Nonadiabatic molecular dynamics study of a complete photoswitching cycle for a full-size diarylethene system

Diarylethene (DAE) photoswitches continue to stay under the spotlight as remarkably stable, ultrafast, and efficient light-driven controlling units for applications in molecular technologies and devices. While tremendous amount of work has been put into rationalizing their performance, several fundamental questions about their switching mechanism remain. In this work, we undertake the challenge to provide, for the first time, the real-time theoretical description of a full-size DAE photoswitch operation dynamics, which becomes possible with employment of the cutting-edge multi-reference semi-empirical ODM2/MRCI methodology. To this end, we perform on-the-fly NAMD simulations of the cyclization and cycloreversion reaction for a flagship DAE system: 1,2-Bis(2-methyl-3-benzothienyl) perfluorocyclopentene, known as BT. Eventually, we obtain very good agreement of predicted photoswitching quantum yields with available experimental data, reporting the efficiency of the ring-opening and the efficiency of the ring-closure transformations, as compared to the 50% and 30% efficiencies, respectively, reported by Ishibashi et al. (J. Phys. Chem. C 2016, 120, 2, 1170–1177). On this grounds, we complement the existing view on the BT photoswitching with explicit predictions of the branching ratio at the reactive conical intersection, and by qualitative estimation of a side relaxation through quasi-degeneration seam. We believe that our results finally open prospects for future wide-range theoretical studies on DAE photoswitching, eventually providing researchers with a long-awaited tool to understand and control their operation.