High-efficiency electrophosphorescent fluorene-alt-carbazole copolymers N-grafted with cyclometalated Ir complexes

Article abstract of DOI:10.1021/ma0474473

A series of electrophosphorescent conjugated fluorene-alt-carbazole copolymers are synthesized by Suzuki polycondensation. A diketone-ended alkyl chain which is grafted in the N-position of carbazole serves as a ligand to form a pendant cyclometalated Ir complex with 1-phenylisoquinoline (Piq), 2-naphthylpyridine (Napy), and 2-phenylquinoline (Phq). The PL efficiencies of PFCzIrPiq and PFCzIrPhq copolymers are around 60% and 70%, respectively. EL emission from the backbone of PFCzIrPiq and PFCzIrPhq copolymers is completely quenched even though the Ir complex contents in the polymers are as low as 0.5 mol %. The device of PFCzIrPiq05 copolymer shows the highest external quantum efficiency of 4.9% ph/el and the luminous efficiency of 4.0 cd/A with 240 cd/m² at a bias voltage of 7.7 V and a peak emission of 610 nm. The device efficiency of PFCzIrPiq05 copolymer still remains high (QE _ext = 3.4% ph/el and LE = 2.9 cd/A) with a luminance of 2978 cd/m² even at a current density of 100 mA/cm². The enhancement of the device performance could be due to the higher triplet energy and meanwhile to suitable HOMO and LUMO levels for efficient charge injection by introducing a carbazole unit into the polyfluorene backbone at the 3,6-linkage and blending PBD into the copolymers.

Full text of DOI:10.1021/ma0474473

4072
Macromolecules 2005, 38, 4072-4080
High-Efficiency Electrophosphorescent Fluorene-alt-carbazole
Copolymers N-Grafted with Cyclometalated Ir Complexes
Jiaxing Jiang, Changyun Jiang, Wei Yang,* Hongyu Zhen, Fei Huang, and
Yong Cao
Institute of Polymer Optoelectronic Materials and Devices, South China University of Technology, Key
Laboratory of Specially Functional Materials and Advanced Manufacturing Technology, Guangzhou
510640, P. R. China
Received December 12, 2004; Revised Manuscript Received March 14, 2005
ABSTRACT: A series of electrophosphorescent conjugated fluorene-alt-carbazole copolymers are syn-
thesized by Suzuki polycondensation. A diketone-ended alkyl chain which is grafted in the N-position of
carbazole serves as a ligand to form a pendant cyclometalated Ir complex with 1-phenylisoquinoline (Piq),
2-naphthylpyridine (Napy), and 2-phenylquinoline (Phq). The PL efficiencies of PFCzIrPiq and PFCzIrPhq
copolymers are around 60% and 70%, respectively. EL emission from the backbone of PFCzIrPiq and
PFCzIrPhq copolymers is completely quenched even though the Ir complex contents in the polymers are
as low as 0.5 mol %. The device of PFCzIrPiq05 copolymer shows the highest external quantum efficiency
of 4.9% ph/el and the luminous efficiency of 4.0 cd/A with 240 cd/m2 at a bias voltage of 7.7 V and a peak
emission of 610 nm. The device efficiency of PFCzIrPiq05 copolymer still remains high (QE
) 3.4%
ext
ph/el and LE ) 2.9 cd/A) with a luminance of 2978 cd/m2 even at a current density of 100 mA/cm2. The
enhancement of the device performance could be due to the higher triplet energy and meanwhile to suitable
HOMO and LUMO levels for efficient charge injection by introducing a carbazole unit into the polyfluorene
backbone at the 3,6-linkage and blending PBD into the copolymers.
Introduction
azole (PBD). These results demonstrate that high
external quantum efficiency can also be realized by
using conjugated polymer as host materials.
Electrophosphorescent light-emitting diodes (LEDs)
have been attracting much attention because of their
high quantum efficiency.1 Unlike electrofluorescence,
electrophosphorescence can make full use of both singlet
and triplet excitons owing to strong spin-orbital cou-
pling of heavy-metal ions in phosphorescent complexes.
As a result, electrophosphorescence can theoretically
approach 100% internal quantum efficiency.1b The green
OLEDs with bis(2-phenylpyridine)iridium(III) acetyl-
acetonate [(ppy)2Ir(acac)] doped into 3-phenyl-4-(1′-
naphthyl)-5-phenyl-1,2,4-triazole (TAZ) show a high
external quantum efficiency of 19% ph/el (photo/election)
and a power efficiency of 60 lm/W.2 Phosphorescent dyes
can also be doped into polymer host materials to use
the dopants as emissive centers since it allows light-
emitting diodes (LEDs) to be made with a spin-coating
or printing technique. The yellow-green PLEDs with
tris(9,9-dihexyl-2-(pyridinyl-2′)fluorene)iridium(III) [Ir-
(dpf)3] doped into a blend of nonconjugated poly(vinyl-
carbazole) (PVK) with 2-tert-butylphenyl-5-biphenyl-
1,3,4-oxadiazole show an external quantum efficiency
of 10% ph/el and a luminous efficiency (LE) of 36 cd/A.3
O’Brien and co-workers4 achieved an external quantum
efficiency of 3.5% and a luminous efficiency of <1.0 cd/A
with a maximum emission at 646 nm by doping plati-
num(II) porphyrins (PtOEP) into conjugated poly(9,9-
dioctylfluorene). Jiang et al.5 achieved an external
quantum efficiency of 12% ph/el and a luminous ef-
ficiency of 5.2 cd/A, with a maximum emission at 624
nm for electrophosphorescent PLEDs by doping iridium-
(III) bis(1-phenylisoquinolyl)-N,C2′) acetylacetonate [(piq)2-
Ir(acac)] into conjugated poly(9,9-dioctylfluorene) (PFO)
and 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadi-
Although the devices with phosphorescent dye doped
into a small molecule or polymer host are successful in
the realization of high-efficiency O(P)LEDs, there exist
serious problems, such as complexity in fabrication
procedure and fast decay of efficiency with the increase
in current density which might become more serious
during a long-term operation due to the intrinsic
instability of such blend systems. A solution to this
problem is to introduce a phosphorescent dye into the
polymer chain. Lee et al.6 synthesized nonconjugated
polyethylene main chain with directly attached phen-
ylpyridine to side chain as a ligand and pendant
N-vinylcarbazole as host materials. High external quan-
tum efficiency of 4.4% ph/el was achieved at current
density of 6.4 mA/cm2. A similar approach of using
nonconjugated main chain with pendant diketone was
reported by Tokito et al.7 By carefully designing the
multilayer device structure, selecting the electron trans-
port material for the emissive layer and optimizing the
content of the iridium complex unit in the phosphores-
cent polymer chain, high external quantum efficiencies
of 5.5%, 9%, and 3.5% in red, green, and blue PLEDs
were respectively achieved. The phosphorescent conju-
gated polymers based on polyfluorene backbone with
diketone pendant attached to the 9-carbon position of
fluorene were reported by Chen et al.8 The device from
polymer grafted with 1.3 mol % iridium(III) bis(2-(2′-
benzothienyl)pyridinato-N,C3′) acetylacetonate complex
[(btp)2Ir(acac)] in diketone pedant attached to the
9-position of fluorene unit has shown a high external
quantum efficiency of 1.59% ph/el and a power efficiency
of 2.8 cd/A at 7.0 V with luminance of 65 cd/m2 and peak
emission at 610 nm. Recently, a series of main-chain-
type well-defined oligo- and polyfluorenyl bis-cyclo-
* Corresponding author: e-mail pswyang@scut.edu.cn; Tel +86-
20-87112321; Fax +86-20-87114535.
10.1021/ma0474473 CCC: $30.25 © 2005 American Chemical Society
Published on Web 04/07/2005

Macromolecules, Vol. 38, No. 10, 2005
Fluorene-alt-carbazole Copolymers 4073
13C NMR (CDCl3) δ (ppm): 138.73, 129,72, 124.54, 123.69,
113.05, 112.66.
metalated Ir complexes was reported by Sandee et al.9
An external quantum efficiency of 1.5% ph/el with a
peak emission of 610 nm was obtained by introducing
the (btp)2Ir(acac) complex covalently into the poly(9,9′-
dioctylfluorene) backbone.
3,6-Dibromo-9-(11-dodecaneone)carbazole (3). To a
solution of sodium hydride (2.5 g, 61.6 mmol, 60%) in 50 mL
of THF, 3,6-dibromocarbazole (10 g, 30.8 mmol) in 20 mL of
THF was added dropwise. The mixture was refluxed for 1.5 h
under a N2 atmosphere, and then 12-bromodo-2-decaneone (1)
(8 g, 30.8 mmol) in 10 mL of THF was added dropwise to the
mixture. The mixture was refluxed for another 12 h and cooled
to room temperature. Then it was extracted with dichlo-
romethane followed by washing with water. The oil phase was
separated and dried overnight with MgSO4. The solvent was
removed by evaporation, and the crude products were purified
by silica column chromatography to give 9.4 g of white solid
In this paper, a series of alternating copolymers from
fluorene and N-alkylcarbazole at the 3,6-linkage were
synthesized by Suzuki polycondensation. A part of
N-alkylcarbazole units were replaced by a diketone
group ended to provide a ligand for the formation of Ir
complexes in side chain in the presence of 1-phenyliso-
quinoline (Piq), 2-naphthylpyridine (Napy), and 2-phen-
ylquinoline (Phq). We expect that the incorporation of
diketone-alkyl group into the N-position of a carbazole
unit can substantially raise the flexibility and reactivity
of a diketone group to the iridium core due to more
rotating freedom of diketone-alkyl around the nitrogen
atom. On the other hand, the fluorene-alt-carbazole
segment is used as a polymer backbone because the
HOMO level of carbazole-based copolymers can be tuned
by the substitution at the 3-, 6-, and 9-position, while
the triplet level remains sufficiently high to accom-
modate even blue triplet emitters.10
1
(yield, 60%). H NMR (CDCl3) δ (ppm): 8.11 (s, 2H), 7.53 (d,
2H), 7.22 (m, 2H) (carbazole ring), 4.21 (t, 2H, N-CH2), 2.37
(t, 2H), 2.10 (s, 3H, -CH3), 1.82-1.19 (m, 16H) (aliphatic). 13
C
NMR (CDCl3) δ (ppm): 209.21 (C-keto form), 139.25, 128.95,
123.38, 123.16, 111.89, 110.36 (carbazole ring), 43.75 (N-CH2),
43.27, 29.83, 29.34, 29.30, 29.24, 29.14, 29.09, 28.81, 27.15,
23.81 (-CH3) (aliphatic). Anal. Calcd for C24H29NOBr2: C,
56.81; H, 5.72; N, 2.76. Found: C, 56.27; H, 5.63; N, 2.71.
3,6-Dibromo-9-(14-trifluoro-11,13-tetradecyldiketone)-
carbazole (4). Sodium methoxide (1.7 g, 31.6 mmol) in 5 mL
of methanol was added dropwise to a solution of 3,6-dibromo-
9-(11-dodecaneone)carbazole (3) (8 g, 15.8 mmol) in 50 mL of
methyl tert-butyl ether. The mixture was refluxed for 1.5 h
under a N2 atmosphere, and then ethyl trifluoroacetate (20
mL) was added dropwise to the mixture. The mixture was
refluxed for another 12 h, cooled to room temperature, and
poured into ice water. The aqueous layer was acidified with
diluted acetic acid. The diketone was extracted with dichlo-
romethane followed by neutralization with a solution of
NaHCO3. The organic phase was separated and dried over-
night with MgSO4. The solvent was removed by evaporation,
and the crude products were purified by silica column chro-
matography to give 5.0 g of white solid (yield, 80%). 1H NMR
(CDCl3) δ (ppm): 14.42 (s, 1H, enol form, -OH), 8.12 (d, 2H),
7.51 (m, 2H), 7.25 (t, 2H) (carbazole ring), 5.88 (s, 1H, enol
form, -CH), 4.23 (t, 2H, keto form, -CH2), 2.37 (t, 2H), 1.82-
1.20 (m, 16H) (aliphatic). 13C NMR (CDCl3) δ (ppm): 197.55
(C-keto form), 175.77, 175.41 (C-enol form), 118.49, (keto form,
-CF3), 115.68, (enol form, -CF3), 139.36, 129.05, 123.51,
123.31, 111.99, 110.41, (carbazole ring), 95.69 (enol form,
-CH), 43.31 (N-CH2), 38.44 (keto form, -CH2), 29.73, 29.34,
29.30, 29.24, 29.15, 29.02, 28.85, 27.21, 25.46 (aliphatic). Anal.
Calcd for C26H28NO2Br2F3: C, 51.74; H, 4.64; N, 2.32. Found:
C, 51.21; H, 4.32; N, 2.28.
Experimental Section
Materials and Measurements. All manipulations involv-
ing air-sensitive reagents were performed under an atmo-
sphere of dry argon. All reagents, unless otherwise specified,
were obtained from Aldrich, Acros, and TCI Co. and were used
as they were received. 1H and 13C NMR spectra were recorded
on a Bruker DRX 400 spectrometer operating respectively at
400 and 100 MHz, with tetramethylsilane as a reference.
Direct injection mass spectra were recorded by the electron
spray impact (ESI) method on a LCQ DECA XP liquid
chromatograph-mass spectrometer (Thremo Co.). Molecular
weight determination was obtained using a Waters GPC 2410
in tetrahydrofuran via a calibration curve of polystyrene
standards. Elemental analyses were performed on Vario EL
elemental analysis instrument (Elementar Co.). The iridium
contents analyses were determined by using a Philips (Magix
PRO) sequential X-ray fluorescence spectrometry (XRF), with
a rhodium tube operated at 60 kV and 50 mA, a LiF 200
crystal, and a scintillation counter. Iridium(III) 2,4-pentanedi-
onate (from Alfa Aesar Co.) was used as a standard. Samples
were pressed as homogeneous tablets (diameter ) 30 mm) of
compressed (375 MPa) powder of the copolymers. UV-vis
absorption spectra were recorded on a HP 8453 spectropho-
tometer. Cyclic voltammetry was carried out on a potentiostat/
galvanostat model 283 (Princeton Applied Research) with
platinum electrode at a scan rate of 50 mV/s against Ag/AgCl
reference electrode with nitrogen-saturated solution of 0.1 M
tetrabutylammonium hexafluorophosphate (Bu4NPF6) in ace-
tonitrile (CH3CN).
2-Naphthylpyridine (5). To a solution of R-naphthalene
(10.36 g, 50 mmol) in 50 mL of THF, n-BuLi (32 mL, 50 mmol)
was added dropwise at -80 °C. The mixture was warmed to
-50 °C, and stirring was continued for 0.5 h. ZnCl2 (6.8 g, 50
mmol) with 50 mL of THF was added dropwise. The mixture
was allowed to warm to 25 °C and stirred for another 1.5 h.
The mixture solution of 2-bromopyridine (8 g, 50 mmol) and
tetrakis(triphenylphosphine)palladium (0.9 g) in 50 mL of THF
was added dropwise. The reaction mixture was stirred for 2 h
at room temperature. Then it was neutralized by 10% NaHCO3
to make the solution neutral followed by extracting with ethyl
acetate. The combined organic layers were washed by water
and dried overnight with MgSO4. The solvent was removed
by a rotary evaporator, and the crude products were purified
by silica chromatography to give 3.0 g (yield, 60%) of yellow
12-Bromo-2-dodecaneone (1). 11-Bromoundecane acid (10
g, 37.7 mmol) was dissolved in 300 mL of THF. The solution
was cooled to -78 °C, and a 1.6 M solution of CH3Li (47.1 mL,
75.4 mmol) in diethyl ether was added dropwise. After stirring
for 2 h, the reaction mixture was allowed to warm to 0 °C and
quenched with saturated ammonium chloride followed by
extraction with ether. The ether phase was separated, dried
with MgSO4, and concentrated. Purification by silica column
chromatography gave the product in colorless oil (7.0 g, yield
1
oil product. H NMR (CDCl3) δ (ppm): 8.78 (d, 1H, pyridine
ring), 8.06 (d, 1H), 7.91, (d, 1H), 7.81, (m, 1H), (naphthalene
ring), 7.76 (t, 2H) (pyridine ring), 7.67 (m, 2H), 7.52 (m, 1H),
7.48 (m, 1H), 7.31 (t, 2H), (naphthalene ring), 7.28 (m, 1H,
pyridine ring). 13C NMR (CDCl3) δ (ppm): 159.21, 149.12,
136.32, 123.21, 121.92 (pyridine ring), 138.40, 133.91, 131.12,
128.83, 128.31, 127.42, 126.41, 125.82, 125.51, 125.21 (naph-
thalene ring). Anal. Calcd for C15H11N: C, 87.81; H, 5.36; N,
6.83. Found: C, 87.46, H, 5.84; N, 6.80.
1
70%). H NMR (CDCl3) δ (ppm): 3.35 (t, 2H, Br-CH2), 2.36
(t, 2H), 2.10 (s, 3H, -CH3), 1.85-1.25 (m, 16H). 13C NMR
(CDCl3) δ (ppm): 209.1 (C-keto form), 43.61, 34.13, 33.92,
32.71, 29.72, 29.22, 29.18, 29.02, 28.60, 28.03, 23.72 (-CH3).
Anal. Calcd for C12H23OBr: C, 54.75; H, 8.74. Found: C, 55.28;
H, 8.70.
3,6-Dibromocarbazole (2) was prepared according to the
published procedure.11 1H NMR (CDCl3) δ (ppm): 8.12 (s, 1H,
N-H), 8.05 (d, 2H), 7.54 (m, 2H), 7.25 (t, 2H) (carbazole ring).
1-Phenylisoquinoline (6). 1-Chloroisoquinoline (8.0 g, 48.9
mmol) was added into a solution of tetrakis(triphenylphos-
phine)palladium (1.7 g, 1.4 mmol) in 100 mL of ethylene glycol

4074 Jiang et al.
Macromolecules, Vol. 38, No. 10, 2005
dimethyl ether. The mixture was stirred for 10 min under an
argon atmosphere to give a yellow/green solution. Benzenebo-
ronic acid (6.0 g, 48.9 mmol) in 10 mL of ethanol was added to
the mixture to give a light red solution. The sodium carbonate
solution (97.8 mmol, 2 M) was added to the mixture and
refluxed for 16 h. Then the mixture was allowed to cool to room
temperature and extracted by dichloromethane. The oil phase
was washed with water and dried overnight with MgSO4. The
solvent was removed by rotary evaporator, and the crude
products were purified by silica chromatography to give 5.4 g
(yield, 52%) of yellow needle product. 1H NMR (CDCl3) δ
(ppm): 8.59 (d, 1H, isoquinoline ring, N-CH), 8.09 (d, 1H,
benzene ring), 7.84 (d, 1H), 7.67 (d, 1H), 7.62 (t, 1H), 7.52 (m,
1H) 7.48 (m, 1H) (isoquinoline ring), 7.36-7.23 (m, 4H,
benzene ring). 13C NMR (CDCl3) δ (ppm): 160.75, 142.23,
136.87, 129.98, 127.58, 127.15, 126.98, 126.73, 119.89 (iso-
quinoline ring), 139.61, 129.92, 128.57, 128.33 (benzene ring).
Anal. Calcd for C15H11N: C, 87.81; H, 5.36; N, 6.83. Found:
C, 87.52; H, 5.75; N, 6.78.
Chloride-Bridged Dimers [(Piq)2Ir-(µ-Cl)2Ir(Piq)2 (7a),
Piq ) 1-Phenylisoquinoline], [(Napy)2Ir-(µ-Cl)2Ir(Napy)2
(7b), Napy ) 2-Naphthylpyridine], and [(Phq)2Ir-(µ-
Cl)2Ir(Phq)2 (7c), Phq ) 2-Phenylquinoline] (7a, 7b, and
7c) were synthesized according to the published procedures.12
3,6-Dibromo-9-(iridium(III)bis(1-phenylisoquinoline-
N,C2′))-14-trifluoro-11,13-tetradecyldiketone)carbazole
(8a). Chloride-bridged dimer (7a) (0.45 g, 0.354 mmol), 4 (0.54
g, 0.885 mmol), and sodium carbonate (100 mg) were mixed
and refluxed in 2-ethoxyethanol (30 mL) for 16 h under a N2
atmosphere. The solution was cooled to room temperature and
filtered before washing with water and hexane. The crude
products were purified by silica chromatography (40% dichlo-
romethane and 60% petroleum ether). 1H NMR (CDCl3) δ
(ppm): 8.95 (d, 2H, isoquinoline ring), 8.36 (d, 2H), 8.25 (d,
2H), (benzene ring), 8.13 (m, 1H, carbazole ring), 7.85 (m, 1H),
7.71 (m, 1H), (benzene ring), 7.64-6.36 (m, 16H), 5.53 (s, 1H,
-CH), 4.20 (t, 2H, N-CH2), 2.12 (t, 2H), 1.77-0.76 (m, 16H).
13C NMR (CDCl3) δ (ppm): 195.11, 185.51 (C-keto form),
173.05, 168.98, 149.01, 146.43, 127.25, 126.92, 126.72, 123.48,
123.36 (isoquinoline ring), 140.18, (-CF3), 139.34, 137.28,
134.04, 130.81, 129.67, 129.03 (benzene ring), 123.29, 121.15,
120.81, 119.96, 111.98, 110.38 (carbazole ring), 95.57 (-CH),
43.34 (N-CH2), 34.13, 31.24, 29.18, 28.98, 28.81, 28.57, 27.16,
26.25, 22.62. Anal. Calcd for C56H47Br2N3F3O2Ir: C, 55.91; H,
3.91; N, 3.49. Found: C, 57.06; H, 4.49; N, 3.30. Mass (ESI),
m/z: 1202.2 (M+).
3,6-Dibromo-9-(iridium(III)bis(2-(1′-naphthylpyridine-
N,C2′))-14-trifluoro-11,13-tetradecyldiketone)carbazole
(8b) was synthesized by a similar method for 8a. Chloride-
bridged dimer (7b) (0.7 g, 0.551 mmol), 4 (0.83 g, 1.377 mmol),
and sodium carbonate (100 mg) were used for the preparation.
1H NMR (CDCl3) δ (ppm): 8.55 (d, 2H), 8.47 (m, 2H), 8.12 (d,
2H),7.80 (m, 2H), 7.62-6.24 (m, 18H), 5.59 (s, 1H), 4.21 (t,
2H), 2.05 (t, 2H), 1.77-0.83 (m, 16H). 13C NMR (CDCl3) δ
(ppm): 193.25, 184.35 (C-keto form), 160.12, 148.51, 137.73,
123.48, 121.21 (pyridine ring), 139.34, 132.19, 131.56, 131.25,
129.71, 129.02, 128.58, 126.42, 125.12 (naphthalene ring),
140.15 (-CF3), 139.23, 123.28, 122.62, 122.41, 111.97, 110.39
(carbazole ring), 94.48 (-CH), 42.25 (N-CH2), 34.15, 31.74,
29.71, 29.45, 28.97, 28.57, 27.16, 26.26, 22.52. Anal.Calcd for
C56H47Br2N3F3O2Ir: C, 55.91; H, 3.91; N, 3.49. Found: C,
57.28; H, 4.60; N, 3.16. Mass (ESI), m/z: 1202.4 (M+).
3,6-Dibromo-9-(iridium(III)bis(2-phenylquinoline-
N,C2′))-14-trifluoro-11,13-tetradecyldiketone)carbazole
(8c) was synthesized by using chloride-bridged dimer (7c) (0.5
g, 0.393 mmol), 4 (0.593 g, 0.983 mmol), and sodium carbonate
(100 mg) by the method as mentioned above. 1H NMR (CDCl3)
δ (ppm): 8.31 (d, 1H, quinoline ring), 8.17 (d, 1H, benzene
ring), 8.13 (m, 2H), 8.06 (m, 2H) (carbazole ring), 7.92-7.23
(m, 14H), 6.93 (t, 2H), 6.62 (m, 2H), 6.54 (d, 1H), 6.48 (d, 1H),
5.29 (s, 1H, -CH), 4.24 (t, 2H, N-CH2), 2.37 (t, 2H), 1.79-
0.84 (m, 16H). 13C NMR (CDCl3) δ (ppm): 194.12, 186.68 (C-
keto form), 160.05, 151.98, 141.01, 132.43, 124.25, 123.92,
122.72, 121.48, 121.32 (quinoline ring), 142.14, 129.83, 129.75,
128.58, 127.79, 126.46 (benzene ring), 141.15 (-CF3), 139.33,
123.88, 123.52, 122.61, 121.97, 110.45 (carbazole ring), 96.42
(-CH), 43.23 (N-CH2), 34.14, 31.46, 29.70, 28.12, 28.04, 27.15,
25.58, 22.61, 22.49. Anal. Calcd for C56H47Br2N3F3O2Ir: C,
55.91; H, 3.91; N, 3.49. Found: C, 56.60; H, 4.29; N, 3.43. Mass
(ESI), m/z: 1202.3 (M+).
3,6-Dibromo-9-hexanecarbazole (9) was prepared ac-
cording to the published procedures.11 1H NMR (CDCl3) δ
(ppm): 8.09 (s, 2H), 7.53 (d, 2H), 7.24 (d, 2H) (carbazole ring),
4.17 (t, 2H, N-CH2), 1.81-1.24 (m, 8H), 0.85 (t, 3H, -CH3).
13C NMR (CDCl3) δ (ppm): 139.2, 128.9, 123.4, 123.1, 111.9,
110.3 (carbazole ring), 43.3 (N-CH2), 31.4, 28.8, 26.8, 22.5,
13.9 (-CH3). Anal. Calcd for C18H19Br2N: C, 52.81; H, 4.64;
N, 3.42. Found: C, 52.72; H, 4.83; N, 3.22.
2,7-Dibromofluorene (10) and 2,7-dibromo-9,9-di-
octylfluorene (11) were prepared according to the published
procedures.13
2,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9,9-
dioctylfluorene (12) was prepared following the published
procedure from 2,7-dibromo-9,9-dioctylfluorene (11).14 The
resulted boronic ester was recrystallized from methanol and
further purification by column chromatography (silica gel, 10%
ethyl acetate in hexane) to give a white solid product (yield,
50%); mp 128-131 °C. 1H NMR (CDCl3) δ (ppm): 7.81 (d, 2H),
7.76 (s, 2H), 7.72 (d, 2H) (fluorene ring), 1.97 (m, 4H), 1.37 (s,
24H, -CH3), 1.22-0.98 (m, 20H), 0.81 (t, 6H), 0.54 (m, 4H)
(aliphatic). 13C NMR (CDCl3) δ (ppm): 150.85, 144.32, 134.06,
129.27, 121.67, 119.75 (fluorene ring), 84.12, 55.56 (C9-fluorene
ring), 40.49, 32.15, 30.32, 29.57, 25.33, 23.97, 22.98, 14.47
(aliphatic). Anal. Calcd for C41H64O4B2: C, 76.74; H, 10.04.
Found: C, 76.43; H, 9.95.
General Procedures of Suzuki Polycondensation, Tak-
ing PFCzIrPiq05 as an Example. 2,7-Bis(4,4,5,5-tetra-
methyl-1,3,2-dioxaborolan-2-yl)-9,9-dioctylfluorene (12) (642
mg, 1.0 mmol), 3,6-dibromo-9-(iridium(III)bis(1-phenylisoquin-
oline-N,C2′))-14-trifluoro-11,13-tetradecyldiketone)carbazole (8a)
(12 mg, 0.01 mmol), 3,6-dibromo-9-hexanecarbazole (9) (405
mg, 0.99 mmol), and tetrakis(triphenylphosphine)palladium
(5 mg) were dissolved in the mixture of toluene/THF(10 mL)
and stirred for 0.5 h, and then Et4NOH (20%) aqueous solution
(4 mL) was added. The mixture was heated to 100 °C and
stirred for 2 days under an argon atmosphere. Then the
polymer was capped by adding 2-(4,4,5,5-tetramethyl-1,3,2-
dioxaborolan-2-yl)-9,9-dioctylfluorene (100 mg) by stirring for
12 h and then bromobenzene (1 mL) followed by heating for
another 12 h. The whole mixture was poured into methanol.
The precipitated polymer was recovered by filtration and
purified by silica column chromatography with toluene to
remove small molecular complex and catalyst residue (yield,
50%). 1H NMR (CDCl3) δ (ppm): 8.52 (s, 2H), 7.87 (d, 2H),
7.85 (m, 2H) (fluorene ring), 7.79 (d, 2H), 7.75 (m, 2H), 7.27
(s, 2H) (carbazole ring), 4.25 (s, 2H, N-CH2), 2.25 (t, 2H), 1.93
(m, 4H), 1.55-1.14 (t, 20H), 0.92-0.77 (m, 16H) (aliphatic).
13C NMR (CDCl3) δ (ppm): 151.69, 140.84, 140.65, 139.55,
133.10, 126.14, 125.53, 123.63, 121.67, 119.88, 118.96, 109.04
(fluorene and carbazole ring), 55.35 (C9-fluorene ring), 43.42,
40.63, 31.79, 31.63, 30.10, 29.23, 29.05, 27.02, 23.90, 22.58,
14.01 (aliphatic). Anal. Calcd for (C29H40)50(C18H19N)49.5 (C56-
H47N3F3O2Ir)0.5: C, 88.16; H, 9.19; N, 2.21. Found: C, 8 8.02;
H, 9.38; N, 1.79.
PFCzIrPiq1. 2,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lan-2-yl)-9,9-dioctylfluorene (12) (642 mg, 1.0 mmol), 3,6-
dibromo-9-(iridium(III)bis(1-phenylisoquinoline-N,C2′))-14-tri-
fluoro-11,13-tetradecyldiketone)carbazole (8a) (24 mg, 0.02
mmol), and 3,6-dibromo-9-hexanecarbazole (9) (411 mg, 0.98
mmol) were used in the polymerization. 1H NMR (CDCl3) δ
(ppm): 8.52 (s, 2H), 8.49 (d, 2H), 7.86 (m, 2H) (fluorene ring),
7.76 (d, 2H), 7.53 (m, 2H), 7.37 (d, 2H) (carbazole ring), 4.39
(s, 2H, N-CH2), 2.15 (t, 2H), 1.97 (m, 4H), 1.52-1.09 (t, 20H),
0.93-0.76 (m, 16H) (aliphatic). 13C NMR (CDCl3) δ (ppm):
151.71, 141.05, 140.86, 140.42, 139.57, 133.11, 126.17, 125.54,
123.65, 121.69, 119.90, 118.97, 109.06 (fluorene and carbazole
ring), 55.37 (C9-fluorene ring), 40.65, 40.51, 31.81, 31.65, 30.12,
29.25, 29.08, 27.04, 23.92, 23.83, 22.61, 14.04 (aliphatic). Anal.
Calcd for (C29H40)50(C18H19N)49(C56H47N3F3O2Ir)1: C, 87.78; H,
9.12; N, 2.23. Found: C, 87.14; H, 9.38; N, 1.60.

Macromolecules, Vol. 38, No. 10, 2005
Fluorene-alt-carbazole Copolymers 4075
PFCzIrPiq2. 2,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lan-2-yl)-9,9-dioctylfluorene (12) (642 mg, 1.0 mmol), 3,6-
dibromo-9-(iridium(III)bis(1-phenylisoquinoline-N,C2′))-14-tri-
fluoro-11,13-tetradecyldiketone)carbazole (8a) (48 mg, 0.04
mmol), and 3,6-dibromo-9-hexanecarbazole (9) (402 mg, 0.96
mmol) were used in the polymerization. 1H NMR (CDCl3) δ
(ppm): 8.52 (s, 2H), 7.85 (t, 2H), 7.78 (d, 2H) (fluorene ring),
7.75 (d, 2H), 7.53 (m, 2H), 7.25 (s, 2H) (carbazole ring), 4.41
(s, 2H, N-CH2), 2.16 (t, 2H), 1.97 (d, 4H), 1.51-1.10 (m, 20),
0.93-0.77 (m, 16H) (aliphatic). 13C NMR (CDCl3) δ (ppm):
151.72, 140.87, 140.42, 139.58, 133.12, 126.18, 125.55, 123.66,
121.69, 119.89, 118.97, 109.06 (fluorene and carbazole ring),
55.37 (C9-fluorene ring), 43.43, 40.65, 31.81, 31.65, 30.12,
29.26, 29.08, 27.04, 23.92, 22.61, 14.03 (aliphatic). Anal. Calcd
for (C29H40)50(C18H19N)48(C56H47N3F3O2Ir)2: C, 87.07; H, 8.99;
N, 2.26. Found: C, 87.20; H, 9.29; N, 1.92.
PFCzIrNapy05. 2,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lan-2-yl)-9,9-dioctylfluorene (12) (1.0 mmol), 3,6-dibromo-9-
hexanecarbazole (9) (0.99 mmol), and 3,6-dibromo-9-(iridium-
(III)bis(2-(1′-naphthylpyridine-N,C2′))-9-(14-trifluoro-11,13-
tetradecyldiketone)carbazole (8b) (0.01 mmol) were used in
the polymerization. 1H NMR (CDCl3) δ (ppm): 8.52 (s, 2H),
7.84 (d, 2H), 7.78 (t, 2H) (fluorene ring), 7.74 (t, 2H), 7.52 (d,
2H), 7.24 (s, 2H) (carbazole ring), 4.39 (s, 2H, N-CH2), 2.16
(t, 2H), 1.97 (m, 4H), 1.58-1.09 (m, 20H), 0.92-0.76 (m, 16H)
(aliphatic). 13C NMR (CDCl3) δ (ppm): 151.71, 140.86, 140.42,
139.57, 133.11, 126.17, 125.54, 123.65, 121.69, 119.91, 118.97,
109.06 (fluorene and carbazole ring), 55.37 (C9-fluorene ring),
40.65, 31.81, 31.65, 30.12, 29.26, 29.08, 27.04, 23.92, 22.61,
109.06 (fluorene and carbazole ring), 55.37 (C9-fluorene ring),
43.42, 40.65, 31.81, 31.65, 30.12, 29.25, 29.08, 27.04, 23.92,
22.61, 14.03 (aliphatic). Anal. Calcd for (C29H40)50(C18H19N)49.5
(C56H47N3F3O2Ir)0.5 C, 88.16; H, 9.19; N, 2.21. Found: C,
87.56; H, 9.40; N, 1.75.
-
:
PFCzIrPhq1. 2,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lan-2-yl)-9,9-dioctylfluorene (12) (0.50 mmol), 3,6-dibromo-9-
hexanecarbazole (9) (0.49 mmol), and 3,6-dibromo-9-(iridium-
(III)bis(2-phenylquinoline-N,C2′))-14-trifluoro-11,13-tetradec-
yldiketone)carbazole (8c) (0.01 mmol) were used in this
1
polymerization. H NMR (CDCl3) δ (ppm): 8.52 (s, 2H), 7.87
(t, 2H), 7.79 (m, 2H) (fluorene ring), 7.75 (d, 2H), 7.55 (t, 2H),
7.25 (s, 2H) (carbazole ring), 4.41 (s, 2H, N-CH2), 2.17 (t, 2H),
1.97 (t, 4H), 1.48-1.14 (m, 20H), 0.93-0.77 (m, 16H) (ali-
phatic). 13C NMR (CDCl3) δ (ppm): 151.72, 140.87, 140.43,
139.58, 133.12, 126.18, 125.56, 123.66, 121.71, 119.91, 118.97,
109.06 (fluorene and carbazole ring), 55.37 (C9-fluorene ring),
43.41, 40.66, 31.82, 31.66, 30.13, 29.26, 29.08, 27.04, 23.93,
22.61, 14.04 (aliphatic). Anal. Calcd for (C29H40)50(C18H19N)49-
(C56H47N3F3O2Ir)1: C, 87.78; H, 9.12; N, 2.23. Found: C, 87.20;
H, 9.24; N, 1.69.
PFCzIrPhq2. 2,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lan-2-yl)-9,9-dioctylfluorene (12) (0.50 mmol), 3,6-dibromo-9-
hexanecarbazole (9) (0.48 mmol), and 3,6-dibromo-9-(iridium-
(III)bis(2-phenylquinoline-N,C2′))-14-trifluoro-11,13-tetradec-
yldiketone)carbazole (8c) (0.02 mmol) were used in this
1
polymerization. H NMR (CDCl3) δ (ppm): 8.85 (s, 2H), 7.87
(d, 2H), 7.79 (d, 2H) (fluorene ring), 7.75 (d, 2H), 7.56 (d, 2H),
7.26 (s, 2H) (carbazole ring), 4.23 (s, 2H, N-CH2), 2.15 (t, 2H),
1.92 (t, 4H), 1.55-1.14 (m, 20H), 0.93-0.77 (m, 16H) (ali-
phatic). 13C NMR (CDCl3) δ (ppm): 151.69, 140.82, 140.40,
139.55, 133.09, 126.15, 125.54, 123.63, 121.67, 119.87, 118.95,
109.04 (fluorene and carbazole ring), 55.34 (C9-fluorene ring),
40.62, 31.79, 31.63, 30.10, 29.23, 29.06, 27.02, 23.90, 22.58,
14.01 (aliphatic). Anal. Calcd for (C29H40)50(C18H19N)48(C56H47-
N3F3O2Ir)2: C, 87.07; H, 8.99; N, 2.26. Found: C, 87.28; H,
9.34; N, 1.94.
14.04 (aliphatic). Anal. Calcd for (C29H40
)
50(C18H19N)49.5
-
(C56H47N3F3O2Ir)0.5
: C, 88.16; H, 9.19; N, 2.21. Found: C,
87.78; H, 8.85; N, 1.60.
PFCzIrNapy1. 2,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lan-2-yl)-9,9-dioctylfluorene (12) (0.5 mmol), 3,6-dibromo-9-
hexanecarbazole (9) (0.49 mmol), and 3,6-dibromo-9-(iridium-
(III)bis(2-(1′-naphthylpyridine-N,C2′))-9-(14-trifluoro-11,13-
tetradecyldiketone)carbazole (8b) (0.01 mmol) were used in the
1
polymerization. H NMR (CDCl3) δ (ppm): 8.52 (d, 2H), 7.86
PFCz. 2,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-
9,9-dioctylfluorene (12) (0.50 mmol) and 3,6-dibromo-9-hex-
anecarbazole (9) (0.50 mmol) were used in this polymerization.
1H NMR (CDCl3) δ (ppm): 8.52 (s, 2H), 7.84 (d, 2H), 7.79 (d,
2H) (fluorene ring), 7.72 (m, 2H), 7.53 (d, 2H), 7.24 (m, 2H)
(carbazole ring), 4.38 (s, 2H, N-CH2), 2.13 (d, 2H), 1.95 (t,
4H), 1.52-0.74 (m, 24 H) (aliphatic). 13C NMR (CDCl3) δ
(ppm): 151.69, 140.83, 140.40, 139.55, 133.09, 126.14, 123.63,
121.66, 119.87, 118.93, 109.04 (fluorene and carbazole ring),
56.94 (N9-carbazole ring), 55.34 (C9-fluorene ring), 40.62, 31.78,
31.62, 30.11, 29.23, 29.05, 27.02, 23.89, 22.57, 14.01 (aliphatic).
Anal. Calcd for (C29H40)50(C18H19N)50: C, 88.54; H, 9.26; N, 2.19;
Found: C, 88.03; H, 9.33; N, 1.88.
(t, 2H), 7.78 (m, 2H) (fluorene ring), 7.74 (d, 2H), 7.53 (t, 2H),
7.24 (s, 2H) (carbazole ring), 4.40 (s, 2H, N-CH2), 2.16 (t, 2H),
1.97 (m, 4H), 1.48-1.09 (m, 20), 0.93-0.76 (m, 16) (aliphatic).
13C NMR (CDCl3) δ (ppm): 151.72, 140.86, 140.42, 139.57,
133.11, 126.18, 125.54, 123.65, 121.69, 119.90, 118.97, 109.06
(fluorene and carbazole ring), 55.37 (C9-fluorene ring), 40.65,
31.81, 31.65, 30.12, 29.25, 29.08, 27.04, 23.92, 22.60, 14.03
(aliphatic). Anal. Calcd for (C29H40)50(C18H19N)49(C56H47N3F3O2-
Ir)1: C, 87.78; H, 9.12; N, 2.23. Found: C, 87.50; H, 9.46; N,
1.56.
PFCzIrNapy2. 2,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lan-2-yl)-9,9-dioctylfluorene (12) (0.5 mmol), 3,6-dibromo-9-
hexanecarbazole (9) (0.48 mmol), and 3,6-dibromo-9-(iridium-
(III)bis(2-(1′-naphthylpyridine-N,C2′))-9-(14-trifluoro-11,13-
tetradecyldiketone)carbazole (8b) (0.02 mmol) were used in the
PFO. 2,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-
9,9-dioctylfluorene (12) (0.50 mmol) and 2,7-dibromo-9,9-
dioctylfluorene (11) (0.50 mmol) were used in this polymeri-
1
1
polymerization. H NMR (CDCl3) δ (ppm): 8.52 (s, 2H), 7.87
zation. H NMR (CDCl3) δ (ppm): 7.85 (d, 2H), 7.78 (s, 2H),
(d, 2H), 7.86 (d, 2H) (fluorene ring), 7.79 (m, 2H), 7.75 (d, 2H),
7.27 (s, 2H) (carbazole ring), 4.38 (s, 2H, N-CH2), 2.15 (t, 2H),
1.95 (t, 4H), 1.52-1.13 (m, 20H), 0.92-0.77 (m, 16H) (ali-
phatic). 13C NMR (CDCl3) δ (ppm): 151.69, 148.16, 140.84,
140.40, 139.55, 133.09, 126.17, 125.50, 123.63, 121.67, 119.88,
118.95, 109.04 (fluorene and carbazole ring), 55.35 (C9-fluorene
ring), 40.62, 31.79, 31.63, 30.10, 29.23, 29.06, 27.02, 23.90,
22.58, 14.09 (aliphatic). Anal. Calcd for (C29H40)50(C18H19N)48-
(C56H47N3F3O2Ir)2: C, 87.07; H, 8.99; N, 2.26. Found: C, 87.32;
H, 9.02; N, 1.99.
7.73 (d, 2H) (fluorene ring), 1.95 (m, 4H), 1.22-0.98 (m, 20H),
0.83 (t, 6H), 0.55 (m, 4H) (aliphatic). 13C NMR (CDCl3) δ
(ppm): 150.92, 144.52, 134.16, 129.31, 121.17, 119.84 (fluorene
ring), 55.58 (C9-fluorene ring), 40.42, 32.11, 30.27, 29.47, 25.24,
23.87, 22.86, 14.53 (aliphatic). Anal. Calcd for C29H40: C, 89.69;
H, 10.31. Found: C, 88.78; H, 9.63.
PFIrPiq05. 2,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-
2-yl)-9,9-dioctyl-fluorene (12) (642 mg, 1.0 mmol), 3,6-dibromo-
9-(iridium(III) bis(1-phenylisoquinoline-N,C2′))-14-trifluoro-
11,13-tetradecyldiketone)carbazole (8a) (12 mg, 0.01 mmol),
and 2,7-dibromo-9,9-dioctylfluorene (11) (543 mg, 0.99 mmol)
PFCzIrPhq05. 2,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lan-2-yl)-9,9-dioctylfluorene (12) (1.0 mmol), 3,6-dibromo-9-
hexanecarbazole (9) (0.99 mmol), and 3,6-dibromo-9-(iridium-
(III)bis(2-phenylquinoline-N,C2′))-14-trifluoro-11,13-tetradec-
yldiketone)carbazole (8c) (0.01 mmol) were used in this
1
were used in this polymerization. H NMR (CDCl3) δ (ppm):
8.52 (s, 2H), 7.84 (d, 2H), 7.79 (d, 2H) (fluorene ring), 2.13 (d,
2H), 1.95 (t, 4H), 1.52-0.74 (m, 24 H) (aliphatic). 13C NMR
(CDCl3) δ (ppm): 151.69, 139.55, 133.09, 126.14, 118.93, 109.04
(fluorene ring), 55.34 (C9-fluorene ring), 31.78, 31.62, 30.11,
29.23, 29.05, 27.02, 23.89, 22.57, 14.01 (aliphatic). Anal. Calcd
for (C29H40)99.5(C56H47N3F3O2Ir)0.5: C, 89.36; H, 10.23. Found:
C, 89.03; H, 9.53.
1
polymerization. H NMR (CDCl3) δ (ppm): 8.52 (s, 2H), 7.86
(d, 2H), 7.78 (t, 2H) (fluorene ring), 7.74 (m, 2H), 7.53 (d, 2H),
7.24 (s, 2H) (carbazole ring), 4.40 (s, 2H, N-CH2), 2.16 (t, 2H),
1.97 (t, 4H), 1.58-1.13 (m, 20H), 0.92-0.76 (m, 16H) (ali-
phatic). 13C NMR (CDCl3) δ (ppm): 151.72, 140.86, 140.42,
139.57, 133.11, 126.17, 125.55, 123.65, 121.69, 119.91, 118.96,
PFIrPhq2. 2,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-
2-yl)-9,9-dioctylfluorene (12) (642 mg, 1.0 mmol), 3,6-dibromo-

4076 Jiang et al.
Macromolecules, Vol. 38, No. 10, 2005
Scheme 1. Synthetic Route for the Copolymers and Molecular Structures of Different Backbone-Based
Copolymers and PBD
Table 1. Structural Properties of the Copolymers
9-(iridium(III)bis(2-phenylquinoline-N,C2′))-14-trifluoro-11,13-
tetradecyldiketone)carbazole (8c) (48 mg, 0.04 mmol), and 2,7-
dibromo-9,9-dioctylfluorene (11) (526 mg, 0.96 mmol) were
DOF/Cz/CzIr (molar ratio)
comonomer in composition in
1
used in this polymerization. H NMR (CDCl3) δ (ppm): 8.53
copolymers
Mw (×103) PDI
feed ratio
copolymera
(s, 2H), 7.83 (d, 2H), 7.81 (d, 2H) (fluorene ring), 2.12 (d, 2H),
1.96 (t, 4H), 1.51-0.73 (m, 24 H) (aliphatic). 13C NMR (CDCl3)
δ (ppm): 151.66, 139.51, 133.08, 126.15, 118.93, 109.02 (fluo-
rene ring), 55.32 (C9-fluorene ring), 31.75, 31.62, 30.11, 29.23,
29.05, 27.02, 23.88, 22.53, 14.02 (aliphatic). Anal. Calcd for
(C29H40)98(C56H47N3F3O2Ir)2: C, 88.34; H: 10.01. Found: C,
88,17; H, 9.45.
PFO
51.3
12.5
11.5
5.1
13.2
12.4
7.1
11.8
12.3
14.1
18.8
16.7
16.5
2.0
PFCz
1.9 50:50
56.5:43.5
PFCzIrPiq05
PFCzIrPiq1
PFCzIrPiq2
PFCzIrNapy05
PFCzIrNapy1
PFCzIrNapy2
PFCzIrPhq05
PFCzIrPhq1
PFCzIrPhq2
PFIrPiq05
2.1 50:49.5:0.5
1.7 50:49:1
2.1 50:48:2
2.1 50:49.5:0.5
1.8 50:49:1
2.1 50:48:2
2.1 50:49.5:0.5
2.0 50:49:1
2.2 50:48:2
2.1 99.5:0:0.5
1.9 98:0:2
50:49.6:0.4
50:49.2:0.8
50:48.8:1.2
50:49.8:0.2
50:49.6:0.4
50:48.7:1.3
50:49.8:0.2
50:49.3:0.7
50:48.7:1.3
99.6:0:0.4
98.8:0:1.2
Results and Discussion
Synthesis and Characterization of Polymers.
The synthetic route of the copolymers is shown in
Scheme 1. The monomers with Ir complex monomers
were synthesized from 3,6-dibromo-9-(14-trifluoro-11,13-
tetradecyldiketone)carbazole (4) and the corresponding
iridium chloride-bridged dimers. The copolymers from
fluorene, carbazole, and iridium complex-attached car-
bazole units were prepared by Suzuki polycondensation.
The feed ratios of Ir complexes in the polycondensation
are 0, 0.5, 1, and 2 mol %, and the corresponding
polymers are named PFO, PFCz, PFIrPiq05, PFC-
zIrPiq05, PFCzIrPiq1, PFCzIrPiq2, PFCzIrNapy05, PFC-
zIrNapy1, PFCzIrNapy2, PFCzIrPhq05, PFCzIrPhq1,
PFCzIrPhq2, and PFIrPhq2, respectively.
PFIrPhq2
a Calculated from the nitrogen and iridium content in copoly-
mers.
fluorescence spectrometry (XRF). Therefore, the molar
ratios of Ir complexes in the copolymers were calculated
by combining elemental analysis with XRF data. Actual
compositions of the copolymers and the feed ratios of
the comonomers are listed in Table 1. The results
indicate that actual Ir complex content in the copolymer
is substantially lower than that of the feed ratio of the
monomers. The weight-average molecular weights of
these copolymers are from 5100 to 18 000 with a
polydispersity index (PDI) from 1.7 to 2.2, which is
consistent with a polycondensation reaction.
The iridium content in the copolymers was ap-
proximately estimated by using of the sequential X-ray

Macromolecules, Vol. 38, No. 10, 2005
Fluorene-alt-carbazole Copolymers 4077
(CV) in the solution of 0.1 M tetrabutylammonium
hexafluorophosphate (Bu4NPF6) in acetonitrile (CH3-
CN). The CV curves were referenced to an Ag quasi-
reference electrode, which was calibrated using the
ferrocene/ferrocenium redox couple (0.35 V vs Ag/AgCl)
as an internal standard prior to measurements. The
photophysical and electrochemical properties of the Ir
complexes and the redox potentials of the copolymers
derived from the onset in the cyclic voltammetry are
summarized in Table 2. The onset of oxidation potentials
of PFO and PFCz is observed respectively at 1.38 and
1.07 V. The HOMO and LUMO levels of polymers can
be estimated using the equations EHOMO ) -e(Eox
+
4.38) (eV) and ELUMO ) -e(Ered+ 4.38) (eV).17a Therefore,
the HOMO levels of PFO and PFCz are respectively
estimated at -5.76 and -5.45 eV. The results show that
the introduction of a carbazole unit into the polyfluorene
main chain leads to the rise in HOMO, which implies a
much lower barrier for the hole injection. The onset of
oxidation potential of the carbazole-based copolymers
with Ir complexes is almost constant at about 1.1 V
against Ag/AgCl reference electrode, which is consistent
with that of the PFCz. This peak is attributed to
p-doping of the fluorene-alt-carbazloe backbone. HOMO
and LUMO levels are respectively estimated at -5.5 and
-2.2 eV (Table 2). That the cabarzole-based copolymers
have an irreversible n-doping process indicates that the
electron-charged (n-doped) state of these polymers is
unstable. The similar behavior has been reported for
the polymer with the same backbone of P(F-alt-Cz).17
Unfortunately, the redox peaks failed to be recorded
corresponding to the Ir complex in all of the copolymers,
obviously due to the low Ir complex content. The
oxidation potentials for the Ir complexes (Piq)2Ir(acaF),
(Napy)2Ir(acaF), and (Phq)2Ir(acaF) were observed re-
spectively at 0.85, 0.90, and 0.95 V (Table 2). Suppose
there are no great changes in the HOMO level of the Ir
complexes grafted into host polymer chains; the HOMO
level of the Ir complexes must fall within the band gap
of the host polymer. Therefore, the grafted Ir complexes
will function as both a hole and an electron trap.18
The photoluminescent (PL) spectra of the copolymers
are shown in Figure 2. All of the copolymers emit light
of λmax ) 580-610 nm. Slight emission differences in
these copolymers are related to the nature of the
ligands. In Figure 2, the intense emission peaked at
about 420 nm from host unit can be observed for those
copolymers with low Ir complex content of 0.5 mol %.
This indicates that the energy transfer from main chain
to the Ir complex connected on the alkyl side chain is
incomplete because the average distance from a photo-
excited polymer chain to the nearest Ir complex is too
large.19 The relative intensities at the peak of 420 nm
vary with the Ir complex contents in the copolymers.
With the increase of Ir complex content in copolymers,
the emission intensity of 420 nm from the main chain
descends. The emission of PFCz segments in copolymers
almost quenched completely for the copolymers with the
Ir complex content of 2 mol %, which indicates that
energy transfer from the main chain to the Ir complex
becomes complete. The PL efficiencies and the maxi-
mum emission wavelength of the copolymers are listed
in Table 2. The PL efficiencies of PFCzIrPiq and
PFCzIrPhq copolymers are as high as 60-70%, much
higher than that of the host polymers (PFCz), which
should be owed to the full energy transfer from the PFCz
segments to the Ir complexes in the copolymers. How-
Figure 1. (a) UV-vis absorption spectra of Ir complexes and
PL spectrum of PFCz in film. (b) UV-vis absorption spectra
of PFO, PFCz, and copolymers in film.
Optical and Electrochemical Properties. Figure
1a shows the UV-vis absorption spectra of the Ir
complexes [(Piq)2Ir(acaF), (Napy)2Ir(acaF), and (Phq)2Ir-
(acaF)] and the PL spectrum of fluorene-alt-carbazole
copolymer (PFCz). The Ir complexes have similar ab-
sorption spectra with broad bands from 270 to 490 nm.
The intense absorption peaks below 350 nm are at-
tributed to the spin-allowed singlet state 1π-π* transi-
tion of cyclometalated ligands, and the weak absorption
peaks around 420 nm can be assigned to the spin-
allowed singlet metal-to-ligand charge-transfer (1MLCT)
transition.15 The strong absorption peaks of 465 nm for
(Phq)2Ir(acaF), 478 nm for (Napy)2Ir(acaF), and 488 nm
for (Piq)2Ir(acaF) are due to the triplet metal-to-ligand
charge-transfer (3MLCT) transition.16 The spin-forbid-
3
den MLCT transition is gained by mixing it with the
higher spin-allowed 1MLCT transition through the
strong spin-orbit coupling of iridium. Figure 1a indi-
cates that the PL emission spectrum of the host polymer
(PFCz) and the absorption spectra of the guests (Ir
complexes) show good spectra overlap. Therefore, the
efficient Fo¨rster energy transfer from the PFCz host to
the Ir complex guests can be expected. Figure 1b shows
the absorption spectra of the electrophosphorescent
copolymers and that of the host polymers (PFO and
PFCz). The absorption spectrum of PFCz shows a blue
shift of 40 nm compared to that of PFO. This is due to
the interruption of delocalization of the π-electrons along
the polymer backbone by the 3,6-carbazole linkages.10b
These absorption spectra show no essential differences
among these complex copolymers with low Ir complex
contents. The absorption of the complex copolymers red
shifts around 10 nm in comparison with that of the host
copolymer (PFCz). From the onset of the absorption
peaks, the optical band gap of the complex copolymers
was estimated at 3.12 eV, which is a little less than that
of the host copolymer (3.14 eV) (Table 2).
The electrochemical behavior of the Ir complexes and
the polymers was investigated by cyclic voltammetry

4078 Jiang et al.
Macromolecules, Vol. 38, No. 10, 2005
Table 2. Optical and Electrochemical Properties of Polymers and Ir Complexes
photoluminescence
copolymers
λmax abs [nm]
Ega (eV)
Eox (V)
Ered (V)
HOMO (eV)
LUMO (eV)
λPL (nm)
QPL (%)
PFO
385
2.85
3.14
3.12
3.12
3.12
3.12
3.12
3.12
3.12
3.12
3.12
2.88
3.12
1.38
1.07
1.11
1.14
1.09
1.08
1.11
1.09
1.15
1.08
1.15
1.36
1.37
0.85
0.90
0.95
-2.16
-2.11
-2.12
-2.15
-2.07
-2.14
-2.12
-2.10
-2.18
-2.13
-2.10
-2.17
-2.18
-5.76
-5.45
-5.49
-5.52
-5.47
-5.46
-5.49
-5.47
-5.53
-5.46
-5.53
-5.74
-5.75
-5.23
-5.28
-5.33
-2.22
-2.27
-2.26
-2.23
-2.31
-2.24
-2.26
-2.28
-2.20
-2.25
-2.28
-2.21
-2.20
435
45
42
56
58
61
29
21
20
65
74
75
60
62
PFCz
345
420
PFCzIrPiq05
PFCzIrPiq1
PFCzIrPiq2
PFCzIrNapy05
PFCzIrNapy1
PFCzIrNapy2
PFCzIrPhq05
PFCzIrPhq1
PFCzIrPhq2
PFIrPiq05
350
420, 610
610
610
350
350
350
415, 595
415, 595
415, 595
420, 580
580
350
350
350
350
350
580
385
435, 610
580
PFIrPhq2
350
(Piq)2Ir(acaF)b
(Napy)2Ir(acaF)b
(Phq)2Ir(acaF)b
303, 358, 488
300, 356, 478
280, 350, 465
610
595
580
a Estimated from the onset of absorption edge responsible for copolymers. b Data in CH2Cl2 solution (10-5 mol/L) of 0.1 mol/L n-Bu4NPF6.
Figure 2. PL spectra of copolymers in film for PFCzIrPiq (a),
Figure 3. EL spectra of copolymers for PFCzIrPiq (a),
PFCzIrNapy (b), and PFCzIrPhq (c).
PFCzIrNapy (b), and PFCzIrPhq (c). Device structure: ITO/
PEDOT/copolymer + PBD(30 wt %)/Ba/Al.
ever, PFCzIrNapy shows much lower PL efficiency
(20%) than that of the other two copolymers, which
should be owed to the incomplete energy transfer
(Figure 2b).
sponding Ir complex emission. This indicates that there
occurs the efficient energy transfer from the host to the
guest. Like the case of PL emission, PFCzIrNapy shows
less efficient energy transfer. The PFCzIrNapy05 co-
polymer shows clearly the emission peaked at 420 nm
from the main chain, which completely quenches at the
Ir complex content of 2 mol % in the feed ratio. The
substantial difference of energy transfer efficiencies
between the PL and EL for the copolymers implies that
different mechanisms are involved.19 Under photoexci-
tation, the singlet excited states are created on the main
chain and subsequently transfer to the metal-organic
complex by Fo¨rster energy transfer. In contrast, the
electrons and holes are trapped on the Ir complex after
Device Performances. The devices were fabricated
in the configuration below. ITO/PEDOT/copolymer +
PBD (30 wt %)/Ba/Al. PBD was blended with copolymers
to improve the electron-transporting capability of the
copolymers.20 The EL spectra of the copolymers are
shown in Figure 3. In the case of PFCzIrPiq and
PFCzIrPhq, EL emission from the backbone of the
copolymers completely quenches even though the Ir
complex content is as low as 0.5 mol % in the feed ratio.
There is only one emission peak at 610 nm for PFC-
zIrPiq and 580 nm for PFCzIrPhq due to the corre-

Macromolecules, Vol. 38, No. 10, 2005
Fluorene-alt-carbazole Copolymers 4079
Table 3. Device Performances of the Copolymersa
b
maximal QEext
J ) 100 mA/cm2 c
copolymers
bias (V)
J (mA/cm2)
L (cd/m2)
QEext (%)
LE (cd/A)
bias (V)
L (cd/m2)
QEext (%)
LE (cd/A)
PFCzIrPiq05
PFCzIrPiq1
7.7
8.0
9.5
6.0
7.5
5.2
6.5
5.7
8.0
5.9
6.1
240
127
228
55
325
53
108
55
448
4.9
2.4
1.5
0.4
0.6
1.1
1.1
1.7
2.7
4.0
2.1
1.2
0.5
0.9
1.6
1.5
2.3
3.1
10.7
12.1
11.0
7.5
2978
1089
826
3.4
1.3
1.2
0.2
0.5
0.6
0.5
0.7
1.3
2.9
1.1
0.8
0.3
0.7
1.0
1.1
1.5
2.5
PFCzIrPiq2
21.8
11.8
35.8
3.5
PFCzIrNapy05
PFCzIrNapy1
PFCzIrNapy2
PFCzIrPhq05
PFCzIrPhq1
PFCzIrPhq2
352
8.2
854
912
1053
1492
2546
7.1
6.1
8.0
1.5
8.2
10.6
10.1
a Device structure: ITO/PEDOT/copolymer + PBD(30 wt %)/Ba/Al. b Device performances at the maximal external quantum efficiency.
c Device performances when the current density is 100 mA/cm2.
Table 4. Device Performances of Different Backbone-Based Copolymers
efficiency
copolymers
λEL max (nm)
bias (V)
J (mA/cm2)
L (cd/m2)
QEext (%)
LE (cd/A)
PFCzIrPiq05a
610
610
610
610
580
580
580
580
7.1
7.7
5.4
4.7
7.2
8.0
6.5
6.7
5.3
5.9
6.3
5.9
5.4
10.6
4.5
7.4
80
240
44
2.3
4.9
0.7
1.5
1.2
2.8
0.4
1.1
1.9
4.0
0.6
1.3
1.4
3.1
0.5
1.2
PFCzIrPiq05: PBDb
PFIrPiq05a
PFIrPiq05: PBDb
PFCzIrPhq2a
62
234
448
112
126
PFCzIrPhq2: PBDb
PFIrPhq2a
PFIrPhq2: PBDb
a Device structure: ITO/ PEDOT/copolymer/Ba/Al. b Device structure: ITO/ PEDOT/copolymer + PBD(30 wt %)/Ba/Al.
the injection of the electrons from the cathode and the
holes from the opposite anode in the device.3,19
The device performances of the copolymers are listed
in Table 3. Like other phosphorescent PLEDs,4a,21,22 the
device performance shows a strong dependence on the
Ir complex content. The best device performance is
observed for PFCzIrPiq05 with Ir complex content of
0.5 mol % in the feed ratio, which is much lower than
that of the same Ir complex doped system.5 A maximum
external quantum efficiency of 4.9% ph/el and a lumi-
nous efficiency of 4.0 cd/A with a luminance of 240 cd/
m2 are achieved at a current density of 5.9 mA/cm2. The
efficiency of this device remains as high as QEext ) 3.4%
pl/el and LE ) 2.9 cd/A with a luminance of 2978 cd/m2
at a current density of 100 mA/cm2 (Table 3). The device
of PFCzIrPhq2 shows QEext ) 2.7% ph/el and LE ) 3.1
cd/A with a luminance of 448 cd/m2 at the current
density of 10.6 mA/cm2. At the current density of 100
mA/cm2, the efficiency of this device still remained QEext
) 1.3% pl/el and LE ) 2.5 cd/A with a luminance of 2546
cd/m2. The device based on PFCzIrNapy2 shows much
lower external quantum efficiencies of 1.1% with lumi-
nous efficiencies of 1.6 cd/A.
The fluorene-based copolymer PFIrPiq05 and PFIr-
Phq2 were synthesized for comparison. The molecular
structures are shown in Scheme 1. Table 4 shows that
the quantum efficiencies of the devices with PBD are
higher than those of the device without PBD. It is a fact
that the buildup of space-charge due to trapping of holes
on the Ir complex is largely inhibited by supplying a
large number of electrons via efficient injection and
transport from blended with PBD.18 The device perfor-
mances of the carbazole-based copolymers PFCzIrPiq05
and PFCzIrPhq2 are superior to those of the fluorene-
based copolymer PFIrPiq05 and PFIrPhq2. This indi-
cates that carbazole unit in the backbone is necessary
due to the raised HOMO level of the copolymer making
the hole injection easier and having a higher triplet level
than phosphorscent guest to prevent triplet energy
transfer from the guest to the host by the introduction
Figure 4. Luminance and external quantum efficiency vs
current density for PFCzIrPiq (a), PFCzIrNapy (b), and
PFCzIrPhq (c). Device structure: ITO/PEDOT/copolymer +
PBD(30 wt %)/Ba/Al.
of carbazole unit at the 3,6-linkage into polyfluorene
main chain.10 Therefore, the device performances were
improved.

4080 Jiang et al.
Macromolecules, Vol. 38, No. 10, 2005
74, 442. (d) Adachi, C.; Baldo, M. A.; Forrest, S. R.; Thompson,
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Figure 4 shows the luminance and the external
quantum efficiency of the devices as a function of
current density for PFCzIrPiq, PFCzIrNapy, and PFC-
zIrPhq copolymers with different Ir complex content in
the polymers. Unlike other electrophosphorescent PLEDs,
the external quantum efficiencies of phosphorescent
grafting copolymers show a gentle decay with the
increasing in current density due to the depressing
triplet-triplet annihilation of the copolymers.21,22 That
less decay in the device performances with the increase
in current density than that in devices with Ir complex
blended into polymer host indicates that grafting of
phosphorescent complexes into host copolymer backbone
could inhibit the concentration quenching at the high
current density due to the complex aggregation.21
(2) Adachi, C.; Baldo, M. A.; Thompson, M. E.; Forrest, S. R. J.
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Conclusion
The high-efficiency electrophosphorescent copolymers
were synthesized based on carbazole-alt-fluorene as a
main chain and Ir complex as a side group. The efficient
energy transfer from the main chain to the Ir complex
connected on the side chain of the polymers was
observed. EL emission from the main chain is com-
pletely quenched even at Ir complex content as low as
0.5 mol % for PFCzIrPiq and PFCzIrPhq copolymers.
The device of PFCzIrPiq05 copolymer shows the highest
external quantum efficiency of 4.9% ph/el and the
luminous efficiency of 4.0 cd/A with 240 cd/m2 at a bias
voltage of 7.7 V and peak emission at 610 nm. The
device of PFCzIrPhq2 shows QEext ) 2.7% ph/el and LE
) 3.1 cd/A with the luminance of 448 cd/m2 at a current
density of 10.6 mA/cm2. The device efficiency of PFC-
zIrPiq05 copolymer remains high (QEext ) 3.4% ph/el
and LE ) 2.9 cd/A) at the current density of 100 mA/
cm2. The enhancement of the device performance could
be due to the higher triplet energy and meanwhile to
suitable HOMO and LUMO levels for efficient charge
injection by introducing the carbazole unit into poly-
fluorene backbone at the 3,6-linkage and blending PBD
into the copolymers.
(15) Su, Y. J.; Huang, H. L.; Li, C. L.; Chien, C. H.; Tao, Y. T.;
Chou, P. T.; Datta, S.; Liu, R. S. Adv. Mater. 2003, 15, 884.
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Acknowledgment. The authors are grateful to the
Ministry of Science and Technology of China (No.
2002CB613403), the National Natural Science Founda-
tion of China (No. 50173008), and the Natural Science
Foundation of Guang-dong Province (No. 11545) for
their financial support to our work.
(17) (a) Li, Y.; Ding, J. F.; Day, M.; Tao, Y.; Lu, J. P.; D’iorio, M.
Chem. Mater. 2004, 16, 2165. (b) Liu, B.; Yu, W.; Lai, Y.;
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Adv. Mater. 1999, 11, 1349.
Supporting Information Available: 1H NMR spectra of
monomers (4, 8a-8c) and representative polymers, cyclic
voltammetry (CV) curves, and X-ray fluorescence (XRF) spec-
tra of polymers. This material is available free of charge via
the Internet at http://pubs.acs.org.
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