A three-state label programmed using a three-color microsphere of structural, fluorescent and dye colors

It is highly challenging to create a security label that carries different information in three states, visible light, ultraviolet (UV) light, and after UV light removal, for anti-counterfeiting and encryption purposes. Herein, we report a three-state anti-counterfeiting system constructed using the selective reflection principle of cholesteric liquid crystals (CLCs) and the photoisomerization principle of spiropyran (SP). Under UV light irradiation, colorless SP transforms into colored merocyanine (MC) and displays fluorescent color simultaneously. Due to the instability of MC, it can be transformed back to colorless SP under visible light or heating conditions. By doping SP into the CLC matrix, uniform mixture microspheres (three-state ink) were generated using a microfluidic chip. Under visible light, the CLC structural color of the three-state ink was displayed, which can be determined by the chiral agent's concentration. Under UV light irradiation, the three-state ink displays the fluorescent color of MC. After UV light removal, the three-state ink showed the combined information of the CLC structural color and MC dye color. Therefore, this three-state ink displays completely independent programming information under visible or UV light. After UV light removal, the displayed information is the combination of the first two states. Compared with simple single-state and dual-state anti-counterfeiting methods, this challenging-to-replicate and easy-to-identify three-state ink has enormous potential in the field of anti-counterfeiting and encryption.