Effect of Edge Functionalization on the Bottom-Up Synthesis of Nano-Graphenes
Effect of Edge Functionalization on the Bottom-Up Synthesis of Nano-Graphenes
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边缘功能化对自下而上合成纳米石墨烯的影响
DOI：
10.1002/cphc.201900510
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发表时间：
2019
期刊：
影响因子：
2.9
通讯作者：
Shintaro Sato
中科院分区：
文献类型：
--
作者：
Manabu Ohtomo;Hironobu Hayashi;Kenjiro Hayashi;Hideyuki Jippo;Juanjuan Zhu;Ryunosuke Hayashi;Junichi Yamaguchi;Mari Ohfuchi;Hiroko Yamada;Shintaro Sato
我们证明了边缘功能化对纳米碳材料表面乌尔曼耦合的影响。与众所周知在Au（111）上形成蒽聚合物和扶手椅边缘石墨烯纳米带的10，10 ′-二溴-9，9 ′-联蒽基（DBBA）不同，（10-溴蒽-9-基）蒽[2，3-B：7，6-B′]二噻吩（BABAT）及其异构体，其具有与DBBA类似的结构，其中一个蒽被蒽并二噻吩取代，发现在Au上于200 °C退火后形成分子内C-C键而不是长蒽聚合物（111）。使用第一原理密度泛函理论研究了该机制，其揭示了在BABAT的情况下表面聚合不是动力学优选的。BABAT分子内C-C键的反应速率比DBBA快206倍。另一方面，DBBA双自由基中的分子内C−C键不会发生，因为逆反应更快。通过参考BABAT双自由基的电子密度，可以得出结论，噻吩官能化改变了BABAT自由基中的电子密度分布，促进了亲电加成，导致在200 °C退火后分子内的C-C键合。这些结果表明，自由基部分的设计在表面Ullmann型偶联中特别重要。
We demonstrate the effect of edge functionalization on the on‐surface Ullmann coupling of nano‐carbon materials. Unlike 10,10′‐Dibromo‐9,9′‐bianthryl (DBBA), which is widely known to form anthracene polymers and armchair‐edge graphene nanoribbons on Au(111), newly‐developed precursor named 5‐bromo‐11(10‐bromoanthracene‐9‐yl)anthra[2,3‐b : 7,6‐b′]dithiophene (BABAT) with isomers, which has similar structure as DBBA with one anthracene substituted with anthradithiophene, was found to make intramolecular C−C bonding instead of long anthracene polymers after annealing at 200 °C on Au(111). The mechanism was investigated using first‐principle density functional theory, which revealed that on‐surface polymerization is not kinetically preferred in case of BABAT. The reaction rate of intramolecular C−C bonding of BABAT is ∼206 times faster than that of DBBA. The intramolecular C−C bonding in DBBA biradicals, on the other hand, do not take place because of faster reverse reaction. By referring to electron density of BABAT biradicals, it was concluded that thiophene functionalization modifies distribution of electron density in BABAT radicals and facilitates electrophilic addition, leading to intramolecular C−C bonding after 200 °C annealing. These results indicate that the design of radical moiety is particularly important in the on‐surface Ullmann‐type coupling.