Photothermal response and precise control of circularly polarized luminescence via double-layered films based on cholesteric liquid crystals†

Abstract

The regulation of the performance of circularly polarized luminescence (CPL) materials has long been a subject of considerable interest. However, achieving simultaneous photothermal responsiveness and precise control of CPL performance remains a challenge. To address this issue, a double-layered film strategy is employed, where the overlap between the emission band of a luminescent layer, exhibiting non-polarized or circularly polarized luminescence, and the selective absorption and reflection bands of a cholesteric liquid crystal (N*-LC) layer with stimuli-responsive properties is utilized to achieve photothermal response and precise regulation of CPL performance. The non-chiral luminescent compound and the CPL copolymer are used as the first layer, combined with N*-LC polymers Azo(x)–Mt(y) synthesized in this work, to prepare the double-layered films NI/Azo(x)–Mt(y) and Py/Azo(x)–Mt(y). Non-polarized or circularly polarized fluorescence is emitted from the first-layered film upon light excitation, allowing static regulation of CPL performance after passing through selective absorption and selective reflection of the second-layered N*-LC film. Additionally, the CPL signals of double-layered films are further precisely regulated in terms of on–off, inversion, intensity, and wavelength by adjusting the Azo(x)–Mt(y) copolymer composition. Furthermore, under different photothermal conditions, the CPL wavelength and intensity of double-layered films are dynamically regulated by stimulating Azo(x)–Mt(y), as azobenzene mesogens undergo trans–cis isomerization.