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

Abstract

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 (ΔE) between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) alone could not explain the variation in electrical conductivity; however, ΔE 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.

Keywords:

• azo bis-aldehyde
• carrier movement
• conductivity
• IR spectra
• PM3 method
• polymer–dopant interaction
• poly-Schiff bases

Acknowledgments

The authors thank Professor J. S. Parmar, Head, Department of Chemistry, Sardar Patel University, Gujarat, India, for providing the necessary facilities to carry out this work. The authors are indebted to Dr. D. K. Kanchan and Manish Jayswal of Department of Physics, Faculty of Science, Maharaja Sayajirao University, Vadodara, Gujarat, for their help to obtain the conductivity of the polymers. The authors gratefully acknowledge the help rendered by Sophisticated Instrumentation Centre for Advanced Research and Testing (SICART), Vallabh Vidyanagar, Gujarat, to obtain the IR spectra and the C,H,N analysis of the dyes. Part of the work was carried out with the financial assistance (Ref. No. F12-26/2001[SR-1]) provided by University Grants Commission (UGC), New Delhi. The authors thank UGC for the assistance provided.