468195 Coarse-Grained Model of Conformational Disorder Effects on the Intra-Chain Electronic Properties of Polythiophenes

Wednesday, November 16, 2016: 1:00 PM
Golden Gate 2 (Hilton San Francisco Union Square)
Joel Bombile, Michael J. Janik and Scott T. Milner, Chemical Engineering, The Pennsylvania State University, University Park, PA

Polythiophenes are semiconductors with potential applications as active elements in organic electronic devices. Like other organic semiconductors, the widespread usage of these polymers is limited by a low performance relative to their inorganic counterparts. A key source of difficulties in developing high-performing polymeric semiconductors is the limited understanding of how conformational disorder affects their optoelectronic properties. A high level of conformational disorder is inherent to these soft materials. 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 atomic coordinates changes. Particularly important are dihedral rotations and moiety distortions, which are known to disrupt extended electronic states. The initial stage of our model successfully captures the effects of dihedral rotations on the valence and conduction states of the chains. The model, which coarse-grains the chains at the level of a thiophene ring, is parameterized using density functional theory (DFT) calculations of the one-dimensional band structures for chains with imposed periodic variations in dihedral angles. In a first application, this model is used to compute the optical absorption spectrum of poly(3-hexylthiophene) (P3HT) chains in solution, and successfully reproduces the broadening of the absorption edge as a result of dihedral disorder. We extend the model to include the effects of thiophene ring vibrational distortions. The extended model combined with the variational method is used to predict the formation and properties of polarons and excitons in P3HT, in a cost effective way.

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See more of this Session: Conjugated Polymers
See more of this Group/Topical: Materials Engineering and Sciences Division