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Exploring synthetic approaches to non-alternant ring topologies in graphene nanostructures

Subject Area Polymer Materials
Term from 2019 to 2023
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 429265950
 
Final Report Year 2023

Final Report Abstract

Local departure from the pristine honeycomb lattice of graphene via the introduction of non-alternant ring topologies has lasting influences in the form of local alterations in intrinsic properties, e.g. 1) odd-membered rings locally break the bipartite character of honeycomb lattice inducing modifications in the Bloch wavefunctions, 2) local curvature and strain fields may lead to altered overlap of pz orbitals leading to changes in π-electron densities, and 3) the Dirac equation used to describe the behavior of electrons in a honeycomb lattice has to be locally modified, to name a few. Such factors, taken together, imply that the introduction of non-alternant ring topologies provides a novel route to tailor the intrinsic electronic, transport, optical, and chemical properties of pristine graphene nanostructures. However, so far, the synthesis of non-alternant rings has been achieved mostly via the non-equilibrium route, and there is thus an impending need to undertake a rational approach toward their precision fabrication. In this joint Swiss-German proposal, we have brought together the TU Dresden, a leader in synthetic nanocarbon, and leaders in fundamental and applied surface science at Empa to establish a new field of research in exploring synthetic approaches to nonalternant ring topologies in graphene nanostructures, especially azulene-embedded NGs. The Empa is known for having the largest availability of UHV surface science equipment worldwide. Within this project period, different classes of azuleneembedded NGs with closed-shell or open-shell ground states were synthesized with the combination of in-solution and on-surface chemistry, including cyclohepta[def]fluorene-based diradicaloids, azulene-embedded [10]helicene as well as non-benzenoid nanographenes with the defect-induced π-magnetism, etc. We also develop a modular synthetic strategy towards diverse azulene-embedded PAHs by a tandem Suzuki coupling and base-promoted Knoevenagel-type condensation with good yields and great structural versatility. Moreover, we also obtained the azulene-embedded graphene nanoribbons from the predesigned precursors, in which the related works are under preparation. Overall, this proposal has stimulated the mobility of researchers between both countries within this key and strategic field of research, which opened up a new research direction in nanographene chemistry.

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