Synthesis of fused phenylcarbazole phosphine oxide based high triplet energy host materials

Article abstract of DOI:10.1016/j.tet.2010.07.008

High triplet energy host materials based on novel fused phenylcarbazole core structure and diphenylphosphine oxide were synthesized and the physical properties of the host materials were investigated. A high triplet energy of 2.95 eV was obtained from the fused phenylcarbazole based host materials and the energy levels could be manipulated using the diphenylphosphine oxide group. The fused phenylcarbazole based high triplet energy host materials showed excellent morphological stability at high temperature. High triplet energy host materials based on novel fused phenylcarbazole core structure and diphenylphosphine oxide were synthesized and a high triplet energy of 2.95 eV could be obtained from the host materials.

Full text of DOI:10.1016/j.tet.2010.07.008

Tetrahedron 66 (2010) 7295e7301
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Tetrahedron
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Synthesis of fused phenylcarbazole phosphine oxide based high triplet
energy host materials
*
Soon Ok Jeon, Jun Yeob Lee
Department of Polymer Science and Engineering, Dankook University, 126, Jukjeon-dong, Suji-gu, Yongin-si, Gyeonggi-do 448-701, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
High triplet energy host materials based on novel fused phenylcarbazole core structure and diphenyl-
phosphine oxide were synthesized and the physical properties of the host materials were investigated.
A high triplet energy of 2.95 eV was obtained from the fused phenylcarbazole based host materials and
the energy levels could be manipulated using the diphenylphosphine oxide group. The fused phenyl-
carbazole based high triplet energy host materials showed excellent morphological stability at high
temperature.
Received 26 April 2010
Received in revised form 1 July 2010
Accepted 2 July 2010
Available online 14 July 2010
Keywords:
Ó 2010 Elsevier Ltd. All rights reserved.
Fused phenylcarbazole
High triplet energy
Phosphine oxide
Morphological stability
1. Introduction
were also developed and high quantum efficiency was reported in
the deep blue PHOLED.11,18 Silane type materials were also effective
Phosphorescent organic light-emitting diodes (PHOLEDs) are
better than fluorescent organic light-emitting diodes (OLEDs) in
terms of quantum efficiency.1e11 Theoretically, PHOLEDs show four
times higher quantum efficiency than fluorescent OLEDs as the
triplet excited state as well as the singlet excited state can
contribute to the light emission. Therefore, there have been many
researches about PHOLEDs. In particular, many recent researches
were devoted to the development of deep blue PHOLEDs as the
quantum efficiency of deep blue PHOLEDs is still not high compared
with that of red or green PHOLEDs.11e15
The quantum efficiency of deep blue PHOLEDs is mainly de-
termined by the host and dopant materials in the emitting layer.
The host should have high triplet energy for an energy transfer to
the dopant and have proper energy levels for charge injection from
charge transport layers. The management of the highest occupied
molecular orbital (HOMO) and the lowest unoccupied molecular
orbital (LUMO) of the host material as well as the triplet energy
level was carried out using various core structures. carbazole type
core structures were found to be useful to obtain high triplet energy
and several derivatives with the carbazole core structure were
developed.5,16,17 N,N-Dicarbazolyl-3,5-benzene is one of carbazole
derivatives with the high triplet energy of 2.9 eV.5 Recently, car-
bazole type host materials with diphenylphosphine oxide groups
as high triplet energy materials for deep blue PHOLEDs even
though the hole injection was difficult due to the deep HOMO level
of the Si based host material.7,8
In this work, a fused phenylcarbazole type core structure was
developed as a high triplet energy core structure with good ther-
mal/morphological stability and the physical properties of the host
materials modified with diphenylphosphine oxide were in-
vestigated. It was demonstrated that high triplet energy of 2.95 eV
for deep blue PHOLED application could be obtained using the
fused phenylcarbazole core structure, and stable morphological
and thermal stability could be realized in the fused phenylcarbazole
based host materials.
2. Experimental
2.1. Synthesis
2.1.1. Synthesis of 9-(2-bromophenyl)-9H-carbazole (1). 9-Carbazole
(14.77 g, 88.3 mmol), 2-bromoiodobenzene (50 g, 176 mmol), cup-
per iodide (8.41 g, 44.1 mmol), and potassium carbonate (24.32 g,
176 mmol) were dissolved in anhydrous xylene under nitrogen
atmosphere. The reaction mixture was stirred for 12 h at 120 ꢀC.
The mixture was diluted with dichloromethane and washed with
distilled water (100 mL) three times. The organic layer was dried
over anhydrous MgSO4 and evaporated in vacuo to give the crude
product, which was purified by column chromatography using
* Corresponding author. Tel./fax: þ82 31 8005 3585; e-mail address: leej17@
dankook.ac.kr (J.Y. Lee).
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.07.008

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S.O. Jeon, J.Y. Lee / Tetrahedron 66 (2010) 7295e7301
n-hexane as an eluent and recrystallized by methanol. The final
white powdery product was obtained in 45% yield.
(4-bromophenyl)-8H-indolo[3,2,1-de]acridine
(3)
(2.5 g,
3.53 mmol) in THF (20 mL). The reaction flask was cooled to ꢁ78 ꢀC
and n-BuLi (2.5 M in hexane, 3.53 mL) was added dropwise slowly.
The whole solution was stirred for 3 h followed by addition of
a solution of chlorodiphenylphophine (1.95 g, 8.84 mmol) under
argon atmosphere. The resulting mixture was gradually warmed to
ambient temperature and quenched by methanol (7 mL). The
mixture was extracted with dichloromethane. The combined or-
ganic layers were dried over magnesium sulfate, filtered, and
evaporated under reduced pressure. The white powdery product
was obtained to 1.7 g (62%). It was dissolved in dichloromethane
(20 mL) and hydrogen peroxide (4 mL), which was stirred over-
night at room temperature. The organic layer was separated and
washed with dichloromethane and water. The extract was evapo-
rated to dryness affording a white solid, which was further purified
by column chromatography to yield 1.18 g of chemically pure
SPCPO2.
2.1.2. Synthesis of 8,8-diphenyl-8H-indolo[3,2,1-de]acridine (SPC). 9-
(2-Bromophenyl)-9H-carbazole (1) (2.1 g, 6.6 mmol) was dissolved
in 20 mL of anhydrous tetrahydrofuran under argon and cooled to
ꢁ78 ꢀC and n-butyllithium (2.5 M in hexanes, 3.4 mL) was added
dropwise slowly. Stirring was continued for 2 h at ꢁ78 ꢀC, followed
by the addition of a solution of benzophenone (1.5 g, 8.5 mmol) in
THF (10 mL) under an argon atmosphere. The resulting mixture was
gradually warmed to ambient temperature and quenched by adding
saturated, aqueous NaHCO3 (20 mL). The mixture was extracted
with dichloromethane. The combined organic layers were dried
over magnesium sulfate, filtered, and evaporated under reduced
pressure. A yellow powdery product was obtained. The crude resi-
due was placed in another two-necked flask was dissolved in acetic
acid (20 mL). A catalytic amount of aqueous HCl (5 mol %, 12 N) was
then added and the whole solution was refluxed for 12 h. After
cooling to ambient temperature, purification by silica gel chroma-
tography using dichloromethane/n-hexane gave a white powder.
SPC yield 70%, mp 248 ꢀC. Tg 84.9 ꢀC. 1H NMR (200 MHz, CDCl3):
SPCPO2 yield 62%, Tg 153.1 ꢀC. 1H NMR (200 MHz, CDCl3):
d
8.15e8.09 (t, 3H), 7.97e7.93 (d, 1H), 7.69e7.60 (m, 7H), 7.49e7.26
(m, 21H), 7.16e7.06 (m, 5H), 7.00e6.96 (m, 2H). 13C NMR (200 MHz,
CDCl3): 149.905, 138.736, 137.571, 137.085, 133.297, 132.617,
d
d
8.14e8.07 (t, 2H), 7.94e7.91 (d, 1H), 7.59e7.48 (t, 1H), 7.42e7.19
131.452, 130.772, 129.704, 129.315, 129.024, 128.830, 128.150,
127.955, 127.276, 126.790, 126.499, 126.110, 125.772, 124.945,
123.682, 123.196, 122.419, 122.128, 121.060, 120.865, 119.409,
118.243,115.135,114.455,113.970,113.290, 57.347. MS (FAB) m/z 808
[(MþH)þ]. Anal. Calcd for C55H39NO2P2: C, 81.77; H, 4.87; N, 1.73.
Found: C, 81.02; H, 5.06; N, 1.87.
(m, 11H), 7.07e7.03 (m, 7H). 13C NMR (200 MHz, CDCl3):
d
146.409,
138.930, 137.862, 137.182, 132.423, 131.646, 130.966, 129.898,
128.538, 128.247, 127.470, 126.207, 123.488, 122.905, 121.934,
120.865, 118.923, 117.758, 115.329, 114.067, 112.998, 67.739, 57.347.
MS (FAB) m/z 407 [(MþH)þ]. Anal. Calcd for C31H21N: C, 91.37; H,
5.19; N, 3.44. Found: C, 90.92; H, 5.19; N, 3.72.
2.1.5. Measurements. The 1H and 13C nuclear magnetic resonance
(NMR) were recorded on a Varian 200 (200 MHz) spectrometer and
the mass spectra were recorded using a JEOL, JMS-AX505WA
spectrometer in FAB mode. Ultraviolet-visible (UVevis) and pho-
toluminescence (PL) spectra of the SPCPO1 and SPCPO2 were
obtained from UVevis spectrophotometer (Shimadzu, UV-2501PC)
and fluorescence spectrophotometer (HITAXHI, F-7000). The en-
ergy level of the SPCPO1 and SPCPO2 was measured with a cyclic
voltameter. Glass transition temperature (Tg) measurements of the
SPCPO1 and SPCPO2 were carried out using differential scanning
calorimeter (Mettler DSC 822) at a heating rate of 10 ꢀC/min under
nitrogen atmosphere.
Hole only devices with a device configuration of indium tin
oxide (100 nm)/SPCPO1 or SPCPO2 (100 nm)/Au (100 nm) and
electron only device with a device configuration of indium tin oxide
(100 nm)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (5 nm)/
SPCPO1 or SPCPO2 (100 nm)/LiF (1 nm)/Al (100 nm).
2.1.3. Synthesis of 8-(4-(diphenylphosphoryl)phenyl)-8-phenyl-8H-
indolo[3,2,1-de]acridine (SPCPO1). Intermediate compound 2 was
synthesized according to the same synthetic procedure as the SPC
except that 4-bromobenzophenone was used instead of benzo-
phenone. Into a 100 mL, two-neck flask, was placed a 8-(4-bromo-
phenyl)-8-phenyl-8H-indolo[3,2,1-de]acridine (2) (2.0 g, 4.1 mmol)
in THF (20 mL). The reaction flask was cooled to ꢁ78 ꢀC and n-BuLi
(2.5 M in hexane, 2.13 mL) was added dropwise slowly. The whole
solutionwas stirred at this temperature for 3 h, followed by addition
of a solution of chlorodiphenylphophine (1.17 g, 5.34 mmol) under
argon atmosphere. The resulting mixture was gradually warmed to
ambient temperature and quenched by methanol (7 mL). The mix-
ture was extracted with dichloromethane. The combined organic
layers were dried over magnesium sulfate, filtered, and evaporated
under reduced pressure. A white powdery product was obtained to
1.21 g (50%). It was dissolved in dichloromethane (20 mL) and hy-
drogen peroxide (4 mL), which was stirred overnight at room
temperature. The organic layer was separated and washed with
dichloromethane and water. The extract was evaporated to dryness
affording a white solid, which was further purified by column
chromatography to yield 1.19 g of chemically pure SPCPO1.
3. Results and discussion
The fused phenylcarbazole unit was designed as a core structure,
which has a high triplet energy and thermal/morphological stability.
The fused phenylcarbazole unit can be synthesized by ring closing
reaction of the 9-(2-bromophenyl)-9H-carbazole with diphenylke-
tone derivatives as shown in Scheme 1. In this work, 4-bromo-
benzophenone and 4,40-dibromobenzophenone were reacted with
the 1 to synthesize the SPCPO1 and SPCPO2. The brominated fused
phenylcarbazole compounds, 2 and 3, were modified with diphe-
nylphosphine oxide to synthesize high triplet energy bipolar host
materials as the diphenylphosphine oxide has electron transport
properties compared with the hole transport type fused phenyl-
carbazole core unit.11,18e20 The SPCPO1 and SPCPO2 could be suc-
cessively synthesized by the ring closing reaction followed by the
phosphonation reaction and a high purity over 99% could be
obtained after purification by column chromatography.
SPCPO1 yield 50%, Tg 126.4 ꢀC. 1H NMR (200 MHz, CDCl3):
d
8.15e8.09 (m, 3H), 7.96e7.92 (d, 1H), 7.69e7.60 (m, 4H), 7.55e7.29
(m, 12), 7.26e7.22 (m, 4H), 7.17e7.04 (m, 6H). 13C NMR (200 MHz,
CDCl3): 150.488, 145.826, 138.736, 137.085, 133.492, 132.617,
d
132.035, 131.452, 130.966, 129.898, 129.218, 129.024, 128.538,
128.150, 127.858, 127.470, 126.790, 126.402, 126.013, 123.585,
123.002, 122.225, 121.934, 120.768, 119.117, 117.952, 115.135,
114.261, 113.970, 113.096, 57.250. MS (FAB) m/z 608 [(MþH)þ]. Anal.
Calcd for C43H30NOP: C, 84.99; H, 4.98; N, 2.30. Found: C, 82.33; H,
4.96; N, 2.34.
2.1.4. Synthesis of 8,8-bis(4-(diphenylphosphoryl)phenyl)-8H-indolo
[3,2,1-de]acridine (SPCPO2). Intermediate compound 3 was syn-
thesized according to the same synthetic procedure as the SPC
except that 4,40-dibromobenzophenone was used instead of
benzophenone. Into a 100 mL two-neck flask, was placed a 8,8-bis
Molecular simulation of the SPCPO1 and SPCPO2 was carried
out to understand the molecular orbital distribution in the two host
materials. Density functional theory (DFT) calculations were

S.O. Jeon, J.Y. Lee / Tetrahedron 66 (2010) 7295e7301
7297
O
N
H+
N
OH
SPC
N
O
I
Br
N
H+
H
Br
Br
n-BuLi
Li
OH
N
N
N
Amination
Br
Br
2
1
O
N
N
H+
Br
Br
OH
Br
Br
Br
Br
3
N
N
N
N
CH2Cl2
H2O2
n-BuLi
P Cl
N
N
CH2Cl2
H2O2
n-BuLi
O
P
O
P
P Cl
O
P
P
P
Br
Br
P
Br
SPCPO 1
SPCPO 2
Scheme 1. Synthetic scheme of SPCPO1 and SPCPO2.
performed using a suite of Gaussian 03 program. The nonlocal
density functional of Becke’s 3-parameters employing Leee
orbital (HOMO) and the lowest unoccupied molecular orbital
(LUMO) distribution of the SPCPO1 and SPCPO2. The HOMO was
mainly distributed over the phenylcarbazole unit of the fused
phenylcarbazole, while the LUMO was dispersed over the whole
YangeParr functional (B3LYP) with 6-31G
*
basis sets was used for
the calculation. Figure 1 shows the highest occupied molecular
Figure 1. Simulated HOMO and LUMO distribution of the SPCPO1 and SPCPO2.

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S.O. Jeon, J.Y. Lee / Tetrahedron 66 (2010) 7295e7301
fused phenylcarbazole structure. The LUMO orbital was rather
dispersed in the SPCPO1 and SPCPO2 as the diphenylphosphine
oxide group has strong electron withdrawing character. Comparing
the orbital distribution of the SPCPO1 and SPCPO2, the HOMO was
more localized in the phenylcarbazole unit and the LUMO was more
dispersed in the fused phenylcarbazole unit in the SPCPO2. The
difference of the orbital distribution affected the simulated HOMO
and LUMO levels of the host materials and 0.1 eV energy level shift
downward from the vacuum level was observed in the SPCPO2
compared with SPCPO1 due to the additional diphenylphosphine
oxide group.
UVevis and PL measurements of the SPCPO1 and SPCPO2 were
carried out to study the light absorption and emission properties of
the host materials. UVevis and PL spectra of host materials are
shown in Figure 2. The SPCPO1 and SPCPO2 showed similar
UVevis absorption spectra and two main absorption peaks
assigned to the absorption of the fused phenylcarbazole unit were
observed at 293 nm and 350 nm. The emission peaks of the SPCPO1
and SPCPO2 appeared at 367 nm and 368 nm, respectively. The
HOMO and LUMO were mostly distributed over the fused phenyl-
carbazole unit with little contribution of the diphenylphosphine
oxide group. Therefore, UVevis light was absorbed by the fused
phenylcarbazole core and light emission was also induced from the
fused phenylcarbazole core by UVevis excitation. As the light ab-
sorption and emission happened in the fused phenylcarbazole core
structure, the SPCPO1 and SPCPO2 showed similar UVevis and
emission spectra in spite of different chemical structures. The
bandgap of the SPCPO1 and SPCPO2 could be calculated from the
absorption edge of the UVevis absorption spectra and the bandg-
aps were 3.41 eV and 3.40 eV, respectively. Low temperature PL
measurement of the SPCPO1 and SPCPO2 was also carried out to
obtain the triplet energy of the host materials. The triplet energy of
the two host materials was the same and it was 2.95 eV. It has been
known that the triplet energy of the carbazole core is 3.02 eV and
there was only 0.07 eV decrease of the triplet energy in the SPCPO1
and SPCPO2.21 The high triplet energy of the fused phenylcarbazole
based host materials can be explained by the distorted chemical
structure of spiro connecting unit. The fused phenylcarbazole has
a sp3 carbon atom between the phenylcarbazole and diphenyl unit.
The sp3 carbon separates the phenylcarbazole and phenyl units and
does not extend the conjugation of the phenylcarbazole group.
Therefore, the high triplet energy of the phenylcarbazole unit could
be maintained in the SPCPO1 and SPCPO2 host materials. The
0.07 eV reduction of the triplet energy is originated from the geo-
metrical structure of the phenyl unit in the phenylcarbazole core.
Figure 3 shows the geometrical structure of the SPCPO1 and
3-(diphenylphosphoryl)-9-phenyl-9H-carbazole. The triplet energy
of the PPO1 was 3.02 eV. The angle between the phenyl unit and
carbazole is 28.8ꢀ in the fused phenylcarbazole, while it was 56.3ꢀ
of common phenylcarbazole group. The reduced angle between the
phenyl and carbazole planes of the fused phenylcarbazole slightly
increases the conjugation between the phenyl group in the phe-
nylcarbazole and carbazole unit, resulting in the reduced triplet
energy in SPCPO1. However, the triplet energy of two host mate-
rials was high enough for application as host materials in deep blue
PHOLEDs as the triplet energy of common deep blue emitting
phosphorescent dopant is around 2.8 eV.
Figure 3. Geometrical structure of SPCPO1 compared with phenylcarbazolephosphine
oxide (3-(diphenylphosphoryl)-9-phenyl-9H-carbazole). The angle between the phe-
nyl plane and carbazole plane is shown.
The HOMO levels of SPCPO1 and SPCPO2 were measured with
CV and the LUMO levels were calculated from the HOMO and ab-
sorption edge of UVevis spectra. The HOMO levels of the SPCPO1
and SPCPO2 were ꢁ6.08 eV and ꢁ6.11 eV, respectively. The HOMO
level of the SPCPO2 was shifted by 0.03 eV compared with that of
the SPCPO1. The HOMO level shift of 0.03 eV is due to the addi-
tional diphenylphosphine oxide group with electron withdrawing
character. The LUMO level was also shifted by 0.04 eV by the
phosphine oxide group. All physical properties of the SPCPO1 and
SPCPO2 are summarized in Table 1.
The fused phenylcarbazole core has a rigid structure as the ro-
tation of the phenyl group in the phenylcarbazole is limited by the
spiro structure. The rigidity of the fused phenylcarbazole core may
improve the Tg of the host materials. In addition, the diphenyl-
phosphine group can also improve the Tg of the host materials.20
Figure 2. Uvevis absorption, photoluminescence and low temperature photolumin-
escence spectra of the SPCPO1 (a) and SPCPO2 (b).
Figure
4 shows DSC thermograms of SPCPO1 and SPCPO2

S.O. Jeon, J.Y. Lee / Tetrahedron 66 (2010) 7295e7301
7299
Table 1
Physical properties of SPCPO1 and SPCPO2
Optical analysis
Absorption (nm)
Thermal analysis
Electrical analysis
Emission (nm)
Tg (ꢀC)
Tm (ꢀC)
HOMO (eV)
LUMO (eV)
Bandgap (eV)
ET (eV)
SPCPO1
SPCPO2
293, 350
294, 350
367
368
126
153
d
d
ꢁ6.08
ꢁ6.11
ꢁ2.67
ꢁ2.71
3.41
3.40
2.95
2.95
compared with that of the fused phenylcarbazole core. The fused
phenylcarbazole core showed a Tg of 85 ꢀC and Tm of 248 ꢀC. The Tg
of the SPCPO1 and SPCPO2 was greatly improved by the diphe-
nylphosphine oxide group and the Tgs of the SPCPO1 and SPCPO2
were 127 ꢀC and 153 ꢀC, respectively. Tm was not observed up to
400 ꢀC. The diphenylphosphine oxide group hinders the close
packing of the fused phenylcarbazole core, suppressing the crys-
tallization of the SPCPO1 and SPCPO2. Therefore, it is expected that
the SPCPO1 and SPCPO2 form a stable amorphous morphology.
The surface morphology of the SPCPO1 and SPCPO2 on silicon
wafer was measured with AFM and AFM pictures of the SPCPO1
and SPCPO2 compared with SPC are shown in Figure 5. The
SPCPO1 and SPCPO2 showed smooth surface morphology without
any aggregation or crystallization and the surface roughness of the
SPCPO1 and SPCPO2 was 0.29 nm and 0.17 nm, while the fused
phenylcarbazole core (SPC) showed aggregated morphology with
a surface roughness of 0.40 nm. The fused phenylcarbazole core
showed rather aggregated morphology due to the reduced dihedral
angle as shown in Figure 3. The SPCPO2 showed better surface
roughness than the SPCPO1, indicating that the additional diphe-
nylphosphine oxide group stabilized the surface morphology of the
fused phenylcarbazole. The smooth surface morphology of the
SPCPO1 and SPCPO2 was kept stable and the same AFM data were
obtained even after storage for more than a week. The high Tg and
rigid molecular structure stabilized the surface morphology of the
SPCPO1 and SPCPO2.
The morphological stability of the SPCPO1 and SPCPO2 was
compared with a phenylcarbazole based phosphine oxide com-
pound, 3,6-bis(diphenylphosphoryl)-9-phenyl-9H-carbazole (PPO2).
Thin films of the organic materials were thermally treated at 140 ꢀC
for 5 min and the morphology of the thermally treated thin films
was analyzed with an optical microscope. Figure 6 shows optical
microscope images of SPC, PPO2, SPCPO1, and SPCPO2. The SPC
was significantly crystallized after thermal treatment and aggre-
gated morphology was observed. Crystallization of the PPO2 was
Figure 4. Differential scanning calorimetric thermogram of the SPCPO1 and SPCPO2.
Figure 5. Atomic force microscopic images of the fused phenylcarbazole core, SPCPO1 and SPCPO2.

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S.O. Jeon, J.Y. Lee / Tetrahedron 66 (2010) 7295e7301
Figure 6. Optical microscope images of SPC, PPO2 SPCPO1, and SPCPO2 after thermal treatment at 140 ꢀC for 5 min.
also observed after thermal treatment, while SPCPO1 and SPCPO2
did not show any crystallization of the deposited film. The amor-
phous morphology of the material was kept stable after thermal
treatment at 140 ꢀC. In particular, there was no change of the
morphology of the SPCPO2 even after thermal treatment at 140 ꢀC
for more than 1 h. Therefore, the fused phenylcarbazole based
compounds, SPCPO1 and SPCPO2, showed much better morpho-
logical stability than a phenylcarbazole based compound. The sta-
ble morphology of the SPCPO1 and SPCPO2 is expected to improve
the device stability in device application.
Charge transport properties of the host materials are important
for device application and the hole/electron transport properties of
SPCPO1 and SPCPO2 were studied using hole and electron only
devices. Figure 7 shows current densityevoltage curves of hole only
and electron only devices of SPCPO1 and SPCPO2. The SPCPO2
showed higher electron current density and lower hole current
density than the SPCPO1. The high electron current density of the
SPCPO2 is due to electron deficient two diphenylphosphine oxide
groups, which play a role of electron transport unit. The SPCPO2
showed similar hole and electron current density and it is expected
that the SPCPO2 shows good device performances in device
applications.
4. Conclusions
In conclusion, high triplet energy host materials based on fused
phenylcarbazole core and diphenylphosphine oxide were effec-
tively synthesized and a high triplet energy of 2.95 eV could be
obtained. The triplet energy of the SPCPO1 and SPCPO2 was high
enough for use as hosts for deep blue phosphorescent dopant. In
addition, the novel design combining the fused phenylcarbazole
and diphenylphosphine oxide improved the thermal and mor-
phological stability. Therefore, the SPCPO1 and SPCPO2 are
promising as host materials for deep blue phosphorescent organic
light-emitting diodes.
Supplementary data
0.003
Supplementary data associated with this article can be found in
the online version at doi:10.1016/j.tet.2010.07.008.
SPCPO1-hole
SPCPO2-hole
SPCPO1-electron
SPCPO2-electron
0.002
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0
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1
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Figure 7. Current densityevoltage curves of hole only and electron only devices of
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