Single chain white-light-emitting polyfluorene copolymers containing iridium complex coordinated on the main chain

Article abstract of DOI:10.1021/ma902318t

We report the synthesis of single chain white-light-emitting polyfluorene copolymers containing a novel iridium complex with β-diketonate unit, bis(2-benzothiazol-2-yl-N-ethylcarbazole)iridium-l,3bis(p-bromophenyl)l, 3-propanedione ((bec)₂IrdbmBr), as the red emission unit. The synthesized polyfluorene copolymers containing the carbazole and iridium complex, poly{9,9-bis(4-octyloxyphenyl)fluorene-2,7-diyl-co(N-hexylcarbazole-3, 6-diyl)-co-[bis(2-benzothiazol-2-yl-N-ethylcarbazole)iridium-l, 3-bis(p-bromophenyl)propanedione-l,3-diyl]} (PFCzIrbecs), were synthesized via palladium-catalyzed Suzuki coupling reactions. These polymers were found to be thermally stable and readily soluble in common organic solvents. Interestingly, the synthesized polymers, PFCzIrbec 05 and PFCzIrbec 2, exhibited two strong emission bands in both the blue and red spectral regions. Light-emitting devices based on these polymers were fabricated in an ITO/PEDOT:PSS/poly(TPD)/polymers/ TPBi/LiF/Al configuration. We obtained white light emission from a single polymer chain by incorporating (bec)₂IrdbmBr as the red emission unit into a BOPF and carbazole main chain as the host and blue emission. This device exhibited good performance. In particular, EL device fabricated with PFCzIrbec 2 was found to emit white light consisting of simultaneous blue and red emission with CIE coordinates of (0.31, 0.32), which are close to the standard for white light emission. Moreover, the EL spectrum of PFCzIrbec 2 was stable with respect applied voltage, and CIE coordinates were almost not changed at various driving voltages.

Full text of DOI:10.1021/ma902318t

Macromolecules 2010, 43, 1379–1386 1379
DOI: 10.1021/ma902318t
Single Chain White-Light-Emitting Polyfluorene Copolymers Containing
Iridium Complex Coordinated on the Main Chain
Moo-Jin Park,† Jeonghun Kwak, Jonghee Lee,‡,^ In Hwan Jung,‡ Hoyoul Kong,‡
Changhee Lee, Do-Hoon Hwang,*,§ and Hong-Ku Shim*,‡
†Polymer Science and Engineering Program, Korea Advanced Institute of Science and Technology, Daejeon 305-701,
Korea, ‡Department of Chemistry, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea,
§Department of Applied Chemistry, Kumoh National Institute of Technology, Gumi 730-701, Korea, and
School of Electrical Engineering and Computer Science, Inter-university Semiconductor Research Center,
Seoul National University, Seoul 151-742, Korea. ^ Present address: Convergence Components & Materials Lab.,
Electronics and Telecommunications Research Institute, Daejeon 305-350, Korea
Received October 18, 2009; Revised Manuscript Received December 21, 2009
ABSTRACT: We report the synthesis of single chain white-light-emitting polyfluorene copolymers contain-
ing a novel iridium complex with a β-diketonate unit, bis(2-benzothiazol-2-yl-N-ethylcarbazole)iridium-1,3-
bis(p-bromophenyl)1,3-propanedione ((bec)2IrdbmBr), as the red emission unit. The synthesized polyfluorene
copolymers containing the carbazole and iridium complex, poly{9,9-bis(4-octyloxyphenyl)fluorene-2,7-diyl-co-
(N-hexylcarbazole-3,6-diyl)-co-[bis(2-benzothiazol-2-yl-N-ethylcarbazole)iridium-1,3-bis(p-bromophenyl)-
propanedione-1,3-diyl]} (PFCzIrbecs), were synthesized via palladium-catalyzed Suzuki coupling reactions.
These polymers were found to be thermally stable and readily soluble in common organic solvents.
Interestingly, the synthesized polymers, PFCzIrbec 05 and PFCzIrbec 2, exhibited two strong emission bands
in both the blue and red spectral regions. Light-emitting devices based on these polymers were fabricated in an
ITO/PEDOT:PSS/poly(TPD)/polymers/TPBi/LiF/Al configuration. We obtained white light emission from
a single polymer chain by incorporating (bec)2IrdbmBr as the red emission unit into a BOPF and carbazole
main chain as the host and blue emission. This device exhibited good performance. In particular, EL device
fabricated with PFCzIrbec 2 was found to emit white light consisting of simultaneous blue and red emission
with CIE coordinates of (0.31, 0.32), which are close to the standard for white light emission. Moreover, the
EL spectrum of PFCzIrbec 2 was stable with respect applied voltage, and CIE coordinates were almost not
changed at various driving voltages.
Introduction
Cao et al. reported that phosphorescent chelating copolymers
based on the linkage isomer of 2-(1-naphthalene)pyridine and
In the past few years, conjugated polymers have attracted
scientific and technological interest due to their potential applica-
tions in organic thin-film transistors,1 nonlinear optical devices,2
photovoltaic cells,3 and polymer light-emitting diodes (PLEDs).4
In particular, concern about PLED devices for flat panel display
has increased due to its suitable properties.5 PLEDs have been
found to be of considerable importance as active materials in new
technology fields because their optical and electrical properties
can be adjusted by manipulating their chemical structures.6-9
Recently, polymer blend systems, produced via the combination
of a polymer “host” and a heavy metal complex “guest”, showed
improved device properties compared with conventional fluores-
cent OLEDs.10 The phosphorescent blending system, however,
intrinsically suffers from efficiency and stability limitations due to
energy loss by energy transfer from the host to low-lying triplet
states, aggregation of dopants, even at low doping concentrations,
and potential phase separation, which results in the fast decay of
efficiency with increasing current density.11 To address these
issues, a recent study introduced heavy-metal complexes by
directly incorporation into polymer main chains.12,13 Phosphor-
escent polymer light-emitting diodes (PhPLEDs) containing com-
plexes between metal centers and the polymer main chain,
directly12 or via pendant group,13 have many advantages com-
pared to blend systems that consist of dopants in a host matrix.
2-(2-naphthalene)pyridine-bicycloiridium complexes exhibited
high external efficiencies with no remarkable efficiency decay.12a
To graft metal complexes onto polymer main chains, Yang et al.
reported the introduction of N-alkylcarbazole units with a term-
inal diketone group to provide a ligand for the formation of
iridium complexes in the side chains.13
Single chain white-light-emitting polymers, for use as PLEDs,
offer several advantages, such as simple fabrication processes,
ease of scaling up production, and the absence of material
complications arising from phase separation or the dependence
of electroluminescence the driving voltage. Recently, several
advances in the synthesis of single chain white-light-emitting
polymers containing a phosphorescent unit have been reported.
Yang et al. reported that fluorene-based copolymers containing
fluorenone and an iridium complex on the main chain exhibited
white light emission produced by a fluorenone defect character-
istic in the polymer main chain.14 Peng et al. reported that a
binary copolymer containing red iridium complexes attached to
the side chain of polyfluorene exhibited white light emission.15
This research introduced green emission segments into the main
chain, which assisted an energy transfer process from the fluorene
units to the iridium complex, and strengthened the otherwise
weak green intensity of the emission band. The control of the
monomer feed ratios in this system was difficult because of used
four kinds of monomers and controlled two kinds of monomers
carefully. The single chain polymer without green segments,
*To whom all correspondence may be addressed. E-mail: hkshim@
kaist.ac.kr (H.-K.S.) or dhhwang@kumoh.ac.kr (D.-H.H.).
r 2010 American Chemical Society
Published on Web 01/08/2010
pubs.acs.org/Macromolecules

1380 Macromolecules, Vol. 43, No. 3, 2010
Scheme 1. Synthetic Routes of the (bec)2IrdbmBr
Park et al.
however, is easier to control feed ratio of monomers due to
adjusting only iridium complex.
atmosphere. Differential scanning calorimetric (DSC) measure-
ments were made using TA Q100 instrument and operated
under a nitrogen atmosphere at a heating rate of 10 ꢀC/min.
The number- and weight-average molecular weights of polymers
were determined by gel permeation chromatography (GPC) on
Viscotek T60A instrument, using tetrahydrofuran (THF) as
eluent and polystyrene as standard. Cyclic voltammetry (CV)
was performed on an AUTOLAB/PG-STAT12 model system
with a three-electrode cell in a solution of Bu4NBF4 (0.10 M) in
acetonitrile at a scan rate of 50 mV/s. A film of each polymer was
coated onto a Pt wire electrode by dippng the electrode into a
solution of the polymer. The measurements were calibrated
using ferrocene as standard. EL devices were fabricated on glass
substrates coated with indium-tin oxide (ITO). The device
configuration was ITO/PEDOT:PSS/poly(TPD)/polymer/
TPBi/LiF/Al structures. The procedure for cleaning the ITO
surface included sonication and rinsing in deionized water,
methanol, and acetone. The hole-transporting PEDOT:PSS
layer was spin-coated onto each ITO anode from a solution
purchased from Bayer. The spin-casting yielded uniform PED-
OT:PSS films with thicknesses of ∼40 nm. To help hole trans-
porting ability from anode and PEDOT:PSS, poly(N,N0-bis(4-
butylphenyl)-N,N0-bis(phenyl)benzidine), poly(TPD), stacked
on PEDOT:PSS layer which was purchased from American
Dye Source, Inc. Poly(TPD) solution in chlorobenzene was then
spin-coated onto the PEDOT:PSS layer and yielded uniform
films with thickness of ∼50 nm. Each polymer solution in p-
xylene was then spin-coated onto the poly(TPD) layer. The spin-
casting yielded uniform polymer films with thicknesses of
∼40 nm. A 40 nm thick 2,20,200-(1,3,5-benzinetriyl)-tris(1-phenyl-
1H-benzimidazole) (TPBi) electron transporting layer was
deposited, and a 0.5 nm thick lithium fluoride (LiF) layer and a
100 nm thick aluminum (Al) layer were subsequently deposited
at pressures below 10-6 Torr. EL spectra of the devices were
obtained using a Konica-Minolta CS-1000A. The current-
voltage-luminance characteristics were measured using a
Keithley 236 source-measure unit and a Keithley 2000 multimeter
equipped with a calibrated Si photodiode placed at an angle
normal to the device’s surface. Transient electrophosphore-
scences were measured by a digital oscilloscope (Tektronix
TDS5054B) and a photomultiplier tubes (PMT) through a
Carbazole-containing polymers are important in organic ma-
terials chemistry due to their high stability, processability, and
hole-transporting properties. In particular, carbazole is used as a
host material to take advantage of its high triplet energy level.16
The ligand of the novel iridium complex described here, bis(2-
benzothiazol-2-yl-N-ethylcarbazole)iridium-1,3-bis(p-bromophe-
nyl)1,3-propanedione ((bec)2IrdbmBr), consists of a carbazole
scaffold with a substituted benzothiadiazole moiety. In particu-
lar, substitution at the 2-position in the carbazole was used to
tune the HOMO energy level of the iridium complex. The iridium
metal center is located in the para position with respect to the
nitrogen atom on the 2-position-substituted carbazole. From this
architecture, carbazole may donate electrons from its nitrogen
lone pair to the metal center, raising the HOMO energy level, thus
inducing to a red shift.16
In this article, we report the synthesis of polyfluorene copoly-
mers containing carbazole and novel iridium complexes in the
main chain without the use of green emission segments, such as
fluorenone or benzothiadiazole. We believed that this attempt
was more suitable synthetic procedure for realizing white-light-
emitting polymers due to easier controlled monomer ratios.
Novel iridium complexes with an ancillary dibromo-β-diketonate
unit can be incorporated into the polymer main chain. We
systematically investigated the synthesis, thermal stability, opti-
cal properties, and electrical properties of the resulting polymers.
The synthetic routes to the iridium complex monomers,
(bec)2IrdbmBr, and copolymers, PFCzIrbecs, are shown in the
Schemes 1 and 2.
Experimental Details
Measurements. NMR spectra were recorded using a Bruker
AM 400 MHz spectrometer with tetramethylsilane as an inter-
nal reference. Elemental analysis was performed using an EA
1110 Fisons analyzer. UV-vis and PL spectra were recorded
using Jasco V-530 and Spex Fluorolog-3 spectrofluorometers.
Thermogravimetric analysis (TGA) was carried out using a TA
Q500 analyzer with a heating rate of 10 ꢀC/min under a nitrogen

Article
Macromolecules, Vol. 43, No. 3, 2010 1381
Scheme 2. Synthetic Routes of the Copolymers PFCzIrbecs
monochromator (ARC 275), biasing with an Agilent 8114A
pulse generator. All measurements were carried out at room
temperature under an ambient atmosphere.
Materials. 2-Nitrobiphenyl, 2-aminobenzenethiol, 1-bromooc-
tane, 1-bromohexane, 1-bromoethane, 3,6-dibromocarbazole,
2,7-dibromofluorenone, N,N-dimethylformamide (99.8%, an-
hydrous), dimethyl sulfoxide, bromine, iron(III) chloride, triethyl
of tert-butyllithium (1.7 M in hexane). The mixture was stirred
at -78 ꢀC for 2 h. N,N-Dimethylformamide (2 mL, 24.6 mmol)
was added to the solution, and the resulting mixture was stirred
at -78 ꢀC for 1 h, warmed to room temperature, and stirred for
40 h. The mixture was poured into water, extracted with
dichloromethane, and dried over MgSO4. The solvent was
removed by solvent evaporation, and the residue was purified
by column chromatography using hexane/ethyl acetate (8:2, v/v)
as the eluent. The resulting solid was recrystallized in dichloro-
methane and hexane, and then the yellow solid was dried in
phosphite,
2-isopropoxy-4,4,5,5,-tetramethyl-1,3,2-dioxaboro-
lane, phenol, tetrahydrofuran, N-bromosuccinimide, toluene
(99.8%, anhydrous), Aliquat 336, and tetrakis(triphenylphos-
phine)palladium(0) were purchased from Aldrich. All chemicals
were used without further purification. 4-Bromo-2-nitrobiphenyl
(1), 2-bromo-9H-carbazole (2), 1,3-bis(4-bromophenyl)propane-
1,3-dione (6), 3,6-dibromo-N-hexylcarbazole (8), and 2,7-bis-
(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9,9-bis(4-octyloxy-
phenyl)fluorene (9) were synthesized according to procedures
outlined in the literature.17-19 Solvents with analytical grade were
used during the whole experiments, and all chemicals were used
without further purification.
Synthesis of 2-Bromo-N-ethylcarbazole (3). 2-Bromo-9H-car-
bazole (2) (6 g, 24.4 mmol), sodium hydroxide (5.85 g, 146
mmol), and 1-bromoethane (4 g, 36.7 mmol) were dissolved in
100 mL of dimethyl sulfoxide (DMSO). The reaction mixture
was then stirred at room temperature. After 24 h, the reaction
mixture was extracted using dichloromethane/brine, and then
the organic layer was separated and concentrated. The crude
product was purified by column chromatography using hexane/
ethyl acetate (8:2, v/v) as the eluent. The resulting solid was
recrystallized in dichloromethane and methanol, and then the
white solid was dried in vacuo. The resulting product yield was
73% (4.9 g). 1H NMR (CDCl3, ppm): 8.01 (d, 1H), 7.96 (d, 1H),
7.59 (s, 1H), 7.51 (t, 1H), 7.40-7.37 (m, 2H), 7.30 (t, 1H), 4.30 (q,
2H), 1.45 (t, 3H). 13C NMR (CDCl3, ppm): 140.63, 139.93,
125.98, 122.31, 121.81, 121.77, 121.44, 120.32, 119.25, 119.15,
111.44, 108.56, 37.49, 13.65. Anal. Calcd for C14H12BrN; C,
61.33; H, 4.41; N, 5.11. Found: C, 61.29; H, 4.40; N, 5.05.
Synthesis of N-Ethylcarbazole-2-carbaldehyde (4). Com-
pound 3 (4.5 g, 16.4 mmol) was dissolved in THF (150 mL) at
-78 ꢀC. To a solution was added, by syringe, 20 mL (32.8 mmol)
1
vacuo. The resulting product yield was 76% (2.8 g). H NMR
(CDCl3, ppm): 10.13 (s, 1H), 8.12 (m, 2H), 7.92 (s, 1H), 7.70
(d, 1H), 7.52 (t, 1H), 7.40 (d, 1H), 7.25 (t, 1H) 4.35 (q, 2H), 1.42
(t, 3H). 13C NMR (CDCl3, ppm): 192.51, 141.57, 139.43, 133.70,
128.04, 127.49, 121.87, 121.39, 121.09, 120.44, 119.48, 109.27,
108.85, 37.59, 13.76. Anal. Calcd for C15H13NO: C, 80.69; H,
5.87; N, 6.27. Found: C, 80.59; H, 5.89; N, 6.30.
Synthesis of 2-Benzothiazol-2-yl-N-ethylcarbazole (5). Com-
pound 4 (2.32 g, 10.4 mmol) and 2-aminobenzenethiol (1.33 mL,
12.5 mmol) were dissolved in DMSO (150 mL). The mixture was
stirred at 120 ꢀC for 24 h. The mixture was poured into water,
extracted with dichloromethane, and dried over MgSO4. The
solvent was removed by solvent evaporation, and the residue was
purified by column chromatography using hexane/ethyl acetate
(8:2, v/v) as the eluent. The resulting solid was recrystallized in
dichloromethane and methanol, and then the green solid was
dried in vacuo. The resulting product yield was 42% (1.43 g). 1H
NMR (CDCl3, ppm): 8.26 (s, 1H), 8.16-8.12 (m, 3H), 7.93-7.91
(m, 2H), 7.52 (m, 2H), 7.44-7.42 (m, 2H), 7.27 (t, 1H), 4.45 (q,
2H), 1.50 (t, 3H). 13C NMR(CDCl3, ppm): 169.17, 154.46, 141.24,
140.16, 135.30, 131.05, 126.64, 126.20, 125.48, 124.89, 123.07,
122.62, 121.50, 120.89, 120.70, 119.37, 118.99, 108.79, 107.37,
37.69, 13.84. Anal. Calcd for C21H16N2S: C, 76.80; H, 4.91; N,
8.53; S, 9.76. Found: C, 76.82; H, 4.91; N, 8.56; S, 9.49.
Synthesis of Bis(2-benzothiazol-2-yl-N-ethylcarbazole)iridium-
1,3-bis(p-bromophenyl)1,3-propanedione (7) ((bec)2IrdbmBr). A
mixture of compound 5 (0.7 g, 2.13 mmol), IrCl3 3H2O (0.30 g,
3
0.85 mmol), 2-ethoxyethanol (20 mL), and distilled water (5 mL)
was stirred under argon at 120 ꢀC for 24 h. After cooling, the

1382 Macromolecules, Vol. 43, No. 3, 2010
Park et al.
mixture was poured in the water and washed several times using
petroleum ether. The above μ-chloro-bridged dimer (0.5 g, 0.33
mmol), compound 6 (0.45 g, 1.17 mmol), and anhydrous sodium
carbonate (0.11 g, 1.03 mmol) in 1,2-dichloroethane (20 mL) were
refluxed in an argon atmosphere for 24 h. After cooling to room
temperature, the crude product was flash chromatographed on a
silia gel with a dichloromethane as a eluent and further purified by
recrystallization from dichloromethane and methanol. The result-
ing product yield was 14.3% (0.15 g). 1H NMR (TC-d4, ppm): 8.13
(s, 1H), 8.10 (m, 3H), 7.82 (m, 2H), 7.79 (m, 4H), 7.60 (m, 4H),
7.43-7.24 (m, 8H), 7.23 (m, 3H), 7.11 (m, 3H), 6.72 (s, 1H), 4.11
(q, 4H), 1.49 (t, 6H). m/z = 1228.23 (Mþ).
General Polymerization Procedure. Into 100 mL two-neck
flask were added dibromo compounds and diborolan com-
pound in 25 mL of anhydrous toluene. Water-soluble Pd(0)
complex, tetrakis(triphenylphosphine)palladium (1 mol %),
was transferred into the mixture in a drybox. Subsequently,
2 M aqueous sodium carbonate deaerated for 30 min, and the
phase transfer catalyst, Aliquat 336 (several drops), in toluene
purged under nitrogen for 1 h was transferred via cannula. The
reaction mixture was stirred at 80 ꢀC for 3 days, and then the
excess amount of bromobenzene, the end-capper, dissolved in 1
mL of anhydrous toluene was added and stirring continued for
12 h. The reaction mixture is cooled to about 50 ꢀC and added
slowly to a vigorously stirred mixture of 200 mL of methanol.
The polymer fibers are collected by filtration and reprecipitation
from methanol and acetone. The polymers are purified further
by washing for 2 days in a Soxhlet apparatus with acetone to
remove oligomers and catalyst residues and column chromato-
graphyed with a chloroform solution of the polymer. The
reprecipitation procedure in chloroform/methanol is then re-
peated a several times. The resulting polymers were soluble in
common organic solvents. Yield: 56-60%.
Figure 1. TGA traces of the synthesized PFCzIrbec polymers.
To organize the single chain phosphorescent polymers, we
introduced an ancillary dibromo-β-diketonate unit.11 All
PFCzIrbecs copolymers were end-capped with bromoben-
zene. The feed ratios of the iridium complexes were 0.5, 2, 4,
and 5 mol % quantity of compound 9. All copolymers were
found to be soluble in common organic solvents, such as
tetrahydrofuran (THF), chloroform, and toluene, with no
evidence of gel formation. Each copolymer was spin-coated
onto an indium-tin oxide (ITO) substrate and found to
produce transparent and homogeneous thin films. The
weight-average molecular weights (Mw) of the copolymers,
as determined by gel permeation chromatography using a
polystyrene standard, were found to range from 9100 to
15 400 with polydispersity indices (PDIs) ranging from 1.6 to
2.1. The yields of the copolymers were 56-60%. The thermal
transitions of the polymers were studied by differential scanning
calorimetry (DSC) under a nitrogen atmosphere. The thermo-
grams for PFCzIrbecs showed a glass transition in the range
from 121 to 127 ꢀC, without any features characteristic of the
melting of liquid-crystalline phases. The thermal properties of
the polymers were determined using thermal gravimetric analy-
sis (TGA) under a nitrogen atmosphere. All polymers were
found to exhibit good thermal stability, losing less than 5% of
their weight upon heating from 345 to 400 ꢀC. Interestingly, the
amount of weight loss at the start of thermal decomposition
increased with increasing content of iridium complexes in the
polymer main chain. The TGA traces of the PFCzIrbecs are
shown in Figure 1. The results of the polymerizations of the
synthesized copolymers are summarized in Table 1.
Optical and Electrochemical Properties. The UV-vis
absorption spectra of the PFCzIrbecs exhibited absorption
maxima at 357 nm. In previous reports, the UV-vis ab-
sorption maxima of the PBOPF homopolymer was 391 nm
in the film state.18 The UV-vis absorption maxima of the
PFCzIrbecs measured here were blue-shifted, by ∼34 nm,
with respect to the PBOPF homopolymer.18 We assume
that this effect arose from the ancillary β-diketonate unit
and from the kinked carbazole unit in the polymer main
chain.11,22 An ancillary diketonated and kinked carbazole
unit in the polymer main chain disturbs the conjugation of
the polymer main chain, leading to a shorting of the con-
jugation length of the molecules and hence to a blue shift in
the absorption.23 The intensity of the two other absorption
peaks at 320 and 426 nm increased as the fraction of iridium
complex units increased in the polymer main chain. The
increased absorption intensity at 320 nm was caused by the
ancillary units, and the absorption intensity at 426 nm was
due to the iridium complexes.
PFCzIrbec 05. 2,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lan-2-yl)-9,9-bis(4-octyloxyphenyl)fluorene (9) (1 equiv), 3,6-di-
bromo-N-hexylcarbazole (8) (0.995 equiv), and (bec)2IrdbmBr (7)
(0.005 equiv) were used in this polymerization. 1H NMR (CDCl3,
ppm): aromatic and vinylene; 7.75-6.73 (∼49H), aliphatic;
4.11-3.75 (∼10H), 1.74-0.84 (∼47H).
PFCzIrbec 2. 2,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lan-2-yl)-9,9-bis(4-octyloxy-phenyl)-fluorene (9) (1 equiv), 3,6-
dibromo-N-hexylcarbazole (8) (0.98 equiv), and (bec)2IrdbmBr
(7) (0.02 equiv) were used in this polymerization. 1H NMR
(CDCl3, ppm): aromatic and vinylene; 7.75-6.73 (∼49H), ali-
phatic; 4.11-3.75 (∼10H), 1.74-0.84 (∼47H).
PFCzIrbec 4. 2,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lan-2-yl)-9,9-bis(4-octyloxyphenyl)fluorene (9) (1 equiv), 3,6-di-
bromo-N-hexylcarbazole (8) (0.96 equiv), and (bec)2IrdbmBr (7)
(0.04 equiv) were used in this polymerization. 1H NMR (CDCl3,
ppm): aromatic and vinylene; 7.75-6.73 (∼49H), aliphatic;
4.11-3.75 (∼10H), 1.74-0.84 (∼47H).
PFCzIrbec 5. 2,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lan-2-yl)-9,9-bis(4-octyloxyphenyl)fluorene (9) (1 equiv), 3,6-di-
bromo-N-hexylcarbazole (8) (0.95 equiv), and (bec)2IrdbmBr (7)
(0.05 equiv) were used in this polymerization. 1H NMR (CDCl3,
ppm): aromatic and vinylene; 7.75-6.73 (∼49H), aliphatic;
4.11-3.75 (∼10H), 1.74-0.84 (∼47H).
Results and Discussion
Synthesis and Characterization of the Polymers. The cyclo-
metalated iridium complex ((bec)2IrdbmBr) was synthesized
successfully. First, iridium trichloride hydrate was reacted
with compound 5 to give the μ-chloro-bridged dimeric com-
plex. The iridium complex was subsequently synthesized
by treatment of the dimer with compound 6 (dbmBr) in
1,2-dichloroethane, as shown Scheme 1. The copolymers,
PFCzIrbecs, were prepared via a palladium-catalyzedSuzuki
coupling reaction20 of compounds 7, 8, and 9. The synthetic
routes and structures of the polymers are shown in Scheme 2.

Article
Macromolecules, Vol. 43, No. 3, 2010 1383
Table 2. Summary of the Optical Properties and Energy Levels of the
Synthesized PFCzIrbec Polymers
film, λmax (nm)a
polymer
absorption emission Eonset,ox (V) EHOMO (eV)b
PFCzIrbec 05
PFCzIrbec 2
PFCzIrbec 4
PFCzIrbec 5
357
357
357
359
421
0.83
0.82
0.83
0.86
5.52
5.51
5.52
5.55
453, 642
468, 644
473, 644
a Measured as thin films on fused quartz plate. b Determined from the
onset voltage of the first oxidation potential with reference to ferrocene
at 4.8 eV.
Figure 2. UV-vis absorption (a) and PL emission (b) spectra of the
synthesized PFCzIrbec polymers.
Figure 3. Cyclic voltammograms of the synthesized PFCzIrbec poly-
mers.
The energy levels of their highest occupied molecular
orbitals (HOMOs) and lowest unoccupied molecular orbi-
tals (LUMOs) were characterized by measuring the electro-
chemical properties of PFCzIrbecs using cyclic voltammetry
(CV). A platinum electrode was coated with the polymers
and used as the working electrode. The counter electrode was
a platinum wire, and the reference electrode was an Ag/
AgNO3 (0.01 M) electrode. The electrochemical properties
of the copolymers were investigated in an electrolyte con-
sisting of a solution of 0.1 M tetrabutylammonium tetra-
fluoroborate (TBABF4) in acetonitrile at room temperature
under nitrogen at a scan rate of 50 mV/s. The measurements
were calibrated using ferrocene as the standard.24 Figure 3
shows the oxidation waves and energy levels of the copoly-
mers as a result of the p-type doping. As shown in Figure 3,
the onsets of the PFCzIrbec polymer oxidations in the anodic
scans were found to occur in the range of 0.82-0.86 V,
corresponding to ionization potentials of 5.51-5.55 eV,
respectively. Interestingly, the HOMO energy level de-
creased as the fraction of iridium complex units increased
in the polymer main chain. The conjugation length appeared
to be disturbed by an ancillary and kinked carbazole unit in
the polymer main chain, which led to a shorting of the
conjugation length of the molecules and hence to decreased
a HOMO energy level for the PFCzIrbecs. Unfortunately, a
reduction wave was scarcely obtained. The onsets of oxida-
tion and the energies of the HOMO energy levels of the
PFCzIrbecs are listed in Table 2.
Table 1. Physical Properties of the Synthesized PFCzIrbec Polymers
in the feed
PDIa Td (ꢀC)b yield (%) composition
a
polymer
Mw
PFCzIrbec 05 13 200
1.7
1.7
2.1
1.6
400
389
347
345
58
58
60
56
1:0.995:0.005
1:0.98:0.02
1:0.96:0.04
1:0.95:0.05
PFCzIrbec 2
PFCzIrbec 4
PFCzIrbec 5
10 800
15 400
9 100
a Mw and PDI of the polymers were determined by gel permeation
chromatography using polystyrene standards. b Temperature resulting
in 5% weight loss based on initial weight.
The photoluminescence (PL) spectra for the thin films of
the polymers were quite different from the spectrum of
PBOPF homopolymer. The PL spectrum of PBOPF exhibi-
ted an emission maximum at 420 nm.18 The blue emission
peak for the PFCzIrbec polymers shifted slightly to longer
wavelengths from 421 to 473 nm. Moreover, the emission at
640 nm increased as the fraction of iridium complex units
increased in the polymer main chain. In previous report, the
host segment emission spectra due to fluorene and carbazole
units disappeared in spite of the low iridium complex content
of the polymer main chain.21 Because intramolecular energy
transfer is much more efficient than intermolecular energy
transfer,21a the polymers containing an iridium complex in
the polymer main chain showed full quenching behaviors
about host emission. The our synthesized polymers, PFCzIr-
bec 05 and PFCzIrbec 2, however, exhibited two strong
emission spectra in the blue and red spectral regions, suggest-
ing the presence of partial intra- and intermolecular energy
transfer in the polymer main chain between host and blue
emission segments (fluorene and carbazole units) and
iridium complex with diketonated ancillary. Therefore, ba-
lanced white emission was obtained. The optical properties
of the synthesized polymers are summarized in Table 2.
Electroluminescence Properties and Current-Voltage-
Luminance Characteristics. To investigate the electrical pro-
perties and performances of the copolymers in real devices,
polymer EL devices with the configuration ITO/PEDOT:
PSS (40 nm)/poly(TPD) (50 nm)/polymer (40 nm)/TPBi (40
nm)/LiF (0.5 nm)/Al (100 nm) were fabricated. The EL

1384 Macromolecules, Vol. 43, No. 3, 2010
Park et al.
Figure 4. Electroluminescence spectra of synthesized PFCzIrbec de-
vices.
Figure 6. CIE coordinates of PFCzIrbec 2 device for various driving
voltages.
Figure 5. Electroluminescence spectra of the PFCzIrbec 2 device for
various driving voltages.
emission spectra of the synthesized polymers were slightly
different than the corresponding PL emission spectra, as
shown in Figure 4. In particular, the blue emission of EL
devices was broader than the bluish green emission measured
in the PL experiments. This discrepancy was assumed to
result from the charge trapping effects of the iridium com-
plexes. Such results are common for organic host-guest
systems, in which the low-energy state units act as charge-
trapping sites.20 Additionally, as mentioned the energy
transfer of phosphorescent complexes occurs via competitive
intra- and intermolecular pathways. The polymers that
contained a low fraction of iridium complexes, PFCzIrbec
05 and PFCzIrbec 2, exhibited two strong emission bands in
the range 490 and 650 nm, indicating that PFCzIrbec 05 and
PFCzIrbec 2 contained well-balanced partial intra- and
intermolecular energy transfer pathways in the polymer
main chain. Moreover, the EL emission bands of PFCzIrbec
05 and PFCzIrbec 2 were broad, covering the visible range
from 400 to 750 nm. The peaks in the blue region arose from
the BOPF and carbazole segments, and the peaks in the red
region at 650 nm originated from the iridium complexes.
Of these EL spectra, those of PFCzIrbec 05 and PFCzIrbec 2
consist of well-balanced bluish green and red regions, with CIE
coordinates at 16 V of (0.24, 0.28) and at 15 V of (0.31, 0.32),
respectively, which were close to those of pure white light (0.33,
0.33). Most importantly, the white light emission is stable, and
Figure 7. Voltage-current (V-I) (a) and voltage-luminance (V-L)
(b) characteristics of the synthesized PFCzIrbec polymers.
the EL spectra are insensitive to the driving voltage. The EL
spectrum of PFCzIrbec 2 was stable with respect to the voltage;
the CIE coordinates were found to be (0.29, 0.32), (0.30, 0.32),
and (0.31, 0.32) at various driving voltages. The dependence of
the EL emission spectrum of PFCzIrbec 2 on voltage is shown
in Figure 5. These results indicated that the use of this polymer
ensures color purity in the EL device, which makes these
polymers of great interest for display applications. As men-
tioned above, we have obtained stable white-light-emitting
polymers, without the use of green segments. This approach
to white emission is the first report of the use of iridium
complexes in polymer main chains.
The voltage-current (V-I) and voltage-luminance
(V-L) characteristics of the devices are shown in Figure 7,

Article
Macromolecules, Vol. 43, No. 3, 2010 1385
Table 3. Summary of the EL Device Performances of the Synthesized PFCzIrbec Polymers
polymer
λ
max (nm)
Vturn-on (V)
current efficiency (cd/A)
EQE (%)
CIE coordinates (x, y)a
PFCzIrbec 05
PFCzIrbec 2
PFCzIrbec 4
PFCzIrbec 5
417, 490, 651
415, 495, 651
507, 650
7.5
8.8
7.5
7.2
0.18
0.05
0.26
0.40
0.14
0.04
0.33
0.47
(0.24, 0.28)
(0.31, 0.32)
(0.43, 0.38)
(0.44, 0.38)
505, 651
a Determined from EL spectra (Figure 4).
devices fabricated with PFCzIrbec 2 were found to emit white
light composed of blue and red emission with CIE coordinates of
(0.31, 0.32), which are close to the standard for white light
emission. Partial intra- and intermolecular energy transfer was
believed to occur within the polymer main chain. Moreover, the
EL spectrum of PFCzIrbec 2 was stable with respect to voltage.
Thus, in our present work we successfully realized white-light-
emitting polymers containing iridium complexes in the polymer
main chain, and we obtained stable white-light-emitting polymers
without the use of green segments. These results suggest that
white PLEDs that utilize a single polymer chain have potential
for application in full-color displays.
Acknowledgment. This work was supported by the Korea
Science and Engineering Foundation (KOSEF) grant Funded by
the Korea government (MEST) (No. R11-2007-050-02003-0).
References and Notes
Figure 8. Transient electrophosphorescent spectra of the synthesized
PFCzIrbec 4 device.
(1) (a) Yang, Y.; Heeger, A. J. Nature 1994, 372, 344. (b) Sirringhaus, H.;
Tessler, N.; Friend, R. H. Science 1998, 280, 1741. (c) Babel, A.;
Jenekhe, S. A. J. Am. Chem. Soc. 2003, 125, 13656.
and their performances are summarized in Table 3. The turn-
on voltages of the PFCzIrbec devices ranged from 7.2 to 8.8
V, and their maximum brightness values fell in the range
65-242 cd/m2. The V-I and V-L curves shifted to slightly
higher voltages with increased presence of iridium complexes
in the copolymers. This phenomenon arose from charge-
trapping and resulted in discrepancies between the EL and
PL spectra.25 To investigate the characteristics of the EL
spectra of PFCzIrbecs, the triplet excited-state lifetimes of
PFCzIrbec 4 were measured by transient electrophosphores-
cence measurements. The initial EL decay at 650 nm was
slower than the EL decay at 505 nm. As a consequence, the
spectrum of PFCzIrbec 4, at 650 nm, appeared to be phos-
phorescence emission from the synthesized iridium complex.26
Transient electrophosphorescent spectra of PFCzIrbec 4 are
shown in Figure 8.
(2) Prasad, P. N.; Williams, D. J. Introduction to Nonlinear Effects in
Monomers and Polymers; Wiley: New York, 1991.
(3) (a) Halls, J. J. M.; Walsh, C. A.; Greenham, N. C.; Marseglia, E. A.;
Friend, R. H.; Moratti, S. C.; Holmes, A. B. Nature 1995, 376, 498.
(b) Yu, G.; Gao, J.; Hummelen, J. C.; Wudl, F.; Heeger, A. J. Science
1995, 270, 1789.
(4) (a) Greenham, N. C.; Moratti, S. C.; Bradely, D. D. C.; Friend, R.
H.; Holmes, A. B. Nature 1993, 365, 628. (b) Shim, H. K.; Jin, J. I.
Adv. Polym. Sci. 2002, 158, 194. (c) Mullen, K.; Scherf, U. Organic
Light Emitting Devices: Synthesis, Properties and Applications;
Wiley-VCH: Weinheim, 2006.
(5) Burn, P. L.; Holmes, A. B.; Kraft, A.; Bradley, D. D. C.; Brown, A.
R.; Friend, R. H.; Gymer, R. W. Nature (London) 1992, 356, 47.
(6) Gustafsson, G.; Cao, Y.; Treacy, G. M.; Klavetter, F.; Colaneri,
N.; Heeger, A. J. Nature (London) 1992, 357, 477.
(7) Friend, R. H.; Gymer, R. W.; Holmes, A. B.; Burroughes, J. H.;
Marks, R. N.; Taliani, C.; Bradley, D. D. C.; Dos Santos, D. A.;
ꢀ
Bredas, J. L.; Logdlund, M.; Salaneck, W. R. Nature (London)
Unfortunately, our research did not show high EL device
efficiencies compared other work that contained iridium
complex in the polymer main chain.27 We assumed that
our synthesized copolymers have similar iridium molecular
structure in our previous work that contained iridium com-
plex with diketonated ancillary, and it triplet energy back-
transfer between fluorene or carbazole segments and iridium
unit could occur.11,21b We believe that these electrolumines-
cence characteristics could be further improved in future
work by optimizing the film morphology, layer thickness,
and postproduction treatment conditions.
1999, 397, 121.
(8) Heeger, A. J. Solid State Commun. 1998, 107, 673.
(9) (a) Alam, M. M.; Jenekhe, S. A. Chem. Mater. 2002, 14, 4775.
(b) Milkroyannidis, J. A.; Spiliopoulos, I. K.; Kasimis, T. S.; Kulkarni,
A. P.; Jenehke, S. A. Macromolecules 2003, 36, 9295.
(10) (a) Chen, L.; You, H.; Yang, C.; Zhang, X.; Qin, J.; Ma, D.
J. Mater. Chem. 2006, 16, 3332. (b) Lee, J.; Lee, J.-I.; Chu, H. Y.
ETRI J. 2009, 31, 642.
(11) Park, M.-J.; Lee, J.; Kwak, J.; Jung, I. H.; Park, J.-H.; Kong, H.;
Lee, C.; Hwang, D.-H.; Shim, H.-K. Macromolecules 2009, 42,
5551.
(12) (a) Zhen, H.; Luo, C.; Yang, W.; Song, W.; Du, B.; Jiang, J.; Jiang,
C.; Zhang, Y.; Cao, Y. Macromolecules 2006, 39, 1693. (b) Zhen, H.;
Jiang, C.; Yang, W.; Jiang, J.; Huang, F.; Cao, Y. Chem.;Eur. J. 2005,
11, 5007.
Conclusions
(13) Jiang, J.; Jiang, C.; Yang, W.; Zhen, H.; Huang, F.; Cao, Y.
Macromolecules 2005, 38, 4072.
(14) Zhang, K.; Chen, Z.; Yang, C.; Tao, Y.; Zou, Y.; Qin, J.; Cao, Y.
J. Mater. Chem. 2008, 18, 291.
(15) Xu, Y.; Guan, R.; Jiang, J.; Yang, W.; Zhen, H.; Peng, J.; Cao, Y.
J. Polym. Sci., Part A: Polym. Chem. 2008, 46, 453.
(16) Bettington, S.; Tavasli, M.; Bryce, M. R.; Beeby, A.; Al-Attar, H.;
Monkman, A. P. Chem.;Eur. J. 2007, 13, 1423.
(17) Zhang, K.; Chen, Z.; Zou, Y.; Yang, C.; Qin, J.; Cao, Y. Organo-
metallics 2007, 26, 3699.
We have successfully prepared BOPF-based copolymers con-
taining a novel iridium complex as a comonomer. To organize the
single chain phosphorescent polymers, we introduced an ancil-
lary dibromo-β-diketonate. White light emission was obtained
from a single polymer chain by incorporating bis(2-benzothia-
zol-2-yl-N-ethylcarbazole)iridium-1,3-bis(p-bromophenyl)-1,3-
propanedione ((bec)2IrdbmBr) as the red emission unit into a BOPF
and carbazole main chain as the host and blue emission. Devices
based on this polymer exhibited good device performances. EL
(18) Lee, J.-H.; Hwang, D.-H. Chem. Commun. 2003, 2836.

1386 Macromolecules, Vol. 43, No. 3, 2010
Park et al.
(19) Hwang, D.-H.; Kim, S.-K.; Park, M.-J.; Lee, J.-H.; Koo,
B.-W.; Kang, I.-N.; Kim, S.-H.; Zyung, T. Chem. Mater. 2004,
16, 1298.
(20) Cho, N.-S.; Park, J.-H.; Lee, S.-K.; Lee, J.; Shim, H.-K.; Park, M.-
J.; Hwang, D.-H.; Jung, B.-J. Macromolecules 2006, 39, 177.
(21) (a) Zhang, K.; Chen, Z.; Yang, C.; Gong, S.; Qin, J.; Cao, Y.
Macromol. Rapid Commun. 2006, 27, 1926. (b) Zhang, K.; Chen, Z.;
Yang, C.; Zou, Y.; Gong, S.; Tao, Y.; Qin, J.; Cao, Y. J. Mater. Chem.
2008, 18, 3366.
(24) Pommerehne, J.; Vestweber, H.; Guss, W.; Mahrt, R. F.; Bassler,
H.; Porsch, M.; Daub, J. Adv. Mater. 1995, 7, 551.
(25) (a) Wu, F.-I.; Yang, X.-H.; Neher, D.; Dodda, R.; Tseng, Y.-H.;
Shu, C.-F. Adv. Funct. Mater. 2007, 17, 1085. (b) Uchida, M.;
Adachi, C.; Koyama, T.; Taniguchi, Y. J. Appl. Phys. 1999, 86,
1680. (c) Lane, P. A.; Palilis, L. C.; O'Brien, D. F.; Giebeler, C.; Cadby,
A. J.; Lidzey, D. G.; Campbell, A. J.; Bradley, D. D. C. Phys. Rev. B
2002, 63, 235206. (d) Gong, X.; Ostrowski, J. C.; Moses, D.; Bazan, G.
C.; Heeger, A. J. Adv. Funct. Mater. 2003, 13, 439.
(22) Lu, J.; Tao, Y.; D’iorio, M.; Li, Y.; Ding, J.; Day, M. Macro-
molecules 2004, 37, 2442.
(26) Ikai, M.; Takeuchi, H.; Fujikawa, H.; Taga, Y. R&D Rev. Toyota
CRDL 2006, 41, 63.
(23) Cho, H.-J.; Jung, B.-J.; Cho, N. S.; Lee, J.; Shim, H.-K. Macro-
molecules 2003, 36, 6704.
(27) Chen, Q.; Liu, N.; Ying, L.; Yang, W.; Wu, H.; Xu, W.; Cao, Y.
Polymer 2009, 50, 1430.