On-surface synthesis of carbon nanostructures with non-benzenoid and non-alternant topology

选择性自下而上合成sp2碳纳米结构为获得具有特殊(光电)电子性能的新型材料提供了一条通用的途径。最好的例子包括石墨烯纳米带和纳米石墨烯，它们已经通过原子精度的表面合成成功地制备出来。到目前为止，主要关注的是具有苯环和交替拓扑结构的系统。这些体系由形成六角环的sp2碳原子组成，通过尺寸、形状和边缘结构可以对它们的电子性质进行有限的控制。改变这些sp2碳纳米结构性质的另一种尚未成熟的替代方法是以非六角形的方式改变它们的拓扑结构，例如通过引入五角环和七角环。根据理论考虑和我们对选定体系的实验结果，得到的非苯类和非交替的pi-电子系统具有独特的(光学)电子和其他性质。在这里，我们建议采用溶液合成/表面合成相结合的方法，在超高真空条件下在金属和金属氧化物表面获得结构良好的非苯类和非交替拓扑的sp2碳纳米结构。选择性将通过前体设计、表面相互作用、表面反应动力学控制和其他手段相结合来控制。这种方法结合了希尔特集团在有机合成方面的专业知识和戈特弗里德集团的表面科学能力，并在长期的合作中得到了完善。本提案针对的产品包括长程周期性的蔚蓝和偶氮聚合物、基于蔚蓝和偶氮结构元素的非交替碳纳米带以及非交替的环芳烃。产品的结构和电学性质将通过扫描探针显微镜/光谱、X射线和紫外光电子光谱、X射线吸收光谱以及光学光谱进行详细表征。这些补充技术还将用于监测表面反应和机理研究，旨在进一步发展表面合成原理。

The selective bottom-up synthesis of sp2 carbon nanostructures provides a versatile route to novel materials with unusual (opto)electronic properties. Prime examples include graphene nanoribbons and nanographenes, which have been successfully prepared by on-surface synthesis with atomic precision. So far, the main focus has been on systems with benzenoid and alternant topology. These systems are composed of sp2 carbon atoms forming hexagonal rings, and limited control over their electronic properties is possible through size, shape, and edge structure. An alternative and not yet well-developed method to modify the properties of these sp2 carbon nanostructures is to change their topology in a non-hexagonal manner, for example by introducing pentagonal and heptagonal rings. The resulting non-benzenoid and non-alternant pi-electron systems have unique (opto)electronic and other properties, according to theoretical considerations and our experimental results for selected systems. Here, we propose to employ a combined solution synthesis / on-surface synthesis approach to achieve structurally well-defined sp2 carbon nanostructures with non-benzenoid and non-alternant topology on metal- and metal-oxide surfaces in ultrahigh vacuum. Selectivity will be steered by a combination of precursor design, surface interaction, kinetic on-surface reaction control, and other means. This methodology combines the expertise in organic synthesis from the Hilt group with the surface science competence in the Gottfried group and has been refined during a long-standing collaboration. The products targeted in this proposal include long-range periodic azulene and azupyrene polymers, non-alternant carbon nanoribbons based on azulene and azupyrene structural elements, as well as non-alternant cycloarenes. The structural and electronic properties of the products will be characterized in detail by scanning probe microscopies/spectroscopies, X-ray and UV photoelectron spectroscopies, X-ray absorption spectroscopy, as well as optical spectroscopies. These complementary techniques will also be used for the monitoring of the on-surface reactions and for mechanistic studies, which aim at the further development of the principles of on-surface synthesis.