Exploring New Carbon Allotropes and Nanographenes on Surfaces

Abstract

The quest for planar sp2-hybridized carbon allotropes other than graphene has stimulated substantial research efforts because of their predicted unique mechanical, electronic, and transport properties. However, the syntheses of these nonbenzenoid networks remain challenging due to the lack of reliable protocols for generating nonhexagonal rings. We have developed various on-surface synthesis strategies by which straight polymer chains are linked to form the nonbenzenoid carbon networks. In this way, we synthesized biphenylene network, a new carbon allotrope with 4-6-8-membered rings, which is metallic already at very small dimensions. Similarly, we generated phagraphene nanoribbons, which are based on 5-6-7-membered rings.Acenes are another interesting class of carbon materials that have fascinated chemists and physicists due to their potential for use in organic electronic applications. We show the synthesis of tridecacene (13ac) and pentadecacene (15ac), the longest acenes known to date, via multistep single-molecule manipulation of suitable precursor molecules on Au(111). We find antiferromagnetic open-shell ground state electron configurations for both acenes. 15ac shows a low-bias spin-excitation feature, indicating a singlet-triplet gap of around 124 meV. Investigation of 15ac complexes with up to 6 gold atoms suggest considerable multiradical contributions to the electronic ground state of 15ac.Altering the electronic and magnetic properties of carbon-based nanomaterials can also be achieved by doping with heteroatoms. We present an access to a variety of nitrogen-containing 0D and 1D carbon nanostructures including planar and curved cycloarenes with different cavities as well as N-doped graphene nanoribbons.