Reactive Dynamics in Confined Liquids: Ultrafast Torsional Dynamics of Auramine O in Nanoconfined Water in Aerosol OT Reverse Micelles
Reactive Dynamics in Confined Liquids: Ultrafast Torsional Dynamics of Auramine O in Nanoconfined Water in Aerosol OT Reverse Micelles
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DOI：
10.1021/jp808989f
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发表时间：
2009-02-12
影响因子：
3.3
通讯作者：
Meech, Stephen R.
中科院分区：
文献类型：
--
作者：
Heisler, Ismael A.;Kondo, Minako;Meech, Stephen R.
利用时间分辨率为50 fs的超快荧光上转换技术研究了约束效应对金胺O水溶液超快扭转反应的影响。水溶液被离子表面活性剂限制在纳米级水滴中。扭转运动的数量级慢于在散装水溶液中的限制液滴。随着纳米液滴半径的增加，动力学变得更快，但从未达到体积值，即使当半径大到10 nm时。时间依赖性的荧光光谱的构建和随后使用一维广义Smoluchowski方程进行分析。使用随时间变化的扩散系数实现了数据的准确描述。这是因为介质摩擦反映了跨越反应动力学的广泛时间尺度上的动力学。摩擦恢复表明强烈受阻的运动在受限的液滴，可以定性地与AOT中测量的溶剂化动力学，与金胺O扭转动力学伴随着分子内电荷重新分配一致。
The effects of confinement on the ultrafast torsional reaction of auramine O in aqueous solution are investigated through ultrafast fluorescence up-conversion with 50 fs time resolution. The aqueous solution is confined in nanoscale water droplets by an ionic surfactant. The torsional motion is orders of magnitude slower in the confined droplets than in bulk aqueous solution. The dynamics become faster with increasing radius of the nanodroplet but never reach the bulk value, even when the radius is as large as 10 nm. Time-dependent fluorescence spectra were constructed and subsequently analyzed using a one-dimensional generalized Smoluchowski equation. An accurate description of the data was achieved using a time-dependent diffusion coefficient. This is suggested to arise because the medium friction reflects dynamics on a broad range of time scales spanning the reaction dynamics. The friction recovered suggests strongly hindered motion in the confined droplet and can be qualitatively related to solvation dynamics measured in AOT, consistent with auramine O torsional dynamics being accompanied by intramolecular charge redistribution.