Bioinspired Unclonable 2D Photonic Crystal Patterns with Multimode Reversible Switching for Anticounterfeiting Applications.

The growing demand for information security and product authentication presents significant challenges for anticounterfeiting technologies. Photonic crystal (PC)-based optical anticounterfeiting approaches that enable multimode dynamic color regulation are of great significance for advancing the field of high-level anticounterfeiting. However, the susceptibility to replication and reliance on responsive materials remain key limitations. Inspired by tree rings, an elaborated two-dimensional (2D) PC anticounterfeiting system was proposed in this paper. By integrating 2D PCs with concentric periodic structures using nanospheres of varying sizes with a polyethylene glycol diacrylate 200-vinyl methacrylate (PEGDA-VMA) polymer matrix, a multimodal color changing performance was realized. The resulting "tree-ring" patterns, formed in situ via controlled injection and Marangoni effects, are inherently random and irreplicable, which provide "unclonable" characteristics. The labels exhibit multi-color-switching modes (full immersion and unilateral wetting), enabling brilliant and angle-dependent structural colors without relying on fatigue-prone responsive substrates. This simplified fabrication strategy enhances verification reliability and offers a robust route for advanced anticounterfeiting applications.