title: ESR spin probes in ionic liquids.
abstract: The spin probes 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL), and 2,2,6,6-tetramethyl-4-trimethylammoniumpiperidine-1-oxylIodide (CAT-1) are examined in a number of ionic liquids based on substituted imidazolium cations and tetrafluoroborate and hexafluorophosphate anions, respectively. The reorientation correlation times tau(R) of the spin probes in these systems have been determined by complete spectra simulation and, for rapid reortientation, by analysis of the intensities of the hyperfine lines of the electron spin resonance (ESR) spectra. A comparison of the results with those from the model system glycerol/water and selected organic solvents is made. Additions of diamagnetic and paramagnetic ions allow the conclusion that salt effects and spin exchange are present, and that both are superimposed by motional effects. Specific interactions in the ionic liquids, as well as between the spin-probe molecules and the constituents of the ionic liquids are reflected in the spectra of the spin probes, depending on their molecular structure.
authors.affiliation: Institute of Chemistry, Humboldt University of Berlin, Germany.
authors.forename: Reinhard
authors.initials: R
authors.lastname: Stoesser
authors.forename: Werner
authors.initials: W
authors.lastname: Herrmann
authors.forename: Andrea
authors.initials: A
authors.lastname: Zehl
authors.forename: Veronika
authors.initials: V
authors.lastname: Strehmel
authors.forename: André
authors.initials: A
authors.lastname: Laschewsky
mesh_terms: D000838:Anions; D002412:Cations; D002627:Chemistry, Physical / Q000379:methods*; D003497:Cyclic N-Oxides / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy / Q000295:instrumentation* / Q000379:methods; D007477:Ions; D008280:Magnetics; D008956:Models, Chemical; D008968:Molecular Conformation; D010087:Oxides / Q000737:chemistry; D013113:Spin Labels; D013696:Temperature; D013997:Time Factors
chemical_list: D000838:Anions; D002412:Cations; D003497:Cyclic N-Oxides; D007477:Ions; D010087:Oxides; D013113:Spin Labels; C001803:tempol; C003959:TEMPO