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 state s of an azo dye (Acid Orange 7 (AO)) was performed using picosecond an d nanosecond laser flash photolysis. The excited singlet state lifetim e, estimated from the bleaching recovery, is around 135 ps. The triple t excited state generated by triplet-triplet (T-T) energy transfer sho ws a difference absorption maximum at 650 nm with a lifetime of 20 mus . The oxidized and reduced forms of the dye were generated by reacting AO with pulse radiolytically generated azide (N3.) and e(aq) radicals . These radicals were also detected as the primary intermediates in vi sible-laser-induced photoionization. The photoelectrochemical reductio n of the dye in UV-irradiated TiO2 colloidal suspension results in the irreversible decolorization of the dye.