Synthesis, Molecular Packing, and Thin Film Transistors of Dibenzo[a,m]rubicenes

Article abstract of DOI:10.1021/jacs.5b10687

We herein report an efficient synthesis of dibenzo[a,m]rubicene, a new member of nonplanar cyclopenta-fused polycyclic aromatic hydrocarbon, and its derivatives. It is found that the conformation and molecular packing of dibenzo[a,m]rubicenes in the solid

Full text of DOI:10.1021/jacs.5b10687

Article
pubs.acs.org/JACS
Synthesis, Molecular Packing, and Thin Film Transistors of
Dibenzo[a,m]rubicenes
Xiao Gu, Xiaomin Xu, Huiyan Li, Zhifeng Liu, and Qian Miao*
Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China
S
* Supporting Information
ABSTRACT: We herein report an efficient synthesis of dibenzo[a,m]rubicene, a
new member of nonplanar cyclopenta-fused polycyclic aromatic hydrocarbon, and its
derivatives. It is found that the conformation and molecular packing of
dibenzo[a,m]rubicenes in the solid state can be tuned by the substituting groups,
and the silylethynylated derivatives of dibenzo[a,m]rubicenes function as p-type
organic semiconductors in solution-processed thin film transistors with field effect
mobility of up to 1.0 cm2 V−1 s−1.
bold lines in Figure 1a is similar to [5]helicene (Figure 1b) but
involves less steric hindrance because it has a cyclopentadiene
ring replacing a benzene ring in [5]helicene.7
INTRODUCTION
This study explores dibenzo[a,m]rubicene (1a in Figure 1a), a
new member of cyclopenta-fused polycyclic aromatic hydro-
■
Here we report an efficient synthesis of 1a and its new
derivatives and demonstrate that the conformation and
molecular packing of dibenzo[a,m]rubicenes in the solid state
can be tuned by the substituting groups. It is found that
silylethynylated derivatives 1b and 1c function as p-type
organic semiconductors in solution-processed OTFTs with
field effect mobility of up to 1.0 cm2 V−1 s−1.
RESULTS AND DISCUSSION
■
Synthesis. Shown in Scheme 1 is the synthesis of
dibromodibenzo[a,m]rubicene 2 starting from terephthalate
3, which was prepared from condensation between dimethyl
Scheme 1. Synthesis of 2
Figure 1. Structures of dibenzo[a,m]rubicene (1a) and related
molecules. (a) 1a with the angularly fused pentacyclic moiety
highlighted; (b) rubicene and [5]helicene; (c) new derivatives of 1a.
carbons (CP-PAHs).1 Dibenzo[a,m]rubicene was not docu-
mented, although its 3,12-tert-butyl-substituted derivatives were
reported in 2009.2 Dibenzo[a,m]rubicene can be regarded as a
fragment of C70 and formally results from fusing two benzene
rings to rubicene (Figure 1b), a planar CP-PAH discovered in
the 1920s3 and recently reported as a p-type semiconductor in
organic thin film transistors (OTFTs).4,5 Unlike rubicene, 1a is
out of plane because of overcrowding in the two fjord regions
and thus can be regarded as an analogue of double helicenes.6
The angularly fused pentacyclic moiety in 1a as shown with
Received: October 13, 2015
Published: December 11, 2015
© 2015 American Chemical Society
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acetonedicarboxylate and benzil8 and the subsequent Diels−
Alder reaction with diphenylacetylene by modification of the
reported method.9 Heating 3 with methanesulfonic acid
resulted in diketone 4, which, as reported earlier, was prepared
from diethyl 2,3,5,6-tetraphenylterephthalate in two steps
(hydrolysis followed by cyclization).9 The two carbonyl groups
of 4 reacted with CBr4 in the Corey−Fuchs reaction,10 yielding
5, which cyclized in an intramolecular Heck-type reaction to
give 2. It was necessary to have this intramolecular Heck-type
reaction completed within 15 min. Otherwise, prolonged
heating led to debromination of 2.
isomerization. Moreover, the twisted-to-anti interconversion of
1a occurs through a partially planar transition state (TS), as
shown in Figure 2. The energy barrier between twisted-1a and
Starting from 2, unsubstituted and functionalized dibenzo-
[a,m]rubicenes were easily synthesized, as shown in Scheme 2.
Scheme 2. Synthesis of 1a−e
Figure 2. Molecular models of twisted-1a and anti-1a and the
transition state as optimized at the B3LYP/6-31G(d,p) level of DFT.
the transition state is calculated as 29 kJ mol−1, which
corresponds to a large rate constant (5.2 × 107 s−1) at room
temperature (298.15 K), as estimated using the Eyring equation
k = κ(kBT/h)exp(−ΔG⧧/RT)
and assuming a value of unity for the transmission coefficient
(κ).14 These calculations indicate that the dominating con-
former of 1a−e is the twisted conformer, which is
interconverted with the anti conformer very fast at room
temperature.
Optical and Electronic Properties. Both 1a and 1e
formed yellow solutions in common organic solvents, emitting
yellow fluorescence with similar fluorescence quantum yields
(18.6 and 17.5%, respectively, as measured in CH2Cl2). In
contrast, the orange solutions of 1b−d in common organic
solvents emitted weaker orange fluorescence with a lower
fluorescence quantum yield (2% as measured in CH2Cl2) in
relation to the presence of silylethynyl substituents. Since
silylethynylated dibenzo[a,m]rubicenes 1b−d exhibited almost
identical UV−vis absorption and fluorescence spectra, Figure 3
only shows the absorption and fluorescence spectra of 1a, 1b,
and 1e in CH2Cl2 at the same concentration. It is found that
Lithium−halogen exchange on 2 followed by treatment with
dilute acid led to 1a, and the Sonogashira and Suzuki coupling
reactions of 2 resulted in 1b−d and 1e, respectively. Silyl
groups of different sizes are introduced in 1b−d to tune the
packing motifs of dibenzo[a,m]rubicenes, as inspired by
Anthony’s silylethynylated pentacenes.11 Cyclization on the
positions ortho and para to the methoxyl groups of 1e in a
Scholl-type reaction12 can, in principle, result in aromatic
bowls. However, attempted oxidative cyclodehydrogenation of
1e with FeCl3 or DDQ−methanesulfonic acid did not lead to
cyclization.
Conformations. As an analogue of double helicenes,
dibenzo[a,m]rubicene can, in principle, adopt two stable
conformations, namely, twisted or anti-folded, depending on
the helicity of the two fjord regions. To find what kind of
conformation 1a−e adopt at room temperature, molecular
structures of 1a−e were calculated at the B3LYP/6-31G(d,p)
level of density functional theory (DFT).13 As summarized in
Table S2 in the Supporting Information, it is found that the
twisted conformers of 1a−e are all thermodynamically more
stable than the corresponding anti-folded conformers by 12.8 to
14.6 kJ mol−1, which corresponds to equilibrium constants in
the range of 175 to 361 at 25 °C for the anti-to-twisted
Figure 3. UV−vis absorption (solid lines) and fluorescence (dashed
lines) spectra of 1a, 1b, and 1e in solutions (5 × 10−6 M in CH2Cl2).
The fluorescence spectra of 1a, 1b, and 1e were recorded with
excitation at 445, 473, and 451 nm, respectively.
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Table 1. Absorption, Reduction Potentials, and Frontier Molecular Orbital Energy Levels of 1a−e
f
experimental
calculated
HOMO (eV)
LUMO (eV)
gap (eV)
a
a
b
c
d
e
λmax (nm)
λedge (nm)
Ered (V)
LUMO (eV)
HOMO (eV)
gap (eV)
twisted
anti
twisted
anti
twisted
anti
1a
1b
1c
1d
1e
445
473
473
473
451
508
551
551
551
515
−1.80
−1.57
−1.56
−1.57
−1.83
−3.30
−3.53
−3.54
−3.53
−3.27
−5.74
−5.78
−5.79
−5.78
−5.68
2.44
2.25
2.25
2.25
2.41
−5.67
−5.65
−5.66
−5.63
−5.50
−5.69
−5.66
−5.66
−5.63
−5.51
−2.68
−2.89
−2.89
−2.87
−2.53
−2.67
−2.88
−2.89
−2.86
−2.53
2.99
2.76
2.77
2.76
2.97
3.02
2.78
2.77
2.77
2.98
a
The wavelength of maximum absorption in the visible light region (λmax) and the wavelength of absorption edge (λedge) from a 5 × 10−6 M solution
b
c
in CH2Cl2. Half-wave potential versus ferrocenium/ferrocene for the first reduction wave. Estimated from LUMO = −5.10 − Ered (eV).
d
e
f
Calculated from the HOMO−LUMO gap and the LUMO energy level. HOMO−LUMO gap estimated from λedge. Calculated at the B3LYP level
of DFT with 6-311++G(d,p)//6-31G(d,p) basis sets.
the absorption spectrum of 1b is red-shifted by 28 nm relative
to that of 1a, as measured from the longest wavelength
absorption maxima, while the absorption spectrum of 1e
exhibits a much smaller red shift relative to that of 1a, likely
because the substituting phenyl groups are almost orthogonal
to the polycyclic backbone with poor conjugation. As shown in
Figure 3, the fluorescence spectra of 1a, 1b, and 1e exhibit
Stokes shifts of 0.43, 0.44, and 0.38 eV, respectively. These
large Stokes shifts are in agreement with the fact that 1a−e are
flexible molecules with a small energy barrier between the
twisted and anti conformations.
The redox behaviors of 1a−e in solution were investigated
with cyclic voltammetry. In the test window of cyclic
voltammetry, 1a−e did not exhibit any oxidation waves. 1a−c
and 1e all exhibited one quasi-reversible reduction wave, while
1d exhibited two quasi-reversible reduction waves (Figure S1 in
the Supporting Information). Based on the first reduction
potential15 as well as the absorption edges found from the UV−
vis absorption spectra, the energy levels of the highest occupied
molecular orbital (HOMO) and the lowest unoccupied
molecular orbital (LUMO) for 1a−e are estimated and
summarized in Table 1. The frontier molecular orbitals of
1a−e were also calculated with both the twisted and anti
conformations. As summarized in Table 1, the twisted and anti
conformers of each molecule have essentially the same HOMO
and LUMO energy levels. As shown in the Supporting
Information, the wave functions of HOMO and LUMO in
1a−e are all delocalized over the entire π-backbone and
essentially do not differ in the twisted and anti conformers. The
calculated HOMO energy levels are in good agreement with
the experimental values, while the calculated LUMO energy
levels are higher than the corresponding experimental values by
a larger degree similar to the reported CP-PAHs.16 The
calculated HOMO and LUMO energy levels of 1a are both
lower than the reported values of rubicene (−5.29 eV for
HOMO and −2.54 eV for LUMO)4 as a result of chromophore
expansion by benzoannulation as well as deviation from
planarity.
Figure 4. Crystal structure of 1a showing (a) P-enantiomer and (b)
π−π stacking. C atoms are shown as ellipsoids at the 50% probability
level. In (b), M-enantiomers are shown in yellow and the P-
enantiomers in blue.
Figure 4b, the crystal of 1a consists of segregated stacks of M-
and P-enantiomers (shown in yellow and blue, respectively),
and molecules of the same chirality stack with each other in one
stack. Since the polycyclic backbone of 1a can be regarded as
two benzo[b]fluorene subunits joined by the central benzene
ring, the π-to-π distance in a stack of 1a can be determined by
measuring the distance between the benzo[b]fluorene planes or
the distance between the central benzene planes of two
neighboring molecules. It is found that the stack of 1a is
associated with a π-to-π distance of 3.64 Å as measured from
the distance between the two benzo[b]fluorene planes of
neighboring molecules.
With essentially the same twisted backbone, 1b−d also exist
as a pair of enantiomers in racemic crystals. However, instead of
forming segregated stacks, M- and P-enantiomers of 1b form π-
stacked columns with an alternate arrangement, as shown in
Figure 5a. The π-to-π distance in this column is not measured
because neither the central benzene rings nor the benzo[b]-
fluorene planes in the neighboring molecules of 1b are parallel
with each other. Instead, intermolecular contacts shorter than
double the van der Waals radius of carbon are found between
carbon atoms in the alternate π-stack of 1b, as also shown in
Figure 5a. Moreover, this type of π-stacking involves a rotation
of the P-enantiomer relative to the M-enantiomer below it, as
Crystal Structures. Single crystals of 1a qualified for X-ray
crystallography were grown by cooling its hot solution in
toluene, and those of 1b−e were grown from solutions in
CH2Cl2−ethyl acetate by slow evaporation of solvents. As
found from the crystal structures, the dibenzo[a,m]rubicene
backbone of 1a−d adopts a twisted conformation, while that of
1e adopts an anti conformation in the crystals. With a twisted
conformation, 1a is a chiral molecule forming a racemic crystal.
Figure 4a shows the P-enantiomer of 1a having its fjord regions
distorted with torsion angles of 13.9 and 16.2°. As shown in
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Figure 5. (a) Side view and (b) top view of the π−π stacking of 1b in
the crystal. Hydrogen atoms are removed for clarification, and C and
Si atoms are shown as ellipsoids at the 50% probability level. The M-
enantiomers are shown in yellow and the P-enantiomers in blue.
Figure 7. Molecular packing of 1e in the single crystal. Carbon and
oxygen atoms are shown as gray and red ellipsoids at the 50%
probability level, and hydrogen atoms are shown as white balls.
shown in Figure 5b. With the trimethylsilyl group of 1b
replaced by a t-butyldimethylsilyl group, 1c exhibits essentially
the same molecular packing as 1b, as found from its crystal
structure. In contrast, further increasing the size of substituting
groups leads to a very different molecular packing in the crystal
structure of 1d likely because the bulky triisopropylsilyl groups
of 1d cannot be accommodated in the columnar stacking of 1b
and 1c. As shown in Figure 6, molecules of 1d form shifted π-
molecules of 1e are separated with a large distance of 3.95 Å
between the central benzene rings of the polycyclic framework.
Semiconductor Properties. The HOMO energy levels
and π−π stacking of 1a−d suggest that they can, in principle,
function as p-type semiconductors. On the other hand, the
large π-to-π distance of 1e suggests an unfavorable molecular
packing for organic semiconductors. To test the potential
semiconductor properties of dibenzo[a,m]rubicenes in OTFTs,
we first attempted to dip-coat thin films 1a−e on a highly
doped silicon substrate, which had a layer of SiO2 on the
surface as a dielectric. However, only 1b and 1c formed
continuous films, while 1a, 1d, and 1e formed isolated
crystalline or amorphous domains on SiO2. It was found that
the dip-coated films of 1b and 1c on SiO2 functioned as p-type
semiconductors, exhibiting a field effect mobility of up to 1 ×
10−3 and 2 × 10−4 cm2 V−1 s−1, respectively. To improve the
quality of organic films, we replaced the conventional SiO2 with
a high-k dielectric layer of AlOy/TiOx,17 which was modified
with a self-assembled monolayer (SAM) of 12-cyclohexyldo-
decylphosphonic acid (CDPA) to provide a dielectric surface
with high molecular ordering and good wettability by common
organic solvents.18 As shown in Figure 8a, thin films of 1b
consisting of aligned crystalline fibers were formed by
immersing the CDPA/AlOy/TiOx substrate into a solution of
1b (2 mg mL−1) in 1:1 (v/v) CH2Cl2−acetone and then
pulling it up with a constant speed of 1.3 μm s−1. Under the
Figure 6. Crystal structure of 1d showing π−π stacking. Hydrogen
atoms are removed for clarification. Carbon atoms in the polycyclic
backbone are shown as ellipsoids at the 50% probability level, and
silylethynyl substituents are shown as capped sticks. The M-
enantiomers are shown in yellow and the P-enantiomers in blue.
stacks with an alternate arrangement of M- and P-enantiomers.
The π-to-π distances between the adjacent M- and P-
enantiomers of 1d are 3.47 and 3.56 Å as measured from the
distance between the two benzo[b]fluorene planes.
With a phenyl-substituting group, 1e has an achiral anti-
folded backbone of dibenzo[a,m]rubicene in the crystals. The
torsion angle between the substituting phenyl group and the
polycyclic backbone is about 80°. As twisted-1e dominates in
the solution and converts to anti-1e fast, the presence of anti-1e
in the crystals is likely a result from closer packing of anti-1e
that accompanies lower solubility. The molecular packing of 1e
is dominated by an edge-to-face interaction between the
substituting phenyl group and the polycyclic backbone, as
shown in Figure 7. The distance between the hydrogen atom in
the phenyl and the carbon atom in the polycyclic backbone is
2.67 Å, which is shorter than the sum of the van der Waals radii
(2.79 Å). With such edge-to-face interaction, the adjacent
Figure 8. (a) Reflection polarized light micrograph for a dip-coated
film of 1b; (b) drain current (IDS) versus gate voltage (VGS) with drain
voltage (VDS) at −3 V for the best-performing OTFT of 1b with an
active channel of W = 1 mm and L = 150 μm measured in air.
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same condition, except a higher pulling speed (5.0 μm s−1), 1c
formed high-quality thin films with similar morphology, as
shown in Figure S2 in the Supporting Information. In contrast,
on the CDPA/AlOy/TiOx dielectric, 1a, 1d, and 1e still could
not form continuous films suitable for OTFTs, although varied
concentrations and pulling speeds were tested. Instead, 1a
formed poorly connected needle-shaped crystallites, while 1d
and 1e formed discrete amorphous domains, likely in relation
to their molecular packing. The fabrication of OTFTs was
completed by depositing a layer of gold on the film of 1b or 1c
through a shadow mask to form top-contact source and drain
electrodes. As measured in ambient air from at least 20
channels for each compound, 1b and 1c both functioned as p-
type semiconductors with a field effect mobility of 0.8 0.2
and 0.2 0.1 cm2 V−1 s−1, respectively. The highest mobility of
1b is 1.0 cm2 V−1 s−1 as extracted from the transfer I−V curve
shown in Figure 8b, using the equation
indicating a highly ordered film with the (110) plane parallel to
the substrate surface. As found from the AFM image (Figure
S10 in the Supporting Information), the film of 1c consisted of
similar microstripes of ca. 1 μm wide but were rougher than
that of 1b. Section analysis revealed a molecular step of ca. 1.6
nm high, which is in agreement with the d spacing of 16.1 Å.
The XRD and AFM indicate that molecules of 1c stand on the
surface of the CDPA/AlOy/TiOx dielectric with an orientation
slightly different than that of 1b but still stack in a column
roughly parallel to the surface, as shown in Figure S12 in the
Supporting Information. The AFM section analysis on the film
of 1c also shows deeper grain boundaries, which may account
for the lower mobility of 1c in thin films. In comparison to the
films on CDPA/AlOy/TiOx, the dip-coated film of 1b on bare
SiO2 exhibited the (200) and (400) diffractions in addition to
the (010), (040), and (050) diffractions, while the dip-coated
film of 1c on bare SiO2 exhibited the (020) and (040)
diffractions in addition to the (110), (330), and (550)
diffractions. The existence of an extra set of diffraction peaks
indicates that molecules of 1b are not uniformly oriented in the
film on bare SiO2, and neither do those of 1c. In comparison to
the films on CDPA/AlOy/TiOx, the dip-coated films of 1b and
1c on bare SiO2 contained much rougher microstripes that
accompany much deeper grain boundaries, as found from their
AFM images (Figure S11 in the Supporting Information).
Therefore, the much lower mobility for the films of 1b and 1c
on bare SiO2 can be explained as a result of poorer crystallinity
and morphology.
IDS = (μWCi/2L)(VGS − V )2
th
where IDS is the drain current, μ is field effect mobility, Ci is the
capacitance per unit area (210 nF cm−2) for the CDPA/AlOy/
TiOx dielectric, W is the channel width, L is the channel length,
and VGS and Vth are the gate and threshold voltage, respectively.
In comparison to 1b, 6,13-bis((triisopropylsilyl)ethynyl)-
pentacene, a benchmark p-type semiconductor, in solution-
processed transistors on the same CDPA/AlOy/TiOx dielectric
exhibited a higher field effect mobility (1.64 0.55 cm2 V−1
s−1),18 while rubicene in vacuum-deposited bottom-contact
OTFTs on bare SiO2 exhibited a lower mobility (0.32 0.04
cm2 V−1 s−1).4
CONCLUSION
■
To better understand the measured field effect mobilities of
1b and 1c in relation to their assemblies in the solid state, their
thin films were investigated with UV−vis absorption spectros-
copy, X-ray diffraction (XRD), and atomic force microscopy
(AFM). The dip-coated film of 1b on a quartz plate, similar to
that of 1c, exhibited a broadened and red-shifted absorption
spectrum relative to that of the solution, as shown in Figure S5
in the Supporting Information. This can be attributed to
electronic delocalization between π-stacked molecules in the
solid state, in agreement with the crystal structures.19,20 X-ray
diffraction patterns from the films of 1b on CDPA/AlOy/TiOx
(Figure S6 in the Supporting Information) exhibited peaks at
2θ = 4.51 (d spacing of 19.6 Å), 2θ = 18.09 (d spacing of 4.9
Å), and 2θ = 22.66 (d spacing of 3.9 Å). These peaks
correspond to the (010), (040), and (050) diffractions as
derived from the single-crystal structure of 1b, indicating a
highly ordered film with the b axis perpendicular to the
substrate surface. The AFM image for the film of 1b (Figure
S10 in the Supporting Information) revealed a smooth surface
containing highly ordered flat microstripes of ca. 1 μm wide.
Section analysis revealed a molecular step of ca. 1.9 nm high,
which is in agreement with the d spacing of 19.6 Å and the
molecular length of 1b (19.5 Å) as measured between the two
trimethylsilyl groups from the crystal structure. The XRD and
AFM indicate that molecules of 1b adopt an edge-on
orientation on the surface of the CDPA/AlOy/TiOx dielectric
and have their π-backbones stacked in a column roughly
parallel to the surface. X-ray diffraction patterns from the films
of 1c on CDPA/AlOy/TiOx (Figure S7 in the Supporting
Information) exhibited peaks at 2θ = 5.48 (d spacing of 16.1
Å), 2θ = 16.48 (d spacing of 5.4 Å), and 2θ = 27.63 (d spacing
of 3.2 Å). These peaks correspond to (110), (330), and (550)
diffractions as derived from the single-crystal structure of 1c,
In conclusion, the above study puts forth a new class of
polycyclic arenes containing fused five-membered rings. We
have developed an efficient synthesis of dibenzo[a,m]rubicene
and its derivatives and demonstrated that the conformation and
molecular packing of dibenzo[a,m]rubicenes in the solid state
are dependent on the substituting groups. With a nonplanar
conjugated backbone, 1b and 1c function as p-type organic
semiconductors in solution-processed OTFTs exhibiting a field
effect mobility of up to 1.0 cm2 V−1 s−1, which is higher than
those of the reported semiconductors based on CP-PAHs.4,21
This finding, together with a few reports on organic
semiconductors with nonplanar polycyclic conjugated back-
bones,22−25 suggests that a planar π-backbone is not the only
choice for designing high-mobility organic semiconductors.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/jacs.5b10687.
Experimental details of synthesis and characterization,
fabrication and characterization of organic thin film
transistors, and NMR spectra (PDF)
Crystallographic information files for 1a (CIF)
Crystallographic information files for 1b (CIF)
Crystallographic information files for 1c (CIF)
Crystallographic information files for 1d (CIF)
Crystallographic information files for 1e (CIF)
AUTHOR INFORMATION
Corresponding Author
*miaoqian@cuhk.edu.hk
■
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(15) The commonly used formal potential of the redox couple of
ferrocenium/ferrocene (Fc+/Fc) in the Fermi scale is −5.1 eV, which
is calculated on the basis of an approximation neglecting solvent effects
using a work function of 4.46 eV for the normal hydrogen electrode
(NHE) and an electrochemical potential of 0.64 V for Fc+/Fc versus
NHE. See: Cardona, C. M.; Li, W.; Kaifer, A. E.; Stockdale, D.; Bazan,
G. C. Adv. Mater. 2011, 23, 2367−2371.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank Ms. Hoi Shan Chan (The Chinese University of
Hong Kong) for the single-crystal crystallography. This work
was supported by the Research Grants Council of Hong Kong
(CRF C4030-14G) and the Chinese University of Hong Kong
(the Faculty Strategic Development Scheme from the Faculty
of Science and the One-Off Funding for Research from
Research Committee).
(16) (a) Wood, J. d.; Jellison, K. L.; Finke, A. D.; Wang, L.; Plunkett,
K. N. J. Am. Chem. Soc. 2012, 134, 15783−15789. (b) Chaolumen;
Murata, M.; Sugano, Y.; Wakamiya, A.; Murata, Y. Angew. Chem., Int.
Ed. 2015, 54, 9308−9312.
(17) Su, Y.; Wang, C.; Xie, W.; Xie, F.; Chen, J.; Zhao, N.; Xu, J. ACS
Appl. Mater. Interfaces 2011, 3, 4662−4667.
(18) Liu, D.; He, Z.; Su, Y.; Diao, Y.; Mannsfeld, S. C. B.; Bao, Z.; Xu,
J.; Miao, Q. Adv. Mater. 2014, 26, 7190−7196.
REFERENCES
■
(19) Miao, Q.; Chi, X.; Xiao, S.; Zeis, R.; Lefenfeld, M.; Steigerwald,
M. L.; Siegrist, T.; Nuckolls, C. J. Am. Chem. Soc. 2006, 128, 1340−
1345.
(1) For recent examples of CP-PAHs, see: (a) Chase, D. T.; Rose, B.
D.; McClintock, S. P.; Zakharov, L. N.; Haley, M. M. Angew. Chem.,
Int. Ed. 2011, 50, 1127−1130. (b) Chase, D. T.; Fix, A. G.; Rose, B. D.;
Weber, C. D.; Nobusue, S.; Stockwell, C. E.; Zakharov, L. N.;
Lonergan, M. C.; Haley, M. M. Angew. Chem., Int. Ed. 2011, 50,
11103−11106. (c) Shimizu, A.; Tobe, Y. Angew. Chem., Int. Ed. 2011,
50, 6906−6910. (d) Zhang, Q.; Kawasumi, K.; Segawa, Y.; Itami, K.;
Scott, L. T. J. Am. Chem. Soc. 2012, 134, 15664−15667. (e) London,
G.; von Wantoch Rekowski, M.; Dumele, O.; Schweizer, W. B.;
Gisselbrecht, J.-P.; Boudon, C.; Diederich, F. Chem. Sci. 2014, 5, 965−
972. (f) Liu, E.-C.; Chen, M.-K.; Li, J.-Y.; Wu, Y. T. Chem. - Eur. J.
2015, 21, 4755−4761. (g) Sbargoud, K.; Mamada, M.; Marrot, J.;
Tokito, S.; Yassar, A.; Frigoli, M. Chem. Sci. 2015, 6, 3402−3409.
(h) Nobusue, S.; Miyoshi, H.; Shimizu, A.; Hisaki, I.; Fukuda, K.;
Nakano, M.; Tobe, Y. Angew. Chem., Int. Ed. 2015, 54, 2090−2094.
(i) Dutta, A. K.; Linden, A.; Zoppi, L.; Baldridge, K. K.; Siegel, J. S.
Angew. Chem., Int. Ed. 2015, 54, 10792−10796.
(20) Lim, S.-H.; Bjorklund, T. G.; Spano, F. C.; Bardeen, J. C. Phys.
Rev. Lett. 2004, 92, 107402.
(21) (a) Kawase, T.; Fujiwara, T.; Kitamura, C.; Konishi, A.; Hirao,
Y.; Matsumoto, K.; Kurata, H.; Kubo, T.; Shinamura, S.; Mori, H.;
Miyazaki, E.; Takimiya, K. Angew. Chem., Int. Ed. 2010, 49, 7728−
7732. (b) Chase, D. T.; Fix, A. G.; Kang, S. J.; Rose, B. D.; Weber, C.
D.; Zhong, Y.; Zakharov, L. N.; Lonergan, M. C.; Nuckolls, C.; Haley,
M. M. J. Am. Chem. Soc. 2012, 134, 10349−10352. (c) Nishida, J.-i.;
Tsukaguchi, S.; Yamashita, Y. Chem. - Eur. J. 2012, 18, 8964−8970.
(d) Xia, H.; Liu, D.; Xu, X.; Miao, Q. Chem. Commun. 2013, 49,
4301−4303.
(22) Ball, M.; Zhong, Y.; Wu, Y.; Schenck, C.; Ng, F.; Steigerwald,
M.; Xiao, S.; Nuckolls, C. Acc. Chem. Res. 2015, 48, 267−276.
(23) Xiao, S.; Myers, M.; Miao, Q.; Sanaur, S.; Pang, K.; Steigerwald,
M. L.; Nuckolls, C. Angew. Chem., Int. Ed. 2005, 44, 7390−7394.
(2) Hseuh, H.-H.; Hsu, M.-Y.; Wu, T.-L.; Liu, R.-S. J. Org. Chem.
2009, 74, 8448−8451.
(3) (a) Pummerer, R.; Ulrich, H. M. Ber. Dtsch. Chem. Ges. 1925, 58,
1806−1808. (b) Schlenk, W.; Karplus, M. Ber. Dtsch. Chem. Ges. 1928,
61, 1675−1680.
(4) Lee, H.; Zhang, Y.; Zhang, L.; Mirabito, T.; Burnett, E. K.;
Trahan, S.; Mohebbi, A. R.; Mannsfeld, S. C. B.; Wudl, F.; Briseno, A.
L. J. Mater. Chem. C 2014, 2, 3361−3366.
(24) Gsanger, M.; Oh, J. H.; Konemann, M.; Hoffken, H. W.; Krause,
̈
̈
̈
A.-M.; Bao, Z.; Wurthner, F. Angew. Chem., Int. Ed. 2010, 49, 740−
̈
743.
(25) Shan, L.; Liu, D.; Li, H.; Xu, X.; Shan, B.; Xu, J.-B.; Miao, Q.
Adv. Mater. 2015, 27, 3418−3423.
(5) Dithiarubicene, which has two benzene rings in rubicene replaced
by two thiophene rings, was also recently reported. See: Mohebbi, A.
R.; Wudl, F. Chem. - Eur. J. 2011, 17, 2642−2646.
(6) For recent examples of double helicenes, see: (a) Fujikawa, T.;
Segawa, Y.; Itami, K. J. Am. Chem. Soc. 2015, 137, 7763−7768.
(b) Kashihara, H.; Asada, T.; Kamikawa, K. Chem. - Eur. J. 2015, 21,
6523−6527. (c) Lutke Eversloh, C.; Liu, Z.; Muller, B.; Stangl, M.; Li,
̈
̈
C.; Mullen, K. Org. Lett. 2011, 13, 5528−5531.
̈
(7) Dougherty, K. J.; Kraml, C. M.; Byrne, N.; Porras, J. A.; Bernhard,
S.; Mague, J. T.; Pascal, R. A., Jr Tetrahedron 2015, 71, 1694−1699.
(8) White, D. M. J. Org. Chem. 1974, 39, 1951−1952.
(9) Merlet, S.; Birau, M.; Wang, Z. Y. Org. Lett. 2002, 4, 2157−2159.
(10) For examples of synthesis of polycylic arenes using the Corey−
Fuchs reaction with similar conditions, see: (a) Donovan, P. M.; Scott,
L. T. J. Am. Chem. Soc. 2004, 126, 3108−3112. (b) Loo, Y.-L.;
Hiszpanski, A. M.; Kim, B.; Wei, S.; Chiu, C.-Y.; Steigerwald, M. L.;
Nuckolls, C. Org. Lett. 2010, 12, 4840−4843. (c) Cheung, K. Y.; Xu,
X.; Miao, Q. J. Am. Chem. Soc. 2015, 137, 3910−3914.
(11) (a) Anthony, J. E.; Brooks, J. S.; Eaton, D. L.; Parkin, S. R. J. Am.
Chem. Soc. 2001, 123, 9482−9483. (b) Anthony, J. E.; Eaton, D. L.;
Parkin, S. R. Org. Lett. 2002, 4, 15−18.
(12) Luo, J.; Xu, X.; Mao, R.; Miao, Q. J. Am. Chem. Soc. 2012, 134,
13796−13803.
(13) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648−5652.
(b) Miehlich, B.; Savin, A.; Stoll, H.; Preuss, H. Chem. Phys. Lett. 1989,
157, 200−206. (c) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B: Condens.
Matter Mater. Phys. 1988, 37, 785−789.
(14) Anslyn, E. V.; Dougherty, D. A. Modern Physical Organic
Chemistry; University Science Books: Sausalito, CA, 2004; Chapter 7.
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DOI: 10.1021/jacs.5b10687
J. Am. Chem. Soc. 2015, 137, 16203−16208