Soluble polynorbornenes with pendant carbazole derivatives as host materials for highly efficient blue phosphorescent organic light-emitting diodes

Article abstract of DOI:10.1002/pola.26005

We report novel host polymers for a high-efficiency polymer-based solution-processed phosphorescent organic light-emitting diode with typical blue-emitting dopant bis(4,6-difluorophenylpyridinato-N,C²) iridium(III) picolinate (FIrpic). The host

Full text of DOI:10.1002/pola.26005

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
Soluble Polynorbornenes with Pendant Carbazole Derivatives as Host
Materials for Highly Efficient Blue Phosphorescent Organic
Light-Emitting Diodes
Jun Ha Park,1 Tae-Wook Koh,2 Youngkyu Do,1 Min Hyung Lee,3 Seunghyup Yoo2
1Department of Chemistry, KAIST, Daejeon 305-701, Republic of Korea
2Department of Electrical Engineering, KAIST, Daejeon 305-701, Republic of Korea
3Department of Chemistry and Energy Harvest-Storage Research Center, University of Ulsan, Ulsan 680-749, Republic of Korea
Correspondence to: M. H. Lee (E-mail: lmh74@ulsan.ac.kr), Y. Do (E-mail: ykdo@kaist.ac.kr), S. Yoo (E-mail: syoo@ee.kaist.ac.kr)
Received 13 July 2011; accepted 30 January 2012; published online
DOI: 10.1002/pola.26005
ABSTRACT: We report novel host polymers for a high-efficiency
polymer-based solution-processed phosphorescent organic
light-emitting diode with typical blue-emitting dopant bis(4,6-
difluorophenylpyridinato-N,C2)iridium(III) picolinate (FIrpic).
The host polymers, soluble polynorbornenes with pendant car-
bazole derivatives, N-phenyl-9H-carbazole (P1), N-biphenyl-9H-
carbazole (P2), and 9,90-(1,3-phenylene)bis-9H-carbazole (mCP)
(P3) are efficiently synthesized by vinyl addition polymerization
of norbornene monomers using Pd(II) catalyst in combination
with 1-octene chain transfer agent. The polymers exhibit high
thermal stability with high decomposition (Td5 > 410 ꢀC) and
glass transition temperatures (Tg ꢁ 268 ꢀC). The HOMO (ca.
ꢂ5.5 to ꢂ5.7 eV) and LUMO (ca. ꢂ2.0 to ꢂ2.1 eV) levels with
the high triplet energy of about 2.7–3.0 eV suggest that the
polymers are suitable for a host material for blue emitters.
Among the solution-processed devices that were fabricated
based on the emissive layers containing the P1ꢂP3 host doped
with various concentrations of FIrpic (7–13 wt %), the best de-
vice with P3 host exhibits power efficiency of 3.0 lm Wꢂ1
and external quantum efficiency of 4.0% at
a luminance
of 1000 cd mꢂ2 that is outstanding among the polymeric rivals.
C
V
2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem
000: 000–000, 2012
KEYWORDS: addition polymerization; carbazole; catalysis; host;
light-emitting diodes (LED); polynorbornene
INTRODUCTION Phosphorescent heavy metal complexes
have attracted considerable attention as electroactive materi-
als in organic light-emitting diodes (OLEDs).1(a–e)–3 Strong
spin–orbit coupling caused by heavy metal atoms results in
efficient intersystem crossing from singlet to triplet excited
state, allowing the complexes to harvest both singlet and tri-
plet excitons. Thus, phosphorescent OLEDs (PhOLEDs) based
on heavy metal complexes can theoretically achieve up to
four times higher internal quantum efficiency than that of
fluorescent OLEDs.2–4 However, it is well known that phos-
phorescent complexes with relatively longer lifetime may
lead to triplet–triplet (T–T) annihilation and concentration
quenching, and thereby decrease in device performance.5(a–c)
To surmount these problems, phosphorescent complexes are
usually adopted as dopants dispersed into appropriate host
materials that should fulfill some essential requirements: (i)
higher triplet energy level (ET) than that of phosphorescent
emitters, which prevent backward energy transfer from
guest into host and confine triplet excitons in the guest
materials;6(a–e) (ii) morphological and thermal stabilities that
extend the device’s operational lifetime.7 Thus, to improve
the efficiency of the PhOLEDs, development of efficient host
materials is also equally important to development of effi-
cient phosphorescent emitters. Although excellent perform-
ances have been realized with the devices based on small
molecular host materials of carbazole derivatives such as
9,90-(1,10-biphenyl)-4,40-diylbis-9H-carbazole (CBP),2,8 9,90-
(1,3-phenylene)bis-9H-carbazole (mCP),9,10 and 3,5-bis(9-car-
bazolyl)-tetraphenylsilane (SimCP),11 polymeric host materi-
als are also of great interest owing to their good solution
processability required for large area or flexible OLEDs by
spin coating and inkjet printing12(a–c) for mass production of
high-efficiency OLEDs applicable to information displays and
lightings. In this aspect, many studies about conjugated and
nonconjugated polymeric hosts have been investigated exten-
sively in the red13(a–g) and green14,15(a,b) PhOLED devices
that showed high device efficiency comparable to that of
small molecular host materials.
For blue phosphorescent OLED devices, however, polymeric
host materials have rarely been reported and moreover, the
performances of these devices based on the polymeric hosts
Additional Supporting Information may be found in the online version of this article.
C
V
2012 Wiley Periodicals, Inc.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 000, 000–000
1

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
SCHEME 1 Conditions: (i) 3-bromocarbazole, Cu, 18-crown-6, K2CO3, o-dichlorobenzene, reflux. (ii) 2 t-BuLi, THF, ꢂ78 ꢀC. [Pd(II)] ¼
[(NHC)Pd(g3-allyl)][SbF6].
have lagged far behind that of vacuum-deposited device-
s.14,16,17(a,b) These results might be explained by the phos-
phorescence quenching caused by Dexter triplet energy
back-transfer from the emitter to the host material. This
back-transfer results from the failure in satisfying the
requirement that conjugated and nonconjugated polymers
used as host materials should have higher triplet energy
than typical blue phosphorescent emitters, such as bis(4,6-
difluorophenylpyridinato-N,C2)iridium(III) picolinate, FIrpic
(ET ¼ 2.65 eV).9,18(a,b),19 To realize efficient blue PhOLEDs,
therefore, designing a new type of polymeric host material
possessing high triplet energy as well as good charge carrier
transport properties will be crucial.
host candidates by Feng et al.,23 mCP moieties in the copoly-
mers were used as the host for green emitter, not for blue
emitter, and no device performances based on such copoly-
mers were reported.
In this study, we designed norbornene monomers functional-
ized with mono- and biscarbazole derivatives and used them
in the vinyl addition polymerization with the help of palla-
dium(II) catalyst to provide the highly efficient polymeric
host materials for the blue PhOLEDs. Details of synthesis,
characterization, as well as its use as host materials in actual
PhOLEDs are described to demonstrate that the proposed
approach can afford blue PhOLEDs with high performance.
Recently, we reported that vinyl-type polynorbornenes with
various side groups that possess hole-transporting or host
property can function as efficient materials for OLEDs appli-
cations.20–22 In particular, it was revealed that polynorbor-
nenes with CBP side groups as host material show excellent
device performance in green PhOLEDs, which is comparable
to that of identical device based on molecular CBP con-
structed by vacuum deposition technique.20 Despite the suc-
cessful demonstration in green PhOLEDs, the triplet energy
of the polynorbornene with CBP side groups (2.60 eV) is
lower than those of typical blue emitters,20 indicating it is
not adequate for blue PhOLEDs.9,19 Hence, vinyl-type poly-
norbornenes bearing side-chain carbazole derivatives with
high triplet energy (>2.65 eV) is required as polymeric host
materials to achieve efficient blue PhOLEDs. This led us to
consider a new candidate for side-chain carbazole groups
such as mCP (ET ¼ 2.90 eV).9 Although norbornene-based
copolymers incorporating mCP groups produced via ring-
opening metathesis polymerization have been investigated as
RESULTS AND DISCUSSION
Synthesis and Characterization
Synthetic routes toward norbornene monomers bearing car-
bazole derivatives (M1–M3) and the corresponding polymers
P1ꢂP3 are depicted in Scheme 1. As the carbazole moiety,
mCP,9,10 the well-known molecular host material for blue tri-
plet emitter in PhOLEDs, as well as monocarbazole ana-
logues such as N-phenyl-9H-carbazole and N-biphenyl-9H-
carbazole, were introduced for M3, and M1 and M2, respec-
tively. The starting materials, 9-(4-bromophenyl)-9H-carba-
zole (1),24 9-(40-bromo-biphenyl-4-yl)-9H-carbazole (2),25
and 9-(3-iodophenyl)carbazole (3a)26 were prepared accord-
ing to the modified procedures described in the literatures.
Ullmann coupling reaction between 3-bromocarbazole and
3a gave the key intermediate 9-[3-(9H-carbazol-9-yl)phenyl]-
3-bromo-9H-carbazole (3). Lithiation of 1ꢂ3 with 2 equiv of
tert-butyllithium followed by subsequent treatment with 5-
norbornene-2-pentyl bromide afforded the M1ꢂM3
2
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 000, 000–000

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
TABLE 1 Polymerization Result of the Monomers (M12M3)
with Pd(II) Catalysta
c
d
Conversion
(%)
10ꢂ3
Tg
Td5
b
b
Polymer
Mw
Mw/Mn
(ꢀC)
(ꢀC)
e
P1a
P2f
P3g
55
54
49
224
356
488
2.50
2.90
3.17
–
410
420
441
e
–
268
a
Conditions: catalyst
¼
[(NHC)Pd(g3-allyl)Cl]/AgSbF6; [Pd]/[AgSbF6]
¼
1/1.5; [Pd] ¼ 2.5 lmol; [Mon.]/[Pd] ¼ 1000; chain transfer agent (1-octene)
¼ 0.05 mol %; solvent: 17 mL of chlorobenzene; Tp ¼ 25 ꢀC; tp ¼ 20 h.
b
Determined by GPC.
Determined by DSC.
c
d
Determined by TGA at 5% weight loss.
e
Not observed up to decomposition temperature.
f
[Pd] ¼ 2.1 lmol.
FIGURE 2 UVꢂvis absorption and PL spectra of the polymers
(P1ꢂP3) in dilute CH2Cl2 solution.
g
[Pd] ¼ 1.7 lmol.
On the basis of our published polymerization procedure,22
the homopolymerization reactions of M1ꢂM3 were investi-
gated using cationic Pd(II) catalyst derived from the in situ
reaction of N-heterocyclic carbene (NHC; N,N0-bis(2,6-diiso-
propylphenyl)-imidazol-2-ylidene) complex, [(NHC)Pd(g3-
allyl)Cl]27 with AgSbF6 in the presence of 0.05 mol % of 1-
octene chain transfer agent (Table 1). This catalytic system
led to moderate monomer conversion of 49–55% under the
given conditions. It can be also seen that an increase of
steric bulkiness of side group results in the slight lower
monomer conversion. The resulting polymers (P1ꢂP3) are
highly soluble in common organic solvents such as chloro-
form, dichloromethane, tetrahydrofuran, and chlorobenzene
at ambient temperature. The chemical structures of polymers
monomers in good yield (72%, 67%, and 77%, respectively)
after purification by column chromatography. The analysis of
the proton signals in the vinyl region (d ¼ 6.0 ppm) of 1H
NMR spectra further confirms that the monomers consist of
a mixture of endo and exo isomers (ca. 2:1 ratio) following
the composition of 5-norbornene-2-bromide starting material
(Supporting Information Figs. S3ꢂS5).
1
were confirmed by H and 13C NMR spectroscopy as well as
elemental analysis. In particular, the absence of vinyl proton
peaks around d 6.0 ppm and peak broadening in the ali-
phatic region, which is indicative of a rigid polymer back-
bone, for P1ꢂP3 support the formation of vinyl-type poly-
norbornene with pendant carbazole groups (Supporting
Information Figs. S6ꢂS8). Gel permeation chromatography
(GPC) measurements indicate that all the polymers have
high molecular weight (Mw) ranging from 2.24 ꢃ 105 to 4.88
ꢃ 105 g molꢂ1. The narrow polydispersity index (PDI, Mw/
Mn) of 2.5–3.2 is in agreement with the involvement of the
single active catalytic species in the polymerization.
Thermal, Photophysical, and Electrochemical Properties
Thermal properties of the polymers (P1ꢂP3) were charac-
terized using thermogravimetric analysis (TGA) and differen-
tial scanning calorimetry (DSC; Fig. 1).
TGA measurements reveal that they possess high thermal
stability with decomposition temperature (Td5, correspond-
ing to 5% weight loss) above 410 ꢀC. It is notable that the
Td5 value increases with increasing the size of the carbazole
moiety (Table 1). DSC aꢀnalysis shows high glass transition
temperature (Tg) of 268 C for P3 without any other crystal-
lization and melting peaks while no distinct glass transition
temperatures are observed for the P1 and P2 polymers from
DSC measurements. We also note that the high Tg of P3 is
FIGURE 1 (a) TGA and (b) DSC curves of the polymers
(P1ꢂP3).
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 000, 000–000
3

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
TABLE 2 Photophysical and Electrochemical Data of the Polymers (P12P3)
Polymer
kabs (nm) (log e)a
kem (nm)b
kphos (nm)c
Eg (eV)d
ET (eV)e
Eox (eV)f
HOMOg/LUMOh (eV)
P1
P2
P3
a
294 (4.68), 330 (4.03), 342 (4.06)
295 (4.58), 342 (3.93)
348, 364
350, 365
351, 367
416
463
418
f
3.52
3.51
3.51
2.98
2.68
2.97
0.87
0.83
0.73
ꢂ5.67/ꢂ2.15
ꢂ5.63/ꢂ2.12
ꢂ5.53/ꢂ2.02
293 (4.58), 328 (3.93), 340 (3.95)
Absorption measured in CH2Cl2 (2.0 ꢃ 10ꢂ5 M).
Recorded in CH2Cl2 (2.0 ꢃ 10ꢂ6 M) at 298 K.
Recorded in CH2Cl2 glass at 77 K.
The onset of the oxidation wave in CV curves.
b
c
g
h
Calculated from the Eox
Estimated from the HOMO and band-gap (Eg) energies.
.
d
e
Estimated from the absorption edge.
Triplet energy level estimated from the highest energy phosphores-
cence peak.
mainly attributed to the rigid polynorbornene backbone as
molecular mCP itself has a relatively low Tg of 60 C.
indicate that the formation of possible low-energy aggrega-
tion in the excited state between the side-chain carbazole
groups is affected by steric factors of pendant carbazole moi-
ety such as size and planarity. In fact, these observations are
in parallel with those found in the previous reports for the
luminescent polynorbornenes bearing triarylamine side
groups.20–22
28
ꢀ
The UVꢂvis absorption and photoluminescent (PL) spectra
of the polymers (P1ꢂP3) in dilute dichloromethane solution
are shown in Figure 2. While P1 and P3 exhibit very similar
absorption features with the major absorption peaks at 294
and 293 nm along with the vibronic shoulders at 342 and
340 nm, respectively, P2 shows its main absorption peak at
295 nm with broad absorption in the region of 300–350 nm
(Table 2). The lowest energy absorption at 342 nm for P2 is
similar to those for P1 and P3. These peaks are assigned to
the spin-allowed pꢂp* transitions of the pendant carbazole
groups. The optical band gaps (Eg) of P1ꢂP3, as determined
from the absorption onset wavelength, were estimated to be
very similar, affording about 3.52, 3.51, and 3.51 eV, respec-
tively. In the PL spectra obtained at room temperature,
P1ꢂP3 display two vibronic emissions centered at 350 and
365 nm under excitation with 292 nm. While the PL spectra
of P1 and P2 exhibit an additional weak broadening in the
lower energy region (420–500 nm) presumably ascribable to
excited-state aggregation or excimer formation between the
neighboring carbazole moieties, the PL spectrum of P3 does
not show an apparent broadening, as also evidenced from
the almost identical absorption and emission features of P3
and M3 (Supporting Information Fig. S10). This finding may
The PL spectra measured in a frozen CH2Cl2 matrix at 77 K
were used to determine triplet energies (ET) of P1ꢂP3.
Although the prompt PL spectra of P1 and P2 exhibit rela-
tively strong and distinct phosphorescence bands at 77 K
allowing for the determination of triplet energy (Supporting
Information Fig. S11), the PL spectrum of P3 featured broad
phosphorescence which is overlapped with fluorescence
bands (Fig. 3). Thus, we measured delayed PL spectra of
polymers at 77 K and found that all fluorescence bands
clearly disappeared, leaving structured phosphorescence
bands. By taking the highest energy phosphorescence peak
as the transition of T1 ! S0, the triplet energies of polymers
were estimated. While the ET of P1 and P3 is estimated to
FIGURE 3 Prompt and delayed (10 ms) PL spectra of P3 in
FIGURE 4 Cyclic voltammograms of (a) P1, (b) P2, and (c) P3
in CH2Cl2 at a scan rate of 50 mV sꢂ1
.
dilute CH2Cl2 solution at 77 K.
4
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 000, 000–000

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
ces D1ꢂD5 based on polymeric emissive layers containing
P1ꢂP3 host doped with various concentration of FIrpic
were fabricated according to the following configuration:
ITO/poly-3,4-ethylenedioxythiophene:poly-styrenesulfonate
(PEDOT:PSS, 40 nm)/polymeric emissive layer (40 nm)/
2,20,2"-(1,3,5-phenylene)tris(1-phenyl-1H-benzimidazole) (TPBi,
15 nm)/4,7-diphenyl-1,10-phenanthroline (Bphen, 35 nm)/LiF
(1 nm)/Al (100 nm), where D1ꢂD3 with 7 wt % FIrpic con-
centration and D4, D5 with 10 wt %, 13 wt %, respectively
(Supporting Information Fig. S12 for device structure illustra-
tion). P3 doped with FIrpic coated on top of PEDOT:PSS layer
showed excellent film quality with surface roughness smaller
than 1 nm as can be seen in the atomic force microscopy
(AFM) image of spin-coated P3 doped with 10 wt % of FIrpic
on PEDOT:PSS coated ITO substrate (Supporting Information
Fig. S13). For performance comparison, device D6 with small
molecular mCP host doped with 7 wt % concentration of
FIrpic was fabricated by vacuum deposition method.11 All
devices D1ꢂD6 were fabricated in the identical device struc-
ture for fair comparison between different host materials.
FIGURE 5 Electroluminescence spectra of devices (D1ꢂD6)
with P1ꢂP3 and molecular mCP hosts doped with FIrpic.
be about 2.98 and 2.97 eV, respectively, comparable to that
reported for molecular mCP (2.90 eV),9 the ET value of P2 is
calculated to be about 2.68 eV, which is lower than those of
P1 and P3 despite the very similar optical band gap with
those of P1 and P3. Nevertheless, all ET values are higher
than that of typical blue phosphorescent emitter (FIrpic, ET
¼ 2.65 eV), thus indicating that all polymers could act as
suitable host materials for blue emitters. Electrochemical
behaviors of the polymers (P1ꢂP3) were investigated by
cyclic voltammetry (CV) measurements. As shown in Figure
4, all polymers exhibit an irreversible oxidation process as
typically observed for the carbazole derivatives with unpro-
tected 3,6-positions.29 When compared with the oxidation
peaks for P1 and P2 which have a similar oxidation poten-
tial, P3 undergoes facile oxidation with a cathodic shift by
>0.1 V probably due to the electron donating effect of the
second carbazole group. Combining the UVꢂvis absorption
spectra and the oxidation onset potentials, the HOMO and
LUMO levels are calculated to be about ꢂ5.5 to ꢂ5.7 eV and
ꢂ2.0 to ꢂ2.1 eV, respectively, which are also in good agree-
ment with those reported for molecular mCP (Table 2).30
As shown in Figure 5, devices D1ꢂD6 show similar electro-
luminescence spectra, which clearly indicate that light emis-
sion originates only from phosphorescent dopant FIrpic and
not from the host materials. Among the devices D1ꢂD3 fab-
ricated based on the emissive layers containing the different
polymer host P1ꢂP3 doped with the same concentration of
FIrpic (7 wt %), device D3 with P3 host displays highest
performances in terms of external quantum efficiency (gEQE
)
and power efficiency (gPE), although P1 and P2 also func-
tion as good hosts for FIrpic (Table 3 and Supporting Infor-
mation Fig. S14). According to the gEQE and gPE values sum-
marized in Figure 6(a,b) and Table 3, device D4 with 10 wt
%-dopant ratio exhibits the best performances among
D3ꢂD5 with P3 host. The best device among the D4 devi-
ces tested affords gEQE of 4.0% and gPE of 3.0 lm Wꢂ1, at a
luminance of 1000 cd mꢂ2. The observed device perform-
ance is significantly higher than that of the previously
reported polymer-based solution-processed blue-emitting
PhOLEDs.14,17(a,b)
The reason for higher gEQE of D4 device compared to D3
and D5 devices can be found in the current densi-
tyꢂvoltageꢂluminance (JꢂVꢂL) curve in Figure 7, where D4
shows similar luminance to D3 and D5 while exhibiting the
Device Fabrication and Performance Analysis
To explore the possibility of the polymers for a host material
in blue PhOLEDs, P1ꢂP3 was tested in real PhOLEDs. Devi-
TABLE 3 Device Performance of PhOLEDs Based on P12P3 and mCP Hosts
Conc. of
Vturn-on
(V)b
Lmax
(cd mꢂ2
EQEmax
(%)
PEmax
(lm Wꢂ1
)
Device
Host
FIrpic (wt %)
CIE (x, y)a
)
D1
D2
D3
D4
D5
D6
a
P1
7
0.193, 0.378
0.186, 0.358
0.189, 0.399
0.202, 0.397
0.196, 0.415
0.174, 0.389
8.1
6.7
6.5
6.6
6.3
5.2
1,800
3,800
5,000
4,600
4,900
10,400
1.9
2.5
3.2
4.3
3.5
6.2
1.3
2.0
2.5
3.4
2.9
8.3
P2
7
P3
7
P3
10
13
7
P3
mCP
Measured at 14 mA cmꢂ2-current density.
Applied voltage at the luminance of 1 cd mꢂ2
.
b
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 000, 000–000
5

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
charge transport properties of P3. Space-charge-limited-con-
duction (SCLC) method was applied to obtain both hole and
electron mobility of P3 and the result is shown in Figure
8.32(a–c) The famous ‘‘V2-dependence’’ of SCLC current was
not observable in the molecular mCP case and thus it was
difficult to extract mobilities of mCP in this work. Neverthe-
less, comparisons with the literature mobility values33
obtained at the average electric field corresponding to the
SCLC region of P3 in this study indicate that calculated effec-
tive hole and electron mobility values of P3 (2.0 ꢃ 10ꢂ4 cm2
Vꢂ1 sꢂ1 and 7.0 ꢃ 10ꢂ5 cm2 Vꢂ1
s
ꢂ1, respectively) with
dielectric constant of P3 set as that of mCP34 are one order
of magnitude lower than those of molecular mCP. Thus, the
overall lower device efficiencies of D4 than D6 can be
explained by carrier transport property of P3 that is poorer
than that of molecular mCP. The lower mobility of P3 is con-
sidered to result partly from the difficulty in purity control
in polymers as opposed to small molecules, which can be
purified by the well-defined thermal-gradient sublimation
technique. The impurities are expected to function as carrier
traps, lowering the effective carrier mobility of P3. This
degraded carrier transport property will limit the current
flow at a given voltage and is likely to increase the operating
voltage and/or compromise the subtle balance between elec-
trons and holes, decreasing the EQE values accordingly.
FIGURE 6 (a) Statistical box plot of external quantum effi-
ciency (gEQE) and (b) power efficiency (gPE) for D3ꢂD6 with P3
or mCP hosts, measured at a luminance of 1000 cd mꢂ2. Val-
ues in the parentheses indicate doping concentration of guest
FIrpic.
current density that is only about half of the current density
of D3. It has been reported that doping host materials hav-
ing high hole mobility but low electron mobility with dop-
ants having high electron mobility can induce decrease in
hole mobility and increase in electron mobility in the host
materials.31 Thus, it can be easily understood that there will
be an optimal doping percentage point where the numbers
of injected holes and electrons are relatively well matched,
enabling high brightness at low current density, and thus
maximizing the device efficiency—which is the case of D4.
Although device D4 overtook its polymeric rivals as shown
above, performance values are still behind than those of vac-
uum-deposited device D6 (gEQE ¼ 5.5%, gPE ¼ 6.7 lm Wꢂ1
at a luminance of 1000 cd mꢂ2). The lower power efficiency
of device D4 compared to D6 can be explained easily by
higher operating voltage of polymeric devices (including
turn-on voltage) than molecular mCP based device (Support-
ing Information Fig. S15 for JꢂVꢂL curve of D6). Further-
more, to follow up the factors that result in the lower exter-
nal quantum efficiency of D4, single carrier devices (both
hole-only and electron-only) were fabricated to analyze
FIGURE 7 (a) Current densityꢂluminanceꢂapplied voltage
(JꢂVꢂL) and (b) External quantum efficiencyꢂluminance (gEQE
L) curves of devices (D3ꢂD5) with P3 hosts doped with FIrpic.
–
6
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 000, 000–000

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
K2CO3 (9.40 g, 68.0 mmol), an o-dichlorobenzene solution of
carbazole (2.84 g, 17.0 mmol) and 1,3-diiodobenzene (11.2
g, 34.0 mmol) was added at room temperature. The reaction
mixture was heated to reflux and stirred for 24 h. After cool-
ing to room temperature, the reaction mixture was filtered
over a silica bed and the filtrate was evaporated to dryness.
The crude product was purified by column chromatography
on silica (eluent: CH2Cl2/n-hexane ¼ 1/4), which afforded
the product as white solid. Yield ¼ 3.01 g (48%).
1H NMR (CDCl3): d 7.22–7.35 (m, 3H), 7.36–7.45 (m, 4H),
7.52–7.57 (m, 1H), 7.79 (dt, J ¼ 7.7/2.1 Hz, 1H), 7.93 (t, J ¼
3.1 Hz, 1H), 8.15 (dt, J ¼ 7.9/1.3 Hz, 2H). 13C NMR (CDCl3):
d 94.55, 109.58, 120.28, 120.35, 123.48, 126.08, 126.42,
131.23, 135.98, 136.43, 138.96, 140.55. HR EI-MS: m/z calcd
for C18H12IN, 369.0014; found, 369.0015.
FIGURE 8 J ꢃ d versus V/d plots for hole-only devices (left) and
electron-only devices (right) with P3 and molecular mCP layers.
d is the thickness of corresponding P3 and mCP layers, where
100 nm of mCP for both hole-only and electron-only devices,
and 122/106 nm of P3 for hole-only/electron-only devices,
respectively. Hole-only and electron-only device structures are
ITO/PEDOT:PSS/P3 or mCP/WO3/Al, and Al/Ca/P3 or mCP/Ca/Al.
Synthesis of 9-[3-(9H-Carbazol-9-yl)phenyl]-3-bromo-9H-
carbazole (3)
To the o-dichlorobenzene (50 mL) slurry containing copper
(0.29 g, 4.5 mmol), 18-crown-6 (0.59 g, 2.2 mmol), and
K2CO3 (3.70 g, 26.8 mmol), an o-dichlorobenzene solution of
3-bromocarbazole (1.65 g, 6.7 mmol) and 1 (2.95 g, 8.0
mmol) was added at room temperature. The reaction mix-
ture was heated to reflux and stirred for 30–36 h. After cool-
ing to room temperature, the reaction mixture was filtered
over a silica bed and the filtrate was evaporated to dryness.
The crude product was purified by column chromatography
on silica (eluent: CH2Cl2/n-hexane ¼ 1/3), which afforded
the product as white powder. Yield ¼ 2.38 g (73%).
EXPERIMENTAL
General Considerations
All operations were performed under an inert nitrogen atmos-
phere using standard Schlenk and glovebox techniques. Anhy-
drous grade solvents (Aldrich) were dried by passing through
an activated alumina column and stored over activated molecu-
lar sieves (5 Å). Spectrophotometric-grade dichloromethane
was used as received from Aldrich. Commercial reagents were
used without any further purification after purchasing from
Aldrich (carbazole, N-bromosuccinimide, 1,3-diiodobenzene,
copper, potassium carbonate, 18-crown-6, t-butyllithium (1.7
M solution in pentanes), and Strem (AgSbF6). 3-Bromocarba-
zole,35 9-(4-bromophenyl)-9H-carbazole (1),24 9-(40-bromo-
biphenyl-4-yl)-9H-carbazole (2),25 5-norbornene-2-pentyl
bromide (endo/exo ¼ 2:1),36(a,b) and allylchloro[N,N0-bis(2,6-
diisopropylphenyl)-imidazol-2-ylidene]palladium(II) ([(NHC)Pd
(g3-allyl)Cl])27 were analogously synthesized according to the
published procedures. 1-Octene (Aldrich) was purified by pass-
ing through an activated alumina column and stored over acti-
vated molecular sieves (5 Å). CDCl3 from Cambridge Isotope
Laboratories was used after drying over activated molecular
sieves (5 Å). NMR spectra of compounds were recorded on a
1H NMR (CDCl3): d 7.28–7.42 (m, 4H), 7.43–7.58 (m, 7H), 7.61–
7.67 (m, 1H), 7.70–7.74 (m, 1H), 7.77 (t, J ¼ 2.1 Hz, 1H), 7.84 (t,
J ¼ 8.0, 1H), 8.09 (d, J ¼ 7.7 Hz, 1H), 8.17 (d, J ¼ 7.7 Hz, 2H),
8.26 (d, J ¼ 1.9 Hz, 1H). 13C NMR (CDCl3): d 109.54, 109.84,
111.09, 113.05, 120.36, 120.44, 120.57, 120.67, 122.45, 123.15,
123.59, 125.16, 125.29, 125.63, 126.13, 126.84, 128.75, 131.25,
138.83, 139.22, 139.44, 140.49, 140.89. HR EI-MS: m/z calcd for
C30H19BrN2, 486.0732; found, 486.0732.
Synthesis of M1
To the THF slurry (50 mL) containing 1 (2.26 g, 7.0 ꢀmmol),
2 equiv of t-BuLi (8.2 mL) was slowly added at ꢂ78 C. The
reaction mixture was stirred at this temperature for 2 h and
then allowed to warm to room temperature. A THF solution
(10 mL) of 5-norbornene-2-pentyl bromide (2.03 g, 8.4
mmol) was slowly added via cannula at 0 ꢀC. The reaction
mixture was allowed to warm to room temperature and
stirred overnight. After the addition of a saturated aqueous
solution of NH4Cl (30 mL), the organic portion was sepa-
rated, and the aqueous layer was further extracted with
ether (2ꢃ 30 mL). The combined organic portions were
dried over MgSO4, filtered, and evaporated to dryness,
affording an oily residue. The crude product was purified by
column chromatography on silica (eluent: CH2Cl2/n-hexane
¼ 1/4), which afforded M1 as yellow oil. Yield ¼ 2.04 g
(72%, mixture of endo and exo isomers [2/1]).
1
Bruker Avance 400 spectrometer (400.13 MHz for H, 100.62
MHz for 13C) at ambient temperature. Chemical shifts are given
in ppm and are referenced against external Me4Si (1H, 13C). HR
EI-MS measurement (JEOL JMS700) was performed at Korea
Basic Science Institute (Daegu). UVꢂvis and photolumines-
cence spectra were recorded on a Jasco V-530 and a Spex Fluo-
rog-3 Luminescence spectrophotometer, respectively, in CH2Cl2
with a 1-cm quartz cuvette at ambient temperature. CV experi-
ment was performed using an AUTOLAB/PGSTAT12 system.
AFM measurements were performed on a NanoMan (Veeco).
Synthesis of 9-(3-Iodophenyl)carbazole (3a)
To the o-dichlorobenzene (50 mL) slurry containing copper
(0.72 g, 11.3 mmol), 18-crown-6 (1.50 g, 5.7 mmol), and
1H NMR (CDCl3): d 0.69–0.76 (m), 1.23–1.67 (m) (10H),
1.82–2.25 (m, 3H), 2.86 (t, J ¼ 8.3 Hz, 2H), 2.96 (d, J ¼ 9.6
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 000, 000–000
7

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
Hz, 2H), 6.15 (dd, J ¼ 5.8/2.8 Hz, Hendo), 6.23 (dd, J ¼ 5.8/
2.9 Hz, Hexo), 6.29–6.31 (m, Hexo), 6.33 (dd, J ¼ 5.8/2.9 Hz,
was poured into the large volume of acidified methanol (5%
v/v, 300 mL) to precipitate the polymer. After stirring for 1
h, the precipitated polymer was collected by filtration and
washed with methanol (3ꢃ 50 mL). The polymers were puri-
fied by dissolving in CHCl3 and reprecipitating into metha-
nol/acetone (v/v ¼ 4/1), which was repeated three times.
The obtained polymers were finally dried in a vacuum oven
H
endo) (2H), 7.42–7.47 (m, 2H), 7.48–7.73 (m, 8H), 8.33 (d, J
¼ 7.5 Hz, 2H). 13C NMR (CDCl3): d 28.11, 28.48, 29.10,
31.07, 32.42, 33.07, 34.68, 35.59, 36.47, 38.72, 41.84, 42.49,
45.20, 45.38, 46.32, 49.54, 109.64, 109.72, 119.65, 119.82,
120.15, 123.18, 123.29, 125.73, 125.82, 126.77, 126.95,
129.61, 129.70, 132.31, 135.05, 136.09, 136.84, 140.76
140.93, 142.11. HR EI-MS: m/z calcd for C30H31N, 405.2457;
found, 405.2448.
ꢀ
at 70 C to constant weight.
P1: 1H NMR (CDCl3): d 0.5–2.1 (br, 15H), 2.2–3.0 (br, 4H),
7.17 (bs, 10H), 8.02 (bs, 2H). 13C NMR (CDCl3): d 25.5–49.6
(br), 109.62, 119.69, 120.19, 123.20, 125.73, 126.82, 129.56,
135.16, 140.84, 141.85. Anal. calcd for P1: C, 88.84; H, 7.70;
N, 3.45. Found: C, 88.30; H, 7.86; N, 3.74.
Synthesis of M2
A procedure analogous to that for M1 was used with 2 (2.39
g, 6.0 mmol) to afford M2 as yellow oil. Yield ¼ 1.94 g
(67%, mixture of endo and exo isomers [2/1]).
P2: 1H NMR (CDCl3): d 0.5–2.2 (br, 15H), 2.3–2.9 (br, 4H),
7.17 (bs, 8H), 7.41 (bs, 6H), 8.02 (bs, 2H). 13C NMR (CDCl3):
d 26.1–49.3 (br), 109.67, 119.89, 120.25, 123.34, 125.83,
126.88, 127.11, 128.04, 128.89, 136.52, 137.53, 139.78,
140.67, 142.13. Anal. calcd for P2: C, 89.77; H, 7.32; N, 2.91.
Found: C, 89.57; H, 7.50; N, 3.15.
1H NMR (CDCl3): d 0.46–0.52 (m), 1.02–1.47 (m) (10H),
1.60–2.05 (m, 3H), 2.52 (s), 2.67–2.82 (m) (4H), 5.93 (dd, J
¼ 5.6/2.8 Hz, Hendo), 6.02 (dd, J ¼ 5.6/2.8 Hz, Hexo), 6.07–
6.11 (m, Hexo), 6.12 (dd, J ¼ 5.6/2.9 Hz, Hendo) (2H), 7.26–
7.35 (m, 4H), 7.42–7.53 (m, 4H), 7.57–7.65 (m, 4H), 7.78–
7.83 (m, 2H), 8.16 (d, J ¼ 7.3 Hz, 2H). 13C NMR (CDCl3): d
28.51, 28.73, 29.60, 31.47, 32.43, 33.10, 34.73, 35.63, 36.52,
38.75, 41.86, 42.52, 45.21, 45.41, 46.33, 49.56, 109.83,
119.89, 119.94, 120.27, 123.38, 125.91, 126.93, 127.11,
127.25, 128.25, 128.47, 128.92, 128.99, 132.39, 136.16,
136.52, 136.88, 137.54, 140.25, 140.87, 142.51. HR EI-MS:
m/z calcd for C36H35N, 481.2770; found, 481.2773.
P3: 1H NMR (CDCl3): d 0.4–2.1 (br, 15H), 2.2–3.1 (br, 4H),
7.18 (bs, 6H), 7.28 (bs, 8H), 7.75 (bs, 2H), 8.00 (bs, 3H). 13C
NMR (CDCl3): d 26.5–49.7 (br), 109.31, 109.54, 119.64,
120.17, 123.44, 124.80, 125.26, 125.98, 126.67, 130.81,
134.69, 138.81, 139.33, 140.42. Anal. calcd for P3: C, 88.38;
H, 6.71; N, 4.91. Found: C, 88.24; H, 6.57; N, 4.94.
Polymer Analysis
1H and 13C NMR spectra of the polymer were recorded on a
Bruker Avance 400 spectrometer at ambient temperature in
CDCl3. The molecular weight (Mw) and molecular weight dis-
tribution (Mw/Mn) of the polymer were analyzed by GPC on
a Viscotek T60A equipped with UV and RI detectors using
THF as an eluent at 35 ꢀC and calibrated with narrow poly-
styrene standards as a reference. TGA was performed under
N2 atmosphere using a TA Instrument Q500 at a heating rate
of 20 ꢀC minꢂ1 from 50 to 800 ꢀC. DSC measurement was
performed on a TA Instrument Q100. Any thermal history in
the polymer was eliminated by the first heating the samples
at 20 ꢀC minꢂ1, and then recording the second DSC scan at
Synthesis of M3
A procedure analogous to that for M1 was used with 4 (1.95
g, 4.0 mmol) to afford M3 as white solid. Yield ¼ 1.76 g
(77%, mixture of endo and exo isomers [2/1]).
1H NMR (CDCl3): d 0.47–0.53 (m), 1.02–1.47 (m) (10H),
1.65–2.05 (m, 3H), 2.51 (s), 2.71–2.88 (m) (4H), 5.92 (dd, J
¼ 5.5/2.8 Hz, Hendo), 6.02 (dd, J ¼ 5.5/2.7 Hz, Hexo), 6.07–
6.09 (m, Hexo), 6.11 (dd, J ¼ 5.8/2.9 Hz, Hendo) (2H), 7.26–
7.36 (m, 4H), 7.40–7.50 (m, 4H), 7.52–7.58 (m, 3H), 7.66–
7.75 (m, 2H), 7.80–7.86 (m, 2H), 7.96 (s, 1H), 8.14 (d, J ¼
7.7 Hz, 1H), 8.16 (d, J ¼ 7.6 Hz, 2H). 13C NMR (CDCl3): d
29.55, 28.77, 29.56, 32.32, 32.41, 33.08, 34.74, 35.96, 36.54,
38.73, 41.83, 42.50, 45.19, 45.39, 46.32, 49.53, 109.36,
109.60, 109.67, 119.74, 120.09, 120.25, 120.29, 120.32,
120.40, 123.55, 123.56, 123.65, 125.12, 125.29, 125.55,
126.10, 126.87, 131.07, 137.14, 132.40, 135.04, 135.07,
136.12, 136.82, 136.89, 138.98, 139.26, 139.57, 140.58,
140.72. HR EI-MS: m/z calcd for C42H38N2, 570.3035; found,
570.3035.
ꢂ1
ꢀ
10 C min to the decomposition temperature.
Cyclic Voltammetry
CV measurement was performed with a three-electrode cell
configuration consisting of platinum working and counter
electrodes and a Ag/AgNO3 (0.1 M in CH3CN) reference elec-
trode at room temperature. The solvent was CH2Cl2 and 0.1
M tetrabutylammonium hexafluorophosphate was used as
the supporting electrolyte. The oxidation potentials were
recorded at a scan rate of 50 mV sꢂ1 and reported with ref-
erence to the ferrocene/ferrocenium (Fc/Fcþ) redox couple.
Polymerization Procedure
An activated catalyst solution (2.0 mM) was prepared in situ
by the addition of chlorobenzene (6.0 mL) to the mixture of
[(NHC)Pd(g3-allyl)Cl] and 1.5 equiv AgSbF6 followed by stir-
ring for 2 h at room temperature. The filtered solution of the
activated catalyst (1.7–2.5 lmol) was introduced into the
chlorobenzene solution containing prescribed amounts of
monomers (M1–M3) ([Mon.]/[Pd] ¼ 1000) and 1-octene
(0.05 mol % to monomer) to initiate polymerization. The po-
lymerization was performed at 25 ꢀC for 20 h. The mixture
Device Fabrication and Analysis
Glass substrates precoated with 150-nm-thick ITO were
cleaned using soapy water, deionized water, acetone, and iso-
propyl alcohol in an ultrasonic bath, and treated by air
plasma using a plasma cleaner (PDC-32G, Harrick Plasma).
An aqueous dispersion of PEDOT:PSS (Baytron AI4083, H.C.
Starck) was spun (2500 rpm for 30 s) onto the substrates.
8
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 000, 000–000

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
The samples were then dried on a hotplate (140 ꢀC) for 10
min. P1ꢂP3 doped with FIrpic was spin coated onto the
substrates from a chlorobenzene solution (0.9 wt %) at
of the NRF (No. 2009-0093818 for M. H. Lee) funded by the
Korea Ministry of Education, Science and Technology are grate-
fully acknowledged. Authors are also thankful to Samsung Mo-
bile Display for the financial support.
ꢀ
3000 rpm and then dried at 80 C on a hot plate for 10 min
in the glovebox filled with N2. The film thickness of spin-
coated layers was determined with AFM and was measured
to be about 40 nm. After drying process, a sample coated
with P3 and samples with only PEDOT:PSS coated were
brought into a thermal evaporation chamber (HS-1100, Digi-
tal Optics & Vacuum), which is enclosed by a glovebox filled
with N2. Using a selective shadow mask, 40-nm-thick mCP
layer was codeposited with FIrpic onto the samples with
PEDOT:PSS. Then, the shadow masks were changed with the
ones having an opening for all samples. In such way, TPBi
(15 nm), Bphen (35 nm), LiF (1 nm), and Al (100 nm) were
successively deposited on top of each emissive layers
(P1ꢂP3 and mCP doped with FIrpic) at the same time. Vac-
uum deposition was done under high vacuum (ꢄ7 ꢃ 10ꢂ7
torr) with the following deposition rates: 0.4–0.8 Å sꢂ1 for
TPBi and Bphen, 0.3–0.5 Å sꢂ1 for LiF, and 1–3 Å sꢂ1 for Al
electrode. Thus devices with following configurations were
fabricated: ITO/PEDOT:PSS/(P1ꢂP3 or mCP doped with
FIrpic)/TPBi/Bphen/LiF/Al. Using the same method, single
carrier (hole- and electron-only) devices were fabricated
with following configurations: ITO/PEDOT:PSS/(P3 or mCP)/
WO3/Al and Al/Ca/(P3 or mCP)/Ca/Al, respectively. EL spec-
tra were obtained with a fiber optic spectrometer (EPP2000,
StellarNet). Currentꢂvoltage (JꢂV) and luminanceꢂvoltage
(LꢂV) characteristics were recorded on a source-measure
unit (Keithley 2400) and a calibrated photodiode (FDS100,
Thorlab). All measurement was done in an N2-filled
glovebox.
REFERENCES AND NOTES
1 (a) Chi, Y.; Chou, P.-T. Chem. Soc. Rev. 2010, 39, 638–655; (b)
Lowry, M. S.; Bernhard, S. Chem. Eur. J. 2006, 12, 7970–7977; (c)
€
Kohler, A.; Wilson, J. S.; Friend, R. H. Adv. Mater. 2002, 14,
701–707; (d) Lamansky, S.; Djurovich, P.; Murphy, D.; Abdel-
Razzaq, F.; Lee, H. E.; Adachi, C.; Burrows, P. E.; Forrest, S. R.;
Thompson, M. E. J. Am. Chem. Soc. 2001, 123, 4304–4312; (e)
Baldo, M. A.; Thompson, M. E.; Forrest, S. R. Nature 2000, 403,
750–753.
2 Baldo, M. A.; Lamansky, S.; Burrows, P. E.; Thompson, M. E.;
Forrest, S. R. Appl. Phys. Lett. 1999, 75, 4–6.
3 Baldo, M. A.; O’Brien, D. F.; You, Y.; Shoustikov, A.; Sibley,
S.; Thompson, M. E.; Forrest, S. R. Nature 1998, 395,
151–154.
4 Adachi, C.; Baldo, M. A.; Thompson, M. E.; Forrest, S. R. J.
Appl. Phys. 2001, 90, 5048–5051.
5 (a) Reineke, S.; Walzer, K.; Leo, K. Phys. Rev. B 2007, 75,
125328; (b) Kawamura, Y.; Brooks, J.; Brown, J. J.; Sasabe, H.;
Adachi, C. Phys. Rev. Lett. 2006, 96, 017404; (c) Baldo, M. A.;
Adachi, C.; Forrest, S. R. Phys. Rev. B 2000, 62, 10967–10977.
€
6 (a) Kohler, A.; Beljonne, D. Adv. Funct. Mater. 2004, 14,
11–18; (b) Pina, J.; Seixas de Melo, J.; Burrows, H. D.; Monk-
man, A. P.; Navaratnam, S. Chem. Phys. Lett. 2004, 400,
441–445; (c) Chen, F.-C.; He, G.; Yang, Y. Appl. Phys. Lett. 2003,
82, 1006–1008; (d) Cleave, V.; Yahioglu, G.; Barny, P. L.; Hwang,
D.-H.; Holmes, A. B.; Friend, R. H.; Tessler, N. Adv. Mater. 2001,
13, 44–47; (e) Cleave, V.; Yahioglu, G.; Le Barny, P.; Friend, R.
H.; Tessler, N. Adv. Mater. 1999, 11, 285–288.
7 Tokito, S.; Noda, K.; Fujikawa, H.; Taga, Y.; Kimura, M.; Shi-
mada, K.; Sawaki, Y. Appl. Phys. Lett. 2000, 77, 160–162.
CONCLUSIONS
€
8 Brunner, K.; van Dijken, A.; Borner, H.; Bastiaansen, J. J. A.
We have demonstrated a novel type of highly efficient blue
phosphorescent OLEDs based on polymeric host–dopant
guest system. The soluble polynorbornenes bearing carba-
zole side groups were used as the polymeric host materials
and have been synthesized by the vinyl addition polymeriza-
tion of norbornene monomers using Pd(II) catalyst in combi-
nation with 1-octene chain transfer agent. The polymers pos-
M.; Kiggen, N. M. M.; Langeveld, B. M. W. J. Am. Chem. Soc.
2004, 126, 6035–6042.
9 Holmes, R. J.; Forrest, S. R.; Tung, Y.-J.; Kwong, R. C.;
Brown, J. J.; Garon, S.; Thompson, M. E. Appl. Phys. Lett.
2003, 82, 2422–2424.
10 Adamovich, V.; Brooks, J.; Tamayo, A.; Alexander, A. M.;
Djurovich, P. I.; D’Andrade, B. W.; Adachi, C.; Forrest, S. R.;
Thompson, M. E. New J. Chem. 2002, 26, 1171–1178.
sessed
high
thermal
stability,
excellent
solution
processability, and large triplet energy inherited from the
parent polynorbornene backbone and the attached carbazole
side groups. Among the polymers, the one bearing mCP side
groups (P3) proved to be a potential candidate for an
adequate host material for the typical blue dopant guest
such as FIrpic, displaying high external quantum efficiency
and power efficiency in PhOLEDs. Although the lower charge
carrier mobilities than those of molecular mCP led to overall
inferior device performances, the performances are best
among the reported devices based on other polymeric host
systems.
11 Yeh, S. J.; Wu, M. F.; Chen, C. T.; Song, Y. H.; Chi, Y.; Ho,
M. H.; Hsu, S. F.; Chen, C. H. Adv. Mater. 2005, 17, 285–289.
12 (a) Sirringhaus, H.; Kawase, T.; Friend, R. H.; Shimoda, T.;
Inbasekaran, M.; Wu, W.; Woo, E. P. Science 2000, 290,
2123–2126; (b) Friend, R. H.; Gymer, R. W.; Holmes, A. B.; Bur-
roughes, J. H.; Marks, R. N.; Taliani, C.; Bradley, D. D. C.; Santos,
D. A. D.; Bredas, J. L.; Logdlund, M.; Salaneck, W. R. Nature 1999,
397, 121–128; (c) Gustafsson, G.; Cao, Y.; Treacy, G. M.; Klavetter,
F.; Colaneri, N.; Heeger, A. J. Nature 1992, 357, 477–479.
13 (a) Vicente, J.; Gil-Rubio, J.; Zhou, G.; Bolink, H. J.; Arias-
Pardilla, J. J. Polym. Sci. Part A: Polym. Chem. 2010, 48,
3744–3757; (b) Zhen, H.; Luo, C.; Yang, W.; Song, W.; Du, B.;
Jiang, J.; Jiang, C.; Zhang, Y.; Cao, Y. Macromolecules 2006,
39, 1693–1700; (c) Wu, F.-I.; Shih, P.-I.; Tseng, Y.-H.; Chen,
G.-Y.; Chien, C.-H.; Shu, C.-F.; Tung, Y.-L.; Chi, Y.; Jen, A. K.-Y.
J. Phys. Chem. B 2005, 109, 14000–14005; (d) Jiang, C.; Yang,
W.; Peng, J.; Xiao, S.; Cao, Y. Adv. Mater. 2004, 16, 537–541;
Financial supports from the National Research Foundation of
Korea (No. 2010-0008264 for Y. Do and No. 2010-0007796 for
M. H. Lee), the ERC program of the NRF (No. R11-2007-045-
01001-0 for S. Yoo) and the Priority Research Centers Program
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 000, 000–000
9

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
(e) Sandee, A. J.; Williams, C. K.; Evans, N. R.; Davies, J. E.;
24 Koene, B. E.; Loy, D. E.; Thompson, M. E. Chem. Mater.
1998, 10, 2235–2250.
€
Boothby, C. E.; Kohler, A.; Friend, R. H.; Holmes, A. B. J. Am.
Chem. Soc. 2004, 126, 7041–7048; (f) Gong, X.; Ostrowski, J. C.;
Bazan, G. C.; Moses, D.; Heeger, A. J.; Liu, M. S.; Jen, A. K.-Y.
Adv. Mater. 2003, 15, 45–49; (g) Chen, X.; Liao, J.-L.; Liang, Y.;
Ahmed, M. O.; Tseng, H.-E.; Chen, S.-A. J. Am. Chem. Soc.
2003, 125, 636–637.
25 Nomura, M.; Shibasaki, Y.; Ueda, M.; Tugita, K.; Ichikawa,
M.; Taniguchi, Y. Synth. Met. 2005, 148, 155–160.
26 Su, S.-J.; Sasabe, H.; Takeda, T.; Kido, J. Chem. Mater.
2008, 20, 1691–1693.
27 Viciu, M. S.; Navarro, O.; Germaneau, R. F.; Kelly, R. A., III;
Sommer, W.; Marion, N.; Stevens, E. D.; Cavallo, L.; Nolan, S.
P. Organometallics 2004, 23, 1629–1635.
14 Fei, T.; Cheng, G.; Hu, D.; Lu, P.; Ma, Y. J. Polym. Sci. Part
A: Polym. Chem. 2009, 47, 4784–4792.
15 (a) Yeh, H.-C.; Chien, C.-H.; Shih, P.-I.; Yuan, M.-C.; Shu, C.-
F. Macromolecules 2008, 41, 3801–3807; (b) Chen, Y.-C.; Huang,
G.-S.; Hsiao, C.-C.; Chen, S.-A. J. Am. Chem. Soc. 2006, 128,
8549–8558.
28 Tsai, M.-H.; Hong, Y.-H.; Chang, C.-H.; Su, H.-C.; Wu, C.-C.;
Matoliukstyte, A.; Simokaitiene, J.; Grigalevicius, S.; Grazulevi-
cius, J. V.; Hsu, C.-P. Adv. Mater. 2007, 19, 862–866.
29 Li, W.; Qiao, J.; Duan, L.; Wang, L.; Qiu, Y. Tetrahedron
2007, 63, 10161–10168.
16 Fei, T.; Cheng, G.; Hu, D.; Dong, W.; Lu, P.; Ma, Y. J. Polym.
Sci. Part A: Polym. Chem. 2010, 48, 1859–1865.
30 Thoms, T.; Okada, S.; Chen, J.-P.; Furugori, M. Thin Solid
Films 2003, 436, 264–268.
17 (a) Wu, Z.; Xiong, Y.; Zou, J.; Wang, L.; Liu, J.; Chen, Q.;
Yang, W.; Peng, J.; Cao, Y. Adv. Mater. 2008, 20, 2359–2364; (b)
Shao, K.-F.; Xu, X.-J.; Yu, G.; Liu, Y.-Q.; Yang, L.-M. Chem. Lett.
2006, 35, 404–405.
31 Noh, S.; Suman, C. K.; Hong, Y.; Lee, C. J. Appl. Phys. 2009,
105, 033709.
18 (a) Rausch, A. F.; Thompson, M. E.; Yersin, H. Inorg. Chem.
2009, 48, 1928–1937; (b) Tokito, S.; Iijima, T.; Suzuri, Y.; Kita,
H.; Tsuzuki, T.; Sato, F. Appl. Phys. Lett. 2003, 83, 569–571.
32 (a) Yun, C.; Cho, H.; Kang, H.; Lee, Y. M.; Park, Y.; Yoo, S.
Appl. Phys. Lett. 2009, 95, 053301–053303; (b) Kiy, M.; Losio, P.;
Biaggio, I.; Koehler, M.; Tapponnier, A.; Gunter, P. Appl. Phys.
¨
Lett. 2002, 80, 1198–1200; (c) Shen, Y.; Klein, M. W.; Jacobs, D.
B.; Campbell Scott, J.; Malliaras, G. G. Phys. Rev. Lett. 2001,
86, 3867–3870.
19 Adachi, C.; Kwong, R. C.; Djurovich, P.; Adamovich, V.;
Baldo, M. A.; Thompson, M. E.; Forrest, S. R. Appl. Phys. Lett.
2001, 79, 2082–2084.
33 Hsiao, C.-H.; Liu, S.-W.; Chen, C.-T.; Lee, J.-H. Org. Electron.
2010, 11, 1500–1506.
20 Park, J. H.; Yun, C.; Koh, T.-W.; Do, Y.; Yoo, S.; Lee, M. H. J.
Mater. Chem. 2011, 21, 5422–5429.
34 Nayak, P. K.; Periasamy, N. Org. Electron. 2009, 10,
532–535.
21 Park, M. H.; Yun, C.; Huh, J. O.; Do, Y.; Yoo, S.; Lee, M. H.
Synth. Met. 2010, 160, 2000–2007.
35 Smith, K.; James, D. M.; Mistry, A. G.; Bye, M. R.; Faulkner,
D. J. Tetrahedron 1992, 48, 7479–7488.
22 Park, J. H.; Yun, C.; Park, M. H.; Do, Y.; Yoo, S.; Lee, M. H.
Macromolecules 2009, 42, 6840–6843.
23 Feng, K.; Zuniga, C.; Zhang, Y.-D.; Kim, D.; Barlow, S.;
Marder, S. R.; Brdas, J. L.; Weck, M. Macromolecules 2009, 42,
6855–6864.
36 (a) Gabert, A. J.; Verploegen, E.; Hammond, P. T.; Schrock,
R. R. Macromolecules 2006, 39, 3993–4000; (b) Stubbs, L. P.;
Weck, M. Chem. Eur. J. 2003, 9, 992–999.
10
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 000, 000–000