A donor-accepter conducting copolymer with a very low band gap and high intrinsic conductivity

Conducting polymers with very small band gaps have been prepared by the electrochemical copolymerization of 4-dicyanomethylene-4H-cyclopenta[2,1-b;3,4-b']dithiophene (1) with 3,4-ethylenedioxythiophene (2). Strong evidence that the materials formed are true copolymers rather than polymer blends is obtained from Raman spectroscopy and cyclic voltammetry. Both of these techniques also show that the copolymer composition can be controlled by varying the polymerization potential, with the ratio of 1:2 in the copolymer increasing with increasing potential. In situ conductivity measurements as a function of potential clearly show that the copolymers have significantly higher intrinsic conductivities than either homopolymer. Band gaps estimated from these intrinsic conductivities range from 0.33 to <0.16 eV. Band gaps for the 3,4-ethylenedioxythiophene-rich copolymers are too low to be accurately estimated but appear to be close to zero. Cyclic voltammograms are consistent with such low band gaps.