A Disposable Thermally Triggered Photonic Crystal Anti‐Counterfeiting Tag with Irreversible Response and Multi‐Step Color Changes

Abstract Thermochromic photonic crystal (PC) is a promising material for anti‐counterfeiting applications, but there are still challenges to further improve the anti‐counterfeiting performance and the practicability in usage. Here, a disposable thermally triggered PC anti‐counterfeiting tag with irreversible response and multi‐step color changes is developed based on the thermochromic Silica/(Polyethylene glycol‐Ethoxylated trimethylolpropane triacrylate) (SiO 2 /(PEG‐ETPTA)) double‐layer film. The fast and irreversible thermal response come from the quick melting and infiltration of PEG‐ETPTA into the PCs upon heating. The multi‐step color change at different temperatures originated from the regioselective control of the UV curing degree of the PEG‐ETPTA layer and the resulting thermochromic temperature of the double‐layer film. Therefore, the invisible PC pattern on the tag can be revealed part by part upon heating and became invisible again after overheating, which offered diversified visual effects and enhanced anti‐counterfeiting performances.