Highly efficient yellow phosphorescent OLEDs based on two novel bipolar host materials

Article abstract of DOI:10.1039/c5nj00939a

Two bipolar host materials, N¹-(naphthalen-1-yl)-N¹,N⁴-diphenyl-N⁴-(4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl)naphthalene-1,4-diamine (NONP) and N¹-(naphthalen-1-yl)-N¹,N⁴-diphenyl-N⁴-(3-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl)naphthalene-1,4-diamine (NONM), comprising a hole-transporting N¹-(naphthalen-1-yl)-N¹,N⁴-diphenylnaphthalene-1,4-diamine (NPNA2) donor and an electron-transporting 1,3,4-oxadiazole (OXD) acceptor at different phenyl bridge positions, have been synthesized. NONP (glass transition temperature T_g= 127°C) and NONM (T_g= 105°C) exhibit high morphological stability. The theoretical calculations on both hosts show that the HOMOs (highest occupied molecular orbitals) are mainly dispersed on the electron-donating groups, and the LUMOs (lowest unoccupied molecular orbitals) are predominantly dispersed on the electron-accepting units, suggesting bipolar charge transporting property. Two yellow phosphorescent organic light-emitting diodes (PHOLEDs, ITO (indium tin oxide)/TAPC (1,1-bis[4-(di-p-tolylamino) phenyl]cyclohexane, 40 nm)/host: Ir(bt)₂(acac) (bis(2-phenylbenzothiozolato-N,C²′) iridium(acetylacetonate), 15 wt%, 20 nm)/TmPyPB (1,3,5-tri(m-pyrid-3-yl-phenyl) benzene, 40 nm)/LiF (1 nm)/Al (100 nm)) fabricated using NONP and NONM as the host and Ir(bt)₂(acac) as the emitter exhibit maximum current efficiencies (η_c,max) of 43.2 and 44.4 cd A^-1, respectively, with low current efficiency roll-off. The values of 40.4 and 43.6 cd A^-1can still be achieved at the luminance of 3000 cd m^-2, respectively.

Full text of DOI:10.1039/c5nj00939a

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Highly efficient yellow phosphorescent OLEDs
based on two novel bipolar host materials†
Cite this:DOI: 10.1039/c5nj00939a
Song Zhang, Qiu-Lei Xu, Jing-Cheng Xia, Yi-Ming Jing, You-Xuan Zheng* and
Jing-Lin Zuo
1
1
4
4
Two bipolar host materials, N -(naphthalen-1-yl)-N ,N -diphenyl-N -(4-(5-phenyl-1,3,4-oxadiazol-2-
1
1
4
4
yl)phenyl)naphthalene-1,4-diamine (NONP) and N -(naphthalen-1-yl)-N ,N -diphenyl-N -(3-(5-phenyl-
,3,4-oxadiazol-2-yl)phenyl)naphthalene-1,4-diamine (NONM), comprising hole-transporting
N -(naphthalen-1-yl)-N ,N -diphenylnaphthalene-1,4-diamine (NPNA2) donor and an electron-transporting
,3,4-oxadiazole (OXD) acceptor at different phenyl bridge positions, have been synthesized. NONP (glass
transition temperature T = 127 1C) and NONM (T = 105 1C) exhibit high morphological stability. The
1
a
1
1
4
1
g
g
theoretical calculations on both hosts show that the HOMOs (highest occupied molecular orbitals) are
mainly dispersed on the electron-donating groups, and the LUMOs (lowest unoccupied molecular orbitals)
are predominantly dispersed on the electron-accepting units, suggesting bipolar charge transporting
property. Two yellow phosphorescent organic light-emitting diodes (PHOLEDs, ITO (indium tin oxide)/TAPC
Received (in Montpellier, France)
2
0
15th April 2015,
(1,1-bis[4-(di-p-tolylamino) phenyl]cyclohexane, 40 nm)/host: Ir(bt)
iridium(acetylacetonate), 15 wt%, 20 nm)/TmPyPB (1,3,5-tri(m-pyrid-3-yl-phenyl) benzene, 40 nm)/LiF (1 nm)/
Al (100 nm)) fabricated using NONP and NONM as the host and Ir(bt) (acac) as the emitter exhibit maximum
current efficiencies (Zc,max) of 43.2 and 44.4 cd A , respectively, with low current efficiency roll-off. The
2
(acac) (bis(2-phenylbenzothiozolato-N,C )
Accepted 27th July 2015
DOI: 10.1039/c5nj00939a
2
ꢀ1
ꢀ1
ꢀ2
www.rsc.org/njc
values of 40.4 and 43.6 cd A can still be achieved at the luminance of 3000 cd m , respectively.
3
host material. The design of appropriate host materials is of great
importance for highly efficient OLEDs, and it should meet some
Introduction
T
In the last few years, the organic light-emitting diode (OLEDs) basic requirements: (a) sufficiently high triplet energy (E ) for
industry has enjoyed fast growth, as OLEDs are widely considered ensuring exothermic energy transfer from the host material to the
4
to be the leading next-generation display and lighting technology. dopant and efficient exciton confinement, (b) a high morphological
Among these devices, tremendous efforts have been made to stability (especially, a high glass transition temperature (T )),
g
improve the phosphorescent organic light-emitting diodes (PHO- (c) suitable energy level match-ups with adjacent layers to reduce
5
LEDs) because they can reach 100% internal quantum efficiency interfacial energy barriers, and (d) decent charge carrier transport
by harvesting both electro-generated singlet and triplet excitons properties to increase the opportunity for electron and hole
1
6
for emission. The emissive layer of a PHOLED is usually doped recombination within the emitting layer.
with an organometallic complex, which contains heavy metal For OLEDs, if only one type of charge carrier is preferentially
atoms (usually iridium). The interaction between the heavy metal injected and transported, recombination of the opposite
and organic molecules can result in more efficient emitters with charges will be shifted out of the emissive layer, lowering the
7
longer lifetime. However, the emission lifetime and high concen- device efficiency. Therefore, bipolar hosts have attracted consi-
tration of these heavy metal complexes easily lead to undesired derable interest in the area of OLEDs because they can provide
efficiency roll-off at high current density during the operation of a more balance in electron and hole fluxes and help increase the
2
8
device. Therefore, to achieve highly efficient electrophosphores- probability of carrier recombination. A simple and viable
cence by reducing competitive factors such as concentration strategy for designing bipolar hosts is to simultaneously incor-
quenching and triplet–triplet annihilation, phosphorescent emitters porate electron donor (D) and electron acceptor (A) subunits in
of heavy-metal complexes are usually doped uniformly in an organic one molecular skeleton without lowering the E resulting from
T
6
intramolecular charge transfer. In this case, the introduction
of a twisted molecular conformation may be an efficient strategy to
State Key Laboratory of Coordination Chemistry, Collaborative Innovation Center
achieve high triplet energy.
of Advanced Microstructures, School of Chemistry and Chemical Engineering,
1
The dimer of N-phenyl-1-naphthylamine, N -(naphthalen-1-
Nanjing University, Nanjing 210093, P. R. China. E-mail: yxzheng@nju.edu.cn
Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nj00939a
1
4
†
yl)-N ,N -diphenylnaphthalene-1,4-diamine (NPNA2) has been
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The thermal properties of NONP and NONM were character-
ized by thermogravimetric analysis (TGA, Fig. 1) and differen-
tial scanning calorimetry (DSC, Fig. 1). TGA of NONP and
NONM showed a decomposition temperature (T ) corre-
d
sponding to 5% weight loss as high as 424 1C and 375 1C,
respectively. More importantly, high glass transition tempera-
g g
tures are observed in NONP (T = 127 1C) and NONM (T =
106 1C). This can be partly due to the molecular structures
contained in the hole-transporting unit NPNA2, which increase
molecular asymmetry and molecular weight. This demon-
strated that the two host materials are capable of forming
uniform amorphous films, one of the key factors for highly
efficient PHOLEDs.
Scheme 1 Synthetic routes of NONP and NONM.
characterized to have high triplet energy, excellent hole-
9
transporting ability and high thermal stability. The 1,3,4-oxadiazole Photophysical properties
(
OXD) derivatives are well established electron-transporting
Photophysical properties of NONP and NONM were examined
by UV-vis and photoluminescence (PL) spectrometry (Fig. 2 and
Table 1). The absorption spectra of NONP, NONM and
and hole-blocking materials used in OLEDs due to the
electron-withdrawing nature of this aromatic heterocycle mole-
cule. In this study, the hole-transporting NPNA2 and electron-
transporting 1,3,4-oxadiazole moieties were selected for the
construction of two new bipolar compounds (Scheme 1),
N -(naphthalen-1-yl)-N ,N -diphenyl-N -(4-(5-phenyl-1,3,4-oxadiazol-
2
1
naphthalene-1,4-diamine (NONM), to study the effects of the
positions of 1,3,4-oxadiazole on the phenyl bridge. As the yellow
phosphors play the indispensable role in achieving high effi-
ciencies in two-color, all-phosphor white organic light-emitting
1
0
2
Ir(bt) (acac) were tested in dichloromethane solution. The two
short-wavelength absorptions peaking at 268 and 276 nm in
NONP and NONM can be attributed to the p–p* transitions
from the electron-donating NPNA2 moiety to the electron-
accepting OXD unit (intramolecular charge transfer). The
longer-wavelength absorptions observed at 351 nm for NONP
and 372 nm for NONM are attributed to the NPNA2-centered
1
1
4
4
1
-yl)phenyl) naphthalene-1,4-diamine (NONP) and N -(naphthalen-
1
4
4
-yl)-N ,N -diphenyl-N -(3-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl)
n–p* transition. The absorption bands of (bt)
2
Ir(acac) at 441
and 481 nm belong to the absorption transition from ground
1
3
13
state to singlet MLCT and triplet MLCT excited states.
2
diodes, the yellow phosphor Ir(bt) (acac) (bis(2-phenylbenzo-
2
0
11
thiozolato-N,C )iridium(acetylacetonate)) was chosen as emitter
in this study. In our previous report, we fabricated devices
with hosts connecting triphenylsilane, NPNA2 moieties and
Ir(bt)
2
(acac) as guest, which achieved a maximum current
ꢀ
1 12
efficiency of 40.8 cd A
.
Unfortunately, those materials are
hole transport hosts. Therefore, we introduce the more electron-
deficient moiety OXD to develop the bipolar property of the hosts
and expect to achieve higher efficiencies of PHOLEDs. The triplet
energy levels of the two novel host materials are higher than
Ir(bt) (acac), and efficient energy transfer from the host materials
2
to the Ir(bt) (acac) is expected.
2
Results and discussion
Synthesis and thermal property
Scheme 1 shows the synthetic routes and structures of NONP
and NONM. The starting materials, 2-(4-bromophenyl)-5-
phenyl-1,3,4-oxadiazole and 2-(3-bromophenyl)-5-phenyl-1,3,4-
oxadiazole, were synthesized from the ring-closing reaction of
N-benzoyl-4-bromobenzohydrazide and N-benzoyl-4-bromobenzo
hydrazide, respectively, which were prepared by hydrazinolysis of
1
1
4
benzoyl chloride. N -(naphthalen-1-yl)-N ,N -diphenyl naphthalene-
1
9
,4-diamine (NPNA2) was synthesized as reported previously.
Buchwald-Hartwig crossing-coupling of 2-(4-bromophenyl)-5-
phenyl-1,3,4-oxadiazole and 2-(3-bromophenyl)-5-phenyl-1,3,4-
oxadiazole with NPNA2 gave NONP and NONM with yields
higher than 60%.
Fig. 1 TGA (a) and DSC (b) thermograms of NONP (black line) and NONM
(red line).
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2
Fig. 2 UV-vis spectra of NONP, NONM and Ir(bt) (acac) in dichloro-
methane solution at room temperature; photoluminescence spectra of
NONP, NONM and Ir(bt) (acac) in dichloromethane solution at 298 K;
2
phosphorescence spectra of NONP and NONM at 40 K.
The fluorescence spectra of NONP and NONM and the
phosphorescence spectrum of Ir(bt)
are also shown in Fig. 2. The maximum emission peak of
Ir(bt) (acac) is located at 560 nm with a slight shoulder at
97 nm. The emission peaks of NONP and NONM at room
2
(acac) at room temperature
Fig. 3 Spatial distributions of the HOMO and LUMO levels for NONP and
NONM.
2
5
temperature are 444 and 447 nm, respectively. There is a good
overlap between the emission bands of NONP and NONM and
the MLCT absorption of Ir(bt) (acac), suggesting a possible
2
energy transfer from NONP and NONM to Ir(bt) (acac), which
2
2
can be confirmed by the emission spectra of Ir(bt) (acac) doped
in NONP and NONM dichloromethane solutions with different
doping concentrations (Fig. S1, ESI†). The triplet state lifetimes
(t) for the two hosts are in millisecond scale at 40 K (Table 1,
Fig. S2, ESI†). Low-temperature PL measurement was detected
at 40 K (Fig. 2) to calculate the triplet energies of the NONP and
NONM as 2.71 and 2.73 eV, respectively (Table 1). These
energies are higher than the triplet energy of the common
14
Fig. 4 Cyclic voltammograms of NONP and NONM in dichloromethane
solution with 0.1 M TBAPF as supporting electrolyte.
6
yellow phosphorescent dopant Ir(bt)
NONP and NONM can be appropriate hosts for Ir(bt)
carriers can be well confined in the emissive layers.
2
(acac) (E
T
= 2.2 eV). Hence,
2
(acac), and
To gain insight into the geometric and electric properties of has almost complete separation of the HOMO and LUMO due
the compounds, quantum chemistry calculation was performed to the steric effects in meta-linkage through the benzene unit.
1
5
using the TDDFT/B3LYP/6-31G(d**) method. As shown in The two host materials both have potential to show bipolar
Fig. 3, their HOMOs (highest occupied molecular orbitals) are property, which is an important factor for enhancing the
1
6
localized predominantly on the electron-rich NPNA2 unit and efficiency and lowering the operating voltage of PHOLEDs.
the attached buffer unit of benzene, and the LUMOs (lowest
Cyclic voltammetry (CV) was performed to study the electro-
unoccupied molecular orbitals) are localized predominantly on chemical property of NONP and NONM. Fig. 4 shows that
electron-deficient OXD fragments. And, having minor differ- both compounds have two reversible reduction and oxidation
ences in electronic properties, the photoluminescent features behaviors, indicating good electrochemical stability and the
1
7
between the two hosts were also similar. Compared with the potential to have bipolar carrier-transporting property. The
slight overlap between HOMO and LUMO for NONP, NONM HOMO energy levels of the two compounds were calculated
Table 1 Photophysical data of compounds NONP and NONM
a
g
b
b
c
T
d
Compound
T
d
/T
(1C)
Absorption labs (nm)
Emission lem (nm)
E
(eV)
t (ms)
HOMO (eV)
LUMO (eV)
NONP
NONM
424/127
375/105
268/351
276/372
444
447
2.71
2.73
1.2, 13.9
1.04, 14.8
ꢀ5.27
ꢀ5.25
ꢀ2.33
ꢀ2.30
a
b
c
T
g
: glass transition temperature, T
d
: decomposition temperature. Measured in dichloromethane solution at 298 K. Triplet energy: estimated
d
from the highest-energy peaks of the 40 K phosphorescence spectra. Measured in zeonex at 40 K, lex = 380 nm.
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from onset potentials of oxidation as ꢀ5.27 and ꢀ5.25 eV for
NONP and NONM, respectively, by comparing with ferrocene
(
Fc) (HOMO = ꢀ(E + 4.8) eV). The corresponding LUMO levels
ox
calculated from the HOMO values and the band gaps (estimated
to be 2.94 and 2.95 eV from the edge of UV-vis absorption) were
found to be approximately ꢀ2.33 (NONP) and ꢀ2.30 eV (NONM),
respectively. Thus, theoretically low hole and electron injection
barriers between the widely used hole-transporting layer (1,1-bis[4-
1
8
(
di-p-tolylamino)phenyl]cyclohexane) (TAPC, ꢀ5.50/ꢀ2.0 eV)
or the electron-transporting layer 1,3,5-tri(m-pyrid-3-yl-phenyl)-
1
9
benzene (TmPyPB, ꢀ6.68/ꢀ2.73 eV) and the hosts can be
realized.
OLED performance
Fig. 6 Energy level diagram of yellow PHOLEDs and molecular structures
The charge-transporting property of the two compounds was of materials used.
investigated by fabricating hole-only and electron-only devices.
The hole-only devices (HODs) have the configuration of ITO
The molecule structures and energy level diagrams of the
materials and devices are shown in Fig. 6. TAPC and TmPyPB
were used as the hole- and electron-transporting layers, respec-
(
indium tin oxide)/host (30 nm)/TAPC (60 nm)/Al (100 nm),
while the electron-only devices (EODs) have the configuration
of ITO/TmPyPB (60 nm)/host (30 nm)/LiF (1 nm)/Al (100 nm).
A TAPC or TmPyPB layer was used to prevent electron or hole
injection from the cathode or anode, respectively. We also
fabricated TAPC-only and TmPyPB-only devices. The current
density versus voltage curves for these devices are shown in
Fig. 5. As the current densities of TAPC and TmPyPB are much
larger than HODs and EODs, the effect of TAPC and TmPyPB on
charge transport can be neglected. In HODs and EODs, both
NONP and NONM-based devices showed a smaller difference in
current density between HODs and EODs. This indicates that
the two compounds are capable of transporting holes and
electrons, and they exhibit bipolar character by the introduc-
tion of the hole transport unit NPNA2 and the electron-drawing
moiety OXD. The hole and electron current densities of NONM
were slightly higher than those of NONP, which indicates that
NONM shows better performance than NONP in terms of
charge transport. This can be attributed to the asymmetric
substitution at the meta position, which is an effective strategy
2
tively. Ir(bt) (acac) was used as the phosphor emitter with the
optimized doping concentration of 15 wt%, which is a little
20
higher than common yellow devices. This is because more
electrons were trapped directly at the dopant molecules at
higher doping level due to the low LUMO level of Ir(bt) (acac),
2
which provided an additional channel for electron transport
21
through hopping between the dopant sites. Accordingly, a
higher dopant concentration, such as 15 wt%, improved the
22
charge balance and energy transfer from host to guest.
The EL spectra of the NONP- and NONM-based yellow
PHOLEDs showed a main peak at 562 nm and a slight shoulder
peak at 595 nm from Ir(bt) (acac) (Fig. 7); both devices emit
2
yellow light with Commission Internationale de l’Eclairage
(CIE) color coordinates of (0.49, 0.51). This means that the host
materials undergo highly efficient exothermic energy transfer
from the host to dopant in the emitting layer upon electrical
excitation. Additionally, no other emission bands were observed
in the devices, which is partly due to the well-balanced charge
1
7
for the design of high-performance bipolar host materials.
22
density in the emission zone.
The electroluminescence (EL) performance of the bipolar
As shown in Fig. 8a, the current density–voltage–luminance
host materials NONP and NONM were evaluated with devices
having the common structure ITO/TAPC (40 nm)/ host: Ir(bt) (acac)
(
(
J–V–L) characteristic curves of the NONP- and NONM-based
2
devices demonstrate that the turn-on voltage is only 2.7 V. One
important reason for such low turn-on voltage is the bipolar
15 wt%, 20 nm)/TmPyPB (40 nm)/LiF (1 nm)/Al (100 nm).
Fig. 5 Current density versus voltage for the hole-only (HOD) and the
electron-only (EOD) devices.
Fig. 7 EL spectra of NONP- and NONM-based yellow PHOLEDs.
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the current density–voltage curves of the HODs and EODs shown
in Fig. 5.
All the devices show good performance for emission in the
yellow region, better than our previous results using silane-based
9
hole transport host materials. Furthermore, the device using
para-linked host NONP achieves a maximum current efficiency
ꢀ
1
(Zc,max) of 43.2 cd A , a maximum power efficiency (Zp,max) of
ꢀ
1
3
5.7 lm W and a maximum external quantum efficiency (EQE)
ꢀ
2
of 12.9% with a maximum luminance of 70 156 cd m at
1.7 V (Table 2). In comparison, the device using meta-linked
NONM as host exhibits slightly higher efficiencies with a Z
1
c,max
ꢀ
1
ꢀ1
of 44.4 cd A , a Zp,max of 35.9 lm W , an EQE of 13.5% and a
ꢀ
2
maximum brightness of 65 737 cd m at 10.1 V, which can be
elucidated from the following two aspects. First, the compound
NONM appears to have a better balance of electron- and hole-
transporting properties than that of compound NONP, which
may result in balanced charge densities and a broad distribution
of recombination regions within the emitting layer. Second,
the slightly higher triplet energy of NONM (2.73 eV) could more
efficiently suppress adverse energy back-transfer from the
Ir(bt) (acac) to the host than that of NONP (2.71 eV), conse-
2
quently resulting in better performance. This result also proved
that the efficiencies were improved by only changing the
position of the substituents.
It is worth mentioning that the current efficiency roll-off
ratios for both devices are mild. For example, at the luminance
ꢀ
2
of 3000 cd m , the current efficiency values of NONP- and
ꢀ1
NONM-based devices are still as high as 40.4 and 43.6 cd A
,
respectively. This can be attributed to the balanced charge
density and efficient exciton recombination in the broad area
2
3
of the emitting zone.
Conclusions
Fig. 8 (a) Current density–voltage–luminance (J–V–L), (b) current efficiency–
Two new bipolar materials, NONP and NONM, comprising the
hole-transporting unit N -(naphthalen-1-yl)-N ,N -diphenyl-
naphthalene-1,4-diamine and the electron-transporting moiety
c p
luminance (Z –L) and power efficiency–luminance (Z –L), and (c) external
quantum efficiency–luminance (EQE–L) characteristics of the PHOLEDs with
NONP and NONM.
1
1
4
1,3,4-oxadiazole, were successfully synthesized. Both materials
showed sufficiently high triplet energy, good thermal ability
transporting property of the hosts. Another reason is the suitable and balanced charge mobility. Used as hosts for yellow PHO-
HOMO and LUMO energy levels of the two hosts, which better LEDs with low efficiency roll-off, the device bearing meta-linked
match the work function of the hole-transporting layer TAPC and NONM performed with a maximum current efficiency of
ꢀ
1
ꢀ1
the electron-transporting layer TmPyPB, improving the charge 44.4 cd A , a maximum power efficiency of 35.9 lm W , a
injection of the device. The current density of the yellow PHOLED maximum external quantum efficiency of 13.5%, and a maxi-
ꢀ2
with NONM as the host was higher than that of the yellow mum luminance of 70 156 cd m – a little higher than that
PHOLED with NONP as the host, which is in agreement with of the para-linked host NONP-based device, which showed a
Table 2 Electroluminescence performance of the devices based on NONP and NONM
b
c
d
e
L
max (voltage)
Z
c,max (luminance)
Z
c,L3000
Zp,max (luminance)
[lm W (cd m )]
a
ꢀ2
ꢀ1
ꢀ2
ꢀ1
ꢀ1
ꢀ2
f
g
Host
V
turn-on (V)
[cd m (V)]
[cd A (cd m )]
[cd A
]
EQEmax [%]
CIE [x, y]
NONP
NONM
2.7
2.7
70 156 (11.7)
65 737 (10.1)
43.2 (612)
44.4 (1703)
40.4
43.6
35.7 (612)
35.9 (556)
12.9
13.5
0.49, 0.51
0.49, 0.51
a
ꢀ2
b
c
d
V
turn-on: turn-on voltage recorded at a luminance of 1 cd m
.
L
max: maximum luminance.
Z
c,max: maximum current efficiency.
Z
c,L3000
:
ꢀ2
e
f
g
current efficiency at 3000 cd m
. Zp,max: maximum power efficiency. EQEmax: maximum external quantum efficiency. Measured at 8 V.
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maximum current efficiency of 44.4 cd A , a maximum power POCl
NJC
ꢀ
1
3
(15 mL) in a 100 mL flask was refluxed under nitrogen for
ꢀ1
efficiency of 35.9 lm W , a maximum external quantum 5 h. The excess POCl
3
was then distilled out, and the residue
was poured into water. The crude product was collected by
These results indicate that this work provides a way to design ideal filtration and purified by recrystallization from chloroform/
ꢀ
2
efficiency of 13.5%, and a maximum brightness of 65 737 cd m
.
host materials for yellow PHOLEDs.
hexane to give white, needle-like crystals (1.21 g, yield: 85%).
1
H NMR (500 MHz, CDCl
.04 (d, J = 8.5 Hz, 2H), 7.71 (d, J = 8.5 Hz, 2H), 7.57 (td, J = 8.7,
4.9 Hz, 3H). MALDI-TOF MS (FAB, m/z) calcd for C H BrN O:
3
) d 8.18–8.16 (m, 1H), 8.16 (s, 1H),
8
Experimental
Materials and measurements
1
4
9
2
+
299.990. Found: 300.458 [M] .
2
-(3-Bromophenyl)-5-phenyl-1,3,4-oxadiazole. 2-(3-Bromo-
1
13
H NMR and C NMR spectra were measured on a Bruker AM
00 spectrometer. Mass spectra (MS) were obtained with
phenyl)-5-phenyl-1,3,4-oxadiazole was prepared according to
the same procedure as compound 2-(4-bromophenyl)-5-phenyl-
5
MALDI-TOF (Bruker Daltonic Inc.). High-resolution electro-
spray ionisation mass spectra (HR ESI-MS, Agilent 6540 UHD
Accurate-Mass Q-TOF LC/MS) were recorded for the compounds.
TGA and DSC measurements were carried out on the STA 449F3
1,3,4-oxadiazole, but 3-bromobenzoyl hydrazine instead of
4
-bromobenzoyl hydrazine was used as a starting material.
1
H NMR (500 MHz, CDCl
3
) d 8.31 (d, J = 1.3 Hz, 1H), 8.20–
.15 (m, 2H), 8.12 (dd, J = 7.8, 0.9 Hz, 1H), 7.72 (dd, J = 8.0,
.9 Hz, 1H), 7.61–7.55 (m, 3H), 7.45 (t, J = 7.9 Hz, 1H). MALDI-
BrN O: 299.990. Found:
8
0
(NETZSCH) and 823e (METTLER), respectively. Absorption and
emission spectra were measured on a Shimadzu UV-3100 and
a Hitachi F-4600 luminescence spectrophotometer, respectively.
The low-temperature phosphorescence spectra were measured
with an Edinburgh Instruments FLS-920 spectrophotometer at
TOF MS (FAB, m/z) calcd for C14
H
9
2
+
300.479 [M] .
1
1
4
4
N -(Naphthalen-1-yl)-N ,N -diphenyl-N -(4-(5-phenyl-1,3,4-
oxadiazol-2-yl)phenyl)naphthalene-1,4-diamine (NONP). Pd (dba)
2
3
4
6
0 K. Cyclic voltammetric experiments were carried out with CHI
00E system (Chenhua, Shanghai) using three-electrode cell
t
(
0.09 g, 0.10 mmol), NPNA2 (0.04 g, 1.0 mmol), Li BuO (0.32 g,
.0 mmol) and 2-(4-bromophenyl)-5-phenyl-1,3,4-oxadiazole
0.36 g, 1.2 mmol) were added into a 50 mL two-neck flask.
The flask was evacuated and backfilled with nitrogen. O-xylene
4
(
assemblies in de-aerated dichloromethane solution with tetra-
butylammoniumperchlorate as supporting electrolyte and at a
ꢀ
1
scan rate of 100 mV s . Each oxidation potential was calibrated
using ferrocene as reference.
t
3
(20 mL) and P Bu (1.23 mL, 0.4 mmol, 10% in n-hexane) were
injected. The mixture was heated at 140 1C for 48 h and
extracted twice with CH Cl at room temperature. The mixed
2
2
OLED fabrication and measurement
organic solution was washed with brine, and the solid obtained
was purified with column chromatography on SiO using ethyl
acetate and petroleum ether (v : v = 1 : 50) as eluant to afford a
Organic chemicals used for OLEDs were generally purified by
high-vacuum, temperature gradient sublimation. The devices
were fabricated by vacuum deposition of the materials at
2
1
yellowish solid NONP (67%). H NMR (500 MHz, CDCl
3
) d 8.12
ꢀ
6
1
1
0
Torr onto an ITO glass substrate (a sheet resistance of
(ddd, J = 19.7, 16.7, 8.5 Hz, 4H), 7.95 (td, J = 13.6, 8.1 Hz, 4H),
ꢀ
1
ꢀ1
5 O square ) with a deposition rate of 1–2 Å s . The
7
7
4
2
.75 (d, J = 8.3 Hz, 1H), 7.54 (dd, J = 10.9, 4.7 Hz, 3H), 7.50 (d, J =
.1 Hz, 1H), 7.41 (ddd, J = 15.8, 12.2, 7.6 Hz, 4H), 7.35–7.30 (m,
H), 7.21–7.16 (m, 3H), 7.14–7.09 (m, 2H), 7.03 (d, J = 8.9 Hz,
phosphor and host were co-evaporated to form a 20 nm emitting
layer from two separate sources. The LiF and Al were deposited
ꢀ1
with deposition rates of 0.1 and 3 Å s , respectively. The
characteristics of the devices were measured with a computer-
controlled KEITHLEY 2400 source meter with a calibrated silicon
diode in air without device encapsulation. The CIE coordinates
were calculated using a testing program of the Spectra scan PR650
spectrophotometer.
13
H), 6.93 (t, J = 7.3 Hz, 2H), 6.80 (d, J = 8.0 Hz, 2H). C NMR
3
(126 MHz, CDCl ) d[ppm] 164.71, 163.91, 151.52, 150.35,
1
1
1
1
1
6
46.75, 144.68, 144.08, 139.44, 135.29, 132.48, 131.64, 131.42,
30.27, 129.55, 129.06, 129.02, 128.55, 128.16, 127.84, 126.93,
26.78, 126.65, 126.34, 126.13, 125.92, 125.28, 125.21, 125.13,
24.43, 124.32, 124.22, 124.08, 123.95, 120.99, 120.58, 119.04,
15.27. HR ESI-MS (m/z) calcd for C H N O: 657.2649. Found:
4
6
32 4
Syntheses
+
57.2650 [M + 1] .
1
1
4
4
All reactions were performed under nitrogen. Solvents were
N -(Naphthalen-1-yl)-N ,N -diphenyl-N -(3-(5-phenyl-1,3,4-
carefully dried and distilled from appropriate drying agents oxadiazol-2-yl)phenyl)naphthalene-1,4-diamine (NONM). Compound
prior to use for the synthesis of ligands. NPNA2 was synthesized NONM was prepared according to the same procedure as compound
9
according to our previous report.
NONP, but 2-(3-bromophenyl)-5-phenyl-1,3,4-oxadiazole was used
2
-(4-Bromophenyl)-5-phenyl-1,3,4-oxadiazole. Benzoyl chloride instead of 2-(4-bromophenyl)-5-phenyl-1,3,4-oxadiazole as a start-
1
(
4
(
5 mmol, 0.70 g) was added dropwise to a solution of ing material with a yield of 60%. H NMR (500 MHz, CDCl
-bromobenzoyl hydrazine (5 mmol, 1.08 g) and triethylamine (d, J = 8.5 Hz, 1H), 8.10 (dd, J = 6.7, 1.6 Hz, 3H), 8.03 (d, J = 8.1 Hz,
5 mmol, 0.50 g) in chloroform (8 mL) at room temperature. 1H), 7.91 (d, J = 8.4 Hz, 1H), 7.86–7.84 (m, 1H), 7.74 (d, J = 8.2 Hz,
3
) d 8.14
The resulting mixture was stirred for 1 h and then filtered. The 1H), 7.69 (d, J = 7.7 Hz, 1H), 7.59–7.51 (m, 3H), 7.48 (d, J = 8.1 Hz,
collected solid was washed with water and ethanol to give the 2H), 7.43–7.30 (m, 7H), 7.19–7.09 (m, 6H), 7.04 (t, J = 7.3 Hz,2H),
13
product N-benzoyl-4-bromobenzohydrazide (1.51 g, yield: 95%). 6.91 (t, J = 7.3 Hz, 1H), 6.80 (d, J = 7.4 Hz, 2H). C NMR (126 MHz,
A mixture of N-benzoyl-4-bromobenzo-hydrazide (1.51 g) and CDCl ) d[ppm] 150.37, 149.28, 147.68, 144.67, 143.68, 140.10,
3
New J. Chem.
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NJC
Paper
1
1
1
1
35.26, 132.54, 131.66, 130.24, 129.96, 129.43, 129.04, 128.51,
27.65, 126.94, 126.76, 126.56, 126.30, 126.15, 126.08, 125.83,
25.27, 125.18, 125.08, 124.85, 124.60, 124.37, 124.22, 123.96,
2013, 23, 3096; (h) H. C. Ting, Y. M. Chen, H. W. You,
W. Y. Hung, S. H. Lin, A. Chaskar, S. H. Chou, Y. Chi,
R. H. Liu and K. T. Wong, J. Mater. Chem., 2012, 22, 8399;
(i) H. F. Chen, T. C. Wang, S. W. Lin, W. Y. Hung, H. C. Dai,
H. C. Chiu, K. T. Wong, M. H. Ho, T. Y. Cho, C. W. Chen and
C. C. Lee, J. Mater. Chem., 2012, 22, 15620; ( j) H. F. Chen,
L. C. Chi, W. Y. Hung, W. J. Chen, T. Y. Hwu, Y. H. Chen,
S. H. Chou, E. Mondal, Y. H. Liu and K. T. Wong, Org.
Electron., 2012, 13, 2671; (k) S. J. Su, C. Cai and J. Kido,
J. Mater. Chem., 2012, 22, 3447.
F. Dumur and F. Goubard, New J. Chem., 2014, 38, 2204.
Y.-L. Liao, C.-Y. Lin, K.-T. Wong, T.-H. Hou and W.-Y. Hung,
Org. Lett., 2007, 9, 4511.
S. Zhang, L.-S. Xue, Y.-M. Jing, X. Liu, G.-Z. Lu, X. Liang,
H.-Y. Li, Y.-X. Zheng and J.-L. Zuo, Dyes Pigm., 2015, 118, 1.
22.78, 122.56, 120.84, 120.47, 119.71, 118.91. HR ESI-MS (m/z)
+
calcd for C H N O: 657.2649. Found: 657.2627 [M + 1] .
46 32 4
Acknowledgements
This work was supported by the National Natural Science
Foundation of China (21371093, 91433113), the Major State Basic
Research Development Program (2011CB808704, 2013CB922101)
and the Natural Science Foundation of Jiangsu Province
7
8
(BK20130054).
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1
0 S.-H. Cheng, S.-H. Chou, W.-Y. Hung, H.-W. You, Y.-M.
Chen, A. Chaskar, Y.-H. Liu and K.-T. Wong, Org. Electron.,
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