Facile bottom-up synthesis of coronene-based 3-fold symmetrical and highly substituted nanographenes from simple aromatics

Article abstract of DOI:10.1021/ja413018f

A facile and efficient self-sorting assemble (CSA) strategy has been paved for bottom-up construction of the 3-fold symmetrical and highly substituted hexa-cata-hexabenzocoronenes (c-HBCs), the trithieno analogues, and larger disc-shaped PAHs from simple

Full text of DOI:10.1021/ja413018f

Article
pubs.acs.org/JACS
Facile Bottom-Up Synthesis of Coronene-based 3‑Fold Symmetrical
and Highly Substituted Nanographenes from Simple Aromatics
Qiang Zhang, Hanqing Peng, Guishan Zhang, Qiongqiong Lu, Jian Chang, Yeye Dong, Xianying Shi,
and Junfa Wei*
Key Laboratory of Applied Surface and Colloid Chemistry (Ministry of Education), Key Laboratory for Macromolecular Science of
Shaanxi Province, School of Chemistry and Chemical Engineering, Shaanxi Normal University, Xi’an 710062, P. R. China
S
* Supporting Information
ABSTRACT: A facile and efficient self-sorting assemble
(CSA) strategy has been paved for bottom-up construction
of the 3-fold symmetrical and highly substituted hexa-cata-
hexabenzocoronenes (c-HBCs), the trithieno analogues, and
larger disc-shaped PAHs from simple chemicals using benzylic
carbons as tenon joints and a novel FeCl3-mediated AAA
process as a key step. The structures of the as-prepared c-
HBCs and related NGs were clearly identified by spectral
analyses and X-ray crystallographic studies. Moreover, these
can be envisaged to serve as new launching platforms for the
construction of larger and more complex π-conjugated
molecules and supramolecular architectures because of the
modifiable and symmetrical decorations.
taken together with numerous other works, make p-HBCs the
most studied large disc-shaped PAHs.
INTRODUCTION
■
Large polycyclic aromatic hydrocarbons (PAHs) or nano-
graphenes (NGs) have kindled great excitement for their
unique electronic and self-assembly properties in a variety of
fields of scientific and technological applications.1 Of particular
interest should be coronene-based NGs, such as hexa-peri-
hexabenzocoronene (planar HBC or p-HBC, also known as
“superbenzene”, Chart 1) and hexa-cata-hexabenzocoronene
In stark contrast with the prosperity of p-HBCs, however, c-
HBC, the twin sister of p-HBC, remains relatively ignored,
despite of its first synthesis by Clar and Stephen7 near half a
century ago. Recently, the Nuckolls group has reported the
parent c-HBC and a variety of its substituted derivatives8 and
disclosed their unique nonplanar structure and intriguing
electronic and self-assembly properties,9 such as their strong
tendency to self-assemble to nanowires8a and nanotubes6d and
to form shape-complementary complexes with C60.8d,9h More-
over, c-HBCs were found to be able to form bowls9b or
hemisphere.9k Even with these striking properties and
potentials, the c-HBC chemistry is far from being well-
documented.8a We believe that the sluggish development of
c-HBC chemistry can be ascribed mainly, if not purely, to the
lack of a convenient and efficient approach for their synthesis.
Although recent elegant work of Nuckolls et al. provided a
quick access to the c-HBC scaffold from pentacene
quinones,8a,b,9b the reported strategy give only mirror-sym-
metrically rather than C3 symmetrically substituted c-HBC
derivatives. Facile synthesis of substituted PAHs is the
precondition for the development of superior organic materials,
and the electronic optical, thermal, and morphological
properties of organic materials are closely related to their
aromatic structures and substitutional patterns. Clearly, a facile
synthesis of c-HBCs with different pattern and degree of
Chart 1. Structures of Coronene, p-HBC, and c-HBC
(contorted HBC, or c-HBC).1a−d Since the synthetic break-
through of p-HBCs by Mullen et al.2 in 1995, impressive
̈
progress has been achieved and a cornucopia of elegant p-HBC
derivatives and more complex PAHs with different shape and
size have been reported,3 even a giant molecular graphene
containing 222 carbon atoms4 and structurally uniform
graphene nanoribbons (GNRs) up to 12 nm in length.5
Many of them have shown potential applications from next-
generation electronic devices (e.g., field-effect transistors, light-
emitting diodes, and solar cells) to bioimaging.6 These works,
Received: December 27, 2013
Published: February 6, 2014
© 2014 American Chemical Society
5057
dx.doi.org/10.1021/ja413018f | J. Am. Chem. Soc. 2014, 136, 5057−5064

Journal of the American Chemical Society
Article
substitution from simple and readily available compounds is
highly desired for creating prosperity for this family of PAHs
and related compounds.
Scheme 1. New Synthesis Involving the CSA Strategy for c-
HBCs and Large NGs
a
In planning a facile strategy that provides coronene-based
NGs, for example, c-HBCs, we were attracted by their 3-fold
symmetry and thus created our synthetic concept, the covalent
self-sorting assembly (CSA) strategy, for construction of these
NG cores based on the retrosynthesis shown in Chart 2. We
Chart 2. Retrosynthetic Analysis of the Contorted HBC (up)
and Conceptual Illustration of the CSA Strategy for the
Construction of 3-Fold Symmetric NGs (down)
a
Conditions: (i) PdCl2, Na2CO3, Me2CO/H2O, rt 12 h, then 37-38
°C, 3 d, 64−83%; (ii) 10 mol % FeCl3, Ac2O, CH2Cl2, MeNO2, Ar, rt;
then excess FeCl3. The newly formed bonds are highlighted in colored
bold.
assumed this CSA chemistry could be accomplished by means
of mortise-and-tenon joints, that is, three benzyl tenons
automatically were mated into three mortises that correspond
to the “cove-regions” between the central ring and branched
rings of an appropriate starburst dendritic aromatic molecule,
for example, sym-tribenzylbenzene (TBBs 2, Chart 2).
This approach, if successful, would conveniently provide not
only c-HBCs having the pattern and degree of substitution
different from the reported ones but also hetero analogs and
even larger, more complex NGs with 3-fold symmetry. It
should be noted that the rim decorations may serve as
solubilizing groups. More significantly, they permit fine-tuning
of the molecular and supramolecular properties and extending
the aromatic π-systems via altering the reactants or
functionalizing the final products. Also noteworthy is that our
CSA strategy distinguishes itself from other protocols reported
for access to NGs by dodging the preparation of corresponding
oligophenylene precursors.
Total synthesis involving the CSA strategy for c-HBCs and
large NGs is a concise two-step reaction sequence. As depicted
in Scheme 1, TBB 2, which can be readily accessed, for
example, through Suzuki cross coupling reaction of 1,3,5-
tri(bromomethyl)-benzene 1 and 3,4-dialkoxyphenyl boronic
acid, is covalently self-sorting assembled with three arylalde-
hyde molecules into the polycyclic aromatic architectures. Far
different from the reported strategies currently used for
constructing c-HBCs and other NGs, the logic of our strategy
derives from the recognition that 7 (i.e., the central ring and the
6 external rings) of the 13 rings necessary to constitute the
entire aromatic scaffold of c-HBCs are provided directly by
simple benzene building blocks, that is, sym-tri(bromomethyl)-
benzene 1, arylboronic acids and arylaldehydes, while the
remaining 6 hexagonal grids, which are slotted in between the
central and the peripheral rings, can be constructed by C−C
bond formation reactions, that is, Friedel−Crafts10 and Scholl
reactions.11 The feasibility of such a design should be enhanced
by preinstalling appropriate ring-activating/directing/blocking
groups, such as alkoxy groups, on the aromatic rings of the
starting boronic acids and/or aldehydes.
RESULT AND DISCUSSION
■
Synthesis of c-HBCs and the Heteroanalogues. The
starburst mortise adaptors, TBB 2a−f, were synthesized in
good yields by a 3-fold Suzuki coupling reaction of 1,3,5-
tri(bromomethyl)benzene 1 with 3,4-dialkoxyphenyl boronic
acid by the method borrowed from B. P. Bandgar et al.12 with
some modifications. For realization of the CSA concept, we
carried out the assembly of TBB 2a and 3,4-dimethoxybenzal-
dehyde using FeCl3 as catalyst/oxidant and acetic anhydride as
dehydrator in a DCM/CH3NO2 solution at room temperature
under argon atmosphere. To our delight, the TBB and the three
arylaldehyde molecules covalently self-assemble into the
requisite c-HBC 3a in an excellent yield (entry 1, Table 1).
5058
dx.doi.org/10.1021/ja413018f | J. Am. Chem. Soc. 2014, 136, 5057−5064

Journal of the American Chemical Society
Article
by dropwise addition of 15.6 equiv of the FeCl3/CH3NO2
solution over ca. 1 h to the reaction mixture and stirring an
additional 12 h before quenching by methanol.
Table 1. c-HBCs and Larger PAHs Synthesized by the CSA
Method
a
b
entry
R1/R2
R3/R4 or R
PAH
yield
As seen from Table 1, the desired c-HBCs were expediently
achieved from the TBBs bearing different alkoxy groups and
various benzaldehyde building blocks using this CSA protocol,
most in high yields. Electron-rich aromatic aldehydes are
favorable to give the hunted c-HBCs; while electron-poor ones
hinder the assemble reaction (entries 8 and 10). These results
suggest that our FeCl3-mediated CSA chemistry follows a
parallel trend as for electrophilic aromatic substitution and
oxidative cyclodehydrogenation reactions. Yet, 3,4-difluoroben-
zaldehyde delivers the hexafluorinated c-HBC 3c smoothly
(entry 3). Owing to solubility issue, this compound was not
further purified by columnar chromatography, but it was found
to be sufficiently pure for spectral analysis after thoroughly
rinsing with methanol. Noteworthy, 3c has electron-rich and
-poor rings alternately fused on the coronene core, providing a
rare example of alternate push−pull structure.
The CSA method can also be comfortably applied to the
mono- and nonsubstituted aldehydes (Table 1, entries 5−9, 11,
18 and 19) to deliver the related c-HBCs in good yields. This
result indicates that the competing side reactions such as
intermolecular Scholl chemistry on the bare positions of the
rim are insignificant in this process. In the case of 4-
(trifluoromethyl)benzaldehyde, the reaction afforded a low
yield (entry 10), presumably because of the strong electron-
withdrawing nature of the trifluoromethyl group which reduces
the reactivity of the attached benzene ring toward Friedel−
Crafts and Scholl reactions. Still, the reaction is quite effective
considering that the 39% isolated yield of the product
represents a 92% yield per C−C bond formed.
1
OCH3/OCH3
OCH3/OCH3
CH3/CH3
F/F
3a
3b
3c
3d
3e
3f
90%
93%
2
c
3
95%
4
Br/OCH3
CH3/H
97%
92%
95%
5
6
C(CH3)3/H
F/H
c
7
3g
3h
3i
94%
8
Cl/H
82%
86%
39%
9
Br/H
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
CF3/H
3j
c
H/H
3k
3l
88%
OC4H9/OC4H9
OC8H17/OC8H17
OC12H25/OC12H25
OC4H9/OC4H9
CH3/CH3
F/F
95%
77%
68%
94%
87%
92%
90%
81%
91%
80%
51%
86%
82%
32%
49%
47%
36%
47%
53%
3m
3n
3o
3p
3q
3r
OC4H9/OC4H9
Br/H
H/H
3s
3t
OC6H13/OC6H13
OC8H17/OC8H17
OC12H25/OC12H25
OC4H9/OCH3
OC6H13/OC6H13
OC8H17/OC8H17
OC12H25/OC12H25
OC4H9/OCH3
Br/OCH3
H
3u
3v
3w
3x
4a
4b
4c
5a
5b
OCH3/OCH3
OC4H9/OC4H9
OC6H13/OC6H13
OCH3/OCH3
H
H
t-Bu
OC4H9/OC4H9
OC6H13/OC6H13
t-Bu
The c-HBCs decorated with phase-forming and solubilizing
long-aliphatic chains were also accessible using this concept in
satisfactory yields (entries 13, 14, and 20−22).
The TBB with the branched phenyl rings bearing two
different groups contentedly affords the anticipated c-HBCs
with mixed substitution of each peripheral benzo ring (entries
23 and 24). Such multisubstituted c-HBCs provide a promise to
selective modification of the anellated benzo rings or extending
their π-systems.
t-Bu
5c
b
a
Conditions is the same as those shown in Scheme 1. Isolated yields
c
by column chromatography, unless otherwise noted. Yields by
filtration and washing with methanol, the product is pure enough
for NMR analysis.
Such a one-step 6-fold self-sorting tenoning annulation is
definitely highly efficient, especially if one considers that a total
of 12 C−C bonds and 6 benzene rings are constructed in a
single step. In this unprecedented process, four 3-fold
transformations take place in tandem, that is, Friedel−Crafts
hydroarylation and intramolecular alkylation, dehydrogenative
aromatization and intramolecular Scholl reaction. So, this
protocol may also be referred to as a direct annulation-
aromatization-annulation (AAA) process.
Switching benzaldehydes to thienaldehydes, we anticipated
to attain a novel heteroversion of c-HBCs, sym-tribenzote-
trathieno-coronenes (TBTTCs), wherein coronene core is
alternately fused by thieno- and benzo-rings (Scheme 1, central
raw), unlike Nuckolls’ dibenzotetrathienocoronene
(DBTTC)9b and Mullen’s hexathienocoronene (HTC).13 But
̈
unfortunately, exposure of 2-thienaldehyde to TBB 2b under
the same conditions led to TBTTC 4b (m/z 1050.6) and a
byproduct (m/z 970.6) that can be ascribed tentatively to
excision of a thiophene ring. Similar results were found when
using 5-methyl-2-thienaldehyde as the starting aldehyde (Figure
S1 and Scheme S7 in the Supporting Information). We
surmised the loss of thiophene units as a result of retro-
Friedel−Crafts reaction during the CSA process (Figure S2 in
the Supporting Information). Considering that the 3-isomer
may be more robust toward this unwanted reaction, we tried to
exploit 3-thienaldehyde instead of the 2-isomer and succeeded
in assembling 4b with 49% yield as a single regioisomer (entry
26). The simplicity of NMR spectra clearly elucidates its 3-fold
symmetry in solution and thereby divulged the high
regioselectivity of the Scholl cyclization. In analogy, TBB 2c
and 2a with 3-thienaldehyde gave 4c and 4a in 47% and 32%
1
The H NMR spectrum of 3a exhibits as being very simple
and symmetrical; only two singlets appear at 8.78 and 4.20
ppm. The 13C NMR spectrum showed six singles attributable to
methoxy groups and five sets of the aromatic carbon atoms.
These results are fully consistent with its 6-fold symmetry. In
the MALDI-TOF spectrum, the molecular ion of m/z 960.3
was observed as a sole peak. The ultimate confirmation was
provided by X-ray crystallography.
Pleased with these results, we applied this concept to the
synthesis of c-HBCs with various substitution symmetries and
peripheral decorations using different aryl boronic acids and
arylaldehydes to explore the generality of our protocol. A series
of c-HBCs was comfortably attained (Table 1). In most cases,
the reaction was carried out with acetic anhydride and a
catalytic amount of FeCl3 in DCM/CH3NO2 solution, followed
5059
dx.doi.org/10.1021/ja413018f | J. Am. Chem. Soc. 2014, 136, 5057−5064

Journal of the American Chemical Society
Article
yields (entries 27 and 25), respectively. The susceptibility of
thiophene ring toward side reactions may be blamed for the low
yields.
evaporation of their solutions in different solvents (see the X-
ray crystallographic analysis in the Supporting Information).
We were also fortunate enough to obtain a crystal of 5c, which,
to the best of our knowledge, is hitherto the largest discoid NG
molecule with all-hexagonal grids to be represented by X-ray
crystal structure.
X-ray crystallographic outcomes unambiguously show that, in
analogy to the unsubstituted c-HBC reported by Nuckolls et
al.,8a the dodecaalkoxy substituted c-HBCs 3a and 3t (Figure
1A and B) have the as-expected nonplanar aromatic structure
Synthesis of HBCCs. Spurred by the successful assembly of
the c-HBCs, we turned to the construction of larger π-disks
using our CSA concept. It can be foreseen that, upon
installation of 9,10-phenanthro- moieties, the newly formed
[5]helicene fjord regions of the intermediary c-HBC could be
further stitched into hexagons via removing the fjord hydrogens
with sufficient FeCl3, thus elaborating a new NG species that
has 72 aromatic carbon atoms, 25 fused benzene rings, 3-fold
symmetric substitution and all-armchair periphery. This
hitherto unknown disk may be formally viewed as a hexa-
peri-hexabenzocircumcoronene (HBCC, 5). Markedly, HBCC
5 has the greatest number (12 rings) of aromatic sextets and no
formal nonaromatic double bonds in the structure, being a full-
benzenoid PAH according to the Clar’s π-sextet rule.15
The hexahexoxy substituted TBB 2c and 3,6-di-tert-butyl-9-
phenanthraldehyde were chosen to avoid the solubility issue.
The application of our CSA conditions, however, led to a
mixture of incompletely dehydrogenated intermediates, of
which the main MALDI ion is eight mass units higher than
the molecular mass of the expected 5c, meaning that eight
hydrogen atoms were left unremoved or four fjords unclosed.
Resubmitting this mixture, after simply wishing with water and
drying with Na2SO4, to the Scholl reaction by adding fresh
FeCl3/MeNO2 solution, we obtained the hunted 5c smoothly
in 56% yield. The MALDI molecular ion at m/z 1825.3 (hoped
1
1825.1) and unambiguous H and 13C NMR spectra were
consistent with the expected structure. That HBCC 5c was
definitely in hand derived from X-ray crystal analysis.
Concurrently, we also tested the one-pot synthesis of the
HBCC by increasing the dosage of FeCl3 and found that, with
120 equiv FeCl3 in the Scholl coupling, which is five times the
stoichiometric requirement, dodeca-cyclized 5c was accessed
successfully in 53% yield (entry 30). It is striking that in this
case 18 new C−C bonds (Scheme 1, colored bold red and
purple) and 12 benzene rings are formed in one pot. The 53%
isolated yield was not very high yet reasonable for access to
such a large compact PAH via such a multifold reaction step,
particularly in view of 96.5% average yield per bond or 94.8%
per rings formed. In this regard, it further highlights the merit
inherent to our CSA chemistry. The methoxy and n-butoxy
analogues, 5a and 5b, were accessed in satisfactory yields
following the same procedure (entries 28 and 29) and were
identified by NMR and MS analyses. However, with 9-
phenanthraldehyde, neither the one-pot synthesis nor resubmit-
ting protocol succeeded in offering the desired product in pure
form, instead a complex mixture contaminated by partially
dehydrogenated species and chlorinated byproducts. Both 5b
and 5c are readily soluble in common solvents while 5a is less
soluble. They all exhibit a red fluorescence on TLC plate or in
DCM solution under 365 nm ultraviolet light, different from
the c-HBCs derived from monocyclic arylaldehydes.
Figure 1. X-ray molecular structures of c-HBCs (A) 3a and (B) 3t and
(C) TBTTC 4b (3a and 3t was measured at room temperature while
4b at 105 K. Hydrogen atoms are omitted for clarity; oxygen is
depicted in red and sulfur in yellow).
The successful synthesis of the c-HBCs and related PAHs
exemplifies the application of our concept in rapid bottom-up
construction of polyaromatic architectures and suggest its
potential in the creation of new NG species with a variation in
functional groups and aromatic frameworks since a wide range
of aryl aldehydes and boronic acids are commercially available
or preparatively accessible.
with a double-trefoil shape and an inversion center. The fused
benzo-moieties are bent away from planarity in an alternate up
and down arrangement because of the sterically congested
cove-regions. The central and peripheral rings are essentially
flat while the in-between benzofused rings adopt boat-
conformations with a mean fold angle of 18.2° in 3a and
18.1° in 3t and the C−C bonds attached on the central ring are
shorter than those on the exterior rings, as observed in the bare
c-HBC.8a The average splay angle at cove-region is 41.6° in 3a
X-Ray Crystallographic Studies. Single crystals of c-
HBCs 3a and 3t and TBTTC 4b were obtained by slow
5060
dx.doi.org/10.1021/ja413018f | J. Am. Chem. Soc. 2014, 136, 5057−5064

Journal of the American Chemical Society
Article
and 41.1° in 3t, comparable to that of bare c-HBC (42.0°).9c
Each ortho-methoxy group is almost coplanar with the attached
benzo ring. In 3t, two of the six hexoxys are out-of-plane with
respect to the benzo-units while the others are coplanar and,
notably, each two opposite oriented side-chains are inversion-
related in conformation, forming a centrosymmetric pair.
Introduction of the side chains has no marked effect on the
shape of the aromatic core.
The hetero analogue, TBTTC 4b, also adapts the up−down
conformation (Figure 1C); three thieno-units bend to one side
while three benzo-units bend to the opposite. The small size of
thiophene ring leads to a noticeably flattening of the core in
comparison with c-HBCs 3a and 3t. In the crystal, this twisted,
chiral core molecule no longer holds the C3 symmetry, unlike
the case in solution. Neither splay angles at cove regions nor
distortion of equivalent parts of the molecule are identical
(Table S17 in the Supporting Information). Three intra-
molecular H-bonds were observed in the sulfur-containing bay
regions. Each pair of enantiomeric molecules forms a cofacial,
slipped, racemic dimer from their benzofused sides and in a
centrosymmetric head-to-tail arrangement (Figure S8 in the
Supporting Information). The interlayer distance in the dimer
is 3.44 Å, slightly longer than that of DBTTC (3.3 Å)9b and
HTC (3.37 Å).13
X-ray analysis of HBCC 5c ascertained the devised structure
and demonstrated its nonplanar and asymmetrical geometry in
the crystalline state (Figure 2A). Both deplanarization and
desymmetrization of the aromatic framework essentially stem
from the alkoxyl substituents overcrowding at the bay regions:
they force the neighboring benzene rings to deviate from
planarity and concurrently are themselves compelled to bend
out of the plane of the attached benzo-unit. The alkoxyl groups
are twisted about CAr−O bonds with torsion angles of 68−82°
and placed in an “up−up−down−up−down−up” pattern,
leading to not only the curvature and asymmetry but also the
inequivalent distortion of the molecule. In fact, only eight
benzene rings, including the central ring, keep their own carbon
atoms coplanar within 0.018 Å while the others are
deplanarized ranging from 0.023 to 0.054 Å. Noteworthy is
that the edge affixing the cisoid vicinal dialkoxyl groups is
seriously lifted up; no torsional angles of the bays, including
those unsubstituted, are alike.
Even so, the all-benzenoid nature of the core3j,8a,16 is
observed from the discrepancy between the discrepancy
between inter- and intrabenzenoid C−C bonds (1.44−1.47 Å
and 1.38−1.42 Å, respectively) (Table S21 in the Supporting
Information). The tert-butyl groups keep in the same plane of
the attached benzene rings and might trivially influence the
distortion. In tramolecular H-bonds were observed between
oxygen and hydrogen atoms.
Figure 2. X-ray molecular structure of HBCC 5c and the dimers in the
crystal. (A) Overall view. (B) Side-view of the π···π and C−H···π
dimers, looking along the slipping direction of the molecules
(Sustituents and hydrogen atoms are omitted for clarity except for
the ones shown). (C) Top-view of the π···π dimer, looking down the
planes of two enantiomers (Measured at 100 K; Hydrogen atoms are
omitted for clarity; oxygen is depicted in red).
Inspection of the crystal packing of 5c (Figure 2B and C)
illustrates that two molecules form a slipped cofacial dimer and
are inversion related. In other words, the dimer is a racemate of
two conformational enantiomers. Inside the dimer, two
opposite conformers are stacked from the less crowded sides
and slipped by 3.57 Å along a p-quaterphenyl unit, forming a
concave-convex complementarity with a π-overlap of about 14
hexagons. The center−center distance is 4.87 Å and the
separation between the mean planes of the central rings is 3.33
Å, close to the layer distance in graphite (3.35 Å). This is
characteristic for a pronounced π−π interaction between two
aromatic cores. The side-chains placed outside the dimers
impede the interdimer π−π interactions but provide favored
aliphatic C−H···π interactions with the neighboring dimer.
Interestingly, the hexoxyl chains adjust themselves with the
topography of the nearest aromatic ring to facilitate the contact
of the C−H bonds with the π-system. A series of 22 hydrogen
atoms of four hexoxyl groups between two π−π dimers are
involved in the cooperative interactions with atom-to-plane
distances of 2.67−2.94 Å (Table S24, Figures S10 and S11 in
the Supporting Information).
The size of the aromatic core, defined here as the mean
distance of the p-quaterphenyl motifs, is 1.55 nm. It hence
should serve as a new discogen possessing a π-system larger
than both p- and c-HBCs.
5061
dx.doi.org/10.1021/ja413018f | J. Am. Chem. Soc. 2014, 136, 5057−5064

Journal of the American Chemical Society
Article
Spectral and Thermal Properties. The spectral properties
of some c-HBCs, TBTTCs and HBCCs were summarized in
the Supporting Information. The typical spectra of 3a, 4b and
5c are shown in Figure 3.
Information). Both absorbance and emission maxima for the
HBCCs are red-shifted by ca. 80 nm as compared to the c-
HBCs.
The thermogravimetric analysis of several representatives
reveals that they are stable to above 300 °C (Table S29 and
Figure S14 in the Supporting Information), being thermally
robust. Most of them exhibit sufficient solubility in ordinary
organic solvents (e.g., DCM, chloroform, toluene, and THF) to
consent usual spectroscopic analysis and chromatographical
isolation.
CONCLUSION
■
We have paved a facile and efficient approach, based on the
CSA strategy for access to 3-fold symmetrical and highly
substituted c-HBCs from very simple chemicals using benzylic
carbons as annulating partners, as an effective alternative to the
reported approach. The total synthesis is composed of 2 steps
of multifold transformations, both under mild conditions and in
good to excellent yields. These merits make the c-HBCs one of
the most accessible large polycyclic aromatic molecules and,
more significantly, render the method a simple and versatile
tool to be controlled in the hands of chemists and materials
scientists. Also remarkable is that our method is amenable to
creating the hetero-c-HBCs and large molecular graphenes. So
it provides simple access to coronene-based PAHs that are
substituted both in the periphery and at the aromatic core. X-
ray analysis reveals their intriguing structural properties.
Furthermore, the good accessibility and modifiable symmetric
decorations of the synthesized PAHs allow them to serve as
new launching platforms for going to even larger aromatic
architectures with defined shape, size and periphery. We believe
that this method will promote the development of c-HBC
chemistry, along with the Nuckolls’ approach. Further efforts to
expand the synthetic diversification of this strategy and the
synthetic uses of the as-prepared NGs are ongoing.
Figure 3. Normalized spectra of c-HBC 3a (green) and TBTTC 4b
(blue) and HBCC 5c (red profile). A: UV−visible spectra (4.00 μM
for 3a and 4b; 2.00 μM for 5c; all in DCM); B: emission and
excitation (dashed line) spectra (rt., 0.40 μM in DCM).
EXPERIMENT SECTION
■
General experimental details, synthesis and characterization for all
compounds, X-ray crystallographic data for some products, and
physicochemical data can be found in the Supporting Information. The
synthetic details are exemplified by the synthesis of 2a, 3a, 4b, and 5c
below.
c-HBC 3a and its heteroversion TBTTC 4b exhibit almost
indistinguishable spectral natures in UV−visible and fluores-
cence spectra. They display three strong absorption bands
around λmax 250, 390, and 420 nm, similar to Clar’s,7
Nuckoll’s,9f and Mullen’s results.13,14 For 3a, the strongest
̈
General Synthesis of 1,3,5-Tri(3,4-dialkoxybenzyl)benzenes
(TBBs). A mixture of arylboronic acid, Na2CO3 in 40 mL acetone−
water (1:1) was stirred at room temperature until it became
homogeneous. Then, it was cooled in an ice bath and degassed by
bubbling Ar for 15 min. To this mixture was added 1,3,5-tris(bromo-
methyl)benzene 1 and PdCl2 at 0 °C and it was stirred at rt for 12 h
and 37−38 °C for 3 days under argon atmosphere. After completion of
the reaction (monitored by TLC), acetone was removed under
reduced pressure and the product was extracted with diethyl ether and
dried with anhydrous Na2SO4. Removal of the ether on a rotary
evaporator furnished the crude product, which was further purified by
column chromatography (silica gel). 1,3,5-Tris(3,4-dimethoxybenzyl)-
benzene (TBB 2a) was prepared from 3,4-dimethoxyphenylboronic
acid and 1 and purified by column chromatography (silica gel, PE:EA
= 2:1, v/v). White solid (yield 83%). Mp 112−114 °C; 1H NMR (300
MHz, CDCl3): δ 6.85 (s, 3H), 6.79−6.76 (d, J = 9.0 Hz, 3H), 6.70−
6.67 (d, J = 9.0 Hz, 3H), 6.65 (s, 3H), 3.84 (s, 18H), 3.78 (s, 6H); 13C
NMR (75 MHz, CDCl3): δ 148.8, 147.3, 141.5, 133.7, 127.1, 120.7,
112.2, 111.2, 55.8, 55.7, 41.3; HR-MS (ESI): m/z calcd for (C33H36O6
+ Na) 551.2410, found 551.2398.
absorption maximum is at wavelength of 390 nm with a molar
extinction coefficient (εmax) of 2.3 × 106 M−1 cm−1, probably
due to the conjugation of peripheral methoxy substituents. The
emission spectra exhibit a strong green fluorescence with three
maxima at λmax 510, 550, and 580 nm with Stokes shifts near
120 nm (Figure 3B). The emission spectral features of 4b
resemble those of 3a, except for slight blue-shifts.
HBCC 5c shows three strong absorption bands around 250,
450, and 480 nm, typical of large aromatic molecules.
Compared with those of c-HBCs, these bands are drastically
red-shifted and the absorption coefficients at the maxima of ca.
450 nm are much higher (for 5c, εmax 3.2 × 106 M−1cm−1).
Apparently, the extended size of the π-system contributes the
red-shift and the enhanced intensity of the absorption bands.
The HBCCs display a strong yellow fluorescence in DCM
(Figure 3B). Two strong emission maxima of 5c were observed
at around 590 and 630 nm, respectively, with Stokes shifts in
excess of 150 nm. The fluorescence quantum yield of 5c in
DCM is 24%, relative to a standard of Rhodamine B in 2.0 μM
ethanol (Table S28 and Figure S13 in the Supporting
General Procedures for the Synthesis of c-HBCs. To a solution
of 3,4-dimethoxybenzaldehyde (100 mg, 1.65 mmol) and Ac2O (0.47
mL, 5 mmol) in 350 mL DCM was added a solution of FeCl3 (16.2
5062
dx.doi.org/10.1021/ja413018f | J. Am. Chem. Soc. 2014, 136, 5057−5064

Journal of the American Chemical Society
Article
mg, 0.1 mmol) in CH3NO2 (1 mL) while stirring at rt, followed by
dropwise addition over 1 h of TBB 2a (0.5 mmol, 264 mg) in DCM
(50 mL). The resulting mixture was stirred at rt overnight and then
degassed with Ar for 15 min. A second portion of FeCl3 (1.26 g, 7.2
mmol, in 20 mL CH3NO2) solution was added dropwise over 1 h
under Ar atmosphere and stirred for 12 h. Then, cold CH3OH (100
mL) was added with stirring to quench the reaction and the mixture
was poured into cold water (500 mL). The biphasic mixture was
separated and the aqueous layer was extracted three times with DCM.
The combined organic layers were washed with water, dried by
Na2SO4, filtered, and rotoevaporated in vacuo. The residue was
purified by chromatography (silica gel, DCM:EA = 10:1, v/v) to give
3a as a yellow solid (432 mg, yield 90%). Mp > 300 °C; 1H NMR (300
MHz, CDCl3): δ 8.78 (s, 12H), 4.20 (s, 24H); 13C NMR (75 MHz,
CDCl3): δ 148.4, 125.0, 123.7, 120.4, 109.0, 56.1; MS (MALDI-TOF)
(CHCA): m/z calcd for C60H48O12: 960.3 (M+), found: 960.3.
General Procedures for the Synthesis of c-TBTTCs. To a
solution of 3-thienaldehyde (0.9 mmol) and Ac2O (0.2 mL, 2 mmol)
in 350 mL DCM was added a solution of FeCl3 (16.2 mg, 0.1 mmol)
in CH3NO2 (1 mL) while stirring at rt, followed by dropwise addition
over 1 h of TBB 2c (0.20 mmol) in DCM (50 mL). The resulting
mixture was stirred at rt overnight and then degassed with Ar for 15
min. A second portion of FeCl3 (1.26 g, 7.2 mmol, in 20 mL
CH3NO2) solution was added dropwise over 1 h under Ar atmosphere
and stirred for 4 h. Then, cold CH3OH (100 mL) was added with
stirring to quench the reaction and the mixture was poured into cold
water (500 mL). The biphasic mixture was separated and the aqueous
layer was extracted three times with DCM. The combined organic
layers were washed with water, dried by Na2SO4, filtered, and
rotoevaporated in vacuo. The residue was purified by chromatography
(silica gel, PE:DCM = 1:1, v/v) to give 4b as a yellowish brown
material is available free of charge via the Internet at http://
pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*weijf@snnu.edu.cn
■
Present Address
Key Laboratory of Applied Surface and Colloid Chemistry
(Ministry of Education), Key Laboratory for Macromolecular
Science of Shaanxi Province, School of Chemistry and
Chemical Engineering, Shaanxi Normal University, Xi’an,
710062, P. R. China.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by National Foundation of Natural
Science in China (Grant No. 21072123 and 21272145),
Fundamental Research Funds for the Central Universities
(Grant No. GK261001095), Innovation Funds of Graduate
Programs, SNU (Grant No. 2010CXB002) and Innovative
Research Team in University of China (IRT 1070). We are also
grateful to Prof. Lawrence T. Scott in the Department of
Chemistry, Boston College and Prof. C. He at the University of
Chicago for their fruitful discussions and advice on the project.
REFERENCES
■
1
(1) (a) Wu, J.; Pisula, W.; Mullen, K. Chem. Rev. 2007, 107, 718−
747. (b) Watson, M. D.; Fechtenkotter, A.; Mullen, K. Chem. Rev.
̈
powder (99 mg, 49% yield). Mp > 300 °C; H NMR (400 MHz,
̈
CDCl3): δ 9.12 (s, 3H), 8.67−8.66 (d, J = 5.6 Hz, 3H), 8.62(s, 3H),
7.77−7.76 (d, J = 5.6 Hz, 3H), 4.49−4.46 (t, J = 6.6 Hz, 6H), 4.39−
4.36 (t, J = 6.6 Hz, 6H), 2.12−2.04 (m, 12H), 1.76−1.67 (m, 12H),
1.16−1.10 (m, 18H); 13C NMR (100 MHz, CDCl3): δ 149.4, 148.7,
135.3, 134.0, 126.8, 125.0, 124.1, 123.7, 122.2, 121.0, 111.5, 108.3,
69.2, 69.1, 315, 31.4, 19.5, 19.4, 14.0; MS (MALDI-TOF) (CHCA):
2001, 101, 1267−1300. (c) Seyler, H.; Purushothaman, B.; Jones, D.
J.; Holmes, A. B.; Wong, W. W. H. Pure Appl. Chem. 2012, 84, 1047−
1067. (d) Feng, X.; Pisu la, W.; Mullen, K. Pure Appl. Chem. 2009, 81,
̈
2203−2224. (e) Wang, J.-L.; Yan, J.; Tang, Z.-M.; Xiao, Q.; Ma, Y.;
Pei, J. J. Am. Chem. Soc. 2008, 130, 9952−9962. (f) Pisula, W.; Feng,
+
X.; Mullen, K. Adv. Mater. 2010, 22, 3634−3649. (g) Kawasumi, K.;
̈
m/z calcd for C66H66O6S3: 1050.4 (M ), found: 1050.6.
Zhang, Q.; Segawa, Y.; Scott, L. T.; Itami, K. Nat. Chem. 2013, 5, 739−
General Procedures for the Synthesis of HBCCs. To a solution
of 3,6-di-tert-butyl-9-phenanthraldehyde (114.5 mg, 0.36 mmol) and
Ac2O (0.24 mL, 2.5 mmol) in 350 mL DCM was added a solution of
FeCl3 (8.1 mg, 0.05 mmol, 10 mol %) in CH3NO2 (1 mL) while
stirring at rt, followed by dropwise addition of a solution of TBB 2c
(0.1 mmol, 94.8 mg) in 50 mL DCM. The resulting mixture was
allowed to stir for 48 h at rt. Then it was degassed with Ar for 10 min
and then added dropwise a second portion of FeCl3 (1.92 g, 12 mmol)
solution in 20 mL CH3NO2 over 1 h under Ar atmosphere. After being
stirred at 0 °C for an additional 4 h, the mixture was added 100 mL
CH3OH with stirring and then poured into cold water. The biphasic
mixture was separated and the aqueous layer was extracted three times
with DCM. The combined organic layers were washed with water,
dried by Na2SO4, filtered, and rotoevaporated in vacuo. The residue
was purified by chromatography (silica gel, PE:DCM = 10:1) to give
744. (h) Chen, L.; Hernandez, Y.; Feng, X.; Mullen, K. Angew. Chem.,
̈
Int. Ed. 2012, 51, 7640−7654. (i) Wei, J.; Han, B.; Guo, Q.; Shi, X.;
Wang, W.; Wei, N. Angew. Chem., Int. Ed. 2010, 49, 8209−8213. (j) Li,
J.; Kastler, M.; Pisula, W.; Robertson, J. W. F.; Wasserfallen, D.;
Grimsdale, A. C.; Wu, J.; Mullen, K. Adv. Funct. Mater. 2007, 17,
̈
2528−2533. (k) Jin, W.; Fukushima, T.; Kosaka, A.; Niki, M.; Ishii, N.;
Aida, T. J. Am. Chem. Soc. 2005, 127, 8284−8285. (l) Jin, W.;
Yamamoto, Y.; Fukushima, T.; Ishii, N.; Kim, J.; Kato, K.; Takata, M.;
Aida, T. J. Am. Chem. Soc. 2008, 130, 9434−9440. (m) Mullen, K.;
̈
Rabe, J. P. Acc. Chem. Res. 2008, 41, 511−520.
(2) Stabel, A.; Herwig, P.; Mullen, K.; Rabe, J. P. Angew. Chem., Int.
̈
Ed. 1995, 34, 1609−1611.
(3) (a) Iyer, V. S.; Wehmeier, M.; Brand, J. D.; Keegstra, M. A.;
Mullen, K. Angew. Chem., Int. Ed. 1997, 36, 1604−1607. (b) Dotz, F.;
̈
̈
1
Brand, J. D.; Ito, S.; Gherghel, L.; Mullen, K. J. Am. Chem. Soc. 2000,
̈
5c as a brick-red solid (97 mg, 53 % yield). Mp > 300 °C; H NMR
122, 7707−7717. (c) Schmidt-Mende, L.; Fechtenkotter, A.; Mullen,
̈
̈
(400 MHz, CDCl3): δ 10.77 (s, 6H), 9.70 (s, 6H), 4.48−4.45 (t, J =
4.5 Hz, 12H), 2.40−1.98 (m, 12H), 1.94 (s, 54H), 1.60−1.37 (m,
36H), 0.95−0.91 (t, 18H); 13C NMR (100 MHz, CDCl3): δ 151.0,
149.1, 130.1, 129.3, 124.6, 124.2, 123.4, 123.0, 120.8, 120.3, 119.4,
74.7, 36.2, 32.4, 31.9, 25.8, 22.7, 14.0; MS (MALDI-TOF) (CHCA):
m/z calcd for C132H144O6: 1825.1 (M+), found: 1825.3.
K.; Moons, E.; Friend, R. H.; MacKenzie, J. D. Science 2001, 293,
1119−1122. (d) Wasserfallen, D.; Kastler, M.; Pisula, W.; Hofer, W.
A.; Fogel, Y.; Wang, Z.; Mullen, K. J. Am. Chem. Soc. 2006, 128, 1334−
̈
1339. (e) Fogel, Y.; Kastler, M.; Wang, Z.; Andrienko, D.; Bodwell, G.
J.; Mullen, K. J. Am. Chem. Soc. 2007, 129, 11743−11749. (f) Wang,
̈
Z.; Tomovic, Z.; Kastler, M.; Pretsch, R.; Negri, F.; Enkelmann, V.;
Mullen, K. J. Am. Chem. Soc. 2004, 126, 7794−7795. (g) Wu, J.;
̈
ASSOCIATED CONTENT
Fechtenkotter, A.; Gauss, J.; Watson, M. D.; Kastler, M.;
̈
■
Fechtenkotter, C.; Wagner, M.; Mullen, K. J. Am. Chem. Soc. 2004,
̈
̈
S
* Supporting Information
126, 11311−11321. (h) Kastler, M.; Pisula, W.; Wasserfallen, D.;
General experimental, synthetic details and characterization
including the copies of NMR and MS spectra for all products
and intermediate compounds, X-ray crystallographic data for
products 3a, 3t, 4b and 5c, and physicochemical data. This
Pakula, T.; Mullen, K. J. Am. Chem. Soc. 2005, 127, 4286−4296.
(i) Wong, W. W. H.; Subbiah, J.; Puniredd, S. R.; Purushothaman, B.;
̈
Pisula, W.; Kirby, N.; Mullen, K.; Jones, D. J.; Holmes, A. B. J. Mater.
̈
Chem. 2012, 22, 21131−21137. (j) Li, J.; Kastler, M.; Pisula, W.;
5063
dx.doi.org/10.1021/ja413018f | J. Am. Chem. Soc. 2014, 136, 5057−5064

Journal of the American Chemical Society
Article
Robertson, J. W. F.; Wasserfallen, D.; Grimsdale, A. C.; Wu, J.; Mullen,
Ahn, S.; Kim, J. B.; Schenck, C.; Hiszpanski, A. M.; Oh, S.; Schiros, T.;
Loo, Y.-L.; Nuckolls, C. J. Am. Chem. Soc. 2013, 135, 2207−2212.
(k) Rim, K. T.; Siji, M.; Xiao, S.; Myers, M.; Carpentier, V. D.; Liu, L.;
Su, C.; Steigerwald, M. L.; Hybertsen, M. S.; McBreen, P. H.; Flynn, G.
W.; Nuckolls, C. Angew. Chem., Int. Ed. 2007, 46, 7891−7895. (l) Hill,
J. P.; Jin, W.; Kosaka, A.; Fukushima, T.; Ichihara, H.; Shimomura, T.;
Ito, K.; Hashizume, T.; Ishii, N.; Aida, T. Science 2004, 304, 1481−
1482. (m) Harris, K. D.; Xiao, S.; Lee, C. Y.; Strano, M. S.; Nuckolls,
C.; Blanchet, G. B. J. Phys. Chem. C 2007, 111, 17947−17951.
(n) Hiszpanski, A. M.; Lee, S. S.; Wang, H.; Woll, A. R.; Nuckolls, C.;
Loo, Y.-L. ACS Nano 2013, 7, 294−300. (o) Schiros, T.; Kladnik, G.;
Prezzi, D.; Ferretti, A.; Olivieri, G.; Cossaro, A.; Floreano, L.; Verdini,
A.; Schenck, C.; Cox, M.; Plunkett, K.; Delongchamp, D.; Nuckolls,
C.; Morgante, A.; Cvetko, D.; Kymissis, I. Adv. Funct. Mater. 2013, 3,
894−902. (p) Kang, S. J.; Kim, J. B.; Chiu, C.-Y.; Ahn, S.; Schrios, T.;
Lee, S. S.; Yager, K. G.; Toney, M. F.; Loo, Y. -L.; Nuckolls, C. Angew.
Chem., Int. Ed. 2012, 51, 8594−8597. (q) Mynar, J.; Yamamoto, T.;
Kosaka, A.; Fukushima, T.; Ishii, N.; Aida, T. J. Am. Chem. Soc. 2008,
130, 1530−1531.
̈
K. Adv. Funct. Mater. 2007, 17, 2528−2563. (k) Dossel, L. F.; Kamm,
̈
V.; Howard, I. A.; Laquai, F.; Pisula,
́
W.; Feng, X.; Li, C.; Takase, M.;
Kudernac, T.; Feyter, S. D.; Mullen, K. J. Am. Chem. Soc. 2012, 134,
5876−5886. (l) Mativetsky, J. M.; Kastler, M.; Savage, R. C.; Gentilini,
D.; Palma, M.; Pisula, W.; Mullen, K.; Samori, P. Adv. Funct. Mater.
2009, 19, 2486−2494. (m) Wong, W. W. H.; Ma, C.-Q.; Pisula, W.;
Yan, C.; Feng, X.; Jones, D. J.; Mullen, K.; Janssen, R. A. J.; Bauerle, P.;
Holmes, A. B. Chem. Mater. 2010, 22, 457−466. (n) Jones, D. J.;
Purushothaman, B.; Ji, S.; Holmes, A. B.; Wong, W. W. H. Chem.
Commun. 2012, 48, 8066−8068. (o) Yin, M.; Shen, J.; Pisula, W.;
Liang, M.; Zhi, L.; Mullen, K. J. Am. Chem. Soc. 2009, 131, 14618−
14619. (p) Feng, X.; Wu, J.; Enkelmann, V.; Mullen, K. Org. Lett.
̈
̈
̈
̈
̈
2006, 8, 1145−1148. (q) Yan, X.; Cui, X.; Li, B.; Li, L. Nano Lett.
2010, 10, 1869−1873. (r) Kastler, M.; Schmidt, J.; Pisula, W. J. Am.
Chem. Soc. 2006, 128, 9526−9534. (s) Feng, X.; Pisula, W.; Takase,
M.; Dou, X.; Enkelmann, V.; Wagner, M. Chem. Mater. 2008, 20,
2872−2874. (t) Feng, X.; Pisula, W.; Ai, M.; Groper, S.; Rabe, J. P.;
̈
Mullen, K. Chem. Mater. 2008, 20, 1191−1193. (u) Feng, X.; Wu, J.;
̈
(10) Goossens, R.; Smet, M.; Dehaen, W. Tetrahedron Lett. 2002, 43,
6605−6608.
Ai, M.; Pisula, W.; Zhi, L.; Rabe, J. P.; Mullen, K. Angew. Chem. 2007,
119, 3093−3096. (v) Boukhvalov, D. W.; Feng, X. L.; Mullen, K. J.
̈
̈
(11) (a) Grzybowski, M.; Skonieczny, K.; Butenschon, H.; Gryko, D.
̈
Phys. Chem. C 2011, 115, 16001−16005. (w) Zhang, W.; Jin, W.;
Fukushima, T.; Ishii, N.; Aida, T. J. Am. Chem. Soc. 2013, 135, 114−
117. (x) Yamamoto, Y.; Fukushima, T.; Saeki, A.; Seki, S.; Tagawa, S.;
Ishii, N.; Aida, T. J. Am. Chem. Soc. 2007, 129, 9276−9277. (y) Feng,
T. Angew. Chem., Int. Ed. 2013, 52, 9900−9930. (b) Zhai, L.; Shukla,
R.; Wadumethrige, S. H.; Rathore, R. J. Org. Chem. 2010, 75, 4748−
4760.
(12) Bandgar, B. P.; Bettigeri, S. V.; Phopase, J. Tetrahedron Lett.
X.; Pisula, W.; Kudernac, T.; Wu, D.; Zhi, L.; Feyter, S. D.; Mullen, K.
̈
2004, 45, 6959−6962.
(13) (a) Chen, L.; Puniredd, S. R.; Tan, Y.-Z.; Baumgarten, M.;
Zschieschang, U.; Enkelmann, V.; Pisula, W.; Feng, X.; Klauk, H.;
J. Am. Chem. Soc. 2009, 131, 4439−4448.
(4) Simpson, C. D.; Brand, J. D.; Berresheim, A. J.; Przybilla, L.;
Rader, H. J.; Mullen, K. Chem.Eur. J. 2002, 8, 1422−1429.
̈
̈
Mullen, K. J. Am. Chem. Soc. 2012, 134, 17869−17872. (b) Chen, L.;
̈
(5) Yang, X.; Dou, X.; Rouhanipour, A.; Zhi, L.; Rader, H. J.; Mullen,
̈
̈
Mali, K. S.; Puniredd, S. R.; Baumgarten, M.; Parvez, K.; Pisula, W.;
K. J. Am. Chem. Soc. 2008, 130, 4216−4217.
Feyter, S. D.; Mullen, K. J. Am. Chem. Soc. 2013, 135, 13531−13537.
̈
(6) (a) Zhang, C.; Liu, Y.; Xiong, X.; Peng, L.; Gan, L.; Chen, C.; Xu,
H. Org. Lett. 2012, 14, 5912−5915. (b) Hill, J.; Jin, W.; Kosaka, A.;
Fukushima, T.; Ichihara, H.; Shimomura, T.; Ito, K.; Hashizume, T.;
Ishii, N.; Aida, T. Science 2004, 304, 1481−1482. (c) Diez-Perez, I.; Li,
Z.; Hihath, J.; Li, J.; Zhang, C.; Yang, X.; Zang, L.; Dai, Y.; Feng, X.;
(14) Chen, L.; Mali, K. S.; Puniredd, S. R.; Baumgarten, M.; Parvez,
K.; Pisula, W.; Feyter, S. D.; Mullen, K. J. Am. Chem. Soc. 2013, 135,
̈
13561−13567.
(15) Rieger, R.; Mullen, K. J. Phys. Org. Chem. 2010, 23, 315−325.
(16) Li, Z.; Lucas, N. T.; Wang, Z.; Zhu, D. J. Org. Chem. 2007, 72,
3917−3920.
̈
Mullen, K.; Tao, N. Nat. Commun. 2010, 1, 1−5. (d) Yamamoto, Y.;
̈
Fukushima, T.; Suna, Y.; Ishii, N.; Saeki, A.; Seki, S.; Tagawa, S.;
Taniguchi, M.; Kawai, T.; Aida, T. Science 2006, 314, 1761−1764.
(e) Mynar, J.; Yamamoto, T.; Kosaka, A.; Fukushima, T.; Ishii, N.;
Aida, T. J. Am. Chem. Soc. 2008, 130, 1560−1561.
(7) Clar, E.; Stephen, J. F. Tetrahedron 1965, 21, 467−470.
(8) (a) Xiao, S.; Myers, M.; Miao, Q.; Sanaur, S.; Pang, K.;
Steigerwald, M. L.; Nuckolls, C. Angew. Chem., Int. Ed. 2005, 44,
7390−7394. (b) Xiao, S.; Tang, J.; Beetz, T.; Guo, X.; Tremblay, N.;
Siegrist, T.; Zhu, Y.; Steigerwald, M. L; Nuckolls, C. J. Am. Chem. Soc.
2006, 128, 10700−10701. (c) Plunkett, K. N.; Godula, K.; Nuckolls,
C.; Tremblay, N.; Whalley, A. C.; Xiao, S. Org. Lett. 2009, 11, 2225−
2228. (d) Loo, Y.-L.; Hiszpanski, A. M.; Kim, B.; Wei, S.; Chiu, C.-Y.;
Steigerwald, M. L.; Nuckolls, C. Org. Lett. 2010, 12, 4840−4843.
(9) (a) Xiao, S.; Kang, S.; Zhong, Y.; Zhang, S.; Scott, A.; Moscatelli,
A.; Turro, N.; Steigerwald, M.; Li, H.; Nuckolls, C. Angew. Chem., Int.
Ed. 2013, 52, 4558−4562. (b) Chiu, C.-Y.; Kim, B.; Gorodetsky, A. A.;
Sattler, W.; Wei, S.; Sattler, A.; Steigerwald, M.; Nuckolls, C. Chem. Sci.
2011, 2, 1480−1486. (c) Whalley, A. C.; Plunkett, K. N.; Gorodetsky,
A. A.; Schenck, C. L.; Chiu, C.-Y.; Steigerwald, M. L.; Nuckolls, C.
Chem. Sci. 2011, 2, 132−135. (d) Xiao, S.; Kang, S.; Wu, Y.; Ahn, S.;
Kim, J.; Loo, Y-L; Siegrist, T.; Steigerwald, M.; Li, H.; Nuckolls, C.
Chem. Sci. 2013, 4, 2018−2013. (e) Guo, X.; Myers, M.; Xiao, S.;
Lefenfeld, M.; Steiner, R.; Tulevski, G. S.; Tang, J.; Baumert, J.;
Leibfarth, F.; Yardley, J. T.; Steigerwald, M. L.; Kim, P.; Nuckolls, C.
Proc. Natl. Acad. Sci. U.S.A. 2006, 103, 11452−11456. (f) Cohen, Y. S.;
Xiao, S.; Steigerwald, M. L.; Nuckolls, C.; Kagan, C. R. Nano Lett.
2006, 6, 2838−2841. (g) Guo, X.; Xiao, S.; Myers, M.; Miao, Q.;
Steigerwald, M. L.; Nuckolls, C. Proc. Natl. Acad. Sci. U.S.A. 2009, 106,
691−696. (h) Tremblay, N. J.; Gorodetsky, A. A.; Cox, M. P.; Schiros,
T.; Kim, B.; Steiner, R.; Bullard, Z.; Sattler, A.; So, W.-Y.; Itoh, Y.;
Toney, M. F.; Ogasawara, H.; Ramirez, A. P.; Kymissis, I.; Steigerwald,
M. L.; Nuckolls, C. ChemPhysChem 2010, 11, 799−803. (j) Kang, S. J.;
5064
dx.doi.org/10.1021/ja413018f | J. Am. Chem. Soc. 2014, 136, 5057−5064