Synthesis of high-triplet-energy host polymer for blue and white electrophosphorescent light-emitting diodes

Article abstract of DOI:10.1021/ma5015929

A high-triplet-energy host polymer consisting of 9-(4-(bis(9-(2-ethylhexyl)-9H-carbazol-3-yl)methyl)phenyl)-9H-carbazole and tetraphenylsilane units was designed and synthesized. The triplet energy (2.67 eV) is one of the highest values reported for conju

Full text of DOI:10.1021/ma5015929

Article
pubs.acs.org/Macromolecules
Synthesis of High-Triplet-Energy Host Polymer for Blue and White
Electrophosphorescent Light-Emitting Diodes
†
,§
†
†
†
†
‡
,‡
Fei Xu, Ji-Hoon Kim, Hee Un Kim, Jae-Ho Jang, Kyoung Soo Yook, Jun Yeob Lee,*
,
and Do-Hoon Hwang*
†
Department of Chemistry and Chemistry Institute for Functional Materials, Pusan National University, Busan 609-735, Korea
Department of Polymer Science & Engineering and Center for Photofunctional Energy Materials, Dankook University, Yongin,
‡
Gyeonggi 448-701, Korea
§
Beijing Key Laboratory of Ionic Liquids Clean Process, State Key Laboratory of Multiphase Complex System, Institute of Process
Engineering, Chinese Academy of Sciences, Beijing 100190, China
*
S Supporting Information
ABSTRACT: A high-triplet-energy host polymer consisting of 9-
4-(bis(9-(2-ethylhexyl)-9H-carbazol-3-yl)methyl)phenyl)-9H-car-
(
bazole and tetraphenylsilane units was designed and synthesized.
The triplet energy (2.67 eV) is one of the highest values reported
for conjugated polymer hosts. Suitable highest occupied molecular
orbital (HOMO) and lowest unoccupied molecular orbital
(
LUMO) levels of −5.61 and −2.24 eV, respectively, were also
observed. Blue phosphorescent polymers were obtained by
2
introducing bis[2-(4,6-difluorophenyl)pyridinato-N,C ′]iridium-
(
III) picolinate (FIrpic) into the host polymer while white
phosphorescent polymers were synthesized by introducing red
2
emissive bis[2-phenylquinoline-N,C ′]iridium(III) picolinate
(
(Phq) Irpic) into the blue phosphorescent one. Polymer light-
2
emitting devices with the configuration ITO/PEDOT:PSS/PVK/
EML/TSPO1/LiF/Al [ITO, indium tin oxide; PEDOT, poly(3,4-
ethylenedioxythiophene); PSS, poly(styrenesulfonic acid); PVK,
poly(N-vinylcarbazole); EML, the emitting layer was composed of
polymer or polymer and 1,3-bis[5-(4-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene (OXD-7) in a doping ratio of 2:1); TSPO1,
diphenylphosphine oxide-4-(triphenylsilyl)pheny] were subsequently fabricated. Efficient energy transfer from the host polymer
to the blue and red iridium(III) complexes was observed owing to the high triplet energy of the host. One of the fabricated blue
phosphorescent devices had a maximum luminous efficiency of 3.57 cd/A.
INTRODUCTION
green, and red) are indispensable. To date, a number of red and
green phosphorescent polymers have been reported, with
maximum quantum efficiencies (EQEs) reaching 18.0% and
■
Solution-processable organic light-emitting diodes (OLEDs)
have recently attracted significant attention for application to
6
−9
1
,2
15.3%, respectively.
However, fewer blue phosphorescent
next-generation displays and solid-state lighting because the
typical vapor deposition method for fabricating OLEDs has
critical drawbacks such as low utilization of expensive OLED
materials, high manufacturing cost, and limitation to its
scalability. Over the past decades, numerous efforts have
focused on developing light-emitting materials for solution-
processable OLEDs. Among these, single phosphorescent
polymers, in which heavy metal complexes are incorporated
into the polymer via covalent bonds, have recently become
popular because with these materials, 100% internal quantum
efficiency can be theoretically achieved owing to the strong
spin−orbit coupling effect, and phase segregation and triplet−
polymers have been reported thus far, which crucially limits the
10,11
commercial application of single phosphorescent polymers.
The most difficult issue for blue phosphorescent polymers is
the lack of suitable host polymers with a high triplet energy
1
2
level (ET) because most conjugated host polymers have E s
T
13−15
lower than that of a blue dopant.
The E should be higher
T
because, otherwise, triplet excitons trapped on the blue dopant
will transfer to the triplet state of the host polymer after
electrical excitation. As a result, all triplet excitons cannot be
utilized for light emission. On the other hand, if the E of the
T
3
−5
triplet aggregation can be effectively inhibited.
For application in display and solid state lighting, single
phosphorescent polymers with three primary colors (blue,
Received: August 6, 2014
Revised: October 12, 2014
Published: October 23, 2014
©
2014 American Chemical Society
7397
dx.doi.org/10.1021/ma5015929 | Macromolecules 2014, 47, 7397−7406

Macromolecules
Article
Scheme 1. Synthetic Routes for Host and Iridium Complex Monomers
host polymer is higher than that of the blue dopant, triplet
excitons trapped on the host polymer can transfer to the triplet
state of the blue dopant. Therefore, triplet excitons trapped not
only on the blue dopant but also on the host polymer can
induce light emission, and high electroluminescence (EL)
efficiency can be achieved. Additionally, the synthesis of all-
phosphorescent white-emitting polymers remains a challenge
owing to the lack of a suitable host polymer for a blue
structure. As anticipated, an E of 2.67 eV was observed for the
synthesized host polymer PCztPSi, which is higher than that of
T
the well-known blue iridium(III) complex, bis[2-(4,6-
2
difluorophenyl)pyridinato-N,C ′]iridium(III) picolinate
(FIrpic, 2.60 eV). This value is also higher than most of the
E
s reported for conjugated host polymers such as a poly(m-
T
phenylene) derivative tethering carbazole unit (E = 2.64
T
26
27
eV), poly(3,6-carbazole) (ET = 2.60 eV), and poly(3,6-
fluorene) (ET = 2.58 eV). In addition, blue and all-
phosphorescent white-emitting polymers are obtained by
2
8
1
6,17
dopant.
Thus, the development of high-E host polymers
T
for blue and white phosphorescent polymers is very urgent and
important. Recently, two bipolar blue host polymers with the
introducing FIrpic and red emissive bis[2-phenylquinoline-
2
N,C ′]iridium(III) picolinate ((Phq) Irpic) into the synthesized
highest reported E (2.96 eV) were synthesized by Wang and
2
T
1
8−20
host polymer as pendent groups. Efficient energy transfer from
the host backbone to the blue and red phosphors is observed
owing to the high ET of the host polymer. The synthesis,
thermal stability, and optical and electrical properties of the
synthesized polymers were systematically investigated. The
synthetic routes to the iridium complex and host monomers are
shown in Scheme 1, and that for the polymers are shown in
Scheme 2.
co-workers.
Breakthroughs in EL performance for both
blue and all-phosphorescent white-emitting polymers were
obtained with EQEs of 9.0% and 7.0%, respectively.
In this work, we designed and synthesized a novel high-ET
host polymer through the typical Suzuki polymerization
2
1−24
method
by utilizing a small carbazole-based molecular
host and tetraphenylsilane. 9-(4-(Bis(9-(2-ethylhexyl)-9H-
carbazol-3-yl)methyl)phenyl)-9H-carbazole 9-(2-ethylhexyl)-3-
yl)methyl)phenyl)-9H-carbazole was introduced into the
RESULTS AND DISCUSSION
polymer backbone as a high-E host unit through modification
■
T
25
of the 3,6-position of carbazole. Brunner et al. reported that
Synthesis and Characterization. The synthetic routes
and chemical structures of the monomers and polymers are
outlined in Schemes 1 and 2, respectively. The host monomer
M1 was synthesized with a moderate yield from 3,6-dibromo-9-
(4-(bis(9-(2-ethylhexyl)-9H-carbazol-3-yl)methyl)phenyl)-9H-
the E of conjugated polymers was mainly determined by the
T
longest poly(p-phenylene) chains. Thus, tetraphenylsilane units
(
i.e., linkage group) were alternately polymerized with
carbazole to block the extended π-conjugation of the backbone
and limit the longest poly(p-phenylene) chain to a biphenyl
carbazole and bis(pinacolato)diboron using PdCl (dppf) as
2
7
398
dx.doi.org/10.1021/ma5015929 | Macromolecules 2014, 47, 7397−7406

Macromolecules
Article
Scheme 2. Synthetic Routes for Polymers (R = 2-Ethylhexyl)
Table 1. Structural and Thermal Properties of PCztPSi-Based Polymers
c
M1:M2 or M1:M2:M3 [mol %]
feed ratio [%]
Mw (×103)
a
PDI
Td [°C]
b
yield [%]
actual ratio [%]
copolymer
PCztPSi
17.2
12.3
13.4
12.7
12.4
2.25
1.87
1.91
1.77
1.74
469
456
453
458
446
65
52
58
45
46
50/0
50/0
PCztPSiB2.5
50/2.5
50/5
50/2.1
50/4.5
PCztPSiB5
PCztPSiB5R0.6
PCztPSiB7.5R0.7
50/5/0.6
50/7.5/0.7
50/4.5/−
50/6.0/−
a
b
Molecular weights were determined by GPC using polystyrene standards. Obtained from TGA measurements. T values were recorded at 5%
d
c
1
weight loss. The iridium contents in polymers were estimated by H NMR.
catalyst. The iridium complex monomers M2 and M3 were
the red iridium monomer M3 were 0.6 and 0.7 mol %,
respectively. As shown in the inset of Figure S2, the intensities
29
synthesized via the method reported by Nonoyama. Iridium
trichloride hydrate was initially reacted with 2-(2,4-
difluorophenyl)pyridine or 2-phenylquinoline to give the blue
or red (μ-chloro)-bridged iridium(III) dimers, respectively.
Compounds M2 and M3 were subsequently synthesized by
treatment of the dimers with compound 5 in 2-ethoxyethanol
with 53% and 76% yield, respectively. The formation of M1−
of the H , H , H , and H proton peaks of M2 increased with
a
b
b′
d
increasing feed ratio. The actual FIrpic content of the polymer
1
was determined by comparing the integration of the H NMR
signal at 5.69 ppm from the H proton of the main ligand of the
b
iridium complex (Figure S2) with that at 6.10 ppm from the Hc
proton of carbazole units (Figures S3 and S4). In contrast, the
1
M3 was confirmed by H (compounds 1−5 and M1−M4; see
actual (Phq) Irpic content of white-emitting polymers cannot
2
Figure S1 in the Supporting Information) and 13C NMR
spectroscopy and FAB-MS spectrometry.
be determined from the NMR spectra owing to its very low
feed ratio. The existence of the (Phq) Irpic unit was ensured by
2
The PCztPSi-based polymers were prepared via a palladium-
catalyzed Suzuki coupling reaction between dibromoaryl and
diborolanylaryl monomers. The host polymer is designated as
PCztPSi. The blue phosphorescent polymers are designated as
PCztPSiB2.5 and PCztPSiB5, where the corresponding feed
ratios of the blue iridium monomer M2 were 2.5 and 5 mol %,
respectively.
All-phosphorescent white-emitting polymers are designated
as PCztPSiB5R0.6 and PCztPSiB7.5R0.7, where the corre-
sponding feed ratios of M2 were 5 and 7.5 mol % while those of
observing its characteristic photoluminescence (PL) and EL
emission bands at the emission spectra of the (Phq) Irpic-
2
containing white-light-emitting polymers. Feed ratios and actual
monomer contents are listed in Table 1. As in other reported
iridium-containing polymers, the actual iridium complex
content of the polymers was slightly lower than the monomer
feed ratio, possibly because of the low reactivity of the
monomer toward polycondensation. All polymers were found
to be soluble in common organic solvents, such as
tetrahydrofuran (THF), chloroform, and toluene, with no
7
399
dx.doi.org/10.1021/ma5015929 | Macromolecules 2014, 47, 7397−7406

Macromolecules
Article
evidence of gel formation. The weight-average molecular
weights (M ) of the polymers, as determined by gel permeation
w
chromatography (GPC) using a polystyrene standard, ranged
from 12 300 to 17 200 with polydispersity indices (PDIs) of
1
.74−2.25 after the purification processes. The yields from
polymerization were 45%−65%. The synthesized polymers
1
13
were characterized by H NMR (Figures S3 and S4), C NMR,
and elemental analysis, and results were in good accordance
with the polymer structures.
The thermal transitions of the PCztPSi host polymer were
studied by differential scanning calorimetry (DSC) under a
nitrogen atmosphere as shown in Figure S5. No discernible
exothermic and endothermic peaks were observed between 0
and 300 °C, suggesting good stability in this temperature range.
The thermal properties of PCztPSi-based polymers were
determined using thermal gravimetric analysis (TGA) as
shown in Figure S6 and summarized in Table 1. All polymers
exhibited good thermal stability, losing less than 5% of their
weight upon heating to ∼440 °C in TGA under a nitrogen
atmosphere. The thermal properties of the polymers are
summarized in Table 1. The high thermal stability and
amorphous natures of polymers are highly desirable for
OLEDs, particularly for fabrication by solution process.
Optical and Electrochemical Properties. To study the
triplet energy level of the synthesized host polymer PCztPSi,
the PL spectra in toluene were measured at room temperature
and 77 K as shown in Figure 1. At 77 K, the emission peak at
Figure 2. (a) Absorption and (b) PL spectra of host (PCztPSi) and
blue-emitting (PCztPSiB2.5 and PCztPSiB5) polymers in film state.
from the host backbone to FIrpic within the polymer chain was
inefficient in solution state. In contrast, as shown in Figure 2b,
there were two distinct PL peaks at 401 and 474 nm in the film
state, which were assigned to the emissions from the host
polymer backbone and pendent FIrpic unit, respectively. The
blue emissions observed from polymers PCztPSiB2.5 and
PCztPSiB5 coincided with that of the pristine FIrpic.
Furthermore, the relative intensity of the emission from the
host polymer to the FIrpic unit noticeably decreased with
increasing iridium content. This demonstrates that the energy
transfer from the host polymer backbone to the FIrpic unit
efficiently occurred in the rigid thin film and the triplet energy
back transfer from FIrpic to the polymer was inhibited owing to
Figure 1. PL spectra of host polymer (PCztPSi) in toluene at room
and low temperatures (77 K).
4
2
65 nm was used to determine the E of PCztPSi, which was
.67 eV. This value was higher than those obtained for FIrpic
T
the high E of the latter.
T
(
E = 2.60 eV) and (Phq) Irpic (E = 2.11 eV), which indicates
The UV−vis absorption and PL spectra of all-phosphor-
escent white-emitting polymers (PCztPSiB5R0.6 and
PCztPSiB7.5R0.7) in dichloromethane solution and film states
are shown in Figure S8 and Figure 3, respectively. As in the
blue phosphorescent polymers, the white ones exhibited
identical strong π−π* absorption peaks at 303 nm in both
solution and film states. MLCT transitions from the Ir
complexes were too weak to be discernible because of the
low iridium complex content. In the solution state, the emission
from the host backbone at 394 nm was dominant as shown in
Figure S8b. Blue emission from FIrpic can be observed at
T
2
T
that the triplet energy back transfer from FIrpic and (Phq) Irpic
to PCztPSi would be efficiently prevented.
2
The ultraviolet−visible absorption (UV) and PL spectra of
PCztPSi and the blue phosphorescent polymers (PCztPSiB2.5
and PCztPSiB5) in dichloromethane solution and film state are
shown in Figure S7 and Figure 2, respectively. In both
dichloromethane solution and film states, all polymers
displayed strong π−π* absorption peaks at 302−303 nm
while the low-energy absorption bands for the metal-to-ligand
charge transfer (MLCT) transition in FIrpic were too weak to
be discernible owing to the low Ir content of the polymers. In
the copolymer solution in dichloromethane, the major emission
was observed at around 394 nm from the host polymer while
no clear emission was observed at around 470 nm from the
incorporated FIrpic unit as shown in Figure S7b. These
observations indicate that the intramolecular energy transfer
30
around 470 nm while red emission from (Phq) Irpic cannot be
2
evidently observed. This indicates that the energy transfer from
the host polymer to the (Phq) Irpic unit was less effective than
2
that to FIrpic. In contrast, three emission peaks at around 398,
473, and 577 nm were found in the PL spectra of the film state
of PCztPSiB5R0.6 and PCztPSiB7.5R0.7, which can be ascribed
7
400
dx.doi.org/10.1021/ma5015929 | Macromolecules 2014, 47, 7397−7406

Macromolecules
Article
phosphorescent polymer PCztPSi5R0.6. However, when the
ratio of the FIrpic unit further increased to 7.5%, the Φ
pl
decreased again. It could be rationalized by the greater
tendency of triplet−triplet annihilation at higher Ir(III)
concentration.
The electrochemical properties of the polymers were studied
by cyclic voltammetry (CV), and the oxidation waves of the
polymers are shown in Figure S10. The onset of the oxidation
waves was between 0.88 and 0.89 V. According to the literature,
the HOMO level can be estimated from the onset oxidation
potential using the following equation: HOMO = −(4.8 +
E
− E ), where E
and E are the potentials of the
ox,onset Fc
34
ox,onset
Fc
polymer and ferrocene, respectively. The calculated HOMO
levels were −5.60 to −5.61 eV, while the LUMO levels were
−
2.23 to −2.30 eV. The onset oxidation potentials and energy
levels of the polymers are listed in Table 2.
EL Device Properties. To evaluate the electroluminescence
performance, the synthesized polymers were used as the
emitting layer (EML) in phosphorescent polymer light-emitting
diodes (PhPLEDs) fabricated with the configuration (device I)
ITO/PEDOT:PSS/PVK/polymer/TSPO1/LiF/Al [ITO, indi-
um tin oxide; PEDOT, poly(3,4-ethylenedioxythiophene); PSS,
poly(styrenesulfonic acid); PVK, poly(N-vinylcarbazole);
TSPO1, 4-(triphenylsilyl)phenyldiphenylphosphine oxide] as
shown in Figure 4. PVK and TSPO1 were used as the hole-
Figure 3. (a) Absorption and (b) PL spectra of white-emitting
(
PCztPSiB5R0.6 and PCztPSiB7.5R0.7) polymers in film state.
to emissions from the host polymer, M2, and M3, respectively
Figure S9). Moreover, the emissions originating from FIrpic
(
and (Phq) Irpic became dominant in the film state, with
2
intensities increasing gradually with increasing Ir complex
content. According to the difference between the PL spectra of
the solution and film states, we speculate that the reduction in
the distance between FIrpic and (Phq) Irpic as the state shifted
2
from solution to solid would favor Dexter energy transfer from
FIrpic to (Phq) Irpic.
2
Figure 4. Configuration of PhPLED and molecular structures of hole-
transporting (PVK) and triplet-exciton-blocking (TSPO1) materials.
Furthermore, the PL quantum yields (Φ ) of the polymer
pl
films were measured at 310 nm excitation wavelength. The Φ s
pl
of the polymers are in the range of 6.7−14.2%. Similar with the
31−33
previous reported iridium-containing polymers,
the Φ of
transporting and exciton-blocking layers, respectively. Figure 5
illustrates the possible energy transfer paths of triplet excitons
inside the PCztPSi-based polymers as well as exciton
confinement by PVK and TSPO1. The triplet energies of
PVK (E = 3.00 eV) and TSPO1 (E = 3.36 eV) were higher
pl
PCztPSiB2.5 decreased to 6.7% as introducing 2.5% of FIrpic
unit into the host polymer PCztPSi (Φ = 9.5%), possibly due
to the energy lost during the exciton transfer from singlet to
triplet state. As the ratio of the iridium content in the polymer
pl
T
T
increased more than 2.5%, the Φ of the polymer increased.
than that of the host polymer PCztPSi (E = 2.67 eV), leading
to effective confinement of triplet excitons within the EML.
pl
T
The highest Φ of 14.2% was observed from the white
pl
Table 2. Optical and Electrochemical Properties of PCztPSi-Based Polymers
a
a
b
c
c
d
e
copolymer
PCztPSi
λmax,abs [nm]
λPL [nm]
401
Φpl [%]
Eox,onset [V]
HOMO [eV]
LUMO [eV]
Eg [eV]
ET [eV]
303
303
303
303
303
9.5
6.7
0.89
0.88
0.89
0.89
0.89
−5.61
−5.60
−5.61
−5.61
−5.61
−2.24
−2.23
−2.25
−2.27
−2.30
3.37
3.37
3.36
3.34
3.31
2.67
PCztPSiB2.5
400, 474
PCztPSiB5
401, 475
8.4
PCztPSiB5R0.6
PCztPSiB7.5R0.7
398, 473, 577
401, 474, 573
14.2
10.4
a
b
c
Measured in film. Φ of the thin films measured under the excitation of a 150 W xenon light source (310 nm). HOMO levels were calculated
pl
d
from CV potentials using ferrocene as a standard [HOMO = −(4.8 + E
−
− E ) eV]. LUMO levels were derived via the equation E = HOMO
ox,onset
Fc
g
e
LUMO, where E obtained from the absorption spectra. Measured in toluene at low temperature (77 K).
g
7
401
dx.doi.org/10.1021/ma5015929 | Macromolecules 2014, 47, 7397−7406

Macromolecules
Article
the polymer backbone were observed. In the case of the white
phosphorescent polymers PCztPSiB5R0.6 and
PCztPSiB7.5R0.7, the host emission also disappeared com-
pletely as shown in Figure 6b. The triplet excitons, formed by
both electrical injection and energy transfer, were trapped in
the iridium complex because of the difference in the E (Figure
T
5
) and HOMO/LUMO energy levels of the host and Ir
complexes. White emissions originating from FIrpic and
Phq) Irpic were observed with two emission peaks at 471
(
2
and 578 nm, respectively. In particular, the intensity ratios for
FIrpic and (Phq) Irpic did not change significantly from PL to
2
Figure 5. Triplet energy levels of materials included in white
PhPLEDs. Possible energy flow in the device is also shown.
EL as in other reported all-fluorescent and fluorescent/
3
,4
phosphorescent hybrid white-emitting polymers.
The current density−voltage−luminance characteristics of
the PCztPSi series of polymers are shown in Figure 7. Low
Additionally, inefficient back-transfer of triplet excitons from
FIrpic (2.60 eV) and (Phq) Irpic (2.11 eV) to the host polymer
2
can be expected, owing to the high triplet energy level of the
host backbone. The EL spectra of the fabricated devices are
shown in Figure 6. In contrast to the PL spectra of the
Figure 7. Current density−voltage−luminance characteristics of (a)
host (PCztPSi), blue-emitting (PCztPSiB2.5, PCztPSiB5, and
PCztPSiB5:OXD-7) and (b) white-emitting (PCztPSiB5R0.6,
PCztPSiB5R0.6:OXD-7, PCztPSiB7.5R0.7, and PCztPSi-
B7.5R0.7:OXD-7) polymers.
Figure 6. EL spectra of (a) host (PCztPSi), blue-emitting
(
PCztPSiB2.5, PCztPSiB5, and PCztPSiB5:OXD-7) and (b) white-
emitting (PCztPSiB5R0.6, PCztPSiB5R0.6:OXD-7, PCztPSiB7.5R0.7,
and PCztPSiB7.5R0.7:OXD-7) polymers.
PhPLED turn-on voltages in the range of 5.5−7.5 V were
observed, which can be attributed to the good charge injection
of the device. The highest luminance from the blue and white
2
polymers, efficient energy transfer from the host backbone to
the iridium complex was observed with both blue and white
phosphorescent polymers. The substantial difference in the PL
and EL spectra indicates that the predominant mechanism of
the EL devices was charge trapping rather than energy transfer.
In the case of the copolymer PCztPSi, two emission peaks were
observed at 396 nm from the host backbone and at 599 nm due
to exciplex emission. With the introduction of the iridium
complex monomer into PCztPSi, the emission from the host
backbone expectedly decreased. In the case of the blue
phosphorescent polymers PCztPSiB2.5 and PCztPSiB5, the
emission peak from FIrpic was observed at 472 nm. At an
iridium complex content of 5%, no additional emissions from
PhPLEDs was observed with PCztPSiB5 (368 cd/m ) and
2
PCztPSiB7.5R0.7 (315 cd/m ). The luminous efficiency (LE)
and EQE as functions of luminance are shown in Figure 8 and
Figure S11, respectively, and device performances are
summarized in Table 3. Among PCztPSi, PCztPSiB2.5, and
PCztPSiB5, the latter had the best device performance, with a
maximum EQE of 1.73%, maximum LE of 3.57 cd/A,
maximum power efficiency (PE) of 1.32 lm/W, and
Commission Internationale de L’Eclairage (CIE) coordinates
of (0.18, 0.36). As the FIrpic content increased, the EQE and
LE of the PhPLEDs gradually increased. Between
PCztPSiB5R0.6 and PCztPSiB7.5R0.7, the latter exhibited the
best device performance, with a maximum EQE of 1.07%,
7
402
dx.doi.org/10.1021/ma5015929 | Macromolecules 2014, 47, 7397−7406

Macromolecules
Article
the EL spectra of the blended system were similar to those of
the pure polymers, and no emissions from OXD-7 were
observed, which indicates complete energy transfer from the
OXD-7 to the polymers. After introducing the electron-
transport material OXD-7, the turn-on voltages were decreased
about 0.5−1.5 V as shown in Figure 7 and Table 3, which could
be attributed to the improved charge injection of the device.
The highest luminance from the PhPLEDs (device II) was
2
observed with PCztPSiB5R0.6:OXD-7 (317 cd/m ). The
luminous efficiency and EQE as functions of luminance are
also shown in Figure 8 and Figure S11, respectively. In the case
of blue-emitting polymer PCztPSiB5, the device performance
was slightly improved by introducing OXD-7 up to the
maximum EQE of 1.75%. For the white-emitting polymers, the
device performances were much improved about 2 times. In the
case of PCztPSiB5R0.6, the EQE was increased from 0.69% to
1
.72%. The device fabricated using PCztPSiB5R0.6:OXD-7
exhibited the best device performances with a maximum EQE
of 1.72%, maximum LE of 4.06 cd/A, maximum PE of 2.04 lm/
W, and CIE coordinates of (0.44, 0.41), which is close to the
standard CIE coordinates for warm white-light emission (0.44,
0
.40).
To investigate the relationship between film morphology and
device performance, tapping-mode atomic force microscopy
AFM) measurements were applied on the pure polymers and
(
polymers doped with OXD-7 as shown in Figure S12. The
root-mean-square (RMS) surface roughness values were
observed in the range of 0.53−1.30 nm. After blending with
OXD-7, the film morphology turned more smooth, and the
lowest surface roughness value was observed from PCztPSi-
B5R0.6:OXD-7 blend film.
Figure 8. Luminous efficiency−luminance curves of (a) host
(
PCztPSi), blue-emitting (PCztPSiB2.5, PCztPSiB5, and PCztPSi-
B5:OXD-7) and (b) white-emitting (PCztPSiB5R0.6, PCztPSi-
B5R0.6:OXD-7, PCztPSiB7.5R0.7, and PCztPSiB7.5R0.7:OXD-7)
polymers.
CONCLUSION
■
2
The host polymer PCztPSi, having a high triplet energy level of
.67 eV, was designed and synthesized. Using this as a host,
maximum LE of 2.26 cd/A, maximum PE of 0.96 lm/W, and
CIE coordinates of (0.33, 0.37), which is close to the standard
CIE coordinates for white light emission (0.33, 0.33).
blue and white phosphorescent polymers were synthesized by
introducing the blue iridium complex FIrpic and red iridium
complex (Phq) Irpic into the side chain of the backbone.
2
In order to further optimize the device structure, we
fabricated another series of PhPLEDs with the configuration
PhPLEDs were fabricated using the PCztPSi-based polymers.
Efficient energy transfer from the host backbone to the blue
and red iridium complexes was observed, which can be
attributed to the higher triplet energy level of the host
backbone. Among the blue PhPLEDs, the best performance
was observed using PCztPSiB5, with a maximum EQE of
1.73%, maximum LE of 3.57 cd/A, and CIE coordinates of
(0.18, 0.36). On the other hand, among the white PhPLEDs,
the best performance was observed using PCztPSiB5R0.6
doped with OXD-7. Our results provide a novel avenue for the
(
device II) of ITO/PEDOT:PSS/PVK/polymer:OXD-7(2:1)/
TSPO1/LiF/Al [OXD-7,1,3-bis[5-(4-tert-butylphenyl)-1,3,4-
oxadiazol-2-yl]benzene]. Polymers PCztPSiB5, PCztPSiB5R0.6,
and PCztPSiB7.5R0.7, which showed good EL performances at
device I were studied. OXD-7 was introduced to improve the
electron-transporting capability, and the doping ratio of the
polymer to OXD-7 was 2:1. The performances of the fabricated
EL devices are summarized in Table 3. As shown in Figure 6,
Table 3. EL Device Performance of PCztPSi-Based Polymers
c
d
Lmax [cd/m2]
copolymer
Vturn‑on [V]
λmax,EL [nm]
CIE [x, y]
EQEmax [%]
LEmax [cd/A]
PEmax [lm/W]
a
PCztPSi
5.5
5.5
6.5
7.5
6.5
5.5
6.0
6.0
396, 599
472
(0.45, 0.31)
(0.19, 0.34)
(0.18, 0.36)
(0.43, 0.40)
(0.33, 0.37)
(0.23, 0.33)
(0.44, 0.41)
(0.32, 0.37)
68
217
368
309
315
218
317
300
0.30
0.87
1.73
0.69
1.07
1.75
1.72
1.54
0.41
1.66
3.57
1.55
2.26
3.45
4.06
3.30
0.20
0.75
1.32
0.51
0.96
1.78
2.04
1.55
a
PCztPSiB2.5
a
PCztPSiB5
473
a
PCztPSiB5R0.6
471, 578
471, 578
473
a
PCztPSiB7.5R0.7
b
PCztPSiB5:OXD-7
PCztPSiB5R0.6:OXD-7
b
472, 578
473, 574
b
PCztPSiB7.5R0.7:OXD-7
a
b
c
Device I: ITO/PEDOT:PSS/PVK/polymer/TSPO1/LiF/Al. Device II: ITO/PEDOT:PSS/PVK/polymer:OXD-7(2:1)/TSPO1/LiF/Al. The
2
d
voltage at a luminance of 1 cd/m . At the maximum luminous efficiency.
7
403
dx.doi.org/10.1021/ma5015929 | Macromolecules 2014, 47, 7397−7406

Macromolecules
Article
design of polymer host material with high E for efficient blue
and white electrophosphorescent light-emitting diodes.
112.9, 111.7, 109.0, 108.9, 56.5, 47.5, 39.5, 31.0, 28.8, 24.4, 23.1, 14.1,
T
1
0.9.
Synthesis of 3,6-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-
2
-yl)-9-(4-(bis(9-(2-ethylhexyl)-9H-carbazol-3-yl)methyl)-
EXPERIMENTAL SECTION
phenyl)-9H-carbazole (M1). A mixture of compound 3 (3.0 g, 3.0
■
mmol), bis(pinacolato)diboron (2.0 g, 7.5 mmol), PdCl (dppf) (0.075
2
Materials. Iridium(III) chloride and carbazole were purchased
from Alfa Aesar. Bis(pinacolato)diboron was obtained from TCI
Chemicals. Tetrakis(triphenylphosphine)palladium(0) [Pd(PPh ) ]
g, 0.09 mmol), and potassium acetate (1.8 g, 18.6 mmol) in DMF (70
mL) was stirred for 3 days at 80 °C. After the reaction mixture has
cooled, it was poured into water and extracted with diethyl ether. The
organic layer was washed with brine three times and dried over
magnesium sulfate. After the solvent was removed under pressure, the
crude product was purified through column chromatography using
hexane/ethyl acetate (9:1, v/v) as eluent and recrystallized in
3
4
was purchased from Strem Chemicals. 4-Bromobenzaldehyde, 1,1′-
bis(diphenylphosphino)ferrocene]dichloropalladium(II)
[
PdCl (dppf)], 2-(2,4-difluorophenyl)pyridine, and tetraethylammo-
2
nium hydroxide solution (20 wt % Et NOH in H O) were obtained
4
2
from Aldrich. All reagents were used without further purification.
Acetic acid (AcOH) was purchased from Daejung, and 2-
ethoxyethanol and nitrobenzene were obtained from Junsei Chemical.
Anhydrous toluene was purchased from Aldrich, and N,N-
dimethylformamide (DMF) was obtained from Alfa Aesar. 2-
Ethoxyethanol was used after purging with dry nitrogen for 10 min.
dichloromethane and methanol to afford the product as a white
1
solid. Yield: 1.38 g (42%). H NMR (CDCl , 300 MHz): δ 8.70 (s,
3
2
7
4
1
1
4
1
H), 8.02 (d, 2H), 7.99 (s, 2H), 7.85 (d, 2H), 7.55−7.36 (m, 14H),
.17 (t, 2H), 6.09 (s, 1H), 4.17 (d, 4H), 2.07 (m, 2H), 1.41−1.25 (m,
1
3
0H), 0.95−0.83 (m, 12H). C NMR (CDCl , 75 MHz): δ 145.1,
3
3
5
43.0, 141.3, 139.7, 135.0, 134.8, 132.1, 131.0, 128.0, 127.4, 126.6,
25.5, 123.1, 122.8, 122.6, 121.0, 120.3, 118.6, 109.3, 108.9, 83.6, 56.6,
7.5, 39.5, 31.0, 28.8, 24.9, 24.4, 23.1, 14.1, 10.9. FAB-MS: m/z =
3
,6-Dibromo-9-(8-bromooctyl)carbazole, bis(4-bromophenyl)-
36 37
diphenylsilane (M4), methyl 6-hydroxypicolinate, 2-phenylquino-
38
29
line, and iridium dimers were prepared according to the literature.
+
064.89 (M ).
All manipulations involving IrCl ·3H O and other Ir(III) species were
3
2
Synthesis of Methyl 6-(8-(3,6-Dibromo-9H-carbazol-9-yl)-
octyloxy)picolinate (4). 3,6-Dibromo-9-(8-bromooctyl)carbazole
performed in an atmosphere of dry nitrogen.
Synthesis of 4-(9H-Carbazol-9-yl)benzaldehyde (1). Carba-
zole (4.0 g, 23.9 mmol), 4-bromobenzaldehyde (5.4 g, 28.7 mmol),
K CO (19.8 g, 143.5 mmol), and copper powder (1.5 g, 23.9 mmol)
(1.0 g, 1.8 mmol), methyl 6-hydroxypicolinate (0.34 g, 2.2 mmol),
K CO (3.1 g, 22.4 mmol), and KI (0.28 g) were mixed in acetone (35
2
3
2
3
mL) and refluxed for 24 h. After cooling, the mixture was poured into
water and extracted with dichloromethane. The organic layer was
washed with brine three times and then dried over magnesium sulfate.
After removal of the solvent, the crude product was purified through
were dissolved in nitrobenzene (100 mL) under a nitrogen
atmosphere and refluxed for 24 h. The mixture was then cooled to
room temperature, and the solvent was removed by distillation.
Ammonia solution was subsequently added to the crude product, and
the mixture was stirred for another 2 h. The crude solution was poured
into water, extracted with dichloromethane/brine, dried over
magnesium sulfate, and concentrated in vacuo. The residue was
purified through column chromatography using hexane/dichloro-
methane (3:1, v/v) as eluent and then recrystallized in dichloro-
column chromatography using hexane/ethyl acetate (10:1, v/v) as
1
eluent to give compound 4. Yield: 0.66 g (61%). H NMR (CDCl ,
3
3
2
00 MHz): δ 8.12 (s, 2H), 7.70−7.63 (m, 2H), 7.55 (d, 2H), 7.25 (d,
H), 6.89 (d, 1H), 4.33 (t, 2H), 4.22 (t, 2H), 3.94 (s, 3H), 1.81−1.68
13
(m, 4H), 1.50−1.24 (m, 8H). C NMR (CDCl , 75 MHz): δ 165.7,
3
163.7, 145.3, 139.2, 139.0, 128.9, 123.3, 123.2, 118.5, 115.2, 111.8,
110.3, 66.2, 52.7, 43.2, 29.2, 29.1, 28.8, 27.1, 25.9.
methane and hexane to afford the product as a yellow solid. Yield: 4.48
1
g (69%). H NMR (CDCl , 300 MHz): δ 10.12 (s, 1H), 8.17−8.13
3
13
(
m, 4H), 7.78 (d, 2H), 7.54−7.30 (m, 6H). C NMR (CDCl , 75
MHz): δ 191.1, 143.5, 140.1, 134.7, 131.5, 126.9, 126.3, 124.1, 121.1,
Synthesis of 6-(8-(3,6-Dibromo-9H-carbazol-9-yl)octyloxy)-
picolinic Acid (5). To a suspension of compound 4 (0.6 g, 1.0 mmol)
in methanol (10 mL) was added a solution of NaOH (0.14 g, 3.5
mmol) in water (10 mL). The mixture was heated at reflux for 5 h and
gradually became clear. After completion of the reaction, the organic
phase was evaporated under reduced pressure. The aqueous phase was
acidified with concentrated HCl. The mixture was poured into water
and extracted with ethyl acetate, and the combined organic layer was
dried over magnesium sulfate. The solvent was removed by rotary
3
1
20.9, 109.9.
Synthesis of 4-(3,6-Dibromo-9H-carbazol-9-yl)-
benzaldehyde (2). Compound 1 (3.5 g, 12.9 mmol) was dissolved
in dichloromethane (100 mL), after which Br (1.0 mL, 38.7 mmol) in
2
dichloromethane (5 mL) was added dropwise to the flask at 0 °C. The
mixture was continuously stirred at room temperature for another 6 h.
The crude solution was quenched with saturated NaOH solution and
poured into water, extracted with dichloromethane/brine, dried over
magnesium sulfate, and concentrated in vacuo. The residue was
1
evaporation to gain compound 5. Yield: 0.53 g (90%). H NMR
(CDCl , 300 MHz): δ 10.5 (br, 1H), 8.12 (s, 2H), 7.82−7.78 (m, 2H),
3
recrystallized in dichloromethane and methanol to afford the product.
7.55 (d, 2H), 7.27 (d, 2H), 6.99 (d, 1H), 4.25 (m, 4H), 1.82−1.72 (m,
1
13
Yield: 4.76 g (86%). H NMR (CDCl , 300 MHz): δ 10.12 (s, 1H),
4H), 1.50−1.24 (m, 8H). C NMR (CDCl , 75 MHz): δ 168.3, 163.7,
3
3
8
.24 (s, 2H), 8.18 (d, 2H), 7.71 (d, 2H), 7.51 (d, 2H), 7.35 (d, 2H).
145.3, 139.2, 139.0, 128.9, 123.3, 123.2, 118.5, 115.2, 111.8, 110.3,
66.2, 52.7, 29.2, 29.1, 28.8, 27.1, 25.9.
Synthesis of Bis[2-(4,6-difluorophenyl)pyridinato-N,C ′]-
1
3
C NMR (CDCl , 75 MHz): δ 193.0, 145.7, 141.3, 134.5, 131.2,
3
2
1
27.3, 125.6, 123.8, 123.1, 120.3, 112.9.
Synthesis of 3,6-Dibromo-9-(4-(bis(9-(2-ethylhexyl)-9H-car-
iridium(III)(6-(8-(3,6-dibromo-9H-carbazol-9-yl)octyloxy)-
picolinate) (M2). Compound 5 (0.54 g, 0.9 mmol), sodium
carbonate (0.45 g, 4.2 mmol), and blue iridium dimer (0.51 g, 0.42
mmol) were dissolved in 2-ethoxyethanol and refluxed under a
nitrogen atmosphere for 12 h. After cooling to room temperature, the
crude solution was poured into water, extracted with dichloro-
methane/brine, dried over magnesium sulfate, and concentrated in
vacuo. The residue was purified through column chromatography using
dichloromethane as eluent and recrystallized in dichloromethane and
bazol-3-yl)methyl)phenyl)-9H-carbazole (3). To a mixture of
compound 2 (2.0 g, 4.7 mmol) and 9-(2-ethylhexyl)carbazole (3.3 g,
11.8 mmol) in AcOH (100 mL), HCl (25 mL, 35.0−37.0%) was
added slowly. The reaction mixture was refluxed for 48 h and then
poured in water and filtered. The deposit was dissolved in
dichloromethane and extracted with dichloromethane/brine three
times. The organic layer was dried over magnesium sulfate. After
removing the solvent by evaporation, the residue was purified through
column chromatography using hexane/dichloromethane (3:1, v/v) as
1
hexane to afford the product as a yellow solid. Yield: 0.57 g (53%). H
eluent and recrystallized in dichloromethane and methanol to afford
NMR (CDCl , 300 MHz): δ 8.66 (d, 1H), 8.27 (q, 2H), 8.15 (s, 2H),
3
1
the product as a white solid. Yield: 3.44 g (76%). H NMR (CDCl ,
8.01 (d, 1H), 7.90 (t, 1H), 7.73 (m, 2H), 7.64 (d, 1H), 7.56 (d, 2H),
7.28 (d, 2H), 7.11 (t, 1H), 6.93 (t, 1H), 6.82 (d, 1H), 6.33 (m, 2H),
3
3
1
2
7
1
00 MHz): δ 8.18 (s, 2H), 8.01 (d, 2H), 7.95 (s, 2H), 7.50−7.38 (m,
4H), 7.33 (d, 2H), 7.17 (t, 2H), 6.08 (s, 1H), 4.15 (d, 4H), 2.07 (m,
5.70 (d, 1H), 5.39 (d, 1H), 4.25 (t, 2H), 3.60 (m, 2H), 1.82 (m, 2H),
13
13
H), 1.41−1.25 (m, 16H), 0.95−0.83 (m, 12H). C NMR (CDCl3,
5 MHz): δ 145.7, 141.3, 139.8, 139.7, 134.6, 134.5, 131.2, 129.3,
27.3, 126.5, 125.6, 123.8, 123.1, 122.8, 122.6, 121.0, 120.3, 118.6,
1.25−0.97 (m, 10H). C NMR (CDCl , 75 MHz): δ 173.3, 165.1,
3
164.0, 161.2, 154.4, 154.3, 151.0, 150.5, 150.5, 148.9, 148.2, 141.6,
139.2, 138.0, 137.8, 129.0, 123.4, 123.2, 123.1, 122.4, 122.2, 121.7,
7
404
dx.doi.org/10.1021/ma5015929 | Macromolecules 2014, 47, 7397−7406

Macromolecules
Article
1
4
21.1, 114.1, 113.9, 113.7, 113.5, 111.9, 110.3, 109.6, 98.0, 95.9, 69.5,
121.0, 120.3, 118.9, 118.6, 110.4, 108.9, 106.5, 56.5, 47.5, 39.5, 31.0,
28.8, 24.4, 23.1, 14.1, 10.9. Element Anal. Found: C, 85.69; H, 7.26; N,
4.27.
PCztPSiB5R0.6. M1 (0.40 g, 0.38 mmol), M4 (0.165 g, 0.33
mmol), M2 (43.1 mg, 0.038 mmol), and M3 (5.3 mg, 0.0045 mmol)
were used for polymerization. Yield: 45%. 1H NMR (300 MHz,
+
3.2, 29.0, 28.8, 28.7, 27.3, 26.9, 25.2. FAB-MS: m/z = 1147.25 (M ).
2
Synthesis of Bis[2-phenylquinoline-N,C ′]iridium(III)(6-(8-
(3,6-dibromo-9H-carbazol-9-yl)octyloxy)picolinate) (M3). Com-
pound 5 (0.60 g, 1.0 mmol), sodium carbonate (0.50 g, 4.7 mmol),
and red iridium dimer (0.60 g, 0.47 mmol) were dissolved in 2-
ethoxyethanol and refluxed under a nitrogen atmosphere for 12 h.
After cooling to room temperature, the crude solution was poured into
water, extracted with dichloromethane/brine, dried over magnesium
sulfate, and concentrated in vacuo. The residue was purified through
column chromatography using dichloromethane as eluent and
recrystallized in dichloromethane and hexane to afford the product
as a reddish orange solid. Yield: 0.84 g (76%). H NMR (CDCl , 300
MHz): δ 8.87 (d, 1H), 8.15 (s, 2H), 8.12−7.98 (m, 5H), 7.91 (d, 1H),
CDCl ): δ 8.43 (br, 2H), 8.17 (br, 0.18H), 7.98 (br, 4H), 7.80−7.60
3
(br, 12H), 7.53 (br, 6H), 7.39 (br, 14H), 7.19 (br, 4H), 6.31 (br,
0.18H), 6.09 (br, 1H), 5.67 (br, 0.09H), 5.39 (br, 0.09H), 4.37 (br,
0.18H), 4.15 (br, 4H), 2.06 (br, 2H), 1.43−1.20 (m, 16H), 0.87 (br,
12H). 13C NMR (CDCl , 75 MHz): δ 145.1, 142.9, 141.3, 140.9,
3
139.7, 136.9, 136.4, 135.3, 134.8, 134.4, 133.1, 132.0, 131.0, 129.5,
128.7, 127.9, 127.4, 126.8, 126.5, 125.5, 124.0, 122.8, 122.6, 121.1,
120.5, 118.9, 118.7, 110.4, 108.9, 56.6, 47.5, 39.6, 31.0, 28.8, 24.4, 23.0,
14.0, 11.0. Element Anal. Found: C, 85.02; H, 7.45; N, 3.36.
PCztPSiB7.5R0.7. M1 (0.40 g, 0.38 mmol), M4 (0.155 g, 0.34
mmol), M2 (64.6 mg, 0.056 mmol), and M3 (6.2 mg, 0.0052 mmol)
were used for polymerization. Yield: 46%. 1H NMR (300 MHz,
1
3
7
7
4
.76 (t, 2H), 7.67 (t, 2H), 7.54 (d, 2H), 7.45 (m, 3H), 7.36 (t, 1H),
.22 (d, 2H), 6.88 (m, 3H), 6.76 (d, 1H), 6.59 (m, 3H), 6.16 (d, 1H),
.21 (t, 2H), 3.60 (m, 2H), 1.82 (m, 2H), 1.25−0.97 (m, 10H).
13
C
NMR (CDCl , 75 MHz): δ 172.9, 171.3, 170.4, 163.9, 152.0, 151.7,
3
1
1
1
1
2
49.3, 147.2, 146.4, 146.1, 140.6, 139.2, 138.4, 138.3, 134.9, 133.1,
31.5, 129.5, 129.4, 129.1, 129.0, 128.6, 127.7, 127.5, 127.2, 126.9,
26.3, 126.1, 125.9, 125.6, 125.3, 123.4, 123.2, 121.8, 119.8, 119.7,
17.1, 115.7, 111.9, 110.3, 108.2, 69.1, 43.2, 29.1, 28.9, 28.8, 27.6, 27.0,
5.6. FAB-MS: m/z = 1175.31 (M ).
General Procedure for Suzuki Polymerization with
CDCl ): δ 8.43 (br, 2H), 8.17 (br, 0.24H), 7.98 (br, 4H), 7.80−7.60
3
(br, 12H), 7.51 (br, 6H), 7.41 (br, 14H), 7.16 (br, 4H), 6.31 (br,
0.24H), 6.10 (br, 1H), 5.69 (br, 0.12H), 5.40 (br, 0.12H), 4.37 (br,
0.24H), 4.16 (br, 4H), 2.06 (br, 2H), 1.43−1.20 (m, 16H), 0.88 (br,
+
13
12H). C NMR (CDCl , 75 MHz): δ 145.1, 142.9, 141.3, 140.9,
3
139.7, 136.9, 136.4, 135.3, 134.8, 134.4, 133.1, 132.0, 131.0, 129.6,
PCztPSiB2.5 as Example. In a 50 mL two-necked flask, M1 (0.40
g, 0.38 mmol), M4 (0.18 g, 0.36 mmol), M2 (21.5 mg, 0.019 mmol),
Pd(PPh ) (13 mg), and tetrabutylammonium bromide (TBAB) (12.1
mg, 0.038 mmol) were dissolved in toluene (5 mL), after which
tetraethylammonium hydroxide solution (5 mL, 20 wt % Et NOH in
1
1
28.7, 127.9, 127.3, 126.8, 126.5, 125.5, 124.0, 122.8, 122.6, 121.1,
20.5, 118.9, 118.7, 110.4, 108.8, 56.7, 47.5, 39.6, 31.0, 28.8, 24.4, 23.0,
3
4
14.1, 11.0. Element Anal. Found: C, 84.96; H, 7.67; N, 3.30.
Device Fabrication. Devices with the ITO/PEDOT:PSS/PVK/
EML/TSPO1/LiF/Al configuration were fabricated using the
synthesized polymers (Figure 4) as follows. ITO glass substrates
were consecutively washed with acetone, detergent, distilled water, and
4
H O) was added. The mixture was heated to 110 °C and stirred for 36
2
h under an argon atmosphere. The polymer was then capped by
adding phenylboronic acid and stirring the reaction mixture
continuously for 6 h. Bromobenzene was subsequently added, and
the mixture was continuously stirred for another 6 h. The whole
mixture was poured into methanol. The precipitated polymer was
recovered by filtration and purification by silica column chromatog-
raphy with chloroform. The polymer was then purified further by
Soxhlet extraction with acetone as solvent to remove oligomers. The
reprecipitation procedure with chloroform/methanol was repeated
several times. The resulting polymer was soluble in common organic
2
-propanol. After ultraviolet/ozone treatment for 10 min, a 60 nm
thick layer of PEDOT doped with PSS (PEDOT:PSS, CH8000) was
spin-coated onto the ITO substrates. The spin-coated film was baked
at 140 °C for 10 min. A 10 nm thick layer of PVK in chlorobenzene
was spin-coated onto the PEDOT:PSS layer and baked at 120 °C for
1
0 min. Two kinds of emitting layers were prepared: one is pure
polymers, and another is polymers dopped with OXD-7. Polymers or
polymers with the OXD-7 in a dopping ratio of 2:1 were dissolved in
toluene, filtered through a 0.50 μm polytetrafluoroethylene (hydro-
phobic) syringe filter, spin-coated onto the PVK layer, and baked at
120 °C for 10 min. The active layers were around 40 nm thick, as
determined using an Alpha-Step IQ surface profiler (KLA Tencor).
TSPO1, which acts as a high-triplet-energy exciton-blocking layer
(HBL) with electron transport properties, was subsequently deposited
solvents such as chloroform and toluene. The polymer yield was 52%.
1
H NMR (300 MHz, CDCl ): δ 8.41 (br, 2H), 8.16 (br, 0.09H), 7.96
3
(
4
br, 4H), 7.80−7.60 (br, 12H), 7.50 (br, 6H), 7.37 (br, 14H), 7.15 (br,
H), 6.31 (br, 0.09H), 6.07 (br, 1H), 5.69 (br, 0.04H), 5.39 (br,
0
1
1
1
1
2
4
.04H), 4.36 (br, 0.09H), 4.13 (br, 4H), 2.03 (br, 2H), 1.43−1.20 (m,
6H), 0.88 (br, 12H). 13C NMR (CDCl , 75 MHz): δ 145.1, 142.9,
39
3
on the emissive layer. Finally, lithium fluoride (LiF) was deposited as
41.3, 140.9, 139.7, 137.0, 136.4, 135.2, 134.8, 134.4, 133.1, 132.0,
31.0, 129.6, 128.8, 127.9, 127.4, 126.7, 126.5, 125.5, 123.9, 122.8,
22.6, 121.0, 120.3, 118.9, 118.6, 110.4, 108.9, 56.6, 47.5, 39.5, 31.0,
8.8, 24.4, 23.1, 14.1, 10.9. Element Anal. Found: C, 86.41; H, 7.29; N,
.15.
an electron-injecting layer (EIL) at an evaporation rate of 1 Å/s, and
aluminum was deposited by vacuum evaporation on top of the film
through a mask at a deposition rate of 5 Å/s.
1
13
Measurements. H and C NMR spectra were recorded using a
Varian Mercury Plus 300 MHz spectrometer. The chemical shifts were
expressed as parts per million (ppm), with chloroform as an internal
standard (δ 7.26 ppm). The fast atom bombardment mass spectra
were measured using a ZMS-DX303 mass spectrometer (FAB-MS;
JEOL LTD). Elemental analysis was performed using a Vario Micro
Cube at the Korea Basic Science Institute (Busan, Korea.) The
PCztPSi. M1 (0.40 g, 0.38 mmol) and M4 (0.19 g, 0.38 mmol)
were used for polymerization. Yield: 65%. 1H NMR (300 MHz,
CDCl ): δ 8.41 (br, 2H), 7.96 (br, 4H), 7.80−7.60 (br, 12H), 7.50 (br,
3
6
H), 7.37 (br, 14H), 7.15 (br, 4H), 6.07 (br, 1H), 4.13 (br, 4H), 2.03
13
(
br, 2H), 1.43−1.20 (m, 16H), 0.88 (br, 12H). C NMR (CDCl , 75
3
MHz): δ 145.1, 142.9, 141.3, 140.9, 139.7, 137.0, 136.5, 135.3, 134.8,
number- (M ) and weight-average molecular weights and polydisper-
n
1
1
5
34.4, 133.2, 132.0, 131.0, 129.6, 128.8, 127.9, 127.4, 126.8, 126.5,
25.6, 124.0, 122.8, 122.6, 121.0, 120.4, 118.9, 118.6, 110.4, 108.9,
6.6, 47.5, 39.5, 31.0, 28.8, 24.4, 23.1, 14.1, 10.9. Element Anal. Found:
sity indices of the polymers relative to a polystyrene standard were
determined via gel permeation chromatography using a Waters high-
pressure GPC assembly (Model M590). Thermal analyses were
e
C, 86.63; H, 7.27; N, 4.09.
performed using a Mettler Toledo TGA/SDTA 851 under a N
2
PCztPSiB5. M1 (0.40 g, 0.38 mmol), M4 (0.17 g, 0.34 mmol), and
atmosphere, with heating and cooling rates of 10 °C/min. Ultraviolet−
visible absorption was recorded using a Shimadzu UV−vis
spectrophotometer (UV-1800). Photoluminescence emission spectra
were recorded using a Hitachi F-7000 fluorescence spectrophotometer.
The PL quantum yields were measured using a Quantaurus-QY
C11347−11 (Hamamatsu Photonics) at 310 nm excitation wavelength
from 150 W xenon light source. Cyclic voltammetry using a CH
Instruments electrochemical analyzer was carried out in an acetonitrile
M2 (43.1 mg, 0.038 mmol) were used for polymerization. Yield: 58%.
1
H NMR (300 MHz, CDCl ): δ 8.41 (br, 2H), 8.16 (br, 0.18H), 7.96
3
(
br, 4H), 7.80−7.60 (br, 12H), 7.50 (br, 6H), 7.37 (br, 14H), 7.15 (br,
4
0
1
1
1
H), 6.31 (br, 0.18H), 6.07 (br, 1H), 5.69 (br, 0.09H), 5.39 (br,
.09H), 4.36 (br, 0.18H), 4.13 (br, 4H), 2.03 (br, 2H), 1.43−1.20 (m,
6H), 0.88 (br, 12H). 13C NMR (CDCl , 75 MHz): δ 142.9, 141.3,
3
40.9, 139.7, 136.9, 136.4, 135.2, 134.8, 134.4, 133.1, 131.9, 131.0,
29.6, 128.8, 127.9, 127.4, 126.7, 126.5, 125.5, 123.9, 122.8, 122.6,
(CH CN) solution containing 0.10 M tetrabutylammonium tetra-
3
7
405
dx.doi.org/10.1021/ma5015929 | Macromolecules 2014, 47, 7397−7406

Macromolecules
Article
fluoroborate (TBABF ) as supporting electrolyte. A Pt plate, Pt wire,
(15) Schulz, G. L.; Chen, X.; Chen, S.-A.; Holdcroft, S. Macro-
molecules 2006, 39, 9157−9165.
4
and Ag/AgNO electrode were used as the working, counter, and
3
reference electrodes, respectively. Atomic force microscopy was
performed using SPM L-Trace II operating in the tapping mode in
air. The current density−voltage−luminance (I−V−L) characteristics
and EL spectra of the PhPLEDs were measured using a Keithley 2400
source measurement unit and CS 1000 spectrophotometer.
(16) Zhang, K.; Chen, Z.; Yang, C.; Zou, Y.; Gong, S.; Tao, Y.; Qin,
J.; Cao, Y. J. Mater. Chem. 2008, 18, 3366−3375.
́
(17) Poulsen, D. A.; Kim, B. J.; Ma, B.; Zonte, C. S.; Frechet, J. M. J.
Adv. Mater. 2010, 22, 77−82.
(18) Ma, Z.; Chen, L.; Ding, J.; Wang, L.; Jing, X.; Wang, F. Adv.
Mater. 2011, 23, 3726−3729.
ASSOCIATED CONTENT
Supporting Information
H NMR spectra of compounds (1-5), monomers (M1-M4),
(19) Shao, S.; Ding, J.; Wang, L.; Jing, X.; Wang, F. J. Am. Chem. Soc.
■
2
012, 134, 20290−20293.
(20) Shao, S.; Ding, J.; Wang, L.; Jing, X.; Wang, F. J. Am. Chem. Soc.
012, 134, 15189−15192.
21) Han, W.-S.; Son, H.-J.; Wee, K.-R.; Min, K.-T.; Kwon, S.; Suh, I.-
H.; Choi, S.-H.; Jung, D. H.; Kang, S. O. J. Phys. Chem. C 2009, 113,
9686−19693.
22) Schrogel, P.; Tomkevici
Ko
*
S
1
2
(
and polymers, DSC and TGA curves, absorption and PL
spectra in dichloromethane solution, cyclic voltammograms,
AFM images, and efficiency−luminance curves. This material is
available free of charge via the Internet at http://pubs.acs.org.
1
(
̈
̌
̇
ene, A.; Strohriegl, P.; Hoffmann, S. T.;
̈
hler, A.; Lennartz, C. J. Mater. Chem. 2011, 21, 2266−2273.
AUTHOR INFORMATION
Corresponding Authors
E-mail: dohoonhwang@pusan.ac.kr (D.-H.H.).
E-mail: leej17@dankook.ac.kr (J.Y.L.).
(23) Moon, B.-J.; Yook, K. S.; Lee, J. Y.; Shin, S.; Hwang, S.-H. J.
Lumin. 2012, 132, 2557−2560.
(
■
24) Koech, P. K.; Polikarpov, E.; Rainbolt, J. E.; Cosimbescu, L.;
*
Swensen, J. S.; Ruden, A. L. V.; Padmaperuma, A. B. Org. Lett. 2010,
2, 5534−5537.
25) Brunner, K.; Dijken, A. V.; Bo
Kiggen, N. M. M.; Langeveld, B. M. W. J. Am. Chem. Soc. 2004, 126,
*
1
Notes
(
̈
rner, H.; Bastiaansen, J. J. A. M.;
The authors declare no competing financial interest.
6
035−6042.
ACKNOWLEDGMENTS
(26) Liu, J.; Pei, Q. Macromolecules 2010, 43, 9608−9612.
(
■
27) Dijken, A. V.; Bastiaansen, J. J. A. M.; Kiggen, N. M. M.;
This work was supported by the Industrial Strategic
Technology Development Program (No. 10039141, Develop-
ment of core technologies for organic materials applicable to
OLED lighting with high color rendering index) funded by the
Ministry of Knowledge Economy (MKE, Korea), the Center
for Advanced Soft-Electronics funded by the Ministry of
Science, ICT and Future Planning as Global Frontier Project
CASE-2014M3A6A5060936), and a National Research
Foundation (NRF) grant funded by the Korean government
NRF-2014R1A2A2A01007318).
Langeveld, B. M. W.; Rothe, C.; Monkman, A.; Bach, I.; Sto
Brunner, K. J. Am. Chem. Soc. 2004, 126, 7718−7727.
28) Wu, Z.; Xiong, Y.; Zou, J.; Wang, L.; Liu, J.; Chen, Q.; Yang, W.;
̈
ssel, P.;
(
Peng, J.; Cao, Y. Adv. Mater. 2008, 20, 2359−2364.
(
(
T.; Wong, K.-T.; Chen, C.-C.; Wu, C.-C. Dalton Trans. 2009, 6472−
6475.
(31) Zhang, K.; Chen, Z.; Zou, Y.; Yang, C.; Qin, J.; Cao, Y.
Organometallics 2007, 26, 3699−3707.
(
29) Nonoyama, M. J. Organomet. Chem. 1975, 86, 263−267.
30) Hung, J.-Y.; Chi, Y.; Pai, I.-H.; Yu, Y.-C.; Lee, G.-H.; Chou, P.-
(
(
32) Zhang, K.; Chen, Z.; Yang, C.; Zou, Y.; Gong, S.; Qin, J.; Cao, Y.
J. Phys. Chem. C 2008, 112, 3907−3913.
33) Zhen, H.; Jiang, C.; Yang, W.; Jiang, J.; Huang, F.; Cao, Y.
Chem.Eur. J. 2005, 11, 5007−5016.
34) Leriche, P.; Frere, P.; Cravino, A.; Alev
Org. Chem. 2007, 72, 8332−8336.
35) Ma, Z.; Ding, J.; Cheng, Y.; Xie, Z.; Wang, L.; Jing, X.; Wang, F.
Polymer 2011, 52, 2189−2197.
36) Hu, D.; Lu, P.; Wang, C.; Liu, H.; Wang, H.; Wang, Z.; Fei, T.;
Gu, X.; Ma, Y. J. Mater. Chem. 2009, 19, 6143−6148.
37) Wang, Y.; Tan, H.; Liu, Y.; Jiang, C.; Hu, Z.; Zhu, M.; Wang, L.;
Zhu, W.; Cao, Y. Tetrahedron 2010, 60, 1483−1488.
38) Zhao, Q.; Jiang, C.-Y.; Shi, M.; Li, F.-Y.; Yi, T.; Cao, Y.; Huang,
C.-H. Organometallics 2006, 25, 3631−3638.
39) Jeon, S. O.; Jang, S. E.; Son, H. S.; Lee, J. Y. Adv. Mater. 2011,
3, 1436−1441.
REFERENCES
■
(
(
1) Chen, X.; Liao, J.-L.; Liang, Y.; Ahmed, M. O.; Tseng, H.-E.;
Chen, S.-A. J. Am. Chem. Soc. 2003, 125, 636−637.
́
2) Furuta, P. T.; Deng, L.; Garon, S.; Thompson, M. E.; Frechet, J.
(
̀
́ ̂
eque, O.; Roncali, J. J.
(
M. J. J. Am. Chem. Soc. 2004, 126, 15388−15389.
3) Park, M. J.; Lee, J.; Park, J. H.; Lee, S. K.; Lee, J. I.; Chu, H. Y.;
Hwang, D. H.; Shim, H. K. Macromolecules 2008, 41, 3063−3070.
4) Jiang, J. X.; Xu, Y. H.; Yang, W.; Guan, R.; Liu, Z. Q.; Zhen, H.
Y.; Cao, Y. Adv. Mater. 2006, 18, 1769−1773.
5) Park, M.-J.; Kwak, J.; Lee, J.; Jung, I. H.; Kong, H.; Lee, C.;
Hwang, D.-H.; Shim, H.-K. Macromolecules 2010, 43, 1379−1386.
6) Chien, C.-H.; Liao, S.-F.; Wu, C.-H.; Shu, C.-F.; Chang, S.-Y.;
Chi, Y.; Chou, P.-T.; Lai, C.-H. Adv. Funct. Mater. 2008, 18, 1430−
439.
7) Liu, J.; Yu, L.; Zhong, C.; He, R.; Yang, W.; Wu, H.; Cao, Y. RSC
Adv. 2012, 2, 689−696.
8) Ying, L.; Xu, Y.; Yang, W.; Wang, L.; Wu, H.; Cao, Y. Org.
Electron. 2009, 10, 42−47.
9) Park, J. H.; Koh, T.-W.; Chung, J.; Park, S. H.; Eo, M.; Do, Y.;
Yoo, S.; Lee, M. H. Macromolecules 2013, 46, 674−682.
10) Kimyonok, A.; Domercq, B.; Haldi, A.; Cho, J.-Y.; Carlise, J. R.;
(
(
(
(
(
(
(
(
(
2
1
(
(
(
(
Wang, X.-Y.; Hayden, L. E.; Jones, S. C.; Barlow, S.; Marder, S. R.;
Kippelen, B.; Weck, M. Chem. Mater. 2007, 19, 5602−5608.
(
11) Fei, T.; Cheng, G.; Hu, D.; Dong, W.; Lu, P.; Ma, Y. J. Polym.
Sci., Part A: Polym. Chem. 2010, 48, 1859−1865.
12) Xu, F.; Kim, J.-H.; Kim, H. U.; Mi, D.; Cho, Y. J.; Lee, J. Y.;
Yoon, U. C.; Hwang, D.-H. Synth. Met. 2013, 178, 10−17.
13) Zhang, K.; Tao, Y.; Yang, C.; You, H.; Zou, Y.; Qin, J.; Ma, D.
Chem. Mater. 2008, 20, 7324−7331.
14) Zhang, K.; Chen, Z.; Zou, Y.; Gong, S.; Yang, C.; Qin, J.; Cao, Y.
Chem. Mater. 2009, 21, 3306−3314.
(
(
(
7
406
dx.doi.org/10.1021/ma5015929 | Macromolecules 2014, 47, 7397−7406