Smart covalent organic frameworks: integrating solid-state chromism for visual monitoring and multi-mode antibacterial action for food preservation.

Currently, intelligent packaging systems are predominantly designed for specific places with limited functional, typically emphasizing singular indication or preservation capabilities. In this research, a covalent organic framework (COF) with irreversible solid coloration, antibacterial, photothermal and photodynamic properties is developed, which can be simultaneously used as time-temperature indicator to achieve quick response code and active package materials. The COF exhibited gradually enhanced light absorption (79.58%), reduced band energy, endowing superior photothermal conversion (37.75%) and reactive oxygen species generation (99.5%) capabilities that achieve broad-spectrum antibacterial performance (100% antibacterial within 5 min). When integrated into packing, the composite antibacterial film exhibited outstanding preservation performance for beef and kumquat, where the shelf life was extended 4 times more than that of commercial film. The COF has good biocompatibility and commercial prospects, and can simultaneously realize the time-temperature indicator and preservation of food, which provides a new strategy for the innovative development of food safety.