Effects of Solubilized Water on the Relaxation Dynamics Surrounding 6-Propionyl-2-(N,N-dimethylamino)naphthalene Dissolved in 1-Butyl-3-methylimidazolium Hexafluorophosphate at 298 K

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• 作者：Sheila N. Baker ; Gary A. Baker ; Chase A. Munson ; Fei Chen ; Eric J. Bukowski ; Alexander N. Cartwright ; and Frank V. Bright
• 刊名：Industrial & Engineering Chemistry Research
• 出版年：2003
• 出版时间：December 10, 2003
• 年：2003
• 卷：42
• 期：25
• 页码：6457 - 6463
• 全文大小：138K
• 年卷期：v.42,no.25(December 10, 2003)
• ISSN：1520-5045

文摘

We report on the picosecond time-resolved fluorescence of 6-propionyl-2-(N,N-dimethylamino)naphthalene (PRODAN) dissolved in 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆]) at 298 K as a function of solubilized water in the [bmim][PF₆] phase. The observed solventrelaxation dynamics can be described by three components with apparent relaxation times thatoccur over a large time regime (<15 ps to >10 ns). The average relaxation dynamics becomefaster as the water concentration in the [bmim][PF₆] phase increases. Libration and vibration,ion ballistic motion, ion local basin exploration, and ion basin hopping, ion diffusion, and/or theultrafast relaxation from water (or other small molecules/impurities) are suggested as possiblereasons for the yet unquantified sub-15-ps dynamics. The sub-nanosecond dynamics areconsistent with [PF₆] anion relaxation. This process was found to be water-dependent, slowingas the amount of solubilized water in the [bmim][PF₆] phase increased. We speculate that thisslowing arises from the formation of 1:2 H-bonded [PF₆]···HOH···[PF₆] complexes. Thenanosecond dynamics are consistent with the cation, decreasing slightly with an increase inthe amount of solubilized water. We suggest that the decrease in this relaxation time arisesfrom a decrease in the bulk viscosity on adding water.