Fast switching, high contrast multichromic polymers from alkyl-derivatized dithienylpyrrole and 3,4-ethylenedioxythiophene

Article abstract of DOI:10.1016/j.electacta.2011.11.079

In this report we disclose the synthesis and characterization of optoelectronic properties of a novel conducting polymer based on 1-(2-ethyl-hexyl)-2,5-di-thiophen-2-yl-2,3-dihydro-1H-pyrrole, (SNS-HE). Additionally, copolymers based on SNS-HE and 3,4-ethylenedioxythiophene (EDOT) were electrochemically synthesized and characterized. Cyclic voltammetry, FTIR, spectroelectrochemistry analyses confirmed that the resulting polymers were true copolymers having distinct electrochromic properties from that of the parent homopolymers. Depending on the synthesis conditions, the SNS-HE based polymers exhibited optical band gaps ranging from 2.32 to 1.70 eV and the copolymers displayed multichromism within a wide range of the visible spectrum. The copolymers revealed shorter switching times (around 0.5 s) and higher optical contrast (around 36%). Our studies have shown that color of the copolymers could be easily tuned by controlled increase in copolymerization potential. Moreover, a prototype of the all solid state poly(SNS-HE-EDOT)/PEDOT complementary electrochromic device was fabricated in order to investigate the utilization of these polymers. These devices exhibited short switching times with reasonable open circuit memory under atmospheric conditions.

Full text of DOI:10.1016/j.electacta.2011.11.079

Electrochimica Acta 61 (2012) 50–56
Contents lists available at SciVerse ScienceDirect
Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
Fast switching, high contrast multichromic polymers from alkyl-derivatized
dithienylpyrrole and 3,4-ethylenedioxythiophene
∗
Pinar Camurlu , Cemil Gültekin, Zeynep Bicil
Akdeniz University, Department of Chemistry, 07058, Antalya, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 14 September 2011
Received in revised form
In this report we disclose the synthesis and characterization of optoelectronic properties of a novel con-
ducting polymer based on 1-(2-ethyl-hexyl)-2,5-di-thiophen-2-yl-2,3-dihydro-1H-pyrrole, (SNS-HE).
Additionally, copolymers based on SNS-HE and 3,4-ethylenedioxythiophene (EDOT) were electro-
chemically synthesized and characterized. Cyclic voltammetry, FTIR, spectroelectrochemistry analyses
confirmed that the resulting polymers were true copolymers having distinct electrochromic proper-
ties from that of the parent homopolymers. Depending on the synthesis conditions, the SNS-HE based
polymers exhibited optical band gaps ranging from 2.32 to 1.70 eV and the copolymers displayed multi-
chromism within a wide range of the visible spectrum. The copolymers revealed shorter switching times
1
5 November 2011
Accepted 19 November 2011
Available online 29 November 2011
Keywords:
Conducting polymer
Electrochemical copolymerization
(around 0.5 s) and higher optical contrast (around 36%). Our studies have shown that color of the copoly-
1
2
3
-(2-Ethyl-hexyl)-2,5-di-thiophen-2-yl-
,3-dihydro-1H-pyrrole
,4-Ethylenedioxythiophene
mers could be easily tuned by controlled increase in copolymerization potential. Moreover, a prototype
of the all solid state poly(SNS-HE-EDOT)/PEDOT complementary electrochromic device was fabricated
in order to investigate the utilization of these polymers. These devices exhibited short switching times
with reasonable open circuit memory under atmospheric conditions.
Electrochromism
©
2011 Elsevier Ltd. All rights reserved.
1
. Introduction
polymerization. Due to monomers’ low oxidation potentials their
electrochemical polymerizations were easily accomplished. How-
ever, to our best knowledge, in literature there is only a single
study [19] involving an amine functionalized alkyl substituted
SNS derivative. It is known that introduction of an alkyl group
into a conducting polymer could be used to manipulate the elec-
trochromic properties of the polymer, due to inductive electronic
effects and interchain interactions between the chains [20], Keep-
ing this in mind, in this study we investigated electrochemical
and electrochromic properties of ethyl–hexyl functionalized SNS
derivative.
Besides chemical tailoring, copolymerization also provides an
effective method for controlling of properties of conducting poly-
mers. Contrary to synthetic approach, copolymerization is an easy,
facile method to combine the electrochromic properties of the
parent polymers [21]. In literature there are several studies that
investigate copolymerization and tune the color of the conducting
polymers via copolymerization. Among those utilization of 3,4-
ethylenedioxythiophene (EDOT) has dominated literature owing
to EDOT’s rapid switching ability and high stability. Since most of
the conducting polymers display color variations simply between
two colors, it is crucial for potential applications to obtain a mul-
tichromic conducting polymer with short switching time and high
stability.
Conducting polymers are a class of polymer which generally
joins the typical properties of conventional polymers with those of
electronically conducting materials [1]. Utilization of these materi-
als in numerous applications including, biosensors [2], actuators
[
3] and electrochromic devices [4] has been proposed. There-
fore remarkable effort has been performed for achieving new
polymers which meet the criteria for commercial applications. Gen-
erally, tuning of polymer properties goes through specific structural
changes in the polymer, like use of different polymer backbones or
modification of polymers through utilization of specific functional
groups [5].
In recent years an emerging class of conducting polymer,
poly(2,5-dithienylpyrrole) derivatives (SNS) has been investigated
for their electrochromic properties by several groups. In litera-
ture there are studies in which various SNS derivatives containing
substituted phenyl derivatives [6–13], aryl derivatives [14,15],
BODIPY [16], 1,10-phenanthrolinyl [17], anthraquinone [18] have
been investigated. Among those, especially substituted phenyl
derivatives revealed soluble conducting polymers upon chemical
∗ Corresponding author. Tel.: +90 242 3102308; fax: +90 242 2278911.
E-mail addresses: pcamurlu@akdeniz.edu.tr, pinarcamurlu@gmail.com
In the present work, 1-(2-ethyl-hexyl)-2,5-di-thiophen-2-yl-
2,3-dihydro-1H-pyrrole (SNS-HE) (Scheme 1) was synthesized
(
P. Camurlu).
0
013-4686/$ – see front matter © 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.electacta.2011.11.079

P. Camurlu et al. / Electrochimica Acta 61 (2012) 50–56
51
O
S
Cl
Cl
2
+
O
AlCl 3
S
+
H N
2
Toluene
Reflux
S
S
N
O
O
S
SNS-HE
Scheme 1. The synthetic route of SNS-HE.
and its structure was analyzed by several methods ( H, 13C
NMR, FTIR, mass spectroscopy). Electrochemical polymerization
of SNS-HE was achieved and the resultant homopolymer was
investigated for its electrochromic properties. Then a novel mul-
ticolored electrochromic copolymer based on SNS-HE and EDOT
was achieved by electrochemical copolymerization. The resultant
copolymer films exhibit four different colors with the varia-
tion of the applied potential with enhanced switching time and
optical contrast together with precisely adjustable band gap. More-
over, utilization of the copolymers on electrochromic devices was
performed through construction of absorption/transmission type
electrochromic devices.
1
[23]. FT-IR (KBr, cm ): 3101, 2919, 1733, 1654, 1514, 1353,
1316, 1191, 1057, 953, 860, 788, 741, and 633. MS calculated
−1
for C12H10O S (m/z) calculated: 250.34, found: 250.3. SNS-HE
2
2
was synthesized according to literature [19] by refluxing 1,4-di(2-
thienyl)-1,4-butanedione (2 mmol, 0.5 g), 2-ethyl-1-hexylamine
(3.2 mmol, 0.52 mL) and 0.2 g propanoic acid in toluene (20 mL)
for 24 h under N2 atmosphere. The solvent was evaporated
and later it was purified on a silica gel column (eluting with
dichloromethane/hexane, 3/1) to yield title compound (1-(2-ethyl-
hexyl)-2,5-di-thiophen-2-yl-2,3-dihydro-1H-pyrrole) as a yellow
−
1
oily (45%). FT-IR (KBr, cm ): 3104, 3070, 2958, 2929, 2870, 2860,
−
1
1460, 1422, 1380, 1305, 1200, 1040, 840, 760 and 695 cm
H NMR (in CDCl ) (ı/ppm): 7.21 ppm (d, 2H), 6.96 ppm (t, 4H),
.
1
3
2
. Experimental
6.23 ppm (s, 2H), 4.02 ppm (d, 2H) 1.33 ppm (m, 1H), 0.97 ppm (m,
2
H), 0.85 ppm (m, 6H), 0.67 ppm (t, 3H) and 0.47 ppm (t, 3H).13
C
2.1. General
NMR (in CDCl ) (ı/ppm): 134.59, 128.10, 126.15, 124.95, 124.10,
3
1
09.81, 48.2, 38.5, 29.3, 27.2, 21.7, 12.9, 22.5 and 9.4 ppm. MS cal-
All chemicals were purchased from Aldrich, Merck Chemical as
culated for C20H25N1S2 (m/z) calculated: 343,5, found: 343,4.
analytical grade. Lithium perchlorate (LiClO ) was electroanalyti-
4
cal grade and thiophene, succinyl chloride, 2-ethyl-1-hexylamin,
3
,4-ethylenedioxythiophene (EDOT) were used as received. Ace-
2.4. Synthesis of homopolymer (poly(SNS-HE))
tonitrile (ACN) was distilled over calcium hydride and kept on 4 A˚
molecular sieves. The gel electrolyte [22] was prepared according
to previously reported methods.
Poly(SNS-HE) films were prepared potentiodynamically on ITO
electrodes, using 0.01 M monomer in a solution containing LiClO4
in acetonitrile (ACN). A platinum wire was used as the counter elec-
trode and Ag/Ag+ electrode calibrated against ferrocene was used
as the reference electrode. During the electrochemical process, the
color of the solution in the vicinity of working the electrode dark-
ened progressively. However, as the polymerization proceeded,
part soluble oligomers became insoluble and deposited on the
working electrode. Electrochromic measurements; spectroelectro-
chemistry, and switching studies of the polymer films deposited on
ITO (both the homopolymer and the copolymer) were performed
using a UV-cuvette with three-electrodes placed in the sample
compartment of a spectrophotometer. In these studies platinum
and Ag wires were used as the counter and reference electrodes
respectively due to geometrical restrictions.
2.2. Equipments
NMR spectra were recorded with a Bruker Spectrospin Avance
1
DPX-400 Spectrometer at 400 MHz for H NMR and 100 MHz for
13
C NMR. Chemical shifts (ı) were given relative to tetramethylsi-
lane (TMS) as the internal standard. Mass spectroscopy (MS) was
performed on DP-MS 5973 HP quadruple MS. The FTIR spectra were
recorded on a Brucker Tensor 27 spectrometer. Ivium stat poten-
tiostat/galvanostat was used to supply a constant potential during
electrochemical synthesis and cyclic voltammetry. Spectroelec-
trochemical and kinetic studies of the polymers were performed
on Varian Cary 100 UV–vis spectrophotometer. Colorimetry mea-
surements were recorded on a Minolta CS-100A Chroma Meter
in a proper box having D-50 illumination. Measurements were
performed with a 0/0 (normal/normal) viewing geometry as rec-
ommended by CIE.
2.5. Synthesis of copolymers (poly(SNS-HE-EDOT))
EDOT was used as the comonomer for the synthesis of conduct-
ing copolymer of SNS-HE. SNS-HE (50 mg) was dissolved in 5 ml of
ACN and 5 ␮L of EDOT was introduced into the electrolysis cell hav-
ing the same electrode system utilized in homopolymers synthesis.
The films were either prepared potentiodynamically scanning the
potential between 0.0 V and 1.3 V or potentiostatically at 1.1–1.4 V
on ITO glass electrodes.
2
1
.3. Synthesis of
-(2-ethyl-hexyl)-2,5-di-thiophen-2-yl-2,3-dihydro-1H-pyrrole
(
SNS-HE)
1
,4-di(2-thienyl)-1,4-Butanedione was synthesized according
to literature starting from thiophene and 1,4-dichlorobutanedione

5
2
P. Camurlu et al. / Electrochimica Acta 61 (2012) 50–56
2.6. Construction of electrochromic device (ECD)
Both anodically poly(SNS-HE-EDOT) and cathodically (PEDOT)
coloring polymers were electrochemically deposited onto the ITO-
coated glass slide in 0.1 M LiClO /ACN electrolyte solution at 1.2 V.
4
The redox sites of these polymer films were matched by step-
ping the potentials between 0.0 V and +1.8 V for the copolymer
and −1.2 to +1.2 V for PEDOT. ECDs were built by arranging two
electrochromic polymer films (one doped, the other neutral) facing
each other separated by a gel electrolyte.
3
. Results and discussion
3.1. Monomer synthesis
1
-(2-Ethyl-hexyl)-2,5-di-thiophen-2-yl-2,3-dihydro-1H-
pyrrole (SNS-HE) was synthesized by two-step synthetic route,
as shown in Scheme 1. The first step involves synthesis of
1
,4-di(2-thienyl)-1,4-butanedione through thiophene and 1,4-
dichlorobutanedione and the second step includes a Paal–Knorr
reaction between 1,4-di(2-thienyl)-1,4-butanedione and 2-ethyl-
1
-hexylamine in toluene. Structural investigation of monomer was
1
13
performed via H, C NMR, FTIR and MS analyses. The monomer
is yellow oil at room temperature.
3.2. Electrochemical polymerization
Typical successive cyclic voltammogram (CV) of the monomer
during the process of electrochemical polymerization is shown in
Fig. 1a The monomer revealed an irreversible oxidation at around
1
.0 V, signifying the formation of radical cation of the monomer
through its SNS moiety and the increase in the redox wave cur-
rents implied that the amount of the polymer on the electrode was
increased. Such behavior is in accordance with the previous stud-
ies based on other SNS derivatives [19]. During potential scanning,
homogeneous, adherent thin film coating on the electrode was
observed by the naked eye and the color of the solution close to the
working electrode changed probably due to dissolved oligomers.
Additional proof of homopolymerization was achieved via com-
parison of FTIR spectra of the monomer and the polymer. FTIR
−
1
spectra of SNS-HE revealed typical signals at 3104–3070 cm
2
,
−1
958–2860 cm due to C–H stretching of aromatic and aliphatic
moieties. The stretching of C C, C–C and C–N, C–S bonds was signi-
−
1
−1
fied by the appearance of peaks at 1577–1422 cm and 1340 cm ,
6
−1
95 cm , respectively. Upon homopolymerization most of the
characteristic peaks were maintained, except the peaks regarding
C–H stretching of thiophene moiety which indicated that the poly-
merization mainly proceeds through 2,5 positions of the monomer
−
1
[
24]. In addition, the broad band centered at 1645 cm and the
Fig. 1. Potentiodynamic electropolymerization of (a) SNS-HE, (b) SNS-HE and EDOT,
−1
(c) EDOT in 0.1 M LiClO /ACN at a scan rate of 100 mV s−1 vs Ag/Ag+.
intense band at 1085 cm revealed formation of polyconjugation
and presence dopant anion, respectively.
4
Copolymerization is often used to achieve novel polymers
having different properties that are expected to embody the advan-
tages of both of the parent polymers, widen the application
fields and display better electrochromic properties. In litera-
ture copolymerization of EDOT with other monomers such as
Fig. 1b and c displays potentiodynamic scans of the monomer
in the presence of EDOT and pure EDOT in LiClO /ACN system with
4
−
1
ITO working electrode at a scan rate of 100 mV s , respectively.
During potentiodynamic scan the anodic peaks of the copolymer
appeared at 1.0 V and 0.67 V. As seen redox potentials of copolymer
are noticeably different from PEDOT and poly(SNS-HE) which could
be interpreted as a proof for the formation of a true copolymer.
Moreover, FTIR spectrum of the copolymer revealed presence of
3
[
-methylthiophene [25], N-ethylcarbazole [26], N-methylpyrrole
27], 5-cyanoindole [28], pyrene [29], SNS derivatives [11,30,31]
has been reported. Hence, we attempted to incorporate the EDOT
with in SNS-HE units through electrochemical copolymerization
in order to enhance the film forming ability of SNS-HE. Since the
electrochemical copolymerization of the monomers is expected to
be based on already known coupling reactions of radical cations,
it is necessary to achieve the reactive radical cations of each
comonomer within the same potential window.
−
1
a new peak at 1199–1109 cm due to asymmetric and symmetric
C–O–C stretching of etheric units that stem from comonomer EDOT,
−
1
respectively. In addition, the broad band centered at 1653 cm and
−
1
the intense band at 1085 cm revealed the formation of polycon-
jugation and presence dopant anion, respectively. Thus, existence

P. Camurlu et al. / Electrochimica Acta 61 (2012) 50–56
53
Fig. 3. Spectroelectrochemistry of poly(SNS-HE) film on an ITO coated glass slide in
monomer-free 0.1 M LiClO4/ACN electrolyte solution (a) 0.6 V, (b) 1.0 V, (c) 1.2 V, (d)
1.3 V, (e) 1.4 V and (f)1.5 V vs Ag wire.
3.3. Electrochromic properties
Spectroelectrochemical analyses of poly(SNS-HE) were per-
formed in order to elucidate the electronic transitions and changes
in optical properties upon redox switching. The spectral behavior
(Fig. 3) of the poly(SNS-HE) was investigated by UV–vis spectropho-
tometer in a monomer-free electrolyte system while incrementally
increasing the applied potential between 0.0 and 1.5 V. In the neu-
tral state, poly(SNS-HE) showed a single broad absorption peak
at 360 nm, which corresponded to the ␲–␲* inter band transi-
tion (Eg = 2.32 eV) and the polymer appeared yellow in color. At
1
.5 V the homopolymer appeared in bluish gray color revealing two
absorptions at around 360 and 602 nm, indicating that the polymer
film could not be fully oxidized. Hence, upon several redox switch-
ing the polymer lost their electroactivity and did not display color
change.
Fig. 2. Cyclic voltammograms of the copolymer on ITO electrode in 0.1 M LiClO4/ACN
at various scan rates vs Ag/Ag .
+
On the other hand, poly(SNS-HE-EDOT), synthesized at 1.2 V,
revealed maximum absorption at 492 nm (Fig. 4) with a band gap
of 1.70 eV. Upon increase in the applied potential, the peak height
of the interband transition was suppressed and simultaneously a
new absorption peak appeared at around 773 nm due to charge car-
rier band formations. Beyond 0.8 V the spectrum was overwhelmed
by the broad transition entailing to the NIR region most probably
indicating bipolaron formation. The copolymer displayed distinct
multichromism (Fig. 4), revealing reddish brown, yellowish green
and blue colors in neutral, mid and highly oxidized states. Hence,
we can infer that incorporation of EDOT units with in SNS-HE chain
allowed us to overcome the limitations of poly(SNS-HE).
In order to explore the effect of polymerization potential on
electrochromic properties, several copolymers were synthesized
at different (1.1, 1.2, 1.3, 1.4 V) applied potentials without chang-
ing the comonomer feed ratio and solvent–electrolyte system. All
the polymers revealed similar spectral features (not given) having
of these distinctive peaks confirms the formation SNS-HE-EDOT
copolymer [32,33].
The electroactivity of the copolymer sample (synthesized at
1
.3 V) was studied in monomer free supporting electrolyte system.
Cyclic voltammograms and plots of wave current density vs poten-
tial scan rate are illustrated in Fig. 2. As seen both the anodic and
cathodic current densities of the copolymer show a linear depen-
dence with the scan rate, having an anodic and cathodic regration
fit of R = 0.999; R = 0.999, respectively. On the contrary, current den-
sity vs square root of the scan rate (not given) revealed an anodic
regration fit of R = 0.992 and cathodic regration fit of R = 0.992. The
linearity of the wave currents with potential scan rate is a character-
istic of mass transfer in the electroactive film on the electrode. Such
observation indicates that migration of the electroactive species is
not diffusion controlled, the electroactive polymer is well adhered
and electrode supported [34].
Table 1
Electrochromic properties of the copolymers and the device.
Materiala
ꢀmaxb (nm)
Egc (eV)
Switching time (s)d t100, t95, t90
Optical contrast (T%)
L, a, be
Poly(SNS-HE-EDOT)-1.1 V
Poly(SNS-HE-EDOT)-1.2 V
Poly(SNS-HE-EDOT)-1.4 V
PEDOT-1.2 V
450
492
522
586
1.72
1.70
1.76
1.57
–
0.87, 0.59, 0.50
0.60, 0.37, 0.29
0.69, 0.53, 0.49
26.52
17.58
36.43
47, 9, 15 (n) 54, −6, 23 (i) 52, −1, 0 (o)
37,17, −4 (n) 61, -3, 17 (i) 57,-2,-12 (o)
31, 12, 3 (n) 52, −9, 25 (i) 45, −2, −11 (o)
ECD
461, 605
1.0, 0.44, 0.37
26.59
46, −6, 33 (n)35, −12, 8 (i)26, −4, −10 (o)
a
Applied potentail during copolymerization.
For the neutral polymer films.
Band gap, estimated from the optical absorption band edge of the films.
The switching time of the copolymers at t100: 100%, t95: 95%, t90: 90% of ultimate contrast.
Colorimetry study results at n: neutral, i: intermediate, o: oxidized states.
b
c
d
e

5
4
P. Camurlu et al. / Electrochimica Acta 61 (2012) 50–56
Fig. 4. Spectroelectrochemistry of poly(SNS-HE-EDOT) film on an ITO coated glass
slide in monomer-free 0.1 M LiClO4/ACN electrolyte solution at applied potentials
(
a) −0.2 V, (b) 0.0 V, (c) 0.2 V, (d) 0.3 V, (e) 0.4 V, (f) 0.6 V, (g) 0.7 V, (h) 0.8 V, (i) 1.2 V
and (j) 1.6 V vs Ag wire.
a strong band in the visible region at their neutral state and a broad
band extending into the NIR in their doped state. Fig. 5 represents
the normalized spectra of the neutral copolymers. As seen, all the
copolymer films exhibited a broad transition showing significant
shift of peak maxima between 450 nm and 522 nm (Table 1) with
the increase in polymerization potential from 1.1 V to 1.4 V. The
positions of these bands define the color of the copolymers, which
range from reddish brown to violet (results of the colorimetric
measurement as also provided) upon variation of polymerization
potential. In accordance with the literature [21,30,31,35] this indi-
cates that the composition of the copolymer changes with the
change in polymerization potential. The higher the applied poten-
tial, the more EDOT units are incorporated into the copolymer film.
The switching ability of the copolymers was evaluated by mon-
itoring the changes in the percent transmittance of the polymers
as a function of time. Fig. 6a–c represents the percent transmit-
tance change, applied potential profile and the current density of
the copolymer (synthesized at 1.4 V) as a function of time. As seen
the optical contrast was calculated to be 36.43% at 522 nm and the
Fig. 5. Normalized UV–vis spectrum of copolymers (in neutral state) synthesized at
different polymerization potentials.
device revealed continual, regular current alternations upon repet-
itive cycling. Such persistent and uniform redox behavior could
be considered as a sign of high stability. The switching time of
the copolymer was measured at 90% of ultimate contrast and it
Fig. 6. (a) Transmittance (%), (b) current density, (c) applied potential, during repetitive electrochromic switching, (d) transmittance (%) of a single switch of the copolymer
deposited at 1.4 V on ITO electrode, monitored at 522 nm in 0.1 M LiClO4/ACN.

P. Camurlu et al. / Electrochimica Acta 61 (2012) 50–56
55
Fig. 9. Open circuit memory of poly(SNS-HE-EDOT)/PEDOT device monitored at
6
05 nm and 461 nm while a pulse of 1.0 V and −0.2 V was applied for 1 s every 200 s
Fig. 7. Optoelectrochemical spectra of poly(SNS-HE-EDOT)/PEDOT ECD at applied
potentials of (a) −0.2 V, (b) 0.0 V, (c) 0.2 V, (d) 0.4 V, (e) 0.6 V, (f) 0.8 V, (g) 0.9 V, (h)
to recover respectively.
1
.0 V, (i) 1.1 V, (j) 1.2 V, (k) 1.3 V, (l) 1.4 V and (m) 1.5 V.
polymers while applying the potential in square wave form
was found to be 0.4 s. Such definition was proposed [36] due to
limitation of human eye to perceive any variations beyond this
limit. Moreover, we have also investigated the switching ability
of the other copolymer (Table 1) films synthesized under different
polymerization potentials. It was observed that all the copolymers
presented fast switching times with parallel coloring and bleaching
processes.
(between 0.0 V and 1.5 V) with a residence time of 5 s. The opti-
cal contrast of the device, measured as the difference between T%
in the extreme forms, was found to be 26.6%. The time required to
reach 95% of ultimate T% was 0.44 s.
Open circuit memory (also called optical memory) is described
as the time at which an electrochromic material maintains its color
after the removal the applied electric field [22]. After polarizing
the device in one color and removing the electric field; the device
is expected to reveal color persistence at the induced state. In order
to evaluate such property, we applied 1 s pulse of 1.0 V (for blue)
or −1.2 V (for brown) and then kept the device under open-circuit
condition for 200 s while simultaneously probing the percent trans-
mittance as a function of time. As seen in Fig. 9 the optical properties
of the device remained almost the same for extended periods of
time for the brown state of the device where the copolymer layer
is in neutral and PEDOT is in its oxidized state. However this is not
eligible for the case of blue colored state.
3.4. Electrochromic device (ECD) application and characterization
Nowadays the scientific community is committed to the devel-
opment of electrochromic devices since it is operational under
a wide range of viewing angles and lighting conditions with
low-power requirements. Therefore, we fabricated a prototype
of the all solid state complementary electrochromic device in
order to investigate the electrochromic performance of SNS-HE
based polymers in ITO/poly(SNS-HE-EDOT)/PEDOT/ITO configu-
ration. Fig. 7 shows the spectroelectrochemistry study of such
ECD between −0.2 and 1.5 V bias to copolymer layer. At −0.2 V
a well defined transition at 461 nm was observed and the device
revealed brown color owing to the copolymer film that is in neu-
tral state. Since this is a dual type device at this point PEDOT
layer is expected to be in its oxidized state showing no signifi-
cant transitions in visible region. Upon stepwise increase in the
applied potential copolymer layer started oxidize and a new peak
at 605 nm emerged due to neutralization of PEDOT layer. Upon
further amplification of the potential (beyond 1.0 V), the spec-
trum was overwhelmed by the ␲–␲* transitions of PEDOT and the
device displayed blue color. Moreover, switching time and opti-
cal contrast of the device were evaluated (Fig. 8) in the case of
4. Conclusions
Herein, we reported the synthesis and characterization of
a alkyl substituted SNS derivative namely,1-(2-Ethyl-hexyl)-2,5-
di-thiophen-2-yl-2,3-dihydro-1H-pyrrole (SNS-HE). Poly(SNS-HE)
was grafted on ITO electrode via electrochemical polymeriza-
tion and the homopolymer displayed yellow-gray transition upon
switching. Additionally, electrochemical copolymerization of SNS-
HE and EDOT was achieved in 0.1 M LiClO /ACN system under
4
different potentiostatic conditions. Investigation of electrochromic
properties of the both the homopolymer and the copolymers were
performed via spectroelectrochemistry and kinetic studies. The
resultant copolymer revealed enhanced optic contrast, switching
time compared to parent polymer and multichromism throughout
the entire visible region, displaying violet, yellow, green, and blue
colors upon variation of the applied potential. Moreover, we suc-
cessfully established the utilization of poly(SNS-HE-EDOT) in dual
type electrochromic devices. The device exhibited short switching
time with reasonable optical memory under atmospheric condi-
tions. To sum up, our studies have shown that we could tune the
color of the polymers by changing the polymerization potential
and SNS-HE based polymers are promising candidates as elec-
trochromic materials.
Acknowledgement
We are grateful to Akdeniz University (Project no:
2
008.01.0105.009) for the support of this study. We would
Fig. 8. Electrochromic switching, transmittance (%) change monitored at 605 nm
for poly(SNS-HE-EDOT)/PEDOT ECD between 0.0 V and 1.5 V.
like to thank to Yusuf Nur for the mass spectroscopy analysis.

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Appendix A. Supplementary data
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