Smart Anti‐Counterfeiting Inks: Controlled Luminescence Polarization and Its Fixation by Photoisomerization and Subsequent Photopolymerization of Cyanostilbene‐Based Liquid Crystal Monomers
Jahyeon Koo, Minwook Kim, Jaeseok Hyeong, Dongmin Yu, Sanghee Kim, Junhwa Jang, Mintaek Oh, Youngjae Wi, Hyeyoon Ko, Kwang‐Un Jeong
Abstract
Abstract To identify and protect authentics from counterfeits, anti‐counterfeiting materials are developed. In spite of many advances in luminescent anti‐counterfeiting materials, there is still a need for easily processible, multilevel anti‐counterfeiting materials. Here, the study reports a novel strategy for the production of smart anti‐counterfeiting inks and films using a cyanostilbene‐based liquid crystal (LC) monomer (CSRM). This smart ink is prepared by mixing CSRM and conventional nematic LC monomers. The optimized ink with a nematic mesophase is uniaxially oriented by simple shear coating for high transmittance and linearly polarized light emission. Upon subsequent irradiation with 365 nm UV light using a photomask, a phase transition to an isotropic state occurs by photoisomerization of CSRM in selected areas, resulting in unpolarized photoluminescence in those areas. Two optically different regions (UV treated and untreated) can be permanently fixed by photopolymerization under 460 nm blue light. Multilevel anti‐counterfeiting labels programmed by simple shear coating, molecular self‐assembly, selective photoisomerization, and photopolymerization fixation can provide a new insight in developing smart anti‐counterfeiting inks and films.