Porous Nanographenes, Graphene Nanoribbons, and Nanoporous Graphene Selectively Synthesized from the Same Molecular Precursor

We demonstrate a family of molecular precursors based on 7,10-dibromo-triphenylenes that can selectively produce different varieties of atomically precise porous graphene nanomaterials through the use of different synthetic environments. Upon Yamamoto polymerization of these molecules in solution, the free rotations of the triphenylene units around the C-C bonds result in the formation of cyclotrimers in high yields. In contrast, in on-surface polymerization of the same molecules on Au(111) these rotations are impeded, and the coupling proceeds toward the formation of long polymer chains. These chains can then be converted to porous graphene nanoribbons (pGNRs) by annealing. Correspondingly, the solution-synthesized cyclotrimers can also be deposited onto Au(111) and converted into porous nanographenes (pNGs) via thermal treatment. Thus, both processes start with the same molecular precursor and end with a porous graphene nanomaterial on Au(111), but the type of product, pNG or pGNR, depends on the specific coupling approach. We also produced extended nanoporous graphenes (NPGs) through the lateral fusion of highly aligned pGNRs on Au(111) that were grown at high coverage. The pNGs can also be synthesized directly in solution by Scholl oxidative cyclodehydrogenation of cyclotrimers. We demonstrate the generality of this approach by synthesizing two varieties of 7,10-dibromo-triphenylenes that selectively produced six nanoporous products with different dimensionalities. The basic 7,10-dibromo-triphenylene monomer is amenable to structural modifications, potentially providing access to many new porous graphene nanomaterials. We show that by constructing different porous structures from the same building blocks, it is possible to tune the energy band gap in a wide range.

Synthesis and properties of a nanographene-embedded conjugated macrocyclic nanoring via the Scholl reaction

Direct π-extension by the Scholl reaction for solution-based growth of armchair edges in curved macrocyclic hydrocarbon nanostructures is a great challenge. To date, several attempts at direct π-extension of small highly strained macrocycles have failed. Herein, we report a fixed two-bond approach for direct functionalization of small strained macrocyclic nanorings. The reaction occurs selectively to produce large π-extended molecular crowns with high yields. The design of these precursors features two peripheral C-C bonds that are readily incorporated into the extended aromatic moiety to overcome strain-induced side reactions, such as 1,2-phenyl shift. The crown-shaped macrocycle 10 showed a significant redshift (∼100 nm for absorption) compared with its precursor. This synthesis strategy could pave the way towards the π-extension of strained conjugated macrocycles and their potential applications in electron-transport devices.

Topologically diverse polycyclic aromatic hydrocarbons from pericyclic reactions with polyaromatic phospholes

Topologically divers PAHs with planar, twisted and negatively curved topologies were obtained from polycyclic phospholes using pericyclic reactions.

Laterally stretched polycyclic aromatic hydrocarbons: synthesis of dibenzophenanthroheptaphene and tetrabenzotriphenylenopyranthrene derivatives

The synthesis of new extended trapezoidal PAHs is shown. Tetra-alkylation of the most stretched derivative induces a contorted structure.