Mechanistic Study of the Photochemical Isomerization Reactions of Silabenzene

The mechanisms for photochemical isomerization reactions were examined theoretically using a model system of a parent silabenzene with CAS­(6,6)/6-311G­(d) and MP2-CAS-(6,6)/6-311++G­(3df,3pd)//CAS­(6,6)/6-311G­(d) methods. Five reaction pathways leading to five types of photoisomers have been investigated. The theoretical computations indicate that conical intersections play a prominent role in the photoisomerization of silabenzenes. The model investigations reveal that the preferred reaction route for silabenzene should result in the corresponding silabenzvalene, rather than the Dewar silabenzene isomer. Moreover, the theoretical computations suggest that all of the photochemical mechanisms of silabenzene should proceed as follows: reactant → Franck–Condon region → conical intersection → photoproduct. In other words, the photochemical mechanism for silabenzene should be a barrierless, single-step process. The computational results agree well with available experimental observations.