Dynamic Role of Conical Intersection Topographies in Nonadiabatic Photodissociation of 2-Substituted Thiophenols^†

Using a reduced dimensional quantum model, the photodissociation dynamics of thiophenol and its ortho-substituted derivatives, namely, 2-fluorothiophenol (2-FTP) and 2-methoxythiophenol (2-MTP), has been studied based on the newly constructed 3-state (^1\pi\pi, ^1\pi\pi^*, and ^1\pi\sigma^*) coupled diabatic potential energy matrices, of which diabatization is achieved by a neural network fitting method. It is found that the strong substituent effect on the photodissociation dynamics in terms of dissociation rates is ascribed to quite different conical intersection (CI) topographies on the dissociation pathways. The calculated lifetimes (τ) and associated kinetic isotope effects (τ_D/τ_H) of the lowest-lying resonances are in good qualitative agreement with experiment. Moreover, nonadiabatic effects in the photodissociation dynamics of thiophenol, 2-FTP, and 2-MTP are found to be dominated by the barriers formed by the CIs and nearby saddle points, shedding light on the dynamic role of CI topographies in the photodissociation.