Reflection-influenced circularly polarised luminescence in dye-embedded polymer-stabilised cholesteric liquid crystal films

Abstract

A phenothiazine derivative TPT with two triphenylethylene groups was prepared through the Suzuki coupling reaction. Obvious aggregation-induced emission in a DMF–H₂O mixture and strong sky-blue solid-state emission were observed for TPT. Cholesteric liquid crystal (CLC) mixtures were prepared with the addition of the dye TPT, a chiral additive (CA) in nematic LC242. By changing the concentration of CA, a series of luminescent and structurally coloured polymer-stabilised CLC films (TPT-PSCLCs) were obtained after photopolymerisation. Diffuse reflectance circular dichroism spectra of the TPT-PSCLC films confirmed the formation of right-handed supramolecular helical structures. The circularly polarised luminescence handedness and the luminescent dissymmetry factors (g_lum) were influenced by both the position and the intensity of the selective Bragg reflection band. A relatively high g_lum value of up to 0.80 was obtained for a TPT-PSCLC film. A composite system by stacking a TPT-PMMA film and a PSCLC film with different substrates was fabricated, verifying the chiral optical filtering effect of the PSCLC system. A high g_lum value of up to 1.63 was successfully achieved. Moreover, the stacking of a fluorescent film with the PSCLC-coated PET film was useful for the large-area preparation of CPL materials. This work not only gives us a deep understanding of the interaction between the circularly polarised light and achiral dye, but also reveals the chiral optical filtering effect of PSCLC films.