On-Surface Synthesis of Regular 2D Polymers – Novel Structures, Properties, and Synthetic Routes

项目目标是开发、研究和建立在超高真空条件下在惰性固体表面合成规则功能二维聚合物的新方法。第一部分的合成是通过直接沉积多自由基进行的，多自由基通过在表面添加物反应成C-C键合网络。这些自由基是由卤素取代基解离沉积后的前体分子在自由基沉积源（RaDeS）中产生的。新设计的RaDeS具有一个集成的冷却阶段，减少了多自由基的热能，足以允许在弱相互作用的表面上进行固定吸附。因此，与传统使用的金属表面相比，由于高单体迁移率和低反应温度的结合，可以预期具有特殊结构质量的2D聚合物的生长。合成主要集中在石墨表面，二维聚合物的结构表征将主要通过高分辨率扫描探针显微镜进行。从根本上研究了分子结构和最重要的反应参数沉积速率和反应温度对聚苯二维聚合物的影响。功能二维聚合物的合成将基于这些经验：共轭二维聚合物是由噻吩基单体合成的。它们的电子结构将通过隧道能谱和光电子能谱进行局部表征。基于卟啉的二维聚合物是由已建立的四苯基卟啉前体合成的，并通过表面金属化进行合成后的功能化。最后，我们将探索用直接沉积自由基的方法合成碳同素异形体石墨烯。由于卤化前体太不稳定，将评估使用三甲基硅基作为替代离去基。在第二部分中，将探索在稀有气体气氛中加热而不是在通常的真空条件下加热作为一种新的合成方法。由此产生的解吸温度的提高使迄今为止由于排出物过早解吸而失败的表面上的反应成为可能。研究了两种模式反应：(1)Melem缩合反应合成氮化碳。在对反应条件进行基础研究后，在可逆条件下进行反应，以规则的二维聚合物为目标。(2)硫醇在惰性表面的脱质子反应，目的是合成二硫化物桥接的二维聚合物。因此，动态共价化学将有助于平衡成规则结构。

Project aim is to develop, study and establish novel methods for the synthesis of regular functional 2D polymers on inert solid surfaces under ultra-high vacuum conditions. The syntheses in the first part are carried out through the direct deposition of poly-radicals that react into C-C bonded networks through additions on the surfaces. These radicals are generated from precursor molecules in a radical-deposition-source (RaDeS) upon deposition by the dissociation of halogen-substituents. The newly devised RaDeS features an integrated cooling stage that reduces the thermal energy of the poly-radicals sufficiently to allow for stationary adsorption on weakly interacting surfaces. Thereby, the growth of 2D polymers with exceptional structure quality can be expected, owing to the combination of high monomer mobility and low reaction temperatures, as compared to the conventionally used metal surfaces. Syntheses are focused on graphitic surfaces and structural characterization of the 2D polymers will be primarily carried out by high-resolution Scanning-Probe-Microscopy.The impact of molecular structure and the most important reaction parameters deposition rate and reaction temperature is fundamentally studied on polyphenylene 2D polymers. The synthesis of functional 2D polymers will be based on these experiences: conjugated 2D polymers are synthesized from thiophene based monomers. Their electronic structure will be characterized locally by tunneling spectroscopy and globally by photoelectron spectroscopy. Porphyrin-based 2D polymers are synthesized from established tetraphenylporphyrin precursors and post-synthetically functionalized by on-surface metalation. Finally, we will explore synthesis of the carbon allotrope graphdiyene by direct deposition of radicals. Since halogenated precursors are too unstable, using trimethylsilyl as alternative leaving group will be evaluated.In the second part, heating in a noble-gas atmosphere instead of the usual vacuum conditions will be explored as a novel synthesis approach. The resulting increase of desorption temperatures enables reactions on surfaces that have failed thus far due to premature desorption of the educts. Two model reactions will be studied: (1) Melem condensation for the synthesis of carbon nitrides. After fundamental research on the reaction conditions, regular 2D polymers will be targeted by carrying out the reaction under reversible conditions. (2) Deprotonation of thiols on inert surfaces with the goal to synthesize disulfide-bridged 2D polymers. Thereby, dynamic covalent chemistry shall facilitate equilibration into regular structures.