High-efficiency electrophosphorescent copolymers containing charged iridium complexes in the side chains

Article abstract of DOI:10.1002/chem.200601811

A convenient approach to novel charged Ir polymers for opto-electronic devices to achieve red emission was developed. 2-(Pyridin-2-yl)-benzimidazole units grafted into the side chains of macroligands (PFCz and PFP) served as ligands for the formation of charged Ir complex pendants with 1-phenylisoquinoline (1-piq). The charged Ir polymers (PFPIrPiq and PFCzIrPiq) showed exclusive Ir(1-piq)₂(N-[2-(pyridin-2-yl)benzimidazole]hexyl) ⁺BF₄^- (IrPiq) emission, with the peak at 595 nm. The best device performances were obtained from PFCzIrPiq4 with the device configuration of ITO/PEDOT:PSS/PFCzIr-Piq4+PBD (30 wt%)/TPBI/Ba/Al (PBD: 5-(4-tert-butylphenyl)-2-(bi-phenyl-4-yl)-1,3,4-oxadiazole; TPBI: 1,3,5-tris-(2-N-phenylbenzimidazolyl)-benzene). A maximum external quantum efficiency (EQE) of 7.3% and a luminous efficiency (LE) of 6.9 cd A^-1 with a luminance of 138 cd m^-2 were achieved at a current density of 1.9 mA cm^-2. The efficiencies remained as high as EQE = 3.4% and LE = 3.3 cd A^-1 with a luminance of 3770 cd m^-2 at a current density of 115 mA cm^-2. The single-layer devices based on charged Ir polymers also showed high efficiency with the high work-function metal Ag as cathode. The maximum external quantum efficiencies of the devices were 0.64 % and 0.66% for PFPIrPiq2 and PFPIrPiq10, respectively. A possible mechanism of an electrochemical cell associated with its electrochemical redox pathway for single-layer devices has been proposed. The results showed that the charged Ir polymers are promising candidate materials for polymer optoelectronic devices.

Full text of DOI:10.1002/chem.200601811

DOI: 10.1002/chem.200601811
High-Efficiency Electrophosphorescent Copolymers Containing Charged
Iridium Complexes in the Side Chains
Bin Du, Lei Wang, HongBin Wu, Wei Yang,* Yong Zhang, RanSheng Liu,
[
a]
MingLiang Sun, Junbiao Peng,* andYong Cao
À2
Abstract: A convenient approach to
novel charged Ir polymers for opto-
Piq4+PBD (30 wt%)/TPBI/Ba/Al
(PBD: 5-(4-tert-butylphenyl)-2-(bi-
phenyl-4-yl)-1,3,4-oxadiazole; TPBI:
3770 cdm
at a current density of
À2
115 mAcm . The single-layer devices
based on charged Ir polymers also
showed high efficiency with the high
work-function metal Ag as cathode.
The maximum external quantum effi-
ciencies of the devices were 0.64% and
0.66% for PFPIrPiq2 and PFPIrPiq10,
respectively. A possible mechanism of
an electrochemical cell associated with
its electrochemical redox pathway for
single-layer devices has been proposed.
The results showed that the charged Ir
polymers are promising candidate ma-
terials for polymer optoelectronic devi-
ces.
A
C
H
T
R
E
U
N
G
electronic devices to achieve red emis-
sion was developed. 2-(Pyridin-2-yl)-
benzimidazole units grafted into the
side chains of macroligands (PFCz and
PFP) served as ligands for the forma-
tion of charged Ir complex pendants
with 1-phenylisoquinoline (1-piq). The
charged Ir polymers (PFPIrPiq and
1,3,5-tris-(2-N-phenylbenzimidazolyl)-
benzene). A maximum external quan-
tum efficiency (EQE) of 7.3% and a
À1
luminous efficiency (LE) of 6.9 cdA
À2
with a luminance of 138 cdm were
achieved at
1.9 mAcm . The efficiencies remained
a
current density of
À2
PFCzIrPiq)
showed
exclusive
as high as EQE=3.4% and LE=
À1
Ir(1-piq) {N-[2-(pyridin-2-yl)benzimida-
A
C
H
T
R
E
U
N
G
3.3 cdA
with
a
luminance of
2
+
À
zole]hexyl} BF4 (IrPiq) emission, with
the peak at 595 nm. The best device
performances were obtained from
PFCzIrPiq4 with the device configura-
Keywords: host–guest systems
·
iridium · luminescence · N ligands ·
polymers
tion
of
ITO/PEDOT:PSS/PFCzIr-
Introduction
plexes in their main chains and side chains have been stud-
[3]
ied extensively, while many reports have recently focused
on different types of electrophosphorescent polymers based
on neutral iridium complexes for optoelectronic applica-
tions, due to their relatively short phosphorescent lifetimes
and high luminous efficiencies. Nonconjugated polymers
with attached neutral iridium complex pendants have been
Electrophosphorescent polymers containing transition metal
complexes have attracted much attention since researchers
realized their potential practical applications in the prepara-
tion of high-efficiency polymer light-emitting diodes
PLEDs). Strong spin–orbit coupling of transition metal
ions in complexes can provide relatively short lifetimes of
triplet metal-to-ligand charge-transfer ( MLCT) states,
thereby theoretically achieving nearly 100% internal quan-
tum efficiency. The chemistry and photophysics of poly-
mers containing ruthenium bipyridyl and terpyridyl com-
[1]
(
[4]
reported by Lee and Tokito. High external quantum effi-
ciencies based on those polymers were achieved in red,
green, and blue PLEDs. Phosphorescent conjugated poly-
mers based on polyfluorene backbones with neutral iridium
complex pendants attached to the 9-carbon position of fluo-
3
[2]
[5]
rene were reported by Chen, and well defined main-chain-
type oligo- and polyfluorenyl biscyclometalated iridium
[6]
complexes were reported by Sandee. Fluorene-alt-carba-
zole copolymers with 1-phenylisoquinoline–Ir complexes
grafted in the carbazole N-position and chelating copoly-
mers based on iridium complexes in the main chain can ach-
[
a]B. Du, L. Wang, Dr. H. Wu, Prof. W. Yang, Y. Zhang, R. Liu, M. Sun,
Prof. J. Peng, Prof. Y. Cao
Institute of Polymer Optoelectronic Materials and Devices
Key Lab of Special Functional Materials, Ministry of Education
South China University of Technology, Guangzhou, 510640 (China)
Fax : (+86)20-8711-0606
[7,8]
ieve high external quantum efficiencies in PLEDs.
Neutral iridium complexes have attracted much more in-
terest than ionic iridium complexes, probably due to their
E-mail: pswyang@scut.edu.cn
psjbpeng@scut.edu.cn
7432
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Chem. Eur. J. 2007, 13, 7432 – 7442

FULL PAPER
compatibility with hydrophobic matrices and their lack of
counterions, which can result in time delays between the
switch-on and the observed emission in display-related ap-
plications. However, charged iridium complexes also show
excellent electrochemical, photochemical, and thermal sta-
bility, good charge-transport properties, long-lived excited
fluorenes containing charged iridium complexes in their
backbones have received a great deal of attention. Soluble
p-conjugated polymers with charged iridium complexes in
[12]
their backbones have been synthesized.
The polymers
showed efficient energy transfer and good redox reversibili-
ty and film formation.
[9]
states, and good photoluminescence (PL) efficiencies.
Although a considerable number of studies have focused
on charged Ir polymers, p-conjugated polymers with charg-
ed iridium complexes in their side chains had not previously
been reported, while even less was known about the photo-
physical properties of those polymers in the preparation of
optoelectronic devices. In the work reported here, polymers
with charged iridium complexes in their side chains were
successfully synthesized. 2-(Pyridin-2-yl)benzimidazole and
1-phenylisoquinoline were selected as ligands because the
obtained metal complexes often show attractive chemical
They have been regarded as promising candidates for appli-
cation in solid-state electroluminescent devices, due to the
presence in them of a single, solution-processable layer
sandwiched with high efficiency between two air-stable elec-
trodes. Recently, light-emitting diodes (LEDs) and solid
light-emitting electrochemical cells (LECs) based on charg-
ed iridium complexes have shown some distinct advantages
over electroluminescent devices based on neutral iridium
[10]
complexes.
[13,14]
Charged iridium complexes of low molecular weight are
doped into a polymeric matrix for the polymer light-emit-
ting diode fabrication process, and these devices are found
to be significantly less efficient than those with neutral com-
and physical properties.
Their synthesis and characteri-
zation are described, together with detailed studies of the
electroluminescent properties.
[10]
plexes. The difference in efficiency is probably attributa-
ble to the ionic content and the charge-trapping properties
Results andDiscussion
[10b]
of charged iridium complexes. Recently, Brunner et al.
have reported that the low efficiencies and high switch-on
voltages of charged-complex-based devices could be over-
come by utilizing a hole-blocking layer to modify the charge
injection and charge transport.
Synthesis andstructural characterization : The synthetic
routes to the macroligands (PFCz and PFP) are shown in
Scheme 1. 3,6-Dibromo-9-{N-[2-(pyridin-2-yl)benzimidazo-
le]hexyl)carbazole was synthesized through a coupling reac-
tion between 2-(pyridin-2-yl)benzimidazole and 3,6-dibro-
mo-9-(6-bromohexyl)carbazole in the presence of sodium
Although devices from phosphorescent dyes doped into
polymeric host materials showed high efficiency in polymer
[1g,7b]
[15]
light-emitting diodes,
device performance from blend
hydroxide by the published procedure.
systems is always limited by phase separation and aggrega-
tion of dopants. This problem is even more serious for
charged complexes doped into a neutral wide-band-gap po-
lymer host, since polar charged iridium complexes have
poorer compatibility with typical hydrophobic host poly-
mers. Therefore, a polymeric host incorporating covalently
bonded phosphorescent chromophores has been regarded as
an efficient solution with the additional benefits of excellent
The macroligands were synthesized by Suzuki polycon-
densation. The feed ratios of monomer (4 or 5) to 6 were
50:50 and the corresponding macroligands were named
PFCz and PFP, respectively. All the macroligands readily
dissolve in common organic solvents such as chloroform,
THF, toluene, and xylene. The number-average molecule
weights (M ) of PFCz and PFP are 23305 and 6987, respec-
n
tively, with polydispersity indexes (PDIs) of 1.63 and 1.74.
The synthetic routes to the model charged iridium com-
[5–8]
solution processability and stability.
Charged Ir complex
+
molecules covalently attached to polymer main chains or
side chains would be forced to separate from each other and
so should be more homogeneously dispersed into the poly-
plex
Ir(1-piq) {N-[2-(pyridin-2-yl)benzimidazole]-hexyl}
A
H
R
U
G
2
À
BF4 (IrPiq) and the corresponding charged Ir polymers are
depicted in Scheme 2. The polymers containing charged iri-
dium complexes of different composition in their side chains
were directly prepared by heating the chloride-bridged iridi-
[12]
mer matrix.
The performances of PLEDs based on co-
polymers containing Ir complexes can be further improved
by the choice of a suitably charged iridium complex, the
match of the iridium complex with the host backbone, and
optimization of the device structure.
The study of polymeric materials functionalized with coor-
dinating charged iridium moieties is currently a rapidly ex-
panding field in macromolecular chemistry. Solution-proc-
um dimer and the macroligand PFP at reflux solvent in the
À
presence of NaBF . The resulting solution was concentrat-
4
ed, and the concentrate was dropped into methanol to pre-
cipitate the polymer. After precipitation, all polymers were
washed with methanol at reflux in a Soxhlet extractor for
2 d, in order to remove the chloride-bridged iridium dimers
À
essable
iridium
monoterpyridine–PEG-functionalized
(III) complexes and phosphorescent side-chain func-
charged
and NaBF4 in polymers; the corresponding polymers were
A
C
H
T
R
E
U
N
G
named PFPIrPiq2, PFPIrPiq4, and PFPIrPiq10, respectively.
The charged iridium complex contents in the polymers were
estimated by X-ray fluorescence spectrometry (XRF), and
the results indicated that the actual iridium complex con-
tents in the polymers were lower than the feed ratios
tionalized poly(norbornene)s containing charged iridium
complexes as light-emitting polymeric materials have been
[11]
successfully synthesized,
but these novel nonconjugated
polymers do not have the advantages of conjugated poly-
mers, such as fluent charge transportability. Recently, poly-
1
(Table 1). The weak H NMR signal of the H atom in the
Chem. Eur. J. 2007, 13, 7432 – 7442
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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7433

W. Yang, J. Peng et al.
centered (LC) transitions and
the absorption band in the
4
20–500 nm region might be
due to the spin-allowed singlet
metal-to-ligand charge-transfer
1
[20]
(
MLCT) transitions
spin-forbidden triplet metal-to-
ligand charge transfer
MLCT) transitions of the iri-
and
3
(
[21]
dium complex.
There is
good overlap between the ab-
sorption of the guest IrPiq and
the PL spectra of the host mac-
roligands (PFCz and PFP), as
shown in Figure 1, so efficient
Fçrster energy transfer from
the singlet excited state of the
1
host to the MLCT band of the
iridium complex can be expect-
ed.
Scheme 1. Synthetic routes to macroligands.
[7]
In Figure 2, the absorption
spectra of the charged Ir poly-
mers show no essential differ-
ences from those of their host
macroligands, obviously as a
result of the low Ir complex
content in the polymers. The
absorption of the polymers
(
PFCzIrPiq10) was red-shifted
by only 2 nm in relation to
that of the host macroligand
(
PFCz). The absorption peaks
at 346 and 371 nm can be at-
tributed to the p–p* transi-
tions of PFCz and PFP back-
bones, respectively, while the
peak at 317 nm is due to the
pendant 2-(pyridin-2-yl)benzi-
midazole group in comparison
with the absorption of 2-[N-
(
pyridin-2-yl)hexyl]benzimida-
zole. The blue shift (Dl=
0 nm) of the absorption peak
3
of PFCz in relation to the PFP
backbone implies that the con-
jugation length of the PFCz
Scheme 2. Synthetic routes to charged Ir polymers.
Table 1. Compositions of copolymers containing iridium complexes.
IrPiq unit is observable in the charged copolymers with high
contents of Ir complex (PFCzIrPiq10 or PFPIrPiq10).
Polymer
Ir complex content [mol%]
[
a]
[b]
in feed ratio
in polymer
PFPIrPiq2
PFPIrPiq4
PFPIrPiq10
PFCzIrPiq4
PFCzIrPiq10
2
4
10
4
10
1.5
2.7
9.0
2.56
10.7
Optical andelectrochemical properties : The absorption
spectrum of the charged iridium complex (IrPiq) in film is
shown in Figure 1. There are broad bands from 270 to
500 nm, the most intense at l<300 nm, and moderately in-
tense bands at longer wavelengths. The absorption bands
[
a]Chloride-bridged Ir-dimer/repeated unit of macroligand. [b]IrPiq/re-
1
(
l<300 nm) are mainly due to spin-allowed p–p* ligand-
peated unit of macroligand.
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Electrophosphorescent Copolymers
FULL PAPER
Figure 1. UV/Vis absorption spectrum of IrPiq and PL spectra of macroli-
gands in films.
Figure 3. PL spectra of charged Ir polymer a) PFPIrPiq and b) PFCzIrPiq
in films.
show high PL efficiencies (in Table 2), relative to IrPiq com-
plex (QPL %=5.4%) because the concentration quenching
and T–T annihilation are greatly decreased. It is also shown
that the incorporation of a space between the polymer host
and phosphorescent guest might be a good design principle
for achieving electrophosphorescent polymers with higher
Figure 2. UV/Vis absorption spectra of charged Ir polymers in film.
[7d]
backbone effectively decreases, as the linear p-system is in-
PL efficiencies.
Figure 4 shows the PL spectra for the
[22]
terrupted by the carbazole unit at the 3,6-linkage.
blends of IrPiq doped in host PFP. The IrPiq contents in
PFP were 2, 4, and 10 mol%, respectively (actual Ir con-
tents: 1.5, 2.7 and 9 mol%), in relation to the corresponding
charged iridium copolymers of the same composition. In
contrast with the copolymer with the charged Ir complex in-
corporated into the side chain, in which host emission was
almost completely quenched for PFPIrPiq4 (Figure 3), the
blend with 10 mol% complex shows incomplete quenching
with a moderate host emission peaking at 420 nm. This
shows that much more efficient energy transfer occurs in the
charged iridium copolymers than in the blend system. This
The photoluminescence (PL) spectra of the charged poly-
mers are shown in Figure 3. The maximum emission peak of
the charged polymers is at 595 nm, the same as the PL emis-
sion of the IrPiq complex doped in the macroligand PFP
(
Figure 4). In Figure 3, the emission peak at 420 nm can be
observed for the PFP-based copolymers with low Ir complex
content of 2 mol% (actual Ir content: 1.5 mol%). This im-
plies that the energy transfer from the main chain to the Ir
complex attached at the alkyl side chain of the PFP is in-
complete, probably because the average distance from a
photoexcited polymer chain to
the nearest Ir complex is too
[7]
Table 2. Optical and electrochemical properties of macroligands and charged Ir polymers.
long.
The emissions both
opt
[a]
from the PFCz and from the
PFP backbone are completely
quenched for copolymers with
l
max (Abs)
l
max (PL)
PL
Eg
E
ox
HOMO
LUMO
Polymer
[nm] [[[enVe[Vm%V][ ]e]] V]
PFCz
PFP
346
317, 371
346
428
420
595
595
595
595
595
30
43
43
41
42
54
34
3.12
3.01
3.09
3.10
3.03
3.03
3.03
0.95
1.28
0.98
0.95
1.29
1.31
1.30
À5.35
À5.68
À5.38
À5.35
À5.69
À5.71
À5.70
À2.23
À2.67
À2.29
À2.25
À2.66
À2.68
À2.67
Ir
complex
contents
of
PFCzIrPiq4
PFCzIrPiq10
PFPIrPiq2
PFPIrPiq4
PFPIrPiq10
4
mol%, which indicates that
348
the energy transfer becomes
complete with increasing Ir
complex content in the copoly-
mers. The charged Ir polymers
317, 371
317, 371
317, 371
[a]Calculated from HOMO level and the optical band gap.
Chem. Eur. J. 2007, 13, 7432 – 7442
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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7435

W. Yang, J. Peng et al.
Electrophosphorescent properties: Double-layer devices
with the configuration of ITO/PEDOT:PSS (50 nm)/poly-
mers+PBD (30 wt%) (75 nm)/Ba (4 nm)/Al
A
H
R
U
G
fabricated. PBD was doped to improve the electron-trans-
[24a]
porting capability of the polymers.
As can be seen in
Figure 5, EL emission from the polymer backbones was
Figure 4. PL spectra for PFP/IrPiq blends in films.
in turn indicates a great advantage of incorporation of
charged complexes covalently into polymer side chains, be-
cause the complexes are distributed more homogeneously in
the polymer host, while in the blend system Ir complexes
are easily aggregated due to poor compatibility between the
hydrophobic conjugated host polymer and polar charged
[7,8,12]
IrPiq complexes.
The electrochemical characteristics of the macroligand
and Ir polymer thin films coated onto Pt electrodes were in-
vestigated by cyclic voltammetry (CV). The highest occu-
pied molecular orbital (HOMO) levels were calculated by
the empirical formula EHOMO =Àe
A
T
E
N
is the onset oxidation potential versus a saturated calomel
electrode (SCE). As no reversible n-doping process was ob-
served in the cyclic voltammograms, the LUMO levels were
estimated from the HOMO values and values of optical
Figure 5. EL spectra of devices fabricated from a) PFPIrPiq and b)
PFCzIrPiq.
opt
opt
band gaps (Eg ) by ELUMO =EHOMO+Eg . The optical band
completely quenched even though the actual IrPiq content
of PFPIrPiq2 was as low as 1.5 mol%, which indicates that
there is efficient energy transfer from the host to the guest
or charge trapping. Similar PL and EL spectra phenomena
were observed by Chen when neutral iridium complex pend-
opt
gap was obtained from Eg =1240/ledge, where ledge is the
onset value of the absorption spectrum of the solid film in
[16,23]
the long-wavelength direction.
The electrochemical data
for the polymers are summarized in Table 2. The HOMO
and LUMO levels of the charged Ir polymers showed no es-
sential differences from those in their corresponding macro-
ligands, which further indicated that the attachment of IrPiq
in the side chain did not alter the backbone and conjugation
[5]
ants were attached to the 9-carbon position of fluorene.
Emission peaks at 595 nm were observed for PFCzIrPiq and
PFPIrPhq. The emissions from devices are dominated by iri-
dium complex phosphorescent emissions, which are almost
identical in peak position and line-width for all polymers.
The device performances are shown in Table 3. The devices
produced from PFP-based polymers have higher efficiencies
than those from PFCz-based polymers. A maximum external
quantum efficiency of 1.3% and a luminous efficiency of
[7,23c]
length of the host polymer.
Unfortunately, the redox
peaks of IrPiq in all Ir polymers proved to be unrecordable,
obviously due to the low Ir complex contents in the poly-
mers. For isolated IrPiq, the measurements were carried out
at room temperature in argon-saturated acetonitrile solu-
tions containing tetrabutylammonium hexafluorophosphate
À1
1.2 cdA were achieved from PFPIrPiq2. For PFCzIrPiq
(
Bu NPF ; 0.1m) with platinum working electrodes at a scan
devices, because of the lower hole injection barrier (ca.
0.15 eV; Figure 7b) at the PEDOT:PSS/PFCzIrPiq interface
and the good hole transporting capabilities of carbazole-
4
6
À1
rate of 50 mVs and IrPiq concentrations of about 2”
1
À4
0
m. An oxidation wave at +1.10 V vs. SCE was recorded.
[24b,25]
The HOMO level of IrPiq is evaluated at À5.5 eV. The
based polymers,
the holes are majority carriers unlike
LUMO level (À3.2 eV) was obtained from the onset of ab-
the PFPIrPiq devices. On the other hand, from CV measure-
ments, it is clear that the HOMO level of the IrPiq complex
is lower than that of PFCz, which means that IrPiq cannot
trap holes in PFCzIrPiq polymers. However, for PFPIrPiq
devices, the lower HOMO level of PFP makes IrPiq com-
[7e]
sorption and HOMO level.
On the assumption of no
great changes in the LUMO level of the IrPiq grafted into
host polymer chains, the grafted Ir complex will function as
an electron trap.
7436
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Electrophosphorescent Copolymers
FULL PAPER
Table 3. Device performances of charged Ir polymers in different configurations.
device components provide
further insight into the roles
played by the functional mate-
rial TPBI in the device
À2
Polymer
Turn-on
V]
EQEmax
[%]
LEmax
[cdA
L
[cdm
max
À2
J=30 mAcm
À1
[
]
]
Bias
V]
L
LE
EQE
[%]
À2
À1
[
[cdm
]
[cdA ]
(
Figure 7). As shown in
[
a]
PFPIrPiq2
PFPIrPiq4
11
9.5
11
9
9.5
11
10
10.5
10
1.3
1.1
1.0
0.6
0.5
4.1
4.7
2.6
7.3
5.7
1.2
1.0
0.9
0.5
0.5
3.9
4.5
2.4
6.9
5.4
262
537
461
986
577
476
1396
764
4004
3945
17
13
16
15
14
20
17
19
20
17
251
297
266
140
137
467
916
479
1452
1380
0.8
0.9
0.7
0.5
0.4
1.5
2.7
1.5
4.5
4.5
0.8
1.0
0.9
0.5
0.5
1.6
2.8
1.6
4.7
4.6
Figure 7 and Table 3, the cur-
rent-voltage characteristic is
shifted to higher voltage and
the device performances are
obviously enhanced after inser-
tion of a TPBI layer. Similar J-
V characteristics can be ob-
served for the devices pro-
duced from other Ir polymers
(not shown here). Preliminary
device performances are sum-
marized in Table 4. The best
PFPIrPiq10
PFCzIrPiq4
PFCzIrPiq10
[
b]
PFPIrPiq2
PFPIrPiq4
PFPIrPiq10
PFCzIrPiq4
PFCzIrPiq10
9.5
[
a]ITO/PEDOT:PSS/polymer +PBD
A
H
R
U
G
A
H
R
U
G
Al.
device performances were obtained from PFCzIrPiq4. A
maximum external quantum efficiency of 7.3% and a lumi-
À1
À2
nous efficiency of 6.9 cdA with a luminance of 138 cdm
À2
were achieved at a current density of 1.9 mAcm . The effi-
ciencies of this device remained as high as EQE=3.4% and
À1
À2
LE=3.3 cdA with a luminance of 3770 cdm at a current
À2
density of 115 mAcm . The PFCzIrPhq10 device showed
EQE=5.7% and LE=5.4 cdA
21 cdm at a current density of 5.9 mAcm . At a current
density of 100 mAcm , the efficiencies of this device re-
À1
with a luminance of
À2
À2
3
À2
Figure 6. Schematic diagrams of the device configurations and the molec-
ular formula of TPBI.
plex trap the holes in PFPIrPiq polymers. As a result, hole
and electron currents are significantly unbalanced in
PFCzIrPiq devices, leading to lower device efficiencies than
in PFPIrPiq. In order to enhance PFCz-based device per-
formances, it is necessary to achieve hole injection/transport
attenuation or electron flux enhancement, which can shift
the recombination zone away from the cathode interface.
One method for testing this assumption is by inserting an
organic hole-blocking and electron-transporting layer be-
tween the emissive layer and the cathode. A suitable materi-
al for such a layer is TPBI, which can be vacuum-evaporat-
ed on top of the polymer layer prior to vacuum evaporation
at the cathode. TPBI has a very low-lying HOMO level at
À6.2 eV (hence its hole-blocking capabilities) and a large
HOMO–LUMO energy difference of 3.4 eV (hence its exci-
ton-blocking capabilities). Multi-layer devices with the con-
figuration of ITO/PEDOT:PSS (50 nm)/polymers+PBD
(
(
30 wt%) (75 nm)/TPBI (50 nm)/Ba (4 nm)/Al (150 nm)
structure A, as shown in Figure 6) were fabricated. The
HOMO energy level of TPBI is 0.85 eV higher than that of
PFCz, which produces a high hole barrier and obstructs the
hole transport. The J–V curves and energy diagrams of
Figure 7. J-V curves of devices based on a) PFCzIrPiq and b) energy dia-
gram of the device components.
Chem. Eur. J. 2007, 13, 7432 – 7442
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
7437

W. Yang, J. Peng et al.
Table 4. Device performances with different cathodes.
of PFP and TPBI (À5.68 eV vs
À6.2 eV), TPBI is a less effi-
cient hole blocker for the
PFPIrPiq device. The increases
in efficiencies of all devices are
due to the reductions of both
hole current and metal cathode
À2
À2
Polymer
Turn-on [V]EQE
max [%]L
max [cdm
]
J=35 mAcm
À2
À1
Bias [V]L [cdm
]LE [cdA
]EQE [%]
[
%]
PFPIrPiq2
PFPIrPiq10
PFPIrPiq2
PFPIrPiq10
[
a]
14
13
11
11
0.83
150
96
200
176
19.5
17.6
17.5
16
87
0.25
0.5
0.3
0.5
0.4
0.33
0.64
0.66
45
86
67
0.13
0.22
0.19
[
b]
quenching.
A
reservoir of
[
a]ITO/PEDOT:PSS/polymer/Ba/Al.[b]ITO/polymer/Ag.
holes builds up within the
layer close to the TPBI layer
and the holes are shielded
À1
mained EQE=3.4% and LE=3.2 cdA with a luminance
of 3330 cdm . The luminance (L) and the external quantum
efficiency (EQE) of the devices as a function of current den-
from annihilation at the cathode by the TPBI layer.
Although high luminous efficiency was obtained at small
current densities (typically less than 10 mAcm ), the
À2
À2
sity (J) for PFPIrPiq and PFCzIrPiq are shown in Figure 8.
maxima of luminance of all the devices based on the poly-
mers with charged iridium complexes in their side chains
were lower than those of some previously reported PLEDs
with doped neutral phosphorescent red or red-orange iridi-
um complexes as emitters. As shown in Table 3 and Fig-
À2
ure 8b, maximum luminances of 4004 cdm for PFCzIrPiq4
À2
and 3945 cdm for PFCzIrPiq10 devices were observed at
À2
the current density of around 150 mAcm when TPBI was
employed as hole-blocking layer. The devices showed rela-
tively higher EL brightness in relation to devices produced
[26a]
from the red phosphorescent conjugated poly
A
H
R
U
G
con-
taining charged iridium complexes in the backbones, proba-
bly owing to the high PL efficiencies.
The efficiencies of the devices decayed at a high rate with
varying current density or operating voltage, as shown in
Figure 8. A similar phenomenon has been reported in devi-
ces based on charged iridium, ruthenium, and osmium com-
plexes. A voltage above the redox potential of the charged
transition metal complexes can lead to the fast degradation
[26b]
of devices. Bardꢁs group
vices containing charged [Ru
action with water and the subsequent production of [Ru-
reported that degradation of de-
2
+
A
H
R
U
G
2
+
A
H
R
U
G
A
H
R
U
the degradation in the charged iridium complex-based devi-
ces are not completely understood at present. A similar
mechanism might be at work in our charged Ir polymers.
Another possible mechanism leading to low EL lumi-
nance in the devices might arise from multi-particle annihi-
lation processes, such as triplet-triplet annihilation
Figure 8. L–J–QE curves of the devices fabricated from a) PFPIrPiq and
b) PFCzIrPiq.
[26c]
[26d]
(TTA),
triplet-polaron quenching,
and field-assisted
[26e]
dissociation of excitons at high electric fields.
These deg-
radations in high current density regions can be remedied
by reducing long radiative lifetimes of triplet excited states
by chemical modifications. Materials modification is ongoing
and improvement should be expected.
EL spectra of the devices produced from IrPiq doped into
a PFP host are shown in Figure 9. Comparison of the EL
spectra of the devices produced from corresponding charged
copolymers (Figure 5) with those of the blends reveals that
the former show much more efficient energy transfer than
the latter. When the doping concentration is 4 mol%, the
host emission is not completely quenched, while the host
emission of the charged copolymer containing 2 mol% IrPiq
The device performances of the carbazole-based PFCzIrPiq
are obviously superior to those of the benzene-based PFPIr-
Piq. When a hole-blocking TPBI layer was deposited on the
top of active layer, the situation was reversed, which is prob-
ably due to significantly reduced hole current in the
PFCzPiq-based devices, as the HOMO level of TPBI
(
À6.2 eV) is much lower than that of PFCzIrPiq (À5.35 eV).
As a result of a more balanced hole and electron current,
the efficiencies of PFCzIrPiq devices with a TPBI layer are
significantly increased. For PFPIrPiq devices, in contrast, be-
cause of the smaller difference between the HOMO levels
7438
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ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2007, 13, 7432 – 7442

Electrophosphorescent Copolymers
FULL PAPER
is quenched completely (Figure 5). This further indicates the
advantage of a covalently connected charged phosphores-
cent dye in a conjugated polymer side chain. This result is
consistent with that reported in chelating polymers with
[8]
neutral Ir complexes in their conjugated backbones.
Figure 10. J–V curves of PFPIrPiq devices with Ag or Ba/Al cathodes.
There are many functions in which charged iridium com-
plexes could significantly improve electron and hole injec-
tion in devices associated with an electrochemical cell mech-
Figure 9. EL spectra of the devices fabricated from PFP/IrPiq blends.
Device structure: ITO/PEDOT:PSS (50 nm)/(PFP/IrPiq)+PBD (30 wt%)
[9–11]
anism.
In the emitting layer, we speculated that the in-
(
75 nm)/TPBI (50 nm)/Ba (4 nm)/Al (150 nm).
troduction of charged IrPiq into the polymer made electro-
chemical doping at the interface of the film/electrode possi-
[28]
ble
or the formation of an ionic space charge layer
[29]
Despite the enhanced device performance, as shown in
easy, which lowered the barrier to hole and electron injec-
tion.
Table 3, the turn-on and operating voltages for all devices
based on the resulting polymers are very high. This could be
attributable to a charge-trapping mechanism, energetically
favored, as inferred from the energy level. To remedy this
problem, reducing the content of iridium complex, utilizing
proper heat annealing treatment to relieve space charge
build-up, and selection of a good electron injection-cathode
Conclusion
High-efficiency electrophosphorescent copolymers contain-
ing charged iridium complexes—with a 2-(pyridin-2-yl)ben-
zimidazole moiety in the polymer side chain directly coordi-
nating with a chloride-bridged iridium dimer of 1-phenyliso-
quinoline—were synthesized. A maximum external quantum
[27]
could be good choices. These efforts are in progress and
will be reported in a forthcoming paper.
The single-layer light-emitting devices based on PFPIr-
Piq2 and PFPIrPiq10 were fabricated with the configuration
of ITO/polymer/Ag (structure B, as shown in Figure 6).
Large hole and electron injection barriers between the poly-
mer and the electrodes are expected. The device performan-
ces at around 35 mAcm with Ba/Al and Ag as cathodes
are summarized in Table 4. For the single-layer device based
on PFPIrPiq2, a quantum efficiency of 0.5% and a luminous
À1
efficiency of 7.3% and a luminous efficiency of 6.9 cdA
À2
with a luminance of 138 cdm were achieved from PFCzIr-
Piq4 at a current density of 1.9 mAcm . The efficiencies of
À2
this device remained as high as EQE=3.4% and LE=
À2
À1
À2
3.3 cdA with a luminance of 3770 cdm at a current den-
À2
sity of 115 mAcm . The enhancement of the device per-
formances could be attributed to the balanced charge injec-
tion and transport achieved through insertion of a layer of
TPBI. The maximum external quantum efficiencies of
single-layer devices were 0.64% and 0.66% for PFPIrPiq2
and PFPIrPiq10, respectively, with Ag as cathode. The en-
couraging results obtained with the devices indicate that the
copolymers containing charged iridium complexes are prom-
ising in optoelectronic applications.
À1
À2
efficiency of 0.22 cdA with 86 cdm were reached at the
current density of 35 mAcm , the same as those of the Ba/
À2
Al device. Similar results were obtained with PFPIrPiq10.
The maximum external quantum efficiencies (EQEmax) of
the single-layer devices were 0.64% and 0.66% from PFPIr-
Piq2 and PFPIrPiq10, respectively, while EQEmax of the
double-layer devices with Ba as cathode were 0.83 and
0
.33%, respectively. The maximum luminance of the single-
À2
layer device was approximately 200 cdm , whereas that of
the double-layer device was only 150 cdm . Figure 10 com-
À2
Experimental Section
pares J–V for PFPIrPiq devices with Ba or Ag as cathode.
The results clearly indicate that the electron and hole injec-
tions from ITO/polymer/Ag device are comparable to those
from a low work function Ba cathode with a slight decrease
of the operating voltage.
1
13
Measurements: H and C NMR spectra were recorded on a Bruker
DRX 300 spectrometer operating at 300 and 75 MHz, respectively, with
tetramethylsilane as a reference. EI-MS were recorded on a LCQ
DECA XP Liquid Chromatograph/Mass Spectrometer (Thremo Group).
Chem. Eur. J. 2007, 13, 7432 – 7442
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
7439

W. Yang, J. Peng et al.
The molecular weight of the polymers was determined with a Waters
GPC 2410 instrument in tetrahydrofuran (THF) by use of a calibration
curve of polystyrene standards. Elemental analyses were performed on a
Vario EL elemental analysis instrument (Elementar Co.). The iridium
contents analyses were determined with a Philips (Magix PRO) sequen-
tial X-ray fluorescence (XRF) spectrometer, with a rhodium tube operat-
ed at 60 kV and 50 mA, a LiF 200 crystal, and a scintillation counter.
Py-H), 8.49 (t, J=7.9 Hz, 1H; Py-H), 7.92–7.87 (m, 2H; Py-H), 7.39–
7.26 ppm (m, 4H; Ar-H).
[15]
3
,6-Dibromo-9-{N-[2-(pyridin-2-yl)benzimidazole]-hexyl}carbazole (4):
A mixture of 3,6-dibromo-9-(6’-bromohexyl)carbazole (4.88 g, 10 mmol),
-(pyridin-2-yl)benzimidazole (1.95 g, 10 mmol), sodium hydroxide
0.44 g, 11 mmol), and dimethyl sulfoxide (30 mL) was stirred and heated
at 1308C for 24 h under argon. It was subsequently poured into ice water
100 mL). After extraction with CH Cl (3”30 mL), the organic layer
was washed with water and dried over anhydrous MgSO , and the solvent
2
(
Iridium(III) 2,4-pentanedionate (from Alfa Aesar Co.) was used as a
A
C
H
T
R
E
U
N
G
(
2
2
standard. UV/Vis absorption spectra were recorded on a HP 8453 spec-
trophotometer. Cyclic voltammetry was carried out on a potentiostat/gal-
vanostat model 283 (Princeton Applied Research) with a platinum elec-
4
was then evaporated. The resulting residue was purified by silica gel
column chromatography (petroleum ether/ethyl acetate 2:1) to give a
À1
trode at a scan rate of 50 mVs against a saturated calomel electrode
1
white solid product (2.7 g, 43%). H NMR (300 MHz, CDCl
3
): d=8.54–
(
SCE) with a nitrogen-saturated solution of tetrabutylammonium hexa-
8
8
.52 (d, J=4.8 Hz, 1H; Py-H), 8.43–8.40 (d, J=7.9 Hz, 1H; Py-H), 8.15–
.14 (d, J=1.8 Hz, 2H; Cz-H), 7.87–7.81 (m, 2H; Py-H), 7.54–7.51 (dd,
fluorophosphate (Bu NPF , 0.1m) in acetonitrile (CH CN). Absolute PL
4
6
3
efficiencies were measured in an integrating sphere (IS-080, Labsphere)
under the 325 nm line of a HeCd laser. Photoluminescence (PL) spectra
was recorded with a CCD spectrophotometer (Instaspec 4, Oriel) with
J=1.9 Hz, 2H; Cz-H), 7.39–7.28 (m, 4H; Ar-H), 7.22–7.19 (m, 2H; Cz-
H), 4.80 (t, J=7.3 Hz, 2H; benzimidazole N-CH ), 4.20 (t, J=7.0 Hz,
H; Cz N-CH ), 1.88–1.33 ppm (m, 8H; CH ) (aliphatic); C NMR
75 MHz, CDCl ): d=150.63, 149.74, 148.51, 142.58, 139.24, 136.80,
136.54, 129.05, 124.67, 123.74, 123.73, 123.50, 122.60, 120.15, 112.02,
110.30, 110.09, 45.20 (Bm N-CH ), 43.12 (Cz N-CH ), 29.85, 28.72, 26.80,
2
13
2
(
2
2
3
25 nm excitation by a HeCd laser.
3
Materials: Reactions involving air-sensitive reagents were performed
under dry argon. All reagents, unless otherwise specified, were obtained
from Aldrich, Acros, and TCI Co, and were used as received. 1-Phenyli-
2
2
26.53 ppm (aliphatic); elemental analysis (%) calcd for C30
26 4 2
H N Br : C
[
17]
soquinoline (1-piq) was prepared by the published procedure.
,6-Dibromo-9-(6’-bromohexyl)carbazole (1): 3,6-Dibromocarbazole
10 g, 30.8 mmol) in dry THF (50 mL) was added dropwise to a solution
of sodium hydride (2.47 g, 61.6 mmol, 60%) in dry THF (50 mL). The
mixture was heated at reflux under N for 1.5 h, and the resulting mix-
ture was then added dropwise to 1,6-dibromohexane (90 mmol) in THF
10 mL). The reaction mixture was heated at reflux for another 24 h and
59.80, H 4.32, N 9.30; found: C 59.89, H 4.50, N 9.30.
3
(
1,4-Dibromo-2-methoxy-5-{N-[2-(pyridin-2-yl)benzimidazole]-hexyloxy}-
benzene (5): This compound was prepared by the same procedure as
1
used to make 4 (yield 65%). H NMR (300 MHz, CDCl
3
): d=8.71–8.69
(d, J=4.7 Hz, 1H; Py-H), 8.44–8.41 (d, J=8.0 Hz, 1H; Py-H), 7.84–7.81
(m, 2H; Py-H), 7.44–7.29 (m, J=6.8 Hz, 4H; Ar-H), 7.10–7.07 (d, J=
2
(
5.8 Hz, 2H; Ar-H), 4.89–4.84 (t, J=7.4 Hz, 2H; benzimidazole N-CH
3.90–3.87 (t, J=6.3 Hz, 2H; OCH ), 3.82 (s, 3H; OCH ), 1.94–1.20 ppm
); C NMR (75 MHz, CDCl ): d=150.73, 150.54, 150.06,
2
),
was then allowed to cool to room temperature. It was extracted with di-
chloromethane, followed by washing with water. The oil phase was sepa-
2
3
1
3
(m, 10H; CH
2
3
rated and dried overnight with MgSO
evaporation, and the crude product was purified by silica column chro-
matography to give a white solid (9.1 g, 60%). H NMR (300 MHz,
4
. The solvent was removed by
149.85, 148.66, 142.63, 136.79, 136.63, 124.71, 123.73, 123.27, 122.55,
120.11, 118.66, 117.01, 111.27, 110.46, 110.20, 70.11, 57.01, 45.32, 29.94,
1
28.93, 26.60, 25.65 ppm; elemental analysis (%) calcd for C25
C 53.67, H, 4.48, N 7.51; found: C 53.64, H 4.51, N 7.35.
25 3 2 2
H N O Br :
CDCl
.1 Hz, J
Cz N-CH
3
): d=8.14 (d, J=1.8 Hz, 2H; Cz-H), 7.52 (m, 2H), 7.20 (t, J
=2.5 Hz, 2H; Cz-H), 4.23–4.21 (t, J =6.9 Hz, J =7.2 Hz, 2H;
), 3.33–3.30 (m, 2H; Br-CH ), 1.85–1.81 ppm (m, 8H; CH
): d=139.28, 129.07, 123.49, 123.30,
12.05, 110.32 (carbazole ring), 43.13 (N-CH ), 33.56, 32.46, 28.68, 27.81,
6.36 ppm; elemental analysis (%) calcd for C18 : C 44.26, H 3.70,
1
=
6
2
1
2
2,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9,9-dioctylfluorene
(6): This compound was prepared by the published procedure and the ob-
2
2
2
)
1
3
(
aliphatic); C NMR (75 MHz, CDCl
3
tained boronic ester was recrystallized from methanol to give a white
[
7]1
1
2
2
solid product (yield 50%).
3
H NMR (300 MHz, CDCl ): d=7.81 (m,
H
18NBr
3
2H), 7.76 (s, 2H), 7.72 (m, 2H) (fluorene ring), 1.97 (m, 4H), 1.37 (s,
N 2.86; found: C 44.75, H 3.83, N 2.85.
,4-Dibromo-2-methoxy-5-[(6’-bromo)hexyloxy]benzene (2): A solution
of bromine (0.64 g, 4.1 mmol) in chloroform (50 mL) was slowly added at
24H; CH ), 1.22–0.98 (m, 20H), 0.81 (t, J=6.7 Hz, 6H), 0.54 ppm (m,
3
1
3
1
4H) (aliphatic); C NMR (75 MHz, CDCl
129.27, 121.68, 119.75 (fluorene ring), 84.12, 55.56 (C
40.49, 32.15, 30.32, 29.60, 25.29, 24.01, 23.03, 14.46 ppm (aliphatic); ele-
3
): d=150.85, 144.32, 134.06,
9
-fluorene ring),
0
2
8C to
a solution of 1-(6-bromohexyloxy)-4-methoxybenzene (5.6 g,
0 mmol) in chloroform (100 mL). The mixture was stirred at room tem-
mental analysis (%) calcd for C41
H
64
O
4
B
2
: C 76.74, H 10.04; found: C
perature for 24 h and the mixture was neutralized with iced aqueous
KOH. After washing with water, diluted hydrochloride acid solution, and
76.43, H 9.95.
Tetrakis(1-phenylisoquinoline-N,C2’) (m-chlorobridged)diiridium
ACHTREUNG
(III) (7):
brine, the organic layer was dried over MgSO
followed by recrystallization from ethanol, afforded a white solid (6.5 g,
4
. Removal of the solvent,
Iridium trichloride hydrate (1.318 g, 3.8 mmol) and 1-phenylisoquinoline
(1.915 g, 9.4 mmol) were dissolved in a mixture of 2-ethoxyethanol and
water (3:1, 20 mL), and the mixture was then heated at reflux for 24 h
under argon. The solution was allowed to cool to room temperature, and
the deep red precipitate was collected on a glass filter frit. The precipi-
tate was washed with ethanol and ethyl ether to form a dark red power
(2.134 g, 90%), which was used directly for the next step without purifi-
cation.
1
7
5%). H NMR (300 MHz, CDCl
J=6.4 Hz, 2H; OCH ), 3.87 (s, 3H; OCH
Br-CH ), 1.93–1.54 ppm (m, 8H; CH ) (aliphatic); C NMR (75 MHz,
CDCl ): d=150.57, 150.05, 118.67, 117.01, 111.28, 110.42, 70.08, 57.01,
3.77, 32.66, 28.94, 27.83, 25.21 ppm; elemental analysis (%) calcd for
Br : C 35.10, H 3.82; found: C 35.13, H 4.06.
-(Pyridin-2-yl)benzimidazole (3):
3
): d=7.11 (s, 2H; Ar-H), 4.01–3.96 (t,
2
3
), 3.47–3.43 (t, J=7.1 Hz, 2H;
1
3
2
2
3
3
C
13
H
17
O
2
3
[
14]
2
Picolinic acid (40.0 mmol, 4.92 g)
2-(Pyridin-2-yl)-N-hexylbenzimidazole (8): A mixture of 1-bromohexane
(15 mmol) and 2-(pyridin-2-yl)benzimidazole (1.95 g, 10 mmol), sodium
hydroxide (0.44 g, 11 mmol), and dry dimethyl sulfoxide (30 mL) was
stirred and heated at 1308C for 24 h under argon. It was subsequently
poured into ice water (100 mL). After extraction with CH Cl (3”
and o-phenylenediamine (40.0 mmol, 4.32 g) were added to polyphos-
phoric acid (85%, 100 mL), and the mixture was then heated to 1908C.
After 8 h, the solution was cooled and added to ice water (1000 mL). The
solution was made alkaline (pH 10, NaOH) and allowed to stir overnight,
forming a purple/lavender precipitate, which was filtered and collected.
Further purification to remove any excess o-phenylenediamine was ach-
ieved by reprecipitation. The lavender precipitate was dissolved in
sodium carbonate solution (10%, 200 mL) and stirred to dissolve all of
the material. The pH of the solution was brought from 11 to 7.8, resulting
in the reprecipitation of the lavender product. The precipitate was col-
lected by filtration, dried, and weighed. The product was further purified
2
2
30 mL), the organic layer was washed with water and dried over anhy-
drous Na SO . The solvent was then evaporated and the obtained residue
2
4
was purified by silica gel column chromatography (1.12 g, 40%).
1
H NMR (300 MHz, CDCl ): d=8.72–8.69 (m, 1H, Py-H), 8.44–8.41 (d,
3
J=8.0 Hz, 1H; Py-H), 7.88–7.83 (m, 2H; Py-H), 7.49–7.28 (m, 1H; Ar-
H), 7.45–7.28 (m, 3H), 4.87–4.82 (t, J=7.6 Hz, 2H; N-CH ), 1.92–1.87
2
1
3
(m, 2H), 1.36–1.27 (m, 6H), 0.89–0.85 ppm (m, 3H); C NMR (75 MHz,
CDCl ): d=150.68, 148.63, 136.77, 136.59, 124.73, 123.71, 123.64, 123.23,
122.53, 120.03, 110.25, 45.47, 31.72, 30.40, 26.48, 22.50, 13.98 ppm.
by column chromatography and recrystallization to give a white solid
3
1
(
1.95 g, 25%). H NMR (300 MHz, CDCl
3
): d=8.54 (d, J=4.8 Hz, 1H;
7440
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ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2007, 13, 7432 – 7442

Electrophosphorescent Copolymers
FULL PAPER
2
{N-[2-(2-benzimidazole)pyridine]hexyl}BF (9):
4À
[18]
In a round-
Cl] (0.10 g,
units)
diiridium
and
tetrakis(1-phenylisoquinoline-N,C2’)(m-chlorobridged)-
Ir
A
C
H
T
R
E
U
N
G
(1-piq)
À5
bottomed flask, dichloro-bridged iridium dimer [Ir
7
A
H
R
U
G
2
2
A
H
R
U
G
À5
.8”10 mol) and 2-(pyridin-2-yl)-N-hexylbenzimidazole (2.0 equiv)
The mixture was heated at reflux under argon for 24 h. As the chelation
were mixed together in THF (25 mL). The solution was then heated at
progressed, the red solid dissolved to form a red clear solution. Excess
À
reflux overnight under an inert atmosphere. After the mixture had
NaBF
4
was dissolved in methanol (5 mL) and added dropwise into the
À
cooled to room temperature, excess NaBF
4
in methanol was added
reaction mixture. The reaction mixture was kept stirring over a period of
4 h and the resulting solution was concentrated and dropped into metha-
dropwise and the mixture was stirred for 4 h, counterion exchange from
À
À
Cl to BF
dissolved in CH
precipitated in hexane. The product was purified by recrystallization
4
was performed, the solvent was removed, and the solid was
nol to precipitate the polymer. The crude product was washed thoroughly
À
Cl (20 mL). The CH Cl solution was filtered off and
2
2
2
with hot methanol to remove the residual NaBF
4
. The solids were dis-
2
solved in toluene and precipitated in hexane again. The desired complex
was filtered to produce an orange-red solid, which was washed with
methanol in a Soxhlet extractor for 2 d and dried under vacuum at room
temperature.
1
from ethanol (0.1 g, 70%). H NMR (300 MHz, CDCl
H), 8.75–8.72 (m, 2H), 8.42–8.22 (m, 3H), 7.92–7.71 (m, 7H), 7.61–7.54
m, 2H), 7.44–7.31 (m, 5H), 7.19–7.11 (m, 2H), 7.01–6.88 (m, 3H), 6.46–
.44 (m, 1H), 6.32–6.29 (m, 1H), 6.04–6.01 (m, 1H), 5.01- 4.88 (m, 3H),
3
): d=9.07–8.89 (m,
2
(
1
6
2
1
1
1
1
1
PFPIrPiq2: H NMR (300 MHz, CDCl ): d=8.63 (br), 8.43–8.40 (d),
3
1
3
.10–0.89 ppm (m, 11H); C NMR (75 MHz, CDCl
3
): d=154.72, 151.83,
7.85–7.15 (m), 4.81 (br, N-CH ), 3.98 (br, OCH ), 3.80 (br, OCH ), 1.91–
2
2
3
51.54, 150.86, 146.83, 146.23, 145.75, 140.90, 140.63, 140.54, 139.23,
36.85, 136.87, 136.56, 133.03, 132.16, 131.62, 131.36, 130.86, 130.71,
30.40, 129.92, 128.66, 128.53, 128.01, 127.62, 127.52, 126.85, 126.33,
26.25, 126.10, 125.92, 125.21, 122.33, 121.92, 121.80, 121.77, 118.32,
11.63, 46.18, 31.36, 29.90, 26.33, 22.36, 13.90 ppm; elemental analysis
0.81 (m); elemental analysis (%) found: C 82.20, H 7.85, N 5.30; weight-
average molecular weight (M ): 19000 and polydispersity index (PDI):
w
1.9.
1
PFPIrPiq4: H NMR (300 MHz, CDCl
3
): d=8.63 (br), 8.42–8.40 (d),
), 3.88 (br, OCH ), 3.80 (br, OCH ), 1.91–
.81 (m); elemental analysis (%) found: C 80.78, H 7.45, N 5.28; weight-
7
0
.86–7.15 (m), 4.81 (br, N-CH
2
2
3
(
4
%) calcd for C48
.15, N 6.84; MS (EI): m/z:: 880; found: 880 [MÀBF
H
41
F
4
IrN
5
B: C 59.70, H 4.25, N 7.26; found: C 59.40, H
À
4
] .
+
average molecular weight (M
w
): 21600 and polydispersity index (PDI):
General procedures for the synthesis of macroligands, with PFCz as an
example: 2,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9,9-dioctyl-
fluorene (632 mg, 1.0 mmol), 3,6-dibromo-9-(N-(2-(pyridin-2-yl)benzimi-
dazole)hexyl)carbazole (602 mg, 1.0 mmol), and tetrakis(triphenylphos-
phine)palladium (5 mg) were dissolved in toluene/THF (10 mL, 3:1) and
2.1.
1
PFPIrPiq10: H NMR (300 MHz, CDCl
3
): d=8.93 (d), 8.84 (t), 8.63 (br),
8
6
0
.43–8.40 (d), 8.31–8.28 (d), 8.23–8.21 (d), 7.85–7.15 (m), 6.92–6.89 (d),
.45–6.43 (d), 4.81 (br, N-CH ), 3.98 (br, OCH ), 3.80 (br, OCH ), 1.91–
.81 (m); elemental analysis (%) found: C 79.79, H 7.45, N 5.48; weight-
): 22000 and polydispersity index (PDI):
2
2
3
4
stirred for 0.5 h, and then Et NOH aqueous solution (20%, 4 mL) was
average molecular weight (M
.7.
PFCzIrPiq4: H NMR (300 MHz, CDCl
w
added. The mixture was heated to 1008C and stirred for 2 d under argon.
The polymer was then capped by addition of 2-(4,4,5,5-tetramethyl-1,3,2-
dioxaborolan-2-yl)-9,9-dioctylfluorene (100 mg), the mixture was stirred
for 12 h, and the polymer was then capped with bromobenzene (1 mL),
followed by heating for another 12 h. The mixture was poured into
stirred methanol (200 mL) to generate plenty of light-yellow precipitates.
The solid was collected by filtration and then dissolved in toluene and
washed twice with dilute NaHCO solution. The careful reprecipitation
3
procedure in acetone/methanol was repeated several times. The polymer
was further purified by washing with acetone at reflux in a Soxhlet for 2–
1
1
3
): d=8.54–8.38 (m), 7.88–7.62
m), 7.57–7.49 (m), 6.26–6.23 (m), 4.82 (br, benzimidazole N-CH ), 4.39
br, Cz N-CH ), 2.45–2.20 (m), 1.97–0.78 (m, aliphatic); elemental analy-
(
(
2
2
sis (%) found: C 83.58, H 8.05, N 6.94; weight-average molecular weight
(
M
w
): 5400 and polydispersity index (PDI): 1.6.
1
PFCzIrPiq10: H NMR (300 MHz, CDCl
3
): d=8.93 (d), 8.84 (t), 8.54–
8
6
4
.38 (m), 8.31–8.28 (d), 8.23–8.21 (d), 7.88–7.62 (m), 7.57–7.49 (m), 6.92–
.89 (d), 6.45–6.43 (d), 6.26–6.23 (m), 4.82 (br, benzimidazole N-CH ),
.39 (br, Cz N-CH ), 2.45–2.20 (m), 1.97–0.78 (m, aliphatic); elemental
2
2
3
days. The light-yellow solid was dried under vacuum at room tempera-
analysis (%) found: C 81.58, H 8.01, N 6.85; weight-average molecular
weight (M ): 7300 and polydispersity index (PDI): 1.8.
ture (0.43 g, 52%).
w
1
PFCz (yield 52%): H NMR (300 MHz, CDCl
.43–8.40 (d, J=7.9 Hz, 1H), 7.87–7.74 (m, 10H), 7.51–7.41 (m, 6H) (flu-
orene ring, carbazole ring, and 2-(pyridin-2-yl)benzimidazole ring), 4.84
br, 2H; benzimidazole N-CH ), 4.38 (br, 2H; Cz N-CH ), 1.92 (m, 4H),
.69–1.13 (m, 20H), 1.14–0.78 ppm (m, 18H) (aliphatic); C NMR
75 MHz, CDCl ): d=151.70, 150.72, 149.82, 148.60, 142.68, 140.80,
3
): d=8.56–8.53 (m, 3H),
Device fabrication andcharacterization : The polymers were dissolved in
p-xylene and filtered (0.45 mm filter). Patterned glass substrates coated
with indium tin oxide (ITO) were cleaned with acetone, detergent, dis-
tilled water, and propan-2-ol, and subsequently in an ultrasonic bath.
After treatment with oxygen plasma, poly(3,4-ethylenedioxythiophene)
8
(
1
(
2
2
1
3
3
(
PEDOT) doped with poly(styrenesulfonic acid) (PSS; Batron-P 4083,
1
1
40.34, 139.57, 136.74, 136.60, 133.11, 126.17, 125.60, 124.65, 123.70,
23.62, 123.27, 122.54, 121.64, 120.16, 119.93, 118.99, 110.13, 109.02 (fluo-
Bayer AG) (150 nm) was spin-coated onto the ITO substrate, which was
followed by drying in a vacuum oven at 808C for 8 h. A thin film of poly-
mers was spin-coated on top of the PEDOT. The film thicknesses of the
active layers were around 75–80 nm, measured with an Alfa Step 500 sur-
face profiler (Tencor). A thin layer of TPBI (50 nm), a layer of Ba (4–
rene, carbazole, and 2-(pyridin-2-yl)benzimidazole ring), 68.01, 55.36 (C
fluorene ring), 45.27 (Bem N-CH ), 40.67 (Cz N-CH ), 31.81, 30.13, 29.92,
9.26, 29.03, 26.95, 26.70, 25.62, 24.01, 22.61, 14.10 ppm (aliphatic); ele-
9
-
2
2
2
mental analysis (%) calcd for C59
H
66
N
4
: C 85.30, H 7.95, N 6.75; found:
5
nm), and a layer of Al (150 nm) were subsequently vacuum-evaporated
C 84.62, H 8.14, N 6.05.
onto the top of the EL polymer layer under vacuum. Device performance
was measured in a dry box. Current–voltage (I–V) characteristics were
recorded with a Keithley 236 source meter. EL spectra were recorded
with an Oriel Instaspec IV CCD Spectrograph. Luminance was measured
with a PR 705 photometer (Photo Research). The external quantum effi-
ciencies were determined with a Si photodiode with calibration in an in-
tegrating sphere (IS 080, Labsphere).
1
PFP (yield 60%): H NMR (300 MHz, CDCl
3
): d=8.65–8.63 (d, J=
4
2
.7 Hz, 1H; Py-H), 8.44–8.41 (d, J=8.0 Hz, 1H; Py-H), 7.87–7.82 (m,
H; Py-H), 7.79–7.42 (m, 5H; Ar-H), 7.42–7.14 (m, 8H; Ar-H), 4.84–4.81
=7.3 Hz, J =7.1 Hz, 2H; N-CH ), 4.0 (br, 2H; OCH ), 3.80 (br,
H; OCH ), 1.91–1.76 (m, 6H), 1.44–1.29 (m, 6H), 1.16–0.91 (m, 21H),
.83–0.61 ppm (m, 9H); C NMR (75 MHz, CDCl
(
t, J
1
2
2
2
3
0
1
1
1
3
3
1
3
3
): d=151.16, 150.76,
50.51, 149.82, 148.59, 142.69, 139.91, 137.07, 136.71, 136.63, 131.68,
28.04, 124.66, 123.60, 123.26, 122.50, 120.13, 119.42, 116.96, 115.52,
10.17, 69.77, 56.84, 55.03 (C
0.28, 30.01, 29.36, 28.93, 26.50, 25.70, 24.13, 22.59, 14.05 ppm; elemental
: C 82.34, H 8.26, N 5.46; found: C
9
-fluorene ring), 45.33, 40.60, 32.15, 31.84,
analysis (%) calcd for C54
2.33, H 8.33, N 5.01.
65 3 2
H N O
8
Acknowledgements
General procedures for the preparation of the polymers containing
charged iridium complex in their side chains, with PFPIrPiq4 as an ex-
The authors are grateful to the Ministry of Science and Technology of
China (No. 2002CB613403) and the National Natural Science Foundation
[
19]
À4
ample: Polymer PFP (250 mg, 3.178”10 mol according to repeated
Chem. Eur. J. 2007, 13, 7432 – 7442
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
7441

W. Yang, J. Peng et al.
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Received: December 17, 2006
Revised: April 4, 2007
Published online: June 21, 2007
7
7442
www.chemeurj.org
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2007, 13, 7432 – 7442