Surface-confined crown ether-capped gold nanoclusters: investigation on their electrochemical behavior

A new ligand 18-crown-6–aminoethanethiol (18C6–AET), in which crown ether–ammonium ion interaction was exploited, had been designed and synthesized. An estimated HOMO–LUMO gap of 0.259 eV for the 18C6–AET complex indicated a definite interaction between 18C6 and AET. Consequently, multivalent interactions interplayed for the stabilization of gold nanoclusters resulting in confined cationic clusters having a diameter in 2–5-nm range in aqueous medium. The modified indium tin oxide electrodes with immobilized 18C6–AET-capped gold nanoclusters represented a metal–insulator–semiconductor junction across which the characteristic interfacial electron transport was unraveled. A heterogeneous electron transfer rate constant of 5.082 s−1 with a transfer coefficient of 0.51 was obtained for the quasi-reversible process, complying with a core-to-core electron hopping transport along with through-bond tunneling across the linker.