Weigelt Sigrid, Bombis Christian, Busse Carsten, Knudsen Martin M, Gothelf Kurt V, Laegsgaard Erik, Besenbacher Flemming, Linderoth Trolle R
Interdisciplinary Nanoscience Center (iNANO) and Department of Physics and Astronomy, University of Aarhus, Ny Munkegade, DK-8000 Aarhus C, Denmark.
ACS Nano. 2008 Apr;2(4):651-60. doi: 10.1021/nn7004365.
Self-assembly of organic molecules on solid surfaces under ultrahigh vacuum conditions has been the focus of intense study, in particular utilizing the technique of scanning tunneling microscopy. The size and complexity of the organic compounds used in such studies are in general limited by thermal decomposition in the necessary vacuum sublimation step. An interesting alternative approach is to deposit smaller molecular precursors, which react with each other on the surface and form the building blocks for the subsequent self-assembly. This has however hitherto not been explored to any significant extent. Here, we perform a condensation reaction between aldehyde and amine precursors codeposited on a Au(111) surface. The reaction product consists of a three-spoke oligo-phenylene-ethynylene backbone with alkyl chains attached through imine coupling. We characterize the self-assembled structures and molecular conformations of the complex reaction product and find that the combined reaction and self-assembly process exhibits pronounced kinetic effects leading to formation of qualitatively different molecular structures depending on the reaction/assembly conditions. At high amine flux/low substrate temperature, compact triimine structures of high conformational order are formed, which inherit organizational motifs from structures formed from one of the reactants. This suggests a topochemical reaction. At low amine flux/high substrate temperature, open porous networks with a high degree of conformational disorder are formed. Both structures are entirely different from that obtained when the triimine product synthesized ex-situ is deposited onto the surface. This demonstrates that the approach of combined self-assembly and on-surface synthesis may allow formation of unique structures that are not obtainable through self-assembly from conventionally deposited building blocks.
在超高真空条件下，有机分子在固体表面的自组装一直是深入研究的焦点，特别是利用扫描隧道显微镜技术。此类研究中使用的有机化合物的尺寸和复杂性通常受到必要的真空升华步骤中热分解的限制。一种有趣的替代方法是沉积较小的分子前体，这些前体在表面上相互反应并形成后续自组装的构建单元。然而，迄今为止尚未对其进行任何显著程度的探索。在此，我们在共沉积在Au(111)表面的醛和胺前体之间进行缩合反应。反应产物由一个三辐条的寡聚亚苯基乙炔主链组成，烷基链通过亚胺偶联连接。我们对复杂反应产物的自组装结构和分子构象进行了表征，发现反应和自组装的联合过程表现出明显的动力学效应，根据反应/组装条件导致形成性质不同的分子结构。在高胺通量/低衬底温度下，形成了具有高构象有序性的紧密三亚胺结构，其继承了由一种反应物形成的结构的组织基序。这表明是一种拓扑化学反应。在低胺通量/高衬底温度下，形成了具有高度构象无序的开放多孔网络。这两种结构与将非原位合成的三亚胺产物沉积到表面上时获得的结构完全不同。这表明自组装和表面合成相结合的方法可能允许形成通过从传统沉积的构建单元进行自组装无法获得的独特结构。
