The dielectric response of room-temperature ionic liquids: Effect of cation variation

TY - JOUR

T1 - The dielectric response of room-temperature ionic liquids: Effect of cation variation

AU - Weingaertner, Hermann

AU - Sasisanker, Padmanabhan

AU - Daguenet, Corinne

AU - Dyson, Paul J.

AU - Krossing, Ingo

AU - Slattery, John M.

AU - Schubert, Thomas

PY - 2007/5/10

Y1 - 2007/5/10

N2 - In continuation of recent work on the dielectric response of imidazolium-based ionic liquids (ILs) (J. Phys. Chem. B, 2006, 110, 12682), we report on the effect of cation variation on the frequency-dependent dielectric permittivity up to 20 GHz of ionic liquids. The salts are comprised of pyrrolidinium, pyridinium, tetraalkylammonium, and triethylsulfonium cations combined with the bis-((trifluoromethyl)sulfonyl)imide anion. The dielectric spectra resemble those observed for imidazolium salts with the same anion. In all cases, the major contribution results from a diffusive low-frequency response on the time scale of several 100 ps, which shows a broadly distributed kinetics similar to that of spatially heterogeneous states in supercooled and glassy systems rather than that observed in fluid systems. There is evidence for a weak secondary process near 10-20 ps. Perhaps the most interesting difference to imidazolium salts is founded in the missing portions of the spectra due to processes beyond the upper cutoff frequency of 20 GHz. These are lower than that observed for imidazolium-based salts and seem to vanish for tetraalkylammonium and triethylsulfonium salts. As for imidazolium salts, the extrapolated static dielectric constants are on the order of epsilon(S) congruent to 10-13, classifying these ILs as solvents of moderate polarity.

AB - In continuation of recent work on the dielectric response of imidazolium-based ionic liquids (ILs) (J. Phys. Chem. B, 2006, 110, 12682), we report on the effect of cation variation on the frequency-dependent dielectric permittivity up to 20 GHz of ionic liquids. The salts are comprised of pyrrolidinium, pyridinium, tetraalkylammonium, and triethylsulfonium cations combined with the bis-((trifluoromethyl)sulfonyl)imide anion. The dielectric spectra resemble those observed for imidazolium salts with the same anion. In all cases, the major contribution results from a diffusive low-frequency response on the time scale of several 100 ps, which shows a broadly distributed kinetics similar to that of spatially heterogeneous states in supercooled and glassy systems rather than that observed in fluid systems. There is evidence for a weak secondary process near 10-20 ps. Perhaps the most interesting difference to imidazolium salts is founded in the missing portions of the spectra due to processes beyond the upper cutoff frequency of 20 GHz. These are lower than that observed for imidazolium-based salts and seem to vanish for tetraalkylammonium and triethylsulfonium salts. As for imidazolium salts, the extrapolated static dielectric constants are on the order of epsilon(S) congruent to 10-13, classifying these ILs as solvents of moderate polarity.

KW - SOLVATION DYNAMICS

KW - MOLECULAR-DYNAMICS

KW - COUMARIN-153

KW - SPECTROSCOPY

KW - HEXAFLUOROPHOSPHATE

KW - FEMTOSECOND

KW - CONSTANT

KW - ROTATION

KW - NITRATE

KW - POLAR

U2 - 10.1021/jp0671188

DO - 10.1021/jp0671188

M3 - Article

SN - 1520-6106

VL - 111

SP - 4775

EP - 4780

JO - Journal of Physical Chemistry B

JF - Journal of Physical Chemistry B

IS - 18

ER -