Li Qingrun, Yi Sijing, Chen Xiao
Key Laboratory of Colloid and Interface Chemistry, Ministry of Education, Shandong University, Jinan 250100, China.
College of Arts and Sciences, Shanxi Agricultural University, Taigu 030801, China.
ACS Omega. 2019 Jun 5;4(6):9843-9849. doi: 10.1021/acsomega.9b01215. eCollection 2019 Jun 30.
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 ([Cmim]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 [Cmim]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 [Cmim]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.
柔软发光材料因其自组装和可控特性而备受关注。为探索其简便有效的制备方法，我们在此报道了一种部分两亲性的铕β-二酮配合物（Eu(III)）与1-十二烷基-3-甲基咪唑阳离子作为抗衡离子，在质子离子液体硝酸乙铵中自组装形成发光囊泡和溶致液晶（LLC）。一个有趣的结果是相应两亲物1-十二烷基-3-甲基咪唑溴化物（[Cmim]Br）在该配合物诱导下形成囊泡，这在过去鲜有报道。正是Eu(III)与咪唑基团之间的相互作用改变了[Cmim]Br的临界堆积参数，最终导致囊泡的形成。与Eu(III)溶液相比，所获得的囊泡聚集体表现出增强的荧光强度和寿命。同时，在较高[Cmim]Br浓度下发现了具有更好荧光性质的六方LLC相。所获得的光物理数据证实，含Eu(III)聚集体的有序度可有效提高配体的能量转移效率。LLC更好的发光性质源于其对Eu(III)的稳定和结合作用比囊泡中更强，这可能是由于LLC中分子堆积更紧密所致。此处给出的结果不仅将扩展在离子液体中构建含镧系发光柔软材料的策略，还可为更好地理解有序聚集体对发光性质的影响提供参考。
