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

Developing structurally well‐defined, noble‐metal‐free photocatalysts that combine high stability with efficient charge utilization remains a key challenge for sustainable hydrogen (H 2 ) production. Herein, we report isoreticular two‐dimensional metal–covalent organic frameworks (MCOFs) termed Cu 3 ‐PDA, Cu 3 ‐NDA, and Cu 3 ‐ADA (PDA = 1,4‐phenylenediamine; NDA = 2,6‐naphthalenediamine; ADA = 2,6‐anthracenediamine), assembled from preorganized planar trinuclear Cu 3 ‐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 Cu 3 ‐NDA delivers exceptional noble‐metal‐free H 2 evolution of 31,328 μmol g −1  h −1 , 4‐fold and 2.7‐fold higher than Cu 3 ‐PDA and Cu 3 ‐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.