Reactions of excited-state benzophenone ketyl radical in a room-temperature ionic liquid.
The photochemistry of the benzophenone ketyl radical in D(1) excited state, BPH(D(1)), was studied by means of two-color dual-pulse laser flash photolysis (355 and 532 nm) in a room-temperature ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide (Bmim-TFSA), and in methanol. Upon excitation with the 532 nm pulse, BPH(D(1)) emitted strong fluorescence. The transient absorption and fluorescence spectra of BPH(D(1)) were measured with nanosecond and sub-nanosecond time resolution, respectively. The observed Stokes shift was 1700 cm(-1) in Bmim-TFSA, and this shift was close to that in acetonitrile. The fluorescence lifetime of BPH(D(1)) was determined to be 5 ns in Bmim-TFSA, and again the value was close to that in acetonitrile. The rate constant of the reaction of BPH(D(1)) with CCl(4) in Bmim-TFSA was determined to be (2.1 +/- 0.4) x 10(9) M(-1) s(-1), which was 10 times the rate constant calculated on the basis of the bulk viscosity of Bmim-TFSA. The results are discussed in terms of the effective microscopic viscosity of the ionic liquid that was recently reported for the cage effect.
Division of Material Science, Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa 920-1192, Japan. ktkenji@t.kanazawa-u.ac.jp
Kenji
K
Takahashi
Hiroaki
H
Tezuka
Shingo
S
Kitamura
Toshifumi
T
Satoh
Ryuzi
R
Katoh
D001577:Benzophenones / Q000737:chemistry*; D005609:Free Radicals; D007093:Imidazoles / Q000737:chemistry; D052578:Ionic Liquids / Q000737:chemistry*; D010782:Photolysis; D012997:Solvents / Q000737:chemistry; D013050:Spectrometry, Fluorescence; D013696:Temperature; D014783:Viscosity
C525963:1-butyl-3-methylimidazolium; D001577:Benzophenones; D005609:Free Radicals; D007093:Imidazoles; D052578:Ionic Liquids; D012997:Solvents; C047723:benzophenone