Effective host materials for blue/white organic light-emitting diodes by utilizing the twisted conjugation structure in 10-phenyl-9,10-dihydroacridine block

Article abstract of DOI:10.1002/asia.201500235

Two new 10-phenyl-9,10-dihydroacridine derivatives attached by dibenzothiophene (DBT) and dibenzofuran (DBF) were synthesized. The influence of the substituents of these materials was studied by theoretical calculations (DFT calculation) and experimental

Full text of DOI:10.1002/asia.201500235

CHEMISTRY
AN ASIAN JOURNAL
Accepted Article
Title: Effective Host Materials for Blue/White Organic Light Emitting Diodes by Utili-
zing Conjugation Twisted Structure in 10-Phenyl-9,10-Dihydroacridine Block
Authors: Xiang-Yang Liu; Feng Liang; Lin-Song Cui; Xiao-Dong Yuan; Zuoquan Ji-
ang; Liang-Sheng Liao
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To be cited as: Chem. Asian J. 10.1002/asia.201500235
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Chemistry - An Asian Journal
10.1002/asia.201500235
FULL PAPERS
DOI: 10.1002/asia.200((will be filled in by the editorial staff))
Effective Host Materials for Blue/White Organic Light Emitting Diodes by Utilizing
Conjugation Twisted Structure in 10-Phenyl-9,10-Dihydroacridine Block
Xiang-Yang Liu, Feng Liang, Lin-Song Cui, Xiao-Dong Yuan, Zuo-Quan Jiang,* Liang-Sheng
Liao,*
Dedication ((optional))
Abstract: Two new 10-phenyl-9,10- hosts for phosphorescent organic light- and TPhAc, respectively. The white
dihydroacridine derivatives attached by emitting diodes. To evaluate the device based on host FPhAc was
dibenzothiophene
(DBT)
and electroluminescent (EL) performance achieved higher performance with
dibenzofuran (DBF) are synthesized. of these materials, FIrpic based blue maximum EQE of 24.7% than used
The influence of the substituents of PHOLEDs and two-color white TPhAc as host material.
these materials is studied by theoretical PHOLEDs (FIrpic and PO-01 as the
calculations (DFT calculation) and dopants) were fabricated using the
experimental measurements. Thanks to common device structures. High
the twisted N-phenyl ring, both external quantum efficiencies (EQE) of
molecules possess sufficiently high 21.1% and 20.9% for FIrpic based blue
triplet energies and are suitable for PHOLEDs were achieved by FPhAc
Keywords: Dibenzothiophene •
Dibenzofuran • Host material •
Twisted • Blue phosphorescent
organic light-emitting diode •
selection of host materials is very important for the high efficient
blue PHOLEDs.2f-2h In recent years, high external quantum
efficiency blue PHOLEDs were achieved based on new device
structures, phosphor emitters or host materials.3 In this regard, most
of the host materials in PHOLEDs rely on the aromatic amine
derivatives,3,4 e.g. the common used triphenylamine (TPA) and 9-
phenyl-9H-carbazole (PhCz). Bin et al. reported a FIrpic-based
OLED with an high external quantum efficiency of 29% by using a
PhCz-based host material SitCz.3a Lee et al. also reported the high
external quantum efficiency of 30% for FIrpic-based devices hosted
by PhCz derivatives.3b-3d The former (TPA) has a free fan-like
configuration and the latter (PhCz) can be viewed as a rigidified
TPA via direct C-C linkage between 2, 2’-positions. This tiny
change in structure leads to many different properties, such as
conjugation degree, distributions of frontier molecular orbitals and
derivation ways in chemical modifications.1i,4g Both TPA and PhCz
blocks are widely studied but another triphenylamine derivative,
named 10-phenyl-9,10-dihydroacridine (PhAc), is less reported up
to now. From the view of structure, PhAc is also a rigid TPA with 2,
2’- positions connected by a nonconjugated sp3 carbon atom. This
carbon has neither donating nor accepting attribute, thus we can
predict that it has little effect on original frontier molecular orbitals
of TPA. The N-phenyl ring, similar to that of PhCz, will possess
nearly perpendicular configuration to the backbone.4g-4i Even though,
PhAc is more like TPA than PhCz because PhCz can also act as
electron-rich biphenyl in some cases.4l,4m Additionally, the
bridgehead carbon atom on PhAc can be further modified for
functional materials. In this way, Lee et. al. prepared a series of
hole-transport materials with high triplet energies based on PhAc
core.5,6 Our group combined PhAc with fluorene in spiro-structure
Introduction
Organic light-emitting diodes (OLEDs) with unique structure and
favorable properties (such as ultra-thin, light weight, low drive
voltage, low power consumption, high brightness, full-color
emission, rapid response, and flexibility, etc.) have been rapidly
developed into next-generation display and solid-state lighting
technology.1 Since the ratio of electron-generated singlet and triplet
excitons formed in device is approximately 1:3, the efficiency of
conventional fluorescent OLEDs are limited within 25% in internal
quantum efficiency (IQE) while the efficiency of phosphorescent
OLEDs (PHOLEDs) can, in theory, achieve nearly 100% IQE by
utilizing both excitons.1c,1d,2 To get highly efficient PHOLEDs, a
host/dopant system is important to disperse triplet emitters. Up to
now, the red and green PHOLEDs has already been achieved the
20% theoretical external quantum efficiency, and various host and
high efficiency dopant materials have been developed to realize the
high efficiency red and green PHOLEDs. However, compared to red
and green PHOLEDs, highly efficient blue PHOLEDs are hard to
obtain due to the large energy gaps of blue phosphors, and the
X-Y. Liu, F. Liang, L-S. Cui, X-D. Yuan, Dr. Z-Q. Jiang, Prof. Dr. L-S. Liao
Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices
Institute of Functional Nano & Soft Materials (FUNSOM)Soochow University,
Suzhou 215123 (P.R. China)
Fax:(+86) 0512-65882846
E-mail: zqjiang@suda.edu.cn; lsliao@suda.edu.cn
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Chemistry - An Asian Journal
10.1002/asia.201500235
to develop blue host materials, in which the fluorene precursor was
elaborately selected to control the conjugation degree.4g-4i However,
the work about derivation on the N-phenyl ring of PhAc is rarely
reported. As aforementioned, this phenyl ring has little effect on the
coplanar 9,10-dihydroacridine because of the twisted configuration,
which is crucial to control molecular conjugation. That will be
another effective way to design high-triplet-energy hosts. The high-
triplet-energy hosts are vital important to achieve highly efficient
blue or white PHOLEDs, which are widely acknowledged as the
most difficult issue in this research area. The structures of three
building blocks TPA, PhCz and PhAc are described in Scheme 1.
efficiency (EQE) for FIrpic based blue PHOLEDs were achieved by
FPhAc and TPhAc, respectively. Finally, to further assess the
performance of these materials, two-color white PHOLEDs were
fabricated using FIrpic and PO-01 as the dopants. The device based
on host FPhAc was achieved higher performance with maximum
efficiencies of 67.0 cd A-1, 53.8 lm W-1, and 24.7%. The white
PHOLEDs also showed low drive voltages of 4.11 and 4.28 V at
1000 cd m-2 for the devices based on FPhAc and TPhAc,
respectively.
Results and Discussion
Synthesis and Structural Characterization
Although there are some work were studied the properties of PhAc
derivatives served as hole-transporting materials for OLEDs,4,5
however, they used the synthetic method (Scheme 3), which will be
limited the position of the substituents and the possibility of
derivative work on the nitrogen atom of acridine. In this work, we
take the new synthetic strategy (Scheme 3) and can be getting the
different derivative on the nitrogen atom. The synthetic routes to
obtain the target materials are outlined in Scheme 3. The key
intermediate of 10-(3-bromophenyl)-9,9-diphenyl-9,10-dihydro-
acridine was readily afforded through the classic Buchwald−
Hartwig C−N coupling reaction between 1-bromo-3-iodobenzene
and 9,9-diphenyl-9,10-dihydroacridine in moderate yield. At last,
the final products can be obtained via Pd-catalyzed Suzuki−Miyaura
coupling reaction between 10-(3-bromophenyl)-9,9-diphenyl-9,10-
dihydroacridine and the corresponding boronic acid of dibenzofuran
(DBF) and dibenzothiophene (DBT) in good yields.
TPA
PhCz
PhAc
Scheme 1. Molecular structures of triphenylamine (TPA), 9-phenyl-9H-carbazole
(PhCz), and 10-phenyl-9,10-dihydroacridine (PhAc).
Recently, the other heterocyclic structures similar to carbazole
were applied to building the new host materials,7-9 e.g. dibenzofuran
(DBF)7,9 and dibenzothiophene (DBT).7c,8,9 The structures of
carbazole, DBF and DBT are shown in Scheme 2. Compared to
carbazole, DBF and DBT also possess high triplet energies of 3.04
and 3.10 eV, respectively. However, the electron-donating ability of
DBF and DBT might be less than carbazole.9 The possible reason is
the stronger electronegativity of the O atom in DBF and it will be
limited the electron donating ability of DBF. Due to the S atom has
a much lower electronegativity that makes DBT has a much stronger
aromaticity compared to DBF or carbazole and it also reduces the
ability of electron donating for DBT.9 These properties will make
DBF and DBT more neutral than carbazole.
Scheme 2. Molecular structures of carbazole, dibenzofuran (DBF), and
dibenzothiophene (DBT)
By combining PhAc with another two heterocyclic blocks
dibenzofuran (DBF) and dibenzothiophene (DBT), two novel host
materials, FPhAc and TPhAc, were designed and synthesized by
incorporating PhAc with DBF and DBT units. DBF and DBT also
possess high triplet energies of 3.04 and 3.10 eV, respectively; and
they are positioned as meta-substituents of PhAc to reduce
molecular conjugation degree. On the other hand, DBF and DBT are
relatively neutral blocks as compared to nitrogen heterocycles,
which could modulate the properties of PhAc-based blocks. Their
thermal behaviour, electrochemical properties, the charge-
transporting abilities, and the devices performances were
investigated. In electroluminescent evaluations, both host materials
present high efficiencies in blue and white PhOLEDs with common
device structures. High efficiencies of 46.5 cd A-1, 38.9 lm W-1 and
21.1% and 45.5 cd A-1, 35.9 lm W-1 and 20.9% for current
efficiency (CE), power efficiency (PE) and external quantum
Scheme 3. Synthetic routes and chemical structures of the materials.
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10.1002/asia.201500235
Thermal Properties
orbital (HOMO) and lowest unoccupied molecular orbital (LUMO)
distributions. The HOMOs of FPhAc and TPhAc are localized at the
electron-rich acridine centers, and the LUMOs are distributed on the
DBF and DBT units with N-phenyl ring acts as separation group.
Both materials have similar HOMO levels because of the same
distributions, which means the heterocyclic structure of DBF and
DBT are almost no contribution for the HOMO energy levels. But
the DBF/DBT moiety in FPhAc/TPhAc can remarkably reduce the
LUMO by 0.74 and 0.83 eV, respectively. It is recognized that due
to the S atom has a much lower electronegativity and the
involvement of an S atom in the conjugation make DBT has a much
stronger aromaticity than DBF.9 Based on the optimize of the
molecular structure, we found, the angle between the two planes of
the phenyl and the 9,10-dihydroacridine is near 90o (about 84o),
which means this phenyl ring has little effect on the acridine core.
FPhAc and TPhAc have shown the similar results. However, the
dihedral angles between phenyl plane and the ring compound plane
are 37o and 47o for FPhAc and TPhAc, respectively. The possible
reason of this phenomenon is the S atom has much larger size in
DBT than O atom in DBF, so that the interaction between the
phenyl and the DBT is stronger and the dihedral angle between
these two planes is bigger.
The thermal properties of FPhAc and TPhAc were measured by
differential scanning calorimetry (DSC) and thermogravimetric
analysis (TGA), both materials exhibited good thermal stabilities.
The glass transition temperature (Tg, Figure 1) was measured as 100
oC for FPhAc, whilst TPhAc showed slightly higher Tg of 105 C.
o
The thermal decomposition temperatures (Td, corresponding to 5%
weight loss, Figure 1) of FPhAc and TPhAc are 394 and 408 C,
o
respectively, which exhibited similar trend to Tg. These data show
slight difference, indicating that it is the PhAc core other than the
DBF or DBT appending groups determines thermal stabilities. It is
worth noting that both molecular FPhAc and TPhAc present Tg are
obvious higher than those of classical host materials for blue
PHOLEDs, such as mCP or CBP.4q,4r Therefore both of these
compounds could be used as potential stable organic host materials
for PHOLEDs under vacuum evaporation due to the high Tg and Td.
Figure 1. DSC and TGA (inset) curves of FPhAc and TPhAc.
Photophysical Properties
Figure 2 shows the UV-vis absorption and photoluminescence (PL)
spectra of FPhAc and TPhAc at room temperature in toluene
solution and the phosphorescence spectra measured in 2-MeTHF
solution at 77 K. The data of photophysical properties of FPhAc and
TPhAc are summarized in Table 1. In the absorption spectra, the
maximum absorption wavelengths (Abs λmax) are 300 and 297 nm
for FPhAc and TPhAc, respectively, and the absorption onset of
TPhAc is red-shifted by 11 nm as compared to FPhAc. As a result,
the optical band gap (Eg) of TPhAc (3.50 eV) is smaller than that of
FPhAc (3.61 eV). On the other hand, the PL spectra of FPhAc and
TPhAc are almost identical to each other with the maximum
emission wavelengths (PL λmax) at 410 and 408 nm, respectively.
The highest vibronic bands of phosphorescence spectra at 77 K for
FPhAc and TPhAc are at 451 and 463 nm, then the triplet energies
(ET) are calculated as 2.75 and 2.68 eV for FPhAc and TPhAc,
respectively.
Figure 2. UV-vis absorption and PL spectra of FPhAc and TPhAc in toluene solution at
10-5 M; phosphorescence spectra measured in a frozen 2-MeTHF matrix at 77 K.
Electrochemical Properties
The electrochemical behavior of FPhAc and TPhAc was measured
by cyclic voltammetry (CV) method using typically tri-electrode
configuration with ferrocene as the internal standard in
dichloromethane solution (Figure 3). Based on these results, the
HOMO levels of these materials are calculated as 5.54 eV from the
onset of the first oxidation waves. These values are almost the same,
indicating that the nature of the DBF and DBT ring has almost no
influence on the HOMO energy levels. In other word, the DBF and
DBT ring are almost no contribution for the HOMOs. These
experimental results are in conformity with DFT calculation result.
And the LUMO energy levels can be calculated from the HOMOs
and the optical Egs, which are 2.01 and 2.11 eV of FPhAc and
TPhAc, respectively.
DFT Simulation
To better understand the electronic distributions of FPhAc and
TPhAc, DFT calculations were utilized to simulate their FMO
spatial distributions at a B3LYP/6-31G(d) level. As Figure S7
illustrates, these materials have similar highest occupied molecular
In order to get more reliable energy levels, ultraviolet
photoemission spectroscopy (UPS) was used to determine the
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10.1002/asia.201500235
HOMO levels (Figure 4). The HOMO levels of FPhAc and TPhAc
are 5.72 and 5.78 eV, respectively. And the LUMO levels of these
materials are 2.19 and 2.36 eV, respectively. The UPS schematic
diagram shows the HOMO levels can be gained via this equation
EHOMO = hν – Ek, hν is the light energy of the light source and
normally we used He I as the light source (hν = 21.2 eV); Ek is the
kinetic energy distribution of the photo-electrons. The LUMO
energies levels can be calculated by ELUMO = Eg – EHOMO, Eg is the
optical energy gap at film state (Figure S8). These results are
consistent with the CV results DFT calculation.
To evaluate the electroluminescent (EL) properties of FPhAc and
TPhAc as host materials, bis(4,6-(difluorophenyl)pyrudinato-
N,C')picolinate iridium(III) (FIrpic) based blue phosphorescent
OLEDs were fabricated using this simple device structure (Figure
S8): ITO/HAT-CN (10 nm)/TAPC (40 nm)/Host: 15% FIrpic (20
nm)/TmPyPB (40 nm)/Liq (2 nm)/Al (120 nm). FPhAc (B1) and
TPhAc (B2) were doped with 15% FIrpic as the emitting layer
(EML). In order to prevent the spread of the triplet excitons and to
confine it in the EML, 1,1-bis[4-[N',N'-di(p-tolyl)amino]phenyl]
cyclohexane (TAPC) and 1,3,5-tri[(3-pyridyl)phen-3-yl]benzene
(TmPyPB), which have a high triplet energies (ET) and good hole
and electron transporting mobility, served as hole transporting layer
(HTL)/electron blocking layer (EBL) and electron transporting layer
(ETL)/hole blocking layer (HBL), respectively. And to make sure
the efficient of carrier injection, dipyrazino[2,3-f:2',3'-
h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile (HAT-CN) and 8-
hydroxyquinolinolatolithium (Liq) were utilized as the hole
injection (HIL) and electron injection layers (EIL), respectively.
Figure 5 shows current density-voltage-luminance characteristic
curves (a, b) and external quantum efficiency, current efficiency and
power efficiency versus luminance curves (c, d) for devices B1-2
and W1-2. The detailed electroluminescence characteristics data are
summarized in Table 2. The blue and white devices shows relatively
lower drive voltages of 4.52/4.67 V and 4.62/4.49 V at 1000 cd m-2
for FPhAc and TPhAc based devices, respectively. The EL spectra
of these devices show relatively greenish blue emission with CIE
coordinates of (0.17, 0.39) for device B1 and (0.16, 0.39) for device
B2 compared to the typical FIrpic based devices (Figure S12),
which means that only the FIrpic emission peak was observed
without any emission from the hosts of FPhAc and TPhAc. Such
finding strongly indicated that the process of excitons formed under
holes and electrons recombination and the excitons emission process
were efficiently confined inside the emitting layer, which could be
attributed to the high ETs and appropriate HOMO/LUMO energy
levels for the hosts. The CIE coordinates for W1 and W2 are (0.33,
0.46) and (0.36, 0.48), respectively.
Figure 3. Cyclic voltammetry (CV) curves of FPhAc and TPhAc.
Figure 5c illustrates the efficiencies of the blue phosphorescent
devices. High efficiencies were achieved by these blue devices. The
maximum efficiency of device using FPhAc as host material (B1)
reached 46.5 cd A-1 for the current efficiency (CE), 38.9 lm W-1 for
the power efficiency (PE), and 21.1% for the external quantum
efficiency (EQE). The device based on host TPhAc (B2) shows
similar performance, with slightly lowered maximum efficiency of
45.5 cd A-1, 35.9 lm W-1, and 20.9% for CE, PE, and EQE,
respectively.
In order to further evaluate the performance of FPhAc and TPhAc,
we also fabricated the two-color white phosphorescent OLEDs using
FIrpic and bis(4-phenylthieno[3,2-c]pyridinato-N,C2')acetylacetona-
teiridium(III) (PO-01) as blue and yellow dopants, respectively. The
device structure is similar to the blue devices: ITO/HAT-CN (10
nm)/TAPC (40 nm)/TCTA (10 nm)/Host: 15% FIrpic: 0.5% PO-01
(15 nm)/TmPyPB (40 nm)/Liq (2 nm)/Al (120 nm). Figure 5d
illustrates the efficiencies of the white phosphorescent devices. The
detailed EL performance data are summarized in Table 2. Similar to
the blue devices, high efficiencies were achieved by white devices
based on FPhAc and TPhAc. The maximum efficiency of the
devices based on FPhAc (W1) reached 67.0 cd A-1 for the current
efficiency (CE), 53.8 lm W-1 for the power efficiency (PE) and
24.7% for the external quantum efficiency (EQE). The devices
based on TPhAc (W2) shows similar performance, with slightly
Figure 4. UPS schematic diagram and UPS spectra of FPhAc and TPhAc.
Electroluminescent Properties
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Chemistry - An Asian Journal
10.1002/asia.201500235
lowered maximum CE, PE and EQE for 55.0 cd A-1, 44.0 lm W-1
and 19.4%, respectively.
Table 1.Physical Properties of FPhAc and TPhAc.
[a]
[a]
Abs λmax
/nm
PL λmax
/nm
Host
Tg[b]/oC
Td[c]/oC
Eg[d]/eV
ET[e]/eV
HOMO[f]/eV
LUMO[g]/eV
FPhAc
TPhAc
300
410
100
105
394
408
3.61/3.53
3.50/3.42
2.75
2.68
-5.72
-5.78
-2.19
-2.36
297
408
[a] Measured in toluene solution at room temperature. [b] Tg: Glass transition temperature. [c] Td: Decomposition temperature. [d] Eg: Band gaps, calculated from the corresponding
absorption onset at solution/film state. [e] ET: Measured in 2-MeTHF glass matrix at 77 K. [f] HOMO levels, calculated from UPS data. [g] LUMO levels, calculated from the
HOMO and Eg at film state.
Figure 5. Current density-voltage-luminance characteristic curves and external quantum
efficiency (EQE), current efficiency (CE) and power efficiency (PE) versus luminance
curves for devices B1-2 (a, c) and W1-2 (b, d).
Conclusion
In conclusion, two novel host materials, FPhAc and TPhAc, were
synthesized and fully characterized. High efficiencies were achieved
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Chemistry - An Asian Journal
10.1002/asia.201500235
of PHOLEDs using these new host materials. The best performances
of blue and white devices based on TPhAc were 21.1% and 24.7%
for EQE, respectively. These results demonstrate the potential of 10-
phenyl-9,10-dihydroacridine (PhAc) block, when it is intendedly
modified from the nitrogen atom, it can form new materials with
separated HOMO/LUMO and thus lead to high triplet host materials
for highly efficient blue and white PHOLEDs.
Table 2. Electroluminescence characteristics of the devices.
V[b]
CE
PE
EQE[c]
[%]
CIE[d]
[x, y]
[c]
[c]
Device[a]
Host
[V]
[cd A-1]
[lm W-1]
B1
B2
FPhAc
TPhAc
FPhAc
TPhAc
4.52
4.67
4.62
4.49
46.5, 42.3, 33.5
45.5, 40.0, 29.8
67.0, 62.2, 55.7
55.0, 52.5, 47.1
38.9, 29.3, 18.0
35.9, 26.9, 15.2
53.8, 42.4, 28.3
44.3, 36.9, 24.6
21.1, 19.3, 15.3
20.9, 18.5, 13.8
24.7, 22.9, 20.5
19.4, 18.6, 16.4
0.17, 0.39
0.16, 0.39
0.33, 0.46
0.36, 0.48
W1
W2
[a] The notation 1 and 2 in devices B1 and B2 indicates the corresponding devices fabricated with FPhAc and TPhAc as the host respectively. Device configuration: B1 and B2:
ITO/HAT-CN (10 nm)/TAPC (40 nm)/TCTA (10 nm)/Host:15% FIrpic (20 nm)/TmPyPB (40 nm)/Liq (2 nm)/Al (120 nm); W1 and W2: ITO/HAT-CN (10 nm)/TAPC (45
nm)/Host: 15 wt% FIrpic: 0.5% PO-01 (15 nm)/TmPyPB (40 nm)/Liq (2 nm)/Al (120 nm). [b] Voltages at 1000 cd m-2. [c] Efficiencies in the order of the maxima, at 1000 cd m-2
and at 5000 cd m-2. [d] CIE coordinates measured at 5 mA cm-2.
After 1 h reaction at 0 oC, the mixture was gradually warmed up to room temperature
overnight. The reaction was quenched by water (5 mL). Put the mixture into 50 mL
water, the product was extracted with EtOAc (350 mL), the combined organic layers
Experimental Section
were washed with brine and dried over anhydrous sodium sulfate (NaSO4). Filtrated and
General Information
evaporated under reduce pressure to afford a yellow oil or yellow soild (14 g), which
was directly used in the next reaction without further purification. The crude product
was dissolved in 100 mL acetic acid (HOAc) under 70 oC and 10 mL hydrochloric acid
(HCl) was added dropwise under stirred. The mixture was reaction overnight at 70 oC.
After the reaction cooling to room temperature, filtered and washed with absolute ethyl
alcohol, and dried under vacuum to give 9,9-diphenylacridane as white power (12 g).
90% yield. 1H NMR (400 MHz, CDCl3): δ 6.25 (s, 1H), 6.86 (m, 9H), 7.16 (m, 8H) ppm.
13C NMR (100 MHz, CDCl3): δ 30.1, 56.7, 120.2, 125.6, 126.2, 127.1, 127.4, 127.6,
127.6, 127.9, 128.5, 130.0, 130.2, 130.2, 139.7, 146.0, 149.3 ppm.10 MS m/z: 334.16.
Anal. calcd for C25H19N (%): C 90.06, H 5.74, N 4.20; found: C 90.05, H 5.68, N 4.32.
All chemicals and reagents were used as received from commercial sources without
further purification. THF was purified by PURE SOLV (Innovative Technology)
purification system. 1H NMR and 13C NMR spectra were recorded on a Bruker 400
spectrometer at room temperature. Mass spectra were recorded on a Thermo ISQ mass
spectrometer using a direct exposure probe. UV-vis absorption spectra were recorded on
a Perkin Elmer Lambda 750 spectrophotometer. PL spectra and phosphorescent spectra
were recorded on
a Hitachi F-4600 fluorescence spectrophotometer. Differential
scanning calorimetry (DSC) was performed on a TA DSC 2010 unit at a heating rate of
10 oC min-1 under nitrogen. The glass transition temperatures (Tg) were determined from
the second heating scan. Thermogravimetric analysis (TGA) was performed on a TA
SDT 2960 instrument at a heating rate of 10 oC min-1 under nitrogen. Temperature at
5% weight loss was used as the decomposition temperature (Td). Cyclic voltammetry
(CV) was carried out on a CHI600 voltammetric analyzer at room temperature.
Deaerated dichloromethane was used as solvent for oxidation scan with
tetrabutylammonium hexafluorophosphate (TBAPF6) (0.1 M) as the supporting
electrolyte. The cyclic voltammograms were obtained at scan rate of 0.1 V s-1. Ultra-
Violet Photoemission Spectroscopy (UPS) analysis were carried out with an unfiltered
He I (21.2 eV) gas discharge lamp and a hemispherical analyzer, which made by
KRATOS ANALYTICAL SHIMADZU GROUP COMPANY. DFT calculations were
performed using B3LYP/6-31g(d) basis set using Gaussian 09.
Preparation of 10-(3-bromophenyl)-9,9-diphenyl-9,10-dihydroacridine
9,9-diphenylacridane (10 g, 30 mmol), 1-bromo-3-iodobenzene (12.7 g, 45 mmol),
tris(dibenzylidene-acetone)dipalladium(0) (Pd2(dba)3, 0.27 g, 0.3 mmol), 2-
dicyclohexylphosphino-2',6'-dimethoxy-1,1'-biphenyl (S-Phos, 0.37 g, 0.9 mmol),
sodium t-butoxide (t-BuONa, 5.76 g, 60 mmol) were dissolved in toluene under argon
and heated to 110 oC. After 20 h reaction under stirring, the reaction was cooled to room
temperature and 200 mL water was added. The product was extracted with
dichloromethane (DCM, 3100 mL), the combined organic layers were washed with
brine and dried over anhydrous sodium sulfate (NaSO4). Filtered and evaporated under
reduced pressure. The crude product was purified by column chromatography using
petroleum ether/dichloromethane (2/1, v/v) to give 10-(3-bromophenyl)-9,9-diphenyl-
9,10-dihydroacridine as a white crystalline power (12.45 g).
85% yield. 1H NMR (400 MHz, CDCl3): δ 6.39-6.41 (d, J = 8.4 Hz, 2H), 6.86-6.92 (m,
4H), 6.96-6.98 (m, 4H), 6.96-7.00 (m, 4H), 7.01-7.09 (m, 3H), 7.20-7.26 (m, 8H), 7.36-
7.40 (t, J = 8.0 Hz, 1H), 7.56-7.59 (m, 1H) ppm. 13C NMR (100 MHz, CDCl3): δ 114.03,
120.50, 123.58, 126.38, 126.97, 127.70, 129.79, 130.15, 130.40, 131.54, 131.75, 134.53,
141.86, 142.20, 146.33 ppm. MS m/z: 488.40. Anal. calcd for C31H22BrN (%): C 76.23,
H 4.54, N 2.87; found: C 76.28, H 4.68, N 2.92.
Synthesis and Characterization
1-bromo-3-iodobenzene, dibenzofuran-4-boronic acid and dibenzothiophene-4-boronic
acid were commercially available. THF was purified by PURE SOLV (Innovative
Technology) purification system. Other reactants or reagents were used as received.
Preparation of 9,9-diphenylacridane
Methyl anthranilate (20 g, 132 mmol), iodobenzene (26.9 g, 132 mmol), K2CO3 (36.4 g,
264 mmol), and copper powder (0.17 g, 2.64 mmol) was scattered in 1,2-
dichlorobenzene (o-DCB) and stirred for 10 hours at 180 °C under argon. After the
reaction cooling to room temperature, filtered and washed with dichloromethane (DCM).
Remove the solvent under reduced pressure and the crude product was purified by
column chromatography using petroleum ether/dichloromethane (2/1, v/v) to afford the
pure product as a colourless oil (23 g). This product was used in the next step needn’t to
further purification.
77% yield. 1H NMR (400 MHz, CDCl3): δ 3.89 (s, 3H), 6.66-6.78 (m, 1H), 7.06-7.10 (t,
J = 7.6, 7.2 Hz, 1H), 7.23-7.25 (m, 3H), 7.28-7.35 (m, 3H), 7.94-7.97 (m, 1H), 7.47 (s,
1H) ppm. 13C NMR (100 MHz, CDCl3): δ 168.95, 147.97, 140.79, 134.12, 131.65,
129.39, 123.58, 122.54, 117.12, 114.04, 111.92, 51.79 ppm. MS m/z: 227.10. Anal.
calcd for C14H13NO2 (%): C 73.99, H 5.77, N 6.16; found: C 73.78, H 5.88, N 6.32.
Preparation of 10-(3-(dibenzo[b,d]furan-4-yl)phenyl)-9,9-diphenyl-9,10-dihydroacrid-
ine
10-(3-bromophenyl)-9,9-diphenyl-9,10-dihydroacridine (3 g, 6.1 mmol), dibenzofuran-
4-boronic acid (1.6 g, 7.3 mmol) and tetrakis(triphenylphosphine)palladium(0)
(Pd(PPh3)4, 0.35 g, 0.3 mmol) were dissolved in THF under argon, and then 2 M K2CO3
(THF/Water = 5/1, v/v) was added. The resulting solution was heated at 70 oC overnight.
After cooled to room temperature, the mixture was evaporated to remove solvents. The
residue was washed with water and extracted with dichloromethane for 3 times. The
organic layer was collected and evaporated. The crude product was purified by
chromatography on silica gel using petroleum ether as eluent to afford of 10-(3-
(dibenzo[b,d]furan-4-yl)phenyl)-9,9-diphenyl-9,10-dihydroacridine (FPhAc) as a white
powder (3.0 g).
86% yield. 1H NMR (400 MHz, CDCl3): δ 6.64-6.66 (m, 2H), 6.87-6.94 (m, 4H), 7.02-
7.11 (m, 7H), 7.19-7.28 (m, 7H), 7.32-7.47 (m, 3H), 7.53-7.57 (m, 2H), 7.63-7.67 (t, J =
8.0, 7.6 Hz, 1H), 7.71 (m, 1H), 7.91-7.97 (m, 2H), 8.04-8.07 (m, 1H) ppm. 13C NMR
(100 MHz, CDCl3): δ 111.85, 114.28, 120.11, 120.18, 120.67, 122.84, 123.21, 124.00,
The colourless oil (10 g, 44 mmol) was dissolved in 180 mL tetrahydrofuran (THF) in a
500 mL Schlenk tube under argon and cooled to 0 oC, and then phenylmagnesium
chloride (PhMgCl, 2 M in THF, 66 mL, 132 mmol) was added dropwise under stirred.
6

Chemistry - An Asian Journal
10.1002/asia.201500235
124.62, 125.06, 126.23, 126.55, 126.87, 127.60, 128.47, 129.70, 129.96, 130.27, 130.43,
131.55 ppm. MS m/z: 575.70. Anal. calcd for C43H29NO (%): C 89.71, H 5.08, N 2.43;
found: C 89.78, H 5.26, N 2.52.
25, 645-650. l) Y.-X. Zhang, L. Ding, X.-Y. Liu, Z.-Q. Jiang, H. Chen, S.-J. Ji,
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10-(3-(dibenzo[b,d]thiophen-4-yl)phenyl)-9,9-diphenyl-9,10-dihydroacridine (TPhAc)
was prepared in a similar manner with FPhAc. The result to afford a white power.
80% yield. 1H NMR (400 MHz, CDCl3): δ 6.59-6.61 (d, J = 8.0 Hz, 2H), 6.87-6.93 (m,
4H), 7.00-7.03 (m, 4H), 7.07-7.43 (m, 3H), 7.18-7.27 (m, 7H), 7.44-7.57 (m, 5H), 7.63-
7.67 (t, J = 8.0, 7.6 Hz, 1H), 7.81-7.85 (m, 2H), 8.13-8.18 (m, 2H) ppm. 13C NMR (100
MHz, CDCl3): δ 111.85, 114.28, 120.11, 120.18, 120.67, 122.84, 123.21, 124.00,
126.23, 127.60, 128.47, 129.70, 129.96, 130.27, 130.76, 131.55, 138.64, 141.08, 142.24,
146.46, 153.20, 156.06 ppm. MS m/z: 591.70. Anal. calcd for C43H29NS (%): C 87.27,
H 4.94, N 2.37; found: C 87.20, H 4.98, N 2.42.
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Device Fabrication and Testing
Bis(4,6-(difluorophenyl)pyrudinato-N,C')picolinateiridium(III) (FIrpic), 1,1-bis[4-
[N',N'-di(p-tolyl)amino]-phenyl]cyclohexane (TAPC), 1,3,5-tri[(3-pyridyl)phen-3-
yl]benzene (TmPyPB), dipyrazino[2,3-f:2',3'-h]-quinoxaline-2,3,6,7,10,11-hexacarbo-
nitrile (HAT-CN), 8-hydroxyquinolinolatolithium (Liq) and bis(4-phenylthieno[3,2-
c]pyridinato-N,C2')acetylacetonateiridium(III) (PO-01) were commercially available.
The OLEDs were fabricated on the indium-tin oxide (ITO) coated transparent glass
substrates, the ITO conductive layer having a thickness of ca. 100 nm and a sheet
resistance of ca. 30 Ω per square. The substrates was cleaned with ethanol, acetone and
deionized water, and then dried in an oven, finally exposed to UV ozone for 30 min. All
of the organic materials and metal layers under a vacuum of ca. 10-6 Torr. Four identical
OLED devices were formed on each of the substrates and the emission area of 0.09 cm2
for each unit. The EL performances of the blue and white devices were measured with a
PHOTO RESEARCH SpectraScan PR 655 PHOTOMETER and a KEITHLEY 2400
SourceMeter constant current source at room-temperature.
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Acknowledgements
We thank to the financial support from the Natural Science Foundation of China (Nos.
21202114 and 61177016). This project is also funded by Collaborative Innovation
Center (CIC) of Suzhou Nano Science and Technology, Soochow University, and by
the Priority Academic Program Development of the Jiangsu Higher Education
Institutions (PAPD).
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Chemistry - An Asian Journal
10.1002/asia.201500235
Entry for the Table of Contents (Please choose one layout only)
Layout 2:
Catch Phrase
Maintain high
triplet energy
Xiang-Yang Liu, Feng Liang, Lin-
Song Cui, Xiao-Dong Yuan, Zuo-
Quan Jiang,* Liang-Sheng
24.7% EQE / white OLED
Increase thermal stability
Liao,*………...… Page – Page
Two new 10-phenyl-9,10-
Effective Host Materials for
dihydroacridine derivatives attached
Blue/White Organic Light
by dibenzothiophene (DBT) and
Emitting Diodes by Utilizing
dibenzofuran (DBF) are synthesized.
Conjugation Twisted Structure in
Thanks to the twisted N-phenyl ring,
10-Phenyl-9,10-Dihydroacridine
both molecules possess sufficiently
Block
high triplet energies and are suitable
for hosts for phosphorescent organic
light-emitting diodes with maximum
efficiency of 24.7% achieved.
8