Linkage Multi-functionalization in Covalent Organic Frameworks via Criss-Cross 1,3-Dipolar Cycloaddition.

Introducing functional groups to skeletons of covalent organic frameworks (COFs) is fundamentally important to create specific properties and functions for this class of crystalline porous polymers. The strategy of multi-functionalization could introduce multiple functional groups in one-step but has rarely been developed for polymers. Herein, we report a novel linkage conversion strategy which could simultaneously install multiple functional groups into a single site of azine-linked COFs. This strategy is based on criss-cross 1,3-dipolar cycloaddition reaction between azine linkages in COFs and multifarious alkynes carrying different functional groups. Its general applicability and high efficiency have been demonstrated by the successful construction of more than 10 COFs with widespread functional groups, for which homo-type and hetero-type functional groups could be introduced. This study provides a general and powerful tool to introduce highly dense functional groups into nanopores of COFs, enabling the further exploration of their applications bestowed by the functional groups.