Electron Transport Through Composite Monolayers

Well-organized thiol monolayers on electrode surfaces are prepared using the Langmuir–Blodgett and self-assembly methods. Planned modification of the molecules building the monolayer allow the electron tunneling efficiency across the monolayer to be controlled. The barrier properties of the monolayers are probed by electrochemical methods. The extent of blocking for all systems under study indicates that contribution of the electroactive molecules that find direct access to the electrode surface can be neglected. These observations permit us to use the monolayers for the determination of the kinetic parameters of Fe(CN)^3– ₆ and IrCl^2– ₆ ion reduction. Such monolayers are employed for the studies of long-range electron transport. We show that insertion of amide bonds in appropriate positions of the alkyl chains of all molecules building the monolayer makes it possible to create a lateral hydrogen-bond network linking the internal amide groups in the monolayer and contributing to the electronic coupling between the redox probe and the electrode. The relation between the location of the amide moiety in the molecule and its importance for the electron tunneling efficiency through the intervening organic medium is discussed.