Journal of Physical Chemistry

Observation of ultrafast energy transfer from the accessory bacteriochlorophylls to the special pair in photosynthetic reaction centers

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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. © 1995 American Chemical Society.