Electrical Conduction Study of Polymers with Indophenine Repeating Units

Abstract

It has been established that the dark conduction of isatin-[thiophene]-indophenine and of three polymers in which it is a repeating unit is described by the expression [sgrave] = [sgrave] exp (Eact/kT). The indophenine repeating units in the polymers are connected with a single bond, an oxygen atom, or a methylene group. The electronic spectra in solution and in the solid state indicate that these bonds between the basic units do not interrupt the conjugation along the chain. There is no correlation between the activation energy calculated from optical data and the thermal activation energy of conduction. The latter is considered as a sum of the energy necessary for the generation of the carriers and the energies needed to overcome the intramolecular and intermolecular potential barriers. The values of the parameters characteristic of the semiconducting properties are determined in the first place by the structure of the polymers as a solid body. Crystallinity tends to improve the electrophysical properties. The participation of heteroatoms and groups in the polymer chain, provided they do not interrupt the conjugation, has a favorable effect in cases where their presence improves the intermolecular interaction. A “compensation effect” is to be observed for all substances in vacuum and in air. The experimental data are best explained by the hopping model of electrical conduction.