Electrochemical, Magnetic, and Electrical Properties of α,ω-Capped Sexithiophene Films. Part 3. Conduction in Poly(bis-terthienyl-B)s (B = Ethane, Disulfide, Diacetylene, Acetylene, Ethylene)

Electrochemical oxidation of bis-terthienyl-B (B = ethane, disulfide, diacetylene, acetylene, ethylene) has been investigated. Monomers without and with 3,3 ''-dialkylsubstitution are regularly coupled to polymers alternating sexithiophene and B moieties. The corresponding terthienyl homopolymers have also been produced for comparison. The polymers obtained are characterized by cyclic voltammetry, EQCM, UV-vis, and FTIR spectroscopy, in situ ESR and in situ conductivity. The conductivities of p-doped polymers with ethane or disulfide bridges fall in a narrow range (1-5 x 10(-2) S cm(-1)) and are practically the same as those of alpha,omega-dimethylsexithiophene (1 x 10(-2) S cm(-1)), suggesting that conduction proceeds without the help of the links via a direct redox hopping between sexithiophene blocks of adjacent polymer chains. In the cases of diacetylene and acetylene, conduction changes from redox to bipolaron-type but only in the case of ethylene the conductivity jumps to high values (1-5 S cm(-1)) corresponding to those of the polymers without the bridging moiety B, i.e., with shortened thiophene rings. DFT calculations of the bridge energy levels account for this result.