Energy Transfer Pathways in Reaction Center upon FemtosecondExcitation of Accessory Bacteriochlorophylls

The energy transfer pathways from the excited accessory
bacteriochlorophylls (B^*) within native and modified (pheophytin-exchanged) reaction center isolated from Rhodobacter
sphaeroides (RS601) have been investigated by using the femtosecond pump-probe technique. For native RS601, B^* decays with time constant of 240 fs, followed by a partial recovery of the ground state bleaching with time scale of about 2 ps. In modified RS601(Phe), however, B^* decays with time constant of 800 fs for magic angle (54.7°) polarization configuration. In addition to the general assumption of energy transfer pathway from B^* to the special pair P, an alternative pathway for energy transfer probably operates as well.