The ESR-spectra recorded during irradiation (436 mµ) of solutions of nitrobenzene, o-, m-, p- dinitrobenzene, and trinitrobenzene in tetrahydrofuran exhibit a hyperfine pattern which can be derived from the negative radical ion of the nitro- and polynitro aromatic compounds in ion-pairs with the n-donor cation (e. g. THF·+), generated by a transfer of an electron from the donor molecule to the acceptor molecule. Owing to the strong interionic interaction of the radical ions in the ion-pairs the photoinduced ESR spectra are quite different from the ESR spectra produced by electrolytic reduction of nitrobenzenes. The ESR spectra may be explained by a strong coupling of the donor cation (THF+, dioxane+, diphenylether+, or di-tert.-butylether+) with the 14N nucleus of a single dominant NO2-group. The nonequivalence of the NO2-groups in the photoinduced radical ion-pairs between nitrobenzenes and n-donor cations is more significant than in ionpairs between an alkali-metal ion and nitrobenzenes, owing to the small size of the radius of Ol + (ca. 0.9 Å) in the donor cation (e. g. THF·+). The ESR spectra of nitrobenzene- and trinitrobenzene- in ion-pairs with THF+ or dioxane+ yield an additional small splittitng constant (0.22 to 0.44 G) according to an interionic coupling interaction with an α-proton of THF·+ in the ion-pair. A hydrogen transfer from THF to a NO2-group (WARD 2) has not been established with certainty and needs not to be taken into account from some points of view. The THF·+ signal becomes undetectable because of an electron exchange THF·++THF ↔ THF+THF·+, since there is a large excess of THF molecules. Quantitative details of the change of the signal-intensity during irradiation, and of the influence of temperature will be published in a following publication.