Circularly Polarized Luminescence of Cholesteric Liquid Crystal Polymer Networks with a Europium(III) Complex as an Emitter.

A coordination complex, Eu(CCdbm)(phen), with strong emission and a high quantum yield (QY ∼ 51.9%) was synthesized. The Eu complex, as a fluorescent emitter, was embedded in cholesteric liquid crystal polymer networks (CLCNs). A series of free-standing Eu-CLCN films were obtained, generating a typical sharp emission band corresponding to the Eu complex. Tunable handedness of circularly polarized luminescence (CPL) with high || values (up to 0.63) was observed. A series of CPL-active CLCN-coated PET films were also prepared (|| values up to 0.63), which can be used for large-area preparations. Moreover, by stacking an emitter-embedded PMMA layer and a CLCN layer, a composite system was built, and a large || value (∼1.42) was achieved. Fluorescence patterns were prepared, and distinct images of CLCN films were recognized under both daylight and UV light. This work not only demonstrated that coordination compounds could be incorporated with CLCN films to prepare CPL-active materials with high || values but also provided a new perspective for emissive CLCN materials used for anticounterfeiting and encryption.