OBSERVATION OF ULTRAFAST ENERGY-TRANSFER FROM THE ACCESSORY BACTERIOCHLOROPHYLLS TO THE SPECIAL PAIR IN PHOTOSYNTHETIC REACTION CENTERS

The energy transfer from accessory bacteriochlorophyll molecules (B) t o the special pair (P) in the reaction center of Rb. capsulatus and Rb , sphaeroides R26 has been time-resolved using 23 fs pulses. In both r eaction centers, the B transient bleaching decays biexponentially, wi th a fast component of approximately 100 fs which gives a characterist ic time scale for excitation energy transfer from B to P. In Rb. caps ulatus, the amplitudes for this component and a 360 +/- 40 fs decay of uncertain origin reported in previous experiments are approximately e qual. Several models for the two components are discussed.