Synthesis of a novel fluorescent and ion sensitive monomer bearing quinoxaline moieties and its electropolymerization

Article abstract of DOI:10.1016/j.reactfunctpolym.2011.02.008

A novel terthienyl based fluorescent polymer bearing pendant quinoxaline moieties directly attached to the 3-positions of the central thiophene ring was synthesized by electrochemical polymerization of 4-((2,5-dithiophen-2-yl) thiophen-3-yl)pyrrolo[1,2-a]quinoxaline (TT-Q). The corresponding polymer was characterized by cyclic voltammetry, FT-IR and UV-vis spectroscopy. The polymer exhibits a reversible redox behavior (Ep^1/2 = 1.05 V) accompanied with a reversible electrochromic behavior; yellowish orange in the neutral state and green in the oxidized state. Band gap of polymer was found (E_g = 1.94 eV). Moreover, the sensitivity of both the monomer and its polymer towards metal cations was investigated by monitoring the change in the fluorescence intensity. Among various common ions, both the monomer and its polymer were found to be selective towards Fe³⁺ ions by quenching the fluorescence efficiency with a Stern-Volmer constant (K_sv) of (2.7 × 10³ M^-1) and (5.0 × 10³ M^-1) for monomer and polymer solutions, respectively. Crown Copyright

Full text of DOI:10.1016/j.reactfunctpolym.2011.02.008

Reactive & Functional Polymers 71 (2011) 579–587
Contents lists available at ScienceDirect
Reactive & Functional Polymers
journal homepage: www.elsevier.com/locate/react
Synthesis of a novel fluorescent and ion sensitive monomer bearing
quinoxaline moieties and its electropolymerization
⇑
Buket Bezgin Çarba ßs , Arif Kivrak, Metin Zora, Ahmet M. Önal
Department of Chemistry, Middle East Technical University, TR-06531 Ankara, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 30 July 2010
Received in revised form 27 January 2011
Accepted 27 February 2011
Available online 5 March 2011
A novel terthienyl based fluorescent polymer bearing pendant quinoxaline moieties directly attached to
the 3-positions of the central thiophene ring was synthesized by electrochemical polymerization of
4-((2,5-dithiophen-2-yl)thiophen-3-yl)pyrrolo[1,2-a]quinoxaline (TT-Q). The corresponding polymer
was characterized by cyclic voltammetry, FT-IR and UV–vis spectroscopy. The polymer exhibits a revers-
1
/2
ible redox behavior (Ep = 1.05 V) accompanied with a reversible electrochromic behavior; yellowish
orange in the neutral state and green in the oxidized state. Band gap of polymer was found (E = 1.94 eV).
g
Keywords:
Quinoxaline
Electrochemical polymerization
Fluorescent polymer
Electrochromics
Ion sensitivity
Moreover, the sensitivity of both the monomer and its polymer towards metal cations was investigated
by monitoring the change in the fluorescence intensity. Among various common ions, both the monomer
3
+
and its polymer were found to be selective towards Fe ions by quenching the fluorescence efficiency
3
ꢁ1
3
ꢁ1
with a Stern–Volmer constant (Ksv) of (2.7 ꢀ 10 M ) and (5.0 ꢀ 10 M ) for monomer and polymer
solutions, respectively.
Ó 2011 Elsevier Ltd. All rights reserved.
1
. Introduction
Quinoxalines are interesting functional materials due to their
[15,16], brings the advantage of tuning the optoelectronic proper-
ties of the polymer. When the trimeric precursor contains donor
and acceptor substituents in an alternating manner, the photovol-
taic and electrochromic properties are greatly affected [17].
Conjugated polymers with alternating donor–acceptor repeat-
ing units have been widely studied to tailor the photovoltaic and
electrochromic properties of the polymers [18–21]. Combining a
strong donor with a strong acceptor not only lowers the band
gap, but also increases the possible redox states for the conjugated
polymer. Thus, the resulting hybrid material will exhibit multiple
redox states in a small potential range. In 2004, Sonmez and his
coworkers were able to synthesize neutral state green polymer
fluorescence properties with high quantum yields. The interest
on these materials lies not only on the fact that they can be utilized
as fluorescence probes in some chemosensors [1] but also their
potential use in high technology applications including light emit-
ting devices and solar cells [2–5]. Some quinoxaline derivatives are
able to coordinate to various anionic species [6,7], and therefore
they can be used as metal ion chelators [8–10]. In some cases,
these applications might require the integration of quinoxaline
moieties into a polymer matrix. Therefore, it might be interesting
to incorporate the quinoxaline moiety as a pendant group to a con-
jugated polymer chain. Among conjugated polymers, polythio-
phenes are widely used because of their environmental stability
and good electrical and optical properties [11]. Furthermore, the
relative easiness of their functionalization makes polythiophenes
attractive in the field of molecular tailoring for the desired proper-
ties [12]. Although there exists a large number of reports related to
the electrochemical or chemical polymerization of various substi-
tuted thiophene derivatives, thiophene oligomers are also em-
ployed to avoid overoxidation of polythiophene [13,14]. The use
of thiophene oligomers, in the form of dimeric and trimeric precur-
sors, which has been developed by Reynolds and coworkers
via electrochemical polymerization of
a precursor monomer
obtained by combining electron rich and electron poor units [22].
Algı and Cihaner investigated the effect of donor and acceptor units
on the intrinsic properties of polymer by using Se or S containing
acceptor unit together with a thiophene or thiophene based donor
unit [23].
Quinoxalines, due to presence of two unsaturated nitrogen
atoms, have high electron affinities and are strong acceptor groups.
This property together with their thermal stability makes quinox-
alines as an attractive candidate for the synthesis of low band gap
polymers [5,24]. Due to their high electron affinities, they are also
promising electron transport materials in multilayer organic light
emitting devices [26,27] and several copolymers containing quin-
oxalines either in the main chain or as pendant groups on the main
chain has been reported [25–31]. Quinoxaline containing polymers
prepared via condensation reaction were first used as heat and
⇑
Corresponding author. Tel.: +90 312 2103188; fax: +90 312 2103200.
E-mail address: aonal@metu.edu.tr (A.M. Önal).
1
381-5148/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.reactfunctpolym.2011.02.008

5
80
B.B. Çarba ßs et al. / Reactive & Functional Polymers 71 (2011) 579–587
Scheme 1. Synthetic route of 4-((5-thiophen-2-yl)thiophen-3-yl)pyrrolo[1,2-a]quinoxaline (DT-Q).
chemical resistant materials and applied later in polymer light
emitting devices [32,33]. Karastatiris et al. investigated the photo-
physical and emissive properties of poly(p-phenylene) derivatives
containing quinoxaline moieties and reported that these materials
exhibits greenish-yellow electroluminescence [6]. Thermal and
optical properties of 2,7-carbazole and quinoxaline based alternat-
ing copolymers were investigated by Morin and Leclerc [31] and
the low band gap of quinoxaline containing copolymer was attrib-
uted to the strong intramolecular interaction between donor and
acceptor groups.
An indium-tin oxide (ITO, Delta Tech. 8–12
X
, 0.7 cm ꢀ 5 cm)
coated by the polymer film was used as the working electrode.
Prior to spectroelectrochemical investigations, the polymer films
were switched between neutral and doped states several times in
order to equilibrate its redox behavior in monomer-free electro-
lytic solution. Electroanalytical measurements were performed
using a Gamry PCI4/300 potentiostat–galvanostat. The electro-
optical spectra were monitored on a Hewlett–Packard8453A diode
array spectrometer. FT-IR spectra were recorded on Nicolet 510
FT-IR with an attenuated total reflectance (ATR). NMR spectra were
Herein, we present our results concerning the synthesis and
characterization of new fluorescent materials; 4-(thiophen-3-yl)-
pyrrolo[1,2-a]quinoxaline (MT-Q), 4-((5-thiophen-2-yl)thiophen-
3
recorded on a Bruker NMR Spectrometer (DPX-400) in CDCl , and
fluorescence measurements were recorded on a Varian Cary
Eclipse Fluorescence Spectrophotometer. The quenching experi-
ments were performed by successive additions of metal ions (each
3
-yl)pyrrolo[1,2-a]quinoxaline (DT-Q) and 4-((2,5-dithiophen-2-
ꢁ
5
yl)thiophen-3-yl)pyrrolo[1,2-a]quinoxaline (TT.Q) (Scheme 1).
Among them, the polymerization of TT-Q was feasible by electro-
chemical means to give poly(4-((2,5-dithiophen-2-yl)thiophen-3-
yl)pyrrolo[1,2-a]quinoxaline, P(TT-Q). Furthermore, the fluores-
cence properties of both the monomer and its polymer were inves-
tigated in dimethylformamide (DMF). The effect of various metal
cations on the fluorescence intensity was also determined.
2–10 mM) to the solution of TT-Q (1.0 ꢀ 10 M) and P(TT-Q) in
DMF at room temperature, and the fluorescence spectra were mea-
sured after excitation at 350 and 500 nm, respectively. Photo-
graphs of the monomer and polymer solutions films were taken
by using a Canon digital camera.
2.1. Synthesis of monomers, MT-Q, DT-Q and TT-Q
2.1.1. 4-(Thiophen-3-yl)pyrrolo[1,2-a]quinoxaline (MT-Q)
2
. Experimental
This compound was synthesized from 1-(2-aminophenyl)pyr-
role and thiophene-3-carboxaldehyde according to known proce-
1
All chemicals were purchased from Aldrich Chemical and used
3
dure [34]. H NMR (400 MHz, CDCl ): d 8.08 (dd, J = 2.9 Hz,
as received. 0.1 M tetrabutylammonium hexafluorophosphate
TBAPF dissolved in dichloromethane (DCM) was used as
J = 1.0 Hz, 1H, H-1), 8.02 (dd, J = 7.8 Hz, J = 1.4 Hz, 1H, H-9), 7.98
(s, 1H, H10), 7.85 (m, 2H, H-6 and H-12), 7.50 (m, 3H, H-7, H-8
(
6
)
electrolyte solution. Cyclic voltammetry (CV) was performed in a
three-electrode cell equipped with a platinum (0.02 cm ) working
and H-13), 7.12 (dd, J = 4.0 Hz, J = 1.0 Hz, 1H, H-3), 6.91 (dd,
2
13
J = 3.9 Hz, J = 2.8 Hz, 1H, H-2).
3
C NMR (100 MHz, CDCl ): d
electrode, a platinum wire counter electrode and Ag/AgCl in 3 M
NaCl(aq) solution as a reference electrode. Repetitive cycling or
constant potential electrolysis was used to obtain the polymer
films. For electro-optical studies, platinum and silver (calibrated
externally using 5 mM solution of ferrocene/ferrocenium couple)
wires were used as counter and reference electrodes, respectively.
149.4, 140.3, 136.2, 130.2, 128.2, 127.6, 127.3, 126.7, 126.1,
129.5, 129.4, 114.8, 114.2, 113.8, 108.3.
2.1.2. 4-(5-Bromothiophen-3-yl)pyrrolo[1,2-a]quinoxaline (1)
To a solution of 4-(thiophen-3-yl)pyrrolo[1,2-a]quinoxaline
(MT-Q) (100 mg, 0.4 mmol) in 10 ml of glacial acetic acid was
Scheme 2. Synthetic route of 4-((2,5-dithiophen-2-yl)thiophen-3-yl)pyrrolo[1,2-a]quinoxaline (TT-Q).

B.B. Çarba ßs et al. / Reactive & Functional Polymers 71 (2011) 579–587
581
added dropwise a solution of bromine (320 mg, 0.103 ml, 2 mmol)
at room temperature. The mixture was warmed and stirred at
flask in 4:1 DMF/H
2
O (4 ml) was added PdCl
2
(PPh
3
)
2
(21 mg,
0.03 mmol). The solution was stirred for 5 min at room tempera-
ture and then heated to 100 °C until TLC revealed complete conver-
sion of the starting material. The mixture was concentrated under
reduced pressure and the resulting crude product was purified by
flash chromatography over silica gel eluting with hexane/ethyl
acetate (9:1, v/v) to give a solid assigned as 4-((5-thiophen-2-
yl)thiophen-3-yl)pyrrolo[1,2-a]quinoxaline (DT-Q) (71 mg, 70%).
6
0 °C. When reaction was over, the mixture was poured into cold
water and extracted with ethyl acetate. Organic phase was washed
two times with Na SO , and then dried with MgSO . After the
2
3
4
filtration, the solvent was removed on a rotary evaporator and
the residue was purified by flash chromatography over silica gel
eluting with hexane/ethyl acetate (9:1, v/v) to give a solid identi-
fied as 4-(5-bromothiophen-3-yl)pyrrolo[1,2-a]quinoxaline (1)
Synthetic route for the DT-Q synthesis is given in Scheme 1. 1
NMR (400 MHz, CDCl ): d 8.08 (dd, J = 2.9 Hz, J = 1.2 Hz, 1H, H-1),
H
1
(
100 mg, 76%). H NMR (400 MHz, CDCl
3
): d 9.27 (m, 1H, H-10),
3
8
.05 (m, 1H, H-9), 8.00 (dd, J = 2.9 Hz, J = 1.2 Hz, 1H, H-1), 7.73
8.03 (dd, J = 8.1 Hz, J = 1.4 Hz, 1H, H-9), 7.83 (dd, J = 5.0 Hz,
J = 1.2 Hz, 1H, thiophenès H), 7.58 (dd, J = 5.1 Hz, J = 1.2 Hz, 1H, thi-
ophenès H), 7.51 (m, 2H, H-6 and H-7), 7.41 (td, J = 7.7 Hz,
J = 1.3 Hz, 1H, H-8), 7.25 (m, 4H, H-3 and thiophenès H), 6.94 (d,
(
dd, J = 5.0 Hz, J = 1.2 Hz, 1H, H-6), 7.48 (m, 3H, H-7, H-8 and H-
1
3
1
2), 7.09 (d, J = 4.3 Hz, 1H, H-3), 6.89 (d, J = 4.3 Hz, 1H, H-2);
): d 148.8, 139.0, 137.0, 130.1, 128.4, 128.2,
27.4, 127.0, 126.5, 126.3, 126.1, 119.5, 115.4, 109.5, 99.9.
C
NMR (100 MHz, CDCl
1
3
1
3
J = 4.1 Hz, 1H, H-2); C NMR (100 MHz, CDCl
1
1
3
): d 149.7, 140.0,
37.4, 134.8, 130.3, 129.7, 129.2, 128.3, 128.2, 128.1, 127.7,
27.2, 126.7, 126.1, 125.4, 124.4, 118.9, 116.1, 108.2.
2
(
.1.3. 4-((5-Thiophen-2-yl)thiophen-3-yl)pyrrolo[1,2-a]quinoxaline
DT-Q)
To a solution of 4-(5-bromothiophen-3-yl)pyrrolo[1,2-a]quin-
oxaline (1) (100 mg, 0.3 mmol), 2-thienylboronic acid (46 mg,
.36 mmol) and KHCO (42 mg, 0.42 mmol) in a round-bottomed
2.1.4. Synthesis of trithiophene-quinoxaline monomer (TT-Q)
2.1.4.1. 2,5-dibromothiophene-3-carbaldehyde (3). This compound
was prepared from 3-thiophenecarboxaldehyde (2) according to
0
3
ꢁ
1
Fig. 1. Cyclic voltammogram comparison of oxidation potentials of (a) MT.Q, (b) DT-Q and (c) TT-Q on a Pt disc electrode at 100 mV s in 0.1 M TBAPF
6
/acetonitrile (dashed
curve: peak clipping after the first oxidation potentials of MT.Q, DT-Q and TT-Q).

5
82
B.B. Çarba ßs et al. / Reactive & Functional Polymers 71 (2011) 579–587
a literature procedure (350 mg, 47%) [35]. 1H NMR (400 MHz,
CDCl ) d
): d 9.80 (s, 1H), 7.34 (s, 1H); 13C NMR (400 MHz, CDCl
83.2, 139.3, 128.7, 124.2, 113.4.
2 3 2
(2 ml) was added PdCl (PPh ) (26 mg, 0.037 mmol). The solution
3
3
was stirred for 5 min at room temperature and then heated to
100 °C until TLC revealed complete conversion of the starting
material. The mixture was concentrated under reduced pressure
and the resulting crude product was purified by flash chromatogra-
phy over silica gel eluting with hexane/ethyl acetate (19:1, v/v) to
1
0
0
00
0
2
.1.4.2. [2,2 ;5 ,2 ]-Terthiophene-3 -carbaldehyde (4). To a solution
of the 2,5-dibromothiophene-3-carbaldehyde (3) (100 mg,
.37 mmol), 2-thienylboronic acid (46 mg, 0.36 mmol) and KHCO
51.8 mg, 0.52 mmol) in a round-bottomed flask in 4:1 DMF/H
0
0
00
0
give a solid identified as [2,2 ;5 ,2 ]-terthiophene-3 -carbaldehyde
0
3
1
(
4) (86 mg, 83%). H NMR (400 MHz, CDCl
3
): d 10.1 (s, 1H), 7.56
(
2
O
Fig. 2. Repeated potential scan electropolymerization of 2 mM TT-Q on a Pt disc electrode at 100 mV sꢁ1 in 0.1 M TBAPF
6
/DCM.
2
Fig. 3. Scan rate dependence of P(TT-Q) film (25 mC/cm ) on a Pt disc electrode in 0.1 M TBAPF
6
/DCM at different scan rates between 20 mV/s and 200 mV/s. (Inset:
a c
Relationship of anodic (I ) and cathodic (I ) current peaks as a function of scan rate).

B.B. Çarba ßs et al. / Reactive & Functional Polymers 71 (2011) 579–587
583
(
s, 1H), 7.49 (dd, J = 5.1 Hz, J = 1.1 Hz, 1H), 7.30 (m, 2H), 7.21 (dd,
3. Results and discussion
J = 3.62 Hz, J = 1.1 Hz, 1H), 7.15 (dd, J = 5.2 Hz, J = 3.7 Hz, 1H), 7.04
13
(
dd, J = 5.1 Hz, J = 3.7 Hz, 1H);
C NMR (400 MHz, CDCl
3
): d
3.1. Electrochemical polymerization of TT-Q
1
1
85.2, 146.1, 137.8, 136.9, 135.7, 132.2129.4, 128.9, 128.5, 128.2,
25.9, 125.1, 122.5.
First of all, the redox behaviors of three different thiophene
derivatives (4-(thiophen-3-yl)pyrrolo[1,2-a]quinoxaline (MT-Q),
4
-((5-thiophen-2-yl)thiophen-3.yl)pyrrolo[1,2-a]quinoxaline (DT-
2
.1.4.3. 4-((2,5-Dithiophen-2-yl)thiophen-3-yl)pyrrolo[1,2-a]quinoxa-
0
0
00
Q) and 4-((2,5-dithiophen-2-yl)thiophen-3-yl)pyrrolo[1,2-a]quin-
oxaline (TT-Q)) were investigated by CV in 0.1 M TBAPF dissolved
in acetonitrile and the results are depicted in Fig. 1. The voltammo-
gram of TT-Q exhibited one reversible oxidation peak at about
line (TT-Q). This compound was synthesized from [2,2 ;5 ,2 ]-ter-
thiophene-3 -carbaldehyde (4) according to known literature
procedure [23]. Synthetic route for the TT-Q synthesis is given
in Scheme 2. H NMR (400 MHz, CDCl
0
6
1
3
): d 8.14 (dd, J = 7.8 Hz,
1
.10 V and another irreversible peak at 1.30 V vs Ag/AgCl during
J = 1.2 Hz, 1H, H-9), 7.96 (m, 1H, H-1), 7.90 (d, J = 8.0 Hz, 1H,
the first anodic scan. Due to high electron affinity, the reversible
peak most probably corresponds to the loss of electron from quin-
oxaline moiety. On the other hand, the irreversible peak at 1.30 V
was assigned to oxidation of terthienyl system. A close inspection
of Fig. 1a–c, clearly indicates that the irreversible peak shifts to
more positive potentials with decreasing number of thiophene
groups in the monomer. These results were in well agreement with
H-6), 7.55 (m, 2H, H-7 and H-8), 7.50 (s, 1H, thiophenès H),
7
.29 (m, 3H, thiophenès H), 7.14 (d, J = 5.2 Hz, 1H, thiophenès
H), 7.08 (m, 1H, H-3), 6.90 (dd, J = 5.1 Hz, J = 3.8 Hz, 1H, thi-
1
3
ophenès H), 6.82 (m, 1H, H-2), 6.76 (m, 1H, thiophenès H);
NMR (400 MHz, CDCl ): d 150.3, 136.6, 135.9, 135.7, 135.2,
35.0, 134.9, 130.2, 128.3, 127.9, 127.8, 127.5, 127.1, 126.8,
26.33, 126.3, 125.8, 125.4, 125.0, 114.6, 114.1, 113.8, 108.7.
C
3
1
1
2
6
Fig. 4. Electronic absorption spectra of P(TT-Q) on ITO (25 mC/cm ) in 0.1 M TBAPF /DCM solution during anodic oxidation of the polymer film.
Table 1
Voltammetric and spectroelectrochemical data for P(TT-Q) recorded in DCM containing 0.1 M TBAPF
6
.
k/nm at charge 25 mC/cm2
T
T
D
%T OD
D
CE (cm /C)
2
Reduced state
Oxidized state
bleached
colored
4
7
043
12
32
39.40
77.21
45.32
47.20
68.18
73.5
7.41
6.51
26.79
0.0784
0.054
0.2017
114
123
426
1

5
84
B.B. Çarba ßs et al. / Reactive & Functional Polymers 71 (2011) 579–587
the electronic nature of each monomer: the oxidation potential
was shifted to lower positive values with increasing -conjugation
36].
Next, we focused on the electropolymerization of MT-Q, DT-Q
and TT-Q monomers in dichloromethane (DCM) containing 0.1 M
TBAPF as supporting electrolyte via potential cycling. During
repetitive anodic scans of TT-Q monomer, in the range of
0.00–1.55 V, a new reversible redox couple appeared at about
1.00 V. An increase in the current intensities of this new redox cou-
ple was also noted (Fig 2), indicating both the formation of an elec-
troactive P(TT-Q) polymer film on the surface of the Pt disc
working electrode and also an increase in the thickness of the poly-
mer film. However, in the case of monomers MT-Q and DT-Q, no
new redox couple with increasing intensity and no polymer film
p
[
6
ꢁ
5
Fig. 5. The Stern–Volmer plots of TT-Q 1.0 ꢀ 10 M in the presence of various metal ions (each 2–10 mM). Metal ion solutions were prepared from Fe(NO
3
)
3
ꢂ9H
2
O,
ꢁ
5
Cu(NO )
3 2
ꢂ3H
2
O, Ni(NO
3
)
2
ꢂ6H
2
3 2
O, Zn(NO ) ꢂ6H
2
O, LiClO
4
, ferrocene and AgNO
3
in DMF. (Inset: The fluorescence emission spectra of TT-Q 1.0 ꢀ 10 M in DMF with successive
ꢁ
3
ꢁ3
3+
addition of (a) 2–10 mM, (b) 2.0 ꢀ 10 to 10.0 ꢀ 10 mM Fe ions. The excitation wavelength is 350 nm for TT-Q.
Fig. 6. The Stern–Volmer plots of P(TT-Q) in the presence of various metal ions (each 2–10 mM). Metal ion solutions were prepared from Fe(NO
3
)
3
ꢂ9H
2
O, Cu(NO
3
)
2
ꢂ3H
2
O,
ꢁ
5
Ni(NO
3 2
) ꢂ6H
2
O, Zn(NO
3 2
)
ꢂ6H
2
O, LiClO
4
, ferrocene and AgNO
3
in DMF. (Inset: The fluorescence emission spectra of PTT-Q 1.0 ꢀ 10 M in DMF with successive addition of
ꢁ
3
ꢁ3
3+
(
a) 2–10 mM, (b) 2.0 ꢀ 10 to 10.0 ꢀ 10 mM Fe ions. The excitation wavelength is 500 nm for P(TT-Q).

B.B. Çarba ßs et al. / Reactive & Functional Polymers 71 (2011) 579–587
585
formation were noted. Therefore, we focused our interest on the
TT-Q monomer for the further investigations.
Since one of the important characteristics of an electrochromic
material is its electrochemical/optical stability upon multiple
switching in a short response time [37], these parameters for elec-
trochemically synthesized P(TT-Q) film was investigated under a
square wave input of 0.0–1.3 V in 10 s intervals by monitoring
the visible transmittance at 412, 732 and 1043 nm and the results
are tabulated in Table 1. It is found that the polymer film showed a
reversible response between a potential range from 0.0 V (neutral)
to +1.3 V (oxidized) with a response time of 1.50 s at 95% of the
In order to elucidate the redox behavior of the polymer P(TT-Q),
the coated electrode was washed with DCM to remove the mono-
mer and oligomeric species and then it was placed into monomer-
free electrolyte solution. The polymer film exhibited a reversible
redox couple (Ep,a = 1.23 V and Ep,c = 1.18 V) with a half peak
potential of 1.05 V and the peak currents were linearly propor-
tional to the scan rate indicating a non-diffusional redox process
and a well-adhered electroactive polymer film (Fig. 3 and its inset).
Formation of P(TT-Q) via potential cycling was also confirmed by
recording the FT-IR spectra of both monomer and its polymer. It
maximum transmittance and the optical contrast (D%T) was calcu-
lated as 7.41%, 9.51% and 26.79% at 412, 732 and 1043 nm, respec-
tively. Coloration efficiency (CE) is a useful term for measuring the
power efficiency of the electrochromic devices and can be calcu-
lated via optical density using the following equations at a given
wavelength [38];
ꢁ
1
is noteworthy to mention that disappearance of 704 cm
3
and
116 cm peaks in the polymer spectrum indicates that polymer-
ization proceeds via C-5 position of external thiophene units. Fur-
ꢁ1
ꢁ1
thermore, presence of a new peak at about 835 cm indicates the
ꢁ
CEðkÞ ¼
D
ODðkÞ=Q
d
and
D
ODðkÞ ¼ log½TOXðkÞ=TredðkÞꢄ
presence of dopant ion PF .
6
where Q
d
is the injected/ejected charge during a redox process, Tox
and Tred are the transmittance in the oxidized and the neutral states,
respectively.
3.2. Electro-optical properties of P(TT-Q)
On the basis of these equations, P(TT-Q) exhibited CE of 114 and
2
To reveal the electro-optical properties of the polymer film,
123 cm /C at 412 and 732 nm respectively. On the other hand, at
2
optical changes were monitored while going from the neutral to
the oxidized states. The P(TT-Q) film was coated on ITO via poten-
tial cycling and optical features of the film were elaborated in the
monomer-free electrolyte solution by recording the changes in the
absorption spectra under a variety of voltage pulses after neutral-
ization at 0.0 V and results are shown in Fig. 4. As seen from Fig. 4,
1043 nm, its CE was found to be relatively high (426 cm /C) at
95% of the full switch, which indicated that the P(TT-Q) might be
a good candidate for electrochromic and optical device application.
3.3. Fluorescence study
the neutral state polymer film has a well defined absorption band
Since the electrochemically obtained P(TT-Q) was found to be
soluble in DMF its fluorescence property was investigated in this
solvent. Although the monomer exhibits an emission at about
520 nm when excited at 350 nm, its polymer has a relatively
intense emission at about 585 nm when excited at 500 nm, corre-
sponding to orange color. These results indicate that the polymer is
an orange emitter and may find applications in various fields, such
as light emitting diode, organic lasers and electroluminescent
materials. Binding affinities of TT-Q and P(TT-Q) towards various
ions were evaluated by monitoring the change in the fluorescence
ꢃ
at 410 nm ascribed to the
lower energy end of this band, the band gap (E
1
p
–
p
transition and from the onset of
) was found to be
.94 eV. Upon electrochemical oxidation, the P(TT-Q) film shows
g
a simultaneous decrease in the absorbance at 410 nm, which is
accompanied with a color change from yellowish orange to green.
A new intensifying band at 700 nm was also noted, indicating the
formation of charge carriers, with increasing applied potentials.
Beyond 0.50 V another new band in the near IR region was also
noted.
Fig. 7. KSV values of P(TT-Q) in the presence of Fe3+, Cu2+, Ag , Ni2+, Fe2+, Zn2+, Li+ (each 2–10 mM in DMF). (Inset: KSV values of TT-Q in the presence of Cu2+, Ag , Ni2+, Fe2+
Zn , Li (each 2–10 mM in DMF)).
+
+
,
2+
+

5
86
B.B. Çarba ßs et al. / Reactive & Functional Polymers 71 (2011) 579–587
Fig. 8. KSV values of P(TT-Q) in the presence of Fe3+, Cu2+, Ag , Ni2+, Fe2+, Zn2+, Li (each 2–10 mM in DMF). (Inset: KSV values of P(TT-Q) in the presence of Cu2+, Ag , Ni2+, Fe2+
Zn , Li (each 2–10 mM in DMF)).
+
+
+
,
2+
+
seen by naked eye under UV lamp. The emission color of TT-Q in
DMF, for example, turned from green to colorless after the addition
3
+
of Fe ions. Also, the addition of this ion to the polymer solution
causes a quenching in the intensity of the orange color emission
of the polymer (Fig. 9).
4
. Conclusion
In summary, three fluorescent monomers, MT-Q, DT-Q and TT-
Q, based on thienyl systems bearing pendant quinoxaline moieties
were synthesized. Among them, only electrochemical polymeriza-
6
tion of TT-Q was feasible in DCM-TBAPF , solvent-electrolyte sys-
tem, yielding a fluorescent polymer, P(TT-Q). Studies on the
electro-optical properties of the polymer film revealed that P(TT-
Q) shows a reversible redox couple with a band gap of 1.94 eV
and electrochromic response during p-doping with a relatively
3
+
Fig. 9. Emission colors of (1) TT.Q, (2) TT-Q in the presence of Fe ion (3), P(TT-Q),
(
3
+
4) P(TT-Q) in the presence of Fe ion in DMF under handheld UV lamp.
2
high coloration efficiency (426 cm /C at 1043 nm). Furthermore,
intensity upon successive addition of metal ions and the results are
depicted in the form of Stern–Volmer plots in Figs. 5 and 6, respec-
tively. Inset of Fig. 5 shows the emission spectra of TT-Q in DMF
upon successive addition of Fe3 ion with an excitation wavelength
of 350 nm (Fig. 5). As seen from inset a of Fig. 5, the addition of the
fluorescence of both monomer, TT-Q, and its polymer were found
3
+
to be highly sensitive towards Fe ions which make them a prom-
3
+
ising sensor candidate for Fe ion detection, besides the use of
+
P(TT-Q) in electronic and optical applications.
3
+
Fe ion resulted in a gradual decrease in the intensity of the fluo-
rescence maximum at 520 nm due to electron or energy transfer
between metal ion and TT-Q fluorophore, and a maximum quench-
ing efficiency of 95% was obtained. The fluorescence quenching re-
sponse of P(TT-Q) emission upon adding Fe3+ ions was also
determined and the results are depicted in the inset of Fig. 6.
References
[1] C.K. Jang, Y.H. Lee, S.Y. Han, J.Y. Jaung, Dyes Pigments 79 (2008) 101.
[
2] T. Yamamoto, K. Sugiyama, T. Kushida, T. Inoue, J. Am. Chem. Soc. 118 (1996)
3930.
[
3] T. Yamamoto, Macromol. Rapid Commun. 23 (2002) 583.
[4] N. Blouin, A. Michaud, D. Gendron, S. Wakim, E. Blair, R. Neagu-Plesu, M.
Belletete, G. Durocher, Y. Tao, M. Leclerc, J. Am. Chem. Soc. 130 (2008) 732.
[5] A. Gadisa, W. Mammo, L.M. Andersson, S. Admassie, F. Zhang, M.R. Andersson,
O. Inganäs, Adv. Funct. Mater. 17 (2007) 3836.
[6] P. Karastatiris, J.A. Mikroyannidis, I.K. Spiliopoulos, A.P. Kulkarni, S.A. Jenekhe,
Macromolecules 37 (2004) 7867.
As there is no quenching effect for lower concentration of ion
Fe3+ to the monomer (Inset b of Fig. 5), polymer has more quench-
ing effect (Inset b of Fig. 6).
The Stern–Volmer quenching constant, KSV, was also deter-
mined and the results are depicted in Figs. 7 and 8 for monomer
and polymer solutions, respectively [39]. It is noteworthy that
the fluorescence of TT-Q and PTT-Q is not significantly influenced
[
7] C.G. Bangcuyo, J.M. Ellsworth, U. Evans, M.L. Myrick, U.H.F. Bunz,
Macromolecules 36 (2003) 546.
[
8] Y.J. Mikata, M. Wakamatsu, S. Yano, Dalton Trans. (2005) 545.
[9] T. Lazarides, T.A. Miller, J.C. Jeffery, T.K. Ronson, H. Adams, M.D. Ward, Dalton
Trans. (2005) 528.
2
+
2+
2+
2+
+
+
by the addition of Cu , Ni , Zn , Fe , Li and Ag ions indicating
that both the monomer and its corresponding polymer can be uti-
lized for fluorometric detection of Fe3 . This behavior can be clearly
[
10] L. Wang, X.J. Zhu, W.Y. Wong, J.P. Guo, W.K. Wong, Z.Y. Li, Dalton Trans. 9
(
2005) 3235.
+
[11] X. Zhan, Polym. Chem. 1 (2010) 409.

B.B. Çarba ßs et al. / Reactive & Functional Polymers 71 (2011) 579–587
587
[
12] K. Wagner, L.L. Crowe, P. Wagner, S. Gambhir, A.C. Partridge, J.C. Earles, T.M.
Clarke, K.C. Gordon, D.L. Officer, Macromolecules 43 (2010) 3817.
13] J. Roncali, Chem. Rev. 92 (1992) 711.
[26] C.B. Black, B. Andrioletti, A.C. Try, C. Ruiperez, J.L. Sessler, J. Am. Chem. Soc. 121
(1999) 10438.
[27] X. Zhan, Y. Liu, X. Wu, S. Wang, D. Zhu, Macromolecules 35 (2002)
2529.
[
[
14] S. Jin, S. Cong, G. Xue, H. Xiong, B. Mansdorf, S.Z.D. Cheng, Adv. Mater. 14
(
2002) 1492.
[28] S.H. Jung, D.H. Suh, H.N. Cho, Polym. Bull. 50 (2003) 251.
[29] M. Jonforsen, T. Johansson, O. Inganas, M.R. Andersson, Macromolecules 35
(2002) 1638.
[
[
15] G.A. Sotzing, J.R. Reynolds, P.J. Steel, Chem. Mater. 8 (1996) 882.
16] L.B. Groenendaal, J. Friedrich, D. Freitag, H. Pielartzik, J.R. Reynolds, Adv. Mater.
1
2 (2000) 481.
[30] B.H. Lee, J.Y. Jaung, J.-W. Cho, K.J. Yoon, Polym. Bull. 50 (2003) 9.
[31] J.F. Morin, M. Leclerc, Macromolecules 35 (2002) 8413.
[32] P.M. Hergenrother, H.H. Levine, J. Polym. Sci. Part A-1 5 (1967) 1453.
[33] D. O’Brien, M.S. Weaver, D.G. Lidzey, D.D.C. Bradley, Appl. Phys. Lett. 69 (1996)
881.
[34] C. Zhang, Z. Wang, Appl. Organometal. Chem. 23 (2008) 9.
[35] M. Pomerantz, H. Yang, Y. Cheng, Macromolecules 28 (1995) 5706.
[36] B. Rasch, W. Vielstich, J. Electroanal. Chem. 370 (1994) 109.
[37] P.M.S. Monk, R.J. Mortimer, D.R. Rosseinsky, Electrochromism: Fundamentals
and Applications, VCH, Weinheim, 1995.
[
[
17] J. Roncali, P. Blanchard, P. Frére, J. Mater. Chem. 15 (2005) 1589.
18] T.T. Steckler, K.A. Abboud, M. Craps, A.G. Rinzler, J.R. Reynolds, Chem.
Commun. 46 (2007) 4904.
19] L. Huo, Y. Zhou, Y. Li, Macromol. Rapid Commun. 29 (2008) 1444.
20] X. Guo, F.S. Kim, S.A. Jenekhe, M.D. Watson, J. Am. Chem Soc. 131 (2009) 7206.
21] J. Peet, M.L. Senatore, A.J. Heeger, G.C. Bazan, Adv. Mater. 21 (2009) 1521.
22] G. Sonmez, C.K.F. Shen, Y. Rubin, F. Wudl, Angew. Chem. Int. Ed. 43 (2004)
[
[
[
[
1
498.
[
[
23] F. Algi, A. Cihaner, Adv. Funct. Mater. 18 (2008) 3583.
24] H. Yi, R.G. Johnson, A. Iraqi, D. Mohamad, R. Royce, D.G. Lidzey, Macromol.
Rapid. Commun. 29 (2008) 1804.
[38] B.D. Reeves, C.R.G. Greiner, A.A. Argun, A. Cirpan, T.D. McCarley, J.R. Reynolds,
Macromolecules 37 (2004) 7559.
[
25] P. Anzenbacher, A.C. Try, H. Miyaji, K. Jursiková, V.M. Lynch, M. Marquez, J.L.
Sessler, J. Am. Chem. Soc. 122 (2000) 10268.
[39] J.R. Lakowicz, Principles of Fluorescence Spectroscopy, Kluwer Academic/
Plenum Publishers, New York, 1999.