SINGLET-TRIPLET ENERGY GAPS OF QUINONOIDAL DINITRENES

Singlet-triplet energy gaps of phenylene-1,4-dinitrene (1), biphenyl-4 ,4'-dinitrene (2), stilbene-4,4'-dinitrene (3), and azobenzene-4,4'-di nitrene (4) were determined from temperature dependence of ESR signal intensities. These quinonoidal dinitrenes show interesting features: ( 1) the energy gap of 1 is comparable to that of 2, and (2) the gap of 4 is almost one-half of the gap of 3. The results are qualitatively ex plained by magnitudes of polarized pi spins.