Photochromic alginate biomaterials doped with sodium spiropyran carboxylate: fabrication and fluorescence characterization of films and fibers

Spiropyran-based photochromic materials hold promises for smart windows and anti-counterfeiting, but their application is often hindered by complex, polluting chemical grafting. To address this, we developed a green, aqueous-phase physical doping strategy to incorporate sodium spiropyran carboxylates ( 4a – 4c ) into sodium alginate (SA) via non-covalent interactions. The resulting films ( SA/4a – SA/4c ), with doping concentrations of 0.5–5.0 mol%, show tunable fluorescence. Adding glycerol enhances the performance, red-shifting the emission peak from 430 nm to 440 nm and increasing the fluorescence lifetime from 3.13 ns to 3.44 ns. The films exhibit excellent stability over 20 cycles. Crucially, these materials can be Ca 2+ -crosslinked into fluorescent microspheres and stimuli-responsive fibers for information encryption and smart textiles, offering a degradable and more sustainable alternative to conventional solvent-based and chemically grafted systems.