Electronic spectroscopy of highly-polar aromatics.* II. Luminescence of nitroanilines

Abstract

The luminescences of isomeric nitroanilines and their N‐methylated derivatives, as observed in glassy media at 77°K, are reported. The o‐ and m‐derivatives fluoresce only. The p‐derivatives may fluoresce only, phosphoresce only, or show both a fluorescence and a phosphorescence whose relative intensities are dependent on the polarity of the medium and the exciting wavelength. These p‐derivatives which possess the largest ground‐state dipole moments exhibit the largest phosphorescence yields; they also exhibit a dependence of φ p /φ f on excitation energies which lie within the wavelength compass of the lowest‐energy absorption band, a ``red‐edge'' effect, and different fluorescence and phosphorescence excitation spectra. Some suggestions as to the interpretation of these effects are made.