Open-shell donors (1, 2) carrying a nitronyl nitroxide group (NN) at the para position of N, N’-dimethyl- or diphenylaniline were prepared and thier one-electron oxidation states were investigated by means of the ESR spectroscopic measurement. The cation diradicals of 1 and 2 turned out to be the ground state triplet species based on the non-disjoint character of thier electronic structures consisted of two non-degenerated SOMOs.