Abstract: Poly[(thiophene)methene]s are the conjugated polymer with very narrow bandgap. Three poly[(3-alkylthiophene)methane]s: poly[(3-butylthiophene-2,5-diyl)][(p-nitro)benzylidenequinomethane-2,5-diyl](PBTNBQ), poly[(3-butylthiophene-2,5-diyl)][(p-N,N-dimethyl-amino)benzylidenequinomethane-2,5-diyl](PBTDMABQ) and poly[(3-octylthiophene-2,5-diyl)][( p-N,N-dimethylamino)benzylidenequinomethane-2,5-diyl](POTDMABQ) are synthesized through three steps. The products are then characterized by IR spectrum, UV-Vis absorption spectrum and ¹H NMR. The results indicate that there is a part quino-structure in poly[(3-alkylthiophene-2,5-diyl)benzylidene](PATB). The absorption peak at 1 653 cm^-1 in IR spectrum, the enlarged absorption of 450-600 nm in UV-Vis absorption spectrum imply that the quino-structure is really formed in this three conjugated polymers. According to the function ofE_gand hν, the bandgaps of these three polymers are calculated by two models which show theE_gas 1.63 and 1.84 eV for PBTNBQ, 1.44 and 1.75 eV for PBTDMABQ, 1.32 and 1.69 eV for POTDMABQ, respectively.

Key words: Poly[(3-alkylthiophene)methene]s, Narrow bandgap conjugated polymer, Band gap width, Synthesis, Characterization