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Recombination of Photogenerated Lophyl Radicals in Imidazolium‐Based Ionic Liquids
Author(s) -
Strehmel Veronika,
Wishart James F.,
Polyansky Dmitry E.,
Strehmel Bernd
Publication year - 2009
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.200900594
Subject(s) - ionic liquid , hexafluorophosphate , radical , chemistry , density functional theory , flash photolysis , ionic bonding , photochemistry , imide , ion , solvent , computational chemistry , organic chemistry , reaction rate constant , catalysis , kinetics , physics , quantum mechanics
Abstract Laser flash photolysis is applied to study the recombination reaction of lophyl radicals in ionic liquids in comparison with dimethylsulfoxide as an example of a traditional organic solvent. The latter exhibits a similar micropolarity as the ionic liquids. The ionic liquids investigated are 1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ( 1 ), 1‐hexyl‐3‐methylimidazolium hexafluorophosphate ( 2 ), and 1‐butyl‐3‐methylimidazolium tetafluoroborate ( 3 ). The recombination of the photolytic generated lophyl radicals occur significantly faster in the ionic liquids than expected from their macroscopic viscosities and is a specific effect of these ionic liquids. On the other hand, this reaction can be compared with the macroscopic viscosity in the case of dimethylsulfoxide. Activation parameters obtained for lophyl radical recombination suggest different, anion‐dependent mechanistic effects. Quantum chemical calculations based on density functional theory provide a deeper insight of the molecular properties of the lophyl radical and its precursor. Thus, excitation energies, spin densities, molar volumes, and partial charges are calculated. Calculations show a spread of spin density over the three carbon atoms of the imidazolyl moiety, while only low spin density is calculated for the nitrogens.