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.