Photochemical processes: potential energy surface topology and rationalization using VB arguments

The development of quantum chemical methods capable of treating excited and ground states of organic molecules in a balanced way has prompted many applications in the field of mechanistic organic photochemistry. In this paper, we review a few representative computational results which illustrate the currently emerging concept of a photochemical (and photophysical) reaction pathway. In particular, we focus on the shape (topology) of the potential energy surface along the excited state branch of the reaction path as well as on the shape and nature of the photochemical funnel where decay to the ground state occurs. The chemical effect of different topologies and their origin in terms of simple valence bond ideas are discussed. (C) 2001 Elsevier Science B.V. All rights reserved.