Hannover 2010 – scientific programme
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MO: Fachverband Molekülphysik
MO 14: Femtosecond Spectroscopy II
MO 14.3: Talk
Wednesday, March 10, 2010, 14:45–15:00, F 102
New insights into the excited state relaxation network by simulation of Pump-DFWM in carotenoids — •Marie Marek1,2, Tiago Buckup1,2, and Marcus Motzkus1,2 — 1Physikalisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, D-69120 Heidelberg, Germany — 2Physikalische Chemie, Philipps-Universität, D-35043 Marburg, Germany
Carotenoids are together with chlorophylls the most abundant natural pigments and play a key role in photosynthetic light-harvesting complexes. However, the exact relaxation following excitation with visible light is still not clear, despite extensive spectroscopic investigations. For the exploration of the excited states dynamics of these complex molecules we used pump-degenerate four wave mixing (pump-DFWM). Pump-DFWM is a two-dimensional technique where the system is promoted to the excited state by an initial pump pulse and the subsequent dynamics is probed by a DFWM sequence. By simulating the pump-DFWM signal of several carotenoids, namely β-carotene and lycopene, and comparing the results with the experimental data we gain detailed knowledge about the internal conversion between the S2 and S1 state. We observe an additional very fast component directly after excitation of S2 in both carotenoids. For lycopene, this component is populated from the S2 state in an ultrashort time scale with a time constant of about 20 fs and which decays to S1 with the 140 fs generally ascribed to the S2 lifetime. We discuss the nature of this component with respect to new theoretical and experimental investigations.[1]
[1] E. Ostroumov et al., PRL 103 (2009) 108302.