Modulating In‐Plane Conjugation and Core Polarity in Naphthalimide‐Based Covalent Organic Frameworks Enables Efficient H 2 O 2 Photosynthesis

ABSTRACT Efficient photocatalytic H 2 O 2 production is a sustainable alternative to the anthraquinone process, yet designing photocatalysts with both high activity and selectivity is extremely challenging. Covalent organic frameworks (COFs) offer modular architectures and tunable electronic structures, but precise electronic modulation for maximizing H 2 O 2 photosynthesis is rarely attained. Here we report a series of naphthalimide‐based donor–acceptor COFs with systematically engineered cores. Among them, NDI–B–COF (benzene core) delivers an outstanding H 2 O 2 yield of 11,025 μmol g −1 h −1 (with sacrificial agent), far surpassing its nitrogen‐ and triazine‐core analogs. This performance stems from synergistic effects of an extended in‐plane conjugation and a reduced core polarity, which collectively enhance charge separation, directional carrier transport, and *OH intermediate formation, thereby lowering the barrier for two‐electron water oxidation. These findings establish a clear structure–property–activity correlation and offer a general strategy for developing highly efficient metal‐free photocatalysts.