title: Nonadiabatic simulation study of photoisomerization of azobenzene: detailed mechanism and load-resisting capacity.
abstract: Nonadiabatic dynamical simulations were carried out to study cis-to-trans isomerization of azobenzene under laser irradiation and/or external mechanical loads. We used a semiclassical electron-radiation-ion dynamics method that is able to describe the coevolution of the structural dynamics and the underlying electronic dynamics in a real-time manner. It is found that azobenzene photoisomerization occurs predominantly by an out-of-plane rotation mechanism even under a nontrivial resisting force of several tens of piconewtons. We have repeated the simulations systematically for a broad range of parameters for laser pulses, but could not find any photoisomerization event by a previously suggested in-plane inversion mechanism. The simulations found that the photoisomerization process can be held back by an external resisting force of 90-200 pN depending on the frequency and intensity of the lasers. This study also found that a pure mechanical isomerization is possible from the cis-to-trans state if the azobenzene molecule is stretched by an external force of approximately 1250-1650 pN. Remarkably, the mechanical isomerization first proceeds through a mechanically activated inversion, and then is diverted to an ultrafast downhill rotation that accomplishes the isomerization. Implications of these findings to azobenzene-based nanomechanical devices are discussed.
authors.affiliation: National Key Laboratory for Surface Physics, Institute of Modern Physics, Fudan University, Shanghai 200433, China.
authors.forename: Junfeng
authors.initials: J
authors.lastname: Shao
authors.forename: Yibo
authors.initials: Y
authors.lastname: Lei
authors.forename: Zhenyi
authors.initials: Z
authors.lastname: Wen
authors.forename: Yusheng
authors.initials: Y
authors.lastname: Dou
authors.forename: Zhisong
authors.initials: Z
authors.lastname: Wang
mesh_terms: D001391:Azo Compounds / Q000737:chemistry*; D004583:Electrons; D006358:Hot Temperature; D007834:Lasers; D008956:Models, Chemical; D055668:Photochemical Processes; D013237:Stereoisomerism; D013314:Stress, Mechanical
chemical_list: D001391:Azo Compounds; C009850:azobenzene