Smart Anti‐Counterfeiting Inks: Controlled Luminescence Polarization and Its Fixation by Photoisomerization and Subsequent Photopolymerization of Cyanostilbene‐Based Liquid Crystal Monomers

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.

Light‐Driven Sign Inversion of Circularly Polarized Luminescence Enabled by Dichroism Modulation in Cholesteric Liquid Crystals

“…This corresponds well to the isomerization of the α‐cyanostyrene moiety from trans to cis ‐configuration. [ 15 ] The emission intensities ( λ ex = 350 nm) and QY (from 7.5% to 6.8%) also weakened in response to the UV light stimulus (Figure 2b), confirming the photoresponsiveness of KG. The 1 H NMR spectra are displayed in Figure 2c, indicating that only 18% of the trans ‐cyanostyrene chain was transformed to cis form during UV irradiation.…”

“…The photophysical properties of KG were first investigated through UV‐visible (UV‐vis) absorption and FL spectra in the tetrahydrofuran (THF) solvent at a fixed concentration of 10 −5 mol L −1 . As shown in Figure a, initial KG exhibited an obvious absorption band at 350 nm, which could be attributed to the absorption of the α‐cyanostyrene chain, [ 15 ] while the absorption peak at 580 nm was possibly caused by the perylene diimide skeleton. [ 16 ] Upon irradiation with 365 nm UV light (20 mW cm −2 ) for 15 min, the absorption peak at 350 nm weakened (Figure 2a).…”

Photochemically and Thermally Programmed Optical Multi‐States from a Single Diacetylene‐Functionalized Cyanostilbene Luminogen

“…[35][36][37] Furthermore, a little restricted TICT of cis-DACSM induces a relatively enhanced emission band at 410 nm (Figure S13c, Supporting Information). [35,36] The emergence of cis-DACSM upon UV irradiation is also evidenced by 1 H NMR analysis in Figure S14 (Supporting Information). [35,37] Having established the photophysical/chemical behaviors of DACSM solution, we analyzed DACSM thin films to observe optical spectral changes of SA-DACSM upon 365 nm light irradiation.…”

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

“…1 These technologies can provide a higher level of anti-counterfeiting capabilities, effectively safeguarding the rights of consumers and the interests of businesses. Over the past few decades, researchers have developed a wide range of anti-counterfeiting technologies based on different principles, 2 including utilizing biometric features for anti-counterfeiting, 3–5 and utilizing the unique properties of nano materials for anti-counterfeiting. 6,7 Additionally, there are chemical anti-counterfeiting technologies 8,9 such as fluorescent inks and thermochromic inks.…”