An Unconventional Approach Imparting Structurally Well-Defined Photoluminescent Gold Clusters With Water Solubility

Well-defined gold clusters that are water-soluble and photoluminescent are promising candidates for diverse applications in biological systems. We present here an unconventional approach that imparts water solubility to atomically precise gold clusters, which is achieved through de novo surface modification with dimethoxymethyl (formaldehyde dimethyl acetal) groups. By attaching dimethoxymethyl on pyridyl groups in [(C)(Au-dppy)₆Ag₂](BF₄)₄ (1, dppy = 2-pyridyldiphenylphosphine), the solubility of resulted cluster [(C)(Au-L^a)₆Ag₂](BF₄)₄ (2a, L^a = 2-(4-dimethoxymethylpyridyl)diphenylphosphine) in water is significantly enhanced, while its molecular structure and intense photoluminescence (PL) are well reserved. Notably, 2a exhibits a high quantum yield (QY) of 32.7% in H₂O under ambient conditions. The universality of this approach is demonstrated by the addition of dimethoxymethyl groups on C@Au₆Ag₂-, C@Au₆Ag₄-, and C@Au₆-type clusters, giving water-soluble products whose identities have been confirmed by single-crystal x-ray diffraction (SCXRD) and ESI-MS in H₂O. Furthermore, cell imaging results indicate that 2a can enter the nucleus of living cells in aqueous medium, which is accumulated in the nucleolus. This approach is anticipated to serve as a highly practical means for modifying the water solubility of atomically precise metal clusters toward bioimaging and related applications.