Understanding the structure and configurations of small-molecule organic semiconductor (OSC) materials is essential in modifying their material properties. Here, we use density functional theory (DFT) to explore the impact of intramolecular noncovalent interactions on the isomerization and structure of the benzodithiophene (BDT) trimer. Fluorine substitutions modify the dihedral coupling between BDTs on the same molecule, thereby significantly increases charge mobility up to 13.2 cm² V^–1 s^–1. In the fluorinated isomers, the formation of hydrogen bonds overcomes the repulsive S···S interaction in the syn-conformer, leading to a more planar backbone structure. To validate the DFT simulations, we simulated inelastic neutron scattering (INS) spectroscopy of different anti- and syn-isomers in mixed configuration crystals and compared them to measured INS. Two main messages emerge from this study. (1) Although the through space interaction of fluorine with sulfur is the main contributor to dihedral planarization, H-bonding formed through selective fluorination plays a critical role. (2) A crystal structure that includes a mixture of several configurations could have significant mobility, while the dihedral disorder is mitigated by configurations that are energetically very similar. Our investigation reveals that both syn- and anti-conformers are common in the BDT-trimer crystal, demonstrating that isomeric or configuration purity is not a prerequisite for high charge mobility over 10 cm² V^–1 s^–1. This work provides a fundamental understanding of the interplay between intramolecular interactions, isomerization, and side chain effects in OSC materials, guiding the design of new generations of OSC materials.

中文翻译：

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优化有机半导体晶体分子间和长距离堆积的设计规则


了解小分子有机半导体（OSC）材料的结构和配置对于改变其材料性能至关重要。在这里，我们利用密度泛函理论（DFT）探讨分子内非共价相互作用对苯并二噻吩（BDT）三聚体异构化和结构的影响。氟取代改变了同一分子上 BDT 之间的二面体耦合，从而显着提高电荷迁移率高达 13.2 cm ² V ^–1 s ^–1 。在氟化异构体中，氢键的形成克服了顺式异构体中排斥的S·S相互作用，从而形成更平坦的主链结构。为了验证 DFT 模拟，我们模拟了混合构型晶体中不同反式和顺式异构体的非弹性中子散射 (INS) 光谱，并将它们与测量的 INS 进行比较。这项研究得出了两个主要信息。 (1)虽然氟与硫的空间相互作用是二面体平坦化的主要贡献者，但通过选择性氟化形成的氢键起着关键作用。 (2) 包含多种构型混合的晶体结构可能具有显着的迁移率，而能量上非常相似的构型可以减轻二面体无序。我们的研究表明，顺式构象和反构象在 BDT 三聚体晶体中都很常见，这表明异构体或构型纯度并不是超过 10 cm ² V ^–1 。这项工作提供了对 OSC 材料中分子内相互作用、异构化和侧链效应之间相互作用的基本了解，指导新一代 OSC 材料的设计。