Pure and saturated red electroluminescent polyfluorenes with dopant/host system and PLED efficiency/color purity trade-offs

Article abstract of DOI:10.1002/adfm.201000840

Three kinds of red electroluminescent (EL) polymers based on polyfluorene as blue host and 2,1,3-benzothiadiazole derivatives with different emission wavelengths as red dopant units on the side chain are designed and synthesized. The influence of the photoluminescence (PL) efficiencies and emission wavelengths of red dopants on the EL efficiencies and color purities of the resulting polyfluorene copolymers of dopant/host system is investigated by adjusting the electron donating ability of the donor units in D-;r-A-D typed 2,1,3-benzothiadiazole derivatives. The devices of these red-emitting polymers realize remarkable EL efficiency/color purity trade-offs. The single-layer devices with the configuration of ITO/PEDOT:PSS/Polymer/Ca/Al show pure red emission at 624 nm with a luminous efficiency of 3.83 cd A^-1 and CIE of (0.63, 0.35) for PFR1, saturated red emission at 636 nm with a luminous efficiency of 2.29 cd A^-1 and CIE of (0.64, 0.33) for PFR2, respectively. By introduction of an additional electron injection layer PF-EP(Ethanol soluble phosphonate-functionalized polyfluorene), high performance pure and saturated red emission two-layer devices (ITO/PEDOT:PSS/Polymer/PF-EP/ LiF/ Al) were achieved with maximum luminous efficiencies of 5.50 cd A ^-1 and CIE of (0.62, 0.35) for PFR1, 3.10 cd A^-1 and CIE of (0.63, 0.33) for PFR2, respectively, which are the best results for pure and saturated fluorescent red EL polymers reported so far.

Full text of DOI:10.1002/adfm.201000840

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Pure and Saturated Red Electroluminescent Polyfluorenes
with Dopant/Host System and PLED Efficiency/Color
Purity Trade-Offs
By Lei Chen, Baohua Zhang, Yanxiang Cheng, Zhiyuan Xie, Lixiang Wang,* Xiabin Jing,
and Fosong Wang
Compared to inorganic and small molec-
ular organic light-emitting diodes, PLEDs
can be conveniently manufactured by solu-
tion processing techniques such as spin
coating or ink-jet printing, which is very
important for low cost, flexible and large-
area displays. For full color displays, three
basic color-red, green and blue are required.
Compared with green and blue emissive
polymers, the development of red EL con-
jugated polymers is far behind in terms of
both color purity and EL efficiency. Most
red-emitting conjugated polymers are real-
ized by incorporating red fluorophores,
such as 2,1,3-benzothiadiazole deriva-
tives,[7–9] 2,1,3-benzoselenadiazole deriva-
tives,[9–11] 2,1,3-naphthaselenadiazole,[12]
cyanovinyl-containingunits,[13,14] 3,4-diphe-
nylmaleimide derivatives[15] and phenothi-
azine derivatives,[16] perylene-containing
dyes,[17] etc., into backbones, side chains
or end groups of conjugated polymers.
Due to the nature of red emissive mate-
rials, the red fluorophores emitting
longer wavelength are more extensively
π-conjugated or stronger polar com-
Three kinds of red electroluminescent (EL) polymers based on polyfluorene
as blue host and 2,1,3-benzothiadiazole derivatives with different emission
wavelengths as red dopant units on the side chain are designed and synthe-
sized. The influence of the photoluminescence (PL) efficiencies and emission
wavelengths of red dopants on the EL efficiencies and color purities of the
resulting polyfluorene copolymers of dopant/host system is investigated by
adjusting the electron donating ability of the donor units in D-π-A-D typed
2,1,3-benzothiadiazole derivatives. The devices of these red-emitting poly-
mers realize remarkable EL efficiency/color purity trade-offs. The single-layer
devices with the configuration of ITO/PEDOT:PSS/Polymer/Ca/Al show pure
red emission at 624 nm with a luminous efficiency of 3.83 cd A−1 and CIE
of (0.63, 0.35) for PFR1, saturated red emission at 636 nm with a luminous
efficiency of 2.29 cd A−1 and CIE of (0.64, 0.33) for PFR2, respectively. By
introduction of an additional electron injection layer PF-EP(Ethanol soluble
phosphonate-functionalized polyfluorene), high performance pure and satu-
rated red emission two-layer devices (ITO/PEDOT:PSS/Polymer/PF-EP/LiF/
Al) were achieved with maximum luminous efficiencies of 5.50 cd A−1 and CIE
of (0.62, 0.35) for PFR1, 3.10 cd A−1 and CIE of (0.63, 0.33) for PFR2, respec-
tively, which are the best results for pure and saturated fluorescent red EL
polymers reported so far.
pounds, which usually have lower fluorescence quantum yields
(ΦPL). Meanwhile, they are highly susceptible to concentra-
tion quenching in solid state because of the intermolecular
dipole–dipole interactions or π–π stacking.[18] So, the devices
of red polymers with red enough emission wavelengths to
achieve excellent CIE coordinates usually show inferior EL effi-
ciencies. Until now, all of the fluorescent pure and saturated
red-emitting polymers show EL efficiencies no more than
2.0 cd A−1.[12,16,19,20]
Recently, our group has reported a new approach to design
high efficiency EL polymers of dopant/host system with molec-
ular dispersion feature by covalently attaching small amounts
of dopant units to the side chain of polyfluorene host.[21–25] By
this means, the problems of phase separation in physical blend
material systems[26–28] and voltage dependence of the EL spec-
trum existing in multilayer devices[29–32] will be avoided due
to the homogeneous distribution of the dopant units in the
polymer host. Meanwhile, the concentration quenching effect
aforementioned will be partly suppressed because of the low
1. Introduction
Since the pioneering work of Burroughes et al. in 1990,[1]
polymer light emitting diodes (PLEDs) based on conjugated poly-
mers have attracted widely research interest for their potential
applications in full color flat-panel displays and illuminations.[2–6]
∗
[ ] Dr. L. Chen, Dr. B. Zhang, Prof. Y. Cheng, Prof. Z. Xie,
Prof. L. Wang, Prof. X. Jing, Prof. F. Wang
State Key Laboratory of Polymer Physics and Chemistry
Changchun Institute of Applied Chemistry
Chinese Academy of Sciences
Changchun 130022 (P. R. China)
E-mail: lixiang@ciac.jl.cn
Dr. L. Chen, Dr. B. Zhang
Graduate School of the Chinese Academy of Sciences
Beijing 100039 (P. R. China)
DOI: 10.1002/adfm.201000840
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content of dopant units, so highly efficient blue,[21] green,[22]
red[23] and white[24,25] PLEDs have been realized by using
dopant/host strategy. However, for red-emitting polymers,[23]
the key problem in our previous report is that we haven’t real-
ized the EL efficiency/color purity trade-offs. We find that highly
efficient PLED (5.10 cd A−1) is not red enough (orange-red
emission at 615 nm, CIE of (0.59, 0.39)), and deep-red PLED
at 645 nm is not so efficient (1.70 cd A−1), which is clearly cor-
responding to the PL efficiencies and emission wavelengths of
the red dopant units. Thus, optimization of red dopant units
is very important for realizing red PLEDs EL efficiency/color
purity trade-offs.
In this article, we report a series of red EL polymers based
on polyfluorene as blue host and 2,1,3-benzothiadiazole deriva-
tives with fine-tuned PL efficiencies and emission wavelengths
as red dopant units on the side chain, aiming at tuning the
EL efficiencies and color purities of the resulting polyfluorene
copolymers of dopant/host system and realizing the optimiza-
tion of red PLEDs EL efficiency/color purity trade-offs. The dif-
ference between this article and previous study is on achieving
excellent PLEDs EL efficiency/color purity trade-offs for red
fluorescent polymers based on polyfluorene as blue host and
2,1,3-benzothiadiazole derivatives as red dopant. As a result,
the single-layer devices of these polymers (ITO/PEDOT:PSS/
Polymer/Ca/Al) show pure red emission at 624 nm with a
luminous efficiency of 3.83 cd A−1 and CIE of (0.63, 0.35) for
PFR1, and saturated red emission at 636 nm with a lumi-
nous efficiency of 2.29 cd A−1 and CIE of (0.64, 0.33) for PFR2
respectively. Furthermore, by using ethanol soluble phospho-
nate-functionalized polyfluorene (PF-EP) as the electron injec-
tion layer (EIL) reported in our previous study,[33] high per-
formance two-layer devices (ITO/PEDOT:PSS/Polymer/PF-EP/
LiF/Al) are obtained with maximum luminous efficiencies
of 5.50 cd A−1 and CIE of (0.62, 0.35) for pure red emission
(PFR1), and 3.10 cd A−1 and CIE of (0.63, 0.33) for saturated red
emission (PFR2), respectively. To the best of our knowledge,
these are the highest efficiencies of pure and saturated red fluo-
rescent EL polymers reported so far.
2. Result and Discussion
2.1. Molecular Design
We designed a series of saturated red emission model com-
pounds (MCs), as shown in Scheme 1, by introducing different
alkoxy groups to increasing the electron donating ability of
4-(5-(4-(N-phenyl-N-(4-methoxy)phenylamino)phenyl)thienyl-2)-
7-(4-(diphenylamino)phenyl)-2,1,3-benzothiadiazole (MC-R2)
reported in our previous work, which show high PL efficiency
(59%), but orange-red emission at 620 nm. Firstly, we designed
MCR1 by incorporating two methoxy groups to the triphe-
nylamine segment of MC-R2, which will lead to about 10 nm
redshift according to our experience.[24,34] Secondly, we designed
MCR2 by changing the thiophene unit of MC-R2 to 3,4-ethylene-
dioxythiophene (EDOT) unit, which will lead to more than 10 nm
redshift due to the stronger electron-donating effect of the eth-
ylenedioxy bridge compared to dialkoxy groups.[35] Thirdly, for
comparison, we designed MCR3 by adopting above-mentioned
two modifications at the same time. Thus, we hope to obtain
saturated red dopants with fine-tuned PL efficiencies and emis-
sion wavelengths. Then we obtained red polymers through
covalently attaching these red dopant units to the side chain of
polyfluorene using alkyl spacers. The contents of the red dopant
units have been controlled to be 0.3 mol% in order to achieve
almost complete energy transfer from polyfluorene host to red
dopant units and suppress the concentration quenching effect.
Thus, high EL efficiencies of these polymers with superior CIE
coordinates will be expected.
2.2. Synthesis and Characters
The synthetic routes of the red MCs, monomers and cor-
responding polymers are outlined in Scheme 2. The tert-
butyldimethylsilyl (TBS) group protected intermediates were
all synthesized by Stille coupling. The TBS groups are stable
H3CO
OCH3
H3CO
host
λ = 615 nm ΦPL= 59%
λ = 631 nm ΦPL= 45%
0.997
0.003 n
C8H17
C8H17
C6H13
N
N
N
N
S
S
N
N
N
N
dopant
O
R
S
S
MC-R2
MCR1
OCH3
OCH3
N
N
PFR1 R1 =
S
N
N
S
OCH3
λ = 640 nm ΦPL= 37%
λ = 650 nm ΦPL= 31%
O
O
O
O
N
N
PFR2 R2 =
PFR3 R3 =
H3CO
H3CO
OCH3
S
N
N
S
O
O
O
O
OCH3
N
N
N
N
S
S
N
N
N
N
N
N
S
S
S
OCH3
N
N
MCR2
MCR3
S
OCH3
Scheme 1. Chemical structure of red model compounds and polymers.
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H3CO
H3CO
H3CO
O
O
O
O
O
O
iii
iv
i
ii
H2N
Br
N
Br
N
B
N
Br
SnBu3
S
S
N
N
S
3
7
1
2
4
H3CO
H3CO
H3CO
TBSO
TBSO
iv
iv
N
HO
TBSO
TBSO
N
SnBu3
vii
S
S
8
v
vi
N
H
N H
N
Br
TBSO
TBSO
vii
4
O
O
O
O
5
6
N
N
SnBu3
S
S
9
10
CH3O-R2
ix
MCR2
O
O
vii
10
viii
TBSO-R2
HO-R2
N
Br
iii
N
R2 =
N
S
N
N
11
12
13
S
N
N
14
Br
Br
S
Monomer R2
O
R2
CH3O-R1
OCH3
ix
MCR1
viii
viii
TBSO-R1
HO-R1
iii
N
N
R1 =
S
15
16
14
N
N
vii
H3CO
Br
Br
S
OCH3
8
N
Br
Monomer R1
O
R1
vii
8
N
N
S
H3CO
CH3O-R3
OCH3
ix
O
O
MCR3
TBSO-R3
HO-R3
N
N
R3 =
iii
14
S
17
18
N
N
S
Br
Br
OCH3
Monomer R3
O
R3
Br
O
B
O
O
iii
0.497n Br
Br
B
Br
0.500n
0.003n
0.997
0.003
n
O
C8H17
C8H17
C6H13
C8H17
C8H17
C8H17
C8H17
20
19
PFR1
PFR2
PFR3
Monomer R1
Monomer R2
Monomer R3
O
R
O
R
H3CO
S
S
N
Br
Br
Br
N
N
n
n
N
N
C8H17
C8H17
N
N
S
S
Br
O
P
O
P
O
MC-R3
11
14
O PF-EPO
O
PFO
Scheme 2. Synthetic routes of the model compounds, monomers, polymers and chemical structure of the intermediates (11, 14) as well as PFO and
PF-EP. (Reagents and conditions: i) CuCl, 1,10-phenanthroline monohydrate, KOH, toluene, reflux; ii) Pd(dppf)Cl2, KOAc, DMF, 80 °C; iii) Pd(PPh3)4,
2 M K2CO3, Aliquat 336, toluene, 90 °C; iv) a) n-BuLi, THF, −78 °C, b) (n-Bu)3SnCl; v) a) N(C2H5)3, DCM, 0 °C, b) TBSCl, r.t.; vi) Pd2(dba)3, rac-binap,
NaOBu-t, toluene, 100 °C; vii) Pd(PPh3)4, toluene, 100 °C; viii) 6 M HCl, THF, r.t.; ix) CH3I, K2CO3, acetone, reflux.
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T a b le 1 . Photophysical, electrochemical properties, and energy levels of the RMCs.
onset
onset
red
E
[V] [b]
EHOMO [eV]
−5.05
E
[V]
ELUMO [eV]
−3.14
Eg [eV]
1.91
λ
abs [nm] [a]
511
λ
emi [nm]
Φ
PL [%]
49
oxd
MCR1
MCR2
MCR3
631
0.71
−1.20
−1.21
−1.23
519
640
37
0.67
0.63
1.88
−5.01
−3.13
529
650
31
1.85
−4.96
−3.11
[a] Measured in around 10−6 M toluene solution. [b] Measured in 10−3 M CH2Cl2 solution, n-Bu4NClO4 as supporting electctrolyte.
to n-BuLi and could be easily deprotected using aqueous HCl
without affecting other alkoxy groups to get corresponding
hydroxylated intermediates, which were then methylated by
CH3I to synthesize the three red MCs: MCR1, MCR2, and
MCR3. The hydroxylated intermediates could also react with
2,7-dibromo-9-hexyl-9-(6-bromohexyl)fluorene (14) to afford the
three red monomers, Monomer R1, Monomer
We also explored the electrochemical properties of all the
polymers films spin-coated on a glassy-carbon working elec-
trode. As shown in Table 2, incorporating a small amount of
red dopant units to the side chain of PFO almost doesn’t affect
the electrochemical properties of the resulting polymers, which
have similar HOMO and LUMO energy levels as PFO.
R2 and Monomer R3 with high yields. All
the red polymers were synthesized by classic
palladium-catalyzed Suzuki polyconden-
(a)
MCR1
MCR2
sation of 2,7-dibromo-9,9-dioctylfluorene
(19), 2,7-bis(trimethyleneborate)-9,9-dioctyl-
fluorene (20) and the corresponding red
monomers and sequentially end-capped by
phenylboronic acid and bromobenzene. The
number-average molecular weights (Mn) of
PFR1, PFR2 and PFR3, as determined by gel
permeation chromatography (GPC) with pol-
ystyrene as standards, range from 36 700 to
53 400 with polydispersities (PDI) ranging
from 2.52 to 2.91. All these polymers show
good thermal stability as PFO with thermal
degradation temperature (Td) around 430 °C
(Table 1).
MCR3
PFO
2
1
-1
-2
-3
Potential (V vs Ag/AgCl)
2.3. Electrochemical Properties
-2.13eV
Cyclic voltammetry measurements have been
demonstrated to investigate the energy levels
of the three red MCs, the results are shown
in Figure 1a. Their onset oxidation voltages
and onset reduction voltages as well as the
highest occupied molecular orbital (HOMO)
and lowest unoccupied molecular orbital
(LUMO) energy levels are listed in Table 1,
which clearly shows that both of the HOMO
and LUMO energy levels of the three model
compounds are increased due to enhanced
electron donating abilities of donor units,
but the increasing amplitudes of the HOMO
energy levels are higher than the LUMO
energy levels. As shown in Figure 1b, the
HOMO and LUMO energy levels of all the
three model compounds are located between
those of PFO, as a result, effective charge
trapping of the red dopants in the EL process
will be expectable.
(b)
-2.89eV
-3.11eV
-3.13eV
-3.14eV
MCR1
MCR2
MCR3
-4.97eV
-5.01eV
-5.05eV
-5.20eV
-5.80eV
PFO
ITO/PEDOT
Ca/Al
Figure 1. Cyclic voltammetry (a) and energy levels (b) of model compounds and PFO.
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T a b le 2 . Characters of the red polymers and PFO.
onset
red
PDI
2.5
2.6
2.9
2.5
Eooxndset [V] [a]
1.37
EHOMO [eV]
−5.80
E
[V]
E LUMO [eV]
−2.13
Mn (× 104)
T d [°C]
430
PFO
4.1
4.7
3.7
5.3
−2.30
−2.32
−2.32
−2.33
PFR1
PFR2
PFR3
433
1.37
−5.80
−2.11
431
1.38
−5.81
−2.11
430
1.38
−5.81
−2.09
[a] Measured in film state, using 0.1 M n-Bu4NClO4 in CH3CN as supporting electctrolyte solution.
2.4. Photophysical Properties
MCR2. More importantly, all of them show saturated red emis-
sion with high ΦPL values in dilute toluene solution (listed in
Table 2). The results coincide with our expectation very well,
demonstrating that our molecular design can really obtain
saturated red dopants with fine-tuned PL efficiency/emission
wavelength trade-offs. We find that MCR2 and MCR3 have
similar emission wavelengths but higher ΦPL values (37% and
31%) compared to the deep-red MC-R3 (24%, see in Scheme 2)
reported in our previous work, indicating that it is a better
choice to realize longer wavelength emission by alternating π-
conjugated thiophene unit by alkoxy groups. It’s probably due
to the heavy atom effect of the sulfur atom[36,37] and/or the
decrease of rigidity of the molecule with more thiophene units,
both of which will lead to more nonradiative decay process and
lower PL quantum yield for MC-R3. As shown in Figure 2a, the
absorption spectrum of all these red MCs have good overlap
with the PL spectrum of PFO, so efficient Förster energy
transfer from polyfluorene host to red dopant units in PL and
EL processes is expected.
The absorption spectra of PFR1, PFR2, PFR3 and PFO
in films are shown in Figure 3a. All the red polymers exhibit
similar absorption spectra as PFO with a peak absorption wave-
length at 393 nm attributed to the π–π∗ transition of the polyflu-
orene backbone, and there are no obvious signals of the charge
transfer state absorption of the red dopant units at around
511 nm/519 nm/529 nm. Figure 3b shows the PL spectra of the
polymers in films with an excitation wavelength at 380 nm. The
PL spectra of all the red polymers exhibit not only blue emis-
sion from the polyfluorene backbone but also red emission
from the dopant units. Since the absorption of the red dopant
units in the polymers almost can’t be detected, we attribute the
red emission of the polymers to the efficient Förster energy
transfer from polyfluorene host to the red dopant units in the
PL process. Furthermore, the relative intensity of red emission
for PFR1, PFR2, and PFR3 decrease successively, mainly due to
the PL quantum efficiencies of the three red dopant units and
the spectral overlap between the PL spectrum of polyfluorene
host and the absorption spectra of the three red dopant units
decrease sequentially as well.
Figure 2 shows the absorption spectrum and PL spectrum of the
three red MCs, their corresponding peak emission wavelengths
are listed in Table 2. Comparing with MC-R2, the introduction
of two methoxy groups (MCR1) leads to 12 nm red-shift of
absorption spectrum and 11 nm red-shift of PL spectrum, alter-
nating thiophene unit by EDOT unit (MCR2) leads to 20 nm
red-shift of absorption spectrum and 20 nm red-shift of PL
spectrum, respectively. MCR3 has another 10 nm redshift
of both absorption spectrum and PL spectrum compared to
1.2
1.0
0.8
0.6
0.4
0.2
0.0
1.2
1.0
0.8
0.6
0.4
0.2
0.0
(a)
PFO
MCR1
MCR2
MCR3
400
450
500
550
600
650
700
Wavelength (nm)
(b)
1.0
0.8
0.6
0.4
0.2
0.0
MCR1
MCR2
MCR3
2.5. EL Properties
550
600
650
700
750
800
In order to investigate the EL properties of the red polymers,
we fabricated single-layer devices with a configuration of ITO/
PEDOT:PSS(40 nm)/Polymer(90 nm)/Ca(10 nm)/Al(100 nm).
Unlike the PL spectra, the EL spectra of all the polymers predom-
inantly exhibit pure red emission attributed to the red dopant
Wavelength (nm)
Figure 2. Absorption spectra of RMCs in dilute toluene solution and
PL spectrum of PFO in film state (a) and PL spectra of RMCs in dilute
toluene solution (b).
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(a)
(a)
PFO
1.0
1.0
0.8
0.6
0.4
0.2
0.0
PFR1
PFR2
PFR3
PFR1
PFR2
PFR3
0.8
0.6
0.4
0.2
0.0
300
350
400
450
500
550
600
400
500
600
700
Wavelength (nm)
Wavelength (nm)
(b)
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
(b)
PFO
1.0
0.8
0.6
0.4
0.2
0.0
PFR1
PFR2
PFR3
6V
8V
10V
12V
400
450
500
550
600
650
700
750
400
500
600
700
Wavelength (nm)
Wavelength (nm)
Figure 3. Absorption (a) and PL (b) spectrum of the red polymers and
PFO in film states.
Figure 4. EL spectra of the devices of the red polymers (a) and EL spectra
at different voltages of the device of PFR1 (b).
units with negligible blue emission from polyfluorene backbone
(Figure 4a). It’s because there is only Förster energy transfer
from polyfluorene to the red dopants in the PL process. While,
in the EL process, the direct charge trapping on the red dopant
units also contribute to the red emission due to their LUMO/
HOMO energy levels lie between the LUMO/HOMO energy
levels of polyfluorene. All the polymers show pure red emis-
sion with maximum emission wavelengths at 624 nm, 636 nm,
and 652 nm for PFR1, PFR2, and PFR3, respectively (Table 3).
The CIE coordinates of the devices of these polymers are
demonstrated to be (0.63, 0.35), (0.64, 0.33), (0.65, 0.32), which
are close to the standard red (0.64, 0.33) demanded by the Euro-
pean Broadcasting Union (EBU). Moreover, the EL spectral
shape of the devices of these polymers keeps almost unchanged
at different voltages, just like the EL spectra of PFR1 shown
in Figure 4b. Meanwhile, the CIE chromaticity coordinates of
the device of PFR1 just change from (0.635, 0.352) at 6.5 V to
(0.625, 0.351) at 12.0 V.
Table
3 outlined the EL performance of the single-
layer devices of the red polymers. All the devices of these
T a b le 3 . EL performance of the single layer devices of the red polymers.
Luminous Efficiency [cd A− 1] [b] Power Efficiency [lm W−1] [c] Maximum Brightness [cd m− 2
]
λ
max [nm]
624
Turn-on Voltage [V] [a]
CIE (x, y) [d]
PFR1
PFR2
PFR3
6.5
6.5
6.5
3.83
2.29
1.71
1.15
0.80
0.57
5393
2792
2193
(0.63, 0.35)
(0.64, 0.33)
(0.65, 0.32)
636
652
[a] At the brightness of 1.0 cd m−2. [b] Maximum values. [c] At the maximum LE. [d] Measured at 8.0 V.
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10000
1000
100
10
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
300
250
200
150
100
50
PFR1
PFR2
PFR3
PFR1
PFR2
PFR3
0
1
6
8
10
12
14
16
18
20
Voltage (v)
0
50
100
150
200
Current Density ( mA/cm2)
Figure 5. Voltage–current density–brightness curves of the devices of the
red polymers.
Figure 6. Dependence of the luminous efficiencies on the current densi-
ties of the devices of the polymers.
polymers show high EL efficiencies with pure red emission.
For example, the devices of PFR1 shows pure red emission
with the CIE coordinates of (0.63, 0.35) at 8.0 V, turn on voltage
of 6.5 V, maximum brightness of 5393 cd m−2 (Figure 5). At a
current density of 3.02 mA cm−2 , it exhibits a maximum lumi-
nous efficiency of 3.83 cd A−1 , power efficiency of 1.09 lm W− 1 .
The devices of PFR2 emits saturated red light with the CIE
coordinates of (0.64, 0.33) at 8.0 V, turn on voltage of 6.5 V,
maximum brightness of 4453 cd m−2 . At a current density of
1.38 mA cm−2 , it has a maximum luminous efficiency of
2.29 cd A−1 , power efficiency of 0.80 lm W−1. The devices of PFR3
emits deep-red light with the CIE coordinates of (0.65, 0.32)
at 8.0 V, turn on voltage of 6.7 V, maximum brightness of
2593 cd m−2 . At a current density of 1.74 mA cm−2 , it achieves a
maximum luminous efficiency of 1.71 cd A−1 , power efficiency
of 0.57 lm W−1 . The devices of PFR1 and PFR2 achieve remark-
able EL luminous efficiencies with excellent CIE coordinates, at
a brightness of 100 cd m−2 , the EL luminous efficiency of PFR1
and PFR2 is up to 3.78 cd A− 1 and 2.14 cd A−1 (Figure 6), which
are superior to that of previously reported fluorescent red-light
emitting polymer devices. Thus, we have realized highly effi-
cient pure red polymer light-emitting devices with excellent EL
efficiency/color purity trade-offs by introduction of these satu-
rated red dopants with fine-tuned PL efficiencies and emission
wavelengths.
the electron injection layer (EIL) to fabricate two-layer devices of
the red polymers with a structure of ITO/PEDOT:PSS(40nm)/
EML(80 nm)/PF-EP(10 nm)/LiF(1 nm)/Al(100 nm). The EL
performances of the devices of the red polymers using PF-EP
as the EIL are summarized in Table 4. The multilayer device
of PFR1 shows turn on voltage of 4.5 V, and maximum bright-
ness of 10800 cd cm−2 (Figure 7). At a current density of
0.30 mA cm−2 , it exhibits a maximum luminous efficiency
of 5.50 cd A−1, a maximum power efficiency of 3.14 lm W−1
(Figure 8), all of which are superior to the device of PFR1
using Ca/Al as the cathode. The EL efficiencies of the multi-
layer devices of PFR2 and PFR3 are improved as well. Even at
a brightness of 100 cd m−2 , the EL luminous efficiency of the
multilayer devices of PFR1 and PFR2 still remain as high as
4.45 cd A−1 and 2.64 cd A− 1 . The detailed optimizing mecha-
nism is still in researching, however, the following aspects may
contribute to the improvement of the EL performances of the
devices: i) Promoted electron injection. PF-EP can facilitate
electron injection from the cathode because the phosphonate
groups in the pendants have a strong coordinating power to
aluminum.[33,38] ii) Suppressed electrode quenching. It has been
proved that the excitons recombination zone is located close to
the EML/PF-EP interface,[39] therefore, the excitons quenching
by low band-gap PEDOT and metal cathode can be effectively
avoided. Further research about the devices using PE-EP as EIL
will be reported later.
To further improve the EL performance of the devices of
the polymers, we use an alcohol-soluble conjugated polymer,
poly[9,9-bis(6′-diethoxylphosphorylhexyl) -fluorene] (PF-EP) as
T a b le 4 . EL performance of the multilayer devices of the red polymers.
Luminous Efficiency [cd A−1] [b] Power Efficiency [lm W−1] [c]
Maximum Brightness [cd m− 2
]
λ
max [nm]
624
Turn-on Voltage [V] [a]
EQE [%]
5.51
CIE (x, y) [d]
(0.62, 0.35)
(0.63, 0.33)
(0.64, 0.32)
PFR1
PFR2
PFR3
4.5
4.5
5.0
5.50
3.10
2.05
3.14
1.62
0.87
10800
6115
3395
3.88
636
3.37
652
[a] At the brightness of 1.0 cd m−2. [b] Maximum values. [c] At the maximum LE. [d] Measured at 6.0 V.
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10000
1000
100
10
3. Conclusions
PFR1
PFR2
PFR3
700
600
500
400
300
200
100
0
In conclusion, we have synthesized a series of red EL polymers
based on polyfluorene as blue host and 2,1,3-benzothiadiazole
derivatives with different emission wavelengths as red dopants
on the side chain. By adjusting the electron donating ability of
the donor units in these D-π-A-D typed 2,1,3-benzothiadiazole
derivatives, the resulting polyfluorene copolymers with fine-
tuned PL efficiencies and emission wavelengths led to the opti-
mization of red PLEDs EL efficiency/color purity trade-offs.
Pure and saturated red emission single-layer PLED devices
(ITO/PEDOT:PSS/Polymer/Ca/Al) are achieved with maximum
luminous efficiencies of 3.83 cd A−1 and CIE of (0.63, 0.35) for
PFR1, 2.29 cd A−1 , and CIE of (0.64, 0.33) for PFR2, respec-
tively. By introduction of ethanol soluble PF-EP as the elec-
tron injection layer, high performance two-layer devices with
the configuration of ITO/PEDOT:PSS/Polymer/PF-EP/LiF/Al
show pure red emission at 624 nm with a luminous efficiency
of 5.50 cd A− 1 and CIE of (0.62, 0.35) for PFR1, saturated red
emission at 636 nm with a luminous efficiency of 3.10 cd A−1
and CIE of (0.63, 0.33) for PFR2, respectively. To the best of our
knowledge, these are the best results for pure and saturated red
fluorescent polymers reported so far.
1
4
5
6
7
8
9
10
11
12
Voltage (V)
Figure 7. Voltage–current density–brightness curves of the multilayer
devices of the red polymers.
6
(a)
PFR1
PFR2
PFR3
5
4
3
2
1
0
4. Experimental Section
Synthesis: All reagents were purchased from Aldrich, Acros, or Alfa
and used directly without any further purification. Tetrahydrofuran (THF)
used for reaction iv and toluene used for Suzuki polycondensation were
purified according to standard procedures. Synthetic routes of 11 and 14
have been reported previously,[23] 2,7-dibromo-9,9-dioctylfluorene (19)
and 2,7-bis-(trimethyleneborate)-9,9-diocty-fluorene (20) were prepared
according to literature.[40]
(4-Bromo-phenyl)-di-(4-methoxyphenyl)-amine (1): A mixture of
4-bromobenzenamine (17.2 g, 100 mmol), 1-iodo-4-methoxybenzene
(56.2 g, 240 mmol), CuCl (1.0 g, 10 mmol), 1,10-phenanthroline
monohydrate (1.9 g, 10 mmol), KOH (28 g, 500 mmol), and p-xylene
(250 mL) were heated to reflux in a 500 mL bottom flask. After being
stirred for 20 h, the reaction mixture was cooled to around 100 °C, 2 M
HCl was added to the flask slowly, extracted with CH2Cl2 and filtered. The
organic filtrate was washed with brine and dried with anhydrous Na2SO4.
The solvent was removed and the residue was sequentially purified by
column chromatography (eluent: petrol ether (PE)/CH2Cl2 5:1) and
recrystallization from methanol to afford a white needle crystal. Yield:
15.2 g (56.7%). 1H NMR (400 MHz, CDCl3, δ): 7.23 (br, 2H), 7.02 (br, 4H),
6.82 (d, J = 8.4 Hz, 6H), 3.79 (s, 6H). MALDI-TOF (m/z): 383.1 [M+]
(4-(4,4,5,5-Tetramethyl-(1,3,2)dioxaborolan-2-yl)-phenyl)-di-(4-
methoxyphenyl)-amine (2): A mixture of 1 (7.7 g, 20 mmol), Pd(dppf)
Cl2·CH2Cl2 (0.41 g, 5 mmol), diborane pinacol ester (6.1 g, 24 mmol)
and KOAc (6.0 g, 60 mmol) in 100 mL DMF was heated to 80 °C for
12 h. After cooling, DMF solvent was removed by vacuum distillation.
The reaction mixture was dissolved in CH2Cl2, washed with water and
then dried over anhydrous Na2SO4. After removing the solvent, the
residue was purified by column chromatography (eluent: PE/ethyl acetate
10:1) to afford a white needle crystal. Yield: 7.1 g (81.2%). 1H NMR
(400 MHz, CDCl3, δ): 7.60 (br, 2H), 7.05 (br, 4H), 6.83 (d, J = 8.0 Hz, 6H),
3.80 (s, 6H), 1.32 (s, 12H). MALDI-TOF (m/z): 431.2 [M+]
0
50
100
150
200
Current Density ( mA/cm2)
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
(b)
PFR1
PFR2
PFR3
0
50
100
150
200
4-(4-(Di-(4-methoxyphenyl)amino)phenyl)-7-bromo-2,1,3-
benzothiadiazole (3): A mixture of 2 (3.4 g, 8 mmol), Pd(PPh3)4 (0.139 g,
0.12 mmol), 4,7-dibromo-2,1,3-benzothiadiazole (3.6 g, 12 mmol),
Aliquat 336 (60 mg) in a two phase solvent of 2 M K2CO3 (25 mL) and
toluene (75 mL) was heated to 90 °C and stirred in dark for 12 h. After
cooling, the mixture was washed with brine and dried with anhydrous
Current Density ( )
cd/cm2
Figure 8. Dependence of the luminous efficiencies (a) and power effi-
ciencies (b) on the current densities of the multilayer devices of the
polymers.
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Na2SO4. The residue was purified by column chromatography (eluent: PE/
CH2Cl2 4:1) to give a red solid. Yield: 2.8 g (67.5%). 1H NMR (400 MHz,
CDCl3, δ): 7.88 (d, J = 8.0 Hz, 1H), 7.76 (br, 2H), 7.52 (br, 1H), 7.11
(br, 4H), 6.88 (br, 6H), 3.82 (s, 6H). MALDI-TOF (m/z): 517.0 [M+]
3-benzothiadiazole (12): Compound 12 was synthesized following the
same procedure for 7 using 11 and 10 instead of 6 and tributyl(thiophen-
2-yl)stannane to give a violet-red solid. Yield: 1.5 g (95.1%). 1H NMR
(300 MHz, CDCl3, δ): 8.44 (d, J = 7.5 Hz, 1H), 7.89 (d, J = 8.7 Hz, 2H),
7.71 (dd, J = 5.6 Hz, 2H), 7.32–7.18 (m, 13H), 7.10–6.96 (m, 9H),
6.78 (d, J = 8.7 Hz, 2H), 4.47–4.40 (m, 4H), 1.00 (s, 9H), 0.22 (s, 6H).
MALDI-TOF (m/z): 892.3 [M+]
4-(5-(4-(N-Phenyl-N-(4-hydroxyphenyl)amino)phenyl)-3,4-
ethylenedioxythienyl-2)-7-(4-(diphenylamino)phenyl)-2,1,3-benzothiadiazole
(13): A mixture of 12 (0.72 g, 0.83 mmol), 6 M HCl (30 mL) and THF
(60 mL) was stirred vigorously overnight. After workup, the reaction
mixture was extracted with CH2Cl2, washed with brine and dried over
anhydrous Na2SO4. The residue was purified by column chromatography
(eluent: CH2Cl2) to afford a violet-red solid. Yield: 0.7 g (94.7%). 1H
NMR (400 MHz, CDCl3, δ): 7.88 (br, 3H), 7.70 (br, 3H), 7.29 (d, J =
8.0 Hz, 6H), 7.22–7.18 (m, 10H), 7.05 (br, 4H), 7.11–7.04 (m, 4H),
6.78 (br, 3H), 4.46 (br, 4H). MALDI-TOF (m/z): 778.2 [M+]
Tributyl(3,4-ethylenedioxythienyl-2)stannane (4): To
a solution of
3,4-ethylenedioxythiophene (7.1 g, 50 mmol) in dry THF (150 mL)
at −78 °C, 2.9 M n-butyllithium (19.0 mL, 55 mmol, in hexane) was
added dropwise. After stirring for 1 h, (n-Bu)3SnCl (16.2 mL, 60 mmol)
was added slowly to it. The reaction mixture was warmed up to room
temperature and stirred overnight. After removing the THF solvent, the
residue was dissolved in PE and filtered. The solvent was evaporated
to afford a product of brown oil and the stannic derivative was used
without any further purification in the Stille coupling reactions. Yield:
25.4 g (99%). MALDI-TOF (m/z): 455.1 [M + 23Na+].
N-(4-(Tert-butyldimethylsilyloxy)phenyl)benzenamine
(5): To
a
suspension of 4-(phenylamino)phenol (11.1 g, 60 mmol) in CH2Cl2 (50 mL)
at 0 °C, N(C2H5)3 (10.1 mL, 72 mmol) was added and the suspension
became a transparent solution. After stirred for 20 minutes, tert-
butyldimethylsilylchloride (10.9 g, 72 mmol) dissolved in CH2Cl2 (50 mL)
was added dropwise. The mixture was warmed to room temperature and
stirred overnight. After filtering, the filtrate was washed with water and
dried over anhydrous Na2SO4. The solvent was evaporated and the residue
was purified by column chromatography (eluent: PE/CH2Cl2 3:1) to give a
white solid. Yield: 15.4 g (86.4%). 1H NMR (300 MHz, DMSO-d6, δ): 7.85
(s, 1H), 7.16 (t, J = 8.0 Hz, 2H), 7.00–6.92 (m, 4H), 6.77–6.69 (m, 3H),
0.95 (s, 9H), 0.17 (s, 6H). MALDI-TOF (m/z): 299.2 [M+]
4-(5-(4-(N-Phenyl-N-(4-(tert-butyldimethylsilyloxy)phenyl)amino)
phenyl)-thienyl-2)-7-(4-(di-(4-methoxyphenyl)-amino)phenyl)-2,1,3-
benzothiadiazole (15): Compound 15 was synthesized following the
same procedure for 7 using 3 and 8 instead of 6 and tributyl(thiophen-
1
2-yl)stannane to give a deep-red solid. Yield: 0.87 g (95.7%). H NMR
(300 MHz, CDCl3, δ): 8.09 (s, 1H), 7.90 (d, J = 7.2 Hz, 1H), 7.82 (d, J =
8.4 Hz, 2H), 7.66 (d, J = 6.6 Hz, 2H), 7.54 (d, J = 8.4 Hz, 2H), 7.33–
7.23 (m, 4H), 7.11–7.02 (m, 4H), 6.87 (d, J = 9.3Hz, 2H), 6.79 (d, J =
8.7 Hz, 2H), 3.82 (s, 6H), 1.00 (s, 9H), 0.22 (s, 6H). MALDI-TOF (m/z):
894.3 [M+]
4-(5-(4-(N-Phenyl-N-(4-hydroxyphenyl)amino)phenyl)-thienyl-2)-
7-(4-(di-(4-methoxyphenyl)-amino)-phenyl)-2,1,3-benzothiadiazole
(16): Compound 16 was synthesized following the same procedure for
13 using 15 instead of 12 to give a deep-red solid. Yield: 0.65 g (92.3%).
1H NMR (400 MHz, CDCl3, δ): 8.10 (br, 2H), 7.82 (d, J = 8.0 Hz, 4H),
7.67 (br, 3H), 7.13 (br, 6H), 7.05 (br, 4H),6.87 (d, J = 8.4 Hz, 7H), 6.78
(br, 3H), 3.82 (s, 6H). MALDI-TOF (m/z): 780.2 [M+]
4-(5-(4-(N-Phenyl-N-(4-(tert-butyldimethylsilyloxy)phenyl)amino)
phenyl)-3,4-ethylenedioxythienyl-2)-7-(4-(di-(4-methoxyphenyl)-amino)
phenyl)-2,1,3-benzothiadiazole (17): Compound 12 was synthesized
following the same procedure for 7 using 3 and 10 instead of 6 and
tributyl(thiophen-2-yl)stannane to give a violet-red solid. Yield: 2.0 g
(94.2%). 1H NMR (400 MHz, CDCl3, δ): 7.82 (d, J = 8.4 Hz, 2H), 7.68 (d, J =
7.6 Hz 3H), 7.23 (d, J = 7.6 Hz, 2H), 7.13 (d, J = 8.8 Hz, 5H), 7.09–6.99
(m, J = 8.8 Hz, 9H), 6.86 (d, J = 9.2 Hz, 5H), 6.77 (d, J = 8.4 Hz, 2H),
4.46 (br, 4H), 3.82 (s, 6H), 1.00 (s, 9H), 0.22 (s, 6H). MALDI-TOF (m/z):
952.3 [M+]
4-Bromo-N-(4-(tert-butyldimethylsilyloxy)-phenyl)-N-phenylbenzenamine
(6): 6 was synthesized according to literature.[41] A solution of 5 (6.0 g,
20 mmol), 1-bromo-4-iodobenzene (14.2 g, 50 mmol), Pd2(dba)3
(0.061 g, 0.067mmol), rac-binap (0.124 g, 0.200 mmol), NaOBu-t (3.8 g,
40 mmol) in toluene (100 mL) was stirred vigorously overnight at 100 °C.
The reaction mixture was then cooled to room temperature and filtered.
The filtrate was washed with water, dried over anhydrous Na2SO4,
concentrated in vacuo to give a colorless solid. The residue was then
purified by column chromatography (eluent: PE/CH2Cl2 6:1) to afford a
1
colorless oil. Yield: 1.3 g (57.6%). H NMR (400 MHz, CDCl3, δ): 7.64
(d, J = 8.0 Hz, 2H), 7.23 (t, J = 8.0 Hz, 2H), 7.07 (d, J = 8.0 Hz, 2H),
7.01–6.95 (m, 5H), 6.76 (d, J = 8.4 Hz, 2H), 0.99 (s, 9H), 0.21 (s, 6H).
2-(4-(N-Phenyl-N-(4-(tert-butyldimethylsilyloxy)phenylamino)
phenylthiophene (7): A mixture of 6 (1.2 g, 2.4 mmol), tributyl(thiophen-
2-yl)stannane (0.74 g, 2.0 mmol), Pd(PPh3)4 (22.5 mg, 0.01 mmol)
and toluene (30 mL) was heated to 100 °C and stirred in the dark for
24 h. After workup, the mixture was poured to saturated aqueous KF and
stirred vigorously for 3 h to remove the residual noxious organic stannic
derivatives. After filtering, the filtrate was extracted with diethyl ether,
washed with brine and dried with anhydrous Na2SO4. The residue was
purified by column chromatography (eluent: PE/CH2Cl2 5:1) to afford
4-(5-(4-(N-Phenyl-N-(4-hydroxyphenyl)amino)phenyl)-3,4-
ethylenedioxythienyl-2)-7-(4-(di-(4-methoxyphenyl)amino)phenyl)-2,1,3-
benzothiadiazole (18): Compound 18 was synthesized following the
same procedure for 13 using 17 instead of 12 to give a violet-red solid.
1
an olive oil. Yield: 0.74 g (82.1%). H NMR (400 MHz, CDCl3, δ): 7.44
1
(d, J = 8.8 Hz, 2H), 7.23–7.19 (m, 4H), 7.08–6.96 (d, 8H), 6.77(d, J =
8.8 Hz, 2H), 0.99 (s, 9H), 0.21 (s, 6H). MALDI-TOF (m/z): 457.2 [M+]
Tributyl(5-(4-(N-phenyl-N-(4-(tert-butyldimethylsilyloxy)phenyl)amino)
phenyl)-thienyl-2)stannane (8): Compound 8 was synthesized following
the same procedure for 4 using 7 instead of 3,4-ethylenedioxythiophene to
give a brown oil. Yield: 1.2 g (99%). MALDI-TOF (m/z): 747.3 [M+]
2-(4-(N-Phenyl-N-(4-(tert-butyldimethylsilyloxy)phenyl)amino)phenyl)-
3,4-ethylenedioxythiophene (9): Compound 9 was synthesized following
the same procedure for 7 using 4 instead of tributyl(thienyl-2)stannane
Yield: 1.1 g (92.5%). H NMR (400 MHz, CDCl3, δ): 7.81 (br, 3H), 7.71
(br, 4H), 7.13 (d, J = 8.8 Hz, 6H), 7.05 (d, J = 8.4 Hz, 4H), 6.86 (d, J =
8.8 Hz, 7H), 6.78 (br, H), 4.46 (br, 4H), 3.82 (s, 6H). MALDI-TOF (m/z):
838.2 [M+]
4-(5-(4-(N-Phenyl-N-(4-methoxyphenyl)amino)phenyl)-thienyl-2)-7-(4-
(di-(4-methoxyphenyl)amino)phenyl)-2,1,3-benzothiadiazole (MCR1):
A
mixture of 16 (0.16 g, 0.20 mmol), K2CO3 (1.38 g, 10.00 mmol), CH3I
(2.00 mL, 32.10 mmol) and acetone (50 mL) was heated to 60 °C for
6 h. After workup, the acetone solvent was evaporated, the mixture was
extracted with CH2Cl2 and filtered. The filtrate was evaporated and the
residue was purified by flash column chromatography (eluent: CH2Cl2)
to afford a deep-red solid. Yield: 0.15 g (95.7%). 1H NMR (400 MHz,
CDCl3, δ): 8.10 (d, J = 3.6 Hz, 1H), 7.89 (d, J = 7.6 Hz, 1H), 7.83
(d, J = 8.8 Hz, 2H), 7.66 (d, J = 7.6 Hz, 1H), 7.54 (d, J = 8.8 Hz, 2H),
7.31 (d, J = 4.0 Hz, 1H), 7.26 (t, J = 8.0 Hz, 2H), 7.16–7.10 (m, 8H),
7.07–6.97 (m, 5H), 6.87 (dd, J = 5.8 Hz, 6H), 3.82 (s, 9H). Anal. Calcd.
For C49H38N4O3S2: C, 74.03; H, 4.82; N, 7.05; Found: C,73.85; H, 4.94; N,
6.98. MALDI-TOF (m/z): 794.2 [M+]
1
to give a yellow solid. Yield: 4.6 g (78.6%). H NMR (300 MHz, CDCl3,
δ): 7.54 (d, J = 8.7 Hz, 2H), 7.21 (t, J = 8.2 Hz, 2H), 7.07–6.93 (m, 7H),
7.76 (d, J = 8.7 Hz, 2H), 6.23 (s, 1H), 4.29–4.20 (m, 4H), 0.99 (s, 9H),
0.21 (s, 6H). MALDI-TOF (m/z): 515.3 [M+]
Tributyl(5-(4-(N-phenyl-N-(4-(tert-butyldimethylsilyloxy)phenyl)amino)
phenyl)-3,4-ethylenedioxythienyl-2)stannane (10): Compound 10 was
synthesized following the same procedure for 4 using 9 instead of
3,4-ethylenedioxythiophene to give a brown oil. Yield: 4.5 g (99%).
MALDI-TOF (m/z): 805.1 [M+]
4-(5-(4-(N-Phenyl-N-(4-(tert-butyldimethylsilyloxy)phenyl)amino)
phenyl)-3,4-ethylenedioxythienyl-2)-7-(4-(diphenylamino)phenyl)-2,1,
4-(5-(4-(N-Phenyl-N-(4-methoxyphenyl)amino)phenyl)-3,4-
ethylenedioxythienyl-2)-7-(4-(diphenylamino)phenyl)-2,1,3-benzothiadiazole
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(MCR2): MCR2 was synthesized following the same procedure for MCR1
using 13 instead of 16 to give a violet-red solid. Yield: 0.37 g (98.2%).
1H NMR (400 MHz, CDCl3, δ): 8.44 (d, J = 8.0 Hz, 1H), 7.89 (d, J =
4.8 Hz, 2H), 7.71 (dd, J = 5.6 Hz, 2H), 7.31–7.18 (m, 13H), 7.12–7.04 (m,
8H), 6.98 (t, J = 7.2 Hz, 1H), 6.86 (d, J = 5.2 Hz, 2H), 4.47–4.39 (m, 4H),
3.82 (s, 9H). Anal. Calcd. For C49H36N4O3S2: C, 74.22; H, 4.58; N, 7.07;
Found: C, 73.95; H, 4.62; N, 6.98. MALDI-TOF (m/z): 792.2 [M+]
4-(5-(4-(N-Phenyl-N-(4-methoxyphenyl)amino)phenyl)-3,4-
ethylenedioxythienyl-2)-7-(4-(di-(4-methoxyphenyl)-amino)phenyl)-2,1,3-
benzothiadiazole (MCR3): MCR3 was synthesized following the same
procedure for MCR1 using 18 instead of 16 to give a violet-red solid. Yield:
0.36 g (98.5%). 1H NMR (400 MHz, CDCl3, δ): 8.42 (d, J = 8.0 Hz, 1H),
7.83 (d, J = 8.8 Hz, 2H), 7.69 (t, J = 8.4 Hz, 3H), 7.24 (t, J = 8.6 Hz,
2H), 7.15–7.04 (m, 12H), 6.98 (t, J = 7.2 Hz, 1H), 6.86 (d, J = 8.8 Hz,
6H), 4.46–4.40 (m, 4H), 3.82 (s, 9H). Anal. Calcd. For C51H40N4O5S2: C,
71.81; H, 4.73; N, 6.57; Found: C, 71.39; H, 4.81; N, 6.51. MALDI-TOF
(m/z): 852.2 [M+]
Monomer R1: Monomer R1 was synthesized using the same reaction
conditions as Suzuki coupling for 3. Here it is a reaction between a
brominated alkane and a phenolic hydroxyl group to give a alkyl aryl
ether, and can be effectively catalyzed by Pd(PPh3)4. The residue was
purified by column chromatography (eluent: PE/CH2Cl2 1:1) to afford a
deep-red solid. Yield: 0.65 g (85.6%). 1H NMR (300 MHz, CDCl3, δ): 8.09
(br, 1H), 7.84 (br, 3H), 7.66 (br, 1H), 7.53 (d, J = 8.4 Hz, 4H), 7.46 (d, J =
5.7 Hz, 4H), 7.32–7.08 (m, 15H), 6.89–6.79 (m, 7H), 3.82 (s, 8H), 1.97–
1.89 (m, 4H), 1.65–1.56 (m, 2H), 1.26–1.05 (m, 10H), 0.88–0.76 (m, 5H)
0.61 (br, 4H). Anal. Calcd. For C73H66Br2N4O3S2: C, 68.97; H, 5.23; N,
4.41; Found: C, 69.43; H, 5.25; N, 4.37. MALDI-TOF (m/z): 1268.3 [M+]
Monomer R2: Monomer R2 was synthesized following the same
procedure for Monomer R1 using 13 instead of 16 to give a violet-red
solid. Yield: 0.45 g (81.2%). 1H NMR (300 MHz, CDCl3, δ): 7.89 (br,
2H), 7.70 (br, 3H), 7.52 (d, J = 8.7 Hz, 2H), 7.47–7.44 (m, 4H), 7.29–
7.27 (m, 6H), 7.20 (t, J = 7.2 Hz, 9H),7.06 (t, J = 7.2 Hz, 4H), 6.80 (br,
5H), 4.47 (br, 4H), 3.82 (s, 2H), 1.97–1.89 (m, 4H), 1.65–1.56 (m, 2H),
1.26–1.05 (m, 10H), 0.88–0.76 (m, 5H), 0.61 (br, 4H). Anal. Calcd. For
C73H64Br2N4O3S2: C, 69.08; H, 5.08; N, 4.41; Found: C, 69.13; H, 5.14; N,
4.38. MALDI-TOF (m/z): 1266.3 [M+]
20 (0.2792 g, 0.500 mmol) and Monomer R1 (0.0038 g, 0.003 mmol)
were used in the polymerization. GPC: Mn = 4.7 × 104, PDI = 2.5. PFR2:
red fiber. 19 (0.2726 g, 0.497 mmol), 20 (0.2792 g, 0.500 mmol) and
Monomer R2 (0.0038 g, 0.003 mmol) were use in the polymerization.
GPC: Mn = 3.7 × 104, PDI = 2.9. PFR3: violet-red fiber. 19 (0.2726 g,
0.497 mmol), 20 (0.2792 g, 0.500 mmol) and Monomer R3 (0.0040 g,
0.003 mmol) were used in the polymerization. GPC: Mn = 5.3 × 104,
1
PDI = 2.5. PFR1, PFR2 and PFR3 showed similar H NMR and element
analysis results as those of PFO.
Measurement and Characterization: 1H NMR spectra were recorded
with a Bruker AV300 or AV400 NMR spectrometer. The elemental
analyses were performed using a Bio-Rad elemental analysis system.
The number- and weight-average molecular weights of the polymers
were determined by gel permeation chromatography (GPC) using a
Waters 410 instrument with polystyrene as standard and THF as eluent.
UV-Vis absorption spectra were measured by a Perkin-Elmer Lambda
35 UV/Vis spectrometer. PL spectra were recorded by a Perkin-Elmer
LS50B spectrofluorometer. MALDI-TOF was measured by a Bruker
Daltonics Flexanalysis system. Cyclic voltammograms of polymer films
on glassy carbon electrodes were recorded on an EG&G 283 (Princeton
Applied Research) potentiostat/galvanostat system at room temperature
in a solution of n-Bu4NClO4 (0.10 M) in fresh acetonitrile at a scan rate of
100 mV/s. A Pt wire and an Ag/AgCl electrode were used as the counter
electrode and the reference electrode, respectively. Cyclic voltammograms
of small organic molecules were carried out with their solution in fresh
CH2Cl2. Other conditions were the same as for polymer films except
that a Pt disc was used as the working electrode. The EL spectra and
current–voltage and brightness–voltage characteristics of the devices
were measured with a Spectrascan PR650 spectrophotometer in the
forward direction and a computer-controlled Keithley 2400 instrument
under ambient conditions. The external quantum yields were calculated
from the brightness, current density and EL spectrum, assuming a
Lambertian distribution.
Device Fabrication: ITO glass plates were degreased in an ultrasonic
acetone solvent bath and then dried in a heating chamber at 120 °C. The
PEDOT:PSS was spin-coated on the cleaned ITO at 3000 rpm for 60 s
and then baked for 20 min at 120 °C to give an approximate thickness of
40 nm. The polymer layer (approximately 90 nm) was then spin-coated
on to the PEDOT/ITO coated glass substrate in fresh toluene solution
(15 mg mL−1) under ambient atmosphere. Finally, a thin layer of calcium
(10 nm) followed by a layer of aluminium (100 nm) was deposited in
a vacuum thermal evaporate or through a shadow mask at a pressure
of 3 × 10−3 – 5 × 10−3 Pa. The active area of the diodes was around
12 mm2. For the multilayer device, PF-EP was spin coated on the
emissive layer from ethanol (3 mg/mL−1 ) and annealed at 70 °C for
30 min. Then 1 nm of LiF and 100 nm of Al were deposited at a pressure
of 4 × 10−4 Pa successively.
Monomer R3: Monomer R3 was synthesized following the same
procedure for Monomer R1 using 18 instead of 16 to give a violet-red
solid. Yield: 0.77 g (83.5%). 1H NMR (300 MHz, CDCl3, δ): 7.82 (br, 2H),
7.70 (br, 3H), 7.52 (d, J = 8.7 Hz, 2H), 7.47–7.44 (m, 4H), 7.33 (t, J =
2.4 Hz, 1H), 7.13 (br, 12H), 6.86 (d, J = 8.1 Hz, 4H), 6.80 (br, 3H), 4.47
(br, 4H), 3.82 (s, 8H), 1.97–1.89 (m, 4H), 1.65–1.56 (m, 2H), 1.26–1.05
(m, 10H), 0.88–0.76 (m, 5H) 0.61 (br, 4H). Anal. Calcd. C75H68Br2N4O5S2:
C, 67.76; H, 5.16; N, 4.21; Found: C, 68.13; H, 5.24; N, 4.16. MALDI-TOF
(m/z): 1326.3 [M+]
General Procedure of the Suzuki Polycondensation: A mixture of
2,7-dibromo-9,9-dioctylfluorene
(18),
2,7-bis-(1,3,2-dioxaborinane-
2-yl)-9,9-dioctylfluorene (19) and corresponding red-unit-containing
comonomer with corresponding feed ratios, Aliquat 336 (0.10 g,
0.25 mmol), Pd(PPh3)4 (11.0 mg, 0.01 mmol) under argon was added
degassed 2 M aqueous K2CO3 (2 mL) and degassed toluene (6 mL).
The resulting mixture was stirred in the dark at 90 °C for 48 h, and
then sequentially end-capped with 0.1 M phenylboronic acid (2 mL)
and bromobenzene (1 mL), stirring for 12 h for each addition. After
cooling, the reaction mixture was poured into methanol and filtered.
The precipitate was collected and dissolved in CH2Cl2, washed with
water and dried with anhydrous Na2SO4. After evaporating most of the
solvent, the residue was precipitated in stirred methanol solvent to give
a fiber-like solid. The polymer was further purified by Soxhlet extraction
with acetone for 24 h. The reprecipitation procedure in CH2Cl2-methanol
was then repeated several times. The final product was obtained after
drying in vacuum with a yield of 56%–70%.
Acknowledgements
This work was supported by the Changchun Institute of Applied
Chemistry, Chinese Academy of Sciences (CX07QZJC-24), the National
Natural Science Foundation of China (No.50803062, 60977026), the
Science Fund for Creative Research Groups (No.20621401), and the 973
Project (2009CB623601).
Received: April 28, 2010
Published online: July 29, 2010
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Adv. Funct. Mater. 2010, 20, 3143–3153
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