Lei Nana, Yi Sijing, Wang Jiao, Li Qintang, Chen Xiao
Key Laboratory of Colloid and Interface Chemistry, Shandong University, Ministry of Education , Jinan 250100, China.
College of Art and Sciences, Shanxi Agricultural University , Taigu 030801, China.
J Phys Chem B. 2017 Dec 28;121(51):11528-11536. doi: 10.1021/acs.jpcb.7b10701. Epub 2017 Dec 13.
Hybridization of polyoxometalates (POMs) with cationic surfactants offers the opportunity to greatly improve their functionalities as well as processabilities. Here, a surfactant-encapsulated Eu-containing POM complex (SEP) was formed via electrostatic interaction between 1-octadecyl-3-methylimidazolium bromide (OB) and Na(EuWO)·32HO (EuW). SEP was first self-assembled in a protic ionic liquid to prepare the soft aggregates to fundamentally avoid the fluorescence quenching by water molecules. The structures and photophysical properties of SEP or aggregates were investigated thoroughly by NMR and FTIR spectroscopy, optical and electron microscopy, small-angle X-ray scattering, and fluorescence measurements. The formed gel-like aggregates were found to compose of three-dimensional networks of microribbons with an interdigitated layered molecular packing of SEP, which was different from the usual inverse bilayer model of POM hybrids in common organic solvents. Compared to EuW solid or its aqueous solution, both SEP and its aggregates exhibited intense red luminescence with much improved lifetime and quantum efficiency. In addition, the soft aggregates exhibited an efficient energy transfer and an obviously enhanced monochromaticity, owning to the organized arrangement of EuW units and a confined microenvironment to isolate them from each other between adjacent layers. The obtained results will not only present a useful reference to the aggregation behavior of POM hybrids in ionic liquids, but also provide an easy way to design EuW luminescent soft materials based on the nonaqueous media.
多金属氧酸盐（POMs）与阳离子表面活性剂的杂化提供了极大改善其功能以及加工性能的机会。在此，通过1-十八烷基-3-甲基咪唑溴盐（OB）与Na(EuWO)·32HO（EuW）之间的静电相互作用形成了一种表面活性剂包裹的含铕POM配合物（SEP）。SEP首先在质子离子液体中自组装以制备软聚集体，从根本上避免水分子导致的荧光猝灭。通过核磁共振（NMR）、傅里叶变换红外光谱（FTIR）、光学和电子显微镜、小角X射线散射以及荧光测量等手段对SEP或聚集体的结构和光物理性质进行了深入研究。发现形成的凝胶状聚集体由微带的三维网络组成，SEP具有相互交错的层状分子堆积结构，这与常见有机溶剂中POM杂化物通常的反相双层模型不同。与EuW固体或其水溶液相比，SEP及其聚集体均表现出强烈的红色发光，其寿命和量子效率都有显著提高。此外，由于EuW单元的有序排列以及相邻层之间将它们彼此隔离的受限微环境，软聚集体表现出高效的能量转移和明显增强的单色性。所得结果不仅将为POM杂化物在离子液体中的聚集行为提供有用的参考，而且还将提供一种基于非水介质设计EuW发光软材料的简便方法。
