Assessing the dynamics of hemithioindigo-based photoswitches using multi-state molecular mechanics

We outline a multi-state molecular mechanics model for describing hemithioindigo- based photoswitches in the ground and excited (S1) states, respectively. While retaining near quantum mechanical accuracy of the related Born-Oppenheimer potential energy profiles, the computational efficiency of our approach offers ns-scale molecular dynamics simulation runs featuring extended statistics of complex systems. Contrasting a series of different environments, we elucidate the explicit solvent effect on photoinduced Z-E switching in terms of both energetics and kinetic aspects. Using thousands of trajectories, isomerization ratios and relaxation times are directly assessed from statistical sampling. On this basis, in-depth mechanistic understanding is achieved via trajectory committor analyses that unravel the key descriptors of the Z- E isomerization process.