QUENCHING OF SINGLET OXYGEN ((1)DELTA(G)) BY HUMIC SUBSTANCES

The quenching of singlet oxygen (O-2 (1) Delta(g)) by humic substances (HSs) of different origins has been investigated by measurements of t he singlet oxygen luminescence at 1270 nm. A Stern-Volmer analysis of the quenching of the emission by HSs shows a strong deviation from the expected linearity. The deviation is explained by an interaction betw een the sensitizer and the HSs. In fact, fluorescence and laser flash photolysis experiments show a large contribution of a static quenching of sensitizer excited state by the HSs. Moreover, the efficiency of s inglet oxygen quenching depends on the origin of the HS sample.