Molecular-level properties of ionic liquids (ILs) draw an increasing interest. Several informative experimental approaches for investigation of nano/miscrostructuring phenomena and local viscosity/rigidity of ILs use probe molecules sensitive to microenvironment along with suitable detection techniques. In this work, we for the first time investigate capabilities of photoexcited triplet fullerenes to probe local properties of ILs, with time-resolved electron paramagnetic resonance (TR EPR) being a sensitive detection tool. We have selected C₆₀ and its derivative phenyl-C₆₁-butyric acid methyl ester (PCBM) as probes and ILs [Bmim]BF₄ and [C₁₀mim]BF₄ as solvents. C₆₀ and PCBM demonstrate different sensitivities to microenvironment in ILs. Spin dynamics of photoexcited C₆₀ is strongly contributed by pseudorotation of the Jahn–Teller axis, making its use as a probe for microenvironment challenging. This behavior is strongly suppressed in PCBM, which, in addition, is more soluble in ILs than C₆₀. The in-depth analysis of variable-temperature two-dimensional TR EPR data shows that spectral shapes are sensitive to the restricted mobility of PCBM in ILs. In this way, the information on local environment and heterogeneities in ILs can be obtained by TR EPR. PCBM usefully complements the other spin probes previously implemented for EPR studies in ILs. It is larger in size and in addition allows high-sensitivity TR EPR measurements up to a room temperature, which is an important improvement for characterization of heterogeneities in room-temperature ILs.

中文翻译：

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离子液体中光激发富勒烯的时间分辨电子顺磁共振研究

离子液体（ILs）的分子水平特性引起了越来越多的关注。用于研究纳米级/微结构现象和IL的局部粘度/刚度的几种有用的实验方法使用对微环境敏感的探针分子以及合适的检测技术。在这项工作中，我们首次研究了光激发三重态富勒烯探测IL的局部特性的能力，其中时间分辨电子顺磁共振（TR EPR）是灵敏的检测工具。我们选择了C ₆₀及其衍生物苯基C ₆₁丁酸甲酯（PCBM）作为探针，选择了ILs [Bmim] BF ₄和[C ₁₀ mim] BF ₄作为溶剂。C ₆₀PCB和PCBM对IL中的微环境表现出不同的敏感性。光激发的C _60的自旋动力学是由Jahn-Teller轴的伪旋转强烈贡献的，使其用作挑战微环境的探针。此行为在PCBM中得到了强烈抑制，此外，与C ₆₀相比，其在IL中的溶解度更高。。可变温度二维TR EPR数据的深入分析表明，光谱形状对IL中PCBM受限制的迁移率敏感。这样，可以通过TR EPR获得有关IL中局部环境和异质性的信息。PCBM可以有效地补充先前用于ILs中EPR研究的其他自旋探针。它的尺寸更大，此外还允许在室温下进行高灵敏度的TR EPR测量，这对于表征室温IL的异质性而言是一项重要的改进。