title: Excited-state ring-opening mechanism of cyclic ketones: a MS-CASPT2//CASSCF study.
abstract: We have employed complete active space self-consistent field (CASSCF) and its second-order perturbation (MS-CASPT2) methods to study the S1 and T1 excited-state ring-opening mechanisms and S1 excited-state deactivation channels of cyclopropanone, cyclobutanone, cyclopentanone, and cyclohexanone. On the basis of optimized minima, transition states, conical intersections, refined energies, and relaxed two-dimensional S1 and T1 potential energy surfaces, we find that, with the ring-strain decrease from cyclopropanone to cyclohexanone, (1) the ring-opening S1 and T1 barrier increases from 0.0 and 0.0 to 19.7 and 10.4 kcal/mol, respectively; (2) the electronic state responsible for the dominant ring-opening reaction varies from the S1 state of cyclopropanone to the T1 state of cyclopentanone and cyclohexanone; and (3) the S1 ring opening gradually becomes inefficient even blocked in cyclopentanone and cyclohexanone. This work shows that these dissimilar excited-state dynamics could originate from different ring strain of small cyclic ketones.
authors: Key Laboratory of Theoretical and Computational Photochemistry, Ministry of Education, College of Chemistry, Beijing Normal University, Beijing 100875, China.
authors: Shu-Hua
authors: SH
authors: Xia
authors: Key Laboratory of Theoretical and Computational Photochemistry, Ministry of Education, College of Chemistry, Beijing Normal University, Beijing 100875, China.
authors: Xiang-Yang
authors: XY
authors: Liu
authors: Key Laboratory of Theoretical and Computational Photochemistry, Ministry of Education, College of Chemistry, Beijing Normal University, Beijing 100875, China.
authors: Qiu
authors: Q
authors: Fang
authors: Key Laboratory of Theoretical and Computational Photochemistry, Ministry of Education, College of Chemistry, Beijing Normal University, Beijing 100875, China.
authors: Ganglong
authors: G
authors: Cui