Charge separation in photosynthesis via a spin exchange coupling mechanism

Abstract

A new mechanism for the primary photoinduced charge separation in photosynthesis is proposed. It involves as a real intermediate between the excited special pair state P^* and the primary charge separated state P⁺ H_L ^– a trip-trip-singlet B^T B_L ^T, which consists of a triplet on the dimer P and a further triplet on the monomer B_L. Both combine to a singlet. The electron transfer is caused by spin exchange couplings. The transient spectrum of the short lived intermediate, formerly taken as evidence for the charge transfer state P⁺ B_L ^–, is reinterpreted as a transient excitation of this trip-trip singlet.