Micro-environmental fine-tuning of electronic and kinetic properties of photochromic dyes

Despite the recognition of the importance of Spiropyran (SP)-Merocyanine (MC) photochromic materials in molecular switching, the majority of studies have been reported in solution with relatively few in the solid-state as required in modern displays and other devices. In contrast, the present work bridges solution, condensed phase and solid-phase media and is to our knowledge the first micro-environmental study on electronic and kinetic effects for the SP-MC system. Expanding on our previous work we have investigated the photochromic properties of an SP molecule (1b) attached to a 100 μm commercially available polystyrene micro-particle (Wang Resin). The thermal MC → SP reversion kinetics (5a,b → 4a,b and 2a,b → 1a,b) which reflect the critical lifetime of the open MC form were measured. Reduction in k_obs of thermal reversion, MC → SP, up to two orders of magnitude, and a blue-shift up to 58 nm was observed with the potential for tailoring or fine tuning. The use of polymeric micro-particles in controlling both electronic and kinetic properties of photochromic molecular switches has been highlighted.