Theoretical models for the selectivity of organic singlet and triplet photoreactions

Abstract

In nonadiabatic photoreactions in solution, the geometry at the decay region from the excited to the ground state is decisive for the outcome of the reaction. From a mechanistic point of view, this "reactive structure", i.e., the structure of the conical intersection accessible on the excited state of a singlet photoreaction or the region of geometries favorable for intersystem crossing in a triplet photoreaction, plays a similar role as the transition state in a thermal reaction. Consequences for the selectivity of singlet and triplet photoreactions are discussed.