CASSCF and CASMP2 study on the photoisomerization mechanisms of [tris(trialkylsilyl)silyl]cyclotetrasilene and related cyclobutene molecules

Abstract

The mechanisms for photochemical isomerization reactions are studied theoretically using the model systems, cyclotetrasilene and cyclobutene, both of which feature one four-membered-ring and one double bond, using the CAS(6,6)/6-311G(d) and CAS-MP2-(6,6)/6-311++G(3df,3pd) methods. The mechanisms, which are governed by the conical intersection concept, play a crucial role in these photorearrangement reactions, and explain the reaction pathways. The model computations demonstrate that the preferred reaction path for the photoisomerization reactions for both cyclotetrasilene and cyclobutene is as follows: four-membered-ring reactant → Franck–Condon region → conical intersection → butterfly-like photoproduct. These results allow a number of predictions to be made.