Synthesis and spectroelectrochemical properties of two new dithienylpyrroles bearing anthraquinone units and their polymer films

Article abstract of DOI:10.1016/j.electacta.2010.07.012

Two new kinds of dithienylpyrroles bearing anthraquinone units have been prepared by the Knorr-Paal condensation between 1,4-di(thiophen-2-yl)butane-1,4- dione and 1-/2-amino-anthraquinone. The corresponding polymer films were successfully synthesized via electropolymerization. The electrochemical, electro-optical properties and electrochromic behavior of the two polymer films were further investigated by thermogravimetric analysis, cyclic voltammetry and UV-vis absorption spectra. The results demonstrated that the two polymer films were thermally stable up to nearly 300°C. Both the two electroactive polymer films presented a stable and well-defined reversible redox process as well as multicolor electrochromic change from yellow (in the reduced state) to grey (in the neutral state) and then to blue (in the oxidized state).

Full text of DOI:10.1016/j.electacta.2010.07.012

Electrochimica Acta 55 (2010) 6933–6940
Contents lists available at ScienceDirect
Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
Synthesis and spectroelectrochemical properties of two new dithienylpyrroles
bearing anthraquinone units and their polymer films
Gang Wang, Xiangkai Fu∗, Jing Huang, Liu Wu, Qiuliang Du
College of Chemistry and Chemical Engineering, Research Institute of Applied Chemistry Southwest University, The Key Laboratory of Applied Chemistry of Chongqing Municipality,
Key Laboratory of, Eco-environments in Three Gorges Reservoir Region (Ministry of Education), Chongqing 400715, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 8 June 2010
Received in revised form 5 July 2010
Accepted 5 July 2010
Available online 25 July 2010
Two new kinds of dithienylpyrroles bearing anthraquinone units have been prepared by the Knorr–Paal
condensation between 1,4-di(thiophen-2-yl)butane-1,4-dione and 1-/2-amino-anthraquinone. The cor-
responding polymer films were successfully synthesized via electropolymerization. The electrochemical,
electro-optical properties and electrochromic behavior of the two polymer films were further inves-
tigated by thermogravimetric analysis, cyclic voltammetry and UV–vis absorption spectra. The results
demonstrated that the two polymer films were thermally stable up to nearly 300 ◦C. Both the two elec-
troactive polymer films presented a stable and well-defined reversible redox process as well as multicolor
electrochromic change from yellow (in the reduced state) to grey (in the neutral state) and then to blue
(in the oxidized state).
Keywords:
Dithienylpyrroles
Polythienylpyrroles
Aminoanthraquinone
Electropolymerization
Electrochromic materials
© 2010 Elsevier Ltd. All rights reserved.
1. Introduction
electrochemical polymerization of them which exhibited relatively
lower oxidation potential (which made its electropolymerization
Conducting polymers have continued to fascinate many sci-
entists due to their synthetic accessibility and ease of modified
architecture which can control the polymer’s spectroelectrochem-
ical properties. Owing to their excellent spectroelectrochemical
properties, conducting polymers have been widely used in elec-
trochromic displays [1,2] and smart windows [3], rechargeable
batteries, light emitting diodes (LEDs), toxic waste cleanup, sensors,
corrosion inhibitors, field effect transistors (FETs), electromagnetic
interference (EMI) shielding, etc. [4].
Polythienylpyrrole derivatives, as a kind of hybrid conduct-
ing polymer materials, are assembled and functionalized through
the central pyrrole unit to which different substituents could be
introduced [5,6]. Moreover, the new hybrid polymer materials
have received much attention due to their synthetic and modified
accessibility, high environmental stability, long cycle life, easy pro-
cessability, multichromic properties and various applications on
donor–acceptor (D–A) molecular materials [7–10], electrochemi-
cal sensors [11–14], electrochromic and fluorescent materials etc.
[15–25] in academic research.
easier and avoided over oxidation problems) and electrochromic
and fluorescence properties. In addition, anthraxquinone deriva-
tives showed excellent performance on electron transfer and
electrochromism etc. [26–30]. Based on these reports, two
new hybrid materials 1-(2,5-di (thiophen-2-yl)-1H-pyrrol-1-yl)-
anthraquinone (SNS-1AQ) and 2-(2,5-di (thiophen -2-yl)-1H-
pyrrol-1-yl)-anthraquinone (SNS-2AQ) in which anthraquinone
moieties were introduced to the central pyrrole ring of the SNS
monomer, were synthesized and corresponding polymer films
PSNS-1AQ and PSNS-2AQ were prepared by electropolymerization,
and their spectroelectrochemical properties were also character-
ized and compared.
2. Experimental details
2.1. General
All chemicals and reagents used in this paper, unless other-
wise specified, were purchased from Aldrich, Aladdin, and TCI
Chemical Co. and used as received. All the solvents were fur-
ther purified before use. All important compounds synthesized
were characterized by 1H NMR, 13C NMR and APCI-MS. 1H NMR
spectra were measured on a Bruker AV300 (300 MHz) spectrom-
eter at the ambient temperature with tetramethylsilane (TMS) as
an internal standard. 13C NMR spectra were recorded on Bruker
Recently, Atilla Cihaner et al. [15–20] reported the synthesis
of several SNS derivatives by the Knorr–Paal condensation and
∗
Corresponding author. Tel.: +86 2368253704; fax: +86 2368254000.
E-mail address: fxk@swu.edu.cn (X. Fu).
0013-4686/$ – see front matter © 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.electacta.2010.07.012

6934
G. Wang et al. / Electrochimica Acta 55 (2010) 6933–6940
Scheme 1. Synthesis of 1-/2-(2,5-di(thiophen-2-yl)-1H-pyrrol-1-yl)-anthraquinone. (a) SOCl2,10 h, reflux. (b) AlCl3,CH2Cl2,18–20 ◦C, 24 h. (c1/c2) PTSA, toluene, reflux, 72 h.
AV300 (75 MHz) spectrometer at the ambient temperature and
chemical shifts were recorded in ppm from the solvent resonance
employed as the internal standard. Atmospheric pressure chemical
ionization mass spectra were obtained on a Bruker HCT Mass Spec-
trometer. Melting points were determined by differential scanning
calorimetry (TAQ100) at a heating rate of 10 ◦C/min under Ar atmo-
sphere. Infrared spectroscopic measurements were performed in
the range 4000–400 cm−1 on a Bruker Tensor 27 FTIR Spectrom-
eter. UV spectra were performed on a Unico UV-4802H UV–vis
spectrophotometer connected to a computer. Thermogravimetric
analysis (TGA) was performed under dynamic N2 atmosphere at
a heating rate of 10 ◦C/min, from room temperature to 1000 ◦C.
Cyclic voltammetry was carried out on CHI 650B electrochemical
workstation using three-electrode system.
2.2. General procedure for the synthesis of SNS-1AQ and SNS-2AQ
A
solution of 1.0 mmol 1,4-di(thiophen-2-yl)-butane-
1,4-dione [6], 1.0 mmol amine(1-aminoanthraquinone or
2-aminoanthraquinone) and 0.1 mmol p-toluenesulfonic acid
in 100 mL dry toluene were heated under reflux in a Dean-Stark
apparatus until all the starting materials were consumed (TLC).
The flask was cooled to room temperature and the solvent was
removed under reduced pressure. The resulted residue was
filtered through a short pad of silica gel by eluting with DCM
(CH2Cl2) to give crude SNS derivatives. Then the crude product
was purified by silica gel column chromatography, eluting with
dichloromethane/petroleum = 2/1 (Scheme 1).
2.3. 1-(2,5-di(thiophen-2-yl)-1H-pyrrol-1-yl)-anthraquinone
(SNS-1AQ)
Following the general procedure the product was obtained as
an black-brown solid (yield, 48%). 223–224 ◦C. 1H NMR(300 M,
CDCl3): ıH 8.52 (d, J = 7.6 Hz, 1H), 8.23 (d, J = 6.3 Hz, 1H), 8.07–8.09
(t, J1 = 7.4 Hz, J2 = 5.9 Hz, 1H), 7.81–7.86 (t, J1ꢀ = 7.7 Hz, J2ꢀ = 7.7 Hz,
Fig. 1. Repeated scan electropolymerization of (a) SNS-1AQ (b) SNS-2AQ in 0.01 M
TBAP/DCM vs. Ag/AgCl at a scan rate of 100 mV/s.

G. Wang et al. / Electrochimica Acta 55 (2010) 6933–6940
6935
Fig. 2. (a) Redox behavior of PSNS-1AQ film at different scan rates and (b) relationship of anodic and cathodic current peaks as a function of scan rate in 0.01 M TBAP/DCM.
(c) Redox behavior of PSNS-2AQ film at different scan rates and (d) relationship of anodic and cathodic current peaks as a function of scan rate in 0.01 M TBAP/DCM.
1H), 7.70–7.74 (q, 3H), 6.95 (d, J = 4.8 Hz, 2H), 6.71–6.75 (t, 4H),
6.59 (d, J = 2.7 Hz, 2H). 13C NMR (75 MHz, CDCl3): ıC 182.6, 181.1,
138.3, 137.9, 135.1, 134.5, 134.4, 134.1, 133.9, 133.8, 132.4, 131.4,
129.1, 128.9, 127.5, 126.8, 126.7, 124.7 124.3, 110.6. FTIR (KBr,
cm−1): 3107, 3085, 3070, 1670, 1580, 1411, 1315, 1279, 1162, 1111,
966, 773, 708, 687. APCI-MS (m/z): 437(M+). UV/vis (DCM): ꢀmax1
256 nm, ꢀmax2 332 nm, lgε1 4.39, lgε2 4.15.
solution was used to elaborate redox behavior and electropoly-
merization of the two monomers: SNS-1AQ and SNS-2AQ. The
monomers (0.2 mM) were successfully electropolymerized via
repetitive cycling voltammogram or constant potential electroly-
sis (1.2 V, 30 min) in three-electrode system using platinum disk
(0.02 cm2) as working electrodes, platinum wire as counter elec-
trodes and Ag/AgCl in 3 M NaCl (aq) solution as a reference.
In order to investigate the electrochemical properties exactly,
the polymer films coated on the working electrodes were
washed with DCM after electropolymerization to remove unre-
acted monomer and oligomeric species and then transferred into
monomer-free electrolyte solution. The indium-tin oxide (ITO.
50 ꢁ/ꢀ, 0.7 cm × 5 cm) electrodes were used as substrate for the
polymer films to deposition. UV–vis spectra and cyclic voltamme-
try were used to investigate spectroelectrochemical measurements
which were carried out to consider absorption spectra of the poly-
mer films under applied voltage. The spectroelectrochemical cell
was made up of three-electrode system including a quartz cuvette,
an Ag wire (pseudo-RE) which was calibrated externally using a
1 mM solution of ferrocene/ferrocenium coupled in an electrolyte
solution, Pt wire counter electrode (CE) and ITO glass as trans-
parent working electrode (WE). The polymer films on the ITO
glass were switched between neutral and doped states several
times in monomer-free electrolyte solution (TBAP/DCM) to study
the electrochemical redox behavior, electro-optical properties and
reversibility.
2.4. 2-(2,5-di(thiophen-2-yl)-1H-pyrrol-1-yl)-anthraquinone
(SNS-2AQ)
Following the general procedure the product was obtained as an
orange solid (yield, 65%). 219–220 ◦C. 1H NMR (300 M, CDCl3): ıH
8.28–8.34 (t, 3H), 8.20 (s, 1H), 7.80–7.83 (t, 2H), 7.64 (d, J = 8.1 Hz,
1H), 7.08 (d, J = 4.8 Hz, 2H), 6.80–6.82 (t, 2H), 6.56–6.59 (t, 2H). 13
C
NMR (75 MHz, CDCl3): ıC 182.4, 182.1, 143.8, 135.1, 134.4, 134.3,
134.1, 134.0, 133.5, 133.4, 133.0, 129.8, 128.4, 128.3, 127.4, 127.1,
125.6, 125.0, 111.2. FTIR (KBr, cm−1): 3103, 3074, 1671, 1593, 1491,
1405, 1331, 1289, 1160, 1111, 961, 766, 709, 677. APCI-MS (m/z):
437 (M+). UV/vis (DCM): ꢀmax1 255 nm, ꢀmax2 327 nm, lgε1 4.36,
lgε2 4.06.
2.5. Electropolymerization and characterization
0.01 M tetrabutylammonium perchlorate (TBAP)/DCM which
was distilled over CaH2 under N2 atmosphere) as electrolyte

6936
G. Wang et al. / Electrochimica Acta 55 (2010) 6933–6940
3. Results and discussion
3.1. Electropolymerization of SNS-1AQ and SNS-2AQ
In order to study the redox behaviors of the two polymer films,
the corresponding monomers were scanned electropolymeriza-
tion via cyclic voltammetry. As the electropolymerization time
increased, the thickness of PSNS-1AQ and PSNS-2AQ film increased
and their colors changed from light brown-grey to light violet then
to blue-violet. It was reported that the oxidation of dithienylpyr-
role systems do not significantly affected by the groups substituted
on the N-position of the central pyrrole ring [15,16,18]. As shown
in Fig. 1, in the first cycle, a single irreversible oxidation peak was
observed for SNS-1AQ and SNS-2AQ at 0.95 V and 0.94 V, respec-
tively. The results were well in agreement with the redox behavior
of SNS (Eox = 0.94 V) reported by Ferraris and Hanlon [29]. This
result confirmed that anthraquinone units had no contributions
to the electronic structure of the dithienylpyrrole trimeric sys-
tem. Moreover, a new reversible redox couple was observed after
repeated cycle and the current value of this reversible peak con-
tinued to intensify after consecutive cycles for the two monomers,
which was attributed to the formation of an electroactive polymer.
As seen in Fig. 2, the polymer films exhibited a single and well-
defined reversible redox couple (Ep,1/2) that was centered at about
0.7 V for PSNS-1AQ and 0.58 V for PSNS-2AQ. In addition, both of the
two polymer films retained their promising reversible and well-
defined properties even at higher scan rates or after hundreds of
cycles between their redox states (reduced and oxidized states).
Furthermore, it was found that both anodic and cathodic current
responses of the two polymer films increased linearly as the scan
rate increased, which demonstrated that the redox process was
non-diffusional and the electroactive polymers were well adhered
to the working electrodes surface [15–18,23–25].
Fig. 3. FTIR spectra of SNS-1AQ and SNS-2AQ as well as their corresponding poly-
mers.
3.3. Thermogravimetric analysis of PSNS-1AQ and PSNS-2AQ
Fig. 4 showed the high-resolution TGA curves of the two poly-
mers at a heating rate of 10 ◦C/min, from room temperature to
1000 ◦C. The three curves reflected the whole weight-loss process
of the two polymers. An initial weight loss was observed in the TG
curve for the two polymers between room temperature and about
150–200 ◦C that could be assigned to the loss of variable amounts of
solvent or water adsorbed or loosely bonded to the polymer chains.
The percentage assigned to the solvent/water loss was about 1% for
PSNS-1AQ and 0.7% for PSNS-2AQ, respectively. The polymers were
stable up to nearly 300 ◦C where the first significant weight loss
3.2. FTIR study
It was reported that there were three characteristic peaks of
SNS units at 679 cm−1 for ␣-H of thiophene rings, 770 cm−1 for
␤-H of pyrrole ring and 843 cm−1for ␤/␤’-H of thiophene rings
in SNS derivatives and the analogous peaks were observed at
687 cm−1, 772 cm−1, 845 cm−1 and 676 cm−1, 766 cm−1, 843 cm−1
in SNS-1AQ and SNS-2AQ, respectively [15–20]. Comparing with
the monomers, the FTIR spectra of the polymers revealed
that electropolymerization mainly proceeded via SNS units and
anthraquinone subunits remained unchanged during polymeriza-
tion. For example, in the spectra of the PSNS-1AQ and PSNS-2AQ,
the disappearance of the peaks at 687 cm−1
,
676 cm−1 and
3106 cm−1, 3103 cm−1 which were attributed to ␣-H of thiophene
rings in the monomers of SNS-1AQ and SNS-2AQ, confirmed the
␣-coupling between the external thiophene rings. Therefore, the
corresponding polymers had linear chains due to the proceeding
polymerization via ␣–␣ linkages. However, all the other peaks
in the spectra of the polymer films almost remained unchanged
upon polymerization, but with some peaks weakened, widened
and red shifted, which unambiguously indicated the presence
of anthraquinone subunits in the polymer backbone: 3070 cm−1
(Ar, C–H)s, 1670 cm−1 (C O)s, 1580 cm−1and 1470 cm−1(Ar,
C
C)s, 1112 cm−1 (C–O)s, 807 cm−1(Ar, C–H)ı (1,2,3-substituted
benzene ring), 772 cm−1 (Ar, C–H)ı (1,2-substituted benzene
ring) for PSNS-1AQ, while 3074 cm−1 (Ar, C–H)s, 1671 cm−1
(C O)s, 1593 cm−1 and 1490 cm−1 (Ar, C C)s, 1110 cm−1 (C–O)s,
884 cm−1 and 801 cm−1 (Ar, C–H)ı (1,2,4-substituted benzene
ring), 766 cm−1 (Ar, C–H)ı (1,2-substituted benzene ring) for
PSNS-2AQ. In addition, the strong peaks at 1089 cm−1, 625 cm−1
and 1092 cm−1, 622 cm−1 in the two polymer spectra were due to
Fig. 4. High-resolution TGA of (a) PSNS-1AQ and (b) PSNS-2AQ under nitrogen
−
atmosphere. Heating rate: 10 ◦C/min from room temperature to 1000 ◦C.
the presence of ClO4 dopant [15,16,18,19,23] (Fig. 3).

G. Wang et al. / Electrochimica Acta 55 (2010) 6933–6940
6937
Fig. 5. UV–vis absorbtion spectra of (a) PSNS-1AQ and (b) PSNS-2AQ films on ITO
glass. Inset: UV–vis absorbtion spectra and photos of (a) SNS-1AQ and (b) SNS-2AQ
in DCM.
Fig. 6. (a) UV/vis/NIR spectroelectrochemistry for PSNS-1AQ on ITO glass; Pt wire
counter electrode, Ag/AgCl reference electrode, TBAP/DCM supporting electrolyte
(0.01 M): (aꢀ) −1.2 V; (bꢀ) −1.0 V; (cꢀ) −0.8 V; (dꢀ) −0.6 V; (eꢀ) −0.4 V; (fꢀ) −0.2; (gꢀ)
0 V; (hꢀ) 0.2 V; (iꢀ) 0.4 V; (jꢀ) 0.6 V; (kꢀ) 0.8 V; (lꢀ) 1.0 V; (mꢀ) 1.2 V. Inset: Multichromic
behavior of PSNS-1AQ at +1.0 V (dark blue-purple), +0.7 V (light blue-purple), 0 V
(light yellow-green), −0.5 V (light yellow), −1.0 V (orange-yellowish). (b) UV/vis/NIR
spectroelectrochemistry for PSNS-2AQ on ITO glass; Pt wire counter electrode,
Ag/AgCl reference electrode, TBAP/DCM supporting electrolyte (0.01 M): (a) −1.2 V;
(b) −1.0 V; (c) −0.8 V; (d) −0.6 V; (e) −0.4 V; (f) −0.2; (g) 0 V; (h) 0.2 V; (i) 0.4 V;
(j) 0.6 V;(k) 0.8 V; (l) 1.0 V; (m) 1.2 V. Inset: Multichromic behavior of PSNS-2AQ
at +1.0 V (blue-grayish), +0.6 V (light blue-grayish), 0 V (light gray), −0.4 V (light
yellow-grayish), −1.0 V (dark orange-yellowish). (For interpretation of the refer-
ences to color in this figure legend, the reader is referred to the web version of the
article.)
(in the TG and DTG curves) corresponding to a strong calorimetric
absorption peak (in the DSC curve) was observed. This weight loss
(about 45% and 50% for PSNS-1AQ and PSNS-2AQ in the range of
200–300 ◦C) could be tentatively attributed to the lack of dopant
as it was explained in similar research work based on conducting
polymers [31]. After the dopant loss step, the two polymers showed
a constant decrease of weight (about 21% and 34% for PSNS-1AQ and
PSNS-2AQ in the range of 300–800 ◦C) due to the degradation of the
polymer backbone. The residue of the different polymers at 800 ◦C
was 12% for PSNS-1AQ and 31% for PSNS-2AQ. The two polymers
were found to be very stable against to thermal effect. Comparing
to PSNS-1AQ, PSNS-2AQ film was more stable against to thermal
effect possibly due to stereo-hindrance effect which decreased the
stablity of the molecule structure of PSNS-1AQ.
ically deposited polymer films, PSNS-1AQ and PSNS-2AQ exhibited
similar ꢀmax (corresponding to the ␲–␲* transition) at 411 nm and
414 nm respectively. As seen in Fig. 5, the absorption bands belong-
ing to SNS moiety shifted from 332 nm and 327 nm in the two
monomers to 411 nm and 414 nm in the corresponding polymers.
However, the absorption band of anthraquinone moiety was not
affected by the polymerization. The ꢀmax of the polymer was much
higher than that of the corresponding monomer, which was caused
by increasing of the conjugation length in the polymer. And this is
a typical trend in conducting polymers [31].
3.4. Spectroelectrochemistry properties of PSNS-1AQ and
PSNS-2AQ
The absorption spectra of PSNS-1AQ and PSNS-2AQ films on ITO
glass (in the neutral state), together with that of the corresponding
monomers in DCM, were represented in Fig. 5, inset. The absorption
maximum (ꢀmax) in the spectra of monomers SNS-1AQ and SNS-
2AQ were similar (256, 332 nm and 255, 327 nm in DCM which
were due to the ␲–␲* transition of the anthraquinone and SNS
moieties, respectively). Also, for the corresponding electrochem-
The optical band gap of polymeric products was calculated from
their low energy absorption edges (ꢀonset) according to Planck
equation (Eg = 1241/ꢀonset) [32]. It was observed that the ꢀmax and
ꢀonset of the absorption spectra of PSNS-1AQ were at 411 nm and

6938
G. Wang et al. / Electrochimica Acta 55 (2010) 6933–6940
Table 1
Electrical and optical data for SNS derivatives and their polymers.
Polymer
Em,ox (V)
Ep,1/2 (V)
ꢀp (nm)
Eg (eV)
Reduced state
Oxidized state
PSNS
PSNS-1AQ
PSNS-2AQ
0.94
0.95
0.94
0.6
0.7
0.58
430
414
411
2.61
2.20
2.13
Yellow orange
Dark orange-yellowish
Dark yellow
Dark blue
Dark blue-purple
Dark blue-purple
588 nm, corresponded to a band gap of 2.11 eV. While for PSNS-
2AQ, the ꢀmax and ꢀonset of the absorption spectra were observed
at 414 nm and 596 nm, corresponded to a band gap of 2.08 eV. As
shown in Table 1, the Eg values are 2.11 and 2.08 eV for PSNS-1AQ
and PSNS-2AQ, respectively, which were smaller than that of the
unsubstitued PSNS (Eg = 2.61 eV) [17].
another two bands intensified at 780 nm and 890 nm. For the two
polymer films, the five intensified bands indicated the formation
of polarons and bipolarons on the polymer backbone (Scheme 2),
respectively [16–18,22,25].
3.5. Switching and stability of PSNS-1AQ and PSNS-2AQ
Spectroelectrochemical study on PSNS-1AQ and PSNS-2AQ film
was carried out by varying the voltage between +1.2 V and −1.2 V.
For monitoring the electrochromic process, five potential points
were chosen for each of the two polymer films and correspond-
ing electrochromic photos were taken and recorded. Both of the
two polymers revealed multicolor electrochromism exhibiting sev-
eral colored states between yellow (in the reduced state), grey (in
the neutral state) and blue (in the oxidized state) (Fig. 6a and b).
Moreover, it was found that when the voltage applied to PSNS-
1AQ film, the valance band-conduction band (␲–␲* transition) at
411 nm was diminished and another three bands intensified at
520 nm, 650 nm and 900 nm. While to PSNS-2AQ film, the valance
band-conduction band (␲–␲* transition) diminished at 414 nm and
Switching and stability are two important properties of an elec-
trochromic material. In order to investigate these properties, the
PSNS-1AQ and PSNS-2AQ film were switched by repeated potential
steps between the reduction (−1.0 V) and oxidized states (+1.0 V)
with a residence time of 10 s in the electrolyte solution.
The optical contrast is given as the transmittance difference
between the reduced and oxidized states and is reported as ꢂT%
which was monitored as a function of time at the wavelength in the
visible region. The maximum ꢂT% in the visible region (at 780 nm)
was found 18% for PSNS-1AQ and 16.5% for PSNS-2AQ, respec-
tively. As seen in Fig. 7, the transmittance–time curves for the two
polymer films started to be stable after several repeated potential
Scheme 2. The electropolymerization doping and redox process of SNS-1AQ and SNS-2AQ.

G. Wang et al. / Electrochimica Acta 55 (2010) 6933–6940
6939
Fig. 7. (a) Optical transmittance changes and (b) optical switching studies for PSNS-1AQ film was monitored at 780 nm in 0.1 M TBAP/DCM. (c) Optical transmittance changes
and (d) optical switching studies for PSNS-2AQ film was monitored at 780 nm in 0.1 M TBAP/DCM.
CE was calculated to be 0.15 and 105 cm2/C for PSNS-1AQ, 0.13 and
98 cm2/C for PSNS-2AQ, respectively.
steps. This result was possibly due to the doping–undoping process
(Scheme 2) which needed some time to become stable. Quantifica-
tion of switching time was performed by defining a change in 95%
of the total absorbance span, since the naked eye could not distin-
guish the color change after this point. The optical response time in
PSNS-1AQ was approximately 4 s for the oxidation process (blue-
grayish) and approximately 4 s for the reduction process (dark
orange-yellowish) while PSNS-2AQ needed also approximately 3 s
to be oxidized (dark blue -purple) and approximately 3 s to be
reduced (orange-yellowish).
It was found that both of the two polymer films showed a paral-
lel coloring and bleaching process, which meant a parallel kinetics
of dopantion diffusion in the oxidation and reduction process. How-
ever, both polymers presented fast switching time in the range of
a few seconds, and the slight discrepancy in the time required to
achieve 95% of the coloring and decoloring states may be due to the
conditions of electrodeposition and the resulting thickness of the
polymer films [31].
4. Conclusions
In summary, two new dithienylpyrrole compounds bearing
anthraquinone units (SNS-1AQ and SNS-2AQ) were synthesized by
the Knorr–Paal condensation, corresponding polymer films PSNS-
1AQ and PSNS-2AQ were prepared by electropolymerized. All the
dithienylpyrrole hybrid compounds and polymer films were well
characterized. The polymer films PSNS-1AQ and PSNS-2AQ were
studied comparatively and which were found that PSNS-1AQ and
PSNS-2AQ films performed similar spectroelectrochemical proper-
ties. Both of the two polymer films were thermally stable up to
nearly 300 ◦C, and showed a well-defined reversible redox process
and stable electrochromic behavior (yellow in the reduced state,
grey in the neutral state and blue in the oxidized state) which can
make them amenable for electrochromic devices.
Furthermore, the optical density (ꢂOD) and colouration effi-
ciency (CE) at 780 nm can be calculated using the following
equations [33].
Acknowledgements
All authors herein are grateful to the support from National
Ministry of Science and Technology Innovation Fund for High-tech
Small and Medium Enterprise Technology (No. 09C26215112399)
and National Ministry of Human Resources and Social Security
Start-up Support Projects for Students Returned to Business, Office
of Human Resources and Social Security Issued 2009 (143).
Tcolored
ꢂOD
Qd
ꢂOD = log
and CE =
Tbleached
where Qd is the injected/ejected charge during a redox step; Tcolored
and Tbleached are the transmittance in the oxidized and neutral
states, respectively. On the basis of these equations, the ꢂOD and

6940
G. Wang et al. / Electrochimica Acta 55 (2010) 6933–6940
References
[17] A. Cihaner, F. Algı, Electrochim. Acta 54 (2009) 1702.
[18] A. Cihaner, O. Mertb, A.S. Demirb, Electrochim. Acta 54 (2009) 1333.
[19] A. Cihaner, F. Algi, Electrochim. Acta 54 (2008) 665.
[20] A. Cihaner, F. Algı, Electrochim. Acta 54 (2008) 786.
[21] S. Tarkuc, E. Sahmetlioglu, C. Tanyeli, I.M. Akhmedov, L. Toppare, Sens. Actua-
tors B 121 (2007) 622.
[22] E. Yildiz, P. Camurlu, C. Tanyeli, I. Akhmedov, L. Toppare, J. Electroanal. Chem.
612 (2008) 247.
[23] A. Yavuz, B. Bezgin, L. Aras, A.M. Önal, J. Electroanal. Chem. 639 (2010) 116.
[24] M. Ak, E. Sahmetliog˘luc, L. Toppare, J. Electroanal. Chem. 621 (2008) 55.
[25] S. Koyuncua, C. Zaferb, E. Sefera, F.B. Koyuncua, S. Demicb, I. Kayaa, E. Ozdemira,
S. Icli, Synth. Met. 159 (2009) 2013.
[26] W. Qiao, J. Zheng, Y. Wang, Y. Zheng, N. Song, X. Wan, Z.Y. Wang, Org. Lett. 10
(2008) 1697.
[27] B.L. Sui, X.K. Fu, J. Solid State Electrochem. 13 (2009) 1889.
[28] B.L. Sui, X.K. Fu, Dyes Pigment 83 (2009) 1.
[29] J.P. Ferraris, T.R. Hanlon, Polymer 30 (1989) 1319.
[30] S. Wang, E.K. Todd, M. Birau, J. Zhang, X. Wan, Z.Y. Wang, Chem. Mater. 17
(2005) 6388.
[31] C.P. Gonzalo, M. Salsamendi, J.A. Pomposo, H.J. Grande, E.Y. Schmidt, Y.Y.
Rusakov, B.A. Trofimov, Macromolecules 41 (2008) 6886.
[32] K. Colladet, M. Nicolas, L. Goris, L. Lutsen, D. Vanderzande, Thin Solid Films 7
(2004) 451.
[1] H.J. Byker, Electrochim. Acta 46 (2001) 2015.
[2] R.J. Mortimer, A.L. Dyer, J.R. Reynolds, Displays 27 (2006) 2.
[3] R. Baetens, B.P. Jelle, A. Gustavsend, Sol. Energy Mater. Sol. Cells 94 (2010) 87.
[4] K. Gurunathan, A.V. Murugan, R. Marimuthu, U.P. Mulik, D.P. Amalnerkar,
Mater. Chem. Phys. 61 (1999) 173.
[5] P.E. Just, K.I. Chane-Ching, P.C. Lacaze, Tetrahedron 58 (2002) 3468.
[6] L.F. Schweiger, K.S. Ryder, D.G. Morris, A. Glidle, J.M. Cooper, J. Mater. Chem. 10
(2000) 107.
[7] J. Nakazaki, I. Chung, M.M. Matsushita, T. Sugawara, R. Watanabe, A. Izuoka, Y.
Kawada, J. Mater. Chem. 13 (2003) 1011.
[8] J.H. Lin, A. Elangovan, T.I. Ho, J. Org. Chem. 70 (2005) 7397.
[9] K. Ogura, R. Zhao, M.T. Jiang, M. Akazome, S.J. Matsumotoa, K. Yamaguchi,
Tetrahedron Lett. 44 (2003) 3595.
[10] K. Ogura, R. Zhao, T. Mizuoka, M. Akazome, S.J. Matsumoto, Org. Biomol. Chem.
21 (2003) 3845.
[11] G. Cooke, J.F. Garety, S. Mabruk, G. Rabani, V.M. Rotello, G. Surpateanud, P.
Woisel, Tetrahedron Lett. 47 (2006) 783.
[12] G. Cooke, J.F. Garety, S. Mabruk, V. Rotello, G. Surpateanuc, P. Woisel, Chem.
Commun. 23 (2004) 2722.
[13] S. Tuncagil, S. Kıralp, S. Varıs, L. Toppare, React. Funct. Polym. 68 (2008)
710–717.
[33] B.D. Reeves, C.R.G. Greiner, A.A. Argun, A. Cirpan, T.D. McCarley, J.R. Reynolds,
Macromolecules 37 (2004) 7559.
[14] N.A. Lengkeek, J.M. Harrowfield, G.A. Koutsantonis, Synth. Met. 160 (2010) 72.
[15] A. Cihaner, F. Algi, Electrochim. Acta 53 (2008) 2574.
[16] A. Cihaner, F. Algı, J. Electroanal. Chem. 614 (2008) 101.