Fluorescence depolarization dynamics in the B850 complex of purple bacteria

The fluorescence anisotropic decay is modeled for the B850 bacteriochlorophyll a complex of the purple bacterium Rhodopseudomonas acidophila. Structural information is combined with experimental data to derive a Hamilton operator which models the S-0-S-1 excitation energy transfer between the pigments as well as the energy dissipation into the protein environment. The time-resolved fluorescence signal is determined from the solutions of the equations of motion for the one-exciton density matrix. Nonsecular terms in the Redfield relaxation tensor are shown to have a dramatic influence on the calculated time scales for depolarization.