Microhydration Dynamics in Molecular Photoswitches: Equilibrium State Reconfiguration in Imine-Based Architectures

Abstract

The functional performance of a molecular photoswitch relies strongly on its ability to undergo structural changes in solution. In this context, microsolvation studies in the gas phase provide access to the conformational panorama of these systems in a size-controlled hydrated environment. Here, we exploit this gas-phase vantage point alongside quantum-chemistry calculations to study the structural properties and microhydration dynamics of camphorquinone imine, a chiral molecule holding the functionality to engage in a motor-like function upon light activation. Using molecular rotational resonance spectroscopy with supersonic jets, we detect and analyze the first- and second-order water complexes of the chiral imine. Our findings reveal that initial hydration steps significantly impact the equilibrium between open (E) and closed (Z) forms, culminating in a reversal of relative stability for the switch states. Despite being captured at rotational temperatures near 1 K, we find that water molecules exhibit notable mobility due to the lack of prominent stabilizing secondary interactions. Additionally, the assignment of a key higher-energy closed (Z) water complex provides insights into the energy required for switching between (E) and (Z) states during collisional cooling. We discuss these effects and rationalize them in terms of molecular forces and internal dynamics governing early solvation.