Cholesteric liquid crystal doped with spiropyran and zinc ions for multi-state anti-counterfeiting

Abstract

With the development of the information age, counterfeit products are rampant. Therefore, the development and application of anti-counterfeiting and information encryption still face significant challenges. Based on the selective reflection of cholesteric liquid crystals (CLC) and the photoisomerization principles of spiropyran (SP) and Zn²⁺, SP or SP/Zn²⁺ mixtures are doped into CLC to form multi-mode anti-counterfeiting inks. Under different stimuli (such as UV irradiation, removal of UV, natural light exposure, heating at 55 °C, heating at 65 °C, and DC voltage), this ink exhibits various responses. Utilizing these characteristics, we first created exquisite anti-counterfeiting patterns, which obtained five different label photos through light or temperature control. Additionally, we further used the ink to create a triple “security label”, which can only be recognized as the correct QR code when both conditions are met simultaneously. It is worth mentioning that by changing the ratio of chiral agent, a range of colors can be obtained to meet more complex anti-counterfeiting requirements. Liquid crystal (LC) cells with the ink were soldered onto a designed circuit board to achieve advanced information encryption. Finally, utilizing LC microspheres, a triple “security label” was created. Therefore, this multi-mode anti-counterfeiting ink can display completely independent programmed information under six different stimulus responses, all of which are reversible. Compared to simple single-state anti-counterfeiting techniques, this advanced multimodal anti-counterfeiting technology significantly improves the security level of practical applications in the field of anti-counterfeiting.