Spin and charge control in conjugated ionic oligomers: DFT and EPR study

Abstract

The initial oxidized trans-polyacetylene and polythiophene-based conjugated oligomers, as well as their composites with polycyclic aromatic hydrocarbons, were studied by density functional theory (DFT) and electron paramagnetic resonance methods. The relative electronic density and spin population of each oligomer atom are obtained within the framework of different formalisms. The stabilization of different spin charge carriers in different poly(3-alkylthiophene)-based oligomers is shown. The role of the hybridization of the molecular orbitals of oligomers in stabilizing these charge carriers on an oligomer chain is analyzed. The main parameters of the spin Hamiltonian of spin charge carriers formed in compounds with various structures and morphologies are determined. A significant change in the electronic and magnetic properties of these charge carriers is shown to occur upon the modification of oligomers with graphene-like polycyclic aromatic hydrocarbons owing to hyperfine coupling of their extended π-conjugated structures. Magic numbers of some graphene-like additives with stabilized structural and electronic parameters were determined. This interaction is initiated by spin polarization, depends on the polycyclicity of the aromatic additive, and is characterized by several extremes. This effect was assumed to arise as a result of cross-coupling of oligomers and graphene-like subsystems with enhanced stability and electronic or/and magnetic properties. It enhances their hyperfine exchange coupling, and it affects a barrier for the spin magnetization switching. Such composite spin-filter functionality can be used in fully organic spin‒controlled molecular devices. This should have an impact on the wide fields of fully organic spintronics, nanotechnology, and quantum devices by controlling and manipulating spin and charge.