Electrosynthesis of novel polyheterocycles

Abstract

The electropolymerisation of a wide-range of derivatised (E)-styrylthiophenes, pyrroles and furans has been investigated. Stable coherent films of low conductivity (σ: 1Q^-6 S cm^-1), which were characterised by a number of electrochemical, spectroscopic and microscopic techniques, were formed. The polymers were redox inactive as shown by cyclic voltammetry. This was possibly due to oxidation of the alkene spacer linkage resulting in formation of a crosslinked polymeric matrix in which the conjugation of the backbone had been disrupted.
To protect the double bond from electro-oxidation, without causing a disruption in planarity, an electron withdrawing nitrile group was introduced at the alkene spacer linkage. Electropolymerisation of (Z)-α,β-diarylacrylonitriles containing one heterocyclic species produced thick adherent films, but in the majority of cases, the nitrile substituent was unable to suppress oxidation of the double bond and crosslinked redox inactive films of low conductivity (σ: 10^-6 S cm^-1) were produced. In contrast, electropolymerisation of (Z)-α,β-diarylacrylonitriles containing two heterocycles produced highly doped redox active polymers of enhanced conductivity ( σ: 10^-4 S cm^-1). Dendritic structures, thought to be the result of unidirectional polymer growth via α,α'-linkages, were observed in some cases.
Density functional theory (DFT) was used to predict the outcome of electropolymerisation reactions by calculating the Π-spin density distribution of monomeric radical cations in order to determine coupling positions in resultant polymers. High positive Π-spin densities were found at the alkene spacer linkage of (E)-styrylheterocycles, suggesting crosslinking reactions via the double bond during electropolymerisation, in agreement with experimental observations. In contrast, DFT calculations of some (Z)-α,β-2-diarylacrylonitriles containing two heterocycles showedhigh n-spin density located at the heterocyclic a-positions, a prerequisite for the formation of α,α'-linkages necessary for electroactivity.
The electropolymerisation of some sterically hindered five member heterocycles (2,5- dimethylthiophene and 1, 1',1 " ,1 "'-silanetetrayltetrakis-1H -pyrrole) illustrated the importance of α, α-linkages and extended conjugation in polymer conduction.
Final studies addressed the use of polymers for enzyme immobilisation. STM investigations of enzymes such as the 51 kD/66 kD heterodimer and 66 kD/66 kD homodimer of the HIV -1 reverse transcriptase and RNNDNA hybrids, which may be used in the immobilisation studies, on an n-MoTe2 substrate were carried out. AFM studies of poly((E)-2-styrylpyrrole), an extremely smooth polymer, revealed a microcorrugated topology with features of heights ranging from 2-5 nm and widths of approx. 80 nm.

Date of Award	Feb 1995
Original language	English
Awarding Institution	University of Portsmouth
Supervisor	Sheelagh A. Campbell (Supervisor)