Charge separation in photosynthesis via a spin exchange coupling mechanism

TL;DR

This paper proposes a novel spin exchange coupling mechanism for charge separation in photosynthesis, involving a trip-trip-singlet intermediate state that reinterprets previous spectral evidence.

Contribution

It introduces a new charge separation mechanism based on spin exchange couplings and identifies a specific trip-trip-singlet intermediate as key.

Findings

Reinterprets transient spectra as a trip-trip singlet excitation.

Proposes a spin exchange coupling mechanism for electron transfer.

Suggests a new intermediate state in photosynthetic charge separation.

Abstract

A new mechanism for the primary photoinduced charge separation in photosynthesis is proposed. It involves as real intermediate between the excited special pair state P* and the primary charge separated state P+HL- a trip-trip-singlet PTBLT, which consists of a triplet on the dimer P and a further triplet on the monomer BL. 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+BL-, is reinterpreted as a transient excitation of this trip-trip singlet.