On the early charge separation and recombination processes in bacterial reaction centers

A new mechanism for the rapid initial charge separation in bacterial reaction centers is investigated. It can be characterized as a combined exciton-electron transfer mechanism. It involves as first step the deactivation of the initially excited dimer (BC_LPBC_MP)^* together with a charge transfer transition between the accessory monomer BC_LA and the pheophytine BP_L leading to the state BC⁺_LABP^-_L. This first step is followed by a rapid electron transfer from the dimer to the cation BC⁺_LA. It is shown that this mechanism is consistent with the pertinent experimental facts from absorption and emission spectra as well as time resolved measurements related to the initial charge separation and subsequent recombination processes.