Cationic Covalent Organic Framework for Photocatalytic Defluorinative Amination of Fluoroarenes

Covalent organic frameworks (COFs)-a unique class of crystalline, porous materials-are distinguished for their structural tunability, large surface area, high chemical stability, and tunable functionalities, which can be modified through pre- or post-synthetic modifications. These features make COFs highly attractive platforms for heterogeneous photocatalysis and electrocatalysis. Building on these inherent advantages, we strategically modulated the electronic structure of a bipyridine-based COF (Tp-Bpy) via simple one-step methylation to yield a dicationic, highly electron-deficient framework (Tp-Bpy-Me). This post-synthetic modification preserved the structural integrity of COF and introduced profound changes to its electronic environment, including a notable upward (positive) shift in the valence band position. Consequently, the cationic Tp-Bpy-Me COF exhibited an exceptional ability to activate one of the most inert bonds in organic chemistry, the C─F bond, under visible light irradiation. This study establishes Tp-Bpy-Me as a robust and efficient heterogeneous photocatalyst for defluorinative C─N bond formation across a broad range of substrates, including various fluoroarenes and nucleophiles. Remarkably, the photocatalytic transformation proceeds even under natural sunlight, highlighting its potential for sustainable, energy-efficient applications. To the best of our knowledge, this work is the first successful demonstration of C─F bond activation toward C─N bond formation using a COF-based photocatalyst.