Electric field-induced circularly polarised luminescence switching in chiral nematic liquid crystals with negative dielectric anisotropy

An emissive chiral nematic liquid crystal (N*-LC-MBBA/CPDI) was fabricated by doping an achiral nematic liquid crystal (<i>N</i>-LC), namely <i>N</i>-(4-methoxybenzylidene)-4-butylaniline (MBBA), which exhibits a negative dielectric anisotropy (Δ<i>ε</i> < 0), with the chiral luminophore <i>N</i>,<i>N</i>'-bis(1-cyclohexylethyl)perylene-3,4,9,10-tetracarboxylic diimide (CPDI). In contrast to the previously reported emissive chiral <i>N</i>-LC (N*-LC-6CB/CPDI) composed of a positive dielectric anisotropy <i>N</i>-LC, N*-LC-MBBA/CPDI exhibited no circularly polarised luminescence (CPL) in the absence of a direct current (DC) electric field. However, upon the application of a DC electric field, a pronounced CPL signal emerged due to helical axis reorientation in the chiral nematic host. Under the optimised conditions, the system displayed a high dissymmetry factor with |<i>g</i>_CPL| values reaching up to 0.36. Moreover, the CPL response was reversible and continuously switchable upon electric field modulation. Overall, this study presents an effective strategy for the development of functional CPL-switching devices based on the DC field-driven control of <i>N</i>*-LCs.