Analysis of mixed solvent effects on the properties of singlet oxygen (1Δg)

The photophysical behaviour of singlet oxygen ((1)Delta(g)) in mixed solvents was rationalized by characterizing the media in the light of the pure solvent scales. We have analysed the rate constants for phosphorescence, k(p) in the oxygen molecule reported by Bilski et al. and found that there is no general relationship between k(p)/n(2) and the polarizability of the medium. We have also studied the rate constant of quenching of singlet oxygen by triethylamine. As expected, it was found to be insensitive to basicity, to increase with increasing dipolarity/polarizability and to decrease with increasing acidity of the medium. One other major quencher of singlet oxygen is azide anion. The description of the rate constant of quenching of oxygen by azide ion, extended to all measured data (i.e., both binary, ternary, and quaternary mixtures), allows one to conclude that the rate of the process increases with increasing dipolarity and decreases with increasing ability of the reaction medium to establish specific interactions. (C) 2004 Elsevier B.V. All rights reserved.