Dresden 2011 – wissenschaftliches Programm
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MO: Fachverband Molekülphysik
MO 1: Biomolecules
MO 1.1: Vortrag
Montag, 14. März 2011, 10:30–10:45, TOE 317
Two-photon fluorescence excitation (TPF) spectroscopy of photosynthetic pigments and pigment-protein complexes — •Alexander Betke1, Bernd Voigt1, Heiko Lokstein2, and Ralf Menzel1 — 1Institut für Physik und Astronomie / Photonik, Univ. Potsdam — 2Institut für Biochemie und Biologie, Univ. Potsdam
Chlorophylls and carotenoids are light-harvesting pigments and essential structural components of photosynthetic pigment-protein complexes. Due to the optically forbidden character of the lowest excited singlet state (S1/21Ag−) of relevant carotenoids for one-photon excitation from the electronic ground state (S0/11Ag−), the relative energy position of the carotenoid S1 state cannot be readily investigated by conventional spectroscopic techniques. This state, however, was generally assumed to be at least partly involved into excitation energy transfer to adjacent chlorophyll molecules, based on its supposed close energetic proximity to the chlorophyll S1 (Qy) state. The carotenoid S0- to S1-transition is two-photon allowed and consequently individual spectral peaks in the TPF spectra (detected by chlorophyll fluorescence) of several light-harvesting complexes are usually ascribed to this transition. However, from direct comparison to TPF spectra of relevant chlorophylls in solution we infer that there is no effective energy transfer from the carotenoid 21Ag− state onto chlorophyll Qy. We conducted TPF studies with the plant major light-harvesting complex and chlorophylls in solution. In particular we discuss the progression of chlorophyll states in TPF spectra, which is considerably different from that in one-photon absorption or -fluorescence excitation spectra.