Effect of interchain hydrogen bonding on electron transfer through alkanethiol monolayers containing amide bonds

Two-component self-assembled monolayers (SAMs) were designed as model systems for the studies of the factors controlling long-range electron-transfer processes. The monolayers, which were attached to a gold electrode, consisted of two components: an alkanethiol with an amide moiety in the chain and an electroactive terminal ferrocene group and a nonelectroactive thiol acting as the diluent of the electroactive centers. The diluent was either a simple alkanethiol or an alkanethiol containing an amide group. The rates of electron transfer for the electroactive ferrocene group were calculated using the data obtained by voltammetry and chronoamperometry. Upon substitution of the diluent alkanethiol for an alkanethiol containing an amide group, the rate constant of the oxidation of ferrocene headgroups increased more than 3 times, while the reorganization energy remained unchanged. The increased electronic coupling between ferrocene and the electrode was ascribed as due to the contribution of the hydrogen bond network linking internal amide groups in the monolayer.