Electrical Conductivity in Polyazomethines: A Novel Mechanism Derived from All Valence MO Calculation and IR Study of Polymer-Dopant Interaction

A simple mechanism is proposed to explain the variation of electrical conductivity in polyazomethines. The results of semiempirical, all valence, molecular orbital calculations obtained from the PM3 method have been employed to arrive at the mechanism. The difference of energy (Delta E) between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) alone could not explain the variation in electrical conductivity; however, Delta E together with the LUMO electron density at the atoms that lie on the continuous chain could account for the electrical conductivity in these polymers. The LUMO electron density on these centers may be visualized as the carrier movement. In certain polymers there are intrinsic holes in HOMO. The movement of these intrinsic holes also adds to the electrical conduction. The polyazomethines are prepared by the condensation of diamines with azo bis-aldehydes. A few of these polymers were doped with silver nanoparticles. Many of the doped polymers showed substantial enhancement in conductivity. Strong polymer-dopant interaction, identified by IR spectroscopy, is proposed to be responsible for the increase in conductivity.