Synthesis and properties of polythiophene bearing an alkylsulfonic acid ester at the side chain

Introduction of an alkylsulfonic acid moiety into the side chain of polythiophene was carried out. Synthesis of 2,5-dihalothiophene bearing an alkylsulfonate group at the 3-position was performed. The reaction of 2-chloro-5-iodothiophene with a Grignard reagent to form organometallic monomer of the corresponding thiophene followed by nickel(II)-catalyzed cross-coupling polymerization lead to head-to-tail-type regioregular polythiophene. The ester group at the side chain was converted into alkali metal sulfonate by treatment with NaI or metal hydroxides (Li, Na, K). The obtained metal salts were successfully transformed to sulfonic acid by the treatment with ion exchange resin. The electric conductivity of the regioregular polythiophene bearing sulfonic acid was remarkably improved ca. 102 times from the corresponding metal salts. (106 times higher than sulfonate ester)