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 and thiophene, investigating the influence of the phosphonium RTILs on the polymerized film properties.³ However, electrosynthesis of polyselenophene in phosphonium RTILs has not been examined. In this work, we report the electropolymerization of selenophene in triethylpentylphosphonium FSA (P₂₂₂₅-FSA) (Fig. 1) and the effect of the phosphonium RTIL on the polyselenophene 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 selenophene 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.

Figure 2 showed the cyclic voltammograms for the electropolymerization of selenophene in P₂₂₂₅-FSA. In the first cycle, the oxidation peak current value of about 0.2 mA was shown around +1.7 V vs Ag/Ag⁺, and the current decayed with each cycle. This closely resembles the electrochemical behavior observed in CVs using π-conjugated aromatic compounds such as pyrrole and thiophene as substrates. ³ After 10 cycles, a black thin film was grown on the surface of the working electrode, and the oxidation current observed in this CV seems to be due to the electropolymerization reaction of selenophene. Furthermore, we will discuss the comparison between the behaviors in various quaternary onium based ionic liquids from the viewpoint of the morphology of the polymer film grown on the working electrode.

References

1. K. Sekiguchi, et al, J. Electroanal. Chem., 1, 557 (2003).
2. K. Tsunashima, et al, ECS Electrochem. Lett., 3, G1 (2014).
3. K. Nishihata, et al, ECS Trans., 75, 99 (2016).
4. K. Tsunashima, et al, Electrocheml. Commun., 13, 178 (2011).