Stuyver Thijs, Danovich David, Shaik Sason
Department of Organic Chemistry and the Lise Meitner-Minerva Centre for Computational Quantum Chemistry , The Hebrew University , Jerusalem 91904 , Israel.
Algemene Chemie , Vrije Universiteit Brussel , Pleinlaan 2 , 1050 Brussels , Belgium.
J Phys Chem A. 2019 Aug 15;123(32):7133-7141. doi: 10.1021/acs.jpca.9b06096. Epub 2019 Jul 31.
The present contribution uses a valence bond (VB) perspective to consider the captodative substitution strategy, a method to enhance the diradical character of (potentially aromatic) compounds. We confirm the qualitative reasoning that has generally been used to rationalize the diradical-character-enhancing effect of captodative substitution: this type of substitution scheme disproportionally stabilizes specific Dewar/diradical(oid) VB structures, thus increasing their weight in the full ground-state wave function. Furthermore, we assess the effect of captodative substitution on the aromaticity of the considered compound. We observe a clear trade-off between diradical character and aromaticity for our model systems: as one of these properties increases, the other decreases. This finding is especially significant within the field of single-molecule electronics because it enables unification of the previously observed inverse proportionality between the aromaticity of a compound and the magnitude of conductance through that molecule, with the observed proportionality between diradical character and the magnitude of conductance associated with a compound. To some extent, both properties, i.e., aromaticity and diradical character, appear to be the flip-sides of the same coin.
本文采用价键（VB）视角来探讨捕获-给体取代策略，这是一种增强（潜在芳香性）化合物双自由基特性的方法。我们证实了通常用于解释捕获-给体取代增强双自由基特性效应的定性推理：这种取代方案能不成比例地稳定特定的杜瓦/双自由基（类）VB结构，从而增加它们在整个基态波函数中的权重。此外，我们评估了捕获-给体取代对所考虑化合物芳香性的影响。对于我们的模型体系，我们观察到双自由基特性和芳香性之间存在明显的权衡：当其中一个性质增加时，另一个性质就会降低。这一发现在单分子电子学领域尤为重要，因为它能够将先前观察到的化合物芳香性与通过该分子的电导大小之间的反比例关系，与观察到的双自由基特性与化合物相关电导大小之间的正比例关系统一起来。在某种程度上，芳香性和双自由基特性这两个性质似乎是同一枚硬币的两面。
