| 1. |
- Billsten, Helena, et al.
(författare)
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Dynamics of vibrational relaxation in the S-1 state of carotenoids having 11 conjugated C=C bonds
- 2002
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Ingår i: Chemical Physics Letters. - 0009-2614. ; 355:5-6, s. 465-470
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Tidskriftsartikel (refereegranskat)abstract
- Transient absorption spectra and kinetics in the 470-650 nm region were recorded for lycopene, P-carotene and zeaxanthin, all carotenoids with 11 conjugated double bonds, in two solvents with different polarity. Analysis of the red wing of the carotenoid SI-S, transition revealed presence of a pronounced shoulder at early delay times. The kinetics recorded at this low-energy shoulder of the SI-S, transition yields an additional decay component of 500-800 fs in addition to the main S, decay. This dynamics is ascribed to a vibrational relaxation in the S, state of the carotenoids. (C) 2002 Elsevier Science B.V. All rights reserved.
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| 2. |
- Papagiannakis, E, et al.
(författare)
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A Near-Infrared Transient Absorption Study of the Excited-State Dynamics of the Carotenoid Spirilloxanthin in Solution and in the LH1 Complex of Rhodospirillum rubrum.
- 2003
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 107:40, s. 11216-11223
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Tidskriftsartikel (refereegranskat)abstract
- The spectroscopic properties of spirilloxanthin in an nhexane solution and bound to the core light-harvesting LH1) complex of Rhodospirillum rubrum were studied by near infrared ultrafast transient absorption spectroscopy. Global analysis of the kinetic traces measured after excitation of spirilloxanthin to the S2 (1Bu +) state enabled us to estimate the species-associated difference spectra that correspond to the excited-state absorption signals originating from the S1 (2Ag-) and S2 states. Analysis of the absorption originating from the S2 state has provided further insight into the characterization of the spirilloxanthin excited states, while by analyzing the profile of the S1-S2 transition, we place the energy of the S1 state of all-trans-spirilloxanthin at 11 500 cm-1, both in solution and in the LH1 complex. This low value excludes excitation energy transfer from the S1 state of spirilloxanthin to bacteriochlorophyll in the LH1 complex of Rs. rubrum and explains the observed low energy transfer efficiency from spirilloxanthin to bacteriochlorophyll in that complex. Our results indicate that the S* state of spirilloxanthin, which was recently found both in solution and in the LH1 complex (Gradinaru, C. C., et al. Proc. Natl. Acad. Sci. U.S.A. 2001, 98, 2364), does not exhibit detectable spectral features in the near-infrared region.
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| 3. |
- Polivka, Tomas, et al.
(författare)
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Carotenoid S(1) state in a recombinant light-harvesting complex of Photosystem II.
- 2002
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Ingår i: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 41:2, s. 439-450
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Tidskriftsartikel (refereegranskat)abstract
- The carotenoid species lutein, violaxanthin, and zeaxanthin are crucial in the xanthophyll-dependent nonphotochemical quenching occurring in photosynthetic systems of higher plants, since they are involved in dissipation of excess energy and thus protect the photosynthetic machinery from irreversible inhibition. Nonetheless, important properties of the xanthophyll cycle carotenoids, such as the energy of their S(1) electronic states, are difficult to study and were only recently determined in organic solvents [Polívka, T. (1999) Proc. Natl. Acad. Sci. U.S.A. 96, 4914. Frank, H. A. (2000) Biochemistry 39, 2831]. In the present study, we have determined the S(1) energies of three carotenoid species, violaxanthin, lutein, and zeaxanthin, in their LHCII (peripheral light-harvesting complex of photosystem II) protein environment by constructing recombinant Lhcb1 (Lhc = light-harvesting complex) proteins containing single carotenoid species. Within experimental error the S(1) energy is the same for all three carotenoids in the monomeric LHCII, 13,900 +/- 300 cm(-1) (720 +/- 15 nm), thus well below the Q(y)() transitions of chlorophylls. In addition, we have found that, although the S(1) lifetimes of violaxanthin, lutein, and zeaxanthin differ substantially in solution, when incorporated into the LHCII protein, their S(1) states have in fact the same lifetime of about 11 ps. Despite the similar spectroscopic properties of the carotenoids bound to the LHCII, we observed a maximal fluorescence quenching when zeaxanthin was present in the LHCII complex. On the basis of these observations, we suggest that, rather than different photochemical properties of individual carotenoid species, changes in the protein conformation induced by binding of carotenoids with distinct molecular structures are involved in the quenching phenomena associated with Lhc proteins.
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| 4. |
- Polívka, Tomáš, et al.
(författare)
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Direct observation of the S1 level of the carotenoid spheroidene using near-infrared femtosecond spectroscopy
- 2001
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Ingår i: Ultrafast Phenomena XII. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 9783642625121 - 9783642565465 ; 66, s. 668-670
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Bokkapitel (refereegranskat)abstract
- In this work, we have determined the energy of the S1 state of the carotenoid spheroidene. The energy of this state is 13,400 ± 90 cm-1 at both 293 K and 186 K, showing that there is no temperature-induced shift of the S1 level. A discrepancy of about 800 cm-1 between the S1 energy determined here and that obtained from previous fluorescence and resonance Raman measurements is explained in terms of the different conformational species co-existing in the S1 excited state.
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| 5. |
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| 6. |
- Polívka, Tornáš, et al.
(författare)
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Near-infrared time-resolved study of the S-1 state dynamics of the carotenoid spheroidene
- 2001
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 105:5, s. 1072-1080
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Tidskriftsartikel (refereegranskat)abstract
- Using a novel experimental approach based on near-infrared femtosecond absorption spectroscopy, we have determined the energy of the S-1 state of the carotenoid spheroidene. The energy of this state is 13 400 +/- 90 cm(-1) at both 293 and 186 K, showing that there is no temperature-induced shift of the S-1 level. A discrepancy of about 800 cm(-1) between the S-1 energy determined here and that obtained from previous fluorescence and resonance Raman measurements is explained in terms of the different conformational species coexisting in the S-1 excited state. Measurements of kinetics in the near-infrared region revealed that at least three relaxation processes take place after excitation of spheroidene into its S-2 state. Ultrafast S-2 --> S-1 internal conversion occurs within the first 300 fs, followed by vibrational cooling in the SI state, which occurs on a time scale of similar to 700 fs. The S-1 lifetime is 8 ps at 293 K, in good agreement with previous measurements of the S-1 --> S-N transition. A somewhat longer S-1 lifetime of 9.5 ps is observed at 186 K.
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| 7. |
- Polivka, Tomas, et al.
(författare)
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The carotenoid S-1 state in LH2 complexes from purple bacteria Rhodobacter sphaeroides and Rhodopseudomonas acidophila: S-1 energies, dynamics, and carotenoid radical formation
- 2002
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 106:42, s. 11016-11025
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Tidskriftsartikel (refereegranskat)abstract
- Using near-infrared femtosecond absorption spectroscopy, we have determined the S-1 energies of the carotenoids spheroidene and rhodopin glucoside in LH2 complexes of purple bacteria. The S-1 energies in the LH2 complexes yield values of 13400 +/- 100 cm(-1) for spheroidene and 12550 +/- 150 cm(-1) for rhodopin glucoside, which are very close to the S-1 energies obtained for both carotenoids in solution. The 850 cm(-1) difference between the S-1 energies of these two carotenoids significantly affects the energy transfer pathways within the LH2 complexes. The S-1 energy of spheroidene in the LH2 complex of Rhodobacter (Rb.) sphaeroides is high enough to allow efficient energy transfer from the S, state to bacteriochlorophylls, resulting in a substantial shortening of the spheroidene S-1 lifetime in the LH2 complex (1.7 ps) compared with the lifetime in solution (8.5 ps). Rhodopin glucoside, which occurs in Rhodopseudomonas (Rps.) acidophila, has an S-1 energy in the LH2 complex too low for efficient S-1-mediated energy transfer and therefore the S-2 state becomes the main energy donor in LH2 complexes containing this carotenoid. In addition, a distinct carotenoid spectral band not observed in solution, was detected at around 960 nm in the LH2 complex of Rb. sphaeroides. This band is assigned to a spheroidene radical cation, which is formed in similar to200 fs and decays within 8 ps. The yield of the spheroidene radical formation is estimated to be in the range of 5-8%.
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| 8. |
- Ruseckas, A., et al.
(författare)
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Luminescence from inter-chain aggregates in polythiophene films
- 2001
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Ingår i: Synthetic Metals. - 0379-6779 .- 1879-3290. ; 119:1-3, s. 603-604
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Tidskriftsartikel (refereegranskat)abstract
- We report time-resolved photoluminescence of two polythiophene derivatives with different chain packing. Emission of inter-chain aggregates is distinguished from that of intra-chain singlet excitons. The aggregate luminescence is shifted towards lower energies relative to that of intra-chain exciton by 0.17 eV, and the Huang-Rhys factor of the coupling to the intra-chain C double bondC vibration is S = 1.5. The excitonic coupling in aggregates is of intermediate strength.
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| 9. |
- Ruseckas, Arvydas, et al.
(författare)
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Luminescence quenching by inter-chain aggregates in substituted polythiophenes
- 2001
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Ingår i: Journal of Photochemistry and Photobiology, A: Chemistry. - 1873-2666 .- 1010-6030. ; 144:1, s. 3-12
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Tidskriftsartikel (refereegranskat)abstract
- Time-resolved photo luminescence spectra measured in solid films of two polythiophene derivatives with different chain packing allow to distinguish emission of intra-chain excitations from the luminescence of inter-chain aggregates. Aggregate luminescence is red shifted by about 0.1 eV relative to intra-chain emission and shows vibronic coupling to the C=C bond stretch with the Huang-Phys factor of S approximate to 1.5, which is twice bigger than that of the intra-chain emission. Combining time resolved luminescence data with femtosecond transient absorption, we show that the dynamic quenching of the luminescence in films with dense chain packing is mainly due to excitation energy transfer to aggregates. The radiative lifetime of the lowest excited state of the aggregate with the optical gap of 1.84-1.9 eV is estimated to be about 20 ns. The aggregate contribution to the total luminescence in the polythiophene films with dense chain packing is about 50% and does not change significantly with temperature. (C) 2001 Elsevier Science B.V. All rights reserved.
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| 10. |
- Theander, M., et al.
(författare)
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High luminescence from a substituted polythiophene in a solvent with low solubility
- 2001
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Ingår i: Chemical Physics Letters. - 0009-2614 .- 1873-4448. ; 337:4-6, s. 277-283
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Tidskriftsartikel (refereegranskat)abstract
- Steady-state and rime-resolved photoluminescence (PL) is used to probe different states of order in highly regular poly(3-(2'-methoxy-5'-octylphenyl)thiophene) (POMeOPT). In a good solvent (chloroform) the polymer has a PL yield of 0.33 and in a solvent with low solubility (mixture of chloroform and toluene) a new phase appears with higher PL yield (0.50). The new phase is attributed to micro-crystals formed by the regular part of the polymer which have low solubility in toluene. The crystallites have highly structured and redshifted electronic transitions compared with chains which are dissolved. (C) 2001 Published by Elsevier Science B.V.
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