A computational study of the photosomerization reactions of bicyclic cyclopropene

The mechanisms of the photochemical isomerization reactions were investigated theoretically using a model system of bicyclic cyclopropene 1 using the CASSCF (six-electron/six-orbital active space) and MP2-CAS methods and the 6-311(d,p) basis set. Our model investigations suggest that the preferred reaction route for 1 is as follows: reactant -> Franck-Condon region -> conical intersection -> intermediate -> transition state -> photoproduct. In particular, the conical intersection mechanism found in this work gives a good explanation and supports the experimental observations. In addition, we suggest a cyclic vinylcarbene model, which can be used as a guide tool to predict the location at which conical intersections are likely to occur, as well as the conformations of the photoisomerization products. (C) 2009 Elsevier B. V. All rights reserved.