Interplay of Aromaticity and Antiaromaticity in N-Doped Nanographenes
Interplay of Aromaticity and Antiaromaticity in N-Doped Nanographenes
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DOI：
10.1021/acs.jpca.9b11315
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发表时间：
2020-01-30
影响因子：
2.9
通讯作者：
Sundholm, Dage
中科院分区：
文献类型：
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作者：
Benkyi, Isaac;Staszewska-Krajewska, Olga;Sundholm, Dage
通过应用两种不同的计算程序-GIMIC和NICS评估了三种围绕吡咯并[3，2-B]吡咯核构建的非平面、完全共轭氮杂纳米石墨烯的芳香性。我们检查计算的磁感应电流密度（GIMIC）和核独立化学位移（NICS）。这三种表面上相似的分子之间的结构差异导致显着不同的芳香族特性。GIMIC分析表明，所研究的碗状二氮杂纳米石墨烯的3.9 nA/T的外周向异性环电流最强，其次是缺乏七元环的双[6]螺旋烯，并且对于具有七元环的双[5]螺旋烯几乎不存在。然而，最大的区别是，在两个不完全稠合的分子中，中心吡咯环具有约4.1 nA/T的显著的向阻电流，而在二氮杂纳米石墨烯中没有这样的电流。此外，当从双[5]螺旋烯移动到二氮杂纳米石墨烯时，七元环的反芳香性增加（从-2.4 nA/T到-6.0 nA/T）。所有研究系统的NICS pi，zz-XY-scan分析得出的感应电流与GIMIC结果定性一致。细微的差异可能源于GIMIC中的σ电子电流或由于系统的非平面性而导致的NICS pi，zz值的不准确性，但总体情况是相似的。
The aromaticity of three nonplanar, fully conjugated aza-nanographenes built around a pyrrolo[3,2-b]pyrrole core is assessed through the application of two different computational procedures-GIMIC and NICS. We examine the calculated magnetically induced current densities (GIMIC) and nucleus-independent chemical shifts (NICS). The structural differences between these three apparently similar molecules lead to significantly different aromatic properties. GIMIC analysis indicates that the peripheral diatropic ring current of 3.9 nA/T for the studied bowl-shaped diaza-nanographene is the strongest, followed by the double [6]helicene which lacks seven-membered rings, and is practically nonexistent for the double [5]helicene possessing seven-membered rings. The biggest difference however is that in the two not-fully-fused molecules, the central pyrrole rings possess a significant diatropic current of about 4.1 nA/T, whereas there is no such current in the diaza-nanographene. Moreover, the antiaromaticity of the seven membered rings is increasing while moving from double [5]helicene to diaza-nanographene (from -2.4 to -6.0 nA/T). The induced currents derived from NICS pi,zz-XY-scan analysis for all of the studied systems are in qualitative agreement with the GIMIC results. Subtle differences may originate from sigma-electron currents in GIMIC or inaccuracy of NICS pi,zz values due to the nonplanarity of the systems, but the general picture is similar.