A bipolar host containing 1,2,3-triazole for realizing highly efficient phosphorescent organic light-emitting diodes

Article abstract of DOI:10.1039/c0nj00091d

We have developed a novel host material, 9,9′-(2-((4-phenyl-1,2,3- triazol-1-yl)methyl)biphenyl-4,4′-diyl)biscarbazole (CBP-TA), for realizing highly efficient blue phosphorescent OLEDs. The maximum external quantum efficiency of the OLED device developed using CBP-TA doped with a blue phosphorescent material was 30% greater than that of a CBP-based device. This enhanced external quantum efficiency resulted from the bipolar properties of the new host, owing to which well-balanced hole and electron transport through the emitting layer was achieved. The excellent bipolar carrier transport properties of the new host were experimentally verified using various OLED device data.

Full text of DOI:10.1039/c0nj00091d

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www.rsc.org/njc | New Journal of Chemistry
A bipolar host containing 1,2,3-triazole for realizing highly efficient
phosphorescent organic light-emitting diodes
Myoung Ki Kim, Jongchul Kwon, Tae-Hyuk Kwon and Jong-In Hong*
Received (in Montpellier, France) 4th February 2010, Accepted 22nd March 2010
First published as an Advance Article on the web 27th April 2010
DOI: 10.1039/c0nj00091d
We have developed a novel host material, 9,90-(2-((4-phenyl-1,2,3-triazol-1-yl)methyl)biphenyl-
4,40-diyl)biscarbazole (CBP-TA), for realizing highly efficient blue phosphorescent OLEDs. The
maximum external quantum efficiency of the OLED device developed using CBP-TA doped with
a blue phosphorescent material was 30% greater than that of a CBP-based device. This enhanced
external quantum efficiency resulted from the bipolar properties of the new host, owing to which
well-balanced hole and electron transport through the emitting layer was achieved. The excellent
bipolar carrier transport properties of the new host were experimentally verified using various
OLED device data.
To overcome these issues, we designed a unique bipolar host
material, 9,90-(2-((4-phenyl-1,2,3-triazol-1-yl)methyl)biphenyl-
4,40-diyl)biscarbazole (CBP-TA), that is obtained by coupling
Introduction
Organic light-emitting diodes (OLEDs) have attracted
considerable attention owing to a number of advantages, such
4,40-N,N0-dicarbazolebiphenyl (CBP; an electron donor) and
as high brightness, high contrast, low power consumption, low
cost,1,2 and a wide range of applications in full-color flat-panel
1,2,3-triazole (an electron acceptor with a high electron affi-
nity). The external quantum efficiency (EQE) when CBP-TA
displays and solid-state lighting.3,4 In particular, phosphorescent
was used as the host for iridium(III) bis(4,6-(difluorophenyl)-
pyridinato-N,C20) picolinate(FIrpic) blue phosphorescent
materials are more attractive compared to fluorescent materials
as they can reach an internal quantum efficiency of 100%
OLEDs was 30% greater than the EQE when CBP alone
through the radiative recombination of both singlet and
was used as the host. The FIrpic-doped CBP-TA device
triplet excitons. Highly efficient blue-emitting materials still
exhibited a stable blue emission at Commission Internationale
need to be developed if high performance OLEDs are to be
de l’Eclairage (CIE) coordinates of (0.17, 0.35) with a high
current efficiency of 9.0 cd Aꢀ1 and a power efficiency of
commercialized. Efficient blue-emitting materials are important
6.9 lm Wꢀ1. The efficiency of the FIrpic-doped CBP-TA device
not only as blue emitters themselves but also as hosts for other
emitters, particularly in phosphorescent OLEDs.5–8
was higher than that of the FIrpic-doped CBP device. The
In order to improve phosphorescent blue emission, it is vital
increased OLED efficiency results from the bipolar properties
to prevent reverse energy transfer from the emitter back to the
of CBP-TA.
host and to effectively confine triplet excitons to the triplet
emitter molecules. This can be achieved by ensuring that the
triplet excited state of the host material is higher than that of
the triplet emitter.9 An alternative method for improving the
performance of OLEDs is to use bipolar host materials.
Bipolar host materials contribute to the balanced transport
of carriers to the triplet emitter and help increase the probability
of carrier recombination.10,11
Results and discussion
The molecular structure of CBP-TA is shown in Scheme 1.
CBP-TA was synthesized according to Scheme 2.
Fig. 1a shows the UV absorption of CBP-TA, and
photoluminescence (PL) spectra at 293 and 77 K of CBP
and CBP-TA in 2-methyltetrahydrofuran. The fluorescence
emission maximum wavelengths of CBP and CBP-TA appear
at 365 and 362 nm, respectively, and the phosphorescence
Carbazole derivatives have been utilized in the construction
of highly photoconductive amorphous organic materials and
thus have been used as hole transport materials in OLEDs via
radical cation species or as host materials.12 Due to its high
triplet energy (ca. 3.0 eV), carbazole is a good candidate for a
blue phosphorescent host material. However, carbazole is a
well-known electron donor. This may result in unbalanced
carrier injection and transport into the emitting layer, thus
limiting device performance.13
Department of Chemistry, College of Natural Sciences, Seoul
National University, Seoul 151-747, Korea. E-mail: jihong@snu.ac.kr;
Fax: +82 2-889-1568; Tel: +82 2-880-6682
Scheme 1 The molecular structures of CBP (left) and CBP-TA
(right).
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Scheme 2 The synthesis of CBP-TA: (a) CuI, K3PO4, (ꢂ)-trans-1,2-
diaminocyclohexane, toluene; (b) n-BuLi, trimethylborate, THF;
(c) 1a, Na2CO3, 2-dicyclohexylphosphino-20-methylbiphenyl, tris-
(dibenzylidene acetone)dipalladium(0), toluene; (d) NBS, CCl4;
(e) NaN3, DMF; (f) phenyl acetylene, Cu(SO4)2, L-ascorbic acid
sodium salt, THF, H2O.
triplet emission of CBP and CBP-TA appears at 454 and 439 nm,
respectively, which was determined by taking the first emission
peak of phosphorescence as the transition energy of T1 - S0.14
The triplet emission (triplet energy 2.71 eV, the arrow in
Fig. 1b) of CBP-TA is blue-shifted compared to that of CBP
(triplet energy 2.56 eV). The PL spectrum of CBP-TA shows a
blue shift at 293 and 77 K compared to that of CBP because of
the electron deficient 1,2,3-triazole unit, indicating an increase
in the singlet–triplet band gap (Fig. 1b).
The HOMO energy value of CBP-TA was estimated by
cyclic voltammetry (CV). This electrochemical experiment was
referenced with respect to a silver wire as the quasi-reference
electrode (AgQRE) at room temperature and then calibrated
to a standard hydrogen electrode (SHE) using ferrocene
(Fc/Fc+). Acetonitrile solutions for CV contained a 2 mm
diameter Pt working electrode, a Pt counterelectrode and a
0.1 M TBAPF6 (tetra-n-butylammoniumhexafluorophosphate)
supporting electrolyte. The oxidation potential of CBP-TA
was observed at E1/2 = 1.51 V vs. SHE. The HOMO energy
level of CBP-TA (ꢀ6.00 eV) was calculated from E1/2 after
correction of the vacuum energy level (4.49 eV). The LUMO
level of CBP-TA, which was determined from the HOMO level
and the cross section wavelength between the absorption and
emission spectra, is 2.5 eV. The HOMO and LUMO levels of
CBP were determined to be 5.9 and 2.6 eV, respectively. These
electrochemical data confirm that the presence of the 1,2,3-
triazole unit leads to an increase in the energy band gap.
In order to evaluate the electroluminescence (EL) and
charge transporting properties of CBP-TA, we designed several
OLED device structures, which are described in Table 1.
Organic layers were fabricated by high vacuum (10ꢀ7 torr)
thermal evaporation onto a patterned ITO glass pre-cleaned in
a UV-ozone chamber. A 10 nm-thick film of copper phthalo-
cyanine (CuPc) and a 30 nm-thick film of 4,40-bis[N-(1-
naphthyl)-N-phenyl-amino]-biphenyl (a-NPD) served as the
hole injection layer (HIL) and hole transport layer (HTL),
respectively. The emitting layer (EML) was prepared by
co-evaporating the CBP or CBP-TA host and 6 wt% FIrpic
Fig. 1 (a) Optical absorption spectra and PL spectra of CBP-TA and
CBP at 293 K. (b) PL spectra of CBP-TA and CBP at 77 K; the inset
shows the energy band gap of CBP-TA and CBP.
dopant. Next, a 30 nm-thick 4-biphenyloxolatoaluminium(III)-
bis(2-methyl-8-quinolinato)4-phenylphenolate (Balq) layer, func-
tioning as both a hole blocking layer (HBL) and an electron
transporting layer (ETL), was deposited; this was then followed
by the deposition of LiF as an electron injection layer (EIL).
Finally, after changing the metal mask, a 100 nm-thick
aluminium film was deposited on the EIL and then encapped.
A Keithly 2400 source meter attached to a computer was used
to operate the device.
First, we examined devices 1 and 2, having CBP-TA or CBP
as the host for FIrpic, which was sandwiched between the
HTL and ETL.15 The maximum efficiencies of devices 1 and 2
were 5.4% (9.2 cd Aꢀ1) and 4.2% (7.5 cd Aꢀ1), respectively.
Both devices exhibited a bright blue emission with a peak at
472 nm from the emission of FIrpic at CIE coordinates of
(0.17, 0.35). It is important to note that the current density of
device 1 was less than that of device 2; this can be explained by
the higher charge injection barrier of CBP-TA compared to
that of CBP (Fig. 1b). However, the luminance and efficiency
of device 1 were higher than those of device 2 (Fig. 2). We
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Table 1 Layer structures and EL performance data of the OLED devices (units: nm)
Turn-on
voltage/Vb
P. E./
lm Wꢀ1d
C. E./
cd Aꢀ1e
Emission peaks/
nm
CIE
coordinates
Devicea
1
EML
ETL
Q. E. (%)c
5.4
CBP-TA:
6% Firpic (30)
CBP:
6% Firpic (30)
CBP-TA:
6% Firpic (60)
CBP:
6% Firpic (60)
CBP-TA:
6% Firpic (30)
CBP:
6% Firpic (30)
CBP-TA:
6% Ir(ppy)3 (30)
CBP:
6% Ir(ppy)3 (30)
Balq (30)
4.6
6.9
6.4
—
9.0
7.5
—
472, 500
472, 500
472, 500
472, 500, 530
472, 500
472, 500, 530
512
(0.17, 0.35)
(0.17, 0.35)
(0.18, 0.34)
(0.22, 0.41)
(0.21, 0.36)
(0.30, 0.44)
(0.32, 0.61)
(0.32, 0.61)
2
3
4
5
6
7
8
Balq (30)
4.2
n.d.f
—
4.2
—
Alq3 (30)
Alq3 (30)
n.d.
—
—
—
CBP-TA (20)/Alq3 (30)
CBP (20)/Alq3 (30)
Balq (30)
—
n.d.
—
—
—
—
n.d.
19.9
10.2
5.0
4.8
7.2
3.7
6.5
3.3
Balq (30)
512
a
b
Device structure of 1–8: CuPc (10 nm)/NPD (30 nm)/EML/ETL/LiF (1 nm)/Al (100 nm). Voltage at 1 cd. Maximum quantum efficiency.
c
d
e
f
Maximum power efficiency. Maximum luminance efficiency. Not determined. We fabricated devices 3–6 for the purpose of comparing
emission peaks and CIEs with those of CBP-based devices.
expected the performance of device 1 to be better than that of
device 2 owing to the improved carrier balance in device 1. The
improved carrier balance of device 1 is due to the bipolar
properties of CBP-TA, which consists of both electron donor
and electron acceptor units.14,16 The efficiency of the examined
devices may be lower than that of phosphorescent OLED
devices fabricated using other hosts;9–11,13,16 this is because,
in the current study, we only compared the performance
of devices 1 and 2, which comprised CBP-TA and CBP,
respectively, as the hosts in order to confirm whether the
bipolar host CBP-TA contributed to the device performance.
In order to verify the bipolar carrier transport properties of
CBP-TA, we fabricated devices 3 and 4, in which Alq3 was
used as the ETL instead of Balq. Fig. 3a shows the normalized
EL spectra of devices 3 and 4 at identical driving voltages. The
EL spectrum of device 4 includes three peaks, two at 472 and
500 nm due to FIrpic emission, and one at 530 nm due to Alq3
emission, at CIE coordinates of (0.22, 0.41). This indicates
that some of the electrons do not penetrate the CBP layer,
because of which carrier recombination occurs at Alq3.13 In
contrast, the EL spectrum of device 3 shows only two peaks at
472 and 500 nm, which are attributed to FIrpic emission at
CIE coordinates of (0.17, 0.34). This is because carrier
recombination occurs mainly in the EML, indicating the
strong bipolar properties of CBP-TA and the well-balanced
hole and electron transport through CBP-TA (Fig. 3a).13,17
To further investigate the bipolar properties of CBP-TA, we
fabricated devices 5 and 6, in which CBP-TA and CBP,
respectively, were inserted between EML and Alq3. In the
case of device 6, we observed an emission from Alq3 because of
a small degree of carrier recombination at Alq3. On the other
hand, in the case of device 5, no emission from Alq3 was
observed and an emission from FIrpic was predominant,
thereby indicating that most of the electrons penetrated the
CBP-TA layer and little carrier recombination had occurred at
Alq3 (Fig. 3b). This confirms that CBP-TA has excellent
bipolar properties and therefore contributes significantly to
Fig. 2 Plots of current efficiency vs. current density for devices 1 and
2; the inset shows the plot of current density vs. voltage for devices
1 and 2.
the balanced transport of holes and electrons in OLED
devices.14,17
To further verify the well-balanced hole and electron
transport through CBP-TA, we fabricated an electron-only
device with the structure ITO/CBP or CBP-TA/Balq/LiF/Al.
As shown in Fig. 4, the turn-on voltage of the CBP-TA-based
device is higher than that of the CBP-based device, and the
current density of the CBP-TA-based device is less than that of
the CBP-based device because of the higher charge injection
barrier of CBP-TA. However, the luminance vs. current
density of the CBP-TA-based device is higher than that of
the CBP-based device. This result indicates that although
CBP-TA reduces the charge injection capability, CBP-TA
contributes to the balanced transport of holes and electrons
because of its bipolar properties.17
It is well known that to enhance the performance of
OLEDs, the triplet excited state of the host material should
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order to demonstrate that the high efficiency of the
CBP-TA-based device results from the bipolar properties of
CBP-TA, and not from its high triplet excited state, we
fabricated devices 7 and 8 using fac-tris(2-phenylpyridine)-
iridium (Ir(ppy)3) instead of FIrpic. Since the triplet excited
state of Ir(ppy)3 is 2.4 eV,18 reverse energy transfer from
phosphorescent emitter Ir(ppy)3 to the CBP host was prevented.
Thus, the triplet excited state, which is lower for CBP
compared to CBP-TA, does not significantly contribute to a
decrease in device efficiency. Nevertheless, the emission
efficiency of device 7 (19.9 cd Aꢀ1), which comprises CBP-TA,
is approximately twice that of device 8 (10.2 cd Aꢀ1), which
comprises CBP. This implies that the higher efficiency of
device 7 results not only from a higher triplet excited state
but also from the stronger bipolar properties of CBP-TA
compared to those of CBP.
While 1,2,3-triazole provides CBP-TA with better bipolar
properties, the CV data revealed that CBP-TA is electro-
chemically less stable than CBP. Also, the OLED device based
on CBP-TA is less stable that the CBP-based OLED device. It
is very likely that the introduction of a methylene linkage
or/and a triazole unit into CBP reduces the electrochemical
stability of CBP-TA.
Conclusion
In summary, we have synthesized a unique bipolar host
material, CBP-TA, which was obtained by coupling CBP
and 1,2,3-triazole. The EQE of the FIrpic-based blue
phosphorescent OLEDs increased by 30% when CBP-TA
was used as the host instead of CBP. This is because the
new host exhibited excellent bipolar properties, owing to
which well-balanced hole and electron transport through the
emitting layer were achieved. These excellent bipolar transport
properties and the resulting high performance of the device
containing CBP-TA as the host suggest that efficient and
versatile host materials for high performance OLEDs can be
generated by coupling an electron donor with an electron
acceptor.
Fig. 3 (a) EL spectra of devices 3 and 4. (b) EL spectra of devices 5
and 6.
Experimental section
Synthesis
1H and 13C NMR spectra were recorded using an Bruker
1
Avance 300 MHz spectrometer in CDCl3. H NMR chemical
shifts in CDCl3 were referenced to CHCl3 (7.27 ppm), and
13C NMR chemical shifts in CDCl3 reported relative to CHCl3
(77.23 ppm). UV-vis spectra were recorded on a Beckman
DU650 spectrophotometer. Fluorescence spectra were recorded
on a Jasco FP-7500 spectrophotometer. Mass spectra were
obtained using a MALDI-TOF MS from Bruker. High
resolution masses were measured by FAB mass using a
JEOL HP 5890 series instrument. Analytical thin layer
chromatography was performed using Kieselgel 60F-254
plates from Merck. Column chromatography was carried
out on Merck silica gel 60 (70–230 mesh). All solvents and
reagents were commercially available and used without further
purification unless otherwise noted.
Fig. 4 Plots of current luminance vs. current density for devices 9 and
10; the inset shows the plots of current density vs. voltage for devices 9
and 10. Device 9: ITO/CBP-TA (30 nm)/Balq (20 nm)/LiF (1 nm)/Al
(100 nm). Device 10: ITO/CBP (30 nm)/Balq (20 nm)/LiF (1 nm)/Al
(100 nm).
be higher than that of the phosphorescent emitter.9 Moreover,
the CBP-TA-based device might show a better performance
than the CBP-based device because the triplet excited state of
CBP-TA (2.71 eV) is higher than that of CBP (2.56 eV).16 In
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9-(4-Bromo-3-methyl-phenyl)-9H-carbazole (1b). To
a
heated in an oil bath at 110 1C for 24 h. The reaction mixture
was cooled to ambient temperature, diluted with ethyl acetate
(2–3 mL) and filtered through a plug of Celites, eluting with
additional ethyl acetate (10–20 mL). The filtrate was concentrated
and the resulting residue purified by column chromatography,
eluting with methylene chloride and hexane. Yield: 1.54 g,
37%. 1H NMR (300 MHz, acetone-d6): d (ppm) 8.26 (d, 9 Hz,
4H), 7.88–7.80 (m, 4H), 7.74–7.64 (m, 3H), 7.58–7.49 (m, 8H),
7.36–7.31 (t, 4H), 2.58 (s, 3H).
screw-capped test tube were added CuI (0.46 g, 0.24 mmol),
carbazole (2.949 g, 17 mmol), K3PO4 (7.74 g, 30 mmol) and
toluene, followed by nitrogen bubbling for 10–20 min.
2,5-Dibromotoleune (5 g, 20 mmol) and (ꢂ)-trans-1,2-diamino-
cyclohexane (0.48 ml, 3.9 mmol) were then successively added
under a stream of nitrogen. The reaction tube was sealed and
the contents stirred while being heating in an oil bath at
110 1C for 24 h. The reaction mixture was cooled to ambient
temperature, diluted with ethyl acetate (2–3 mL) and filtered
through a plug of Celites, eluting with additional ethyl acetate
(10–20 mL). The filtrate was concentrated and the resulting
residue purified by column chromatography, eluting with
methylene chloride and hexane. Yield: 4.62 g, 81%. 1H
NMR (300 MHz, acetone-d6): d (ppm) 8.20 (d, 9 Hz, 2H),
7.88 (d, 9 Hz, 1H), 7.63 (s, 1H) 7.45–7.43 (m, 5H), 7.43–7.29
(m, 2H), 2.54 (s, 3H).
9,90-(2-Bromomethyl)biphenyl-4,40-diyl)biscarbazole (4). A
mixture of 9,90-(2-methyl)biphenyl-4,40-diyl)biscarbazole
(0.3 g, 0.6 mmol), NBS (0.138 g, 0.7 mmol) and AIBN
(0.0098 g, 0.05 mmol) was refluxed in CCl4 for 10 h. After
cooling to room temperature, the solvent was evaporated
under high vacuum and dissolved in methylene chloride. The
organic phase was washed with water and dried over Na2SO4.
The solvent was evaporated to give the crude product, which
was then column chromatographed on silica gel, eluting
with methylene chloride and hexane, to provide the desired
9-(4-Bromophenyl)-9H-carbazole (1a). To a screw-capped
test tube were added CuI (0.650 mg, 0.31 mol), carbazole
(3.54 g, 2 mmol), K3PO4 (10.24 g, 4 mol) and toluene, followed
by nitrogen bubbling for 10–20 min. 1,4-Dibromobenzene
(5 g, 21.2 mmol) and (ꢂ)-trans-1,2-diaminocyclohexane
(0.637 ml, 5.2 mmol) were then successively added under a
stream of nitrogen. The reaction tube was sealed and the
contents stirred while being heating in an oil bath at 110 1C
for 24 h. The reaction mixture was cooled to ambient
temperature, diluted with ethyl acetate (2–3 mL) and filtered
through a plug of Celites, eluting with additional ethyl acetate
(10–20 mL). The filtrate was concentrated and the resulting
residue purified by column chromatography, eluting with
1
product. Yield: 0.168 g, 48%. H NMR (300 MHz, CDCl3):
d (ppm) 8.20 (d, 9 Hz, 4H), 7.86–7.75 (m, 5H), 7.67–7.62 (d, 2H),
7.59–7.56 (d, 4H), 7.52–7.47 (t, 4H), 7.38–7.33 (t, 4H), 4.67
(s, 2H).
9,90-(2-Azidomethyl)biphenyl-4,40-diyl)biscarbazole (5).
A
mixture of 4 (2 g, 3.46 mmol) and NaN3 (2.25 g, 34,6 mmol)
in DMF was stirred at 70 1C for 10 h. After cooling to room
temperature, the solvent was evaporated under high vacuum
and dissolved in methylene chloride. The organic phase was
washed with water and dried over Na2SO4. The solvent was
evaporated to give the crude product, which was column
chromatographed on silica gel, eluting with methylene
chloride and hexane, to provide the desired product. Yield:
1.58 g, 85%. 1H NMR (300 MHz, CDCl3): d (ppm) 8.28 (d, 9 Hz,
4H), 7.91–7.80 (m, 5H), 7.69–7.65 (d, 2H), 7.58–7.55 (m, 4H),
7.52–7.33 (t, 8H), 4.70 (s, 2H).
1
methylene chloride and hexane. Yield: 5.53 g, 83%. H NMR
(300 MHz, DMSO-d6): d (ppm) 8.25 (d, 9 Hz, 2H), 7.86
(d, 9 Hz, 2H), 7.61 (d, 9 Hz, 2H), 7.42 (m, 4H), 7.30 (m, 2H).
4-Carbazol-9-yl-2-methyl-phenyl-4-boronic acid (2). To a
stirred solution of 1b (3 g, 8.54 mmol) in dry THF under
N2, cooled with dry ice and an acetone bath, was added
n-BuLi (5.21 ml, 0.1 mmol) dropwise. After completion of
the addition, the orange mixture was stirred 15 min and
trimethyl borate (28.6 ml, 20 mmol) added. The reaction flask
was kept in the cooling bath for 30 min and then allowed to
warm to room temperature. 3 h later, the solvent was removed
by evaporation under reduced pressure. Next, 1 N HCl was
added and stirred for 30 min. The solvent was evaporated and
the residues separated by flash column chromatography,
eluting with methylene chloride and methanol. Yield: 1.3 g,
50%. 1H NMR (300 MHz, DMSO-d6): d (ppm) 8.25 (d, 9 Hz,
2H), 7.86 (d, 9 Hz, 2H), 7.61 (d, 9 Hz, 2H), 7.42 (m, 4H), 7.30
(m, 2H).
9,90-(2-((4-Phenyl-1,2,3-triazol-1yl)methyl)biphenyl-4,40diyl)-
biscarbazole (6; CBP-TA). A mixture of 5 (3 g, 5.56 mmol),
phenyl acetylene (0.68 g, 6.67 mmol), copper(II) sulfate penta-
hydrate (0.42 g, 1.67 mmol) and L-ascorbic acid sodium salt
(0.33 g, 1.67 mmol) in THF and water was stirred at 100 1C for
15 h. After cooling to room temperature, the solvent was
evaporated under high vacuum and dissolved in methylene
chloride. The organic phase was washed with water and dried
over Na2SO4. The solvent was then evaporated to give the
crude product, which was column chromatographed on silica
gel, eluting with methylene chloride and hexane, to provide the
desired product. Yield: 1.5 g, 42%. 1H NMR(300 MHz,
(CD3)2CO): d (ppm) 8.53 (s, 1H), 8.27 (t, J = 6 Hz, 4H),
7.80 (t, J = 6 Hz, 6H), 7.75 (s, 1H), 7.72 (s, 1H), 7.57–7.48 (m,
8H), 7.45–7.71 (m, 8H), 5.93 (s, 2H). 13C NMR (125 MHz,
CDCl3): d (ppm) 146.41, 140.05, 139.69, 139.24, 137.95,
136.63, 136.35, 135.45, 132.07, 130.76, 130.60, 128.80,
127.83, 126.64, 126.61, 126.24, 126.08, 125.136, 122.90,
122.79, 121.98, 120.59, 120.52, 120.33, 120.14, 109.78,
109.67, 51.26. MALDI-TOF MS calc. for C451H31N5: 641.25
g molꢀ1, found: 641.28 g molꢀ1. HRMS (FAB) calc. for
9,90-(2-Methyl)biphenyl-4,40-diyl)biscarbazole (3). To
a
screw-capped test tube were added 2 (0.939 mg, 2.9 mmol),
1a (1 g, 2.97 mmol), Na2CO3 (2.051 g, 90 mmol) and toluene,
followed by nitrogen bubbling for 10–20 min. 2-Dicyclohexyl-
phosphino-20-methylbiphenyl (0.12 mmol) and tris(dibenzylidene
acetone)dipalladium(0) (0.135 mg, 0.43 mmol) were then
successively added under a stream of nitrogen. The reaction
tube was quickly sealed and the contents stirred while being
C
451H31N5: 641.2579 g molꢀ1, found: 641.2579 g molꢀ1
.
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7 X. H. Zhang, M. W. Liu, O. Y. C. S. Lee, H. L. Kwong, S. T. Lee
and S. K. Wu, Chem. Phys. Lett., 2003, 369, 478.
8 C. H. Chuen and Y. T. Tao, Appl. Phys. Lett., 2004, 85, 4609.
9 (a) R. J. Holmes, S. R. Forrest, Y.-J. Tung, R. C. Kwong,
J. J. Brown, S. Garon and M. E. Thompson, Appl. Phys. Lett.,
2003, 82, 2422; (b) Tokito, S. Iijima, T. Suzuki, Y. Kita, H. Tsuzuki
and T. Sato, Appl. Phys. Lett., 2003, 83, 569.
10 (a) J. M. Hancock, A. P. Gifford, Y. Zhu, Y. Lou and
S. A. Jenekhe, Chem. Mater., 2006, 18, 4924; (b) T. H. Huang,
J. T. Lin, L. Y. Chen and C. C. Wu, Adv. Mater., 2006, 18, 602.
11 C. C. Wu, Y. T. Lin, K. T. Wong, R. T. Chen and Y. Y. Chien,
Adv. Mater., 2004, 16, 61.
Acknowledgements
This work was supported by the Basic Science Research
Program through the National Research Foundation of Korea
(NRF) grant funded from the Ministry of Education, Science
and Technology (MEST) of Korea for the Center for Next
Generation Dye-Sensitized Solar Cells (no. 2010-0001842), the
Samsung SDI-SNU grant and the Seoul R&BD Program
(10543). We acknowledge the BK21 fellowship grants to
J. K. and T.-H. K.
12 J. Kwon, T.-H. Kwon, H. S. Cho, M. K. Kim, I.-S. Shin,
D.-Y. Shin, S. J. Park and J.-I. Hong, New J. Chem., 2008, 32,
1368.
13 S. J. Su, H. Sasabe, T. Takeda and J. Kido, Chem. Mater., 2008,
20, 1691.
14 M.-H. Tsai, H.-W. Lin, H.-C. Su, T.-H. Ke, C.-C. Wu, F.-C. Fang,
Y.-Li. Liao, K.-T. Wong and C.-I. Wu, Adv. Mater., 2006, 18,
1216.
15 C. Adachi, R. C. Kwong, P. Djurovich, V. Adamovich,
M. A. Baldo, M. E. Thompson and S. R. Forrest, Appl. Phys.
Lett., 2001, 79, 2082.
16 S. Tao, C. S. Lee, S. T. Lee and X. Zhang, Appl. Phys. Lett., 2007,
91, 013507.
17 J. H. Lee, H. H. Tsai, M. K. Leung, C. C. Yang and C. C. Chao,
Appl. Phys. Lett., 2007, 90, 243501.
18 Y. Y. Noh, C. L. Lee and J.-J. Kim, J. Chem. Phys., 2003, 118,
2853.
References
1 C. W. Tang and S. A. VanSlyke, Appl. Phys. Lett., 1987, 51, 913.
2 C. W. Tang, S. A. VanSlyke and C. H. Chen, J. Appl. Phys., 1989,
65, 3610.
3 J. H. Burroughes, D. D. C. Bradley, A. R. Broun, R. N. Marks,
K. Mackay, R. H. Friend, P. L. Burn and A. B. Holmes, Nature,
1990, 347, 539.
4 M. A. Baldo, M. E. Thompson and S. R. Forrest, Nature, 2000,
403, 750.
5 (a) M. A. Baldo, D. F. O’Brien, Y. You, A. Shoustikov, S. Sibley,
M. E. Thompson and S. R. Forrest, Nature, 1998, 395, 151;
(b) Watanabe, S. Ide and N. Kido, Jpn. J. Appl. Phys., 2007, 46, 1186.
6 K. Okumoto, H. Kanno, Y. Hamaa, H. Takahashi and K. Shibata,
Appl. Phys. Lett., 2006, 89, 063504.
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This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2010
1322 | New J. Chem., 2010, 34, 1317–1322