Nitronyl Nitroxyl Diradical with Pyrene Backbone: Synthesis, Quantum Chemical and X/Q-Band EPR Study

We report the synthesis and EPR and quantum chemical study of a new nitronyl nitroxyl diradical with a pyrene backbone. EPR at the X- and Q-bands indicates weak dipolar coupling between electron spins, the magnitude of which is comparable to hyperfine interactions in nitronyl nitroxide moieties. Quantum chemical calculations predict weak ferromagnetic interaction between radical fragments, which is nevertheless large on the EPR scale. Using additional Q-band measurements on the reference monoradical to accurately determine the g- and A-tensor components and results of quantum chemical calculations, the X/Q-band spectra of the diradical were satisfactorily modelled using a D-value of 82 MHz. The spectroscopic information obtained can be useful in the design of polyradical systems with similar backbones.