3A Cyanide-Bridged Ru-Fe Supramolecular Photocatalyst for Efficient CO₂ Reduction

Supramolecular control over electron transfer is a key challenge in artificial photosynthesis. Here, we report a cyano-bridged Ru-Fe supramolecular photocatalyst that self-assembles in solution through spontaneous coordination. This preorganized architecture enables ultrafast excited-state electron transfer from Ru to Fe via a static oxidative quenching pathway, as revealed by pump-probe transient absorption spectroscopy showing sub-picosecond formation of the reduced Fe species, in contrast to the reductive quenching mechanisms commonly observed in related systems. Remarkably, reversible coordination of CO₂ to the supramolecular adduct can be directly monitored by electronic absorption spectroscopy, providing rare experimental access to substrate binding within a molecular photocatalytic system. Under visible-light irradiation, the system achieves highly efficient CO₂-to-CO conversion (AQY 18%), with CO selectivity exceeding 95%, suggesting an intrinsic preference of the supramolecular photocatalyst for CO formation. These findings establish cyano bridging as a powerful design principle for constructing supramolecular photocatalysts, enabling both mechanistic transparency and enhanced performance. More broadly, this strategy defines a modular platform that can be extended to a wide range of catalysts and photocatalytic transformations.