title: Ultrafast excited state dynamics of fucoxanthin: excitation energy dependent intramolecular charge transfer dynamics.
abstract: Carotenoids containing a carbonyl group in conjugation with their polyene backbone are naturally-occurring pigments in marine organisms and are essential to the photosynthetic light-harvesting function in aquatic algae. These carotenoids exhibit spectral characteristics attributed to an intramolecular charge transfer (ICT) state that arise in polar solvents due to the presence of the carbonyl group. Here, we report the spectroscopic properties of the carbonyl carotenoid fucoxanthin in polar (methanol) and nonpolar (cyclohexane) solvents studied by steady-state absorption and femtosecond pump-probe measurements. Transient absorption associated with the optically forbidden S(1) (2(1)A) state and/or the ICT state were observed following one-photon excitation to the optically allowed S(2) (1(1)B) state in methanol. The transient absorption measurements carried out in methanol showed that the ratio of the ICT-to-S(1) state formation increased with decreasing excitation energy. We also showed that the ICT character was clearly visible in the steady-state absorption in methanol based on a Franck-Condon analysis. The results suggest that two spectroscopic forms of fucoxanthin, blue and red, exist in the polar environment.
authors.affiliation: Department of Physics, Graduate School of Science, Osaka City University, 3-3-138 Sugimoto, Osaka 558-8585, Japan. kosumi@sci.osaka-cu.ac.jp
authors.forename: Daisuke
authors.initials: D
authors.lastname: Kosumi
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Kusumoto
authors.forename: Ritsuko
authors.initials: R
authors.lastname: Fujii
authors.forename: Mitsuru
authors.initials: M
authors.lastname: Sugisaki
authors.forename: Yoshiro
authors.initials: Y
authors.lastname: Iinuma
authors.forename: Naohiro
authors.initials: N
authors.lastname: Oka
authors.forename: Yuki
authors.initials: Y
authors.lastname: Takaesu
authors.forename: Tomonori
authors.initials: T
authors.lastname: Taira
authors.forename: Masahiko
authors.initials: M
authors.lastname: Iha
authors.forename: Harry A
authors.initials: HA
authors.lastname: Frank
authors.forename: Hideki
authors.initials: H
authors.lastname: Hashimoto
mesh_terms: D004735:Energy Transfer; D056004:Molecular Dynamics Simulation; D024341:Xanthophylls / Q000737:chemistry*
chemical_list: D024341:Xanthophylls; C025164:fucoxanthin