Moore and More ›› 2025, Vol. 1 ›› Issue (1): 16-25.DOI: 10.1007/s44275-024-00008-x

• ORIGINAL ARTICLES • Previous Articles    

Impact of the alkyl side-chain length on solubility, interchain packing, and charge-transport properties of amorphous π-conjugated polymers

Qingqing Dai1, Xingyou Lang2, Jean-Luc Brédas3, Tonghui Wang2, Qing Jiang2   

  1. 1. Key Laboratory of Bionic Engineering, Ministry of Education, Jilin University, Changchun, 130022, China;
    2. Key Laboratory of Automobile Materials, Ministry of Education, and School of Materials Science and Engineering, Jilin University, Changchun, 130022, China;
    3. Department of Chemistry and Biochemistry, The University of Arizona, Tucson, AZ, 85721-0041, USA
  • Received:2024-04-19 Revised:2024-06-19 Accepted:2024-06-20 Online:2024-08-20 Published:2024-08-20
  • Contact: Jean-Luc Brédas,E-mail:jlbredas@arizona.edu;Tonghui Wang,E-mail:twang@jlu.edu.cn
  • Supported by:
    National Key R&D Program of China (No. 2023YFB3003001).

Impact of the alkyl side-chain length on solubility, interchain packing, and charge-transport properties of amorphous π-conjugated polymers

Qingqing Dai1, Xingyou Lang2, Jean-Luc Brédas3, Tonghui Wang2, Qing Jiang2   

  1. 1. Key Laboratory of Bionic Engineering, Ministry of Education, Jilin University, Changchun, 130022, China;
    2. Key Laboratory of Automobile Materials, Ministry of Education, and School of Materials Science and Engineering, Jilin University, Changchun, 130022, China;
    3. Department of Chemistry and Biochemistry, The University of Arizona, Tucson, AZ, 85721-0041, USA
  • 通讯作者: Jean-Luc Brédas,E-mail:jlbredas@arizona.edu;Tonghui Wang,E-mail:twang@jlu.edu.cn
  • 作者简介:Qingqing Dai received her Ph.D. in Materials Science in 2014 at Jilin University. She worked as a postdoc at King Abdullah University of Science & Technology (2015-2016), the Georgia Institute of Technology (2017-2020), and The University of Arizona (2020-2021), respectively. Currently, she is a lecturer at Key Laboratory of Bionic Engineering, Ministry of Education, Jilin University. Her current research interests focus on the computational characterization of surface/interface properties of materials.
    Xingyou Lang received his Ph.D. in Materials Science in 2007 at Jilin University. He worked as a postdoc and assistant professor at Tohoku University (2007-2011). Currently, he is a professor at School of Materials Science and Engineering, Jilin University. His research interests focus on nanoporous metal-based materials for energy storage and conversion.
    Jean-Luc Brédas received his B.Sc. (1976) and Ph.D. (1979) degrees from University of Namur, Belgium. In 1988, he was appointed Professor at The University of Mons, Belgium, where he established the Laboratory for Chemistry of Novel Materials. While keeping an “Extraordinary Professorship” appointment in Mons, he joined The University of Arizona in 1999. In 2003, he moved to the Georgia Institute of Technology where he became Regents’ Professor of Chemistry and Biochemistry and held the Vasser-Woolley and Georgia Research Alliance Chair in Molecular Design. Between 2014 and 2016, he joined King Abdullah University of Science and Technology (KAUST) as a Distinguished Professor and served as Director of the KAUST Solar & Photovoltaics Engineering Research Center. He returned to Georgia Tech in 2017 before moving back to the University of Arizona in 2020 where he is currently Regents Professor in the Department of Chemistry and Biochemistry.
    Jean-Luc Brédas is an elected member of the International Academy of Quantum Molecular Science, the Royal Academy of Belgium, and the European Academy of Sciences. Recent honors include the 2013 American Physical Society David Adler Lectureship Award in the Field of Materials Physics, the 2016 American Chemical Society Award in the Chemistry of Materials, the 2019 Alexander von Humboldt Research Award, the 2020 Materials Research Society Materials Theory Award, and the 2021 Centenary Prize of the Royal Society of Chemistry. He is an Honorary Professor of the Institute of Chemistry of the Chinese Academy of Sciences and holds an Adjunct Professorship at the Georgia Institute of Technology. He was Editor for Chemistry of Materials, published by the American Chemical Society, between 2008 and 2021; since June 2022, he has served as Scientific Editor for Materials Horizons, the flagship materials journal of the Royal Society of Chemistry. He has published over 1 200 scientific articles, which have garnered nearly 140 000 citations (h-index: 170) according to Google Scholar.
    Tonghui Wang received his Ph.D. in Materials Science in 2014 at Jilin University. He worked as a postdoc at the King Abdullah University of Science & Technology (2014-2016) and the Georgia Institute of Technology (2017-2020), and as a research scientist at The University of Arizona (2020-2021) in the group of Professor Jean-Luc Brédas. Currently, he is a full professor at School of Materials Science and Engineering, Jilin University. His current research interests focus on the multi-scale simulation studies in the field of organic photovoltaics and catalysis.
    Qing Jiang obtained his Ph.D. in Chemistry from University of Stuttgart, Germany in 1990. Since 1992, he has been a professor at School of Materials Science and Engineering, Jilin University, China. His research interests focus on synthesis of nanomaterials as well as their applications in catalysis, energy storage, and conversion, and interface thermodynamics and kinetics of nanomaterials.
  • 基金资助:
    National Key R&D Program of China (No. 2023YFB3003001).

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Abstract: Increasing the length of alkyl side chains is a typical way to improve the solubility of π-conjugated polymers designed for use in solution-processed devices. However, these modifications have also been reported to alter the film morphology. Given that the mechanism leading to improved solubility is not well documented yet and the nanoscale (local) morphologies of amorphous π-conjugated polymer films are difficult to characterize experimentally, here, we combine molecular dynamics simulations and long-range corrected density functional theory calculations to examine at the molecular scale the impact that the alkyl side-chain length has on polymer solubility and film morphologies. As a representative example, we consider poly(thieno[3,4-c]pyrrole-4,6-dione-alt-3,4-difluorothiophene) (PTPD[2F]T) with two different lengths of the alkyl side chains on the thieno[3,4-c]pyrrole-4,6-dione (TPD) moieties, i.e., 2-hexyldecyl (2HD) and 2-decyltetradecyl (2DT). A detailed analysis of polymer-solvent and polymer-polymer interactions provides a picture that describes the underlying mechanism for improved solubility in going from 2HD to 2DT. We then underline an intrinsic characteristic that decreasing the side-chain length brings a greater extent of backbone planarity and lesser side chain-TPD interactions, which leads to higher interchain π-π packing density and order, while the interchain π-π packing patterns remain similar in the two films. These morphologies are discussed in terms of the charge-transport properties between neighboring PTPD[2F]T chains, which point to a higher electron mobility in the PTPD[2F]T films with shorter alkyl side chains. Overall, our findings offer guidance in the field of solution-processed electronic devices by pointing out that the polymer alkyl side-chain length could be minimized to improve carrier mobility while ensuring polymer solubility.

Key words: π-conjugated polymers, Alkyl side-chain length, Solubility, Local morphology, Molecular dynamics simulations, Density functional theory calculations

摘要： Increasing the length of alkyl side chains is a typical way to improve the solubility of π-conjugated polymers designed for use in solution-processed devices. However, these modifications have also been reported to alter the film morphology. Given that the mechanism leading to improved solubility is not well documented yet and the nanoscale (local) morphologies of amorphous π-conjugated polymer films are difficult to characterize experimentally, here, we combine molecular dynamics simulations and long-range corrected density functional theory calculations to examine at the molecular scale the impact that the alkyl side-chain length has on polymer solubility and film morphologies. As a representative example, we consider poly(thieno[3,4-c]pyrrole-4,6-dione-alt-3,4-difluorothiophene) (PTPD[2F]T) with two different lengths of the alkyl side chains on the thieno[3,4-c]pyrrole-4,6-dione (TPD) moieties, i.e., 2-hexyldecyl (2HD) and 2-decyltetradecyl (2DT). A detailed analysis of polymer-solvent and polymer-polymer interactions provides a picture that describes the underlying mechanism for improved solubility in going from 2HD to 2DT. We then underline an intrinsic characteristic that decreasing the side-chain length brings a greater extent of backbone planarity and lesser side chain-TPD interactions, which leads to higher interchain π-π packing density and order, while the interchain π-π packing patterns remain similar in the two films. These morphologies are discussed in terms of the charge-transport properties between neighboring PTPD[2F]T chains, which point to a higher electron mobility in the PTPD[2F]T films with shorter alkyl side chains. Overall, our findings offer guidance in the field of solution-processed electronic devices by pointing out that the polymer alkyl side-chain length could be minimized to improve carrier mobility while ensuring polymer solubility.

关键词: π-conjugated polymers, Alkyl side-chain length, Solubility, Local morphology, Molecular dynamics simulations, Density functional theory calculations

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