New series of light-emitting polyquinolines containing 9,9′-spirobifluorene Units

Article abstract of DOI:10.1021/ma050741q

A new series of polyquinoline copolymers (P1-P5) containing 9,9'-spirobifluorene in the main chain were synthesized via Friedlaender reactions. The emission colors of the polymers were readily tuned from blue to yellow by changing the conjugated counits. Excellent EL performances were obtained for P5, probably because the proper donor/acceptor pairs were rightly matched, and the charge transport was significantly balanced. The devices based on P5 showed a maximum external quantum efficiency of 0.63% and a maximum photometric efficiency of 1.85 cd/A (at a brightness of 140 cd/m²). Yellow-green EL with narrow full width at the half-maximum (fwhm < 70 nm) and the highest maximum luminance (1768 cd/m²) among the currently reported polyquinolines was obtained for P5.

Full text of DOI:10.1021/ma050741q

Macromolecules 2005, 38, 6915-6922
6915
New Series of Light-Emitting Polyquinolines Containing
9,9′-Spirobifluorene Units
Bing Huang,† Jun Li,† Zuoquan Jiang,† Jingui Qin,*,† Gui Yu,‡ and Yunqi Liu‡
Department of Chemistry, Wuhan University, Wuhan 430072, China, and Institute of Chemistry
Chinese Academy of Science, Beijing 100080, China
Received April 9, 2005; Revised Manuscript Received June 2, 2005
ABSTRACT: A new series of polyquinoline copolymers (P1-P5) containing 9,9′-spirobifluorene in the
main chain were synthesized via Friedla¨nder reactions. The emission colors of the polymers were readily
tuned from blue to yellow by changing the conjugated counits. Excellent EL performances were obtained
for P5, probably because the proper donor/acceptor pairs were rightly matched, and the charge transport
was significantly balanced. The devices based on P5 showed a maximum external quantum efficiency of
0.63% and a maximum photometric efficiency of 1.85 cd/A (at a brightness of 140 cd/m2). Yellow-green
EL with narrow full width at the half-maximum (fwhm < 70 nm) and the highest maximum luminance
(1768 cd/m2) among the currently reported polyquinolines was obtained for P5.
Introduction
center, and two fluorene moieties are perpendicular to
each other. This structure feature would be expected to
minimize the close π-stacking in solid state. A series of
spiro-annulated small molecules12-14 and polymers15-18
based on 9,9′-spirobifluorene have been synthesized and
demonstrated to be amorphous with high thermal and
morphological stability and high PL efficiency. When
being applied into OLEDs, such spiro-annulated materi-
als are effective to improve the stability, color purity,
and quantum efficiency of the devices.12-18 Chiang et
al.15 developed a series of polyquinolines containing 9,9′-
spirobifluorene units, which possess high thermal sta-
bility and good solubility in common solvents. However,
they just investigated PL properties of these polymers
and did not further study the EL properties.
On the other hand, it is vital to properly balance the
charge injection and transporting ability so as to achieve
high efficiency in OLEDs.19 There have been reports on
the use of bipolar pairs of electron-withdrawing (hole
transport)/electron-rich (electron transport) moieties
such as oxadiazole/carbazole20 and oxadiazole/thiophene21
toward the achievement of “bipolar” or “p-n” lumines-
cent polymers, which can remarkably improve the
efficiency. In light of these observations, we synthesized
a series of spiro-based polyquinolines with electron-
withdrawing/electron-rich pairs in the chains. Because
the 9,9′-spirobifluorene units served as a conjugation
interrupt in these polymers, the emission colors were
effectively tuned between blue and yellow by changing
the conjugated length and the electronic structures of
the conjugated counits in these polymers. To choose the
right pair of electron-withdrawing/electron-rich moieties
and tune the emission band, electron-rich groups such
as carbazole, fluorene, bithiophene, and phenothiazine
were introduced into the copolymers. The optical, lu-
minescent, and electrochemical properties of these new
polyquinoline copolymers were studied.
Semiconducting polymers are of wide current interest
for applications in electronic and optoelectronic devices
including light-emitting diodes (LEDs),1,2,6-8 thin film
transistors,3a-c and photovoltaic cells.3d,e The vast ma-
jority of synthetic effort and structure-property studies
in the field have to date been devoted to polymeric
semiconductors having p-type (electron donor, hole
transport)1,2 properties. n-Type (electron acceptor, elec-
tron transport) polymeric semiconductors are urgently
needed for developing more efficient and high-perfor-
mance plastic electronic and optoelectronic devices.
Molecules and polymers containing oxadiazole,4a,b
benzothiadiazole,4c quinoxaline,4d and anthrazoline4e,f
are some of the electron transport materials that have
been explored for LED applications thus far. It has been
well-known that polyquinolines (PQs) are intrinsic good
n-type semiconducting polymers.6-10,25 The polyquino-
lines also have outstanding thermal and oxidative
stability, excellent mechanical strength, low relative
permittivity, and low moisture absorption.5-11 On the
basis of their optical and electric properties, polyquino-
lines have been studied for their potential uses in
electroluminescent devices,6-8,15,25 electrochromic cells,9
photovoltaic devices,6c chemosensors,10 and nonlinear
optics.11 Many polyquinolines were developed since
1970s,5 and their electroluminescent and photophysical
properties have also been recently investigated.6-8
However, these polyquinolines showed poor electro-
luminescent performance (maximum luminance < 300
cd/m2)6-8 and broad electroluminescence because the
formation of aggregates and excimers in solid films even
incorporating large hindrance substituents (long alkoxy
or alkyl).6-8
It has been reported that spirobifluorene can be
introduced into small compounds or polymeric chains
to effectively suppress aggregate-forming tendency.12-18
9,9′-Spirobifluorene contains two biphenyl units con-
nected by tetrahedral bonding carbon atom at the
Results and Discussion
Synthesis and Characterization. The bisacetyl
monomers 2, 3, 4, 5, and 6 were synthesized according
to a general procedure via the Friedel-Crafts acylation
with acetyl chloride in CS2 or acetic anhydride/phos-
phoric acid, as shown in Scheme 1. P1-P5 were
† Wuhan University.
‡ Chinese Academy of Science.
* To whom correspondence should be addressed: Tel +86-27-
68764117; Fax +86-27-68756757; e-mail jgqin@whu.edu.cn.
10.1021/ma050741q CCC: $30.25 © 2005 American Chemical Society
Published on Web 07/06/2005

6916 Huang et al.
Macromolecules, Vol. 38, No. 16, 2005
Scheme 1. Synthesis of Monomers 2-6
Scheme 2. Synthesis of Copolymers P1-P5
synthesized using a condensation scheme based on acid-
catalyzed Friedla¨nder6-11,15c reaction, as shown in
Scheme 2. An equimolar mixture of the appropriate
bisacetyl monomer and the bis(o-aminoketone) monomer
1 was reacted in an acid medium of diphenyl phosphate
(DPP) and m-cresol at 140 °C for 72 h under argon. The
resulting viscous polymer solution was diluted with
CHCl3 and precipitated into ethanol containing 10%
triethylamine, followed by Soxhlet extraction with the
same solution to obtain the polymers in good yields (56-
93%). The structures of these polymers were character-
ized by 1H NMR, 13C NMR, and FT-IR spectroscopy. The
proton signals from the amino and acetyl groups in the
monomer structures are not observed, indicating that
no significant amount of monomeric residue remained.
The disappearance of characteristic doublet absorption
bands of amine (3472, 3341 cm-1), carbonyl stretchings
of acetyl (1656-1710 cm-1), and benzophenone (1628
cm-1) units of the monomers and the appearance of
strong bands between 1600 and 1400 cm-1 due to the
imine (CdN) group and characteristic of the quinoline
ring confirmed the complete polymerization.6,7 The
isolated polymeric materials, even those with rigid
biphenyl or bithiophene linkages in the backbone,
exhibited good solubility in a variety of solvents such
as chloroform, tetrahydrofuran (THF), formic acid, and
m-cresol. These results demonstrated that the introduc-
tion of a 9,9′-spirobiflorene unit into the polymer main
chain was highly effective in enhancing the solubility
of the polyquinolines. These copolymers were subjected
to laser scattering (LS) analysis by gel permeation
chromatography with THF as an eluent to yield weight-
average molecular weights (Mw’s) of (3.8-5.0) × 104. The
crystallinity of the polyquinolines was evaluated by
wide-angle X-ray diffraction experiments. All the poly-
mers displayed amorphous diffraction patterns owing
to the kinked 9,9′-spirobiflorene structure. The thermal
properties of the copolymers were investigated through

Macromolecules, Vol. 38, No. 16, 2005
Light-Emitting Polyquinolines 6917
Table 1. Molecular Weights and Thermal Properties of
Polyquinolines P1-P5
polymer
Mw (×104)
PD (Mw/Mn)
Tg (°C)
Td (°C)a
P1
P2
P3
P4
P5
5.0
4.4
5.0
3.8
4.5
1.10
1.10
1.09
1.07
1.24
243
259
320
376
222
540
525
535
420
370
a Onset decomposition temperature measured by TGA under
nitrogen.
Table 2. Photophysical Properties of Polyquinolines
P1-P5
solution λmax (nm)
thin film λmax (nm)
Figure 2. UV-vis absorption spectra of P1-P5 in solid state.
polymer
abs
emis
abs
emis
æFa (sol)
P1
P2
P3
P4
P5
382
442
400
405 (428)
(492) 520
442
384
443
401
391
410
435
0.28
0.38
0.32
0.51
0.16
542
447 (544)
510
550
388, 406 418 (442)
410 546
a Solution quantum yields were measured relative to quinine
bisulfate (in 1.0 M H2SO4).
Figure 3. PL spectra of P1-P5 in THF.
Figure 1. UV-vis absorption spectra of P1-P5 in THF.
DSC and TGA, and the results are tabulated in Table
1. DSC was performed in the range from ambient
temperature to 400 °C (except for P5, DSC was per-
formed up to 300 °C). All the polymers have high glass
transition temperatures, in the range 222-320 °C. As
TGA revealed, these polymers also exhibit high decom-
position temperatures of 370-540 °C. These results
reflect the high thermal stability of these spiro-
annulated polymers.
Optical Properties. The photophysical characteris-
tics of P1-P5 were investigated in solution and in solid
state. The absorption and emission spectral data for the
polymers in THF and in the films casting from solution
are summarized in Table 2. The absorption spectra of
the polyquinolines in diluted THF solutions and in films
are illustrated in Figures 1 and 2, respectively. All the
polymers show the maximum absorption in the range
382-442 nm in THF, attributed to π-π* transition. In
THF, the absorption spectra of P2, P3, and P5, which
contain a strong electron donor (bithiophene, carbazole,
and phenothiazine, respectively), are red-shifted com-
pared to the other polymers. The absorption spectra of
the solutions in THF are nearly identical to the corre-
sponding spin-coating films. Thus, the electronic transi-
tions of the polymers are primarily determined by their
molecular structures, which are insignificantly affected
by their aggregation states. The optical band gaps (Eg)
of the polymers are determined to be 2.36-2.98 eV from
the film absorption spectra.
Figure 4. PL spectra of P1-P5 in solid state.
Figure 3 shows the PL spectra of polymers in THF
solutions. In THF, P1 and P4 emit strong blue fluores-
cence around 405-418 nm with a vibronic fine struc-
ture, P3 emits blue fluorescence around 442 nm, P2
emits strong green fluorescence with two peaks at 495
and 523 nm, and P5 shows yellow-green fluorescence
around 550 nm under photoexcitation. These polymers
show solution PL efficiencies in THF varying from 0.16
to 0.51. For P2, P3, and P5, a major reason for their
low emission quantum yield is their donor-acceptor
nature and the consequent intramolecular charge trans-
fer (ICT) which is known to be an important lumines-
cence quenching mechanism in such donor-acceptor
systems.6c,e
Figure 4 shows the PL spectra of polymers in the solid
states. All the photophysical data are summarized in
Table 2. Very broad emissive spectra and very large red
shifts in thin films compared to solutions, which are
normally observed in fully conjugated polyquinolines,6-8
are not observed in our spiro-linked polyquinolines.

6918 Huang et al.
Macromolecules, Vol. 38, No. 16, 2005
Though the solid-state PL emission spectra of the
polymers showed substantial red shifts by 4-92 nm
relative to dilute solutions, it is probably due to excimer
formation rather than aggregation, judging by the lack
of spectral shift in the absorption spectra for the solution
by comparison to the solid state. The similarity of
emission spectral peak maxima in PL and EL spectra
further supports a lack of substantial interchain elec-
tronic interactions. As shown in Figure 4, P1 and P4
in solid states exhibit featureless emissions, assigned
to intermolecular excimers. Thin film of the carbazole-
linked polymer (P3) exhibits dual fluorescence, which
was also observed in some carbazole-linked polyquino-
line and oligomer.6c The blue emission band is very
similar to the dilute solution emission band of P3 in
THF. On the basis of this similarity, we assign the blue
emission band to singlet emission from P3. The feature-
less yellow emission band around 544 nm can be also
assigned to an intermolecular excimer. A possible reason
is that the spin-coated thin films of P3 were semicrys-
talline, allowing highly ordered regions to coexist with
amorphous regions with consequent different molecular
packing and different emitting species.6c Surprisingly
for P5, the solid-state emission is very similar to the
dilute solution emission. Thus, the aggregates or exci-
mers are almost completely suppressed, probably due
to the steric hindrance from the long length alkyl chain
of phenothiazine units and the spiro-linked structures
in P5. The solid-state emission appears to be from an
intramolecular exciton with strong charge-transfer char-
acter. The PL emission blue shift of P2 relative to P5,
which is the opposite of the absorption spectra relation-
ship of the two materials, allows us to assign bithiophene-
linked polymer (P2) emission to the dominance of
intermolecular excimer. Because of insights provided by
the previously discussed emission features of these
copolymers, the interchain electronic interactions of the
polymers are weak.
Figure 5. Cyclic voltammograms of P1-P5 films coated on
platinum plate electrodes in acetonitrile containing 0.1 M
Bu4NPF6. Scan rate: 100 mV/s.
carbazole, and phenothiazine), decreases in the oxida-
tion potential and energy band gap are observed, as
expected initially. On the other hand, for P2 and P5,
obvious decrease in the oxidative onset potential and
increase in the reductive onset potential are observed,
which result in smaller energy gaps than P1 and P4.
From Table 3, we could find all the polymers have low
LUMO energy levels (-2.73 to -3.03 eV). Their rela-
tively high electron affinity and good solubility in both
aprotic organic solvents (THF, chloroform, etc.) and
protonic solvents (formic acid, etc.) make them very
attractive for use as electron transport materials in
multilayer device architectures.6e P2, P3, and P5 also
demonstrate hole transport properties with high HOMO
energy levels from -5.07 to -5.45 eV. These data
suggested P2, P3, and P5 are characteristic of bipolar
property, which could obtain excellent EL performances
when serving as emissive layer in OLEDs. These results
were further checked by the EL properties in the next
part. Once again, the HOMO and LUMO energy levels
of the polymers could be easily adjusted in the range of
0.3-1.0 eV by verifying the monomers.
Electrochemical Properties. When materials are
served as an emissive layer for OLEDs or as a donor
(or acceptor) component in organic photovoltaic devices
(OPVDs), matches of their valence band (HOMO) and
conduction band (LUMO) energy levels with work
functions of the electrodes are of paramount importance.
Cyclic voltammetry is employed to investigate the redox
behaviors of the polymers. Regarding the energy level
of the SCE reference, one can calculate the LUMO and
HOMO energies with the assumption that the energy
level of SCE is 4.4 eV below vacuum.27 In Figure 5, P1-
P4 show irreversible n-doping processes and irreversible
(for P1 and P3) or quasi-reversible (for P2 and P4)
oxidation processes, while P5 exhibits a reversible
reduction and oxidation process. From the onset poten-
tials of the oxidation and reduction processes, the band
gaps of the polymers are estimated to be 3.19, 2.42, 2.60,
3.18, and 2.13 eV for P1-P5, respectively. According
Electroluminescence. LEDs with configurations
of ITO/polymer(60 nm)/Alq(30 nm)/Al(100 nm), ITO/
PEDOT(50 nm)/polymer(60 nm)/Al(100 nm), or ITO/
PEDOT(50 nm)/polymer(60 nm)/Alq(30 nm)/Al(100 nm)
were fabricated to study the electroluminescence prop-
erties of copolymers. The device performances are
summarized in Table 4. The devices based on P4 were
first investigated. Figure 7 shows the current voltage-
brightness characteristic of the devices. The device of
ITO/PEDOT/P4/Al demonstrates a blue-greenish emis-
sion as shown in Figure 6, with a maximum external
quantum efficiency of 0.014% at 4 cd/m2 and 17 V bias.
The bilayer device of ITO/P4/Alq/Al using Alq as
electron transport layer shows a decrease of turn-on
voltage and an improvement of the luminance up to 302
cd/m2, as illustrated in Figure 7, and the maximum
external quantum efficiency is 6 times (0.21%) higher
than that of the device of ITO/PEDOT/P4/Al. The EL
spectra of devices based on P4 show similar spectra
around 500 nm, close to the PL spectrum in thin film,
as shown in Figure 6, and shows narrow emissions
(fwhm e 90 nm). The aggregate formation was success-
fully prevented compared to the reported fluorene-linked
polyquinoline,7c which showed broad EL emission band
about 100-200 nm.
to the empirical equations proposed by Leeuw et al.,28
ïx
ionization potential (IP, HOMO levels) ) -([Eonset
]
+
4.4) eV and electron affinities (EA, LUMO levels) )
-([Eonset
]
red + 4.4) eV, where [Eonset ïx and [Eonset red are
]
]
the onset potentials for the oxidation and reduction of
the polymer vs the reference electrode, the LUMO and
HOMO energy levels are estimated. The electrochemical
data of the polymers are summarized in Table 3. The
electrochemical properties of P1 and P4 are quite
similar, with large energy band gaps. As for P2, P3,
and P5, by insertion of the electron donors (bithiophene,
Since P2, P3, and P5 possess electron-deficient/
electron-rich moieties, they might be employed in OLED

Macromolecules, Vol. 38, No. 16, 2005
Light-Emitting Polyquinolines 6919
Table 3. Electrochemical Properties of Polyquinolines P1-P5a
polymer
Eredo (V)
Eredonset (V)
LUMO (eV)b
Eoxpeak (V)
Eoxonset (V)
HOMO (eV)c
Egel (eV)d
Egopt (eV)e
P1
P2
P3
P4
P5
-1.61
-1.37
-1.61
-1.67
-1.46
-2.79
-3.03
-2.79
-2.73
-2.94
2.08
1.40
1.30
1.75
0.87
1.58
1.05
0.99
1.51
0.67
-5.98
-5.45
-5.39
-5.91
-5.07
3.19
2.42
2.60
3.18
2.13
2.97
2.40
2.83
2.98
2.36
-1.78
-1.96
-1.92
a All potentials vs SCE. b Determined from the onset reduction potential. c Determined from the onset oxidation potential. d Electro-
onset
.
chemical band gap estimated using Egel ) Eoxonset - Ered e Optical band gap, calculated from the absorption edge of the UV-vis spectrum.
Table 4. Performance of Single-Layer and Double-Layer LEDs Based on Polyquinolines P3-P5
device structure
Vona (V)
Bmaxb (cd/m2)
ηmaxc (%)
PEmaxd (cd/A)
λElmaxe (nm)
fwhm (nm)
ITO/P3/Alq/Al
ITO/PEDOT/P4/Al
ITO/P4/Alq/Al
ITO/P5/Alq/Al
ITO/PEDOT/P5/Alq/Al
6
16
9
1529
57
302
1768
583
0.47
1.22
0.028
0.21
1.09
1.85
509
501
506
559
561
76
90
82
69
65
0.014
0.085
0.37
5
6
0.63
a Turn-on voltage, defined as the voltage needed for brightness of 1 cd/m2. b Maximum brightness. c Maximum external quantum
efficiency. d Maximum photometric efficiency. e EL emission maximum.
Figure 8. Current density and luminance vs applied voltage
Figure 6. Normalized EL spectra of devices based on P4.
of ITO/P3/Alq/Al device.
Figure 9. Normalized EL spectra of devices based on P5.
12 V, respectively, but Alq serves as the emitting layer
and P3 serves as the hole-transporting layer material.
This observation clearly suggested that P3 transported
holes better than it carried electrons, attributed to the
high HOMO energy level of P3. Choosing proper elec-
tron transport materials (such as TPBI or BCP) instead
of Alq would help to explore the emitting properties of
P3 further. Surprising for P5, it is very easy to obtain
a yellow emission in a device of ITO/PEDOT/P5/Al, as
showed in Figure 9. It was reported that this kind of
Figure 7. Current density and luminance vs applied voltage
phenothiazine-phenylquinoline donor-acceptor poly-
mer showed no emission in the single-layer device.6c To
improve the device performance, two devices using Alq
as electron transport material with a configuration of
ITO/P5/Alq/Al and ITO/PEDOT/P5/Alq/Al were fabri-
cated. The EL spectra of these devices (Figure 9) are
similar to that of the single-layer device and PL
spectrum of thin film (Figure 4), and all show very
narrow emissions (fwhm < 70 nm). Figure 10 showed
the current voltage-brightness characteristic of the
devices. For the device of ITO/P5/Alq/Al, the turn-on
voltage is 5 V, and the brightness reached 1768 cd/m2
of ITO/PEDOT/P4/Al (a) and ITO/P4/Alq/Al (b).
as electron-transporting, hole-transporting, or bifunc-
tional materials. Initially, for P2, the single- or double-
layer devices are hardly to observe emission due to the
poor efficiency, as bithiophene is a strong donor and the
effect of ICT is dominant.6c,e For P3, the single-layer
device shows weak emission. A double-layer device with
a configuration of ITO/P3/Alq/Al exhibits improved EL
performance (Figure 8), and the maximum external
quantum efficiency and the maximum photometric
efficiency reach 0.47% and 1.22 cd/A at 487 cd/m2 and

6920 Huang et al.
Macromolecules, Vol. 38, No. 16, 2005
maximum photometric efficiency of 1.85 cd/A (at a
brightness of 140 cd/m2). Yellow-green EL with narrow
fwhm (<70 nm) was successfully achieved, and the
highest maximum luminance (1768 cd/m2) among the
currently reported polyquinolines was obtained for P5.
The spiro-structure modification may be a promising
approach to reduce the interchain interactions and
improve the color purity of polyquinolines as EL materi-
als.
Experimental Section
Materials. The synthesis of monomer 1 was reported by
Chiang and Shu in detail.15c Compounds 2,23 3,24 4,6c 5,25 and
DPP26 (diphenyl phosphate) were prepared as described in the
literature. THF was distilled from Na-K alloy, and m-cresol
was purified by distillation under reduced pressure. CS2 was
dried over CaCl2 and freshly distilled prior to use. Acetyl
chloride was distilled with molecular sieve (4 A) before use.
All other chemicals were used as received unless otherwise
stated.
10-n-Hexylphenothiazine. Phenothiazine (2.0 g, 0.01 mol)
was added to a suspension of potassium hydroxide (9.0 g, 0.1
mol) in 30 mL of dimethylformamide under an argon atmo-
sphere. After 1 h of vigorous stirring, n-hexyl bromide (2.5 g,
0.015 mol) wad added. The reaction was carried out overnight,
poured into water, and the extracted with chloroform. The
extract was dried with Na2SO4 and then concentrated under
reduced pressure. The crude product was purified by column
chromatography on a silica gel column using petroleum ether
as an eluent. Colorless oil was obtained (2.1 g, 74%). 1H NMR
(300 MHz, CDCl3): δ 7.09 (d, 4 H, J ) 7.5 Hz), 6.84 (dd, 4 H,
J ) 18, 7.5 Hz), 3.80 (t, 2 H, J ) 6.6 Hz), 1.78 (t, 2 H,J ) 6.6
Hz), 1.25-1.40 (m, 6 H), 0.86 (t, 3 H, J ) 6.6 Hz).
2,7-Diacetyl-10-n-hexylphenothiazine (5). The proce-
dure was similar to the literature6c with modification. To a
mixture of 10-n-hexylphenothiazine (2.10 g, 7.4 mmol) and
AlCl3 (2.96 g, 22.2 mmol) in 20 mL of CS2 in an ice-water
bath was added dropwise acetyl chloride (1.7 mL, 22.2 mmol)
in 5 mL of CS2. After addition, the mixture was stirred for
further 30 min and refluxed overnight. Thereafter, CS2 was
removed and the aluminum chloride complex was decomposed
with a solution of crushed ice and concentrated hydrochloric
acid, and then the mixture was extracted with chloroform. The
organic layer was separated, washed with water, and dried
over anhydrous Na2SO4, and the solvent was removed to
dryness. The crude product was purified on silica gel column
with chloroform as eluent. 0.72 g (30%) of orange solid was
collected. 1H NMR (300 MHz, CDCl3): δ 7.73 (dd, 2 H, J )
10.2, 1.8 Hz), 7.64 (d, 2 H, J ) 1.8 Hz), 6.84 (d, 2 H, J ) 10.2
Hz), 3.88 (t, 2 H, J ) 4.2 Hz), 2.52 (s, 6 H), 1.80 (m, 2 H),
1.25-1.44 (m, 6 H), 0.88 (t, 3 H, J ) 6 Hz).
General Procedure for Polymerization. All the copoly-
mers were synthesized according to the general literature
procedures for polyquinolines.15c A mixture of 1 equimolar
monomer 1, 1 equimolar bisacetyl monomer, 25 equimolar
diphenyl phosphate (DPP), and appropriate freshly distilled
m-cresol was flushed with argon with stirring for about 20 min
and heated from room temperature to 140 °C over about a 30
min period. It was maintained at this temperature for 72 h
under an argon atmosphere. After cooling, the resulting
viscous solution was diluted with chloroform and added
dropwise into an agitated solution of ethanol containing 10%
v/v of triethylamine. The collected polymer was purified by
precipitating from chloroform into a solution of ethanol
containing 10% v/v of triethylamine three times. The polymer
was then continuously extracted in a Soxhlet extractor for 24
h with an ethanol solution containing 10% v/v of triethylamine
and then dried at 80 °C under vacuum to give the product.
Figure 10. Current density and luminance vs applied voltage
of ITO/PEDOT/P5/Alq/Al (a) and ITO/P5/Alq/Al (b).
(the highest maximum luminance among the currently
reported polyquinolines) at a bias voltage of 11.5 V and
a current density of 204 mA/cm2, corresponding to an
external quantum efficiency of 0.2%. The maximum
external quantum efficiency is 0.37% at 694 cd/m2 and
6 V. For the device of ITO/PEDOT/P5/Alq/Al, the
maximum external quantum efficiency and the maxi-
mum photometric efficiency reach 0.63% and 1.85 cd/A
at 140 cd/m2 and 10.5 V, respectively. The higher
efficiency than that of the device without PEDOT layer
may be attributed to the good balance of charge trans-
port and injection. Comparing P5 to P2 and P3, though
the three copolymers similar possess donor/acceptor
structures and demonstrated bipolar properties, only P5
could easily obtain good EL performances, which was
probably because the proper donor/acceptor pairs were
chosen in P5 and the charge transport was balanced.
Considering all of the measurements were performed
under ambient atmosphere at room temperature, we
believed that better device performance would be pos-
sible with further optimization on device fabrication.
The devices based on P4 and P5 all demonstrate narrow
EL emissions (fwhm about 65-90 nm); thus, the intro-
duction of spiro-units into polymeric backbones will be
a promising approach to reduce the aggregates and
improve the EL color purity.
Conclusions
We have described the synthesis and luminescence
of a series of new polyquinoline copolymers (P1-P5)
containing 9,9′-spirobifluorene in the main chain. In
these copolymers, the spiro moieties not only reduced
the interchain aggregates, resulting in good solubility
in common organic solvents and high thermal stability,
but also effectively controlled the conjugated length. The
electronic and EL properties of these polymers can be
readily manipulated by simply varying the nature of the
counits. When the proper donor/acceptor pairs were
rightly matched and the charge transport was signifi-
cantly balanced (for P5), excellent EL performances
were obtained. The devices based on P5 showed a
maximum external quantum efficiency of 0.63% and a
P1 (74%). 1H NMR (300 MHz, CDCl3): δ 6.84 (br, 2 H), 7.13
(br, 2 H), 7.35 (br, 2 H), 7.56-7.62 (br m, 16 H), 7.76 (br, 2 H),
7.86 (br, 2 H), 8.08 (br, 2 H), 8.28 (br, 2 H). 13H NMR (75 MHz,
CDCl3): δ 68.3, 116.0, 116.8, 119.2, 121.2, 124.3, 125.0, 125.4,

Macromolecules, Vol. 38, No. 16, 2005
Light-Emitting Polyquinolines 6921
126.4, 127.4, 127.9, 128.5, 129.0, 129.9, 138.5, 139.0, 140.7,
140.9, 141.3, 149.3, 149.8, 152.2, 155.6.
parameter analyzer. All of the measurements were performed
under ambient atmosphere at room temperature.
P2 (82%). 1H NMR (300 MHz, CDCl3): δ 6.80 (br, 2 H), 7.09
(br, 4 H), 7.32 (br, 2 H), 7.42 (br, 4 H), 7.58 (br m, 12 H), 7.80
(br, 2 H), 8.42 (br, 2 H). 13H NMR (75 MHz, CDCl3): δ 68.0,
117.2, 118.7, 12.3, 125.9, 126.1, 126.3, 127.5, 129.8, 130.1,
130.9, 139.8, 141.3, 141.6, 142.0, 145.6, 150.2, 150.8, 152.1,
153.4.
Acknowledgment. This work was supported by the
National Science Foundation of China, the Scientific
Research Foundation for the Overseas Chinese Scholars,
State Education Ministry of China, and the National
Fundamental Key Research Program of China (973
Project).
1
P3 (56%). H NMR (300 MHz, CDCl3): δ 0.87 (br m, 2 H),
1.27 (br m, 2 H), 1.79 (br m, 2 H), 4.22 (br, 2 H), 6.87 (br, 2
H), 7.14 (br, 2 H), 7.35 (br, 4 H), 7.61 (br m, 8 H), 7.71 (br, 4
H), 7.89 (br, 4 H), 8.24 (br, 2 H), 8.32 (br, 2 H), 8.75 (br, 2 H).
13H NMR (75 MHz, CDCl3): δ 14.1, 20.6, 31.3, 43.3, 65.5, 109.5,
116.1, 119.4, 119.8, 121.2, 123.7, 125.0, 125.3, 125.8, 126.0,
128.5, 128.7, 129.1, 130.0, 130.9, 139.3, 140.2, 141.3, 141.8,
142.0, 149.3, 149.5, 150.0, 152.2, 157.0.
Supporting Information Available: 1H and 13C NMR
spectra, XRD spectra, and DSC curves of polymers. This
material is available free of charge via the Internet at http://
pubs.acs.org.
1
P4 (75%). H NMR (300 MHz, CDCl3): δ 0.54-0.65 (br m,
References and Notes
10 H), 0.87 (br m, 12 H), 1.96 (br, 4 H), 6.82 (d, 2 H, J ) 6
Hz), 7.12 (br, 2 H), 7.35 (br, 2 H), 7.59 (br, 4 H), 7.67 (br m, 10
H), 7.77 (br, 2 H), 7.87 (d, 2 H, J ) 6.6 Hz), 7.96 (br, 2 H),
8.00 (d, 2 H, J ) 7.2 Hz), 8.27 (br, 2 H). 13H NMR (75 MHz,
CDCl3): δ 14.3, 22.9, 24.1, 29.9, 31.8, 40.8, 55.9, 65.5, 116.1,
119.6, 120.5, 121.2, 125.0, 125.5, 126.3, 126.7, 128.5, 128.7,
129.0, 129.9, 138.7, 139.2, 140.6, 141.0, 142.1, 149.3, 149.4,
149.9, 152.1, 156.6.
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Varian Unity 300 MHz spectrometer using CDCl3 as solvent.
IR spectra were obtained as KBr pellets on a Nicolet-170
SKFT-IR spectrometer. Wide-angle X-ray diffraction (WAXD)
patterns were obtained at room temperature on a Shimadzu
XRD 6000 powder diffractometer with Cu KR1 radiation (λ )
1.540 56 nm) by a graphic monochromator. Differential scan-
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instrument under nitrogen at a heating rate of 15 °C/min with
gas flow of 20 mL/min. Thermogravimetric analysis (TGA) was
performed with a Shimadzu-DT 40 instrument at a heating
rate of 20 °C/min under static argon with a gas flow of 50 mL/
min. UV-vis absorption spectra were recorded on a Hitachi
U-3010 UV-vis recording spectrophotometer. PL and EL
spectra were performed on a Hitachi F-4500 fluorescence
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by gel permeation chromatography with multiangle static light
scattering (GPC-MASLS). GPC-MALLS measurements were
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a pump P100 (Thermo Separation Products, San Jose, CA)
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