The nature of electronic coupling between ferrocene and gold through alkanethiolate monolayers on electrodes: The importance of chain composition, interchain coupling, and quantum interference

Cyclic voltammetry was used to measure electron-transfer rate constants of self-assembled mixed monolayers. on gold electrodes formed by coadsorption of a redox-active ferrocene-based alkanethiol [(eta (C5H5)-C-5)Fe(eta (C5H4)-C-5)-. CO2(CH2)(5)X(CH2)(6)SH, where X = -CH2- or -O-] and a diluent alkanethiol [CH3(CH2)(4)Y(CH2)(6)SH, where Y = -CH2- or -O-]. The replacement of a methylene link by an ether link in the redox-active component leads to a significant reduction in the rate of electron transfer and results from a decrease in the electronic coupling through the chain. The corresponding replacement in the diluent leads to a smaller, but measurable, decrease in rate constant-suggesting that intermolecular electronic coupling pathways also contribute to the electron transfer.