BETA,BETA-DISUBSTITUTED OLIGOTHIOPHENES, A NEW OLIGOMERIC APPROACH TOWARDS THE SYNTHESIS OF CONDUCTING POLYMERS

The electropolymerization of methylthio-substituted oligothiophenes 2- 4 has been studied. Theoretical and experimental results reveal that o nly 4,4'-disubstituted derivatives yield polymeric films. The reason f or this is that electron-donating methylthio (= methylsulphonyl) subst ituents in the 'outer' beta-positions of the starting compounds 2-4, w hich cause high spin densities at the corresponding a-C atoms, favour fast coupling steps between the reacting oligomers during all stages o f the electropolymerization. All data clearly indicate that the electr opolymerization of donor-substituted thiophenes is not a chain propaga tion process but a series of successive 'dimerization' steps. The resu lting polymers have been characterized by voltammetric measurements, i n situ conductivity experiments and spectroelectrochemistry. (C) 1998 Elsevier Science S.A. All rights reserved.