Thermally Induced Self-Doping of pi-Conjugated Polymers Bearing a Pendant Neopentyl Sulfonate Group

A regioregular head-to-tail (HT)-type polythiophene was synthesized by the deprotonative nickel-catalyzed cross-coupling polymerization of 2-chlorothiophene bearing a neopentyl benzenesulfonate group at the 3-position. The obtained HT-regioregular polymer was found to dissolve in chloroform or THF, while it became soluble in water upon heating at 185 degrees C for 10 min by the liberation of the protected neopentyl group. The thin film of the polymer showed a remarkable improvement in conductivity of ca. 10(3) times before/after heating, suggesting the thermally induced intramolecular doping of polythiophene by the formed sulfonic acid at the side chain. The related doping was also observed in a poly(phenylacetylene) derivative, which was synthesized by rhodium-catalyzed polymerization. Copolymerization of such thiophene- and acetylene-bearing neopentyl sulfonate with 3-alkylthiophene and phenylacetylene, respectively, produced the corresponding statistical copolymers, demonstrating the formal self-doping of poly(3-alkylthiophene) and poly(phenylacetylene).