The chemical stability and the low-lying singlet and triplet excited states of BN-n-acenes (n = 1–7) were studied using single reference and multireference methodologies. From the calculations, descriptors such as the singlet-triplet splitting, the natural orbital (NO) occupations and aromaticity indexes are used to provide structural and energetic analysis. The boron and nitrogen atoms form an isoelectronic pair of two carbon atoms, which was used for the complete substitution of these units in the acene series. The structural analysis confirms the effects originated from the insertion of a uniform pattern of electronegativity difference within the molecular systems. The covalent bonds tend to be strongly polarized which does not happen in the case of a carbon-only framework. This effect leads to a charge transfer between neighbor atoms resulting in a more strengthened structure, keeping the aromaticity roughly constant along the chain. The singlet-triplet splitting also agrees with this stability trend, maintaining a consistent gap value for all molecules. The BN-n-acenes molecules possess a ground state with monoconfigurational character indicating their electronic stability. The low-lying singlet excited states have charge transfer character, which proceeds from nitrogen to boron.

中文翻译：

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BN-n-并苯的结构稳定性和低位单线态和三线态，n = 1–7

BN- n -acenes ( n = 1–7) 使用单参考和多参考方法进行了研究。从计算中，单重态-三重态分裂、自然轨道 (NO) 占据和芳香性指数等描述符用于提供结构和能量分析。硼和氮原子形成两个碳原子的等电子对，用于完全取代并苯系列中的这些单元。结构分析证实了这种效应源于在分子系统中插入了统一的电负性差异模式。共价键倾向于强烈极化，这在纯碳框架的情况下不会发生。这种效应会导致相邻原子之间的电荷转移，从而形成更坚固的结构，从而使链上的芳香性大致保持不变。单重态-三重态分裂也符合这种稳定性趋势，为所有分子保持一致的间隙值。BN-正并苯分子具有单构型特征的基态，表明它们的电子稳定性。低位单重激发态具有电荷转移特性，从氮到硼。