Synthetic Tailoring of Graphene Nanostructures with Zigzag-Edged Topologies: Progress and Perspectives

Abstract

Experimental and theoretical investigations have revealed that the chemical and physical properties of graphene are crucially determined by their topological structures. Therefore, the atomically precise synthesis of graphene nanostructures is essential. A particular example is graphene nanostructures with zigzag-edged structures, which exhibit unique (opto)electronic and magnetic properties owing to their spin-polarized edge state. Recent progress in the development of synthetic methods and strategies as well as characterization methods has given access to this class of unprecedented graphene nanostructures, which used to be purely molecular objectives in theoretical chemistry. Thus, clear insight into the structure-property relationships has become possible as well as new applications in organic carbon-based electronic and spintronic devices. In this Minireview, we discuss the recent progress in the controlled synthesis of zigzag-edged graphene nanostructures with different topologies through a bottom-up synthetic strategy.

Keywords: bottom-up synthesis; doping; graphene nanoribbons; magnetism; nanographenes.

Figure 1

a) Different edge structures of graphene. b) In ZGNRs, the edge magnetism can be tailored by the ribbon width. ^[24]

Figure 2

The chemical structures of representative zigzag‐edged HBCs.

Figure 3

Circumacene‐based NGs with full zigzag‐edged structures.

Figure 4

Phenalenyl radical (8) and its resonance forms, biphenalenyls 9–11 and their resonance forms, and zethrene (12).

Figure 5

Chemical structures of zigzag‐edged NGs based on bisanthene.

Figure 6

Chemical structures of the zigzag‐edged NGs based on bisanthene.

Scheme 1

a) Synthesis of bistetracene 17. b) Structural formula of 23. c) Time‐dependent UV/Vis spectra of 17 under ambient conditions. ^[81]

Scheme 2

a) Synthetic route towards peri‐tetracene 18 and 4CN‐7 through Diels–Alder reactions of 18. b) Time‐dependent UV/Vis absorption spectra of 18. ^[65]

Figure 7

a) Synthesis of 19 on a gold surface. b) STM image of 29. c,d) STM images of 19. e) nc‐AFM image of 19. ^[67]

Figure 8

The nomenclature of higher triangular‐shaped nanographenes.

Scheme 3

Synthesis of triangulene t ‐Bu 30 with three tert‐butyl groups. ^[91]

Figure 9

a) Synthesis of triangulene 30 on a surface. b) AFM images of 30 on NaCl. c) AFM images of 30 on Cu. d) AFM images of 30 on Xe. e) The differential conductance dI/dV(V) of 30. f‐h) STM images of 30 at different voltages (f: V=−1.4 V; g: V=0.1 V; h:V=1.85 V). ^[92]

Figure 10

a) STM image of [4]triangulene (31). b) DFT‐simulated geometry of 31 on the Au(111) surface. c) dI/dV spectrum of 31 (blue curve). ^[68]

Scheme 4

Synthetic route towards [4]triangulene 31. ^[68]

Figure 11

Structural characterization of 32 on a) Cu(111) and b) Au(111) surfaces. c) dI/dV spectra of 32 (solid blue line). d,e) Experimental dI/dV maps performed at different energy positions (d: −0.62 V; e: 1.07 V). ^[94]

Scheme 5

The synthetic route towards [5]triangulene 32. ^[94]

Figure 12

a) dI/dV and b) d² I/dV ² spectra of 53. c) Spin excitation of 53. S _z denotes the spin projection quantum number. ^[99]

Figure 13

a) The formation of di‐53 by the linear fusion of 53. b) High‐resolution STM image of di‐53. c,d) Ultrahigh‐resolution STM images of di‐53. ^[99]

Scheme 6

a) Schematic illustration of the difference between white and black (or unstarred and starred) vertices for triangulene and Clar's goblet 53. b) The synthetic route towards bowtie‐shaped nanographene 53. Insert: ultrahigh‐resolution STM image of 53. ^[99]

Figure 14

Chemical structures of the rhombus nanographenes.

Scheme 7

Synthesis of 55 and 56. ^[102]

Figure 15

a) UV/Vis absorption spectra of 54, 55, and 56. ^[102] b) UV/Vis absorption spectra of 57 and 58. ^[103]

Scheme 8

Synthesis of 57 and 58. ^[103]

Figure 16

Isoelectronic structure of B‐N and C=C units.

Scheme 9

a) The resonance structures of AMY 1. b) Synthesis of 79. ^[116]

Scheme 10

Solution‐based synthesis of 82, on‐surface synthesis of N‐doped HBC 83, ^[121] and polyaromatic azaullazine chain 84. ^[122] Blue: NICS(1) value.

Scheme 11

a) NBN‐edged structure and its radical cation and isoelectronic structures. b) Synthetic routes towards NBN‐doped 88. c) The possible oxidation process of 88. ^[123]

Scheme 12

Synthesis of NBN‐doped 94.^[123

Scheme 13

Synthesis of six‐membered B₃NO₂ heterocycles 97 and 98. ^[124] .

Scheme 14

Synthesis of BNB‐edged 103 with mesityl groups. ^[126]

Scheme 15

The synthetic route towards 6‐ZGNR from the U‐shaped monomer 105 with two preinstalled methyl groups. ^[69]

Figure 17

a) STM image of Polymer‐1. b) STM image of 6‐ZGNR. c) nc‐AFM image of 6‐ZGNR. d) STM image of 6‐ZGNR on NaCl monolayer islands. ^[69]

Figure 18

a) STM image of 106. b) STM image of polymers poly‐1. c) STM image of ZGNR1. d) nc‐AFM image of ZGNR1. e) STM image of ZGNR2. f) nc‐AFM image of ZGNR2. ^[137]

Scheme 16

Synthetic strategy for NBN‐doped ZGNR1 and ZGNR2. ^[137]

Scheme 17

a) On‐surface synthesis of GNR1. b) 7‐AGNR‐extended GNR1. c) 7‐AGNR‐extended GNR3. ^[139]