1,2,4-Triazole derivatives as host materials for blue and green phosphorescent organic light-emitting devices

Article abstract of DOI:10.1016/j.tet.2016.06.005

A novel host material, namely 9-(6-(3-phenyl-5-(pyridin-2-yl)-4H-1,2,4-triazol-4-yl)hexyl)-9H-carbazole (PPHCZ) was designed and synthesized by incorporating 1, 2, 4-triazol as the electron-withdrawing moiety and carbazole as electron-donating moiety using hexyl as bridge. The photophysical, electrochemical, thermal properties and performances in phosphorescent organic light-emitting devices (PhOLED) were thoroughly characterized. PPHCZ with a high triplet energy level (3.01?eV) exhibited an obvious intermolecular interaction in thin film. Green and blue PhOLEDs using fac-tris(2-phenylpyridine)iridium and iridium(III) bis(4,6-difluorophenyl)-pyridinato [Formula presented],C²′]picolinate as phosphorescent dopants have been fabricated.

Full text of DOI:10.1016/j.tet.2016.06.005

Tetrahedron xxx (2016) 1e6
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1,2,4-Triazole derivatives as host materials for blue and green
phosphorescent organic light-emitting devices
Huixia Xu a ,*, Peng Sun a , Kexiang Wang a , Yanqin Miao b, Tingting Yang a,b,
,
b
,
b
,
b
a,
Hua Wang , Bingshe Xu , Wai-Yeung Wong a
a
,
b
a
,
b
,c
a
Key Laboratory of Interface Science and Engineering in Advanced Materials, Ministry of Education, Taiyuan University of Technology, Taiyuan 030024,
PR China
Shanxi Research Center of Advanced Materials Science and Technology, Taiyuan 030024, PR China
b
c
Institute of Molecular Functional Materials, Department of Chemistry and Institute of Advanced Materials, Hong Kong Baptist University, Waterloo
Road, Hong Kong, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel host material, namely 9-(6-(3-phenyl-5-(pyridin-2-yl)-4H-1,2,4-triazol-4-yl)hexyl)-9H-carbazole
Received 5 April 2016
Received in revised form 1 June 2016
Accepted 3 June 2016
Available online xxx
(
PPHCZ) was designed and synthesized by incorporating 1, 2, 4-triazol as the electron-withdrawing
moiety and carbazole as electron-donating moiety using hexyl as bridge. The photophysical, electro-
chemical, thermal properties and performances in phosphorescent organic light-emitting devices
(
PhOLED) were thoroughly characterized. PPHCZ with a high triplet energy level (3.01 eV) exhibited an
obvious intermolecular interaction in thin film. Green and blue PhOLEDs using fac-tris(2-phenylpyridine)
iridium and iridium(III) bis(4,6-difluorophenyl)-pyridinato eN,C ]picolinate as phosphorescent dopants
have been fabricated.
Keywords:
2
0
Host materials
Light-emitting device
Carbazole
Ó 2016 Published by Elsevier Ltd.
1. Introduction
phene and dibenzofuran/carbazole hybrids et al.11,12 The 1,2,4-
triazole derivatives have been proved to be excellent electron-
Phosphorescent organic light-emitting devices (PhOLED) have
attracted considerable interests due to their high efficiency and
great applications in the next generation full-color flat-panel dis-
plays.1 In the design of highly efficient PhOLEDs, the selection of
a proper host material is of great importance. In general, to prevent
back energy transfer from dopant to host, the host materials should
transport and hole-block materials due to the electron-deficient
13,14
triazole moiety.
transport material of 3,5-bis(4-(diphenylphosphoryl)phenyl)-4-
phenyl-4H-1,2,4-triazole (TPO) with high E of 2.86 eV and high
J. Zhuang et al. in 2013 reported an electron-
e3
T
ꢀ
15
glass transition temperature (133 C).
In this paper, we designed and synthesized a novel host material
have a wider energy gap (E
g
) and larger triplet level (E
T
) than
of
9-(6-(3-phenyl-5-(pyridin-2-yl)-4H-1,2,4-triazol-4-yl)hexyl)-
dopant.4 Therefore, to attain efficient blue PhOLEDs, the de-
9H-carbazole (PPHCz) with the electron-donating carbazole and
electron-withdrawing triazole ligands. Two functional groups were
connected by hexyl in order to improve the solubility of blue bi-
polar host. PPHCz can be used as the host matrix to fabricate the
green- and blue-emitting PhOLEDs.
velopment of appropriate host materials has become a challenge
because of intrinsic wide E of blue-emitting dopant.
g
5
,6
Bipolar hosts with electron-donating and electron-withdrawing
moieties have drawn much attention due to excellent charge-
transport capabilities to make the charge recombination zone
7,8
within the emissive layer. Carbazole possessing high triplet en-
ergy level (E >2.9 eV) and excellent electron-donating properties
2
2
. Experimental
T
were widely used as the structural moieties in blue hosts. Several
bipolar hosts for sky-blue phosphorescent devices were reported
.1. Syntheses of 9-(6-(3-phenyl-5-(pyridin-2-yl)-4H-1,2,4-
triazol-4-yl)hexyl)-9H-carbazole (PPHCZ)
9
10
including oxide/carbazole, pyrimidine/carbazole dibenzothio-
All materials were used as received from commercial suppliers
without further purification. Synthetic routes are outlined in
Scheme 1.
*
Corresponding author. E-mail address: xuhuixia@tyut.edu.cn (H. Xu).
http://dx.doi.org/10.1016/j.tet.2016.06.005
040-4020/Ó 2016 Published by Elsevier Ltd.
0
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2
H. Xu et al. / Tetrahedron xxx (2016) 1e6
Scheme 1. Molecular structure and synthetic routes of PPHCz.
2
.1.1. 9-(6-Bromohexyl)-9H-carbazole (L1). A mixture solution of
2H), 7.40 (d, 2H, J¼8.4 Hz), 7.24e7.21 (m, 2H), 4.31 (t, 2H, J¼7.2 Hz),
3.35 (t, 2H, J¼7.2 Hz), 1.92e1.78 (m, 2H), 1.50e1.37 (m, 2H).
The synthetic route of 2-(5-phenyl-4H-1,2,4-triazol-3-yl)pyri-
dine (L2) can be found in Ref. 16.
carbazole (5.0 g, 30 mmol), 1, 6-dibromohexane (36.0 g, 150 mmol),
tetrabutyl ammonium bromide (TBAB) (1.0 g, 3 mmol), toluene
(
40 mL) and KOH (25 mL, 50%) was heated to reflux for 12 h. After
cooling to room temperature, the mixture was poured into the water
50 mL) and extracted with CH Cl . The organic extracts were
washed with water and dried over MgSO . The crude product was
subjected to silica gel column chromatography using an 8:1 mixture
of petroleum ether and CH Cl as the eluent. The white crystals of 9-
6-bromohexyl)-9H-carbazole (7.7 g) were obtained. Yield: 78%, H
NMR (600 MHz, CDCl ):
8.11(dt, 2H, J¼7.8 Hz,1.2 Hz), 7.47e7.44 (m,
(
2
2
2.1.2. 9-(6-(3-Phenyl-5-(pyridin-2-yl)-4H-1,2,4-triazol-4-yl)hexyl)-
9H-carbazole (PPHCZ). A mixture of L2 (2.22 g, 10 mmol),
TBAB(0.32 g, 1 mmol), and 30 mL toluene were stirred for 30 min. 2
M KOH solution was added and stirred for another 30 min at room
temperature under nitrogen atmosphere. The L1, which was dis-
solved in 10 mL toluene, were added slowly into solution and
refluxed for 24 h. The water was added after cooling to room
temperature. After removal of the solvent, the residue was purified
4
2
2
1
(
3
d
by column chromatography on silica gel using as the eluent to give
1
a white powder. Yield: 80%. H NMR (600 MHz, CDCl
3
)
d
8.52 (ddd,
¼1.1 Hz, 1H), 8.18e8.15
¼0.7 Hz, 2H), 7.82 (td, J¼7.8,
¼1.8 Hz, 1H), 7.47e7.42 (m, 4H), 7.42e7.39 (m, 1H), 7.37 (dt, J¼8.2,
¼0.9 Hz, 2H), 7.29 (ddd, J¼7.6, J ¼4.8, J ¼1.2 Hz, 1H), 7.22 (ddd,
¼7.0, J ¼1.0 Hz, 2H), 4.87e4.81 (m, 2H), 4.28 (t, J¼7.2 Hz,
H), 2.00e1.83 (m, 4H), 1.43 (dd, J¼6.6, J
600 MHz, CDCl ): 163.59, 151.11, 151.70, 151.13, 143.32, 139.78,
34.15, 131.91, 131.41, 129.25, 128.48, 126.89, 126.80, 125.75, 123.22,
21.66, 111.50, 53.56, 45.78, 32.88, 31.77, 29.72, 29.17. FTIR (KBr,
J
(
1
¼4.8, J
2
¼1.8, 0.9 Hz, 1H), 8.30 (dt, J
1
¼7.9, J
2
m, 2H), 8.10 (ddd, J¼7.8, J
2
¼1.2, J
3
J
J
2
2
2
3
J¼7.9, J
2
3
13
2
2
¼3.0 Hz, 4H). C NMR
(
3
d
1
1
ꢁ1
cm ): 3416, 3049, 2926, 2825, 1590, 1466, 1322, 1227, 1153, 1128,
015, 920, 846, 793, 723. Anal. Calcd for C31 (%): C, 78.95; H,
1
29 5
H N
6.20; N, 14.85; found: C, 79.60; H, 6.10; N, 14.62.
2.2. General information
1
H NMR data were recorded with Switzerland Bruker DRꢂ600
NMR spectrometers. FTIR spectra were measured with a Nicolet
7199B spectrometer in KBr pellets in the range of 4000e400 cm
Fig. 1. UVevis absorption and emission spectra in toluene, CH
2
Cl
2
, THF solutions
ꢁ
1
ꢁ
5
.
(
10
M), neat thin film at room temperature and phosphorescence spectra in 2-
ꢁ
5
MeTHF solutions (10 M) at 77 K with 1 ms delay.
C, H and N microanalysis were carried out with an Elemental Vario
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H. Xu et al. / Tetrahedron xxx (2016) 1e6
3
Fig. 2. The optimized molecular structure and frontier molecular orbitals (HOMO and LUMO) distribution for PPHCz.
Table 1
Photophysical properties of PPHCz
ꢀ
E
g
(eV)d
Compound
Abs peaks (nm)
Emission (nm)
T
d
( C)
HOMO (eV)
Solution a
Film b
Solution
350, 367
Film
77 K c
PPHCz
290, 336, 347
299, 333, 349
353, 374, 411, 435,
411, 435, 439, 463, 473
330
ꢁ6.0
3.57
a
ꢁ5
Measured in CH
2
Cl
2
solution (1ꢂ10 M).
b
Films were made on quartz substrates with thicknesses of 80 nm.
Measured in 2-MeTHF at 77 K.
Determined from UV-visible absorption and emission spectra in CH Cl .
2 2
c
d
EL Elemental analyzer. UVevis absorption spectra were recorded by
Lambda Bio 40. The Photoluminescence (PL) spectra in different
solutions and in thin film were examined by HORIBA FluouoMax-4
spectrophotometer. The low-temperature phosphorescence spec-
tra were measured on an Edinburgh F-980 spectrometer at 77 K in
2
-methyltetrahydrofuran (2-MeTHF). The thin solid films used for
absorption and PL spectra measurements were vacuum vapor de-
posited on quartz substrates with thickness of 80 nm. Thermog-
ravimetric analysis (TGA) was undertaken using a Netzsch TG
ꢀ
2
09F3 under dry nitrogen atmosphere heating at a rate of 10 C/
min.
Theoretical calculation of PPHCz was carried out by using the
Gaussian 03 package. The ground state structure were optimized by
density functional theory (DFT) in B3LYP/6-31G(d) basis sets. The-
oretical prediction for molecular orbital distributions of PPHCz was
acquired based on the optimized structure.
Cyclic voltammetry (CV) was carried out in CH Cl solution with
2 2
chromatographic purity at room temperature using a CHI 660E
voltammetry analyzer. Tetrabutylammonium hexafluorophosphate
(
TBAPF6) (0.1 M) was used as the supporting electrolyte. The
platinum wire is used as working electrode. The platinum electrode
Fig. 4. Cyclic voltammograms in CH
2
Cl
2
for oxidation.
Fig. 3. TGA and DTG curves of HPPCz.
Fig. 5. Current density-voltage curves of hole- and electron-only devices of PPHCz.
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4
H. Xu et al. / Tetrahedron xxx (2016) 1e6
Fig. 6. Energy levels diagram of PhOLEDs and molecular structures of materials.
is the counter and a calomel electrode is the reference with
ferrocenium-ferrocene (Fc /Fc) as the internal standard. The scan
3. Characterization of materials
þ
rate for CV curves is 100 mV/s.
3.1. Photophysical properties
2
Devices with area of 3ꢂ3 mm were fabricated by vacuum de-
ꢁ
4
position (3ꢂ10 Pa) onto indium tin oxide (ITO) glass substrate.
The ITO glass substrate was cleaned with deionized water, acetone,
and ethanol in turn, and dried. To evaluate the bipolar property of
PPHCz, the hole- and electron-only devices were fabricated with
the structures ITO/NPB(20 nm)/PPHCz(30 nm)/NPB(20 nm)/
Al(200 nm) and ITO/TPBi(20 nm)/PPHCz(30 nm)/TPBi(20 nm)/
LiF(1 nm)/Al(200 nm). And then the green- and blue-emitting de-
vices were fabricated by using fac-tris(2-phenylpyridine)iridium
2 2
UVevis absorption spectra of PPHCz in dilute toluene, CH Cl
and tetrahydrofuran (THF) solutions show the similar absorptions
where the bands around 293, 331 and 345 nm, are displayed in
Fig. 1. The absorption around 293 nm can be attributed to the
transition local electron transition of carbazole and triazole. The
absorption peaks at 331 and 345 nm can be assigned to the ne
pep*
p*
12
transitions of carbazoles. The E
g
calculated from the interaction
solution of PPHCz is 3.57 eV.
absorption and PL spectra in CH Cl
2
2
0
2
Ir(ppy)
3
and iridium(III)bis(4,6-(difluorophenyl) pyridinato-N,C )
Both absorption and fluorescence spectra of PPHCz are studied
in different solutions with different polarities to detect sol-
vatochromic possibility. Upon optical excitation at 290 nm, the
maximum peaks at emission spectra of PPHCz in solutions are lo-
cated at 351 and 367 nm with the much weaker peaks at 411 and
435 nm. The absorption and emission spectra in different solutions
picolinate (FIrpic) as dopants. The electroluminescent (EL) spectra
and CIE coordinates were measured by PR-655 spectrophotometer.
The voltageecurrent density (VeJ) characteristics of PhOLEDs were
recorded using Keithley 2400 Source Meter and ST-900M Spot
Brightness Meter.
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H. Xu et al. / Tetrahedron xxx (2016) 1e6
5
energy of the phosphorescence spectrum as 3.01 eV. All spectra
data are summary in Table 1.
3.2. Thermal property
The thermal stability of PPHCz was examined by TGA and DTG.
As displayed in Fig. 3, its onset decomposition temperature (T
d
,
ꢀ
corresponding to 5% weight loss) appears at 330 C, indicating that
PPHCz is favorable for fabrication of OLED devices by vacuum
thermal evaporation.
3.3. Electrochemical property
2 2
The electrochemical property of PPHCz was studied in CH Cl
through CV, in Fig. 4. The HOMO energy level (EHOMO¼ꢁ6.0 eV) was
ox
ox
calculated from equation of E
¼ ꢁ4:8 ꢁ eðEc ꢁ E ÞV, where
HOMO
f
ox
E
was the first oxidation peaks measured from CV curves and was
the oxidation peak of ferrocene (Ec ¼ 1:6 V and Ef ¼ 0:4 V). So,
the LUMO energy level of ELUMO¼ꢁ2.43 eV was obtained by
c
ox
ox
Fig. 7. EL spectra of green and blue devices at voltage of 8 V.
ELUMO¼E
g
ꢁEHOMO
.
almost do not change with solvent polarity, indicating that no
significant charge-transfer from donor to acceptor occurs due to the
introduction of non-conjugate hexyl. In order to verify this point,
the molecular structure of PPHCz was optimized by means of the
B3LYP with the 6-31G (d) basis set and the electronic distributions
of HOMO and LUMO are displayed in Fig. 2 (HOMO: the highest
occupied molecular orbital; LUMO: the lowest unoccupied molec-
ular orbital). HOMO is mainly distributed on the carbazole. While,
LUMO dominates all on the 2-(5-phenyl-4H-1,2,4-triazol-3-yl)pyr-
idine. There is little distribution on the hexyl, indicated that hexyl
can break the conjugation between electron-donating and
electron-withdrawing moieties in this compound.
3
.4. Electroluminescent performances
To investigate the charge-transport property of PPHCz, we
prepared electron- and hole-only devices with the structures of
ITO/NPB(20 nm)/PPHCz(30 nm)/NPB(20 nm)/Al(200 nm) and ITO/
TPBi(20 nm)/PPHCz(30 nm)/TPBi(20 nm)/LiF(1 nm)/Al(200 nm).
However, a pronounced change is detected in fluorescence
spectra of thin film. The emission peaks of thin film at 411 and
4
35 nm become stronger than that at 351 and 367, suggesting that
the intermolecular interactions occur in solid state. To obtain triplet
emission, the low-temperature PL spectrum was measured in
a frozen 2-methyltetrahydrofuran matrix at 77 K and is also shown
in Fig. 1. The emission bands below 411 nm should be assigned the
fluorescence from the singlet excited state compared with the PL in
thin film at room temperature. The fluorescence spectrum at 77 K
exhibits the well-defined vibronic peaks, which is reported in other
host materials.17 Therefore, E
was estimated from the highest-
T
Fig. 9. Current efficiency-current density-power efficiency of green (a) and blue (b)
Fig. 8. Voltageecurrent density-luminance characteristics for PhOLEDs.
PhOLEDs.
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6
H. Xu et al. / Tetrahedron xxx (2016) 1e6
Table 2
EL performances of green and blue PhOLEDs
Dopant
lmax (nm)
Vturnꢁon (V)
L
max (cd/m2)
h
c(max) (cd/A)
h
p (max) (lm/W)
CIE (x, y)
Ir(ppy)
FIrpic
3
515
470, 496
4.0
4.2
12,597
3328
14.0
11.5
8.0
7.6
0.37, 0.55
0.24, 0.40
0
0
NPB (N, N -bis(naphthalen)-N,N -bis(phenyl)-benzidine) was used
as hole-transport layer; and TPBi [1,3,5-tris(2-
peaks at emission spectra of PPHCz in different solutions are lo-
cated at 351, 367 nm and the emission peaks appeared at 353, 374,
411 and 435 nm in thin solid film. PPHCz exhibited the wide energy
gap (3.57 eV). The blue PhOLED was fabricated using FIrpic as
dopant and PPHCZ as host with the maximum luminance, maxi-
Nphenylbenzimidazolyl)-benzene] were used as electron-
transport materials. The hole and electron current density-voltage
curves of PPHCz are shown in Fig. 5. The hole-only device ex-
hibits higher carrier current density than the electron-only device
at the same voltage due to the weak electron deficient group of
2
mum current and power efficiencies of 12,597 cd/m , 14.0 cd/A and
8.0 lm/W.
1
,2,4-triazol and the strong electron donating of carbazole.
PPHCz was evaluated as the bipolar host material for green and
blue PhOLEDs doped with Ir(ppy) and FIrpic. The devices config-
urations were as follows: ITO/NPB (30 nm)/TCTA (10 nm)/PPHCz:
Ir(ppy) (6 %wt, 30 nm)/TPBi (35 nm)/LiF (1 nm)/Al (200 nm) and
ITO/NPB (30 nm)/TCTA (10 nm)/PPHCz: FIrpic (8 %wt, 30 nm)/TPBi
35 nm)/LiF (1 nm)/Al (200 nm). NPB was used as hole-transport
layer; and TPBi were used as electron-transport materials. TCTA
Tris(4-carbazoyl-9-ylphenyl)amine] can reduce the hole injection
Acknowledgements
3
This work was financially supported by the International Sci-
ence and Technology Cooperation Program of China
(2012DFR50460); National Natural Science Foundation of China
(21071108, 60976018, 61274056 and 61205179); Natural Science
Foundation of Shanxi Province (2015021070); Program for Chang-
jiang Scholar and Innovation Research Team in University
(IRT0972); and Shanxi Provincial Key Innovative Research Team in
Science and Technology (201513002-10).
3
(
[
barrier from NPB to the host. The molecular structures of all ma-
terials and energy levels in PhOLEDs are displayed in Fig. 6.
The maximum peaks at EL spectra of green PhOLED is located at
5
15 nm with the CIE coordinate of (0.37, 0.55), which means
a typical Ir(ppy) emission feature. In blue device, the emission
peaks of 470 and 496 nm were observed with CIE of (0.24, 0.40),
References and notes
3
1. Ho, C.-L.; Wong, W.-Y. New J. Chem. 2013, 37, 1665.
2. Tao, P.; Li, W.-L.; Zhang, J.; Guo, S.; Zhao, Q.; Wang, H.; Wei, B.; Liu, S.-J.; Zhou,
X. H.; Xu, B. S.; Huang, W. Adv. Funt. Mater. 2016, 26, 881.
18
which is consistent with PL of FIrpic, as shown in Fig. 7. There are
no residual emission peaks from other functional layers suggests
a complete energy transfer from host to dopant.
3. Yook, K. S.; Lee, J. Y. Adv. Mater. 2014, 26, 4218.
4. Yin, X.; Zhang, T.; Peng, Q.; Zhou, T.; Zeng, W.; Zhu, Z.; Xie, G.; Li, F.; Ma, D.;
Yang, C. J. Mater. Chem. C 2015, 3, 7589.
The current densityevoltageeluminance (VeJeL) character-
istics and efficiency versus current density curves of green- and
blue-emitting PhOLEDs are shown in Figs. 8 and 9. The green
device has a lower turn-on voltage (Vturnꢁon¼4.0 V, corre-
5. Zhuang, J.; Li, W.; Su, W.; Liu, Y.; Shen, Q.; Liao, L.; Zhou, M. Org. Electron. 2012,
13, 2210.
6. Kang, J. S.; Hong, T. R.; Kim, H. J.; Son, Y. H.; Bin, J. K.; Lee, B. S.; Yang, J. H.; Kim,
J. W.; Cho, M. J.; Kwon, J. H.; Choi, D. H. Org. Electron. 2015, 26, 218.
7. Chou, H. H.; Cheng, C.-H. Adv. Mater. 2010, 22, 2468.
2
sponding to 1 cd/m ) than that of blue-emitting device based
8. Han, C.; Zhang, Z. S.; Xu, H.; Xie, G. H.; Li, J.; Zhao, Y.; Deng, Z. P.; Liu, S. Y.; Yan,
FIrpic device (4.2 V). The green-emitting PhOLEDs exhibited
a maximum luminance (Lmax) of 12,597 cd/m at 7.8 V, and
P. F. Chem.dEur. J. 2013, 19, 141.
. Sapochak, L. S.; Padmaperuma, A. B.; Cai, X.; Male, J. L.; Burrows, P. E. J. Phys.
Chem. C 2008, 112, 7989.
0. Lee, Y.-T.; Chang, Y.-T.; Lee, M.-T.; Chiang, P.-H.; Chen, C.-T. J. Mater. Chem. C
2014, 2, 382.
1. Xie, Y.-M.; Cui, L.-S.; Zu, F.-S.; Igbari, F.; Xue, M.-M.; Jiang, Z.-Q.; Liao, L.-S. Org.
Electron. 2015, 26, 25.
2. Mondal, E.; Hung, W.-Y.; Dai, H.-C.; Chen, H.-F.; Hung, P.-Y.; Wong, K. T. Tetra-
hedron 2014, 70, 6328.
2
9
a maximum current efficiency (
a peak power efficiency ( ) of 8.0 lm/W. The blue-emitting
device based on FIrpic achieved Lmax of 3328 cd/m , maximum
of 11.5 cd/A and maximum of 7.6 lm/W, respectively. The
c
h ) of 14.0 cd/A, corresponding to
1
h
p
2
1
h
c
h
p
1
detailed performances of green- and blue-emitting PhOLEDs are
summarized in Table 2.
13. Kido, J.; Hongawa, K.; Okuyama, K.; Nagai, K. Appl. Phys. Lett. 1993, 63, 2627.
1
4. Hung, M. C.; Liao, J. L.; Chen, S. A.; Chen, S. H.; Su, A. C. J. Am. Chem. Soc. 2005,
27, 14576.
5. Zhuang, J.; Su, W.; Wu, W.; Li, W.; Shen, Q.; Zhou, M. Tetrahedron 2013, 69, 9038.
6. Xu, H. X.; Yue, Y.; Qu, L. T.; Hao, Y. Y.; Wang, H.; Chen, L. Q. Dyes Pigments 2013,
9, 67.
7. Li, W.; Li, J.; Liu, D.; Wang, F.; Zhang, S. J. Mater. Chem. C 2015, 3, 12529.
8. Lee, J.; Park, H.; Park, K.-M.; Kim, J.; Lee, J.-Y.; Kang, Y. Dyes Pigments 2015, 12,
235.
1
4
. Conclusions
1
1
9
In summary, a novel bipolar green and blue host material of 9-
1
1
(
6-(3-phenyl-5-(pyridin-2-yl)-4H-1,2,4-triazol-4-yl)hexyl)-9H-car-
bazole (PPHCZ) has been designed and synthesized. The maximum
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