Extended Huckel calculations on the Pi system of polyaniline

The pi molecular orbitals of aniline are used in a tight-binding calculation, within the extended Huckel methodology, to find the energy band structure of head-to-tall polyaniline. The highest occupied band, the 3b1, is also the widest band with width=1.7eV. This band can be depopulated either by oxidation or protonation to give a metal-like conductive state. Alternately, oxidation can lead to quinoid-like defect sites along the polymer chain that give midgap states that could be responsible for conductivity. The lowest unoccupied state is the localized 2a2 orbital positioned 3.0eV above the top of the 3b1 band. Because of the localized nature of this state, reductive doping should not be an effective method for improving the conductivity of polyaniline. © 1986