Achiral Dichroic Dyes-mediated Circularly Polarized Emission Regulated by Orientational Order Parameter through Cholesteric Liquid Crystals

It is noteworthy that cholesteric liquid crystal (CLC) platforms have been witnessed in high-performance circularly polarized luminescence (CPL) behaviors through the highly organized chiral co-assembled arrangement of achiral dyes. However, most CPL-active design strategies are closely relative to the helix co-assembly structure of CLC rather than achiral dyes. Herein, we developed an intriguing regulation strategy for CPL-active CLC materials. They were regulated using the orientational order parameter (SF) of achiral dichroic dyes as an incisive probe for the order arrangement degree of achiral dyes in CLC media. The I-shaped phenothiazine derivative PHECN dye (SF=0.30) emitted a strong CPL signal (|glum|=0.47). In contrast, the T-shaped derivative (PHEBen) dye (SF=0.09) showed a weak circular polarization level (|glum|=0.07) at similar CLC textures. Most interestingly, this kind of dichroic PHECN dye with a higher SF could greatly improve the contrast ratio of CPL (Delta glum=0.47) and emission intensity (Delta FL=46.0 %) at direct-current electric field compared with the T-shaped PHEBen (Delta glum=0.07 and Delta FL=1.0 %) in CLC. This work demonstrates that an induced CPL emission can be mediated using achiral dichroic dye, which will open a new avenue for developing excellent CPL-active display materials. A strategy was developed for regulating circularly polarized luminescence performance by increasing the order parameter value of achiral dichroic dye in cholesteric liquid crystal media without changing the helical superstructure. Additionally, the circularly polarized luminescence and fluorescence intensity response (contrast ratio) was also improved as the order parameter value increased under the DC electric field. Efficient encryption could be achieved by modulating the structure of achiral dichroic dyes in cholesteric liquid crystals.+image

Automated summary

Cholesteric liquid crystal platforms have achieved high-performance circularly polarized luminescence (CPL) through the organized arrangement of achiral dyes. This study developed a regulation strategy for CPL-active CLC materials by using the orientational order parameter of achiral dichroic dyes. The results showed that increasing the order parameter value of the dichroic dye improved the CPL emission and contrast ratio in CLC, opening a new avenue for developing excellent CPL-active display materials.