Ultrafast Energy Transfer from Chlorophyll c2 to Chlorophyll a in Fucoxanthin-Chlorophyll Protein Complex

Light-harvesting in fucoxanthin-chlorophyll protein (FCP) of diatoms is performed by a cluster of chromophores: chlorophylls a (Chl a), chlorophylls c(2) (Chl c(2)), and carotenoids fucoxanthins. It is well-known that energy captured by fucoxanthin is transferred to Chl a on a subpicosecond time scale. However, the energy flow channel connecting Chl c(2) and Chl a remained elusive. In this study, the energy transfer between Chl c(2) and Chl a molecules in the FCP complex from the diatom algae C. meneghiniana at room temperature is investigated using pump probe and coherent two-dimensional electronic spectroscopy. Measured dynamics of the absorption band associated with the Q(y) transition of the Chl c(2) reveals an ultrafast energy transfer pathway to CM a. This conclusion is supported by the theoretical simulations based on the effective oscillator model.