Sustainable approach for optical band gap modulation and enhanced optoelectronic performance in PVA films via four O’clock flower dye extracts

The global textile industry is increasingly focused on reducing the environmental footprint of synthetic dyes, making a switch to bio-based dyeing materials a key priority for sustainable textile applications. This work describes the preparation of eco-friendly, high-performance dye-doped polymer (DDP) films using a natural dye extracted from Mirabilis jalapa (MJ) (four o’clock flower), embedded in a polyvinyl alcohol (PVA) polymer. Purple-colored composite films were fabricated using a green aqueous extraction method and a low-cost solution-casting technique and were reinforced with chitosan to protect against antimicrobial instability. FTIR spectroscopy revealed shifts in the O–H stretching band following MJ dye incorporation, indicating changes in the hydrogen-bonding environment and intermolecular interactions within the PVA matrix. X-ray diffraction (XRD) analysis showed a reduction in the characteristic PVA diffraction peak at 2θ ≈ 19.5°, indicating a decrease in the structural ordering of the polymer chains. This structural transition is also reflected in a dramatic reduction of the characteristic XRD diffraction peak at 2θ ≈ 19.5 o , and the increase of the Urbach energy ( E b ) from 0.3315 to 1.0342 eV. Optical characterization shows a pronounced redshift in the absorption spectra after dye incorporation, indicating a transition from an insulating to a semiconducting regime. The optical energy gap ( E G ) was significantly modified, that is 6.05 eV in the pure PVA material and decreasing to 3.65 eV for the highly dye doped PVA materials. Furthermore, the MJ dye increased the refractive index, dielectric constant, and plasma frequency, indicating improved light-matter interaction and charge-carrier density. The PVA: MJ dye-doped films have a high figure of merit (FOM) and optimized thermal emissivity, making them versatile and sustainable materials for advanced technologies, such as organic light-emitting diodes and flexible photonic sensors. The outcomes of this study establish that green chemistry and optoelectronic engineering are a scalable pathway to functional macromolecules without the ecological footprint of the petroleum-based additives. Clinical trial number Not applicable.