Electronic Substituent Effects in Quenching of1O2by Diaryl Tellurides

Singlet-oxygen quenching by a series of substituted diaryl tellurides was investigated in 10% aqueous methanol by monitoring the competitive inhibition of oxidation of 1,3-diphenylisobenzofuran. The extent of quenching of the sensitizer triplet state was determined by repeating the analysis in both air- and O 2 -saturated solutions and by laser flash-photolysis experiments. A Hammett analysis of the rate of quenching as a function of substituent constant (σ) gave a ρ value of −0.5, which is significantly lower than the ones reported for other chalcogenides. Although this value does not dispute the existence of a charge-transfer intermediate, it suggests that a strong contribution from the heavy-atom effect of Te is present and that Te is relatively insensitive to inductive electronic substituent effects. The efficiency of chemical quenching in the system was estimated to be 2−9% of the overall quenching of 1 O 2 .