Conjugation‐Controlled Ion Response in One‐Dimensional Covalent Organic Frameworks for Seawater Photocatalysis

Photocatalytic hydrogen evolution from seawater offers a sustainable route for energy production, yet the role of dissolved ions in modulating carrier dynamics remains poorly understood. Herein, we demonstrate conjugation‐controlled ion responses that regulate charge separation in one‐dimensional covalent organic frameworks (1D COFs) through ion‐induced polarization for seawater photocatalysis. Two COFs featuring localized (DHP‐COF) and extended (DHPD‐COF) conjugation are constructed. In natural seawater, DHP‐COF achieves 246.9 mmol g −1 h −1 for hydrogen evolution, 5.03‐fold higher than in pure water (49.1 mmol g −1 h −1 ), whereas DHPD‐COF shows only 2.48‐fold enhancement (from 38.9 to 96.5 mmol g −1 h −1 ), revealing markedly stronger ion‐responsive sensitivity in the locally conjugated framework. Mechanistic investigations reveal that localized conjugation preserves spatially inhomogeneous polar domains arising from segmented π‐electron distribution, enabling strong coupling with seawater ions and thereby amplifying local dipoles to generate enhanced internal electric fields for efficient charge separation. In contrast, extended π‐delocalization leads to electronic homogenization that attenuates ion‐induced polarization. Beyond hydrogen production, this system simultaneously achieves chemoselective hydrogenation of α , β ‐unsaturated carbonyl compounds to high‐value pharmaceutical intermediates in natural seawater/CH 3 OH. These findings establish conjugation‐controlled ion response as a key design principle for charge separation in saline photocatalysis and provide general guidelines for environment‐adaptive catalysts.