Electrochemical Fabrication of Poly(6-aminoindole)–Graphene Oxide Nanostructures on Transparent Electrodes

The nanochemistry, sensor, and organic electronics development leads to a constant search for easier-to-synthesize, cheaper polymer composite materials with new physicochemical properties. Materials based on the heteroaromatic compounds containing an aromatic ring (conjugated system) and a nitrogen atom are arousing the intense interest of researchers since the electronic properties of conjugated polymers are similar to those of inorganic semiconductors. Polyaminoindole (PAIn), among the substances of this class, has a relatively high electrical conductivity, good thermal stability, and a slower rate of degradation compared to other conducting polymers [1]. Surfaces covered with a thin layer of polyaminoindole exhibit catalytic properties during the electrooxidation of organic substances, are stable in aqueous solutions, and inhibit corrosion due to the good adhesion of the polymer film to the metal surface [2]. Composite materials based on PAIn are used in the electrochemical immunosensors with ultrahigh sensitivity manufacturing [3] and lithium-ion rechargeable batteries [4]. It was reported that poly(6-aminoindole) surface films at gold show reversible redox activity accompanied by color changes [5]. However, the electrochemical deposition of this indole derivative, especially in the presence of doping components, needs to be studied and improved. In this work, we investigated the influence of graphene oxide (GO) on the conditions of electrochemical polymerization of 6-aminoindole, the features of the polymer chain structure.

Poly(6-aminoindole) films were obtained on flexible optically transparent substrates of polyethylene terephthalate covered with a thin conductive layer of indium-tin oxide (PET-ITO). Polymerization was carried out by potential sweep mode in acidic media. It was established that monomer electrooxidation takes place in the range of potentials of 0.6-0.8 V vs. Ag/AgCl and leads to the formation of uniform polymeric films. According to IR spectroscopy, the polymerization of 6-aminoindole occurs due to the formation of a C-N bond in the 1,3 positions along the molecule chain, while the amino-group does not participate in the joining process. The electrochemical behavior of PAIn doped with GO was studied in the range of potentials E = -0.9... + 1.0 V. The possibility of catalytic electrooxidation of reduced GO on the PAIn film was revealed. The SEM images of poly(6-aminoindole) films obtained in the presence of GO clearly show very different morphologies with dissimilar particle sizes compared to the unmodified PAIn film. The ordered grid formation of GO uniformly distributed over the film surface is observed. In addition, with an increase in the potential sweep, the PAIn/GO interfacial boundary becomes thinner.