Highly efficient green light emitting polyfluorene incorporated with 4-diphenylamino-1,8-naphthalimide as green dopant

Article abstract of DOI:10.1039/b514359d

The dopant/host methodology, which enables efficient tuning of emission color and enhancement of the electroluminescence (EL) efficiency of organic light emitting diodes (OLEDs) based on small molecules, is applied to the design and synthesis of highly efficient green light emitting polymers. Highly efficient green light emitting polymers were obtained by covalently attaching just 0.3-1.0 mol% of a green dopant, 4-(N,N-diphenyl) amino-1,8-naphthalimide (DPAN), to the pendant chain of polyfluorene (the host). The polymers emit green light and exhibit a high photoluminescence (PL) quantum yield of up to 0.96 in solid films, which is attributed to the energy transfer from the polyfluorene host to the DPAN dopant unit. Single layer devices (device configuration: ITO/PEDOT/Polymer/Ca/Al) of the polymers exhibit a turn on voltage of 4.8 V, luminance efficiency of 7.43 cd A^-1, power efficiency of 2.96 lm W^-1 and CIE coordinates at (0.26, 0.58). The good device performance can be attributed to the energy transfer and charge trapping from the polyfluorene host to the DPAN dopant unit as well as the molecular dispersion of the dopant in the host. The device performance is fairly comparable to that of state-of-the-art green light emitting poly(fluorene-co-benzothiadiazole), indicating that the covalently attached dopant/host polymer system is very promising for the development of highly efficient electroluminescent polymers of tunable emission color. The Royal Society of Chemistry 2006.

Full text of DOI:10.1039/b514359d

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www.rsc.org/materials | Journal of Materials Chemistry
Highly efficient green light emitting polyfluorene incorporated with
4-diphenylamino-1,8-naphthalimide as green dopant
Jun Liu, Guoli Tu, Quanguo Zhou, Yanxiang Cheng, Yanhou Geng, Lixiang Wang,* Dongge Ma,
Xiabin Jing and Fosong Wang
Received 10th October 2005, Accepted 5th January 2006
First published as an Advance Article on the web 25th January 2006
DOI: 10.1039/b514359d
The dopant/host methodology, which enables efficient tuning of emission color and enhancement
of the electroluminescence (EL) efficiency of organic light emitting diodes (OLEDs) based on
small molecules, is applied to the design and synthesis of highly efficient green light emitting
polymers. Highly efficient green light emitting polymers were obtained by covalently attaching
just 0.3–1.0 mol% of a green dopant, 4-(N,N-diphenyl) amino-1,8-naphthalimide (DPAN), to the
pendant chain of polyfluorene (the host). The polymers emit green light and exhibit a high
photoluminescence (PL) quantum yield of up to 0.96 in solid films, which is attributed to the
energy transfer from the polyfluorene host to the DPAN dopant unit. Single layer devices (device
configuration: ITO/PEDOT/Polymer/Ca/Al) of the polymers exhibit a turn on voltage of 4.8 V,
luminance efficiency of 7.43 cd A21, power efficiency of 2.96 lm W21 and CIE coordinates at
(0.26, 0.58). The good device performance can be attributed to the energy transfer and charge
trapping from the polyfluorene host to the DPAN dopant unit as well as the molecular dispersion
of the dopant in the host. The device performance is fairly comparable to that of state-of-the-art
green light emitting poly(fluorene-co-benzothiadiazole), indicating that the covalently attached
dopant/host polymer system is very promising for the development of highly efficient
electroluminescent polymers of tunable emission color.
and stability of OLEDs.22 This strategy has also been applied
Introduction
to tune the emission color of electroluminescent polymers.24–26
Electroluminescent polymers have received much attention in
By covalently attaching the dopant unit (perylene derivatives)
academia and industry due to their applications in the genera-
to a polymer host (polyfluorene) to form a single polymer, Ego
tion of new display technologies.1–4 Among them, fluorene-
et al have elegantly tuned the emission color of polyfluorene
from blue to green, orange and red.24 The great success of
based polymers have attracted particular attention in recent
dopant/host OLEDs based on small molecules22 also directed
years because of their high photoluminescence (PL) and
electroluminescence (EL) efficiency, good thermal and chemi-
our research towards electroluminescence polymers with the
cal stability, and color tunability within the entire visible
dopant/host system. Recently, we have developed colorfast
spectrum.1–4 Normally, polyfluorene emits blue light with
and efficient blue electroluminescent polymers with this
system.27 Also, we have adopted the dopant/host system to
large band gap. In order to tune the emission color of poly-
achieve white emission from a single polymer.28–30 In this
fluorene, a common and successful approach is to incorporate
narrow bandgap units into the main chain of polyfluorene.5–19
article, we report a novel highly efficient green light emitting
The narrow bandgap units are always aromatic heterocycles,
polyfluorene with the dopant/host system.
such as benzothiadiazole,5–8 naphthoselenadiazole,14 bithio-
4-(N, N-Diphenyl)amino-1,8-naphthalimide (DPAN),
a
phene,18 etc. In particular, poly(fluorene-co-benzothiadiazole)
emits green light with good electron injection and transporting
properties. Devices of poly(fluorene-co-benzothiadiazole)
exhibit high luminance efficiency and long lifetime.5–8
derivative of the dye 1,8-naphthalimide,31,32 was selected as
the dopant because of its high PL quantum yield. Moreover,
DPAN has the ability to form a dopant/host system with
polyfluorene. The absorption spectrum of DPAN sufficiently
overlaps with the emission spectrum of polyfluorene, favour-
ing the Fo¨rster energy transfer from polyfluorene to DPAN.33
Also, the LUMO and HOMO energy levels of DPAN lie
between those of polyfluorene, favouring the charge trapping
of the DPAN dopant unit.34,35 The dopant molecule was
attached to the pendant chain of polyfluorene by an alkyl
spacer with a low content of 0.3–1 mol%, avoiding the
quenching effect of the dopant unit. This molecular design
brings the molecular dispersion of the dopant in the host,24
which is different from blending36–38 the dopant with the host
because the former case can achieve higher efficiency and
The dopant/host emitter system is a common strategy to
tune the emission color of organic light emitting diodes
(OLEDs) based on small molecules.20–23 The energy transfer
and charge trapping from the host to the dopant molecule
allows the emission to originate from the dopant and the
emission properties are dominated by the dopant. Moreover,
the dopant/host system is found to enhance the EL efficiency
State Key Laboratory of Polymer Physics and Chemistry, Changchun
Institute of Applied Chemistry, Chinese Academy of Sciences, and
Graduate School of Chinese Academy of Sciences, Changchun 130022,
P. R. China. E-mail: lixiang@ciac.jl.cn; Fax: +86-431-5685653
This journal is ß The Royal Society of Chemistry 2006
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better spectral stability without phase separation.27–30
A
with different feed ratios of the three monomers. In the
photoluminescence quantum yield up to 0.96 was observed
for the neat films of the polymers. To our best knowledge,
these materials are the most efficient light-emitting polymers
reported to date. Polymer light emitting diodes (PLEDs) with
a non-optimized single-layer device structure of ITO/PEDOT/
polymer/Ca/Al have been fabricated and a high luminance
efficiency of 7.43 cd A21 with CIE coordinates of (0.26, 0.58)
is demonstrated. This performance is fairly comparable to that
of the state-of-the-art green light emitting poly(fluorene-co-
benzothiadiazole) in similar device configurations,5 and
indicates that polyfluorenes of the dopant/host system are
very promising for the development of highly efficient electro-
luminescent polymers with tunable emission color.
copolymers, the DPAN was attached to the pendant chain
of polyfluorene without affecting the electronic properties
of polyfluorene backbone. All the polymers were thoroughly
purified before characterization and device fabrication.
Structural characterization of the polymers was carried out
with H NMR, 13C NMR and elemental analysis. In the H
NMR spectra, the signals at 4.60, 4.32 and 3.97 ppm are all
attributed to the DPAN unit, from which we can calculate its
actual content. For PFG40, the exact content of DPAN unit is
0.033, which is close to the feed ratio of 0.040 of the monomer
5, indicating that the incorporation of DPAN unit into
polyfluorene is very efficient in the polymerization process.
For PFG3, PFG5, PFG10, the contents of DPAN unit are too
1
1
1
low to give accurate contents from H NMR spectra due to
experimental error. Therefore, the actual content of DPAN in
the polymers is assumed to be the same with the feed ratios.
For comparison, we have also synthesized poly(9,9-dioctyl-
fluorene-2,7-yl) homopolymer (PF) and the model compound
4-(N, N-diphenyl)amino-9-decyl-1,8-naphthalimide (GMC).
The number-average molecular weight (Mn) of the polymers,
Result and discussion
Synthesis and characterization
As shown in Scheme 1, the 4-diphenylylamino-1,8-naphthal-
imide dopant unit was first attached to a phenyl ring and then
copolymerized into polyfluorene by Suzuki condensation39
Scheme 1 Synthetic route for monomers and polymers. Reagents and conditions: (i) 1-bromooctane, KOH, ethanol, reflux; (ii) 1,2-
dibromoethane, KOH (aq., 2 M), tetra(n-butyl)ammonium bromide, toluene, 90 uC; (iii) bromine, dichloromethane; (iv) KOH, DMSO, 120 uC; (v)
iodobenzene, K2CO3, CuI, 18-crown-6, DMPU, 190 uC; (vi) Pd(PPh3)4, Aliquat 336, toluene, K2CO3 (aq., 2 M), 90 uC; (vii) 1-bromodecane, KOH,
DMSO, 120 uC.
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Table 1 The content of DPAN unit, number average molecular
weight (Mn), polydispersity (PDI), thermal decomposition tempera-
ture (Td), photoluminescence quantum efficiency (WPL) of PF, PFG3,
PFG5, PFG10 and PFG40
Polymer
Content
Mn
PDI
Td
WPL
PF
0
28000
25600
24800
20200
18600
1.87
1.65
1.69
1.56
1.86
434
432
432
433
431
0.45
0.89
0.96
0.83
0.23
PFG3
PFG5
PFG10
PFG40
0.003
0.005
0.01
0.04
determined by gel permeation chromotagraphy (GPC) with
polystyrene as standard, is in the range of 20 200 to 28 000
with the polydispersity from 1.56 to 1.87 (Table 1). All these
polymers show good thermal stability with thermal decom-
position temperature higher than 430 uC. All these polymers
are soluble in common organic solvent, such as chloroform,
toluene and THF.
Fig. 2 UV-Vis absorption spectra of polymers in solid film.
Electrochemical properties
Cyclic voltammetry of all polymers in solid films was
carried out in acetonitrile with n-Bu4NClO4 (0.10 M) as the
electrolyte. PFG3, PFG5, PFG10 all exhibited identical redox
behavior with that of PF, indicating that the incorporation
of small amount of DPAN has negligible effect on the redox
properties of the resulting polymers. Fig. 1 shows the cyclic
voltagramms of PF and the model compound GMC. Based on
the onset potential of oxidation and reduction process, and
according to the formula (EHOMO = 2(Eox + 4.34) eV and
ELUMO = 2(Ered + 4.34) eV),40 we can estimate the HOMO
and LUMO energy levels of PF and GMC. The HOMO
and the LUMO levels of GMC are 25.61 and 23.20 eV,
respectively, and are above and below the corresponding
values of PF that exhibit a HOMO level of 25.81 eV and a
LUMO level of 22.12 eV, indicating possible charge trapping
of the DPAN units in the electroluminescence process.34,35
Fig. 3 UV-Vis absorption spectra of the model compound GMC in
PMMA (1023 M) and photoluminescence spectrum of homopolymer
PF in film.
attributed to the p–p* transition of the polymer backbone
(Fig. 2). No absorption by the DPAN unit (lmax = 444 nm
for the model compound as shown in Fig. 3) is observed. In
contrast, the PL spectra of the copolymers with an excitation
at 380 nm, as illustrated in Fig. 4a, exhibit a strong emission
Photophysical properties
For photophysical measurements, a polymer film with a
thickness of approximately 70 nm was spin-coated on quartz
from a chloroform solution (10 mg ml21). Similar to the
results obtained by cyclic voltammetry characterization, all the
DPAN-containing polymers have identical UV-Vis absorption
spectra with PF with an absorption maximum at 393 nm
Fig. 4 Photoluminescence (a) and electroluminescence (b) spectra of
Fig. 1 Cyclic voltagramms of PF and GMC.
polymers with different contents of DPAN unit.
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peak from DPAN at 520 nm and only a weak emission peak
from the polyfluorene backbone at 420/440 nm. The weak
emission peaks from polyfluorene backbone decrease with
increasing content of naphthalimide units from 0.3 to
1.0 mol%. The incorporation of DPAN into polyfluorene
leads to little change in the absorption spectra but results in
a great change in the PL spectra. This is due to the Fo¨rster
energy transfer from the polyfluorene backbone to the DPAN
unit because of the efficient overlap of the absorption
spectrum of GMC with PL spectrum of PF (see Fig. 3).33
The PL spectrum of PFG40 is dominated by total emission
from the DPAN unit with the peak at 532 nm. This redshift
results from the interaction of the DPAN unit due to its
high content.
of the EL and PL spectra of the same polymer indicates that
the contribution of blue emission from the polyfluorene
backbone in the EL spectrum is much smaller compared to
the PL spectrum. This difference is attributed to different
mechanisms in the EL and PL processes. In the former case,
both charge trapping and energy transfer contribute to the
emission from DPAN. However, in the latter case, charge
trapping does not occur and only energy transfer is involved.
Color purity of these copolymers was excellent, indicated by
their CIE coordinates (see Table 2) and a narrow full width at
half maximum (FWHM) of 66 nm. For example, the CIE
coordinates (0.26, 0.58) of PFG3 are very close to those of
the standard green (0.26, 0.65) demanded by the National
Television System Committee (NTSC).
The performance data of all the devices are listed in Table 2.
The device of the homopolymer PF exhibited a turn-on voltage
of 3.2 V, whereas the copolymers exhibited turn on voltages of
4.8 to 8.2 V with increasing DPAN content from PFG3 to
PFG10. The increase of the turn-on voltage with increasing
DPAN concentration is due to the charge trapping of the
DPAN unit. At low operating voltages, the electrons (holes)
injected from the cathode (anode) are trapped by the DPAN
unit in the region near the cathode (anode) and cannot migrate
to recombination with each other. Therefore, higher voltages
are needed for the device to emit light. A luminance efficiency
of 0.84 cd A21, a power efficiency of 0.58 lm W21 and a
maximum brightness of 2201 cd m22 for PF are much higher
than those of polyfluorene homopolymer reported by other
groups42 and are comparable with those of triaryl amine end-
capped polyfluorenes in similar device structures.43 All devices
based on the copolymers exhibited efficient green emission
Photoluminescence quantum yield (WPL) of the polymers
and GMC in the solid states were measured by means of an
integrated sphere (according to the method of ref. 41) with an
excitation at 409 nm (Table 1). GMC dispersed in PMMA film
with a concentration of 1023 M gave a quantum yield of 0.90,
which is comparable to that of other efficient light-emitters. As
listed in Table 1, the WPL value of the four copolymers, PFG3,
PFG5, PFG10 and PFG40, in neat films is 0.89, 0.96, 0.83 and
0.23, respectively. The low photoluminescence quantum yield
of PFG40 is due to the quenching effect of the dopant unit
because of its high content. The WPL value of PFG3, PFG5,
PFG10 is much higher than that of PF, 0.45, and other
fluorene-based polymers ever reported.5–24 These remarkable
WPL of PFG3, PFG5, PFG10 is attributed to the Fo¨rster
energy transfer from polyfluorene to the DPAN unit and the
high PL efficiency of the DPAN unit. This result also indicates
that a low content of dopant unit is important to achieve
high PL efficiency of the resulting polymers. The relatively
lower WPL value at 0.3 and 1.0 mol% is possibly due to the
incomplete energy transfer in the former case and the presence
of concentration quenching in the latter case.
with luminance efficiency ranging from 4.48 to 7.43 cd A21
.
A weak dependence of luminance efficiency on current
density was observed (see Fig. 5). In particular, the device
fabricated with PFG3 has a turn on voltage of 4.8 V, a current
efficiency of 7.43 cd A21, a power efficiency of 2.96 lm W21
and a maximum brightness of 21 595 cd m22 (see Fig. 6).
These values are comparable to those of poly(fluorene-co-
benzothiadiazole).5 It is worth noting that the content of
DPAN in PFG3 is only 0.3 mol% and that an increase of
DPAN’s content leads to an increase of the onset voltage and a
decrease of EL efficiency. Hence, our result indicates that a
low content of dopant unit is enough to tune the emission
color of polyfluorene and is crucial to realize good EL
performance of the devices.
Electroluminescence properties
To investigate the EL properties of the polymers, single-layer
devices were fabricated with
a configuration of ITO/
PEDOT(50 nm)/polymer(70 nm)/Ca(10 nm)/Al(100 nm).
PFG40 was not further characterized because of its low PL
quantum yield. The polymer layer was prepared following the
same procedure for preparation of polymer films for photo-
physical measurements; except that PEDOT treated ITO glass
substrates were used. The EL spectra of the polymers
are illustrated in Fig. 4b. PFG3, PFG5, PFG10 all exhibit
predominant green emission from the DPAN units and only
negligible blue emission from the polyfluorene backbone,
indicating that only a very small amount of dopant unit is
needed to tune the emission color of polyfluorene. Comparison
The excellent EL performance of PFG3 is principally
attributed to the energy transfer and charge trapping from
polyfluorene to highly fluorescent DPAN unit, which enhances
the radiative decay rate of singlet excitons. In addition, the
charge trapping of the DPAN units also enhances the EL
efficiency by increasing the recombination probability of
Table 2 Electroluminescence performance of the devices of PF, PFG3, PFG5, and PFG10
Polymer
Onset voltage/V
Maximum brightness/cd m22
Luminous efficiency/cd A21
Power efficiency/lm W21
CIE (x,y)
PF
3.2
4.8
5.4
8.2
2201
0.84
7.43
6.18
4.48
0.58
2.96
2.30
1.27
(0.16, 0.09)
(0.26, 0.58)
(0.27, 0.59)
(0.28, 0.60)
PFG3
PFG5
PFG10
21595
17596
15639
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beginning, the device performance almost levels off at approxi-
mately 50 min. Most importantly, during the operation, the
EL spectra remained unchanged and the CIE coordinates kept
within the range of (0.260–0.261, 0.581–0.582).
In comparison, we fabricated another device with 0.3 mol%
GMC blended with PF as emissive materials. The device
showed the turn on voltage of 5.0 V and maximum luminance
efficiency of 4.62 cd A21 and power efficiency of 1.82 lm W21
.
This performance is inferior to that of PFG3, indicating that
the molecular dispersion of dopant in the host material is
important to realize highly efficient PLEDs.
Conclusion
Fig. 5 Dependence of luminance efficiency on current density of the
In summary, we have developed a series of highly efficient
green light emitting polyfluorenes by covalently attaching
very small amounts of a highly fluorescent dopant unit, 4-(N,
N-diphenyl)amino-1,8-naphthalimide, to the pendant chain of
polyfluorene. The attachment of 0.3–1 mol% of dopant unit
results in little change of the absorption spectrum and
electrochemical properties of the resulting polymers but results
in a great change in the emission properties due to energy
transfer and charge trapping from polyfluorene to DPAN unit.
The resulting polymers exhibits high photoluminescence
quantum yields in solid films. Non-optimized single layer
device of these polymers achieved a luminance efficiency of
7.43 cd A21, which is fairly comparable to those of the state-
of-art green light-emitting poly(fluorene-co-benzothiadiazole)
with similar device structure. Both Fo¨rster energy transfer and
charge trapping and high photoluminescence quantum yields
of the copolymers as well as molecular dispersion of the
dopant are responsible for the efficient green light emission.
Our results indicate that polyfluorene with dopant/host system
is very promising for achieving excellent electroluminescence
performance with tunable emission color.
devices based on polymers with different contents of DPNA unit.
Fig. 6 Voltage–current density–brightness curve of the device based
on PFG3.
charge carriers. The electron and/or holes trapped by DPAN
units causes a build up in local charge density, which enhances
the possibility of attracting oppositive charge carriers. That
is, DPAN offers an effective recombination site for electrons
and holes.
Experimental
In order to evaluate the stability of these polymers, the
device of PFG3 was encapsulated with a cover glass and epoxy
and the performance is shown in Fig. 7. At a constant current,
the brightness decreases and the voltage is observed to increase
from an initial brightness of 800 cd m22. After this rapid
reduction of brightness and increase of driving voltage at the
Materials
All the reagents and solvents used for the syntheses were
purchased from Aldrich and Acros companies and used
without further purification except for tetrahydrofuran
(THF), which was dried over sodium/benzophenone.
2,7-dibromo-9,99-dioctylfluorene (6), 2,7-bis(trimethylene
boronate)-9,99-dioctylfluorene (7) were synthesized according
to the procedure from the literature.25 All reactions were
performed under a dry argon atmosphere.
4-Octyloxy phenol (1)
A mixture of hydroquinone (11.0 g, 100 mmol) and potassium
hydroxide (11.2 g, 200 mmol) in 200 ml ethanol was heated
under reflux with stirring. 1-Bromooctane (15.44 g, 80 mmol)
in 20 ml ethanol was added dropwise to the stirred solution.
The mixture had been refluxed for 14 h. After cooled to room
temperature, the mixture was poured into 500 ml 1 M HCl and
extracted with chloroform. The organic layer was washed
with brine and dried over anhydrous sodium sulfate. After the
solvent had been removed by rotary evaporation, the residual
Fig. 7 Dependence of the brightness and voltage on the operation
time of the device of PFG3 under constant current stress.
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was recrystallized from hexane to afford the titled compound
1
as a white crystal. Yield: 11.2 g (63%). H NMR (300 MHz,
J = 7.9 Hz), 7.20 (s, 1H), 7.01 (s, 1H), 6.90 (d, 1H, J = 8.1 Hz),
4.65 (t, 2H, J = 6.1 Hz), 4.29 (t, 2H, J = 6.1 Hz), 3.90 (t, 2H, J =
6.5 Hz), 1.79 (m, 2H), 1.70–1.20 (m, 10H), 0.88 (t, 3H, J =
7.0 Hz). 13C NMR (300 MHz, CDCl3) d (ppm): 163.6, 162.9,
149.4, 148.5, 148.4, 132.9, 130.6, 128.8, 126.1, 123.9, 121.8,
119.0, 117.8, 117.3, 110.6, 110.3, 110.1, 108.5. 69.2, 66.0, 37.6,
30.7, 28.2, 28.1, 24.9, 21.6, 13.1. The signal at 37.6 ppm in 13C
NMR indicates that the alkylation occurs at the imide nitrogen
not the primary amine. Anal. calcd: C, 54.39; H, 4.89; N, 4.53.
Found: C, 54.28; H, 4.71; N, 4.82. Electrospray ionization
mass spectrum (ESI-MS): [M + H]+: calcd: 617.1; found: 617.4.
CDCl3) d (ppm): 6.78 (m, 4H), 4.39 (br, 1H), 3.89 (t, 2H, J =
6.5 Hz), 1.75 (m, 2H), 1.50–1.20 (m, 10H), 0.88 (t, 3H, J =
6.9 Hz). Anal. calcd: C, 75.63; H, 9.97. Found: C, 74.27;
H, 9.70.
1-(2-Bromoethyloxy)-4-(octyloxy)benzene (2)
A
mixture of 1,2-dibromoethane (18.8 g, 100 mmol),
4-(octyloxy)phenol (1) (4.44 g, 20 mmol), tetra(n-butyl)ammo-
nium bromide (0.32 g, 1 mmol), 50 ml toluene and 50 ml 2 M
aqueous potassium hydroxide was stirred at 90 uC for 12 h.
After cooled to room temperature, the mixture was extracted
with chloroform. The organic layer was washed with water
and dried over anhydrous sodium sulfate. After the solvent
had been removed by rotary evaporation, the residual was
recrystallized from ethanol to afford the titled compound as a
white crystal. Yield: 3.16 g (48.4%). 1H NMR (300 MHz,
CDCl3) d (ppm): 6.84 (m, 4H), 4.23 (t, 2H, J = 6.3 Hz), 3.90 (t,
2H, J = 6.6 Hz), 3.61 (t, 2H, J = 6.3 Hz), 1.75 (m, 2H), 1.50–
1.20 (m, 10H), 0.88 (t, 3H, J = 6.9 Hz). Anal. calcd: C, 58.36;
H, 7.65. Found: C, 58.18; H, 7.23.
1,4-Dibromo-2-(octyloxy)-5-(2-(4-diphenylamino-1,8-
naphthalimide-9-yl)ethyloxy)benzene (5)
A
mixture of 1,4-dibromo-2-(octyloxy)-5-(2-(4-amino-1,8-
naphthalimide-9-yl)ethyloxy)benzene (4) (0.618 g, 1.0 mmol),
iodobenzene (1.020 g, 5.0 mmol), potassium carbonate (0.414 g,
3.0 mmol), 18-crown-6 (0.015 g, 0.05 mmol), copper iodide
(0.038 g, 0.2 mmol), 0.30 mL DMPU was stirred at 190 uC
for 48 h. After cooled to room temperature, the mixture was
dissolved in chloroform and washed with brine. The organic
layer was dried over anhydrous Na2SO4. After the solvent had
been removed, the crude product was purified with column
chromatography on silica gel to afford the titled compound as
an orange-red solid. Yield: 0.151 g (19%). 1H NMR (300 MHz,
CDCl3): d (ppm) 8.55 (dd, 1H, J = 7.3 Hz, J = 0.8 Hz), 8.52 (d,
1H, J = 8.1 Hz) 8.18 (d, 1H, J = 8.5 Hz), 7.49 (dd, 1H, J =
8.5 Hz, J = 7.3 Hz), 7.37 (d, 1H, J = 8.0 Hz), 7.30–7.23 (m,
4H), 7.12–7.00 (m, 8H), 4.68 (t, 2H, J = 5.8 Hz), 4.30 (t, 2H, J =
5.8 Hz), 3.90 (t, 2, J = 6.1 Hz H), 1.77 (m, 2H), 1.50–1.25 (m,
10H), 0.88 (t, 3H, J = 7.0 Hz). 13C NMR (300 MHz, CDCl3) d
(ppm): 164.3, 163.7, 153.2, 152.4, 151.0, 148.4, 132.4, 131.5,
131.4, 130.4, 129.6, 129.4, 128.0, 126.3, 125.4, 124.2, 123.9,
123.2, 123.1, 122.8, 118.6, 118.3 , 70.3, 66.9, 38.9, 31.8, 29.7,
29.2, 29.1, 26.0, 22.7, 14.1. Anal. calcd: C, 62.35; H, 4.97; N,
3.64. Found: C, 62.12; H, 4.76; N, 3.53. ESI-MS: [M + H]+:
calcd: 769.1; found: 769.4.
1,4-Bibromo-2-(octyloxy)-5-(2-bromoethyloxy)benzene (3)
A solution of 1-(2-bromoethyloxy)-4-(octyloxy)benzene (2)
(3.29 g, 10 mmol) in 50 ml dichloromethane was stirred
under room temperature. Bromine (4.80 g, 30 mmol) in 20 ml
dichloromethane was added dropwise. The mixture was
stirred under dark for 10 h. Then the mixture was washed
subsequently with aqueous sodium hydrogen sulfate and
brine, and then dried over anhydrous sodium sulfate. After
the solvent had been removed by rotary evaporation, the
residual was recrystallized from ethanol to give the titled
1
compound as a white crystal. Yield: 4.11 g (84%). H NMR
(300 MHz, CDCl3) d (ppm): 7.09 (s, 2H), 4.28 (t, 2H, J =
6.3 Hz), 3.95 (t, 2H, J = 6.6 Hz), 3.73 (t, 2H, J = 6.3 Hz), 1.75
(m, 2H), 1.50–1.20 (m, 10H), 0.91 (t, 3H, J = 6.9 Hz). 13C
NMR (300 MHz, CDCl3) d (ppm): 154.0, 152.1, 68.9, 68.6,
31.8, 29.4, 29.3, 26.1, 22.7, 14.11. Anal. calcd: C, 39.45; H,
4.76. Found: C, 40.00; H, 4.30.
General procedure of Suzuki polymerization39
A
mixture of 2,7-dibromo-9,9-dioctylfluorene (6), 2,7-
bis(trimethylene boronate)-9,99-dioctylfluorene (7),
1,4-dibromo-2-(octyloxy)-5-(2-(4-diphenylamino-1,8-naphthal-
imide-9-yl)ethyloxy)benzene (5) with corresponding feed
ratio, Aliquat 336 (0.05 g, 0.12 mmol), tetrakis(triphenyl-
phosphine)palladium (2.3 mg) under argon was added 2.5 ml
2 M aqueous potassium carbonate and 7 ml toluene. The
mixture was stirred at 90 uC for 48 h and at 60 uC for
another 24 h and then poured into methanol. The precipitate
was collected by filtration, dried and then dissolved in
dichloromethane. The solution was washed with water and
dried over anhydrous Na2SO4. After most of the solvent had
been removed, the residue was poured into stirred methanol
to give a fiber-like solid. The polymer was further purified
by extracting with acetone for 24 h. The reprecipitation
procedure in dichloromethane–methanol was then repeated
several times. The final product, a light yellow fiber, was
obtained after drying in vacuum with a yield of 45–60%. PF
1H NMR (300 MHz, CDCl3) d (ppm) 7.87 (d, 2H), 7.72 (br,
1,4-Dibromo-2-(octyloxy)-5-(2-(4-amino-1,8-naphthalimide-9-
yl)ethyloxy)benzene (4)
Into a stirred solution of 4-amino-1,8-naphthalimide (2.12 g,
10 mmol) in 60 ml DMSO was added potassium hydroxide
powder (0.56 g, 10 mmol). After 10 min, 1,4-dibromo-2-
(octyloxy)-5-(2-bromoethyloxy) benzene (3) (5.38 g, 11 mmol)
was added and the mixture was stirred at 120 uC for another
3 h. After cooling to room temperature, the mixture was
poured into water and extracted with ethyl acetate. The
organic layer was separated and washed with brine and then
dried over anhydrous sodium sulfate. After the solvent had
been removed by rotary evaporation, the dark yellow solid was
purified with column chromatography on silica gel to afford
1
the titled compound as a yellow solid. Yield: 4.39 g (71%). H
NMR (300 MHz, CDCl3) d (ppm): 8.63 (d, 1H, J = 7.3 Hz),
8.45 (d, 1H, J = 8.1 Hz), 8.12 (d, 1H, J = 8.4 Hz), 7.68 (t, 1H,
1436 | J. Mater. Chem., 2006, 16, 1431–1438
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4H), 2.10 (br, 4H), 1.14 (br, 24H), 0.81 (t, 6H). 13C NMR
(300 MHz, CDCl3) d (ppm): 151.4, 110.1, 139.7, 125.8,
121.1, 119.6, 55.0, 40.0, 31.4, 29.7, 28.8, 23.5, 22.2, 13.7.
Anal. calcd: C, 89.69; H, 10.31. Found: C, 89.08; H, 10.02.
PFG3, PFG5, PFG10 showed the similar 1H NMR and
elemental analysis results with those of PF. PFG40 1H
NMR (300 MHz, CDCl3) d (ppm) 8.53 (br, 0.032H), 7.83 (d,
2H), 7.68 (br, 4H), 7.49 (br, 0.60H), 7.38 (br, 0.28H), 6.92
(br, 0.34H), 4.60 (br, 0.062H), 4.32 (br, 0.068H), 3.97 (br,
0.062H), 2.11 (br, 4H), 1.14 (br, 24H), 0.81 (t, 6H). Anal.
calcd: C, 88.85; H, 10.00; N, 0.32. Found: C, 88.11; H, 9.71;
N, 0.60.
Instruments
1H NMR and 13C NMR spectra were recorded with Bruke
Avance 300 NMR spectrometer. The elemental analysis was
performed using a Bio-Rad elemental analysis system. The
number- and weight-average molecular weights of the poly-
mers were determined by gel permeation chromotagraphy
(GPC) with a Waters 410 instrument with polystyrene as
standards and THF as eluent. UV-Vis absorption, photo-
luminescence and electroluminescence spectra were measured
by Perkin-Elmer Lambda 35 Uv/Vis spectrometer and Perkin-
Elmer LS50B spectrofluorometer, respectively. Cyclic voltam-
mograms of polymer films on Pt plate were recorded on an
EG&G 283 (Princeton Applied Research) at room temperature
in a solution of n-Bu4NClO4 (0.10 M) in acetonitrile at a
scan rate of 100 mV s21. A Pt wire and an Ag/AgCl electrode
were used as the counter electrode and the reference electrode,
respectively. Thermal gravimetric analysis (TGA) was per-
formed under a nitrogen atmosphere at a heating rate of
10 uC min21 through the use of Perkin-Elmer-TGA 7. The
current–voltage and brightness–voltage curves of devices were
measured using a Keithley 2400/2000 current/voltage source
unit calibrated with a silicon photodiode.
4-Amino-9-N-decyl-1,8-naphthalimide (8)
Into a solution of 4-amino-1,8-naphthalimide (2.12 g, 10 mmol)
in 60 ml DMSO was added potassium hydroxide (0.56 g,
10 mmol) at 120 uC. After 10 min, 1-bromodecane (2.21 g,
10 mmol) was added and the mixture was kept stirring for 12 h.
After cooled to room temperature, the mixture was poured
into water and extracted with ethyl acetate. The organic layer
was collected and washed with brine and dried over anhydrous
Na2SO4. The crude product was further purified by column
chromatography on silica gel to give the title compound as a
yellow solid. Yield: 2.50 g (71%). 1H NMR (300 MHz, CDCl3)
d (ppm): 8.60 (d, 1H, J = 7.3 Hz), 8.42 (d, 1H, J = 8.4 Hz), 8.10
(d, 1H, J = 8.4 Hz), 7.66 (t, 1H, J = 7.8 Hz), 6.89 (d, 1H, J =
8.1 Hz),4.93 (br, 2H), 4.15 (t, 2H, J = 7.6 Hz), 1.74–1.18
(m,16H), 0.87 (t, 3H, J = 6.7 Hz). 13C NMR (300 MHz,
CDCl3) d (ppm): 163.5, 163.0 148.4, 132.7, 130.3, 128.7, 125.9,
123.8, 122.0, 119.0, 110.9, 108.4, 39.3, 30.8, 28.5, 28.4, 28.2,
27.2, 26.2, 21.6, 13.1. The signal at 39.3 ppm in 13C NMR
indicates that the alkylation occurs at the imide nitrogen not
at the primary amine. Anal. calcd: C, 74.97; H, 8.01; N, 7.95.
Found: C, 74.43; H, 7.90; N, 8.20. Matrix-assisted laser
desorption/ionization mass spectrometry (MALTI-TOF MS):
calcd: 352.2; found: 352.2.
Device fabrication
The indium–tin oxide (ITO) glass plates were degreased in
ultrasonic solvent bath and then dried in a heating chamber at
the temperature of 120 uC. The poly(styrene sulfonic acid)
doped poly(ethylenedioxythiophene) was spin-coated on the
treated ITO at 3000 rms for 60 s and then baked for 15 min
at 120 uC to give an approximate thickness of 50 nm. The
polymer layer (approximately 70 nm) was then spin-coated
onto the PEDOT/ITO coated glass substrate in chloroform
solution (10 mg ml21) at ambient atmosphere. Finally, a thin
layer of calcium (10 nm) followed by a layer of aluminum
(100 nm) is deposited in a vacuum thermal evaporator through
a shadow mask at a pressure of 3 6 1025 Torr. The active area
of the diodes is 16 mm2.
4-N,N-Diphenylamino-9-decyl-1,8-naphthalimide (GMC)
A mixture of 4-amino-9-decyl-1,8-naphthalimide (0.704 g,
2.0 mmol), iodobenzene (4.080 g, 20.0 mmol), potassium
carbonate (0.828 g, 6.0 mmol), 18-crown-6 (0.030 g,
0.11 mmol), copper iodide (0.076 g, 0.4 mmol), 0.30 mL
DMPU had been stirred at 190 uC for 12 h. After cooled to
room temperature, the mixture was dissolved in chloroform.
The organic solution was washed with brine and dried over
anhydrous Na2SO4. The crude product was purified by column
chromatography on silica gel to give the title compound
as an orange-red solid. Yield: 0.796 g (79%). 1H NMR
(300 MHz, CDCl3) d (ppm): 8.55–8.48 (m, 2H), 8.17 (dd, 1H,
J = 8.6 Hz, J = 1.0 Hz), 7.49 (dd, 1H, J = 7.3 Hz, J = 8.5 Hz),
7.37 (d, 1H, J = 8.0 Hz), 7.24 (m, 4H), 7.04 (m, 6H), 4.17 (t,
2H, J = 7.5 Hz), 1.18–1.74 (m,16H), 0.87 (t, 3H, J = 6.9 Hz).
13C NMR (300 MHz, CDCl3) d (ppm): 163.2, 162.7, 149.7,
147.4, 131.0, 130.2, 130.0, 129.3, 128.5, 127.0, 125.3, 124.5,
122.8, 122.6, 122.3, 117.8, 39.4, 30.9, 28.5, 28.4, 28.3, 27.2,
26.2, 21.7, 13.1. Anal. calcd: C, 80.92; H, 7.19; N, 5.55. Found:
C, 79.41; H, 7.15; N, 5.40. MALTI-TOF MS calcd: 504.2;
found: 504.2.
Acknowledgements
This work is supported by the National Natural Science
Foundation of China (No. 20574067) and 973 Project
(2002CB613402). The authors thank Dr Aldred P. Matthew
for fruitful discussion.
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