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.
Takahashi
Kenji
K
Division of Material Science, Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa 920-1192, Japan. ktkenji@t.kanazawa-u.ac.jp
Tezuka
Hiroaki
H
Kitamura
Shingo
S
Satoh
Toshifumi
T
Katoh
Ryuzi
R
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