The electrosynthesis and characterisation of functionalised polyindoles

• Main Author: Thomson, Alastair David
• Published: University of Edinburgh 1997
• Subjects: 547.7
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.662886

The aim of the work presented in this thesis was to investigate the electropolymerisation of indole and various substituted indole monomers, with the objective of electrosynthesising, characterising and functionalising indole-based conducting polymers for possible use as sensor devices. It was found that on electropolymerisation, all of the substituted indole monomers studied formed asymmetric cyclic trimer species. A mechanism was proposed invoking a 3-3' dimer intermediate to explain the nature of the trimer formed. These trimers were believed to initially form in solution and then deposit on to the electrode surface where they could link to form a polymer film consisting of linked trimer units. The polymer film then facilitated the formation of trimers on the film surface. The electronic nature of the substituents was found to control the reactivity of the trimers, and a correlation was found between the electron withdrawing / donating nature of the substituent and the observed potential of the trimer one electron redox reaction. The lyophilicity of the trimer substituents was found to affect the relative solubility of the trimers which controlled the rate of initial adsorption of trimers on to the electrode surface and the rate of desorption of free trimers from the polymer film. It was discovered that for the electropolymerisation of indoles with highly solubilising substituents, a pre-formed polymer layer could be used to encourage the deposition of trimers on to the film and decrease their desportion rate. This was also used to limit any passivation effects noted for electropolymerisation on platinum. The linking mechanism of all the substituted cyclic trimers studied is believed to be very similar. This was tested by studies carried out on the electropolymerisation of N-methylindole. These studies showed that the major product of the N-methylindole electropolymerisation was a highly soluble cyclic trimer species, in addition there was also an appreciable amount of linear polymer produced from the energetically destabilised sterically hindered 3-3'dimer. The absence of any linking of the N-methylindole trimers suggested that the nitrogen positions in the trimer are involved in the linking reaction observed for all of the other substituted indoles studied.