Knowledge Bank

Diazaphenanthrene, sym-tetrazine, and pyridazine differ from many aromatic heterocyclie compounds in that they fluoresce but do not phosphoresce with significant quantum yields. The low-lying singlet and triplet states of diazaphenanthrene are located and assigned by means of polarized absorption studies on single crystals. The lowest triplet state is shown to be $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\pi \pi \ast (B1)$ and to be mixing strongly with the $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}n\pi \ast$ state. Some interesting solvent effects on the emission properties of orthodiazines are presented with the aim of understanding the radiationless processes involved.