Complete solvation response of coumarin 153 in ionic liquids.
Complete solvation response of coumarin 153 in ionic liquids.
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DOI：
10.1021/jp305430a
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发表时间：
2013-04
期刊：
影响因子：
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通讯作者：
Xin-Xing Zhang;Min Liang;N. Ernsting;M. Maroncelli
中科院分区：
文献类型：
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作者：
Xin-Xing Zhang;Min Liang;N. Ernsting;M. Maroncelli
香豆素153的动态斯托克斯位移，测量宽带荧光上转换（80 fs分辨率）和时间相关单光子计数（至20 ns）的组合，用于确定21咪唑，吡咯烷和其他各种离子液体的完整溶剂化响应。这样得到的响应函数显示出一个明显的双峰字符组成的亚皮秒分量，占10-40%的响应，和一个慢得多的组件在很宽的时间范围内放松。与快速分量相关的时间与离子质量相关，确认其起源于惯性溶剂运动。与许多以前的研究一致，较慢的组分与溶剂粘度相关，表明其起源在于溶剂的扩散，结构重组。一个简单的介电连续模型的预测所观察到的响应函数的比较表明，在偶极溶剂中，溶剂化和介电弛豫涉及密切相关的分子动力学。然而，与偶极溶剂相反，介电连续预测系统地低估溶剂化时间至少2-4倍。
The dynamic Stokes shift of coumarin 153, measured with a combination of broad-band fluorescence upconversion (80 fs resolution) and time-correlated single photon counting (to 20 ns), is used to determine the complete solvation response of 21 imidazolium, pyrrolidinium, and assorted other ionic liquids. The response functions so obtained show a clearly bimodal character consisting of a subpicosecond component, which accounts for 10-40% of the response, and a much slower component relaxing over a broad range of times. The times associated with the fast component correlate with ion mass, confirming its origins in inertial solvent motions. Consistent with many previous studies, the slower component is correlated to solvent viscosity, indicating that its origins lie in diffusive, structural reorganization of the solvent. Comparisons of observed response functions to the predictions of a simple dielectric continuum model show that, as in dipolar solvents, solvation and dielectric relaxation involve closely related molecular dynamics. However, in contrast to dipolar solvents, dielectric continuum predictions systematically underestimate solvation times by factors of at least 2-4.