Covalently immobilized 1,4-phenylenediamine on 11-mercaptoundecanoic acid-coated gold: Effect of surface-confined monomers on the chemical in situ deposition of polyaniline and its derivatives

We present the study of polyaniline, poly(2-methoxyaniline), and poly(2,5-dimethoxyaniline) chemical deposition in situ on gold electrodes coated with thiol monolayers containing 4-aminophenyl groups in terminal positions. The thiol. monolayers were prepared by self-assembly of 11-mercaptoundecanoic acid on gold with subsequent covalent attachment of 1,4-phenylenediamine molecules through the formation of a peptide bond with use of 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide as catalyst. Thus, the immobilized monomer molecules (H2N-C6H4-NHOC-C10H20SH) could act as nucleation sites for subsequent polymer formation by the chemical in situ method. The deposition process of polymers was investigated with a quartz crystal microbalance. The electronic properties of such obtained polymers were studied by cyclic voltammetry. Particularly interesting behavior was observed for polyaniline, which exhibited unique voltammetric curves. We assigned this unusual behavior as the result of covalent attachment of some polymer chains to the surface.