Size Matters: Influence of Gold-to-Ligand Ratio and Sulfur-Sulfur Distance of Linear Thioether Heptamers on the Size of Gold Nanoparticles

A systematic investigation of two parameters steering the size of linear octadentate heptamer-coated gold nanoparticles (AuNPs) is presented, being i) the chemical structure (sulfur-sulfur distance) of the coating thioether heptamer ligand and ii) the ratio of ligand to tetrachloroauric acid (HAuCl4) reduced during the formation of the AuNPs. For this purpose, a novel terphenyl-based thioether heptamer (Ter) is synthesized via an end-capping oligomerization strategy, comprising an increased distance between neighboring sulfur atoms in the ligand backbone compared to the meta-xylene- (Xyl) and tetraphenylmethane- (TPM) based heptamers. While for both investigated parameters a clear trend to various-sized NPs is shown, a stronger influence in the resulting sizes is observed by alteration of ligand to gold-ratio. Remarkable processability- and long-term stability-features were observed for AuNPs stabilized by the bulky tetraphenylmethane-based heptamer (TPM).