Physical Quenching and Chemical Reaction of Singlet Molecular Oxygen with Azo Dyes

Article abstract of DOI:10.1021/jo00264a006

The quenching rate constants of singlet oxygen liefetime by dialkylamino azo dyes 1 and tautomeric azo dyes 2 and 5 (as well as azo- and hydrazone-model methylated derivatives 3 and 4) were determined by measuring the 1.27-μm ¹O2 emission lifetime, and the values obtained are in the range 10⁶ - 10⁸ M^-1 s^-1.The quenching involves a charge-transfer interaction, and different correlations with the oxidation potentials of the two classes of azo dyes are observed.Chemical reactions take place with a rate in the range 10³ - 10⁴ M^-1 s^-1 and are rationalized as a secondary pathway for the charge-transfer complex between ¹O2 and the azo dye.Products include dealkylated amino azo dyes 6 from 1; compounds arising from the fragmentation of the aryl-azo bond, viz., benzenes 7 and phenoles 8 from 1 and 2; and 1,4-naphthoquinone 10 as well as the dimer 9 and the oxidized cyclic derivative 11 from 2.The methoxy derivative 3 yields an endoperoxide, which rearranges to a 1,2-naphthoquinone derivative 14.The results are discussed in comparison with the currently accepted mechanism for the reaction of ¹O2 with azo dyes.