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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) to 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 reaction centers, the B* transient bleaching decays biexponentially, with a fast component of approximately 100 fs which gives a characteristic time scale for excitation energy transfer from B* to P. In Rb. capsulatus, the amplitudes for this component and a 360 {+-} 40 fs decay of uncertain origin reported in previous experiments are approximately equal. Several models for the two components are discussed. 33 refs., 2 figs.