Mandal Prasun K, Samanta Anunay
School of Chemistry, University of Hyderabad, Hyderabad 500 046, India.
J Phys Chem B. 2005 Aug 11;109(31):15172-7. doi: 10.1021/jp051844d.
While the imidazolium ionic liquids have been studied for some time, little is known about the pyrrolidinium ionic liquids. In this work, steady-state and picosecond time-resolved fluorescence behavior of three electron donor-acceptor molecules, coumarin-153 (C153), 4-aminophthalimide (AP), and 6-propionyl-2-dimethylaminonaphthalene (PRODAN), has been studied in a pyrrolidinium ionic liquid, N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide, abbreviated here as [bmpy][Tf2N]. The steady-state fluorescence data of the systems suggest that the microenvironment around these probe molecules, which is measured in terms of the solvent polarity parameter, E(T)(30), is similar to that in 1-decanol and that the polarity of this ionic liquid is comparable to that of the imidazolium ionic liquids. All three systems exhibit wavelength-dependent fluorescence decay behavior, and the time-resolved fluorescence spectra show a progressive shift of the fluorescence maximum toward the longer wavelength with time. This behavior is attributed to solvent-mediated relaxation of the fluorescent state of these systems. The dynamics of solvation, which is studied from the time-dependent shift of the fluorescence spectra, suggests that approximately 45% of the relaxation is too rapid to be measured in the present setup having a time resolution of 25 ps. The remaining observable components of the dynamics consist of a short component of 115-440 ps (with smaller amplitude) and a long component of 610-1395 ps (with higher amplitude). The average solvation time is consistent with the viscosity of this ionic liquid. The dynamics of solvation is dependent on the probe molecule, and nearly 2-fold variation of the solvation time depending on the probe molecule could be observed. No correlation of the solvation time with the probe molecule could, however, be observed.
虽然咪唑鎓离子液体已经被研究了一段时间，但对于吡咯烷鎓离子液体却知之甚少。在这项工作中，研究了三种电子供体 - 受体分子，香豆素 - 153（C153）、4 - 氨基邻苯二甲酰亚胺（AP）和6 - 丙酰基 - 2 - 二甲基氨基萘（PRODAN）在吡咯烷鎓离子液体N - 丁基 - N - 甲基吡咯烷双（三氟甲磺酰）亚胺（在此简称为[bmpy][Tf2N]）中的稳态和皮秒时间分辨荧光行为。系统的稳态荧光数据表明，这些探针分子周围的微环境（根据溶剂极性参数E(T)(30)测量）与在1 - 癸醇中的微环境相似，并且这种离子液体的极性与咪唑鎓离子液体的极性相当。所有这三个系统都表现出波长依赖性荧光衰减行为，并且时间分辨荧光光谱显示荧光最大值随时间逐渐向更长波长移动。这种行为归因于这些系统荧光态的溶剂介导弛豫。从荧光光谱的时间依赖性位移研究的溶剂化动力学表明，在本具有25 ps时间分辨率的装置中，大约45%的弛豫太快而无法测量。动力学的其余可观测成分包括一个115 - 440 ps的短成分（幅度较小）和一个610 - 1,395 ps的长成分（幅度较高）。平均溶剂化时间与这种离子液体的粘度一致。溶剂化动力学取决于探针分子，并且可以观察到溶剂化时间根据探针分子有近2倍的变化。然而，未观察到溶剂化时间与探针分子之间的相关性。
