Photochemical rearrangement reactions of bicyclic molecules that contain a cyclopropane ring

The mechanisms of photochemical rearrangement reactions are studied theoretically using a model system of bicyclic molecules that features a cyclopropane ring that is in proximity to a double bond moiety (such as C?C or C ?O group), using the M06-L method and the 6-311G(d,p) basis set. The theoretical findings show that intersystem crossing is vital to successfully interpret the mechanisms. This theoretical research also shows that the photoisomerization mechanism should proceed as follows: Rea-S-0 FC-T-1 Min-T-1 TS1-T-1 T-1/S-0 Int1-S-0 TS2-S-0 Int2-S-0 TS3-S-0 Pro-S-0. The theoretical evidence in this work confirms the experimental results for both [3.1.0] and [5.1.0] bicyclic molecules. The theoretical observations also predict that for both [2.1.0] and [4.1.0] systems, the quantum yields of the tautomeric keto forms are greater than those of the corresponding enol isomers.