Abstract
Multiple fused pentagon–heptagon pairs are frequently found as defects at the grain boundaries of the hexagonal graphene lattice and are suggested to have a fundamental influence on graphene-related materials. However, the construction of sp2-carbon skeletons with multiple regularly fused pentagon–heptagon pairs is challenging. In this work, we found that the pentagon–heptagon skeleton of azulene was rearranged during the thermal reaction of an azulene-incorporated organometallic polymer on Au(111). The resulting sp2-carbon frameworks were characterized by high-resolution scanning probe microscopy techniques and feature novel polycyclic architectures composed of multiple regularly fused pentagon–heptagon pairs. Moreover, the calculated analysis of its aromaticity revealed a peculiar polar electronic structure.
Highlights
Multiple fused pentagon−heptagon pairs are frequently found as defects at the grain boundaries of the hexagonal graphene lattice and are suggested to have a fundamental influence on graphene-related materials
I n the hexagonal lattice of graphene, nanostructures of fused pentagon−heptagon pairs are found as defects at grain boundaries.[1−6] Numerous calculations have suggested that controlling these “defect” structures is essential for tuning the properties of graphene-based materials.[5,7−15] The unsaturated pentagon−heptagon bicyclic hydrocarbon, named azulene, is a classic of organic chemistry.[16]
On-surface synthesis is emerging as a new method with remarkable success in fabricating novel sp2-carbon nanostructures that are often inaccessible by conventional organic synthesis.[25−30] Typically, molecular precursors are sublimed onto metal surfaces under ultrahigh vacuum (UHV) conditions, followed by thermally induced surface-catalyzed reactions.[25,31,32]
Summary
Did not find fully closed nanorings (Figure S3). there were several nanostructures (5) arising from polymeric precursors (Figure 3a). The formed radical species attacked the neighboring azulenediyl moieties, triggering a chain reaction through repetitive steps of homoallyl-cyclopropylcarbinyl-radical-rearrangement/1,2-hydrogen-shift/interazulenediyl-radical-attack (Scheme S1). This sequence would eventually lead to an sp2-carbon skeleton with multiple fused pentagon−heptagon pairs. Our results can pave the way for new sp2carbon frameworks with nonhexagons Investigation of their potentially intriguing properties, such as an open-shell electronic structure, will be promising for spintronic applications.[21,34,61] the precise construction of multiple fused pentagon−heptagon pairs can facilitate the understanding of topologically nontrivial defects in graphene.[6].
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