Theory of Charge Transfer in Aromatic Donor–Acceptor Crystals

Abstract

A narrow‐band, localized model is developed for charge transfer (CT) interactions in 1:1 stacks of planar, π‐electron donors (D) and acceptors (A). The inequivalence of D and A sites and the Madelung constant for the ionic lattice are treated phenomenologically. The electronic states, for arbitrary CT in the aromatic D–A stacks, are found self‐consistently by an equation‐of‐motion method. The ground‐state charge density and the band structures correspond to primarily neutral, ···DADA···, diamagnetic or to primarily ionic, ···D⁺A⁻D⁺A⁻···, paramagnetic one‐dimensional semiconductors. The activation energies for CT and for semiconduction, together with the CT stabilization, are found self‐consistently. In ionic lattices, CT is shown to provide an activation energy for paramagnetism of the proper magnitude. When the sites are equivalent, the theory reduces to a half‐filled Hubbard model, and the self‐consistent solutions are in good agreement with exact results.