Light harvesting complex II B850 excitation dynamics.

The dynamics of excitation energy transfer within the B850 ring of light harvesting complex 2 from Rhodobacter sphaeroides and between neighboring B850 rings is investigated by means of dissipative quantum mechanics. The assumption of Boltzmann populated donor states for the calculation of intercomplex excitation transfer rates by generalized Forster theory is shown to give accurate results since intracomplex exciton relaxation to near-Boltzmann population exciton states occurs within a few picoseconds. The primary channels of exciton transfer between B850 rings are found to be the five lowest-lying exciton states, with non-850 nm exciton states making significant contributions to the total transfer rate.