Spectral and Luminescent Properties of Bis(hydroxyazomethine)s of Angular Structure

The spectral and luminescent properties of solutions of bis(hydroxyphenylazomethine)s (I and II) and bis(hydroxynaphthylazomethine)s (III and IV) of the benzene and pyridine series in toluene and ethanol have been studied. The keto–enol equilibrium in pyridine azomethine II in the ground state weakly depends on the presence of the pyridine N atom, whereas the influence of pyridine is significant for pyridine azomethine IV. In solutions of I and II in both solvents, two luminescence bands are observed from the enol (E*) and (K*) keto forms, the ratio of which depends on the excitation wavelength. Luminescence in solutions of III and IV is determined by the formation of K*, and predominant short-wavelength luminescence from E* is added to the luminescence spectrum only in a solution of III in toluene in the case of short-wavelength excitation. The solvent and the pyridine atom were found to affect the position of the emission bands, with the influence being more pronounced for compound II than for IV. For all compounds I–IV, luminescence in alcohol is an order of magnitude more intense than in toluene.