A new synthetic route to soluble polyquinolines with tunable photophysical, redox, and electroluminescent properties

Article abstract of DOI:10.1021/ma051280b

A new monomer bearing dialkyl groups, 3,3′-dinonanoylbenzidine, when copolymerized with diacetyl monomers gave six new alternating conjugated copolymers, poly(2,2′-arylene-4,4′-bis(4-alkyl-quinolines))s, which are soluble in organic solvents. The thermal,

Full text of DOI:10.1021/ma051280b

Macromolecules 2005, 38, 9539-9547
9539
A New Synthetic Route to Soluble Polyquinolines with Tunable
Photophysical, Redox, and Electroluminescent Properties
Christopher J. Tonzola, Maksudul M. Alam, and Samson A. Jenekhe*
Department of Chemical Engineering and Department of Chemistry, University of Washington,
Seattle, Washington 98195-1750
Received June 17, 2005; Revised Manuscript Received September 11, 2005
ABSTRACT: A new monomer bearing dialkyl groups, 3,3′-dinonanoylbenzidine, when copolymerized with
diacetyl monomers gave six new alternating conjugated copolymers, poly(2,2′-arylene-4,4′-bis(4-alkyl-
quinolines))s, which are soluble in organic solvents. The thermal, electrochemical, photophysical, and
electroluminescent properties of the new polyquinolines varied with the arylene linkage, including
p-phenylene, 4,4′-biphenylene, stilbene, 5,5′-bithienylene, bis(thienyl)vinylene, and 3,7-phenothiazinylene.
The new conjugated polymers combined high glass transition temperature (110-254 °C) with quasi-
reversible electrochemical reduction from which 2.72-3.00 eV electron affinities were estimated. The
optical band gap varied from 2.19 to 2.86 eV whereas the photoluminescence emission maximum varied
from blue-green (477 nm) to deep red (646 nm). Some of the new polymers with alternating donor-
acceptor architecture showed strong intramolecular charge transfer. Electroluminescence of moderate
brightness (up to 209 cd/m2) was achieved with blue-green, green, yellow, orange, and deep red colors
depending on the arylene linkage of the copolymer. The new polyquinolines were also demonstrated as
useful electron transport materials for the enhancement of polymer light-emitting diodes.
Introduction
Solubility in organic solvents also allows for the prepa-
ration of blends with other conjugated polymerssan
attractive route to efficient photovoltaic and light-
emitting materials where both n-type and p-type func-
tionalities are needed.12 Furthermore, soluble polyquin-
olines can be used as the host in guest-host systems
with either fluorescent or phosphorescent emissive
dopants as has been done with other soluble polymers.13
To achieve solubility in organic solvents, alkyl-substi-
tuted arylene groups6c,d,8b,c,9,10 have been incorporated
into the polymer backbone or the pendant phenyl group
on the bis(4-phenylquinoline) has been alkylated.8a
Alternatively, our group has synthesized a series of A-B
monomers that self-polymerized into soluble regioregu-
lar poly(4-alkylquinoline)s.7 Although polyquinolines
have been studied for over three decades, novel archi-
tectures such as diblock and triblock copolymers14 that
facilitate self-assembly and side-chain polymers15 are
still being explored. Similarly, the library of arylene
groups being incorporated into quinoline copolymers is
being expanded and becoming more exotic.8-10,16
New and improved conjugated polymer semiconduc-
tors are necessary for the advancement of the rapidly
growing field of organic electronics.1-5 One area of great
need is the development of new n-type conjugated
polymers with good electron transport properties and a
range of electron affinities or lowest unoccupied molec-
ular orbital (LUMO) energy levels.1,2 For use as electron
transport materials in organic light-emitting diodes
(OLEDs) a desirable range of the electron affinity (EA)
is 2.7-3.4 eV, whereas much higher values (EA ∼ 3.8-
4.5 eV) are necessary for Ohmic contacts in photovoltaic
cells and field effect transistors.2,3d,4 Our group and
others have previously shown that poly(phenylquino-
line)s6 and poly(alkylquinoline)s7 are excellent electron
transport materials for OLEDs due in part to their
suitable EA values (2.6-3.0 eV) and rugged photochemi-
cal and thermal stability (Tg > 100 °C). Improved
solubility, processability, and modulation of the elec-
tronic and photonic properties are of current interest
in the development of polyquinolines as n-type semi-
conductors for organic electronics.6c,d,7-10
This paper reports a new synthetic route to organic-
solvent-soluble conjugated polyquinolines incorporating
bis(4-alkylquinoline) units through a new A-A mono-
mer, 3,3′-dinonanoylbenzidine. A series of six new
alternating conjugated copolymers, poly(2,2′-arylene-
4,4′-bis(4-alkylquinoline))s, whose structures are shown
in Chart 1, exemplify the new synthetic methodology.
Diverse n-type conjugated polymers that are soluble in
organic solvents can thus be obtained by variation of
the arylene linkage which facilitates the tuning of the
electronic and optical properties. The arylene linkages
shown in the polymers of Chart 1 include p-phenylene,
4,4′-biphenylene, stilbene, 5,5′-bithienylene, bis(thienyl)-
vinylene, and 3,7-phenothiazinylene, and they allowed
the variation of the electron affinity in the 2.7-3.0 eV
range, the glass transition in the 110-254 °C range,
and the electroluminescence color from blue-green,
green, yellow, and orange to deep red.
Early efforts to address the problem of processing
conjugated poly(phenylquinoline)s into thin films suit-
able for nonlinear optics, optoelectronics, and electronics
exploited their solubility in protonic acids (e.g., formic
acid) and solubility of their Lewis acid complexes in
aprotic organic solvents.11 Processability from formic
acid allowed the poly(phenylquinoline)s to be success-
fully used in bilayer OLED devices with emissive p-type
(hole transport) polymers such as poly(p-phenylenevi-
nylene) (PPV)6a,b and poly(2-methoxy-5-(2′-ethyl-hexyl-
oxy)-1,4-phenylenevinylene) (MEH-PPV).6c-f,7 Recent
synthetic work has targeted organic-solvent-soluble
polyquinolines in an effort to enhance processability and
to permit more comprehensive characterization (e.g.,
solution spectroscopy on the neutral, nonprotonated
species and gel permeation chromatography).6c,d,7-10
* Corresponding author. E-mail: jenekhe@u.washington.edu.
10.1021/ma051280b CCC: $30.25 © 2005 American Chemical Society
Published on Web 10/19/2005

9540 Tonzola et al.
Chart 1. Structures of New Polyquinolines
Macromolecules, Vol. 38, No. 23, 2005
Scheme 2. Synthesis of New Polymers
Diheptanoylbenzidine (8) was initially used to synthe-
size several polymers containing bis(4-hexylquinoline);
however, only PSHQ (Chart 1) was sufficiently soluble
in organic solvents and incorporated in the present
study. The resulting products of polymerization were
precipitated into 10% triethylamine/ethanol and ex-
tracted on a Soxhlet apparatus with 20% triethylamine/
ethanol for 2 days to remove the diphenyl phosphate
(DPP) acid catalyst.
Scheme 1. Synthesis of New Monomers
1H NMR and FT-IR spectra of the polymers confirmed
the proposed structures. Thermogravimetric analysis
(TGA) also indicated high purity with <2% weight loss
at the decomposition temperatures (TD). The weight-
average molecular weights (Mw), based on polystyrene
standards and gel permeation chromatography (GPC),
are shown in Table 1. The Mw values range from 10 000
for PPZOQ to 33 900 for PBOQ, and the polydispersities
were in the range of 1.26-4.90. These Mw values are
generally lower than those previously reported for
soluble poly(phenylquinoline)s6c,d but are similar to
those of poly(4-alkylquinoline)s.7 This indicates that
replacing the phenyl group with an alkyl chain at the
keto position of the A-A monomer may decrease the
reactivity of the monomer. The much larger and broader
molecular weight of PBOQ compared to the others
reflects the geometry and reactivity of diacetylbiphenyl
as also observed in prior phenylated polyquinolines.11
The TGA thermogram of PBOQ is shown in Figure
1, indicating a decomposition temperature of 419 °C.
The decomposition temperature (TD) of the remaining
polymers was in the range of 400-477 °C (Table 1).
Typical second heating differential scanning calorimetry
(DSC) scans for PPOQ and PBOQ are shown in Figure
2; these polymers show glass transitions (Tg) of 127 and
141 °C, respectively. The Tg of the remaining polymers
was between 110 and 254 °C (Table 1). Notably, the
hexyl-substituted PSHQ had a significantly higher Tg
(254 °C) than the octyl-substituted polyquinolines (Tg
< 170 °C), and PPZOQ (Tg ) 110 °C), which contains
both a decyl chain and two octyl chains per repeat unit,
has the lowest Tg. Poly(phenylquinoline)s typically have
glass transitions between 200 and 400 °C.11 The pres-
ence and length of alkyl chains has a significant effect
on the glass transition as evidenced in a series of poly-
(phenylquinoline)s containing dialkylbithiophene moi-
eties in the main chain;6c,d it was observed that the Tg
decreased with increasing chain length. The high glass
transitions of the new polyquinolines (>110 °C) suggest
that they could withstand the joule heating associated
with the operation of organic electronic devices.
Results and Discussion
Synthesis and Characterization. The syntheses of
the new monomers 5 and 7 are outlined in Scheme 1.
The reaction of alkylmagnesium bromide with N-(tri-
fluoroacetyl)-5-bromoanthranilic acid (2) is the crucial
step in achieving o-(amino keto) functionality. Attempts
to synthesize the monomer via Friedel-Crafts acylation
of aniline, 4-bromoaniline, and benzidine were unsuc-
cessful. N-Protected-5-bromo-2-nonanoylaniline (3) was
coupled under Stille conditions and then deprotected to
achieve the 3,3′-dinonanoylbenzidine (5). The overall
yield of the four-step synthesis was 24%. Initial work
targeted the 3,3′-diheptanoylbenzidine monomer (8), the
synthesis of which is described elsewhere.10 However,
the poly(2,2′-(arylene)-6,6′-bis(4-hexylquinolines)) based
on 8 had poor solubility,10 leading us to increase the
length of the alkyl chain from hexyl to octyl in the
present study. Diacetyl monomers were copolymerized
with the (o-amino keto)-functionalized 3,3′-dinonanoyl-
benzidine (5) to yield the new polyquinolines containing
bis(4-octylquinoline) in the main chain (Scheme 2). 3,3′-
Electrochemical Properties. Cyclic voltammetry
was performed on thin films of the polymers coated onto
Pt wire. Representative cyclic voltammograms (CVs) of
four of the new polyquinolines are shown in Figure 3,
and the corresponding electrochemical redox data are
collected in Table 2. CV scans on the polymers showed
quasi-reversible reduction waves, similar to those of

Macromolecules, Vol. 38, No. 23, 2005
Table 1. Physical Properties of New Polyquinolines
Soluble Polyquinolines 9541
abs
abs
em
em
λ
λ
λ
λ
max
max
max
max
TD
(°C)
Tg
(°C)
(soln)
(nm)
ꢀ
(film)
(nm)
Eogpt
(eV)
(soln)
(nm)
(film)
(nm)
polymer
MW (104)
PDI
(104 M-1 cm-1
)
φf (soln)
φf (film)
PPOQ
1.5
3.3
1.9
1.5
1.1
1.0
1.82
4.90
2.74
1.45
1.50
1.26
421
419
477
400
445
414
127
141
254
128
163
110
375
372
398
436
453
414
2.3
2.4
1.4
2.3
1.0
1.5
386
385
409
443
454
429
2.85
2.86
2.67
2.35
2.19
2.29
417
413
431
483
502
538
493
477
524
615
646
576
.18
.13
.11
.16
.20
.24
.05
.06
.04
.01
.07
.08
PBOQ
PSHQ
PBTOQ
PBTVOQ
PPZOQ
properties of the polymers. PPOQ did not exhibit an
oxidation wave in the potential range scanned in the
CVs whereas PBOQ and PSHQ (Figure 3a,b) had
irreversible oxidation peaks. PBTOQ (Figure 3d) and
PBTVOQ, with thiophene linkages, showed a slight
reversibility in their oxidation waves, similar to that
observed in analogous poly(phenylquinoline)s.17 PPZOQ,
with the electron-rich phenothiazine group, showed a
quasi-reversible oxidation peak (Figure 3c). The solid-
onset
state ionization potential (IP), estimated as IP ) E
ox
onset
+ 4.4, where E
is the onset oxidation potential vs
ox
SCE, varied from 5.17 eV for PPZOQ to 5.96 eV for
PBOQ. The electrochemically derived band gap (Eegl) of
the new polyquinolines (Table 2) was 2.30-3.14 eV.
These values, as well as the estimated HOMO/LUMO
levels, showed good agreement with previously reported,
structurally similar poly(phenylquinoline)s.17,19 This
indicates that the alkyl substitution at the 4-position
had negligible effect on the electronic structure of the
polymers.
Figure 1. TGA curve of PBOQ at a scan rate of 10 °C/min.
Photophysical Properties. Absorption spectra of
the six new polyquinolines in THF solution are shown
in Figure 4a. The lowest energy absorption bands of
most of the polymers are from π-π* transitions by
virtue of their large molar extinction coefficients (ꢀ) (ꢀmax
) (1.0-2.3) × 104 M-1 cm-1). However, the lowest
energy absorption bands of PBTOQ, PPZOQ, and
PBTVOQ, which have a clear donor-acceptor architec-
ture, can be interpreted in terms of intramolecular
charge transfer (ICT).19,20 The absorption maxima
(λambasx) of the polymers varies from 372 to 453 nm. The
phenylene-, biphenylene-, and stilbene-linked polymers
abs
max
abs
max
have the lowest λ
values (372-398 nm). The λ
of
PPZOQ, PBTOQ, and PBTVPQ show significant red
shifts relative to these polymers because the donor-
acceptor architecture of the latter polymers facilitates
large ICT. Donor-acceptor architectures in conjugated
polymers is a well-known route to lowering the band
gap of semiconducting polymers.11,19,20
Figure 2. Second heating DSC curves of PPOQ and PBOQ
(rate ) 10 °C/min).
previously reported polyquinolines.6c,d,7,17 The formal
reduction potential (Ered°′ ) (Epa + Epc)/2) varied from
-2.0 V (vs SCE) for PPZOQ (Figure 3c) to -1.56 V for
PBTVOQ. The onset reduction potential followed a trend
similar to that of Ered°′ in which PBTOQ and PBTVOQ
have the most positive values. The solid-state electron
affinity (EA) was estimated using the following relation-
The thin film optical absorption spectra of the poly-
mers are shown in Figure 4b. The solid-state absorption
bands are red-shifted by 1-15 nm compared to their
corresponding solution spectra. This phenomenon of
increased electronic delocalization in thin films com-
pared to solution is indicative of increased planarity of
the polymer backbones in the solid state. The λmax of
the polymer thin films is in the range of 385-454 nm.
Optical band gaps (Eogpt) determined from the absorp-
tion edge of the thin film spectra are also shown in Table
1. The Eogpt values range from 2.19 to 2.86 eV, with
PBTOQ (2.35 eV) and PBTVOQ (2.19 eV) having the
lowest values. These band gap values are in fair
agreement with those determined from cyclic voltam-
metry (Table 2). A comparison of the solid-state absorp-
tion spectra of the present poly(bis(4-alkylquinoline))s
to analogous poly(phenylquinoline)s shows a blue shift
onset
red
onset
is the onset
red
ship: EA ) E
+ 4.4, where E
reduction potential vs SCE.17,18 The EA values range
from 2.72 eV for PPZOQ to 3.00 eV for PBTVOQ,
reflecting the modulation of the LUMO level by the
arylene linkage. These values agree well with other
polyquinolines which have been found to be useful
n-type materials for OLEDs.6b,7,10
The electron-accepting bis(quinoline) moiety is present
in all the polymers (Chart 1), which explains the little
variation in electron affinity. However, variation of the
arylene linkage provided a modulation of the oxidative

9542 Tonzola et al.
Macromolecules, Vol. 38, No. 23, 2005
Figure 3. Cyclic voltammograms of thin films of PBOQ (a), PSHQ (b), PPZOQ (c), and PBTOQ (d) on Pt electrode. (0.1 M TBAF6
in MeCN; scan rate ) 60 mV/s).
Table 2. Electrochemical Properties of New Polyquinolinesa,b
polymer
Eredo′ (V)
Eorendset (V)
EA (eV)
Epoxeak (V)
Eoonxset (V)
IP (eV)
Eegl (eV)
PPOQ
-1.72
-1.78
-1.66
-1.57
-1.56
-2.00
-1.62
-1.58
-1.48
-1.42
-1.40
-1.68
2.78
2.82
2.92
2.98
3.00
2.72
n.o.
n.o.
n.o.
n.o.
PBOQ
1.92
1.52
1.43
1.31
0.99
1.56
1.21
1.03
0.90
0.77
5.96
5.61
5.43
5.30
5.17
3.14
2.63
2.45
2.30
2.53
PSHQ
PBTOQ
PBTVOQ
PPZOQ
a All potentials vs SCE. b Polymers were coated onto Pt wire; 0.1 M TBAPF6/MeCN. Scan rate ) 60 mV/s.
of 7-19 nm.11,19 This indicates that the π-orbitals of the
phenyl side group have some electronic interaction with
those of the backbone quinoline unit.
of these polymers (11-24%) are low, they are compa-
rable to those of other soluble polyquinolines.6b,7,10
The PL emission spectra of the polymer thin films are
shown Figure 5b. All the PL emission spectra have
The dilute solution (10-6 M) photoluminescence (PL)
spectra of the polymers in THF are shown in Figure 5a.
Five of the polymers have highly structured emission
bands whereas the emission band of PPZOQ is struc-
tureless. The emission maximum varies from 413 nm
for PPOQ and 538 nm for PPZOQ. The PL quantum
yield (φf) of the polymers in dilute solution in THF was
11-24% (Table 1). The Stokes shift is between 33 and
49 nm for the polymers, except PPZOQ in which it is
124 nm. Previously, the analogous phenothiazylene-
linked poly(phenylquinoline) (PPZPQ)19a was not stud-
ied in solution in the neutral state. However, the solid-
state emission of PPZPQ and that of a model compound
were established to be due to intramolecular excitons
with strong charge-transfer character. We believe that
ICT also explains the large Stokes shift in the PL
emission of PPZOQ. Although the PL quantum yields
broad and structureless line shapes, with emission
em
max
maxima (λ ) from 477 nm (PBOQ) to 646 nm
(PBTVOQ). Thus, variation of the arylene linkage
effectively tunes the PL emission color of the polymers.
Five of the polymers showed an increased Stokes shift
relative to that observed in solution. These features of
the thin film PL emission spectra are indicative of
aggregation effects and significant excimer formation.21
However, PPZOQ thin films displayed approximately
the same Stokes shift as in solution, indicating that the
PL emission arises from an intramolecular charge-
transfer excited state. A rough estimate of the solid-
state fluorescence quantum efficiencies of these films
without an integrated sphere shows that they are low
(1-8%), consistent with other polyquinolines.6c,d,7,10

Macromolecules, Vol. 38, No. 23, 2005
Soluble Polyquinolines 9543
Figure 4. Optical absorption spectra of new polyquinolines
Figure 5. Photoluminescence (PL) spectra of new polyquino-
lines in dilute THF (10-6 M) solutions (a) and as thin films
(b). All polymers were excited at their respective absorption
maximum.
in dilute THF (10-6 M) solutions (a) and as thin films (b).
Electroluminescence and Electron Transport
Properties. We investigated the intrinsic electrolumi-
nescence (EL) of the new polyquinolines by using poly-
The brightness of the OLEDs was 69-209 cd/m2, and
the external quantum efficiency (EQE) was 0.01-0.05%
(Table 3). The device efficiency and brightness are in
accord with the poor fluorescence quantum yields of thin
films and the large barrier to hole injection into the
n-type polymers. The OLED performance of the new
polyquinolines is comparable to those of previous
polyquinoline devices.6c,d,7,10,22
n-Type (electron transport) polymers that can be used
in bilayer OLED architectures with organic-solvent
soluble emissive polymers are relatively scarce, al-
though some polypyridines, polyquinolines, and poly-
quinoxalines that are soluble in formic acid have been
explored.3a,6,7 Such an electron transport material (ETM)
can increase device performance by reducing the barrier
to electron injection, by blocking holes, and by moving
the recombination zone away from the cathode. We have
investigated the electron transport properties of the new
polyquinolines by using MEH-PPV as the emissive
polymer in LEDs of the type ITO/PEDOT/MEH-PPV/
polyquinoline/Al. The film thickness of the polyquino-
lines as an electron transport layer in these diodes was
in the range of 55-60 nm. These OLEDs showed EL
spectra characteristic of MEH-PPV, having an emission
peak at about 580 nm as exemplified in Figure 6b. The
diodes showed no emission from the polyquinoline layer,
(ethylenedioxythiophene)/poly(styrenesulfonic
acid)
(PEDOT) thin film on indium tin oxide (ITO) as the
anode, poly(N-vinylcarbazole) (PVK) as the hole trans-
port layer, the spin-coated polyquinoline as the emissive
layer, and aluminum as the cathode: ITO/PEDOT/PVK/
polyquinoline/Al. The film thicknesses of the emissive
polyquinolines were ∼75 nm. Representative EL spectra
of four of the polymers are shown in Figure 6a. Emission
EL
max
maxima (λ ) varied from 513 to 656 nm (Table 3),
indicating that we can effectively tune the emission color
from blue-green to red by varying the arylene linkage.
The EL maxima for PPOQ, PBOQ, and PSHQ are
between 513 and 580 nm. The EL spectra for these
polymers are considerably red-shifted 36-87 nm, rela-
tive to the PL spectra. The 551-656 nm EL maxima of
PBTOQ, PBTVOQ, and PPZOQ are more consistent
with the PL maxima.
The voltage-current and voltage-luminance curves
for all six polyquinoline OLEDs are shown in Figure 7.
The turn-on voltage (electric field) of the diodes was
8.5-12 V (∼1.2 × 106 V/cm). PPZOQ, which has the
smallest barrier to hole injection (IP ) 5.17 eV), has
the lowest turn-on voltage. The generally high turn-on
voltages of these diodes are because of the large film
thicknesses and the large barriers for charge injection.

9544 Tonzola et al.
Macromolecules, Vol. 38, No. 23, 2005
Figure 6. Electroluminescence (EL) spectra of selected
polyquinolines in ITO/PEDOT/PVK/polyquinoline/Al diodes (a)
and for a ITO/PEDOT/MEH-PPV/PPOQ/Al diode (b).
Figure 7. Current density-voltage characteristics (a) and
luminance-voltage characteristics (b) for ITO/PEDOT/PVK/
polyquinoline/Al diodes.
indicating that recombination was occurring strictly in
the MEH-PPV. The current-voltage and luminance-
voltage characteristics of the MEH-PPV diodes using
the new polyquinolines as electron transport materials
are shown in Figure 8. The turn-on voltage (electric
field) of these LEDs was 4.5-8.0 V (∼9 × 105 V/cm).
The best performance was found in diodes using
PBTVOQ as the electron transport material, achieving
a brightness of 740 cd/m2 and an external quantum
efficiency of 0.12%. PSHQ based diodes had a similar
brightness (659 cd/m2) and efficiency (0.11%) but a lower
turn-on voltage of 4.5 V. This represents an increase in
both brightness and efficiency over single-layer MEH-
PPV devices or single-layer polyquinoline diodes. Diodes
using the other polyquinolines as ETMs had bright-
nesses of 451-557 cd/m2 and EL device efficiencies
(EQEs) between 0.08 and 0.11%. It is reasonable to
conclude that the performance of all the MEH-PPV
diodes incorporating these polyquinolines as ETMs is
in the same range. The performance of these diodes is
equal to or higher than other recent work where
polyquinolines were employed strictly as the electron
transport layer with emissive MEH-PPV.6e,f However,
these results are considerably lower than those based
on polyquinolines incorporating a bis(phenylquinoline)
and a regioregular dialkylbithiophene in the backbone.6c,d
The molecular weights of those previous polyquinolines
were significantly higher ((1.9-14.9) × 104) than the
present materials.6c,d The lower molecular weights of the
Table 3. Electroluminescent Device Properties of New Polyquinolines
as an emissive materiala
as an electron transport materialb
Lmax
Jmax
Lmax
Jmax
EL
max
EL
max
polymer
(cd/m2)
λ
(nm)
(mA/cm2)
Von (V)
EQE (%)
(cd/m2)
λ
(nm)
(mA/cm2)
Von (V)
EQE (%)
PPOQ
209
176
127
25
580
208
184
205
110
479
500
11
12
11
9.5
9
0.05
0.04
0.03
0.005
0.01
0.02
451
557
659
n.o.
740
470
580
580
585
500
500
500
n.o.
500
496
7.5
8
4.5
n.o.
7.5
7
0.09
0.08
0.11
n.o.
0.12
0.08
PBOQ
513
578
610
656
551
PSHQ
PBTOQ
PBTVOQ
PPZOQ
n.o.
69
578
575
81
8.5
a Polyquinolines were in diodes of the type ITO/PEDOT/PVK/polyquinoline/Al. b The polyquinolines were in diodes of the type ITO/
PEDOT/MEH-PPV/polyquinoline/Al.

Macromolecules, Vol. 38, No. 23, 2005
Soluble Polyquinolines 9545
were obtained from bilayer OLEDs based on MEH-PPV
as the emitter and the new polyquinolines as the
electron transport layer.
The bis(4-alkylquinoline) platform demonstrated here
allows the ready synthesis of diverse new soluble
polyquinolines; it thus opens the door to further explo-
ration of this n-type building block in new materials for
organic electronics. New polymer structures incorporat-
ing more exotic arylene linkages may allow the optimi-
zation of the materials for improved performance in
optoelectronic devices. Furthermore, optimization of the
reaction conditions should lead to higher molecular
weight polymers and could likely increase device per-
formance.
Experimental Section
Materials. Diacetylbenzene, diacetylbiphenyl, 5-bromo-
anthranilic acid (1), 1-bromooctane, hexamethylditin, diphenyl
phosphate (DPP), m-cresol, and Pd(PPh3)4 were purchased
from Aldrich and were used as received with the exception of
m-cresol, which was distilled prior to polymerization.
Synthetic Procedures. N-Trifluoroacetyl-5-bromoanthra-
nilic acid (2),23 4,4′-diacetylstilbene,24 1,2-bis(5-acetyl-2-thienyl)-
ethylene,11b 10-decylphenothiazine,25 and 3,3′-heptanoylben-
zidine (8)10 were synthesized according to literature procedures.
N-(Trifluoroacetyl)-5-bromo-3-nonanoylaniline (3). 5
equiv of an ethereal solution of the octylmagnesium bromide
was added to 11 g (35.0 mmol) of 2 in 500 mL of anhydrous
THF at 0 °C. The reaction was refluxed overnight and then
poured into water/CH2Cl2 mixture. The organic layer was
separated and concentrated, washed with 1 M NaOH and
water, and dried with MgSO4, and the solvent was removed
to yield an orange oil. The oil was purified on silica gel column
(2:1 hexanes:CH2Cl2) to yield 9.3 g of pale orange oil (56%).
1H NMR (499 MHz, CDCl3, 298 K) δ (ppm): 12.89 (s, 1H); 8.67
(s, 1H); 8.14 (d, 1H); 7.74 (d, 1H); 3.05 (d, 2H); 1.75 (t, 2H);
1.35 (m, 6H); 0.92 (t, 3H).
N,N-(Trifluoroacetyl)-3,3′-dinonanoylbenzidine (4). 13.9
g (35.3 mmol) of 3, 6.0 g (18.3 mmol) of [Me3Sn]2, and 0.62 g
(0.54 mmol) of Pd(PPh3)4 in 200 mL of anhydrous toluene were
refluxed overnight. The reaction mixture was poured into CH2-
Cl2, and the resulting crystals were collected, dissolved in CH2-
Cl2, washed with H2O several times, and dried, and the solvent
was evaporated to yield an orange solid which was recrystal-
lized from a mixture of CH2Cl2/MeOH to yield 6.0 g of orange
needles (56%). 1H NMR (499 MHz, CDCl3, 298 K) δ (ppm):
12.89 (s, 2H); 8.76 (s, 2H); 8.07 (d, 2H); 7.75 (d, 2H); 3.05 (d,
4H); 1.75 (t, 4H); 1.35 (m, 12H); 0.92 (t, 6H). Calcd for
C30H34F6N2O4: C, 62.19; H, 6.45; F, 17.36; N, 4.27; O, 9.75.
Found: C, 62.32; H, 6.10; N, 4.33.
Figure 8. Current density-voltage characteristics (a) and
luminance-voltage characteristics (b) for ITO/PEDOT/MEH-
PPV/polyquinoline/Al diodes.
present polyquinolines may account for their poorer
performance as ETMs, compared to our previously
reported materials, since the electron affinities of the
two classes of polyquinolines are comparable.
Conclusions
3,3′-Dinonanoylbenzidine (5). 3.0 g (4.9 mmol) of 4 and
6.0 g (56.6 mmol) of Na2CO3 were added to a deareated solution
of 30 mL of H2O and 100 mL of EtOH. The reaction mixture
was refluxed for 3 days, poured into water/CH2Cl2 mixture,
washed with water, and dried with MgSO4, and the solvent
We have devised a new synthetic route to soluble
n-type conjugated polyquinolines. Synthesis of the key
o-amino keto-functionalized monomer, 3,3′-dinonanoyl-
benzidine (5), was achieved by reacting alkylmagnesium
bromide with the appropriate carboxylic acid. The new
polymers derived from this monomer contained bis(4-
alkylquinoline) in the main chain, facilitating solubility
in organic solvents. The polymers had glass transitions
of 110-254 °C and decomposed at above 400 °C, proving
them to be thermally robust materials suitable for
application in organic electronic devices. By varying the
arylene linkage in poly(2,2′-arylene-6,6′-bis(4-alkylquin-
oline))s from p-phenylene to bis(thienyl)vinylene, the
optical band gap, redox properties, and electrolumines-
cence color could be tuned over a wide range. The
electron affinity or LUMO energy level of the polymers
was in the range 2.72-3.00 eV, and blue-green, green,
yellow, orange, and red electroluminescence colors were
achieved with moderate brightness and efficiency. En-
hanced electroluminescence efficiency and brightness
1
was removed to yield 1.9 g of yellow needles (88%). H NMR
(499 MHz, CDCl3, 298 K) δ (ppm): 7.88 (s, 2H); 7.47 (d, 2H);
6.75 (d, 2H); 6.32 (s, 4H); 3.02 (d, 4H); 1.79 (t, 4H); 1.35 (m,
12H); 0.93 (t, 6H). FT-IR (NaCl, cm-1): 3435, 3323, 2920, 2852,
1651, 1624, 1552, 1481, 1258, 1179, 968, 820. Calcd for
C26H36N2O2: C, 77.54; H, 9.54; N, 6.03; O, 6.89. Found: C,
77.57; H, 9.29; N, 6.07.
2,7-Diacetyl-10-decylphenothiazine (7). 10.5 g (80.0
mmol) of AlCl3 was slowly added to a mixture of 12.3 g (36.2
mmol) of 10-decylphenothiazine (6) and 6.5 g (82.0 mmol) of
acetyl chloride in CS2 at 0 °C. The reaction was stirred at room
temperature for 3 h and then poured into ice. The product was
extracted into CH2Cl2 (3 × 100 mL) and then eluted through
silica gel column with CH2Cl2. The yellow solid was recrystal-
lized twice from hexanes to yield 5.3 g (39%) of yellow needles.
FT-IR (NaCl, cm-1): 2917, 2849, 1670, 1565, 1476, 1355, 1266,
1
1238, 796. H NMR (499 MHz, CDCl3, 298 K) δ (ppm): 7.70
(m, 4H), 6.90 (d, 2H), 3.92 (t, 2H), 2.55 (s, 6H), 2.49 (m, 2H),

9546 Tonzola et al.
Macromolecules, Vol. 38, No. 23, 2005
1.83 (m, 2H), 1.27 (m, 14H), 0.91 (d, 3H). Calcd for C22H29NS:
C, 77.82; H, 8.61; N, 4.13; S, 9.44. Found: C, 77.53; H, 8.51;
N, 3.77.
in air at room temperature. In solution, the fluorescence
quantum yield in 10-6
M THF was determined using a
perylene standard (87%). A rough estimate of the fluorescence
quantum yield in the solid state was achieved by comparing
the thin film of the polymer with a thin film of 9,10-
diphenylanthracene in poly(methyl methacrylate) as a refer-
ence standard (83%).26
General Procedure for Polymerization. 1 equiv of the
diacetyl monomer, 1 equiv of 3,3′-dinonanoylbenzidine, 6.0 g
of diphenyl phosphate, and 3 g of m-cresol were added to a
cylindrical reaction vessel. The reactor was purged with argon
for 20 min. The mixture was mechanically stirred under static
argon as the temperature was gradually raised to 140 °C over
a period of 12 h. The polymerization mixture was stirred at
this temperature for 72 h and then precipitated into 10%
triethylamine/ethanol. The precipitate was collected by vacuum
filtration and extracted on a Soxhlet apparatus for 72 h with
20% triethylamine/ethanol. The polymer was dissolved in
CHCl3 and precipitated into ethanol, collected by vacuum
filtration, and dried at 60 °C in a vacuum for 24 h.
Poly(2,2′-(p-phenylene)-6,6′-bis(4-octylquinoline))
(PPOQ). 570 mg of yellow solid recovered (90% yield). 1H NMR
(499 MHz, CDCl3, 298 K) δ (ppm): 8.18 (d, 2H); 8.09 (s, 2H);
7.99 (d, 2H); 7.77 (s, 2H); 7.61 (d, 2H); 7.54 (d, 2H); 2.60 (s,
4H); 1.70 (m, 4H); 1.35 (m, 20H); 0.77 (t, 6H). FT-IR (NaCl,
cm-1): 3059, 2924, 2853, 1593, 1553, 1495, 1347, 1298, 1240,
1107, 1015, 826, 754.
Cyclic Voltammetry. Cyclic voltammetry experiments
were done on an EG&G Princeton Applied Research poten-
tiostat/galvanostat (model 273A). Data were collected and
analyzed by the model 270 Electrochemical Analysis System
Software on a PC computer. A three-electrode cell was used
in all experiments as previously described.17,18 Platinum wire
electrodes were used as both counter and working electrodes,
and silver/silver ion (Ag in 0.1 M AgNO3 solution, Bioanalytical
System, Inc.) was used as a reference electrode. The Ag/Ag+
(AgNO3) reference electrode was calibrated at the beginning
of the experiments by running cyclic voltammetry on ferrocene
as the internal standard in an identical cell without any
polymer on the working electrode. By means of the internal
ferrocenium/ferrocene (Fc+/Fc) standard, the potential values,
obtained in reference to Ag/Ag+ electrode, were converted to
the saturated calomel electrode (SCE) scale. The films of all
polymers were coated on the Pt working electrode by dipping
the Pt wire into the viscous solution in chloroform and then
drying it in a vacuum oven at 80 °C for 8 h. An electrolyte
solution of 0.1 M TBAPF6 in acetonitrile was used in all
experiments. All solutions in the three-electrode cell were
purged with ultrahigh-purity N2 for 10-15 min before each
experiment, and a blanket of N2 above the solution was used
during the experiment.
Poly(2,2′-(4,4′-diphenylene)-6,6′-bis(4-octylquino-
line)) (PBOQ). 585 mg of yellow solid recovered (85% yield).
1H NMR (499 MHz, CDCl3, 298 K) δ (ppm): 8.22 (d, 2H); 8.11
(s, 2H); 8.01 (d, 2H); 7.78 (s, 2H); 7.71 (d, 4H); 7.60 (d, 4H);
2.67 (s, 4H); 1.66 (m, 4H); 1.28 (m, 20H); 0.85 (t, 6H). FT-IR
(NaCl, cm-1): 3032, 2924, 2853, 1593, 1495, 1354, 1005, 825.
Poly(2,2′-(4,4′-stilbene)-6,6′-bis(4-hexylquinoline))
(PSHQ). 3,3′-Diheptanoylbenzidine was used in place of 3,3′-
dinonanoylbenzidine. 0.450 g (87%) of pale yellow powder was
1
recovered. H NMR (499 MHz, CDCl3, 298 K) δ (ppm): 8.21
Fabrication and Characterization of LEDs. Two types
of OLEDs were fabricated and evaluated: ITO/PEDOT/PVK/
polyquinoline/Al and ITO/PEDOT/MEH-PPV/polyquinoline/
Al. Sequential spin-coating of the layers onto a cleaned ITO-
coated glass substrate was used to fabricate the devices. A thin
layer of poly(ethylenedioxythiophene)-poly(styrenesulfonate)
(PEDOT) (∼40 nm) was first spin-coated from its solution in
water onto ITO and dried at 80 °C in a vacuum for 12 h. For
ITO/PEDOT/PVK/polyquinoline/Al devices, PVK thin film was
spin-coated from a 0.5 wt % solution in CHCl3 onto the PEDOT
layer and dried at 50 °C in a vacuum for 10 h. In the case of
ITO/PEDOT/MEH-PPV/polyquinoline/Al devices, the MEH-
PPV thin film was spin-coated from a 0.5 wt % solution in
CHCl3 onto the PEDOT layer and dried at 50 °C in a vacuum
for 10 h. A thin film of the polyquinoline was then spin-coated
from a 0.5 wt % solution in formic acid onto the MEH-PPV
thin film. The multilayer thin films were dried in a vacuum
at 80 °C for 10 h before deposition of the aluminum electrode
under vacuum (3 × 10-6 Torr). A 100 nm thick aluminum layer
was thermally deposited to form active diode areas of 0.2 cm2
(5 mm diameter).
(d, 2H); 8.11 (s, 2H); 8.01 (d, 2H); 7.66 (s, 2H); 7.55 (d, 4H);
7.43 (d, 4H); 3.75 (dd, 2H); 2.68 (s, 4H); 1.68 (m, 4H); 1.28 (m,
12H); 0.85 (t, 6H).
Poly(2,2′-(5-(2-thien-2-ylethenyl)thien-2-yl)-6,6′-bis(4-
hexylquinoline)) (PBTOQ). 330 mg of orange solid recovered
(51% yield). 1H NMR (499 MHz, CDCl3, 298 K) δ (ppm): 8.35
(d, 2H); 8.17 (s, 2H); 8.06 (d, 2H); 7.54 (s, 2H); 7.05 (d, 4H);
6.93 (d, 4H); 2.67 (s, 4H); 1.66 (m, 4H); 1.28 (m, 20H); 0.91 (t,
6H). FT-IR (cm-1): 2924, 2854, 1653, 1558, 1541, 1457, 1357,
1227, 1194, 1041, 926, 852, 721, 667.
Poly(2,2′-(5-(2-thien-2-ylethenyl)thien-2-yl)-6,6′-bis(4-
hexylquinoline)) (PBTVOQ). 370 mg of orange solid recov-
ered (86% yield). 1H NMR (499 MHz, CDCl3, 298 K) δ (ppm):
8.35 (d, 2H); 8.17 (s, 2H); 8.06 (d, 2H); 7.54 (s, 2H); 7.05 (d,
4H); 6.93 (d, 4H); 3.33 (dd, 2H); 2.67 (s, 4H); 1.66 (m, 4H);
1.28 (m, 20H); 0.91 (t, 6H). FT-IR (cm-1): 2920, 2902, 1585,
1544, 1456, 1421, 1022, 826, 699, 621.
Poly(2,2′-(10-decylphenothiazine-2,7-diyl)-6,6′-bis(4-oc-
tylquinoline)) (PPZOQ). 470 mg of orange solid recovered
(75% yield). 1H NMR (499 MHz, CDCl3, 298 K) δ (ppm): 8.31
(d, 2H); 8.27 (s, 2H); 8.03 (d, 2H); 7.77 (s, 2H); 7.61 (d, 2H);
7.31 (d, 2H); 7.03 (s, 2H); 3.65 (d, 2H); 2.68 (s, 4H); 1.83 (m,
2H); 1.28 (m, 38H); 1.05 (t, 3H) 0.88 (t, 6H). FT-IR (NaCl,
cm-1): 3059, 2924, 2853, 1593, 1495, 1466, 1347, 1015, 841.
General. 1H NMR spectra were recorded on a Bruker DRX-
499 at 499 MHz using CDCl3 as the solvent. Fourier trans-
formation infrared (FT-IR) spectroscopy was done on a film
on a NaCl plate using a Perkin-Elmer 1720 FT-IT spectrom-
eter. Thermogravimetric analysis of the polymers was con-
ducted on a TA Instruments Q50 TGA. A heating rate of 10
°C/min under flowing N2 was used with runs being conducted
from room temperature to 800 °C. Differential scanning
calorimetry (DSC) was run on a TA Instruments Q100 DSC
under flow of N2. The heat-cool-heat method was used with
an initial heat rate of 20 °C/min and a cooling rate of 10 °C/
min and a final heating rate of 10 °C/min. All reported
transitions were based upon the second heating.
The film thickness was measured by using an Alpha step
profilometer (model 500, KLA-Tencor, San Jose, CA), which
has a resolution of (1 nm. Electroluminescence (EL) spectra
were measured on a Photon Technology International Inc.
(PTI) Instrument fluorimeter. The electrical characteristics of
the devices were measured on an HP4155A semiconductor
parameter analyzer together with a Grasby S370 optometer
equipped with a calibrated luminance sensor head. The EL
quantum efficiencies of the diodes were measured by using
the procedures similar to those previously reported.27 All the
fabrications and measurements were done under ambient
laboratory conditions.
Acknowledgment. C.T. thanks Angela P. Gifford
for her assistance in purifying new materials and Dr.
XiangXing Kong for supplying the N-decylphenothiaz-
ine. This research was supported by the NSF STC-
MDITR at the University of Washington, the NSF (CTS-
0437912), and in part by the Air Force Office of
Scientific Research (Grant F49620-03-1-0162).
Photophysics. Optical absorption spectra were obtained
by using a Lambda-900 UV/vis/near-IR spectrophotometer
(Perkin-Elmer). Steady-state photoluminescence (PL) studies
were done by using a Photon Technology International Inc.
(PTI) instrument and a Xe lamp (75 W) as the excitation source

Macromolecules, Vol. 38, No. 23, 2005
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