Small gold nanoparticles (∼1.4–2.2 nm core diameters) exist at an exciting interface between molecular and metallic electronic structures. These particles have the potential to elucidate fundamental physical principles driving nanoscale phenomena and to be useful in a wide range of applications. Here, we study the optoelectronic properties of aqueous, phosphine-terminated gold nanoparticles (core diameter = 1.7 ± 0.4 nm) after ligand exchange with a variety of sulfur-containing molecules. No emission is observed from these particles prior to ligand exchange, however the introduction of sulfur-containing ligands initiates photoluminescence. Further, small changes in sulfur substituents produce significant changes in nanoparticle photoluminescence features including quantum yield, which ranges from 0.13 to 3.65% depending on substituent. Interestingly, smaller ligands produce the most intense, highest energy, narrowest, and longest-lived emissions. Radiative lifetime measurements for these gold nanoparticle conjugates range from 59 to 2590 μs, indicating that even minor changes to the ligand substituent fundamentally alter the electronic properties of the luminophore itself. These results isolate the critical role of surface chemistry in the photoluminescence of small metal nanoparticles and largely rule out other mechanisms such as discrete (Au(I)—S—R)<i><sub>n</sub></i> impurities, differences in ligand densities, and/or core diameters. The results from these experiments are then applied to the less noble coinage metals (e.g. silver and copper) which share the same valence electronic configuration as gold. We then demonstrate that copper and silver nanoparticles of analogous size, shape, and surface chemistries as gold nanoparticles exhibit comparable luminescent properties, a critical step in the design of cost-effective luminescent particles.

Ligand-mediated near-infrared photoluminescence of small diameter copper, silver, and gold nanoparticles

256th National Meeting (2018)

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