近日，我组设计了一种环境友好型、多模式和相互切换的手性光子薄膜。该研究为先进防伪材料的设计提供了新思路。
早在中国古代，防伪标签（如水印、指纹和笔迹）就已广泛与文化、经济和军事交织在一起。创新的防伪技术对于市场稳定、医疗健康和社会可持续发展具有重要意义。目前的防伪标签主要集中在使用发光或结构色材料，如荧光染料、量子点、钙钛矿、室温磷光和纳米印迹光子阵列，通过物理化学刺激、多色组合或复杂图案实现编码安全。然而，由于自身的空间结构限制，这些防伪编码仅仅停留在一维或者二维的信息传递。
相比之下，偏振衍生的手性发光材料将大量有关视觉特征和空间结构的信息整合到一种复合材料中。那么，每种信息都可以进行编码或集成，从而大大提高防伪水平。为此，该团队将强手性的纤维素纳米晶体（CNC）系统和强发光的稀土配合物进行结合，制备出携带四种光学信息的手性光子复合膜。所获得的材料展现出可调节的结构色、明亮的荧光、手性光学变异行为和右旋圆偏振发光（CPL）特性。基于这些多级光学状态、湿度响应荧光或结构颜色、柔韧性和耐用性的综合特性，该光学系统在钞票防伪中表现出先进的应用潜力。同时，该材料还具有强CPL发射（不对称因子高达–0.36）、高绝对量子产率（67%）和偏振敏感的手性光学特性，这些研究将推动CNC光子材料在手性光学器件、光学探测器、视觉保护和手性传感等方面的应用。
相关研究成果以“Multimodal, Convertible, and Chiral Optical Films for Anti-Counterfeiting Labels”为题，于近日发表在Advanced Functional Materials上。该工作的第一作者是博士研究生张福生。上述工作得到国家自然科学基金、大连化物所创新基金、兴辽英才计划等项目的支持。（文/图 张福生、李琼雅）
Multimodal, Convertible, and Chiral Optical Films for Anti-Counterfeiting Labels
Fusheng Zhang, Qiongya Li, Cunli Wang, Dongdong Wang, Mengyuan Song, Zan Li, Xingya Xue, Gang Zhang, Guangyan Qing*
Adv. Funct. Mater. 2022, DOI: 10.1002/adfm.202111406
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.
