Soluble Graphene Nanoribbons from Planarization of Oligophenylenes

Article abstract of DOI:10.1002/chem.201604778

A solution-based chemical synthesis of two graphene nanoribbons with armchair edges is reported. The precursor oligophenylene molecules are synthesized and subjected to oxidative cyclodehydrogenation to afford the target molecules, G-1 and G-2. These molecules have good solubility in organic solvents, and show a large redshift in their absorption edge (up to 185 nm) and emission maximum (up to 125 nm) after planarization. Fibrous structures are formed upon self-assembly of molecules through columnar π–π stacking. Such molecular assemblies may be useful for various applications.

Full text of DOI:10.1002/chem.201604778

A Journal of
Accepted Article
Title: Soluble Graphene Nanoribbons From Planarization of
Oligophenylenes
Authors: choong ping sen and Suresh Valiyaveettil
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Soluble Graphene Nanoribbons From Planarization of
Oligophenylenes
Choong Ping Sen, and Suresh Valiyaveettil*
Abstract: A solution-based chemical synthesis of two graphene
nanoribbons with armchair edge is reported. The precursor
oligophenylene molecules were synthesized and subjected to
oxidative cyclodehydrogenation to afford target molecules, G-1 and
G-2. These molecules have good solubility in organic solvents, and
showed a large red-shift in absorption edge (up to 185 nm) and
emission maximum (up to 125 nm) after planarization. Fibrous
structures were formed through self-assembly of molecules via
columnar π – π stacking. Such molecular assembles may be useful
for various applications.
iron(III) chloride to afford target molecules G-1 and G-2 (Figure
1). Alkoxy groups are attached on the periphery of the molecules
to improve the solubility in organic solvents and ease of
purification. Also, the electron-donating alkoxy groups should
enhance the reactivity towards oxidative cyclodehydrogenation.
The main advantage of our method is the high solubility and
versatile strategy for introducing multiple functional groups on
target molecules.
Introduction
Soluble graphene nanoribbons (GNRs) have attracted
considerable interests owing to their extraordinary electronic,
thermal, and mechanical properties which make them potential
candidates for applications in field-effect transistors,[1]
optoelectronics,[2] sensors,[3] catalysis,[4] composites,[5] and
energy storage devices.[6] The well-defined chemical structure of
GNRs can be obtained from solution-based bottom-up synthesis,
which has many advantages over the top-down approaches In
addition, the optical, electrochemical, and electronic properties
of GNRs can be tuned by varying their size and symmetries.[7]
GNRs can be conveniently synthesized by using solution-
mediated intramolecular oxidative cyclodehydrogenation of
oligo- or polyphenylene precursors,[8] in the presence of Lewis
acid catalysts such as iron(III) chloride. However, the success of
such method is highly dependent on the electronic nature and
structure of the precursor molecules.[9] For example, the
intramolecular cyclodehydrogenation of o-phenylene is difficult
owing to the skeletal rearrangements of the phenyl groups.[10]
On the other hand, the oxidative cyclodehydrogenation of ortho-
phenylene will afford GNRs with armchair edges. Different
strategies had been reported for cyclodehydrogenation of o-
phenylenes such as photochemical dehydrohalogenation or
stepwise cyclodehydrogenation.[11] In a pioneering approach,
Müllen’s group reported many elegant solution syntheses of
GNRs and explored their applications.[8a, 8d, 8e, 11c, 12]
Figure 1. Bottom-up approach for synthesis of GNRs G-1 and G-2 from
planarization of oligophenylenes.
Results and Discussion
Synthesis and Characterization
The synthetic routes of precursor molecules (9 - 12) are given in
Schemes 1 and 2. The Suzuki-Miyaura[13] coupling between
borylated compound 1 and 2-bromo-1,4-diiodobenzene to afford
compound 2 in 42% yield. A subsequent Miyaura borylation[14] of
Herein, we report the synthesis of soluble GNRs with two
different sizes via extension of π conjugation in one direction.
The dimer and trimer oligophenylenes were prepared and
oxidative cyclodehydrogenation was achieved in presence of
compound
2 with bis(pinacolato)diboron to give borylated
compound 3 in 60% yield. The Suzuki-Miyaura coupling of
compound 4 and 2-bromo-1,4-diiodobenzene was attempted to
afford compound 5. However, mixed products of mono-, di-, and
tricoupled compounds were isolated, which led to a low yield
(19%) of target compound 5. This is attributed to the more
reactive borylated compound 4 incorporated with dialkoxy
groups. In order to resolve this issue, the Suzuki-Miyaura
coupling condition was optimized by using a palladium salt
(PdCl2(PPh3)2) and Na2CO3 in a mixture of THF/H2O/Aliquat®
336 at reflux temperature. This improved the product yield of
[*]
C. P. Sen and Prof. Dr. S. Valiyaveettil*
Department of Chemistry
National University of Singapore
3 Science Drive 2, Singapore 117543.
E-mail: chmsv@nus.edu.sg
Supporting information for this article is given via a link at the end of
the document.
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compound 5 to 50%. Subsequently, compound 5 was subjected
to borylation to afford compound 6 in 86% yield.
substitution of trimethylsilyl groups with iodo groups in presence
of excess iodine monochloride to afford compound 8 in 90%
yield. A subsequent Suzuki-Miyaura coupling of compound 8
with borylated compound 3 or 6 gave trimers 11 or 12 in 56 –
59% yields. All precursor molecules were fully characterized by
1H, 13C NMR spectroscopy, mass spectrometry and elemental
analyses (SI, Figure S1-S40).
Scheme 1. Synthesis of target compounds
1
- 6. (i) Pd(PPh3)4,
dimethoxyethane, 2M aqueous K2CO3 solution, 80 °C, 18 h, 42%; (ii)
bis(pinacolato)diboron, Pd(dppf)Cl2, KOAc, 1,4-dioxane, 80 °C, 18 h, 60%; (iii)
PdCl2(PPh3)2, Aliquat® 336, THF, 2M aqueous Na2CO3 solution, 70 °C, 18 h,
50%; (iv) bis(pinacolato)diboron, Pd(dppf)Cl2, KOAc, 1,4-dioxane, 90 °C, 24 h,
86%.
Scheme 3. Oxidative cyclodehydrogenation of 11-14 to afford G-1 (33%) and
G-2 (41%). (i) FeCl3, DCM, MeNO2, r.t, 18 h.
The intramolecular oxidative cyclodehydrogenation of
compounds 9 – 12 was attempted by using anhydrous iron(III)
chloride in a mixture of DCM / MeNO2 at room temperature
(Scheme 3). The reaction mixture was bubbled with a gentle
stream of nitrogen for 2 hours for the removal of gaseous HCl.
After stirring for 18 hours, methanol was added to stop the
reaction and the obtained precipitate was filtered, followed by
washing with methanol to remove excess iron(III) chloride. The
cyclodehydrogenation of compound
9 to form G-1 was
successful as evident from MALDI-TOF analysis, where the
molecular ion peak (G-1, m/z 962.1) with loss of 8 protons
(dimer 9, m/z 970.1) was observed (SI, Figure S42). G-1 exhibits
good solubility in organic solvent and was further purified by
using column chromatography with hexane/DCM as eluent. The
chemical structure of G-1 was characterized using NMR, MALDI-
TOF, and elemental analyses (SI, Figure S41-42). In order to
study the dimer system with catechol groups, oxidative
cyclodehydrogenation of dimer 10 was also attempted. However,
MALDI-TOF analysis showed that dimer 10 treated with iron(III)
chloride had resulted in a mixture of by-products with no cyclized
products. The side reaction is possibly due to having a larger
number of activating alkoxy groups on dimer 10. Further
characterization of by-products was not done owing to the
tedious purifications.
Scheme 2. Synthesis of target compounds 7 – 12. (i) Ni(cod)2, 2,2-bipyridyl,
cod, THF, 80 °C, 18 h, 68% for 9, 72% for 10; (ii) Pd(PPh3)4, dimethoxyethane,
2M aqueous K2CO3 solution, 70 °C, 18 h, 62%; (iii) iodine monochloride,
CHCl3, r.t, 1 h, 90%; (iv) for 11, Pd(PPh3)4, dimethoxyethane, 2M aqueous
K2CO3 solution, 80 °C, 24 h, 59%; for 12, PdCl2(PPh3)2, dimethoxyethane, 2M
aqueous Na2CO3 solution, 80 °C, 24 h, 56%.
Nickel-catalyzed Yamamoto homocoupling[15] of aromatic
halides compound 2 or compound 5, was carried out to obtain
dimers 9 or 10 in 68% and 72% yields, respectively. On the
other hand, the trimers 11 and 12 were prepared in a few steps.
On the other hand, attempt to cyclodehydrogenate trimer 11
by using anhydrous iron(III) chloride had resulted in partially
cyclized product as shown by MALDI-TOF analysis (SI, Figure
A
Suzuki-Miyaura
coupling
of
1,4-diiodo-2,5-
bis(trimethylsilyl)benzene with two equivalents of borylated
compound 1 gave compound 7 in 62% yield, followed by a
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S43). Other attempts to cyclodehydrogenate trimer 11 by using
excess iron(III) chloride, different types of solvents, other Lewis
acids such as aluminium(III) chloride, molybdenum(III) chloride,
The solution state absorption and emission spectra of G-1
and G-2 were recorded in chloroform at room temperature
(Figure 2). G-1 showed a red-shift in absorption maximum at
305 nm as compared to that of precursor dimer 9 (280 nm, SI,
Figure S47) owing to the extended π-conjugation induced by
planarization. G-1 also showed a red-shift in emission maximum
from 360 nm to 485 nm upon planarization. The geometry of G-1
was optimized by using density functional theory (DFT) at the
B3LYP/6-31g (d, p) level (Figure 3). G-1 has a slightly out-of-
plane conformation owing to the steric hindrance between
alkoxy group and adjacent hydrogen atom on the phenyl ring.
Similar steric effect had been reported in other polycyclic
aromatic systems substituted with solubilizing groups.[17] On the
other hand, the unsubstituted G-1 exhibits a planar conformation
as revealed from DFT calculation. This explains the blue-shift in
absorption for G-1 as compared to that of unsubstituted G-1
(λmax = 324 nm in trichlorobenzene).[18]
or antimony(V) chloride, were unsuccessful and gave
a
complicated mixture of partially cyclized product and unidentified
by-products. It is conceivable that the trimer 11 could undergo
skeletal rearrangement of phenyl groups, which resulted in
partially cyclized product.[10]
The trimer 12 substituted with dialkoxy groups was designed
to direct the intramolecular bond formation and enhance the
overall electron-donating property of the trimer system for
oxidative cyclodehydrogenation. As expected, the MALDI-TOF
analysis (SI, Figure S45) showed the presence of cyclized
product G-2 with a loss of 16 protons (m/z 1952.1) as compared
to trimer 12 (m/z 1968.5). G-2 is highly soluble in organic
solvents and was purified by using column chromatography on
1
silica gel with DCM as eluent. H NMR spectrum of G-2 showed
simpler signals in comparison to that of compound 12 (SI, Figure
S44).
(a)
(b)
Side View
Top View
Photophysical Properties
Absorption and emission spectra of precursor dimer and
trimer, 9 and 10 were recorded in chloroform (SI, Figure S46).
The dimer 9 showed absorption maximum and emission maxima
at 280 nm and 360 nm, respectively. On the other hand, dimer
10 incorporated with dialkoxy groups showed red-shifts in
absorption and emission maxima to 305 nm and 400 nm,
respectively, which is attributed to higher HOMO energy level for
dimer 10. The trimer 11 showed a small red-shift (5 nm) in
absorption maximum (λmax = 285 nm) as compared to the dimer
9 (λmax = 280 nm), indicating no conjugation between three
terphenyl chains. This is expected because the trimer 11 is in
twisted and cruciform-type conformation as observed in other
systems.[16] Similarly, the trimer 12 exhibited negligible changes
in absorption maximum (λmax = 304 nm) as compared to dimer
10 (λmax = 305 nm).
(d) Side View
Top View
(c)
Figure 3. Geometry optimization of unsubstituted (a and b) and substituted (c
and d) G-1 by using DFT calculation at the B3LYP/6-31g (d, p) level.
Table 1. Summary of photophysical properties of G-1 and G-2.
Absorption
CHCl3
Emission
CHCl3
0.8
0.4
0.0
0.8
0.4
0.0
Thin film
[b]
[c]
λmax
(nm)
ε[a]
λonset
Eg
λmax
(nm)
ϕf[d]
(%)
(M-1cm -1
)
(nm)
446
(eV)
2.78
G-1
G-2
305
10 350
27 100
485
41.5
54.9
368, 385,
472, 500
508,
545
550
2.25
300 400 500 600 700 800
Wavelength (nm)
[a] ε extinction coefficient was calculated by dividing absorbance with
concentration (M) and cuvette path length (1 cm). for G-2, the ε was
calculated at 385 nm. [b] λonset was calculated from the intersection of the
tangent lines drawn to the lowest energy absorption edge to the baseline in
thin film. [c] Eg = 1240/ λonset. [d] ϕf, fluorescence quantum yields were
determined in chloroform using fluorescein (0.1 M NaOH, quantum yield of
0.85) as a reference.[19]
Figure 2. Normalized absorption spectra of G-1 (-■-) and G-2 (-●-), and
normalized emission spectra of G-1 (- -▲- -) and G-2 (- -▼- -) recorded in
chloroform.
G-2 showed four absorption peaks at around 368 nm, 385
nm, 472 nm, and 500 nm in chloroform, and emission peaks at
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508 nm and 545 nm, respectively, with significant red-shifts as
compared to those of precursor 12 and target molecule G-1, due
to the extended conjugation. Also, G-2 showed a red-shift in
absorption maximum when compared with alkoxy-substituted
A)
B)
D)
hexa-peri-hexabenzocoronene
(λmax
=
380
nm
in
dichloromethane).[20] Similar to G-1, the steric hindrance
between alkoxy groups and aromatic protons resulted in a small
distortion of the edges on G-2 (SI, Figure S48). The optical band
gaps of G-1 and G-2 were estimated to be 2.78 eV and 2.25 eV,
respectively, in thin films (SI, Figure S47). All photophysical
properties of G-1 and G-2 are summarized in Table 1.
10 µm
1 µm
C)
2 nm
2 1/nm
Electrochemical Properties
The redox properties of the G-1 and G-2 were evaluated by
using cyclic voltammetry (CV) with a platinum working electrode,
a platinum wire counter electrode, and an Ag/AgCl reference
electrode, in
a
solution of 0.1
M
tetrabutylammonium
hexafluorophosphate in anhydrous dichloromethane and at a
scan rate of 100 mVs-1 (SI, Figure 49).
5 nm
20 nm
1.9 nm
The potentials were calibrated using ferrocene/ferocenium
ion redox couple as internal reference. The onset of oxidation
(Eoxonset) and reduction (Eredonset) were used to estimate HOMO
(EHOMO) and LUMO (ELUMO) energy levels using the equation
EHOMO = -(4.8 + Eoxonset) and ELUMO = -(4.8 + Eredonset) by
assuming the absolute HOMO energy level of ferrocene to be -
4.8 eV relative to the vacuum level. All electrochemical
properties of molecules are summarized in Table 2. G-1 showed
a quasi-reversible oxidation at +1.71 V and reduction at -1.60 V,
which correspond to HOMO and LUMO energy levels of -5.68
eV and -2.97 eV, respectively. In contrast, G-2 showed a quasi-
reversible oxidation at +1.13 V and irreversible reduction at -0.99
V, respectively. The HOMO and LUMO energy levels of G-2
Figure 4. Optical (A), SEM (B) and TEM (C) images of the G-2 fibers, which
were obtained by drop-casting the G-2 solution in THF : MeOH (4:1) on the
substrates. TEM image (D) and the SAED pattern (inset) of the film formed by
drop-casting the dilute G-2 solution in hexane.
Self-assembly Properties
Self-assembly of G-1 and G-2 were investigated using optical
microscopy and scanning electron microscopy (SEM). A few
drops of G-1 or G-2 solutions (0.2 mg/mL) in THF : MeOH (4:1)
were dropcasted on a glass substrate and the solvent was
allowed to evaporate slowly under ambient conditions. Both G-1
and G-2 solutions gave fibrous structures with ~ 500 nm in
diameter and up to few hundred microns in length (Figure 4, and
SI, Figure S50). The transmission electron microscopy (TEM)
image of the G-2 fibers revealed an ordered nanofibers with
diameter of ~2 nm (Figure 4C, and inset), which is in good
agreement to the molecular size of G-2 as estimated from DFT
calculation (SI, Figure S48). Many such fibers are packed to
form a thick nanofiber as a result from the assembly of π-
were
estimated
to
be
-5.24
eV
and
-3.53 eV. The electrochemical band gaps of the molecules are
similar to the estimated optical band gaps. Such differences are
explained based on the extended conjugation and presence of
electron-donating alkoxy groups on G-2 as compared to that of
G-1. On the other hand, the observed changes in LUMO energy
level of G-2 indicate stronger affinity to accept electron.
stacked columnar arrays of the G-2 molecules, which had been
21]
reported for other flat molecules.[8a,
The dispersion of G-2
Table 2. Summary of electrochemical properties of G-1 and G-2.
nanoribbons in hexane was sonicated and deposited on a
copper grid for TEM imaging. Unfortunately, the high-energy
electron beam melted the G-2 nanoribbons. The presence of
hexagonal patterns was observed from the selected area
electron diffraction (SAED, Figure 4D, inset) with a lattice
spacing of 0.43 nm. In addition, A single set of hexagonal spots
was obtained, which suggests the presence of monolayer
GNRs.[22] Such monolayer GNRs will be useful for potential
applications such as organic electronics.
[a]
[b]
Eox
Ered
Eox, onset
(V)
Ered,
HOMO[
c] (eV)
LUM
O[c]
(eV)
[d]
Eg
[a]
[b]
(V)
onset
(eV)
(V)
(V)
G-1
G-2
+1.71
+1.13
-1.60
-0.99
+1.41
+0.97
-1.30
-0.74
-5.68
-5.24
-2.97
-3.53
2.71
1.71
[a] Eox and Ered were determined from the maxima of oxidation and reduction
waves. [b] Eox,
and Ered,
were estimated from onset potentials of
onset
onset
oxidation and reduction peaks. [c] Electrochemical HOMO = -(Eox,calib + 4.8) eV
and electrochemical LUMO = -(Ered,calib + 4.8) eV, where Eox,calib and Ered,calib
were estimated from Eox,
and Ered,
after calibration with
onset
onset
ferrocene/ferocenium ion (Fc/Fc+). [d] Eg electrochemical band gap = LUMO –
HOMO.
Conclusions
In summary, two soluble GNRs molecules (G-1 and G-2) were
successfully synthesized by oxidative cyclodehydrogenation.
The success of the oxidative cyclodehydrogenation is dependent
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on the chemical structures of substrate and thus a proper design
of substrate is required. G-1 and G-2 showed red-shifts in both
absorption and emission maxima upon planarization. G-1 and G-
2 exhibited distorted structures owing to the steric hindrance
between alkoxy groups and adjacent aromatic protons as
revealed from DFT studies. The molecules were self-assembled
into nanofibers due to the strong columnar π – π stacking. Such
soluble GNRs can be explored for the fabrication of various
devices in the future.
(40 mL) was stirred at 90 °C for 18 hours. The reaction mixture
was poured into diethyl ether (60 mL) and washed with water (2
x 30 mL) and brine solution, dried over anhydrous sodium
sulfate, filtered, and concentrated under reduced pressure. The
crude product was purified on a silica gel column using hexane
1
as eluent to afford a colorless liquid (5.82 g, yield 63%). H NMR
(400 MHz, CDCl3) δ 7.36 (d, J = 9.0 Hz, 2H), 6.77 (d, J = 9.0 Hz,
2H), 3.91 (t, J = 6.6 Hz, 2H), 1.77 (m, 2H), 1.49 – 1.40 (m, 2H),
1.38 – 1.25 (m, 8H), 0.90 (t, J = 6.9 Hz, 3H). 13C NMR (101 MHz,
CDCl3) δ 158.28, 132.18, 116.32, 112.56, 68.29, 31.81, 29.34,
29.23, 29.18, 26.01, 22.65, 14.09. Elemental analysis calculated
(%) for C14H21BrO: C, 58.95; H, 7.42; Found: C, 59.91; H, 7.35.
Experimental Section
Compound 1
Materials
4-Bromo-1-n-octyloxybenzene
(3.86
g,
13.5
mmol),
All starting materials and reagents were purchased from Sigma-
Aldrich and used without further purification. Solvents used for
spectroscopic measurements were HPLC grade. Preparative
separations were performed by column chromatography on
silica gel grade 60 (0.040 – 0.063 mm) from SiliCycle.
bis(pinacolato)diboron (7.56 g, 29.8 mmol), Pd(dppf)Cl2 (0.66 g,
0.81 mmol) and KOAc (3.99 g, 40.6 mmol) were added to a
round bottom flask under nitrogen atmosphere. 1,4-Dioxane (50
mL) was added via syringe and the reaction mixture was stirred
at 80 °C for 18 hours. The reaction mixture was diluted with ethyl
acetate (60 mL), washed with water (2 x 25 mL) and brine
solution, dried over anhydrous sodium sulfate, filtered, and
concentrated under reduced pressure. The crude product was
purified on a silica gel column using a mixture of 10% DCM in
hexane as eluent to afford a pale-yellowish liquid (3.95 g, yield
Instrumentation
1H NMR and 13C NMR spectra were recorded on a Bruker
Avance AV300 (300 MHz), a Bruker Avance AV400 (400 MHz),
or a Bruker Avance AV500 (500 MHz) NMR instruments using
deuterated solvents from Cambridge Isotope Laboratories. The
chemical shifts were reported in part per million or ppm with
referenced to the residual solvent peak: s = singlet, d = doublet,
t = triplet, m = multiplet, and br = broad. Electron ionization high
1
88%). H NMR (300 MHz, CDCl3) δ 7.73 (d, J = 8.7 Hz, 2H),
6.88 (d, J = 8.7 Hz, 2H), 3.97 (t, J = 6.6 Hz, 2H), 1.83 – 1.73 (m,
2H), 1.50 – 1.43 (m, 2H), 1.33 (s, 12H), 1.32 – 1.23 (m, 8H),
0.88 (t, J = 6.9 Hz, 3H). 13C NMR (101 MHz, CDCl3) δ 161.78,
136.49, 113.88, 83.49, 67.80, 31.81, 29.35, 29.23, 26.03, 24.86,
22.65, 14.08. HR-MS (EI): M+ (C20H33BO3) Calculated m/z
resolution mass spectra (EI–HRMS) were obtained on
a
Finnigan TSQ7000. Atmospheric-pressure chemical ionization
(APCI) high resolution mass spectra (APCI-HRMS) were
obtained on Bruker MicrOTOF-QII. Matrix assisted laser
desorption ionization-time of flight (MALDI-TOF) mass spectra
were recorded on a Bruker Autoflex III TOF/TOF with reflectron
analyzers in positive ionization mode. Elemental analysis was
carried out on Elementar Vario Micro Cube. Absorption spectra
=332.2523, Found m/z
=
332.2531. Elemental analysis
calculated (%) for C20H33BO3: C, 72.29; H, 10.01; Found: C,
71.89; H, 9.87.
Compound 2
Compound 1 (1.60 g, 4.81 mmol), 2-bromo-1,4-diiodobenzene
(0.89 g, 2.18 mmol), and Pd(PPh3)4 (0.10 g, 0.087 mmol) were
added to a pre-degassed mixture of dimethoxyethane (25 mL)
and 2M aqueous K2CO3 solution (10 mL) under nitrogen
atmosphere. The reaction mixture was stirred at 80 °C for 18
hours, cooled, and diluted with ethyl acetate (40 mL). The
organic fraction was washed with water (2 x 20 mL) and brine
solution, dried over anhydrous sodium sulfate, filtered, and
concentrated under reduced pressure. The crude product was
purified on a silica gel column using a mixture of 15% DCM in
were measured on
a
UV-1800 Shimadzu UV-VIS
spectrophotometer with an optical filter that is calibrated at a
bandwidth of 1 nm. Emission spectra were measured on a RF-
5301PC Shimadzu spectrofluorophotometer with analytical
grade solvents. Cyclic voltammograms were recorded with a
computer controlled CHI electrochemical analyzer at a constant
scan rate of 100 mV/s. The potentials were calibrated using
ferrocene/ferocenium ion redox couple as internal reference.
The onset of oxidation (Eoxonset) and reduction (Eredonset) were
used to estimate HOMO (EHOMO) and LUMO (ELUMO) energy
levels using the equation EHOMO = -(4.8 + Eoxonset) and ELUMO = -
(4.8 + Eredonset). Scanning Electron micrograph was recorded on
1
hexane as eluent to afford a white solid (0.52 g, yield 42%). H
NMR (300 MHz, CDCl3) δ 7.85 (d, J = 1.8 Hz, 1H), 7.52 (d, J =
8.8 Hz, 2H), 7.53 – 7.50 (m, 1H), 7.38 (d, J = 8.8 Hz, 2H), 7.35
(m, 1H), 6.98 (d, J = 5.5 Hz, 2H), 6.95 (d, J = 5.5 Hz, 2H), 4.01 (t,
J = 5.8 Hz, 4H), 1.87 – 1.74 (m, 4H), 1.53 – 1.44 (m, 4H), 1.42 –
1.22 (m, 16H), 0.90 (t, J = 6.9 Hz, 6H). 13C NMR (126 MHz,
CDCl3) δ 159.20, 158.74, 141.23, 140.29, 133.03, 131.58,
131.52, 131.11, 130.58, 128.05, 125.56, 123.22, 114.96, 113.95,
68.17, 68.05, 31.87, 29.74, 29.42, 29.37, 29.33, 29.29, 26.14,
26.11, 22.70, 14.13. HRMS (APCl, +ve, (M +H)+) : (C34H46BrO2)
Calculated m/z = 565.2676, Found m/z = 565.2680. Elemental
a
JEOL JSM-6701F Field Emission Scanning Electron
Microscope (SEM). Transmission electron micrograph was
recorded on a JEOL JEM-3011.
Synthetic procedures
4-Bromo-1-n-octyloxybenzene
A
solution of 4-bromophenol (5.60 g, 32.4 mmol), 1-
bromooctane (8.73 g, 45.2 mmol), potassium carbonate (8.90 g,
64.3 mmol), and potassium iodide (2.10 g, 12.7 mmol) in DMF
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analysis calculated (%) for C34H45BrO2: C, 72.20; H, 8.02;
Found: C, 72.40; H, 7.96.
and concentrated under reduced pressure. The crude product
was purified on a silica gel column using a mixture of 20% DCM
in hexane, followed by a 30% DCM in hexane as eluents to
afford a pale-yellowish liquid (1.82 g, yield 79%). 1H NMR (500
MHz, CDCl3) δ 7.38 (dd, J = 7.9, 1.4 Hz, 1H), 7.29 (d, J = 1.4 Hz,
1H), 6.87 (d, J = 8.0 Hz, 1H), 4.02 (t, J = 6.6 Hz, 4H), 1.81 (m,
4H), 1.50 – 1.43 (m, 4H), 1.33 (s, 12H), 1.38 – 1.24 (m, 16H),
0.88 (t, J = 6.9 Hz, 6H). 13C NMR (126 MHz, CDCl3) δ 152.00,
148.56, 128.64, 119.55, 112.79, 105.00, 83.56, 69.29, 68.92,
31.84, 31.82, 29.42, 29.41, 29.37, 29.29, 29.27, 29.21, 26.06,
26.00, 24.86, 22.67, 22.66, 14.09. HR-MS (EI): M+ (C28H49BO4)
Calculated m/z =460.3724, Found m/z = 460.3725. Elemental
analysis calculated (%) for C28H49BO4: C, 73.03; H, 10.73;
Found: C, 72.62; H, 10.48.
Compound 3
Compound 2 (0.37 g, 0.65 mmol), bis(pinacolato)diboron (0.67
g, 2.64 mmol), Pd(dppf)Cl2 (0.05 g, 0.06 mmol) and KOAc (0.52
g, 5.33 mmol) were added to a round bottom flask under
nitrogen atmosphere. 1,4-Dioxane (25 mL) was added via
syringe and the reaction mixture was stirred at 80 °C for 18
hours, cooled, and diluted with ethyl acetate (30 mL). The
organic fraction was washed with water (2 x 15 mL) and brine
solution, dried over anhydrous sodium sulfate, filtered, and
concentrated under reduced pressure. The crude product was
purified on a silica gel column using a mixture of 15% DCM in
hexane, followed by 5% ethyl acetate in hexane as eluent to
afford a yellow sticky liquid (0.24 g, yield 60%). 1H NMR (300
Compound 5
MHz, CDCl3) δ 7.87 (d, J = 2.0 Hz, 1H), 7.59 (dd, J = 2.0, 8.0 Hz, Compound 4 (0.94 g, 2.04 mmol), 2-bromo-1,4-diiodobenzene
1H), 7.57 (d, J = 8.7 Hz, 2H), 7.40 (d, J = 8.0 Hz, 1H), 7.35 (d, J
= 8.7 Hz, 2H), 6.97 (d, J = 8.7 Hz, 2H), 6.92 (d, J = 8.7 Hz, 2H),
4.00 (t, J = 6.6 Hz, 4H), 1.81 (m, 4H), 1.53 - 1.43 (m, 4H), 1.41 –
1.27 (m, 16H), 1.25 (s, 12H), 0.90 (t, J = 6.9 Hz, 6H). 13C NMR
(126 MHz, CDCl3) δ 158.66, 158.45, 145.49, 138.34, 135.34,
133.32, 132.80, 130.11, 129.33, 128.37, 128.11, 114.75, 113.96,
83.75, 68.16, 68.13, 31.82, 31.61, 29.67, 29.40, 29.37, 29.33,
29.32, 29.25, 26.08, 24.65, 22.65, 14.08. HR-MS (EI): M+
(C40H57BO4) Calculated m/z =612.4350, Found m/z = 612.4355.
Elemental analysis calculated (%) for C40H57BO4: C, 78.41; H,
9.38; Found: C, 79.01; H, 9.42.
(0.42 g, 1.03 mmol), Aliquat® 336 (0.5 mL), and PdCl2(PPh3)2
(0.02 g, 0.028 mmol) were added to a pre-degassed mixture of
THF (15 mL) and 2M aqueous Na2CO3 solution (4 mL) under
nitrogen atmosphere. The reaction mixture was stirred at 70 °C
for 18 hours, cooled, and diluted with ethyl acetate (30 mL). The
organic fraction was washed with water (2 x 15 mL) and brine
solution, dried over anhydrous sodium sulfate, filtered, and
concentrated under reduced pressure. The crude product was
purified on a silica gel column using a mixture of 20% DCM in
1
hexane as eluent to afford a white solid (0.42 g, yield 50%). H
NMR (500 MHz, CDCl3) δ 7.84 (d, J = 1.8 Hz, 1H), 7.51 (dd, J =
7.9, 1.8 Hz, 1H), 7.37 (d, J = 7.9 Hz, 1H), 7.14 (d, J = 2.1 Hz,
1H), 7.12 (s, 1H), 7.01 (d, J = 1.8 Hz, 1H), 6.96 (m, 3H), 4.11 –
4.02 (m, 8H), 1.90 – 1.81 (m, 8H), 1.55 – 1.45 (m, 8H), 1.42 –
1.25 (m, 32H), 0.95 – 0.87 (m, 12H). 13C NMR (126 MHz, CDCl3)
δ 149.46, 149.36, 148.83, 148.36, 141.50, 140.53, 133.49,
132.28, 131.46, 131.22, 125.65, 123.08, 121.90, 119.64, 115.63,
114.11, 113.11, 113.05, 69.58, 69.40, 69.38, 69.23, 31.82, 29.68,
29.39, 29.35, 29.30, 29.27, 26.07, 26.05, 22.66, 14.07. HRMS
(APCl, +ve, (M +H)+) : (C50H78BrO4) Calculated m/z = 821.5078,
Found m/z = 821.5076. Elemental analysis calculated (%) for
C50H77BrO4: 73.05; H, 9.44; Found: C, 72.95; H, 9.38.
4-Bromo-1,2-bis(octyloxy)benzene
A
solution of 4-bromocatechol (1.63 g, 8.63 mmol), 1-
bromooctane (6.60 g, 34.2 mmol), and potassium carbonate
(4.70 g, 34.0 mmol) in acetone (40 mL) was stirred at 70 °C for
18 hours, cooled, and poured into ethyl acetate (30 mL). The
organic fraction was washed with water (2 x 15 mL) and brine
solution, dried over anhydrous sodium sulfate, filtered, and
concentrated under reduced pressure. The crude product was
purified on a silica gel column using a mixture of 5% ethyl
acetate in hexane as eluent to afford a colorless liquid (2.07 g,
yield 58%). 1H NMR (500 MHz, CDCl3) δ 6.99 (d, J = 9.1 Hz, 1H),
6.97 (s, 1H), 6.73 (d, J = 9.1 Hz, 1H), 3.98 – 3.93 (t, J = 6.6 Hz,
4H), 1.80 (m, 4H), 1.45 (m, 4H), 1.40 – 1.23 (m, 16H), 0.89 (t, J
Compound 6
Compound 5 (0.22 g, 0.27 mmol), bis(pinacolato)diboron (0.41
= 7.0, 6H). 13C NMR (126 MHz, CDCl3) δ 150.11, 148.43, 123.47, g, 1.62 mmol), Pd(dppf)Cl2 (0.01 g, 0.012 mmol) and KOAc
118.15, 117.06, 115.29, 112.83, 69.68, 69.60, 69.44, 31.81,
29.35, 29.33, 29.25, 29.16, 29.07, 25.99, 25.98, 25.93, 22.66,
14.08. Elemental analysis calculated (%) for C22H37BrO2: C,
63.91; H, 9.02; Found: C, 63.99; H, 9.09.
(0.15 g, 1.53 mmol) were added to a round bottom flask under
nitrogen atmosphere. 1,4-Dioxane (8 mL) was added via syringe
and the reaction mixture was stirred at 90 °C for 24 hours,
cooled, and diluted with ethyl acetate (25 mL). The organic
fraction was washed with water (2 x 15 mL) and brine solution,
dried over anhydrous sodium sulfate, filtered, and concentrated
under reduced pressure. The crude product was purified on a
silica gel column using a mixture of 3% ethyl acetate in hexane
as eluent to afford a yellow sticky liquid (0.20 g, yield 86%). 1H
NMR (500 MHz, CDCl3) δ 7.82 (d, J = 2.0 Hz, 1H), 7.58 (dd, J =
8.0, 2.0 Hz, 1H), 7.40 (d, J = 8.0 Hz, 1H), 7.18 – 7.14 (m, 2H),
6.99 (d, J = 2.0 Hz, 1H), 6.95 (d, J = 8.9 Hz, 1H), 6.93 – 6.87 (m,
2H), 4.11 – 3.99 (m, 8H), 1.89 – 1.78 (m, 8H), 1.49 (m, 8H), 1.40
– 1.25 (m, 32H), 1.23 (s, 12H), 0.93 – 0.83 (m, 12H). 13C NMR
Compound 4
4-Bromo-1,2-bis(octyloxy)benzene (2.07 g, 5.0 mmol),
bis(pinacolato)diboron (1.52 g, 5.99 mmol)), Pd(dppf)Cl2 (0.15 g,
0.18 mmol) and KOAc (1.5 g, 15.0 mmol) were added to a round
bottom flask under nitrogen atmosphere. 1,4-Dioxane (25 mL)
was added via syringe and the reaction mixture was stirred at
80 °C for 18 hours, cooled, and diluted with ethyl acetate (30
mL). The organic fraction was washed with water (2 x 25 mL)
and brine solution, dried over anhydrous sodium sulfate, filtered,
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10.1002/chem.201604778
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(126 MHz, CDCl3) δ 149.36, 148.87, 148.70, 148.46, 145.82,
138.78, 136.30, 134.23, 132.64, 129.24, 128.41, 121.67, 119.82,
115.25, 114.29, 113.83, 113.58, 83.76, 69.67, 69.63, 69.49,
69.35, 31.85, 29.43, 29.40, 29.30, 26.08, 24.68, 22.67, 14.09.
HRMS (APCl, +ve, (M +H)+) : (C56H90BO6) Calculated m/z =
869.6834, Found m/z = 869.6842. Elemental analysis calculated
(%) for C56H89BO6: C, 77.39; H, 10.32; Found: C, 76.98; H,
10.22.
for 18 hours under nitrogen atmosphere, cooled, and
concentrated under reduced pressure. The crude product was
purified on a silica gel column using a mixture of 15% DCM in
hexane as eluent to afford a white solid (0.07 g, yield 68%). 1H
NMR (500 MHz, CDCl3) δ 7.65 (d, J = 1.9 Hz, 2H), 7.55 (d, J =
8.7 Hz, 3H), 7.52 (dd, J = 8.0, 1.9 Hz, 3H), 7.21 (d, J = 8.0 Hz,
2H), 6.96 (d, J = 8.7 Hz, 4H), 6.63 (d, J = 8.8 Hz, 4H), 6.57 (d, J
= 8.8 Hz, 4H), 4.00 (t, J = 6.6 Hz, 4H), 3.89 (m, 4H), 1.81 (m,
8H), 1.47 (m, 8H), 1.30 (m, 32H), 0.90 (m, 12H). 13C NMR (126
MHz, ) δ 158.85, 157.67, 140.44, 139.20, 139.08, 133.27,
132.96, 130.37, 130.32, 130.25, 129.86, 128.04, 128.02, 127.92,
127.90, 127.04, 125.54, 114.91, 114.87, 114.82, 114.78, 114.14,
113.80, 68.22, 68.12, 31.92, 29.48, 29.47, 29.40, 29.34, 26.16,
26.14, 22.75, 14.19. HRMS (APCl, +ve, (M +H)+) : (C68H91O4)
Calculated m/z = 971.6912, Found m/z = 971.6904. Elemental
analysis calculated (%) for C68H90O4: C, 84.07; H, 9.34; Found:
C, 84.19; H, 9.29.
Compound 7
1,4-Diiodo-2,5-bis(trimethylsilyl)benzene (0.50 g, 1.05 mmol),
compound 1 (0.77 g, 2.32 mmol), and Pd(PPh3)4 (0.10 g, 0.087
mmol) were added to
a
pre-degassed mixture of
dimethoxyethane (12 mL) and 2M aqueous K2CO3 solution (3
mL) under nitrogen atmosphere. The reaction mixture was
stirred at 70 °C for 18 hours, cooled, and diluted with ethyl
acetate (25 mL). The organic fraction was washed with water (2
x 15 mL) and brine solution, dried over anhydrous sodium
sulfate, filtered, and concentrated under reduced pressure. The
crude product was purified on a silica gel column using a mixture
of 5% DCM in hexane as eluent to afford a white solid (0.41 g,
yield 62%). 1H NMR (300 MHz, CDCl3) δ 7.43 (s, 2H), 7.26 (d, J
= 8.7 Hz, 4H), 6.93 (d, J = 8.7 Hz, 4H), 4.01 (t, J = 6.6 Hz, 4H),
1.88 – 1.74 (m, 4H), 1.52 – 1.44 (m, 4H), 1.41 – 1.24 (m, 16H),
0.90 (s, 6H), 0.01 (s, 18H). 13C NMR (75 MHz, CDCl3) δ 158.39,
146.41, 139.02, 136.93, 135.87, 130.48, 113.71, 68.09, 31.82,
29.39, 29.33, 29.25, 26.08, 22.66, 14.10, 0.58. HR-MS (EI): M+
Compound 10
A solution of compound 5 (0.13 g, 0.16 mmol), 2,2-bipyridyl
(0.05 g, 0.33 mmol) in THF (3 mL) was added with 1,5-
cyclooctadiene (3 drops) and Ni(cod)2 (0.09 g, 0.33 mmol) under
nitrogen atmosphere. The reaction mixture was stirred at 80 °C
for 18 hours under nitrogen atmosphere, cooled, and
concentrated under reduced pressure. The crude product was
purified on a silica gel column using a mixture of 30% DCM in
1
hexane as eluent to afford a white solid (0.085 g, yield 72%). H
(C40H62O2Si2) Calculated m/z =630.4288, Found m/z = 630.4287. NMR (400 MHz, CDCl3) δ 7.71 (d, J = 2.0 Hz, 2H), 7.51 (dd, J =
Elemental analysis calculated (%) for C40H62O2Si2: C, 76.13; H,
9.90; Found: C, 76.51; H, 9.97.
8.1, 2.0 Hz, 2H), 7.25 (d, J = 8.1 Hz, 2H), 7.16 (m, 4H), 6.95 (d,
J = 8.1 Hz, 2H), 6.57 (d, J = 8.3 Hz, 2H), 6.29 – 6.20 (m, 4H),
4.05 (m, 12H), 3.92 (t, J = 6.7 Hz, 4H), 1.90 – 1.77 (m, 16H),
1.49 (m, 16H), 1.30 (m, 64H), 0.88 (m, 24H). 13C NMR (101 MHz,
CDCl3) δ 149.56, 149.02, 148.19, 147.44, 140.65, 139.58,
139.45, 133.63, 133.54, 130.87, 130.13, 129.64, 128.82, 125.72,
121.44, 119.50, 114.94, 114.25, 113.50, 112.91, 69.56, 69.49,
69.46, 68.63, 68.17, 31.86, 29.47, 29.46, 29.42, 29.32, 26.15,
26.10, 26.08, 26.00, 22.69, 14.09. HRMS (APCl, +ve, (M +H)+) :
Compound 8
A solution of compound 7 (0.32 g, 0.51 mmol) in chloroform (16
mL) was added with iodine monochloride (1 M in DCM, 2.0 mL,
2.00 mmol) dropwise under nitrogen atmosphere at room
temperature. The reaction mixture was stirred at room
temperature for 1 hour, diluted with DCM (20 mL), and extracted
with aqueous sodium thiosulfate solution. The organic fraction
was washed with water (2 x 15 mL) and brine solution, dried
over anhydrous sodium sulfate, filtered, and concentrated under
reduced pressure. The crude product was purified from
precipitation in DCM/MeOH to afford a white solid (0.34 g, yield
90%). 1H NMR (300 MHz, CDCl3) δ 7.84 (s, 2H), 7.29 (d, J = 8.7
Hz, 4H), 6.95 (d, J = 8.7 Hz, 4H), 4.01 (t, J = 6.6 Hz, 4H), 1.88 –
1.76 (m, 4H), 1.49 (m, 4H), 1.32 (m, 16H), 0.90 (t, J = 6.7 Hz,
6H). 13C NMR (75 MHz, CDCl3) δ 159.01, 146.45, 140.21,
(C100H155O8) Calculated m/z
= 1484.1716, Found m/z =
1484.1714. Elemental analysis calculated (%) for C100H154O8: C,
80.92; H, 10.46; Found: C, 80.90; H, 10.25.
Compound 11
Compound 3 (0.10 g, 0.16 mmol), compound 8 (0.06 g, 0.08
mmol), and Pd(PPh3)4 (0.007 g, 0.006 mmol) were added to a
pre-degassed mixture of dimethoxyethane (5 mL) and 2M
aqueous K2CO3 solution (2 mL) under nitrogen atmosphere. The
134.58, 130.35, 113.94, 98.70, 68.06, 31.82, 29.37, 29.29, 29.25, reaction mixture was stirred at 80 °C for 24 hours, cooled, and
26.08, 22.66, 14.11. HR-MS (EI): M+ (C34H44I2O2) Calculated m/z
=738.1431, Found m/z 738.1446. Elemental analysis
calculated (%) for C34H44I2O2: C, 55.30; H, 6.01; Found: C,
54.90; H, 6.02.
diluted with ethyl acetate. The organic fraction was washed with
water (2 x 5 mL) and brine solution, dried over anhydrous
sodium sulfate, filtered, and concentrated under reduced
pressure. The crude product was purified on a silica gel column
using a mixture of 10% DCM in hexane, followed by a mixture of
2% ethyl acetate in hexane as eluents to afford a white solid
(0.07 g, yield 59%). 1H NMR (300 MHz, CDCl3) δ 7.75 (d, J = 1.8
Hz, 2H), 7.59 (d, J = 8.9 Hz, 2H), 7.56 – 7.45 (m, 5H), 7.39 (s,
2H), 7.20 (m, 2H), 6.95 (d, J = 8.9 Hz, 5H), 6.65 (s, 5H), 6.63 –
6.51 (m, 9H), 4.05 – 3.84 (m, 12H), 1.77 (m, 12H), 1.44 (m, 12H),
=
Compound 9
A solution of compound 2 (0.12 g, 0.21 mmol), 2,2-bipyridyl
(0.12 g, 0.77 mmol) in THF (10 mL) was added with 1,5-
cyclooctadiene (3 drops) and Ni(cod)2 (0.22 g, 0.80 mmol) under
nitrogen atmosphere. The reaction mixture was stirred at 80 °C
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10.1002/chem.201604778
Chemistry - A European Journal
FULL PAPER
1.30 (s, 48H), 0.95 – 0.85 (m, 18H). 13C NMR (126 MHz, CDCl3 )
δ 158.85, 158.70, 157.82, 157.71, 140.13, 139.46, 139.28,
139.19, 138.91, 133.24, 133.21, 133.05, 132.79, 130.27, 130.20,
130.06, 129.53, 128.02, 127.96, 127.91, 125.53, 114.89, 113.85,
113.57, 68.20, 68.14, 31.92, 31.91, 31.90, 29.52, 29.48, 29.45,
29.38, 29.37, 29.35, 29.34, 29.32, 26.17, 26.14, 22.75, 22.74,
14.18, 14.17, 14.16. HRMS (APCl, +ve, (M +H)+) : (C102H135O6)
Calculated m/z = 1456.0253, Found m/z = 1456.0257. Elemental
analysis calculated (%) for C102H134O6: C, 84.13; H, 9.28; Found:
C, 83.99; H, 9.23.
mixture. The reaction mixture was stirred overnight at room
temperature, followed by addition of methanol (25 mL). The
precipitate was filtered and washed with methanol to remove
excess iron (III) chloride. The crude product was purified on a
silica gel column using a mixture of 50% DCM in hexane as
1
eluent to afford orange wax-like solid (0.029 g, yield 41%). H
NMR (400 MHz, CD2Cl2) δ 7.73 (dd, J = 5.8, 3.4 Hz, 2H), 7.58
(dd, J = 5.8, 3.4 Hz, 2H), 7.31 (d, J = 2.5 Hz, 2H), 7.09 (dd, J =
8.3, 2.5 Hz, 2H), 6.63 (d, J = 8.3 Hz, 2H), 4.26 (d, br, 20H), 1.98
(br, 20H), 1.51 – 1.19 (br, 100H), 0.93 (br, 30H). MALDI-TOF:
(C134H182O10) Calculated m/z = 1952.3, Found m/z = 1952.1.
Elemental analysis calculated (%) for C134H182O10: C, 82.41; H,
9.39; Found: C, 79.98; H, 9.29.
Compound 12
Compound 6 (0.16 g, 0.18 mmol), compound 8 (0.06 g, 0.08
mmol), and PdCl2(PPh3)2 (0.002 g, 0.003 mmol) were added to a
pre-degassed mixture of dimethoxyethane (8 mL) and 2M
aqueous Na2CO3 solution (1.5 mL) under nitrogen atmosphere.
The reaction mixture was stirred at 80 °C for 24 hours, cooled,
and diluted with ethyl acetate (20 mL). The organic fraction was
washed with water (2 x 5 mL) and brine solution, dried over
anhydrous sodium sulfate, filtered, and concentrated under
reduced pressure. The crude product was purified on a silica gel
column using a mixture of 2% ethyl acetate in hexane as eluent
to afford a sticky liquid (0.09 g, yield 56%). 1H NMR (300 MHz,
CDCl3) δ 7.71 (s, 1H), 7.65 – 7.27 (m, 6H), 7.15 (m, 5H), 7.08 –
6.77 (m, 5H), 6.75 – 6.48 (m, 7H), 6.47 – 6.10 (m, 4H), 3.93 (br,
20H), 1.82 (br, 20H), 1.47 (br, 12H), 1.28 (br, 88H), 0.88 (br,
30H). 13C NMR (75 MHz, CDCl3) δ 167.28, 149.33, 148.86,
139.42, 139.35, 139.26, 139.06, 133.80, 130.77, 130.05, 129.76,
128.71, 127.90, 126.97, 119.44, 114.20, 113.15, 69.48, 69.38,
68.09, 38.68, 31.74, 31.52, 30.29, 29.59, 29.31, 29.20, 28.85,
25.98, 23.68, 22.88, 22.57, 13.98, 10.86. HRMS (APCl, +ve, (M
+H)+) : (C134H199O10) Calculated m/z = 1968.5058, Found m/z =
1968.5050. Elemental analysis calculated (%) for C134H198O10: C,
81.74; H, 10.14; Found: C, 81.90; H, 10.25.
Acknowledgements
The authors would like to thank Department of Chemistry,
National University of Singapore (NUS) for technical supports.
CPS is grateful for the research scholarship from NUS. The
authors also acknowledge Mr. Bhargava Samarth and Ms.
Sriramulu Deepa for their helps in SEM and TEM studies.
Keywords: Graphene nanoribbons • oligophenylenes •
cyclodehydrogenation • self-assembly • columnar π stacking
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Compound 9 (0.07 g, 0.076 mmol) was dissolved in anhydrous
DCM (20 mL) under nitrogen atmosphere at room temperature.
[8]
A
solution of iron (III) chloride (0.37 g, 2.28 mmol) in
nitromethane (5 mL) was added dropwise to the reaction mixture.
The reaction mixture was stirred overnight at room temperature,
followed by addition of methanol (20 mL). The precipitate was
filtered and washed with methanol to remove excess iron (III)
chloride. The crude product was purified on a silica gel column
using a mixture of 50% DCM in hexane as eluent to afford a
yellowish wax-like solid (0.024 g, yield 33%). 1H NMR (300 MHz,
CD2Cl2) δ 9.10 (br, 2H), 8.26 (br, 2H), 7.82 (br, 5H), 7.17 (br, 5H),
4.14 (br, 8H), 1.90 (br, 8H), 1.44 (br, 40H), 0.95 (br, 12H).
[9]
MALDI-TOF: (C66H82O4) Calculated m/z = 962.6, Found m/z = [10]
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2008, 64, 11370-11378.
962.1. Elemental analysis calculated (%) for C68H82O4: C, 84.78;
H, 8.58; Found: C, 86.79; H, 8.21.
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G-2
Compound 12 (0.07 g, 0.036 mmol) was dissolved in
anhydrous DCM (33 mL) under nitrogen atmosphere at room
[12]
temperature. A solution of iron (III) chloride (0.267 g, 1.65 mmol)
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in nitromethane (0.8 mL) was added dropwise to the reaction
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Chemistry - A European Journal
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Entry for the Table of Contents
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Soluble graphene nanoribbons
are prepared from the oxidative
cyclodehydrogenation of
precursor oligophenylenes. Self-
assembly of the molecule into
ordered nanofibers is studied.
Choong Ping Sen, and Suresh
Valiyaveettil*
2 nm
Page No. – Page No.
Soluble Graphene Nanoribbons
from Planarization of
Oligophenylenes
20 nm
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