Synthesis of conjugated polymer containing bipyridine and oxadiazole groups and its metal ion sensing property

Article abstract of DOI:10.1080/15421401003598025

A new polybipyridine linked with oxadiazole and 2,5-didecyloxybenzene was prepared via simple condensation and ring closing reaction. The polymer P2 is basically an amorphous material with thermal decomposition temperature greater than 500C. Introduction of didecyloxy group into the rigid oxadiazole backbone resulted in better solubility in common organic solvents such as THF, chloroform, and DMF. UV-vis and fluorescence spectroscopy were employed to investigate the optical properties both solution in the presence of a variety of metal cations, in which the polymer would be a good candidate for optical sensory material for metal ion.

Full text of DOI:10.1080/15421401003598025

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Synthesis of Conjugated Polymer
Containing Bipyridine and Oxadiazole
Groups and Its Metal Ion Sensing
Property
Young-Shin Kim a b , Na Young Kwon b , Dai Gun Kim c , Minjung Lee d
& Taek Seung Lee e
a Aekyung ChemTech Co., Ltd. R&D Center , Yuseong-gu, Daejeon,
Korea
b Organic and Optoelectronic Materials Laboratory, Department
of Advanced Organic Materials and Textile System Engineering ,
Chungnam National University , Daejeon, Korea
c Organic and Optoelectronic Materials Laboratory, Department of
Nanotechnology , Chungnam National University , Daejeon, Korea
d Department of Oriental Medicine and Food Biotechnology ,
Joongbu University , Kumsan-gun, Chungnam, Republic of Korea
e Organic and Optoelectronic Materials Laboratory, Department of
Advanced Organic Materials and Textile System Engineering and
Graduate School of Analytical Science and Technology (GRAST) ,
Chungnam National University , Daejeon, Korea
Published online: 19 Apr 2010.
To cite this article: Young-Shin Kim , Na Young Kwon , Dai Gun Kim , Minjung Lee & Taek Seung
Lee (2010) Synthesis of Conjugated Polymer Containing Bipyridine and Oxadiazole Groups
and Its Metal Ion Sensing Property, Molecular Crystals and Liquid Crystals, 519:1, 43-53, DOI:
10.1080/15421401003598025
To link to this article: http://dx.doi.org/10.1080/15421401003598025
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Mol. Cryst. Liq. Cryst., Vol. 519: pp. 43–53, 2010
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421401003598025
Synthesis of Conjugated Polymer Containing
Bipyridine and Oxadiazole Groups and
Its Metal Ion Sensing Property
YOUNG-SHIN KIM,1,2 NA YOUNG KWON,2 DAI GUN
KIM,3 MINJUNG LEE,4 AND TAEK SEUNG LEE5
1Aekyung ChemTech Co., Ltd. R&D Center, Yuseong-gu,
Daejeon, Korea
2Organic and Optoelectronic Materials Laboratory, Department
of Advanced Organic Materials and Textile System Engineering,
Chungnam National University, Daejeon, Korea
3Organic and Optoelectronic Materials Laboratory, Department
of Nanotechnology, Chungnam National University, Daejeon, Korea
4Department of Oriental Medicine and Food Biotechnology, Joongbu
University, Kumsan-gun, Chungnam, Republic of Korea
5Organic and Optoelectronic Materials Laboratory, Department
of Advanced Organic Materials and Textile System Engineering
and Graduate School of Analytical Science and Technology
(GRAST), Chungnam National University, Daejeon, Korea
A new polybipyridine linked with oxadiazole and 2,5-didecyloxybenzene was
prepared via simple condensation and ring closing reaction. The polymer P2 is
basically an amorphous material with thermal decomposition temperature greater
than 500ꢀC. Introduction of didecyloxy group into the rigid oxadiazole backbone
resulted in better solubility in common organic solvents such as THF, chloroform,
and DMF. UV-vis and fluorescence spectroscopy were employed to investigate the
optical properties both solution in the presence of a variety of metal cations, in
which the polymer would be a good candidate for optical sensory material for
metal ion.
Keywords Bipyridine; conjugated polymers; metal ion; sensors
Introduction
Conjugated polymers with fluorescent properties are highly recognized as functional
organic materials due to the advantage with which the substance is able to integrate
its electronic and optical characteristics. Therefore, these materials are frequently
Address correspondence to Taek Seung Lee, Organic and Optoelectronic Materials
Laboratory, Department of Advanced Organic Materials and Textile System Engineering,
Chungnam National University, Daejeon 305-764, Korea. Tel.: þ82-42-821-6615; Fax:
þ82-42-823-3736; E-mail: tslee@cnu.kr
43

44
Y.-S. Kim et al.
applied to fields that use electronic properties resulting from p-conjugated structures
such as organic light emitting diodes (OLED) and organic solar cells [1–5].
Among the various conjugated polymers the ones with 1,3,4-oxadiazole struc-
tures show diverse characteristics such as thermal and chemical stability in addition
to mechanical strength and rigidity allowing them to be used in carbon fibers,
high-performance fibers, reinforcing materials, and gas separation membranes [6,7].
It is understood that oxadiazole shows such characteristics because it’s structures
resemble the characteristics of phenyl structures [8]. Hence recently, there has been
much study on applying conjugated polymers with oxadiazole structures to eletro-
optics. Specifically, related to the development of the multi-level structure of OLED
(ITO=HTL=EL=ETL=metal) it is studied and developed widely as ETL [9]. However,
multi-layered OLED’s have many limitations when selecting materials, like a suitable
solvent to produce the multi-layer structure. Many researchers continue to resolve the
current limitations and, as a result, researchers are attempting to simplify multi-
layered OLED’s to single-layered OLED’s (ITO=EL=metal) [10,11].
The most important aspect of simulating a single-layered OLED is the hole and
electrons provided by the anode and cathode, and the balanced insertion of electrons
into the emitting layer. Typical conjugated polymers used as organic emitting mate-
rials have better hole transporting abilities than electron transporting abilities due to
a high lowest unoccupied molecular orbital (LUMO) energy level. Therefore, in
order to increase the efficiency of organic luminescence it is important to design
the organic luminescent material to have electron transporting abilities. Thus, it is
for this reason, that the introduction of an oxadiazole structure that can give
electron transporting abilities to conjugated polymers is so important.
Besides, conjugated polymers have a unique optical property (UV-vis and
fluorescence spectra) and signal amplification ability that are advantageous for an
analytical tool. An important characteristics is that conjugated polymers and metal
ions such as 2,20-bipyridyl and 4-hydroxybipyridyl can chelate with metal ions,
which can lead to conformation changes. This means that the optical properties of
conjugated polymers can be altered due to the chelation between the polymer and
metal ions. These conjugated polymers, that can form chelation with metal ions,
are used as ion-recognizing materials in various studies [12,13].
In this study, we synthesized P2 containing oxadiazole groups which have an
n-type semiconducting property due to electron deficiency and bipyridine groups
for chelation with metal ion by means of thermal cyclization of precursor polymer
P1. We investigated the efficiency of the polymer’s ability as an ion-recognition
material toward metal ions.
Experimental
Materials and Reagent
2,5-Dihydroxyterephtalic acid (1), 1-bromodecane, hydrazine hydrate, 5,50-dimethyl-
2,20-dypyridyl used for monomer synthesis were purchased from Aldrich and used
without further purification. Sulfuric acid, nitric acid, hydrochloric acid, potassium
carbonate, potassium dichromate, potassium hydroxide, magnesium sulfate, triethy-
lamine, and N,N0-dimethylformamide (DMF) were purchased from Duksan Pure
Chemicals Co. or Samchun Pure Chemical and used without additional purification
procedures. Distilled deionized water was used in polymer synthesis and ion

Conjugated Polymer for Metal Ion Sensing
45
recognition experiment. Ethyl ether and thionyl chloride were purified by conven-
tional distillation method.
Instrumentation
1H NMR spectra were collected on a Bruker DRX-300 spectrometer with
tetramethylsilane as an internal standard (Korea Basic Science Institute). UV-vis
absorption spectra were recorded on a PerkinElmer Lambda 35 spectrometer.
Infrared absorption analysis was carried out with the FT-IR Matsson Genesis II.
Gel Permeation Chromatography (GPC, solvent: THF, reference material:
polystyrene) was used to measure the molecular weight of the polymer. Fluorescence
spectrum was recorded in PerkinElmer LS45.
Synthesis
Diethyl-2,5-dihydroxylterephthalate (2) [14]. 5 g (25 mmol) of 1 and 200 mL of
ethanol were stirred in a 500 mL 3-neck-round flask. Then, the temperature of the
flask was increased to 80ꢀC. After the solid in the flask was completely dissolved,
13 mL (250 mmol) of sulfuric acid was slowly added and the flask was charged
with nitrogen. The reaction mixture was stirred vigorously for 24 hr. After the
reaction, the flask was cooled to room temperature and the solid precipitate was
obtained by filtration. The solid precipitate was then recrystallized in ethanol
twice. The solid obtained was vacuum dried at 50ꢀC. The obtained 2 is light
1
green-colored and the yield was 5.9 g (92%). H NMR (CDCl3, ppm): 10.2 (s, 2H,
OH); 7.5 (s, 2H, aromatic); 4.4 (m, 4H, CH2); 1.4 (t, 6H, CH3).
Diethyl-2,5-didecyloxyterephthalate (3) [14]. 5 g (20 mmol) of 2 and 200 mL of
DMF were stirred in a 500 mL 3-neck-round flask and heated to 80ꢀC until the
solid within the flask was completely dissolved. After the solid was completely
dissolved, 13.6 g (100 mmol) of potassium carbonate was put into the flask with
20.5 mL (98.5 mmol) of 1-bromodecane and maintained for 96 hr. After the
reaction the flask was cooled to room temperature and the solid precipitate was
isolated by filtration. The obtained solution was evaporated in rotary evaporator.
The solid 3 obtained after removing the solvent was recrystallized twice in ethanol
to obtain a pure substance. The obtained 3 was a white solid (yield 9.0 g (86%)).
1H NMR (DMSO-d6, ppm): 6.8 (s, 2H, aromatic); 3.7 (m, 4H, COOCH2); 3.3 (t,
4H, OCH2); 2.4-1.1 (broad, 32H, alkyl); 0.7 (broad, CH3).
2,5-Bis(decyloxy)terephthalohydrazide (4). 100 mL of methanol and 16.3 mL
(524 mmol) hydrazine hydrate were placed in a 500 mL 3-neck-round flask and the
temperature was raised to 65ꢀC. During the vigorous stirring of the solution, 7 g
(13.1 mmol) of 3 in 200 mL of methanol was added and reacted for 24 hr. After
the reaction, the solvent was removed by evaporation to 50 mL. Then the solution
was cooled to room temperature and the solid precipitate was filtered. The solid
was recrystallized twice in ethanol. The obtained compound was white and the
yield was 6.0 g (91%). 1H NMR (CDCl3, ppm): 9.2 (s, 2H, NH); 7.8 (s, 2H,
aromatic); 4.2 (t, 4H, OCH2); 2.0-1.3 (broad, 36H, alkyl and NH2); 0.9 (t, 6H, CH3).
5,50-Dicarboxyl-2,20-bipyridine (6) [15]. 125 mL of sulfuric acid was slowly stirred
in 500 mL beaker and then 5.0 g (20.5 mmol) of 5 was placed within the beaker.

46
Y.-S. Kim et al.
The beaker was then heated to 80ꢀC while 24 g (81.5 mmol) of potassium dichromate
was added portionwise. After the addition of potassium dichromate, the beaker was
cooled to 40ꢀC and then the solution was slowly poured into 800 mL of ice water with
vigorous stirring. The solid precipitate was washed with water four times. The solid
obtained after the filtration was dried in a vacuum at 60ꢀC. The dried solid and
170 mL of nitric acid (50%) were placed in a 250 mL beaker and heated to 140ꢀC
with stirring for 4 hr. After the reaction, the solution was cooled to room
temperature and then was slowly added to a 2 L beaker filled with ice. When the
ice was completely melted the solution was diluted with 1 L of water. The
precipitate was filtered, washed with water 5 times, and finally with acetone twice.
The obtained solid was vacuum dried at 40ꢀC to afford white solid (yield 5.6 g (90%)).
5,50-Dicarbonyl chloride-2,20-bipyridine (7). 100 mL of distilled thionyl chloride and
2.5 g (10.2 mmol) of 6 were placed in a 250 mL 3-neck-round flask. Three drops of
DMF were added and the temperature was raised to reflux and left to react for
24 hr. After the reaction the solution was cooled to room temperature and a
needle-shaped precipitate was formed. The solid was filtered using a glass funnel.
Then the solid was recrystallized in n-heptane. Finally, it was vacuum dried at
room temperature affording 7 as a needle-shaped white crystal (yield 2.3 g (79%)).
1H NMR (DMSO-d6, ppm): 9.0 (s, 2H, aromatic); 8.4 (d, 2H, aromatic); 8.3 (d,
2H, aromatic).
P1. 10 mL of chloroform and 1.1 g (2.1 mmol) of 4 were stirred in a 100 mL
3-neck-round flask and the solid was completely dissolved. 1.0 mL (7.2 mmol)
of triethylamine was added to the flask with vigorous stirring. 0.6 g (2.1 mmol) of
7 dissolved in chloroform was added. The polymerization took place for an hour.
After the polymerization, the solution was poured into 700 mL of methanol resulting
in a solid precipitate. The solid precipitate was isolated through filtration and
washed with water twice and in methanol three times. Then it was dried in a vacuum
oven for 24 hours at 50ꢀC. The P1 was light yellow and the yield was 0.9 g (59%).
P2. 10 mL of phosphorus oxychloride and 0.5 g (0.7 mmol) of P1 were put into a
50 mL 3-neck-round flask with vigorous stirring. The temperature was raised to
100ꢀC and the reaction was maintained for 24 hr. After the reaction, the flask was
cooled to room temperature and the solution was slowly poured into 500 mL of
ice water resulting in the formation of a solid precipitate. The solid precipitate
was isolated by filtration and washed with water twice and with acetone respectively
1
and dried in vacuum at 50ꢀC. The P2 was yellow-colored (yield 0.4 g (80%)). H
NMR (DMSO-d6, ppm): 8.8-8.5 (d, 4H, aromatic); 7.8 (d, 2H, aromatic); 6.7-6.5
(d, 2H, aromatic); 4.1 (t, 4H, OCH2); 2.0-1.3 (broad, 32H, alkyl); 0.9 (t, 6H, CH3).
Ion Recognition Properties
The P2 was dissolved in chloroform and the concentration was varied depending on
the metal ion used. To analyze the polymer solution’s light absorption property, 1 cm
cuvette cells were used to test for the path length of light. To obtain the absorption
spectrum, 3 mL of the polymer solution was used and the measured wavelength
range was 250–700 nm. The same cuvette cells and the same volume of solution were
used to study the absorption properties of the polymer solution as well as to study
the fluorescence properties of the polymer solution.

Conjugated Polymer for Metal Ion Sensing
47
The change in optical property due to the formation of a polymer-metal complex
compound was measured within the 250–700 mn range for absorption spectrum and
357–700 nm range for fluorescent spectrum. The metal ions used were Fe3þ, Cu2þ
,
Co2þ, Ni2þ, Cr3þ, Zn2þ, Cd2þ, Al3þ, and Mg2þ
.
Results and Discussion
Heterocyclic amines with 2,20-bipyridine exhibit two important features. The first
one is related to the fact that the unshared electron pair can react separately and this
is known as ‘p-deficiency.’ The second feature is that such unshared electron pairs
act as ligands that can form chelation with various metal ions [16]. Since the dis-
covery of bipyridyl ligand in the late 19th century, it has been widely used for the
coordinate bonding of metal ions. It has been proved that the chelation between
metal ions with bipyridyl groups can alter the UV-vis and the fluorescent spectra.
Also, theoretically, the two pyridyl rings can form a dihedral angle of 20ꢀ near the
molecules. However, the chelation between such molecules and metal ions result in
more planar bipyridyl ring conformation. It has been found that such chelation will
eventually increase the conjugated length of the molecule resulting in red shift within
the peak absorption wavelength in the UV-vis spectrum [17].
Regarding the design of the P2 molecular structure, 2,20-bipyridyl rings were
introduced to give ion recognizing abilities using ionochromic effect. The 2,20-bipyridyl
rings were introduced to make the polymer into a effective conjugated structure thus
giving it a signal amplification and therefore increase it’s sensitivity towards metal ions.
Finally, by incorporating alkoxy groups into the main chain of the polymers, it was
possible to enhance the solubility allowing it to be applied to more diverse fields.
In this study, the synthesis of conjugated polymers with 1,3,5-oxydiazoles was
achieved through condensation polymerization of dihydrazide radical monomer
(4) and diacid chloride monomer (7) to produce a polymer precursor (P1). Then
the intermediate polymer was cyclized into P2. The general method of cyclization
was related to dehydration in hydrazide to form oxydiazole compound using phos-
phorous oxychloride. The didodecyloxy group present in the side chain improved the
solubility and therefore showed complete dissolution of P2 in chloroform, DMF,
and DMSO, on the while P2 was not soluble in THF and acetone. The synthetic
scheme of the monomer for the polymer is described in Scheme 1.
1
The compounds for monomer synthesis and P2 were analyzed using H NMR
and they were in good agreement with our expectation. P1, that has a hydrazide
structure in the main chain, did not dissolve due to the intermolecular bonding
1
and therefore could not be analyzed by the H NMR. The KBr pellet was used to
check the cyclization by studying the IR spectrum of precursor polymer P1 and
cyclized polymer P2. Figure 1(a) and (b) show the IR spectra of P1 and P2 respect-
ively. In the aforementioned IR spectrum, the characteristic band of hydrazide
ꢁ1
(ꢁCONHNHCOꢁ) was shown at 1680 cmꢁ1 (amide C O) and 3250 cm (amide
=
NꢁH). However, in the spectrum of P2, as a result of cyclization, the bands disap-
peared from the spectrum. This leads to the conclusion that hydrazide in P1 was
successfully cyclized as to give 1,3,4-oxadiazole structures. Also the observation
of disappearance of NH proton signals of hydrazide in H NMR spectrum of P2
confirms the aforementioned conclusion.
Thermogravimetric analysis was carried out by heating to 900ꢀC under the
nitrogen flow (Fig. 2). Through this thermogram it can be known that compound
1

48
Y.-S. Kim et al.
Scheme 1. Synthesis of monomers and polymers.
Figure 1. Infrared spectra of precursor polymer (a) P1 and (b) P2.

Conjugated Polymer for Metal Ion Sensing
49
Figure 2. TGA thermograms of the precursor polymer P1 (solid) and P2 (dotted) under
nitrogen atmosphere.
thermal decomposition temperature (onset Td) of P1 was found to be 482.3ꢀC and
that of P2 to be 592.4ꢀC. As can be seen on the TGA thermogram, the polymer with
oxadiazole structure showed significantly increased the decomposition temperature.
It can be observed that the decomposition temperature P2 is much higher than that
of P1 and it conforms that the decomposition temperature of main-chain oxadiazole
polymers is located between 400–600ꢀC. This predicts that as 1,3,4-oxadiazole poly-
mers can be used as heat-resistant materials. Glass transition temperature (Tg) and
melting temperature (Tm) were not found in DSC measurement showing that the
polymers are amorphous.
GPC revealed that number-average molecular weight (Mn) of P1 was found to
be 5,210 and weight-average molecular weight (Mw) was 9,330. Mn of P2 was found
to be 4,770 and Mw to be 8,920. Thus, it can be thought that there was a slight
decrease in the molecular weight through cyclization.
UV-vis spectrum of P2 showed absorption maximum (kmax) at 337 nm with a
shoulder at approximately 360 nm in the chloroform. When excited at 337 nm, it
showed a emission maximum at 425 nm and a band-edge reached to approximately
600 nm. Figure 3 illustrates the absorption and fluorescence spectra of P2 solution in
chloroform.
In order to study the metal-recognition ability of P2, various amounts of metal
ions were continuously added into the solution to investigate the changes in the
absorption and fluorescence spectra. Figure 4 shows the change of the UV-vis spec-
trum in relation to the addition of ferric nitrate (4.0 ꢂ 10ꢁ5 M) dissolved in methanol.
In the spectrum, as the concentration Fe3þ within the polymer solution increased
there was no change in the absorption wavelength of P2. However, the overall
absorption was remarkably increased. This linearly proportional increase in absor-
bance is due to the increase in the formation of polymer-metal complex with the
increase of Fe3þ ions within the polymer solution. Therefore, it can be concluded
that P2 is an efficient candidate for an ion-recognizing material quantitatively and
qualitatively toward Fe3þ
.

50
Y.-S. Kim et al.
Figure 3. Absorption (solid) and emission spectra (dotted) of the P2 solution in chloroform
(excitation wavelength 337 nm).
Similarly, when Cu2þ ion is added to the P2 in chloroform solution to a variable
concentration, the absorption in UV-vis spectrum increases. However, the extent of
the increament was smaller compared to that of Fe3þ. Figure 5 illustrates the change
in UV-vis spectrum of the solution when cupric sulfate (4.0 ꢂ 10ꢁ5 M) solution
dissolved in methanol is added. Similar to the case with Fe3þ ion, Cu2þ ion can alter
the conformation structure of P2.
Figure 6 illustrates the change in UV-vis spectrum due to the addition of cobalt
(II) chloride hexahydrate (1.0 ꢂ 10ꢁ6 M) in methanol into P2 solution. This spectrum
shows some difference from those of Fe3þ and Cu2þ ions in that the absorbance
Figure 4. Absorption spectra of the P2 solution in chloroform (6.0 ꢂ 10ꢁ4 M) at room
temperature upon addition of Fe3þ. [Fe3þ] ¼ 0; 0.40; 0.80; 1.20; 1.60; 2.00; 2.40; 2.80; 3.20;
3.60; 4.00 ꢂ 10ꢁ4 M.

Conjugated Polymer for Metal Ion Sensing
51
Figure 5. Absorption spectra of the P2 solution in chloroform (6.0 ꢂ 10ꢁ4 M) at room
temperature upon addition of Cu2þ. [Cu2þ] ¼ 0; 0.40; 0.80; 1.20; 1.60; 2.00; 2.40; 2.80; 3.20;
3.60; 4.00 ꢂ 10ꢁ4 M.
linearly decreases. This relationship reveals that this polymer solution carries both
the selectivity and the sensitivity that is needed for it to be used as an ion-recognition
material. Nevertheless, in the case with other metal ions, that is with Ni2þ, Cr3þ
Zn2þ, Cd2þ, Al3þ, and Mg2þ the optical changes were negligible.
,
For the purpose of diversifying the optical signals in response to molecular
recognition, changes in the fluorescent spectrum of the polymer molecule recognition
material and metal ion complex compound was measured. Figure 7 compares the
Figure 6. Absorption spectra of the P2 solution in chloroform (7.0 ꢂ 10ꢁ4 M) at room
temperature upon addition of Co2þ. [Co2þ] ¼ 0; 0.10; 0.20; 0.30; 0.40; 0.50; 0.60; 0.70; 0.80;
0.90 ꢂ 10ꢁ5 M.

52
Y.-S. Kim et al.
Figure 7. Fluorescence quenching of the P2 solution in chloroform (8.65 ꢂ 10ꢁ9 M) by
addition of various metal cation. f0 corresponds to the fluorescence intensity of P2 solution
without metal ion and f corresponds to the fluorescence intensity of the P2 solution with
metal ion.
fluorescence quenching depending on the concentration of various metal ions.
Increasing Fe3þ, Cu2þ, and Co2þ ion concentration to P2 polymer solution it can
be seen that the fluorescence quenching took place proportionally. There was no
change in the emission wavelength and only the decrease in the fluorescent intensity
at 425 nm was observed. It was found that the most significant quenching was
observed in the case of copper ion.
Such changes in fluorescence intensity are due to the conformation changes in
the bipyridyl groups due to the metal-bipyridyl complex formation in the polymer
main chain. Such conformation change in the bipyridyl group is an important fea-
ture because when the metal-ligand forms a complex, the electron density in the
bipyridyl group as well as the electron conductivity changes. Through the optical
characteristics (absorbance and fluorescence) measured through the complex formed
between the polymer material and the metal ion, it is confirmed that P2 is a material
that can recognize metal ions such as Fe3þ, Cu2þ, and Co2þ ions.
Conclusion
To obtain a polymer that can recognize ions, a fluorescent conjugated polymer con-
taining bipyridine and oxydiazole was synthesized. Oxadiazole units were introduced
by cyclization of their precursot hydrazide group and due to the long alkoxy side
chain the solubility was improved. Studying the absorption spectrum of the polymer,
there are significant changes in the absorbance depending on the type of metal ion.
The polymer has emission wavelength of 425 nm and therefore shows a blue fluores-
cence. Depending on the concentration of metal ions the level of fluorescence
quenching varied, presumably due to metal ion interaction with bipyridine ligand.
Therefore, the fluorescent conjugated polymers P2 can possibly be used as a metal
ion-detecting material.

Conjugated Polymer for Metal Ion Sensing
53
Acknowledgment
Financial support from the National Research Foundation (NRF) funded by the
Korea Government (MEST) is gratefully acknowledged (No. R01-2007-000-10740-0
and 2009-008146).
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