Dresden 2011 – scientific programme
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MO: Fachverband Molekülphysik
MO 9: Femtosecond Spectroscopy II
MO 9.7: Talk
Tuesday, March 15, 2011, 12:15–12:30, TOE 317
Dependence of the ultrafast initial dynamics of carotenoids on the conjugation length (N) studied by multidimensional spectroscopy — •Marie S. Marek, Tiago Buckup, and Marcus Motzkus — Physikalisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, D-69120 Heidelberg, Germany.
Determination of the detailed energy dissipation pathway in carotenoids following photoexcitation proved to be particularly challenging for optical spectroscopy. Specifically the question whether additional dark states between the well known S2 and S1 states participate in the relaxation is highly controversial. Application of pump-degenerate four wave mixing (pump-DFWM) to β-carotene and lycopene in combination with numerical simulations based on the Brownian oscillator model already gave strong evidence for an additional electronic state located energetically below S2 and playing a role in the deactivation process. Here, we further investigate the interplay between the conjugation length N of carotenoids and the involved electronic states in the very early dynamics by using DFWM and pump-DFWM. We concentrate on carotenoids with N = 10 (spheroidene) and 11 (lycopene), for which a crossing of the S2 state with dark states is proposed. Raman active modes in spheroidene and lycopene differ on the dependence of their amplitude and frequency on the population relaxation. For spheroidene, high-frequency Raman active modes are present directly after the excitation of S2 and show almost no dependence on the population relaxation. This is in contrast to lycopene, where state specific modes can be identified.