title: Combining the Advantages of Alkene and Azo E-Z Photoisomerizations: Mechanistic Insights into Ketoimine Photoswitches.
abstract: We carried out CASPT2//(TD)DFT and CASPT2//CASSCF studies on the working mechanism of imine switches, including a camphorquinone-derived ketoimine (shortened as k-Imine) switch designed by Lehn as well as a model camphorquinone alkene-imine (a-Imine) proposed in this study. Under the experimental conditions (light irradiation with 455 and 365 nm for E and Z, respectively), k-Imine is excited to the S1:(nN,π*) state and then decays toward a perpendicular intermediate following the C═N bond rotation coordinate. During the bond rotation, a mild energy barrier caused by the strong interaction of S1:(nN,π*) and S2:(nO,π*) states will more or less slow down the rotation speed of k-Imine. The large difference in irradiation light wavelength supports k-Imine as a two-way photoswitch. The photoisomerization of a-Imine obeys a similar but fully barrierless pattern while requiring a higher excitation energy to reach the (nN,π*) state. The good directionality of thermal isomerization toward E(a-Imine), plus the barrierless photoisomerization, allows for the design of a thermal and photo-operated switch. For both imines, a minimal-energy crossing point (MECI) located at the perpendicular region, with low relative energy and close to the rotary path, ensures the directionality of C═N bond rotation and confirms imines as optimal candidates for photoswitches and motors.
authors.affiliation: Key Laboratory for Macromolecular Science of Shaanxi Province, School of Chemistry & 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 & 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 & 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 & Chemical Engineering, Shaanxi Normal University , Xi'an, Shaanxi 710062, People's Republic of China.
authors.forename: Minjuan
authors.initials: M
authors.lastname: Liu
authors.affiliation: Key Laboratory for Macromolecular Science of Shaanxi Province, School of Chemistry & Chemical Engineering, Shaanxi Normal University , Xi'an, Shaanxi 710062, People's Republic of China.
authors.forename: Hongjuan
authors.initials: H
authors.lastname: Wang
authors.affiliation: Key Laboratory for Macromolecular Science of Shaanxi Province, School of Chemistry & 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: Key Laboratory for Macromolecular Science of Shaanxi Province, School of Chemistry & Chemical Engineering, Shaanxi Normal University , Xi'an, Shaanxi 710062, People's Republic of China.
authors.forename: Fengyi
authors.identifier: http://orcid.org/0000-0002-9462-701X
authors.initials: F
authors.lastname: Liu