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/CH₃OH. 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.