A series of soluble conjugated poly(heteroarylene methines) with varying number of 2,5-thienylene rings have been synthesized, characterized, and shown to have small intrinsic optical and electrochemical bandgaps. The conjugated polymers containing alternating aromatic and quinoid heteroarylene moieties in the main chain were prepared by oxidative dehydrogenation of precursor poly-(heteroarylene methylenes) with 2,3-dicyano-5,6-dichloro-1,4-benzoquinone (DDQ). The optical and electrochemical properties of the conjugated poly(heteroarylene methines), such as bandgap, redox potentials, ionization potential, and electron affinity, were found to be significantly modified by the size of the quinoid moieties in the main chain and the type of donor or acceptor side group at the methine carbon. Some of the poly(heteroarylene methines) have intrinsic bandgaps (E(g)) that are significantly smaller than found for the parent polythiophene (E(g) similar to 2 eV) : PBTHBQ (E(g) = 1.14 eV); PBTBQ (E(g) 1.27 eV); PBTTBQ (E(g) = 1.31 eV); and PBTNBQ (E(g) = 1.45 eV). These same four polymers have peak oxidation potentials in the range 0.29-0.54 V (eV) and peak reduction potentials in the range -1.82 to -1.49 V (SCE). The electrical conductivity of iodine-doped thin films of PBTBQ, PBTNBQ, and PBTHBQ was 6 X 10(-3), 2.2 X 10(-3), and 1.6 x 10(-1) S/cm, respectively, compared to a conductivity of less than 10(-7) S/cm for the undoped materials. These results confirm that conjugated poly(heteroarylene methines) are small-bandgap conducting polymers which can be prepared by oxidative dehydrogenation of precursors.