Photochemistry of textile azo dyes. Spectral characterization of excited state, reduced and oxidized forms of Acid Orange 7

The spectral characterization of the singlet and triplet excited states of an azo dye (Acid Orange 7 (AO)) was performed using picosecond and nanosecond laser flash photolysis. The excited singlet state lifetime, estimated from the bleaching recovery, is around 135 ps. The triplet excited state generated by triplet—triplet (TT) energy transfer shows a difference absorption maximum at 650 nm with a lifetime of μs. The oxidized and reduced forms of the dye were generated by reacting AO with pulse radiolytically generated azide (N3) and eaq radicals. These radicals were also detected as the primary intermediates in visible-laser-induced photoionization. The photoelectrochemical reduction of the dye in UV-irradiated TiO2 colloidal suspension results in the irreversible decolorization of the dye.