Flexible and enhanced multicolor-emitting films co-assembled by lanthanide complexes and a polymerizable surfactant in aqueous solution

Abstract

Lanthanide complex doped lyotropic liquid crystals (LLCs) are soft materials which are impressive due to their excellent luminescence efficiencies and stabilities. The introduction of lanthanide complexes into polymerizable LLCs, however, may produce organized films with better optical and mechanical properties through in situ photopolymerization. An environmentally friendly strategy to fabricate flexible multicolor-emitting films has been developed through co-assembling red-/green-emitting trisdipicolinate lanthanide complexes [choline]₃[Ln(DPA)₃] (Ln–DPA, Ln = Eu, Tb) into LLC matrices mainly via electrostatic interaction and further photopolymerization. The LLCs were constructed from a polymerizable surfactant, 3-dodecyl-1-vinylimidazolium bromide (C₁₂VIMBr), in aqueous solution. The maintenance of the well-defined LLC nanostructures in the luminescent films was validated by small-angle X-ray scattering (SAXS) as well as scanning electron microscopy (SEM) measurements. Remarkably, the lifetime and absolute luminescence quantum efficiency of such films have been improved significantly compared with those of the corresponding solid Eu–DPA complex or in aqueous solution and LLC matrices. Through tuning the molar ratio of Eu–DPA to Tb–DPA complexes, the emission color of the films could be finely-tailored between red and green in the CIE chromaticity diagram. Furthermore, the films also possessed certain mechanical strength and stability against pH, metal ions, and temperature, indicating their potential application as robust luminescent materials.