Urban Mateusz, Durka Krzysztof, Górka Patrycja, Wiosna-Sałyga Gabriela, Nawara Krzysztof, Jankowski Piotr, Luliński Sergiusz
Department of Physical Chemistry, Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw, Poland.
Department of Molecular Physics, Faculty of Chemistry, Lodz University of Technology, Żeromskiego 116, 90-924 Łódź, Poland.
Dalton Trans. 2019 Jun 28;48(24):8642-8663. doi: 10.1039/c9dt01332f. Epub 2019 May 24.
A series of 8 luminescent borafluorene complexes were extensively studied both experimentally and theoretically in order to elucidate the effect of organoboron moiety rigidification on the physicochemical properties of these compounds. Due to the spiro geometry of the boron atom, borafluorene and ligand units are perpendicularly aligned, which considerably affects the flexibility of the molecule as well as its solid-state structure. Through comparative analysis with close diphenyl analogues, we show how these structural features influence the thermal, photoluminescent and charge mobility behaviour of the studied compounds. Crystal structural analysis revealed that the molecules are connected mostly through C-HO and C-Hπ interactions formed between perpendicularly aligned borafluorene and ligand moieties from neighboured molecules, serving as a complementary donor and acceptor of electron density, respectively. This also efficiently prevents molecules from engaging in unfavoured π-stacking contact. Furthermore, structural analysis suggests that borafluorene complexes possess a considerable degree of flexibility due to OBN heterocycle distortions and mutual borafluorene-ligand plane movements. The magnitude of these effects strictly depends on the ligand structure and may lead either to enhancing or lowering the quantum yield value with respect to BPh analogues, while the absorption and emission wavelength are slightly affected. The measured photophysical parameters for solid-state samples showed that the studied complexes are much better emitters in their crystalline states that in amorphous films. The TD-DFT and NTO calculations revealed a significant change in frontier molecular distribution, with the HOMO localized on the borafluorene moiety. However, as the HOMO-LUMO transition is geometrically not favoured, excitation occurred from HOMO-1 localized on the ligand. Finally, aggregation effects were discussed based on supramolecular arrangements in crystal structures and charge transfer rates obtained from theoretical calculations in the framework of the Marcus-Hush approximation. They suggest that borafluorene complexes are much better electron carriers with respect to non-annulated BPh complexes.
为了阐明有机硼部分刚性化对这些化合物物理化学性质的影响，对一系列8种发光硼芴配合物进行了广泛的实验和理论研究。由于硼原子的螺环几何结构，硼芴和配体单元垂直排列，这极大地影响了分子的柔韧性及其固态结构。通过与密切相关的二苯基类似物进行比较分析，我们展示了这些结构特征如何影响所研究化合物的热、光致发光和电荷迁移行为。晶体结构分析表明，分子主要通过相邻分子垂直排列的硼芴和配体部分之间形成的C-HO和C-Hπ相互作用相连，分别作为电子密度的互补供体和受体。这也有效地防止了分子进行不利的π堆积接触。此外，结构分析表明，由于OBN杂环畸变和硼芴-配体平面的相互移动，硼芴配合物具有相当程度的柔韧性。这些效应的大小严格取决于配体结构，相对于BPh类似物，可能导致量子产率值升高或降低，而吸收和发射波长受到轻微影响。固态样品的光物理参数测量表明，所研究的配合物在结晶态下比在非晶薄膜中是更好的发光体。TD-DFT和NTO计算揭示了前沿分子分布的显著变化，HOMO定域在硼芴部分。然而，由于HOMO-LUMO跃迁在几何上不利，激发发生在配体上的HOMO-1。最后，基于晶体结构中的超分子排列和在Marcus-Hush近似框架下从理论计算获得的电荷转移速率，讨论了聚集效应。结果表明，相对于非稠合的BPh配合物，硼芴配合物是更好的电子载体。
