Derivatization of Carbon Surfaces by Anodic Oxidation of Arylacetates. Electrochemical Manipulation of the Grafted Films

Abstract

Electrochemical oxidation of the corresponding carboxylates (Kolbe reaction) offers a simple and efficient means to solidly attach a monolayer of arylmethyl groups on carbon surfaces. The starting molecules are easily accessible, and the presence of appropriate substituents on the phenyl rings makes this type of derivatization a convenient starting point for further chemical modifications. The extent of the surface modification can be followed by cyclic voltammetry as a function of the number of successive potential cycles. The presence of the groups on the surface, their arrangement, and their concentration are determined by the same technique as well as by X-ray photoelectron spectroscopy and scanning electron tunneling microscopy after transfer of the derivatized electrode into a pure electrolyte solution. The fact that reductive and oxidative cyclic voltammograms of the derivatized electrodes can be obtained demonstrates that the grafted groups are in electrical contact with the electrode by means of electron hopping to or from the aryl moieties they contain. After the electrode has been passivated at the potential whereby anodic oxidation occurs, a second, more positive wave appears. Oxidation at the potential of this second wave triggers a further grafting process leading to a denser film. Electrochemical manipulations allow not only the attachment of electroactive films on the carbon surface but also their erasing by setting the electrode potential at a value where the attached groups are oxidized.