Understanding Structure–Property Correlation in Monocationic and Dicationic Ionic Liquids through Combined Fluorescence and Pulsed-Field Gradient (PFG) and Relaxation NMR Experiments

Steady state, time-resolved fluorescence and NMR experiments are carried out to gain deeper insights into the structure–property correlation in structurally similar monocationic and dicationic room-temperature ionic liquids (RTILs). The excitation wavelength dependent fluorescence response of fluoro...

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Published in:The journal of physical chemistry. B 2015-11, Vol.119 (44), p.14221-14235
Main Authors: Kumar Sahu, Prabhat, Ghosh, Arindam, Sarkar, Moloy
Format: Article
Language:English
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Summary:Steady state, time-resolved fluorescence and NMR experiments are carried out to gain deeper insights into the structure–property correlation in structurally similar monocationic and dicationic room-temperature ionic liquids (RTILs). The excitation wavelength dependent fluorescence response of fluorophore in 1-methy-3-propyllimidazolium bis­(trifluoromethylsulfonyl)­amide [C3MIm]­[NTf2] is found to be different from that of 1,6-bis­(3-methylimidazolium-1-yl)­hexane bis­(trifluoromethylsulfonyl)­amide [C6(MIm)2]­[NTf2]2 and 1-hexyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­amide [C6MIm]­[NTf2]. The outcomes of the present solvent dynamics study in [C3MIm]­[NTf2] when compared with those in [C6(MIm)2]­[NTf2]2 and in [C6MIm]­[NTf2] from our previous studies (Phys. Chem. Chem. Phys. 2014, 16, 1291812928) indicate the involvement of dipolar rotation of imidazolium cation during solvation. To correlate the findings of solvation dynamics study with the dipolar rotation of the imidazolium ring, pulsed-field gradient (PFG)-NMR technique for translational diffusion coefficient measurement and 1H as well as 19F spin–lattice relaxation measurements are employed. NMR investigation reveals that an ultrafast component of solvation can be related to the dipolar rotation of imidazolium cation; hence, the role of dipolar rotation of cations in governing the dynamics of solvation in ILs cannot be ignored. Analysis of the rotational relaxation dynamics data by the Stokes–Einstein–Debye hydrodynamic theory unveils distinctive features of solute–solvent interaction in [C3MIm]­[NTf2] and [C6(MIm)2]­[NTf2]2.
ISSN:1520-6106
1520-5207
DOI:10.1021/acs.jpcb.5b07357