Chiral nematic liquid crystals (N*-LC) doped with achiral fluorescent aromatic molecules emit strong circularly polarized luminescence (CPL) and act as a reversible CPL switch that can be regulated by turning the applied direct-current electric field on and off.

Chiral liquid crystals (LCs) are essential for optoelectronic devices. Two representative achiral luminescent compounds, pyrene and perylene, are doped into a mixed chiral nematic LC (N*-LC) comprising achiral LC 4′-pentyl-4-biphenylcarbonitrile (5CB) and chiral LC 2-octyl-4-[4-(hexyloxy)benzoyloxy]benzoate (2OHBB). Consequently, despite being achiral luminescent materials, the doped pyrene and perylene successfully generate strong circularly polarized luminescence (CPL) from the resulting chiral N*-LC composed of 5CB and 2OHBB. The rotation direction of the extracted CPL can be controlled by the chirality of the LC molecule 2OHBB. Furthermore, these N*-LCs demonstrate continuous and reversible CPL responses depending on the presence or absence of a direct current (DC) electric field. This result demonstrates the successful design of a CPL LC system, where the rotation direction of CPL can be controlled not only by the chirality of 2OHBB, but also through the ON–OFF–ON switching of the DC electric field. This behavior is attributed to a reversible transition from a helical structure to another ordered structure (chiral nematic phase to chiral nematic phase transition). This study provides an effective strategy for controlling CPL properties by exposing N*-LC to DC electric fields and for developing functional CPL devices.