Jorner Kjell, Jahn Burkhard O, Bultinck Patrick, Ottosson Henrik
Department of Chemistry - Ångström Laboratory , Uppsala University , Box 523 , 751 20 Uppsala , Sweden . Email:
SciClus GmbH & Co. KG , Moritz-von-Rohr-Str. 1a , 07745 Jena , Germany.
Chem Sci. 2018 Feb 19;9(12):3165-3176. doi: 10.1039/c7sc05009g. eCollection 2018 Mar 28.
Cyclic conjugation that occurs through-space and leads to aromatic properties is called homoaromaticity. Here we formulate the homoaromaticity concept for the triplet excited state (T) based on Baird's 4 rule and validate it through extensive quantum-chemical calculations on a range of different species (neutral, cationic and anionic). By comparison to well-known ground state homoaromatic molecules we reveal that five of the investigated compounds show strong T homoaromaticity, four show weak homoaromaticity and two are non-aromatic. Two of the compounds have previously been identified as excited state intermediates in photochemical reactions and our calculations indicate that they are also homoaromatic in the first singlet excited state. Homoaromaticity should therefore have broad implications in photochemistry. We further demonstrate this by computational design of a photomechanical "lever" that is powered by relief of homoantiaromatic destabilization in the first singlet excited state.
通过空间发生并导致芳香性的环状共轭被称为同芳香性。在此，我们基于贝尔德规则4为三重激发态（T）阐述同芳香性概念，并通过对一系列不同物种（中性、阳离子和阴离子）进行广泛的量子化学计算对其进行验证。通过与著名的基态同芳香分子比较，我们发现所研究的化合物中有五种表现出强烈的T同芳香性，四种表现出弱同芳香性，两种是非芳香性的。其中两种化合物先前已被确定为光化学反应中的激发态中间体，我们的计算表明它们在第一单线态激发态中也是同芳香性的。因此，同芳香性在光化学中应具有广泛的意义。我们通过计算设计一种光机械“杠杆”进一步证明了这一点，该“杠杆”由第一单线态激发态中同反芳香性失稳的缓解提供动力。
