Synthesis and Characterization of Peralkylated Pyrrole-Fused Azacoronene
Synthesis and Characterization of Peralkylated Pyrrole-Fused Azacoronene
复制标题
全烷基化吡咯稠合氮杂苯的合成与表征
DOI：
10.1021/acs.joc.0c03042
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
Uno Hidemitsu
中科院分区：
文献类型：
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作者：
Oki Kosuke;Takase Masayoshi;Kobayashi Nagao;Uno Hidemitsu
为了研究六聚吡咯六氮杂冠烯(HPHAC)的本质性质，合成了一个比含芳基的HPHAC小12个周边乙基的六聚吡咯六氮杂冠烯(HPHAC)。X-射线衍射分析表明，由于烷基与HPHAC核之间的CH-−π相互作用，HPHAC具有平面结构和紧密堆积。与以前报道的带有12个外围芳基的HPHAc相比，这种富含电子的π体系在低电位下表现出可逆的多步氧化，并且容易与7，7，8，8-四氰基-对奎诺二甲烷形成单阳离子和电荷转移(CT)络合物。这些氧化物种在晶态下的吡咯单元的键长变化明显，表明电荷和自旋离域。从磁性判据的观点来看，~(13)C核磁共振谱中的中心碳信号的明显前场移动证实了整体芳香性。在UV-Vis/NIR光谱中，只观察到HPhAc2+的近红外吸收，而没有观察到结构相似的环[6]吡咯。磁性圆二色谱测量和含时密度泛函理论计算表明，从中心苯环到外部吡咯环的CT跃迁是分子的广谱吸收。
A hexapyrrolohexaazacoronene (HPHAC) with 12 less-bulky peripheral ethyl groups than its aryl-containing HPHAC counterpart was synthesized to investigate the innate character of HPHAC. X-ray diffraction analysis revealed that HPHAC had a planar structure and close packing because of CH−π interactions between the alkyl groups and the HPHAC core. Compared to the previously reported HPHAC decorated with 12 peripheral aryl groups, this electron-rich π-system exhibited reversible multistep oxidations at low potentials and easily formed mono- and dicationic salts and charge-transfer (CT) complexes with 7,7,8,8-tetracyano-p-quinodimethane. These oxidized species exhibited clear changes in the bond-length alternation of the pyrrole units in the crystal state, indicating charge and spin delocalization. The distinct upfield shift of the central carbon signal of the dication in the13C NMR spectrum affirms the global aromaticity from the viewpoint of a magnetic criterion. In the UV–vis/NIR spectra, broad absorption in the NIR region was observed only for HPHAC2+and not the structurally similar cyclo[6]pyrrole. Magnetic circular dichroism measurements and time-dependent density functional theory calculations revealed that the broad absorption was assigned to the CT transition from the central benzene ring to the outer pyrrole rings.