Isoreticular Metal–Covalent Organic Frameworks With Engineered π-Conjugation for Efficient Photocatalytic Hydrogen Production

Abstract

Developing structurally well-defined, noble-metal-free photocatalysts that combine high stability with efficient charge utilization remains a key challenge for sustainable hydrogen (H₂) production. Herein, we report isoreticular two-dimensional metal–covalent organic frameworks (MCOFs) termed Cu₃-PDA, Cu₃-NDA, and Cu₃-ADA (PDA = 1,4-phenylenediamine; NDA = 2,6-naphthalenediamine; ADA = 2,6-anthracenediamine), assembled from preorganized planar trinuclear Cu₃-cluster nodes and aromatic diamine linkers with systematically extended π-conjugation. All three frameworks preserve identical topology and stacking while allowing a single-variable modulation of linker length and conjugation to tune light harvesting and charge separation. Under visible light irradiation, the moderately conjugated Cu₃-NDA delivers exceptional noble-metal-free H₂ evolution of 31,328 μmol g⁻¹ h⁻¹, 4-fold and 2.7-fold higher than Cu₃-PDA and Cu₃-ADA, respectively, ranking among the best COF-based photocatalysts. Photoelectrochemical measurements and theoretical analyses indicate that an appropriately extended π-extension promotes delocalized electron transport and suppresses recombination, achieving the best balance between carrier separation and interfacial transfer. This work establishes a tractable platform to correlate conjugation engineering with photocatalytic activity in MCOFs and offers a general design paradigm based on cluster-node engineering and reticular conjugation control.

Keywords

π-conjugation / charge transfer / metal–covalent organic frameworks / photocatalytic hydrogen production

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2026 The Author(s). Electron published by Harbin Institute of Technology and John Wiley & Sons Australia, Ltd.