Pure blue electroluminescent poly(aryl ether)s with dopant-host systems

Article abstract of DOI:10.1002/pola.24828

A series of novel arylene ether polymers (P5F-BCzVFs) containing both pentafluorene (5F) and distyrylarylene derivative (BCzVF) units in the side chains for efficient pure blue light emission were prepared by a facile, metal-free condensation polymerization. The emission spectra indicated that color tuning could be achieved through efficient Foerster energy transfer from the deep-blue 5F host to the pure-blue BCzVF dopant. Single-layer polymer light-emitting diodes (PLEDs) based on P5F-BCzVFs (ITO/(PEDOT:PSS)/polymer/Ca/ Al) exhibited voltage-independent and stable pure blue emission with a Commission International de L'Eclairage (CIE) coordinate of (0.15, 0.15), a maximum brightness of 3576 cd/m², and a maximum luminous efficiencies of 2.15 cd/A, respectively. As most polymers with dopant-host systems, the luminous efficiencies of all P5F-BCzVFs surpassed that of the host-only polymer (P5F), due to the energy transfer and charge trapping from the host to the dopant.

Full text of DOI:10.1002/pola.24828

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ARTICLE
Pure Blue Electroluminescent Poly(aryl ether)s with Dopant–Host
Systems
Chunlei Bian,1,2 Guoxin Jiang,1 Hui Tong,1 Yanxiang Cheng,1 Zhiyuan Xie,1 Lixiang Wang,1
Xiabin Jing,1 Fosong Wang1
1State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of
Sciences, Changchun 130022, People’s Republic of China
2Graduate School of Chinese Academy of Sciences, Beijing 100039, People’s Republic of China
Correspondence to: L.-X. Wang (E-mail: lixiang@ciac.jl.cn) or H. Tong (E-mail: chemtonghui@ciac.jl.cn)
Received 14 April 2011; accepted 26 May 2011; published online 7 July 2011
DOI: 10.1002/pola.24828
ABSTRACT: A series of novel arylene ether polymers (P5F-
BCzVFs) containing both pentafluorene (5F) and distyrylarylene
derivative (BCzVF) units in the side chains for efficient pure
blue light emission were prepared by a facile, metal-free con-
densation polymerization. The emission spectra indicated that
(0.15, 0.15), a maximum brightness of 3576 cd/m2, and a maxi-
mum luminous efficiencies of 2.15 cd/A, respectively. As most
polymers with dopant-host systems, the luminous efficiencies
of all P5F-BCzVFs surpassed that of the host-only polymer
(P5F), due to the energy transfer and charge trapping from the
C
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color tuning could be achieved through efficient Forster energy
¨
host to the dopant. 2011 Wiley Periodicals, Inc. J Polym Sci
transfer from the deep-blue 5F host to the pure-blue BCzVF
dopant. Single-layer polymer light-emitting diodes (PLEDs)
based on P5F-BCzVFs (ITO/(PEDOT:PSS)/polymer/Ca/Al) exhib-
ited voltage-independent and stable pure blue emission with a
Commission International de L’Eclairage (CIE) coordinate of
Part A: Polym Chem 49: 3911–3919, 2011
KEYWORDS: energy transfer; host-guest systems; light-emitting
diodes (LED); pure blue electroluminescent; photophysics;
PLED; poly(aryl ether)s; polyethers
INTRODUCTION Polymer light-emitting diodes (PLEDs) have
attracted much attention because of their potential applica-
tion in the large-area, flat-panel display field.1–12 For full-
color display, blue, green, and red fluorophores with high
emission efficiency and high color purity are required. In
particular, blue light-emitting polymers are essential as blue
light sources for PLEDs or polymer hosts for green and red
dopants.13,14 Most of research about blue light-emitting poly-
mers focused on fluorene-based polymers, owing to their
high photoluminescence (PL) efficiency and wide
bandgap.15–22 Nevertheless, low electroluminescence (EL)
device efficiency and poor EL color stability during device
operation hamper their further application.23–26 Moreover,
the human eyes is not very sensitive to the deep blue emis-
sion of typical polyfluorenes (415 nm).27,28
polyfluorene derivative that contain bis(2,2-diphenylvinyl) fluo-
rene as a pendant with a maximum external quantum effi-
ciency of 1.06% with color coordinates of (0.15, 0.17). A poly-
fluorene derivative that contains 1 mol % 2-hexylbenzotriazole
(HBT) in the main chain has been reported by Cao et al.40 and
its PLED exhibited a luminance efficiency of 2.69 cd/A with a
color coordinate of (0.15, 0.17). Our group reported a series of
blue polyfluorene derivatives of dopant-host systems and their
single-layer PLEDs with the luminance efficiency of 3.43 cd/A,
the maximum brightness of 6539 cd/m2, and CIE coordinates
of (0.15, 0.16).41
However, most of these blue-emission polymers polymerized
by expensive transition metal catalysts, and the removing of
the residual catalysts is still a great challenge.42,43 In previous
works, our group have reported novel poly(aryl ether)s (PAEs)
with pentafluorene (5F) in the side chains (P5F), which exhib-
ited the similar EL performance with polyfluorenes.44 In this
article, we report a series of pure blue poly (aryl ether)s (P5F-
BCzVFs) containing dopant/host systems by a traditional con-
densation reaction without any metal catalysts. Pentafluorene
(5F) and distyrylarylene derivative (BCzVF) units are attached
orthogonally to the main chains of the polymers as pendant
Development of EL polymers with dopant-host systems have
been proved to be a successful strategy to tune colors and to
enhance the efficiency and stability of PLEDs.29–33 In most
cases, polyfluorene were used as the host material, and highly
efficient red, green, and sky blue EL polymers have been
reported.34–38 However, very few works are about pure blue
emission EL polymers.39–41 Shu and coworkers39 reported a
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SCHEME 1 Synthesis of poly(aryl ether)s. (i) n-BuLi, DMF, THF; (ii) LiAlH4, THF; (iii) CBr4, PPh3, THF; (iv) P(OEt)3, reflux; (v) NaOH
(50% aq), bromoethane, Tetrabutylammonium bromide, toluene; (vi) DMF, POCl3; (vii) t-BuOK, THF; (viii) K2CO3, toluene, DMAc,
140 ꢁC and then 170 ꢁC.
groups (Scheme 1). Poly(aryl ether) was selected as the poly-
mer skeleton due to the ease of synthesis and purification and
also because of its high thermal stability, and excellent film for-
mation capability.45 Effective energy transfer from the deep
blue pentafluorene units to the pure blue BCzVF units may
occur, leading to their emission predominantly from BCzVF.
The pure blue emission at 445 nm is more sensitive for
human eyes than that of polyfluorenes. In addition, the orthog-
onally connect style between pendant groups and the main
chains of poly(aryl ether)s induce a big steric hindrance that
can reduce the p-p stacking and depress the crystalline tend-
ency of polymers, which may result in stable and efficient blue
electroluminescence.
2,7-Dibromo-9,9-bis(4-fluoro-3-(trifluoromethyl)phenyl)fluorine
and monomer 5F were synthesized as previously described.44
All other reagents and solvents were used as received from
commercial sources without further purification.
9,9-Bis(4-fluoro-3-(trifluoromethyl)phenyl)fluorine-2,7-
dicarbaldehyde (1)
To a solution of 2,7-dibromo-9,9-bis(4-fluoro-3-(trifluorome-
thyl)phenyl)fluorine (6g, 9.3 mmol) in anhydrous THF (250
mL) was slowly added n-BuLi (8.9 mL,2.5 M in hexane, 22.2
mmol) at ꢀ78 ꢁC. The mixture was stirred at ꢀ78 ꢁC for 2
h. N,N-Dimethylformamide (DMF) (4 mL) was added to the
ꢁ
solution, and the resulting mixture was stirred at ꢀ78 C for
1 h, warmed to room temperature and stirred overnight fol-
lowed by quenching with 250 mL of HCl (2.0 M). After
extraction with dichloromethane three times, dried over an-
hydrous Na2SO4. Solid residues collected by evaporating off
the solvent were purified by column chromatography on
silica gel to afford the target compound with a yield of 75%.
EXPERIMENTAL
Material
Dimethylacetamide (DMAc) were dried and distilled from
finely powdered calcium hydride. Tetrahydrofuran (THF)
and toluene were distilled over sodium/ benzophenone.
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1H NMR (300 MHz, CDCl3): d 8.08 (d, 2H, J ¼ 7.9 Hz), 8.03
(dd, 2H, J ¼ 7.9 Hz, 1.2 Hz), 7.85 (s, 2H), 7.46–7.41 (m, 2H),
7.28 (dd, 2H, J ¼ 6.4 Hz, 2.3 Hz), 7.18 (t, 2H, J ¼ 9.2 Hz).
cooled to room temperature, extracted with dichlorome-
thane, and then combined organic layers were dried with
Na2SO4. After the solvent had been removed by rotary evap-
oration, the residue was purified by column chromatography
on silica gel to give the target compound. Yield: 84%.
2,7-Bis(bromomethyl)-9,9-bis(4-fluoro-3-(trifluoromethyl)-
phenyl)fluorine (3)
The solution of lithium aluminium hydride (4.5 mmol) in
THF was added dropwise to a solution of 9,9-Bis(4-fluoro-3-
1H NMR (400 MHz, CDCl3): d 10.09 (s, 1H), 8.60 (s, 1H),
8.15 (d, 1H, J ¼ 7.6 Hz), 8.00 (dd, 1H, J ¼ 8.8 Hz, 1.2 Hz),
7.53 (t, 1H, J ¼ 7.2 Hz), 7.46 (d,1H, J ¼ 5.6 Hz), 7.44 (d, 1H,
J ¼ 5.2 Hz), 7.32 (t, 1H, J ¼ 7.6 Hz), 4.37 (q, 4H, J ¼ 9.3 Hz),
1.45 (t, 6H, J ¼ 7.2 Hz).
(trifluoromethyl)phenyl)fluorine-2,7-dicarbaldehyde
(7.5
mmol) in THF (150 mL). The resulting mixture was stirred
at room temperature for 1 h. Then the mixture was poured
into water slowly and extracted with diethyl ether. The or-
ganic extracts were dried with anhydrous Na2SO4. After the
solvent had been removed, the crude compound 2 was dis-
solved in THF, then tetrabromomethane (CBr4) (9.3 mmol)
and triphenylphosphine (PPh3) (9.3 mmol) was added
quickly at room temperature. After the addition was com-
plete, the mixture was stirred for1h at room temperature
and then added dichloromethane and water. The organic
layer was extracted with dichloromethane, and the combined
organic layers were dried with Na2SO4. After the solvent had
been removed by rotary evaporation, the residue was puri-
fied by column chromatography on silica gel to give the tar-
get compound 3. Yield: 88%.
BCzVF
The solution of potassium tert-butoxide in anhydrous THF
was dropped to a stirred solution of compound 4 and 9-
ethyl-3-carbazolcarboxaldehyde in anhydrous THF under
nitrogen at room temperature, then the mixture was heated
under reflux for 6 h, cooled, and then dropped to water. The
precipitate was purified by column chromatography to give
the target compound with a yield of 60%.
1H NMR (300 MHz, CDCl3): d 8.23 (s, 2H), 8.12 (d, 2H, J ¼
7.5 Hz), 7.79 (d, 2H, J ¼ 7.8 Hz), 7.66 (d, 4H, J ¼ 7.8 Hz),
7.51–7.37 (m, 12H), 7.25 (d, 4H, J ¼ 9.3 Hz), 7.20–7.13 (m,
4H), 4.37 (q, 4H, J ¼ 9.3 Hz), 1.45 (t, 6H, J ¼ 7.2 Hz). MS
(MALDI-TOF): m/z: 928.3[Mþ].
1H NMR (300 MHz, CDCl3): d 7.91 (d, 2H, J ¼ 10.7 Hz),
7.59–7.54 (m, 2H), 7.42 (s, 2H), 7.41 (d, 2H, J ¼ 8.1 Hz),
7.30 (dd, 2H, J ¼ 6.7 Hz, 2 Hz), 4.50 (d, 2H, J ¼ 5.4 Hz).
General Polymerization Procedure
To a mixture of 4,40-dihydroxydiphenylpropane, 5F and
BCzVF with a determined feed ratio, toluene (2 mL), DMAc
(1.5 mL), and K2CO3 (0.58 g, 0.42 mmol) in a two-necked 20
mL glass reacꢁtor equipped with a Dean-Stark trap was
heated to 140 C for 3 h then enhanced to 170 ꢁC for extra
24 h. Then the mixture was cooled to room temperature and
diluted with 50 mL dichloromethane. The organic portion
was washed with water, dried with anhydrous MgSO4, and
concentrated into 2 mL. The polymer was precipitated with
methanol, followed by purification with Soxhlet extraction
with acetone and precipitated into methanol twice. The
resulting polymers are green or light-yellow solid with a
yield of 70–80%.
2,7-Bis(diethoxyphosphorylmethyl)-9,9-bis
(4-fluoro-3-(trifluoromethyl)phenyl)fluorine (4)
A mixture of 3 (3.ꢁ7 mmol) and triethyl phosphate (5 mL)
was heated at 150 C for 15 h. Excess triethyl phosphite was
evaporated under vacuum, and the residue was added to
hexane. The precipitate was purified by column chromatog-
raphy on silica gel with ethyl acetate to give the target com-
pound 4. Yield: 97%.
1H NMR (300 MHz, CDCl3): d 7.66 (d, 2H, J ¼ 7.8 Hz), 7.36–
7.20 (m, 6H), 7.05 (t, 2H, J ¼ 9 Hz), 3.94–3.74 (m, 8H), 3.06
(d, 2H, J ¼ 21.6 Hz), 1.04 (t, 12H, J ¼ 7.2 Hz).
P5F
N-Ethylcarbazole (5)
Yield: 73%. 1H NMR (400 MHz, CDCl3): d7.87(d, 2H, J ¼ 7.8
Hz), 7.78-7.60 (m, 24H),7.51–7.50 (m, 4H), 7.35–7.28 (m, 6H),
7.15 (d, 4H, J ¼ 8.4 Hz), 6.91 (d, 4H, J ¼ 8.4 Hz), 6.79-6.77 (m,
2H), 2.04-2.00 (m, 16H), 1.58 (s, 6H), 1.18-0.71 (m, 120H);
Anal. Calcd: H, 8.49; C, 84.98; Found: H, 8.34; C, 84.62.
A mixture of carbazole (42 mmol), toluene (40 mL), 50% of
the sodium hydroxide solution (25 mL), bromoethane (48
mmol) and Tetrabutylammonium bromide (0.5 g) was heated
under reflux for 16 h, cooled and extracted with dichlorome-
thane. The combined organic layers were dried with Na2SO4.
After the solvent had been removed by rotary evaporation,
the residue was purified by column chromatography on silica
gel to give the target compound. Yield: 90%.
P5F-BCzVF1
Yield: 80%. 1H NMR (400 MHz, CDCl3): d 8.21 (ArAH, weak
peak of BCzVF units), 8.11 (ArAH, weak peaks of BCzVF
units), 7.86 (ArAH), 7.77-7.63 (ArAH), 7.53 (ArAH), 7.36-
7.33 (ArAH), 7.17 (ArAH), 6.94 (ArAH), 6.80 (ArAH), 4.33
(m, CH2 of BCzVF units), 2.05 (m, CH2 of 5F units), 1.61 (s,
CH3), 1.18-0.71(m, CH2 and CH3). Anal. Calcd: H, 8.49; C,
84.93. Found: H, 8.47; C, 84.96.
1H NMR (400 MHz, CDCl3): d 8.06 (d, 2H, J ¼ 7.6 Hz), 7.58
(t, 2H, J ¼ 7.6 Hz), 7.50 (d, 2H, J ¼ 8.4 Hz), 7.35 (t, 2H, J ¼
7.6 Hz), 4.37 (q, 4H, J ¼ 9.3 Hz), 1.45 (t, 6H, J ¼ 7.2 Hz).
N-Ethyl-3-aldehyde Carbazole (6)
To a stirred solution of N-ethylcarbazole (30 mmol) of 50
mL N,N-Dimethylformamide was added dropwise 7 mL (75
P5F-BCzVF3
ꢁ
mmol) of phosphorusoxychloride (POCl3) at 0 C for 30 min,
Yield: 75%. 1H NMR (400 MHz, CDCl3): d 8.22 (ArAH, weak
peak of BCzVF units), 8.11 (ArAH, weak peaks of BCzVF
ꢁ
then enhanced to 98 C for extra 2 h. Then the mixture was
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TABLE 1 Molecular Weights and Thermal Properties of
units), 7.87 (ArAH), 7.78-7.64 (ArAH), 7.54 (ArAH), 7.36-
7.33 (ArAH), 7.17 (ArAH), 6.94 (ArAH), 6.80 (ArAH), 4.33
(m, CH2 of BCzVF units), 2.05 (m, CH2 of 5F units), 1.61 (s,
CH3), 1.18-0.71 (m, CH2 and CH3). Anal. Calcd: H, 8.69; C,
84.46. Found: H, 8.43; C, 84.88.
Polymers
Polymer
Mn ꢃ 104a
Mw ꢃ 104a
PDI
Td (ꢁC)b
P5F
10.2
4.0
3.9
2.0
4.4
23.8
7.3
5.8
3.7
7.0
2.3
1.8
1.5
1.8
1.6
424
416
415
423
418
P5F-BCzVF1
P5F-BCzVF3
P5F-BCzVF5
P5F-BCzVF10
a
P5F-BCzVF5
Yield: 72%. 1H NMR (400 MHz, CDCl3): d 8.20 (ArAH, weak
peak of BCzVF units), 8.09 (ArAH, weak peaks of BCzVF
units), 7.86 (ArAH), 7.77-7.62 (ArAH), 7.51 (ArAH), 7.36-
7.28 (ArAH), 7.14 (ArAH), 6.92 (ArAH), 6.78 (ArAH), 4.31
(m, CH2 of BCzVF units), 2.03 (m, CH2 of 5F units), 1.59 (s,
CH3), 1.18-0.71 (m, CH2 and CH3). Anal. Calcd: H, 8.60; C,
84.92. Found: H, 8.40; C, 84.84.
Molecular weights were determined by GPC, eluting with THF, by
comparison with polystyrene standards.
b
Temperature at which a 5% weight loss occurred was determined at a
heating rate of 10 ꢁC /min under a nitrogen atmosphere.
P5F-BCzVF10
Yield: 71%. 1H NMR (400 MHz, CDCl3): d 8.23 (ArAH, weak
peak of BCzVF units), 8.08 (ArAH, weak peaks of BCzVF
units), 7.86 (ArAH), 7.77-7.62 (ArAH), 7.51 (ArAH), 7.36-
7.30 (ArAH), 7.14 (ArAH), 6.92 (ArAH), 6.78 (ArAH), 4.31
(m, CH2 of BCzVF units), 2.02 (m, CH2 of 5F units), 1.59 (s,
CH3), 1.18-0.72 (m, CH2 and CH3). Anal. Calcd: H, 8.25; C,
84.83. Found: H, 8.31; C, 84.72.
ent conditions using a Keithley 2400/2000 current/voltage
source unit with a calibrated silicon photodiode.
RESULTS AND DISCUSSION
Synthesis and Characterization of the Polymers
The synthesis of monomers and polymers are illustrated in
Scheme 1. Compound 4 was synthesized with a total yield
more than 60% beginning from 2,7-Dibromo-9,9-bis(4-flu-
Measurement and Characterization
1H NMR spectra were recorded on a Bruker AV300 or
AV400 NMR spectrometer. Mass spectra were obtained on a
LDI-1700 matrix-assisted laser desorption/ionization time-
of-flight (MALDI TOF) mass spectrometer (American Linear
Scientific). Gel permeation chromatography (GPC) was per-
formed by a Waters 410 instrument with polystyrene as
standard and THF as eluent. The elemental analysis was per-
formed using a Bio-Radele mental analysis system. The UV/
vis absorption and PL spectra were obtained on a Perkin–
Elmer Lambda 35 UV/vis spectrometer and a Perkin–Elmer
LS50B luminescence spectrometer, respectively. The cyclic
voltammetry was recorded on an EG&G model 283 potentio-
stat/galvanostat system at room temperature using a Ag/
AgCl electrode as the reference electrode, a platinum wire as
the auxiliary electrode, and a platinum plate as the working
electrode in acetonitrile solution of (n-Bu)4NClO4 (0.1 M)
with the scan rate of 100 mV/s. Thermal properties of the
polymers were obtained using Perkin–Elmer DSC7 and TGA7
equipment at a heating/cooling rate of 10 ꢁC/min under a
nitrogen atmosphere.
oro-3-(trifluoromethyl)-phenyl)fluorene.
The
monomers
BCzVF was synthesized by Horner-Emmons coupling reac-
tion in a yield of 60%. All the polymers were synthesized by
the nucleophilic displacement reaction as the traditional
PAEs. Compared with the Suzuki or Yamamoto coupling reac-
tions, their purification process is very simple, and there is
no need to use chromatography or other special techniques
to remove metal catalyst residues. As shown in Scheme 1, 5F
and BCzVF were attached to the main chains of poly(aryl
ether)s through two phenyl rings at the 9-position of the
central fluorene unit. Due to the sp3 characteristic of the
bridge carbon (9-position) of fluorene, all fluorophores
locate nearly orthogonally to the poly(aryl ether)s main
chain, and the main chain of poly(aryl ether)s primarily
serves as a skeleton, and the optical properties mainly
depend on the side chains. The orthogonally linkage also
leads to a big steric hindrance that will reduce the p-p stack-
ing of polymer chains and depressing the crystalline tend-
ency of polymers. The monomer molar feed ratios of the
BCzVF units to the pentafluorene units are 0:100, 1:100,
3:100, 5:100, and 10:100, and the corresponding polymers
are referred to as P5F, P5F-BCzVF1, P5F-BCzVF3, P5F-
BCzVF5, and P5F-BCzVF10, respectively. The actual ratios of
the BCzVF units to 5F units in the resulting polymers were
estimated by 1H NMR spectra and the results are in good
agreement with the monomer feed ratios.
Device Fabrication and Characterization
PLEDs were fabricated with
a configuration of ITO/
PEDOT:PSS/polymers/Ca/Al. The poly(styrene sulfonic acid)
doped poly(ethylenedioxythiophene) (PEDOT:PSS) layer was
spin-coated directly onto the cleaned IꢁTO at 3000 rpm for
60 s and then baked for 30 min at 120 C to give an approx-
imate thickness of 50 nm. Then the polymer layer (ꢂ100
nm) was spin-coated on to the PEDOT:PSS/ITO coated glass
substrate in fresh toluene solution (20 mg/mL) under ambi-
ent atmosphere. Finally a 10 nm thick calcium layer and a
100 nm thick aluminum layer were deposited by thermal
sublimation under a vacuum level of 10ꢀ4 Torr. The electro-
luminescence (EL) spectra and current-voltage and bright-
ness-voltage curves of devices were measured under ambi-
Gel permeation chromatography (GPC) revealed the weight-
average molecular weight (Mw) of (3.7–23.8) ꢃ 104 with
polydispersities (Mw/Mn) of 1.5–2.3 for the five polymers as
shown in Table 1. The thermal properties of these five
copolymers by thermogravimetric analysis (TGA) and differ-
ential scanning calorimetry (DSC) were investigated with a
scan rate of 10 ꢁC/min under nitrogen atmosphere. As
shown in Figure 1 and Table 1, all polymers are thermally
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TABLE 2 Optical Properties of Compounds 5F and BCzVF
kabs, max
(nm)a
kPL, max
(nm)a
UFL
(%)b
FWHM
(nm)c
Compound
5F
370
405 (425)
413 (436)
445 (472)
95
59
48
49
BCzVF
a
Solution spectra were measured in toluene with a concentration of
10ꢀ5 M.
b
Fluorescence quantum efficiency (UFL) was measured in toluene with
a concentration of 10ꢀ7 M and 9,10-diphenylanthracene (U ¼ 0.9) as the
standard.
c
Full width at half-maximum.
Figure 3 presents the absorption spectra and PL spectra of
P5F-BCzVFs in toluene solution. The absorption spectra of
P5F-BCzVFs are identical to P5F, which demonstrate that the
absorption of all the polymers mainly originate from the
absorption of 5F units, perhaps due to the low amounts of
BCzVF units in the polymers. The PL spectra of P5F-BCzVFs
in solution show that incomplete energy transfer happened
from the 5F units to BCzVF units. With increasing BCzVF
content in P5F-BCzVFs, the relative intensity of the deep
blue emission from 5F becomes weaker gradually, and the
emission peak is red-shifted as well.
FIGURE 1 TGA curves of the polymers P5F, P5F-BCzVF1, P5F-
BCzVF3, P5F-BCzVF5, P5F-BCzVF10.
stable and have the onset decomposition temperatures (Td)
of about 420 ꢁC in N2. DSC data indicate that the polymer
P5F exhibits a glass transition temperature at 84 ꢁC, which
46
ꢁ
is higher than that of poly(9,9-dicotylfluorene) (75 C). We
did not find any phase transition signals during repeated
heating/cooling DSC cycles for P5F-BCzVFs from room tem-
ꢁ
perature to 300 C. In addition, all the polymers are soluble
The absorption spectra of P5F-BCzVFs in film (Fig. 4) are
similar to those in solution (Table 3). Unlike their toluene
solutions, even for P5F-BCzVF1, the intensity of the emission
from 5F is already suppressed significantly in thin film.
These results clearly indicate that much more efficient Fo¨r-
ster energy transfer happen in film compared to dilute solu-
tion. With the increasing of BCzVF content, the emission
from 5F units is quenched completely, and their PL spectra
are similar to that of BCzVF, suggesting that the PL emission
of P5F-BCzVFs in thin film is majorly from BCzVF.
in common solvents such as dichloromethane, chloroform,
toluene, and tetrahydrofuran.
Optical Properties
The absorption and PL spectra of the monomers are shown
in Figure 2, and the spectral data are summarized in Table 2.
In toluene solution, 5F and BCzVF exhibited the absorption
maxima at 370 and 405 nm, respectively. The PL emission
peak of BCzVF spectrum is at 445 nm while 5F’s emission
peak is at 413 nm. The full width at half-maximum (FWHM)
value of BCzVF is only about 49 nm, and the PL quantum
yields of BCzVF is 0.59 relative to 9,10-diphenylanthracene
in cyclohexane (Uf ¼ 0.9). In addition, as shown in Figure 2,
the emission spectrum of 5F and the absorption spectrum of
BCzVF display a good overlap, which will facilitate efficient
energy transfer from 5F to BCzVF.
We also studied spectral stability of P5F-BCzVFs after ther-
mal annealing at 200 ꢁC under vacuum for 10 h. As shown
in Figure 5, different from polyfluorene,47 the PL spectra of
P5F-BCzVFs are almost same before and after thermal
annealing, indicating their excellent spectral stability.
FIGURE 2 Normalized absorption and PL spectra of 5F and
FIGURE 3 Normalized absorption and PL spectra of the poly-
BCzVF in toluene.
mers in toluene.
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TABLE 3 Optical Properties of the Polymers
kabs, max (nm)b
kPL, max (nm)c
FWHM
(nm)a
Polymer
Solution Film Solution Film
P5F
52
55
58
60
369
370
370
370
370
370
370
370
370
370
413 (435) 419 (442)
413 (437) 443 (470)
415 (437) 449 (475)
439 (415) 449 (472)
442 (415) 449 (474)
P5F-BCzVF1
P5F-BCzVF 3
P5F-BCzVF 5
P5F-BCzVF 10 59
a
Full width at half-maximum of PL spectra of the polymers in film.
Evaluated in 10ꢀ5 M toluene solution.
b
c
Prepared by spin-coating from a toluene solution.
further investigated the electrochemical behavior of the poly-
mer thin films spin-coated on a glassy carbon electrode. The
polymers show the similar electrochemical properties of 5F,
perhaps also due to the low contents of BCzVF units. As
shown in Figure 6, the LUMO and HOMO energy levels of
BCzVF lie between those of 5F, suggesting favorable charge
trapping of BCzVF units for P5F-BCzVF will happen in the EL
process.48
FIGURE 4 Normalized absorption and PL spectra of the poly-
mers in the solid state.
Electrochemical Properties
The electrochemical properties of monomers 5F and BCzVF
were investigated by means of cyclic voltammetry (CV) with
a typical three-electrode cell using ferrocene as the internal
standard (Fig. 6). From the onset oxidation and reduction
potentials in the cyclic voltammogram, the highest occupied
molecular orbital (HOMO) and the lowest unoccupied molec-
ular orbital (LUMO) energy levels of the monomers can be
estimated. 5F and BCzVF show the HOMO levels of ꢀ5.8 and
ꢀ5.5 eV, LUMO levels of ꢀ2.1 and ꢀ2.3 eV, respectively. We
Electroluminescent Properties
The PLEDs based on P5F-BCzVFs were fabricated with a sin-
gle-layer configuration of ITO/(PEDOT:PSS)/polymer/Ca/Al,
and all the EL data are summarized in Table 4. As shown in
Figure 7, the EL spectrum of the device based on P5F is
FIGURE 5 Normalized film-state PL spectra of the polymers before (solid) and after annealing at 200 ꢁC for 10 h (dash) under
vacuum.
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dinates fall in the pure blue region. In addition, they show
narrow EL spectra with the FWHM smaller than 60 nm, indi-
cating their excellent color purity. Moreover, their EL spectra
are voltage-independent. Taking P5F-BCzVF3 as an example,
its EL spectra are very stable with the same CIE coordinates
of (0.15, 0.15) from 6 to 10 V (Fig. 8). For P5F-BCzVF10, its
emission peak is at 479 nm with the corresponding CIE
coordinate at (0.16, 0.21), which even deviated from the
pure blue region.
The luminous efficiency-current density curves of the poly-
mers are shown in Figure 9. In comparison with the low lu-
minous efficiency (0.61 cd/A) of P5F, P5F-BCzVF1, P5F-
BCzVF3, P5F-BCzVF5, and P5F-BCzVF10 exhibit much higher
luminous efficiencies up to 2.15 cd/A, demonstrating the
advantage of dopant-host systems. The turn-on voltages are
increased from 4.2 V to 5.5 V, with the increasing of BCzVF
content in the polymers, perhaps due to the charge trapping
of the dopant units.49 The maximum brightness of all the
P5F-BCzVFs devices was in the range of 2342–4035 cd/m2,
also much higher than that of the P5F device (875 cd/m2).
The enhanced performance of P5F-BCzVFs relative to P5F
should be attributed to both the energy transfer and the
charge trapping from the 5F host to the BCzVF dopant as
other highly efficient EL polymers with dopant-host systems.
Among these P5F-BCzVF copolymers, the device based on
P5F-BCzVF3 (Fig. 10) is the best one, which emits pure blue
FIGURE 6 LUMO and HOMO energy levels of 5F and BCzVF.
similar to its PL spectrum with the emission peak at 420 nm
and the CIE coordinate (0.16, 0.10), which is also located in
the deep blue region. With the increasing of BCzVF content,
the EL spectra are red shifted gradually. Even for P5F-
BCzVF1, the emission from 5F is nearly complete quenched
due to efficient energy transfer. The EL emissions of P5F-
BCzVF1, P5F-BCzVF3, and P5F-BCzVF5 exhibit blue emission
peaks around 440-460 nm and their corresponding CIE coor-
TABLE 4 EL Performance Data of the Devices with the Configuration of ITO/PEDOT: PSS/Polymer/Ca/Al
a
b
c
Polymer
kEL, max (nm)
Von (V)
Lmax (cd/m2)
LEmax (cd/A)
CIE (x, y)
FWHMd (nm)
P5F
420 (442)
445 (470)
447 (471)
448 (476)
479 (453)
4.4
4.2
4.2
5.0
5.5
875
2472
3576
2342
4035
c
0.61
1.66
2.15
1.99
1.44
0.16, 0.10
0.15, 0.12
0.15, 0.15
0.15, 0.16
0.16, 0.21
48
49
54
57
63
P5F-BCzVF1
P5F-BCzVF3
P5F-BCzVF5
P5F-BCzVF10
a
Onset voltage at the brightness of 1 cd/m2.
Maximum brightness.
Maximum luminous efficiency.
Full width at half-maximum.
b
d
FIGURE 8 Normalized EL spectra of ITO/PEDOT/P5F-BCzVF3/Ca/
FIGURE 7 Normalized EL spectra of the polymers.
Al at different voltages.
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with the CIE coordinates of (0.15, 0.15), a maximum lumi-
nous efficiency of 2.15 cd/A, and a maximum brightness of
3576 cd/m2. In addition, the EL spectra of P5F-BCzVFs ex-
hibit good color stability at different voltage. All of these
results demonstrate that these highly efficient, color-stable,
pure blue emissive poly(aryl ether)s are promising candi-
dates for blue EL polymers.
This work was supported by the Chang chun Institute of
Applied Chemistry, Chinese Academy of Sciences (CX07QZJC-
24), the National Natural Science Foundation of China
(No.60977026), the Science Fund for Creative Research Groups
(No.20921061), and the 973 Project (2009CB623601).
REFERENCES AND NOTES
1 Burroughes, J. H.; Bradley, D. D. C.; Brown, A. R.; Marks, R.
N.; Mackay, K.; Friend, R. H.; Burns, P. L.; Holmes, A. B. Nature
1990, 347, 539–541.
FIGURE 9 Current density-luminous efficiency curves of the
devices based on the polymers.
2 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 1999, 397, 121–128.
3 Yang, Y.; Heeger, A. J. Nature 1994, 372, 344–346.
4 Cao, Y.; Parker, I. D.; Yu, G.; Zhang, C.; Heeger, A. J. Nature
1999, 397, 414–417.
5 Jenekhe, S. A.; Lu, L.; Alam, M. M. Macromolecules 2001, 34,
7315–7324.
6 Zhu, Y.; Alam, M. M.; Jenekhe, S. A. Macromolecules 2002,
35, 9844–9846.
7 Kraft, A.; Grimsdale, A. C.; Holmes, A. B. Angew Chem Int Ed
1998, 37, 402–428.
8 Mikroyannidis, J. A.; Fakis, M.; Spiliopoulos, I. K. J Polym Sci
Part A: Polym Chem 2009, 47, 3370–3379.
9 Ying, L.; Ye, T.; Yu, C.; Ma, D.; Chen, Z.; Dai, Y.; Li, Y. J
Polym Sci Part A: Polym Chem 2010, 48, 5930–5937.
FIGURE 10 Voltage-brightness-current density plots of the de-
10 Grimsdale, A. C.; Chan, K. L.; Martin, R. E.; Jokisz, P. G.;
Holmes, A. B. Chem Rev 2009, 109, 897–1091.
vice based on the polymer P5F-BCzVF3.
11 Lei, T.; Luo, J.; Wang, L.; Ma, Y.; Wang, J.; Cao, Y.; Pei, J.
New J Chem 2010, 34, 699–707.
light with the CIE coordinates (0.15, 0.15), a remarkable
maximum brightness of 3576 cd/m2, a luminous efficiency
up to 2.15 cd/A.
12 Kim, H.; Schulte, N.; Zhou, G.; Mullen, K.; Laquai, F. Adv
Mater 2011, 23, 894–897.
¨
13 McGehee, M. D.; Bergstedt, T.; Zhang, C.; Saab, A. P.;
O’Regan, M. B.; Bazan, G. C.; Srdanov, V. I.; Heeger, A. J. Adv
Mater 1999, 11, 1349–1354.
CONCLUSIONS
14 Li, A.; Li, Y.; Cai, W.; Zhou, G.; Chen, Z.; Wu, H.; Wong, W.
Y.; Yang, W.; Peng, J.; Cao, Y. Org Electron 2010, 11, 529–534
In summary, we have designed and synthesized a series of
novel poly(aryl ether)s (P5F-BCzVFs) with dopant-host sys-
tems containing pentafluorene as the host and BCzVF as the
dopant by a facile, metal-free condensation polymerization.
The PL spectra of the polymers in film indicated that color
tuning can be realized through efficient energy transfer from
pentafluorene to BCzVF. And all the polymers showed good
15 Scherf, U.; List, E. J. W. Adv Mater 2002, 14, 477–487.
16 Neher, D. Macromol Rapid Commun 2001, 22, 1366–1385.
17 Bernius, M. T.; Inbasekaran, M.; O’Brien, J.; Wu, W. S. Adv
Mater 2000, 12, 1737–1750.
18 Marsitzky, D.; Vestberg, R.; Blainey, P.; Tang, B. T.; Hawker,
C. J.; Carter, K.R. J Am Chem Soc 2001, 123, 6965–6972.
ꢁ
emission color stability even after annealing at 200 C under
19 Lee, J.; Cho, H. J.; Jung, B. J.; Cho, N. S.; Shim, H. K. Mac-
vacuum for 10 h. Their EL emission peaks are located
around 440–460 nm with a narrow FWHM below 60 nm,
both of which endowed these poly(aryl ether)s with sensi-
tive blue emissions to human eyes and good color purity. In
comparison with P5F, the luminous efficiencies of the EL
devices based on P5F-BCzVFs are significantly improved. The
devices based on P5F-BCzVF3 exhibit pure blue emissions
romolecules 2004, 37, 8523–8529.
20 Wong, W. Y.; Liu, L.; Cui, D.; Leung, L. M.; Kwong, C.F.; Lee,
T. H.; Ng, H. F. Macromolecules 2005, 38, 4970–4976.
21 Wong, W. Y. Coord Chem Rev 2005, 249, 971–997.
22 Wong, W. Y.; Ho, C. L. Coord Chem Rev 2009, 253,
1709–1758.
23 Montilla, F.; Mallavia, R. Adv Funct Mater 2007, 17, 71–78.
3918
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2011, 49, 3911–3919

WWW.POLYMERCHEMISTRY.ORG
ARTICLE
24 Zeng, G.; Yu, W.-L.; Chua, S.-J.; Huang, W. Macromolecules
36 Yang, J.; Jiang, C.; Zhang, Y.; Yang, R.; Yang, W.; Hou, Q.;
2002, 35, 6907–6914.
Cao, Y. Macromolecules 2004, 37, 1211–1218.
25 Becker, K.; Lupton, J. M.; Feldmann, J.; Nehls, B. S.; Gal-
brecht, F.; Gao, D.; Scherf, U. Adv Funct Mater 2006, 16,
364–370.
37 Yang, R.; Tian, R.; Yan, J.; Zhang, Y.; Yang, J.; Hou, Q.; Yang,
W.; Zhang, C.; Cao, Y. Macromolecules 2005, 38, 244–253.
38 Tang, R.; Tan, Z. A.; Li, Y.; Xi, F. Chem. Mater. 2006, 18,
26 Gaal, M.; List, E. J. W.; Scherf, U. Macromolecules 2003, 36,
1053–1061.
4236–4337.
39 Su, H. J.; Wu, F. I.; Shu, C. F. Macromolecules 2004, 37,
27 Setayesh, S.; Marsitzky, D.; Mullen, K. Macromolecules
¨
7197–7202.
2000, 33, 2016–2020.
40 Sun, M.; Niu, Q.; Yang, R.; Du, B.; Liu, R.; Yang, W.; Peng,
28 Jacob, J.; Sax, S.; Piok, T.; List, E. J. W.; Grimsdale, A. C.;
J.; Cao, Y. Eur Polym J 2007, 43, 1916–1922.
Mullen, K. J Am Chem Soc 2004, 126, 6987–6995.
¨
41 Guo, X.; Cheng, Y.; Xie, Z.; Geng, Y.; Wang, L.; Jing, X.;
Wang, F. Macromol Rapid Commun 2009, 30, 816–825.
29 Liu, J.; Cao, J.; Shao, S.; Xie, Z.; Cheng, Y.; Geng, Y.; Wang,
L.; Jing, X.; Wang, F. J Mater Chem 2008, 18, 1659–1666.
42 Nielsen, K. T.; Bechgaard, K.; Krebs, F. C. Macromolecules
30 Huang, S. T.; Liaw, D. J.; Hsieh, L. G.; Chang, C. C.; Leung,
M. K.; Wang, K. L.; Chen, W. T.; Lee, K. R.; Lai, J. Y.; Chan, L.
H.; Chen, C. T. J Polym Sci Part A: Polym Chem 2009, 47,
6231–6245.
2005, 38, 658–659.
43 Craig, M. R.; de Kok, M. M.; Hofstraat, J. W.; Schenning, A.
P. H. J.; Meijer, E. W. J Mater Chem 2003, 13, 2861–2862.
44 Jiang, G.; Yao, B.; Geng, Y.; Cheng, Y.; Xie, Z.; Wang, L.;
Jing, X.; Wang, F. Macromolecules 2006, 39, 1403–1409.
31 Lee, J. I.; Klaerner, G.; Davey, M. H.; Miller, R. D. Synth.Met.
1999, 102, 1087–1088.
45 Hay, A. S. Prog Polym Sci 1995, 24, 45–80.
32 Liu, J.; Min, C.; Zhou, Q.; Cheng, Y.; Wang, L.; Ma, D.; Jing,
46 Lee, J. H.; Hwang, D. H. Chem Commun 2003, 2836–2837.
X.; Wang, F. Appl Phys Lett 2006, 88, 083505–083507.
47 Katsis, D.; Geng, Y. H.; Ou, J. J.; Culligan, S. W.; Trajkovska,
A.; Chen, S. H.; Rothberg, L. J. Chem Mater 2002, 14,
1332–1339.
33 Liu, J.; Tu, G.; Zhou, Q.; Cheng, Y.; Geng, Y.; Wang, L.; Ma,
D.; Jing, X.; Wang, F. J Mater Chem 2006, 16, 1431–1438.
34 Huang, F.; Hou, L.; Wu, H.; Wang, X.; Shen, H.; Cao, W.;
48 Suzuki, H.; Hoshino, S. J Appl Phys 1996, 79, 8816–8822.
Yang, W.; Cao, Y. J Am Chem Soc 2004, 126, 9845–9853.
35 Herguth, P.; Jiang, X.; Liu, M. S.; Jen, A. K.-Y. Macromole-
49 Uchida, M.; Adachi, C.; Koyama, T.; Taniguchi, Y. J. Appl
cules 2002, 35, 6094–6100.
Phys 1999, 86, 1680–1687.
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