Electrochemical Approach for Constructing a Monolayer of Thiophenolates from Grafted Multilayers of Diaryl Disulfides

An electrochemical approach is presented for constructing a monolayer or near monolayer of molecules on conducting surfaces by degradation of a multilayer film formed via reduction of aryldiazonium salts. Usually, grafting of surfaces employing aryldiazonium salts results in the formation of intertwined multilayers in a difficult controllable polymerization reaction. However, if the chemical system selected contains a cleavable group, a subsequent degradation of the polymeric network may allow the formation of a thin reactive molecular layer. As chemical systems, diazonium salts of diaryl disulfides (ArSSAr) were selected to produce surface-confined thiophenolates, but an extension of the approach to include other functionalities is straightforward. The thiophenolates (ArS - ) may be reversibly oxidized to disulfides to establish a covalently attached ArSSAr/ArS - redox pair at the surface. Analysis of the surfaces was carried out by means of cyclic voltammetry, X-ray photoelectron spectroscopy, and atomic force microscopy.