Photosensitizing properties and reactivity of aryl azo naphtol dyes towards singlet oxygen

Quantum yields ϕΔ of singlet oxygen (1O2) formation have been determined for 10 aryl azo naphtol dyes by flash photolysis. The 1O2 NIR luminescence signals at 1275 nm sensitized by the dyes were compared with the signal obtained with the reference sensitizer, phenalenone. All aryl azo naphtols photosensitize the generation of 1O2, but with very low quantum yields 4 × 10−4 ≤ ϕΔ ≤ 5 × 10−2. Overall rate constants of 1O2 quenching could be determined for six of these dyes by flash photolysis. A linear correlation between the logarithms of these rate constants and the oxidation potentials of the quenchers could be established, thus indicating that quenching probably involves a charge-transfer mechanism. The roles of 1O2 on the photofading of azo dyes and on the photodegradation of consumer products are discussed.