Multichromic polymers of benzotriazole derivatives: Effect of benzyl substitution

Article abstract of DOI:10.1016/j.electacta.2010.11.052

Two electroactive monomers 1-benzyl-4,7-di(thiophen-2-yl))-2H-benzo[d][1,2, 3]triazole (BBTA) and 2-benzyl-4,7-di(thiophen-2-yl))-2H-benzo[d][1,2,3]triazole (BBTS) were synthesized with satisfactory yields. The effect of substitution site on electrochemic

Full text of DOI:10.1016/j.electacta.2010.11.052

Electrochimica Acta 56 (2011) 2263–2268
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Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
Multichromic polymers of benzotriazole derivatives:
Effect of benzyl substitution
Basak Yigitsoya, S.M. Abdul Karimd, Abidin Balana, Derya Barana, Levent Topparea,b,c,∗
a Department of Chemistry, Middle East Technical University, 06531 Ankara, Turkey
b Department of Biotechnology, Middle East Technical University, 06531 Ankara, Turkey
c Department of Polymer Science and Technology, Middle East Technical University, 06531 Ankara, Turkey
d Department of Arts and Sciences, Ahsanullah University of Science and Technology, Dhaka 1208, Bangladesh
a r t i c l e i n f o
a b s t r a c t
Article history:
Two electroactive monomers 1-benzyl-4,7-di(thiophen-2-yl))-2H-benzo[d][1,2,3]triazole (BBTA) and
2-benzyl-4,7-di(thiophen-2-yl))-2H-benzo[d][1,2,3]triazole (BBTS) were synthesized with satisfactory
yields. The effect of substitution site on electrochemical and optical properties was investigated with
cyclic voltammetry and spectroelectrochemical studies. Results showed that position of pendant group
alters the electronic structure of the resulting polymer causing different optical and electrochemical
behaviors. Symmetrically positioned benzyl unit on benzotriazole moiety resulted in a neutral state red
polymer, PBBTS, having multi-colored property in its different oxidized and reduced states. Its analogue
PBBTA exhibited maximum absorption at 390 nm in its neutral state and also revealed multicolored elec-
trochromic property upon stepwise oxidation. Very different optical band gap values were calculated:
1.55 eV and 2.25 eV for PBBTS and PBBTA, respectively.
Received 12 September 2010
Received in revised form 7 November 2010
Accepted 13 November 2010
Available online 23 November 2010
Keywords:
Benzotriazole
Electrochromism
Multicolored electrochromism
Conjugated polymers
Substitution effect
© 2010 Elsevier Ltd. All rights reserved.
1. Introduction
of the spectrum. Rarely, when more than two redox states, absorb-
ing in the visible, are electrochemically accessible, the ECP exhibits
Conjugated polymers are great nominees for plastic electron-
ics due to the fact that the structural modifications on this class
of materials enable color-tuning by adjusting band gap [1], high
optical contrasts [2], fast switching times [3] and processabil-
ity [4]. Hence, design of electroactive monomers is a key tool
to determine the electrochemical and optical properties of the
final conducting polymers. Donor–acceptor (DA) approach is com-
monly claimed to be a useful method to synthesize low band
gap polymers which have multiple red-ox states at low potentials
[5,6].
Electrochromic polymers (ECPs) reveal reversible color change
upon appropriate external bias. Since energy gap between HOMO
and LUMO levels lies in the visible region, most of conducting poly-
mers are colored in their neutral states. Redox switching results in
new optical absorption bands due to electronic charge transport
and incorporation of counter ions into polymer chains. Upon oxi-
dation or reduction conducting polymers are considered as doped
with counter ions and their structures change into a delocalized
␲-electron band structure [7]. This structural change results in for-
mation of new optical absorption bands in the lower energy part
multicolored electrochromism [8]. This is a consequence of high
energy absorption of polaronic states which also tails into the vis-
ible region. It is important to remark that although all conjugated
polymers have potential to exhibit two colors, only a few show
multi-colored states.
In the context of color tuning concept, DAD type monomers
with electropolymerizable heterocyclics at both sides of the A
unit symmetrically were studied quite extensively up to date and
effects of different D and A groups were investigated. Several exam-
ples of electron deficient groups coupled with electron donating
groups such as ethylenedioxythiophene (EDOT) and thiophene (Th)
revealed either better optical contrast, lower band gap and switch-
ing time or both p-type and n-type doping compared to pristine
polymers polythiophene (PTh) and PEDOT [9–13]. Recently, syn-
thesis and optoelectronic properties of new DAD type polymers
bearing benzotriazole (BTz) as the A unit were reported by our
group [14,15]. These BTz based DAD type polymers were seen
to be ambipolar due to the electron accepting nature of imine
containing triazole ring which also provides a possible alkylation
position to improve solubility. BTz containing polymers were also
studied by other research groups for solar cell and electrochromic
applications recently [16–18]. Poly(2-dodecyl-4,7-di(thiophen-2-
yl)-2H-benzo[d][1,2,3]triazole) (PTBT) as an example of BTz based
polymers revealed multicolored electrochromism with the ability
to switch between all RGB colors, black and transmissive states
∗
Corresponding author at: Department of Chemistry, Middle East Technical Uni-
versity, 06531 Ankara, Turkey. Tel.: +90 3122103251; fax: +90 3122103200.
E-mail address: toppare@metu.edu.tr (L. Toppare).
0013-4686/$ – see front matter © 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.electacta.2010.11.052

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B. Yigitsoy et al. / Electrochimica Acta 56 (2011) 2263–2268
which make this polymer unique among numerous electrochromic
conjugated polymers [15].
Here we report electrochemical and optical properties of
poly(1-benzyl-4,7-di(thiophen-2-yl))-2H-benzo[d][1,2,3]triazole)
room temperature under an argon atmosphere. The mixture
was refluxed for 48 h, cooled, and concentrated on the rotary
evaporator. The residue was subjected to column chromatography
(hexane/CH2Cl2, 1:1, Rf, 0.43) to afford an yellow solid (0.168 g, 71%
yield). 1H NMR (400 MHz, CDCl3, TMS)) ı 8.27 (d, 1H, J = 3.7 Hz),
7.51 (d, 1H, J = 7.5 Hz), 7.36 (d, 1H, J = 5.1 Hz), 7.32 (d, 1H, J = 5.1 Hz),
7.27 (d, 1H, J = 7.5 Hz), 7.17–7.15 (m, 1H), 7.13-6.98 (m, 5H), 6.80
(d, 1H, J = 3.5 Hz), 6.55 (d, 1H, J = 6.6 Hz), 5.66 (s, 2H) 13C NMR
(100 MHz, CDCl3, TMS) ı 52.03, 115.93, 119.44, 125.61, 125.66,
125.71, 125.78, 126.08, 126.67, 127.22, 127.37, 127.48, 129.91,
130.75, 134.63, 136.39, 137.77, 142.59. MS (m/z): 373.5 [M+].
2-Benzyl-4,7-di(thiophen-2-yl))-2H-benzo[d][1,2,3]triazole
(PBBTA)
and
poly(2-benzyl-4,7-di(thiophen-2-yl))-2H-
benzo[d][1,2,3]triazole) (PBBTS). Polymers were synthesized
electrochemically from their corresponding monomers. Reported
spectroelectrochemical results showed that both polymers are
multicolored electrochromics with low working potential range.
Structural and substitutional effects on electrochromic properties
of polymers were highlighted in detail.
(BBTS): 2-Benzyl-4,7-dibromo-1H-benzo[d][1,2,3]triazole (3)
(120 mg, 0.327 mmol) and tributyl(thiophen-2-yl)stannane
(610 mg, 1.63 mmol) were dissolved in dry THF (40 mL).
The solution was purged with argon for 30 min and
2. Experimental
2.1. General
dichlorobis(triphenylphosphine)-palladium(II)
(60 mg,
All chemicals were purchased from Aldrich except anhy-
drous tetrahydrofuran (THF) which was purchased from Acros.
0.085 mmol) was added at room temperature under an argon
atmosphere. The mixture was refluxed for 15 h, cooled, and con-
centrated on the rotary evaporator. The residue was subjected to
column chromatography (hexane/CHCl3, 2:1, Rf, 0.35) to afford an
bright yellow solid (118 mg, 96%). 1H NMR (400 MHz, CDCl3, TMS)
ı 8.01 (s, 2H), 7.53 (s, 2H), 7.41 (d, 2H, J = 6.6 Hz), 7.28 (m, 4H), 7.17
(s, 1H), 7.09 (m, 2H), 5.89 (s, 2H). 13C NMR (100 MHz, CDCl3, TMS)
ı 60.55, 122.98, 133.74, 125.58, 127.13, 128.13, 128.34, 128.54,
128.82, 134.80, 139.88, 142.50 MS (m/z): 373.5 [M+].
4,7-Dibromobenzo[1,2,5]thiadiazole
[19],
3,6-dibromo-1,2-
phenylenediamine [20], tributyl(thiophen-2-yl)stannane [21],
4,6-dibromo-1,2,3-benzotriazole (1) [22] were synthesized accord-
ing to previously described methods. Electropolymerization was
performed with a Voltalab 50 potentiostat in a three electrode cell
consisting of platinum wire or indium tin oxide (ITO) coated glass
as the working electrode, platinum wire as the counter electrode,
and an Ag wire as the pseudo reference electrode. Electrodeposi-
tion was performed in a 0.1 M solution of tetrabutylammonium
hexafluoroborate (TBAPF6) in acetonitrile–dichloromethane mix-
ture (95:5, v/v). UV–vis–NIR spectra were recorded on a Varian
Cary 5000 spectrophotometer at a scan rate of 2000 nm/min. 1H
and 13C NMR spectra were recorded on a Bruker Spectrospin
Avance DPX-400 spectrometer and chemical shifts were given
relative to tetramethylsilane (TMS). Mass analysis was carried
out on a Bruker time-of-flight (TOF) mass spectrometer with an
electron impact ionization source.
3. Results and discussion
3.1. Synthesis
The design of the molecules is based on the donor–acceptor
approach. Benzotriazoles are considered to act as electron with-
drawing groups owing to electron deficient –N N– and –C N–
moieties and thiophene acts as the electron rich donor group
[23,24]. The substitution pattern of monomers was decided accord-
ing to previous investigations on alkyl substituted benzotriazoles
[15] which have notable properties. Benzyl pendant group was
substituted from two available sites of benzotriazole in order to
investigate substitution effect.
Although benzylation of benzotriazole resulted in substitution
from both 1 and 2 positions of the triazole ring, bromination
of 1-substituted product was not possible with the previously
reported procedures for the bromination of N-functionalized ben-
zotriazoles. In order to obtain 1-benzyl-1H-benzo[d][1,2,3]triazole
a more convenient synthetic route was selected where starting
material was benzothiadiazole. In this method, benzothiadia-
zole was brominated from 4,7 positions in high yield and later
brominated compound was reduced to 3,6-dibromobenzene-1,2-
diamine. Then dibromo benzotriazole (1) was formed in the
presence of sodium nitride (NaNO2) in acetic acid. From the
benzylation of (1) both 1-benzyl-1H-benzo[d][1,2,3]triazole and
2-benzyl-1H-benzo[d][1,2,3]triazole were obtained.
2.2. Synthesis
1-Benzyl-4,7-dibromo-1H-benzo[d][1,2,3]triazole (2) and 2-
Benzyl-4,7-dibromo-1H-benzo[d][1,2,3]triazole (3): Benzyl bromide
(575 mg, 3.4 mmol) was added to a solution of 4,6-dibromo-1,2,3-
benzotriazole (500 mg, 1.8 mmol), potassium t-butoxide (224 mg,
2 mmol) in ethanol (20 mL) and the reaction mixture was stirred
for 12 h at room temperature. The reaction was monitored by
thin layer chromatography (TLC). After removal of the solvent
by evaporation, the residue was dissolved in CH2Cl2 and washed
with water and then with brine. The organic layer was dried
over MgSO4 and the solvent was evaporated under reduced
pressure. The residue was subjected to column chromatography
(CH2Cl2:hexane = 1:1) to obtain 2 (Rf, 0.23) as a light pink solid in
47% yield (308 mg) and 3 (Rf, 0.43) as a white solid in 28% yield
(187 mg). Overall yield is 75%. 2: 1H NMR (400 MHz, CDCl3, TMS) ı
7.39 (d, 1H, J = 8 Hz), 7.33 (d, 1H, J = 8 Hz), 7.24 (m, 2H), 7.19 (s, 1H),
7.13 (m, 2H), 6.10 (s, 2H). 13C NMR (100 MHz, CDCl3, TMS) ı 51.71,
100.76, 112.10, 126.00, 127.07, 127.23, 127.83, 130.99, 131.32,
134.75, 145.05. MS (m/z): 367 [M+]. 3: 1H (400 MHz, CDCl3, TMS)
ı 7.41 (s, 1H), 7.40 (s, 1H), 7.30–7.26 (m, 4H), 7.19 (s, 1H), 5.86
(s, 2H). 13C NMR (100 MHz, CDCl3, TMS) ı 59.41, 108.61, 126.94,
127.34, 127.39, 128.23, 132.38, 142.57. MS (m/z): 367 [M+].
The brominated compounds
2 and 3 were coupled with
tributyl(thiophen-2-yl)stannane in the presence of Pd catalyst to
obtain final desired products, 2-benzyl-4,7-di(thiophen-2-yl)-2H-
benzo[d][1,2,3]triazole (BBTS) and 1-benzyl-4,7-di(thiophen-2-
yl)-1H-benzo[d][1,2,3]triazole (BBTA). The intermediate products
and final products were characterized by 1H ad 13C NMR spec-
troscopy. The synthetic route was outlined in Scheme 1.
1-Benzyl-4,7-di(thiophen-2-yl))-2H-benzo[d][1,2,3]triazole
(BBTA): 1-Benzyl-4,7-dibromo-1H-benzo[d][1,2,3]triazole (2)
(0.233 g, 0.635 mmol) and tributyl(thiophen-2-yl)stannane
(1.185 g, 3.175 mmol) were dissolved in dry THF (50 mL). The solu-
tion was purged with argon for 30 min and dichlorobis(tripheny-
lphosphine)-palladium(II) (60 mg, 0.085 mmol) was added at
3.2. Cyclic voltammetry
In order to determine redox reactions during electrochem-
ical polymerization and film deposition, monomers; BBTS and

B. Yigitsoy et al. / Electrochimica Acta 56 (2011) 2263–2268
2265
Fig. 2. Single scan cyclic voltammograms of PBBTS films between 1.2 V and −2.1 V
using ACN as the solvent and 0.1 M TBAPF6 as supporting electrolyte at a scan rate of
100 mV s−1. Colors observed for p-type doping (a) red; (b) purple; (c) gray; (d) blue.
And n-type doping (e) red; (f) brown; (g) blue; (h) gray. (For interpretation of the
references to color in this figure legend, the reader is referred to the web version of
the article.)
reversible redox peaks were evolved and the anodic and cathodic
currents were increased as a result of regular growth of PBBTS on
ITO electrode. The resulting polymer was oxidized and reduced
reversibly at 1.05 V and 0.9 V, respectively in a monomer free
solution (Fig. 2). The polymer changed colors between red and
blue upon p-type doping/dedoping. The whole process requires
ca. 24 mC/cm2. Single scan cyclic voltammetry in monomer free,
0.1 M TBAPF6/ACN solution showed that PBBTS was also n-type
dopable (Fig. 2) when the polymer was cycled between negative
potentials. The n-type doping property was determined for PBBTS
with a reversible couple at −2.02 V and −1.21 V vs. Ag wire refer-
ence electrode. The red polymer in the neutral state turned into
brown and blue when partially reduced and finally gray color was
observed for PBBTS upon further reduction.
Scheme 1. Synthetic route to monomers BBTA and BBTS.
BBTA were initially subjected to cyclic voltammetry (CV) in 0.1 M
tetrabutylammonium hexafluorophosphate (TBAPF6) solution in
acetonitrile/dichloromethane (ACN:DCM) (5:95, v:v) on indium tin
oxide (ITO) coated glass slides. 5% dichloromethane was used to
enhance the solubility of BBTS and BBTA in the electrolytic medium
owing to poor solubility of the monomers in acetonitrile.
Fig. 1 shows typical cyclic voltammogram recorded during con-
tinuously applied cyclic scans for BBTS. In the first cycle, BBTS
exhibited an irreversible monomer oxidation at 1.33 V vs. Ag wire
pseudo-reference electrode (50 mV vs. Fc/Fc+/V). After the first run,
Cyclic voltammetry of BBTS led to the formation of the corre-
sponding polymer PBBTS, whereas BBTA did not form well adhered
film on ITO even continuous scans were applied (Fig. 3a). Therefore,
BBTA was polymerized at 1.5 V constant potential vs. the same ref-
erence electrode where the homogenous film formation took place
on ITO. This process takes 2 min with a total of 220 ␮A comprising
ca. 26 mC/cm2. Later, the p-doping electrochemistry was probed
by oxidative cycling of the polymer film, PBBTA between 0.5 V and
1.65 V in a monomer free environment (Fig. 3b). PBBTA has a broad
oxidation peak at 1.30 V and a clear reduction peak at 1.05 V. PBBTA
does not have n-type doping property due to differences in the elec-
tronic characteristic and enhanced possibility of ␲ interaction on
the polymer backbone with respect to the PBBTS.
3.3. Spectroelectrochemistry
In order to observe the polymer characteristics upon applied
external bias, spectroelectrochemistry studies of PBBTS and PBBTA
were performed in a monomer free 0.1 M TBAPF6 solution.
Spectroelectrochemistry of PBBTS showed ꢀmax at 504 nm
which corresponds to red color for the neutral polymer. As the
potential was increased gradually, new electronic transitions pro-
Fig. 1. Repetitive cyclic voltammogram of the 0.01 M BBTS between 0.0 to +1.5 V at
100 mV s−1 in 0.1 M TBAPF6/CH2Cl2/ACN on an ITO electrode.

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B. Yigitsoy et al. / Electrochimica Acta 56 (2011) 2263–2268
Fig. 3. (a) The cyclic voltammogram of the 0.01 M BBTA between −0.3 to +1.7 V at 100 mV s−1 in 0.1 M TBAPF6/CH2Cl2/ACN on an ITO electrode. (b) Single scan cyclic
voltammogram of PBBTA film between 0.5 V and 1.65 V at 100 mV s−1 in 0.1 M TBAPF6/ACN on an ITO electrode.
gressively intensified at 685 nm owing to the formation of charge
carriers such as polarons. Since these transitions lie in the visible
region of the electromagnetic spectrum, PBBTS showed multicol-
ored states in its intermediate doping levels. Red color of the
polymer film turned into purple and than gray upon oxidation.
Moreover, further oxidation of PBBTS resulted in blue color due to
increased absorption at 685 nm together with a diminished neu-
tral state absorption. Compared to previously reported polymer
PTBT [15], green color was not detected for PBBTS in its partially
oxidized forms since the absorptions were not distinct at around
500 and 680 nm, which is essential for green color. Band gap of
PBBTS was determined as 1.55 eV from the onset value of lowest
energy transition in the visible region (Fig. 4). Additionally, since
PBBTS is both p and n dopable, its band gap was also calculated
from CV data as 1.9 eV. The electrochemical band gap of PBBTS
is higher than its optical gap. This is a common trend observed
in conjugated polymers and is usually attributed to the creation
of free ions in the electrochemical experiment rather than a neu-
tral optically induced excited state. The most important property
of PBBTS is that it shows multicolored charged states during n-
doping process. Normally both p and n type dopable polymers tend
to have multicolored states however, these kind of polymers are
rather rare. PBBTS showed three different reduced state colors and
Fig. 5. Spectroelectrochemistry of PBBTA film on an ITO coated glass slide in
monomer-free, 0.1 M TBAPF6/ACN electrolyte–solvent couple at applied potentials
and corresponding color observed at neutral and doped states.
Fig. 4. Spectroelectrochemistry of PBBTS film on an ITO coated glass slide in
monomer-free, 0.1 M TBAPF6/ACN electrolyte–solvent couple at applied potentials
(V) (a) 0.0; (b) 0.1; (c) 0.2; (d) 0.3; (e) 0.4; (f) 0.5; (g) 0.6; (h) 0.7; (i) 0.8; (j) 0.9; (k)
1.0; (l) 1.1; (m) 1.2.
Fig. 6. ꢁT% change monitored at 504 nm for PBBTS in 0.1 M TBAPF6/ACN.

B. Yigitsoy et al. / Electrochimica Acta 56 (2011) 2263–2268
2267
Fig. 7. ꢁT% change monitored at 1225 nm and 1300 nm for (a) PBBTS and (b) PBBTA in 0.1 M TBAPF6/ACN, respectively.
turned back to its original neutral state color when compen-
sated. This clearly confirms that the negative charge formation is
taking place on the polymer backbone and n-doping process is
reversible.
In addition to percent transmittance changes of electrochromic
materials upon doping/dedoping processes, how quickly these
materials change their colors and achieve full contrast are also
important. Considering that the PBBTS is a multicolored elec-
trochromic, PBBTS showed notable switching properties in visible
region. The switching times at 504 nm and 1225 nm were calcu-
lated as 0.6 s and 1.2 s for PBBTS which refer to four different color
transitions within that period. For PBBTA, the switching time was
recorded as 0.9 s at 1300 nm.
The in situ spectroelectrochemistry of PBBTA was performed
between 0.5 V and 1.45 V in a monomer free ACN/0.1 M TBAPF6
solution. The ꢀmax for the ␲–␲* transition in neutral state was
found to be 390 nm and the electronic band gap (Eg) was calcu-
lated as 2.25 eV from the onset potential for the neutral film at
551 nm. Although the maximum absorption is not totally in the
visible region, since absorbance tails into 450 nm, PBBTA reveals
yellow color in its neutral state. Upon stepwise oxidation, the inten-
sity of absorptions corresponding to charge carriers simultaneously
increased and observed at around 640 nm and 1230 nm for polarons
and bipolarons, respectively (Fig. 5). As a result of the structural
change of the polymer film upon oxidation, PBBTA altered its color
from yellow to gray. For PBBTA, the increase in the NIR region was
not as high as the symmetric PBBTS. Since benzyl unit was placed
to 2-position of benzotriazole unit, it may resulted in a steric hin-
drance for counter-ion injection and increased the possibility of ␲
interaction between pendant groups and the polymer backbone.
Thus, the insertion of dopant ions to the polymer structure upon
oxidation became less preferred.
4. Conclusions
Two benzotriazole and thiophene containing DAD type
monomers (BBTS and BBTA) with benzyl pendant groups were
synthesized successfully and polymerized electrochemically. Their
electrochemical and optical properties were characterized by cyclic
voltammetry and spectroelectrochemistry. The results revealed
that the position of pendant group clearly alter the optoelec-
tronic properties of the resulting polymers. All studies confirmed
that symmetrical substitution of pendant groups results in better
electrochemical properties, percent transmittance changes, faster
switching times and repetitive doping/dedoping processes.
Higher band gap and blue shifted absorptions of PBBTA com-
pared to PBBTS suggested that the effective conjugation length is
shorter in PBBTA than that of PBBTS [25].
References
[1] I. Schwendeman, R. Hickman, G. Sonmez, P. Schottland, K. Zong, D. Welsh, J.R.
Reynolds, Chem. Mater. 14 (2002) 3118.
[2] S.A. Sapp, G.A. Sotzing, J.R. Reynolds, Chem. Mater. 10 (1998) 2101.
[3] A. Kumar, D.M. Welsh, M.C. Morvant, F. Piroux, K.A. Abboud, J.R. Reynolds,
Chem. Mater. 10 (1998) 896.
3.4. Electrochromic contrast and switching studies
[4] G. Sonmez, H.B. Sonmez, C.K.F. Shen, R.W. Jost, Y. Rubin, F. Wudl, Macro-
molecules 38 (2005) 669.
[5] U. Salzner, J. Phys. Chem. B 106 (2002) 9214.
[6] H.A.M. van Mullekom, J.A.J.M. Vekemans, E.E. Havinga, E.W. Meijer, Mater. Sci.
Eng. R32 (2001) 1.
[7] J. Roncali, Chem. Rev. 92 (1992) 711.
[8] C.L. Gaupp, J.R. Reynolds, Macromolecules 36 (2003) 6305.
[9] A. Durmus, G.E. Gunbas, P. Camurlu, L. Toppare, Chem. Commun. (2007) 3246.
[10] D. Aldakov, M.A. Palacios, P. Anzenbacher, Chem. Mater. 17 (2005) 5238.
[11] P. Blanchard, J.M. Raimundo, J. Roncali, Synth. Met. 119 (2001) 527.
[12] A. Durmus, G.E. Gunbas, L. Toppare, Chem. Mater. 19 (2007) 6247.
[13] G.E. Gunbas, A. Durmus, L. Toppare, Adv. Funct. Mater. 18 (2008) 2026.
[14] A. Balan, G. Gunbas, A. Durmus, L. Toppare, Chem. Mater. 20 (2008) 7510.
[15] A. Balan, D. Baran, G. Gunbas, A. Durmus, F. Ozyurt, L. Toppare, Chem. Commun.
(2009) 6768.
[16] Z. Zhang, B. Peng, B. Liu, C. Pan, Y. Li, Y. He, K. Zhou, Y. Zou, Polym. Chem. 1
(2010) 1441.
[17] B. Peng, A. Najari, B. Liu, P. Berrouard, D. Gendron, Y. He, K. Zhou, M. Leclerc, Y.
Zou, Macromol. Chem. Phys. 211 (2010) 2026.
Electrochromic switching studies were carried out in order to
monitor the percent transmittance changes as a function of time
and to calculate the switching times of the polymers at their
maximum absorptions (ꢀmax) by stepping potentials repeatedly
between their fully neutral and oxidized states within 5 s time
intervals. The switching time is calculated from the kinetic stud-
ies to determine the time required for switching between oxidized
and neutral states.
At its dominant wavelength in the visible region (504 nm),
PBBTS showed 44% percent transmittance change (Fig. 6). On the
contrary to PBBTS, PBBTA has no worthy difference in percent trans-
mittances since the PBBTA film could not be reduced and oxidized
successively due to the difficulty in charge injection/ejection pro-
cesses. In NIR region PBBTS and PBBTA revealed 73% (1225 nm)
and 38% (1300 nm) transmittance which are significant for elec-
trochromic materials to be used for NIR applications (Fig. 7) [26,27].
Optical stabilities of the polymers are reasonable since PBBTS loses
5% of its original contrast whereas PBBTA loses ca. 8% of the initial
contrast upon consecutive 30 full switches.
[18] D. Baran, A. Balan, S. Celebi, B.M. Esteban, H. Neugebauer, N.S. Sariciftci, L.
Toppare, Chem. Mater. 22 (2010) 2978.
[19] A.B. Da Silveria Neto, A. Lopes Sant’Ana, G. Ebeling, S.R. Gonclaves, E.V.U. Costa,
H.F. Quina, J. Dupont, Tetrahedron 61 (2005) 10975.
[20] Y. Tsubata, T. Suzuki, T. Myashi, Y. Yamashita, J. Org. Chem. 57 (1992) 6749.
[21] S.S. Zhu, T.M. Swager, J. Am. Chem. Soc. 119 (1997) 12568.
[22] A. Tanimoto, T. Yamamoto, Adv. Synth. Catal. 346 (2004) 1818.

2268
B. Yigitsoy et al. / Electrochimica Acta 56 (2011) 2263–2268
[23] G.R. Newkome, W.W. Paudler, Contemporary Heterocyclic Chemistry, John
Wiley, New York, 1982.
[24] S.H. Ahn, M. Czae, E.R. Kim, H. Lee, S.H. Han, J. Noh, M. Hara, Macromolecules
34 (2001) 2522.
[26] A.M. McDonagh, S.R. Bayly, D.J. Riley, M.D. Ward, J.A. McCleverty, M.A. Cowin,
C.N. Morgan, R. Varrazza, R.V. Penty, I.H. White, Chem. Mater. 12 (2000) 2523.
[27] H. Meng, D. Tucker, S. Chaffins, Y. Chen, R. Helgeson, B. Dunn, F. Wudl, Adv.
Mater. 15 (2003) 146.
[25] S.D.D.V. Rughooputh, S. Hotta, A.J. Heeger, F. Wudl, J. Polym. Sci., Part B: Polym.
Phys. 25 (1987) 1071.