Star-Shaped Single-Polymer Systems with Simultaneous RGB Emission: Design, Synthesis, Saturated White Electroluminescence, and Amplified Spontaneous Emission

Article abstract of DOI:10.1021/acs.macromol.6b00020

A three-armed star-shaped single-polymer system comprising tris(4-(3-hexyl-5-(7-(4-hexylthiophen-2-yl)benzo[c][1,2,5]thiadiazol-4-yl)thiophen-2-yl)phenyl)amine (TN) as red emissive cores, benzothiadiazole (BT) as green emissive dopants, and polyfluorene (

Full text of DOI:10.1021/acs.macromol.6b00020

Article
pubs.acs.org/Macromolecules
Star-Shaped Single-Polymer Systems with Simultaneous RGB
Emission: Design, Synthesis, Saturated White Electroluminescence,
and Amplified Spontaneous Emission
†
†
†
†
†
,†,‡
Cheng-Fang Liu, Yuanda Jiu, Jianyun Wang, Jianpeng Yi, Xin-Wen Zhang, Wen-Yong Lai,*
,
†,‡
and Wei Huang*
†Key Laboratory for Organic Electronics and Information Displays (KLOEID) & Institute of Advanced Materials (IAM), Jiangsu
National Synergetic Innovation Center for Advanced Materials (SICAM), Nanjing University of Posts & Telecommunications, 9
Wenyuan Road, Nanjing 210023, China
‡
Key Laboratory of Flexible Electronics (KLOFE) & Institute of Advanced Materials (IAM), Jiangsu National Synergetic Innovation
Center for Advanced Materials (SICAM), Nanjing Tech University (NanjingTech), 30 South Puzhu Road, Nanjing 211816, China
*
S Supporting Information
ABSTRACT: A three-armed star-shaped single-polymer sys-
tem comprising tris(4-(3-hexyl-5-(7-(4-hexylthiophen-2-yl)-
benzo[c][1,2,5]thiadiazol-4-yl)thiophen-2-yl)phenyl)amine
(
TN) as red emissive cores, benzothiadiazole (BT) as green
emissive dopants, and polyfluorene (PF) as blue arms was
successfully developed, in which the construction of the star-
shaped architectures can depress intermolecular interactions
and concentration quenching. The thermal, photophysical,
electrochemical, electroluminescent, and amplified sponta-
neous emission (ASE) properties of the synthesized polymers
are systematically investigated. The modulation of the doping
concentration of TN and BT can guarantee the partial energy
transfer in a star-shaped single-polymer system, further
achieving saturated white emission. Consequently, a current
−
1
efficiency of 2.41 cd A and Commission Internationale d’Eclairage (CIE) coordinates of (0.34, 0.35) were recorded for TN-
R3G4 with 0.03 mol % red core and 0.04 mol % green dopants. The saturated white emission is likely to result from the fine
control of partial energy transfer and suppressed intermolecular interactions due to the construction of such a star-shaped single-
2
polymer system. What is more, TN-R3G4 shows impressive ASE characteristics with relatively low threshold of 63 ± 5 μJ/cm ,
which demonstrates the potential as gain media for organic lasing applications. Our results have provided new insights and better
understanding into the photophysical and optoelectronic behaviors of the resulting star-shaped single-polymer systems with
simultaneous RGB emission.
INTRODUCTION
To address these issues, great efforts have been made to a
■
(
12−16
single-polymer system
based on the insufficient energy
During the past decade, white polymer light-emitting diodes
WPLEDs) have gained remarkable attention because of their
various applications in full-color displays and solid-state
transfer because phase separation of chromophores can be
largely suppressed by incorporating RGB emissive species into a
single-polymer chain. Recently, many groups have concentrated
on linear single-polymer systems to accomplish white emission,
in which the energy transfer can be fine-tuned by modulating the
contents of various emissive components, further manifesting
comparably stable bias-independent EL spectra. Wang and co-
1
−5
lighting. The most widely employed methods for fabricating
WPLEDs have been reported, which involve the multilayer
system with sequential deposition of red, green, and blue (RGB)
6
emissive species and physical blends such as polymer−small
7
,8
molecule blend systems, polymer−organometallic complex
12
9
10,11
workers developed a novel method in which a green-emitting
component was attached to the pendant chain and a red-emitting
component was incorporated into the blue-emitting polyfluor-
ene backbone, realizing white emission with maximum current
blend systems, and polymer−polymer blend systems.
The
multilayer device may encounter the mixing of adjacent layers,
which is detrimental to the device performance. In contrast, the
blended devices have undergone significant development in
efficiency and brightness. However, the phase behavior is
sensitive to the driving voltages and operational conditions,
thus resulting in unstable electroluminescence (EL) spectra and
color coordinates.
Received: January 4, 2016
Revised: March 6, 2016
©
XXXX American Chemical Society
A
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Scheme 1. Synthetic Routes toward the Core Structure TN
−
1
efficiency of 1.59 cd A and CIE coordinates of (0.31, 0.34). Lee
investigation on the novel materials with saturated and stable
white emission is still going on.
In this article, we reported white EL from a star-shaped single-
polymer system synthesized by introducing polyfluorene (PF) as
blue emissive arms and 2,1,3-benzothiadiazole (BT) as green
emissive dopants onto tris(4-(3-hexyl-5-(7-(4-hexylthiophen-2-
yl)benzo[c][1,2,5]thiadiazol-4-yl)thiophen-2-yl)phenyl)amine
1
3
et al. developed a copolymer comprising 9,9-dihexylfluorene as
blue emissive species and 2-(2,6-bis{2-[1-(9,9-dihexyl-9H-
fluoren-2-yl)-1,2,3,4-tetrahydroquinolin-6-yl]vinyl}pyran-4-
ylidene)malononitrile (DCMF) as orange emissive species. The
electroluminescent devices showed maximum current efficiency
of 0.60 cd A−1 and CIE coordinates of (0.33, 0.31). Generally
(
TN) as the red emissive core. Here, TN was selected as the core
speaking, linear single-polymer systems have suppressed phase
separation and bias-independent EL performance but encounter
low efficiency and unsaturated white emission in comparison to
the blend systems. Therefore, it is imperative to develop novel
white-light-emitting single-polymer materials with improved
efficiency and saturated emission.
According to previous studies in our group, monodisperse
conjugated star-shaped macromolecules have been developed
with high purity, well-defined chemical structures, good solution
because of its saturated red emission. Blue PF arms were used in
the system due to their high photoluminescence efficiency and
good thermal and electrochemical stability. BT units were widely
applied in the design of novel materials for green light emission.
The synthesis, thermal stability, photophysical, electrochemical,
and electroluminescent characteristics and amplified sponta-
neous emission (ASE) properties of these resulting polymers
were studied in detail. By modulating the content of TN and BT,
we controlled the insufficient energy transfer from the blue arms
to the green and red species, therefore achieving saturated white
emission with simultaneous blue (442 nm), green (495 nm), and
red (625/608 nm) emission. A single-emissive-layer device based
on the polymer (TN-R3G4) achieved high-color-quality white
EL with a current efficiency of 2.41 cd A− and CIE coordinates
of (0.34, 0.35). Interestingly, typical ASE behaviors could also be
detectable from the resulting star-shaped single-polymer system
with low content of red and green emissive dopants in films. A
17−23
processability, and excellent optoelectronic characteristics.
It is notable to mention that PLEDs based on these
macromolecules exhibited highly efficient blue and red emission.
Thus, making use of the star-shaped architectures, we can
incorporate various emissive components to ensure the
insufficient energy transfer, further realizing white emission.
Star-shaped polymer systems have attracted much interest owing
to the highly branched architectures, suppressed intermolecular
1
2
4−29
2
interactions, and improved solid-state luminescence.
relatively low threshold of 63 ± 5 μJ/cm with ASE peaks at 448
Hyperbranched copolymers with phenylene units as the blue
host and benzothiadiazole derivatives as red and green
nm was recorded for TN-R3G4, showing great promise for
organic lasing applications.
30
chromophores were developed by Kim’s group, demonstrating
white EL with CIE coordinates of (0.32, 0.35). WPLEDs based
on these copolymers exhibited a maximum luminous efficiency
RESULTS AND DISCUSSION
The synthetic routes toward the model compounds and the
resulting polymers are shown in Schemes 1 and 2. A (arm-
■
−1
(
LE) of 0.21 cd A , which still need further optimization to
3
satisfy the requirements of commercial applications. The
three)-type core structure was obtained from bromination of the
B
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a
Scheme 2. Schematic Illustrations and Synthetic Routes of TN-RxGy
a
x means the contents of TN as red dopants, and y denotes the contents of BT as green dopants.
star-shaped red emissive molecule (TN) with N-bromo-
succinimide (NBS). According to Suzuki polycondensation,
star-shaped polymers were synthesized from an AB type 9,9-
dioctylfluorene monomer, a green 2,1,3-benzothiadiazole
synthesized polyfluorene homopolymer (PF) and poly(9,9-
dihexylfluorene-co-benzothiadiazole) (PFB) as model com-
pounds.
As revealed by thermogravimetric analysis (TGA) and
differential scanning calorimetry (DSC) measurements in Figure
monomer, and an A -type red emissive core. The polymers are
3
named as TN-RxGy, where x means the contents of TN as red
dopants and y denotes the contents of BT as green dopants. The
doping concentration of TN and BT was controlled to tune the
relative intensity of the blue, green, and red emission. For TN-
R5G8, TN-R5G12, and TN-R5G15, the content of the red unit
was fixed at 0.05 mol % while the content of the green dopants
was controlled as 0.08, 0.12, and 0.15 mol % (Table S1),
respectively. The similar adjustment in doping concentration was
applied for TN-R3G2 and TN-R3G4. By comparison, we also
S1a,b, TN has the decomposition temperature (T , correspond-
ing to 5% weight loss) of 402 °C. The glass transition
d
temperature (T ) was noticed at 157 °C. Moreover, the resulting
g
polymers exhibited excellent thermal stability as shown in Figure
S2. In order to unravel the packing structures in condensed states
of the polymers, wide-angle X-ray diffraction (WXRD) measure-
ments were implemented. The results confirmed that all the
polymers possessed typical amorphous characteristics (Figure
S3).
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Figure 1. (a) Absorption spectra and PL spectra of TN and BT in dilute solutions. (b) PL spectra of PF and PFB in solid films. (c) Energy levels of TN
and PF.
Figure 2. (a) UV−vis absorption and PL spectra of the star-shaped polymers in THF solutions. (b) PL spectra of the star-shaped polymers in solid films.
Figure 1a shows the absorption and photoluminescence (PL)
spectra of TN and BT in dilute solutions. Two well-resolved
absorption bands at 329 and 477 nm are observed for TN. BT
shows absorption peak at 351 nm and the PL emission peak at
Under this circumstance, the energy transfer has become
complete in the process, which is disadvantageous to generate
white emission. In contrast, TN-R3G4 exhibits the balance of
RGB emission with optimized contents in such a star-shaped
single-polymer system.
480 nm. Figure 1b shows PL spectra of PF and PFB in solid films.
The absorption spectra of all the polymers in Figure 2a show
peaks at around 384 nm, which are attributed to the π−π*
transition of PF backbones. Since the doping concentration is
extremely low, the absorption of red dopants at 475/457 nm and
green dopants at 353 nm can be hardly detected. In dilute
solutions, these polymers have similar PL spectra to PF because
of the fluorene segment. Nevertheless, the polymers in the films
show PL spectra with red emission from TN core, green emission
from BT dopants, and blue emission from PF arms (Figure 2b).
The doping concentration of the red and green dopants were
adjusted to generate partial energy transfer, thus achieving white
EL. It is indicated that the different contents of the red TN core
and green BT units significantly affect the PL spectra. Increasing
the doping concentration resulted in obvious enhancement of
the relative intensity of the red and green emission. For instance,
TN-R5G15 has the highest intensity of the green emission in this
system, originating from the high contents of BT green dopants.
Figure 1c shows the lowest unoccupied molecular orbital
(LUMO) and highest occupied molecular orbital (HOMO)
energy levels of TN and PF. Both of HOMO and LUMO energy
levels of TN are situated between the HOMO/LUMO energy
levels of PF, implying efficient charge trapping in EL process. The
electrochemical properties of polymers are shown in Figure S4
and summarized in Table S3. The results suggest that the energy
levels could be barely affected by the doping concentration
because of the extremely low contents.
To study the EL properties of the resulting polymers, single-
emissive-layer devices with configuration of indium−tin oxide
(ITO)/poly(3,4-ethylenedioxythiophene):poly(styrene-
sulfonate) (PEDOT:PSS) (40 nm)/polymer (80 nm)/1,3,5-
tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBI) (30 nm)/
LiF (1 nm)/Al (80 nm) were fabricated. The devices were
thermally annealed at 120 °C for 10 min in a vacuum box before
the LiF/Al cathode was evaporated. As shown in Figure 3a, the
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Figure 3. (a) EL spectra and (b) voltage−current density of the devices based on TN-RxGy.
Figure 4. EL characteristics of TN-RxGy with the configuration of ITO/PEDOT:PSS/polymer/TPBI/LiF/Al: (a) brightness−voltage characteristics;
b) current efficiency−current density characteristics; (c) EQE−voltage characteristics; (d) current efficiency−voltage characteristics.
(
Table 1. EL Performance of the Devices
GPC
turn-on voltage
current efficiency
power efficiency
maximum brightness
EQE
[%]
−
1
−1
−2
[
V]
[cd A
]
[lm W
]
[cd m
]
Mn
PDI
CIE (x, y)
TN-R5G8
TN-R5G12
TN-R5G15
TN-R3G2
TN-R3G4
TN-blended
8
8
8
4
5
5
1.04
1.64
2.90
1.41
2.41
0.71
0.29
0.66
0.93
1.24
1.33
0.27
3041
3712
4546
400
0.69
0.56
0.61
0.63
1.05
0.25
9248
9436
1.54
1.88
1.97
1.79
1.83
(0.31, 0.40)
(0.28, 0.42)
(0.30, 0.36)
(0.33, 0.35)
(0.34, 0.35)
(0.31, 0.47)
9430
10990
11256
1833
1250
blue, green, and red emission of the EL spectra can be assigned as
an individual emission from PF, BT, and TN, respectively. The
relative intensity of the peaks in the EL spectra of TN-RxGy can
be fine-tuned by varying the contents of the dopants. For TN-
R3G2 and TN-R3G4 with the same doping concentration of red
core, the relative intensity of the green emission band in the EL
spectra increases by increasing the content of green dopants,
which is attributed to more energy transfer from the blue arms to
the green dopants. A similar phenomenon can also be observed
for the case of TN-R5G8, TN-R5G12, and TN-R5G15.
Therefore, adjusting the doping concentration is an effective
methodology to generate partial energy transfer with the aim to
realize high-quality white emission in such a star-shaped single-
polymer system. According to the EL spectra, the CIE
coordinates of (0.34, 0.35) were recorded form TN-R3G4,
which are very close to the values of standard white emission
(0.33, 0.33). More importantly, the EL spectra of TN-R3G4 are
quite stable with variation in CIE coordinates of (±0.02, ±0.02)
by increasing the bias from 6 to 13 V. Voltage−current density
characteristics of the devices are shown in Figure 3b.
Figure 4 shows the brightness−voltage, current efficiency−
current density, EQE−voltage, and current efficiency−voltage
curves of the devices of TN-RxGy. The detailed data of the
corresponding devices are summarized in Table 1. In this system,
E
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current efficiency and maximum brightness are enhanced by
increasing the doping concentration, manifesting the suppressed
concentration quenching in the doping concentration range.
Among these, the device based on TN-R3G4 showed much
better white emission with a turn-on voltage of 5.0 V, a maximum
and dominated the relaxation decay. It thus should be associated
with dominant blue emissive species. The prolonged τ may be
2
attributed to the exciton migration from the blue emissive species
to the green or red emissive dopants. It is worthwhile to mention
that the resulting star-shaped single-polymer system exhibited
quite similar decay patterns in dilute solutions, suggesting little
impact of such a rather low content of green and red dopants on
the photophysical characteristics.
−2
brightness of 1833 cd m , a maximum current efficiency of 2.41
−1
−1
cd A , and a power efficiency of 1.33 lm W .
As a comparison experiment, we have physically blended 0.03
mol % TN into PFB and fabricated a device with the blend as the
emissive layer. As shown in Table 1 and Figure S5, the EL spectra
exhibited bias dependence. The CIE coordinates of TN-blended
samples change from (0.24, 0.31) to (0.31, 0.47) by increasing
the bias from 6 to 13 V. In addition, the devices based on TN-
blended samples showed a current efficiency of 0.71 cd A− and a
maximum EQE of 0.25%. The performance is much worse than
those based on the star-shaped single-polymer systems (TN-
R3G4). We can deduce from the results that phase separation
and concentration quenching could be significantly suppressed
in such a star-shaped single-polymer system in comparison to the
blend system, giving rise to the improved EL performance.
To investigate the excited state relaxation processes of the
synthesized polymers, the fluorescence transients of TN-RxGy in
dilute solutions and in films were recorded as plotted in Figure 5.
In addition, the fluorescence transients of the films of TN-
RxGy could also be well described by employing a double-
exponential decay model with two decay components. The
various decay lifetimes in the inset are related with different
radiative transition in the system. The shorter τ is about 3 times
as short as that observed for solution, while the extracted longer τ
is slightly longer than that in solution. To be specific, the shorter
τ correlates with the rapid excited state relaxation in an early stage
due to the possible more efficient exciton radiation in films.
Keeping in mind the molecular aggregation in films, the longer τ
varying from about 2 ns can be ascribed to the aggregated states.
High-efficiency and thermally stable conjugated light-emitting
polymers have stood out as prominent active materials for
1
19,20,31−34
organic solid-state lasing.
To get further insights into
the photophysical properties of the resulting star-shaped single-
polymer systems, the amplified spontaneous emission (ASE)
characteristics of TN-RxGy have been investigated consequently.
In order to quantify our results, the pulse energy of exciting light
at which the full width at half-maximum (fwhm) intensity of the
emission spectrum drops to half of its PL value was defined as the
35
ASE threshold. As shown in Figures 6a and 6b, since the
spectral narrowing emerges only with very high pump energy up
2
to 3338 μJ/cm , it is indicated that no ASE characteristics are
observed for TN-R5G8. In the case of TN-R5G12, the fwhm has
dropped dramatically from 27 to 4 nm when pumped above a
2
threshold intensity of 264 ± 10 μJ/cm . As shown in Figure 6c,
the output emission is amplified when the energy of pumped
laser pulse is above the threshold. TN-R5G15 has the same ASE
characteristics as TN-R5G12 with a threshold intensity of 164 ±
2
1
0 μJ/cm and the ASE peak at 448 nm (Figure 6e). Meanwhile,
as depicted in Figures 6g and 6i, TN-R3G2 and TN-R3G4 have
2
the threshold of 114 ± 10 and 63 ± 5 μJ/cm with the ASE peaks
at 448 and 448 nm, respectively. In addition, Figures 6b, 6d, 6f,
6
h, and 6j show the emission spectra for the planar waveguide of
TN-R5G8, TN-R5G12, TN-R5G15, TN-R3G2, and TN-R3G4
with various pump fluences, and the corresponding normalized
spectra are depicted in the inset, demonstrating the spectral
narrowing. According to the results, the doping concentration
plays an important role in ASE characteristics of TN-RxGy. The
absence of ASE in TN-R5G8 needs further exploring, and
detailed investigation is desirable to clarify the possible reason in
this system. Among all these materials, TN-R3G4 with saturated
white emission has displayed the lowest threshold of 63 ± 5 μJ/
Figure 5. Fluorescence transients of (a) THF solution (10− M) and (b)
the films of TN-RxGy measured at the fluorescence band maxima
collected at 421 and 447 nm, respectively.
5
2
2
cm , which is comparable to that of PF (50 ± 5 μJ/cm , Figure
S6). The results indicated that TN-R3G4 holds great potential as
attractive gain media for organic lasing applications. More
importantly, this star-shaped single-polymer system was deemed
as an attractive platform to investigate the influence of various
emissive species with different contents on the energy transfer, in
which ASE behaviors could be fine-tuned by adjusting the
corresponding concentrations.
The corresponding transient lifetimes are calculated as listed in
the inset. Based on the analysis, the excited state relaxation of
TN-RxGy in dilute solutions can be approximated using double-
exponential decay profiles, exhibiting a fast component at τ (TN-
1
R5G8) = 0.74 ns (85.79%), τ (TN-R5G12) = 0.72 ns (86.48%),
1
τ (TN-R5G15) = 0.71 ns (83.07%), τ (TN-R3G2) = 0.74 ns
1
1
(
86.01%), τ (TN-R3G4) = 0.71 ns (86.66%) and a longer
1
component at τ (TN-R5G8) = 1.95 ns (14.21%), τ (TN-
2
2
CONCLUSIONS
In conclusion, a three-armed star-shaped single-polymer system
consisting of TN as red emissive cores, PF as blue emissive arms,
R5G12) = 2.33 ns (13.52%), τ (TN-R5G15) = 2.02 ns (16.93%),
■
2
τ (TN-R3G2) = 2.23 ns (13.99%), τ (TN-R3G4) = 2.17 ns
2
2
(
13.34%). The shorter τ for all the polymers are quite similar
1
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Figure 6. Full width at half-maximum (fwhm) of the emission spectrum (left, solid spheres) and the corresponding output intensity (right, solid
triangles) for (a) TN-R5G8, (c) TN-R5G12, (e) TN-R5G15, (g) TN-R3G2, and (i) TN-R3G4 as a function of the pump energy density, indicating its
pump threshold. The emission spectra for the planar waveguide of (b) TN-R5G8, (d) TN-R5G12, (f) TN-R5G15, (h) TN-R3G2, and (j) TN-R3G4
with various pump fluences and the corresponding normalized spectra shown in the inset.
and BT as green emissive units was designed and synthesized.
According to PL and EL studies, partial energy transfer has
played a critical role in achieving good-quality white emission
from three primary emissive species. As a result, an appropriate
choice of the doping concentration of TN and BT can facilitate
partial energy transfer from the blue components to the red and
green dopants, realizing saturated white EL with good CIE
coordinates. A current efficiency of 2.41 cd A− and CIE
1
G
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coordinates of (0.34, 0.35) were obtained for a single-emissive-
layer device based on TN-R3G4. It is notable to mention that
their CIE coordinates match well with the values of standard
saturated white emission (0.33, 0.33). Keeping all the results in
mind, we believe that the star-shaped single-polymer systems
appear quite promising to realize high-performance WPLEDs,
originating from the fine control of incomplete energy transfer
and the suppression of intermolecular interactions and phase
separation. Interestingly, the resulting star-shaped single-
polymer system with low content of red and green emissive
dopants demonstrated typical ASE behaviors. A relatively low
PFB. 3 (0.25 g, 0.50 mmol), 4 (0.30 g, 0.50 mmol), and BT2Br (0.2
−3
−4
mL, 1.0 × 10 M solution in toluene, 2.0 × 10 mmol) were used in the
4
polymerization. GPC: M = 1.19 × 10 , PDI = 1.96 (polystyrene as
n
standard).
TN-R5G8. 3 (0.25 g, 0.50 mmol), 4 (0.30 g, 0.50 mmol), BT2Br (0.8
−3
−4
mL, 1.0 × 10 M solution in toluene, 8.0 × 10 mmol), and TN3Br
−4
−4
(
2.5 mL, 2 × 10 M solution in toluene, 5.0 × 10 mmol) were used in
the polymerization. GPC: M = 9248, PDI = 1.54.
n
TN-R5G12. 3 (0.25 g, 0.50 mmol), 4 (0.30 g, 0.50 mmol), BT2Br (1.2
−
3
−4
mL, 1.0 × 10 M solution in toluene, 12.0 × 10 mmol), and TN3Br
−4
−4
(
2.5 mL, 2 × 10 M solution in toluene, 5.0 × 10 mmol) were used in
the polymerization. GPC: M = 9436, PDI = 1.88.
n
2
TN-R5G15. 3(0.25 g, 0.50 mmol), 4 (0.30 g, 0.50 mmol), BT2Br (1.5
threshold of 63 ± 5 μJ/cm with ASE peaks at 448 nm was
−
3
−4
mL, 1.0 × 10 M solution in toluene, 15.0 × 10 mmol), and TN3Br
recorded for TN-R3G4, showing great promise for organic lasing
applications. Our results have provided new insights and better
understanding into the photophysical and optoelectronic
behaviors of the resulting star-shaped single-polymer systems
with simultaneous RGB emission.
−4
−4
(
2.5 mL, 2 × 10 M solution in toluene, 5.0 × 10 mmol) were used in
the polymerization. GPC: M = 9430, PDI = 1.97.
n
TN-R3G2. 3 (0.25 g, 0.50 mmol), 4 (0.30 g, 0.50 mmol), BT2Br (0.2
−
3
−4
mL, 1.0 × 10 M solution in toluene, 2.0 × 10 mmol), and TN3Br
−4
−4
(1.5 mL, 2 × 10 M solution in toluene, 3.0 × 10 mmol) were used in
4
the polymerization. GPC: M = 1.10 × 10 , PDI = 1.79.
n
TN-R3G4. 3 (0.25 g, 0.50 mmol), 4 (0.30 g, 0.50 mmol), BT2Br (0.4
EXPERIMENTAL SECTION
−3
−4
■
mL, 1.0 × 10 M solution in toluene, 4.0 × 10 mmol), and TN3Br
1
−4
−4
H NMR spectra were recorded on a 400 MHz spectrometer.
(1.5 mL, 2 × 10 M solution in toluene, 3.0 × 10 mmol) were used in
4
Chloroform (δ 7.26) was used as an internal standard for chloroform-
d. Fluorescent spectra were recorded on a Shimadzu-5301PC
fluorescent spectrometer. UV−vis spectra were recorded on a
Shimadzu-3600 spectrometer. Compounds 2, 4, 7, 8, and 11 were
synthesized according to the literature, and the methods for the
determination of association constants were reported in our previous
the polymerization. GPC: M = 1.13 × 10 , PDI = 1.83.
n
1
All these polymers showed similar H NMR spectra and elemental
1
analysis results. For example, PF: H NMR (400 MHz, CDCl ) δ (parts
3
per million; ppm): 7.87 (d, 2H), 7.72 (br, 4H), 2.10 (br, 4H), 1.14 (br,
24H), 0.81 (t, 6H). Analysis calculated: C 89.69, H 10.31. Found: C
89.08, H 10.02. The contents of green- and red-light-emitting dopant
17−23
1
papers.
TN was synthesized from the Suzuki method.
units in these polymers were too low to be detected using H NMR and
Synthesis of tris(4-(5-(7-(5-bromo-4-hexylthiophen-2-yl)benzo[c]-
elemental analysis.
[
1,2,5]thiadiazol-4-yl)-3-hexylthiophen-2-yl)phenyl)amine (TN3Br):
Device Fabrication and Characterization. OLEDs were
fabricated on prepatterned indium−tin oxide (ITO) with the sheet
resistance of 10−20 Ω/sq. The substrate was ultrasonic cleaned with
acetone, detergent, deionized water, and 2-propanol. Before the film
coating, the substrate was treated by oxygen plasma treatment for 4 min.
The poly(ethylenedioxythiophene)−poly(styrenesulfonic acid) (PE-
DOT:PSS) film with thickness of about 40 nm was spin-coated onto the
ITO glass. PEDOT:PSS film was dried at 80 °C for 3 h in the vacuum
oven. The solution of TN-RxGy polymers in chloroform was prepared
under a nitrogen atmosphere and spin-coated onto the PEDOT:PSS
layer, resulting in the emitting layer with an approximate thickness of 80
nm. Soon afterward, a thin layer of TPBI (30 nm) as an electron
injection cathode and the subsequent LiF (1 nm)/aluminum (80 nm)
layers were thermally deposited by vacuum evaporation through a mask
at a base pressure below 2 × 10 Pa. The luminance of the device was
measured with a calibrated photodiode. External quantum efficiency was
measured by the integrating sphere. Luminance was calibrated after the
encapsulation of devices with UV-curing epoxy and thin cover glasses.
The Commission Internationale d’Eclairage (CIE) coordinates were
calculated using 1931 observer parameters.
A mixture of TN (0.50 g, 0.30 mmol) was dissolved in CH Cl (100
2
2
mL). Then, NBS (0.16 g, 0.96 mmol) in DMF (5 mL) was added
dropwise. Upon complete, the mixture was stirred for an additional 3 h
in dark before it was diluted with CH Cl , washed with 10% aqueous
HCl solution and saturated aqueous NaCl solution, dried (Na SO ), and
evaporated. The resulting residue was purified by silica gel column
chromatography using hexane/CH Cl (8:1) as eluent to give TN3Br as
a dark red solid (0.42 g, 76%). H NMR (400 MHz, CDCl ), δ (ppm):
8
2
(
2
2
2
4
2
2
1
3
.10 (s, 3H), 7.69−7.77 (m, 9H), 7.46−7.48 (d, 2H), 7.25 (s, 6H),
.76−2.80 (t, 6H), 2.61−2.65 (t, 6H), 1.64−1.78 (m, 12H), 1.33−1.42
1
3
m, 36H), 0.89−0.91 (t, 18H). C NMR (100 MHz, CDCl ), δ (ppm):
3
1
1
3
52.47, 152.35, 146.60, 143.00, 139.61, 139.52, 138.73, 136.70, 130.57,
30.08, 129.25, 127.83, 126.06, 124.96, 124.89, 124.77, 124.19, 111.31,
1.93, 31.66, 29.70, 29.36, 22.69, 14.10. Anal. Calcd for C H Br N S :
−4
96
102
3
7 9
C 61.26, H 5.46, N 5.21, S 15.33. Found: C 61.20, H 5.66, N 5.46, S
5.11.
General Procedures for the Synthesis of the Polymers. To a
1
mixture of 2,7-dibromo-9,9-dihexyl-9H-fluorene (3) (quantities given
below), 2,2′-(9,9-dihexyl-9H-fluorene-2,7-diyl)bis(4,4,5,5-tetramethyl-
1
As for ASE characterization, all samples were optically pumped at 355
nm by using an optical parameteric oscillator (OPO), which was
,3,2-dioxaborolane) (4), and Pd(PPh ) (11.5 mg, 0.01 mmol) under
3 4
N was added a drop of Aliquat 336, 2 M aqueous potassium carbonate
2
3+
pumped by a frequency-tripled pulsed Q-switched Nd :YAG laser
system with 5 ns-output pulses at a repetiton rate of 10 Hz. The raw
pulsed beam from the OPO passed through an adjustable slit to be
spatially formed and then was focused with a cylindrical lens (with focal
length f = 10 cm) to form a 4.1 mm × 440 μm stripe-shaped excitation
area on the sample. The pump energy incident on the sample was tuned
by the insertion of a set of calibrated neutral density filters into the beam
path. The emission was collected from the edge of the slab waveguide by
a fiber-coupled spectrograph and recorded by a charge coupled device
(
2.5 mL), and degassed toluene (5 mL). Solutions of tris(4-(5-(7-(5-
bromo-4-hexylthiophen-2-yl)benzo[c][1,2,5] thiadiazol-4-yl)-3-hexyl-
thiophen-2-yl)phenyl)amine (TN3Br) and solutions of 4,7-dibromo-
benzo[c][1,2,5]thiadiazole (BT2Br) were also added. The mixture was
stirred at 90 °C for 48 h and then poured into methanol. The precipitate
was collected by using filtration, dried, and then dissolved in
dichloromethane. The solution was washed with water and dried over
anhydrous Na SO . After most of the solvent had been removed, the
2
4
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 THF/methanol was then repeated several
times. The final product, a light orange-colored fiber, was obtained after
drying in a vacuum with a yield of 60−80%. THF was used as the eluent
solvent for the GPC measurements.
(CCD) detector.
ASSOCIATED CONTENT
■
* Supporting Information
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.macro-
mol.6b00020.
PF. 3 (0.25 g, 0.50 mmol) and 4 (0.30 g, 0.50 mmol) were used in the
polymerization. Gel-permeation chromatography (GPC): M = 2.47 ×
1
n
4
0 , polydispersity index (PDI) = 2.09 (polystyrene as standard).
H
DOI: 10.1021/acs.macromol.6b00020
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
TGA and DSC curves of TN and TN-RxGy; CV data of
Article
Efficient Energy Transfer from a Conjugated Polymer. Adv. Funct.
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10) Granstrom, M.; Inganas, O. White Light Emission from a Polymer
Blend Light Emitting Diode. Appl. Phys. Lett. 1996, 68, 147−149.
11) Tasch, S.; List, E. J. W; Ekstrom, O.; Graupner, W.; Leising, G.;
TN and TN-RxGy; XRD patterns of TN-RxGy; EL
(
characteristics of devices based on 0.03 mol % TN blended
1
into PFB; ASE and emission characteristics of PF films; H
(
NMR, 13C NMR and MALDI-TOF mass spectra of TN
Schlichting, P.; Rohr, U.; Geerts, Y.; Scherf, U.; Mullen, K. Efficient
White Light-emitting Diodes Realized with New Processable Blends of
Conjugated Polymers. Appl. Phys. Lett. 1997, 71, 2883−2885.
(12) Liu, J.; Zhou, Q. G.; Cheng, Y. X.; Geng, Y. H.; Wang, L. X.; Ma,
D. G.; Jing, X. B.; Wang, F. S. The First Single Polymer with
Simultaneous Blue, Green, and Red Emission for White Electro-
luminescence. Adv. Mater. 2005, 17, 2974−2978.
1
and TN3Br; H NMR of TN-RxGy (PDF)
AUTHOR INFORMATION
Corresponding Authors
E-mail iamwylai@njupt.edu.cn (W.-Y.L.).
Email: wei-huang@njtech.edu.cn (W.H.).
■
*
*
(
13) Lee, S. K.; Jung, B. J.; Ahn, T.; Jung, Y. W.; Lee, J. I.; Kang, I. N.;
Author Contributions
C.-F.L. and Y.J. contributed equally to this work.
Lee, J.; Park, J. H.; Shim, H. K. White Electroluminescence from a Single
Polyfluorene Containing Bis-DCM Units. J. Polym. Sci., Part A: Polym.
Chem. 2007, 45, 3380−3390.
Notes
(14) Tsami, A.; Yang, X. H.; Galbrecht, F.; Farrell, Tony.; Li, H. B.;
The authors declare no competing financial interest.
Adamczyk, S.; Heiderhoff, R.; Balk, L. J.; Neher, D.; Holder, E. Random
Fluorene Copolymers with On-chain Quinoxaline Acceptor Units. J.
Polym. Sci., Part A: Polym. Chem. 2007, 45, 4773−4785.
ACKNOWLEDGMENTS
■
The authors acknowledge financial support from the National
Key Basic Research Program of China (973 Program,
(15) Shekhar, S.; Aharon, E.; Tian, N.; Galbrecht, F.; Scherf, U.;
Holder, E.; Frey, G. L. Decoupling 2D Inter- and Intrachain Energy
Transfer in Conjugated Polymers. ChemPhysChem 2009, 10, 576−581.
2
014CB648300), the National Natural Science Foundation of
(16) Kanelidis, I.; Ren, Y.; Lesnyak, V.; Gasse, J. C.; Frahm, R.;
China (21422402, 20904024, 51173081, 61136003), the Natural
Science Foundation of Jiangsu Province (BK20140060,
BK20130037, BM2012010), Program for Jiangsu Specially-
Appointed Professors (RK030STP15001), Program for New
Century Excellent Talents in University (NCET-13-0872),
Specialized Research Fund for the Doctoral Program of Higher
Education (20133223110008, and 20113223110005), the
Synergetic Innovation Center for Organic Electronics and
Information Displays, the Priority Academic Program Develop-
ment of Jiangsu Higher Education Institutions (PAPD), the
NUPT “1311 Project”, the Six Talent Plan (2012XCL035), the
Eychmueller, A.; Holder, E. Arylamino-Functionalized Fluorene- and
Carbazole-Based Copolymers: Color-Tuning Their CdTe Nanocrystal
Composites from Red to White. J. Polym. Sci., Part A: Polym. Chem.
2
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011, 49, 392−402.
17) Lai, W. Y.; Zhu, R.; Fan, Q. L.; Hou, L. T.; Cao, Y.; Huang, W.
Monodisperse Six-Armed Triazatruxenes: Microwave-Enhanced Syn-
thesis and Highly Efficient Pure-Deep-Blue Electroluminescence.
Macromolecules 2006, 39, 3707−3709.
(18) Lai, W.-Y.; He, Q. Y.; Zhu, R.; Chen, Q. Q.; Huang, W. Kinked
Star-Shaped Fluorene/Triazatruxene Co-oligomer Hybrids with
Enhanced Functional Properties for High-Performance, Solution-
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333 Project (BRA2015374), and the Qing Lan Project of Jiangsu
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19) Xia, R. D.; Lai, W.-Y.; Levermore, P. A.; Huang, W.; Bradley, D. D.
C. Low-Threshold Distributed-Feedback Lasers Based on Pyrene-
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