STRUCTURE, ENERGY-SPECTRA AND MAGNETIC-PROPERTIES OF POLY(M-ANILINE)S

The energy spectra and magnetic properties of a large class of one-dim ensional poly(m-aniline)s (PMA) and further model polymers are investi gated theoretically. The band structure of those PMA's which are aza-a nalogs of the alternant non-classical (non-Kekule) hydrocarbons (polym ers) is characterized by a wide gap in which there is a narrow half-fi lled band (HFB). The different contributions to the effective spin exc hange between the unpaired electrons in the HFB: Coulomb (Hund), kinet ic and indirect exchange interactions are calculated. While it has bee n shown earlier that PMA exhibits a net spin exchange of ferromagnetic nature, this approach enables a detailed understanding of the influen ce of substituents on the nitrogen centers and changes in the aromatic bridging unit. The ferromagnetic nature of the spin coupling in the s ingly bridged PMA models therebye prevails independent of the structur al changes. The HFB width of those PMA's which are derivatives (aza-an alogs) of ladder-type non-alternant hydrocarbons is very large and the Wannier functions are delocalized. For this group of polymers the del ocalized, non-magnetic state is favored and, therefore; they may be go od candidates for testing electrical conduction.