Engineering Ag6 Cluster-Based Donor-Acceptor Heterojunctions Into Hydrogen-Bonded Organic Frameworks for Photocatalytic H2O2 Production.

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.