Molecular alloying of titanium–oxo clusters for linker-free S-scheme interfaces

Heterojunction engineering is one of the most effective strategies for enhancing charge separation and improving the performance of photo-functional materials. However, such heterojunction functionality has been almost exclusively realized in extended solids, and how to translate this concept into atomically precise molecular systems remains an open question. Here, we employ two isostructural yet electronically distinct titanium-oxo clusters, Ti 12 Mn 6 O 18 (Bz) 30 and Ti 12 Cr 6 O 18 (Bz) 30 (denoted as TiMn and TiCr, respectively; Bz denotes C 6 H 5 CO 2 ), as modular nanosized building blocks to construct molecular alloys that form eutectic molecular alloys across the entire compositional range. Free from covalent or ionic linkages, TiMn and TiCr achieve spontaneous Fermi-level equilibration solely through intimate intermolecular packing, thereby establishing an S-scheme junction at the molecular scale. This markedly enhances charge-carrier separation, carrier lifetime, and interfacial charge-transport kinetics, leading to substantially increased photocurrents, accelerated reactive oxygen species generation, and significantly improved elimination of representative waterborne micropollutants. The emergent functionality originates from local electronic complementarity and low-resistance intermolecular charge-transport channels facilitated by ligand π–π interactions, whereas long-range crystalline order is not essential. Our findings suggest a convenient approach for developing nanocluster-level functional donor–acceptor systems without relying on extended frameworks or on covalent fusion between the building units.