Ligand effects on the optical and chiroptical properties of the thiolated Au18 cluster

Abstract

The effect of chiral and achiral ligands protecting the inner Au₉ core of the Au₁₈(SR)₁₄ cluster is studied based on density functional theory (DFT) and its corrected long-range interaction (DFT-D) approach. It was found that the electronic properties (energy levels) depend on the specific ligands, which induce distinct distortions on the Au–S framework. However, the substitution of S-c-C₆H₁₁ as SCH₃ ligands may be considered to be correct given the obtained resemblance to the displayed bonding, optical and chiroptical properties. A further comparison of the CD and UV spectra displayed by the Au₁₈ cluster protected by chiral and achiral ligands attests that more intense profiles are featured by ligands including phenyl rings and/or oxygen atoms such that the Au₁₈ cluster protected by either achiral meta-mercaptobenzoic acid (m-MBA) or achiral SPh ligands displays more intense UV and CD signals. These results provide new insight into the effect of ligands on thiolated gold clusters.