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Doped Conductive Polymers: Modeling of Polythiophene with Explicitly Used Counterions

Authors


  • We thank the Israel Science Foundation, the MINERVA Foundation and the Helen and Martin Kimmel Center for Molecular Design for financial support. M. B. is the incumbent of the Recanati career development chair, a member ad personam of the Lise Meitner-Minerva Center for Computational Quantum Chemistry and acknowledges support from a DuPont Young Professor Award. Supporting Information is available online from Wiley InterScience or from the author.

Abstract

The effect of counterions on the properties and structure of conducting polymers was studied by using a series of Cl3 doped polythiophenes (PTs) as a case example. Hybrid density functional theory (DFT) with periodic boundary conditions (PBC) at the B3LYP/6–31G(d) level has been used. This is the first theoretical study of infinitely long doped PT using DFT with counterions explicitly taken into account. The balance between charge carrier states was addressed by studying the singlet and triplet state unit cells of differently doped PTs. The relative isomer energies, density of states diagrams, bond length alternation, and charge distribution patterns were analyzed. Interestingly, the position of the counterion is flexible over the polymer chain and the electronic structure of the polymer and, consequently, optical properties are sensitive to the position of the counterion. A bipolaron electronic configuration is preferred at high dopant concentrations (one dopant per six or less thiophene rings) while a polaron pairs configuration is preferred at low dopant concentrations (one dopant per ten or more thiophene rings) which is in line with many experimental observations.

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