Rational Synthesis of Photocatalytic Acridinium‐Based Covalent Organic Frameworks via Single‐Atom Skeletal Editing

Abstract The rational synthesis of covalent organic frameworks (COFs) with customized functionalities and enhanced stability requires innovative bond‐forming strategies beyond conventional dynamic covalent chemistry. Herein, we report a novel single‐atom skeletal editing approach to construct acridinium‐based crystalline COFs through an irreversible Katritzky‐type reaction. This strategy enables precise transformation of 9,9′‐(2,3,5,6‐tetramethyl‐1,4‐phenylene)bis(3,6‐di‐tert‐butylxanthylium) with either 1,3,5‐tris(4‐aminophenyl)benzene (TAPB) or 1,2,4,5‐tetra(4‐aminophenyl)benzene (TADB) into acridinium‐linked COFs, denoted as Acr‐TAPB and Acr‐TADB, respectively. The transformation proceeds via a unique single‐atom oxygen‐to‐nitrogen replacement, converting the xanthylium precursor into acridinium frameworks. The resulting COFs exhibit high crystallinity, robust stability, strong redox ability, and efficient charge separation. Notably, Acr‐TADB functions as a highly effective metal‐free photocatalyst for oxidative nucleophilic substitution and [3 + 2] cycloaddition reactions, supporting gram‐scale synthesis in both batch and flow reactors with excellent stability. This work establishes skeletal editing as a powerful strategy for engineering functionalized COF architectures for advanced applications.