Polyheterocycles containing beta,beta'-linkages - electrosynthesis and peroperties of poly(2,5-dimethylthiophene)

The intrinsically conducting polymer, polythiophene, contains primarily alpha,alpha'-linkages, although some alpha,beta' and beta,beta'-linkages are known to occur. In the current study, the electrochemical behaviour of 2,5-dimethylthiophene, a thiophene compound bearing methyl groups at both the alpha-positions normally required for monomer coupling, is investigated. A thick black film was electrodeposited on the anode surface as a result of electrochemical polymerisation. XPS studies showed that the polymer was doped, with a ratio of 3.9 monomer units to each dopant anion. The film was redox inactive with a conductivity of 10(-6) S cm(-1). The tow conductivity was attributed to limited conjugation of pi-electrons along the polymer backbone due to steric effects and the presence of the beta,beta'-linkages. Oligomeric solution species of up to five monomer units, formed during electropolymerisation, were characterised by mass spectrometry.