Light-Induced Manipulation of Circularly Polarized Luminescence Color and Intensity via the Photonic Bandgap Effect

The development of smart circularly polarized luminescence (CPL) systems with dynamically tunable emission properties presents both a significant challenge and a compelling opportunity in advanced photonics. Herein, we report a light-responsive CPL system fabricated by dispersing achiral Coumarin 6 and a photochromic spiropyran derivative within a self-organized chiral nematic liquid crystal (N*-LCs) matrix. The regular helical superstructure of the N*-LCs host not only induces the emergence of pronounced CPL signals from the achiral dopants but also provides a photonic bandgap (PBG). Through the efficient Förster resonance energy transfer (FRET) process from the donor Coumarin 6 to the photoisomerized merocyanine form of the acceptor, the CPL emission is reversibly switched from green to red upon UV light irradiation. Concurrently, the luminescence dissymmetry factor (g _lum) is significantly enhanced from 0.2 to 0.95, which is attributed to the precise spectral alignment of the new red emission with the PBG center of the chiral medium. This strategy of leveraging the photonic effect for amplification, combined with a photon-controlled FRET, enables dynamic and reversible tuning of both the color and g _lum of CPL, offering a versatile platform for applications in programmable optical encryption and next-generation anticounterfeiting technologies.