A FEMTOSECOND STUDY OF ELECTRONIC STATE DYNAMICS OF FUCOXANTHIN AND IMPLICATIONS FOR PHOTOSYNTHETIC CAROTENOID-TO-CHLOROPHYLL ENERGY-TRANSFER MECHANISMS

The electronic state dynamics and absorption properties of the carotenoid fucoxanthin are examined, both in vitro and in vivo. An S2 lifetime of 0.15 ps and an S1 lifetime of 40 ps are measured for fucoxanthin dissolved in ethanol. Fluorescence emission from both S2 and S1 is observed, allowing corroboration of the direct measure of the S2 lifetime and determination of the S1 --> S0 oscillator strength. Emission from the S2 state of carotenoids in thylakoid membranes of Phaeodactylum tricornutum is also seen, but S1 emission in vivo is obscured by chlorophyll a (chl a) fluorescence. These new results, together with previous time-resolved and two-photon excitation results, are discussed and the importance of considering Coulomb coupling as a mechanism for carotenoid-to-chl a energy transfer is demonstrated, at least for Phaeodactylum tricornutum.