4399-88-6Relevant articles and documents
Laser flash photolysis and integral equation theory to investigate reactions of dilute solutes with oxygen in supercritical fluids
Roberts,Zhang,Chateauneuf,Brennecke
, p. 6553 - 6560 (1995)
The absolute reactivity of triplet benzophenone (3BP) and benzyl free radical (PhCH2) toward molecular oxygen (O2) in supercritical CO2 and CHF3 has been measured by laser flash photolysis (LFP). The
EPR investigation of persistent radicals produced from the photolysis of dibenzyl ketones adsorbed on ZSM-5 zeolites
Turro, Nicholas J.,Lei, Xue-Gong,Jockusch, Steffen,Li, Wei,Liu, Zhiqiang,Abrams, Lloyd,Ottaviani, M. Francesca
, p. 2606 - 2618 (2007/10/03)
Photolysis of ketones (1, 1-oMe, 2, 2-oMe, 3, and 4) adsorbed on ZSM-5 zeolites produces persistent carbon-centered radicals that can be readily observed by conventional steady-state EPR spectroscopy. The radicals are persistent for time periods of seconds to many hours depending on the supramolecular structure of the initial radical@zeolite complex and the diffusion and reaction dynamics of radicals produced by photolysis. The structures of the persistent radicals responsible for the observed EPR spectra are determined by a combination of alternate methods of generation of the same radical, by deuterium substitution, and by spectral simulation. A clear requirement for persistence is that the radicals produced by photolysis must either separate and diffuse from the external to the internal surface or be generated within the internal surface and separate and diffuse apart. The persistence of radicals located on the internal surface is the result of inhibition of radical-radical reactions. Radicals that are produced on the external surface and whose molecular structure prevents diffusion into the internal surface are transient because radical-radical reactions occur rapidly on the external surface. The reactions of the persistent radicals with oxygen and nitric oxide were directly studied in situ by EPR analysis. In the case of reaction with oxygen, persistent peroxy radicals are formed in high yield. The addition of nitric oxide scavenges persistent radicals and leads initially to a diamagnetic nitroso compound, which is transformed into a persistent nitroxide radical by further photolysis. The influence of variation of radical structure on transience/persistence is discussed and correlated with supramolecular structure and reactivity of the radicals and their parent ketones.
Quenching of singlet oxygen by oxygen- and sulfur-centered radicals: Evidence for energy transfer to peroxyl radicals in solution
Darmanyan, Alexandre P.,Gregory, Daniel D.,Guo, Yushen,Jenks, William S.,Burel, Laure,Eloy, Dominique,Jardon, Pierre
, p. 396 - 403 (2007/10/03)
Quenching of singlet oxygen luminescence at 1.27 μm by PhS., PhSO., and peroxyl radicals PhOO., t-BuOO., PhCH2OO., Ph2CHOO. and Ph3COO. was studied in liquid solution. The quantum yields of decomposition of different initiators which lead to the formation of free radicals were measured by using nanosecond transient absorption. This allowed determination of singlet oxygen O2(1Δ(g)) quenching rate constants by the radicals. They are 8 M-1 s-1 for the sulfur-centered radicals and (2-7) x 109 M-1 s-1 for peroxyl radicals in acetonitrile. The rapid quenching is attributed to energy transfer quenching by the peroxyls, which have an n → π* transition leading to a low-lying 2A' state above their 2A'' ground state. PhSO. is shown computationally not to have such a low-lying 2A' state. There may be a very low-lying 2B1 state, for PhS., but it is apparently not an efficient acceptor of electronic energy from O2(1Δ(g)).
