Fluorene- and benzimidazole-based blue light-emitting copolymers: Synthesis, photophysical properties, and PLED applications

Article abstract of DOI:10.1002/pola.25984

Blue light-emitting materials are receiving considerable academic and industrial interest due to their potential applications in optoelectronic devices. In this study, blue light-emitting copolymers based on 9,9'-dioctylfluorene and 2,2'-(1,4-phenylene)-bis(benzimidazole) moieties were synthesized through palladium-catalyzed Suzuki coupling reaction. While the copolymer consisting of unsubstituted benzimidazoles (PFBI0) is insoluble in common organic solvents, its counterpart with N-octyl substituted benzimidazoles (PFBI8) enjoys good solubility in toluene, tetrahydrofuran, dichloromethane (DCM), and chloroform. The PFBI8 copolymer shows good thermal stability, whose glass transition temperature and onset decomposition temperature are 103 and 428 °C, respectively. Its solutions emit blue light efficiently, with the quantum yield up to 99% in chloroform. The electroluminescence (EL) device of PFBI8 with the configuration of indium-tin oxide/poly(ethylenedioxythiophene): poly(styrene sulfonic acid)/PFBI8/1,3,5-tris(1-phenyl-1H-benzimidazole-2-yl) benzene/LiF/Al emits blue light with the maximum at 448 nm. Such unoptimized polymer light-emitting diode (PLED) exhibits a maximum luminance of 1534 cd/m² with the current efficiency and power efficiency of 0.67 cd/A and 0.20 lm/W, respectively. The efficient blue emission and good EL performance make PFBI8 promising for optoelectronic applications. 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 A conjugated polymer based on 9,9'-dioctylfluorene and N-octyl substituted 2,2'-(1,4-phenylene)- bis(benzimidazole) moieties (PFBI8) was synthesized. Its solutions emit blue light efficiently, with the quantum yield up to 99% in chloroform. It is also morphologically and thermally stable, with glass transition temperature and decomposition temperature as high as 103 and 428 °C, respectively. The polymer light-emitting diode using PFBI8 as the active emitting layer exhibits blue emission (448 nm) with the maximum luminance, current efficiency and power efficiency of 1534 cd/m², 0.67 cd/A, and 0.20 lm/W, respectively. Copyright

Full text of DOI:10.1002/pola.25984

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Fluorene- and Benzimidazole-Based Blue Light-Emitting Copolymers:
Synthesis, Photophysical Properties, and PLED Applications
Haifeng Zhu,1 Hui Tong,2 Yongyang Gong,1 Shiyang Shao,2 Chunmei Deng,3 Wang Zhang
Yuan,1 Yongming Zhang1
1School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, No. 800, Dongchuan Road, Shanghai 200240,
China
2State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of
Sciences, 5625 Renmin Street, Changchun 130022, China
3Zhong Guan Cun, Bei Yi Jie 2, Haidian District, Chinese Chemical Society, Beijing 100190, China
Correspondence to: Y. Zhang (E-mail: ymzsjtu@yahoo.com.cn) or W. Z. Yuan (E-mail: wzhyuan@sjtu.edu.cn)
Received 17 November 2011; accepted 24 January 2012; published online 23 February 2012
DOI: 10.1002/pola.25984
ABSTRACT: Blue light-emitting materials are receiving consider-
able academic and industrial interest due to their potential appli-
cations in optoelectronic devices. In this study, blue light-
emitting copolymers based on 9,90-dioctylfluorene and 2,20-(1,4-
phenylene)-bis(benzimidazole) moieties were synthesized
through palladium-catalyzed Suzuki coupling reaction. While the
copolymer consisting of unsubstituted benzimidazoles (PFBI0) is
insoluble in common organic solvents, its counterpart with N-
octyl substituted benzimidazoles (PFBI8) enjoys good solubility
in toluene, tetrahydrofuran, dichloromethane (DCM), and chloro-
form. The PFBI8 copolymer shows good thermal stability,
whose glass transition temperature and onset decomposition
temperature are 103 and 428 ꢀC, respectively. Its solutions emit
blue light efficiently, with the quantum yield up to 99% in chlo-
roform. The electroluminescence (EL) device of PFBI8 with the
configuration of indium-tin oxide/poly(ethylenedioxythiophene):-
poly(styrene sulfonic acid)/PFBI8/1,3,5-tris(1-phenyl-1H-benzimid-
azole-2-yl)benzene/LiF/Al emits blue light with the maximum at
448 nm. Such unoptimized polymer light-emitting diode (PLED)
exhibits a maximum luminance of 1534 cd/m2 with the current
efficiency and power efficiency of 0.67 cd/A and 0.20 lm/W,
respectively. The efficient blue emission and good EL
performance make PFBI8 promising for optoelectronic applica-
C
V
tions.
2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym
Chem 50: 2172–2181, 2012
KEYWORDS: benzimidazole; conjugated polymers; copolymeriza-
tion; light-emitting diodes (LED)
INTRODUCTION Conjugated polymers have received increas-
ing attentions due to their potential applications in such
optoelectronic devices as organic light-emitting diodes
(OLEDs),1–4 solid-state lasers,5,6 chemosensors and biosen-
sors,7 organic field effect transistors,8–10 photovoltaic devi-
ces,11–13 and so on. Furthermore, their solution-processable
property affords the possibility for the fabrication of low-
cost large area electronics. Particularly, emissive conjugated
polymers are attracting considerable interests due to their
light-emitting capability, solution processability, film-forming
property, and morphology stability,14–16 which render them
suitable for the fabrication of flexible, large-area OLEDs via
spin-coating, screen, and/or inkjet printing.
ces in full-color display applications or as hosts for exother-
mic energy transfer to lower-energy fluorophores.18–20 Com-
pared with red and green-lighting PLEDs, the development
of stable blue light-emitting PLEDs21 remains the subject of
intense research in both academia and industry.22
Among various known blue emitters, polyfluorenes (PFs) and
derivatives have been widely researched as the most promising
blue light-emitting materials due to their high luminescence
efficiency, excellent chemical, and thermal stabilities.23–25 Par-
ticularly, poly(dialkylfluorene)s, such as poly(9,90-dioctylfluor-
ene) (PFO), have played a leading role in the evolution of
commercial technology.26 Furthermore, PFO has good hole-
transport properties, whose hole mobility is on the order of
10ꢁ3 cm2/Vs. However, its electron-transport capability is
poor.27 To improve the electron transport properties of PFs,
varying electron-withdrawing segments such as oxadizole,28,29
triazole,30 quinoxaline,31 pyridine,32 and dibenzo[a,c]phena-
zine27 have been introduced into the PFs backbone.
Polymer light-emitting diodes (PLEDs) show potential appli-
cations in the next generation of flexible, low-cost, and high-
efficiency flat-panel displays and lighting technologies.3,17 Ef-
ficient blue light-emitting PLEDs are of particular interest
because they are highly desirable for use as blue light sour-
C
V
2012 Wiley Periodicals, Inc.
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SCHEME 1 Synthetic routes to copolymers PFBI0 and PFBI8.
Imidazole ring is a noncenter symmetrical structure with elec-
tron deficient characteristic. Imidazole and its imidazolium cat-
ion containing conjugated oligomers and polymers exhibit in-
triguing optical properties and can be used as chemosensors
and biosensors.33 Suitable conjugation of imidazole with elec-
tron-donating moieties may produce dyads with excellent intra-
molecular charge transfer (ICT) property. Benzimidazole-based
molecules, such as 1-methyl-2-(anthryl)-inidazo[4,5-f][1,10]-
phenanthroline34 and 1,3,5-tris(1-phenyl-1H-benzimidazole-2-
yl)benzene (TPBI) are reported to show large bandgap and
effective electron-transport property. Thus, it is expected that
combination of fluorene and benzimidazole moieties can gener-
ate new polymers with high emission efficiency and effective
charge transport property. However, due to the rigid skeleton
and strong intermolecular hydrogen bonding, benzimidazole-
and glass transition temperature are as high as 428 and
103 ꢀC, respectively. It emits blue light in solvents with a
quantum yield up to 99% in CHCl3. The PLED device with
suitable configuration of PFBI8 exhibits a maximum lumi-
nance of 1534 cd/m2 with the current efficiency and power
efficiency of 0.67 cd/A and 0.20 lm/W, respectively.
RESULTS AND DISCUSSION
Synthesis and Characterization
The synthetic routes to monomers and copolymers are outlined
in Scheme 1. All reactions proceeded smoothly and desired
products were obtained successfully in high yields (65–92%).
The products were characterized spectroscopically, with satis-
factory data obtained. The synthesis of N-octyl substituted 2,20-
(1,4-phenylene)-bis(benzimidazole) (7) started with commer-
cially available 2-nitroaniline (1). To obtain compound 2, it is
essential to add less than 1 equiv of N-bromosuccinimide (NBS)
to prevent the formation of dibromination products which are
difficult to remove.38 Compound 5 was synthesized according to
the previously reported approach.39 The reaction comprises two
stages: at the first stage, intermediate bis(Schiff bases) is
obtained by low-temperature solution condensation of 4-bromo-
1,2-benzenediamine with terephthalaldehyde under anhydrous
and anaerobic conditions; at the second stage, 5 is attained by
cyclodehydrogenation of bis(Schiff base) under air using FeCl3 as
catalyst. For this reaction, mild reaction conditions rather than
such strong acid as polyphosphoric acid at elevated temperature
were chosen to avoid the CABr bond breakage.
based compounds usually exhibit serious molecular aggregation
36
and poor solubility. Previously, Yoshino35 and Inganas pro-
€
posed the alkyl chain decoration method to improve the solubil-
ity of rigid conjugated poly(thiophene)s. Therefore, substitution
of the hydrogen atoms in benzimidazole by alkyl chains is
expected to not only suppress the molecular interaction and
aggregation but also improve its solubility.37
In this study, fluorene- and benzimidazole-based copolymers
were designed and synthesized through facile Suzuki
coupling of 9,9-dioctylfluorene-2,7-diboronic acid with
unsubstituted or N-octyl-substituted 2,20-(1,4-phenylene)-
bis(benzimidazole), yielding copolymers PFBI0 and PFBI8,
respectively (Scheme 1). While PFBI0 shows poor solubility
in common solvents because of intense intramolecular and
intermolecular interactions, PFBI8 exhibits excellent solubil-
ity due to the diminished interactions. Also, PFBI8 enjoys
good thermal stability, whose decomposition temperature
Theoretically, compound 5 has three isomers due to 1,3-shift of
the NH hydrogen in the imidazole ring (Chart 1), which is con-
firmed by the 1H NMR spectrum. As depicted in Figure 2(A),
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CHART 1 NH exchange-induced isomers of the benzimidazole
ring and their N-alkyl-substituted counterpart.
FIGURE 2 1H NMR spectrum of 7 in CDCl3. The solvent peak is
marked with asterisk.
two singlet peaks corresponding to NH resonance are
observed at d 13.26 and 13.22. Meanwhile, protons Ha and
Hc (see Chart 1) both exhibit two separate peaks at d 7.88/
7.71 and 7.63/7.51 [see the magnified inset in Fig. 1(A)],
respectively, thus duly verifying the existence of the isomers.
as blocking agents at the end of the polymerizations. Poly-
merization between 5 and 10 resulted in toluene soluble
PFBI0 in the schlenk tube after 48 h. However, the copoly-
mer became insoluble in common organic solvents [dichloro-
methane (DCM), tetrahydrofuran (THF), CHCl3, N,N-dimethyl-
formamide (DMF)] after precipitation, which should be
caused by the strong intramolecular and intermolecular
interactions of the polymer chains.
1
It is also proved by the H NMR spectrum [Fig. 1(B)] of 5 in
DMSO/trifluoroacetic acid (TFA) mixture, where emerged
peaks at d 8.02 and 7.62 are observed for Ha and Hc, respec-
tively, due to the restricted tautomeric change of the benzim-
idazole ring by TFA.40
To enhance the solubility of the rigid conjugated polymers,
flexible alkyl chains are often introduced as pendants to
reduce the intramolecular and intermolecular interactions
between polymer chains and promote their solvating
power.35–37 Herein, N-octyl substituents were incorporated
into the imidazole ring to destroy the hydrogen bonds. The
resulting copolymer PFBI8 was successfully obtained in
moderate yield (65%) and molecular weight (Mw ¼ 14,500)
with the polydispersity index of 2.1. Such polymer shows
expected good solubility in toluene, THF, chloroform, DMF,
and so on. The chemical structure of PFBI8 was verified by
1H NMR and 13C NMR (see Experimental Section for details).
Thermal properties of PFBI8 were evaluated by differential
NaH-promoted deprotonation of the NH groups in bis(benzi-
midazole) 5 and subsequent addition of 1-bromooctane and
substitution by N-octyl group offered 7 in satisfactory yield.
Figure 2 shows the 1H NMR spectrum of 7 in CDCl3. The
0
0
separated peaks at d 7.97/7.59 and 7.68/7.32 for Ha and Hc
indicate that there are also isomers, namely, Form A and
Form B (Chart 1). Through integration of such peaks, the ra-
tio of Form A to Form B is estimated to be ꢂ 1:1, suggesting
the random proton exchange process.
The copolymers were synthesized via the Pd(PPh3)4-cata-
lyzed Suzuki coupling reaction in toluene (Scheme 1). Phe-
nylboronic acid and bromobenzene were added in sequence
FIGURE 1 1H NMR spectra of 5 in (A) DMSO-d6 and (B) DMSO-d6/TFA mixture.
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PFBI8 is composed of electron rich fluorene and electron
deficient imidazole moieties, which readily offer ICT charac-
teristic for the copolymer. Therefore, the absorption and
emission properties of PFBI8 in varying solvents were stud-
ied. As shown in Figure 4(A), the absorption maxima (kabs
)
associated with the p-p* transition of the backbone of PFBI8
in toluene, THF, and CHCl3 are 358, 357, and 354 nm,
respectively, exhibiting little solvent effect. Such absorption
bands are much blue shifted compared with those of PFO in
toluene (387 nm) and chloroform (391 nm),27 suggesting
the much shorter effective conjugation length of PFBI8 than
PFO. Meanwhile, the slight difference of the absorptions also
reveals the similar ground-state electronic structures of
PFBI8 in different solvents, indicative of a small dipole
moment associated with the ICT transition. The absorption
peak of its solid thin film is 363 nm, which is slightly red-
shifted when compared to those in solvents due to the inter-
molecular interactions.
Figure 4(B) depicts the solution and film emission spectra of
PFBI8. With increased solvent polarity, the emission peak of
PFBI8 is shifted from 426 nm in toluene to 430 nm in THF,
and then 435 nm in CHCl3, exhibiting a bathochromic effect.
These emission maxima are comparable or even red-shifted
when compared to those of PFO, which emits at 414/438 and
416/439 nm in toluene and CHCl3,27 respectively, although
PFBI8 is less conjugated than PFO (see absorption part). Such
phenomenon should be ascribed to the ICT effect of PFBI8.
FIGURE 3 TGA and DSC thermograms of PFBI8 under nitrogen
at a scanning rate of 20 ꢀC/min.
scanning calorimetry (DSC) and thermogravimetric analysis
(TGA). As can be seen from Figure 3, the glass transition
temperature (Tg) and onset decomposition temperature (Td)
of PFBI8 are 103 and 428 ꢀC, respectively, indicative of its
excellent morphological and thermal stability. Such perform-
ances are even better than those of PFO homopolymer,
The thin film emission maximum of PFBI8 is further red-
shifted to 450 nm due to aggregation and interaction of the
molecules. It is noticeable that the CIE coordinates of the
photoluminescent (PL) emission of the PFBI8 film is (0.15,
0.12), which is quite close to the National Television System
Committee standard blue of (0.14, 0.08). Moreover, no new
long wavelength peak or shoulder emerges for the thin-film
spectrum of PFBI8, which is distinctly different form PFO,
whose thin film shows emission maxima at 435, 460, and
490 nm, corresponding to the 0-0, 0-1 transitions, and exci-
mers, respectively.24(b),27 The lack of long-wavelength exci-
mer emission of PFBI8 suggests that the introduction of
benzimidazole units into the PFO main chain can effectively
depress the intermolecular interactions between fluorene
units, thus favoring the achievement of high-efficiency blue
solid emitters with excellent color purity.
27
ꢀ
whose Tg and Td are 66 and 407 C, respectively. The rela-
tively high Tg and Td values of PFBI8 favored its potential
applications in optoelectronic devices.
Photophysical Properties
As monomer 7 has three isomers, PFBI8 copolymer chains
should include such isomers. To evaluate this stereoisomer
effect on photophysical properties of PFBI8, HOMO, and
LUMO energy levels of 7a–7c (Chart 2) were calculated by
B3LYP/6-31g(d) (Gaussian 09, DFT theory) method. The
HOMO/LUMO levels are ꢁ5.76/ꢁ1.67, ꢁ5.84/ꢁ1.66, and
ꢁ5.90/ꢁ1.66 eV for 7a, 7b, and 7c, respectively, suggesting
their similar electronic structures. Most likely, the result indi-
cates that different PFBI8 molecules have similar photophysi-
cal properties.
CHART 2 Three isomers of 7 and their calculated HOMO/LUMO energy levels and energy gaps (Eg).
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FIGURE 4 (A) Absorption and (B) emission spectra of copolymer PFBI8 in different solvents and in film state. Concentration ¼
10ꢁ6 M; Excitation wavelength ¼ 355 nm.
For quantitatively assessing the emissions, fluorescence
quantum efficiencies (U) of PFBI8 were determined by using
9,10-diphenylanthracene (DPA) as standard (U ¼ 90% in
cyclohexane) according to eq 1:
reference electrodes, respectively. Polymer film was fabri-
cated by dropping the PFBI8 chloroform solution onto the
working electrode. The cyclic voltammogram of PFBI8 film is
shown in Figure 5. The onset oxidation peak is 1.95 eV.
According to the equation of EHOMO ¼ ꢁ(EOX þ 4.4) eV42
with the ferrocene oxidation as the standard, the HOMO level
of PFBI8 is determined to be ꢁ6.35 eV. Meanwhile, from the
film absorption edge of 430 nm, the band gap of PFBI8 is
calculated to be 2.88 eV, thus giving a LUMO level of ꢁ3.47
eV. These HOMO/LUMO energy levels for PFO are ꢁ5.78/
ꢁ2.12, which are much higher than those of PFBI8, suggest-
ing that electron-accepting benzimidazole units lowered the
energy levers of PFO.
ꢀ
ꢁꢀ ꢁꢀ
ꢁ
AST
AP
FP
gP
Up ¼ UST
(1)
FST
gST
where the subscripts ST and p denote the standard and the
polymer solution specimens, respectively. U, A, F, and g are
the fluorescence quantum efficiency, the absorbance at the ex-
citation wavelength, the integral over the emission spectrum,
and the refractive index of the solvent, respectively. To avoid
the aggregation or concentration caused quenching effect, the
absorbance of DPA and PFBI8 solutions lower than 0.05 at
the excitation wavelength (355 nm) must be guaranteed
(herein, 0.026, 0.035, 0.043, and 0.045 for DPA in cyclohex-
ane, TPBI8 in CHCl3, THF, and toluene, respectively).
Electroluminescence
The high-efficiency blue emission and excellent thermal sta-
bility of PFBI8 promoted us to explore its application in
PLEDs. As benzimidazoles possess good electron transport
The results are summarized in Table 1. Clearly, the U value
of PFBI8 in toluene is 35%, which is much lower than that
of PFO in toluene (85%).27 However, it is greatly enhanced
with increasing solvent polarity, with the values being 80%
in THF and almost unity (99%) in chloroform, which are
higher than that of PFO in CHCl3 (79%).25(b) Normally, ICT
luminogens show high-efficiencies in nonpolar solvents and
decreased quantum yields in polar solvents.27,41 The oppo-
site effect of PFBI8 might be ascribed to the populated radia-
tive transitions of the excitons in polar solvents.
TABLE 1 Photophysical Properties of PFBI8a
Solvent
kabs (nm)
kem (nm)
U (%)
PFBI8
Toluene
THF
358
357
354
363
426
35
80
99
–
430
435
450
CHCl3
Film
PFO
Toluene
CHCl3
Film
387
391
389
414, 438
416, 439
85
79b
–
Electrochemical Properties
The electrochemical behavior of PFBI8 was examined by
cyclic voltammetry (CV) using a standard three-electrode
electrochemical cell in 0.1 M tetrabutylammonium hexfluoro-
phosphate in acetonitrile at a scan rate of 50 mV/s. A glassy
carbon electrode, a platinum wire, and an Ag/Agþ (satu-
rated) electrode were used as the working, encounter, and
435, 460, 490
a
The solution quantum efficiency (U) values of PFBI8 were determined
by using 9,10-diphenylanthracene (DPA) (U ¼ 90% in cyclohexane) as
27
standard. All data for PFO are from ref.
.
b
Data from ref. 25(b).
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FIGURE 5 Cyclic voltammogram curve of the PFBI8 film in
0.1 M tetrabutylammonium hexfluorophosphate (TBAPF6) in
acetonitrile at a scan rate of 50 mV/s.
FIGURE 7 Voltage–current density–luminance plots for the
devices with general configurations of ITO/PEDOT:PSS/PFBI8/X:
X ¼ Ca/Al (device I), LiF/Al (device II), and TPBI/LiF/Al (device
III).
property, we thus first constructed an OLED with the config-
uration of indium-tin oxide (ITO)/ poly(ethylenedioxythio-
phene) (PEDOT):poly(styrene sulfonic acid)(PSS)/PFBI8
(100 nm)/Ca/Al (device I) without an electron-transporting
layer, where PFBI8 serves as emitter and PEDOT:PSS works
as hole-injecting and -transporting layers, respectively. The
electroluminescence (EL) spectra of the device under varying
voltages are shown in Figure 6. Clearly, with increased volt-
age, the EL maxima is slightly red-shifted from 444 (11 V) to
452 nm (14 V) with much broader emission. The device per-
formances are given in Figures 7 and 8 and summarized in
Table 2. The turn-on voltage (Von), maximum luminance
(Lmax), maximum current efficiency (CEmax), and power effi-
ciency (PEmax) of the device are 9.3 V, 134 cd/m2, 0.073 cd/
A, and 0.018 lm/W, respectively.
the weakness of Ca metal, a more stable bilayered LiF/Al
cathode was adopted. The resulting ITO/PEDOT:PSS/PFBI8
(100 nm)/LiF/Al device (device II) is turned on at 10.2 V
with the EL maximum of 448 nm (almost identical under
different voltages). Lmax, CEmax, and PEmax of the device are
183 cd/m2, 0.081 cd/A, and 0.023 lm/W, respectively, which
are much better than those of device I.
Devices I and II could produce moderate luminance even
without an electron-transporting layer; however, the low effi-
ciencies suggest the charge transport is not well balanced.
Therefore, to further improve the device performance, elec-
tron-transporting TPBI was utilized to construct the device
with the configuration of ITO/PEDOT:PSS/PFBI8 (50 nm)/
TPBI (50 nm)/LiF/Al (device III). The EL spectra of the
device are peaked at 448 nm [Fig. 6(C)], which is nearly
independent on the operating voltage, indicating a stable
blue emission.
Though low work-function Ca is often used to enhance elec-
tron injection into organic materials in PLEDs, it is not stable
in air and sometimes may react with and diffuse into organic
materials, leading to the device deterioration. To overcome
FIGURE 6 EL spectra of (A) device I, (B) device II, and (C) device III at different voltages.
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FIGURE 8 Plots of (A) current efficiency and (B) power efficiency versus current density for the devices with general configurations
of ITO/PEDOT:PSS/PFBI8/X: X ¼ Ca/Al (device I), LiF/Al (device II), and TPBI/LiF/Al (device III).
As shown in the voltage–current density–luminance (V–J–L)
characteristics and the efficiency curves in Figures 7 and 8,
device III exhibited a Lmax of 1534 cd/m2 at 13.3 V, a CEmax of
0.67 cd/A at 92.3 mA/cm2, and a PEmax of 0.20 lm/W. The
significant improvement in device performance should be
ascribed to the enhanced electron injection and transport
property and thus better charge balance in the device. The
blue efficient EL emission demonstrated the applicability of
PFBI8 as stable and highly efficient blue PLEDs. It should be
pointed out that the EL devices of PFBI8 were unoptimized,
and thus better performance including the brightness and effi-
ciency can be achieved through further optimizations as inter-
layer modification,43 anode modification,44 tuning drift mobil-
ity and charge balance,45 and other engineering efforts.46
excess of injected electrons on the molecule,47 and the other
possibility might be ascribed to the increased radiative decay
from longer conjugated segments with increasing voltage.
Nevertheless, almost voltage independent EL spectra for de-
vice II exclude the latter one. With an additional electron-
transporting layer of TPBI, the emission spectrum of device
III displays slight voltage-dependent effect when compared
to device I due to decreased cavity effect. Therefore, it is
understandable that broader emissions of devices I and III
compared to device II owing to the cavity effect caused by
an excess of injected electrons in PFBI8.
EXPERIMENTAL
It is also noted that devices I–III give EL maxima at 444,
448, and 448 nm, respectively. Moreover, remarkably form
PFO, no new defect or excimer emission at long wavelength
at high bias was observed for PFBI8 devices, indicating their
high color purity and relatively good EL stability. However,
while the EL spectrum of device I is voltage dependent, giv-
ing broadened emission at longer wavelength with increasing
bias, that of device II exhibits no voltage dependence. Con-
sidering the only difference between devices I and II lies in
the cathode, one possible explanation that has been cited in
the literature is that of the cavity effect when there is an
Materials
2-Nitroaniline, terephthalaldehyde, NBS, potassium carbon-
ate, 1-bromooctane, stannous chloride dehydrate, hydrochlo-
ric acid, DMF, N,N-dimethylacetamide (DMAc), THF, chloro-
form, toluene were purchased from Sinapharm (China). THF
was purified by distillation from sodium in the presence of
benzophenone. DMF and DMAc were dried by being refluxed
over and distilled under reduced pressure from calcium
hydrides. Sodiumhydride (60% oil dispersion), ferric trichlo-
ride anhydrous, and triisopropylborate were purchased from
Aaladdin (China). Palladium-tetrakis(triphenyl phosphine)
TABLE 2 EL Performance of PFBI8-Based Devicesa
Device
kmax (nm)b
Von (V)a
Lmax (cd/m2)b
CEmax (cd/A)b
PEmax (lm/W)b
CIE (x,y)c
I
444
448
448
9.3
10.2
8.2
134
183
0.073
0.081
0.67
0.018
0.023
0.20
(0.17, 0.16)
(0.17, 0.16)
(0.20, 0.21)
II
III
a
1,534
c
Device configuration: ITO/PEDOT:PSS/PFBI8/X: X ¼ Ca/Al (device I),
CIE coordinates are taken at 11 V.
LiF/Al (device II), and TPBI/LiF/Al (device III).
b
kmax ¼ EL peak, Von ¼ turn on voltage, Lmax ¼ maximum luminance, CEmax
¼ maximum current efficiency, and PEmax ¼ maximum power efficiency.
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and n-butyllithium were obtained from J&K Chemical and
were used without further purification.
DMSO-d6, d): 13.25 (s, NAH), 13.20 (s, NAH), 8.33 (s, Ar-H),
7.87 (s, Ar-H), 7.71 (s, Ar-H), 7.65 (d, J ¼ 8.0 Hz), 7.53 (d,
J ¼ 8.0 Hz), 7.38 (m, Ar-H). 1H NMR (400 MHz, DMSO-d6
þ
Synthesis of 4-Bromo-2-nitroaniline (2)
TFA, d): 8.42 (s, 4H), 8.01(d, Jmeta ¼ 2 Hz, 2H), 7.76 (d,
Jortho ¼ 8.4 Hz, 2H), 7.62 (dd, Jmeta ¼ 2 Hz, Jortho ¼ 8.4 Hz,
2H). 13C NMR (100 MHz, DMSO-d6, TFA, d): 149.11, 134.84,
132.74, 129.09, 127.69, 118.71, 117.60, 116.53.
Compound
2 was prepared by a modified literature
method.38 2-Nitroaniline (27.6 g, 0.2 mol) was dissolved in
80 mL of glacial acetic acid in a 150-mL three-necked flash
ꢀ
with magnetic stirring at 50 C. Then, NBS (35.6 g, 0.2 mol)
Synthesis of Compound 7
was added into the solution over 30 min. The mixture was
stirred for 3 h and then poured into 500 mL of ice-water,
yielding orange–yellow precipitates. The crude product was
filtered, washed with water, and recrystallized from ethanol
to give orange needles. The yield was 40 g (92%).
Into a 50-mL three-necked round bottom flask, 0.468 g of 5
(1 mmol) and 15 mL of anhydrous DMF were placed. About
0.048 g of NaH (60% oil dispersion, 3 mmol) was added to
the solution. The mixture was stirred at room temperature
for half an hour until gas evolution ceased. Then 3 mmol of
1-bromooctane in 5 mL of anhydrous DMF was added drop-
wise and stirred at 60 ꢀC for 6 h. The mixture was poured
into brine and extracted with chloroform. The organic layer
was dried with anhydrous MgSO4 overnight. After filtration,
the solvent was evaporated and an off-white solid was
obtained. The crude product was purified by column chro-
matography using chloroform/methanol (20/1 by volume)
as eluent. An off-white solid was attained. The yield was
0.58 g (83%). Because compound 5 has three isomers, corre-
spondingly, compound 7 also has three isomers.
1H NMR (400 MHz, CDCl3, d): 8.26 (d, Jmeta ¼ 2.4 Hz, 1H),
7.42 (dd, Jortho ¼ 8.8 Hz, Jmeta ¼ 2.4 Hz, 1H), 6.73 (d, Jortho
¼
8.8 Hz, 1H), 6.11 (s, 2H). 13C NMR (100 MHz, CDCl3, d)
143.90, 138.74, 132.52, 128.45, 120.62, 108.00.
Synthesis of 4-Bromo-1,2-benzenediamine (3)
Compound 3 was prepared according the literature proce-
dure.38 Stannous chloride dehydrate (47 g, 207 mmol) was
dissolved in 80 mL of concentrated hydrochloric acid in a
150-mL three-necked flask with magnetic stirring at 60 ꢀC.
Then, 4-bromo-2-nitroaniline (15 g, 69 mmol) was added
into the solution. Stirring was continued at this temperature
for a further hour. After the mixture cooled to room temper-
ature, 50% of sodium hydroxide solution was added slowly
until the pH ¼ 12. The temperature was maintained below
25 ꢀC in the ice-water bath during the alkalization process.
The white solid was precipitated and filtered, redissolved in
dichloromethane, and washed with brine. The organic layer
was dried over MgSO4. After filtration, the solvent was
removed by rotary evaporation to give a white solid. Recrys-
tallization of the crude product from cyclohexane resulted
flat, pinkish needles. The yield was 10.2 g (79%).
1H NMR (400 MHz, CDCl3, d): 7.96 (d, J ¼1.6 Hz), 7.86 (s,
4H), 7.69 (d, J ¼ 8.4 Hz), 7.58 (d, J ¼ 1.6 Hz), 7.42 (m, 2H),
7.30 (d, J ¼ 8.8 Hz), 7.22 (q, J ¼ 8.0 Hz, 4H), 1.79 (brs, 4H),
1.22 (s, 20H), 0.84 (m, 6H). 13C NMR (100 MHz, CDCl3, d):
153.84, 153.52, 144.60, 142.28, 137.02, 134.91, 131.99,
129.92, 126.29, 123.09, 121.54, 116.50, 115.78, 113.51,
111.68, 45.36, 31.86, 30.09, 29.27, 29.23, 26.94, 22.79, 14.26.
Synthesis of 9,9-Dioctyl-2,7-dibromofluorene (9)
Compound
9 was prepared by a modified literature
method.48 To a mixture of tetrabutylammonium bromide
(TBAB, 0.5 g, 1.6 mmol) and aqueous 50 wt % sodium
hydroxide (30 mL), 2,7-dibromoflurene (8, 12.0 g, 37 mmol)
and 1-bromooctane (6, 15.7 g, 81.5 mmol) were added
under stirring at 70 ꢀC for 24 h. Then the mixture was
cooled to room temperature, poured into brine, and
extracted with methylene chloride. The organic phase
washed with water, dried over magnesium sulfate. After re-
moval of solvent, the residue was purified by column chro-
matography on silica gel (hexane) and then recrystallized
1H NMR (400 MHz, CDCl3, d): 6.82 (d, Jmeta ¼ 2.0 Hz, 1H),
6.81 (dd, Jortho ¼ 8.0 Hz, Jmeta ¼ 2.0 Hz, 1H), 6.57 (d, Jortho
¼
8.0 Hz, 1H), 3.35 (s, 4H). 13C NMR (100 MHz, CDCl3, d)
136.62, 133.89, 122.82, 119.25, 118.15, 112.10.
Synthesis of 2,2-(1,4-Phenylene)-bis(5-
bromobenzimidazole) (5)
Compound 5 was prepared according to the previously
reported proceduce.35 Into a 50-mL three-necked round bot-
tom flask, 2.99 g of 4-bromo-1,2-benylenediamine (16 mmol)
and 20 mL of DMAc were placed under nitrogen. The solu-
tion was cooled to ꢁ15 ꢀC. Then, 1.07 g of terephthalalde-
hyde (4, 8 mmol) in 10 mL of DMAc was added dropwise.
After stirring for 1 h at ꢁ10 ꢀC, the mixture was slowly
(ethanol) to give white needles. The yield was 17
g
(85%).1H NMR (400 MHz, CDCl3, d): 7.52 (d, J ¼ 8 Hz, 2H),
7.46–7.44 (m, 4H), 1.93–1.89 (m, 4H), 1.26–1.05 (m, 20H),
0.83 (t, J ¼ 8 Hz, 6H), 0.64–0.54 (m, 4H). 13C NMR (100
MHz, CDCl3, d): 152.77, 139.28, 130.36, 126.39, 121.68,
121.33, 55.91, 40.37, 31.98, 30.08, 29.42, 29.38, 23.85,
22.82, 14.29.
ꢀ
warmed to 20 C in 4 h, and then stirred for another 5 h at
room temperature. Subsequently, ferric trichloride anhydrous
(1.3 mg, 0.08 mmol) was added, and the mixture was
bubbled with air for 6 h. Finally, the mixture was poured
into ice-water. The solid precipitated out of the mixture was
collected by filtration, and recrystallized from a DMF/water
mixture. An off-white solid was obtained. Because of the NH
proton exchange in the imidazole ring, compound 5 has
three isomers. The yield was 2.8 g (75%).1H NMR (400 MHz,
Synthesis of 9,9-Dioctylfluorene-2,7-diboronic acid (10)
Compound 10 was prepared according the literature
method.49 Into a 250-mL one-necked round bottom flask, 5 g
of 2,7-dibromo-9,9-dioctylfluorene (9.1 mmol) and 150 mL
of THF under nitrogen were placed. n-BuLi (10 mL) inꢀhex-
ane (2.5 M) was slowly dropped into the flask at ꢁ78 C in
30 min under stirring. The mixture was stirred at this
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temperature for 4 h, then 6.5 mL of triisopropylborate (28.3
mmol) was injected under ꢁ78 ꢀC. One hour later, the mix-
ture was warmed to room temperature and stirred overnight.
Then 2 M HCl (50 mL) was added, and the mixture was
stirred at room temperature for 4 h. Then, the product was
extracted into ether. The organic layer was dried over MgSO4
and solvent was removed by evaporator giving a white solid,
which was recrystallized form acetonitrile to yield white crys-
tals of compound 10.The yield was 3.5 g (80%).
1H NMR (400 MHz, acetone-d6, d): 7.99 (s, 2H), 7.90 (dd,
J3–4 ¼ 1.2 Hz, J1–3¼7.6 Hz, 2H), 7.80 (dd, J ¼ 0.8 Hz, J ¼ 7.6
Hz), 7.14 (s, 4H), 1.3–1.0 (m, 24H), 0.78 (t, J ¼ 7.2 Hz),
0.66–0.56 (m, 6H). 13C NMR (100 MHz, DMSO-d6, d): 150.08,
143.02, 133.57, 129.08, 119.63, 54.86, 31.78, 29.98, 29.29,
29.19, 24.19, 24.05, 22.67, 14.54.
using a polystyrene standards eluting with THF. TGA and
DSC measurements were conducted on TA Q5000 instrument
and Netzsch DSC 200 under nitrogen at a heating and cool-
ing rate of 20 ꢀC/min, respectively. CV measurement was
conducted on a three-electrode Autolab (PGSTA302) work-
station in a solution of Bu4NPF6 (0.1 M) in acetonitrile at a
scan of 50 mV/s at room temperature.
Fabrication of the PLEDs
The indium-tin oxide (ITO) glass plates were cleaned in an ul-
trasonic solvent bath and then baked in a heating chamber at
ꢀ
120 C, and treated with O2 plasma for 25 min before use. A
50-nm thick ITO-modifying layer of PEDOT/PSS was spin-
coated (2500 rpm) on top of the ITO and then baked for
20 min at 120 ꢀC. Thin film of PFBI8 was spin-coated
(1500 rpm) from its solution in chlorobenzene (15 mg/mL).
The substrate was then thermally annealed in vacuum at
Polymerization
ꢀ
90 C for 30 min. After being cooled, the substrate was trans-
Into a 25-mL schlenk tube, compound 7 (138.5 mg, 0.2 mmol),
9,9-dioctylfluorene-2,7-diboronic acid (10, 95.7 mg, 0.2 mmol),
and Aliquat 336 (16 mg) were added. The tube was evac-
uated and flushed with nitrogen three times. Toluene (5 mL)
and saturated aqueous sodium carbonate (1 mL) were
injected. The mixture was stirred for 30 min at 100 ꢀC. The
Pd(PPh3)4 (11.6 mg, 0.01 mmol) in 1 mL of tꢀoluene was
added. The resulting mixture was stirred at 100 C for 48 h.
Then, benzeneboronic acid and phenylbromide were added
in sequence as end-capping regents to react for another two
12 h. The mixture was cooled to room temperature,
extracted with dichloromethane, and washed with water sev-
eral times. The organic layer was dried with anhydrous mag-
nesium sulfate over night. The solution was condensed and
added into methanol through a cotton filter, and fibrous pre-
cipitates were formed. The crude product was filtered,
washed with excess methanol, and dried. Then it was puri-
fied by a Soxhlet extraction in acetone foꢀr 24 h. The pure co-
polymer was dried under vacuum at 45 C overnight. A light
yellow solid was obtained. The yield was 120 mg (65%).
ferred to a vacuum thermal evaporator. For device I, a 10-nm
thick layer of Ca was deposited at a pressure of 2 ꢃ 10ꢁ3 Pa
through a mask, and another layer of 100-nm thick Al was de-
posited on the top as a protecting layer for Ca. For device II, 1-
nm LiF and 100-nm of Al were deposited on the substrate at a
pressure of 4 ꢃ 10ꢁ4 Pa, successively. For device III, a 50-nm
layer of TPBI was deposited on the substrate before deposi-
tion of LiF and Al. The thickness of PFBI8 of devices I and II
was 100 nm, and 50 nm for device III.
CONCLUSIONS
In Summary, a novel soluble blue-emitting copolymer PFBI8
containing hole transporting fluorene and electron-transport-
ing benzimidazole segments has been synthesized through
Suzuki coupling reaction. PFBI8 possesses good solubility,
high thermal stability, and efficient emission, whose quantum
yield is up to 0.99 in CHCl3. While the PL emission peak of
PFBI8 film is 450 nm with almost standard blue CIE coordi-
nates (0.15, 0.12), its EL maximum is 448 nm in the PLED of
ITO/PEDOT:PSS/PFBI8/TPBI/LiF/Al. The device exhibits a
maximum luminance of 1534 cd/m2 with the current effi-
ciency and power efficiency of 0.67 cd/A and 0.20 lm/W,
respectively. The efficient pure blue emission makes PFBI8
promising for blue light-emitting PLED applications.
1H NMR (400 MHz, CDCl3, d): 8.17–7.36 (m, 16H, Ar-H), 4.36
(brs, 4H, ANACH2), 2.3–0.6 (m, 64H). 13C NMR (100 MHz,
CDCl3, d): 153.63, 153.54, 152.05, 144.05, 142.90, 140.84,
140.13, 137.59, 137.12, 136.64, 135.47, 132.23, 129.91,
128.98, 127.41, 126.54, 123.13, 122.96, 122.22, 120.37,
120.24, 118.70, 110.59, 108.85, 55.52, 45.41, 40.69, 32.00,
31.93, 30.31, 29.93, 29.47, 29.33, 27.05, 24.21, 22.83.
This work was financially supported by the ‘‘12th 5-year’’
National Key Technologies R&D Program of China
(2011BAE08B00), the National Science Foundation of China
(21104044), the Ph.D. Programs Foundation of Ministry of Edu-
cation of China (20110073120040), the Start-up Foundation
for New Faculties of Shanghai Jiao Tong University, and the
Shanghai Leading Academic Discipline Project (No. B202).
Measurements
1H and 13C NMR spectra were recorded on a MERCURY plus
400 spectrometer in deuterated solvent at room tempera-
ture. UV–vis absorption and emission measurements were
performed on a TU-1901 UV–vis spectrophotometer and a
Perkin-Elmer LS 50B luminescence spectrometer, respec-
tively. PL quantum yields (Us) of PFBI8 in different solvents
were measured using DPA as standard (U ¼ 90% in cyclo-
hexane). To avoid the aggregation or concentration caused
quenching effect, the absorbance of DPA and PFBI8 solutions
lower than 0.05 at the excitation wavelength must be guar-
anteed. The molecular weights of the polymer were deter-
mined with Waters 410 gel permeation chromatography
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.
2 Friend, R. H.; Gymer, R. W.; Holmes, A. B.; Burroughes, J. H.;
Marks, R. N.; Taliani, C.; Bradley, D. D. C.; Santos, D. A.; Bre’-
das, J. L.; Lo´ gdlund, M.; Salaneck, W. R. Nature 1999, 397, 121.
2180
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 50, 2172–2181

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
3 Kraft, A.; Grimsdale, A. C.; Holmes, A. B. Angew. Chem. Int.
Ed. 1998, 37, 402–428.
27 Zhu, Y.; Gibbons, K. M.; Kulkarni, A. P.; Jenekhe, S. A. Mac-
romolecules 2007, 40, 804–813.
4 Xie, L. H.; Deng, X. Y.; Chen, L.; Chen, S. F.; Liu, R. R.; Hou,
X. Y.; Wong, K. Y.; Ling, Q. D.; Huang, W. J. Polym. Sci. Part A:
Polym. Chem. 2009, 47, 5221–5229.
28 Mikroyannidis, J. A.; Gibbons, K. M.; Kulkarni, A. P.;
Jenekhe, S. A. Macromolecules 2007, 41, 663–674.
29 Oyston, S.; Wang, C.; Hughes, G.; Batsanov, A. S.; Pere-
pichka, I. F.; Bryce, M. R.; Ahn, J. H.; Pearson, C.; Petty, M. C.
J. Mater. Chem. 2005, 15, 194–203.
5 McGehee, M. D.; Heeger, A. J. Adv. Mater. 2000, 12,
1655–1668.
6 Hide, F.; Diaz-Garcia, M. A.; Schwartz, B. J.; Andersson, M.
R.; Qibing, P.; Heeger, A. J. Science 1996, 273, 1833–1836.
30 Tsai, L.-R.; Chen, Y. J. Polym. Sci. Part A: Polym. Chem.
2007, 45, 4465–4476.
7 Zhou, Q.; Swager, T. M. J. Am. Chem. Soc. 1995, 117,
12593–12602.
31 Kulkarni, A. P.; Zhu, Y.; Jenekhe, S. A. Macromolecules
2005, 38, 1553–1563.
8 Dimitrakopoulos, C. D.; Kymissis, J.; Purushothaman, S.;
Neumayer, D. A.; Duncombe, P. R.; Laibowitz, R. B. Adv. Mater.
1999, 11, 1372–1375.
32 Yang, W.; Huang, J.; Liu, C.; Niu, Y.; Hou, Q.; Yang, R.; Cao,
Y. Polymer 2004, 45, 865–872.
33 (a) Yamamoto, T.; Uemura, T.; Tanimoto, A.; Sasaki, S. Mac-
romolecules 2003, 36, 1047–1053; (b) Ho, H. A.; Leclerc, M. J.
Am. Chem. Soc. 2003, 125, 4412–4413; (c) Masaya, T.; Takuya,
N.; Tsuyoshi, K. Macromolecules 2009, 42, 8068–8075; (d)
Takagi, K.; Sugihara, K.; Isomura, T. J. Polym. Sci. Part A:
Polym. Chem. 2009, 47, 4822–4829; (e) Takagi, K.; Isomura, T.;
Ito, Y.; Sakaida, M.; Nagano, S. Seki, T. J. Polym. Sci. Part A:
Polym. Chem. 2011, 49, 4993–5000; (f) Toba, M.; Nakashima, T.;
Kawai, T. J. Polym. Sci. Part A: Polym. Chem. 2011, 49,
1895–1906.
9 Horowitz, G.; Hajlaoui, R.; Delannoy, P. J. Phys. III 1995, 5,
355–371.
10 Horowitz, G.; Hajlaoui, R.; Fichou, D.; El Kassmi, A. J. Appl.
Phys. 1999, 85, 3202–3206.
11 Ma, W.; Yang, C.; Gong, X.; Lee, K.; Heeger, A. J. Adv.
Funct. Mater. 2005, 15, 1617–1622.
12 Reyes-Reyes, M.; Kim, K.; Carroll, D. L. Appl. Phys. Lett.
2005, 87, 083506.
13 Li, G.; Shrotriya, V.; Huang, J.; Yao, Y.; Moriarty, T.; Emery,
K.; Yang, Y. Nat. Mater. 2005, 4, 864–865.
34 Wang, R. Y.; Jia, W. L.; Aziz, H.; Vamvounis, G.; Wang, S.;
Hu, N. X.; Popovic, Z. D.; Coggan, J. A. Adv. Funct. Mater.
2005, 15, 1483–1487.
14 Muller, C. D.; Falcou, A.; Reckefuss, N.; Rojahn, M.; Wieder-
hirn, V.; Rudati, P.; Frohne, H.; Nuyken, O.; Becker, H.; Meer-
holz, K. Nature 2003, 421, 829–833.
35 Yoshino, K.; Nakajima, S.; Gu, H. B.; Sugimoto, R.-I. Jpn. J.
Appl. Phys. 1987, 26, L2046–L2048.
15 Hughes, G.; Bryce, M. R. J. Mater. Chem. 2005, 15, 94–107.
16 Zhao, X. G.; Zhan, X. W. Chem. Soc. Rev. 2011, 40, 3728–3743.
€
36 Andersson, M. R.; Pei, Q.; Hjertberg, T.; Inganas, O.;
¨
€
Wennerstrom, O.; Osterholm, J. E. Synth. Met. 1993, 55, 1227–1231.
17 Bernius, M. T.; Inbasekaran, M.; O’Brien, J.; Wu, W. Adv.
Mater. 2000, 12, 1737–1750.
37 Yamaguchi, I.; Osakada, K.; Yamamoto, T. Macromolecules
1997, 30, 4288–4294.
18 Lin, Y.; Chen, Z. K.; Ye, T. L.; Dai, Y. F.; Ma, D. G.; Ma, Z.;
Liu, Q. D.; Chen, Y. Polymer 2010, 51, 1270–1278.
38 Wilson, J.; Hunt, F. Aust. J. Chem. 1983, 36, 2317–2325.
39 Leyden, R. N.; Loonat, M. S.; Neuse, E. W.; Sher, B. H.; Wat-
kinson, W. J. J. Org. Chem. 1983, 48, 727–731.
19 Wang, B.; Shen, F.; Lu, P.; Tang, S.; Zhang, W.; Pan, S.; Liu,
M.; Liu, L.; Qiu, S.; Ma, Y. J. Polym. Sci. Part A: Polym. Chem.
2008, 46, 3120–3127.
40 Berrada, M.; Carriere, F.; Abboud, Y.; Abourriche, A.; Bena-
mara, A.; Lajrhed, N.; Kabbaj, M. J. Mater. Chem. 2002, 12,
3551–3559.
20 Wang, E.; Li, C.; Peng, J.; Cao, Y. J. Polym. Sci. Part A:
Polym. Chem. 2007, 45, 4941–4949.
41 Lakowicz, J. R. Principles of Fluorescence Spectroscopy,
3rd ed.; Springer: New York, 2006, pp 205–235.
21 Liu, B.; Huang, W. Thin Solid Films 2002, 417, 206–210.
22 Lu, J.; Tao, Y.; D’Iorio, M.; Li, Y.; Ding, J.; Day, M. Macromo-
lecules 2004, 37, 2442–2449.
42 Neher, D. Macromol. Rapid Commun. 2001, 22, 1365–1385.
43 Kim, Y. H.; Lee, W.; Cai, G.; Baek, S. J.; Han, S.-H.; Lee, S.-
H. J. Nanosci. Nanotech. 2008, 8, 4842–4845.
23 (a) Kreyenschmidt, M.; Klaerner, G.; Fuhrer, T.; Ashenhurst,
J.; Karg, S.; Chen, W. D.; Lee, V. Y.; Scott, J. C.; Miller, R. D.
Macromolecules 1998, 31, 1099–1103; (b) Fukuda, M.; Sawada,
K.; Yoshino, K. J. Polym. Sci. Part A: Polym. Chem. 1993, 31,
2465–2471; (c) Fukuda, M.; Sawada, K.; Yoshino, K. Jpn.
J. Appl. Phys. 1989, 28, L1433–L1435.
44 Yan, H.; Huang, Q.; Cui, J.; Veinot, J. G. C.; Kern, M. M.;
Marks, T. J. Adv. Mater. 2003, 15, 835–838.
45 Chin, B. D.; Suh, M. C.; Lee, S. T.; Chung, H. K.; Lee, C. H.
Appl. Phys. Lett. 2004, 84, 1777–1779.
46 Veinot, J. G. C.; Marks, T. J. Acc. Chem. Res. 2005, 38,
632–643.
24 (a) Scherf, U.; List, E. J. W. Adv. Mater. 2002, 14, 477–487;
(b) Kim, D. Y.; Cho, H. N.; Kim, C. Y. Prog. Polym. Sci. 2000, 25,
1089–1139 and references therein.
47 Burrows, P. E.; Shen, Z.; Bulovic, V.; McCarty, D. M.; Forrest,
S. R.; Cronin, J. A.; Thompson, M. E. J. Appl. Phys. 1996, 79,
7991–8006.
25 (a) Peng, Q.; Xie, M.; Huang, Y.; Lu, Z.; Xiao, D. J. Polym.
Sci. Part A: Polym. Chem. 2004, 42, 2985–2993; (b) Ranger, M.;
Rondeau, D.; Leclerc, M. Macromolecules 1997, 30, 7686–7691.
48 Song, S.; Jin, Y.; Kim, S. H.; Shim, J. Y.; Son, S.; Kim, I.;
Lee, K.; Suh, H. J. Polym. Sci. Part A: Polym. Chem. 2009, 47,
6540–6551.
26 (a) Cho, S. Y.; Grimsdale, A. C.; Jones, D. J.; Watkins, S. E.;
Holmes, A. B. J. Am. Chem. Soc. 2007, 129, 11910–11911; (b)
Ohmori, Y.; Uchida, M.; Muro, K.; Yoshino, K. Jpn. J. Appl.
Phys. 1991, 30, L1941–L1943.
49 Perepichka, I. I.; Perepichka, I. F.; Bryce, M. R.; Palsson, L. O.
Chem. Commun. 2005,3397–3399.
WWW.MATERIALSVIEWS.COM
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