Photophysical characterization of natural cis-carotenoids

Andersson, PA (författare)

Takaichi, S (författare)

Cogdell, RJ (författare)

(creator_code:org_t)

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Abstract Ämnesord

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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.

Av författaren/redakt...: Andersson, PA; Takaichi, S; Cogdell, RJ; Gillbro, Tomas

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