Million-Turnover Photocatalysis Enabled by Far-Red-Light-Responsive Gold Nanoclusters.

In recent years, numerous photocatalytic systems have been developed to promote a wide range of organic transformations mediated by singlet oxygen. However, conventional blue-light photosensitizers encounter significant challenges in large-scale synthesis, primarily due to the limited penetration depth of high-energy photons. Herein, we report an atomically precise Au27 nanocluster featuring a novel superatomic core built from an icosahedral Au13 and a tetrahedral Au4, allowing for highly efficient singlet oxygen generation under far-red-light irradiation. While its overall structure closely resembles that of Au25 nanoclusters with a single icosahedral Au13 core, the incorporation of a tetrahedral Au4 building unit through ligand engineering markedly enhances intersystem crossing efficiency and aligns transition energies for effective O2 sensitization, affording an internal quantum yield of 0.37% at 740 nm. Compared with previous light-driven systems, our ten-gram-scale, cluster-based photochemical process reduces catalyst loading by four orders of magnitude (10,000-fold), requiring only 13 nmol of photocatalyst, and achieves turnover numbers greater than one million. This study establishes a new paradigm in photocatalyst design, demonstrating how atomic-level structural control can enable far-red-light-driven organic transformations with substantially enhanced catalytic performance.