Green approach to synthesizing a novel dye-doped polymer based on chitosan with desired optical properties

Abstract The present study attempts to turn trash into treasure in the field of optical materials. Natural dyes derived from red Nerium oleander flower were utilized to prepare films of chitosan (CS)/doped oleander dye with varying dye concentrations (5–15 ml) by solution casting method. The FTIR structure analyses showed that the extracted dye was enriched with essential functional groups of OH, NH, C = O, and C = C, whereas for the dye-doped films the OH band suppressed and became wider, which suggested the formation of hydrogen bonding. The XRD established that the dried dye had an almost amorphous structure and for the dye-doped films the main CS peak shifted toward a greater 2θ with a broader intensity. The morphological examination revealed a miscible phase blend of the dye-doped films. The analysis of UV–Visible optical data showed a direct energy gap value of 5.45 eV for CS, which shrunk to 2.05 eV for the dye doped CS films. The addition of the natural dye caused an increment in the number of charge carriers from 9.7 ×1055 to 93.6×1055 m3/kg. This is consistent with the expansion of Urbach tails and enhancement of the index of refraction. Thermogravimetric analysis (TGA) confirmed the enhancement of CS thermal stability by incorporation the oleander dye. The overall analysis of the optical properties indicated that natural dyes derived from waste flowers are an ideal dopant to modify the band structure of functional polymers compared to other traditional fillers (such as ceramics, salts, nanoparticles, etc.).