Experimental and Theoretical Determination of the Optical Gap of the Au144(SC2H4Ph)60 Cluster and the (Au/Ag)144(SC2H4Ph)60 Nanoalloys.

Abstract

Au144PET60 and Au144-xAgxPET60 (PET = SC2H4Ph, phenylethylthiolate, and 30 ≤ x ≤ 53) clusters were studied by optical spectroscopy and linear response time-dependent density functional theory. Spectra of thin dry films were measured in order to reveal the onset for electronic absorption. The optical gap of the Au144PET60 cluster was determined at 0.19 ± 0.01 eV, which agrees well with the computed energy for the first optical transition at 0.32 eV for a model cluster Au144(SH)60 when the line width of individual transitions is taken into account. The optical gaps for the Au144-xAgxPET60 alloy clusters were observed in a range of 0.12-0.26 eV, in good agreement with the calculations giving 0.16-0.36 eV for the lowest-energy optical transitions for corresponding Au144-xAgx(SH)60 models. This indicates that the gap is only moderately affected by doping Au with Ag. This work constitutes the first accurate determination of the fundamental spectroscopic gap of these compounds.