ABSTRACT Conical intersections (CIs) are key features of electronic states that govern ultrafast photochemical processes, and efficient nonradiative transitions can occur through them. In this study, the photochemical electrocyclic ring‐closure reaction of 1,3‐cycloheptadiene conformers with Cs and C 2 point groups that yields bicyclo3.2.0heptene is analysed. The reaction pathways are mapped by optimizing reactants, products, transition states, and conical intersections. A disrotatory transition state (TS) was identified, connecting the Cs‐reactant to the Cs‐product, while a conrotatory TS links the Cs‐product to the transient cis, trans‐cyclohepta‐1,3‐diene intermediate. Interpolation studies indicate that only the Cs‐product pathway is viable as the route from CI‐S 1 /S 0 to the C 2 ‐product has a high activation barrier, whereas the Cs‐product pathway proceeds without such an obstacle. Surface hopping simulations is employed from the S 1 state for both Cs and C 2 conformers. The simulations consistently yielded the Cs photoproduct, with quantum yields of 7% and 2% from Cs and C 2 ‐conformer, respectively, which can be attributed to differences in S 1 ‐S 0 hopping near the CI‐S 1 /S 0 region. Overall, these results emphasize the decisive role of conical intersections in dictating product formations in photochemical reactions, providing mechanistic insights relevant to the development of molecular electronics, photopharmacology, and solar energy conversion.
Morang et al. (Sun,) studied this question.