Sugosh Prabhu - Rotational Diffusion of Nonpolar and Charged Solutes in Propylammonium Nitrate–Propylene Glycol Mixtures: Does the Organized Structure of the Ionic Liquid Influence Solute Rotation?

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      Publication Details (including relevant citation   information):

        Radiation & Photochemistry Division, Bhabha Atomic Research Centre, Trombay,     Mumbai 400 085, India 
    J. Phys. Chem. B, 2014, 118 (10), pp 2738–2745
    Publication Date (Web): February 21, 2014
    Copyright © 2014 American Chemical Society


        Rotational diffusion of two structurally similar nonpolar and   charged solutes has been examined in mixtures of an ionic liquid   and an organic solvent of comparable size and viscosity with an   intent to find out whether the organized structure of the former   influences solute rotation. To this effect, temperature-dependent   fluorescence anisotropies of 9-phenylanthracene (9-PA) and   rhodamine 110 (R110) have been measured in n-propylammonium   nitrate (PAN), propylene glycol (PG), and also four different   compositions of PAN–PG mixtures. Analysis of the data carried out   with the aid of Stokes–Einstein–Debye (SED) hydrodynamic theory   indicates that the reorientation times of 9-PA and R110 scale   more or less linearly with the ratio of viscosity to temperature   and are found to be independent of the mole fraction of PAN. In   other words, apart from the viscosity and temperature, rotational   diffusion of both the solutes is not affected by the composition   of PAN–PG mixtures. It has also been observed that the   reorientation times of R110 are significantly longer compared to   those of 9-PA due to the specific interactions prevailing between   the cationic solute and PAN–PG mixtures. However, the important   finding of this work is that, even though PAN forms an organized   structure, rotational diffusion of the solute molecules is   similar in both the ionic liquid and the organic solvent. The   disordered lamellar structure present in PAN probably does not   offer compact organized domains unlike ionic liquids with long   alkyl chains wherein solute rotation is influenced   significantly.

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