Electrochemical studies of the terminally substituted alkanethiol monolayers formed on a gold electrode: Effects of the terminal group on the redox responses of Fe(CN) 3−6, Ru(NH 3) 3+6 and ferrocenedimethanol

Abstract

Self-assembled monolayers of the alkanethiols having OH, COOH and NH 2 terminal group were formed on a gold electrode via a sulfur attachment. The effects of their terminal groups on the redox responses of Fe(CN) 3− 6, Ru(NH 3) 3+ 6 and 1,1′-ferrocenedimethanol (FcDM 0) aqueous solutions were investigated by cyclic voltammetry. The voltammetric response of Fe(CN) 3− 6 was decreased in the order of NH 2 > OH > COOH terminal group. In contrast, the response of Ru(NH 3) 3+ 6 was increased in the order of NH 2 < OH < COOH. In the case of FcDM 0, the response was in the order of COOH > OH > NH 2. These results were discussed in relations to the effect of charged terminal group on (a) the shift of the potential drop across the diffuse layer and (b) the change of the concentration of redox species at the electrode surface which is caused by the electrostatic interaction between the terminal group and ionic redox species.