Covalent Organic Frameworks with Pendant Azo Groups on Pore Walls for Synergistic Photothermal–Photodynamic Antibacterial Preservation

Photoresponsive covalent organic framework (COF) plays an increasingly important role in food applications due to its controllability. This study aims to prepare an azo-based COF with synergistic photothermal/photodynamic properties by introducing stimulus-responsive azo groups into the periodic pore via the one-step synthesis method. The COF can achieve a 100% inhibition rate against four common pathogenic bacteria under only 5 min of light irradiation. The developed COF-based antibacterial film demonstrates remarkable preservation efficacy, extending the shelf life of pork samples to 144 h under ambient conditions (25 °C). Furthermore, the fabricated azo COF card exhibits excellent portability and practical application, providing an additional 12 h extension of food preservation duration. These prominent properties are attributed to its unique structure. The azo groups within the pores serving as active sites possess strong light absorption capabilities, enabling effective electron-energy transfer and greatly enhancing the intersystem crossing process. Especially, the azo COF has superior light absorption ability, lower bandgap energy, stronger photothermal conversion efficiency (38.54%), and photodynamic performance. The low-cost monomer, simple preparation process, and prominent photothermal and photodynamic properties make the COF an ideal candidate for innovative applications in food preservation.