Multimodal, Convertible, and Chiral Optical Films for Anti-Counterfeiting Labels

Designing a sustainable security model that carries multilevel information with numerous optical states will significantly enhance anti-counterfeiting abilities to deter counterfeits, ranging from artworks, currencies, and foods to medicines, but is enormously challenging. Herein, ambient-friendly, large-area, quadruple-level, and chiral luminescent materials are prepared by incorporating lanthanide complexes wrapped in poly(ethylene glycol) matrix into chiral nematic cellulose nanocrystal (CNC) films through a co-assembly strategy. Due to the regulation of the chiral nematic structures, the composite films enable full-color structural colors and tunable fluorescence. Notably, the brightest fluorescent film radiates right-handed circularly polarized luminescence with an asymmetric factor over -0.36, a lifetime up to 510 mu s, and an absolute quantum yield up to 66.7%. More interestingly, a fascinating chiro-optical behavior ranging from azure to khaki can be controlled by a polarizing filter at given 0 degrees and 90 degrees rotation angles. This anti-counterfeiting system showcases the comprehensive properties of bright and responsive photoluminescence, quadruple and convertible color, and flexible and solvent-resistant abilities. This CNC-derived photonic material can act as the multimodal security label on a model banknote, which greatly facilitates its development for practical applications.

Automated summary

In this study, lanthanide complexes wrapped in a poly(ethylene glycol) matrix were combined with chiral nematic cellulose nanocrystal films to create ambient-friendly, large-area, quadruple-level, and chiral luminescent materials. These materials exhibit full-color structural colors, tunable fluorescence, and chiro-optical behavior controlled by a polarizing filter.