Nonadiabatic molecular dynamics simulations shed light on the timescale of furylfulgide photocyclisation

The sequence of events during the photocyclisation of furylfulgides is not fully understood, and there is a significant disparity between ring closing timescales determined with the use of transient absorption spectroscopy [Siewertsen et al., Phys. Chem. Chem. Phys., 2011, 13, 3800] and the timescale estimated on the basis of nonadiabatic molecular dynamics (NAMD) simulations [Kochman et al., Phys. Chem. Chem. Phys., 2022, 24, 18103]. With a view to resolving this issue, in the present study I report NAMD simulations of the photorelaxation process of a model furylfulgide with a bulky alkyl substituent at carbon atom C3. I employed a pattern recognition algorithm in order to automate the analysis of the simulated trajectories. According to the simulation results, the bulky alkyl group causes a substantial increase in the photocyclisation quantum yield, but the timescale of ring closing is only marginally affected. I discuss the implications of these findings in light of the available spectroscopic data. Furylfulgide photocyclisation is one of the fastest known photoisomerisation reactions. In this study, I use surface hopping simulations aided by pattern recognition analysis to verify spectroscopic estimates of its timescale.