Highly Fluorescent Au25-xAgx Nanoclusters Protected with Poly(ethylene glycol) - and Zwitterion-Modified Thiolate Ligands

We describe the growth and characterization of highly fluorescing, near-infrared-emitting nanoclusters made of bimetallic Au_25-xAg_x cores, prepared using various monothiol-appended hydrophobic and hydrophilic ligands. The reaction uses well-defined triphenylphosphine-protected Au₁₁ clusters (as precursors), which are reacted with Ag(I)-thiolate complexes. The prepared nanoclusters are small (diameter < 2nm, as characterized by TEM) with emission peak at 760 nm and long lifetime (~12 µs). The quantum yield measured for these materials was 0.3 - 0.4 depending on the ligand. XPS measurements show the presence of both metal atoms in the core, with measured binding energies that agree with reported values for nanocluster materials. The NIR emission combined with high quantum yield, small size and ease of surface functionalization afforded by the coating, make these materials suitable to implement investigations that address fundamental questions and potentially useful for biological sensing and imaging applications.