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Tailoring Bond Topologies in Open-Shell Graphene Nanostructures

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journal contribution
posted on 05.11.2018, 00:00 by Shantanu Mishra, Thorsten G. Lohr, Carlo A. Pignedoli, Junzhi Liu, Reinhard Berger, José I. Urgel, Klaus Müllen, Xinliang Feng, Pascal Ruffieux, Roman Fasel
Polycyclic aromatic hydrocarbons exhibit a rich spectrum of physicochemical properties depending on the size and, more critically, on the edge and bond topologies. Among them, open-shell systemsmolecules hosting unpaired electron densitiesrepresent an important class of materials for organic electronic, spintronic, and optoelectronic devices, but remain challenging to synthesize in solution. We report the on-surface synthesis and scanning tunneling microscopy- and spectroscopy-based study of two ultralow-gap open-shell molecules, namely peri-tetracene, a benzenoid graphene fragment with zigzag edge topology, and dibenzo­[a,m]­dicyclohepta­[bcde,nopq]­rubicene, a nonbenzenoid nonalternant structural isomer of peri-tetracene with two embedded azulene units. Our results provide an understanding of the ramifications of altered bond topologies at the single-molecule scale, with the prospect of designing functionalities in carbon-based nanostructures via engineering of bond topology.