Embedding non-hexagonal rings into sp2-hybridized carbon networks is considered a promising strategy to enrich the family of low-dimensional graphenic structures. However, non-hexagonal rings are energetically unstable compared to the hexagonal counterparts, making it challenging to embed non-hexagonal rings into carbon-based nanostructures in a controllable manner. Here, we report an on-surface synthesis of graphene-like nanoribbons with periodically embedded four- and eight-membered rings. The scanning tunnelling microscopy and atomic force microscopy study revealed that four- and eight-membered rings are formed between adjacent perylene backbones with a planar configuration. The non-hexagonal rings as a topological modification markedly change the electronic properties of the nanoribbons. The highest occupied and lowest unoccupied ribbon states are mainly distributed around the eight- and four-membered rings, respectively. The realization of graphene-like nanoribbons comprising non-hexagonal rings demonstrates a controllable route to fabricate non-hexagonal rings in nanoribbons and makes it possible to unveil their unique properties induced by non-hexagonal rings.

We report the synthesis and characterization of two hexapole [7]helicenes (H7Hs). Single crystal X-ray diffraction unambiguously confirms the molecular structure. H7H absorbs light, with distinct Cotton effect, from ultraviolet to the near-infrared (λ = 618 nm). Cyclic voltammetry reveals nine reversible redox states, consecutively from -2 to +6. These chiroptical and electronic properties of H7H are inaccessible from helicene's small homologues.

Tailoring functionalized nanostructures at the atomic scale is of importance in nanotechnology. We report on the controllable fabrication of linear polyphenyl wires by direct C–H activation and C–C coupling of para-sexiphenyl (p-6P) on an anisotropic Au(110) surface. Because of the one-dimensional spatial constraint at the surface, the equivalent C–H bonds of p-6P molecules were differentiated with various reaction probabilities. Consequently, linear polymerization of p-6P was achieved via C–C bonding at the meta-sites, with the kink formation every 6 phenylene units. On the other hand, branched polymerization was efficiently suppressed. Among such kinked polyphenyl wires, the trans conformation is predominant, compared with the cis conformation. Furthermore, exclusive C–C bond formation at the p-6P para-sites has been promoted by the neighboring terphenyl radicals, which possess reactive para-sites, resulting in the formation of straight para-polyphenyl wires instead of kinked ones. Our study demonstrates that the surface steric effect can be applied to guide the pathway of on-surface synthesis toward desired covalently bonded nanostructures.

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Linear alkanes undergo different C-C bond chemistry (coupling or dissociation) thermally activated on anisotropic metal surfaces depending on the choice of the substrate material. Owing to the one-dimensional geometrical constraint, selective dehydrogenation and C-C coupling (polymerization) of linear alkanes take place on Au(110) surfaces with missing-row reconstruction. However, the case is dramatically different on Pt(110) surfaces, which exhibit similar reconstruction as Au(110). Instead of dehydrogenative polymerization, alkanes tend to dehydrogenative pyrolysis, resulting in hydrocarbon fragments. Density functional theory calculations reveal that dehydrogenation of alkanes on Au(110) surfaces is an endothermic process, but further C-C coupling between alkyl intermediates is exothermic. On the contrary, due to the much stronger C-Pt bonds, dehydrogenation on Pt(110) surfaces is energetically favorable, resulting in multiple hydrogen loss followed by C-C bond dissociation.