Modeling the Structural and Electronic Properties of an Optically Active Regioregular Polythiophene

Abstract

A comprehensive theoretical study about the structural and electronic molecular properties of the optically active regioregular poly[(R)-3-(4-(4-ethyl-2-oxazolin-2-yl)phenyl)thiophene] and its model oligomers has been developed with use of quantum mechanical calculations. Results show two stable arrangements for the investigated oligomers. The first one consists of a plain structure with all the inter-ring dihedral angles arranged in a syn-gauche+ conformation rather than the anti-gauche+ typically found in substituted polythiophenes. This produces a reduction of the steric repulsions allowing the formation of a π-stacking alignment between phenyl groups of adjacent monomers. The second is a helical structure with six repeating units per turn that is constructed by alternating the syn-gauche+ and syn-gauche− conformations. The lowest π−π* transition energy predicted for an idealized polymer chain, which was derived from Density Functional Theory calculations, is in agreement with the reported experimental values obtained by UV−vis spectroscopy.