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

Abstract

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. Thioaldehydeketene was experimentally inferred as a product, which is confirmed by the simulations reported herein.[a] Dr.

Tracking the ultraviolet-induced photochemistry of thiophenone during and after ultrafast ring opening

“…To determine the possible connections between these critical structures and the relaxation pathways of thiophenone following UV photoexcitation, linear interpolations in internal coordinates (LIICs) were performed using XMS(4)-CASPT2(10/8) (see Computational Details). Starting from the FC geometry, the LIICs smoothly connect the different critical points and confirm that photoexcited thiophenone (S 2 ) molecules can relax efficiently towards the S 0 state via the S 2 /S 1 and S 1 /S 0 seams of intersection in the C-S bond extension coordinate 28 . The energies of the low-lying (i.e.…”

“…In the present experiment, gas-phase thiophenone molecules are excited to the optically bright S 2 electronic state by a UV pulse (λ ≈ 265 nm). The excited molecules evolve through one or more conical intersections at progressively greater C-S bond separations en route back to the S 0 -state PES, where they can adopt the original closed-ring or several possible open-ring geometries 18,28 , some of which are sketched in Fig. 1.…”

Role of Multistate Intersections in Photochemistry

“…43,44 We have taken 2(5H)-thiophenone (2TP) as a representative of these heteroatom-containing molecules and performed the combined QTMF and MM (QTMF/MM) nonadiabatic dynamics simulations to study its photodissociation in CH 3 CN. 43 Among the QTMF/MM-simulated 448 reactive trajectories, the nonadiabatic transition from 1 ππ* to 1 πσ* was observed in only the 14 trajectories. The QTMF/ MM simulation reveals that the nonadiabatic transition occurs in the 1 ππ*/ 1 πσ* region with little probability (∼0.03), and the 1 ππ*/ 1 πσ* intersection plays only a minor role in the photoinduced ring-opening reaction of 2(5H)-thiophenone, which is quite different from the mechanism proposed experimentally.…”

“…Different spectroscopic and imaging techniques have been employed to explore photodissociation reactions of small molecules containing heteroatom, such as phenol, thiophenol, thioanisole, thiophene, thiophenone, furanone, and their derivatives. The intersection between the 1 ππ* and 1 πσ*­( 1 nσ*) excited states has been recognized as key to understanding the detailed mechanism of these photoreactions. , We have taken 2­(5H)-thiophenone (2TP) as a representative of these heteroatom-containing molecules and performed the combined QTMF and MM (QTMF/MM) nonadiabatic dynamics simulations to study its photodissociation in CH 3 CN . Among the QTMF/MM-simulated 448 reactive trajectories, the nonadiabatic transition from 1 ππ* to 1 πσ* was observed in only the 14 trajectories.…”

Monitoring the Evolution of Relative Product Populations at Early Times during a Photochemical Reaction

“…Among these ketenes, an exotic episulfide species, 2-(2-thiiranyl)-ketene, involving an S-containing three-membered ring, has been predicted to dominate at early times following the nonradiative deexcitation (Scheme 1). 22,25,26 The formation of a three-membered ring from a fivemembered cyclic species following the absorption of a 266 nm photon, with 4.65 eV of energy, might appear to challenge chemical intuition. Our recent TRPES studies using suitably short probe wavelengths 22 succeeded in resolving the ultrafast nonradiative decay of 2(5H)-thiophenone from its second excited singlet electronic state (S 2 , with n(S)π* character in the Franck−Condon region) following photoexcitation at 266 nm (Figure 1A) and in revealing the formation of acyclic photoproducts.…”