Chiral luminescent nematic liquid crystals emit strong CPL signals and act as a reversible CPL switch regulated by turning the applied DC electric field on and off.

Abstract

To obtain chiral luminescent nematic liquid crystals (N*-LCs), two sets of chiral perylene luminescent materials (R,R)/(S,S)-N,N′-bis(1-cyclohexylethyl)perylene-3,4,9,10-tetracarboxylic diimide [(R,R)/(S,S)-CPDI] and (R,R)/(S,S)-N,N′-bis(1-phenylethyl)perylene-3,4,9,10-tetracarboxylic diimide [(R,R)/(S,S)-BPP] were prepared and doped into a nematic liquid crystal (N-LC), 5CB. The obtained liquid crystals N*-LC-CPDI and N*-LC-BPP emitted stronger circularly polarized luminescence (CPL) signals than the CPDI- and BPP-containing chiral poly(methyl methacrylate) (PMMA) luminescent films owing to higher helical twist power. When a direct current (DC) electric field was applied to N*-LC, a reversible CPL response was obtained due to the field-induced phase transition from the chiral nematic phase to the nematic phase. This demonstrated the successful construction of an ′′on-off-on′′ CPL system based on a DC electric field and was attributed to the change in the liquid crystalline organization from a uniformly lying helical structure to a planar one. This work can provide an effective strategy for the development of functional CPL devices in which the CPL can be regulated by applying a DC electric field to the N*-LC.