State Key Laboratory of Coordination Chemistry, Jiangsu Key Laboratory of Advanced Organic Materials, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China.
School of Chemistry and Chemical Engineering, Henan Normal University, Xinxiang, Henan 453007, China.
J Am Chem Soc. 2023 Feb 15;145(6):3577-3587. doi: 10.1021/jacs.2c12526. Epub 2023 Feb 6.
Aromatic polycyclic systems have been extensively utilized as structural subunits for the preparation of various functional molecules. Currently, aromatics-based polycyclic systems are predominantly generated from the extension of two-dimensional (2D) aromatic rings. In contrast, polycyclic compounds based on the extension of three-dimensional (3D) aromatics such as boron clusters are less studied. Here, we report three types of boron cluster-cored tricyclic molecular systems, which are constructed from a 2D aromatic ring, a 3D aromatic -carborane, and an alkyne. These new tricyclic compounds can be facilely accessed by Pd-catalyzed B-H activation and the subsequent cascade heteroannulation of carborane and pyridine with an alkyne in an isolated yield of up to 85% under mild conditions without any additives. Computational results indicate that the newly generated ring from the fusion of the 3D carborane, the 2D pyridyl ring, and an alkyne is non-aromatic. However, such fusion not only leads to a H chemical shift considerably downfield shifted owing to the strong diatropic ring current of the embedded carborane but also devotes to new/improved physicochemical properties including increased thermal stability, the emergence of a new absorption band, and a largely red-shifted emission band and enhanced emission efficiency. Besides, a number of bright, color-tunable solid emitters spanning over all visible light are obtained with absolute luminescence efficiency of up to 61%, in contrast to aggregation-caused emission quenching of, e.g., Rhodamine B containing a 2D-aromatics-fused structure. This work demonstrates that the new hybrid conjugated tricyclic systems might be promising structural scaffolds for the construction of functional molecules.
芳香多环体系已被广泛用作制备各种功能分子的结构单元。目前，基于芳香族的多环体系主要是通过二维（2D）芳香环的扩展来生成的。相比之下，基于三维（3D）芳香族如硼簇的多环化合物研究较少。在这里，我们报告了三种基于硼簇核的三环分子体系，它们由一个 2D 芳香环、一个 3D 芳香族 -卡硼烷和一个炔烃组成。这些新的三环化合物可以通过 Pd 催化的 B-H 活化和随后的硼烷和吡啶与炔烃的级联杂环化在温和条件下以高达 85%的分离产率轻松获得，无需任何添加剂。计算结果表明，由 3D 卡硼烷、2D 吡啶环和炔烃融合形成的新环是非芳香的。然而，这种融合不仅导致由于嵌入的卡硼烷的强对角环电流导致 H 化学位移显著向高场移动，而且还赋予了新的/改进的物理化学性质，包括增加的热稳定性、新吸收带的出现、以及发射带的大幅度红移和发射效率的提高。此外，获得了许多明亮、可调颜色的固态发射器，其绝对发光效率高达 61%，而含有 2D-芳香族融合结构的罗丹明 B 等则会发生聚集诱导的发射猝灭。这项工作表明，新的杂化共轭三环体系可能是构建功能分子的有前途的结构支架。
