Poly(3-arylthiophenes): Syntheses of monomers and spectroscopic and electrochemical characterization of the corresponding polymers

Several arylthiophene derivatives were synthesized using the Kumada cross-c oupling reaction and electropolymerized at a platinum electrode with the ai m of investigating the effect of the number of thiophene unit and substitut ion pattern of the monomers on the spectroscopic and charge storage propert ies of the resulting polymers. The electrochemical oxidation of these monom ers showed a decrease of the anodic peak potential as the number of thiophe ne units is increased: 1.2-1.4, 1.0, and 0.75 V for the mono-, bi-, and ter thiophene, respectively. The polymers having one phenyl ring per thiophene unit displayed a larger band gap with the exception ofpoly-3-phenyl-thiophe ne, which showed a much smaller band gap. The lower band gap for the later can be explained by the higher reactivity of the cation radical(as evidence d bg;a high oxidation potential) which led to a highly conjugated polymer. The cyclic voltammograms of the same polythiophene derivatives is character ized by a significant charge unbalance between the doping and undoping char ge and most showed a limited cycle lifetime. On the other hand, poly-3-phen yl thiophene, poly-3 '-(1-naphthyl)-2,2 ': 5 ' ,2 " -terthiophene are the m ore stable and also show a relatively good balance between doping and undop ing charge for both the p- and n-doping redox processes. The highest voltam metric charge density evaluated by considering the weight of monomer unit w as recorded for poly-3-phenyl thiophene despite the fact that some poly ter thiophene derivatives have a lower phenyl ring/thiophene unit ratio.