Picosecond deactivation of azo dye excited states in solution and in cellulose

Ultrafast time-resolved UV–visible absorption spectroscopy has been used to study four model azo dyes and five commercial azo dyes. All of the dyes have been found to show strong bleaching of their ground-state absorption bands on photoexcitation, with recovery lifetimes of 1–5 ps in aqueous solution that are attributed to rapid and efficient non-radiative decay; two commercial azo dyes deposited in cellophane have been found to show an additional longer-lived component with a lifetime of >50 ps that is attributed to the effects of intermolecular interactions with the cellulosic environment.