In situ UV–vis spectroelectrochemical study of dye doped nanostructure polypyrrole as electrochromic film

In the present work, the electrosynthesis and the spectroelectrochemical characterization of eriochrome cyanine R (ECR) doped polypyrrole (PPy) were described. Nanostructured PPy–ECR film was electrochemically deposited onto fluorine doped tin oxide (FTO) coated/glass electrode from aqueous solution containing a water-soluble trianionic dye, ECR, as dopant. The surface morphology was studied using scanning electron microscopy (SEM) analysis. Dye doped polymer film showed spherical morphology with primary particles 70–90 nm in size and 900 nm thicknesses. The main characteristics of PPy–ECR film include uniformity, stability and adherent on FTO electrodes, which are better compared to that of PPy film. In situ UV–vis spectroelectrochemistry was used as a powerful tool in analyzing the evolution of the neutral, polaron and bipolaron states in prepared polymer films as they were redox cycled (from −0.6 V to +0.6 V) in NaClO4. As the polymers gets oxidized, the intensity of the π–π* transition (neutral state) decreases while the charge carrier bands at longer wavelengths (polaron band and bipolaron band) increases in intensity and the color of the polymers change. We found that these variations are more intense in the case of dye doped to those of PPy. The spectroelectrochemical studies showed that the electrochromic properties of dye doped polymer (PPy–ECR) such as optical contrast (27%), switching time (⩽1.5 s) and film stability (100 cycles) were greatly enhanced relative to the PPy film.