Electronic Substituent Effects in Quenching of¹O₂by Diaryl Tellurides

Abstract

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 O2-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 1O2.

Quantitative structure‐activity relationships for oxidation reactions of organic chemicals in water

“…Reviews focusing on Hammett‐type relationships for singlet oxygen reactivity [66,106] included 10 reported relationships. These exhibited reaction constants ( p ) ranging from −1.7 to −0.8 for various series of aromatic compounds, but a value of −0.5 has also been observed for diaryl tellurides in a 90% methanol/10% water mixture [107].…”

Reversible oxidation of a water-soluble tellurophene

“…Tellurium-containing dyes are known singlet oxygen photosensitizers due to their strong absorption properties and the presence of the heavy tellurium atom. 4,10 Since 1 can be oxidized by H 2 O 2 we were interested in determining whether it could photosensitize singlet oxygen and undergo subsequent oxidation. A solution of 1 in water (under ambient atmosphere) was irradiated with blue light (447 nm LED) overnight.…”

Photosensitized oxygenation of diaryl tellurides to telluroxides and their oxidizing properties

“…6 However, there are no synthetic studies on the photosensitized formation of telluroxides from simple tellurides and molecular oxygen. In this paper, we describe photosensitized oxygenation of diaryl tellurides to the corresponding teluroxides and the first example of the oxidation of simple alcohols by chalcogen oxides.…”

“…It was shown by Detty and coworkers that the organotellurium compounds act as a chemical quencher of singlet oxygen and afford the corresponding telluroxides or their hydrates. 6 However, there are no synthetic studies on the photosensitized formation of telluroxides from simple tellurides and molecular oxygen. In this paper, we describe photosensitized oxygenation of diaryl tellurides to the corresponding teluroxides and the first example of the oxidation of simple alcohols by chalcogen oxides.…”