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Luminescent Vesicles and Lyotropic Liquid Crystals in Ethylammonium Nitrate from a Partially Amphiphilic Eu Complex

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journal contribution
posted on 05.06.2019, 15:05 by Qingrun Li, Sijing Yi, Xiao Chen
Soft luminescent materials have attracted much attention because of their self-assembled and controllable properties. To explore their facile and effective fabrication ways, we report here the self-assembling of luminescent vesicles and lyotropic liquid crystals (LLCs) in a protic ionic liquid, ethylammonium nitrate, by a partially amphiphilic europium β-diketonate complex (Eu­(III)) with a 1-dodecyl-3-methylimidazolium cation as the counter ion. An interesting result came from the complex-induced vesicle formation of corresponding amphiphile, 1-dodecyl-3-methylimidazolium bromide ([C12mim]­Br), which has been rarely reported in the past. It was the interaction between the Eu­(III) and imidazolium group that changed the critical packing parameter of [C12mim]­Br, which finally resulted in the occurrence of vesicles. The obtained vesicle aggregates exhibited enhanced fluorescence intensity and lifetime compared to those of Eu­(III) solution. Meanwhile, a hexagonal LLC phase with better fluorescence properties was found at higher [C12mim]Br concentration. The obtained photophysical data confirmed that the order degree of Eu­(III)-containing aggregates could effectively increase the energy transition efficiency of ligands. The better luminescent properties of LLC resulted from the stronger stabilizing and binding effects on Eu­(III) in LLC than that in vesicles, which might be caused by closer molecular packing in LLC. The results presented here will not only expand the strategy of constructing lanthanide-containing luminescent soft materials in ionic liquids but also provide reference to better understand the effect of organized aggregates on luminescence properties.