Photoswitchable Imines: From Molecular Design to Out-of-Equilibrium Systems

Imines (RCH=NR’) are well-known for their dynamic-covalent properties and are widely used in the field of self-assembly and in designing self-healing materials due to their reversible condensation/hydrolysis behavior. However, despite being structurally similar to azo-based photoswitches, which are capable of E/Z photoisomerization, their photoswitching capabilities have long been overlooked. The two questions that I sought to answer during my PhD studies were: (1) Can imines themselves function as efficient, reliable photoswitches? (2) Can imines be used to drive dynamic-covalent systems into non-equilibrium steady states (NESS) under light irradiation? We have demonstrated that arylimines can be optimized to exhibit robust photoswitching behavior, achieving near-quantitative E-to-Z isomerization under visible light and Z-to-E thermal half-lives of up to 25 hours at room temperature. Further development of imine-based photoswitches, including iminobispyrazoles (IBPs) and N-Alkyl imines, provided deeper insights into the design rules of photoswitchable imines. Building on these findings, we showed that coupling imine photoisomerization to a thermodynamically controlled transimination reaction enables the light-driven operation of an “information ratchet”, in which the system is driven away from equilibrium into a NESS under continuous irradiation. Furthermore, by integrating this light-responsive transimination with a second, non-photoresponsive reaction, the entire coupled network can be driven to a NESS under light irradiation, effectively transducing photon energy into a higher chemical potential via a reaction cascade.