Hamburg 2009 – wissenschaftliches Programm
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MO: Fachverband Molekülphysik
MO 13: Molekülphysik Poster 1
MO 13.30: Poster
Dienstag, 3. März 2009, 16:30–19:00, VMP 8 Foyer
Optically ‘Dark’ States of Xanthophylls in the Major Plant Light-Harvesting Complex Studied by Femtosecond Two-Photon Excitation Spectroscopy — •Alexander Betke1, Bernd Voigt1, Heiko Lokstein1,2, and Ralf Menzel1 — 1Institut für Physik und Astronomie / Photonik, Universität Potsdam — 2Institut für Biochemie und Biologie, Universität Potsdam
Carotenoids (Xanthophylls) play crucial roles in photosynthesis: i.e., as accessory light-harvesting pigments and photoprotectors. To understand these functions it is vital to know the energetic positions of their lowest excited singlet states, S1 (21 Ag−). Since one-photon absorption is forbidden for the S0 (21 Ag−) → S1 (21 Ag−) transition, the xanthophyll S1 state is optically ‘dark’ and cannot be readily investigated by conventional spectroscopic techniques. This transition, however, is two-photon allowed. Two-photon absorption (TPA) of tunable near-infrared fs-pulses is used to investigate the role of the xanthophylls ‘dark’ states in excitation energy transfer (EET) and dissipation in light-harvesting complexes. TPA can either be monitored by chlorophyll fluorescence (provided that EET onto chlorophyll occurs) or by probing transient absorption changes. A detailed study of two-photon-excitation of the plant major light-harvesting complex (LHC II) containing different xanthophyll-cycle pigment complements (violaxanthin, zeaxanthin) and of these pigments in solution will be given using both techniques. Implications for the photoprotective non-photochemical quenching (NPQ) mechanism will be discussed. This research is supported by the DFG (SFB 429, TP A2).