Synthesis and physical properties of meta-terphenyloxadiazole derivatives and their application as electron transporting materials for blue phosphorescent and fluorescent devices

Article abstract of DOI:10.1039/c2jm33376g

Two m-terphenyloxadiazole-based electron transporting materials, bis(2-tert-butyl-1,3,4-oxadiazole-5-diyl)-3,3′-m-terphenyl (tOXD-mTP) and bis(2-(4-tert-butylphenyl)-1,3,4-oxadiazole-5-diyl)-3,3′-m-terphenyl (tpOXD-mTP) were synthesized and characterized. These two molecules contained two oxadiazolyl groups and a m-terphenyl linkage as the core structure achieving high triplet energy gaps (E_T) of 2.83 and 2.90 eV, respectively. The application of tOXD-mTP and tpOXD-mTP as the electron transporting materials (ETM) in bis(4′,6′-difluorophenylpyridinato)-iridium(iii) picolinate (FIrpic)-based blue phosphorescent light-emitting devices effectively confines the triplet exciton in the emitting layers. One of the electroluminescent (EL) devices using FIrpic as the dopant showed an excellent current efficiency of 43.3 cd A^-1 and an external quantum efficiency (EQE) of 23.0% with CIE (Commission International de l'Eclairage) coordinates of (0.13, 0.29). The bis(4′,6′-difluorophenylpyridinato)-iridium(iii) tetra(1-pyrazolyl)borate (FIr6)-based deeper blue EL device exhibited a high current efficiency of 42.5 cd A^-1 and external quantum efficiency of 25.0% with CIE coordinates of (0.14, 0.23). These two tOXD-mTP and tpOXD-mTP based devices show device efficiencies two to three times higher than that based on the well-known electron transporting material 1,3-bis[(4-tertbutylphenyl)-1, 3,4-oxadiazolyl]phenylene (OXD-7).

Full text of DOI:10.1039/c2jm33376g

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PAPER
Synthesis and physical properties of meta-terphenyloxadiazole derivatives and
their application as electron transporting materials for blue phosphorescent
and fluorescent devices†
a
a
a
Cheng-An Wu,ab Ho-Hsiu Chou, Cheng-Hung Shih, Fang-Iy Wu, Chien-Hong Cheng, a Heh-Lung Huang,b
*
Teng-Chih Chaob and Mei-Rurng Tsengb
Received 25th May 2012, Accepted 29th June 2012
DOI: 10.1039/c2jm33376g
Two m-terphenyloxadiazole-based electron transporting materials, bis(2-tert-butyl-1,3,4-oxadiazole-5-
diyl)-3,30-m-terphenyl (tOXD-mTP) and bis(2-(4-tert-butylphenyl)-1,3,4-oxadiazole-5-diyl)-3,30-m-
terphenyl (tpOXD-mTP) were synthesized and characterized. These two molecules contained two
oxadiazolyl groups and a m-terphenyl linkage as the core structure achieving high triplet energy gaps
(ET) of 2.83 and 2.90 eV, respectively. The application of tOXD-mTP and tpOXD-mTP as the electron
transporting materials (ETM) in bis(40,60-difluorophenylpyridinato)-iridium(III) picolinate (FIrpic)-
based blue phosphorescent light-emitting devices effectively confines the triplet exciton in the emitting
layers. One of the electroluminescent (EL) devices using FIrpic as the dopant showed an excellent
current efficiency of 43.3 cd Aꢀ1 and an external quantum efficiency (EQE) of 23.0% with CIE
(Commission International de l’Eclairage) coordinates of (0.13, 0.29). The bis(40,60-
difluorophenylpyridinato)-iridium(III) tetra(1-pyrazolyl)borate (FIr6)-based deeper blue EL device
exhibited a high current efficiency of 42.5 cd Aꢀ1 and external quantum efficiency of 25.0% with CIE
coordinates of (0.14, 0.23). These two tOXD-mTP and tpOXD-mTP based devices show device
efficiencies two to three times higher than that based on the well-known electron transporting material
1,3-bis[(4-tertbutylphenyl)-1,3,4-oxadiazolyl]phenylene (OXD-7).
readily move from the electron injection layer and the highest
1. Introduction
occupied molecular orbital (HOMO) should also be low enough
Organic light emitting diodes (OLEDs) have been extensively
to block the hole transport. Generally, the hole mobility of hole
studied for application in displays and lighting. The devices
transporting material is several orders greater than electron
based on phosphorescent emitters benefit from the ability to
mobility of the electron transporting material in a device. Hence
harvest both singlet and triplet excitons leading to an internal
the balance of hole and electron in a device is another important
quantum efficiency as high as 100%.1 In the design of highly
issue to be considered.3
efficient phosphorescent devices, the selection of a proper elec-
The requirement of ETM for blue phosphorescent electrolu-
tron transporting material (ETM) is of great importance. Due to
minescent devices is of particular importance. In addition to a
the fact that the triplet exciton of the dopant or host material
large triplet energy gap and very low HOMO level, the material
generally has a long diffusion length to the adjacent layer, the
should have a relatively high glass transition temperature (Tg).
ETM should have a sufficient triplet state energy gap (ET) to
prevent the diffusion to the electron transporting layer (ETL).2
Several types of ETM are known to date. Recently, Kido’s group
reported a series of pyridine derivatives as ETMs to confine the
In addition, the lowest unoccupied molecular orbital (LUMO) of
triplet excitons for sky-blue bis(40,60-difluorophenylpyridinato)-
the ETM should be low enough for the conducting electron to
iridium(III) picolinate (FIrpic)-based devices. The device external
quantum efficiencies (EQEs) are near or over 20%. The ET of
aDepartment of Chemistry, National Tsing Hua University, Hsinchu 30013,
these pyridine-type materials is 2.6–3.0 eV. The second pyridine
Taiwan. E-mail: chcheng@mx.nthu.edu.tw; Fax: +886-3-572469; Tel:
type of ETM is bipyridyl triazole-based materials, these also
+886-3-5721454
show good thermal stability and device performance.4 Other
bMaterial and Chemical Research Laboratories, Industrial Technology
electron transporting type functional groups like phosphine
oxide, phosphine sulfide,5 quinoxaline,6 triazine,7 benzimida-
zolyl8 and phenanthroline9 have been reported. The oxadiazole-
based materials also have a wide energy gap and are often
employed as the host or electron transporting materials in
Research Institute, Chutung, Hsinchu 31040, Taiwan
† Electronic supplementary information (ESI) available: The UV-vis
absorption and fluorescence data; 1H, 13C-NMR spectra;
crystallographic information file of tOXD-mTP. CCDC 883144. For
ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/c2jm33376g
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Scheme 1 Synthesis of m-terphenyl oxadiazole derivatives tOXD-mTP and tpOXD-mTP.
OLEDs.10 In this series, 1,3-bis[(4-tertbutylphenyl)-1,3,4-oxa-
diazolyl]phenylene (OXD-7) is very commonly used in device
fabrication.11 However, the glass transition temperature of
OXD-7 is low and the triplet state energy gap of OXD-7 is not
large enough for the triplet exciton confinement in deeper blue
EL devices. Thus, it is a challenge to design oxadiazole-based
ETMs with a larger ET than that of OXD-7 and yet also having a
high glass transition temperature. In this paper, we wish to report
the synthesis of two meta-terphenyloxadiazole derivatives
tOXD-mTP and tpOXD-mTP. These materials show higher Tg
and ET than OXD-7. It appears that the combination of meta-
terphenyl and oxadiazole moieties is able to keep the triplet
energy gap at very high values. The application of these
compounds as the ETM for phosphorescent blue devices ach-
ieves excellent device performance, even with the deeper blue
dopant bis(40,60-difluorophenylpyridinato)-iridium(III) tetra(1-
pyrazolyl)borate (FIr6). Moreover, the materials can also be
used as the ETM for deep blue fluorescent electroluminescent
devices with excellent efficiencies.
Fig. 1 The ORTEP drawing of tOXD-mTP.
As shown in Fig. 1, the dihedral angles between the first and
second and second and third m-phenylenes in the terphenyl
group are 48ꢁ and 32ꢁ indicating substantial disruption of the
conjugation between the aromatic rings.
2.2 Thermal properties
The thermal properties of tOXD-mTP and tpOXD-mTP were
investigated by thermal gravimetric analysis (TGA) and differ-
ential scanning calorimetry (DSC). The decomposition temper-
atures (Td, corresponding to 5% weight loss) of tOXD-mTP and
tpOXD-mTP were 328 and 416 ꢁC, respectively. The Td value of
2. Results and discussion
2.1 Synthesis and crystal structure
Scheme 1 shows the synthetic steps for the preparation of the
meta-terphenyloxadiazole derivatives, tOXD-mTP and tpOXD-
mTP. 5-(3-Bromophenyl)-1H-tetrazole was prepared by heating
the corresponding aryl nitrile with NaN3 and acetic acid in
refluxing n-butanol for two days. Then the tetrazole and pivaloyl
chloride was refluxed in the presence of pyridine for 24–48 h to
obtain the (bromophenyl)(tert-butyl)oxadiazole intermediate.12
Similarly, the (bromophenyl)(tert-butylphenyl)oxadiazole inter-
mediate was obtained by using the corresponding reagents. In the
last step, (bromophenyl)(tert-butyl)oxadiazole and (bromophe-
nyl)(tert-butylphenyl)oxadiazole were treated with 1,3-phenyl-
enediboronate under Suzuki-type cross-coupling conditions to
give tOXD-mTP and tpOXD-mTP, respectively, in good yields.
1
These compounds were characterized by H-NMR, 13C-NMR
and DEPT spectroscopy, mass spectrometry and elemental
analysis. In addition, the molecular structure of tOXD-mTP was
determined by single-crystal X-ray crystallographic analysis.13
Fig. 2 The UV-vis absorption and fluorescence spectra of the thin film
(30 nm) on quartz.
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tOXD-mTP is close to that of OXD-7 of 330 C, but tpOXD-
tOXD-mTP shows a highly non-coplanar conformation15 due to
the sterically hindered m-phenylene connection in the solid state,
while OXD-7 is expected to be more coplanar for the three rings
centered at oxadiazolyl moiety because of the sterically more
open 5-membered oxadiazolyl ring (Fig. 3). The coplanar
structure of OXD-7 should lead to greater intramolecular p-
conjugation and intermolecular p–p overlapping. The HOMO
levels were determined by a photoelectron spectrometer and the
values for tOXD-mTP and tpOXD-mTP are 6.05 and 5.83 eV,
respectively. The LUMO levels were then estimated by sub-
tracting the energy gap from the HOMO levels and the values are
listed in Table 1.
ꢁ
mTP appears to have a much higher Td, likely due to the presence
of two extra phenyl rings in tpOXD-mTP. Similar to the trend of
Td, the glass transition temperature (Tg) of tpOXD-mTP
(107 ꢁC) is larger than that of tOXD-mTP (63 ꢁC). However, the
Tg of OXD-7 was not detected by the DSC measurement.
The higher Td and Tg of tpOXD-mTP are apparently due to the
presence of two extra rigid phenyl rings and its larger molecular
size compared with tOXD-mTP.
2.3 Photophysical properties
The absorption and photoluminance of terphenyloxadiazole
structures in thin film and solution were analyzed by UV-vis and
photoluminescence (PL) measurements as shown in Fig. 2. These
materials exhibited absorption bands of 250–330 nm assigned to
p–p* transitions of the oxadiazole moiety.14 The PL spectra,
To understand the electron transporting character of these
compounds, three electron-only devices were fabricated. The
devices consist of the following structure: ITO/BCP (10 nm)/
OXDs (50 nm)/LiF (1 nm)/Al (100 nm), where BCP ¼ 2,9-
dimethyl-4,7-diphenyl-1,10-phenanthroline. The current density
versus voltage curves (see ESI†) show that the tOXD-mTP- and
tpOXD-mTP-based devices gave lower current densities than the
OXD-7-based one in these three electron-only devices, likely due
to the relatively non-coplanar conformation and low intermo-
lecular p–p overlapping of these two meta-terphenyl
compounds.
which were measured in dichloromethane, show
a peak
maximum at 341 nm for tOXD-mTP and at 345 nm for tpOXD-
mTP. The thin-film PL spectrum is red-shifted slightly to 347 nm
for tOXD-mTP and by a larger degree to 375 nm for tpOXD-
mTP. The observed mild red-shift of the PL spectrum of tOXD-
mTP in the thin film relative to in solution indicated that the p–p
interaction between molecules in the thin film is weak. The
presence of the two t-butyl groups at the end of the molecules
appears to play an important role to prevent strong intermo-
lecular p–p interaction in the thin film state. On the other hand,
the larger degree of red shift from 345 to 375 nm for tpOXD-mTP
suggests that the aromatic chain consisting of five m-phenylene
units and two oxadiazole moieties of the molecule has led to
substantial intermolecular p–p interaction in the thin film state.
The singlet state energy gaps (Eg) of these two materials are
calculated from the thresholds of the thin film UV spectra and
are 3.86 and 3.65 eV, respectively. On the other hand, the triplet
energy gaps were calculated from the highest-energy peak
maximum of the phosphorescent spectra measured at low
temperature. Both tOXD-mTP and tpOXD-mTP revealed very
high triplet energy gaps of 2.83 and 2.90 eV, respectively. It is
interesting to compare the energy gaps of tOXD-mTP and OXD-
7 which have exactly the same molecular weight. As shown in
Table 1, both the singlet and triplet energy gaps of tOXD-mTP
are higher than the corresponding values of OXD-7 by 0.16 eV.
A possible reason for this observation is that the meta-phenylene
moieties in tOXD-mTP disrupt very effectively the p-conjuga-
tion between the two functional groups connected to a m-
phenylene moiety. Another reason for the observation is that
3. Performance of electroluminescent devices
In order to find the suitability of these terphenyloxadiazole
derivatives as the ETMs in PhOLEDs, we fabricated devices A
and B by using FIrpic as the dopant emitter, BCPO as the host,16
and tOXD-mTP and tpOXD-mTP as the ETMs. In addition, we
also fabricated device C using OXD-7 as the ETM for compar-
ison. The devices consist of the layers: ITO/NPB (30 nm)/mCP
(20 nm)/BCPO: 8% FIrpic (25 nm)/ETMs (50 nm)/LiF (1 nm)/Al
(100 nm), where NPB ¼ N,N0-di(1-naphthyl)-N,N0-diphenyl-
(1,10-biphenyl)-4,40-diamine, mCP
¼
N,N0-dicarbazolyl-3,5-
benzene and BCPO
phosphine oxide.
¼
bis-(4-(N-carbazolyl)phenyl)phenyl-
As shown by the I–V–L curves of these three devices in Fig. 4,
device A using tOXD-mTP as the electron transporting material
gave a very low current density compared to devices B and C
using tpOXD-mTP and OXD-7 as the electron transporting
material, respectively. It is interesting to note that B and C
provide a very similar current density at the same applied
voltage. The low intermolecular p–p stacking of the tOXD-mTP
thin film leading to low electron mobility of the layer likely
Table 1 Optical and thermal properties of tOXD-mTP and tpOXD-mTP
a,b
labs (nm)
d
lphos (nm)
g
h
i
Compd
lflb,c (nm)
341 (347)
345 (375)
348 (370)
Es/ETe (eV)
HOMOf (eV)
6.05
LUMO (eV)
2.19
Tm (ꢁC)
Tg (ꢁC)
Td (ꢁC)
tOXD-mTP
tpOXD-mTP
OXD-7
251 (252)
288 (270)
292 (290)
440
423
466
3.86
2.83
3.65
2.90
3.70
2.67
181
63
328
416
331
5.83
2.18
N.D.
240
107
N.D.
5.98
2.28
a
Absorption maxima measured in CH2Cl2 solution at concentration ¼ 1 ꢂ 10ꢀ5 M. b Wavelengths in parentheses are for thin films with thickness of 300
nm. c Fluorescence maxima measured in CH2Cl2 solution at concentration ¼ 1 ꢂ 10ꢀ5 M. d The high-energy phosphorescence maxima at 77 K in 2-
e
methyltetrahydrofuran. Estimated from the absorption threshold and high-energy emission maxima in the phosphorescence spectra. Determined
f
by a photoelectron spectrometer. Melting point. h Glass transition temperature. i Decomposition point.
g
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Fig. 3 The device structures and the materials structures for blue EL devices.
accounts for the very low current density of device A. The low p–
p stacking of tOXD-mTP in the thin film is also supported by the
very small red-shift of its emission from 341 in solution to 347 nm
in the thin film of tOXD-mTP.
due to the fact that tOXD-mTP and tpOXD-mTP have a higher
triplet energy gap to achieve better exciton confinement in the
emission layer17 and suppress the triplet exciton quenching near
the emitting layer/ETL interface.18 Device A exhibits a relatively
low efficiency roll-off. At luminance of 3000 cd cmꢀ2, the EQE is
maintained at more than 20% and the current efficiency is ꢃ40 cd
Devices A and B have achieved excellent EQEs of 23.0 and
20.7% with current efficiencies of 43.3 and 40.3 cd Aꢀ1, respec-
tively. However, the corresponding efficiency of the OXD-7-
based device C is only about one half of the values of A and B
(see Table 2). The higher efficiency of devices A and B is probably
A
ꢀ1. Due to its higher ionization potential, tOXD-mTP is
expected to block the holes more effectively and to enhance
charge recombination in the emission layer. This blocking action
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Table 2 Performances of oxadiazole-based phosphorescent OLEDsa
Deviceb
Host/dopant (wt%)/ETL
Vonc (V)
L (cd mꢀ2, V)
hext (%, V)
hc (cd Aꢀ1, V)
hp (lm Wꢀ1, V)
CIE, 8 V (x, y)
A
B
C
D
E
F
BCPO/FIrpic (8)/tOXD-mTP
BCPO/FIrpic (8)/tpOXD-mTP
BCPO/FIrpic (8)/OXD-7
BCPO/Fir6 (8)/tOXD-mTP
BCPO/Fir6 (8)/tpOXD-mTP
BCPO/Fir6 (8)/OXD-7
3.9
3.3
3.9
4.3
3.9
5.1
13 943, 17.5
32 778, 18.0
13 280, 16.0
13 068, 17.0
29 353, 17.5
11 147, 15.0
23.0, 7.0
20.7, 3.5
11.4, 5.5
25.0, 8.0
20.4, 5.0
8.9, 9.5
43.3, 8.0
40.3, 4.0
22.7, 5.5
42.5, 8.0
38.7, 5.0
14.7, 9.5
31.7, 4.0
36.2, 4.0
16.4, 4.0
25.7, 4.5
27.7, 4.0
5.3, 8.5
0.13, 0.29
0.13, 0.30
0.18, 0.43
0.14, 0.23
0.14, 0.26
0.14, 0.22
a
The luminescence (L), external quantum efficiency (hext), current efficiency (hc) and power efficiency (hp) are the maximum values of the device. b The
cathode of the general device is LiF (1 nm)/Al (100 nm); the structure of devices A–F: NPB (30 nm)/mCP (20 nm)/emitting layer (25 nm)/ETM (50 nm).
c
The applied voltage (Von) required for a brightness of 1 cd mꢀ2
.
To see whether tOXD-mTP and tpOXD-mTP can also be
applied as the ETMs in blue fluorescent OLEDs, we fabricated
devices G–J consisting of the layers: ITO/NPNPB (80 nm)/NPB
(10 nm)/DMPPP: 5% BCzVBi (40 nm)/ETM (20 nm)/LiF (1 nm)/
Al (100 nm), where NPNPB ¼ N,N0-di-phenyl-N,N0-di-[4-(N,N-
di-phenyl-amino)phenyl]benzidine, DMPPP ¼ 1-(2,5-dimethyl-
4-(1-pyrenyl)phenyl) pyrene and BCzVBi ¼ 4,40-bis(9-ethyl-3-
carbazovinylene)-1,10-biphenyl. In these devices, only the
material in the electron transporting layer was varied. The device
Fig. 4 The I–V–L curves of devices A–C and devices D–F.
is particularly effective at higher voltages and the roll-off is
diminished.
To see the capability of these materials as an electron trans-
porting material for deeper blue phosphorescent devices, FIr6
was chosen as the dopant for devices D–F of which the config-
uration is the same as that of devices A–C, respectively. Device D
showed an excellent maximum EQE and current efficiency of
25.0% and 42.5 cd Aꢀ1, respectively, with CIE coordinates of
(0.14, 0.23) at 8 V. Device E also revealed a high external
quantum efficiency and current efficiency of 20.4% and 38.7 cd
A
ꢀ1, respectively. For comparison, device F using OXD-7 for the
electron transporting layer showed an EQE of only 8.9%. The I–
V–L curves of devices A–F are also shown in Fig. 4, while the
EQEs and current efficiencies vs. luminance of these devices are
displayed in Fig. 5.
Fig. 5 External quantum efficiency and current efficiency versus lumi-
nance for devices A–F.
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Table 3 Performances of oxadiazole-based OLEDsa
Deviceb
Host/dopant (wt%)/ETL
Vonc (V)
L (cd mꢀ2, V)
hext (%, V)
hc (cd Aꢀ1, V)
hp (lm Wꢀ1, V)
CIE, 8 V (x, y)
G
H
I
DMPPP/BCzVBi (5)/tOXD-mTP
DMPPP/BCzVBi (5)/tpOXD-mTP
DMPPP/BCzVBi (5)/OXD-7
DMPPP/BCzVBi (5)/BAlq
4.6
3.7
3.7
4.9
14 245, 15.0
41 419, 17.5
28 825, 16.0
40 694, 18.5
8.4, 10.5
7.3, 9.5
7.0, 10.0
6.0, 13.5
9.9, 10.5
9.8, 10.0
8.7, 11.0
8.1, 13.5
3.3, 8.5
4.7, 5.0
3.4, 5.5
2.2, 10.5
0.15, 0.14
0.14, 0.16
0.15, 0.15
0.14, 0.16
J
a
The luminescence (L), external quantum efficiency (hext), current efficiency (hc) and power efficiency (hp) are the maximum values of the device. b The
cathode of the general device is LiF (1 nm)/Al (100 nm); the structure of devices G–I: NPNPB (80 nm)/NPB (10 nm)/emitting layer (40 nm)/ETM (20
nm). c The applied voltage (Von) required for a brightness of 1 cd mꢀ2
.
and 1,3-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl) benzene
(2.94 g, 8.92 mmol) and dry dimethyl sulfoxide (DMSO) (40 mL)
were added to a 100 mL two-necks flask. The reaction was stirred
at 80–120 ꢁC under nitrogen until the staring material dis-
appeared as monitored by TLC. After cooling to room temper-
ature, the catalyst was removed by filtration and washed with
chloroform. The crude product was extracted with H2O five to
six times to remove the DMSO. The organic layer was dried over
MgSO4, filtered and concentrated under reduced pressure and
then purified by a silica gel column using a mixture of hexane and
EA (2 : 1) as eluent to give the desired product in 78% yield.
Fig. 6 The I–V–L curves of devices G–J.
performances are summarized in Table 3, while the I–V–L curves
of these devices are shown in Fig. 6. Device G using tOXD-mTP as
the ETM reveals the highest EQE of 8.4% (Fig. 7) and current
efficiency of 9.9 cd Aꢀ1, but with the smallest current density at the
same applied voltage among these blue fluorescent devices G–J.
Device H gave the highest current density, second highest EQE of
7.3% and the highest power efficiency of 4.7 lm Wꢀ1. As expected,
devices I and J using OXD-7 and BAlq as the ETM, respectively,
showed lower device efficiency. The trend of the performance of
these fluorescent devices is similar to that of the phosphorescent
ones. The results indicate that both tOXD-mTP and tpOXD-mTP
are also highly efficient ETMs for blue fluorescent devices.
4. Conclusions
Two new meta-terphenyl oxadiazole compounds tOXD-mTP
and tpOXD-mTP were successfully synthesized and character-
ized. These compounds have larger triplet state energies than the
well known OXD-7. The use of these meta-terphenyloxadiazoles
as the ETMs for FIrpic and FIr6-based blue phosphorescent
devices has greatly improved the device performance, ca. two to
three times higher than that of the OXD-7-based devices. In
addition, these meta-terphenyloxadiazoles can also be success-
fully applied as the ETMs for blue fluorescent devices leading to
very high device efficiencies.
5. Experimental
5.1 Procedure for the synthesis of tOXD-mTP
2-(3-Bromophenyl)-5-tert-butyl-1,3,4-oxadiazole (5 g, 17.85
Fig. 7 External quantum efficiency and current efficiency versus lumi-
mmol), K2CO3 (12.31 g, 89.27 mmol), PdCl2(PPh3)2 (10 mol%)
nance for devices G–J.
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tpOXD-mTP was prepared by a procedure similar to that of
tOXD-mTP. The yield is 76%.
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1
tOXD-mTP. H-NMR (400 MHz, CDCl3, d): 8.31 (s, 2H),
8.05–8.03 (d, J ¼ 8 Hz, 2H), 7.87 (s, 1H), 7.81–7.79 (d, J ¼ 8
Hz, 2H), 7.68–7.66 (d, J ¼ 8 Hz, 2H), 7.62–7.58 (m, 3H), 1.50
(s, 18H). 13C-NMR (100 MHz, CDCl3, d): 173.27, 164.49,
141.85, 140.79, 130.30, 129.53, 129.50, 126.81, 126.15, 125.80,
125.47, 124.82, 32.50, 28.25; HRMS (FAB) calcd for
C30H30N4O2 (M+ + 1): 479.2447. Found: 479.2457. Anal. calcd
for C30H30N4O2: C 75.29, H 6.32, N 11.71; found: C 75.41, H
6.41, N 11.55%.
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S. R. Forrest, Nature, 2006, 440, 908; (b) N. Matsusue, S. Ikame,
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tpOXD-mTP. 1H-NMR (400 MHz, CDCl3, d): 8.41 (s, 2H),
8.14–8.12 (d, J ¼ 8 Hz, 2H), 8.09–8.07 (d, J ¼ 8 Hz, 4H), 7.92 (s,
1H), 7.84–7.82 (d, J ¼ 8 Hz, 2H), 7.68–7.66 (d, J ¼ 8 Hz, 2H), 7.64–
7.53 (m, 7 H), 1.34 (s, 18H). 13C-NMR (100 MHz, CDCl3, d):
164.72, 164.20, 155.32, 141.80, 140.63, 130.35, 129.57, 129.53,
127.18, 126.75, 126.04, 125.99, 125.81, 125.51, 124.57, 120.95,
35.01, 31.04. HRMS (EI) calcd for C42H38N4O2 (M+): 630.2995.
Found: 630.2995. Anal. calcd for C42H38N4O2: C 79.97, H 6.07, N
8.88; found: C 79.77, H 6.20, N 8.87%.
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5.2 Physical property measurements
UV-vis absorption spectra were recorded using a Hitachi U-3300
spectrophotometer. PL spectra and phosphorescent spectra at 77
K were measured on a Hitachi F-4500 spectrophotometer. The
electrochemical properties of the OXDs derivatives were
measured by Riken Keiki Co. ACII spectrometer. The HRMS
were measured on a MAT-95XL HRMS or a JEOL JMS-700
Mstation. Elemental analysis was measured on an Elementar
vario EL III. The glass transition temperatures of the compounds
were determined by DSC under nitrogen atmosphere using a
DSC-Q10 instrument. The decomposition temperatures were
determined by TGA using TGA-Q500 instrument.
5.3 OLED fabrication and measurements
Organic chemicals used for fabricating devices were generally
purified by high-vacuum, gradient temperature sublimation. The
EL devices were fabricated by vacuum deposition of the mate-
rials at 10ꢀ6 Torr onto a glass precoated with a layer of indium
tin oxide with a sheet resistance of 30 U per square. The depo-
sition rate for organic compounds is 1–2 A sꢀ1. The cathode
ꢀ
consisting of Al/LiF was deposited by evaporation of LiF with a
deposition rate of 0.1 A sꢀ1 and then by evaporation of Al metal
ꢀ
with a rate of 3 A sꢀ1. The effective area of the emitting diode was
ꢀ
9.00 mm2. Current, voltage, and light intensity measurements
were made simultaneously using a Keithley 2400 source meter
and a Newport 1835-C optical meter equipped with a Newport
818-ST silicon photodiode. Electroluminescence spectra were
measured on a Hitachi F-4500 fluorescence spectrophotometer
(see ESI,† S12).
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We thank the Ministry of Economy (100-EC-17-A-08-S1-042)
and the National Science Council of the Republic of China
(NSC-100-2119-M-007-010-MY3) for support of this research.
17798 | J. Mater. Chem., 2012, 22, 17792–17799
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