Excited states and reduced and oxidized forms of a textile diazo dye, naphthol blue black. Spectral characterization using laser flash photolysis and pulse radiolysis studies

The excited singlet and triplet states of a diazo textile dye (Naphthol Blue Black) have been investigated by pico and nanosecond flash photolysis. The excited singlet state shows a difference absorption maximum at 500 nm and has a lifetime of 25–30 ps in ethanol. The triplet excited state generated by triplet-triplet energy transfer shows an absorption maxima at 710–730 nm. The oxidized form as well as the reduced form of the diazo dye have been generated pulse radiolytically by reacting with azide and eaq radicals, respectively. Preliminary results of the photoelectrochemical irreversible reduction of Naphthol Blue Black in colloidal TiO2 are also reported.