Nitrogen and proton hyperfine interactions in the triplet state of azanaphthalenes at zero field

The zero field optically detected ESR and ENDOR spectra of the triplet state of 1,8−diazanaphthalene are presented and completely interpreted in terms of a spin Hamiltonian which includes proton hyperfine interactions. The latter are shown to be of considerable importance at zero field even in systems containing quadrupolar nitrogen nuclei. The previously unassigned features in the zero field spectra of diazanaphthalenes are explained and some new assignments are proposed in quinoline.