Curved Polycyclic Aromatic Molecules That Are π-Isoelectronic to Hexabenzocoronene
Curved Polycyclic Aromatic Molecules That Are π-Isoelectronic to Hexabenzocoronene
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DOI：
10.1021/ja3054354
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发表时间：
2012-08-22
影响因子：
15
通讯作者：
Miao, Qian
中科院分区：
文献类型：
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作者：
Luo, Jiye;Xu, Xiaomin;Miao, Qian
这里报道了两种弯曲的pi-分子，它们是pi-等电子的平面六苯并冠烯(HBC)，但由于嵌入的七元环或由于峡区的原子拥挤而被迫脱离平面。在HBC中嵌入一个七角形分子会产生一种新的马鞍形分子1，就平均高斯曲率而言，其pi主干的弯曲程度略低于先前报道的[7]环烯，但令人惊讶的是，它比[7]环烯要坚硬得多。在新的六苯并(HBP)2a，b的衍生物中，过度拥挤的峡区导致手性扭曲和反折叠构象。1和2a，b的成功合成与将烷氧基引入到六苯基苯的前所未有的位置有关。发现2b的红色扭曲异构体在高温下异构化为黄色的反折叠构象。这一发现以及对热异构化热力学和动力学的研究，加深了人们对HBP构象的早期认识。在晶体中，1缺乏相邻分子之间的pi-pi相互作用，而扭曲的-2a既表现出面对面的相互作用，也表现出边对面的pi-pi相互作用。Twisted-2b被发现在薄膜晶体管中起到p型半导体的作用，但1的薄膜似乎是绝缘的，这可能是由于缺乏pi-pi相互作用。通过对1中三种不同类型的曲率和2b的两种异构体的研究，揭示了pi面曲率在决定前线分子轨道能级及其pi-pi相互作用中的作用，因此在设计新的有机半导体时需要考虑。
Reported here are two types of curved pi-molecules that are pi-isoelectronic to planar hexabenzocoronene (HBC) but are forced out of planarity either by an embedded seven-membered ring or by atom crowding at the fjord region. Embedding a heptagon in HBC leads to a novel saddle-shaped molecule 1, whose pi-backbone is slightly less curved than the previously reported [7]circulene in terms of the average Gauss curvature, but surprisingly much more rigid than [7]circulene. Overcrowded fjord regions in novel derivatives of hexabenzoperylene (HBP) 2a,b lead to both chiral twisted and antifolded conformers. The successful synthesis of 1 and 2a,b is related to introducing alkoxyl groups to unprecedented positions of hexaphenylbenzenes. It is found that the red twisted isomer of 2b isomerizes at elevated temperature to the yellow anti-folded conformer. This finding along with the study on the thermodynamics and kinetics of the thermal isomerization has improved the early understandings on the conformation of HBP. In the crystals, 1 lacks pi-pi interactions between neighboring molecules, while twisted-2a exhibits both face-to-face and edge-to-face pi-pi interactions. Twisted-2b is found to function as a p-type semiconductor in thin film transistors, but the thin films of 1 appear insulating presumably due to lacking pi-pi interactions. By exploring three different types of curvatures in 1 and the two isomers of 2b, this study has revealed that the curvature of pi-face plays a role in determining the frontier molecular orbital energy levels and it pi-pi interactions and thus needs to be considered when one designs new organic semiconductors.