Versatile transformations of alkylamine-derivatized glassy carbon electrodes using aryl isocyanates

The reaction between a nucleophilic 4-(2-aminoethyl)phenyl-tethered glassy carbon surface and various para-substituted aryl isocyanates [ONC-PhX; X = NO(2), COPh, Cl, H, and NMe(2)] has been studied in toluene. It is demonstrated that the nucleophilic addition reaction is relatively fast occurring within two hours while providing an efficient and versatile route for derivatizing alkylamine-functionalized surfaces. An often overlooked issue in surface reactions is the possibility for competing physisorption processes. In such cases, the solution-based reactants become adsorbed to the surface or embedded in the grafted layer rather than chemically bonded to the surface. It is shown that for two of the aryl isocyanates (X = NO(2) and COPh) this physical adhesion can be so strong that even prolonged ultrasonic treatment cannot remove the adsorbant. However, a single potential excursion is capable of desorbing most of the physisorbed layers. The isocyanate-based method is also compared with the well-known approaches involving diazonium salts for assembling similar chemical systems directly. It is concluded that the method can be used advantageously not only in cases, where such approaches should fall short, but also if the goal is to achieve better control of the positioning of, e.g., redox active molecules in a well-defined layer with the ultimate goal of obtaining distinct electrochemical responses.