An Electrochemically Prepared Small-Bandgap Poly(biheteroarylidenemethine):  Poly{bi[(3,4-ethylenedioxy)thienylene]methine}

The electrochemical polymerization of bis(2-thienyl)methanes carrying substituents either on the methylene carbon or on the thiophene rings is reported. Poly(dithienylenemethylene)s are formed which undergo in-situ dehydrogenation to poly(dithienylenemethine)s. Bis(3,4-ethylenedioxythienyl)methane gave a very low-gap material (0.4 V onset-based bandgap). This value is much lower than those previously reported for chemically prepared materials having the same conjugated backbone but carrying different substituents. The unsubstituted bis(2-thienyl)methane gives a similar low-gap polymer as well, but overoxidation and probably misjunction defects are present. No polymer was formed in the case of 2,2‘-bis(2-thienyl)propane, for which the possibility of producing a conjugated polymer is precluded by the lack of at least one hydrogen atom on the carbon bridging the thiophene units. Full electrochemical and optical characterization data for the polymers are reported, and the polymerization and p- and n-doping processes are discussed.