Spectral-luminescence and acid-base properties of 4,7-diaminocoumarins

The absorption and luminescence spectra of a series of 4,7-diaminocoumarins have been investigated in ethanol and acetonitrile solution. The pk_a ^I and pk_a ^II values for several of the compounds have been measured. It has been found that the site of primary protonation is the nitrogen atom in the 7-position, and that the second protonation reaction occurs at the lactone oxygen atom. The effects of steric and electronic factors on the spectral-luminescence and acid-base characteristics of these compounds are discussed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1610–1618, December, 1990.