Two low band-gap polymers (gap energy similar to 1 eV) based on carbon-bridged dithienyl monomers have been investigated by density functional theory (B3LYP/6-31G) and semiempirical/CI methods. Theoretical absorption spectra from monomers to pentamers were obtained and showed good agreement with the experimental spectra of the polymers. Comparison with data for oligomers of CDM and BDT (dithiophene derivatives indicated that the new polymers have a small band gap and could fulfill the conditions for n-dopability. (c) 2005 Elsevier B.V. All rights reserved.759416998791