Energy Tranfer in the Photosynthetic Reaction Center

Abstract

For isolated photosynthetic reaction centers from the photosynthetic bacterium Rhodobacter sphaeroides R26, pump-probe experiments with 20–25 fs pulses near 800 nm yield an initial anisotropy of 0.4 which decays in ~80 fs. The initial anisotropy decay is assigned to dipole reorientation by electronic energy transfer from the accessory bacteriochlorophylls (B) to the upper exciton state (P₊) of the special pair. This ~80 fs energy transfer step excites vibrational wavepackets assigned to P₊ on the basis of their anisotropy. B→P₊ energy transfer is followed by ~150 fs internal conversion to the lower exciton state (P_-) of the special pair.