On the opto-electronic properties of phosphine and thiolate-protected undecagold nanoclusters

We present here a detailed time-dependent density-functional theory investigation aimed at systematically dissecting the electronic spectra of two thiolate and phosphine protected undecagold nanoclusters. Calculations performed on the experimental structures of Au-11(PPh3)(7)Cl-3 and Au-11(PPh3)(7)(SPyr)(3) show that ligands have negligible contributions in the visible region. Metal -> ligand charge transfer transitions appear at energies well above the visible threshold, while transitions with some small ligand -> metal and ligand -> ligand character occur sporadically at even higher energies. Thus, the conjugation effect between the pi-electrons of the ligand and electrons of gold, recently hypothesized to interpret the spectra of phosphine and thiolate-protected nanoclusters, is not confirmed by the results of this study.