Spin–spin interaction between phenoxyl radicals through σ–π system

Compounds having two p-phenoxyl radicals bridged by a 1,2-diphenylenedisilanylene unit in m,p- and p,p- fashions were synthesized and the intramolecular spin–spin interaction was examined by Curie plots of ESR signal intensities due to the ΔMS=±2 transition at low temperature. It was found that bridging two phenoxyl radicals at meta and para positions of the bridge led to triplet ground state or degeneracy of triplet/singlet states. In contrast, two phenoxyl radicals put at both para positions interacted in an antiferromagnetic fashion through the diphenylenedisilanylene bridge, to realize singlet ground state.