On-Surface Covalent Linking of Organic Building Blocks on a Bulk Insulator
On-Surface Covalent Linking of Organic Building Blocks on a Bulk Insulator
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DOI：
10.1021/nn2033192
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发表时间：
2011-10-01
期刊：
影响因子：
17.1
通讯作者：
Kuehnle, Angelika
中科院分区：
文献类型：
--
作者：
Kittelmann, Markus;Rahe, Philipp;Kuehnle, Angelika
超高真空表面合成为在表面上制备热稳定和化学稳定的分子结构提供了一种很有前途的策略。管道的二维限制，在没有溶剂的情况下在更高（或更低）温度下工作的可能性，以及表面的模板效应，都有可能制备出在溶液中无法获得的化合物。此外，共价连接的共轭分子允许有效的电子传递，因此，对未来的分子电子学应用特别感兴趣。考虑到这些应用，电绝缘衬底必须提供分子结构与衬底表面的充分解耦。然而，到目前为止，表面合成仅在金属衬底上实现。在这里，我们展示了有机分子在块状绝缘体上的共价连接，即方解石。我们故意利用卤化物取代苯甲酸添加剂的羧酸基与表面钙离子之间的强静电相互作用来防止分子解吸并达到均解裂解温度。这允许芳基自由基和分子间偶联的形成。通过改变卤化物取代的数目和位置，我们合理地设计了得到的结构，揭示了直线结构、之字形结构和二聚体，从而为共价连接提供了明确的证据。我们的研究结果为开发分子电子学和光学应用的表面合成迈出了重要的一步，这些应用需要电绝缘而不是金属支撑衬底。
On-surface synthesis in ultrahigh vacuum provides a promising strategy for creating thermally and chemically stable molecular structures at surfaces. The two-dimensional confinement of the educts, the possibility of working at higher (or lower) temperatures in the absence of solvent, and the templating effect of the surface bear the potential of preparing compounds that cannot be obtained in solution. Moreover, covalently linked conjugated molecules allow for efficient electron transport and are, thus, particularly interesting for future molecular electronics applications. When having these applications in mind, electrically insulating substrates are mandatory to provide sufficient decoupling of the molecular structure from the substrate surface. So far, however, on-surface synthesis has been achieved only on metallic substrates. Here we demonstrate the covalent linking of organic molecules on a bulk insulator, namely, calcite. We deliberately employ the strong electrostatic interaction between the carboxylate groups of halide-substituted benzoic adds and the surface calcium cations to prevent molecular desorption and to reach homolytic cleavage temperatures. This allows for the formation of aryl radicals and intermolecular coupling. By varying the number and position of the halide substitution, we rationally design the resulting structures, revealing straight lines, zigzag structures, and dimers, thus providing clear evidence for the covalent linking. Our results constitute an important step toward exploiting on-surface synthesis for molecular electronics and optics applications, which require electrically insulating rather than metallic supporting substrates.