Molecular Nanographenes E-Book
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- Herausgeber: Wiley-VCH
- Kategorie: Fachliteratur
- Sprache: Englisch
Explore the world’s most powerful materials with nanographene research
Graphene, comprised of a single layer of carbon atoms in a honeycomb nanostructural arrangement, is the thinnest and strongest material yet known to science. Despite that this pristine carbon allotrope exhibits a variety of outstanding properties, its zero bandgap prevents its use for some optoelectronic applications. Fragments of graphene, or nanographenes, have shown a great potential to obviate these problems, thus paving the way for the development of chiroptical and optoelectronic properties.
Molecular Nanographenes constitutes a comprehensive overview on the synthesis of these materials and their properties. Covering their widely varying morphologies, their potential applications, and their valuable chiroptical and photophysical features, it also analyzes multiple approaches to obtain nanographene by using both top-down and bottom-up methodologies. The result is a one-stop shop for materials scientists and other researchers interested in these emergent and fascinating materials.
Molecular Nanographenes readers will also find:
- A careful distinction between top-down and bottom-up approaches to nanographene synthesis
- Detailed discussion of nanographene configurations including planar, bilayer, helical, nanobelt, and many other geometries
- An authorial team with pioneering research experience in the study of nano-sized graphenes and their synthesis
Molecular Nanographenes is ideal for materials scientists, polymer chemists, solid state chemists, organic chemists, and any other researchers looking to work with shape and size-controlled flakes of graphenes.
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Veröffentlichungsjahr: 2025
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Table of Contents
Cover
Table of Contents
Title Page
Copyright
Foreword
Preface
1 Aromaticity and Antiaromaticity in Nanographenes: An Overview
1.1 Introduction
1.2 Global and Local Aromaticity
1.3 Methods to Quantify Aromaticity
1.4 The Analysis of Aromaticity in Nanographene Systems
1.5 Concluding Remarks
Acknowledgments
References
2 Covalent Patterned Functionalization of Graphene
2.1 Introduction
2.2 Substrate‐Mediated Chemical Patterning
2.3 Tip‐Induced Patterned Functionalization
2.4 Lithography‐assisted Molecular Engineering
2.5 Laser Writing
2.6 Conclusion
References
3 Nanographenes by Bottom‐up Approach: The Scholl Reaction
3.1 Introduction
3.2 Planar Nanographenes
3.3 Heterocyclic Analogs of Planar Nanographenes
3.4 Nonplanar, Curved, and Twisted Nanographenes
3.5 Heterocyclic Analogs of Nonplanar Nanographenes
3.6 Surface‐assisted (cyclo)Dehydration
3.7 Summary and Outlook
Acknowledgment
References
4 Racemization Barriers in Chiral Molecular Nanographenes
4.1 Introduction
4.2 Structural Motifs for Chirality in Nanographenes
4.3 Classification of Chiral Molecular NGs According to Their Isomerization Barriers
4.4 Flexible Nanographenes (<5 kcal mol
−1
)
4.5 Nanographenes with Spectroscopically Detectable Chirality (5–20 kcal mol
−1
)
4.6 Isolable Nanographenes (20–35 kcal mol
−1
)
4.7 Rigid Nanographenes (>35 kcal mol
−1
)
4.8 Enantioselective Synthesis of Rigid Molecular Nanographenes
4.9 Conclusion
References
5 Synthesis of Helicenes
5.1 Introduction
5.2 Characteristics of Helicenes
5.3 Synthetic Methodologies
5.4 Advanced Helicene Architectures
5.5 Summary and Outlook
Acknowledgment
References
6 Carbon Nanobelt History and Chemistry
6.1 Introduction
6.2 Synthetic Attempts to CNBs
6.3 Synthesis of CNBs
6.4 Synthesis of Related Aromatic Nanobelts
6.5 Synthesis of Topological Aromatic Nanobelts
6.6 Conclusion
References
7 Negatively Curved Nanographenes
7.1 Introduction
7.2 Negatively Curved Nanographenes Containing Seven‐Membered Rings
7.3 Negatively Curved Nanographenes Containing Eight‐Membered Rings
7.4 Structures and Stereochemical Dynamics and Properties
7.5 Negatively Curved Molecular Nanocarbons beyond Nanographenes and Bottom‐up Approaches to Carbon Schwarzites
7.6 Conclusion and Outlook
References
8 From PAH‐based Cyclophanes to Nanographenophanes
8.1 Introduction
8.2 Synthetic Considerations
8.3 Pentacenophanes (C
22
)
8.4 Indeno[2,3‐
b
]triphenylenophanes (C
25
)
8.5 Dibenzo[
c,l
]chrysenophanes (C
26
)
8.6 Dibenzo[
f,j
]picenophanes (C
30
) and Tetrabenz[
a,c,h,j
]anthracenes (C
30
)
8.7 Teropyrenophanes (C
36
)
8.8 A π‐Extended Azacorannulenophane (C
36
N)
8.9 Hexabenzocoronenophanes (C
42
)
8.10
hept
‐Hexabenzocoronenophanes (C
43
)
8.11 Summary and Outlook
References
9 Bilayer and Multilayer Nanographenes: Synthesis and Properties
9.1 Introduction
9.2 Van der Waals Molecular Nanographenes
9.3 Bilayers from Fused Radicals
9.4 Covalently Linked Bilayers
9.5 Conclusions
References
10 Large π‐Extended Carbon Nanorings: From Syntheses to Properties
10.1 Introduction
References
11 Nanographenes with Multiple Zigzag Edges
11.1 Introduction
11.2
Peri
‐Acenes
11.3 Triangular Nanographenes
11.4
Peri
‐acenoacenes
11.5 Circumarenes
11.6 Conclusion
References
12 Synthesis of Graphene Nanoribbons, Nanographenes, and Fused Aromatic Networks Through the Formation of Pyrazine Rings
12.1 Introduction
12.2 Graphene Nanoribbons and Nanographenes
12.3 Fused Aromatic Networks
12.4 Conclusions
References
13 Conjugated Nanohoops: Synthesis, Properties, and Applications
13.1 Introduction
13.2 Synthetic Strategies to Conjugated Nanohoops
13.3 Properties of Conjugated Nanohoops
13.4 Applications of Conjugated Nanohoops
13.5 Conclusions
References
14 Chiral Polycyclic Aromatic Compounds with Monkey Saddle Topologies
14.1 Introduction
14.2 Saddle Mathematics
14.3 Synthesis
14.4 X‐Ray Crystal Structures of Monkey Saddle PAHs
14.5 NICS and ACID Plots
14.6 Inversion Barriers and Chiroptical Properties
14.7 Other Monkey Saddle PAHs and Related Systems
14.8 Summary and Outlook
References
15 On‐Surface Synthesis of π‐Conjugated Polymers
15.1 Introduction
15.2 Content
15.3 Conclusions
References
16 Merging Organic Chemistry with Surface Science for the Preparation of Nanographenes
16.1 Introduction
16.2 Scanning Probe Microscopies for the Characterization of Nanographenes Obtained by Solution‐Phase Chemistry
16.3 Combining Solution‐Phase and On‐Surface Chemistry for the Synthesis of Nanographenes
16.4 Concluding Remarks
References
17 Chiral Materials from Twistacenes and Helicenes
17.1 Introduction
17.2 Twistacene‐based Materials
17.3 Helicene‐Based Materials
17.4 Future Directions
References
18 Nanographene Diradicals
18.1 Introduction
18.2 On the Origin of the Diradical State in Monocyclic Conjugated Hydrocarbons: The Case of Cyclobutadiene
18.3 Nanographene Diradical Made from Mixtures of Quinoidal Bonding States and Nonbonding States
18.4 The Diradical State in All‐Zig‐zag Polycyclic Conjugated Hydrocarbons: On the Reversed Aromatic→Quinoidal Way to Open‐Shell Nanographenes
18.5 The Diradical State as a Result of Zig‐zag Versus Arm‐chair Structures with “Mobile” Quinoidal Rings with Quinoidal → Aromatic Transformation in the Diradical State
18.6 Conclusions
Acknowledgments
References
19 Circularly Polarized Luminescence (CPL) in Nanographenes
19.1 Introduction
19.2 (1 × HBC)‐Based Chiral Nanographenes
19.3 (1 × HBC)‐Based Heteroatom‐Doped Chiral Nanographenes
19.4 2 × HBC‐Based Chiral Nanographenes
19.5 3 × HBC‐based Chiral Nanographenes
19.6 4 × HBCs‐based Chiral Nanographenes and Beyond
19.7 Summary Table and Outlook
Acknowledgments
References
20 Redox Properties of Nanographenes
20.1 Introduction
20.2 Planar Nanographene Fragments
20.3 Contorted Nanographenes with Positive and Negative Curvatures
Acknowledgments
References
21 Kekulé and Non‐Kekulé Nanographenes: A Magnetic Perspective
21.1 Introduction
21.2 Stable Open‐Shell Kekulé NGs (
S
= 0) as Quantum Units
21.3 Concealed Non‐Kekulé Nanographenes (
S
= 0)
21.4 Obvious Non‐Kekulé Nanographenes (
S
> 0)
21.5 Engineering of Magnetic Coupling in Non‐Kekulé Nanographenes
21.6 Summary and Outlook
Acknowledgments
References
Index
End User License Agreement
List of Tables
Chapter 5
Table 5.1 Examples of other synthetic approaches to helicenes involving ioni...
Table 5.2 Examples of other synthetic approaches to helicenes employing tran...
Table 5.3 Examples of other synthetic approaches to helicenes employing orga...
Chapter 8
Table 8.1 Some series of PAH and their lengths (peripheral C–H not included)...
Chapter 19
Table 19.1 Summary of the photophysical properties reported for the compound...
List of Illustrations
Chapter 1
Figure 1.1 The molecular structure of (a) hexabenzocoronene (HBC) and (b) ci...
Figure 1.2 The ring currents in circumcoronene computed with the NICS2BC met...
Figure 1.3 Two (a,b) out of the five Kekulé resonance structures of phenanth...
Figure 1.4 (a) A hyperhomodesmotic reaction for estimating the ASE of [
N
]ann...
Figure 1.5 Composite maps showing the π‐ring currents in D
6h
[
N
]annulenes (
N
Figure 1.6 Dependence of the bond length alternation (BLA, in Å) in cyclo[18...
Figure 1.7 Localization domains and bifurcation diagram of the benzene molec...
Figure 1.8 Plot of the global aromaticity of 24π‐electron carboporphine visu...
Figure 1.9 The diatropic (clockwise, blue) and paratropic (anticlockwise, re...
Figure 1.10 (a) X‐ray crystallographic structure of a nanographene with sele...
Figure 1.11 (a) The NICS‐XY‐scan method applied to coronene along the
X
axis...
Figure 1.12 (a) A cove‐edged (Clar π‐sextets highlighted in blue) and the an...
Figure 1.13 (a) Aromaticity analysis of [12]infinitene using
B
ind
surfaces (...
Figure 1.14 Aromaticity analysis of an overcrowded triply fused carbo[7]heli...
Figure 1.15 (a) Aromaticity analysis of Itami's grossly warped nanographene ...
Chapter 2
Figure 2.1 Schemic illustration of substrate‐induced patterned functionaliza...
Figure 2.2 The reaction sequence of substrate‐based bottom‐patterned fluorin...
Figure 2.3 (a) Illustration of the Diels–Alder reaction between graphene and...
Figure 2.4 Sketch of lithography‐assisted patterned hydrogenation of graphen...
Figure 2.5 Graphical representation of covalent patterning of graphene based...
Figure 2.6 Schematic diagram for the preparation of multiply patterned graph...
Figure 2.7 Reaction sequence for the preparation of hierarchically patterned...
Figure 2.8 Large‐scale STM image of the highly ordered maleimide entities fo...
Figure 2.9 Schematic description of spatially resolved fluorination of graph...
Figure 2.10 (a) Scheme of the chemical 2D patterning of graphene via laser w...
Figure 2.11 Sketch of the laser writing procedure for the fabrication of pat...
Chapter 3
Figure 3.1 Hexa‐
peri
‐hexabenzocoronene synthesis utilizing Fe‐mediated Schol...
Figure 3.2 Reagents and conditions: (a) FeCl
3
, CH
2
Cl
2
, CH
3
NO
2
, RT; (b) DDQ, ...
Figure 3.3 Reagents and conditions: (a) Cu(OTf)
2
, AlCl
3
, CS
2
, 30 °C.
Figure 3.4 Reagents and conditions: (a) DDQ, TfOH, CH
2
Cl
2
, 0 °C.
Figure 3.5 Reagents and conditions: (a) FeCl
3
, CH
2
Cl
2
, RT; (b) FeCl
3
, CH
2
Cl
2
Figure 3.6 Reagents and conditions: (a) FeCl
3
, CH
3
NO
2
, CH
2
Cl
2
, RT.
Figure 3.7 Reagents and conditions: (a) FeCl
3
, CH
2
Cl
2
, CH
3
NO
2
, RT.
Figure 3.8 Reagents and conditions: (a) DDQ, Sc(OTf)
3
, TfOH, 1,2‐dichloroben...
Figure 3.9 Unexpected Scholl reaction of 13. Reaction conditions: (a) DDQ, T...
Figure 3.10 Reagents and conditions: (a) DDQ, CH
2
Cl
2
, TfOH, 20°C; (b) DDQ, ...
Figure 3.11 Exemplary Scholl reaction of 18 accompanied by forming two octag...
Figure 3.12 Reagents and conditions: (a) FeCl
3
, CH
2
Cl
2
, RT; (b) FeCl
3
, BF
3
·O...
Figure 3.13 Cyclization conditions: (a) FeCl
3
,CH
3
NO
2
,CH
2
Cl
2
, RT; then hydraz...
Figure 3.14 Cyclization conditions: (a) DDQ, Sc(OTf)
3
, toluene, 80°C; (b) D...
Figure 3.15 Reagents and conditions: (a) DDQ, Sc(OTf)
3
, toluene, 55°C. Ar =...
Figure 3.16 Reagents and conditions: (a) FeCl
3
, CH
3
NO
2
, CH
2
Cl
2
, RT.
Figure 3.17 Reagents and conditions: (a) DDQ, TfOH, CH
2
Cl
2
, 0°C to RT; (b) ...
Figure 3.18 Saddle‐shaped nanographenes. Reagents and conditions: (a) FeCl
3
...
Figure 3.19 Bowl‐shaped nanographenes. Reagents and conditions: (a) DDQ (6e...
Figure 3.20 Carbohelicenes. Reagents and conditions: (a) DDQ (1.2–2.0equiv....
Figure 3.21 Superhelicenes. Reagents and conditions: (a) DDQ (1.0–7.8equiv....
Figure 3.22 Nanosolenoid. Reagents and conditions: (a) DDQ (1.4equiv./bond)...
Figure 3.23 Nanobelts. Reagents and conditions: (a) FeCl
3
(100 equiv.), CH
2
C...
Figure 3.24 π‐Extended 1,4‐dihydropyrrolo[3,2‐
b
]pyrroles. Reagents and condi...
Figure 3.25 Heterohelicenes. Reagents and conditions: (a) DDQ (4.5equiv.), ...
Figure 3.26 Heterosuperhelicenes. Reagents and conditions: (a) DDQ (1.1–1.2...
Figure 3.27 Boron‐containing nanographenes. Reagents and conditions: (a) DDQ...
Figure 3.28 The most known example of the on‐surface synthesis of atomically...
Figure 3.29 Reagents and conditions: (a) DDQ (3.6 equiv.), CH
2
Cl
2
/CF
3
SO
3
H (9...
Chapter 4
Figure 4.1 [5]Circulene (corannulene) and [7]circulene, examples of molecule...
Figure 4.2 Helicenes with different numbers of
ortho
‐fused benzene rings: [5...
Figure 4.3 Examples of carbon nanobelts. According to the rolling mode CNBs ...
Figure 4.4 Supertwistacene [41], showing the helical twist around the main a...
Figure 4.5 (a) Molecular nanographenes with [4]helicenes. (b) Molecular nano...
Figure 4.6 Comparison of negative curved nanographenes' racemization barrier...
Figure 4.7 (a) [8]Circulene and [8]circulene‐based curved nanographene synth...
Figure 4.8 (a) Monkey saddle nanographenes reported by Mastalerz. (b) Chiral...
Figure 4.9 (a) Helical nanographenes with narrow cove‐edges due to the prese...
Figure 4.10 (a) Configurationally stable molecular nanographenes containing ...
Figure 4.11 (a) Rigid molecular nanographenes reported by Martín et al. [76]...
Figure 4.12 First chiral molecular nanographene involving five stereogenic c...
Chapter 5
Figure 5.1 [6]Helicene
1
as the first intended and iconic representative of ...
Scheme 5.1 Photocyclodehydrogenation of stilbene‐type precursors to phenanth...
Scheme 5.2 Examples of helicene synthesis using photocyclodehydrogenation me...
Scheme 5.3 Examples of azahelicene synthesis using photocyclodehydrogenation...
Scheme 5.4 Examples of thiahelicene synthesis using photocyclodehydrogenatio...
Scheme 5.5 Synthesis of PDI [6]helicene
25
[94].
Scheme 5.6 The Scholl reaction in the synthesis of dibenzo[7]helicene
27
[11...
Scheme 5.7 Transition metal‐catalyzed intramolecular [2+2+2] cycloisomer...
Scheme 5.8 Transition metal‐catalyzed intramolecular [2+2+2] cycloisomer...
Scheme 5.9 Stoichiometric asymmetric synthesis of enantiopure fully aromatic...
Scheme 5.10 Catalytic asymmetric synthesis of enantioenriched dibenzohelicen...
Scheme 5.11 Diels–Alder [4+2] cycloaddition of (hetero)aromatic (bis)vinyl...
Scheme 5.12 Asymmetric Diels–Alder [4+2] cycloaddition of hydroaromatic (b...
Scheme 5.13 Pt‐catalyzed hydroarylation of alkynes/diynes to form the [6]hel...
Scheme 5.14 Enantioselective Au‐catalyzed multiple hydroarylation of diynes/...
Scheme 5.15 Enantioselective Au‐catalyzed hydroarylation of diynes to form t...
Scheme 5.16 Synthesis of cationic dioxa[6]helicene
81
, azaoxa[6]helicene
82
...
Scheme 5.17 Conformationally locked [4]helicene derivatives: synthesis of [4...
Scheme 5.18 Organometallic complexes of helicenes: cyclometalated platina[6]...
Scheme 5.19 Borahelicenes: the preparation of azabora[7]helicene
91
[198].
Figure 5.2 The longest helicenes and their congeners prepared to date: [16]h...
Figure 5.3 Examples of π‐extended helicenes: pyreno[7]helicene
96
[73], oxa[...
Figure 5.4 Examples of multiple helicenes: the naphtho‐fused double[7]helice...
Figure 5.5 Example of helicenoid twistacenes: supertwistacene
114
[270] (hel...
Figure 5.6 Examples of helicene‐based macrocycles: Enantiopure cyclotrimer
1
...
Chapter 6
Figure 6.1 Nanographene and a carbon nanotube.
Figure 6.2 Graphene nanoribbon and carbon nanobelt.
Figure 6.3 History of nanobelt synthesis.
Figure 6.4 Synthesis of (6,6)CNB, (8,8)CNB, and (12,12)CNB.
Figure 6.5 Structures of (
n
,
m
)CNB.
Figure 6.6 Structures of related nanobelts.
Figure 6.7 Structures of topological aromatic nanobelts.
Chapter 7
Figure 7.1 (a) A unit cell of carbon schwarzite P216; (b) partial structure ...
Scheme 7.1 Synthesis of heptagon‐embedded HBC (
1
).
Scheme7.2 Synthesis of
4a/b
and
5a/b
.
Scheme 7.3 Synthesis of
9
.
Scheme 7.4 (a) Synthesis of
15
; (b) synthesis of
20
.
Scheme 7.5 Synthesis of
24a–c
and structures of
25
and
26
.
Scheme 7.6 (a) Synthesis of circulene, Adapted from [7]; (b) synthesis of ci...
Scheme 7.7 (a) Synthesis of
33a/b
; (b) synthesis of
35
.
Scheme 7.8 (a) Synthesis of
37
; (b) synthesis of
39
.
Scheme 7.9 Synthesis of
42
and the structures of
43–47
.
Scheme 7.10 Synthesis of
49
.
Scheme 7.11 Synthesis of
53
.
Scheme 7.12 Synthesis of
55
.
Figure 7.2 Structures of cyclooctatetraene, tetraphenylene, and [8]circulene...
Scheme 7.13 (a) Synthesis of
57a/b
; (b) synthesis of
59
.
Scheme 7.14 (a) Synthesis of
62a/b/c
; (b) synthesis of
64
.
Scheme 7.15 Synthesis of
67
a and
70
b.
Scheme 7.16 (a) Synthesis of
59
in an inward approach; (b) synthesis of
73
....
Scheme 7.17 Synthesis of
75
.
Scheme 7.18 (a) Synthesis of
77
; (b) synthesis of
79
.
Figure 7.3 (a) Structures of
62b
and
80
; (b) molecular packing of
62b
in the...
Scheme 7.19 Synthesis of aromatic nanobelts and nanorings containing seven‐ ...
Figure 7.4 Structures of molecular nanocarbon merging a negatively curved na...
Figure 7.5 Negatively curved nanobelt
93
and nanocage
94
. The skeleton of
79
Chapter 8
Figure 8.1 Two series of compounds that evolve from cyclophanes to cyclic ol...
Scheme 8.1 Durola's synthesis of cyclic oligoarylene
14
and Watanabe's cycli...
Scheme 8.2 Wu and Isobe's synthesis of figure‐of eight PAH 17.
Figure 8.2 Cyclic oligoarylenes
18
and
19
.
Figure 8.3 Summary of cyclophane‐forming strategies.
Scheme 8.3 Tilley's synthesis of pentacenophane 24.
Figure 8.4 Trimeric pentacenophanes
25
–
27
.
Scheme 8.4 Tanaka's enantioselective synthesis of indeno[2,3‐
b
]triphenylenop...
Figure 8.5 Infinitene (
36
) and some of its C
48
H
24
constitutional isomers
37
–
Scheme 8.5 Itami and Ito's synthesis of dibenzo[
c.l
]chrysenophanes
43
–
48
and...
Scheme 8.6 (a) Durola's observation of a regioselective Scholl reaction. (b)...
Scheme 8.7 Merner's synthesis of dibenzo[
f,j
]picenophanes
53d
–
f
and tetraben...
Scheme 8.8 Synthetic approaches to the 1,1,
n
,
n
‐tetramethyl[
n
](2,11)teropyren...
Scheme 8.9 Synthesis of tetrabromide
65
and radical cation
62c
+
•
, ...
Scheme 8.10 Synthesis of pyridinophane
72
and its protonation.
Scheme 8.11 Bodwell and Ito's synthesis of π‐extended azacorannulenophane
78
Figure 8.6 (a) Overlapping structures of
78
(pink) and
74
(gray) calculated ...
Scheme 8.12 Müllen's synthesis of hexa‐
peri
‐hexabenzocoronenophanes
83
and
8
...
Scheme 8.13 Akine and Nabeshima's synthesis of hexa‐
peri
‐hexabenzocoronenoph...
Scheme 8.14 Isobe and Wu's synthesis of hexa‐
peri
‐hexabenzocoronenophanes
93
Scheme 8.15 Isobe and Wu's synthesis of hexa‐
peri
‐hexabenzocoronenophanes
93
Scheme 8.16 Blanco and Campaña's synthesis of
hept
‐HBC cyclophanes
102
and
1
...
Chapter 9
Figure 9.1 Persistent graphene bilayers
1
and
2
, stabilized by supramolecula...
Figure 9.2 Single crystal X‐ray structure of coronoid persistent van der Waa...
Figure 9.3 Selenium annulation of HBC derivative providing a bowl structure ...
Figure 9.4 Van der Waals bilayer
5
formed by homoaggregation of trisimide na...
Figure 9.5 Supramolecular multilayers formed by heteroaggregation of nanogra...
Figure 9.6 Diradical character of open‐shell bilayer nanographene
8
and its ...
Figure 9.7 Nanographenoid radical of hexapyrrolohexaazacoronene fused with s...
Figure 9.8 Bilayer nanographenes covalently connected through aliphatic link...
Figure 9.9 Toward helical bilayer nanographenes. First helical overlapped bi...
Figure 9.10 Family of helical bilayer nanographenes (HBNGs)
14
,
12
, and
15
w...
Figure 9.11 Potassium and rubidium organometallic bilayers
16
and
17
formed ...
Figure 9.12 Nonbenzoid [10]helicene containing bilayer nanographene
18
.
Figure 9.13 Helical trilayer nanographenes: [8]helicene‐containing nanograph...
Chapter 10
Figure 10.1 Reported examples of carbon nanorings “integrating naphthalene u...
Figure 10.2 Reported examples of double‐layer CPPs bearing partially hydroge...
Figure 10.3 Reported examples of carbon nanorings “integrating anthracene or...
Figure 10.4 Reported examples of carbon nanorings “integrating pyrene or per...
Figure 10.5 Reported examples of carbon nanorings “integrating other PAHs an...
Figure 10.6 The synthetic pathways for accessing [
n
]cyclo‐PAH macrocycles as...
Figure 10.7 The cyclonaphthylenes reported by (a) Cram, (b) Isobe, (c) Itami...
Figure 10.8 Reported examples of (a and b) [4]cyclochrysenylenes, (c) [4]cyc...
Figure 10.9 The examples of carbon nanorings consisting solely of PAHs repor...
Scheme 10.1 Du's synthesis of longitudinal π‐extended poly(
para
‐phenylene)‐b...
Figure 10.10 Longitudinally π‐extended CPP‐based polymers prepared by Du's g...
Scheme 10.2 Tovar and Jasti's synthesis of π‐extended CPP‐based polymer
62
v...
Scheme 10.3 Jasti's synthesis of π‐extended CPP‐based polymers
63
was perfor...
Chapter 11
Figure 11.1 The representative edge structures of nanographenes.
Figure 11.2 (a) Nomenclature and (b) chemical structures and the representat...
Figure 11.3 Synthetic route toward teranthene and quateranthene derivatives:...
Figure 11.4 Synthetic route toward tertetracene: (a) Pd(PPh
3
)
4
, K
2
CO
3
, tolue...
Figure 11.5 (a) Selected bond lengths of the backbone (in Å). The red/pink n...
Figure 11.6 Synthetic routes toward
peri
‐tetracene derivatives: (a) Pd(PPh
3
)
Figure 11.7 Attempted synthesis of
peri
‐pentacene derivatives: (a) Wu's appr...
Figure 11.8 Synthetic route toward
peri
‐heptacene derivatives.
Figure 11.9 (a) Structures of triangular nanographenes with three zigzag edg...
Figure 11.10 (a) A general structure of [
m
,
n
]
peri
‐acenoacenes. (b) Represent...
Figure 11.11 (a) Structures of representative circumarenes. (b) On‐surface s...
Figure 11.12 Synthetic routes for the preparation of circumcoronene derivati...
Figure 11.13 (a) Selected bond lengths of
73
(in Å) from the X‐ray crystallo...
Figure 11.14 Synthetic route toward circumpentacene derivative
76
. (a) (i)
n
Figure 11.15 (a) VT
1
H NMR spectra (aromatic region) of
1
in [D
8
] THF. (b) F...
Chapter 12
Scheme 12.1 Cyclocondensation reaction between
ortho
‐diamines and
ortho
‐quin...
Scheme 12.2 Synthesis of
NR‐10
,
NR‐20
, and
NR‐30
.
Scheme 12.3 Synthesis of
NR‐20
,
NR‐40
, and
NR‐60
.
Figure 12.1 Chemical structures of
SNG‐G
0
,
SNG‐G
1
, and
SNG‐G
...
Figure 12.2 Chemical structures of
NR‐13
,
NR‐33
, and
NR‐53
Scheme 12.4 Synthesis of
NR‐27
,
NR‐67
, and
NR‐147
.
Scheme 12.5 Synthesis of C
2
N.
Scheme 12.6 Synthesis of
aza‐COF‐1
.
Scheme 12.7 Synthesis of aza‐CMP.
Scheme 12.8 Synthesis of TIPS‐CMP.
Scheme 12.9 Synthesis of
C
5
N
and of
[30]KL‐FAN
.
Scheme 12.10 Synthesis of
CS‐COF
.
Scheme 12.11 General structure of the 2D FANs reported by the group of Hober...
Scheme 12.12 Synthesis of
[90]KL‐FAN
.
Chapter 13
Scheme 13.1 Two strategies for nanohoop formation overcoming their strain en...
Scheme 13.2 Pt‐mediated synthesis of [8]CPP by Yamago et al. [8].
Scheme 13.3 Au‐mediated synthesis of [6]CPP by Tsuchido et al. [21].
Scheme 13.4 Ni‐mediated synthesis of PF[
n
]CPPs
10
by Itami and co‐workers [3...
Scheme 13.5 Synthesis of [9]‐, [12]‐, and [18]CPP by Jasti et al. [6].
Scheme 13.6 Size‐selective synthesis of [12]CPP by Itami and co‐workers [35]...
Figure 13.1 Calculated (B3LYP/6‐31G*) HOMO and LUMO energies of [
n
]CPPs (blu...
Figure 13.2 Calculated frontier molecular orbital energies of the conjugated...
Figure 13.3 Examples of a chiral conjugated nanohoop and a lemniscular deriv...
Figure 13.4 Left: Size of C
60
and C
70
and dimension of the spheres in which ...
Figure 13.5 The porphyrin‐[10]CPP host can bind the fullerene C
60
to form a ...
Figure 13.6 Molecular structures (top) and solid‐state packing of [
n
]CPPs in...
Figure 13.7 (a) Structure of [10]CPP‐based derivatives; (b) device stack of
Figure 13.8 Schematic presentation of growth experiments. Spin‐coated [12]CP...
Chapter 14
Figure 14.1 Examples of PAHs as cut‐outs of various carbon allotropes. (a) T...
Figure 14.2 Denotation of the edges of PAHs [8]/with permission of John Wile...
Figure 14.3 Visualization of the different curvatures of the [5]‐ to [8]circ...
Figure 14.4 Examples of negatively curved PAHs with incorporated seven‐membe...
Scheme 14.1 Synthesis of chiral PAHs
4
–
6
by Campaña and co‐workers [27]/John...
Figure 14.5 Schematic representation of three surfaces with different Gaussi...
Figure 14.6 Overview of all saddle topologies from
n
=2 to 8. Adapted from ...
Scheme 14.2 PAH synthetic strategy by condensation as a key step [31]/John W...
Scheme 14.3 Synthesis of the bromotruxene precursor in four steps starting f...
Scheme 14.4 Synthesis of PAH monkey saddles
17
,
18,
and
21
from tribromotrux...
Figure 14.7 Solid‐state structure of
17
. (a) Top view of the (
R
a
,
R
a
,
R
a
) enan...
Figure 14.8 Solid‐state structure of
21
. (a–c) Different views of the (
S
a
,
S
a
Figure 14.9 Calculated NICS(1)
av
values (top) and ACID plots (bottom) of mon...
Figure 14.10 Calculated energy profile of the enantiomerization of the (
S
a
,
S
Figure 14.11 CD spectra the (
S
a
,
S
a
,
S
a
) and (
R
a
,
R
a
,
R
a
) enantiomers of monkey ...
Figure 14.12 Hexa‐
cata
‐hexabenzocoronenes
22
and its conformation found in t...
Figure 14.13 Formula and solid‐state structure of monkey saddle shaped PAH
2
...
Figure 14.14 (a) Selected examples of positively curved
N
‐PACs [37, 53, 54]....
Figure 14.15 Giant aza monkey saddle PAHs
30
(a) and
27
(b) [50]. Mesityl (l...
Figure 14.16 From monkey saddle PAHs to conjugated chiral open cages.
Chapter 15
Figure 15.1 Synthesis of ethynylene‐anthracene wires on Au(111). (a) Reactio...
Figure 15.2 Electronic structure of ethynylene‐anthracene wires on Au(111). ...
Figure 15.3 Topological quantum phase transition in the acene polymer family...
Figure 15.4 On‐surface synthesis and electronic and topological characteriza...
Figure 15.5 Topological phase transition of cumulene‐linked pentacene polyme...
Figure 15.6 Synthesis of cumulene‐linked periacene polymers (P3 and P4) on A...
Figure 15.7 Synthesis of pentalene‐linked π‐conjugated polymers (P5) on Au(1...
Figure 15.8 Synthesis of N‐containing π‐conjugated polymers (P6 and P7) by e...
Figure 15.9 Synthesis of cumulene‐linked 1D nonbenzenoid π‐conjugated polyme...
Figure 15.10 Structural characterization of ethynylene‐like linked pentacene...
Chapter 16
Figure 16.1 (a) Scanning probe microscope with a CO‐functionalized tip. AFM ...
Figure 16.2 Synthesis in solution and AFM characterization on surface of: (a...
Figure 16.3 Surface‐assisted cyclodehydrogenation reactions to obtain graphe...
Figure 16.4 Selected examples of on‐surface Ullmann couplings to obtain dive...
Figure 16.5 Additional reactions used for the on‐surface preparation of grap...
Figure 16.6 Porous nanographenes obtained by combining Ullmann couplings and...
Chapter 17
Figure 17.1 (a) Ladder‐type conjugation that is contorted into two helical n...
Figure 17.2 Synthesis of twistacene‐based graphene nanoribbons. (a)
hPDI[2]
...
Figure 17.3 (a) Dimethoxy
hPDI
(
hPDI
x
OMe
2
) ribbon series. (b) Molecular mode...
Figure 17.4 Structures from single‐crystal X‐ray diffraction of a 1 : 1 mixt...
Figure 17.5 (a) Structures of
c
hPDI[2]
s. (b) CD spectra of (
R
)‐
1
,(
S
)‐
1
, and ...
Figure 17.6 (a) Structure of
c
hPDI[2]
.
(
b) CD spectra of electrochemical swi...
Figure 17.7 (a) UV–Vis and (b) CD spectra of
c
hPDI[2]
(pink),
c
hPDI[2]
1–
...
Figure 17.8 (a) Schematic of a photodetector to demonstrate the sharpness in...
Figure 17.9 (a) Design of
PHATN
. (b) Key for building blocks. (c) PDI (red) ...
Figure 17.10 (a) Schematic illustration of our novel molecular nanoribbons,
Figure 17.11 Synthesis of the PDI‐based helicenes
NPnH
series (
n
= 2–5).
Figure 17.12 Structures of the
NPDH
,
NP3H
,
NP4H
, and
NP5H
containing 2, 3, 4...
Chapter 18
Figure 18.1 (a) Tschitschibabin diradical and the competition between closed...
Figure 18.2 Singlet to triplet energy gap (Δ
E
ST
) and diradical character in ...
Figure 18.3 Hückel energy distribution of the electronic states of squared C...
Figure 18.4 (a) Multiconfigurational character of the ground electronic stat...
Figure 18.5 Schematic representation of the electronic configurations in the...
Figure 18.6 Zethrene derivatives: zethrene, heptazethrene, octazethrene, and...
Figure 18.7 Construction of the frontier molecular orbitals of zethrene from...
Figure 18.8 For the HOMO of zethrene, the red regions are those associated w...
Figure 18.9 Left: electronic configuration mixing giving way to the diradica...
Figure 18.10 Bisphenalenylene derivatives extended by central para‐benzo, pa...
Figure 18.11 Construction of the frontier molecular orbitals of bisphenaleny...
Figure 18.12 Left: electronic configuration mixing giving way to the diradic...
Figure 18.13 Evolution of the frontier molecular orbitals obtained by the si...
Figure 18.14 Formation of
di‐2
from dimerization of
2
and the qualitat...
Figure 18.15 Graphene nanoribbons with several topological phases such as di...
Figure 18.16 Higher‐order Peierls distortion toward a full benzoquinoidal st...
Figure 18.17 Chemical structures of [n,m]acenoacenes: anthracene, [2,3]anthr...
Figure 18.18 Evolution of the frontier molecular orbitals of anthracene to p...
Figure 18.19 HOMO and LUMO orbitals of anthanthrene highlighting the zig‐zag...
Figure 18.20 Left: electronic configuration mixing giving way to the diradic...
Figure 18.21 Chemical structure of the oligorylene with 12 naphthalene repea...
Figure 18.22 Evolution of the frontier molecular orbitals of naphthalene to ...
Figure 18.23 Left: electronic configuration mixing giving way to the diradic...
Figure 18.24 Chemical structure of the oligoanthenes; bisanthene, teranthene...
Figure 18.25 Representation of the para‐ and ortho‐quinoidal forms in the cl...
Figure 18.26 Evolution of the frontier molecular orbitals of anthracene to p...
Figure 18.27 Electronic configuration mixing giving way to the diradical sta...
Figure 18.28 Decomposition of the delocalized HOMO and LUMO orbitals of quat...
Figure 18.29 Chemical structures hexabenzocoronene (right, HBCN) and circump...
Figure 18.30 Frontier molecular orbitals (HOMO) of circumpentacene from peri...
Figure 18.31 Union of two [3]triangulene in their triple ground electronic s...
Chapter 19
Figure 19.1 Chemical representation of graphene, graphene quantum dots and t...
Figure 19.2 Structural motifs that furnish chiral nanographenes.
Figure 19.3 Schematic representation a pair of enantiomeric chiral nanograph...
Figure 19.4 Hexabenzotriphenylene (HBT,
1
) and double [6]helicenes in HBC (
2
Figure 19.5 Chiral HBCs bearing a single carbohelicene (
4
,
5
) and bowl (
6
) o...
Figure 19.6 π‐Extended chiral nanographenes bearing double [6]helicenes.
Figure 19.7 Heteroatom‐doped chiral HBCs.
Figure 19.8 BN‐doped chiral nanographenes.
Figure 19.9 2‐HBCs based chiral nanographenes.
Figure 19.10 Examples of bilayer nanographenes.
Figure 19.11 3‐HBCs based chiral nanographenes.
Figure 19.12 4×HBCs based chiral nanographenes.
Chapter 20
Scheme 20.1 Several representative 2D and 3D molecular nanographenes: (a) he...
Figure 20.1 Depictions of (a) corannulene and (c) [8]CPP. Structures of (b) ...
Figure 20.2 (a) Depiction of triphenylene. (b) Structures of mono‐reduced pr...
Figure 20.3 (a) Depiction of coronene. (b) Geometry comparison of neutral co...
Figure 20.4 (a) Depiction of HBC. (b) Structure of triply reduced HBC with K
Scheme 20.2 Depictions of positive/zero/negative curvature. The arrows show ...
Scheme 20.3 Depictions of (a) tetrabenzo[
b
,
h
,
n
,
t
]tetraphenylene (C
40
H
24
) and...
Figure 20.5 (a) Depiction of Cor‐NG. The blue and orange arrows show [4]heli...
Figure 20.6 (a) Depiction of buckycatcher. (b) Geometry comparison of neutra...
Figure 20.7 (a) Depiction of WNG. Structures of (b) mono‐reduced, (c) doubly...
Figure 20.8 (a) Depiction of WNG. (b) Structure of doubly reduced WNG produc...
Scheme 20.4 Twofold reduction of COT, along with the geometry change.
Scheme 20.5 Twofold oxidation of octamethoxytetraphenylene (OMT), along with...
Figure 20.9 (a) Depiction of OPTBCOT. (b) Structure of tetra‐reduced product...
Figure 20.10 (a) Depiction of OPTBCOT. Structures of doubly reduced products...
Figure 20.11 (a) Depiction of OB8C. (b) Structure of penta‐reduced OB8C with...
Figure 20.12 (a) Depiction of [10]HBNG. Structures of triply reduced [10]HBN...
Chapter 21
Figure 21.1 (a) The Ovchinnikov's rule applied to Kekulé and non‐Kekulé NGs....
Figure 21.2 (a) Chemical structures of diradical
1
and monoradical
2
. (b) Pu...
Figure 21.3 (a) Chemical structures of open‐shell graphene radicaloids
3
,
4
,...
Figure 21.4 (a) On‐surface synthesis of Clar's goblet (
7
) on Au(111). (b) Co...
Figure 21.5 In‐solution and on‐surface synthesis of phenalenyl radical. (a) ...
Figure 21.6 (a) On‐surface synthesis of olympicenyl radical (
13
) from the co...
Figure 21.7 (a) On‐surface synthesis of spin ½ nanographene (
19
) by introduc...
Figure 21.8 (a) Structures of [3]triangulene (
20
) and its derivatives
20a
–
d
....
Figure 21.9 (a) On‐surface synthesis of [3]triangulene (
20
). (b) nc‐AFM imag...
Figure 21.10 On‐surface synthesis of [
n
]triangulene and their ultra‐high‐res...
Figure 21.11 (a) On‐surface synthesis [7]triangulene quantum ring
33
from pr...
Figure 21.12 (a) Chemical structure of achieved nanographene with an embedde...
Figure 21.13 Chemical structures of achieved non‐Kekulé NG dimers and their ...
Figure 21.14 On‐surface synthesis of diphenalenyl (
40
) from 2H‐diphenalenyl ...
Figure 21.15 On‐surface synthesis of [3]triangulene dimers and trimers and t...
Figure 21.16 (a) On‐surface synthesis of [3]triangulene‐based spin chains
49
Guide
Cover
Table of Contents
Title Page
Copyright
Foreword
Preface
Begin Reading
Index
End User License Agreement
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Molecular Nanographenes
Synthesis, Properties, and Applications
Edited by Nazario Martín and Colin P. Nuckolls
Editors
Nazario MartínUniversidad Complutense de MadridPlaza de las Ciencias28040 MadridSpain
Colin P. NuckollsColumbia University3000 BroadwayNew YorkNY 10027, USA
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Print ISBN: 978‐3‐527‐35322‐4ePDF ISBN: 978‐3‐527‐84499‐9ePub ISBN: 978‐3‐527‐84500‐2oBook ISBN: 978‐3‐527‐84501‐9
Foreword
I have tremendously enjoyed reading this book, its topic is at the forefront of modern science, it is interdisciplinary, but still strongly synthesis‐driven, and it is of both fundamental and practical relevance. I congratulate the editors on the overarching concept and on their selection of leading researchers as authors.
Chemistry is today experiencing not one, but many groundbreaking developments. Their key driving forces are the digital revolution, the enormous advances in both synthesis and theory as well as the unfolding interactions with biomedicine and materials science. What has accompanied this blooming progress is the increasing structural complexity of molecules, assemblies and particles together with the ability of emerging nanosciences to visualize such objects in real space. In these endeavours, the regular hexagon of benzene has served as a powerful module, for example, when varying the size and dimensionality of macromolecules. The occurrence of benzene building blocks in so‐called carbon nanostructures, from carbon allotropes up to carbon fibers, strongly suggests a brief historical review. What comes to mind then are the discovery of benzene by Faraday, the recognition of benzene and its derivatives as a new family of “aromatic” compounds by Hofmann, the pyrolysis of benzoic acid and determination of the molecular benzene formula as C6H6 by Mitscherlich, and the structural description of benzene proposed by Kekulé. Benzene is also the constituent of polycyclic aromatic hydrocarbons (PAHs). Remarkably enough, Clar, the founder of modern PAH chemistry, has recognized a relation between benzene ring fusion pattern and stability. While PAHs had thus played a major role in the development of modern organic chemistry, they had lost much of their appeal by the end of the last century and turned into preferred objects of toxicology. The revival of PAHs began with two events: the ability of organic chemists to increase the size of the polycycles and the groundbreaking detection of graphene as prototypical two‐dimensional material by Geim and Novoselov. PAHs thus adopted a new role as molecularly defined model fragments of graphene.
Before I look closer at the world of such nanographenes and molecules derived therefrom, aromaticity demands some more attention. Put simply, aromaticity is a characteristic of cyclic or polycyclic compounds that exhibit higher stability than expected from their formulation as conjugated π‐systems. From early on, however, aromaticity has seen quite different definitions in the literature, one based on structural concepts such as the Kekulé formula or the Robinson sextet and the other based on properties, be it a flavor, a particular (aromatic) reactivity, or a diatropic ring current. Today, the notion of global aromaticity gives firm evidence of the viability of the idea. Annulenes as higher homologues of benzene have been employed as test cases of aromaticity and of Hückel's rule, although the application of aromaticity to anything else than benzene and benzenoid compounds has been questioned. Free benzene does not occur naturally, but many industrial processes commence with the functionalization of benzene. There is thus no doubt that the huge variety of compounds which contain the benzene ring as a constituent has a tremendous scientific, industrial, and societal impact.
Benzene and most PAHs are flat, confined to the world of flatland, the land which E. A. Abbott in his “Romance of Many Dimensions” defines as the land without shadow. They are thus said to lack the attraction coming with chirality. This is no longer true, however, when the two‐dimensional sheet is distorted in the third dimension. Consider the atropisomerism of oligophenyls, the helicity of nanographenes, or the bending of PAHs to curved sheets.
Benzene is thus indispensable in the search for the design of structural complexity and for chemically moving along length scales. While π,π‐stacking or other weak intermolecular forces can serve as tools, the role of modern synthetic protocols for carbon‐carbon bond formation can hardly be overestimated. Advanced organic, organometallic, and organocatalytic methods allow the coupling of different aryl units and new cycloaddition reactions as well as aromatization and de‐aromatization processes. Two synthetic concepts that are instrumental for carbon nanostructure generation, but less established in organic chemistry should be mentioned. One is interfacial synthesis. This comprises the deposition of molecules, for example, at the air‐water interface or on metal substrates and their subsequent thermal treatment. The metal acts to promote homolytic bond cleavage and subsequent coupling of radical intermediates under ultra‐high vacuum conditions. Next to its role as catalyst, the metal can also stabilize otherwise elusive products and, more importantly, allow the visualization and manipulation of nanosized molecules by methods such as scanning tunnelling microscopy (STM) and non‐contact atomic force microscopy (nc‐AFM). The other concept is the “materials science” approach utilizing, for example, solvothermal, lithographic or pyrolytic protocols. Pyrolysis reactions are sometimes looked down as crude mix‐and‐bake techniques, but have great value, in particular when executed in preorganized phases. It is this wealth of synthetic methods from different fields of chemistry, which has stimulated a systematic increase in the size of carbon nanostructures into one, two, or three dimensions (1D, 2D, or 3D). An early, though still small example is that of hexa‐peri‐hexabenzocoronenes (HBCs) as soluble “superbenzenes” which sheds light upon synthetic, structural and functional aspects of carbon nanostructure research at the same time: these disc‐shaped molecules can be obtained by the oxidative cyclodehydrogenation of non‐planar oligophenylene precursors. They form stable discotic mesophases and their characterization by scanning probe methods has furnished current/potential curves at the single‐molecule level on the way to emerging nanoelectronics.
In the past decades, the well‐known, carbon‐rich polyphenylenes and polycyclic aromatic hydrocarbons (PAHs) have been extended to other carbon allotropes, namely the 0D fullerenes (1985) and 1D carbon nanotubes (CNTs) (1991). As already mentioned, these were followed by the most recent 2D graphene (2004). Although exhibiting different dimensionalities, they all contain fused benzene rings and, most importantly, they connect the realm of molecules with those of discrete particles and bulk materials. Actually, these new carbon nanostructures, starting with the seminal molecule of fullerene C60, were received by the community with great excitement and have profoundly promoted further developments of modern nanoscience and nanotechnology. Furthermore, their physical properties allow them to serve as active components of organic electronic devices, charge‐storage systems, and biomedical sensors. There is still much undiscovered territory out there since structural imagination has pointed toward further carbon allotropes made from benzene moieties. Attractive examples are cubic graphite in which each benzene is part of three crossing poly‐para‐phenylene chains and graphynes or graphdiynes in which benzenes are connected by acetylene or diacetylene bridges, respectively.
The disruptive discovery of 2D graphene as a new nanoform of carbon also paved the way toward unknown monolayer materials currently involving a variety of chemical elements of the Periodic Table and unveiling the emergent field of 2D materials. Nevertheless, despite the outstanding chemical and physical properties of pristine graphene, its zero electronic bandgap between the conduction (CB) and valence (VB) bands has prevented some important applications. A good case can be made for field effect transistors as omnipresent elements of printed circuits. While its outstanding charge‐carrier mobility would make graphene an important semiconductor in such “switches,” its use is severely obstructed by currents being always “on” due to the vanishing bandgap.
In sharp contrast to pristine graphene, the geometric confinement of electrons occurring in smaller lattice structures at the nanometer scale, the so‐called nanographenes (NGs), graphene nanoribbons (GNRs) and graphene quantum dots (GQDs) increases the HOMO‐LUMO energy gap, thus significantly broadening the scope of these nanocarbons for potential applications.
In a kind of top‐down approach, NGs could be synthesized by cutting carbon flakes out of graphene, and GNRs could be obtained by slicing open carbon nanotubes. Both procedures utilized harsh chemical conditions but failed to offer reliable size and shape control. A powerful alternative is the bottom‐up approach which starts from benzene‐based, monomeric building blocks and uses the methods of modern organic synthesis. It is this precision synthesis which allows the rational variation of size and morphology of graphene molecules and thus the fine control of their electronic and optical properties. Next to the length and width of ribbons, their edge‐structures play an important role, in particular, for adding the spin degree of freedom to NG‐based circuitry and for establishing exotic quantum states. Not only planar single layers, but also bowls, saddles and bilayers can be made, holes can be drilled and heteroatoms can be incorporated en route to carbon‐based molecular nanographenes. These structural modifications can also be regarded as defects in the bulk material. Such emerging cross‐talk between the fields of carbon molecules and carbon materials is particularly important for the so‐called defect engineering which is, indeed, a key concept of materials science. Size limits, in turn, are not easy to define for such synthetic aromatic compounds endowed with a graphitized area at the nanometer scale, usually defined as 1–100 nm.
The rapid development of molecularly defined carbon nanostructures makes this book a rich source of information for scientists of different backgrounds and, more importantly, can serve as starting point for a myriad of new research ideas.
Klaus Müllen
Max Planck Institute forPolymer ResearchMainz, Germany
Preface
Although the initial idea for editing a book devoted to one of the most appealing nanocarbon structures such as the so‐called molecular nanographenes stemmed from the 8th EuChemS Chemistry Congress (ECC8) held in Lisbon, Portugal, in 2022, the realization and writing of the chapters contained in this book occurred through 2024, and, eventually, the edition and publication is occurring in the current year 2025. As the editors of this successful venture, we like mentioning these years since last year 2024 we celebrated the first centennial of the less‐known paper published by J. D. Bernal reporting the structure of graphite (Proc. R. Soc. London A1924, 106, 749). Graphite, the material used in pencil lead, is composed of countless layers stacked one upon the other.
In 2004 A. Geim and K. Novoselov (Science2004, 306, 666) were able to isolate one (and a few) of these layers from graphite, despite the prediction denying the possible existence of graphene (N. D. Mermin, Phys. Rev. 1968, 176, 250) due to the lack of stability. Thus, we were very happy to celebrate the 20 years of the discovery of graphene (J. Am. Chem. Soc. 2024, 146, 32 222) as a new carbon allotrope, paving the way to a new and disruptive two‐dimensional (2D) π‐conjugated material of one carbon atom thickness. Furthermore, the outstanding properties found in graphene encouraged the search for other 2D materials from other elements of the Periodic Table, giving rise to a wide variety of 2D materials formed by one, or more, elements.
This year 2025 is another date for celebration not only within the chemical community but also by the whole scientific community. It was in 1825 when Michael Faraday (Phil. Trans. R. Soc. London1825, 115, 440), a universal scientist, discovered benzene, the foundational aromatic compound and probably among the most singular and fascinating molecules, since it opened the family of aromatic compounds not only to the chemical community but, most importantly, to the industry and the society. Today, benzene is everywhere forming part of more complex molecules used for a huge variety of areas such as health, energy, material science, electronics, food, and biomolecules, thereby fulfilling the ultimate goal of science.
Following benzene, polycyclic aromatic hydrocarbons (PAHs) are organic molecules composed of multiple fused benzene rings. These compounds retain the aromatic features of benzene, including stability due to electron delocalization, and they exhibit electronic and optical properties based on their size and arrangement. PAHs are naturally formed through the incomplete combustion of organic matter, such as during wildfires or volcanic activity, but they can also be synthetically engineered to achieve specific properties for industrial and scientific applications. Small PAHs have been well‐known substances since the nineteenth century, but as they grow in size and complexity, their properties change. For example, while smaller systems like naphthalene and anthracene exhibit discrete energy levels due to their limited conjugation, larger PAHs such as coronene or longer acenes display semi‐metallic properties akin to those of graphene.
The synthesis and study of PAHs have paved the way for the development of nanographenes (NGs), offering insights into how molecular structure impacts properties such as electron conductivity, fluorescence, chirality, and chemical reactivity. These insights are essential for designing NGs with specific functionalities and emphasize the critical role of atomistic‐level control in creating advanced materials with tunable properties, as will be presented throughout the 21 chapters comprising this book.
The smallest and most frequently investigated graphene molecule, hexa‐peri‐hexabenzocoronene (HBC), was simultaneously described by A. Halleux (Helv. Chim. Acta1958, 41, 1177) and E. Clar (Proc. Chem. Soc. 1958, 150). This flat structure formed by 42 carbon atoms was for a long time the largest fully characterized polyaromatic hydrocarbon. However, the development of different methodologies based on stepwise organic synthesis has made possible the monodisperse preparation of PAHs with different sizes and shapes. As a beautiful and challenging NG, one of the pioneers in the preparation of molecular graphene fragments, Klaus Müllen, reported one of the largest structures described at that time, formed by 222 carbon atoms and a diameter of 3 nm (Chem. Eur. J. 2002, 8, 1424), thus showing the potential of organic synthesis for obtaining large graphene molecules.
The book is organized in four main areas: fundamental concepts, synthesis, properties, and applications, all of them involving several chapters written by authoritative scientists that are currently leading this scientific area all over the world. Therefore, as guest editors, we like to express our gratitude to the many top scientists who have agreed to participate in this venture. Their collaboration and efforts have been the key to achieving this outstanding and pioneering book in which, for the first time, the chemistry and properties of these molecular NGs are brought together for the enjoyment of the reader.
Our gratitude is also extended to Wiley and to the editors who have guided and supported us from the very first steps to the final edition of this book. The result nicely pays the efforts and dedication to this fantastic venture. Finally, we hope that this book on these new carbon‐based materials be stimulus for young researchers and put new heart into other colleagues to develop new chemical concepts and imaginative molecular architectures for expanding the interest in these fascinating heirs of benzene.
Nazario Martín and Colin P. Nuckolls
Editors
1Aromaticity and Antiaromaticity in Nanographenes: An Overview
Albert Artigas and Miquel Solà
Universitat de Girona, Institut de Química Computacional i Catàlisi, Departament de Química, C/Maria Aurèlia Capmany, 69, Girona, 17003 Catalonia, Spain
1.1 Introduction
In 2010, Geim and Novosolev were awarded the Nobel Prize in Physics for the discovery of graphene. Graphene is an allotrope of carbon consisting of a single layer of carbon atoms arranged in a two‐dimensional (2D) hexagonal lattice nanostructure, reminiscent of a honeycomb [1]. Despite having remarkable chemical and physical characteristics, its zero band‐gap prevents it from being used as a functional material. One way to open this band‐gap is the confinement of its electrons in smaller structures called nanographenes, which are tiny fragments of graphene with a minimum size of 1 nm. Nanographenes hold promise for unprecedented physical properties [2], from spin transport [3] to magnetism [4] and from exotic quantum states [5] to stable biexcitonic states [6] (for more information, see the Properties and Applications of Molecular Nanographenes part of this book). By adding defects in the form of 5‐ to 10‐membered rings in the hexagonal lattice, or by the inclusion of sterically strained helical motifs, their structural possibilities can be further extended from the two to the three dimensions in which nanographenes can be chiral [7]. For applications, nanographenes must be structurally perfect and narrow enough. And, of course, they have to be stable. This stability is the result of a combination of several factors such as size, topology, defects, and functionalization. Among these factors, aromaticity plays an important role.
In the realm of aromaticity, misunderstandings and disagreements over its definition and the aromatic nature of specific systems are frequent. Although the concept of aromaticity has been known for nearly two centuries, there is no way to measure it experimentally. The definition of aromaticity has been the subject of numerous studies, reviews, and conferences in the chemical community, although a general consensus has not been reached yet. In a recent perspective [8], some authors even consider that a universal definition of aromaticity is impractical or noncompatible with the general laws constituting chemical theory. Probably, the most accepted definition of aromaticity to date was given in 2005 by Chen et al. [9], who defined this concept as “a manifestation of electron delocalization in closed circuits, either in two or in three dimensions. This results in energy lowering, often quite substantial, and a variety of unusual chemical and physical properties. These include a tendency toward bond length equalization, unusual reactivity, and characteristic spectroscopic features”. It is clear from this definition that electron delocalization and energetic stabilization are the two most fundamental properties of aromatic compounds. The presence of ring currents, symmetry, unusual reactivity, and characteristic spectroscopic features are properties that most aromatic compounds share, but they are not as fundamental as the electron delocalization and stabilization.
Nanographenes are constituted by a relatively large number of rings (most of them six‐membered rings, 6‐MRs). Hexabenzocoronene (HBC) with 13 6‐MRs and circumcoronene with nineteen 6‐MRs are still considered polycyclic aromatic hydrocarbons (), but they are close to the limit (see Figure 1.1). Systems with more than 20 fused 6‐MRs can be considered nanographenes, although the frontier between PAHs and nanographenes is fuzzy and smaller systems are often referred as nanographenes in the literature [10].
Figure 1.1 The molecular structure of (a) hexabenzocoronene (HBC) and (b) circumcoronene with their Clar π‐sextets labeled with a circle in purple.
1.2 Global and Local Aromaticity
Some of the 6‐MRs in nanographenes are clearly aromatic and this type of aromaticity is named local aromaticity. Some nanographenes can show important electron delocalization through long circuits and we can refer to this type of aromaticity as global or macrocyclic. This is exemplified in Figure 1.2 for circumcoronene. The local ring currents in the 6‐MRs having a Clar π‐sextet (vide infra) are undoubtedly identified, together with a global ring current following the perimeter of the molecule that is also clearly depicted.
Figure 1.2 The ring currents in circumcoronene computed with the NICS2BC method.
Source: Reproduced with permission from Gershoni‐Poranne and Tsybizova [11]. John Wiley & Sons.
Clar's π‐sextet rule [12] is an empirical guideline that provides a straightforward method for assessing the local aromatic character of individual rings within PAHs. It states that the Kekulé resonance structure with the largest number of disjoint aromatic π‐sextets, that is benzene‐like moieties, is the most important resonance structure for the characterization of PAHs (and nanographenes) properties. Aromatic π‐sextets were defined by Clar as six π‐electrons localized in a single benzene‐like ring separated from adjacent rings by formal C—C single bonds. For instance, the application of this rule to phenanthrene indicates that its outer rings are expected to have a higher local aromaticity than the central ring (Figure 1.3). This result was confirmed using different measures of local aromaticity [13]. Clar's π‐sextet rule also predicts high stability for HBC of Figure 1.1a because it is made only from rings that are either π‐sextets or empty rings. These types of systems are called claromatic [14]. In contrast, circumcoronene (Figure 1.1b) has rings with a double bond that are neither π‐sextets nor empty rings. These are the most reactive rings and the double bonds are the ones expected to participate, for instance, as dienophiles in Diels–Alder reactions. In 1984, Glidewell and Lloyd proposed to extend the Clar π‐sextet rule to nonbenzenoid polycyclic conjugated hydrocarbons (PCHs). Glidewell and Lloyd's rule [15] states that the total population of π‐electrons in conjugated polycyclic systems tends to form the smallest 4n + 2 groups of π‐electrons and to avoid the formation of the smallest 4n groups.
Figure 1.3
