Department of Chemistry, Indian Institute of Technology, Kharagpur 721 302, WB, India.
Spectrochim Acta A Mol Biomol Spectrosc. 2013 Feb;102:371-8. doi: 10.1016/j.saa.2012.10.036. Epub 2012 Nov 1.
Understanding ion transport dynamics, structure of surfactant aggregates in ionic liquids or ionic liquid/water solutions are quite interesting and potentially important due to widespread applications of surfactant-based systems. In this manuscript we have investigated the effect of 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF(4)) addition on solvent and rotational relaxation of coumarin-153 (C-153) and coumarin-480 (C-480) in aqueous solution of sodium 1,4-bis(2-ethylhexyl) sulfosuccinate (NaAOT) using steady state and picosecond time resolved fluorescence spectroscopy. The strong adsorption of the bmim(+) at the interface and the role of the ionic liquid particularly the cation bmim(+) in the modification of the interfacial geometry were probed by the analysis of decay parameters and the rotational relaxation parameters. Since the addition of the NaAOT in water-bmimBF(4) mixture above critical micellar concentration (48 mM, obtained from observing pyrene fluorescence) causes strong adsorption of the ionic liquid particularly the cation bmim(+), the average solvation time, particularly the slow component increases significantly. More importantly we have found the probe dependent solvation dynamics due to the different location of the probe molecules, C-153 and C-480. C-153 being hydrophobic in nature resides in the stern layer and the adsorption of the bmim(+) at the interface modifies stern layer more effectively. So we have observed more pronounced change in solvation dynamics in case of C-153 compared to that in case of C-480. The fluorescence anisotropy decays of the probe molecules were found to be biexponential in nature. The anisotropy decay was interpreted by using a model which consists of the wobbling (rotational) and translational diffusion of the dye coupled with the rotational motion of the micelle as a whole.
由于基于表面活性剂的系统具有广泛的应用，因此了解离子传输动力学、表面活性剂在离子液体或离子液体/水溶液中的聚集结构是非常有趣和潜在重要的。在本手稿中，我们使用稳态和皮秒时间分辨荧光光谱法研究了 1-丁基-3-甲基咪唑四氟硼酸盐（bmimBF(4)）对香豆素-153（C-153）和香豆素-480（C-480）在十二烷基硫酸钠（NaAOT）水溶液中溶剂和旋转松弛的影响。通过分析衰减参数和旋转松弛参数，探测了 bmim(+)在界面上的强吸附以及离子液体（特别是阳离子 bmim(+)）在修饰界面几何形状方面的作用。由于在临界胶束浓度（48 mM，通过观察芘荧光获得）以上，NaAOT 在水-bmimBF(4)混合物中的添加导致离子液体，特别是阳离子 bmim(+)的强烈吸附，平均溶剂化时间，特别是慢组分显著增加。更重要的是，我们发现由于探针分子 C-153 和 C-480 的不同位置，存在探针依赖性的溶剂化动力学。C-153 本质上是疏水性的，位于 Stern 层，界面上 bmim(+)的吸附更有效地修饰 Stern 层。因此，与 C-480 相比，我们观察到 C-153 中溶剂化动力学的变化更为显著。探针分子的荧光各向异性衰减被发现具有双指数性质。各向异性衰减通过使用一个模型进行解释，该模型由染料的摆动（旋转）和扩散与胶束的整体旋转运动耦合。
