Electron transfer through self-assembled monolayers of alkaneselenols and alkanethiols on mercury electrode

The kinetics of long-range electron transfer through self-assembled monolayers of n-alkanethiols and n-alkaneselenols (SAMs) was studied via voltammetry of hexaammineruthenium (III) on a hanging mercury drop electrode (HMDE). Electron tunneling rates across the both monolayer films decay exponentially with thickness with a tunneling coefficient beta. = 1.1 per CH2. Gradual additions of aliphatic alcohols to the solution result in a decrease of the long-range electron transfer rate, by a maximum of 7-fold, dependent upon the alcohol concentration, but independent of the thickness of the n-alkanethiol monolayer (SAM) and the alcohol's chain length. The mechanism involving competitive adsorption of the alcohol on the SAM surface is proposed to interpret the kinetic data. Electron tunneling rates across n-alkanethiol monolayers are approximately 4-fold larger than the rates measured on n-alkaneselenol monolayers containing the same number of carbon atoms signifying the importance of head-group contact in electron transfer through SAMs.