Electrochemical Rectification Using Mixed Monolayers of Redox-Active Ferrocenyl Dendrimers and n-Alkanethiols

A strategy for constructing a dendrimer-based electrochemical current rectifier that permits current flow in only one direction is described. This approach is based on the insulating properties of n -alkanethiol self-assembled monolayers and the ability of redox-active ferrocenyl dendrimers to mediate electron transfer. The dendrimer-based rectifying layer is prepared by direct adsorption of second-, third-, or fourth-generation ferrocene-functionalized poly(propylene imine) dendrimers onto Au surfaces, followed by adsorption of n -hexadecanethiol. Reflection infrared spectroscopy, ellipsometry, and electrochemical measurements are used to characterize the resulting two-component monolayers. The surface coverage of ferrocenyl dendrimers in the two-component monolayers is estimated to be about 50% of maximum coverage. Cyclic voltammetry in electrolyte solutions containing the redox-active probes Fe(CN) 6 4 -, Fe(bpy) 3 2+, and Co(bpy) 3 2+ reveals that the ferrocenyl dendrimer/ n -alkanethiol-modified electrodes exhibit excellent barrier properties that prevent direct oxidation/reduction of the solution-phase redox molecules. Electrochemical current rectification occurs via mediated electron transfer across the surface-confined ferrocenyl dendrimers.