Interplay between Aromaticity and Radicaloid Character in Nitrogen-Doped Oligoacenes Revealed by High-Level Multireference Methods,The Journal of Physical Chemistry A

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Interplay between Aromaticity and Radicaloid Character in Nitrogen-Doped Oligoacenes Revealed by High-Level Multireference Methods
The Journal of Physical Chemistry A ( IF 2.7 ) Pub Date : 2018-11-14 00:00:00 , DOI: 10.1021/acs.jpca.8b09046
Max Pinheiro ₁ , Anita Das ₂ , Adelia J. A. Aquino _{2,

3,

4} , Hans Lischka _{2,

4,

5} , Francisco B. C. Machado ₁

Affiliation

Aromaticity is a multivariable concept in organic chemistry that plays a central role for understanding the structure, stability, and reactivity of polycyclic aromatic hydrocarbons (PAHs). Several types of PAHs are characterized as singlet biradicaloid species and their chemical stability is intimately linked to the degree of aromatic character. In this study, theoretically designed routes to tune the biradical character (and thereby its chemical stability) of nitrogen-substituted octacenes have been investigated on the basis of the high-level multireference averaged quadratic coupled-cluster MR-AQCC method necessary for the appropriate description of polyradicaloid systems. The influence of nitrogen centers on the aromaticity of octacene is probed through structural (HOMA) and electron localization (ELF) indices by comparing the N- against NH-doping cases. These analyses reveal that the aromaticity and biradical character of octacene is only slightly affected by replacing one pair of CH groups with N atoms, i.e., by N-doping. However, a significant aromatic stabilization can be obtained when NH-doping is applied at the inner octacene rings; this is also accompanied by an overall decrease of the open-shell character, as evidenced by the gradual quenching of the unpaired electrons and increase in the singlet–triplet splittings when the NH doping groups are moved toward the center of the octacene molecule. Our findings aid in the rational design of new PAH compounds with balanced biradicaloid character and chemical stability which is important, e.g., for practical applications in organic solar cells based on the singlet-fission mechanism.

中文翻译：

高水平多参考方法揭示氮掺杂寡聚体的芳香性和自由基基团之间的相互作用

芳香性是有机化学中的一个多变量概念，对于理解多环芳烃（PAHs）的结构，稳定性和反应性起着核心作用。几种类型的PAHs被表征为单重双自由基类，其化学稳定性与芳香性程度密切相关。在这项研究中，基于适当描述所必需的高级多参考平均二次耦合簇MR-AQCC方法，研究了理论上设计的途径来调节氮取代辛烷的双自由基特性（从而调节其化学稳定性）。多自由基系统。通过比较N-和NH掺杂的情况，通过结构（HOMA）和电子局部化（ELF）指数来探讨氮中心对并八苯芳香性的影响。这些分析表明，通过用N原子取代一对CH基团，即通过N掺杂，对并辛基的芳香性和双自由基特性仅稍有影响。但是，当在内部并八苯环上进行NH掺杂时，可以获得显着的芳族稳定度。当NH掺杂基团移向并八苯分子的中心时，未配对电子的逐渐猝灭和单重态-三重态分裂的增加也证明了开壳特性的整体降低。

更新日期：2018-11-14

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