The open-shell character y of a molecule correlates with its physical properties, such as singlet fission and nonlinear optical responses. In this study, we investigated the effect of various radical substituents on the y of polyaromatic hydrocarbons (PAHs) using occupation numbers of natural orbitals calculated at the LC-UBLYP(μ=0.33)/6-311G(d,p) level of theory. It was found that radical substituents significantly altered the y of PAHs compared to non-radical substituents. Specifically, substituting methyl-type radicals such as the dicyanomethyl radical decreased the y value, while substituting allyl-2-yl-type radicals such as nitronyl nitroxide increased it. In addition, we also evaluated the correlation between the y and the HOMO–LUMO gaps and between the y and the spin-state energy gaps.

中文翻译：

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自由基取代基对多环芳烃开壳层特性影响的理论研究

分子的开壳层特征y与其物理性质相关，例如单线态裂变和非线性光学响应。在这项研究中，我们利用LC-UBLYP( μ =0.33)/6-311G(d,p)理论水平计算的自然轨道占据数，研究了各种自由基取代基对多环芳烃(PAHs) y的影响。。研究发现，与非自由基取代基相比，自由基取代基显着改变了 PAH 的y 。具体而言，取代甲基型基团例如二氰基甲基基团降低了y值，而取代烯丙基-2-基型基团例如硝基硝基氧则增加了y值。此外，我们还评估了y与HOMO-LUMO能隙之间以及y与自旋态能隙之间的相关性。