Room temperature ionic liquids in electrosynthesis and spectroelectrochemical characterization of poly(para-phenylene)

Room temperature ionic liquids (RTILs) were used in electrochemical polymerization and in doping studies (oxidation and reduction) of poly(para-phenylene) (PPP). Cyclic voltammetry was used simultaneously with Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy. Electropolymerization and doping of PPP were done by potential scanning in acetonitrile (ACN + 0.1 M TBAPF6), 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) and butylmethylpyrrolidinium bis (trifluoromethylsulfonyl) imide ([BMP][Tf2N]). The cyclic voltammograms recorded during polymerization of the PPP film indicate that the best film growth was achieved in [BMIM][PF6]. The films made in [BMP][Tf2N] were more stable than films made in ACN (0.1 M TBAPF6). Results from p-doping studies show that doping can be made at higher potentials in RTILs than in ACN (0.1 M TBAPF6). It was also found that n-doping can be performed in RTILs at higher negative potentials (−2.2 V) than in ACN (0.1 M TBAPF6) (−1.8 V). The best n-doping response was achieved in [BMP][Tf2N]. Also, n-doping in [BMIM][PF6] was better than in ACN (0.1 M TBAPF6). The in situ ATR-FTIR spectroscopy was used to study p- and n-doping of PPP films. During both p- and n-doping the spectra indicated formation of infrared active vibration bands (IRAV) in the wavenumber region 1600–800 cm−1. The obtained IRAV bands correlate to the theoretical modes calculated by Zerbi and co-workers according to the effective conjugation coordinate theory (ECC). All these results indicate that RTILs are good solvents in spectroscopic and electrochemical studies of conducting polymers.