Synthesis of Two-Dimensional Polymers by On-Surface Photopolymerization

本项目的目标是通过在固体表面上的拓扑化学光聚合来促进有机二维聚合物(2DP)的合成。我们的合成路线是基于两步方案：(1)单体自组装成具有光活性的官能团定位的可聚合单层；(2)通过分子间环加成反应的光化学激发将共价交联成2DP。用高分辨率扫描隧道显微镜进行了结构表征。由于环加成引起的局域电子结构的强烈变化，可以清楚地识别出个别新形成的共价键。这是在分子水平上研究聚合反应的基础。此外，还利用局部红外吸收光谱(Nano-FTIR)对光反应进行了检测。该项目的第一部分建立在我们对FANTRIP(氟化三苯并三乙烯)单体的丰富经验的基础上。在初步实验中，我们证明了石墨光激发载流子环加成反应的可逆性。详细的机理研究将研究基本方面，尤其是利用键的可逆性通过自我修复过程来提高结构质量。在近场显微镜金属化探头作用下，等离子体场增强可以实现超衍射极限的光刻。对钝化Au(111)表面的初步研究表明：反应速度提高了两个数量级，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电荷载流子激发来解释。我们期待从不同波长和光照强度的研究中获得基本的见解，尤其是促进完全聚合。局部注入载流子的实验提供了更多的洞察力，因为它们允许分开研究电子和空穴诱导的化学。其他2DP的探索是表面光聚合的重要里程碑。初步实验确定了一种非常适合于进一步研究的单体。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衬底上的自组装。随后将在块状绝缘子表面进行合成。最后，将评估已建立的将2DP转移到替代底物上的方法的适用性。这对于今后探索2DP的应用相关性质是非常重要的第一步。

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.