Electropolymerisation of indole-5-carboxylic acid

Abstract

The electrochemical oxidation and polymerisation of indole-5-carboxylic acid have been studied in acetonitrile in the concentration range 10–100 mmol dm^–3. The initial product of this oxidation is an insoluble trimer which is deposited onto the electrode surface. Further oxidation of this trimer occures on the electrode to form a polymer containing linked trimer units. The degree of trimer linkage is determined by the time of deposition; the proportion of trimer in a film of any given thickness can therefore be controlled by varying the rotation speed of the electrode or the bulk monomer concentration.

Redox reaction of these layers involves oxidation and reduction of the trimer centres. It appears that the extent of electronic delocalisation between these redox centres in the polymer is small. Cyclic voltammetric studies indicate that polymer produced by the oxidation of pure trimer or by extraction from the deposited film show narrower redox peaks indicative of a more homogeneous morphology than the deposited layer.