Optically Tunable Multistable Liquid Crystal Grating for Anti‐Counterfeiting through Multilayer Continuous Phase Analysis

Abstract

AbstractOptically tunable liquid‐crystal (LC) gratings have remarkable applications in the field of image analysis for anti‐counterfeiting. However, existing tunable LC gratings suffer from limited adjustable ranges and weak stability. The spacing variability and accuracy of the grating cannot satisfy the demands of continuous analysis. This study presents a novel approach to anti‐counterfeiting through multilayer continuous phase analysis (MCPA) based on the continuous multistable states of the LC grating. This optically tunable LC grating featuring continuous multistable states is successfully prepared using a novel optically tunable chiral dopant, tetra(n‐hex‐azo), which exhibits an exceptionally slow conformational relaxation rate (half‐life: 78.02 h). By exposing the LC grating to ultraviolet irradiation with an intensity of 0.1054 mW cm−2, the fringe spacing can be continuously and widely tuned between 0 and 250 µm, which enhances the ultraslow conformational relaxation of tetra(n‐hex‐azo). Four representative spacings (50, 55, 60, and 65 µm) are selected to construct four‐layer MCPA gratings, enabling simultaneous decoding of a four‐layer latent image for the first time. The mechanism of the MCPA grating is investigated through control experiments and theoretical simulations. This study demonstrates a facile, precise, and efficient approach for complex information encryption and anti‐counterfeiting.