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Title: Rotational diffusion of nondipolar solutes in ionic liquids: Influence of nature of anion on solute rotation
Authors: Dutt, G B
Keywords: Ionic liquids;Fluorescence anisotropy;Hydrogen bonding;Nondipolar solutes;Reorientation time;Rotational diffusion;Size effects;Specific interactions
Issue Date: Jun-2010
Publisher: CSIR
Abstract: Rotational diffusion of two structurally similar nondipolar solutes, viz., 2,5-dimethyl-1,4-dioxo-3,6-diphenylpyrrolo [3,4-c]pyrrole (DMDPP) and 1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DPP) has been examined in two ionic liquids, (1-butyl-3-methylimidazolium octylsulfate ([bmim+][OS]) and 1-butyl-3-methylimidazolium nitrate ([bmim+][NO])), to understand the influence of the nature of the anion on solute rotation. It has been observed that the rotation of DPP is slower as compared to that of DMDPP in [bmim+][OS] as well as in [bmim+][NO] by a factor of 2.5 and 1.7, respectively. The slow rotation of DPP is due to the strong hydrogen bonding interactions between the two NH groups of the solute and the respective anions of the ionic liquids. Comparison of the viscosity normalized reorientation times of DMDPP in [bmim+][OS] and [bmim+][NO] indicates that the rotation of the solute is slower by a factor of 2 in nitrate as compared to that in octylsulfate. The faster rotation of DMDPP in [bmim+][OS] has been rationalized on the basis of size effects. Quasihydrodynamic theories of Gierer-Wirtz and Dote-Kivelson-Schwartz have been invoked to assimilate the results in a qualitative manner. In contrast, the viscosity normalized reorientation times of DPP in  [bmim+][NO] are longer only by factor of 1.3 as compared to the ones measured in [bmim+][OS], which is due to the stronger hydrogen bonding interactions between DPP and the nitrate ion.
Page(s): 705-713
Appears in Collections:IJC-A Vol.49A(05-06) [May-June 2010]

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