Engineering Ag₆ Cluster-Based Donor-Acceptor Heterojunctions Into Hydrogen-Bonded Organic Frameworks for...

Atomically precise coinage metal nanoclusters possess well-defined structures and distinctive optoelectronic properties. However, their assembly through weak van der Waals interactions often results in inefficient charge migration and rapid electron-hole recombination. Hydrogen-bonded organic frameworks (HOFs) offer an alternative strategy to integrate functional clusters into ordered crystalline materials while preserving molecular isolation. Herein, we report the first example of coinage-metal-cluster-based donor-acceptor (D-A) heterojunction engineered into a HOF. A tailored Ag₆ cluster serves as the electron-rich donor, and 4,4'-bipyridine (BPY) acts as the electron-deficient acceptor. Directional N─H···N hydrogen bonds guide the assembly into a crystalline Ag₆-HOF, which retains the intrinsic structure of the Ag₆ clusters while creating hydrogen-bonded channels for enhanced inter-cluster charge transport. Photoelectrochemical studies and density functional theory calculations reveal an S-scheme heterojunction, with the highest occupied molecular orbital (HOMO) localized on the Ag₆ cluster and the lowest unoccupied molecular orbital (LUMO) on the BPY linker. This electronic configuration promotes spatial charge separation, extends visible-light absorption, and significantly boosts photocatalytic H₂O₂ production compared to the individual components. The work demonstrates hydrogen-bond-directed assembly as a precise and versatile approach to design cluster-based heterojunctional materials with tunable electronic structures and enhanced photocatalytic performance.