Characterization of bisazo compounds employing ultrafast spectroscopy Original Research Article

Fluorenone-based bisazo compounds with different substituents have been investigated in various organic solvents and in a solid state by means of absorption, fluorescence and picosecond time-resolved absorption pump–probe spectroscopy. The bisazo compounds were found to coexist in azo–enol and hydrazone–quinone (HQ) tautomeric forms. Absorption spectra of the two forms were determined and excited-state properties were characterized. The azo–enol tautomeric form has a short, of tens of ps, excited-state lifetime and shows strong excited-state absorption, whereas stimulated emission is weak or absent. The HQ tautomeric form has a longer excited-state lifetime and shows sizeable stimulated emission. The main spectroscopic features of bisazo molecules in a solid state are similar to those in solutions, however, the excited-state relaxation is influenced by the specific solid phase effects. The lifetimes of the HQ form molecules in solutions differ by more than 10 times for bisazo compounds with different substituents and correlate with the photosensitivity of xerographic layers based on these compounds.