Molecular design for polyionic organic ferromagnets and syntheses of model oligomers; Exploitation of topological superdegeneracy of π-BCO's and π-ABCO's, and high spin characterization by FT pulsed ESR/ESTN spectroscopy as a novel experimental technique

Abstract

The conceptual proposals of organic magnetism/molecule-based magnetism in terms of non-charged open-shell units were made as early as 1960's. One of the highlighted advances has been that the use of topological-symmetry requirement in the electron network of it-conjugated homoatomic neutral hydrocarbon systems gives rise to the unlimited number of the degeneracy in non-bonding molecular orbitals (coined as topological degeneracy). This paper deals with the π-topological version of an approach to purely organic polyionic polymer ferromagnets, emphasizing that molecular design exploits the topological pseudo superdegeneracy of π-bonding and -antibonding crystal orbitals (π-BCOs and π-ABCOs; π-bands) appearing close to zero energy in heteroatomic π-conjugated organic systems, for pofycationic and poryanionic organic polymer ferromagnets, respectively. The appearance of the BCOs and ABCOs close to zero energy as well as their pseudo degeneracy is due to heteroperturbation. Their superdegeneracy arises from the topological nature of the electron network of π-conjugation. Oxidation and reduction states of polymers designed according to the topological approach are expected to undergo dynamic spin polarization, leading to high-spin ground states for porycationic and poryanionic model porymers, respectively. One-dimensional and two-dimensional star-burst model oligomers with heteroatoms in π-conjugation were designed and synthesized Their electronic high-spin ground states have been identified by means of Electron Spin Transient Nutation (ESTN) spectroscopy based on FT pulsed ESR technique to which recently we have exerted ourselves in order to obtain technical advances in molecular spin science underlying the research field of molecule-based magnetism. Most of the poryionic high-spin species have been generated by wet processes, i.e., chemical reaction in solution. In this study, the poryketone-based poryanionic high-spin species have been generated also by a dry process, i.e., electron attachment via γ-irradiation in organic glasses.