Energy spectra and magnetic properties of radialenes, dendralenes and their poly-radical ions. A new class of polaronic high-spin π-systems

Abstract

Abstract The energy spectra of infinite radialenes (RA) and dendralenes (DE) — the simplest one-dimensional π-systems possessing non-degenerate ground states — are theoretically investigated. Three factors, a topological, a geometrical, and a correlational, contribute to the energy gap of 3.6 eV. The charge density distribution of the Jahn-Teller active mono-cation of the [3]RA and the charged [6]RA, and the charged [6]DE is studied. The polymers derived from the poly-radical ions of infinite RAs possess a narrow half-filled band (HFB) within the energy gap. The different contributions to the effective spin exchange interaction between the unpaired electrons in the HFB: the potential exchange, the kinetic exchange, and the indirect exchange (due to the spin polarization) were calculated. In all cases the effective spin exchange is positive, i.e. the ground state of the polymers is a high-spin one. The ferromagnetic interaction within the HFB is due to the predominant role of the direct Coulomb exchange. A juxtaposition between the structural principle of the polaronic high-spin systems considered here and Fukutome's polaronic high-spin systems is discussed.