Synthesis of Two-Dimensional Polymers by On-Surface Photopolymerization

本课题的目标是通过拓扑化学光聚合在固体表面上合成有机二维聚合物（2DP）。我们的合成路线是基于两个阶段的方案：(1)单体自组装成具有光活性定位功能部分的可聚合单层；(2)通过光化学激发分子间环加成反应，共价交联成2DP。通过高分辨率扫描隧道显微镜进行结构表征。由于环加成引起的局部电子结构的强烈变化，可以清楚地识别单个新形成的共价键。这是在分子水平上研究聚合的基础。此外，用局部红外吸收光谱（纳米ftir）检测了光反应。该项目的第一部分建立在我们在fantrip（氟化蒽三甲烯）单体方面的丰富经验之上。在初步实验中，我们已经证明了石墨中光激发高能载流子的环加成的可逆性。详细的机制研究将调查基本方面，尤其是利用债券可逆性，通过自我修复过程提高结构质量。在近场显微镜的金属化探针下，通过等离子体场增强可以实现超过衍射极限的光刻。对钝化Au（111）表面的初步研究显示了有趣的结果：反应速率提高了两个数量级，但聚合度停滞在25%。这些意想不到的结果可以用金属中的热荷载流子激发来解释。我们期望从可变波长和照明强度的研究中获得基本见解，尤其是促进完全聚合。局部注入载流子的实验有望带来更多的见解，因为它们允许对电子和空穴诱导的化学进行单独的研究。其他2DP的发现是表面光聚合的一个重要里程碑。初步的实验已经确定了一个非常合适和有前途的单体进行进一步的研究。在应用方面，宏观单晶2DP的合成是一个重要的里程碑。我们的目标是优化石墨基板上的自组装。随后将在大块绝缘体表面上进行合成。最后，将评估将2DP转移到替代基板的既定方法的适用性。这是未来探索2DP应用相关性质非常重要的第一步。

The goal of this project is to advance the synthesis of organic two-dimensional polymers (2DP) by topochemical photopolymerization on solid surfaces. Our synthetic route is based on a two-staged protocol: (1) self-assembly of monomers into a polymerizable monolayer with photoactive positioning of functional moieties; (2) covalent cross-linking into the 2DP by photochemical excitation of intermolecular cycloaddition reactions. Structural characterization is performed by high-resolution scanning tunneling microscopy. Due to the strong change in the local electronic structure caused by the cycloaddition, individual newly formed covalent bonds can be clearly identified. This is the basis for studies of polymerization at the molecular level. In addition, the photoreaction is detected by local infrared absorption spectroscopy (nano-FTIR). The first part of the project builds on our extensive experience with the fantrip (fluorinated anthracene triptycene) monomer. In preliminary experiments, we have demonstrated the reversibility of cycloaddition by photoexcited energetic charge carriers in graphite. Detailed mechanistic studies will investigate fundamental aspects, not least to exploit the bond reversibility to improve structural quality through self-healing processes. Photolithography beyond the diffraction limit will be achieved by plasmonic field enhancement under metallized probes of near-field microscopes. Preliminary studies on passivated Au(111) surfaces showed interesting results: The reaction rate is enhanced by two orders of magnitude, but the degree of polymerization stagnates at 25%. These unexpected results can be interpreted in terms of hot charge carrier excitation in the metal. We expect fundamental insights from studies with variable wavelength and illumination intensity, not least to facilitate complete polymerization. Experiments with local injection of charge carriers promise additional insights, as they allow the separate study of electron- and hole-induced chemistry. The exploration of other 2DP is an important milestone for on-surface photopolymerization. Preliminary experiments have identified a very suitable and promising monomer for further studies. In terms of applications, the synthesis of macroscopic monocrystalline 2DP is an important milestone. Our targeted approach is to optimize the self-assembly on graphitic substrates. This will be followed by synthesis on bulk insulator surfaces. Finally, the applicability of established methods for transferring 2DP to alternative substrates will be evaluated. This is a very important first step for the future exploration of application relevant properties of 2DP.