Electrografting of aryl amines on graphitic surfaces: An alternative to diazonium salts?

Aryl amines have recently been shown to be effectively grafted with the use of Lewis bases. Hence, they have been proposed as a potential alternative to aryl diazonium salts for the covalent modification of surfaces. In this work we compare grafting efficiencies of aryl amines, such as 4-bromoaniline (4-BA), with aryl diazonium salts, such as 4-bromobenzene diazonium (4-BBD), on carbon-based surfaces, namely highly oriented pyrolytic graphite (HOPG) and graphene. The Lewis base 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) was employed to improve the grafting of 4-BA to the surfaces. The systems were studied with a range of techniques to confirm grafting of the organic molecules to the carbon surfaces, such as cyclic voltammetry, atomic force microscopy, scanning tunnelling microscopy and Raman spectroscopy. Density functional theory calculations demonstrate that the C-C bond is more favoured than the C-N bond. The grafting density of the aryldiazonium salts on graphite and graphene surfaces is much higher compared to aryl amines with or without the use of a Lewis base. Consequently, selection of the appropriate precursor for efficient covalent functionalization of a surface is required.