Paramagnetic resonance in phosphorescent diazanaphthalenes

The E.P.R. spectra of 1,6-diazanaphthalene in its lowest triplet state have been observed for solid solutions in durene single crystals. The triplet guest is shown to replace a host durene molecule with its normal, and long and short in-plane axes approximately parallel with the corresponding axes of the replaced host molecule. The deviations from perfect substitution are small, and correspond to a rotation of a few degrees about the normal to the molecular plane, and a smaller rotation about an axis closely parallel to the long axis of the host molecule. Two such energetically distinct substitutions are observed. Each has different fine-structure parameters, but identical hyperfine structure. From an examination of this nuclear hyperfine structure, an estimate of 0·14 was obtained for the spin density on the nitrogen atom in the 1-position.