Lanthanide Containing Ionic Liquid Crystals: EuBr2, SmBr3, TbBr3 and DyBr3 in C(12)mimBr

Doping the ionic liquid crystal C(12)mimBr with various lanthanide halides yields interesting novel liquid crystalline and luminescent materials. The thermal phase behavior of all compounds was investigated by hot-stage polarizing optical microscopy and differential scanning calorimetry and the photophysical properties were determined by luminescence spectroscopy. C(12)mimBr itself is an ionic liquid crystal that shows bluish-white emission upon excitation with UV light due to transitions in the imidazolium it-system. Doping lanthanide bromides into C(12)mimBr with concentrations of about 1 mol-% does not affect the liquid crystalline behavior of the host materials to a great extent and room temperature liquid crystals are obtained. All materials show an appreciable luminescence. EuBr2 in C(12)mimBr yields a material, which shows a blue emission originating from 4f-5d-transitions. SmBr3-doped samples show a red and TbBr3 samples a green luminescence. Upon doping C(12)mimBr with DyBr3 an orange luminescent liquid crystalline material is obtained. Most interestingly the emission color for the TbBr3 and DyBr3 containing materials can be tuned from bluish-white (mainly C(12)mimBr emission) to green (for TbBr3) and orange-yellow (for DyBr3) depending on the wavelength of the excitation light used.