Abstract
The energy spectra and magnetic properties of a large class of one‐dimensional poly(m‐aniline)s (PMA) and further model polymers are investigated theoretically. The band structure of those PMA's which are aza‐analogs of the alternant non‐classical (non‐Kekulé) hydrocarbons (polymers) is characterized by a wide gap in which there is a narrow half‐filled band (HFB). The different contributions to the effective spin exchange between the unpaired electrons in the HFB: Coulomb (Hund), kinetic and indirect exchange interactions are calculated. While it has been shown earlier that PMA exhibits a net spin exchange of ferromagnetic nature, this approach enables a detailed understanding of the influence of substituents on the nitrogen centers and changes in the aromatic bridging unit. The ferromagnetic nature of the spin coupling in the singly bridged PMA models therebye prevails independent of the structural changes. The HFB width of those PMA's which are derivatives (aza‐analogs) of ladder‐type non‐alternant hydrocarbons is very large and the Wannier functions are delocalized. For this group of polymers the delocalized, non‐magnetic state is favored and, therefore, they may be good candidates for testing electrical conduction.