Comparative OHD-RIKES Study of the Low-Frequency (0-250 cm-1) Vibrational Dynamics of Dibenzyl- and Monobenzyl-Substituted Imidazolium Ionic Liquids and Benzene/Dimethylimidazolium Mixtures

Lianjie Xue, George Tamas, E. L. Quitevis

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Abstract

The low-frequency (0-450 cm-1) Kerr spectra of 1-benzyl-3-methylimidazolium bis[(trifluoromethane)sulfonyl]amide ([BnzC1im][NTf2]) and 1,3-dibenzylimidazolium bis[(trifluoromethane)sulfonyl]amide ([(Bnz)2im][NTf2]) and 2:1 and 1:1 mixtures of benzene in 1,3-dimethylimidazolium bis[(trifluoromethane)sulfonyl]amide ([C1C1im][NTf2]) were measured by the use of optical heterodyne-detected Raman-induced Kerr effect spectroscopy (OHD-RIKES). Surprisingly, the line-shape of the intermolecular part of the height-normalized Kerr spectrum is the same for both the 1:1 and 2:1 C6H6/[C1C1im][NTf2] mixtures, which may be a signature of the local liquid structure being characterized by π-stacked benzene-cation complexes. The intermolecular part of the Kerr spectrum of [BnzC1im][NTf2] is lower in intensity, higher in frequency, and broader than that of the 1:1 C6H6/[C1C1im][NTf2] mixture. Similarly, the intermolecular part of the Kerr spectrum of [(Bnz)2im][NTf2] is lower in intensity, higher in frequency, and broader than that of the 2:1 C6H6/[C1C1im][NTf2] mixture. These results are explained in terms of the increased restriction of the intermolecular motion of benzene in going from being free in the mixtures to being tethered to the imidazolium ring in the benzyl-substituted ionic liquids.

Original languageEnglish
Pages (from-to)514-524
Number of pages11
JournalACS Sustainable Chemistry and Engineering
Volume4
Issue number2
DOIs
StatePublished - Feb 1 2016

Keywords

  • Aromatic compounds
  • Exfoliation of graphite
  • Femtosecond nonlinear spectroscopy
  • Intermolecular dynamics
  • Optical Kerr effect
  • π-Stacking

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