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Charge Trapping in Imidazolium Ionic Liquids
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Section:Abstract
Room-temperature ionic liquids (ILs) are a promising class of solvents for applications ranging from photovoltaics to solvent extractions. Some of these applications involve the exposure of the ILs to ionizing radiation, which stimulates interest in their radiation and photo- chemistry. In the case of ILs consisting of 1,3-dialkylimidazolium cations and hydrophobic anions, ionization, charge transfer and redox reactions yield charge-trapped species thought to be radicals resulting from neutralization of the constituent ions. Using computational chemistry methods and the recent results on electron spin resonance (ESR) and transient absorption spectroscopy of the ionized ILs, we argue that electron localization in the imidazolium ILs yields a gauche dimer radical cation with the elongated C(2)−C(2) bond. This species is shown to absorb in the near-infrared and the visible regions and accounts for the observed ESR spectra. We suggest that the excess electron in these aromatic ILs is localized as such a dimeric ion, and consider the chemical implications of this attribution. We also suggest that three-electron N−N bonding with the formation of a dimer radical anion occurs for amide anions, such as dicyanamide, when the parent anion traps holes; steric hindrance prevents the analogous reaction for bis(triflyl)amide anion. For another anion of practical importance, bis(oxalato)borate, a pathway involving the elimination of CO2 is suggested. Together, these results indicate the unanticipated tendency of the ILs to localize primary charges as radical ions as opposed to neutral radicals. Thus, it appears that secondary chemistry in the ionized ILs may be dominated by radical ion reactions, similarly to the previously studied conventional organic liquids, depending on the composition of the IL.
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This article has been cited by 9 ACS Journal articles (5 most recent appear below).
Dry Excess Electrons in Room-Temperature Ionic Liquids
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Claudio J. Margulis, Harsha V. R. Annapureddy, Pablo M. De Biase, David Coker, Jorge Kohanoff, and Mario G. Del PópoloJournal of the American Chemical Society2011 133 (50), 20186-20193In this article, we describe general trends to be expected at short times when an excess electron is generated or injected in different room-temperature ionic liquids (RTILs). Perhaps surprisingly, the excess electron does not localize systematically on ...
Radiation and Radical Chemistry of NO3–, HNO3, and Dialkylphosphoric Acids in Room-Temperature Ionic Liquids
Ilya A. Shkrob, Timothy W. Marin, S. D. Chemerisov, and J. F. WishartThe Journal of Physical Chemistry B2011 115 (37), 10927-10942Radiation and Radical Chemistry of NO3–, HNO3, and Dialkylphosphoric Acids in Room-Temperature Ionic Liquids
Ilya A. Shkrob, Timothy W. Marin, S. D. Chemerisov, and J. F. WishartThe Journal of Physical Chemistry B2011 115 (37), 10927-10942Hydrophobic room-temperature ionic liquids (ILs) are considered as possible replacements for molecular diluents for nuclear separations, as well as the basis of new separations processes. Such applications may put the solvents both in high radiation ...
Radiation Induced Redox Reactions and Fragmentation of Constituent Ions in Ionic Liquids. 2. Imidazolium Cations
Ilya A. Shkrob, Timothy W. Marin, Sergey D. Chemerisov, Jasmine L. Hatcher, and James F. WishartThe Journal of Physical Chemistry B2011 115 (14), 3889-3902Radiation Induced Redox Reactions and Fragmentation of Constituent Ions in Ionic Liquids. 2. Imidazolium Cations
Ilya A. Shkrob, Timothy W. Marin, Sergey D. Chemerisov, Jasmine L. Hatcher, and James F. WishartThe Journal of Physical Chemistry B2011 115 (14), 3889-3902In part 1 of this study, radiolytic degradation of constituent anions in ionic liquids (ILs) was examined. The present study continues the themes addressed in part 1 and examines the radiation chemistry of 1,3-dialkyl substituted imidazolium cations, ...
On the Radiation Stability of Crown Ethers in Ionic Liquids
Ilya A. Shkrob, Timothy W. Marin, and Mark L. DietzThe Journal of Physical Chemistry B2011 115 (14), 3903-3911On the Radiation Stability of Crown Ethers in Ionic Liquids
Ilya A. Shkrob, Timothy W. Marin, and Mark L. DietzThe Journal of Physical Chemistry B2011 115 (14), 3903-3911Crown ethers (CEs) are macrocyclic ionophores used for the separation of strontium-90 from acidic nuclear waste streams. Room temperature ionic liquids (ILs) are presently being considered as replacements for traditional molecular solvents employed in ...
Radiation Induced Redox Reactions and Fragmentation of Constituent Ions in Ionic Liquids. 1. Anions
Ilya A. Shkrob, Timothy W. Marin, Sergey D. Chemerisov, and James F. WishartThe Journal of Physical Chemistry B2011 115 (14), 3872-3888Radiation Induced Redox Reactions and Fragmentation of Constituent Ions in Ionic Liquids. 1. Anions
Ilya A. Shkrob, Timothy W. Marin, Sergey D. Chemerisov, and James F. WishartThe Journal of Physical Chemistry B2011 115 (14), 3872-3888Room temperature ionic liquids (IL) find increasing use for the replacement of organic solvents in practical applications, including their use in solar cells and electrolytes for metal deposition, and as extraction solvents for the reprocessing of spent ...
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History
- Published In Issue April 23, 2009
- Article ASAPMarch 26, 2009
- Received: December 30, 2008
Revised: January 29, 2009
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