Tetrapyridophenazine-Based Vinylene-Linked Covalent Organic Frameworks for Efficient Sequential Photocatalysis and Continuous-Flow Synthesis.

Abstract

Vinylene-linked covalent organic frameworks (COFs) are promising photocatalysts because their conjugated sp2-carbon frameworks combine exceptional chemical stability with efficient charge transport. However, the limited reversibility of C═C bond formation narrows the scope of polymerizable monomers, restricting the structural diversity and electronic tunability of vinylene-linked COFs. Here, we report a molecular design strategy based on a planar, electron-deficient, nitrogen-rich tetrapyridophenazine (TTPhz) building block for constructing vinylene-linked COFs. Knoevenagel polycondensation of a polymerizable TTPhz monomer with aromatic dialdehydes affords three highly crystalline COFs with tunable donor-acceptor interactions and electronic structures. The optimized fluorinated framework, TTPhz-COF-3, exhibits efficient charge separation and transport, enabling a previously unreported one-pot sequential photocatalytic synthesis of 2,3-dihydrobenzofuran derivatives from arylboronic acids through tandem aerobic hydroxylation and oxidative [3 + 2] cycloaddition. The catalyst displays broad substrate scope, excellent recyclability, and enables gram-scale continuous-flow synthesis of a key intermediate of the natural product (±)-conocarpan with a 4-fold higher turnover frequency than the corresponding batch process. This work expands the structural and functional scope of vinylene-linked COFs and establishes molecular building-block design as a general strategy for developing advanced crystalline organic photocatalysts.