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Impact of Side Chains of Conjugated Polymers on Electronic Structure: A Case Study

Institut für Physikalische Chemie, Albert-Ludwigs-Universität Freiburg, Albertstraße 21, 79104 Freiburg, Germany
Institut für Makromolekulare Chemie, Albert-Ludwigs-Universität Freiburg, Stefan-Meier-Straße 31, 79104 Freiburg, Germany
Author to whom correspondence should be addressed.
Current address: Institut für Chemie, Technische Universität Chemnitz, Straße der Nationen 62, 09111 Chemnitz, Germany.
Polymers 2019, 11(5), 870;
Received: 28 February 2019 / Revised: 26 April 2019 / Accepted: 8 May 2019 / Published: 13 May 2019
(This article belongs to the Special Issue Synthesis and Application of Conjugated Polymers)
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Processing from solution is a crucial aspect of organic semiconductors, as it is at the heart of the promise of easy and inexpensive manufacturing of devices. Introducing alkyl side chains is an approach often used to increase solubility and enhance miscibility in blends. The influence of these side chains on the electronic structure, although highly important for a detailed understanding of the structure-function relationship of these materials, is still barely understood. Here, we use time-resolved electron paramagnetic resonance spectroscopy with its molecular resolution to investigate the role of alkyl side chains on the polymer PCDTBT and a series of its building blocks with increasing length. Comparing our results to the non-hexylated compounds allows us to distinguish four different factors determining exciton delocalization. Detailed quantum-chemical calculations (DFT) allows us to further interpret our spectroscopic data and to relate our findings to the molecular geometry. Alkylation generally leads to more localized excitons, most prominent only for the polymer. Furthermore, singlet excitons are more delocalized than the corresponding triplet excitons, despite the larger dihedral angles within the backbone found for the singlet-state geometries. Our results show TREPR spectroscopy of triplet excitons to be well suited for investigating crucial aspects of the structure-function relationship of conjugated polymers used as organic semiconductors on a molecular basis. View Full-Text
Keywords: side chains; electronic structure; triplet states; electron paramagnetic resonance; delocalization side chains; electronic structure; triplet states; electron paramagnetic resonance; delocalization

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Matt, C.; Lombeck, F.; Sommer, M.; Biskup, T. Impact of Side Chains of Conjugated Polymers on Electronic Structure: A Case Study. Polymers 2019, 11, 870.

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