King David, Le Matthew C, Arnaiz Yan P, Cox Seonghyeok L, Smith Jakob, Han Haesook, Bhowmik Pradip K
Department of Chemistry and Biochemistry, University of Nevada Las Vegas, 4505 S. Maryland Parkway, Box 454003, Las Vegas, NV 89154, United States.
J Ion Liq. 2024 Dec;4(2). doi: 10.1016/j.jil.2024.100125. Epub 2024 Nov 9.
Dicationic ionic liquids (DILs) are emerging as a powerful, next-generation approach to designing applied ILs because of their superior physicochemical properties as well as their diverse complexity and tunability for task specific applications. DILs are scarce in the literature compared to monocationic ILs (MILs), and one of their main issues is their expected tendency to possess higher melting temperatures. A series of 1,4-bis[2-(4-pyridyl)ethenyl] benzene and 1,4-bis[2-(2-pyridyl)ethenyl]benzene quaternary salts (Q-BPEBs) with different counterions (bromide, tosylate, and triflimide) and carbon chain lengths (C, C, and C) have been synthesized for their potential as DILs with strong photoluminescent properties in the solid state. All Q-BPEB salts demonstrated robust thermal stabilities as determined by thermogravimetric analysis (TGA). The differential scanning calorimetry (DSC) thermograms for Q-BPEB tosylates and triflimides displayed crystalline polymorphisms before melting transitions as verified by polarizing optical microscopy (POM). The Q-BPEB bromide and tosylate salts all showed high melting points of above >170 °C because of their dicationic rigid structures and strong ionic interactions of their anions. Once the Q-BPEB tosylates were exchanged with triflimide ions, - isomers , and still possessed very high melting points (>225 °C), however, the - isomers , and exhibited melting points lower than 100 °C, classifying them as DILs. Their photoluminescent properties were also studied in methanol with the emission values of λ = 476-482 nm for the - isomers and those of λ = 448-453 nm for the - isomers. In the solid state, the Q-BPEB salts exhibited strong fluorescence with quantum yields of up to 50 %. The relatively simple synthesis of these fluorescent dicationic organic salts and ILs are pertinent towards the scarcity of these materials in the literature and provide a deeper insight on the design of fluorescent ILs containing more than one charge center.
双阳离子离子液体（DILs）正作为一种强大的下一代方法出现，用于设计应用离子液体，因为它们具有优异的物理化学性质，以及针对特定任务应用的多样复杂性和可调性。与单阳离子离子液体（MILs）相比，DILs在文献中较为稀少，其主要问题之一是它们预期具有较高熔点的倾向。已经合成了一系列具有不同抗衡离子（溴化物、对甲苯磺酸盐和三氟甲磺酰亚胺）和碳链长度（C、C和C）的1,4 - 双[2 - （4 - 吡啶基）乙烯基]苯和1,4 - 双[2 - （2 - 吡啶基）乙烯基]苯季铵盐（Q - BPEBs），以研究它们作为具有固态强发光性质的DILs的潜力。通过热重分析（TGA）确定，所有Q - BPEB盐都表现出强大的热稳定性。通过偏光显微镜（POM）验证，Q - BPEB对甲苯磺酸盐和三氟甲磺酰亚胺的差示扫描量热法（DSC）热谱图在熔融转变前显示出晶体多晶型性。由于其双阳离子刚性结构及其阴离子的强离子相互作用，Q - BPEB溴化物和对甲苯磺酸盐都显示出高于170°C的高熔点。一旦Q - BPEB对甲苯磺酸盐与三氟甲磺酰亚胺离子交换， - 异构体 、 和 仍然具有非常高的熔点（>225°C），然而， - 异构体 、 和 表现出低于100°C的熔点，将它们归类为DILs。还在甲醇中研究了它们的发光性质， - 异构体的发射值为λ = 476 - 482 nm， - 异构体的发射值为λ = 448 - 453 nm。在固态下，Q - BPEB盐表现出强荧光，量子产率高达50%。这些荧光双阳离子有机盐和离子液体相对简单的合成方法与文献中这些材料的稀缺性相关，并为设计含有多个电荷中心的荧光离子液体提供了更深入的见解。
