Structural Studies of Polythiophenes: An Ab Initio Evaluation of Coupling Through α and β Carbons
Abstract
Extensive studies have been done both fundamentally and practically on conducting polymers like polythiophene (PT). Once positively doped, PT is relatively stable in air, due in part to the resonance effect of the sulfur which acts to stabilize a carbonium ion on the polymer chain (Yang & Chien, 1995). The drastic changes in electrical, optical and magnetic properties upon doping (Castillon, 2000) have attracted much attention from both theoretical and practical physicists.In the undoped state, polythiophene is an insulator with a band gap of about 2.0 eV (Castillon, 2000) and can be used as heterojunction together with polypyrrole (PPy). Their combination exhibits excellent rectifying characteristics (Castillon, 2000). PT stable films can be prepared by either an electrochemical, or a chemical method (Roncalia, 1992).
Like polypyrrole, the neutral polythiophene as observed in the infrared (lR) and a Carbon13 NMR spectrum has shown that α-α' carbon linkages predominate (Roncalia, 1992; Yurtsener, 1999). Thus, the commonly accepted structure of PT is a linear chain of monomers bonded by α-α'' carbons.
This paper investigates the most probable carbon coupling during polymerization. The thermodynamical probabilities of linking α and β carbons in dimers through pentamers of polythiophenes were determined employing ab initio method.
Published
2012-07-04
Issue
Section
Articles
Submission of a manuscript implies: that the work described has not been published before (except in the form of an abstract or as part of a published lecture, review, or thesis); that it is not under consideration for publication elsewhere; that its publication has been approved by all co-authors, if any, as well as by the responsible authorities at the institute where the work has been carried out; that, if and when the manuscript is accepted for publication, the authors agree to the automatic transfer of the copyright to the publisher; that the manuscript will not be published elsewhere in any language without the consent of the copyright holders; that written permission of the copyright holder is obtained by the authors for material used from other copyrighted sources; and that any costs associated with obtaining this permission are the authors’ responsibility.