Synthesis and chemosensory properties of terpyridine-containing diblock polycarbazole through RAFT polymerization

Article abstract of DOI:10.1016/j.reactfunctpolym.2015.06.008

This paper describes the synthesis of a terpyridine-containing diblock copolymer, poly(N-vinylcarbazole)-block-poly[4′-((4-vinylphenyl) phenyl)-2,2′:6′,2″- terpyridine] (poly(VK₁₅-b-TPY₄)), using the macro-chain transfer agent VK macro-CTA, and employing two-step reverse addition-fragmentation transfer (RAFT) polymerization. We examined the effect of terpyridine units on sensory characteristics of fluorescent chemosensors. VK macro-CTA and diblock copolymer poly(VK₁₅-b-TPY₄) both exhibited moderate thermal stability, with thermal decomposition temperatures of 5% weight losses at approximately 307°C and 378°C, respectively, suggesting that the enhancement of thermal stability was attributed to the incorporation of terpyridine segments into the block copolymer. Poly(VK₁₅-b-TPY₄) exhibited higher sensitivities to Ni^{2 +} and Mn^{2 +} ions, with Stern-Volmer constants (K_sv) of 2.58 × 10⁵ M^{- 1} and 2.57 × 10⁵ M^{- 1}, respectively. Adding a Zn^{2 +} ion not only caused partial fluorescence enhancement (3.2-fold quantum efficiency) but also induced a bathochromic shift of emission peak by approximately 56 nm (from 429 nm to 485 nm), indicating that the Zn^{2 +}-terpyridine complex reduced the twist and vibration of the C-C polymer backbone and enhanced the charge transfer from donors to acceptors because of the more planar and rigid structure. Our results suggest that poly(VK₁₅-b-TPY₄) is a promising material for chemosensory applications.

Full text of DOI:10.1016/j.reactfunctpolym.2015.06.008

Reactive and Functional Polymers 93 (2015) 130–137
Contents lists available at ScienceDirect
Reactive and Functional Polymers
journal homepage: www.elsevier.com/locate/react
Synthesis and chemosensory properties of terpyridine-containing
diblock polycarbazole through RAFT polymerization
b
b
b
b
Ruey-Shin Juang a, Po-Chih Yang b, , Hua-Wen Wen , Cheng-Yi Lin , Sih-Ciao Lee , Ting-Wei Chang
⁎
a
Department of Chemical and Materials Engineering, Chang Gung University, Kwei-Shan 33302, Taoyuan, Taiwan
Department of Chemical Engineering and Materials Science, Yuan Ze University, Chung-Li 32003, Taoyuan, Taiwan
b
a r t i c l e i n f o
a b s t r a c t
Article history:
This paper describes the synthesis of a terpyridine-containing diblock copolymer, poly(N-vinylcarbazole)-block-
poly[4′-((4-vinylphenyl) phenyl)-2,2′:6′,2″- terpyridine] (poly(VK15-b-TPY4)), using the macro-chain transfer
agent VK macro-CTA, and employing two-step reverse addition-fragmentation transfer (RAFT) polymerization.
We examined the effect of terpyridine units on sensory characteristics of fluorescent chemosensors. VK macro-
CTA and diblock copolymer poly(VK15-b-TPY4) both exhibited moderate thermal stability, with thermal decom-
position temperatures of 5% weight losses at approximately 307 °C and 378 °C, respectively, suggesting that the
enhancement of thermal stability was attributed to the incorporation of terpyridine segments into the block
copolymer. Poly(VK15-b-TPY4) exhibited higher sensitivities to Ni2+ and Mn2+ ions, with Stern–Volmer con-
stants (Ksv) of 2.58 × 105 M−1 and 2.57 × 105 M−1, respectively. Adding a Zn2+ ion not only caused partial fluo-
rescence enhancement (3.2-fold quantum efficiency) but also induced a bathochromic shift of emission peak by
approximately 56 nm (from 429 nm to 485 nm), indicating that the Zn2+-terpyridine complex reduced the twist
and vibration of the C–C polymer backbone and enhanced the charge transfer from donors to acceptors because
of the more planar and rigid structure. Our results suggest that poly(VK15-b-TPY4) is a promising material for
chemosensory applications.
Received 24 November 2014
Received in revised form 10 June 2015
Accepted 14 June 2015
Available online 21 June 2015
Keywords:
Diblock copolymer
Chemosensor
Terpyridine
Reversible-fragmentation chain transfer
polymerization (RAFT)
© 2015 Elsevier B.V. All rights reserved.
1. Introduction
many metal ions in low oxidation states because of dπ\\pπ* bonding
modes.
The growth of chemosensors for sensing various analytes by apply-
ing color or fluorescence intensity has increased and chemosensors
have attracted particular attention for various environmental applica-
tions during the past decade because of their high analyte sensitivity
and ease of measurement [1–3]. Fluorescent chemosensors based on
conjugated polymers have been developed for measuring pH and
detecting metal ions and biological species. These detection properties
arise because the fluorescence properties of the chemosensor depend
on coupling between the receptors on the polymer and detected
analytes [4,5]. A chemosensor comprises a receptor (the recognition
site) and a fluorophore group (the signal source). The signal translates
the recognition event into the fluorophore group [6–8]. Polymer-
based optical sensors offer several crucial advantages over low
molecular-weight molecules, including transformation and amplifica-
tion of the fluorescent signal [9]. The high sensitivity is mainly acquired
by the highly conjugated polymer chain through which the signal is
transformed and amplified. Fluorescent pyridine-based derivatives
such as 1,10-phenanthroline [10,11], 2,2′-bipyridine [12–15], and
2,2′:6′,2″-terpyridine [16–19] have high binding affinities toward
In recent years, the use of controlled/living radical polymerization
(CLRP) methods (e.g., atom transfer radical polymerization (ATRP)
[20–22], nitroxide-mediated radical polymerization (NMP) [23], and
reversible addition-fragmentation chain transfer (RAFT) polymeriza-
tion [24–26]) has increased extensively in the preparation of block poly-
mers, because using these methods yields advantages such as a simple
experimental setup, a wide range of functional monomers, and complex
macromolecular architectures with well-defined end groups of narrow
polydispersity in the CLRP methods [27,28]. RAFT polymerization is a
well-established CLRP method that exhibits numerous appealing char-
acteristics for controlling the synthesis of a wide variety of macromolec-
ular architectures and for maintaining molecular weight control,
narrow molecular weight distributions, and functionality [29]. The
absence of catalysts and the ease of scaling up make RAFT one of the
most versatile CLRP techniques. To our best knowledge, only a few stud-
ies on the synthesis of the fluorescent chemosensor polymers using
RAFT methods have been done. Zhao et al. [30] employed the RAFT tech-
nique to prepare thermo- and pH-responsive fluorescent polymers
(PCN51 and PCN250). Their results verified that PCN250 shows absor-
bance enhancement or decrease at different pH values. However, the
fluorescence intensity of this copolymer demonstrates enhancement
with a rise in temperature if pH values are in the range of 4–10. In
⁎
Corresponding author.
E-mail address: pcyang@saturn.yzu.edu.tw (P.-C. Yang).
http://dx.doi.org/10.1016/j.reactfunctpolym.2015.06.008
1381-5148/© 2015 Elsevier B.V. All rights reserved.

R.-S. Juang et al. / Reactive and Functional Polymers 93 (2015) 130–137
131
addition, fluorescence suppression of PCN250 was observed with
high proton concentration. Tian et al. [31] synthesized a polymer
chemosensor (PNa) containing a naphthalimide signal moiety and
piperazinyl ring recognition moiety for detecting protons through
RAFT polymerization. PNa and its corresponding monomer (Na)
showed both fluorescence enhancement in a low proton concentra-
tion and fluorescence suppression in a high proton concentration,
which can be observed by both the naked eyes and optical responses.
In our previous study [32], we examined the effect of microwave
heating on the polymerization kinetics of a 4-acetoxystyrene-based
macro-chain transfer agent (macro-CTA) and investigated the effects
of azobenzene on the E/Z photoisomerization, as well as the self-
assembly behavior of a diblock copolymer in a THF/H2O solution by
using RAFT polymerization. In this study, we employed a two-step
RAFT polymerization technique to synthesize a macro-CTA, VK macro-
CTA, and a novel terpyridine-based block polymer, poly(VK15-b-TPY4).
We examined the effect of a terpyridine unit on the optoelectronic
properties of polymers and on the sensory characteristics of fluorescent
chemosensors. Poly(VK15-b-TPY4) takes advantage of luminescence
properties of the carbazole-based polymer chain and metal ion-
coordinating ability of the terpyridine unit to yield a highly effec-
tive transition-metal chemosensor. In the present system, we
found that poly(VK15-b-TPY4) exhibiting a pendant terpyridine
unit shows highly selective response to specific metal cations
(Mn2+ and Ni2+). Moreover, adding a Zn2+ ion not only caused
partial fluorescence enhancement but also induced a broad red-
shifted emission peak in the range of 400–650 nm, indicating that
the Zn2+–TPY complex reduced the twist and vibration of the C–C
polymer backbone and enhanced the charge transfer from donors
to acceptors because of the higher planarization and rigidity of
structure compared with the pristine poly(VK15-b-TPY4). Our re-
sults suggest that poly(VK15-b-TPY4) has potential applications in
chemosensors.
was used for calibration. Thermal analysis was performed using a differ-
ential 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 heating rate of
20 K/min using a Perkin Elmer TGA-7 thermal analyzer. UV/visible
absorption spectra were measured using a Jasco V-670 spectrophotom-
eter and photoluminescence (PL) spectra were obtained using an OBB
Quattro II fluorescence spectrophotometer. Fluorescence quantum
yields of compounds in chloroform using 9,10-diphenylanthracene
(λex = 350 nm) as the standard were estimated at room temperature
by the dilution method (1 × 10−7 M, assuming a quantum efficiency
of unity). Cyclic voltammograms were recorded with a voltammetric
analyzer (model CV-50 W from BAS) at room temperature under
nitrogen atmosphere with a scanning rate of 100 mV/s. The measur-
ing cell comprised polymer-coated ITO as the working electrode, Ag/
AgCl electrode as the reference electrode, and platinum wire elec-
trode as the auxiliary electrode. The electrodes were immersed in
acetonitrile containing 0.1 M tetrabutylammonium perchlorate
((n-Bu)4NClO4) as electrolyte. The energy levels were calculated
using the ferrocene (FOC) value of −4.8 eV with respect to vacuum
level, which is defined as zero. All the computational calculations
were performed at B3LYP/6-31G* level using density functional the-
ory (DFT) with Gaussian 09 program [36]. The DFT calculations on
the model compounds based on VKTPY and VKTPY-Zn2+ were per-
formed using default-spin.
2.3. Fluorescent titration of polymer
Fluorescent titration experiments were carried out in THF solution.
The chloride salts of Li+, Mg2+, Ca2+, Fe3+, Al3+, Ba2+, Ag+, Pb2+
,
Mn2+, Ni2+, and Zn2+ (5.0 × 10−5 M) were dissolved in distilled
water. Titration was done by adding the metal ion solution to a test
tube with polymer solution. The final concentration of polymer was
1.0 × 10−6 M. Titration of the metal ions was terminated until no
2. Experimental
2.1. Materials
Synthetic routes for the target terpyridine-based monomer
(2) are shown in Scheme 1. The target intermediate, 4′-(4-
bromophenyl)-2,2′:6′,2″-terpyridine (1), was synthesized follow-
ing the processes reported previously [33–35]. Synthetic routes
for the target macro-CTAs (VK macro-CTAs) and diblock copolymer
(poly(VK15-b-TPY4)) are shown in Scheme 2. The polymers were
synthesized following the procedures reported in the supporting
information. 9-Vinylcarbazole (Sigma-Aldrich, 98%) and 2,2′-
azoisobutyronitrile (AIBN, 98%, Sigma-Aldrich) were recrystallized
from methanol twice. All organic solvents and reagents were pur-
chased from Acros, Alfa, and Aldrich Chemical Co. and used without
further purification. S-(Thiobenzoyl)thioglycolic acid (CTA, 99%,
Sigma-Aldrich) and other chemical reagents were used as received
unless otherwise noted. Toluene (Acros, 99.5%) and tetrahydrofu-
ran (THF, N99.9%, Sigma-Aldrich) were dried with appropriate dry-
ing agents, calcium hydride or sodium, then distilled under
reduced pressure and stored over 4 Å molecular sieves before use.
2.2. Measurements
1H NMR (400 MHz) spectra were recorded on a Bruker AMX-400 FT-
NMR, and chemical shifts were reported in ppm using tetramethylsilane
(TMS) as an internal standard. Elemental analysis was carried out on a
Heraeus CHN–O rapid elemental analyzer. Number-average molecular
weight (Mn) and polydispersity index (PDI) of polymers were measured
with a gel permeation chromatograph (GPC), model CR4A from
Shimadzu, using tetrahydrofuran (THF) as an eluent and the rate of elu-
tion was 1.0 ml min−1. Polystyrene standard (1000–136000 g mol−1
)
Scheme 1. Synthetic routes of terpyridine-based monomer (2).

132
R.-S. Juang et al. / Reactive and Functional Polymers 93 (2015) 130–137
Scheme 2. Synthetic routes of VK macro-CTA and poly(VK-b-TPY).
change in the fluorescence intensity was observed. The Stern–Volmer
constant (Ksv) was estimated according to following equation:
copolymer (poly(VK15-b-TPY4)). Scheme 1 outlines the synthetic
routes for synthesizing the required monomer (2). We prepared 4′-
(4-bromophenyl)-2,2′:6′,2″-terpyridine (1) in 40.5% yield by using
the Kröhnke-type condensation reaction of 4-bromobenzaldehyde
with 2-acetylpyridine in the presence of potassium hydroxide. The
target monomer, 4′-((4-vinylphenyl)phenyl)-2,2′:6′,2″-terpyridine
(2), was prepared by reacting 4′-(4-bromophenyl)-2,2′:6′,2″-
terpyridine (1) and 4-vinylbenzeneboronic acid at 80 °C. Reaction
was performed under Suzuki coupling conditions using Pd(PPh3)4
as the catalyst. This creates monomer 2 with a yield of 31.1%. Chem-
ical structure and constitutional composition of the synthesized
monomer were confirmed by 1H NMR spectroscopy. Fig. S1 shows
the 1H NMR spectrum of monomer 2 in CDCl3. The 1H NMR spectrum
of monomer 2 shows characteristic chemical shifts of the vinyl group
doublet of doublets (dd; Ha, Hb, and Hc) at 5.25–6.79 ppm and the
terpyridyl singlet (Hh) and doublet proton signals (Hi and Hl) at
8.78 ppm and 8.64–8.75 ppm, respectively. The molecular structures
ðIo=IÞ ¼ 1 þ Ksv½Qꢀ
ð1Þ
where Io and I are the intensities of PL spectrum without and with a
quencher, respectively, Ksv is the Stern–Volmer constant (quenching
coefficient), and [Q] is the concentration of the quencher ions.
3. Results and discussion
3.1. Synthesis of monomer and macromolecular chain transfer agents (VK
macro-CTAs)
This study investigated the structural effect on the polymeriza-
tion kinetics during the RAFT polymerizations of 9-vinylcarbazole
(VK macro-CTAs) and sensory characteristics of the diblock
Table 1
Molecular weights and polydispersity data for VK macro-CTAs.a
Table 2
Polymerization results of VK macro-CTA and diblock copolymer.
Entry
[M]0:[CTA]0:[I]0
Conv.
(%)b
Mn (g mol−1
)
PDIc
Mn(th) (g mol−1
)
(×103)c
(×103)d
Polymer
Mn(GPC)
PDIb
Mn(NMR)
Tg
Td
x:yf
x:yg
c
(×103)b
(×103)
(°C)d
(°C)e
1
2
3
4
5
100:1:1
100:3:1
100:1:3
500:1:1
300:1.5:1
17.8
21.4
5.07
28.6
9.27
2.17
1.13
0.68
15.38
2.92
1.68
1.40
1.74
1.81
1.30
3.65
1.59
1.19
27.77
3.79
VK macro-CTAa
Poly(VK-b-TPY)
2.92
3.49
1.30
1.49
3.03
4.67
195
229
307
378
14:0
14:2
15:0
15:4
a
Feed molar ratio of [M]0: [CTA]0: [I]0 = 300: 1.5: 1.
b
c
Mn and PDI of the polymers were determined by GPC.
Mn of the polymers was determined by 1H NMR spectroscopy.
Phase transition temperature was obtained at a scanning rate of 20 K min−1 under ni-
a
Reaction temperature was 60 °C. Reaction solvent was THF. [M]: monomer, CTA: chain
transfer agent, I: AIBN.
d
b
Conversion = [Mo − M]/[Mo]. Values were calculated by 1H NMR.
Mn and PDI of the polymers were determined by GPC using polystyrene standards in
trogen atmosphere.
c
e
Decomposition temperature of 5% weight loss was measured by TGA.
f
THF.
Ratio of block length in copolymer was calculated by GPC.
d
g
Mn(th) = [M]0 × Mm × conversion/[CTA]o + CTAm
.
Ratio of block length in copolymer was calculated by 1H NMR spectroscopy.

R.-S. Juang et al. / Reactive and Functional Polymers 93 (2015) 130–137
133
respectively. As expected, the Mn values of VK macro-CTAs were
considerably low (Mn ≤ 2 × 104). We attributed the lower values to
the steric effects and stable resonance of carbazole radicals, resulting
in reducing polymerization reactivity. This suggests that in RAFT
polymerization, the monomer/CTA ratios, CTA/initiator ratios, sol-
ute/solvent solubility, and temperature play vital roles in determin-
ing the monomer conversion, molecular weight, and polydispersity
[37].
Fig. S2 shows the 1H NMR spectrum of the VK macro-CTA (i.e., entry
5 in Table 1), which was recorded in CDCl3. The degree of polymeriza-
tion (DP) of the VK macro-CTA was controlled by adjusting the molar
ratio of monomer to CTA, and its value was calculated based on the
integral ratio of protons Ha (at approximately 4.56–5.18 ppm) derived
from the carbazole monomer to methylene protons Hb in the CTA
agent (at 2.16 ppm). The DP value of macro-CTA was approximately
15, indicating that the moiety of the RAFT agent was attached to the
ends of the macro-CTAs. The Mn(NMR) of the VK macro-CTA calculated
from Fig. S2 was 3030 g mol−1 by applying the following equation:
Fig. 1. DSC traces of polymers at a heating rate of 20 °C min−1 in nitrogen.
MnðNMRÞ ¼ ½ð2Ha=HbÞ þ 1ꢀ ꢁ Mn;VK þ Mn;CTA
ð1Þ
of the synthesized compounds were also supported by elemental
analysis results.
where Ha: integral of carbazole protons (–CH), Hb: integral of methylene
protons, Mn,VK: molecular weight of VK, and Mn,CTA: molecular weight of
CTA. The Mn determined by GPC was 2920 g mol−1. Consequently, the
VK macro-CTA chains end-capped with CTA group were approximately
96.4%.
The VK macro-CTAs were conducted using RAFT polymerization and
were reacted in THF at 60 °C using 9-vinylcarbazole monomer with var-
ious molar ratios of [M]0/[CTA]0/[AIBN]0. Table 1 lists the VK macro-CTA
polymerization results and Scheme 2 shows the synthetic routes in-
volved in the synthesis of macro-CTAs and diblock copolymer. The
macro-CTA structures were characterized using GPC and 1H NMR spec-
troscopy. As shown in Table 1, when [M]0/[CTA]0/[AIBN]0 = 100/1/1,
the number-average molecular weight (Mn) and polydispersity index
(PDI) of VK macro-CTA was 2.17 × 103 g mol−1 and 1.68, respectively.
However, we observed that when [M]0/[CTA]0/[AIBN]0 = 100/3/1, the
Mn and PDI of VK macro-CTA (i.e., entry 2 in Table 1) decreased to
1.13 × 103 g mol−1 and 1.40, respectively. By contrast, when we
changed the ratio of [CTA]0/[AIBN]0 to 1/3 and fixed the [M]0/
[CTA]0 ratio to 100/1, the Mn decreased from 1.13 × 103 g mol−1 to
6.8 × 102 g mol−1 and the PDI increased from 1.40 to 1.74. These re-
sults indicate that when [CTA]0/[AIBN]0 = 1/3 ~ 1 (entries 1 and 3 in
Table 1), the amount of CTA is too low compared to the number of
generated radicals to ensure a fast equilibrium between dormant
and active species. The high concentration of initiator (i.e., entry 3
in Table 1) also results in more initiator-derived polymer chains
being formed during the polymerization, thus inducing a broad poly-
dispersity. Additionally, a high [CTA]0/[AIBN]0 ratio resulted in a long
polymerization inhibition period and induced a decrease of mono-
mer conversion but improved the control over polydispersity. This
observation is explained by the effectively rapid chain transfer rate
of propagated chains, leading to the formation of lower Mn. The
molecular weights of VK macro-CTA can be controlled by adjusting
the molar ratio of monomer to CTA. When the monomer concentra-
tion changed to 5-fold compared to that of entry 1 (i.e., [M]0/[CTA]0/
[AIBN]0 = 500/1/1), the Mn of VK macro-CTA increased from to
2.17 × 103 g mol−1 to 15.38 × 103 g mol−1 but induced a slight
increase in the PDI value (1.81). When [M]0/[CTA]0/[AIBN]0 = 300/
1.5/1, the Mn and PDI decreased to 2.92 × 103 g mol−1 and 1.30,
3.2. Synthesis and thermal properties of diblock copolymer (poly(VK15-b-
TPY4))
The diblock copolymer poly(VK15-b-TPY4) was prepared by apply-
ing the second-step RAFT polymerization method, using VK macro-
CTA (i.e., entry 5 in Table 1) as the macro-RAFT agent, and AIBN as the
initiator in the THF at 60 °C. Fig. S3 shows the 1H NMR spectrum of
the poly(VK15-b-TPY4) in CDCl3. The molar ratio of the two diblock
lengths was calculated at 15:4 by comparing the integrated peak areas
of carbazole protons (Ha: 4.58–5.20 ppm) to those of the terpyridyl pro-
tons (Hb: 8.16–8.85 ppm) in monomer 2. The poly(VK15-b-TPY4) spec-
trum shown in Fig. S3 confirms that the RAFT agent had attached to the
end of the polymer chain.
Table 2 lists the Mn of poly(VK15-b-TPY4) as 3.49 × 103 g mol−1 and
lists the corresponding PDI, determined according to GPC, as 1.49. The
VK macro-CTA and poly(VK15-b-TPY4) showed glass transition temper-
atures (Tg) of 195 °C and 229 °C, respectively (Fig. 1). Poly(VK15-b-TPY4)
exhibited moderate thermal stability at thermal decomposition temper-
atures (Td; at 5% weight losses) of approximately 378 °C in a nitrogen
atmosphere. These results indicate that terpyridyl groups can be incor-
porated into block copolymers to enhance the thermal stability of
polymers.
3.3. Optical properties
Optical properties of the polymers were investigated using absorp-
tion and PL spectroscopies, in both solution and film states, to determine
the structural effect of the terpyridine-based monomer, as summarized
in Table 3 and Fig. 2. The polymers exhibit strong UV–vis absorption
Table 3
Optical properties of polymers.
d
Polymer
UV–vis λmax (solution, nm)a
UV–vis λmax (film, nm)
PL λmax (solution, nm)b
PL λmax (film, nm)
Stokes Shiftc
Φ )
PL (×10−2
VK macro-CTA
poly(VK15-b-TPY4)
333
286
350
305
439
429
456
450
106
145
0.3
2.0
a
Measured in THF solution (1 × 10−5 M).
b
c
The excitation wavelengths were 350 nm for all polymers.
Stokes shift = PL(film)/nm − UV(film)/nm.
d
These values of quantum efficiency were estimated by using 9,10-diphenylanthracene as a standard (1 × 10−7 M, assuming a quantum efficiency of unity).

134
R.-S. Juang et al. / Reactive and Functional Polymers 93 (2015) 130–137
Table 4
Electrochemical data of polymers.
opt
Polymer
UV–vis λonset E(ox) (V) vs. EHOMO
ELUMO Eg
(eV)c (eV)d
(nm)a
FOC
(eV)b
VK macro-CTA
poly(VK15-b-TPY4) 398
405
0.17
0.22, 0.43
−4.97
−1.91 3.06
−5.02, −5.23e −1.90 3.12
a
Onset wavelength of compounds in absorption spectra.
EHOMO = −(E(ox), FOC + 4.8) eV.
b
c
ELUMO = (EHOMO + Egopt) eV.
d
e
Band gaps are estimated from onset absorption in the solid state (Eogpt = 1240.8/λonset).
The molecular orbital was HOMO-1.
states, originating from aggregate formation through intrachain or
interchain interactions.
In solution, the emission spectra of VK macro-CTA and poly(VK15-b-
TPY4) have maxima at 439 and 429 nm, respectively, on excitation at a
wavelength of 350 nm, as shown in Fig. 2a. In the film states (Fig. 2b),
the PL spectra of the two polymers are red-shifted by approximately
17 and 21 nm, respectively, from the corresponding solution spectra, in-
dicating that the shift is probably attributable to the formation of aggre-
gation and excimers. Poly(VK15-b-TPY4) exhibits greater Stokes shift
(145 nm) than that of VK macro-CTA (106 nm). We attributed this dif-
ference to donor–acceptor interactions that occur between the carba-
zole donor and the terpyridine acceptor groups. The PL quantum
yields of VK macro-CTA and poly(VK15-b-TPY4) in THF, which were es-
timated using 9,10-diphenylanthracene as a reference, are 3.0 × 10−3
and 2.0 × 10−2, respectively. The results indicate that the terpyridyl
group on poly(VK15-b-TPY4) led to an increase in the fluorescence
intensity of the polymer, which we attributed to the resonance effect
of the 2,2′:6′,2″-(terpyridyl)phenyl groups, leading to the formation of
higher quantum yield.
3.4. Electrochemical properties
Fig. 3 shows estimated cyclic voltammograms (CV) for the polymer
films coated on ITO working electrodes, and Table 4 summarizes the
electrochemical data. The highest occupied molecular orbital (HOMO)
and lowest unoccupied molecular orbital (LUMO) energy levels were
estimated according to the equations EHOMO = −(Eox + 4.8) eV and
ELUMO = EHOMO + Egopt, where Eox is the onset oxidation potential
regarding the standard ferrocene/ferrocenium (FOC) redox system.
The optical band gaps (Eogpt) were determined according to the onset
absorption wavelength. As shown in Table 4, the onset oxidation poten-
tial of VK macro-CTA was observed at approximately 0.17 V; however,
the onset oxidation potentials for poly(VK15-b-TPY4) shifted slightly
to 0.22 and 0.43 V. The increased oxidation potential in poly(VK15-b-
TPY4) may have originated from the introduction of electron-
withdrawing terpyridyl segments. The estimated HOMO and LUMO
energy levels of VK macro-CTA are −4.97 and −1.91 eV, respective-
ly. However, the molecular orbital levels of poly(VK15-b-TPY4) are
−5.02/−5.23 (HOMO/HOMO-1) and −1.90 eV (LUMO).
Fig. 2. Normalized UV–visible absorption and PL spectra of polymers (a) in solution and
(b) in thin films.
bands in THF solution at 286–333 nm, corresponding to the π–π* elec-
tronic transition of the polymer backbone. The absorption peak of
poly(VK15-b-TPY4) is blue-shifted 47 nm relative to that of VK macro-
CTA, and appears at 286 nm, probably because of the conformational
distortion of terpyridine blocks, thereby leading to the observed
bathochromic shift of absorption peak. In the film states, the absorption
maxima are slightly red-shifted (17–19 nm) relative to the solution
3.5. Ion sensing properties
Generally, polyvinylcarbazoles (PVKs) are promising blue light-
emitting materials widely used in PLEDs because of their optically active
carbazole groups in the side chains. Terpyridine-functionalized polymers
are commonly employed as molecular hosts to complex with transition
metal cations. Poly(VK15-b-TPY4) is a diblock copolymer consisting of
two various block lengths, emission carbazoles, and terpyridine blocks.
Fig. 4 shows the effect of complexation with various metal ions (Li+
,
Mg2+, Ca2+, Fe3+, Al3+, Ba2+, Ag+, Pb2+, Mn2+, Ni2+, and Zn2+) on
the PL spectra of poly(VK15-b-TPY4) in a THF/H2O solution. The PL inten-
sity of the poly(VK15-b-TPY4) solution decreased significantly by adding
Ni2+, Mn2+, Ag+, or Fe3+ ions (Fig. 4a), indicating that these metal ions
lead to an efficient fluorescence quenching of the polymer chain. In
Fig. 3. Cyclic voltammograms of polymer films coated on ITO glass at a scanning rate of
100 mV/s.

R.-S. Juang et al. / Reactive and Functional Polymers 93 (2015) 130–137
135
Fig. 4. (a) Photoluminescence spectra, (b) PL response profiles, and (c) fluorescence colors of poly(VK-b-TPY) in the presence of various metal ions (excitation: 350 nm). Concentration of
polymer: 10−6 M in THF, concentration of metal ions: 5.0 × 10−5 M.
particular, poly(VK15-b-TPY4) is quenched completely by Ni2+ and Mn2+
ions, thus indicating its high selectivity toward these two cations. These
results suggest that after being linked to the polymer side chain, the
terpyridine chelating moieties could effectively transfer the energy from
the polymer backbone to the Ni2+ or Mn2+ ions, thus resulting in the
fluorescence quenching of the polymer. In addition, the quenching mech-
anism of poly(VK15-b-TPY4) could be attributed to the photoexcited ener-
gy transfer of the polymer chain [38,39]. Thus, poly(VK15-b-TPY4) could
be utilized as a polymer chemosensor for metal ions. In the presence of
Mg2+ or Ca2+, the PL intensity and spectral pattern of the polymer
show no obvious changes, whereas adding Li+, Al3+, Ba2+, or Pb2+
results in a slight decrease of the PL intensity. Fig. 4b shows their corre-
sponding PL response profiles (i.e., Io/I) of poly(VK15-b-TPY4) in the pres-
ence of various metal ions with an ion concentration of 5.0 × 10−5 M. The
emission color of fluorescence response to various metal ions was visible,
as shown in Fig. 4c. This indicates that the charge density, diameter, and
paramagnetic property of the metal ions, quenching mechanism, and che-
lating capability of ligands substantially influence the decreased fluores-
cence emission, thereby leading to the observed variation in chelating
these ions that accompany terpyridine units [40]. This also leads to the
formation of a stable terpyridine-ion complex because of its high charge
density. Furthermore, the obtained results were substantially different
from those for poly(VK15-b-TPY4) binding with Zn2+ ions, exhibiting
enhanced green emission (i.e., λem = 485 nm) and a bathochromic shift
of approximately 56 nm. The quantum efficiency (ΦPL) of poly(VK15-b-
TPY4) solution was increased from 2.0 × 10−2 to 6.4 × 10−2 (i.e., 3.2-
fold). Fig. 5 shows the conformations of model compound VKTPY
(i.e., repeating unit x = 1 and y = 1 in Scheme 2) before and after binding
with Zn2+. After chelation with Zn2+, the angle among the three nitrogen
atoms in the terpyridyl unit changing from 128.7° to 98.6° leads the
terpyridyl unit approaching closer and becoming more planar because
of the coordination interaction within the terpyridyl unit and Zn2+. Addi-
tionally, the dihedral angle (0.16°) between two neighboring pyridine
rings with binding Zn2+ was smaller than that without Zn2+ (38.7°).
These results indicate that the more highly planar and rigid terpyridine-
Zn2+ complex reduced the twist and vibration of the C–C polymer back-
bone and enhanced the charge transfer from donors to acceptors [41–43].
To quantitatively evaluate the fluorescence quenching and sensitiv-
ity of the polymer toward these cations, the PL intensities and Stern–
Volmer constants (Ksv) of poly(VK15-b-TPY4) in the presence of various
concentrations of Ni2+ and Mn2+ ions were measured. As shown in
ability. Consequently, the smaller diameters (Ni2+: 1.44 Å; Mn2+
:
1.60 Å) and higher charges (Ni2+: 1.91; Mn2+: 1.55) of Ni2+ and Mn2+
ions might play vital roles in determining the strong coordination of

136
R.-S. Juang et al. / Reactive and Functional Polymers 93 (2015) 130–137
Fig. 5. B3LYP optimized structure of VKTPY (left) and VKTPY-Zn2+ (right) complex. Carbon atoms are gray, oxygen atoms are red, nitrogen atoms are blue, and sulfur atoms are yellow.
(For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Fig. 6, the PL intensities decrease with an increasing Ni2+ or Mn2+ con-
centration. When the Ni2+ and Mn2+ concentrations are greater than
2.6 × 10−5 M and 1.8 × 10−5 M, respectively, the slope of the Stern–
Volmer plot turns noticeably upward, which we attributed to a strong
terpyridine chelation to the transition metal ions. The Stern–Volmer
constants (Ksv) for poly(VK15-b-TPY4) in the presence of a low concen-
tration of Ni2+ and Mn2+ ions (below approximately 2.0 × 10−5 M) are
2.58 × 105 M−1 and 2.57 × 105 M−1, respectively. Table 5 summarizes
the emission wavelengths and ΦPL of polymer solutions in the pres-
ence of various cations. Poly(VK15-b-TPY4)-Ni2+ or a poly(VK15-b-
TPY4)-Mn2+ complex exhibited considerably low PL intensity and
identical ΦPL values from 2.0 × 10−2 to 6.0 × 10−4 (i.e., 97.0% ΦPL
loss). Our results indicate that the distinct cation-response proper-
ties are responsible for various coordination strengths between
different transition metal ions and the terpyridyl substituted li-
gands. Therefore, poly(VK15-b-TPY4) is a promising chemical sen-
sor for transition metal cations.
4. Conclusions
We synthesized and characterized a terpyridine-containing diblock
copolymer (poly(VK15-b-TPY4)) by using a RAFT polymerization tech-
nique. We evaluated the effect of terpyridine units on optical properties
of the diblock copolymer and sensory characteristics of a fluorescent
chemosensor. Poly(VK15-b-TPY4) exhibited moderate thermal stability
at a thermal decomposition temperature of 5% weight loss at approxi-
mately 378 °C, suggesting that introducing terpyridine groups to the
polymer chain enhanced the intermolecular interaction. The diblock
polymer poly(VK15-b-TPY4) exhibited high selectivity toward Ni2+
and Mn2+ ions, and its Stern–Volmer constants (Ksv) for Ni2+ and
Mn2+ ions were 2.58 × 105 M−1 and 2.57 × 105 M−1, respectively.
These results suggested that poly(VK15-b-TPY4) containing the terpyridyl
group is a promising chemosensory material.
Acknowledgments
The authors are thankful for the Ministry of Science and Technology
(MOST), Taiwan, for its financial aid through projects NSC100-2113-M-
115-001-MY2 and Most103-2221-E-155-072.
Fig. 6. PL spectra of poly(VK-b-TPY) in the presence of various concentrations of (a) Ni2+
and (b) Mn2+ ions. Concentration of polymer: 10−6 M in THF; inset: Stern–Volmer plot of
PL quenching with various concentration of ions.

R.-S. Juang et al. / Reactive and Functional Polymers 93 (2015) 130–137
137
Table 5
Emission wavelengths and quantum efficiencies of poly(VK15-b-TPY4) solutions in the presence of various cations.
Complex
Pa
P–Li+
P–Mg2+
P–Ca2+
P–Fe3+
P–Al3+
P–Pb2+
P–Ag+
P–Ba2+
P–Ni2+
P–Mn2+
P–Zn2+
485
PL λmax (nm)b
429
427
1.7
427
1.9
431
2.0
425, 561
0.7
433
1.6
462
1.0
435
0.09
430
1.7
423
0.06
427
0.06
Φ (×10−2
)
2.0
6.4
c
a
P means diblock copolymer, poly(VK15-b-TPY4).
b
c
The excitation wavelengths were 350 nm for all polymers.
These values of quantum efficiency were estimated by using 9,10-diphenylanthracene as a standard (1 × 10−7 M, assuming a quantum efficiency of unity).
[25] A.B. Lowe, C.L. McCormick, Prog. Polym. Sci. 32 (2007) 283–351.
[26] C. Boyer, V. Bulmus, J. Liu, T.P. Davis, M.H. Stenzel, C. Barner-Kowollik, J. Am. Chem.
Soc. 129 (2007) 7145–7154.
Appendix A. Supplementary data
Supplementary data to this article can be found online at http://dx.
doi.org/10.1016/j.reactfunctpolym.2015.06.008.
[27] M. Kamigaito, T. Ando, M. Sawamoto, Chem. Rev. 101 (2001) 3689–3746.
[28] W.A. Braunecker, K. Matyjaszewski, Prog. Polym. Sci. 32 (2007) 93–146.
[29] C. Boyer, V. Bulmus, T.P. Davis, V. Ladmiral, J. Liu, S.B. Perrier, Chem. Rev. 109 (2009)
5402–5436.
References
[30] G. Liu, W. Zhou, J. Zhang, P. Zhao, J. Polym. Sci. A Polym. Chem. 50 (2012)
2219–2226.
[1] T. Gunnlaugsson, M. Glynn, G.M. Tocci, P.E. Kruger, F.M. Pfeffer, Coord. Chem. Rev.
250 (2006) 3094–3117.
[31] J. Jiang, B. Leng, X. Xiao, P. Zhao, H. Tian, Polymer 50 (2009) 5681–5684.
[32] P.C. Yang, H.C. Chen, H.W. Wen, P.I. Wu, J. Polym. Sci. A Polym. Chem. 52 (2014)
3107–3117.
[33] Y. Zhang, C.B. Murphy, W.E. Jones Jr., Macromolecules 35 (2002) 630–636.
[34] P.D. Vellis, J.A. Mikroyannidis, C.N. Lo, C.S. Hsu, J. Polym. Sci. A Polym. Chem. 46
(2008) 7702–7712.
[2] X. Chen, Y. Zhou, X. Peng, J. Yoon, Chem. Soc. Rev. 39 (2010) 2120–2135.
[3] A.W. Czarnik (Ed.), Fluorescent chemosensors for ion and molecular recognition,
ACS Symposium Series 538American Chemical Society, Washington, DC, 1993.
[4] A.P. de Silva, H.Q.N. Gunaraten, T. Gunnlaugsson, A.J.M. Huxley, C.P. McCoy, J.T.
Rademacher, T.E. Rice, Chem. Rev. 97 (1997) 1515–1566.
[5] D.T. McQuade, A.E. Pullen, T.M. Swager, Chem. Rev. 100 (2000) 2537–2574.
[6] H. Tong, L.X. Wang, X.B. Jing, F.S. Wang, Macromolecules 35 (2002) 7169–7171.
[7] T. Yasuda, I. Yamaguchi, T. Yamamoto, Adv. Mater. 15 (2003) 293–296.
[8] J.W.Y. Lam, B.Z. Tang, Acc. Chem. Res. 38 (2005) 745–754.
[9] S.W. Thomas, G.D. Joly, T.M. Swager, Chem. Rev. 107 (2007) 1339–1386.
[10] E. Holder, G. Trapp, J.C. Grimm, V. Schurig, E. Lindner, Tetrahedron Asymmetry 13
(2002) 2673–2678.
[35] H.P. Zhou, F.X. Zhou, P. Wu, Z. Zheng, Z.P. Yu, Y. Chen, Y. Tu, L. Kong, J. Wu, Y. Tian,
Dyes Pigments 91 (2011) 237–247.
[36] 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. 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, Ö. Farkas, J.B. Foresman, J.V. Ortiz, J.
Cioslowski, D.J. Fox, Gaussian 09, Revision D.01, Gaussian, Inc., Wallingford CT, 2009.
[37] M.L.T. Sordi, I.C. Riegel, M.A. Ceschi, A.H.E. Müller, C.L. Petzhold, Eur. Polym. J. 46
(2010) 336–344.
[11] U.S. Schubert, C. Eschbaumer, Angew. Chem. Int. Ed. 41 (2002) 2892–2926.
[12] E. Holder, G. Schoetz, V. Schurig, E. Lindner, Tetrahedron Asymmetry 12 (2001)
2289–2293.
[13] E. Holder, M.A.R. Meier, V. Marin, U.S. Schubert, J. Polym. Sci. A Polym. Chem. 41
(2003) 3954–3964.
[14] V. Marin, E. Holder, M.A.R. Meier, R. Hoogenboom, U.S. Schubert, Macromol. Rapid
Commun. 25 (2004) 793–798.
[15] V. Marin, E. Holder, R. Hoogenboom, E. Tekin, U.S. Schubert, Dalton Trans. (2006)
1636–1644.
[38] B. Valeur, Effects of intermolecular photophysical process on fluorescence emission,
Molecular Fluorescence: Principles and Applications, Wiley-VCH, Weinheim, 2001
(Chapter 4).
[16] E. Holder, V. Marin, M.A.R. Meier, U.S. Schubert, Macromol. Rapid Commun. 25
(2004) 1491–1496.
[17] S. Bonnet, J.P. Collin, M. Koizumi, P. Mobian, J.P. Sauvage, Adv. Mater. 18 (2006)
[39] R. Dobrawa, M. Lysetska, P. Ballester, M. Grune, F. Wurthner, Macromolecules 38
1239–1250.
(2005) 1315–1325.
[18] E.C. Constable, Aust. J. Chem. 59 (2006) 1–2.
[40] J.E. House, Inorganic Chemistry, Academic Press (Elsevier), Burlington, MA, 2008.
[41] A.R. Rabindranath, A. Maier, M. Schäfer, B. Tieke, Macromol. Chem. Phys. 210 (2009)
659–668.
[42] N.W. Alcock, P.R. Barker, J.M. Haider, M.J. Hannon, C.L. Painting, Z. Pikramenou, E.A.
Plummer, K. Rissanen, P. Saarenketo, J. Chem. Soc. Dalton Trans. (2000) 1447–1461.
[43] A. Fermi, G. Bergamini, M. Roy, M. Gingras, P. Ceroni, J. Am. Chem. Soc. 136 (2014)
6395–6400.
[19] A. Wild, A. Winter, F. Schlütter, U.S. Schubert, Chem. Soc. Rev. 40 (2011) 1459–1511.
[20] K. Matyjaszewski, J. Xia, Chem. Rev. 101 (2001) 2921–2990.
[21] Y. Mei, K.L. Beers, M.H.C. Byrd, D.L. VanderHart, N.R. Washburn, J. Am. Chem. Soc.
126 (2004) 3472–3476.
[22] L. Ayres, K. Koch, P.H.H.M. Adams, J.C.M. van Hest, Macromolecules 38 (2005)
1699–1704.
[23] C.J. Hawker, A.W. Bosman, E. Harth, Chem. Rev. 101 (2001) 3661–3688.
[24] B.S. Lokitz, A.J. Convertine, R.G. Ezell, A. Heidenreich, Y. Li, C.L. McCormick, Macro-
molecules 39 (2006) 8594–8602.