Dynamic Responsive Poly(methyl Methacrylate)-Spiropyran Microspheres via Membrane Emulsification for Advanced Solid-State Photochromic Anticounterfeiting

Photochromic materials have garnered significant attention for applications in anticounterfeiting and information encryption. However, their practical utilization in solid states remains challenging due to restricted molecular isomerization. In this work, we successfully synthesized PMMA-SP microspheres via a membrane emulsification-solvent evaporation approach, which enables efficient and reversible solid-state photochromism. Under UV irradiation, the microspheres undergo a rapid color transition from pale pink to deep purple, accompanied by enhanced fluorescence emission, and revert to their original state upon exposure to visible light. Furthermore, flexible PVA/PMMA-SP composite films were fabricated, allowing reversible and high-contrast photopatterning through the photomasks. Notably, these films exhibit distinct color changes, even under natural sunlight, providing a straightforward authentication feature. Collectively, this study offers a facile and scalable strategy for designing rewritable photochromic materials with considerable potential for advanced optical security applications.