title: Different conical intersections control nonadiabatic photochemistry of fluorene light-driven molecular rotary motor: A CASSCF and spin-flip DFT study.
abstract: We report the light-driven isomerization mechanism of a fluorene-based light-driven rotary motor (corresponding to Feringa's 2nd generation rotary motor, [M. M. Pollard et al., Org. Biomol. Chem. 6, 507-512 (2008)]) at the complete active space self-consistent field (CASSCF) and spin-flip time-dependent density functional theory (TDDFT) (SFDFT) levels, combined with the complete active space second-order perturbation theory (CASPT2) single-point energy corrections. The good consistence between the SFDFT and CASSCF results confirms the capability of SFDFT in investigating the photoisomerization step of the light-driven molecular rotary motor, and proposes the CASPT2//SFDFT as a promising and effective approach in exploring photochemical processes. At the mechanistic aspect, for the fluorene-based motor, the S1/S0minimum-energy conical intersection (MECIs) caused by pyramidalization of a fluorene carbon have relatively low energies and are easily accessible by the reactive molecule evolution along the rotary reaction path; therefore, the fluorene-type MECIs play the dominant role in nonadiabatic decay, as supported by previous experimental and theoretical works. Comparably, the other type of MECIs that results from pyramidalization of an indene carbon, which has been acting as the dominant nonadiabatic decay channel in the stilbene motor, is energetically inaccessible, thus the indene-type MECIs are "missing" in previous mechanistic studies including molecular dynamic simulations. A correlation between the geometric and electronic factors of MECIs and that of the S1energy profile along the C═C rotary coordinate was found. The findings in current study are expected to deepen the understanding of nonadiabatic transition in the light-driven molecular rotary motor and provide insights into mechanistic tuning of their performance.
authors.affiliation: Key Laboratory for Macromolecular Science of Shaanxi Province, School of Chemistry and Chemical Engineering, Shaanxi Normal University, Xi'an, Shaanxi 710062, People's Republic of China.
authors.forename: Yuanying
authors.initials: Y
authors.lastname: Li
authors.affiliation: Key Laboratory for Macromolecular Science of Shaanxi Province, School of Chemistry and Chemical Engineering, Shaanxi Normal University, Xi'an, Shaanxi 710062, People's Republic of China.
authors.forename: Fengyi
authors.initials: F
authors.lastname: Liu
authors.affiliation: Key Laboratory for Macromolecular Science of Shaanxi Province, School of Chemistry and Chemical Engineering, Shaanxi Normal University, Xi'an, Shaanxi 710062, People's Republic of China.
authors.forename: Bin
authors.initials: B
authors.lastname: Wang
authors.affiliation: Key Laboratory for Macromolecular Science of Shaanxi Province, School of Chemistry and Chemical Engineering, Shaanxi Normal University, Xi'an, Shaanxi 710062, People's Republic of China.
authors.forename: Qingqing
authors.initials: Q
authors.lastname: Su
authors.affiliation: Key Laboratory for Macromolecular Science of Shaanxi Province, School of Chemistry and Chemical Engineering, Shaanxi Normal University, Xi'an, Shaanxi 710062, People's Republic of China.
authors.forename: Wenliang
authors.initials: W
authors.lastname: Wang
authors.affiliation: Fukui Institute for Fundamental Chemistry, Kyoto University, Kyoto 606-8103, Japan.
authors.forename: Keiji
authors.initials: K
authors.lastname: Morokuma