Combined Quantum Trajectory Mean‐Field and Molecular Mechanical (QTMF/MM) Nonadiabatic Dynamics Simulations on the Photoinduced Ring‐Opening Reaction of 2(5H)‐Thiophenone

Abstract

AbstractIn the present work, the direct ab initio quantum trajectory mean‐field and molecular mechanical (QTMF/MM) nonadiabatic dynamics approach has been numerically implemented and used to simulate the photo‐induced ring‐opening process of 2(5H)‐thiophenone in CH3CN solution. Meanwhile, the subsequent processes in the S0 state have been simulated employing a quantum mechanics/molecular mechanics (QM/MM) adiabatic dynamics method that is derived from the direct ab initio QTMF/MM nonadiabatic dynamics approach. Upon irradiation at 267 nm, 2(5H)‐thiophenone is initially populated to its bright 1ππ* state. Subsequently, the ring‐opening reaction is predicted to be an ultrafast process with a time constant of about 228 fs. As a result, the ring‐opening reaction proceeds mainly along the diabatic S2(1ππ*) pathway and the solute‐solvent interaction has little influence on this initial process. Meanwhile, the 1ππ*→1πσ* transition takes place with little probability via the 1πσ*/1ππ* conical intersection and the 1πσ* excited state plays a minor role in the ring‐opening reaction, which is quite different from those reported for many heterocyclic molecules. Reformation of the parent molecule in the S0 state is determined to have a quantum yield of 33.9 % within the simulated period of 3.5 ps, which is considerably underestimated in comparison with a value of ∼60.0 % inferred experimentally. Thioaldehyde‐ketene was experimentally inferred as a product, which is confirmed by the simulations reported herein.