ULTRAFAST SPECTROSCOPY OF THE PRIMARY ELECTRON AND ENERGY-TRANSFER PROCESSES IN THE REACTION-CENTER OF PHOTOSYSTEM-II

The picosecond fluorescence kinetics of the D1-D2-cyt-b559 photosystem II reaction center(RC)complex with 6 Chl/2 Pheo have been characterized upon preferential excitation of the special pair P680 at 685 nm. The component with largest amplitude had a lifetime of 3 +/- 1 ps and is attributed to the process of primary charge separation. In the short time range two further lifetimes of 19 +/- 2 and 67 +/- 5 ps were resolved in addition. The 19 ps component is attributed mainly to energy transfer from the antenna Chl(s) present in the preparation of RCs with 6 Chl/2 Pheo to the reaction center pigments. The 67 ps component may have a mixed origin. Upon preferential excitation of the antenna Chls at 650 nm also a slow energy transfer of about 22 ps is observed, together with a 5 ps component that shows negative amplitudes in its decay-associated spectrum (DAS). From femtosecond transient absorption data,we infer an ultrafast anisotropy decay of about 0.5 ps which is assigned to energy transfer among the immediate pigments of the reaction center (primary donor and accessory Chls and/or pheophytins).