Excitation Energy-Transfer Dynamics of Brown Algal Photosynthetic Antennas

Fucoxanthin–chlorophyll-<i>a</i>/<i>c</i> protein (FCP) complexes from brown algae Cladosiphon okamuranus TOKIDA (Okinawa Mozuku in Japanese) contain the only species of carbonyl carotenoid, fucoxanthin, which exhibits spectral characteristics attributed to an intramolecular charge-transfer (ICT) property that arises in polar environments due to the presence of the carbonyl group in its polyene backbone. Here, we investigated the role of the ICT property of fucoxanthin in ultrafast energy transfer to chlorophyll-<i>a</i>/<i>c</i> in brown algal photosynthesis using femtosecond pump–probe spectroscopic measurements. The observed excited-state dynamics show that the ICT character of fucoxanthin in FCP extends its absorption band to longer wavelengths and enhances its electronic interaction with chlorophyll-<i>a</i> molecules, leading to efficient energy transfer from fucoxanthin to chlorophyll-<i>a</i>