Tandem Ring-Closing/Ring-Opening Chemistry for Linkage Reprogramming in Covalent Organic Frameworks

The linkages connecting building blocks largely dictate the accessible chemical space of covalent organic frameworks (COFs). However, synthesizing new linkages typically relies on linkage-specific condensations that require distinct monomer pairs. Here, we present a controllable tandem ring-closing/ring-opening (RCRO) strategy that enables linkage reprogramming of COFs from a single imine-linked precursor. Through a domino sequence involving intramolecular oxidative ring-closing followed by nucleophilic ring-opening, imine linkages are selectively transformed into benzoxazinone- and bis-benzamide-linked frameworks while preserving long-range crystallinity. This RCRO process allows divergent access to multiple robust linkages, is compatible with extended linkers, and enables systematic modulation of framework connectivity and porosity without altering the precursor chemistry. The resulting COFs exhibit pronounced linkage-dependent properties, including rapid iodine vapor adsorption in bis-benzamide-linked frameworks and efficient photocatalytic H2O2 production in the benzoxazinone-linked COF. By establishing tandem RCRO reactions as a viable mode of linkage engineering in extended crystalline frameworks, this work opens a general pathway for efficient and divergent exploration of COF structures and functions.