We present a theoretical design for a series of multifunctional nanomaterials that exhibit superior performance in singlet fission (SF) as well as exceptional nonlinear optical (NLO) performance. Our study focuses on a systematic investigation into the aromaticity, diradical character, excited state transition and (hyper)polarizability of the [n]benzocyclobutadiene carbon nanobelt system. To provide further guidance for designing multifunctional nanomaterials, our quantum chemical calculations propose empirical rules regarding the influence of aromatics on SF and NLO: Through an exploration of SF properties, we observed significant diradical character with radical sites exclusively located at anti-aromatic positions. Furthermore, these anti-aromatic positions serve as transition sites for excited state transitions to achieve the necessary low triplet excited states energy for SF. Then, by conducting calculations on NLO properties, we ascertain that the main tensor components of first-order hyperpolarizability (βtotal) and second-order hyperpolarizability (γtotal) come from the anti-aromatic region. However, there exists a contrasting impact of anti-aromaticity on first- and second-order hyperpolarizability density. The positive and negative contributions to first-order hyperpolarizability density mainly come from both aromatic and anti-aromatic regions while for second-order hyperpolarizability density it is contradictory. This study elucidates the role of aromatic sites in multifunctional nanomaterials with respect to diradical sites, excited state transition regions, and (hyper)polarizability density distribution.

中文翻译：

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[n] 苯并环丁二烯碳纳米带结构-性能关系的理论研究：芳香性、单线态裂变和（高）极化率


我们提出了一系列多功能纳米材料的理论设计，这些材料在单线态裂变 （SF） 中表现出卓越的性能以及卓越的非线性光学 （NLO） 性能。我们的研究重点是系统研究 [n] 苯并环丁二烯碳纳米带系统的芳香性、双自由基特性、激发态转变和（超）极化性。为了为设计多功能纳米材料提供进一步的指导，我们的量子化学计算提出了关于芳烃对 SF 和 NLO 影响的经验规则：通过对 SF 特性的探索，我们观察到自由基位点仅位于反芳烃位置的显着双自由基特性。此外，这些反芳烃位置用作激发态跃迁的过渡位点，以实现 SF 所需的低三重态激发态能量。然后，通过对 NLO 特性进行计算，我们确定一阶超极化率 （βtotal） 和二阶超极化率 （γtotal） 的主要张量分量来自反芳香族区域。然而，反芳香性对一阶和二阶超极化密度存在相反的影响。对一阶超极化密度的正负贡献主要来自芳香族和反芳香族区域，而对于二阶超极化密度，则是矛盾的。本研究阐明了多功能纳米材料中芳香族位点在双自由基位点、激发态过渡区和（超）极化密度分布方面的作用。