Construction of novel benzoxazine-linked covalent organic framework with antimicrobial activity via postsynthetic cyclization

Organic framework materials have shown increasingly promising applications in biomedicine, such as drug delivery and release. In this work, we first synthesized a new hydroxyl-containing imine-linked two-dimensional covalent organic framework (COF) through solvothermal synthesis. Then, the imine group was converted into a benzoxazine group using a cyclization reaction. The results show that the postsynthetic modification did not change the basic framework of the original COF and did not affect the basic properties of the original COF. At the same time, the new benzoxazine group obtained by cyclization gave the COF good antibacterial activity against Escherichia coli and Staphylococcus aureus. The COF efficiency after cyclization was improved, and its antibacterial activity against both bacteria was over 90% compared with the imine-linked COF. Moreover, the benzoxazine-linked COF crystal structure and pore structures were retained, leaving the drug delivery and release functions unaffected. A benzoxazine-linked COF has never been reported because it cannot be synthesized by a direct reaction method. The work in this paper shows that the COFs that cannot be directly synthesized can be obtained through specific postsynthetic modification reactions. This means that more functional COFs can be obtained based on existing COFs, and the diversity of COF types and their potential applications can be further enriched and expanded.