Ab initio study of ladder-type polymers polythiophene and polypyrrole

TL;DR

This study uses ab initio methods to analyze the electronic properties of polythiophene and polypyrrole polymers, revealing contrasting band gap behaviors in ladder-type structures due to structural and charge density effects.

Contribution

It provides a comparative ab initio analysis of ladder-type and unconstrained polymers, highlighting differences in band gap variations and charge density effects.

Findings

Ladder-type polythiophene has a larger band gap than unconstrained polythiophene.

Ladder-type polypyrrole has a smaller band gap than unconstrained polypyrrole.

Charge density and bond length alternation explain the band gap differences.

Abstract

This article presents an \textit{ab initio} study of four polymers, polythiophene, polypyrrole, ladder-type polythiophene, and ladder-type polypyrrole. Upon an analysis of the variation of the band gap when comparing the unconstrained and the ladder-type polymers, a discrepancy was found between the thiophene and the pyrrole polymer families. For polythiophene, the ladder-type polymer has a larger gap than the unconstrained polymer whereas the opposite is found for the pyrrole polymers. The structural properties and the charge densities using the Bader charge analysis of these four compounds are investigated. The different band gap behaviors in thiophene and pyrrole polymers can be explained in terms of the competition between the bond length alternation and the effect of the charge density in the carbon backbone.