To enhance the third nonlinear optical properties of poly(thiophene methine), we synthesized a new kind of poly(3-butylthiophene methine) with azo side groups: poly[(3-butylthiophene-2,5-diyl)-p-(N,N-dimethylamino)azobenzylidenequin omethane] (PBTDMABQ). PBTDMABQ and its intermediate product were characterized with IR, ultraviolet-visible, and H-1-NMR spectroscopy. The band gaps of PBTDMABQ were calculated to be 1.94 and 2.06 eV with two different models. The thermal stability, determined by thermogravimetric analysis, indicated that PBTDMABQ decomposed above 345 degrees C. (c) 2005 Wiley Periodicals, Inc.