Protection of 2-(3-thienyl)ethanol with 3-thienylacetic acid and hard cross-linked conducting films by electropolymerization of the ester

The ester (compound 1) of 2-(3-thienyl)ethanol (T-etOH) with 3-thienylacetic acid was synthesized as a monomer whose two thiophene groups could be electropolymerized independently, becoming members of different polymer chains in a highly cross-linked highly insoluble polymer. Indeed, 1 was electropolymerized successfully alone and together with 3-methylthiophene (3MeT). Films of poly(1) are hard (3H, as opposed to <6B for poly(3MeT)), and the close proximity of the polymeric strands creates π-stacking interactions. The behavior of 1 suggests that by: (a) limiting the potential used for the oxidation of monomeric esters of T-etOH at the foot of their oxidation waves (<1.8 V versus Ag/AgCl) and (b) compensating for the decrease in the electrogenerated radical concentration by increasing the monomer concentration, practically all esters of T-etOH should be electropolymerizable. This was confirmed by durable film formation from the archetypical ester of T-etOH, the 2-(3-thienyl)ethyl acetate (T-etOAc), whose homoelectropolymerization is reported for the first time.