Anion effect on the electrochemical characteristics of a gold electrode modified with a self-assembled monolayer of ferrocenylhexanethiol in aqueous and dichloromethane solutions

The electrochemical characteristics of a gold electrode modified with a self-assembled monolayer (SAM) of ferrocenylhexanethiol were investigated in aqueous and dichloromethane solutions containing various anions, i.e. HSO4− (or SO42−), ClO4−, and PF6−. In all the cases, a pair of redox peaks corresponding to the redox of a ferrocene moiety in a SAM was observed. The peak positions depended on the anions in the solution. While the redox potential measured in the aqueous solutions shifted more positively in the anion order of PF6−, ClO4−, and HSO4−, that measured in dichloromethane shifted more negatively in this order. The origin of this anion effect on the redox potentials in the aqueous and dichloromethane solutions was discussed by comparing the electrochemical characteristics of the results for ferrocene dissolved in dichloromethane.