Spectroscopic study of wemple-didomenico empirical formula and taucs model to determine the optical band gap of dye-doped polymer based on chitosan: Common poppy dye as a novel approach to reduce the optical band gap of biopolymer

This study investigates the effect of a natural dye extracted from common poppy (Papaver rhoeas) waste flowers on the optical properties of chitosan (CS) films. The extraction of natural dyes from waste flowers can be considered a new field for research in green chemistry. CS films are flexible and biodegradable but have low optical activity and band gap, limiting their applications in optical devices. The doped CS polymer with different concentrations of Papaver rhoeas dye exhibited enhanced optical properties. Also, 30 % glycerol was added as a plasticizer to omit film brittleness. The FTIR examinations is helpful to propose a mechanism that explains the interaction of the dye with the host polymer. The UV-vis spectroscopic examination establish that the optical characteristics of the films can be modified by adjusting the dye concentration. Furthermore, optical absorption properties are described using the Tauc non-direct transition model, revealing an approximate optical band gap of 1.64 eV. This band gap defines the energy required for electron transitions, elucidating the material's electronic characteristics. The extinction coefficient (k) and refractive index (n) of the CS-doped films' shows a dispersion behavior at visible regions of EM radiation. The Wemple-DiDomenico single oscillator model was used to investigate the n dispersion and determine the oscillator energy equivalent to the optical band gap. Additionally, calculations have been performed on optical dielectric properties and optical conductivity. The Urbach energy was measured and used to detect the structure of the films. The findings underscore the potential applications of these natural dye-doped CS films in eco-friendly materials and optical devices.