Department of Chemistry, Indian Institute of Technology Hyderabad, Sangareddy 502285, Telangana, India.
J Phys Chem B. 2022 Jul 28;126(29):5523-5533. doi: 10.1021/acs.jpcb.2c03561. Epub 2022 Jul 14.
We have monitored the impacts of an increment in the alkyl chain length of the imidazolium-based tetrafluoroborate ionic liquids on the local deuteroxyl probe modes of interest. For this study, we have taken 1-ethyl-3-methylimidazolium tetrafluoroborate [EMIm][BF], 1-butyl-3-methylimidazolium tetrafluoroborate [BMIm][BF], 1-octyl-3-methylimidazolium tetrafluoroborate [OMIm][BF], and 1-decyl-3-methylimidazolium tetrafluoroborate [DMIm][BF] ionic liquid solutions with 5% HOD in HO as the vibrational reporter of the associated ultrafast system dynamics. Classical molecular dynamics (MD) simulations were employed to determine molecular structure and dynamic properties, while the spectral profiles were derived by applying the wavelet analysis of classical trajectories. Spatial distribution functions reveal the heterogeneity within the molecular structures of the ionic liquids (ILs) with varying alkyl chain lengths. The intense position of the spectral peak, the frequency corresponding to the shoulder peak, and the spectral linewidth of the O-D stretch distribution are not influenced by the increment in the cationic chain length. In addition, the ionic liquid (IL) [BMIm][BF] exhibits a notable trend; the dynamic timescales are longer than the other studied systems. Therefore, we have performed the Voronoi decomposition analysis of the ionic and the polar-apolar domains, symmetrically increasing the length of alkyl chains on the IL cations. Domain analysis reveals structural microheterogeneity; the anions form discrete domains, and the ionic liquid constituting cations form continuous domains irrespective of the alkyl chain length on the imidazolium cations. Therefore, this computational ultrafast spectroscopy study aids in forming a molecular-level picture of the ionic liquid cations and anions in the liquid phase, providing a detailed interpretation of the spectral properties of the probe stretching vibrations.
我们监测了咪唑鎓四氟硼酸酯离子液体烷基链长度增加对感兴趣的局部氘代探针模式的影响。在这项研究中，我们采用了 1-乙基-3-甲基咪唑四氟硼酸酯[EMIm][BF]、1-丁基-3-甲基咪唑四氟硼酸酯[BMIm][BF]、1-辛基-3-甲基咪唑四氟硼酸酯[OMIm][BF]和 1-癸基-3-甲基咪唑四氟硼酸酯[DMIm][BF]离子液体，其中 5%的 HOD 在 HO 中作为关联超快系统动力学的振动报告分子。采用经典分子动力学（MD）模拟确定分子结构和动态特性，而通过对经典轨迹的小波分析得出光谱轮廓。空间分布函数揭示了具有不同烷基链长度的离子液体（IL）分子结构的异质性。光谱峰的强度位置、肩峰对应的频率以及 O-D 伸缩分布的光谱线宽不受阳离子链长增加的影响。此外，离子液体（IL）[BMIm][BF]表现出显著的趋势；动态时间尺度长于其他研究体系。因此，我们对离子和极性-非极性域进行了 Voronoi 分解分析，对称地增加了 IL 阳离子上的烷基链长度。域分析揭示了结构微异质性；阴离子形成离散的域，而构成阳离子的离子液体无论在咪唑阳离子上的烷基链长度如何，都形成连续的域。因此，这项超快光谱学的计算研究有助于形成离子液体阳离子和阴离子在液相中的分子水平图像，对探针伸缩振动的光谱性质提供详细的解释。
