External control of photocleavage reactivity in polymer networks to reconcile photodegradability and photostability

Abstract Owing to the high spatiotemporal resolution of light, photocontrol has attracted considerable interest in the field of polymer science. Consequently, various photoreactive moieties that undergo bond cleavage or structural transformations upon light irradiation have been developed to achieve excellent photocontrollability. However, highly photoresponsive materials are intrinsically unstable under light exposure, thus restricting long-term use and resulting in a fundamental trade-off between photoreactivity and photostability. This Focus Review summarizes our recent strategies to address this trade-off, focusing on cooperative reactions induced by combined light and acid stimuli and controllable photoreactivity based on reversible intramolecular isomerization. By examining the reactivity of small molecules and incorporating them as crosslinks in polymer network materials, on-demand control over photoreactivity and photostability can be achieved. These polymer systems show significant promise for diverse functional applications, including light-induced degradation and processing, and are even suitable for light-irradiated environments.