Studying electronic transport in polyazulene–ionic liquid systems using infrared vibrational spectroscopy

Abstract

This paper presents an in situ spectroelectrochemical characterization of polyazulene (PAz) and PAz–C₆₀ composite films using Fourier Transform Infrared Attenuated Total Reflection (FTIR-ATR) spectroscopy. In situFTIR-ATR spectra were recorded simultaneously as the films were charged and discharged electrochemically. The aim was to clarify how the use of ILs and the addition of C₆₀ affected the electronic transport and structural changes occurring in PAz during electrochemical charging. We found that electrosynthesis of PAz in an IL lowered the oxidation potential of the film and improved its electroactivity. The FTIR-ATR data also suggest that PAz with a longer effective conjugation length is obtained during electrosynthesis when using ILs. With in situFTIR-ATR it is possible to quite accurately determine the onset potential for oxidation/reduction. These values are important since they determine the suitability of the polymer for a specific application. Our experiments indicate that two types of charge carriers are formed during electrochemical oxidation of PAz in an IL. Furthermore, their formation is strongly affected by the addition of C₆₀ into the film. The type of charge carrier formed affects the electronic and possibly also ionic transport within the film. The inclusion of C₆₀ into PAz influenced the optical and structural properties considerably. In situFTIR-ATR is also an extremely useful method for studying the potential stability of an IL during electrochemical cycling. We showed that cathodic decomposition of N,N-butyl-methyl-pyrrolidinium bis(trifluoromethylsulfonyl)imide ([BMP][Tf₂N]) occurs at less negative potentials than those determined electrochemically.