Shape memory photonic gels enable reversible regulation of photoluminescence: Towards multiple anti-counterfeiting

Rampant counterfeit products have seriously threatened worldwide public security. It is highly desirable yet challenging to develop advanced encryption and anti-counterfeiting strategies. Herein, a fluorophore-doped shape memory photonic gel (SMPG) for high-end multi-mode anti-counterfeiting purposes is developed by synergistically utilizing two collaborative optical signals of structural color and photoluminescence (PL). The SMPG is prepared by polymerizing mixed monomers of poly(ethylene glycol) methacrylate (PEGMA) and trimethylolpropane ethoxylate triacrylate (ETPTA) in the presence of self-assembled silica nanoparticles (NPs) array, followed by doping Rhodamine B (RhB) in the polymeric matrix and selectively etching the silica NPs. The regular macroporous structures of RhB-doped SMPG can be destroyed temporarily after drying and restored after solvent triggering, and such a variation is reversible, repeatable, and stable. We show that dry RhB-doped SMPG is highly transparent under natural light and exhibits PL under UV light, while wet RhB-doped SMPG exhibits vivid and angle-dependent structural color under natural light and a depressed PL under UV light because of the inhibition of the appearance of photonic bandgap (PBG). As a proof-of-concept, various shapes of anti-counterfeiting tags can be prepared by laser engraving technology, significantly improving the security of anti-counterfeiting tags and shows great potential in the high-end anti-counterfeiting fields.