Polymers and oligomers with substituted 2,5-thienylene units. Preparation and electrical conductivity properties

Ni-catalyzed dehalogenation polycondensation of 3-formyl-, 3-hydroxyiminomethyl- and 3-cyano-2,5-dibromothiophene with zinc affords oligo(3-formyl-2,5-thienylene) (2a), oligo-(3-hydroxyiminomethyl-2,5-thienylene) (2b), and oligo(3-cyano-2,5-thienylene) (2c). Electrochemical polymerization of 3-methoxythiophene and 3,4-dimethoxythiophene give blueblack films of oligo(3-methoxy-2,5-thienylene) (2d) and poly(3,4-dimethoxy-2,5-thienylene) (2e). Iodine adducts of 2a–2c show electrical conductivity values between 1,8 · 10−11 and 8,8 · 10−8 S · cm−1. Doped 2d shows electrical conductivity of 2 · 10−1 S · cm−1, whereas doped 2e exhibits an electrical conductivity between 1,5 and 30 S · cm−1. Doping of undoped 2d and 2e causes profound changes in their IR and NMR spectra, colour, and electrical conductivity properties.