Synthesis and characterization of polyazopyrrole. A novel narrow-bandgap polypyrrole with proton-exchange properties

Anodic coupling of 2,2′-azopyrrole, N,N′-dimethyl-2,2′-azopyrrole and pyrrolyl-2-aldazine has been performed in acetonitrile. The resulting polymer films were investigated by cyclic voltammetry (CV), UV-Vis-NIR spectroscopy, FT-IR reflection-absorption spectroscopy and in situ conductivity. Polyazopyrrole is the first reported narrow-bandgap pyrrole-based polymer (Eg ≈ 1.0 eV). It undergoes reversible oxidation without significant changes in the visible region but with strongly enhanced absorption in the NIR region. The CV of polyazopyrrole displays a two-step oxidation process with a finite potential window of conductivity (maximum conductivity 2 × 10−2 S cm−1). In the oxidized form polyazopyrrole easily dissociates its NH protons. Its acidic properties are no longer displayed in its N,N′-dimethyl-substituted homologue and in poly (pyrrolyl-2-aldazine).