Studies on the CHCL 3 ‐soluble fraction of polythiophene and its conductivity on doping with iodine

The CHCl 3 ‐soluble fraction of polythiophene, prepared by catalytic coupling of thienyl Grignard reagent, was characterized by VPO, GPC, TLC, 1 H NMR, and WAXS measurements. Iodine doping of this polymer shows a maximum conductivity of the order of 5 Ω −1 · cm −1 , much higher than that of I 2 ‐doped compact powder pellets of the insoluble polymer. IR spectra of slightly I 2 ‐doped polythiophene show two new strong absorption bands, one at 1360–1380 cm −1 and the other at 1140 cm −1 . XPS results indicate that the C 1st peak does not change after doping while the profile of the S 2p peak changes markedly. This suggests that in I 2 ‐doped polythiophene the positive charge is localized on the S atom. Combined results of the change of the I 3d XPS peak profile and the Raman spectrum in the low frequency region suggest that iodine in doped polythiophene is present in the form of the I 2 moleculre and the I‐ion, in contrast to polyacetylene where iodine exists in the form of I 3 − and I 5 − anions.