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

选择性自底向上合成sp2碳纳米结构为具有不同寻常（光电）电子特性的新型材料提供了一条通用途径。典型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和交替拓扑结构的系统。这些系统由sp2碳原子组成，形成六边形环，并且可以通过尺寸，形状和边缘结构对其电子特性进行有限的控制。另一种尚未完善的方法是通过非六边形的方式改变sp2碳纳米结构的拓扑结构，例如通过引入五边形和七边形环。根据理论考虑和我们对所选系统的实验结果，所得到的非苯类和非交替pi电子系统具有独特的（光电）电子和其他性质。在此，我们提出采用溶液合成/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上制备具有非苯类和非交替拓扑结构的sp2碳纳米结构。选择性将由前驱体设计、表面相互作用、表面动力学反应控制和其他手段的组合来控制。这种方法结合了希尔特小组在有机合成方面的专业知识和戈特弗里德小组的表面科学能力，并在长期合作中得到了改进。本提案的目标产品包括长周期的azulene和azupyrene聚合物，基于azulene和azupyrene结构元素的非交替碳纳米带，以及非交替环芳烃。产品的结构和电子性能将通过扫描探针显微镜/光谱学、x射线和紫外光电子能谱、x射线吸收能谱以及光谱学进行详细表征。这些互补的技术也将用于表面反应的监测和机理研究，其目的是进一步发展表面合成的原理。

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.