Fusheng Zhang, Qiongya Li, Cunli Wang, Dongdong Wang, Mengyuan Song, Zan Li, Xingya Xue, Gang Zhang and Guangyan Qing*

Adv. Funct. Mater. 2022, 32, 2204487

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 chirooptical 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.