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

In 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 CH 3 CN solution. Meanwhile, the subsequent processes in the S 0 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 1 ππ * 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 S 2 ( 1 ππ * ) pathway and the solute‐solvent interaction has little influence on this initial process. Meanwhile, the 1 ππ * → 1 πσ * transition takes place with little probability via the 1 πσ * / 1 ππ * conical intersection and the 1 πσ * 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 S 0 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.