Berlin 2008 – wissenschaftliches Programm
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BP: Fachverband Biologische Physik
BP 5: Photobiophysics
BP 5.1: Vortrag
Montag, 25. Februar 2008, 16:15–16:30, PC 203
Optically "Dark" States of Carotenoids in the Major Plant Light-Harvesting Complex Investigated by Femtosecond Two-Photon Fluorescence Excitation Spectroscopy — •Alexander Betke1, Bernd Voigt1, Heiko Lokstein2, and Ralf Menzel1 — 1Institut für Physik/Photonik, Universität Potsdam, Germany — 2Institut für Biologie, Universität Potsdam, Germany
Carotenoids play several important roles in photosynthetic organisms: as structural components of pigment-protein-complexes, as accessory light-harvesting pigments, and in photoprotection. To understand the latter two functions and the underlying mechanism(s) it is vital to know the energetic positions of the first exited singlet state S1 (21Ag−) of relevant xanthophylls (carotenoids). Because single photon absorption is symmetry-forbidden for the S0 (11Ag−) → S1 (21Ag−) transition, the carotenoid 21Ag− state cannot be readily investigated by conventional spectroscopy. This transition, however, is two-photon allowed. Moreover, the carotenoid S1 state is assumed to lie close to the lowest excited chlorophyll singlet state. Thus, simultaneous two-photon absorption of tuneable fs-NIR-pulses being monitored by chlorophyll fluorescence is a useful approach to study the role of the "dark" states in excitation energy transfer and dissipation in light-harvesting complexes. Two-photon excitation spectra of the plant major light-harvesting complex (LHC II) with different xanthophyll-cycle pigment complements (violaxanthin, zeaxanthin) will be presented and implications for the photoprotective mechanism will be discussed. This research is supported by the DFG (SFB 429, TP A2).