Synthesis and chemosensory properties of two-arm truxene-functionalized conjugated polyfluorene containing terpyridine moiety

Article abstract of DOI:10.1039/c6ra15965f

We report the responsive fluorescence chemosensory phenomena of a truxene-functionalized conjugated polymer (P1) with pendant terminal terpyridine (tpy) groups as receptors for metal ions synthesized via a Suzuki polymerization reaction. We examined the s

Full text of DOI:10.1039/c6ra15965f

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Synthesis
and
chemosensory
conjugated
properties
of
twoꢀarm
containing
truxeneꢀfunctionalized
terpyridine moiety
polyfluorene
PoꢀChih Yang*, HuaꢀWen Wen, ChihꢀWei Huang and YiꢀNing Zhu
Department of Chemical Engineering and Materials Science, Yuan Ze University,
ChungꢀLi, Taoyuan City 32003, Taiwan
* Corresponding author. Tel.: +886 3 4638800; fax: +886 3 4559373.
Eꢀmail address: pcyang@saturn.yzu.edu.tw (P.ꢀC. Yang).
1

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Graphical abstract
Purple
λex = 300 nm
λex = 300 nm
λem= 393 nm
Dark
C6H13
C6H13
C6H13
C6H13
C3H7
C3H7
C3H7
C3H7
C3H7
C3H7
C3H7
C3H7
C3H7
C3H7
C3H7
C3H7
Fe3+
N
N
Fluorescent
quenching
Strong
fluorescent
N
N
N
N
Fe3+
2

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ABSTRACT
We report the responsive fluorescence chemosensory phenomena of
a
truxeneꢀfunctionalized conjugated polymer (P1) with pendant terminal terpyridine (tpy)
groups as receptors of metal ions synthesized through Suzuki polymerization. We
examined the structural effect of tpy units on the sensory characteristics of fluorescent
chemosensors. The weightꢀaverage molecular weight (Mw) of P1 was 1.08
×
104
g/mol, with the corresponding polydispersity index being 2.25. P1 exhibited high
o
thermal stability with the thermal decomposition temperature being 334.6 C at 5%
polymer weight loss. Photoluminescence titrations demonstrated that P1 exhibited
high sensing ability to Fe3+ ions, with a Stern–Volmer constant of 1.14
×
106 Mꢀ1. The
limit of detection of Fe3+ was estimated at 2.13 10ꢀ7 M. The first stepwise
×
association constant (Ka1) for the P1/Fe3+ complex was 4.48 × 105 Mꢀ1. The
fluorescence of the P1 solution that was quenched by Fe3+ ions recovered on the
addition of trace CNꢀ anions because of the considerably high stability constant of the
CNꢀ–Fe3+ complex. Our results suggest that the synthesized polymer is a promising
material for chemosensory applications.
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Introduction
In recent decades, the development of conjugated polymers has attracted increasing
attention, because of their use as highly sensitive fluorescent chemosensors for
sensing various analytes, measuring pH, and detecting metal ions and biological species
in environmental applications by applying color or fluorescence intensities.1ꢀ8
Fluorescent chemosensors generally contain three components: (1) a receptor, which is
a sorting or recognition site for selecting analytes reliably; (2) a fluorophore, the
luminescent properties of which should be changed completely after being combined
with the target substance; and (3) an appropriate linker, which couples the two parts.9
Fluorescent chemosensors offer several crucial advantages over lowꢀmolecularꢀweight
compounds. For instance, the chemical signals that are converted into electronic or
optical signals when these conjugated polymers bind with an analyte can be
transformed and enhanced effectively.10 Additionally, the fluorophore of a conjugated
polymer used as a fluorescent chemosensor is always bonded at the conjugated
backbone, along which the excitons can diffuse easily, resulting in the fluorescence
intensity and bathochromic or hypsochromic shifts of fluorescence wavelengths of
these polymers changing more markedly.11ꢀ15 To date, series of conjugated polymers
have been synthesized to detect cations, anions, and pH by incorporating specific
receptors in polymers such as alkyl ethers,16 crown ethers,17 quinolones,18
bipyridines,19,20 and terpyridines (tpys).21,22
The 5Hꢀdiindeno[1,2ꢀa:1’,2’ꢀc]fluorine (truxene) unit, a C3h symmetric polycyclic
polyarene with a rigid planar πꢀconjugated configuration, has gained considerable
interest and been developed in the past decade as an optoelectronic functional
template in the fields of organic lightꢀemitting diodes, organic photovoltaics,
transistors, and chemosensors.23 The truxene core is particularly suitable as a scaffold
because its extended πꢀdelocalized system can cause a substantial shift in the absorption
spectrum toward the visible region. Because of their dπ–pπ* backꢀbonding of the metal
ions to pyridines and a chelation effect useful for multinuclear supramolecular
construction, 2,2’;6’,2’’ꢀtpy units have a high binding affinity toward transitionꢀmetal
ions.24,25 These supramolecular complexes between the tpy ligands and metal ions
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have been thoroughly investigated because of their relevant optical, electronic and
magnetic properties.26ꢀ28 Many studies have investigated tpy units as recognition sites,
and it has been widely demonstrated that the choice of ligands has a marked influence
on the detection of metal ions in biological and environmental systems.29,30 Combining
these fluorophores consisting of truxene and tpy units affords a new platform for
developing metallodendrimers and starꢀshaped macromolecules. However, thus far,
only a few studies have reported on these molecules, whose structures contain truxene
and tpy units.31ꢀ33 Pei et al.31 prepared a series of linear and starꢀshaped rigid
conjugated tpy ligands containing truxene or fluorene as the core with various
linkages through coupling reactions. Additionally, their findings on the involved
photophysical properties indicates that these compounds emit strong blue fluorescence
in solutions, thereby providing potential for materials such as the hosts for
constructing novel functionalized metallic materials in examining energy and
electronꢀtransfer processes.
In this work, we used Suzuki coupling polymerization to synthesize a novel rigid
linear truxeneꢀfunctionalized conjugated copolymer with pendant tpy groups (P1). We
examined the structural effect of the tpy groups on the sensory characteristics of
fluorescent chemosensors. Although many studies have investigated conjugated
polymers carrying tpy units as recognition sites,24,25 research on linear truxeneꢀbased
conjugated polymers with tpy recognition units is lacking. In contrast to previous
studies, our contributions differ in that P1 benefits from the strong conjugation and
luminescence properties of the asymmetric twoꢀarmꢀsubstituted truxene monomer (M1)
to yield enhanced sensing ability when mediated with metal ions. In this study, we
found that P1 demonstrated a highly selective response and rapid, sensitive recognition
to Fe3+ with a marked fluorescence change from bright purple to dark in the THFꢀH2O
mixture. The Stern–Volmer constant (Ksv) and limit of detection (LOD) were 1.14
Mꢀ1 and 2.13 10ꢀ7 M, respectively. In addition, the resulting P1ꢀFe3+ complex
×
106
×
exhibited a markedly selective fluorescence restoration with cyanide ions (CNꢀ), making
this polymer a promising material for highꢀpotential chemosensory applications.
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Experimental
Materials
Synthetic routes for the truxeneꢀbased monomer and polymer are shown in Schemes 1
and 2. The terpyridineꢀfunctionalized compound
4’ꢀ(4ꢀbromophenyl)ꢀ2,2’:6’,2”ꢀterpyridine (1), and the truxeneꢀfunctionalized
compounds,
5Hꢀdiindeno[1,2ꢀa:1’,2’ꢀc]fluorene
(3)
and
5,5,10,10,15,15ꢀhexapropylꢀ10,15ꢀdihydroꢀ5Hꢀdiindeno[1,2ꢀa:1’,2’ꢀc]fluorene
(4)
were synthesized following the processes reported previously.34ꢀ37 Tetrahydrofuran
(THF) and toluene were purified and distilled from sodium prior.
N,Nꢀdimethylformamide (DMF) was dried with appropriate drying agents, calcium
hydride or sodium, then distilled under reduced pressure and stored over 4 Å
molecular sieves before use. 1ꢀBromopropane (Aldrich, 98.5%), 3ꢀphenylpropionic
acid (Acros, 99.0%), bromine (Acros, 99.8%), bis(pinacolato)diboron (B2Pin2) (Acros,
95.0%), Pd(dppf)2Cl2 (Alfa, 99.0%) and other reagents were purchased from
commercial Chemical Co. and used without further purification.
Measurements
All new compounds were identified by NMR and elemental analysis (EA). NMR
spectra were recorded on a Bruker AMXꢀ500 (1H NMR: 500 MHz, 13C NMR: 125
MHz) spectrometer with CDCl3 as solvent, and chemical shifts (δ) were reported in
ppm using tetramethylsilane (TMS) as an internal standard. Elemental analysis was
performed on a Heraeus CHNꢀO rapid elemental analyzer. Fast Atom Bombardment
mass spectra (FABMS) were obtained on a JEOL JMSꢀ700 mass spectrometer.
Weightꢀaverage molecular weight (Mw) and polydispersity index (PDI) of polymer
were measured with a gel permeation chromatograph (GPC), model CR4A from
Shimadzu, using tetrahydrofuran (THF) as an eluent and the rate of elution was 1.0 ml
minꢀ1; the instrument was calibrated with polystyrene standards (1000–136000 g/mol).
Thermal analysis was performed using a differential scanning calorimeter (Perkin
Elmer DSC 7) at a scanning rate of 20 K/min under nitrogen atmosphere.
Thermogravimetric analysis (TGA) was performed under nitrogen atmosphere at a
6

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heating rate of 20 K/min using a Perkin Elmer TGAꢀ7 thermal analyzer. UVꢀvis
absorption spectra were measured with a Jasco Vꢀ670 spectrophotometer.
Fluorescence properties were detected with an OBB Quattro II fluorescence
spectrophotometer. Fluorescence quantum yield (ΦPL) of P1 in solution were estimated
at room temperature with poly(9,9ꢀdihexylfluorene) (PF) as the standard (ΦPL = 1.0).
Cyclic voltammograms (CV) were recorded with a voltammetric analyzer (model
CVꢀ50W from BAS) at room temperature under nitrogen atmosphere with a scanning
rate of 100 mV/s. The measuring cell comprised platinum wire as the working
electrode, Ag/AgNO3 electrode as the reference electrode, and platinum wire
electrode as the auxiliary electrode. The electrodes were immersed in acetonitrile
containing 0.1 M (nꢀBu)4NClO4 as electrolyte. All the computational calculations
were performed at B3LYP/6ꢀ31G* level using density functional theory (DFT) with
Gaussian 09 program.38
Synthesis of intermediates and monomer
Synthesis of 4’ꢀ(4ꢀbromophenyl)ꢀ2,2’:6’,2”ꢀterpyridine (1). Yield: 40.5%. Tm =
162.0 oC. 1HꢀNMR (CDCl3, 500 MHz): δH (ppm) = 7.49 (t, 2H), 7.80 (d, 2H), 7.92 (d,
13
2H), 8.01 (t, 2H), 8.75 (d, 4H), 8.81 (s, 2H). C NMR (CDCl3, 125 MHz, δ in ppm):
118.7, 121.5, 123.5, 124.0, 129.0, 132.2, 137.1, 149.1, 156.0. FABMS (m/z) 388 M+.
Synthesis
of
4’ꢀ(4ꢀ(4,4,5,5ꢀtetramethylꢀ1,3,2ꢀdioxaborolanꢀ2ꢀyl)phenyl)ꢀ
2,2’:6’,2’’ꢀterpyridine (2). A mixture of 1 (0.39 g, 1.0 mmol), bis(pinacolato)diboron
(B2Pin2) (0.30 g, 1.2 mmol), K2CO3 (0.69 g, 5.0 mmol), Pd(dppf)2Cl2 (43 mg, 0.070
mmol) and DMF (30 mL) was carefully degassed. The mixture was stirred for 24 h at
o
90 C under N2. Water (400 mL) was added, and the crude product was filtered and
washed with water. After dried, the crude product was dissolved in chloroform,
washed with a saturated solution of EDTA and purified by recrystallized from ethanol
1
to afford 2 as a white solid (0.24 g, 55.2%). H NMR (CDCl3, 500 MHz): δH (ppm) =
1.36 (s, 12H), 7.34 (t, 2H, J = 4.0 Hz), 7.83ꢀ7.92 (m, 6H), 8.65 (d, 2H, J = 8.0 Hz),
8.70ꢀ8.74 (m, 4H). 13C NMR (CDCl3, 125 MHz, δ in ppm): 21.5, 83.3, 118.7, 121.6,
123.5, 124.0, 129.1, 132.2, 137.2, 149.1, 156.1. FABMS (m/z) 435 M+.
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Synthesis of 2ꢀbromoꢀ5,5,10,10,15,15ꢀhexapropylꢀ10,15ꢀdihydroꢀ5Hꢀdiindeno
[1,2ꢀa:1’,2’ꢀc]fluorene (5). To a stirred solution of 4 (0.59 g, 1.0 mmol) in
chloroform (20 mL), a solution of bromine (0.08 g, 0.5 mmol) in 10 mL of chloroform
was added dropwise at room temperature. After 12 h, the mixture was washed with a
saturated sodium thiosulfate solution and brine. After removal of the solvent, the
1
crude product was purified by recrystallized from ethanol to afford 5 (30.2%). H
NMR (CDCl3, 500 MHz): δH (ppm) = 0.51 (m, 30H), 2.00ꢀ2.11 (m, 6H), 2.73ꢀ2.94 (m,
6H), 7.36ꢀ7.42 (m, 5H), 7.44ꢀ7.51 (m, 3H), 8.32ꢀ8.40 (m, 3H). 13C NMR (CDCl3, 125
MHz, δ in ppm): 14.6, 17.3, 39.3, 56.2, 121.2, 124.7, 125.7, 126.0, 126.4, 129.5, 130.1,
137.6, 138.4, 138.8, 140.3, 145.1, 154.0, 156.4. FABMS (m/z) 672 M+.
Synthesis
of
4’ꢀ(4ꢀ(5,5,10,10,15,15ꢀhexapropylꢀ10,15ꢀdihydroꢀ5Hꢀ
diindeno[1,2ꢀa:1’,2’ꢀc]fluorenꢀ2ꢀyl)phenyl)ꢀ2,2’:6’,2’’ꢀterpyridine (6). A mixture
of 2 (0.87 g, 2.0 mmol), 5 (1.35 g, 2.0 mmol), tetrakis(triphenyl phosphine)palladium
(Pd(PPh3)4) (69 mg, 0.06 mmol), K2CO3 (2M, 6 mL) and toluene (20 mL) was
carefully degassed. The mixture was stirred for 12 h at 90 oC under N2. After removal
of the solvent, the crude product was purified by recrystallized from ethanol/CH2Cl2
1
(1:5, v/v) to give 6 as a white solid (1.14 g, 63.2%). H NMR (CDCl3, 500 MHz): δH
(ppm) = 0.50 (m, 30H), 1.92ꢀ2.23 (m, 6H), 2.65ꢀ3.00 (m, 6H), 7.16ꢀ7.61 (m, 11H),
7.67ꢀ7.91 (m, 6H), 8.03ꢀ8.22 (m, 2H), 8.59 (s, 2H), 8.61ꢀ8.76 (d, 4H). 13C NMR
(CDCl3, 125 MHz, δ in ppm): 14.7, 17.7, 38.3, 46.4, 118.1, 120.9, 124.2, 125.9, 126.8,
127.9, 128.4, 130.5, 134.9, 135.9, 137.0, 139.9, 140.8, 141.1, 147.8, 148.3, 149.2, 152.1,
155.4, 156.1. FABMS (m/z) 901 M+.
Synthesis of 4’ꢀ(4ꢀ(7,12ꢀdibromoꢀ5,5,10,10,15,15ꢀhexapropylꢀ10,15ꢀdihydroꢀ
5Hꢀdiindeno[1,2ꢀa:1’,2’ꢀc]fluorenꢀ2ꢀyl)phenyl)ꢀ2,2’:6’,2’’ꢀterpyridine (M1). To a
stirred solution of 6 (0.45 g, 0.5 mmol) in chloroform (15 mL), a solution of bromine
(0.32 g, 2.0 mmol) in 10 mL of chloroform was added dropwise at room temperature.
After 12 h, the mixture was washed with a saturated sodium thiosulfate solution and
brine. Removal of the solvent gave a yellow solid. Recrystallization from
o
1
ethanol/CH2Cl2 (1:5, v/v) afforded a white solid (0.18 g, 34.0%). Tm = 168.6 C. H
NMR (CDCl3, 500 MHz): δH (ppm) = 0.43ꢀ0.56 (m, 30H), 1.92ꢀ2.12 (m, 6H),
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2.65ꢀ2.89 (m, 6H), 7.26ꢀ7.61 (m, 11H), 7.84ꢀ8.19 (m, 6H), 8.60 (s, 2H), 8.62ꢀ8.76 (d,
4H). Anal. Calcd. (%) for C66H65Br2N3: C, 74.78; H, 6.18; N, 3.96. Found: C, 74.92; H,
6.22; N, 4.01. 13C NMR (CDCl3, 125 MHz, δ in ppm): 14.7, 17.6, 38.3, 46.4, 118.1,
120.9, 124.1, 125.9, 126.8, 127.9, 130.5, 134.9, 135.9, 137.1, 139.9, 140.7, 141.1, 147.8,
148.3, 149.2, 152.1, 155.4, 156.1. Anal. Calcd. (%) for C66H65Br2N3: C, 74.78; H, 6.18;
N, 3.96. Found: C, 74.84; H, 6.09; N, 4.01. FABMS (m/z) 1060 M+.
Synthesis of conjugated polymer
Synthesis
of
poly[2,7ꢀ(5,5,10,10,15,15ꢀhexapropylꢀ10,15ꢀdihydroꢀ5Hꢀ
diindeno[1,2ꢀa:1’,2’ꢀc]fluorene)ꢀaltꢀ4’ꢀphenylꢀ2,2’:6’,2’’ꢀterpyridine] (P1). The
conjugated polymer P1 was prepared using palladiumꢀcatalyzed Suzuki coupling
o
reactions of monomers A/M1 in toluene at 90 C using Pd(PPh3)4 as the catalyst. A
mixture of A (0.29 g, 0.5 mmol), M1 (0.53 g, 0.5 mmol), Pd(PPh3)4 (49 mg, 0.04
mmol), K2CO3 (2M, 2 mL) and toluene (7 mL) was carefully degassed. The mixture
o
was stirred for 72 h at 90 C under N2. Then, bromobenzene (0.08 g, 0.5 mmol) and
phenylboronic acid (0.06 g, 0.5 mmol) were added for the end capping by refluxing
subsequently for 6 h each. The mixture was cooled to room temperature. After
removal of the solvent, the residue was filtered in CH3OH (500 mL) to precipitate out
the polymer. The resulting precipitate was placed in a Soxhlet apparatus and extracted
with refluxed CH3OH for 72 h and then was dried in vacuum to give 0.23 g (44.3%).
1
Mw = 1.08 × 104 g/mol, PDI = 2.25. H NMR (CDCl3, 500 MHz): δH (ppm) =
0.35ꢀ0.98 (br, CH3 and CH2), 1.76ꢀ2.44 (br, CH2), 2.69ꢀ3.12 (br, CH2), 7.27ꢀ9.10 (br,
ArꢀH). Anal. Calcd. (%) from feed (C25H32)(C66H65N3): C, 76.31; H, 6.78; N, 2.94.
Found: C, 75.84; H, 6.54; N, 2.82.
Fluorescent titration with metal ions
Fluorescent titration experiments were performed in THF solutions. Stock solutions (1.0
× 10ꢀ3 M) of the chloride or nitrate salts of Ag+, Al3+, Ba2+, Ca2+, Fe2+, Fe3+, K+, Mg2+,
Mn2+, Ni2+, Pb2+, Li+, and Zn2+ in deionized water were prepared. Titrations were
performed by adding separately stock solutions to a test tube containing polymer
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solution. All optical measurements were conducted immediately after the test solutions
were prepared and thoroughly mixed. The final concentration of the polymer was 1.0 ×
10ꢀ6 M. The percentage of water in THF was approximately 1.0%. The Stern–Volmer
constant (Ksv) was estimated according to following equation:
(Io/I) = 1 + Ksv [Q]
(1)
where Io and I are the intensities of PL spectra without and with a quencher, respectively,
Ksv is the Stern–Volmer constant (quenching coefficient), and [Q] is the concentration of
the quencher ions. The stabilization of P1ꢀFe3+ complex (1.0 × 10ꢀ6 M in THF) was
ꢀ
2
2
−
ꢀ
−
−
studied in the presence of some anions, including F , Cl−, Br−, NO3 , SO4 , S , and CN
(2.0 × 10ꢀ5 M). The limit of detection (LOD) of P1 was calculated on the basis of
fluorescence titrations. To obtain the slope, the fluorescence emission at 393 nm was
plotted as a concentration of Fe3+. The LOD was calculated using the following
equation:
Limit of detection (LOD) = 3σ/S
(2)
where σ is the standard deviation of the blank signal, and S is the slope between the
fluorescence intensity versus [Fe3+].
Results and Discussion
Synthesis of intermediates and monomer
Scheme 1 outlines the synthetic routes of the tpyꢀfunctionalized monomer M1. The
bromoꢀfunctionalized compound 5, 2ꢀbromoꢀ5,5,10,10,15,15ꢀhexapropylꢀ10,15ꢀ
dihydroꢀ5Hꢀdiindeno[1,2ꢀa:1’,2’ꢀc]fluorene, was prepared through the bromination
reaction
of
compound
4
(5,5,10,10,15,15ꢀhexapropylꢀ10,15ꢀdihydroꢀ5Hꢀ
diindeno[1,2ꢀa:1’,2’ꢀc]fluorene) with bromine at room temperature. The crude product
was purified by recrystallized from ethanol to afford 5, thus creating compound 5 with
a
yield
of
30.2%.
We
prepared
4’ꢀ(4ꢀ(5,5,10,10,15,15ꢀhexapropylꢀ10,15ꢀdihydroꢀ5Hꢀdiindeno[1,2ꢀa:1’,2’ꢀc]fluorenꢀ
2ꢀyl)phenyl)ꢀ2,2’:6’,2’’ꢀterpyridine (6) in a 63.2% yield by using the Suzuki coupling
reaction
of
4’ꢀ(4ꢀ(4,4,5,5ꢀtetramethylꢀ1,3,2ꢀdioxaborolanꢀ2ꢀyl)phenyl)ꢀ
2,2’:6’,2’’ꢀterpyridine (2) with compound 5 in the presence of potassium carbonate at
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o
90 C. The reaction was performed using Pd(PPh3)4 as the catalyst. The target
monomer, 4’ꢀ(4ꢀ(7,12ꢀdibromoꢀ5,5,10,10,15,15ꢀhexapropylꢀ10,15ꢀdihydroꢀ5Hꢀ
diindeno[1,2ꢀa:1’,2’ꢀc]fluorenꢀ2ꢀyl)phenyl)ꢀ2,2’:6’,2’’ꢀterpyridine (M1), was
prepared in a procedure similar to that for compound 5, except that compound 6 was
used instead of compound 4, resulting in M1 in a 34.0% yield. The chemical
structures and constitutional composition of the synthesized monomer were confirmed
using proton nuclear magnetic resonance (1H NMR) spectroscopy. Fig. S1a shows the
1H NMR spectrum of M1 and the corresponding structural assignments. The
characteristic chemical shifts of δ = 8.62ꢀ8.76 (Ha) and δ = 8.60 ppm (Hb) were
attributed to the terpyridyl doublet and singlet proton signals in M1, respectively, and
those of δ = 2.65ꢀ2.89, 1.92ꢀ2.12 and 0.43ꢀ0.56 ppm were ascribed to the aliphatic
methylene (Hc and Hd) and methyl (He) groups of the truxene unit, respectively. 13C
NMR measurements (Fig. S2) were adapted to confirm the structure of the
intermediates 1 and 5. Fig. S3 and Fig. S4 show the FABMS (Fast Atom
Bombardment Mass Spectroscopy) mass spectra of two representative
tpyꢀfunctionalized intermediate 1 and monomer M1, respectively. In addition, the
chemical structures of the synthesized monomer were also confirmed using elemental
analysis.
Scheme 1
Synthesis and thermal properties of polymer
P1 was successfully synthesized from M1 and A through a palladiumꢀmediated
Suzuki coupling reaction (Scheme 2). Fig. S1b shows the 1H NMR spectrum of P1 in
CDCl3. The 1H NMR spectrum of P1 exhibited peaks at approximately 8.97ꢀ9.10 ppm,
which were assigned to shifts to the ortho and meta positions labeled Ha of the pyridine
unit, whereas the protons (Hb) were the two aromatic protons of the
2,2’:6’,2’’ꢀterpyridyl segment at 8.82ꢀ8.96 ppm. The other aromatic protons appeared at
1
7.27ꢀ8.54 ppm. Finally, the H NMR spectrum of P1 had the alkyl group peaks at
approximately 2.69ꢀ3.12, 1.94ꢀ2.38, 0.78ꢀ0.95 and 0.40ꢀ0.66 ppm assigned to the
aliphatic protons labeled Hc, Hd+e, Hf, and Hg+h. The weightꢀaverage molecular weight
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(Mw) of P1 was 1.08 × 104 g molꢀ1 with a corresponding polydispersity index of 2.25
(Table 1). The molar percentage of the tpyꢀfunctionalized monomer (M1) in P1 was
estimated at approximately 44.5% according to the integrated peak areas of the aliphatic
group of truxene (Hc and Hd) and the methylene protons of fluorene (He). The estimated
molar percentage of M1 in the polymer was lower than that of the feed (50.0%),
indicating that the lower percentage was attributed to the steric effect and
electron–deficient character of the tpy monomer, resulting in reduced monomer
reactivity. P1 exhibited high thermal stability with the thermal decomposition
o
temperature (Td) being 334.6 C at 5% polymer weight loss (Fig. 1). The residual
weight of P1 at 800 oC was approximately 61.2%, indicating high thermal stability.
Scheme 2, Figure 1, Table 1
Optical and electrochemical properties
Fig. 2 shows the absorption and PL spectra of P1 in THF (1.0 × 10ꢀ6 M) and in thin
films spinꢀcoated from THF solutions (10 mg/mL) with the corresponding data
summarized in Table 2. In THF, P1 exhibited the main absorption peaks at 284 and
309 nm, which resulted from a π–π* transition of the truxene units, consistent with a
finding reported in the literature.39 Another weak transition shoulder in P1 was
observed at approximately 363 nm, which was attributed to the intramolecular charge
transfer (ICT) between the truxene donor groups and the tpy acceptor, leading to the
observed ICT interaction and bathochromic shift.40,41 In the film state, the absorption
maximum of P1 was redꢀshifted (ca. 53 nm) relative to the solution state, resulting from
aggregation caused by intraꢀchain or interchain interactions. The fluorescence
maximum of P1 in THF was 393 nm. In the film state, the emission maximum was
situated at 433 nm, implying that excimers or exciplexes form in the film state. Table 2
lists the Stokes shift of P1 at 96 nm, and the large shift may result from structural
differences between the ground and excited states as well as migrated excitons in the
segments of the chain, where the ring rotates more flexibly.
Fig. S5 depicts the estimated cyclic voltammogram of P1 in CH2Cl2 at a scanning
rate of 100 mV/s, and Table 3 presents a summary of the electrochemical data. The
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highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital
(LUMO) energy levels were evaluated according to the equations EHOMO = –(Eox+ 4.8)
eV and ELUMO = EHOMO + Egopt, where Eox is the onset oxidation potential regarding
opt
the standard ferrocene/ferrocenium (FOC) redox system. The optical band gap (Eg
)
was determined based on the onset absorption wavelength. The onset oxidation peaks
of P1 were observed at approximately 0.27 and 0.55 V. We attributed these two
oxidation potentials of P1 to the charge delocalization of extended πꢀsystems of the
truxene and fluorene groups, respectively. The estimated molecular orbital levels of P1
are –5.07/–5.35 (HOMO/HOMOꢀ1) and –2.06 eV (LUMO). The optical bandgap
(Egopt) value for P1, determined according to the onset of absorption in the solution
state, was 3.01 eV (412 nm).
Figure 2, Table 2, Table 3
Theoretical calculations
To obtain further insight into the electronic effect of polymer on the molecular
geometry and electronic structure, density functional theory (DFT) calculations were
performed using the B3LYP/6ꢀ31G* method to predict the minimumꢀenergy
conformations and the frontier molecular orbitals of the model compounds of P1. As
presented in Fig. S6, the optimized structures of the model compound (i.e., repeating
unit n =1 in Scheme 2) revealed that the HOMO for P1 is nearly delocalized on the
whole backbone of the model compound, whereas the LUMO is mainly located on the
tpy unit, indicating the efficient charge separation of the model compound. According
to DFT calculations, the HOMO and LUMO values of P1 were ‒5.49 and ‒1.52 eV,
respectively. This also means that the theoretical bandgap (Egthe) value for P1 was
3.97 eV. This result was different from the data of the UVꢀvis absorption and CV
opt
experiments (i.e., Eg = 3.01 eV), for which we attributed the larger bandgap to the
small repeating unit number (i.e., n =1) of the model compound. Additionally, we
found that the model compound exhibited high coplanar arrangement, in which the
largest dihedral angle was only 36.8o between truxene and tpy units, indicating that
the efficient conjugation effect between truxene and tpy units was induced and leads
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to the effective ICT.
Ion sensing properties
The tpy groups are generally employed as ligands to combine metal cations for
generating complexes. Fig. 3a shows the effect of complexation with various metal
ions (Ag+, Al3+, Ba2+, Ca2+, Fe2+, Fe3+, K+, Mg2+, Mn2+, Ni2+, Pb2+, Li+, and Zn2+) on
the fluorescence spectra of P1 in THFꢀH2O solution. The fluorescence intensity of the
P1 solution decreased significantly on the addition of Fe2+, Fe3+, Ag+, Zn2+, or Ni2 ions
(Fig. 3a), indicating that the tpy chelating moiety in the side chain effectively
transferred energy from the conjugated polymer backbone to these cations, thus leading
to the fluorescence quenching of P1. In particular, P1 was quenched completely by
Fe3+ ions with an ion concentration of 5.0 × 10ꢀ5 M, indicating their high selectivity
toward this cation. The quenching mechanism of polymer can be attributed to the
photoinduced energy transfer occurring in a collision (dynamic quenching) between the
excited fluorophore and metal ions. We also attributed the quenching behavior to strong
cation binding between Fe3+ ions and the tpy chelating groups; the binding results
from the effective energy transfer migration between the receptors and polymer chains.
Thus, P1 can be used in polymer chemosensors for detecting metal ions.
Fig. 3b shows the photoluminescence response profiles (i.e., Io/I) of P1 in the
presence of various metal ions with an ion concentration of 5.0 × 10ꢀ5 M. The
emission colors of fluorescence responses to various metal ions were visible (Fig. 3d).
We found that P1 showed high sensitivity toward Fe3+ with a marked fluorescence
change from bright purple to dark in the THFꢀH2O mixture. These results indicated that
the shorter diameter (1.28 Å) and higher charge (1.83) of Fe3+ might lead to a higher
electronꢀaccepting capability and consequently more stable complexes. Moreover,
these two factors (i.e., diameter and charge) might play a vital role in determining the
coordination strength of Fe3+ ions accompanying tpy units.42 The five electrons (Fe3+:
d5 electron configuration) may be present as two orbitals occupied by pairs of
electrons and one having single occupancy, leading to the innerꢀorbital complex,
which was more stable than the other host/metal complexes.43 The ΦPL value of P1 in
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the presence of Fe3+ ions decreased by approximately 99.8% (i.e., from 1.82 to 0.6 ×
10ꢀ2). Moreover, adding Zn2+ ions induced a broad redꢀshifted emission in the range of
500ꢀ600 nm for P1, which was ascribed to the enhancement of the ICT processes.
Adding metal ions (Ag+, Al3+, Ca2+, Fe2+, Fe3+, K+, Mg2+, Ni2+, and Li+) into P1 led to
a new emission peak at approximately 601 nm, which is attributable to the
phosphorescence derived from the P1ꢀmetal ion complexes.44ꢀ46 These results also
indicated that these shifts were ascribed to the similar energy level of metal ions and
truxene triplets and to the spinꢀorbit coupling induced by the metal ions,45 or to the
formation of the polymeric selfꢀassembled structure by the metal ion coordination,
which hinders intramolecular rotations and motions of the core chromophore and
favors radiative deactivation of the luminescent excited state.46
Figure 3a, Figure 3b, Figure 3c, Figure 3d
To quantitatively evaluate the fluorescence quenching attained by adding Fe3+, the
fluorescence spectra and the response of P1 to titration with Fe3+ were studied in THF.
The emission intensities at 393 nm (i.e., I393 nm) gradually decreased with increasing
Fe3+ concentrations (Fig. 4a). The slope of the Stern–Volmer plot turned noticeably
upward (i.e., static quenching), resulting from strong tpy chelation to the transition
metal ions, when Fe3+ concentrations were greater than 2.0 × 10ꢀ5 M. Ksv for P1 in the
presence of low Fe3+ concentrations (below approximately 1.5 × 10ꢀ5 M) was 1.14 × 106
Mꢀ1. The estimated detection limit for P1 toward Fe3+ was as low as 2.13 × 10ꢀ7 M,
enabling P1 to be a selective and sensitive Fe3+ probe. As shown in Fig. 3b, a new
absorption peak at 580 nm appeared in P1 solution when it was titrated with Fe3+ ions.
The color of P1 solution under sunlight changed from colorless to purple (Fig. 3c),
suggesting that P1 can be employed as a useful probe for detecting Fe3+ ions. The first
stepwise association constant (Ka1) for the P1−Fe3+ complex was calculated following
the photoluminescence titration experiment.47,48 The Ka1 of this system for P1 was
4.48 × 105 Mꢀ1 at 393 nm (Fig. 4a).
Figure 4a, Figure 4b
Fig. 5 shows the specificity of P1 (1.0 × 10ꢀ6 M in THF) toward Fe3+ ions with
various cations (1.0 × 10ꢀ5 M in water). We examined whether P1 can retain the sensing
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response to Fe3+ in the presence of the competitive cations. The changes in the
enhanced ratio of fluorescence intensity (i.e., Io/I) of polymer were measured on the
addition of other metal ions. No responses were found, as shown by the black bars in
this figure. Adding 1.0 × 10ꢀ5 M of Fe3+ in P1 solutions then yielded 160ꢀ to 310ꢀfold
emission enhancements with and without other metal ions, respectively (Fig. 5, red
bars). In other words, the presence of other metal ions seemed to have no effect on the
response of P1 toward Fe3+. Therefore, the fluorescence interference titration indicated
that the Fe3+ꢀdependent fluorescence response of P1 was not affected by other transition
metal ions.
Figure 5
To determine whether the P1−Fe3+ complex can be used as an anion selective
ꢀ
2ꢀ
probe, the response of the complex toward anions (Fꢀ, Clꢀ, Brꢀ, NO3 , SO4 , S2ꢀ, and
CNꢀ) was investigated (Fig. 6a). The fluorescence response profiles (i.e., I/Io) of
P1−Fe3+ complexes in the presence of CNꢀ anions with a concentration of 2.0 × 10ꢀ5
M are provided in Fig. 6b. These data illustrate that the fluorescence intensity of the
P1−Fe3+ complex increased considerably on the addition of CNꢀ ions, whereas
complexation with other anions induced no obvious shift in the emission peak because
of the poor coordination of Fe3+ with these anions. However, in the presence of S2ꢀ,
the PL spectrum of the P1−Fe3+ complex exhibited a slight increase in the
fluorescence intensity. The complex demonstrated a markedly selective fluorescence
“turnꢀon” behavior exclusively with CNꢀ ions, indicating that CNꢀ ions could
effectively coordinate with Fe3+ instead of P1. This finding is attributed to the high
stability of the Fe3+–CNꢀ complex.49,50 Hence, the fluorescence intensities of P1 could
be revived by the transformation from the polymerꢀFe3+ complex (quenched) to the free
polymer (revived). When the concentration of added CNꢀ was 1.8 × 10ꢀ5 M, the
fluorescence intensity recovered by up to 48.6% of the original intensity, whereas
adding S2ꢀ led to a recovery of up to 6.5% of the original intensity (Fig. 7). In addition,
addition of other anions induced a recovery of approxiately 0.1% of the original
intensity, enabling P1 to be used as a sensitive CNꢀ sensor.
Figure 6a, Figure 6b, Figure 7
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Conclusions
In summary, a new truxeneꢀfunctionalized conjugated copolymer with tpy groups as
receptors (P1) was synthesized, and its corresponding optical and sensory
characteristics were evaluated. P1 exhibited high thermal stability with the thermal
o
decomposition temperature being 334.6 C at 5% weight loss. P1 exhibited high
sensitivity toward Fe3+ ions (“turnꢀoff”) with a Stern–Volmer constant (Ksv) of 1.14
106 Mꢀ1 and an LOD of 2.13 10ꢀ7 M. Furthermore, the polymerꢀFe3+ complex
×
×
demonstrated particularly selective fluorescence restoration (“turnꢀon”) abilities with
CNꢀ ions. These results indicate that P1 can meet the selective requirements for
environmental applications and be sufficiently sensitive to detect Fe3+ ions in
environmental water samples, including drinking water.
Acknowledgements
Financial support for this work by grants from the Ministry of Science and
Technology, Taiwan (Nos. 103ꢀ2221ꢀEꢀ155ꢀ072 and 105ꢀ2221ꢀEꢀ155ꢀ079) is
gratefully appreciated.
Notes and references
1 P. G. Del Rosso, M. J. Romagnoli, M. F. Almassio and C. A. Barbero, Sens. Actuators
B, 2014, 203, 612–620.
2 Y. Yang, G. Zhang, H. Luo, J. Yao, Z. Liu and D. Zhang, ACS Appl. Mater. Interfaces,
DOI: 10.1021/acsami.5b08078, 2015.
3 Y. Zhou, L. Tang, G. Zeng, C. Zhang, Y. Zhang and X. Xie, Sens. Actuators B, 2016,
223, 280–294.
4 O. S. Wolfbeis, Chem. Soc. Rev., 2015, 44, 4743–4768.
5 M. Saleem and K. H. Lee, RSC Adv., 2015, 5, 72150–72287.
6 S. Cao, Z. Pei, Y. Xu, R. Zhang and Y. Pei, RSC Adv., 2015, 5, 45888–45896.
7 L. Zhang, X. Lou, Y. Yu, J. Qin and Z. Li, Macromolecules, 2011, 44, 5186–5193.
8 X. Lou, Y. Zhang, S. Li, D. Ou, Z. Wan, J. Qin and Z. Li, Polym. Chem., 2012, 3,
17

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Page 18 of 30
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1446–1452.
9 Y. Long, H. Chen, H. Wang, Z. Peng, Y. Yang, G. Zhang, N. Li, F. Liu and J. Pei, Anal.
Chim. Acta., 2012, 744, 82–91.
10 Z. Chen, Q. Wang, X. Wu, Z. Li and Y. B. Jiang, Chem. Soc. Rev., 2015, 44,
4249–4263.
11 C.M. Darr, V. Korampally, B. Chen, K. Gangopadhyay, S. Gangopadhyay, Sens.
Actuators B, 2014, 202, 1088–1096.
12 A. C. Bhasikuttan and J. Mohanty, Chem. Commun., 2015, 51, 7581–7597.
13 L. Qin, B. Lu, J. Xu, G. Zhang and S. Zhang, RSC Adv., 2014, 4, 28368–28376.
14 C. Kaewtong, N. Niamsa, B. Pulpoka and T. Tuntulani, RSC Adv., 2014, 4,
52235–52240.
15 D. Mao, X. Liu, Q. Qiao, W. Yin, M. Zhao, J. M. Cole, J. Cui and Z. Xu, Analyst,
2015, 140, 1008–1013.
16 A. Balamurugan, V. Kumar and M. Jayakannan, Chem. Commun., 2014, 50,
842–845.
17 G. Xiang, L. Wang, W. Cui, X. An and L. Zhou, Sens. Actuators B, 2014, 196,
495–503.
18 H. Kim, G. R. You, G. J. Park, J. Y. Choi, I. Noh, Y. Kim, S. J. Kim, C. Kim and R. G.
Harrison, Dyes Pigm., 2015, 113, 723–729.
19 F. Jin, W. Shu, X. Yu, Y. Zhang, L. Sun, Y. Liu, D. Tao, H. Zhou and Y. Tian, Dyes
Pigm., 2015, 121, 379–384.
20 A. Bellusci, M. Ghedini, L. Giorgini, F. Gozzo, E. I. Szerb, A. Crispini and D.
Pucci, Dalton Trans., 2009, 7381–7389.
21 S. Jing, C. Zheng, S. Pu, C. Fan and G. Liu, Dyes Pigm., 2014, 107, 38–44.
22 Z. B. Zheng, S. Y. Kang, Y. Zhao, N. Zhang, X. Yi and K. Z. Wang, Sens. Actuators
B, 2015, 221, 614–624.
23 F. Goubard, and F. Dumur, RSC Adv., 2015, 5, 3521–3551.
24 M. Zheng, H. Tao, Z. Xie, L. Zhang, X. Jing and Z. Sun, ACS Appl. Mater.
Interfaces, 2013, 5, 1078–1083.
25 S. Karmakar, D. Maity, S. Mardanya and S. Baitalik, Dalton Trans., 2015, 44,
18

Page 19 of 30
RSC Advances
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18607–18623.
26 U. S. Schubert, H. Hofmeier and G. R. Newkome, Modern Terpyridine Chemistry,
WileyꢀVCH, Weinheim, Germany, 2006.
27 A. Wild, A. Winter, F. Schlütter and U. S. Schubert, Chem. Soc. Rev., 2011, 40,
1459–1511.
28 E. C. Constable, Chem. Soc. Rev., 2007, 36, 246–253.
29 P. Mahato, S. Saha, P. Das, H. Agarwalla and A. Das, RSC Adv., 2014, 4,
36140–36174.
30 Y. Zhou and J. Yoon, Chem. Soc. Rev., 2012, 41, 52–67.
31 S. C. Yuan, H. B. Chen, Y. Zhang and J. Pei, Org. Lett., 2006, 8, 5701–5704.
32 B. Ventura, A. F. Barigelletti, S. Diring and R. Ziessel, Inorg. Chem., 2010, 49,
8333–8346.
33 J. L. Wang, Y. T. Chan, C. N. Moorefield, J. Pei, D. A. Modarelli, N. C. Romano
and G. R. Newkome, Macromol. Rapid Commun., 2010, 31, 850–855.
34 S. K. Lee, D. H. Hwang, B. L. Jung, N. S. Cho, J. Lee, J. D. Lee and H. K. Shim,
Adv. Funct. Mater., 2005, 15, 1647–1655.
35 F. Dumur, C. R. Mayer, E. Dumas, F. Miomandre, M. Frigoli and F. Sécheresse, Org.
Lett., 2008, 10, 321–324.
36 X. Y. Cao, H. Zi, W. Zhang, H. Lu and J. Pei, J. Org. Chem., 2005, 70,
3645–3653.
37 J. Pei, J. L. Wang, X. Y. Cao, X. H. Zhou and W. B. Zhang, J. Am. Chem. Soc.,
2003, 125, 9944–9945.
38 Gaussian 09, Revision A.1, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E.
Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G. A.
Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A. F. Izmaylov, J.
Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J.
Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J. A.
Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K.
N. Kudin, V. N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A.
Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M.
19

RSC Advances
Page 20 of 30
View Article Online
DOI: 10.1039/C6RA15965F
Klene, J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.
E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L.
Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg,
S. Dapprich, A. D. Daniels, O. Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski,
and D. J. Fox, Gaussian, Inc., Wallingford CT, 2009.
39 Y. Wu, X. Hao, J. Wu, J. Jin and X. Ba, Macromolecules, 2010, 43, 731–738.
40 P. Leriche, A. Frère, A. Cravino, O. Alévêque and J. Roncali, J. Org. Chem., 2007,
72, 8332–8336.
41 Y. J. Cheng, S. H. Yang and C. S. Hsu, Chem. Rev., 2009, 109, 5865–5923.
42 J. E. House, Inorganic Chemistry, Academic press, Elsevier, Burlington, MA, 2008.
43 Y. Cui, Q. Chen, D. D. Zhang, J. Cao and B. H. Han, J. Polym. Sci. Part A: Polym.
Chem., 2010, 48, 1551–1556.
44 B. Du, D. Fortin and P. D. Harvey, Inorg. Chem., 2011, 50, 11493–11505.
45 B. Ventura, A. Barbieri, F. Barigelletti, S. Diring and R. Ziessel, Inorg. Chem., 2010,
49, 8333–8346.
46 A. Fermi, G. Bergamini, M. Roy, M. Gingras and P. Ceroni, J. Am. Chem. Soc., 2014,
136, 6395–6400.
47 M. Brzezinski and T. Biela, Macromolecules, 2015, 48, 2994–3004.
48 Z. Qu, H. Jin, Y. Guo, S. Li, H. Li, Y. Li, X. Wang and G. Yang, J. Phys. Chem. B,
2012, 116, 2048–2058.
49 Q. Zeng, P. Cai, Z. Li, J. Qin and B. Z. Tang, Chem. Commun., 2008, 1094–1096.
50 X. Lou, D. Ou, Q. Li and Z. Li, Chem. Commun., 2012, 48, 8462–8477.
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Br
N
N
N
Pd(dppf)2Cl2
O
O
KOH, NH4OH
EtOH
Br
N
+
B
N
K2CO3
N
N
O
CHO
1
2
C3H7
C3H7
C3H7
C3H7
CH2CH2COOH
C3H7 C3H7
C3H7 C3H7
PPA
Br2
BuLi
PPA
O
C3H7Br
CHCl3
C3H7
C3H7
Br
C3H7
C3H7
4
5
3
Br
C3H7
C3H7
C3H7
C3H7
Br
C3H7
C3H7
C3H7
C3H7
C3H7
C3H7
C3H7
C3H7
Br2
CHCl3
Pd(PPh3)4
+
2
5
N
N
6
N
N
N
N
M1
Scheme 1 Synthetic routes of terpyridineꢀsubstituted monomer (M1).
Br
C6H13
C6H13
C6H13
C3H7
C3H7
C3H7
C3H7
C6H13
O
O
n
Br
Pd(PPh3)4
+
B
B
O
O
C3H7
C3H7
C3H7
C3H7
C3H7
C3H7
C3H7
C3H7
A
N
N
N
N
N
N
P1
M1
Scheme 2 Synthetic routes of conjugated polymer (P1).
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100
90
80
70
60
50
200
400
600
800
o
Temperature ( C)
o
Fig. 1 TGA thermogram of P1 at a heating rate of 20 C minꢀ1 under nitrogen
atmosphere.
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1.0
0.8
0.6
0.4
0.2
1.0
0.8
0.6
0.4
0.2
300
400
500
600
Wavelength (nm)
Fig. 2 Normalized UVꢀvis absorption and PL spectra of P1 in THF solution (solid line)
and in film (dotted line).
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(a)
(b)
160
140
120
100
80
P1
Ba2+
Fe2+
Fe3+
Mn2+
Pb2+
Ni2+
3.0
2.5
2.0
1.5
1.0
0.5
0.0
Al3+
Ag+
Ca2+
K+
Li+
Mg2+
Zn2+
60
40
20
0
+
Al3
Mg2
+
+
+
+
Ca2
Fe3
+
Ni2
+
Ag+
+
Pb2
+
+
200
300
400
500
600
Li
K+
+
Zn2
Mn2
Fe2
Ba2
Wavelength (nm)
P1
(c)
P1 Li+ Mg2+ Al3+ K+ Ca2+ Mn2+ Fe3+ Fe2+ Ni2+ Zn2+ Ag+ Ba2+ Pb2+
(d)
Fig. 3 (a) Photoluminescence spectra, (b) PL response profiles, and images of P1 in
the presence of various cations under (c) sunlight and (d) UV excitation (λex = 300
nm). Concentration of polymer: 1.0 × 10ꢀ6 M in THF, concentration of metal ions: 5.0
× 10ꢀ5 M.
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(a)
400
300
200
100
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0
0
5
10
15
20
25
-6
3+
C
Fe
(10 mol/L)
300
400
500
Wavelength (nm)
600
(b)
0.40
0.32
0.24
0.16
0.08
0.00
400
500
600
700
800
Wavelength (nm)
Fig. 4 (a) Photoluminescence and (b) absorption spectra of P1 in the presence of
various concentrations of Fe3+ ions; Inset in (a): SternꢀVolmer plot of PL quenching
with various concentrations of Fe3+ ions. Concentration of polymer: 1.0 × 10ꢀ6 M in
THF.
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300
250
200
150
100
50
0
with Fe3+
without Fe3+
Al3+ Ag+ Ca2+ K+ Li+ Mg2+ Ba2+ Fe2+ Mn2+ Pb2+ Co2+ Ni2+ Zn2+
Fig. 5 Fluorescent quenching rate of P1 in the present of different cations with and
without Fe3+ ions in THF solution. The black bars represent the addition of the
appropriate metal ion (1.0 × 10ꢀ5 M in water) to a solution of polymer (1.0 × 10ꢀ6 M in
THF). The red bars represent the subsequent addition of Fe3+ (1.0 ×10ꢀ5 M in water) to
the former solution.
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RSC Advances
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DOI: 10.1039/C6RA15965F
(a)
P1
3.0
2.5
2.0
1.5
1.0
0.5
0.0
P1+Fe3+
P1+Fe3++CN-
-
P1+Fe3++SO42
P1+Fe3++NO3-
P1+Fe3++F-
P1+Fe3++Cl-
P1+Fe3++Br-
P1+Fe3++S2-
350
400
450
500
550
600
650
Wavelength (nm)
(b)
350
300
250
200
150
100
20
15
10
5
0
P1 +Fe3+ +Fe3+ +Fe3+ +Fe3+ +Fe3+ +Fe3+ +Fe3+ +Fe3+
CN_ NO3- F- Cl- Br- +S2-
SO42-
+
+
+
+
+
+
Fig. 6 (a) Photoluminescence spectra and (b) PL response profiles of P1–Fe3+ in the
presence of various anions.
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DOI: 10.1039/C6RA15965F
P1+Fe3+
3
2
1
0
P1+Fe3++0.1
P1+Fe3++0.3
P1+Fe3++0.6
P1+Fe3++1.2
P1+Fe3++3.0
P1+Fe3++6.0
P1+Fe3++9.0
µ
M CN-
µ
M CN-
µ
µ
M CN-
M CN-
µ
M CN-
µ
µ
M CN-
M CN-
M CN-
P1+Fe3++18.0
P1
µ
350
400
450
500
550
600
650
Wavelength (nm)
Fig. 7 Photoluminescence spectra of P1–Fe3+ in the presence of various
concentrations of CNꢀ anions.
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DOI: 10.1039/C6RA15965F
Table 1 Molecular weight and thermal properties of conjugated polymer
b
c
Polymer
Yield (%)
Mwa (×104) PDIa
Tg (oC)
Td (oC)
44.3
1.08 2.25
113.5
334.6
P1
a Mw and PDI of the polymer were determined by gel permeation chromatography using
polystyrene standards in THF. b Glass transition temperatures by DSC under N2 at a
heating rate of 20oC/min. c The temperatures at 5% weight loss.
Table 2 Optical electrochemical properties of polymer
a
a
b
b
UVꢀvis λmax
sol’n (nm)
UVꢀvis λmax
film (nm)
PL λmax
PL λmax
Stokes
d
Polymer
ΦPL
sol’n (nm) film (nm) shiftc
284, 309, 363s 337
393
433
96
1.82
P1
a Measured in THF solution (1.0 × 10ꢀ6 M). Superscript s means the wavelength of the
b
c
shoulder. The excitation wavelength was 300 nm in THF for polymer. Stokes shift
= PL(film)/nm − UV(film)/nm. d These values of quantum yield were measured using PF
as a standard (1.0 × 10ꢀ7 M, assuming a quantum yield of unity).
29