Polymerization of Two Unsymmetrical Isomeric Monomers Based on Thieno[3,4-b]thiophene Containing Cyanovinylene Spacers

Two cyanovinylene-containing isomeric monomers were prepared by the Knoevenagel condensation of 4- and 6-formylthieno[3,4- b ]thiophene with thiophene-2-acetonitrile, and these monomers were electrochemically polymerized to yield two low-band-gap (1.2 eV) conjugated polymers. The onsets for oxidation of the conjugated polymers were found to have shifted ca. 0.6 V higher compared to the parent poly(thieno[3,4- b ]thiophene) and the onset for reduction increased by ca. 0.1 V. Both polymers, according to spectroscopic evidence, were found to be deep blue in the neutral state and transmissive sky blue in the oxidized form, and these polymers exhibit stable n-doping behavior.