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Issue 18, 2016
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Tight binding model of conformational disorder effects on the optical absorption spectrum of polythiophenes

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Abstract

Semiconducting polymers are soft materials with many conformational degrees of freedom. The limited understanding of how conformational disorder affects their optoelectronic properties is a key source of difficulties that limits their widespread usage in electronic devices. We develop a coarse-grained approach based on the tight binding approximation to model the electronic degrees of freedom of polythiophene chains, taking into account conformational degrees of freedom. Particularly important is dihedral disorder, which disrupts extended electronic states. Our tight binding model is parameterized using density functional theory (DFT) calculations of the one-dimensional band structures for chains with imposed periodic variations in dihedral angles. The model predicts valence and conduction bands for these chain conformations that compare well to DFT results. As an initial application of our model, we compute the optical absorption spectrum of poly(3-hexylthiophene) chains in solution. We observe a broadening of the absorption edge resulting from dihedral disorder, just shy of the experimental broadening. We conclude that the effects of molecular disorder on the optoelectronic properties of conjugated polymer single chains can be mostly accounted for by torsional disorder alone.

Graphical abstract: Tight binding model of conformational disorder effects on the optical absorption spectrum of polythiophenes

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Article information


Submitted
05 Feb 2016
Accepted
06 Apr 2016
First published
12 Apr 2016

Phys. Chem. Chem. Phys., 2016,18, 12521-12533
Article type
Paper

Tight binding model of conformational disorder effects on the optical absorption spectrum of polythiophenes

J. H. Bombile, M. J. Janik and S. T. Milner, Phys. Chem. Chem. Phys., 2016, 18, 12521
DOI: 10.1039/C6CP00832A

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