Spiropyran-functionalized alginate biomaterials with light-responsive fluorescence

Spiropyran (SP), a classical photochromic molecule, exhibits reversible structural isomerization under stimuli such as light irradiation, pH changes, and solvent variations. However, its practical application in solid-state materials is still hindered by challenges such as molecular aggregation and fluorescence quenching. In this work, we developed photochromic SP-grafted sodium alginate derivatives via a green and efficient synthetic strategy, which combines the stimuli-responsive properties of SP with the processability of alginate. Through sequential amidation under mild conditions, carboxylated SPs were grafted onto sodium alginate, enabling the synthesis of novel biomaterials with tunable fluorescence. The synthesized biomaterials exhibit reversible color changes under UV/visible light. Processed into films, fibers, and microspheres via ionic crosslinking with Ca²⁺, these materials showcased applications in fluorescence patterning, textile integration, and solvent detection.