Thermally irreversible, photochromic dithienylethene-alt-dihexyloxyphenylenevinylene and dithienylethene-alt-didodecyloxy-phenylenevinylene copolymers have been synthesized via the Horner and Wittig reactions, respectively. Both polymers are photochromic in solution and in the solid state. Electronic spectra show that the materials are highly conjugated in both states and the large pi-delocalization along the main chain when the diarylethene moiety is in the closed form gives a decrease of the ring-opening quantum yield. The increase in molecular weight relative to other backbone dithienylethene polymers allows the preparation of good quality films without the use of supporting polymer matrices; this is an important achievement for the technological application of these photochromic materials.