Highly transmissive and conductive poly[(3,4­alkylenedioxy)pyrrole­2,5­diyl] (PXDOP) films prepared by air or transition metal catalyzed chemical oxidation

Abstract

Poly[(3,4-ethylenedioxy)pyrrole-2,5-diyl] (PEDOP) and poly[(3,4-propylenedioxy)pyrrole-2,5-diyl] (PProDOP) were synthesized by in situ chemical polymerization yielding highly transmissive, conductive and electroactive thin films. PProDOP coatings exhibit a surface resistivity of 16 kΩ □−1 at 60% and 58 kΩ □−1 at 99.9% relative luminance (measured by colorimetry). Many factors were found to impact the formation of the films, including pH, temperature, nature of the dopant ion, and nature of the oxidizing agent. The best combination of dopant ion–oxidant was obtained for anthraquinone-2-sulfonic acid (AQSA)–copper chloride which yielded the most conductive films (σ = 10 S cm−1). A doping level of about 25–30% was determined by X-ray photoelectron spectroscopy (XPS) for PEDOP and PProDOP films. Scanning electron microscopy (SEM) and profilometry indicate homogenous film deposition with total surface coverage attained in films as thin as 40–70 nm with a compact and smooth morphology. Spectroelectrochemistry of chemically prepared (oxidized) and subsequently electrochemically reduced PProDOP films showed the disappearance of the π–π* transition, evident as two maxima at 485 nm and 518 nm upon electrochemical doping. The band gap, measured as the onset of the π–π* transition was 2.2 eV. Since the oxidation potential of EDOP is relatively low (+0.6 V vs. Ag/Ag+), it was possible to obtain conducting films of PEDOP using air as the oxidizing agent for the polymerization. This result is of particular importance since very few conducting polymers can be obtained by such an environmentally friendly process.