Photolysis of para,para’-diazide precursors in 2-methyltetrahydrofuran gives biradical ESR spectra assignable to quinonoidal dinitrenes with excited triplet biradical states. The zero field splitting (zfs) parameters for the biradicals at 77 K are as follows : 1,4-phenylenedinitrene (D/hc = 0.169 dm(-1), E/hc = 0.004 cm(-1)); 4,4’-biphenyldinitrene (D/hc = 0.188 cm(-1), E/hc less than or equal to 0.002 cm(-1)); 4,4’-stilbenedinitrene (D/hc = 0.122 cm(-1), E/hc < 0.002 cm(-1)); 1,4-bis(p-nitrenophenyl)buta-1,3-diene (D/hc = 0.0865 cm(-1), E/hc < 0.002 cm(-1)); 1,8-bis(p-nitrenophenyl)octa-1,3,5,7-tetraene (D/hc = 0.0442 cm(-1), E/hc < 0.001 cm(-1)). These zfs parameters are inconsistent with simple dipole-dipole analysis of the ESR spectra in localized biradicals, but are reconcilable with a spin-polarized model involving the x-electrons of the biradicals.