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  • Solvent-dependent activation of intermediate excited states in the energy relaxation pathways of spheroidene.

Solvent-dependent activation of intermediate excited states in the energy relaxation pathways of spheroidene.

Physical chemistry chemical physics : PCCP (2012-02-15)
Margherita Maiuri, Dario Polli, Daniele Brida, Larry Lüer, Amy M LaFountain, Marcel Fuciman, Richard J Cogdell, Harry A Frank, Giulio Cerullo
ABSTRACT

In carotenoids internal conversion between the allowed (S(2)) and forbidden (S(1)) excited states occurs on a sub-picosecond timescale; the involvement of an intermediate excited state(s) (S(x)) mediating the process is controversial. Here we use high time resolution (sub-20 fs) broadband (1.2-2.5 eV) pump-probe spectroscopy to study the solvent dependence of excited state dynamics of spheroidene, a naturally-occurring carotenoid with ten conjugated double bonds. In the high polarizability solvent, CS(2), we find no evidence of an intermediate state, and the traditional three-level (S(0), S(1), S(2)) model fully accounts for the S(2)→ S(1) process. On the other hand, in the low polarizability solvent, cyclohexane, we find that rapid (~30 fs) relaxation to an intermediate state, S(x), lying between S(1) and S(2) is required to account for the data. We interpret these results as due to a shift of the S(2) energy, which positions the state above or below the energy of S(x) in response to changes in solvent polarizability.

MATERIALS
Product Number
Brand
Product Description

Supelco
Carbon disulfide solution, certified reference material, 5000 μg/mL in methanol
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