Technische Universität Chemnitz, Institut für Chemie, Fakultät für Naturwissenschaften, Chemnitz, Germany.
Technische Universität Berlin, Institut für Chemie, Berlin, Germany.
Nat Chem. 2023 Mar;15(3):377-385. doi: 10.1038/s41557-022-01121-w. Epub 2023 Jan 26.
Homoaromatic compounds possess an interrupted π system but display aromatic properties due to through-space or through-bond interactions. Stable neutral homoaromatic hydrocarbons have remained rare and are typically unstable. Here we present the preparation of a class of stable neutral homoaromatic molecules, supported by experimental evidence (ring current observed by NMR spectroscopy and equalization of bond lengths by X-ray structure analysis) and computational analysis via nucleus-independent chemical shifts (NICS) and anisotropy of the induced current density (ACID). We also show that one homoaromatic hydrocarbon is a photoswitch through a reversible photochemical [1, 11] sigmatropic rearrangement. Our computational analysis suggests that, upon photoswitching, the nature of the homoaromatic state changes in its perimeter from a more pronounced local 6π homoaromatic state to a global 10π homoaromatic state. These demonstrations of stable and accessible homoaromatic neutral hydrocarbons and their photoswitching behaviour provide new understanding and insights into the study of homoconjugative interactions in organic molecules, and for the design of new responsive molecular materials.
具有离域π 体系的休克尔芳香性化合物由于空间或键的相互作用而表现出芳香性。稳定的中性休克尔芳香烃仍然很少见，而且通常不稳定。在这里，我们通过实验证据（NMR 光谱观察到的环流和 X 射线结构分析中键长的均衡）和核独立化学位移（NICS）和感应电流密度各向异性（ACID）的计算分析，提出了一类稳定中性休克尔芳香分子的制备方法。我们还表明，一种休克尔烃是通过可逆光化学 [1,11] 西格玛重排的光开关。我们的计算分析表明，在光开关后，休克尔状态的性质在其周边从更明显的局部 6π 休克尔状态变为全局 10π 休克尔状态，从而改变了休克尔状态的性质。这些稳定且易于获得的中性休克尔芳香烃及其光开关行为的证明为有机分子中同共轭相互作用的研究以及新型响应性分子材料的设计提供了新的理解和见解。
