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

Abstract 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 µs, 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° and 90° 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.