Single‐Site Defect Engineering in Covalent Organic Frameworks Enables Extended Directional Charge Transfer Pathway for Efficient Photocatalytic Hydrogen Evolution

ABSTRACT Covalent organic frameworks (COFs) have emerged as promising photocatalysts for hydrogen production. Defect engineering has been identified as an effective approach to break structural symmetry and improve charge transfer. Nonetheless, achieving atomically precise construction of defects in COFs while preserving structural integrity to achieve efficient directional charge carrier migration remains challenging. Herein, we introduce an innovative “single‐site defects” (SSD) strategy to construct functionalized single ring‐cleavage defect sites that enable directional charge transfer in COFs. As a proof of concept, a series of SSD‐based CTF‐1 (covalent triazine frameworks) was developed by functionalizing the defect sites with various substituents. Notably, the amide‐functionalized d‐CTF(CONH 2 ) exhibits the highest hydrogen evolution activity of 17.6 mmol g −1 h −1 , representing a 6.3‐fold enhancement over pristine CTF‐1. Mechanistic investigations reveal that the SSD structure enhances the built‐in electric field and redirects the local charge transfer into an extended directional transfer pathway surrounding the SSD, while the preserved long‐range order ensures efficient charge transport, collectively boosting charge separation efficiency. In contrast to traditional defect engineering approaches, this strategy for the first time provides a universal design principle for the atomically precise construction and functionalization of defects that enable the modulation of charge transfer for target reactions.