K. Kwak, D. Lee
J. Phys. Chem. Lett., 2012, 3 (17), pp 2476–2481
We report the synthesis and electrochemical characterization of a new water-soluble Au25 cluster protected with (3-mercaptopropyl)sulfonate. The presence of sulfonate terminal groups on the surface of the cluster enabled facile phase transfer of the water-soluble cluster to organic phase by ion-pairing with hydrophobic counterions. The phase-transferred form of the water-soluble Au25 cluster was found to retain its integrity and allowed investigation of its electrochemical properties in organic media. The voltammetric investigation of the phase-transferred Au25 cluster in mixtures of CH2Cl2 and toluene has revealed that the cluster exhibits the characteristic Au25 peak pattern, but the electrochemical HOMO–LUMO energy gap of the cluster varies from 1.39 to 1.66 V depending on the solvent polarity. The origin of the solvent dependence is explained by the electrostatic field effect of the sulfonate anion on the redox potentials of the Au25 cluster.