GENERATION OF SINGLET OXYGEN BY 2,2'/5',2''-TERTHIOPHENE AND SOME OF ITS DERIVATIVES

The kinetics of oxygen quenching of the lowest triplet states of 2,2':5',2#-terthiophene and several of its substituted derivatives in 95% ethanol were analysed as part of an investigation of the chemical and physicochemical basis of the phototoxicity of these compounds. Overall bimolecular rate constants and singlet oxygen (O-2((1) Delta(g))) formation quantum yields were measured by laser flash photolysis and time-resolved phosphorescence detection. With the exception of one compound, both parameters proved to be almost independent of the chemical nature, position and number of substituents, thus failing to indicate an explanation for the very large differences in phototoxicity observed between the various derivatives during in vivo experiments. On the basis of the measured kinetic parameters, a schematic description of the mechanism of interaction with oxygen of these compounds in their lowest triplet states is proposed.