Switching of circularly polarised luminescence in perylene-diimide-based chiral liquid crystals induced by electric fields and heating.

Two pairs of chiral perylene-based luminescent materials, namely ()/()-,'-bis(1-phenylethyl)perylene-3,4,9,10-tetracarboxylic diimide [()/()-BPP] and ()/()-,'-bis(1-cyclohexylethyl)perylene-3,4,9,10-tetracarboxylic diimide [()/()-CPDI], were doped into a nematic liquid crystal with a low phase transition temperature, 4'-hexyl-4-biphenylcarbonitrile. The resultant luminescent chiral nematic liquid crystals (N*-LCs) exhibited a circularly polarised luminescence (CPL) stronger than that of chiral poly(methyl methacrylate)-based luminescent films containing BPP and CPDI. Both N*-LCs displayed reversible CPL property responses (CPL intensity and CPL sign inversion) upon the application of a direct-current (DC) electric field (due to a chiral nematic phase → nematic phase transition) and heating (due to a chiral nematic phase → isotropic phase transition). Thus, an on-off-on CPL system controlled by DC electric fields and thermal stimuli was constructed based on a transition from a uniformly aligned helical structure to another orientational arrangement. This work provides an effective strategy for the development of functional CPL devices based on CPL control N*-LC exposure to DC electric fields or heat.