Completely soluble azo-dye-substituted thiophenic copolymers through proper molecular design

Copolymerizations at various feed ratios between azo-dye-substituted thiophenes and 3-hexylthiophene under FeCl3-based oxidative conditions have been conducted. It is shown that when the molecular structure of the dye is properly designed, completely soluble copolymers, with molecular weigths ranging around 104 as Mn and dye-substituted monomer content up to 50% in a molar ratio, may be prepared, as well as a completely soluble homopolymer. In addition, the so-obtained polymers evidenced excellent filmability from a variety of solvents. The dye-substituted monomer content of the soluble copolymers has been assessed by 1H NMR analysis via a convenient choice of the reference signals. In the completely soluble copolymers the dye-substituted monomer content is well correlated to the feed within a range between 0 and 75% of dye-substituted unit in the feed, which corresponds to a 0-50% range in the copolymer composition, still conserving satisfactory molecular weights. Following these observations and analyzing the characteristics of the polymers, a lower reactivity of the dye-functionalized unit toward 3-hexylthiophene was evidenced in the used reaction conditions, and some hypotheses on this finding are presented.