A new ITO-compatible side chain-functionalized multielectrochromic polymer for use in adaptive camouflage-like electrochromic devices

Article abstract of DOI:10.1016/j.reactfunctpolym.2018.07.024

In this study, a new electroactive monomer, 3-(2-[4-(2,5-di-2-thienyl-1H-pyrrol-1-yl)phenyl]ethyl-thio)propanoic acid (SNSPA), was synthesized and then deposited onto the ITO/glass surface by an electrochemical process. When positive potentials were applied on the polymer film of SNSPA, the film at the neutral state turned from orange to green (0.6 V) and then to blue (1.1 V) because of the presence of polaronic and bipolaronic species on the SNS main chain of the polymer. At the last stage, a complementary electrochromic device was constructed by using poly(SNSPA) as the anode layer and PEDOT:PSS as the cathode layer. A fast response time (about 0.5 s) and a high stability of about 98% were obtained at the end of 1000 cycles. The capability of the proposed polymer to undergo reversible color change among brown, green, and blue is a significant property for use as an adaptive camouflage material for all conditions of sand, forest, and sea for military applications.

Full text of DOI:10.1016/j.reactfunctpolym.2018.07.024

ReactiveandFunctionalPolymers131(2018)174–180
Contents lists available at ScienceDirect
Reactive and Functional Polymers
journal homepage: www.elsevier.com/locate/react
A new ITO-compatible side chain-functionalized multielectrochromic
polymer for use in adaptive camouflage-like electrochromic devices
⁎
Sermet Koyuncua, Fatma Baycan Koyuncub,c,
a
Department of Chemical Engineering, Faculty of Engineering, Canakkale Onsekiz Mart University, 17100, Canakkale, Turkey
Department of Chemistry, Faculty of Sciences and Arts, ÇanakkaleOnsekiz Mart University, 17020 Çanakkale, Turkey
Polymeric Materials Research Laboratory, Çanakkale Onsekiz Mart University, 17020 Çanakkale, Turkey
b
c
A R T I C L E I N F O
A B S T R A C T
Keywords:
In this study, a new electroactive monomer, 3-(2-[4-(2,5-di-2-thienyl-1H-pyrrol-1-yl)phenyl]ethyl-thio)propa-
noic acid (SNSPA), was synthesized and then deposited onto the ITO/glass surface by an electrochemical pro-
cess. When positive potentials were applied on the polymer film of SNSPA, the film at the neutral state turned
from orange to green (0.6 V) and then to blue (1.1 V) because of the presence of polaronic and bipolaronic
species on the SNS main chain of the polymer. At the last stage, a complementary electrochromic device was
constructed by using poly(SNSPA) as the anode layer and PEDOT:PSS as the cathode layer. A fast response time
(about 0.5 s) and a high stability of about 98% were obtained at the end of 1000 cycles. The capability of the
proposed polymer to undergo reversible color change among brown, green, and blue is a significant property for
use as an adaptive camouflage material for all conditions of sand, forest, and sea for military applications.
Electrochromic polymers
2,5-di-(2-thienyl)-1H-pyrrole
Adaptive camouflage
1. Introduction
time, optical density variations, percent transmittance/luminescence
changes, low power requirement, high coloration efficiency (CE), and
With the discovery of the first conductive polymer polyacetylene by
Heeger et al. [1], a new door has been opened for the technology and
semi-conducting polymers with a conjugated structure; these polymers
have been widely used in many areas such as light-emitting diodes [2],
solar cells [3, 4], field effect transistors [5, 6], and electrochromic
materials [7, 8]. Semi-conducting polymers are usually colored because
of the presence of conjugated main chain; hence, the energy gap be-
tween their HOMO-LUMO levels corresponds to the energy of the
visible region [9, 10]. The neutral state color of conjugated polymers is
important especially for use in electrochromic materials because of the
observation of reversible optical changes in absorption or permeability
during electrochemical switching and the change in color [11]. Al-
though the initial studies on electrochromic materials have started with
inorganic compounds such as tungsten trioxide (WO3) [12] and iridium
dioxide (IrO2) [13], today electroactive polymers can be widely used
because of their some advantages such as structurally controllable
HOMO–LUMO band gap, solution processability, high contrast ratio,
and fast response time [14, 15].
easy chemical structure modification for color adjustment [17]. Be-
sides, the most important disadvantage of electrochromic devices
(ECDs) fabricated from conducting polymers is high stability against
atmospheric condition and switching voltage [18]. For this purpose,
conjugated polymers functionalized with subunits such as siloxane,
carboxylic acid, and phosphonic acid compatible with ITO/glass surface
are good alternatives to eliminate this problem [19–21].
2,5-di-(2-thienyl)-1H-pyrrole (SNS) derivatives are very well known
electroactive structure in the literature [22, 23]. Conjugated polymers
containing SNS moiety are often used in electrochromic applications
because of simple synthetic strategy, low oxidation potential, and re-
versible redox behavior [24–26]. The SNS-based polymers have dif-
ferent colors at the neutral state and generally converted to dark blue
upon electrochemical oxidation [26]. In addition, the optical and
electrochemical properties and also electrochromic performances can
be easily adjusted by attaching second electroactive moiety on the side
chain [27–30].
In this work, a new SNS-based electroactive polymer film containing
carboxyl subunit compatible with the ITO/glass surface was prepared
by electrochemical process. The AFM image shows that a well-ordered
polymer film can be obtained by using potentiodynamic electro-
chemical polymerization onto the ITO/glass surface. Spectro-
Polymeric electrochromics have been extensively studied for the last
20 years; nevertheless, the materials cannot be commercialized at the
desired level [16]. There are some important reasons to use these ma-
terials in commercial electrochromic applications, such as fast response
⁎
Corresponding author at: Department of Chemical Engineering, Faculty of Engineering, Canakkale Onsekiz Mart University, 17100 Canakkale, Turkey.
E-mail address: fatmabaycan@hotmail.com (F.B. Koyuncu).
https://doi.org/10.1016/j.reactfunctpolym.2018.07.024
Received 12 June 2018; Received in revised form 29 July 2018; Accepted 30 July 2018
Availableonline31July2018
1381-5148/©2018ElsevierB.V.Allrightsreserved.

S. Koyuncu, F.B. Koyuncu
ReactiveandFunctionalPolymers131(2018)174–180
Fig. 1. Camouflage like poly(SNSPA)-PEDOT:PSS based complementary ECD.
electrochemical measurements revealed multielectrochromic behavior
during the electrochemical oxidation process. Further, the prepared
poly(SNSPA)-PEDOT:PSS-based complementary ECD presented low
response time and high contrast ratio in the visible region, with re-
versible color change among soil-like brown, vegetation-like green, and
sea-like blue. Because of this property, the device has multiple ca-
mouflage abilities, thus making it suitable for sand, forest, and sea
surface conditions [31, 32] (Fig. 1).
recorded using an Analytic Jena Speecord S-600 diode-array spectro-
photometer [34]. PTI QM1 fluorescence spectrophotometer was used in
the photoluminescence measurements, and all the measurements were
made at a concentration of 3 × 10−5 M THF solution at 25 °C.
A Nanosurf Naio atomic force microscope (AFM) was used for the
investigation of SNSPA polymer film surface. AFM measurements were
made in noncontact mode (wave mode) at ambient conditions and
room temperature scanned in a 10 μm × 10 μm measurement area. The
AFM system was protected with an acoustic chamber to avoid electro-
magnetic noise.
2. Experimental
Spectro-electrochemical measurements of SNSPA polymer film were
made from absorption spectra obtained by applying a potential to this
polymer film on the ITO/glass conducting surface [35]. These mea-
surements were carried out in a spectro-electrochemical cell including a
quartz cuvette, an Ag wire as the reference, and a Pt wire as the counter
electrode in 0.1 M TBAPF6 supporting electrolyte in acetonitrile. Col-
orimetry measurements were made by using a chromameter module
(standard illuminator D65, field of view 10° observer) on an Analytic
Jena Specord S600 UV–vis spectrophotometer with viewing geometry
as recommended by International Commision on Illumination (CIE).-
Color can be described in terms of three characteristics: luminance (L),
hue (a), and saturation (b), according to the CIE system [36]. These
values were given in the neutral, intermediate, and fully oxidized states
of the SNSPA polymer film on the ITO/glass surface and its ECDs.
2.1. Materials and instrumentation
All chemicals were purchased from Aldrich and TCI Chemical, and
they were used without further purification. The syntheses and char-
acterizations of 1,4-bis(2-tiyenil)butan-1,4-dione (1) were previously
described in the literature [23]. Finaly, the SNSPA was synthesized in
three steps (Scheme 1).
Fourier-transform infrared spectra (FT-IR) were recorded on a
Agilent Cary 630 FT-IR by using an attenuated total reflectance (ATR)
module (4000–650 cm−1). 1H NMR spectrum was recorded on a Bruker
Advance DPX-400 at 25 °C in d-CHCl3 solutions. A biologic SP50 po-
tentiostat–galvanostat system was used in the electrochemical mea-
surements. The electrochemical cell consisted of a Ag wire as the re-
ference electrode, a Pt wire as the counter electrode, and glassy carbon
as the working electrode (WE) immersed in 0.1 M tetrabutylammonium
hexafluorophosphate (TBAPF6) as the supporting electrolyte.
The electrochemical measurements were realized under argon at-
mosphere. Further, the oxidation and reduction onset potentials de-
termined by cyclic voltammetry (CV) were used for the HOMO-LUMO
2.2. Synthesis of 1-(4-ethenylphenyl)-2,5-di(thiophen-2-yl)-1H-pyrrole
(SNSP)
1,4-Dithiophene-2-yl-butane-1,4-dione (1.5 g, 6 mmol), 4-vinylani-
line (0.783 g, 6,6 mmol), and p-toluenesulfonic acid (20.4 mg,
1.2 mmol) in 60 mL dry toluene were added in a flask under argon at-
mosphere. The reaction mixture was refluxed for 5 h by using a
Dean–Stark apparatus until all the starting materials were consumed. It
was then cooled, and toluene as a solvent was removed by a rotary
evaporator. The residue was purified by column chromatography
band gap calculations by using the equation
EHOMO = −e
(Eox − EFc) + (−4.8 eV), with the ferrocene redox couple E(Fc/
Fc+) = 0.44 V as the inner standard [33]. On the other hand, the op-
tical band gaps (Eg) of SNSPA and the corresponding polymer were
calculated by using their absorption edges of the UV–Vis spectra
175

S. Koyuncu, F.B. Koyuncu
ReactiveandFunctionalPolymers131(2018)174–180
O
S
S
(1)
Cl
S
(a)
+
Cl
O
O
O
NH2
a) AlCl3, DCM, 0oC,
b) Toluene, PTSA,110oC,
c) Dioxane, DMPA,
(b)
CH2
S
N
(c)
S
S
O
N
OH
HS
S
SNSPA
S
CH2
O
SNSP
OH
Scheme 1. Synthetic route to SNSPA electroactive monomer.
added to a Schlenk tube. The reaction mixture was degassed by argon
under vacuum. DMPA (0.01 g, 0.04 mmol) was then added, and the
reaction mixture was stirred at room temperature under 366 nm UV
light for an hour. The mixture was poured into 100 mL of methanol, and
the solvent was removed under reduced pressure. The residue was
purified by column chromatography through silica gel by eluting with a
chloroform: methanol (9:1) mixture. Yield: 0.622 g, 70%, gray product.
FT-IR (cm−1): 3096, 3061 (CeH aromatic); 2917, 2847 (CeH ali-
phatic); 1707(C]O carboxyl); 1586, 1488 (C]C aromatic); 684 (CeS
thiophene);1H NMR (CHCl3-d): δ ppm, 8.16 (d, 2H, Ar-Ha); 8.13 (t, 2H,
Ar-Hb); 7.87 (d, 2H, Ar-Hc); 6.92 (d, 2H, AreHe); 6.90 (d, 2H, AreHf),
6.26 (s, 2H, Ar-Hd); 3.86 (d, 2H, Hj); 3.57 (d, 2H, Hi); 3.31 (d, 2H, Hh),
2.72 (d, 2H, Hg);13C NMR (CHCl3-d): δ ppm 179.2 (COOH), 143.4,
135.6, 134.1, 132.8, 130.9, 128.3, 121.8, 119.3, 118.4, 109.1, 36.8,
34.7, 31.6, 27.3.
2.4. Electrochemical polymerization of SNSPA
Repeated scan electrochemical polymerization was carried out by
using an acetonitrile solution of 2.0 × 10−3 M SNSPA monomer and
0.1 M TBAPF6. In addition, a platinum wire was used as the counter and
Ag wire as the reference electrode. Poly(SNSPA) film was obtained by
performing repetitive cycling for 20 times at potentials between 0 and
0.9 V and a scan rate of 100 mV/s (Fig. 2). A new redox couple with a
Fig. 2. Repeated potential scans of SNSPA in 0.1 M TBAHF6 in acetonitrile, scan
rate 100 mV/s.
through silica gel by eluting with a chloroform: hexane(1:2) mixture.
Yield: 0.846 g, 42%, light yellow product.
FT-IR (cm−1): 3104, 3068 (CeH aromatic); 3024 (CeH vinyl); 1508,
1482 (C]C aromatic); 652 (CeS thiophene);1H NMR (CHCl3-d): δ ppm,
8.12 (d, 2H, Ar-Ha); 8.08 (t, 2H, Ar-Hb); 7.81 (d, 2H, Ar-Hc); 7.11 (d,
2H, AreHf), 7.08 (d, 2H, AreHe); 6.26 (s, 2H, Ar-Hd); 6,11, 5.52,
5.25(m, 3H, CeH vinyl subunit). 13C NMR (CHCl3-d): δ ppm 144.2,
136.8, 134.7, 134.2, 130.6, 128.7, 123.4, 121.6, 118.8, 117.6, 109.1,
106.8.
half wave potential (Em,
ox) of 0.48 V was observed, and the re-
1/2
versible peaks intensified after each successive cycle, which clearly
indicates the deposition of poly(SNSPA) on the ITO-glass working
electrode surface. The prepared polymer film was then rinsed with
acetonitrile to remove electrolyte salt and other impurities. Thus, the
SNSPA polymer film could be directly formed on the ITO-glass surface
(8–12 Ω, 0.8 cm × 5 cm and 4 cm × 5 cm).
2.3. Synthesis of 3-(2-[4-(2,5-di-2-thienyl-1H-pyrrol-1-yl)phenyl]ethyl-
thio)propanoic acid (SNSPA)
2.5. ECD fabrication
The ECD was fabricated in a sandwich configuration by using a
transparent ITO-glass substrate (active area: 5 cm2) as anode and
cathode materials. First, PEDOT–PSS was spin coated from aqueous
solution (Clevios pH 500 - Heraeus) onto the ITO-glass surface (5 cm2)
SNSP was functionalized according to the procedures published by
Cakir et al. for thiol-ene click reaction [37]. SNSP (0.667 g, 2 mmol),-
mercaptopropionic acid (0.53 g, 5 mmol) and 1,4 dioxane (10 mL) were
176

S. Koyuncu, F.B. Koyuncu
ReactiveandFunctionalPolymers131(2018)174–180
Fig. 3. AFM image of poly(SNSPA) thin film surface; a) Topography image b) 3D image.
with 2000 rpm spin rate. On the other hand, poly(SNSPA) was de-
posited onto another ITO-glass surface by potentiodynamic electro-
chemical process. After the process, the polymer film of poly(SNSPA)
was rinsed with acetonitrile to remove electrolyte salt. The conducting
gel electrolyte was prepared from LiClO4:ACN:poly (methyl methacry-
late) (PMMA, Mw: 15,000):1,2-propylene carbonate in the ratio of
3:70:7:20 by weight. Finally, the gel electrolyte was spread over each
face, and individual ITO/glass layers were stacked face to face [38, 39].
reduction peak negatively shifted to Ep,
red= − 1.70, Ep,
a
red= − 1.76 V, and Ep, 1/2ox= − 1.73 V in poly(SNSPA). On the other
c
hand, a reversible oxidation peak was defined at Em, aox= 0.79 V, Em,
ox=0.63 V, and Em, 1/2ox= 0.71 V for SNSPA, and because of extended
c
conjugation after polymerization, the oxidation was observed at lower
potentials; Ep, ox= 0.71 V, Ep, ox=0.51 V, and Ep, ox= 0.61 V for
a
c
1/2
poly(SNSPA) in the anodic regime. Furthermore, the electrochemical
band gaps of SNSPA and corresponding polymer were calculated by
using onset values of their redox potentials (Table 1).
3. Results and discussion
3.3. Optical properties
3.1. Thin film properties
The optical properties of SNSPA were investigated by bot UV–vis
absorption and fluorescence spectroscopy recorded with a concentra-
tion of 2 × 10−6 M solution in THF (Fig. 5). On the other hand, the
poly(SNSPA) film on ITO/glass surface was rinsed in THF to obtain the
SNSPA polymer solution. SNSPA exhibited three distinct absorption
bands at 232, 268 and 337 nm. The transition at 337 nm is more intense
than that at the neighboring band at 268 nm because SNSPA bears both
SNS-conjugated system containing thiophene and pyrrole photoactive
moieties and –COOH as subunit. In the UV–vis absorption spectrum of
poly(SNSPA), a 185 nm red shift was observed after polymerization
because of the extended conjugation on the electroactive SNSPA
polymer main chain. Finally, the optical band gap (Eg) of SNSPA and
poly(SNSPA) calculated from their absorption edges were found to be
2.11 eV and 1.90 eV, respectively (Table 1). Photoluminescence beha-
vior of SNSPA and poly(SNSPA) were also investigated in the same
conditions with exciting their low-energy absorption maxima. In the
photoluminescence spectrum of SNSPA, two distinct emission bands
were observed at 378 and 422 nm. Besides, the spectrum of poly
(SNSPA) exhibited emission maxima at 628 nm relative to the corre-
sponding monomer SNSPA because of a red shift in absorbance. Finally,
it is clearly observed that blue light emission of the SNSPA solution in
THF turned into green after polymerization (Fig. 5) (Table 2).
The surface morphology of poly(SNSPA) film obtained by the
electrochemical deposition process was examined by AFM (Fig. 3). As
provided in the literature, during electrochromic switching, the elec-
trolyte ions are injected/ejected upon the polymer film formed on the
ITO-glass WE surface [40, 41]. Because of this feature, the electro-
chromic performance can be affected by the polymer film surface
roughness [42–44]. The AFM image of poly(SNSPA) exhibits a uniform
structure because the polymer could be regularly attached to the ITO-
glass surface through a compatible –COOH subunit. Overall, the root
mean surface roughness of the polymer was found to be 0.4 nm with
234 nm polymer film thickness. Consequently, a well-defined thin film
surface and uniform roughness are great advantages for electrochromic
applications.
3.2. Electrochemical properties
The electrochemical properties of SNSPA monomer and the corre-
sponding polymer were investigated by CV (Fig. 4). During the cathodic
scan regime, a semi-reversible reduction peak attributed to carboxyl
subunit at Em, red= − 1.45, Em, red= − 1.51 V, and Em,
1/
a
c
ox= − 1.48 V was observed in the CV of SNSPA monomer. This
2
Fig. 4. Redox behavior of SNSPA (a) and poly(SNSPA) (b) in 0.1 M TBAPF6/acetonitrile electrolyte solution at a scan rate of 100 mV/s, vs. Ag wire.
177

S. Koyuncu, F.B. Koyuncu
ReactiveandFunctionalPolymers131(2018)174–180
Table 2
Electrochromic parameters for poly-(SNSPA) and prepared ECD.
Table 1
'
HOMO and LUMO energy levels, electrochemical (Eg ) and optical band gap (Eg)
values of SNSPA and poly(SNSPA).
Material
Optical contrast
Response time Optical
Coloration
change (ΔT%)
(s)
activity
after
efficiency,
Molecule
HOMO LUMO
Optical band
gap
Electrochemical band gap
(eV)
(cm2 C−1
)
(eV)
(eV)
5000 cycles
(%)
(eV)
SNSPA
Poly(SNSPA) −4.71
−5.91
−3.80 3.18
−2.81 2.13
2.11
1.90
poly(SNSPA)
%ΔT:
56%Tneutral:
Oxidation
1.7 s
97
82
Thin film
98%Toxidation
42
at 860 nm
%ΔT:
:
:
Reduction
1.2 s
3.4. Spectroelectrochemical properties
poly(SNSPA)-
PEDOT:PSS
ECD
Oxidation
0.65 s
Reduction
0.45 s
98
434
The electrochromic behavior of the poly(SNSPA) film on the ITO-
glass surface was investigated by spectro-electrochemical technique. At
the neutral state, the poly(SNSPA) film is in orange color, which ab-
sorbs the blue-green region on the visible spectrum. Depending on the
applied positive potential, while the intensity of the absorption band at
about 430 nm was decreased, the absorption band around 650 nm
gradually intensified between 0 and 0.6 V. As a result, the orange color
of the poly(SNSPA) film (L*:93.49; a:-1.30; b: 54.44) was turned into
green (L*:73.38; a:-13.29; b: 4.23) at the intermediate state. With fur-
ther increase in the potential from 0.6 to 1.1 V, the band at 860 nm was
intensified, and the green color of the polymer film converted to dark
blue (L*:62.74; a:-0.88; b:-21,63) at fully oxidized state (Fig. 6). This
multielectrochromic behavior has great advantage in potential appli-
cations.
54%Tneutral
:
98%Toxidation
44
at 600 nm
On the other hand, the ECD was prepared in sandwich configuration
by ITO-glass/PEDOT:PSS//LiClO4 gel electrolyte//poly(SNSPA)/ITO-
glass device construction. PEDOT:PSS and poly(SNSPA) layers were
prepared by spin coating and electrochemical deposition process, re-
spectively. Then, in the second step, an LiClO4-based gel electrolyte was
spread over the face of each layer. Finally, electroactive material-coated
ITO-glass layers were stacked face to face. Spectroelectrochemical be-
havior of ECD under an applied potential of −1.0–1.2 is presented in
Fig. 7. During the coloration process of dual-type ECD, poly(SNSPA)
and PEDOT:PSS layers were oxidized and reduced, respectively. At the
neutral state, poly(SNSPA) layer was orange and PEDOT:PSS layer was
light blue; therefore, the color of the ECD was light brown (L*:70.21; a:
4.35; b: 15.98). When a potential of −1.0 to 0.7 V was applied, the new
band at about 740 nm was intensified; hence, the light brown color of
ECD turned into green (L*:67.79; a: −1.54; b: 2.53) at the intermediate
state. At higher potentials from 0.7 to 1.2 V, the new band at about
540 nm was intensified because of the simultaneous oxidation of poly
(SNPA) and reduction of PEDOT:PSS. As the spectral signatures of
PEDOT:PSS layers became dominant at the fully oxidized state, the
color of ECD converted to dark blue (L*:64.73; a: 2.92; b:-2.29) (Fig. 8).
The kinetic studies of SNSPA polymer film and the ECD were carried
out by detecting the changes in the electro-optical responses during
redox potential switching. Poly(SNSPA) film was investigated by al-
terations that occurred in the transmittance (increments of the ab-
sorption band at 860 nm with respect to time), while switching the
potential step wisely between neutral (0 V) and oxidized states (1.1 V)
Fig. 6. Electronic absorption spectra and the color change of poly(SNSPA) in
the anodic regime on ITO/glass surface in 0.1 M TBAPF6/acetonitrile.
with a residence time of 5 s. Response time to color change and the
percentage transmittance change (ΔT%) of the polymer film during the
potential switching were determined (Fig. 7). The ΔT% of poly(SNSPA)
at 860 nm between neutral (at 0 V) and oxidized states (at 1.1 V) was
detected as 56%. In addition, the oxidation and reduction response
times were measured as 1.7 and 1.2 s, respectively. In addition, optical
activity against applied potentials and their related life time are very
important parameters for electrochromic applications. It was de-
termined that poly-(SNSPA) showed an optical activity of about 97% at
the end of 1000 potential switching cycles between 0 and 1.1 V. On the
other hand, ΔT% of poly(SNSPA)-PEDOT:PSS-based ECD at 600 nm
was 54% between −1.0 and 1.2 V. The response time against trans-
mittance changes in this regime was measured as 0.65 and 0.45 s.
Fig. 5. UV–Vis absorption and fluorescence spectra of SNSPA (a) and poly(SNSPA) (b) in THF.
178

S. Koyuncu, F.B. Koyuncu
ReactiveandFunctionalPolymers131(2018)174–180
Fig. 7. Electronic absorption spectra and the color change of poly(SNSPA)-PEDOT:PSS-based ECD scanning potentials between −1.0 and 1.2 V.
Fig. 8. Electrochromic switching and optical absorbance monitored (a) at 860 nm for poly(SNSPA) between 0 V and 1.1 V (b) at 600 nm for poly
(SNSPA):PEDOT:PSS-based ECD.
Further, the ECD achieved an excellent optical activity of 98% after
5000 cycles with a residence time of 5 s (Fig. 8). The high stability and
fast response time of ECD against electrochromic switching are great
advantages for its use in electrochromic applications.
Acknowledgment
The authors would like to thank Çanakkale Onsekiz Mart University
for financial support (Project Number: 2016/1083).
The CE is also important for electrochromic application. The CE was
calculated as follows: CE = ΔOD/Qd and ΔOD = log (Tcolored/Tbleached),
where Qd is the injected/ejected charge between neutral and oxidized
states and Tcolored and Tbleached are the transmittance in the oxidized and
neutral states, respectively [38]. By using these equations, the CEs were
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–COOH subunit compatible with a ITO-glass surface was synthesized
and then directly coated onto the ITO-glass surface by potentiodynamic
electrochemical process. Multielectrochromic behavior among orange,
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