Electropolymerization of Thiophene in a Bis(fluorosulfonyl)Amide Based Phosphonium Ionic Liquid

Abstract

Room-temperature ionic liquids (RTILs) have been regarded as potential electrolytic media for electropolymerization processes.1 Many kinds of RTILs have been investigated for the electropolymerizations. For example, we have reported that a bis(fluorosulfonyl)amide (FSA) anion based imidazolium ionic liquid promoted the electropolymerization reaction of pyrrole and the anion doping into the polymerized film, improving the conductivity of the film.2 We also have applied the phosphonium based RTILs to the electropolymerization of pyrrole, investigating the influence of the phosphonium RTILs on the polymerized film properties.3 However, electrosynthesis of polythiophene in phosphonium RTILs has not been examined. In this work, we report the electropolymerization of thiophene in triethylpentylphosphonium FSA (P2225-FSA) and the effect of the phosphonium RTIL on the polythiophene film properties.P2225-FSA was prepared according to the procedure we have previously reported,4 and dried under high vacuum at 80°C for 6 h before use. The electropolymerization of thiophene in P2225-FSA was carried out by cyclic voltammetry (CV) method using a three-electrode cell equipped with a working electrode of platinum or transparent glass electrode and an IL-based Ag/Ag+ reference electrode.Fig. 1 showed the cyclic voltammograms for the electropolymerization of thiophene in P2225-FSA. It was found that an irreversible oxidation peak was observed and maintained even when the cycle was repeated, forming the polythiophene film on the electrode surface. It is noted that the peak current at 2.2 V vs Ag/Ag+ was enhanced by cycling, which seems likely to be attributed to the efficient anion doping into the polymerized film grown on the working electrode surface. Fig. 2 depicted a SEM image of the polythiophene film grown in P2225-FSA. A uniform surface of the film grown in P2225-FSA was observed when compared to that in an organic solvent based electrolyte, which is closely similar to the result previously found in the electropolymerization of pyrrole. The electrochemical activity and thermal stability of the polythiophene film obtained will be discussed.