Ultrafast Dynamics in Spatially Confined Photoisomerization: Accelerated Simulations through Machine Learning Models

This study sheds light on the exploration of photoresponsive host-guest systems, highlighting the intricate interplay between confined spaces and photosensitive guest molecules. Conducting nonadiabatic molecular dynamics (NAMD) simulations based on electronic structure calculations for such large systems remains a formidable challenge. Leveraging machine learning (ML) as an accelerator for NAMD simulations, we analytically constructed excited-state potential energy surfaces along relevant collective variables to investigate photoisomerization processes efficiently. Combining the QM/MM methodology with ML-based NAMD simulations, we elucidated reaction pathways and identified key degrees of freedom as reaction coordinates leading to conical intersections. Comparing the behavior of the guest molecule (benzopyran) in the gas phase with its confinement within cucurbit[5]uril, our findings reveal a delayed photoisomerization rate and reduced isomerization yield within confined spaces. The results underscore the effectiveness of ML models in simulating trajectory evolution cost-effectively. This research offers a practical approach to accelerate NAMD simulations in large-scale systems of photochemical reactions, with potential applications in other host-guest complex systems.