Relative Fraction of Excited-State Oxygen Formed as Sigma (+) Molecular State inSolution-Phase Photosensitized Reactions

摘要

The relative fraction F sub sigma of excited state oxygen formed as b(1)sigma subg(+) was determined for a series of triplet state photosensitizers in CCI4 solutions. Oxygen excited states were formed by energy transfer from aromatic ketones whose triplet-state energies ET ranged from 53 to 75 kcal/mol. F sub sigma was determined by monitoring the intensities of(a) O2(b(1) sigma sub g (-)) fluorescence at 1926 nm O2(b(1) sigma sub g(+)) (right arrow) O2(a(1) delta sub g) and (b) O2(a(1 delta sub g) phosphorescence at 1270 nm O2(a(1) delta sub g) (right arrow) O2(X(1) sigma sub g (-). Ketone-dependent changes in F sub sigma are not consistent with predictions made by Kearns et al. over 25 years ago. Specifically, F sub sigma values from high ET ketones were found to be smaller than, not equivalent to those obtained by using a low ET ketone. These data may