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Indian Journal of Chemistry -Section A (IJC-A) >
IJC-A Vol.49A [2010] >
IJC-A Vol.49A(05-06) [May-June 2010] >
| Title: | Solvation dynamics in imidazolium and phosphonium ionic liquids: Effects of solute motion |
| Authors: | Kashyap, Hemant K
Biswas, Ranjit |
| Keywords: | Theoretical chemistry
Ionic liquids
Solvation dynamics
Solute motion
Phosphonium ionic liquids
Imidozolium ionic liquids
Dipolar cations |
| Issue Date: | Jun-2010 |
| Publisher: | CSIR |
| Abstract: | Experimental and simulation results of
solvation dynamics in ionic liquids have so far been explained in terms of
translational motion of the ions constituting the ionic liquids under
investigation. A recent theoretical study [Kashyap & Biswas, J Phys Chem B, 114 (2010) 254] has indicated that while translational
motion of the constituent ions is indeed responsible for Stokes’ shift dynamics
of a polar solute probe in non-dipolar ionic liquids (such as phosphonium ionic
liquids), fast orientational relaxation of dipolar ions significantly affects
the spectral dynamics in imidazolium ionic liquids. Herein, we investigate the
effects of rotational and translational motions of a dissolved dipolar probe on
the Stokes’ shift dynamics in these representative non-dipolar and dipolar
ionic liquids. Theoretical results presented here suggest that while the
probe-motion accelerates the solvation-rate in non-dipolar ionic liquids twice
over the fixed solute values, it plays a secondary role in dipolar ionic solvents. The sensitivity to the solute’s
self-motion of the rate of solvation has been found to be linked to the
solute-cation size ratio and is decoupled from the initial ultrafast response
in dipolar ionic liquids. This work also explains the reasons for not observing
the effects of solute motion in simulation study of solvation dynamics in the
imidazolium ionic liquid considered herein. Careful analyses of the effects of
solute motion further support the fact that rotation of dipolar solvent
species, like in conventional polar solvents, dictates the initial phase of
solvation of a dipolar probe in imidazolium and other dipolar ionic liquids. In
addition, probe size dependence is predicted in non-dipolar ionic liquids, such
as phosphonium ionic liquids. |
| Page(s): | 685-694 |
| Source: | IJC-A Vol.49A(05-06) [May-June 2010]
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