High-Efficiency Saturated Red Emitting Polymers Derived from Fluorene and Naphthoselenadiazole

Article abstract of DOI:10.1021/ma035743u

A variety of novel light-emitting copolymers derived from 9,9-dioctylfluorene (DOF) and 2,1,3-naphthozoselenadiazole (NSeD) were prepared by the palladium-catalyzed Suzuki coupling reaction. The feed ratios of DOF to NSeD were 99.9:0.1, 99.5:0.5, 99:1, 98:2, 95:5, and 85:15. All of the polymers are soluble in common organic solvents and highly fluorescent in solid state. Devices based on the copolymers emit saturated red light, and the emission slightly red-shifted gradually with increasing NSeD's contents. The maximal external quantum efficiency of the polymer light-emitting devices (PLED) reaches 3.1%, and luminous efficiency is greater than 1.0 cd/A with emission maximum at 657 nm and Commission Internationale de L'Eclairage (CIE) coordinates of (0.64, 0.33). This is the highest efficiency with saturated red emission for a single-layer device with nonblend type emitter reported so far in the scientific literature. This indicates that the new EL polymers based on fluorene and naphthoselenadiazole are promising as a red emitter in polymer light-emitting displays.

Full text of DOI:10.1021/ma035743u

Macromolecules 2004, 37, 1211-1218
1211
High-Efficiency Saturated Red Emitting Polymers Derived from
Fluorene and Naphthoselenadiazole
J ia n Ya n g, Ch a n gyu n J ia n g, Yon g Zh a n g, Ren qia n g Ya n g, Wei Ya n g,
Qion g Hou , a n d Yon g Ca o*
Polymer Optoelectronic Materials and Devices, South China University of Technology,
Guangzhou, China 510640
Received November 20, 2003; Revised Manuscript Received December 4, 2003
ABSTRACT: A variety of novel light-emitting copolymers derived from 9,9-dioctylfluorene (DOF) and
2,1,3-naphthozoselenadiazole (NSeD) were prepared by the palladium-catalyzed Suzuki coupling reaction.
The feed ratios of DOF to NSeD were 99.9:0.1, 99.5:0.5, 99:1, 98:2, 95:5, and 85:15. All of the polymers
are soluble in common organic solvents and highly fluorescent in solid state. Devices based on the
copolymers emit saturated red light, and the emission slightly red-shifted gradually with increasing NSeD’s
contents. The maximal external quantum efficiency of the polymer light-emitting devices (PLED) reaches
3.1%, and luminous efficiency is greater than 1.0 cd/A with emission maximum at 657 nm and Commission
Internationale de L’Eclairage (CIE) coordinates of (0.64, 0.33). This is the highest efficiency with saturated
red emission for a single-layer device with nonblend type emitter reported so far in the scientific literature.
This indicates that the new EL polymers based on fluorene and naphthoselenadiazole are promising as
a red emitter in polymer light-emitting displays.
In tr od u ction
phene,13-16 ethylenedioxythiophene,16-18 and benzothia-
diazole.11,19-21 For example, red-emitting alternating
copolymer of fluorene and 4,7-di-2-thienyl-2,1,3-ben-
zothiadiazole (DBT) has been reported in the patent
literature by the Dow Chemical group.22 Significant
enhancement in efficiency (up to 1.4%) with emission
peak at 663 nm for the PFO-DBT copolymer was
recently reported by our group.11 Cambridge Display
Technology (CDT)23 announced a saturated red emitter
with high external quantum efficiency of 3% and power
efficiency of 1.2 Lm/W with emission peak at 650 nm,
though the detailed chemical structure was not dis-
closed. Recently we reported the synthesis and proper-
ties of copolymers with 9,9-dioctylflourene as a main
chain building unit and the selen-containing heterocycle
2,1,3-benzoselenadiazole (BSeD) as the narrow-band-
gap component.12 We have shown that, in replacement
of sulfur by selenium in the aromatic heterocycles, EL
emission of the device from the resulting polymer is red-
shifted about 50-60 nm in comparison with the corre-
sponding sulfur analogue. For example, devices from
polyfluorene copolymer with 15% molar ratio of BSeD
unit emits orange-red light with λmax ) 582 nm in
contrast to 530 nm for copolymer with 15% of its sulfur
analogue, benzothiadiazole.11a To move emitter further
to saturated red side, the utilization of comonomer with
more narrow band gap than benzoselenodiazole is
necessary.
Since the initial discovery of conjugated polymer
electroluminescence reported by Burroughes et al.,
polymer light-emitting diodes (PLEDs) have attracted
considerable interest because of their potential applica-
tion in flat panel displays.1 PLEDs can now achieve high
brightness and efficiency. Their operation lifetime is
improving rapidly.2 PLEDs offer advantages of low turn-
on and operating voltages and wide viewing angles. The
range of colors available from PLEDs spans the entire
visible spectrum. It is believed that PLED technology
is one of the most promising for next generation large-
area flat panel displays.3
Conjugated polymers with aromatic or heterocyclic
units generally absorb light with wavelengths of 300-
500 nm due to π-π* transitions.4 A high QE, a color
purity, and a material stability are essential for the full-
color flat panel application. During the past 10 years, a
variety of opto-electroactive conjugated backbone struc-
tures, such as poly(p-phenylenevinylene) (PPV),5 poly-
(p-phenylene) (PPP),6 polythiophene (PT),7 and polyflu-
orene (PF),8 have been prepared. Among them, poly(9,9-
di-n-alkylflourene) attracts special attention as a blue-
light-emitting polymer, for it shows highly efficient
photoluminescence (PL) and electroluminescence (EL),
excellent thermal and oxidative stability, and good
solubility in common organic solvents.8 Normally, poly-
fluorene homopolymers have a large band-gap and emit
blue light. Significant efforts have been made to tune
color to longer wavelength for fluorene-based poly-
mers.9-12 Compared with a high-efficiency green poly-
fluorene emitter reported in the scientific literature, the
polymer emitter with saturated red emission remains
a great challenge. A method of tuning emission color of
polyfluorenes over entire visible region is incorporating
narrow band-gap comonomer into polyfluorene back-
bone. Most widely used narrow-band-gap comonomers
are varieties of aromatic heterocycles such as thio-
In this paper we synthesized a new conjugated Se-
containing heterocyclic monomer 2,1,3-naphthoselena-
dizole (NSeD) (structure in Scheme 1) which has more
extended p-conjugation than benzoselenadiazole. On the
basis of this new monomer, a series of novel copolymers
derived from PFO and NSeD were synthesized by the
palladium-catalyzed Suzuki coupling method. A special
feature of Suzuki coupling is that it allows an alternat-
ing type of copolymer to be obtained in the case of A-B
comonomers, while typical cross-coupling of dibromides
provides a multiblock copolymer. In the case of Suzuki
coupling, each individual narrow-band-gap unit is sepa-
* Corresponding author. E-mail: poycao@scut.edu.cn.
10.1021/ma035743u CCC: $27.50 © 2004 American Chemical Society
Published on Web 01/16/2004

1212 Yang et al.
Sch em e 1. Syn th etic Rou te of
Macromolecules, Vol. 37, No. 4, 2004
ular weights of these polymers are relatively high, from
8000 to 60 000 with a polydispersity index (Mw/Mn) from
2.09 to 3.09, consistent with a polycondensation reac-
tion. The Se contents of these polymers were measured
by atomic absorption spectroscopy, and the results are
listed in Table 1. We note that the calculated actual
copolymer composition based on independent N and Se
measurements is very close to the experimental error.
Once the monomer 4,7-dibromo-2,1,3-naphthoselena-
diazole (5) used in the copolymerization is equal to or
greater than 2%, the actual composition of the NSeD
in the copolymer is remarkably reduced in comparison
with that of the monomer feed ratio. The low solubility
of monomer NSeD in toluene is responsible for the low
NSeD incorporation ratio. The molecular weights of 6f
were less than those of other copolymers. A slightly
higher actual NSeD content in 0.1% feed ratio must be
related to inaccuracy caused by the analytical method.
4,7-Dibr om o-2,1,3-n a p h th oselen a d ia zole
rated on both sides by wide-band-gap segments, when
the narrow-band-gap component is less than or equal
to 50% in the copolymer. The 2,1,3-naphthoselenadizole
unit in the copolymer is isolated from both sides by
fluorene host segment functions as a powerful exciton
trap which allows efficient intramolecular energy trans-
fer from the fluorene segment to the NSeD unit.
Saturated red emission at the maximum wavelength of
657 nm was obtained. The highest external quantum
efficiency of device fabricated with this type of copolymer
is of 3.1% ph/el, and luminous efficiency is of 0.9 cd/A.
To the best of our knowledge, this is the highest
efficiency reported so far for nondoped fluorescent
polymer LEDs in the scientific literature.
Op tica l P r op er ties a n d Electr och em ica l Ch a r -
a cter istics. The UV-vis absorption properties of the
conjugated polymers based on 9,9-dioctylflourene and
naphthoselenadiazole are presented in Table 2. Two
absorption bands peaked at 390 and 550 nm were ob-
served for PFO-NSeD copolymers in chloroform solu-
tion (5 × 10-5 M) (Figure 1a). The peak positions are
insensitive to NSeD content in contrast to the magni-
tudes of the two bands. Compared with the absorption
spectrum of pure PFO, the 390 nm peak in PFO-NSeD
copolymers can be identified due to fluorene segments.
The intensities of the 550 nm band increase linearly
with the NSeD content, suggesting that NSeD units
contribute to the 550 nm absorption band. The absorp-
tion peak of 550 nm is hardly seen for copolymers with
0.1 and 0.5% NSeD content. Table 2 shows the molar
absorption coefficients in CHCl3 solution for both fluo-
rene and NSeD peaks. The NSeD unit has a similar
absorption coefficient as the fluorene unit (Table 2). This
forms a sharp contrast with the polyfluorene copolymers
with other narrow-band-gap comonomers, such as 2,1,3-
benzoselenadiazole (BSeD) and dithienbenzothiadiazole
(DBT) units, which show much higher molar absorption
coefficients than the fluorene segment.11a As in other
wide-narrow-band-gap copolymers, the narrow band
unit in the solid-state films shows less absorption
intensity than in the solution. Thereby the NSeD peak
is much less evident for copolymers with low NSeD
content (0.1-1%). Figure 1b shows that absorption
spectra in solid-state film are slightly red-shifted (around
10 nm) in comparison with that in solution. From onset
Resu lt a n d Discu ssion
Syn th esis a n d Ch a r a cter iza tion . The general syn-
thetic routes toward the monomers and polymers are
outlined in Scheme 1 and Scheme 2. Monomers 2 and 3
were prepared following the already published proce-
dure.22,24,25 2,3-Diamino-1,4-dibromonaphthalene (4) was
synthesized, with some modification, according to the
method described by J ohansson et al.26 4,7-Dibromo-
2,1,3-naphthoselenadizole (5) was prepared from 4 and
SeO2 in hot ethanol.
Conjugated copolymers derived from 2,7-dibromo-9,
9-dioctylfluorene (2), 2,7-bis (4,4,5,5-tetramethyl-1,3,2-
dioxaborolan-2-yl)-9,9-dioctylfluorene (3), and 4,7-di-
bromo-2,1,3-naphthoselenadiazole (5) have been pre-
pared by using palladium-catalyzed Suzuki coupling
methods. The utilization of 2,7-bis(4,4,5,5-tetramethyl-
1,3,2-dioxaborolan-2-yl)-9,9-dioctylfluorene (3) simplified
their purification by column chromatography combined
with the advantage of the presence of a protecting group
on the boronic acid moieties. The comonomer ratios of
PFO to NSeD are 99.9:0.1, 99.5:0.5, 99:1, 98:2, 95:5, and
85:15, and the corresponding copolymers are named
6a -f, respectively. The resulted copolymers are readily
soluble in CHCl3, THF, and toluene. The average molec-
Sch em e 2. Syn th etic Rou te of Cop olym er s

Macromolecules, Vol. 37, No. 4, 2004
Red Emitting Polymers 1213
Ta ble 1. Molecu la r Weigh ts of th e Cop olym er s a n d N a n d Se Con ten t in th e Cop olym er s
N content
in the feed
N content
in the
Se content
in the feed
Se content
in the
NSeD content
in the copolymers in the copolymers (%)
NSeD content
Mn
composition copolymers composition copolymers
(%) according
to Se content
according to N
content
copolymers
(×103) Mw/Mn
(%)
(%)
(%)
(%)
PFO-NSeD 0.1 (6a )
PFO-NSeD 0.5 (6b)
PFO-NSeD 1 (6c)
PFO-NSeD 2 (6d )
PFO-NSeD 5 (6e)
PFO-NSeD 15 (6f)
21
60
24
23
18
8
2.23
3.09
2.46
2.32
2.09
2.61
0.0072
0.036
0.072
0.14
0.37
1.15
0.013
0.030
0.069
0.081
0.28
0.02
0.10
0.20
0.41
1.02
3.25
0.04
0.08
0.20
0.24
0.40
2.02
0.20
0.40
1.00
1.17
1.96
10.86
0.18
0.42
0.96
1.13
3.82
9.54
0.82
Ta ble 2. UV-Vis P r op er ties of Cop olym er s in CHCl3
The electrochemical behavior of the copolymers was
investigated by cyclic voltammetry (CV) (Figure 2).
Table 3 summarizes oxidation and reduction potentials
derived from the onset in the cyclic voltammograms of
the copolymers. We can record only one p-doping process
and one n-doping process. The onset of oxidation process
is about 1.32-1.40 V, which is very close to the data
reported for polyfluorene homopolymer, Eox ) 1.4 V and
Ip ) 5.8 eV.27 This peak is attributed to p-doping of PFO
segments. The onset of n-doping processes of copolymers
is -(0.72-0.78) V. Since the reduction potential for
polyfluorene homopolymer was observed typically at
-2.28 V,27 the reduction wave at -(0.72-0.78) V must
be attributed to the reduction process for the NSeD unit.
We were unable to record a second reduction wave
corresponding to the fluorene segment. It is probably
due to the instability of the reduced state of these
copolymers at higher negative voltage. HOMO and
LUMO levels calculated by empirical formulas (EHOMO
) -e(Eox + 4.4) eV and ELUMO ) -e(Ered + 4.4) eV)28
are also listed in Table 3. The HOMO and LUMO levels
are almost identical for copolymer of different composi-
tion. From the obtained oxidation and reduction poten-
tial, we estimate electrochemical band gap at ca. 2.06-
2.16 eV for copolymers (Table 3). This value is close to
the optical band gap determined for NSeD unit from
absorption spectra in the solid film (Table 3).
molar absorption coeff,
ꢀa (mol-1 L cm-1
)
copolymers
λabs/nm
fluorene
NSeD
PFO-NSeD 0.1 (6a )
PFO-NSeD 0.5 (6b)
PFO-NSeD 1 (6c)
PFO-NSeD 2 (6d )
PFO-NSeD 5 (6e)
PFO-NSeD 15 (6f)
391
391
385, 556
390, 559
389, 555
353, 563
2.67 × 104
2.71 × 104
3.85 × 104
3.47 × 104
2.69 × 104
3.30 × 104
1.8 × 104
3.80 × 104
3.47 × 104
5.53 × 104
a
Molar absorption coefficient of each comonomer was calculated
according to the equation log(I0/I) ) ꢀcd, where ꢀ is the molar
absorption coefficient and c is the molar concentration of corre-
sponding chromophore (moles of fluorene or NSeD unit in a liter
of copolymer solution (mol/L)).
P h ot olu m in escen ce P r op er t ies. Photolumines-
cence spectra (Figure 3a) of copolymers in 1 × 10-3
M
solution of chloroform were taken under an excitation
of 325 nm by using a Fluorolog-3 spectrofluorometer
(J obin Yvon). At this concentration, PL response is
dominated by PFO segment for copolymers PFO-
NSeD0.1 and PFO-NSeD0.5. For copolymer PFO-
NSeD1 an additional PL emission peak can be observed
at around 700 nm. The intensity of this PL peak
increases with increasing the NSeD concentration in the
copolymers. We can attribute the 700 nm emission to
the NSeD unit. This indicates that the efficient energy
transfer from the excitons created on the PFO segment
to the narrow-band-gap unit, NSeD, is highly efficient.
Figure 3b shows the dependence of PL profile of
copolymer PFO-NSeD5 on the copolymer concentration
in the CHCl3 solution. The PL peak at 700 nm increases
dramatically with increasing copolymer concentration
in the solution. We note that even at a very high
concentration of 1 × 10-3 m/L the considerable contri-
bution of PFO emission remains. Compared with PFO-
DBT copolymer reported previously,11a complete quench-
ing of host emission was observed at a dilute concentra-
tion of 4 × 10-4 m/L for the copolymer of PFO-DBT1
in the solution. This indicates either less efficient
intrachain energy transfer in PFO-NSeD copolymer or
less interchain interaction between PFO-NSeD chains
in the solution. The photoluminescence (PL) spectra of
the copolymers in thin film, produced under the excita-
F igu r e 1. (a) UV-vis absorption spectra for the copolymers
in the CHCl3 solution (5 × 10-5 M). (b) UV-vis absorption
spectra for the copolymers in solid-state films.
of two peaks we can estimate the optical band gap
corresponding to fluorene segment and NSeD unit at
around 3.0 and 2.0 eV, respectively (Table 3).

1214 Yang et al.
Macromolecules, Vol. 37, No. 4, 2004
Ta ble 3. UV-Vis P r op er ties a n d Electr och em ica l P r op er ties of th e Cop olym er s
copolymers
optical band gapb/eV
band gapc/eV
Eox/V
Ered/V
HOMO/eV
LUMO/eV
PFOa
2.95
2.95
2.95
2.95
2.95
2.95, 1.96
2.95, 1.95
3.61
2.16
2.14
2.12
2.12
2.08
2.06
1.39
1.38
1.36
1.40
1.36
1.34
1.32
-2.22
-0.78
-0.78
-0.72
-0.76
-0.74
-0.74
-5.79
-5.78
-5.76
-5.80
-5.76
-5.74
-5.72
-2.18
-3.62
-3.62
-3.68
-3.64
-3.66
-3.66
PFO-NSeD 0.1 (6a )
PFO-NSeD 0.5 (6b)
PFO-NSeD 1 (6c)
PFO-NSeD 2 (6d )
PFO-NSeD 5 (6e)
PFO-NSeD 15 (6f)
a
b
Polyfluorene (PFO) homopolymer. Estimated from the onset wavelength of optical absorption in solid-state film. c Calculated from
oxidation and reduction potential.
than that of its sulfur analogue, probably due to a great
Se radius.
In Table 4, we list the absolute PL efficiency mea-
sured in the integrating sphere and the maximum
emission wavelength of the copolymer in a thin film.
The PL efficiency initially increases with increasing the
NSeD content, reaching a maximum of 84% for PFO-
NSeD2. With further increase in NSeD content to 5%
the PL efficiency starts to decrease. The initial increase
in PL efficiency is probably due to disturbing PFO chain
regularity by incorporation of big size Se-containing
heterocycles. The further decrease in PL efficiency after
passing maximum is due to concentration quenching of
heavy metals. We note in the report by Hou et al.11a that
PL efficiency of PFO-DBT copolymer has a much lower
PL efficiency (11.4 and 12.5% for PFO-DBT1 and
PFO-DBT5, respectively) than the Se-containing poly-
mer. This again indicates that the interchain interaction
for Se-containing copolymers is remarkably reduced due
to large Se atomic size in comparison with its sulfur
analogue.
F igu r e 2. Cyclic voltammograms of the copolymers films on
glassy carbon in 0.1 mol/L Bu4NPF6, CH3CN solution.
Electr olu m in escen ce P r op er ties. Devices from
PFO-NSeD copolymers are fabricated with configura-
tion ITO/PEDT/PFO-NSeD/Ba/Al. Figure 5 shows EL
tion of 325 nm line of the HeCd laser, are presented in
Figure 3c. Similar to the PL emission in solution, PL
spectra in the solid state consist of two peaks corre-
sponding to both fluorene and NSeD segments, respec-
tively. For PFO-NSeD0.1, the PL spectrum was domi-
nated by PFO emission, while the emission of NSeD at
634 nm was very weak. The intensity of the 660-700
nm peak increases dramatically with increasing NSeD
composition in the copolymer in the solid state. For the
copolymer PFO-NSeD0.5 the relative intensities of
PFO and NSeD components become equal (Figure 3c).
When NSeD content in the copolymer increases to 1%
(PFO-NSeD1), PFO emission decreases significantly.
Since PFO-NSeD1 has an average molecular weight
Mn ) 24 000, around 62 units per chain (Table 1),
statistically, only two copolymer chains from three can
have one NSeD unit in a chain, while one out of three
polymer chains should be PFO homopolymer. To com-
pletely quench PFO emission including PFO homopoly-
mer, interchain interaction (interchain energy transfer)
is absolutely necessary in this case. By comparing PL
spectra in the solution and in the solid state (Figure
3a,c), it is obvious that the relative intensity of NSeD
to PFO in the solid state (Figure 3c) is much higher than
that in solution. This clearly indicates the importance
of interchain interaction in this case. PFO emission in
the solid-state film was completely quenched for PFO-
NSeD5. We note that for the PFO-DBT copolymer11a
PFO emission at solid state was completely quenched
at concentration of 1% of DBT content in the copolymer
PFO-DBT1. This fact again indicates that the inter-
chain interaction between PFO-NSeD chains is weaker
spectra of such devices. In contrast to PL spectra, EL
emission consists exclusively of red emission peaked at
around 640-670 nm originating from the NSeD unit
for copolymers with NSeD content equal to or greater
than 0.5%. PFO host emission is completely quenched
at 0.5% NSeD concentration in the copolymer. Even for
copolymer PFO-NSeD0.1, EL emission responsible for
PFO emission in the region of 400-460 nm is much
weaker than the emission at 640 nm originating from
the NSeD unit. The emission peaks are red-shiftted from
634 nm for PFO-NSeD0.1 to 672 nm for PFO-NSeD15.
McGehe29 and O’Brien30 reported a large difference
between PL and EL spectra at low doping concentration
region for Eu-complex/CNPPP and PtOEP/PFO devices,
respectively. For these systems the host PL emissions
were quenched completely only at much higher doping
concentration than that for EL spectra. They explained
that the difference between PL and EL processes has a
different recombination zone. Recently, many authors31-33
attributed similar results observed for phosphorescent
dye-doped PLEDs to that the dominant emission mech-
anism in phosphorescent dye-doped PLEDs is charge
trapping (rather than Fo¨rster transfer) followed by
recombination on Ir-complex molecules. According to
Gong et al.,33 the hole and electron trapping mechanism
is most favorable if the HOMO level of the guest is above
that of the host and if LUMO level of the guest is below
that of the host. This argument can be used for in-
tramolecular trapping systems. The LUMO level of the
NSeD unit in PFO-NSeD copolymer is around 3.70 eV,
much less than the LUMO level of PFO homopolymer
(2.7 eV). The HOMO level of PFO-NSeD copolymer is

Macromolecules, Vol. 37, No. 4, 2004
Red Emitting Polymers 1215
Ta ble 4. Absolu te P L Efficien cies Mea su r ed in th e
In tegr a tin g Sp h er e
polymers
λ
Plsmax/nm
QPLsmax (%)
PFO
432
47.0
33.0
68.7
77.4
84.0
52.7
33.6
PFO-NSeD 0.1 (6a )
PFO-NSeD 0.5 (6b)
PFO-NSeD 1 (6c)
PFO-NSeD 2 (6d )
PFO-NSeD 5 (6d )
PFO-NSeD 15 (6f)
423, 634
438, 645
423, 647
420, 656
421, 671
422, 681
in PFO-NSeD copolymer occurs mainly via intramo-
lecular trapping, which must be a very quick and
efficient process. Intermolecular interaction is also
important for low-NSeD content copolymers (<0.5%).
The external EL efficiencies in the device of configu-
ration ITO/PEDT/PFO-NSeD/Ba/Al vary with the co-
polymer composition. The device performance is listed
in Table 5. The external quantum efficiencies (EQE)
increase initially with NSeD content and then decrease.
The best device performance is observed for devices
fabricated with PFO-NSeD1 copolymer. It is worth-
while to note that dependence of EL efficiency on the
copolymer composition coincides with the PL change
pattern (Table 3). Figure 5 shows external quantum
efficiency and luminance as a function of current density
for device with PFO-NSeD1. As can be seen from
Figure 5, the device shows a high external quantum
efficiency of around 3.0% without significant decay in
efficiency over wide range up to high current density
(270 mA/cm2). The highest external EL quantum ef-
ficiencies was 3.1% and luminous efficiency of 0.91 cd/A
with the luminance of 906 cd m-2 at current density of
98 mA/cm2 and at the bias voltage of 8.9 V (Table 4).
The highest luminance can reach 2104 cd m-2 at 9.8 V.
To the best of our knowledge, this is the highest
efficiency with saturated red emission for a single-layer
device with nonblend type emitter reported so far in the
scientific literature.
Con clu sion
A novel EL polymer, poly(9,9-dioctylfluorene-co-naph-
thoselenadiazole), was successfully synthesized. The
efficient energy transfer due to exciton trapping on
narrow-band-gap NSeD sites has been observed. EL
emission from PFO segment was completely quenched
at very low NSeD content (0.5%). Saturated red emis-
sion at the maximum wavelength of 657 nm was
obtained. The highest external quantum efficiency is of
3.1% photon/electron, and luminous efficiency is of 0.9
cd/A with 908 cd/m2. To the best of our knowledge, this
is the highest efficiency reported so far for nondoped
fluorescent polymer LEDs. We further demonstrated
that improvement in PL and EL efficiency in compari-
son with its sulfur analogue could be attributed to the
reduction in interchain interaction due to larger atomic
size of the selenium atom.
F igu r e 3. (a) PL spectra of PFO-NSeD copolymers in
solution (1 × 10-3 M in chloroform). (b) PL spectra of PFO-
NSeD5 copolymers in chloroform solution with different
concentrations of copolymer. (c) PL spectra for the copolymers
in the thin films.
Exp er im en ta l Section
around 5.7 eV (Table 1), which is slightly above the
HOMO of the host 5.77 eV. Thus, energy level alignment
of guest and host components in the copolymer chain is
favorable for intra- and intermolecular trapping in the
PFO-NSeD copolymers.
On the basis of the results described above, the
concentration dependence of PL spectra in solution and
solid state (Figure 3), and EL spectra of copolymer of
different composition (Figure 4), we conclude that
energy transfer from host PFO segment to NSeD unit
Ma ter ia ls a n d Mea su r em en t. All manipulations involving
air-sensitive reagents were performed under an atmosphere
of dry argon. All reagents, unless otherwise specified, were
obtained from Aldrich, Acros, and TCI Chemical Co. and were
used as received. All solvents were carefully dried and purified
1
under nitrogen flow. H and 13C NMR spectra were recorded
on a Varian Inova 500 or Bruker DRX 400 spectrometer
operating respectively at 500 and 100 MHz and were refer-
enced to tetramethylsilane. GPC was obtained through a
Waters GPC 2410 in tetrahydrofuran using a calibration curve

1216 Yang et al.
Macromolecules, Vol. 37, No. 4, 2004
F igu r e 4. EL spectra of PFO-NSeD copolymers.
temperature and extracted with ether. The extract was washed
with saturated sodium chloride solution and dried with
anhydrous magnesium sulfate. Evaporation of the solvent and
purification by flash column with hexane as eluent gave with
crystal; mp 49-50 °C.
2,7-Bis(4,4,5,5-tetr a m a th yl-1,3,2-d ioxa bor ola n -2-yl)-9,9-
d ioctylflu or en e (3). n-Butyllithium (23 mL of a 1.6 M
solution in hexane, 36.8 mmol) was added dropwise into a
solution of 2 (6.0 g, 10.9 mmol) in tetrahydrofuran (THF,150
mL) at -78 °C under an atmosphere of dry argon. The mixture
was stirred at -78 °C for 1 h, and then 2-isopropoxy-4,4,5,5-
tetramethyl-1,3,2-dioxaborolane (25 mL, 123.24 mmol) was
injected promptly into the flask. The mixture was stirred at
-78 °C for 2 h, and then the reaction was allowed to stand
overnight at room temperature. The mixture was poured into
water and was extracted with ether. The extract was washed
with brine and dried over anhydrous magnesium sulfate. After
evaporation of the solvent, the residue was recrystallized from
THF and methanol and gave a white crystal (5.2 g, 74.0%);
F igu r e 5. External quantum efficiency and luminance of ITO/
PEDT/PFO-NSeD1/Ba/Al device.
of polystyrene standards. Elemental analyses were performed
on a Vario EL elemental analysis instrument (Elementar Co.)
or an ANTEK7000 elemental analysis instrument (ANTEK
Co.). The elemental selenium analysis was recorded on a
polarized Zeeman atomic absorption spectrophotometer (Hi-
tachi Co., J apan). UV-vis absorption spectra were recorded
on a HP 8453 spectrophotometer. The PL quantum yields were
determined in an Integrating Sphere IS080 (LabSphere) with
325 nm excitation of a HeCd laser (Melles Griot). PL an EL
spectra were recorded on an Instaspec 4 CCD spectrophotom-
eter (Oriel Co.). Cyclic voltammetry was carried out on a
CHI660A electrochemical workstation with platinum elec-
trodes at a scan rate of 50 mV/s against a calomel reference
electrode with nitrogen-saturated solution of 0.1 M tetrabu-
tylammonium hexafluorophosphate (Bu4NPF6) in acetonitrile
(CH3CN).
1
mp 128-130 °C. H NMR (500 MHz, CDCl3): δ (ppm): 7.83
(d, 2H), 7.75 (d, 2H), 1.92 (m, 4H), 1.35 (s, 24H), 1.25-1.01
(m, 20H), 0.81 (t, 6H), 0.60 (m, 4H). 13C NMR (100 MHz,
CDCl3) δ (ppm): 151.92, 144.50, 134.90, 128.92, 119.54, 82.53,
55.54, 41.05, 32.78, 30.40, 29.61, 25.41, 44.10, 23.20, 14.78.
Anal. Calcd for C41H64O4B2: C, 76.74; H, 10.04. Found: C,
76.68; H, 10.15.
1,4-Dibr om o-2,3-d ia m in oa p h th a len e (4). A mixture of
0.75 mL of bromine (2.36 g, 14.7 mmol) and 20 mL of glacial
acetic acid was added dropwise into a solution of 1.04 g of 2,3-
diaminophthalene (6.58 mmol) in 30 mL of glacial acetic, with
vigorous stirring at room temperature. After 1 h, the precipi-
tate was filtered and washed subsequently with 50 mL of
glacial acetic acid, 100 mL of 2 wt % sodium carbonate solution,
and 100 mL of water. A yellow powder was obtained after
drying (1.84 g, 88.5%); mp 95-97 °C. 1H NMR (500 MHz,
CDCl3) δ (ppm): 8.02 (q,2H), 7.41 (q, 2H), 4.33 (s, 4H). 13C
NMR (100 MHz, CDCl3) δ (ppm): 134.94, 128.27, 126.08,
2,7-Dibr om oflu or en e (1).22 Bromine (31.4 g, 0.196 mol)
in 20 mL of chloroform was added dropwise into a suspension
solution containing fluorene (15.0 g, 0.091 mol), iron power
(80 mg, 1.43 mmol), and 100 mL of chloroform. The flask was
cooled by ice water, and the temperature was controlled under
5 °C. The reaction was allowed to stand for 2 h. The product
was filtered and recrystallizd with chloroform, giving white
crystal (27.3 g, 93.2%); mp 161-163 °C.
125.43, 106.90. Anal. Calcd for C10H8Br2 N : C, 37.97; H, 2.53;
2
N, 8.86. Found: C, 38.50; H, 2.60; N, 9.01.
4,7-Dibr om o-2,1,3-n a p h th oselen a d izole (5). A solution
of selenious oxide (0.34 g, 3.06 mmol) in 10 mL of water was
added dropwise into a mixture of 4 (0.8 g, 2.53 mmol) and 200
mL of ethanol at 70 °C, and the temperature was maintained
for 2 h. The mixture was cooled to room temperature overnight,
and the precipitate was filtered and recrystallized in acetic
ether and gave a purple solid (0.91 g, 91%); mp 264-265 °C.
2,7-Dibr om o-9,9-d ioct ylflu or en e (2).22 1-Bromooctane
(18.6 g, 0.097 mol) was dropped into a suspension of 1 (15.0 g,
0.046 mol) and benzyltriethylemmonium chloride (0.09 g 0.39
mmol) in DMSO (200 mL) and sodium hydroxide (15 mL of
50 wt %). The mixture was stirred vigorously for 3 h at a room

Macromolecules, Vol. 37, No. 4, 2004
Red Emitting Polymers 1217
Ta ble 5. Device P er for m a n ce of P F O-NSeD
device performance
copolymers
CIE x, y
λmax (EL)/nm
bias/V
current density/mA cm-2
luminance/cd m-2
QEext (%)
PFO-NSeD 0.1 (6a )
PFO-NSeD 0.5 (6b)
PFO-NSeD 1 (6c)
PFO-NSeD 2 (6d )
PFO-NSeD 5 (6e)
PFO-NSeD 15 (6f)
0.37, 0.34
0.61, 0.35
0.64, 0.33
0.67, 0.32
0.68, 0.31
0.69, 0.30
634
645
657
659
662
672
6.7
6.27
8.9
7.6
13.1
6.7
30.0
33.3
98.0
7.3
33.3
33.3
1870
980
908
22.5
165
20.3
0.56
0.30
3.10
1.14
0.35
0.22
1H NMR (500 MHz, CDCl3) δ (ppm): 7.48 (d,2H), 8.29 (d,2H).
Anal. Calcd for C10H4Br2N2Se: C, 30.69; H, 1.02; N, 7.16; Se,
20.20. Found: C, 30.84; H, 1.16; N, 7.31; Se, 20.05.
126.17, 121.53, 119.95, 55.35, 40.39, 31.79, 30.04, 29.21, 24.35,
23.94, 22.95, 14.03.
P oly[2,7-(9,9-d ioctylflu or en e)-co-4,7-(2,1,3-n a p h th ose-
len a d izole)] (6e). 2,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lan-2-yl)-9,9-dioctylfluorene (3) (0.50 equiv), 2,7-dibromo-9,9-
dioctylfluorene (2) (0.45 equiv), and 4,7-dibromo-2,1,3-benzo-
selenadiazole (5) (0.05 equiv) were used in this polymerization.
Element Anal. Found: C, 87.05%; H, 9.98%; N, 0.28%. Atomic
Gen er a l P r oced u r e of P olym er iza tion . Carefully puri-
fied 2,7-dibromo-9,9-dioctylfluorene (2), 2,7-bis(4,4,5,5-tetra-
mathyl-1,3,2-dioxaborolan-2-yl)-9,9-dioctylfluorene (3), 4,7-
dibromonaphthoselenadizole (5), (PPh3)4Pd(0) (0.5-2.0 mol %),
and several drops of Aliquat 336 were dissolved in a mixture
of toluene and aqueous 2 M Na2CO3. The solution was refluxed
with vigorous stirring for 72 h under an argon atmosphere.
At the end of polymerization, 2,7-bis(4,4,5,5-tetramathyl-1,3,2-
dioxaborolan-2-yl)-9,9-dioctylfluorene was added to remove
bromine end groups, and bromobenzene was added as a
monofunctional end-capping reagent to remove boracic ester
end group because boron and bromine units could quench
emission and contribute to excimer formation in LED applica-
tion. The mixture was then poured into methanol. The
precipitated material was filtered and washed for 24 h with
acetone to remove oligomers and catalyst residues. The result-
ing polymers were soluble in THF, CHCl3, and toluene. Yield:
45-80%.
P oly[2,7-(9,9-d ioctylflu or en e)-co-4,7-(2,1,3-n a p h th ose-
len a d izole)] (6a ). 2,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lan-2-yl)-9,9-dioctylfluorene (3) (0.50 equiv), 2,7-dibromo-9,9-
dioctylfluorene (2) (0.499 equiv), and 4,7-dibromo-2,1,3-
benzoselenadiazole (5) (0.001 equiv) were used in this
polymerization. Element Anal. Found: C, 89.55%; H, 10.92%;
N, 0.013%. Atomic absorption spectra for Se: 0.04%. 1H NMR
(500 MHz, CDCl3) δ (ppm): 7.86, 7.70, 2.15, 1.55,1.16-1.22,
0.83. 13C NMR (100 MHz, CDCl3) δ (ppm): 152.21, 140.90,
140.43, 126.55, 121.89, 120.36, 55.74, 40.79, 32.19, 30.43,
29.62, 24.31, 23.00, 14.46.
1
absorption spectra for Se: 0.40%. H NMR (500 MHz, CDCl3)
δ (ppm): 7.82, 7.66, 7.50, 7.01, 2.11, 1.37, 1.12-1.23, 0.80. 13
C
NMR (100 MHz, CDCl3) δ (ppm): 152.21, 140.90, 140.26,
126.48, 121.85, 120.36, 55.74, 32.19, 30.44, 29.63, 24.35, 23.00,
14.47.
P oly[2,7-(9,9-d ioctylflu or en e)-co-4,7-(2,1,3-n a p h th ose-
len a d izole)] (6f). 2,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lan-2-yl)-9,9-dioctylfluorene (3) (0.50 equiv), 2,7-dibromo-9,9-
dioctylfluorene (2) (0.35 equiv), and 4,7-dibromo-2,1,3-benzo-
selenadiazole (5) (0.15 equiv) were used in this polymerization.
Element Anal. Found: C, 86.02%; H, 8.86%; N, 0.82%. Atomic
1
absorption spectra for Se: 2.02%. H NMR (500 MHz, CDCl3)
δ (ppm): 7.85, 7.70, 7.51, 2.15, 1.59, 1.43, 1.36, 1.16, 1.50, 0.84,
0.73. 13C NMR (100 MHz, CDCl3) δ (ppm): 151.82, 140.54,
140.03, 126.17, 121.52, 119.96, 55.35, 40.36, 31.78, 30.03,
29.201, 24.95, 22.58, 14.02.
Device F a br ica tion a n d Ch a r a cter iza tion . LED was
fabricated on prepatterned indium-tin oxide (ITO) with sheet
resistance 10-20 Ω/0. The substrate was ultrasonically
cleaned with acetone, detergent, deionized water, and 2-pro-
panol, subsequently. Oxygen plasma treatment was taken
for 10 min as the final step of cleaning to improve the con-
tact angle just before film forming. Onto the ITO glass a layer
of poly(ethylenedioxythiophene)-poly(styrenesulfonic acid)
(PEDOT:PSS) film with a thickness of 50 nm was spin-coated
from its aqueous dispersion (Baytron P 4083, Bayer AG),
aiming to improve the hole injection and to avoid possibility
of leaking. Solution of PFO-NSeD copolymers in toluene were
prepared in nitrogen-filled drybox and spin-coated on top of
the ITO/PEDOT:PSS surface. A typical thickness of emitting
layer was 70-80 nm. Then a thin layer of barium as an
electron injection cathode, and subsequently 200 nm aluminum
protection layers were thermally deposited by vacuum evapo-
ration through a mask at a base pressure below 2 × 10-4 Pa.
The deposition speed and the thickness of the barium and
aluminum layers were monitored with a thickness/rate meter
model STM-100 (Sycon Instrument, Inc.). The cathode area
defines the active area of the device. A typical active area of
devices in this study is 0.15 mm2. The EL layer spin-coating
process and the device performance tests were taken within a
glovebox (Vacuum Atmosphere Co.) with nitrogen circulation.
P oly[2,7-(9,9-d ioctylflu or en e)-co-4,7-(2,1,3-n a p h th ose-
len a d izole)] (6b). 2,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lan-2-yl)-9,9-dioctylfluorene (3) (0.50 equiv), 2,7-dibromo-9,9-
dioctylfluorene (2) (0.495 equiv), and 4,7-dibromo-2,1,3-
benzoselenadiazole (5) (0.005 equiv) were used in this
polymerization. Element Anal. Found: C, 88.41%; H, 10.48%;
1
N, 0.03%. Atomic absorption spectra for Se: 0.08%. H NMR
(500 MHz, CDCl3) δ (ppm): 7.84, 7.70, 2.15, 1.55, 1.16-1.27,
0.83. 13C NMR (100 MHz, CDCl3) δ (ppm): 152.21, 140.91,
140.41, 126.58, 121.88, 120.32, 55.74, 40.80, 32.19, 30.40,
29.62, 24.33, 23.00, 14.47.
P oly[2,7-(9,9-d ioctylflu or en e)-co-4,7-(2,1,3-n a p h th ose-
len a d izole)] (6c). 2,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lan-2-yl)-9,9-dioctylfluorene (3) (0.50 equiv), 2,7-dibromo-9,9-
dioctylfluorene (2) (0.49 equiv), and 4,7-dibromo-2,1,3-benzo-
selenadiazole (5) (0.01 equiv) were used in this polymerization.
Element Anal. Found: C, 88.21%; H, 10.15%; N, 0.069%.
1
Atomic absorption spectra for Se: 0.20%. H NMR (500 MHz,
I-V characteristics were measured with
a computerized
CDCl3) δ (ppm): 7.82, 7.66, 7.55, 7.45, 7.33, 7.01, 2.11, 1.12-
1.23, 0.79, 0.52. 13C NMR (100 MHz, CDCl3) δ (ppm): 152.21,
140.92, 140.06, 126.54, 121.80, 120.35, 55.74, 32.19, 30.44,
29.63, 24.35, 23.00, 16.05, 14.47.
Keithley 236 source measure unit. The luminance of device
was measured with calibrated photodiode. The external quan-
tum efficiency was verified by measurement in the integrating
sphere (IS-080, Labsphere), and luminance was calibrated by
using a PR-705 SpectraScan spectrophotometer (Photo Re-
search) after encapsulation of devices with UV-curing epoxy
and thin cover glass.
P oly[2,7-(9,9-d ioctylflu or en e)-co-4,7-(2,1,3-n a p h th ose-
len a d izole)] (6d ). 2,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lan-2-yl)-9,9-dioctylfluorene (3) (0.50 equiv), 2,7-dibromo-9,9-
dioctylfluorene (2) (0.48 equiv), and 4,7-dibromo-2,1,3-benzo-
selenadiazole (5) (0.02 equiv) were used in this polymerization.
Element Anal. Found: C, 87.60%; H, 10.23%; N, 0.081%.
Ack n ow led gm en t. This work is sponsored by Min-
istry of Science and Technology of China (#2002CB-
613402) and the National Natural Science Foundation
of China (#50028302).
1
Atomic absorption spectra for Se: 0.24%. H NMR (500 MHz,
CDCl3) δ (ppm): 7.86, 7.70, 2.14, 1.56, 1.16, 0.84, 0.63. 13C
NMR (100 MHz, CDCl3) δ (ppm): 151.83, 140.53, 140.03,

1218 Yang et al.
Macromolecules, Vol. 37, No. 4, 2004
Cao, Y. Appl. Phys. Lett. 2003, 82, 2163-2165. (c) Yang, W;
Hou, Q.; Liu, C.; Niu, Y.; Huang, J .; Yang, R.; Cao, Y. J .
Mater. Chem. 2003, 13, 1351-1355.
Refer en ces a n d Notes
(1) (a) 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 (London) 1990, 347, 539-541. (b) Ziemelis, K. Nature
(London) 1999, 399, 408-11. (c) Heeger, A. J . Solid State
Commun. 1998, 107, 673-679. (d) Sugura, J . L. Acta Polym.
1998, 49, 319-344.
(2) (a) Braun, D.; Heeger, A. J . Appl. Phy. Lett. 1991, 58, 982-
1984. (b) Heeger, A. J . Angew. Chem., Int. Ed. 2001, 40,
2591-2611.
(3) (a) Pei, Q.; Yu, G.; Zhang, C.; Yang, Y.; Heeger, A. J . Science
1995, 269, 1086. (b) Herold, M.; Gmeiner, J .; Schworer, M.
Acta Polym. 1994, 451, 92. (c) 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 (London) 1990, 347,
539-541. (d) Braun, D.; Heeger, A. J . Appl. Phys. Lett. 1991,
58, 1982. (e) Kraft, A.; Grimsdale, A. C.; Holmes, A. B. Angew.
Chem., Int. Ed. 1998, 37, 402-428. (f) Burns, P. L.; Holmes,
A. B.; Kraft, A.; Bradley, D. D. C.; Brown, A. R.; Friend, R.
H.; Gywer, R. W. Nature (London) 1992, 356, 47.
(12) Yang, R.; Tian, R.; Yang, Y.; Hou, Q.; Cao, Y. Macromolecules
2003, 36, 7453.
(13) Liu, B.; Yu, W. L.; Lai, Y. H.; Huang, W. Macromolecules
2000, 33, 8945-8952.
(14) Tsuie, B.; Reddinger, J . L.; Sotzing, G. A.; Soloducho, J .;
Katritzky, A. R.; Reynolds, J . R. J . Mater. Chem. 1999, 9,
2189-2200.
(15) Liu, B.; Yu, W. L.; Lai, Y. H.; Huang, W. Chem. Mater. 2001,
13, 1984-1991.
(16) Donat-Bouillud, A.; Le´vesque, I.; Tao, Y.; D’Iorio, M. Chem.
Mater. 2000, 12, 1931-1936.
(17) Le´vesque, I.; Donat-Bouillud, A.; Tao, Y.; D’Iorio, M.; Beaupre´,
S.; Blondin, P.; Ranger, M.; Bouchard, J .; Leclerc, M. Synth.
Met. 2001, 122, 79-81.
(18) Leclerc, M. J . Polym. Sci., Part A: Polym. Chem. 2001, 39,
2867-2873.
(19) Kitamura, C.; Tanaka, S.; Yamashita, Y. Chem. Mater. 1996,
8, 570-578.
(4) Kim, D. Y.; Cho, H. N.; Kim, C. Y. Prog. Polym. Sci. 2000,
25, 1089.
(20) Herguth, P.; J iang, X.; Liu, M. S.; J en, A. K.-Y. Macromol-
ecules 2002, 35, 6094-6100.
(5) (a) 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 (London) 1990, 347, 539-541. (b) Doi, S.; Kuwabara,
M.; Noguchi, T. Synth. Met. 1993, 57, 4174. (c) J ohansson,
D. M.; Srdanov, G.; Yu, G.; Theander, M.; Inganas, O.;
Anderson, M. R. Macromolecules 2000, 33, 2525-2529.
(6) (a) Rehahn, M.; Schluter, A.; Wegner, G.; Feast, W. J . Polymer
1989, 30, 1054-1059. (b) Yang, Y.; Pei, Q.; Heeger, A. J . J .
Appl. Phys. 1996, 79, 934-939.
(7) (a) Pei, J .; Yu, W. L.; Ni, J .; Lai, Y. H.; Huang, W.; Heeger,
A. J . Macromolecules 2001, 34, 7241-7248. (b) Groenendaal,
L. B.; J onas, F.; Freitag, D.; Pielartzik, H.; Reynolds, J . R.
Adv. Mater. 2000, 12, 482-494.
(8) (a) Fukuda, M.; Sawada, K.; Yoshino, K. J . Polym. Sci., Part
A: Polym. Chem. 1993, 31, 2465-2471. (b) Pei, Q.; Yang, Y.
J . Am. Chem. Soc. 1996, 118, 7416-7417. (c) Kameshima,
H.; Nemoto, N.; Endo, T. J . Polym. Sci., Part A: Polym. Chem.
2001, 39, 3143-3150. (d) Scherf, U.; List, E. J . W. Adv. Mater.
2002, 14, 477-487.
(9) (a) Tesller, N.; Medvedev, V.; Kazes, M.; Kan, S.; Banin, U.
Science 2002, 295, 1506. (b) Virgili, T.; Lidzey, D. G.;
Bradeley, D. D. C. Adv. Mater. 2000, 12, 58. (c) Slooff, L. H.;
Polman, A.; Cacialli, F.; Friend, R. H.; Hebbink, G. A.; Veggel,
F. C. J . M.; Reinhoudt, D. N. Appl. Phys. Lett. 2001, 78, 2122.
(10) (a) Beaupre, M. Leclerc Adv. Funct. Mater. 2002, 12, 193.
(b) Levesque, L.; Bouillud, A. D.; Tao, Y.; Iorio, M. D.;
Beaupre, S.; Blondin, P.; Ranger, M.; Buchard, J .; Leclerc,
M. Synth. Met. 2001, 12, 279. (c) Bernius, M.; Inbasekaran,
M.; Woo, E.; Wu, W.; Wujkowski, L. J . Mater. Sci.: Mater.
Electron. 2000, 11, 111.
(21) Campbell, A. J .; Bradley, D. D. C. Appl. Phys. Lett. 2001, 79,
2133-2135.
(22) Woo, E. P.; Inbasekaran, M.; Shiang, W.; Roof, G. R. WO 99
05184, 1997.
(23) Millard, I. S. Synth. Met. 2000, 111, 119-123.
(24) Lee, J . K.; Klaerner, G.; Miller, R. D. Chem. Mater. 1997,
11, 1083.
(25) Ranger, M.; Rondeau, D.; Leclerc, M. Macromolecules 1997,
30, 7686-7691.
(26) J ohansson, K.; Andersson, O¨ .; Olin, Å. Analyst 1995, 120,
423-429.
(27) J anietz, S.; Bradley, D. D. C.; Grell, M.; Giebeler, C.;
Inbasekaran, M.; Woo, E. P. Appl. Phys. Lett. 1998, 73, 2453-
2455.
(28) Leeuw, D. M.; Simenon, M. M. J .; Brown, A. R.; Einerhand,
R. E. F. Synth. Met. 1997, 87, 53.
(29) McGehee, M. D.; Bergstedt, T. T.; Zhang, C.; Saab, A. P.;
O’Regan, M. B.; Bazan, G. C.; Srdanov, V. I.; Heeger, A. J .
Adv. Mater. 1999, 11, 1349-1354.
(30) O’Brien, D. F.; Giebler, C.; Fletcher, R. B.; Cadlby, J .; Palilis,
L. C.; Lidzey, D. G.; Lane, P. A.; Bradley, D. D. C.; Blau, W.
Synth. Met. 2001, 116, 379-383.
(31) Lane, P. A.; Palilis, L. C.; O’Brien, D. F.; Giebeler, C.; Cadby,
A. J .; Lidzey, D. G.; Campbell, A. J .; Blau, W.; Bradley, D.
D. C. Phys. Rev. B 2001, 63, 235206.
(32) Tessler, N.; Ho, P. K. H.; Cleave, V.; Pinner, D. J .; Friend, R.
H.; Yahioglu, G.; Le. Barny, P.; Gray, J .; de Souza, M.;
Rumbles, G. Thin Solid Films 2000, 363, 64.
(33) Gong, J . C.; Ostrowski, D.; Moses, G. C.; Bazan, A. J .; Heeger,
Adv. Funct. Mater. 2003, 13, 439.
(11) (a) Hou, Q.; Xu, Y.; Yang, W.; Yuan, M.; Peng, J .; Cao, Y. J .
Mater. Chem. 2002, 12, 887-2892. (b) Niu, Y.-H; Hou, Q.;
MA035743U