Experimental and Theoretical Investigations of Surface-Assisted Graphene Nanoribbon Synthesis Featuring Carbon-Fluorine Bond Cleavage
Experimental and Theoretical Investigations of Surface-Assisted Graphene Nanoribbon Synthesis Featuring Carbon-Fluorine Bond Cleavage
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DOI：
10.1021/acsnano.7b02316
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发表时间：
2017-06-01
期刊：
影响因子：
17.1
通讯作者：
Yamada, Hiroko
中科院分区：
文献类型：
--
作者：
Hayashi, Hironobu;Yamaguchi, Junichi;Yamada, Hiroko
边缘氟化石墨烯纳米带有望表现出诱人的结构和电子性质，然而，这还需要实验证明。因此，为了提供进一步的实验见解，我们利用扫描隧道显微镜和X射线光电子能谱分析，探索了一个含有部分氟化中心单元的三聚体作为前驱体分子，表明在超高真空条件下，Au(111)在350℃下热处理后，通过表面反应形成了部分边缘的氟化聚菲。在400℃下进一步的热处理会导致部分边氟化聚菲的环脱氢形成石墨烯纳米带，从而导致碳氟键的断裂，尽管它的解离能很高。大量的理论计算揭示了以脱氟为基础的反应机理，结果表明，由于H原子迁移到聚菲中含氟菲单元的末端碳而获得的关键中间结构，在显著降低碳氟键解离活化能方面起着至关重要的作用。这些结果表明，中间态的暂态结构对合成边缘氟化石墨烯纳米带具有重要意义。
Edge-fluorinated graphene nanoribbons are predicted to exhibit attractive structural and electronic properties, which, however, still need to be demonstrated experimentally. Hence, to provide further experimental insights, an anthracene trimer comprising a partially fluorinated central unit is explored as a precursor molecule, with scanning tunneling microscopy and X-ray photoelectron spectroscopy analyses, indicating the formation of partially edge fluorinated polyanthrylenes via on-surface reactions after annealing at 350 degrees C on Au(111) under ultrahigh-vacuum conditions. Further annealing at 400 degrees C leads to the cyclodehydrogenation of partially edge-fluorinated polyanthrylenes to form graphene nanoribbons, resulting in carbon fluorine bond cleavage despite its high dissociation energy. Extensive theoretical calculations reveal a defluorination-based reaction mechanism, showing that a critical intermediate structure, obtained as a result of H atom migration to the terminal carbon of a fluorinated anthracene unit in polyanthrylene, plays a crucial role in significantly lowering the activation energy of carbon fluorine bond dissociation. These results suggest the importance of transient structures in intermediate states for synthesizing edge-fluorinated graphene nanoribbons.