Synthesis and electrostatic Nano-Assembly of water-soluble Polybenzothiadiazole derivatives with long-wavelength emission in the solid states

Article abstract of DOI:10.1166/jnn.2010.2961

We have synthesized APBT and APTBT containing benzothiadiazole units by Suzuki cross-coupling reaction with good yield. The polymers showed blue emission colors in aqueous solutions, while long wavelength shift was observed in the solid state due to facilitated exciton migration. APBT and APTBT are water-soluble and highly-fluorescent conjugated polymers with negatively charged sulfonate side chains and thus they can be electrostatically assembled with oppositely charged polyelectrolyte such as cationic polymer, poly(dimethyldiallylammonium chloride) (PDAC) via layerby- layer (LbL) deposition technique on a glass slide. According to the increased the number of bilayer, we found that the assembled film exhibited larger enhancement of the long wavelength emission relative to the blue emission, due to the increased excition migration. Copyright

Full text of DOI:10.1166/jnn.2010.2961

Copyright © 2010 American Scientific Publishers
All rights reserved
Printed in the United States of America
Journal of
Nanoscience and Nanotechnology
Vol. 10, 6977–6980, 2010
Synthesis and Electrostatic Nano-Assembly of
Water-Soluble Polybenzothiadiazole Derivatives with
Long-Wavelength Emission in the Solid States
1
ꢀ2
3
1
4
Jung Hyo Lee , Dai Geun Kim , Geun Seok Jang , Won Seok Lyoo ,
1
5
1ꢀ∗
Won Ho Park , Minjung Lee , and Taek Seung Lee
1Organic and Optoelectronic Materials Laboratory, Department of Advanced Organic Materials and
Textile System Engineering, Chungnam National University, Daejeon 305-764, Korea
2
Samsung Cheil Industries Inc., 332-2 Gocheon-dong, Uiwang, Gyeonggi-do 437-711, Korea
3
Organic and Optoelectronic Materials Laboratory, Department of Nanotechnology, Chungnam National University,
Daejeon 305-764, Korea
4
School of Textile, Yeungnam University, Gyeongsan, Gyeongbuk 712-749, Korea
5
Department of Oriental Medicine and Food Biotechnology, Joongbu University, 101 Daehack-ro,
Chubu-myon, Kumsan-gun, Chungnam 312-702, Korea
We have synthesized APBT and APTBT containing benzothiadiazole units by Suzuki cross-coupling
reaction with good yield. The polymers showed blue emission colors in aqueous solutions, while
long wavelength shift was observed in the solid state due to facilitated exciton migration. APBT
and APTBT are water-s oD l ue bl il ve e ar ne dd hb i yg hI lny g- fleu no t rae st co e: nMt cc oM n aj us gt ea tr e Ud np i ov l ey mr s ei t rys with negatively charged
sulfonate side chains aI nP d: 5t h. 8u .s 4 7t h. e2 y3 5c aOn n b: eM eo l ne c, t1r o3 s tJa ut inc a 2l l 0y 1 a6 s s0 e0 m: 3b 0l e: 0d 6with oppositely charged
polyelectrolyte such as ca tCi o on pi cy pr i og l hy mt : eA r ,m p eo rl yi c( ad inm Se tch i ye l dn itai fl il cy l aP mu mb loi sn hi ue mr schloride) (PDAC) via layer-
by-layer (LbL) deposition technique on a glass slide. According to the increased the number of
bilayer, we found that the assembled film exhibited larger enhancement of the long wavelength
emission relative to the blue emission, due to the increased excition migration.
Keywords: Water-Soluble Conjugated Polymers, Fluorescence, Self-Assembled Multilayer Film,
Layer-by-Layer Deposition.
1
. INTRODUCTION
as electrostatic interaction with oppositely charged species,
1
0ꢀ11
a high sensitivity toward fluorescence quenchers
fluorescence change with aggregation.
and
In the past decade, fluorescent conjugated polymers are
being extensively investigated for their potential appli-
cations in the fields of optoelectronics, microelectronics,
and chemical and biological sensors. Especially, water-
soluble conjugated polymers have been attracted a great
deal of attention because of their unique optoelectronic
properties, which may serve as a basis for a new gener-
ation of optoelectronic devices and biochemical detection
12
One of the frequently utilized methods for obtain-
ing conjugated polymers with a small band gap is the
incorporation of benzothiadiazole groups into the poly-
mer backbone, resulting in a remarkable red-shift due to
intramolecular alternating electron donor–acceptor struc-
ture, which has potential applications in LED, photovoltaic
1
–5
13
devices, and sensors.
6
7
such as DNA, proteins, and biological agents.
LbL self-assembly between oppositely charged species
is a well-known method to precisely controlled nanometer-
Their peculiar properties stem from the combination
of optoelectronic properties of conventional conjugated
polymers and water solubility induced by ionic nature of
polyelectrolytes.8 Their optoelectronic properties can be
easily tuned through the structural alteration of the con-
jugated structure of the polymer backbones, and the ionic
functionality endows them with exceptional features such
1
4
scale composite films. This technique has also been
employed to incorporate chromophoric subunits into the
ꢀ9
1
5–17
multilayer films.
In this study, we have designed and synthesized
water-soluble anionic conjugated poly(para-phenylene)s
containing benzothiadiazole (BT) unit or thienylbenzoth-
iadiazole (TBT) unit in the polymer backbones, and we
report a polyelectrolyte self-assembly multilayered film by
∗
Author to whom correspondence should be addressed.
J. Nanosci. Nanotechnol. 2010, Vol. 10, No. 10
1533-4880/2010/10/6977/004
doi:10.1166/jnn.2010.2961
6977

Synthesis and Electrostatic Nano-Assembly of Water-Soluble Polybenzothiadiazole Derivatives
Lee et al.
alternate adsorption of positively charged PDAC and the
negatively charged polymers on a glass substrate.
2.3.2. Synthesis of APTBT
26.1 mg (0.057 mmol) of 2, 300 mg (0.514 mmol) of
3, and 188 mg (0.571 mmol) of 4 were dissolved in
2
. EXPERIMENTAL DETAILS
a mixture of 8 ml of DMF, 12 ml of 2 M Na CO
aqueous solution in a three-necked round-bottom flask.
2 3
2
.1. Materials
After addition of 3.5 mg (0.003 mmol) of Pd(PPh ꢁ ,
3
4
ꢀ
the reaction mixture was stirred under argon at 100 C
for 48 h. The same purification method was employed
as described for APBT. 162 mg of the red solid was
The benzothiadiazole monomers, 4,7-dibromo-2,1,3-
benzothiadiazole (1) and 4,7-bis(5-bromothiophen-2-
yl)benzo-2,1,3-thiadiazole (2) and ionic monomers,
1
obtained in 53% yield. H NMR (300 MHz, D O): ꢂ
2
ppm
1
,4-dibromo-2,5-bis(4-sulfonatobutoxy) benzene sodium
8
.1–7.3 (br, 3.1H), 7.2–6.7 (br, 2H), 4.0 (br, 2.8H), 3.0
salt (3) were synthesized according to the previously
1
3
published methods.1
8–20
(br, 3H), 2.0–1.5 (br, 5H). C-NMR (D
1
6
2
O): ꢂppm 150.17,
30.56, 128.85, 128.26, 120.40, 117.63, 114.98, 68.97,
5.76, 51.21, 49.86, 43.04, 27.93, 23.14, 21.30, 20, 87.
Other reagents were purchased
from Aldrich and Acros without further purification.
Anal. Calcd. (%) for C H N S O Na C, 49.24;
H, 4.27; N, 0.57; S, 13.79. Found: C, 43.48; H, 4.84;
N, 0.40; S, 11.66.
2
0
20ꢃ8 0ꢃ2 2ꢃ1 7ꢃ2
1ꢃ8ꢄ
2
.2. Characterization
1H NMR spectra were collected on a Bruker DRX-300
spectrometer with tetramethylsilane as an internal standard
2.4. Layer-by-Layer Deposition (Spin-Assembly
(Korea Basic Science Institute). UV-vis absorption spectra
Method)
were recorded on a PerkinElmer Lambda 35 spectrome-
ter. Photoluminescence spectra were obtained from a Var-
ian Cary Eclipse fluorescence spectrophotometer equipped
with a Xenon flash lamp excitation source.
The layer-by-layer films were deposited consisting of a
cyclic repetition according to the following steps:
(
1
1) spin-casting an aqueous PDAC solution ([RU] = 5ꢃ0×
−
2
0
M) onto a glass substrate at 400 and 3000 rpm for
2
.3. Polymerization
the first 10 s and the following 60 s, respectively,
Delivered by Ingenta to: McMaster University
(
2) rinsing with deionized water and drying with a stream
IP: 5.8.47.235 On: Mon, 13 Jun 2016 00:30:06
All the polymers were synthesized via Suzuki cross-
coupling reaction.
Copyright: American S co i fe nd rt iyf i cn iPt r uo bg el i ns ,h ers
(
5
3) spin-casting an aqueous polymer solution ([RU] =
−
2
ꢃ0×10 M) onto a glass substrate at 400 and 3000 rpm
2
.3.1. Synthesis of APBT
for the first 10 s and the following 60 s, respectively, and
4) final rinsing with deionized water and drying by blow-
(
2
3
6.5 mg (0.090 mmol) of 1, 474.4 mg (0.812 mmol) of
, and 356.4 mg (1.08 mmol) of 1,4-benzenediboronic
ing of dry nitrogen. The buildup of a multilayered film
was monitored by UV/vis absorption spectroscopy.
acid bis(pinacol) ester 4 were dissolved in a mixture
of 6 ml of DMF and 9 ml of 2 M Na CO aque-
2
3
ous solution in a three-necked round-bottom flask. After
3
. RESULTS AND DISCUSSION
addition of 3.5 mg (0.003 mmol) of Pd(PPh ꢁ , the reac-
3
4
ꢀ
tion mixture was stirred under argon at 100 C for
8 h. After the reaction, the reaction mixture was cooled
The synthetic procedures for the preparation for monomers
and polymers are illustrated in Scheme 1. 1 was easily
obtained via bromination of commercially available
2,1,3-benzothiadiazole with good yield according to the
published methods. 2 was obtained via the bromination
of 4,7-bis(thiophen-2-yl)benzo-2,1,3-thiadiazole with
NBS in a mixture of THF and acetic acid. 3 was
synthesized according to the previously published
methods.
4
and slowly added to 500 ml of methanol/acetone/ether
mixture (10:40:50 v:v:vꢁ, and precipitates were filtered.
The polymer was dissolved in water and reprecipitated
in methanol/acetone/ether twice. Finally, the polymer
was purified through dialysis against water (Millipore
1
8
1
9
TM
Nanopure ꢁ using a 1.24 KD MWCO cellulose mem-
2
0
brane for 3 days. After the dialysis, the polymer solu-
Poly{[4ꢀ7-(2ꢀ1ꢀ3-benzothiadiazole)-alt-1ꢀ4-
tion was freeze-dried and 360 mg of the yellow solid
phenylene]-co-[2ꢀ5-bis(4-sulfonatobutoxy)-1ꢀ4-phenylene
sodium salt-alt-1ꢀ4-phenylene]} (APBT) and poly{[4ꢀ7-
(bis (thiophen-2-yl) benzo-2ꢀ1ꢀ3-thiadiazole)-alt-1ꢀ4-
phenylene]-co-[2ꢀ5-bis(4sulfonatobutoxy)-1ꢀ4-phenylene
sodium salt-alt-1ꢀ4-phenylene]} (APTBT) were synthe-
sized by the palladium-catalyzed Suzuki cross-coupling
reaction. The molar ratio (m) in the copolymer APBT
and APTBT were determined by elemental analysis and
1
was obtained in 58% yield. H NMR (300 MHz, D O):
2
ꢂppm 8.1–7.3 (br, 3H), 7.2–6.7 (br, 2H), 3.9 (br, 2H),
1
3
2
1
6
.8 (br, 2.5H), 1.7–1.3 (br, 4.7H). C-NMR (D O): ꢂ
2 ppm
55.14, 150.35, 138.15, 131.05 129.65, 115.59, 70.27,
9.44, 51.15, 28.10, 21.43, 21.31. Anal. Calcd. (%) for
C19ꢃ2H20ꢃ4N S O Na1ꢃ8ꢄ: C, 48.87; H, 4.33; N,0.59;
0ꢃ2 1ꢃ9 7ꢃ2
S, 12.91. Found: C, 46.85; H, 5.13; N, 0.59; S, 10.41.
6
978
J. Nanosci. Nanotechnol. 10, 6977–6980, 2010

Lee et al.
Synthesis and Electrostatic Nano-Assembly of Water-Soluble Polybenzothiadiazole Derivatives
SO3–Na+
each other only intra-chain exciton migration was possible.
However, in the film state, the conjugated polymer chains
were aggregated within close proximity to each other, thus
S
N
N
O
O
O
O
O
Br
Br
Br
Br
B
B
21
inter-chain exciton migration also became possible. The
O
1
3
4
three-dimensional random walk available to an exciton in a
polymer film enabled the exciton to sample a much greater
number of different sites than by the one-dimensional ran-
dom walk available to an exciton in dilute, well-dissolved
polymer solutions. Therefore, an exciton in a conjugated
polymer is much more likely to find a low-energy exci-
ton trap site if the polymer is in its solid state than in a
solution state.
+
–
Na O S
3
SO3–Na+
S
N
N
O
Pd(0)
DMF, 2MNa CO
2
3
m
n
O
APBT
+
–
Na O S
3
S
N
N
Pd(0)
S
S
Br
Br
3
4
Properly designed polyelectrolytes were reported as LbL
film due to electrostatic attraction. The polymers can be
DMF, 2MNa CO
2
3
22
2
N
combined with commercially available cationic polymers
and anionic polymers such as PDAC and sulfonated poly-
mers (APBT and APTBT) to form nano-scale multilay-
ers. With APBT and APTBT, we attempted to provide
a self-assembled LbL film for changes in absorbance and
fluorescence intensity upon increased bilayer. The process
was repeated five times to assemble five bilayers on the
glass slide. The UV-vis spectra of the bilayers are shown in
Figure 1. The increase of absorption with increasing num-
ber of bilayers indicates the multilayer deposition process.
Figure 2 shows consecutive increase in fluores-
cence intensity of the films upon increased bilayer of
SO3–Na+
S
N
O
S
S
m
n
O
+
–
Na O S
3
APTBT
Scheme 1. Synthetic methods for APBT and APTBT.
found to be approximately 8 mol%. The polymers have
number-average molecular weights ranging from 13,000
to 15,000. The chemical structures of the polymers were
confirmed by H-NMR, and C-NMR spectra. For APBT,
the peaks at 7.7–8.1 ppm can be as sI Pi g:n 5e .d 8 t. o4 7t h. 2e 3p 5r o Ot o nn :s Mo fo n, 13 Jun 2016 00:30:06
1
13
Delivered by Ingenta to: McMaster University
(
a) 0.10
Copyright: American Scientific Publishers
BT unit and the peaks at 6.9–7.5 ppm to phenylene units.
The optical absorption and fluorescence emission data
of the polymers in aqueous solution are shown in Table I.
APBT has two absorption maxima at 321 and 415 nm in
∗
aqueous solution, corresponding to the ꢅ–ꢅ transitions of
0
0
.05
the phenylene unit (short wavelength absorption) and the
BT unit (long wavelength absorption). APTBT has broad
absorption band around 500–600 nm, which is assigned
to TBT units. A solid film of APTBT shows red-shifted
absorption about 20 nm compared to that in aqueous solu-
tion. The fluorescence spectrum of APBT shows emission
maximum around 429 nm in aqueous solution and two
emission bands around 412 nm and 538 nm are observed
in the fluorescence spectrum of the thin film. In the case
of APTBT, the fluorescence spectrum shows emission
maximum around 422 nm in aqueous solution and two
emission bands around 415 nm and 653 nm are observed
in the fluorescence spectrum of the thin film. In aque-
ous solution, since the polymer chains were isolated from
.00
300
400
500
600
Wavelength ( nm )
(
b) 0.3
0.2
0
0
.1
.0
Table I. Photophysical properties of the polymers.
UV (nm)
PL (nm)
a
a
Solution
Film
Solution
Film
300
400
500
600
700
APBT
APTBT
321, 415
330, 512
343, 435
350, 525
429
422
412, 538
415, 653
Wavelength ( nm )
Fig. 1. Absorption spectra of LbL self-assembled films (1 to 5 bilayers)
of (a) PDAC/APBT and (b) PDAC/APTBT.
a
Measured in aqueous solution.
J. Nanosci. Nanotechnol. 10, 6977–6980, 2010
6979

Synthesis and Electrostatic Nano-Assembly of Water-Soluble Polybenzothiadiazole Derivatives
(
Lee et al.
a) 800
with APBT and APTBT using the LbL assembly method.
PDAC/polymer LbL film shows the fluorescence enhance-
ment of the green or red emission band relative to the
blue emission band as the number of bilayers increased.
The results demonstrate that enhanced exciton transport
between conjugated polymer bilayers increases the possi-
bility that an exciton would find a specific site (BT unit
and TBT unit) among the conjugated polymer bilayers.
5
bilayers
6
4
2
00
00
00
0
1 bilayer
Acknowledgment: Financial support from the National
Science Foundation (NRF) grant funded by the Korea gov-
ernment (MEST) (No. R01-2007-000-10740-0 and 2009-
400
500
600
700
800
Wavelength (nm)
008146) was greatly acknowledged.
(
b) 800
References and Notes
5
bilayers
6
4
2
00
00
00
0
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8
9
PDAC/APBT or PDAC/APTBT. The fluorescence spectra
of PDAC/APBT LbL film show the larger increment of the
green emission band (535 nm) relative to that of blue emis-
sion band (415 nm) as the number of PDAC/APBT bilay-
ers increased (Fig. 2(a)). In the case of PDAC/APTBT
LbL film, the fluorescence spectra also exhibited larger
enhancement of the red emission band (650 nm) relative
to the blue emission band (420 nm) as the number of
PDAC/APTBT bilayers increased (Fig. 2(b)).
Along with the increase in the fluorescence intensity,
slight red-shift was observed as well according to the
increased the number of bilayers, presumably due to the
possible aggregation.
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4
. CONCLUSION
We synthesized novel water-soluble anionic polybenzoth-
iadiazole derivatives containing BT units (APBT) and
TBT units (APTBT). The polymers showed blue emis-
sion colors in aqueous solutions, but green or red emission
color was observed in the thin film. We have described a
procedure for preparing for highly emissive films coated
22. O. Mermut and C. J. Barrett J. Phys. Chem. B 107, 2525 (2003).
Received: 31 December 2008. Accepted: 10 July 2009.
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J. Nanosci. Nanotechnol. 10, 6977–6980, 2010