Osnabrück 2002 – scientific programme
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MO: Molekülphysik
MO 1: Elektronische Übergänge
MO 1.1: Talk
Monday, March 4, 2002, 14:00–14:15, HS 01/E01
Two-Photon Excitation study of Peridinin in Benzene and Perdinin Chlorophyll Protein — •Joerg Zimmermann1, Patricia A. Linden1, Harsha M. Vaswani1, Roger Hiller2, and Graham R. Fleming1 — 1University of California, Berkeley, Department of Chemistry — 2Macquarie University, School of Biological Sciences, Australia
Peridinin chlorophyll protein (PCP) is a unique light harvesting protein found in dynoflagellates that contains a large amount of the carotenoid peridinin. Carotenoids have unusual spectroscopic properties due to their approximate C2h symmetry, which makes transitions to their S1 (S2) states one-photon forbidden (allowed). To gain information about one-photon forbidden electronic states in peridinin, fluorescence excitation spectra were measured after two-photon excitation (TPE) for isolated peridinin in benzene and PCP. The samples were excited using 920-1320nm light. Fluorescence of the isolated peridinin S1 state was then measured at 750nm. In PCP, the excited peridinin transfers energy to chlorophyll whose fluorescence was monitored at 670nm. Surprisingly, two-photon absorption was observed in both the peridinin S1 and S2 regions, with the spectrum slightly red-shifted in the protein sample. The peridinin S1 energy was found to be higher than that of typical light harvesting carotenoids, making its S1 state lie very close in energy to its S2 state. We suggest that the two-photon character of the one-photon allowed S2 state is due to the polar groups present in peridinin, which cause a change in dipole moment upon excitation. Electronic structure calculations support these results.