Thiol-Terminated Di-, Tri-, and Tetraethylene Oxide Functionalized Gold Nanoparticles: A Water-Soluble, Charge-Neutral Cluster

A series of gold nanoclusters stabilized by ligands containing short ethylene oxide oligomers of fixed length were prepared and characterized. The thiols CH 3 (OCH 2 CH 2 ) n SH (where n = 2, 3, and 4) were substituted onto the surface of 1.8-nm hexanethiol-capped gold clusters by a thiol-exchange reaction, and the resulting nanoclusters were characterized by NMR, FTIR, and UV/vis spectroscopies; TGA; and TEM analysis. A degree of ligand exchange greater than 99% was achieved, and the gold core diameter remained unchanged in the final material. Of particular interest, the cluster with n = 2 was water-insoluble, whereas those with n = 3 or 4 were water-soluble. The thin-film electrical conductivities of these clusters were compared with those of alkanethiol-capped clusters of similar chain lengths and found to be roughly 1 order of magnitude greater. In a chemical vapor sensor configuration, this series of clusters displayed strong electrical responses that showed a correlation between the length of the ethylene oxide ligand and the polarity of the vapor.