Tailoring β-ketoenamine covalent organic framework with azo for blue light-driven selective oxidation of amines with oxygen

Covalent organic frameworks (COFs) present bright prospects as visible light photocatalysis with abundant active sites and exceptional stability. Tailoring an established COF with a photoactive group is a prudent means to extend visible light absorption. Here, a β-ketoenamine COF, TpBD-COF, constructed with 1,3,5-triformylphloroglucinol (Tp) and 4,4′-biphenyldiamine (BD), is tailored with azo to validate this tactic. By the insertion of azo into BD, TpAzo-COF is successfully constructed with Tp and 4,4′-azodianiline (Azo). Intriguingly, the insertion of azo enhances π-conjugation, thereby facilitating visible light absorption and intramolecular electron transfer. Moreover, TpAzo-COF, characterized by an appropriate electronic structure and an impressive specific surface area of 1855 m2/g, offers substantial active sites conducive to the reduction of oxygen (O2) to superoxide. Compared with TpBD-COF, TpAzo-COF exhibits superior performance for the blue light-driven oxidation of amines with O2. Superoxide, the critical reactive oxygen species, controls the selective formation of product imines. This work foreshadows the remarkable capacity of tailoring COFs with a photoactive group toward broad visible light photocatalysis.