| 1. |
- Andersson, PA, et al.
(författare)
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Photophysical characterization of natural cis-carotenoids
- 2001
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Ingår i: PHOTOCHEMISTRY AND PHOTOBIOLOGY. - 0031-8655. ; 74:4, s. 549-57
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Tidskriftsartikel (refereegranskat)abstract
- By means of steady-state fluorescence spectroscopy we explore the photophysics of two lowest lying singlet excited states in two natural 15-cis-carotenoids, namely phytoene and phytofluene, possessing three and five conjugated double bonds (N), respectively. The results are interpreted in relation to the photophysics of all-trans-carotenoids with varying N. The fluorescence of phytofluene is more Stokes-shifted relative to that of phytoene, and is ascribed to the forbidden S-1 --> S-0 transition, with its first excited singlet state (S-1) lying 3340 cm(-1) below the dipole allowed second excited singlet state (S-2), at 77 K. For phytoene the S-2 and S-1 potential surfaces are closer in energy, probably giving rise to the mixed S-2 and S-1 fluorescence characteristics. The origin of phytoene fluorescence is discussed and is suggested to be due to the S-1 --> S-0 transition; with the S-1 state located 1100 cm(-1) below S-2 at 77 K. The dependence of the fluorescence quantum yield on temperature and viscosity shows that large amplitude molecular motions are involved in the radiationless relaxation process of phytoene. The transition dipole moment of absorption and emission are parallel in phytoene and nonparallel in phytofluene.
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| 2. |
- 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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