Division of Theoretical Chemistry, IFM, Linköping University, SE-581 83 Linköping, Sweden.
Phys Chem Chem Phys. 2023 Jun 28;25(25):16763-16771. doi: 10.1039/d3cp00842h.
Excited-state aromaticity (ESA) and antiaromaticity (ESAA) are by now well-established concepts for explaining photophysical properties and photochemical reactivities of cyclic, conjugated molecules. However, their application is less straightforward than the corresponding process by which the thermal chemistry of such systems is rationalized in terms of ground-state aromaticity (GSA) and antiaromaticity (GSAA). Recognizing that the harmonic oscillator model of aromaticity (HOMA) provides an easy way to measure aromaticity on geometric grounds, it is therefore notable that this model is yet to be parameterized for excited states. Against this background, we here present a new parameterization of HOMA - termed HOMER - for the T state of both carbocyclic and heterocyclic compounds based on high-level quantum-chemical calculations. Considering CC, CN, NN and CO bonds and testing the parametrization using calculated magnetic data as reference, we find that the description of ESA and ESAA by HOMER is superior to that afforded by the original HOMA scheme, and that it reaches the same overall quality as HOMA does for GSA and GSAA. Furthermore, we demonstrate that the derived HOMER parameters can be used for predictive modeling of ESA and ESAA at very different levels of theory. Altogether, the results highlight the potential of HOMER to facilitate future studies of ESA and ESAA.
激发态芳香性（ESA）和反芳香性（ESAA）现已成为解释环状共轭分子光物理性质和光化学反应性的成熟概念。然而，它们的应用并不像用基态芳香性（GSA）和反芳香性（GSAA）来合理化这些体系的热化学过程那样直接。人们认识到，芳香性的谐振子模型（HOMA）为从几何角度衡量芳香性提供了一种简单的方法，因此值得注意的是，该模型尚未针对激发态进行参数化。在此背景下，我们在这里提出了一种新的基于高精度量子化学计算的 HOMA 参数化方法（称为 HOMER），用于描述碳环和杂环化合物的 T 态。考虑 CC、CN、NN 和 CO 键，并使用计算得到的磁数据作为参考来测试参数化，我们发现 HOMER 对 ESA 和 ESAA 的描述优于原始 HOMA 方案，并且与 HOMA 对 GSA 和 GSAA 的描述质量相当。此外，我们证明了衍生的 HOMER 参数可用于在非常不同的理论水平上对 ESA 和 ESAA 进行预测建模。总之，这些结果突出了 HOMER 在促进未来 ESA 和 ESAA 研究方面的潜力。
