Voltammetry and electron-transfer dynamics in a molecular melt of a 1.2 nm metal quantum dot.

New molecular melts of nanoparticles have been obtained by place exchanging thiolated poly(ethyleneglycol, MW = 350) ligands into the monolayer shells of the quantum dot nanoparticle Au38(phenylethylthiolate)24. These melts are nearly monodisperse in monolayer protected Au clusters with core diameters of approximately 1.2 nm. LiClO4 electrolyte can be dissolved in the melt via the PEG component of the protecting monolayer, producing an ionically conductive nanophase and enabling voltammetry of the undiluted, semisolid nanoparticle molecular melt. The optical and electrochemical charging properties of the small nanoparticles have molecule-like characteristics (as opposed to quantized double layer charging) both in dilute fluid-solvent solutions and as undiluted melts. Potential step chronoamperometry shows that electronic charge is transported through the melt by diffusion-like core-core electron hopping reactions with a rate constant of 2 x 104 s-1.