Density Functional Theory Studies on Structure, Ligand Exchange, and Optical Properties of Ligand-Protected Gold Nanoclusters: Thiolate versus Selenolate

Atomically precise thiolate-protected Au nanoclusters (NCs), i.e. Au_<i>m</i>(SR)_<i>n</i>, have attracted intensive research interest during the past few years. Recently, the synthesis and isolation of selenolate-protected gold clusters (Au_<i>m</i>(SeR)_<i>n</i>) via the ligand exchange of thiolate with selenol were achieved, which demonstrated identical compositions to those of thiolate-protected Au NCs. In this study, we perform a comprehensive theoretical study on the structure, electronic structure, and electronic optical absorption properties of 11 selenolate-protected gold clusters on the basis of density functional theory (DFT) calculations. Our results propose that the selenolate-protected Au NCs with framework structure identical to the thiolated ones are stable local minima. The ligand effect is proposed to understand the distinct geometrical structures of Au₂₄(SeR)₂₀ and Au₂₄(SR)₂₀ NCs. In addition, the optical absorption properties of thiolate- and selenolate-protected Au NCs are compared via the time-dependent density functional theory (TD-DFT). The results indicate that two types of Au NCs possess similar shape of electronic optical absorption spectra and electronic structure. The excitation wavelength dependent intermolecular electron transfer between the Au₂₅(ER)⁻ (E = S and Se) and O₂ is revealed as well