Bipolar tetraarylsilanes as universal hosts for blue, green, orange, and white electrophosphorescence with high efficiency and low efficiency roll-off

Article abstract of DOI:10.1002/adfm.201002066

A series of tetraarylsilane compounds, namely p-BISiTPA (1), m-BISiTPA (2), p-OXDSiTPA (3), m-OXDSiTPA (4), are designed and synthesized by incorporating electron-donating arylamine and electron-accepting benzimidazole or oxadiazole into one molecule via

Full text of DOI:10.1002/adfm.201002066

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Bipolar Tetraarylsilanes as Universal Hosts for Blue, Green,
Orange, and White Electrophosphorescence with High
Efficiency and Low Efficiency Roll-Off
Shaolong Gong, Yonghua Chen, Jiajia Luo, Chuluo Yang,* Cheng Zhong,
Jingui Qin, and Dongge Ma*
1. Introduction
A series of tetraarylsilane compounds, namely p-BISiTPA (1), m-BISiTPA (2),
Phosphorescent organic light-emitting
p-OXDSiTPA (3), m-OXDSiTPA (4), are designed and synthesized by incorpo-
diodes (PhOLEDs) have attracted intense
rating electron-donating arylamine and electron-accepting benzimidazole or
interest because they can approach 100%
oxadiazole into one molecule via a silicon-bridge linkage mode. Their thermal,
photophysical and electrochemical properties can be finely tuned through the
different groups and linking topologies. The para-disposition compounds 1 and
3 display higher glass transition temperatures, slightly lower HOMO levels and
triplet energies than their meta-disposition isomers 2 and 4, respectively. The
silicon-interrupted conjugation of the electron-donating and electron-accepting
segments gives these materials the following advantages: i) relative high triplet
energies in the range of 2.69–2.73 eV; ii) HOMO/LUMO levels of the com-
pounds mainly depend on the electron-donating and electron-accepting groups,
respectively; iii) bipolar transporting feature as indicated by hole-only and
electron-only devices. These advantages make these materials ideal universal
hosts for multicolor phosphorescent OLEDs. 1 and 3 have been demonstrated
as universal hosts for blue, green, orange and white electrophosphorescence,
exhibiting high efficiencies and low efficiency roll-off. For example, the devices
hosted by 1 achieve maximum external quantum efficiencies of 16.1% for blue,
22.7% for green, 20.5% for orange, and 19.1% for white electrophosphores-
cence. Furthermore, the external quantum efficiencies are still as high as 14.2%
for blue, 22.4% for green, 18.9% for orange, and 17.4% for white electrophos-
phorescence at a high luminance of 1000 cd m−2 . The two-color, all-phosphor
white device hosted by 3 acquires a maximum current efficiency of 51.4 cd A−1 ,
and a maximum power efficiency of 51.9 lm W−1 . These values are among the
highest for single emitting layer white PhOLEDs reported till now.
internal quantum efficiency by utilizing
both singlet and triplet excitons.[1–3]
Recently, green and red PhOLEDs with
100% internal quantum efficiency have
been reported,[4–6] but highly efficient and
stable blue PhOLEDs have yet to be devel-
oped. Furthermore, the low efficiency and
instability of blue PhOLEDs has become a
bottleneck in the development of efficient
and stable white PhOLEDs. To achieve
highly efficient electrophosphorescence,
phosphorescent emitters of heavy-metal
complexes are usually doped into a suit-
able host material by reducing competitive
factors such as concentration quenching
and triplet-triplet annihilation.[7] Given
this, a universal host for blue, green, and
red phosphors is vital for the realization
of white PhOLEDs. However, the design
of such universal host is a considerable
challenge. As a host for blue phosphor,
its triplet energy level must be larger than
photon energies of blue light (≥2.7 eV)
to maintain effective exothermic energy
transfer from host to guest.[8] On the other
hand, as a host for green or red phosphor,
a triplet energy higher than blue phos-
phor may not be desirable because a high triplet energy gener-
ally signifies a large electrical bandgap, i.e., a low-lying highest
occupied molecular orbital (HOMO) and/or high-lying lowest
occupied molecular orbital (LUMO) level, which may cause
large energy barriers between adjacent layers.[9] Therefore, in a
universal host for blue, green, and red phosphors, a compro-
mise must be reached between high triplet energy and appro-
priate HOMO/LUMO levels.
S. Gong, J. Luo, Prof. C. Yang, C. Zhong, Prof. J. Qin
Department of Chemistry
Hubei Key Lab on Organic and Polymeric Optoelectronic Materials
Wuhan University
Wuhan 430072, People’s Republic of China
E-mail: clyang@whu.edu.cn
Y. Chen, Prof. D. Ma
Carbazole-based compounds have been widely utilized as the
hostmaterialsforbluePhOLEDs.[10,11]Additionally,tetraarylsilane
compounds with ultrahigh singlet (∼4.5 eV) and triplet (∼3.5 eV)
energies have been reported as host materials for deep blue
electrophosphorescence,[12] but their poor charge-transporting
ability and very high hole-injection barrier hamper their further
State Key Laboratory of Polymer Physics and Chemistry
Changchun Institute of Applied Chemistry
Chinese Academy of Sciences
Changchun 130022, People’s Republic of China
E-mail: mdg1014@ciac.jl.cn
DOI: 10.1002/adfm.201002066
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usage as host materials. To reduce the hole-injection barrier,
p-type tetraarylsilane compounds synthesized by introducing
the carbazole moiety have been recently reported as hosts for
blue PhOLEDs.[13,14] Unfortunately, problems still remain in
terms of low efficiency and large efficiency roll-off due to the
imbalance of carrier injection and transport. To address this
issue, a bipolar host can play an important role because it could
facilitate the balanced transport of both hole and electron, and
broaden the exciton-formation zone, consequently improving
the device performance and reduce efficiency roll-off.[15,16] In
this context, we designed and synthesized a series of tetraar-
ylsilane compounds by integrating electron-donating arylamine
and electron-accepting benzimidazole or oxadiazole into one
molecule. We anticipate that the electron-donating and electron-
accepting moieties would impart the material with bipolar
transporting characteristics; meanwhile, the whole molecule
would maintain relative high triplet energy owing to silicon-
interrupted conjugation of two segments. We also expect that
different groups and linking modes of the electron-donor and
electron-acceptor would finely tune their photophysical and
electrochemical properties, and consequently modulate their
triplet energies and HOMO/LUMO levels to some extent. We
will present a comprehensive investigation that encompasses
the thermal, photophysical, and electrochemical properties of
the compounds as well as the theoretical modeling, and dem-
onstrate the applicability of these materials as universal hosts
for blue, green, and orange phosphors, and finally for all-
phosphor white OLEDs.
2. Results and Discussion
2.1. Synthesis and Characterization
The synthetic routes and chemical structures of the compounds,
(4-{diphenyl[4-(1-phenyl-1H-benzimidazol-2-yl)phenyl]silyl}phenyl)
diphenylamine (p-BISiTPA, 1), (3-{diphenyl[3-(1-phenyl-1H-benz-
imidazol-2-yl)phenyl]silyl}phenyl)diphenylamine (m-BISiTPA, 2),
{4-[{4-[5-(4-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]phenyl}(diphenyl)
silyl]phenyl}diphenylamine (p-OXDSiTPA, 3), {3-[{3-[5-(4-tert-
butylphenyl)-1,3,4-oxadiazol-2-yl]phenyl}(diphenyl)silyl]phenyl}
diphenylamine (m-OXDSiTPA, 4), are depicted in Scheme 1. The
electron-withdrawing benzimidazole or oxadiazole moiety was
Br
N
Si
Si
N
N
N
N
Pd(OAc) / BuONa/( Bu) PHBF
2 t
t
3
4
diphenylamine toluene, reflux
Br
N
Si
N
Si
N
N
N
O
O
N
N
N
N
Si
N
Si
N
p-BISiTPA, 1
m-BISiTPA, 2
N
N
O
Si
N
N
N
Si
N
O
m-OXDSiTPA, 4
p-OXDSiTPA, 3
Scheme 1. Synthesis and molecular structures of 1–4.
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a)
exhibit high thermal decomposition temperatures (Td, corre-
sponding to 5% weight loss) in the range of 376–415 °C. Their
glass-transition temperatures (Tg) range from 77 to 102 °C,
which are substantially higher than those of tetraarylsilane
compounds (26–53 oC),[12] indicating that the introduction of
benzimidazole or oxadiazole moiety improves their morpholo-
gical stability. Additionally, 1 and 3 with a para-disposition
linkage show significantly higher Tg values than 2 and 4 with a
meta-disposition connection.
100
1
2
3
4
80
60
40
20
0
2.3. Photophysical Properties
100 200 300 400 500 600 700
Temperature (oC)
Figure 2 shows the electronic absorption and fluorescence
spectra of the compounds in dilute toluene and CH2Cl2
solution. The absorption peaks around 300 nm for all com-
pounds are consistent with the triphenylamine-centered
π–π∗ transition. In addition, no charge transfer absorp-
tion band from the electron-donating triphenylamine to
the electron-withdrawing benzimidazole or oxadiazole
group can be observed,[18] indicating the disruption of the
π-conjugation between the two parts owing to the silicon-
bridge linkage mode.
b)
1
102 oC
2
79 oC
3
100 oC
4
77 oC
The four compounds show emission peaks in the range of
372–408 nm in low-polarity toluene solution. In more polar
CH2Cl2 solution, all of the compounds display pronounced
dual emission bands simultaneously (Figure 2b): the emis-
sion peaks in the range of 358–387 nm can be assigned to the
π–π∗ transitions; the emissions at longer wavelengths around
450–506 nm originate from donor–acceptor charge transfer
transitions.[19] The charge transfer transitions of 2 and 4 are
partially blocked due to the meta-disposition linkage, which
results in the blue-shifts of the charge transfer bands with
respect to the para-disposition isomers 1 and 3, respectively.
Moreover, the charge transfer emission shift between 1 and
2 is smaller than that between 3 and 4, since the benzimida-
zole unit in 1 and 2 is a weaker electron-accepting unit than
the oxadiazole unit in 3 and 4. Their phosphorescence spectra
were measured in a frozen 2-methyltetrahydrofuran matrix at
77 K (Figure 3), and the triplet energy levels were estimated
from the highest-energy vibronic sub-band of the phospho-
rescence spectra. All of the compounds show higher triplet
energy levels (2.69 eV for 1, 2.73 eV for 2, 2.70 eV for 3, and
2.72 eV for 4) than that of blue phosphor iridium(III) bis(4,6-
(difluorophenyl)pyridine-N,C2’) picolinate (FIrpic, 2.65 eV),[20]
which implies they could serve as host materials for the blue
triplet emitter.
60
80
100
120
Temperature (oC)
Figure 1. a) TGA thermograms of 1–4 recorded at a heating rate of
10 °C min−1 . b) DSC traces of 1–4 recorded at a heating rate of 10 °C min−1 .
firstly introduced to the silicon-containing skeleton, and then the
electron-donating diphenylamine segment was connected to the
skeleton through the palladium-catalyzed C–N coupling reaction
of the corresponding bromide intermediates with diphenylamine
in good yields (72–80%).[17] For 1 and 3, the electron-donor and
acceptor units locate at the para-disposition of the silicon, while for
2 and 4, the two units situate in the meta-disposition of the silicon.
The chemical structures of all of the compounds were fully charac-
terized by 1H NMR and 13C NMR spectroscopy, mass spectrometry,
and elemental analysis (see the Experimental Section).
2.2. Thermal Properties
The thermal properties of the compounds were investigated by
thermogravimetric analysis (TGA) and differential scanning
calorimetry (DSC) (Figure 1 and Table 1). The four compounds
T a b le 1 . Physical data of 1–4.
Compound
HOMO/LUMOexpe) (eV)
5.27/NA
HOMO/LUMOcalf) (eV)
5.22/1.78
ETg) (eV)
2.69
Tga) (°C)
102
Tdb) (°C)
405
λabsc) (nm) λem, maxc) (nm) λabsd) (nm)
λem, maxd)(nm)
363, 473
1
2
3
4
308
301
299
295
372
380
408
393
306
301
298
294
79
376
387, 450
5.25/NA
5.11/1.70
2.73
100
415
359, 506
5.30/2.34
5.30/2.18
2.70
77
384
358, 474
5.25/2.26
5.09/2.12
2.72
a)Obtained from DSC measurements; b)Obtained from TGA measurements; c)Measured in toluene; d)Measured in CH2Cl2; e)Determined from the onset of oxidation/reduc-
tion potentials; f)Values from DFT calculation; g)Measured in 2-methyltetrahydrofuran at 77 K.
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a)
a)
1
2
3
4
1.0
1.0
0.8
0.6
0.4
0.2
0.0
1
2
3
0.8
0.6
0.4
0.2
0.0
4
-0.5
0.0
0.5
1.0
250 300 350 400 450 500 550 600
Wavelength (nm)
Potential vs. Fc/Fc+ (V)
b)
b)
1
3
4
1.0
1.0
2
3
4
0.8
0.6
0.4
0.2
0.0
0.8
0.6
0.4
0.2
0.0
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
Potential vs. Fc/Fc+ (V)
250 300 350 400 450 500 550 600 650
Wavelength (nm)
Figure 4. Cyclic voltammograms of 1–4 in a) CH2Cl2 for oxidation and
b) THF for reduction.
Figure 2. UV-vis absorption and PL spectra of 1–4 in a) toluene solution
at 5 × 10−6 M and b) CH2Cl2 solution at 5 × 10−6 M.
2.4. Electrochemical Properties
The HOMO/LUMO energy levels were estimated from the
onsets of the oxidation and reduction potentials with regard to
the energy level of ferrocene (4.8 eV below vacuum), respec-
tively (Table 1). The four compounds exhibit similar HOMO
levels (5.25–5.30 eV), which are much higher than the ∼7.0 eV
of the tetraarylsilane compounds previously reported,[12] and
even higher than that of widely used hole transporting mate-
rial 1, 4-bis[(1-naphthylphenyl)amino]biphenyl (NPB, 5.4 eV).[22]
The LUMO level of 4 (2.26 eV) is slightly higher than that of
3 (2.34 eV), which could be attributed to the different linking
modes.
Cyclic voltammetry (CV) was performed to investigate the elec-
trochemical properties of the compounds (Figure 4). During the
anodic scan in dichloromethane, the four compounds all exhibit
one quasi-reversible, one-electron oxidation process, which can
be assigned to the oxidation of the arylamine moiety.[21] Upon
cathodic sweeping in THF, 3 and 4 exhibit reversible reduction
waves (Figure 4b), arising from the reduction of the n-type oxa-
diazole segments;[4b] while 1 and 2 exhibit no reduction wave.
4
2.5. Theoretical Calculations
1
3
To understand the structure-property relationship of the com-
pounds at the molecular level, the geometry were optimized at
B3LYP/6–31G(d) level, and the electronic properties of the com-
pounds were calculated at τ-HCTHhyb/6–311++G(d, p) level (for
details, see the Experimental Section). According to DFT calcu-
lations, the HOMO orbitals are mainly located on the electron-
donating triphenylamine moiety, while the LUMO orbitals are
mainly distributed on the electron-accepting benzimidazole or
oxadiazole moiety (Figure 5). All of the compounds have almost
completeseparationoftheHOMOandLUMOathole-andelectron-
transporting moieties, which can be rationalized by the disrup-
tion of the π-conjugation between the electron-donating and
2
3
2
1
4
0
350
400
450
500
550
600
650
Wavelength(nm)
Figure 3. The phosphorescence spectra of 1–4 in
methyltetrahydrofuran matrix at 77 K.
a frozen 2-
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Figure 5. Calculated spatial distributions of the HOMO and LUMO levels of 1–4.
2.6. Electroluminescent Devices
electron-accepting moiety. The complete separation is preferable
for efficient hole- and electron-transporting properties, and the
prevention of reverse energy transfer.[23] The calculated HOMO/
LUMO values are in the range of 5.09–5.30/1.70–2.18 eV,
which correlate with the experimental data (Table 1).
To evaluate the bipolar character of the compounds, we
fabricated hole-only devices with the structure of ITO/MoO3
(10 nm)/NPB (80 nm)/4,4’,4’’-tri(N-carbazolyl)triphenylamine
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a)
2
3
4
5
6
2.26
3.0
30
2.3
2.3 2.3
LUMO
2.7
2.34
p-BISiTPA, 1
25
20
15
10
5
hole-only device
electron-only device
LiF/Al
ITO
5.25
5.7
5.3
5.3
5.4
5.7
0
5
10
15
20
25
30
6.2
HOMO
Voltage (V)
b)
Figure 7. Energy level diagrams for devices C and D.
25
20
15
10
5
p-OXDSiTPA, 3
hole only device
electron only device
meta-disposition2achievesamaximumcurrentefficiency(ηc,max
of 31.4 cd A−1 , a maximum power efficiency (ηp, max) of
21.0lmW−1 andamaximumexternalquantumefficiency(ηext,max
of 14.6%. In comparison, device A using para-disposition 1 as
the host exhibits higher performance with ηc.max of 35.1 cd A−1 ,
ηp.max of 26.1 lm W−1 , and ηext.max of 16.1%. The same trend
can be observed for devices C and D. Device C hosted by para-
disposition 3 displays substantially higher efficiencies (ηc.max of
36.9 cd A−1 , ηp.max of 31.4 lm W−1 , and ηext.max of 14.5%) than
device D hosted by meta-disposition 4 (ηc.max of 26.7 cd A−1 , ηp.max
)
)
0
5
10
15
20
25
30
Voltage (V)
Figure 6. Current density versus voltage characteristics of the hole-only
and electron-only devices for a) 1 and b) 3.
a)
A
B
C
104
400
(TCTA, 5 nm)/1 or 3 (20 nm)/1,3,5-tris(N-phenylbenzimidazol-
2-yl)benzene (TPBI, 40 nm)/MoO3 (40 nm)/Al (100 nm) and
electron-only devices with the configuration of ITO/TPBI
(40nm)/NPB(80nm)/TCTA(5nm)/1or3(20nm)/TPBI(40nm)/
LiF (1 nm)/Al (100 nm). For the hole-only devices, most of the
electrons can be impeded and only holes can be injected from
the anode to the organic layer, because of the large energy injec-
tion barrier between the MoO3 (LUMO = 2.3 eV) and Al (4.3 eV)
layers. In the case of the electron-only devices, the TPBI layer,
which has a low-lying HOMO level of 6.2 eV, was used to pre-
vent hole-injection from the ITO anode (4.8 eV) to the organic
layers. Figure 6a and 6b show current density versus voltage
curves of the devices for 1 and 3, respectively. It is obvious that
the two compounds are capable of transporting both electron
and hole, and exhibit bipolar transporting nature.
D
103
300
102
200
101
100
100
0
2
4
6
8
10
12
14
16
Voltage (V)
b)
100
100
10
We initially examined the performance of FIrpic-based blue
phosphorescent devices (devices A-D) with the structures of
ITO/MoO3 (10 nm)/NPB (80 nm)/TCTA (5 nm)/host 1–4:
FIrpic (8 wt%, 20 nm)/TPBI (40 nm)/LiF (1 nm)/Al (100 nm).
NPB and TPBI were used as the hole- and electron-transporting
layers, respectively; TCTA was used as electron/exciton-blocking
layer; MoO3 and LiF served as hole- and electron-injecting layer,
respectively; FIrpic doped in host 1–4 was used as the emitting
layer, respectively. Figure 7 depicts the relative energy levels
of the materials employed in the devices. Figure 8 shows the
current density–voltage–brightness (J–V–L) characteristics and
efficiency versus current density curves for the devices, and
the EL data are summarized in Table 2. Device B hosted by
10
1
1
A
B
C
D
0.1
0.01
0.01
0.1
1
10
100
Current Density (mA/cm2)
Figure 8. a) Current density-voltage-brightness characteristics for devices
A-D. b) External quantum efficiency and power efficiency versus current
density curves for devices A-D.
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T a b le 2 . Electroluminescence characteristics of the devices.a)
max [cd m−2 ] (V at Lmax, V)
17798 (14.1)
15421 (15.7)
26439 (13.7)
16870 (13.9)
48066 (10.1)
47073 (13.3)
48331 (10.9)
47574 (11.1)
47756 (13.1)
45417 (12.7)
45398 (14.5)
35770 (13.9)
ηcb) [cd A−1
]
ηpb) [lm W−1
]
ηextb) [%]
Device
Host/Guest
1/Ir-B
V
on [V]
CIE [x,y]c)
0.18, 0.32
0.17, 0.31
0.19, 0.39
0.19, 0.38
0.35, 0.62
0.36, 0.60
0.35, 0.62
0.35, 0.62
0.52, 0.48
0.51, 0.49
0.38, 0.44
0.36, 0.45
L
A
B
C
D
E
F
G
H
I
3.5
3.7
3.1
3.3
3.1
3.3
2.7
2.9
3.1
2.9
3.1
2.9
35.1, 35.1, 31.1
31.4, 31.3, 27.6
36.9, 36.9, 34.4
26.7, 26.5, 25.5
86.9, 84.7, 85.8
70.8, 67.9, 69.7
75.5, 75.3, 74.8
84.2, 81.4, 83.1
57.8, 57.3, 53.2
52.4, 52.3, 50.4
51.8, 51.7, 47.3
51.4, 46.2, 40.4
26.1, 24.5, 15.5
21.0, 20.1, 12.2
31.4, 28.3, 18.3
20.3, 18.5, 12.3
72.4, 71.8, 57.3
45.4, 45.4, 35.9
77.8, 71.6, 52.2
70.4, 69.1, 51.2
51.9, 43.9, 29.3
48.7, 44.4, 31.0
42.7, 37.8, 25.2
51.9, 35.4, 22.2
16.1, 16.1, 14.2
14.6, 14.6, 12.9
14.5, 14.5, 13.5
10.7, 10.6, 10.2
22.7, 22.1, 22.4
19.3, 18.5, 19.0
19.7, 19.6, 19.5
21.9, 21.2, 21.7
20.5, 20.4, 18.9
17.9, 17.9, 17.2
19.1, 19.1, 17.4
18.3, 16.4, 14.3
2/Ir-B
3/Ir-B
4/Ir-B
1/Ir-G
2/Ir-G
3/Ir-G
4/Ir-G
1/Ir-O
J
3/Ir-O
K
L
1/Ir-B+Ir-O
3/Ir-B+Ir-O
a)Abbreviations: Von: turn-on voltage; Lmax: maximum luminance; V: voltage; ηext: external quantum efficiency; ηc: current efficiency; ηp: power efficiency; CIE [x, y]: Commis-
;
sion International de I’Eclairage coordinates; b)Order of measured value: maximum, then values at 100 and 1000 cd m−2 c)Measured at 7 V.
of 20.3 lm W−1 , and ηext.max of 10.7%) (Table 2). These values are
a)
105
104
103
102
101
100
150
100
50
E
F
G
H
much higher than those of the comparable blue device using the
conventional host of mCP, which achieves ηc.max of 15.4 cd A−1 ,
ηp.max of 10.4 lm W−1 , and ηext.max of 6.2% (Figure S1). It is
worth noting that these devices show a low external quantum
efficiency roll-off (Figure 8b). For example, when the brightness
reaches 1000 cd m−2 , ηext still remains as high as 14.2% with a
efficiency roll-off value of 11.8% for device A, and 13.5% with
a roll-off value of 6.9% for device C. The Commission Interna-
tional de I’Eclairage (CIE) coordinates vary little for the devices
based on the same type of host; however, they vary significantly
for the devices based on the different type of host [(0.18, 0.32) for
A and (0.17, 0.31) for B; (0.19, 0.39) for C and (0.19, 0.38) for D].
This could be attributed to the recombination zone shift in
devices owing to the different charge transporting abilities of
the hosts.[24]
0
2
4
6
8
10
12
14
Voltage (V)
b)
100
10
1
100
10
To test the applicability of the hosts as a green phosphores-
cent emitter, we fabricated device E-H by using 1–4 as the hosts
and 9 wt% iridium(III) bis(2-phenylpyridinato-N,C2’) acetylac-
etonate [(ppy)2Ir(acac)] as the dopant, with an identical device
structure as device A. Figure 9 shows the J–V–L characteristics
and curves of external quantum efficiency and power efficiency
versus current density. Excellent performance of green electro-
phosphorescence can be achieved for devices E-H (Table 2). For
example, devices E and H obtain ηc.max as high as 86.9 cd A−1
(ηp.max of 72.4 lm W−1 , ηext.max of 22.7%) and 84.2 cd A−1 (ηp.max
of 70.4 lm W−1 , ηext.max of 21.9%), respectively. These values are
substantially higher than those of the comparable green device
using the host of mCP (ηc.max of 66.8 cd A−1 , ηp.max of 59.2 lm W−1 ,
and ηext.max of 17.2%, Figure S2). Remarkably, devices E and
H still exhibit over 20% external quantum efficiencies (20.6%
for device E and 20.1% for device H) at the extremely high
luminance of 10 000 cd m−2 .
1
E
F
G
H
0.1
0.01
0.01
0.1
1
10
100
Current Density (mA/cm2)
Figure 9. a) Current density-voltage-brightness characteristics for devices
E-H. b) External quantum efficiency and power efficiency versus current
density curves for devices E-H.
benzoimidazol-N,C3)iridium acetylacetonate [(fbi)2Ir(acac)] as
the dopant; these devices achieved better performances for
blue electrophosphorescence. The J–V–L characteristics and
curves of external quantum efficiency and power efficiency
versus current density are displayed in Figure 10 with the key
parameters summarized in Table 2. The turn-on voltage of
To further evaluate the suitability of the compounds as host
materials for low energy triplet emitters, we fabricated two
orange phosphorescent devices (devices I and J) by using 1
and 3 as the hosts, with the same configuration as device A but
using 8 wt% bis(2-(9,9-diethyl-9H-fluoren-2-yl)-1-phenyl-1H-
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35 770 cd m−2 at 13.9 V, 51.4 cd A−1 , 51.9 lm W−1 , and 18.3% for
device L with 3 as host. The devices efficiencies are remark-
ably higher than those of the comparable white device using
the conventional host of mCP (ηc.max of 42.6 cd A−1 , ηp.max of
24.3 lm W−1 , and ηext.max of 14.7%, Figure S4), and among the
highest for single emitting layer WOLEDs reported till now.[26]
Similar to the behavior of the orange devices, device L has
a lower turn-on voltage of 2.9 V relative to device K (3.1 V),
in consequence, device L exhibits a significantly higher
power efficiency than device K. Additionally, both devices
K and L exhibit a significantly reduced efficiency roll-off at
high brightness compared to our previously reported results
under the similar device structures using the conventional
host material of mCP,[26b] in which ηext drops to 12.3% with
a roll-off value of 36.3% at the luminance of 1000 cd m−2 ; at
the luminance of 10 000 cd m−2 , ηext declined to only 6.3%.
In this work, ηext of device K at the luminance of 1000 cd m−2
is still as high as 17.4% with a roll-off value of 8.9%; at the
extremely high luminance of 10 000 cd m−2 , ηext is still 12.2%;
while ηext of device L is 14.3% at 1000 cd m−2 and 9.7% at
10 000 cd m−2 . The high efficiencies and low efficiency roll-off at
high luminance for devices K and L can be attributed to the
use of the bipolar host which may result in balanced charge
fluxes and a broad distribution of recombination regions
within the emitting layer. In addition, devices K and L show
good color stability (Figure 11c and 11d). When the voltage
increases from 8 to 12 V, the CIE coordinates slightly vary
from (0.37, 0.43) to (0.36, 0.43) for device K, and from
(0.35, 0.45) to (0.34, 0.45) for device L. Affected by the two-
color system, the color-rendering index (CRI) of the WOLEDs
is not high (67 for device K and 60 for device L).
105
104
103
102
101
100
a)
I
J
300
200
100
0
2
4
6
8
10
12
14
Voltage (V)
b)
100
10
1
100
10
1
I
J
0.1
0.01
0.01
0.1
1
10
100
Current Density (mA/cm2)
Figure 10. a) Current density–voltage–brightness characteristics for
devices I and J. b) External quantum efficiency and power efficiency versus
current density curves for devices I and J.
device J (Von = 2.9 V) is lower relative to device I (Von = 3.1 V).
This can be attributed to the low-lying LUMO level of the host
3, which is better matched with the TPBI layer. Both devices
exhibit high performance with a rather low efficiency roll-off
at high brightness. For instance, device I exhibits ηp.max of
51.9 lm W−1 , ηext.max of 20.5%, with a external quantum effi-
ciency roll-off of 7.8% at the luminance of 1000 cd m−2 ; while
device J displays ηp.max of 48.7 lm W−1 , ηext.max of 17.9%, with a
external quantum efficiency roll-off of 3.9% at the luminance
of 1000 cd m−2 . The devices efficiencies are much higher than
those of the comparable orange device hosted by CBP (ηc.max
of 45.0 cd A−1 , ηp.max of 31.6 lm W−1 , and ηext.max of 15.8%,
Figure S3), and among the highest for orange PhOLEDs ever
reported.[25]
In terms of the applicability of the host materials for
multicolor triplet emitters, we demonstrated two-color and
all-phosphor WOLEDs (devices K and L) with the configu-
ration of ITO/MoO3 (10 nm)/NPB (80 nm)/TCTA (5 nm)/1
or 3: 8 wt% FIrpic: 0.67 wt% (fbi)2Ir(acac) (20 nm)/TPBI
(40 nm)/LiF (1 nm)/Al (100 nm). FIrpic and (fbi)2Ir(acac) were
co-doped into the bipolar host 1 or 3 as the single emitting
layer. Figure 11 shows the J–V–L characteristics and curves of
external quantum efficiency and power efficiency versus cur-
rent density. Device K with 1 as host achieves a maximum
brightness of 45 398 cd m−2 at 14.5 V, ηc.max of 51.8 cd A−1 ,
ηp.max of 42.7 lm W−1 , and ηext.max of 19.1%; these values are
3. Conclusions
In summary, we have developed a new molecular design
strategy for bipolar host material by incorporating both elec-
tron donor and acceptor into the silicon-bridged structure.
The bipolar tetraarylsilane compounds achieve a compromise
between a high triplet energy, bipolar transporting nature,
and carrier-injection barrier; therefore, these compounds can
be utilized as universal host materials for multicolor phos-
phors. We have successfully fabricated highly efficient blue,
green, orange, and white electrophosphorescence by using
the tetraarylsilane compounds as host materials. The devices
hosted by 1 achieve maximum external quantum efficien-
cies of 16.1% for blue, 22.7% for green, 20.5% for orange,
and 19.1% for white electrophosphorescence. The two-color,
all-phosphor white device hosted by 3 acquires a maximum
current efficiency of 51.4 cd A−1 , and a maximum power
efficiency of 51.9 lm W−1 , which are among the highest for
single emitting layer white PhOLEDs reported till now. We
also note that all the devices exhibit low efficiency roll-off at
high luminance. For example, the external quantum efficien-
cies of devices hosted by 1 are still as high as 14.2% for blue,
22.4% for green, 18.9% for orange and 17.4% for white elec-
trophosphorescence at a high luminance of 1000 cd m−2 . This
can be attributed to the usage of the bipolar tetraarylsilane
compounds as hosts.
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105
104
103
102
101
100
a)
c)
600
8 V, (0.37, 0.43), 4774 cd/m 2
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
K
L
10 V, (0.37, 0.43), 11940 cd/m 2
12 V, (0.36, 0.43), 24295 cd/m 2
500
400
300
200
100
0
400 450 500 550 600 650 700 750
Wavelength (nm)
2
4
6
8
10
12
14
16
Voltage (V)
b)
100
10
1
d)
8 V, (0.35, 0.45), 5623 cd/m 2
10 V, (0.34, 0.45), 13297 cd/m 2
12 V, (0.34, 0.45), 25264 cd/m 2
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
100
10
1
K
L
0.1
0.01
0.01
0.1
1
10
100
1000
400 450 500 550 600 650 700 750
Wavelength (nm)
Current Density (mA/cm2)
Figure 11. a) Current density-voltage-brightness characteristics for devices K and L. b) External quantum efficiency and power efficiency versus current
density curves for devices K and L. c) The normalized EL spectra of device K at various voltages. d) The normalized EL spectra of device L at various
voltages.
the 6–31G(d) atomic basis set. Then the electronic structures were
4. Experimental Section
General Information: 1H NMR and 13C NMR spectra were measured
calculated at τ-HCTHhyb/6–311++G(d, p) level.[29] Molecular orbitals
were visualized using Gaussview.
on a MECUYR-VX300 spectrometer. Elemental analyses of carbon,
hydrogen, and nitrogen were performed on a Vario EL III microanalyzer.
LC-Mass spectra were measured on a Waters ZQ-Mass ESI. UV-Vis
absorption spectra were recorded on a Shimadzu UV-2500 recording
spectrophotometer. PL spectra were recorded on a Hitachi F-4500
fluorescence spectrophotometer. Differential scanning calorimetry (DSC)
was performed on a NETZSCH DSC 200 PC unit at a heating rate of
10 °C min−1 from 20 to 300 °C under argon. The glass transition
temperature (Tg) was determined from the second heating scan.
Thermogravimetric analysis (TGA) was undertaken with a NETZSCH STA
449C instrument. The thermal stability of the samples under a nitrogen
atmosphere was determined by measuring their weight loss while heating
at a rate of 10 °C min−1 from 25 to 800 °C. Cyclic voltammetry (CV) was
carried out in nitrogen-purged dichloromethane (oxidation scan) at room
temperature with a CHI voltammetric analyzer. Tetrabutylammonium
hexafluorophosphate (TBAPF6) (0.1 M) was used as the supporting
electrolyte. The conventional three-electrode configuration consists of a
platinum working electrode, a platinum wire auxiliary electrode, and an
Ag wire pseudo-reference electrode with ferrocenium–ferrocene (Fc+/Fc)
as the internal standard. Cyclic voltammograms were obtained at
scan rate of 100 mV s−1 . The onset potential was determined from the
intersection of two tangents drawn at the rising and background current
of the cyclic voltammogram.
Device Fabrication and Measurement: The hole-injection material
MoO3, hole-transporting material 1,4-bis[(1-naphthylphenyl)amino]
biphenyl (NPB), electron/exciton-blocking material 4,4’,4’’-tri(N-
carbazolyl)triphenylamine (TCTA), and electron-transporting
material
1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene
(TPBI)
were commercially available. Commercial ITO (indium tin oxide)
coated glass with sheet resistance of 10 Ω per square was used
as the starting substrates. Before device fabrication, the ITO glass
substrates were pre-cleaned carefully and treated by oxygen plasma
for 2 min. Then the sample was transferred to the deposition
system. MoO3 (10 nm) was firstly deposited to ITO substrate,
followed by NPB (80 nm), TCTA (5 nm), emissive layer, and TPBI
(40 nm). Finally, a cathode composed of lithium fluoride (1 nm) and
aluminum (100 nm) was sequentially deposited onto the substrate
in the vacuum of 10−6 Torr. The L–V–J of the devices was measured
with a Keithley 2400 Source meter and a Keithley 2000 Source
multimeter equipped with a calibrated silicon photodiode. The EL
spectra were measured by JY SPEX CCD3000 spectrometer. The EQE
values were calculated according to previously reported methods.[30]
All measurements were carried out at room temperature under
ambient conditions.
Materials: 2-{4-[(4-bromophenyl)(diphenyl)silyl]phenyl}-1-phenyl-
1H-benzimidazole,
1-phenyl-1H-benzimidazole,
phenyl}-5-(4-tert-butylphenyl)-1,3,4-oxadiazole,2-{3-[(3-bromophenyl)
2-{3-[(3-bromophenyl)(diphenyl)silyl]phenyl}-
Computational Details: The geometrical and electronic properties were
performed with the Gaussian 09 program package.[27] The calculation
was optimized by means of the B3LYP (Becke three parameters hybrid
functional with Lee-Yang-Perdew correlation functionals)[28] with
2-{4-[(4-bromophenyl)(diphenyl)silyl]
(diphenyl)silyl]phenyl}-5-(4-tert-butylphenyl)-1,3,4-oxadiazole
were
prepared according to previously reported procedures.[31]
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(4-{diphenyl[4-(1-phenyl-1H-benzimidazol-2-yl)phenyl]silyl}phenyl)
diphenylamine (1): A mixture of 2-{4-[(4-bromophenyl)(diphenyl)silyl]
phenyl}-1-phenyl-1H-benzimidazole (1.82 g, 3.00 mmol), diphenylamine
(0.54 g, 3.20 mmol), Pd(OAc)2 (13 mg, 0,06 mmol), tBuONa (0.35 g,
3.60 mmol), (tBu)3PHBF4 (52 mg, 0.18 mmol), and toluene (20 mL) was
refluxed under argon for 18 h. After cooling, the mixture was extracted
with CH2Cl2, and the organic layer was dried over anhydrous Na2SO4.
After removal of the solvent, the residue was purified by column
chromatography on silica gel using ethyl acetate/petroleum (1:5 by vol.)
as the eluent to give a white powder. Yield: 72%. 1H NMR (300 MHz,
CDCl3) δ [ppm]: 8.35 (d, J = 8.1 Hz, 1H), 7.80 (d, J = 8.1 Hz, 2H), 7.67–7.57
(m, 6H), 7.52–7.34 (m, 12H), 7.32–7.27 (m, 8H), 7.14 (d, J = 7.8 Hz, 4H),
7.07–7.00 (m, 4H). 13C NMR (75 MHz, CDCl3) δ [ppm]: 152.28, 149.45,
147.52, 142.69, 137.52, 137.42, 137.16, 137.02, 136.63, 134.35, 130.74,
130.25, 129.93, 129.62, 129.06, 128.82, 128.17, 127.67, 125.44, 123.90,
123.77, 123.54, 121.75, 119.99, 110.84. MS (ESI): m/z 696 [M + H]+.
Anal. calcd for C49H37N3Si (%): C 84.57, H 5.36, N 6.04; found: C 84.72,
H 5.12, N 5.95.
(3-{diphenyl[3-(1-phenyl-1H-benzimidazol-2-yl)phenyl]silyl}phenyl)
diphenylamine (2): 2 was prepared according to the same procedure as
1 but using 2-{3-[(3-bromophenyl)(diphenyl)silyl]phenyl}-1-phenyl-1H-
benzimidazole. Yield: 74%. 1H NMR (300 MHz, CDCl3) δ [ppm]: 7.86
(d, J = 7.5 Hz, 2H), 7.51–7.46 (m, 2H), 7.39–7.37 (m, 4H), 7.32–7.22
(m, 13H), 7.18–7.07 (m, 8H), 7.04 (d, J = 8.1 Hz, 4H), 6.97–6.91 (m,
4H). 13C NMR (75 MHz, CDCl3) δ [ppm]: 153.10, 148.12, 147.79, 143.40,
137.86, 137.57, 137.50, 137.16, 136.80, 135.15, 134.95, 133.94, 132.19,
131.59, 131.03, 130.22, 130.11, 129.93, 129.71, 129.42, 128.78, 128.66,
128.39, 127.67, 125.75, 124.59, 123.92, 123.58, 123.26, 120.34, 111.02.
MS (ESI): m/z 696 [M + H]+. Anal. calcd for C49H37N3Si (%): C 84.57, H
5.36, N 6.04; found: C 84.76, H 5.34, N 6.03.
of China (973 Program 2009CB623602 and 2009CB930603), the Open
Research Fund of State Key Laboratory of Polymer Physics and Chemistry,
Changchun Institute of Applied Chemistry, Chinese Academy of Sciences,
and the Fundamental Research Funds for the Central Universities of
China for financial support.
Received: September 30, 2010
Revised: November 21, 2010
Published online: February 10, 2011
[1] M. A. Baldo, D. F. O’Brien, Y. You, A. Shoustikov, S. Sibley,
M. E. Thompson, S. R. Forrest, Nature 1998, 395, 151.
[2] a) M. A. Baldo, S. Lamansky, P. E. Burrows, M. E. Thompson,
S. R. Forrest, Appl. Phys. Lett. 1999, 75, 4; b) X. Yang, D. Neher,
in Organic Light Emitting Devices (Eds.: K. Müllen, U. Scherf),
Wiley-VCH, Weinheim, 2006, pp. 333–367.
[3] a) A. Köhler, J. Wilson, R. Friend, Adv. Mater. 2002, 14, 701;
b) T. Tsuzuki, S. Tokito, Adv. Mater. 2007, 19, 276; c) S.-J. Su,
E. Gonmori, H. Sasabe, J. Kido, Adv. Mater. 2008, 20, 4189.
[4] a) H. Sasabe, T. Chiba, S.-J. Su, Y.-J. Pu, K.-I. Nakayama, J. Kido,
Chem. Commun. 2008, 5821; b) Y. Tao, Q. Wang, C. Yang, C. Zhong,
K. Zhang, J. Qin, D. Ma, Adv. Funct. Mater. 2010, 20, 304.
[5] a) C. Adachi, M. A. Baldo, M. E. Thompson, S. R. Forrest, J. Appl.
Phys. 2001, 90, 5048; b) Y. Z. Li, W. J. Xu, G. Z. Ran, G. G. Qin, Appl.
Phys. Lett. 2009, 95, 033307.
[6] a) C.-H. Chien, F.-M. Hsu, C.-F. Shu, Y. Chi, Org. Electron. 2009, 10,
871; b) Y. Tao, Q. Wang, L. Ao, C. Zhong, J. Qin, C. Yang, D. Ma, J.
Mater. Chem. 2010, 20, 1759.
{4-[{4-[5-(4-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]phenyl}(diphenyl)
silyl]phenyl}diphenylamine (3): 3 was prepared according to the same
procedure as 1 but using 2-{4-[(4-bromophenyl)(diphenyl)silyl]phenyl}-
5-(4-tert-butylphenyl)-1,3,4-oxadiazole. Yield: 73%. 1H NMR (300 MHz,
CDCl3) δ [ppm]: 8.13 (d, J = 7.5 Hz, 2H), 8.06 (d, J = 8.4 Hz, 2H), 7.75
(d, J = 8.1 Hz, 2H), 7.60–7.54 (m, 6H), 7.46–7.38 (m, 8H), 7.30–7.25
(m, 4H), 7.15 (d, J = 7.8 Hz, 4H), 7.06–7.03 (m, 4H), 1.37 (s, 9H). 13C
NMR (75 MHz, CDCl3) δ [ppm]: 164.60, 164.27, 155.26, 149.19, 147.08,
139.67, 137.10, 136.80, 136.19, 133.68, 129.69, 129.23, 127.88, 126.66,
125.96, 125.81, 125.08, 124.65, 123.43, 121.35, 120.96, 34.97, 31.00. MS
(ESI): m/z 704 [M + H]+. Anal. calcd for C48H41N3OSi (%): C 81.90, H
5.87, N 5.97; found: C 82.11, H 5.73, N 5.86.
{3-[{3-[5-(4-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]phenyl}(diphenyl)
silyl]phenyl}diphenylamine (4): 4 was prepared according to the same
procedure as 1 but using 2-{3-[(3-bromophenyl)(diphenyl)silyl]phenyl}-
5-(4-tert-butylphenyl)-1,3,4-oxadiazole. Yield: 80%. 1H NMR (300 MHz,
CDCl3) δ [ppm]: 8.26 (s, 1H), 8.18 (d, J = 7.8 Hz, 1H), 8.00 (d, J = 8.1 Hz,
2H), 7.67 (d, J = 7.2 Hz, 1H), 7.55–7.35 (m, 14H), 7.30–7.25 (m, 2H),
7.17–7.15 (m, 5H), 7.07 (d, J = 7.8 Hz, 4H), 6.97–6.92 (m, 2H), 1.36 (s,
9H). 13C NMR (75 MHz, CDCl3) δ [ppm]: 164.96, 164.72, 155.62, 147.84,
147.81, 139.78, 136.72, 136.63, 136.33, 134.67, 134.64, 133.55, 131.74,
130.62, 130.22, 129.52, 129.36, 128.86, 128.37, 127.10, 126.40, 125.42,
124.55, 123.93, 123.13, 121.40, 35.41, 31.48. MS (ESI): m/z 704 [M +
H]+. Anal. calcd for C48H41N3OSi (%): C 81.90, H 5.87, N 5.97; found: C
82.28, H 5.65, N 6.06.
[7] M. A. Baldo, C. Adachi, S. R. Forrest, Phys. Rev. B: Condens. Matter
Mater. Phys. 2000, 62, 10967.
[8] a) A. B. Padmaperuma, L. S. Sapochak, P. E. Burrows, Chem. Mater.
2006, 18, 2389; b) S.-J. Su, H. Sasabe, T. Takeda, J. Kido, Chem.
Mater. 2008, 20, 1691.
[9] a) R. J. Holmes, B. W. D’Andrade, S. R. Forrest, X. Ren, J. Li,
M. E. Thompson, Appl. Phys. Lett. 2003, 83, 3818; b) Z. Q. Gao,
M. Luo, X. H. Sun, H. L. Tam, M. S. Wong, B. X. Mi, P. F. Xia,
K. W. Cheah, C. H. Chen, Adv. Mater. 2009, 21, 688.
[10] a) S.-J. Yeh, M.-F. Wu, C.-T. Chen, Y.-H. Song, Y. Chi, M.-H. Ho,
S.-F. Hsu, C. H. Chen, Adv. Mater. 2005, 17, 285; b) M.-H. Tsai,
Y.-H. Hong, C.-H. Chang, H.-C. Su, C.-C. Wu, A. Matoliukstyte,
J. Simokaitiene, S. Grigalevicius, J. V. Grazulevicius, C.-P. Hsu, Adv.
Mater. 2007, 19, 862.
[11] a) J. Ding, B. Zhang, J. Lü, Z. Xie, L. Wang, X. Jing, F. Wang, Adv.
Mater. 2009, 21, 4983; b) S. Ye, Y. Liu, J. Chen, K. Lu, W. Wu, C. Du,
Y. Liu, T. Wu, Z. Shuai, G. Yu, Adv. Mater. 2010, 22, 4167.
[12] X. Ren, J. Li, R. J. Holmes, P. I. Djurovich, S. R. Forrest,
M. E. Thompson, Chem. Mater. 2004, 16, 4743.
[13] M.-H. Tsai, H.-W. Lin, H.-C. Su, T.-H. Ke, C.-c. Wu, F.-C. Fang,
Y.-L. Liao, K.-T. Wong, C.-I. Wu, Adv. Mater. 2006, 18, 1216.
[14] M.-F. Wu, S.-J. Yeh, C.-T. Chen, H. Murayama, T. Tsuboi, W.-S. Li,
I. Chao, S.-W. Liu, J.-K. Wang, Adv. Funct. Mater. 2007, 17, 1887.
[15] a) Y. Tao, Q. Wang, C. Yang, Q. Wang, Z. Zhang, T. Zou, J. Qin,
D. Ma, Angew. Chem. Int. Ed. 2008, 47, 8104; b) S.-y. Takizawa,
V. A. Montes, P. Anzenbacher, Jr., Chem. Mater. 2009, 21,
2452.
Supporting Information
[16] a) F.-M. Hsu, C.-H. Chien, C.-F. Shu, C.-H. Lai, C.-C. Hsieh,
K.-W. Wang, P.-T. Chou, Adv. Funct. Mater. 2009, 19, 2834;
b) H.-H. Chou, C.-H. Cheng, Adv. Mater. 2010, 22, 2468.
[17] J. F. Hartwig, Acc. Chem. Res. 1998, 31, 852.
Supporting Information is available from the Wiley Online Library or
from the author.
[18] a) C.-H. Chen, W.-S. Huang, M.-Y. Lai, W.-C. Tsao, J. T. Lin, Y.-H. Wu,
T.-H. Ke, L.-Y. Chen, C.-C. Wu, Adv. Funct. Mater. 2009, 19, 2661;
b) Y. Tao, Q. Wang, Y. Shang, C. Yang, L. Ao, J. Qin, D. Ma, Z. Shuai,
Chem. Commun. 2009, 77.
Acknowledgements
We thank the National Natural Science Foundation of China (Project
Nos. 90922020 and 50773057), the National Basic Research Program
[19] D.-R. Bai, X.-Y. Liu, S. Wang, Chem. Eur. J. 2007, 13, 5713.
©
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Adv. Funct. Mater. 2011, 21, 1168–1178
2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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[20] R. J. Holmes, S. R. Forrest, Y. J. Tung, R. C. Kwong, J. J. Brown,
S. Garon, M. E. Thompson, Appl. Phys. Lett. 2003, 82, 2422.
[21] P.-I. Shih, C.-H. Chien, F.-I. Wu, C.-F. Shu, Adv. Funct. Mater. 2007,
17, 3514.
[22] M. E. Kondakova, T. D. Pawlik, R. H. Young, D. J. Giesen,
D. Y. Kondakov, C. T. Brown, J. C. Deaton, J. R. Lenhard, K. P. Klubek,
J. Appl. Phys. 2008, 104, 094501.
[23] Z. Ge, T. Hayakawa, S. Ando, M. Ueda, T. Akiike, H. Miyamoto,
T. Kajita, M.-a. Kakimoto, Adv. Funct. Mater. 2008, 18,
584.
[24] a) S. O. Jeon, K. S. Yook, C. W. Joo, J. Y. Lee, Appl. Phys. Lett. 2009,
94, 013301; b) J. Lee, J.-I. Lee, J. Y. Lee, H. Y. Chu, Org. Electron.
2009, 10, 1529.
X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng,
J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda,
J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao,
H. Nakai, T. Vreven, J. A. Montgomery, Jr., J. E. Peralta, F. Ogliaro,
M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov,
R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J. C. Burant,
S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene,
J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo,
R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi,
C.Pomelli,J.W.Ochterski,R.L.Martin,K.Morokuma,V.G.Zakrzewski,
G. A. Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels,
O. Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski, D. J. Fox,
Gaussian Inc., Wallingford CT, 2009.
[25] a) C.-L. Ho, W.-Y. Wong, Q. Wang, D. Ma, L. Wang, Z. Lin, Adv.
Funct. Mater. 2008, 18, 928; b) Y. Tao, Q. Wang, C. Yang, C. Zhong,
J. Qin, D. Ma, Adv. Funct. Mater. 2010, 20, 2923.
[26] a) J. Lee, J.-I. Lee, J. Y. Lee, H. Y. Chu, Appl. Phys. Lett. 2009, 94,
193305; b) Q. Wang, J. Ding, D. Ma, Y. Cheng, L. Wang, X. Jing,
F. Wang, Adv. Funct. Mater. 2009, 19, 84.
[27] Gaussian 09, Revision A.01, M. J. Frisch, G. W. Trucks, H. B. Schlegel,
G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani,
V. Barone, B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato,
[28] a) A. D. Becke, Phys. Rev. A 1988, 38, 3098; b) C. Lee, W. Yang,
R. G. Parr, Phys. Rev. B 1988, 37, 785.
[29] A. D. Boese, N. C. Handy, J. Chem. Phys. 2002, 116, 9559.
[30] S. R. Forrest, D. D. C. Bradley, M. E. Thompson, Adv. Mater. 2003,
15, 1043.
[31] a) Z. Ge, T. Hayakawa, S. Ando, M. Ueda, T. Akiike, H. Miyamoto,
T. Kajita, M.-a. Kakimoto, Chem. Mater. 2008, 20, 2532; b) X. Zheng,
Z. Li, Y. Wang, W. Chen, Q. Huang, C. Liu, G. Song, J. Fluorine Chem.
2003, 123, 163.
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