Characterization of bisazo compounds employing ultrafast spectroscopy

Fluorenone-based bisazo compounds with different substituents have been inv estigated in various organic solvents and in a solid state by means of abso rption, fluorescence and picosecond time-resolved absorption pump-probe spe ctroscopy. The bisazo compounds were found to coexist in azo-enol and hydra zone-quinone (HQ) tautomeric forms. Absorption spectra of the two forms wer e determined and excited-state properties were characterized. The azo-enol tautomeric form has a short, of tens of ps, excited-state lifetime and show s strong excited-state absorption, whereas stimulated emission is weak or a bsent. The HQ tautomeric form has a longer excited-state lifetime and shows sizeable stimulated emission. The main spectroscopic features of bisazo mo lecules in a solid state are similar to those in solutions, however, the ex cited-state relaxation is influenced by the specific solid phase effects. T he lifetimes of the HQ form molecules in solutions differ by more than 10 t imes for bisazo compounds with different substituents and correlate with th e photosensitivity of xerographic layers based on these compounds. (C) 2001 Elsevier Science B.V. All rights reserved.