Focal Conics Enabling Unprecedented Modulation of Circularly Polarized Luminescence for Anti‐Counterfeiting Applications

ABSTRACT Chiral photonic materials have attracted considerable attention for advanced optics and information security owing to their unique light‐matter interactions. Hydroxypropyl cellulose (HPC), a bio‐based chiral liquid crystal, can self‐assemble into structurally colored films exhibiting a photonic bandgap (PBG) with a right‐handed twist. Current research primarily focuses on its planar texture, particularly its capability to enable left‐handed circularly polarized luminescence (CPL), while the optical properties of focal conic textures induced by internal stress remain poorly understood. This study presents a facile thermal induction method to reversibly induce the formation of focal conic textures in methacrylate‐functionalized HPC (HPC‐MA) films. The texture morphology and the PBG characteristics can be tuned by concentration, temperature difference (ΔT), and relaxation time. We discover that the focal conic texture is capable of transforming fluorescence located on the short‐wavelength side outside the PBG to a significant negative CPL signal (g lum = −0.1). Leveraging the multi‐dimensional differences in structural color, polarized texture, and CPL activity between planar and focal conic textures, complex optical patterns, and multilevel information encryption can be achieved. This work reveals a new mechanism for modulating CPL via defect engineering and opens a novel pathway to high‐security optical anti‐counterfeiting materials.