Spin-triplet excitons in 1,3-diphenyl-7-(fur-2-yl)-1,4-dihydro-1,2,4-benzotriazin-4-yl

7-(Fur-2-yl)benzotriazinyl 1 is the first example of a hydrazyl radical dimer with a thermally accessible triplet state. The triplet exciton (|D| = 0.018 cm(-1), |E| = 0.001 cm(-1)) was observed by solid-state VT-EPR spectroscopy between 5 and 140 K. VT crystallography, DFT calculations and magnetic susceptibility studies reveal a strong temperature dependence of the intra-dimer exchange interaction with J/k ~ -254 + 0.0007T(2).