Tunable Helix Inversion and Circularly Polarized Luminescence in Cholesteric Liquid Crystal Copolymers with Room-Temperature Phosphorescence

Abstract

Circularly polarized luminescence (CPL) polymer materials have received widespread attention due to their high stability and excellent processability. However, most of reported intrinsic CPL polymer materials show low luminescence dissymmetry factor (g lum ) values and are difficult to effectively regulate luminescent properties. This article proposes a simple strategy to synthesize luminescent cholesteric liquid crystal (N*-LC) copolymers Bi(x)-Mt(y)-Py(0.01) with large g lum values and tunable performance by copolymerizing nematic liquid crystal monomer MA4BiCN, chiral monomer MC0Mt, and luminescent monomer MC6Py. Regulation and inversion of chiral helix structure and CPL performance of copolymers are achieved by altering the relative content of chiral and liquid crystal components. Meanwhile, g lum values are further amplified and reversed through selective reflection. With an increase of chiral component, helix structures of Bi(x)-Mt(y)-Py(0.01) change from left-handed to right-handed, accompanied by reversal of CPL signal. For Bi(0.79)-Mt(0.20)-Py(0.01), solid-state fluorescence quantum yield can achieve 41.5%, and a negative CPL signal (g lum = −0.40) is detected in 10 μm film. When film thickness increases to 150 μm, the CPL signal is reversed to positive, attributed to enhanced selective reflection, and g lum is amplified to 0.66. Additionally, a red room-temperature phosphorescence with a 278.2 ms long lifetime is observed.