Gold clusters smaller than 2 nm exhibit unique quantum size effects with discrete electronic energy levels, and possess both semiconducting and molecule-like characteristics. Exciting optical, electrochemical and catalytic properties are observed in gold clusters because of their discrete electronic transitions. In recent work, we have shown unique optical transitions in the gold-clusters using ultrafast luminescence and temperature-dependent absorption measurements. In the present work, measurements are aimed at understanding of both ligand and solvent effects on the optical transitions. Here we used bi-icosahedral Au25 clusters ([Au25(PPh3)10(X)5Cl2]2+; X- thiolated ligands) as the systems to investigate both ligand and solvent mediated effects These Au25 clusters were synthesized using five different thiolated ligands to investigate how the ligand affects optical properties and four different solvents used to investigate the solvent mediated properties of the clusters. Temperature-dependent absorption measurements of bi-Au25 in aprotic (toluene) and protic (ethanol, TFE and 2-butanol) were carried out to understand the influence of solvent hydrogen bonding on the low energy absorption. In toluene, both low and high energy absorption bands shift to higher energies consistent with electron-phonon relaxation. However in protic solvents of ethanol, TFE and 2-butanol, the low energy absorption shows zig-zag trend with high to low high energy shifts with a decrease in temperature.

Solvent and ligand effect on ultrafast and temperature-dependent optical properties of bi-icosahedral Au25 clusters

251st National Meeting (2016)

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