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.