Theoretical exploration of 4π-Photocyclization Mechanism of α-Tropone Derivatives

In this study, we employed ab initio methods to investigate the 4π-photocyclization process of substituted α-tropones. Our findings suggest that the initial stages of this reaction occur from low-energy excited states such as S2 and S3, as the barriers in higher-energy excited states are prohibi-tively high. Additionally, we observed that the presence of acid catalysts or substitution of tro-pones with electron-donating groups reduces the energy barriers. Regarding the formation of bicy-clo[3.2.0]hepta-3,6-dien-2-one derivatives, both T1/S0 and S1/S0 crossings were identified as plau-sible pathways for this deactivation process. Specifically, electron-donating groups on the tro-pones promote degeneracy between S1 and S0 states during the return to the ground state. Moreo-ver, T1/S0 crossing systems were consistently observed across all investigated scenarios.