Synthesis and Characterization of Azulenes Substituted by Stable Radical

Abstract

Stable organic radicals have been extensively used in the design of molecular magnets. Alkenyl and/or aryl conjugated nitroxides and nitronyl nitroxides have been well characterized from the viewpoint of electronic structure in the conjugated system, i.e., spin polarization and spin delocalization, the degree of which greatly depend on the nature of the organic group introduced. It is an important issue for us to construct azulene-conjugated stable radicals. Such molecules attract interest from the viewpoint of electronic effect of the radical unit on the azulene nucleus and of intermolecular interaction through the azulene nuclei since azulene, isomeric non-alternant hydrocarbon of naphthalene, has high electron affinity, low ionization potential and low aromatic resonance energy together with the dipole moment vector (1 D) whose negative end is toward its five-membered ring. To the best of our knowledge, synthesis of azulene-conjugated stable radicals have not appeared yet. We report here the synthesis and characterization of azulenyl nitronyl nitroxides .