodes (OLEDs), has been investigated in detail by optical spectroscopy. Studies at temperatures from T = 1.5 K to T = 300 K were carried out in CH(2)Cl(2) and tetrahydrofuran (THF). In CH(2)Cl(2), two discrete sites were observed at cryogenic temperatures and studied by site-selective, high-resolution spectroscopy. The investigations reveal that the molecules located at the two sites exhibit distinctly different photophysical properties. For example, the three substates I, II, and III of the emitting triplet state T(1) of the low-energy site A show a distinctly larger zero-field splitting (ZFS) and exhibit shorter individual decay times than observed for the high-energy site B. The vibrational satellite structures in the emission spectra of the substates I(A) and I(B) exhibit clear differences in the ranges of metal-ligand (M-L) vibrations. For the compound studied in a polycrystalline THF host, giving only strongly inhomogeneously broadened spectra, the ZFS parameters and substate decay times vary in a similar range as observed for the two discrete sites in the CH(2)Cl(2) matrix. Thus, the amount of ZFS, the emission decay times, and also the intensities of the M-L vibrational satellites are affected by the matrix cage, that is, the host environment of the emitting complex. These properties are discussed with respect to variations of spin-orbit coupling routes. In particular, changes of d-orbital admixtures, that is, differences of the metal-to-ligand charge transfer (MLCT) character in the emitting triplet, play an important role. The matrix effects are expected to be also of importance for FIrpic and other Ir(III) compounds when applied as emitters in amorphous OLED matrixes. PMID:19235957

  16. The photophysics of monomeric bacteriochlorophylls c and d and their derivatives: properties of the triplet state and singlet oxygen photogeneration and quenching

    NASA Technical Reports Server (NTRS)

    Krasnovsky, A. A. Jr; Cheng, P.; Blankenship, R. E.; Moore, T. A.; Gust, D.

    1993-01-01

    Measurements of pigment triplet-triplet absorption, pigment phosphorescence and photosensitized singlet oxygen luminescence were carried out on solutions containing monomeric bacteriochlorophylls (Bchl) c and d, isolated from green photosynthetic bacteria, and their magnesium-free and farnesyl-free analogs. The energies of the pigment triplet states fell in the range 1.29-1.34 eV. The triplet lifetimes in aerobic solutions were 200-250 ns; they increased to 280 +/- 70 microseconds after nitrogen purging in liquid solutions and to 0.7-2.1 ms in a solid matrix at ambient or liquid nitrogen temperatures. Rate constants for quenching of the pigment triplet state by oxygen were (2.0-2.5) x 10(9) M-1 s-1, which is close to 1/9 of the rate constant for diffusion-controlled reactions. This quenching was accompanied by singlet oxygen formation. The quantum yields for the triplet state formation and singlet oxygen production were 55-75% in air-saturated solutions. Singlet oxygen quenching by ground-state pigment molecules was observed. Quenching was the most efficient for magnesium-containing pigments, kq = (0.31-1.2) x 10(9) M-1 s-1. It is caused mainly by a physical process of singlet oxygen (1O2) deactivation. Thus, Bchl c and d and their derivatives, as well as chlorophyll and Bchl a, combine a high efficiency of singlet oxygen production with the ability to protect photochemical and photobiological systems against damage by singlet oxygen.

  17. Non-adiabatic and intersystem crossing dynamics in SO2. II. The role of triplet states in the bound state dynamics studied by surface-hopping simulations.

    PubMed

    Mai, Sebastian; Marquetand, Philipp; González, Leticia

    2014-05-28

    The importance of triplet states in the photorelaxation dynamics of SO2 is studied by mixed quantum-classical dynamics simulations. Using the SHARC method, standing for Surface Hopping including ARbitrary Couplings, intersystem crossing (ISC) processes caused by spin-orbit coupling are found occurring on an ultrafast time scale (few 100 fs) and thus competing with internal conversion. While in the singlet-only dynamics only oscillatory population transfer between the (1)B1 and (1)A2 states is observed, in the dynamics including singlet and triplet states we find additionally continuous ISC to the (3)B2 state and to a smaller extent to the (3)B1/(3)A2 coupled states. The populations obtained from the dynamics are discussed with respect to the overall nuclear motion and in the light of recent TRPEPICO studies [I. Wilkinson, A. E. Boguslavskiy, J. Mikosch, D. M. Villeneuve, H.-J. Wörner, M. Spanner, S. Patchkovskii, and A. Stolow, "Excited state dynamics in SO2. I. Bound state relaxation studied by time-resolved photoelectron-photoion coincidence spectroscopy," J. Chem. Phys. 140, 204301 (2014)]. PMID:24880275

  18. Theory of enhanced proximity effect by midgap Andreev resonant state in diffusive normal-metal/triplet superconductor junctions

    NASA Astrophysics Data System (ADS)

    Tanaka, Y.; Kashiwaya, S.; Yokoyama, T.

    2005-03-01

    Enhanced proximity effect by the midgap Andreev resonant state (MARS) in a diffusive normal-metal/insulator/triplet superconductor (DN/TS) junction is studied based on the Keldysh-Nambu quasiclassical Greens-function formalism. By choosing a p -wave superconductor as a typical example of the TS, conductance of the junction and the spatial variation of the quasiparticle local density of states (LDOS) in the DN are calculated as the function of the magnitudes of the resistance Rd , Thouless energy in the DN, and the transparency of the insulating barrier. The resulting conductance spectrum has a zero-bias conductance peak (ZBCP) and the LDOS has a zero energy peak (ZEP) except for ?=?/2 (0????/2) , where ? denotes the angle between the lobe direction of the p -wave pair potential and the normal to the interface. The widths of the ZBCP and the ZEP are reduced with the increase of Rd while their heights are drastically enhanced. These peaks are revealed to be suppressed by applying a magnetic field. When the magnitude of Rd / R0 is sufficiently large, the total zero voltage resistance of the junction is almost independent of the Rd for ???/2 . The extreme case is ?=0 , where total zero voltage resistance is always R0 /2 . We also studied the charge transport in px +i py -wave junctions, where only the quasiparticles with perpendicular injection feel the MARS. Even in this case, the resulting LDOS in the DN has a ZEP. Thus the existence of the ZEP in the LDOS of the DN region is a remarkable feature for DN/TS junctions which have never been expected for the DN/singlet superconductor junctions where the MARS and proximity effect compete with each other. Based on these results, a crucial test to identify triplet pairing superconductors based on tunneling experiments is proposed.

  19. Toward the Understanding of the Photophysics and Photochemistry of 1-Nitronaphthalene under Solar Radiation: The First Theoretical Evidence of a Photodegradation Intramolecular Rearrangement Mechanism Involving the Triplet States.

    PubMed

    Giussani, Angelo

    2014-09-01

    1-Nitronaphthalene belongs to the class of nitrated polycyclic aromatic hydrocarbons, and constitutes an atmospheric pollutant commonly found in urban environments due to its production during incomplete combustions. On the basis of CASPT2//CASSCF quantum chemical calculations, the photophysics and photochemistry of the system under solar exposure have for the first time been studied. According to the characteristics of the incident radiation (either UVA or UVB, both present in the portion of the solar spectrum reaching the earth), a different excited state will be mainly populated. In both cases, the main decay path undertaken by the corresponding bright state leads to an efficient intersystem crossing process toward the (3)(πOπ*) triplet excited state. The population of the triplet manifold is then identified as the primary photoinduced process in the title molecule, not only after UVA interaction but also under UVB exposure. From the (3)(πOπ*) state, the system can either decay in a radiationless manner to the original ground state minimum, or undergo a photodegradation process mediated by the presence of an accessible singlet-triplet crossing region characterized by the formation of a oxaziridine ring. The determination of such a photodegradation path constitutes the first theoretical evidence supporting the hypothesis formulated almost 50 years ago in the seminal work of Chapman et al. (J. Am. Chem. Soc. 1966, 88, 5550), according to which the photolysis undertaken by nitrated polycyclic aromatic hydrocarbons proceeds through an intramolecular rearrangement mechanism, here characterized on the triplet manifold. PMID:26588542

  20. Influence of ionic strength on triplet-state natural organic matter loss by energy transfer and electron transfer pathways.

    PubMed

    Parker, Kimberly M; Pignatello, Joseph J; Mitch, William A

    2013-10-01

    Triplet state excited natural organic matter chromophores ((3)NOM*) are important reactive intermediates in indirect photochemical processes, yet the impact of salt concentrations relevant to estuarine and marine environments on (3)NOM* is poorly understood. The formation rates, pseudo-first-order loss rate constants, and steady-state concentration of (3)NOM* were monitored using the sorbate probe method in synthetic matrices with increasing ionic strength (IS) to seawater values using seawater halides or other salts. The steady-state concentration of (3)NOM* approximately doubled at seawater IS, regardless of the salt used, due to a decrease in the (3)NOM* decay rate constant. The electron transfer-mediated degradation of 2,4,6-trimethylphenol (TMP) by (3)NOM* was significantly slowed at higher IS. A model is proposed wherein high IS slows intra-organic matter electron transfer pathways, an important (3)NOM* loss pathway, leading to longer (3)NOM* lifetimes. Although IS did not appear to impact energy transfer pathways directly, the higher (3)NOM* steady-state concentrations promote energy transfer interactions. The observed decrease in decay rate constant, increase in steady-state concentration of (3)NOM* at high IS, and the inhibition of electron transfer pathways should be considered when determining the fate of organic pollutants in estuarine and marine environments. PMID:23952218

  1. Photophysical studies of triplet exciton processes in pure polymer films: Technical progress report for the period February 1985-July 26, 1986. [Poly (N-vinylcarbazole) (PVCA)

    SciTech Connect

    Burkhart, R.D.

    1986-01-01

    An integrated system has been constructed to conduct experiments on time resolved photoluminescence processes into the low microsecond time regime. It is specifically designed for investigations of triplet photophysical processes in polymers and it is very sensitive providing, for the first time, triplet-triplet absorption spectra of poly(N-vinylcarbazole). A primary mission for this system is the direct detection of excited triplets using triplet-triplet absorption spectroscopy. Both spectroscopic and kinetic characteristics of polymeric triplet states have been investigated with this system. Quantitative measurements have been made of molar absorptivities, triplet quantum yields and specific rate constants for both radiative and radiationless transitions for poly(4-((vinyloxy) carbonyl)-carbazole) (PFCZ) and ot its monomeric analogue (MFCZ). In addition, specific rate constants for triplet-triplet annihilation have been evaluated for several polymers and molecularly doped polymeric systems. Additional studies include computer assisted resolution of the excimeric phosphorescence of poly(N-vinylcarbazole) and the synthesis of end-capped polystyrene molecules in order to investigate intramolecular exciton transfer. Work is also under way to determine contributions from intermolecular and intramolecular triplet exciton migration in very concentrated solutions of poly(2-vinylnaphthalene). 6 refs., 3 figs.

  2. ODMR and optical investigation of the lowest triplet state of thioxanthone

    NASA Astrophysics Data System (ADS)

    Griesser, Hans J.; Bramley, Richard

    1982-02-01

    Highly resolved phosphorescence and optical-microwave double-resonance spectra of thioxanthone are reported. In contrast to related molecules, not only the z sublevel, but also the y sublevel carries substantial oscillator strength, whereas intersystem crossing still is highly selective, reaching the z sublevel only. A new zero-field resonance assignment is given.

  3. Reversal of Hckel (anti)aromaticity in the lowest triplet states of hexaphyrins and spectroscopic evidence for Baird's rule

    NASA Astrophysics Data System (ADS)

    Sung, Young Mo; Yoon, Min-Chul; Lim, Jong Min; Rath, Harapriya; Naoda, Koji; Osuka, Atsuhiro; Kim, Dongho

    2015-05-01

    The reversal of (anti)aromaticity in a molecule's triplet excited state compared with its closed-shell singlet ground state is known as Baird's rule and has attracted the interest of synthetic, physical organic chemists and theorists because of the potential to modulate the fundamental properties of highly conjugated molecules. Here we show that two closely related bis-rhodium hexaphyrins (R26H and R28H) containing [26] and [28] ?-electron peripheries, respectively, exhibit properties consistent with Baird's rule. In the ground state, R26H exhibits a sharp Soret-like band and distinct Q-like bands characteristic of an aromatic porphyrinoid, whereas R28H exhibits a broad absorption spectrum without Q-like bands, which is typical of an antiaromatic porphyrinoid. In contrast, the T-T absorption of R26H is broad, weak and featureless, whereas that of R28H displays an intense and sharp Soret-like band. These spectral signatures, in combination with quantum chemical calculations, are in line with qualitative expectations based on Baird's rule.

  4. Radio frequency measurements of tunnel couplings and singlet-triplet spin states in Si:P quantum dots

    NASA Astrophysics Data System (ADS)

    House, M. G.; Kobayashi, T.; Weber, B.; Hile, S. J.; Watson, T. F.; van der Heijden, J.; Rogge, S.; Simmons, M. Y.

    2015-11-01

    Spin states of the electrons and nuclei of phosphorus donors in silicon are strong candidates for quantum information processing applications given their excellent coherence times. Designing a scalable donor-based quantum computer will require both knowledge of the relationship between device geometry and electron tunnel couplings, and a spin readout strategy that uses minimal physical space in the device. Here we use radio frequency reflectometry to measure singlet-triplet states of a few-donor Si:P double quantum dot and demonstrate that the exchange energy can be tuned by at least two orders of magnitude, from 20 μeV to 8 meV. We measure dot-lead tunnel rates by analysis of the reflected signal and show that they change from 100 MHz to 22 GHz as the number of electrons on a quantum dot is increased from 1 to 4. These techniques present an approach for characterizing, operating and engineering scalable qubit devices based on donors in silicon.

  5. Photochemistry on surfaces: Fluorescence emission of monomers and dimers and triplet state absorption of acridine orange adsorbed on microcrystalline cellulose

    NASA Astrophysics Data System (ADS)

    Wilkinson, F.; Worrall, D. R.; Ferreira, L. F. Vieira

    1992-02-01

    Prompt fluorescence as well as delayed fluorescence emission of acridine orange was detected at room temperature from samples where this dye is adsorbed on microcrystalline cellulose. Ground state absorption studies provided evidence for dimer formation of the dye when adsorbed on cellulose, and the equilibrium constant for dimerisation was determined as 1.60.1 10 6mol -1g. At low loadings of acridine orange on cellulose (<1 ?mol g -1) the fluorescence emission is mainly due to the monomer and is similar to that observed in ethanolic solutions where little aggregation occurs, and peaks at 530 nm. A linear dependence of the fluorescence intensity on the amount of light absorbed by the dye was established for these "diluted" samples. However, at higher loadings (>20 ?mol g -1), the fluorescence intensity decreases, and the emission is broad with its maximum at 620 nm, and is mainly due to the dimer. By assuming that the excited monomer and dimer of acridine orange are the only emitting species, it was possible to determine the fluorescence quantum yields for these two species when adsorbed on microcrystalline cellulose as 0.950.05 and 0.400.10, respectively. Pulsed emission studies at room temperature in the millisecond time-range also revealed monomer and dimer emissions on this longer time-scale. These are shown to be due to thermally activated delayed fluorescence arising from the triplet states of monomer and dimer acridine orange as confirmed by diffuse reflectance transient absorption studies.

  6. Radio frequency measurements of tunnel couplings and singlet-triplet spin states in Si:P quantum dots.

    PubMed

    House, M G; Kobayashi, T; Weber, B; Hile, S J; Watson, T F; van der Heijden, J; Rogge, S; Simmons, M Y

    2015-01-01

    Spin states of the electrons and nuclei of phosphorus donors in silicon are strong candidates for quantum information processing applications given their excellent coherence times. Designing a scalable donor-based quantum computer will require both knowledge of the relationship between device geometry and electron tunnel couplings, and a spin readout strategy that uses minimal physical space in the device. Here we use radio frequency reflectometry to measure singlet-triplet states of a few-donor Si:P double quantum dot and demonstrate that the exchange energy can be tuned by at least two orders of magnitude, from 20??eV to 8?meV. We measure dot-lead tunnel rates by analysis of the reflected signal and show that they change from 100?MHz to 22?GHz as the number of electrons on a quantum dot is increased from 1 to 4. These techniques present an approach for characterizing, operating and engineering scalable qubit devices based on donors in silicon. PMID:26548556

  7. Radio frequency measurements of tunnel couplings and singlettriplet spin states in Si:P quantum dots

    PubMed Central

    House, M. G.; Kobayashi, T.; Weber, B.; Hile, S. J.; Watson, T. F.; van der Heijden, J.; Rogge, S.; Simmons, M. Y.

    2015-01-01

    Spin states of the electrons and nuclei of phosphorus donors in silicon are strong candidates for quantum information processing applications given their excellent coherence times. Designing a scalable donor-based quantum computer will require both knowledge of the relationship between device geometry and electron tunnel couplings, and a spin readout strategy that uses minimal physical space in the device. Here we use radio frequency reflectometry to measure singlettriplet states of a few-donor Si:P double quantum dot and demonstrate that the exchange energy can be tuned by at least two orders of magnitude, from 20??eV to 8?meV. We measure dotlead tunnel rates by analysis of the reflected signal and show that they change from 100?MHz to 22?GHz as the number of electrons on a quantum dot is increased from 1 to 4. These techniques present an approach for characterizing, operating and engineering scalable qubit devices based on donors in silicon. PMID:26548556

  8. Linear dichroism in triplet singlet difference spectra of photosynthetic pigment protein complexes, monitored with absorbance-detected magnetic resonance: correction for non-ideal optical effects

    NASA Astrophysics Data System (ADS)

    Louwe, R. J. W.; Vrieze, J.; van der Vos, R.; Aartsma, T. J.; Hoff, A. J.

    1999-06-01

    The non-sinusoidal modulation of the photo-elastic modulator used for measurements of the linear dichroism in absorption-detected magnetic resonance (LD-AMDR) causes an experimental error in determining the angles of the triplet spin-sublevel axes relative to the optical dipole transition moment that can be be as large as 20. We have obtained an analytical correction for this error. The error analysis was applied to LD-ADMR experiments on the carotenoidless mutant R26 of Rhodobacter (Rb.) sphaeroides. The corrected angles of the triplet x- and y-axis with respect to the optical transition dipole moment at 896 nm of R26 are 864 and 223, respectively.

  9. Effect of SiO2 and zeolite surfaces on the excited triplet state of benzophenone, BT; a spectroscopic and kinetic study.

    PubMed

    Thomas, J Kerry

    2004-05-01

    Laser flash photolysis has been used to study the triplet excited state of benzophenone B(T), on various surfaces, SiO(2), zeolites NaY, KY, NaX and KX, and in rigid media at room temperature, polyethylene and polymethylmethacrylate. The studies point to similarities of the spectroscopy and kinetics of B(T) in fluid solution, in a solid matrix (polymers) and on a SiO(2) surface. However, stark differences are observed for B(T) in zeolites where the absorption spectrum mimics that of the protonated ketone, and the reactivities of B(T) with C(6)H(12) and CH(3)OH are an order of magnitude smaller than those in liquid C(6)H(12) and CH(3)OH. Inclusion of ammonia, which blocks acidic sites in the zeolite, produces a triplet spectrum which is similar to that in polar solution. The reactivity of the triplet with ammonia in a zeolite is also comparable to that observed for this reaction in polar solution. These data are discussed in terms of the interaction of benzophenone with acidic sites in the zeolites, and to restrictions placed on the reactants in the zeolite cages. The blocking of the zeolite acidic sites by ammonia produces spectral and kinetic data (reactivity with NH(3)) of the triplet that are comparable to those observed in solution. This is one of the few cases where zeolites inhibit rather than promote reactions of a solute adsorbed in them. PMID:15122366

  10. Low temperature pulsed EPR study at 34 GHz of the triplet states of the primary electron donor P865 and the carotenoid in native and mutant bacterial reaction centers of Rhodobacter sphaeroides

    PubMed Central

    Marchanka, Aliaksandr; Paddock, Mark; Lubitz, Wolfgang; van Gastel, Maurice

    2008-01-01

    The photosynthetic charge separation in bacterial reaction centers occurs predominantly along one of two nearly symmetric branches of cofactors. Low temperature EPR spectra of the triplet states of the chlorophyll and carotenoid pigments in the reaction center of Rb. sphaeroides R-26.1, 2.4.1 and two double mutants GD(M203)/AW(M260) and LH(M214)/AW(M260) have been recorded at 34 GHz to investigate the relative activities of the A and B branches. The triplet states are found to derive from radical pair and intersystem crossing mechanisms and the rates of formation are anisotropic. The former mechanism is operative for Rb. sphaeroides R-26.1, 2.4.1 and mutant GD(M203)/AW(M260) and indicates that A-branch charge separation proceeds at temperatures down to 10 K. The latter mechanism, derived from the spin polarization and operative for mutant LH(M214)/AW(M260) indicates that no long-lived radical pairs are formed upon direct excitation of the primary donor and that virtually no charge separation at the B-branch occurs at low temperatures. When the temperature is raised above 30 K, B-branch charge separation is observed, which is at most 1% of A-branch charge separation. B-branch radical pair formation can be induced at 10 K with low yield by direct excitation of the bacteriopheophytin of the B-branch at 590 nm. The formation of a carotenoid triplet state is observed. The rate of formation depends on the orientation of the reaction center in the magnetic field and is caused by a magnetic field dependence of the oscillation frequency by which the singlet and triplet radical pair precursor states interchange. Combination of these findings with literature data provides strong evidence that the thermally activated transfer step on the B-branch occurs between the primary donor, P865, and the accessory bacteriochlorophyll, whereas this step is barrierless down to 10 K along the A-branch. PMID:18052205

  11. Communication: DMRG-SCF study of the singlet, triplet, and quintet states of oxo-Mn(Salen)

    SciTech Connect

    Wouters, Sebastian Van Speybroeck, Veronique; Van Neck, Dimitri; Bogaerts, Thomas; Van Der Voort, Pascal

    2014-06-28

    We use CHEMPS2, our free open-source spin-adapted implementation of the density matrix renormalization group (DMRG) [S. Wouters, W. Poelmans, P. W. Ayers, and D. Van Neck, Comput. Phys. Commun. 185, 1501 (2014)], to study the lowest singlet, triplet, and quintet states of the oxo-Mn(Salen) complex. We describe how an initial approximate DMRG calculation in a large active space around the Fermi level can be used to obtain a good set of starting orbitals for subsequent complete-active-space or DMRG self-consistent field calculations. This procedure mitigates the need for a localization procedure, followed by a manual selection of the active space. Per multiplicity, the same active space of 28 electrons in 22 orbitals (28e, 22o) is obtained with the 6-31G{sup *}, cc-pVDZ, and ANO-RCC-VDZP basis sets (the latter with DKH2 scalar relativistic corrections). Our calculations provide new insight into the electronic structure of the quintet.

  12. Statistical Enrichment of Epigenetic States Around Triplet Repeats that Can Undergo Expansions

    PubMed Central

    Essebier, Alexandra; Vera Wolf, Patricia; Cao, Minh Duc; Carroll, Bernard J.; Balasubramanian, Sureshkumar; Bodén, Mikael

    2016-01-01

    More than 30 human genetic diseases are linked to tri-nucleotide repeat expansions. There is no known mechanism that explains repeat expansions in full, but changes in the epigenetic state of the associated locus has been implicated in the disease pathology for a growing number of examples. A comprehensive comparative analysis of the genomic features associated with diverse repeat expansions has been lacking. Here, in an effort to decipher the propensity of repeats to undergo expansion and result in a disease state, we determine the genomic coordinates of tri-nucleotide repeat tracts at base pair resolution and computationally establish epigenetic profiles around them. Using three complementary statistical tests, we reveal that several epigenetic states are enriched around repeats that are associated with disease, even in cells that do not harbor expansion, relative to a carefully stratified background. Analysis of over one hundred cell types reveals that epigenetic states generally tend to vary widely between genic regions and cell types. However, there is qualified consistency in the epigenetic signatures of repeats associated with disease suggesting that changes to the chromatin and the DNA around an expanding repeat locus are likely to be similar. These epigenetic signatures may be exploited further to develop models that could explain the propensity of repeats to undergo expansions. PMID:27013954

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

    PubMed

    Svoboda, Ond?ej; Slav?ek, 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

  14. Laser spectroscopy of HfO: Linkage of the triplet state manifolds

    SciTech Connect

    Kaledin, L.A.; McCord, J.E.; Heaven, M.C.

    1995-12-31

    The wavelength-resolved fluorescence excitation technique has been used to record the (0,0) band of the b{sup 3}{Pi}{sub 1} - X{sup 1}{Sigma}{sup +} electronic transition of HfO at a resolution of 0.03 cm{sup -1}. Previously, this transition has been assigned as a B{sup 1}{Pi}-X{sup 1}{Sigma}{sup +} electronic transition. The principal constants (in cm{sup -1}) obtained from recent and previous analyses are discussed. Ligand field theory (LFT) calculations were used to suggest electronic configurations for the excited states of HfO. New electronic assignments based on LFT predictions for the F and E states are indicated in parentheses.

  15. Properties of the triplet metastable states of the alkaline-earth-metal atoms

    SciTech Connect

    Mitroy, J.; Bromley, M.W.J.

    2004-11-01

    The static and dynamic properties of the alkaline-earth-metal atoms in their metastable state are computed in a configuration interaction approach with a semiempirical model potential for the core. Among the properties determined are the scalar and tensor polarizabilities, the quadrupole moment, some of the oscillator strengths, and the dispersion coefficients of the van der Waals interaction. A simple method for including the effect of the core on the dispersion parameters is described.

  16. Toward enabling large-scale open-shell equation-of-motion coupled cluster calculations: triplet states of β-carotene

    SciTech Connect

    Hu, Hanshi; Bhaskaran-Nair, Kiran; Apra, Edoardo; Govind, Niranjan; Kowalski, Karol

    2014-10-02

    In this paper we discuss the application of novel parallel implementation of the coupled cluster (CC) and equation-of-motion coupled cluster methods (EOMCC) in calculations of excitation energies of triplet states in beta-carotene. Calculated excitation energies are compared with experimental data, where available. We also provide a detailed description of the new parallel algorithms for iterative CC and EOMCC models involving single and doubles excitations.

  17. Overview of helium-like structure measurements: A focus on the N = 2 triplet states

    SciTech Connect

    Berry, H.G.; Dunford, R.W.

    1992-01-01

    We present a comprehensive analysis of existing measurements of the 1s2s [sup 3]S[sub 1] [minus] 1s2p[sup 3]P[sub 0,1,2] transition energies in heliumlike ions for nuclear charges Z=2 to Z=92. We find agreement with the standard unified calculations of [vert bar]Drake except for the transitions from the 1s2p [sup 3]P[sub o] state. We find a deviation equal to 2.3x(Z/10)[sup 4] cm[sup [minus]1] for the most precise existing measurements.

  18. Narrow Energy Gap between Triplet and Singlet Excited States of Sn2+ in Borate Glass

    PubMed Central

    Masai, Hirokazu; Yamada, Yasuhiro; Suzuki, Yuto; Teramura, Kentaro; Kanemitsu, Yoshihiko; Yoko, Toshinobu

    2013-01-01

    Transparent inorganic luminescent materials have attracted considerable scientific and industrial attention recently because of their high chemical durability and formability. However, photoluminescence dynamics of ns2-type ions in oxide glasses has not been well examined, even though they can exhibit high quantum efficiency. We report on the emission property of Sn2+-doped strontium borate glasses. Photoluminescence dynamics studies show that the peak energy of the emission spectrum changes with time because of site distribution of emission centre in glass. It is also found that the emission decay of the present glass consists of two processes: a faster S1-S0 transition and a slower T1-S0 relaxation, and also that the energy difference between T1 and S1 states was found to be much smaller than that of (Sn, Sr)B6O10 crystals. We emphasize that the narrow energy gap between the S1 and T1 states provides the glass phosphor a high quantum efficiency, comparable to commercial crystalline phosphors. PMID:24345869

  19. Narrow energy gap between triplet and singlet excited states of Sn2+ in borate glass.

    PubMed

    Masai, Hirokazu; Yamada, Yasuhiro; Suzuki, Yuto; Teramura, Kentaro; Kanemitsu, Yoshihiko; Yoko, Toshinobu

    2013-01-01

    Transparent inorganic luminescent materials have attracted considerable scientific and industrial attention recently because of their high chemical durability and formability. However, photoluminescence dynamics of ns(2)-type ions in oxide glasses has not been well examined, even though they can exhibit high quantum efficiency. We report on the emission property of Sn(2+)-doped strontium borate glasses. Photoluminescence dynamics studies show that the peak energy of the emission spectrum changes with time because of site distribution of emission centre in glass. It is also found that the emission decay of the present glass consists of two processes: a faster S1-S0 transition and a slower T1-S0 relaxation, and also that the energy difference between T1 and S1 states was found to be much smaller than that of (Sn, Sr)B6O10 crystals. We emphasize that the narrow energy gap between the S1 and T1 states provides the glass phosphor a high quantum efficiency, comparable to commercial crystalline phosphors. PMID:24345869

  20. Narrow Energy Gap between Triplet and Singlet Excited States of Sn2+ in Borate Glass

    NASA Astrophysics Data System (ADS)

    Masai, Hirokazu; Yamada, Yasuhiro; Suzuki, Yuto; Teramura, Kentaro; Kanemitsu, Yoshihiko; Yoko, Toshinobu

    2013-12-01

    Transparent inorganic luminescent materials have attracted considerable scientific and industrial attention recently because of their high chemical durability and formability. However, photoluminescence dynamics of ns2-type ions in oxide glasses has not been well examined, even though they can exhibit high quantum efficiency. We report on the emission property of Sn2+-doped strontium borate glasses. Photoluminescence dynamics studies show that the peak energy of the emission spectrum changes with time because of site distribution of emission centre in glass. It is also found that the emission decay of the present glass consists of two processes: a faster S1-S0 transition and a slower T1-S0 relaxation, and also that the energy difference between T1 and S1 states was found to be much smaller than that of (Sn, Sr)B6O10 crystals. We emphasize that the narrow energy gap between the S1 and T1 states provides the glass phosphor a high quantum efficiency, comparable to commercial crystalline phosphors.

  1. The effect of the structure and conformational dynamics on quenching of triplet states of porphyrins and their chemical dimers by molecular oxygen and on singlet oxygen generation

    NASA Astrophysics Data System (ADS)

    Ivashin, N. V.; Shchupak, E. E.; Sagun, E. I.

    2015-01-01

    Quantum-chemical calculations are performed to analyze the factors affecting rate constant k T of quenching of the lowest triplet state by molecular oxygen and quantum yield ?? of singlet oxygen generation in chemical dimers of porphyrins bound by phenyl spacers at one of the meso positions (OEP)2-Ph, (TPP)2, and their Zn complexes. It is established that, for both types of dimers, the triplet excitation is localized on one of the macrocycles. The steric hindrance of macrocycles at the site of the phenyl ring of (OEP)2-Ph, (ZnOEP)2-Ph, and their monomeric analogues OEP-Ph and ZnOEP-Ph facilitates its rotation by 90 in the triplet state. The lowest triplet state energy in this ( U) conformation is lower than 7800 cm-1, which makes impossible electronic excitation energy transfer to molecular oxygen. The potential barrier of transformation to the U conformation is considerably lower for dimers than for monomers. Because of this, the rate of conformational transformations for dimers is higher and some of the (OEP)2-Ph and (ZnOEP)2-Ph molecules have time to transform into the new U conformation before diffusion collision with O2 molecules in solution. This leads to a noticeable decrease in ?? in accordance with experimental data. It is shown that the behavior of k T in the series of the studied dimers, their monomeric analogues, and relative compounds corresponds to the model of dipole-dipole electronic excitation energy transfer 1(3M⋯3?{g/-}) ? 1(1M0⋯1?g) in collisional complexes.

  2. Effect of zeolite properties on ground-state and triplet-triplet absorption, prompt and oxygen induced delayed fluorescence of tetraphenylporphyrin at gas/solid interface

    NASA Astrophysics Data System (ADS)

    Levin, P. P.; Costa, Silvia M. B.; Lopes, J. M.; Serralha, F. N.; Ribeiro, F. Ramôa

    2000-08-01

    The ground-state and transient absorption, prompt and delayed fluorescence of tetraphenylporphyrin (TPP) adsorbed onto the external surface of different zeolites was monitored using diffuse-reflectance steady-state and laser flash photolysis. The delayed fluorescence (DF) of TPP detected in the presence of O 2 is attributed to the energy transfer from 3TPP to 3O 2 to form 1O 2 and subsequent energy transfer from 1O 2 to some other 3TPP within the organised molecular ensembles on the zeolite surface. The spectroscopic and kinetic parameters, namely the yield of DF (2-20% relative to prompt fluorescence), depend on the zeolite properties: the observed differences were correlated with the acid-base properties of the two zeolite series studied in this work (KA, NaA, CaA) and (NaA, NaX, NaY).

  3. Effect of zeolite properties on ground-state and triplet-triplet absorption, prompt and oxygen induced delayed fluorescence of tetraphenylporphyrin at gas/solid interface.

    PubMed

    Levin, P P; Costa, S M; Lopes, J M; Serralha, F N; Ribeiro, F R

    2000-08-01

    The ground-state and transient absorption, prompt and delayed fluorescence of tetraphenylporphyrin (TPP) adsorbed onto the external surface of different zeolites was monitored using diffuse-reflectance steady-state and laser flash photolysis. The delayed fluorescence (DF) of TPP detected in the presence of O2 is attributed to the energy transfer from 3TPP to 3O2 to form 1O2 and subsequent energy transfer from 1O2 to some other 3TPP within the organised molecular ensembles on the zeolite surface. The spectroscopic and kinetic parameters, namely the yield of DF (2-20% relative to prompt fluorescence), depend on the zeolite properties: the observed differences were correlated with the acid-base properties of the two zeolite series studied in this work (KA, NaA, CaA) and (NaA, NaX, NaY). PMID:10952136

  4. Role of the vibrational coupling of /sup 3/n. pi. * and /sup 3/. pi pi. * states in reactions resulting in the formation of triplet exciplexes of phenazine compounds with dimethylaniline

    SciTech Connect

    Osipov, V.V.; Usacheva, M.N.; Dilung, I.I.

    1986-11-01

    The relationship between the nature of the reactive triplet state of phenazine, as well as its mono-, di-, and tetrabenzo derivatives, and their reactivity in the formation of triplet exciplexes with amines has been investigated. It has been shown that the reactivity of triplet excited states of phenazines is determined mainly by the presence of vibrational mixing of the lower T/sub 1/ and T/sub 2/ triplet states with different electronic configurations and the position of the T/sub 2/ level. The total reaction rate is determined by the sum of the rates of the processes with the participation of the T/sub 1/ and T/sub 2/ states.

  5. Ab initio analysis of the transition states on the lowest triplet H2O2 potential surface

    NASA Astrophysics Data System (ADS)

    Karkach, Sergei P.; Osherov, Vladimir I.

    1999-06-01

    The lowest triplet H2O2 potential surface was analyzed for the transition and minimum-energy structures in the range from -0.2 to +5.4 eV with respect to the H2+O2 energy. All the transition structures, the reaction pathways, and the local minima were found to have planar configurations for the atoms. We focus on the transition structures responsible for the main bimolecular chemical reactions formally possible on this surface: H2+O2?2HO, H+HO2, and H2O+O; H+HO2?2HO and H2O+O; and 2HO?H2O+O. For these reactions, activation energies and rate constants in the transition state approximation were evaluated. Our computed rate constants confirm the recommended values for the H+HO2?H2+O2 and HO+HO?H2O+O reactions. The results obtained refute the elementary character of the H+HO2?H2O+O process and call into question the possibility of chain initiation in the H2/O2 system by means of a bimolecular reaction. Most likely, the chain initiation in the gas phase is owing to trimolecular reactions H2+2O2?2HO2, 2HO+O2. Special attention was paid to accurate prediction of electronic energies in the transition structures. A new procedure developed, "extrapolation to zero high-level correction," results in very realistic activation energies. Predictions of molecular energies are coincident with those from the widely used G2 scheme but have smaller uncertainty.

  6. Neutron interferometric measurement of the scattering length difference between the triplet and singlet states of n -3He

    NASA Astrophysics Data System (ADS)

    Huber, M. G.; Arif, M.; Chen, W. C.; Gentile, T. R.; Hussey, D. S.; Black, T. C.; Pushin, D. A.; Shahi, C. B.; Wietfeldt, F. E.; Yang, L.

    2014-12-01

    We report a determination of the n -3He scattering length difference Δ b'=b1'-b0'=[-5.411 ±0.031 (statistical)±0.039 (systematic)] fm between the triplet and singlet states using a neutron interferometer. This revises our previous result Δ b'=[-5.610 ±0.027 (statistical)±0.032 (systematic)] fm obtained using the same technique in 2008 [Huber et al., Phys. Rev. Lett. 102, 200401 (2009), 10.1103/PhysRevLett.102.200401; Huber et al., Phys. Rev. Lett. 103, 179903(E) (2009), 10.1103/PhysRevLett.103.179903]. This revision is attributable to a reanalysis of the 2008 experiment that now includes a systematic correction caused by magnetic-field gradients near the 3He cell which had been previously underestimated. Furthermore, we more than doubled our original data set from 2008 by acquiring 6 months of additional data in 2013. Both the new data set and a reanalysis of the older data are in good agreement. Scattering lengths of low-Z isotopes are valued for use in few-body nuclear effective field theories, provide important tests of modern nuclear potential models, and, in the case of 3He, aid in the interpretation of neutron scattering from quantum liquids. The difference Δ b' was determined by measuring the relative phase shift between two incident neutron polarizations caused by the spin-dependent interaction with a polarized 3He target. The target 3He gas was sealed inside a small, flat-windowed glass cell that was placed in one beam path of the interferometer. The relaxation of 3He polarization was monitored continuously with neutron transmission measurements. The neutron polarization and spin-flipper efficiency were determined separately using 3He analyzers and two different polarimetry analysis methods. A summary of the measured scattering lengths for n -3He with a comparison to nucleon interaction models is given.

  7. Aqueous benzene-diols react with an organic triplet excited state and hydroxyl radical to form secondary organic aerosol.

    PubMed

    Smith, Jeremy D; Kinney, Haley; Anastasio, Cort

    2015-04-21

    Chemical processing in atmospheric aqueous phases, such as cloud and fog drops, can play a significant role in the production and evolution of secondary organic aerosol (SOA). In this work we examine aqueous SOA production via the oxidation of benzene-diols (dihydroxy-benzenes) by the triplet excited state of 3,4-dimethoxybenzaldehyde, (3)DMB*, and by hydroxyl radical, ?OH. Reactions of the three benzene-diols (catechol (CAT), resorcinol (RES) and hydroquinone (HQ)) with (3)DMB* or ?OH proceed rapidly, with rate constants near diffusion-controlled values. The two oxidants exhibit different behaviors with pH, with rate constants for (3)DMB* increasing as pH decreases from pH 5 to 2, while rate constants with ?OH decrease in more acidic solutions. Mass yields of SOA were near 100% for all three benzene-diols with both oxidants. We also examined the reactivity of atmospherically relevant mixtures of phenols and benzene-diols in the presence of (3)DMB*. We find that the kinetics of phenol and benzene-diol loss, and the production of SOA mass, in mixtures are generally consistent with rate constants determined in experiments containing a single phenol or benzene-diol. Combining our aqueous kinetic and SOA mass yield data with previously published gas-phase data, we estimate a total SOA production rate from benzene-diol oxidation in a foggy area with significant wood combustion to be nearly 0.6 ?g mair(-3) h(-1), with approximately half from the aqueous oxidation of resorcinol and hydroquinone, and half from the gas-phase oxidation of catechol. PMID:25797024

  8. Theory of Pairing Assisted Spin Polarization in Spin-Triplet Equal Spin Pairing: Origin of Extra Magnetization in Sr2RuO4 in Superconducting State

    NASA Astrophysics Data System (ADS)

    Miyake, Kazumasa

    2014-05-01

    It is shown that an extra magnetization is induced by an onset of the equal-spin-pairing of spin triplet superconductivity if the energy dependence of the density of states of quasiparticles exists in the normal state. It turns out that the effect is observable in Sr2RuO4 due to the existence of van Hove singularity in the density of states near the Fermi level, explaining the extra contribution in the Knight shift reported by Ishida et al. It is also quite non-trivial that this effect exists even without external magnetic field, which implies that the time reversal symmetry is spontaneously broken in the spin space.

  9. A first detection of singlet to triplet conversion from the 1 1B u- to the 1 3A g state and triplet internal conversion from the 1 3A g to the 1 3B u state in carotenoids: dependence on the conjugation length

    NASA Astrophysics Data System (ADS)

    Rondonuwu, Ferdy S.; Watanabe, Yasutaka; Fujii, Ritsuko; Koyama, Yasushi

    2003-07-01

    Subpicosecond time-resolved absorption spectra were recorded in the visible region for a set of photosynthetic carotenoids having different numbers of conjugated double bonds ( n), which include neurosporene ( n=9), spheroidene ( n=10), lycopene ( n=11), anhydrorhodovibrin ( n=12) and spirilloxanthin ( n=13). Singular-value decomposition and global fitting of the spectral-data matrices lead us to a branched relaxation scheme including both (1) the singlet internal conversion in the sequence of 1 1B u+ ? 1 1B u- ? 2 1A g- ? 1 1A g-(ground), and (2) the singlet-to-triplet conversion of 1 1B u- ? 1 3A g followed by triplet internal conversion of 1 3A g ? 1 3B u.

  10. Photophysics of singlet and triplet intraligand excited states in [ReCl(CO)3(1-(2-pyridyl)-imidazo[1,5-α]pyridine)] complexes.

    PubMed

    Blanco-Rodríguez, Ana María; Kvapilová, Hana; Sýkora, Jan; Towrie, Michael; Nervi, Carlo; Volpi, Giorgio; Záliš, Stanislav; Vlček, Antonín

    2014-04-23

    Excited-state characters and dynamics of [ReCl(CO)3(3-R-1-(2-pyridyl)-imidazo[1,5-α]pyridine)] complexes (abbreviated ReGV-R, R = CH3, Ph, PhBu(t), PhCF3, PhNO2, PhNMe2) were investigated by pico- and nanosecond time-resolved infrared spectroscopy (TRIR) and excited-state DFT and TD-DFT calculations. Near UV excitation populates the lowest singlet state S1 that undergoes picosecond intersystem crossing (ISC) to the lowest triplet T1. Both states are initially formed hot and relax with ∼20 ps lifetime. TRIR together with quantum chemical calculations reveal that S1 is predominantly a ππ* state localized at the 1-(2-pyridyl)-imidazo[1,5-α]pyridine (= impy) ligand core, with impy → PhNO2 and PhNMe2 → impy intraligand charge-transfer contributions in the case of ReGV-PhNO2 and ReGV-PhNMe2, respectively. T1 is predominantly ππ*(impy) in all cases. It follows that excited singlet and corresponding triplet states have to some extent different characters and structures even if originating nominally from the same preponderant one-electron excitations. ISC occurs with a solvent-independent (CH2Cl2, MeCN) 20-30 ps lifetime, except for ReGV-PhNMe2 (10 ps in CH2Cl2, 100 ps in MeCN). ISC is 200-300 times slower than in analogous complexes with low-lying MLCT states. This difference is interpreted in terms of spin-orbit interaction and characters of orbitals involved in one-electron excitations that give rise to S1 and T1 states. ReGV-R present a unique case of octahedral heavy-metal complexes where the S1 lifetime is long enough to allow for separate spectroscopic characterization of singlet and triplet excited states. This study provides an insight into dynamics and intersystem crossing pathways of low-lying singlet and triplet excited states localized at bidentate ligands bound directly to a heavy metal atom. Rather long (1)IL lifetimes indicate the possibility of photonic applications of singlet excited states. PMID:24669762

  11. Efficient enhancement of the visible-light absorption of cyclometalated Ir(III) complexes triplet photosensitizers with Bodipy and applications in photooxidation and triplet-triplet annihilation upconversion.

    PubMed

    Sun, Jifu; Zhong, Fangfang; Yi, Xiuyu; Zhao, Jianzhang

    2013-06-01

    We report molecular designing strategies to enhance the effective visible-light absorption of cyclometalated Ir(III) complexes. Cationic cyclometalated Ir(III) complexes were prepared in which boron-dipyrromethene (Bodipy) units were attached to the 2,2'-bipyridine (bpy) ligand via -C?C- bonds at either the meso-phenyl (Ir-2) or 2 position of the ? core of Bodipy (Ir-3). For the first time the effect of ? conjugating (Ir-3) or tethering (Ir-2) of a light-harvesting chromophore to the coordination center on the photophysical properties was compared in detail. Ir(ppy)2(bpy) (Ir-1; ppy = 2-phenylpyridine) was used as model complex, which gives the typical weak absorption in visible range (? < 4790 M(-1) cm(-1) in region > 400 nm). Ir-2 and Ir-3 showed much stronger absorption in the visible range (? = 71,400 M(-1) cm(-1) at 499 nm and 83,000 M(-1) cm(-1) at 527 nm, respectively). Room-temperature phosphorescence was only observed for Ir-1 (?(em) = 590 nm) and Ir-3 (?(em) = 742 nm). Ir-3 gives RT phosphorescence of the Bodipy unit. On the basis of the 77 K emission spectra, nanosecond transient absorption spectra, and spin density analysis, we proposed that Bodipy-localized long-lived triplet excited states were populated for Ir-2 (?T = 23.7 ?s) and Ir-3 (87.2 ?s). Ir-1 gives a much shorter triplet-state lifetime (0.35 ?s). Complexes were used as singlet oxygen ((1)O2) photosensitizers in photooxidation. The (1)O2 quantum yield of Ir-3 (?? = 0.97) is ca. 2-fold of Ir-2 (?? = 0.52). Complexes were also used as triplet photosensitizer for TTA upconversion; upconversion quantum yields of 1.2% and 2.8% were observed for Ir-2 and Ir-3, respectively. Our results proved that the strong absorption of visible light of Ir-2 failed to enhance production of a triplet excited state. These results are useful for designing transition metal complexes that show effective strong visible-light absorption and long-lived triplet excited states, which can be used as ideal triplet photosensitizers in photocatalysis and TTA upconversion. PMID:23327589

  12. Triplet properties and interactions of the primary electron donor and antenna chromophores in membranes of Heliobacterium chlorum, studied with ADMR spectroscopy.

    PubMed

    Vrieze, J; van de Meent, E J; Hoff, A J

    1998-10-20

    The triplet states of antenna and reaction center bacteriochlorophyll (BChl) g in membranes of Heliobacterium chlorum were studied by optically detected magnetic resonance in zero magnetic field, using absorbance detection. A variety of triplet states was detected, which were all localized on single BChl g chromophores as concluded from a comparison with the triplet state of monomeric BChl g in organic solvents. With the aid of the microwave-induced absorbance difference spectra, we assign a triplet state with zero-field splitting parameters |D| = 727.5 and |E| = 254. 5 MHz to that of the primary donor. The low |E| value indicates that the BChls of the primary donor are monoligated. The intensities of the zero-field transitions were strongly dependent on the redox state of the secondary electron acceptors. A triplet state with |D| = 690-705 MHz and |E| =230 MHz, present under all redox conditions, is associated with antenna BChl g absorbing at 814 nm. Its triplet yield was independent of the redox conditions; we conclude therefore that the antenna chromophores absorbing at 814 nm are not connected with the reaction center at cryogenic temperatures (1.2 K). In addition, relatively strong signals were detected belonging to triplet states with |D| and |E| of 663-680 and 220-227 MHz, respectively, whose amplitudes were dependent on the redox conditions. Triplet states with these zero-field splitting parameters are located on antenna chromophores absorbing between 798-814 nm; their zero-field transitions and absorbance difference spectra indicate a considerable heterogeneity. The concentration of triplet states of antenna chromophores absorbing around 800 nm decreased markedly upon prolonged excitation at 1.2 K. This phenomenon is attributed to quenching of excitations on antenna pigments by stable charge separation in the closely connected reaction center, possibly involving a low-quantum yield menaquinone electron acceptor. PMID:9778366

  13. 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.

  14. 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(?-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(?-P2O5H2)4 + 2H](2-) is the first example of a photoexcited multianion for which ESETD has been observed following ISC. PMID:26851919

  15. Photophysics of N-ethylcarbazole in fluid solution. Evidence for solvent dependence and triplet excimer formation

    SciTech Connect

    Haggquist, G.W.; Burkhart, R.D. )

    1993-03-18

    The photoexcitation of N-ethylcarbazole (NEC) in fluid solutions of cyclohexane, N,N-dimethylformamide (DMF), ethanol, paraffin oil, and mixtures of glycerol with either ethanol or DMF has been carried out using 308-nm pulses from a XeCl excimer laser. Emission spectra recorded at 70 [mu]s or longer after the excitation pulse depend upon the solvent. In ethanol and DMF red-shifted, structureless bands appear at these longer delay times which are attributed to delayed excimer fluorescence. No such bands are found using cyclohexane. In glycerol/ethanol or glycerol/DMF (90/10 (v/v)) monomeric delayed fluorescence is found at delay times of 70 [mu]s or less, but at delay times from 700 [mu]s to 3.8 ms a prominent band at 500 nm is observed which is attributed to emission from triplet excimers. Transient absorption spectra of NEC in cyclohexane recorded at delay times from 1 to 20 [mu]s after the excitation pulse are entirely attributable to the carbazolyl triplet state. In ethanol and DMF, however, additional bands corresponding to radical cations and anions of NEC are also found. A broad band observed near 500 nm is provisionally assigned to the triplet excimer. Kinetic decays of the absorption signals due to triplets were fit to concurrent first-order and second-order processes whereas those due to the radical anion were fit to a biexponential decay. It is proposed that delayed excimer fluorescence arises from recombination of cation dimers and radical anions and that triplet excimers are formed by recombination of geminate ion pairs to form a monomeric triplet and a ground-state partner, followed by interaction of the triplet and the same partner. The primary mechanism for ion formation is thought to involve electron transfer from multiply excited molecules to ground-state species. 34 refs., 10 figs., 1 tab.

  16. 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

  17. 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.

  18. 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.

  19. Spin-multiplicity of a moderately coupled triplet-doublet spin pair in a biphenylene-linked porphyrin dimer

    NASA Astrophysics Data System (ADS)

    Asano, Motoko S.; Ishizuka, Kazuhiko; Kaizu, Youkoh

    2006-05-01

    Electron spin transient nutation spectroscopy has been applied to a moderately coupled excited triplet and doublet spin-pair. In a biphenylene-linked copper(II)-free base porphyrin dimer, laser irradiation of either the free base half or the copper half, leads to excitation to the excited states and relaxation to the lowest excited state of the dimer. In this lowest excited state, the free base moiety in the lowest triplet state is coupled to the copper porphyrin ground doublet state, and thus forming a triplet-doublet spin pair. Time-resolved electron paramagnetic resonance (TREPR) spectra of the dimer in frozen solution at 40 K show much wider spectral width and a prominent band in the centre of the spectra than either of those for the free base monomer triplet or that of the copper(II) monomer porphyrin. These features are quite different from the strongly-coupled and weakly-coupled triplet-doublet spin pairs. Transient nutation method by pulsed EPR is used to examine the spin-multiplicity of the excited state in the dimer at three magnetic field positions. It was found that spin-multiplicity depends largely on the magnetic field. This is rationalized in terms of an intermediate size of coupling. In such intermediate coupling cases, the degree of mixing of the triplet and doublet basis wavefunctions depends greatly on the relative orientation between magnetic field and molecular axis because the ratio of the coupling size to an energy difference between the unperturbed species, triplet and doublet, varies with magnetic field direction. A splitting of TREPR spectra in partially oriented samples suggests that exchange coupling |J| is around 10 mT, which reasonably matches the results of the pulsed experiments.

  20. 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.

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

    NASA Astrophysics Data System (ADS)

    Zafra, José Luis; González Cano, Rafael C.; Ruiz Delgado, M. Carmen; Sun, Zhe; Li, Yuan; López Navarrete, Juan T.; Wu, Jishan; Casado, Juan

    2014-02-01

    A analysis of the electronic and molecular structures of new molecular materials based on zethrene is presented with particular attention to those systems having a central benzo-quinoidal core able to generate Kekulé biradicals whose stability is provided by the aromaticity recovery in this central unit. These Kekulé biradicals display singlet ground electronic states thanks to double spin polarization and have low-energy lying triplet excited states also featured by the aromaticity gain. Pro-aromatization is also the driving force for the stabilization of the ionized species. Moreover, the low energy lying singlet excited states also display a profound biradical fingerprint allowing to singlet exciton fission. These properties are discussed in the context of the size of the zethrene core and of its substitution. The work encompasses all known long zethrenes and makes use of a variety of experimental techniques, such as Raman, UV-Vis-NIR absorption, transient absorption, in situ spectroelectrochemistry and quantum chemical calculations. This study reveals how the insertion of suitable molecular modules (i.e., quinoidal) opens the door to new intriguing molecular properties exploitable in organic electronics.

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

    PubMed

    Zafra, José Luis; González Cano, Rafael C; Ruiz Delgado, M Carmen; Sun, Zhe; Li, Yuan; López Navarrete, Juan T; Wu, Jishan; Casado, Juan

    2014-02-01

    A analysis of the electronic and molecular structures of new molecular materials based on zethrene is presented with particular attention to those systems having a central benzo-quinoidal core able to generate Kekulé biradicals whose stability is provided by the aromaticity recovery in this central unit. These Kekulé biradicals display singlet ground electronic states thanks to double spin polarization and have low-energy lying triplet excited states also featured by the aromaticity gain. Pro-aromatization is also the driving force for the stabilization of the ionized species. Moreover, the low energy lying singlet excited states also display a profound biradical fingerprint allowing to singlet exciton fission. These properties are discussed in the context of the size of the zethrene core and of its substitution. The work encompasses all known long zethrenes and makes use of a variety of experimental techniques, such as Raman, UV-Vis-NIR absorption, transient absorption, in situ spectroelectrochemistry and quantum chemical calculations. This study reveals how the insertion of suitable molecular modules (i.e., quinoidal) opens the door to new intriguing molecular properties exploitable in organic electronics. PMID:24511967

  3. The photoexcited triplet state of sapphyrin dication: Unusual spin alignment in monomers and spin delocalization in dimers

    SciTech Connect

    Levanon, H. |; Michaeli, S.; Regev, A.; Galili, T.; Cyr, M.; Sessler, J.L.

    1990-01-31

    Sapphyrin (Sap) and its stable dicationic form, Sap{sup 2+}, originally prepared by Woodawrd and Johnson, are large porphyrin-like systems which exhibit unique photophysical and photochemical properties. We report on the triplet diode detection, by time-resolved CW EPR, of (Sap{sup 2+}){sup T} randomly oriented in toluene (as monomers), ethanol (as dimers), and partially oriented in a nematic liquid crystal (as monomers). The substantial reduction of both zero-field splitting (ZFS) parameters (D and E) in the dimer, is interpreted in terms of spin delocalization (charge transfer) among the monomers within the dimer, (Sap{sup 2+}){sub 2}. The EPR line shape of Sap{sup 2+} in the liquid crystal suggests that, unlike other known porphyrinoid systems, the ZFS term D is associated with the in-plane alignment of the triplet spins along the C{sub 2v} symmetry axis, Z.

  4. Geminate and nongeminate recombination of triplet excitons formed by singlet fission.

    PubMed

    Bayliss, Sam L; Chepelianskii, Alexei D; Sepe, Alessandro; Walker, Brian J; Ehrler, Bruno; Bruzek, Matthew J; Anthony, John E; Greenham, Neil C

    2014-06-13

    We report the simultaneous observation of geminate and nongeminate triplet-triplet annihilation in a solution-processable small molecule TIPS-tetracene undergoing singlet exciton fission. Using optically detected magnetic resonance, we identify recombination of triplet pairs directly following singlet fission, as well as recombination of triplet excitons undergoing bimolecular triplet-triplet annihilation. We show that the two processes give rise to distinct magnetic resonance spectra, and estimate the interaction between geminate triplet excitons to be 60 neV. PMID:24972236

  5. Electronic excited states and electronic spectra of biphenyl: a study using many-body wavefunction methods and density functional theories.

    PubMed

    Fukuda, Ryoichi; Ehara, Masahiro

    2013-10-28

    The low-lying electronic excited states of biphenyl were studied using the symmetry-adapted cluster-configuration interaction (SAC-CI), complete active space self-consistent field (CASSCF), complete active space perturbation theory of the second-order (CASPT2), and the time-dependent density functional theory (TDDFT). The molecular geometries in the ground and excited states were optimized using the SAC-CI and TDDFT for singlet and triplet states. The energies of vertical excitations, emissions, and adiabatic transitions were calculated. The TDDFT calculations significantly underestimated the excitation energy of the 1(1)B1 state, while the SAC-CI and CASPT2 provided essentially similar results. The present SAC-CI and CASPT2 calculations concluded that the lowest singlet state of isolated biphenyl is the 1(1)B3 state that takes a planar geometry and the second lowest state is the 1(1)B2 state with a twisted geometry. The present results were consistent with the previous experimental findings. The 1(1)B1 state that has a charge-separated biracial character in the vertical excitation relaxed into a planar quinoid structure in which bond alternations were emphasized. The other states took a benzenoid structure. The ultraviolet (UV) absorption and circular dichroism (CD) spectra below 7 eV were calculated with the SAC-CI method. The valence-Rydberg mixings were found to be significant in the second and higher series of excited states. PMID:24022338

  6. Thiol-Activatable Triplet-Triplet Annihilation Upconversion with Maleimide-Perylene as the Caged Triplet Acceptor/Emitter.

    PubMed

    Mahmood, Zafar; Zhao, Jianzhang

    2016-01-15

    Efficient thiol-activated triplet-triplet annihilation (TTA) upconversion system was devised with maleimide-caged perylene (Py-M) as the thiol-activatable triplet acceptor/emitter and with diiodoBodipy as the triplet photosensitizer. The photophysical processes were studied with steady-state UV-vis absorption spectroscopy, fluorescence spectroscopy, electrochemical properties, and nanosecond transient absorption spectroscopy. The triplet acceptor/emitter Py-M shows week fluorescence (?F = 0.8%), and no upconversion (?UC = 0%) was observed. The quenching of fluorescence of Py-M is due to photoinduced electron-transfer (PET) process from perylene to maleimide-caging unit, which quenches the singlet excited state of perylene. The fluorescence of Py-M was enhanced by 200-fold (?F = 97%) upon addition of thiols such as 2-mercaptoethanol, and the ?UC was increased to 5.9%. The unique feature of this thiol-activated TTA upconversion is that the activation is based on addition reaction of the thiols with the caged acceptor/emitter, and no side products were formed. The previously reported cleavage approach gives side products which are detrimental to the TTA upconversion. With nanosecond transient absorption spectroscopy, we found that the triplet excited state of Py-M was not quenched by any PET process, which is different from singlet excited state (fluorescence) of Py-M. The results are useful for study of the triplet excited states of organic chromophores and for activatable TTA upconversion. PMID:26694534

  7. Kinetic Monte Carlo study of triplet-triplet annihilation in organic phosphorescent emitters

    NASA Astrophysics Data System (ADS)

    van Eersel, H.; Bobbert, P. A.; Coehoorn, R.

    2015-03-01

    The triplet-triplet annihilation (TTA) rate in organic phosphorescent materials such as used in organic light-emitting diodes is determined predominantly either by the rate of single-step Frster-type triplet-triplet interactions, or by multi-step triplet diffusion. We show how kinetic Monte Carlo simulations may be used to analyze the role of both processes. Under steady state conditions, the effective triplet-triplet interaction rate coefficient, kTT, which is often regarded as a constant, is found to depend actually on the number of excitons lost upon a triplet-triplet interaction process and to show a significant higher-order dependence on the triplet volume density. Under the conditions encountered in transient photoluminescence (PL) studies, kTT is found to be effectively constant in the case of diffusion-dominated TTA. However, for the case of single-step TTA, a strongly different decay of the emission intensity is found, which also deviates from an analytic expression proposed in the literature. We discuss how the transient PL response may be used to make a distinction between both mechanisms. The simulations are applied to recently published work on the dye concentration dependence of the TTA rate in materials based on the archetypal green emitter tris[2-phenylpyridine]iridium (Ir(ppy)3).

  8. Ground and Excited State Spectra of a Quantum Dot

    NASA Astrophysics Data System (ADS)

    Stewart, D. R.; Sprinzak, D.; Patel, S. R.; Marcus, C. M.; Duruoz, C. I.; Harris, J. S.

    1998-03-01

    We present linear and nonlinear magnetoconductance measurements of the ground and excited state spectra for successive electron occupancy in a gate defined lateral quantum dot. Previous measurementsfootnote D.R. Stewart, D. Sprinzak, C.M. Marcus, C.I. Duruoz and J.S. Harris Jr., Science 278, (1997). showed a direct correlation between the mth excited state of the N-electron system and the ground state of the (N+m)-electron system for m up to 4, consistent to a large degree with a single-particle picture. Here we report quantitative deviations of the excited state spectra from the spectrum of ground state magnetoconductances, attributed to many-body interactions in the finite system of N ~200 electrons. We also describe the behaviour of anticrossings in the ground state magnetoconductances. We acknowledge the support of JSEP (DAAH04-94-G-0058), ARO (DAAH04-95-1-0331), ONR-YIP (N00014-94-1-0622) and the NSF-PECASE program. D.S. acknowledges the support of MINERVA grant.

  9. 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.

  10. Theory of triplet-triplet annihilation in optically detected magnetic resonance

    NASA Astrophysics Data System (ADS)

    Keevers, T. L.; McCamey, D. R.

    2016-01-01

    Triplet-triplet annihilation allows two low-energy photons to be upconverted into a single high-energy photon. By essentially engineering the solar spectrum, this allows solar cells to be made more efficient and even exceed the Shockley-Quiesser limit. Unfortunately, optimizing the reaction pathway is difficult, especially with limited access to the microscopic time scales and states involved in the process. Optical measurements can provide detailed information: triplet-triplet annihilation is intrinsically spin dependent and exhibits substantial magnetoluminescence in the presence of a static magnetic field. Pulsed optically detected magnetic resonance is especially suitable, since it combines high spin sensitivity with coherent manipulation. In this paper, we develop a time-domain theory of triplet-triplet annihilation for complexes with arbitrary spin-spin coupling. We identify unique "Rabi fingerprints" for each coupling regime and show that this can be used to characterize the microscopic Hamiltonian.

  11. Magnetic Field Effects on Triplet-Triplet Annihilation in Solutions: Modulation of Visible/NIR Luminescence

    PubMed Central

    Mani, Tomoyasu; Vinogradov, Sergei A.

    2013-01-01

    Photon upconversion based on sensitized triplet-triplet annihilation (TTA) presents interest for such areas as photovoltaics and imaging. Usually energy upconversion is observed as p-type delayed fluorescence from molecules whose triplet states are populated via energy transfer from a suitable triplet donor, followed by TTA. Magnetic field effects (MFE) on delayed fluorescence in molecular crystals are well known; however, there exist only a few examples of MFE on TTA in solutions, and all of them are limited to UV-emitting materials. Here we present MFE on TTA-mediated visible and near infrared (NIR) emission, sensitized by far-red absorbing metalloporphyrins in solutions at room temperature. In addition to visible delayed fluorescence from annihilator, we also observed NIR emission from the sensitizer, occurring as a result of triplet-triplet energy transfer back from annihilator, termed delayed phosphorescence. This emission also exhibits MFE, but opposite in sign to the annihilator fluorescence. PMID:24143268

  12. Bound state spectra and properties of the doublet states in three-electron atomic systems

    NASA Astrophysics Data System (ADS)

    Frolov, Alexei M.; Ruiz, Mara Beln; Wardlaw, David M.

    2014-07-01

    The bound state spectra of the doublet states in three-electron atomic systems are investigated. By using different variational expansions we determine various bound state properties in these systems. Such properties include the electron-nucleus and electron-electron delta-functions and cusp values. The general structure of the bound state spectra in several three-electron atomic systems (Li, Be+, C3+ and F6+) is investigated with the use of the Hylleraas-Configuration Interaction and the Configuration Interaction wave functions. The advantage of our Configuration Interaction based procedure is that it provides high numerical accuracy for all rotationally excited states, including the bound states with L?7.

  13. Auroral N{sub 2} emissions and the effect of collisional processes on N{sub 2} triplet state vibrational populations

    SciTech Connect

    Morrill, J.S.; Benesch, W.M.

    1996-01-01

    Previous model results have shown that the N{sub 2} triplet vibrational level populations in the aurora are strongly affected by cascade and quenching by atomic and molecular oxygen. As the aurora penetrates to lower altitudes (less than 100 km) the role of quenching by atomic oxygen becomes less important and processes involving N{sub 2} collisions begin to play a more prominent part. The authors are developing a model which will yield steady state vibrational level populations for both the singlet and triplet valence states of N{sub 2}. The model currently provides results for the seven low-lying N{sub 2} triplet states (A {sup 3}{Sigma}{sub u}{sup +}, B {sup 3}{Pi}{sub g}, W {sup 3}{Delta}{sub u}, B{prime}{sup 3}{Sigma}{sub u}, C{sup 3}{Pi}{sub u}, D{sup 3}{Sigma}{sub u}{sup +}, and E{sup 3}{Sigma}{sub g}{sup +}). These states are responsible for auroral emissions from the UV (Vegard-Kaplan (VK), second positive (2PG)) through the visible to the infrared (first positive (1PG), infrared afterglow (IRA), Wu-Benesch (WB)). The authors have included two additional collisional processes in the current model which were not treated previously. These are the intersystem collisional transfer of excitation (ICT) between the B state and the A, W, and B{prime} states and vibrational redistribution within the A state vibrational manifold, both due to collisions with ground state N{sub 2}. The present work compares the current model results with those of a previous model as well as ground, airborne, and rocket observations. The comparison between N{sub 2}(A) (VK) and N{sub 2}(B) (1PG) vibrational level populations predicted by this model and a number of auroral observations indicate that the current model achieves a significant improvement in the fit between calculation and observation. 81 refs., 12 figs., 2 tabs.

  14. Single-shot readout and relaxation of singlet and triplet states in exchange-coupled 31P electron spins in silicon.

    PubMed

    Dehollain, Juan P; Muhonen, Juha T; Tan, Kuan Y; Saraiva, Andre; Jamieson, David N; Dzurak, Andrew S; Morello, Andrea

    2014-06-13

    We present the experimental observation of a large exchange coupling J ? 300 ?eV between two (31)P electron spin qubits in silicon. The singlet and triplet states of the coupled spins are monitored in real time by a single-electron transistor, which detects ionization from tunnel-rate-dependent processes in the coupled spin system, yielding single-shot readout fidelities above 95%. The triplet to singlet relaxation time T(1) ? 4 ms at zero magnetic field agrees with the theoretical prediction for J-coupled 31P dimers in silicon. The time evolution of the two-electron state populations gives further insight into the valley-orbit eigenstates of the donor dimer, valley selection rules and relaxation rates, and the role of hyperfine interactions. These results pave the way to the realization of two-qubit quantum logic gates with spins in silicon and highlight the necessity to adopt gating schemes compatible with weak J-coupling strengths. PMID:24972221

  15. Understanding the Photoreactivity of Dissolved Organic Carbon in Natural Waters: The Role of the Triplet Excited-State of Allochthonous and Autochthonous DOC

    NASA Astrophysics Data System (ADS)

    Cottrell, B. A.; Timko, S. A.; Robinson, A. K.; Weiden, L. M.; Cooper, W.

    2012-12-01

    The photochemical reactivity of DOC in sunlit waters is a major factor for the in situ processing of DOC itself and trace contaminants in streams, lakes and the ocean. There is an increasing interest in the use of wetlands to mitigate contaminant removal. Laser flash photolysis is used to determine the reaction rate constants of dissolved organic carbon (DOC) with emerging contaminants in natural waters. DOC, produced by the decomposition of plant and microbial material, is one of the most complex naturally occurring mixtures. DOC plays a major role in the global carbon cycle, the sequestration and transport of trace chemicals and contaminants, and the biogeochemistry of natural waters. Hydrolysis, direct photolysis and reactions with singlet oxygen and the hydroxyl radical account for up to 25% of the photo reactivity of natural organic matter. The remaining 75% is attributed to reactions with the triplet-excited state of DOC (3DOC*). In this study, 1H NMR is used to characterize DOC from the Black River (NC), the San Joaquin Wetlands (Irvine, CA), and coastal seawater (Crystal Cove, CA). These sites encompass both allochthonous and autochthonous organic matter from catchment, wetlands, and marine waters. We then determine the reaction rate constants of known triplet state reactants and pharmaceuticals with the 3DOC* in the natural waters and with the DOC isolated by solid phase extraction. Studies of 3DOC* could provide a measure of DOC reactivity, essential in the design of constructed wetlands for contaminant removal.

  16. On the solid-state NMR spectra of naproxen

    NASA Astrophysics Data System (ADS)

    Czernek, Ji?

    2015-01-01

    Two previous measurements of the 13C and 1H NMR isotropic chemical shifts in crystalline naproxen, which is an important pharmaceutical compound, are confronted with the results obtained from several theoretical approaches capable of the proper treatment of solid-phase effects. In the underlying geometrical optimizations, two crystal structures are considered. The agreement between the data sets is quantified, including an evaluation of the similarity between the experimental solid-state NMR spectra. The 13C-1H heteronuclear correlations are analyzed, and their various assignments are discussed employing the statistical treatment of the differences between the measured and theoretical isotropic chemical shifts.

  17. Narrow chaotic compound autoionizing states in atomic spectra

    SciTech Connect

    Flambaum, V.V.; Gribakina, A.A.; Gribakin, G.F.

    1996-09-01

    Simultaneous excitation of several valence electrons in atoms gives rise to a dense spectrum of compound autoionizing states (AIS). These states are almost chaotic superpositions of large numbers of many-electron basis states built of single-electron orbitals. The mean level spacing {ital D} between such states is very small (e.g., {ital D}{lt}0.01 eV for the numerical example of {ital J}{sup {pi}}=4{sup {minus}} states of Ce just above the ionization threshold). The autoionization widths of these states estimated by perturbations, {gamma}=2{pi}{vert_bar}{ital W}{vert_bar}{sup 2}, where {ital W} is the Coulomb matrix element coupling the AIS to the continuum, are also small, but comparable with {ital D} in magnitude: {gamma}{approximately}{ital D}. Hence the nonperturbative interaction of AIS with each other via the continuum is very essential. It suppresses greatly the widths of the autoionizing resonances ({Gamma}{approx_equal}{ital D}{sup 2}/3{gamma}{lt}{ital D}), and leads to the emergence of a {open_quote}{open_quote}collective{close_quote}{close_quote} doorway state which accumulates a large share of the total width. This state is in essence a modified single-particle continuum decoupled from the resonances due to its large width. Narrow compound AIS should be a common feature of atomic spectra at energies sufficient for excitation of several electrons above the ground-state configuration. The narrow resonances can be observed as peaks in the photoabsorption, or, in electron-ion scattering, as Fano-type profiles on the background provided by the wide doorway-state resonance. It is also shown that the statistics of electromagnetic and autoionization amplitudes involving compound states are close to Gaussian. {copyright} {ital 1996 The American Physical Society.}

  18. Enhanced triplet formation in polyfluorene blends

    NASA Astrophysics Data System (ADS)

    Ford, Thomas

    2005-03-01

    Formation of triplet excitons may be an important loss mechanism in organic light-emitting diodes (LEDs) and photovoltaics. Here we use photoinduced absorption spectroscopy to study the generation of triplet excitons after photoexcitation of a blend of the fluorene-based conjugated polymers poly(9,9'-dioctylfluorene-co-benzothiadiazole) (F8BT) and poly(9,9'-dioctylfluorene-co-bis-N,N'-(4-butylphenyl)-bis-N,N'-phenyl-1,4-phenylene-diamine) (PFB). The triplet generation rate is found to be 10 times higher in F8BT:PFB than in F8BT alone. We attribute this effect to increased intersystem crossing in the charge-separated states formed at the polymer/polymer heterojunctions in the blend. Applying an electric field dissociates these states and thus reduces the rate of triplet state formation. We will discuss the implications of this result for the operation of polymer blend LEDs and photovoltaics.

  19. Ab initio calculation of the NH(3sigma-)-NH(3sigma-) interaction potentials in the quintet, triplet, and singlet states.

    PubMed

    Dhont, Guillaume S F; van Lenthe, Joop H; Groenenboom, Gerrit C; van der Avoird, Ad

    2005-11-01

    We present the ab initio potential-energy surfaces of the NH-NH complex that correlate with two NH molecules in their 3sigma- electronic ground state. Three distinct potential-energy surfaces, split by exchange interactions, correspond to the coupling of the S(A) = 1 and S(B) = 1 electronic spins of the monomers to dimer states with S = 0, 1, and 2. Exploratory calculations on the quintet (S = 2), triplet (S = 1), and singlet (S = 0) states and their exchange splittings were performed with the valence bond self-consistent-field method that explicitly accounts for the nonorthogonality of the orbitals on different monomers. The potential surface of the quintet state, which can be described by a single Slater determinant reference function, was calculated at the coupled cluster level with single and double excitations and noniterative treatment of the triples. The triplet and singlet states require multiconfiguration reference wave functions and the exchange splittings between the three potential surfaces were calculated with the complete active space self-consistent-field method supplemented with perturbative configuration interaction calculations of second and third orders. Full potential-energy surfaces were computed as a function of the four intermolecular Jacobi coordinates, with an aug-cc-pVTZ basis on the N and H atoms and bond functions at the midpoint of the intermolecular vector R. An analytical representation of these potentials was given by expanding their dependence on the molecular orientations in coupled spherical harmonics, and representing the dependence of the expansion coefficients on the intermolecular distance R by the reproducing kernel Hilbert space method. The quintet surface has a van der Waals minimum of depth D(e) = 675 cm(-1) at R(e) = 6.6a0 for a linear geometry with the two NH electric dipoles aligned. The singlet and triplet surfaces show similar, slightly deeper, van der Waals wells, but when R is decreased the weakly bound NH dimer with S = 0 and S = 1 converts into the chemically bound N2H2 diimide (also called diazene) molecule with only a small energy barrier to overcome. PMID:16292903

  20. Favorable performance of the DFT methods in predicting the minimum-energy structure of the lowest triplet state of WF{sub 4}

    SciTech Connect

    Gutowski, M.

    1999-06-15

    The tetrahedral structure of the lowest triplet state of the WF{sub 4} complex was examined using different variants of the density functional theory (DFT) and conventional ab initio methods. The low-level, conventional, ab initio methods, such as SCF, MP2, MP3, and CISD, predict the tetrahedral structure to be a minimum, whereas the DFT schemes predict an imaginary frequency for the e vibrational mode. Only after recovering electron correlation effects at the MP4 and higher levels, the conventional electronic structure methods also predict the T{sub d} structure to be a second-order stationary point. This is not the correlation but the exchange part of the DFT functionals which is responsible for the discrepancy between the DFT and low-level, conventional, ab initio predictions. The lowering of symmetry to C{sub 2v} leads to a minimum on the lowest triplet potential energy surface and the electronic energy difference between the T{sub d} and C{sub 2v} stationary points amounts to 0.85 and 0.96 kcal/mol at the B3LYP and CCSD(T) levels, respectively.

  1. Aromaticity Changes along the Lowest-Triplet-State Path for C?C Bond Rotation of Annulenyl-Substituted Olefins Probed by the Electron Localization Function

    NASA Astrophysics Data System (ADS)

    Villaume, Sbastien; Ottosson, Henrik

    2009-10-01

    The ?-contribution to the electron localization function (ELF?) was used to analyze changes in the aromaticity of annulenyl-substituted olefins in their lowest triplet state (T1) when the structure around the olefin C?C bond is twisted from planar to a structure (3p*) at which the planes of the two RR'C units are perpendicular. The ring closure bifurcation value and the range in the bifurcation values of the ELF? basins serve as (anti)aromaticity indicators directly linked to the electronic structure. Both Hckel's 4n + 2 ?-electron rule for aromaticity in the singlet ground state (S0) and Baird's 4n ?-electron rule for aromaticity in the lowest ??* triplet state are applied. Three olefins with S0 aromatic (T1 antiaromatic) substituents and four olefins with T1 aromatic (S0 antiaromatic) substituents were studied using the ELF? topology at the OLYP/6-311G(d,p) density functional theory level. The changes in the substituent ELF? bifurcation values upon rotation about the olefin bond in the T1 state reveal that aromatic character is recovered for the first three olefins and that it is reduced for the latter ones. These changes in aromatic character are reflected in the shapes of the T1 potential energy surfaces as a twist away from planar structures in olefins with T1 antiaromatic substituents is energetically favorable, but that in olefins with T1 aromatic substituents is unfavorable. Hence, aromaticity change is a driver for a photochemical reaction as for many ground-state reactions.

  2. Poly(p-phenylene vinylene) in light-emitting diodes: Nature of the lowest singlet and triplet excited states and effects of derivatization

    SciTech Connect

    Cornil, J.; Beljonne, D.; Bredas, J.L.

    1995-12-01

    Poly(p-phenylene vinylene), PPV, has attracted a tremendous interest in the past few years, especially in the field of optic and electro-optic devices such as light-emitting diodes (LED`s). Here we focus our attention on three issues of prime importance when studying PPV (or its oligomers) as an emitting layer. The first topic deals with the modelling of the nature of the lowest singlet excited state (from which fluorescence originates) and of the lowest triplet excited states (also reached by the system following recombination of the charge carriers). In a second part, we analyze the way the optical transitions are affected by derivatization; we modulate the locations of the frontier levels by fixing {pi}-donor (methoxy) and {pi}-acceptor (cyano) substituents along the conjugated backbone. Finally, we investigate the metallization of the cyano-PPVs, by aluminum or alkali metals.

  3. Quasiclassical asymptotics and coherent states for bounded discrete spectra

    SciTech Connect

    Gorska, K.; Penson, K. A.; Horzela, A.; Blasiak, P.; Duchamp, G. H. E.; Solomon, A. I.

    2010-12-15

    We consider discrete spectra of bound states for nonrelativistic motion in attractive potentials V{sub {sigma}}(x)=-|V{sub 0}| |x|{sup -}{sigma}, 0<{sigma}{<=}2. For these potentials the quasiclassical approximation for n{yields}{infinity} predicts quantized energy levels e{sub {sigma}}(n) of a bounded spectrum varying as e{sub {sigma}}(n){approx}-n{sup -}2{sigma}/(2-{sigma}). We construct collective quantum states using the set of wavefunctions of the discrete spectrum assuming this asymptotic behavior. We give examples of states that are normalizable and satisfy the resolution of unity, using explicit positive functions. These are coherent states in the sense of Klauder and their completeness is achieved via exact solutions of Hausdorff moment problems, obtained by combining Laplace and Mellin transform methods. For {sigma} in the range 0 < {sigma}{<=} 2/3 we present exact implementations of such states for the parametrization {sigma}= 2(k-l)/(3k-l) with k and l positive integers satisfying k>l.

  4. 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.

  5. Low-energy chlorophyll states in the CP43 antenna protein complex: simulation of various optical spectra. II.

    PubMed

    Reppert, Mike; Zazubovich, Valter; Dang, Nhan C; Seibert, Michael; Jankowiak, Ryszard

    2008-08-14

    The CP43 protein complex of the core antenna of higher plant photosystem II (PSII) has two quasidegenerate "red" absorption states. It has been shown in the accompanying paper I (Dang, N. C., et al. J. Phys. Chem. B 2008, 112, 9921.) that the site distribution functions (SDFs) of red-states A and B are uncorrelated and the narrow holes are burned in subpopulations of chlorophylls (Chls) from states A and B that are the lowest-energy pigments in their particular CP43 complexes and cannot further transfer energy downhill. In this work, we present the results of a series of Monte Carlo simulations using the 3.0-A structure of the PSII core complex from cyanobacteria (Loll, B., et al. Nature 2005, 303, 1040.) to model absorption, emission, persistent, and transient hole burned (HB) spectra. At the current structural resolution, we found calculated site energies (obtained from INDO/S calculations) to be only suggestive because their values are different for the two monomers of CP43 in the PS II dimer. As a result, to probe the excitonic structure, a simple fitting procedure was employed to optimize Chl site energies from various starting values corresponding to different A/B pigment combinations to provide simultaneously good fits to several types of optical spectra. It is demonstrated that the shape of the calculated absorption, emission, and transient/persistent hole-burned spectra is consistent with experimental data and our model for excitation energy transfer between two quasi-degenerate lowest-E states (A and B) with uncorrelated SDFs discussed in paper I. Calculations revealed that absorption changes observed near 670 nm in the non-line-narrowed persistent HB spectra (assigned to photoconversion involving Chl-protein hydrogen-bonding by Hughes (Biochemistry 2006, 45, 12345.) are most likely the result of nonphotochemical hole-burning (NPHB) accompanied by the redistribution of oscillator strength due to modified excitonic interactions. We argue that a unique redistribution of oscillator strength during the NPHB process helps to assign Chls contributing to the low-energy states. It is demonstrated that the 4.2 K asymmetric triplet-bottleneck (transient) hole is mostly contributed to by both A and B states, with the hole profile described by a subensemble of pigments, which are the lowest-energy pigments (B s- and A s-type) in their complexes. The same lowest-energy Chls contribute to the observed fluorescence spectra. On the basis of our excitonic calculations, the best Chl candidates that contribute to the low-energy A and B states are Chl 44 and Chl 37, respectively. PMID:18642950

  6. Assignment of IR bands of isolated and protein-bound Peridinin in its fundamental and triplet state by static FTIR, time-resolved step-scan FTIR and DFT calculations

    NASA Astrophysics Data System (ADS)

    Mezzetti, Alberto; Kish, Elizabeth; Robert, Bruno; Spezia, Riccardo

    2015-06-01

    The vibrational properties of Peridinin in its fundamental state and in the excited triplet state have been investigated by DFT calculations and static and time-resolved FTIR spectroscopy. The infrared spectrum of Peridinin in its fundamental state has been explored in the whole 2000-600 cm-1 range, and interpreted in term of molecular vibrations. In particular, new infrared bands have been identified and assigned to specific molecular vibrations. 3Peridinin molecular vibrations have also been investigated by DFT calculations. In addition, putative IR bands belonging to Peridinin and 3Peridinin have been identified in the step-scan FTIR difference spectrum of the Peridinin-Chlorophyll a-Protein from Amphidinium carterae, where light induce formation of a triplet state localized on one or more Peridinins. The exact nature of the triplet state formed in Peridinin-Chlorophyll a-Protein from dinoflagellates, in particular the possible involvement in this triplet state of 3Chlorophyll a, has been largely debated in the last few years (see Carbonera et al., 2014 [3]); time-resolved differential FTIR experiments have played a key role in this debate. Identification of IR marker bands for the main molecule (Peridinin) implicated in this photophysical process is therefore particularly important and makes this study a significant step towards the full understanding of Peridinin-Chlorophyll-a-Proteins photophysics.

  7. Negative Polaron and Triplet Exciton Diffusion inOrganometallic Molecular Wires

    SciTech Connect

    Schanze, K.S.; Miller, J.; Keller, J.M.; Sean McIlroy, S.; Sreearuothai, P.; Danilov, E.O.; Jiang, H.; Glusac, K.D.; Miller, J.R.

    2011-07-27

    The dynamics of negative polaron and triplet exciton transport within a series of monodisperse platinum (Pt) acetylide oligomers is reported. The oligomers consist of Pt-acetylide repeats, [PtL{sub 2}-C {triple_bond} C-Ph-C {triple_bond} C-]{sub n} (where L = PBu{sub 3} and Ph = 1,4-phenylene, n = 2, 3, 6, and 10), capped with naphthalene diimide (NDI) end groups. The Pt-acetylide segments are electro- and photoactive, and they serve as conduits for transport of electrons (negative polaron) and triplet excitons. The NDI end groups are relatively strong acceptors, serving as traps for the carriers. Negative polaron transport is studied by using pulse radiolysis/transient absorption at the Brookhaven National Laboratory Laser-Electron Accelerator Facility (LEAF). Electrons are rapidly attached to the oligomers, with some fraction initially residing upon the Pt-acetylide chains. The dynamics of transport are resolved by monitoring the spectral changes associated with transfer of electrons from the chain to the NDI end group. Triplet exciton transport is studied by femtosecond-picosecond transient absorption spectroscopy. Near-UV excitation leads to rapid production of triplet excitons localized on the Pt-acetylide chains. The excitons transport to the chain ends, where they are annihilated by charge separation with the NDI end group. The dynamics of triplet transport are resolved by transient absorption spectroscopy, taking advantage of the changes in spectra associated with decay of the triplet exciton and rise of the charge-separated state. The results indicate that negative polarons and excitons are transported rapidly, on average moving distances of 3 nm in less than 200 ps. Analysis of the dynamics suggests diffusive transport by a site-to-site hopping mechanism with hopping times of 27 ps for triplets and <10 ps for electrons.

  8. Energy harvesting of non-emissive triplet excitons in tetracene by emissive PbS nanocrystals.

    PubMed

    Thompson, Nicholas J; Wilson, Mark W B; Congreve, Daniel N; Brown, Patrick R; Scherer, Jennifer M; Bischof, Thomas S; Wu, Mengfei; Geva, Nadav; Welborn, Matthew; Voorhis, Troy Van; Bulović, Vladimir; Bawendi, Moungi G; Baldo, Marc A

    2014-11-01

    Triplet excitons are ubiquitous in organic optoelectronics, but they are often an undesirable energy sink because they are spin-forbidden from emitting light and their high binding energy hinders the generation of free electron-hole pairs. Harvesting their energy is consequently an important technological challenge. Here, we demonstrate direct excitonic energy transfer from 'dark' triplets in the organic semiconductor tetracene to colloidal PbS nanocrystals, thereby successfully harnessing molecular triplet excitons in the near infrared. Steady-state excitation spectra, supported by transient photoluminescence studies, demonstrate that the transfer efficiency is at least (90 ± 13)%. The mechanism is a Dexter hopping process consisting of the simultaneous exchange of two electrons. Triplet exciton transfer to nanocrystals is expected to be broadly applicable in solar and near-infrared light-emitting applications, where effective molecular phosphors are lacking at present. In particular, this route to 'brighten' low-energy molecular triplet excitons may permit singlet exciton fission sensitization of conventional silicon solar cells. PMID:25282507

  9. Energy harvesting of non-emissive triplet excitons in tetracene by emissive PbS nanocrystals

    NASA Astrophysics Data System (ADS)

    Thompson, Nicholas J.; Wilson, Mark W. B.; Congreve, Daniel N.; Brown, Patrick R.; Scherer, Jennifer M.; Bischof, Thomas S.; Wu, Mengfei; Geva, Nadav; Welborn, Matthew; Voorhis, Troy Van; Bulović, Vladimir; Bawendi, Moungi G.; Baldo, Marc A.

    2014-11-01

    Triplet excitons are ubiquitous in organic optoelectronics, but they are often an undesirable energy sink because they are spin-forbidden from emitting light and their high binding energy hinders the generation of free electron-hole pairs. Harvesting their energy is consequently an important technological challenge. Here, we demonstrate direct excitonic energy transfer from ‘dark’ triplets in the organic semiconductor tetracene to colloidal PbS nanocrystals, thereby successfully harnessing molecular triplet excitons in the near infrared. Steady-state excitation spectra, supported by transient photoluminescence studies, demonstrate that the transfer efficiency is at least (90 ± 13)%. The mechanism is a Dexter hopping process consisting of the simultaneous exchange of two electrons. Triplet exciton transfer to nanocrystals is expected to be broadly applicable in solar and near-infrared light-emitting applications, where effective molecular phosphors are lacking at present. In particular, this route to ‘brighten’ low-energy molecular triplet excitons may permit singlet exciton fission sensitization of conventional silicon solar cells.

  10. Triplet-triplet energy transfer from chlorophylls to carotenoids in two antenna complexes from dinoflagellate Amphidinium carterae.

    PubMed

    Kvíčalová, Zuzana; Alster, Jan; Hofmann, Eckhard; Khoroshyy, Petro; Litvín, Radek; Bína, David; Polívka, Tomáš; Pšenčík, Jakub

    2016-04-01

    Room temperature transient absorption spectroscopy with nanosecond resolution was used to study quenching of the chlorophyll triplet states by carotenoids in two light-harvesting complexes of the dinoflagellate Amphidinium carterae: the water soluble peridinin-chlorophyll protein complex and intrinsic, membrane chlorophyll a-chlorophyll c2-peridinin protein complex. The combined study of the two complexes facilitated interpretation of a rather complicated relaxation observed in the intrinsic complex. While a single carotenoid triplet state was resolved in the peridinin-chlorophyll protein complex, evidence of at least two different carotenoid triplets was obtained for the intrinsic light-harvesting complex. Most probably, each of these carotenoids protects different chlorophylls. In both complexes the quenching of the chlorophyll triplet states by carotenoids occurs with a very high efficiency (~100%), and with transfer times estimated to be in the order of 0.1ns or even faster. The triplet-triplet energy transfer is thus much faster than formation of the chlorophyll triplet states by intersystem crossing. Since the triplet states of chlorophylls are formed during the whole lifetime of their singlet states, the apparent lifetimes of both states are the same, and observed to be equal to the carotenoid triplet state rise time (~5ns). PMID:26801214

  11. Quantitative comparison of villin headpiece subdomain simulations and triplettriplet energy transfer experiments

    PubMed Central

    Beauchamp, Kyle A.; Ensign, Daniel L.; Das, Rhiju; Pande, Vijay S.

    2011-01-01

    As the fastest folding protein, the villin headpiece (HP35) serves as an important bridge between simulation and experimental studies of protein folding. Despite the simplicity of this system, experiments continue to reveal a number of surprises, including structure in the unfolded state and complex equilibrium dynamics near the native state. Using 2.5ms of molecular dynamics and Markov state models, we connect to current experimental results in three ways. First, we present and validate a novel method for the quantitative prediction of triplettriplet energy transfer experiments. Second, we construct a many-state model for HP35 that is consistent with previous experiments. Finally, we predict contact-formation time traces for all 1,225 possible triplettriplet energy transfer experiments on HP35. PMID:21768345

  12. NO A{sup 2}{Sigma}{sup +}-X{sup 2}II chemiluminescence produced from the reaction of excited NO{sub 2} with acetylene and its derivatives in their triplet states

    SciTech Connect

    Sisk, Wade; Endo; Hiromu; Shibuya, Kazuhiko; Obi, Kinichi

    1992-08-06

    This paper discusses how reacting excited NO{sub 2} with acetylene and its derivatives produced NO(A{sup 2}{Sigma}{sup +}) by a NO A{sup 2}{sigma}{sup +}-X{sup 2}II chemiluminescence produced by a triplet-state mechanism, with acetylene > methylacetylene > ethylacetylene > phenylacetylene > benzene in terms of efficiency. 22 refs., 8 figs., 2 tabs.

  13. Singlet--Triplet Excitations and High-Field Magnetization in CuTe2O5

    NASA Astrophysics Data System (ADS)

    Wang, Zhe; Schmidt, Michael; Goncharov, Yurii; Skourski, Yurii; Wosnitza, Joachim; Berger, Helmuth; Nidda, Hans-Abrecht Krug von; Loidl, Alois; Deisenhofer, Joachim

    2011-12-01

    By measuring the THz electron spin resonance (ESR) transmission spectra and high-field magnetization on the spin-gapped system CuTe2O5, we identified the singlet--triplet excitations in the dimerized non-magnetic ground state. The determined spin-gap value of h?0=4.94 meV at the ? point (Q?0) is significantly smaller than the strongest antiferromagnetic exchange interaction between the Cu ions predicted by theoretical investigations. We also observed the critical field Hc1a^{*}=37.6 T for H\\perpbc-plane and Hc1bc=40.6 T for H\\parallelbc-plane at the onset of non-zero magnetization, consistent with the gap value and corresponding anisotropic g-factors determined previously. The observed singlet--triplet excitations in Faraday and Voigt configurations suggest a mixing of the singlet state with the Sz=0 triplet state and the Sz= 1 triplet states, respectively, due to the Dzyaloshinskii--Moriya (DM) interaction with a DM vector perpendicular to the crystalline bc-plane.

  14. Electronic states and spectra of BiH

    NASA Astrophysics Data System (ADS)

    Setzer, Klaus-Dieter; Fink, Ewald H.; Hill, Christian; Brown, John M.

    2015-06-01

    Emission spectra of bismuth monohydride (BiH) radicals excited by energy transfer from O2(a1?g) or NF(a1?) or by a DC discharge in a mixture of bismuth vapor and hydrogen in a fast-flow system were studied in the wavenumber range from 4000 to 25 000 cm-1 with a Fourier-transform spectrometer. The X21 ? X10+ transition between the spin components of the X3?- ground state was remeasured at high spectral resolution and signal/noise. Six bands of the ?v = 0 and +1 sequences near 4950 and 6600 cm-1 have been observed. The low-J lines of these bands are split into up to 10 hfs components due to magnetic hyperfine structure splitting of the X21 levels. In addition to the previously observed electric dipole lines, weak magnetic dipole lines show up in the ?v = 0 but not in the ?v = +1 bands. The intensities of the ?v = +1 bands are about a factor of 10 higher than expected from Franck-Condon factors indicating that the electric dipole transition moment ?X2-X1 shows a strong dependence on internuclear distance. Near 5450 cm-1, the 0-0 and 1-1 bands of the transition a2 ? X21 from the hitherto unknown first excited state a1?(a2) to the upper component of the ground state have been observed. The lines in these bands show the magnetic hfs splitting of both the a2 and X21 states. In the visible range near 21 300 and 16 300 cm-1, the 0-0 and 1-1 bands of the b0+ ? X10+ system and the 0-0 band of the b0+ ? X21 transition likewise have been measured at high resolution. The lines of the latter band also show the hfs splitting of the X21 state. Least-squares fits have yielded rotational and vibrational constants of the X10+, X21, a2, and b0+ states as well as hfs parameters of the X21 and a2 states and the electronic energy of the hitherto unknown a1?(a2) level.

  15. Reactive photoinduced species in estuarine waters. Characterization of hydroxyl radical, singlet oxygen and dissolved organic matter triplet state in natural oxidation processes.

    PubMed

    al Housari, Fadi; Vione, Davide; Chiron, Serge; Barbati, Stphane

    2010-01-01

    This paper describes the reactive photo-induced species (RPS) hydroxyl radical (HO*), singlet oxygen ((1)O(2)) and chromophoric dissolved organic matter triplet state ((3)CDOM*) in fresh water (Canal Fumemorte) and estuarine water (Vaccars), sampled in the Camargue region, southern France. Experiments were conducted with a medium-pressure Hg lamp in a glass photoreactor (lambda > 290 nm, 220 W m(-2) irradiance between 290 and 400 nm). Steady-state concentration and initial production rate of RPS were determined for HO* and for (1)O(2). HO* and (1)O(2) were indirectly identified in the presence of benzene and furfuryl alcohol, respectively, as specific probes. The steady-state measured concentration of HO* was (1.72 +/- 0.01) x 10(-16) M and (9.41 +/- 0.12) x 10(-17) M for Vaccars and Canal waters samples, respectively, and the respective concentrations of (1)O(2) was (2.06 +/- 0.22) x 10(-13) M and (5.44 +/- 0.04) x 10(-14) M. The interference of (3)CDOM* or other species in the determination of (1)O(2) with furfuryl alcohol, and of (1)O(2) in the quantification of (3)CDOM* with 2,4,6-trimethylphenol was also quantitatively assessed. We developed a kinetic model describing the solar photo-transformation of xenobiotic organic compounds induced by the three different photooxidants HO*, (1)O(2) and (3)CDOM*. PMID:20062847

  16. Ab initio study of nonhomogeneous broadening of the zero-field splitting of triplet guest molecules in diluted glasses

    NASA Astrophysics Data System (ADS)

    Loboda, Oleksandr; Minaev, Boris; Vahtras, Olav; Ruud, Kenneth; gren, Hans

    2003-08-01

    Nonhomogeneous broadening of phosphorescence lines and microwave signals in optical detection of magnetic resonance (ODMR) has been calculated using multiconfigurational self-consistent field wave functions and the polarized continuum model. The solvent effects on the zero-field splitting (ZFS) parameters in the low-lying triplet states of aza-aromatic molecules are found to be linearly dependent on the solvent-induced shifts in the phosphorescence frequency in agreement with experimental data. The main contribution to the ZFS originates in the dipolar interaction of the two electron spins, the spin-spin coupling. The spin-orbit coupling (SOC) contribution to the ZFS parameter is much larger for the 3n?* state of pyrazine compared to the 3??* states of quinoline. The second-order SOC contribution to the splitting of the 3n?* state in the pyrazine molecule does not show any appreciable dependence on the dielectric constant of the solvent. This raises doubts about earlier theories for explaining the inhomogeneous broadening in triplet-state spectra based exclusively on the SOC-induced mixing of the singlet and triplet states. We complete the interpretation of the ODMR spectrum of pyrazine by calculating the hyperfine coupling (HFC) tensors in the lowest triplet state using the UB3LYP hybrid functional. An appreciable solvent-induced rotation of the anisotropic HFC tensor axes has been obtained for the 3n?* state of pyrazine, in particular for 13C and 14N nuclei. This produces additional nonhomogeneous broadening not only in electron-nuclear double resonance spectra, but also in electron paramagnetic resonance signals because the anisotropic HFC perturbation results in an intensity redistribution among the magnetic transitions between the spin sublevels. A small in-plane rotation of the ZFS tensor axes upon solvation has been predicted for quinoline. Rotation of the magnetic axes induced by the interaction with isotropic solvents can provide a new mechanism for spin-lattice relaxation in the triplet state.

  17. Direct observation of triplet energy transfer from semiconductor nanocrystals.

    PubMed

    Mongin, Cdric; Garakyaraghi, Sofia; Razgoniaeva, Natalia; Zamkov, Mikhail; Castellano, Felix N

    2016-01-22

    Triplet excitons are pervasive in both organic and inorganic semiconductors but generally remain confined to the material in which they originate. We demonstrated by transient absorption spectroscopy that cadmium selenide semiconductor nanoparticles, selectively excited by green light, engage in interfacial Dexter-like triplet-triplet energy transfer with surface-anchored polyaromatic carboxylic acid acceptors, extending the excited-state lifetime by six orders of magnitude. Net triplet energy transfer also occurs from surface acceptors to freely diffusing molecular solutes, further extending the lifetime while sensitizing singlet oxygen in an aerated solution. The successful translation of triplet excitons from semiconductor nanoparticles to the bulk solution implies that such materials are generally effective surrogates for molecular triplets. The nanoparticles could thereby potentially sensitize a range of chemical transformations that are relevant for fields as diverse as optoelectronics, solar energy conversion, and photobiology. PMID:26798011

  18. Excited-state properties of trans-(9-anthryl)ethylenes. Effects of geometric distortion about single bond

    SciTech Connect

    Bhattacharyya, K.; Chattopadhyay, S.K.; Baral-Tosh, S.; Das, P.K.

    1986-06-05

    The singlet- and triplet-related photophysical properties of four trans-1,2-diarylethylenes, containing methyl, phenyl, 1-naphthyl, and 9-anthryl group as one substituent and 9-anthryl group as the other, have been studied by steady-state and time-correlated fluorescence measurements, laser flash photolysis, and pulse radiolysis. The results show pronounced effects of the photoexcitation-induced geometric distortion (about the anthryl-to-ethylene single bond) in rendering fluorescence and triplet-triplet absorption spectra broad and structureless, and in enhancing radiationless processes from singlets, triplets, and exciplexes (with N,N-dimethylaniline). The shortening of triplet lifetimes, and the triplet quenching behaviors toward ferrocene, di-tert-butylnitroxy radical, and oxygen, are also explainable in terms of the torsional relaxation; these effects are similar to, but less pronounced than, those arising from double bond twisting in smaller arylethylene triplets. No photophysical anomaly attributable to ground-state rotamerism is observed in fluid solutions.

  19. Gas phase dynamics of triplet formation in benzophenone.

    PubMed

    Spighi, Gloria; Gaveau, Marc-André; Mestdagh, Jean-Michel; Poisson, Lionel; Soep, Benoît

    2014-05-28

    Benzophenone is a prototype molecule for photochemistry in the triplet state through its high triplet yield and reactivity. We have investigated its dynamics of triplet formation under the isolated gas phase conditions via femtosecond and nanosecond time resolved photoelectron spectroscopy. This represents the complete evolution from the excitation in S2 to the final decay of T1 to the ground state S0. We have found that the triplet formation can be described almost as a direct process in preparing T1, the lowest reacting triplet state, from the S1 state after S2 → S1 internal conversion. The molecule was also deposited by a pick-up technique on cold argon clusters providing a soft relaxation medium without evaporation of the molecule and the mechanism was identical. This cluster technique is a model for medium influenced electronic relaxation and provides a continuous transition from the isolated gas phase to the relaxation dynamics in solution. PMID:24728443

  20. Dependence of the Efficiency of Triplet-Triplet Energy Transfer on the Distance Between the Donor and Acceptor

    NASA Astrophysics Data System (ADS)

    Ibraev, N. Kh.; Seliverstova, E. V.; Artyukhov, V. Ya.

    2015-01-01

    The triplet-triplet and singlet-singlet energy transfer is investigated both experimentally and theoretically in the anthracene - Nile red system. Quantum-chemical investigations of the special features in the formation of electronically excited states and photoprocesses in the donor-acceptor pair are performed. It is demonstrated that atypical distance dependence of the efficiency of triplet-triplet energy transfer in the Langmuir-Blodgett multilayered thin films is caused by additional quenching of donor particles due to the process of energy transfer to acceptor centers by the inductive-resonant mechanism.

  1. 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

  2. Photoinduced electron transfer and electron-mediating systems from aromatic amines to triplet states of C60 and C70 in the presence of a viologen dication.

    PubMed

    Sasaki, Yoshiko; Araki, Yasuyuki; Fujitsuka, Mamoru; Ito, Osamu; Hirao, Akiko; Nishizawa, Hideyuki

    2003-02-01

    Photoinduced electron transfer between fullerenes (C60 and C70) and various aromatic amines (AA's) in the absence and presence of a viologen dication has been studied by the transient absorption method in the visible and near-IR regions. Electron-transfer takes place from AA's to the triplet states of fullerenes (3C60* and 3C70*) giving the anion radicals of fullerenes (C60*- and C70*-) and the radical cations of AA's (AA*+). The rate constants and efficiencies of electron transfer are quite high, because of the high electron-donor abilities of AA's as their low oxidation potentials indicate. The absorption bands of AA*+ appeared also in the near-IR region indicating that the radical-cation center (hole) delocalizes over the entire region of each AA. On addition of an octylviologen dication (OV2+) to C60/C70-AA systems, the electron-mediating process from C60*- and C70*- to OV2+ occurs yielding the viologen radical cation (OV*+) with longer lifetime. PMID:12664974

  3. Solvent effects on the thioxanthone triplet quenching by vinyl monomers

    NASA Astrophysics Data System (ADS)

    Fouassier, J. P.; Jacques, P.; Encinas, M. V.

    1988-07-01

    The quenching rate constants for the deactivation of triplet thioxanthone by methyl methacrylate and N-vinyl-2-pyrrolidone undergo a drastic decrease when the solvent polarity increases. This variation is represented by the ?*, ?, ? scale of solvent polarity. The contribution to this solvent effect of vibronic coupling between nearby n?* and ??* states of thioxanthone triplets is considered.

  4. Simultaneous analysis of the Ballik-Ramsay and Phillips systems of C{sub 2} and observation of forbidden transitions between singlet and triplet states

    SciTech Connect

    Chen, Wang; Kawaguchi, Kentarou; Tang, Jian; Bernath, Peter F.

    2015-02-14

    6229 lines of the Ballik-Ramsay system (b{sup 3}?{sub g}{sup ?}a{sup 3}?{sub u}) and the Phillips system (A{sup 1}?{sub u}X{sup 1}?{sub g}{sup +}) of C{sub 2} up to v = 8 and J = 76, which were taken from the literature or assigned in the present work, were analyzed simultaneously by least-squares fitting with 82 Dunham-like molecular parameters and spin-orbit interaction constants between the b{sup 3}?{sub g}{sup ?} and X{sup 1}?{sub g}{sup +} states with a standard deviation of 0.0037 cm{sup ?1} for the whole data set. As a result of the deperturbation analysis, the spin-orbit interaction constant A{sub bX} was determined as 6.333(7) cm{sup ?1} and the energy difference between the X{sup 1}?{sub g}{sup +} and a{sup 3}?{sub u} states was determined as 720.008(2) cm{sup ?1} for the potential minima or 613.650(3) cm{sup ?1} for the v = 0 levels with Merer and Browns N{sup 2} Hamiltonian for {sup 3}? states, which is about 3.3 cm{sup ?1} larger than the previously determined value. Due to this sizable change, a new energy-level crossing was found at J = 2 for v = 3 (F{sub 1}) of b{sup 3}?{sub g}{sup ?} state and v = 6 of X{sup 1}?{sub g}{sup +} state, where the strong interaction causes a nearly complete mixing of the wave functions of the b{sup 3}?{sub g}{sup ?} and X{sup 1}?{sub g}{sup +} states and the forbidden transitions become observable. Using the predictions of our deperturbation analysis, we were able to identify 16 forbidden transitions between the singlet and triplet states at the predicted frequencies with the expected intensities, which verifies our value for the energy difference between the X{sup 1}?{sub g}{sup +} and a{sup 3}?{sub u} states.

  5. Triplet-sensitized and thermal isomerization of all-trans, 7-cis, 9-cis, 13-cis, and 15-cis isomers of. beta. -carotene: Configurational dependence of the quantum yield of isomerization via the T sub 1 state

    SciTech Connect

    Kuki, Michitaka; Koyama, Yasushi ); Nagae, Hiroyoshi )

    1991-09-19

    The products of triplet-sensitized photoisomerization (excitation at 337 mn of the sensitizer, anthracene) and thermal isomerization of {beta}-carotene in {eta}-hexane, starting from the all-trans, 7-cis, 9-cis, 13-cis, and 15-cis isomers, were analyzed by HPLC. Direct photoisomerization (excitation at 488 and 337 mn) was also examined for comparison. Three different isomerization patterns were found in both triplet-sensitized and thermal isomerization: pattern A, cis to trans isomerization around each cis bond; pattern B, trans to cis isomerization in the central part of the conjugated chain; and pattern C, cis to another cis isomerization. In the T{sub 1} state, the pattern A isomerization was predominant even for the peripheral-cis (7-cis and 9-cis) isomers and its efficiency was extremely high for the central-cis (13-cis and 15-cis) isomers. In the S{sub 0} state, the pattern B isomerization, instead, was predominant for the peripheral-cis isomers, and the pattern A isomerization was predominant only for the central-cis isomers. The quantum yields of triplet-sensitized isomerization (decrease of the starting isomer per triplet species generated) were determined to be as follows: all-trans, 0.04; 7-cis, 0.12; 9-cis, 0.15; 13-cis, 0.87; and 15-cis, 0.98. Carbon-carbon {pi} bond orders of model polyenes in the T{sub 1} and S{sub 0} states were calculated by using the Pariser-Parr-Pople CI theory; bond lengths were optimized by using a bond order-bond length relationship. Isomerization characteristics in the T{sub 1} and S{sub 0} states observed were discussed based on the results of the calculations.

  6. N2 triplet band emissions in the dayglow of Venus, Mars, and Titan

    NASA Astrophysics Data System (ADS)

    Jain, Sonal Kumar; Bhardwaj, Anil

    2012-07-01

    Vegard-Kaplan (VK) and Second Positive emissions of N_2 are common features in the terrestrial dayglow and aurora and have been studied extensively. Recent discoveries of N_2 triplet band emissions on Mars by SPICAM/Mars-Express and on Titan by Cassini UVIS have led planetary scientists to look for the processes governing the N_2 triplet band emissions in different planetary atmospheres. Present work deals with the modeling of N_2 triplet band emission on Mars, Venus, and Titan. A model for N_2 triplet band emissions has been developed and used to explain the recent observations of N_2 Vegard-Kaplan (VK) (A^3?_u^+ - X^1?^+_g ) band on Mars and Titan. Steady state photoelectron fluxes and volume excitation rates have been calculated using the Analytical Yield Spectra technique. Since interstate cascading is important for triplet states of N_2, the population of any given level of N_2 triplet states is calculated under statistical equilibrium considering direct excitation, cascading, and quenching effects. Relative population of all vibrational levels of each triplet state is calculated in the model. Line of sight intensities and height-integrated overhead intensities have been calculated for VK, First Positive ( B^3?_g - A^3?^+_u ), Second Positive ( C^3?_u - B^3?_g ), Wu-Benesch (W^3?_u - B^3?_g), Reverse First Positive, Herman--Kaplan (E ? A), E ? B, and E ? C bands of N_2. The N_2 VK band span wavelength range from far ultraviolet to visible, and some transitions even originate at wavelength more than 1000 nm . Our calculations show that the overhead intensity of VK bands in the wavelength range 400--800, 300--190, 200--300, and 150--200 nm are 22%, 39%, 35%, and 4% of the total VK band emission. Emissions between 600 and 800 nm wavelength consist of about 50% of the total First Positive band system. Major portion of Second Positive band emissions lie in wavelengths between 300 and 400 nm, which is more than 90% of the total Second Positive band overhead intensity. On Mars, a reduction in the N_2 density by a factor of 3 in the Mars thermospheric general circulation model is required to obtain agreement between calculated limb profiles of VK (0-6) and the SPICAM/MEX observation. On Titan, the calculated intensity of N_2 VK band in 150--190 nm wavelength range is in good agreement with the Cassini-UVIS observation. Calculations are also carried out on Venus using this model. Calculated intensities on Venus are about factor of 10 higher than that on Mars. The results will be presented and discussed.

  7. Triplet dark matter from leptogenesis

    NASA Astrophysics Data System (ADS)

    Heo, Jae Ho; Kim, C. S.

    2014-04-01

    A triplet dark matter candidate from thermal leptogenesis is considered with building a model. The model is based on the standard two-Higgs-doublet model and seesaw mechanism with Higgs triplets. The parameters (couplings and masses) are adjusted for the observed small neutrino mass and the leptogenesis. Dark matter particles can annihilate and decay in this model. The time evolution of the dark matter number is governed by (co)annihilations in the expanding universe, and its mass is constrained by the observed relic density. The dark matter can decay into final states with three leptons (two charged leptons and one neutrino). We investigate whether the decay in a galaxy can account for cosmic ray anomalies in the positron and electron spectrum. A noticeable point is that if the dark matter decays into each lepton with different branching ratios, cosmic ray anomalies in AMS-02 measurements of the positron fraction and the Fermi LAT measurements of the electrons-plus-positrons flux could be simultaneously accounted for from its decay products.

  8. Chemical characterization of SOA formed from aqueous-phase reactions of phenols with the triplet excited state of carbonyl and hydroxyl radical

    SciTech Connect

    Yu, Lu; Smith, Jeremy; Laskin, Alexander; Anastasio, Cort N.; Laskin, Julia; Zhang, Qi

    2014-01-01

    Phenolic compounds, which are emitted in significant amounts from biomass burning, can undergo fast reactions in atmospheric aqueous phases to form secondary organic aerosol (aqSOA). In this study, we investigate the reactions of phenol and two methoxy-phenols (syringol and guaiacol) with two major aqueous phase oxidants – the triplet excited states of an aromatic carbonyl (3C*) and hydroxyl radical (•OH). We thoroughly characterize the low-volatility species produced from these reactions and interpret their formation mechanisms using aerosol mass spectrometry (AMS), desorption electrospray ionization mass spectrometry (DESIMS), and ion chromatography (IC). A large number of oxygenated molecules are identified, including oligomers containing up to six monomer units, functionalized monomer and oligomers with carbonyl, carboxyl, and hydroxyl groups, and small organic acid anions (e.g., formate, acetate, oxalate, and malate). The average atomic oxygen-to-carbon (O/C) ratios of phenolic aqSOA are in the range of 0.85-1.23, similar to those of low-volatility oxygenated organic aerosol (LV-OOA) observed in ambient air. The aqSOA compositions are overall similar for the same precursor, but the reactions mediated by 3C* are faster than •OH-mediated reactions and produce more oligomers and hydroxylated species at the point when 50% of the phenol had reacted. Profiles determined using a thermodenuder indicate that the volatility of phenolic aqSOA is influenced by both oligomer content and O/C ratio. In addition, the aqSOA shows enhanced light absorption in the UV-vis region, suggesting that aqueous-phase reactions of phenols are likely an important source of brown carbon in the atmosphere, especially in regions influenced by biomass burning.

  9. Chemical characterization of SOA formed from aqueous-phase reactions of phenols with the triplet excited state of carbonyl and hydroxyl radical

    NASA Astrophysics Data System (ADS)

    Yu, L.; Smith, J.; Laskin, A.; Anastasio, C.; Laskin, J.; Zhang, Q.

    2014-08-01

    Phenolic compounds, which are emitted in significant amounts from biomass burning, can undergo fast reactions in atmospheric aqueous phases to form secondary organic aerosol (aqSOA). In this study, we investigate the reactions of phenol and two methoxy-phenols (syringol and guaiacol) with two major aqueous phase oxidants - the triplet excited states of an aromatic carbonyl (3C*) and hydroxyl radical (\\centerdot OH). We thoroughly characterize the low-volatility species produced from these reactions and interpret their formation mechanisms using aerosol mass spectrometry (AMS), nanospray desorption electrospray ionization mass spectrometry (nano-DESI MS), and ion chromatography (IC). A large number of oxygenated molecules are identified, including oligomers containing up to six monomer units, functionalized monomer and oligomers with carbonyl, carboxyl, and hydroxyl groups, and small organic acid anions (e.g., formate, acetate, oxalate, and malate). The average atomic oxygen-to-carbon (O / C) ratios of phenolic aqSOA are in the range of 0.85-1.23, similar to those of low-volatility oxygenated organic aerosol (LV-OOA) observed in ambient air. The aqSOA compositions are overall similar for the same precursor, but the reactions mediated by 3C* are faster than \\centerdot OH-mediated reactions and produce more oligomers and hydroxylated species at the point when 50% of the phenol had reacted. Profiles determined using a thermodenuder indicate that the volatility of phenolic aqSOA is influenced by both oligomer content and O / C ratio. In addition, the aqSOA shows enhanced light absorption in the UV-vis region, suggesting that aqueous-phase reactions of phenols are likely an important source of brown carbon in the atmosphere, especially in regions influenced by biomass burning.

  10. Chemical characterization of SOA formed from aqueous-phase reactions of phenols with the triplet excited state of carbonyl and hydroxyl radical

    NASA Astrophysics Data System (ADS)

    Yu, L.; Smith, J.; Laskin, A.; Anastasio, C.; Laskin, J.; Zhang, Q.

    2014-12-01

    Phenolic compounds, which are emitted in significant amounts from biomass burning, can undergo fast reactions in atmospheric aqueous phases to form secondary organic aerosol (aqSOA). In this study, we investigate the reactions of phenol (compound with formula C6H5OH)), guaiacol (2-methoxyphenol), and syringol (2,6-dimethoxyphenol) with two major aqueous-phase oxidants - the triplet excited states of an aromatic carbonyl (3C*) and hydroxyl radical (· OH). We thoroughly characterize the low-volatility species produced from these reactions and interpret their formation mechanisms using aerosol mass spectrometry (AMS), nanospray desorption electrospray ionization mass spectrometry (nano-DESI MS), and ion chromatography (IC). A large number of oxygenated molecules are identified, including oligomers containing up to six monomer units, functionalized monomer and oligomers with carbonyl, carboxyl, and hydroxyl groups, and small organic acid anions (e.g., formate, acetate, oxalate, and malate). The average atomic oxygen-to-carbon (O / C) ratios of phenolic aqSOA are in the range of 0.85-1.23, similar to those of low-volatility oxygenated organic aerosol (LV-OOA) observed in ambient air. The aqSOA compositions are overall similar for the same precursor, but the reactions mediated by 3C* are faster than · OH-mediated reactions and produce more oligomers and hydroxylated species at the point when 50% of the phenolic compound has reacted. Profiles determined using a thermodenuder indicate that the volatility of phenolic aqSOA is influenced by both oligomer content and O / C ratio. In addition, the aqSOA shows enhanced light absorption in the UV-visible region, suggesting that aqueous-phase reactions of phenols may contribute to formation of secondary brown carbon in the atmosphere, especially in regions influenced by biomass burning.

  11. Chemical characterization of SOA formed from aqueous-phase reactions of phenols with the triplet excited state of carbonyl and hydroxyl radical

    DOE PAGESBeta

    Yu, L.; Smith, J.; Laskin, A.; Anastasio, C.; Laskin, J.; Zhang, Q.

    2014-12-23

    Phenolic compounds, which are emitted in significant amounts from biomass burning, can undergo fast reactions in atmospheric aqueous phases to form secondary organic aerosol (aqSOA). In this study, we investigate the reactions of phenol (compound with formula C6H5OH)), guaiacol (2-methoxyphenol), and syringol (2,6-dimethoxyphenol) with two major aqueous-phase oxidants – the triplet excited states of an aromatic carbonyl (3C*) and hydroxyl radical (· OH). We thoroughly characterize the low-volatility species produced from these reactions and interpret their formation mechanisms using aerosol mass spectrometry (AMS), nanospray desorption electrospray ionization mass spectrometry (nano-DESI MS), and ion chromatography (IC). A large number of oxygenatedmore » molecules are identified, including oligomers containing up to six monomer units, functionalized monomer and oligomers with carbonyl, carboxyl, and hydroxyl groups, and small organic acid anions (e.g., formate, acetate, oxalate, and malate). The average atomic oxygen-to-carbon (O / C) ratios of phenolic aqSOA are in the range of 0.85–1.23, similar to those of low-volatility oxygenated organic aerosol (LV-OOA) observed in ambient air. The aqSOA compositions are overall similar for the same precursor, but the reactions mediated by 3C* are faster than · OH-mediated reactions and produce more oligomers and hydroxylated species at the point when 50% of the phenolic compound has reacted. Profiles determined using a thermodenuder indicate that the volatility of phenolic aqSOA is influenced by both oligomer content and O / C ratio. In addition, the aqSOA shows enhanced light absorption in the UV–visible region, suggesting that aqueous-phase reactions of phenols may contribute to formation of secondary brown carbon in the atmosphere, especially in regions influenced by biomass burning.« less

  12. Chemical characterization of SOA formed from aqueous-phase reactions of phenols with the triplet excited state of carbonyl and hydroxyl radical

    DOE PAGESBeta

    Yu, L.; Smith, J.; Laskin, A.; Anastasio, C.; Laskin, J.; Zhang, Q.

    2014-08-19

    Phenolic compounds, which are emitted in significant amounts from biomass burning, can undergo fast reactions in atmospheric aqueous phases to form secondary organic aerosol (aqSOA). In this study, we investigate the reactions of phenol and two methoxy-phenols (syringol and guaiacol) with two major aqueous phase oxidants – the triplet excited states of an aromatic carbonyl (3C*) and hydroxyl radical (·OH). We thoroughly characterize the low-volatility species produced from these reactions and interpret their formation mechanisms using aerosol mass spectrometry (AMS), nanospray desorption electrospray ionization mass spectrometry (nano-DESI MS), and ion chromatography (IC). A large number of oxygenated molecules are identified,more » including oligomers containing up to six monomer units, functionalized monomer and oligomers with carbonyl, carboxyl, and hydroxyl groups, and small organic acid anions (e.g., formate, acetate, oxalate, and malate). The average atomic oxygen-to-carbon (O / C) ratios of phenolic aqSOA are in the range of 0.85–1.23, similar to those of low-volatility oxygenated organic aerosol (LV-OOA) observed in ambient air. The aqSOA compositions are overall similar for the same precursor, but the reactions mediated by 3C* are faster than ·OH-mediated reactions and produce more oligomers and hydroxylated species at the point when 50% of the phenol had reacted. Profiles determined using a thermodenuder indicate that the volatility of phenolic aqSOA is influenced by both oligomer content and O / C ratio. In addition, the aqSOA shows enhanced light absorption in the UV-vis region, suggesting that aqueous-phase reactions of phenols are likely an important source of brown carbon in the atmosphere, especially in regions influenced by biomass burning.« less

  13. Mapping Agricultural Crops with AVIRIS Spectra in Washington State

    NASA Technical Reports Server (NTRS)

    Green, Robert O.; Pavri, Betina; Roberts, Dar; Ustin, Susan

    2000-01-01

    Spectroscopy is used in the laboratory to measure the molecular components and concentrations of plant constituents to answer questions about the plant type, status, and health. Imaging spectrometers measure the upwelling spectral radiance above the Earth's surface as images. Ideally, imaging spectrometer data sets should be used to understand plant type, plant status, and health of plants in an agricultural setting. An Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data set was acquired over agricultural fields near Wallula, Washington on July 23rd, 1997. AVIRIS measures upwelling radiance spectra through 224 spectral channels with contiguous 10-nm sampling from 400 to 2500 run in the solar-reflected spectrum. The spectra are measured as images of 11 by up to 800 km with 20-m spatial resolution. The spectral images measured by AVIRIS represent the integrated signal resulting from: the solar irradiance; two way transmittance and scattering of the atmosphere; the absorptions and scattering of surface materials; as well as the spectral, radiometric and spatial response functions of AVIRIS. This paper presents initial research to derive properties of the agricultural fields near Wallula from the calibrated spectral images measured by AVIRIS near the top of the atmosphere.

  14. Ground-state features in the THz spectra of molecular clusters of ?-HMX.

    PubMed

    Huang, Lulu; Shabaev, Andrew; Lambrakos, Samuel G; Massa, Lou

    2012-10-01

    We present calculations of absorption spectra arising from molecular vibrations at THz frequencies for molecular clusters of the explosive HMX using density functional theory (DFT). The features of these spectra can be shown to follow from the coupling of vibrational modes. In particular, the coupling among ground-state vibrational modes provides a reasonable molecular-level interpretation of spectral features associated with the vibrational modes of molecular clusters. THz excitation from the ground state is associated with frequencies that characteristically perturb molecular electronic states, in contrast to frequencies, which are usually substantially above the mid-infrared (mid-IR) range, that can induce appreciable electronic-state transition. Owing to this characteristic of THz excitation, one is able to make a direct association between local oscillations about ground-state minima of molecules, either isolated or comprising a cluster, and THz absorption spectra. The DFT software program GAUSSIAN was used for the calculations of the absorption spectra presented here. PMID:23031709

  15. Spin polarization in quantum Hall state obtained by Kerr rotation spectra

    SciTech Connect

    Ito, H.; Seo, M.; Fukuoka, D.; Oto, K.; Muro, K.; Hirayama, Y.; Kumada, N.

    2011-12-23

    We developed a novel system for a high sensitive measurement of Kerr rotation spectra, and Kerr rotation spectra of quantum Hall system in AlGaAs/GaAs 17 nm quantum well were measured. Spin polarization of quantum Hall states was obtained by integrating the spectra, since Kerr rotation spectra reflect spin population of electrons. The spin polarization decreased rapidly on both sides of {nu} = 1, which is ascribed to Skyrmion effect. However, the spin polarization present a flat region around {nu} = 1 which means a quantum Hall ferromagnet is not fully spin polarized.

  16. 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.

  17. State flip at exceptional points in atomic spectra

    NASA Astrophysics Data System (ADS)

    Menke, Henri; Klett, Marcel; Cartarius, Holger; Main, Jrg; Wunner, Gnter

    2016-01-01

    We study the behavior of nonadiabatic population transfer between resonances at an exceptional point in the spectrum of the hydrogen atom. It is known that, when the exceptional point is encircled, the system always ends up in the same state, independent of the initial occupation within the two-dimensional subspace spanned by the states coalescing at the exceptional point. We verify this behavior for a realistic quantum system, viz., the hydrogen atom in crossed electric and magnetic fields. It is also shown that the nonadiabatic hypothesis can be violated when resonances in the vicinity are taken into account. In addition, we study nonadiabatic population transfer in the case of a third-order exceptional point, in which three resonances are involved.

  18. Enhanced triplet exciton generation in polyfluorene blends

    NASA Astrophysics Data System (ADS)

    Ford, T. A.; Avilov, I.; Beljonne, D.; Greenham, N. C.

    2005-03-01

    Photoinduced absorption spectroscopy is used to study the intersystem crossing in a blend consisting of the fluorene-based conjugated polymers poly( 9,9' -dioctylfluorene- co -benzothiadiazole) (F8BT) and poly( 9,9' -dioctylfluorene- co -bis- N,N' -(4-butylphenyl)-bis- N,N' -phenyl-1,4-phenylene-diamine) (PFB). The intersystem crossing efficiency is found to be 10 times higher in F8BT:PFB than in F8BT alone. We attribute this effect to enhanced increased intersystem crossing in the charge-separated states formed at the polymer/polymer heterojunctions in the blend. Applying an electric field dissociates these states and thus reduces the rate of triplet state formation. We also perform time-dependent density functional theory quantum chemical calculations to determine the T1?Tn absorption cross section and to estimate the triplet yield.

  19. A comparison between Stark maps and scaled spectra of highly perturbed Rydberg states in Ba

    NASA Astrophysics Data System (ADS)

    Vasilescu, Camelia; Bates, Kenn; Masae, Jumpei; Schumacher, Douglass

    2001-05-01

    We have studied the Stark effect in Ba Rydberg states, exciting from 6s^2arrow 5d6parrow 6snd, with n near 27. Data showing energy dependent absorption strengths (spectra) were acquired in two different ways. We have measured Stark spectra (electric field F=constant) and scaled energy spectra (\\varepsilon =E/?F=constant). In the latter, the applied electric field and the excitation energy are varied simultaneously. We show that one can obtain a time domain representation by Fourier transforming the Stark spectra and that this representation is similar to the scaled spectra with comparable peak structure. The time domain data have peaks whose location is controlled by Kepler, Stark, and other characteristic times, whereas in the scaled spectra, the peaks are located at the scaled actions of contributing periodic orbits. We also show that, starting from the Stark map, one can obtain scaled energy spectra by interpolating between data taken at different fields strengths. Comparing the scaled spectra obtained by these two methods, we have found resonable agreement. This means, in principle, that past Stark maps of various systems can be converted to scaled spectra without redoing the experiment, depending on the resolution desired.

  20. Experimental Study of the Triplet Synchronization of Coupled Nonidentical Mechanical Metronomes

    PubMed Central

    Jia, Ji; Song, Zhiwen; Liu, Weiqing; Kurths, Jürgen; Xiao, Jinghua

    2015-01-01

    Triplet synchrony is an interesting state when the phases and the frequencies of three coupled oscillators fulfill the conditions of a triplet locking, whereas every pair of systems remains asynchronous. Experimental observation of triplet synchrony is firstly realized in three coupled nonidentical mechanical metronomes. A more direct method based on the phase diagram is proposed to observe and determine triplet synchronization. Our results show that the stable triplet synchrony is observed in several intervals of the parameter space. Moreover, the experimental results are verified according to the theoretical model of the coupled metronomes. The outcomes are useful to understand the inner regimes of collective dynamics in coupled oscillators. PMID:26598175

  1. Experimental Study of the Triplet Synchronization of Coupled Nonidentical Mechanical Metronomes.

    PubMed

    Jia, Ji; Song, Zhiwen; Liu, Weiqing; Kurths, Jrgen; Xiao, Jinghua

    2015-01-01

    Triplet synchrony is an interesting state when the phases and the frequencies of three coupled oscillators fulfill the conditions of a triplet locking, whereas every pair of systems remains asynchronous. Experimental observation of triplet synchrony is firstly realized in three coupled nonidentical mechanical metronomes. A more direct method based on the phase diagram is proposed to observe and determine triplet synchronization. Our results show that the stable triplet synchrony is observed in several intervals of the parameter space. Moreover, the experimental results are verified according to the theoretical model of the coupled metronomes. The outcomes are useful to understand the inner regimes of collective dynamics in coupled oscillators. PMID:26598175

  2. Proximity effect in ferromagnet/triplet p-wave superconductor structures

    NASA Astrophysics Data System (ADS)

    Li, Hong; Yang, Wei; Yang, Xinjian; Qin, Minghui

    2007-02-01

    The superconducting proximity effect in normal metal/insulator/ferromagnet/triplet p-wave superconductor (N/I/FP) structures is studied based on an extended Blonder Tinkham Klapwijk (BTK) theory. Three kinds of pairings for the P side are chosen: p, p, p+ip waves. The transition from the 0 to ? state is found in the conductance spectra with increasing the thickness of F or the ferromagnetic exchange energy. The large amplitude of the normalized conductance suggests the possible coexistence of the ferromagnetism and p-wave superconductivity in a small region near the F/P interface induced by the proximity effect.

  3. Limits to the applicability of the rule of equality to unity of the sum of quantum yields of fluorescence and transition to the triplet state for complex organic molecules in the condensed phase (A review)

    NASA Astrophysics Data System (ADS)

    Ermolaev, V. L.; Sveshnikova, E. B.

    2015-10-01

    For different classes of molecules, we have estimated from experimental data the lower limit of the height of S 1 levels for which the rule q fl + q T = 1 ( q fl is the fluorescence quantum yield, q T is the quantum yield of formation of the triplet state) begins to be violated; i.e., direct nonradiative transition from the S 1-state to the ground state appears, the quantum yield of which exceeds measurement errors. We have found that, for compounds of different classes, this limit varies from 15000 to 21000 cm-1. It has been shown that the difference in the limit may be explained in terms of the inductive resonance theory of nonradiative transitions, which takes into account the localization of the electronic transition, its rate constant, and the overlap of the vibronic spectrum of the molecule with the vibrational spectrum of high-frequency vibrations taking into account the variation in the rate constant of the intersystem crossing transition to the triplet state.

  4. The influence of polymer structure on triplet luminescence

    SciTech Connect

    Burkhart, R.D.; Burrows, J.A.J.

    1987-01-01

    Triplet luminescence spectroscopy has been used to probe interactions between pendant groups of polymer chains. A styrene polymer was synthesized with naphthyl and phenylcarbonyl chromophores at the terminal positions. Information about inter- and intramolecular energy transfer was obtained from phosphorescence spectra in MTHF solutions at 77/sup 0/K. (DLC)

  5. Rotational spectra of the X 2Sigma(+) states of CaH and CaD

    NASA Technical Reports Server (NTRS)

    Frum, C. I.; Oh, J. J.; Cohen, E. A.; Pickett, H. M.

    1993-01-01

    The rotational spectra of the 2Sigma(2+) ground states of calcium monohydride and monodeuteride have been recorded in absorption between 250 and 700 GHz. The gas phase free radicals have been produced in a ceramic furnace by the reaction of elemental calcium with molecular hydrogen or deuterium in the presence of an electrical discharge. The molecular constants including the rotational constant, centrifugal distortion constants, spin-rotation constants, and magnetic hyperfine interaction constants have been extracted from the spectra.

  6. Peculiarity of triplet-triplet energy transfer from 2-(2'-hydroxy-phenyl)benzoxazole to diacetyl. Evidence for radiative keto-enol transitions 3K∗→ 1E and 1E→ 1K∗

    NASA Astrophysics Data System (ADS)

    Nickel, Bernhard; Walla, Peter J.

    1998-10-01

    In the triplet-triplet energy transfer (TTET) from a donor D to an acceptor A, 3D∗+ 1A→ 1D+ 3A∗, the maximum transferable energy is equal to the maximum energy that can be emitted as phosphorescence 3D∗→ 1D. A peculiarity was expected for the TTET from 2-(2'-hydroxyphenyl)benzoxazole (HBO), which has two isoenergetic lowest triplet states, an enol triplet state 3E∗ and a keto triplet state 3K∗, with completely different phosphorescence spectra: 3E∗→ 1E (origin at 22400 cm -1) and 3K∗→ 1K (origin at ˜17500 cm -1). If the triplet energy of an acceptor A is between these two origin values, like in the case of diacetyl (19700 cm -1), then the TTET from HBO to A should be predominantly due to the process 3E∗+ 1A→ 1E+ 3A∗. The TTET from HBO, meta-methyl-HBO ( m-MeHBO, 3K∗≳300 cm -1 above 3E∗) and ortho-methyl-HBO ( o-MeHBO, 3K∗≳600 cm -1 below 3E∗) to diacetyl was studied in 3-methylpentane from 110 to 280 K, which corresponds to a viscosity range of more than three orders of magnitude. The postulated peculiarity of TTET was observed at low viscosity. At low temperature and high viscosity, however, the kinetic differences in the TTET from the three donors disappear. The TTET from o-MeHBO to diacetyl at low temperature is assigned to the process 3K∗+ 1A→ 1E+ 3A∗, which corresponds to a keto-enol phosphorescence 3K→ 1E. The temperature dependence of the second-order rate constant for TTET can be satisfactorily described with a kinetic model, whose distinctive feature is a finite rate of the triplet-state tautomerization 3K∗⇌ 3E∗. The only essentially donor-specific parameter is the energy difference between 3E∗ and 3K∗. The principal possibility of radiative keto-enol or enol-keto transitions has been verified: The phosphorescence excitation spectrum of m-MeHBO in a xenon matrix exhibits in the near UV a weak band that can be assigned to the transition 1E→ 1K∗.

  7. In vivo absorption spectra of the two stable states of the Euglena photoreceptor photocycle.

    PubMed

    Barsanti, Laura; Coltelli, Primo; Evangelista, Valtere; Passarelli, Vincenzo; Frassanito, Anna Maria; Vesentini, Nicoletta; Santoro, Fabrizio; Gualtieri, Paolo

    2009-01-01

    Euglena gracilis possesses a simple but sophisticated light detecting system, consisting of an eyespot formed by carotenoids globules and a photoreceptor. The photoreceptor of Euglena is characterized by optical bistability, with two stable states. In order to provide important and discriminating information on the series of structural changes that Euglena photoreceptive protein(s) undergoes inside the photoreceptor in response to light, we measured the in vivo absorption spectra of the two stable states A and B of photoreceptor photocycle. Data were collected using two different devices, i.e. a microspectrophotometer and a digital microscope. Our results show that the photocycle and the absorption spectra of the photoreceptor possess strong spectroscopic similarities with a rhodopsin-like protein. Moreover, the analysis of the absorption spectra of the two stable states of the photoreceptor and the absorption spectrum of the eyespot suggests an intriguing hypothesis for the orientation of microalgae toward light. PMID:18764888

  8. Ground and Excited State Alkyl CH Stretch IR Spectra of Straight-Chain Alkylbenzenes

    NASA Astrophysics Data System (ADS)

    Hewett, Daniel M.; Korn, Joseph A.; Zwier, Timothy S.

    2015-06-01

    Vibrational spectra of alkanes in the CH stretch region are often complicated by Fermi resonance with the overtone of the CH bends. This complication has made the CH stretch region difficult to use as a spectroscopic tool for assigning structures to experimental infrared spectra. A first-principles model accounting for Fermi resonance has been developed by Sibert and co-workers, and has been successfully implemented to predict the CH stretch region of alkyl groups in a variety of settings (both -CH2- and -CH3). We have recorded jet-cooled, single-conformation infrared spectra of a series of straight chain alkylbenzenes having chain lengths of two carbons and longer, serving as a foundation for further tests and refinement of the theoretical model. Ground and excited state IR spectra of these alkylbenzenes were acquired using fluorescence dip infrared spectroscopy. A novel approach for taking the excited state spectra that utilizes the gain of a second, infrared-induced fluorescence peak will be discussed and compared to the typical depletion spectra, using ethylbenzene as a prototypical system.

  9. Venus - Stein Triplet Crater

    NASA Technical Reports Server (NTRS)

    1990-01-01

    The Magellan synthetic aperture radar (SAR) imaged this unique 'triplet crater,' or 'crater field' during orbits 418-421 on 21 September 1990. These craters are 14 kilometers, 11 kilometers, and 9 kilometers in diameter, respectively, and are centered at latitude -30.1 degrees south and longitude 345.5 degrees east. The Magellan Science Team has proposed the name Stein for this crater field after the American author, Gertrude Stein. This name has not yet been approved by the International Astronomical Union. The crater field was formed on highly fractured plains. The impacts generated a considerable amount of low viscosity 'flows' thought to consist largely of shock-melted target material along with fragmented debris from the crater. The three craters appear to have relatively steep walls based on the distortion in the image of the near and far walls of the craters in the Magellan radar look direction (from the left). The flow deposits from the three craters extend dominantly to the northeast (upper right).

  10. Control of magnetism in singlet-triplet superconducting heterostructures

    NASA Astrophysics Data System (ADS)

    Romano, Alfonso; Gentile, Paola; Noce, Canio; Vekhter, Ilya; Cuoco, Mario

    2016-01-01

    We analyze the magnetization at the interface between singlet and triplet superconductors and show that its direction and dependence on the phase difference across the junction are strongly tied to the structure of the triplet order parameter as well as to the pairing interactions. We consider equal spin helical, opposite spin chiral, and mixed symmetry pairing on the triplet side and show that the magnetization vanishes at ? =0 only in the first case, follows approximately a cos? behavior for the second, and shows higher harmonics for the last configuration. We trace the origin of the magnetization to the magnetic structure of the Andreev bound states near the interface, and provide a symmetry-based explanation of the results. Our findings can be used to control the magnetization in superconducting heterostructures and to test symmetries of spin-triplet superconductors.

  11. The electronic spectrum of Si3 I: triplet D(3h) system.

    PubMed

    Reilly, N J; Kokkin, D L; Zhuang, X; Gupta, V; Nagarajan, R; Fortenberry, R C; Maier, J P; Steimle, T C; Stanton, J F; McCarthy, M C

    2012-05-21

    We report the measurement of a jet-cooled electronic spectrum of the silicon trimer. Si(3) was produced in a pulsed discharge of silane in argon, and the excitation spectrum examined in the 18 000-20 800 cm(-1) region. A combination of resonant two-color two-photon ionization (R2C2PI) time-of-flight mass spectroscopy, laser-induced fluorescence/dispersed fluorescence, and equation-of-motion coupled-cluster calculations have been used to establish that the observed spectrum is dominated by the 1(3)A(1)" - ã (3)A(2)' transition of the D(3h) isomer. The spectrum has an origin transition at 18,600 ± 4 cm(-1) and a short progression in the symmetric stretch with a frequency of ∼445 cm(-1), in good agreement with a predicted vertical transition energy of 2.34 eV for excitation to the 1(3)A(1)" state, which has a calculated symmetric stretching frequency of 480 cm(-1). In addition, a ∼505 cm(-1) ground state vibrational frequency determined from sequence bands and dispersed fluorescence is in agreement with an earlier zero-electron kinetic energy study of the lowest D(3h) state and with theory. A weaker, overlapping band system with a ∼360 cm(-1) progression, observed in the same mass channel (m/z = 84) by R2C2PI but under different discharge conditions, is thought to be due to transitions from the (more complicated) singlet C(2v) ground state ((1)A(1)) state of Si(3). Evidence of emission to this latter state in the triplet dispersed fluorescence spectra suggests extensive mixing in the excited triplet and singlet manifolds. Prospects for further spectroscopic characterization of the singlet system and direct measurement of the energy separation between the lowest singlet and triplet states are discussed. PMID:22612095

  12. Sensitized and heavy atom induced production of acenaphthylene triplet: A laser flash photolysis study

    SciTech Connect

    Samanta, A.; Fessenden, R.W. )

    1989-07-27

    The triplet state of acenaphthylene has been examined by nanosecond laser flash photolysis using sensitization and heavy atom perturbation techniques. Although acenaphthylene does not form any observable triplet upon direct flash excitation, a transient with microsecond lifetime ({lambda}{sub max} = 315 nm) is observable when a solution of the sample is excited by sensitizers (benzophenone, thioxanthone, benzil). This transient is ascribed to the triplet of acenaphthylene on the basis of its quenching behavior toward oxygen, ferrocene, azulene, and {beta}-carotene. Quantitative data concerning the triplet-triplet absorption and quenching constants are presented. The triplet energy is estimated to lie between 46 and 47 kcal/mol. The triplet can also be produced by direct excitation in solvents containing heavy atoms (ethyl bromide, ethyl iodide). The triplet yield is found to increase with an increase of the amount of the heavy atom containing solvent. No saturation limit is obtained. These facts together with the effect of heavy atoms on the T{sub 1} {yields} S{sub 0} process allow the differing behavior of ethyl bromide and ethyl iodide on the photodimerization process of acenaphthylene to be explained. Triplet-state parameters (extinction coefficient and triplet yield) have been estimated in these solvents by the energy-transfer technique and actinometry.

  13. Dimethyl ether: laboratory spectra up to 2.1 THz. Torsion-rotational spectra within the vibrational ground state

    NASA Astrophysics Data System (ADS)

    Endres, C. P.; Drouin, B. J.; Pearson, J. C.; Müller, H. S. P.; Lewen, F.; Schlemmer, S.; Giesen, T. F.

    2009-09-01

    Dimethyl ether (CH_3OCH_3) is one of the largest organic molecules detected in the interstellar medium. As an asymmetric top molecule with two methyl groups which undergo large amplitude motions and a dipole moment of μ=1.3 D, it conveys a dense spectrum throughout the terahertz region and contributes to the spectral line confusion in astronomical observations at these frequencies. In this paper, we present rotational spectra of dimethyl ether in its ground vibrational states, which have been measured in the laboratory and analyzed covering frequencies up to 2.1 THz. The analysis is based on an effective Hamiltonian for a symmetric two-top rotor and includes experimental data published so far. Frequency predictions are presented up to 2.5 THz for astronomical applications with accuracies better than 1 MHz. Table A.1 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/504/635

  14. Spectroscopic Characterization and Reactivity of Triplet and Quintet Iron(IV) Oxo Complexes in the Gas Phase

    PubMed Central

    Andris, Erik; Jašík, Juraj; Gómez, Laura

    2016-01-01

    Abstract Closely structurally related triplet and quintet iron(IV) oxo complexes with a tetradentate aminopyridine ligand were generated in the gas phase, spectroscopically characterized, and their reactivities in hydrogen‐transfer and oxygen‐transfer reactions were compared. The spin states were unambiguously assigned based on helium tagging infrared photodissociation (IRPD) spectra of the mass‐selected iron complexes. It is shown that the stretching vibrations of the nitrate counterion can be used as a spectral marker of the central iron spin state. PMID:26878833

  15. Spectra of random operators with absolutely continuous integrated density of states

    SciTech Connect

    Rio, Rafael del E-mail: delriomagia@gmail.com

    2014-04-15

    The structure of the spectrum of random operators is studied. It is shown that if the density of states measure of some subsets of the spectrum is zero, then these subsets are empty. In particular follows that absolute continuity of the integrated density of states implies singular spectra of ergodic operators is either empty or of positive measure. Our results apply to Anderson and alloy type models, perturbed Landau Hamiltonians, almost periodic potentials, and models which are not ergodic.

  16. Simultaneous detection of two triplets: a time-resolved resonance Raman study.

    PubMed

    Pandey, Rishikesh; Umapathy, Siva

    2012-08-23

    Solvents are known to affect the triplet state structure and reactivity. In this paper, we have employed time-resolved resonance Raman (TR3) spectroscopy to understand solvent-induced subtle structural changes in the lowest excited triplet state of thioxanthone. Density functional theory (DFT) combined with the self-consistent reaction field (SCRF) implicit solvation model has been used to calculate the vibrational frequencies in the solvents. Here, we report a unique observation of the coexistence of two triplets, which has been substantiated by the probe wavelength-dependent Raman experiments. The coexistence of two triplets has been further supported by photoreduction experiments carried out at various temperatures. PMID:22803611

  17. Low temperature emission spectra of optically nonlinear N-benzyl-2-methyl-4-nitroaniline crystal

    NASA Astrophysics Data System (ADS)

    Piela, Katarzyna; Kozankiewicz, Boles?aw; Lipi?ski, Jzef; Magdalena Szostak, M.

    2012-08-01

    The fluorescence and phosphorescence spectra of N-benzyl-2-methyl-4-nitroaniline (BNA) orthorhombic crystal were measured between 5 and 200 K. The fluorescence spectrum of BNA in a Shpol'skii matrix of n-heptane was also recorded at 5 K. The electronic absorption spectra parameters such as singlet and triplet state energies, dipole moments and oscillator strengths were calculated by semi-empirical and TD DFT methods. The calculated energies of singlet and triplet states and electronic transitions in the BNA molecule were compared with the experimental results. The phosphorescence decay time was estimated to be 270 ms at 5 K. It is presumed that the disappearance of vibronic structure above 30 K observed in the fluorescence spectra is caused by the nitro group vibrations while the structured phosphorescence originates from the trap states. The role of molecular shape towards emission processes in BNA crystal in terms of structure-property relationship is discussed.

  18. Time-resolved resonance Raman spectra of free-base tetraarylporphyrins: effects of the peripheral substituents

    NASA Astrophysics Data System (ADS)

    Jeoung, Sae Chae; Kim, Dongho; Ahn, Kwang-Hyun; Cho, Dae Won; Yoon, Minjoong

    1995-08-01

    Time-resolved resonance Raman spectra of free-base tetraarylporphyrins were obtained to investigate the peripheral substituent effect on the structural changes in the excited states. The aryl mode of H 2-tetratoluylporphyrin in the excited triplet state was more strongly enhanced relative to that of H 2-tetramesitylporphyrin. These results are discussed in terms of the difference in the steric hindrance inhibiting the electron delocalization of the porphyrin in the excited states.

  19. Wide range double photoionisation spectra of N2 and CO2

    NASA Astrophysics Data System (ADS)

    Eland, J. H. D.; Plogmaker, S.; Lablanquie, P.; Penent, F.; Palaudoux, J.; Nicolas, C.; Robert, E.; Miron, C.; Feifel, R.

    2016-02-01

    Using a magnetic bottle time-of-flight electron spectrometer we have measured double photoionisation spectra of N2 and CO2 covering the range from threshold up to the triple ionisation energies. The experiments demonstrate the use of a new asynchronous chopper in eight-bunch mode of the synchrotron radiation source SOLEIL. For CO22+ some broad bands in the Auger spectra are found to have multiple resolved counterparts in the photoionisation spectrum. All the bands in the Auger spectra have counterparts in the photoionisation spectra, where extra bands attributed to triplet states are present. In the spectrum of N22+ we suggest reassignment of one band.

  20. Binding energies of the ground triplet state a^3? _u^+ of Rb2 and Cs2 in terms of the generalized Le Roy-Bernstein near-dissociation expansion

    NASA Astrophysics Data System (ADS)

    Sovkov, V. B.; Ivanov, V. S.

    2014-04-01

    Formulae of Le Roy-Bernstein near-dissociation theory are derived in a general isotope-invariant form, applicable to any term in the rotational expansion of a diatomic ro-vibrational term value. It is proposed to use the generalized Le Roy-Bernstein expansion to describe the binding energies (ro-vibrational term values) of the ground triplet state a^3? _u^+ of alkali metal dimers. The parameters of this description are determined for Rb2 and Cs2 molecules. This approach gives a recipe to calculate the whole variety of the binding energies with characteristic accuracies from 1 10-3 to 1 10-2 cm-1 using a relatively simple algebraic equation.

  1. Binding energies of the ground triplet state a{sup 3}?{sub u}{sup +} of Rb{sub 2} and Cs{sub 2} in terms of the generalized Le RoyBernstein near-dissociation expansion

    SciTech Connect

    Sovkov, V. B.; Ivanov, V. S.

    2014-04-07

    Formulae of Le RoyBernstein near-dissociation theory are derived in a general isotopeinvariant form, applicable to any term in the rotational expansion of a diatomic ro-vibrational term value. It is proposed to use the generalized Le RoyBernstein expansion to describe the binding energies (ro-vibrational term values) of the ground triplet state a{sup 3}?{sub u}{sup +} of alkali metal dimers. The parameters of this description are determined for Rb{sub 2} and Cs{sub 2} molecules. This approach gives a recipe to calculate the whole variety of the binding energies with characteristic accuracies from ?1 10{sup ?3} to 1 10{sup ?2} cm{sup ?1} using a relatively simple algebraic equation.

  2. Unraveling the electronic structure, spin states, optical and vibrational spectra of malaria pigment.

    PubMed

    Ali, Md Ehesan; Oppeneer, Peter M

    2015-06-01

    A detailed knowledge of the electronic structure and magnetic and optical properties of hemozoin, the malaria pigment, is essential for the design of effective antimalarial drugs and malarial diagnosis. By employing state-of-the-art electronic structure calculations, we have performed an in-depth investigation of the malaria pigment. Specifically, molecular bond lengths and spin states of the two Fe(III) heme centers and their exchange interaction, the UV/Vis absorption spectrum, and the IR vibrational spectra were calculated and compared with available experimental data. Our density functional theory (DFT)-based calculations predict a singlet ground spin state that stems from an S=5/2 spin state on each of the Fe heme centers with a very weak antiferromagnetic exchange interaction between them. Our theoretical UV/Vis and IR spectra provide explanations for various spectroscopic studies of hemozoin and ?-hematin (a synthetic analogue of hemozoin). A good comparison of calculated and measured properties demonstrates the convincing unveiling of the electronic structure of the malaria pigment. Based on the predicted vibrational spectra, we propose a unique spectral band from the nuclear resonance vibrational spectroscopy (NRVS) results that could be used as a key fingerprint for malarial detection. PMID:25933355

  3. 'Blueberry' Triplets Born in Rock

    NASA Technical Reports Server (NTRS)

    2004-01-01

    This microscopic image, taken at the outcrop region dubbed 'Berry Bowl' near the Mars Exploration Rover Opportunity's landing site, shows the sphere-like grains or 'blueberries' that fill Berry Bowl. Of particular interest is the blueberry triplet, which indicates that these geologic features grew in pre-existing wet sediments. Other sphere-like grains that form in the air, such as impact spherules or ejected volcanic material called lapilli, are unlikely to fuse along a line and form triplets. This image was taken by the rover's microscopic imager on the 46th martian day, or sol, of its mission.

  4. Bringing light into the dark triplet space of molecular systems.

    PubMed

    Ge, Jing; Zhang, Qun; Jiang, Jun; Geng, Zhigang; Jiang, Shenlong; Fan, Kaili; Guo, Zhenkun; Hu, Jiahua; Chen, Zongwei; Chen, Yang; Wang, Xiaoping; Luo, Yi

    2015-05-21

    A molecule or a molecular system always consists of excited states of different spin multiplicities. With conventional optical excitations, only the (bright) states with the same spin multiplicity of the ground state could be directly reached. How to reveal the dynamics of excited (dark) states remains the grand challenge in the topical fields of photochemistry, photophysics, and photobiology. For a singlet-triplet coupled molecular system, the (bright) singlet dynamics can be routinely examined by conventional femtosecond pump-probe spectroscopy. However, owing to the involvement of intrinsically fast decay channels such as intramolecular vibrational redistribution and internal conversion, it is very difficult, if not impossible, to single out the (dark) triplet dynamics. Herein, we develop a novel strategy that uses an ultrafast broadband white-light continuum as a excitation light source to enhance the probability of intersystem crossing, thus facilitating the population flow from the singlet space to the triplet space. With a set of femtosecond time-reversed pump-probe experiments, we report on a proof-of-concept molecular system (i.e., the malachite green molecule) that the pure triplet dynamics can be mapped out in real time through monitoring the modulated emission that occurs solely in the triplet space. Significant differences in excited-state dynamics between the singlet and triplet spaces have been observed. This newly developed approach may provide a useful tool for examining the elusive dark-state dynamics of molecular systems and also for exploring the mechanisms underlying molecular luminescence/photonics and solar light harvesting. PMID:25916946

  5. Sulphur Kβ emission spectra reveal protonation states of aqueous sulfuric acid

    PubMed Central

    Niskanen, Johannes; Sahle, Christoph J.; Ruotsalainen, Kari O.; Müller, Harald; Kavčič, Matjaž; Žitnik, Matjaž; Bučar, Klemen; Petric, Marko; Hakala, Mikko; Huotari, Simo

    2016-01-01

    In this paper we report an X-ray emission study of bulk aqueous sulfuric acid. Throughout the range of molarities from 1 M to 18 M the sulfur Kβ emission spectra from H2SO4 (aq) depend on the molar fractions and related deprotonation of H2SO4. We compare the experimental results with results from emission spectrum calculations based on atomic structures of single molecules and structures from ab initio molecular dynamics simulations. We show that the S Kβ emission spectrum is a sensitive probe of the protonation state of the acid molecules. Using non-negative matrix factorization we are able to extract the fractions of different protonation states in the spectra, and the results are in good agreement with the simulation for the higher part of the concentration range. PMID:26888159

  6. Sulphur Kβ emission spectra reveal protonation states of aqueous sulfuric acid

    NASA Astrophysics Data System (ADS)

    Niskanen, Johannes; Sahle, Christoph J.; Ruotsalainen, Kari O.; Müller, Harald; Kavčič, Matjaž; Žitnik, Matjaž; Bučar, Klemen; Petric, Marko; Hakala, Mikko; Huotari, Simo

    2016-02-01

    In this paper we report an X-ray emission study of bulk aqueous sulfuric acid. Throughout the range of molarities from 1 M to 18 M the sulfur Kβ emission spectra from H2SO4 (aq) depend on the molar fractions and related deprotonation of H2SO4. We compare the experimental results with results from emission spectrum calculations based on atomic structures of single molecules and structures from ab initio molecular dynamics simulations. We show that the S Kβ emission spectrum is a sensitive probe of the protonation state of the acid molecules. Using non-negative matrix factorization we are able to extract the fractions of different protonation states in the spectra, and the results are in good agreement with the simulation for the higher part of the concentration range.

  7. The state of absorbed hydrogen in the structure of reduced copper chromite from the vibration spectra.

    PubMed

    Khassin, Alexander A; Kustova, Galina N; Jobic, Herv; Yurieva, Tamara M; Chesalov, Yury A; Filonenko, Georgii A; Plyasova, Lyudmila M; Parmon, Valentin N

    2009-08-01

    The reduction of copper chromite, CuCr(2)O(4), is followed by means of thermogravimetric analysis. The reduced state is studied by means of FT IR spectroscopy, Raman spectroscopy and inelastic neutron scattering. The reduction of copper occurs in two stages: absorption of hydrogen at 250-400 degrees C and dehydration of the reduced state at above 450 degrees C. The measured vibrational spectra prove that a considerable amount of hydrogen is absorbed by the oxide structure with absorbed protons stabilized in OH and HOH-groups (geminal protons). Three groups of vibration bands are observed in the INS spectra, which can be assigned to stretching, bending and libration vibrations. An increase in the reduction temperature of copper chromite results in softening of the stretching and hardening of the bending vibrations, what can be related to the strengthening of hydrogen bonding. PMID:19606318

  8. Sulphur K? emission spectra reveal protonation states of aqueous sulfuric acid.

    PubMed

    Niskanen, Johannes; Sahle, Christoph J; Ruotsalainen, Kari O; Mller, Harald; Kav?i?, Matja; itnik, Matja; Bu?ar, Klemen; Petric, Marko; Hakala, Mikko; Huotari, Simo

    2016-01-01

    In this paper we report an X-ray emission study of bulk aqueous sulfuric acid. Throughout the range of molarities from 1?M to 18?M the sulfur K? emission spectra from H2SO4?(aq) depend on the molar fractions and related deprotonation of H2SO4. We compare the experimental results with results from emission spectrum calculations based on atomic structures of single molecules and structures from ab initio molecular dynamics simulations. We show that the S K? emission spectrum is a sensitive probe of the protonation state of the acid molecules. Using non-negative matrix factorization we are able to extract the fractions of different protonation states in the spectra, and the results are in good agreement with the simulation for the higher part of the concentration range. PMID:26888159

  9. Bimolecular hydrogen abstraction from phenols by aromatic ketone triplets.

    PubMed

    Lathioor, Edward C; Leigh, William J

    2006-01-01

    Absolute rate constants for hydrogen abstraction from 4-methylphenol (para-cresol) by the lowest triplet states of 24 aromatic ketones have been determined in acetonitrile solution at 23 degrees C, and the results combined with previously reported data for roughly a dozen other compounds under identical conditions. The ketones studied include various ring-substituted benzophenones and acetophenones, alpha,alpha,alpha-trifluoroacetophenone and its 4-methoxy analog, 2-benzoylthiophene, 2-acetonaphthone, and various other polycyclic aromatic ketones such as fluorenone, xanthone and thioxanthone, and encompass n,pi*, pi,pi*(CT) and arenoid pi,pi* lowest triplets with (triplet) reduction potentials (E(red)*) varying from about -10 to -38 kcal mol(-1). The 4-methylphenoxyl radical is observed as the product of triplet quenching in almost every case, along with the corresponding hemipinacol radical in most instances. Hammett plots for the acetophenones and benzophenones are quite different, but plots of log k(Q) vs E(red)* reveal a common behavior for most of the compounds studied. The results are consistent with reaction via two mechanisms: a simple electron-transfer mechanism, which applies to the n,pi* triplet ketones and those pi,pi* triplets that possess particularly low reduction potentials, and a coupled electron-/proton-transfer mechanism involving the intermediacy of a hydrogen-bonded exciplex, which applies to the pi,pi* ketone triplets. Ketones with lowest charge-transfer pi,pi* states exhibit rate constants that vary only slightly with triplet reduction potential over the full range investigated; this is due to the compensating effect of substituents on triplet state basicity and reduction potential, which both play a role in quenching by the hydrogen-bonded exciplex mechanism. Ketones with arenoid pi,pi* states exhibit the fall-off in rate constant that is typical of photoinduced electron transfer reactions, but it occurs at a much higher potential than would be normally expected due to the effects of hydrogen-bonding on the rate of electron-transfer within the exciplex. PMID:16042506

  10. Sn(IV) Schiff base complexes: triplet photosensitizers for photoredox reactions.

    PubMed

    Grusenmeyer, Tod A; King, Albert W; Mague, Joel T; Rack, Jeffrey J; Schmehl, Russell H

    2014-12-21

    We present the synthesis and characterization of a series of four fluorescent Sn(iv) Schiff base complexes, which also possess long-lived triplet excited states. The complexes absorb visible light (λmax = 420 to 462 nm) and the optical properties are easily tunable without laborious synthetic elaboration. The triplet excited states are not luminescent, but can be observed and followed using nanosecond transient absorption spectroscopy. The lifetimes of the triplet excited states are on the order of 500 μs-10 ms in PMMA matrices. The triplet state energies were estimated via energy transfer reactions with a series of organic triplet acceptors. In addition, the photoexcited complexes react with electron donors and acceptors in solution. These results demonstrate the potential for the development of photosensitizers based on main group elements with high spin orbit coupling constants. PMID:25043697

  11. A study of the electronic states of pyrimidine by electron energy loss spectroscopy

    NASA Astrophysics Data System (ADS)

    Linert, Ireneusz; Zubek, Mariusz

    2015-03-01

    The electron energy loss spectra were measured in pyrimidine at the constant electron residual energy varied from 15 meV to 10 eV and in the scattering angle range 0-180. The spectra were analysed applying an iteration fitting procedure to resolve the energy loss bands corresponding to excitation of the electronic states of pyrimidine. The vertical excitation energies of the singlet states of pyrimidine and of a number of the triplet states were determined. The presently observed triplet states were tentatively assigned.

  12. Rotationally resolved photoelectron spectra in resonance enhanced multiphoton ionization of Rydberg states of NH

    SciTech Connect

    Wang, K.; Stephens, J.A.; McKoy, V. ); de Beer, E.; de Lange, C.A.; Westwood, N.P.C. )

    1992-07-01

    Results of combined theoretical and experimental studies of photoelectron spectra resulting from (2+1) resonance enhanced multiphoton ionization (REMPI) via the {ital f} {sup 1}{Pi}(3{ital p}{sigma}), {ital g} {sup 1}{Delta}(3{ital p}{pi}), and {ital h} {sup 1}{Sigma}{sup +}(3{ital p}{pi}) Rydberg states of NH are reported. The overall agreement between these calculated and measured spectra is encouraging. Strong {Delta}{ital N}={ital N}{sup +}{minus}{ital N}{prime}=even peaks, particularly for {Delta}{ital N}=0, are observed in these spectra. Low-energy Cooper minima are predicted to occur in the l=2 wave of the {ital k}{pi}({sup 1}{Sigma}{sup +}), {ital k}{pi}({sup 1}{Sigma}{sup {minus}}), and {ital k}{pi}({sup 1}{Delta}) photoelectron channels for the {ital f} state, the {ital k}{pi}({sup 1}{Delta}), {ital k}{delta}({sup 1}{Pi}), and {ital k}{delta}({sup 1}{Phi}) channels for the {ital g} state, and the {ital k}{pi}({sup 1}{Sigma}{sup +}) and {ital k}{delta}({sup 1}{Pi}) channels for the {ital h} state of NH. Depletion of the {ital d} wave (l=2) contributions to the photoelectron matrix element in the vicinity of these Cooper minima subsequently enhances the relative importance of the odd l waves. The observed {Delta}{ital N} transitions are also affected by strong l mixing in the electronic continuum induced by the nonspherical molecular potential. Interference of continuum waves between degenerate ionization channels also determines the spectral pattern observed for photoionization of the {ital f} {sup 1}{Pi} state of NH. Photoelectron angular distributions and the angular momentum compositions of photoelectron matrix elements provide further insight into the origin of these Cooper minima.

  13. Identification of a triplet pair intermediate in singlet exciton fission in solution.

    PubMed

    Stern, Hannah L; Musser, Andrew J; Gelinas, Simon; Parkinson, Patrick; Herz, Laura M; Bruzek, Matthew J; Anthony, John; Friend, Richard H; Walker, Brian J

    2015-06-23

    Singlet exciton fission is the spin-conserving transformation of one spin-singlet exciton into two spin-triplet excitons. This exciton multiplication mechanism offers an attractive route to solar cells that circumvent the single-junction Shockley-Queisser limit. Most theoretical descriptions of singlet fission invoke an intermediate state of a pair of spin-triplet excitons coupled into an overall spin-singlet configuration, but such a state has never been optically observed. In solution, we show that the dynamics of fission are diffusion limited and enable the isolation of an intermediate species. In concentrated solutions of bis(triisopropylsilylethynyl)[TIPS]--tetracene we find rapid (<100 ps) formation of excimers and a slower (∼ 10 ns) break up of the excimer to two triplet exciton-bearing free molecules. These excimers are spectroscopically distinct from singlet and triplet excitons, yet possess both singlet and triplet characteristics, enabling identification as a triplet pair state. We find that this triplet pair state is significantly stabilized relative to free triplet excitons, and that it plays a critical role in the efficient endothermic singlet fission process. PMID:26060309

  14. Identification of a triplet pair intermediate in singlet exciton fission in solution

    PubMed Central

    Stern, Hannah L.; Musser, Andrew J.; Gelinas, Simon; Parkinson, Patrick; Herz, Laura M.; Bruzek, Matthew J.; Anthony, John; Friend, Richard H.; Walker, Brian J.

    2015-01-01

    Singlet exciton fission is the spin-conserving transformation of one spin-singlet exciton into two spin-triplet excitons. This exciton multiplication mechanism offers an attractive route to solar cells that circumvent the single-junction Shockley–Queisser limit. Most theoretical descriptions of singlet fission invoke an intermediate state of a pair of spin-triplet excitons coupled into an overall spin-singlet configuration, but such a state has never been optically observed. In solution, we show that the dynamics of fission are diffusion limited and enable the isolation of an intermediate species. In concentrated solutions of bis(triisopropylsilylethynyl)[TIPS]—tetracene we find rapid (<100 ps) formation of excimers and a slower (∼10 ns) break up of the excimer to two triplet exciton-bearing free molecules. These excimers are spectroscopically distinct from singlet and triplet excitons, yet possess both singlet and triplet characteristics, enabling identification as a triplet pair state. We find that this triplet pair state is significantly stabilized relative to free triplet excitons, and that it plays a critical role in the efficient endothermic singlet fission process. PMID:26060309

  15. Spectra in Coherent States with Excited-de Sitter Mode during Inflation

    NASA Astrophysics Data System (ADS)

    Mohsenzadeh, M.; Yusofi, E.

    2016-03-01

    We use an excited-de Sitter mode as the fundamental mode function for the far past time limit during inflation, to study the corrections of spectra of curvature perturbation. Excited-de Sitter mode is actually the approximate solution of the inflaton field equation that asymptotically approaches to the de Sitter mode function in the first approximation. We build coherent state over excited-de Sitter mode. Then, we compute spectrum of the curvature perturbation with this coherent state as the initial state. We show that in this case, the spectrum of curvature perturbation is scale dependent. As a important result of using this coherent state, we find a non-zero non-Gaussian one-point function as a possible tiny source for generation of anisotropy in CMB from the initial mode in the string or Planck scale.

  16. Non-Markovian Quantum State Diffusion for temperature-dependent linear spectra of light harvesting aggregates.

    PubMed

    Ritschel, Gerhard; Suess, Daniel; Mbius, Sebastian; Strunz, Walter T; Eisfeld, Alexander

    2015-01-21

    Non-Markovian Quantum State Diffusion (NMQSD) has turned out to be an efficient method to calculate excitonic properties of aggregates composed of organic chromophores, taking into account the coupling of electronic transitions to vibrational modes of the chromophores. NMQSD is an open quantum system approach that incorporates environmental degrees of freedom (the vibrations in our case) in a stochastic way. We show in this paper that for linear optical spectra (absorption, circular dichroism), no stochastics is needed, even for finite temperatures. Thus, the spectra can be obtained by propagating a single trajectory. To this end, we map a finite temperature environment to the zero temperature case using the so-called thermofield method. The resulting equations can then be solved efficiently by standard integrators. PMID:25612697

  17. Non-Markovian Quantum State Diffusion for temperature-dependent linear spectra of light harvesting aggregates

    SciTech Connect

    Ritschel, Gerhard; Mbius, Sebastian; Eisfeld, Alexander; Suess, Daniel; Strunz, Walter T.

    2015-01-21

    Non-Markovian Quantum State Diffusion (NMQSD) has turned out to be an efficient method to calculate excitonic properties of aggregates composed of organic chromophores, taking into account the coupling of electronic transitions to vibrational modes of the chromophores. NMQSD is an open quantum system approach that incorporates environmental degrees of freedom (the vibrations in our case) in a stochastic way. We show in this paper that for linear optical spectra (absorption, circular dichroism), no stochastics is needed, even for finite temperatures. Thus, the spectra can be obtained by propagating a single trajectory. To this end, we map a finite temperature environment to the zero temperature case using the so-called thermofield method. The resulting equations can then be solved efficiently by standard integrators.

  18. Long-lived, colour-triplet scalars from unnaturalness

    NASA Astrophysics Data System (ADS)

    Barnard, James; Cox, Peter; Gherghetta, Tony; Spray, Andrew

    2016-03-01

    Long-lived, colour-triplet scalars are a generic prediction of unnatural, or split, composite Higgs models where the spontaneous global-symmetry breaking scale f ≳ 10 TeV and an unbroken SU(5) symmetry is preserved. Since the triplet scalars are pseudo NambuGoldstone bosons they are split from the much heavier composite-sector resonances and are the lightest exotic, coloured states. This makes them ideal to search for at colliders. Due to discrete symmetries the triplet scalar decays via a dimension-six term and given the large suppression scale f is often metastable. We show that existing searches for collider-stable R-hadrons from Run-I at the LHC forbid a triplet scalar mass below 845 GeV, whereas with 300 fb-1 at 13 TeV triplet scalar masses up to 1.4 TeV can be discovered. For shorter lifetimes displaced-vertex searches provide a discovery reach of up to 1.8 TeV. In addition we present exclusion and discovery reaches of future hadron colliders as well as indirect limits that arise from modifications of the Higgs couplings.

  19. Infrared Spectra and Density Functional Calculations for Singlet CH2═SiX2 and Triplet HC-SiX3 and XC-SiX3 Intermediates in Reactions of Laser-Ablated Silicon Atoms with Di-, Tri-, and Tetrahalomethanes.

    PubMed

    Cho, Han-Gook; Andrews, Lester

    2016-03-21

    Reactions of laser-ablated silicon atoms with di-, tri-, and tetrahalomethanes in excess argon were investigated, and the products were identified from the matrix infrared spectra, isotopic shifts, and density functional theory energy, bond length, and frequency calculations. Dihalomethanes produce planar singlet silenes (CH2═SiX2), and tri- and tetrahalomethanes form triplet halosilyl carbenes (HC-SiX3 and XC-SiX3). The Si-bearing molecules identified are the most stable, lowest-energy product in the reaction systems. While the C-Si bond in the silene is a true double bond, the C-Si bond in the carbene is a shortened single bond enhanced by hyperconjugation of the two unpaired electrons on C to σ*(Si-X) orbitals, which contributes stabilization through a small amount of π-bonding and reduction of the HCSi or XCSi angles. The C-Si bond lengths in these carbenes (1.782 Å for HC-SiF3) are between the single-bond length in the unobserved first insertion intermediate (1.975 Å for CHF2-SiF) and the double-bond length in the silene (1.704 Å for CHF═SiF2). The silicon s(2)p(2) and titanium s(2)d(2) electron configurations produce similar primary products, but the methylidyne with Ti has a bond to carbon stronger than that of the halosilyl carbene. PMID:26918739

  20. 6-Aminouracil: Geometries and spectra in the isolated state and in the solid state simulation. A comparison with 5-aminouracil

    NASA Astrophysics Data System (ADS)

    Palafox, M. Alcolea; Rastogi, V. K.

    2016-03-01

    FT-IR and FT-Raman spectra of 6-aminouracil were recorded in the solid state in the regions 3500-0 cm-1 and 4000-400 cm-1, respectively. The unit cell reported by X-ray in the crystal was reproduced theoretically by density functional theoretical calculations as a tetramer form. To correct the overestimation of the theoretical wavenumbers of 6-aminouracil were used specific scaling equations determined from the molecule of uracil. These scaled frequencies obtained were employed in the reassignment of several Raman and Infrared experimental bands. In the comparison of these experimental values the percentage of error is very small in most of the wavenumbers. A correlation between the geometric parameters, charge distribution and vibrational spectra of 6-aminouracil and 5-aminouracil molecules was shown.

  1. 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 individual BChl pigments within that photosynthetic antenna complex are accessed via their triplet state dynamics. It is found that the currently used exciton model of FMO needs to be revised. It is also shown that triplet excited states can be readily transferred between the molecules. It is proposed that the triplet energy transfer between the BChl molecules can also serve as a protection mechanism. Finally, it is inferred that at least one of the BChl molecules within the FMO has a triplet state energy that is lower than that of singlet oxygen. This effectively prevents the formation of singlet oxygen and protects the complex from oxidative damage. The energy of BChl is apparently lowered by the specific protein environment, as in solution its energy is measured to be somewhat higher than the energy of singlet oxygen. Finally, the results of the triplet energy transfer within the cytochrome b6f complex are presented. This part of the work is not conclusive, and some of the problems encountered in experiments are described, as well as a new method of sample degassing developed for this type of study is presented.

  2. Analysis of PANDA Passive Containment Cooling Steady-State Tests with the Spectra Code

    SciTech Connect

    Stempniewicz, Marek M

    2000-07-15

    Results of post test simulation of the PANDA passive containment cooling (PCC) steady-state tests (S-series tests), performed at the PANDA facility at the Paul Scherrer Institute, Switzerland, are presented. The simulation has been performed using the computer code SPECTRA, a thermal-hydraulic code, designed specifically for analyzing containment behavior of nuclear power plants.Results of the present calculations are compared to the measurement data as well as the results obtained earlier with the codes MELCOR, TRAC-BF1, and TRACG. The calculated PCC efficiencies are somewhat lower than the measured values. Similar underestimation of PCC efficiencies had been obtained in the past, with the other computer codes. To explain this difference, it is postulated that condensate coming into the tubes forms a stream of liquid in one or two tubes, leaving most of the tubes unaffected. The condensate entering the water box is assumed to fall down in the form of droplets. With these assumptions, the results calculated with SPECTRA are close to the experimental data.It is concluded that the SPECTRA code is a suitable tool for analyzing containments of advanced reactors, equipped with passive containment cooling systems.

  3. Intensity formulas for triplet bands

    NASA Technical Reports Server (NTRS)

    Budo, A.

    1982-01-01

    Previous work in this area is surveyed and the mathematics involved in determining the quantitative intensity measurements in triplet bands is presented. Explicit expressions for the intensity distribution in the branches of the 3 Sigma-3 Pi and 1 Sigma-3Pi bands valid for all values of the coupling constant Y of the 3 Pi terms are given. The intensity distribution calculated according to the formulas given is compared with measurements of PH, 3 Pi-3 Sigma. Good quantitative agreement is obtained.

  4. Electronic spectra and excited state dynamics of pentafluorophenol: Effects of low-lying ??(?) states.

    PubMed

    Karmakar, Shreetama; Mukhopadhyay, Deb Pratim; Chakraborty, Tapas

    2015-05-14

    Multiple fluorine atom substitution effect on photophysics of an aromatic chromophore has been investigated using phenol as the reference system. It has been noticed that the discrete vibronic structure of the S1?S0 absorption system of phenol vapor is completely washed out for pentafluorophenol (PFP), and the latter also shows very large Stokes shift in the fluorescence spectrum. For excitations beyond S1 origin, the emission yield of PFP is reduced sharply with increase in excess vibronic energy. However, in a collisional environment like liquid hydrocarbon, the underlying dynamical process that drives the non-radiative decay is hindered drastically. Electronic structure theory predicts a number of low-lying dark electronic states of ??(?) character in the vicinity of the lowest valence ??(?) state of this molecule. Tentatively, we have attributed the excitation energy dependent non-radiative decay of the molecule observed only in the gas phase to an interplay between the lowest ??(?) and a nearby dissociative ??(?) state. Measurements in different liquids reveal that some of the dark excited states light up with appreciable intensity only in protic liquids like methanol and water due to hydrogen bonding between solute and solvents. Electronic structure theory methods indeed predict that for PFP-(H2O)n clusters (n = 1-11), intensities of a number of ??(?) states are enhanced with increase in cluster size. In contrast with emitting behavior of the molecule in the gas phase and solutions of nonpolar and polar aprotic liquids, the fluorescence is completely switched off in polar protic liquids. This behavior is a chemically significant manifestation of perfluoro effect, because a very opposite effect occurs in the case of unsubstituted phenol for which fluorescence yield undergoes a very large enhancement in protic liquids. Several dynamical mechanisms have been suggested to interpret the observed photophysical behavior. PMID:25978887

  5. Heavy vector triplets: bridging theory and data

    NASA Astrophysics Data System (ADS)

    Pappadopulo, Duccio; Thamm, Andrea; Torre, Riccardo; Wulzer, Andrea

    2014-09-01

    We introduce a model-independent strategy to study narrow resonances which we apply to a heavy vector triplet of the Standard Model (SM) group for illustration. The method is based on a simplified phenomenological Lagrangian which reproduces a large class of explicit models. Firstly, this allows us to derive robust model-independent phenomenological features and, conversely, to identify the peculiarities of different explicit realizations. Secondly, limits on ? BR can be converted into bounds on a few relevant parameters in a fully analytic way, allowing for an interpretation in any given explicit model. Based on the available 8 TeV LHC analyses, we derive current limits and interpret them for vector triplets arising in weakly coupled (gauge) and strongly coupled (composite) extensions of the SM. We point out that a model-independent limit setting procedure must be based on purely on-shell quantities, like ? BR. Finite width effects altering the limits can be considerably reduced by focusing on the on-shell signal region. We illustrate this aspect with a study of the invariant mass distribution in di-lepton searches and the transverse mass distribution in lepton-neutrino final states. In addition to this paper we provide a set of online tools available at a dedicated webpage [1].

  6. The singlet-triplet absorption and photodissociation of the HOCl, HOBr, and HOI molecules calculated by the MCSCF quadratic response method

    SciTech Connect

    Minaev, B.F.

    1999-09-09

    The molecular absorption spectra of hypochlorous, hypobromous, and hypoiodous acids have been studied by multiconfiguration self-consistent field (MCSCF) calculations with linear and quadratic response techniques. The complete form of the spin-orbit coupling (SOC) operator is accounted. The singlet-triplet transition to the lowest triplet state {sup 3}A{double{underscore}prime} {l{underscore}arrow} X{sup 1}A{prime} is shown to be responsible for the weak long-wavelength tail absorption and photodissociation in these molecules. The transition is polarized along the O-X bond (X = Cl, Br, I) and has an oscillator strength equal 6 x 10{sup {minus}6}, 8 x 10{sup {minus}5}, and 2 x 10{sup {minus}4} for hypochlorous, hypobromous, and hypoiodous acids, respectively. The second singlet-triplet transition {sup 3}A{prime} {l{underscore}arrow} X{sup 1}A{prime} comes to the region of the first singlet-singlet {sup 1}A{double{underscore}prime} {l{underscore}arrow} X{sup 1}A{prime} absorption and contributes significantly to the total cross-section at wavelengths {lambda} {approx} 300--320 nm (X = Cl), {lambda} {approx} 340--360 nm (X = Br), and {lambda} {approx} 400 nm (X = I). In the last case the singlet-triplet transition {sup 3}A{prime} {l{underscore}arrow} X{sup 1}A{prime} produces predominant contribution to HOI absorption in the visible region. All states are dissociative, so the singlet-triplet absorption contributes to the yield of photolysis in the important near-UV and visible region close to the intense solar actinic flux. Contributions to the removal mechanisms for atmospheric HOCl, HOBr, and HOI species are shortly discussed. The minor loss process of ozone in troposphere because of the HOI reservoir sink is getting evident on the ground of this calculations. The importance of SOC accounting for atmospheric photochemistry problems is stressed.

  7. Infrared laser spectroscopy of jet-cooled carbon clusters: structure of triplet C6

    NASA Technical Reports Server (NTRS)

    Hwang, H. J.; Van Orden, A.; Tanaka, K.; Kuo, E. W.; Heath, J. R.; Saykally, R. J.

    1993-01-01

    We report the first structural characterization of the triplet isomer of C6. Forty-one rovibrational/fine structure transitions in the nu 4(sigma u) antisymmetric stretch fundamental of the C6 cluster have been measured by diode laser absorption spectroscopy of a supersonic carbon cluster beam. The observed spectrum is characteristic of a centrosymmetric linear triplet state with cumulene-type bonding. The measured ground state rotational constant B0 = 0.048 479 (10)cm-1 and the effective bond length r(eff) = 1.2868 (1) angstroms are in good agreement with ab initio predictions for the linear triplet (3 sigma g-) state of C6.

  8. 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.

  9. Magnetic chains on a triplet superconductor.

    PubMed

    Sacramento, P D

    2015-11-11

    The topological state of a two-dimensional triplet superconductor may be changed by an appropriate addition of magnetic impurities. A ferromagnetic magnetic chain at the surface of a superconductor with spin-orbit coupling may eliminate the edge states of a finite system giving rise to localized zero modes at the edges of the chain. The coexistence/competition between the two types of zero modes is considered. The reduction of the system to an effective 1d system gives partial information on the topological properties but the study of the two sets of zero modes requires a two-dimensional treatment. Increasing the impurity density from a magnetic chain to magnetic islands leads to a finite Chern number. At half-filling small concentrations are enough to induce chiral modes. PMID:26459719

  10. Polar propagating optical phonon states and their dispersive spectra in wurtzite nitride superlattices: Quantum size effect

    NASA Astrophysics Data System (ADS)

    Zhang, L.; Shao, Peng-Ming

    2010-12-01

    The polar optical phonon states of propagating (PR) modes in wurtzite GaN/Al xGa 1- xN superlattices (SLs) are investigated within the dielectric continuum model framework. It is proved that the PR phonon modes only appear in wurtzite GaN/Al xGa 1- xN SL with a small x Al mole ratio concentration (such as x<0.34). The analytical phonon states of PR modes and their dispersive equation in the wurtzite GaN/Al xGa 1- xN SL structures are obtained. Numerical calculations on the dispersive spectra of PR modes and their electrostatic potential properties as well as the quantum size effect are performed for a wurtzite GaN/Al 0.15Ga 0.85N SL. Results reveal that dispersive curves of PR modes in SLs form frequency bands. As the well width of GaN well-layer increases, the frequency bands of PR modes become steeper and narrower. The discussion of electrostatic potentials shows that the wavelength of PR phonon modes with a phase qL=π (0) is 2L ( L). With the increase of the SL well width, the wave-node number of the PR phonon modes in the barrier regions increases. The present theoretical scheme and numerical results are quite useful for analyzing the dispersive spectra of PR phonon modes and their polaronic effect in wurtzite GaN/AlGaN SL structures.

  11. Influence of wetting state on optical reflectance spectra of Si nanopillar arrays

    NASA Astrophysics Data System (ADS)

    Gwon, Minji; Kim, Sujung; Li, Jiaqi; Xu, Xiumei; Kim, Sun-Kyung; Lee, Eunsongyi; Kim, Dong-Wook; Chen, Chang

    2015-12-01

    Finite-difference time-domain (FDTD) simulations showed that the reflectance spectra of crystalline Si nanopillar (NP) arrays with diameters of 40, 70, 100, and 130 nm differed depending on wetting state. The observed reflectance dips of the 40-nm-diameter NP array were in good agreement with those estimated from destructive interference conditions at the top and bottom of the NPs: the NP arrays were treated as a homogeneous medium with an effective permittivity according to the effective medium approximation model. In contrast, the dip positions of the FDTD-simulated spectra for 70-, 100-, and 130-nm-diameter NP arrays deviated from the results of interference calculations, particularly for short wavelengths. This suggested that Mie resonances in individual NPs significantly increased the absorption cross-section at the resonant wavelengths, which was sensitive to the refractive index of the surrounding medium (i.e., the wetting state). Optical reflectance measurements provide an easy and efficient means of inspecting the wetting behavior of non-flat surfaces.

  12. Investigating Velocity Spectra at the Hugoniot State of Shock Loaded Heterogeneous Materials

    NASA Astrophysics Data System (ADS)

    Lajeunesse, Jeff; Borg, John; Stewart, Sarah; Thadhani, Naresh

    2015-06-01

    Hugoniot states achieved in heterogeneous materials have shown oscillations in particle velocity about an averaged state for both experimental and simulated data. These oscillations arise from the scattering of the transmitted shock wave due to the presence of internal interfaces within heterogeneous materials. The goal of this work is to determine if the spectra of oscillatory behavior can be associated to characteristic length scales of the corresponding un-shocked heterogeneous material. Similarities between different types of shock-loaded materials are compared such as sand, concrete, aluminum foam, and layered composites. I would like to acknowledge the AFOSR under grant: FA9550-12-1-0128, ``Dynamic High-Pressure Behavior of Hierarchical Heterogenous Geological Granular Materials'' and the D.o.D. Supercomputing Resource Center.

  13. Experimental and theoretical study of the electronic states and spectra of SbNa

    NASA Astrophysics Data System (ADS)

    Setzer, K. D.; Fink, E. H.; Liebermann, H.-P.; Buenker, R. J.; Alekseyev, A. B.

    2015-12-01

    Gas-phase emission spectra of the hitherto unknown free radical SbNa were measured in the NIR region with a Fourier-transform spectrometer. The emissions were observed from a fast-flow system in which antimony vapor in argon or neon carrier gas was passed through a microwave discharge and mixed with sodium vapor in an observation tube. Seven transitions from five low-lying excited states A12, A21, A30+, A40-, and B2 to the X10+ and/or X21 components of the X3Σ- ground state have been observed and analyzed. In parallel to the experiments, relativistic configuration interaction calculations of potential energy curves, vibrational constants, bond lengths, transition moments and radiative lifetimes were carried out to aid in the analysis of the experimental data.

  14. Experimental and theoretical study of the electronic states and spectra of NaAs

    NASA Astrophysics Data System (ADS)

    Setzer, K. D.; Fink, E. H.; Alekseyev, A. B.; Liebermann, H.-P.; Buenker, R. J.

    2016-02-01

    Gas-phase emission spectra of the hitherto unknown free radical NaAs were measured in the NIR region with a Fourier-transform spectrometer. The emissions were observed from a fast-flow system in which arsenic vapor in argon carrier gas was passed through a microwave discharge and mixed with sodium vapor in an observation tube. Seven transitions from all five Ω components of the low-lying A3Π and a1Δ excited states (A12, A21, A30+, A40-, a2) to the X10+ and/or X21 components of the X3Σ- ground state have been observed and analysed. With the help of parallel relativistic configuration interaction calculations all observed spectral features could be assigned and analyzed.

  15. Analysis of the energy spectra of ground states of deformed nuclei in the rare-earth region

    NASA Astrophysics Data System (ADS)

    A. Okhunov, A.; I. Turaeva, G.; A. Kassim, H.; U. Khandaker, M.; Noora, B. Rosli

    2015-04-01

    The 62Sm, 64Gd, 66Dy, 70Yb, 72Hf and 74W nuclei are classified as deformed nuclei. Low-lying bands are one of the most fundamental excitation modes in the energy spectra of deformed nuclei. In this paper a theoretical analysis of the experimental data within the phenomenological model is presented. The energy spectra of ground states are calculated. It is found that the low-lying spectra of ground band states are in good agreement with the experimental data. Supported by IIUM University Research Grant Type B (EDW B13-034-0919) and MOHE Fundamental Research Grant Scheme (FRGS13-074-0315)

  16. Reactivity of aromatic amines with triplet 1,8-dihydroxyanthraquinone: A laser flash photolysis study

    NASA Astrophysics Data System (ADS)

    Pan, Yang; Gao, Yuhe; Yan, Lei; Pan, Hu; Chen, Jiafu; Yu, Shuqin

    2007-01-01

    The property of the lowest excited triplet states of 1,8-dihydroxyanthraquinone (DHAQ) was investigated by using time-resolved laser flash photolysis at 355 nm in organic solvents, i.e. acetonitrile and cyclohexane. The transient absorption spectra of the excited triplet DHAQ were obtained in acetonitrile, which have an absorption maximum at 480 nm and two broad absorption bands around 350 and 650 nm. 3DHAQ * is efficiently quenched by triphenylamine (TPA) via photoinduced electron transfer pathway, which was testified by the finding of TPA radical cation. In addition, aniline derivatives such as N, N-dimethylaniline (DMA), 3,5, N, N-tetramethylaniline (TMA), 4-dimethylaminobenzoic acid (DMABA) and dimethyl- p-toluidine (DMT) could also quench 3DHAQ * rapidly. Evidence for electron transfer interaction with anilines in acetonitrile was obtained from transient spectral characterization of formed radicals. Experimental kq values approach the diffusion-controlled rate limit, and decrease significantly from DMT (1.85 10 10 M -1 s -1) to DMABA (1.95 10 9 M -1 s -1). These kq values depend on the charge density on the "N" atom of anilines, which could be quantified by Hammett ? constant.

  17. Understanding Singlet and Triplet Excitons in Acene Crystals from First Principles

    NASA Astrophysics Data System (ADS)

    Rangel Gordillo, Tonatiuh; Sharifzadeh, Sahar; Kronik, Leeor; Neaton, Jeffrey

    2014-03-01

    Singlet fission, a process in which two triplet excitons are formed from a singlet exciton, has the potential to increase the solar cell efficiencies above 100%. Efficient singlet fission has been reported in larger acene crystals, such as tetracene and pentacene, in part attributable to their low-lying triplet energies. In this work, we use many-body perturbation theory within the GW approximation and the Bethe-Salpeter equation approach to compute quasiparticle gaps, low-lying singlet and and triplet excitations, and optical absorption spectra across the entire acene family of crystals, from benzene to hexacene. We closely examine the degree of localization and charge-transfer character of the low-lying singlets and triplets, and their sensitivity to crystal environment, and discuss implications for the efficiency of singlet fission in this systems. This work supported by DOE and computational resources provided by NERSC.

  18. Photosensitization of triplet carotenoid in photosynthetic light-harvesting complex of photosystem II

    SciTech Connect

    Nechushtai, R.; Thornber, J.P.; Patterson, L.K.; Fessenden, R.W.; Levanon, H.

    1988-03-10

    A laser photolysis study, on the nanosecond time scale, has been carried out on the major light-harvesting chlorophyll-protein complex of photosystem II (LHC II..beta..). The transient triplet absorption of the isolated LHC II..beta.. has been compared to those of its constituent chromophores in dilute micellar aqueous solutions, namely, chlorophyll a, chlorophyll b, chlorophyll a + chlorophyll b, and chlorophyll a + ..beta..-carotene. The results indicate that the carotenoid in the LHC II..beta.. is photosensitized by triplet chlorophyll a and that the decay of the transient triplet absorption exhibits two transients, one in the approx. 50-ns range and the other in the approx. 10..mu..s time scales. The former transient is light-intensity dependent and is attributed to an annihilation process between two triplets of chlorophyll a, while the latter is due to the decay of the triplet carotenoid to its ground state.

  19. Ultrafast dissociation of triplets in pentacene induced by an electric field

    NASA Astrophysics Data System (ADS)

    Srimath Kandada, Ajay Ram; Petrozza, Annamaria; Lanzani, Guglielmo

    2014-08-01

    Singlet fission into a pair of triplet excitons in pentacene is envisaged to be a potential carrier multiplication route in organic photovoltaics. In order to shed light on the dissociation dynamics of the triplet states we performed electric field induced pump-probe experiments on polycrystalline films of pentacene. We find that the nascent triplet pair formed immediately after the fission process is susceptible to dissociation in the presence of the electric field. By measuring the temporal dynamics of the dissociation, we estimate its binding energy to be approximately 320 meV. After about 2 ps the triplets diffuse away from each other and the field assisted dissociation is substantially reduced. Our results suggest that if the nascent triplet pairs could be harvested at the interface in a device, the efficiency of the process would be higher.

  20. Influence of ground-state scattering properties on photoassociation spectra near the intercombination line of bosonic ytterbium

    SciTech Connect

    Borkowski, M.; Ciurylo, R.; Tojo, S.; Enomoto, K.; Takahashi, Y.

    2010-10-29

    We study theoretically the properties of photoassociation spectra near the {sup 1}S{sub 0}-{sup 3}P{sub 1} inter-combination line of bosonic ytterbium. We construct a mass scaled model of the excited state interaction potential that well describes bound state energies obtained in a previous photoassociation experiment. We then use it to calculate theoretical photoassociation spectra in a range of ultracold temperatures using semianalytical theory developed by Bohn and Julienne.Photoassociation spectra not only give us the energies of excited bound states, but also provide information about the behavior of the ground state wavefunction. In fact, it can be shown that within the so-called reflection approximation the line intensity is proportional to the ground state wavefunction at the transition's Condon point. We show that in the case of ytterbium, the rotational structure of the photoassociation spectra depends heavily on the behavior of the ground-state wavefunction. The change of the scattering length from one isotope to another and the resulting occurence of shape resonances in higher partial waves determines the appearance and disapperance of rotational components, especially in the deeper lying states, whose respective Condon points lie near the ground state centrifugal barrier. Thus, photoassociation spectra differ qualitatively between isotopes.

  1. Influence of ground-state scattering properties on photoassociation spectra near the intercombination line of bosonic ytterbium

    NASA Astrophysics Data System (ADS)

    Borkowski, M.; Ciury?o, R.; Julienne, P. S.; Tojo, S.; Enomoto, K.; Takahashi, Y.

    2010-10-01

    We study theoretically the properties of photoassociation spectra near the 1S0-3P1 inter-combination line of bosonic ytterbium. We construct a mass scaled model of the excited state interaction potential that well describes bound state energies obtained in a previous photoassociation experiment. We then use it to calculate theoretical photoassociation spectra in a range of ultracold temperatures using semianalytical theory developed by Bohn and Julienne. Photoassociation spectra not only give us the energies of excited bound states, but also provide information about the behavior of the ground state wavefunction. In fact, it can be shown that within the so-called reflection approximation the line intensity is proportional to the ground state wavefunction at the transition's Condon point. We show that in the case of ytterbium, the rotational structure of the photoassociation spectra depends heavily on the behavior of the ground-state wavefunction. The change of the scattering length from one isotope to another and the resulting occurence of shape resonances in higher partial waves determines the appearance and disapperance of rotational components, especially in the deeper lying states, whose respective Condon points lie near the ground state centrifugal barrier. Thus, photoassociation spectra differ qualitatively between isotopes.

  2. [Probabilistic calculations of biomolecule charge states that generate mass spectra of multiply charged ions].

    PubMed

    Raznikova, M O; Raznikov, V V

    2015-01-01

    In this work, information relating to charge states of biomolecule ions in solution obtained using the electrospray ionization mass spectrometry of different biopolymers is analyzed. The data analyses have mainly been carried out by solving an inverse problem of calculating the probabilities of retention of protons and other charge carriers by ionogenic groups of biomolecules with known primary structures. The approach is a new one and has no known to us analogues. A program titled "Decomposition" was developed and used to analyze the charge distribution of ions of native and denatured cytochrome c mass spectra. The possibility of splitting of the charge-state distribution of albumin into normal components, which likely corresponds to various conformational states of the biomolecule, has been demonstrated. The applicability criterion for using previously described method of decomposition of multidimensional charge-state distributions with two charge carriers, e.g., a proton and a sodium ion, to characterize the spatial structure of biopolymers in solution has been formulated. In contrast to known mass-spectrometric approaches, this method does not require the use of enzymatic hydrolysis or collision-induced dissociation of the biopolymers. PMID:26510600

  3. Formation of ultracold {sup 7}Li{sup 85}Rb molecules in the lowest triplet electronic state by photoassociation and their detection by ionization spectroscopy

    SciTech Connect

    Altaf, Adeel Dutta, Sourav; Lorenz, John; Prez-Ros, Jess; Chen, Yong P.; Elliott, D. S.

    2015-03-21

    We report the formation of ultracold {sup 7}Li{sup 85}Rb molecules in the a{sup 3}?{sup +} electronic state by photoassociation (PA) and their detection via resonantly enhanced multiphoton ionization (REMPI). With our dual-species Li and Rb magneto-optical trap apparatus, we detect PA resonances with binding energies up to ?62 cm{sup ?1} below the {sup 7}Li?2s?{sup 2}S{sub 1/2}?+?{sup 85}Rb 5p?{sup 2}P{sub 1/2} asymptote. In addition, we use REMPI spectroscopy to probe the a{sup 3}?{sup +} state and excited electronic 3{sup 3}? and 4{sup 3}?{sup +} states and identify a{sup 3}?{sup +} (v? = 713), 3{sup 3}? (v{sub ?}? = 010), and 4{sup 3}?{sup +} (v{sub ?}? = 05) vibrational levels. Our line assignments agree well with ab initio calculations. These preliminary spectroscopic studies on previously unobserved electronic states are crucial to discovering transition pathways for transferring ultracold LiRb molecules created via PA to deeply bound rovibrational levels of the electronic ground state.

  4. Particle diffusion and localized acceleration in inhomogeneous AGN jets - I. Steady-state spectra

    NASA Astrophysics Data System (ADS)

    Chen, Xuhui; Pohl, Martin; Bttcher, Markus

    2015-02-01

    We study the acceleration, transport, and emission of particles in relativistic jets. Localized stochastic particle acceleration, spatial diffusion, and synchrotron as well as synchrotron self-Compton (SSC) emission are considered in a leptonic model. To account for inhomogeneity, we use a 2D axisymmetric cylindrical geometry for both relativistic electrons and magnetic field. In this first phase of our work, we focus on steady-state spectra that develop from a time-dependent model. We demonstrate that small isolated acceleration region in a much larger emission volume are sufficient to accelerate particles to high energy. Diffusive escape from these small regions provides a natural explanation for the spectral form of the jet emission. The location of the acceleration regions within the jet is found to affect the cooling break of the spectrum in this diffusive model. Diffusion-caused energy-dependent inhomogeneity in the jets predicts that the SSC spectrum is harder than the synchrotron spectrum. There can also be a spectral hardening towards the high-energy section of the synchrotron spectrum, if particle escape is relatively slow. These two spectral hardening effects indicate that the jet inhomogeneity might be a natural explanation for the unexpected hard ?-ray spectra observed in some blazars.

  5. Triplet energy transfer in photoexcited diketones

    SciTech Connect

    Francesco, J.V.

    1992-01-01

    The rate at which excitation energy transfers between chromophores of diketones was investigated. Energy transfer (ET) was induced by irradiation of the diketones with 313nm and 366nm ultraviolet light. The most significant aspect of this work is the assignment of rates for both exothermic and endothermic ET between the chromophores of a diketone molecule. By varying the most influential factors which determine ET rates, the difference in energy between the triplet excited states of each chromophore ([Delta]E) and the length of the alkyl tether linking the chromophores, two trends emerged. First, as the [Delta]E increased between two interacting chromophores within a given bichromophoric series of compounds, exothermic ET increased and endothermic ET decreased. Second,as the alkyl tether length connecting the two chromophores increased, both the exothermic and endothermic ET rates decreased. Intramolecular ET rates were derived by fitting the experimental photokinetic data with mathematical models.

  6. OptaDOS: A tool for obtaining density of states, core-level and optical spectra from electronic structure codes

    NASA Astrophysics Data System (ADS)

    Morris, Andrew J.; Nicholls, Rebecca J.; Pickard, Chris J.; Yates, Jonathan R.

    2014-05-01

    We present OptaDOS, a program for calculating core-electron and low-loss electron energy loss spectra (EELS) and optical spectra along with total-, projected- and joint-density of electronic states (DOS) from single-particle eigenenergies and dipole transition coefficients. Energy-loss spectroscopy is an important tool for probing bonding within a material. Interpreting these spectra can be aided by first principles calculations. The spectra are generated from the eigenenergies through integration over the Brillouin zone. An important feature of this code is that this integration is performed using a choice of adaptive or linear extrapolation broadening methods which we show produces higher accuracy spectra than standard fixed-width Gaussian broadening. OptaDOS may be straightforwardly interfaced to any electronic structure code. OptaDOS is freely available under the GNU General Public licence from http://www.optados.org.

  7. Computational Study of Absorption Spectra of the Photoconvertible Fluorescent Protein EosFP in Different Protonation States.

    PubMed

    Imhof, Petra

    2012-11-13

    Absorption spectra of the green-to-red convertible fluorescent protein EosFP have been computed in a hybrid quantum mechanical/molecular mechanical (QM/MM) framework. The experimentally observed absorption maximum at ?390 nm is well reproduced by the protein with a neutral chromophore, and the anionic form is computed to absorb close to the experimentally determined maximum at ?500 nm. Absorption of a zwitterionic form is calculated to lie in the same spectral region; however, this species cannot be unambiguously assigned to the experimental spectra. Variation of the protonation states of residues surrounding the chromophore do not have significant impact on the positions of the absorption maxima. In particular, protonation of Glu212 leaves the calculated spectra largely unaffected. This is consistent with the spectra of the E212Q mutant, which differ from the wild-type spectra only in the intensities but not in the positions of the absorption bands. PMID:26605635

  8. Spectroscopic study on deuterated benzenes. I. Microwave spectra and molecular structure in the ground state.

    PubMed

    Kunishige, Sachi; Katori, Toshiharu; Baba, Masaaki; Nakajima, Masakazu; Endo, Yasuki

    2015-12-28

    We observed microwave absorption spectra of some deuterated benzenes and accurately determined the rotational constants of all H/D isotopomers in the ground vibrational state. Using synthetic analysis assuming that all bond angles are 120, the mean bond lengths were obtained to be r0(C-C) = 1.3971 and r0(C-H) = r0(C-D) = 1.0805 . It has been concluded that the effect of deuterium substitution on the molecular structure is negligibly small and that the mean bond lengths of C-H and C-D are identical unlike small aliphatic hydrocarbons, in which r0(C-D) is about 5 m shorter than r0(C-H). It is considered that anharmonicity is very small in the C-H stretching vibration of aromatic hydrocarbons. PMID:26723666

  9. Spectroscopic study on deuterated benzenes. I. Microwave spectra and molecular structure in the ground state

    NASA Astrophysics Data System (ADS)

    Kunishige, Sachi; Katori, Toshiharu; Baba, Masaaki; Nakajima, Masakazu; Endo, Yasuki

    2015-12-01

    We observed microwave absorption spectra of some deuterated benzenes and accurately determined the rotational constants of all H/D isotopomers in the ground vibrational state. Using synthetic analysis assuming that all bond angles are 120°, the mean bond lengths were obtained to be r0(C-C) = 1.3971 Å and r0(C-H) = r0(C-D) = 1.0805 Å. It has been concluded that the effect of deuterium substitution on the molecular structure is negligibly small and that the mean bond lengths of C-H and C-D are identical unlike small aliphatic hydrocarbons, in which r0(C-D) is about 5 mÅ shorter than r0(C-H). It is considered that anharmonicity is very small in the C-H stretching vibration of aromatic hydrocarbons.

  10. Lowest triplet (n,π{sup *}) state of 2-cyclohexen-1-one: Characterization by cavity ringdown spectroscopy and quantum-chemical calculations

    SciTech Connect

    McAnally, Michael O.; Zabronsky, Katherine L.; Stupca, Daniel J.; Phillipson, Kaitlyn; Pillsbury, Nathan R.; Drucker, Stephen

    2013-12-07

    The cavity ringdown (CRD) absorption spectrum of 2-cyclohexen-1-one (2CHO) was recorded over the range 401.5–410.5 nm in a room-temperature gas cell. The very weak band system (ε ⩽ 0.1 M{sup −1} cm{sup −1}) in this spectral region is due to the T{sub 1}(n, π*) ← S{sub 0} electronic transition. The 0{sub 0}{sup 0} origin band was assigned to the feature observed at 24 558.8 ± 0.3 cm{sup −1}. We have assigned 46 vibronic transitions in a region extending from −200 to +350 cm{sup −1} relative to the origin band. For the majority of these transitions, we have made corresponding assignments in the spectrum of the deuterated derivative 2CHO-2,6,6-d{sub 3}. From the assignments, we determined fundamental frequencies for several vibrational modes in the T{sub 1}(n, π{sup *}) excited state of 2CHO, including the lowest ring-twisting (99.6 cm{sup −1}) and ring-bending (262.2 cm{sup −1}) modes. These values compare to fundamentals of 122.2 cm{sup −1} and 251.9 cm{sup −1}, respectively, determined previously for the isoconfigurational S{sub 1}(n, π{sup *}) excited state of 2CHO and 99 cm{sup −1} and 248 cm{sup −1}, respectively, for the S{sub 0} ground state. With the aid of quantum-mechanical calculations, we have also ascertained descriptions for these two modes, thereby resolving ambiguities appearing in the previous literature. The ring-twisting mode (ν{sub 39}) contains a significant contribution from O=C–C=C torsion, whereas the ring-bending mode (ν{sub 38} in the ground state) involves mainly the motion of C-5 with respect to the plane containing the other heavy atoms. The CRD spectroscopic data for the T{sub 1}(n, π{sup *}) state have allowed us to benchmark several computational methods for treating excited states, including time-dependent density functional theory and an equation-of-motion coupled cluster method. In turn, the computational results provide an explanation for observed differences in the T{sub 1}(n, π{sup *}) vs. S{sub 1}(n, π{sup *}) ring frequencies.

  11. Experimental and theoretical study of the electronic states and spectra of BiLi

    NASA Astrophysics Data System (ADS)

    Setzer, K. D.; Fink, E. H.; Liebermann, H.-P.; Buenker, R. J.; Alekseyev, A. B.

    2015-06-01

    Gas phase emission spectra of the hitherto unknown free radical BiLi were measured in the NIR range with a Fourier-transform spectrometer. The emissions were observed from a fast-flow system in which bismuth vapor in argon carrier gas was passed through a microwave discharge and mixed with lithium vapor in an observation tube. Two systems of blue-degraded bands observed in the range 6900-9800 cm-1 are assigned to the transitions A3?(A20+) ? X3?-(X10+, X21). The ?v = 0, +1, and -1 sequences of both systems were measured at high spectral resolution. Rotational and vibrational analyses of 12 bands have yielded the spectroscopic parameters of the X10+, X21, and A20+ states including a hfs splitting parameter of the X21 state. In order to aid in the analysis of the experimental data, a series of relativistic configuration interaction calculations has been carried out to obtain spectroscopic parameters and potential curves for the low-lying states of BiLi and also electric dipole transition moments connecting them.

  12. The energies and kinetics of triplet carotenoids in the LH2 antenna complexes as determined by phosphorescence spectroscopy

    NASA Astrophysics Data System (ADS)

    Rondonuwu, Ferdy S.; Taguchi, Tokio; Fujii, Ritsuko; Yokoyama, Kyosuke; Koyama, Yasushi; Watanabe, Yasutaka

    2004-01-01

    The triplet (T 1) states of carotenoids (Cars) and bacteriochlorophyll a (BChl) in the LH2 antenna complexes from Rhodobacter sphaeroides G1C, Rba. sphaeroides 2.4.1 and Rhodospirillum molischianum, containing neurosporene, spheroidene and lycopene, respectively, were examined by stationary-state and time-resolved phosphorescence spectroscopy. The T 1 energies of Cars were determined, irrespective of the Car or BChl excitation, to be 7030 cm -1 (neurosporene), 6920 cm -1 (spheroidene) and 6870 cm -1 (lycopene), respectively, whereas that of BChl to be 7590 cm -1. In the Rba. sphaeroides G1C, the Car and BChl triplet states decayed in similar time constant as the BChl Q y state, a fact which indicates that the pair of triplet states decays through the triplet-triplet annihilation mechanism.

  13. First-principles calculation of ground and excited-state absorption spectra of ruby and alexandrite considering lattice relaxation

    NASA Astrophysics Data System (ADS)

    Watanabe, Shinta; Sasaki, Tomomi; Taniguchi, Rie; Ishii, Takugo; Ogasawara, Kazuyoshi

    2009-02-01

    We performed first-principles calculations of multiplet structures and the corresponding ground-state absorption and excited-state absorption spectra for ruby (Cr3+:α-Al2O3) and alexandrite (Cr3+:BeAl2O4) which included lattice relaxation. The lattice relaxation was estimated using the first-principles total energy and molecular-dynamics method of the CASTEP code. The multiplet structure and absorption spectra were calculated using the configuration-interaction method based on density-functional calculations. For both ruby and alexandrite, the theoretical absorption spectra, which were already in reasonable agreement with experimental spectra, were further improved by consideration of lattice relaxation. In the case of ruby, the peak positions and peak intensities were improved through the use of models with relaxations of 11 or more atoms. For alexandrite, the polarization dependence of the U band was significantly improved, even by a model with a relaxation of only seven atoms.

  14. Singlet, triplet, electron and hole transport along single polymer chains

    NASA Astrophysics Data System (ADS)

    Bird, Matthew; Mauro, Gina; Zaikowski, Lori; Li, Xiang; Reid, Obadiah; Karten, Brianne; Asaoka, Sadayuki; Chen, Hung-Cheng; Cook, Andrew R.; Rumbles, Garry; Miller, John R.

    2015-08-01

    The diffusion of singlet and triplet excitons along single polyfluorene chains in solution has been studied by monitoring their transport to end traps. Time-resolved transient absorption and steady state fluorescence were used to determine fractions of excitons that reach the end caps. In order to accurately determine the singlet diffusion coefficient, the fraction of polymer ends that have end traps was determined through a combination of NMR and triplet quenching experiments. The distributions of polymer lengths were also taken into account and the resulting analysis points to a surprisingly long singlet diffusion length of 34 nm. Experiments on triplet transport also suggest that the entire 100nm+ chain is accessible to the triplet during its lifetime suggesting a lack of hindrance by defects or traps on this timescale. Time Resolved Microwave Conductivity measurements were also performed on a series of different length oligo- and polyfluorenes in solution allowing a global fit to be performed to extract an accurate intrachain mobility of 1.1 cm2/Vs.

  15. Production of N2 Vegard-Kaplan and other triplet band emissions in the dayglow of Titan

    NASA Astrophysics Data System (ADS)

    Bhardwaj, Anil; Jain, Sonal Kumar

    2012-04-01

    Recently the Cassini Ultraviolet Imaging Spectrograph (UVIS) has revealed the presence of N2 Vegard-Kaplan (VK) band A3?u+-X1?g+ emissions in Titan's dayglow limb observation. We present model calculations for the production of various N2 triplet states (viz., A3?u+,B3?g,C3?u,E3?u,W3?u, and B3?u ) in the upper atmosphere of Titan. The Analytical Yield Spectra technique is used to calculate steady state photoelectron fluxes in Titan's atmosphere, which are in agreement with those observed by the Cassini's CAPS instrument. Considering direct electron impact excitation, inter-state cascading, and quenching effects, the population of different levels of N2 triplet states are calculated under statistical equilibrium. Densities of all vibrational levels of each triplet state and volume production rates for various triplet states are calculated in the model. Vertically integrated overhead intensities for the same date and lighting conditions as reported by the UVIS observations for N2 Vegard-Kaplan A3?u+-X1?g+, First Positive B3?g-A3?u+, Second Positive (C3?u - B3?g), Wu-Benesch (W3?u - B3?g), and Reverse First Positive bands of N2 are found to be 132, 114, 19, 22, and 22 R, respectively. Overhead intensities are calculated for each vibrational transition of all the triplet band emissions of N2, which span a wider spectrum of wavelengths from ultraviolet to infrared. The calculated limb intensities of total and prominent transitions of VK band are presented. The model limb intensity of VK emission within the 150-190 nm wavelength region is in good agreement with the Cassini UVIS observed limb profile. An assessment of the impact of solar EUV flux on the N2 triplet band emission intensity has been made by using three different solar flux models, viz., Solar EUV Experiment (SEE), SOLAR2000 (S2K) model of Tobiska (Tobiska, W.K. [2004]. Adv. Space Res. 34, 1736-1746), and HEUVAC model of Richards et al. (Richards, P.G., Woods, T.N., Peterson, W.K. [2006]. Adv. Space Res. 37 (2), 315-322). The calculated N2 VK band intensity at the peak of limb intensity due to S2K and HEUVAC solar flux models is a factor of 1.2 and 0.9, respectively, of that obtained using SEE solar EUV flux. The effects of higher N2 density and solar zenith angle on the emission intensity are also studied. The model predicted N2 triplet band intensities during moderate (F10.7 = 150) and high (F10.7 = 240) solar activity conditions, using SEE solar EUV flux, are a factor of 2 and 2.8, respectively, higher than those during solar minimum (F10.7 = 68) condition.

  16. Excited-state Raman spectroscopy with and without actinic excitation: S{sub 1} Raman spectra of trans-azobenzene

    SciTech Connect

    Dobryakov, A. L.; Quick, M.; Ioffe, I. N.; Granovsky, A. A.; Ernsting, N. P.; Kovalenko, S. A.

    2014-05-14

    We show that femtosecond stimulated Raman spectroscopy can record excited-state spectra in the absence of actinic excitation, if the Raman pump is in resonance with an electronic transition. The approach is illustrated by recording S{sub 1} and S{sub 0} spectra of trans-azobenzene in n-hexane. The S{sub 1} spectra were also measured conventionally, upon n?* (S{sub 0} ? S{sub 1}) actinic excitation. The results are discussed and compared to earlier reports.

  17. Scalar triplet on a domain wall

    NASA Astrophysics Data System (ADS)

    Gani, V. A.; Lizunova, M. A.; Radomskiy, R. V.

    2016-02-01

    We consider a model with a real scalar field with polynomial self-interaction of the fourth degree and a coupled scalar triplet. We demonstrate that there is an exact analytic solution in the form of a domain wall with a localised configuration of the scalar triplet coupled to the wall. We study some properties of this solution.

  18. Definition and determination of the triplet-triplet energy transfer reaction coordinate

    SciTech Connect

    Zapata, Felipe; Marazzi, Marco; Castaño, Obis; Frutos, Luis Manuel; Acuña, A. Ulises

    2014-01-21

    A definition of the triplet-triplet energy transfer reaction coordinate within the very weak electronic coupling limit is proposed, and a novel theoretical formalism is developed for its quantitative determination in terms of internal coordinates The present formalism permits (i) the separation of donor and acceptor contributions to the reaction coordinate, (ii) the identification of the intrinsic role of donor and acceptor in the triplet energy transfer process, and (iii) the quantification of the effect of every internal coordinate on the transfer process. This formalism is general and can be applied to classical as well as to nonvertical triplet energy transfer processes. The utility of the novel formalism is demonstrated here by its application to the paradigm of nonvertical triplet-triplet energy transfer involving cis-stilbene as acceptor molecule. In this way the effect of each internal molecular coordinate in promoting the transfer rate, from triplet donors in the low and high-energy limit, could be analyzed in detail.

  19. Doublet-triplet fermionic dark matter

    NASA Astrophysics Data System (ADS)

    Dedes, Athanasios; Karamitros, Dimitrios

    2014-06-01

    We extend the Standard Model (SM) by adding a pair of fermionic SU(2) doublets with opposite hypercharge and a fermionic SU(2) triplet with zero hypercharge. We impose a discrete Z2 symmetry that distinguishes the SM fermions from the new ones. Then, gauge invariance allows for two renormalizable Yukawa couplings between the new fermions and the SM Higgs field, as well as for direct masses for the doublet (MD) and the triplet (MT). After electroweak symmetry breaking, this model contains, in addition to SM particles, two charged Dirac fermions and a set of three neutral Majorana fermions, the lightest of which contributes to dark matter (DM). We consider a case where the lightest neutral fermion is an equal admixture of the two doublets with mass MD close to the Z-boson mass. This state remains stable under radiative corrections thanks to a custodial SU(2) symmetry and is consistent with the experimental data from oblique electroweak corrections. Moreover, the amplitudes relevant to spin-dependent or spin-independent nucleus-DM particle scattering cross sections both vanish at tree level. They arise at one loop at a level that may be observed in near future DM direct detection experiments. For Yukawa couplings comparable to the top quark, the DM particle relic abundance is consistent with observation, not relying on coannihilation or resonant effects, and has a mass at the electroweak scale. Furthermore, the heavier fermions decay to the DM particle and to electroweak gauge bosons making this model easily testable at the LHC. In the regime of interest, the charged fermions suppress the Higgs decays to diphotons by 45%-75% relative to SM prediction.

  20. Prenatally diagnosed monochorionic diamniotic triplet pregnancy.

    PubMed

    Yonetani, Naoto; Ishii, Keisuke; Mabuchi, Aki; Sasahara, Jun; Hayashi, Shusaku; Mitsuda, Nobuaki

    2015-08-01

    We present an extremely rare case of monochorionic diamniotic (MD) triplet pregnancy diagnosed via ultrasonography at the end of the first trimester that resulted in delivery of three healthy newborns. Ultrasonography for a 34-year-old woman at 12 weeks of gestation showed three fetuses and one placenta with a T-sign at the initial segment of the dividing membrane. Color Doppler examination revealed umbilical cord entanglement between two fetuses in one sac in addition to another sac containing one fetus. Therefore, this was diagnosed as MD triplet pregnancy. The triplets were delivered by cesarean section at 35 weeks of gestation and were healthy without neurological morbidities at the age of 28 days. Histopathological examination also revealed an MD triplet placenta. The possibility of MD triplet pregnancy should be recognized, although it is rare. PMID:25832331

  1. Asynchronous MASSLF spectroscopy: A convenient method for assigning solid-state carbon-13 CPMAS spectra

    SciTech Connect

    Webb, G.G.; Zilm, K.W. )

    1989-03-29

    A two-dimensional solid-state NMR technique is presented which permits assignment of {sup 13}C CPMAS spectra on the basis of the number of protons bonded to a carbon center. The method is similar to several other methods that have become popular for accurately determining C-H or N-H bond distances in solids and for following molecular motions in polymers. These techniques, referred to collectively as MASSLF spectroscopy, rely on the use of MAS NMR to resolve dipolar coupled patterns that would normally overlap in static one-dimensional spectra. The dipolar coupled patterns generated by these techniques are sufficiently sensitive that small variations in C-H distances in organic solids can be accurately measured. The patterns are, however, much more sensitive to the number of protons directly bonded to the carbon center. Under conditions of fast magic angle spinning, methylenes typically exhibit twice the number of sidebands as methines, and rapidly rotating methyl groups and nonprotonated carbons usually exhibit only one set of sidebands. The method presented here determines the number of methylenes, methines, and methyl plus nonprotonated carbons contributing to a resonance by taking advantage of the fact that the dipolar patterns have characteristic and predictable relative sideband intensities. A new MASSLF pulse sequence is used in this work that differs from previous sequences by not requiring synchronization with the MAS rotation. In addition the sequence conveniently allows for a much wider bandwidth in the dipolar dimension and produces the effect of quadrature detection in this frequency domain without the need for multiple data sets.

  2. Analysis of source spectra, attenuation, and site effects from central and eastern United States earthquakes

    SciTech Connect

    Lindley, G.

    1998-02-01

    This report describes the results from three studies of source spectra, attenuation, and site effects of central and eastern United States earthquakes. In the first study source parameter estimates taken from 27 previous studies were combined to test the assumption that the earthquake stress drop is roughly a constant, independent of earthquake size. 200 estimates of stress drop and seismic moment from eastern North American earthquakes were combined. It was found that the estimated stress drop from the 27 studies increases approximately as the square-root of the seismic moment, from about 3 bars at 10{sup 20} dyne-cm to 690 bars at 10{sup 25} dyne-cm. These results do not support the assumption of a constant stress drop when estimating ground motion parameters from eastern North American earthquakes. In the second study, broadband seismograms recorded by the United States National Seismograph Network and cooperating stations have been analysed to determine Q{sub Lg} as a function of frequency in five regions: the northeastern US, southeastern US, central US, northern Basin and Range, and California and western Nevada. In the third study, using spectral analysis, estimates have been made for the anelastic attenuation of four regional phases, and estimates have been made for the source parameters of 27 earthquakes, including the M{sub b} 5.6, 14 April, 1995, West Texas earthquake.

  3. Franck-Condon analysis of the S0 --> T1 absorption and phosphorescence spectra of biphenyl and bridged derivatives

    NASA Astrophysics Data System (ADS)

    Negri, Fabrizia; Zgierski, Marek Z.

    1992-11-01

    The equilibrium geometry and the vibrational force field of the ground and the lowest triplet electronic states of biphenyl and three bridged derivatives-biphenylene, fluorene and phenanthrene-are computed by using an updated version of the QCFF/PI (Quantum Chemical Force Field/? electron) Hamiltonian. The displacement parameters between T1 and S0 are obtained and used to model the S0?T1 absorption and the phosphorescence spectra. The calculated Franck-Condon envelopes are found to be in excellent agreement with the vibrational structure of the observed spectra. The common features of the phosphorescence spectra of biphenyl and fluorene are related to the same orbital nature of the lowest triplet state. The observed asymmetry between the phosphorescence and singlet-triplet absorption spectra of biphenyl is reproduced when the twisted equilibrium geometry of S0 is considered. It is shown that evidence of the nonplanarity of the ground state of biphenyl is manifested by the lower intensity of the band observed in the phosphorescence at 747 cm-1 with respect to the intensity of the same band in fluorene. The increased vibrational activity calculated in the lower frequency region for biphenylene and phenanthrene agrees with the observed spectra and reflects the different orbital nature of the lowest triplet state of the two strongly perturbed bridged derivatives with respect to biphenyl and fluorene. From the analysis of the computed vibrational frequencies, it is suggested that the false origin of the symmetry forbidden phosphorescence of biphenylene is due to the lowest out-of-plane mode of au symmetry.

  4. Dominant second harmonic in the Josephson current--phase relation: Manifestation of the long-range spin-triplet proximity effect in SFF'S junctions

    NASA Astrophysics Data System (ADS)

    Radovic, Zoran; Trifunovic, Luka; Knezevic, Milos

    2012-02-01

    We present theoretical study of the Josephson effect and pairing correlations in planar SFF'S junctions that consist of conventional superconductors connected through two metallic monodomain ferromagnets. Both singlet and triplet pair amplitudes, the Josephson current-phase relations, and density of states for arbitrary orientation of magnetizations are calculated from the self-consistent solutions of Eilenberger equations in the clean limit and for moderate disorder in ferromagnets. We find that in highly asymmetric SFF'S junctions the long-range spin-triplet proximity effect manifests itself as a dominant second harmonic in the Josephson current-phase relation [1] and gives distinctive tunneling conductance spectra [2]. Unambiguous detection of the long-range spin-triplet proximity effect by tunneling spectroscopy and experimental realization of the Josephson junctions ground state degeneracy (like at 0-pi transtions) is accessible for small interface roughness and moderate disorder in ferromagnets at low temperatures. [4pt] [1] L. Trifunovic, Z. Popovic and Z. Radovic, Phys. Rev. B 84, 064511 (2011).[0pt] [2] M. Knezevic, L. Trifunovic, and Z. Radovic (to be published).

  5. Impedance spectra classification for determining the state of charge on a lithium iron phosphate cell using a support vector machine

    NASA Astrophysics Data System (ADS)

    Jansen, P.; Vergossen, D.; Renner, D.; John, W.; Götze, J.

    2015-11-01

    An alternative method for determining the state of charge (SOC) on lithium iron phosphate cells by impedance spectra classification is given. Methods based on the electric equivalent circuit diagram (ECD), such as the Kalman Filter, the extended Kalman Filter and the state space observer, for instance, have reached their limits for this cell chemistry. The new method resigns on the open circuit voltage curve and the parameters for the electric ECD. Impedance spectra classification is implemented by a Support Vector Machine (SVM). The classes for the SVM-algorithm are represented by all the impedance spectra that correspond to the SOC (the SOC classes) for defined temperature and aging states. A divide and conquer based search algorithm on a binary search tree makes it possible to grade measured impedances using the SVM method. Statistical analysis is used to verify the concept by grading every single impedance from each impedance spectrum corresponding to the SOC by class with different magnitudes of charged error.

  6. Singlet and triplet instability theorems

    NASA Astrophysics Data System (ADS)

    Yamada, Tomonori; Hirata, So

    2015-09-01

    A useful definition of orbital degeneracyform-degeneracyis 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.

  7. Singlet and triplet instability theorems.

    PubMed

    Yamada, Tomonori; Hirata, So

    2015-09-21

    A useful definition of orbital degeneracyform-degeneracyis 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

  8. Perturbations to the intersystem crossing of proflavin upon binding to DNA and poly d(A-IU) from triplet-delayed emission spectroscopy.

    PubMed Central

    Lee, W E; Galley, W C

    1988-01-01

    The steady-state prompt fluorescence, phosphorescence and delayed fluorescence spectra and triplet lifetimes of free proflavin and proflavin bound to native DNA and alternating poly d(A-IU) were obtained as a function of temperature in a buffer-glycerol solvent. The intensity of the proflavin E-type delayed fluorescence (DF) relative to both the phosphorescence (Ph) and the prompt fluorescence (F) was observed to increase with temperature, and plots of both ln (DF/Ph) and ln (DF/(F.tau T] as a function of 1/T were linear over a wide range of temperatures. Although the activation energies for the thermal repopulation of the proflavin excited singlet state from the triplet obtained from the slopes of these plots were essentially unchanged on binding, perturbations to the S1----T1 intersystem crossing rate constants extracted from the intercepts at infinite temperature were observed. The marked enhancement of the intersystem crossing that occurs with binding to the iodinated polynucleotide reflects an external heavy atom perturbation upon the intercalated dye which also induces a shortening in the triplet lifetime. With proflavin bound to DNA an enhancement to the S1----T1 intersystem crossing, though lesser in magnitude than for poly d(A-IU), is observed but with no change to the triplet lifetime. The well-studied fluorescence quenching of DNA-bound proflavin is a result of this increase in the intersystem crossing. It is proposed that these non-heavy atom enhancements in the intersystem crossing are due to distortions of the molecular plane of the bound proflavin molecule. In total these analyses provide a complete description of the excited state processes of the proflavin molecule and their variations with temperature. PMID:3224148

  9. Polaron pair mediated triplet generation in polymer/fullerene blends.

    PubMed

    Dimitrov, Stoichko D; Wheeler, Scot; Niedzialek, Dorota; Schroeder, Bob C; Utzat, Hendrik; Frost, Jarvist M; Yao, Jizhong; Gillett, Alexander; Tuladhar, Pabitra S; McCulloch, Iain; Nelson, Jenny; Durrant, James R

    2015-01-01

    Electron spin is a key consideration for the function of organic semiconductors in light-emitting diodes and solar cells, as well as spintronic applications relying on organic magnetoresistance. A mechanism for triplet excited state generation in such systems is by recombination of electron-hole pairs. However, the exact charge recombination mechanism, whether geminate or nongeminate and whether it involves spin-state mixing is not well understood. In this work, the dynamics of free charge separation competing with recombination to polymer triplet states is studied in two closely related polymer-fullerene blends with differing polymer fluorination and photovoltaic performance. Using time-resolved laser spectroscopic techniques and quantum chemical calculations, we show that lower charge separation in the fluorinated system is associated with the formation of bound electron-hole pairs, which undergo spin-state mixing on the nanosecond timescale and subsequent geminate recombination to triplet excitons. We find that these bound electron-hole pairs can be dissociated by electric fields. PMID:25735188

  10. Polaron pair mediated triplet generation in polymer/fullerene blends

    PubMed Central

    Dimitrov, Stoichko D.; Wheeler, Scot; Niedzialek, Dorota; Schroeder, Bob C.; Utzat, Hendrik; Frost, Jarvist M.; Yao, Jizhong; Gillett, Alexander; Tuladhar, Pabitra S.; McCulloch, Iain; Nelson, Jenny; Durrant, James R.

    2015-01-01

    Electron spin is a key consideration for the function of organic semiconductors in light-emitting diodes and solar cells, as well as spintronic applications relying on organic magnetoresistance. A mechanism for triplet excited state generation in such systems is by recombination of electron-hole pairs. However, the exact charge recombination mechanism, whether geminate or nongeminate and whether it involves spin-state mixing is not well understood. In this work, the dynamics of free charge separation competing with recombination to polymer triplet states is studied in two closely related polymer-fullerene blends with differing polymer fluorination and photovoltaic performance. Using time-resolved laser spectroscopic techniques and quantum chemical calculations, we show that lower charge separation in the fluorinated system is associated with the formation of bound electron-hole pairs, which undergo spin-state mixing on the nanosecond timescale and subsequent geminate recombination to triplet excitons. We find that these bound electron-hole pairs can be dissociated by electric fields. PMID:25735188

  11. A designed room-temperature triplet ligand from pyridine-2,6-diyl bis(tert-butyl nitroxide).

    PubMed

    Kawakami, Hinako; Tonegawa, Asato; Ishida, Takayuki

    2016-01-28

    The magnetic study on newly developed 4-mesitylpyridine-2,6-diyl bis(tert-butyl nitroxide) shows that almost the whole population has a ground triplet state at room temperature, and the ability of complex formation as a tridentate triplet ligand was proven with a diamagnetic yttrium(iii) ion. PMID:26615801

  12. Photochromic dibenzobarrlenes: long-lived triplet biradical intermediates.

    PubMed

    Sajimon, Meledathu C; Ramaiah, Danaboyina; Suresh, Cherumuttathu H; Adam, Waldemar; Lewis, Frederick D; George, Manapurathu V

    2007-08-01

    Upon exposure to UV light, the disubstituted dibenzobarrelene derivative 1a turns green in the solid phase and reverts back to its original pale-yellow color within several hours in the dark. The lifetime of the colored species in degassed benzene at room temperature is 37 +/- 2 s (Ea for decoloration is 14.5 +/- 0.7 kcal mol-1 and log A is 8.92 +/- 0.5 s-1) and highly sensitive to molecular oxygen; the Stern-Volmer quenching constant is 6.9 +/- 0.2 x 108 M-1 s-1. Similarly, the disubstituted dibenzobarrelenes 1b and 1c exhibited pink coloration when exposed to UV light in the solid phase. On the basis of combined experimental and theoretical evidence, it is proposed that upon photoexcitation the excited singlet state of 1a undergoes rapid intersystem crossing to its triplet state, followed by intramolecular delta-H abstraction, to yield the triplet biradical intermediate (3)2. Upon prolonged irradiation, 2 undergoes cyclization to the alcohol 3, which affords the enone 4 as the final photoproduct. The delta-H abstraction on the triplet-state potential energy surface, calculated at the B3LYP/6-31G* level of density functional theory (DFT), has an activation energy of 18.5 kcal/mol. Further, the absorption spectrum of the triplet biradical (3)2, obtained from time-dependent DFT calculations, displays an intense absorption maximum at 670 nm, which is in good agreement with the observed absorption peak at 700 nm. The molecular-orbital analysis of the triplet diradical (3)2 suggests that its long-wavelength absorption involves the transition of the unpaired electron from the comparatively localized benzyl-type HOMO to the extensively conjugated benzoyl-type LUMO. The present experimental and theoretical results strongly support the intervention of a long-lived triplet biradical (3)2 in the photochromism of appropriately substituted dibenzobarrelenes. PMID:17625852

  13. The fate of the triplet excitations in the Fenna-Matthews-Olson complex.

    PubMed

    Kihara, Shigeharu; Hartzler, Daniel A; Orf, Gregory S; Blankenship, Robert E; Savikhin, Sergei

    2015-05-01

    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. Experiments reveal microsecond triplet excited-state energy transfer between the bacteriochlorophyll (BChl) pigments, but show no evidence of triplet energy transfer to molecular oxygen, which is known to produce highly reactive singlet oxygen and is the leading cause of photo damage in photosynthetic proteins. The FMO complex is exceptionally photo stable despite the fact it contains no carotenoids, which could effectively quench triplet excited states of (bacterio)chlorophylls and are usually found within pigment-protein complexes. It is inferred that the triplet excitation is transferred to the lowest energy pigment, BChl 3, within the FMO complex, whose triplet state energy is shifted by pigment-protein interactions below that of the singlet oxygen excitation. Thus, the energy transfer to molecular oxygen is blocked and the FMO does not need carotenoids for photo protection. PMID:25856694

  14. 7Li and 13C solid-state NMR spectra of lithium cuprates.

    PubMed

    Jost, Steffen; Khnen, Martin; Gnther, Harald

    2006-10-01

    7Li and 13C solid-state MAS NMR spectra of three lithium cuprates with known X-ray structures--lithium([12]crown-4)2 dimethyl and diphenyl cuprate (1,2) and lithium(thf)4-[tris(trimethylsilyl) methyl]2 cuprate (3)--have been measured and analysed with respect to the quadrupolar coupling constants of lithium-7, chi(7Li), and the asymmetry parameters of the quadrupolar interactions, eta(7Li), as well as the 6, 7Li and 13C chemical shifts. The chi(7Li) values of 23, 30, and 18 kHz for 1, 2 and 3, respectively, are in line with the high symmetry around the lithium nucleus in the solvent-separated structures and may be used as reference data for this structural motif. Calculations based on charges derived from ab initio 6-31 G* HF computations using the point charge model (PCM) and the program GAMESS support the experimental findings. PMID:16835893

  15. Acquiring impedance spectra from diode-coupled primary batteries to determine health and state of charge

    NASA Astrophysics Data System (ADS)

    Christophersen, Jon P.; Morrison, John L.; Morrison, William H.

    The U.S. Army uses BA5590 Lithium Sulfur Dioxide primary batteries for portable electronic systems. There remains a need, however, for technology that can rapidly assess these batteries and estimate their remaining state of health after being used without degrading them to determine if there is remaining useful life for additional missions. This allows the full range of charge to be consumed before the battery is recycled or disposed. Impedance spectroscopy measurements have been shown to be a useful diagnostic tool, but standard methods cannot be applied to the BA5590 batteries because of the up-front electronics. The BA5590 module is diode-coupled and a charge-neutral excitation signal would be half-wave rectified and completely corrupt the results. However, a rapid impedance spectrum measurement technique has been developed that can be used for the BA5590s based on the addition of a small discharge bias load super-imposed on the sinusoidal excitation signal. The feasibility of this approach was initially simulated and then successfully applied to cell strings on four fresh BA5590 modules. The results clearly showed consistent and repeatable impedance spectra with no significant impact on the SOC as a result of the measurement. Details of this measurement technique and discussion of the preliminary results are presented.

  16. Spectra, energy levels, and energy transition of lanthanide complexes with cinnamic acid and its derivatives.

    PubMed

    Zhou, Kaining; Feng, Zhongshan; Shen, Jun; Wu, Bing; Luo, Xiaobing; Jiang, Sha; Li, Li; Zhou, Xianju

    2016-04-01

    High resolution spectra and luminescent lifetimes of 6 europium(III)-cinnamic acid complex {[Eu2L6(DMF)(H2O)]·nDMF·H2O}m (L=cinnamic acid I, 4-methyl-cinnamic acid II, 4-chloro-cinnamic acid III, 4-methoxy-cinnamic acid IV, 4-hydroxy-cinnamic acid V, 4-nitro-cinnamic acid VI; DMF=N, N-dimethylformamide, C3H7NO) were recorded from 8K to room temperature. The energy levels of Eu(3+) in these 6 complexes are obtained from the spectra analysis. It is found that the energy levels of the central Eu(3+) ions are influenced by the nephelauxetic effect, while the triplet state of ligand is lowered by the p-π conjugation effect of the para-substituted functional groups. The best energy matching between the ligand triplet state and the central ion excited state is found in complex I. While the other complexes show poorer matching because the gap of (5)D0 and triplet state contracts. PMID:26802538

  17. Higgs triplets and limits from precision measurements

    SciTech Connect

    Chen, Mu-Chun; Dawson, Sally; Krupovnickas, Tadas; /Brookhaven

    2006-04-01

    In this letter, they present the results on a global fit to precision electroweak data in a Higgs triplet model. In models with a triplet Higgs boson, a consistent renormalization scheme differs from that of the Standard Model and the global fit shows that a light Higgs boson with mass of 100-200 GeV is preferred. Triplet Higgs bosons arise in many extensions of the Standard Model, including the left-right model and the Little Higgs models. The result demonstrates the importance of the scalar loops when there is a large mass splitting between the heavy scalars. It also indicates the significance of the global fit.

  18. 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

  19. Heats of Formation of Triplet Ethylene, Ethylidene, and Acetylene

    SciTech Connect

    Nguyen, M.T.; Matus, M.H.; Lester Jr, W.A.; Dixon, David A.

    2007-06-28

    Heats of formation of the lowest triplet state of ethylene and the ground triplet state of ethylidene have been predicted by high level electronic structure calculations. Total atomization energies obtained from coupled-cluster CCSD(T) energies extrapolated to the complete basis set limit using correlation consistent basis sets (CBS), plus additional corrections predict the following heats of formation in kcal/mol: Delta H0f(C2H4,3A1) = 80.1 at 0 K and 78.5 at 298 K, and Delta H0f(CH3CH,3A") = 86.8 at 0 K and 85.1 at 298 K, with an error of less than +-1.0 kcal/mol. The vertical and adiabatic singlet-triplet separation energies of ethylene were calculated as Delta ES-T,vert = 104.1 and Delta ES-T,adia = 65.8 kcal/mol. These results are in excellent agreement with recent quantum Monte Carlo (DMC) values of 103.5 +- 0.3 and 66.4 +- 0.3 kcal/mol. Both sets of computational values differ from the experimental estimate of 58 +- 3 kcal/mol for the adiabatic splitting. The computed singlet-triplet gap at 0 K for acetylene is Delta ES-T,adia(C2H2) = 90.5 kcal/mol, which is in notable disagreement with the experimental value of 82.6 kcal/mol. The heat of formation of the triplet is Delta H0f(C2H2,3B2) = 145.3 kcal/mol. There is a systematic underestimation of the singlet-triplet gaps in recent photodecomposition experiments by ~;;7 to 8 kcal/mol. For vinylidene, we predict Delta H0f(H2CC,1A1) = 98.8 kcal/mol at 298 K (exptl. 100.3 +- 4.0), Delta H0f(H2CC,3B2) = 146.2 at 298 K, and an energy gap Delta ES-T-adia(H2CC) = 47.7 kcal/mol.

  20. Large isotropic exchange interactions from E.P.R. on doublet-triplet organometallic molecular pairs in diamagnetic host-lattices

    NASA Astrophysics Data System (ADS)

    Hulliger, Jürg

    In order to study exchange interactions between representative paramagnetic metal-π-complexes of the ferrocene type, bis-(benzene)-vanadium(S = 1/2) - nickelocene(S = 1) and cyclopentadienyl-cycloheptatrienyl-vanadium(S = 1/2) - nickelocene(S = 1) doublet-triplet pairs in a diamagnetic ruthenocene lattice have been investigated by low temperature X-band E.P.R. Single crystal and powder spectra of bi-doped ruthenocene (˜1 per cent S = 1/2 and ˜4-12 per cent S = 1) samples clearly revealed the existence of several different ferro- or antiferromagnetically coupled molecules in neighbouring lattice sites (called 'pairs'), and from these experiments surprisingly large isotropic exchange constants J in the range of -4·7 to 7·9 cm-1 (ℌex = JSD · ST) could be determined. Thereby a large axial zero-field splitting of 33·6 cm-1 on nickelocene triplet allowed a pair ground state description in terms of an effective spin hamiltonian with S' = 1/2, I' = 7/2. Due to a strong dependence of the new effective g- and A-tensors on J, (S = 1/2) - nickelocene doublet-triplet molecular pairs have turned out to be unique systems to measure exchange interactions with E.P.R.

  1. Control of triplet supercurrent in superconductor/ferromagnet hybrid systems

    NASA Astrophysics Data System (ADS)

    Martinez, William; Pratt, W. P., Jr.; Birge, Norman O.

    2015-03-01

    A lot of excitement has been generated in superconductor/ferromagnet (S/F) systems since long-range spin-triplet correlations (LRTCs) were predicted. Despite the many breakthroughs so far in this field, the ability to control the triplet generation reliably still needs to be realized before these devices can be used in technological applications. One possible direction to control the state in such structures is to manipulate the magnetizations of the various F layers within, specifically to switch between colinear and non-colinear directions between the layers. In this work, we report on the progress made to control LRTC generation in such a way. Supported by the DOE-BES under grant DE-FG-02-06ER46341.

  2. Charge separation in triplet C[sub 60]/TMPD exciplexes

    SciTech Connect

    Grzeskowiak, K.N.; Smirnov, S.N.; Braun, C.L. )

    1994-06-02

    A transient dc photoconductivity technique was used to demonstrate the formation of dipolar exciplexes of the triplet C[sub 60] state with N,N,N[prime],N[prime]-tetramethyl-1,4-phenylendiamine (TMPD) in toluene. The dipole moment of the [sup 3]C[sub 60]/TMPD exciplex was measured to be 35 [+-] 4D. Unit charges separated by 7.1 [angstrom] the center-to-center distance estimated for C[sub 60] in van der Waals contact with TMPD, correspond to a dipole moment of 34D. This implies that the triplet exciplex has essentially complete charge transfer. The lifetime of the exciplex was determined to be 7 [+-] 2 ns. 24 refs., 3 figs.

  3. Boron Subphthalocyanines as Triplet Harvesting Materials within Organic Photovoltaics.

    PubMed

    Castrucci, Jeffrey S; Josey, David S; Thibau, Emmanuel; Lu, Zheng-Hong; Bender, Timothy P

    2015-08-01

    Singlet fission, the generation of two excited triplet states from a single absorbed photon, is currently an area of significant interest to photovoltaic researchers. In this Letter, we outline how a polychlorinated boron subphthalocyanine, previously hypothesized to be an effective harvester of singlet fission derived triplets from pentacene, is relatively efficient at facilitating the process. As expected, we found a major increase in photocurrent generation at the expense of device voltage. For a direct point of comparison, we also have paired the same polychlorinated boron subphthalocyanine with α-sexithiophene to probe the alternative technique of complementary absorption engineering. The sum of these efforts have let us present new guidelines for the molecular design of boron subphthalocyanine for organic photovoltaic applications. PMID:26267212

  4. TRIO (Triplet Ionospheric Observatory) Mission

    NASA Astrophysics Data System (ADS)

    Lee, D.; Seon, J.; Jin, H.; Kim, K.; Lee, J.; Jang, M.; Pak, S.; Kim, K.; Lin, R. P.; Parks, G. K.; Halekas, J. S.; Larson, D. E.; Eastwood, J. P.; Roelof, E. C.; Horbury, T. S.

    2009-12-01

    Triplets of identical cubesats will be built to carry out the following scientific objectives: i) multi-observations of ionospheric ENA (Energetic Neutral Atom) imaging, ii) ionospheric signature of suprathermal electrons and ions associated with auroral acceleration as well as electron microbursts, and iii) complementary measurements of magnetic fields for particle data. Each satellite, a cubesat for ion, neutral, electron, and magnetic fields (CINEMA), is equipped with a suprathermal electron, ion, neutral (STEIN) instrument and a 3-axis magnetometer of magnetoresistive sensors. TRIO is developed by three institutes: i) two CINEMA by Kyung Hee University (KHU) under the WCU program, ii) one CINEMA by UC Berkeley under the NSF support, and iii) three magnetometers by Imperial College, respectively. Multi-spacecraft observations in the STEIN instruments will provide i) stereo ENA imaging with a wide angle in local times, which are sensitive to the evolution of ring current phase space distributions, ii) suprathermal electron measurements with narrow spacings, which reveal the differential signature of accelerated electrons driven by Alfven waves and/or double layer formation in the ionosphere between the acceleration region and the aurora, and iii) suprathermal ion precipitation when the storm-time ring current appears. In addition, multi-spacecraft magnetic field measurements in low earth orbits will allow the tracking of the phase fronts of ULF waves, FTEs, and quasi-periodic reconnection events between ground-based magnetometer data and upstream satellite data.

  5. The Auger (Autoionization) Decay of Excited States in Spectra of Multicharged Ions: Relativistic Theory

    SciTech Connect

    Svinarenko, A. A.; Nikola, L. V.; Prepelitsa, G. P.; Tkach, T.; Mischenko, E.

    2010-10-29

    Relativistic method of calculating the characteristics of the Auger decay in the atomic spectra, based on the S-matrix Gell-Mann and Low formalism, is used for estimating the transition energies and autoionization probabilities in spectra of the Fe ion with one vacancy above the core 1s{sup 2}2s{sup 2}2p{sup 6}3s{sup 2}3p{sup 6}.

  6. Photochemical studies of alkylammonium molybdates. Part 12. O?Mo charge-transfer triplet-states-initiated self-assembly to {Mo154} ring- and tube-molybdenum-blues

    NASA Astrophysics Data System (ADS)

    Yamase, T.; Prokop, P.; Arai, Y.

    2003-08-01

    The chemically induced dynamic electron-spin-polarization technique is employed in order to investigate the primary steps of the photoredox reaction between polyoxomolybdates and alkylammonium cations as both proton and electron-donors in solutions. An observation of emissive electron-spin-polarization signals of alkylamino radical cations for the photoredox reaction between polyoxomolybdates and alkylammonium cations in solutions reveals that the O?Mo ligand-to-metal charge-transfer triplet states are involved in the transfers of both proton and electron from alkylammonium cation to polyoxomolybdate anions. Prolonged photolysis of aqueous solutions containing [Mo36O112(H2O)16]8-, [iPrNH3]+, and LaCl3 at pH 1.0 leads to formation of two kinds of {Mo154} molybdenum-blues, [Mo28VMo126VIO462H28(H2O)70]156.5H2O (1) and [iPrNH3]8 [Mo28VMo126VIO458H12(H2O)66]127H2O (2), which were X-ray crystallographically characterized. The former exhibits the intact car-tire-shaped {Mo154} ring structure (with thickness of about 1.1 nm and with outer- and inner-rings of approximately 3.5- and 2.3-nm diameters, respectively) derived formally from the dehydrated cyclic heptamerization of four-electron reduced building blocks of {Mo22} (?[Mo4VMo18VIO70H12(H2O)10]) with overall symmetry of D7d. The anion for the latter, [Mo28VMo126VIO458H12(H2O)66]8- (2a), exhibits a nanotube structure of {Mo154} rings, each inner ring of which contains a bis(?-oxo)-linkaged [MoO2(?-O)(?-H2O)MoO2]2+ unit replacing one of seven [Mo(H2O)O2(?-O)Mo(H2O)O2]2+linker units. The neighboring {Mo154} rings are connected by six Mo-O-Mo bridge between inner-rings consisting of 7 head- and 14 linkers-MoO6 octahedra for each.

  7. Triplet-triplet energy transfer in fucoxanthin-chlorophyll protein from diatom Cyclotella meneghiniana: insights into the structure of the complex.

    PubMed

    Di Valentin, Marilena; Meneghin, Elena; Orian, Laura; Polimeno, Antonino; Bchel, Claudia; Salvadori, Enrico; Kay, Christopher W M; Carbonera, Donatella

    2013-10-01

    Although the major light harvesting complexes of diatoms, called FCPs (fucoxanthin chlorophyll a/c binding proteins), are related to the cab proteins of higher plants, the structures of these light harvesting protein complexes are much less characterized. Here, a structural/functional model for the "core" of FCP, based on the sequence homology with LHCII, in which two fucoxanthins replace the central luteins and act as quenchers of the Chl a triplet states, is proposed. Combining the information obtained by time-resolved EPR spectroscopy on the triplet states populated under illumination, with quantum mechanical calculations, we discuss the chlorophyll triplet quenching in terms of the geometry of the chlorophyll-carotenoid pairs participating to the process. The results show that local structural rearrangements occur in FCP, with respect to LHCII, in the photoprotective site. PMID:23856166

  8. Theoretical Studies of Singlet and Triplet Formation in Polymer LEDs.

    NASA Astrophysics Data System (ADS)

    Mazumdar, Sumit

    2002-03-01

    Spin statistics for electron-hole recombination in polymer LEDs suggest that the singlet excited state is formed with a probability of only 0.25. Recent experiments by several groups, however, indicate, that the probability of formation of the singlet is considerably larger than this. We present a comprehensive theory of the formation cross-sections of the singlet and triplet excitons in conjugated polymers. Within our model, electron correlations influence the relative yields of the singlet and triplet excitons in a profound manner. We have carried out the dynamics of the electron-hole recombination in pair of simple conjugated organic molecules, both with noninteracting electrons and within the Pariser-Parr-Pople model with interacting electrons. The formation cross-section for the singlet exciton is considerably larger than the triplet for the correlated electron case. Numerical results as well as simple physical interpretations of theoretical and experimental results will be presented. This work was supported in part by NSF DMR-0101659 and CSIR, India.

  9. A simple method for analyzing 51V solid-state NMR spectra of complex systems.

    PubMed

    Fenn, Annika; Wchtler, Maria; Breitzke, Hergen; Buchholz, Axel; Lippold, Ines; Plass, Winfried; Buntkowsky, Gerd

    2011-09-01

    Five vanadium complexes as models for biological systems were investigated using (51)V-MAS-NMR spectroscopy. All spectra show an uncommon line shape, which can be attributed to a shorter relaxation time of the satellite transition in contrast to the central one. A method for the reliable analysis of such kind of spectra is presented for the first time and the most important NMR parameters of the investigated complexes (quadrupolar coupling constant C(Q), asymmetry of the EFG tensor ?(Q), isotropic chemical shift ?(iso), chemical shift anisotropy ?(?) and asymmetry of the CSA tensor ?(?)) are presented. These results are of particular importance with respect to the analysis of the (51)V-MAS-NMR spectra of vanadium moieties in biological matrices such as vanadium chloroperoxidase, which show hitherto unexplained low intensity of the satellite sideband pattern. PMID:21601435

  10. Scalar triplet flavored leptogenesis: a systematic approach

    NASA Astrophysics Data System (ADS)

    Aristizabal Sierra, D.; Dhen, Mikal; Hambye, Thomas

    2014-08-01

    Type-II seesaw is a simple scenario in which Majorana neutrino masses are generated by the exchange of a heavy scalar electroweak triplet. When endowed with additional heavy fields, such as right-handed neutrinos or extra triplets, it also provides a compelling framework for baryogenesis via leptogenesis. We derive in this context the full network of Boltzmann equations for studying leptogenesis in the flavored regime. To this end we determine the relations which hold among the chemical potentials of the various particle species in the thermal bath. This takes into account the standard model Yukawa interactions of both leptons and quarks as well as sphaleron processes which, depending on the temperature, may be classified as faster or slower than the Universe Hubble expansion. We find that when leptogenesis is enabled by the presence of an extra triplet, lepton flavor effects allow the production of the B-L asymmetry through lepton number conserving CP asymmetries. This scenario becomes dominant as soon as the triplets couple more to leptons than to standard model scalar doublets. In this case, the way the B-L asymmetry is created through flavor effects is novel: instead of invoking the effect of L-violating inverse decays faster than the Hubble rate, it involves the effect of L-violating decays slower than the Hubble rate. We also analyze the more general situation where lepton number violating CP asymmetries are present and actively participate in the generation of the B-L asymmetry, pointing out that as long as L-violating triplet decays are still in thermal equilibrium when the triplet gauge scattering processes decouple, flavor effects can be striking, allowing to avoid all washout suppression effects from seesaw interactions. In this case the amount of B-L asymmetry produced is limited only by a universal gauge suppression effect, which nevertheless goes away for large triplet decay rates.

  11. Quantum calculations of highly excited vibrational spectrum of sulfur dioxide. III. Emission spectra from the C 1B2 state

    NASA Astrophysics Data System (ADS)

    Xie, Daiqian; Ma, Guobin; Guo, Hua

    1999-11-01

    We report quantum mechanical calculations of the X?C emission spectra of SO2 at the red wing of the C absorption band. The near equilibrium potential energy surface of the C 1B2 state is deduced by fitting experimental vibrational frequencies using an exact quantum mechanical Hamiltonian. Low-lying vibrational eigenenergies on this double minimum potential agree well with experimental frequencies and the corresponding eigenstates show some interesting features. Both spectral positions and intensities of the X?C transitions are obtained up to 16 000 cm-1 using a Chebyshev based spectral method, which does not explicitly construct vibrational eigenfunctions in the X state. The emission spectra are in reasonably good agreement with experimental measurements.

  12. Effect of nearest-neighbor ions on excited ionic states, emission spectra, and line profiles in hot and dense plasmas

    NASA Technical Reports Server (NTRS)

    Salzmann, D.; Stein, J.; Goldberg, I. B.; Pratt, R. H.

    1991-01-01

    The effect of the cylindrical symmetry imposed by the nearest-neighbor ions on the ionic levels and the emission spectra of a Li-like Kr ion immersed in hot and dense plasmas is investigated using the Stein et al. (1989) two-centered model extended to include computations of the line profiles, shifts, and widths, as well as the energy-level mixing and the forbidden transition probabilities. It is shown that the cylindrical symmetry mixes states with different orbital quantum numbers l, particularly for highly excited states, and, thereby, gives rise to forbidden transitions in the emission spectrum. Results are obtained for the variation of the ionic level shifts and mixing coefficients with the distance to the nearest neighbor. Also obtained are representative computed spectra that show the density effects on the spectral line profiles, shifts, and widths, and the forbidden components in the spectrum.

  13. Singlet-triplet annihilation in single LHCII complexes.

    PubMed

    Gruber, J Michael; Chmeliov, Jevgenij; Krger, 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 ?s) 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

  14. Restricted active space calculations of L-edge X-ray absorption spectra: From molecular orbitals to multiplet states

    NASA Astrophysics Data System (ADS)

    Pinjari, Rahul V.; Delcey, Mickal G.; Guo, Meiyuan; Odelius, Michael; Lundberg, Marcus

    2014-09-01

    The metal L-edge (2p ? 3d) X-ray absorption spectra are affected by a number of different interactions: electron-electron repulsion, spin-orbit coupling, and charge transfer between metal and ligands, which makes the simulation of spectra challenging. The core restricted active space (RAS) method is an accurate and flexible approach that can be used to calculate X-ray spectra of a wide range of medium-sized systems without any symmetry constraints. Here, the applicability of the method is tested in detail by simulating three ferric (3d5) model systems with well-known electronic structure, viz., atomic Fe3+, high-spin [FeCl6]3- with ligand donor bonding, and low-spin [Fe(CN)6]3- that also has metal backbonding. For these systems, the performance of the core RAS method, which does not require any system-dependent parameters, is comparable to that of the commonly used semi-empirical charge-transfer multiplet model. It handles orbitally degenerate ground states, accurately describes metal-ligand interactions, and includes both single and multiple excitations. The results are sensitive to the choice of orbitals in the active space and this sensitivity can be used to assign spectral features. A method has also been developed to analyze the calculated X-ray spectra using a chemically intuitive molecular orbital picture.

  15. Restricted active space calculations of L-edge X-ray absorption spectra: From molecular orbitals to multiplet states

    SciTech Connect

    Pinjari, Rahul V.; Delcey, Mickaël G.; Guo, Meiyuan; Lundberg, Marcus; Odelius, Michael

    2014-09-28

    The metal L-edge (2p → 3d) X-ray absorption spectra are affected by a number of different interactions: electron-electron repulsion, spin-orbit coupling, and charge transfer between metal and ligands, which makes the simulation of spectra challenging. The core restricted active space (RAS) method is an accurate and flexible approach that can be used to calculate X-ray spectra of a wide range of medium-sized systems without any symmetry constraints. Here, the applicability of the method is tested in detail by simulating three ferric (3d{sup 5}) model systems with well-known electronic structure, viz., atomic Fe{sup 3+}, high-spin [FeCl{sub 6}]{sup 3−} with ligand donor bonding, and low-spin [Fe(CN){sub 6}]{sup 3−} that also has metal backbonding. For these systems, the performance of the core RAS method, which does not require any system-dependent parameters, is comparable to that of the commonly used semi-empirical charge-transfer multiplet model. It handles orbitally degenerate ground states, accurately describes metal-ligand interactions, and includes both single and multiple excitations. The results are sensitive to the choice of orbitals in the active space and this sensitivity can be used to assign spectral features. A method has also been developed to analyze the calculated X-ray spectra using a chemically intuitive molecular orbital picture.

  16. Restricted active space calculations of L-edge X-ray absorption spectra: from molecular orbitals to multiplet states.

    PubMed

    Pinjari, Rahul V; Delcey, Mickaël G; Guo, Meiyuan; Odelius, Michael; Lundberg, Marcus

    2014-09-28

    The metal L-edge (2p → 3d) X-ray absorption spectra are affected by a number of different interactions: electron-electron repulsion, spin-orbit coupling, and charge transfer between metal and ligands, which makes the simulation of spectra challenging. The core restricted active space (RAS) method is an accurate and flexible approach that can be used to calculate X-ray spectra of a wide range of medium-sized systems without any symmetry constraints. Here, the applicability of the method is tested in detail by simulating three ferric (3d(5)) model systems with well-known electronic structure, viz., atomic Fe(3+), high-spin [FeCl6](3-) with ligand donor bonding, and low-spin [Fe(CN)6](3-) that also has metal backbonding. For these systems, the performance of the core RAS method, which does not require any system-dependent parameters, is comparable to that of the commonly used semi-empirical charge-transfer multiplet model. It handles orbitally degenerate ground states, accurately describes metal-ligand interactions, and includes both single and multiple excitations. The results are sensitive to the choice of orbitals in the active space and this sensitivity can be used to assign spectral features. A method has also been developed to analyze the calculated X-ray spectra using a chemically intuitive molecular orbital picture. PMID:25273421

  17. Collision-induced light scattering spectra and ground state potential of gaseous xenon

    NASA Astrophysics Data System (ADS)

    Abdel Kader, Mohamed Sayed

    2008-09-01

    Polarized and depolarized collision-induced light scattering spectra of xenon gas at room temperature 295 K with the pressure second virial coefficients, viscosity and thermal conductivity have been used for deriving the empirical models of the pair-polarizability trace and anisotropy and the interaction potential. Theoretical zeroth and second moments of the binary spectra using various models for the pair polarizabilities and interatomic potential are compared with the experimental values performed by Frommhold's group. In addition, vibrational energy levels, self diffusion coefficients and second virial dielectric constants calculated for these models are compared with experimental ones. The results show that these models are the most accurate models reported to date for this system.

  18. Triplet correlation functions in liquid water

    NASA Astrophysics Data System (ADS)

    Dhabal, Debdas; Singh, Murari; Wikfeldt, Kjartan Thor; Chakravarty, Charusita

    2014-11-01

    Triplet correlations have been shown to play a crucial role in the transformation of simple liquids to anomalous tetrahedral fluids [M. Singh, D. Dhabal, A. H. Nguyen, V. Molinero, and C. Chakravarty, Phys. Rev. Lett. 112, 147801 (2014)]. Here we examine triplet correlation functions for water, arguably the most important tetrahedral liquid, under ambient conditions, using configurational ensembles derived from molecular dynamics (MD) simulations and reverse Monte Carlo (RMC) datasets fitted to experimental scattering data. Four different RMC data sets with widely varying hydrogen-bond topologies fitted to neutron and x-ray scattering data are considered [K. T. Wikfeldt, M. Leetmaa, M. P. Ljungberg, A. Nilsson, and L. G. M. Pettersson, J. Phys. Chem. B 113, 6246 (2009)]. Molecular dynamics simulations are performed for two rigid-body effective pair potentials (SPC/E and TIP4P/2005) and the monatomic water (mW) model. Triplet correlation functions are compared with other structural measures for tetrahedrality, such as the O-O-O angular distribution function and the local tetrahedral order distributions. In contrast to the pair correlation functions, which are identical for all the RMC ensembles, the O-O-O triplet correlation function can discriminate between ensembles with different degrees of tetrahedral network formation with the maximally symmetric, tetrahedral SYM dataset displaying distinct signatures of tetrahedrality similar to those obtained from atomistic simulations of the SPC/E model. Triplet correlations from the RMC datasets conform closely to the Kirkwood superposition approximation, while those from MD simulations show deviations within the first two neighbour shells. The possibilities for experimental estimation of triplet correlations of water and other tetrahedral liquids are discussed.

  19. Triplet correlation functions in liquid water

    SciTech Connect

    Dhabal, Debdas; Chakravarty, Charusita; Singh, Murari; Wikfeldt, Kjartan Thor

    2014-11-07

    Triplet correlations have been shown to play a crucial role in the transformation of simple liquids to anomalous tetrahedral fluids [M. Singh, D. Dhabal, A. H. Nguyen, V. Molinero, and C. Chakravarty, Phys. Rev. Lett. 112, 147801 (2014)]. Here we examine triplet correlation functions for water, arguably the most important tetrahedral liquid, under ambient conditions, using configurational ensembles derived from molecular dynamics (MD) simulations and reverse Monte Carlo (RMC) datasets fitted to experimental scattering data. Four different RMC data sets with widely varying hydrogen-bond topologies fitted to neutron and x-ray scattering data are considered [K. T. Wikfeldt, M. Leetmaa, M. P. Ljungberg, A. Nilsson, and L. G. M. Pettersson, J. Phys. Chem. B 113, 6246 (2009)]. Molecular dynamics simulations are performed for two rigid-body effective pair potentials (SPC/E and TIP4P/2005) and the monatomic water (mW) model. Triplet correlation functions are compared with other structural measures for tetrahedrality, such as the O–O–O angular distribution function and the local tetrahedral order distributions. In contrast to the pair correlation functions, which are identical for all the RMC ensembles, the O–O–O triplet correlation function can discriminate between ensembles with different degrees of tetrahedral network formation with the maximally symmetric, tetrahedral SYM dataset displaying distinct signatures of tetrahedrality similar to those obtained from atomistic simulations of the SPC/E model. Triplet correlations from the RMC datasets conform closely to the Kirkwood superposition approximation, while those from MD simulations show deviations within the first two neighbour shells. The possibilities for experimental estimation of triplet correlations of water and other tetrahedral liquids are discussed.

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

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

    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.

  1. Iridium-Based High-Sensitivity Oxygen Sensors and Photosensitizers with Ultralong Triplet Lifetimes.

    PubMed

    Jiang, Xinpeng; Peng, Jiang; Wang, Jianchun; Guo, Xinyan; Zhao, Dahui; Ma, Yuguo

    2016-02-17

    The photophysics of a series of bichromophoric molecules featuring an intramolecular triplet energy transfer between a triscyclometalated iridium(III) complex and covalently linked organic group are studied. By systematically varying the energy gap (0.1-0.3 eV) between the donor (metal complex) and acceptor (pyrene unit), reversible triplet energy transfer processes with equilibrium constant K ranging from ca. 500 to 40?000 are established. Unique photophysical consequences of such large K values are observed. Because of the highly imbalanced forward and backward energy transfer rates, triplet excitons dominantly populate the acceptor moiety in the steady state, giving rise to ultralong luminescence lifetimes up to 1-4 ms. Because the triscyclometalated Ir and triplet pyrene groups both impart relatively small nonradiative energy loss, decent phosphorescence quantum yields (? = 0.1-0.6) are attained in spite of the exceptionally prolonged excited states. By virtue of such precious combination of long-lived triplet state and high ?, these bichromophoric molecules can serve as highly sensitive luminescent sensors for detecting trace amount of O2 and as potent photosensitizers for producing singlet oxygen even under low-oxygen content conditions. PMID:26592255

  2. Ultrabright fluorescent OLEDS using triplet sinks

    DOEpatents

    Zhang, Yifan; Forrest, Stephen R; Thompson, Mark

    2013-06-04

    A first device is provided. The first device further comprises an organic light emitting device. The organic light emitting device further comprises an anode, a cathode, and an emissive layer disposed between the anode and the cathode. The emissive layer further comprises an organic host compound, an organic emitting compound capable of fluorescent emission at room temperature, and an organic dopant compound. The triplet energy of the dopant compound is lower than the triplet energy of the host compound. The dopant compound does not strongly absorb the fluorescent emission of the emitting compound.

  3. Excited state dipole moments of chloroanilines and chlorophenols from solvatochromic shifts in electronic absorption spectra: Support for the concept of excited state group moments

    NASA Astrophysics Data System (ADS)

    Prabhumirashi, L. S.; Satpute, R. S.

    The dipole moments of isomeric o-, m- and p-chloroanilines and chlorophenols in electronically excited L a and L b states are estimated from solvent induced polarization shifts in electronic absorption spectra. It is observed that ? e( L a) > ? e( L b) > ? g, which is consistent with the general theory of polarization red shift. The ? es are found to be approximately co-linear with the corresponding ? gs. The concept of group moments is extended to aromatic molecules in excited states. This approach is found to be useful in understanding correlations among the excited states of mono- and disubstituted benzenes.

  4. Solid state photochemistry of polycarbonates

    NASA Technical Reports Server (NTRS)

    Gupta, A.; Rembaum, A.; Moacanin, J.

    1978-01-01

    The quantum yield of photoFries rearrangement in a polycarbonate film has been analyzed as a function of temperature and humidity on the basis of previously reported (Koyler and Mann, 1977) experimental data. Results indicate that in the homogeneous amorphous phase, photoFries rearrangement is a concerted process proceeding either from the pi star reversed arrow n singlet, in which case it must be subject to considerable self quenching, or from a triplet, presumably the first triplet since the lifetime of higher triplets is expected to be very short in the solid phase. If the parent excited state is the first triplet, chain scission is possibly an independent process, probably occurring from the pi star reversed arrow n singlet. Evidence of chain scission on photodegradation in the solid state includes loss of C-O and C-C bond intensities revealed in the Fourier transform infrared spectra, gel permeation chromotography elution profiles of degraded film samples dissolved in CHCl3, and a decrease in tensile strength and T sub g as photodegradation proceeds. Chain scission is apparently inhibited as photoFries products accumulate.

  5. Improved Cell Typing by Charge-State Deconvolution of matrix-assisted laser desorption/ionization Mass Spectra

    SciTech Connect

    Wilkes, Jon G.; Buzantu, Dan A.; Dare, Diane J.; Dragan, Yvonne P.; Chiarelli, M. Paul; Holland, Ricky D.; Beaudoin, Michael; Heinze, Thomas M.; Nayak, Rajesh; Shvartsburg, Alexandre A.

    2006-05-30

    Robust, specific, and rapid identification of toxic strains of bacteria and viruses, to guide the mitigation of their adverse health effects and optimum implementation of other response actions, remains a major analytical challenge. This need has driven the development of methods for classification of microorganisms using mass spectrometry, particularly matrix-assisted laser desorption ionization MS (MALDI) that allows high throughput analyses with minimum sample preparation. We describe a novel approach to cell typing based on pattern recognition of MALDI spectra, which involves charge-state deconvolution in conjunction with a new correlation analysis procedure. The method is applicable to both prokaryotic and eukaryotic cells. Charge-state deconvolution improves the quantitative reproducibility of spectra because multiply-charged ions resulting from the same biomarker attaching a different number of protons are recognized and their abundances are combined. This allows a clearer distinction of bacterial strains or of cancerous and normal liver cells. Improved class distinction provided by charge-state deconvolution was demonstrated by cluster spacing on canonical variate score charts and by correlation analyses. Deconvolution may enhance detection of early disease state or therapy progress markers in various tissues analyzed by MALDI.

  6. Calcium triplet metallicity calibration for stars in the Galactic bulge

    NASA Astrophysics Data System (ADS)

    Vásquez, S.; Zoccali, M.; Hill, V.; Gonzalez, O. A.; Saviane, I.; Rejkuba, M.; Battaglia, G.

    2015-08-01

    Aims: We present a new calibration of the calcium II triplet equivalent widths versus [Fe/H], constructed upon K giant stars in the Galactic bulge. This calibration will be used to derive iron abundances for the targets of the GIBS survey, and is in general especially well suited for solar and supersolar metallicity giants, which are typical of external massive galaxies. Methods: About 150 bulge K giants were observed with the GIRAFFE spectrograph at the VLT with a resolution of R ~ 20 000 and at R ~ 6000. In the first case, the spectra allowed us to directly determine the Fe abundances from several unblended Fe lines, deriving what we call here high-resolution [Fe/H] measurements. The low-resolution spectra allowed us to measure equivalent widths of the two strongest lines of the near-infrared calcium II triplet at 8542 and 8662 Å. Results: By comparing the two measurements, we derived a relation between calcium equivalent widths and [Fe/H] that is linear over the metallicity range probed here, - 1 < [Fe/H] < +0.7. By adding a small second-order correction based on literature globular cluster data, we derived the unique calibration equation [Fe/H] CaT = -3.150 + 0.432W' + 0.006W'2, with an rms dispersion of 0.197 dex, valid across the whole metallicity range -2.3 < [Fe/H] < +0.7. Based on observations taken with ESO telescopes at the La Silla Paranal Observatory under programme ID 385.B-0735(B).Full Table 2 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/580/A121

  7. Mass spectra of four-quark states in the hidden charm sector

    NASA Astrophysics Data System (ADS)

    Patel, Smruti; Shah, Manan; Vinodkumar, P. C.

    2014-08-01

    Masses of the low-lying four-quark states in the hidden charm sector ( are calculated within the framework of a non-relativistic quark model. The four-body system is considered as two two-body systems such as diquark-antidiquark ( - and quark-antiquark-quark-antiquark ( - q molecular-like four-quark states. Here, the Cornell-type potential has been used for describing the two-body interactions among Q - q , - , Q - , Qq - and Q - q , with appropriate string tensions. Our present analysis suggests the following exotic states: X(3823) , Z c(3900) , X(3915) , Z c(4025) , (4040) , Z 1(4050) and X(4160) as Q - q molecular-like four-quark states, while Z c(3885) , X(3940) and Y(4140) as the diquark-antidiquark four-quark states. We have been able to assign the JPC values for many of the recently observed exotic states according to their structure. Apart from this, we have identified the charged state Z(4430) recently confirmed by LHCb as the first radial excitation of Zc(3885) with G = + 1 and Y(4360) state as the first radial excitation of Y(4008) with G = - 1 and the state as the first radial excitation of the state.

  8. MEASUREMENTS OF MECHANICAL TRIPLET VIBRATIONS IN RHIC.

    SciTech Connect

    MONTAG,C.; BRENNAN,M.; BUTLER,J.; BONATI,R.; KOELLO,P.

    2002-06-02

    Mechanical vibrations of the RHIC interaction region triplets has been identified as the dominant source of orbit jitter for frequencies up to 20 Hz. We report the results of detailed measurements that were performed to characterize these effects. We discuss the impact on beam dynamics and possible cures.

  9. One Interesting Family of Diophantine Triplets

    ERIC Educational Resources Information Center

    Deshpande, M. N.

    2002-01-01

    In this note properties of two sequences generated by the recurrence relation G[subscript n] +2 = 4 G[subscript n] +1 - G[subscript n], are studied. It is shown that one of the sequences leads to a family of diophantine triplets. Some interesting properties of these sequences are also established.

  10. Relative Pose Estimation Using Image Feature Triplets

    NASA Astrophysics Data System (ADS)

    Chuang, T. Y.; Rottensteiner, F.; Heipke, C.

    2015-03-01

    A fully automated reconstruction of the trajectory of image sequences using point correspondences is turning into a routine practice. However, there are cases in which point features are hardly detectable, cannot be localized in a stable distribution, and consequently lead to an insufficient pose estimation. This paper presents a triplet-wise scheme for calibrated relative pose estimation from image point and line triplets, and investigates the effectiveness of the feature integration upon the relative pose estimation. To this end, we employ an existing point matching technique and propose a method for line triplet matching in which the relative poses are resolved during the matching procedure. The line matching method aims at establishing hypotheses about potential minimal line matches that can be used for determining the parameters of relative orientation (pose estimation) of two images with respect to the reference one; then, quantifying the agreement using the estimated orientation parameters. Rather than randomly choosing the line candidates in the matching process, we generate an associated lookup table to guide the selection of potential line matches. In addition, we integrate the homologous point and line triplets into a common adjustment procedure. In order to be able to also work with image sequences the adjustment is formulated in an incremental manner. The proposed scheme is evaluated with both synthetic and real datasets, demonstrating its satisfactory performance and revealing the effectiveness of image feature integration.

  11. Synthesis of triplet-triplet annihilation upconversion nanocapsules under protective conditions.

    PubMed

    Katta, Kartheek; Busko, Dmitry; Avlasevich, Yuri; Muñoz-Espí, Rafael; Baluschev, Stanislav; Landfester, Katharina

    2015-06-01

    Triplet-triplet annihilation upconversion (TTA-UC) nanocapsules are synthesized under oxygen-protective conditions (i.e., complete darkness and argon atmosphere) by free-radical miniemulsion polymerization. These conditions help to exclude the oxidation of the emitter molecules caused by singlet oxygen, generated during the synthesis at daylight conditions and oxygen-rich environment. Subsequently, keeping all the other experimental conditions the same, samples synthesized at protective conditions demonstrate substantially increased UC efficiency. These experimental facts strongly support the hypothesis that posterior removing of oxygen from TTA-UC nanocapsules is not sufficient to obtain reproducible and sustainable UC results. The schematic representation shows the influence of sunlight on the formation of singlet oxygen and its effect on the triplet-triplet annihilation upconversion process. PMID:25630569

  12. Quenching excited triplet C{sub 60} fullerene by tetracyanoethylene in benzonitrile

    SciTech Connect

    Nadtochenko, V.A.; Denisov, N.N.; Rubtsov, I.V.; Lobach, A.S.; Moravsky, A.P.

    1994-01-01

    The main photophysical properties of C{sub 60} fullerene: The absorption spectra of excited singlet C{sub 60}, the inter-combinational conversion time, the quantum yield of triplet C{sub 60}, the triplet-triplet absorption spectra, and the channels and rate constants of the deactivation of triplet C{sub 60} have been established. The photochemical properties of C{sub 60} fullerene have been investigated to a lesser degree. C{sub 60} is known to be readily reduced (E{sub 1/2} = {minus}0.4 in relation to Ag/Ag{sup +}), in particular, photochemically. For example, photoexcitation of charge-transfer complexes of C{sub 60} with amines gives the radical anion C{sup {minus}}{sub 60} which is also formed in reactions of photoexcited C{sub 60} fullerene. The formation of the radical cation C{sup +}{sub 60} under the action of light has been detected in the reaction with colloidal TiO{sub 2}. The radical ion C{sup +}{sub 60} has been obtained in a homogeneous photochemical process: the reaction of unexcited C{sub 60} with excited singlet N-methylacridinium hexafluorophosphate or with the biphenyl radical cation generated in the reaction with excited singlet N-methylacridinium hexafluorophosphate. The formation of C{sup +}{sub 60} with an electron acceptor in a homogeneous process has not so far been observed. The purpose of this work has been to study the quenching of triplet {sup 3}C{sub 60} with an electron acceptor, tetracyanoethylene (TCNE), which is known to oxidize unsaturated or aromatic hydrocarbons in photochemical reactions.

  13. Electronic spectra of GdF reanalyzed by decomposing state functions according to f-shell angular momentum

    NASA Astrophysics Data System (ADS)

    Yamamoto, Shigeyoshi; Tatewaki, Hiroshi

    2011-04-01

    The electronic structure of the GdF molecule was studied by means of four-component relativistic configuration interaction (CI) calculations [S. Yamamoto, H. Tatewaki, and T. Saue, J. Chem. Phys. 129, 244505 (2008), 10.1063/1.3039794]. To analyze the electronic spectra more accurately, the CI wave function is decomposed according to the angular momentum (?f) generated from the (4f)7 electrons. The weight of a specified ?f is referred to as the "f-shell Omega component weight." This ?f plays a crucial role in classifying the strong electronic transitions from the upper states (0.7 eV-3.0 eV) to the lower states (0.55 eV). For these transitions, the upper and lower states have almost identical ?f weights. This appears to be a necessary condition for a transition to be strong. The same condition is expected to hold for other lanthanide linear molecules. A point charge model is also studied, acting as a simplified model of GdF; it successfully reproduces the spectra of GdF, justifying studies based on ligand field theory.

  14. Enhanced triplet-triplet annihilation in bicomponent organic systems by using a gap plasmon resonator

    NASA Astrophysics Data System (ADS)

    Park, Jun Kue; Lee, Gi Yong; Jung, Kinam; Ko, Doo-Hyun; Han, Il Ki; Ko, Hyungduk

    2015-07-01

    The triplet-triplet annihilation (TTA) efficiency in bicomponent organic systems is investigated by employing a gap plasmon resonator. In our structure, strong absorption peaks arising from coupling between localized surface plasmons and surface plasmon polaritons closely overlap the Q band of porphyrin, leading to higher triplet concentrations within the film. We find that at ultralow excitation intensities on the order of watts per square centimeter (W cm-2), TTA becomes predominant for the organic system on a gap plasmon resonator. A strong surface-enhanced Raman scattering intensity is observed in this substrate, verifying the near-field enhancement.The triplet-triplet annihilation (TTA) efficiency in bicomponent organic systems is investigated by employing a gap plasmon resonator. In our structure, strong absorption peaks arising from coupling between localized surface plasmons and surface plasmon polaritons closely overlap the Q band of porphyrin, leading to higher triplet concentrations within the film. We find that at ultralow excitation intensities on the order of watts per square centimeter (W cm-2), TTA becomes predominant for the organic system on a gap plasmon resonator. A strong surface-enhanced Raman scattering intensity is observed in this substrate, verifying the near-field enhancement. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr02813b

  15. How disorder controls the kinetics of triplet charge recombination in semiconducting organic polymer photovoltaics.

    PubMed

    Bittner, Eric R; Lankevich, Vladimir; Glinas, Simon; Rao, Akshay; Ginger, David A; Friend, Richard H

    2014-10-14

    Recent experiments by Rao et al. (Nature, 2013, 500, 435-439) indicate that recombination of triplet charge-separated states is suppressed in organic polymer-fullerene based bulk-heterojunction (BHJ) photovoltaic cells exhibiting a high degree of crystallinity in the fullerene phase relative to systems with more disorder. In this paper, we use a series of Frenkel-exciton lattice models to rationalize these results in terms of wave-function localization, interface geometry, and density of states. In one-dimensional co-linear and co-facial models of the interface, increasing local energetic disorder in one phase localizes the interfacial triplet charge-transfer ((3)CT) states and increases the rate at which these states relax to form lower-energy triplet excitons. In two dimensional BHJ models, energetic disorder within the fullerene phase plays little role in further localizing states pinned to the interface. However, inhomogeneous broadening introduces strong coupling between the interfacial (3)CT and nearby fullerene triplet excitons and can enhance the decay of these states in systems with higher degrees of energetic disorder. PMID:24922118

  16. EMITTING ELECTRONS SPECTRA AND ACCELERATION PROCESSES IN THE JET OF Mrk 421: FROM THE LOW STATE TO THE GIANT FLARE STATE

    SciTech Connect

    Yan Dahai; Zhang Li; Fan Zhonghui; Zeng Houdun; Yuan Qiang

    2013-03-10

    We investigate the electron energy distributions (EEDs) and the acceleration processes in the jet of Mrk 421 through fitting the spectral energy distributions (SEDs) in different active states in the frame of a one-zone synchrotron self-Compton model. After assuming two possible EEDs formed in different acceleration models: the shock-accelerated power law with exponential cut-off (PLC) EED and the stochastic-turbulence-accelerated log-parabolic (LP) EED, we fit the observed SEDs of Mrk 421 in both low and giant flare states using the Markov Chain Monte Carlo method which constrains the model parameters in a more efficient way. The results from our calculations indicate that (1) the PLC and LP models give comparably good fits for the SED in the low state, but the variations of model parameters from low state to flaring can be reasonably explained only in the case of the PLC in the low state; and (2) the LP model gives better fits compared to the PLC model for the SED in the flare state, and the intra-day/night variability observed at GeV-TeV bands can be accommodated only in the LP model. The giant flare may be attributed to the stochastic turbulence re-acceleration of the shock-accelerated electrons in the low state. Therefore, we may conclude that shock acceleration is dominant in the low state, while stochastic turbulence acceleration is dominant in the flare state. Moreover, our result shows that the extrapolated TeV spectra from the best-fit SEDs from optical through GeV with the two EEDs are different. It should be considered with caution when such extrapolated TeV spectra are used to constrain extragalactic background light models.

  17. Electronic spectra and excited-state dynamics of 4-fluoro-N,N-dimethylaniline

    NASA Astrophysics Data System (ADS)

    Fujiwara, Takashige; Reichardt, Christian; Aaron Vogt, R.; Crespo-Hernndez, Carlos E.; Zgierski, Marek Z.; Lim, Edward C.

    2013-10-01

    Concerted ultrafast time-resolved spectroscopic experiments and ab initio computational (TDDFT) studies of the electronic transitions of 4-fluoro-N,N-dimethylaniline (FDMA) have been performed to investigate the mechanism of photo-induced intramolecular charge transfer (ICT). The compound FDMA shows dual fluorescence from a ??? state and a closely-lying twisted intramolecular charge transfer (TICT) state in both n-hexane and acetonitrile. The very similar lifetimes observed for the two emission bands indicate that the ??? and the TICT states are effectively in thermal equilibrium at room temperature.

  18. Nucleon, Delta and Omega excited state spectra at three pion mass values

    SciTech Connect

    John Bulava, Robert G. Edwards, Balint Joo, David G. Richards, Eric Engelson, Huey-Wen Lin, Colin Morningstar, Stephen J. Wallace

    2010-06-01

    The energies of the excited states of the Nucleon, Delta and Omega are computed in lattice QCD, using two light quarks and one strange quark on anisotropic lattices. The calculations are performed at three values of the pion mass: 392(4), 438(3) and 521(3) MeV. We employ the variational method with a basis of about ten interpolating operators enabling six energies to be distinguished clearly in each irreducible representation of the octahedral group. We compare our calculations of nucleon excited states with the low-lying experimental spectrum. There is reasonable agreement for the pattern of states.

  19. Unification without doublet triplet splitting

    NASA Astrophysics Data System (ADS)

    Kilian, W.; Reuter, J.

    2006-11-01

    Matter-Higgs unification in string-inspired supersymmetric grand unified theories predicts the existence of colored states in the Higgs multiplets and calls for two extra generations of Higgs-like fields ('unhiggses'). If these states are present near the TeV scale, gauge-coupling unification points to the existence of two distinct scales, 1015 GeV where right-handed neutrinos and a Pati-Salam symmetry appear, and 1018 GeV where complete unification is achieved. Baryon-number conservation, while not guaranteed, can naturally emerge from an underlying flavor symmetry. Collider signatures and dark-matter physics may be drastically different from the conventional MSSM.

  20. 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)

  1. Radical-mediated dehydrogenation of bile acids by means of hydrogen atom transfer to triplet carbonyls.

    PubMed

    Miro, P; Marin, M L; Miranda, M A

    2016-02-24

    The aim of the present paper is to explore the potential of radical-mediated dehydrogenation of bile salts (BSs), which is reminiscent of the enzymatic action of hydroxysteroid dehydrogenase enzymes (HSDH). The concept has been demonstrated using triplet carbonyls that can be efficiently generated upon selective UVA-excitation. Hydrogen atom transfer (HAT) from BSs to triplet benzophenone (BP) derivatives gave rise to radicals, ultimately leading to reduction of the BP chromophore with concomitant formation of the oxo-analogs of the corresponding BSs. The direct reactivity of triplet BP with BSs in the initial step was evaluated by determining the kinetic rate constants using laser flash photolysis (LFP). The BP triplet decay was monitored (λmax = 520 nm) upon addition of increasing BS concentrations, and the obtained rate constant values indicated a reactivity of the methine hydrogen atoms in the order of C-3 < C-12 < C-7. The steady-state kinetics of the overall process, monitored through the disappearance of the typical BP absorption band at 260 nm, was much faster under N2 than under O2, also supporting the role of the oxygen-quenchable triplet in the dehydrogenation process. Furthermore, irradiation of deaerated aqueous solutions of sodium cholate in the presence of KPMe provided the oxo-analogs, 3[O],7[O]-CA, 3[O]-CA and 7[O]-CA, arising from the HAT process. PMID:26833240

  2. Composite spectra: XX. 45 Cancri. Two stars with very similar masses but quite different evolutionary states

    NASA Astrophysics Data System (ADS)

    Griffin, R. E. M.; Griffin, R. F.

    2015-02-01

    From accurate radial-velocity measurements covering 11 circuits of the orbit of the composite-spectrum binary 45 Cnc, together with high-resolution spectroscopy spanning nearly 3 circuits, we have (i) isolated cleanly the spectrum of the early-type secondary, (ii) classified the component spectra as G8 III and A3 III, (iii) derived the first double-lined orbit for the system and a mass ratio (M_1/M_2) of 1.035 0.01, and (iv) extracted physical parameters for the component stars, deriving the masses and (log) luminosities of the G star and A star as 3.11 and 3.00 M?} R?, and 2.34 and 2.28 L?, respectively, with corresponding uncertainties of 0.10 M? R? and 0.09 L?. Since the mass ratio is close to unity, we argue that the more evolved component is unlikely to have been a red giant long enough to have made multiple ascents of the RGB, an argument that is supported somewhat by the rather high eccentricity of the orbit (e = 0.46) and the evolutionary time-scales of the two components, but chiefly by the presence of significant Li I in the spectrum of the cool giant.

  3. Hydrophobic-Radical Influence on the Structure and Vibrational Spectra of Zwitterionic Glycine and Alanine in the Condensed State

    NASA Astrophysics Data System (ADS)

    Ten, G. N.; Kadrov, D. M.; Baranov, V. I.

    2014-05-01

    The structure and vibrational spectra of zwitterionic glycine and alanine in aqueous solution and the solid state were calculated in the B3LYP/6-311++G(d,p) approximation. The environment infl uence was taken into account by two methods, i.e., the self-consistent reaction fi eld (SCRF) model and a clear accounting for the effects of hydrogenbonds (complexes with water molecules). The geometric, energetic, and spectral characteristics required to establish that a hydrophobic radical affected the ability of glycine and alanine to form H-bonds were determined. It was found by comparison with experiment that zwitterionic glycine and alanine in the condensed states had to be surrounded with three water molecules, one of which was situated between the N+H3 and COO- ions, in order to calculate their vibrational (IR and Raman) spectra. The formation energies of the alanine complexes with water were 56.47 kcal/ mol and 12.55 kcal/mol greater than those of glycine for formation of a complex with one water molecule situated between the ionized groups and with three water molecules, respectively.

  4. Photoluminescence spectra of ZnS:X- (X = F and I) nanoparticles synthesized via a solid-state reaction

    NASA Astrophysics Data System (ADS)

    Chen, Zhong; Li, Xiao Xia; Du, Guoping; Yu, Quanmao

    2014-04-01

    ZnS:X- (X = F and I) nanoparticles have been prepared successfully via a solid-state method at low temperature, and the effects of doping with X- on the photoluminescence (PL) properties of ZnS nanoparticles have been investigated. X-ray powder diffraction (XRD), energy-dispersive X-ray spectrum (EDS), transmission electron microscope (TEM), ultraviolet-visible diffusion reflection spectra, and emission and excitation spectra were used to characterize the crystal structure, chemical compositions, diameter, surface states, and optical properties of ZnS:X- (X = F and I) nanoparticles. XRD studies showed the phase singularity of ZnS:X- particles having zinc-blende (cubic) structure with an average crystallite size 4.7-11.0 nm. The results indicated that the PL of doping halogen ZnS nanoparticles can be enhanced remarkably by controlling suitable halogen doping, and the most intense emission was obtained when X/Zn = 0.3 and 0.45 under 387 nm excitation corresponding to X = F and I, respectively. The emission intensity of ZnS:F- (F/Zn = 0.3) nanoparticles was higher than that of ZnS:I- (I/Zn = 0.45), and exhibited strong emission with an intensity about 9 times higher than the undoped nanoparticles. It was found that the PL of ZnS nanoparticles doped with various halogens was decreased with the increase of the halogen ion radius.

  5. Studies on reaction of amino acids and triplet thioxanthone derivatives by laser flash photolysis.

    PubMed

    Zhu, Hongping; Wang, Wenfeng; Yao, Side

    2006-11-01

    Excitation of the thioxanthone derivatives (TXs), 2, 4-diethylthioxanthone (DETX) and 2-(2,3-epoxypropyloxy) thioxanthone (ETX) in acetonitrile/water mixture solution (1:1, v/v) upon 355 nm laser flash produced the triplet of TXs ((3)TXs(*)). Characteristic absorption spectra of (3)TXs(*)(590 nm) were recorded and rate constants of (3)TXs(*) quenched by O(2) and by its ground state were determined (9.8 x 10(9) M(-1) s(-1), 7.3 x 10(9) M(-1) s(-1) and 2.6 x 10(8) M(-1) s(-1), 2.2 x 10(8) M(-1) s(-1) respectively). The reactions of some amino acids oxidized by (3)TXs(*) were carried out. It has been found that tryptophan (Trp) and tyrosine (Tyr) can quench (3)TXs(*) via electron transfer process and related quenching rate constants were obtained. (3)TXs(*) induced protein damage was investigated using electrophoresis and significant levels of dimerisation were observed under aerobic and anaerobic conditions. The influence of photo-sensitizer's structure on photo-oxidation of amino acid and protein has been discussed. PMID:16586012

  6. Excited state dipole moments of N, N-dimethylaniline from thermochromic effect on electronic absorption and fluorescence spectra

    NASA Astrophysics Data System (ADS)

    Kawski, A.; Kukli?ski, B.; Bojarski, P.

    2006-01-01

    The effect of temperature on absorption and fluorescence spectra of N, N-dimethylaniline (DMA) in ethyl acetate has been studied for temperature ranging from 293 to 388 K. The permittivity ? and refractive index n of the solvent decrease with temperature increase and the absorption and fluorescence bands are blue shifted (so-called "thermochromic shift"). Based on this phenomenon, the dipole moment ?e in the excited singlet state and the Onsager interaction radius a for DMA were determined using the Bilot and Kawski theory [L. Bilot, A. Kawski, Z. Naturforsch. 17a (1962) 621; 18a (1963) 10, 256]. For the known dipole moment in the ground state ?g = 1.61 D and for ?/ a3 = 0.54 ( ? is the polarizability of the solute) the average value of ?e = 3.55 D and a = 3.1 were determined. The obtained values for DMA are compared with the experimental values determined by other authors.

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

    PubMed

    Arulmozhiraja, Sundaram; Coote, Michelle L; Hasegawa, Jun-Ya

    2015-11-28

    Electronic structures of azaindole were studied using symmetry-adapted cluster configuration interaction theory utilizing Dunning's cc-pVTZ basis set augmented with appropriate Rydberg spd functions on carbon and nitrogen atoms. The results obtained in the present study show good agreement with the available experimental values. Importantly, and contrary to previous theoretical studies, the excitation energy calculated for the important n-?(?) state agrees well with the experimental value. A recent study by Pratt and co-workers concluded that significant mixing of ?-?(?) and n-?(?) states leads to major change in the magnitude and direction of the dipole moment of the upper state vibrational level in the 0,0 + 280 cm(-1) band in the S1?S0 transition when compared to that of the zero-point level of the S1 state. The present study, however, shows that all the four lowest lying excited states, (1)Lb ?-?(?), (1)La ?-?(?), n-?(?), and ?-?(?), cross each other in one way or another, and hence, significant state mixing between them is likely. The upper state vibrational level in the 0,0 + 280 cm(-1) band in the S1?S0 transition benefits from this four-state mixing and this can explain the change in magnitude and direction of the dipole moment of the S1 excited vibrational level. This multistate mixing, and especially the involvement of ?-?(?) state in mixing, could also provide a route for hydrogen atom detachment reactions. The electronic spectra of benzimidazole, a closely related system, were also investigated in the present study. PMID:26627956

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

    NASA Astrophysics Data System (ADS)

    Arulmozhiraja, Sundaram; Coote, Michelle L.; Hasegawa, Jun-ya

    2015-11-01

    Electronic structures of azaindole were studied using symmetry-adapted cluster configuration interaction theory utilizing Dunning's cc-pVTZ basis set augmented with appropriate Rydberg spd functions on carbon and nitrogen atoms. The results obtained in the present study show good agreement with the available experimental values. Importantly, and contrary to previous theoretical studies, the excitation energy calculated for the important n-?? state agrees well with the experimental value. A recent study by Pratt and co-workers concluded that significant mixing of ?-?? and n-?? states leads to major change in the magnitude and direction of the dipole moment of the upper state vibrational level in the 0,0 + 280 cm-1 band in the S1?S0 transition when compared to that of the zero-point level of the S1 state. The present study, however, shows that all the four lowest lying excited states, 1Lb ?-??, 1La ?-??, n-??, and ?-??, cross each other in one way or another, and hence, significant state mixing between them is likely. The upper state vibrational level in the 0,0 + 280 cm-1 band in the S1?S0 transition benefits from this four-state mixing and this can explain the change in magnitude and direction of the dipole moment of the S1 excited vibrational level. This multistate mixing, and especially the involvement of ?-?? state in mixing, could also provide a route for hydrogen atom detachment reactions. The electronic spectra of benzimidazole, a closely related system, were also investigated in the present study.

  9. Coherent transient in dressed-state and transient spectra of Autler-Townes doublet

    SciTech Connect

    Zhang Lianshui; Feng Xiaomin; Fu Guangsheng; Li Xiaowei; Han Li; Manson, Neil B.; Wei Changjiang

    2004-12-01

    In this paper we present a theoretical study of the time-dependent probe response in the presence of a strong pump field in a three-level pump-probe configuration. Two situations are investigated: a cw pump with a pulsed probe field and a pulsed pump with a cw probe field. The results are explained as dressed-state nutation and nutation by dynamic Stark switching. Dressed-state quantum beats are also an important feature for both situations. Furthermore, when a 90 deg. phase shift after a {pi}/2 period is introduced in the pulsed probe field, there is a spin locking in the dressed-state transition. Our results give a satisfactory theoretical account of a previous experimental observation [Wei et al., Phys. Rev. Lett. 74, 1083 (1995)].

  10. 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

  11. 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.

  12. Singlet-Triplet Excitations in the Unconventional Spin-Peierls TiOBr Compound

    NASA Astrophysics Data System (ADS)

    Clancy, J. P.; Gaulin, B. D.; Adams, C. P.; Granroth, G. E.; Kolesnikov, A. I.; Sherline, T. E.; Chou, F. C.

    2011-03-01

    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 Spallation Neutron Source at Oak Ridge National Laboratory. 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 results represent the first direct measurement of the singlet-triplet energy gap in TiOBr, which has a value of Eg=21.21.0meV.

  13. Fermiophobia in a Higgs triplet model

    SciTech Connect

    Akeroyd, A. G.; Diaz, Marco A.; Romero Maltrana, D.; Rivera, Maximiliano A.

    2011-05-01

    A fermiophobic Higgs boson can arise in models with an extended Higgs sector, such as models with scalars in an isospin triplet representation. In a specific model with a scalar triplet and spontaneous violation of lepton number induced by a scalar singlet field, we show that fermiophobia is not a fine-tuned situation, unlike in two higgs doublet models. We study distinctive signals of fermiophobia which can be probed at the LHC. For the case of a small Higgs mass, a characteristic signal would be a moderate B(H{yields}{gamma}{gamma}) accompanied by a large B(H{yields}JJ) (where J is a Majoron), the latter being an invisible decay. For the case of a large Higgs mass there is the possibility of dominant H{yields}ZZ, WW and suppressed H{yields}JJ decay modes. In this situation, B(H{yields}ZZ) is larger than B(H{yields}WW), which differs from the SM prediction.

  14. Singlets and triplets in hybrid nanodevices

    NASA Astrophysics Data System (ADS)

    Agranovich, V. M.; Dubovskii, O. A.; La Rocca, G. C.

    2014-05-01

    An organic material thin layer can be used to resonantly absorb light and nonradiatively transfer excitation to an adjacent inorganic quantum well the optical nonlinearities of which can in this way be turned on more efficiently than by direct optical pumping. We theoretically consider this process in a hybrid structure based on crystalline tetracene in which the singlet exciton energy is close to twice the one of a triplet exciton and thermally activated singlet exciton fission into two triplets can be efficient. We investigate how the temperature dependence of the singlet exciton diffusion length affects the functional properties of such hybrid organic-inorganic nanostructures based on tetracene. We show how temperature activated fission opens a new possibility to turn on and off the indirect pumping due to energy transfer from the organic into the inorganic subsystem.

  15. Electronic structure of some adenosine receptor antagonists. III. Quantitative investigation of the electronic absorption spectra of alkyl xanthines

    NASA Astrophysics Data System (ADS)

    Moustafa, H.; Shalaby, Samia H.; El-sawy, K. M.; Hilal, Rifaat

    2002-07-01

    Quantitative and comparative investigation of the electronic absorption spectra of theophylline, caffeine and their derivatives is reported. The spectra of theophylline, caffeine and theobromine were compared to establish the predominant tautomeric species in solution. This comparison, analysis of solvent effects and assignments of the observed transitions via MO computations indicate the exits of only one tautomeric species in solution that is the N7 form. A low-lying triplet state was identified which corresponds to a HOMO-LUMO transition. This relatively long-lived T 1 state is always less polar than the ground state and may very well underlie the photochemical reactivity of alkyl xanthines. Substituents of different electron donating or withdrawing strengths and solvent effects are investigated and analyzed. The present analysis is facilitated via computer deconvolution of the observed spectra and MO computation.

  16. Triplet Superconductivity in the One-Dimensional Hubbard Model with Modulated Kinetic Hopping at Weak Coupling

    NASA Astrophysics Data System (ADS)

    Ding, Hanqin; Zhang, Jun

    2015-12-01

    We construct a theoretical model for one-dimensional interacting electrons by modulating electronic kinetic hopping in the weak-coupling regime. The use of bosonization and renormalization group analysis allows us to obtain the phase diagram. The induced three-body attraction gives rise to a triplet superconducting phase in the ground state.

  17. Surface-state spectra from thick-oxide MOS tunnel junctions

    NASA Technical Reports Server (NTRS)

    Ma, T. P.; Barker, R. C.

    1974-01-01

    The conductance and capacitance of thick-oxide MOS tunnel junctions (SiO2 thickness 40 to 65 A) have been measured from 35 Hz to 210 kHz. It is demonstrated that the use of a thick-oxide MOS tunnel junction makes it possible to obtain the surface-state data throughout the whole silicon band gap with better resolution and better sensitivity than the conventional MOS capacitance techniques. A slight departure from equilibrium may occur in the voltage range where large tunnel current flows. Corrections to the energy scale must be made in this voltage range. A method for the evaluation of the junction quality is discussed. The simplified equivalent circuits necessary for the calculation of surface-state data are constructed under various bias conditions by an approach different from that used in a previously published work. The present work supports the model that at least some of the observed surface states are a consequence of the diffusion of contact metals into the oxide.

  18. Twin and Triplet Drugs in Opioid Research

    NASA Astrophysics Data System (ADS)

    Fujii, Hideaki

    Twin and triplet drugs are defined as compounds that contain respectively two and three pharmacophore components exerting pharmacological effects in a molecule. The twin drug bearing the same pharmacophores is a "symmetrical twin drug", whereas that possessing different pharmacophores is a "nonsymmetrical twin drug." In general, the symmetrical twin drug is expected to produce more potent and/or selective pharmacological effects, whereas the nonsymmetrical twin drug is anticipated to show both pharmacological activities stemming from the individual pharmacophores (dual action). On the other hand, nonsymmetrical triplet drugs, which have two of the same pharmacophores and one different moiety, are expected to elicit both increased pharmacological action and dual action. The two identical portions could bind the same receptor sites simultaneously while the third portion could bind a different receptor site or enzyme. This review will mainly focus on the twin and triplet drugs with an evaluation of their in vivo pharmacological effects, and will also include a description of their pharmacology and synthesis.

  19. Initial- versus final-state effects in the narrow-band spectra of heavy-fermion systems

    SciTech Connect

    Gumhalter, B. ); Zlatic, V. )

    1990-10-01

    The {ital f}-electron spectral density of heavy-fermion systems, as observed by x-ray photoelectron spectroscopy (XPS) and bremsstrahlung isochromat spectroscopy (BIS), is discussed in terms of initial- and final-state effects. The properties of the initial state, described by the periodic Anderson model, are obtained from the adiabatic perturbation theory, with the on-site correlation {ital U}{sub {ital f}{ital f}} taken as the expansion parameter. In the final state the transient effects following the sudden ionization of the system in XPS or BIS are discussed by using the time-dependent perturbation expansion. The overall spectral shapes, as would be observed experimentally, turn out to be given as a convolution of the adiabatic spectral function, which reflects the many-body interactions in the initial state, and the shape function, which accounts for the nonadiabatic effects following the destruction of the charge neutrality in XPS and BIS. Our treatment allows us to explain the position and the shape of the {ital f}-derived peaks in the XPS spectra of actinide intermetallics and to remove the conceptual difficulty in understanding the data acquired independently from thermodynamic (low-energy) and spectroscopic (high-energy) measurements of heavy fermions within a unified framework.

  20. Dressing effects in the attosecond transient absorption spectra of doubly excited states in helium

    NASA Astrophysics Data System (ADS)

    Argenti, L.; Jimnez-Galn, .; Marante, C.; Ott, C.; Pfeifer, T.; Martn, F.

    2015-06-01

    Strong-field manipulation of autoionizing states is a crucial aspect of electronic quantum control. Recent measurements of the attosecond transient absorption spectrum (ATAS) of helium dressed by a few-cycle visible pulse [C. Ott et al., Nature (London) 516, 374 (2014), 10.1038/nature14026] provide evidence of the inversion of Fano profiles. With the support of accurate ab initio calculations that reproduce the results of the latter experiment, here we investigate the new physics that arise from ATAS when the laser intensity is increased. In particular, we show that (i) previously unnoticed signatures of the dark 2 p21S doubly excited state are observed in the experimental spectrum, (ii) inversion of Fano profiles is predicted to be periodic in the laser intensity, and (iii) the ac Stark shift of the higher terms in the s p2,n + autoionizing series exceeds the ponderomotive energy, which is the result of a genuine two-electron contribution to the polarization of the excited atom.

  1. Electronic spectra and excited state dynamics of pentafluorophenol: Effects of low-lying πσ{sup ∗} states

    SciTech Connect

    Karmakar, Shreetama; Mukhopadhyay, Deb Pratim; Chakraborty, Tapas

    2015-05-14

    Multiple fluorine atom substitution effect on photophysics of an aromatic chromophore has been investigated using phenol as the reference system. It has been noticed that the discrete vibronic structure of the S{sub 1}←S{sub 0} absorption system of phenol vapor is completely washed out for pentafluorophenol (PFP), and the latter also shows very large Stokes shift in the fluorescence spectrum. For excitations beyond S{sub 1} origin, the emission yield of PFP is reduced sharply with increase in excess vibronic energy. However, in a collisional environment like liquid hydrocarbon, the underlying dynamical process that drives the non-radiative decay is hindered drastically. Electronic structure theory predicts a number of low-lying dark electronic states of πσ{sup ∗} character in the vicinity of the lowest valence ππ{sup ∗} state of this molecule. Tentatively, we have attributed the excitation energy dependent non-radiative decay of the molecule observed only in the gas phase to an interplay between the lowest ππ{sup ∗} and a nearby dissociative πσ{sup ∗} state. Measurements in different liquids reveal that some of the dark excited states light up with appreciable intensity only in protic liquids like methanol and water due to hydrogen bonding between solute and solvents. Electronic structure theory methods indeed predict that for PFP-(H{sub 2}O){sub n} clusters (n = 1-11), intensities of a number of πσ{sup ∗} states are enhanced with increase in cluster size. In contrast with emitting behavior of the molecule in the gas phase and solutions of nonpolar and polar aprotic liquids, the fluorescence is completely switched off in polar protic liquids. This behavior is a chemically significant manifestation of perfluoro effect, because a very opposite effect occurs in the case of unsubstituted phenol for which fluorescence yield undergoes a very large enhancement in protic liquids. Several dynamical mechanisms have been suggested to interpret the observed photophysical behavior.

  2. Triplet proximity effect and odd-frequency pairing in graphene

    NASA Astrophysics Data System (ADS)

    Linder, Jacob; Black-Schaffer, Annica M.; Sudb, Asle

    2010-07-01

    We study the interplay between proximity-induced superconductivity and ferromagnetism in graphene by self-consistently solving the Bogoliubov de Gennes equations on the honeycomb lattice. We find that a strong triplet proximity effect is generated in graphene, leading to odd-frequency pairing correlations. These odd-frequency correlations are clearly manifested in the local density of states of the graphene sheet, which can be probed via scanning tunnel microscope measurements. Motivated by recent experiments on S|N|S graphene Josephson junctions, we also study the spectrum of Andreev bound states formed in the normal region due to the proximity effect. Our results may be useful for interpreting spectroscopic data and can also serve as a guideline for future experiments.

  3. BROADBAND EMISSION SPECTRA FROM THE CYGNUS X-3 JET IN THE SOFT SPECTRAL STATE

    SciTech Connect

    Zhang, Jian-Fu; Lu, Ju-Fu E-mail: lujf@xmu.edu.cn

    2015-02-01

    In order to understand the main observational characteristics of the Galactic X-ray binary Cygnus X-3, we propose a radiation model in which high-energy electrons accelerate in the dissipation zone of a jet and produce nonthermal broadband emissions. Broadband spectral energy distributions are computed to compare the AGILE and Fermi LAT data with the multi-band data during soft X-ray spectral states. By fitting observations at different locations of the jet, we find that the emission region is rather compact and should be located at a distance of about one orbital radius. Our results can explain the current multi-frequency observations and also predict the TeV band emission. The model could be tested by a polarization measurement at IR band, and/or by a correlation study between the GeV and TeV bands once very-high-energy observations are available.

  4. Exchange-only optimized effective potential calculation of excited state spectra for He and Be atoms.

    SciTech Connect

    Desjarlais, Michael Paul; Muller, Richard Partain

    2006-02-01

    The optimized effective potential (OEP) method allows orbital-dependent functionals to be used in density functional theory (DFT), which, in particular, allows exact exchange formulations of the exchange energy to be used in DFT calculations. Because the exact exchange is inherently self-interaction correcting, the resulting OEP calculations have been found to yield superior band-gaps for condensed-phase systems. Here we apply these methods to the isolated atoms He and Be, and compare to high quality experiments and calculations to demonstrate that the orbital energies accurately reproduce the excited state spectrum for these species. These results suggest that coupling the exchange-only OEP calculations with proper (orbital-dependent or other) correlation functions might allow quantitative accuracy from DFT calculations.

  5. Hindered and modulated rotational states and spectra of adsorbed diatomic molecules

    NASA Astrophysics Data System (ADS)

    Shih, Y. T.; Chuu, D. S.; Mei, W. N.

    1996-10-01

    Both vertical and horizontal adsorption configurations of a diatomic molecule were modeled as the rigid rotor with which the spatial motion was confined by a finite conical well. In addition to the polar hindering potential, a sinusoidal azimuthal modulation, which bears the local symmetry of the adsorption site, was incorporated. Eigenfunctions for different models were expressed analytically in terms of the hypergeometric functions, and eigenvalues were solved numerically. We found that the rotational energy levels exhibit oscillatory behavior when plotted as functions of the hindrance angle. This particular phenomenon was interpreted as the occurrence of resonance transmission of the rotor wave function at certain hindrance condition. We also found that the rotational levels were grouped into bands when the azimuthal modulation strength was increased. The solutions were used to calculate the rotational-state distribution of desorbed molecules, and agreement with the previous experiment was obtained.

  6. Hindered and modulated rotational states and spectra of adsorbed diatomic molecules

    SciTech Connect

    Shih, Y.T.; Chuu, D.S.; Mei, W.N.

    1996-10-01

    Both vertical and horizontal adsorption configurations of a diatomic molecule were modeled as the rigid rotor with which the spatial motion was confined by a finite conical well. In addition to the polar hindering potential, a sinusoidal azimuthal modulation, which bears the local symmetry of the adsorption site, was incorporated. Eigenfunctions for different models were expressed analytically in terms of the hypergeometric functions, and eigenvalues were solved numerically. We found that the rotational energy levels exhibit oscillatory behavior when plotted as functions of the hindrance angle. This particular phenomenon was interpreted as the occurrence of resonance transmission of the rotor wave function at certain hindrance condition. We also found that the rotational levels were grouped into bands when the azimuthal modulation strength was increased. The solutions were used to calculate the rotational-state distribution of desorbed molecules, and agreement with the previous experiment was obtained. {copyright} {ital 1996 The American Physical Society.}

  7. Intra-molecular triplet energy transfer is a general approach to improve organic fluorophore photostability.

    PubMed

    Zheng, Qinsi; Jockusch, Steffen; Rodrguez-Calero, Gabriel G; Zhou, Zhou; Zhao, Hong; Altman, Roger B; Abrua, Hctor D; Blanchard, Scott C

    2016-02-10

    Bright, long-lasting and non-phototoxic organic fluorophores are essential to the continued advancement of biological imaging. Traditional approaches towards achieving photostability, such as the removal of molecular oxygen and the use of small-molecule additives in solution, suffer from potentially toxic side effects, particularly in the context of living cells. The direct conjugation of small-molecule triplet state quenchers, such as cyclooctatetraene (COT), to organic fluorophores has the potential to bypass these issues by restoring reactive fluorophore triplet states to the ground state through intra-molecular triplet energy transfer. Such methods have enabled marked improvement in cyanine fluorophore photostability spanning the visible spectrum. However, the generality of this strategy to chemically and structurally diverse fluorophore species has yet to be examined. Here, we show that the proximal linkage of COT increases the photon yield of a diverse range of organic fluorophores widely used in biological imaging applications, demonstrating that the intra-molecular triplet energy transfer mechanism is a potentially general approach for improving organic fluorophore performance and photostability. PMID:26700693

  8. Intra-molecular Triplet Energy Transfer is a General Approach to Improve Organic Fluorophore Photostability

    PubMed Central

    Zheng, Qinsi; Jockusch, Steffen; Rodríguez-Calero, Gabriel G.; Zhou, Zhou; Zhao, Hong; Altman, Roger B.; Abruña, Héctor D.; Blanchard, Scott C.

    2015-01-01

    Bright, long-lasting and non-phototoxic organic fluorophores are essential to the continued advancement of biological imaging. Traditional approaches towards achieving photostability, such as the removal of molecular oxygen and the use of small-molecule additives in solution, suffer from potentially toxic side effects, particularly in the context of living cells. The direct conjugation of small-molecule triplet state quenchers, such as cyclooctatetraene (COT), to organic fluorophores has the potential to bypass these issues by restoring reactive fluorophore triplet states to the ground state through intra-molecular triplet energy transfer. Such methods have enabled marked improvement in cyanine fluorophore photostability spanning the visible spectrum. However, the generality of this strategy to chemically and structurally diverse fluorophore species has yet to be examined. Here, we show that the proximal linkage of COT increases the photon yield of a diverse range of organic fluorophores widely used in biological imaging applications, demonstrating that the intra-molecular triplet energy transfer mechanism is a potentially general approach for improving organic fluorophore performance and photostability. PMID:26700693

  9. Final-State Projection Method in Charge-Transfer Multiplet Calculations: An Analysis of Ti L-Edge Absorption Spectra.

    PubMed

    Kroll, Thomas; Solomon, Edward I; de Groot, Frank M F

    2015-10-29

    A projection method to determine the final-state configuration character of all peaks in a charge transfer multiplet calculation of a 2p X-ray absorption spectrum is presented using a d(0) system as an example. The projection method is used to identify the most important influences on spectral shape and to map out the configuration weights. The spectral shape of a 2p X-ray absorption or L2,3-edge spectrum is largely determined by the ratio of the 2p core-hole interactions relative to the 2p3d atomic multiplet interaction. This leads to a nontrivial spectral assignment, which makes a detailed theoretical description of experimental spectra valuable for the analysis of bonding. PMID:26226507

  10. Rotational Spectra of Urea in its Ground and First Excited Vibrational States

    NASA Astrophysics Data System (ADS)

    Thomas, Jessica; Medvedev, Ivan; Kisiel, Zbigniew

    2014-06-01

    Urea is an important terrestrial bio-molecule, which has been tentatively detected in the interstellar medium. To match the much improved range and sensitivities of modern sub-millimeter telescopes a broad laboratory assay of rotational transitions needs to be recorded in order to aid in the definitive identification of this molecule. This paper focuses on the spectroscopic assignment of the rotational transitions of urea in the 207-500 GHz range which belong to its ground and first excited vibrational states. Remijan, A.J., L.E. Snyder, B.A. McGuire, H.-L. Kuo, L.W. Looney, D.N. Friedel, G.Y. Golubiatnikov, F.J. Lovas, V.V. Ilyushin, E.A. Alekseev, S.F. Dyubko, B.J. McCall, and J.M. Hollis, Observational Results of a Multi-Telescope Campaign in Search of Interstellar Urea [NH22CO]. The Astrophysical Journal, 2014. 783(2): p. 77

  11. Correlations between metal spin states and vibrational spectra ofatrinuclear Fe(II) complex exhibiting spin crossover

    NASA Astrophysics Data System (ADS)

    Gerasimova, Tatiana P.; Katsyuba, Sergey A.; Lavrenova, Ludmila G.; Pelmenschikov, Vladimir; Kaupp, Martin

    2015-12-01

    Combined IR spectroscopic/quantum-chemical analysis of a 4-propyl-1,2,4-triazole trinuclear Fe(II) complex capable of reversible thermal spin crossover has revealed mid-IR bands of the ligand sensitive to the Fe(II) spin state. The character of the correlations found between the intensity and peak position of the triazole bands and the spin state of the metal center depends neither on the identity of the metal nor on the nuclearity of the complex. The found spectral correlations therefore allow analysis of various similar complexes. This is illustrated by the example of experimental IR spectra reported earlier for Fe(II), Co(II), Ni(II), Cu(II) and Zn(II) complexes with triazole ligands. Quantum-chemical IR spectral simulations further suggest that certain ligand bands vary between the states with the same total molecular spin, but different distribution of the spin density between the metal centers. However these variations are too subtle to discriminate between the spin transitions of the central and peripheral Fe(II) ions. The experimentally revealed mid-IR markers are therefore conclusive only for the total molecular spin.

  12. Assigning States in the Jahn-Teller Coupled Infrared Spectra of CH_3O and CD_3O

    NASA Astrophysics Data System (ADS)

    Johnson, Britta; Sibert, Edwin

    2014-06-01

    The ground tilde{X}^2E vibrations of the methoxy radical have intrigued both experimentalists and theorists alike due to the presence of a conical intersection at the C3v molecular geometry. This conical intersection causes methoxy's vibrational spectrum to be strongly influenced by Jahn-Teller coupling, this leading to large amplitude vibrations and extensive mixing of the two lowest electronic states. This coupling combined with spin-orbit and Fermi couplings greatly complicates the assignments of states. In this talk we describe our efforts to assign the states of both CH_3O and CD_3O. Using the potential energy force field and calculated spectra of Nagesh and Sibert^1 as a starting point, vibrational mixing is considered using various zero-order representations. When the zero-order states are the diabatic normal mode states, there is sufficient mode mixing that the normal mode quantum numbers are no longer good labels. The mixing of the zero-order states can be reduced by including additional terms in the zero-order Hamiltonian, H^o. We consider the choice of including the first order Jahn-Teller coupling between one of the three degenerate normal modes. As the rocking motion has the largest Jahn-Teller coupling, this is the coupling that is included in H^o. Although the normal mode quantum numbers of the rocking basis functions are no longer good quantum numbers, due to the Jahn-Teller induced vibronic mixing, the zero-order states can be labeled with the linear Jahn-Teller quantum numbers.^2 This work extends these ideas by considering an H^o that includes linear Jahn-Teller coupling between two sets of degenerate vibrations. Plots of the resulting zero-order states are presented, and the spectral transitions recently observed3 for both CH_3O and CD_3O in a p-H_2 matrix are assigned using these basis functions. The extent of state-mixing found for the full Hamiltonian H for various choices of H^o is illustrated via the use of correlation diagrams obtained by plotting the eigenvalues of H^o + ? (H-H^o) as a function of ? where ? varies from zero to one. [^1] Nagesh, J.; Sibert, E. L. J. Phys. Chem. A, 2012, 116, 3846-3855. [^2] Barckholtz, T. A.; Miller, T. A. Int. Revs. in Phys. Chem., 1998, 17, 435-524. [^3] Yu-Fang Lee, Wei-Te Chou, and Yuan-Pern Lee (private communication).

  13. Skew quadrupole errors in the RHIC IR triplets

    SciTech Connect

    Tepikian, S.; Peggs, S.

    1993-12-31

    From simulation studies of the RHIC lattice, we found that skew quadrupole errors and quadrupole roll misalignments in the IR triplets (where the {beta} function can be large) produce large vertical dispersions. A simple model, using only one triplet, is applied to obtain sensitivities of vertical dispersion to skew quadrupole errors. This study revealed that measuring the vertical dispersion in the triplets is a good tool for the diagnosis of local skew quadrupole correction.

  14. Exchange interaction between the triplet exciton and the localized spin in copper-phthalocyanine.

    PubMed

    Wu, Wei

    2014-06-14

    Triplet excitonic state in the organic molecule may arise from a singlet excitation and the following inter-system crossing. Especially for a spin-bearing molecule, an exchange interaction between the triplet exciton and the original spin on the molecule can be expected. In this paper, such exchange interaction in copper-phthalocyanine (CuPc, spin-) was investigated from first-principles by using density-functional theory within a variety of approximations to the exchange correlation, ranging from local-density approximation to long-range corrected hybrid-exchange functional. The magnitude of the computed exchange interaction is in the order of meV with the minimum value (1.5 meV, ferromagnetic) given by the long-range corrected hybrid-exchange functional CAM-B3LYP. This exchange interaction can therefore give rise to a spin coherence with an oscillation period in the order of picoseconds, which is much shorter than the triplet lifetime in CuPc (typically tens of nanoseconds). This implies that it might be possible to manipulate the localized spin on Cu experimentally using optical excitation and inter-system crossing well before the triplet state disappears. PMID:24929382

  15. Exchange interaction between the triplet exciton and the localized spin in copper-phthalocyanine

    SciTech Connect

    Wu, Wei

    2014-06-14

    Triplet excitonic state in the organic molecule may arise from a singlet excitation and the following inter-system crossing. Especially for a spin-bearing molecule, an exchange interaction between the triplet exciton and the original spin on the molecule can be expected. In this paper, such exchange interaction in copper-phthalocyanine (CuPc, spin-1/2 ) was investigated from first-principles by using density-functional theory within a variety of approximations to the exchange correlation, ranging from local-density approximation to long-range corrected hybrid-exchange functional. The magnitude of the computed exchange interaction is in the order of meV with the minimum value (1.5 meV, ferromagnetic) given by the long-range corrected hybrid-exchange functional CAM-B3LYP. This exchange interaction can therefore give rise to a spin coherence with an oscillation period in the order of picoseconds, which is much shorter than the triplet lifetime in CuPc (typically tens of nanoseconds). This implies that it might be possible to manipulate the localized spin on Cu experimentally using optical excitation and inter-system crossing well before the triplet state disappears.

  16. On the absorption and emission spectra for the purine chromophore in weakly perturbative environments

    NASA Astrophysics Data System (ADS)

    Cataln, J.

    2004-08-01

    The absorption spectra for the purine chromophore in the gas phase and in 2-methylbutane, decalin and 1-chlorobutane at room temperature and of these solutions at lower temperatures exposed not only the behaviour of the chromophore in the first n,? * and ?,? * excited electronic states, but also whether the chromophore adopted an aggregate structure, and allowed their photophysical characterization. The spectrum for the chromophore in decalin matrices at low temperatures revealed a highly structured phosphorescence. The first triplet state for the chromophore is for the first time shown to be an n,? * state rather than a ?,? * state as widely assumed previously. The long phosphorescence lifetime observed, 1.1 s, is not intrinsic to this state but rather a result of the slow generation of the phosphorescent state.

  17. Rotationally resolved photoelectron spectra in resonance enhanced multiphoton ionization of HCl via the F 1Δ2 Rydberg state

    NASA Astrophysics Data System (ADS)

    Wang, Kwanghsi; McKoy, V.

    1991-12-01

    Results of studies of rotational ion distributions in the X 2Π3/2 and X 2Π1/2 spin-orbit states of HCl+ resulting from (2+1') resonance enhanced multiphoton ionization (REMPI) via the S(0) branch of the F 1Δ2 Rydberg state are reported and compared with measured threshold-field-ionization zero-kinetic-energy spectra reported recently [K. S. Haber, Y. Jiang, G. Bryant, H. Lefebvre-Brion, and E. R. Grant, Phys. Rev. A (in press)]. These results show comparable intensities for J+=3/2 of the X 2Π3/2 ion and J+=1/2 of the X 2Π1/2 ion. Both transitions require an angular momentum change of ΔN=-1 upon photoionization. To provide further insight into the near-threshold dynamics of this process, we also show rotationally resolved photoelectron angular distributions, alignment of the ion rotational levels, and rotational distributions for the parity components of the ion rotational levels. About 18% population is predicted to occur in the (+) parity component, which would arise from odd partial-wave contributions to the photoelectron matrix element. This behavior is similar to that in (2+1) REMPI via the S(2) branch of the F 1Δ2 state of HBr and was shown to arise from significant l mixing in the electronic continuum due to the nonspherical molecular ion potential. Rotational ion distributions resulting from (2+1) REMPI via the S(10) branch of the F 1Δ2 state are also shown.

  18. Pump-probe photoionization detection of singlet and triplet decay in anisole and p-cresol in a supersonic free jet

    SciTech Connect

    Lipert, R.J.; Colson, S.D.; Sur, A.

    1988-01-14

    The singlet and triplet decay of anisole and p-cresol in a supersonic free jet were determined by delayed photoionization mass spectrometry. A biexponential decay was observed in p-cresol yielding a triplet lifetime of 400 +/- 10 ns and a singlet life less than or equal to 5 ns. Very different behavior was observed for anisole. Evidence suggests the triplet state is decaying at a rate approximately 10 times greater than in p-cresol while the anisole S/sub 1/ state decays at least 5 times more slowly than the p-cresol S/sub 1/.

  19. A new medium for triplet-triplet annihilated upconversion and photocatalytic application.

    PubMed

    Ye, Changqing; Wang, Jingjing; Wang, Xiaomei; Ding, Ping; Liang, Zuoqin; Tao, Xutang

    2016-01-27

    Since the triplet-triplet annihilated upconversion (TTA-UC) materials work efficiently only in degassing organic solvents, it is of significance to find a new medium without toxicity and volatility and that promotes TTA-UC. Here, we firstly reported the effect of an OH-containing medium on low power upconversion and found that in alcohol solvent containing ?-cyclodextrin (?-CD), the phosphorescence lifetime (?p) of the sensitizer (PdTPP) and the fluorescence quantum yield (?f) of the acceptor (DPA) were enhanced with the increase in the number of OH-groups of the medium. A large triplet-triplet quenching constant (kq, 1.91 10(9) M(-1) s(-1)) and high upconversion efficiency (?UC, ?36%) of PdTPP/DPA were obtained under the excitation of a diode laser (532 nm, 60 mW cm(-2)). Under our green-to-blue upconversion irradiation, in a demonstration experiment the photocurrent was recorded at 0.09 ?A cm(-2), resulting from photocatalytic water splitting by a Cd0.7Zn0.3S photoanode and a Pt counter-electrode in a photoelectrochemical cell. The importance of this study suggests that upconversion-powered photoelectrochemistry possesses potential application for hydrogen generation from water under excitation of sun energy. PMID:26580451

  20. A versatile detector system to measure the change states, mass compositions and energy spectra of interplanetary and magnetosphere ions

    NASA Technical Reports Server (NTRS)

    Gloeckler, G.

    1977-01-01

    An instrument is described for measuring the mass and charge state composition as well as the energy spectra and angular distributions of 0.5 to 350 kev/charge ions in interplanetary space and in magnetospheres of planets such as Jupiter and earth. Electrostatic deflection combined with a time-of-flight and energy measurement allows three-parameter analysis of output signals from which the mass, charge states, and energy are determined. Post-acceleration by 30 kV extends the energy range of the detector system into the solar wind and magnetosphere plasma regime. Isotopes of H and He are easily resolved as are individual elements up to Ne and the dominant elements up to and including Fe. This instrument has an extremely large dynamic range in intensity and is sensitive to rare elements even in the presence of high intensity radiation, and is adapted for interplanetary, deep-space, and out-of-the-ecliptic missions, as well as for flights on spacecraft orbiting Jupiter and earth.

  1. Resistively detected NMR spectra of the crystal states of the two-dimensional electron gas in a quantizing magnetic field

    NASA Astrophysics Data System (ADS)

    Côté, R.; Simoneau, Alexandre M.

    2016-02-01

    Transport experiments on the two-dimensional electron gas (2DEG) confined into a semiconductor quantum well and subjected to a quantizing magnetic field have uncovered a rich variety of uniform and nonuniform phases such as the Laughlin liquids, the Wigner, bubble, and Skyrme crystals, and the quantum Hall stripe state. Optically pumped nuclear magnetic resonance (OP-NMR) has also been extremely useful in studying the magnetization and dynamics of electron solids with exotic spin textures such as the Skyrme crystal. Recently, it has been demonstrated that a related technique, resistively-detected nuclear magnetic resonance (RD-NMR), could be a good tool to study the topography of the electron solids in the fractional and integer quantum Hall regimes. In this work, we compute theoretically the RD-NMR line shapes of various crystal phases of the 2DEG and study the relation between their spin density and texture and their NMR spectra. This allows us to evaluate the ability of the RD-NMR to discriminate between the various types of crystal states.

  2. Quasiparticle energies, excitons, and optical spectra of few-layer black phosphorus

    NASA Astrophysics Data System (ADS)

    Tran, Vy; Fei, Ruixiang; Yang, Li

    2015-12-01

    We report first-principles GWBetheSalpeter-equation (BSE) studies of excited-state properties of few-layer black phosphorus (BP) (phosphorene). With improved GW computational methods, we obtained converged quasiparticle band gaps and optical absorption spectra by the single-shot (G0W0) procedure. Moreover, we reveal fine structures of anisotropic excitons, including the series of one-dimensional like wave functions, spin singlettriplet splitting, and electronhole binding energy spectra by solving BSE. An effective-mass model is employed to describe these electronhole pairs, shedding light on estimating the exciton binding energy of anisotropic two-dimensional semiconductors without expensive ab initio simulations. Finally, the anisotropic optical response of BP is explained by using optical selection rules based on the projected single-particle density of states at band edges.

  3. Rydberg-blockade effects in Autler-Townes spectra of ultracold strontium

    NASA Astrophysics Data System (ADS)

    DeSalvo, B. J.; Aman, J. A.; Gaul, C.; Pohl, T.; Yoshida, S.; Burgdörfer, J.; Hazzard, K. R. A.; Dunning, F. B.; Killian, T. C.

    2016-02-01

    We present a combined experimental and theoretical study of the effects of Rydberg interactions on Autler-Townes spectra of ultracold gases of atomic strontium. Realizing two-photon Rydberg excitation via a long-lived triplet state allows us to probe the regime where Rydberg state decay presents the dominant decoherence mechanism. The effects of Rydberg interactions are observed in shifts, asymmetries, and broadening of the measured atom-loss spectra. The experiment is analyzed within a one-body density-matrix approach, accounting for interaction-induced level shifts and dephasing through nonlinear terms that approximately incorporate correlations due to the Rydberg blockade. This description yields good agreement with our experimental observations for short excitation times. For longer excitation times, the loss spectrum is altered qualitatively, suggesting additional dephasing mechanisms beyond the standard blockade mechanism based on pure van der Waals interactions.

  4. Pd(II) phthalocyanine-sensitized triplet-triplet annihilation from rubrene.

    PubMed

    Singh-Rachford, Tanya N; Castellano, Felix N

    2008-04-24

    Upconverted yellow singlet fluorescence from rubrene (5,6,11,12-tetraphenylnapthacene) was generated from selective excitation (lambdaex = 725 nm) of the red light absorbing triplet sensitizer palladium(II) octabutoxyphthalocyanine, PdPc(OBu)8, in vacuum degassed toluene solutions using a Nd:YAG/OPO laser system in concert with gated iCCD detection. The data are consistent with upconversion proceeding from triplet-triplet annihilation (TTA) of rubrene acceptor molecules. The TTA process was confirmed by the quadratic dependence of the upconverted delayed fluorescence intensity with respect to incident light, measured by integrating the corresponding kinetic traces as a function of the incident excitation power. In vacuum degassed toluene solutions, the red-to-yellow upconversion process is stable under continuous long wavelength irradiation and is readily visualized by the naked eye even at modest laser fluence (0.6 mJ/pulse). In aerated solutions, however, selective excitation of the phthalocyanine sensitizer leads to rapid decomposition of rubrene into its corresponding endoperoxide as evidenced by UV-vis (in toluene), 1H NMR (in d6-benzene), and MALDI-TOF mass spectrometry, consistent with the established reactivity of rubrene with singlet dioxygen. The upconversion process in this triplet sensitizer/acceptor-annihilator combination was preliminarily investigated in solid polymer films composed of a 50:50 mixture of an ethyleneoxide/epichlorohydrin copolymer, P(EO/EP). Films that were prepared under an argon atmosphere and maintained under this inert environment successfully achieve the anticipated quadratic incident power dependence, whereas air exposure causes the film to deviate somewhat from this dependence. To the best of our knowledge, the current study represents the first example of photon upconversion using a phthalocyanine triplet sensitizer, furthering the notion that anti-Stokes light-producing sensitized TTA appears to be a general phenomenon as long as proper energy criteria are met. PMID:18336014

  5. Acceleration of guanine oxidation under visible light irradiation by photon upconversion based on triplet-triplet annihilation.

    PubMed

    Tanaka, Kazuo; Kitamura, Narufumi; Inafuku, Kenichi; Chujo, Yoshiki

    2009-01-01

    We report the fluorescent polymer complex which can show fluorescence emission at 380 nm with the excitation of 520 nm in aqueous media. This photon upconversion based on triplet-triplet annihilation can efficiently take place via inter-molecular energy transfers between the Ru complex as a sensitizer and anthracene molecules as an emitter captured into the water-soluble network polymers. We performed the oxidation reaction of 2'-deoxyguanosine by riboflavin in the presence of the polymer complex with the visible light irradiation. It was clearly indicated that oxidative decomposition can be accelerated by UV light generation via upconversion based on triplet-triplet annihilation. PMID:19749321

  6. Reaction of Triplet Phenylnitrene with Molecular Oxygen.

    PubMed

    Mieres-Prez, Joel; Mendez-Vega, Enrique; Velappan, Kavitha; Sander, Wolfram

    2015-12-18

    Triplet carbenes react with molecular oxygen with rates that approach diffusion control to carbonyl O-oxides, whereas triplet nitrenes react much slower. For investigating the reaction of phenylnitrene with O2, the nitrene was generated by flash vacuum thermolysis (FVT) of phenylazide and subsequently isolated in O2-doped matrices. FVT of the azide produces the nitrene in high yield and with only minor contaminations of the rearranged products that are frequently observed if the nitrene is produced by photolysis. The phenylnitrene was isolated in solid Ar, Xe, mixtures of these rare gases with O2, and even in pure solid O2. At temperatures between 30 and 35 K an extremely slow thermal reaction between the nitrene and O2 was observed, whereas at higher temperatures, solid Ar and O2 rapidly evaporate. Only O2-doped Xe matrices allowed us to anneal at temperatures above 40 K, and at these temperatures, the nitrene reacts with O2 to produce nitroso O-oxide mainly in its syn conformation. Upon visible light irradiation (450 nm), the nitroso oxide rapidly rearranges to nitrobenzene. PMID:26524191

  7. Tetralogy of Fallot in monozygotic triplets

    SciTech Connect

    Victorica, B.E.; Kumar, A.; Zori, R.T.

    1994-09-01

    Tetralogy of Fallot (TOF), like most other congenital heart defects, is considered to be of multifactorial inheritance. Occasional families with multiple affected members in one or more generations above been described. A stronger genetic influence in the causation of isolated TOF is also supported by recent demonstration of microdeletions in chromosome 22q11 region. Deletions in this region are also responsible for DiGeorge and velocardiofacial syndrome as well as CHARGE association. We report a set of monozygotic triplets born to healthy parents at 35 weeks of gestation. There was no family history of congenital heart defects. All three had TOF with left aortic arch (documented by cardiac catheterization in 2 and echocardiography in all 3). The degree of right ventricular outflow obstruction varied from mild to complete atresia needing prostaglandin infusion and a subsequent Blalock-Taussig shunt in one. No features of DiGeorge syndrome or any other congenital defects were present. High resolution chromosome analysis of peripheral blood lymphocytes of these infants revealed normal 46,XY male karyotype. Fluorescent in situ hybridization (FISH) using probe D22S75, which maps to chromosome 22q11.2 did not detect any deletion. This pedigree suggests a de novo mutation causing TOF in all 3 monozygotic triplets. Although there is no deletion demonstrable in DiGeorge critical region, a smaller deletion or mutation in this region cannot be excluded.

  8. Reducing the incidence of twins and triplets.

    PubMed

    Wimalasundera, R C; Trew, G; Fisk, N M

    2003-04-01

    Multiple pregnancy rates remain high after assisted conception because of a misconceived assumption that transferring three or more embryos will maximize pregnancy rates. Maternal morbidity is sevenfold greater in multiple pregnancies than in singletons, perinatal mortality rates are fourfold higher for twins and sixfold higher for triplets, while cerebral palsy rates are 1-1.5% in twin and 7-8% in triplet pregnancies. Therefore, multiple pregnancies must be considered a serious adverse outcome of assisted reproductive techniques. Primary prevention of multiple pregnancies is the solution. The overwhelming evidence presented in this chapter demonstrates that limiting the embryo transfer in in vitro fertilization to two embryos would significantly reduce adverse maternal and perinatal outcomes by reducing the incidence of high order multiple pregnancies without reducing take-home-baby rates. Secondary prevention by multifetal pregnancy reduction is effective, but not acceptable to all patients. New developments in blastocyst culture, single embryo transfer, embryo cryopreservation and pre-implantation aneuploidy exclusion, should allow improvements in pregnancy rates without increasing multiple pregnancies. PMID:12758102

  9. Far infrared spectra of solid state L-serine, L-threonine, L-cysteine, and L-methionine in different protonation states.

    PubMed

    Gaillard, Thomas; Trivella, Aurlien; Stote, Roland H; Hellwig, Petra

    2015-11-01

    In this study, experimental far infrared measurements of L-serine, L-threonine, L-cysteine, and L-methionine are presented showing the spectra for the 1.0-13.0 pH range. In parallel, solid state DFT calculations were performed on the amino acid zwitterions in the crystalline form. We focused on the lowest frequency far infrared normal modes, which required the most precision and convergence of the calculations. Analysis of the computational results, which included the potential energy distribution of the vibrational modes, permitted a detailed and almost complete assignment of the experimental spectrum. In addition to characteristic signals of the two main acid-base couples, CO2H/CO2(-) and NH3(+)/NH2, specific side chain contributions for these amino acids, including CCO and CCS vibrational modes were analyzed. This study is in line with the growing application of FIR measurements to biomolecules. PMID:26056980

  10. How to calculate linear absorption spectra with lifetime broadening using fewest switches surface hopping trajectories: A simple generalization of ground-state Kubo theory

    SciTech Connect

    Petit, Andrew S.; Subotnik, Joseph E.

    2014-07-07

    In this paper, we develop a surface hopping approach for calculating linear absorption spectra using ensembles of classical trajectories propagated on both the ground and excited potential energy surfaces. We demonstrate that our method allows the dipole-dipole correlation function to be determined exactly for the model problem of two shifted, uncoupled harmonic potentials with the same harmonic frequency. For systems where nonadiabatic dynamics and electronic relaxation are present, preliminary results show that our method produces spectra in better agreement with the results of exact quantum dynamics calculations than spectra obtained using the standard ground-state Kubo formalism. As such, our proposed surface hopping approach should find immediate use for modeling condensed phase spectra, especially for expensive calculations using ab initio potential energy surfaces.

  11. Dual enhancement of electroluminescence efficiency and operational stability by rapid upconversion of triplet excitons in OLEDs.

    PubMed

    Furukawa, Taro; Nakanotani, Hajime; Inoue, Munetomo; Adachi, Chihaya

    2015-01-01

    Recently, triplet harvesting via a thermally activated delayed fluorescence (TADF) process has been established as a realistic route for obtaining ultimate internal electroluminescence (EL) quantum efficiency in organic light-emitting diodes (OLEDs). However, the possibility that the rather long transient lifetime of the triplet excited states would reduce operational stability due to an increased chance for unwarranted chemical reactions has been a concern. Herein, we demonstrate dual enhancement of EL efficiency and operational stability in OLEDs by employing a TADF molecule as an assistant dopant and a fluorescent molecule as an end emitter. The proper combination of assistant dopant and emitter molecules realized a "one-way" rapid Frster energy transfer of singlet excitons from TADF molecules to fluorescent emitters, reducing the number of cycles of intersystem crossing (ISC) and reverse ISC in the TADF molecules and resulting in a significant enhancement of operational stability compared to OLEDs with a TADF molecule as the end emitter. In addition, we found that the presence of this rapid energy transfer significantly suppresses singlet-triplet annihilation. Using this finely-tuned rapid triplet-exciton upconversion scheme, OLED performance and lifetime was greatly improved. PMID:25673259

  12. Non-linear advanced control of the LHC inner triplet heat exchanger test unit

    NASA Astrophysics Data System (ADS)

    Viuela, E. Blanco; Cubillos, J. Casas; de Prada Moraga, C.; Cristea, S.

    2002-05-01

    The future Large Hadron Collider (LHC) at CERN will include eight interaction region final focus magnet systems, the so-called "Inner Triplet," one on each side of the four beam collision points. The Inner Triplets will be cooled in a static bath of pressurized He II nominally at 1.9 K. This temperature is a control parameter and has very severe constraints in order to avoid the transition from the superconducting to normal resistive state. The main difference in these special zones with respect to a regular LHC cell is higher dynamic heat load unevenly distributed which modifies largely the process characteristics and hence the controller performance. Several control strategies have already been tested at CERN in a pilot plant (LHC String Test) which reproduced a LHC half-cell. In order to validate a common control structure along the whole LHC ring, a Nonlinear Model Predictive Control (NMPC) has been developed and implemented in the Inner Triplet Heat Exchanger Unit (IT-HXTU) at CERN. Automation of the Inner Triplet setup and the advanced control techniques deployed based on the Model Based Predictive Control (MBPC) principle are presented.

  13. Dual enhancement of electroluminescence efficiency and operational stability by rapid upconversion of triplet excitons in OLEDs

    PubMed Central

    Furukawa, Taro; Nakanotani, Hajime; Inoue, Munetomo; Adachi, Chihaya

    2015-01-01

    Recently, triplet harvesting via a thermally activated delayed fluorescence (TADF) process has been established as a realistic route for obtaining ultimate internal electroluminescence (EL) quantum efficiency in organic light-emitting diodes (OLEDs). However, the possibility that the rather long transient lifetime of the triplet excited states would reduce operational stability due to an increased chance for unwarranted chemical reactions has been a concern. Herein, we demonstrate dual enhancement of EL efficiency and operational stability in OLEDs by employing a TADF molecule as an assistant dopant and a fluorescent molecule as an end emitter. The proper combination of assistant dopant and emitter molecules realized a one-way rapid Frster energy transfer of singlet excitons from TADF molecules to fluorescent emitters, reducing the number of cycles of intersystem crossing (ISC) and reverse ISC in the TADF molecules and resulting in a significant enhancement of operational stability compared to OLEDs with a TADF molecule as the end emitter. In addition, we found that the presence of this rapid energy transfer significantly suppresses singlet-triplet annihilation. Using this finely-tuned rapid triplet-exciton upconversion scheme, OLED performance and lifetime was greatly improved. PMID:25673259

  14. Quantum Monte Carlo study of the singlet-triplet transition in ethylene

    SciTech Connect

    El Akramine, Ouafae; Kollias, Alexander C.; Lester, Jr., William A.

    2003-01-23

    A theoretical study is reported of the transition between the ground state ({sup 1}A{sub g}) and the lowest triplet state (1{sup 3}B{sub 1u}) of ethylene based on the diffusion Monte Carlo (DMC) variant of the quantum Monte Carlo method. Using DMC trial functions constructed from Hartree-Fock, complete active space self-consistent field and multi-configuration self-consistent field wave functions, we have computed the atomization energy and the heat of formation of both states, and adiabatic and vertical energy differences between these states using both all-electron and effective core potential DMC. The ground state atomization energy and heat of formation are found to agree with experiment to within the error bounds of the computation and experiment. Predictions by DMC of the triplet state atomization energy and heat of formation are presented. The adiabatic singlet-triplet energy difference is found to differ by 5 kcal/mol from the value obtained in a recent photodissociation experiment.

  15. Integrin triplets of marine sponges in human brain receptor heteromers.

    PubMed

    Tarakanov, Alexander O; Fuxe, Kjell G; Borroto-Escuela, Dasiel O

    2012-09-01

    Based on our theory, we have discovered main triplets of amino acid residues in cell-adhesion receptors of marine sponges, which appear also as homologies in several receptor heteromers of human brain. The obtained results strengthen our hypothesis that these triplets may "guide-and-clasp" receptor-receptor interactions. PMID:22573093

  16. Triplet excimer formation of triphenylamine and related chromophores in polystyrene films

    SciTech Connect

    Burkhart, R.D.; Jhon, Namin )

    1991-09-19

    The phosphorescence of triphenylamine (TPA) and of the (N,N-diphenylamino) phenylmethyl ester of 2-methylpropanoic acid (DAPM) was investigated in polystyrene films at temperatures from 20 to 230 k. Their phosphorescence spectra at low temperatures are similar to those recorded in rigid glassy solvents at 77 K, but as the temperature is raised, a new phosphorescence band at 470 mn grows in and the low-temperature band gradually disappears. The new emission is due to an excimeric triplet since it is similar to one found earlier from the polymeric analogue of DAPM and is also similar to the totally excimeric phosphorescence of crystalline TPA at 77K. Rates of excimer formation and dissociation were determined as a function of temperature as were the corresponding activation energies. Triplet exciton migration is not the rate-limiting step in excimer formation. The activation energies for dissociation of the triplet excimers were found to depend upon the concentration of the amine. For DAPM the evidence suggests that excimers formed in dilute samples are in a strained configuration which relaxes slowly compared to the excimer lifetime.

  17. Solvent effects on the absorption and fluorescence spectra of coumarins 6 and 7 molecules: determination of ground and excited state dipole moment.

    PubMed

    Raikar, U S; Renuka, C G; Nadaf, Y F; Mulimani, B G; Karguppikar, A M; Soudagar, M K

    2006-11-01

    Absorption and fluorescence emission spectra of coumarins 6 and 7 were recorded in solvents with different solvent parameters, viz., dielectric constant epsilon and refractive index n. The fluorescence lifetime of these dyes were measured in butanol at higher values of viscosity over temperature. Experimental ground and excited state dipole moments are determined by means of solvatochromic shift method and also the excited state dipole moments are determined in combination with ground state dipole moments. It was determined that dipole moments of the excited state were higher than those of the ground state in both the molecules. PMID:16524762

  18. Three-Triplet Model with Double SU(3) Symmetry

    DOE R&D Accomplishments Database

    Han, M. Y.; Nambu, Y.

    1965-01-01

    With a view to avoiding some of the kinematical and dynamical difficulties involved in the single triplet quark model, a model for the low lying baryons and mesons based on three triplets with integral charges is proposed, somewhat similar to the two-triplet model introduced earlier by one of us (Y. N.). It is shown that in a U(3) scheme of triplets with integral charges, one is naturally led to three triplets located symmetrically about the origin of I{sub 3} - Y diagram under the constraint that Nishijima-Gell-Mann relation remains intact. A double SU(3) symmetry scheme is proposed in which the large mass splittings between different representations are ascribed to one of the SU(3), while the other SU(3) is the usual one for the mass splittings within a representation of the first SU(3).

  19. Triplet-exciton fine structure of anthracene: high-resolution optical measurements

    NASA Astrophysics Data System (ADS)

    Port, H.; Rund, D.

    1980-01-01

    The optical transitions to the magnetic sublevels of the lowest triplet exciton Davydov component in anthracene are spectrally resolved in photoexcitation at 1.8 K. This allows, for the first time, the direct analysis of the properties of the individual magnetic substates in zero-field and in low magnetic fields. From polarized excitation spectra the ordering of the zero-field spin sublevels and the associated absolute signs of the zero-field splitting parameters are determined. The zerofield intensities are compared with the predictions of spin-orbit coupling theory.

  20. Photoelectron spectra of 2-thiouracil, 4-thiouracil, and 2,4-dithiouracil

    NASA Astrophysics Data System (ADS)

    Ruckenbauer, Matthias; Mai, Sebastian; Marquetand, Philipp; González, Leticia

    2016-02-01

    Ground- and excited-state UV photoelectron spectra of thiouracils (2-thiouracil, 4-thiouracil, and 2,4-dithiouracil) have been simulated using multireference configuration interaction calculations and Dyson norms as a measure for the photoionization intensity. Except for a constant shift, the calculated spectrum of 2-thiouracil agrees very well with experiment, while no experimental spectra are available for the two other compounds. For all three molecules, the photoelectron spectra show distinct bands due to ionization of the sulphur and oxygen lone pairs and the pyrimidine π system. The excited-state photoelectron spectra of 2-thiouracil show bands at much lower energies than in the ground state spectrum, allowing to monitor the excited-state population in time-resolved UV photoelectron spectroscopy experiments. However, the results also reveal that single-photon ionization probe schemes alone will not allow monitoring all photodynamic processes existing in 2-thiouracil. Especially, due to overlapping bands of singlet and triplet states the clear observation of intersystem crossing will be hampered.

  1. Photoelectron spectra of 2-thiouracil, 4-thiouracil, and 2,4-dithiouracil.

    PubMed

    Ruckenbauer, Matthias; Mai, Sebastian; Marquetand, Philipp; Gonzlez, Leticia

    2016-02-21

    Ground- and excited-state UV photoelectron spectra of thiouracils (2-thiouracil, 4-thiouracil, and 2,4-dithiouracil) have been simulated using multireference configuration interaction calculations and Dyson norms as a measure for the photoionization intensity. Except for a constant shift, the calculated spectrum of 2-thiouracil agrees very well with experiment, while no experimental spectra are available for the two other compounds. For all three molecules, the photoelectron spectra show distinct bands due to ionization of the sulphur and oxygen lone pairs and the pyrimidine ? system. The excited-state photoelectron spectra of 2-thiouracil show bands at much lower energies than in the ground state spectrum, allowing to monitor the excited-state population in time-resolved UV photoelectron spectroscopy experiments. However, the results also reveal that single-photon ionization probe schemes alone will not allow monitoring all photodynamic processes existing in 2-thiouracil. Especially, due to overlapping bands of singlet and triplet states the clear observation of intersystem crossing will be hampered. PMID:26896982

  2. The speed limit for protein folding measured by triplettriplet energy transfer

    PubMed Central

    Bieri, Oliver; Wirz, Jakob; Hellrung, Bruno; Schutkowski, Mike; Drewello, Mario; Kiefhaber, Thomas

    1999-01-01

    A direct measure of intramolecular chain diffusion is obtained by the determination of triplettriplet energy-transfer rates between a donor and an acceptor chromophore attached at defined points on a polypeptide chain. Single exponential kinetics of contact formation are observed on the nanosecond time scale for polypeptides in which donor and acceptor are linked by repeating units of glycine and serine residues. The rates depend on the number of peptide bonds (N) separating donor and acceptor and show a maximum for the shortest peptides (N = 3) with a time constant (? = 1/k) of 20 ns. This sets an upper limit for the speed of formation of the first side-chain contacts during protein folding. PMID:10449738

  3. Mouse models of triplet repeat diseases.

    PubMed

    Bates, Gillian P; Hay, David G

    2004-01-01

    Since their discovery in 1991, triplet repeat mutations have been found to be the cause of genomic fragile sites, two of which are linked to mental retardation, myotonic dystrophy, and several late-onset neurodegenerative diseases. In all cases, these mutations exhibit gametic and/or somatic instability once they have expanded into the mutant range. The mutations are located in coding and noncoding gene regions and have been found to act by dominant and recessive mechanisms. A wide range of mouse models has been generated to understand both of the mechanisms that underlie repeat instability and the molecular pathogenesis of the diseases. Mouse models have proved extremely useful in these goals and are now also being used for the preclinical testing of therapeutic compounds. This chapter reviews the successes and limitations of the approaches that have been developed. PMID:15201445

  4. Experimental aspects in acquisition of wide bandwidth solid-state MAS NMR spectra of low-? nuclei with different opportunities on two commercial NMR spectrometers.

    PubMed

    Jakobsen, Hans J; Bildse, Henrik; Gan, Zhehong; Brey, William W

    2011-08-01

    The acquisition and different appearances observed for wide bandwidth solid-state MAS NMR spectra of low-? nuclei, using (14)N as an illustrative nucleus and employing two different commercial spectrometers (Varian, 14.1T and Bruker, 19.6T), have been compared/evaluated and optimized from an experimental NMR and an electronic engineering point of view, to account for the huge differences in these spectra. The large differences in their spectral appearances, employing the recommended/standard experimental set-up for the two different spectrometers, are shown to be associated with quite large differences in the electronic design of the two types of preamplifiers, which are connected to their respective probes through a 50? cable, and are here completely accounted for. This has led to different opportunities for optimum performances in the acquisition of nearly ideal wide bandwidth spectra for low-? nuclei on the two spectrometers by careful evaluation of the length for the 50? probe-to-preamp cable for the Varian system and appropriate changes to the bandwidth (Q) of the NMR probe used on the Bruker spectrometer. Earlier, we reported quite distorted spectra obtained with Varian Unity INOVA spectrometers (at 11.4 and 14.1T) in several exploratory wide bandwidth (14)N MAS NMR studies of inorganic nitrates and amino acids. These spectra have now been compared/evaluated with fully analyzed (14)N MAS spectra correspondingly acquired at 19.6T on a Bruker spectrometer. It is shown that our upgraded version of the STARS simulation/iterative-fitting software is capable of providing identical sets for the molecular spectral parameters and corresponding fits to the experimental spectra, which fully agree with the electronic measurements, despite the highly different appearances for the MAS NMR spectra acquired on the Varian and Bruker spectrometers. PMID:21704544

  5. A theoretical study on the molecular structure of biphenylene in its first excited singlet and triplet states: quantum chemical calculations on the structural changes of an antiaromatic molecule upon excitation

    NASA Astrophysics Data System (ADS)

    Zimmermann, Ralf

    1996-03-01

    The structural changes accompanying the electronic excitation of the antiaromatic biphenylene molecule were studied by semiempirical quantum chemical calculations, using the AM1 hamiltonian with configuration interaction (S 1, S 2, T 1, T 2, X + states). The largest bond length differences of the molecular states investigated were observed within the central four-membered ring. Potential curves of the CC bonds which connect the two benzene rings have been calculated for all molecular states investigated. For the S 0 and S 1 states, potential hypersurfaces, using the two different bond lengths of the central four-membered "cyclobutadiene" subsystem as variables, were presented. Furthermore, the geometry of 1,3-cyclobutadiene in different states (S 0, S 1, T 1, X + states) was investigated with the AM1-CI hamiltonian and compared with recent 6-31G ? MC-SCF ab initio results.

  6. Benzophenone Ultrafast Triplet Population: Revisiting the Kinetic Model by Surface-Hopping Dynamics

    PubMed Central

    2016-01-01

    The photochemistry of benzophenone, a paradigmatic organic molecule for photosensitization, was investigated by means of surface-hopping ab initio molecular dynamics. Different mechanisms were found to be relevant within the first 600 fs after excitation; the long-debated direct (S1 → T1) and indirect (S1 → T2 → T1) mechanisms for population of the low-lying triplet state are both possible, with the latter being prevalent. Moreover, we established the existence of a kinetic equilibrium between the two triplet states, never observed before. This fact implies that a significant fraction of the overall population resides in T2, eventually allowing one to revisit the usual spectroscopic assignment proposed by transient absorption spectroscopy. This finding is of particular interest for photocatalysis as well as for DNA damages studies because both T1 and T2 channels are, in principle, available for benzophenone-mediated photoinduced energy transfer toward DNA. PMID:26821061

  7. Inverted singlet-triplet qubit coded on a two-electron double quantum dot

    NASA Astrophysics Data System (ADS)

    Mehl, Sebastian; DiVincenzo, David P.

    2014-11-01

    The sz=0 spin configuration of two electrons confined at a double quantum dot (DQD) encodes the singlet-triplet qubit (STQ). We introduce the inverted STQ (ISTQ) that emerges from the setup of two quantum dots (QDs) differing significantly in size and out-of-plane magnetic fields. The strongly confined QD has a two-electron singlet ground state, but the weakly confined QD has a two-electron triplet ground state in the sz=0 subspace. Spin-orbit interactions act nontrivially on the sz=0 subspace and provide universal control of the ISTQ together with electrostatic manipulations of the charge configuration. GaAs and InAs DQDs can be operated as ISTQs under realistic noise conditions.

  8. Doping-Induced Ferromagnetism and Possible Triplet Pairing in d4 Mott Insulators

    NASA Astrophysics Data System (ADS)

    Chaloupka, Ji?; Khaliullin, Giniyat

    2016-01-01

    We study the effects of electron doping in Mott insulators containing d4 ions such as Ru4 +, Os4 +, Rh5 +, and Ir5 + with J =0 singlet ground state. Depending on the strength of the spin-orbit coupling, the undoped systems are either nonmagnetic or host an unusual, excitonic magnetism arising from a condensation of the excited J =1 triplet states of t2g 4. We find that the interaction between J excitons and doped carriers strongly supports ferromagnetism, converting both the nonmagnetic and antiferromagnetic phases of the parent insulator into a ferromagnetic metal, and further to a nonmagnetic metal. Close to the ferromagnetic phase, the low-energy spin response is dominated by intense paramagnon excitations that may act as mediators of a triplet pairing.

  9. Benzophenone Ultrafast Triplet Population: Revisiting the Kinetic Model by Surface-Hopping Dynamics.

    PubMed

    Marazzi, Marco; Mai, Sebastian; Roca-Sanjun, Daniel; Delcey, Mickal G; Lindh, Roland; Gonzlez, Leticia; Monari, Antonio

    2016-02-18

    The photochemistry of benzophenone, a paradigmatic organic molecule for photosensitization, was investigated by means of surface-hopping ab initio molecular dynamics. Different mechanisms were found to be relevant within the first 600 fs after excitation; the long-debated direct (S1 ? T1) and indirect (S1 ? T2 ? T1) mechanisms for population of the low-lying triplet state are both possible, with the latter being prevalent. Moreover, we established the existence of a kinetic equilibrium between the two triplet states, never observed before. This fact implies that a significant fraction of the overall population resides in T2, eventually allowing one to revisit the usual spectroscopic assignment proposed by transient absorption spectroscopy. This finding is of particular interest for photocatalysis as well as for DNA damages studies because both T1 and T2 channels are, in principle, available for benzophenone-mediated photoinduced energy transfer toward DNA. PMID:26821061

  10. Doping-Induced Ferromagnetism and Possible Triplet Pairing in d^{4} Mott Insulators.

    PubMed

    Chaloupka, Ji?; Khaliullin, Giniyat

    2016-01-01

    We study the effects of electron doping in Mott insulators containing d^{4} ions such as Ru^{4+}, Os^{4+}, Rh^{5+}, and Ir^{5+} with J=0 singlet ground state. Depending on the strength of the spin-orbit coupling, the undoped systems are either nonmagnetic or host an unusual, excitonic magnetism arising from a condensation of the excited J=1 triplet states of t_{2g}^{4}. We find that the interaction between J excitons and doped carriers strongly supports ferromagnetism, converting both the nonmagnetic and antiferromagnetic phases of the parent insulator into a ferromagnetic metal, and further to a nonmagnetic metal. Close to the ferromagnetic phase, the low-energy spin response is dominated by intense paramagnon excitations that may act as mediators of a triplet pairing. PMID:26799042

  11. Action spectra of photosystems II and I and quantum yield of photosynthesis in leaves in State 1.

    PubMed

    Laisk, Agu; Oja, Vello; Eichelmann, Hillar; Dall'Osto, Luca

    2014-02-01

    The spectral global quantum yield (YII, electrons/photons absorbed) of photosystem II (PSII) was measured in sunflower leaves in State 1 using monochromatic light. The global quantum yield of PSI (YI) was measured using low-intensity monochromatic light flashes and the associated transmittance change at 810nm. The 810-nm signal change was calibrated based on the number of electrons generated by PSII during the flash (4O2 evolution) which arrived at the PSI donor side after a delay of 2ms. The intrinsic quantum yield of PSI (yI, electrons per photon absorbed by PSI) was measured at 712nm, where photon absorption by PSII was small. The results were used to resolve the individual spectra of the excitation partitioning coefficients between PSI (aI) and PSII (aII) in leaves. For comparison, pigment-protein complexes for PSII and PSI were isolated, separated by sucrose density ultracentrifugation, and their optical density was measured. A good correlation was obtained for the spectral excitation partitioning coefficients measured by these different methods. The intrinsic yield of PSI was high (yI=0.88), but it absorbed only about 1/3 of quanta; consequently, about 2/3 of quanta were absorbed by PSII, but processed with the low intrinsic yield yII=0.63. In PSII, the quantum yield of charge separation was 0.89 as detected by variable fluorescence Fv/Fm, but 29% of separated charges recombined (Laisk A, Eichelmann H and Oja V, Photosynth. Res. 113, 145-155). At wavelengths less than 580nm about 30% of excitation is absorbed by pigments poorly connected to either photosystem, most likely carotenoids bound in pigment-protein complexes. PMID:24333386

  12. Effects of state-selective charge-exchange processes on the He-like spectra from the Alcator C tokamak

    SciTech Connect

    Kato, T.; Masai, K. ); Fujimoto, T. ); Koike, F. ); Kaellne, E. ); Marmar, E.S.; Rice, J.E. )

    1991-11-15

    The effects of a low-energy charge-exchange process between hydrogenlike ions and neutral hydrogen on x-ray spectra of He-like argon ions from the Alcator C tokamak are investigated. Dependences of charge-exchange cross sections on both the principal and angular momentum quantum numbers {ital n} and {ital l} are estimated from the observed spectra, taking cascade effects into account with the use of a collisional radiative model.

  13. Temperature dependent fluorescence spectra arise from change in excited-state intramolecular proton transfer potential of 4?-N,N-dimethylamino-3-hydroxyflavone-doped acetonitrile crystals

    NASA Astrophysics Data System (ADS)

    Furukawa, Kazuki; Yamamoto, Norifumi; Hino, Kazuyuki; Sekiya, Hiroshi

    2016-01-01

    The effect of intermolecular interaction on excited-state intramolecular proton transfer (ESIPT) in 4?-N,N-dimethylamino-3-hydroxyflavone (DMHF) doped in acetonitrile crystals was investigated by measuring the temperature dependence of fluorescence excitation and fluorescence spectra. A solid/solid phase transition of DMHF-doped acetonitrile crystals occurred in the temperature between 210 and 218 K. Significant differences in the spectral profiles and shifts in the fluorescence spectra were observed in the low- and high-temperature regions of the phase transition. The temperature dependence of the ESIPT potential of DMHF is discussed.

  14. Signatures of triplet supercurrents in hybrid S/F structures

    NASA Astrophysics Data System (ADS)

    Richard, Caroline; Houzet, Manuel; Meyer, Julia; Spsms-Cea/Ujf Grenoble Team

    2014-03-01

    While ferromagnetism and conventional superconductivity appear as antagonist phases, the proximity effect in hybrid S/F structures offers a unique opportunity to study their interplay. In particular, spin-triplet odd-frequency superconducting correlations may be induced in a diffusive ferromagnet. We study the Josephson effect through a long ferromagnetic bilayer in the diffusive regime. For a non-collinear magnetization of the bilayer, we find that the current phase relation is dominated by its second harmonic, and corresponds to the long-range coherent propagation of two triplet pairs. Here, the superharmonicity is a signature of the Josephson coupling between a singlet superconductor and an effective triplet superconductor induced at the end of the ferromagnetic bilayer attached to the other lead. Then, we further study the critical current flowing between such two effective triplet reservoirs through a conventional superconducting layer. As a result of the competition between triplet/triplet and triplet/singlet couplings and under quite general conditions, we find that the critical current exhibits a maximum in the vicinity of the superconducting transition of the central layer.

  15. Potential energy surface of triplet N2O2.

    PubMed

    Varga, Zoltan; Meana-Paeda, Rubn; Song, Guoliang; Paukku, Yuliya; Truhlar, Donald G

    2016-01-14

    We present a global ground-state triplet potential energy surface for the N2O2 system that is suitable for treating high-energy vibrational-rotational energy transfer and collision-induced dissociation. The surface is based on multi-state complete-active-space second-order perturbation theory/minimally augmented correlation-consistent polarized valence triple-zeta electronic structure calculations plus dynamically scaled external correlation. In the multireference calculations, the active space has 14 electrons in 12 orbitals. The calculations cover nine arrangements corresponding to dissociative diatom-diatom collisions of N2, O2, and nitric oxide (NO), the interaction of a triatomic molecule (N2O and NO2) with the fourth atom, and the interaction of a diatomic molecule with a single atom (i.e., the triatomic subsystems). The global ground-state potential energy surface was obtained by fitting the many-body interaction to 54?889 electronic structure data points with a fitting function that is a permutationally invariant polynomial in terms of bond-order functions of the six interatomic distances. PMID:26772574

  16. Potential energy surface of triplet N2O2

    NASA Astrophysics Data System (ADS)

    Varga, Zoltan; Meana-Pañeda, Rubén; Song, Guoliang; Paukku, Yuliya; Truhlar, Donald G.

    2016-01-01

    We present a global ground-state triplet potential energy surface for the N2O2 system that is suitable for treating high-energy vibrational-rotational energy transfer and collision-induced dissociation. The surface is based on multi-state complete-active-space second-order perturbation theory/minimally augmented correlation-consistent polarized valence triple-zeta electronic structure calculations plus dynamically scaled external correlation. In the multireference calculations, the active space has 14 electrons in 12 orbitals. The calculations cover nine arrangements corresponding to dissociative diatom-diatom collisions of N2, O2, and nitric oxide (NO), the interaction of a triatomic molecule (N2O and NO2) with the fourth atom, and the interaction of a diatomic molecule with a single atom (i.e., the triatomic subsystems). The global ground-state potential energy surface was obtained by fitting the many-body interaction to 54 889 electronic structure data points with a fitting function that is a permutationally invariant polynomial in terms of bond-order functions of the six interatomic distances.

  17. Triplet correlations among similarly tuned cells impact population coding.

    PubMed

    Cayco-Gajic, Natasha A; Zylberberg, Joel; Shea-Brown, Eric

    2015-01-01

    Which statistical features of spiking activity matter for how stimuli are encoded in neural populations? A vast body of work has explored how firing rates in individual cells and correlations in the spikes of cell pairs impact coding. Recent experiments have shown evidence for the existence of higher-order spiking correlations, which describe simultaneous firing in triplets and larger ensembles of cells; however, little is known about their impact on encoded stimulus information. Here, we take a first step toward closing this gap. We vary triplet correlations in small (approximately 10 cell) neural populations while keeping single cell and pairwise statistics fixed at typically reported values. This connection with empirically observed lower-order statistics is important, as it places strong constraints on the level of triplet correlations that can occur. For each value of triplet correlations, we estimate the performance of the neural population on a two-stimulus discrimination task. We find that the allowed changes in the level of triplet correlations can significantly enhance coding, in particular if triplet correlations differ for the two stimuli. In this scenario, triplet correlations must be included in order to accurately quantify the functionality of neural populations. When both stimuli elicit similar triplet correlations, however, pairwise models provide relatively accurate descriptions of coding accuracy. We explain our findings geometrically via the skew that triplet correlations induce in population-wide distributions of neural responses. Finally, we calculate how many samples are necessary to accurately measure spiking correlations of this type, providing an estimate of the necessary recording times in future experiments. PMID:26042024

  18. Triplet correlations among similarly tuned cells impact population coding

    PubMed Central

    Cayco-Gajic, Natasha A.; Zylberberg, Joel; Shea-Brown, Eric

    2015-01-01

    Which statistical features of spiking activity matter for how stimuli are encoded in neural populations? A vast body of work has explored how firing rates in individual cells and correlations in the spikes of cell pairs impact coding. Recent experiments have shown evidence for the existence of higher-order spiking correlations, which describe simultaneous firing in triplets and larger ensembles of cells; however, little is known about their impact on encoded stimulus information. Here, we take a first step toward closing this gap. We vary triplet correlations in small (approximately 10 cell) neural populations while keeping single cell and pairwise statistics fixed at typically reported values. This connection with empirically observed lower-order statistics is important, as it places strong constraints on the level of triplet correlations that can occur. For each value of triplet correlations, we estimate the performance of the neural population on a two-stimulus discrimination task. We find that the allowed changes in the level of triplet correlations can significantly enhance coding, in particular if triplet correlations differ for the two stimuli. In this scenario, triplet correlations must be included in order to accurately quantify the functionality of neural populations. When both stimuli elicit similar triplet correlations, however, pairwise models provide relatively accurate descriptions of coding accuracy. We explain our findings geometrically via the skew that triplet correlations induce in population-wide distributions of neural responses. Finally, we calculate how many samples are necessary to accurately measure spiking correlations of this type, providing an estimate of the necessary recording times in future experiments. PMID:26042024

  19. Fluorescence excitation and ultraviolet absorption spectra and theoretical calculations for benzocyclobutane: Vibrations and structure of its excited S1(?,?*) electronic state

    PubMed Central

    Shin, Hee Won; Ocola, Esther J.; Kim, Sunghwan; Laane, Jaan

    2014-01-01

    The fluorescence excitation spectra of jet-cooled benzocyclobutane have been recorded and together with its ultraviolet absorption spectra have been used to assign the vibrational frequencies for this molecule in its S1(?,?*) electronic excited state. Theoretical calculations at the CASSCF(6,6)/aug-cc-pVTZ level of theory were carried out to compute the structure of the molecule in its excited state. The calculated structure was compared to that of the molecule in its electronic ground state as well as to the structures of related molecules in their S0 and S1(?,?*) electronic states. In each case the decreased ? bonding in the electronic excited states results in longer carbon-carbon bonds in the benzene ring. The skeletal vibrational frequencies in the electronic excited state were readily assigned and these were compared to the ground state and to the frequencies of five similar molecules. The vibrational levels in both S0 and S1(?,?*) states were remarkably harmonic in contrast to the other bicyclic molecules. The decreases in the frequencies of the out-of-plane skeletal modes reflect the increased floppiness of these bicyclic molecules in their S1(?,?*) excited state. PMID:25669377

  20. Fluorescence excitation and ultraviolet absorption spectra and theoretical calculations for benzocyclobutane: Vibrations and structure of its excited S{sub 1}(π,π{sup *}) electronic state

    SciTech Connect

    Shin, Hee Won; Ocola, Esther J.; Laane, Jaan; Kim, Sunghwan

    2014-01-21

    The fluorescence excitation spectra of jet-cooled benzocyclobutane have been recorded and together with its ultraviolet absorption spectra have been used to assign the vibrational frequencies for this molecule in its S{sub 1}(π,π{sup *}) electronic excited state. Theoretical calculations at the CASSCF(6,6)/aug-cc-pVTZ level of theory were carried out to compute the structure of the molecule in its excited state. The calculated structure was compared to that of the molecule in its electronic ground state as well as to the structures of related molecules in their S{sub 0} and S{sub 1}(π,π{sup *}) electronic states. In each case the decreased π bonding in the electronic excited states results in longer carbon-carbon bonds in the benzene ring. The skeletal vibrational frequencies in the electronic excited state were readily assigned and these were compared to the ground state and to the frequencies of five similar molecules. The vibrational levels in both S{sub 0} and S{sub 1}(π,π{sup *}) states were remarkably harmonic in contrast to the other bicyclic molecules. The decreases in the frequencies of the out-of-plane skeletal modes reflect the increased floppiness of these bicyclic molecules in their S{sub 1}(π,π{sup *}) excited state.