CHARGE SEPARATION IN PHOTOSYNTHESIS VIA A SPIN-EXCHANGE COUPLING MECHANISM

A new mechanism for the primary photoinduced charge separation in phot osynthesis 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 t o a singlet. The electron transfer is caused by spin exchange coupling s. The transient spectrum of the short lived intermediate, formerly ta ken as evidence for the charge transfer state P+ B-L(-) is reinterpret ed as a transient excitation of this trip-trip singlet.