Electrosynthesis of Poly(para)phenylene in an Ionic Liquid: Cyclic Voltammetry and in Situ STM/Tunnelling Spectroscopy Studies

Abstract

The electropolymerization of benzene in the air and water-stable ionic liquid 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate (HMIm)FAP is investigated. The study comprises cyclic voltammetry, IR and in situ STM/tunnelling spectroscopy measurements. The IR results indicate that poly(para)phenylene is the end product of the electropolymerization of benzene in the employed ionic liquid. The resulting conjugation lengths of the product fall between 19 and 21. A polymer reference electrode is used successfully for the electrochemical polymerization of benzene. The first in situ STM results show that the electropolymerization of benzene in the ionic liquid can be probed on the nanoscale and the band gap of the prepared polymer can be determined. The electrodeposited polymer film obtained at a constant potential of 1.0 V vs PPP (polyparaphenylene) exhibits a band gap of 2.9+/-0.2 eV.

Regular poly(para-phenylene) films bound to gold surfaces through the electrochemical reduction of diazonium salts followed by electropolymerization in an ionic liquid

“…On the whole, the values for the number of repeat units are consistent with those reported for electrochemically-grown PPP films [36,43].…”

“…As a preliminary experiment, a PPP film was prepared by oxidation of biphenyl (à. poorly adherent to the surface as already described in the literature [33,43]. Figure 1 (right, bottom) shows the IRRAS spectrum of the film.…”

“…Figure 1 (right, bottom) shows the IRRAS spectrum of the film. It is fully similar to that described in the literature for a regular PPP [43]. The out of the plane vibrations of the aromatic hydrogens are characteristic of the substitution of the aromatic ring [48] and a thorough analysis of these vibration band allow to assess the formation of regular PPP material in contrast to disordered PP.…”

“…Indeed, Endres et al [42,43], and Ivaska et al [44], successfully used imidazolium-based ionic liquids to produce PPP onto platinum or gold electrodes. For instance, by using the 1-hexyl-3-methylimidazolium tris(pentafluorethyl)trifluorophosphate ionic liquid as electrolyte, in a glove box, a thick PPP film was deposited at a Pt substrate from the electrochemical oxidation of benzene [42].…”

“…For instance, by using the 1-hexyl-3-methylimidazolium tris(pentafluorethyl)trifluorophosphate ionic liquid as electrolyte, in a glove box, a thick PPP film was deposited at a Pt substrate from the electrochemical oxidation of benzene [42]. The resulting PPP film was highly regular with a conjugation length ranging between 19 and 21 [43]. However, the electrosynthesized PPP film is not covalently bound to the substrate.…”