Rimmele Martina, Nogala Wojciech, Seif-Eddine Maryam, Roessler Maxie M, Heeney Martin, Plasser Felix, Glöcklhofer Florian
Department of Chemistry, Imperial College London London W12 0BZ UK
Centre for Processable Electronics, Imperial College London London W12 0BZ UK.
Org Chem Front. 2021 Jun 22;8(17):4730-4745. doi: 10.1039/d1qo00901j. eCollection 2021 Aug 23.
π-Conjugated macrocycles are molecules with unique properties that are increasingly exploited for applications and the question of whether they can sustain global aromatic or antiaromatic ring currents is particularly intriguing. However, there are only a small number of experimental studies that investigate how the properties of π-conjugated macrocycles evolve with systematic structural changes. Here, we present such a systematic experimental study of a set of [2.2.2.2]cyclophanetetraenes, all with formally Hückel antiaromatic ground states, and combine it with an in-depth computational analysis. The study reveals the central role of local and global aromaticity for rationalizing the observed optoelectronic properties, ranging from extremely large Stokes shifts of up to 1.6 eV to reversible fourfold reduction, a highly useful feature for charge storage/accumulation applications. A recently developed method for the visualization of chemical shielding tensors (VIST) is applied to provide unique insight into local and global ring currents occurring in different planes along the macrocycle. Conformational changes as a result of the structural variations can further explain some of the observations. The study contributes to the development of structure-property relationships and molecular design guidelines and will help to understand, rationalize, and predict the properties of other π-conjugated macrocycles. It will also assist in the design of macrocycle-based supramolecular elements with defined properties.
π共轭大环是具有独特性质的分子，这些性质越来越多地被用于各种应用中，而它们是否能维持全局芳香或反芳香环电流的问题尤其引人关注。然而，仅有少数实验研究探讨了π共轭大环的性质如何随系统结构变化而演变。在此，我们展示了对一组[2.2.2.2]环芳四烯的系统性实验研究，这些化合物均具有形式上的休克尔反芳香基态，并将其与深入的计算分析相结合。该研究揭示了局部和全局芳香性在解释所观察到的光电性质方面的核心作用，这些性质范围从高达1.6 eV的极大斯托克斯位移到可逆的四倍降低，这是电荷存储/积累应用中非常有用的一个特征。一种最近开发的化学屏蔽张量可视化方法（VIST）被用于深入了解沿着大环在不同平面中出现的局部和全局环电流。结构变化导致的构象变化可以进一步解释一些观察结果。这项研究有助于建立结构-性质关系和分子设计准则，并将有助于理解、合理化和预测其他π共轭大环的性质。它还将协助设计具有特定性质的基于大环的超分子元件。
