Assessing the Dynamics of Hemithioindigo-Based Photoswitches Using Multistate Molecular Mechanics

We outline a multistate molecular mechanics model for describing hemithioindigo-based photoswitches in the ground and excited (T₁) 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 Z-E switching from the triplet-surface in terms of both energetics and kinetic aspects. Using thousands of trajectories, isomerization ratios and vibrational 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.