Asymmetric anthracene-based blue host materials: Synthesis and electroluminescence properties of 9-(2-naphthyl)-10-arylanthracenes

Article abstract of DOI:10.1039/c0jm02877k

A series of bulky aryl-substituted asymmetric anthracene blue host materials, 9-(2-naphthyl)-10-(3-(1-naphthyl)phenyl)anthracene, where phenyl was varied from H (5a), Me (5b), Ph (5e), and 1-Naph (5f) at the 6-position and Me (5c) at the 2-position, was s

Full text of DOI:10.1039/c0jm02877k

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PAPER
www.rsc.org/materials | Journal of Materials Chemistry
Asymmetric anthracene-based blue host materials: synthesis and
electroluminescence properties of 9-(2-naphthyl)-10-arylanthracenes†
*
Kyung-Ryang Wee, Won-Sik Han, Ju-Eun Kim, Ae-Li Kim, Soonnam Kwon and Sang Ook Kang
Received 30th August 2010, Accepted 11th October 2010
DOI: 10.1039/c0jm02877k
A series of bulky aryl-substituted asymmetric anthracene blue host materials, 9-(2-naphthyl)-10-(3-(1-
naphthyl)phenyl)anthracene, where phenyl was varied from H (5a), Me (5b), Ph (5e), and 1-Naph (5f)
at the 6-position and Me (5c) at the 2-position, was synthesized by Suzuki coupling reaction between
10-(2-naphthyl)anthracene-9-boronic acid and 1-(3-iodophenyl)naphthalene derivatives. A less bulky
aryl-substituted anthracene, 9-(2-naphthyl)-10-(2,5-diphenyl)phenyl)anthracene (5d), was also
synthesized for comparison. All asymmetric anthracenes showed high glass transition temperatures in
the range of 84–153 ꢀC. The photophysical and electrochemical properties in solution showed that the
substituent at the 10-positions of the anthracene unit did not influence the blue emission of 420 nm and
HOMO–LUMO energy level (5.5–2.5 eV). However, a gradual decrease of bathochromic shift in solid
state PL was observed from the increaseg of the substituent bulkiness, exhibiting 5e (18 nm) # 5f
(19 nm) < 5c (25 nm) # 5b (26 nm) < 5a (30 nm) < 5d (41 nm), respectably. When 5a was used as a blue
host material in the multilayered device structure of ITO/DNTPD/NPD/host:dopant (9%)/PyPySPyPy/
LiF/Al, enhanced OLED device performance was observed, showing a luminous current efficiency of
9.9 cd Aꢁ1, power efficiency of 6.3 lm Wꢁ1 at 20 mA cmꢁ2, deep blue color coordinates of (0.14, 0.18),
and a 932 h device lifetime at L0 ¼ 3000 cd mꢁ2
.
on anthracenes, several issues need to be resolved. It is important
to avoid strong intermolecular forces, such as hydrogen bonding
or p–p stacking, between the molecules in the film state.13
Accordingly, we expected that the introduction of the bulky
substituent leads to larger intermolecular distances and is
a hindrance in packing and, therefore, produces amorphous
behavior. Another strategy for designing amorphous materials is
the synthesis of asymmetric molecules, enabling an increase in the
number of conformers. This approach comes from the assump-
tion that increasing the number of conformers necessitates high
energy for crystallization, favoring the stability of amorphous
films.14 As a result, the asymmetric nonplanar anthracene struc-
ture provides a steric hindrance to the close-packing of the
molecules, with low crystallization behavior in the solid state;
thus, it enables formation of smooth and pinhole-free thin films.
In this study, we report the synthesis and characterization of
a series of asymmetric anthracene derivatives, 9-(2-naphthyl)-10-
arylanthracene (5a–5f), as blue host materials for OLEDs. These
Introduction
Since the pioneering report of Tang et al., organic light emitting
devices (OLEDs) have attracted enormous interest because of
their high efficiency, pure color reproduction, fast response, and
wide viewing angle.1 Full-color displays require red, green, and
blue emission of relatively equal stability, efficiency, and color
purity. Although significant improvements in OLED perfor-
mance have been achieved over the past decades, further
improvement is required. In particular, the performance of blue
OLEDs is relatively poor compared with red and green OLEDs;
thus, it is necessary to improve their performance for display or
lighting applications.2 Recently, a number of fluorescent blue
emitting materials, such as styrylarylene,3 fluorene,4 fluoran-
thene,5 quinoline,6 quinoxaline,7 triarylamines,8 pyrene,9 and
diarylanthracence10 derivatives have been reported. Among
these, anthracene and its derivatives has been the subject of
investigation because of their excellent photoluminescence,
electroluminescence, and electrochemical properties.11 However,
they fail to provide dense films, and the thin films tend to be
crystallized producing rough surfaces, grain boundaries, or pin
holes that lead to current leakage.12 To prevent such problems
and improve device lifetime with highly efficient electrolumine-
scence properties, we carefully designed asymmetric anthracene
materials, containing a bulky aryl group substituted at the 10-
position, as shown in Chart 1. To achieve amorphous films based
Department of Advanced Material Chemistry, Korea University, Sejong,
Chungnam, 339–700, South Korea. E-mail: sangok@korea.ac.kr; Fax:
+82 41 867 5396; Tel: +82 41 860 1334
† Electronic supplementary information (ESI) available: 1H and 13C
NMR spectroscopic data, and calculation data for compounds. See
DOI: 10.1039/c0jm02877k
Chart 1 Structures of the asymmetric and bulky aryl-substituted
anthracene derivatives (5a–5f).
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compounds show high thermal stability and good amorphous
film forming capability with moderate fluorescence quantum
yields. Based on using these asymmetric anthracenes as host
materials, blue fluorescence OLEDs have been fabricated with
a 6,12-bis(di(3,4-dimethylphenyl)amino)chrysene dopant. The
5a-based device exhibits highly efficient blue emission (0.14, 0.18)
with luminous current efficiency of 9.9 cd Aꢁ1, power efficiency
of 6.3 lm Wꢁ1 at 20 mA cmꢁ2 and reduced efficiency roll off at
high luminance and a stable device lifetime.
Finally, a series of bulky aryl-substituted asymmetric 9-(2-
naphthyl)-10-phenylanthracene derivatives, 5a–5f, where phenyl
was varied with methyl, phenyl, and naphthyl at the 2,3,6-posi-
tion, was obtained by Suzuki–Miyaura coupling using 4a–4f and
10-(2-naphthyl)anthracene-9-boronic acid. The details of this
synthesis are given in the experimental section. All 5a–5f
compounds were isolated by flash column chromatography with
yields ranging from 70 to 87%, and further purified by train
sublimation. Their compositions were confirmed based on
elemental and high resolution mass analyses. The structures were
1
authenticated based on functional group analysis of the H and
13C NMR spectra.
Results and discussion
Synthesis
Thermal properties
The synthesis of asymmetric anthracene derivatives, 5a–5f, was
accomplished according to the synthetic routes given in Scheme
1. Initially, 2,3,6-substituted nitrobenzenes, 2a–2f, were obtained
via Pd(0)-mediated Suzuki–Miyaura coupling reactions between
1a–1d and phenylboronic acid or 1-naphthylboronic acid.
Compounds 2a, 2b, and 2c were prepared by reacting 1-naph-
thylboronic acid and 1a–1c, respectively; compounds 2d, 2e, and
2f were obtained in moderate yields by reacting 1d and different
equivalents of phenylboronic acid or 1-naphthylboronic acid.
Hydrogenation of 2a–2f with hydrogen gas in the presence of
a catalytic amount of Pd/C afforded 2,3,6-substituted anilines,
3a–3f, in quantitative yields. The subsequent Sandmeyer reaction
using 3a–3f with p-toluenesulfonic acid and NaNO2 produced
the desired 2,3,6-substituted iodobenzenes, 4a–4f, in 51–68%
yield.
The thermal properties of 5a–5f were determined by differential
scanning calorimetry (DSC) analysis as listed in Table 1. A
heating rate of 10 ꢀC minꢁ1 was used after the first melting, which
was followed by rapid cooling to room temperature. As shown in
Fig. 1, the first heating cycle revealed a Tm for 5a, 5b, 5c, 5d, 5e,
and 5f in the order of 288, 294, 164, 219, 242, and 292 ꢀC,
respectively. In subsequent heating cycles, weak endothermic
transitions associated with Tg were found in the order of 116,
125, 84, 123, 126, and 153 ꢀC for 5a, 5b, 5c, 5d, 5e, and 5f,
respectively. It was noted that the Tg of the anthracene deriva-
tives increase in proportion to the size of the substituent groups
at the 10-position of the anthracene molecules, except for
compound 5c. In particular, no distinct crystallization tempera-
ture was observed in this series when the temperature was swept
continuously between 30 and 350 ꢀC with the exception of 5f.
These experiments demonstrate that it is possible to get stable
glasses from these materials. Therefore, a stable device lifetime
can be expected for OLEDs using these asymmetric anthracenes
since it has been demonstrated that high Tg materials lead to
enhanced device stability and lifetime.15
Photophysical properties
The photophysical properties of each anthracene compound
were examined by UV-vis absorption and photoluminescence
(PL) in the solution and film states. Table 1 summarizes the
spectroscopic data. The UV-vis absorption spectrum (Fig. 2a)
shows that all of the anthracene derivatives exhibited the char-
acteristic vibronic structure at approximately 397, 376, and
358 nm, which was attributed to the anthracene molecule. The
Scheme 1 Synthetic route towards 9-(2-naphthyl)-10-arylanthracene
derivatives (5a–5f).
Table 1 Photophysical properties of 9-(2-naphthyl)-10-phenylanthracene derivatives (5a–5f)
labs (nm)
lem [FWHM] (nm)
Sola
Filmb
Sola
Filmb
Ffc
Tg/Tc/Tm (ꢀC)
d
Compound
5a
5b
5c
5d
5e
5f
396.8, 376.2, 358.5
396.7, 376.2, 357.8
396.9, 376.2, 357.7
399.3, 378.6, 359.5
399.6, 378.6, 359.4
399.5, 378.6, 359.7
401.7, 380.6, 359.5
400.3, 379.5, 360.4
402.0, 382.5, 358.5
402.3, 381.1, 359.4
403.4, 382.3, 362.2
405.1, 383.5, 364.1
421.1 [54]
416.4 [52]
417.4 [52]
420.0 [53]
421.0 [53]
425.0 [54]
451.0 [53]
441.9 [53]
441.8 [53]
461.1 [42]
438.8 [60]
443.9 [57]
0.81
0.78
0.78
0.82
0.84
0.82
116/—/288
125/—/294
84/—/164
123/—/219
126/—/242
153/194/292
a
b
c
In CH2Cl2. Prepared by a vapor deposition method. Relative to 9,10-diphenylanthracene as standards in CH2Cl2 at room temperature.
Determined by differential scanning calorimetry (DSC).
d
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PL wavelengths of all compounds were similar to those found in
9,10-diphenylanthracene,16 which could be assigned unambigu-
ously to the lowest p–p* transition of the anthracene chromo-
phore in the molecule, as shown in Fig. 2b. This suggests there is
little or negligible electronic communication between the
anthracene and periphery group because the twisted bulky aryl
unit blocks the extending p-conjugation of the 9,10-diary-
lanthracene.
Moreover, the PL emission spectrum of these anthracenes was
sufficiently overlapped with the UV-vis absorption of the dopant
materials of 6,12-bis(di(3,4-dimethylphenyl)amino)chrysene17
(DACrs), as shown in Fig. 3. Therefore, efficient energy transfer
Fig. 1 DSC traces of 5a–5f were recorded at a heating rate of 10 ꢀC
minꢁ1
€
from the anthracene host to the blue dopant through a Forster
.
energy transfer was expected, suggesting that anthracenes act as
a good host material in OLED devices using chrysene dopant
materials.18
The PL spectra of the anthracenes (5a–5f) in thin solid film
on quartz plates are shown in Fig. S1† and the inset of Fig. 2b.
The maximum emission peaks of 5a–5f in thin films were
slightly red-shifted, but not significantly, compared to those
acquired in a dilute solution, exhibiting values in the range of
18 to 41 nm. The reduced spectral shifts in the solid state
spectra imply that the intermolecular interactions were weak
due to the twisted asymmetrically bound aryl groups.
Furthermore, a gradual decrease of red-shift effects was
observed with an increase of the substituent bulkiness, exhibi-
ting 5e (18 nm) # 5f (19 nm) < 5c (25 nm) # 5b (26 nm) < 5a
(30 nm) < 5d (41 nm), respectively. As a result, the introduction
of a twisted bulky aryl group at the 10-position of the
anthracene not only prevents red-shifted emissions in the solid
state due to molecular interactions, but also enables the
formation of stable amorphous thin films.
Fig. 2 (a) UV/vis absorbance, (b) photoluminescence spectra of 5a–5f in
CH2Cl2 solution. (Inset: film PL spectrum of 5e).
Electrochemical properties
The electrochemical properties of 5a–5f were examined by cyclic
voltammetry (CV). Table 2 summarizes the CV results, which
were obtained in CH2Cl2 containing 0.1 M tetrabutylammonium
perchlorate (TBAP) at a scan rate of 0.1 V sꢁ1. All scans are
shown in Fig. 4. The potential values of the first redox wave in
both the positive and negative directions represent Eox and Ered
,
respectively. All anthracenes exhibited reversible oxidation
peaks. Moreover, a distinct cathodic reduction process was
recorded when the electrode potential was swept continuously
between 0.0 and ꢁ2.5 V.
Fig. 3 6,12-Bis(di(3,4-dimethylphenyl)amino)chrysene dopant UV/vis
(red line) and PL (blue line) spectrum in solution. (dashed line: 5a PL
spectrum).
Table 2 Oxidation and reduction potentials of 5a–5f in CH2Cl2 solution containing 0.1 M TBAP
Oxidation (V)a
Reduction (V)a
b
HOMO (eV)c
LUMO (eV)c
ox
red
opt
Eg (eV)
Entry
Epa
Epc
Eon
Epc
Eon
5a
5b
5c
5d
5e
5f
0.84
0.82
0.81
0.81
0.80
0.79
0.75
0.75
0.74
0.74
0.74
0.72
0.70
0.70
0.69
0.69
0.70
0.68
ꢁ2.50
ꢁ2.50
ꢁ2.52
ꢁ2.52
ꢁ2.52
ꢁ2.53
ꢁ2.36
ꢁ2.36
ꢁ2.37
ꢁ2.37
ꢁ2.37
ꢁ2.39
3.02
3.02
3.03
3.01
3.00
3.00
ꢁ5.50
ꢁ5.50
ꢁ5.49
ꢁ5.49
ꢁ5.50
ꢁ5.48
ꢁ2.48
ꢁ2.48
ꢁ2.46
ꢁ2.48
ꢁ2.50
ꢁ2.48
Epa¼ anodic peak potential; Epc ¼ cathodic peak potential; Eonset ¼ onset potential. b Optical bandgap Egopt from the absorption edge. c The HOMO
a
and LUMO levels were determined using the following equations: EHOMO (eV) ¼ ꢁe(Eonsetox + 4.8), ELUMO (eV) ¼ ꢁe(EHOMO ꢁ Egopt).
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Fig. 4 Cyclic voltammetry of 5a–5f in CH2Cl2 solution containing 0.1 M
TBAP.
Fig. 6 HOMO–LUMO energy levels obtained from the Dmol3 calcula-
tion.
The HOMO and LUMO energy levels of these anthracene
derivatives were determined by CV experiments. From the first
oxidation onset potential, the HOMO energy levels of 5a–5f were
estimated to be ca. ꢁ5.48 to ꢁ5.50 eV. The LUMO energy levels
were calculated to be in the range of ꢁ2.46 to ꢁ2.50 eV from the
absorption edge of the optical absorption spectra of 5a–5f. All
compounds of anthracene derivatives have wide optical energy
band gaps (Eg) of 3.0–3.1 eV, as determined from the edge of the
UV-vis absorption spectra. As expected, CV experiments suggest
that there is no significant electronic communication between the
anthracene and the periphery group. The photophysical and
electrochemical properties of 5a–5f indicate that the bulky
substituent at the 10-positions of the anthracene does not influ-
ence the blue emission or energy level of the anthracene core
without significant excimer emission in the solid state.
summarize the calculated results and representative HOMO and
LUMO diagrams for 5a–5f. The calculated geometries of 5a–5f
show that the 9-(2-naphthyl)anthracene and phenyl units at the
10-position of anthracene are significantly twisted against each
other because of the bulky 2,3,6-substituted phenyl group,
resulting in a three-dimensional structure in each molecule.
These geometric characteristics can effectively prevent inter-
molecular interactions, such as hydrogen bonding or p–p
stacking between the molecules.
The electron densities of the HOMO and LUMO are mostly
localized on the anthracene unit, implying that the absorption
and emission processes can only be attributed to the p–p* tran-
sition at the anthracene unit. Molecular orbital analysis clearly
indicates that the substituent at the 10-positions of the anthracene
unit does not alter the energy level of the anthracene unit.
Theoretical calculations
Electroluminescent properties
The electronic structure of these compounds was further
investigated by performing quantum chemical calculations at the
Density Functional Theory (DFT) level, as implemented in the
Dmol3 package.19 The HOMO–LUMO levels of 5a–5f were
calculated using double numerical plus d-functions (DND), and
the geometries were optimized under the same conditions. No
atom was omitted from the detailed study of the bond lengths
and angles of the optimized structure. Fig. 5 and Fig. 6
The asymmetric anthracenes, 5a, 5b, 5e, and 5f were evaluated as
blue host materials by fabricating multi-layer OLED devices with
DACrs dopant. As shown in Fig. 7, all devices were fabricated
with the following configuration: ITO/DNTPD (65 nm)/NPB
(20 nm)/host:DACrs (9%) (35 nm)/PyPySPyPy (20 nm)/LiF
(1 nm)/Al (100 nm), where ITO (indium tin oxide) was the anode,
DNTPD (N,N-[p-di(m-tolyl)aminophenyl]-N,N-diphenylbenzi-
dine) served as a hole-injection layer, NPB (N,N-bis-(naph-
thalen-1-yl)-N,N-bis(phenyl)benzidine) as a hole transport layer,
host (MADN, 5a, 5b, 5e, and 5f) and dopant (DACrs) as
an emitting layer, PyPySPyPy (2,5-bis(20,200-bipyridin-6-yl)-1,1-
dimethyl-3,4-diphenylsilacyclopentadiene) as an electron trans-
port layer, and LiF:Al as the composite cathode.
Fig. 5 Representative HOMO–LUMO orbital diagrams of 5a–5f
obtained from the Dmol3 calculation.
Fig. 7 The device structure and materials used in this study.
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Fig. 9 Device operational stability for the lifetime of the ref (MADN),
5a, 5b, 5e, and 5f based device at 3000 cd mꢁ2 brightness.
Fig. 8 The I–V–L curve of the 5a (a), 5b (b), 5e (c), and 5f (d) based
aryl-substituted asymmetric anthracene based devices showed
a more stable lifetime than that of the MADN based device. For
example, the 5a based device under a constant current density of
38 mA cmꢁ2 with L0 ¼ 3000 cd mꢁ2 dropped to about 2450 cd mꢁ2
after operating continually for 215 h and with the driving voltage
increased by 1.1 V, while the MADN based device dropped to
about 2040 cd mꢁ2 after operating continually for 215 h.
Assuming the scalable law of Coulombic degradation22 and by
estimation of its extrapolated profile, driving at a normalized L0
value of 3000 cd mꢁ2, the t1/2 values for the MADN and 5a
based device without considering any accelerating factor23 for
a blue device, are projected to be 429 h and 932 h, respectively.
The longer lifetime of bulky aryl-substituted asymmetric
anthracene based devices may be attributed to the better
thermal stability and no significant intermolecular interaction in
the solid state.
device. (The insets denote the current efficiency and EL spectrum).
Fig. 8 show the current–voltage–luminance (I–V–L) charac-
teristics of the anthracene host based devices with a 9% ratio of
dopant; their device characteristics at 20 mA cmꢁ2 are listed in
Table 3.
The EL spectra for all devices were featureless with the
maximum peak at 467 nm with CIE coordinates of x ¼ 0.14 and
y ¼ ꢂ0.18. The similarity of the PL of DACrs and EL spectra
suggests that the EL was attributed to emissions from the radi-
ation decay of the excited singlet state of the DACrs dopant. In
addition, negligible EL color shift was observed when the driving
voltage was increased from 3 to 11 V. It also suggests that the
electron–hole pairs for recombination are well confined in the
blue emitter region. In the I–V–L curves, the bulky aryl-
substituted anthracene (5a, 5b, 5e, and 5f) based device showed
better performance than that of a common blue host material, 2-
methyl-9,10-di(2-naphthyl)anthracene20 (MADN). In particular,
as shown in Fig. 8a, a 5a-based device showed promising
performance compared with previous blue devices,21 exhibiting
a turn-on potential of 3.0 V and a maximum brightness of
49360 cd mꢁ2 at 555 mA cmꢁ2 (11 V), as well as maximum current
Conclusions
In summary, a series of asymmetric anthracene blue host mate-
rials, 9-(2-naphthyl)-10-arylanthracene, 5a–5f, was synthesized
and characterized. By employing these asymmetric anthracenes
as a host material of DACrs-based blue OLEDs, the reduced
efficiency roll-off at high luminance and stable lifetime were
observed. This results suggest that the introduction of a sterically
bulky unit at the 10-position of the anthracene provides an
effective handle to prevent the close-packing of the molecules in
the solid state and thus enables formation of stable amorphous
thin films. Further studies, focusing on additional structural
tuning of the anthracene series with the aim of improving the
amorphous properties and high quantum efficiency, as well as
device optimization, are currently underway.
and power efficiencies of up to 10.1 cd Aꢁ1 and 6.4 lm Wꢁ1
,
respectively. Moreover, the device efficiency showed no signifi-
cant fall-off from low current density to a higher current density.
This result might be due to less intermolecular interaction of
anthracenes in the solid state.
The operational lifetime of the four blue devices under an
initial brightness of 3000 cd mꢁ2 was examined after encapsula-
tion in the nitrogen-purged glove box. A MADN based device
was also examined for comparison. As shown in Fig. 9, bulky
Table 3 EL performance of an anthracene host with a 9% doping ratio at 20 mA cmꢁ2
a
b
hex
c
d
e
9% doping
Von
V
hlum
hpw
Lmax
CIE (x, y)
MADN (ref)
2.7
2.9
3.0
2.9
2.9
5.6
5.0
5.2
5.5
5.4
5.8
7.3
5.9
6.9
7.1
7.2
9.9
7.6
8.7
9.2
4.3
6.3
4.5
5.3
5.8
50 080
49 360
36 410
39 400
38 710
0.14, 0.18
0.14, 0.18
0.14, 0.18
0.14, 0.17
0.14, 0.17
5a
5b
5e
5f
a
Turn-on voltage (V). b External quantum efficiency (%). c Luminance efficiency (cd Aꢁ1). d Power efficiency (lm Wꢁ1). e Maximum luminance (cd mꢁ2).
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1-(4-Methyl-3-nitrophenyl)naphthalene (2b).
A
procedure
Experimental
analogous to the preparation of 2a was used, but starting from 4-
bromo-1-methyl-2-nitrobenzene (2.14 g, 9.90 mmol). 2b was
obtained as a pale yellow powder. Yield: 62% (0.92 g).1H NMR
(CDCl3) d 8.13 (s, 1H), 7.95–7.90 (m, 2H), 7.81 (d, 1H), 7.64 (d,
1H), 7.57–7.41 (m, 5H), 2.71 (s, 3H). Anal. calcd. for
C17H13NO2: C, 77.55; H, 4.98; N, 5.32; O, 12.15. Found: C,
77.52; H, 4.95; N, 5.30.
General procedures
All reactions were carried out under an argon atmosphere.
1
Solvents were distilled from appropriate reagents. The H and
13C spectra were recorded on a Varian Mercury 300 spectro-
meter operating at 300.1 and 75.4 MHz, respectively. All proton
and carbon chemical shifts were measured relative to the
internal residual benzene and chloroform from the lock solvent
(99.5% C6D6, 99.9% CDCl3). The elemental analyses were per-
formed using a Carlo Erba Instruments CHNS-O EA 1108
analyzer. High Resolution Tandem Mass Spectrometry (Jeol
LTD JMS-HX 110/110A) was performed by the Seoul Branch
of the Korean Basic Science Institute. The absorption and
photoluminescence spectra were recorded on a SHIMADZU
UV-3101PC UV-VIS-NIR scanning spectrophotometer and
1-(2-Methyl-3-nitrophenyl)naphthalene (2c).
A
procedure
analogous to the preparation of 2a was used, but starting from 1-
bromo-2-methyl-3-nitrobenzene (2.14 g, 9.90 mmol). 2c was
1
obtained as a pale yellow oil. Yield: 62% (0.92 g). H NMR
(CDCl3) d 7.94–7.92 (m, 3H), 7.58–7.49 (m, 3H), 7.46–7.41 (m,
2H), 7.37–7.31 (m, 2H), 2.16 (s, 3H). C17H13NO2: C, 77.55; H,
4.98; N, 5.32; O, 12.15. Found: C, 77.50; H, 4.97; N, 5.31.
a
VARIAN Cary Eclipse fluorescence spectrophotometer,
1,4-Diphenyl-2-nitrobenzene (2d). A procedure analogous to
the preparation of 2a was used, but starting from 1,4-dibromo-2-
nitrobenzene (2.78 g, 9.90 mmol) and 2.2 equiv. phenylboronic
acid (2.66 g, 21.78 mmol). 2d was obtained as a pale yellow
respectively. The absorption spectra of the solution were
measured in CH2Cl2 and the corresponding fluorescence
emissions were determined at each excitation wavelength
(labsmax/nm). 9,10-Diphenylanthracene (Ff ¼ 0.90) was used as
the standard for determining the quantum yields (1 to 4 ꢃ
10ꢁ6 M in CH2Cl2). The thermal stability of the compound was
measured by differential scanning calorimetry (Q20, TA). A
heating rate of 10 ꢀC minꢁ1 was used after first melting the
compound followed by rapid cooling to room temperature.
Cyclic voltammetry (CV) was performed in an electrolyte con-
taining 1 mM of the electro-active compounds and 0.1 M
tetrabutylammonium perchlorate (TBAP) at room temperature
under a N2 atmosphere using a BAS 100B electrochemical
analyzer. Platinum, platinum wire, and Ag|AgNO3 (0.1 M) were
used as the working, counter, and reference electrodes,
respectively. All potentials were calibrated to the ferrocene/
ferrocenium (Fc|Fc+) redox couple. 3-Bromonitrobenzene, 4-
bromo-1-methyl-2-nitrobenzene, 1-bromo-2-methyl-3-nitroben-
zene, 1,4-dibromo-2-nitrobenzene, phenylboronic acid and
1-naphthylboronic acid were purchased and used as received.
10-(2-Naphthyl)anthracene-9-boronic acid was prepared using
the method reported in the literature.24
1
powder. Yield: 92% (2.50 g). H NMR (CDCl3) d 8.08 (s, 1H),
7.84 (d, 1H), 7.65 (d, 2H), 7.53–7.49 (m, 3H), 7.46–7.42 (m, 4H),
7.39–7.35 (m, 2H). Anal. calcd. for C18H13NO2: C, 78.53; H,
4.76; N, 5.09; O, 11.62. Found: C, 78.52; H, 4.74; N, 5.08.
1-Phenyl-4-(1-naphthyl)-2-nitrobenzene (2e). A stirred mixture
of 1,4-dibromo-2-nitrobenzene (2.78 g, 9.90 mmol), 1 equiv.
phenylboronic acid (1.22 g, 10.00 mmol), Pd(PPh3)4 (0.34 g,
3 mol%), and K2CO3 (4.10 g, 29.66 mmol) in toluene (160 nm)
were added to a mixture of toluene (160 nm) and deionized water
(40 mL) was refluxed for 12 h under an inert atmosphere. The
mixture was cooled to room temperature and quenched with
H2O. The organic layer was extracted with CH2Cl2 (3 ꢃ 30 mL)
and dried over magnesium sulfate. The solvent was removed
under reduced pressure, and the residue purified by silica gel
column chromatography. After the first coupling was complete,
a procedure analogous to the preparation of 2a was used to
obtain 2e as a pale yellow powder. Yield: 81% (2.61 g). 1H NMR
(CDCl3) d 8.00 (s, 1H), 7.97–7.89 (m, 3H), 7.76 (d, 1H), 7.60–7.42
(m, 10H). Anal. calcd. for C22H15NO2: C, 81.21; H, 4.65; N, 4.30;
O, 9.83. Found: C, 81.20; H, 4.64; N, 4.27.
Synthesis
1-(3-Nitrophenyl)naphthalene (2a). 3-Bromonitrobenzene
(2.00 g, 9.90 mmol), 1-naphthylboronic acid (1.88 g,
10.88 mmol), Pd(PPh3)4 (0.34 g, 3 mol%), and K2CO3 (4.10 g,
29.66 mmol) were added to a mixture of DME (100 mL). After
adding deionized water (25 mL), the resulting mixture was
refluxed for 12 h under an inert atmosphere. The mixture was
cooled to room temperature and quenched with H2O. The
organic layer was extracted with CH2Cl2 (3 ꢃ 30 mL) and dried
over magnesium sulfate. The solvent was removed under reduced
pressure, and the residue purified by silica gel column chroma-
tography using CH2Cl2/hexane (1 : 2) as the eluent. 2a was
obtained as a yellow solid (2.34 g, 95%). 1H NMR (CDCl3) d 8.39
(s, 1H), 8.32 (d, 1H), 7.97–7.93 (m, 2H), 7.86 (d, 1H), 7.79 (d,
1H), 7.70–7.66 (m, 1H), 7.59–7.53 (m, 2H), 7.51–7.44 (m, 2H).
Anal. calcd. for C16H11NO2: C, 77.10; H, 4.45; N, 5.62; O, 12.84.
Found: C, 77.04; H, 4.42; N, 5.63.
1,4-Di(1-naphthyl)-2-nitrobenzene (2f). A procedure analogous
to the preparation of 2a was used, but starting from 1,4-dibromo-
2-nitrobenzene (2.78 g, 9.90 mmol) and 2.2 equiv. of 1-naph-
thylboronic acid (3.76 g, 21.78 mmol). 2f was obtained as a pale
yellow powder. Yield: 94% (3.49 g).1H NMR (CDCl3) d 8.26 (s,
1H), 8.03–7.96 (m, 6H), 7.86 (d, 1H), 7.69–7.49 (m, 9H). Anal.
calcd. for C26H17NO2: C, 83.18; H, 4.56; N, 3.73; O, 8.52. Found:
C, 83.17; H, 4.54; N, 3.73.
Aniline derivatives (3a–3f). Nitrobenzene derivatives (2a–2f),
ethanol (150 ml), ethyl acetate (100 ml), and 10% palladium on
charcoal (1.0 g) were placed in a 500 mL Parr bottle. The bottle
was then placed on a Parr hydrogenation apparatus. The sample
was evacuated and filled with hydrogen, and the process repeated
three times. The tank and bottle were then filled with hydrogen to
30 psi. The shaker was started, and hydrogenation was allowed
1120 | J. Mater. Chem., 2011, 21, 1115–1123
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to proceed for five hours. After safely venting the hydrogen from
the bottle, the resulting solution was filtered through celite and
the catalyst washed carefully with 20 mL of ethanol. The filtrate
was transferred to a flask and solvent was removed under
reduced pressure. After dissolving in CH2Cl2, the solution was
filtered again through silica gel and the resulting solvent was
removed under reduced pressure to obtain 3a–3f as a white
powder in quantitative yield.
3-(1-Naphthyl)iodobenzene (4a). Yield: 62% (1.63 g). 1H NMR
(CDCl3) d 7.93–7.84 (m, 3H), 7.66 (s, 1H), 7.59–7.49 (m, 3H),
7.46–7.34 (m, 4H). Anal. calcd. for C16H11I: C, 58.20; H, 3.36; I,
38.44. Found: C, 58.19; H, 3.33.
2-Methyl-5-(1-naphthyl)iodobenzene (4b). Yield: 54% (1.48 g).
1H NMR (CDCl3) d 7.97 (s, 1H), 7.91–7.85 (m, 3H), 7.54–7.45
(m, 3H), 7.40–7.34 (m, 3H), 2.54 (s, 3H). Anal. calcd. for
C17H13I: C, 59.32; H, 3.81; I, 36.87. Found: C, 59.31; H, 3.78.
1
3-(1-Naphthyl)aniline (3a). H NMR (CDCl3) d 8.03 (d, 1H),
7.87 (d, 1H), 7.67–7.39 (m, 6H), 7.25 (d, 1H), 6.78 (d, 1H), 6.71 (s,
1H), 3.56 (s, -NH2-). Anal. calcd. for C16H11NO2: C, 77.10; H,
4.45; N, 5.62; O, 12.84. Found: C, 77.11; H, 4.44; N, 5.59.
2-Methyl-3-(1-naphthyl)iodobenzene (4c). Yield: 58% (1.60 g).
1H NMR (CDCl3) d 7.95–7.87 (m, 3H), 7.55–7.48 (m, 2H), 7.41
(d, 2H), 7.31–7.22 (m, 2H), 6.98 (t, 1H), 2.14 (s, 3H). Anal. calcd.
for C17H13I: C, 59.32; H, 3.81; I, 36.87. Found: C, 59.29; H, 3.80.
1
2-Methyl-5-(1-naphthyl)aniline (3b). H NMR (CDCl3) d 7.96
1
2,5-Diphenyliodobenzene (4d). Yield: 51% (1.45 g). H NMR
(d, 1H), 7.88 (d, 1H), 7.83 (d, 1H), 7.58–7.41 (m, 4H), 7.19 (d,
1H), 6.92–6.88 (m, 2H), 3.78 (s, -NH2-), 2.32 (s, 3H). Anal. calcd.
for C17H13NO2: C, 77.55; H, 4.98; N, 5.32; O, 12.15. Found: C,
77.52; H, 4.95; N, 5.30.
(CDCl3) d 8.20 (s, 1H), 7.61 (d, 2H), 7.49ꢂ7.36 (m, 10H). Anal.
calcd. for C18H13I: C, 60.69; H, 3.68; I, 35.63. Found: C, 60.68;
H, 3.67.
1
2-Methyl-3-(1-naphthyl)aniline (3c). H NMR (CDCl3) d 7.91
2-Phenyl-5-(1-naphthyl)iodobenzene (4e). Yield: 68% (2.21 g).
1H NMR (CDCl3) d 8.12 (s, 1H), 7.98–7.88 (m, 4H), 7.57–7.41
(m, 10H). Anal. calcd. for C22H15I: C, 65.04; H, 3.72; I, 31.24.
Found: C, 65.01; H, 3.72.
(d, 1H), 7.87 (d, 1H), 7.55–7.46 (m, 3H), 7.41–7.34 (m, 2H), 7.14
(t, 1H), 6.83 (d, 1H), 6.76 (d, 1H), 3.67 (s, -NH2-), 1.84 (s, 3H).
Anal. calcd. for C17H13NO2: C, 77.55; H, 4.98; N, 5.32; O, 12.15.
Found: C, 77.54; H, 4.97; N, 5.31.
2,5-Di(1-naphthyl)iodobenzene (4f). Yield: 50% (1.83 g). 1H
NMR (CDCl3) d 8.19 (s, 1H), 8.05 (t, 1H), 7.98–7.92 (m, 5H),
7.63–7.44 (m, 10H). Anal. calcd. for C26H17I: C, 68.43; H, 3.76; I,
27.81. Found: C, 68.42; H, 3.75.
2,5-Diphenylaniline (3d). 1H NMR (CDCl3) d 7.62 (d, 2H), 7.51
(d, 2H), 7.46–7.43 (m, 4H), 7.37–7.32 (m, 2H), 7.24 (d, 1H), 7.13
(d, 1H), 7.08 (s, 1H), 3.77 (s, -NH2-). Anal. calcd. for
C18H13NO2: C, 78.53; H, 4.76; N, 5.09; O, 11.62. Found: C,
78.53; H, 4.72; N, 5.07.
Asymmetric bulky aryl-substituted anthracenes (5a–5f).
4.0 mmol of iodobenzene (4a–4f), 10-(2-naphthyl)anthracene-9-
boronic acid (1.74 g, 5.00 mmol), Pd(PPh3)4 (0.14 g, 3 mol%),
and K2CO3 (1.66 g, 12.01 mmol) were added to a mixture of
toluene (80 mL). After adding deionized water (20 mL), the
resulting mixture was refluxed for 12 h under an inert atmo-
sphere. The mixture was cooled to room temperature and
quenched with H2O. The organic layer was extracted with
CH2Cl2 (3 ꢃ 30 mL) and dried over magnesium sulfate. The
solvent was removed under reduced pressure, and the residue
purified by silica gel column chromatography using dichloro-
methane/hexane (1 : 7) as eluent, and further purified by train
sublimation under 5.4 ꢃ 10ꢁ5 Torr.
1
2-Phenyl-5-(1-naphthyl)aniline (3e). H NMR (CDCl3) d 8.08
(d, 1H), 7.91 (d, 1H), 7.86 (d, 1H), 7.59–7.45 (m, 7H), 7.44–7.36
(m, 2H), 7.25 (d, 1H), 6.97 (d, 1H), 6.91 (s, 1H), 3.62 (s, -NH2-).
Anal. calcd. for C22H15NO2: C, 81.21; H, 4.65; N, 4.30; O, 9.83.
Found: C, 81.19; H, 4.63; N, 4.27.
2,5-Di(1-naphthyl)aniline (3f). 1H NMR (CDCl3) d 8.12 (d,
1H), 7.93–7.79 (m, 5H), 7.60–7.47 (m, 8H), 7.23 (d, 1H), 6.99 (d,
1H), 6.95 (s, 1H), 3.55 (s, -NH2-). Anal. calcd. for C26H17NO2: C,
83.18; H, 4.56; N, 3.73; O, 8.52. Found: C, 83.19; H, 4.56; N,
3.72.
Iodobenzenes derivatives (4a–4f). 8.00 mmol of the anilines
(3a–3f) was added to a solution of p-TsOH$H2O (3.44 g,
18.08 mmol) in MeCN (24 mL). The resulting suspension of
amine salt was cooled to 0 ꢀC and a solution of NaNO2
(0.83 g, 12.03 mmol) and KI (2.49 g, 15.00 mmol) in H2O
(4 mL) was gradually added to it. The reaction mixture was
stirred for 30 min then allowed to cool to room temperature
and stirred for 12 h. Then H2O (50 mL), NaHCO3 (1 M; until
pH ¼ 9–10) and Na2S2O3 (2 M, 20 mL) was added to the
reaction mixture. The precipitated aromatic iodide was
extracted with Et2O (3 ꢃ 30 mL) and dried over magnesium
sulfate. The solvent was removed under reduced pressure, and
the residue purified by silica gel column chromatography
using hexane as the eluent, obtaining 4a–4f as a white powder
in moderate yield.
9-(2-Naphthyl)-10-(3-(1-naphthyl)phenyl)anthracene
(5a).
1
Yield: 76% (1.54 g, white powder). H NMR (C6D6) d 8.31 (d,
1H), 8.08 (d, 2H), 7.88–7.85 (m, 3H), 7.76 (d, 2H), 7.71–7.70 (m,
1H), 7.67–7.60 (m, 4H), 7.52–7.49 (d, 2H), 7.46–7.43 (m, 2H),
7.36–7.27 (m, 5H), 7.20–7.19 (m, 2H), 7.13–7.11 (m, 2H). 13C
NMR (C6D6) 141.4, 140.1, 139.8, 139.7, 137.5, 137.4, 137.0,
134.4, 133.9, 133.3, 133.2, 133.1, 132.1, 130.6, 130.5, 130.46,
130.45, 130.42, 129.7, 129.5, 129.4, 128.6, 128.5, 128.4, 128.3,
128.2, 128.0, 127.5, 127.4, 127.3, 126.5, 126.4, 126.3, 126.2, 125.9,
125.6, 125.5, 125.4. HRMS(FAB) calcd for C40H26: 506.2035.
Found: 506.2030 [M]+. Anal. calcd for C40H26: C, 94.83; H, 5.17.
Found: C, 94.82; H, 5.16.
9-(2-Naphthyl)-10-(2-methyl-5-(1-naphthyl)phenyl)anthracene
(5b). Yield: 63% (1.31 g, white powder). 1H NMR (C6D6): d 8.36
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(t, 1H), 7.95–7.92 (m, 2H), 7.89–7.85 (m, 2H), 7.79–7.71 (m, 4H),
7.66 (d, 1H), 7.60 (d, 1H), 7.54–7.47 (m, 3H), 7.39–7.26 (m, 7H),
7.19–7.16 (m, 2H), 7.11–7.10 (m, 2H), 2.05 (d, 3H). 13C NMR
(C6D6) 140.1, 139.1, 138.9, 137.4, 137.3, 137.0, 136.98, 136.91,
134.4, 133.9, 133.3, 133.2, 133.1, 132.1, 130.7, 130.5, 130.4, 130.2,
129.89, 129.87, 129.7, 128.5, 128.4, 128.3, 128.2, 128.1, 127.6,
127.4, 126.8, 126.53, 126.50, 126.3, 126.2, 125.8, 125.7, 125.6,
125.58, 125.54, 125.53, 19.55, 19.54. HRMS(FAB) calcd for
C41H28: 520.2191. Found: 520.2185 [M]+. Anal. calcd for C41H28:
C, 94.58; H, 5.42. Found: C, 94.56; H, 5.42.
130.3, 130.2, 130.1, 129.7, 129.6, 129.33, 129.31, 128.6, 128.5,
128.33, 128.30, 128.17, 128.14, 128.0, 127.8, 127.6, 127.4, 127.3,
127.12, 127.08, 126.64, 126.61, 126.5, 126.3, 126.2, 126.1, 126.0,
125.67, 125.64, 125.51, 125.49, 125.44, 125.40, 125.16, 125.14,
125.0, 124.7, 124.6. HRMS(FAB) calcd for C50H32: 632.2504.
Found: 632.2498 [M]+. Anal. calcd for C50H32: C, 94.90; H, 5.10.
Found: C, 94.89; H, 5.08.
Device fabrication and characterization
The OLED devices were fabricated on glass substrates precoated
with a 150 nm thick indium tin oxide (ITO) layer with a sheet
resistance of ꢂ10 U per square. The ITO glass was precleaned
using a conventional solvent cleaning method. The ITO surface
was cleaned again with a UV ozone treatment immediately before
depositing the HIL layer. 2-Methyl-9,10-di(2-naphthyl)-
anthracene (MADN) was used as a reference material because it
is used widely as a blue EML host material. The organic, LiF, and
Al layers were deposited sequentially onto the substrate without
breaking the vacuum. The other commercially available organic
materials were used as received. The current–voltage character-
istics of the OLEDs were measured using a source measure unit
(Keithley 236). The electroluminescence spectra, luminance, and
CIE color coordinates were measured using a spectroradiometer
(Photo Research PR650). Assuming Lambertian emission, the
external quantum efficiency (EQE) was calculated from the
luminance, current density, and electroluminescence spectrum.
9-(2-Naphthyl)-10-(2-methyl-3-(1-naphthyl)phenyl)anthracene
(5c). Yield: 41% (0.85 g, white powder). 1H NMR (C6D6) d 8.09–
8.07 (m, 1H), 8.01–7.97 (m, 2H), 7.89–7.82 (m, 2H), 7.77–7.75
(m, 2H), 7.72–7.67 (m, 3H), 7.63 (t, 1H), 7.50 (d, 1H), 7.47–7.42
(m, 3H), 7.36–7.25 (m, 7H), 7.20 (t, 1H), 7.14–7.10 (m, 2H), 1.87
(d, 3H). 13C NMR (C6D6) 141.5, 140.3, 139.5, 137.4, 137.18,
137.16, 137.09, 137.05, 136.9, 136.8, 134.1, 133.9, 133.1, 132.62,
132.61, 131.1, 130.7, 130.53, 130.50, 130.49, 130.47, 130.3,
130.28, 130.22, 130.21, 129.74, 129.70, 128.6, 128.4, 128.3,
128.22, 128.20, 128.1, 127.6, 127.1, 126.9, 126.7, 126.5, 126.3,
126.2, 126.1, 126.0, 125.9, 125.7, 125.6, 125.5, 17.5, 17.4.
HRMS(FAB) calcd for C41H28: 520.2191. Found: 520.2177 [M]+.
Anal. calcd for C41H28: C, 94.58; H, 5.42. Found: C, 94.54; H,
5.39.
9-(2-Naphthyl)-10-(2,5-diphenyl)phenyl)anthracene (5d). Yield:
49% (1.04 g, white powder). 1H NMR (C6D6) d 8.00 (d, 2H), 7.83
(s, 1H), 7.78–7.63 (m, 8H), 7.54–7.46 (m, 3H), 7.34–7.26 (m, 5H),
7.20 (t, 2H), 7.13 (t, 2H), 7.04–7.01 (m, 2H), 6.79–6.73 (m, 2H),
6.70–6.67 (m, 1H). 13C NMR (C6D6) 142.7, 142.6, 141.4, 141.3,
140.55, 140.53, 140.44, 140.40, 138.4, 137.6, 136.9, 136.8, 136.7,
133.85, 133.81, 133.1, 131.4, 131.2, 130.7, 130.5, 130.48, 130.42,
129.8, 129.7, 129.01, 129.02, 128.7, 128.4, 128.3, 128.2, 128.1,
127.9, 127.8, 127.57, 127.50, 127.35, 127.33, 127.30, 127.0,
126.98, 126.95, 126.46, 126.43, 126.2, 125.6, 125.3. HRMS(FAB)
calcd for C42H28: 532.2191. Found: 532.2179 [M]+. Anal. calcd
for C42H28: C, 94.70; H, 5.30. Found: C, 94.65; H, 5.28.
Acknowledgements
This work was supported by the National Research Foundation
of Korea (NRF) grant funded by the Korean government
(MEST) (No. 2010-0018456) and ERC Program (No. 2010-
0001842). We are also grateful for the support from WCU
Program (R31-10035).
Notes and references
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2008, 47, 581.
3 (a) M.-T. Lee, C.-H. Liao, C.-H. Tsai and C. H. Chen, Adv. Mater.,
2005, 17, 2493; (b) Y. Duan, Y. Zhao, P. Chen, J. Li, S. Liu, F. He
and Y. Ma, Appl. Phys. Lett., 2006, 88, 263503.
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C.-C. Wu and K.-T. Wong, Adv. Mater., 2005, 17, 992; (b)
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Mater., 2006, 18, 325.
9-(2-Naphthyl)-10-(2-phenyl-5-(1-naphthyl)phenyl)anthracene
(5e). Yield: 69% (1.60 g, white powder). 1H NMR (C6D6) d 8.37
(t, 1H), 8.07 (d, 2H), 7.77–7.56 (m, 10H), 7.56–7.50 (m, 1H), 7.48
(t, 2H), 7.42–7.26 (m, 10H), 7.04–6.99 (m, 2H), 6.80–6.68 (m,
2H).13C NMR (C6D6) 142.6, 141.8, 141.7, 141.5, 141.2, 140.3,
139.7, 138.5, 137.9, 137.8, 137.5, 137.4, 136.7, 136.4, 136.3, 134.6,
134.4, 133.8, 133.7, 133.1, 132.1, 130.7, 130.6, 130.5, 130.4, 130.1,
129.7, 128.7, 128.6, 128.2, 127.54, 127.52, 127.26, 127.23, 127.0,
126.4, 126.2, 125.9, 125.6, 125.3. HRMS(FAB) calcd for C46H30:
582.2348. Found: 582.2328 [M]+. Anal. calcd for C46H30: C,
94.81; H, 5.19. Found: C, 94.78; H, 5.18.
6 C. J. Tonzola, A. P. Kukarni, A. P. Gifford, W. Kaminsky and
S. A. Jenekhe, Adv. Funct. Mater., 2007, 17, 863.
7 (a) C.-T. Chen, Y. Wei, J.-S. Lin, M. V. R. K. Moturu, W.-S. Chao,
Y.-T. Tao and C.-H. Chien, J. Am. Chem. Soc., 2006, 128, 10992; (b)
Y. Wei, S. Samori, S. Tojo, M. Fujitsuka, J.-S. Lin, C.-T. Chen and
T. Majima, J. Am. Chem. Soc., 2009, 131, 6698.
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K. Chan, J. Li and Y. Chi, Adv. Funct. Mater., 2007, 17, 1028.
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B. Peng, W. Wei, Y. Cao and W. Huang, J. Phys. Chem. C, 2009,
113, 4641; (b) K.-R. Wee, H.-C. Ahn, H.-J. Son, W.-S. Han,
J.-E. Kim, D. W. Cho and S. O. Kang, J. Org. Chem., 2009, 74, 8472.
9-(2-Naphthyl)-10-(2,5-di(1-naphthyl)phenyl)anthracene (5f).
Yield: 71% (1.79 g, white powder).1H NMR (C6D6) d 8.50 (t,
1H), 8.37 (d, 1H), 8.29 (d, 1H), 8.11 (d, 1H), 7.79–7.68 (m, 8H),
7.64 (t, 1H), 7.60–7.57 (m, 1H), 7.51–7.44 (m, 2H), 7.41–7.28 (m,
10H), 7.24 (t, 1H), 7.17–7.08 (m, 2H), 6.93 (m, 1H), 6.79–6.68 (m,
2H). 13C NMR (C6D6) 140.7(5), 140.6(8), 140.4, 139.8, 139.4,
138.4, 138.3, 137.2, 136.8, 136.6, 136.5, 134.9, 134.4, 134.1, 133.7,
133.0, 132.5, 132.4, 132.27, 132.24, 132.1, 131.37, 131.34, 130.4,
1122 | J. Mater. Chem., 2011, 21, 1115–1123
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