Ultrafast energy transfer and charge separation dynamics in PSII-dimer from Thermosynechococcus vulcanus

Cyanobacterial photosynthetic apparatus efficiently capture sunlight, and the energy is subsequently transferred to photosystem I (PSI) and II (PSII), to produce electrochemical potentials. PSII is a unique membrane protein complex that photo-catalyzes oxidation of water and majorly contains photosynthetic pigments of chlorophyll a and carotenoids. In the present study, the ultrafast energy transfer and charge separation dynamics of PSII from a thermophilic cyanobacteria Thermosynechococcus vulcanus have been investigated by femtosecond pump-probe spectroscopic measurements. The results demonstrated that the pheophytin anion Pheo D1 − generates with 43.0 ps at 140 K (14.8 ps at 296 K) and the secondary electron transfer to quinone: Pheo D1 − Q A →Pheo D1 Q A − occurs with 650 ps at 296 K upon excitation into the Q y band of chlorophyll a at 670 nm. On the other hand, an inefficient β-carotene → chlorophyll a energy transfer (33%) occurred after excitation to the S 2 state of β-carotene at 500 nm. Instead, the carotenoid triplet state appeared in an ultrafast timescale after excitation at 500 nm.