Modulation of optical band gap and conductivity of polyindoles with concentrations of FeCl3 and APS

Abstract

Conducting Polyindoles (PIn-I and PIn-II) samples were synthesized via chemical oxidative polymerization in aqueous solution at a range of concentrations (0.3–0.9 M) of anhydrous FeCl3 and Ammonium persulfate (APS) at 25 ± 1 °C. Techniques such as FTIR spectrograph confirm various bond absorptions which give the identity of PIns, the morphology has been examined by SEM and XRD, while the thermal analysis of the prepared sample was studied by employing TGA-DSC. UV–Vis spectroscopy has been used to analyze complex optical parameters like band gap, refractive index, dielectric constant, and optical conductivity. The produced PIns exhibit absorption around 340–410 nm and results in the optical band gap in the range of 2.906 to 2.929 eV for the PIn-I series (with FeCl3) and 2.673 to 2.734 eV for the series of PIn-II (with APS). The samples synthesized employing 0.3 M FeCl3 and 0.9 M APS were found to have the lowest optical band gap energies of 2.906 eV and 2.673 eV, respectively. The experimental studies reveal that the optical conductivity, particle size, and crystallinity of PIn can be optimized with the different types of oxidants and their varying concentrations. The results conclude that the oxidizing agents having high reduction potential offer better electron transport and thus lower band gap and high optical conductivity. Due to the above-mentioned optical band gaps and high environmental stability, PIns have potential applications in optical devices.