The electron paramagnetic resonance of polyradicals

The chemical synthesis and the characterisation of the organic polyradicals build up a representative part of the research in the field of magnetic mo lecular materials. For such single molecule units bearing two or more radic al spins submitted to magnetic exchange interaction, the knowledge of the s pin multiplicity of the magnetic ground state is of crucial interest. The v arious ways for the EPR techniques, e.g. CW-EPR, FT-EPR (Transient Spin Nut ation), and ENDOR, to answer this question and others are reviewed. The bas ic contributions to the EPR response of an organic polyradical are summaris ed. Some results have been selected in the literature as illustrating examp les, from the primary example of the biradical up to the (semi)infinite sys tems (dendrimers, polymers) through the oligoradical molecules (triradicals , tetraradicals,...).