Proton-Mediated Kinetic Equilibrium Synthesis of High-Crystalline Vinylene-Linked Covalent Organic Frameworks for...

Vinylene-linked covalent organic frameworks (COFs) are considered as one of the most promising COF materials due to their full π-conjugation and excellent stability. However, the irreversibility of carbon-carbon double bond formation can lead to uncontrolled nucleation and growth, limiting crystal growth and structural regulation of vinylene-linked COFs. Here, we leverage reversible protonation reactions between carboxylic acids and N-heteroaromatic precursors to realize controlled synthesis of vinylene-linked COFs and investigate their crystallization process in depth. Carboxylic acid acts as a modulator to precisely regulate the acidity of the melt polymerization system, which can slow the polymerization and nucleation rates, providing opportunities to correct molecular misconnection and promote the formation of thermodynamically more stable crystal structures. The synthesized N-heteroaromatic vinylene-linked COFs exhibited unprecedented crystal domains, with a maximum size up to 0.33 μm. The 15 N-heteroaromatic vinylene-linked COFs with high crystalline quality and excellent photochemical properties were successfully synthesized via this strategy. When used as a catalyst for oxygen reduction reactions, the new 2,2',6,6'-tetramethyl-4,4'-bipyridine/4,4″-p-terphenyldicarboxaldehyde (TMBP-TPDA) exhibited excellent performance, achieving a H₂O₂ generation rate of 17.53 mmol g^-1 h^-1 in pure water, surpassing existing COF-based photocatalysts. This study is not only searching for an efficient formula but also exploring and understanding the inherent laws of the reaction, paving the way for precise regulation and practical application of vinylene-linked COFs.