On-Surface Synthesis of C144 Hexagonal Coronoid with Zigzag Edges

Abstract

Coronoids as polycyclic aromatic macrocycles enclosing a cavity have attracted a lot of attention due to their distinctive molecular and electronic structures. They can be also regarded as nanoporous graphene molecules whose electronic properties are critically dependent on the size and topology of their outer and inner peripheries. However, because of their synthetic challenges, the extended hexagonal coronoids with zigzag outer edges have not been reported yet. Here, we report the on-surface synthesis of C144 hexagonal coronoid with outer zigzag edges on a designed precursor undergoing hierarchical Ullmann coupling and cyclodehydrogenation on the Au(111) surface. The molecular structure is unambiguously characterized by bond-resolved noncontact atomic force microscopy imaging. The electronic properties are further investigated by scanning tunneling spectroscopy measurements, in combination with the density functional theory calculations. Moreover, the values of the harmonic oscillator model of aromaticity are derived from calculations that suggest that the molecular structure is ideally represented by Clar's model. Our results provide approaches toward realizing a hexagonal coronoid with zigzag edges, potentially inspiring fabrication of hexagonal zigzag coronoids with multiple radical characters in the future.

Molecular nanoarchitectonics: unification of nanotechnology and molecular/materials science

“…Especially, extended hexagonal coronoids with zigzag outer edges still pose synthetic challenges. Sun, Yan, Yu, and co-workers have successfully synthesized a C144 hexagon with a zigzag outer edge by hierarchical Ullmann coupling and cyclodehydrogenation on a Au (111) surface (Figure 11) [127]. The precursors of this synthesis are methylnaphthalene, methylbenzene, and 3,5-dibromobenzene at 300 K on the Au (111) surface with a thickness less than a single layer.…”

“…Figure 11:On-surface synthesis of a C144 hexagon with a zigzag outer edge by hierarchical Ullmann coupling and cyclodehydrogenation on a Au(111) surface. Figure11was adapted with permission from[127], Copyright 2022 American Chemical Society. This content is not subject to CC-BY-4.0.…”

Wide Tuning of Magnetic Exchange Coupling in Nanographenes through Orbital-Symmetry Engineering

“…Magnetism in nanographenes attracts a lot of attention due to its unique properties such as weak spinorbit coupling and long spin coherence time, 1,2 compared with conventional magnetism originating from d-or f-block elements. With the advanced developments of on-surface synthesis, [3][4][5][6][7][8][9] nanographenes can be precisely fabricated with well-de ned -electron topologies upon the design of molecular precursors, [10][11][12][13] which are ideal models for investigating carbon-based magnetism and the underlying mechanism of magnetic exchange interaction. 14 To induce magnetism in nanographenes, embedding substitutional heteroatoms [15][16][17][18] or incorporating pentagon rings [19][20][21][22][23] have been employed in nanographenes upon on-surface synthesis.…”

Density functional and graph theory computations of vibrational, electronic, and topological properties of porous nanographenes

“…Porous nanographenes in several forms such as graphene molecular belts with multiple pores, porous 2D nanosheets of graphenes, tessellations of kekulenes and other polyarenes, and large extended polyarenes such as kekulenes are of considerable interest in recent years, as they exhibit novel electronic and optical properties. [1][2][3][4][5][6][7][8][9][10][11] They appear to be promising materials for transport and sequestration of environmentally toxic metal ions, pollutants, hydrogen purification, and several other applications. [1][2][3][4][5][6][7][8][9][10][11] The synthesis of kekulene, [12][13][14][15][16] a circumcised polycyclic aromatic compound with a central hole and the related nonalternant septulene, [16] has paved the way for the advent of several other holey nanographenes with intriguing electronic and optical properties.…”

“…[1][2][3][4][5][6][7][8][9][10][11] They appear to be promising materials for transport and sequestration of environmentally toxic metal ions, pollutants, hydrogen purification, and several other applications. [1][2][3][4][5][6][7][8][9][10][11] The synthesis of kekulene, [12][13][14][15][16] a circumcised polycyclic aromatic compound with a central hole and the related nonalternant septulene, [16] has paved the way for the advent of several other holey nanographenes with intriguing electronic and optical properties. Furthermore, these experiments have stimulated significant theoretical interest related to aromaticity and superaromaticity.…”