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Near-Infrared Time-Resolved Study of the S 1 State Dynamics of the Carotenoid Spheroidene

2001; American Chemical Society; Volume: 105; Issue: 5 Linguagem: Inglês

10.1021/jp002206s

1520-6106

Tomáš Polı́vka, Donatas Zigmantas, Harry A. Frank, James A. Bautista, Jennifer L. Herek, Yasushi Koyama, Ritsuko Fujii, Villy Sundström,

Molecular spectroscopy and chirality

Using a novel experimental approach based on near-infrared femtosecond absorption spectroscopy, 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 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 coexisting in the S1 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 S2 state. Ultrafast S2→S1 internal conversion occurs within the first 300 fs, followed by vibrational cooling in the S1 state, which occurs on a time scale of ∼700 fs. The S1 lifetime is 8 ps at 293 K, in good agreement with previous measurements of the S1 → SN transition. A somewhat longer S1 lifetime of 9.5 ps is observed at 186 K.