Mesomorphic and luminescence properties of side chain cholesteric liquid crystalline polymers containing Eu(III) and Tb(III) ions

Luminescent cholesteric liquid crystalline polymers consisting of the lanthanide ions covalently attached to cholesteric polysiloxanes are prepared. Cholesteric liquid crystalline monomer and 4-(allyloxy)benzoic acid grafted to poly(methylhydrogeno)siloxane is used as one of the precursors for the preparation of the lanthanide-containing cholesteric liquid crystalline polymers. The chemical structures of the monomers are characterised by Fourier transform infrared, ¹H NMR and elemental analyses. The mesomorphic properties and phase behaviour are investigated by differential scanning calorimetry, thermogravimetric analysis, polarising optical microscopy and X-ray diffraction. The polymers containing <3 mol% of the lanthanide ions reveal reversible mesomorphic phase transition, wide mesophase temperature ranges and high thermal stability. The introductions of the lanthanide ions do not change the liquid crystalline state of polymer systems; on the contrary, the polymers are enabled with the significant luminescent properties. With the lanthanide ions contents ranging between 1 and 3 mol%, luminescent intensity and luminescent lifetimes of polymers gradually increased. The temperature dependence of luminescent intensity was studied in the liquid crystalline phase.