Ab initio investigation of the cyclodehydrogenation process for polyanthrylene transformation to graphene nanoribbons
Ab initio investigation of the cyclodehydrogenation process for polyanthrylene transformation to graphene nanoribbons
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DOI：
10.1038/s41524-019-0228-6
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发表时间：
2019-09-06
影响因子：
9.7
通讯作者：
Bernholc, Jerzy
中科院分区：
文献类型：
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作者：
Xiao, Zhongcan;Ma, Chuanxu;Bernholc, Jerzy
石墨烯纳米带（GNR）可以由分子前体以原子精度合成。一个突出的例子是 7 原子宽的扶手椅 GNR，由 10,10'-二溴-9,9'-联二蒽 (DBBA) 前体在金属基底上通过脱卤/聚合和环化脱氢制成。我们通过使用密度泛函理论和微移弹性带方法评估各种反应途径的能量分布来研究环化脱氢过程的关键方面。金属基底通过为产物提供更强的吸附并促进H脱附而发挥关键的催化作用。对于在 Au 上额外的 GNR 层上的聚蒽，下面的 GNR 将其与 Au 基底隔离并增加反应势垒，使聚蒽“准独立”。然而，正电荷注入可以诱导局部环化脱氢。我们发现这是由于通过芳烃离子机制和有利的轨道对称性稳定了中间态。这些结果为 GNR 合成过程中金属基底和电荷注入对环化脱氢的影响提供了机制见解，并为新石墨结构的设计和生长提供了指导。
Graphene nanoribbons (GNRs) can be synthesized from molecular precursors with atomic precision. A prominent case is the 7-atom-wide armchair GNR made from 10,10'-dibromo-9,9'-bianthryl (DBBA) precursors on metal substrates through dehalogenation/polymerization followed by cyclodehydrogenation. We investigate the key aspects of the cyclodehydrogenation process by evaluating the energy profiles of various reaction pathways using density functional theory and the nudged elastic band method. The metal substrate plays a critical catalytic role by providing stronger adsorption for products and facilitating H desorption. For polyanthrylene on an extra layer of GNR on Au, the underlying GNR insulates it from the Au substrate and increases the reaction barriers, rendering the polyanthrylene "quasi-freestanding". However, positive charge injection can induce localized cyclodehydrogenation. We find that this is due to the stabilization of an intermediate state through an arenium ion mechanism and favorable orbital symmetries. These results provide mechanistic insight into the effects of the metal substrate and charge injection on cyclodehydrogenation during GNR synthesis and offer guidance for the design and growth of new graphitic structures.